Power Conversion Equipment

Abstract

To effectively use low loss elements in an H bridge motor drive system obtained by combining switching elements with different loss characteristics.SOLUTION: A first inverter is connected in parallel with a DC power supply and comprises a plurality of first switching elements for every phase of a rotary electric machine. A second inverter is connected in parallel with the DC power supply and comprises a plurality of second switching elements for every phase of the rotary electric machine. A control device controls the first and second inverters. The plurality of first switching elements and the plurality of second switching elements have mutually different loss characteristics. When the switching elements with smaller loss are defined as low loss elements, and the switching elements with larger loss are defined as high loss elements, the control device controls the first and second inverters so that the number of times of switching of one of the first and second inverters corresponding to the inverters on a side of using the low loss elements becomes more than the number of times of switching of the other of the first and second inverters corresponding to the inverters on a side of using the low loss elements.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device. [Background technology]

[0002] Patent Document 1 discloses an open winding system for driving a three-phase induction motor or the like. This open winding system includes first and second inverters that convert DC power from a DC power source into AC power, and an open winding connected between the AC output terminals of the first inverter and the second inverter. A control device for the open winding system controls each switching element of the first and second inverters so that the losses of the switching elements are equal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-093077 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a power conversion device (also referred to as an "H-bridge motor drive system" for convenience) having a configuration in which the coils (windings) of each phase are driven by an H-bridge inverter, such as the open winding system described in Patent Document 1, it is possible to use a mixture of switching elements with different loss characteristics in consideration of the balance between cost and efficiency. When such a configuration is adopted, it is difficult to effectively use each switching element by a method of controlling each switching element of the first and second inverters so that the losses of each switching element are equal.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to enable effective use of low-loss elements in an H-bridge motor drive system that combines switching elements with different loss characteristics. [Means for solving the problem]

[0007] A power conversion device according to a first aspect of the present disclosure converts power supplied from a DC power source to a rotating electric machine having open windings with coils of multiple phases, and includes a first inverter, a second inverter, and a control device. The first inverter is connected in parallel with the DC power source and includes a plurality of first switching elements capable of switching between a first high potential point and one end of the coil and between one end of the coil and a first low potential point for each phase of the rotating electric machine. The second inverter is connected in parallel with the DC power source and includes a plurality of second switching elements capable of switching between a second high potential point and the other end of the coil and between the other end of the coil and a second low potential point for each phase of the rotating electric machine. The control device controls the first and second inverters. The plurality of first switching elements and the plurality of second switching elements are configured to have different loss characteristics from each other. When the multiple first switching elements and multiple second switching elements having smaller losses are referred to as low-loss elements and the ones having larger losses are referred to as high-loss elements, the control device controls the first and second inverters so that the number of times that one of the first and second inverters corresponding to the inverter using the low-loss elements is switched is greater than the number of times that the other of the first and second inverters corresponding to the inverter using the high-loss elements is switched. The current flowing through each of the coils of the multiple phases is defined as positive when it flows from the first inverter side to the second inverter side. The control device includes a control signal generating unit that generates control signals for each of the multiple first switching elements and the multiple second switching elements for each of the multiple phases. nothing. The control signal generating unit, when a fundamental modulation wave of a voltage command for each phase based on a drive command for the rotating electric machine is 0 or more, compares the fundamental modulation wave with a first carrier signal varying between 0 and 1 to generate control signals for first switching elements that respectively constitute the upper arm and the lower arm of the first inverter, while turning off and on, respectively, the control signals for second switching elements that respectively constitute the upper arm and the lower arm of the second inverter, and, when the fundamental modulation wave is less than 0, compares a first corrected modulation wave obtained by adding 1 to the fundamental modulation wave with the first carrier signal to generate control signals for first switching elements that respectively constitute the upper arm and the lower arm of the first inverter, while turning on and off, respectively, the control signals for second switching elements that respectively constitute the upper arm and the lower arm of the second inverter. do .

[0008] A power conversion device according to a second aspect of the present disclosure converts power supplied from a DC power source to a rotating electric machine having open windings with coils of multiple phases, and includes a first inverter, a second inverter, and a control device. The first inverter is connected in parallel with the DC power source and includes a plurality of first switching elements capable of switching between a first high potential point and one end of the coil and between one end of the coil and a first low potential point for each phase of the rotating electric machine. The second inverter is connected in parallel with the DC power source and includes a plurality of second switching elements capable of switching between a second high potential point and the other end of the coil and between the other end of the coil and a second low potential point for each phase of the rotating electric machine. The control device controls the first and second inverters. The plurality of first switching elements and the plurality of second switching elements are configured to have different loss characteristics from each other. When the multiple first switching elements and multiple second switching elements having smaller losses are referred to as low-loss elements and the ones having larger losses are referred to as high-loss elements, the control device controls the first and second inverters so that the number of times that one of the first and second inverters corresponding to the inverter using the low-loss elements is switched is greater than the number of times that the other of the first and second inverters corresponding to the inverter using the high-loss elements is switched. The current flowing through each of the coils of the multiple phases is defined as positive when it flows from the first inverter side to the second inverter side. The control device includes a control signal generating unit that generates control signals for each of the multiple first switching elements and the multiple second switching elements for each of the multiple phases. nothing.The control signal generating unit, when a fundamental modulation wave of a voltage command for each phase based on a drive command for the rotating electric machine is less than 0, compares the fundamental modulation wave with a second carrier signal varying between -1 and 0 to generate control signals for second switching elements that respectively constitute the upper arm and the lower arm of the second inverter, while turning off and on, respectively, the control signals for first switching elements that respectively constitute the upper arm and the lower arm of the first inverter, and, when the fundamental modulation wave is 0 or more, compares a second corrected modulation wave obtained by adding -1 to the fundamental modulation wave with the second carrier signal to generate control signals for second switching elements that respectively constitute the upper arm and the lower arm of the second inverter, while turning on and off, respectively, the control signals for first switching elements that respectively constitute the upper arm and the lower arm of the first inverter. do .

[0009] The power conversion device may further include a switch disposed between the first inverter and the second inverter, for switching between a current conduction state and a current cutoff state. The first inverter may include a plurality of first switching elements each of which is a low-loss element.

[0010] The plurality of first switching elements and the plurality of second switching elements may be configured to have different loss characteristics due to differences in materials.

[0011] The plurality of first switching elements and the plurality of second switching elements may be configured to have different loss characteristics due to differences in chip areas. Effect of the Invention

[0012] According to the power conversion device of the present disclosure, in an H-bridge motor drive system in which switching elements with different loss characteristics are combined on an inverter-by-inverter basis, the first and second inverters are controlled so that the number of times that one of the first and second inverters corresponding to the inverter using low-loss elements is switched is greater than the number of times that the other of the first and second inverters corresponding to the inverter using high-loss elements is switched, thereby making it possible to effectively utilize the low-loss elements and reduce inverter losses. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating a schematic configuration of a power conversion device according to a first embodiment. [Diagram 2] 1A is a time chart showing a method for generating a control signal in a general switching control (comparative example), and FIG. 1B is a time chart showing a method for generating a control signal in a characteristic switching control according to the first embodiment. [Diagram 3] 13 is a diagram illustrating the relationship between the modulated wave and the on / off states of the connection points U1 and U2 in the comparative example. FIG. [Figure 4] 5 is a flowchart showing a procedure for generating a control signal by a control signal generating unit according to the first embodiment. [Diagram 5] 11 is a time chart showing a method of generating a control signal when the number of switching operations of the second switching element SW2 on the second inverter side is increased. [Figure 6] 3A and 3B are diagrams for explaining the effect of the first embodiment over the comparative example shown in FIG. [Figure 7] FIG. 11 is a diagram illustrating a schematic configuration of a power conversion device according to a second embodiment. [Figure 8] FIG. 11 is a diagram showing a control state of a power conversion device during Y-connection driving. [Figure 9] FIG. 13 is a diagram illustrating a schematic configuration of a power conversion device according to a first modification of the second embodiment. [Figure 10] FIG. 13 is a diagram illustrating a schematic configuration of a power conversion device according to a second modification of the second embodiment. [Figure 11] FIG. 1 is a diagram illustrating a schematic configuration of a power conversion device applied to a five-phase rotating electric machine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] In each embodiment described below, elements common to each drawing are given the same reference numerals, and duplicated descriptions are omitted or simplified. In addition, when the number, quantity, amount, range, etc. of each element is mentioned in the embodiments described below, the technical idea of ​​the present disclosure is not limited to the mentioned number, unless otherwise specified or clearly specified in principle. In addition, the structures, steps, etc. described in the embodiments described below are not necessarily essential to the technical idea of ​​the present disclosure, unless otherwise specified or clearly specified in principle.

[0015] 1. First embodiment 1-1. Configuration of power conversion device Fig. 1 is a diagram illustrating a schematic configuration of a power conversion device 100 according to embodiment 1. In Fig. 1, an electric motor 1, a DC power source 2 (e.g., a battery), and a smoothing capacitor 3 are illustrated together with the power conversion device 100. The power conversion device 100 is configured to convert power supplied from the DC power source 2 to the electric motor 1.

[0016] The electric motor 1 is mounted on an electric vehicle such as an electric car or a hybrid car, and generates torque for driving drive wheels (not shown) of the electric vehicle. The electric motor 1 is an example of a "rotating electric machine" according to the present disclosure. The rotating electric machine is not limited to an electric motor, and may be, for example, a generator, or a motor generator having both a function as an electric motor and a function as a generator.

[0017] The electric motor 1 is a three-phase electric motor with open windings, and has three coils 4 (a U-phase coil 4U, a V-phase coil 4V, and a W-phase coil 4W). That is, the electric motor 1 has a configuration in which both ends of the coils 4 of each phase are open.

[0018] The power conversion device 100 includes a first inverter 10, a second inverter 30, and a control device 60. The first inverter 10 and the second inverter 30 are each connected in parallel to a DC power source 2. More specifically, the first inverter 10 is disposed closer to the DC power source 2 than the second inverter 30. The above-mentioned smoothing capacitor 3 is connected between the DC power source 2 and the first inverter 10.

[0019] 1-1-1. First and second inverters The first inverter 10 is a three-phase inverter that switches the energization of the coil 4 of each phase. The first inverter 10 includes a plurality of first switching elements 12, 14, 16, 18, 20, and 22 that can open and close (turn on and off) between a first high potential point H1 of the first inverter 10 and one end of the coil 4, and between one end of the coil 4 and a first low potential point L1 of the first inverter 10, for each phase of the motor 1. In this embodiment, the first switching elements 12, 14, 16, 18, 20, and 22 are collectively referred to as "first switching elements SW1."

[0020] More specifically, the first inverter 10 includes a first switching element 12 provided between a first high potential point H1 and a connection point U1 corresponding to the U-phase coil 4U, and a first switching element 14 provided between the connection point U1 and a first low potential point L1. One end of the U-phase coil 4U is connected to the connection point U1 between the U-phase first switching elements 12 and 14.

[0021] The first inverter 10 also includes a first switching element 16 provided between a first high potential point H1 and a connection point V1, and a first switching element 18 provided between the connection point V1 and a first low potential point L1, corresponding to the V-phase coil 4V. One end of the V-phase coil 4V is connected to the connection point V1 between these V-phase first switching elements 16 and 18.

[0022] Furthermore, the first inverter 10 includes a first switching element 20 provided between the first high potential point H1 and a connection point W1 corresponding to the W-phase coil 4W, and a first switching element 22 provided between the connection point W1 and a first low potential point L1. One end of the W-phase coil 4W is connected to the connection point W1 between the W-phase first switching elements 20 and 22.

[0023] The second inverter 30 is a three-phase inverter that switches the energization of the coil 4 of each phase, similar to the first inverter 10. The second inverter 30 includes a plurality of second switching elements 32, 34, 36, 38, 40, and 42 that can open and close (turn on and off) between a second high potential point H2 of the second inverter 30 and the other end of the coil 4, and between the other end of the coil 4 and a second low potential point L2 of the second inverter 30, for each phase of the motor 1. In this embodiment, the second switching elements 32, 34, 36, 38, 40, and 42 are collectively referred to as "second switching element SW2."

[0024] More specifically, the second inverter 30 includes a second switching element 32 provided between the second high potential point H2 and a connection point U2 corresponding to the U-phase coil 4U, and a second switching element 34 provided between the connection point U2 and a second low potential point L2. The other end of the U-phase coil 4U is connected to the connection point U2 between the U-phase second switching elements 32 and 34.

[0025] The second inverter 30 also includes a second switching element 36 provided between the second high potential point H2 and the connection point V2, and a second switching element 38 provided between the connection point V2 and the second low potential point L2, corresponding to the V-phase coil 4V. The other end of the V-phase coil 4V is connected to the connection point V2 between these V-phase second switching elements 36 and 38.

[0026] Furthermore, the second inverter 30 includes a second switching element 40 provided between the second high potential point H2 and a connection point W2 corresponding to the W-phase coil 4W, and a second switching element 42 provided between the connection point W2 and a second low potential point L2. The other end of the V-phase coil 4W is connected to the connection point W2 between the W-phase second switching elements 40 and 42.

[0027] The on / off of the first switching element SW1 and the second switching element SW2 is controlled by the control device 60. When the first switching element SW1 and the second switching element SW2 are turned on, they allow current to flow from the high potential side to the low potential side, and when they are turned off, they cut off the current.

[0028] The first high potential point H1 of the first inverter 10 is connected to the positive electrode of the DC power supply 2. The first high potential point H1 and the second high potential point H2 of the second inverter 30 are connected by a high potential side connection line 50. The first low potential point L1 of the first inverter 10 is connected to the negative electrode of the DC power supply 2. The first low potential point L1 and the second low potential point L2 of the second inverter 30 are connected by a low potential side connection line 52.

[0029] As described above, the first inverter 10 and the second inverter 30 are connected in an H-bridge configuration with each phase of the first and second inverters 10, 30 being connected via each phase of the electric motor 1 (i.e., configured as an H-bridge inverter). In the following description, the direction of current flowing through each of the coils 4 of each of the three phases is defined as positive when it flows from the first inverter 10 side to the second inverter 30 side. In this configuration, the voltage applied across the coils 4 can be set to a positive power supply voltage Vdc, a negative power supply voltage Vdc, or 0, depending on the switching state of the first inverter 10 and the second inverter 30.

[0030] 1-1-2. Loss characteristics of the first and second switching elements In this embodiment, the first switching element SW1 on the first inverter 10 side and the second switching element SW2 on the second inverter 30 side are configured to have different loss characteristics due to differences in materials.

[0031] Specifically, the first switching element SW1 is, for example, an insulated gate bipolar transistor (IGBT) with a diode (freewheel diode) 24. The material of the IGBT is, for example, Si (silicon). The diode 24 allows current to flow from a low potential side to a high potential side. On the other hand, the second switching element SW2 is, for example, a metal oxide semiconductor field effect transistor (MOSFET) made of SiC (silicon carbide). The MOSFET includes a diode (parasitic diode) 44. In this embodiment, the first switching element SW1 and the second switching element SW2 are configured to have different loss characteristics by mixing an IGBT made of Si and a MOSFET made of SiC in each inverter.

[0032] 1-1-3.Control device The control device 60 controls the first and second inverters 10, 30 configured as described above. The control device 60 is connected to a current detector 62, a voltage detector 64, and a rotation angle sensor (not shown) along with the first inverter 10 and the second inverter 30. The control device 60 includes a CPU (Central Processing Unit), a memory, and a non-volatile storage unit, and performs various types of arithmetic processing. The arithmetic processing in the control device 60 may be realized by software processing in which a pre-stored program is executed by the CPU, or may be realized by hardware processing using a dedicated electronic circuit.

[0033] The current detector 62 includes a current detection element such as a Hall element for each phase of the electric motor 1, and detects the current flowing through each coil 4. The voltage detector 64 detects the power supply voltage (DC voltage across the smoothing capacitor 3) Vdc. In addition, the rotation angle sensor detects the rotation electrical angle θ of the output shaft of the electric motor 1.

[0034] The control device 60 includes a control signal generating unit 60a. The control signal generating unit 60a generates a control signal (PWM (Pulse Width Modulation) signal) for controlling the on / off of the first switching element SW1 and the second switching element SW2 in order to control the first and second inverters 10 and 30. The PWM signal is generated for each phase of the motor 1 based on a rotational electrical angle θ of the motor 1, a current value of each phase, and a voltage command value for each phase that is generated based on a torque command value. Then, the control device 60 generates and outputs a gate signal for controlling the on / off of the first switching element SW1 and the second switching element SW2 in response to the generated PWM signal. The first switching element SW1 and the second switching element SW2 are turned on and off in response to the PWM signal, so that the DC power from the DC power source 2 is converted into AC power and supplied to the motor 1. More specifically, a voltage is applied to the coil 4 of each phase. This drives the motor 1.

[0035] As described above, the power conversion device 100 of this embodiment has a configuration in which the coils 4 of each phase of the motor 1 are driven by an H-bridge inverter (H-bridge motor drive system). In this configuration, by appropriately controlling the switching of each phase of the first and second inverters 10, 30, it is possible to appropriately control the voltage applied to each phase of the motor 1 and drive the motor 1.

[0036] 1-2.Characteristics of switching control Here, the first switching element SW1 or the second switching element SW2, whichever has smaller loss, is referred to as the “low-loss element,” and the other, which has larger loss, is referred to as the “high-loss element.” The loss here typically refers to switching loss and conduction loss.

[0037] The switching control of the first switching element SW1 and the second switching element SW2 in this embodiment has the following features: That is, the control device 60 controls the first and second inverters 10, 30 so that the number of times of switching of one of the first and second inverters 10, 30 corresponding to the inverter on the side using low-loss elements is greater than the number of times of switching of the other of the first and second inverters 10, 30 corresponding to the inverter on the side using high-loss elements.

[0038] In this embodiment, as described later with reference to FIG. 4, it is assumed that which of the first switching element SW1 and the second switching element SW2 corresponds to the low-loss element is not uniform, but varies depending on the amount of current of each switching element SW1, SW2 which changes depending on the operating point of the motor 1.

[0039] Fig. 2(A) is a time chart showing a method of generating a control signal (PMW signal) in a general switching control (comparative example), and Fig. 2(B) is a time chart showing a method of generating a control signal (PWM signal) in a characteristic switching control according to the first embodiment. Note that in Fig. 2, the method of generating a PWM signal is explained using the U phase as an example, but the same is true for the other V and W phases. Also, the comparative example has the same circuit configuration as the power conversion device 100 of the first embodiment, but differs from the first embodiment in the method of generating a PWM signal.

[0040] First, a comparative example will be described with reference to Fig. 2(A). The U-phase modulated wave Vu (sine wave, for example) shown in Fig. 2(A) is obtained by normalizing a U-phase voltage command value based on a drive command (torque command, for example) of the electric motor 1 by 1 / 2 the power supply voltage Vdc. The first carrier signal C1 and the second carrier signal C2 (carrier wave) are triangular waves, for example. The first carrier signal C1 is generated so as to vary in the range from 0 to 1, and the second carrier signal C2 is generated so as to vary in the range from -1 to 0.

[0041] The control signal generating unit in the comparative example compares the U-phase modulated wave Vu with the first carrier signal C1 to generate PWM signals for the first switching elements 12 and 14 on the first inverter 10 side. Specifically, when the U-phase modulated wave Vu is larger than the first carrier signal C1, the control signal generating unit turns on the connection point U1 (see FIG. 1) of the first inverter 10 (i.e., turns on the first switching element 12 constituting the upper arm and turns off the first switching element 14 constituting the lower arm). On the other hand, when the U-phase modulated wave Vu is smaller than the first carrier signal C1, the control signal generating unit turns off the connection point U1 (i.e., turns off the first switching element 12 constituting the upper arm and turns on the first switching element 14 constituting the lower arm).

[0042] Furthermore, the control signal generating unit in the comparative example compares the U-phase modulated wave Vu with the second carrier signal C2 to generate PWM signals for the second switching elements 32 and 34 on the second inverter 30 side. Specifically, when the U-phase modulated wave Vu is larger than the second carrier signal C2, the control signal generating unit turns off the connection point U2 (see FIG. 1) of the second inverter 30 (i.e., turns off the second switching element 32 constituting the upper arm and turns on the second switching element 34 constituting the lower arm). On the other hand, when the U-phase modulated wave Vu is smaller than the second carrier signal C2, the control signal generating unit turns on the connection point U2 (i.e., turns on the second switching element 32 constituting the upper arm and turns off the second switching element 34 constituting the lower arm).

[0043] Fig. 3 is a diagram showing the relationship between the modulated wave and the on / off states of the connection points U1 and U2 in the comparative example. As described above with reference to Fig. 2(A), according to the comparative example, when the U-phase modulated wave Vu is larger than the first carrier signal C1, the connection point U1 is turned on and the connection point U2 is turned off. When the U-phase modulated wave Vu is between the first carrier signal C1 and the second carrier signal C2, both the connection points U1 and U2 are turned off. Also, when the U-phase modulated wave Vu is smaller than the second carrier signal C2, the connection point U1 is turned off and the connection point U2 is turned on.

[0044] According to the comparative example shown in FIG. 2(A) described above, the first and second inverters 10, 30 are controlled so that the number of switching operations of the first inverter 10 and the second inverter 30 are equal to each other.

[0045] Next, the operation of the control signal generating unit 60a of this embodiment will be described with reference to FIG. 2(B). Here, a method for increasing the number of switching times of the first inverter 10 compared to that of the second inverter 30 will be described. In order to increase the number of switching times of the first inverter 10, the control signal generating unit 60a sets the modulated waves (U-phase modulated wave Vu and first corrected modulated wave Vu_new1) so that they fall within the amplitude range from 0 to 1 as shown in FIG. 2(B). Specifically, when the U-phase modulated wave Vu (basic modulated wave of voltage command) is 0 or more (solid line), the control signal generating unit 60a uses the U-phase modulated wave Vu (basic modulated wave) as it is. On the other hand, when the U-phase modulated wave Vu (basic modulated wave) is less than 0 (dashed line), the first corrected modulated wave Vu_new1 obtained by adding 1 to the basic modulated wave is set.

[0046] Then, when the U-phase modulated wave Vu (basic modulated wave) is 0 or more (solid line), the control signal generating unit 60a generates the PWM signals of the first switching elements 12 and 14 constituting the upper arm and lower arm on the first inverter 10 side by comparing the U-phase modulated wave Vu with the first carrier signal C1 as in the comparative example. Also, when the fundamental modulated wave is 0 or more, the control signal generating unit 60a turns off the connection point U2 of the second inverter 30 (i.e., turns off the second switching element 32 constituting the upper arm and turns on the second switching element 34 constituting the lower arm).

[0047] On the other hand, when the U-phase modulated wave Vu (basic modulated wave) is less than 0 (dashed line), the control signal generating unit 60a compares the first corrected modulated wave Vu_new1 with the first carrier signal C1 to generate PWM signals for the first switching elements 12 and 14 constituting the upper and lower arms on the first inverter 10 side, respectively. Specifically, when the first corrected modulated wave Vu_new1 is greater than the first carrier signal C1, the control signal generating unit 60a turns on the connection point U1, and when the first corrected modulated wave Vu_new1 is smaller than the first carrier signal C1, the control signal generating unit 60a turns off the connection point U1. In addition, when the fundamental modulated wave is less than 0, the control signal generating unit 60a turns on the connection point U2 of the second inverter 30.

[0048] According to the method of generating the PWM signal described with reference to FIG. 2(B), the number of switching operations of the first inverter 10 can be increased compared to that of the second inverter 30 while maintaining the applied voltage of the motor 1 at the same level as that of the comparative example. More specifically, according to this method, when the U-phase modulated wave Vu (basic modulated wave) is less than 0 (dashed line), the connection point U2 of the second inverter 30 is continuously turned on and a PWM signal on the first inverter 10 side is generated by comparing the first corrected modulated wave Vu_new1 with the first carrier signal C1, so that a voltage equivalent to that of the comparative example shown in FIG. 2(A) can be applied to the motor 1. In this way, according to this method, a PWM signal in which switching is biased toward the first inverter 10 side can be easily generated.

[0049] FIG. 4 is a flowchart showing a procedure for generating a control signal (PWM signal) by the control signal generating unit 60a according to the first embodiment.

[0050] 4, first in step S100, the control signal generating unit 60a (control device 60) extracts (obtains) the current operating point of the electric motor 1. This operating point is specified by, for example, the torque and rotation speed of the electric motor 1. Thereafter, the process proceeds to step S102.

[0051] In step S102, the control signal generating unit 60a determines which of the first inverter 10 and the second inverter 30 should have its switching count increased. Specifically, which inverter should have its switching count increased (in other words, which inverter should have its loss increased) is determined, for example, according to the current amounts of the switching elements SW1 and SW2 that change according to the current operating point of the motor 1. More specifically, in a current amount range in which the first switching element SW1 is a low-loss element, the number of switching times of the first switching element SW1 is increased and the number of switching times of the second switching element SW2 is decreased by the processes in the following steps S104 to S114. On the other hand, in a current amount range in which the second switching element SW2 is a low-loss element, the number of switching times of the second switching element SW2 is increased and the number of switching times of the first switching element SW1 is decreased by the processes in the following steps S116 to S126.

[0052] When it is determined to increase the number of switching operations of the first switching element SW1 (step S102; Yes), the control signal generating unit 60a determines in step S104 whether the modulated wave Vx of the current command is equal to or greater than 0. The "modulated wave Vx" indicates a modulated wave of x phase, and in a three-phase example, x has three variables U, V, and W. The processes of steps S106 and S108 following step S104 and the processes of steps S110 to S114 correspond to the example shown in FIG. 2(B) described above.

[0053] In step S104, if the modulated wave Vx (corresponding to the "basic modulated wave" according to the present disclosure) is equal to or greater than 0 (solid line in FIG. 2(B)), the control signal generating unit 60a compares the modulated wave Vx with the first carrier signal C1 in step S106 to generate a control signal (i.e., the above-mentioned PWM signal) for the first inverter 10. In the following step S108, the control signal generating unit 60a sets the x-phase connection point X2 (U2, V2, and W2) of the second inverter 30 to OFF.

[0054] On the other hand, when the modulated wave Vx (basic modulated wave) is less than 0 in step S104 (dashed line in FIG. 2B), the control signal generating unit 60a sets a first corrected modulated wave Vx_new1 in step S110. The first corrected modulated wave Vx_new1 is obtained by adding 1 to the modulated wave Vx (basic modulated wave).

[0055] In step S112 following step S110, the control signal generating unit 60a compares the first corrected modulated wave Vx_new1 with the first carrier signal C1 to generate a control signal (PWM signal) for the first inverter 10. In the following step S114, the control signal generating unit 60a sets the x-phase connection point X2 of the second inverter 30 to ON.

[0056] On the other hand, when it is determined to increase the number of switching times of the second switching element SW2 (step S102; No), in step S116, the control signal generating unit 60a determines whether or not the modulated wave Vx is less than 0. The processes of steps S118 and S120 following step S116, and the processes of steps S122 to S126 will be described with reference to FIG.

[0057] Fig. 5 is a time chart showing a method for generating a control signal (PWM signal) when increasing the number of switching operations of the second switching element SW2 on the second inverter 30 side. In the method shown in Fig. 5, in order to increase the number of switching operations of the second inverter 30, the modulated waves (the modulated wave Vx and the second corrected modulated wave Vx_new2) are set to fall within the amplitude range from -1 to 0, as shown in Fig. 5.

[0058] When the modulated wave Vx (basic modulated wave) is less than 0 in step S116 (solid line in FIG. 5), the control signal generating unit 60a compares the modulated wave Vx (basic modulated wave) with the second carrier signal C2 in step S118 to generate a control signal (PWM signal) for the second inverter 30. More specifically, as shown in FIG. 5, when the modulated wave Vx is greater than the second carrier signal C2, the control signal generating unit 60a turns off the connection point X2 of the second inverter 30 (i.e., turns off the second switching element SW2 constituting the upper arm and turns on the second switching element SW2 constituting the lower arm). On the other hand, when the modulated wave Vx is smaller than the second carrier signal C2, the control signal generating unit 60a turns on the connection point X2 (i.e., turns on the second switching element SW2 constituting the upper arm and turns off the second switching element SW2 constituting the lower arm).

[0059] In the following step S120, the control signal generating unit 60a sets the x-phase connection point X1 (U1, V1, and W1) of the first inverter 10 to OFF.

[0060] On the other hand, when the modulated wave Vx (basic modulated wave) is equal to or greater than 0 in step S116 (dotted line in FIG. 5), the control signal generating unit 60a sets a second corrected modulated wave Vx_new2 in step S122. The second corrected modulated wave Vx_new2 is obtained by adding −1 to the modulated wave Vx (basic modulated wave).

[0061] In step S124 following step S122, the control signal generating unit 60a compares the second corrected modulated wave Vx_new2 with the second carrier signal C2 to generate a control signal (PWM signal) for the second inverter 30. More specifically, as shown in Fig. 5, when the second corrected modulated wave Vx_new2 is larger than the second carrier signal C2, the control signal generating unit 60a turns off the connection point X2. On the other hand, when the second corrected modulated wave Vx_new2 is smaller than the second carrier signal C2, the control signal generating unit 60a turns on the connection point X2.

[0062] In the following step S126, the control signal generating unit 60a sets the x-phase connection point X1 of the first inverter 10 to ON.

[0063] In addition, according to the method of generating the PWM signal described with reference to FIG. 5 (steps S116 to S126), the number of switching operations of the second inverter 30 can be increased compared to that of the first inverter 10 while maintaining the applied voltage of the motor 1 equivalent to that of the comparative example (see FIG. 2(A)). More specifically, according to this method, when the modulated wave Vx (basic modulated wave) is equal to or greater than 0 (dashed line), the connection point X1 of the first inverter 10 is continuously turned on and a PWM signal on the second inverter 30 side is generated by comparing the second corrected modulated wave Vu_new2 with the second carrier signal C2, so that a voltage equivalent to that of the comparative example can be applied to the motor 1. In this way, according to this method, a PWM signal in which the occurrence of switching is biased toward the second inverter 30 side can be easily generated.

[0064] 1-3.Effects As described above, in the power conversion device 100 according to the first embodiment, in the H-bridge motor drive system, switching elements with different loss characteristics are mixed and used on an inverter-by-inverter basis by utilizing differences in materials. The first and second inverters 10, 30 are controlled so that the number of times of switching one of the first and second inverters 10, 30 corresponding to the inverter on the side using low-loss elements is greater than the number of times of switching the other of the first and second inverters 10, 30 corresponding to the inverter on the side using high-loss elements. This makes it possible to effectively utilize the low-loss elements and reduce inverter losses (switching losses and conduction losses).

[0065] The effect of reducing inverter loss will be described in more detail with reference to FIG. 6. FIG. 6 is a diagram for explaining the effect of the first embodiment with respect to the comparative example shown in FIG. 2(A). An example of the effect shown in FIG. 6 shows a simulation result in an example where the first switching element SW1 corresponds to a high-loss element and the second switching element SW2 corresponds to a low-loss element. The switching control of this embodiment is a control that concentrates (biases) the occurrence of switching on one inverter (in this example, the second inverter 30) (i.e., on the low-loss element side). For this reason, as shown in FIG. 6, due to the reduction in the number of switching operations of the high-loss element (the first switching element SW1), the switching loss on the first inverter 10 side is significantly reduced compared to the comparative example. In addition, although the switching loss on the second inverter 30 side increases due to the concentration of switching compared to the comparative example, the increase is suppressed to a low amount because it is the low-loss element side. And, the conduction loss of the second inverter 30 is also reduced compared to the comparative example. As a result, the loss of the entire inverter is reduced by 14% compared to the comparative example. Furthermore, even if the switching control of this embodiment is performed, the voltage applied to the motor 1 is equivalent to that of the comparative example, and therefore the loss (motor loss) of the motor 1 is equivalent. Therefore, according to the power conversion device 100 of this embodiment, the total loss in the H-bridge motor drive system, including the loss of the motor 1, can be reduced.

[0066] As described above, according to this embodiment, in an H-bridge motor drive system in which switching elements with different loss characteristics are combined, it becomes possible to effectively utilize low-loss elements. More specifically, it is possible to reduce the loss of the H-bridge motor drive system by effectively utilizing low-loss elements while reducing the use of low-loss elements to reduce costs. This leads to improved electric power consumption of electric vehicles equipped with the H-bridge motor drive system.

[0067] 1-4.Other configuration examples with different loss characteristics In the above-described first embodiment, the first switching element SW1 and the second switching element SW2 are configured to have different loss characteristics due to differences in materials. However, instead of such an example utilizing differences in materials, the "plurality of first switching elements" and the "plurality of second switching elements" according to the present disclosure may be configured to have different loss characteristics due to differences in chip areas.

[0068] 2. Second embodiment 7 is a diagram illustrating a schematic configuration of a power conversion device 200 according to the second embodiment. The power conversion device 200 differs from the power conversion device 100 according to the first embodiment in the points described below.

[0069] Specifically, the power conversion device 200 includes first and second inverters 210, 230 instead of the first and second inverters 10, 30. In this embodiment, the first switching elements SW1 (212, 214, 216, 218, 220, and 222) on the first inverter 210 side are MOSFETs made of SiC, contrary to the example shown in Fig. 1. Also, the second switching elements SW2 (232, 234, 236, 238, 240, and 242) on the second inverter 230 side are IGBTs made of Si, contrary to the example shown in Fig. 1.

[0070] Moreover, unlike the power conversion device 100, the power conversion device 200 includes a switch 202. The switch 202 is disposed on the high potential side connection line 50. The switch 202 is turned on and off by the control device 60. The switch 202 is, for example, a semiconductor switch (an IGBT as one example). Alternatively, the switch 202 may be, for example, a mechanical switch such as a relay. In this manner, the power conversion device 200 includes the switch 202 that is disposed between the first inverter 210 and the second inverter 230 and switches between a conductive state and a cut-off state of a current.

[0071] According to the power conversion device 200 having the above-mentioned configuration, by continuously keeping the switch 202 on, it is possible to perform open connection driving in an H-bridge configuration, similarly to the power conversion device 100 of the embodiment 1. Then, by similarly executing the process of the flowchart shown in Fig. 4 for the power conversion device 200, it is possible to effectively utilize low-loss elements and reduce inverter losses (switching losses and conduction losses).

[0072] Moreover, according to the power conversion device 200, Y-connection driving can also be performed in a desired Y-connection driving region. FIG. 8 is a diagram showing the operating state of the power conversion device 200 during Y-connection driving. When performing Y-connection driving, the control device 60 keeps the switch 202 off. Moreover, the control device 60 keeps the second switching elements 232, 236, and 240 constituting the upper arm of the second inverter 230 on, and keeps the second switching elements 234, 238, and 242 constituting the lower arm of the second inverter 230 off. This allows the second inverter 230 to operate as the neutral point of each coil 4 of the motor 1.

[0073] In addition, in the power conversion device 200, a SiC MOSFET is disposed on the first inverter 210 side as a low-loss element. Therefore, by performing Y-connection driving in a driving region in which the SiC MOSFET functions as a low-loss element, switching can be performed only by the low-loss element during Y-connection driving. This makes it possible to further reduce inverter loss.

[0074] 9 is a diagram illustrating a schematic configuration of a power conversion device 300 according to a first modification of the embodiment 2. The power conversion device 300 differs from the power conversion device 200 according to the embodiment 2 in that a switch 302 is additionally provided.

[0075] Specifically, the switch 302 is disposed on the low potential side connection line 52. The switch 302 is, for example, a semiconductor switch (an IGBT as one example) like the switch 202. The switch 302 is turned on and off by the control device 60. The switch 302 also corresponds to one example of the "switch" according to the present disclosure.

[0076] The power conversion device 300 having the switches 202 and 302 on both the high potential side and the low potential side, respectively, can also perform Y-connection driving by, for example, the following method. That is, the control device 60 keeps the switches 202 and 302 off continuously. The control device 60 also keeps the second switching elements 232, 236, and 240 constituting the upper arm of the second inverter 230 off continuously, and keeps the second switching elements 234, 238, and 242 constituting the lower arm of the second inverter 230 on continuously. This allows the second inverter 230 to operate as the neutral point of each coil 4 of the motor 1. Alternatively, the control device 60 may operate as the neutral point of each coil 4 by keeping the second switching elements 232, 236, and 240 constituting the upper arm on continuously, and keeping the second switching elements 234, 238, and 242 constituting the lower arm off continuously.

[0077] 10 is a diagram illustrating a schematic configuration of a power conversion device 400 according to a second modification of the embodiment 2. The power conversion device 400 differs from the power conversion device 200 according to the embodiment 2 in that the power conversion device 400 includes switches 402 and 404 instead of the switch 202.

[0078] Specifically, the switches 402 and 404 are disposed on the high potential side connection line 50 and the low potential side connection line 52, respectively. These switches 402 and 404 are, for example, semiconductor switches, and are configured to be able to control the conduction / cutoff of bidirectional current. The switches 402 and 404 are turned on and off by the control device 60. Such bidirectional switches 402 and 404 may be used as another example of the "switch" according to the present disclosure for enabling Y-connection drive.

[0079] 3. Other embodiments In the above-mentioned first and second embodiments, the power conversion device 100 and the like applied to the three-phase electric motor 1 have been described as an example. However, the "rotating electric machine" according to the present disclosure may be, for example, a five-phase rotating electric machine.

[0080] 11 is a diagram that illustrates a schematic configuration of a power conversion device 500 that is applied to a five-phase rotating electric machine. The power conversion device 500 differs from the power conversion device 100 according to the first embodiment in the points that will be described below.

[0081] 11 shows a five-phase motor 5 with open windings as an example of a five-phase rotating electric machine. The motor 5 has five-phase coils 6. The power conversion device 500 includes first and second inverters 510 and 520 instead of the first and second inverters 10 and 30.

[0082] The first inverter 510 and the second inverter 520 are five-phase inverters that switch the current supply to the coil 6 of each phase. The first inverter 510 includes a plurality of first switching elements SW1 that can open and close (ON / OFF) between the first high potential point H1 and one end of the coil 6, and between the one end of the coil 6 and the first low potential point L1, for each phase of the motor 5. These first switching elements SW1 are, for example, Si IGBTs. The second inverter 520 includes a plurality of second switching elements SW2 that can open and close (ON / OFF) between the second high potential point H2 and the other end of the coil 6, and between the other end of the coil 6 and the second low potential point L2, for each phase of the motor 5. These second switching elements SW2 are, for example, SiC MOSFETs.

[0083] Furthermore, the "power conversion device" according to the present disclosure is not limited to the above-mentioned three-phase and five-phase examples, and may be similarly applied to a rotating electric machine having an n-phase coil, such as six or nine phases. In addition, each of the power conversion devices 200, 300, and 400 described in the second embodiment may be modified so as to be similarly applied to a rotating electric machine having an n-phase coil, such as five phases. [Explanation of symbols]

[0084] 1, 5 Electric motor (rotating motor) 2 DC power supply 3. Smoothing capacitor 4, 6 Motor coil 10, 210, 510 1st inverter 12, 14, 16, 18, 20, 22, 212, 214, 216, 218, 220, 222, SW1 First switching element 24, 44 Diode 30, 230, 520 2nd inverter 32, 34, 36, 38, 40, 42, 232, 234, 236, 238, 240, 242, SW2 Second switching element 50 High potential side connection wire 52 Low potential side connection wire 60 Control device 60a Control signal generating unit of control device 62 Current detector 64 Voltage Detector 100, 200, 300, 400, 500 Power Converter 202, 302, 402, 404 Switches H1 First high potential point H2 2nd high potential point L1 1st low potential point L2 2nd low potential point U1, V1, W1 Connection points of one end of each phase coil to the first inverter U2, V2, W2 Connection points of the other end of each phase coil to the second inverter

Claims

1. A power conversion device that converts power supplied from a DC power source to a rotating electric machine having an open winding with multiple phase coils, a first inverter connected in parallel with the DC power supply, the first inverter including a plurality of first switching elements for each phase of the rotating electric machine, the first switching elements being capable of switching between a first high potential point and one end of the coil, and between one end of the coil and a first low potential point, a second inverter including a plurality of second switching elements connected in parallel to the DC power supply and capable of opening and closing between a second high potential point and the other end of the coil and between the other end of the coil and a second low potential point for each phase of the rotating electric machine; A control device for controlling the first and second inverters; Equipped with The first switching elements and the second switching elements are configured to have different loss characteristics from each other, when one of the plurality of first switching elements and the plurality of second switching elements having a smaller loss is referred to as a low-loss element and one of the plurality of second switching elements having a larger loss is referred to as a high-loss element, the control device controls the first and second inverters such that a number of times of switching of one of the first and second inverters corresponding to an inverter using the low-loss element is greater than a number of times of switching of the other of the first and second inverters corresponding to an inverter using the high-loss element, A direction of a current flowing through each of the coils of the multiple phases is defined as a positive direction from the first inverter side to the second inverter side, the control device includes a control signal generation unit that generates control signals for the first switching elements and the second switching elements for each of the multiple phases, The control signal generating unit when a fundamental modulation wave of a voltage command for each phase based on a drive command for the rotating electric machine is equal to or greater than 0, a first carrier signal varying between 0 and 1 is compared with the fundamental modulation wave to generate control signals for first switching elements constituting upper and lower arms of the first inverter, while turning off and on control signals for second switching elements constituting upper and lower arms of the second inverter, respectively; When the fundamental modulated wave is less than 0, a first corrected modulated wave obtained by adding 1 to the fundamental modulated wave is compared with the first carrier signal to generate control signals for first switching elements constituting the upper arm and the lower arm of the first inverter, while turning on and off control signals for second switching elements constituting the upper arm and the lower arm of the second inverter, respectively. A power conversion device comprising:

2. A power conversion device that converts power supplied from a DC power source to a rotating electric machine having an open winding with multiple phase coils, a first inverter connected in parallel with the DC power supply, the first inverter including a plurality of first switching elements for each phase of the rotating electric machine, the first switching elements being capable of switching between a first high potential point and one end of the coil, and between one end of the coil and a first low potential point, a second inverter including a plurality of second switching elements connected in parallel to the DC power supply and capable of opening and closing between a second high potential point and the other end of the coil and between the other end of the coil and a second low potential point for each phase of the rotating electric machine; A control device for controlling the first and second inverters; Equipped with The first switching elements and the second switching elements are configured to have different loss characteristics from each other, when one of the plurality of first switching elements and the plurality of second switching elements having a smaller loss is referred to as a low-loss element and one of the plurality of second switching elements having a larger loss is referred to as a high-loss element, the control device controls the first and second inverters such that a number of times of switching of one of the first and second inverters corresponding to an inverter using the low-loss element is greater than a number of times of switching of the other of the first and second inverters corresponding to an inverter using the high-loss element, A direction of a current flowing through each of the coils of the multiple phases is defined as a positive direction from the first inverter side to the second inverter side, the control device includes a control signal generation unit that generates control signals for the first switching elements and the second switching elements for each of the multiple phases, The control signal generating unit when a fundamental modulation wave of a voltage command for each phase based on a drive command of the rotating electric machine is less than 0, the fundamental modulation wave is compared with a second carrier signal that varies between -1 and 0 to generate control signals for second switching elements that respectively constitute the upper arm and the lower arm of the second inverter, while turning off and on control signals for first switching elements that respectively constitute the upper arm and the lower arm of the first inverter, When the fundamental modulated wave is equal to or greater than 0, a second corrected modulated wave obtained by adding -1 to the fundamental modulated wave is compared with the second carrier signal to generate control signals for second switching elements constituting the upper and lower arms of the second inverter, while turning on and off control signals for first switching elements constituting the upper and lower arms of the first inverter, respectively. A power conversion device comprising:

3. The power conversion device further includes a switch disposed between the first inverter and the second inverter, the switch switching between a current conduction state and a current cutoff state, The first switching elements included in the first inverter are the low loss elements.

3. The power conversion device according to claim 1 or 2.

4. The first switching elements and the second switching elements are configured to have different loss characteristics due to differences in materials.

4. The power conversion device according to claim 1, wherein the first and second power supplies are connected to each other.

5. The first switching elements and the second switching elements are configured to have different loss characteristics due to differences in chip areas.

4. The power conversion device according to claim 1, wherein the first and second power supplies are connected to each other.

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