Power converter

Abstract

This prevents the element temperature of specific switching elements in the first and second inverters from becoming excessively high. [Solution] A power conversion device connected to a power storage device and a motor having a three-phase open winding comprises a first inverter connected to the power line to which the power storage device is connected and to one end of the three-phase open winding, a second inverter connected to the power line and to the other end of the three-phase open winding, and a control device that generates PWM signals for multiple switching elements of the first and second inverters using modulated waves and carrier waves for each phase based on the torque command of the motor to control the first and second inverters. The control device varies the carrier frequency of the carrier wave for each phase of the first and second inverters based on the variation in element temperature of each switching element of the first and second inverters.

Description

Technical Field

[0001] This disclosure relates to a power conversion device.

Background Art

[0002] Conventionally, a power conversion device has been proposed that includes a first inverter that converts DC power from a first power source into AC power, a second inverter that converts DC power from a second power source into AC power, and a motor driven by the AC power from the first and second inverters (see Patent Document 1). In this power conversion device, switching signals for driving the first and second inverters are generated based on the comparison between modulation waves indicating the first and second voltage commands and the first and second carrier waves. In this case, based on the operating point of the motor, the first and second carrier frequencies, which are the frequencies of the first and second carrier waves, are set to be different from each other.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such a power conversion device, the element temperatures of the switching elements in each phase of the first and second inverters may vary. If only the element temperature of a specific switching element in the first and second inverters becomes significantly high, it may be necessary to limit the output of the motor for component protection.

[0005] The main object of the power conversion device of this disclosure is to suppress only the element temperature of a specific switching element in the first and second inverters from becoming significantly high.

Means for Solving the Problems

[0006] The power conversion device of this disclosure employs the following means to achieve the main objective described above.

[0007] The power conversion device of this disclosure, A power conversion device connected to an energy storage device and a motor having a three-phase open winding, A first inverter connected to the power line to which the energy storage device is connected and connected to one end of the three-phase open winding, A second inverter connected to the aforementioned power line and connected to the other end of the three-phase open winding, A control device that generates PWM signals for multiple switching elements of the first and second inverters using the modulated waves and carrier waves of each phase based on the torque command of the motor, and controls the first and second inverters. Equipped with, The control device varies the carrier frequency of the carrier wave for each phase of the first and second inverters based on the variation in the element temperature of the switching elements of the first and second inverters. This is the gist of it.

[0008] In the power conversion device of this disclosure, the carrier frequency of the carrier wave is varied for each phase of the first and second inverters based on the variation in the element temperature of each switching element of the first and second inverters. This makes it possible to suppress the phenomenon where only the element temperature of specific switching elements in the first and second inverters becomes excessively high.

[0009] In the power conversion device of the present disclosure, the control device may set the carrier frequency for each phase of the first and second inverters such that it decreases as the element temperature increases.

[0010] In the power conversion device of the present disclosure, the control device may lower the carrier frequency of the current concentration phase based on the electrical angle of the motor when the motor is locked compared to when it is not locked.

[0011] In the power conversion device of the present disclosure, the control device may set the carrier frequency for each phase of the first and second inverters such that it decreases as the cumulative value of the absolute value of the phase current over a predetermined time increases. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram of an electric vehicle equipped with a power converter according to an embodiment of the present disclosure. [Figure 2] This is a block diagram showing an example of a functional block in the control of the first and second inverters 22 and 24 by the ECU. [Figure 3] This is an explanatory diagram showing an example of a carrier frequency setting map. [Modes for carrying out the invention]

[0013] Embodiments for implementing this disclosure will be described with reference to the drawings. Figure 1 is a schematic diagram of an electric vehicle 10 equipped with a power converter 20 according to an embodiment of this disclosure. As shown in the figure, the electric vehicle 10 of the embodiment includes a battery 12 as an energy storage device, a motor 18, a power converter 20, and an electronic control unit (hereinafter referred to as "ECU") 50 as a control device.

[0014] The battery 12 is configured as, for example, a lithium-ion secondary battery or a nickel-metal hydride secondary battery and is connected to the power line 16 (positive electrode line 16p and negative electrode line 16n). The motor 18 is configured as a three-phase AC motor and comprises a rotor with permanent magnets embedded in the rotor core and a stator with three-phase (U-phase, V-phase, W-phase) coils (three-phase open windings) wound around the stator core. The rotor is connected to a drive shaft which is linked to the drive wheels via a differential gear.

[0015] The power converter 20 comprises first and second inverters 22 and 24, first and second capacitors 30 and 32, and changeover switches 34p and 34n. The first and second inverters 22 each comprise six transistors T11-T16 and T21-T26 as multiple switching elements, and six diodes D11-D16 and D21-D26 connected in parallel to each of the six transistors T11-T16 and T21-T26. For example, MOSFETs and IGBTs can be used as transistors T11-T16 and T21-T26. The transistors T11-T16 and T21-T26 are arranged in pairs, with two transistors each acting as the source and sink sides with respect to the positive side line 16p and the negative side line 16n. Each connection point of the pair of transistors T11-T16 is connected to each of the three-phase coils of the motor 18. Each of the connection points of the pair of transistors T21-T26 is connected to the other end of each of the three-phase coils of the motor 18. Hereafter, transistors T11-T13 may be referred to as the "first upper arm," transistors T14-T16 as the "first lower arm," transistors T21-T23 as the "second upper arm," and transistors T24-T26 as the "second lower arm."

[0016] The first and second capacitors 30 and 32 are connected to the power line 16 near the first and second inverters 22 and 24, respectively. In this embodiment, the power line 16 is connected in the following order from left to right in Figure 1: battery 12, first capacitor 30, first inverter 22, second inverter 24, and second inverter 24. The changeover switches 34p and 34n are provided between the first and second inverters 22 and 24 on the positive side line 16p and the negative side line 16n, respectively. For example, semiconductor switches or isolated switches can be used as changeover switches 34p and 34n.

[0017] The ECU50 is a microcomputer equipped with a CPU, ROM, RAM, flash memory, input / output ports, and communication ports, as well as various drive circuits and logic ICs. Signals from various sensors are input to the ECU50. For example, the ECU50 receives the voltage Vb of battery 12 from voltage sensor 12v, the current Ib of battery 12 from current sensor 12i, and the temperature αb of battery 12 from temperature sensor 12t. The ECU50 also receives the rotational position θm of the rotor of motor 18 from rotational position sensor 18a, and the phase currents Iu, Iv, and Iw of each phase of motor 18 from current sensors 18u, 18v, and 18w. The ECU50 also receives the temperatures αi11 to αi16 and αi21 to αi26 of transistors T11 to T16 and T21 to T26 from temperature sensors 22t1 to 22t6 and 24t1 to 24t6. The ECU 50 also receives the voltage VH from the first capacitor 30 via the voltage sensor 30V, and the voltage VL from the second capacitor 32 via the voltage sensor 32V. The ECU 50 also receives the on / off signal from the power switch, the shift position SP which is the operating position of the shift lever 61 from the shift position sensor 62, the accelerator opening Acc which is the amount the accelerator pedal 63 is pressed down from the accelerator pedal position sensor 64, the brake pedal position BP which is the amount the brake pedal 65 is pressed down from the brake pedal position sensor 66, and the vehicle speed V from the vehicle speed sensor 67.

[0018] ECU50 outputs various control signals. For example, ECU50 outputs control signals to transistors T11-T16 of the first inverter 22, transistors T21-T26 of the second inverter 24, and selector switches 34p and 34n. ECU50 calculates the state of charge (SOC) of battery 12 based on the integrated value of the current Ib of battery 12. ECU50 calculates the electrical angle θe and rotational speed Nm of motor 18 based on the rotational position θm of the rotor of motor 18. ECU50 uses the electrical angle θe of motor 18 to perform coordinate transformation (3-phase to 2-phase transformation) of the phase currents Iu, Iv, and Iw of each phase to the d-axis and q-axis currents Id and Iq.

[0019] In the electric vehicle 10 of the embodiment, the ECU 50 sets a required torque Td* required for running based on the accelerator opening Acc and the vehicle speed V, and sets a torque command Tm* for the motor 18 so as to run with the set required torque Td*. Then, basically, the first and second inverters 22, 24 are controlled so that the changeover switches 34p, 34n are in the on state and the motor 18 is driven by the torque command Tm*.

[0020] Next, the operation of the electric vehicle 10 of the embodiment, particularly the control of the first and second inverters 22, 24, will be described. FIG. 2 is a block diagram showing an example of functional blocks in the control of the first and second inverters 22, 24 by the ECU 50. As shown in the figure, the ECU 50, in cooperation with hardware such as a CPU and a plurality of programs (software) installed in a ROM or a flash memory, functions as a current command setting unit 71, a current control unit 72, a dq-uvw conversion unit 73, a temperature maximum value selection unit 74, a carrier frequency setting unit 75, and a PWM conversion unit 76.

[0021] The current command setting unit 71 sets current commands Id*, Iq* for the d-axis and q-axis based on the torque command Tm* of the motor 18. For example, the torque command Tm* is applied to a current command map previously determined by experiments, analysis, etc. as the relationship between the torque command Tm* and the current commands Id*, Iq* for the d-axis and q-axis, and the corresponding current commands Id*, Iq* for the d-axis and q-axis are derived and set from the current command map.

[0022] The current control unit 72 calculates voltage commands Vd*, Vq* for the d-axis and q-axis by current feedback control so that the difference between the currents Id, Iq for the d-axis and q-axis and the current commands Id*, Iq* for the d-axis and q-axis from the current command setting unit 71 is canceled out.

[0023] The dq-uvw conversion unit 73 performs a coordinate transformation (2-phase to 3-phase transformation) of the d-axis and q-axis voltage commands Vd* and Vq* from the current control unit 72 into phase voltage commands Vu*, Vv*, and Vw* for each phase using the electrical angle θe of the motor 18. Furthermore, it calculates the duty cycle commands Du*, Dv*, and Dw* (modulated waves) for each phase by dividing the phase voltage commands Vu*, Vv*, and Vw* for each phase by the voltage VH of the first capacitor 30 (power line 16).

[0024] The maximum temperature selection unit 74 sets the element temperatures αi1u, αi1v, αi1w, αi2u, αi2v, and αi2w for each phase of the first and second inverters 22 and 24, respectively, based on the temperatures αi11 to αi16 and αi21 to αi26 of transistors T11 to T16 and T21 to T26 of the first and second inverters 22 and 24. Specifically, the maximum values ​​of the temperatures αi11 and αi14 of transistors T11 and T14 are set to the element temperature αi1u of the U phase of the first inverter 22. The maximum values ​​of the temperatures αi12 and αi15 of transistors T12 and T15 are set to the element temperature αi1v of the V phase of the first inverter 22. The maximum values ​​of the temperatures αi13 and αi16 of transistors T13 and T16 are set to the element temperature αi1w of the W phase of the first inverter 22. The maximum temperatures αi21 and αi24 of transistors T21 and T24 are set to the U-phase element temperature αi2u of the second inverter 24. The maximum temperatures αi22 and αi25 of transistors T22 and T25 are set to the V-phase element temperature αi2v of the second inverter 24. The maximum temperatures αi23 and αi26 of transistors T23 and T26 are set to the W-phase element temperature αi2w of the second inverter 24.

[0025] The carrier frequency setting unit 75 sets the carrier frequencies fc1u, fc1v, fc1w, fc2u, fc2v, fc2w for each phase of the first and second inverters 22 and 24, respectively, based on the element temperatures αi1u, αi1v, αi1w, αi2u, αi2v, αi2w for each phase of the first and second inverters 22 and 24, respectively, from the temperature maximum value selection unit 74. The carrier frequency is the frequency of the carrier wave (triangular wave) used for comparison with the duty cycle command (modulated wave) described above when generating the PWM signal for each transistor. For example, the relationship between element temperatures αi1u, αi1v, αi1w, αi2u, αi2v, αi2w (collectively referred to as element temperature αi) and carrier frequencies fc1u, fc1v, fc1w, fc2u, fc2v, fc2w (collectively referred to as carrier frequency fc) is determined by applying the element temperature αi to a predetermined carrier frequency setting map, which is determined through experiments or analyses, and the corresponding carrier frequency fc is derived from the map. Figure 3 is an explanatory diagram showing an example of a carrier frequency setting map. As shown in the figure, in the region where the element temperature αi is below the threshold αilo, the value fchi is set for the carrier frequency fc. Furthermore, in the region where the element temperature αi is higher than the threshold αilo but below the threshold αihi, the carrier frequency fc is set so that as the element temperature αi increases, the value fchi gradually decreases towards a smaller value fclo. In addition, in the region where the element temperature αi is above the threshold αihi, the value fclo is set for the carrier frequency fc. In other words, for setting the PWM signal of each transistor, the carrier frequencies fc1u, fc1v, fc1w, fc2u, fc2v, and fc2w are set such that they decrease as the element temperature αi1u, αi1v, αi1w, αi2u, αi2v, and αi2w increases.

[0026] The PWM conversion unit 76 generates PWM signals S11~S16 and S21~S26 for transistors T11~T16 and T21~T26 using the duty cycle commands Du*, Dv*, and Dw* for each phase from the dq-uvw conversion unit 73 and the carrier frequencies fc1u, fc1v, fc1w, fc2u, fc2v, and fc2w for each phase from the carrier frequency setting unit 75. Specifically, it generates PWM signals S11 and S14 for transistors T11 and T14 using the comparison result between the duty cycle command Du* for the U phase and the carrier wave (triangular wave) of carrier frequency fc1u, and generates PWM signals S21 and S24 for transistors T21 and T24 using the comparison between the duty cycle command Du* and the carrier wave of carrier frequency fc2u. The PWM signals S12 and S15 for transistors T12 and T15 are generated using the comparison result between the V-phase duty cycle command Dv* and the carrier wave (triangular wave) of carrier frequency fc1v, and the PWM signals S22 and S25 for transistors T22 and T25 are generated using the comparison between the duty cycle command Dv* and the carrier wave of carrier frequency fc2v. The PWM signals S13 and S16 for transistors T13 and T16 are generated using the comparison result between the W-phase duty cycle command Dw* and the carrier wave (triangular wave) of carrier frequency fc1w, and the PWM signals S23 and S26 for transistors T23 and T26 are generated using the comparison between the duty cycle command Dw* and the carrier wave of carrier frequency fc2w. Once the PWM signals S11-S16 and S21-S26 for transistors T11-T16 and T21-T26 are generated in this way, they are used to control the switching of transistors T11-T16 and T21-T26. As described above, the carrier frequency fc is set so that it decreases as the element temperature αi increases. For example, for the U phase of the first inverter 22, the carrier frequency fc1u is set so that it decreases as the element temperature αiu1 increases. Therefore, for the U phase of the first inverter 22, when the element temperature αiu1 is low, the controllability of the U phase can be improved by increasing the carrier frequency fc1u, and when the element temperature αiu1 is high, a further increase in the element temperature αiu1 can be suppressed by lowering the carrier frequency fc1u. The same applies to the V phase and W phase of the first inverter 22 and the U phase, V phase and W phase of the second inverter 24.

[0027] Due to manufacturing variations (variations in heat generation characteristics) of transistors T11-T16 and T21-T26 of the first and second inverters 22 and 24, even if the carrier frequencies fc1u, fc1v, fc1w, fc2u, fc2v, and fc2w of each phase of the first and second inverters 22 and 24 are kept constant, the element temperatures αi1u, αi1v, αi1w, αi2u, αi2v, and αi2w may vary. Taking this into account, in this embodiment, the carrier frequencies fc1u, fc1v, fc1w, fc2u, fc2v, and fc2w are set for each phase of the first and second inverters 22 and 24 such that they decrease as the element temperature αi1u, αi1v, αi1w, αi2u, αi2v, and αi2w increases. This makes it possible to suppress the phenomenon where the temperature of only specific transistors T11-T16 and T21-T26 in the first and second inverters 22 and 24 becomes excessively high. As a result, it is possible to suppress the occurrence of the situation where the temperature of only specific transistors becomes excessively high, necessitating the output limiting of the motor 18 to protect the components.

[0028] In the power converter 20 mounted on the electric vehicle 10 of the embodiment described above, PWM signals for transistors T11-T16 and T21-T26 of the first and second inverters 22 and 24 are generated using the duty cycle commands Du*, Dv*, Dw* for each phase based on the torque command Tm* of the motor 18 and the carrier wave, thereby controlling the first and second inverters 22 and 24. In this case, for each phase of the first and second inverters 22 and 24, the carrier frequencies fc1u, fc1v, fc1w, fc2u, fc2v, fc2w are set such that they decrease as the element temperature αi1u, αi1v, αi1w, αi2u, αi2v, αi2w increases. This makes it possible to suppress the temperature of only a specific transistor among the transistors T11-T16 and T21-T26 of the first and second inverters 22 and 24 from becoming excessively high.

[0029] In the embodiment described above, the carrier frequency setting unit 75 sets the carrier frequencies fc1u, fc1v, fc1w, fc2u, fc2v, fc2w for each phase of the first and second inverters 22 and 24 such that the higher the element temperature αi1u, αi1v, αi1w, αi2u, αi2v, αi2w, the lower the carrier frequencies become. However, the embodiment is not limited to this.

[0030] For example, when motor 18 is locked, the current-concentrated phase may be identified based on the electrical angle θe of motor 18, and the carrier frequency of that current-concentrated phase may be lower than when motor 18 is not locked. The locked state of motor 18 is detected, for example, when the absolute value of the rotational speed Nm of motor 18 is less than or equal to the threshold Nmref and the absolute value of the torque command Tm* of motor 18 is greater than or equal to the threshold Tmref. When motor 18 is locked, a current with a large absolute value continues to flow in the current-concentrated phase corresponding to the electrical angle θe of motor 18, and the element temperature of the current-concentrated phase tends to be higher than the element temperatures of the other phases. Therefore, by lowering the carrier frequency of the current-concentrated phase compared to when motor 18 is not locked, it is possible to suppress the temperature of only specific transistors among transistors T11~T16 and T21~T26 of the first and second inverters 22 and 24 from becoming excessively high.

[0031] Furthermore, for each phase of the first and second inverters 22 and 24, the carrier frequencies fc1u, fc2u, fc1v, fc2v, fc1w, and fc2w may be set such that the larger the integrated values ​​Iusum, Ivsum, and Iwsum (absolute values ​​of phase currents Iu, Iv, and Iw) over a predetermined time, the lower the carrier frequencies become. It is assumed that the larger the integrated values ​​Iusum, Ivsum, and Iwsum, the higher the element temperatures αi1u, αi2u, αi1v, αi2v, αi1w, and αi2w become. Therefore, by setting the carrier frequencies fc1u, fc2u, fc1v, fc2v, fc1w, and fc2w so that the larger the integrated values ​​Iusum, Ivsum, and Iwsum, it is possible to suppress the phenomenon where only the temperature of specific transistors among the transistors T11-T16 and T21-T26 of the first and second inverters 22 and 24 becomes exceptionally high.

[0032] In the embodiment described above, the power converter 20 mounted on the electric vehicle 10 is provided with first and second capacitors 30 and 32, but is not limited to this. For example, the second capacitor 32 may be omitted.

[0033] In the embodiment described above, the power converter 20 mounted on the electric vehicle 10 is provided with changeover switches 34p and 34n, but is not limited to this. For example, it is not necessary to provide at least one of the changeover switches 34p and 34n.

[0034] In the embodiment described above, the power converter 20 was provided as being mounted on an electric vehicle 10 equipped with a motor 18, but it is not limited to this. For example, it may be provided as a power converter mounted on a hybrid vehicle that has an engine in addition to the same hardware configuration as the electric vehicle 10. Alternatively, it may be provided as a power converter mounted on a fuel cell vehicle that has a fuel cell in addition to the same hardware configuration as the electric vehicle 10.

[0035] The correspondence between the main elements of the embodiment and the main elements of the invention described in the section on means for solving the problem will be explained. In the embodiment, the battery 12 corresponds to the "energy storage device", the motor 18 corresponds to the "motor", the power converter 20 corresponds to the "power converter", the first inverter 22 corresponds to the "first inverter", the second inverter 24 corresponds to the "second inverter", and the ECU 50 corresponds to the "control device".

[0036] Furthermore, the correspondence between the main elements of the embodiment and the main elements of the invention described in the section on means for solving the problem is merely an example to specifically explain the form in which the embodiment implements the invention described in the section on means for solving the problem, and does not limit the elements of the invention described in the section on means for solving the problem. In other words, the interpretation of the invention described in the section on means for solving the problem should be based on the description in that section, and the embodiment is merely one specific example of the invention described in the section on means for solving the problem.

[0037] Although the embodiments for implementing this disclosure have been described above, this disclosure is not limited in any way to these embodiments, and it is of course possible to implement it in various forms without departing from the gist of this disclosure. [Industrial applicability]

[0038] This disclosure can be used in industries such as the manufacturing of power conversion equipment. [Explanation of Symbols]

[0039] 10 Electric vehicle, 12 Battery, 12i, 18u, 18v, 18w Current sensor, 12t, 22t1~22t6, 24t1~24t6 Temperature sensor, 12v, 30v, 32v Voltage sensor, 16 Power line, 16n Negative side line, 16p Positive side line, 18 Motor, 20 Power converter, 18a Rotation position sensor, 22 First inverter, 24 Second inverter, 30 First capacitor, 32 Second capacitor, 34n, 34p Changeover switch, 50 ECU, 60 Power switch, 61 Shift lever, 62 Shift position sensor, 63 Accelerator pedal, 64 Accelerator pedal position sensor, 65 Brake pedal, 66 Brake pedal position sensor, 67 Vehicle speed sensor, 71 Current command setting unit, 72 Current control unit, 73 DQ-UVW conversion unit, 74 Temperature maximum value selection section, 75 Carrier frequency setting section, 76 PWM conversion section, D11~D16, D21~D26 Diodes, T11~T16, T21~T26 Transistors.

Claims

1. A power conversion device connected to an energy storage device and a motor having a three-phase open winding, The first inverter is connected to the power line to which the energy storage device is connected and is connected to one end of the three-phase open winding, A second inverter connected to the aforementioned power line and to the other end of the three-phase open winding, A control device that generates PWM signals for multiple switching elements of the first and second inverters using the modulated waves and carrier waves of each phase based on the torque command of the motor, and controls the first and second inverters. Equipped with, The control device varies the carrier frequency of the carrier wave for each phase of the first and second inverters based on the variation in the element temperature of the switching elements of the first and second inverters. Power converter.

2. A power conversion device according to claim 1, The control device sets the carrier frequency for each phase of the first and second inverters such that it decreases as the element temperature increases. Power converter.

3. A power conversion device according to claim 1, The control device, when the motor is locked, lowers the carrier frequency of the current concentration phase based on the electric angle of the motor compared to when it is not locked. Power converter.

4. A power conversion device according to claim 1, The control device sets the carrier frequency for each phase of the first and second inverters such that the carrier frequency decreases as the cumulative value of the absolute value of the phase current over a predetermined time increases. Power converter.

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