Power conversion device

Abstract

To relax shock accompanying change in a modulation scheme or dead time.SOLUTION: A power conversion device 1 includes: a current control unit 120 that calculates and outputs a voltage command value from a current command value of a motor 2; a PWM signal generation unit 160 that generates a PWM signal based on the voltage command value; and an inverter 3 that drives the motor 2 by switching based on the PWM signal. The power conversion device 1 includes a modulation scheme switching unit 150 that switches a modulation scheme of the inverter 3 and an error component compensation unit 180 that adds a compensation voltage command value to the voltage command value when the modulation scheme is switched. The error component compensation unit 180 cancels an error component of the voltage command value caused by switching of the modulation method with a compensation voltage command value.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a power conversion device that drives a motor based on PWM control of an inverter.

Background Art

[0002] Conventionally, a power conversion device that drives a motor based on PWM control of an inverter has been known. In this type of power conversion device, a three-phase modulation method or a two-phase modulation method is adopted. The three-phase modulation method is a modulation method with large switching losses, and the two-phase modulation method can reduce the switching losses to 2 / 3 compared to the three-phase modulation method. However, in the two-phase modulation method, it is difficult to output an accurate voltage vector in the low-speed range or the high-speed range. Therefore, a method of driving the motor while switching between the three-phase modulation method and the two-phase modulation method according to the operating conditions has been proposed (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, if the modulation method is switched and changed during the driving of the motor, the current may suddenly change due to the switching shock, and there is a risk of overcurrent flowing or demodulation occurring.

[0005] An object of the present invention is to provide a power conversion device that can mitigate the shock associated with a change in the modulation method or dead time.

Means for Solving the Problems

[0006] The present invention relates to a power conversion device including a current control unit that calculates and outputs a voltage command value from a current command value of a motor, a PWM signal generation unit that generates a PWM signal based on the voltage command value, and an inverter that drives the motor by switching based on the PWM signal. The power conversion device includes at least one of a modulation method switching unit that switches the modulation method of the inverter and a dead time specifying unit that specifies an arbitrary dead time of the inverter, and an error component compensation unit that adds a compensation voltage command value to the voltage command value when the modulation method is switched or the dead time is changed. The error component compensation unit cancels an error component of the voltage command value caused by the switching of the modulation method or the change of the dead time with the compensation voltage command value. The power conversion device is characterized by this.

Effect of the Invention

[0007] According to the present invention, it is possible to mitigate the shock associated with the switching of the modulation method or the change of the dead time.

Brief Description of the Drawings

[0008]

Figure 1

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Figure 13

Mode for Carrying Out the Invention

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] [Power Conversion Device] As shown in FIG. 1, a power conversion device 1 according to an embodiment includes an inverter 3 connected to a motor 2 and a control device 100 that drives the motor 2 based on PWM control of the inverter 3. The motor 2 is a three-phase permanent magnet synchronous motor that drives an electric compressor used in an air conditioner of an electric vehicle or the like, but the application of the motor 2 is not limited to this.

[0011] [Inverter] The inverter 3 is configured to include a plurality of switching elements 4A to 4F. One ends of the three-phase windings 5U, 5V, and 5W provided in the motor 2 are respectively connected to one end side of the inverter 3. The other ends of the windings 5U, 5V, and 5W are connected at the midpoint. The other end side of the inverter 3 is connected to a battery 8, which is a DC power source, via a positive power line 6 and a negative power line 7. The inverter 3 applies a voltage to the windings 5U, 5V, and 5W based on the switching of the switching elements 4A to 4F by PWM control of the control device 100 to drive the motor 2.

[0012] Specifically, the inverter 3 includes a U-phase half-bridge circuit 9U, a V-phase half-bridge circuit 9V, and a W-phase half-bridge circuit 9W. In each phase's half-bridge circuit 9U, 9V, and 9W, switching elements 4A to 4C of the upper arm and switching elements 4D to 4F of the lower arm are respectively arranged. Further, each of the switching elements 4A to 4F incorporates a freewheeling diode connected in antiparallel.

[0013] In the U-phase half-bridge circuit 9U, the switching element 4A of the upper arm and the switching element 4D of the lower arm are connected in series, and this connection point is connected to one end side of the U-phase winding 5U of the motor 2. In the V-phase half-bridge circuit 9V, the switching element 4B of the upper arm and the switching element 4E of the lower arm are connected in series, and this connection point is connected to one end side of the V-phase winding 5V of the motor 2. In the W-phase half-bridge circuit 9W, the switching element 4C of the upper arm and the switching element 4F of the lower arm are connected in series, and this connection point is connected to one end side of the W-phase winding 5W of the motor 2. Note that the inductor 10 interposed in the positive power supply line 6 and the capacitor 11 connected between the positive power supply line 6 and the negative power supply line 7 constitute a noise filter.

[0014] [Control device] Next, as shown in FIG. 2, the control device 100 includes subtractors 101 and 102, adders 103 to 106, a current control unit 120, a non-interference control unit 130, a coordinate conversion unit 140, a modulation method switching unit 150, a PWM signal generation unit 160, a gate driver 170, and an error component compensation unit 180.

[0015] The current control unit 120 includes a PI control unit 121 for the d-axis and a PI control unit 122 for the q-axis. The subtractor 101 inputs the deviation obtained by subtracting the d-axis current response value i d * from the d-axis current command value i d to the PI control unit 121 for the d-axis. Also, the subtractor 102 inputs the deviation obtained by subtracting the q-axis current response value i q * from the q-axis current command value i q to the PI control unit 122 for the q-axis. The PI control unit 121 for the d-axis and the PI control unit 122 for the q-axis perform PI calculations using the deviations input from the subtractors 101 and 102 and output the d-axis voltage and the q-axis voltage. Specifically, the PI control unit 121 for the d-axis and the PI control unit 122 for the q-axis each include P control elements 121b and 122b and I control elements (integral elements) 121a and 122b.

[0016] The P control elements 121b and 122b output a value obtained by multiplying the input deviation by K P (K P is a design parameter). That is, the P control elements 121b and 122b calculate the output value to make the current deviation zero, so the outputs of the P control elements 121b and 122b affect the responsiveness. Also, the I control elements 121a and 122a integrate the input deviation and output a value that is K i times (K i is a design parameter). That is, the I control elements 121a and 122a calculate the output value to make the integrated value of the deviation zero, so the outputs of the I control elements 121a and 122b affect the disturbance suppression performance.

[0017] The adder 103 adds the value output by the P control element 121b of the PI control unit 121 on the d-axis to the value output by the I control element 121a and inputs it to the non-interference control unit 130. Also, the adder 104 adds the value output by the P control element 122b of the PI control unit 122 on the q-axis to the value output by the I control element 122a and inputs it to the non-interference control unit 130. The non-interference control unit 130 calculates and outputs the d-axis voltage command value V d * and the q-axis voltage command value V q * after eliminating the interference between the dq axes based on the input values from the adders 103 and 104. The coordinate conversion unit 140 converts the d-axis voltage command value V d * and the q-axis voltage command value V q * input from the non-interference control unit 130 into the U-phase voltage command value V u * , the V-phase voltage command value V v * , and the W-phase voltage command value V w * .

[0018] The modulation method switching unit 150 switches the modulation method between a three-phase modulation method and a two-phase modulation method based on a predetermined switching condition. As shown in FIG. 3, in the three-phase modulation method, the number of switchings in each control cycle is 6 times. As shown in FIG. 4, in the two-phase modulation method, the number of switchings in each control cycle is 4 times. That is, the three-phase modulation method is a modulation method with large switching losses, and the two-phase modulation method can reduce the switching losses to 2 / 3 compared with the three-phase modulation method. However, in the two-phase modulation method, it is difficult to output an accurate voltage vector in the low-speed range and the high-speed range. Therefore, the control device 100 drives the motor while switching between the three-phase modulation method and the two-phase modulation method according to the operating conditions.

[0019] The PWM signal generation unit 160 generates a PWM signal based on the U-phase voltage command value V input from the modulation method switching unit 150 u ** , the V-phase voltage command value V v ** , and the W-phase voltage command value V w ** and the dead time specified by the dead time setting unit 160a described later. The gate driver 170 switches the switching elements 4A to 4F of the inverter 3 based on the PWM signal input from the PWM signal generation unit 160. Thereby, the motor 2 is driven based on the PWM control of the inverter 3.

[0020] [Switching shock] When the switching elements 4A to 4F of the upper and lower arms of the inverter 3 are simultaneously turned on, a through current may flow and cause damage. Therefore, when switching the switching elements 4A to 4F, a dead time (simultaneous OFF period) is provided to prevent simultaneous ON. The error in motor control due to the dead time is mainly suppressed by the I control elements 121a and 122a of the current control unit 120. However, when the modulation method is switched from a three-phase modulation method to a two-phase modulation method, or from a two-phase modulation method to a three-phase modulation method, the way the error due to the dead time appears changes. For this reason, there is a delay in suppressing the dead time error by the I control elements 121a and 122a. This delay causes the current to oscillate due to voltage disturbance and becomes a factor in the switching shock.

[0021] [Error Component Compensation Unit] To mitigate the above switching shock, the control device 100 includes an error component compensation unit 180 and adders 105 and 106. The adder 105 is arranged downstream of the adder 103 and adds the compensation voltage command value V d mod of the d-axis output from the error component compensation unit 180 to the output value of the PI control unit 121 of the d-axis. Also, the adder 106 is arranged downstream of the adder 104 and adds the compensation voltage command value V q mod of the q-axis output from the error component compensation unit 180 to the output value of the PI control unit 122 of the q-axis.

[0022] When the modulation method is switched, the error component compensation unit 180 outputs the compensation voltage command value V d mod of the d-axis to the adder 103 and outputs the compensation voltage command value V q mod of the q-axis to the adder 106. That is, the error component compensation unit 180 compensates for the error components of the voltage command values V d * , V q * caused by the switching of the modulation method with the compensation voltage command values V d mod , V q modcancels it at to mitigate the shock associated with the switching of the modulation method. The compensation voltage command value V d mod , V q mod The error component to be canceled at is the error component generated by the delay of the I control elements 121a and 122a of the PI control units 121 and 122 at the time of switching the modulation method. In other words, at the time of switching the modulation method, the dead time compensation component integrated in the I control elements 121a and 122a is used as the compensation voltage command value V d mod , V q mod is instantaneously compensated at to mitigate the shock associated with the switching of the modulation method.

[0023] Immediately after the modulation method is switched, it is necessary to instantaneously perform dead time error compensation with the compensation voltage command value V d mod , V q mod However, after the modulation method is switched, it is preferable to gradually shift to the dead time error compensation by the I control elements 121a and 122a. The compensation voltage command value V d mod , V q mod for performing such dead time error compensation can use, for example, a value obtained by multiplying the unit compensation voltage command value V unit mod generated through a first-order low-pass filter from the modulation method switching flag by the correction coefficients K d mod , K q mod for each of the dq axes. Note that although the low-pass filter is described in the continuous system, it is actually implemented after discretization.

[0024] The unit compensation voltage command value V unit modAs can be seen from the waveform, it outputs 1 at the moment when the switching flag becomes 1, and then becomes a signal that decays exponentially. As a result, after instantaneously relaxing the switching shock, it can gradually shift to the dead time error compensation by the I control elements 121a and 122a. Note that the unit compensation voltage command value V unit mod The bandwidth of the low-pass filter that generates is made sufficiently slower than the bandwidth of the current control unit 120 so that the I control elements 121a and 122a can perform dead time error compensation following the decrease of the unit compensation voltage command value V unit mod .

[0025] Next, an example of the calculation formula for calculating the unit compensation voltage command value V unit mod , the compensation voltage command value V d mod , V q mod , and the coefficients K d mod , K q mod is shown.

[0026]

Equation

[0027]

Equation

[0028]

Equation

[0029]

Equation

[0030]

Equation

[0031] [Number]

[0032] [Number]

[0033] [Number]

[0034] Here, V dc is the DC link voltage, T d is the dead time, F PWM is a variable depending on the modulation method after the modulation method switching, F PWM ′ is a variable depending on the modulation method before the modulation method switching. Note that the coefficient K d mod , K q mod may be calculated by the above calculation formula, or may be determined by trial and error to obtain an optimal value, and may be set to a larger or smaller value in consideration of parameter fluctuations.

[0035] [Verification of the Effect of an Embodiment] Next, the verification of the effect of this embodiment performed by simulation will be described with reference to FIGS. 6 to 9.

[0036] FIG. 6 shows the motor rotation speed ω rm , d-axis current i d , q-axis current i q and three-phase current UVW- phase in a power conversion device according to a conventional example when switching from a three-phase modulation method to a two-phase modulation method during motor driving. As shown in FIG. 6, in the power conversion device according to the conventional example, the switching from the three-phase modulation method to the two-phase modulation method was performed at 50 ms. In the conventional example, immediately after the switching of the modulation method, a steep fluctuation regarded as a switching shock occurred in the q-axis current i q and the three-phase current W- phase , and the motor rotation speed ω rmhas propagated up to.

[0037] FIG. 7 shows the motor rotational speed ω, the d-axis current i rm , the q-axis current i d , and the three-phase currents UVW- q when the power conversion device 1 according to the present embodiment switches from a three-phase modulation method to a two-phase modulation method during motor driving. As shown in FIG. 7, in the power conversion device 1 according to the present embodiment, similar to the conventional example, the switching from the three-phase modulation method to the two-phase modulation method was performed at 50 ms. In the present embodiment, it was confirmed that the steep fluctuations between the q-axis current i phase and the three-phase current W- q were suppressed, and the fluctuations in the motor speed were also suppressed. phase

[0038] FIG. 8 shows the d-axis voltage (the output voltage V of the I control element on the d-axis d i ), the q-axis voltage (the output voltage V of the I control element on the q-axis q i ), and the dq-axis voltage command values V d ref , V q ref when the power conversion device according to the conventional example switches from a three-phase modulation method to a two-phase modulation method during motor driving. As shown in FIG. 8, in the conventional example, although the output voltage V q i of the I control element on the q-axis fluctuates at the time of switching the modulation method and responds to compensate for it, the slope indicated by the change in the output voltage V q i is large.

[0039] FIG. 9 shows the d-axis voltage (the output voltage V of the I control element on the d-axis d i ), the q-axis voltage (the output voltage V of the I control element on the q-axis q i ), the compensation voltage V q mod ), and the dq-axis voltage command values V d ref , Vq ref is shown. As shown in FIG. 9, under the simulation conditions for verification of this embodiment, when switching the modulation method, at the output voltage V of the I control element 122a on the q-axis q i only the compensation voltage command value V q mod is instantaneously added. As a result, the change in the output voltage V of the I control element 122a on the q-axis q i is suppressed, avoiding a switching shock. Also, the output voltage V of the I control element 122a on the q-axis q i performs compensation for the dead time error component in accordance with the attenuation of the compensation voltage command value V q mod .

[0040] [Modification Example] As described above, the power conversion device 1 according to an embodiment of the present invention has been described. However, the present invention is not limited to the configuration of the above embodiment. For example, since the dead time error component of the voltage command value can occur not only when switching the modulation method but also when changing the dead time, the present invention can also be applied to a power conversion device provided with a dead time setting unit 160a that designates an arbitrary dead time.

[0041] Hereinafter, a modification example including the dead time setting unit 160a will be described with reference to FIGS. 10 to 13. However, for configurations common to the above embodiment, the same reference numerals as those in the above embodiment may be used, and the description of the above embodiment may be incorporated by reference. The error component compensation unit 180 of the modification example outputs a compensation voltage command value V for the d-axis to the adder 103 and a compensation voltage command value V for the q-axis to the adder 106 when the dead time is changed. That is, the error component compensation unit 180 compensates for the error components of the voltage command values V d mod , V q mod caused by the change in the dead time with the compensation voltage command values V d * , V q * . d mod , Vq mod Cancels it and reduces the shock associated with the switching of the modulation method.

[0042] Compensation voltage command value V d mod , V q mod The error component to be canceled by is the error component generated by the delay of the I control elements 121a and 122a of the PI control units 121 and 122 at the time of switching the dead time. In other words, at the time of switching the dead time, the dead time compensation component integrated in the I control elements 121a and 122a is used as the compensation voltage command value V d mod , V q mod By instantaneously compensating with, the shock associated with the change in the dead time is reduced. Immediately after the dead time is changed, the compensation voltage command value V d mod , V q mod needs to instantaneously perform dead time error compensation at, but after the dead time is changed, it is preferable to gradually shift to the dead time error compensation by the I control elements 121a and 122a.

[0043] The compensation voltage command value V that performs such dead time error compensation d mod , V q mod For example, as shown in FIG. 5, is the unit compensation voltage command value V generated from the dead time switching flag through a first-order low-pass filter unit mod multiplied by the correction coefficients K for each of the dq axes d mod , K q mod can be used. Although the low-pass filter is described in the continuous system, in practice, it is implemented after discretization.

[0044] Unit compensation voltage command value V unit modAs can be seen from the waveform, it outputs 1 at the moment when the switching flag becomes 1, and then becomes a signal that decays exponentially. As a result, after instantaneously relaxing the switching shock, it can gradually shift to dead-time error compensation by the I control elements 121a and 122a. Note that the band of the low-pass filter that generates the unit compensation voltage command value V unit mod should be made sufficiently slower than the band of the current control unit 120 so that the I control elements 121a and 122a can perform dead-time error compensation following the decrease in the unit compensation voltage command value V unit mod . The calculation formula for calculating the unit compensation voltage command value V unit mod and the compensation voltage command value V d mod , V q mod is the same as that of the power conversion device 1 according to the above embodiment. However, since the calculation formulas for calculating the coefficients K d mod , K q mod are slightly different, an example is shown below.

[0045]

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[0046]

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[0047]

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[0048]

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[0049]

Number

[0050] Here, V dc is the DC link voltage, ΔT d is the dead time change amount, T d is the dead time after change, T d ′ is the dead time before change, F PWM is a variable depending on the modulation method, and θ Im is the phase of the current vector command value.

[0051] [Verification of the Effect of the Modified Example] Next, the verification of the effect of the modified example performed by simulation will be described with reference to FIGS. 10 to 13.

[0052] FIG. 10 shows the motor rotation speed ω rm , d-axis current i d , q-axis current i q and three-phase current UVW- phase when the dead time is switched during motor drive in the power conversion device according to the conventional example. As shown in FIG. 10, in the power conversion device according to the conventional example, the dead time was switched from 3 μs to 1.5 μs at 50 ms. In the conventional example, immediately after the switching of the modulation method, a steep fluctuation regarded as a switching shock occurred in the q-axis current i q and the three-phase current W- phase and propagated up to the motor rotation speed ω rm .

[0053] FIG. 11 shows the motor rotation speed ω rm , d-axis current i d , q-axis current i q and three-phase current UVW- phase when the dead time is switched during motor drive in the power conversion device 1 according to the present embodiment. As shown in FIG. 11, in the power conversion device according to the modified example, the dead time was switched from 3 μs to 1.5 μs at 50 ms in the same manner as in the conventional example. In the modified example, it was confirmed that the steep fluctuations between the q-axis current i q and the three-phase current W- phase seen in the conventional example were suppressed, and the fluctuation of the motor speed was also suppressed.

[0054] FIG. 12 shows the d-axis voltage (the output voltage V of the I control element on the d-axis) when the dead time is switched during motor driving in a conventional power conversion device. d i ), the q-axis voltage (the output voltage V of the I control element on the q-axis) q i ) and the dq-axis voltage command values V d ref , V q ref . As shown in FIG. 12, in the conventional example, although the output voltage V of the I control element on the q-axis q i varies at the time of dead time switching and responds to compensate for it, the slope indicated by the change in the output voltage V q i is large.

[0055] FIG. 13 shows the d-axis voltage (the output voltage V of the I control element on the d-axis) when the dead time is switched during motor driving in a power conversion device according to a modified example. d i ), the q-axis voltage (the output voltage V of the I control element on the q-axis) q i and the compensation voltage V q mod ) and the dq-axis voltage command values V d ref , V q ref . As shown in FIG. 13, under the simulation conditions for verifying the modified example, at the time of dead time switching, the compensation voltage command value V q i is instantaneously added only to the output voltage V of the I control element 122a on the q-axis. As a result, the change in the output voltage V of the I control element 122a on the q-axis q mod is suppressed, avoiding the switching shock. Also, the output voltage V of the I control element 122a on the q-axis q i compensates for the dead time error component in accordance with the attenuation of the compensation voltage command value V q i . q mod

Explanation of Signs

[0056] 1 Power conversion device 2 Motor 3 Inverter 4A~4F Switching elements 5U, 5V, 5W Windings 8 Battery 100 Control device 101, 102 Subtractors 103~106 Adders 120 Current control unit 121, 122 PI control units 121a, 122a I control elements 121b, 122b P control elements 130 Non-interference control unit 140 Coordinate conversion unit 150 Modulation method switching unit 160 PWM signal generation unit 170 Gate driver 180 Error component compensation unit

Claims

1. A power conversion device comprising: a current control unit that calculates and outputs a voltage command value from a current command value of a motor; a PWM signal generation unit that generates a PWM signal based on the voltage command value; an inverter that drives the motor by switching based on the PWM signal, wherein: at least one of a modulation method switching unit that switches the modulation method of the inverter and a dead time setting unit that designates an arbitrary dead time for the inverter; an error component compensation unit that adds a compensation voltage command value to the voltage command value when the modulation method is switched or the dead time is changed; the error component compensation unit cancels an error component of the voltage command value caused by switching of the modulation method or change of the dead time with the compensation voltage command value; A power conversion device characterized by the above.

2. The error component compensation unit according to claim 1, wherein the error component compensation unit compensates for an error component generated by a delay due to an integral element of the current control unit when the modulation method is switched or the dead time is changed. The power conversion device according to claim 1, characterized by the above.

3. The error component compensation unit according to claim 1, wherein after compensating for the error component with the compensation voltage command value, the error component compensation unit attenuates the compensation voltage command value over time. The power conversion device according to claim 1, characterized by the above.

4. The modulation method switching unit according to claim 1, wherein the modulation method switching unit switches between a three-phase modulation method and a two-phase modulation method. The power conversion device according to claim 1, characterized by the above.

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