Power conversion device and air-conditioning device

Abstract

This power conversion device (10) comprises: a converter (11) that rectifies an alternating current input from an AC power supply (30) and outputs a direct current; a DC reactor (14) that removes a harmonic component included in the output of the converter (11); a smoothing capacitor (12) that smooths the output of the converter (11); and an inverter (13) that drives a motor (40) by converting the direct current output from the converter (11) into an alternating current and outputting the alternating current to the motor (40), and a clamp circuit (16) that absorbs regenerative energy from the motor (40). The clamp circuit (16) has an electrolytic capacitor (16a) connected in parallel to the smoothing capacitor (12) via a diode (18), and heat generated in the DC reactor (14) is transmitted to the electrolytic capacitor (16a) during an operation for converting the power supplied from the AC power supply (30) and outputting the converted power to the motor (40).

Description

Power conversion device and air conditioning device

[0001] The present disclosure relates to a power conversion device that converts power supplied from an AC power supply and outputs the converted power to a load, and an air conditioner.

[0002] A power conversion device that converts power supplied from an AC power source and outputs it to a load includes a clamp circuit for absorbing regenerative energy from the load. The clamp circuit includes an electrolytic capacitor connected in parallel with a smoothing capacitor that smoothes the output of a converter that rectifies AC current input from the AC power source and outputs DC current.

[0003] Electrolytic capacitors have the characteristic that their capacitance decreases as the temperature drops. Therefore, if a power conversion device is expected to be used in a low-temperature environment, it is necessary to design the capacitor with a larger capacitance in advance, taking into account the decrease in capacitance.

[0004] If an electrolytic capacitor with a large capacitance is used in a power converter, the power converter will become larger and more expensive.

[0005] Patent Document 1 discloses a power conversion device in which a resistive element that generates heat when current is applied to the power conversion device is placed around an electrolytic capacitor, and the heat from the resistive element is transferred to the electrolytic capacitor, thereby suppressing a drop in the temperature of the electrolytic capacitor and suppressing a decrease in capacitance.

[0006] Patent No. 6978661

[0007] However, in the power conversion device disclosed in Patent Document 1, the resistive elements are a voltage dividing resistor used for voltage detection and a balancing resistor provided for the purpose of equalizing the voltage divided by the series-connected capacitors. Generally, the voltage dividing resistor used for voltage detection and the balancing resistor are not components that function to realize the main operation of converting power supplied from an AC power source and outputting it to a load. Therefore, from the viewpoint of energy conservation, it is desirable to reduce the power consumption of the balancing resistor. In the power conversion device disclosed in Patent Document 1, reducing the power consumption of the balancing resistor reduces the heating effect of the electrolytic capacitor, making it difficult to suppress the decrease in capacitance. Therefore, there was a problem in that attempting to suppress the decrease in capacitance by suppressing the decrease in capacitor temperature resulted in increased power consumption.

[0008] The present disclosure has been made in view of the above, and has an object to provide a power conversion device that can suppress a decrease in the capacitance of an electrolytic capacitor used in a clamp circuit with low power consumption.

[0009] In order to solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure includes a converter that rectifies AC current input from an AC power source and outputs DC current, a DC reactor that removes harmonic components from the converter output, a smoothing capacitor that smoothes the converter output, an inverter that converts the DC current output from the converter into AC current and outputs the AC current to the load, thereby driving the load, and a clamp circuit that absorbs regenerative energy from the load. The clamp circuit has an electrolytic capacitor connected in parallel to the smoothing capacitor via a diode. The anode of the diode is connected to a node on the high-potential side of the smoothing capacitor, and the cathode of the diode is connected to the anode of the electrolytic capacitor. Heat generated in the DC reactor during the operation of converting power supplied from the AC power source and outputting it to the load is transferred to the electrolytic capacitor.

[0010] The power conversion device according to the present disclosure has an effect of being able to suppress a decrease in the capacitance of an electrolytic capacitor used in a clamp circuit with low power consumption.

[0011] 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 the installation of a DC reactor in a power conversion device according to embodiment 1. FIG. 3 is a diagram showing an example of the hardware configuration for realizing the inverter control unit provided in the power conversion device according to embodiment 1. FIG. 4 is a diagram showing an example of the installation of a DC reactor in a power conversion device according to embodiment 2. FIG. 5 is a diagram showing an example of the installation of a DC reactor in a power conversion device according to embodiment 3. FIG. 6 is a diagram showing an example of the installation of a DC reactor in a power conversion device according to embodiment 4.

[0012] Hereinafter, a power conversion device and an air conditioner according to an embodiment will be described in detail with reference to the drawings.

[0013] First Embodiment. Fig. 1 is a diagram showing the configuration of a power conversion device according to a first embodiment. As shown in Fig. 1, an AC power supply 30, which is a power source, and a motor 40, which is a load, are connected to the power conversion device 10. The AC power supply 30 is, for example, a commercial power supply that supplies three-phase AC power having U, V, and W phases. The motor 40 is, for example, a permanent magnet synchronous motor that is driven by three-phase AC power having U, V, and W phases. Here, the motor 40 is given as an example of the load of the power conversion device 10, but the load of the power conversion device 10 may be other equipment.

[0014] Power conversion device 10 according to the first embodiment includes converter 11 that rectifies AC current input from AC power supply 30 and outputs DC current, DC reactor 14 that removes harmonic components included in the output of converter 11, and smoothing capacitor 12 that smoothes the output of converter 11. Power conversion device 10 also includes inverter 13 that converts the DC current output from converter 11 into AC current and outputs the AC current to motor 40 to drive motor 40, clamp circuit 16 that absorbs regenerative energy from motor 40, bus voltage detection unit 15 that detects a bus voltage, and inverter control unit 8.

[0015] Operation commands such as a speed command and a torque command are input to the inverter control unit 8 from the outside. The inverter control unit 8 outputs a drive switch signal to the inverter 13 based on the input operation commands. As a method for controlling the speed and torque of the motor 40, for example, vector control, which uses a dq coordinate system to feedback control the current flowing through the motor 40, is known. The inverter control unit 8 is not limited to vector control and may use other methods. That is, the inverter control unit 8 may use constant V / f control, which outputs a voltage proportional to the operating frequency of the motor 40, or direct torque control, which controls the magnetic flux and torque of the motor 40.

[0016] The inverter 13 is configured with a full-bridge circuit including, for example, six switching elements 13a. Specifically, the switching elements 13a are connected in series to form a series body. Three series bodies are connected in parallel to form a full-bridge circuit. A freewheeling diode 13b is connected in anti-parallel to each switching element 13a. Each switching element 13a performs an on / off operation independently of the others in accordance with a drive switch signal input from the inverter control unit 8. This on / off operation converts direct current into alternating current. Examples of the switching elements 13a include an insulated gate bipolar transistor (IGBT) and a metal-oxide-semiconductor field-effect transistor (MOSFET), but other elements may also be used.

[0017] The bus voltage detector 15 outputs the detected bus voltage to the inverter controller 8. As is generally known, the bus voltage can be detected by observing the value obtained by dividing the bus voltage by a resistor.

[0018] The converter 11 includes a plurality of diodes 11a, 11b, 11c, 11d, 11e, and 11f.

[0019] The clamp circuit 16 includes an electrolytic capacitor 16a connected in parallel with the smoothing capacitor 12, a discharge resistor 16b that discharges the electrolytic capacitor 16a, and a diode 18. The discharge resistor 16b is connected in parallel to the electrolytic capacitor 16a. The clamp circuit 16 is connected to the cathode of the diode 18, and the DC reactor 14 and the smoothing capacitor 12 are connected to the anode of the diode 18. Specifically, the anode of the diode 18 is connected to the high-potential node of the smoothing capacitor 12, and the cathode of the diode 18 is connected to the anode of the electrolytic capacitor 16a.

[0020] Since the electrolytic capacitor 16a is connected in parallel to the smoothing capacitor 12 via the diode 18, only the discharge resistor 16b consumes the energy of the electrolytic capacitor 16a, and therefore, even if the energy consumption of the motor 40 increases, the voltage across the electrolytic capacitor 16a remains substantially smooth.

[0021] Since the smoothing capacitor 12 and the electrolytic capacitor 16a are connected via the diode 18, part of the energy of the regenerative power is absorbed by the electrolytic capacitor 16a, which has a large capacity, and therefore the voltage rise is suppressed.

[0022] In the operation of converting the power input from the AC power supply 30 and outputting it to the motor 40, a main circuit current flows through the DC reactor 14, causing the temperature of the DC reactor 14 to rise due to copper loss, which is a power loss due to a resistance component present in the DC reactor 14, and iron loss, which is a power loss due to a change in magnetic flux linked to a fluctuation in the current flowing through the DC reactor 14. The amount of heat generated by the DC reactor 14 is often greater than the amount of heat generated by the discharge resistor 16b.

[0023] The DC reactor 14 is installed at a position where heat generated during normal operation, which is an operation of converting power input from the AC power supply 30 and outputting it to the motor 40, is transferred to the electrolytic capacitor 16a. Here, when a first temperature, which is the surface temperature during normal operation of the electrolytic capacitor 16a in the direction of the DC reactor 14 installed at the first position, is compared with a second temperature, which is the surface temperature during normal operation of the electrolytic capacitor 16a in the direction of the DC reactor 14 installed at a second position farther from the electrolytic capacitor 16a than the first position, if the first temperature is higher than the second temperature, the first position can be considered to be a position where heat generated during normal operation is transferred to the electrolytic capacitor 16a.

[0024] FIG. 2 is a diagram illustrating an example of the placement of a DC reactor in the power conversion apparatus according to the first embodiment. The open arrows in FIG. 2 indicate the flow of air heated by the DC reactor 14. The DC reactor 14 is located upstream of the electrolytic capacitor 16a in the flow of air heated by the DC reactor 14. For example, the DC reactor 14 is located inside the housing 20 of the power conversion apparatus 10, outside the substrate 21 on which the electrolytic capacitor 16a is mounted, and below the electrolytic capacitor 16a. By placing the DC reactor 14 below the electrolytic capacitor 16a, the air heated by the DC reactor 14 forms an ascending air current and passes around the electrolytic capacitor 16a, thereby efficiently heating the electrolytic capacitor 16a. Note that if the DC reactor 14 generates a large amount of heat and the electrolytic capacitor 16a can be heated by radiant heat from the DC reactor 14, the DC reactor 14 does not need to be placed below the electrolytic capacitor 16a.

[0025] The heat generated in the DC reactor 14 is transferred to the electrolytic capacitor 16a, thereby heating the electrolytic capacitor 16a, and thus the decrease in capacitance due to a decrease in temperature of the electrolytic capacitor 16a is suppressed.

[0026] In the power conversion device 10 according to the first embodiment, the electrolytic capacitor 16a is heated by heat generated in the DC reactor 14, not by heat generated in the discharge resistor 16b, and therefore there is no need to increase the power consumption of the discharge resistor 16b to increase the amount of heat generated in the discharge resistor 16b. Therefore, the power conversion device 10 according to the first embodiment can suppress a decrease in the capacitance of the electrolytic capacitor 16a with low power consumption. Therefore, compared to a power conversion device that heats the electrolytic capacitor by heat generated in the discharge resistor, the power conversion device 10 according to the first embodiment can obtain equivalent output performance even when using a small, inexpensive electrolytic capacitor 16a with a small capacitance.

[0027] Next, a hardware configuration of the inverter control unit 8 included in the power conversion device 10 will be described. Fig. 3 is a diagram showing an example of a hardware configuration realizing the inverter control unit included in the power conversion device according to the first embodiment. The inverter control unit 8 is realized, for example, by the processing circuit shown in Fig. 3. The inverter control unit 8 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.

[0028] The processor 91 may be a computing device such as an arithmetic unit, a microprocessor, a microcomputer, a CPU (Central Processing Unit), or a DSP (Digital Signal Processor). The memory 92 may be a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Only Memory), or an EEPROM (Electrically Erasable Programmable Read Only Memory). The storage device 93 stores a program for executing a process for controlling the inverter 13. 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 inverter control unit 8.

[0029] Second Embodiment Fig. 4 is a diagram showing an example of installation of a DC reactor in a power conversion device according to a second embodiment. The power conversion device 10 according to the second embodiment differs from the power conversion device 10 according to the first embodiment in that it includes a wind generator 19 inside the housing 20. The white arrows in Fig. 4 indicate the airflow generated by the wind generator 19. The DC reactor 14 is installed upstream of the electrolytic capacitor 16a in the flow of the airflow generated by the wind generator 19. When the wind generator 19 is operating, the temperature of the electrolytic capacitor 16a is higher than the temperature of the electrolytic capacitor 16a when the wind generator 19 is stopped.

[0030] In addition to a propeller fan that generates airflow by rotating a propeller, an axial fan or a sirocco fan can be used as the wind generating device 19. The wind generating device 19 may also have a structure in which the fan is provided at a position different from the airflow outlet.

[0031] In the power conversion device 10 according to the second embodiment, the air heated by the DC reactor 14 can pass around the electrolytic capacitor 16a even if the DC reactor 14 is not positioned below the electrolytic capacitor 16a, which increases the degree of freedom in the installation position of the DC reactor 14.

[0032] Embodiment 3. Fig. 5 is a diagram showing an example of installation of a DC reactor in a power conversion device according to embodiment 3. In a power conversion device 10 according to embodiment 3, a DC reactor 14 and an electrolytic capacitor 16a are mounted on a common substrate 21 inside a housing 20. The white arrows in Fig. 5 indicate the flow of air heated by the DC reactor 14.

[0033] Conventionally, the DC reactor 14 is large and has a certain weight. Therefore, when mounted on the substrate 21, there is a risk that the substrate 21 may be damaged by vibrations generated during transportation or by vibrations generated by the operation of the equipment. For this reason, the DC reactor 14 is often fixed to a metal plate constituting the housing 20 and connected to the substrate 21 by wiring, and a certain distance is often maintained between the DC reactor 14 and the electrolytic capacitor 16a. However, when the rated power of the power conversion device 10 is small, the reactor elements constituting the DC reactor 14 may be sized to be mountable on the substrate 21. Furthermore, by reducing the size of the reactor elements constituting the DC reactor 14 and connecting multiple reactor elements in series, it is possible to mount the DC reactor 14 on the substrate 21 without reducing the reactance of the DC reactor 14 as a whole, while reducing the risk of damage to the substrate 21 due to vibrations.

[0034] By mounting the DC reactor 14 and the electrolytic capacitor 16a on a common substrate 21, heat can be transferred from the DC reactor 14 to the electrolytic capacitor 16a by thermal conduction through the patterned copper foil portion of the substrate 21. In addition, since the DC reactor 14 can be placed physically close to the electrolytic capacitor 16a, the electrolytic capacitor 16a can be heated efficiently.

[0035] Fourth Embodiment Fig. 6 is a diagram showing an example of the placement of a DC reactor in a power conversion device according to a fourth embodiment. The power conversion device 10 according to the fourth embodiment differs from the power conversion device 10 according to the third embodiment in that a heat conduction member 50 is placed between the DC reactor 14 and the electrolytic capacitor 16a. The hollow arrows in Fig. 6 indicate the flow of air heated by the DC reactor 14.

[0036] The heat conducting member 50 is made of a material having a higher thermal conductivity than air, such as silicon, but is not limited to this.

[0037] Although the example given here is a structure in which the DC reactor 14 is mounted on the same substrate 21 as the electrolytic capacitor 16a, the DC reactor 14 may be mounted on a substrate different from the substrate 21 on which the electrolytic capacitor 16a is mounted.

[0038] In the power conversion device 10 according to the fourth embodiment, heat is transferred from the DC reactor 14 to the electrolytic capacitor 16a not only through the air heated by the heat generated from the DC reactor 14 but also through the heat conduction member 50, thereby enabling efficient heating of the electrolytic capacitor 16a.

[0039] Embodiment 5 Fig. 7 is a configuration diagram that schematically shows the configuration of an air conditioning apparatus according to embodiment 5. As shown in Fig. 7, an air conditioning apparatus 60 according to embodiment 5 includes an indoor unit 600 installed indoors, an outdoor unit 900 installed outdoors, and refrigerant piping 700 for circulating refrigerant between the indoor unit 600 and the outdoor unit 900. The outdoor unit 900 is capable of communicating with the indoor unit 600 via a communication line (not shown).

[0040] 8 is a diagram showing the configuration of an outdoor unit of an air conditioning apparatus according to embodiment 5. An outdoor unit 900 of an air conditioning apparatus 60 according to embodiment 5 includes a power conversion apparatus 10 according to any one of embodiments 1 to 4.

[0041] The outdoor unit 900 includes a compressor 901 incorporating the motor 40 shown in any one of the first to fourth embodiments, a four-way valve 902, an expansion valve 903, and an outdoor heat exchanger 904.

[0042] Inside the compressor 901, a compression mechanism 911 that compresses the refrigerant and a motor 40 that operates the compression mechanism 911 are provided.

[0043] The outdoor unit 900 can perform heating or cooling operation by switching the four-way valve 902. The compression mechanism 911 is driven by a motor 40 that is variably controlled in speed.

[0044] The indoor unit 600 includes an indoor heat exchanger 601 .

[0045] During heating operation, as shown by the solid arrow, the refrigerant is pressurized by the compression mechanism 911 and sent out, passes through the four-way valve 902, the indoor heat exchanger 601, the expansion valve 903, the outdoor heat exchanger 904 and the four-way valve 902 and returns to the compression mechanism 911.

[0046] During cooling operation, as shown by the dashed arrow, the refrigerant is pressurized by the compression mechanism 911 and sent out, passes through the four-way valve 902, the outdoor heat exchanger 904, the expansion valve 903, the indoor heat exchanger 601 and the four-way valve 902 and returns to the compression mechanism 911.

[0047] During heating operation, the indoor heat exchanger 601 acts as a condenser to release heat, and the outdoor heat exchanger 904 acts as an evaporator to absorb heat. During cooling operation, the outdoor heat exchanger 904 acts as a condenser to release heat, and the indoor heat exchanger 601 acts as an evaporator to absorb heat. The expansion valve 903 reduces the pressure of the refrigerant to expand it.

[0048] The air conditioning device 60 of embodiment 5 is equipped with a power conversion device 10 of any of embodiments 1 to 4, and therefore is able to suppress the decrease in capacity of the electrolytic capacitor 16a due to a decrease in temperature, reduce the power consumption in the power conversion device 10, and achieve low power consumption.

[0049] 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.

[0050] 8 inverter control unit, 10 power conversion device, 11 converter, 11a, 11b, 11c, 11d, 11e, 11f, 18 diode, 12 smoothing capacitor, 13 inverter, 13a switching element, 13b reflux diode, 14 DC reactor, 15 bus voltage detection unit, 16 clamp circuit, 16a electrolytic capacitor, 16b discharge resistor, 19 wind generator, 20 housing, 21 circuit board, 30 AC power supply, 40 motor, 50 heat conduction member, 60 air conditioner, 91 processor, 92 memory, 93 storage device, 600 indoor unit, 601 indoor heat exchanger, 700 refrigerant piping, 900 outdoor unit, 901 compressor, 902 four-way valve, 903 expansion valve, 904 outdoor heat exchanger, 911 compression mechanism.

Claims

1. A power conversion device comprising: a converter that rectifies AC current input from an AC power supply and outputs DC current; a DC reactor that removes harmonic components contained in the output of the converter; a smoothing capacitor that smoothes the output of the converter; an inverter that converts the DC current output from the converter into AC current and outputs the AC current to the load, thereby driving the load; and a clamp circuit that absorbs regenerative energy from the load, wherein the clamp circuit has an electrolytic capacitor connected in parallel to the smoothing capacitor via a diode, the anode of the diode being connected to a node on the high potential side of the smoothing capacitor and the cathode of the diode being connected to the anode of the electrolytic capacitor, and heat generated in the DC reactor is transferred to the electrolytic capacitor during an operation of converting power supplied from the AC power supply and outputting it to the load.

2. The power conversion device according to claim 1, wherein the DC reactor is installed upstream of the electrolytic capacitor in the flow of air heated by the DC reactor.

3. The power conversion device according to claim 1 or 2, further comprising a wind generating device that generates an airflow from the DC reactor toward the electrolytic capacitor, wherein the temperature of the electrolytic capacitor when the wind generating device is operating is higher than the temperature of the electrolytic capacitor when the wind generating device is stopped.

4. The power conversion device according to any one of claims 1 to 3, wherein the DC reactor and the electrolytic capacitor are mounted on a common substrate.

5. The power conversion device according to any one of claims 1 to 4, further comprising a heat conduction member disposed between the DC reactor and the electrolytic capacitor.

6. An air conditioner equipped with a power conversion device according to any one of claims 1 to 5.

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