Power conversion device and method of controlling the same

Abstract

The present invention provides a power conversion device capable of suppressing an increase in current flowing in a motor even if a voltage command exceeds an amplitude of a carrier. To achieve the above object, a power conversion device converts a direct-current voltage into a voltage based on a voltage command by an operation of a switching circuit, thereby performing drive control of a three-phase motor, and includes a direct-current voltage detector that detects the direct-current voltage; a norm generator that generates a norm of the voltage command based on the voltage command; a modulation wave generator that generates a first modulation wave based on the detected direct-current voltage and the norm of the voltage command; and a control signal generator that generates a control signal that controls the operation of the switching circuit based on the first modulation wave and a carrier, the modulation wave generator generating, for one phase, the first modulation wave having a size of 1 / 2 of the detected direct-current voltage at a time of a maximum value or a minimum value of the voltage command, and generating, for the remaining two phases, the first modulation wave having a size based on the detected direct-current voltage and the norm of the voltage command.

Description

Technical Field

[0001] This invention relates to power conversion devices. Background Technology

[0002] As background technology in this field, there is Japanese Patent Application Publication No. 10-248262 (Patent Document 1).

[0003] Patent document 1 describes a power conversion device that, without increasing the high-order harmonics of the output voltage, increases the fundamental frequency component of the output voltage and reduces torque ripple during motor drive using a simple control circuit. The device includes a comparator and an adder. The comparator compares the magnitudes of the three-phase voltage commands, and the adder uses the comparator to obtain the intermediate value after removing the maximum and minimum values. The adder then adds the intermediate value multiplied by half to each phase voltage command, and uses the output of the adder as the new voltage command value.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 10-248262 Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] The technology in Patent Document 1 can reduce the peak value of the voltage command, thus increasing the maximum value of the fundamental component of the output voltage by increasing the voltage command. However, when the output of the above adder exceeds the amplitude of the carrier wave, there is a problem that the fundamental component of the output voltage is lower than the voltage command, and the current flowing in the motor increases.

[0009] Therefore, the present invention aims to provide a power conversion device and its control method that can suppress the increase of current flowing in a motor even when the voltage command exceeds the amplitude of the carrier wave.

[0010] Technical means to solve the problem

[0011] As one example of achieving the above objective, a power conversion device is provided that converts DC voltage into a voltage based on a voltage command through the operation of a switching circuit, thereby performing drive control of a three-phase motor. The device includes: a DC voltage detector for detecting the DC voltage; a norm generator for generating a voltage command norm based on the voltage command; a modulation wave generator for generating a first modulation wave based on the detected DC voltage and the voltage command norm; and a control signal generator for generating a control signal for controlling the operation of the switching circuit based on the first modulation wave and a carrier wave. The modulation wave generator generates a first modulation wave with a magnitude of 1 / 2 of the detected DC voltage for one phase at the moment of the maximum or minimum value of the voltage command, and generates first modulation waves with magnitudes based on the detected DC voltage and the voltage command norm for the other two phases.

[0012] Invention Effects

[0013] Using this invention, a power conversion device and its control method can be provided that can suppress the increase of current flowing in the motor even if the voltage command exceeds the amplitude of the carrier wave. Attached Figure Description

[0014] Figure 1 This is a structural diagram of the electric motor drive system of Example 1.

[0015] Figure 2 This is a structural diagram of the DC power supply in Example 1, where a virtual neutral point is introduced.

[0016] Figure 3 This is a diagram showing the relationship between existing voltage commands and carrier waves.

[0017] Figure 4 This is a diagram showing the relationship between the voltage command and the first modulation wave in Embodiment 1.

[0018] Figure 5 This is a structural diagram of the electric motor drive system of Example 2.

[0019] Figure 6 This is a structural diagram of the electric motor drive system of Example 3.

[0020] Figure 7 This is a diagram showing the relationship between the voltage command and the fourth modulation wave in Embodiment 3.

[0021] Figure 8 This is a structural diagram of the electric motor drive system of Example 4. Detailed Implementation

[0022] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0023] As a premise for the following explanation, let the reference phase of the three phases be phase U, and the phases with a phase difference of ±2π / 3 rad relative to phase U be phase V and phase W, respectively.

[0024] Furthermore, when the sum of the three phases is zero, the Euclidean norm of the three phases (hereinafter referred to as the norm) can be obtained by squaring the absolute value of each phase and taking the square root of their sum. When the sum of the three phases is not zero, the norm can be obtained by removing the zero-phase portion from each phase. The zero-phase portion can be obtained by dividing the sum of the three phases by 3. In the following text, "three phases" refers to the case after removing the zero-phase portion. When the three phases are transformed into a two-phase fixed coordinate system (Clarke transformation), and further into a two-phase rotating coordinate system (Park transformation), the norm can be obtained by squaring the absolute value of each phase and taking the square root of their sum.

[0025] Furthermore, the norms of the three-phase phase voltages can be multiplied by √2 / √3, and the norms of the phase voltages in the two-phase fixed coordinate system and the two-phase rotating coordinate system can be multiplied by the values ​​corresponding to the coefficients multiplied during the Park transformation, so that they can be consistent with the amplitudes of the three-phase phase voltages. Therefore, in this embodiment, the norms of the three-phase phase voltages, the norms of the phase voltages in the two-phase fixed coordinate system, the norms of the phase voltages in the two-phase rotating coordinate system, and the amplitudes of the three-phase phase voltages are considered as the same physical quantity.

[0026] In addition, in the case of a two-phase fixed coordinate system or a two-phase rotating coordinate system, it can be inversely transformed into a three-phase system and treated as a three-phase system.

[0027] Example 1

[0028] Figure 1 This is a structural diagram of the electric motor drive system in this embodiment.

[0029] The motor drive system of this embodiment includes a DC power supply 1000, a power conversion device 1010, and a three-phase motor 1020. The power conversion device 1010 converts the DC voltage supplied from the DC power supply 1000 into a voltage based on a voltage command 1030 to drive and control the three-phase motor 1020.

[0030] Figure 1 In the power conversion device 1010, there are DC voltage detector 1040, phase generator 1050, norm generator 1060, modulation wave generator 1070, carrier generator 1080, control signal generator 1090, and switching circuit 1100.

[0031] The DC voltage detector 1040 detects the DC voltage input to the switching circuit 1100 and outputs the detected DC voltage 1110.

[0032] Phase generator 1050 generates voltage command phase 1120 based on voltage command 1030. Voltage command phase 1120 can be obtained, for example, by performing a Clarke transform on voltage command 1030 and taking its arctangent. Phase generator 1050 may not be required if voltage command phase 1120 is known.

[0033] Norm generator 1060 generates voltage command norm 1130 based on voltage command 1030.

[0034] The modulation wave generator 1070 generates the first modulation wave 1140 based on the voltage command phase 1120, the voltage command norm 1130, and the detected DC voltage 1110.

[0035] Carrier generator 1080 generates carrier 1150. In this embodiment, carrier 1150 uses a triangular wave with a period within the fundamental period of voltage command 1030 or first modulation wave 1140, but a sawtooth wave can also be used.

[0036] The control signal generator 1090 generates a control signal 1160 to control the on / off state of the switching circuit 1100 by comparing the first modulated wave 1140 with the carrier wave 1150. Furthermore, this control signal 1160 is modulated using a method known as PWM (Pulse Width Modulation), which is well-known to those skilled in the art; therefore, details of the control signal generator 1090 are omitted.

[0037] The switching circuit 1100 switches on and off according to the control signal 1160, converting the DC voltage supplied from the DC power supply 1000 into a voltage based on the voltage command 1030.

[0038] In addition, a DC power supply 1000 is used in this embodiment, but a single-phase or multi-phase AC power supply can also be used instead of the DC power supply 1000. In this case, a rectifier circuit and a smoothing circuit are added to the power conversion device 1010. The AC voltage output from the AC power supply is rectified by the rectifier circuit and smoothed by the smoothing circuit, thereby obtaining a DC voltage.

[0039] The 1020 three-phase motor includes three-phase induction motors, three-phase permanent magnet synchronous motors, and three-phase synchronous reluctance motors.

[0040] Regarding the voltage command 1030 for driving control of the three-phase motor 1020, it can be obtained, for example, through constant V / f control (in the case of a three-phase induction motor only), or through sensorless vector control by adding a current detector to the power conversion device 1010 to detect the current flowing in the three-phase motor 1020. Alternatively, it can be obtained through vector control by adding the aforementioned current detector and a position detector to the power conversion device 1010 to detect the rotor position of the three-phase motor 1020. The current detector is used to detect the three-phase current, but in addition to directly detecting the three-phase current, it can also be used to detect two-phase current and determine the remaining phase based on the sum of the three phases being zero. Alternatively, a shunt resistor can be provided on the positive or negative side of the switching circuit 1100, and the three-phase current can be obtained from the current flowing in the shunt resistor. The position detector can obtain the rotor position by detecting the rotor speed of the three-phase motor 1020 and utilizing the calculus-integral relationship between speed and position.

[0041] The effects of this embodiment will be explained below. For the sake of simplicity, as... Figure 2 As shown, a virtual neutral point 2170 is introduced in the DC power supply 1000. In this case, the DC power supplies 2000 and 2001 output half the voltage of the DC power supply 1000, and it can be assumed that the amplitude of the carrier wave 1150 is half the output voltage of the DC power supply 1000.

[0042] First, let’s explain the case where the technology of this embodiment is not used, that is, the case where the voltage command 1030 is input to the control signal generator 1090 instead of the first modulation wave 1140 (hereinafter referred to as the prior art).

[0043] In the control signal generator 1090, the voltage command 1030, which is a modulation wave, is compared with the carrier wave 1150 to output a control signal 1160, but if Figure 3 As shown, when the amplitude of voltage command 1030 increases, although voltage command 1030 should be as shown by the dashed line, it is limited by the amplitude of carrier wave 1150, and the output is control signal 1160, which is equivalent to the solid line of voltage command 1030.

[0044] When the voltage command as the modulation wave is a sine (cosine) wave, and the percentage (hereinafter referred to as voltage utilization) between the voltage command norm 1130 and half of the voltage output from the DC power supply 1000 exceeds 100%, the norm of the voltage applied to the three-phase motor 1020 (hereinafter referred to as the output voltage norm) will be less than the voltage command norm 1130 because it is limited by the amplitude of the carrier wave 1150 as described above. While the fundamental component of the output voltage can be increased by up to 2 / √3 times compared to the prior art when using the technology described in Patent Document 1, the output voltage norm will still be less than the voltage command norm 1130 when the voltage utilization exceeds 200 / √3%, similar to the prior art. Consequently, the current flowing in the three-phase motor 1020 increases.

[0045] Next, the use of the technology in this embodiment will be described.

[0046] Figure 4 This diagram illustrates the relationship between the voltage command 1030 and the first modulated wave 1140 generated by the modulated wave generator 1070 in this embodiment. In the modulated wave generator 1070, a wave is generated as shown in the diagram. Figure 4 The convex waveform shown, which is in phase with the voltage command 1030, is output as the first modulation wave 1140. While it is preferable that the voltage command 1030 and the first modulation wave 1140 are in phase, the observed voltage will be as follows, provided the voltage (pulsed) applied to the three-phase motor 1020 is demodulated according to the period of its voltage pulses (which is the same as the period of the carrier wave 1150). Figure 4 The convex waveform shown is not limited to this. In addition, since the phase difference of the three phases is ±2π / 3 rad, it is also possible to generate a convex waveform for one phase, while the other two phases generate convex waveforms with a phase difference of ±2π / 3 rad.

[0047] like Figure 4 As shown, when the amplitude A, representing the maximum value of the convex waveform generated by the modulation wave generator 1070, is 1 / 2 of the DC voltage (the amplitude of the carrier 1150), and its two ends B are the difference between 3 / 2 of the voltage command norm 1130 and 1 / 2 of the DC voltage (the amplitude of the carrier 1150), if the voltage utilization rate is within 400 / 3%, then compared with the prior art, the voltage utilization rate with the voltage command norm 1130 being consistent with the output voltage norm is 4 / 3 times (=(400 / 3%) / (100%)).

[0048] Compared with the technology in Patent Document 1, the voltage utilization rate of the voltage command norm 1130 being consistent with the output voltage norm is 2 / √3 times (=(400 / 3%) / (200 / √3%)).

[0049] Furthermore, even when the voltage utilization rate reaches 400 / 3% or higher, it is able to suppress the decrease in the output voltage norm compared with the prior art and the technology in Patent Document 1.

[0050] Furthermore, the relationship among the three phases of the first modulation wave 1140 generated by the modulation wave generator 1070 is as follows: for one phase (referred to as the maximum phase or the minimum phase), a first modulation wave with a magnitude of 1 / 2 of the DC voltage is generated at the moment when the voltage command is at its maximum or minimum value. For the other two phases, since the phase difference is ±2π / 3 rad, a first modulation wave with a magnitude based on the difference between 3 / 2 of the voltage command norm 1130 and 1 / 2 of the DC voltage is generated, that is, based on the DC voltage and the voltage command norm.

[0051] As described above, by using the technology of this embodiment, even if the voltage command 1030 exceeds the amplitude of the carrier wave 1150, the increase in the current flowing in the three-phase motor 1020 can be suppressed.

[0052] Example 2

[0053] Figure 5 This is a structural diagram of the electric motor drive system in this embodiment. Figure 5 China for and Figure 1 Structures with the same function are labeled with the same markings and their descriptions are omitted. Figure 5 Zhongyu Figure 1 The difference lies in that it has a voltage utilization calculator 5180, a zero-phase voltage injector 5190, and a modulation wave controller 5200.

[0054] Figure 5 In the middle, the voltage utilization calculator 5180 calculates the voltage utilization based on the voltage command norm 1130 and the detected DC voltage 1110, and outputs it as the calculated voltage utilization 5210.

[0055] The zero-phase voltage injector 5190 injects a zero-phase voltage into the voltage command 1030 and outputs it as the second modulation wave 5140. The injected zero-phase voltage may include, for example, the value described in Patent Document 1, "a comparator compares the magnitudes of the three-phase voltage commands, obtains the intermediate value after removing the maximum and minimum values ​​using the comparator, and multiplies the intermediate value by half", or the third harmonic of the voltage command 1030, and the difference between the maximum phase of the voltage command 1030 and half of the detected DC voltage 1110, or the difference between the minimum phase of the voltage command 1030 and half of the detected DC voltage 1110 multiplied by -1, etc., but it may also be zero, that is, the voltage command 1030 is output as is as the second modulation wave 5140.

[0056] The modulation wave controller 5200 controls the switching between the first modulation wave 1140 and the second modulation wave 5140 based on the calculated voltage utilization rate 5210, and outputs the third modulation wave 5141.

[0057] In addition, the carrier 1150 generated by the carrier generator 1080 in this embodiment uses a triangular wave with a period within the fundamental period of the voltage command 1030, the first modulation wave 1140, the second modulation wave 5140, or the third modulation wave 5141, but a sawtooth wave can also be used.

[0058] In addition, the control signal generator 1090 of this embodiment generates a control signal 1160 to control the on / off state of the switching circuit 1100 by comparing the third modulation wave 5141 with the carrier wave 1150.

[0059] The following describes the switching control between the first modulation wave 1140 and the second modulation wave 5140 based on the calculated voltage utilization rate 5210.

[0060] As described above, in the prior art, if the calculated voltage utilization rate 5210 is within 100%, and in the technology of Patent Document 1, if the calculated voltage utilization rate 5210 is within 200 / √3%, then the voltage command norm 1130 is consistent with the output voltage norm. Therefore, if the calculated voltage utilization rate 5210 is less than or equal to 100% to 200 / √3%, then the second modulation wave 5140 is output as the third modulation wave 5141, and if it exceeds 100% to 200 / √3%, then the first modulation wave 1140 is output as the third modulation wave 5141. Thus, it is possible to apply a voltage equivalent to a sine (cosine) wave to the three-phase motor 1020 while keeping the voltage command norm 1130 consistent with the output voltage norm and when the calculated voltage utilization rate 5210 is low.

[0061] Furthermore, when switching between the first modulation wave 1140 and the second modulation wave 5140, to prevent modulation wave discontinuity, the transition from the second modulation wave 5140 to the first modulation wave 1140 can be made according to the calculated voltage utilization rate 5210 if it exceeds 100% to 200 / √3%. Additionally, as described above, by using the technique of this embodiment, if the calculated voltage utilization rate 5210 is within 400 / 3%, the voltage command norm 1130 is consistent with the output voltage norm, so the transition to the first modulation wave 1140 can be completed when the calculated voltage utilization rate 5210 is 400 / 3%.

[0062] Example 3

[0063] Figure 6 This is a structural diagram of the electric motor drive system in this embodiment. Figure 6 China for and Figure 1Structures with the same function are labeled with the same markings and their descriptions are omitted.

[0064] Figure 6 Zhongyu Figure 1 The difference lies in the presence of a modulation wave generator 1330. The power conversion device 6010 has a modulation wave generator 1330, a control signal generator 1090, and a switching circuit 1100.

[0065] The modulation wave generator 1330 generates a fourth modulation wave 1340 based on the norm of the voltage command 1030 (hereinafter referred to as the voltage command norm).

[0066] In this embodiment, the control signal generator 1090 generates a control signal 1160 to control the on / off state of the switching circuit 1100 by comparing the fourth modulation wave 1340 with the carrier wave 1150.

[0067] In the modulation wave generator 1330, the voltage command norm and the voltage command phase (hereinafter referred to as voltage phase) are calculated according to the voltage command, and a square wave with amplitude based on the voltage command norm and phase based on the voltage phase is generated and output as the fourth modulation wave 1340.

[0068] Figure 7 This is a diagram illustrating the relationship between the voltage command and the fourth modulation wave in this embodiment. For example... Figure 7 As shown, it is preferable that the voltage command 1030 and the fourth modulation wave 1340 have the same phase. However, it is not limited to this as long as the voltage (pulse-like) applied to the three-phase motor 1020 is demodulated according to the period of its voltage pulse (which is the same as the period of the carrier wave 1150) and the observed voltage is a square wave. The voltage phase can be obtained, for example, by transforming the three-phase AC coordinates into two-phase AC (Clarke transform) and taking the arctangent. Since the phase difference of the three phases is ±2π / 3 rad, a square wave of one phase is generated, and the other two phases generate square waves with a phase difference of ±2π / 3 rad. When the voltage command norm and voltage phase are known in advance, the voltage command norm and voltage phase can also be directly input to the modulation wave generator 1330 instead of the voltage command 1030.

[0069] When the amplitude of the square wave generated by the modulation wave generator 1330, i.e. the amplitude of the fourth modulation wave 1340, is 3 / 4 of the voltage command norm, if the voltage utilization rate is within 400 / 3%, the voltage command norm is consistent with the output voltage norm. Therefore, compared with the prior art, the voltage utilization rate with the voltage command norm consistent with the output voltage norm is 4 / 3 times (=(400 / 3%) / (100%)).

[0070] Compared with the technology in Patent Document 1, the voltage utilization rate with the voltage command norm being consistent with the output voltage norm is 2 / √3 times (=(400 / 3%) / (200 / √3%)).

[0071] Furthermore, even when the voltage utilization rate reaches 400 / 3% or higher, it is able to suppress the decrease in the output voltage norm compared with the prior art and the technology in Patent Document 1.

[0072] As described above, by using the technology of this embodiment, even if the voltage command 1030 exceeds the amplitude of the carrier wave 1150, the increase in the current flowing in the three-phase motor 1020 can be suppressed.

[0073] Example 4

[0074] Figure 8 This is a structural diagram of the electric motor drive system in this embodiment. Figure 8 China for and Figure 5 , Figure 6 Common parts are marked with the same label and their descriptions are omitted.

[0075] exist Figure 8 In the process, the power conversion device 8010 for driving control of the three-phase motor 1020 includes a DC voltage detector 1040, a voltage utilization calculator 5180, a modulation wave generator 1330, a zero-phase voltage injector 5190, a control signal generator 5390, and a switching circuit 1100.

[0076] The voltage utilization calculator 5180 calculates the voltage utilization rate 5210 based on the voltage command 1030 and the detected DC voltage 1110. If the voltage command norm is known in advance, it can also be directly input into the voltage utilization calculator 5180 instead of the voltage command 1030.

[0077] The zero-phase voltage injector 5190 injects zero-phase voltage into the voltage command 1030 and outputs it as the fifth modulation wave 1341.

[0078] The control signal generator 5390 controls the switching between the fourth modulation wave 1340 and the fifth modulation wave 1341 based on the calculated voltage utilization 5210. It generates a control signal 1160 to control the on / off state of the switching circuit 1100 by comparing the switched modulation wave with the carrier wave. Generally, the carrier wave is a triangular wave with a period within the fundamental period of the switched modulation wave. A sawtooth wave can also be used instead of a triangular wave.

[0079] The following describes the switching control between the fourth modulation wave 1340 and the fifth modulation wave 1341 based on the calculated voltage utilization rate 5210.

[0080] As described above, in the prior art, if the calculated voltage utilization rate 5210 is within 100%, and in the technology of Patent Document 1, if the calculated voltage utilization rate 5210 is within 200 / √3%, then the voltage command norm and the output voltage norm are consistent. Therefore, if the calculated voltage utilization rate 5210 is less than or equal to 100% to 200 / √3%, the fifth modulation wave 1341 is selected, and if it exceeds 100% to 200 / √3%, the fourth modulation wave 1340 is selected. By comparing the selected modulation wave with the carrier wave, it is possible to apply a voltage equivalent to a sine (cosine) wave to the three-phase motor 1020 while keeping the voltage command norm consistent with the output voltage norm and the calculated voltage utilization rate 5210 low.

[0081] Furthermore, when switching between the fourth modulation wave 1340 and the fifth modulation wave 1341, to prevent modulation wave discontinuity, the transition between the fourth modulation wave 1340 and the fifth modulation wave 1341 can be made according to the calculated voltage utilization rate 5210 if the calculated voltage utilization rate 5210 exceeds 100% to 200 / √3%. Additionally, as described above, by using the technique of this embodiment, if the calculated voltage utilization rate 5210 is within 400 / 3%, the voltage command norm and the output voltage norm are consistent, so the transition to the fourth modulation wave can be completed when the calculated voltage utilization rate 5210 is 400 / 3%.

[0082] The embodiments have been described above, but the present invention is not limited to the above embodiments and includes various modifications. For example, the above embodiments have been described to facilitate understanding of the present invention, but are not limited to having all the structures described. In addition, a part of the structure of one embodiment can be replaced with the structure of another embodiment, and the structure of another embodiment can be added to the structure of one embodiment. Furthermore, for a part of the structure of each embodiment, other structures can be added, deleted, or replaced.

[0083] In addition, the above-mentioned structures and functions can be implemented by software, which is a program that the processor interprets and executes to implement each function, or by hardware, for example, through integrated circuit design.

[0084] Explanation of reference numerals in the attached figures

[0085] 1000: DC power supply; 1010: Power conversion device; 1020: Three-phase motor; 1030: Voltage command; 1040: DC voltage detector; 1050: Phase generator; 1060: Norm generator; 1070: Modulation wave generator; 1080: Carrier generator; 1090: Control signal generator; 1100: Switching circuit; 1110: Detecting DC voltage; 1120: Voltage command phase; 1130: Voltage command norm; 1140: First modulation wave; 1150: Carrier, 1160: Control signal, 1330: Modulation wave generator, 1340: Fourth modulation wave, 1341: Fifth modulation wave, 2000: DC power supply, 2001: DC power supply, 2170: Virtual neutral point, 5010: Power conversion device, 5140: Second modulation wave, 5141: Third modulation wave, 5180: Voltage utilization calculator, 5190: Zero-phase voltage injector, 5200: Modulation wave controller, 5210: Calculate voltage utilization, 5390: Control signal generator.

Claims

1. A power conversion device that converts DC voltage into voltage based on voltage commands through the operation of a switching circuit, thereby driving and controlling a three-phase motor, characterized in that, comprising: a direct-current voltage detector that detects the direct-current voltage; a norm generator that generates a voltage command norm from the voltage command; a modulation wave generator that generates a first modulation wave from the detected direct-current voltage and the voltage command norm; a voltage utilization rate calculator that calculates a voltage utilization rate from the voltage command and the direct-current voltage; a zero-phase voltage injector that injects a zero-phase voltage into the voltage command to generate a second modulation wave; a modulation wave controller that generates a third modulation wave based on the first modulation wave, the second modulation wave, and the voltage utilization rate; and a control signal generator that generates a control signal that controls the operation of the switching circuit from the third modulation wave and a carrier wave, wherein the modulation wave generator generates, for one phase, a first modulation wave that is 1 / 2 the detected direct-current voltage at a time of a maximum value or a minimum value of the voltage command, and generates, for the remaining two phases, a first modulation wave whose magnitude is based on the detected direct-current voltage and the voltage command norm.

2. The power conversion device according to claim 1, wherein the first modulation wave for the remaining two phases generated by the modulation wave generator is a modulation wave whose magnitude is the difference between 3 / 2 the voltage command norm and 1 / 2 the detected direct-current voltage.

3. The power conversion device according to claim 1, wherein the modulation wave controller generates the second modulation wave as the third modulation wave when the voltage utilization rate is equal to or less than 200 / √3%, and generates the first modulation wave as the third modulation wave when the voltage utilization rate exceeds 200 / √3%.

4. The power conversion device according to claim 1, wherein the modulation wave controller generates the second modulation wave as the third modulation wave when the voltage utilization rate is equal to or less than 200 / √3%, and generates the third modulation wave that transitions from the second modulation wave to the first modulation wave when the voltage utilization rate exceeds 200 / √3%.

5. The power conversion device according to claim 4, wherein the modulation wave controller transitions from the second modulation wave to the first modulation wave in accordance with the voltage utilization rate.

6. The power conversion device according to claim 5, wherein the modulation wave controller completes the transition to the first modulation wave when the voltage utilization rate is 400 / 3% for the transition from the second modulation wave to the first modulation wave. comprising:

7. A control method for a power conversion device, comprising converting DC voltage into a voltage based on a voltage command through the operation of a switching circuit, thereby performing drive control of a three-phase motor, characterized in that, detecting the direct-current voltage; generating a voltage command norm from the voltage command; generating, for one phase, a first modulation wave that is 1 / 2 the detected direct-current voltage at a time of a maximum value or a minimum value of the voltage command, and generating, for the remaining two phases, a first modulation wave whose magnitude is based on the detected direct-current voltage and the voltage command norm; calculating a voltage utilization rate from the voltage command and the direct-current voltage; injecting a zero-phase voltage into the voltage command to generate a second modulation wave; generating a third modulation wave based on the first modulation wave, the second modulation wave, and the voltage utilization rate; and generating a control signal that controls the operation of the switching circuit from the third modulation wave and a carrier wave. generating a third modulation wave based on the first modulation wave, the second modulation wave, and the voltage utilization rate; and generating a control signal that controls the operation of the switching circuit based on the third modulation wave and a carrier wave.

8. The control method of a power conversion device according to claim 7, wherein: the first modulation wave of the remaining two phases is a modulation wave whose magnitude is the difference between 3 / 2 of the norm of the voltage command and 1 / 2 of the detected DC voltage.

9. The control method of a power conversion device according to claim 7, wherein: the second modulation wave is generated as the third modulation wave when the voltage utilization rate is equal to or less than 200 / √3%, and the first modulation wave is generated as the third modulation wave when the voltage utilization rate exceeds 200 / √3%.

10. The control method of a power conversion device according to claim 7, wherein: the second modulation wave is generated as the third modulation wave when the voltage utilization rate is equal to or less than 200 / √3%, and the third modulation wave is generated in transition from the second modulation wave to the first modulation wave when the voltage utilization rate exceeds 200 / √3%.

11. The control method of a power conversion device according to claim 10, wherein: the transition from the second modulation wave to the first modulation wave is performed in accordance with the voltage utilization rate.

12. The control method of a power conversion device according to claim 11, wherein: the transition to the first modulation wave is completed at the voltage utilization rate of 400 / 3% for the transition from the second modulation wave to the first modulation wave.

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