Power Conversion Device

Abstract

To provide a power converter capable of improving a command value of two-phase modulation to suppress steep fluctuation of the command value, thereby improving electromagnetic noise.SOLUTION: A control device 21 is provided with a command value calculation unit 30 that calculates a three-phase modulation command value for generating a phase voltage of each phase, and calculates a two-phase modulation command value that turns on lower arm switching elements 18D to 18F of a phase in which the three-phase modulation command value is minimum, and stops switching. The command value calculation unit has a command value correction unit 35 that adds, to the two-phase modulation command value of each phase, a correction to fix the two-phase modulation command value of a phase in which the two-phase modulation command value is maximum in a predetermined specified section that includes a phase position at which the phase, in which the lower arm switching element is turned on and switching is stopped, is changed over.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power conversion device that generates a three-phase AC output using an inverter circuit. [Background technology]

[0002] Conventional power conversion devices for driving motors have comprised a three-phase inverter circuit using upper and lower arm switching elements for each of the UVW phases, and have controlled the switching elements of each phase using PWM (Pulse Width Modulation) to apply a voltage waveform (three-phase AC output) that is close to a sine wave to the motor to drive it.

[0003] Furthermore, power conversion devices that use a method called two-phase modulation have also been proposed for the purpose of reducing loss and heat generation in switching elements. This two-phase modulation power conversion device fixes the ON / OFF states of the upper and lower arm switching elements of one of the UVW phases and controls while modulating the ON / OFF states of only the upper and lower arm switching elements of the other two phases, thereby reducing the number of switching operations of the switching elements compared to three-phase modulation, thereby reducing switching loss and heat generation and performing PWM control (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-149660 Summary of the Invention [Problem to be solved by the invention]

[0005] In a power conversion device that performs PWM control using a constant-frequency carrier signal, noise components tend to concentrate at the carrier frequency. For this reason, methods are often used in which the carrier frequency is set to 20 kHz, which is outside the audible range, or 10 kHz or higher, which is difficult for humans to perceive as noise. However, when using line modulation such as the two-phase modulation method mentioned above, the pulse width of the output PWM signal no longer changes like a sine wave, and the PWM pulse width can change abruptly.

[0006] This pulse width is the command value for generating the phase voltage of each phase, and abrupt changes in this command value cause large variations in the timing at which the PWM signal is generated. This variation in the timing at which the PWM signal is generated causes momentary noise components at frequencies higher and lower than the carrier frequency, resulting in noise characteristics centered around the carrier frequency having sidebands on both sides of 10 kHz and 20 kHz, as shown in the upper part of Figure 6. These sideband components of the noise centered around the carrier frequency cause the problem of harsh electromagnetic noise.

[0007] The present invention has been made to solve the above-mentioned conventional technical problems, and aims to provide a power conversion device that can suppress sudden fluctuations in the command value and improve electromagnetic noise by improving the command value of two-phase modulation. [Means for solving the problem]

[0008] A power conversion device of the present invention includes an inverter circuit that generates a three-phase AC output by switching upper and lower arm switching elements of each phase, and a control device that controls the switching of the upper and lower arm switching elements of each phase of the inverter circuit, wherein the control device includes a command value calculation unit that calculates a three-phase modulation command value to generate a phase voltage for each phase, and calculates a two-phase modulation command value that turns on the lower arm switching element of the phase for which the three-phase modulation command value is smallest to stop switching, or that turns on the upper arm switching element of the phase for which the command value is largest to stop switching, and the command value calculation unit includes a command value correction unit that adds a correction to the two-phase modulation command value of each phase to fix the two-phase modulation command value of the phase for which the two-phase modulation command value is largest, in a predetermined specified interval including the phase where the phase for stopping switching is switched by turning on the lower arm switching element, or that adds a correction to the two-phase modulation command value of each phase to fix the two-phase modulation command value of the phase for which the two-phase modulation command value is smallest, in a predetermined specified interval including the phase where the phase for stopping switching is switched by turning on the upper arm switching element.

[0009] The power conversion device of the invention of claim 2 is characterized in that in the above invention, the phase at which the phase at which the lower arm switching element is turned on and switching is stopped changes is any one of 0°, 120°, 240°, or a combination of two of them, or all of them, when the voltage phase is based on the U phase, and the phase at which the upper arm switching element is turned on and switching is stopped is any one of 60°, 180°, 300°, or a combination of two of them, or all of them, when the voltage phase is based on the U phase.

[0010] The power conversion device of the invention of claim 3 is characterized in that in each of the above inventions, the command value correction unit sets a specified interval from the phase at which the phase at which switching is stopped changes and a specified phase width, and has a judgment unit that judges whether the current phase is included in the specified interval.

[0011] The power conversion device of the invention of claim 4 is characterized in that in each of the above inventions, the command value corrector changes the width of the specified section so that it becomes narrower as the modulation rate increases and becomes wider as the modulation rate decreases.

[0012] The power conversion device of the invention of claim 5 is characterized in that in each of the above inventions, the command value corrector sets the width of the specified section to 60° or less.

[0013] The power conversion device of the invention of claim 6 is characterized in that in each of the above inventions, the command value calculation unit has a phase voltage command calculation unit that calculates a phase voltage command value for each phase, and a pulse width command calculation unit that calculates a pulse width command value for each phase as a three-phase modulation command value from the phase voltage command value for each phase, and the pulse width command calculation unit calculates a two-phase modulation command value that stops switching by turning on the lower arm switching element of the phase for which the pulse width command value is smallest, or stops switching by turning on the upper arm switching element of the phase for which the pulse width command value is largest, and the command value correction unit applies correction to the two-phase modulation command value for each phase calculated by the pulse width command value.

[0014] The power conversion device of the invention of claim 7 is characterized in that in the inventions of claims 1 to 5, the command value calculation unit has a phase voltage command calculation unit that calculates a phase voltage command value for each phase as a three-phase modulation command value, and a pulse width command calculation unit that calculates a pulse width command value for each phase from the phase voltage command value for each phase, the phase voltage command calculation unit calculates a two-phase modulation command value that either turns on the lower arm switching element of the phase for which the phase voltage command value is smallest to stop switching, or turns on the upper arm switching element of the phase for which the phase voltage command value is largest to stop switching, and the command value correction unit applies correction to the two-phase modulation command value for each phase calculated by the phase voltage command value.

[0015] The power conversion device of the invention of claim 8 is characterized in that in the invention of claim 6 or claim 7, phase voltages at the connection points of the upper and lower arm switching elements of each phase are applied to the motor as three-phase AC outputs, and the phase voltage command calculation unit calculates instantaneous values ​​of phase voltage command values ​​of each phase using magnetic pole position information of the motor for each control period.

[0016] The power conversion device of the invention of claim 9 is characterized in that in the inventions of claims 6 to 8, the command value correction unit adds narrow pulse avoidance processing to the two-phase modulation command value, which prevents the pulse width command value of each phase from becoming narrower than the minimum pulse width that can be output or wider than the maximum pulse width.

[0017] The power conversion device of the present invention according to claim 10 is characterized in that in each of the above inventions, phase voltages at the connection points of the upper and lower arm switching elements of each phase are applied to the motor as three-phase AC outputs. [Effects of the Invention]

[0018] According to the present invention, in a power conversion device including an inverter circuit that generates a three-phase AC output by switching upper and lower arm switching elements of each phase, and a control device that controls the switching of the upper and lower arm switching elements of each phase of the inverter circuit, the control device calculates a three-phase modulation command value to generate a phase voltage of each phase, and includes a command value calculation unit that calculates a two-phase modulation command value to turn on the lower arm switching element of the phase for which the three-phase modulation command value is smallest and stop switching, or to turn on the upper arm switching element of the phase for which the command value is largest and stop switching, and the command value calculation unit includes a command value correction unit that adds a correction to the two-phase modulation command value of each phase to fix the two-phase modulation command value of the phase for which the two-phase modulation command value is largest, in a predetermined specified interval including the phase for switching the phase for switching the lower arm switching element to the ON state and stop switching, or adds a correction to the two-phase modulation command value of each phase to fix the two-phase modulation command value of the phase for which the two-phase modulation command value is smallest, in a predetermined specified interval including the phase for switching the phase for switching the upper arm switching element to the ON state and stop switching.

[0019] Such correction by the command value correction unit makes it possible to make the change in the two-phase modulation command value gentle in a predetermined specified interval including a phase where the phase at which the lower arm switching element is turned on and switching is stopped changes, or in a predetermined specified interval including a phase where the phase at which the upper arm switching element is turned on and switching is stopped changes, thereby suppressing abrupt changes and suppressing sideband waves.

[0020] This makes it possible to effectively reduce electromagnetic noise when the motor is operated by applying a three-phase AC output, as in the tenth aspect of the invention.

[0021] In this case, as in the invention of claim 2, the phase at which the phase at which the lower arm switching element is turned on and switching is stopped is set to any one of 0°, 120°, or 240°, or a combination of two of these, or all of these, in the case of a voltage phase with the U phase as the reference phase, and the phase at which the upper arm switching element is turned on and switching is stopped is set to any one of 60°, 180°, or 300°, or a combination of two of these, or all of these, in the case of a voltage phase with the U phase as the reference phase. This makes it possible to more efficiently suppress sideband waves and reduce the sideband wave components of noise.

[0022] Furthermore, as in the invention of claim 3, if the command value correction unit sets a specified interval from the phase at which the phase at which switching is stopped changes and a specified phase width, and has a judgment unit that judges whether the current phase is included in the specified interval, the judgment unit can accurately determine whether the current phase is within the specified interval, and it becomes possible to more effectively suppress noise generated near the phase at which the phase at which switching is stopped changes.

[0023] Here, the fact that the change in the two-phase modulation command value within the specified range becomes gradual means that the number of times the switching element is switched increases. On the other hand, in the high modulation rate range where operating noise increases, electromagnetic noise due to sideband waves becomes less noticeable.

[0024] Therefore, if the command value correction unit changes the width of the specified section so that it becomes narrower the higher the modulation rate and wider the lower the modulation rate, as in the invention of claim 4, it becomes possible to narrow the specified section in areas where the modulation rate is high, thereby suppressing an increase in the number of switching times of the switching element, and to widen the specified section in areas where the rate of change is low, thereby achieving more effective noise reduction.

[0025] Furthermore, as in the invention of claim 5, by the command value correction unit setting the width of the specified section to 60° or less, it becomes possible to correct only the region where the change in the two-phase modulation command value is steep, thereby enabling more effective noise reduction.

[0026] The two-phase modulation command value to which the command value corrector applies correction may be a pulse width command value as in the sixth aspect of the invention, or may be a phase voltage command value as in the seventh aspect of the invention.

[0027] Here, when the phase voltages at the connection points of the upper and lower arm switching elements of each phase are applied to the motor as three-phase AC outputs as in the invention of claim 8, if the phase voltage command calculation unit calculates the instantaneous value of the phase voltage command value of each phase using the magnetic pole position information of the motor for each control period, it becomes possible to sequentially calculate the voltage command value required to drive the motor while suppressing electromagnetic noise, and the advantages of the present invention can be obtained more effectively.

[0028] Furthermore, as in the invention of claim 9, if the command value correction unit applies narrow-width pulse avoidance processing to the two-phase modulation command value to prevent the pulse width command value of each phase from becoming narrower than the minimum pulse width that can be output or wider than the maximum pulse width, it becomes possible to avoid the inconvenience of not being able to output a targeted pulse width. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is an electrical circuit diagram of a power conversion device according to an embodiment of the present invention. [Figure 2]FIG. 10 is a diagram showing pulse width command values ​​Cu, Cv, and Cw of the UVW phases for each modulation value. [Figure 3] FIG. 3 is a diagram showing pulse width command values ​​Cu, Cv, and Cw of (c) in FIG. 2 and pulse width command values ​​Cu, Cv, and Cw after correction. [Figure 4] 10A and 10B are diagrams illustrating a phase for selecting a phase for fixing a pulse width command value, etc.; [Figure 5] 4 is a flowchart illustrating control of the power conversion device of the present invention (first embodiment). [Figure 6] 10 is a diagram comparing noise characteristics between conventional two-phase modulation and the control of the power conversion device of the present invention. FIG. [Figure 7] FIG. 10 is a diagram showing a minimum pulse width for explaining narrow pulse avoidance processing. [Figure 8] 10 is a diagram showing pulse width command values ​​Cu, Cv, and Cw of each phase, which explains narrow-width pulse avoidance processing. FIG. [Figure 9] FIG. 10 is a diagram illustrating changes in the pulse width command value of each phase under the control of the power conversion device of the present invention when the upper arm switching element of the phase in which the pulse width command value is maximum is turned on to stop switching. [Figure 10] FIG. 10 is a diagram illustrating changes in the pulse width command value of each phase under the control of the power conversion device of the present invention when the lower arm switching element of the phase with the smallest pulse width command value is turned on to stop switching. [Figure 11] FIG. 10 is a diagram showing the pulse width command values ​​of each phase under the control of the power conversion device of the present invention, in which the upper arm switching element of the phase for which the pulse width command value is maximum is turned on to stop switching only for the phase from 120° to 240°, and the lower arm switching element of the phase for which the pulse width command value is minimum is turned on to stop switching for the other phases. [Figure 12] 10 is a flowchart illustrating control of another embodiment of the power conversion device of the present invention (Embodiment 2). DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0031] A power conversion device 1 according to an embodiment of the present invention drives a motor 8 of a so-called inverter-integrated electric compressor that constitutes a refrigerant circuit of a vehicle air conditioner mounted on a vehicle such as an electric car.

[0032] (1) Circuit configuration of power conversion device 1 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, 350 V) 29 into a three-phase AC voltage (three-phase AC output) and applies it to the motor 8. In this case, the motor 8 of the embodiment is an IPMSM (Interior Permanent Magnet Synchronous Motor).

[0033] The inverter circuit 28 includes a U-phase half-bridge circuit 19U, a V-phase half-bridge circuit 19V, and a W-phase half-bridge circuit 19W. Each of the half-bridge circuits 19U to 19W for each phase includes upper arm switching elements 18A to 18C and lower arm switching elements 18D to 18F. Furthermore, a flywheel diode 31 is connected in anti-parallel to each of the switching elements 18A to 18F. In this embodiment, each of the upper and lower arm switching elements 18A to 18F is configured by an insulated gate bipolar transistor (IGBT) or the like incorporating a MOS structure in the gate portion.

[0034] The collectors of the upper arm switching elements 18A to 18C of the inverter circuit 28 are connected to an upper arm power supply 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 a lower arm power supply line (negative bus) 15 of the DC power supply 29 and the smoothing capacitor 32.

[0035] In this case, the emitter of upper arm switching element 18A and the collector of lower arm switching element 18D of U-phase half-bridge circuit 19U are connected in series, the emitter of upper arm switching element 18B and the collector of lower arm switching element 18E of V-phase half-bridge circuit 19V are connected in series, and the emitter of upper arm switching element 18C and the collector of lower arm switching element 18F of W-phase half-bridge circuit 19W are connected in series.

[0036] 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.

[0037] (2) Configuration of the control device 21 Next, the control device 21 is composed of a microcomputer having a processor, and in this embodiment, receives a rotation speed command value from the vehicle's ECU and a motor current (phase current) from the motor 8, and based on these, controls the ON / OFF state (switching) of each of the switching elements 18A to 18F of the inverter circuit 28. Specifically, it controls the gate voltage applied to the gate of each of the switching elements 18A to 18F.

[0038] The control device 21 of the embodiment has a command value calculation unit 30, a PWM signal generation unit 36, a gate driver 37, and current sensors 26A, 26B, and 26C each consisting of a current transformer for measuring the motor currents (phase currents) of each phase flowing through the motor 8, that is, a U-phase current iu, a V-phase current iv, and a W-phase current iw.

[0039] (2-1) Command value calculation unit 30 Command value calculation unit 30 includes a phase voltage command calculation unit 33, a pulse width command calculation unit 34, and a command value correction unit 35, and each of current sensors 26A to 26C is connected to phase voltage command calculation unit 33. In the embodiment, current sensor 26A measures U-phase current iu, current sensor 26B measures V-phase current iv, and current sensor 26C measures W-phase current iw, but it is also possible to measure U-phase current iu using current sensor 26A and V-phase current iv using current sensor 26B, and calculate W-phase current iw from these. Furthermore, the method of detecting the motor current of each phase is not particularly limited, and other methods include measuring the current value of lower arm power supply line 15 using a shunt resistor and having phase voltage command calculation unit 33 estimate the current value and the operating state of motor 8, in addition to measuring it with current sensors 26A to 26C as in the embodiment.

[0040] (2-2) Phase voltage command calculation unit 33 The phase voltage command calculation unit 33 of the command value calculation unit 30 calculates a phase voltage command value Vu for three-phase modulation to generate a U-phase voltage Vu, a V-phase voltage Vv, and a W-phase voltage Vw to be 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 current command value, and the d-axis current and the q-axis current obtained from the phase current. * (Hereinafter, U-phase voltage command value Vu * ), Vv * (Hereinafter, V-phase voltage command value Vv * ), Vw * (Hereinafter, W-phase voltage command value Vw * ) and generate it.

[0041] In this case, the phase voltage command calculation unit 33 calculates the phase voltage command value Vu for each phase using the following formula (I) based on the d-axis voltage Vd and the q-axis voltage Vq obtained from the d-axis current and the q-axis current: * , Vv * , Vw * In equation (I), Vm and θm can be calculated from equation (II). θv is set to θ+θm (θv=θ+θm). θ is the magnetic pole position based on the U phase, θm is the voltage phase difference with respect to the magnetic pole position, and θv is the voltage phase.

[0042]

number

[0043] (2-3) Pulse width command calculation unit 34 The pulse width command calculation unit 34 of the command value calculation unit 30 calculates and outputs the phase voltage command value Vu for each phase calculated and output by the phase voltage command calculation unit 33. * , Vv * , Vw * From this, the pulse width command values ​​Cu1 (U-phase pulse width command value), Cv1 (V-phase pulse width command value), and Cw1 (W-phase pulse width command value) of each phase normalized (corrected to 0 to 1) by the DC voltage Vdc are calculated and output using the following formula (III). These pulse width command values ​​Cu1, Cv1, and Cw1 are values ​​before line-to-line modulation (values ​​without line-to-line modulation), which will be described later, and serve as three-phase modulation command values ​​in this embodiment of the present invention.

[0044]

number

[0045] Furthermore, the pulse width command calculation unit 34 in this embodiment performs line modulation (two-phase modulation in this embodiment) using the pulse width command values ​​Cu1, Cv1, and Cw1 described above, using formula (IV). Cu, Cv, and Cw in formula (IV) are pulse width command values ​​for each phase after line modulation (U-phase pulse width command value Cu, V-phase pulse width command value Cv, and W-phase pulse width command value Cw), which are two-phase modulation command values ​​in this embodiment of the present invention.

[0046]

number

[0047] In addition, Cmod in formula (IV) is a modulation value for performing line-to-line modulation (two-phase modulation). When this modulation value Cmod is 0 (Cmod=0), the pulse width command values ​​Cu, Cv, and Cw are not modulated between lines, i.e., they are the same as the pulse width command values ​​Cu1, Cv1, and Cw1 before line-to-line modulation, and their waveforms are shown in Figure 2(a).

[0048] On the other hand, when the modulation value Cmod is set to the following formulas (V) and (VI), line-to-line modulation is performed, and the waveforms are as shown in (b) and (c) of FIG. 2, respectively. Cmod=1-max(Cu1, Cv1, Cw1) ···(V) Cmod=-min(Cu1, Cv1, Cw1) ···(VI)

[0049] In formula (V), max(Cu1, Cv1, Cw1) means the value of the phase that is the maximum among the pulse-width command values ​​Cu1, Cv1, and Cw1 (the three-phase modulation command values ​​in this embodiment), and in formula (V), this value is subtracted from 1 to obtain Cmod, which is added to all the pulse-width command values ​​Cu1, Cv1, and Cw1. As a result, the pulse-width command value of the maximum phase becomes 1, and the upper arm switching element of that phase is fixed to the ON state. The values ​​of the other two phases have waveforms as shown in FIG. 2(b), and the upper and lower arm switching elements of those two phases are turned ON / OFF, so Cu, Cv, and Cw become the two-phase modulation command values.

[0050] In formula (VI), min(Cu1, Cv1, Cw1) means the value of the phase that is the smallest among the pulse-width command values ​​Cu1, Cv1, and Cw1 (three-phase modulation command values), and in formula (VI), this value Cmod is subtracted from all pulse-width command values ​​Cu1, Cv1, and Cw1, so the pulse-width command value of the smallest phase becomes 0 and the lower-arm switching element of that phase is fixed to the ON state. The values ​​of the other two phases have waveforms as shown in Figure 2(c), and the upper and lower arm switching elements of those two phases are turned ON / OFF, so Cu, Cv, and Cw become the two-phase modulation command values.

[0051] (2-4) Command value correction unit 35 The command value corrector 35 of the command value calculator 30 applies corrections as shown in Fig. 3 to the pulse width command values ​​Cu, Cv, and Cw for each phase calculated by the pulse width command calculator 34. The upper side of Fig. 3 shows waveforms for the case of Fig. 2(c), i.e., for line modulation in which the lower arm switching element of the phase with the smallest pulse width command value Cu1, Cv1, and Cw1 is fixed to the ON state and the upper and lower arm switching elements of the other two phases are turned ON / OFF, but the same is true for the case of Fig. 2(b), i.e., for line modulation in which the upper arm switching element of the phase with the largest pulse width command value Cu1, Cv1, and Cw1 is fixed to the ON state and the upper and lower arm switching elements of the other two phases are turned ON / OFF.

[0052] 2(c), for example, the command value corrector 35 corrects the pulse width command values ​​Cu, Cv, and Cw shown in the upper part of Fig. 3 to waveforms as shown in the lower part of Fig. 3. That is, in the case of Fig. 3, in a predetermined specified section centered on the phase at which the phase at which the lower arm switching element is turned on and switching is stopped changes, correction is applied to all phases to fix the pulse width command values ​​of the phases at which the pulse width command values ​​Cu, Cv, and Cw are maximum, thereby causing the change in the command value of the phase in which the command value decreases to gradually decrease smoothly, and causing the change in the command value of the phase in which the command value increases to gradually increase smoothly (lower part of Fig. 3). This correction operation by the command value corrector 35 will be described in detail later.

[0053] (2-5) PWM signal generation section 36 The PWM signal generating unit 36 ​​receives the pulse width command values ​​Cu, Cv, Cw calculated by the pulse width command calculating unit 34 (the pulse width command values ​​Cu, Cv, Cw corrected by the command value correcting unit 35) and compares the magnitude with the carrier signal to generate and output PWM signals that serve as drive command signals for the U-phase inverter 19U, the V-phase inverter 19V, and the W-phase inverter 19W of the inverter circuit 28.

[0054] Based on the PWM signal output from the PWM signal generating unit 36, 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.

[0055] Each of the switching elements 18A-18F of the inverter circuit 28 is driven to turn on / off based on the gate voltage output from the gate driver 37. That is, when the gate voltage is in the ON state (a predetermined voltage value), the switching element operates ON, and when the gate voltage is in the OFF state (zero), the switching element operates OFF. If the switching elements 18A-18F are the IGBTs described above, the gate driver 37 is a circuit for applying the gate voltage to the IGBTs based on a PWM signal, and is composed of a photocoupler, a logic IC, a transistor, etc.

[0056] 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 a 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 a 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 a W-phase voltage Vw (phase voltage).

[0057] (3) Correction operation of the command value corrector 35 Next, the correcting operation by the command value corrector 35 in this embodiment will be described with reference to FIGS. (3-1) Determination of the specified section by the determination unit 35a The command value corrector 35 has a determiner 35a. The determiner 35a determines whether the current voltage phase θv (the voltage phase θv in formula (I)) is included in the specified interval described above. In this embodiment, the specified interval is centered on the phase at which the phase at which the switching element is turned on and the switching is stopped changes, and is set with a predetermined phase width θw around the center phase. The line modulation differs between the cases of (c) and (b) in FIG. 2.

[0058] 2(c), in which the lower arm switching element of the phase with the smallest pulse width command value Cu1, Cv1, or Cw1 is fixed to the ON state and the upper and lower arm switching elements of the other two phases are turned ON / OFF, when viewed from the voltage phase θv in formula (I), the phase at which the lower arm switching element is turned ON and switching is stopped changes over is always 0°, 120°, or 240°, so the determination unit 35a determines that the current voltage phase θv (current phase) is within the specified interval if the following formulas (VII), (VIII), and (IX) are satisfied. That is, in this case, 0°, 120°, and 240° are the center phases. 0°-θw<θv<0°+θw (VII) 120°-θw<θv<120°+θw (VIII) 240°-θw<θv<240°+θw ···(IX)

[0059] 2(b), in which the upper arm switching element of the phase with the largest pulse width command value Cu1, Cv1, or Cw1 is fixed to the ON state and the upper and lower arm switching elements of the other two phases are turned ON / OFF, when viewed from the voltage phase θv in formula (I), the phase at which the upper arm switching element is turned ON and the phase at which switching is stopped is switched is always 60°, 180°, and 300°, so the determination unit 35a determines that the current voltage phase θv (current phase) is within the specified interval if the following formulas (X), (XI), and (XII) are satisfied. That is, in this case, 60°, 180°, and 300° are the center phases. 60°-θw<θv<60°+θw ···(X) 180°-θw<θv<180°+θw ···(XI) 300°-θw<θv<300°+θw ···(XII)

[0060] In this embodiment, the phase width θw is set so that the width of the specified section is a maximum of 60° (i.e., the width of the specified section is 60° or less). This makes it possible to correct only the region where the two-phase modulation command value (in this embodiment, the pulse width command values ​​Cu, Cv, Cw) changes sharply, as will be described later.

[0061] (3-2) Command value correction operation Then, when the determination unit 35a determines that the current voltage phase θv is within the specified interval, the command value corrector 35 calculates the modulation value Cmod in the formula (IV) using the following formula (XIII).

[0062]

number

[0063] In equation (XIII), Cx1buf is the pulse width command value for the previous carrier cycle, Cx1 is the pulse width command value for the current carrier cycle, and x is selected from u, v, and w. That is, the previous Cu1 is substituted and saved for Cu1buf, the previous Cv1 is substituted and saved for Cv1buf, and the previous Cw1 is substituted and saved for Cw1buf. The command value corrector 35 performs the above substitution for each carrier cycle at a phase outside the specified interval, and does not perform the above substitution when the voltage phase θv falls within the specified interval. In addition, Cn in equation (XIII) is an additional value when narrow-width pulse avoidance processing, which will be described later, is executed. When narrow-width pulse avoidance processing is not executed, the additional value Cn = 0.

[0064] 4 indicates the center phase, and to the right of that is the phase at which the pulse width command value is fixed to a value when it enters a specified interval, as will be described later; the x in formula (XIII) is selected based on this field. To the right of that is the upper and lower arms of the switching elements that are fixed to the ON state, and to the right of that is the positive and negative values ​​of the added value Cn. The phase θa at the right end will be explained later.

[0065] In the case of line modulation in which, for example, as shown in the upper part of FIG. 3 (FIG. 2(c)), the lower-arm switching element of the phase with the smallest pulse-width command values ​​Cu1, Cv1, and Cw1 is fixed to the ON state and the upper and lower-arm switching elements of the other two phases are turned ON / OFF, Cx1buf-Cx1 in formula (XIII) means the value (Cv1buf-Cv1) obtained by subtracting the current pulse-width command value Cv1 from the previous pulse-width command value Cv1buf, where v is selected for x in a specified section with a center phase of 120°, for example.

[0066] That is, when the current voltage phase θv enters the specified interval (120°-θw<θv<120°+θw), if the current pulse width command value Cv1 increases relative to the pulse width command value Cv1buf at the time the current voltage phase θv enters the specified interval, the command value correction unit 35 subtracts that amount from all phases using formula (IV), and if it decreases, the command value correction unit 35 adds that amount to all phases using formula (IV). Then, after entering the specified interval, Cv1 is no longer substituted for Cv1buf, so that the V-phase pulse width command value Cv is fixed to the value (pulse width command value Cv1buf) at the time when the specified interval was entered (the range within the dashed square at the bottom of Figure 3), the U-phase pulse width command value Cu is added with the value of Cv1buf-Cv1, which changes as the phase progresses after entering the specified interval, and is corrected to gradually decrease as shown at the bottom of Figure 3, and the W-phase pulse width command value Cw is also added with the value of Cv1buf-Cv1, which changes as the phase progresses after entering the specified interval, and is corrected to gradually increase as shown at the bottom of Figure 3 (assuming that the above-mentioned added value Cn=0).

[0067] The above-described correction is similar to the case of line modulation in which, as shown in FIG. 2(b), the upper arm switching element of the phase in which the pulse width command value Cu1, Cv1, Cw1 is the largest is fixed to the ON state, and the upper and lower arm switching elements of the other two phases are turned ON / OFF. In this case, the center phases of the specified interval are 60°, 180°, and 300°, and the determination unit 35a determines whether or not the specified interval is present using the above-described formulas (X), (XI), and (XII), and the command value correction unit 35 calculates the modulation value Cmod using formula (XIII).

[0068] In this case, for example, when the current voltage phase θv enters a specified interval (60°-θw<θv<60°+θw), if the current pulse width command value Cw1 increases relative to the pulse width command value Cw1buf at the time the voltage phase θv entered the specified interval, the command value correction unit 35 subtracts that amount from all phases using formula (IV), and if it decreases, the command value correction unit 35 adds that amount to all phases using formula (IV). Then, after entering the specified interval, Cw1 is no longer substituted for Cw1buf, so that the W-phase pulse width command value Cw is fixed to the value (pulse width command value Cw1buf) at the time when the specified interval was entered, the V-phase pulse width command value Cv is corrected to gradually increase by adding the value Cw1buf-Cw1, which changes as the phase progresses after entering the specified interval, and the U-phase pulse width command value Cu is also corrected to gradually decrease by adding the value Cw1buf-Cw1, which changes as the phase progresses after entering the specified interval (as shown in FIG. 9(c). Again, the added value Cn=0).

[0069] The above operation is summarized in a flowchart shown in FIG. 5. In step S1, pulse width command values ​​Cu1, Cv1, and Cw1 are calculated using the aforementioned formulas (I), (II), and (III). Next, in step S2, it is determined whether the voltage phase θv is within the aforementioned specified interval using the aforementioned formulas (VII) to (XII). If it is not within the specified interval, the process proceeds to step S3, where the modulation value Cmod is calculated using the aforementioned formula (V) or (VI). In step S4, line modulation is performed using the aforementioned formula (IV) to calculate pulse width command values ​​Cu, Cv, and Cw. Next, in step S5, the current pulse width command value Cu1 is substituted for Cu1buf, the current pulse width command value Cv1 is substituted for Cv1buf, and the current pulse width command value Cw1 is substituted for Cw1buf. These become the previous values ​​in the next carrier cycle.

[0070] On the other hand, if the voltage phase θv is within the specified interval in step S2, the process proceeds to step S6, where the modulation value Cmod is calculated using the aforementioned formula (XIII). Next, in step S7, line-to-line modulation is performed using the aforementioned formula (IV), and pulse width command values ​​Cu, Cv, and Cw are calculated. After that, the process returns to step S1, so the current pulse width command value Cx1 is not substituted into the aforementioned Cx1buf. Therefore, the pulse width command value is fixed to the value when the maximum or minimum phase enters the specified interval.

[0071] In this way, the command value corrector 35 applies a correction to the pulse width command value of each phase to fix the pulse width command value of the phase at which the pulse width command value (two-phase modulation command value in this case) is maximum in a predetermined specified interval centered on the phase at which the phase at which the lower arm switching element is turned on and switching is stopped changes, or applies a correction to the pulse width command value of each phase to fix the pulse width command value of the phase at which the pulse width command value is minimum in a predetermined specified interval centered on the phase at which the phase at which the upper arm switching element is turned on and switching is stopped changes.

[0072] Such correction by the command value corrector 35 makes it possible to make the change in the pulse width command value within the specified interval gentle, suppressing abrupt changes and suppressing sidebands, thereby effectively reducing electromagnetic noise when operating the motor 8 with a three-phase AC output applied, as in this embodiment.

[0073] In this case, in the embodiment, the phase at which the phase at which the lower arm switching element is turned on and switching is stopped changes is set to 0°, 120°, and 240° in the case of a voltage phase with the U phase as the reference phase, and the phase at which the upper arm switching element is turned on and switching is stopped changes is set to 60°, 180°, and 300° in the case of a voltage phase with the U phase as the reference phase.This makes it possible to more efficiently suppress sideband waves and reduce the sideband wave components of noise.

[0074] In addition, in the embodiment, the command value correction unit 35 has a determination unit 35a that sets a specified interval from the phase at which the phase at which switching is stopped changes and a specified phase width θw, and determines whether the current phase is included in the specified interval.Therefore, the determination unit 35a can accurately determine whether the current phase is within the specified interval, and it becomes possible to more effectively suppress noise generated in the vicinity of the phase at which the phase at which switching is stopped changes.

[0075] 6 is a graph showing a comparison of noise characteristics of conventional two-phase modulation (top) and noise characteristics of the power conversion device 1 of the present invention under the above-described control (bottom). The vertical axis represents noise characteristics. As is clear from this graph, compared to the conventional method (top), the present invention (bottom) is able to suppress sidebands around the carrier frequency (10 kHz in this embodiment).

[0076] In the embodiment, the phase at which the phase at which the lower arm switching element is turned on and switching is stopped is changed over in the case of a voltage phase with the U phase as the reference phase, and the phase at which the upper arm switching element is turned on and switching is stopped is changed over in the case of a voltage phase with the U phase as the reference phase, but the phase is not limited to this. In the former case, the phase may be 0°, 120°, or 240°, or a combination of two of these, and in the latter case, the phase may be 60°, 180°, or 300°, or a combination of two of these, so as to execute the correction operation of the two-phase modulation command value.

[0077] In addition, in the embodiment, the switching phase is set as the center phase of the specified interval, but this is not limiting and the widths before and after may be different. That is, the phase width θw to be subtracted from the switching phase and the phase width θw to be added may be different values, as long as it is possible to determine whether the voltage phase is included in the specified interval including the switching phase. However, it is more effective to set the switching phase as the center phase of the specified interval.

[0078] (4) Controlling the width of the specified section Here, the fact that the pulse width command values ​​Cu, Cv, and Cw (two-phase modulation command values) change more slowly in the specified section means that the number of times the switching elements are switched increases. On the other hand, in an operating region with a high modulation rate, the operating noise of the motor 8 increases, and electromagnetic noise due to sideband waves also becomes less noticeable.

[0079] Therefore, the command value corrector 35 changes the phase width θw described above in accordance with the modulation rate. Specifically, the phase width θw is changed so that the width of the specified interval becomes narrower as the modulation rate increases, and becomes wider as the modulation rate decreases. However, the limit for widening the width of the specified interval is 60° as described above. This narrows the specified interval in areas with a high modulation rate to suppress an increase in the number of switching operations of the switching elements, and widens the specified interval in areas with a low modulation rate, thereby achieving more effective noise reduction.

[0080] (5) Narrow pulse avoidance processing Furthermore, particularly when applying voltage to motor 8 using PWM as in the embodiment, in order to switch the upper arm switching element at the minimum pulse width, as shown by the upper arm voltage in Figure 7(a), it is necessary to switch the lower arm switching element at the pulse width shown below by the lower arm voltage. This is the minimum pulse width that can be output. In other words, even if the upper arm voltage (pulse) is narrow, the lower arm voltage (pulse) will be wide, and it is not possible to output a pulse width narrower than this.

[0081] Therefore, when the pulse width command value from the control device indicates the pulse width of the lower arm voltage, the pulse width command value cannot be output as a small value near 0.0, as shown in Figure 7(a).Furthermore, when the pulse width command value from the control device indicates the pulse width of the upper arm voltage, the pulse width command value cannot be output as a large value near 1.0, as shown in Figure 7(b).

[0082] As described above, when the pulse width command value is 0.0 or near 1.0, there is a possibility that the intended pulse width cannot be output. Therefore, in the present invention, such a pulse width is referred to as a narrow pulse. In order to avoid such a narrow pulse, the command value corrector 35 of the embodiment sets the aforementioned additional value Cn to a value other than 0 and executes narrow pulse avoidance processing such that the pulse width command values ​​Cu, Cv, and Cw (same as those in the lower part of FIG. 3) shown in FIG. 8(a) have waveforms as shown in FIG. 8(b).

[0083] Here, the additional value Cn is a negative value in the case of line modulation in which the upper arm switching element of the maximum phase is fixed to the ON state and the upper and lower arm switching elements of the other two phases are turned ON / OFF, as shown in Figure 4, and a positive value in the case of line modulation in which the lower arm switching element of the minimum phase is fixed to the ON state and the upper and lower arm switching elements of the other two phases are turned ON / OFF. This eliminates the region in which a pulse width command value that is too narrow or too wide to be output is issued, and makes it possible to avoid the inconvenience of not being able to output the desired pulse width.

[0084] The waveforms of the pulse width command values ​​obtained by the above control are shown in Figures 9 and 10. Figure 9 shows the case of line modulation in which the upper arm switching element of the maximum phase is fixed to the ON state, and the upper and lower arm switching elements of the other two phases are turned ON / OFF, while Figure 10 shows the case of line modulation in which the lower arm switching element of the minimum phase is fixed to the ON state, and the upper and lower arm switching elements of the other two phases are turned ON / OFF.

[0085] In addition, (a) in each figure shows the value when the modulation value Cmod=0, (b) shows the value calculated by the formula (IV) when no correction is made by the command value correction unit 35, (c) shows the value when correction is made by the command value correction unit 35 using the formula (XIII) (additional value Cn=0), and (d) shows the pulse width command values ​​Cu, Cv, and Cw of each phase after the narrow pulse avoidance processing described above is performed.

[0086] Here, FIG. 11 shows the pulse width command values ​​Cu, Cv, and Cw for each phase in the case of line modulation in which the upper arm switching element of the phase in which the pulse width command value is maximum is turned on to stop switching only in the phases from 120° to 240°, and the lower arm switching element of the phase in which the pulse width command value is minimum is turned on to stop switching in the other phases.

[0087] Similarly, (a) in Fig. 11 shows the case where the modulation value Cmod = 0. In the case of such line-to-line modulation, the command value corrector 35 performs the same correction operation as described above, with 0° and 180° as the specified interval, and further performs the narrow pulse avoidance process described above, thereby making it possible to reduce electromagnetic noise by producing a waveform such as that shown in (c) in Fig. 11. Note that (b) in Fig. 11 shows the waveform when no correction is performed by the command value corrector 35. [Example]

[0088] (6) Control of other embodiments of the present invention Next, another embodiment (embodiment 2) of the present invention will be described. In the embodiment (embodiment 1) described above, the pulse width command calculation unit 34 of the command value calculation unit 30 performs line modulation to calculate pulse width command values ​​Cu, Cv, and Cw, which are two-phase modulation command values, and the command value correction unit 35 applies corrections to the pulse width command values ​​Cu, Cv, and Cw calculated by the pulse width command calculation unit 34. However, this is not limiting, and the phase voltage command calculation unit 33 may perform line modulation, the command value correction unit 35 may apply corrections to the two-phase modulation command values ​​calculated thereby, and then the pulse width command calculation unit 34 may calculate the pulse width command values. Control in this case will be described below. In this embodiment, too, the circuit configuration of the power conversion device 1 is basically the same as that shown in FIG. 1.

[0089] (6-1) Phase voltage command calculation unit 33 in this embodiment Also in this embodiment, the phase voltage command calculation unit 33 calculates the phase voltage command value Vu for each phase using the above-mentioned formula (I). * , Vv * , Vw * In this embodiment, the phase voltage command value Vu * , Vv * , Vw * is the three-phase modulation command value of the present invention.

[0090] On the other hand, the phase voltage command calculation unit 33 of this embodiment calculates the phase voltage command value Vu of each phase. * , Vv * , Vw * Then, line modulation (two-phase modulation in this embodiment) is performed using the following formula (XIV). ** , Vv ** , Vw ** is the phase voltage command value of each phase after line modulation (U phase voltage command value Vu ** , V-phase voltage command value Vv ** , W-phase voltage command value Vw ** ) which is the two-phase modulation command value in this embodiment of the present invention.

[0091]

number

[0092] In addition, v0 in the formula (XIV) is a modulation value for performing line-to-line modulation (two-phase modulation) in this embodiment. When this modulation value v0=0, the phase voltage command value Vu ** , Vv ** , Vw ** does not perform line modulation, that is, the phase voltage command value Vu before line modulation * , Vv * , Vw * On the other hand, when the modulation value v0 is set to the following formulas (XV) and (XVI), line-to-line modulation is performed.

[0093]

number

[0094] max(Vu * (θv), Vv * (θv), Vw * (θv)) is the phase voltage command value Vu at the voltage phase θv * , Vv * , Vw * In equation (XV), this value is subtracted from Vdc / 2 to obtain v0, which is the maximum value of all phase voltage command values ​​Vu ** , Vv ** , Vw ** , the phase voltage command value of the maximum phase is Vdc / 2, and the upper arm switching element of that phase is fixed to the ON state. Then, the upper and lower arm switching elements of the other two phases are turned ON / OFF, so Vu ** , Vv ** , Vw ** is the two-phase modulation command value.

[0095] min(Vu * (θv), Vv * (θv), Vw * (θv)) is the phase voltage command value Vu at the voltage phase θv * , Vv * , Vw *This means the minimum value of the phase (three-phase modulation command value), and in formula (XVI), this value is subtracted from -Vdc / 2 to obtain v0, which is the voltage command value Vu for all phases. ** , Vv ** , Vw ** Since the phase voltage command value of the minimum phase is -Vdc / 2, the lower arm switching element of that phase is fixed to the ON state. Then, the upper and lower arm switching elements of the other two phases are turned ON / OFF, so Vu ** , Vv ** , Vw ** is the two-phase modulation command value.

[0096] (6-2) Pulse width command calculation unit 34 in this embodiment The pulse width command calculation unit 34 of this embodiment calculates and outputs the phase voltage command value Vu of each phase calculated by the phase voltage command calculation unit 33. ** , Vv ** , Vw ** From the above, the pulse width command values ​​Cu (U-phase pulse width command value), Cv (V-phase pulse width command value), and Cw (W-phase pulse width command value) of each phase normalized (corrected to 0 to 1) by the DC voltage Vdc are calculated and output using the following formula (XVII).

[0097]

number

[0098] The subsequent operations of the PWM signal generator 36 and the gate driver 37 are the same as those in the above-described embodiment.

[0099] (6-3) Command value correction unit 35 in this embodiment In this embodiment, the command value corrector 35 corrects the phase voltage command value Vu of each phase calculated by the phase voltage command calculator 33. ** , Vv ** , Vw **For example, in the case of line modulation in which the lower arm switching element of the minimum phase is fixed to the ON state and the upper and lower arm switching elements of the other two phases are turned ON / OFF, the phase voltage command value Vu is corrected in the same specified section as in the above-mentioned embodiment, centered on the phase in which the phase in which the lower arm switching element is turned ON and the switching is stopped is changed. ** , Vv ** , Vw ** is applied to all phases to fix the phase voltage command value of the phase for which is maximum, thereby causing the change in the command value of the phase for which the command value decreases to gradually decrease smoothly, and the change in the command value of the phase for which the command value increases to gradually increase smoothly.

[0100] (7) Correction operation of the command value corrector 35 in this embodiment The correction operation by the command value corrector 35 in this embodiment will be described below. The operation of the determiner 35a of the command value corrector 35 in this case is the same as in the above-described embodiment, and determines whether the current voltage phase θv (current phase) is within the specified interval using equations (VII) to (XII). However, the pulse width command values ​​Cu1, Cv1, and Cw1 in the above description are the same as the phase voltage command value Vu. * , Vv * , Vw * 4 is also replaced with the phase voltage command value fixed phase. Furthermore, the combination of specified intervals is also the same as in the above-described embodiment.

[0101] (7-1) Command value correction operation In this case as well, if the judgment unit 35a judges that the current voltage phase θv is within the above-mentioned specified interval, the command value correction unit 35 calculates the modulation value v0 in the formula (XIV) using the following formulas (XVIII) and (XIX).

[0102]

number

[0103] Incidentally, formula (XVIII) is the case of line modulation in which the upper arm switching element of the maximum phase is fixed to the ON state and the upper and lower arm switching elements of the other two phases are turned ON / OFF, and formula (XIX) is the case of line modulation in which the lower arm switching element of the minimum phase is fixed to the ON state and the upper and lower arm switching elements of the other two phases are turned ON / OFF.

[0104] The phase θa shown on the right side of FIG. 4 means the phase when the phase enters a specified section in each center phase of FIG. 4, and Vx * (θa) is the phase voltage command value when entering the specified section. * (θa) and Vx * x in (θv) is selected from u, v, or w. Furthermore, Vn in formulas (XVIII) and (XIX) is an additional value when the narrow pulse avoidance process described above in this embodiment is executed, and when the narrow pulse avoidance process is not executed, the additional value Vn=0.

[0105] min(Vu) in formula (XIX) * (θa), Vv * (θa), Vw * (θa)) is the phase voltage command value Vu at the phase θa when entering the specified section. * , Vv * , Vw * This means the minimum value of the phase, and subtracting this from -Vdc / 2 gives equation (XVI) for the phase θa. Also, equation (XIX) gives Vx when it is in the specified range. * (θa) to Vx when voltage phase θv * (θv) is subtracted.

[0106] In the case of formula (XIX), for example, in the specified interval where the center phase is 120°, v is selected as x, and the modulation value v0 is Vv when it enters the specified interval. * (θa) to Vv when voltage phase θv * (θv) is subtracted, and then Vdc / 2 is subtracted again, and the phase voltage command value Vu is obtained at the phase θa when the specified section is entered. * , Vv * , Vw* The value of the smallest phase among these is also subtracted (when the added value Vn=0).

[0107] That is, when the current voltage phase θv falls within the specified interval (120°-θw<θv<120°+θw), the command value corrector 35 calculates the phase voltage command value Vv * (θa) with respect to the current phase voltage command value Vv * If (θv) increases, the amount is subtracted from all phases using formula (XIV), and if it decreases, the amount is added to all phases using formula (XIV). As a result, the phase voltage command value Vv of the V phase is the value (Vv) when it enters the specified section. * (θa)), and the phase voltage command value Vu * Vv changes as the phase advances after entering the specified section. * (θa)-Vv * The value of (θv) is added and corrected to gradually decrease, and the phase voltage command value Vw * Vv also changes as the phase progresses after entering the specified section. * (θa)-Vv * The value of (θv) is added and corrected to gradually increase (assuming that the above-mentioned added value is Vn=0).

[0108] The above correction is performed by adjusting the phase voltage command value Vu * , Vv * , Vw * The same is true for the case of line-to-line modulation, in which the upper arm switching element of the phase with the largest value is fixed to the ON state and the upper and lower arm switching elements of the other two phases are turned ON / OFF. In this case, the center phases of the specified interval are 60°, 180°, and 300°, and the determination unit 35a determines whether or not it is in the specified interval using the above-mentioned formulas (X), (XI), and (XII), and the command value correction unit 35 calculates the modulation value v0 using formula (XVIII).

[0109] In this case, for example, when the current voltage phase θv enters a specified interval (60°-θw<θv<60°+θw), the command value corrector 35 calculates the phase voltage command value Vw *(θa) with respect to the current phase voltage command value Vw * If it increases, the amount is subtracted from all phases according to formula (XIV), and if it decreases, the amount is added to all phases according to formula (XIV). * is the value when it enters the specified section (phase voltage command value Vw * (θa)), and the V-phase voltage command value Vv * Vw changes as the phase advances after entering the specified section. * (θa)-Vw * The value of (θv) is added and corrected to gradually increase, and the phase voltage command value Vu of the U phase is * Vw also changes as the phase progresses after entering the specified section. * (θa)-Vw * The value of (θv) is added and corrected to gradually decrease (when the added value Vn=0).

[0110] The above operation is summarized in a flowchart shown in Figure 12. In step S8, the phase voltage command value Vu is calculated using the above-mentioned formulas (I) and (II). * , Vv * , Vw * Next, in step S9, it is determined whether or not the voltage phase θv is within the specified interval using the above-mentioned formulas (VII) to (XII). If it is not within the specified interval, the process proceeds to step S10, where a modulation value v0 is calculated using the above-mentioned formula (XV) or (XVI). In step S11, line modulation is performed using the above-mentioned formula (XIV) to calculate a phase voltage command value Vu. ** , Vv ** , Vw ** Next, in step S12, the pulse width command values ​​Cu, Cv, and Cw are calculated using the above-mentioned formula (XVII).

[0111] On the other hand, if the voltage phase θv is in the specified interval in step S9, the process proceeds to step S13 to calculate the modulation value v0 using the above-mentioned formula (XVIII) or (XIX). As a result, the phase voltage command value is fixed to the value when the maximum or minimum phase enters the specified interval. After that, the process proceeds to step S11, where line modulation is performed using the above-mentioned formula (XIV) to obtain the phase voltage command value Vu ** , Vv ** , Vw ** In step S12, the pulse width command values ​​Cu, Cv, and Cw are calculated using the above-mentioned formula (XVII).

[0112] As described above, in this embodiment, the command value corrector 35 applies a correction to the phase voltage command value of each phase to fix the phase voltage command value of the phase at which the phase voltage command value (two-phase modulation command value in this case) is maximum in a predetermined specified interval centered on the phase at which the phase at which the lower arm switching element is turned on and switching is stopped, or applies a correction to the phase voltage command value of each phase to fix the phase voltage command value of the phase at which the phase voltage command value is minimum in a predetermined specified interval centered on the phase at which the phase at which the upper arm switching element is turned on and switching is stopped.

[0113] By such correction by the command value corrector 35, it is possible to make the change in the phase voltage command value in the specified section gentle, suppress abrupt changes, and suppress sidebands in this embodiment as well. This similarly makes it possible to effectively reduce electromagnetic noise when the motor 8 is operated by applying a three-phase AC output.

[0114] In particular, in this embodiment, the value at the time of entering the specified interval is restored using the phase θa, so there is no need to substitute the current value for the previous value as in the previous embodiment (embodiment 1), and no value buffer is required. Also, in this embodiment, the above-mentioned control of changing the width of the specified interval and narrow-width pulse avoidance processing are performed.

[0115] Incidentally, the formula (I) used by the phase voltage command calculation unit 33 described above is in a format for calculating an instantaneous voltage command value using the magnetic pole position θ (magnetic pole position information) of the motor 8 for each control period. Therefore, formulas (XV) and (XVI) are in a format that allows calculation using this instantaneous voltage command value. Also, formula (XIII) can be calculated using the instantaneous voltage command value calculated by formula (I). As a result, each calculation in each of the above embodiments is carried out by the phase voltage command calculation unit 33 using the phase voltage command value Vu of each phase calculated as an instantaneous value for each control period. * , Vv * , Vw * This allows the voltage command value required to drive the motor 8 to be calculated sequentially while suppressing electromagnetic noise.

[0116] Furthermore, in the embodiment, the present invention is applied to a power conversion device 1 that controls the drive of a motor 8 of an electric compressor, but the present invention is not limited to this in the inventions other than claims 8 and 10, and is effective when various devices are controlled by an inverter circuit. [Explanation of symbols]

[0117] 1 Power conversion device 8 motors 18A~18F Upper and lower arm switching elements 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 Pulse width command calculation unit 35 Command value correction unit 35a Judgment part 36 PWM signal generation section 37 Gate Driver

Claims

1. A power conversion device including an inverter circuit that generates a three-phase AC output by switching upper and lower arm switching elements of each phase, and a control device that controls the switching of the upper and lower arm switching elements of each phase of the inverter circuit, The control device a command value calculation unit that calculates a three-phase modulation command value for generating a phase voltage of each of the phases, and calculates a two-phase modulation command value for turning on the lower arm switching element of the phase for which the three-phase modulation command value is smallest to stop switching, or for turning on the upper arm switching element of the phase for which the command value is largest to stop switching, The command value calculation unit a command value correcting unit that applies a correction to the two-phase modulation command value of each phase to fix the two-phase modulation command value of a phase for which the two-phase modulation command value is maximum in a predetermined specified section including a phase for which the phase for stopping switching is switched over with the lower arm switching element turned on, or applies a correction to the two-phase modulation command value of each phase to fix the two-phase modulation command value of a phase for which the two-phase modulation command value is minimum in a predetermined specified section including a phase for which the phase for stopping switching is switched over with the upper arm switching element turned on; A power conversion device comprising:

2. 2. The power conversion device according to claim 1, wherein the phase at which the phase at which switching is stopped with the lower arm switching element turned on is switched is any one of 0°, 120°, and 240°, or a combination of two of them, or all of them, in the case of a voltage phase with a U phase as a reference phase, and the phase at which the phase at which switching is stopped with the upper arm switching element turned on is switched is any one of 60°, 180°, and 300°, or a combination of two of them, or all of them, in the case of a voltage phase with a U phase as a reference phase.

3. 3. The power conversion device according to claim 1, wherein the command value correction unit sets the specified interval based on a phase at which the phase at which the switching is stopped switches and a predetermined phase width, and includes a determination unit that determines whether a current phase is included in the specified interval.

4. 4. The power conversion device according to claim 1, wherein the command value corrector changes the width of the specified section so that the width is narrower as the modulation rate increases and wider as the modulation rate decreases.

5. 5. The power conversion device according to claim 1, wherein the command value corrector sets the width of the specified interval to 60 degrees or less.

6. The command value calculation unit a phase voltage command calculation unit that calculates a phase voltage command value for each phase; a pulse width command calculation unit that calculates a pulse width command value for each phase as the three-phase modulation command value from the phase voltage command value for each phase; the pulse width command calculation unit calculates the two-phase modulation command value to turn on the lower arm switching element of the phase in which the pulse width command value is smallest to stop switching, or to turn on the upper arm switching element of the phase in which the pulse width command value is largest to stop switching, and 6. The power conversion device according to claim 1, wherein the command value corrector applies the correction to the two-phase modulation command value for each phase calculated from the pulse width command value.

7. The command value calculation unit a phase voltage command calculation unit that calculates a phase voltage command value for each phase as the three-phase modulation command value; a pulse width command calculation unit that calculates a pulse width command value for each phase from the phase voltage command value for each phase; the phase voltage command calculation unit calculates the two-phase modulation command value to turn on the lower arm switching element of the phase for which the phase voltage command value is minimum to stop switching, or to turn on the upper arm switching element of the phase for which the phase voltage command value is maximum to stop switching, and 6. The power conversion device according to claim 1, wherein the command value corrector applies the correction to the two-phase modulation command value for each phase calculated from the phase voltage command value.

8. The phase voltages at the connection points of the upper and lower arm switching elements of the respective phases are applied to a motor as the three-phase AC output, 8. The power conversion device according to claim 6, wherein the phase voltage command calculation unit calculates an instantaneous value of the phase voltage command value for each phase using magnetic pole position information of the motor for each control period.

9. 9. The power conversion device according to claim 6, wherein the command value correction unit applies narrow-width pulse avoidance processing to the two-phase modulation command value, which prevents the pulse width command value of each phase from becoming narrower than a minimum pulse width that can be output or wider than a maximum pulse width that can be output.

10. 10. The power conversion device according to claim 1, wherein the phase voltages at the connection points of the upper and lower arm switching elements of the respective phases are applied to a motor as the three-phase AC output.

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