JP7502016B2 - POWER CONVERSION DEVICE AND CURRENT CONTROL METHOD THEREFOR - Google Patents

Description

The present invention relates to a power conversion device and a current control method in a power conversion device.

Power conversion devices and filter reactors, which are electrical equipment used to drive railway vehicles, are installed under the floor of the vehicle. In recent years, in order to improve the maintainability of vehicles, the installation of monitoring devices to detect deterioration and failures in rails and overhead lines has been considered. Since the space under the floor of a vehicle is limited, in order to install these monitoring devices on the vehicle, it is necessary to miniaturize the drive electrical equipment.

Power conversion devices use voltage-driven power semiconductors such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). Power semiconductors such as IGBTs and MOSFETs can reduce switching losses through high-speed switching operations, allowing the coolers used in power conversion devices to be made smaller.

The power conversion device has a filter reactor. Although reducing the inductance value is an effective way to make the filter reactor smaller, the slope of the fault current that occurs when the power conversion device fails or the filter reactor has a ground fault increases as the inductance value of the filter reactor decreases. For this reason, it is necessary to reduce the fault current quickly to prevent the substation from tripping.

In addition, in railway vehicles that use DC overhead lines, the voltage of the DC overhead line can fluctuate suddenly. This sudden change in the overhead line voltage causes a resonant current to occur in the filter reactor and the filter capacitor installed in the power conversion device. If the filter reactor is made smaller and its inductance value is reduced, the peak value of this resonant current will increase, and there is a risk that it will exceed the allowable current of the substation. Therefore, technology has been developed to suppress the above-mentioned fault current and resonant current by installing a device consisting of a semiconductor element and a resistor between the DC overhead line and the power conversion device.

For example, Patent Document 1 discloses that "a transistor is connected in parallel with a current-limiting resistor. When the current detection signal from the current sensor exceeds a set value, the transistor is turned OFF to limit the input current, and when the current falls below the set value, a control circuit is provided which turns the transistor ON to short-circuit the current-limiting resistor. Furthermore, a sequential cutoff circuit is provided which turns the transistor OFF when the cutoff condition is met and then releases the DC circuit breaker" (see the abstract of Patent Document 1).

Japanese Patent Application Laid-Open No. 6-70457

However, in Patent Document 1, the filter reactor is connected closer to the overhead line than the semiconductor current reduction device, and the current sensor is connected closer to the load than the filter reactor, so a fault current caused by a ground fault in the filter reactor cannot be detected and the fault current cannot be reduced.

The present invention was made in consideration of the above points, and aims to suppress both fault currents caused by ground faults in filter reactors and resonant currents caused by sudden changes in overhead line voltage in railway vehicles.

In order to solve such problems, in the present invention, a power conversion device includes an inverter that converts DC power supplied from an overhead line into AC power, and a reactor connected to the overhead line side of the inverter. The power conversion device also includes a semiconductor element connected to the overhead line side of the reactor, a resistor connected in parallel to the semiconductor element, a circuit breaker connected to the overhead line side of the semiconductor element and cutting off the DC power, a voltage detection means for detecting the overhead line voltage of the overhead line, and a current detection means for detecting the overhead line current flowing through the overhead line. The power conversion device also includes a control unit that performs a first control for switching-controlling the semiconductor element to perform a chopping operation based on the overhead line voltage detected by the voltage detection means or the overhead line current detected by the current detection means, and a second control for opening the circuit breaker to cut off the DC power after controlling the semiconductor element to be off.

The present invention makes it possible to suppress both fault currents caused by ground faults in filter reactors and resonant currents caused by sudden changes in overhead line voltage in railway vehicles.

FIG. 1 is a schematic diagram of an electric vehicle in a first embodiment. FIG. 2 is a circuit diagram of a drive device according to the first embodiment. 4 shows operational waveforms of the drive device when a fault current is suppressed in the first embodiment. 4 shows operational waveforms of the driving device when suppressing resonance current in the first embodiment. 5 is a flowchart showing an example of processing performed by the driving device when an overhead line voltage is used in the first embodiment. 5 is a flowchart showing an example of processing of the driving device when an overhead line current is used in the first embodiment. FIG. 11 is a circuit diagram of a drive device according to a second embodiment. FIG. 11 is a circuit diagram of a drive device according to a third embodiment. FIG. 13 is a circuit diagram of a drive device according to a fourth embodiment. 13 is a flowchart showing an example of processing performed by a driving device when an overhead line voltage is used in a fourth embodiment. 13 is a flowchart showing an example of processing performed by a driving device when an overhead line current is used in a fourth embodiment. FIG. 13 is a circuit diagram of a drive device according to a fifth embodiment. FIG. 13 is a circuit diagram of a drive device according to a sixth embodiment. 23 is a flowchart showing an example of processing performed by the driving device when a voltage of a secondary winding of a filter reactor is used in the sixth embodiment. FIG. 23 is a diagram illustrating an example of the configuration of a drive device for a railway vehicle (electric vehicle) in a seventh embodiment. FIG. 23 is a diagram showing an example of a timing chart showing the control of each device constituting the drive device in Example 7 (when a sudden change occurs in the main circuit input current (overhead wire current Is) during inverter operation of the drive device). FIG. 23 is a diagram showing an example of a timing chart showing the control of each device constituting the drive device in Example 8 (when a sudden change occurs in the main circuit input current (overhead wire current Is) during inverter operation of the drive device). FIG. 13 is a diagram illustrating an example of the configuration of a drive device for a railway vehicle (electric vehicle) in a ninth embodiment.

The following describes in detail the embodiments of the present invention with reference to the drawings. In each of the drawings for explaining the following embodiments, the same reference numbers indicate elements or processes having the same or similar functions, and subsequent explanations are omitted. Furthermore, each of the embodiments and modified examples can be combined in whole or in part within the scope and consistency of the technical concept of the present invention.

<Configuration of electric vehicle and drive unit>
Fig. 1 is a schematic diagram of an electric vehicle shown in embodiment 1. Fig. 2 is a circuit diagram of a drive device in embodiment 1.

In FIG. 1, in power running operation for accelerating the electric vehicle 100, power is supplied from the overhead line 1, which is a power source, to the vehicle 8 via the current collector 7. As shown in FIG. 2, the DC power supplied from the overhead line 1 is converted from DC power to AC power via the circuit breaker 11, the semiconductor current reducer 10, the filter reactor 9, and the power converter 6. The electric motor 5 is driven by the converted AC power. The driving of the electric motor 5 rotates the wheels 3 and moves the vehicle 8 forward. The electric motor 5 may be either an induction motor or a permanent magnet synchronous motor.

In the regenerative operation for decelerating the electric vehicle 100, the flow of power is the opposite of that in the power running operation. That is, the AC power generated by the electric motor 5 operating as a generator is converted to DC power by the power conversion device 6, and then regenerated to the overhead line 1 via the filter reactor 9, the semiconductor current reduction device 10, the circuit breaker 11, and the current collector 7.

The negative voltage side of the power conversion device 6 is connected to the rail 2 via the wheels 3 as an electrical ground. The electric motor 5 is mounted on a bogie 4, which supports a vehicle 8. In the following, the voltage of the overhead line 1 will be described as 1500 V DC as an example.

The drive device 1S shown in FIG. 2 has a power conversion device 6, a filter reactor 9, a semiconductor current reduction device 10, a circuit breaker 11, a current detection means 12, a voltage detection means 13, and a control logic unit 15. The power conversion device 6 that drives the electric motor 5 has a capacitor 105 and switching elements Q1 to Q6. The switching elements Q1 and Q2 are connected in series to form the U phase, the switching elements Q3 and Q4 are connected in series to form the V phase, and the switching elements Q5 and Q6 are connected in series to form the W phase.

The power conversion device 6 is, for example, an inverter. Diodes D1 to D6 are connected in inverse parallel to the switching elements Q1 to Q6 of the power conversion device 6, respectively. Here, if the switching elements Q1 to Q6 are IGBTs, it is necessary to connect the diodes D1 to D6. If the switching elements Q1 to Q6 are elements having body diodes, such as MOSFETs, it is possible to use the body diodes of the MOSFETs without connecting the diodes D1 to D6. Also, a 2-in-1 element in which series-connected switching elements or diodes are mounted in the same package may be used.

In this embodiment, for example, the inverter itself is called the power conversion device 6, but the drive device 1S including the power conversion device 6, the filter reactor 9, the semiconductor current reduction device 10, the circuit breaker 11, the current detection means 12, the voltage detection means 13, and the control logic unit 15 can also be called a power conversion device.

The switching elements Q1 to Q6 may be voltage-controlled switching elements such as MOSFETs or IGBTs, or current-controlled switching elements such as thyristors. The diodes D1 to D6 may be PN diodes or SBDs (Schottky Barrier Diodes). The semiconductors of the switching elements Q1 to Q10 and the diodes D1 to D10 may be Si (silicon) or SiC (silicon carbide) or GaN (gallium nitride), which are semiconductors with a wider band gap than Si.

The power conversion device 6 supplies AC power to the motor 5 by outputting AC power obtained by converting the input DC power through, for example, PWM (Pulse Width Modulation) control of the U-, V-, and W-phase switching elements Q1 to Q6. PWM control commands are generated by a logic unit (not shown). Here, the filter reactor 9 and capacitor 105 function as a filter circuit, reducing the noise current flowing out to the overhead line 1.

The DC voltage of the overhead line 1 is detected using a voltage detection means 13 such as a voltage sensor. The current flowing from the overhead line 1 to the power conversion device 6 is detected using a current detection means 12 such as a current sensor. The control logic unit 15 outputs a control signal to the semiconductor current reducer 10 and the circuit breaker 11 based on the results of calculation processing using the overhead line voltage value detected by the voltage detection means 13 and/or the overhead line current value detected by the current detection means 12. The control logic unit 15 may be common to the logic unit (not shown) of the power conversion device 6.

In the drive unit 1S of this embodiment, a semiconductor current reducer 10 is connected between the circuit breaker 11 and the filter reactor 9. The semiconductor current reducer 10 is composed of a switching element Q7, a diode D7, and a resistor 101. A cooler (not shown) is connected to the switching element Q7, and the heat generated by the switching element Q7 is cooled by the cooler.

The operation of the power conversion device 6 will now be described. To drive the power conversion device 6, it is necessary to initially charge the capacitor 105. When initially charging the capacitor 105, the switching element Q7 is turned off and the circuit breaker 11 is closed. The charging current for the capacitor 105 flows from the overhead line 1 through the circuit breaker 11, resistor 101, and filter reactor 9. The capacitor 105 is charged by this charging current, and the voltage of the capacitor 105 rises to the voltage of the overhead line 1.

When the capacitor 105 is charged, the switching element Q7 of the semiconductor current reducer 10 is turned on. When the power converter 6 starts operating, DC power is supplied to the power converter 6 from the overhead line 1 via the circuit breaker 11, the switching element Q7, and the filter reactor 9.

<Method of Suppressing Fault Current in the First Embodiment>
Here, since the filter reactor 9 is mounted under the floor of the vehicle 8, its insulation performance may deteriorate due to rain and wind, etc., causing a ground fault. For example, if a ground fault occurs between the filter reactor 9 and the power conversion device 6, a fault current flows from the overhead line 1. Similarly, if any of the U-phase, V-phase, or W-phase of the power conversion device 6 is short-circuited, a fault current flows. Since this fault current flows from the substation that supplies DC power to the overhead line 1, if the fault current exceeds the allowable current of the substation, the supply of power to the overhead line 1 is stopped. In other words, the fault current needs to be reduced and cut off quickly.

The method of suppressing the fault current in the power conversion device of this embodiment will be described using the operating waveforms in Figure 3. Figure 3 shows the operating waveforms of the drive device when suppressing the fault current in Example 1. At time t = t11, due to a ground fault in the filter reactor 9 or a failure in the power conversion device 6, the overhead line voltage Es begins to drop as shown by the straight line 301 in Figure 3, and the fault current begins to flow as shown by the straight line 302. This fault is detected using the current detection means 12 or the voltage detection means 13. If a fault is detected at time t = t11 (or between time t = t11 and time = t12), the switching element Q7 of the semiconductor current reduction device 10 is turned off at time t = t12.

When switching element Q7 is turned off, the overhead line 1 and resistor 101 are connected, so the fault current flowing in from the overhead line is suppressed to a current determined by dividing the voltage of the overhead line 1 by the resistance value of resistor 101. For example, if the DC voltage of the overhead line 1 is 1500 V and the resistance value of resistor 101 is 10 Ω, the current becomes 150 A. After that, at time t = t13, the circuit breaker 11 is opened and the fault current is cut off to 0 A. In addition, since the semiconductor current reducer 10 is connected closer to the overhead line 1 than the filter reactor 9, it is possible to suppress not only the fault current due to a failure of the power conversion device 6 but also the fault current due to a ground fault of the filter reactor 9.

Method for suppressing resonant current according to the first embodiment
On the other hand, the DC voltage of the overhead line 1 may fluctuate suddenly. For example, if the DC voltage of the overhead line 1 rises suddenly from 1500 V to 1800 V, an LC resonant circuit is formed by the filter reactor 9 and the capacitor 105, and a resonant current flows from the overhead line 1. Since reducing the inductance value of the filter reactor 9 increases the positive peak value of the resonant current, it is necessary to suppress it quickly. Since this sudden change in the overhead line voltage is not an accident, it is necessary to continue the operation of the power conversion device 6.

The method of suppressing the resonant current in the power conversion device of this embodiment will be described using the operating waveforms in Figure 4. Figure 4 shows the operating waveforms of the drive device when suppressing the resonant current in Example 1. At time t = t21, a sudden change in the overhead line voltage occurs, and a resonant current as shown by the dashed line 401 in Figure 4 begins to flow. This resonant current is detected using the current detection means 12 or the voltage detection means 13. When the sudden change in the overhead line voltage is detected, the switching element Q7 of the semiconductor current reduction device 10 starts a chopping operation at time t = t22, and continues the chopping operation until time t = t23.

Chopping operation refers to the repeated on and off states of switching element Q7. When switching element Q7 is on, a current flows from overhead line 1 to capacitor 105 due to the potential difference between the DC voltage of overhead line 1 and the voltage of capacitor 105. When switching element Q7 is off, resistor 101 is connected between overhead line 1 and capacitor 105, so the current flowing from overhead line 1 to capacitor 105 is reduced. By performing chopping operation in this way, semiconductor current reduction device 10 functions equivalently as a resistor, and as shown by solid line 402 in Figure 4, the positive peak value of the resonant current can be reduced and the resonant current can be quickly suppressed.

The switching frequency in the chopping operation of the switching element Q7 is a multiple of the commercial power frequency of 50 Hz or 60 Hz. As an example, the switching frequency in the chopping operation of the switching element Q7 is 300 Hz when the commercial power frequency is 50 Hz, and 360 Hz when the commercial power frequency is 60 Hz. The DC voltage of the overhead line 1 is generated by full-wave rectifying the AC commercial power. Therefore, the DC voltage of the overhead line 1 contains multiple components of the frequency of the AC commercial power, and these frequencies are not usually used by signal equipment or communication equipment. In other words, by performing chopping operation of the switching element Q7 at a frequency that is a multiple of the commercial power frequency, the resonant current can be suppressed by the chopping operation without causing any damage to the signal equipment or communication equipment.

As described above, when a fault current occurs, the semiconductor current reducer 10 turns off the switching element Q7 and then opens the circuit breaker 11, thereby quickly reducing and cutting off the fault current. Furthermore, when the overhead line voltage suddenly changes, the semiconductor current reducer 10 chops the switching element Q7 to quickly suppress the resonant current. As a result, even if the inductance value of the filter reactor 9 is reduced, the fault current and resonant current can be suppressed to below the allowable current of the substation.

<Processing of the driving device using overhead line voltage in the first embodiment>
The operation flow of the switching element Q7 will be described with reference to Fig. 5. Fig. 5 is a flowchart showing an example of processing of the drive device when the overhead line voltage is used in the first embodiment. Fig. 5 shows a method of controlling the operation state of the switching element Q7 using the overhead line voltage detection means 13. When using the method of controlling the operation state of the switching element Q7 using the voltage detection means 13, the current detection means 12 can be omitted in the drive device 1S.

As shown in FIG. 5, first, in step S11, the control logic unit 15 detects the overhead line voltage Es of the overhead line 1 using the voltage detection means 13. Next, in step S12, the control logic unit 15 calculates the deviation ΔEs (=Es-Es0) by subtracting the overhead line reference voltage Es0 from the overhead line voltage Es detected in step S11. For example, the control logic unit 15 determines the voltage difference between the overhead line voltage Es sampled at a constant period and the overhead line reference voltage Es0 to be the deviation ΔEs.

Next, in step S13, the control logic unit 15 determines whether the deviation ΔEs calculated in step S12 is, for example, greater than 200 V. If the deviation ΔEs calculated in step S12 is greater than 200 V (step S13: Yes), the control logic unit 15 proceeds to step S14, and if the deviation ΔEs is 200 V or less (step S13: No), the control logic unit 15 proceeds to step S15.

In step S14, the control logic unit 15 causes the switching element Q7 to perform a chopping operation. When step S14 ends, the control logic unit 15 returns the process to step S11.

On the other hand, in step S15, the control logic unit 15 determines whether the deviation ΔEs calculated in step S12 is, for example, less than -200 V. If the deviation ΔEs calculated in step S12 is less than -200 V (step S15: Yes), the control logic unit 15 proceeds to step S16, and if the deviation ΔEs is -200 V or greater (step S13: No), the control logic unit 15 returns to step S11.

In step S16, the control logic unit 15 turns off the switching element Q7 to suppress the fault current to a level that can be interrupted by the circuit breaker 11. Then, in step S17, the control logic unit 15 opens the circuit breaker 11. When step S17 ends, the control logic unit 15 ends the processing of the drive device when the overhead line voltage in Example 1 is used.

As shown in Figure 3, when a ground fault or the like occurs in the filter reactor 9, the overhead line voltage Es drops, causing a deviation ΔEs in the overhead line voltage. A threshold value is set for this deviation ΔEs, and when the deviation ΔEs falls below -200 V, for example, the occurrence of a ground fault is detected, and the switching element Q7 is turned off, and then the circuit breaker 11 is opened.

As shown in Figure 4, when a sudden change in the overhead line voltage occurs, a deviation ΔEs occurs in the overhead line voltage Es. The control logic unit 15 sets a threshold value for this deviation ΔEs, and when the deviation ΔEs becomes higher than 200 V, for example, it detects the occurrence of a sudden change in the overhead line voltage and starts the chopping operation of the switching element Q7. In this way, by detecting the deviation ΔEs in the overhead line voltage Es, it is possible to distinguish between a sudden change in the overhead line voltage and a ground fault.

<Processing of the driving device using overhead line current in the first embodiment>
Fig. 6 shows an operation flow when controlling switching element Q7 using current detection means 12. Fig. 6 is a flowchart showing an example of processing of the drive device when overhead line current is used in embodiment 1. Fig. 6 shows a method of detecting a current flowing in from the overhead line 1 using current detection means 12. When using the method of controlling the operating state of switching element Q7 using current detection means 12, the voltage detection means 13 can be omitted in the drive device 1S.

Here, by connecting the current detection means 12 between the overhead line 1 and the circuit breaker 11, it is possible to detect both a ground fault in the filter reactor 9 and a fault current caused by a failure in the power conversion device 6. For example, if a current detection means is connected between the filter reactor 9 and the power conversion device 6, it is possible to detect a fault current caused by a failure in the power conversion device 6, but it is not possible to detect a ground fault in the filter reactor 9.

As shown in FIG. 6, first, in step S21, the control logic unit 15 detects the overhead line current Is using the current detection means 12. Next, in step S22, the control logic unit 15 calculates the rate of change dIs/dt of the overhead line current Is detected in step S21.

Next, in step S23, the control logic unit 15 determines whether the rate of change dIs/dt calculated in step S22 is greater than, for example, 10 A/ms. If the rate of change dIs/dt calculated in step S22 is greater than 10 A/ms (step S23: Yes), the control logic unit 15 moves the process to step S24. On the other hand, if the rate of change dIs/dt is 10 A/ms or less (step S23: No), the control logic unit 15 returns the process to step S21.

In step S24, the control logic unit 15 causes the switching element Q7 to perform a chopping operation. Then, in step S25, the control logic unit 15 detects the overhead line current Is.

Next, in step S25, the control logic unit 15 determines whether the overhead line current Is detected in step S25 is, for example, greater than 1500 A. If the overhead line current Is detected in step S25 is greater than 1500 A (step S26: Yes), the control logic unit 15 proceeds to step S27, and if the overhead line current Is is 1500 A or less (step S26: No), the control logic unit 15 returns to step S21.

In step S27, the control logic unit 15 causes the switching element Q7 to perform a chopping operation. Then, the control logic unit 15 turns off the chopping operation of the switching element Q7. Then, in step S28, the control logic unit 15 opens the circuit breaker 11. When step S28 ends, the control logic unit 15 ends the processing of the drive device when the overhead line current in Example 1 is used.

As shown in Figure 4, when a sudden change in the overhead line voltage occurs and the overhead line voltage rises, the overhead line current Is begins to rise. This current change rate is detected, and when it exceeds a threshold, the switching element Q7 starts chopping operation. The current change rate is calculated by the control logic unit 15, and for example, the current difference between the overhead line current Is sampled at a constant period and the overhead line reference current Is0 is calculated, and this value is divided by the sampling period to obtain the change rate dIs/dt. Here, it is desirable to set the threshold value for the current change rate taking into account the inductance value of the overhead line 1. As described above, for example, when the current change rate becomes greater than 10 A/ms, the switching element Q7 starts chopping operation.

In FIG. 6, if the change in the overhead line current Is determined in step S23 to have a rate of change dIs/dt exceeding the threshold is a resonant current caused by a sudden change in the overhead line voltage, it can be reduced by the chopping operation of the switching element Q7 in step S24. On the other hand, if the change in the overhead line current Is determined in step S23 to have a rate of change dIs/dt exceeding the threshold is a fault current caused by a ground fault in the filter reactor 9, it cannot be suppressed by the chopping operation of the switching element Q7 in step S24, and the overhead line current Is increases.

As shown in step S25 of FIG. 6, the current in the overhead line 1 is detected by the current detection means 12 even after the chopping operation of the switching element Q7 starts in step S24. Then, as shown in step S26, a threshold value is set for the overhead line current Is of the overhead line 1, and when the threshold value is exceeded, the switching element Q7 is turned off. When the switching element Q7 is turned off, the fault current is reduced by the resistor 101, and the circuit breaker 11 is opened, thereby cutting off the fault current to 0 A.

In this way, when the rate of change dIs/dt of the current in the overhead line 1 becomes equal to or greater than the threshold value, the switching element Q7 is caused to start chopping, and when the overhead line current Is in the overhead line 1 after chopping becomes equal to or greater than the threshold value, the switching element Q7 is turned off and the circuit breaker 11 is opened. This makes it possible to suppress both the resonant current and the fault current. Compared to Patent Document 1, which starts the chopping operation of the switching element Q7 based on the current value of the overhead line 1, this embodiment starts the chopping operation according to the current change rate in the overhead line 1, so the delay time is short and the loss of the switching element Q7 associated with the chopping operation can be reduced.

In the driving device 1S of this embodiment, a semiconductor current reduction device 10 is connected between the filter reactor 9 and the circuit breaker 11 connected to the overhead line 1. This makes it possible to detect and suppress both the fault current caused by a ground fault in the filter reactor 9 and the resonant current caused by a sudden change in the overhead line voltage.

In addition, instead of calculating the rate of change dIs/dt of the overhead line current Is in step S22, the control logic unit 15 may calculate the deviation ΔIs between the reference current Is0 and the overhead line current Is, and may perform a threshold judgment of the deviation ΔIs in step S23. Alternatively, the control logic unit 15 may omit the calculation of the rate of change dIs/dt of the overhead line current Is in step S22, and may perform a threshold judgment of the overhead line current Is itself in step S23. Furthermore, the control logic unit 15 may detect the resonant current and the fault current using the rate of change dEs/dt or deviation ΔEs of the overhead line voltage Es, instead of the rate of change dIs/dt or deviation ΔIs of the overhead line current Is.

Figure 7 is a circuit diagram of the drive device in Example 2. Compared to the semiconductor current reducer 10 of the drive device 2S in Example 1, the semiconductor current reducer 10B in the drive device 2S in Example 2 has a switching element Q8, an anti-parallel diode D8 for the switching element Q8, and a resistor 102 added. The switching element Q8 and the resistor 102 are connected in series. The switching element Q8 and the resistor 102 are also connected in parallel to the switching element Q7 and the resistor 101.

When initially charging the capacitor 105 to drive the power conversion device 6, the switching elements Q7 and Q8 are turned off during the initial charging of the capacitor 105, and a charging current flows from the overhead line 1 to the capacitor 105 via the circuit breaker 11, the resistor 101, and the filter reactor 9. In other words, the resistor 101 acts as a charging resistor for the capacitor 105.

When the initial charging of capacitor 105 is completed, switching elements Q7 and Q8 are turned on. To suppress the resonant current, switching element Q7 is chopped while switching element Q8 is turned on, or to suppress the fault current, switching element Q7 is turned off while switching element Q8 is turned on. At this time, current flows through resistors 101 and 102, so the combined resistance of these becomes the parallel value of resistors 101 and 102.

As described above, in the semiconductor current reducer 10B shown in Example 2, the resistance value of the capacitor 105 during initial charging and the resistance value when the switching element Q7 is off can be switched. When the DC voltage of the overhead line 1 is, for example, 1500 V, the resistance value when charging the capacitor 105 is around 10 Ω to suppress the peak value of the charging current. On the other hand, the resistance value when the switching element Q7 is turned off is set to a few Ω to suppress the surge voltage.

In this way, the semiconductor current reducing device 10B of Example 2, which switches between resistors 101 and 102, can suppress the charging current of capacitor 105 and reduce the surge voltage when switching element Q7 is off.

The processing of the drive device when the overhead line voltage in Example 2 is used, and the processing of the drive device when the overhead line current in Example 2 is used are the same as the flowchart shown in FIG. 5 and the flowchart shown in FIG. 5, respectively.

Figure 8 is a circuit diagram of a drive device in Example 3. Drive device 3S in Example 3 differs from drive device 2S in Example 2 in that a secondary winding is provided in filter reactor 9 and a second power conversion device 14 is connected.

The second power conversion device 14 has the function of suppressing the noise current flowing through the overhead line 1. This noise current is on the order of several amperes, but when the switching element Q7 performs a chopping operation to suppress the resonant current, a ripple current of several tens of amperes may be superimposed on the overhead line 1. However, the second power conversion device 14 does not need to suppress this ripple current. Therefore, in order to reduce the power capacity of the second power conversion device 14, the control logic unit 15 stops the operation of the second power conversion device 14 during the chopping operation of the switching element Q7.

Prior to describing the fourth embodiment, it will be noted that the inductance of the filter reactor 9 can be reduced by combining a semiconductor current reducer (SHB) and an active filter (second power conversion device). The filter reactor 9 has the advantage of being compact with a reduced inductance value, which reduces weight and makes it easier to design the drive unit. However, the filter reactor 9 is required to satisfy the requirements of suppressing the rate of increase (time gradient) of the overhead line current when a fault current occurs, and suppressing return line current noise that flows in the current path from the overhead line to the drive unit and then to the return line, so there is a limit to how much the inductance value can be reduced.

Therefore, by using a semiconductor current reducer (SHB) to suppress the rate of increase (time gradient) of the overhead line current, and an active filter (second power conversion device) to suppress return current noise, the function of the filter reactor 9 can be supplemented, making it possible to reduce the inductance value of the filter reactor 9 to, for example, 4 mH or less, half the conventional value. In this way, in order to reduce the inductance of the filter reactor 9, a combination of a semiconductor current reducer (SHB) and an active filter (second power conversion device) is used in the drive unit.

9 is a circuit diagram of the drive device 4S in Example 4. Compared to the semiconductor current reducer device 10B of the drive device 3S in Example 3, the semiconductor current reducer device 10C of the drive device 4S in Example 4 has a switching element Q9, an anti-parallel diode D9 of the switching element Q9, and a resistor 103 added thereto.

The operation of the power conversion device 6 in this embodiment will be described. To drive the power conversion device 6, the capacitor 105 needs to be initially charged. During the initial charging of the capacitor 105, the switching elements Q7, Q8, and Q9 are turned off, and the circuit breaker 11 is closed. The charging current for the capacitor 105 flows from the overhead line 1 through the circuit breaker 11, the resistor 101, and the filter reactor 9. In other words, the resistor 101 acts as a charging resistor for the capacitor 105. The capacitor 105 is charged by this charging current, and the voltage of the capacitor 105 rises to the voltage of the overhead line 1.

When the initial charging of the capacitor 105 is completed, the switching elements Q7, Q8, and Q9 of the semiconductor current reducer 10C are turned on. When the power converter 6 starts operating, DC power is supplied to the power converter 6 from the overhead line 1 via the circuit breaker 11, the switching element Q7, and the filter reactor 9.

If a ground fault occurs in the filter reactor 9 or a failure occurs in the power conversion device 6, and it is detected that the rate of change dIs/dt of the overhead line current Is, the rate of change dEs/dt of the overhead line voltage Es, or the deviation ΔEs exceeds a threshold value, the chopping operation of the switching element Q7 is performed to suppress the fault current and the resonant current when the overhead line voltage suddenly changes.

During the chopping operation of switching element Q7, a potential fluctuation of the product of the overhead line current Is and the combined resistance of resistors 101, 102, and 103 appears on the primary side of filter reactor 9. This potential fluctuation is applied to second power conversion device 14 according to the coupling coefficient of the primary and secondary windings of filter reactor 9, and second power conversion device 14 outputs a current according to the applied voltage. Since second power conversion device 14 has the function of suppressing noise current flowing in overhead line 1, if it operates in response to the potential fluctuation caused by the chopping operation of switching element Q7 of semiconductor current reducer 10C, the function of suppressing noise current flowing in overhead line 1 will be impaired.

For this reason, in order to reduce the combined resistance of resistors 101, 102, and 103, the resistance value of resistor 103 is set to, for example, 1 Ω or less, and the potential fluctuation during the chopping operation of switching element Q7 is reduced, so that the operation of second power conversion device 14 continues even during the chopping operation of switching element Q7 of semiconductor current reduction device 10C, and the function of suppressing the noise current flowing through overhead line 1 is not impaired. If overhead line current Is increases even after the chopping operation of switching element Q7, or if the rate of change dEs/dt of overhead line voltage Es cannot be suppressed, switching element Q8 is left on, switching elements Q7 and Q9 are turned off, the fault current is reduced by resistors 101 and 102, and the current is then interrupted by circuit breaker 11.

<Processing of the driving device in the fourth embodiment>
Fig. 10 is a flowchart showing an example of processing of the drive device 4S when the overhead line voltage is used in the fourth embodiment. The processing of the drive device 4S when the overhead line voltage is used in the fourth embodiment is different from the flowchart of the first embodiment shown in Fig. 5 in that in step S16B following step S16, the control logic unit 15 turns off the switching element Q9 to perform a current reduction operation. When step S16B is completed, the control logic unit 15 commutates the fault current/resonant current to the resistors 101 and 102 to perform a current reduction operation, then opens the circuit breaker in step S17, turns off the second power conversion device 14 in step S18, and ends the processing of the drive device when the overhead line voltage is used in the fourth embodiment.

Fig. 11 is a flowchart showing an example of processing of the drive device 4S when the overhead line current is used in the fourth embodiment. The processing of the drive device 4S when the overhead line current is used in the fourth embodiment is different from the flowchart of the first embodiment shown in Fig. 6 in that in step S27B following step S27, the switching element Q9 is turned off to perform a current reduction operation. When step S27B is completed, the control logic unit 15 commutates the fault current/resonant current to the resistors 101 and 102 to perform a current reduction operation, then opens the circuit breaker in step S28 and turns off the second power conversion device 14 in step S29, thereby completing the processing of the drive device when the overhead line current is used in the fourth embodiment.

In this way, the semiconductor current reduction device 10C shown in Example 4 can switch between the resistance value during initial charging of the capacitor 105, the resistance value during chopping operation, and the resistance value during current reduction. This allows the second power conversion device 14 to continue operating even when the overhead line voltage suddenly changes, and allows the electric vehicle 100 to continue operating.

12 is a circuit diagram of the drive unit 5S in Example 5. The semiconductor current reducer 10D of the drive unit 5S in Example 5 is different from the semiconductor current reducer 10C of the drive unit 4S in Example 4 in that the resistor 101 functioning as a charging resistor and the resistor 102 functioning as a current reducing resistor are integrated into a resistor 104 for charging/current reducing.

The operation of the power conversion device 6 in this embodiment will be described. During initial charging of the capacitor 105 to drive the power conversion device 6, the switching elements Q7 and Q9 are turned off and the circuit breaker 11 is closed. The charging current for the capacitor 105 flows from the overhead line 1 through the circuit breaker 11, resistor 104, and filter reactor 9. When the initial charging of the capacitor 105 is completed, the switching elements Q7 and Q9 are turned on.

When suppressing the resonant current, switching element Q7 is chopped while switching element Q9 is kept on. After the chopping operation, switching element Q9 is turned off, and the current is reduced by resistor 104, and then the current is cut off by circuit breaker 11.

At this time, during chopping operation, current flows through resistors 104 and 103, and the combined resistance is the parallel value of resistors 104 and 103. As described above, the resistance value of resistor 103 is 1 Ω or less, so the operation of second power conversion device 14 is not hindered by potential fluctuations.

When the fault current is to be reduced, both switching elements Q7 and Q9 are turned off. At this time, the current flows through resistor 104 and is reduced.

Even when resistors 101 and 102 are integrated into resistor 104 as in this embodiment, by switching switching elements Q7 and Q9, it is possible to suppress the charging current when capacitor 105 is charged, suppress the resonant current when a fault current or a sudden change in overhead line voltage occurs, and suppress the voltage applied to second power conversion device 14 during chopping operation. Furthermore, according to this embodiment, by integrating resistors 101 and 102 into resistor 104, it is possible to reduce the size of semiconductor current reduction device 10D.

In the fourth embodiment, the resistance value of resistor 101 is set to about 10 Ω to suppress the peak value of the charging current, and the resistance value of resistor 102 is set to several Ω to suppress the surge voltage. In this embodiment, if the resistance value of resistor 104 is set to about 10 Ω like resistor 101, the surge voltage would destroy switching element Q7, so it is set to several Ω.

Furthermore, when the resistance value of resistor 104 is set to several ohms, the peak value of the charging current will be higher than when resistor 101 is used as the charging resistor as in Example 4. When the peak value of the charging current becomes high, it is necessary to prevent the substation circuit breaker from being tripped by the initial charging current of the filter capacitor (capacitor 105) depending on the length of the train. For this reason, measures such as staggering the charging timing for each car, rather than charging the filter capacitor at the same time for each car in the same train, are required to prevent the peak value of the charging current from tripping the substation circuit breaker.

The process flow of the driving device 5S of the fifth embodiment is the same as that of the fourth embodiment, and is the same as that of FIG. 10 when the overhead line voltage is used, and is the same as that of FIG. 11 when the overhead line current is used.

13 is a circuit diagram of a driving device 6S in Example 6. The driving device 6S in Example 6 is different from the driving device 5S in Example 5 in that the driving device 6S in Example 6 has a means for detecting the voltage of the secondary winding of the filter reactor 9.

The methods for detecting a ground fault in the filter reactor 9 or a short circuit fault in the inverter described in Examples 1 to 5 detect fluctuations in the overhead line voltage and overhead line current at a fixed sampling period, so it takes several times the sampling period to detect a fault. In the main circuit configurations according to Examples 1 to 5, the inductance of the filter reactor is reduced, so when a ground fault or short circuit fault occurs, the slope of the fault current is steep. For this reason, if it takes a long time to detect the fault current, the fault current is already large when it is detected, so the fault current cannot be suppressed, and there is a possibility that the substation will trip.

13 , the drive device 6S is provided with a voltage detection means 16 that detects the voltage of the secondary winding of the filter reactor 9. By providing the voltage detection means 16 in this manner, it is possible to quickly detect both a ground fault in the filter reactor 9 and a fault current due to a short-circuit fault in the power conversion device 6. For example, if a current detection means is connected between the filter reactor 9 and the power conversion device 6, it is possible to detect a fault current due to a short-circuit fault in the power conversion device 6, but it is not possible to detect a fault current due to a ground fault in the filter reactor 9.

By doing this, in this embodiment, compared to detection based on differential processing such as the rate of change dIs/dt of the overhead line current Is and the rate of change dEs/dt of the overhead line voltage Es, accidents are detected without differential processing, making it possible to quickly detect short circuit accidents and ground fault accidents and suppress accident currents and resonant currents.

<Processing of the driving device in the sixth embodiment>
FIG. 14 is a flowchart showing an example of processing by the driving device 6S in the case where the voltage of the secondary winding of the filter reactor in the sixth embodiment is used.

14 , first, in step S31, the control logic unit 15 detects a secondary voltage value (hereinafter referred to as VAFL) of the filter reactor 9 by the voltage detection means 16. Then, in step S32, the control logic unit 15 determines whether the VAFL detected in step S31 is greater than, for example, 200 V. If VAFL is greater than 200 V (step S32: Yes), the control logic unit 15 moves the process to step S33. On the other hand, if VAFL is equal to or less than 200 V (step S32: No), the control logic unit 15 returns the process to step S31.

In step S33, the control logic unit 15 causes the switching element Q7 to perform a chopping operation. Then, in step S34, the control logic unit 15 detects VAFL. Then, in step S35, the control logic unit 15 determines whether the VAFL detected in step S34 is greater than, for example, 200 V. If VAFL is greater than 200 V (step S35: Yes), the control logic unit 15 moves the process to step S36. On the other hand, if VAFL is 200 V or less (step S35: No), the control logic unit 15 returns the process to step S31.

In step S36, the control logic unit 15 turns off the switching element Q7. Then, in step S37, the control logic unit 15 turns off the switching element Q9 and performs a current reduction operation. In step S38 after the current reduction operation, the control logic unit 15 opens the circuit breaker 11 and cuts off the resonant current/fault current.

Next, in step S39, the control logic unit 15 turns off the second power conversion device 14. When step S39 ends, the control logic unit 15 ends the processing of the drive device when the voltage of the secondary winding of the filter reactor in Example 6 is used.

The driving device 6S may be equipped with the semiconductor current reducer 10, 10B, or 10C in the first to fourth embodiments instead of the semiconductor current reducer 10D. In the process flow of the driving device 6S when the semiconductor current reducer 10 or 10B is provided instead of the semiconductor current reducer 10D, step S37 is omitted from the process flow shown in Fig. 14. In the process flow of the driving device 6S when the semiconductor current reducer 10C is provided instead of the semiconductor current reducer 10D, the process flow is the same as the process flow shown in Fig. 14 .

Next, a seventh embodiment in which the operation of the active filter is stopped in order to avoid a surge current flowing into the active filter when the overhead line current suddenly changes, and then the operation of the active filter is promptly resumed will be described with reference to Figs. 15 and 16 .

First, a configuration of a driving device 7S for a railway vehicle (electric vehicle) in the seventh embodiment will be described. Fig. 15 is a diagram showing an example of the configuration of a driving device 7S for a railway vehicle (electric vehicle) in the seventh embodiment.

15 , the drive device 7S differs from the drive device 3S of the third embodiment in that it is provided with an AC switch 53 (ACSW) that separates the output terminal of the second power conversion device 14 (AF: active filter) from the secondary winding 52. When an overcurrent occurs in the overhead line current Is, the AC switch 53 is turned off to block the intrusion path of the surge.

When the semiconductor current reducer 10B is in normal operation and conducting current, it turns on both switching element Q7 (SHBTr1) and switching element Q8 (SHBTr2) and conducts the overhead line current via switching element Q7.

When a fault current occurs, the semiconductor current reducer 10B switches both switching element Q7 and switching element Q8 to the off state, thereby diverting the overhead line current to resistor 101. Because the overhead line current flows through resistor 101, the increase in the overhead line current stops and the fault current begins to decrease. After the overhead line current has attenuated to a level where the circuit breaker 11's capacity is sufficient to interrupt the current, the circuit breaker 11 is turned off, thereby interrupting the overhead line current.

The second power conversion device 14 detects the return current noise contained in the overhead line current using a current sensor (not shown), calculates the output required to cancel it, and performs a noise reduction operation by supplying an output based on the calculation result to a secondary winding 52 (FL2) provided in a filter reactor 9 (FL1) of the main circuit via an AC switch 53. The output of the second power conversion device 14 is injected into the path through which the overhead line current passes via the magnetic coupling between the filter reactor 9 and the secondary winding 52, thereby reducing the return current noise.

The path through which the overhead line current passes and the output terminal of the second power conversion device 14 are connected via magnetic coupling between the filter reactor 9 and the secondary winding 52. Therefore, when the overhead line current changes abruptly, the current passing through the filter reactor 9 also changes abruptly, causing a surge voltage/current to flow into the output terminal of the second power conversion device 14, which may damage the circuit of the second power conversion device 14. For this reason, a means for reducing the intrusion of surges into the second power conversion device 14 is required.

There are several possible means for suppressing surges. Possible measures on the side of the second power conversion device 14 include the following means. The first means is to increase the ratings of elements used in the second power conversion device 14 to enhance the withstand voltage and withstand current characteristics. The second means is to provide an AC switch 53 (ACSW) that separates the output terminal of the second power conversion device 14 from the secondary winding 52, as shown in Fig. 15 , and to cut off the intrusion path of the surge by turning off the AC switch 53 when an overcurrent occurs.

It is preferable that an active filter current reduction resistor 54 (AFDRe) is connected in parallel to the AC switch 53. By connecting the active filter current reduction resistor 54, when the overhead line current changes suddenly while the AC switch 53 is off, the voltage applied to both ends of the AC switch 53 can be suppressed, and the withstand voltage specification required for the AC switch 53 can be reduced.

The smaller the resistance value of the active filter current reduction resistor 54, the more the voltage applied to both ends of the AC switch 53 is reduced, but the current value flowing into the output terminal of the second power conversion device 14 increases, and the AF protection function of the AC switch 53 decreases. For this reason, the resistance value of the active filter current reduction resistor 54 must be determined taking into account both the overcurrent tolerance of the second power conversion device 14 and the overvoltage tolerance of the AC switch 53.

Since railway vehicle drive systems are high-current systems in which overhead line currents of the order of 1000 A flow even during normal operation, the overhead line current Is has a large time gradient (dIs/dt). For this reason, the first method described above is not practical because it results in a large increase in mass and cost due to an increase in the element rating of the second power conversion device 14.

In addition, the second means described above can protect the second power conversion device 14 from overcurrent while the AC switch 53 is off, but there is a problem in that it cannot reduce return current noise, which is the original function of the second power conversion device 14. In order to keep the intensity of return current noise below the interference threshold value for signaling equipment, the second power conversion device 14 basically needs to be operating when the current path from the current collector 7 to the return line is conducting, that is, when both the circuit breaker 11 and the switching element Q7 constituting the semiconductor current reduction device 10B are on. If it is unavoidable to temporarily stop the operation of the second power conversion device 14, it is necessary to resume the operation of the second power conversion device 14 within a time period that does not affect the signaling equipment.

On the other hand, as a surge suppression means on the main circuit side, the time gradient (dIs/dt) of the overhead line current Is can be reduced by the operating sequence of the switching elements constituting the semiconductor current reducer 10B. When a steep change in the overhead line current is detected, the current change can be suppressed by turning off switching element Q7 while switching element Q8 is on, and commutating the overhead line current to resistor 102. As a result, the current change in the filter reactor 9 is suppressed, and the intensity of the inrush voltage and current flowing into the second power conversion device 14 is also suppressed.

By chopping the switching element Q7, it is possible to artificially create a resistance value intermediate between the parallel combined resistance of resistors 101 and 102 and 0Ω. The resistance value of the destination of the overhead line current can be changed continuously, and fluctuations in the overhead line current when switching element Q7 is turned on can be suppressed. When switching element Q7 is turned on after the overhead line current is diverted to resistor 102, the resistance value of the destination changes instantaneously to 0Ω, causing a sudden change in current at the moment switching element Q7 is turned on, which can cause a surge to the second power conversion device 14. However, by changing the conduction rate of the chopping operation stepwise over time, the resistance value of the destination of the diversion can be changed continuously, making it possible to suppress surges without a sudden change in current.

<Control during sudden changes in overhead line current>
Next, a process of stopping the operation of the second power conversion device 14 in order to avoid a surge current flowing into the second power conversion device 14 when the overhead line current suddenly changes, and then quickly restarting the operation of the second power conversion device 14 in the seventh embodiment will be described with reference to Fig. 16. Fig. 16 is a diagram showing an example of a timing chart showing the control of each device constituting the drive device 7S in the seventh embodiment (when a sudden change occurs in the main circuit input current (overhead line current Is) during inverter operation of the drive device 7S). Note that t on the horizontal axis in the figure represents time.

16 , during steady power running operation (t10 to t11), the overhead line current Is>0, and the switching element Q7 (SHBTr1) and the switching element Q8 (SHBTr2) are both on. From t10 to t11, the second power conversion device 14 operates to reduce return current noise so as not to affect signaling devices, the AC switch 53 (ACSW) is on, and the AF control gain indicating the output of the second power conversion device 14 is 100%.

When a sudden change in the overhead line voltage occurs (t11), the overhead line current Is increases with a large time change (dIs/dt) (t11 to t12). When it is detected that the overhead line current Is has changed with a time gradient exceeding a predetermined threshold (t12), the AC switch 53 (ACSW) is turned off to cut off the inrush current path to the second power conversion device 14, and the AF control gain of the second power conversion device 14 is set to 0%, so that the second power conversion device 14 stops operating and is protected. At the same time, the switching element Q7 (SHBTr1) is turned off to commutate the overhead line current Is to the resistor 102. Here, the relationship of the resistance value is resistor 101>resistor 102, so the commutated overhead line current Is flows preferentially through resistor 102. Since the overhead line current Is flows through resistor 102, the time gradient of the overhead line current Is converges to a predetermined range.

When it is detected (t13) that the time gradient of the overhead line current Is has converged to a level within a range where the second power conversion device 14 will not be damaged even if the second power conversion device 14 is operated, the AC switch 53 (ACSW) is turned on. After t13, the AF control gain of the second power conversion device 14 is gradually increased from 0% and returned to 100%.

After a further time has elapsed from t13, when the time gradient of the overhead line current Is converges to a level within a range where the second power conversion device 14 will not be damaged even if the switching element Q7 (SHBTr1) is chopped (t14), the chopping operation of the switching element Q7 (SHBTr1) is performed (t14 to t15). After the chopping operation starts, the conduction rate of the switching element Q7 (SHBTr1) gradually increases and is returned to 100%, i.e., a steady on state.

When the switching element Q7 (SHBTr1) returns to the steady on state (t16), the drive device 7S has returned to the same state as t10, and returns to the normal power running state. The timing at which the switching element Q7 (SHBTr1) returns to the steady on state may be the same as the timing at which the AF output gain of the second power conversion device 14 rises to a value necessary to reduce return current noise so as not to affect the signal equipment.

16 , when it is detected (t13) that the time gradient (dIs/dt) of the overhead line current Is exceeds a predetermined threshold, the chopping operation is not performed immediately, but commutation to the resistor 102 is performed first. This is because, if the chopping operation is performed before the time gradient (dIs/dt) converges within a predetermined range, large amplitude current oscillations at the chopping frequency will flow as the overhead line current Is, which may damage the second power conversion device 14. By performing the chopping operation of the switching element Q7 (SHBTr1) after the time change of the overhead line current Is has sufficiently converged by resistive commutation, the switching element Q7 (SHBTr1) can be smoothly returned to a steady on state without damaging the second power conversion device 14.

According to this embodiment, when a sudden change in the overhead line current is detected, the semiconductor current reducer 10B (SHB) is activated and the second power converter 14 (AF) is stopped, and the time until the second power converter 14 resumes operation is not longer than the time when the signaling equipment does not malfunction, and it is possible to suppress the inflow of surge current into the second power converter 14 due to fluctuations in the overhead line current.

In the seventh embodiment, the chopping operation of the switching element Q7 (SHBTr1) is started after the AC switch 53 (ACSW) is turned on and the AF control gain starts to rise, but this is not limiting, and the AC switch 53 (ACSW) may be turned on and the AF control gain starts to rise after the chopping operation of the switching element Q7 (SHBTr1) starts. This case will be described as an eighth embodiment with reference to FIG. 17 .

FIG. 17 is a diagram showing an example of a timing chart showing the control of each device constituting the drive device 7S in Example 8 (when a sudden change occurs in the main circuit input current (overhead line current Is) during inverter operation of the drive device 7S). In Example 8, differences from Example 7 will be mainly described, and descriptions of commonalities with Example 7 will be omitted or simplified. The configuration of the drive device in Example 8 is the same as that of the drive device 7S in Example 7.

When a steep time gradient (dIs/dt) of the overhead line current Is occurs (t31) and it is detected that the time gradient of this overhead line current Is exceeds a predetermined threshold (t32), the AC switch 53 (ACSW) is turned off and the AF control gain of the second power conversion device 14 is set to 0%, thereby protecting the second power conversion device 14. At the same time, the switching element Q7 (SHBTr1) is turned off and the overhead line current Is is commutated to the resistor 102.

When the time gradient of the overhead line current Is does not converge to within a predetermined range in which the operation of the second power conversion device 14 can be resumed, but converges to a level within a range in which the chopping operation of the switching element Q7 (SHBTr1) does not affect the second power conversion device 14, the chopping operation of the switching element Q7 (SHBTr1) is started (t33). When the time gradient of the overhead line current Is converges to a level within a range in which the operation of the second power conversion device 14 is resumed without damaging the second power conversion device 14 (t34), the AC switch 53 (ACSW) is turned on, and the AF control gain is gradually returned toward 100%. When the AF control gain rises to 100% and the chopping operation of the switching element Q7 (SHBTr1) ends and the steady on state is reached (t35), the drive device 7S returns to the same state as t30.

The chopping operation of the switching element Q7 (SHBTr1) has the effect of continuously changing the resistance value seen from both ends of the semiconductor current reducer 10B (SHB) between the resistance value of the resistor that commutates the overhead line current Is by turning off the switching element Q7 (SHBTr1) and 0Ω. Therefore, during the chopping operation, a resistor is equivalently inserted at the connection position of the semiconductor current reducer 10B (SHB). In the region where the conduction rate of the switching element Q7 (SHBTr1) is high, the equivalent resistance value of the semiconductor current reducer 10B (SHB) decreases, but interference with the signal equipment can be prevented by setting the chopping frequency so that the period is shorter than the time element of the signal equipment. From the above, there is no problem in chopping the switching element Q7 (SHBTr1) before the second power conversion device 14 (AF) is turned on, as in this sequence.

As a modified example of the configuration method of the semiconductor current reducer in the second, third, seventh, and eighth embodiments, a configuration (second configuration) of a semiconductor current reducer 10I shown in Fig. 18 is considered. Fig. 18 is a diagram showing an example of the configuration of a drive unit 9S of a railway vehicle (electric car) in the ninth embodiment.

7, 8, and 15 (first configuration), the semiconductor current reducer 10I is different in the arrangement of the switching element Q8 (SHBTr2) connected in parallel with the switching element Q7 (SHBTr1) and the two resistors. In the first configuration, the switching of the combined resistance of the resistors 101 and 102 by the switching element Q8 (SHBTr2) is performed by connecting the resistors in parallel, whereas in the second configuration, the resistance value is switched by shorting both ends of one resistor 101a of the two resistors 101a and 102a connected in series.

In the embodiment of FIG. 18 as well, by operating each element according to the timing charts (see FIGS. 16 and 17 ) shown in the seventh and eighth embodiments, the same effects as those described in the seventh and eighth embodiments can be obtained.

By applying the drive units 1S to 7S, and 9S of the above-mentioned Examples 1 to 9 to an electric vehicle, it is possible to suppress fault currents and resonance currents in the electric vehicle. In addition, the same effects can be obtained when the drive units 1S to 7S, and 9S of the above-mentioned Examples 1 to 9 are applied to vehicles such as automobiles and construction machines, and elevator devices.

The present invention is not limited to the above-described embodiments, but includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described. It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, replace, integrate, or distribute other configurations to part of the configuration of each embodiment. Furthermore, each process shown in the embodiments may be appropriately distributed or integrated based on processing efficiency or implementation efficiency.

1S, 2S, 3S, 4S, 5S, 6S, 7S, 9S: Drive unit, 1: Overhead line, 2: Rail, 5: Motor, 6: Power converter, 7: Current collector, 8: Vehicle, 9: Filter reactor, 10, 10B, 10C, 10D, 10I: Semiconductor current reduction device, 11: Circuit breaker, 12: Current detection means, 13: Voltage detection means, 14: Second power converter, 15: Control logic unit, 16: Voltage detection means, 52: Secondary winding, 53: AC switch, 54: Active filter current reduction resistor, 100: Electric vehicle, 101, 101a, 102, 102a, 103, 104: Resistor, 105: Capacitor

Claims (17)

An inverter that converts DC power supplied from the overhead line into AC power;
A reactor connected to the overhead line side of the inverter;
A semiconductor element connected to the overhead line side of the reactor;
a resistor connected in parallel to the semiconductor element;
A circuit breaker connected to the overhead line side of the semiconductor device and cutting off the DC power;
A voltage detection means for detecting an overhead line voltage of the overhead line;
a current detection means connected to the overhead line side of the circuit breaker and detecting a current flowing from the overhead line to the inverter;
A control unit performs a first control for switching-controlling the semiconductor element to perform a chopping operation based on the overhead line voltage detected by the voltage detection means or the current detected by the current detection means, and a second control for opening the circuit breaker to cut off the DC power after controlling the semiconductor element to be off,
The control unit is
when it is determined that a voltage difference obtained by subtracting a reference voltage of the overhead line voltage from the overhead line voltage detected by the voltage detection means is greater than a first threshold value , or when it is determined that a rate of change of the current detected by the current detection means is greater than a second threshold value, it is determined that an LC resonant circuit is formed by the reactor and a capacitor for driving the inverter, and a resonant current flows from the overhead line to the inverter, and the first control is performed;
when it is determined that the voltage difference is equal to or less than a third threshold value , or when it is determined that the current is greater than a fourth threshold value , it determines that a fault current has occurred flowing from the overhead line to the inverter due to a ground fault occurring between the reactor and the inverter or a failure of the inverter, and performs the second control. The power conversion device according to claim 1 , wherein the voltage detection means is connected to the overhead line side of the circuit breaker. a circuit connected in parallel to the semiconductor element and including a second semiconductor element and a second resistor connected in series;
The control unit is
The power conversion device according to any one of claims 1 to 2 , characterized in that the first control and the second control are performed in a state in which the second semiconductor element is controlled to be on. The reactor is provided with a secondary winding, and a second power conversion device is connected to the secondary winding to suppress a noise current flowing through the overhead line.
Operate the second power conversion device when suppressing a noise current flowing through the overhead line;
The power conversion device according to any one of claims 1 to 3 , characterized in that, during the first control, an operation of the second power conversion device is stopped. The reactor is provided with a secondary winding, and a second power conversion device is connected to the secondary winding to suppress a noise current flowing through the overhead line.
Operate the second power conversion device when suppressing a noise current flowing through the overhead line;
During the first control, a potential fluctuation appearing in a primary winding of the reactor in response to a chopping operation of the semiconductor element is suppressed, thereby continuing the operation of the second power conversion device ;
During the second control, the operation of the second power conversion device is stopped.
The power conversion device according to any one of claims 1 to 2 . a circuit connected in parallel to the semiconductor element and including a second semiconductor element and a second resistor connected in series; and a circuit connected in parallel to the semiconductor element and including a third semiconductor element and a third resistor connected in series,
The control unit is
performing the first control in a state in which the second semiconductor element and the third semiconductor element are controlled to be on;
The power conversion device according to claim 5 , wherein the second control is performed in a state in which the second semiconductor element is controlled to be on and the third semiconductor element is controlled to be off. The power conversion device according to claim 6 , wherein a resistance value of the third resistor is smaller than each of the resistance values of the resistor and the second resistor. a circuit connected in parallel to the semiconductor element and including a second semiconductor element and a second resistor connected in series;
The control unit is
The power conversion device according to claim 5 , wherein the first control is performed in a state in which the second semiconductor element is controlled to be on, and the second control is performed in a state in which the second semiconductor element is controlled to be off. the resistance value of the resistor is smaller than a predetermined charging resistance value when initially charging a capacitor that is connected between the overhead line voltage side and the negative voltage side of the inverter to drive the inverter and that forms a filter circuit together with the reactor to reduce noise current flowing out to the overhead line;
The power conversion device according to claim 8 , wherein the resistance value of the second resistor is smaller than the resistance value of the resistor. Further, a secondary voltage detection means for detecting a voltage of the secondary winding is provided.
The control unit is
The power conversion device according to any one of claims 5 to 9 , characterized in that the first control and the second control are performed based on the voltage detected by the secondary side voltage detection means. The power conversion device according to any one of claims 1 to 10 , characterized in that a switching frequency in the chopping operation of the semiconductor element is a multiple of a power supply frequency of a commercial power supply that generates the DC power. The reactor is provided with a secondary winding, and a second power conversion device is connected to the secondary winding to suppress a noise current flowing through the overhead line,
Operate the second power conversion device when suppressing a noise current flowing through the overhead line;
When the current changes with a time gradient exceeding a predetermined threshold during operation of the inverter, the semiconductor element is turned off and the second power conversion device is turned off;
The power conversion device according to any one of claims 1 to 2, characterized in that when the time gradient of the current converges to within a predetermined range, the semiconductor element is switched to a steady on-state after starting operation of the second power conversion device from an off-state and a stopped state of the second power conversion device. 13. The power conversion device according to claim 12, wherein, when the time gradient of the current converges within a predetermined range, after starting operation of the second power conversion device from a state in which the semiconductor element is off and a state in which the second power conversion device is stopped, a chopping operation is performed in which a conduction rate of the semiconductor element is increased stepwise over time, and then the semiconductor element is brought into a steady on state. 13. The power conversion device according to claim 12, wherein, when the time gradient of the current converges to within a predetermined range, a chopping operation is started in which a conduction rate of the semiconductor element is increased by changing it stepwise over time from an off state of the semiconductor element and a stopped state of the second power conversion device, and then the operation of the second power conversion device is started and the semiconductor element is brought into a steady on state. A power conversion device as described in any one of claims 12 to 14, characterized in that after operation of the second power conversion device is started, the semiconductor element is put into a steady on state after the output of the second power conversion device rises from 0 % to 100 % . A power conversion device as described in any one of claims 13 to 14, characterized in that the chopping operation of the semiconductor element is started at a timing when the time gradient of the current converges to a range in which the second power conversion device is not damaged even if the semiconductor element is subjected to a chopping operation in which the conduction rate is gradually changed over time and increased . A current control method in a power conversion device, comprising:
The power conversion device is
An inverter that converts DC power supplied from the overhead line into AC power;
A reactor connected to the overhead line side of the inverter;
A semiconductor element connected to the overhead line side of the reactor;
a resistor connected in parallel to the semiconductor element;
A circuit breaker connected to the overhead line side of the semiconductor device and cutting off the DC power;
A voltage detection means for detecting an overhead line voltage of the overhead line;
a current detection means connected to the overhead line side of the circuit breaker and detecting a current flowing from the overhead line to the inverter;
A control unit and
The control unit:
when it is determined that a voltage difference obtained by subtracting a reference voltage of the overhead line voltage from the overhead line voltage detected by the voltage detection means is greater than a first threshold value , or when it is determined that a rate of change of the current detected by the current detection means is greater than a second threshold value , a first control is performed in which an LC resonant circuit is formed by the reactor and a capacitor for driving the inverter, and a resonant current flows from the overhead line to the inverter, and a first control is performed in which the semiconductor element is switched and controlled to perform a chopping operation;
a second control is performed in which, when it is determined that the voltage difference is equal to or less than a third threshold value , or when it is determined that the current is greater than a fourth threshold value , a second control is performed in which the semiconductor element is turned off and then the circuit breaker is opened to cut off the DC power, assuming that a ground fault has occurred between the reactor and the inverter or a malfunction of the inverter has caused a fault current to flow from the overhead line to the inverter.

Images