Electric power conversion device and air conditioner

Abstract

Provided is an electric power conversion device or the like in which improvement of a power supply power factor and reduction of a power supply harmonic current can be achieved. An electric power conversion device (10) comprises: a converter circuit (1) having a plurality of switching elements (Q1-Q6); reactors (21-23); a smoothing capacitor (3); an AC voltage detection unit (4); a current detection unit (5); a DC voltage detection unit (6); and a control unit (7) that performs PWM switching on the plurality of switching elements (Q1-Q6). The control unit (7) stops the PWM switching in a predetermined switching stop section including a zero-cross point of an AC voltage and changes the width of the switching stop section on the basis of the magnitude of the load of a load device (D1).

Description

Power converters and air conditioners

[0001] This disclosure relates to power converters and air conditioners.

[0002] Regarding power conversion devices that convert AC voltage to DC voltage, for example, the technology described in Patent Document 1 is known. Specifically, Patent Document 1 describes determining a first period encompassing the positive and negative peaks of each phase voltage in the AC voltage, and a second period encompassing the zero-crossing point, as the limiting period for each phase, and limiting the control signal during this limiting period.

[0003] International Publication No. 2017 / 199293

[0004] The technology described in Patent Document 1 uniformly sets a predetermined limit period, but there is room for improvement in terms of improving the power factor of the power supply and reducing the harmonic current of the power supply.

[0005] Therefore, the objective of this disclosure is to provide a power conversion device, etc., that improves the power factor of the power source and reduces harmonic currents of the power source.

[0006] To solve the aforementioned problems, the power conversion device according to the present disclosure comprises a converter circuit having a plurality of switching elements connected in a bridge configuration, the input side of which is connected to an AC power source and the output side of which is connected to a load device, a reactor provided in the wiring connecting the AC power source and the converter circuit, a smoothing capacitor for smoothing the voltage on the output side of the converter circuit, an AC voltage detection unit for detecting the AC voltage of the AC power source, a current detection unit for detecting the current flowing through the converter circuit, and a DC voltage detection unit for detecting the DC voltage of the smoothing capacitor, and a control unit that performs PWM switching of the plurality of switching elements based on the detected values ​​of the AC voltage detection unit, the current detection unit and the DC voltage detection unit, and the control unit stops the PWM switching in a predetermined switching stop section including the zero-crossing point of the AC voltage, and changes the width of the switching stop section based on the load size of the load device.

[0007] According to this disclosure, it is possible to provide power conversion devices and the like that improve the power factor of the power source and reduce the harmonic current of the power source.

[0008] This is a configuration diagram of a power converter according to the first embodiment. This is a waveform diagram of the power converter according to the first embodiment when PWM switching is stopped in a predetermined switching stop section including a zero-crossing point. This is a simulation result showing the relationship between the width of the switching stop section and the power factor of the power converter according to the first embodiment. This is a simulation result showing the relationship between the width of the switching stop section and THD in the power converter according to the first embodiment. This is an explanatory diagram showing the relationship between the load size and the width of the switching stop section in the power converter according to the first embodiment. This is an explanatory diagram of another example showing the relationship between the load size and the width of the switching stop section in the power converter according to the first embodiment. This is a functional block diagram of the control unit of the power converter according to the first embodiment. This is a flowchart of the processing performed by the control unit of the power converter according to the first embodiment. This is a configuration diagram of a power converter according to a modified example of the first embodiment. This is a functional block diagram of the control unit of the power converter according to the second embodiment. This is an explanatory diagram showing the relationship between the load size and the operating mode in the power converter according to the second embodiment. This is an explanatory diagram regarding synchronous rectification control of the power converter according to the second embodiment. This is an explanatory diagram showing the current flow in section X1 of Figure 12 in the synchronous rectification control of the power converter according to the second embodiment. This is a waveform diagram of the power supply voltage and power supply current in the full-range switching control of the power converter according to the second embodiment. This is a flowchart of the processing performed by the control unit of the power converter according to the second embodiment. This is a configuration diagram of the air conditioner according to the third embodiment. This is an explanatory diagram showing the relationship between the load magnitude, operating mode, and operating range of the power converter equipped in the air conditioner according to a modified example. This is an explanatory diagram showing the relationship between the load magnitude, operating mode, and operating range of the power converter equipped in the air conditioner according to another modified example.

[0009] <First Embodiment> <Configuration of Power Conversion Device> Figure 1 is a configuration diagram of the power conversion device 10 according to the first embodiment. The power conversion device 10 is a device (DC power supply device) that converts the AC voltage applied from the AC power supply E1 into a DC voltage. The input side of the power conversion device 10 is connected to the three-phase AC power supply E1, and the output side is connected to the load device D1. The load device D1 may include an inverter circuit (not shown) and a motor (not shown), but is not limited to this.

[0010] As shown in Figure 1, the power conversion device 10 includes a converter circuit 1, reactors 21 to 23, a smoothing capacitor 3, an AC voltage detection unit 4, a current detection unit 5, a DC voltage detection unit 6, and a control unit 7.

[0011] Converter circuit 1 is a power converter that converts the AC voltage applied from a three-phase AC power supply E1 into a DC voltage (pulsating DC voltage). The input side of converter circuit 1 is connected to the AC power supply E1 via three-phase wiring Kr, Ks, and Kt. The output side of converter circuit 1 is connected to the load device D1 via the positive DC line K1 and also via the negative DC line K2.

[0012] The converter circuit 1 includes multiple switching elements Q1 to Q6. In the example shown in Figure 1, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) are used as switching elements Q1 to Q6. The switching elements Q1 to Q6 each have parasitic diodes (not shown in the diagram) inside them. The parasitic diodes are the pn junctions located between the source and drain of each switching element Q1 to Q6.

[0013] Furthermore, the types of switching elements Q1 to Q6 are not limited to MOSFETs; other types of switching elements such as IGBTs (Insulated Gate Bipolar Transistors) and bipolar transistors may also be used. In addition, as switching elements Q1 to Q6, in addition to superjunction MOSFETs, SiC, GaN, Ga ２O ３ By using wide-bandgap semiconductor elements such as these, it is possible to increase the speed and efficiency of switching.

[0014] As shown in Figure 1, the converter circuit 1 has a configuration in which the first leg G1, the second leg G2, and the third leg G3 are connected in parallel to the smoothing capacitor 3. The first leg G1 is a series connection of switching elements Q1 and Q4. The source of switching element Q1 and the drain of switching element Q4 are connected, and this connection point P1 is connected to the AC power supply E1 via the R-phase wiring Kr. Similarly, the connection point P2 between the source of switching element Q2 and the drain of switching element Q5 is connected to the AC power supply E1 via the S-phase wiring Ks. In addition, the connection point P3 between the source of switching element Q3 and the drain of switching element Q6 is connected to the AC power supply E1 via the T-phase wiring Kt.

[0015] Furthermore, the connection points of the drains of switching elements Q1, Q2, and Q3 are connected to the load device D1 via the positive DC line K1. The connection points of the sources of switching elements Q4, Q5, and Q6 are connected to the load device D1 via the negative DC line K2.

[0016] Reactors 21 to 23 are elements that store and release energy from the power supplied from the three-phase AC power supply E1, and are used to boost the DC voltage and improve the power factor of the power supply. Reactor 21 is provided in the R-phase wiring Kr that connects the AC power supply E1 and the converter circuit 1. Similarly, reactor 22 is provided in the S-phase wiring Ks, and reactor 23 is provided in the T-phase wiring Kt.

[0017] The smoothing capacitor 3 is an element that smooths the voltage (pulsating DC voltage) on the output side of the converter circuit 1, and is connected to the output side of the converter circuit 1. Specifically, the positive terminal of the smoothing capacitor 3 is connected to the positive DC line K1, and the negative terminal of the smoothing capacitor 3 is connected to the negative DC line K2.

[0018] The AC voltage detection unit 4 detects the power supply voltage Vs (AC voltage) of the AC power supply E1 and is connected to the respective wirings Kr, Ks, and Kt. The current detection unit 5 detects the current flowing through the converter circuit 1. In the example in Figure 1, the power supply current Is flowing through the three-phase wirings Kr, Ks, and Kt of the AC power supply E1 is detected by the current detection unit 5. The DC voltage detection unit 6 detects the DC voltage Edc of the smoothing capacitor 3. The detected values ​​from the AC voltage detection unit 4, the current detection unit 5, and the DC voltage detection unit 6 are output to the control unit 7.

[0019] The control unit 7 is, for example, a microcomputer, and although not shown in the diagram, it is composed of electronic circuits including a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and various interfaces. It reads the program stored in the ROM, loads it into the RAM, and the CPU executes various processes. Based on the detection values ​​of the AC voltage detection unit 4, the current detection unit 5, and the DC voltage detection unit 6, the control unit 7 performs PWM (Pulse Width Modulation) switching of multiple switching elements Q1 to Q6. Here, "PWM switching" means switching the on and off states of the switching elements Q1 to Q6 based on PWM control.

[0020] In the first embodiment, the control unit 7 stops PWM switching in a predetermined switching stop section that includes the zero-crossing point of the power supply voltage (AC voltage) of the AC power supply E1 (see Figure 2). This reduces the switching loss in the switching elements Q1 to Q6 and improves efficiency compared to the case where PWM switching is performed continuously (for example, the waveform diagram in Figure 14). Note that "switching loss" refers to the power loss associated with switching the switching elements Q1 to Q6 on and off.

[0021] Figure 2 shows the waveform when PWM switching is stopped in a predetermined switching stop section including the zero-crossing point. The horizontal axis of the upper and lower waveform diagrams in Figure 2 represents time. The vertical axis of the upper waveform diagram in Figure 2 represents the power supply voltage (AC voltage) of AC power supply E1. The vertical axis of the lower waveform diagram in Figure 2 represents the power supply current (AC current) of AC power supply E1. As shown in Figure 2, the three-phase power supply voltages Vr, Vs, and Vt each have sinusoidal waveforms. The phase difference between power supply voltages Vr and Vs is approximately 120 degrees (similarly for the phase difference between power supply voltages Vs and Vt, and between power supply voltages Vt and Vr).

[0022] The control unit 7 (see Figure 1) identifies the zero-crossing point of the AC voltage based on the value detected by the AC voltage detection unit 4 (see Figure 1). Here, "zero-crossing point" refers to the point where the polarity of the AC voltage switches from positive to negative, or from negative to positive. In short, the point where the AC voltage is approximately zero is the "zero-crossing point". The control unit 7 then stops PWM switching in a predetermined switching stop section that includes the zero-crossing point. Hereafter, this control method will be referred to as "intermittent switching control". In intermittent switching control, PWM switching is performed intermittently with the aforementioned switching stop section in between.

[0023] In the example shown in Figure 2, the width of the switching stop interval (phase angle width) is set to 30 degrees (i.e., 30°) in intermittent switching control. For example, with respect to the zero-crossing point A1 of the R-phase power supply voltage Vr, PWM switching is stopped within a range of +15 degrees on the positive side and -15 degrees on the negative side (the same applies to the other zero-crossing points A2 and A3). As a result, in the switching stop intervals B1, B2, and B3 at the bottom of Figure 2, the R-phase power supply current Ir is approximately zero, and the changes in the S-phase and T-phase power supply currents Is and It are gradual. The same can be said for other switching stop periods that include the zero-crossing points of the S-phase and T-phase power supply voltages.

[0024] In intermittent switching control, PWM switching is intermittently stopped, which reduces switching losses associated with the on / off switching of switching elements Q1 to Q6 (see Figure 1), thereby improving efficiency. The longer the switching stop interval, the greater the effect of reducing switching losses, and thus the higher the efficiency of power conversion. However, the longer the switching stop interval, the more the waveform of the power supply current (AC current) is distorted, the lower the power supply power factor, and the higher the power supply harmonic current (harmonic components contained in the current of the AC power supply E1) tends to be.

[0025] Furthermore, as will be explained below, the inventors have discovered that even if the width of the switching stop interval is the same in intermittent switching control, the power factor of the power supply differs depending on the load size.

[0026] Figure 3 shows the simulation results illustrating the relationship between the width of the switching stop interval and the power factor of the power supply. In Figure 3, the horizontal axis represents the width of the switching stop interval in intermittent switching control (the range of phase angles in the power supply voltage), and the vertical axis represents the power factor of the power supply. In the example in Figure 3, the simulation results are shown for loads (power consumption) of load device D1 (see Figure 1) at 3 kW, 6 kW, and 10 kW.

[0027] As shown in Figure 3, for loads of 3 kW, 6 kW, and 10 kW, the wider the switching stop interval, the lower the power factor of the power supply. This is because the waveform of the power supply current is distorted as the width of the switching stop interval increases. Furthermore, the inventors have found that even with the same width of the switching stop interval (e.g., 80 degrees), the power factor of the power supply decreases as the load decreases. This is thought to be because, as the load decreases (i.e., the power consumption of the load device D1 decreases), it becomes more difficult for charge to be released from the smoothing capacitor 3 to the load device D1, and the DC voltage of the smoothing capacitor 3 does not drop easily. When the DC voltage of the smoothing capacitor 3 does not drop easily, the DC voltage tends to be higher than the power supply voltage (AC voltage), making it difficult for power supply current to flow from the AC side to the DC side, and as a result, the waveform of the power supply current is more likely to be distorted.

[0028] In the example of FIG. 3, when the width of the switching stop interval is in the range of 0 to 60 deg, the influence of the load magnitude (3 [kW], 6 [kW], or 10 [kW]) on the power factor of the power supply is relatively small. However, when the width of the switching stop interval exceeds 60 deg, a large difference in the power factor of the power supply occurs depending on the load magnitude. Also, the wider the width of the switching stop interval, the greater the tendency for the difference in the power factor of the power supply to increase with the load magnitude.

[0029] FIG. 4 shows the simulation results of the relationship between the width of the switching stop interval and THD. The horizontal axis in FIG. 4 is the width of the switching stop interval (the width of the phase angle range in the power supply voltage) in the intermittent switching control, and the vertical axis is THD (Total Harmonics Distortion). Note that THD is an index indicating the degree of distortion in the waveform of the power supply current. For example, the greater the distortion in the waveform of the power supply current, the larger the value of THD. In the example of FIG. 4, the simulation results for the cases where the load (power consumption) of the load device D1 (see FIG. 1) is 3 [kW], 6 [kW], and 10 [kW] are shown.

[0030] As shown in FIG. 4, regardless of whether the load magnitude is 3 [kW], 6 [kW], or 10 [kW], the larger the width of the switching stop interval, the larger the value of THD. In other words, the narrower the width of the switching stop interval, the closer the waveform of the power supply current approaches a sine wave, and thus the lower the THD. Also, even when the length of the width of the switching stop interval is the same (for example, 80 deg), the smaller the load, the higher the THD, and the more likely the power supply harmonic current is to occur.

[0031] Thus, in the intermittent switching control, the smaller the load, the lower the power factor of the power supply (see Fig. 3), and the more likely the power supply harmonic current is to occur (see Fig. 4). Also, the shorter the width of the switching stop section, the higher the power factor of the power supply (see Fig. 3), and the power supply harmonic current is reduced (see Fig. 4). Therefore, in the first embodiment, the smaller the load, the narrower the width of the switching stop section is made by the control unit 7 (see Fig. 1). As a result, while achieving high efficiency in the intermittent switching control, the power factor of the power supply can be improved and the power supply harmonic current can be reduced.

[0032] Fig. 5 is an explanatory diagram showing the relationship between the magnitude of the load and the width of the switching stop section. The horizontal axis of Fig. 5 is the magnitude of the load in the load device D1 (see Fig. 1). Also, the vertical axis of Fig. 5 is the width of the switching stop section in the intermittent switching control. In the example of Fig. 5, the width of the switching stop section is set to be proportional to the magnitude of the load. That is, the control unit 7 (see Fig. 1) narrows the width of the switching stop section as the load of the load device D1 (see Fig. 1) becomes smaller.

[0033] For example, for a predetermined load Ld1 shown in Fig. 5, the width θw1 of the switching stop section stop is set. Incidentally, the "w" included in the symbol of the width θw1 of the switching stop section stop means "width". Thereafter, as the load increases, accordingly, the control unit 7 widens the width of the switching stop section. Also, as the load decreases, accordingly, the control unit 7 narrows the width of the switching stop section. Thus, the control unit 7 (see Fig. 1) changes the width of the switching stop section based on the magnitude of the load of the load device D1 (see Fig. 1). As a result, while reducing the switching loss in the converter circuit 1 (see Fig. 1), the power factor of the power supply can be improved and the power supply harmonic current can be reduced.

[0034] In the example of FIG. 5, the magnitude of the load and the width of the switching stop period have a linear relationship, but it is not limited to this. That is, as long as the width of the switching stop period is set to be narrower as the load becomes smaller, the magnitude of the load and the width of the switching stop period may have a non-linear relationship.

[0035] FIG. 6 is an explanatory diagram of another example showing the relationship between the magnitude of the load and the width of the switching stop period. The horizontal axis and the vertical axis in FIG. 6 are the same as those in FIG. 5. As shown in FIG. 6, as the magnitude of the load changes, the control unit 7 (see FIG. 1) may change the width of the switching stop period step by step. In the example of FIG. 6, in the range of 0 ≤ load < Ld1, the width of the switching stop period is set to zero. In this case, PWM switching is performed over the entire range of the phase angle of the power supply voltage.

[0036] Also, in the range of Ld1 ≤ load < Ld2, the width of the switching stop period is set to a predetermined value θw1 stop In the range of Ld2 ≤ load < Ld3, the width of the switching stop period is set to a predetermined value θw2 stop In the range of Ld3 ≤ load, the width of the switching stop period is set to a predetermined value θw3 stop The magnitude relationship of the predetermined values θw1 stop , θw2 stop , θw3 stop is θw1 stop < θw2 stop < θw3 stop In this way, after dividing the magnitude of the load into a plurality of sections, the control unit 7 may discretely set the width of the switching stop period corresponding to each section.

[0037] FIG. 7 is a functional block diagram of the control unit 7 of the power conversion device. As shown in FIG. 7, the control unit 7 includes, as a functional configuration, a phase calculation unit 71, a DC voltage control unit 72, a vector calculation unit 73, a load determination unit 74, a conduction stop angle calculation unit 75, and a PWM signal generation unit 76.

[0038] The phase calculation unit 71 calculates the phase θs of the power supply voltage Vs (AC voltage) based on the power supply voltage Vs (AC voltage) detected by the AC voltage detection unit 4 (see Figure 1). The DC voltage control unit 72 calculates the phase θs of the power supply voltage Vs based on the DC voltage Edc detected by the DC voltage detection unit 6 (see Figure 1) and a predetermined DC voltage command Edc * Based on that, current correction command I adj This generates the DC voltage command Edc. * This is the target value of the DC voltage of the smoothing capacitor 3 (see Figure 1), and is set appropriately based on the load magnitude. Current correction command I adj The detected DC voltage is set to the DC voltage command Edc * This is the command value for the current used to approach the target value.

[0039] The vector calculation unit 73 receives the power supply current Is, which is the value detected by the current detection unit 5 (see Figure 1), as well as the power supply voltage Vs, the phase θs of the power supply voltage, and the current correction command I. adj Based on this, a predetermined vector calculation is performed, and the d-axis voltage command Vd * and q-axis voltage command Vq * The load determination unit 74 calculates the load at each moment based on predetermined load information.

[0040] Such load information (i.e., load) may include, for example, the current flowing through the converter circuit 1 (power supply current) or the current flowing through the load device D1 (load current). If the load device D1 (see Figure 1) includes an inverter circuit and a motor, the motor's rotational speed, the motor's load torque, and the modulation rate of the inverter circuit may also be used as load information (i.e., load). The aforementioned "modulation rate" is the ratio of the AC voltage (effective value) on the output side of the inverter circuit to the DC voltage of the smoothing capacitor 3.

[0041] The load determination unit 74 determines which of several categories (see Figure 6), such as low load, medium load, and high load, the current load magnitude belongs to. The load determination result information Inf, which is the determination result of the load determination unit 74, is output to the energization stop angle calculation unit 75.

[0042] The power supply stop angle calculation unit 75 calculates the switching stop section θ when performing intermittent switching control based on the phase θs of the power supply voltage and the load determination result information Inf. stop The (range of the power-off angle) is calculated. That is, the power-off angle calculation unit 75 calculates the switching stop section θ as the load decreases. stop The width is narrowed. The power supply stop angle calculation unit 75 then calculates the switching stop section θ stop The power supply voltage is set based on the phase angle. The PWM signal generation unit 76 generates the d-axis voltage command Vd * And, q-axis voltage command Vq * And, the switching stop interval θ stop Based on this, a predetermined PWM signal is generated. The PWM signal generated by the PWM signal generation unit 76 is output to the switching elements Q1 to Q6 (see Figure 1).

[0043] Figure 8 is a flowchart of the process executed by the control unit (see also Figure 1 as appropriate). Note that when "START" is shown in Figure 8, the load device D1 is driven by the DC voltage applied from the power converter 10. Also, the intermittent switching control described above is performed by the control unit 7. In step S101, the control unit 7 sets the switching stop interval based on the load size. As described above, the smaller the load, the narrower the width of the switching stop interval is set.

[0044] In step S102, the control unit 7 generates a predetermined PWM signal. During the switching stop section, which is the result of the processing in step S101, PWM switching is temporarily stopped. After the processing in step S102, the control unit 7 returns to "START" (RETURN). In this way, the series of processes shown in Figure 8 are repeated predetermined times.

[0045] Although not shown in Figure 8, the control unit 7 may stop PWM switching if the DC voltage across the smoothing capacitor 3 (the value detected by the DC voltage detection unit 6) is overvoltage. Similarly, the control unit 7 may stop PWM switching if the current flowing through the converter circuit 1 (see Figure 1) (the value detected by the current detection unit 5) is overcurrent. Such protective control can improve the reliability of the power converter 10. It is assumed that thresholds for the judgment criteria (criteria for determining overvoltage or overcurrent) of the above-mentioned protective control are set in advance.

[0046] <Effects> According to the first embodiment, in addition to boosting the DC voltage by PWM switching, the power factor of the power supply can be improved and the harmonic current of the power supply can be reduced. Furthermore, since switching losses are reduced in intermittent switching control compared to when PWM switching is performed continuously, higher efficiency can be achieved.

[0047] Furthermore, when the control unit 7 stops PWM switching in a predetermined switching stop section including the zero-crossing point, the smaller the load, the narrower the width of the switching stop section (see Figures 5 and 6). This improves the power supply power factor while increasing efficiency and reducing power supply harmonic currents. In addition, since power supply harmonic currents can be reduced by switching the switching elements Q1 to Q6 on and off, passive elements such as reactors 21 to 23 (see Figure 1) and smoothing capacitors 3 (see Figure 1) can be miniaturized and their costs reduced.

[0048] ≪Modified Version of the First Embodiment≫ Figure 9 is a configuration diagram of a power converter 10A according to a modified version of the first embodiment. In Figure 9, a current detection unit 5A for detecting DC current Ish is provided instead of the current detection unit 5 (see Figure 1) described in the first embodiment. For example, a shunt resistor R1 is used as such a current detection unit 5A. The shunt resistor R1 is provided between the converter circuit 1 and the smoothing capacitor 3 in the negative DC line K2. The moment-by-moment detection value of the current detection unit 5A is output to the control unit 7. The control unit 7 performs the intermittent switching control described above based on the detected values ​​of DC current Ish, power supply voltage Vs, and DC voltage Edc. The same effects as the first embodiment are achieved with this configuration as well.

[0049] ≪Second Embodiment≫ The second embodiment differs from the first embodiment in that the control unit 7B (see Figure 10) switches the operating mode of the power converter 10 (see Figure 1) based on the magnitude of the load. Other aspects are the same as the first embodiment. Therefore, the differences from the first embodiment will be explained, and the overlapping parts will be omitted.

[0050] Figure 10 is a functional block diagram of the control unit 7B of the power converter according to the second embodiment. As shown in Figure 10, the control unit 7B includes a phase calculation unit 71, a DC voltage control unit 72, a vector calculation unit 73, a load determination unit 74, an energization stop angle calculation unit 75, and a PWM signal generation unit 76B. The configuration shown in Figure 10 differs from the first embodiment (see Figure 7) in that load determination result information Inf is input from the load determination unit 74 to the PWM signal generation unit 76B.

[0051] The PWM signal generation unit 76B determines the operating mode of the power converter 10 (see Figure 1) based on the load determination result information Inf input from the load determination unit 74. Details of the operating mode will be described later. Furthermore, the PWM signal generation unit 76B generates the d-axis voltage command Vd * And, q-axis voltage command Vq * And, the switching stop interval θ stop Based on this, a predetermined PWM signal is generated so that power conversion is performed in the aforementioned operating mode (an operating mode corresponding to the load size).

[0052] Figure 11 is an explanatory diagram showing the relationship between load magnitude and operating mode. As shown in Figure 11, when the load magnitude is less than a predetermined value I1 (i.e., in the low load region), synchronous rectification control is performed. When the load magnitude is greater than or equal to the predetermined value I1 and less than a predetermined value I2 (i.e., in the medium load region), intermittent switching control, as described in the first embodiment, is performed. When the load magnitude is greater than or equal to the predetermined value I2 (i.e., in the high load region), full-range switching control is performed. Next, synchronous rectification control and full-range switching control will be explained in order.

[0053] <Synchronous Rectification Control> Figure 12 is an explanatory diagram regarding synchronous rectification control. In Figure 12, the horizontal axis of the waveform diagram at the top of the page and the horizontal axis of the time chart at the bottom of the page both represent the phase angle of the power supply voltage (AC voltage). In Figure 12, the vertical axis of the waveform diagram at the top of the page represents the power supply voltage of the AC power supply E1 (see Figure 1). In Figure 12, the vertical axis of the time chart at the bottom of the page represents the ON / OFF state of the switching elements Q1 to Q6 (see Figure 1).

[0054] For example, "Q1: R-Hi" in Figure 1 indicates that the switching element Q1 is connected to the R-phase wiring Kr (see Figure 1) and also to the positive (High) DC line K1 (see Figure 1). Also, for example, "Q4: R-Lo" indicates that the switching element Q4 is connected to the R-phase wiring Kr (see Figure 1) and also to the negative (Low) DC line K2 (see Figure 1).

[0055] Synchronous rectification control is a control method in which, among multiple switching elements Q1 to Q6, the positive switching element corresponding to the phase with the highest instantaneous AC voltage is kept in the ON state, while the negative switching element corresponding to the phase with the lowest instantaneous AC voltage is kept in the ON state. Such synchronous rectification control is performed, for example, when the load is relatively small (see Figure 11).

[0056] As shown in Figure 12, for example, in the interval X1 where the relative magnitudes of the R-phase power supply voltage Vr, the S-phase power supply voltage Vs, and the T-phase power supply voltage Vt are Vr > Vt > Vs, the R-phase switching element Q1 connected to the positive terminal of the smoothing capacitor 3 (see Figure 1) and the S-phase switching element Q5 connected to the negative terminal of the smoothing capacitor 3 are kept in the ON state, while the remaining switching elements are kept in the OFF state. In other words, in synchronous rectification control, the control unit 7B (see Figure 10) keeps the High-side (positive-side) switching element Q1 corresponding to the phase with the highest instantaneous value of the AC voltage (e.g., the R-phase) in the ON state, and keeps the Low-side (negative-side) switching element Q5 corresponding to the phase with the lowest instantaneous value of the AC voltage (e.g., the S-phase) in the ON state.

[0057] Figure 13 is an explanatory diagram showing the current flow in section X1 of Figure 12 in synchronous rectification control. As described above, in section X1 (see Figure 12), switching elements Q1 and Q5 are kept in the ON state, while the remaining switching elements Q2 to Q4 and Q6 are kept in the OFF state. As a result, as shown by the dashed arrow in Figure 13, current flows through the path AC power supply E1 → R-phase reactor 21 → switching element Q1 → smoothing capacitor 3 → switching element Q5 → S-phase reactor 22 → AC power supply E1. As a result, charge is supplied to the smoothing capacitor 3.

[0058] In synchronous rectification control, when current flows through the ON-state switching elements Q1 and Q5, almost no current flows through the parasitic diodes of the switching elements Q1 and Q5, and the current flows through the drift layer with low on-resistance. Furthermore, compared to intermittent switching control and full-range switching control, synchronous rectification control requires fewer switching cycles, thus enabling highly efficient power conversion.

[0059] <Whole-range switching control> Whole-range switching control is a control method that continuously performs PWM switching. Such whole-range switching control is performed, for example, when the load is relatively large (see Figure 11). The control unit 7B (see Figure 10) sets the detected value of the DC voltage detection unit 6 to a predetermined DC voltage command Edc *Set the duty cycle of the PWM switching (duty cycle for each phase angle of the AC voltage) appropriately to approach (see Figure 7).

[0060] Figure 14 shows the waveforms of the power supply voltage and power supply current in full-range switching control. The horizontal axis of the upper and lower waveform diagrams in Figure 14 represents time. The vertical axis of the upper waveform diagram in Figure 14 represents the power supply voltage (AC voltage) of AC power supply E1. The vertical axis of the lower waveform diagram in Figure 14 represents the power supply current (AC current) of AC power supply E1. As shown in Figure 14, in full-range switching control, the waveform of the power supply current becomes sinusoidal. Therefore, compared to the intermittent switching control described above (see Figure 2), the power supply power factor can be further improved and the power supply harmonic current can be further reduced. In addition, in full-range switching control, the DC voltage on the output side of the converter circuit 1 can also be sufficiently boosted.

[0061] When comparing synchronous rectification control, intermittent switching control, and full-range switching control, full-range switching control has the greatest power loss, followed by intermittent switching control and then synchronous rectification control. Furthermore, full-range switching control has the highest power factor, followed by intermittent switching control and then synchronous rectification control.

[0062] Figure 15 is a flowchart of the process executed by the control unit (see also Figure 10 as appropriate). Note that at "START" in Figure 15, the load device D1 is assumed to be driven by the DC voltage from the power converter 10. In step S201, the control unit 7B reads the load information. For example, the power supply current and the load current can be used as such load information. Note that if the load device D1 (see Figure 1) includes an inverter circuit and a motor, the motor's rotational speed and load torque, as well as the modulation rate of the inverter circuit, may be used as load information.

[0063] In step S202, the control unit 7B determines whether the load magnitude based on the load information is less than a first predetermined value. The "first predetermined value" (see also Figure 11) is a threshold value that serves as the criterion for determining whether or not to perform synchronous rectification control, and is set in advance. If the load magnitude is less than the first predetermined value (S202: Yes), the control unit 7B proceeds to step S203. In step S203, the control unit 7B performs synchronous rectification control. By performing synchronous rectification control in this way, switching losses are reduced, and power conversion can be performed with high efficiency.

[0064] Furthermore, if the load magnitude is greater than or equal to the first predetermined value in step S202 (S202: No), the control unit 7B proceeds to step S204. In step S204, the control unit 7B determines whether or not the load magnitude is less than the second predetermined value. The "second predetermined value" (see also Figure 11) is a threshold value that serves as the criterion for determining whether or not to perform intermittent switching control, and is preset as a value greater than the first predetermined value mentioned above.

[0065] If the load magnitude is less than the second predetermined value in step S204 (S204: Yes), the control unit 7B proceeds to step S205. In step S205, the control unit 7B performs intermittent switching control. In the intermittent switching control (S205), the series of processes shown in Figure 8, which was described in the first embodiment, are performed. As described above, in intermittent switching control, the control unit 7B narrows the width of the PWM switching stop interval as the load decreases. This allows the DC voltage to be increased, the power factor of the power supply to be improved, and the power supply harmonic current to be reduced.

[0066] Furthermore, if the load magnitude is greater than or equal to the second predetermined value in step S204 (S204: No), the control unit 7B proceeds to step S206. In step S206, the control unit 7B performs full-range switching control. This further improves the power factor compared to intermittent switching control and also reduces power supply harmonic currents. After performing any of the processes in steps S203, S205, or S206, the control unit 7B returns to "START" (RETURN). In this way, the control unit 7B repeats the series of processes shown in Figure 15 at predetermined intervals.

[0067] <Effects> According to the second embodiment, the control unit 7B switches the operating mode according to the magnitude of the load. Specifically, in the region where the load is relatively small (the region where there is no particular need to boost the DC voltage), the control unit 7B performs synchronous rectification control. This reduces power loss and improves efficiency compared to intermittent switching control and full-range switching control.

[0068] Furthermore, in the moderate load range, the control unit 7B performs intermittent switching control, which increases the DC voltage, improves the power factor, and reduces power harmonic currents. In the heavy load range, the control unit 7B performs full-range switching control, which further enhances the effects of DC voltage increase, power factor improvement, and harmonic current reduction compared to intermittent switching control.

[0069] <<Modification of the Second Embodiment>> In the second embodiment, the control unit 7B performed synchronous rectification control when the load magnitude was less than a first predetermined value (S202: Yes, S203 in Figure 15), but it is not limited to this. For example, instead of synchronous rectification control, the control unit 7B may perform full-wave rectification control.

[0070] <Full-wave rectification control> Full-wave rectification control is a control method that keeps each of the multiple switching elements Q1 to Q6 (see Figure 1) in the off state. In this case, there is no particular need for switching by the switching elements Q1 to Q6, so the switching loss can be reduced even further than with the synchronous rectification control described above. However, in full-wave rectification control, the waveform of the power supply current is distorted, so the power supply power factor becomes lower than with synchronous rectification control, and there is a tendency for power supply harmonic currents to be more likely to occur.

[0071] The control unit 7B (see Figure 10) performs one of the following based on the load magnitude: full-wave rectification control, intermittent switching control, or full-range switching control. Specifically, if the load is less than a first predetermined value, the control unit 7B performs full-wave rectification control. If the load is greater than or equal to the first predetermined value but less than a second predetermined value, the control unit 7B performs intermittent switching control. If the load is greater than or equal to the second predetermined value, the control unit 7B performs full-range switching control. This makes it possible to improve the power factor and reduce power harmonic currents while reducing switching losses.

[0072] ≪Third Embodiment≫ In the third embodiment, an air conditioner equipped with the power converter 10 with the configuration described in the first embodiment will be described.

[0073] Figure 16 is a configuration diagram of the air conditioner 100 according to the third embodiment. The solid arrows in Figure 16 indicate the flow of refrigerant in the heating cycle. The dashed arrows in Figure 16 indicate the flow of refrigerant in the cooling cycle. The air conditioner 100 is a device that performs air conditioning such as cooling and heating operations. As shown in Figure 16, the air conditioner 100 includes a compressor 91, an outdoor heat exchanger 92, an outdoor fan 93, an expansion valve 94, an indoor heat exchanger 95, an indoor fan 96, and a four-way valve 97. In the example in Figure 16, the compressor 91, outdoor heat exchanger 92, outdoor fan 93, expansion valve 94, and four-way valve 97 are installed in the outdoor unit U1. The indoor heat exchanger 95 and indoor fan 96 are installed in the indoor unit U2.

[0074] Furthermore, the air conditioner 100 includes a power converter 10, which has the same configuration as in the first embodiment, in addition to the inverter circuit 8, for use in driving the motor M1 of the compressor 91. The power converter 10 includes a converter circuit 1, a smoothing capacitor 3, an AC voltage detection unit 4, a DC voltage detection unit 6, and a control unit 7. The inverter circuit 8 shown in Figure 16 is a power converter that converts the DC voltage applied from the power converter 10 into a predetermined AC voltage. The output side of the inverter circuit 8 is connected to the three-phase winding of the motor M1. The motor M1 is the driving source for the compressor 91 and is driven by the AC voltage applied from the inverter circuit 8. The "load device" electrically connected to the power converter 10 includes the inverter circuit 8 and the motor M1.

[0075] The compressor 91 is a device that compresses low-temperature, low-pressure gaseous refrigerant and discharges it as high-temperature, high-pressure gaseous refrigerant, and is equipped with a motor M1 as its drive source. For example, a permanent magnet synchronous motor is used as such a motor M1.

[0076] The outdoor heat exchanger 92 is a heat exchanger in which heat exchange takes place between a refrigerant flowing through its heat transfer tubes (not shown) and the outside air. The outdoor fan 93 is a fan that blows outside air into the outdoor heat exchanger 92. The outdoor fan 93 is equipped with an outdoor fan motor 93a, which is its driving source, and is installed near the outdoor heat exchanger 92.

[0077] The expansion valve 94 is a valve that reduces the pressure of the refrigerant condensed in the "condenser" (one of the outdoor heat exchanger 92 and the indoor heat exchanger 95). The refrigerant reduced in pressure by the expansion valve 94 is then led to the "evaporator" (the other of the outdoor heat exchanger 92 and the indoor heat exchanger 95).

[0078] The indoor heat exchanger 95 is a heat exchanger in which heat exchange takes place between a refrigerant flowing through its heat transfer tubes (not shown) and indoor air (air from the air-conditioned room). The indoor fan 96 is a fan that supplies indoor air to the indoor heat exchanger 95. The indoor fan 96 is equipped with an indoor fan motor 96a, which is its driving source, and is installed near the indoor heat exchanger 95.

[0079] The four-way valve 97 is a valve that switches the flow path of the refrigerant according to the operating mode of the air conditioner 100. For example, in the cooling cycle (see dashed arrow in Figure 16), the refrigerant circulates sequentially through the compressor 91, the outdoor heat exchanger 92 (condenser), the expansion valve 94, and the indoor heat exchanger 95 (evaporator). On the other hand, in the heating cycle (see solid arrow in Figure 16), the refrigerant circulates sequentially through the compressor 91, the indoor heat exchanger 95 (condenser), the expansion valve 94, and the outdoor heat exchanger 92 (evaporator).

[0080] <Effects> According to the third embodiment, since the air conditioner 100 is equipped with a power converter 10 having the same configuration as in the first embodiment, the performance and efficiency of the air conditioner 100 can be improved. Therefore, an air conditioner 100 with a high APF (Annual Performance Factor) can be provided.

[0081] <Modifications> Although the power converter 10 and air conditioner 100 according to this disclosure have been described in each embodiment above, the invention is not limited to these descriptions and various modifications can be made. For example, the second embodiment and the third embodiment may be combined to switch the operating mode according to the load size, as shown in Figures 17 and 18.

[0082] Figure 17 is an explanatory diagram showing the relationship between the load size, operating mode, and operating range of the power conversion device in the modified air conditioner. The "intermediate operating range" shown in Figure 17 is an operating range where the load is relatively small. For example, in transitional seasons such as spring and autumn, the air conditioning load is small, and the load on the inverter circuit 8 (see Figure 16) and motor M1 (see Figure 16) is often small. Therefore, the control unit 7 is configured to perform synchronous rectification control in the intermediate operating range. This enables highly efficient power conversion.

[0083] The "rated operation region" shown in Figure 17 is a region where the load is greater than in the intermediate operation region described above, and the motor M1 (see Figure 16) is driven at its rated operation. In this rated operation region, the load on the inverter circuit 8 (see Figure 16) and the motor M1 (see Figure 16) is often moderate, so the control unit 7 performs intermittent switching control. This allows for a boost in DC voltage, as well as improvement of the power supply power factor and reduction of power supply harmonic currents.

[0084] The "high-load operation region" shown in Figure 17 is a region where the load is considerably high. For example, the operating region when performing heating operation when the outside temperature is very low, or when performing cooling operation when the outside temperature is very high, corresponds to the high-load operation region. In such high-load operation regions, the load on the inverter circuit 8 (see Figure 16) and motor M1 (see Figure 16) is often high, so the control unit 7 performs switching control across the entire range. This enables comfortable air conditioning even under high load conditions.

[0085] Figure 18 is an explanatory diagram showing the relationship between the load magnitude, operating mode, and operating range of the power converter in an air conditioner according to another modified example. As shown in Figure 18, intermittent switching control is performed in the rated operating range, and intermittent switching control may also be performed in the high-load operating range where the load is relatively small. As mentioned above, intermittent switching control has lower switching losses compared to full-range switching control, so air conditioning operation at high load can be performed with high efficiency.

[0086] Furthermore, while each embodiment describes the case where a three-phase AC voltage is applied from an AC power source E1 (see Figure 1) to the power converter 10 (see Figure 1), it is not limited to this. That is, each embodiment can also be applied when a single-phase AC voltage is applied from a single-phase AC power source to the power converter 10. In the case where a single-phase AC voltage is applied to the power converter 10, the converter circuit shall be equipped with four switching elements connected in a bridge configuration.

[0087] Furthermore, while each embodiment described a process in intermittent switching control where the width of the switching stop interval is narrowed as the load decreases, the method is not limited to this. In other words, any process that changes the width of the switching stop interval based on the magnitude of the load is sufficient. For example, considering the efficiency of power conversion, a process that narrows the width of the switching stop interval as the load increases may be performed in a portion of the load region.

[0088] Furthermore, although the third embodiment described a case in which the air conditioner 100 (see Figure 16) is equipped with a four-way valve 97, it is not limited to this. That is, the four-way valve 97 may be omitted as appropriate, and the air conditioner may be used for cooling only or heating only. Also, the air conditioner 100 (see Figure 16) described in the third embodiment can be applied to various types of air conditioners such as multi-split air conditioners for buildings, packaged air conditioners, and room air conditioners. In addition, the third embodiment can be applied to other refrigeration cycle devices such as chillers, water heaters, air conditioning and water heating systems, chillers, and refrigerators.

[0089] Furthermore, each embodiment is described in detail for the purpose of clearly illustrating this disclosure and is not necessarily limited to having all the configurations described. In addition, it is possible to add, delete, or replace some of the configurations in each embodiment with other configurations. Moreover, some or all of the above-described configurations, functions, processing units, processing means, etc., may be implemented in hardware, for example, by designing them as integrated circuits. Also, the mechanisms and configurations shown are those deemed necessary for explanation and do not necessarily represent all of the mechanisms and configurations in the product.

[0090] 1 Converter circuit 3 Smoothing capacitor 4 AC voltage detection unit 5, 5A Current detection unit 6 DC voltage detection unit 7, 7B Control unit 8 Inverter circuit 10, 10A Power conversion device 21, 22, 23 Reactor 91 Compressor 92 Outdoor heat exchanger 93 Outdoor fan 94 Expansion valve 95 Indoor heat exchanger 96 Indoor fan 97 Four-way valve 100 Air conditioner D1 Load device E1 AC power supply K1, K2 DC line Kr, Ks, Kt Wiring M1 Motor Q1, Q2, Q3, Q4, Q5, Q6 Switching element

Claims

1. A power converter comprising: a converter circuit having a plurality of switching elements connected in a bridge configuration, the input side of which is connected to an AC power source and the output side of which is connected to a load device; a reactor provided in the wiring connecting the AC power source and the converter circuit; a smoothing capacitor for smoothing the voltage on the output side of the converter circuit; an AC voltage detection unit for detecting the AC voltage of the AC power source; a current detection unit for detecting the current flowing through the converter circuit; and a DC voltage detection unit for detecting the DC voltage of the smoothing capacitor; and a control unit that performs PWM switching of the plurality of switching elements based on the detected values ​​of the AC voltage detection unit, the current detection unit, and the DC voltage detection unit, wherein the control unit stops the PWM switching in a predetermined switching stop section including the zero-crossing point of the AC voltage, and changes the width of the switching stop section based on the load size of the load device.

2. The power conversion device according to claim 1, characterized in that the control unit narrows the width of the switching stop interval as the load decreases.

3. The power converter according to claim 1, characterized in that the control unit performs synchronous rectification control when the load is less than a first predetermined value, performs intermittent switching control when the load is greater than or equal to the first predetermined value and less than a second predetermined value, performs full-range switching control when the load is greater than or equal to the second predetermined value, the synchronous rectification control is a control that maintains the positive switching element corresponding to the phase with the highest instantaneous value of the AC voltage among the plurality of switching elements in an ON state, and maintains the negative switching element corresponding to the phase with the lowest instantaneous value of the AC voltage in an ON state, the intermittent switching control is a control that changes the width of the switching stop interval based on the magnitude of the load, and the full-range switching control is a control that continuously performs the PWM switching.

4. The power conversion device according to claim 1, characterized in that the control unit performs full-wave rectification control when the load is less than a first predetermined value, performs intermittent switching control when the load is greater than or equal to the first predetermined value and less than a second predetermined value, performs full-range switching control when the load is greater than or equal to the second predetermined value, the full-wave rectification control is a control that maintains each of the plurality of switching elements in an off state, the intermittent switching control is a control that changes the width of the switching stop interval based on the magnitude of the load, and the full-range switching control is a control that continuously performs the PWM switching.

5. The power conversion device according to claim 1, characterized in that the control unit stops the PWM switching when the DC voltage of the smoothing capacitor is overvoltage, or when the current flowing through the converter circuit is overcurrent.

6. An air conditioner comprising a power conversion device according to any one of claims 1 to 5, an inverter circuit that converts a DC voltage applied from the power conversion device into an AC voltage, and a motor driven by the AC voltage applied from the inverter circuit, wherein the load device includes the inverter circuit and the motor, and further comprises a compressor driven by the motor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger.

7. The air conditioner according to claim 6, characterized in that the load is the current flowing through the converter circuit, the current flowing through the load device, the rotational speed of the motor, the load torque of the motor, or the modulation rate of the inverter circuit.

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