Direct power conversion device

Abstract

If the following definition is made, that is, fdc is a frequency twice the frequency of a single-phase AC power supply (20), fL is a frequency of periodic load variation, tb=1 / |fdc-n×fL|, wherein n is a positive integer that maximizes tb, then in a power supply half cycle at a time when the peak value of the fundamental wave of the load torque during the tb period is approximately consistent with the peak value of the absolute value of the power supply voltage, the switching elements (Su, Sv, Sw, Sx, Sy, Sz) are controlled so that in a waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the motor current vector, two or more maximum points appear in the power supply half cycle.

Description

Technical Field

[0001] The present disclosure relates to a direct power conversion device. Background Art

[0002] A power conversion device that converts the AC power of an input AC power source into an AC power of a specified frequency can be roughly divided into an indirect power conversion device and a direct power conversion device according to the presence or absence of an energy storage element (a large-capacity capacitor or a large-capacity inductor). The former has an energy storage element (a large-capacity capacitor or a large-capacity inductor), while the latter does not have an energy storage element. In some of the direct power conversion devices, a capacitor with a relatively small capacity is provided in the DC link section. Patent document 1 discloses a torque control technology for suppressing the vibration of a compressor in the direct power conversion device when the load torque changes periodically. In patent document 1, the torque control described as follows is performed: in this torque control, the pulsating component caused by the frequency of the AC power source and the pulsating component synchronized with the load torque change generated during one rotation of the motor are superimposed on the output torque of the motor, thereby causing the output torque of the motor to change according to the load torque change of the motor.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 4192979 Summary of the invention

[0006] -Technical problem to be solved by the invention-

[0007] However, in the torque control, the pulsating component caused by the frequency of the AC power supply and the pulsating component synchronized with the load torque change appear in the motor torque. Therefore, in the torque control, sometimes, the peak values ​​of the two pulsating components overlap with each other, resulting in an excessively high peak value of the motor torque. Since the motor torque and the motor current are roughly proportional, the higher the peak value of the motor torque, the higher the peak value of the motor current.

[0008] An object of the present disclosure is to reduce a peak value of a motor current in a power conversion device.

[0009] -Technical solutions to solve technical problems-

[0010] A first aspect of the present disclosure is a direct power conversion device that converts AC power from a single-phase AC power source 20 input into AC power of a predetermined frequency through switching operations of a plurality of switching elements Su, Sv, Sw, Sx, Sy, and Sz, and supplies the AC power to a motor 30 that drives a load with periodic load fluctuations, and is characterized in that:

[0011] The direct power conversion device includes a control unit 40 for controlling the switch operation.

[0012] If the following definition is made,

[0013] fdc is twice the frequency of the AC power source 20,

[0014] fL is the frequency of the periodic load variation,

[0015] tb=1 / |fdc-n×fL|,

[0016] Among them, n is a positive integer that maximizes tb.

[0017] Then, in the power supply half cycle including the time when the peak value of the fundamental wave of the load torque and the peak value of the absolute value of the power supply voltage are approximately the same during the tb period,

[0018] The control unit 40 controls the switching elements Su, Sv, Sw, Sx, Sy, and Sz so that two or more maximum points appear in a power supply half cycle in a waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the motor current vector.

[0019] In the first aspect, in the power conversion device, the peak value of the motor current can be reduced.

[0020] The second aspect of the present disclosure is a power conversion device based on the disclosure of the first aspect, characterized in that:

[0021] In the power supply half cycle including the moment when the fundamental wave of the load torque reaches the maximum,

[0022] The control unit 40 controls the switching elements Su, Sv, Sw, Sx, Sy, and Sz so that two or more maximum points appear in a power supply half cycle in a waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the motor current vector.

[0023] In the second aspect, the peak value of the motor current can be reduced in the power supply half cycle including the time when the fundamental wave of the load torque reaches the maximum.

[0024] The third aspect of the present disclosure is a power conversion device based on the disclosure of the first aspect, characterized in that:

[0025] The power supply half cycle included in the phase range R of the mechanical angle in which the fundamental wave of the load torque exceeds the prescribed threshold,

[0026] The control unit 40 controls the switching elements Su, Sv, Sw, Sx, Sy, and Sz so that two or more maximum points appear in a power supply half cycle in a waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the motor current vector.

[0027] In the third aspect, the peak value of the motor current can be reduced in the power supply half cycle included in the phase range R of the mechanical angle in which the fundamental wave of the load torque exceeds the predetermined threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a block diagram of a power conversion device.

[0029] Figure 2 An example of the waveforms of the power supply voltage and the DC voltage is shown.

[0030] Figure 3 The compressor load torque, a waveform obtained by adding the average torque to the fundamental wave of the compressor load torque, and the waveform of the average torque are shown.

[0031] Figure 4 The basic data generated according to the first table is shown as a waveform.

[0032] Figure 5 The basic data generated according to the second table is shown as a waveform.

[0033] Figure 6 The waveforms of average torque in the related art, a waveform obtained by adding the fundamental wave of the load torque to the average torque, the motor torque, the vibration suppression component, the higher harmonic component, and the absolute value of the power supply voltage are exemplarily shown.

[0034] Figure 7 The waveforms of the average torque in the first embodiment, the waveform obtained by adding the fundamental wave of the load torque to the average torque, the motor torque, the vibration suppression component, the harmonic component, and the absolute value of the power supply voltage are exemplarily shown.

[0035] Figure 8 The waveforms of average torque in the related art, a waveform obtained by adding the fundamental wave of the load torque to the average torque, the motor torque, the vibration suppression component, the higher harmonic component, and the absolute value of the power supply voltage are exemplarily shown.

[0036] Fig. 9 The waveforms of the average torque, the waveform obtained by adding the fundamental wave of the load torque to the average torque, the motor torque, the vibration suppression component, the harmonic component, and the absolute value of the power supply voltage in the second embodiment are exemplarily shown.

[0037] Fig.10The waveforms of average torque in the related art, a waveform obtained by adding the fundamental wave of the load torque to the average torque, the motor torque, the vibration suppression component, the higher harmonic component, and the absolute value of the power supply voltage are exemplarily shown.

[0038] Fig.11 The waveforms of average torque, a waveform obtained by adding the fundamental wave of load torque to average torque, motor torque, a vibration suppression component, a harmonic component, and an absolute value of power supply voltage in the third embodiment are exemplarily shown. DETAILED DESCRIPTION

[0039] (First Embodiment)

[0040] Figure 1 1 is a block diagram of a power conversion device 10 according to the first embodiment. The power conversion device 10 converts an input AC voltage (power supply voltage v in ) is converted into a predetermined AC voltage. More specifically, the power conversion device 10 is a "direct power conversion device" that does not have an energy storage element (large-capacity capacitor, large-capacity inductor). In this example, an AC voltage is input to the power conversion device 10 from a single-phase AC power source 20. The power conversion device 10 supplies the converted AC voltage to the motor 30.

[0041] like Figure 1 As shown, the power conversion device 10 includes an AC / DC conversion circuit 11, a DC link unit 12, a DC / AC conversion circuit 13, and a control unit 40. The motor 30 is, for example, an IPM motor (Interior Permanent Magnet Motor). In this embodiment, the motor 30 drives a compressor (not shown) of an air conditioner. In the compressor, during the compression stroke of the fluid, a periodic change in the torque of the load (compressor) (a change in the load torque) is generated during one rotation of the motor 30.

[0042] 〈AC / DC conversion circuit〉

[0043] The AC / DC conversion circuit 11 is connected to the AC power source 20 via a reactor L. The AC / DC conversion circuit 11 converts the power supply voltage v from the AC power source 20 to in The AC / DC conversion circuit 11 includes four diodes D1, D2, D3, and D4. The four diodes D1, D2, D3, and D4 are connected in a bridge shape.

[0044] 〈DC link section〉

[0045] The DC link unit 12 has a capacitor C. The capacitor C is connected between a pair of output nodes of the AC / DC conversion circuit 11. The DC link unit 12 is connected to the output of the AC / DC conversion circuit 11 (power supply voltage v after full-wave rectification).in ) generates a DC voltage v dc .

[0046] The capacitance value of the capacitor C is such that the output of the AC / DC conversion circuit 11 can hardly be smoothed. On the other hand, the capacitance value of the capacitor C is such that the ripple voltage (voltage fluctuation corresponding to the switching frequency) caused by the switching action (described later) of the DC / DC conversion circuit 13 can be suppressed. Specifically, the capacitor C has a capacitance value (e.g., about tens of μF) that is about 0.01 times the capacitance value of a smoothing capacitor (e.g., an electrolytic capacitor) used to smooth the output of the AC / DC conversion circuit in a general power conversion device. The capacitor C is, for example, a film capacitor.

[0047] As described above, the output of the AC / DC converter circuit 11 cannot be smoothed in the DC link section 12 by the capacitor C. dc In the middle, there will be a residual voltage with the power supply voltage v in The frequency corresponding to the pulsating component.

[0048] Figure 2 The power supply voltage v in and DC voltage v dc An example of a waveform. In this example, the DC voltage v dc Pulsates in such a way that its maximum value reaches more than twice its minimum value. dc contains a pulsating component, which has a power supply voltage v in The frequency is twice the frequency of the

[0049] 〈DC to AC conversion circuit〉

[0050] The DC-AC conversion circuit 13 converts the DC voltage v generated by the DC link unit 12 into dc The DC-AC conversion circuit 13 supplies the three-phase AC voltage to the motor 30 .

[0051] The DC-AC conversion circuit 13 has six switching elements Su, Sv, Sw, Sx, Sy, Sz and six freewheeling diodes Du, Dv, Dw, Dx, Dy, Dz. The six switching elements Su, Sv, Sw, Sx, Sy, Sz are connected in a bridge shape. As described in detail below, the DC-AC conversion circuit 13 includes three switching legs. The switching leg is formed by connecting two switching elements in series.

[0052] In each of the three switching arms, the midpoint between the switching elements Su, Sv, Sw of the upper arm and the switching elements Sx, Sy, Sz of the lower arm is connected to the coils of each phase (u-phase, v-phase, w-phase coil) of the motor 30. Each of the switching elements Su, Sv, Sw, Sx, Sy, Sz is connected in reverse parallel to a freewheeling diode Du, Dv, Dw, Dx, Dy, Dz.

[0053] 〈Control Department〉

[0054] The control unit 40 controls the AC voltage output by the DC-AC conversion circuit 13 so that the rotation speed ω of the motor 30 reaches the given command value (hereinafter referred to as the rotation speed command value ω*). When controlling the rotation speed ω, the control unit 40 controls the switching action to change the output torque of the motor 30.

[0055] The control unit 40 includes a microcomputer and a storage device. The storage device stores software that operates the microcomputer. The control unit 40 executes the software to function as a speed control unit 41, a coordinate conversion unit 43, a dq axis current control unit 44, a PWM operation unit 45, a torque control unit 48, and a high-order harmonic component superposition unit 50 (see Figure 1 ).

[0056] The speed control unit 41 generates an average value of the torque of the motor 30 (hereinafter referred to as average motor torque T ave ) command value (hereinafter referred to as the average torque command value T ave Specifically, the speed control unit 41 generates an average torque command value T according to the deviation between the rotation speed ω of the motor 30 and the rotation speed command value ω*, for example, by performing PID calculation (proportional, integral, differential). ave *. The speed control unit 41 outputs the average torque command value T to the torque control unit 48. ave *.

[0057] The torque control unit 48 sets the average torque command value T ave * is superimposed with the vibration suppression component to generate a command value for the torque of the motor 30 (hereinafter referred to as the first torque command Tm*). The first torque command Tm* pulsates in synchronization with the load change (torque change) of the compressor. By performing the superposition as described above, a pulsating component synchronized with the load change (torque change) of the compressor will appear in the output torque of the motor 30. The vibration suppression component is a pulsating waveform synchronized with the load change (torque change) of the compressor. The vibration suppression component is obtained by calculating based on the mechanical angle θm of the motor 30. It should be noted that, for example, a sensor can be provided to detect the mechanical angle θm of the motor 30, or the mechanical angle θm of the motor 30 can be calculated based on the motor currents iu, iv, iw and the motor voltages Vu, Vv, Vw.

[0058] Figure 3 The compressor load torque, the waveform obtained by adding the average torque to the fundamental wave of the compressor load torque, and the waveform of the average torque are shown. Figure 3 As shown, among the frequency components included in the waveform of the compressor load torque, the frequency component with the largest amplitude is the fundamental frequency component. In addition, the deviation between the compressor load torque and the motor torque is the excitation torque. The compressor vibrates due to the excitation torque.

[0059] In order to suppress the compressor vibration caused by the fundamental frequency component, which is the frequency component with the largest amplitude among the frequency components included in the waveform of the compressor load torque, the torque control unit 48 generates a first torque command value Tm* that pulsates in synchronization with the fundamental wave of the compressor load torque. If the first torque command value Tm* pulsates in synchronization with the fundamental wave of the compressor load torque, the output torque of the motor 30 pulsates in synchronization with the fundamental wave of the compressor load torque. As a result, the exciting torque that causes the compressor vibration is reduced.

[0060] The harmonic component superposition unit 50 superimposes the first torque instruction Tm* with the harmonic component to generate a torque instruction (hereinafter referred to as the second torque instruction T*). The second torque instruction T* pulsates synchronously with the fundamental wave of the compressor load torque and the voltage variation of the absolute value of the power supply voltage. After the superposition as described above, a pulsating component caused by the frequency of the AC power supply appears in the output torque of the motor. The harmonic component is a pulsating waveform synchronized with the voltage variation of the absolute value of the power supply voltage. The harmonic component is generated based on the power supply phase θin. There are two modes of superposition of the harmonic components performed by the harmonic component superposition unit 50.

[0061] In the first mode (hereinafter referred to as the first mode M1), the first torque command Tm* is modulated in a predetermined power supply half cycle (described later) so that two or more maximum points appear in a waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the motor current vector. Figure 2 As shown in FIG. 1 , a “power supply half cycle” refers to a period from a predetermined zero crossing point of the voltage of the AC power supply 20 to the next zero crossing point (the same applies hereinafter). A “motor current vector” refers to a d-axis current i when controlling the motor 30. d The vector of the q-axis current i q The resultant vector of the vectors .

[0062] In the second mode (hereinafter referred to as the second mode M2), the first torque command Tm* is modulated in a specified power supply half cycle (described later) so that a maximum point appears in the waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the motor current vector.

[0063] In order to realize the above-mentioned mode, the control unit 40 includes a selector 46, a multiplier 47 and a data generating unit 49. In addition, the control unit 40 includes two tables for generating data used for modulation (hereinafter referred to as basic data D). The basic data D is data (signal) containing higher harmonic components.

[0064] One of the two tables is a table for generating basic data D for the first mode M1 (hereinafter referred to as the first table Tb1). The other table is a table for generating basic data D for the second mode M2 ​​(hereinafter referred to as the second table Tb2). In each table, the value of the power supply phase θin and the value of the basic data D under the power supply phase θin are stored in pairs. Each table is configured to take the power supply phase θin as a parameter and output the basic data D corresponding to the power supply phase θin.

[0065] Figure 4 The basic data D generated according to the first table Tb1 is shown as a waveform. Figure 4 In the figure, the horizontal axis is the power supply phase θin. The vertical axis is the value of the modulation amount. Figure 4 As shown in FIG. 1 , according to the basic data D generated by the first table Tb1, a maximum point appears in each of the first and second halves of the power supply half cycle. This waveform (table value) is synthesized by synthesizing the waveforms of the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency in such a way that at least one maximum point appears in each of the first and second halves of the power supply half cycle.

[0066] Figure 5 The basic data D generated according to the second table Tb2 is shown as a waveform. Figure 5 As shown, the basic data D generated from the second table Tb2 has only one maximum point in the power supply half cycle. This waveform (table value) is created using the second harmonic of the power supply frequency in such a way that only one maximum point appears in the power supply half cycle.

[0067] The data generation unit 49 generates a signal (hereinafter referred to as a selection signal) for selecting one of the two tables Tb1 and Tb2 . How the data generation unit 49 generates the selection signal will be described in detail below. The data generation unit 49 outputs the selection signal to the selector 46 .

[0068] The selector 46 outputs one of the outputs of the two tables Tb1 and Tb2 to the multiplier 47 according to the selection signal. The multiplier 47 multiplies the value output by the selector 46 by the first torque command Tm*. The multiplier 47 outputs the multiplication result to the dq axis current control unit 44 as the second torque command T*.

[0069] The coordinate conversion unit 43 derives the d-axis current i of the motor 30 based on the u-phase current iu, the w-phase current iw, and the electrical angle (mechanical angle θm) of the rotor (not shown) of the motor 30. d and q-axis current i q The coordinate conversion unit 43 is used to derive the d-axis current i d and q-axis current i q It should be noted that, for example, a current sensor can be provided to detect the values ​​of the u-phase current iu and the w-phase current iw.

[0070] The dq axis current control unit 44 controls the torque according to the second torque command T* and the d axis current i d , q-axis current i q The d-axis voltage command value v is derived from the phase β command value β* of the motor current vector. d * and q-axis voltage command value v q Specifically, the dq-axis current control unit 44 obtains a target value of the d-axis current (referred to as the d-axis current command value i*) required to obtain the corresponding torque based on the second torque command T*. d *) and the target value of the q-axis current (referred to as the q-axis current command value i q *). The dq axis current control unit 44 uses the d axis current command value i d * and d-axis current i d The deviation is small and the q-axis current command value is different from the q-axis current i q The d-axis voltage command value v is derived in a way that the deviation is small. d * and q-axis voltage command value v q *.

[0071] The PWM operation unit 45 controls the on / off switching of the switching elements Su, Sv, Sw, Sx, Sy, and Sz by so-called PWM (Pulse Width Modulation) control so as to achieve the d-axis voltage command value v d * and q-axis voltage command value v q * The output voltage indicated by the PWM operation unit 45 generates a signal for controlling the on / off of the conduction (hereinafter referred to as the control signal G).

[0072] The time when the switching elements Su, Sv, Sw, Sx, Sy, and Sz are in the on state and the time when they are in the off state are determined by the duty ratio of the control signal G. The PWM operation unit 45 generates a voltage according to the mechanical angle θm and the DC voltage v dc , d-axis voltage command value v d *、q-axis voltage command value v q *、d-axis voltage v d And the q-axis voltage v q, sets the duty ratio of the control signal G supplied to each switching element Su, Sv, Sw, Sx, Sy, Sz.

[0073] When the control signal G is output, each switching element Su, Sv, Sw, Sx, Sy, Sz performs switching operation (on / off operation) at a duty ratio corresponding to the control signal G. The PWM operation unit 45 periodically updates the control signal G. In response to the update, the inverter circuit 13 continues to perform switching operation.

[0074] 〈Mode Selection〉

[0075] The data generation unit 49 selects one of the two tables by outputting a selection signal. Through this selection, the control unit 40 realizes the selection of the first mode M1 and the second mode M2. In the following, for the convenience of explanation, the power supply half cycle for executing the first mode M1 is set as the first power supply half cycle, and the power supply half cycle for executing the second mode M2 ​​is set as the second power supply half cycle. Specifically, the data generation unit 49 selects one of the first table Tb1 and the second table Tb2 by executing the following steps.

[0076] Step 1:

[0077] Data generator 49 obtains a frequency (hereinafter referred to as fdc) twice the frequency of AC power source 20 from power phase θin. Data generator 49 also calculates a frequency (hereinafter referred to as fL) of periodic load variation (here, load variation of the compressor) from mechanical angle θm.

[0078] Step 2:

[0079] Figure 6 The waveforms of the average torque in the prior art, the waveform obtained by adding the fundamental wave of the load torque to the average torque, the motor torque, the vibration suppression component, the higher harmonic component, and the absolute value of the power supply voltage are shown. Since the output torque of the motor 30 is the product of the average torque, the vibration suppression component, and the higher harmonic component, the output torque of the motor 30 includes a pulsating component caused by the frequency of the AC power supply and a pulsating component synchronized with the load torque variation.

[0080] Figure 6 The waveform is a waveform of a conventional power conversion device, and exemplarily shows a waveform in which the power conversion device 10 is operated by always using the second table Tb2 to generate the basic data D in the data generation unit 49. Hereinafter, for convenience of explanation, the example of always operating the power conversion device 10 using the second table Tb2 is referred to as a conventional example.

[0081] If torque control is performed in a direct power conversion device, the pulsating component caused by the frequency of the AC power supply and the pulsating component synchronized with the load torque fluctuation generated during one rotation of the motor will be superimposed. Figure 6 As shown, the waveform of the motor output torque and the waveform of the motor current are waveforms containing beats. In the beat cycle (hereinafter referred to as the beat cycle tb), in the power supply half cycle where the peak values ​​of the two pulsating components overlap, the peak values ​​of the motor output torque and the motor current are large (refer to the circled peak values).

[0082] Specifically, since the output torque of the motor 30 is the product of the average torque, the vibration suppression component, and the high-order harmonic component, Figure 6 As shown in FIG. 1 , in the half-cycle of the power supply where the peak values ​​of the vibration suppression component and the higher harmonic component coincide with each other, the peak values ​​of the motor output torque and the motor current are large. The vibration suppression component is a pulsating waveform synchronized with the fundamental wave of the compressor load torque. The vibration suppression component reaches its peak value at the moment when the fundamental wave of the compressor load torque reaches its peak value (refer to FIG. 1 ). Figure 6 ).

[0083] The harmonic component is a pulsating waveform that is synchronized with the voltage fluctuation of the absolute value of the power supply voltage. The harmonic component reaches its peak when the absolute value of the power supply voltage reaches its peak (see Figure 6 ). In other words, if torque control is performed in the direct power conversion device, the peak values ​​of the motor output torque and the motor current are large (see the circled peaks) in the power supply half cycle where the peak value of the fundamental wave of the compressor load torque coincides with the peak value of the absolute value of the power supply voltage. The data generation unit 49 obtains the beat period tb shown in the following equation.

[0084] tb=1 / |fdc-n×fL|,

[0085] Here, n is a positive integer that maximizes tb. It should be noted that, in this formula, when tb>1, tb=1.

[0086] Step 3:

[0087] The data generating unit 49 obtains the time when the fundamental wave of the load torque reaches a peak value (θm=180°) in all the beat cycles tb based on the mechanical angle θm.

[0088] Step 4:

[0089] The data generating unit 49 obtains the power supply phase θin at each time point obtained in step 3 .

[0090] Step 5:

[0091] The data generating unit 49 obtains a power supply half cycle including a power supply phase θin which is closest to the power supply voltage v among the power supply phases θin obtained in step 4. in The power supply phase θin is the peak value of the absolute value of the load torque (corresponding to 90° or 270° in the value of the power supply phase θin). The power supply half cycle obtained by the data generation unit 49 is the power supply half cycle at the moment when the peak value of the fundamental wave of the load torque and the peak value of the absolute value of the power supply voltage are roughly consistent. In this embodiment, the power supply half cycle at the moment when the peak value of the fundamental wave of the load torque and the peak value of the absolute value of the power supply voltage are roughly consistent is the first power supply half cycle. The power supply half cycle other than the first power supply half cycle is the second power supply half cycle.

[0092] Step 6:

[0093] In the first power supply half cycle, the data generating unit 49 outputs a selection signal to the selector 46 for selecting the first table Tb1 , and in the second power supply half cycle, the data generating unit 49 outputs a selection signal to the selector 46 for selecting the second table Tb2 .

[0094] According to the selection signal, in the first power half cycle, the basic data D from the first table Tb1 is output from the selector 46, and in the second power half cycle, the basic data D from the second table Tb2 is output from the selector 46. In other words, in the first power half cycle, the first mode M1 is executed, and in the second power half cycle, the second mode M2 ​​is executed.

[0095] <Operation example of power conversion device>

[0096] If the power conversion device 10 is started, the AC / DC conversion circuit 11 converts the power supply voltage v in The output of the AC / DC converter circuit 11 is supplied to the DC link unit 12. The DC link unit 12 generates a power supply voltage v in The frequency of the pulsating DC voltage is twice the frequency v dc .

[0097] In the power conversion device 10, the speed control unit 41, the torque control unit 48, the coordinate conversion unit 43, the dq axis current control unit 44, and the harmonic component superposition unit 50 operate. As a result, the control unit 40 generates a d axis voltage command value v d * and q-axis voltage command value v q *. If the d-axis voltage command value v is generated d * and q-axis voltage command value v q *, the PWM operation unit 45 generates a control signal G. As a result, the inverter circuit 13 performs a switching operation according to the control signal G. According to the switching operation, a predetermined AC power is supplied from the inverter circuit 13 to the motor 30 .

[0098] Figure 7 The waveforms of the average torque in this embodiment, the waveform obtained by adding the average torque to the fundamental wave of the load torque, the motor torque, the vibration suppression component, the higher harmonic component, and the absolute value of the power supply voltage are shown. In the power conversion device 10 of this embodiment, the first mode M1 is executed in the first power supply half cycle. In the first mode M1, the basic data D (refer to the first table Tb1) based on the first table Tb1 is used. Figure 4 ) is used for control. On the other hand, in the conventional power conversion device 10, the basic data D (refer to Figure 5 ) is used to control (refer to Figure 6 ).

[0099] exist Figure 6 In the case of the first half-cycle of the power supply, a large peak value (refer to the circled peak value) appears in the output torque at the beat period tb. The power supply half-cycle including the circled peak value includes the moment when the peak value of the fundamental wave of the load torque and the peak value of the absolute value of the power supply voltage are roughly consistent. In other words, the power supply half-cycle including the circled peak value is the first half-cycle of the power supply. On the other hand, Figure 7 In the first power supply half cycle, no large peak value appears in the output torque. In other words, if the basic data D based on the first table Tb1 is used for control, the peak value of the output torque can be reduced.

[0100] like Figure 4 , Figure 5 As shown, the waveform of the basic data D generated according to the first table Tb1 is a waveform with suppressed peak values ​​(roughly a trapezoidal waveform) compared to the waveform of the basic data D generated according to the second table Tb2. Since the output torque of the motor 30 is the product of the average torque, the vibration suppression component, and the higher harmonic component, the peak value of the output torque of the motor 30 can be reduced by setting the waveform of the higher harmonic component to a waveform with suppressed peak values. In other words, in order to reduce the peak value of the output torque of the motor 30, the waveform of the basic data D is set to a waveform with suppressed peak values ​​(roughly a trapezoidal waveform), and for this purpose, the amplitude and phase of the waveforms of the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency need to be appropriately synthesized to generate the waveform of the basic data D.

[0101] Since the output torque and the motor current are roughly proportional, if the basic data D based on the first table Tb1 is used for control, the waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveforms of the absolute value of the output torque and the motor current in the first power supply half cycle is a waveform with two or more maximum points (refer to Figure 7 ). In other words, if the basic data D based on the first table Tb1 is used for control, the peak values ​​of the output torque and the motor current can be reduced.

[0102] It should be noted that in the second power supply half cycle of the second mode M2, the output torque of the motor 30 and the peak value of the motor current are not suppressed. In this case, the waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the output torque and the motor current has one maximum point. Compared with the case of controlling in the first mode M1, the input current (power supply current i in ) has a relatively small level of higher harmonics.

[0103] In summary, the present embodiment is a direct power conversion device, which converts the AC power of the input single-phase AC power source 20 into AC power of a specified frequency through the switching actions of a plurality of switching elements Su, Sv, Sw, Sx, Sy, and Sz, and supplies the AC power to the motor 30 driving the load with periodic load fluctuations, and is characterized in that: the direct power conversion device includes a control unit 40 for controlling the switching action, and if the following definitions are made, that is, fdc is a frequency twice the frequency of the AC power source 20, and fL is the period The frequency of the load change, tb=1 / |fdc-n×fL|, wherein n is a positive integer that maximizes tb. In the power supply half cycle at the moment when the peak value of the fundamental wave of the load torque during the tb period is approximately consistent with the peak value of the absolute value of the power supply voltage, the control unit 40 controls the switching elements Su, Sv, Sw, Sx, Sy, and Sz so that in the waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the motor current vector, two or more maximum points appear in the power supply half cycle.

[0104] <Effects of the present embodiment>

[0105] The power conversion device 10 implements the second mode M2 ​​in the second power half cycle. In other words, the power conversion device 10 does not actively reduce the peak value of the motor current in the second power half cycle. However, the power conversion device 10 reduces the peak value of the motor current at least in the first power half cycle. In the power conversion device 10, even if the peak value of the motor current is not actively reduced in the second power half cycle, the peak value of the motor current will be reduced from the perspective of the overall operation of the power conversion device 10.

[0106] (Second Embodiment)

[0107] In the second embodiment, another configuration example of the control unit 40 is described. In the power supply half cycle including the moment when the fundamental wave of the load torque reaches the maximum, the control unit 40 of the second embodiment controls the switching elements Su, Sv, Sw, Sx, Sy, and Sz so that two or more maximum points appear in the power supply half cycle in the waveform obtained by synthesizing the second harmonic, the fourth harmonic, and the sixth harmonic of the power supply frequency included in the waveform of the absolute value of the motor current vector. In order to realize this control, in this embodiment, the control unit 40 (more specifically, the data generation unit 49) of the first embodiment is changed.

[0108] The data generation unit 49 of this embodiment has a function of detecting the time when the fundamental wave of the load torque reaches a peak value. Specifically, the data generation unit 49 detects the time when the mechanical angle θm reaches 180°. After finding the time when the fundamental wave of the load torque reaches a peak value, the data generation unit 49 generates a selection signal to select the first table Tb1 in the power supply half cycle including the found time.

[0109] Figure 8 The waveforms of the average torque in the conventional power conversion device, the waveform obtained by adding the fundamental wave of the load torque to the average torque, the motor torque, the vibration suppression component, the higher harmonic component, and the absolute value of the power supply voltage are shown as examples. Figure 8 In the waveform diagram, a large peak appears in the output torque (refer to the circled peak). The power supply half cycle including the circled peak includes the moment when the fundamental wave of the load torque reaches its peak. Fig. 9 The waveforms in the waveform diagram are the average torque in this embodiment, the waveform obtained by adding the fundamental wave of the load torque to the average torque, the motor torque, the vibration suppression component, the higher harmonic component, and the absolute value of the power supply voltage.

[0110] In the present embodiment, the first mode M1 is executed in the power supply half cycle including the peak value of the fundamental wave of the load torque. In other words, in the present embodiment, the power supply half cycle including the peak value of the fundamental wave of the load torque is the first power supply half cycle, and the power supply half cycle other than the first power supply half cycle is the second power supply half cycle. In the first mode M1, the basic data D (refer to Figure 4 ) is used for control. Since the output torque and the motor current are roughly proportional, if the basic data D based on the first table Tb1 is used for control, then in the first power supply half cycle, the waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the output torque and the motor current is a waveform with two or more maximum points (refer to Fig. 9 ).

[0111] In other words, if the basic data D based on the first table Tb1 is used for control, the output torque and the peak value of the motor current can be reduced. It should be noted that in this embodiment, the second mode M2 ​​is implemented while the operation of the first mode M1 is not implemented.

[0112] <Effects of the present embodiment>

[0113] As described above, in this embodiment, the peak value of the motor current can be reduced in the power supply half cycle including the time when the fundamental wave of the load torque reaches the maximum.

[0114] In this embodiment, similarly, the power conversion device 10 implements the second mode M2 ​​in the second power half cycle. In other words, the power conversion device 10 does not actively reduce the peak value of the motor current in the second power half cycle. However, the power conversion device 10 reduces the peak value of the motor current at least in the first power half cycle. In the power conversion device 10, even if the peak value of the motor current is not actively reduced in the second power half cycle, the peak value of the motor current will be reduced from the perspective of the overall operation of the power conversion device 10.

[0115] (Third Embodiment)

[0116] In the third embodiment, another configuration example of the control unit 40 is described. In the power supply half cycle within the range of the mechanical angle in which the fundamental wave of the load torque exceeds a predetermined threshold value (torque threshold value Tth described later), the control unit 40 of the third embodiment controls the switching elements Su, Sv, Sw, Sx, Sy, and Sz so that two or more maximum points appear in the power supply half cycle in the waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency included in the waveform of the absolute value of the motor current vector. In order to realize this control, in this embodiment, the control unit 40 (more specifically, the data generation unit 49) of the first embodiment is changed.

[0117] The data generation unit 49 of this embodiment has a function of obtaining a range of mechanical angle θm (hereinafter referred to as phase range R) in which the fundamental wave of the load torque exceeds a predetermined threshold. The data generation unit 49 outputs a selection signal for selecting the first table Tb1 in a power supply half cycle included in the obtained phase range R. Specifically, the data generation unit 49 performs the following steps.

[0118] Step 31:

[0119] The data generation unit 49 obtains the upper limit value of the output torque (hereinafter referred to as the torque upper limit value Tmax). The value of the torque upper limit value Tmax is stored (set) in, for example, a storage device of the control unit 40. As an example of the torque upper limit value Tmax, it can be considered to be set according to the anti-demagnetization ability of the motor 30 or to be set according to the yield strength of the switching elements Su, Sv, Sw, Sx, Sy, and Sz.

[0120] Step 32:

[0121] The data generation unit 49 obtains the threshold value of the fundamental wave of the load torque (hereinafter referred to as the torque threshold value Tth). Motor torque = first torque command Tm*×higher harmonic component, and the first torque command Tm* is a waveform that pulsates synchronously with the fundamental wave of the load torque. Therefore, by comparing the value obtained by dividing the torque upper limit value Tmax by the peak value of the higher harmonic component of the second mode M2 ​​with the waveform obtained by adding the average torque to the fundamental wave of the load torque, it is possible to predict the range of the mechanical angle θm (phase range R) in which the motor torque exceeds the torque upper limit value Tmax when the second mode M2 ​​is always implemented.

[0122] In other words, by comparing the value obtained by dividing the torque upper limit value Tmax by the peak value of the higher harmonic component of the second mode M2 ​​and subtracting the average torque with the fundamental wave of the load torque, when the conventional example is implemented, it is possible to predict the range of the mechanical angle θm (phase range R) in which the motor torque exceeds the torque upper limit value Tmax. The data generation unit 49 obtains the value obtained by dividing the torque upper limit value Tmax by the peak value of the higher harmonic component of the second mode M2 ​​and subtracting the average torque as the torque threshold value Tth.

[0123] Step 33:

[0124] The data generation unit 49 determines the range of the mechanical angle θm (phase range R) in which the first mode M1 should be implemented. Specifically, the data generation unit 49 obtains the phase range in which the fundamental wave of the load torque exceeds the torque threshold Tth as the range R. Here, the phase range R obtained by the data generation unit 49 is set to [θ1, θ2].

[0125] Step 34:

[0126] The data generation unit 49 obtains the power supply voltage v in The moment when the absolute value of reaches the peak value (corresponding to 90° or 270° in the value of the power supply phase θin) is included in the power supply half cycle within the phase range R.

[0127] Fig.10 The waveforms of the average torque in the conventional power conversion device, the waveform obtained by adding the fundamental wave of the load torque to the average torque, the motor torque, the vibration suppression component, the higher harmonic component, and the absolute value of the power supply voltage are shown as examples. Fig.10 In the waveform diagram of , a large peak appears in the output torque (refer to the circled peak). The power supply half cycle including the circled peak is the power supply half cycle included in the phase range R where the fundamental wave of the load torque exceeds the torque threshold value Tth. Fig.11 The waveforms of the average torque, the waveform obtained by adding the fundamental wave of the load torque to the average torque, the motor torque, the vibration suppression component, the harmonic component, and the absolute value of the power supply voltage in this embodiment are exemplarily shown.

[0128] In the present embodiment, the first mode M1 is executed in the power supply half cycle included in the phase range R in which the fundamental wave of the load torque exceeds the torque threshold Tth. In other words, in the present embodiment, the power supply half cycle included in the phase range R in which the fundamental wave of the load torque exceeds the torque threshold Tth is the first power supply half cycle, and the power supply half cycle other than the first power supply half cycle is the second power supply half cycle.

[0129] In the first mode M1, the basic data D (refer to Figure 4 ) is used for control. Since the output torque and the motor current are roughly proportional, if the basic data D based on the first table Tb1 is used for control, then in the first power supply half cycle, the waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the output torque and the motor current is a waveform with two or more maximum points (refer to Fig.11 ).

[0130] In other words, if the basic data D based on the first table Tb1 is used for control, the output torque and the peak value of the motor current can be reduced. It should be noted that in this embodiment, the second mode M2 ​​is implemented while the operation of the first mode M1 is not implemented.

[0131] <Effects of the present embodiment>

[0132] As described above, in the present embodiment, the peak value of the motor current can be reduced in the power supply half cycle included in the phase range R of the mechanical angle θm in which the fundamental wave of the load torque exceeds the torque threshold value Tth.

[0133] In this embodiment, similarly, the power conversion device 10 implements the second mode M2 ​​in the second power half cycle. In other words, the power conversion device 10 does not actively reduce the peak value of the motor current in the second power half cycle. However, the power conversion device 10 reduces the peak value of the motor current at least in the first power half cycle. In the power conversion device 10, even if the peak value of the motor current is not actively reduced in the second power half cycle, the peak value of the motor current will be reduced from the perspective of the overall operation of the power conversion device 10.

[0134] (Other embodiments)

[0135] It should be noted that, when generating the basic data D, for example, a function encapsulated in the software may be used instead of a table.

[0136] Since the output torque and the motor current are in a substantially proportional relationship, for example, the motor current vector may be used for the command value, the upper limit value, and the threshold value instead of the torque command value, the upper limit value, and the threshold value.

[0137] The switching control of the first mode M1 and the second mode M2 ​​described in the above embodiment can also be applied to the matrix converter. The matrix converter is also an example of a direct power conversion device that does not have an energy storage element (large-capacitance capacitor or large-capacitance inductor).

[0138] The use of the power conversion device 10 is not limited to supplying power to a compressor motor, but the power conversion device 10 can be applied to supplying power to motors for various purposes.

[0139] The above embodiments and modifications are described, but it should be understood that various changes can be made to their forms and details without departing from the spirit and scope of the claims. In addition, the above embodiments and modifications can also be appropriately combined and replaced as long as they do not affect the functions of the objects disclosed.

[0140] - Industrial Applicability -

[0141] In summary, the present disclosure is useful for a power conversion device.

[0142] - Explanation of symbols -

[0143] 10 Power conversion device

[0144] 20 AC power supply

[0145] 30 Motor

[0146] 40 Control Department

Claims

1. A direct power conversion device, which converts AC power of a single-phase AC power source (20) input into AC power of a predetermined frequency by switching operations of a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz), and supplies the AC power to a motor (30) driving a load with periodic load fluctuations, characterized in that: The direct power conversion device comprises a control unit (40) for controlling the switch operation. If the following definition is made, fdc is a frequency twice the frequency of the AC power source (20), fL is the frequency of the periodic load variation, tb=1 / |fdc-n×fL|, Among them, n is a positive integer that maximizes tb. Then, in the first power supply half cycle at the moment when the peak value of the fundamental wave of the load torque and the peak value of the absolute value of the power supply voltage are substantially consistent in the period tb, the control unit (40) executes a first mode, in which the switching elements (Su, Sv, Sw, Sx, Sy, Sz) are controlled so that two or more maximum points appear in the power supply half cycle in a waveform obtained by synthesizing the second harmonic, the fourth harmonic, and the sixth harmonic of the power supply frequency included in the waveform of the absolute value of the motor current vector, In a second power supply half cycle other than the first power supply half cycle during period tb, the control unit (40) executes a second mode in which the switching elements (Su, Sv, Sw, Sx, Sy, Sz) are controlled so that there is one maximum point in a waveform obtained by synthesizing the second harmonic, the fourth harmonic, and the sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the motor current vector.

2. The direct power conversion device according to claim 1, characterized in that: In the power supply half cycle including the moment when the fundamental wave of the load torque reaches the maximum, The control unit (40) controls the switching elements (Su, Sv, Sw, Sx, Sy, Sz) so that two or more maximum points appear in a power supply half cycle in a waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the motor current vector.

3. The direct power conversion device according to claim 1, characterized in that: In a power supply half cycle within a phase range (R) of a mechanical angle in which the fundamental wave of the load torque exceeds a predetermined threshold, The control unit (40) controls the switching elements (Su, Sv, Sw, Sx, Sy, Sz) so that two or more maximum points appear in a power supply half cycle in a waveform obtained by synthesizing the second harmonic, fourth harmonic, and sixth harmonic of the power supply frequency contained in the waveform of the absolute value of the motor current vector.

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