JP7618511B2 - Power conversion device and power conversion method - Google Patents

Description

The present invention relates to a power conversion device and a power conversion method for converting power between input and output.

To reduce global energy consumption, there is a demand for high efficiency in power conversion devices that use semiconductor switching elements, such as inverters that drive motors, converters that supply power to inverters, and charging/discharging devices for electric vehicles. These power conversion devices are sometimes configured with multiple power conversion units equipped with switching elements connected in parallel.

For example, Patent Document 1 states, "When IGBT modules are connected in parallel, temperature variations occur in the IGBT chips due to variations in characteristics and structure, and limiting the temperature to the absolute maximum temperature would result in a large device and increased costs. A temperature detector is provided in each module with an embedded temperature detection sensor, and the magnitude of the temperature difference is determined by a comparator. The turn-on timing of the hotter module is delayed by an integrating circuit of resistors and capacitors, thereby lowering the temperature."

JP 2009-159662 A

Generally, a power conversion unit has switching elements called upper and lower arms. The technology described in Patent Document 1 is capable of suppressing temperature imbalance between parallel switching elements. However, there is an issue that the accuracy of detecting the temperature difference between power conversion units is low because there is little temperature imbalance between parallel-connected power conversion units when outputting AC current.

Given the above situation, there was a demand for a method that could detect the temperature difference between power conversion units connected in parallel with high accuracy.

In order to solve the above problem, a power conversion device according to one aspect of the present invention is a power conversion device that includes a plurality of parallel-connected power conversion units, each of which has a first switching element and a second switching element connected in series; a temperature sensor that detects the internal temperature of each power conversion unit; and a signal generation unit that generates an on/off command signal for the control electrodes of the first switching element and the second switching element for each power conversion unit according to the detection result of the temperature sensor, and the signal generation unit uses the temperature sensor to detect the temperature of each power conversion unit when the power conversion device outputs a direct current.

According to at least one aspect of the present invention, a power conversion device detects the temperatures of power conversion units connected in parallel when outputting a direct current, thereby making it possible to detect a temperature difference between the power conversion units with high accuracy.
Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments.

1 is a diagram showing an example of an overall configuration of an elevator system according to an embodiment of the present invention. FIG. 1 is a configuration diagram showing an example of a conventional power conversion device (inverter system) and its drive circuit. 10 is a timing chart showing an example of waveforms of signals measured at each portion when there is no turn operation delay in a switching element between power conversion units connected in parallel. 11 is a timing chart showing an example of waveforms of signals measured at each portion when there is a turn-on delay time variation in switching elements between power conversion units connected in parallel. 10 is a timing chart showing an example of waveforms of signals measured at each portion when there is a variation in turn-off delay time between switching elements in power conversion units connected in parallel; FIG. 2 is a diagram showing an example of speed characteristics with respect to time per operation period of the elevator system according to the embodiment of the present invention. 1 is a configuration diagram showing an example of a power conversion device (inverter system) and its drive circuit according to an embodiment of the present invention. 11 is a diagram showing an example of a direct current output to a motor by a three-phase inverter system during a startup compensation period. FIG. 4 is a graph showing characteristics of detected temperature versus output current of an inverter system; 5 is a flowchart showing an example of a procedure for a process of reducing a temperature difference between power conversion units connected in parallel according to an embodiment of the present invention.

Below, examples of embodiments of the present invention will be described with reference to the accompanying drawings. In this specification and the accompanying drawings, components having substantially the same functions or configurations are designated by the same reference numerals and duplicated descriptions will be omitted.

Power conversion devices can convert DC power to AC power or vice versa by the switching operation of semiconductor elements, and are used in a wide range of fields, including elevators, railways, and automobiles. There is a demand for higher output density in inverter devices, one example of a power conversion device, and power conversion devices are becoming smaller and lighter. As power conversion units (part of a power conversion device), which integrate components such as power semiconductor modules equipped with power semiconductor elements, capacitors, and bus bars, become smaller, there is a growing need to make the drive circuits for driving the power semiconductor elements more compact and less expensive.

In addition, by installing multiple power conversion units that integrate components such as power semiconductor modules, capacitors, bus bars, and gate circuits, the cost of the power conversion device can be reduced by standardizing components and improving output capacity. By increasing the number of power conversion units connected in parallel, it is possible to increase the capacity of the power conversion device.

When power semiconductor modules are connected in parallel, the power semiconductor elements have inherent characteristic variations, such as their turn-on delay time and turn-off delay time, which causes an imbalance in the current values flowing through each power semiconductor element. This causes current to concentrate in some power semiconductor elements, increasing switching losses and conduction losses and causing temperature imbalances.

Conventionally, when power semiconductor elements, i.e. power conversion units, are connected in parallel, it was necessary to take current imbalance into consideration and design the current value to be smaller than the rated current of each power semiconductor element. As a result, it was not possible to make the most of the performance of the power semiconductor elements.

One method for detecting current imbalance is to measure the current of each power semiconductor element using a current sensor, but this requires the same number of current sensors as the number of power semiconductor elements. This results in an increase in cost by the number of additional current sensors. A method is known in which a temperature imbalance occurs when the currents of the power semiconductor elements become unbalanced, and instead of current sensors, a temperature sensor, which is less expensive than a current sensor, is used. However, in elevator systems, DC current output and AC current output are switched depending on the operating state, so the detection result changes depending on the timing of temperature detection. For this reason, a method for detecting temperature is an issue. Below, we will explain a power conversion device according to one embodiment of the present invention, in which a temperature sensor is provided in the power conversion unit.

<One embodiment>
Fig. 1 is a diagram showing an example of the overall configuration of an elevator system according to an embodiment of the present invention. In the illustrated elevator system 1, AC power supplied from a system 2 is input via a filter circuit 3 to a three-phase converter system 10 in which a plurality of power conversion units 12, 13 are connected in parallel. The AC power input to the converter system 10 is converted from AC to DC via the power conversion units 12, 13 in the converter system 10. Then, a three-phase inverter system 11 in which a plurality of power conversion units 14, 15 are connected in parallel drives a motor 5 via a filter circuit 4. The filter circuits 3, 4 remove harmonic components from the input sine wave (square wave).

The load on the motor 5 is an elevator car 7 connected to a rope 6, and a weight 8 to balance the car 7. The power supplied to the motor 5 is consumed to wind up the rope 6 and raise and lower the elevator car 6.

The converter system 10 and the inverter system 11 are controlled by a control circuit 9. The control circuit 9 controls the on/off of the switching elements in the power conversion units 14 and 15 to control the current output to the load.

[Configuration of a conventional power conversion device]
FIG. 2 is a configuration diagram showing an example of a conventional power conversion device and its drive circuit. To prevent the diagram from becoming complicated, only one phase of a bus is shown, and the other phases are omitted. As shown in FIG. 2, in an inverter system 100 which is a power conversion device, power conversion units 14 and 15 are connected in parallel. The input sides of the power conversion units 14 and 15 are connected in parallel to a DC power source 102 (corresponding to the converter system 10), and the output sides are connected to a resistive load 104 and an inductive load 105 of the inverter system 100. The resistive load 104 and the inductive load 105 are provided as output loads. A current sensor 106 is attached to the wiring between the output end of the inverter system 100 and the load.

The power conversion unit 14 includes a capacitor 21, an upper arm gate circuit 22, a lower arm gate circuit 23, an upper arm switching element 24, a lower arm switching element 25, an upper arm switching freewheel diode 26, and a lower arm switching freewheel diode 27. The upper arm switching element 24 and the lower arm switching element 25 are connected in anti-parallel to the upper arm switching freewheel diode 26 and the lower arm switching freewheel diode 27, respectively. The switching leg consisting of the upper arm switching element 24 and the lower arm switching element 25 connected in series is connected in parallel to the capacitor 21.

The connection midpoint between the upper arm switching element 24 and the lower arm switching element 25 is connected to the output terminal T1 via a resistive load 28 and an inductive load 29 connected in series. The output terminals of the upper arm gate circuit 22 and the lower arm gate circuit 23 are connected to the gate terminals (control electrodes) of the upper arm switching element 24 and the lower arm switching element 25, respectively.

The power conversion unit 15 includes a capacitor 31, an upper arm gate circuit 32, a lower arm gate circuit 33, an upper arm switching element 34, a lower arm switching element 35, an upper arm switching freewheel diode 36, and a lower arm switching freewheel diode 37. The upper arm switching element 34 and the lower arm switching element 35 are connected in anti-parallel to the upper arm switching freewheel diode 36 and the lower arm switching freewheel diode 37, respectively. The switching leg consisting of the upper arm switching element 34 and the lower arm switching element 35 connected in series is connected in parallel to the capacitor 31.

The connection midpoint between the upper arm switching element 34 and the lower arm switching element 35 is connected to the output terminal T2 via a resistive load 38 and an inductive load 39 connected in series. The output terminals of the upper arm gate circuit 32 and the lower arm gate circuit 33 are connected to the gate terminals (control electrodes) of the upper arm switching element 34 and the lower arm switching element 35, respectively.

In the following description, the upper arm switching element 24, the lower arm switching element 25, the upper arm switching element 34, and the lower arm switching element 35 may be abbreviated to "switching elements." Furthermore, the upper arm gate circuit 22, the lower arm gate circuit 23, the upper arm gate circuit 32, and the lower arm gate circuit 33 may be abbreviated to "gate circuits."

The switching elements that make up the power conversion units 14 and 15 are, for example, IGBTs (insulated gate bipolar transistors) and MOSFETs (metal oxide semiconductors). The same is true for the switching elements of the power conversion units 12 and 13.

One end of the capacitor 21 of the power conversion unit 14 is connected to one electrode (e.g., positive electrode) of the DC power supply 102, and the other end of the capacitor 21 is connected to the other electrode (e.g., negative electrode) of the DC power supply 102. The other electrode of the DC power supply 102 is connected to the ground 103. The same is true for the capacitor 31 of the power conversion unit 15. The output terminals T1 and T2 are connected to the output terminal T3 (load side) via the resistive load 104 and the inductive load 105. A current sensor 106 that detects the output current is connected to the wiring that connects the resistive load 104 and the inductive load 105 to the output terminal T3.

If the inductance of the inductive load 105 of the inverter system 100 can be substituted by the inductance of the wiring, the inductive load 105 may be omitted. Also, if the load connected to the output terminal T3 has a sufficiently large inductance, such as the motor 5, or has characteristics that can be regarded as a current source, the inductive load 105 may be omitted.

The control circuit section 9 shown in FIG. 1 controls the on/off of the switching elements 24, 25, 34, and 35 included in the power conversion units 14 and 15, and controls the output current Itotal detected by the current sensor 106. The output current Itotal is the sum of the output current I1 of the power conversion unit 14 and the output current I2 of the power conversion unit 15. The control circuit section 9 controls the on/off of each switching element 24, 25, 34, and 35 based on the output current Itotal detected using the current sensor 106. The power conversion units 14 and 15 are provided with gate circuits 22, 23, 32, and 33 that supply gate signals to each of the switching elements 24, 25, 34, and 35. The control circuit section 9 outputs a control command to the gate circuit corresponding to each of the switching elements 24, 25, 34, and 35, and controls the switching operation (on/off) of the switching elements 24, 25, 34, and 35.

The control circuit unit 9 is a controller composed of, for example, a microcomputer. The control circuit unit 9 includes an analog/digital (A/D) conversion circuit 9a that converts the output current Itotal detected by the current sensor 106 into a digital signal, a processor 9b, and a memory 9c. The processor 9b is a processing device such as a CPU (Central Processing Unit). Instead of the CPU, an MPU (Micro-Processing Unit) may be used as the processing device. The memory 9c is a storage device such as a semiconductor memory in which program code (control program) of software that realizes each function according to this embodiment is stored. The control circuit unit 9 includes a network interface (not shown) and receives a target value of the output current (load current) from, for example, an ECU (Electronic Control Unit) of the controlled system. The processor 9b reads out and executes the control program from the memory 9c, and outputs a control command (input signal 101) to the gate circuit corresponding to each switching element 24, 25, 34, 35 based on the current detection value of the current sensor 106 input from the A/D conversion circuit 9a and the target value.

The control circuit unit 9 outputs an input signal 101 as a control command, and the input signal 101 is input to the gate circuits 22, 23, 32, and 33. The gate circuits 22, 23, 32, and 33 generate gate signals (gate voltage pulses) for driving the switching elements 24, 25, 34, and 35 based on the input signal 101, and input the gate signals to the gate terminals of the upper arm switching elements 24 and 34 and the lower arm switching elements 25 and 35. The gate signals are signals (on/off command signals) that command the switching elements to turn on/off.

When the gate signal switches from high to low (turns on), the upper arm switching elements 24, 34 and the lower arm switching elements 25, 35 are turned on, with electrical continuity between the source terminals and drain terminals. Conversely, when the gate signal switches from low to high (turns off), the upper arm switching elements 24, 34 and the lower arm switching elements 25, 35 are turned off, with no electrical continuity between the source terminals and drain terminals.

[Operation waveform when there is no variation in turn operation delay time]
3 is a timing chart showing an example of the waveform of a signal measured at each part when there is no variation in turn operation delay time of the switching elements between the parallel-connected power conversion units 14 and 15. The horizontal axis of FIG. 3 indicates time [s]. The vertical axis of FIG. 3 indicates, from the top, the gate signal of the power conversion unit 14, the gate signal of the power conversion unit 15, the output voltage of the power conversion unit 14, the output voltage of the power conversion unit 15, the output current of the power conversion unit 14, the output current of the power conversion unit 15, the temperature of the power conversion unit 14, and the temperature of the power conversion unit 15. Note that in this specification, the inductive load 105 and the inductance on the load side are sufficiently large, and the current Itotal of the inductive load 105 can be considered constant. Also, the voltage applied to the capacitor 21 and the capacitor 31 becomes equal to the voltage of the DC power source 102.

When gate signals with the same pulse waveform are input to the switching elements 24, 25, 34, and 35 of the power conversion units 14 and 15, if there is no variation in the delay times of these switching elements, the turn-on delay times Ton1 and Ton2 of the output voltages of the power conversion units 14 and 15 are equal. Similarly, the turn-off delay times Toff1 and Toff2 are also equal. As a result, the output currents of the power conversion units 14 and 15 are equal. The temperatures of the power conversion units 14 and 15 are also equal.

[Operation waveform when turn-on delay time varies]
4 is a timing chart showing an example of the waveforms of signals measured at various points when there is a turn-on delay time variation in the switching elements between the parallel-connected power conversion units 14 and 15. The relationship between the horizontal and vertical axes in FIG. 4 is the same as that in FIG.

When gate signals with the same pulse waveform are input to the switching elements 24, 25, 34, and 35 of the power conversion units 14 and 15, there is variation in the turn-on delay times Ton1 and Ton2 of these switching elements (Ton1<Ton2), so the pulse width of the output voltage of the power conversion unit 15 is narrower than that of the power conversion unit 14. As a result, the output current of the power conversion unit 15 is smaller, and the output current of the power conversion unit 14 is larger than that of the power conversion unit 15. This causes the temperature of the power conversion unit 14 to be higher than that of the power conversion unit 15.

[Operation waveform when turn-off delay time varies]
5 is a timing chart showing an example of the waveforms of signals measured at various points when there is a variation in turn-off delay time of the switching elements between the parallel-connected power conversion units 14 and 15. The relationship between the horizontal and vertical axes in FIG. 5 is the same as that in FIG.

When gate signals with the same pulse waveform are input to the switching elements 24, 25, 34, and 35 of the power conversion units 14 and 15, the turn-off delay times Toff1 and Toff2 of these switching elements vary (Toff1<Toff2), so the pulse width of the output voltage of the power conversion unit 15 becomes wider than that of the power conversion unit 14. As a result, the output current of the power conversion unit 15 becomes larger, and the output current of the power conversion unit 14 becomes smaller than that of the power conversion unit 15. As a result, the temperature of the power conversion unit 14 becomes lower than that of the power conversion unit 15.

When the output currents between the parallel-connected power conversion units 14 and 15 become unbalanced, the currents concentrate in some of the switching elements, increasing the switching losses and conduction losses, and causing an imbalance in the temperatures of the switching elements (between the power conversion units 14 and 15).

Therefore, the challenge is to develop a method for detecting an imbalance in the output current between the power conversion units 14 and 15 that is less expensive than the method using the current sensor 106 and that is accurate even when a temperature sensor is used.

[Elevator system speed characteristics]
Fig. 6 is a diagram showing an example of speed characteristics with respect to time per operation period of the elevator system 1. The horizontal axis of Fig. 6 represents time [s], and the vertical axis represents speed [m/s]. As shown in the figure, the elevator system 1 includes a start-up compensation period 150, an acceleration period 151, a constant speed period 152, and a deceleration period 153 in one operation period.

During the startup compensation period 150, the elevator system 1 fixes the motor 5 and causes the motor 5 to generate torque by passing a direct current. At this stage, the motor 5 is still stopped and the car 7 does not move. During the acceleration period 151, the elevator system 1 outputs an alternating current from the power conversion device, and by increasing the frequency of the output current, the rotational speed of the motor 5 is increased, accelerating the car 6. During the constant speed period 152, the elevator system 1 keeps the frequency of the output current constant, thereby keeping the rotational speed of the motor 5 constant. During the deceleration period 153, the elevator system 1 reduces the frequency of the output current, thereby slowing the rotational speed of the motor 5 and decelerating the car 6.

Between the parallel-connected power conversion units 14, 15, there are resistive loads 28, 38 with a resistance component and inductive loads 29, 39 with an inductance component. When DC current is output, the load has no inductance component and only a resistance component, so the cross current flowing between the parallel-connected power conversion units 14, 15 increases, and the imbalance of the output currents of the power conversion units 14, 15 becomes maximum. Here, the greater the imbalance of the output currents of the power conversion units 14, 15, the greater the temperature difference (temperature imbalance) between the power conversion units 14, 15, and the more noticeable the temperature difference becomes.

Therefore, a significant temperature difference occurs between the power conversion units 14, 15 during the startup compensation period 150 when DC current is output, compared to the acceleration period 151, the constant speed period 152, and the deceleration period 153 when AC current is output. Therefore, during the startup compensation period 150, the temperature difference between the power conversion units 14, 15 can be detected with high accuracy. Therefore, by detecting the temperature difference between the power conversion units 14, 15 during the startup compensation period 150 when a cross current is output, the imbalance in the output current between the power conversion units 14, 15 can be detected with high accuracy.

[Configuration of a power conversion device according to an embodiment]
Next, a power conversion device and a drive circuit thereof according to an embodiment of the present invention will be described with reference to FIG.

Figure 7 is a configuration diagram showing an example of a power conversion device and its drive circuit according to one embodiment of the present invention. The inverter system 11, which is a power conversion device, is the same as the conventional inverter system 100 (Figure 2) in that it includes power conversion units 14 and 15, but the control signals (gate voltage pulse widths) supplied to the gate terminals of the gate circuits 22 to 33 are different.

As shown in FIG. 7, the input side of the power conversion units 14, 15 is connected in parallel to the DC power supply 102, and the output side is connected in parallel to the resistive load 104 and the inductive load 105 of the inverter system 11. A current sensor 106 is attached to the wiring on the output side of the inverter system 11. The internal configuration of the power conversion units 14, 15 is the same as the configuration shown in FIG. 2, so the following description will focus on the differences.

In the power conversion unit 14, a temperature sensor 41 is disposed near the upper arm switching element 24 and the lower arm switching element 25. The distance between the upper arm switching element 24 and the lower arm switching element 25 and the temperature sensor 41 is designed to be an appropriate distance for measuring the temperature of the switching elements 24 and 25 through experiments, etc. In addition, in the power conversion unit 15, a temperature sensor 42 is disposed near the upper arm switching element 34 and the lower arm switching element 35. The temperature sensor 41 detects the temperature of the switching elements 24 and 25 of the power conversion unit 14, i.e., the temperature inside the power conversion unit 14, and the temperature sensor 41 detects the switching elements 34 and 35 of the power conversion unit 15, i.e., the temperature inside the power conversion unit 15. The detected temperature information is input to the temperature accumulation unit 121.

The control circuit unit 9 includes a signal generating unit 120 that generates a control signal to be supplied to the gate circuits 22, 23, 32, and 33. The signal generating unit 120 includes a temperature storage unit 121 and an on/off time adjustment unit 122. The temperature storage unit 121 is composed of a processor 9b and a memory 9c, and stores temperature information measured by the temperature sensors 41 and 42. The temperature information stored in the temperature storage unit 121 and the input signal 101 are input to the on/off time adjustment unit 122. The on/off time adjustment unit 122 adjusts the pulse width of the input signal 101 (gate voltage pulse) based on the temperature information and the input signal 101, and supplies the adjusted input signal 101 to each gate circuit 22, 23, 32, and 33 as an on/off command signal. The input signal 101 may be input to the on/off time adjustment unit 122 via the temperature storage unit 121.

Figure 8 shows an example of the DC current output by the three-phase inverter system 11 to the motor 5 during the startup compensation period 150. The phase difference of each phase with respect to the reference axis is determined by the position of the motor 5 (position of the rotating shaft). The motor position during startup compensation is the motor position when the motor 5 stopped in the previous operation mode, and the motor position is irregular. Therefore, the output current of the power conversion units 14, 15 becomes irregular during the startup compensation period 150.

[Temperature characteristics for output current]
Fig. 9 is a graph showing the characteristic (rate of change) of the detected temperature versus the output current of the inverter system 11. In Fig. 9, the horizontal axis represents the magnitude (absolute value) [A] of the output current Itotal of the power conversion device (inverter system 11), and the vertical axis represents the temperature difference ΔT [°C] between the parallel-connected power conversion units 14 and 15.

Hereinafter, in this specification, the temperature characteristic of the inverter system 11 with respect to the output current is referred to as the rate of change. During elevator operation, DC current is output only during the startup compensation period 150. When DC current is output, the imbalance of the output current is greatest, so the temperature difference can be detected with high accuracy. For this reason, it is desirable to detect the temperature difference during startup compensation when DC current is output. However, as explained in FIG. 8, when DC current is output, a different DC output current is obtained each time it is detected depending on the motor position (position of the rotating shaft).

When comparing the temperature difference between the power conversion units 14, 15, it is necessary to compare them using the same DC output current, but because the DC output current is irregular depending on the motor position, it is difficult to compare the temperature difference using the same DC output current. Therefore, the temperature of the power conversion units 14, 15 is detected multiple times and temperature information relative to the DC current is accumulated. Using the accumulated information, the rate of change of the temperature difference between the power conversion units 14, 15 relative to the DC output current can be calculated. Using the rate of change of the temperature difference, it is possible to detect temperature imbalance occurring between the parallel-connected power conversion units 14, 15.

In the inverter system 11, the temperatures of the power conversion units 14 and 15 are detected when DC current is output. The temperature difference between the parallel-connected power conversion units 14 and 15 is calculated from the detected temperatures, and information on the output current and temperature difference is stored. Information on the output current and temperature difference is stored multiple times, at least two times, and the rate of change 200 of the temperature difference relative to the output current is calculated from the detection results.

When the rate of change 200 is large, the temperature imbalance is large and losses are concentrated in some switching elements, so it is necessary to eliminate the imbalance. Therefore, next we will explain how to control the elimination of the imbalance according to the rate of change of the temperature difference.

The imbalance in the output current and temperature of the power conversion units 14 and 15 depends on the pulse width variation of the output voltage of the power conversion units 14 and 15, which occurs due to the delay time variation of the turn operation of the switching elements. Therefore, in order to eliminate the imbalance in the output current, it is necessary to adjust the gate signal supplied to each gate circuit according to the relationship between the rate of change of the temperature difference and the threshold value.

As a method of controlling the elimination of the imbalance according to the rate of change of the temperature difference, for example, when the rate of change 200 exceeds a threshold value, the on/off time adjustment unit 122 performs control to reduce the imbalance by delaying the turn-on time of the power conversion unit on the higher temperature side to narrow the pulse width. After this control, the temperatures of the power conversion units 14, 15 are detected and stored again, and the rate of change of the temperature difference between the power conversion units 14, 15 is calculated to obtain the rate of change 201.

The rate of change 201 after control is lower than the rate of change 200, and the temperature difference changes little with respect to the output current of the inverter system 11, so the temperatures of the power conversion units 14, 15 are equalized. This reduces the temperature imbalance of the power conversion units 14, 15, making it possible to suppress increases in switching loss and conduction loss of some switching elements. If the rate of change of the temperature difference is equal to or lower than the threshold, it is determined that there is no temperature imbalance, and no adjustment is made.

When the rate of change 200 exceeds the threshold, the turn-off time of the power conversion unit on the low temperature side is delayed to widen the pulse width and reduce the rate of change 200. This can be a method of equalizing the temperature between the power conversion units 14 and 15.

In this way, the signal generating unit 120 has the function of correcting at least one of the turn-on time or turn-off time of the on/off command signal depending on the detected temperature imbalance between the power conversion units 14 and 15.

[Example of temperature difference reduction process procedure]
Next, an example of a procedure for a process for reducing the temperature difference between the power conversion units 14, 15 connected in parallel according to an embodiment of the present invention will be described with reference to FIG.

Figure 10 is a flowchart showing an example of the procedure for reducing the temperature difference between the power conversion units 14, 15 connected in parallel. The signal generating unit 120 repeats the following steps S2 to S4 until the count value of the number of detections reaches a predetermined number (multiple times) (S1). First, the signal generating unit 120 determines whether or not it is currently in the startup compensation period 150 (S2), and if it is (Yes in S2), it proceeds to step S3, and if it is not (No in S2), it executes the determination process of step S2 again.

Next, during the startup compensation period 150, the signal generating unit 120 uses the temperature sensors 41, 42 and the current sensor 106 to detect the temperature of the power conversion units 14, 15 and the output current of the inverter system 11, and accumulates the detected temperature and output current information in the temperature accumulation unit 121 (S3). Next, the signal generating unit 120 increments the count value of the number of times the temperature and output current have been detected by "1" (S4).

Next, the signal generating unit 120 calculates the rate of change α of the temperature difference between the power conversion units 14 and 15 with respect to the output current (e.g., the rate of change 200 in FIG. 9) from the accumulated temperature and output current information (S5). If the rate of change α is greater than the threshold value (Yes in S6), the signal generating unit 120 adjusts the gate voltage pulse width (S7). For example, the signal generating unit 120 uses the on/off time adjusting unit 122 to delay the turn-on time of the switching element provided in the power conversion unit on the high temperature side, thereby reducing the rate of change α of the temperature difference between the power conversion units 14 and 15. By reducing the rate of change α, the temperatures of the power conversion units 14 and 15 can be controlled to be more uniform.

On the other hand, if the rate of change α is equal to or less than the threshold value (No in S6), it is determined that there is no temperature imbalance between the power conversion units 14 and 15 or that the difference is slight, and the gate voltage pulse width is not adjusted. After the processing of step S7 or if the judgment in step S6 is No, the processing of this flowchart ends.

According to the power conversion device according to one embodiment of the present invention described above, the inverter system 11 detects the temperature of the power conversion units 14, 15 connected in parallel multiple times when outputting a direct current, and accumulates the temperature in the temperature accumulation unit 121. Then, when the rate of change α of the temperature difference between the power conversion units 14, 15 with respect to the output current exceeds a threshold value, the inverter system 11 adjusts the pulse width of the gate signal of each switching element. As a result, the inverter system 11 according to this embodiment can detect the temperature difference between the power conversion units 14, 15 with higher accuracy than conventional technology.

[Upper and lower arm adjustment according to output current]
Furthermore, it is necessary to adjust the gate signals by switching the upper arm switching elements 24, 34 and the lower arm switching elements 25, 35 depending on the direction of the output current of the inverter system 11. Therefore, next, a method of adjusting the upper and lower arms according to the output current of the inverter system 11 will be described.

When current is output from the inverter system 11, current flows through the upper arm switching elements 24, 34, and when current is drawn into the inverter system 11, current flows through the lower arm switching elements 25, 35. Therefore, the challenge is to find a way to change the arm that adjusts the gate signal depending on the direction of the output current.

Therefore, the current sensor 106 is used to detect whether a current is being output or drawn from the inverter system 11, and the arm that adjusts the gate signal is switched. This makes it possible to suppress the pulse width variation of the gate voltage for the upper and lower arms separately. Whether a current is being output or drawn from the inverter system 11 is determined by the detected current of the current sensor 106.

In this way, the signal generating unit 120 has the function of correcting at least one of the turn-on time or turn-off time of the on/off command signal by switching the upper arm switching elements 24, 25 and the lower arm switching elements 25, 35 according to the output current Itotal of the inverter system 11 through the on/off time adjusting unit 122.

That is, when the inverter system 11 outputs current, the signal generating unit 120 corrects at least one of the turn-on time and the turn-off time of the upper arm switching elements 24, 34 and the lower arm switching elements 25, 35, which correspond to the upper arm. When the inverter system 11 draws current, the signal generating unit 120 corrects at least one of the turn-on time and the turn-off time of the upper arm switching elements 24, 34 and the lower arm switching elements 25, 35, which correspond to the lower arm.

By having such a correction function, the signal generating unit 120 can select the appropriate arm from the lower arm and the upper arm when the inverter system 11 is outputting current and when it is drawing current, and can adjust the delay time of the turning operation.

As described above, the power conversion device (inverter system 11) according to this embodiment is a power conversion device that includes a plurality of parallel-connected power conversion units, each of which has a first switching element (upper arm switching element 24, 34) and a second switching element (upper arm switching element 25, 35) connected in series (power conversion unit 14, 15), a temperature sensor (temperature sensor 41, 42) that detects the internal temperature of each power conversion unit, and a signal generating unit (signal generating unit 120) that generates an on/off command signal (gate signal) for the control electrodes of the first switching element and the second switching element for each power conversion unit according to the detection result of the temperature sensor. The signal generating unit uses the temperature sensor to detect the temperature of each power conversion unit when the power conversion device outputs a direct current.

In addition, in the power conversion device (inverter system 11) according to this embodiment, the time when the DC current is output is the startup compensation period of the motor connected to the power conversion device.

In addition, in the power conversion device (inverter system 11) according to this embodiment, the signal generating unit includes a storage device (temperature storage unit 121) that stores the detected temperature information of each power conversion unit. The power conversion device is configured to store the output current of the power conversion device and the temperature information of each power conversion unit detected by a temperature sensor, calculate the rate of change of the temperature difference between the power conversion units relative to the output current from multiple detection results, and detect a temperature imbalance between the power conversion units by comparing the rate of change of the temperature difference with a threshold value.

According to the power conversion device of the present embodiment described above, the temperature of the power conversion units connected in parallel is detected multiple times and stored when the power conversion device outputs DC current, making it possible to detect the temperature difference between the power conversion units with higher accuracy than with conventional technology.

[Modification]
In the above-described embodiment, the startup compensation period 150 of the motor 5 is used as the time when the inverter system 11 outputs DC current, but other methods may be used. For example, in a system such as the elevator system 1, a DC current output mode may be prepared in the power conversion device (inverter system 11), and when the DC current output mode is selected, the power conversion device may detect the temperature of each power conversion unit when outputting DC current.

In addition, although the present specification has described the configuration of a power conversion device (inverter system 11) in which two power conversion units are connected in parallel, the number of power conversion units connected in parallel may be three or more. In that case, for example, the rate of change in temperature difference between the power conversion units may be calculated for all combinations of multiple combinations of power conversion units, or the rate of change in temperature difference may be calculated only for one or more combinations of power conversion units specified in advance.

Although an example of applying the power conversion device of the present invention to a three-phase inverter system has been described, the power conversion device of the present invention can of course also be applied to a three-phase converter system having power conversion units connected in parallel. The power conversion device of the present invention can also be applied to a single-phase inverter system or single-phase converter system having power conversion units connected in parallel, a boost converter system, or a buck converter system.

Furthermore, the present invention is not limited to the embodiment described above, and of course various other applications and modifications are possible without departing from the gist of the present invention as described in the claims. For example, the embodiment described above describes in detail and specifically the configuration of an inverter system as a power conversion device in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to having all of the components described. In addition, it is also possible to add, replace, or delete other components to part of the configuration of each embodiment.

Furthermore, the above-mentioned configurations, functions, processing units, etc. may be realized in part or in whole in hardware, for example by designing them as integrated circuits. As the hardware, a broad processor device such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) may be used.

In addition, in the above-described embodiment, the control lines and information lines are those that are considered necessary for the explanation, and not all control lines and information lines in the product are necessarily shown. In reality, it can be considered that almost all components are connected to each other.

1...Elevator system, 2...System, 3, 4...Filter circuit, 5...Motor (load), 6...Rope, 7...Cage, 8...Weight, 9...Control circuit section, 9a...A/D conversion circuit, 9b...Processor, 9c...Memory, 10...Converter system, 11...Inverter system, 12-15...Power conversion unit, 21, 31...Capacitor, 22, 23, 32, 33...Gate circuit, 24, 34...Upper arm switching element, 25, 35...Lower arm switching element, 26, 36...Upper arm switching reflux diode , 27, 37...lower arm switching return diode, 14, 15...power conversion unit, 28, 38...resistive load, 29, 39...inductive load, 101...input signal, 102...DC power supply, 103...GND, 104...resistive load (output load), 105...inductive load (output load), 106...current sensor, 120...signal generation unit (control circuit unit), 121...temperature storage unit, 122...on/off time adjustment unit, 150...startup compensation period, 151...acceleration period, 152...constant speed period, 153...deceleration period, 200, 201...rate of change

Claims (7)

a power conversion device including: a plurality of power conversion units connected in parallel, each power conversion unit having a first switching element and a second switching element connected in series; a temperature sensor for detecting an internal temperature of each power conversion unit; and a signal generating unit for generating an on/off command signal for control electrodes of the first switching element and the second switching element for each power conversion unit in accordance with a detection result of the temperature sensor,
the signal generating unit includes a storage device;
The signal generating unit detects, using the temperature sensor, the temperature of each power conversion unit when the power conversion device outputs a direct current , accumulates information on the output current of the power conversion device and temperature information of each power conversion unit detected by the temperature sensor in the storage device, calculates a rate of change of the temperature difference between the power conversion units with respect to the output current from a plurality of detection results, and detects a temperature imbalance between the power conversion units by comparing the rate of change of the temperature difference with a threshold value.
Power conversion equipment. The power conversion device according to claim 1 , wherein the time of output is a startup compensation period of a motor connected to the power conversion device. The signal generating unit
The power conversion device according to claim 1 , further comprising a function of correcting at least one of a turn-on time and a turn-off time of the on/off command signal in response to a detected temperature imbalance between the power conversion units. The signal generating unit
The power conversion device according to claim 3 , further comprising a function of correcting at least one of a turn-on time and a turn-off time of the on/off command signal by switching between the first switching element and the second switching element in accordance with an output current of the power conversion device. The signal generating unit
5. The power conversion device according to claim 4, further comprising a function of correcting at least one of a turn-on time and a turn-off time of a switching element corresponding to an upper arm out of the first switching element and the second switching element when a current is output from the power conversion device, and correcting at least one of a turn-on time and a turn-off time of a switching element corresponding to a lower arm out of the first switching element and the second switching element when a current is drawn into the power conversion device. the motor is a hoist motor that hoists an elevator car by utilizing an output of the power conversion device,
The power conversion device according to claim 2 , wherein the hoist motor is stopped during the output. A power conversion method for a power conversion device including a plurality of power conversion units connected in parallel, each power conversion unit having a first switching element and a second switching element connected in series, a temperature sensor that detects an internal temperature of each power conversion unit, and a signal generation unit that generates an on/off command signal for control electrodes of the first switching element and the second switching element for each power conversion unit in accordance with a detection result of the temperature sensor, comprising:
the signal generating unit includes a storage device;
The signal generating unit detects, using the temperature sensor, the temperature of each power conversion unit when the power conversion device outputs a direct current , accumulates information on the output current of the power conversion device and temperature information of each power conversion unit detected by the temperature sensor in the storage device, calculates a rate of change of the temperature difference between the power conversion units with respect to the output current from a plurality of detection results, and detects a temperature imbalance between the power conversion units by comparing the rate of change of the temperature difference with a threshold value.
Power conversion methods.

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