Power Conversion Device

Abstract

A power conversion device (100) comprises a rectifier unit (2) that converts a three-phase alternating-current voltage into a direct-current voltage, a power converter (6) that converts the direct-current voltage into an alternating-current voltage to control a motor (7), and a control unit (50), wherein the control unit (50) derives, on the basis of a detection value of the three-phase alternating-current voltage, a pulsation included in the direct-current voltage obtained through the full-wave rectification of the three-phase alternating-current voltage as a predicted pulsating voltage value (ΔVdc*), derives a pulsation included in the direct-current voltage as an actual pulsating voltage measurement value (ΔVdc) on the basis of the detection value of the direct-current voltage, and corrects at least one among a D-axis voltage command (Vd*) or a Q-axis voltage command (Vq*) by means of a voltage correction command (ΔVd*, ΔVq*) generated so as to reduce a deviation between the predicted pulsating voltage valve (ΔVdc*) and the actual pulsating voltage measurement value (ΔVdc).

Description

[Technical Field]

[0001] The present application relates to a power conversion device. [Background technology]

[0002] A power conversion device used to drive an AC motor is one that includes a rectifier that rectifies AC power input from a three-phase AC power source such as a commercial power source into DC power, and an inverter that converts this DC power into AC power suitable for the AC motor and outputs it to the AC motor.It is generally known that when a three-phase AC voltage is rectified by a rectifier made of diodes, pulsation occurs in the rectified DC voltage at a frequency six times the frequency of the AC power source. A smoothing capacitor is provided in the DC link connecting the DC output side of the rectifier and the DC input side of the inverter. This smoothing capacitor forms an LC resonant circuit with the inductance component of the AC power supply. When the resonant frequency of this LC resonant circuit is six times the power supply frequency, the DC voltage in the DC link pulsates significantly. In particular, when a small-capacity film capacitor is used as the smoothing capacitor for the purpose of downsizing the device, significant DC voltage pulsation and power supply current distortion often occur, making continuous operation of the power conversion device difficult. To solve these problems, an inverter device as a power conversion device with the following configuration has been disclosed.

[0003] That is, a conventional inverter device includes an inductor connected between a diode bridge serving as a rectifier and an inverter unit, and a capacitor connected to the input terminal of the inverter unit. The control unit of the inverter unit multiplies the voltage across the inductor detected by a voltage detector by a gain (k). The voltage across the inductor multiplied by the gain (k) is subtracted from the signal from the PI controller or the initial value of the voltage control rate (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-29151 A (Figs. 18 and 19) Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional inverter devices such as those described above, the voltage across the inductor connected between the diode bridge and the smoothing capacitor is detected and multiplied by a gain (k), and then the current command signal from the PI controller or the modulation factor, which is the voltage control factor, is corrected. This can improve pulsation in the power supply current and DC voltage. However, with this correction method based on the detected voltage across the inductor, the effectiveness of the control to suppress pulsation decreases as the impedance on the power supply side increases. Furthermore, correcting the current command is difficult to reduce pulsation unless the current control system is designed for extremely high response. Furthermore, in addition to pulsation at a frequency six times the power supply frequency, high-order pulsations exceeding the sixth order, such as those caused by the rectification operation of the rectifier and the resonance of the LC resonant circuit, are also superimposed on the DC link voltage. The above-mentioned conventional correction methods have the drawback of being ineffective in suppressing such pulsation and also in suppressing distortion in the power supply current.

[0006] The present application discloses a technique for solving the above-mentioned problems, and aims to provide a power conversion device that can effectively suppress pulsations occurring in the power supply current and the DC link section. [Means for solving the problem]

[0007] The power conversion device disclosed in the present application comprises: a rectification unit that converts an input three-phase AC voltage into a DC voltage and outputs the DC voltage to a DC bus; a power converter that converts the DC voltage on the DC bus converted by the rectifier unit into an AC voltage to control an electric motor; a control unit that controls the power converter, The control unit converting a current flowing through the electric motor into a D-axis current and a Q-axis current on a two-axis orthogonal coordinate system, generating a D-axis voltage command so that the D-axis current follows the D-axis current command, and generating a Q-axis voltage command so that the Q-axis current follows the Q-axis current command, and controlling the power converter based on the generated D-axis voltage command and Q-axis voltage command; deriving, based on the detected values of the three-phase AC voltage, a pulsation contained in the DC voltage obtained by full-wave rectifying the three-phase AC voltage as a pulsation voltage predicted value, and deriving, based on the detected values of the DC voltage, the pulsation contained in the DC voltage as a pulsation voltage actual measurement value; correcting at least one of the D-axis voltage command and the Q-axis voltage command with a voltage correction command generated so as to reduce a deviation between the predicted pulsation voltage value and the actual pulsation voltage value; This is what we have done. [Effects of the Invention]

[0008] According to the power conversion device disclosed in the present application, pulsation occurring in the power supply current and the DC link section can be effectively suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing a schematic configuration of a power conversion device according to a first embodiment. [Figure 2] 2 is a control block diagram showing the internal configuration of a control unit of the power conversion device according to the first embodiment. FIG. [Figure 3] 2 is a control block diagram showing the configuration of a pulsation suppression control unit of the power conversion device according to the first embodiment. FIG. [Figure 4] 2 is a diagram illustrating an example of a hardware configuration of a control unit as a control device according to the first embodiment. FIG. [Figure 5] 5A and 5B are diagrams showing operational waveforms of a power conversion device of a comparative example. [Figure 6] 6A and 6B are diagrams illustrating operational waveforms of the power conversion device according to the first embodiment. [Figure 7] 7A and 7B are diagrams illustrating operational waveforms of the power conversion device according to the first embodiment. [Figure 8] FIG. 10 is a control block diagram showing the internal configuration of a pulsation suppression control unit of a power conversion device according to a second embodiment. [Figure 9] FIG. 10 is a control block diagram showing the internal configuration of a pulsation suppression control unit of a power conversion device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Embodiment 1 A power conversion device 100 according to the first embodiment will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a power conversion device 100 according to the first embodiment. The power conversion device 100 is provided between a three-phase AC power source 1 such as a commercial power source and a motor 7 serving as an electric motor, and converts AC power from the AC power source 1 into DC power, converts the converted DC power back into AC power, and supplies it to the motor 7 serving as a load. The power conversion device 100 includes a rectifier 2 as a rectifying unit, a DC link unit 5, an inverter 6 as a power converter, and a control unit 50.

[0011] The rectifier 2 is made up of diodes, and performs full-wave rectification on the three-phase AC voltage input from the three-phase AC power supply 1 to convert it into a DC voltage. The DC link unit 5 is provided between the rectifier 2 and the inverter 6, and supplies the DC power converted by the rectifier 2 to the inverter 6. The DC link unit 5 has positive and negative DC buses P and N that connect the DC output side of the rectifier 2 and the DC input side of the inverter 6, a DC reactor 3 connected in series to the positive DC bus P, and a smoothing capacitor 4 provided between the positive and negative DC buses P and N.

[0012] The inverter 6 has six semiconductor elements (not shown), and these semiconductor elements are driven by a drive signal G from the control unit 50 to convert the DC voltage from the DC link unit 5 into an AC voltage with a variable voltage and variable frequency, thereby controlling the motor 7 at any rotation speed.

[0013] The power conversion device 100 further includes a voltage sensor 10 that detects a line voltage Vab of the AC voltage on the AC power supply 1 side, a voltage sensor 11 that detects a DC bus voltage Vdc between DC buses P and N, and a load current sensor 12 that detects load currents Iu, Iv, and Iw flowing through each phase of the motor 7.

[0014] Inputs to the control unit 50 include information on the DC bus voltage Vdc, information on the load currents Iu, Iv, and Iw flowing through the motor 7, and information on the angular velocity ω of the motor 7, as well as information on the line voltage Vab on the AC power source 1 side detected by a voltage sensor 10, which will be described in detail later, and is used to suppress pulsation occurring in the AC power source 1 and the DC link unit 5. The control unit 50 generates a drive signal G for controlling the inverter 6 based on these detected values that are input.

[0015] Although the load current sensor 12 is shown as one that acquires all three-phase load currents Iu, Iv, and Iw, the current of the remaining phase can be calculated by detecting the current of two of the three phases, so it is sufficient to actually detect only two phases. Alternatively, a current sensor can be installed on the negative input side of the semiconductor element of the inverter 6, and the three-phase currents can be calculated by sampling multiple times.

[0016] It is common to insert a DC reactor 3 into the DC bus P to reduce harmonic noise, but in the power conversion device 100 of this embodiment, it is not necessarily required to use the DC reactor 3, and therefore it can be omitted.

[0017] Next, the control unit 50 will be described. 2 is a control block diagram showing the internal configuration of the control unit 50 of the power conversion device 100 according to the embodiment 1. In this embodiment, a control block for performing vector control is employed.

[0018] The control unit 50 includes PI control units 22, 23, and 24 that perform feedback control based on the input deviation, a coordinate conversion unit 25 that converts the two-phase D-axis voltage command Vd* and Q-axis voltage command Vq* into three-phase voltage commands Vu*, Vv*, and Vw*, a PWM control unit 26 that generates a drive signal G that drives the semiconductor elements of the inverter 6 based on the converted voltage commands Vu*, Vv*, and Vw*, a pulsation suppression control unit 30 that performs control to suppress pulsation in the power supply current and the DC link unit 5, and subtractors 21A, 21B, 21C, 21D, and 21E.

[0019] In the control unit 50, the detected load currents Iu, Iv, Iw of the motor 7 are converted by a converter (not shown) into a D-axis current Id and a Q-axis current Iq on a two-axis coordinate system of orthogonal axes. Then, the deviation between the angular velocity command ω*, which is a velocity command, and the angular velocity ω estimated by position sensorless control is calculated by a subtractor 21A, and the PI control unit 22 performs PI control so as to reduce this calculated deviation, thereby deriving the Q-axis current command Iq*.

[0020] The deviation between this Q-axis current command Iq* and the detected Q-axis current Iq is calculated by a subtractor 21B, and the PI control unit 23 performs PI control so that this calculated deviation becomes small, i.e., so that the Q-axis current Iq follows the Q-axis current command Iq*, thereby calculating a Q-axis voltage command Vq*. Similarly, for the D-axis, the deviation between the D-axis current command Id* and the detected D-axis current Id is calculated by a subtractor 21D, and the PI control unit 24 performs PI control so that this calculated deviation becomes small, i.e., so that the D-axis current Id follows the D-axis current command Id*, thereby calculating the D-axis voltage command Vd*.

[0021] Furthermore, a D-axis voltage correction command ΔVd* as a voltage correction command and a Q-axis voltage correction command ΔVq* as a voltage correction command are calculated in the pulsation suppression control unit 30. Details of this pulsation suppression control unit 30 will be described later. Then, a subtractor 21E subtracts the D-axis voltage correction command ΔVd* from the D-axis voltage command Vd* to correct the D-axis voltage command Vd*. Also, a subtractor 21C subtracts the Q-axis voltage correction command ΔVq* from the Q-axis voltage command Vq* to correct the Q-axis voltage command Vq*. The corrected D-axis voltage command Vd* and Q-axis voltage command Vq* are input to a coordinate conversion unit 25.

[0022] The coordinate conversion unit 25 converts the D- and Q-axis rotation coordinates into the U-, V-, and W-stationary coordinates, which are the actual output voltage commands. The voltage commands Vu*, Vv*, and Vw* for each phase obtained by the coordinate conversion are input to the PWM control unit 26. The PWM control unit 26 generates a drive signal G for the semiconductor elements of the inverter 6 based on the input voltage commands Vu*, Vv*, and Vw* for each phase.

[0023] It should be noted that the coordinate conversion unit 25 and the PWM control unit 26 are techniques used in general inverter control, and therefore detailed explanations thereof will be omitted here. Furthermore, although the control block described here does not describe the DQ axis non-interference control that suppresses interference between the D and Q axes, the DQ axis non-interference control may be executed before correcting the voltage commands using the D axis voltage correction command ΔVd* and the Q axis voltage correction command ΔVq* from the pulsation suppression control unit 30.

[0024] Next, the pulsation suppression control unit 30, which is a main part of the power conversion device 100 of this embodiment, will be described in detail. FIG. 3 is a control block diagram showing the configuration of the pulsation suppression control unit 30 of the power conversion device 100 according to the first embodiment.

[0025] The pulsation suppression control unit 30 performs pulsation suppression control to suppress voltage pulsation and current distortion occurring from the AC power supply 1 to the DC link unit 5 . The pulsation suppression control unit 30 includes an amplitude / phase calculation unit 31, a pulsation voltage command calculation unit 32, a D-axis feedback control unit 35 that performs feedback control based on the input deviation, a Q-axis feedback control unit 36, gain adjustment units 37 and 38, and high-pass filters 33A and 33B.

[0026] The pulsation suppression control unit 30 receives two inputs: the detected line voltage Vab on the AC power supply 1 side and the detected DC bus voltage Vdc. The pulsation suppression control unit 30 also receives two outputs: a D-axis voltage correction command ΔVd* and a Q-axis voltage correction command ΔVq*.

[0027] The pulsation suppression control performed by the pulsation suppression control unit 30 will be described below in order, starting from the input of the line voltage Vab. First, the amplitude / phase calculation unit 31 calculates the amplitude Vs and phase θs from the analog voltage signal. A method known as ePLL (enhanced phase looked loop) can be used as a calculation method. Alternatively, the amplitude Vs and phase θs of the AC voltage may be derived using the zero-cross signal of the line voltage Vab. If only negative to positive zero-crossings are detected, a zero-crossing signal is input once per power supply cycle. The phase angle can be calculated using the time T1 between zero-crossings and the time T2 between zero-crossings in the previous cycle, as shown in equation (1) below. The unit is radians [rad].

[0028]

number

[0029] The amplitude Vs can be calculated by integrating the absolute value of the power line voltage Vab between zero crossings and taking the average value, as shown in the following equation (2).

[0030]

number

[0031] In equation (2), π / 2 is a coefficient that converts the average value to the effective value. In this way, the amplitude Vs and phase θs can be derived from the zero-crossing signal by using equations (1) and (2) above.

[0032] It is possible to calculate the amplitude Vs and phase θs using only the zero-crossing signal, without detecting the line voltage Vab in analog form. In this case, the amplitude Vs can be calculated using the average value Vdcave of the DC bus voltage using the following equation (3).

[0033]

number

[0034] K1 is the gain, and normally it should be set to "K1 = π / 3". If the resistance component such as the power supply impedance is large, you can make fine adjustments by increasing K1 slightly. The amplitude Vs and phase θs of the AC voltage calculated by the amplitude / phase calculation unit 31 are input to a pulsating voltage command calculation unit 32 .

[0035] The pulsating voltage command calculation unit 32 can restore the phase voltages Va, Vb, and Vc of the three-phase AC power supply 1 using the input amplitude Vs and phase θs, respectively, as shown in the following equations (4) to (6).

[0036]

number

[0037]

number

[0038]

number

[0039] Then, for the restored phase voltages Va, Vb, and Vc of the three-phase AC power supply 1, the DC bus voltage predicted value Vdc* can be derived by subtracting the minimum phase voltages Va, Vb, and Vc for each phase from the maximum phase voltages Va, Vb, and Vc for each phase. This can be expressed as equation (7).

[0040]

number

[0041] Furthermore, by removing the DC component of the DC bus voltage predicted value Vdc* by the high-pass filter 33A, it is possible to calculate the pulsating voltage predicted value ΔVdc* from which the AC component is extracted. This predicted ripple voltage value ΔVdc* is a predicted value of the AC component contained in the DC bus voltage between DC buses P and N, which is obtained by full-wave rectifying the three-phase AC voltage, and is a pulsation that oscillates at a frequency six times the frequency of the AC voltage of AC power source 1.

[0042] Next, the DC bus voltage Vdc input at the bottom of FIG. 3 will be explained in order. The DC bus voltage Vdc detected by the voltage sensor 11 is passed through a high-pass filter 33B to remove the DC component, and the actual AC component on the DC buses P, N is extracted to derive a ripple voltage actual measurement value ΔVdc.

[0043] The reason for providing the high-pass filters 33A and 33B is that if a DC component remains in the derived predicted pulsating voltage value ΔVdc* and measured pulsating voltage value ΔVdc, it may interfere with the current control shown in Fig. 2, causing the motor control itself to malfunction. For this reason, the insertion of the high-pass filters 33A and 33B is essential. Then, the deviation ΔVerr is obtained by subtracting the actual pulsating voltage value ΔVdc from the predicted pulsating voltage value ΔVdc* by a subtractor 34.

[0044] Here, the measured ripple voltage value ΔVdc, which is the actual measurement value of the actual ripple in the DC link unit 5, has a higher wave height than the predicted ripple voltage value ΔVdc*, which oscillates at a frequency six times the power supply frequency predicted by calculation. Furthermore, this measured ripple voltage value ΔVdc has a waveform that includes higher-order ripples with frequencies exceeding six times the power supply frequency, which are caused by the actual rectification operation of the rectifier 2 and resonance of the LC resonant circuit formed in the actual circuit. Therefore, the deviation ΔVerr, which is derived by subtracting the measured ripple voltage value ΔVdc from the predicted ripple voltage value ΔVdc*, has a waveform that includes sixth-order ripples and higher-order ripples exceeding sixth-order.

[0045] Then, in order to reduce this deviation ΔVerr, that is, to reduce pulsations including sixth-order pulsations and higher-order pulsations beyond sixth-order, feedback control is performed in the D-axis feedback control unit 35 to derive the control variable 35C for the D-axis. Then, in the gain adjustment unit 37, the controlled variable 35C is multiplied by a gain 37G (Vdc / Id) as a first gain that is proportional to the DC bus voltage Vdc and inversely proportional to the D-axis current Id to calculate a D-axis voltage correction command ΔVd*.

[0046] Feedback control usually uses proportional (P) control. If the control band is increased, proportional-differential (PD) control may be used. The P control can be expressed by the following equation (8), and the PD control can be expressed by the following equation (9).

[0047]

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[0048]

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[0049] In the above equations (8) and (9), Kp is a proportional gain as a control gain, and Kd is a differential gain as a control gain. Instead of performing PD control, a configuration may be adopted in which phase lead control performed by a phase lead compensation filter and P control are performed. This phase lead control is a control that advances the control amount derived by P control by a set phase amount, and by compensating for the control delay that occurs depending on the control cycle in which feedback control is performed, the pulsation suppression effect can be improved.

[0050] The same is true for the Q axis, and feedback control is performed in the feedback control unit 36 to calculate the control amount 36C in order to reduce this deviation ΔVerr, i.e., to reduce pulsations including sixth-order pulsations and higher-order pulsations than sixth-order. Then, in the gain adjustment unit 38, the controlled variable 36C is multiplied by a gain 38G (Vdc / Iq) as a first gain that is proportional to the DC bus voltage Vdc and inversely proportional to the Q-axis current Iq to calculate a Q-axis voltage correction command ΔVq*.

[0051] When the DC bus voltage Vdc increases, the D-axis voltage correction command ΔVd* and the Q-axis voltage correction command ΔVq* correct the d-axis voltage and the q-axis voltage to increase in order to increase the output power of the inverter 6. When the DC bus voltage Vdc decreases, the D-axis voltage correction command ΔVd* and the Q-axis voltage correction command ΔVq* correct the d-axis voltage and the q-axis voltage to decrease in order to decrease the output power of the inverter 6. In this way, pulsation suppression control is executed to suppress pulsation in the power supply current and the DC link unit 5.

[0052] Furthermore, the magnitudes of the control amounts 35C and 36C in this embodiment are adjusted by gains 37G and 38G, respectively, which serve as first gains. Such gains 37G and 38G have the effect of making the control effect of the pulsation suppression control constant. The following description will be given taking the gain 37G as an example.

[0053] First, let the output power of the inverter 6 be Pout+ΔPout. The DC component of the output power is Pout, and the pulsating power of the output power is ΔPout. Pout is the DC power generated by normal motor control, and ΔPout is the pulsating power generated to suppress resonance. The output power Pout+ΔPout can be calculated using the following equation (10).

[0054]

number

[0055] where Vd is the DC component of the D-axis voltage, ΔVd is the AC component of the D-axis voltage, Vq is the DC component of the Q-axis voltage, ΔVq is the AC component of the Q-axis voltage, Id is the DC component of the D-axis current, ΔId is the AC component of the D-axis current, Iq is the DC component of the Q-axis current, and ΔIq is the AC component of the Q-axis current.

[0056] Here, the DC component power Pout can be expressed as equation (11).

[0057]

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[0058] ΔPout can be derived from equations (10) and (11), resulting in equation (12).

[0059]

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[0060] In this equation (12), the term ΔV*I, which is the product of the voltage AC component ΔV and the current DC component I, is dominant. Because ΔI does not change significantly even if ΔV is changed due to the motor characteristics, it is possible to approximate by ignoring the ΔI term. This approximation results in equation (13).

[0061]

number

[0062] Next, the input current of the inverter 6 is calculated. If the input power of the inverter 6 is Pin+ΔPin, it can be expressed by the following equation (14).

[0063]

number

[0064] Here, Vdc is the DC voltage component of the DC bus voltage, ΔVdc is the AC component of the DC bus voltage, Idc is the DC component of the inverter input current, and ΔIdc is the AC component of the inverter input current.

[0065] Here, the DC component power Pin can be expressed as the following equation (15).

[0066]

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[0067] ΔPin can be derived from equations (14) and (15), resulting in the following equation (16).

[0068]

number

[0069] Here, if the inverter 6 is properly controlled, the term ΔVdc of the oscillation component of the bus voltage becomes small and the term Vdc*ΔIdc becomes dominant, so that the following equation (17) can be obtained by approximation.

[0070]

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[0071] By placing ΔIdc on the left side and rearranging, it can be expressed as equation (18).

[0072]

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[0073] Since ΔPin and ΔPout are equal, equation (19) can be derived by substituting equation (13) for ΔPin in equation (18).

[0074]

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[0075] From the results of equation (19), it can be seen that if a pulsating voltage ΔVd is intentionally applied to the D-axis to suppress resonance, a pulsating input current ΔIdc is obtained that is proportional to the D-axis current Id and inversely proportional to the DC bus voltage Vdc for this applied pulsating voltage ΔVd. Therefore, it can be seen that if Id and Vdc change, the control amount of ΔIdc also changes.

[0076] Therefore, to keep ΔIdc constant, in the case of the D-axis, it is sufficient to multiply the control variable 35C that imparts a pulsating voltage to the D-axis voltage command Vd* by a gain 37G so that the D-axis voltage command Vd* is proportional to the DC bus voltage Vdc and inversely proportional to the D-axis current Id, as in the case of a gain 37G. Similarly, in the case of the Q-axis, it is sufficient to multiply the control variable 36C that imparts a pulsating voltage to the Q-axis voltage command Vq* by a gain 38G so that the Q-axis voltage command Vq* is proportional to the DC bus voltage Vdc and inversely proportional to the Q-axis current Iq, as in the case of a gain 38G.

[0077] The values of the DC bus voltage Vdc, the D-axis current Id, and the Q-axis current Iq used for the gains 37G and 38G may be average values when the motor 7 is being driven, but are not limited to this. For example, the gains 37G and 38G may be configured so that their values are updated according to the detected values of the DC bus voltage Vdc, the D-axis current Id, and the Q-axis current Iq when the motor 7 is being driven, rather than being predetermined fixed values. The gain 37G adjusts the control amount in the feedback control so that it is proportional to the detected DC bus voltage Vdc and inversely proportional to the D-axis current Id. By adjusting the control amount in this way, even if Vdc and Id change, the control amount of ΔIdc can be kept constant, and the control effect can be maintained more constant. This suppresses variations in the control effect, such as insufficient control amount and pulsation depending on the conditions, and more efficiently suppresses resonance.

[0078] Also, although the configuration has been shown in which gain 37G is inversely proportional to the D-axis current Id and gain 38G is inversely proportional to the Q-axis current Iq, the present invention is not limited to this. As expressed in the above formula (19), as long as both gains 37G and 38G are proportional to at least the DC bus voltage Vdc, the effect of keeping ΔIdc constant to a certain extent can be obtained even if they are not configured to be inversely proportional to the D-axis current Id and the Q-axis current Iq.

[0079] Alternatively, only one of the D-axis voltage command Vd* and the Q-axis voltage command Vq* may be corrected by the voltage correction command. In this case, if there is no need to correct the D-axis voltage command Vd*, control may be performed so that the D-axis voltage correction command ΔVd* is invalid. Alternatively, when performing flux-weakening control or the like and operating with current flowing in the d-axis in addition to the q-axis current, it is advisable to correct both the D-axis voltage command Vd* and the Q-axis voltage command Vq* using the voltage correction command. This makes it possible to suppress resonance even when the motor 7 rotates at high speed, ensuring sound operation of the motor 7 over a wide speed range.

[0080] The hardware configuration of the control unit 50 will now be described. As will be explained below with reference to the drawings, the control unit 50 is generally configured with a microcomputer or the like that executes the control blocks shown in FIGS. FIG. 4 is a diagram showing an example of a hardware configuration of the control unit 50 as the control device according to the first embodiment.

[0081] 3, an example of hardware of the control device is configured with a processor 51 and a storage device 52. The storage device 52 includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory, both of which are not shown. Also, an auxiliary storage device such as a hard disk may be provided instead of flash memory. Processor 51 executes a program input from storage device 52. In this case, the program is input from the auxiliary storage device to processor 51 via a volatile storage device. Processor 51 may output data such as calculation results to a volatile storage device of storage device 52, or may store data in the auxiliary storage device via the volatile storage device.

[0082] Below, we will use the diagram to confirm the effectiveness of pulsation suppression control using actual operating waveforms. FIG. 5 is a diagram showing operational waveforms of a power conversion device of a comparative example in which pulsation suppression control is not performed. Figure 5A shows the power supply current waveform when operated under a low torque load of Id = 0 A and Iq = 30 A. Figure 5B shows the power supply current waveform when operated under a high torque load of Id = 0 A and Iq = 100 A. Both of them generate large pulsations, which confirms that they are resonating.

[0083] FIG. 6 is a diagram showing operational waveforms of the power conversion device 100 of this embodiment that performs pulsation suppression control. Figure 6A shows the power supply current waveform when operated under a low torque load of Id = 0 A and Iq = 30 A. Figure 6B shows the power supply current waveform when operated under a high torque load of Id = 0 A and Iq = 100 A. The feedback control in the pulsation suppression control unit 30 is P control only, and the Q-axis feedback gain is Kp=0.3. Since the D-axis has Id=0 A, compensation is ineffective, so no feedback is performed in this waveform example. That is, in this waveform example, the power conversion device 100 corrects only the Q-axis voltage command Vq* using the Q-axis voltage correction command ΔVq*. Considering both the waveforms in FIG. 6A and FIG. 6B, it is clear that the pulsation has been significantly reduced in both cases, confirming the effectiveness of the pulsation suppression control.

[0084] FIG. 7 shows the operating waveforms when fixed gains of 37G and 38G are applied. Figure 7A shows the power supply current waveform when operating under a low torque load of Id = 0 A and Iq = 30 A. If the gain is adjusted to obtain the same waveform as Figure 6A under these conditions, operating under a high torque load of Id = 0 A and Iq = 100 A will result in the waveform shown in Figure 7B, and the power supply current waveform may oscillate. This confirms that gains of 37G and 38G are important components for stable operation under various operating conditions.

[0085] Because the gain 37G is configured to divide by the D-axis current Id, the D-axis voltage correction command ΔVd* becomes excessively large when the value of the D-axis current Id is small. In that case, clamp control, as described below, can be performed to prevent the value of the D-axis current Id from becoming too small, or control can be performed to disable the D-axis voltage correction command ΔVd* when the D-axis current Id is 0 or infinitesimally small. The same applies to the Q-axis current Iq of the gain 38G.

[0086] When clamp control is performed, for example, when the D-axis current Id or the Q-axis current Iq falls within a set first value range, the value of the D-axis current Id used for gain 37G and the value of the Q-axis current Iq used for gain 38G can be adjusted to exceed the first value range. For example, if the first value range is set to a range from -10 to +10, clamp control is performed in which if the D-axis current Id is -2, the value is clamped to -10.1, and if the Q-axis current Iq is +3, the value is clamped to +10.1. In particular, when the motor 7 is rotating at low or medium speed, Id is often controlled at 0 A, and this phenomenon applies.

[0087] The power conversion device of this embodiment configured as described above has the following features: a rectification unit that converts an input three-phase AC voltage into a DC voltage and outputs the DC voltage to a DC bus; a power converter that converts the DC voltage on the DC bus converted by the rectifier unit into an AC voltage to control an electric motor; a control unit that controls the power converter, The control unit converting a current flowing through the electric motor into a D-axis current and a Q-axis current on a two-axis orthogonal coordinate system, generating a D-axis voltage command so that the D-axis current follows the D-axis current command, and generating a Q-axis voltage command so that the Q-axis current follows the Q-axis current command, and controlling the power converter based on the generated D-axis voltage command and Q-axis voltage command; deriving, based on the detected values of the three-phase AC voltage, a pulsation contained in the DC voltage obtained by full-wave rectifying the three-phase AC voltage as a pulsation voltage predicted value, and deriving, based on the detected values of the DC voltage, the pulsation contained in the DC voltage as a pulsation voltage actual measurement value; correcting at least one of the D-axis voltage command and the Q-axis voltage command with a voltage correction command generated so as to reduce a deviation between the predicted pulsation voltage value and the actual pulsation voltage value; It is something.

[0088] In this way, the control unit derives, based on the detected three-phase AC voltage, the pulsation contained in the DC voltage obtained by full-wave rectifying the three-phase AC voltage as a pulsation voltage prediction value. Furthermore, based on the detected DC voltage of the DC bus, the control unit derives the pulsation contained in the DC voltage as a pulsation voltage measurement value and calculates the deviation between the pulsation voltage prediction value and the pulsation voltage measurement value. This calculated deviation includes a sixth-order harmonic pulsation component resulting from the difference in wave height between the pulsation voltage prediction value and the pulsation voltage measurement value, as well as higher-order pulsations (greater than sixth order) resulting from the rectification operation of the rectifier and the resonance of the LC resonant circuit contained in the pulsation voltage measurement value. The control unit generates a voltage correction command to reduce this calculated deviation and corrects at least one of the D-axis voltage command and the Q-axis voltage command. This effectively suppresses pulsation in the power supply current and pulsation on the DC bus, including higher-order noise, enabling stable and sound continuous operation of the inverter.

[0089] In particular, since the voltage correction command is generated based on the deviation between the predicted ripple voltage value and the actual measured ripple voltage value to reduce this deviation, ripple can be effectively suppressed without relying on the impedance on the power supply side, and the control amount can be reduced, resulting in good tracking performance to the target value. As a result, high-order noise exceeding the sixth order can also be effectively suppressed. Furthermore, because the configuration corrects the D-axis and Q-axis voltage commands rather than the current command, pulsation can be effectively suppressed even when the current control system is not designed for high response, and high-order noise can be effectively reduced.

[0090] In addition, in the power conversion device of the present embodiment configured as described above, The control unit deriving the ripple voltage prediction value by subtracting the minimum phase voltage for each phase from the maximum phase voltage for each phase of the three-phase AC voltage; It is something.

[0091] In this way, a predicted value of the pulsation contained in the DC voltage after full-wave rectification is derived from the phase voltages of the three-phase AC voltage. This makes it possible to accurately derive a predicted value of the pulsation at six times the power frequency, excluding pulsation caused by the rectification operation of the rectifier that occurs in an actual circuit and pulsation caused by LC resonance in the LC circuit formed in an actual circuit.

[0092] In addition, in the power conversion device of the present embodiment configured as described above, The control unit performing feedback control using a set control gain to derive a control amount so as to reduce the deviation, and multiplying the control amount by a first gain configured to be proportional to the voltage of the DC bus to generate the voltage correction command; It is something.

[0093] In this way, by performing feedback control, it is possible to improve the control responsiveness to the target value and effectively suppress high-order noise. Furthermore, by using the first gain configured in proportion to the voltage of the DC bus, the D-axis voltage command and the Q-axis voltage command can be corrected with an appropriate control amount, preventing over-correction or, conversely, under-correction. This enables the power converter to operate stably and soundly continuously. Furthermore, it can accurately suppress small amplitude pulsations when the resonant frequency does not match six times the power supply frequency.

[0094] In addition, in the power conversion device of the present embodiment configured as described above, The control unit generating the voltage correction command for correcting the D-axis voltage command by multiplying the controlled variable by the first gain configured inversely proportional to the D-axis current; The voltage correction command for correcting the Q-axis voltage command is generated by multiplying the controlled variable by the first gain configured inversely proportional to the Q-axis current. It is something.

[0095] By using the first gain configured in this way, it is possible to correct the D-axis voltage command and the Q-axis voltage command with a more appropriate control amount, to keep the control amount of ΔIdc constant, and to maintain a constant control effect. In this way, it is possible to stably eliminate pulsation occurring in the power supply current and the DC link, and to continuously operate the power converter stably and soundly.

[0096] In addition, in the power conversion device of the present embodiment configured as described above, At least one value of the DC bus voltage, the D-axis current, and the Q-axis current, which constitute the first gain, is updated according to a detected value during operation of the power converter. It is something.

[0097] This makes it possible to suppress insufficient control amount and variations in control effect even under various operating conditions such as fluctuations in load current, and to efficiently suppress pulsation.

[0098] In addition, in the power conversion device of the present embodiment configured as described above, The control unit When the D-axis current or the Q-axis current falls within a set first value range, performing clamp control to adjust the value of the D-axis current or the Q-axis current used in the first gain so that the value exceeds the first value range; It is something.

[0099] This makes it possible to prevent excessive control input under various operating conditions, and further to operate the power converter continuously in a stable and sound manner.

[0100] Embodiment 2 Hereinafter, the second embodiment of the present invention will be described with reference to the drawings, focusing on the differences from the first embodiment. The same parts as those in the first embodiment will be assigned the same reference numerals and the description thereof will be omitted. The circuit configuration of the power conversion device of the second embodiment is the same as that of the first embodiment, as shown in Fig. 1. The configuration of the control unit 50 of the second embodiment is also the same as that of the first embodiment, as shown in Fig. 2, but the internal configuration of the pulsation suppression control unit 30 is different.

[0101] FIG. 8 is a control block diagram showing the internal configuration of the pulsation suppression control unit 230 of the power conversion device according to the second embodiment. The pulsation suppression control section 230 of the second embodiment differs from the pulsation suppression control section 30 of the first embodiment in that it includes a feedback control section 235, a gain adjustment section 237, and positive / negative determination sections 239d and 239q as sign functions.

[0102] In particular, unlike the first embodiment, the feedback control unit 235 for suppressing resonance is characterized in that the D-axis and Q-axis are configured identically, and a control variable 235C is derived that is commonly used to generate a D-axis voltage correction command ΔVd* and a Q-axis voltage correction command ΔVq* that correct the D-axis voltage command Vd* and the Q-axis voltage command Vq*, respectively. The feedback control in the feedback control unit 235 normally uses proportional (P) control. If the control band is increased, proportional-differential (PD) control may be used. Instead of PD control, a configuration may be adopted in which proportional (P) control is performed in combination with control using a phase lead compensation filter that advances the control amount by a set phase.

[0103] In this way, the gain adjuster 237 multiplies the control variable 235C used in common for the D axis and the Q axis by the gain 237G (Vdc / (|Id|+|Iq|)) as the first gain used in common for the D axis and the Q axis. This gain 237G is proportional to the DC bus voltage Vdc and inversely proportional to the sum of the absolute value of the D-axis current Id and the absolute value of the Q-axis current Iq.

[0104] Next, for the D-axis, a positive / negative determination unit 239d multiplies the controlled variable by a sign function Sign(Id) that extracts only the polarity of the D-axis current Id, which is a variable, for the controlled variable multiplied by the gain 237G, to generate a voltage correction command ΔVd*. Next, for the Q-axis, a positive / negative determination unit 239q multiplies the controlled variable by a sign function Sign(Iq) that extracts only the polarity of the Q-axis current Iq, which is a variable, for the controlled variable multiplied by the gain 237G, to generate a voltage correction command ΔVq*. The D-axis voltage command Vd* and the Q-axis voltage command Vq* are corrected using the D-axis voltage correction command ΔVd* and the Q-axis voltage correction command ΔVq* thus generated.

[0105] The following describes how the gain 237G and the positive / negative determining units 239d and 239q of this embodiment work. In the first embodiment, it has been confirmed that ΔIdc is derived from the above equation (19).

[0106] In this embodiment, ΔVd given to the voltage command to suppress pulsation, i.e., D-axis voltage correction command ΔVd*, is given by the following equation (20): ΔVq intentionally given to the voltage command to suppress pulsation, i.e., Q-axis voltage correction command ΔVq*, is given by the following equation (21):

[0107]

number

[0108]

number

[0109] ΔVerr is the deviation between the predicted pulsating voltage value ΔVdc* and the actual pulsating voltage value ΔVdc, and corresponds to the output of the subtractor 34. The feedback control performed to derive the above ΔVd* and ΔVq* is shown as a case where only proportional (P) control using a proportional gain Kp is performed.

[0110] Here, the D-axis current Id is normally 0 or a negative value, and Iq is normally a positive value, so the above equations (20) and (21) can be rewritten as the following equations (22) and (23).

[0111]

number

[0112]

number

[0113] Substituting equations (22) and (23) into equation (19) gives equation (24).

[0114]

number

[0115] That is, the output power of the inverter 6 shown by the above equation (19) can be made to have a simple characteristic in which the influence of the physical parameters Vdc, Id, and Iq is canceled, as shown by the above equation (24). By making such adjustments, the control amount of ΔIdc can be kept constant, and depending on the conditions, insufficient control amount, occurrence of pulsation, and variation in control effect can be suppressed, thereby making it possible to efficiently suppress resonance.

[0116] Next, another gain calculation method will be described. The contents of the pulsation suppression control unit are replaced with a pulsation suppression control unit 230A shown in FIG. FIG. 9 is a control block diagram showing the internal configuration of a pulsation suppression control unit 230A of a power conversion device according to the second embodiment. The difference from the pulsation suppression control section 230 shown in FIG. 8 is the gain by which the control amount 235C is multiplied in the gain adjustment sections 237A and 238A.

[0117] For the D axis, the gain adjuster 237A multiplies the control amount 235C by a gain 237AG (|Id| / Id') as a second gain in addition to a gain 237G (Vdc / (|Id|+|Iq|)) as a first gain. In addition, for the Q axis, the gain adjuster 238A multiplies the control amount 235C by a gain 238AG (|Iq| / Iq') as a second gain in addition to a gain 237G (Vdc / (|Id|+|Iq|)) as a first gain.

[0118] The gain 237AG is configured to be proportional to the absolute value of the D-axis current Id and inversely proportional to the value of the D-axis current Id that has been clamped so as to exceed the set first value range. Further, the gain 238AG is configured to be proportional to the absolute value of the Q-axis current Iq and inversely proportional to the value of the Q-axis current Iq that is clamp-controlled to a value that exceeds the set first value range. The denominator Id' of the gain 237AG is the D-axis current Id after limiter processing by clamp control, and the denominator Iq' of 238AG is the Q-axis current Iq after limiter processing by clamp control.

[0119] This limiter processing by clamp control clamps the output so that the absolute values of the D-axis current Id and Q-axis current Iq do not fall within a set first value range. For example, if the first value range is set to -9 A to 9 A, an input of 7 A will be clamped to 9.1 A. Conversely, an input of -7 A will be clamped to -9.1 A. As a result, even if the absolute values of the D-axis current Id and the Q-axis current Iq are small, the voltage command is not corrected excessively. When this block is used, for example, when Id = 0 A, clamp control is executed, resulting in a voltage correction command ΔVd* = 0 V. Conversely, if clamp control is not executed on either the D axis or the Q axis, the operation is the same as the pulsation suppression control configured as shown in Fig. 8.

[0120] In the power conversion device of this embodiment configured as described above, The control unit The voltage correction command for correcting the D-axis voltage command and the Q-axis voltage command is The control amount is generated by multiplying the first gain, which is configured to be inversely proportional to the sum of the absolute value of the D-axis current and the absolute value of the Q-axis current, by the control amount. It is something. In addition, in the power conversion device of this embodiment configured as described above, In the feedback control, the control unit deriving the control amount commonly used for generating the voltage correction command for correcting the D-axis voltage command and the Q-axis voltage command; It is something.

[0121] By using the first gain configured in this way, it is not only possible to correct the D-axis voltage command and the Q-axis voltage command with an appropriate control amount, but also to configure feedback control for both the D-axis and the Q-axis with a single configuration. In this way, the amount of feedback control performed in the control unit can be reduced, and the same first gain can be used for the D-axis and the Q-axis, and a control amount that can be commonly used to generate voltage correction commands that correct the D-axis and the Q-axis voltage commands is derived, thereby simplifying the control configuration and reducing the control load on the control unit. In this way, high-speed response in feedback control is possible, and high-order pulsation can be effectively suppressed.

[0122] In addition, in the power conversion device of this embodiment configured as described above, In a configuration in which the first gain is inversely proportional to the sum of the absolute value of the D-axis current and the absolute value of the Q-axis current, The control unit generating the voltage correction command for correcting the D-axis voltage command by multiplying the control amount commonly used for correcting the D-axis voltage command and the Q-axis voltage command by a sign function that extracts only the polarity of the D-axis current, which is a variable, by the control amount, and generating the voltage correction command for correcting the Q-axis voltage command by multiplying the control amount by a sign function that extracts only the polarity of the Q-axis current, which is a variable; It is something.

[0123] In this way, by configuring the system to generate a voltage correction command by multiplying the same control variable used in common for the D-axis and Q-axis by a sign function that extracts only the polarity of the D-axis and Q-axis currents, the output of the power converter can be controlled using a simple characteristic that multiplies the deviation ΔVerr by the gain Kp. This makes it possible to continuously operate the power converter stably and soundly under a variety of operating conditions.

[0124] In addition, in the power conversion device of this embodiment configured as described above, In a configuration in which the first gain is inversely proportional to the sum of the absolute value of the D-axis current and the absolute value of the Q-axis current, The control unit multiplying the control amount commonly used for correcting the D-axis voltage command and the Q-axis voltage command by a second gain in addition to the first gain; The second gain is The D-axis current is proportional to the absolute value of the D-axis current and inversely proportional to the value of the D-axis current that is clamped and controlled to be a value exceeding a first value range. or, The Q-axis current is proportional to the absolute value of the Q-axis current and inversely proportional to the value of the Q-axis current that is clamped and controlled to be a value that exceeds a set first value range. It is something.

[0125] This prevents excessive correction even when the driving conditions of the motor change, and enables the inverter to operate continuously in a stable and healthy manner while suppressing pulsation.

[0126] Although the present application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are conceivable within the scope of the technology disclosed in this application, including, for example, cases where at least one component is modified, added, or omitted, and cases where at least one component is extracted and combined with a component of another embodiment. [Explanation of symbols]

[0127] 2 Rectifier (rectification unit), 6 Inverter (power converter), 7 Motor (electric motor), 50 Control unit, 37G, 38G Gain (first gain), 100 Power conversion device, P, N DC bus.

Claims

1. a rectification unit that converts an input three-phase AC voltage into a DC voltage and outputs the DC voltage to a DC bus; a power converter that converts the DC voltage on the DC bus converted by the rectifier unit into an AC voltage to control an electric motor; a control unit that controls the power converter, The control unit converting a current flowing through the electric motor into a D-axis current and a Q-axis current on a two-axis orthogonal coordinate system, generating a D-axis voltage command so that the D-axis current follows the D-axis current command, and generating a Q-axis voltage command so that the Q-axis current follows the Q-axis current command, and controlling the power converter based on the generated D-axis voltage command and Q-axis voltage command; deriving, based on the detected values of the three-phase AC voltage, a pulsation contained in the DC voltage obtained by full-wave rectifying the three-phase AC voltage as a pulsation voltage predicted value, and deriving, based on the detected values of the DC voltage, the pulsation contained in the DC voltage as a pulsation voltage actual measurement value; correcting at least one of the D-axis voltage command and the Q-axis voltage command with a voltage correction command generated so as to reduce a deviation between the predicted pulsation voltage value and the actual pulsation voltage value; Power conversion device.

2. The control unit deriving the ripple voltage prediction value by subtracting the minimum phase voltage for each phase from the maximum phase voltage for each phase of the three-phase AC voltage; The power conversion device according to claim 1 .

3. The control unit performing feedback control using a set control gain to derive a control amount so as to reduce the deviation, and multiplying the control amount by a first gain configured to be proportional to the voltage of the DC bus to generate the voltage correction command; The power conversion device according to claim 1 .

4. The control unit performing feedback control using a set control gain to derive a control amount so as to reduce the deviation, and multiplying the control amount by a first gain configured to be proportional to the voltage of the DC bus to generate the voltage correction command; The power conversion device according to claim 2 .

5. The control unit generating the voltage correction command for correcting the D-axis voltage command by multiplying the controlled variable by the first gain configured inversely proportional to the D-axis current; The voltage correction command for correcting the Q-axis voltage command is generated by multiplying the controlled variable by the first gain configured inversely proportional to the Q-axis current. The power conversion device according to claim 3 or 4.

6. The control unit The voltage correction command for correcting the D-axis voltage command and the Q-axis voltage command is a first gain that is inversely proportional to the sum of the absolute value of the D-axis current and the absolute value of the Q-axis current, and is generated by multiplying the control amount by the first gain; The power conversion device according to claim 3 or 4.

7. In the feedback control, the control unit deriving the control amount commonly used for generating the voltage correction command for correcting the D-axis voltage command and the Q-axis voltage command; The power conversion device according to claim 6.

8. In a configuration in which the first gain is inversely proportional to the sum of the absolute value of the D-axis current and the absolute value of the Q-axis current, The control unit a control amount commonly used for correcting the D-axis voltage command and the Q-axis voltage command is multiplied by a sign function that extracts only the polarity of the D-axis current, which is a variable, to generate the voltage correction command for correcting the D-axis voltage command, and a control amount is multiplied by a sign function that extracts only the polarity of the Q-axis current, which is a variable, to generate the voltage correction command for correcting the Q-axis voltage command; The power conversion device according to claim 7.

9. In a configuration in which the first gain is inversely proportional to the sum of the absolute value of the D-axis current and the absolute value of the Q-axis current, The control unit multiplying the control amount commonly used for correcting the D-axis voltage command and the Q-axis voltage command by a second gain in addition to the first gain; The second gain is The D-axis current is proportional to the absolute value of the D-axis current and inversely proportional to the value of the D-axis current that is clamped and controlled to be a value that exceeds a set first value range. or, The Q-axis current is proportional to the absolute value of the Q-axis current and inversely proportional to the value of the Q-axis current that is clamped and controlled to be a value that exceeds a set first value range. The power conversion device according to claim 6.

10. In a configuration in which the first gain is inversely proportional to the sum of the absolute value of the D-axis current and the absolute value of the Q-axis current, The control unit multiplying the control amount commonly used for correcting the D-axis voltage command and the Q-axis voltage command by a second gain in addition to the first gain; The second gain is The D-axis current is proportional to the absolute value of the D-axis current and inversely proportional to the value of the D-axis current that is clamped and controlled to be a value that exceeds a set first value range. or, The Q-axis current is proportional to the absolute value of the Q-axis current and inversely proportional to the value of the Q-axis current that is clamped and controlled to be a value that exceeds a set first value range. The power conversion device according to claim 7.

11. The feedback control is performing any one of proportional control, proportional differential control, and control in which a control for advancing the control amount by a set phase and a proportional control are performed in combination; The power conversion device according to claim 3 or 4.

12. The control unit When the D-axis current or the Q-axis current falls within a set first value range, performing clamp control to adjust the value of the D-axis current or the Q-axis current used in the first gain so that the value exceeds the first value range; The power conversion device according to claim 5 .

13. At least one value of the DC bus voltage, the D-axis current, and the Q-axis current, which constitute the first gain, is updated in accordance with a detected value during operation of the power converter. The power conversion device according to claim 3 or 4.

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