Converter device, control method therefor, and program

Abstract

In the present invention, a converter controller (25) comprises: a mode switching unit (44) that, on the basis of physical quantities that relate to a motor connected to the output side of a smoothing capacitor, selects any one among a plurality of control modes; and a switching control unit (43) that executes, as one of the plurality of control modes, a first control mode in which a positive-electrode-side switching element connected to the positive electrode side of the smoothing capacitor is put into the off state, and a period during which a negative-electrode-side switching element connected to the negative electrode of the smoothing capacitor is driven is switched in accordance with AC voltage phase, and during the drive period, the negative-electrode-side switching element is on / off controlled through a plurality of cycles to boost the voltage across the terminals of the smoothing capacitor.

Description

Converter device, control method thereof, and program

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

[0002] Conventionally, converter devices that convert an AC voltage output from an AC power source into a DC voltage and output the DC voltage have been known. For example, Patent Document 1 discloses a converter device including a bridge circuit composed of four switching elements, a reactor connected to wiring between the 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, for example, synchronous rectification control when the magnitude of a current flowing through the bridge circuit is less than a first threshold, 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 that is greater than the first threshold, and high-speed switching control when the magnitude of the current flowing through the bridge circuit is equal to or greater than the second threshold.

[0003] Patent No. 7044462

[0004] As described in Patent Document 1, in a converter device having a reactor, energy stored in the reactor is released to a smoothing capacitor, which stores charge and boosts the DC voltage. In this case, the DC voltage may become higher than the AC voltage, so it is necessary to perform on / off control of the switching element at appropriate timing to prevent backflow, in which current flows from the smoothing capacitor toward the AC power source. Furthermore, to achieve high efficiency in power conversion, it is necessary to improve the power factor correction effect.

[0005] The present disclosure has been made in consideration of the above circumstances, and aims to provide a converter device, a control method and a program for the same that can easily prevent backflow and improve the power factor correction effect.

[0006] A converter device according to one aspect of the present disclosure includes a bridge circuit including a plurality of bridge-connected switching elements, the bridge circuit converting AC power supplied from an AC power source into DC power and outputting the DC power; a reactor provided in wiring connecting the AC power source and the bridge circuit; a smoothing capacitor connected between output terminals of the bridge circuit; and a converter control unit having a plurality of control modes and controlling the plurality of switching elements in accordance with the control mode. The converter control unit includes a mode switching unit that selects one of a plurality of control modes based on a physical quantity related to a load connected to an output side of the smoothing capacitor, and a switching control unit that executes, as one of the plurality of control modes, a first control mode in which a positive-side switching element connected to a positive electrode of the smoothing capacitor is turned off, a drive period of a negative-side switching element connected to a negative electrode of the smoothing capacitor is switched in accordance with the phase of the AC voltage, and the negative-side switching element is turned on and off a plurality of times during the drive period to boost a voltage across the smoothing capacitor.

[0007] A motor drive device according to one aspect of the present disclosure includes the converter device described above.

[0008] An air conditioner according to one aspect of the present disclosure includes the motor drive device described above, a compressor motor driven by the motor drive device, and a compressor driven by the compressor motor.

[0009] 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 including a plurality of bridge-connected switching elements, which converts AC power supplied from an AC power source into DC power and outputs the DC power, a reactor provided in wiring connecting the AC power source and the bridge circuit, and a smoothing capacitor connected between output terminals of the bridge circuit, wherein the control method includes a plurality of control modes, and a process of selecting one of the plurality of control modes based on a physical quantity related to a load connected to the output side of the smoothing capacitor, and a process of executing, as one of the plurality of control modes, a first control mode in which a positive-side switching element connected to the positive side of the smoothing capacitor is turned off, a drive period of a negative-side switching element connected to the negative side of the smoothing capacitor is switched depending on the phase of the AC voltage, and the negative-side switching element is turned on and off a plurality of times during the drive period to boost the voltage across the smoothing capacitor, performed by a computer.

[0010] A program according to one aspect of the present disclosure is a program for causing a computer to implement the above-described converter device control method.

[0011] According to the present disclosure, backflow can be easily prevented and the power factor can be improved.

[0012] FIG. 1 is a diagram illustrating a configuration of a motor drive device according to an embodiment of the present disclosure. FIG. 2 is a functional configuration diagram illustrating an example of a function provided in a converter control unit according to an embodiment of the present disclosure. FIG. 3 is a diagram illustrating a schematic diagram of an example of a control signal for each switching element in a synchronous rectification mode according to an embodiment of the present disclosure. FIG. 4 is a diagram illustrating a current path in a bridge circuit according to an embodiment of the present disclosure when an AC power supply has positive polarity. FIG. 5 is a diagram illustrating a current path in a bridge circuit according to an embodiment of the present disclosure when an AC power supply has negative polarity. FIG. 6 is a diagram illustrating a schematic diagram of an example of a control signal for each switching element in a horizontal bridgeless mode according to an embodiment of the present disclosure. FIG. 7 is a diagram illustrating a schematic diagram of an example of a control signal for each switching element in a full switching mode according to an embodiment of the present disclosure. FIG. 8 is a diagram for explaining a drive period of each switching element in a full switching mode according to an embodiment of the present disclosure. FIG. 9 is a diagram illustrating an example of a switching condition table according to an embodiment of the present disclosure. FIG. 10 is a diagram illustrating a configuration example of an air conditioner to which a motor drive device according to an embodiment of the present disclosure is applied.

[0013] A converter device, a control method thereof, and a program therefor according to an embodiment of the present disclosure will be described below with reference to the drawings. Fig. 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 the inverter device 3 converts the DC power into three-phase AC power and outputs it to a motor 5, which is a load.

[0014] In the present 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 the 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.

[0015] The converter device 2 includes, for example, a rectifier circuit 21 and a converter control unit 25 that controls the rectifier circuit 21. The rectifier circuit 21 includes, for example, a bridge circuit 200, a reactor L1, and a smoothing capacitor C1.

[0016] The bridge circuit 200 includes a plurality of bridge-connected switching elements Q1 to Q4. 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 each has parasitic diodes D1 to D4 between its source and drain.

[0017] The switching elements Q1 to Q4 are, for example, MOSFETs formed using wide bandgap semiconductors (WBG semiconductors). Here, the WBG semiconductor is, for example, a semiconductor having a bandgap of 3.0 eV or more. Examples of WBG semiconductors include SiC (silicon carbide), Ga ２ O ３ (gallium oxide), GaN (gallium nitride), etc. Generally, WBG semiconductors have smaller switching losses than silicon semiconductors, so by using MOSFETs formed using WBG semiconductors for the switching elements Q1 to Q4, it is possible to reduce losses.

[0018] Furthermore, as the MOSFET, for example, a MOSFET (hereinafter referred to as "SJ-MOSFET") employing a super junction (SJ) structure with a small on-resistance (operating resistance when the MOSFET is operating) may be employed.

[0019] The bridge circuit 200 includes a first arm K1 and a second arm K2. The first arm K1 includes a switching element Q1 and a switching element Q3 connected in series. In the first arm K1, the source of the switching element Q1 and the drain of the switching element Q3 are connected together, and a connection point P1 between these elements is connected to a first terminal of the AC power supply 4 via a reactor L1.

[0020] The second arm K2 has the switching element Q2 and the switching element Q4 connected in series. In the second arm 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 the second terminal of the AC power supply 4.

[0021] The reactor L1 is provided on a 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.

[0022] The smoothing capacitor C1 is connected between the output terminals of the bridge circuit 200. The positive electrode of the smoothing capacitor C1 is connected to the drains of the switching elements Q1 and Q2 via a wiring h2, and the negative electrode is connected to the sources of the switching elements Q3 and Q4 via a wiring 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 Q2 are also referred to as positive-side switching elements, and the switching elements Q3 and Q4 are also referred to as negative-side switching elements.

[0023] The converter device 2 is provided with a current sensor 22 and a voltage sensor 23. The current sensor 22 detects 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 AC voltage, and outputs the detected current value to the converter control unit 25. The voltage sensor 23 detects the AC voltage Vac 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 AC voltage, and outputs the detected voltage value to the converter control unit 25. The current sensor 22 and the voltage sensor 23 may be configured in a known manner as appropriate, and detailed description thereof will be omitted.

[0024] 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, etc. The converter control unit 25 will be described in detail later.

[0025] 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 IPM (Intelligent Power Module) 31 and an inverter control unit 32. The IPM 31 is, for example, a bridge circuit made up of six switching elements. These switching elements are on / off controlled based on control signals (e.g., PWM signals) output from the inverter control unit 32, thereby converting the DC power supplied from the rectifier circuit 21 into three-phase AC power and outputting it to the motor 5, which is a three-phase AC motor. Note that the configuration of the inverter device 3 is merely an example, and any known configuration can be adopted as appropriate.

[0026] Next, the converter control unit 25 will be described in detail. The converter control unit 25 is, for example, a computer and includes a processing circuit. The processing circuit includes, for example, a processor, a main memory, a secondary storage, etc. The converter control unit 25 may also include a communication interface for transmitting and receiving information to and from other devices.

[0027] Examples of processors include a CPU (Central Processing Unit), a microprocessor, a microcomputer, and a DSP (Digital Signal Processor). A primary storage device is composed of writable memory such as a cache memory or a RAM (Random Access Memory), and is used as a working area for reading the processor's execution program and writing data processed by the execution program. A secondary storage device is a non-transitory computer-readable storage medium. Examples of secondary storage devices include a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, and a semiconductor memory.

[0028] A series of processes for realizing the various functions described below is stored in a secondary storage device in the form of a program, for example, and the various functions are realized by a processor reading this program into a main storage device and executing information processing and arithmetic operations. Note that the program may be pre-installed in a secondary storage device, 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.

[0029] Fig. 2 is a functional configuration diagram showing an example of functions included in the converter control unit 25. As shown in Fig. 2, the 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.

[0030] The zero-cross detector 41 outputs a zero-cross signal Sz corresponding to the polarity of the AC voltage Vac detected by the voltage sensor 23. For example, the zero-cross detector 41 outputs a signal of "1" while the AC voltage Vac is positive, and a signal of "0" while the AC voltage Vac is negative. This makes it possible to detect the timing at which the zero-cross signal Sz switches as the zero-cross point.

[0031] The current determination unit 42 determines whether or not a current is flowing through the bridge circuit 200 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. The current determination unit 42 outputs, for example, a signal of "1" during a period when a current is flowing through the bridge circuit 200, and a signal of "0" during a period when a current is not flowing through the bridge circuit 200.

[0032] The switching control unit 43 has a plurality of control modes. The plurality of control modes includes a cross-bridgeless mode as a first control mode. In this embodiment, the plurality of control modes also includes a full-switching mode as a second control mode and a synchronous rectification mode as a third control mode. Each of these control modes will be described later.

[0033] 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 physical quantities 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 obtain such physical quantities related to the motor, the converter control unit 25 is configured to be able to obtain necessary information from a sensor (not shown) provided in the motor 5 and a motor control unit (not shown) that controls the motor 5. The mode switching unit 44 will be described in detail later.

[0034] Next, each control mode executed by the switching control unit 43 will be described.

[0035] (Synchronous Rectification Mode) In the synchronous rectification mode, during a period when the AC voltage Vac is positive, the switching elements Q1 and Q4 are turned on while the switching elements Q2 and Q3 are turned off, and during a period when the AC voltage Vac is negative, the switching elements Q2 and Q3 are turned on while the switching elements Q1 and Q4 are turned off.

[0036] 3 is a diagram schematically illustrating an example of control signals S1 to S4 for the switching elements Q1 to Q4 in the synchronous rectification mode. In FIG. 3, (a) represents the AC voltage Vac, (b) represents the zero-cross signal Sz, (c) represents the AC current Iac, (d) represents the control signal S1 for the switching element Q1, (e) represents the control signal S2 for the switching element Q2, (f) represents the control signal S3 for the switching element Q3, and (g) represents the control signal S4 for the switching element Q4. Note that, in the AC current Iac, currents of opposite phase are shown inverted.

[0037] In the synchronous rectification mode, the switching elements Q1 and Q4 are turned on during a period when the AC voltage Vac is positive and when the AC current Iac is flowing, as shown in Fig. 3. In this case, as shown by the bold 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.

[0038] Furthermore, during a period when the AC voltage Vac is negative and AC current Iac is flowing, the switching elements Q2 and Q3 are turned on. In this case, as shown by the bold line in FIG. 5 , current flows from the second terminal of the AC power supply 4 to the switching element Q2, the smoothing capacitor C1, the switching element Q3, the reactor L1, and the first terminal of the AC power supply 4. Note that the on-periods of the switching elements Q1 to Q4 in the synchronous rectification mode are merely examples and are not limiting. For example, known synchronous rectification control may be appropriately adopted. For example, the negative-side switching elements Q3 and Q4 connected to the negative side of the smoothing capacitor C1 may be controlled to maintain an on-state for approximately half a cycle, regardless of whether AC current Iac is flowing.

[0039] (Horizontal Bridgeless Mode) In the horizontal bridgeless mode, the positive-side switching elements Q1, Q2 connected to the positive side of the smoothing capacitor C1 are turned off, and the drive periods of the negative-side switching elements Q3, Q4 connected to the negative side of the smoothing capacitor C1 are switched in accordance with the phase of the AC voltage Vac, and the negative-side switching elements Q3, Q4 are turned on and off multiple times during the drive period to boost the voltage Vdc across the smoothing capacitor C1. In this embodiment, the drive periods of the negative-side switching elements Q3, Q4 are switched every half cycle of the AC voltage Vac, based on the zero-crossing point.

[0040] FIG. 6 is a diagram schematically illustrating an example of control signals S1 to S4 for the switching elements Q1 to Q4 in the horizontal bridgeless mode. The signal waveforms in FIG. 6 are arranged in the same manner as in FIG. 3 . In the horizontal bridgeless mode, as illustrated in FIG. 6 , during a period when the AC voltage Vac is positive, the switching element Q4 is controlled using pulse amplitude modulation (PAM), while the switching elements Q1 to Q3 are turned off. In this case, when the switching element Q4 is turned on, 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. The switching element Q4 is repeatedly turned on and off, thereby boosting the DC voltage and improving the power factor.

[0041] Furthermore, during a period when the AC voltage Vac is negative, the switching element Q3 is PAM-controlled, while the switching elements Q1, Q2, and Q4 are turned off. In this case, when the switching element Q3 is in the on state, a current flows from the second terminal of the AC power supply 4 to the parasitic diode D2 of the switching element Q2, the smoothing capacitor C1, the switching element Q3, the reactor L1, and the first terminal of the AC power supply 4.

[0042] The PAM control of the switching elements Q3 and Q4 can be performed using any of various known techniques. For example, the control signals S3 and S4 can be 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 Q3 and Q4 that output this PWM signal are then switched every half cycle based on a zero-cross signal. Alternatively, a control method (e.g., Patent No. 7080120) that reduces the distortion rate of the input current by adding phase adjustment to the above-mentioned general PWM technology may be used.

[0043] By performing PAM control on the switching elements Q4 and Q3, it is possible to approximate the current flowing from the AC power supply 4 to the rectifier circuit 21 to a sine wave. In addition, it is also possible to perform boost control, which increases the voltage Vdc across the smoothing capacitor C1 to at least √2 times the effective value of the AC voltage Vac. This improves the power factor and reduces harmonic currents in the power supply. Furthermore, in cross-bridgeless control, the switching elements Q1 and Q2 are turned off. This makes it possible to easily prevent backflow current that may occur due to the boost in the voltage Vdc across the smoothing capacitor C1.

[0044] 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 positive-side switching elements Q1 and Q2 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 Q2 are always kept in the off state, which makes it easy to prevent a backflow of current. Furthermore, by performing PAM control on the switching element Q4, it becomes possible to boost the voltage Vdc across the smoothing capacitor C1 to a desired voltage.

[0045] (Full Switching Mode) In the full switching mode, the drive periods of the switching elements Q1, Q2 are switched every half cycle of the AC voltage Vac based on the zero-crossing point, and during the drive periods of the positive side switching elements Q1, Q2, the positive side switching elements Q1, Q2 and their corresponding negative side switching elements Q4, Q3 are alternately turned on and off, thereby boosting the voltage Vdc across the smoothing capacitor C1.

[0046] 7 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. 7 are arranged in the same manner as in FIG.

[0047] In the full switching mode, the switching elements Q1 and Q4 are PAM controlled during a period when the AC voltage Vac is positive, as shown in Fig. 7. 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 signal of the control signal for the switching element Q4.

[0048] Similarly, during a period when the AC voltage Vac is negative, the switching elements Q2 and Q3 are PAM controlled. Here, if the switching elements Q2 and Q3 are simultaneously turned on, there is a risk of a reverse current flowing. Therefore, the control signal for the switching element Q2 is set to a signal that is an inversion of the control signal for the switching element Q3.

[0049] The process of generating control signals under PAM control is the same as that for the horizontal bridgeless mode described above. That is, control signals generated for the switching elements Q3 and Q4 are inverted and then provided to the switching elements Q2 and Q1, respectively.

[0050] In full switching control, the driving period of the switching elements Q1 to Q4 may be the period during which current flows through the bridge circuit 200. An example of the control signals S1 to S4 for the switching elements Q1 to Q4 in this case is shown in Fig. 8. The arrangement of the signal waveforms in Fig. 8 is the same as that in Fig. 3.

[0051] As shown in FIG. 8 , the switching elements Q1 to Q4 are PAM-controlled during a period when a forward current flows through the bridge circuit 200. Specifically, the timing at which the current determination unit 42 determines that a current is flowing through the bridge circuit 200 is set as the start timing of the drive period for the switching elements Q1 to Q4. In this way, even in full switching mode, by turning on the switching elements Q1 to Q4 only during a period when a current is flowing through the bridge circuit 200, it is possible to more reliably prevent backflow of current. Note that, since no backflow current flows through the negative-side switching elements Q3 and Q4 even if they are on during a period when no current is flowing, the negative-side switching elements Q3 and Q4 may be repeatedly turned on and off regardless of whether or not a current is flowing.

[0052] 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. More specifically, the mode switching unit 44 selects one of the plurality of control modes based on at least one of the required power of the motor 5, the rotation speed of the motor 5, the rotation speed command of the motor 5, the power consumption of the motor 5, and the induced voltage of the motor 5. For example, the mode switching unit 44 selects the cross bridgeless mode when the physical quantity related to the motor 5 is less than a first threshold, and selects the full switching mode when the physical quantity related to the motor 5 is equal to or greater than the first threshold. Furthermore, the mode switching unit 44 selects the synchronous rectification mode when the physical quantity related to the motor 5 is less than a second threshold that is smaller than the first threshold, and selects the cross bridgeless mode when the physical quantity is equal to or greater than the second threshold and less than the first threshold.

[0053] Specifically, the mode switching unit 44 has a switching condition table in which switching conditions and control modes are associated, for example, as shown in Fig. 9, and switches the control mode using this switching condition table. Fig. 9 shows an example of a switching condition table in which the required power Pd of the motor 5 is used as the physical quantity related to the motor. Here, the required power has a relationship of a<b<c<d. Switching is performed in the order of synchronous rectification mode, cross bridgeless mode, and full switching mode, from the lowest required power to the highest required power.

[0054] The value of the required power when switching from the synchronous rectification mode to the horizontal bridgeless mode is set to, for example, the required power that requires a boost in the DC voltage, that is, the required power value when the motor 5 requires a voltage equal to or greater than the voltage Vdc across the smoothing capacitor C1 in the synchronous rectification mode.

[0055] Next, a control method for the converter device 2 according to this embodiment will be described below, taking as an example a case where the synchronous rectification mode is selected as the current execution mode.

[0056] In this case, the current sensor 22 detects the AC current Iac at predetermined sampling intervals, and the voltage sensor 23 detects the AC 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 AC 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 AC current Iac, and outputs a current determination signal Sa based on the detection result to the switching control unit 43.

[0057] The switching control unit 43 generates control signals S1 to S4 based on the zero-cross signal Sz and the current determination signal Sa. That is, the switching control unit 43 generates a control signal that outputs "1" during a period when the current determination signal Sa indicates "1" and outputs "0" during a period when the current determination signal Sa indicates "0." The generated control signals are output to the gate driver 24 as control signals S1 and S4 for the switching elements Q1 and Q4 during a period when the zero-cross signal Sz is "1," and are output to the gate driver 24 as control signals S2 and S3 for the switching elements Q2 and Q3 during a period when the zero-cross signal Sz is "0." The gate driver 24 drives the switching elements Q1 to Q4 based on these control signals S1 to S4, thereby achieving control in the synchronous rectification mode as shown in FIG. 3 .

[0058] 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 exceeds the upper limit value b of the required power in synchronous rectification mode, thereby satisfying the conditions for the cross bridgeless mode, the control mode is switched from the synchronous rectification mode to the cross bridgeless mode.

[0059] In the cross-bridgeless mode, the switching control unit 43 switches between the switching elements Q3 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 S3 for the switching element Q3 while the zero-cross signal Sz is "0." The gate driver 24 then drives the switching elements Q3 and Q4 based on these control signals, thereby achieving control in the cross-bridgeless mode as shown in FIG. 6 .

[0060] 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 exceeds the upper limit value c of the required power for the cross bridgeless mode, thereby satisfying the conditions for the full switching mode, the control mode is switched from the cross bridgeless mode to the full switching mode.

[0061] 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 during the period when 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 S3 for the switching element Q3, 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 during the period when the zero-cross signal Sz is "0." 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. 7 .

[0062] 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.

[0063] As described above, the converter device, control method, and program according to this embodiment include a mode switching unit 44 that selects one of a plurality of control modes based on the power required by the motor 5, and a switching control unit 43 that controls the switching elements Q1 to Q4 based on the control mode selected by the mode switching unit 44. The plurality of control modes include a cross-bridgeless mode (first control mode) in which the positive-side switching elements Q1, Q2 connected to the positive side of the smoothing capacitor C1 are turned off, the drive period of the negative-side switching elements Q3, Q4 connected to the negative side of the smoothing capacitor C1 is switched every half cycle of the AC voltage Vac, and the negative-side switching elements Q3, Q4 are turned on and off a plurality of times during the drive period to boost the voltage Vdc across the smoothing capacitor C1.

[0064] In this way, in the horizontal bridgeless mode, the positive-side switching elements Q1 and Q2 are turned off, making it possible to easily prevent backflow current from flowing from the smoothing capacitor C1 toward the AC power supply 4. Furthermore, by performing PAM control on the negative-side switching elements Q3 and Q4, it is possible to boost the voltage Vdc across the smoothing capacitor C1 and make the current flowing from the AC power supply 4 to the rectifier circuit 21 approximate a sine wave.

[0065] 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.

[0066] For example, in the above-described embodiment, the case where the current flows through the parasitic diodes of the switching elements Q1 to Q4 has been described as an example, but the present invention is not limited to this. For example, a configuration may be adopted in which each of the switching elements Q1 to Q4 is connected in parallel with a diode, and the current flows through these diodes instead of the parasitic diodes described above.

[0067] Furthermore, although the above-described embodiment has a synchronous rectification mode, the synchronous rectification mode may be omitted. In this case, for example, a horizontal bridgeless mode and a full switching mode may be provided, and the horizontal bridgeless mode may be employed even during the period when the above-described synchronous rectification mode is being executed. In this case, the timing of switching between the horizontal bridgeless mode and the full switching mode can be set appropriately depending on the operation.

[0068] In the above-described embodiment, for example, the switching conditions for switching from the lateral bridgeless mode to the full switching mode may be modified as follows.

[0069] [Variation 1] For example, the condition for switching from the lateral bridgeless mode to the full switching mode may be that the period during which a current flows in the forward direction through the bridge circuit 200 (from the AC power supply 4 to the smoothing capacitor C1) is equal to or longer than a predetermined period (predetermined phase angle).

[0070] For example, immediately after switching from the synchronous rectification mode to the horizontal bridgeless mode, the boost operation has just started, and the amount of energy stored in the reactor L1 is not very high. Therefore, as shown in FIG. 6C, for example, the period during which a positive current flows is relatively short. In contrast, by continuing to operate in the horizontal bridgeless mode, the amount of energy stored in the reactor L1 gradually increases, and as the voltage on the AC power supply side rises, the period during which a positive current flows gradually increases (see FIG. 7C, for example).

[0071] Furthermore, since the period during which a forward current flows increases, the period during which a reverse current flows decreases, and therefore, the need to precisely adjust the on-timing (phase) of the positive-side switching elements Q1, Q2 decreases. Therefore, for example, when the period during which a signal "1" is output in the current determination signal Sa output from the current determination unit 42 exceeds a predetermined threshold, the cross-bridgeless mode may be switched to the full-switching mode.

[0072] [Variation 2] The switching condition for switching from the horizontal bridgeless mode to the full switching mode may be set based on, for example, the execution time of the horizontal bridgeless mode. For example, in the horizontal bridgeless mode, the positive-side switching elements Q1 and Q2 are turned off, which makes it easy to prevent reverse current. On the other hand, since rectification is performed using the parasitic diodes D1 and D2 of the positive-side switching elements Q1 and Q2, the voltage drop is larger and efficiency is lower than in the synchronous rectification mode. Heat generation must also be taken into consideration. In consideration of this trade-off, a certain period of time may be set for a transitional state when transitioning from the synchronous rectification mode to the full switching mode, and the mode may be switched to the full switching mode after this certain period has elapsed.

[0073] The idea in this case is that the main control modes are synchronous rectification mode and full switching mode, but when switching from synchronous rectification mode to full switching mode, the voltage of reactor L1 is not so high that it is difficult to prevent backflow, resulting in an unstable state. Therefore, during the temporary period when switching from synchronous rectification mode to full switching mode, the cross bridgeless mode is temporarily adopted to prevent backflow, and after the voltage has stabilized, the mode is switched to full switching mode.

[0074] Although the above-described embodiment has been described with reference to a single-phase (two-phase) configuration, the present invention is not limited to this. 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 supply. In this case, in the above-described bridge circuit 200, a third arm unit having two switching elements connected in series is connected in parallel with the first arm unit K1 and the second arm unit K2. The converter control unit 25 may then switch on / off each switching element included in each arm unit every one-third cycle of the AC voltage supplied from the AC power supply 4, thereby appropriately performing synchronous rectification control and / or PAM control. The number of arms may also be changed as appropriate without departing from the spirit of the present disclosure.

[0075] In the above-described embodiment, whether or not a current is flowing 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 wiring h3, and whether or not a current is flowing through the bridge circuit 200 may be determined by detecting the current flowing through the shunt resistor.

[0076] Fig. 10 is a diagram showing an example of the configuration of an air conditioner to which the motor drive device according to this embodiment is applied. In Fig. 10, the air conditioner 50 includes a refrigerant circuit 51. The refrigerant circuit 51 mainly includes, for example, a compressor 52 that compresses and outputs a refrigerant, a condenser 54, an expansion valve 55, and an evaporator 56. The refrigerant circuit 51 also includes a four-way 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.

[0077] (Additional Notes) The converter device and the control method and program thereof described in the above-described embodiment can be understood, for example, as follows.

[0078] A converter device according to a first aspect of the present disclosure includes a bridge circuit (200) including a plurality of bridge-connected switching elements (Q1 to Q4) and converting AC power supplied from an AC power source (4) into DC power and outputting the DC power, a reactor (L1) provided in a wiring (h1) connecting the AC power source and the bridge circuit, a smoothing capacitor (C1) connected between output terminals of the bridge circuit, and a converter control unit (25) having a plurality of control modes and controlling the plurality of switching elements according to the control mode, and the converter control unit is configured to control a load connected to the output side of the smoothing capacitor. and a switching control unit (43) that executes, as one of the plurality of control modes, a first control mode in which positive-side switching elements (Q1, Q2) connected to the positive side of the smoothing capacitor are turned off, and drive periods of negative-side switching elements (Q3, Q4) connected to the negative side of the smoothing capacitor are switched in accordance with the phase of the AC voltage, and the negative-side switching elements are turned on and off a plurality of times during the drive period to boost the voltage across the smoothing capacitor.

[0079] According to the above aspect, in the first control mode, the positive-side switching element is turned off, so that it is possible to easily prevent a reverse current from flowing from the smoothing capacitor toward the AC power supply. Also, with respect to the negative-side switching element, the drive period is switched depending on the phase of the AC voltage, and the negative-side switching element is controlled to be turned on and off multiple times during the drive period, so that it is possible to boost the voltage across the smoothing capacitor.

[0080] In the converter device according to a second aspect of the present disclosure, in the first aspect, the switching control unit (43) executes, as one of the plurality of control modes, a second control mode in which the drive period of the positive pole side switching elements (Q1, Q2) is switched based on the phase of the AC voltage, and the positive pole side switching elements (Q1, Q2) and the negative pole side switching elements (Q4, Q3) paired with the positive pole side switching elements are alternately turned on and off during the drive period, thereby boosting the voltage across the smoothing capacitor, and the mode switching unit (44) selects the first control mode when a physical quantity related to the load (5) is less than a first threshold value, and selects the second control mode when the physical quantity related to the load is equal to or greater than the first threshold value.

[0081] According to the above aspect, when the physical quantity related to the load is less than the first threshold, the first control mode is selected in which the positive-side switching element is turned off, thereby making it possible to boost the DC voltage while preventing backflow. When the physical quantity related to the load is equal to or greater than the first threshold, the execution mode is switched from the first control mode to the second control mode, making it possible to execute the second control mode in which the positive-side switching element and the negative-side switching element are alternately turned on and off while the DC voltage is boosted. This allows the mode to be switched while the DC voltage is stable, making it possible to easily prevent backflow.

[0082] In the converter device according to the third aspect of the present disclosure, in the second aspect, the switching control unit has a current determination unit (42) that determines whether or not a current is flowing in the bridge circuit when all of the switching elements are in an off state, and the switching control unit (43) sets the timing at which the current determination unit determines that a current is flowing in the bridge circuit as the start timing of the drive period in the second control mode.

[0083] According to the above aspect, in the second control mode, the positive-side switching element can be turned on only during the period when current flows through the bridge circuit, thereby more reliably preventing the flow of reverse current.

[0084] In the converter device according to a fourth aspect of the present disclosure, in the second or third aspect, the switching control unit (43) has, as one of the plurality of control modes, a third control mode in which the switching element is turned on at a timing when a current flows through a parasitic diode (D1 to D4) of the switching element, and the mode switching unit (44) switches from the third control mode to the first control mode when a predetermined switching condition is satisfied while the third control mode is selected, and switches from the first control mode to the second control mode when a predetermined switching condition is satisfied while the first control mode is selected.

[0085] According to the above aspect, the control mode can be transitioned from the third control mode to the second control mode via the first control mode rather than directly from the third control mode to the second control mode. This allows the control mode to be transitioned from the first mode to the second mode when the AC voltage on the input side of the bridge circuit is higher than the DC voltage. As a result, it is possible to effectively and easily prevent backflow current.

[0086] A motor drive device (1) according to a fifth aspect of the present disclosure includes the converter device (2) according to any one of the first to fourth aspects.

[0087] An air conditioner (50) according to a sixth aspect of the present disclosure includes the motor drive device (1) according to the fifth aspect, a compressor motor (5a) driven by the motor drive device (1), and a compressor (52) driven by the compressor motor (5a).

[0088] A control method for a converter device according to a seventh aspect of the present disclosure is a control method for a converter device (2) including a bridge circuit (200) including a plurality of bridge-connected switching elements (Q1 to Q4) and converting AC power supplied from an AC power source (4) into DC power and outputting the DC power, a reactor (L1) provided in wiring connecting the AC power source and the bridge circuit, and a smoothing capacitor (C1) connected between output terminals of the bridge circuit, wherein a computer executes the following processes: selecting one of a plurality of control modes based on a physical quantity related to a load connected to the output side of the smoothing capacitor; and executing, as one of the plurality of control modes, a first control mode in which a positive-side switching element connected to the positive side of the smoothing capacitor is turned off, a drive period of a negative-side switching element connected to the negative electrode of the smoothing capacitor is switched depending on the phase of the AC voltage, and the negative-side switching element is turned on and off a plurality of times during the drive period to boost the voltage across the smoothing capacitor.

[0089] A program according to an eighth aspect of the present disclosure is a program for causing a computer to implement the converter device control method according to the seventh aspect.

[0090] 1: Motor drive device 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 unit 32: Inverter control unit 41: Zero cross detection unit 42: Current determination unit 43: Switching control unit 44: Mode switching unit 50: Air conditioner 51: Refrigerant circuit 52: Compressor 53: Four-way valve 54: Condenser 55: Expansion valve 56: Evaporator 200: Bridge circuit C1: Smoothing capacitor D1: Parasitic diode D2: Parasitic diode D3: Parasitic diode D4: Parasitic diode K1: First arm section K2: Second arm section L1: Reactor Q1 : Switching element (positive side switching element) Q2: Switching element (positive side switching element) Q3: Switching element (negative side switching element) Q4: Switching element (negative side switching element)

Claims

1. A converter device comprising: a bridge circuit having a plurality of bridge-connected switching elements, and converting AC power supplied from an AC power source into DC power and outputting the DC power; a reactor provided in wiring connecting the AC power source and the bridge circuit; a smoothing capacitor connected between output terminals of the bridge circuit; and a converter control unit having a plurality of control modes and controlling the plurality of switching elements in accordance with the control mode, wherein the converter control unit comprises: a mode switching unit that selects one of a plurality of control modes based on a physical quantity related to a load connected to the output side of the smoothing capacitor; and a switching control unit that executes, as one of the plurality of control modes, a first control mode in which a positive-side switching element connected to the positive side of the smoothing capacitor is turned off, and a drive period of a negative-side switching element connected to the negative side of the smoothing capacitor is switched according to the phase of the AC voltage, and the negative-side switching element is turned on and off a plurality of times during the drive period to boost the voltage across the smoothing capacitor.

2. The converter device according to claim 1, wherein the switching control unit executes, as one of the plurality of control modes, a second control mode in which the drive period of the positive pole side switching element is switched based on the phase of the AC voltage, and the positive pole side switching element and the negative pole side switching element paired with the positive pole side switching element are alternately turned on and off during the drive period, thereby boosting the voltage across the smoothing capacitor; and the mode switching unit selects the first control mode when a physical quantity related to the load is less than a first threshold value, and selects the second control mode when the physical quantity related to the load is equal to or greater than the first threshold value.

3. The converter device according to claim 2, wherein the switching control unit has a current determination unit that determines whether or not a current is flowing in the bridge circuit when all of the switching elements are in an off state, and the switching control unit, in the second control mode, sets the timing at which it is determined by the current determination unit that a current is flowing in the bridge circuit as the start timing of the drive period.

4. The converter device according to claim 2, wherein the switching control unit has, as one of the plurality of control modes, a third control mode in which the switching element is turned on at a timing when a current flows through a parasitic diode of the switching element, and the mode switching unit switches from the third control mode to the first control mode when a predetermined switching condition is satisfied while the third control mode is selected, and switches from the first control mode to the second control mode when a predetermined switching condition is satisfied while the first control mode is selected.

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

6. An air conditioner comprising: a motor drive device according to claim 5; a compressor motor driven by said motor drive device; and a compressor driven by said compressor motor.

7. A control method for a converter device including a bridge circuit having a plurality of bridge-connected switching elements, which converts AC power supplied from an AC power source into DC power and outputs the DC power, a reactor provided in wiring connecting the AC power source and the bridge circuit, and a smoothing capacitor connected between output terminals of the bridge circuit, the control method comprising: a process of selecting one of the plurality of control modes based on a physical quantity related to a load connected to the output side of the smoothing capacitor; and a process of executing, as one of the plurality of control modes, a first control mode in which a positive-side switching element connected to the positive side of the smoothing capacitor is turned off, and a drive period of a negative-side switching element connected to the negative side of the smoothing capacitor is switched depending on the phase of the AC voltage, and the negative-side switching element is turned on and off a plurality of times during the drive period to boost the voltage across the smoothing capacitor, performed by a computer.

8. A program for causing a computer to implement the converter device control method according to claim 7.

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