Power conversion device, motor drive device, and refrigeration cycle application device

Abstract

A power conversion device (1) is provided with a step-up / down converter (150) that converts an input voltage into a DC voltage, steps up or steps down the converted DC voltage, and outputs the step-up or step-down DC voltage. The power conversion device (1) applies a bus voltage to a load (100), said bus voltage being output from the step-up / down converter (150) to DC bus bars (420, 422). When an abnormality in the bus voltage is detected during the step-up operation of the step-up / down converter (150), the operation of the step-up / down converter (150) is switched to the step-down operation. When an abnormality in the bus voltage is detected during the step-down operation of the step-up / down converter (150), the operation of the step-up / down converter (150) is switched to the step-up operation.

Description

Power conversion devices, motor drive devices, and refrigeration cycle application equipment

[0001] The present disclosure relates to a power conversion device that performs power conversion, a motor drive device, and a refrigeration cycle application device.

[0002] Conventionally, there are power conversion devices that include a converter and an inverter. Some converters not only convert an input AC voltage to a DC voltage but also boost or buck the input AC voltage while converting it to a DC voltage. Such converters are called "buck-boost converters." Patent Document 1 listed below discloses a technique for a DC brushless motor drive device that controls the output voltage of a buck-boost converter so that a DC brushless motor rotates at a desired speed. In a configuration such as that of the DC brushless motor drive device described in Patent Document 1, it is possible to rotate a DC brushless motor at a desired speed by controlling the operation of the buck-boost converter and the inverter.

[0003] Japanese Patent Application Laid-Open No. 2003-143890

[0004] However, in the DC brushless motor drive device described in Patent Document 1, if the load operation suddenly changes due to an external disturbance or abnormal situation while the step-up / step-down converter is performing a step-up operation to step up the bus voltage or a step-down operation to step down the bus voltage, the bus voltage may rise or fall unexpectedly, and the bus voltage may deviate from the range in which the power converter can continue to operate, which may result in an abnormal shutdown of the power conversion device or a failure of the power conversion device.

[0005] The present disclosure has been made in view of the above, and aims to provide a power conversion device that can prevent abnormal shutdown and failure of the device that may occur due to an abnormal rise or fall in bus voltage.

[0006] In order to solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure includes a buck-boost converter that converts an input voltage into a DC voltage and outputs the converted DC voltage by stepping up or stepping down, and applies a bus voltage output from the buck-boost converter to a DC bus to a DC load. If an abnormality in the bus voltage is detected during boost operation of the buck-boost converter, the operation of the buck-boost converter is switched to buck operation. Also, if an abnormality in the bus voltage is detected during buck operation of the buck-boost converter, the operation of the buck-boost converter is switched to boost operation.

[0007] The power conversion device according to the present disclosure has the advantage of being able to prevent abnormal shutdowns and breakdowns of the device that may occur due to an abnormal rise or fall in bus voltage.

[0008] FIG. 1 is a diagram showing an example of the configuration of a power conversion device according to embodiment 1. FIG. 2 is a diagram showing fluctuations in bus voltage and load power within a normal range during boost operation of the power conversion device according to embodiment 1. FIG. 3 is a diagram showing fluctuations in bus voltage and load power that are considered to be abnormal during boost operation of the power conversion device according to embodiment 1. FIG. 4 is a diagram explaining a control method performed when a sudden decrease in load power occurs during boost operation of the power conversion device according to embodiment 1. FIG. 5 is a flowchart explaining a control method in embodiment 1 performed when a sudden decrease in load power occurs. FIG. 6 is a diagram explaining a control method in embodiment 1 performed when a sudden increase in load power occurs during step-down operation of the power conversion device according to embodiment 1. FIG. 7 is a flowchart explaining a control method in embodiment 1 performed when a sudden increase in load power occurs. FIG. 8 is a diagram showing an example of a hardware configuration for realizing a control unit provided in the power conversion device according to embodiment 1. FIG. 9 is a diagram showing the relationship between the rotation speed of a motor provided in the load shown in FIG. 1 and the voltage generated by the motor. FIG. 10 is a diagram showing an example of the configuration of a power conversion device according to embodiment 3. FIG. 11 is a diagram showing an example of the configuration of a power conversion device according to embodiment 4. FIG. 12 is a diagram showing an example of the configuration of a power conversion device according to embodiment 4. FIG. 13 is a diagram showing an example of the configuration of a refrigeration cycle application device according to embodiment 5.

[0009] Hereinafter, a power conversion device, a motor drive device, and a refrigeration cycle applied device according to embodiments of the present disclosure will be described in detail with reference to the drawings.

[0010] First Embodiment Fig. 1 is a diagram showing an example of the configuration of a power conversion device 1 according to a first embodiment. The power conversion device 1 is connected to an AC power supply 110 and a load 100. The power conversion device 1 converts an AC voltage applied from the AC power supply 110, such as a commercial power supply, into a DC voltage and applies the DC voltage to the load 100. The load 100 is a DC load that operates on a DC voltage. In the example of Fig. 1, the AC power supply 110 is a single-phase AC power supply, but may also be a three-phase AC power supply.

[0011] The power conversion device 1 includes a noise filter 120 and a step-up / step-down converter 150. The step-up / step-down converter 150 includes a rectifier circuit 130, a step-up / step-down circuit 140, a control unit 400, a current detection unit 502, and a voltage detection unit 506. The power conversion device 1 and the load 100 form a motor drive device 2.

[0012] The power conversion device 1 and the load 100 are connected by DC buses 420 and 422. The DC bus 420 is a DC bus on the high potential side, and the DC bus 422 is a DC bus on the low potential side. The load 100 is a DC load that operates on a DC voltage. The DC voltage converted by the power conversion device 1 is applied to the load 100. The load 100 includes an inverter 310, a motor 314, and a current detection unit 504.

[0013] The inverter 310 has six switching elements 311 connected in a three-phase bridge configuration. A freewheeling diode 312 is connected in parallel to each of the six switching elements 311. The switching elements 311 may be, for example, an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET), or a bipolar transistor, but are not limited to these. A DC voltage is applied to the inverter 310 via DC buses 420 and 422. In this document, this DC voltage is referred to as a "bus voltage" as appropriate.

[0014] In the inverter 310, six switching elements 311 are turned on and off under the control of the control unit 400, converting the applied DC voltage into a three-phase AC voltage to drive the motor 314. In this paper, an interior permanent magnet synchronous motor is assumed as the motor 314. Note that although the illustrated motor 314 is a three-phase motor, the motor 314 may also be a single-phase motor. If the motor 314 is a single-phase motor, the inverter 310 is configured with a single-phase bridge circuit.

[0015] The noise filter 120 removes noise from the AC voltage supplied from the AC power supply 110. The noise filter 120 may have a general configuration and is not particularly limited. The noise filter 120 outputs the AC voltage after noise removal to the step-up / step-down converter 150. Note that the noise filter 120 is not an essential component of the power conversion device 1. That is, the power conversion device 1 may be configured without the noise filter 120.

[0016] The step-up / step-down converter 150 is a power converter connected in parallel to both ends of the input terminal of the inverter 310. The step-up / step-down converter 150 converts an input voltage into a DC voltage, and outputs the converted DC voltage to the load 100 by stepping up or down the voltage. The step-up / step-down converter 150 described in the first embodiment is an AC (Alternating Current)-DC (Direct Current) converter. That is, the step-up / step-down converter 150 described in the first embodiment is an AC-DC converter that is connected to the AC power supply 110 and converts the input voltage applied from the AC power supply 110 into a bus voltage.

[0017] The step-up / step-down converter 150 includes a rectifier circuit 130 and a step-up / step-down circuit 140. The rectifier circuit 130 rectifies the noise-removed AC voltage output from the noise filter 120, and outputs the rectified voltage to the step-up / step-down circuit 140. When the AC power supply 110 is a single-phase AC power supply as shown in FIG. 1 , the rectifier circuit 130 is a bridge circuit configured by four rectifier elements 131.

[0018] The step-up / step-down circuit 140 includes a switching element 141, a freewheeling diode 142, a reactor 143, a diode 144, a detection resistor 502a, and a smoothing capacitor 210. The step-up / step-down circuit 140 steps up or steps down the rectified voltage output from the rectifier circuit 130 and outputs the resulting voltage to the inverter 310. In the step-up / step-down circuit 140, the switching element 141 is turned on and off under the control of the control unit 400, and the rectified voltage output from the rectifier circuit 130 is stepped up or down by the switching element 141, the freewheeling diode 142, the reactor 143, and the diode 144. The switching element 141 may be, for example, an IGBT, a MOSFET, a bipolar transistor, or the like, but is not limited to these.

[0019] The smoothing capacitor 210 smoothes the rectified voltage that has been stepped up or down by the switching element 141, the freewheeling diode 142, the reactor 143, and the diode 144, and outputs the smoothed DC voltage to the DC buses 420 and 422. The smoothing capacitor 210 is, for example, an electrolytic capacitor or a film capacitor.

[0020] The smoothing capacitor 210 may be disposed outside the buck-boost converter 150. That is, the smoothing capacitor 210 may be connected to a main circuit inside the buck-boost converter 150, or may be connected to a main circuit outside the buck-boost converter 150 between the buck-boost converter 150 and the inverter 310.

[0021] 1, the step-up / step-down converter 150 is configured by the rectifier circuit 130 and the step-up / step-down circuit 140, but the configuration of the step-up / step-down converter 150 is not limited to the example in Fig. 1. The step-up / step-down converter 150 may be configured such that the rectifier circuit 130 and the step-up / step-down circuit 140 are integrated together.

[0022] The current detection unit 502 is located downstream of the rectifier circuit 130 and detects the rectified current flowing in and out of the rectifier circuit 130. The current detection unit 502 is connected to a detection resistor 502a and detects the rectified current by measuring the current flowing through the detection resistor 502a. Although not shown in the figure, the current detection unit 502 outputs the detected value of the rectified current, i.e., the current value of the rectified current, to the control unit 400.

[0023] The current detection unit 504 is located in the upstream stage of the inverter 310 and detects the inverter input current flowing in and out of the inverter 310. By detecting the inverter input current, it is possible to estimate the motor current flowing in the motor 314. The current detection unit 504 is connected to a detection resistor 504a and detects the inverter input current by measuring the current flowing through the detection resistor 504a. Although not shown in the figure, the current detection unit 504 outputs the detected value of the inverter input current, i.e., the current value of the inverter input current, to the control unit 400. The voltage detection unit 506 detects the bus voltage output by the buck-boost converter 150. Although not shown in the figure, the voltage detection unit 506 outputs the detected value of the bus voltage, i.e., the voltage value of the bus voltage, to the control unit 400.

[0024] The control unit 400 acquires detection values ​​from the current detection units 502 and 504 and the voltage detection unit 506. The control unit 400 uses the acquired detection values ​​to control the operation of the switching element 141 included in the step-up / step-down circuit 140 of the step-up / step-down converter 150 and the switching element 311 included in the inverter 310. The control unit 400 performs control calculations to control the on / off of the switching elements 141 and 311, and generates and outputs control signals to control the on / off of the switching elements 141 and 311. In particular, the control unit 400 calculates a target bus voltage, which is a target value of the bus voltage, by the control calculations, and performs feedback control on the step-up / step-down converter 150 so that the detection value of the voltage detection unit 506 becomes the target bus voltage.

[0025] The power conversion device 1 may further include a current detection unit installed at a position not shown in Fig. 1. The power conversion device 1 may further include a voltage detection unit installed at a position not shown in Fig. 1. The control unit 400 may use detected values ​​from these detection units not shown to control the operation of the switching element 141 included in the step-up / step-down circuit 140 of the step-up / step-down converter 150 and the switching element 311 included in the inverter 310. The positions of the detection units such as the current detection unit and the voltage detection unit further installed in the power conversion device 1 may be similar to the positions of detection units installed in a general power conversion device, and are not particularly limited.

[0026] Next, key points of control in the power conversion device 1 according to the first embodiment will be described with reference to FIGS. 2 to 7 . FIG. 2 is a diagram illustrating fluctuations in the bus voltage and load power within normal ranges during boost operation of the power conversion device 1 according to the first embodiment. FIG. 3 is a diagram illustrating fluctuations in the bus voltage and load power that are considered to be abnormal during boost operation of the power conversion device 1 according to the first embodiment. FIG. 4 is a diagram illustrating a control method performed when a sudden decrease in load power occurs during boost operation of the power conversion device 1 according to the first embodiment. FIG. 5 is a flowchart illustrating the control method performed in the first embodiment when a sudden decrease in load power occurs. FIG. 6 is a diagram illustrating a control method performed when a sudden increase in load power occurs during step-down operation of the power conversion device 1 according to the first embodiment. FIG. 7 is a flowchart illustrating the control method performed in the first embodiment when a sudden increase in load power occurs.

[0027] 2, the upper side shows the waveform of the bus voltage when the power conversion device 1 is performing a boost operation as a solid line, and the target bus voltage calculated by the control unit 400 as a dashed line. The lower side shows the waveform of the load power consumed by the load 100. In both the upper and lower sides, the horizontal axis represents time.

[0028] During operation of the power conversion device 1, if the operation of the buck-boost converter 150 is constant, i.e., if the control signal to the buck-boost converter 150 is always constant, then an increase in load power will cause the bus voltage to decrease, and a decrease in load power will cause the bus voltage to increase. However, in the power conversion device 1 according to embodiment 1, feedback control of the bus voltage is performed on the buck-boost converter 150. Therefore, even if fluctuations in load power occur, the bus voltage can be maintained at the target bus voltage by changing the control signal in response to the fluctuations in the bus voltage. The lower part of Figure 2 shows how the load power decreases normally, but when feedback control of the bus voltage is performed, the bus voltage operates to track the target bus voltage, as shown in the upper part of Figure 2.

[0029] On the other hand, as shown in the lower part of Fig. 3, if some abnormality occurs in the power conversion device 1 and a sudden decrease in load power occurs at a speed that exceeds the control response of the feedback control of the bus voltage, the feedback control of the bus voltage will not be able to keep up, and the bus voltage will deviate from the target bus voltage and suddenly rise, as shown in the upper part of Fig. 3. Although not shown, when the power conversion device 1 is in a step-down operation, the bus voltage may also deviate from the target bus voltage and suddenly drop. This phenomenon is thought to occur when the response value of the bus voltage fluctuation due to an abnormal increase or decrease in load power is higher than the response value of the bus voltage control in the control of the buck-boost converter 150, and some control ingenuity is required to keep the bus voltage within a certain set value range.

[0030] Therefore, in the power conversion device 1 according to the first embodiment, when a sudden decrease in load power occurs and the bus voltage rises sharply during the boost operation of the boost-buck converter 150, the control shown in Figures 4 and 5 is performed to suppress the sudden rise in the bus voltage.

[0031] First, the control unit 400 compares the bus voltage with a threshold value A (step S11). As shown in FIG. 4, the threshold value A is set to a value greater than the target bus voltage. If the bus voltage does not exceed the threshold value A (step S12, Yes), the process returns to step S11, and the process of step S11 is repeated. On the other hand, if the bus voltage exceeds the threshold value A (step S12, No), the control unit 400 forcibly switches the operation of the buck-boost converter 150 to buck operation (step S13).

[0032] After the process of step S13, the control unit 400 compares the bus voltage with threshold C (step S14). As shown in FIG. 4, threshold C is set to a value smaller than the target bus voltage. Therefore, threshold C is smaller than threshold A. If the bus voltage is not lower than threshold C (step S15, Yes), the process returns to step S14, and the process of step S14 is repeated. On the other hand, if the bus voltage is lower than threshold C (step S15, No), the control unit 400 returns the operation of the boost-buck converter 150 to boost operation (step S16). Thereafter, the process returns to step S11, and the process from step S11 is repeated.

[0033] In the determination process of step S12 described above, when the bus voltage is equal to threshold A, the determination is "Yes," but it may also be "No." That is, when the bus voltage is equal to threshold A, the determination may be either "Yes" or "No." In addition, in the determination process of step S15 described above, when the bus voltage is equal to threshold C, the determination is "Yes," but it may also be "No." That is, when the bus voltage is equal to threshold C, the determination may be either "Yes" or "No."

[0034] 5, the processes of steps S11 and S12 correspond to the abnormal rise determination process in the first embodiment, and the processes of steps S14 and S15 correspond to the abnormal rise elimination determination process in the first embodiment. In FIG. 5, an example of the abnormal rise determination process is shown in which the bus voltage is compared with the threshold value A, but the process is not limited to this. Other processes may be used as long as it is possible to determine the abnormal rise. In FIG. 5, an example of the abnormal rise elimination determination process is shown in which the bus voltage is compared with the threshold value C, but the process is not limited to this. Other processes may be used as long as it is possible to determine the elimination of the abnormal rise.

[0035] As described above, in the power conversion device 1 according to the first embodiment, if an abnormality in the bus voltage is detected during the boost operation of the buck-boost converter 150, the operation of the buck-boost converter 150 is forcibly switched to buck operation. Switching the operation of the buck-boost converter 150 to buck operation during the boost operation results in an operation that counteracts the increase in the bus voltage, thereby making it possible to suppress the increase in the bus voltage. Furthermore, although it is anticipated that this operation switch will cause the bus voltage to drop too much, the power conversion device 1 according to the first embodiment does not continue the forcible buck operation, but instead performs a process of returning the operation of the buck-boost converter 150 to boost operation based on a threshold value, i.e., a process of returning to boost operation. This makes it possible to control the bus voltage so that it falls within a desired range near the target bus voltage in a shorter time after the sudden decrease in load power subsides.

[0036] Although the operation diagram shown in FIG. 4 and the flowchart in FIG. 5 assume that the target bus voltage is constant, the value of the target bus voltage may be adjusted during the above-described control. For example, the target bus voltage may be reduced after the bus voltage exceeds threshold A and the operation of the buck-boost converter 150 is switched to buck operation. In this case, the target bus voltage may be reduced more the greater the difference between the value by which the bus voltage exceeds threshold A, i.e., the value at the time when the bus voltage exceeds threshold A, and the peak value at which the bus voltage starts to decrease. When the value by which the bus voltage exceeds threshold A is large, the bus voltage needs to be reduced more quickly. However, if the target bus voltage is controlled to be reduced more after switching to buck operation, it becomes easier to keep the bus voltage within the desired range, and the bus voltage can be reduced within the desired range in a shorter time.

[0037] Similarly, for example, after the bus voltage falls below threshold C and the operation of the buck-boost converter 150 is switched to boost operation, the value of the target bus voltage may be increased. In this case, the greater the difference between the value by which the bus voltage falls below threshold C, i.e., the value at the time when it falls below threshold C and the bottom value at which the bus voltage starts to rise, the greater the increase in the value of the target bus voltage. When the value by which the bus voltage falls below threshold C is large, the bus voltage needs to be increased more quickly. However, if the target bus voltage is controlled to be increased more after switching to boost operation, it becomes easier to keep the bus voltage within the desired range, and the bus voltage can be kept within the desired range in a shorter time.

[0038] Furthermore, in the power conversion device 1 according to the first embodiment, when a sudden increase in load power occurs and the bus voltage drops suddenly during the step-down operation of the step-up / step-down converter 150, the control shown in FIGS. 6 and 7 is performed so that the operation of the power conversion device 1 can be continued.

[0039] First, the control unit 400 compares the bus voltage with a threshold value B (step S21). As shown in FIG. 6, the threshold value B is set to a value smaller than the target bus voltage. If the bus voltage is not lower than the threshold value B (step S22, Yes), the process returns to step S21, and the process of step S21 is repeated. On the other hand, if the bus voltage is lower than the threshold value B (step S22, No), the control unit 400 forcibly switches the operation of the buck-boost converter 150 to boost operation (step S23).

[0040] After the process of step S23, the control unit 400 compares the bus voltage with threshold value D (step S24). As shown in FIG. 6, threshold value D is set to a value greater than the target bus voltage. Therefore, threshold value D is greater than threshold value B. If the bus voltage does not exceed threshold value D (step S25, Yes), the process returns to step S24, and the process of step S24 is repeated. On the other hand, if the bus voltage exceeds threshold value D (step S25, No), the control unit 400 returns the operation of the buck-boost converter 150 to buck operation (step S26). Thereafter, the process returns to step S21, and the process from step S21 is repeated.

[0041] In the determination process of step S22 described above, when the bus voltage is equal to threshold value B, the determination is "Yes," but the determination may also be "No." That is, when the bus voltage is equal to threshold value B, the determination may be either "Yes" or "No." In addition, in the determination process of step S25 described above, when the bus voltage is equal to threshold value D, the determination is "Yes," but the determination may also be "No." That is, when the bus voltage is equal to threshold value D, the determination may be either "Yes" or "No."

[0042] 7, the processes of steps S21 and S22 correspond to the abnormal decrease determination process in the first embodiment, and the processes of steps S24 and S25 correspond to the abnormal decrease elimination determination process in the first embodiment. Although FIG. 7 illustrates an example of the abnormal decrease determination process in which the bus voltage is compared with the threshold value B, the process is not limited to this. Other processes may be used as long as they can determine the abnormal decrease. Furthermore, FIG. 7 illustrates an example of the abnormal decrease elimination determination process in which the bus voltage is compared with the threshold value D, but the process is not limited to this. Other processes may be used as long as they can determine the elimination of the abnormal decrease.

[0043] As described above, in the power conversion device 1 according to the first embodiment, if an abnormality in the bus voltage is detected during the buck operation of the buck-boost converter 150, the operation of the buck-boost converter 150 is forcibly switched to the boost operation. Switching the operation of the buck-boost converter 150 to the boost operation during the buck operation counteracts the bus voltage drop, thereby suppressing the bus voltage drop. Furthermore, although it is anticipated that this operation switch will cause the bus voltage to rise too much, the power conversion device 1 according to the first embodiment does not continue the forcible boost operation, but instead performs a process of returning the operation of the buck-boost converter 150 to the buck operation based on a threshold value, i.e., a process of returning to the buck operation. This makes it possible to control the bus voltage so that it falls within a desired range near the target bus voltage in a shorter time after a sudden increase in load power subsides.

[0044] Although the operation diagram shown in FIG. 6 and the flowchart in FIG. 7 assume that the target bus voltage is constant, the value of the target bus voltage may be adjusted during the above-described control. For example, the target bus voltage may be increased after the bus voltage falls below threshold B and the operation of the buck-boost converter 150 is switched to boost operation. In this case, the target bus voltage may be increased more the greater the difference between the value at which the bus voltage falls below threshold B, i.e., the value at which the bus voltage falls below threshold B, and the bottom value at which the bus voltage starts to rise. When the bus voltage falls below threshold B by a large amount, the bus voltage needs to be increased more quickly. However, if the target bus voltage is controlled to be increased more after switching to boost operation, it becomes easier to keep the bus voltage within the desired range, and the bus voltage can be brought within the desired range in a shorter time.

[0045] Similarly, for example, after the bus voltage exceeds threshold D and the operation of buck-boost converter 150 is switched to buck operation, the value of the target bus voltage may be reduced. In this case, the greater the difference between the value by which the bus voltage exceeds threshold D, i.e., the value at which it exceeds threshold D, and the peak value at which the bus voltage starts to decrease, the greater the reduction in the value of the target bus voltage. When the value by which the bus voltage exceeds threshold D is large, the bus voltage needs to be reduced more quickly. However, if the target bus voltage is controlled to be reduced more after switching to buck operation, it becomes easier to keep the bus voltage within the desired range, and the bus voltage can be kept within the desired range in a shorter time.

[0046] As described above, according to the power conversion device 1 of the first embodiment, if an abnormality in the bus voltage is detected during the boost operation of the buck-boost converter 150, the operation of the buck-boost converter 150 is switched to the buck operation. Specifically, when the bus voltage exceeds threshold A, which is a first threshold value that is higher than the target bus voltage, the operation of the buck-boost converter 150 is switched to the buck operation. This operation suppresses an abnormal rise in the bus voltage in the power conversion device 1. Therefore, by using the power conversion device 1 of the first embodiment, it is possible to prevent abnormal shutdowns and failures of the device that may occur due to an abnormal rise in the bus voltage.

[0047] Furthermore, according to the power conversion device 1 of the first embodiment, if an abnormality in the bus voltage is detected during the buck operation of the buck-boost converter 150, the operation of the buck-boost converter 150 is switched to the boost operation. Specifically, when the bus voltage falls below threshold B, which is a second threshold value that is lower than the target bus voltage, the operation of the buck-boost converter 150 is switched to the boost operation. This operation suppresses an abnormal drop in the bus voltage in the power conversion device 1. Therefore, by using the power conversion device 1 of the first embodiment, it is possible to prevent abnormal shutdowns and failures of the device that may occur due to an abnormal drop in the bus voltage.

[0048] Furthermore, in the power conversion device 1 according to the first embodiment, after an abnormal rise in the bus voltage is detected and the operation of the buck-boost converter 150 is switched to the buck operation, if the bus voltage drops to a third threshold C that is lower than the target bus voltage, the buck operation is stopped and the normal buck operation is resumed. This operation makes it possible to control the bus voltage so that it falls within a desired range around the target bus voltage in a shorter time after the sudden decrease in load power subsides.

[0049] Furthermore, in the power conversion device 1 according to the first embodiment, after an abnormal drop in the bus voltage is detected and the operation of the buck-boost converter 150 is switched to the boost operation, if the bus voltage rises to a fourth threshold D that is higher than the target bus voltage, the boost operation is stopped and the operation returns to the normal buck operation. This operation makes it possible to control the bus voltage so that it falls within a desired range near the target bus voltage in a shorter time after the sudden increase in load power subsides.

[0050] In the power conversion device 1 according to the first embodiment, the control unit 400 may adjust the value of the target bus voltage when performing the above control. Specifically, the control unit 400 may decrease the target bus voltage in the step-down operation as the amount by which the bus voltage exceeds the threshold A increases, or may increase the target bus voltage in the step-up operation as the amount by which the bus voltage falls below the threshold B increases. By using such controls in combination, it becomes possible to bring the bus voltage within a desired range in a shorter time.

[0051] Furthermore, in the power conversion device 1 according to the first embodiment, the operation of the buck-boost converter 150 may be switched to the buck operation or the boost operation when an abnormality occurs in the bus voltage when the response value of the bus voltage fluctuation due to an abnormal rise or fall is higher than the response value of the bus voltage control in the control of the buck-boost converter 150. In this way, the control of the first embodiment can be limited to cases where it is truly necessary, thereby providing the effect of preventing unnecessary reductions in the operating efficiency of the power conversion device 1.

[0052] Finally, a description will be given of the hardware configuration of the control unit 400 included in the power conversion device 1. Fig. 8 is a diagram showing an example of a hardware configuration realizing the control unit 400 included in the power conversion device 1 according to embodiment 1. The control unit 400 is realized by a processor 91 and a memory 92.

[0053] The processor 91 is a CPU (Central Processing Unit, also called a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor)) or a system LSI (Large Scale Integration). Examples of memory 92 include non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), and EEPROM (Electrically Erasable Programmable Read Only Memory). Memory 92 is not limited to these, and may also be a magnetic disk, optical disk, compact disk, minidisc, or DVD (Digital Versatile Disc).

[0054] Second Embodiment In a second embodiment, considerations to be taken into account when determining the thresholds A and B described in the first embodiment will be described.

[0055] First, the threshold value A will be described. The threshold value A is preferably set to a value smaller than the withstand voltage of the power conversion device 1. Setting the threshold value A in this manner can prevent the power conversion device 1 from failing due to operation exceeding the withstand voltage, and it becomes possible to continue the operation of the power conversion device 1 while performing the control described in the first embodiment.

[0056] Next, threshold value B will be described. Threshold value B should be set to a value that exceeds the minimum voltage required to operate motor 314 provided in load 100 at the minimum rotation speed. The reason for setting threshold value B in this manner will be explained with reference to FIG. 9. FIG. 9 is a diagram showing the relationship between the rotation speed of motor 314 provided in load 100 shown in FIG. 1 and the voltage generated by motor 314.

[0057] As described above, the motor 314 used in the motor drive device 2 of the first embodiment is assumed to be an interior permanent magnet synchronous motor. In the interior permanent magnet synchronous motor, the magnets embedded in the motor 314 generate a voltage in response to the rotation speed of the motor 314. As shown in FIG. 9 , the voltage generated by the motor 314 is directly proportional to the rotation speed of the motor 314. Therefore, in order to energize and rotate the motor 314, a voltage equal to or greater than the voltage generated by the motor 314 must be applied to the motor 314 from the inverter 310. Therefore, as described above, the threshold value B is set to a value exceeding the minimum voltage required to operate the motor 314 of the load 100 at the minimum rotation speed. This setting makes it possible to maintain at least the voltage required to operate the motor 314 at the minimum rotation speed, thereby enabling the motor 314 to continue to operate while the rotation speed of the motor 314 is rapidly reduced.

[0058] As described above, according to the power conversion device 1 of embodiment 2, the first threshold value is set to a value smaller than the withstand voltage of the power conversion device 1, so that it is possible to prevent the power conversion device 1 from failing due to operation exceeding the withstand voltage, and it becomes possible to continue operating the power conversion device 1 while performing the control described in embodiment 1.

[0059] Furthermore, according to the power conversion device 1 of embodiment 2, the second threshold value is set to a value that exceeds the minimum voltage required to operate the motor 314 provided in the load 100 at the minimum rotation speed, so that the voltage required to drive the motor 314 at the minimum rotation speed can be maintained, and it becomes possible to continue driving the motor 314 while causing the rotation speed of the motor 314 to drop sharply.

[0060] Third Embodiment In a third embodiment, a case where the power conversion device 1 is connected to a DC power supply will be described.

[0061] FIG. 10 is a diagram showing a configuration example of a power conversion device 1 according to a third embodiment. The power conversion device 1 is connected to a DC power supply 111 and a load 100. The power conversion device 1 converts a first DC voltage applied from the DC power supply 111 into a second DC voltage and applies the second DC voltage to the load 100. The configuration of the power conversion device 1 according to the third embodiment is obtained by deleting the rectifier circuit 130 from the configuration of the power conversion device 1 according to the first embodiment shown in FIG. 1. That is, in the third embodiment, the step-up / step-down converter 150 is a DC-DC converter, i.e., a DC-DC converter. In the step-up / step-down converter 150, the configuration of the step-up / step-down circuit 140 is the same as the configuration of the step-up / step-down circuit 140 according to the first embodiment shown in FIG. 1. In the first embodiment, the noise filter 120 is for AC, but in the third embodiment, the noise filter 120 is for DC. The power conversion device 1 and the load 100 form a motor drive device 2.

[0062] In the third embodiment, the operation of the step-up / step-down circuit 140 included in the step-up / step-down converter 150 and the control content of the control unit 400 are the same as the operation of the step-up / step-down circuit 140 included in the step-up / step-down converter 150 of the first embodiment and the control content of the control unit 400. In the third embodiment, the second DC voltage output from the step-up / step-down converter 150 is output to the DC buses 420, 422 to become the bus voltage.

[0063] As described above, the power conversion device 1 according to the third embodiment is connected to the DC power supply 111 and includes a DC-DC converter that converts the input voltage applied from the DC power supply 111 into a bus voltage, and has functions equivalent to those of the power conversion device 1 according to the first embodiment. Therefore, even if the power conversion device 1 according to the third embodiment is configured to receive power from the DC power supply 111, it is possible to obtain effects equivalent to those of the power conversion device 1 according to the first embodiment, which is configured to receive power from the AC power supply 110.

[0064] Fourth Embodiment In a fourth embodiment, a step-up / step-down circuit 140 provided in a step-up / step-down converter 150 will be described, which has a different configuration from those described in the first to third embodiments.

[0065] Fig. 11 is a first diagram showing a configuration example of a power conversion device 1 according to embodiment 4. Fig. 11 shows an example in which a step-up / step-down converter 150 of the power conversion device 1 employs a Cuk converter circuit as the step-up / step-down circuit 140. As shown in Fig. 11 , the step-up / step-down circuit 140, which is a Cuk converter circuit, includes a switching element 141, a freewheeling diode 142, a reactor 143, a diode 144, a capacitor 145, a reactor 146, a detection resistor 502a, and a smoothing capacitor 210.

[0066] Fig. 12 is a second diagram showing a configuration example of the power conversion device 1 according to embodiment 4. Fig. 12 shows an example in which the step-up / step-down converter 150 of the power conversion device 1 employs a SEPIC (Single Ended Primary Inductor Converter) converter circuit as the step-up / step-down circuit 140. As shown in Fig. 12, the step-up / step-down circuit 140, which is a SEPIC converter circuit, includes a switching element 141, a freewheeling diode 142, a reactor 143, a diode 144, a capacitor 145, a reactor 146, a detection resistor 502a, and a smoothing capacitor 210.

[0067] 11 and 12 show the case where the power supply connected to the power conversion device 1 is an AC power supply 110, but the configuration is also applicable to the case where the power supply connected to the power conversion device 1 is a DC power supply 111, as shown in FIG. 10. The configuration of the step-up / step-down circuit 140 is not limited to the examples in FIGS. 11 and 12. The configuration of the step-up / step-down circuit 140 can also be configured in a manner other than the circuit configurations shown in FIGS. 11 and 12. The power conversion device 1 and the load 100 form a motor drive device 2.

[0068] Fifth Embodiment. FIG. 13 is a diagram showing a configuration example of a refrigeration cycle-applied apparatus 900 according to a fifth embodiment. The refrigeration cycle-applied apparatus 900 according to the fifth embodiment includes the power conversion device 1 described in the first embodiment. The refrigeration cycle-applied apparatus 900 may also include the power conversion device 1 described in the second to fourth embodiments. Hereinafter, an example will be described in which the refrigeration cycle-applied apparatus 900 includes the power conversion device 1 described in the first embodiment. The refrigeration cycle-applied apparatus 900 according to the fifth embodiment can be applied to products equipped with a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters. In FIG. 13, components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

[0069] The refrigeration cycle application equipment 900 includes a compressor 315 incorporating the motor 314 in embodiment 1, 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.

[0070] Inside the compressor 315, a compression mechanism 904 that compresses the refrigerant and a motor 314 that operates the compression mechanism 904 are provided.

[0071] The refrigeration cycle device 900 can perform heating or cooling operation by switching the four-way valve 902. The compression mechanism 904 is driven by a motor 314 that is variably controlled in speed.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 1 Power conversion device, 2 Motor drive device, 91 Processor, 92 Memory, 100 Load, 110 AC power supply, 111 DC power supply, 120 Noise filter, 130 Rectifier circuit, 131 Rectifier element, 140 Step-up / step-down circuit, 141, 311 Switching element, 142, 312 Freewheeling diode, 143, 146 Reactor, 144 Diode, 145 Capacitor, 150 Step-up / step-down converter, 210 Smoothing capacitor, 310 Inverter, 314 Motor, 315 Compressor, 400 Control unit, 420, 422 DC bus, 502, 504 Current detection unit, 502a, 504a Detection resistor, 506 Voltage detection unit, 900 Refrigeration cycle applied equipment, 902 Four-way valve, 904 Compression mechanism, 906 Indoor heat exchanger, 908 Expansion valve, 910 outdoor heat exchanger, 912 refrigerant piping.

Claims

1. A power conversion device comprising a buck-boost converter that converts an input voltage into a DC voltage and outputs the converted DC voltage by stepping up or stepping down, and that applies a bus voltage output from the buck-boost converter to a DC bus to a DC load, wherein if an abnormality in the bus voltage is detected during the step-up operation of the buck-boost converter, the operation of the buck-boost converter is switched to step-down operation, and if an abnormality in the bus voltage is detected during the step-down operation of the buck-boost converter, the operation of the buck-boost converter is switched to step-up operation.

2. The power conversion device according to claim 1, wherein the step-up / step-down converter is an AC / DC converter connected to an AC power source and converts the input voltage applied from the AC power source into the bus voltage.

3. The power conversion device according to claim 1, wherein the step-up / step-down converter is a DC / DC converter connected to a DC power source and converts the input voltage applied from the DC power source into the bus voltage.

4. A power conversion device according to any one of claims 1 to 3, wherein in the event of an abnormality in the bus voltage, the operation of the buck-boost converter is switched to buck operation or boost operation when the response value of bus voltage fluctuations due to an abnormal rise or fall is higher than the response value of bus voltage control in the control of the buck-boost converter.

5. The power conversion device according to any one of claims 1 to 4, wherein when the bus voltage exceeds a first threshold value that is higher than a target bus voltage that is a target value of the bus voltage during boost operation of the buck-boost converter, operation of the buck-boost converter is switched to buck operation, and when the bus voltage falls below a second threshold value that is lower than the target bus voltage during buck operation of the buck-boost converter, operation of the buck-boost converter is switched to boost operation.

6. The power conversion device according to claim 5, wherein, after an abnormal rise in the bus voltage is detected and operation of the buck-boost converter is switched to buck operation, if the bus voltage drops to a third threshold value that is lower than the target bus voltage, the buck operation is stopped and operation is restored to normal boost operation; and, after an abnormal drop in the bus voltage is detected and operation of the buck-boost converter is switched to boost operation, if the bus voltage rises to a fourth threshold value that is higher than the target bus voltage, the boost operation is stopped and operation is restored to normal buck operation.

7. The power conversion device according to claim 5 or 6, wherein the target bus voltage in step-down operation decreases as the bus voltage exceeds the first threshold, and the target bus voltage in step-up operation increases as the bus voltage falls below the second threshold.

8. The power conversion device according to any one of claims 5 to 7, wherein the first threshold value is set to a value smaller than a withstand voltage of the power conversion device.

9. The power conversion device according to any one of claims 5 to 8, wherein the second threshold value is set to a value that exceeds a minimum voltage required to operate a motor provided in the DC load at a minimum rotation speed.

10. A motor drive device comprising the power conversion device according to any one of claims 1 to 9.

11. A refrigeration cycle device comprising the motor drive device according to claim 10.

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