Power converter

Abstract

To provide an electric power conversion device capable of linearly switching between pulse-width modulation which can be high in noise suppression effect, but is limited in percentage modulation and pulse-width modulation which is inferior in noise suppression effect, but can be high in percentage modulation.SOLUTION: An electric power conversion device comprises: a first modulation unit 34 which executes pulse-width modulation for outputting only an odd-numbered voltage vector in one control period to reduce common mode noise; a second modulation unit 35 which executes pulse-width modulation providing higher percentage modulation than the pulse-width modulation thereby and reducing common mode noise; a determination unit 45 which determines zero-voltage output time when a zero-voltage vector is output; and a selection unit 40 which selects the pulse-width modulation by the first modulation unit or the pulse-width modulation by the second modulation unit within one electric angle period based upon the zero-voltage output time that the determination unit determines.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power conversion device that converts a DC voltage into an AC voltage.

Background Art

[0002] Conventionally, various pulse width modulations (PWM) have been proposed to suppress conduction noise propagated to a power supply, and the methods are roughly divided into two categories. One is a method that completely suppresses fluctuations in the common mode voltage, which is a factor of common mode noise, and the other is a method that partially suppresses the fluctuations in the common mode voltage while allowing the fluctuations.

[0003] Examples of the former method include pulse width modulation that outputs only odd voltage vectors or only even voltage vectors. According to this method, it is possible to completely suppress fluctuations in the common mode voltage within a carrier period. There is also pulse width modulation that switches whether to output only odd voltage vectors or only even voltage vectors according to the electrical angle phase. By this method, fluctuations in the common mode voltage can also be greatly suppressed (see, for example, Patent Document 1).

[0004] Examples of the latter method include pulse width modulation that matches the timing of the fall and rise of the phase voltage of another phase with the rise and fall of the phase voltage of a specific phase in the PWM pattern (see, for example, Patent Document 2). Furthermore, fluctuations in the common mode voltage can also be suppressed by pulse width modulation of two-phase modulation in which the switching of one phase is fixed and the switching of the other two phases is performed (see, for example, Patent Document 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

[0006] While the former method (Patent Document 1) is the most effective method for suppressing common-mode voltage fluctuations, it has the drawback of limiting the linear output region (the maximum amplitude at which the voltage vector can complete one rotation with a constant radius) and thus limiting the possible modulation ratios due to restrictions on the voltage vector used. Therefore, it is difficult to apply when driving a compressor motor, or it is necessary to switch the modulation method as described in Patent Document 3 when the rotational speed and modulation ratio are high.

[0007] In contrast, the latter method (Patent Documents 2 and 3) allows the linear output region to be used up to its normal maximum, and can achieve a high modulation rate, but its effect in suppressing common-mode voltage fluctuations is still inferior to that of the former method.

[0008] In Patent Document 3, two-phase modulation and three-phase modulation are switched depending on the operating region. It is conceivable to switch between the former and latter methods described above in a similar manner, but this would result in the problem of a switching shock occurring in the pulse width modulation method.

[0009] The present invention was made to solve the aforementioned conventional technical problems, and aims to provide a power converter that can linearly switch between pulse width modulation, which has a high noise suppression effect but a limited modulation rate, and pulse width modulation, which has an inferior noise suppression effect but can achieve a high modulation rate. [Means for solving the problem]

[0010] The power conversion device of the present invention converts a DC voltage to an AC voltage and comprises an inverter circuit that applies the phase voltage at the connection point of the upper and lower arm switching elements of each phase to a load, and a control device that controls the switching of each switching element, wherein the control device has a first modulation unit that reduces common-mode noise by performing one of the following: pulse width modulation that outputs only odd voltage vectors in one control cycle, or pulse width modulation that outputs only even voltage vectors in one control cycle, or pulse width modulation that switches between pulse width modulation that outputs only odd voltage vectors in one control cycle and pulse width modulation that outputs only even voltage vectors in one control cycle according to the electrical angular phase, and a first modulation unit that reduces common-mode noise than the pulse width modulation by the first modulation unit The modulation rate can be increased. Furthermore, it includes a second modulation unit that performs pulse width modulation capable of reducing common-mode noise, a determination unit that determines the zero voltage output time for which a zero voltage vector is output, and a selection unit that, based on the zero voltage output time determined by the determination unit, selects between pulse width modulation by the first modulation unit and pulse width modulation by the second modulation unit within one electrical angle period. This selection unit selects pulse width modulation by the first modulation unit if the zero voltage output time is greater than or equal to zero, and selects pulse width modulation by the second modulation unit if the zero voltage output time is negative, or selects pulse width modulation by the first modulation unit if the zero voltage output time is positive, and selects pulse width modulation by the second modulation unit if the zero voltage output time is less than or equal to zero. It is characterized by the following:

[0011] The power conversion device of the second invention is the same as the above invention The first modulation unit is characterized by achieving a zero voltage output time in which a zero voltage vector is output by modifying an odd voltage vector or an even voltage vector.

[0012] Third Invention The power conversion device is characterized in that, in each of the above inventions, the first modulation unit switches between pulse width modulation that outputs only odd voltage vectors during one control cycle and pulse width modulation that outputs only even voltage vectors during one control cycle, depending on the control state.

[0013] The fourth inventionThe power conversion device in the above invention includes a phase voltage command calculation unit that calculates the phase voltage command value for each phase, and the first modulation unit is characterized in that, when the sign of the phase with the maximum amplitude of the phase voltage command value is positive, it performs pulse width modulation that outputs only even voltage vectors in one control cycle, and when the sign of the phase with the maximum amplitude of the phase voltage command value is negative, it performs pulse width modulation that outputs only odd voltage vectors in one control cycle.

[0014] The power conversion device of the fifth invention is the same as the inventions of the present invention to the fourth invention. In this configuration, the second modulation unit is characterized by performing pulse width modulation, which outputs only adjacent voltage vectors within one control cycle.

[0015] The sixth invention The power conversion device in the above invention includes a phase voltage command calculation unit that calculates the phase voltage command value for each phase, and the second modulation unit is characterized in that, when the sign of the phase with the maximum amplitude of the phase voltage command value is positive, it performs pulse width modulation that outputs only two even voltage vectors and the odd voltage vector sandwiched between them during one control cycle, and when the sign of the phase with the maximum amplitude of the phase voltage command value is negative, it performs pulse width modulation that outputs only two odd voltage vectors and the even voltage vector sandwiched between them during one control cycle.

[0016] The power conversion device of the seventh invention is the same as the inventions of the present invention to the fourth invention. The second modulation unit is characterized by performing pulse width modulation that synchronizes the rising and falling timings of the phase voltages of other phases with the rising and falling timings of the phase voltages of a specific phase.

[0017] The power conversion device of the eighth invention is the same as the inventions of the present invention to the fourth invention. The second modulation unit is characterized by performing pulse width modulation, which fixes the ON / OFF state of a predetermined one-phase upper / lower arm switching element and modulates the ON / OFF state of the other two-phase upper / lower arm switching elements.

[0018] The ninth invention The power conversion device described above is characterized in that the inverter circuit drives the motor by applying the phase voltage at the connection point of the upper and lower arm switching elements of each phase. [Effects of the Invention]

[0019] According to the present invention, in a power conversion device that converts DC voltage to AC voltage, the device comprises an inverter circuit that applies phase voltages at the connection points of the upper and lower arm switching elements of each phase to a load, and a control device that controls the switching of each switching element, wherein the control device has a first modulation unit that reduces common-mode noise by performing one of the following: pulse width modulation that outputs only odd voltage vectors in one control cycle, or pulse width modulation that outputs only even voltage vectors in one control cycle, or pulse width modulation that switches between pulse width modulation that outputs only odd voltage vectors in one control cycle and pulse width modulation that outputs only even voltage vectors in one control cycle according to the electrical angular phase, and a first modulation unit that reduces common-mode noise than the pulse width modulation by the first modulation unit The modulation rate can be increased. Furthermore, it includes a second modulation unit that performs pulse width modulation capable of reducing common-mode noise, a determination unit that determines the zero voltage output time for outputting a zero voltage vector, and a selection unit that, based on the zero voltage output time determined by the determination unit, selects pulse width modulation by the first modulation unit and pulse width modulation by the second modulation unit within one electrical angle period. Thus, it includes pulse width modulation by the first modulation unit which has a high common-mode noise suppression effect, and pulse width modulation that can reduce common-mode noise but is more effective than pulse width modulation by the first modulation unit. The modulation rate can be increased. This allows for linear (seamless) switching of pulse width modulation by the second modulation unit.

[0020] This makes it possible to minimize switching shocks while simultaneously improving the common-mode noise suppression effect and expanding the operating range, for example. The ninth invention As such, it is extremely effective when driving a motor as a load.

[0021] in this case, The selection unit is configured to either select pulse width modulation by the first modulation unit if the zero voltage output time is greater than or equal to zero, and select pulse width modulation by the second modulation unit if the zero voltage output time is negative, or to select pulse width modulation by the first modulation unit if the zero voltage output time is positive, and select pulse width modulation by the second modulation unit if the zero voltage output time is less than or equal to zero. This makes it possible to smoothly switch between pulse width modulation by the first modulation unit and pulse width modulation by the second modulation unit according to the required modulation rate.

[0022] Also, Second inventionIf the first modulation unit modifies an odd voltage vector or an even voltage vector to achieve a zero voltage output time that outputs a zero voltage vector, then the pulse width modulation of the first modulation unit can completely suppress fluctuations in the common-mode voltage.

[0023] Also, Third Invention As described above, if the first modulation unit switches between pulse width modulation that outputs only odd voltage vectors during one control cycle and pulse width modulation that outputs only even voltage vectors during one control cycle, depending on the control state, it becomes possible to achieve optimal pulse width modulation by the first modulation unit according to the control state.

[0024] In this case, for example The fourth invention As described above, the first modulation unit performs pulse width modulation that outputs only even voltage vectors in one control cycle when the sign of the phase with the maximum amplitude of the phase voltage command value calculated by the phase voltage command calculation unit is positive, and performs pulse width modulation that outputs only odd voltage vectors in one control cycle when the sign of the phase with the maximum amplitude of the phase voltage command value is negative. This allows for appropriate switching between pulse width modulation that outputs only even voltage vectors in one control cycle and pulse width modulation that outputs only odd voltage vectors in one control cycle.

[0025] Here, the pulse width modulation performed by the second modulation unit is: The fifth invention One example is pulse width modulation, which outputs only adjacent voltage vectors within one control cycle. In this case, The sixth invention As described above, the second modulation unit performs pulse width modulation that outputs only two even voltage vectors and the odd voltage vector sandwiched between them during one control cycle when the sign of the phase with the maximum amplitude of the phase voltage command value is positive, and when the sign of the phase with the maximum amplitude of the phase voltage command value is negative, it performs pulse width modulation that outputs only two odd voltage vectors and the even voltage vector sandwiched between them during one control cycle, thereby enabling smooth pulse width modulation by the second modulation unit.

[0026] In addition, the pulse width modulation performed by the second modulation unit includes the following: The seventh invention Pulse width modulation, which synchronizes the rising and falling timings of the phase voltages of other phases with the rising and falling timings of the phase voltages of a specific phase, The eighth invention As shown above, pulse width modulation can be employed to fix the ON / OFF state of a predetermined one-phase upper / lower arm switching element and modulate the ON / OFF state of the other two-phase upper / lower arm switching elements. [Brief explanation of the drawing]

[0027] [Figure 1] This is an electrical circuit diagram of a power conversion device according to one embodiment to which the present invention is applied. [Figure 2] This diagram shows the command values ​​for three-phase AC voltage. [Figure 3] This is a diagram representing the voltage space used to explain the linear output region. [Figure 4] This diagram shows the relationship between voltage vectors and phase voltages. [Figure 5] This is a diagram showing the voltage vector (output basis vector). [Figure 6] Figure 1 is a flowchart illustrating the operation of one embodiment of the control device (Embodiment 1). [Figure 7] This diagram represents the voltage space used to explain IRSPWM with odd voltage vectors. [Figure 8] This figure shows the output region and the values ​​that the function can take. [Figure 9] This diagram illustrates the linear output region of IRSPWM with an odd voltage vector. [Figure 10] This figure shows the output vector and output time of RSPWM with odd voltage vectors. [Figure 11] This figure shows the output vector and output time of NSPWM with odd voltage vectors. [Figure 12] This figure shows an example of an IRSPWM output vector with an odd voltage vector (in the case of RSPWM). [Figure 13] This figure shows an example of an IRSPWM output vector with an odd voltage vector (in the case of NSPWM). [Figure 14] This figure shows the PWM pattern of IRSPWM with odd voltage vectors (in the case of RSPWM). [Figure 15] This figure shows the PWM pattern of IRSPWM with odd voltage vectors (in the case of NSPWM). [Figure 16] This figure shows the modulation waveform of IRSPWM at a low modulation rate using odd voltage vectors. [Figure 17] This figure shows the modulation waveform at high modulation rates for IRSPWM using odd voltage vectors. [Figure 18] This diagram represents the voltage space used to explain IRSPWM with even voltage vectors. [Figure 19] This figure shows the output region and the values ​​that the function can take. [Figure 20] This diagram illustrates the linear output region of IRSPWM with an even voltage vector. [Figure 21] This figure shows the output vector and output time of RSPWM with an even voltage vector. [Figure 22] This figure shows the output vector and output time of NSPWM with an even voltage vector. [Figure 23] This figure shows an example of an IRSPWM output vector using an even voltage vector (in the case of RSPWM). [Figure 24] This figure shows an example of an IRSPWM output vector using an even voltage vector (in the case of NSPWM). [Figure 25] This figure shows the PWM pattern of IRSPWM with an even voltage vector (in the case of RSPWM). [Figure 26] This figure shows the PWM pattern of IRSPWM with an even voltage vector (in the case of NSPWM). [Figure 27] This figure shows the modulation waveform of IRSPWM at a low modulation rate using even voltage vectors. [Figure 28] This figure shows the modulation waveform at high modulation rates for IRSPWM using even voltage vectors. [Figure 29]This figure shows the operating region of IRSPWM based on the total voltage vector (Example 2). [Figure 30] This figure shows the linear output region of IRSPWM based on the total voltage vector. [Figure 31] This figure shows the correspondence between RSPWM and each phase of IRSPWM based on the total voltage vector. [Figure 32] This figure shows the modulation waveform of IRSPWM at a low modulation rate using the total voltage vector. [Figure 33] This figure shows the modulation waveform of IRSPWM at a high modulation rate using the total voltage vector. [Figure 34] This figure shows a pulse width modulation (PWM) pattern in which the rising and falling timings of one phase are synchronized with the falling and rising timings of another phase (Example 3). [Figure 35] This figure shows the linear output region of Figure 34. [Modes for carrying out the invention]

[0028] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Examples]

[0029] The power conversion device 1 in the embodiment to which the present invention is applied drives the motor 8 (load) of a so-called inverter-integrated electric compressor that constitutes the refrigerant circuit of a vehicle air conditioning system mounted on a vehicle such as an electric vehicle.

[0030] (1) Circuit configuration of power converter 1 In Figure 1, the power conversion device 1 of the embodiment includes a three-phase inverter circuit 28 and a control device 21. The inverter circuit 28 is a circuit that converts the DC voltage of a DC power source (vehicle battery: for example, 350V) 29 into a three-phase AC voltage and applies it to the motor 8. In this case, the motor 8 of the embodiment is an IPMSM (Interior Permanent Magnet Synchronous Motor).

[0031] The inverter circuit 28 has a U-phase half-bridge circuit 19U, a V-phase half-bridge circuit 19V, and a W-phase half-bridge circuit 19W. Each phase half-bridge circuit 19U to 19W has upper arm switching elements 18A to 18C and lower arm switching elements 18D to 18F, respectively. Furthermore, each switching element 18A to 18F is connected in antiparallel to a flywheel diode 31. In this embodiment, each upper and lower arm switching element 18A to 18F is composed of an insulated gate bipolar transistor (IGBT) with a MOS structure incorporated into its gate portion.

[0032] The collectors of the upper arm switching elements 18A to 18C of the inverter circuit 28 are connected to the upper arm power line (positive bus) 10 of the DC power supply 29 and the smoothing capacitor 32. On the other hand, the emitters of the lower arm switching elements 18D to 18F of the inverter circuit 28 are connected to the lower arm power line (negative bus) 15 of the DC power supply 29 and the smoothing capacitor 32.

[0033] In this case, the emitter of the upper arm switching element 18A of the U-phase half-bridge circuit 19U and the collector of the lower arm switching element 18D are connected in series, the emitter of the upper arm switching element 18B of the V-phase half-bridge circuit 19V and the collector of the lower arm switching element 18E are connected in series, and the emitter of the upper arm switching element 18C of the W-phase half-bridge circuit 19W and the collector of the lower arm switching element 18F are connected in series.

[0034] Furthermore, the connection point (U-phase voltage Vu) between the upper arm switching element 18A and the lower arm switching element 18D of the U-phase half-bridge circuit 19U is connected to the U-phase armature coil of the motor 8, the connection point (V-phase voltage Vv) between the upper arm switching element 18B and the lower arm switching element 18E of the V-phase half-bridge circuit 19V is connected to the V-phase armature coil of the motor 8, and the connection point (W-phase voltage Vw) between the upper arm switching element 18C and the lower arm switching element 18F of the W-phase half-bridge circuit 19W is connected to the W-phase armature coil of the motor 8.

[0035] (2) Configuration of the control device 21 Next, the control device 21 is composed of a microcomputer with a processor. In this embodiment, it receives a rotation speed command value from the vehicle's ECU and a motor current (phase current) from the motor 8, and controls the ON / OFF state (switching) of each switching element 18A to 18F of the inverter circuit 28 based on these values. Specifically, it controls the gate voltage applied to the gates of each switching element 18A to 18F.

[0036] The control device 21 of this embodiment includes a command value calculation unit 30, a PWM signal generation unit 36, a gate driver 37, and current sensors 26A, 26B, and 26C, which consist of current transformers for measuring the motor currents (phase currents) of each phase flowing through the motor 8: U-phase current iu, V-phase current iv, and W-phase current iw.

[0037] (2-1) Command value calculation unit 30 The command value calculation unit 30 of this embodiment includes a phase voltage command calculation unit 33, a first modulation unit 34, a second modulation unit 35, a selection unit 40, and a determination unit 45, and each current sensor 26A to 26C is connected to the phase voltage command calculation unit 33.

[0038] In the embodiment, the current sensor 26A measures the U-phase current iu, the current sensor 26B measures the V-phase current iv, and the current sensor 26C measures the W-phase current iw. However, the U-phase current iu may be measured by the current sensor 26A, the V-phase current iv may be measured by the current sensor 26B, and the W-phase current iw may be obtained by calculation from these. In addition to measuring with the current sensors 26A to 26C as in the embodiment for the method of detecting the motor current of each phase, there is a method of detecting the current value of the lower arm power line 15 with a shunt resistor and estimating the phase voltage command calculation unit 33 from the current value and the operating state of the motor 8. Therefore, the method of detecting and estimating each phase current is not particularly limited.

[0039] (2-2) Phase voltage command calculation unit 33 The phase voltage command calculation unit 33 in the embodiment generates the U-phase voltage Vu, V-phase voltage Vv, and W-phase voltage Vw applied to the armature coils of each phase of the motor 8 by vector control based on the electrical angle of the motor 8, the d-axis current and q-axis current obtained from the current command value and the phase current, for three-phase modulation phase voltage command values Vu ref (Hereinafter, the U-phase voltage command value Vu ref ), Vv ref (Hereinafter, the V-phase voltage command value Vv ref ), Vw ref (Hereinafter, the W-phase voltage command value Vw ref ) are calculated and output.

[0040] In this case, the phase voltage command calculation unit 33 uses the d-axis voltage command value Vd ref and the q-axis voltage command value Vq ref to calculate the α-axis voltage command value Vα ref and the β-axis voltage command value Vβ ref using the following formula (I), and calculates the voltage command values Vu ref and Vβ ref from these α-axis voltage command value Vα ref and β-axis voltage command value Vβ ref using formula (II) for the voltage command values Vu ref (phase voltage command value) of each phase of UVW.

[0041]

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[0042] The above formula (II) is used with respect to the α-axis as the phase θm and the α-axis voltage command value Vα. ref and β-axis voltage command value Vβ ref Rewriting this using the voltage vector Vm composed of the following, we get the following equation (III).

[0043]

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[0044] Figure 2 shows the voltage command values ​​Vu for each phase calculated using formula (III). ref , Vv ref VW ref The waveform is shown, and Figure 3 shows the linear output region kH. The linear output region is the maximum amplitude at which the voltage vector can complete a clean rotation (draw a circle) in the voltage space diagram shown in Figure 3. Since the voltage space of a three-phase inverter is hexagonal as shown in Figure 3, theoretically the linear output region is the inscribed circle of the hexagon. In this application, the linear output region kH in general three-phase modulation is represented as 1, and the linear output regions of other modulation methods are normalized and discussed.

[0045] Furthermore, by combining the High and Low states of the U-phase voltage Vu, V-phase voltage Vv, and W-phase voltage Vw, they can be represented as eight voltage vectors (output fundamental vectors) V0 to V7, as shown in Figure 4. Of these, V1, V3, and V5 are odd voltage vectors, V2, V4, and V6 are even voltage vectors, and V0 and V7 are zero voltage vectors. When each voltage vector is shown in voltage space, it looks like Figure 5.

[0046] The phase voltage command calculation unit 33 of the embodiment further uses the following equations (IV) and (V) to calculate the two-phase modulated voltage command value Vu for each phase. ref2 , Vv ref2 VW ref2 It is calculating this.

[0047]

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[0048]

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[0049] Note that Vmod in equations (IV) and (V) represents the voltage command value Vu for three-phase modulation. ref , Vv ref VW ref From the voltage command value Vu of two-phase modulation ref2 , Vv ref2 VW ref2 This is a correction value used to calculate the three-phase voltage command value Vu. ref , Vv ref VW ref The smallest value (min) among them is added to Vdc / 2, and in formula (V), the three-phase voltage command value Vu ref , Vv ref VW ref The maximum value (max) among them is subtracted from Vdc / 2.

[0050] And the voltage command value Vu for three-phase modulation ref , Vv ref VW ref If the sign of the phase with the maximum amplitude among the (phase voltage command values) is positive, two-phase modulation is performed by fixing the upper arm switching element of the phase with the maximum amplitude ON using formula (V), and the voltage command value Vu ref , Vv ref VW ref If the phase with the maximum amplitude has a negative sign, two-phase modulation is achieved by using formula (IV) to fix the lower arm switching element of the phase with the maximum amplitude to ON.

[0051] (2-3) First modulation section 34 The first modulation unit 34 of the embodiment performs pulse width modulation, outputting only the odd voltage vectors V1, V3, and V5 from the aforementioned voltage vectors during one control cycle, thereby obtaining the voltage command value Vα ref and Vβ refThe ON times tu, tv, and tw of the upper arm switching elements of each phase are generated directly from this, and the voltage vectors (V1, V3, V5) and their output times are output. In this application, this pulse width modulation will be referred to as RSPWM (Remote State PWM) using odd voltage vectors. This pulse width modulation is based on the concept of instantaneous spatial vector modulation, which performs spatial vector modulation without waiting for the next sampling point.

[0052] The first modulation unit 34 further performs pulse width modulation, outputting only the even voltage vectors V2, V4, and V6 from the aforementioned voltage vectors during one control cycle, thereby generating the voltage command value Vα ref and Vβ ref The ON times tuv, tvw, and twu of the two-phase upper arm switching element are generated directly from this, and the voltage vectors (V2, V4, V6) and their output times are output. In this application, this pulse width modulation will be hereafter referred to as RSPWM with even voltage vectors.

[0053] Furthermore, the first modulation unit 34 performs pulse width modulation by switching between RSPWM using odd voltage vectors and RSPWM using even voltage vectors according to the electrical angular phase. In this application, this pulse width modulation will hereafter be referred to as RSPWM using all voltage vectors. The pulse width modulation by the first modulation unit 34 described above will be described in detail later.

[0054] (2-4) Second modulation section 35 The second modulation unit 35 performs pulse width modulation that achieves a higher modulation rate than the pulse width modulation performed by the first modulation unit 34 and reduces common-mode noise. In the embodiment, the second modulation unit 35 performs pulse width modulation that outputs only adjacent voltage vectors in one control cycle in Figure 5.

[0055] For example, the voltage vector and output time are output for combinations of two odd voltage vectors V1 and V3 and an even voltage vector V2 sandwiched between them in Figure 5, or two odd voltage vectors V3 and V5 and an even voltage vector V4 sandwiched between them in Figure 5, or two odd voltage vectors V5 and V1 and an even voltage vector V6 sandwiched between them in Figure 5. In this application, this pulse width modulation will be referred to below as NSPWM (Near State PWM) using odd voltage vectors.

[0056] Furthermore, for example, the voltage vectors and output times are output for combinations of two even voltage vectors V2 and V4 and an odd voltage vector V3 sandwiched between them in Figure 5, or two even voltage vectors V4 and V6 and an odd voltage vector V5 sandwiched between them in Figure 5, or two even voltage vectors V6 and V2 and an odd voltage vector V1 sandwiched between them in Figure 5. In this application, this pulse width modulation will be hereafter referred to as NSPWM by even voltage vectors. The pulse width modulation by this second modulation unit 35 will also be described in detail later.

[0057] (2-5) Judgment section 45 The determination unit 45 in this embodiment determines the zero voltage output times t0 and t7, which are the times when the zero voltage vector obtained from the calculation by the first modulation unit 34 is output, for each control cycle. The operation of this determination unit 45 will be described in detail later.

[0058] (2-6) Selection section 40 In this embodiment, the selection unit 40 selects, based on the zero-voltage output times t0 and t7 determined by the determination unit 45, the pulse width modulation by the first modulation unit 34 and the pulse width modulation by the second modulation unit 35 within one electrical angle period for each control period. The selected voltage vector and output time are then output to the PWM signal generation unit 36. The operation of this selection unit 40 will be described in detail later.

[0059] (2-7) PWM signal generation section 36 The PWM signal generation unit 36 ​​receives the voltage vector and output time output by the selection unit 40 as input, and compares its magnitude with the carrier signal to generate and output PWM signals that serve as drive command signals for the U-phase inverter 19U, V-phase inverter 19V, and W-phase inverter 19W of the inverter circuit 28.

[0060] The gate driver 37 generates gate voltages for the switching elements 18A and 18D of the U-phase inverter 19U, the gate voltages for the switching elements 18B and 18E of the V-phase inverter 19V, and the gate voltages for the switching elements 18C and 18F of the W-phase inverter 19W, based on the PWM signal output from the PWM signal generation unit 36.

[0061] Then, each switching element 18A to 18F of the inverter circuit 28 is driven ON / OFF based on the gate voltage output from the gate driver 37. That is, when the gate voltage is ON (a predetermined voltage value), the switching element operates ON, and when the gate voltage is OFF (zero), the switching element operates OFF. When the switching elements 18A to 18F are IGBTs as described above, the gate driver 37 is a circuit for applying the gate voltage to the IGBTs based on the PWM signal, and is composed of photocouplers, logic ICs, transistors, etc.

[0062] Then, the voltage at the connection point between the upper arm switching element 18A and the lower arm switching element 18D of the U-phase half-bridge circuit 19U is applied (output) to the U-phase armature coil of the motor 8 as the U-phase voltage Vu (phase voltage), the voltage at the connection point between the upper arm switching element 18B and the lower arm switching element 18E of the V-phase half-bridge circuit 19V is applied (output) to the V-phase armature coil of the motor 8 as the V-phase voltage Vv (phase voltage), and the voltage at the connection point between the upper arm switching element 18C and the lower arm switching element 18F of the W-phase half-bridge circuit 19W is applied (output) to the W-phase armature coil of the motor 8 as the W-phase voltage Vw (phase voltage).

[0063] (3) Operation of the command value calculation unit 30 Next, the operation of the command value calculation unit 30 in this embodiment will be described with reference to Figures 6 to 28. Figure 6 is a flowchart illustrating the overall flow of pulse width modulation (hereinafter referred to as IRSPWM (Instantaneous Remote State PWM) in this application) performed by the command value calculation unit 30. Step S1 is the calculation of the formulas (I) to (V) described above, and the phase voltage command calculation unit 33 calculates the α-axis voltage command value Vα ref and β-axis voltage command value Vβ ref , three-phase modulation voltage command value Vu ref , Vv ref VW ref , two-phase modulated voltage command value Vu ref2 , Vv ref2 VW ref2 Calculate.

[0064] Then, in step S2, the voltage command value Vu of the three-phase modulation described above is used. ref , Vv ref VW ref The system determines whether the sign of the phase with the maximum amplitude (of the phase voltage command value) is positive or negative. In this embodiment, this determination is performed by the first modulation unit 34 and the second modulation unit 35. Then, the voltage command value Vu of the three-phase modulation is determined. ref , Vv ref VW ref If the phase with the maximum amplitude has a negative sign, proceed to step S3 and perform IRSPWM with odd voltage vectors.

[0065] (3-1) IRSPWM using odd voltage vectors In step S3 of this odd voltage vector IRSPWM, the first modulation unit 34 uses the following equations (VI) and (VII) to obtain the voltage command value Vα ref and Vβ refThe ON times tu, tv, and tw of the upper arm switching elements 18A, 18B, and 18C for each phase are calculated. In formula (VI), V1, V3, and V5 are odd voltage vectors, and Ts is one control period. This control period Ts may be one carrier period. However, this control period Ts should be a period sufficiently shorter than one electrical angle period. Also, Su, Sv, and Sw are functions corresponding to the output regions (Sectors) A to C in the voltage space shown in Figure 7, and the correspondence between each output region and the functions Su, Sv, and Sw is shown in Figure 8. These functions Su, Sv, and Sw select the voltage vector in spatial vector modulation. Note that the calculation result of formula (VII) is the same as that of formula (IV), so either can be used in step S3.

[0066]

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[0067] Next, in step S4, the zero voltage output time t0, which is the time during which the zero voltage vector V0 is output, is calculated using formula (VIII), and it is determined whether this zero voltage output time t0 is greater than or equal to zero. This determination is made by the determination unit 45 at the beginning of each control cycle.

[0068]

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[0069] Then, if the zero voltage output time t0 is a value greater than or equal to zero, the process proceeds to step S5 to select RSPWM using odd voltage vectors from the first modulation unit 34. If it is a negative value, the process proceeds to step S7 to select NSPWM using odd voltage vectors from the second modulation unit 35. This selection is made by the selection unit 40 every control cycle based on the determination of the determination unit 45. Note that the determination in step S4 may be modified so that the process proceeds to step S5 if the zero voltage output time t0 is a positive value, and to step S7 if it is a value less than or equal to zero.

[0070] (3-1-1) RSPWM using odd voltage vectors In RSPWM using odd voltage vectors when the zero voltage output time t0 is greater than or equal to zero, the first modulation unit 34 modulates the ON time of each phase's upper arm switching element in step S5 using the following formula (IX). This is done by adding t0 / 3 to all of the ON times tu, tv, and tw. As a result, the zero voltage output time is eliminated, and fluctuations in the common mode voltage Vc of the motor 8 are resolved.

[0071]

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[0072] Then, in step S6, using Figure 10, the first modulation unit 34 determines the odd voltage vectors (V1, V3, V5) and their output times for each output region (Sector). These values ​​are then finally output to the PWM signal generation unit 36 ​​in step S14. Figure 10 shows the relationship between the output region (Sector), voltage vector, and output time of the RSPWM based on the odd voltage vectors.

[0073] Figure 9 shows the linear output region (inner circle) of RSPWM with odd voltage vectors (odd RSPWM). Figure 12 shows, for example, the odd voltage vectors V1, V3, and V5 and their output times in output region A. Furthermore, Figure 14 shows the output patterns of the odd voltage vectors V1, V3, and V5 of RSPWM with odd voltage vectors in output region A (when kH < 2 / 3).

[0074] (3-1-2) NSPWM using odd voltage vectors On the other hand, in NSPWM using odd voltage vectors when the zero voltage output time t0 is a negative value, the second modulation unit 35 uses Figure 11 in step S7 to determine three adjacent voltage vectors and their output times for each output region (Sector). These values ​​are then output to the PWM signal generation unit 36 ​​in step S14. Figure 11 shows the relationship between the output region (Sector), voltage vectors, and output times for NSPWM using odd voltage vectors. In output region A, only odd voltage vectors V1 and V3, and the even voltage vector V2 sandwiched between them are output; in output region B, only odd voltage vectors V3 and V5, and the even voltage vector V4 sandwiched between them are output; and in output region C, only odd voltage vectors V5 and V1, and the even voltage vector V6 sandwiched between them are output.

[0075] Figure 9 also shows the linear output region of NSPWM using odd voltage vectors (outer circle). In NSPWM using odd voltage vectors, the common-mode voltage Vc of motor 8 fluctuates twice, but it can be seen that the linear output region is expanded compared to RSPWM using odd voltage vectors. Figure 13 also shows, for example, odd voltage vectors V1, V2, and V5 in output region A, and their output times. Furthermore, Figure 15 shows the output patterns of each voltage vector V1, V2, and V3 of NSPWM using odd voltage vectors in output region A (when kH≧2 / 3).

[0076] In the IRSPWM using odd voltage vectors in steps S3 to S7, the RSPWM using odd voltage vectors of the first modulation unit 34 and the NSPWM using odd voltage vectors of the second modulation unit 35 are selected for each control cycle within one electrical angle period. This selection is made based on the zero voltage output time t0 obtained from equation (VIII) in step S4. If this zero voltage output time t0 is greater than or equal to zero, it means that the modulation rate is low, and if this state continues, only the RSPWM using odd voltage vectors is selected, and the modulation waveforms of each phase of UVW become as shown in Figure 16, and there is no fluctuation in the common mode voltage Vc (modulation waveform at low modulation rate).

[0077] On the other hand, a negative zero-voltage output time t0 indicates a control state with a high modulation rate. The more control cycles there are where the zero-voltage output time t0 is negative, the more frequently NSPWM with odd voltage vectors is selected (as shown in the phase region enclosed by a rectangle in Figure 17), as seen from the state in Figure 16 to the state in Figure 17. This also causes fluctuations in the common-mode voltage Vc (modulation waveform at high modulation rate).

[0078] In other words, with the IRSPWM using odd voltage vectors in the embodiment, within one electrical angle period, the ratio of RSPWM using odd voltage vectors, which has a high common-mode noise suppression effect, and NSPWM, which can achieve a higher modulation rate but has a lower common-mode noise suppression effect, is switched linearly, that is, seamlessly. This makes it possible to improve the common-mode noise suppression effect and expand the operating range while minimizing the switching shock, and is therefore extremely effective when driving the motor 8 of an electric compressor, as in the embodiment.

[0079] (3-2) IRSPWM using even voltage vectors Meanwhile, in step S2, the voltage command value Vu of the three-phase modulation ref , Vv ref VW ref If the sign of the phase with the maximum amplitude among the (phase voltage command values) is positive, the process proceeds to step S8 and IRSPWM is performed using an even voltage vector. In step S8 of this IRSPWM using an even voltage vector, the first modulation unit 34 uses the following equations (X) and (XI) to calculate the voltage command value Vα ref and Vβ ref From this, calculate the ON times tuv, tvw, and twu of the two-phase upper arm switching element.

[0080]

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[0081] Furthermore, tuv is the ON time of the upper arm switching elements 18A and 18B of the U and V phases, tvw is the ON time of the upper arm switching elements 18B and 18C of the V and W phases, and twu is the ON time of the upper arm switching elements 18C and 18A of the W and U phases. In addition, V2, V4, and V6 in equation (X) are even voltage vectors, and Suv, Svw, and Swu are functions corresponding to the output regions (Sectors) A to C of the voltage space shown in Figure 18. The correspondence between each output region and the functions Suv, Svw, and Swu is shown in Figure 19. These functions Suv, Svw, and Swu select the voltage vector in spatial vector modulation.

[0082] Furthermore, the first modulation unit 34 calculates the OFF times tu (upper bar), tv (upper bar), and tw (upper bar) of the upper arm switching elements 18A, 18B, and 18C of each phase using the following formula (XII). Note that the calculation result of formula (XII) is the same as that of formula (V), so either one may be used in step S8.

[0083]

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[0084] Next, in step S9, the zero voltage output time t7, which is the time for outputting the zero voltage vector V7, is calculated using formula (XIII), and it is determined whether this zero voltage output time t7 is greater than or equal to zero. This determination is made by the determination unit 45 for each control cycle.

[0085]

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[0086] Then, if the zero voltage output time t7 is a value greater than or equal to zero, the process proceeds to step S10 to select RSPWM using an even voltage vector from the first modulation unit 34. If it is a negative value, the process proceeds to step S12 to select NSPWM using an even voltage vector from the second modulation unit 35. This selection is made by the selection unit 40 every control cycle based on the determination of the determination unit 45. Note that the determination in step S9 may be modified so that the process proceeds to step S10 if the zero voltage output time t7 is a positive value, and to step S12 if it is a value less than or equal to zero.

[0087] (3-2-1) RSPWM using even voltage vectors In RSPWM using even voltage vectors when the zero voltage output time t7 is greater than or equal to zero, the first modulation unit 34 modulates the OFF time of each phase's upper arm switching element in step S10 using the following formulas (XIV) and (XV). This is done by adding t7 / 3 to all of the OFF times tu (upper bar), tv (upper bar), and tw (upper bar). As a result, the zero voltage output time is eliminated, and fluctuations in the common mode voltage Vc of the motor 8 are resolved.

[0088]

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[0089] Then, in step S11, using Figure 21, the first modulation unit 34 determines the even voltage vectors (V2, V4, V6) and their output times for each output region (Sector). Finally, in step S14, these values ​​are output to the PWM signal generation unit 36. Figure 21 shows the relationship between the output region (Sector), voltage vector, and output time of the RSPWM based on the even voltage vectors.

[0090] Figure 20 shows the linear output region of RSPWM (even RSPWM) with even voltage vectors (inner circle). Figure 23 shows, for example, the even voltage vectors V2, V4, and V6 and their output times in output region A. Furthermore, Figure 25 shows the output patterns of each voltage vector V4, V2, and V6 of RSPWM with even voltage vectors in output region C (when kH < 2 / 3).

[0091] (3-2-2) NSPWM using even voltage vectors On the other hand, in NSPWM using an even voltage vector when the zero voltage output time t7 is a negative value, the second modulation unit 35 calculates the ON times tu, tv, and tw of the upper arm switching element in step S12 using the following formula (XVI).

[0092]

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[0093] Next, in step S13, using Figure 22, the second modulation unit 35 determines three adjacent voltage vectors and their output times for each output region (Sector). These values ​​are then output to the PWM signal generation unit 36 ​​in step S14. Figure 22 shows the relationship between the output region (Sector), voltage vectors, and output time for NSPWM using even voltage vectors. In output region A, only the even voltage vectors V6 and V2, and the odd voltage vector V1 between them are output; in output region B, only the even voltage vectors V2 and V4, and the odd voltage vector V3 between them are output; and in output region C, only the even voltage vectors V4 and V6, and the odd voltage vector V5 between them are output.

[0094] Figure 20 also shows the linear output region of NSPWM with even voltage vectors (outer circle). In NSPWM with even voltage vectors, the common-mode voltage Vc of motor 8 fluctuates twice, but it can be seen that the linear output region is expanded compared to RSPWM with even voltage vectors. Figure 24 also shows, for example, the even voltage vector V6, odd voltage vector V1, and even voltage vector V2 and their output times in output region A. Furthermore, Figure 26 shows the output patterns of each voltage vector V4, V5, and V6 of NSPWM with even voltage vectors in output region C (when kH≧2 / 3).

[0095] In the IRSPWM using even voltage vectors in steps S8 to S13, the RSPWM using even voltage vectors of the first modulation unit 34 and the NSPWM using even voltage vectors of the second modulation unit 35 are selected for each control cycle within one electrical angle period. This selection is made based on the zero voltage output time t7 obtained from equation (XIII) in step S9. If this zero voltage output time t7 is greater than or equal to zero, it means that the modulation rate is low, and if this state continues, only the RSPWM using even voltage vectors is selected, and the modulation waveforms of each phase of UVW become as shown in Figure 27, and there is no fluctuation in the common mode voltage Vc (modulation waveform at low modulation rate).

[0096] On the other hand, a negative zero-voltage output time t7 indicates a control state with a high modulation rate. The more control cycles there are where the zero-voltage output time t7 is negative, the more frequently NSPWM with even voltage vectors is selected (phase region enclosed by a rectangle in Figure 28), as shown from the state in Figure 27 to the state in Figure 28, and fluctuations in the common-mode voltage Vc also occur (modulation waveform at high modulation rate).

[0097] In other words, even with the IRSPWM using even voltage vectors in the embodiment, within one electrical angle period, the ratio of RSPWM using even voltage vectors, which has a high common-mode noise suppression effect, and NSPWM, which can achieve a higher modulation rate but has a lower common-mode noise suppression effect, is switched linearly, that is, seamlessly. This makes it possible to minimize switching shock while simultaneously improving the common-mode noise suppression effect and expanding the operating range. [Examples]

[0098] (4) IRSPWM using the total voltage vector In this embodiment, the first modulation unit 34 performs either RSPWM using an odd voltage vector or RSPWM using an even voltage vector, and modulates it to a three-phase modulation voltage command value Vu ref , Vv ref VW ref The (phase voltage command value) is configured to switch between cases where the sign of the phase with the maximum amplitude is negative and case where it is positive. However, it is not limited to this, and the RSPWM using odd voltage vectors and RSPWM using even voltage vectors may be switched based on the phase θm with respect to the α axis. In this application, this is referred to as RSPWM using all voltage vectors, and pulse width modulation that selects between this RSPWM using all voltage vectors and the aforementioned NSPWM for each control cycle within one electrical angle period is referred to as IRPWM using all voltage vectors.

[0099] Figure 29 shows the operating region of IRSPWM with the total voltage vector, and Figure 30 shows the linear output region of IRSPWM with the total voltage vector. Figure 31 shows the correspondence between RSPWM with the total voltage vector and each phase. Note that in Figure 29, odd IRSPWM is the operating region of IRSPWM with odd voltage vectors in this case, and even IRSPWM is the operating region of IRSPWM with even voltage vectors in this case.

[0100] As shown in Figure 31, one period of the electrical angle is divided into six regions (330°<θm≦30°, 30°<θm≦90°, 90°<θm≦150°, 150°<θm≦210°, 210°<θm≦270°, 270°<θm≦330°), and RSPWM using odd voltage vectors and RSPWM using even voltage vectors are switched alternately. As a result, the linear output region of RSPWM is expanded compared to when each is performed individually (the innermost circle in Figure 30), as shown by the second innermost circle in Figure 30.

[0101] In this case as well, RSPWM and NSPWM are selected at the zero-voltage output times t0 and t7 as described above. As a result, in the low modulation rate control state, only RSPWM using the full voltage vector is selected, and the modulation waveforms of each phase of UVW are as shown in Figure 32. In this case, the common-mode voltage Vc fluctuates when switching between odd and even RSPWM (modulation waveform at low modulation rate).

[0102] On the other hand, when the control state becomes one with a high modulation rate, as shown in Figure 33 from the state in Figure 32, NSPWM using the entire voltage vector is selected more often (phase region enclosed by a rectangle in Figure 33), and the fluctuation of the common mode voltage Vc becomes even greater (modulation waveform at high modulation rate). However, because the linear output region of RSPWM is expanded, the proportion of NSPWM decreases accordingly, and overall, the common mode noise is reduced compared to the case of Example 1 described above.

[0103] In this case as well, the ratio of RSPWM using the full voltage vector to NSPWM, which can achieve a higher modulation rate but has a less effective common-mode noise suppression, is linear, meaning that it switches seamlessly. This makes it possible to minimize switching shock while simultaneously improving the common-mode noise suppression effect and expanding the operating range. [Examples]

[0104] (5) Other examples of the second modulation unit 35 Furthermore, the pulse width modulation by the second modulation unit 35 is not limited to NSPWM as described in the above embodiment, but may also be pulse width modulation that synchronizes the rising and falling timings of the phase voltages of other phases with the rising and falling timings of the phase voltages of a specific phase.

[0105] The PWM turn in this case is shown in Figure 34, and the linear output region is shown in Figure 35. In this example, the falling timing of the U-phase voltage Vu and the rising timing of the W-phase voltage Vw are synchronized, and the rising timing of the U-phase voltage Vu and the falling timing of the V-phase voltage Vv are synchronized.

[0106] This type of pulse width modulation can reduce the fluctuation of the common-mode voltage Vc to twice during one control period, and furthermore, the linear output region kHz can be set to 2 / (√3). [Examples]

[0107] (6) Yet another example of the second modulation unit 35 Furthermore, as the pulse width modulation by the second modulation unit 35, pulse width modulation using two-phase modulation with the aforementioned formulas (VI) and (V) may be employed. Even with two-phase modulation, the fluctuation of the common-mode voltage Vc can be reduced to four times during the control period.

[0108] Furthermore, in the IRSPWM of the aforementioned embodiment, the voltage command value Vu of the three-phase modulation ref , Vv ref VW ref Of these, the system switches between IRSPWM using odd voltage vectors and IRSPWM using even voltage vectors depending on whether the sign of the phase with the maximum amplitude is negative or positive. The above inventions to the third invention However, it is not limited to that; the switching can also be done using other control states that can determine whether an odd voltage vector or an even voltage vector is appropriate.

[0109] Also, The above invention to the second invention Alternatively, one could choose to execute only one of the IRSPWM methods, rather than switching between odd-numbered voltage vectors and even-numbered voltage vectors.

[0110] Furthermore, although the flowchart in Figure 6 shows a flow in which the calculations of the first modulation unit 34 and the second modulation unit 35 are performed after selection by the selection unit 40, the invention is not limited to this. The calculations of the first modulation unit 34 and the second modulation unit 35 may be performed continuously, and the selection unit 40 may select their outputs and send them to the PWM signal generation unit 36. In either case, the invention is included. Also, in the embodiment, the determination unit 45 and the selection unit 40 determine the zero voltage output time and select RSPWM and NSPWM at each control cycle, but the invention is not limited to this. These may be performed at multiple control cycles (however, for a period sufficiently shorter than one electrical angle cycle).

[0111] Furthermore, although the above embodiments were described using the driving of the motor (load) of an electric compressor as an example, the method is not limited to this and is also effective when driving motors other than the motor of an electric compressor. Except for the ninth invention, The present invention is applicable to various power conversion devices that convert DC voltage to AC voltage using an inverter and apply it to a load. [Explanation of symbols]

[0112] 1. Power converter 8 motors 18A~18F Up / Down Arm Switching Element 19U U-phase inverter 19V V-phase inverter 19W W-phase inverter 21 Control device 28 Inverter Circuit 30 Command value calculation unit 33 Phase voltage command calculation unit 34 First Modulation Section 35 Second Modulation Section 36 PWM signal generation section 37 Gate Driver 40 Selection Section 45 Judgment section

Claims

1. In a power conversion device that converts DC voltage to AC voltage, An inverter circuit that applies the phase voltage at the connection point of the upper and lower arm switching elements of each phase to the load, The system includes a control device that controls the switching of each of the aforementioned switching elements, The control device is A first modulation unit that reduces common-mode noise by performing one of the following: pulse width modulation that outputs only odd voltage vectors in one control cycle, pulse width modulation that outputs only even voltage vectors in one control cycle, or pulse width modulation that switches between pulse width modulation that outputs only odd voltage vectors in one control cycle and pulse width modulation that outputs only even voltage vectors in one control cycle according to the electrical angular phase; A second modulation unit performs pulse width modulation that can achieve a higher modulation rate than the pulse width modulation performed by the first modulation unit and can reduce common-mode noise, A determination unit that determines the zero voltage output time for which a zero voltage vector is output, Based on the zero voltage output time determined by the determination unit, the system includes a selection unit that selects pulse width modulation by the first modulation unit and pulse width modulation by the second modulation unit within one electrical angle period. The selection unit is, A power conversion device characterized in that, when the zero voltage output time is a value of zero or greater, pulse width modulation by the first modulation unit is selected, and when the zero voltage output time is a negative value, pulse width modulation by the second modulation unit is selected, or when the zero voltage output time is a positive value, pulse width modulation by the first modulation unit is selected, and when the zero voltage output time is a value of zero or less, pulse width modulation by the second modulation unit is selected.

2. The power conversion device according to Claim 1, characterized in that the first modulation unit achieves a zero voltage output time by modifying the odd voltage vector or the even voltage vector to output the zero voltage vector.

3. The power conversion device according to claim 1 or 2, characterized in that the first modulation unit switches between pulse width modulation that outputs only odd voltage vectors during one control cycle and pulse width modulation that outputs only even voltage vectors during one control cycle, depending on the control state.

4. A phase voltage command calculation unit that calculates the phase voltage command value for each of the phases, The power converter according to claim 3, characterized in that the first modulation unit performs pulse width modulation to output only the even voltage vectors during one control cycle when the sign of the phase with the maximum amplitude of the phase voltage command value is positive, and performs pulse width modulation to output only the odd voltage vectors during one control cycle when the sign of the phase with the maximum amplitude of the phase voltage command value is negative.

5. The power conversion device according to any one of claims 1 to 4, characterized in that the second modulation unit performs pulse width modulation that outputs only adjacent voltage vectors in one control cycle.

6. A phase voltage command calculation unit that calculates the phase voltage command value for each of the phases, The power converter according to claim 5, characterized in that the second modulation unit performs pulse width modulation that outputs only two even voltage vectors and the odd voltage vector sandwiched between them during one control cycle when the sign of the phase with the maximum amplitude of the phase voltage command value is positive, and performs pulse width modulation that outputs only two odd voltage vectors and the even voltage vector sandwiched between them during one control cycle when the sign of the phase with the maximum amplitude of the phase voltage command value is negative.

7. The power conversion device according to any one of claims 1 to 4, characterized in that the second modulation unit performs pulse width modulation to synchronize the rising and falling timings of the phase voltages of other phases with the rising and falling timings of the phase voltages of a specific phase.

8. The power conversion device according to any one of claims 1 to 4, characterized in that the second modulation unit performs pulse width modulation to fix the ON / OFF state of a predetermined one-phase upper / lower arm switching element and modulate the ON / OFF state of the other two phases of the upper / lower arm switching elements.

9. The power conversion device according to any one of claims 1 to 8, characterized in that the inverter circuit drives the motor by applying the phase voltage at the connection point of the upper and lower arm switching elements of each phase.

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