Power conversion device, and air conditioner outdoor unit

Abstract

This power conversion device (1) comprises: a rectifier unit (130) that rectifies a first AC power supplied from a commercial power supply (110); a capacitor (210) that is connected to the output end of the rectifier unit (130); an inverter (310) that is connected to both ends of the capacitor (210), and that converts the power outputted from the rectifier unit (130) and the capacitor (210) to a second AC power and outputs that to a load having a motor (314); and a control unit (400) that, by controlling the operation of the inverter (310) so that the inverter (310) outputs to the load the second AC power including pulsations according to the pulsations of the power flowing from the rectifier unit (130) to the capacitor (210), performs capacitor load suppression control that suppresses the current flowing to the capacitor (310). The control unit (400) estimates the capacitor load of the capacitor (210) and determines whether to perform capacitor load suppression control on the basis of the estimated value of the capacitor load.

Description

Power conversion device and outdoor unit of air conditioner

[0001] The present disclosure relates to a power conversion device that rectifies AC power supplied from a commercial power source, converts it into AC power, and outputs it, and to an outdoor unit of an air conditioner that includes the same.

[0002] Conventionally, in a power conversion device that rectifies AC power supplied from a commercial power source, converts it into AC power, and outputs it, a smoothing capacitor is used to smooth the power rectified by a rectifier that rectifies the AC current supplied from the commercial power source.

[0003] Patent Document 1 discloses a power conversion device that suppresses the deterioration of a smoothing capacitor by suppressing a large current from flowing through the smoothing capacitor.

[0004] International Publication No. 2022 / 091184

[0005] However, in the power conversion device disclosed in Patent Document 1, the current in the capacitor is suppressed by including pulsation corresponding to the pulsation of the power flowing into the smoothing capacitor in the output from the inverter to the device having the motor. As a result, in the power conversion device disclosed in Patent Document 1, the output of the inverter tends to increase, and loss increases regardless of the magnitude of the capacitor load of the smoothing capacitor, resulting in a problem of reduced energy-saving performance.

[0006] The present disclosure has been made in view of the above, and aims to provide a power conversion device that suppresses deterioration of a smoothing capacitor and also suppresses a decrease in energy-saving performance.

[0007] In order to solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure includes a rectifier that rectifies first AC power supplied from a commercial power source, a capacitor connected to an output terminal of the rectifier, an inverter connected to both ends of the capacitor and converting power output from the rectifier and the capacitor into second AC power and outputting the second AC power to a load having a motor, and a control unit that performs capacitor load suppression control to suppress a current flowing through the capacitor by controlling operation of the inverter so that the second AC power includes pulsation corresponding to pulsation of power flowing from the rectifier to the capacitor. The control unit estimates a capacitor load on the capacitor and determines whether to perform capacitor load suppression control based on the estimated capacitor load.

[0008] The power conversion device according to the present disclosure has the effect of suppressing deterioration of the smoothing capacitor and suppressing a decrease in energy-saving performance.

[0009] FIG. 1 is a diagram showing the configuration of a power conversion device according to embodiment 1; FIG. 2 is a diagram showing an example of each current and the capacitor voltage of the capacitor of the smoothing unit when the control unit of the power conversion device according to embodiment 1 smooths the current output from the rectifier unit in the smoothing unit and keeps the current flowing to the inverter constant; FIG. 3 is a diagram showing an example of each current and the capacitor voltage of the capacitor of the smoothing unit when the control unit of the power conversion device according to embodiment 1 controls the operation of the inverter to reduce the current flowing to the smoothing unit;

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A power conversion device and an outdoor unit of an air conditioner according to embodiments will be described in detail below with reference to the drawings.

[0011] 1 is a diagram showing the configuration of a power conversion device according to a first embodiment. The power conversion device 1 is connected between a commercial power supply 110 and a compressor 315. The power conversion device 1 converts first AC power of a power supply voltage Vs supplied from the commercial power supply 110 into second AC power and supplies the second AC power to the compressor 315. The second AC power may be different from the first AC power in at least one of the amplitude and the phase, or may be the same as the first AC power in both the amplitude and the phase.

[0012] The power conversion device 1 includes a voltage / current detection unit 501, a reactor 120, a rectification unit 130, a voltage detection unit 502, a smoothing unit 200, an inverter 310, current detection units 313a and 313b, and a control unit 400. The compressor 315 is a load device that includes a motor 314 for driving the compressor, to which power is supplied from the power conversion device 1. The motor 314 included in the compressor 315 and the power conversion device 1 constitute a motor drive device 2.

[0013] The voltage / current detection unit 501 detects the voltage and current values ​​of the first AC power supplied from the commercial power supply 110 and outputs the detected voltage and current values ​​to the control unit 400. The voltage of the first AC power is the power supply voltage Vs. The reactor 120 is connected between the voltage / current detection unit 501 and the rectification unit 130. The rectification unit 130 has a bridge circuit configured with rectification elements 131, 132, 133, and 134. The rectification unit 130 rectifies the first AC power supplied from the commercial power supply 110 and outputs the rectified power. In the power conversion device 1 according to the first embodiment, the rectification unit 130 performs full-wave rectification. The voltage detection unit 502 detects the voltage value of the power rectified by the rectification unit 130 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 130 via the voltage detection unit 502. The smoothing unit 200 includes a capacitor 210, which is a smoothing element, and smooths the power rectified by the rectifying unit 130. The capacitor 210 is, for example, an electrolytic capacitor or a film capacitor. The capacitor 210 has a capacity to smooth the power rectified by the rectifying unit 130, and the voltage generated across the capacitor 210 due to the smoothing is not a full-wave rectified waveform of the commercial power source 110, but rather a waveform in which a voltage ripple corresponding 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 mainly twice the frequency of the power supply voltage Vs when the commercial power source 110 is single-phase, and is mainly 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 generated across the capacitor 210 due to smoothing pulsates within a range in which the maximum value of the voltage ripple generated across the capacitor 210 is less than twice the minimum value.

[0014] The inverter 310 is connected to both ends of the capacitor 210 included in the smoothing unit 200. 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 130 and the smoothing unit 200 into second AC power, and outputs the second AC power to the compressor 315. Each of the current detection units 313a and 313b detects 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 value of the remaining one-phase current 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 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. For example, when the compressor 315 is a hermetic compressor used in an air conditioner or the like, the load torque of the compressor 315 can often be considered to be a constant torque load.

[0015] Note that the arrangement of the components of the power conversion device 1 shown in Fig. 1 is an example, and the arrangement of the components is not limited to the example shown in Fig. 1. For example, the reactor 120 may be arranged after the rectifier 130. In the following description, the voltage / current detection unit 501, the voltage detection unit 502, 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 / current detection unit 501, the voltage value detected by the voltage detection unit 502, and the current values ​​detected by the current detection units 313a and 313b may be referred to as detection values.

[0016] The control unit 400 acquires the voltage value and current value of the first AC power from the voltage / current detection unit 501, acquires the voltage value of the power rectified by the rectifier 130 from the voltage detection unit 502, and acquires the current value of the second AC power having the amplitude and phase 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 inverter 310, specifically, the on / off of the switching elements 311a, 311b, 311c, 311d, 311e, and 311f of the inverter 310. In this embodiment, the control unit 400 controls the operation of the inverter 310 so that the second AC power including pulsation corresponding to the pulsation of the power flowing from the rectifier 130 to the capacitor 210 of the smoothing unit 200 is output from the inverter 310 to the compressor 315, which is a load. The pulsation corresponding to the pulsation of the power flowing into capacitor 210 of smoothing unit 200 is, for example, a pulsation that varies depending on the frequency of the pulsation of the power flowing into capacitor 210 of smoothing unit 200. In this way, control unit 400 suppresses the current flowing through capacitor 210 of smoothing unit 200. Note that control unit 400 does not need to use all of the detection values ​​acquired from each detection unit, and may perform control using only some of the detection values.

[0017] It is known that there is a correlation between the capacitor load, which is the amount of charge transfer in capacitor 210, and the amount of fluctuation in the voltage applied to capacitor 210. For this reason, control unit 400 detects the amount of fluctuation in the voltage applied to capacitor 210 by removing the DC component from the voltage across capacitor 210 and extracting the AC component, thereby estimating the capacitor load. Based on the estimated value of the capacitor load, control unit 400 determines whether or not to perform capacitor load suppression control. The capacitor load suppression control will be described later.

[0018] Next, the operation of the control unit 400 included in the power conversion device 1 will be described. In the power conversion device 1 according to the first embodiment, the load generated by the inverter 310 and the compressor 315 can be considered to be a constant load, and the following description will be given assuming that a constant current load is connected to the smoothing unit 200 when viewed in terms of the current output from the smoothing unit 200. Here, as shown in FIG. 1 , the current flowing from the rectifying unit 130 is referred to as current I1, the current flowing to the inverter 310 is referred to as current I2, and the current flowing from the smoothing unit 200 is referred to as current I3. Current I2 is the sum of current I1 and current I3. Current I3 can be expressed as the difference between current I2 and current I1, i.e., current I2 - current I1. The discharge direction of the smoothing unit 200 is considered to be the positive direction, and the charge direction of the smoothing unit 200 is considered to be the negative direction. That is, current may flow into or out of the smoothing unit 200.

[0019] FIG. 2 is a diagram illustrating an example of currents and capacitor voltages of the smoothing unit capacitors when the control unit of the power conversion device according to embodiment 1 smooths the current output from the rectifier unit using the smoothing unit to maintain a constant current flowing through the inverter. From top to bottom, FIG. 2 shows current I1, current I2, current I3, and capacitor voltage Vdc. Note that capacitor voltage Vdc is the voltage of capacitor 210 generated in response to current I3. The vertical axes of currents I1, I2, and I3 represent current values, while the vertical axis of capacitor voltage Vdc represents voltage values. All horizontal axes represent time t. Note that, in practice, carrier components of inverter 310 are superimposed on currents I2 and I3, but are omitted here. The same applies hereinafter. As shown in FIG. 2 , in the power conversion device 1, if current I1 flowing from rectifier 130 is sufficiently smoothed by smoothing unit 200, current I2 flowing through inverter 310 will have a constant current value. However, a large current I3 flows through capacitor 210 of smoothing unit 200, causing degradation. Therefore, in this embodiment, in the power conversion device 1, the control unit 400 controls the current I2 flowing through the inverter 310, that is, controls the operation of the inverter 310, so as to reduce the current I3 flowing through the smoothing unit 200.

[0020] FIG. 3 is a diagram illustrating an example of currents and capacitor voltages of the capacitors of the smoothing unit when the control unit of the power conversion device according to embodiment 1 controls the operation of the inverter to reduce the current flowing through the smoothing unit. From top to bottom, FIG. 3 illustrates current I1, current I2, current I3, and capacitor voltage Vdc. Note that capacitor voltage Vdc is the voltage of capacitor 210 generated in response to current I3. The vertical axes of currents I1, I2, and I3 represent current values, and the vertical axis of capacitor voltage Vdc represents voltage values. All horizontal axes represent time t. The control unit 400 of the power conversion device 1 controls the operation of inverter 310 so that current I2 as shown in FIG. 3 flows through inverter 310. This reduces the frequency component of the current flowing from rectifier 130 to smoothing unit 200, thereby reducing current I3 flowing through smoothing unit 200, compared to the example of FIG. 2 . Specifically, the control unit 400 controls the operation of inverter 310 so that current I2, which includes a pulsating current primarily composed of the frequency component of current I1, flows through inverter 310.

[0021] The frequency component of current I1 is determined by the frequency of the AC current supplied from commercial power supply 110 and the configuration of rectifier 130. Therefore, control unit 400 can set the frequency component of the pulsating current superimposed on current I2 to a component having a predetermined amplitude and phase. The frequency component of the pulsating current superimposed on current I2 has a waveform similar to that of the frequency component of current I1. As control unit 400 brings the frequency component of the pulsating current superimposed on current I2 closer to the frequency component of current I1, it is possible to reduce current I3 flowing through smoothing unit 200 and reduce the pulsating voltage generated in capacitor voltage Vdc.

[0022] Controlling the operation of the inverter 310 by the control unit 400 to control the pulsation of the current flowing through the inverter 310 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 130. 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. The case 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 control as shown in FIG.

[0023] 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 determine the frequency component of the pulsating current superimposed on the current I2 according to the first AC power supplied from the commercial power supply 110. Specifically, the control unit 400 controls the pulsating waveform of the current I2 flowing through the inverter 310 to have 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 supply 110 is single-phase, or a frequency component six times the frequency of the first AC power when the first AC power supplied from the commercial power supply 110 is three-phase. The pulsating waveform may have, for example, the shape of 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, which is an integer multiple of the sine wave frequency, to the pulsating waveform as a predetermined amplitude. The pulsating waveform may also have 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 predetermined values.

[0024] 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.

[0025] The operation of the control unit 400 will be described using a flowchart. FIG. 4 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 1. In step S2, the control unit 400 estimates the capacitor load. In step S3, the control unit 400 determines whether or not it is necessary to suppress the capacitor load. If the control unit 400 determines that it is necessary to suppress the capacitor load, the result of step S3 is Yes, and in step S4, the control unit 400 performs capacitor load suppression control. That is, when the control unit 400 outputs the second AC power from the inverter 310 to the load, the control unit 400 adds pulsation corresponding to the pulsation of the power flowing into the capacitor 210. Note that if the capacitor load suppression control is already being performed, the control unit 400 continues the capacitor load suppression control. On the other hand, if the control unit 400 determines that it is not necessary to suppress the capacitor load, the result of step S3 is No, and in step S5, the control unit 400 does not perform the capacitor load suppression control. That is, when the control unit 400 outputs the second AC power from the inverter 310 to the load, the control unit 400 does not include pulsation corresponding to the pulsation of the power flowing into the capacitor 210. Note that if the capacitor load suppression control is already not being performed, the control unit 400 continues not to perform the capacitor load suppression control.

[0026] Next, a description will be given of the hardware configuration of the control unit 400 included in the power conversion device 1. Fig. 5 is a diagram showing an example of a hardware configuration realizing the control unit included in the power conversion device according to embodiment 1. The control unit 400 is realized by a processor 91 that executes various processes, a memory 92 that is a main memory, and a storage device 93 that stores information.

[0027] The processor 91 may be a computing device such as an arithmetic unit, a microprocessor, a microcomputer, a central processing unit (CPU), or a digital signal processor (DSP). The memory 92 may be a non-volatile or volatile semiconductor memory such as a random access memory (RAM), a read-only memory (ROM), a flash memory, an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM). A program for executing the capacitor load suppression control process is stored in the storage device 93. The processor 91 reads the program stored in the storage device 93 into the memory 92 and executes it. The processor 91 reads the program stored in the storage device 93 into the memory 92 and executes it, thereby realizing the functions of the control unit 400.

[0028] As described above, in the power conversion device 1 according to the first embodiment, the control unit 400 controls the operation of the inverter 310 based on the detection values ​​acquired from each detection unit, and reduces the current I3 flowing through the smoothing unit 200 by superimposing a pulsation of a frequency component corresponding to the frequency component of the current I1 flowing from the rectifier unit 130 on the current I2 flowing through the inverter 310. As a result, the power conversion device 1 can use a capacitor with a smaller ripple current tolerance than when the control according to the first embodiment is not performed, because the current I3 flowing through the smoothing unit 200 is reduced. Furthermore, the power conversion device 1 can use a smaller capacity capacitor 210 than when the control according to 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 with a plurality of capacitors 210, the power conversion device 1 can reduce the number of capacitors 210 constituting the smoothing unit 200.

[0029] In addition, the control unit 400 estimates the capacitor load and determines whether or not to perform capacitor load suppression control based on the estimated value of the capacitor load, so that if the deterioration of the capacitor 210 is within an acceptable range when capacitor load suppression control is not performed, it is possible to prevent losses from occurring due to reducing the capacitor current to suppress the capacitor load.

[0030] Second Embodiment. Fig. 6 is a diagram showing the configuration of a power conversion device according to a second embodiment. The power conversion device 1 according to the second embodiment differs from the power conversion device 1 according to the first embodiment in that it includes a first current detection unit 601 and a second current detection unit 602. The first current detection unit 601 is installed in the rectification unit 130. That is, the first current detection unit 601 is installed closer to the commercial power supply 110 than the capacitor 210. The second current detection unit 602 is installed between the inverters 310. That is, the second current detection unit 602 is installed closer to the compressor 315, which is the load, than the capacitor 210. The control unit 400 calculates the current flowing through the capacitor 210 from the difference between the current value detected by the first current detection unit 601 and the current value detected by the second current detection unit 602, and estimates the capacitor load.

[0031] The power conversion device 1 according to the second embodiment estimates the capacitor load based on the current flowing through the capacitor 210, which is calculated based on the difference between the current value detected by the first current detection unit 601 and the current value detected by the second current detection unit 602, and therefore can estimate the capacitor load more accurately than the power conversion device 1 according to the first embodiment. Therefore, the power conversion device 1 according to the second embodiment can more accurately determine whether or not it is necessary to perform capacitor load suppression control, and can therefore suppress deterioration of the capacitor 210.

[0032] In addition, since the first current detection unit 601 and the second current detection unit 602 are generally installed in the power conversion device 1 for the purpose of motor control and control and protection of the boost circuit, by estimating the capacitor load using the first current detection unit 601 and the second current detection unit 602 installed for motor control and control and protection of the boost circuit, it is possible to eliminate the need to add a new first current detection unit 601 and second current detection unit 602 for estimating the capacitor load.

[0033] Third Embodiment Fig. 7 is a diagram showing the configuration of a power conversion device according to a third embodiment. The power conversion device 1 according to the third embodiment differs from the power conversion device 1 according to the second embodiment in that it includes a first voltage detection circuit 701 and a second voltage detection circuit 702. The first voltage detection circuit 701 is installed between the reactor 120 and the rectifier 130. That is, the first voltage detection circuit 701 is installed closer to the commercial power supply 110 than the capacitor 210. The second voltage detection circuit 702 is installed between the smoothing unit 200 and the inverter 310. That is, the second voltage detection circuit 702 is installed closer to the compressor 315, which is a load, than the capacitor 210.

[0034] The control unit 400 calculates a first power value from the current value detected by the first current detection unit 601 and the voltage value detected by the first voltage detection circuit 701. Therefore, the first current detection unit 601 and the first voltage detection circuit 701 form a first power detection unit 801. The control unit 400 also calculates a second power value from the current value detected by the second current detection unit 602 and the voltage value detected by the second voltage detection circuit 702. Therefore, the second current detection unit 602 and the second voltage detection circuit 702 detect the second power detection unit 802. The first power detection unit 801 is installed closer to the commercial power source 110 than the capacitor 210, and the second power detection unit 802 is installed closer to the compressor 315, which is a load, than the capacitor 210.

[0035] The control unit 400 calculates the power consumption of the capacitor 210 based on the first power value and the second power value, and estimates the capacitor load.

[0036] The power conversion device 1 of embodiment 3 calculates the power consumption in the capacitor 210 based on a first power value calculated from the current value detected by the first current detection unit 601 and the voltage value detected by the first voltage detection circuit 701, and a second power value calculated from the current value detected by the second current detection unit 602 and the voltage value detected by the second voltage detection circuit 702, and estimates the capacitor load.Therefore, compared to the power conversion device 1 of embodiment 2, it is possible to estimate the capacitor load more accurately.

[0037] Fourth Embodiment The circuit configuration of the power conversion device 1 according to the fourth embodiment is the same as that of the power conversion device 1 according to the first embodiment. In the fourth embodiment, a compressor 315, which is a load including a motor 314 receiving power from the power conversion device 1, is applied to an outdoor unit of an air conditioner and compresses a refrigerant flowing through a refrigerant circuit. In the fourth embodiment, the air conditioner including the compressor 315 is operated in one of a plurality of operation modes with different power consumption. The power conversion device 1 according to the fourth embodiment switches whether or not to perform capacitor load suppression control in accordance with the operation mode of the air conditioner. Here, it is assumed that the air conditioner is operated in either a normal operation mode or an energy-saving operation mode, and the control unit 400 performs capacitor load suppression control when the operation mode of the air conditioner is the normal operation mode and does not perform capacitor load suppression control when the operation mode of the air conditioner is the energy-saving operation mode.

[0038] FIG. 8 is a diagram illustrating the operation of the power conversion device according to the fourth embodiment. In FIG. 8 , the mode switching signal is a signal for switching the operation mode of the air conditioner, with a high level corresponding to the normal operation mode and a low level corresponding to the energy-saving operation mode. At time t10, the mode switching signal is high, and the air conditioner is operating in the normal operation mode. Therefore, at time t10, the control unit 400 is performing capacitor load suppression control. At time t11, the control unit 400 changes the mode switching signal from high to low, switching the air conditioner from the normal operation mode to the energy-saving operation mode. Therefore, at time t11, the control unit 400 stops performing capacitor load suppression control. As the control unit 400 stops performing capacitor load suppression control, the capacitor load suppression control amount begins to decrease at time t11. Although the reduction in the capacitor load suppression control amount increases the capacitor load, the input power to the capacitor 210 decreases because the loss in the motor 314 is reduced. At time t12, the control unit 400 changes the mode switching signal from low to high, switching the air conditioner from the energy-saving operation mode to the normal operation mode. Therefore, at time t12, the control unit 400 starts capacitor load suppression control, and the capacitor load suppression control amount begins to increase. As the capacitor load suppression control amount increases, the capacitor load decreases and the input power to the capacitor 210 increases. Because the workload of the motor 314 on the air conditioner's refrigerant circuit does not change depending on the capacitor load suppression control amount, the air conditioning capacity of the air conditioner remains constant regardless of the capacitor load suppression control amount.

[0039] The power conversion device 1 of embodiment 4 switches whether or not to perform capacitor suppression control in accordance with the operating mode of the air conditioner. Therefore, when the input power of the capacitor 210 is small and the capacitor load can be kept small without performing capacitor load suppression control, by not performing capacitor load suppression control, losses in the motor 314 can be reduced and energy-saving performance can be improved.

[0040] Embodiment 5 The circuit configuration of the power conversion device 1 according to embodiment 5 is the same as that of the power conversion device 1 according to embodiment 1. The power conversion device 1 according to embodiment 5 starts the capacitor load suppression control when the capacitor load exceeds a preset capacitor load upper threshold, and stops the capacitor load suppression control when the capacitor load becomes equal to or less than a preset capacitor load lower threshold.

[0041] FIG. 9 is a diagram illustrating the operation of a power conversion device according to the fifth embodiment. In the fifth embodiment, after the capacitor load exceeds the capacitor load upper threshold and capacitor load suppression control is initiated, the power conversion device 1 increases or decreases the capacitor load suppression control amount in accordance with the increase or decrease in input power or capacitor load until the capacitor load falls below the capacitor load lower threshold. At time t20, the control unit 400 performs the capacitor load suppression control. At time t21, the control unit 400 reduces the air conditioning capacity of the air conditioner. This reduces the input power to the capacitor 210 and also reduces the capacitor load. At time t22, the capacitor load falls below the capacitor load lower threshold. This causes the control unit 400 to stop performing the capacitor load suppression control. As the capacitor load suppression control is not performed, the capacitor load increases. At times t23 and t24, the capacitor load does not exceed the capacitor load upper threshold, so the control unit 400 continues not performing the capacitor load suppression control. At time t25, the capacitor load exceeds the capacitor load upper threshold. Therefore, the control unit 400 performs the capacitor load suppression control, and the capacitor load suppression control amount begins to increase. As the capacitor load suppression control amount increases, the capacitor load decreases and the input power to the capacitor 210 increases. At time t26 and time t27, the capacitor load is not equal to or less than the capacitor load lower limit threshold, so the control unit 400 continues to perform the capacitor load suppression control.

[0042] When the capacitor load is low, the power conversion device 1 according to the fifth embodiment can switch to an operation that prioritizes performance over suppressing the capacitor load, thereby improving energy conservation.

[0043] In the first to fifth embodiments, whether or not to perform capacitor load suppression control is switched, but a threshold value that serves as a target value for the capacitor load may be set in advance, and the capacitor load suppression control amount may be continuously changed according to the difference between the threshold value that serves as the target value and the capacitor load.By continuously adjusting the amount of pulsation to be included in the output from inverter 310, rather than whether or not to include the amount of pulsation to be output from inverter 310 to the load, it is possible to operate the air conditioner by achieving a balance between the lifespan of the air conditioner and its air conditioning performance.

[0044] Sixth Embodiment The circuit configuration of the power conversion device 1 according to the sixth embodiment is the same as that of the power conversion device 1 according to the first embodiment. Fig. 10 is a diagram showing the operation of the power conversion device according to the sixth embodiment. The power conversion device 1 according to the sixth embodiment stops the control to suppress the capacitor load when the control amount of the control to suppress the capacitor load, which is necessary to make the capacitor load equal to or less than the target load amount, becomes equal to or less than a predetermined capacitor load suppression control amount threshold, and resumes the output of the control to suppress the capacitor load when the estimated value of the capacitor load exceeds the predetermined capacitor load threshold.

[0045] At time t30, the control unit 400 is performing capacitor load suppression control, and the capacitor load is maintained at the target load amount. At time t31, the control unit 400 begins to reduce the air conditioning capacity of the air conditioner. Therefore, from time t31, the capacitor load suppression control amount also decreases in line with the reduction in air conditioning capacity. At time t32, the capacitor load suppression control amount becomes equal to or less than a predetermined capacitor load suppression control amount threshold. Therefore, the control unit 400 stops the capacitor load suppression control. Therefore, at time t32, the capacitor load suppression control amount decreases to 0. Although the reduction in the capacitor load suppression control amount increases the capacitor load, the input power to the capacitor 210 decreases because the loss of the motor 314 is improved. At times t33 and t34, the capacitor load does not exceed the predetermined capacitor load threshold, so the control unit 400 continues to stop the capacitor load suppression control. At time t35, the capacitor load exceeds a predetermined capacitor load threshold, so the control unit 400 resumes the capacitor load suppression control, and the capacitor load suppression control amount increases. As the capacitor load suppression control amount increases, the capacitor load decreases to the target load amount, and the input power to the capacitor 210 increases. At time t36, the capacitor load suppression control amount is not equal to or less than the predetermined capacitor load suppression control amount threshold, so the control unit 400 continues the capacitor load suppression control.

[0046] The power conversion device 1 of embodiment 6 controls the capacitor load so that it does not exceed a predetermined capacitor load threshold, and when the capacitor load falls below a certain value, allows the capacitor load to deteriorate to a certain value, and by setting the control amount to the minimum necessary amount, it is possible to improve energy saving in operating conditions where the capacitor load is low.

[0047] Seventh Embodiment The circuit configuration of the power conversion device 1 according to the seventh embodiment is the same as that of the power conversion device 1 according to the first embodiment. The power conversion device 1 according to the seventh embodiment continuously changes the capacitor load suppression control amount so that the life of the capacitor 210 estimated from the capacitor load does not fall below a preset period.

[0048] It is known that the life of a capacitor follows Arrhenius' law. Therefore, the life of a capacitor can generally be calculated from the ambient temperature of the capacitor, the voltage applied to the capacitor, and the amount of capacitor current resulting from the heat generated by the capacitor, in addition to constants determined by the capacitor's specifications. The ambient temperature of the capacitor 210 can be calculated by adding the temperature difference between the ambient temperature of the capacitor 210 and the outdoor temperature detected by the air conditioner, which is confirmed in a preliminary evaluation, for example. The voltage applied to the capacitor 210 can be calculated from the value detected by the voltage detection unit 502. The amount of capacitor current can be calculated from the fluctuation of the voltage applied to the capacitor, or from the difference between the amount of system power supply current and the amount of motor current.

[0049] The power conversion device 1 according to the seventh embodiment does not perform the capacitor load suppression control when it is estimated that the life of the capacitor 210 will not fall below a predetermined period, and performs the capacitor load suppression control only when it is estimated that the life of the capacitor 210 will fall below the predetermined period. Therefore, when it is estimated that the life of the capacitor 210 will not fall below the predetermined period, the power conversion device 1 according to the seventh embodiment allows the life of the capacitor 210 to be shortened to the predetermined period and does not perform the capacitor load suppression control, thereby suppressing a decrease in energy saving that would be caused by performing the capacitor load suppression control. As a result, the power conversion device 1 according to the seventh embodiment can ensure that the life of the capacitor 210 is equal to or longer than the predetermined period while suppressing a decrease in energy saving.

[0050] Eighth Embodiment The circuit configuration of the power conversion device 1 according to the eighth embodiment is the same as that of the power conversion device 1 according to the second embodiment. In the power conversion device 1 according to the eighth embodiment, the control unit 400 decomposes the capacitor current into frequency components and changes the control amount of the capacitor load suppression control so that the root of the sum of the squares of the frequency components twice the power supply voltage Vs or the components that are integer multiples of the power supply voltage Vs does not exceed a predetermined constant value. Furthermore, when the root of the sum of the squares of the frequency components twice the power supply voltage Vs or the components that are integer multiples of the power supply voltage Vs is equal to or smaller than the predetermined constant value, the control unit 400 allows the root of the sum of the squares of the frequency components twice the power supply voltage Vs or the components that are integer multiples of the power supply voltage Vs to increase up to the predetermined constant value, and sets the capacitor load suppression control amount to the minimum necessary amount.

[0051] When the current flowing through the capacitor 210 is a ripple current containing multiple frequency components, the ripple current I Ｒ is calculated by the following formula (1): Ｒ is the effective value [Ams] of the ripple current at the specified frequency, and I Ｘ１ From I ＸＮ is the effective value [Ams] of the ripple current at each frequency, and K １ From K Ｎ is a frequency correction coefficient for each frequency component. Since the frequency correction coefficient for each frequency component differs for each capacitor component used as capacitor 210, control unit 400 stores in advance information about the component specifications of the capacitor component used as capacitor 210.

[0052]

[0053] 11 is a diagram illustrating an example of the relationship between the capacitor current and the capacitor load suppression control amount of the power conversion device according to the eighth embodiment. The control unit 400 uses bandpass filters 401 and 402 to decompose the capacitor current into a frequency component twice the power supply voltage Vs and a component that is an integer multiple of the frequency component twice the power supply voltage Vs. The component that is an integer multiple of the frequency component twice the power supply voltage Vs is, for example, a frequency component four times the power supply voltage Vs. The control unit 400 then divides the frequency component twice the power supply voltage Vs by a frequency correction coefficient using a divider 403, and then divides the component that is an integer multiple of the frequency component twice the power supply voltage Vs by the frequency correction coefficient using a divider 404. The control unit 400 then uses an adder 405 to calculate the root of the sum of the squares of the frequency component twice the power supply voltage Vs divided by the frequency correction coefficient and the component that is an integer multiple of the frequency component twice the power supply voltage Vs divided by the frequency correction coefficient. Then, the control unit 400 calculates the difference between the summed value calculated by the adder 405 and a preset threshold value using a subtractor 406, and changes the capacitor load suppression control amount based on the calculation result of the subtractor 406. Note that the summed value calculated by the adder 405 used in the processing by the subtractor 406 is an average value over a preset period of time rather than an instantaneous value, thereby making it possible to prevent the capacitor load suppression control amount from being changed frequently.

[0054] The power conversion device 1 of embodiment 8 varies the control amount based on the magnitude of the root sum of the squares of the frequency component twice the power supply voltage Vs, or the frequency component twice the power supply voltage Vs and its integer multiples, among the multiple frequency components contained in the capacitor current, for which the capacitor load can be efficiently suppressed by control.This makes it possible to prevent a sudden increase in the control amount for preventing the capacitor current from exceeding a certain value, which would result in a loss of energy saving, when the total capacitor load increases due to other frequency components that cannot be efficiently suppressed by control.

[0055] In the above description, the capacitor current is decomposed into a frequency component that is twice the power supply voltage Vs and a component that is an integer multiple of the frequency component that is twice the power supply voltage Vs. However, the capacitor current may be decomposed into a frequency component that is an integer multiple of the power supply voltage Vs. Alternatively, the capacitor current may be decomposed into a frequency component that is an integer multiple of the power supply voltage Vs and a frequency component of the rotation speed of the compressor 315. Alternatively, the capacitor current may be decomposed into a frequency component that is an integer multiple of the power supply voltage Vs and a frequency component that is twice the control period of the inverter 310 or the converter. Alternatively, the capacitor current may be decomposed into at least one of a frequency component that is an integer multiple of the power supply voltage Vs, a frequency component of the rotation speed of the compressor 315, and a frequency component that is twice the control period of the inverter 310 or the converter.

[0056] 12 is a diagram showing the configuration of an outdoor unit of an air conditioner according to embodiment 9. An outdoor unit 900 of an air conditioner according to embodiment 9 includes the power conversion device 1 according to any one of embodiments 1 to 8.

[0057] The outdoor unit 900 of the air conditioner includes a compressor 315 incorporating the motor 314 shown in embodiments 1 to 8, 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.

[0058] Inside the compressor 315, a compression mechanism 904 that compresses the refrigerant and a motor 314 that operates the compression mechanism 904 are provided.

[0059] The outdoor unit 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.

[0060] During heating operation, as shown by the solid arrow, the refrigerant is pressurized by the compression mechanism 904 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.

[0061] During cooling operation, as shown by the dashed arrow, the refrigerant is pressurized by the compression mechanism 904 and sent out, and returns to the compression mechanism 904 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.

[0062] 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.

[0063] The configurations shown in the above embodiments are merely examples of the content, and may be combined with other known technologies, or parts of the configurations may be omitted or modified without departing from the spirit of the invention.

[0064] 1 Power conversion device, 2 Motor drive device, 91 Processor, 92 Memory, 93 Storage device, 110 Commercial power supply, 120 Reactor, 130 Rectification unit, 131, 132, 133, 134 Rectification element, 200 Smoothing unit, 210 Capacitor, 310 Inverter, 311a, 311b, 311c, 311d, 311e, 311f Switching element, 312a, 312b, 312c, 312d, 312e, 312f Freewheel diode, 313a, 313b Current detection unit, 314 Motor, 315 Compressor, 400 Control unit, 401, 402 Bandpass filter, 403, 404 Divider, 405 Adder, 406 Subtractor, 501 Voltage / current detection unit, 502 Voltage detection unit, 601: first current detection unit, 602: second current detection unit, 701: first voltage detection circuit, 702: second voltage detection circuit, 801: first power detection unit, 802: second power detection unit, 900: outdoor unit, 902: four-way valve, 904: compression mechanism, 906: indoor heat exchanger, 908: expansion valve, 910: outdoor heat exchanger, 912: refrigerant piping.

Claims

1. a rectification unit that rectifies a first AC power supplied from a 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 having a motor; a control unit that performs capacitor load suppression control to suppress a current flowing through the capacitor by controlling an operation of the inverter so that the second AC power including a pulsation corresponding to a pulsation of the power flowing from the rectifier to the capacitor is output from the inverter to the load; Equipped with The control unit estimates a capacitor load on the capacitor, and determines whether or not to perform the capacitor load suppression control based on the estimated value of the capacitor load.

2. The power converter of claim 1 , further comprising means for detecting a voltage across the capacitor.

3. a first current detection unit disposed on the commercial power supply side of the capacitor, and a second current detection unit disposed on the load side of the capacitor; The power conversion device according to claim 1 , wherein the control unit estimates the capacitor load based on a detection value of the first current detection unit and a detection value of the second current detection unit.

4. 2. The power conversion device according to claim 1, wherein the control unit decomposes the capacitor current into frequency components, and performs the capacitor load suppression control when a magnitude of the root sum of the squares of at least a frequency component that is twice the power supply voltage frequency or each component that is an integer multiple of the power supply voltage frequency is equal to or greater than a predetermined constant value, and stops the capacitor load suppression control when a magnitude of the root sum of the squares of at least a frequency component that is twice the power supply voltage frequency or each component that is an integer multiple of the power supply voltage frequency is less than a predetermined constant value.

5. a first power estimation unit that is disposed closer to the commercial power supply than the capacitor, and a second power estimation unit that is disposed closer to the load than the capacitor, The power conversion device according to claim 1 , wherein the control unit estimates the capacitor load based on an estimated value of the first power estimating unit and an estimated value of the second power estimating unit.

6. The control unit is The power conversion device according to claim 1 , wherein whether or not the capacitor load suppression control is performed is switched depending on an operation mode of the load.

7. 2. The power conversion device according to claim 1, wherein the control unit starts the capacitor load suppression control when the capacitor load exceeds a preset capacitor load upper threshold, and stops the capacitor load suppression control when the capacitor load becomes equal to or lower than a preset capacitor load lower threshold.

8. The power conversion device according to claim 1 , wherein the control unit continuously adjusts a pulsation amount corresponding to the pulsation of the power flowing into the capacitor in the capacitor load suppression control.

9. The control unit starts the capacitor load suppression control when the capacitor load exceeds a preset capacitor load threshold, and stops the capacitor load suppression control when a capacitor load suppression control amount by the capacitor load suppression control becomes equal to or less than a preset capacitor load suppression control amount threshold.

2. The power conversion device according to claim 1, wherein the capacitor load suppression control continuously adjusts a minimum necessary pulsation amount according to the pulsation of the power flowing into the capacitor so that the estimated value of the capacitor load is equal to or less than a predetermined target load amount.

10. The power conversion device according to claim 1, wherein the control unit continuously adjusts a minimum necessary amount of pulsation according to the pulsation of the power flowing into the capacitor in the capacitor load suppression control so that the life of the capacitor estimated from the capacitor load is equal to or longer than a predetermined period.

11. An outdoor unit of an air conditioner comprising the power conversion device according to any one of claims 1 to 10.

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