JP6984553B2 - Boost converter - Google Patents

Description

The present specification discloses a boost converter capable of offset control of a current sensor.

In HV (Hybrid Vehicle) systems, PHV (Plug-in Hybrid Vehicle) systems, and FC (Fuel Cell) systems, the output voltage of secondary batteries and fuel cells is boosted to a voltage suitable for driving motors by a boost converter. There is. In addition, the power balance is controlled by measuring the charge / discharge current with a current sensor. As a related technique, the technique of Patent Document 1 can be mentioned.

Japanese Unexamined Patent Publication No. 2011-217543

The measured value of the current sensor includes a hysteresis error due to the residual magnetic flux of the magnetic core included in the current sensor. Due to the hysteresis error, the power balance will be out of alignment. In the boost converter connected to the secondary battery, the output current direction from the secondary battery changes in the positive direction (power running) and the negative direction (regeneration) in order to control the regeneration to the secondary battery. Therefore, since the magnetic core can be demagnetized, the hysteresis error can be canceled. However, since the boost converter connected to the fuel cell does not perform regeneration control to the fuel cell, the output current direction from the fuel cell is only in the positive direction (force running). Since the magnetic core of the current sensor cannot be degaussed, the hysteresis error cannot be canceled. The present specification provides a technique for correcting a measurement error due to residual magnetic flux in a current sensor used in a fuel cell.

The boost converter disclosed in the present specification is a boost converter connected to a fuel cell to boost the output voltage of the fuel cell. The boost converter includes a magnetic core and a current sensor that detects the output current of the fuel cell. The boost converter includes a peak hold means for storing the peak value of the output current detected by the current sensor within a certain period of time. The boost converter uses a correction value determined based on the peak value stored by the peak hold means to correct the hysteresis error due to the residual magnetic flux of the magnetic core contained in the output current detected by the current sensor. A correction means is provided.

The output current of the fuel cell is only one direction (power running). Therefore, since the magnetic core of the current sensor that detects the output current of the fuel cell cannot be demagnetized, the value of the hysteresis error due to the residual magnetic flux does not change once it occurs. When a current exceeding the previous maximum current value flows, the hysteresis error increases according to the current value. In the boost converter disclosed in the present specification, the maximum current value is constantly updated by the peak hold means. Then, by determining the correction value based on the peak value stored by the peak hold means, the correction value can be updated every time the maximum current value is updated. Therefore, it is possible to timely cancel the hysteresis error due to the residual magnetic flux that changes according to the current energization history from the detected value of the current sensor by using the correction value. Details and further improvements to the techniques disclosed herein will be described in the "Modes for Carrying Out the Invention" section below.

It is a block diagram of the electric power system of the fuel cell vehicle including the power source system of an Example. It is a waveform diagram of the current flowing through a reactor. It is a waveform diagram of the current charged and discharged from a fuel cell and a secondary battery. It is a figure which shows the hysteresis characteristic of the residual magnetic flux of a magnetic core. It is a figure which shows the hysteresis error curve. It is a flowchart of a concrete operation executed by a controller. It is a figure which shows the relationship of the measured current value, the update flag, and the current peak hold value.

(Structure of power supply system)
The power supply system 2 of the embodiment will be described with reference to the drawings. FIG. 1 shows a block diagram of an electric power system of a fuel cell vehicle 100 including a power supply system 2. In FIG. 1, the circuit other than the motor 22 is the power supply system 2. In FIG. 1, the solid line indicates a power line, and the broken line arrow indicates a signal line.

The fuel cell vehicle 100 runs on the motor 22. The motor 22 is driven by the electric power of the fuel cell 7 or the electric power of the main battery 3. In FIG. 1, the fuel cell 7 is indicated by a simple symbol, but the "fuel cell 7" here is a hydrogen tank for storing hydrogen, a fuel cell stack in which a plurality of fuel cell cells are stacked, and a fuel cell stack. It is an assembly of a plurality of devices such as an oxide gas supply device that supplies an oxide gas to a fuel cell and a fuel gas supply device that supplies a fuel gas to a fuel cell stack.

In general, automobiles are required to have the ability to rapidly change the driving force from zero to the maximum driving force in response to the driver's accelerator work. On the other hand, it is difficult for a fuel cell to change its output rapidly. Therefore, the fuel cell vehicle is equipped with a battery in addition to the fuel cell. The fuel cell vehicle 100 of the embodiment also includes a main battery 3. The main battery 3 is a rechargeable secondary battery, for example, a lithium ion battery or a nickel hydrogen battery.

The output voltage of the fuel cell 7 is, for example, 200 to 300 volts. The output voltage of the main battery 3 is, for example, 300 volts. On the other hand, the maximum drive voltage of the traveling motor 22 is 600 volts. The main battery 3 and the fuel cell 7 are connected in parallel to the inverter 6 via a voltage converter (bidirectional DC-DC converter 10, FC voltage converter 8). The inverter 6 converts the boosted DC power of the main battery 3 and / or the boosted DC power of the fuel cell 7 into AC power suitable for driving the motor 22 and supplies it to the motor 22. The motor 22 is a three-phase AC motor. Hereinafter, for the sake of simplicity, the bidirectional DC-DC converter 10 may be simply referred to as a “DC converter 10”.

(FC voltage converter 8)
The FC voltage converter 8 boosts the DC power voltage of the fuel cell 7 to a voltage suitable for driving the motor and supplies the voltage to the inverter 6. In the FC voltage converter 8, boosting operation is realized by turning the transistor 84 on and off. Since the operation of the FC voltage converter 8 is well known, detailed description thereof will be omitted.

The FC voltage converter 8 includes a reactor 81, a current sensor 82, a rectifier diode 83, a transistor 84, a freewheeling diode 85, and a controller 86. The transistor 84 is an IGBT (Insulated Gate Bipolar Transistor), and no current flows in the reverse direction. A freewheeling diode 85 is connected in antiparallel to the transistor 84. The freewheeling diode 85 is provided to bypass the reverse current of the transistor 84. One end of the reactor 81 is connected to the positive electrode of the fuel cell 7. The other end of the reactor 81 is connected to the midpoint N1 of the series connection of the rectifier diode 83 and the transistor 84 via the current sensor 82. The end of the rectifying diode 83 on the opposite side of the midpoint N1 is connected to the positive electrode 12a. The end of the transistor 84 opposite to the midpoint N1 is connected to the negative electrode 12b and the negative electrode of the fuel cell 7.

The current sensor 82 is a sensor that measures the output current of the fuel cell 7. The current sensor 82 includes a magnetic core (not shown) and a Hall element. The magnetic core is a member for increasing the measurement sensitivity by focusing the magnetic flux generated by the energizing current around the circuit. The Hall element is an element that detects the magnetic field of the magnetic flux focused by the magnetic core.

The measurement data of the current sensor 82 is input to the controller 86. Further, the controller 86 outputs a gate drive signal of the transistor 84. The controller 86 includes an EEPROM 87, a CPU 88, and a RAM 89. The controller 86 functions as a peak hold means and a correction means. The peak hold means is a means for storing the peak value of the measured current measured by the current sensor 82 within a certain period in the RAM 89 and the EEPROM 87. The correction means is a means for correcting the hysteresis error included in the measured current value measured by the current sensor by using the hysteresis correction value determined based on the peak value stored in the RAM 89. The hysteresis error will be described later.

The controller 86 can accurately calculate the target generated power of the fuel cell 7 by using the measured value corrected by the correction means. Then, the gate drive signal generated based on the target generated power can be supplied to the transistor 84.

(DC converter 10)
The DC converter 10 has a step-up function that boosts the power applied to the low-voltage end 11 and outputs it to the high-voltage end 12, and a step-down function that steps down the power applied to the high-voltage end 12 and outputs it to the low-voltage end 11. It has both functions. The step-down function is used when charging the main battery 3 with surplus power that was not used for driving the motor 22 out of the output power of the fuel cell 7. The step-down function is also used when the motor 22 generates electricity using the deceleration energy of the vehicle and when the regenerative power obtained by the power generation is charged to the main battery 3. The step-down operation is realized by turning on / off the transistor 16a on the high potential side, and the step-up operation is realized by turning on / off the transistor 16b on the low potential side. Since the operation of the DC converter 10 is well known, detailed description thereof will be omitted.

The DC converter 10 includes two transistors 16a and 16b, two diodes 17a and 17b, a reactor 15, a filter capacitor 14, and a smoothing capacitor 5. The low voltage end 11 of the DC converter 10 is connected to the main battery 3, and the high voltage end 12 is connected to the inverter 6. A smoothing capacitor 5 is connected in parallel between the DC converter 10 and the inverter 6. The two transistors 16a and 16b are connected in series between the positive electrode 12a and the negative electrode 12b at the high voltage end 12. The transistors 16a and 16b are IGBTs. The diode 17a is connected to the transistor 16a in antiparallel, and the diode 17b is connected to the transistor 16b in antiparallel. One end of the reactor 15 is connected to the midpoint of the series connection of the transistors 16a and 16b. The other end of the reactor 15 is connected to the positive electrode 11a of the low voltage end 11. The filter capacitor 14 is connected between the positive electrode 11a and the negative electrode 11b at the low voltage end 11.

(Characteristics of detected current in fuel cells and secondary batteries)
FIG. 2 shows a waveform diagram of the current flowing through the reactor provided in the boost converter. The vertical axis of FIG. 2 shows the current, and the center is 0A. The reactor current RI1 shown by the solid line is the reactor current of the boost converter connected to the fuel cell. The reactor current RI2 shown by the dotted line is the reactor current of the boost converter connected to the secondary battery. Further, FIG. 3 shows a waveform diagram of the current charged and discharged from the fuel cell and the secondary battery. On the vertical axis of FIG. 2, the upper side shows power running (that is, discharge), and the lower side shows regeneration (that is, charging). The fuel cell current FI shown by the solid line is the current discharged from the fuel cell. The secondary battery current SI shown by the dotted line is the current charged and discharged from the secondary battery.

Secondary batteries can be recharged, but fuel cells cannot. Therefore, as shown in FIGS. 2 and 3, in the boost converter connected to the secondary battery, the reactor current RI2 and the secondary battery current SI are positive (power running) and the secondary battery current SI because the regeneration control to the secondary battery is performed. It changes to negative (regeneration). On the other hand, in the boost converter connected to the fuel cell, the regenerative control to the fuel cell is not performed, so that the reactor current RI1 and the fuel cell current FI are only in the positive direction (force running).

(Characteristics of current sensor)
The general characteristics of the current sensor 82 will be described with reference to FIGS. 4 and 5. The horizontal axis of the graph of FIG. 4 is the energizing current (that is, the measured current), and the vertical axis is the measured value (that is, the output voltage) of the current sensor 82. FIG. 4 shows the hysteresis characteristic of the residual magnetic flux of the magnetic core. Specifically, the curve L1 when the measured current changes from the negative direction to the positive direction and the curve L2 when the measured current changes from the positive direction to the negative direction are different curves. Then, the difference between the curves L1 and L2 becomes a hysteresis error.

The horizontal axis of the graph of FIG. 5 is the energization current (that is, the measured current), and the vertical axis is the hysteresis error. Hysteresis error curves HC1 to HC3 are curves showing the relationship between the energization current and the hysteresis error. The hysteresis error curve HC1 is a curve generated by a negative peak current P11 or a positive peak current P12. The hysteresis error curve HC2 is a curve generated by a negative peak current P21 or a positive peak current P22. The hysteresis error curve HC3 is a curve generated by a negative peak current P31 or a positive peak current P32. The area occupied by the hysteresis error curve on the graph has the characteristic that it increases in proportion to the magnitude of the peak value of the energizing current. That is, the hysteresis error curves HC1 to HC3 are error curves generated by the energization current that gradually increases in this order. As shown in the hysteresis error curve H3 of FIG. 5, the hysteresis error value becomes the maximum value E1 when the measured current is “0A”. Further, at the negative peak current P31 and the positive peak current P32, the hysteresis error value becomes the minimum (0).

Then, as described with reference to FIGS. 2 and 3, in the boost converter connected to the fuel cell, the measured current flows only in the positive direction (power running). Then, the region used in FIG. 5 is only the region A1 in the first quadrant shown by the shaded area. In this case, once the hysteresis error curve occurs, it does not change because it is not degaussed. When a current exceeding the previous maximum current value flows, the area of the hysteresis error curve increases according to the current value. That is, the hysteresis error curve changes only in the direction of increasing from the hysteresis error curve HC1 to HC3.

The hysteresis error curves HC1 to HC3 in FIG. 5 are examples. There are numerous hysteresis error curves for different peak currents. The EEPROM 87 stores a large number of hysteresis error curves as an error map. In other words, the error map can be used to uniquely identify the hysteresis error curve corresponding to a certain peak current value.

(Specific operation example)
An operation example of the power supply system 2 of the embodiment will be described with reference to FIGS. 6 and 7. FIG. 6 shows a flowchart of the process from when the main switch of the vehicle is turned on to when the main switch is turned off. The process of FIG. 6 is started when the main switch (not shown) of the vehicle is turned on. The steps S10 to S30 are processes at the time of system startup, and the steps S40 to S130 are processes during traveling.

In S10, the CPU 88 reads the final current peak hold value of the previous trip from the EEPROM 87 and stores it in the RAM 89 as the current current peak hold value. In S20, the CPU 88 determines a hysteresis error curve corresponding to the current peak hold value and stores it in the RAM 89. As described above, this can be realized by using the error map stored in the EEPROM 87.

In S30, the CPU 88 determines the offset learning value α. The offset learning value α is a value for detecting a detection error when the output current of the fuel cell 7 is 0 and correcting the error. Since the method of determining the offset learning value α is well known, detailed description thereof will be omitted.

In S40, the CPU 88 receives the measured current value I1 from the current sensor 82. As shown in FIG. 7A, the measured current value I1 has a ripple waveform, and there are a plurality of peak values.

In S50, the CPU 88 determines whether or not the peak value of the measured current value I1 exceeds the current peak hold value stored in the RAM 89. And if it exceeds, the update flag is set. If the update flag is set (S50: YES), the process proceeds to S60. In S60, the CPU 88 overwrites and stores the peak value of the measured current value I1 in the RAM 89 as a new current peak hold value. In the example of FIG. 7, at time t1, it is determined that the peak value IP1 of the measured current value I1 exceeds the current peak hold value PH1 stored in the RAM 89, and the update flag F1 is set (FIG. 7B). Therefore, the current peak hold value is updated from PH1 to PH2 (FIG. 7 (C)). Similarly, at time t2, it is determined that the peak value IP2 of the measured current value I1 exceeds the current peak hold value PH2, the update flag F2 is set, and the current peak hold value is updated from PH2 to PH3.

In S70, the CPU 88 determines a hysteresis error curve corresponding to the current peak hold value. As described above, this can be realized by using the error map stored in the EEPROM 87. In S80, the CPU 88 overwrites and stores the determined hysteresis error curve in the RAM 89. This updates the hysteresis error curve. Then proceed to S100.

On the other hand, when the update flag is not set in S50 (S50: NO), the process proceeds to S90 and the hysteresis error curve is maintained as it is. Then proceed to S100.

In S100, the CPU 88 determines the hysteresis correction value β from the measured current value I1 measured in S40 and the stored hysteresis error curve. In S110, the CPU 88 corrects the measured current value I1. Specifically, the offset learning value α determined in S30 and the hysteresis correction value β determined in S100 are added to the measured current value I1.

In S120, the CPU 88 determines whether or not the main switch of the vehicle has been turned off. If a negative judgment is made (S120: NO), the process returns to S40, and if a positive judgment is made (S120: YES), the process proceeds to S130. In S130, the CPU 88 stores the current peak hold value stored in the RAM 89 in the EEPROM 87. As a result, the current peak hold value can be saved until the next trip.

(effect)
In the FC voltage converter 8 disclosed in the present specification, the current peak hold value is constantly updated by the controller 86 functioning as the peak hold means (S60). Then, the optimum hysteresis error curve can be determined by referring to the error map based on the updated current peak hold value (S70), and the hysteresis correction value β is determined from the determined hysteresis error curve. Can be done (S100). Therefore, it is possible to timely cancel the hysteresis error due to the residual magnetic flux that changes according to the current energization history from the measured current value I1.

By storing the current peak hold value of the previous trip in the EEPROM 87 (S130) and reading the final current peak hold value of the previous trip (S10), the hysteresis error curve determined in the previous trip is inherited by the next trip. Is possible (S20). As a result, the error correction amount becomes 0 even though the residual magnetic flux remains in the magnetic core of the current sensor 82, so that the occurrence of a situation in which the error of the measured current value I1 is expanded is suppressed. be able to.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above. The technical elements described herein or in the drawings exhibit their technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the techniques exemplified in the present specification or the drawings can achieve a plurality of purposes at the same time, and achieving one of the purposes itself has technical usefulness.

(Modification example)
In S10, the final current peak hold value of the previous trip is read out, but the present invention is not limited to this mode. For example, the final hysteresis error curve of the previous trip may be read out. In this case, the processing of S20 can be omitted.

2: Power supply system 3: Main battery 6: Inverter 7: Fuel cell 8: FC voltage converter 10: DC converter (bidirectional DC-DC converter) 22: Motor 81: Reactor 82: Current sensor 86: Controller 87: EEPROM 88 : CPU 89: RAM 100: Fuel cell vehicle

Claims (1)

A boost converter that is connected to a fuel cell and boosts the output voltage of the fuel cell.
A current sensor equipped with a magnetic core to detect the output current of the fuel cell,
A peak hold means for storing the peak value of the output current detected by the current sensor within a certain period, and
Using the correction value determined based on the peak value stored by the peak hold means, the hysteresis error due to the residual magnetic flux of the magnetic core included in the output current detected by the current sensor is corrected. Correction means and
A boost converter with.

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