Power conversion device and heat pump device

Abstract

A power conversion device (100) comprises: a power reception terminal (128) capable of being connected to an external power supply (200) that is a DC power supply or an AC power supply; a voltage conversion unit (120) capable of outputting, as a variable DC voltage, an applied voltage applied to the power reception terminal (128); and a load (140) connected to the output side of the voltage conversion unit (120). The voltage conversion unit (120) is provided with: a reactor (121) that accumulates and discharges energy; a short-circuit unit (126) that has a switch (125); and a smoothing unit (123) that smooths the DC voltage. The voltage conversion unit (120) is configured so as to be capable of operating whether the voltage applied via the reactor (121) is a DC voltage or an AC voltage, and is configured so that backflow from the smoothing unit (123) does not occur during operation of the switch (125).

Description

Power conversion device and heat pump device

[0001] The present disclosure relates to a power conversion device that performs power conversion and a heat pump device.

[0002] An example of an application of a heat pump device is an air conditioner. Patent Document 1 listed below discloses a configuration in which, in an air conditioner to which only DC power is input, high-voltage DC power of a first DC voltage value is input to an inverter for driving a compressor in an outdoor unit, and low-voltage DC power of a second DC voltage value lower than the first DC voltage value is input to a power conversion circuit group consisting of a drive circuit for an indoor unit and drive circuits in the outdoor unit other than the inverter for driving the compressor.

[0003] JP 2012-83063 A

[0004] However, in a configuration in which high-voltage DC power is input from an external source to drive the compressor, the technology of Patent Document 1 applies a fixed DC voltage, which means that the DC voltage cannot be varied according to the rotation speed of the compressor, and this poses a problem in that efficiency cannot be improved.

[0005] Furthermore, in the case of the configuration of Patent Document 1, if the positive and negative polarities of the DC voltage are connected in reverse, power will not be supplied and the air conditioner will not operate. Therefore, the technology of Patent Document 1 has issues not only in terms of efficiency but also in terms of installation of the equipment.

[0006] Furthermore, in a transitional power supply environment where AC and DC power distribution coexist, a power conversion device that can operate at both AC and DC voltages is desired. To address this issue, Patent Document 1 discloses a configuration in which a converter circuit is connected between a commercial power source, which is an AC power source, and an inverter for driving a compressor. However, with the technology of Patent Document 1, even if this converter circuit is installed on the supply side of high-voltage DC power, it is not possible to vary the DC voltage value.

[0007] The present disclosure has been made in view of the above, and aims to provide a power conversion device that can vary the voltage value depending on the operating status of the device, regardless of the polarity of the power supply voltage and the power supply specifications.

[0008] In order to solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure includes a power receiving terminal to which an external power source, which is a DC power source or an AC power source, a voltage conversion unit capable of outputting a voltage applied to the power receiving terminal as a variable DC voltage, and a load connected to the output side of the voltage conversion unit. The voltage conversion unit includes a reactor that stores and releases energy, a short-circuiting unit having one or more switches, and a smoothing unit that smooths the DC voltage. The voltage conversion unit is configured to be operable whether the voltage applied via the reactor or the voltage applied without passing through the reactor is a DC voltage or an AC voltage, and is configured so that backflow from the smoothing unit does not occur when the switch is operating.

[0009] The power conversion device according to the present disclosure has the advantage of being able to vary the voltage value depending on the operating status of the device, regardless of the polarity of the power supply voltage and the power supply specifications.

[0010] FIG. 1 is a block diagram showing an example of a hardware configuration for realizing the function of a control unit provided in the power conversion device according to embodiment 1; FIG. 2 is an equivalent circuit diagram for explaining the operation of the power conversion device according to embodiment 1; FIG. 3 is a waveform diagram for explaining the operation of the power conversion device according to embodiment 1; FIG. 4 is a diagram showing an example of a configuration according to a first modified example of a voltage conversion unit provided in the power conversion device shown in FIG. 1; FIG. 5 is a diagram showing an example of a configuration according to a second modified example of a voltage conversion unit provided in the power conversion device shown in FIG. 1; FIG. 6 is a diagram showing an example of a configuration according to a third modified example of a voltage conversion unit provided in the power conversion device shown in FIG. 1;

[0011] Hereinafter, a power conversion device and a heat pump device according to embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0012] First Embodiment. FIG. 1 is a diagram illustrating a configuration example of a power conversion device 100 according to a first embodiment. The power conversion device 100 is configured to receive power from an external power source 200, such as a DC power distribution system or an AC power system. That is, the external power source 200 is a DC power source or an AC power source. The power conversion device 100 has a power receiving terminal 128 to which the external power source 200 can be connected, and is connected to a load 140 via a voltage conversion unit 120. The voltage conversion unit 120 varies the voltage of the external power source 200 and supplies a DC voltage to the load 140 connected to the output side of the voltage conversion unit 120. To achieve this function, the voltage conversion unit 120 is configured to output the voltage applied to the power receiving terminal 128 as a variable DC voltage.

[0013] The voltage conversion unit 120 includes a reactor 121, a rectifier 122, a short-circuit unit 126, and a smoothing unit 123. The rectifier 122 has diodes 152a to 152d connected in a full bridge configuration. When the external power supply 200 outputs a DC voltage, the rectifier 122 receives a first DC voltage and outputs a second DC voltage. When the external power supply 200 outputs an AC voltage, the rectifier 122 rectifies the received AC voltage and outputs the second DC voltage. The first DC voltage is the output voltage when the external power supply 200 outputs a DC voltage, and the second DC voltage is the variable DC voltage described above. The reactor 121 stores and releases energy. The reactor 121 also corrects the power factor of the power supply current flowing between the external power supply 200 and the rectifier 122. The smoothing unit 123 smoothes the DC voltage output by the rectifier 122. An example of the smoothing unit 123 is a capacitor as shown in the figure.

[0014] The short-circuiting unit 126 includes a rectifier circuit 124 having four full-bridge-connected diodes 154a to 154d, and a switch 125 connected in parallel across the rectifier circuit 124. The switch 125 is typically configured with a switching element such as an insulated gate bipolar transistor (IGBT) that conducts in one direction. The rectifier circuit 124 controls the direction of current so that it flows from the upper terminal of the switch 125 to the lower terminal. Note that if a bidirectional switch such as a metal-oxide-semiconductor field-effect transistor (MOSFET) is used as the switch 125, the rectifier circuit 124 can be omitted. When the switch 125 is a switching element, this switching element may be referred to as a "first switching element" in this document.

[0015] The load 140 includes an inverter 141 and a motor 142. A DC voltage converted by the voltage conversion unit 120 is applied to the load 140. The inverter 141 has switching elements 156a to 156f connected in a three-phase bridge. The load 140 is a DC load that operates on a DC voltage, and the applied DC voltage is converted into a three-phase AC voltage by the inverter 141 to operate the motor 142. Note that although the illustrated motor 142 is a three-phase motor, the motor 142 may also be a single-phase motor. When the motor 142 is a single-phase motor, the inverter 141 is configured as a single-phase bridge circuit.

[0016] The control unit 400 controls the operation of the switch 125 of the short-circuiting unit 126 and the switching elements 156a to 156f of the inverter 141 based on the detected value of the current or voltage detected by a current detection unit, a voltage detection unit, etc. (not shown). Examples of the detected current value include the detected value of the motor current flowing through the motor 142, the detected value of the power supply current flowing through the reactor 121, and the detected value of the smoothing unit current flowing through the smoothing unit 123. Examples of the detected voltage value include the detected value of the power supply voltage output by the external power supply 200, the detected value of the smoothing unit voltage applied to the smoothing unit 123, and the detected value of the motor voltage applied to the motor 142.

[0017] Fig. 2 is a block diagram showing an example of a hardware configuration that realizes the functions of the control unit 400 provided in the power conversion device 100 according to embodiment 1. When the functions of the control unit 400 according to embodiment 1 are realized, as shown in Fig. 2, a configuration can be adopted that includes a processor 91 that performs calculations, a memory 92 that stores programs read by the processor 91, and an interface 93 that inputs and outputs signals.

[0018] The processor 91 is an example of a computing means. The processor 91 may be a computing means called a microprocessor, a microcomputer, a CPU (Central Processing Unit), or a DSP (Digital Signal Processor). Examples of the memory 92 include non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), and EEPROM (Electrically EPROM), as well as a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, and a DVD (Digital Versatile Disc).

[0019] The memory 92 stores a program that executes the functions of the control unit 400 in embodiment 1. The processor 91 exchanges necessary information via the interface 93, receives detected values ​​of current or voltage detected by the current detection unit, voltage detection unit, etc., and executes the program stored in the memory 92 to perform the processing described below. The calculation results by the processor 91 can be stored in the memory 92.

[0020] Next, the operation of the power conversion device 100 according to the first embodiment will be further described with reference to Fig. 3 and Fig. 4. Fig. 3 is an equivalent circuit diagram provided for explaining the operation of the power conversion device 100 according to the first embodiment. Fig. 4 is a waveform diagram provided for explaining the operation of the power conversion device 100 according to the first embodiment.

[0021] FIG. 3A shows an equivalent circuit of a normal connection in which a positive voltage is applied to the reactor 121 when the external power supply 200 is a DC power supply. In the normal connection, the circuit elements that contribute to operation are the reactor 121, the diodes 154a and 154d and switch 125 of the short-circuiting unit 126, the diodes 152a and 152d of the rectifying unit 122, and the smoothing unit 123. In the normal connection, as shown by the dashed line in the figure, a short-circuit current flows through the reactor 121, the diode 154a, the switch 125, and the diode 154d. This short-circuit current accumulates energy in the reactor 121. In the normal connection, a charging current flows through the reactor 121, the diode 152a, the smoothing unit 123, and the diode 152d, as shown by the solid line in the figure. This charging current charges the smoothing unit 123. Furthermore, when this charging current flows, the energy stored in reactor 121 is released, making it possible to charge smoothing unit 123 with a voltage higher than the voltage of external power supply 200 .

[0022] 3B shows an equivalent circuit of a reverse connection in which a negative voltage is applied to the reactor 121 when the external power supply 200 is a DC power supply. In the reverse connection, the circuit elements contributing to operation are the reactor 121, the diodes 154b and 154c of the short-circuiting unit 126, the switch 125, the diodes 152b and 152c of the rectifying unit 122, and the smoothing unit 123. In the reverse connection, as shown by the dashed line in the figure, a short-circuit current flows through the path passing through the diode 154c, the switch 125, the diode 154b, and the reactor 121. This short-circuit current accumulates energy in the reactor 121. In the reverse connection, as shown by the solid line in the figure, a charging current flows through the path passing through the diode 152c, the smoothing unit 123, the diode 152b, and the reactor 121. This charging current charges the smoothing unit 123. Furthermore, when this charging current flows, the energy stored in reactor 121 is released, making it possible to charge smoothing unit 123 with a voltage higher than the voltage of external power supply 200 .

[0023] As described above, when the external power supply 200 is a DC power supply, the power conversion device 100 can be operated regardless of whether the connection is normal connection or reverse connection. This operation makes it possible to prevent damage to equipment due to incorrect connection of voltage polarity by using the power conversion device 100 according to the first embodiment.

[0024] Note that when the external power supply 200 is a DC power supply and the voltage of the external power supply 200 is constant, the control unit 400 basically repeatedly outputs a drive pulse with a constant duty ratio at a constant cycle, as shown in the lower part of FIG. 4A. The drive pulse is a drive signal for driving the switch 125 of the short-circuiting unit 126. The duty ratio of the drive pulse is the ratio between the on time and the off time of the drive pulse. In other words, when the external power supply 200 is a DC power supply, the duty ratio of the drive pulse for driving the switch 125 is controlled to a fixed value.

[0025] However, if the duty ratio is fixed, the voltage of the smoothing unit 123 will not be stable. For this reason, the duty ratio is changed appropriately so that the voltage of the smoothing unit 123, which changes depending on the operating state of the load 140, will have a desired value. In this way, it is possible to adjust the voltage value of the DC voltage output by the voltage conversion unit 120 to a desired value.

[0026] Furthermore, if the voltage value of the smoothing unit 123 becomes higher than the voltage value of the external power supply 200, a backflow may occur. Backflow is a phenomenon in which current flows from the smoothing unit 123 toward the external power supply 200. In the case of the configuration of the power conversion device 100 in this paper, including the power conversion device 100 described below, at least one of the diodes 152a to 152d of the rectification unit 122 performs a reverse blocking function, making it possible to prevent such backflow.

[0027] Furthermore, if the operating frequency of switch 125 of short-circuiting unit 126 is high, loss increases due to the recovery operation of diodes 152a to 152d of rectification unit 122. For this reason, it is desirable to use fast recovery diodes with short recovery times as diodes 152a to 152d.

[0028] 3, the power conversion device 100 supports positive and negative connections. Therefore, when an AC voltage whose polarity alternates over time is applied, the rectifier 122 functions as a full-wave rectifier circuit, making it possible to maintain a DC voltage in the smoothing unit 123. Furthermore, by appropriately operating the switch 125 of the short-circuiting unit 126, the energy stored in the reactor 121 can be appropriately varied, making it possible to boost the DC voltage of the smoothing unit 123 to a desired voltage value.

[0029] Furthermore, when the external power supply 200 is an AC power supply, the voltage value output from the external power supply 200 varies in a sinusoidal manner. Therefore, as shown in FIG. 4B , the on-time of the drive pulse is lengthened when the voltage value of the sine wave is near zero, and the on-time of the drive pulse is shortened near the positive or negative peak of the sine wave voltage. That is, the duty ratio of the drive pulse is relatively increased near the zero-crossing points of the sine wave, and the duty ratio of the drive pulse is relatively decreased near the positive or negative peak of the sine wave. By controlling in this manner, it is possible to make the current flowing through the external power supply 200 sinusoidal. Note that the voltage of the smoothing unit 123 varies depending on the operating state of the load 140, so it goes without saying that it is desirable to appropriately change the duty ratio of the drive pulse depending on the state of the load 140 and the voltage of the smoothing unit 123.

[0030] The features of the power conversion device 100 according to the first embodiment described above can be summarized as follows. First, in the power conversion device 100 according to the first embodiment, the operation of the switch 125 of the short-circuiting unit 126 changes depending on the voltage value output by the external power supply 200. Furthermore, when the switch 125 is configured as a first switching element, if the external power supply 200 is a DC power supply, the duty ratio between the on time and the off time of the drive pulse for driving the first switching element is controlled to a fixed value. On the other hand, if the external power supply 200 is an AC power supply, the duty ratio between the on time and the off time of the drive pulse for driving the first switching element changes depending on the voltage value of the AC power supply. Furthermore, in the power conversion device 100 according to the first embodiment, the voltage conversion unit 120 is configured to be operable whether the voltage applied via the reactor 121 is a DC voltage or an AC voltage, and is configured so that backflow from the smoothing unit 123 does not occur when the switch 125 is operating.

[0031] Next, further considerations in configuring the power conversion device 100 according to the first embodiment will be described. First, as described above, it is desirable to select diodes with short recovery times for the diodes 152a to 152d of the rectifier unit 122 in order to reduce recovery loss that occurs when the switch 125 is short-circuited. On the other hand, in the power conversion device 100 according to the first embodiment, it is necessary to consider the case where the external power supply 200 is an AC power supply. When the external power supply 200 is an AC power supply, the rectifier unit 122 performs full-wave rectification. Therefore, from the perspective of reducing conduction loss, diodes or MOSFETs with low forward voltage drop may be used for the diodes 152a to 152d of the rectifier unit 122.

[0032] 4B illustrates an operation in which drive pulses with different duty ratios are continuously output to form a sinusoidal current in the external power supply 200 when the external power supply 200 is an AC power supply. Meanwhile, the short-circuiting unit 126 can be controlled so that the switch 125 performs one or more switching operations during partial sections of each half cycle of the sinusoidal voltage. As the number of switching operations of the switch 125 increases, the proportion of conduction loss in the overall loss increases due to accumulated conduction losses. Therefore, if the proportion of conduction loss is a concern, the rectifier unit 122 may be configured with a MOSFET, and synchronous rectification control may be performed, in which the MOSFET is turned on when the MOSFET diode conducts, thereby conducting current through the channel side of the MOSFET. Synchronous rectification control eliminates conduction loss due to a forward voltage drop across the diode during synchronous rectification, thereby improving the efficiency of the rectifier unit 122.

[0033] Furthermore, in the power conversion device 100 according to the first embodiment, if it is not possible to determine whether the external power supply 200 supplies a DC voltage or an AC voltage, it is difficult to appropriately control the switch 125. Therefore, a voltage detection unit (not shown in FIG. 1 ) converts a signal corresponding to the voltage value applied to the power receiving terminal 128 into a value detectable by the processor 91 of the control unit 400 and outputs the converted signal to the control unit 400. For example, when a DC voltage is applied to the power receiving terminal 128, the voltage detection unit converts the converted signal into a low DC voltage of approximately 0 V to 5 V that can be detected by the processor 91 and outputs the converted signal to the control unit 400. When an AC voltage is applied to the power receiving terminal 128, the voltage detection unit outputs a signal that changes between 0 V and 5 V depending on whether the AC voltage is positive or negative to the control unit 400. This configuration enables the control unit 400 to determine whether a DC voltage or an AC voltage is applied to the power receiving terminal 128, thereby enabling appropriate and reliable control of the power conversion process in the power conversion device 100.

[0034] Furthermore, because the applied voltage differs between when connected to a DC power distribution system and when connected to an AC grid voltage, the operating state of the load 140 changes, resulting in performance variations depending on the connected power source. Even when only a DC power distribution system is connected, the DC voltage output by the DC power distribution system is expected to vary between 300 V and 400 V. For example, in Japan, a DC voltage of 282 V (=√2 × 200 V) is generated by full-wave rectifying an AC grid voltage of 200 V, while in the United States, Australia, and other countries, a DC voltage of 282 V (=√2 × 240 V) is generated by full-wave rectifying an AC grid voltage of 240 V. Therefore, similar issues arise in DC power distribution systems.

[0035] To address this issue, the power conversion device 100 according to the first embodiment adjusts the voltage value using the voltage conversion unit 120, and can boost the voltage to the minimum voltage necessary to drive the load 140. As a result, even if the voltage value applied to the power receiving terminal 128 varies, the performance of the power conversion device 100 is not degraded, and it is possible to provide a product that provides high levels of satisfaction to users.

[0036] 1 is configured to boost the voltage of the external power supply 200, but it may also be configured to lower the voltage of the external power supply 200. Even when the voltage of the external power supply 200 is lowered, the above-described effects can be obtained. However, with regard to the motor 142, the higher the applied voltage, the higher the back electromotive force, and therefore the motor can be driven with a smaller current, and the current flowing through the inverter 141 also becomes smaller. Therefore, if the voltage of the external power supply 200 is increased, the operating efficiency of the power conversion device 100 can be improved.

[0037] Furthermore, to achieve a highly efficient power conversion apparatus 100 that can operate with both DC and AC voltages, a design may be considered in which switching means are provided for one-way current-carrying elements, such as diodes, in the rectifier unit 122 to short-circuit both ends of each element, and the switching means is conductive when the short-circuiting unit 126 is not operating and is not conductive when the short-circuiting unit 126 is operating. Using an electromagnetic contactor as the switching means results in a highly efficient power conversion apparatus 100 because only losses equivalent to contact resistance occur in the electromagnetic contactor. However, using a mechanical switching means such as an electromagnetic contactor may result in excessive current flow through the power conversion apparatus 100 due to its slow switching operation. This is because a delay in opening the switching means when the short-circuiting unit 126 is operated would cause the smoothing unit 123 to enter a short-circuit state with low impedance. Therefore, using a mechanical switching means in the rectifier unit 122 for the purpose of increasing the efficiency of the power conversion apparatus 100 is not a preferable approach.

[0038] In contrast, if the rectifier unit 122 is configured with a MOSFET, the above problem does not occur. Because the MOSFET has a high switching speed, it is possible to reliably prevent a situation in which the MOSFET is conductive when the short-circuit unit 126 is operated. This makes it possible to reliably prevent backflow from the smoothing unit 123 to the external power supply 200 side.

[0039] It is also possible to use an IGBT, which is a unidirectional current-carrying element, instead of a MOSFET, which is a bidirectional element. When an IGBT is used, the collector of the IGBT is connected to the external power supply 200 side and the emitter is connected to the smoothing unit 123 side. However, in the case of an IGBT, a saturation voltage exists between the collector and emitter when the IGBT is conducting, which causes a loss similar to the voltage drop of a diode. Therefore, when replacing a diode with a switching element, it is desirable to use an element such as a MOSFET, which has small loss in the low current region.

[0040] Furthermore, as described above, when a motor with a high back electromotive force is used as the motor 142, the operating efficiency of the power conversion device 100 can be improved. Regardless of the specifications of the external power supply 200, when a motor 142 with a high back electromotive force is used, the reactor 121 is an essential component. Note that when the external power supply 200 is connected, there is a risk of an excessive inrush current flowing when charging the smoothing unit 123. However, if the reactor 121 is provided, it is possible to suppress the inrush current that may flow between the external power supply 200 and the smoothing unit 123.

[0041] Furthermore, when motor 142 is driven at a low speed, there is no need to perform a voltage boosting operation on voltage conversion unit 120. Taking such an operating mode into consideration, a switching means for short-circuiting both ends of reactor 121 may be provided from the viewpoint of improving efficiency. However, when external power supply 200 is a DC power supply and an electromagnetic contactor is used as the switching means, it is desirable to use an electromagnetic contactor that can avoid the problem of contact welding caused by arc discharge.

[0042] As described above, the power conversion device according to the first embodiment includes a power receiving terminal to which an external power source, which is a DC power source or an AC power source, can be connected, a voltage conversion unit capable of outputting the voltage applied to the power receiving terminal as a variable DC voltage, and a load connected to the output side of the voltage conversion unit. The voltage conversion unit includes a reactor that stores and releases energy, a short-circuiting unit having one or more switches, and a smoothing unit that smooths the DC voltage. The voltage conversion unit is configured to be operable whether the voltage applied via the reactor is a DC voltage or an AC voltage, and is configured to prevent backflow from the smoothing unit when the switch is operating. This makes it possible to obtain a power conversion device that can vary the voltage value depending on the operating status of the device, regardless of the polarity of the power supply voltage and the power supply specifications.

[0043] In the power conversion device according to the first embodiment, the switch may be a first switching element. In this configuration, the operation of the first switching element changes depending on the voltage value output by the external power supply. Furthermore, when the external power supply is a DC power supply, the duty ratio between the on time and the off time of a drive pulse for driving the first switching element is controlled to a fixed value. However, when the external power supply is an AC power supply, the duty ratio changes depending on the voltage value of the AC power supply.

[0044] Second Embodiment In a second embodiment, variations in the configuration of the voltage conversion unit 120 will be described with reference to the drawings in Fig. 5 to Fig. 8. Fig. 5 to Fig. 8 are diagrams showing configuration examples according to first to fourth modified examples of the voltage conversion unit 120 provided in the power conversion device 100 shown in Fig. 1. In Fig. 5 to Fig. 8, components that are the same as or equivalent to those in Fig. 1 are denoted by the same reference numerals, and duplicated descriptions will be omitted as appropriate.

[0045] In the first modified example shown in Fig. 5, the four diodes 152a to 152d constituting the rectifier unit 122 are replaced with switching elements 158a to 158d, respectively. Also, in Fig. 5, the short-circuit unit 126 having the rectifier circuit 124 and switch 125 that were present in Fig. 1 has been deleted, but in the configuration of the first modified example, the rectifier unit 122 has the function of the short-circuit unit 126. In this document, the switching elements 158a to 158d may be referred to as "second switching elements."

[0046] When the external power supply 200 is a DC power supply and a positive voltage is applied to the reactor 121 side, the short-circuit current shown in FIG. 3A can be caused to flow by turning on the switching element 158b or the switching element 158c. When a negative voltage is applied to the reactor 121 side, the short-circuit current shown in FIG. 3B can be caused to flow by turning on the switching element 158a or the switching element 158d. When the external power supply 200 is an AC power supply, a similar short-circuit current can be caused to flow by controlling the corresponding element to the ON state depending on whether the voltage polarity is positive or negative. These operations enable the same effects as those of the first embodiment to be achieved even when the power conversion device 100 according to the first modification is used.

[0047] When IGBTs are used for the switching elements 158a to 158d, the short-circuit operation described above is possible, but the current flow direction when the IGBTs are turned on is limited to one direction, so synchronous rectification control that is available with MOSFETs cannot be used. Therefore, when high efficiency is to be achieved, it is desirable to use MOSFETs.

[0048] 6, of the four diodes 152a to 152d that constitute the rectifier unit 122, the diodes 152b and 152d are replaced with switching elements 158b and 158d. In addition, in Fig. 6, the short-circuit unit 126 having the rectifier circuit 124 and the switch 125 that were present in Fig. 1 has been deleted, but in the configuration of the second modified example, the rectifier unit 122 has the function of the short-circuit unit 126.

[0049] When the external power supply 200 is a DC power supply, if a positive voltage is applied to the reactor 121 side, the short-circuit current shown in FIG. 3A can be caused to flow by turning on the switching element 158b. Also, when a negative voltage is applied to the reactor 121 side, the short-circuit current shown in FIG. 3B can be caused to flow by turning on the switching element 158d. Also, when the external power supply 200 is an AC power supply, if the corresponding element is controlled to be on depending on whether the voltage polarity is positive or negative, a similar short-circuit current can be caused to flow. These operations allow the use of the power conversion device 100 according to the second modification to achieve the same effects as those of the first embodiment.

[0050] When IGBTs are used for the switching elements 158b and 158d, the short-circuit operation described above is possible, but the current flow direction when the IGBTs are turned on is limited to one direction, so synchronous rectification control that is available with MOSFETs cannot be used. Therefore, when high efficiency is to be achieved, it is desirable to use MOSFETs.

[0051] 7, of the four diodes 152a to 152d that constitute the rectifier unit 122, the diodes 152c and 152d are replaced with switching elements 158c and 158d. In addition, in Fig. 7, the short-circuit unit 126 having the rectifier circuit 124 and the switch 125 that were present in Fig. 1 has been deleted, but in the configuration of the third modified example, the rectifier unit 122 has the function of the short-circuit unit 126.

[0052] When the external power supply 200 is a DC power supply, if a positive voltage is applied to the reactor 121 side, the short-circuit current shown in FIG. 3A can be caused to flow by turning on the switching element 158c. Also, if a negative voltage is applied to the reactor 121 side, the short-circuit current shown in FIG. 3B can be caused to flow by turning on the switching element 158d. Also, when the external power supply 200 is an AC power supply, if the corresponding element is controlled to be on depending on whether the voltage polarity is positive or negative, a similar short-circuit current can be caused to flow. These operations enable the same effects as those of the first embodiment to be obtained even when the power conversion device 100 according to the third modification is used.

[0053] When IGBTs are used for the switching elements 158c and 158d, the short-circuit operation described above is possible, but the current flow direction when the IGBTs are turned on is limited to one direction, so synchronous rectification control that is available with MOSFETs cannot be used. Therefore, when high efficiency is to be achieved, it is desirable to use MOSFETs.

[0054] 7, of the four diodes 152a to 152d that make up the rectifier 122, the diodes 152c and 152d are replaced with switching elements 158c and 158d, but the diodes 152a and 152b may also be replaced with switching elements 158a and 158b. Even with this replacement, the above-described operation can be performed, and the same effects as those of the first embodiment can be obtained.

[0055] 8 , a reactor 121 is disposed downstream of the rectifier 122, and a short-circuiting unit 126 is disposed between the reactor 121 and the smoothing unit 123. The short-circuiting unit 126 includes a switch 125 and a diode 155a. The diode 155a is a one-way current-carrying element, and is connected in a direction that prevents reverse current from flowing from the smoothing unit 123 side to the external power supply 200 side.

[0056] 8, even when the external power supply 200 is a DC power supply and a positive voltage or a negative voltage is applied to the reactor 121 side, or even when the external power supply 200 is an AC power supply, the voltage of the smoothing unit 123 can be boosted by turning on and off the switch 125 of the short-circuiting unit 126. With these operations, even when the power conversion device 100 according to the fourth modification is used, the same effects as those of the first embodiment can be obtained.

[0057] As described above, the power conversion device according to the second embodiment includes a power receiving terminal to which an external power source, such as a DC power source or an AC power source, can be connected, a voltage conversion unit capable of outputting a voltage applied to the power receiving terminal as a variable DC voltage, and a load connected to the output side of the voltage conversion unit. The voltage conversion unit includes a reactor that stores and releases energy, a short-circuiting unit having one or more switches, and a smoothing unit that smooths the DC voltage, the smoothing unit having at least one second switching element that performs a rectifying operation. The voltage conversion unit is configured to operate whether the voltage applied via the reactor or the voltage applied without passing through the reactor is a DC voltage or an AC voltage, and is configured so that backflow from the smoothing unit does not occur when the switch is operating. This makes it possible to obtain a power conversion device that can adjust the voltage value according to the operating status of the device, regardless of the polarity of the power supply voltage and the power supply specifications.

[0058] In the power conversion device according to the second embodiment, the second switching element may be configured as a MOSFET. When the second switching element is a MOSFET, the forward voltage drop during conduction is reduced, thereby enabling the rectifier unit to operate more efficiently. Furthermore, when the second switching element is a MOSFET, the rectifier unit can operate even more efficiently if synchronous rectification control is also used.

[0059] Third Embodiment. FIG. 9 is a diagram showing a configuration example of a power conversion device 100 according to a third embodiment. In FIG. 9, components that are the same as or equivalent to those in FIG. 8 are denoted by the same reference numerals, and redundant description will be omitted where appropriate. In the power conversion device 100 according to the third embodiment, the configuration of the rectifier unit 122 in FIG. 8 is changed from a full-bridge connection to a three-phase bridge connection. As with the first and second embodiments, the power conversion device 100 according to the third embodiment assumes that power is supplied from an external power source 200, such as a DC power distribution system or an AC power supply system, and further assumes that the AC power supply system may be three-phase. For this reason, the power conversion device 100 has three power receiving terminals 128 that can be connected to a three-phase power supply system. Other functions are equivalent to those of the first embodiment.

[0060] When the external power source 200 is a DC power distribution system, the power conversion device 100 can vary the voltage charged to the smoothing unit 123 by connecting a DC power source to any two of the three power receiving terminals 128 and operating the switch 125 of the short-circuiting unit 126.

[0061] In the power conversion device 100 according to the third embodiment, which is compatible with a three-phase power supply, if the external power supply 200 is a DC power supply, one of the three power receiving terminals 128 will be left unused. Compared to the configuration of FIG. 1 , when attempting to drive the same load 140, current will no longer flow through one phase of the rectifier 122, and the current that has been lost will be added to the other phases. As a result, approximately 1.5 times the current will flow through each of the diodes 152a to 152f of the rectifier 122 compared to when the rectifier 122 is designed for a three-phase power supply. Therefore, heat generation in the rectifier 122 can be addressed by designing it for a DC power supply. For example, it is desirable to select elements with a current rating for the diodes 152a to 152f in the rectifier 122 that has a margin of approximately 1.5 times the current rating when operating with only a three-phase power supply.

[0062] The power conversion device 100 according to the third embodiment can operate when any power supply of any specifications is connected, including when the external power supply 200 is a three-phase power supply system, and can use a variable power supply voltage, so that it can be operated at an optimum operating point according to the operating state of the load 140.

[0063] Furthermore, the power conversion device 100 according to the third embodiment can be manufactured with the same model name and circuit configuration regardless of the type of external power supply 200, which has the advantage of eliminating the need for increased management costs due to an increase in the number of models and individual designs for different power sources. Furthermore, even if a contractor or other person installing the equipment mistakenly connects a different power source, the equipment can still operate normally, thereby achieving high reliability.

[0064] As described above, in the power conversion device according to embodiment 3, a DC power supply, a single-phase AC power supply, or a three-phase AC power supply can be connected to the power receiving terminals, and devices can be manufactured with the same model name and circuit configuration regardless of the type of external power supply, which makes it possible to obtain the effect of eliminating the increase in management costs due to an increase in the number of models and the need for individual designs according to the type of power supply.In order to obtain this effect, the current rating of the rectifying elements provided in the voltage conversion unit is selected to be 1.5 times the current rating per phase when a three-phase AC power supply is connected to the power receiving terminals.

[0065] Fourth Embodiment In a fourth embodiment, a heat pump device will be described as an example of a device to which the power conversion device 100 described in any of the first to third embodiments can be applied. Fig. 10 is a diagram showing a configuration example of a heat pump device 900 according to the fourth embodiment. The heat pump device 900 according to the fourth embodiment includes the power conversion device 100 described in any of the first to third embodiments.

[0066] The heat pump device 900 also includes a refrigeration cycle in which a four-way valve 902 , a compressor 903 , a heat exchanger 906 , an expansion valve 908 , and a heat exchanger 910 are attached via a refrigerant pipe 912 .

[0067] The compressor 903 is provided with a compression mechanism 904 that compresses the refrigerant circulating inside the refrigerant pipe 912, and a motor 905 that operates the compression mechanism 904. The motor 905 is driven by receiving a supply of electric power from the power conversion device 100.

[0068] The heat pump device 900 having such a configuration can be used, for example, in an air conditioner, a heat pump water heater, a refrigerator, a freezer, etc. Although a fan motor is not shown in Fig. 10, the power conversion device 100 described in the first to third embodiments can be used in a motor drive device that drives a fan motor.

[0069] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0070] 91 processor, 92 memory, 93 interface, 100 power conversion device, 120 voltage conversion unit, 121 reactor, 122 rectification unit, 123 smoothing unit, 124 rectification circuit, 125 switch, 126 short-circuit unit, 128 power receiving terminal, 140 load, 141 inverter, 142, 905 motor, 152a to 152f, 154a to 154d, 155a diode, 156a to 156f, 158a to 158d switching element, 200 external power source, 400 control unit, 900 heat pump device, 902 four-way valve, 903 compressor, 904 compression mechanism, 906, 910 heat exchanger, 908 expansion valve, 912 refrigerant piping.

Claims

1. A power conversion device comprising: a power receiving terminal to which an external power source which is a DC power source or an AC power source can be connected; a voltage conversion unit which can output the voltage applied to the power receiving terminal as a variable DC voltage; and a load connected to the output side of the voltage conversion unit, wherein the voltage conversion unit comprises a reactor which stores and releases energy, a short-circuiting unit having one or more switches, and a smoothing unit which smooths the DC voltage, wherein the voltage conversion unit is configured to be able to operate whether the voltage applied via the reactor or the voltage applied without passing through the reactor is a DC voltage or an AC voltage, and is configured so that backflow from the smoothing unit does not occur when the switch is operating.

2. The power conversion device according to claim 1, wherein the switch is formed by a first switching element, and the operation of the first switching element changes depending on the voltage value output by the external power supply.

3. The power conversion device according to claim 2, wherein when the external power supply is a DC power supply, the duty ratio between the on time and the off time of the drive pulse for driving the first switching element is controlled to a fixed value.

4. The power conversion device according to claim 2, wherein, when the external power supply is an AC power supply, the time ratio between the on time and the off time of the drive pulse for driving the first switching element varies according to the voltage value of the AC power supply.

5. The power conversion device according to claim 1, wherein a DC power supply, a single-phase AC power supply or a three-phase AC power supply can be connected to the power receiving terminal, and the current rating of the rectifier element provided in the voltage conversion unit is 1.5 times the current rating per phase when a three-phase AC power supply is connected to the power receiving terminal.

6. The power conversion device according to any one of claims 1 to 5, wherein the voltage conversion unit has at least one second switching element that performs a rectifying operation, and the second switching element is a MOSFET.

7. A heat pump device comprising the power conversion device according to any one of claims 1 to 6.

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