Power conversion device

Abstract

To suppress the harmonics generated in a power supply current with LC resonance in a circuit including a DC link capacitor and a reactor.SOLUTION: A power conversion device (10) includes an inverter circuit (13) that is connected in parallel with a capacitor (C), has switching elements (Su, Sv, Sw, Sx, Sy, Sz), and suppresses LC resonance of a circuit including the capacitor (C) and a reactor (L). During a half-cycle period of LC resonance starting from a transition timing from a non-conductive period in which no current flows from an AC power source (20) to a converter circuit (11) to a conductive period in which current flows from the AC power source (20) to the converter circuit (11), the power conversion device causes a control unit (40) to control the inverter circuit (13) so that an integral value of a current flowing from the capacitor (C) to the inverter circuit (13) becomes 0 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device that converts power output from an AC power supply and supplies the power to a load. [Background technology]

[0002] The power conversion device disclosed in Patent Document 1 includes a rectifier circuit that rectifies and outputs AC output from an AC power source, an inverter circuit having a plurality of switching elements that converts the DC output from the rectifier circuit into AC by switching operations of the switching elements and supplies the AC to a load, a DC link capacitor that is connected between input nodes of the inverter circuit and has a capacitance value set to allow fluctuations in the output voltage of the rectifier circuit and suppress ripple voltage caused by the switching operations, a reactor that is connected between the AC power source and the rectifier circuit, and a control unit that controls the inverter circuit. In this power conversion device, the control unit controls the inverter circuit to have a non-conducting period during which no current flows from the AC power source to the rectifier circuit, thereby reducing the modal current effective value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6566105 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, immediately after the non-conducting period transitions to a conducting period in which current flows from the AC power supply to the rectifier circuit, harmonic components are superimposed on the power supply current flowing from the AC power supply to the rectifier circuit due to LC resonance in a circuit including the DC link capacitor and the reactor.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to suppress harmonics generated in a power supply current due to LC resonance in a circuit including a DC link capacitor and a reactor. [Means for solving the problem]

[0006] A first aspect of the present disclosure includes a rectifier circuit (11) that rectifies and outputs an AC current output from a single-phase AC power supply (20), a first inverter circuit (13) having a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) and converting a DC current output from the rectifier circuit (11) into an AC current by switching operations of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) and supplying the DC current to a first load (30), a DC link capacitor (C) that is connected between input nodes of the first inverter circuit (13) and has a capacitance value set to tolerate fluctuations in an output voltage of the rectifier circuit (11) and suppress a ripple voltage caused by the switching operation, a reactor (L) that is connected between the rectifier circuit (11) and the first inverter circuit (13) or between the AC power supply (20) and the rectifier circuit (11), and a DC link capacitor (C) that is connected between the input nodes of the first inverter circuit (13) and has a capacitance value set to tolerate fluctuations in an output voltage of the rectifier circuit (11) and suppress a ripple voltage caused by the switching operation, and a control unit (40) that controls the first inverter circuit (13) so that there is a non-conduction period in which no current flows through the rectifier circuit (11), and the power conversion device further comprises a resonance suppression unit (13, 14) that is connected in parallel with the DC link capacitor (C) and has at least one switching element (Su, Sv, Sw, Sx, Sy, Sz, 141) and suppresses LC resonance of a circuit including the DC link capacitor (C) and the reactor (L), wherein the control unit (40) controls the resonance suppression unit (13, 14) so ​​that an integral value of a current flowing from the DC link capacitor (C) to the resonance suppression unit (13, 14) becomes 0 or less during a half-cycle period (T1) of the LC resonance, the half-cycle period starting from a transition timing (t1) at which the non-conduction period transitions to a conduction period in which a current flows from the AC power source (20) to the rectifier circuit (11).

[0007] In the first mode, during a half cycle period of the LC resonance starting from the transition timing (t1), the integral value of the current flowing from the DC link capacitor (C) to the resonance suppression unit (13, 14) is controlled to be 0 or less. Therefore, compared with the case where the integral value exceeds 0, the power supply current (i in ) harmonics can be suppressed.

[0008] A second aspect of the present disclosure is characterized in that, in the first aspect, the control unit (40) controls the resonance suppression unit (13, 14) so ​​that the current flowing from the DC link capacitor (C) to the resonance suppression unit (13, 14) is equal to or less than 0 at the transition timing (t1).

[0009] In the second mode, at the transition timing (t1), the current flowing from the DC link capacitor (C) to the resonance suppression unit (13, 14) is set to 0 or less, so that the power supply current (i in ) harmonics can be suppressed.

[0010] A third aspect of the present disclosure is characterized in that, in the first or second aspect, the resonance suppression unit (13, 14) is the first inverter circuit (13) and the first load (30) is a motor (30).

[0011] A fourth aspect of the present disclosure is the third aspect, wherein the motor (30) is a motor (30) for a compressor.

[0012] A fifth aspect of the present disclosure is characterized in that, in the first or second aspect, a resonance suppression circuit (14) is provided having a capacitance element (143) and a switching element (141) for a resonance suppression circuit connected in series with each other and connected in parallel with the DC link capacitor (C), the resonance suppression unit (13, 14) is the resonance suppression circuit (14), and the control unit (40) sets the transition timing (t1) to the timing when the voltage of the capacitance element (143) is higher than the voltage of the DC link capacitor (C).

[0013] In the fifth aspect, by turning on the switching element (141) for the resonance suppression circuit, a current can be caused to flow from the capacitance element (143) to the DC link capacitor (C).

[0014] A sixth aspect of the present disclosure is characterized in that, in the fifth aspect, the resonance suppression circuit (14) further includes a diode (144) connected in parallel with the switching element (141) for the resonance suppression circuit with its cathode facing the capacitive element (143).

[0015] In the sixth aspect, when the switching element (141) for the resonance suppression circuit is turned off, a drop in the voltage of the capacitance element (143) caused by a current flowing out of the capacitance element (143) can be restricted by the diode (144). Also, when the switching element (141) for the resonance suppression circuit is turned off, the capacitance element (143) is charged via the diode (144), so that the voltage of the capacitance element (143) can be made higher than the voltage of the DC link capacitor (C).

[0016] A seventh aspect of the present disclosure is characterized in that, in the fifth or sixth aspect, a second inverter circuit (145) is connected to the capacitive element (143) for converting the voltage of the capacitive element (143) into AC and supplying the AC voltage to a second load (60) different from the first load (30).

[0017] In the seventh aspect, the energy stored in the capacitive element (143) can be supplied to the second load (60).

[0018] An eighth aspect of the present disclosure is any one of the first to fourth aspects, wherein the control unit (40) controls the voltage (v dc The resonance suppression unit (13, 14) is controlled based on the detected value of the resonance suppression unit (13, 14).

[0019] A ninth aspect of the present disclosure includes a rectifier circuit (11) that rectifies and outputs an AC current output from a single-phase AC power supply, an inverter circuit (13) having a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) and converting a DC current output by the rectifier circuit (11) into an AC current by switching operations of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) and supplying the AC current to a load (30), a DC link capacitor (C) that is connected between input nodes of the inverter circuit (13) and has a capacitance value set to tolerate fluctuations in an output voltage of the rectifier circuit (11) and suppress a ripple voltage caused by the switching operation, a reactor (L) that is connected between the rectifier circuit (11) and the inverter circuit (13) or between the AC power supply (20) and the rectifier circuit (11), and a current that flows from the AC power supply (20) to the rectifier circuit (11). and a control unit (40) that controls the inverter circuit (13) to have a non-conduction period in which no current flows, the power conversion device further comprising a resonance suppression unit (13, 14) that is connected in parallel with the DC link capacitor (C) and has at least one switching element (Su, Sv, Sw, Sx, Sy, Sz, 141, 145a) and suppresses LC resonance of a circuit including the DC link capacitor (C) and the reactor (L), wherein the control unit (40) operates the resonance suppression unit (13, 14) to attenuate a physical quantity that correlates to the pulsation of magnetic energy of the reactor (L) due to the LC resonance by more than 80% during a resonance suppression period of three cycles of the LC resonance starting from a transition timing (t1) at which the non-conduction period transitions to a conduction period in which current flows from the AC power source (20) to the rectifier circuit (11).

[0020] In the ninth aspect, during the period of three cycles of the LC resonance starting from the transition timing (t1), the physical quantity correlated with the pulsation of the magnetic energy of the reactor (L) due to the LC resonance is attenuated by more than 80%, so that the power supply current (i in ) harmonics can be suppressed.

[0021] A tenth aspect of the present disclosure includes a rectifier circuit (11) that rectifies and outputs an AC current output from a three-phase AC power supply (20), an inverter circuit (13) having a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) and converting a DC current output by the rectifier circuit (11) into an AC current by switching operations of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) and supplying the DC current to a load, a DC link capacitor (C) that is connected between input nodes of the inverter circuit (13) and has a capacitance value set to allow fluctuations in the output voltage of the rectifier circuit (11) and suppress a ripple voltage caused by the switching operation, a reactor (L) connected between the rectifier circuit (11) and the inverter circuit (13) or between the AC power supply (20) and the rectifier circuit (11), and a reactor (L) that supplies a predetermined phase of the three phases from the AC power supply (20) to the rectifier circuit (11). and a control unit (40) that controls the inverter circuit (13) to have a non-conduction period during which a current of the predetermined phase does not flow, the power conversion device further comprising a resonance suppression unit (13, 14) that is connected in parallel with the DC link capacitor (C) and has at least one switching element (Su, Sv, Sw, Sx, Sy, Sz, 141, 145a) and suppresses LC resonance of a circuit including the DC link capacitor (C) and the reactor (L), wherein the control unit (40) operates the resonance suppression unit (13, 14) to attenuate a physical quantity that correlates to pulsation of magnetic energy of the reactor (L) due to the LC resonance by more than 80% during a resonance suppression period of three periods of the LC resonance starting from a transition timing (t1) at which the non-conduction period transitions to a conduction period during which a current of the predetermined phase flows from the AC power source (20) to the rectifier circuit (11).

[0022] In the tenth aspect, during the period of three cycles of the LC resonance starting from the transition timing (t1), the physical quantity correlated with the pulsation of the magnetic energy of the reactor (L) due to the LC resonance is attenuated by more than 80%, so that the power supply current (i in ) harmonics can be suppressed.

[0023] An eleventh aspect of the present disclosure is the ninth or tenth aspect, characterized in that the physical quantity is an amplitude of a current flowing through the reactor (L) during the resonance suppression period.

[0024] In the eleventh aspect, during the three-cycle period of the LC resonance starting from the transition timing (t1), the amplitude of the current flowing through the reactor (L) due to the LC resonance is attenuated by more than 80%, so that the power supply current (i in ) harmonics can be suppressed.

[0025] A twelfth aspect of the present disclosure includes a rectifier circuit (11) that rectifies and outputs an AC current output from a three-phase AC power supply (20), an inverter circuit (13) having a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) and converting a DC current output by the rectifier circuit (11) into an AC current by switching operations of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) and supplying the DC current to a load (30), a DC link capacitor (C) that is connected between input nodes of the inverter circuit (13) and has a capacitance value set to tolerate fluctuations in the output voltage of the rectifier circuit (11) and suppress ripple voltage caused by the switching operation, a reactor (L) connected between the rectifier circuit (11) and the inverter circuit (13) or between the AC power supply (20) and the rectifier circuit (11), and a pre-cooled inverter circuit (13) that supplies a DC current to a load (30). and a control unit (40) that controls the inverter circuit (13) to have a non-conduction period during which a current of a specified phase among the three phases does not flow, the power conversion device further comprising a resonance suppression unit (13, 14) that is connected in parallel with the DC link capacitor (C) and has at least one switching element (Su, Sv, Sw, Sx, Sy, Sz, 141) and suppresses LC resonance of a circuit including the DC link capacitor (C) and the reactor (L), the control unit (40) controls the resonance suppression unit (13, 14) so ​​that an integral value of a current flowing from the DC link capacitor (C) to the resonance suppression unit (13, 14) becomes 0 or less during a half-cycle period of the LC resonance starting from a transition timing (t1) at which the non-conduction period transitions to a conduction period during which a current of the specified phase flows from the AC power supply (20) to the rectifier circuit (11).

[0026] In the twelfth aspect, during a half cycle period of the LC resonance starting from the transition timing (t1), the integral value of the current flowing from the DC link capacitor (C) to the resonance suppression unit (13, 14) is controlled to be 0 or less. Therefore, compared with the case where the integral value exceeds 0, the power supply current (i in ) harmonics can be suppressed. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a block diagram showing a configuration of a power conversion device according to a first embodiment. [Diagram 2] FIG. 2 shows an example of a power supply current waveform. [Diagram 3] FIG. 3 shows an example of waveforms of a power supply voltage and a DC voltage. [Figure 4] FIG. 4 shows the waveforms of the power supply voltage and the DC voltage under conditions 1 to 3. In FIG. [Diagram 5] FIG. 5 shows the waveforms of the power supply current under conditions 1 to 3. [Figure 6] FIG. 6 shows an example of waveforms of the power supply voltage, the DC voltage, and the inverter current before and after the transition timing in the first embodiment. [Figure 7] FIG. 7 is a diagram equivalent to FIG. 6 when the inverter current at the transition timing is set to a positive value. [Figure 8] FIG. 8 shows the waveform of the current flowing through the reactor due to LC resonance when the damping coefficient is 1000. [Figure 9] FIG. 9 is an enlarged view of the portion X in FIG. [Figure 10] FIG. 10 is a graph showing the relationship between the damping ratio and the proportion of the harmonics relative to the harmonics when the damping ratio is zero. [Figure 11] FIG. 11 is a view corresponding to FIG. 1 of the second embodiment. [Figure 12] FIG. 12 is a block diagram showing a configuration of the repetition control unit. [Figure 13] FIG. 13 is a view corresponding to FIG. 1 of the third embodiment. [Figure 14] FIG. 14 shows waveforms of a DC voltage, a DC voltage command value, a power supply voltage, a compensation amount generated by feedback control of a DC voltage, and a compensation amount generated by repetitive control of a DC voltage in the third embodiment. [Figure 15] FIG. 15 shows the power supply current, the power supply current command value, the inverter current, and the q-axis current in the third embodiment. [Figure 16] FIG. 16 is a view corresponding to FIG. 1 of the fourth embodiment. [Figure 17]FIG. 17 shows waveforms of the DC link voltage, the power supply voltage, and the voltage of the resonance suppression circuit in the fourth embodiment. [Figure 18] FIG. 18 is a view corresponding to FIG. 1 of the fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the following embodiments are essentially preferred examples and are not intended to limit the scope of the present invention, its applications, or its uses.

[0029] (Embodiment 1) FIG. 1 shows a configuration of a power conversion device (10) according to a first embodiment of the present disclosure. The power conversion device (10) converts an input AC voltage (in this example, a power supply voltage (v in )) into a predetermined output AC voltage and supplies it to a motor (30) serving as a first load. In this embodiment, as shown in Fig. 1, the power conversion device (10) includes a reactor (L), a converter circuit (11), a DC link unit (12), an inverter circuit (13), and a control unit (40). The motor (30) is, for example, an Interior Permanent Magnet Motor (IPM motor), and in this embodiment, drives a compressor (not shown) of an air conditioner.

[0030] <Reactor> The reactor (L) is connected between the AC power supply (20) and one input node of the converter circuit (11).

[0031] <Converter circuit> The converter circuit (11) is a rectifier circuit that is connected to an AC power source (20) via a reactor (L) and that full-wave rectifies and outputs an AC signal output from the AC power source (20). In this example, the converter circuit (11) includes four diodes (D1, D2, D3, D4) connected in a bridge configuration. That is, the converter circuit (11) is configured as a diode bridge circuit.

[0032] <DC link section> The DC link unit (12) has a capacitor (C) as a DC link capacitor connected between a pair of input nodes of the inverter circuit (13), and is connected to the output of the converter circuit (11) (i.e., the full-wave rectified power supply voltage (v in )) to obtain the DC voltage (v dc ) to generate a DC voltage (v dc ) is the power supply voltage (v in ) pulsates according to the frequency of the DC voltage (v dc ) is the voltage across the capacitor (C).

[0033] Here, the power supply voltage (v in ) is a pulsating component according to the frequency of the DC voltage (v dc ), the capacitance value of the capacitor (C) in the DC link section (12) is set so as to tolerate fluctuations in the output of the converter circuit (11) and to suppress ripple voltage (voltage fluctuations according to the switching frequency) caused by the switching operation (described later) of the inverter circuit (13). Specifically, the capacitor (C) is made of a small-capacity capacitor (e.g., a film capacitor) having a capacitance value (e.g., about several 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 converter circuit in a general power conversion device. Since the capacitor (C) is configured in this way, the output of the converter circuit (11) is hardly smoothed in the DC link section (12), and as a result, the power supply voltage (v in ) frequency (in this example, the power supply voltage (v in ) is a pulsating component with a frequency twice that of the DC voltage (v dc ) remains at the DC voltage (v dc ) pulsates so that its maximum value is more than twice its minimum value.

[0034] <Inverter circuit> The inverter circuit (13) has six bridge-connected switching elements (Su, Sv, Sw, Sx, Sy, Sz) and six freewheeling diodes (Du, Dv, Dw, Dx, Dy, Dz) to supply a three-phase output AC voltage to the motor (30). To explain in detail, the inverter circuit (13) has three switching legs each formed by connecting two switching elements in series with each other, and in each of the three switching legs, a midpoint between the switching element (Su, Sv, Sw) of an upper arm and the switching element (Sx, Sy, Sz) of a lower arm is connected to a coil of each phase (coil of u-phase, v-phase, w-phase) of the motor (30). In addition, six freewheeling diodes (Du, Dv, Dw, Dx, Dy, Dz) are connected in anti-parallel to each of the six switching elements (Su, Sv, Sw, Sx, Sy, Sz). The inverter circuit (13) has a pair of input nodes connected to both ends of the capacitor (C) of the DC link section (12), and converts the DC output by the converter circuit (11) into AC by the switching action of switching elements (Su, Sv, Sw, Sx, Sy, Sz) and supplies the AC to the motor (30).

[0035] <Control Unit> The control unit (40) is configured using a microcomputer and a memory device in which software for controlling the microcomputer is stored. The control unit (40) controls the output (output AC voltage) of the inverter circuit (13) by controlling the switching operation of the inverter circuit (13) so that the rotation speed (ω) of the motor (30) becomes equal to a given command value (hereinafter, referred to as rotation speed command value (ω*)). In this way, the drive of the motor (30) is controlled.

[0036] In order to realize the above control, as shown in FIG. 1, the control unit (40) includes a first subtraction unit (41), a speed control unit (42), a dq-axis current command calculation unit (43), a second subtraction unit (44), a PI control unit (45), an addition unit (46), a phase conversion unit (47), a coordinate conversion unit (48), a dq-axis current control unit (49), and a PWM calculation unit (50).

[0037] The first subtraction section (41) calculates the deviation between the rotation speed (ω) of the motor (30) and a rotation speed command value (ω*).

[0038] The speed control unit (42) performs, for example, PID calculations (proportional, integral, differential) based on the deviation calculated by the first subtraction unit (41) to generate a command value for an average motor torque (Tm) (hereinafter, average torque command value (Tm*)). The average torque command value (Tm*) is output to a dq-axis current command calculation unit (43).

[0039] The dq-axis current command calculation unit (43) calculates the power supply voltage (v in ) (hereafter referred to as power supply phase (θin)) in ) frequency (for example, 50 Hz) in This power supply current command value (|i in *|) is generated so that when a waveform obtained by extracting and synthesizing the fundamental wave, third harmonic, and fifth harmonic based on the fundamental frequency of the voltage of the AC power source (20) is multiplied by the polarity of the voltage of the AC power source (20), the waveform has two or more maximum points in a half power cycle. in The power supply current command value (|i *|) is generated so as to have a non-conducting period during which no current flows from the AC power supply (20) to the converter circuit (11). in The waveform in Figure 2 shows an example of the power supply current command value (|i in As shown in Figure 2, this power supply current command value (|i in *|), one maximum point appears in each of the first and second halves. in *|) waveform, the power supply current command value (|i in *|) is set to zero. In this way, the power supply current (i in), the existence of a non-conduction period makes it possible to reduce the d-axis current and minimize the effective motor current. In other words, depending on the length of the non-conduction period, it is possible to select whether to minimize the peak of the motor current or to minimize the effective motor current.

[0040] The power supply current command value (|i in * In order to generate the dq-axis current command (θ in ) is calculated (more specifically, calculated at the time of design) and stored in the memory device in the form of a table or function (hereinafter referred to as a table, etc.). in * |) value, the power phase (θ in ) as an argument and reads it out.

[0041] The dq-axis current command calculation unit (43) calculates the q-axis current (i q ) command value (hereafter, q-axis current command value (i q * The pulsation command value (i p * ) is generated. p * The generation of (1) is carried out using the following formulas (1) to (8).

[0042]

number

[0043]

number

[0044]

number

[0045]

number

[0046]

number

[0047]

number

[0048]

number

[0049]

number

[0050] In these formulas, v in is the power supply voltage, i in is the power supply current, v dc and P inv is the output power of the inverter circuit (13), L is the inductance of the reactor (L), and C is the capacitance of the capacitor (C). d is the d-axis current, i q is the q-axis current, T m is the average motor torque, p n indicates the number of motor pole pairs. In these equations, the "(t)" added after each variable indicates that the value of each variable is the value at time t. However, for simplicity, each equation is assumed to have no loss in the converter circuit (11) and the inverter circuit (13).

[0051] For example, the formulas (1) to (4) are derived from the relationship between the current and voltage in each part of the circuit (see FIG. 1) constituting the power conversion device (10). As can be seen from the formulas (1) to (5), the power supply current (i in ) absolute value (i.e., the power supply current command value (|i in* |)) to inverter power (P inv ) can be derived. In addition, the inverter power (P inv ) and the motor output (see the right side of equation (6)) are almost equal, so equation (6) holds. Also, the average motor torque (T m ) can be expressed as in equation (7). As can be seen from equation (7), the d-axis current (i d ) is constant, the average motor torque (T m ) is the q-axis current (i q ) is proportional to

[0052] Therefore, as shown in equation (8), the q-axis current (i q ) is the inverter power (P inv ) is approximately proportional to the inverter power (P inv ) is normalized so that its average value is 1, and the average torque command value (T m * ) to obtain the q-axis current (i q ) is the command value (i.e., the pulsation command value (i p * )) can be calculated.

[0053] The second subtraction unit (44) calculates the DC voltage (v dc ) command value (V dc_c ) to DC voltage (v dc ) predicted value (V dc_p ) to obtain the DC voltage (v dc ) command value (V dc_c ) and predicted value (V dc_p The control unit (40) calculates the deviation from this DC voltage (v dc ) predicted value (V dc_p ) into DC voltage (v dc ) is calculated by referring to the detected value of the DC voltage (v dc ) predicted value (V dc_p ) is the reference DC voltage (v dc ) is based on the detection value of the DC voltage (v dc ) predicted value (V dc_p ) is the reference DC voltage (v dc) is the value one control cycle ahead of the timing at which it was detected.

[0054] The PI control unit (45) adjusts the compensation amount (q-axis current command compensation amount (i comp * In this example, the PI control section (45) calculates and outputs the DC voltage (v dc ) command value (V dc_c ) and predicted value (V dc_p ) based on the deviation from the q-axis current command compensation amount (i comp * The second subtraction unit (44) and the PI control unit (45) constitute a feedback control unit (51).

[0055] The adder (46) calculates the pulsation command value (i p * ) to the q-axis current command compensation amount (i comp * ) and the sum is used as the q-axis current command value (i q * ) to the dq-axis current control unit (49).

[0056] The phase converter (47) converts the DC link current (i dc ) to the u-phase current (i u ) and w-phase current (i w ) and output.

[0057] The coordinate conversion unit (48) converts the u-phase current (i u ) and w-phase current (i w ) and the electrical angle (motor phase) of the rotor (not shown) of the motor (30), a so-called dq transformation is performed to obtain the d-axis current (i d ) and q-axis current (i q ) is derived. Note that the u-phase current (i u ) and v-phase current (i v ) can be directly detected by providing a current sensor, for example.

[0058] The dq-axis current control unit (49) calculates the d-axis current command value (i d *), q-axis current command value (i q *), d-axis current (i d ), and q-axis current (i q ) based on the d-axis voltage command value (v d *) and q-axis voltage command value (v q Specifically, the dq-axis current control unit (49) derives a d-axis current command value (i d *) and d-axis current (i d ) and the q-axis current command value (i q *) and q-axis current (i q ) so that the deviation from the d-axis voltage command value (v d *) and q-axis voltage command value (v q *) is derived.

[0059] The PWM calculation unit (50) generates a control signal (G) for controlling the on / off of switching elements (Su, Sv, Sw, Sx, Sy, Sz) in the inverter circuit (13). Specifically, the PWM calculation unit (50) generates a control signal (G) for controlling the on / off of switching elements (Su, Sv, Sw, Sx, Sy, Sz) in the inverter circuit (13). dc ), d-axis voltage command value (v d *), q-axis voltage command value (v q The PWM calculation unit (50) sets the duty ratio of a control signal (G) to be supplied to each of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) based on the duty ratio (PWM control signal (G)). When the control signal (G) is output, each of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) performs a switching operation (on / off operation) at the duty ratio set by the PWM calculation unit (50). This control signal (G) is periodically updated to control the switching operation in the inverter circuit (13).

[0060] <Operation of the power conversion device> When the power conversion device (10) starts operating, the converter circuit (11) converts the power supply voltage (v in ) is full-wave rectified and output to the DC link unit (12). The DC link unit (12) receives the output of the converter circuit (11) as an input and converts it into a power supply voltage (v in ) pulsating at twice the frequency of thedc ) is generated. As shown in Figure 3, dc ) is a constant value greater than 0 during a predetermined period near the zero crossing (hereinafter referred to as the zero crossing vicinity period (P0)). During this zero crossing vicinity period (P0), in ) is zero, and the DC voltage (v dc ) is the period corresponding to the valley of the pulsation waveform.

[0061] In the power conversion device (10), a dq-axis current command calculation unit (43) calculates a power supply voltage (v in The power supply current command value (|i in The dq-axis current command calculation unit (43) generates the power supply current command value (|i in Based on *|, the pulsation command value (i p On the other hand, the PI control unit (45) generates a power supply current command value (|i in *|) and DC voltage (v dc ) command value (V dc_c ) and predicted value (V dc_p ) so that the deviation from the q-axis current command compensation amount (i comp * ) is calculated. This gives the q-axis current command value (i q *) is calculated.

[0062] In this way, the q-axis current command value (i q When the d-axis current command value (i d *), q-axis current command value (i q *) etc., the d-axis voltage command value (v d *) and q-axis voltage command value (v q *) is generated. As a result, a control signal (G) is generated by the PWM calculation unit (50), and the inverter circuit (13) performs a switching operation in accordance with the control signal (G). As a result, a predetermined AC power is supplied from the inverter circuit (13) to the motor (30), and the motor (30) is driven.

[0063] As described above, in the first embodiment, the control unit (40) controls the inverter circuit (13) so as to have a non-conduction period during which no current flows from the AC power supply (20) to the converter circuit (11).

[0064] FIG. 4 shows the power supply voltage (v) in the circuit of FIG. 1 under condition 1 in which a current flows from the inverter circuit (13) to the capacitor (C), condition 2 in which a current flows from the capacitor (C) to the inverter circuit (13), and condition 3 in which no current flows between the inverter circuit (13) and the capacitor (C). in ) and DC voltage (vdc). in ) waveform is shown.

[0065] From FIG. 5, under condition 1, the power supply current (i in ) can be suppressed most effectively.

[0066] When the non-conduction period is provided as in the first embodiment, LC resonance may occur at a transition timing (t1) (see FIG. 6) when the non-conduction period transitions to a conduction period in which a current flows from the AC power supply (20) to the converter circuit (11). In FIG. 7, the inverter current (i inv ) is a positive value. Therefore, immediately after the transition timing (t1), current flows to the motor (30), and the DC voltage (v dc ) decreases, the energy of the reactor (L) becomes larger than the energy of the capacitor (C), and resonance is likely to occur. Therefore, in the first embodiment, during a half-cycle period (T1) (see FIG. 6) of the LC resonance starting from the transition timing (t1) (see FIG. 6), the inverter current (i inv ) is integrated to be less than or equal to 0. dc ) command value (V dc_c ) to set the DC voltage (v dc ) command value (V dc_c) is the DC voltage (v dc ) is the power supply voltage (v in ) is set to gradually increase along with the absolute value of the inverter current (i inv ) is less than or equal to 0, dc ) command value (V dc_c ) to set the

[0067] Furthermore, in the first embodiment, the inverter current (i inv ) is integrated to be less than or equal to 0. dc ) command value (V dc_c ) is set. Note that the inverter current (i inv ) becomes 0 or less, and during part or all of the period (T2), the inverter current (i inv ) may be made to exceed 0.

[0068] Therefore, in the first embodiment, as shown in FIG. in ) and DC voltage (v dc During the half-cycle period (T1) of the LC resonance starting from the transition timing (t1) at which the inverter current (i inv ) is equal to or less than 0. Also, during the half cycle period (T2) of the LC resonance immediately before the transition timing (t1), the inverter current (i inv ) is equal to or less than 0. This reduces the power supply current (i in ) harmonics can be suppressed. Also, at the transition timing (t1), inv ) is set to 0 or less, so the inverter current (i inv ) exceeds 0, the power supply current (i in ) harmonics can be suppressed. This also makes it possible to reduce the size of the reactor (L).

[0069] In the first embodiment, the DC voltage (v dc ) command value (Vdc_c ) is further set so that the amplitude of the current flowing through the reactor (L) attenuates by more than 80% during the resonance suppression period. Therefore, the control unit (40) operates the inverter circuit (13) to attenuate the amplitude of the current flowing through the reactor (L) by more than 80% during the resonance suppression period of three cycles of the LC resonance starting from the transition timing (t1). In other words, at the end of the resonance suppression period, the amplitude of the current flowing through the reactor (L) is less than 20% of that at the transition timing (t1). The current flowing through the reactor (L) is set to I L The amplitude of the current rise is A, the damping coefficient is B, and the resonance frequency is f LC Then, the current I L is expressed by the following formula:

[0070] I L =Ae -Bt sin(2πf LC t) Figure 8 shows the current I L As shown in Figure 9, the waveform of the current I L is attenuated by a predetermined damping ratio C% for each resonance period. FIG. 10 shows the relationship between the damping ratio C when the resonance frequency is 1950 Hz and the ratio of harmonics to harmonics when the damping ratio C is 0 at the end of the resonance suppression period (the period of three cycles of the LC resonance starting from the transition timing (t1)). By setting the damping ratio C to 40% or more, the harmonics can be reduced to 10% or less of the harmonics when the damping ratio C is 0. The change in the ratio of harmonics to the damping ratio C is large until the damping ratio C reaches 40%, and decreases when the damping ratio C becomes 40% or more. Therefore, it is preferable to set the damping ratio C to 40% or more. Also, in FIG. 9, when the damping ratio C for each resonance period is 40%, the current I L At the end of the resonance suppression period, the amplitude of the current I is reduced by about 80% compared to the first half cycle from the transition timing (t1). Therefore, by setting the damping ratio C to 40% or more, the amplitude of the current I L The amplitude of the signal can be reduced by 80% or more.

[0071] Therefore, in the first embodiment, the amplitude of the current flowing through the reactor (L) is attenuated by more than 80% during the resonance suppression period, so that the power supply current (i in ) harmonics can be suppressed.

[0072] (Embodiment 2) 11 shows a configuration of a power converter (10) according to a second embodiment of the present disclosure. In the second embodiment, the control unit (40) includes a repetitive control unit (52) instead of the PI control unit (45).

[0073] As shown in FIG. 12, the repetitive control unit (52) has a first index generation unit (521), a power supply phase calculation unit (522), a second index generation unit (523), a third subtraction unit (524), a first switching unit (525), a deviation memory unit (526), ​​a second switching unit (527), and a compensation amount calculation unit (528).

[0074] The first index generating unit (521) outputs a switching signal (SW1) that specifies which of K types of phase ranges the current power supply phase (θin) belongs to.

[0075] The power supply phase calculation unit (522) calculates the current power supply phase (θin).

[0076] The second index generation unit (523) calculates the compensation amount this time based on the current power supply phase (θin) calculated by the power supply phase calculation unit (522) as a DC voltage (v dc ) detection value. Specifically, the second index generation unit (523) calculates a power phase (θin) that is 3 / 4 of the pulse width modulation period ahead of the current power phase (θin). Then, the second index generation unit (523) outputs a switching signal (SW2) that specifies which of K phase ranges the calculated power phase (θin) belongs to.

[0077] The third subtraction unit (524) calculates the DC voltage (v dc ) to the detected DC voltage (v dc ) command value (Vdc_c ) to obtain the DC voltage (v dc ) command value (V dc_c ) and DC voltage (v dc ) and calculate the deviation from the detected value.

[0078] The first switch unit (525) selects one of the input terminals of the deviation storage unit (526) in response to the switch signal (SW1) output by the first index generation unit (521). Then, the first switch unit (525) connects the selected input terminal to the output of the third subtraction unit (524).

[0079] The deviation storage unit (526) divides the power supply phase (θin) of 0 to 180° into phase ranges of 0° or more and less than 180° / K, 180° / K or more and less than 360° / K, 360° / K or more and less than 540° / K, and . . . 180°*(K-1) / K or more and less than 180°, and sequentially assigns indexes of 1 to K to each phase range. Also, the deviation input from the first switching unit (525) is stored as the deviation of the phase range specified by the switching signal (SW1).

[0080] The second switching unit (527) outputs, from the deviations stored in the deviation storage unit (526), ​​the deviation that corresponds to the phase range specified by the switching signal (SW2) output by the second index generation unit (523), to the compensation amount calculation unit (528).

[0081] The compensation amount calculation unit (528) calculates the compensation amount (q-axis current command compensation amount (i comp * The compensation amount calculation unit (528) calculates and outputs the q-axis current command compensation amount (i comp * ) is required.

[0082] In the second embodiment, as in the first embodiment, the DC voltage (v dc ) command value (V dc_c ) is set.

[0083] The other configurations are the same as those in the first embodiment, so the same components are given the same reference numerals and detailed descriptions thereof are omitted.

[0084] (Embodiment 3) FIG. 13 shows a configuration of a power conversion device (10) according to a third embodiment of the present disclosure. In the third embodiment, an adder (46) calculates the sum of a q-axis current command compensation amount output by a feedback (FB) control unit (51) multiplied by −1 and a q-axis current command compensation amount output by a repetitive control unit (52) multiplied by −1 as a pulsation command value (i p * ) to

[0085] The other configurations are the same as those in the first embodiment, so the same components are given the same reference numerals and detailed descriptions thereof are omitted.

[0086] Figure 14 shows the DC voltage (v dc ), DC voltage command value (V dc_c ), power supply voltage (v in ), DC voltage (v dc ) feedback control, and the DC voltage (v dc ) is generated by the repetitive control of the power supply current (i in ), power supply current command value (|i in *|), inverter current (i inv ), and q-axis current (i q ) is shown.

[0087] As shown in Figure 14, the DC voltage (v dc ) repetitive control does not cause control delay, so the DC voltage (v dc ) and power supply voltage (v in ) becomes equal to the compensation amount generated by the repetitive control. Therefore, as shown in FIG. 15, at the transition timing (t1), the inverter current (i inv ) can be reduced to 0 or less, and the power supply current (i in ) can reduce the current flowing to the motor (30).

[0088] (Embodiment 4) FIG. 16 shows a configuration of a power conversion device (10) according to a fourth embodiment of the present disclosure. In the fourth embodiment, a resonance suppression circuit (14) serving as a resonance suppression unit is connected in parallel with a capacitor (C). The resonance suppression circuit (14) has a resonance suppression circuit switching element (141), a resistor (142), and a capacitance element (capacitor) (143) that are connected in series in this order from the input node side of the upper arm of the inverter circuit (13). A diode (144) is connected in parallel with the resonance suppression circuit switching element (141) with its cathode facing the capacitance element (143). A fan motor inverter circuit (145) serving as a second inverter circuit that converts the voltage of the capacitance element (143) into AC and supplies the AC voltage to a fan motor (60) serving as a second load different from the motor (30) is connected to the capacitance element (143). The fan motor inverter circuit (145) has at least one switching element (145a).

[0089] The control unit (40) determines the transition timing (t1) to be the timing when the voltage of the capacitive element (143) is higher than the voltage of the capacitor (C).

[0090] The control unit (40) controls the switching element (141) for the resonance suppression circuit so that the integral value of the current flowing from the capacitor (C) to the resonance suppression circuit (14) becomes 0 or less during a half cycle period of the LC resonance starting from the transition timing (t1).

[0091] Furthermore, at the transition timing (t1), the control unit (40) controls the switching element (141) for the resonance suppression circuit so that the current flowing from the capacitor (C) to the resonance suppression circuit (14) becomes zero or less.

[0092] In addition, the control unit (40) operates the switching element (141) for the resonance suppression circuit to attenuate the amplitude of the current flowing through the reactor (L) by more than 80% during a resonance suppression period of three cycles of the LC resonance starting from the transition timing (t1).

[0093] The other configurations are the same as those in the first embodiment, so the same components are given the same reference numerals and detailed descriptions thereof are omitted.

[0094] 17, the voltage of the resonance suppression circuit (14) is maintained at or above the voltage of the capacitor (C). Therefore, by turning on the switching element (141) for the resonance suppression circuit, a current can flow from the capacitance element (143) to the capacitor (C). When the switching element (141) for the resonance suppression circuit is turned off, the diode (144) can prevent a current from flowing out of the capacitance element (143) and a voltage drop of the capacitance element (143). When the switching element (141) for the resonance suppression circuit is turned off, the capacitance element (143) can be charged via the diode (144).

[0095] In addition, since the diode (144) is provided, when the resonance suppression circuit switching element (141) is turned off, the control unit (40) controls the fan motor inverter circuit (145) to supply power to the fan motor (60), thereby reducing the voltage of the capacitance element (143) and the DC voltage (v dc ) (the voltage of the capacitor (C)) can be adjusted to be lower. Therefore, during the period from the time when half a resonance cycle has passed since the transition timing (t1) to the time when one resonance cycle has passed since the transition timing (t1), the DC voltage (v dc ) is the power supply voltage (v in ) when the DC voltage (v dc ) to reduce the power supply voltage (v in ) and DC voltage (v dc ) and the resonance can be reduced. In other words, by controlling the inverter circuit (145) for the fan motor, the DC voltage (v dc ) and reduce resonance. dc ) can also be achieved by controlling the inverter circuit (13).

[0096] (Embodiment 5) 18 illustrates a configuration of a power conversion device (10) according to a fifth embodiment of the present disclosure. In the fifth embodiment, the AC power supply (20) is a three-phase AC power supply.

[0097] The maximum power consumption of the motor (30) is Pmax (W), and the voltage value of the AC power supply (20) is V. in When the load current (V) is (V) and the capacitance of the capacitor (C) is (C(F), if Pmax≧2000 holds, the following equation (9) holds.

[0098]

number

[0099] The transition timing (t1) corresponds to a transition from a non-conductive period, in which current of a specified phase among the three phases does not flow from the AC power source (20) to the converter circuit (11), to a conductive period, in which current of the specified phase flows from the AC power source (20) to the converter circuit (11).

[0100] The other configurations are the same as those in the first embodiment, so the same components are given the same reference numerals and detailed descriptions thereof are omitted.

[0101] In the second to fourth embodiments, similarly to the fifth embodiment, the AC power supply (20) may be a three-phase AC power supply.

[0102] In the first to fifth embodiments, the first load is the compressor motor (30), but may be another load. In the fourth embodiment, the second load is the fan motor (60), but may be another load as long as it is different from the first load.

[0103] Further, in the above first to fifth embodiments, the reactor (L) is connected between the AC power supply (20) and the converter circuit (11). However, the reactor (L) may be connected between the converter circuit (11) and the inverter circuit (13).

[0104] In the above first to fifth embodiments, the control unit (40) operates at least one of the inverter circuit (13), the resonance suppression circuit switching element (141), and the fan motor inverter circuit (145) to attenuate the amplitude of the current flowing through the reactor (L) by more than 80% during the resonance suppression period. However, a physical quantity other than the current flowing through the reactor (L) that correlates with the pulsation of the magnetic energy of the reactor (L) due to LC resonance may be attenuated by more than 80%.

[0105] Although the embodiments have been described above, it will be understood that various modifications of form and details are possible without departing from the spirit and scope of the claims. Furthermore, the above embodiments and modifications may be appropriately combined or substituted as long as the functions of the subject of the present disclosure are not impaired. [Industrial Applicability]

[0106] The present disclosure is useful as a power conversion device that converts power output from an AC power supply and supplies the power to a load. [Explanation of symbols]

[0107] 10 Power conversion device 11 Converter circuit (rectifier circuit) 13 inverter circuit (first inverter circuit, resonance suppression unit) 14 Resonance suppression circuit (resonance suppression section) 141 Switching element for resonance suppression circuit 143 Capacitive element 144 Diode 145 Inverter circuit for fan motor (second inverter circuit) 145a Switching element 20 AC power supply 30 Motor (first load) 40 Control section 60 Fan motor (second load) Su, Sv, Sw, Sx, Sy, Sz Switching elements C capacitor (DC link capacitor) L Reactor t1 Transition timing T1 Period v dc DC voltage

Claims

1. a rectifier circuit (11) that rectifies and outputs an AC current output from a single-phase AC power source (20); a first inverter circuit (13) having a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) and converting a direct current output by the rectifier circuit (11) into an alternating current by switching operations of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) and supplying the alternating current to a first load (30); a DC link capacitor (C) connected between input nodes of the first inverter circuit (13), the DC link capacitor (C) having a capacitance set to allow fluctuations in the output voltage of the rectifier circuit (11) and to suppress a ripple voltage caused by the switching operation; a reactor (L) connected between the rectifier circuit (11) and the first inverter circuit (13) or between the AC power supply (20) and the rectifier circuit (11); a control unit (40) that controls the first inverter circuit (13) so as to have a non-conduction period during which no current flows from the AC power supply (20) to the rectifier circuit (11), a resonance suppression unit (13, 14) connected in parallel with the DC link capacitor (C), having at least one switching element (Su, Sv, Sw, Sx, Sy, Sz, 141), and suppressing LC resonance of a circuit including the DC link capacitor (C) and the reactor (L); the control unit (40) controls the resonance suppression unit (13, 14) so ​​that an integral value of a current flowing from the DC link capacitor (C) to the resonance suppression unit (13, 14) becomes equal to or less than 0 during a half-cycle period (T1) of the LC resonance, the half-cycle period starting from a transition timing (t1) at which a transition occurs from the non-conduction period to a conduction period in which a current flows from the AC power supply (20) to the rectifier circuit (11).

2. 2. The power conversion device according to claim 1, the control unit (40) controls the resonance suppression unit (13, 14) so ​​that a current flowing from the DC link capacitor (C) to the resonance suppression unit (13, 14) is equal to or less than 0 at the transition timing (t1).

3. 2. The power conversion device according to claim 1, the resonance suppression unit (13, 14) is the first inverter circuit (13), The power conversion device, wherein the first load (30) is a motor (30).

4. The power conversion device according to claim 3, The power conversion device, wherein the motor (30) is a motor (30) for a compressor.

5. 2. The power conversion device according to claim 1, a resonance suppression circuit (14) including a capacitance element (143) and a resonance suppression circuit switching element (141) connected in series with each other and connected in parallel with the DC link capacitor (C); the resonance suppression section (13, 14) is the resonance suppression circuit (14), The power conversion device, wherein the control unit (40) sets the transition timing (t1) to a timing when the voltage of the capacitive element (143) is higher than the voltage of the DC link capacitor (C).

6. 6. The power conversion device according to claim 5, a switching element for switching the capacitance element of the capacitance element, the switching element being connected in parallel with the switching element, and a diode connected in parallel with the switching element, the cathode of the diode being connected in parallel with the switching element, the cathode of the diode being connected in parallel with the switching element, the capacitance element being connected in parallel with the switching element.

7. 7. The power conversion device according to claim 6, a second inverter circuit (145) is connected to the capacitive element (143) for converting a voltage of the capacitive element (143) into AC and supplying the AC voltage to a second load (60) different from the first load (30).

8. 2. The power conversion device according to claim 1, The control unit (40) controls the voltage (v dc a resonance suppression unit (13, 14) that controls the resonance suppression unit (13, 14) based on a detected value of the resonance suppression unit (13, 14).

9. a rectifier circuit (11) that rectifies and outputs an AC current output from a single-phase AC power supply; an inverter circuit (13) having a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) for converting a direct current output by the rectifier circuit (11) into an alternating current by switching operations of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) and supplying the alternating current to a load (30); a DC link capacitor (C) connected between input nodes of the inverter circuit (13), the DC link capacitor (C) having a capacitance set to allow fluctuations in the output voltage of the rectifier circuit (11) and to suppress ripple voltage caused by the switching operation; a reactor (L) connected between the rectifier circuit (11) and the inverter circuit (13) or between the AC power supply (20) and the rectifier circuit (11); a control unit (40) that controls the inverter circuit (13) so as to have a non-conduction period during which no current flows from the AC power supply (20) to the rectifier circuit (11), a resonance suppression unit (13, 14) that is connected in parallel with the DC link capacitor (C), has at least one switching element (Su, Sv, Sw, Sx, Sy, Sz, 141, 145a), and suppresses LC resonance of a circuit including the DC link capacitor (C) and the reactor (L); the control unit (40) operates the resonance suppression unit (13, 14) to attenuate by more than 80% a physical quantity correlated to pulsation of magnetic energy in the reactor (L) caused by the LC resonance, during a resonance suppression period of three cycles of the LC resonance starting from a transition timing (t1) at which a transition occurs from the non-conduction period to a conduction period in which a current flows from the AC power supply (20) to the rectifier circuit (11).

10. a rectifier circuit (11) that rectifies and outputs an AC current output from a three-phase AC power source (20); an inverter circuit (13) having a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) for converting a direct current output by the rectifier circuit (11) into an alternating current by switching operations of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) and supplying the alternating current to a load; a DC link capacitor (C) connected between input nodes of the inverter circuit (13), the DC link capacitor (C) having a capacitance set to allow fluctuations in the output voltage of the rectifier circuit (11) and to suppress ripple voltage caused by the switching operation; a reactor (L) connected between the rectifier circuit (11) and the inverter circuit (13) or between the AC power supply (20) and the rectifier circuit (11); a control unit (40) that controls the inverter circuit (13) so that a non-conduction period occurs during which no current of a predetermined phase among the three phases flows from the AC power supply (20) to the rectifier circuit (11), a resonance suppression unit (13, 14) that is connected in parallel with the DC link capacitor (C), has at least one switching element (Su, Sv, Sw, Sx, Sy, Sz, 141, 145a), and suppresses LC resonance of a circuit including the DC link capacitor (C) and the reactor (L); the control unit (40) operates the resonance suppression unit (13, 14) to attenuate a physical quantity correlated to pulsation of magnetic energy of the reactor (L) caused by the LC resonance by more than 80% during a resonance suppression period of three periods of the LC resonance starting from a transition timing (t1) at which the non-conduction period transitions to a conduction period in which a current of the specified phase flows from the AC power supply (20) to the rectifier circuit (11).

11. 11. The power conversion device according to claim 9, The power conversion device, wherein the physical quantity is the amplitude of a current flowing through the reactor (L) during the resonance suppression period.

12. a rectifier circuit (11) that rectifies and outputs an AC current output from a three-phase AC power source (20); an inverter circuit (13) having a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz) for converting a direct current output by the rectifier circuit (11) into an alternating current by switching operations of the switching elements (Su, Sv, Sw, Sx, Sy, Sz) and supplying the alternating current to a load (30); a DC link capacitor (C) connected between input nodes of the inverter circuit (13), the DC link capacitor (C) having a capacitance set to allow fluctuations in the output voltage of the rectifier circuit (11) and to suppress ripple voltage caused by the switching operation; a reactor (L) connected between the rectifier circuit (11) and the inverter circuit (13) or between the AC power supply (20) and the rectifier circuit (11); a control unit (40) that controls the inverter circuit (13) so that a non-conduction period occurs during which no current of a predetermined phase among the three phases flows from the AC power supply (20) to the rectifier circuit (11), a resonance suppression unit (13, 14) connected in parallel with the DC link capacitor (C), having at least one switching element (Su, Sv, Sw, Sx, Sy, Sz, 141), and suppressing LC resonance of a circuit including the DC link capacitor (C) and the reactor (L); the control unit (40) controls the resonance suppression unit (13, 14) so ​​that an integral value of a current flowing from the DC link capacitor (C) to the resonance suppression unit (13, 14) becomes equal to or less than 0 during a half-cycle period of the LC resonance starting from a transition timing (t1) at which a transition occurs from the non-conduction period to a conduction period in which a current of the specified phase flows from the AC power supply (20) to the rectifier circuit (11).

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