JP6248986B2 - Inverter control method and inverter device - Google Patents

Description

  The present invention relates to a method for controlling an inverter and an inverter device.

  The inverter includes a plurality of switching elements, and converts DC power into AC power by turning on / off the plurality of switching elements. The switching element is composed of an element such as an IGBT (Insulated Gate Bipolar Transistor). In an inverter, it is known that a switching loss occurs when a switching element is turned on / off. It is generally known that this switching loss is proportional to the product of the current flowing through the element when it is on (conduction) and the voltage that the element takes when it is off (shut off). Therefore, for example, every time the switching element is turned on / off according to PWM (Pulse Width Modulation) control, there arises a problem that a switching loss proportional to the product of the input voltage and current occurs.

  Patent Document 1 describes a circuit called a so-called three-level inverter. In the three-level inverter, the intermediate potential is interposed, so that the voltage that the switching element takes on is almost halved, so that the switching loss can be reduced to almost half.

JP 2014-107931 A

  According to the above three-level inverter, switching loss can be reduced, but it is necessary to provide an intermediate voltage, and it is necessary to provide many additional elements. Specifically, it is necessary to provide two sets of IGBTs and diodes for each phase of the inverter, and it is necessary to additionally provide a gate driver, a signal line, a logic IC, and the like for driving those elements. As described above, the three-level inverter has a problem of requiring many additional elements.

  An object of the present invention is to reduce switching loss in an inverter. Alternatively, the switching loss in the inverter is reduced by a circuit configuration with few additional elements.

The invention according to claim 1 comprises a plurality of switching elements, wherein the plurality of switching elements are turned on / off to control an inverter that converts DC power supplied from a power source into AC power. The output terminals of the plurality of phases configured by the switching elements are provided with a short-circuit switch that short-circuits the output terminals of the plurality of phases, and the plurality of phases constitute the plurality of phases during the on-period of the short-circuit switch. Inverter characterized by switching at least one switching element for each phase among a plurality of switching elements , wherein the short-circuit switch is a switch that collectively short-circuits the output terminals of the plurality of phases. This is a control method.

  According to a second aspect of the present invention, in the inverter control method according to the first aspect, the short-circuit switch is turned on for a predetermined period for each PWM control cycle of the inverter.

  According to a third aspect of the present invention, in the inverter control method according to the first or second aspect, the operation of the switching element that is switched during the ON period of the short-circuit switch is the negative side of the power source in each phase. The operation of the switching element connected to is switching from on to off, and the operation of the switching element connected to the positive side of the power supply in each individual phase is switching from off to on, or the power supply The operation of the switching element connected to the negative electrode side is switching from off to on, and the operation of the switching element connected to the positive electrode side of the power supply is switching from on to off.

According to a fourth aspect of the present invention, there is provided a power conversion unit that includes a plurality of switching elements, and that converts DC power supplied from a power source into AC power by turning on / off the plurality of switching elements, and the plurality of switching elements. A shorting switch that is provided at an output terminal of a plurality of phases constituted by elements, and short-circuits the output terminals of the plurality of phases; and a plurality of switching elements that constitute the plurality of phases during an ON period of the shorting switch among them, seen including a control unit for switching at least one switching element, a for each phase, the short-circuit switch is a switch for short-circuiting collectively output terminals of the plurality of phases, characterized in that It is an inverter device.

The invention according to claim 5 is the inverter device according to claim 4 , wherein the control unit turns on the short-circuit switch for a predetermined period for each PWM control cycle of the power conversion unit. To do.

  According to the present invention, switching loss in an inverter can be reduced.

It is a figure which shows the inverter apparatus which concerns on embodiment of this invention. It is a figure which shows the structure of a short circuit switch. It is a figure which shows the signal regarding PWM control which concerns on this embodiment. It is a graph which shows the switching loss in the inverter which concerns on this embodiment. It is a figure for demonstrating the switching operation | movement which concerns on this embodiment. It is a figure for demonstrating the switching operation | movement which concerns on this embodiment. It is a figure which shows an equivalent circuit. It is a figure for demonstrating the switching operation | movement which concerns on this embodiment. It is a figure for demonstrating the switching operation | movement which concerns on this embodiment. It is a figure for demonstrating the switching operation | movement which concerns on this embodiment. It is a figure which shows the signal regarding the PWM control which concerns on the comparative example 1. FIG. 6 is a graph showing switching loss in an inverter according to Comparative Example 2. 10 is a diagram for explaining a switching operation according to Comparative Example 2. FIG. 10 is a diagram for explaining a switching operation according to Comparative Example 2. FIG. 10 is a diagram for explaining a switching operation according to Comparative Example 2. FIG. It is a figure which shows the inverter apparatus which concerns on the modification 1. FIG. It is a figure which shows the structure of the short circuit switch which concerns on the modification 1. FIG. It is a figure which shows the signal regarding the PWM control which concerns on the modification 1. FIG. It is a figure which shows the signal regarding the PWM control which concerns on the modification 2. FIG.

  FIG. 1 shows an inverter device according to this embodiment. This inverter device is a device having a function of adjusting power supplied from the DC power supply 10 to the motor MG. Further, the inverter device may have a function of adjusting the power generated by the motor MG and supplied to the DC power supply 10.

  The motor MG is, for example, a three-phase AC synchronous motor, and is driven by electric power supplied from the DC power supply 10. Motor MG includes a stator having three coils of U phase, V phase and W phase, and a rotor (not shown). One end of the three coils of the U phase, the V phase, and the W phase is connected to each other at a midpoint, and the other end is connected to a switching element that constitutes an inverter. The motor MG is used as a drive source of an electric vehicle, a hybrid vehicle, or a fuel cell vehicle, for example.

  The DC power supply 10 is a power supply that supplies a DC voltage. As the DC power supply 10, for example, a chargeable / dischargeable power supply may be used. As a chargeable / dischargeable power source, a lithium ion battery, a nickel metal hydride battery, or the like can be used.

  Here, regarding the power source line of the DC power source 10, the high voltage side line is referred to as a positive electrode side line 12, and the low voltage side line is referred to as a negative electrode side line 14. The line connected to the positive terminal of the DC power supply 10 is the positive electrode side line 12, and the line connected to the negative terminal of the DC power supply 10 is the negative electrode side line 14.

  The inverter includes a plurality of switching elements (switching elements Q11 to Q16), converts the DC power supplied from DC power supply 10 into three-phase AC power, and supplies it to motor MG. The inverter includes a U-phase arm, a V-phase arm, and a W-phase arm arranged in parallel with each other between positive electrode side line 12 and negative electrode side line 14. The U-phase arm is configured by serial connection of switching elements Q11 and Q12, the V-phase arm is configured by serial connection of switching elements Q13 and Q14, and the W-phase arm is configured by serial connection of switching elements Q15 and Q16. ing. In the U-phase arm, switching element Q11 is a switching element belonging to the upper arm, and switching element Q12 is a switching element belonging to the lower arm. Similarly, in the V-phase arm, switching element Q13 is a switching element belonging to the upper arm, and switching element Q14 is a switching element belonging to the lower arm. Similarly, in the W-phase arm, switching element Q15 is a switching element belonging to the upper arm, and switching element Q16 is a switching element belonging to the lower arm.

  The switching elements Q11 to Q16 are, for example, IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs (metal-oxide-semiconductor field-effect transistors). In each switching element, diodes (diodes D11 to D16) that flow current from the emitter side to the collector side are arranged between the collector and the emitter.

  An intermediate point between the switching elements Q11 and Q12 of the U-phase arm is connected to the U-phase coil of the motor MG. An intermediate point between the switching elements Q13 and Q14 of the V-phase arm is connected to the V-phase coil of the motor MG. An intermediate point between switching elements Q15 and Q16 of the W-phase arm is connected to a W-phase coil of motor MG. For example, each of the switching elements Q11 to Q16 is provided with a drive circuit, and the switching elements Q11 to Q16 are subjected to switching control (on or off control) by a corresponding drive circuit based on a control signal from the control unit 24. The Thereby, electric power is converted.

  Note that the inverter may convert AC power generated by the motor MG into DC power and supply it to the DC power supply 10.

  The short-circuit switch 16 is a switch that is provided between the intermediate point of each phase arm and each phase coil, and short-circuits the output terminal of each phase arm. The short-circuit switch 16 is, for example, a three-terminal switch, and has a function of short-circuiting output terminals of the U-phase arm, the V-phase arm, and the W-phase arm at once, and a function of eliminating the short circuit. Specifically, the short-circuit switch 16 includes the intermediate point of the U-phase arm and the U-phase coil, the intermediate point of the V-phase arm and the V-phase coil, and the intermediate point of the W-phase arm and the W-phase coil. Between. The short-circuit switch 16 includes a line 18 connecting the intermediate point of the U-phase arm and the U-phase coil, a line 20 connecting the intermediate point of the V-phase arm and the V-phase coil, and an intermediate point of the W-phase arm and the W-phase. A function of connecting or blocking the line 22 connecting the coil is provided. When the shorting switch 16 is on, the lines 18, 20 and 22 are connected by the shorting switch 16. As a result, the output terminal of the U-phase arm, the output terminal of the V-phase arm, and the output terminal of the W-phase arm are short-circuited. When the shorting switch 16 is off, the connection of the lines 18, 20, and 22 is canceled, and the short circuit is eliminated. For example, the short-circuit switch 16 is provided with a drive circuit, and the short-circuit switch 16 is subjected to switching control (on or off control) by the drive circuit based on a control signal from the control unit 24. Thereby, the short circuit or interruption | blocking of each phase arm is implement | achieved.

  Control unit 24 controls the operation of motor MG by controlling the switching operation of switching elements Q11 to Q16 constituting the inverter. For example, the control unit 24 controls the switching operation of the switching elements Q11 to Q16 so that the motor MG outputs the target torque. In the present embodiment, the control unit 24 controls the switching operation of the switching elements Q11 to Q16 according to PWM control. For example, the control unit 24 generates a PWM signal for turning on or off the switching elements Q11 to Q16 so that the motor MG outputs a target torque. And the control part 24 supplies the PWM signal for each switching element to the drive circuit corresponding to each of the switching elements Q11-Q16. Further, the control unit 24 controls the switching operation of the short-circuit switch 16.

  In the present embodiment, the control unit 24 switches at least one switching element for each individual phase while the short-circuit switch 16 is on. That is, the control unit 24 switches at least one of the switching elements belonging to the upper arm and the switching elements belonging to the lower arm for each phase. As an example, the control unit 24 switches the switching elements Q12, Q14, Q16 belonging to the lower arm from on to off, and switches the switching elements Q11, Q13, Q15 belonging to the upper arm from off to on. Alternatively, the control unit 24 may switch the switching elements Q12, Q14, and Q16 belonging to the lower arm from off to on, and may switch the switching elements Q11, Q13, and Q15 belonging to the upper arm from on to off. This switching control is an example, and other switching control may of course be performed. The control unit 24 turns on the short-circuit switch 16 for a predetermined period and turns off the short-circuit switch 16 in other periods for each PWM control cycle.

  The control unit 24 can be realized using hardware resources such as a processor and an electronic circuit, for example, and a device such as a memory may be used as necessary in the realization. The control unit 24 may be realized by a computer, for example. That is, the function of the control unit 24 may be realized by cooperation of hardware resources such as a CPU, a memory, and a hard disk included in the computer and software (program) that defines the operation of the CPU and the like. The program is stored in a storage device (not shown) via a recording medium such as a CD or DVD, or via a communication path such as a network. As another example, the control unit 24 may be realized by a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), or the like.

  FIG. 2 shows a short-circuit switch 16 as a three-terminal switch. A known switch can be used as the three-terminal switch. For example, the short-circuit switch 16 includes a switching element Q30 configured by an IGBT or the like, and diodes D31 to D36. Diodes D31 and D32 are connected in series, and an intermediate point thereof is connected to U-phase arm line 18. Similarly, diodes D33 and D34 are connected in series, and an intermediate point thereof is connected to the line 20 of the V-phase arm. Similarly, diodes D35 and D36 are connected in series, and the intermediate point thereof is connected to the line 22 of the W-phase arm.

  For example, a driving circuit is provided in the switching element Q30, and the switching element Q30 is subjected to switching control (on or off control) by the driving circuit based on a control signal from the control unit 24. When the switching element Q30 is on, the lines 18, 20, and 22 shown in FIG. 1 are connected, thereby short-circuiting the output terminals of the U-phase arm, V-phase arm, and W-phase arm. On the other hand, when the switching element Q30 is off, the connection of the lines 18, 20, and 22 is eliminated, and the short circuit is eliminated.

  Hereinafter, a specific control method of the inverter will be described.

  FIG. 3 shows an example of signals related to PWM control. The horizontal axis indicates time. The carrier signal 26 is a carrier wave for generating a PWM signal for each phase, and is a sawtooth wave as an example. Specifically, the waveform of the carrier signal 26 is a waveform that repeatedly decreases gradually with time and rapidly increases. Of course, as another example, it may be repeated that the waveform rises with time and falls rapidly.

  The period from the sudden rise of the waveform of the carrier signal 26 to the next rapid rise is defined as one cycle, and this cycle is referred to as a PWM control cycle. That is, the period between the timing when the sawtooth wave suddenly rises (edge timing of the sawtooth wave) and the timing when the sawtooth wave suddenly rises next (next edge timing) is defined as one cycle (PWM control cycle).

  The U-phase duty signal 28, the V-phase duty signal 30, and the W-phase duty signal 32 are signals for generating a PWM signal of a corresponding phase, and are signals according to a command voltage for the corresponding phase. is there. Based on the carrier signal 26, the U-phase duty signal 28, the V-phase duty signal 30, and the W-phase duty signal 32, the control unit 24 performs the U-phase PWM signal 34, the V-phase PWM signal 36, and The W-phase PWM signal 38 is generated.

  The U-phase PWM signal 34 is a PWM signal for controlling the switching operation of the switching elements Q11 and Q12 belonging to the U-phase arm, and is a signal indicating the on / off timing of the switching elements Q11 and Q12. The U-phase PWM signal 34 is generated by comparing the carrier signal 26 with the U-phase duty signal 28. At the timing when the carrier signal 26 and the U-phase duty signal 28 cross each other, the U-phase PWM signal 34 switches between high and low. The control unit 24 supplies the U-phase PWM signal 34 to the drive circuit for the U-phase arm. The drive circuit controls the switching operation of the switching elements Q11 and Q12 belonging to the U-phase arm according to the U-phase PWM signal 34. When the U-phase PWM signal 34 indicates high (High), the drive circuit turns on the switching element Q12 belonging to the lower arm and turns off the switching element Q11 belonging to the upper arm in the U-phase arm. On the other hand, when the U-phase PWM signal 34 indicates Low, the drive circuit turns on the switching element Q11 belonging to the upper arm and turns off the switching element Q12 belonging to the lower arm in the U-phase arm.

  The V-phase PWM signal 36 is a PWM signal for controlling the switching operation of the switching elements Q13 and Q14 belonging to the V-phase arm, and is a signal indicating the on / off timing of the switching elements Q13 and Q14. The V-phase PWM signal 36 is generated by comparing the carrier signal 26 with the V-phase duty signal 30. At the timing when the carrier signal 26 and the V-phase duty signal 30 cross each other, the V-phase PWM signal 36 is switched between high and low. The control unit 24 supplies the V-phase PWM signal 36 to the drive circuit for the V-phase arm. The drive circuit controls the switching operation of the switching elements Q13 and Q14 belonging to the V-phase arm in accordance with the V-phase PWM signal 36. When the V-phase PWM signal 36 indicates high (High), the drive circuit turns on the switching element Q14 belonging to the lower arm and turns off the switching element Q13 belonging to the upper arm in the V-phase arm. On the other hand, when the V-phase PWM signal 36 indicates low, the drive circuit turns on the switching element Q13 belonging to the upper arm and turns off the switching element Q14 belonging to the lower arm in the V-phase arm.

  The W-phase PWM signal 38 is a PWM signal for controlling the switching operation of the switching elements Q15 and Q16 belonging to the W-phase arm, and is a signal indicating the on / off timing of the switching elements Q15 and Q16. The W-phase PWM signal 38 is generated by comparing the carrier signal 26 with the W-phase duty signal 32. At the timing when the carrier signal 26 and the W-phase duty signal 32 cross each other, the W-phase PWM signal 38 switches between high (High) and low (Low). The control unit 24 supplies the W-phase PWM signal 38 to the drive circuit for the W-phase arm. The drive circuit controls the switching operation of the switching elements Q15 and Q16 belonging to the W-phase arm in accordance with the W-phase PWM signal 38. When the W-phase PWM signal 38 indicates high, the drive circuit turns on the switching element Q16 belonging to the lower arm and turns off the switching element Q15 belonging to the upper arm in the W-phase arm. On the other hand, when the W-phase PWM signal 38 indicates low, the drive circuit turns on the switching element Q15 belonging to the upper arm and turns off the switching element Q16 belonging to the lower arm in the W-phase arm.

  As described above, by using a signal having a sawtooth waveform as the carrier signal 26, the PWM signal for each phase is high (High) at the timing when the waveform suddenly rises in the carrier signal 26 (sawtooth edge timing). Switch from low to low. Specifically, at the edge timing of the sawtooth wave, the U-phase PWM signal 34, the V-phase PWM signal 36, and the W-phase PWM signal 38 are switched from high to low and switched. The timing (edge timing of each PWM signal) matches. As a result, the on / off timing (switching operation timing) of each switching element coincides at the sawtooth edge timing. Specifically, at the edge timing of the sawtooth wave, the switching elements Q11, Q13, Q15 are switched from on to off, and the switching elements Q12, Q14, Q16 are switched from off to on.

  If a waveform that rises with time and repeats a sudden drop is used as the waveform of the carrier signal 26, the PWM signal for each phase is low (the edge timing of the sawtooth wave) when the waveform suddenly falls (the edge timing of the sawtooth wave). Switch from Low to High. Thus, at the edge timing of the sawtooth wave, the switching elements Q11, Q13, Q15 are switched from off to on, and the switching elements Q12, Q14, Q16 are switched from on to off.

  The short circuit signal 40 is a signal indicating the on / off timing of the short circuit switch 16. The short circuit signal 40 is generated by the control unit 24, for example. The waveform of the short circuit signal 40 is in a high state in a period before and after the timing (hereinafter referred to as “short circuit period”) including the timing at which the waveform of the carrier signal 26 suddenly rises (edge timing of the sawtooth wave). During a period other than the above, the low state is entered. The control unit 24 supplies the short circuit signal 40 to the drive circuit of the short circuit switch 16. The drive circuit controls the switching operation of the short-circuit switch 16 according to the short-circuit signal 40. When the short circuit signal 40 indicates high, the drive circuit turns on the short circuit switch 16. Thereby, the output terminal of each phase arm is short-circuited during the short-circuit period. On the other hand, when the short circuit signal 40 indicates low, the drive circuit turns off the short circuit switch 16. Thereby, the short circuit of the output terminal of each phase arm is eliminated during a period other than the short circuit period. As an example, the short-circuit period is several microseconds.

  Note that the edge timing of the PWM signal for each phase, that is, the timing at which the PWM signal for each phase switches from high (High) to low (Low), or the PWM signal for each phase changes from low (Low) to high (High). The switching timing may not exactly match. It is only necessary that the edge timing of the PWM signal for each phase is included in the short-circuit period in which the short-circuit signal 40 is high. In other words, the ON / OFF timings of the switching elements Q11 to Q16 belonging to each phase arm may not strictly coincide with each other, and the switching elements Q11 to Q16 are in the short circuit period in which the short circuit switch 16 is in the ON state. May be switched.

  In the present embodiment, switching loss occurs at timings indicated by reference numerals 42, 44, and 46 in one PWM control cycle, and switching is performed by the switching elements Q11 to Q16 during the short-circuit period in which the short-circuit switch 16 is on. There is no loss. Therefore, the number of occurrences of switching loss is reduced, and the total switching loss can be reduced. In the example shown in FIG. 3, the total number of switching losses can be reduced by suppressing the number of occurrences of switching losses to 3 times during one PWM control period. That is, when the short-circuit switch 16 is on, the voltage of the switching elements Q11 to Q16 becomes 0V, or the current flowing through the switching elements Q11 to Q16 due to the current flowing through the short-circuit switch 16 becomes 0A. Switching loss will not occur.

  Hereinafter, the reason why the switching loss does not occur during the short circuit period will be described with reference to FIGS.

  FIG. 4 shows a graph of switching loss in the inverter according to the present embodiment. In the graph in FIG. 4, the horizontal axis indicates time, and the vertical axis indicates switching loss (unit: per unit) generated in the inverter. A graph 48 is a waveform obtained by simulation, and shows a total of switching losses generated in the switching elements Q11 to Q16 and the short-circuit switch 16 in a period before and after the edge timing of the sawtooth wave (carrier signal 26). It is. That is, the graph 48 shows the switching element Q11 in a period before and after the timing at which the U-phase PWM signal 34, the V-phase PWM signal 36, and the W-phase PWM signal 38 are switched from high to low. The total of the switching loss which generate | occur | produces in -Q16 and the short circuit switch 16 is shown. Hereinafter, the periods before and after the sawtooth edge timing are divided into periods A to E, and the operation of the switching elements Q11 to Q16 in each period will be described. In the periods A and E, the short-circuit switch 16 is in an off state, and in the periods B, C, and D, the short-circuit switch 16 is in an on state.

  FIG. 5 shows the states of the switching elements Q11 to Q16 and the short-circuit switch 16 in the period A. In the period A, the U-phase PWM signal 34, the V-phase PWM signal 36, and the W-phase PWM signal 38 are high (High). Therefore, the switching elements Q12, Q14, Q16 belonging to the lower arm are turned on, and the switching elements Q11, Q13, Q15 belonging to the upper arm are turned off. In the period A, the short circuit signal 40 is low. Therefore, the short-circuit switch 16 is in an off state. The arrows in FIG. 5 indicate current paths. In the period A, the current is supplied to the U-phase coil of the motor MG via the U-phase line 18 and is supplied to the V-phase coil and the W-phase coil via the U-phase coil. At this time, the current is supplied to the U-phase line 18 via the diode D12. The current is supplied to the switching element Q14 via the V-phase coil and the V-phase line 20. Similarly, the current is supplied to the switching element Q16 via the W-phase coil and the W-phase line 22. At this stage, no switching loss occurs because no switching operation occurs in the switching elements Q11 to Q16 and the short-circuit switch 16.

  FIG. 6 shows the states of the switching elements Q11 to Q16 and the short-circuit switch 16 in the period B. The period B is a period immediately before the switching elements Q11 to Q16 are switched on / off. In the period B, the U-phase PWM signal 34, the V-phase PWM signal 36, and the W-phase PWM signal 38 are high (High). Therefore, the switching elements Q12, Q14, Q16 belonging to the lower arm are on, and the switching elements Q11, Q13, Q15 belonging to the upper arm are off. Further, in the period B, the short-circuit signal 40 is high. Therefore, the shorting switch 16 is turned on. The arrows in FIG. 6 indicate current paths. In the period B, the current is supplied to the U-phase coil of the motor MG via the U-phase line 18 and is supplied to the V-phase coil and the W-phase coil via the U-phase coil. At this time, the current is supplied to the U-phase line 18 via the diode D12. The current is supplied to the switching element Q14 via the V-phase coil and the V-phase line 20. Similarly, the current is supplied to the switching element Q16 via the W-phase coil and the W-phase line 22. At this stage, the potentials of all terminals of the short-circuit switch 16 are 0V, and the voltage (potential difference between terminals) that the short-circuit switch 16 is responsible for is 0V. Therefore, no switching loss occurs in the short-circuit switch 16. That is, zero voltage switching (lossless) is realized. During the period B, the current flows through the diode D12 in the U-phase arm, so the switching element Q12 may be turned off. The same applies to the operations described below. That is, when a current flows through a diode, the switching element to which the diode is connected may be turned off. Of course, the switching element may be turned on.

  Here, the reason why the zero voltage switching is realized in the period B will be described with reference to FIG. FIG. 7 shows an equivalent circuit of a circuit including the switching elements Q12, Q14, Q16 and the short-circuit switch 16. In the period B, since the current flows through the diode D12, it can be considered that this part is conducting. Further, since the short-circuit switch 16 is in the ON state, the potential between the terminals of the switching elements Q12, Q14, Q16 becomes zero. Therefore, in the period B, zero voltage switching is realized.

  FIG. 8 shows the states of the switching elements Q11 to Q16 and the short-circuit switch 16 in the period C. Period C is a dead time period in which switching elements Q11 to Q16 are turned off. In the period C, the U-phase PWM signal 34, the V-phase PWM signal 36, and the W-phase PWM signal 38 indicate Low. Therefore, the switching elements Q12, Q14, Q16 belonging to the lower arm are turned off. As described above, the switching element Q12 may be turned off in advance during the period B. Further, in order to avoid short circuit of the DC power supply 10, the timing when the switching elements Q12, Q14, Q16 are turned on and the timing when the switching elements Q11, Q13, Q15 are turned on are not completely matched. In the period C (dead time), the switching elements Q11, Q13, Q15 are also turned off. That is, in the period C, all the switching elements are turned off. In the period C, the short-circuit signal 40 is high. Therefore, the shorting switch 16 is turned on. The arrows in FIG. 8 indicate current paths. In the period C, the current is supplied to the U-phase coil via the short-circuit switch 16 and the U-phase line 18, and is supplied to the V-phase coil and the W-phase coil via the U-phase coil. The current is supplied to the short-circuit switch 16 via the V-phase coil and the V-phase line 20. Similarly, the current is supplied to the short-circuit switch 16 via the W-phase coil and the W-phase line 22. At this stage, since the short-circuit switch 16 is on, the voltage that the switching elements Q12, Q14, Q16 are responsible for is 0V. Therefore, even when the switching elements Q12, Q14, Q16 are turned off from on, no switching loss occurs in the switching elements Q12, Q14, Q16. That is, zero voltage switching (lossless) is realized.

  FIG. 9 shows the states of the switching elements Q11 to Q16 and the short-circuit switch 16 in the period D. The period D is a period immediately after the dead time period. In the period D, the U-phase PWM signal 34, the V-phase PWM signal 36, and the W-phase PWM signal 38 are low. Therefore, the switching elements Q12, Q14, Q16 belonging to the lower arm are off, and the switching elements Q11, Q13, Q15 belonging to the upper arm are on. In the period D, the short circuit signal 40 is high. Therefore, the shorting switch 16 is turned on. The arrows in FIG. 9 indicate current paths. In the period D, the current is supplied to the U-phase coil via the short-circuit switch 16 and the U-phase line 18, and is supplied to the V-phase coil and the W-phase coil via the U-phase coil. The current is supplied to the short-circuit switch 16 via the V-phase coil and the V-phase line 20. Similarly, the current is supplied to the short-circuit switch 16 via the W-phase coil and the W-phase line 22. At this stage, since the current flows through the short-circuit switch 16, it does not flow through the switching elements Q11, Q13, Q15 belonging to the upper arm. Therefore, even when the switching elements Q11, Q13, Q15 are turned on from off, no switching loss occurs in the switching elements Q11, Q13, Q15. That is, zero current switching (lossless) is realized.

  FIG. 10 shows the states of the switching elements Q11 to Q16 and the short-circuit switch 16 in the period E. In the period E, the U-phase PWM signal 34, the V-phase PWM signal 36, and the W-phase PWM signal 38 are low. Therefore, the switching elements Q12, Q14, Q16 belonging to the lower arm are turned off, and the switching elements Q11, Q13, Q15 belonging to the upper arm are turned on. In the period E, the short circuit signal 40 is low. Therefore, the shorting switch 16 is turned off. The arrows in FIG. 10 indicate current paths. In the period E, the current is supplied to the U-phase coil via the switching element Q11 and the U-phase line 18, and is supplied to the V-phase coil and the W-phase coil via the U-phase coil. The current flows through the diode D13 via the V-phase coil and the V-phase line 20. Similarly, the current flows through the diode D15 via the W-phase coil and the W-phase line 22. At this stage, since the switching elements Q11, Q13, Q15 belonging to the upper arm are in the ON state, the potentials of all the terminals of the short-circuit switch 16 become the input voltage Vin. Therefore, the voltage (potential difference between terminals) that the shorting switch 16 takes is 0V, and no switching loss occurs in the shorting switch 16. That is, zero voltage switching (lossless) is realized.

  As described above, in the present embodiment, during the ON period of the short-circuit switch 16, the switching elements Q12, Q14, Q16 are switched from on to off, and the switching elements Q11, Q13, Q15 are switched from off to on. As a result, zero voltage switching and zero current switching can be realized, and the occurrence of switching loss can be prevented. For example, as shown in the graph 48 shown in FIG. 4, the total switching loss can be reduced.

(Comparative Example 1)
Next, an inverter device and a control method according to Comparative Example 1 will be described with reference to FIG. The inverter device according to Comparative Example 1 does not include the short-circuit switch 16. It is assumed that the circuit configuration of the inverter other than the short-circuit switch 16 is the same as the circuit configuration shown in FIG.

  FIG. 11 shows signals related to PWM control according to the first comparative example. The horizontal axis indicates time. The carrier signal 50 is a carrier wave for generating a PWM signal for each phase, and is a triangular wave. Specifically, the waveform of the carrier signal 50 is a waveform that repeats gradually increasing with time and then gradually decreasing. A period between the lowest point of the carrier signal 50 and the next lowest point is defined as one cycle (one PWM control cycle).

  The U-phase duty signal 52, the V-phase duty signal 54, and the W-phase duty signal 56 are signals for generating a PWM signal of a corresponding phase, and are signals corresponding to a command voltage for the corresponding phase. is there. Based on the carrier signal 50, the U-phase duty signal 52, the V-phase duty signal 54, and the W-phase duty signal 56, the U-phase PWM signal 58, the V-phase PWM signal 60, and the W-phase PWM A signal 62 is generated.

  The U-phase PWM signal 58 is a PWM signal for controlling the switching operation of the switching elements Q11 and Q12 belonging to the U-phase arm, and is a signal indicating the on / off timing of the switching elements Q11 and Q12. The U-phase PWM signal 58 is generated by comparing the carrier signal 50 and the U-phase duty signal 52. At the timing when the carrier signal 50 and the U-phase duty signal 52 cross each other, the U-phase PWM signal 58 is switched between high and low. The U-phase PWM signal 58 is supplied to the drive circuit for the U-phase arm. The drive circuit controls the switching operation of the switching elements Q11 and Q12 belonging to the U-phase arm according to the U-phase PWM signal 58. When the U-phase PWM signal 58 indicates high (High), the drive circuit turns on the switching element Q12 belonging to the lower arm and turns off the switching element Q11 belonging to the upper arm in the U-phase arm. On the other hand, when the U-phase PWM signal 58 indicates Low, the drive circuit turns on the switching element Q11 belonging to the upper arm and turns off the switching element Q12 belonging to the lower arm in the U-phase arm.

  The V-phase PWM signal 60 is a PWM signal for controlling the switching operation of the switching elements Q13 and Q14 belonging to the V-phase arm, and is a signal indicating the on / off timing of the switching elements Q13 and Q14. The V-phase PWM signal 60 is generated by comparing the carrier signal 50 and the V-phase duty signal 54. At the timing when the carrier signal 50 and the V-phase duty signal 54 cross each other, the V-phase PWM signal 60 is switched between high and low. The V-phase PWM signal 60 is supplied to the drive circuit for the V-phase arm. The drive circuit controls the switching operation of the switching elements Q13 and Q14 belonging to the V-phase arm according to the V-phase PWM signal 60. When the V-phase PWM signal 60 indicates high, the drive circuit turns on the switching element Q14 belonging to the lower arm and turns off the switching element Q13 belonging to the upper arm in the V-phase arm. On the other hand, when the V-phase PWM signal 60 indicates Low, the drive circuit turns on the switching element Q13 belonging to the upper arm and turns off the switching element Q14 belonging to the lower arm in the V-phase arm.

  The W-phase PWM signal 62 is a PWM signal for controlling the switching operation of the switching elements Q15 and Q16 belonging to the W-phase arm, and is a signal indicating the on / off timing of the switching elements Q15 and Q16. The W-phase PWM signal 62 is generated by comparing the carrier signal 50 and the W-phase duty signal 56. At the timing at which the carrier signal 50 and the W-phase duty signal 56 intersect, the W-phase PWM signal 62 switches between high and low. The W-phase PWM signal 62 is supplied to the drive circuit for the W-phase arm. The drive circuit controls the switching operation of the switching elements Q15 and Q16 belonging to the W-phase arm according to the W-phase PWM signal 62. When the W-phase PWM signal 62 indicates high (High), the drive circuit turns on the switching element Q16 belonging to the lower arm and turns off the switching element Q15 belonging to the upper arm in the W-phase arm. On the other hand, when W-phase PWM signal 62 indicates Low, the drive circuit turns on switching element Q15 belonging to the upper arm and turns off switching element Q16 belonging to the lower arm in the W-phase arm.

  In Comparative Example 1, switching loss occurs at timings indicated by reference numerals 64, 66, 68, 70, 72, and 74 during one PWM control period. That is, the number of occurrences of switching loss during one PWM control cycle is six. On the other hand, in this embodiment, as shown in FIG. 3, the number of occurrences can be reduced to three. Therefore, according to the present embodiment, it is possible to reduce the number of occurrences of switching loss by half compared to Comparative Example 1.

(Comparative Example 2)
Next, an inverter device and a control method according to Comparative Example 2 will be described with reference to FIGS. The inverter device according to Comparative Example 2 does not include the short-circuit switch 16. It is assumed that the circuit configuration of the inverter other than the short-circuit switch 16 is the same as the circuit configuration shown in FIG. In Comparative Example 2, it is assumed that the switching operations of the switching elements Q11 to Q16 are controlled according to the signal according to the present embodiment shown in FIG. That is, a U-phase PWM signal 34, a V-phase PWM signal 36, and a W-phase PWM signal 38 are generated using the carrier signal 26 that is a sawtooth wave, and switching of the switching elements Q11 to Q16 is performed according to these PWM signals. The operation shall be controlled. However, in Comparative Example 2, since the short-circuit switch 16 is not used, the output terminals of the respective phases are not short-circuited.

  FIG. 12 shows a graph of switching loss in the inverter according to Comparative Example 2. In the graph in FIG. 12, the horizontal axis represents time, and the vertical axis represents switching loss (unit: per unit) generated in the inverter. Graphs 76 to 82 are waveforms obtained by simulation, and are graphs showing switching losses that occur in the period before and after the edge timing of the sawtooth wave (carrier signal 26). That is, the graphs 76 to 82 are generated in a period before and after the timing when the U-phase PWM signal 34, the V-phase PWM signal 36, and the W-phase PWM signal 38 are switched from high to low. It is a graph which shows the switching loss to do. Specifically, the graph 76 shows the switching loss generated in the switching element Q14, the graph 78 shows the switching loss generated in the switching element Q16, and the graph 80 shows the switching loss in the switching element Q11. It shows the switching loss that occurs. A graph 82 is a graph showing the total switching loss generated in the switching elements Q11 to Q16. Hereinafter, the period before and after the sawtooth edge timing is divided into periods F to H, and the operation of the switching elements Q11 to Q16 in each period will be described.

  FIG. 13 shows the states of the switching elements Q11 to Q16 in the period F. In the period F, the U-phase PWM signal 34, the V-phase PWM signal 36, and the W-phase PWM signal 38 are high. Therefore, the switching elements Q12, Q14, Q16 belonging to the lower arm are turned on, and the switching elements Q11, Q13, Q15 belonging to the upper arm are turned off. Arrows in FIG. 13 indicate current paths. In the period F, the current is supplied to the U-phase coil of the motor MG via the U-phase line 18 and is supplied to the V-phase coil and the W-phase coil via the U-phase coil. At this time, the current is supplied to the U-phase line 18 via the diode D12. The current is supplied to the switching element Q14 via the V-phase coil and the V-phase line 20. Similarly, the current is supplied to the switching element Q16 via the W-phase coil and the W-phase line 22. At this stage, no switching loss occurs because no switching operation occurs in the switching elements Q11 to Q16.

  FIG. 14 shows the states of the switching elements Q11 to Q16 in the period G. The period G is a dead time period, and is a period during which the switching elements Q11 to Q16 are turned off. In the period G, the U-phase PWM signal 34, the V-phase PWM signal 36, and the W-phase PWM signal 38 indicate Low. Therefore, the switching elements Q12, Q14, Q16 belonging to the lower arm are turned off. In addition, in order to avoid a short circuit of the DC power supply 10, the timing when the switching elements Q12, Q14, Q16 are turned on and the timing when the switching elements Q11, Q13, Q15 are turned on do not completely coincide with each other. In G (dead time), the switching elements Q11, Q13, and Q15 are also turned off. That is, in the period G, all the switching elements are turned off. The arrows in FIG. 14 indicate current paths. In the period G, the current is supplied to the U-phase coil via the diode D12 and the U-phase line 18, and is supplied to the V-phase coil and the W-phase coil via the U-phase coil. The current flows through the diode D13 via the V-phase coil and the V-phase line 20. Similarly, the current flows through the diode D15 via the W-phase coil and the W-phase line 22. At this stage, since the current flows through the diode D12, no switching loss occurs in the switching element Q12. However, switching loss occurs in the switching elements Q14 and Q16 when the switching elements Q14 and Q16 are switched from on to off.

  FIG. 15 shows the states of the switching elements Q11 to Q16 in the period H. In the period H, the U-phase PWM signal 34, the V-phase PWM signal 36, and the W-phase PWM signal 38 indicate Low. Therefore, the switching elements Q12, Q14, Q16 belonging to the lower arm are turned off, and the switching elements Q11, Q13, Q15 belonging to the upper arm are turned on. The arrows in FIG. 15 indicate current paths. In the period H, the current is supplied to the U-phase coil via the switching element Q11 and the U-phase line 18, and is supplied to the V-phase coil and the W-phase coil via the U-phase coil. The current flows through the diode D13 via the V-phase coil and the V-phase line 20. Similarly, the current flows to the diode D15 via the W-phase coil and the W-phase line 22. At this stage, since current flows through the diodes D13 and D15, no switching loss occurs in the switching elements Q13 and Q15. However, switching loss occurs in the switching element Q11 when the switching element Q11 is switched from the OFF state to the ON state.

  As described above, in Comparative Example 2, when the switching elements Q12, Q14, and Q16 are switched from the on state to the off state, switching loss occurs in the switching elements Q14 and Q16, and the switching elements Q11, Q13, and Q15 are turned off. When switching from ON to OFF, switching loss occurs in the switching element Q11. Therefore, as shown in FIG. 12, the total switching loss increases.

  Comparing the graph 48 according to the present embodiment shown in FIG. 4 and the graph 82 according to the comparative example 2 shown in FIG. 12, the present embodiment can reduce the total switching loss. It becomes possible.

(Modification 1)
Next, an inverter device according to Modification 1 will be described. FIG. 16 shows an inverter device according to the first modification. This inverter device is a device that includes two inverters and has a function of adjusting power supplied from the DC power supply 10 to the motors MG1 and MG2. The inverter device may have a function of adjusting the power generated by the motors MG1 and MG2 and supplied to the DC power supply 10.

  Motors MG 1 and MG 2 are motors having the same configuration as motor MG shown in FIG. 1 and are driven by electric power supplied from DC power supply 10.

  Here, regarding the power supply line of the DC power supply 10, the high-voltage side lines are referred to as positive-side lines 12a and 12b, and the low-voltage-side lines are referred to as negative-side lines 14a and 14b. The positive electrode side line 12a and the negative electrode side line 14a are power lines for the first inverter, and the positive electrode side line 12b and the negative electrode side line 14b are power lines for the second inverter. A positive electrode side line 12b is connected to the positive electrode side line 12a, and a negative electrode side line 14a is connected to the negative electrode side line 14b.

  The first inverter includes switching elements Q11 to Q16, converts the DC power supplied from DC power supply 10 into three-phase AC power, and supplies it to motor MG1. The first inverter includes a U-phase arm, a V-phase arm, and a W-phase arm arranged in parallel with each other between the positive electrode side line 12a and the negative electrode side line 14a. The U-phase arm is configured by serial connection of switching elements Q11 and Q12, the V-phase arm is configured by serial connection of switching elements Q13 and Q14, and the W-phase arm is configured by serial connection of switching elements Q15 and Q16. ing. Switching elements Q11, Q13, Q15 are switching elements belonging to the upper arm, and switching elements Q12, Q14, Q16 are switching elements belonging to the lower arm. In each switching element, diodes (diodes D11 to D16) that flow current from the emitter side to the collector side are arranged between the collector and the emitter.

  An intermediate point between the switching elements Q11 and Q12 of the U-phase arm is connected to the U-phase coil of the motor MG1. An intermediate point between switching elements Q13 and Q14 of the V-phase arm is connected to the V-phase coil of motor MG1. An intermediate point between switching elements Q15 and Q16 of the W-phase arm is connected to the W-phase coil of motor MG1. For example, each of the switching elements Q11 to Q16 is provided with a drive circuit, and the switching elements Q11 to Q16 are subjected to switching control (on or off control) by a corresponding drive circuit based on a control signal from the control unit 24. The Thereby, electric power is converted.

  The second inverter includes switching elements Q21 to Q26, converts the DC power supplied from DC power supply 10 into three-phase AC power, and supplies it to motor MG2. The second inverter includes a U-phase arm, a V-phase arm, and a W-phase arm arranged in parallel with each other between positive electrode side line 12b and negative electrode side line 14b. The U-phase arm is constituted by a series connection of switching elements Q21 and Q22, the V-phase arm is constituted by a series connection of switching elements Q23 and Q24, and the W-phase arm is constituted by a series connection of switching elements Q25 and Q26. ing. Switching elements Q21, Q23, and Q25 are switching elements belonging to the upper arm, and switching elements Q22, Q24, and Q26 are switching elements belonging to the lower arm. In each switching element, diodes (diodes D21 to D26) that flow current from the emitter side to the collector side are arranged between the collector and the emitter.

  An intermediate point between the switching elements Q21 and Q22 of the U-phase arm is connected to the U-phase coil of the motor MG2. The midpoint of switching elements Q23 and Q24 of the V-phase arm is connected to the V-phase coil of motor MG2. An intermediate point between the switching elements Q25 and Q26 of the W-phase arm is connected to the W-phase coil of the motor MG2. For example, each of the switching elements Q21 to Q26 is provided with a drive circuit, and the switching elements Q21 to Q26 are subjected to switching control (on or off control) by a corresponding drive circuit based on a control signal from the control unit 24. The Thereby, electric power is converted.

  The short-circuit switch 84 is a switch that is provided between the intermediate point of each phase arm and each phase coil and short-circuits the output terminal of each phase arm. The short-circuit switch 84 is, for example, a 6-terminal switch, and has a function of short-circuiting the output terminals of the U-phase arm, V-phase arm, and W-phase arm of the first and second inverters at once, and a function of eliminating the short circuit. It has. Specifically, the short-circuit switch 84 is between the intermediate point of the U-phase arm of the first inverter and the U-phase coil of the motor MG1, and between the intermediate point of the V-phase arm of the first inverter and the V-phase coil of the motor MG1. And between the intermediate point of the W-phase arm of the first inverter and the W-phase coil of the motor MG1. Short-circuit switch 84 is between the middle point of the U-phase arm of the second inverter and the U-phase coil of motor MG2, between the middle point of the V-phase arm of the second inverter and the V-phase coil of motor MG2, and , Between the intermediate point of the W-phase arm of the second inverter and the W-phase coil of the motor MG2. Short-circuit switch 84 connects line 18a connecting the intermediate point of the U-phase arm of the first inverter and the U-phase coil of motor MG1, and connects the intermediate point of the V-phase arm of the first inverter and the V-phase coil of motor MG1. Line 20a, line 22a connecting the intermediate point of the W-phase arm of the first inverter and the W-phase coil of the motor MG1, line 18b connecting the intermediate point of the U-phase arm of the second inverter and the U-phase coil of the motor MG2. , A line 20b connecting the intermediate point of the V-phase arm of the second inverter and the V-phase coil of the motor MG2, and a line 22b connecting the intermediate point of the W-phase arm of the second inverter and the W-phase coil of the motor MG2. , Has a function of connecting or blocking. When the shorting switch 84 is in the ON state, the lines 18a, 20a, 22a, 18b, 20b, and 22b are connected by the shorting switch 84. As a result, the output terminals of the U-phase arm, V-phase arm, and W-phase arm of the first and second inverters are short-circuited. When the short-circuit switch 84 is in the OFF state, the connection of the lines 18a, 20a, 22a, 18b, 20b, and 22b is canceled, and the short circuit is eliminated. For example, the short circuit switch 84 is provided with a drive circuit, and the short circuit switch 84 is switched (ON or OFF controlled) by the drive circuit based on a control signal from the control unit 24. Thereby, the short circuit or interruption | blocking of each phase arm in a 1st and 2nd inverter is implement | achieved.

  The control unit 24 controls the operation of the motor MG1 by controlling the switching operation of the switching elements Q11 to Q16 constituting the first inverter. For example, the control unit 24 controls the switching operation of the switching elements Q11 to Q16 so that the motor MG1 outputs the target torque, and performs the switching operation of the switching elements Q21 to Q26 so that the motor MG2 outputs the target torque. Control. For example, the control unit 24 generates a PWM signal for turning on or off the switching elements Q11 to Q16 so that the motor MG1 outputs the target torque, and the switching element Q21 so that the motor MG2 outputs the target torque. A PWM signal for turning on or off Q26 is generated. And the control part 24 supplies the PWM signal for each switching element to the drive circuit corresponding to each of the switching elements Q11-Q26.

  In the first modification, the control unit 24 causes the switching elements Q11 to Q26 to perform a switching operation while the short-circuit switch 84 is on. For example, the control unit 24 switches the switching elements Q12, Q14, Q16, Q22, Q24, Q26 belonging to the lower arm from on to off, and turns off the switching elements Q11, Q13, Q15, Q21, Q23, Q25 belonging to the upper arm. Switch from to on. Alternatively, the control unit 24 switches the switching elements Q12, Q14, Q16, Q22, Q24, Q26 belonging to the lower arm from off to on, and turns on the switching elements Q11, Q13, Q15, Q21, Q23, Q25 belonging to the upper arm. Switch from to off. For example, the control unit 24 turns on the short-circuit switch 84 for a predetermined period and turns off the short-circuit switch 84 in other periods for each PWM control cycle.

  FIG. 17 shows a short-circuit switch 84 as a 6-terminal switch. A known switch can be used as the 6-terminal switch. For example, the short-circuit switch 84 includes a switching element Q40 configured by an IGBT or the like, and diodes D41 to D52. Diodes D41 to D46 are diodes for the first inverter, and diodes D47 to D52 are diodes for the second inverter. Diodes D41 and D42 are connected in series, and an intermediate point thereof is connected to U-phase arm line 18a. Similarly, diodes D43 and D44 are connected in series, and the intermediate point thereof is connected to the V-phase arm line 20a. Similarly, diodes D45 and D46 are connected in series, and the intermediate point thereof is connected to W-phase arm line 22a. Diodes D47 and D48 are connected in series, and an intermediate point thereof is connected to U-phase arm line 18b. Similarly, diodes D49 and D50 are connected in series, and the intermediate point thereof is connected to the V-phase arm line 20b. Similarly, diodes D51 and D52 are connected in series, and the intermediate point thereof is connected to the line 22b of the W-phase arm.

  For example, the switching element Q40 is provided with a drive circuit, and the switching element Q40 is subjected to switching control (on or off control) by the drive circuit based on a control signal from the control unit 24. When the switching element Q40 is on, the lines 18a, 20a, 22a, 18b, 20b, and 22b shown in FIG. 16 are connected, whereby the U-phase arm, V-phase arm, and W of the first and second inverters are connected. The output terminal of the phase arm is short-circuited. On the other hand, when the switching element Q40 is OFF, the connection of the lines 18a, 20a, 22a, 18b, 20b, and 22b is eliminated, and the short circuit is eliminated.

  FIG. 18 shows an example of signals related to PWM control. The horizontal axis indicates time. The carrier signal 26 is a common carrier wave for generating PWM signals for the first and second inverters, and is a sawtooth wave as an example. Note that separate carrier signals may be used for the first inverter and the second inverter.

  The U-phase duty signal 28a, the V-phase duty signal 30a, and the W-phase duty signal 32a are signals for generating a PWM signal of a corresponding phase in the first inverter, and are used as command voltages for the corresponding phase. The corresponding signal. Similarly, the U-phase duty signal 28b, the V-phase duty signal 30b, and the W-phase duty signal 32b are signals for generating a PWM signal of a corresponding phase in the second inverter. It is a signal according to the command voltage. Based on the carrier signal 26, the U-phase duty signal 28a, the V-phase duty signal 30a, and the W-phase duty signal 32a, the control unit 24 uses the first inverter U-phase PWM signal 34a and V-phase. A PWM signal 36a and a W-phase PWM signal 38a are generated. Similarly, the control unit 24, based on the carrier signal 26, the U-phase duty signal 28b, the V-phase duty signal 30b, and the W-phase duty signal 32b, the U-phase PWM signal 34b for the second inverter, A V-phase PWM signal 36b and a W-phase PWM signal 38b are generated.

  The U-phase PWM signal 34a is a PWM signal for controlling the switching operation of the switching elements Q11 and Q12 belonging to the U-phase arm in the first inverter. When the U-phase PWM signal 34a indicates high (High), the switching element Q12 is turned on and the switching element Q11 is turned off. On the other hand, when the U-phase PWM signal 34a indicates low, the switching element Q11 is turned on and the switching element Q12 is turned off.

  The V-phase PWM signal 36a is a PWM signal for controlling the switching operation of the switching elements Q13 and Q14 belonging to the V-phase arm in the first inverter. When the V-phase PWM signal 36a indicates high (High), the switching element Q14 is turned on and the switching element Q13 is turned off. On the other hand, when the V-phase PWM signal 36a indicates low, the switching element Q13 is turned on and the switching element Q14 is turned off.

  The W-phase PWM signal 38a is a PWM signal for controlling the switching operation of the switching elements Q15 and Q16 belonging to the W-phase arm in the first inverter. When the W-phase PWM signal 38a indicates high (High), the switching element Q16 is turned on and the switching element Q15 is turned off. On the other hand, when the W-phase PWM signal 38a indicates low, the switching element Q15 is turned on and the switching element Q16 is turned off.

  The U-phase PWM signal 34b is a PWM signal for controlling the switching operation of the switching elements Q21 and Q22 belonging to the U-phase arm in the second inverter. When the U-phase PWM signal 34b indicates high (High), the switching element Q22 is turned on and the switching element Q21 is turned off. On the other hand, when the U-phase PWM signal 34b indicates low, the switching element Q21 is turned on and the switching element Q22 is turned off.

  The V-phase PWM signal 36b is a PWM signal for controlling the switching operation of the switching elements Q23 and Q24 belonging to the V-phase arm in the second inverter. When the V-phase PWM signal 36b indicates high (High), the switching element Q24 is turned on and the switching element Q23 is turned off. On the other hand, when the V-phase PWM signal 36b indicates low, the switching element Q23 is turned on and the switching element Q24 is turned off.

  The W-phase PWM signal 38b is a PWM signal for controlling the switching operation of the switching elements Q25 and Q26 belonging to the W-phase arm in the second inverter. When the W-phase PWM signal 38b indicates high (High), the switching element Q26 is turned on and the switching element Q25 is turned off. On the other hand, when the W-phase PWM signal 38b indicates low, the switching element Q25 is turned on and the switching element Q26 is turned off.

  As described above, by using the common carrier signal 26 having a sawtooth waveform, at the timing when the waveform suddenly rises in the carrier signal 26 (edge timing of the sawtooth wave), each phase of the first and second inverters The PWM signal is switched from high to low. Thereby, the on / off timing of each switching element in the first and second inverters coincides at the edge timing of the sawtooth wave. Specifically, the switching elements Q11, Q13, Q15, Q21, Q23, and Q25 are switched from on to off at the sawtooth edge timing, and the switching elements Q12, Q14, Q16, Q22, Q24, and Q26 are switched from off to on. Switch to

  In the first modification, the waveform of the carrier signal 26 may be a waveform that rises with time and repeats a sudden drop. In this case, the PWM signal for each phase of the first and second inverters switches from low to high at the timing when the waveform suddenly drops (sawtooth edge timing). Thereby, at the edge timing of the sawtooth wave, the switching elements Q11, Q13, Q15, Q21, Q23, and Q25 are switched from OFF to ON, and the switching elements Q12, Q14, Q16, Q22, Q24, and Q26 are switched from ON to OFF. .

  The short circuit signal 86 is a signal indicating the on / off timing of the short circuit switch 84. The short circuit signal 86 is generated by the control unit 24, for example. The waveform of the short-circuit signal 86 is in a high state in the period before and after the timing (the edge timing of the sawtooth wave) when the waveform of the carrier signal 26 suddenly rises (short-circuiting period), and in the other periods It becomes a Low state. When the short circuit signal 40 indicates high, the short circuit switch 84 is turned on. Thereby, the output terminal of each phase arm in a 1st and 2nd inverter short-circuits during a short circuit period. On the other hand, when the short circuit signal 40 indicates Low, the short circuit switch 84 is turned off. Thereby, the short circuit of the output terminal of each phase arm in the first and second inverters is eliminated during a period other than the short circuit period. As an example, the short-circuit period is several microseconds.

  Note that also in the first modification, the edge timing of the PWM signal for each phase in the first and second inverters may not exactly match. It suffices if the edge timing of the PWM signal for each phase is included in the short-circuit period in which the short-circuit signal 86 is high.

  According to the modified example 1, as in the above-described embodiment, switching loss does not occur in the switching elements Q11 to 16 and Q21 to 26 during the short circuit period. This reason is the same as the reason according to the above-described embodiment. Also in the first modification, the number of occurrences of switching loss is reduced, and the total switching loss can be reduced. For example, the number of occurrences of switching loss in the first inverter is 3, and the number of occurrences of switching loss in the second inverter is 3. Compared with Comparative Example 1, the number of occurrences of switching loss can be reduced by half.

  In the first modification, the short-circuit switch 84 can collectively short-circuit the output terminals of the U-phase arm, V-phase arm, and W-phase arm of the first and second inverters. Thereby, compared with the case where a separate short-circuit switch is provided for each of the first and second inverters, it is possible to reduce the number of components and reduce the manufacturing cost of the inverter device.

  Note that the control method according to the present embodiment may be applied to three or more inverters. Even in this case, switching loss can be reduced by switching all the switching elements during the short-circuit period. Further, a short-circuit switch that short-circuits all phase output terminals at once may be used.

(Modification 2)
Next, Modification 2 will be described. In the second modification, a triangular wave is used as a carrier wave for generating a PWM signal for each phase. In addition, individual carrier waves are used for individual phases. The phase difference of each carrier wave is controlled so that the switching operation occurs in the switching elements Q11 to Q16 during the short-circuit period in which the short-circuit switch 16 is on.

  FIG. 19 shows signals related to PWM control according to the second modification. The horizontal axis indicates time. The U-phase carrier signal 88 is a carrier wave for generating a U-phase PWM signal. The V-phase carrier signal 90 is a carrier wave for generating a V-phase PWM signal. The W-phase carrier signal 92 is a carrier wave for generating a W-phase PWM signal. These carrier waves are triangular waves. Specifically, the waveforms of these signals are waveforms that gradually increase with time and then gradually decrease.

  The U-phase duty signal 94, the V-phase duty signal 96, and the W-phase duty signal 98 are signals for generating a PWM signal of a corresponding phase, and are signals corresponding to a command voltage for the corresponding phase. is there. The control unit 24 controls the phase difference of the carrier wave for each phase according to the duty signal for each phase. The control unit 24 generates a U-phase PWM signal 100, a V-phase PWM signal 102, and a W-phase PWM signal 104 based on the carrier signal for each phase and the duty signal for each phase.

  The U-phase PWM signal 100 is a PWM signal for controlling the switching operation of the switching elements Q11 and Q12 belonging to the U-phase arm, and is a signal indicating the on / off timing of the switching elements Q11 and Q12. The U-phase PWM signal 100 is generated by comparing the U-phase carrier signal 88 with the U-phase duty signal 94. At the timing when the U-phase carrier signal 88 and the U-phase duty signal 94 intersect, the U-phase PWM signal 100 is switched between high and low. The control unit 24 supplies the U-phase PWM signal 100 to the drive circuit for the U-phase arm. The drive circuit controls the switching operation of the switching elements Q11 and Q12 belonging to the U-phase arm according to the U-phase PWM signal 100. When the U-phase PWM signal 100 indicates high, the drive circuit turns on the switching element Q12 belonging to the lower arm and turns off the switching element Q11 belonging to the upper arm in the U-phase arm. On the other hand, when U-phase PWM signal 100 indicates low, the drive circuit turns on switching element Q11 belonging to the upper arm and turns off switching element Q12 belonging to the lower arm in the U-phase arm.

  The V-phase PWM signal 102 is a PWM signal for controlling the switching operation of the switching elements Q13 and Q14 belonging to the V-phase arm, and is a signal indicating the on / off timing of the switching elements Q13 and Q14. The V-phase PWM signal 102 is generated by comparing the V-phase carrier signal 90 and the V-phase duty signal 96. At the timing when the V-phase carrier signal 90 and the V-phase duty signal 96 cross each other, the V-phase PWM signal 102 is switched between high and low. The control unit 24 supplies the V-phase PWM signal 102 to the drive circuit for the V-phase arm. The drive circuit controls the switching operation of the switching elements Q13 and Q14 belonging to the V-phase arm in accordance with the V-phase PWM signal 102. When the V-phase PWM signal 102 indicates high, the drive circuit turns on the switching element Q14 belonging to the lower arm and turns off the switching element Q13 belonging to the upper arm in the V-phase arm. On the other hand, when the V-phase PWM signal 102 indicates Low, the drive circuit turns on the switching element Q13 belonging to the upper arm and turns off the switching element Q14 belonging to the lower arm in the V-phase arm.

  The W-phase PWM signal 104 is a PWM signal for controlling the switching operation of the switching elements Q15 and Q16 belonging to the W-phase arm, and is a signal indicating the on / off timing of the switching elements Q15 and Q16. The W-phase PWM signal 104 is generated by comparing the W-phase carrier signal 92 and the W-phase duty signal 98. At the timing when the W-phase carrier signal 92 and the W-phase duty signal 98 cross each other, the W-phase PWM signal 104 is switched between high and low. The control unit 24 supplies the W-phase PWM signal 104 to the drive circuit for the W-phase arm. The drive circuit controls the switching operation of the switching elements Q15 and Q16 belonging to the W-phase arm according to the W-phase PWM signal 104. When the W-phase PWM signal 104 indicates high, the drive circuit turns on the switching element Q16 belonging to the lower arm and turns off the switching element Q15 belonging to the upper arm in the W-phase arm. On the other hand, when the W-phase PWM signal 104 indicates low, the drive circuit turns on the switching element Q15 belonging to the upper arm and turns off the switching element Q16 belonging to the lower arm in the W-phase arm.

  The short circuit signal 106 is a signal indicating the on / off timing of the short circuit switch 16. The short circuit signal 106 is generated by the control unit 24, for example. The control unit 24 supplies the short circuit signal 106 to the drive circuit of the short circuit switch 16. The drive circuit controls the switching operation of the short-circuit switch 16 in accordance with the short-circuit signal 106. When the short-circuit signal 106 indicates high (High), the drive circuit turns on the short-circuit switch 16. Thereby, the output terminal of each phase arm short-circuits. On the other hand, when the short circuit signal 106 indicates low, the drive circuit turns off the short circuit switch 16. Thereby, the short circuit of the output terminal of each phase arm is eliminated. As an example, the short-circuit period is several microseconds.

  In the second modification, the control unit 24 controls the phase difference of the carrier signal of each phase according to the change of the duty signal of each phase, and during the short circuit period in which the short circuit switch 16 is on, The phase difference of each carrier signal is controlled so that the PWM signal is switched from high to low. For example, during the short circuit period, the phase difference of the carrier signal of each phase is controlled so that the on / off timing (switching operation timing) of each switching element coincides. As another example, the carrier signal of each phase may be generated so that the PWM signal for each phase is switched from low to high during the short circuit period.

  As in the above embodiment, the PWM signal edge timing for each phase, that is, the timing at which the PWM signal for each phase switches from high to low, or the PWM signal for each phase is low ( The timing of switching from (Low) to High (High) may not exactly match. It is only necessary that the edge timing of the PWM signal for each phase is included in the short-circuit period in which the short-circuit signal 106 is high.

  Also in the modified example 2, switching loss does not occur in the switching elements Q11 to Q16 during the short circuit period. Therefore, the number of occurrences of switching loss is reduced, and the total switching loss can be reduced.

  In addition, the carrier signal for including the edge timing of the PWM signal for each phase in the short-circuit period is not limited to the signal according to the above-described embodiment and Modification 2. Of course, signals other than these can be used as carrier signals as long as the edge timing of the PWM signal can be included in the short-circuit period.

  According to the above embodiment and Modifications 1 and 2, for example, the number of parts can be reduced as compared with a three-level inverter, and the manufacturing cost of the inverter device can be reduced. For example, in the case where two inverters are used, additional parts necessary for reducing switching loss will be described. In the three-level inverter described in Patent Document 1, it is necessary to add 12 switching elements, 12 gate drivers, 12 diodes, and a power supply circuit for outputting an intermediate voltage. On the other hand, in the inverter device according to the modified example 1, switching loss is achieved by adding one switching element (switching element Q40), one gate driver, and twelve diodes (diodes D41 to D52). Can be reduced. As described above, according to the circuit configuration and the control method according to the present embodiment and the modification, it is possible to reduce the switching loss with a smaller number of parts compared to the three-level inverter.

  10 DC power source, 12 positive line, 14 negative line, 16 short circuit switch, Q11 to Q16 switching element, D11 to D16 diode.

Claims (5)

In a method of controlling an inverter comprising a plurality of switching elements and converting the DC power supplied from a power source into AC power by turning on / off the plurality of switching elements,
The output terminals of the plurality of phases configured by the plurality of switching elements are provided with short-circuit switches that short-circuit the output terminals of the plurality of phases.
During the ON period of the short-circuit switch, among the plurality of switching elements constituting the plurality of phases, at least one switching element is switched for each phase ,
The short-circuit switch is a switch that collectively short-circuits the output terminals of the plurality of phases.
An inverter control method characterized by the above. In the control method of the inverter according to claim 1,
For each PWM control cycle of the inverter, the shorting switch is turned on for a predetermined period.
An inverter control method characterized by the above. In the control method of the inverter according to claim 1 or 2,
The operation of the switching element that is switched during the ON period of the short-circuit switch is an operation of the switching element connected to the negative electrode side of the power supply in each phase is switching from ON to OFF, and the operation in the individual phase The operation of the switching element connected to the positive side of the power supply is switching from off to on, or the operation of the switching element connected to the negative side of the power supply is switching from off to on, The operation of the switching element connected to the positive electrode side is switching from on to off,
An inverter control method characterized by the above. A power converter that includes a plurality of switching elements, and converts DC power supplied from a power source into AC power by turning on and off the plurality of switching elements;
A short-circuit switch provided at a plurality of phase output terminals constituted by the plurality of switching elements, and short-circuiting the plurality of phase output terminals;
During the ON period of the short circuit switch, among the plurality of switching elements constituting the plurality of phases, a control unit that switches at least one switching element for each phase;
Only including,
The short-circuit switch is a switch that collectively short-circuits the output terminals of the plurality of phases.
An inverter device characterized by that. The inverter device according to claim 4 ,
The control unit turns on the short-circuit switch for a predetermined period for each PWM control cycle of the power conversion unit.
An inverter device characterized by that.