Converter device and control method thereof

Abstract

To improve a power factor under light load.SOLUTION: The converter controller 25 executes the first control mode when the physical quantity related to the load connected to the output side of the smoothing capacitor is less than the predetermined threshold. The first control mode includes a combination of first control and second control, the first control being control in which the switching elements Q1 and Q4 are turned on and the switching elements Q3 and Q2 are turned off in a period in which the power-supply voltage has a positive polarity and a current flows on the DC bus, and the switching elements Q3 and Q2 are turned on and the switching elements Q1 and Q4 are turned off in a period in which the power-supply voltage Vac has a negative polarity and a current flows on the DC bus, in the second control, at least one of the switching elements Q2 and Q4 is turned on and off a predetermined number of times in each half cycle of the supply voltage Vac before the first control is performed. The converter controller 25 does not perform the synchronous rectification mode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a converter device and a control method thereof. [Background technology]

[0002] 2. Description of the Related Art Conventionally, converter devices are known that convert a power supply voltage output from an AC power supply into a DC voltage and output the DC voltage. For example, Patent Document 1 discloses a converter device including a bridge circuit consisting of four switching elements, a reactor connected to wiring between an AC power source and the bridge circuit, and a smoothing capacitor connected to the output side of the bridge circuit. The converter device described in Patent Document 1 performs synchronous rectification control when the magnitude of the current flowing through the bridge circuit is less than a first threshold, performs partial switching control when the magnitude of the current flowing through the bridge circuit is equal to or greater than the first threshold and less than a second threshold, and performs high-speed switching control when the magnitude of the current flowing through the bridge circuit is equal to or greater than the second threshold. Patent Documents 2 and 3 also disclose converter devices that perform synchronous rectification control under light loads. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7175364 [Patent Document 2] Patent No. 7034373 [Patent Document 3] Patent No. 7044462 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, conventional converter devices perform synchronous rectification control under light loads in order to reduce switching loss as much as possible. However, synchronous rectification control distorts the current waveform, resulting in a deterioration in the power factor. This deterioration in the power factor leads to problems such as reduced energy saving efficiency.

[0005] The present disclosure has been made in view of the above circumstances, and aims to provide a converter device and a control method thereof that can improve the power factor under light load conditions. [Means for solving the problem]

[0006] A converter device according to one aspect of the present disclosure includes a bridge circuit including a plurality of switching elements, a reactor provided in wiring connecting an AC power source and the bridge circuit, a smoothing capacitor connected across a DC bus that is an output side of the bridge circuit, and a converter control unit that controls the plurality of switching elements, wherein the bridge circuit has a first leg in which a first positive side switching element and a first negative side switching element are connected in series, and a second leg in which a second positive side switching element and a second negative side switching element are connected in series, the converter control unit has a plurality of control modes and includes a mode switching unit that selects a first control mode when a physical quantity related to a load connected to the output side of the smoothing capacitor is less than a predetermined threshold, and a switching control unit that controls the plurality of switching elements based on the selected control mode, The control modes are configured by a combination of first control and second control, and the first control is a control that turns on a first positive side switching element and a second negative side switching element while turning off a second positive side switching element and a first negative side switching element during a period when the power supply voltage is positive and a current flows through the DC bus, and turns on a second positive side switching element and a first negative side switching element while turning off a first positive side switching element and a second negative side switching element during a period when the power supply voltage is negative and a current flows through the DC bus, and the second control is a control that turns on and off at least one of the first negative side switching element and the second negative side switching element a predetermined number of times during each half cycle of the power supply voltage before the first control is performed, and the plurality of control modes does not include a synchronous rectification mode.

[0007] A control method for a converter device according to one aspect of the present disclosure is a control method for a converter device including a bridge circuit having a plurality of switching elements, a reactor provided in wiring connecting an AC power source and the bridge circuit, and a smoothing capacitor connected across a DC bus that is an output side of the bridge circuit, wherein the bridge circuit has a first leg in which a first positive side switching element and a first negative side switching element are connected in series, and a second leg in which a second positive side switching element and a second negative side switching element are connected in series, the control method for a converter device including a plurality of control modes, the control method comprising: a mode switching process for selecting a first control mode when a physical quantity related to a load connected to the output side of the smoothing capacitor is less than a predetermined threshold; and a switching control process for controlling the plurality of switching elements based on the selected control mode, the first control mode being selected by a computer; The control modes are configured by a combination of a first control and a second control, and the first control is a control that turns on a first positive side switching element and a second negative side switching element while turning off a second positive side switching element and a first negative side switching element during a period when the power supply voltage is positive and a current flows through the DC bus, and turns on a second positive side switching element and a first negative side switching element while turning off a first positive side switching element and a second negative side switching element during a period when the power supply voltage is negative and a current flows through the DC bus. The second control is a control that turns on and off at least one of the first negative side switching element and the second negative side switching element a predetermined number of times during each half cycle of the power supply voltage before the first control is performed. The plurality of control modes does not include a synchronous rectification mode. [Effects of the Invention]

[0008] According to the present disclosure, the power factor can be improved under light load conditions. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a configuration of a motor drive device according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a functional configuration diagram illustrating an example of functions provided in a converter control unit according to an embodiment of the present disclosure. [Figure 3] FIG. 10 is a diagram illustrating an example of a control signal for each switching element in a partial switching mode according to an embodiment of the present disclosure. [Figure 4] FIG. 10 is a diagram illustrating a current path when a power supply voltage has positive polarity in a first control in a partial switching mode according to an embodiment of the present disclosure. [Figure 5] FIG. 10 is a diagram illustrating a current path when a power supply voltage has negative polarity in a first control in a partial switching mode according to an embodiment of the present disclosure. [Figure 6] FIG. 10 is a diagram illustrating an example of a current path when a power supply voltage has a positive polarity in a second control in a partial switching mode according to an embodiment of the present disclosure. [Figure 7] FIG. 10 is a diagram illustrating a dead time according to an embodiment of the present disclosure. [Figure 8] FIG. 10 is a diagram illustrating an example of a control signal for each switching element in a horizontal bridgeless mode according to an embodiment of the present disclosure. [Figure 9] FIG. 10 is a diagram illustrating an example of a control signal for each switching element in a full switching mode according to an embodiment of the present disclosure. [Figure 10] FIG. 10 is a diagram illustrating an example of a switching condition table according to an embodiment of the present disclosure. [Figure 11] FIG. 10 is a diagram illustrating an example of a control signal for each switching element in a partial switching mode according to a modification of the present disclosure. [Figure 12] FIG. 10 is a diagram illustrating an example of a control signal for each switching element in a partial switching mode according to a modification of the present disclosure. [Figure 13] FIG. 10 is a diagram illustrating an example of a control signal for each switching element in a partial switching mode according to a modification of the present disclosure. [Figure 14] FIG. 10 is a diagram illustrating an example of a control signal for each switching element in a partial switching mode according to a modification of the present disclosure. [Figure 15] 1 is a diagram illustrating an example of a configuration of an air conditioner to which a motor drive device according to an embodiment of the present disclosure is applied. [Figure 16] FIG. 2 is a diagram illustrating an example of a hardware configuration of a converter control unit according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] A converter device and a control method thereof according to an embodiment of the present disclosure will be described below with reference to the drawings. 1 is a diagram showing a schematic configuration of a motor drive device 1 according to an embodiment of the present disclosure. The motor drive device 1 includes a converter device 2 and an inverter device 3. The converter device 2 converts AC power from an AC power source 4 into DC power and outputs the DC power. The inverter device 3 converts the DC power into three-phase AC power and outputs the three-phase AC power to a motor 5, which is a load.

[0011] In this embodiment, a case where single-phase AC power is supplied from the AC power supply 4 to the converter device 2 will be described as an example, but the present invention is not limited to this. For example, three-phase AC power may be supplied from the AC power supply 4. The motor 5 is driven in response to three-phase AC power supplied from the inverter device 3. An example of the motor 5 is a compressor motor used in an air conditioner.

[0012] The converter device 2 includes, for example, a rectifier circuit 21 and a converter control unit 25.

[0013] The rectifier circuit 21 includes, for example, a bridge circuit 200, a reactor L1, and a smoothing capacitor C1.

[0014] The bridge circuit 200 includes a plurality of bridge-connected switching elements Q1 to Q4.

[0015] The switching elements Q1 to Q4 are semiconductor switches such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors), and have parasitic diodes D1 to D4 between their sources and drains.

[0016] The switching elements Q1 to Q4 are, for example, MOSFETs formed using wide bandgap semiconductors (WBG semiconductors). Here, a WBG semiconductor is, for example, a semiconductor having a bandgap of 3.0 eV or more. Examples of WBG semiconductors include SiC (silicon carbide), Ga2O3 (gallium oxide), and GaN (gallium nitride). Generally, WBG semiconductors have smaller switching losses than silicon semiconductors, so using MOSFETs formed using WBG semiconductors for the switching elements Q1 to Q4 makes it possible to reduce losses.

[0017] Furthermore, as the MOSFET, for example, a MOSFET employing a super junction (SJ) structure (hereinafter referred to as "SJ-MOSFET") with a small on-resistance (operating resistance when the MOSFET is operating) may be employed.

[0018] The bridge circuit 200 has a first leg K1 in which a switching element Q1 (first positive side switching element) and a second switching element Q2 (first negative side switching element) are connected in series, and a second leg K2 in which a switching element Q3 (second positive side switching element) and a switching element Q4 (second negative side switching element) are connected in series.

[0019] In the first leg K1, the source of the switching element Q1 and the drain of the switching element Q3 are connected together, and a connection point P1 therebetween is connected to a first terminal of the AC power supply 4 via a reactor L1.

[0020] In the second leg K2, the source of the switching element Q2 and the drain of the switching element Q4 are connected together at a connection point P2, which is connected to a second terminal of the AC power supply 4.

[0021] In this way, the rectifier circuit 21 is configured so that the power supply voltage Vac output by the AC power supply 4 is applied between the connection point P1 and the connection point P2 via the reactor L1.

[0022] In other words, the reactor L1 is provided on the wiring h1 that connects the AC power supply 4 and the bridge circuit 200. The reactor L1 stores the power supplied from the AC power supply 4 as energy and releases this energy to boost the voltage and improve the power factor.

[0023] The smoothing capacitor C1 is connected between the output terminals of the bridge circuit 200. Specifically, the smoothing capacitor C1 is connected between the DC buses h2 and h3, which are the output side of the bridge circuit 200. More specifically, the smoothing capacitor C1 has a positive electrode connected to the drains of the switching elements Q1 and Q2 via the DC bus h2, and a negative electrode connected to the sources of the switching elements Q3 and Q4 via the DC bus h3. The smoothing capacitor C1 smoothes the output from the bridge circuit 200, and a DC voltage with little fluctuation is supplied from the converter device 2 to the inverter device 3. The smoothing capacitor C1 is, for example, an electrolytic capacitor. Hereinafter, in terms of their connection with the smoothing capacitor C1, the switching elements Q1 and Q3 will also be referred to as positive-side switching elements, and the switching elements Q2 and Q4 will also be referred to as negative-side switching elements.

[0024] The converter device 2 is provided with a current sensor 22 and a voltage sensor 23 . The current sensor 22 detects, for example, the AC current Iac input from the AC power supply 4 to the rectifier circuit 21 at a sampling period that is sufficiently shorter than the period of the power supply voltage, and outputs the detected current value to the converter control unit 25. The voltage sensor 23 detects the power supply voltage Vac input to the rectifier circuit 21 from the AC power supply 4 at a sampling period that is sufficiently shorter than the period of the power supply voltage, and outputs the detected voltage value to the converter control unit 25. The current sensor 22 and the voltage sensor 23 are not limited to those described above, and known configurations can be appropriately adopted.

[0025] The converter control unit 25 controls the switching elements Q1 to Q4 of the bridge circuit 200 based on the detected values ​​of the current sensor 22, the voltage sensor 23, and the like. The converter control unit 25 will be described in detail later.

[0026] The inverter device 3 converts the DC power output by the rectifier circuit 21 into three-phase AC power and outputs it to the motor. The inverter device 3 includes, for example, an inverter 31 and an inverter control unit 32. The inverter 31 has, for example, an IPM (Intelligent Power Module). The IPM is, for example, a bridge circuit made up of six switching elements. These switching elements are on / off controlled based on control signals (for example, PWM signals) output from the inverter control unit 32, whereby the DC power supplied from the rectifier circuit 21 is converted into three-phase AC power and output to the motor 5, which is a three-phase AC motor. The configuration of the inverter device 3 is an example, and any known configuration can be appropriately adopted.

[0027] Next, the converter control unit 25 will be described in detail. Fig. 16 is a diagram showing an example of the hardware configuration of the converter control unit 25. As shown in Fig. 16, the converter control unit 25 is, for example, a computer and includes a processing circuit 60. The processing circuit 60 includes, for example, a processor 61, a main memory 62, a secondary storage (memory) 63, etc. The converter control unit 25 may also include a communication interface 64 for transmitting and receiving information to and from other devices. These units are connected directly or indirectly via a bus.

[0028] Examples of the processor 61 include a CPU (Central Processing Unit), a microprocessor, a microcomputer, and a DSP (Digital Signal Processor).

[0029] The main memory device 62 is composed of writable memory such as cache memory or RAM (Random Access Memory), and is used as a working area for reading the execution program of the processor 61 and writing the processing data by the execution program.

[0030] The secondary storage device 63 is a non-transitory computer-readable storage medium. Examples of the secondary storage device 63 include flash memory and SSD (Solid State Drive). Other examples of the secondary storage device 63 include magnetic disks, magneto-optical disks, CD-ROMs, and DVD-ROMs. A plurality of secondary storage devices may be provided, and programs and data for realizing the functions described below may be stored separately in each secondary storage device.

[0031] A series of processes for realizing the various functions described below is stored in the secondary storage device 63 in the form of a program, for example, and the processor 61 reads this program into the main storage device 62 and executes information processing and arithmetic processing to realize the various functions. Note that the program may be pre-installed in the secondary storage device 63, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. Examples of computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories.

[0032] Fig. 2 is a functional configuration diagram showing an example of functions included in converter control unit 25. As shown in Fig. 2, converter control unit 25 includes, for example, a zero-cross detection unit 41, a current determination unit 42, a switching control unit 43, and a mode switching unit 44.

[0033] The zero-cross detector 41 outputs a zero-cross signal Sz corresponding to the polarity of the power supply voltage Vac detected by the voltage sensor 23, for example. The zero-cross detector 41 outputs a signal of "1" during a period when the power supply voltage Vac is positive, and a signal of "0" during a period when the power supply voltage Vac is negative. This makes it possible to detect the timing at which the zero-cross signal Sz switches as a zero-cross point. The zero-cross detector 41 can be omitted. For example, instead of the zero-cross detector 41, the voltage phase may be detected based on the power supply voltage Vac input from the voltage sensor 23.

[0034] The current determination unit 42 determines whether or not a current is flowing through the bridge circuit 200, in other words, the DC buses h2 and h3, based on the AC current Iac detected by the current sensor 22, and outputs a current determination signal Sa indicating the presence or absence of a current. For example, the current determination unit 42 outputs a signal of "1" during a period when a current is flowing through the bridge circuit 200, and outputs a signal of "0" during a period when a current is not flowing through the bridge circuit 200.

[0035] The switching control unit 43 receives the zero-cross signal Sz, the current determination signal Sa, and the voltage detection value of the power supply voltage Vac. The switching control unit 43 has a plurality of control modes. The plurality of control modes includes a partial switching mode as a first control mode. The plurality of control modes may also include a cross-bridgeless mode as a second control mode. The plurality of control modes may also include a full switching mode. Note that the plurality of control modes does not include a synchronous rectification mode. In other words, the converter control unit 25 is configured not to perform synchronous rectification control. The control modes executed by the switching control unit 43 will be described later.

[0036] The mode switching unit 44 selects one of a plurality of control modes based on a physical quantity related to the motor (load) connected to the output side of the smoothing capacitor C1. Examples of the physical quantity related to the motor 5 include the rotation speed of the motor 5, power consumption, required power of the motor 5, and a rotation speed command for the motor 5. In order to acquire such physical quantities related to the motor, the converter control unit 25 is configured to be able to acquire necessary information from a sensor (not shown) provided in the motor 5, the inverter control unit 32 that controls the inverter 31, a higher-level control device (not shown), and the like. The mode switching unit 44 will be described in detail later.

[0037] Next, each control mode executed by the switching control unit 43 will be described.

[0038] (Partial Switching Mode) The partial switching mode is configured by a combination of the first control and the second control PLs, for example, as shown in FIG.

[0039] Fig. 3 is a diagram showing an example of control signals S1 to S4 for switching elements Q1 to Q4 in partial switching mode. In Fig. 3, (a) shows the zero-cross signal Sz, (b) shows AC power Pin, (c) shows AC current Iac, (d) shows control signal S1 for switching element Q1, (e) shows control signal S2 for switching element Q2, (f) shows control signal S3 for switching element Q3, and (g) shows control signal S4 for switching element Q4. Note that in the AC current Iac, currents with opposite phases are shown inverted.

[0040] The first control is a control in which, during a period when the power supply voltage Vac is positive (in other words, when the zero-cross signal Sz is "1") and an AC current Iac flows, the switching elements Q1 and Q4 are turned on while the switching elements Q2 and Q3 are turned off, and similarly, during a period when the power supply voltage Vac is negative and an AC current Iac flows, the switching elements Q2 and Q3 are turned on while the switching elements Q1 and Q4 are turned off.

[0041] That is, in the first control, the switching elements Q1 and Q4 are turned on during a period when the power supply voltage Vac is positive and the AC current Iac is flowing. In this case, as shown by the thick line in Fig. 4, a current flows from the first terminal of the AC power supply 4 to the reactor L1, the switching element Q1, the smoothing capacitor C1, the switching element Q4, and the second terminal of the AC power supply 4.

[0042] 5, the switching elements Q2 and Q3 are turned on during a period when the power supply voltage Vac is negative and the AC current Iac is flowing. In this case, a current flows from the second terminal of the AC power supply 4 to the switching element Q3, the smoothing capacitor C1, the switching element Q2, the reactor L1, and the first terminal of the AC power supply 4.

[0043] The second control PLs is a control for turning on and off at least one of the switching element Q2 and the switching element Q4 a predetermined number of times in each half cycle of the power supply voltage Vac before the first control is performed.

[0044] For example, the switching control unit 43 may turn on and off at least one of the switching element Q2 and the switching element Q4 a predetermined number of times during a period in which the phase of the power supply voltage Vac is between 0° and 45°, and during a period in which the phase of the power supply voltage Vac is between 180° and 225°.

[0045] Specifically, in the second control PLs, the switching control unit 43 turns on and off at least one of the switching element Q2 and the switching element Q4 a predetermined number of times at a predetermined phase and phase width that are set in advance.

[0046] Here, the timing (phase), pulse width, and number of pulses (for example, about 1 to 5) for performing the second control PLs are set in advance. For example, optimal values ​​of these parameters can be determined and set based on the relationship with the power factor through prior testing using an actual device or prior simulation testing. Alternatively, voltage data, current data, etc. during operation may be collected, and the optimal values ​​may be dynamically set by learning from this data using machine learning or the like.

[0047] For example, the switching control unit 43 has information that associates the input current value or physical quantity related to the load (for example, at least one of the output power, the rotation speed of the motor 5, the power consumption, the required power of the motor 5, and the rotation speed command of the motor 5) with various parameters of the second control PLs (for example, at least one of the number of pulses in a half cycle of the power supply voltage, the timing (phase) of the pulses, and the pulse width), and may obtain parameters corresponding to the current operation from this information and perform the second control PLs based on the obtained parameters.

[0048] In the partial switching mode illustrated in FIG. 3, in the second control PLs, when the power supply voltage Vac is positive, the switching element Q2 is turned on twice, and when the power supply voltage Vac is negative, the switching element Q4 is turned on twice.

[0049] By performing the second control PLs, for example, when the power supply voltage Vac has positive polarity, the switching element Q2 is turned on, and as shown in FIG. 6, a current flows to the second terminal of the AC power supply 4 via the first terminal of the AC power supply 4, the reactor L1, the switching element Q2, and the switching element Q4, and energy is stored in the reactor L1.

[0050] Furthermore, when the power supply voltage Vac is negative, switching element Q4 is turned on, causing a current to flow through the second terminal of the AC power supply 4, switching element Q4, switching element Q2, and reactor L1 to the first terminal of the AC power supply 4, and energy is stored in reactor L1.

[0051] Then, the energy stored in the reactor L1 is released to the smoothing capacitor C1 by the first control described above. This causes the voltage Vdc across the smoothing capacitor C1 to increase. As a result, the current waveform can be made closer to the voltage waveform, and the power factor can be improved.

[0052] When the switching element Q2 is on, the switching element Q1 in the same first leg K1 must be off. Similarly, when the switching element Q4 is on, the switching element Q3 in the same second leg K2 must be off.

[0053] For this reason, as shown in Fig. 7, it is necessary to provide a dead time Td to prevent simultaneous on-states of the switching elements Q1 to Q4, taking into consideration the on-off response characteristics of the switching elements Q1 to Q4. Therefore, the various parameters of the second control PLs described above are determined taking into consideration the dead time Td. Also, simultaneous on-states may be avoided by masking the control signals S1 and S3 during the dead time Td.

[0054] The ON periods of the switching elements Q1 to Q4 in the first control are merely examples, and are not intended to be limiting. For example, the switching elements Q2 and Q4 may be controlled to maintain the ON state for approximately half a cycle, regardless of whether or not the AC current Iac is flowing.

[0055] (lateral bridgeless mode) In the horizontal bridgeless mode, the switching elements Q1 and Q3 connected to the positive electrode side of the smoothing capacitor C1 are turned off, and the drive periods of the switching elements Q2 and Q4 connected to the negative electrode side of the smoothing capacitor C1 are switched according to the phase of the power supply voltage Vac. During the drive periods, the switching elements Q2 and Q4 are turned on and off multiple times to boost the voltage Vdc across the smoothing capacitor C1. In this embodiment, the driving period of the negative polarity side switching elements Q2 and Q4 is switched every half cycle of the power supply voltage Vac with the zero crossing point as the reference.

[0056] Fig. 8 is a diagram showing an example of the control signals S1 to S4 of the switching elements Q1 to Q4 in the horizontal bridgeless mode. In Fig. 8, (a) shows the zero-cross signal Sz, (b) shows the AC current Iac, (c) shows the control signal S1 of the switching element Q1, (d) shows the control signal S2 of the switching element Q2, (e) shows the control signal S3 of the switching element Q3, and (f) shows the control signal S4 of the switching element Q4. Note that in the AC current Iac, currents of opposite phase are shown inverted.

[0057] In the horizontal bridgeless mode, as illustrated in FIG. 8, during a period when the power supply voltage Vac is positive, the switching element Q4 is PAM (Pulse Amplitude Modulation) controlled, while the switching elements Q1 to Q3 are turned off. In this case, when the switching element Q4 is in the on state, a current flows from the first terminal of the AC power supply 4 to the reactor L1, the parasitic diode D1 of the switching element Q1, the smoothing capacitor C1, the switching element Q4, and the second terminal of the AC power supply 4. This causes energy to be stored in the reactor L1. Then, when the switching element Q4 is turned off, the energy stored in the reactor L1 is released to the smoothing capacitor C1. Then, by repeatedly turning on and off the switching element Q4, the DC voltage is boosted and the power factor is improved.

[0058] Furthermore, during a period when the power supply voltage Vac is negative, switching element Q2 is PAM controlled, while switching elements Q1, Q3, and Q4 are turned off. In this case, when switching element Q2 is in the on state, current flows from the second terminal of the AC power supply 4 to the parasitic diode D3 of switching element Q3, smoothing capacitor C1, switching element Q2, reactor L1, and the first terminal of the AC power supply 4.

[0059] The PAM control of the switching elements Q2 and Q4 can be performed using any of a variety of well-known techniques. For example, the control signals S2 and S4 are generated using PWM (Pulse Width Modulation) technology. Specifically, a modulated wave representing a sine wave equivalent to the AC current Iac is generated, and the modulated wave is compared with a carrier wave (e.g., a triangular wave) having a predetermined frequency. A control signal (PWM signal: Pulse Width Modulation signal) is generated that is on when the value of the carrier wave exceeds the value of the modulated wave and off when the value of the carrier wave is equal to or less than the value of the modulated wave. The switching elements Q2 and Q4 that output this PWM signal are then switched every half cycle based on the zero-crossing signal. Furthermore, a control method using a technology that reduces the distortion rate of the input current by adding phase adjustment to the general PWM technology described above (for example, Patent No. 7080120) may be used. Furthermore, without being limited to PWM control, a general-purpose port I / O may be used to control the on / off of a switching element based on timing such as time or phase.

[0060] By performing PAM control on the switching elements Q2 and Q4, it is possible to approximate the current flowing from the AC power supply 4 to the rectifier circuit 21 to a sine wave. Additionally, boost control is also possible, which increases the voltage Vdc across the smoothing capacitor C1 to at least √2 times the effective value of the power supply voltage Vac. This improves the power factor and reduces power supply harmonic currents. Furthermore, in cross-bridgeless control, the switching elements Q1 and Q3 are turned off. This makes it easy to prevent backflow currents that may occur due to the boost in the voltage Vdc across the smoothing capacitor C1.

[0061] That is, in the horizontal bridgeless mode, PAM control is performed, which may result in a phenomenon in which the voltage Vdc across the smoothing capacitor C1 is boosted, causing the voltage on the output side of the bridge circuit 200 to be higher than the voltage on the input side. If the switching elements Q1 and Q3 are turned on at an inappropriate time in this state, there is a possibility that a current (backflow current) will flow from the smoothing capacitor C1 toward the AC power supply 4. However, in the horizontal bridgeless mode, the switching elements Q1 and Q3 are always kept in the off state, which makes it easy to prevent a backflow of current, and by PAM control of the switching element Q4, it becomes possible to boost the voltage Vdc across the smoothing capacitor C1 to a desired voltage.

[0062] (Full switching mode) In the full switching mode, the drive periods of the switching elements Q1 and Q3 are switched every half cycle of the power supply voltage Vac based on the zero-crossing point, and during the drive periods of the switching elements Q1 and Q3, the switching elements Q4 and Q2 that are paired with each other are alternately turned on and off, thereby boosting the voltage Vdc across the smoothing capacitor C1.

[0063] 9 is a diagram showing an example of control signals for the switching elements Q1 to Q4 in the full switching mode, where the signal waveforms in FIG. 9 are arranged in the same order as in FIG.

[0064] In full switching mode, the switching elements Q1 and Q4 are PAM controlled while the power supply voltage Vac is positive, as shown in Fig. 9. If the switching elements Q1 and Q4 are turned on simultaneously, a reverse current may flow. Therefore, the control signal for the switching element Q1 is an inverted version of the control signal for the switching element Q4.

[0065] Similarly, when the power supply voltage Vac is negative, switching elements Q2 and Q3 are PAM-controlled. To prevent reverse current from flowing if switching elements Q2 and Q3 are simultaneously turned on, the control signal for switching element Q2 is an inverted version of the control signal for switching element Q3. Furthermore, to prevent switching elements Q1 and Q2, and switching elements Q3 and Q4 from being simultaneously turned on, dead time Td is provided, as described above.

[0066] The process of generating control signals using PAM control is the same as that for the horizontal bridgeless mode described above. That is, the control signals generated for the switching elements Q2 and Q4 are inverted and then provided to the switching elements Q3 and Q1, respectively.

[0067] The mode switching unit 44 selects one of a plurality of control modes based on a physical quantity related to the motor 5 connected to the output side of the smoothing capacitor C1. The mode switching unit 44 selects one of the plurality of control modes based on, for example, at least one of the required power of the motor 5, the rotational speed of the motor 5, the rotational speed command of the motor 5, the power consumption of the motor 5, and the induced voltage of the motor 5.

[0068] For example, when the physical quantity related to the motor 5 is less than the first threshold value, the mode switching unit 44 selects the partial switching mode. Further, when the physical quantity related to the motor is greater than or equal to the first threshold value, the mode switching unit 44 selects the horizontal bridge-less mode. Further, when the physical quantity related to the motor is greater than or equal to the second threshold value which is greater than the first threshold value, the mode switching unit 44 selects the full switching mode.

[0069] Specifically, the mode switching unit 44 has, for example, a switching condition table in which switching conditions as shown in FIG. 10 are associated with control modes, and switches the control mode using this switching condition table. FIG. 10 shows an example of a switching condition table when the required power Pd of the motor 5 is used as the physical quantity related to the motor. Here, the required powers are in the relationship of a < b < c < d. As the required power increases from low to high, the modes are switched in the order of the partial switching mode, the horizontal bridge-less mode, and the full switching mode. Here, a may be zero or may take a value other than zero. When a takes a value greater than zero, in the region where the required power is less than a, it may be possible to perform a diode rectification mode in which rectification is performed only by the parasitic diodes of the switching elements Q1 to Q4.

[0070] The value of the required power at which the mode is switched from the partial switching mode to the horizontal bridge-less mode is set, for example, to the required power at which boosting of the DC voltage is required, that is, the value of the required power when the motor 5 requires a voltage higher than the voltage Vdc across the smoothing capacitor C1 in the synchronous rectification mode.

[0071] Next, a control method for the converter device 2 according to this embodiment will be described. The following description will be given taking as an example a case where the partial switching mode is selected as the current execution mode.

[0072] In this case, the current sensor 22 detects the AC current Iac at predetermined sampling intervals, and the voltage sensor 23 detects the power supply voltage Vac, which are output to the converter control unit 25. In the converter control unit 25, the zero-cross detection unit 41 generates a zero-cross signal Sz based on the voltage detection value of the power supply voltage Vac and outputs it to the switching control unit 43. Furthermore, the current determination unit 42 detects whether or not a current is flowing through the bridge circuit 200 based on the current detection value of the AC current Iac, and outputs a current determination signal Sa based on the detection result to the switching control unit 43. Furthermore, the voltage detection value of the power supply voltage Vac is input to the converter control unit 25.

[0073] The switching control unit 43 performs the first control and the second control described above. Specifically, when the voltage detection value of the power supply voltage Vac reaches a preset phase during a period in which the power supply voltage Vac is positive, the switching control unit 43 first generates a control signal S2 with a predetermined pulse width (second control). As a result, the control signal S2 as shown in Fig. 3 is generated and output to the gate driver 24. As a result, the gate driver 24 drives the switching element Q2 based on the control signal S2, thereby performing the second control PLs as shown in Fig. 3.

[0074] Subsequently, the switching control unit 43 sets the control signals S1 and S4 of the switching elements Q1 and Q4 to "1" (first control) during the period when the zero-cross signal Sz is "1" and the current determination signal Sa is "1". As a result, the control signals S1 and S4 are output to the gate driver 24, and the switching elements Q1 and Q4 are turned on.

[0075] Subsequently, when the voltage detection value of the power supply voltage Vac reaches a preset phase during a period when the power supply voltage Vac is negative, the switching control unit 43 generates a control signal S4 with a predetermined pulse width (second control). As a result, the control signal S4 as shown in Fig. 3 is generated and output to the gate driver 24. As a result, the gate driver 24 drives the switching element Q4 based on the control signal S4, thereby performing the second control PLs as shown in Fig. 3.

[0076] Subsequently, the switching control unit 43 sets the control signals S2 and S3 of the switching elements Q2 and Q3 to "1" (first control) during a period in which the zero-cross signal Sz is "0" and the current determination signal Sa is "1." As a result, the control signals S2 and S3 are output to the gate driver 24, and the switching elements Q2 and Q3 are turned on. Then, in the partial switching mode, the above-described control is repeatedly performed.

[0077] The mode switching unit 44 also acquires the motor's required power Pd as input information at predetermined time intervals and compares this required power Pd with each switching condition registered in the switching condition table. When the required power Pd becomes equal to or exceeds the upper limit value b of the required power for partial switching mode, thereby satisfying the conditions for the cross bridgeless mode, the control mode is switched from the partial switching mode to the cross bridgeless mode.

[0078] In the cross-bridgeless mode, the switching control unit 43 switches between the switching elements Q2 and Q4 to be driven every half cycle based on the zero-cross signal Sz, and generates a PWM signal as a control signal. The generated control signal is provided to the gate driver 24 as a control signal S4 for the switching element Q4 while the zero-cross signal Sz is "1," and is output to the gate driver 24 as a control signal S2 for the switching element Q2 while the zero-cross signal Sz is "0." The gate driver 24 then drives the switching elements Q2 and Q4 based on these control signals, thereby achieving control in the cross-bridgeless mode as shown in FIG. 8.

[0079] The mode switching unit 44 also acquires the motor's required power Pd as input information at predetermined time intervals and compares this required power Pd with each switching condition registered in the switching condition table. When the required power Pd becomes equal to or exceeds the upper limit c of the required power for the cross bridgeless mode, thereby satisfying the conditions for full switching mode, the control mode is switched from the cross bridgeless mode to the full switching mode.

[0080] In the full switching mode, the switching control unit 43 switches between the switching elements Q1, Q4, and Q2, Q3 to be driven every half cycle based on the zero-cross signal Sz, and generates a PWM signal. The generated PWM signal is output to the gate driver 24 as a control signal S4 for the switching element Q4 while the zero-cross signal Sz is "1," and an inverted signal of the PWM signal is output to the gate driver 24 as a control signal S2 for the switching element Q2 while the zero-cross signal Sz is "0," and an inverted signal of the PWM signal is output to the gate driver 24 as a control signal S3 for the switching element Q3. The gate driver 24 drives the switching elements Q1 to Q4 based on these control signals S1 to S4, thereby achieving the full switching mode control shown in FIG. 9.

[0081] As described above, the control mode is dynamically switched depending on the load conditions, thereby realizing appropriate commutation control based on the operating state of the motor 5. Note that the thresholds (a to d) in the direction in which the required power decreases may be provided with hysteresis, which makes it possible to prevent the control mode from being switched frequently.

[0082] As described above, the converter device and the control method thereof according to this embodiment provide the following advantageous effects. That is, the converter device 2 has a plurality of control modes, and includes a mode switching unit 44 that selects a partial switching mode (first control mode) when a physical quantity related to a load connected to the output side of the smoothing capacitor C1 is less than a predetermined threshold, and a switching control unit 43 that controls a plurality of switching elements Q1 to Q4 based on the selected control mode.

[0083] The partial switching mode is configured by a combination of the first control and the second control, and the first control turns on the switching elements Q1 and Q4 while turning off the switching elements Q2 and Q3 during a period when the power supply voltage Vac is positive and current flows through the DC buses h2 and h3. Also, during a period when the power supply voltage Vac is negative and current flows through the DC buses h2 and h3, the first control turns on the switching elements Q2 and Q3 while turning off the switching elements Q1 and Q4. The second control is a control for turning on and off at least one of the switching elements Q2 and Q4 a predetermined number of times in each half cycle of the power supply voltage Vac before the first control is performed.

[0084] In this way, when a physical quantity related to the load (e.g., required power Pd) is less than a predetermined threshold, the partial switching mode is performed, which makes it possible to improve the power factor in the light load region compared to the conventional case in which the synchronous rectification mode is performed. For example, in household air conditioners, operation in the light load region is the most common. Therefore, by improving the power factor in the light load region, it is possible to achieve energy savings. Furthermore, by using MOSFETs formed using WBG semiconductors as the switching elements Q1 to Q4, it is possible to reduce losses, thereby achieving further energy savings.

[0085] Although the present disclosure has been described above using embodiments, the technical scope of the present disclosure is not limited to the scope described in the above embodiments. Various modifications or improvements can be made to the above embodiments without departing from the gist of the present disclosure, and such modifications or improvements are also included in the technical scope of the present disclosure.

[0086] [Variation 1] For example, in the second control PLs of the partial switching mode illustrated in FIG. 3, the switching element Q2 is driven during the period when the power supply voltage Vac is positive, and the switching element Q4 is driven during the period when the power supply voltage Vac is negative, but this is not limited to this.

[0087] For example, as illustrated in FIG. 11, in the second control PLs of the partial switching mode, the switching element Q2 may be driven in a period in which the power supply voltage Vac is positive and in a period in which the power supply voltage Vac is negative.

[0088] Furthermore, as illustrated in FIG. 12, in the second control PLs of the partial switching mode, the switching element Q4 may be driven in a period in which the power supply voltage Vac is positive and in a period in which the power supply voltage Vac is negative.

[0089] Furthermore, as illustrated in FIG. 13, in the second control PLs of the partial switching mode, the switching element Q4 may be driven during a period in which the power supply voltage Vac is positive, and the switching element Q2 may be driven during a period in which the power supply voltage Vac is negative.

[0090] Furthermore, as illustrated in FIG. 14, in the second control signal PLs of the partial switching mode, the switching element Q2 and the switching element Q4 may be driven in periods when the power supply voltage Vac is positive and negative.

[0091] [Variation 2] In the present embodiment, at least one of the switching elements Q2 and Q4 is turned on and off a predetermined number of times before the first control is performed, but this is not limiting. For example, at least one of the switching elements Q2 and Q4 may be turned on and off a predetermined number of times not only before the first control is performed but also after the first control is performed.

[0092] [Variation 3] In this embodiment, in the second control of the partial switching mode, the phase, pulse width, etc. for turning on at least one of the switching element Q2 and the switching element Q4 are set in advance, but this is not limited to this. For example, the difference between the power supply voltage Vac and the voltage of the DC bus may be monitored, and at least one of the switching element Q2 and the switching element Q4 may be turned on when this difference reaches a predetermined value.

[0093] In this way, by monitoring the difference between the power supply voltage Vac and the DC bus voltage, it is possible to predict the timing at which current will flow through the bridge circuit, which makes it possible to turn on at least one of the switching elements Q2 and Q4 at an appropriate timing that suits the current operation.

[0094] [Variation 4] In the present embodiment, the mode switching unit 44 selects the partial switching mode in a region where the physical quantity related to the motor 5 is less than the first threshold, but this is not limited to this. For example, when the physical quantity related to the motor 5 is less than a third threshold that is smaller than the first threshold, the mode switching unit 44 may select the diode rectification mode in which rectification is performed only by the parasitic diodes of the switching elements Q1 to Q4 without performing switching.

[0095] [Variation 5] In the present embodiment, the case where the current flows through the parasitic diodes of the switching elements Q1 to Q4 has been exemplified, but this is not limiting. For example, each of the switching elements Q1 to Q4 may be connected in parallel to a diode, and the current may flow through these diodes instead of the parasitic diodes described above.

[0096] [Variation 6] In the present embodiment, the case of a single phase (two phase) has been described as an example, but the present invention is not limited to this example. For example, the present invention can also be applied to a case where three-phase AC power is supplied from a three-phase AC power source. In this case, in the above-described bridge circuit 200, a third leg having two switching elements connected in series is connected in parallel with the first leg K1 and the second leg K2. Then, the converter control unit 25 switches on / off each switching element included in each leg every ⅓ cycle of the power supply voltage supplied from the AC power source 4, thereby executing a partial switching mode or the like. Furthermore, the number of legs may be changed as appropriate without departing from the gist of the present disclosure.

[0097] [Variation 7] In the above-described embodiment, whether or not a current flows through the bridge circuit 200 is determined based on the AC current Iac, but this is not limiting. For example, a shunt resistor may be provided on the DC bus h3, and whether or not a current flows through the bridge circuit 200 may be determined by detecting the current flowing through the shunt resistor.

[0098] [Variation 8] In the above-described embodiment, the horizontal bridgeless mode is provided between the partial switching mode and the full switching mode, but this is not limiting. For example, the horizontal bridgeless mode may be omitted, and mode switching may be performed between the partial switching mode and the full switching mode. In this case, the switching threshold may be set appropriately, taking into consideration the power factor and switching loss.

[0099] Although several modifications of the converter device 2 according to this embodiment have been described above, this embodiment and the above modifications 1 to 8 can be combined as appropriate.

[0100] [Application example] FIG. 15 is a diagram showing an example configuration of an air conditioner 50 to which the motor drive device 1 according to this embodiment is applied. In FIG. 15, the air conditioner 50 includes a refrigerant circuit 51. The refrigerant circuit 51 mainly includes, for example, a compressor 52 that compresses and sends out a refrigerant, a condenser 54, an expansion valve 55, and an evaporator 56. The refrigerant circuit 51 also includes a switching valve 53 that switches the circulation direction of the refrigerant. The compressor 52 is controlled by a compressor motor 5a that is driven by the motor drive device 1 according to this embodiment.

[0101] (Additional notes) The converter device and the control method thereof described in the above-described embodiment can be understood, for example, as follows.

[0102] A converter device (2) according to a first aspect of the present disclosure includes a bridge circuit (200) including a plurality of switching elements (Q1 to Q4), a reactor (L1) provided in a wiring (h1) connecting an AC power source (4) and the bridge circuit, a smoothing capacitor (C1) connected between DC buses (h2, h3) on the output side of the bridge circuit, and a converter control unit (25) that controls the plurality of switching elements, wherein the bridge circuit has a first leg (K1) in which a first positive-side switching element (Q1) and a first negative-side switching element (Q2) are connected in series, and a second leg (K2) in which a second positive-side switching element (Q3) and a second negative-side switching element (Q4) are connected in series, and the converter control unit has a plurality of control modes, a mode switching unit (44) that selects a first control mode when a physical quantity related to a load (5) connected to the output side of the smoothing capacitor is less than a predetermined threshold, and a converter control unit (25) that controls the plurality of switches (Q1 to Q4) based on the selected control mode. and a switching control unit (43) that controls a switching element, the first control mode being configured by a combination of a first control and a second control (PLs), the first control being a control that turns on a first positive side switching element and a second negative side switching element while turning off a second positive side switching element and a first negative side switching element during a period when a power supply voltage (Vac) is positive and a current flows through the DC bus, and that turns on a second positive side switching element and a first negative side switching element while turning off a first positive side switching element and a second negative side switching element during a period when a power supply voltage is negative and a current flows through the DC bus, and the second control being a control that turns on and off at least one of the first negative side switching element and the second negative side switching element a predetermined number of times during each half cycle of the power supply voltage before the first control is performed, and the plurality of control modes does not include a synchronous rectification mode.

[0103] According to the above aspect, the first control mode is executed when a physical quantity related to the load (e.g., required power Pd) is less than a predetermined threshold. The first control mode is a combination of the first control and the second control. In the second control, before the first control is executed, at least one of the first negative-side switching element and the second negative-side switching element is turned on and off a predetermined number of times. As a result, as illustrated in FIG. 6 , before the first control is executed, the energy stored in the reactor can be stored in the smoothing capacitor, and the voltage across the smoothing capacitor (DC bus voltage) can be boosted. This allows the current waveform to approach the voltage waveform, thereby improving the power factor. As a result, the power factor in the light-load range can be improved compared to the conventional case in which the synchronous rectification mode is executed. For example, in a home air conditioner, operation in the light-load range is most common. Therefore, by improving the power factor in the light-load range, energy can be effectively saved.

[0104] In the converter device according to the second aspect of the present disclosure, in the first aspect, the switching control unit turns on and off at least one of the first negative side switching element and the second negative side switching element a predetermined number of times during a period when the phase of the power supply voltage is greater than or equal to 45° and less than 90°, and during a period when the phase of the power supply voltage is greater than or equal to 225° and less than 270°.

[0105] According to the above aspect, it is possible to turn on and off the negative switching element in the first control in a phase close to the timing at which the positive switching element is turned on, thereby making it possible to make the current waveform closer to the voltage waveform and effectively improve the power factor.

[0106] In the converter device according to the third aspect of the present disclosure, in the first or second aspect, the switching control unit turns on and off at least one of the first negative-side switching element and the second negative-side switching element a predetermined number of times at a predetermined phase and phase width that are set in advance during the second control.

[0107] According to the above aspect, at least one of the first negative-side switching element and the second negative-side switching element is turned on and off a predetermined number of times at a predetermined phase and phase width that are set in advance, so that on / off control can be easily performed. Also, by determining and setting an optimal value for power factor improvement through prior simulation or prior actual device testing, it is possible to further improve the power factor.

[0108] In the converter device according to the fourth aspect of the present disclosure, in the first aspect, the switching control unit, in the second control, turns on and off at least one of the first negative side switching element and the second negative side switching element a predetermined number of times based on the difference between the power supply voltage and the voltage of the DC bus.

[0109] According to the above aspect, it is possible to turn on and off at least one of the first negative-side switching element and the second negative-side switching element a predetermined number of times at appropriate timing depending on the operating state.

[0110] A converter device according to a fifth aspect of the present disclosure is any of the first to fourth aspects, wherein, in the second control, the switching control unit turns on and off the first negative-side switching element a predetermined number of times when the power supply voltage is positive, and turns on and off the second negative-side switching element a predetermined number of times when the power supply voltage is negative.

[0111] According to the above aspect, it is possible to effectively boost the voltage across the smoothing capacitor, thereby making it possible to effectively improve the power factor.

[0112] A converter device according to a sixth aspect of the present disclosure is any one of the first to fifth aspects, wherein, in the second control, the switching control unit turns on and off at least one of the first negative-side switching element and the second negative-side switching element a predetermined number of times in each half cycle of the power supply voltage before and after the first control is performed.

[0113] According to the above aspect, at least one of the first negative-side switching element and the second negative-side switching element is turned on and off a predetermined number of times before and after the first control is performed, so that the current waveform can be made closer to the voltage waveform, which is expected to further improve the power factor.

[0114] A motor drive device (1) according to a seventh aspect of the present disclosure includes the converter device (2) according to any one of the first to fourth aspects.

[0115] An air conditioner (50) according to an eighth aspect of the present disclosure includes the motor drive device (1) according to the seventh aspect, a compressor motor (5a) driven by the motor drive device (1), and a compressor (52) driven by the compressor motor (5a).

[0116] A control method for a converter device (2) according to a ninth aspect of the present disclosure is a control method for a converter device (2) including a bridge circuit (200) having a plurality of switching elements (Q1 to Q4), a reactor (L1) provided in a wiring (h1) connecting an AC power source (4) and the bridge circuit, and a smoothing capacitor (C1) connected between DC buses (h2, h3) that are the output side of the bridge circuit, the bridge circuit having a first leg (K1) in which a first positive side switching element (Q1) and a first negative side switching element (Q2) are connected in series, and a second leg (K2) in which a second positive side switching element (Q3) and a second negative side switching element (Q4) are connected in series, the control method comprising: a mode switching process for selecting a first control mode when a physical quantity related to a load connected to the output side of the smoothing capacitor is less than a predetermined threshold; and a switching process for controlling the plurality of switching elements based on the selected control mode. a switching control process executed by a computer, the first control mode being constituted by a combination of a first control and a second control, the first control being a control for turning on a first positive side switching element and a second negative side switching element while turning off a second positive side switching element and a first negative side switching element during a period when a power supply voltage is positive and a current flows through the DC bus, and turning on a second positive side switching element and a first negative side switching element while turning off a first positive side switching element and a second negative side switching element during a period when a power supply voltage is negative and a current flows through the DC bus, and the second control being a control for turning on and off at least one of the first negative side switching element and the second negative side switching element a predetermined number of times during each half cycle of the power supply voltage before the first control is executed, and the plurality of modes does not include a synchronous rectification mode.

[0117] A program according to a tenth aspect of the present disclosure is a program for causing a computer to implement the converter device control method according to the ninth aspect. [Explanation of symbols]

[0118] 1: Motor drive unit 2: Converter device 3: Inverter device 4: AC power supply 5: Motor 5a: Compressor motor 21: Rectifier circuit 22: Current sensor 23: Voltage sensor 24: Gate driver 25: Converter control section 32: Inverter control unit 41: Zero cross detector 42: Current judgment section 43: Switching control section 44: Mode switching section 50: Air conditioner 51: Refrigerant circuit 52: Compressor 53: Switching valve 54: Condenser 55: Expansion valve 56: Evaporator 60: Processing circuit 61: Processor 62: Main memory 63 :Secondary storage device 64: Communication interface 200: Bridge circuit C1: Smoothing capacitor D1: Parasitic diode D2: Parasitic diode D3: Parasitic diode D4: Parasitic diode K1: First leg K2: Second leg L1: Reactor P1: Connection point P2: Connection point Q1: Switching element Q2: Switching element Q3: Switching element Q4: Switching element

Claims

1. a bridge circuit including a plurality of switching elements; a reactor provided in a wiring that connects an AC power supply and the bridge circuit; a smoothing capacitor connected across a DC bus on the output side of the bridge circuit; a converter control unit that controls the plurality of switching elements; Equipped with the bridge circuit has a first leg in which a first positive side switching element and a first negative side switching element are connected in series, and a second leg in which a second positive side switching element and a second negative side switching element are connected in series, The converter control unit a mode switching unit that has a plurality of control modes and selects a first control mode when a physical quantity related to a load connected to an output side of the smoothing capacitor is less than a predetermined threshold; a switching control unit that controls the plurality of switching elements based on the selected control mode; Equipped with the first control mode is configured by a combination of the first control and the second control, the first control is a control to turn on a first positive side switching element and a second negative side switching element while turning off a second positive side switching element and a first negative side switching element during a period when a power supply voltage has a positive polarity and a current flows through the DC bus, and to turn on a second positive side switching element and a first negative side switching element while turning off a first positive side switching element and the second negative side switching element during a period when a power supply voltage has a negative polarity and a current flows through the DC bus; the second control is a control for turning on and off at least one of the first negative side switching element and the second negative side switching element a predetermined number of times in each half cycle of the power supply voltage before the first control is performed, A converter device in which the plurality of control modes does not include a synchronous rectification mode.

2. 2. The converter device according to claim 1, wherein the switching control unit turns on and off at least one of the first negative-side switching element and the second negative-side switching element a predetermined number of times during a period in which the phase of the power supply voltage is equal to or greater than 45° and less than 90°, and during a period in which the phase of the power supply voltage is equal to or greater than 225° and less than 270°.

3. 2. The converter device according to claim 1, wherein the switching control unit turns on and off at least one of the first negative-side switching element and the second negative-side switching element a predetermined number of times at a predetermined phase and phase width that are set in advance during the second control.

4. 2. The converter device according to claim 1, wherein, in the second control, the switching control unit turns on and off at least one of the first negative-side switching element and the second negative-side switching element a predetermined number of times based on a difference between the power supply voltage and the voltage of the DC bus.

5. 2. The converter device according to claim 1, wherein, in the second control, the switching control unit turns on and off the first negative-side switching element a predetermined number of times when the power supply voltage is positive, and turns on and off the second negative-side switching element a predetermined number of times when the power supply voltage is negative.

6. 2. The converter device according to claim 1, wherein, in the second control, the switching control unit turns on at least one of the first negative-side switching element and the second negative-side switching element a predetermined number of times before and after the first control is performed in each half cycle of the power supply voltage.

7. A motor drive device comprising the converter device according to any one of claims 1 to 4.

8. The motor drive device according to claim 7; a compressor motor driven by the motor drive device; a compressor driven by the compressor motor; An air conditioner equipped with:

9. A control method for a converter device comprising: a bridge circuit including a plurality of switching elements; a reactor provided in wiring connecting an AC power source and the bridge circuit; and a smoothing capacitor connected across a DC bus that is an output side of the bridge circuit, wherein the bridge circuit has a first leg in which a first positive-side switching element and a first negative-side switching element are connected in series, and a second leg in which a second positive-side switching element and a second negative-side switching element are connected in series, a mode switching process including a plurality of control modes, the mode switching process selecting a first control mode when a physical quantity related to a load connected to an output side of the smoothing capacitor is less than a predetermined threshold value; a switching control process for controlling the plurality of switching elements based on the selected control mode; The computer executes the first control mode is configured by a combination of the first control and the second control, the first control is a control to turn on a first positive side switching element and a second negative side switching element while turning off a second positive side switching element and a first negative side switching element during a period when a power supply voltage has a positive polarity and a current flows through the DC bus, and to turn on a second positive side switching element and a first negative side switching element while turning off a first positive side switching element and the second negative side switching element during a period when a power supply voltage has a negative polarity and a current flows through the DC bus; the second control is a control for turning on and off at least one of the first negative side switching element and the second negative side switching element a predetermined number of times in each half cycle of the power supply voltage before the first control is performed, A control method for a converter device, wherein the plurality of control modes does not include a synchronous rectification mode.

10. A program for causing a computer to implement the converter device control method according to claim 9.

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