Power conversion devices, motor drives and refrigeration cycle application equipment

Abstract

A power conversion device (1a) comprises: an inrush current prevention unit (120) that prevents an inrush current; a momentary power failure detection unit (502) that detects a momentary power failure of a commercial power source (110); a rectifying unit (140) that rectifies first AC power supplied from the commercial power source (110); a capacitor (210) connected to the output end of the rectifying unit (140); an inverter (310) that is connected to both ends of the capacitor (210), that converts the power outputted from the rectifying unit (140) and the capacitor (210) to second AC power, and that outputs the second AC power to a compressor (315) having a motor (314); and a control unit (400) that controls the operation of the inverter (310) such that the second AC power, which includes pulsation corresponding to the pulsation of power flowing from the rectifying unit (140) into the capacitor (210), is outputted from the inverter (310) to the compressor (315), said control unit (400) suppressing the current flowing to the capacitor (210).

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device that converts AC power supplied from an AC power source into AC power having a different voltage from the AC power and supplies the converted power to a load, and to a motor drive device and refrigeration cycle application equipment that are equipped with the power conversion device. [Background technology]

[0002] Conventionally, there is a power conversion device that converts AC power supplied from an AC power source into AC power with a different voltage from the AC power and supplies it to a load such as an air conditioner. The power conversion device rectifies the AC power supplied from the AC power source using a diode bridge circuit, smoothes it further using a smoothing capacitor, converts the smoothed power into a desired AC power using an inverter consisting of multiple switching elements, and outputs it to a compressor motor, which is a load.

[0003] Since such power conversion devices are equipped with a relatively large-capacity smoothing capacitor, an inrush current flows when the power is turned on to rapidly charge the smoothing capacitor. If an inrush current flows through a semiconductor component such as a diode bridge, the component may be destroyed due to exceeding its capacity. Therefore, it is necessary to suppress the inrush current by using an inrush current prevention circuit.

[0004] On the other hand, when a momentary power outage occurs, the power conversion device continues to operate and supply power to the compressor motor, which is the load, and the charge in the smoothing capacitor decreases rapidly, causing a drop in the DC bus voltage. When power is restored in this state and normal operation is resumed, a re-inrush current flows as the smoothing capacitor is recharged, and this re-inrush current may also destroy components. For this reason, when a momentary power outage occurs during operation, operation is often stopped once and then restarted after power is restored to continue operation. However, once operation is stopped, the voltage and frequency applied to the compressor motor, which is the load, must be increased from zero again, which causes a problem in that it takes time to restore the state before the momentary power outage.

[0005] In view of this background, a configuration is known that has a means for detecting an instantaneous power outage and suppresses a decrease in DC bus voltage by limiting the power supplied to a load when an instantaneous power outage occurs. For example, Patent Document 1 discloses a power conversion device that has a means for detecting the voltage of an AC power source, reduces a command value of a torque current component at a preset rate according to the reduced amount of electricity when an amount of electricity calculated from the voltage detected by the voltage detection means becomes equal to or less than a first set value, and reduces the command value of the torque current component to zero when the amount of electricity becomes equal to or less than a second set value smaller than the first set value. The power conversion device disclosed in Patent Document 1 can quickly return to a normal state after power is restored from an instantaneous power outage. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2007-49798 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the power conversion device disclosed in Patent Document 1 reduces the torque current only when a momentary power outage is detected, and therefore there is a problem in that a large current flows through the smoothing capacitor during normal operation, accelerating the deterioration of the smoothing capacitor over time.In addition, while it is possible to suppress the ripple change of the capacitor voltage by increasing the capacity of the smoothing capacitor or to use a smoothing capacitor with a high tolerance for deterioration due to ripple, there is a problem in that the device becomes large in size.

[0008] The present disclosure has been made in consideration of the above, and has an object to provide a power conversion device in which deterioration over time of a smoothing capacitor is suppressed without increasing the size of the device. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure includes an inrush current prevention unit that prevents inrush current, an instantaneous power interruption detection unit that detects an instantaneous power interruption of a commercial power supply, a rectification unit that rectifies a first AC power supplied from the commercial power supply, a capacitor connected to an output terminal of the rectification unit, and an inverter connected to both ends of the capacitor and converts the power output from the rectification unit and the capacitor into a second AC power and outputs the second AC power to a load. The power conversion device includes a control unit that controls the operation of the inverter so that the second AC power including pulsation corresponding to the pulsation of the power flowing from the rectification unit to the capacitor is output from the inverter to the load, and suppresses the current flowing to the capacitor. Effect of the Invention

[0010] The power conversion device according to the present disclosure has an advantage of being able to suppress deterioration over time of a smoothing capacitor without increasing the size of the device. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a configuration of a power conversion device according to a first embodiment. [Diagram 2] FIG. 1 is a diagram showing a current flowing from a rectification unit, a current flowing to an inverter, a current flowing from a smoothing unit, and a capacitor voltage of the power conversion device according to the first embodiment. [Diagram 3] FIG. 1 is a diagram showing a current flowing from a rectification unit, a current flowing to an inverter, a current flowing from a smoothing unit, and a capacitor voltage of the power conversion device according to the first embodiment. [Figure 4] FIG. 1 is a diagram showing a current flowing from a rectification unit, a current flowing to an inverter, a current flowing from a smoothing unit, and a capacitor voltage of the power conversion device according to the first embodiment. [Diagram 5] FIG. 1 is a diagram showing a current flowing from a rectification unit, a current flowing to an inverter, a current flowing from a smoothing unit, and a capacitor voltage of the power conversion device according to the first embodiment. [Figure 6] A flowchart showing the operation of a control unit included in the power conversion device according to the first embodiment. [Figure 7]FIG. 1 is a diagram showing an example of a hardware configuration for implementing a control unit included in a power conversion device according to a first embodiment. [Figure 8] FIG. 1 is a diagram showing a configuration of a power conversion device according to a second embodiment. [Figure 9] A flowchart showing the operation of a control unit included in a power conversion device according to a second embodiment. [Figure 10] FIG. 13 is a diagram showing a configuration of a power conversion device according to a modification of the second embodiment. [Figure 11] FIG. 13 is a diagram showing a configuration of a refrigeration cycle application device according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A power conversion device, a motor drive device, and a refrigeration cycle applied device according to embodiments will be described in detail below with reference to the drawings.

[0013] Embodiment 1 FIG. 1 is a diagram showing a configuration of a power conversion device according to a first embodiment. The power conversion device 1a is connected to a commercial power source 110 and a compressor 315. The power conversion device 1a converts a first AC power of a power source voltage Vs supplied from the commercial power source 110 into a second AC power having an amplitude and a phase different from those of the first AC power, and supplies the second AC power to the compressor 315. The power conversion device 1a includes an inrush current prevention unit 120, an instantaneous power interruption detection unit 502, a voltage / current detection unit 501, a reactor 130, a rectification unit 140, a voltage detection unit 503, a smoothing unit 200, an inverter 310, current detection units 313a and 313b, and a control unit 400. The power conversion device 1a and a motor 314 provided in the compressor 315 constitute a motor drive device 2a.

[0014] The inrush current prevention unit 120 is composed of an inrush current prevention element 121 connected in series to the commercial power supply 110, and a switching element 122 connected in parallel to the inrush current prevention element 121. The inrush current prevention element 121 suppresses an inrush current generated when the commercial power supply 110 is turned on to the power conversion device 1a. Examples of the inrush current prevention element 121 include, but are not limited to, a PTC (Positive Temperature Coefficient) thermistor, a cement resistor, and a temperature fuse resistor. The switching element 122 shorts the inrush current prevention element 121 by turning on the switching element 122 during normal operation, thereby suppressing losses that steadily occur in the inrush current prevention element 121. Examples of the switching element 122 include, but are not limited to, a relay, a thyristor, and a triac. The inrush current prevention element 121 may be connected to a path from the commercial power supply 110 to the smoothing unit 200. For example, the inrush current prevention element 121 may be connected closer to the commercial power supply 110 than the rectifier unit 140, or may be connected closer to the motor 314 than the rectifier unit 140. In addition, the inrush current prevention element 121 may be connected to the positive electrode side or the negative electrode side.

[0015] The instantaneous power interruption detection unit 502 detects the voltage of the commercial power supply 110 and outputs the detected value to the control unit 400. The voltage / current detection unit 501 detects the voltage value and current value of the first AC power of the power supply voltage Vs supplied from the commercial power supply 110 and outputs the detected voltage value and current value to the control unit 400. The reactor 130 is connected between the inrush current prevention unit 120 and the rectification unit 140. The rectification unit 140 has a rectification circuit 500 and rectifies and outputs the first AC power of the power supply voltage Vs supplied from the commercial power supply 110. In the power conversion device 1a according to the first embodiment, the rectification circuit 500 is a bridge circuit configured by rectification elements 141, 142, 143, and 144. The rectification unit 140 performs full-wave rectification. The voltage detection unit 503 detects the voltage value of the power rectified by the rectification unit 140 and outputs the detected voltage value to the control unit 400. The smoothing unit 200 is connected to the output terminal of the rectification unit 140 via the voltage detection unit 503. The smoothing unit 200 has a capacitor 210 as a smoothing element, and smoothes the power rectified by the rectification unit 140. The capacitor 210 can be exemplified by, but is not limited to, an electrolytic capacitor and a film capacitor. The capacitor 210 has a capacity to smooth the power rectified by the rectification unit 140. The voltage generated in the capacitor 210 by the smoothing is not a full-wave rectified waveform of the commercial power source 110, but a waveform in which a voltage ripple according to the frequency of the commercial power source 110 is superimposed on a DC component, and does not pulsate significantly. The frequency of this voltage ripple is a component twice the frequency of the power source voltage Vs when the commercial power source 110 is single-phase, and a component six times the frequency when the commercial power source 110 is three-phase. When the power input from the commercial power source 110 and the power output from the inverter 310 do not change, the amplitude of this voltage ripple is determined by the capacitance of the capacitor 210. For example, the voltage ripple generated in the capacitor 210 pulsates in a range in which the maximum value is less than twice the minimum value.

[0016] The inverter 310 is connected to the smoothing unit 200. That is, the inverter 310 is connected to both ends of the capacitor 210. The inverter 310 has switching elements 311a, 311b, 311c, 311d, 311e, and 311f and freewheeling diodes 312a, 312b, 312c, 312d, 312e, and 312f. The inverter 310 turns on and off the switching elements 311a, 311b, 311c, 311d, 311e, and 311f under the control of the control unit 400, converts the power output from the rectifier unit 140 and the smoothing unit 200 into a second AC power having an amplitude and phase different from the first AC power, and outputs the second AC power to the compressor 315. The current detection units 313a and 313b detect a current value of one phase of the three-phase current output from the inverter 310, and outputs the detected current value to the control unit 400. Note that the control unit 400 can calculate the current value of the remaining one phase output from the inverter 310 by acquiring the current values ​​of two phases out of the three phase current values ​​output from the inverter 310. The compressor 315 is a load having a motor 314 for driving the compressor. The motor 314 rotates in accordance with the amplitude and phase of the second AC power supplied from the inverter 310, and performs a compression operation. When the compressor 315 is a hermetic compressor used in an air conditioner, the load torque of the compressor 315 can often be regarded as a constant torque load.

[0017] 1 is an example, and the arrangement of the components in the power conversion device 1a is not limited to the example shown in FIG. 1. For example, the reactor 130 may be arranged after the rectifier 140. In the following description, the voltage and current detection unit 501, the voltage detection unit 503, and the current detection units 313a and 313b may be collectively referred to as "detection units." Furthermore, the voltage value and current value detected by the voltage and current detection unit 501, the voltage value detected by the voltage detection unit 503, and the current value detected by the current detection units 313a and 313b may be referred to as "detection values."

[0018] The control unit 400 acquires the voltage value and current value of the first AC power of the power supply voltage Vs from the voltage / current detection unit 501. The control unit 400 also acquires the voltage value of the power rectified by the rectification unit 140 from the voltage detection unit 503. The control unit 400 also acquires the current value of the second AC power having an amplitude and phase different from the first AC power converted by the inverter 310 from the current detection units 313a and 313b. The control unit 400 uses the detection values ​​detected by the respective detection units to control the operation of the inverter 310, specifically, the on / off of the switching elements 311a, 311b, 311c, 311d, 311e, and 311f of the inverter 310. In the first embodiment, the control unit 400 controls the operation of the inverter 310 so that the inverter 310 outputs the second AC power including pulsation corresponding to the pulsation of the power flowing from the rectifier 140 to the capacitor 210 of the smoothing unit 200 to the compressor 315, which is a load. The pulsation corresponding to the pulsation of the power flowing into the capacitor 210 of the smoothing unit 200 is, for example, pulsation that varies depending on the frequency of the pulsation of the power flowing into the capacitor 210 of the smoothing unit 200. As a result, the control unit 400 suppresses the current flowing into the capacitor 210 of the smoothing unit 200. Note that the control unit 400 does not need to use all the detection values ​​acquired from each detection unit, and may perform control using some of the detection values. Hereinafter, the operation of the control unit 400 will be described separately for normal operation and for instantaneous power interruption detection.

[0019] First, the operation of the control unit 400 during normal operation will be described. In the power conversion device 1a according to the first embodiment, the load generated by the inverter 310 and the compressor 315 can be regarded as a constant load, and the following description will be given on the assumption that a constant current load is connected to the smoothing unit 200 in terms of the current output from the smoothing unit 200. Here, as shown in FIG. 1, the current flowing from the rectifying unit 140 is the current I1, the current flowing to the inverter 310 is the current I2, and the current flowing from the smoothing unit 200 is the current I3. The current I2 is a current obtained by combining the currents I1 and I3. The current I3 can be expressed as the difference between the currents I2 and I1, that is, the current I2-I1. The discharge direction of the smoothing unit 200 is the positive direction of the current I3, and the charge direction of the smoothing unit 200 is the negative direction. That is, the current may flow into the smoothing unit 200 and may flow out of the smoothing unit 200.

[0020] FIG. 2 is a diagram showing the current flowing from the rectifier, the current flowing to the inverter, the current flowing from the smoothing unit, and the capacitor voltage of the power conversion device according to the first embodiment. FIG. 2 shows an example of each current I1, I2, I3 and the capacitor voltage Vdc of the smoothing unit 200 when the current output from the rectifier 140 is smoothed by the smoothing unit 200 and the current I2 flowing to the inverter 310 is made constant. In FIG. 2, the currents I1, I2, I3, and the capacitor voltage Vdc are shown from the top. The capacitor voltage Vdc is generated according to the current I3. The vertical axis of the currents I1, I2, I3 indicates the current value, and the vertical axis of the capacitor voltage Vdc indicates the voltage value. The horizontal axis indicates the time t. The currents I2 and I3 are actually superimposed with the carrier components of the inverter 310, but are omitted here. The same applies to the following. As shown in Fig. 2, in the power conversion device 1a, if the current I1 flowing from the rectification unit 140 is smoothed by the smoothing unit 200, the current I2 flowing to the inverter 310 will have a constant current value. However, a large current I3 flows through the capacitor 210 of the smoothing unit 200, which causes deterioration. For this reason, in the power conversion device 1a according to the first embodiment, the control unit 400 controls the current I2 flowing to the inverter 310 so as to reduce the current I3 flowing to the smoothing unit 200. That is, the control unit 400 controls the operation of the inverter 310 so as to reduce the current I3 flowing to the smoothing unit 200.

[0021] FIG. 3 is a diagram showing the current flowing from the rectifier, the current flowing to the inverter, the current flowing from the smoothing unit, and the capacitor voltage of the power conversion device according to the first embodiment. FIG. 3 shows an example of each of the currents I1, I2, and I3 and the capacitor voltage Vdc of the smoothing unit 200 when the control unit 400 controls the operation of the inverter 310 to reduce the current I3 flowing to the smoothing unit 200. In FIG. 3, the currents I1, I2, and I3 are shown in order from the top. The capacitor voltage Vdc is generated according to the current I3. The vertical axis of the currents I1, I2, and I3 indicates the current value, and the vertical axis of the capacitor voltage Vdc indicates the voltage value. The horizontal axis indicates time t. The control unit 400 of the power conversion device 1a controls the operation of the inverter 310 so that the current I2 shown in FIG. 3 flows to the inverter 310, thereby reducing the frequency component of the current flowing from the rectifier 140 to the smoothing unit 200 and reducing the current I3 flowing to the smoothing unit 200, compared to the example shown in FIG. 2. Specifically, the control unit 400 controls the operation of the inverter 310 so that the current I2 flows through the inverter 310 and includes a pulsating current whose main component is the frequency component of the current I1.

[0022] The frequency component of the current I1 is determined by the frequency of the AC current supplied from the commercial power source 110 and the configuration of the rectifier unit 140. Therefore, the control unit 400 can set the frequency component of the pulsating current superimposed on the current I2 to a component having a predetermined amplitude and phase. The frequency component of the pulsating current superimposed on the current I2 has a waveform similar to that of the frequency component of the current I1. As the control unit 400 brings the frequency component of the pulsating current superimposed on the current I2 closer to the frequency component of the current I1, it is possible to reduce the current I3 flowing through the smoothing unit 200 and reduce the pulsating voltage generated in the capacitor voltage Vdc.

[0023] The control unit 400 controls the operation of the inverter 310 to control the pulsation of the current flowing through the inverter 310, which is the same as controlling the pulsation of the first AC power output from the inverter 310 to the compressor 315. The control unit 400 controls the operation of the inverter 310 so that the pulsation contained in the second AC power output from the inverter 310 is smaller than the pulsation of the power output from the rectifier unit 140. The control unit 400 controls the amplitude and phase of the pulsation contained in the second AC power output from the inverter 310 so that the voltage ripple of the capacitor voltage Vdc, i.e., the voltage ripple generated in the capacitor 210, is smaller than the voltage ripple generated in the capacitor 210 when the second AC power output from the inverter 310 does not contain pulsation corresponding to the pulsation of the power flowing into the capacitor 210. Alternatively, the control unit 400 controls the amplitude and phase of the pulsation contained in the second AC power output from the inverter 310 so that the current ripple flowing in and out of the capacitor 210 is smaller than the current ripple generated in the capacitor 210 when the second AC power output from the inverter 310 does not contain pulsation corresponding to the pulsation of the power flowing into the capacitor 210. Note that "when the second AC power output from the inverter 310 does not contain pulsation corresponding to the pulsation of the power flowing into the capacitor 210" refers to the case where the smoothing unit 200 smoothes the current output from the rectifying unit 140 and keeps the current I2 flowing in the inverter 310 constant, as shown in FIG. 2.

[0024] The AC current supplied from the commercial power source 110 is not particularly limited, and may be single-phase or three-phase. The control unit 400 may determine the frequency component of the pulsating current superimposed on the current I2 according to the first AC power supplied from the commercial power source 110. Specifically, when the first AC power supplied from the commercial power source 110 is single-phase, the control unit 400 controls the pulsating waveform of the current I2 flowing through the inverter 310 to a shape obtained by adding a DC component to a pulsating waveform whose main component is a frequency component twice the frequency of the first AC power. When the first AC power supplied from the commercial power source 110 is three-phase, the control unit 400 controls the pulsating waveform of the current I2 flowing through the inverter 310 to a shape obtained by adding a DC component to a pulsating waveform whose main component is a frequency component six times the frequency of the first AC power. The control unit 400 sets the pulsating waveform of the current I2 to, for example, the absolute value of a sine wave or the shape of a sine wave. In this case, the control unit 400 may add at least one frequency component among the components that are an integer multiple of the sine wave frequency to the pulsating waveform as a predefined amplitude. The control unit 400 may also set the pulsating waveform of the current I2 to a rectangular wave shape or a triangular wave shape. In this case, the control unit 400 may set the amplitude and phase of the pulsating waveform to predefined values.

[0025] The control unit 400 may calculate the amount of pulsation contained in the second AC power output from the inverter 310 using the voltage applied to the capacitor 210 or the current flowing through the capacitor 210, or may calculate the amount of pulsation contained in the second AC power output from the inverter 310 using the voltage or current of the first AC power supplied from the commercial power source 110.

[0026] Next, the operation of the control unit 400 when detecting an instantaneous power interruption will be described. When an instantaneous power interruption occurs, the capacitor voltage in the smoothing unit 200 becomes greater than the voltage supplied from the commercial power supply 110, so that the capacitor 210 is not charged. If the inverter 310 continues to supply power to the load in this state, the capacitor 210 discharges, and the current I3 flows in the positive direction, causing the current to flow out of the smoothing unit 200, resulting in a drop in the capacitor voltage. If the inverter 310 continues to supply the load with the same amount of second AC power as during normal operation, the capacitor voltage drops sharply because the power is supplied only by the charge remaining in the capacitor 210. When power is restored in this state, a re-inrush current occurs because the amount of recharge in the capacitor 210 is large. Therefore, if the control unit 400 is operated to limit the current I2 flowing through the inverter 310 when an instantaneous power interruption occurs, and the second AC power is reduced, the drop in the capacitor voltage can be slowed down, and the re-inrush current at the time of power restoration can be suppressed.

[0027] FIG. 4 is a diagram showing the current flowing from the rectifier, the current flowing to the inverter, the current flowing from the smoothing unit, and the capacitor voltage of the power conversion device according to the first embodiment. FIG. 4 shows an example of each current I1, I2, I3 and the capacitor voltage Vdc of the smoothing unit 200 in the case where the control unit 400 does not limit the current I2 flowing to the inverter 310 when an instantaneous blackout occurs, and the current I2 before the instantaneous blackout occurs is equal to the current I2 during the instantaneous blackout period. FIG. 4 shows, from the top, the current I1, the current I2, the current I3, and the capacitor voltage Vdc. The capacitor voltage Vdc is generated according to the current I3. The vertical axis of the currents I1, I2, I3 indicates the current value, and the vertical axis of the capacitor voltage Vdc indicates the voltage value. All horizontal axes indicate time t. As shown in FIG. 4, when the power supply voltage Vs is cut off when an instantaneous blackout occurs, the current I1 flowing from the rectifier 140 becomes zero. At this time, the current I2 is not limited, so the power output to the load is not reduced and is supplied only by the charge remaining in the capacitor 210, resulting in a large drop in the capacitor voltage. If power is restored in this state, the re-inrush current will be large.

[0028] FIG. 5 is a diagram showing the current flowing from the rectifier, the current flowing to the inverter, the current flowing from the smoothing unit, and the capacitor voltage of the power conversion device according to the first embodiment. FIG. 5 shows an example of the currents I1, I2, and I3 and the capacitor voltage Vdc of the smoothing unit 200 when the control unit 400 controls the operation of the inverter 310 when an instantaneous interruption occurs to reduce the current I2 flowing to the inverter 310. As shown in FIG. 5, when the power supply voltage Vs is cut off when an instantaneous interruption occurs, the current I1 flowing from the rectifier 140 becomes zero. When the instantaneous interruption detection unit 502 detects an instantaneous interruption, the control unit 400 controls the operation of the inverter 310 so as to reduce the absolute value of the current I2 flowing to the inverter 310. At this time, the frequency component of the pulsating current superimposed on the current I2 is the same as the frequency component of the current I1 before the instantaneous interruption occurs, so that the current I3 flowing to the smoothing unit 200 can be reduced, and the absolute value of the current I2 is reduced, so the amount of reduction in the current I3 during the instantaneous interruption is limited. Therefore, the decrease in the capacitor voltage Vdc of the smoothing unit 200 can be made gentler.

[0029] The momentary interruption detection unit 502 constantly monitors the input voltage and realizes a control operation by outputting the state of the input voltage to the control unit 400. The momentary interruption detection unit 502 may detect a zero cross of the input power supply voltage, or may directly monitor the value of the input power supply voltage. When detecting a zero cross of the power supply voltage, the fact that the AC voltage crosses the zero point at a certain period is utilized. The presence or absence of a zero cross point of the power supply voltage is detected, and when the zero cross point is not detected for a preset detection time, the control unit 400 can determine that a momentary interruption of the power supply voltage has occurred. On the other hand, when the value of the input power supply voltage is directly monitored, the control unit 400 determines that a momentary interruption has occurred when the input power supply voltage value falls below a preset value. At this time, the momentary interruption state is detected by a drop in the input voltage, so not only a momentary interruption but also a momentary voltage drop can be detected. Hereinafter, a momentary voltage drop is referred to as a "momentary drop."

[0030] The operation of the control unit 400 will be described using a flowchart. FIG. 6 is a flowchart showing the operation of the control unit included in the power conversion device according to the first embodiment. In step S1, the control unit 400 acquires detection values ​​from each detection unit of the power conversion device 1a. In step S2, the control unit 400 controls the operation of the inverter 310 so that the current I3 flowing through the smoothing unit 200 is reduced based on the acquired detection values. In step S3, the control unit 400 judges whether or not an instantaneous interruption of the power supply voltage has been detected. If an instantaneous interruption of the power supply voltage has been detected, the result is Yes in step S3, and the control unit 400 controls the operation of the inverter 310 so that the drop in the capacitor voltage Vdc is mitigated by limiting the current I2 flowing through the inverter 310. If an instantaneous interruption of the power supply voltage has not been detected, the result is No in step S3, and the control unit 400 ends the process.

[0031] Next, a hardware configuration of the control unit 400 included in the power conversion device 1a will be described. Fig. 7 is a diagram showing an example of a hardware configuration realizing the control unit included in the power conversion device according to the embodiment 1. The control unit 400 is realized by a processor 91 and a memory 92.

[0032] The processor 91 is a CPU (Central Processing Unit), a central processing unit, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, a processor, a DSP (Digital Signal Processor), or a system LSI (Large Scale Integration). The memory 92 can be exemplified by non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPPROM (Erasable Programmable Read Only Memory), and EEPROM (Electrically Erasable Programmable Read Only Memory). The memory 92 is not limited to these, and may be a magnetic disk, an optical disk, a compact disk, a mini disk, or a DVD (Digital Versatile Disc).

[0033] As described above, in the power conversion device 1a according to the first embodiment, the control unit 400 controls the operation of the inverter 310 based on the detection values ​​acquired from the respective detection units, and reduces the current I3 flowing through the smoothing unit 200 by superimposing the pulsation of the frequency component corresponding to the frequency component of the current I1 flowing from the rectification unit 140 on the current I2 flowing through the inverter 310. As a result, the power conversion device 1a can use the capacitor 210 with a smaller ripple current tolerance than when the control of the first embodiment is not performed, because the current I3 flowing through the smoothing unit 200 is reduced. Alternatively, the power conversion device 1a can reduce the capacity of the mounted capacitor 210 compared to when the control of the first embodiment is not performed, because the pulsation voltage of the capacitor voltage Vdc is reduced. For example, when the smoothing unit 200 is configured by a plurality of capacitors 210, the power conversion device 1a can reduce the number of capacitors 210 that configure the smoothing unit 200. Therefore, the power conversion device 1a according to the first embodiment can suppress the aging deterioration of the smoothing capacitor without increasing the size of the device. Furthermore, since the smoothing section 200 can use a low-capacity capacitor 210 or the number of capacitors 210 can be reduced, the component costs of the power conversion device 1a can be reduced.

[0034] Moreover, the power conversion device 1a according to the first embodiment can suppress the pulsating component superimposed on the current I2 flowing through the inverter 310 from becoming excessive by controlling the operation of the inverter 310 so that the pulsation contained in the second AC power becomes smaller than the pulsation of the power output from the rectifier 140. The superimposition of the pulsating component increases the effective value of the current flowing through the inverter 310, the motor 314, etc., compared to a non-superimposed state, but by suppressing the superimposed pulsating component from becoming excessive, it is possible to provide a system in which the current capacity of the inverter 310, an increase in loss of the inverter 310, an increase in loss of the motor 314, etc. are suppressed.

[0035] Moreover, the power conversion device 1a according to the first embodiment can suppress vibration of the compressor 315 caused by pulsation of the current I2.

[0036] Embodiment 2 FIG. 8 is a diagram showing a configuration of a power conversion device according to the second embodiment. The power conversion device 1b is connected to a commercial power source 110 and a compressor 315. The power conversion device 1b converts a first AC power of a power source voltage Vs supplied from the commercial power source 110 into a second AC power having an amplitude and a phase different from those of the first AC power, and supplies the second AC power to the compressor 315. The power conversion device 1b includes an inrush current prevention unit 120, an instantaneous power interruption detection unit 502, a voltage / current detection unit 501, a rectification unit 140, a reactor 130, a boost unit 600, a voltage detection unit 503, a smoothing unit 200, an inverter 310, current detection units 313a and 313b, and a control unit 400. In the power conversion device 1b, the rectification unit 140 is configured by the rectification circuit 500, the reactor 130, and the boost unit 600. Moreover, the power conversion device 1b and the motor 314 provided in the compressor 315 constitute a motor driving device 2b.

[0037] In the power conversion device 1b, the reactor 130 is connected between the rectifier circuit 500 and the boost unit 600. The boost unit 600 has a switching element 611 and a rectifier element 621. The boost unit 600 turns on and off the switching element 611 under the control of the control unit 400, boosts the power output from the rectifier circuit 500, and outputs the boosted power to the smoothing unit 200. Note that, although the boost unit 600 has a configuration including one switching element 611 as an example here, the boost unit 600 may have a configuration including multiple switching elements 611. When the boost unit 600 has multiple switching elements 611, a bridge circuit including multiple rectifier elements is connected in parallel to each of the multiple switching elements 611.

[0038] In this embodiment, the boost unit 600 is controlled by the control unit 400 with full PAM (Pulse Amplitude Modulation) in which the switching element 611 performs a continuous switching operation. The power conversion device 1b performs power factor correction control of the commercial power source 110 by the boost unit 600, and makes the capacitor voltage Vdc of the capacitor 210 of the smoothing unit 200 a voltage higher than the power source voltage Vs. The rectification unit 140 rectifies the first AC power supplied from the commercial power source 110 by the rectification circuit 500 and the boost unit 600, and boosts the voltage of the first AC power supplied from the commercial power source 110. In the power conversion device 1b according to the second embodiment, the rectification circuit 500 and the boost unit 600 are connected in series in the rectification unit 140.

[0039] The control unit 400 obtains the voltage value and the current value of the first AC power of the power supply voltage Vs from the voltage / current detection unit 501, obtains the voltage value of the power boosted by the rectification unit 140 from the voltage detection unit 503, and obtains the current value of the second AC power having an amplitude and a phase different from the first AC power converted by the inverter 310 from the current detection units 313a and 313b. The control unit 400 uses the detection values ​​detected by each detection unit to control the operation of the boost unit 600 of the rectification unit 140, specifically, the on / off of the switching element 611 of the boost unit 600. The control unit 400 also uses the detection values ​​detected by each detection unit to control the operation of the inverter 310, specifically, the on / off of the switching elements 311a, 311b, 311c, 311d, 311e, and 311f of the inverter 310. In the power conversion device 1b according to the second embodiment, the control unit 400 controls the operation of the rectification unit 140. The control unit 400 controls the operation of the rectification unit 140, and performs power factor correction control of the first AC power supplied from the commercial power source 110 and average voltage control of the capacitor 210 of the smoothing unit 200. In this manner, the power conversion device 1b increases the capacitor voltage Vdc of the capacitor 210 by the boosting operation of the boost unit 600, and can expand the possible output voltage range of the inverter 310.

[0040] The power conversion device 1b may detect an instantaneous interruption of the power supply voltage by utilizing the boost ratio of the boost unit 600. When an instantaneous interruption or instantaneous drop occurs in the power supply voltage, the voltage of the first AC power drops. The control unit 400 must boost the voltage output to the inverter 310 by an amount corresponding to the voltage drop in order to perform average voltage control of the smoothing unit 200. Specifically, the control unit 400 is operated so that the ON period of the switching element 611 of the boost unit 600 is lengthened. That is, the control unit 400 is operated so that the energy stored in the reactor 130 becomes larger when the switching element 611 is ON. The control unit 400 determines the boost ratio by comparing the target capacitor voltage with the actual capacitor voltage detected by the voltage detection unit 503, and performs average voltage control. Therefore, if the control unit 400 is operated so as to determine that an instantaneous interruption or instantaneous drop in the power supply voltage occurs when the boost ratio exceeds a preset value, the inrush current at the time of power recovery can be prevented by the control operation shown in the power conversion device 1a according to the first embodiment. In this manner, a momentary interruption or momentary drop in the power supply voltage can be detected without detecting the zero crossing of the input power supply voltage or the value of the input power supply voltage.

[0041] The AC current supplied from the commercial power supply 110 is not particularly limited, and may be single-phase or three-phase. The control unit 400 may calculate the amount of pulsation contained in the second AC power output from the inverter 310 using the voltage applied to the capacitor 210 or the current flowing through the capacitor 210. The control unit 400 may also calculate the amount of pulsation contained in the second AC power output from the inverter 310 using the voltage or current of the first AC power supplied from the commercial power supply 110.

[0042] Furthermore, when the control unit 400 controls the inverter 310 so as to output from the inverter 310 to the compressor 315 a second AC power including a frequency component different from the frequency component of the first AC power supplied from the commercial power source 110, the control unit 400 may superimpose the frequency component included in the second AC power output from the inverter 310 to the compressor 315 on a drive signal for turning on and off the switching element 611 of the boost unit 600. That is, when the first AC power supplied from the commercial power source 110 is single-phase, the control unit 400 controls the operation of the rectification unit 140, specifically, the operation of the switching element 611 of the boost unit 600, so that power including a fluctuating frequency component other than the frequency component twice the frequency of the first AC power is output from the rectification unit 140. Furthermore, when the first AC power supplied from the commercial power source 110 is three-phase, the control unit 400 controls the operation of the rectifier 140, specifically, the operation of the switching element 611 of the boost unit 600, so that the rectifier 140 outputs power including a fluctuating frequency component other than the frequency component six times the frequency of the first AC power, among the power pulsations of the second AC power output from the inverter 310 to the compressor 315. The control unit 400 may control the fluctuating frequency component using a command value for the commercial power source 110. The control unit 400 may also control the fluctuating frequency component to be a component other than an integer multiple up to the 40th order of the frequency of the first AC power supplied from the commercial power source 110. The control unit 400 may also control the fluctuating frequency component to be equal to or less than a preset standard value.

[0043] The operation of the control unit 400 will be described using a flowchart. FIG. 9 is a flowchart showing the operation of the control unit included in the power conversion device according to the second embodiment. In step S11, the control unit 400 acquires detection values ​​from each detection unit of the power conversion device 1b. In step S12, the control unit 400 controls the operation of the inverter 310 so as to reduce the current I3 flowing through the smoothing unit 200 based on the acquired detection values. In step S13, the control unit 400 controls the operation of the boost unit 600 so as to perform power factor correction control of the commercial power source 110 and average voltage control of the capacitor voltage Vdc of the capacitor 210 of the smoothing unit 200 based on the acquired detection values. In step S14, the control unit 400 judges whether or not an instantaneous interruption has been detected. If an instantaneous interruption of the power supply voltage has been detected, the result in step S14 is Yes, and in step S15, the control unit 400 controls the operation of the inverter 310 so as to limit the current I2 flowing through the inverter 310 and to mitigate the drop in the capacitor voltage Vdc. If an instantaneous power interruption is not detected, the result in step S14 is No, and the control unit 400 ends the process.

[0044] Other operations in the power conversion device 1b are similar to those in the power conversion device 1a of embodiment 1. Even in this case, the power conversion device 1b can obtain the same effects as the power conversion device 1a of embodiment 1.

[0045] The power conversion device 1b according to the second embodiment uses the boost section 600 to make the capacitor voltage Vdc of the capacitor 210 in the smoothing section 200 higher than the power supply voltage Vs, and therefore can improve the power factor and increase the energy efficiency compared to the power conversion device 1a according to the first embodiment.

[0046] Here, the power conversion device 1b in which the rectifier circuit 500 and the boost unit 600 are connected in series in the rectifier unit 140 have been described, but the rectifier circuit 500 and the boost unit 600 may be connected in parallel in the rectifier unit 140. FIG. 10 is a diagram showing a configuration of a power conversion device according to a modification of the second embodiment. In the power conversion device 1c according to the modification of the second embodiment, the boost unit 600 has a switching element 611 and rectifier elements 621, 622, 623, and 624. The boost unit 600 is connected to the reactor 130 so that the rectifier circuit 500 and the boost unit 600 are connected in parallel. In the power conversion device 1c according to the modification of the second embodiment in which the rectifier circuit 500 and the boost unit 600 are connected in parallel, the power factor can be improved and the energy efficiency can be increased, similarly to the power conversion device 1b according to the second embodiment.

[0047] Embodiment 3 11 is a diagram showing a configuration of a refrigeration cycle applied device according to embodiment 3. The refrigeration cycle applied device 900 according to embodiment 3 includes the power conversion device 1a described in embodiment 1 or the power conversion device 1b described in embodiment 2. The refrigeration cycle applied device 900 according to embodiment 3 can be applied to products including a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters.

[0048] The refrigeration cycle applied equipment 900 includes a compressor 315 incorporating the motor 314 in the first and second embodiments, a four-way valve 902, an indoor heat exchanger 906, an expansion valve 908, and an outdoor heat exchanger 910, which are attached via refrigerant piping 912.

[0049] Inside the compressor 315, a compression mechanism 904 that compresses the refrigerant, and a motor 314 that operates the compression mechanism 904 are provided.

[0050] The refrigeration cycle device 900 can perform heating or cooling operation by switching the four-way valve 902. The compression mechanism 904 is driven by a motor 314 that is variably controlled in speed.

[0051] During heating operation, as indicated by the solid arrow, the refrigerant is pressurized by the compressor 315 and sent out, passes through the four-way valve 902, the indoor heat exchanger 906, the expansion valve 908, the outdoor heat exchanger 910 and the four-way valve 902 and returns to the compression mechanism 904.

[0052] During cooling operation, as indicated by the dashed arrow, the refrigerant is pressurized by the compression mechanism 904 and sent out, passes through the four-way valve 902, the outdoor heat exchanger 910, the expansion valve 908, the indoor heat exchanger 906 and the four-way valve 902 and returns to the compression mechanism 904.

[0053] During heating operation, the indoor heat exchanger 906 acts as a condenser to release heat, and the outdoor heat exchanger 910 acts as an evaporator to absorb heat. During cooling operation, the outdoor heat exchanger 910 acts as a condenser to release heat, and the indoor heat exchanger 906 acts as an evaporator to absorb heat. The expansion valve 908 reduces the pressure of the refrigerant to expand it.

[0054] The refrigeration cycle application equipment 900 according to the third embodiment includes the power conversion device 1a according to the first embodiment or the power conversion device 1b according to the second embodiment in which deterioration over time of the smoothing capacitor is suppressed, and therefore a longer life can be achieved.

[0055] The configurations shown in the above embodiments are merely examples of the contents, and may be combined with other known technologies. Parts of the configurations may be omitted or modified without departing from the spirit of the invention. [Explanation of symbols]

[0056] 1a, 1b, 1c power conversion device, 2a, 2b motor drive device, 91 processor, 92 memory, 110 commercial power source, 120 inrush current prevention unit, 121 inrush current prevention element, 122, 311a, 311b, 311c, 311d, 311e, 311f, 611 switching element, 130 reactor, 140 rectifier unit, 141, 142, 143, 144, 621, 622, 623, 624 rectifier element, 200 smoothing unit, 210 capacitor, 310 inverter, 312a, 312b, 312c, 312d, 312e, 312f freewheel diode, 313a, 313b current detection unit, 314 motor, 315 compressor, 400 control unit, 500 Rectifier circuit, 501 voltage and current detection unit, 502 momentary power failure detection unit, 503 voltage detection unit, 600 boost unit, 900 refrigeration cycle application equipment, 902 four-way valve, 904 compression mechanism, 906 indoor heat exchanger, 908 expansion valve, 910 outdoor heat exchanger, 912 refrigerant piping.

Claims

1. an inrush current prevention unit that prevents an inrush current; An instantaneous power interruption detection unit that detects an instantaneous power interruption in a commercial power supply; a rectification unit that rectifies a first AC power supplied from the commercial power source; A capacitor connected to an output terminal of the rectifier unit; an inverter connected to both ends of the capacitor, converting power output from the rectifier and the capacitor into second AC power and outputting the second AC power to a load; a control unit that controls an operation of the inverter so that the second AC power including pulsation corresponding to pulsation of the power flowing from the rectifier to the capacitor is output from the inverter to the load, and suppresses a current flowing to the capacitor; the rectifier unit includes a rectifier circuit including a plurality of rectifier elements, and a switching element whose on / off is controlled by the control unit, the rectifier unit being connected between the rectifier circuit and the capacitor, and a boost unit that boosts a voltage of the first AC power after being rectified by the rectifier circuit; The control unit is a power conversion device that controls the operation of the inverter so as to limit the current flowing to the inverter and mitigate the voltage drop of the capacitor when a momentary power outage or momentary voltage drop of the power supply voltage is detected based on the boost ratio of the boost unit.

2. The power conversion device according to claim 1 , wherein the rectifier section includes a rectifier circuit including a plurality of rectifier elements.

3. The control unit is When the first AC power is single-phase, a pulsating waveform of a current flowing through the inverter is controlled to a shape obtained by adding a DC component to the pulsating waveform having a main component of a frequency component twice the frequency of the first AC power, 2. The power conversion device according to claim 1, wherein, when the first AC power is three-phase, the pulsating waveform is controlled to a shape obtained by adding a DC component to the pulsating waveform having a main component of a frequency component six times the frequency of the first AC power.

4. The power conversion device according to claim 3 , wherein the control unit sets the pulsating waveform to a shape of an absolute value of a sine wave or a shape of a sine wave.

5. The power conversion device according to claim 4 , wherein the rectifier adds at least one frequency component among components that are integer multiples of a frequency of the sine wave to the pulsating waveform as a specified amplitude.

6. The power conversion device according to claim 3 , wherein the control unit sets the pulsating waveform to have a rectangular wave shape or a triangular wave shape.

7. The power conversion device according to claim 6 , wherein the rectifier sets the amplitude and phase of the pulsating waveform to specified values.

8. The power conversion device according to claim 1 , wherein the rectification unit and the boost unit are connected in series or in parallel.

9. the boosting unit includes a plurality of the switching elements, The power conversion device according to claim 1 , wherein each of the plurality of rectifying elements is connected in parallel to each of the plurality of switching elements.

10. The power conversion device according to claim 1 , wherein the control unit controls an operation of the rectification unit, and performs a power factor correction control of the first AC power supplied from the commercial power source and an average voltage control of the capacitor.

11. The control unit is When the first AC power is single-phase, an operation of the rectifier is controlled so that power including a fluctuating frequency component other than a frequency component twice the frequency of the first AC power is output from the rectifier, out of the pulsation included in the second AC power output from the inverter; 2. The power conversion device according to claim 1, wherein, when the first AC power is three-phase, an operation of the rectifier is controlled so that power including a fluctuating frequency component other than a frequency component six times a frequency of the first AC power is output from the rectifier, among pulsations included in the second AC power output from the inverter.

12. The power conversion device according to claim 11 , wherein the control unit controls the fluctuating frequency component by using a command value for the commercial power supply.

13. The power conversion device according to claim 11 , wherein the control unit controls the fluctuating frequency component to be a component other than an integer multiple up to a fortieth order of the frequency of the first AC power.

14. The power conversion device according to claim 11 , wherein the control unit controls the fluctuating frequency component to be equal to or less than a preset specified value.

15. 2. The power conversion device according to claim 1, wherein the control unit controls an operation of the inverter so that pulsation contained in the second AC power output from the inverter is smaller than pulsation of the power output from the rectification unit.

16. The rectification unit performs full-wave rectification, The power conversion device according to claim 1 , wherein the voltage generated across the capacitor has a waveform different from a full-wave rectified waveform of the commercial power supply.

17. 2. The power conversion device according to claim 1, wherein the control unit controls an amplitude and a phase of pulsation contained in the second AC power output from the inverter so that a voltage ripple generated in the capacitor is smaller than a voltage ripple generated in the capacitor when the second AC power output from the inverter does not contain a pulsation corresponding to a pulsation of power flowing into the capacitor.

18. 2. The power conversion device according to claim 1, wherein the control unit controls an amplitude and a phase of pulsation contained in the second AC power output from the inverter so that a current ripple flowing into or out of the capacitor is smaller than a current ripple generated in the capacitor when the second AC power output from the inverter does not contain a pulsation corresponding to a pulsation of power flowing into the capacitor.

19. The power conversion device according to claim 1 , wherein the control unit calculates a pulsation amount of the pulsation included in the second AC power output from the inverter, using a voltage applied to the capacitor or a current flowing through the capacitor.

20. The power conversion device according to claim 1 , wherein the control unit calculates a pulsation amount of the pulsation included in the second AC power output from the inverter, using a voltage or a current of the first AC power.

21. The power conversion device according to claim 1 , wherein the capacitor is an electrolytic capacitor or a film capacitor.

22. The power conversion device according to claim 1 , wherein a maximum value of a voltage ripple generated in the capacitor is less than twice a minimum value.

23. The power conversion device according to claim 1 , wherein the momentary power failure detection unit detects a momentary power failure or a momentary voltage drop of the commercial power supply, and outputs a state of an input voltage to the control unit.

24. A motor drive device comprising the power conversion device according to any one of claims 1 to 22.

25. A refrigeration cycle application device comprising the power conversion device according to any one of claims 1 to 22.

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