Power conversion device, motor drive device, and equipment for refrigeration cycle applications

Abstract

A power conversion device (50) comprises: a converter (3) that converts an alternating current into a direct current and that outputs the direct current to a load (130); a capacitor (4) that smooths the output voltage of the converter (3); a shunt resistor (7) and a current detection unit (10) that detect a converter current (I1) which flows between the converter (3) and the low potential side of the capacitor (4); and a control unit (14) that controls the operation of the converter (3). The control unit (14) uses the polarity of a first current to perform a protective operation against the converter (3).

Description

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

[0001] The present disclosure relates to a power conversion device including a converter that converts AC to DC and outputs the DC to a load, a motor drive device including a power conversion device, and refrigeration cycle equipment.

[0002] Power supply current, which is the current supplied from an AC power supply, contains harmonic currents. Harmonic currents are frequency components with frequencies higher than the fundamental frequency. To suppress interference caused by harmonic currents, international regulations have been established for electronic devices that generate harmonic currents. To comply with these regulations, converters take measures to suppress the harmonic currents contained in the power supply current by chopping AC (Alternating Current) or DC (Direct Current).

[0003] Patent Document 1 listed below discloses a power conversion device equipped with a three-phase PWM (Pulse Width Modulation) converter. The three-phase PWM converter is a converter that performs chopping in AC. The use of any converter, not limited to a three-phase PWM converter, controls the power supply current to a sinusoidal waveform, making it possible to suppress power supply harmonics, which are harmonic currents contained in the power supply current.

[0004] Japanese Patent Application Laid-Open No. 2005-151755

[0005] Unlike rectifier circuits, converters have a circuit configuration with upper and lower arm semiconductor elements connected in series. In this circuit configuration, there is a possibility of an upper and lower arm short circuit occurring, where both upper and lower arm semiconductor elements are accidentally turned on at the same time. When an upper or lower arm short circuit occurs, a large short circuit current flows through the upper and lower arm semiconductor elements. If the amount of current flowing through the semiconductor elements exceeds their short circuit resistance, the semiconductor elements will be damaged. Therefore, to prevent damage to the semiconductor elements, it is necessary to quickly detect the upper and lower arm short circuit and take protective action.

[0006] The present disclosure has been made in view of the above, and has an object to provide a power conversion device that can quickly detect a short circuit between the upper and lower arms to protect semiconductor elements.

[0007] In order to solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure includes a converter that converts AC to DC and outputs the converted DC to a load, a capacitor that smoothes the output voltage of the converter, a first current detector that detects a first current flowing between the converter and the low-potential side of the capacitor, and a first control unit that controls the operation of the converter. The first control unit performs a protection operation on the converter based on the polarity of the detected value of the first current.

[0008] The power conversion device according to the present disclosure has the advantage of being able to quickly detect a short circuit between the upper and lower arms and protect the semiconductor elements.

[0009] FIG. 1 is a diagram showing an example of the configuration of a motor drive device including a power conversion device according to embodiment 1; FIG. 2 is a diagram showing the operating waveforms of the main parts of the power conversion device according to embodiment 1; FIG. 3 is a diagram used to explain the main points of the configuration of the power conversion device according to embodiment 1; FIG. 4 is a block diagram showing an example of the hardware configuration for realizing the functions of the control unit according to embodiment 1; FIG. 5 is a diagram showing an example of the configuration of a converter provided in a power conversion device according to embodiment 2;

[0010] 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 accompanying drawings.

[0011] First Embodiment Fig. 1 is a diagram showing an example of the configuration of a motor drive device 100 including a power conversion device 50 according to a first embodiment. The power conversion device 50 according to the first embodiment is a power conversion device that converts AC voltage output from a three-phase power supply 110, which is a three-phase AC power supply, into DC voltage and applies the DC voltage to a load 130. The motor drive device 100 according to the first embodiment is also a drive device that converts DC power output from the power conversion device 50 into AC power and supplies the converted AC power to a motor 120 to drive the motor 120. As shown in the figure, the phases of the three-phase power supply 110 are represented by R, S, and T, and are referred to as the "R phase," the "S phase," and the "T phase," respectively.

[0012] 1, the power conversion device 50 according to the first embodiment includes a converter 3, a capacitor 4, a shunt resistor 7 for current detection, a current detection unit 10, a voltage detection unit 11, a control unit 14 which is a first control unit, and a drive circuit 16 which is a first drive circuit. Also, the motor drive device 100 according to the first embodiment includes the power conversion device 50, and further includes a noise filter 1, a reactor 2, current detectors 5a and 5b, a phase voltage detection unit 6, a control unit 15 which is a second control unit, and a load 130, as shown in FIG.

[0013] The load 130 includes a shunt resistor 8 for current detection, an inverter 9, a current detection unit 12, a drive circuit 17 which is a second drive circuit, current detectors 18a and 18b, and a motor 120. Of the components of the load 130, the shunt resistor 8, the inverter 9, the current detection unit 12, the drive circuit 17, and the current detectors 18a and 18b, excluding the motor 120, are components of the motor drive device 100.

[0014] The converter 3 is electrically connected to the three-phase power supply 110 by electrical wiring 70a, 70b, and 70c, which are first electrical wiring. The noise filter 1 is disposed between the three-phase power supply 110 and the reactor 2. The noise filter 1 operates to reduce noise currents flowing in and out of the power conversion device 50. The reactor 2 is disposed between the noise filter 1 and the converter 3. The reactor 2 is a device including circuit elements that temporarily store electrical energy supplied from the three-phase power supply 110. The reactor 2 also operates to reduce noise currents flowing in and out of the power conversion device 50.

[0015] The current detectors 5a and 5b detect the power supply current, which is an AC current flowing between the three-phase power supply 110 and the power conversion device 50, and output the detected values ​​of the power supply current to the control unit 14. An example of the current detectors 5a and 5b is an ACCT (Alternating Current Transformer). While FIG. 1 illustrates an example in which the current detector 5a detects the R-phase current Ir and the current detector 5b detects the T-phase current It, the present invention is not limited to this example. It is sufficient for the current detectors 5a and 5b to detect the currents of any two of the three phases; the currents of the remaining phases can be calculated by utilizing the fact that the power supply currents are three-phase balanced. The phase voltage detector 6 detects the phase voltages of the three phases, i.e., the R-phase voltage Vr, the S-phase voltage Vs, and the T-phase voltage Vt, output from the three-phase power supply 110, and outputs the detected values ​​to the control unit 14.

[0016] The capacitor 4 is electrically connected to the converter 3 by electrical wiring 72a and 72b, which are second electrical wirings. The converter 3 converts the AC voltage output from the three-phase power supply 110 into a DC voltage and outputs it to the electrical wirings 72a and 72b. The electrical wirings 72a and 72b are called "DC buses," and the voltage between the electrical wirings 72a and 72b is called "bus voltage."

[0017] The output voltage of converter 3 is applied across capacitor 4. Capacitor 4 smoothes the output voltage of converter 3. Capacitor 4 is electrically connected to electrical wires 72a and 72b by electrical wires 74a and 74b, which are third electrical wires, respectively. Therefore, in the configuration of FIG. 1 , the capacitor voltage, which is the voltage across capacitor 4, is equal to the bus voltage. The connection point between electrical wire 74a and electrical wire 72a forms terminal P, and the connection point between electrical wire 74b and electrical wire 72b forms terminal N. Terminal P is the high-potential side terminal of capacitor 4, and terminal N is the low-potential side terminal of capacitor 4. The voltage smoothed by capacitor 4 is applied to inverter 9.

[0018] The voltage detection unit 11 detects the bus voltage Vdc and outputs the detected value of the bus voltage Vdc to the control units 14 and 15. The current detection unit 10 detects the converter current I1, which is a first current flowing between the converter 3 and the terminal N of the capacitor 4. In the configuration of FIG. 1 , the converter current I1 flows through the shunt resistor 7, so the current detection unit 10 detects this current. The current detection unit 10 converts the voltage value generated by the converter current I1 flowing through the shunt resistor 7 into a current value and outputs it to the control unit 14. In this document, the shunt resistor 7 and the current detection unit 10 will be collectively referred to as the "first current detector" where appropriate.

[0019] The converter 3 includes six semiconductor elements Q1 to Q6 that are connected in a three-phase bridge configuration. The semiconductor elements Q1 and Q2 are connected in series in this order, and a connection point 3a between the semiconductor elements Q1 and Q2 is electrically connected to the R phase of the three-phase power supply 110. The semiconductor elements Q3 and Q4 are connected in series in this order, and a connection point 3b between the semiconductor elements Q3 and Q4 is electrically connected to the S phase of the three-phase power supply 110. The semiconductor elements Q5 and Q6 are connected in series in this order, and a connection point 3c between the semiconductor elements Q5 and Q6 is electrically connected to the T phase of the three-phase power supply 110.

[0020] In this document, the semiconductor elements Q1, Q3, and Q5 arranged on the upper side of the circuit diagram may be referred to as "upper arm elements," and the semiconductor elements Q2, Q4, and Q6 arranged on the lower side of the circuit diagram may be referred to as "lower arm elements." Also, in this document, the side of three-phase power supply 110 where connection points 3a to 3c are located, as viewed from converter 3, may be referred to as the "AC side," and the side of load 130 may be referred to as the "DC side."

[0021] The semiconductor elements Q1 to Q6 each include a diode D1 to D6 connected in parallel. The diodes D1 to D6 are connected so that their anodes are located on the AC side and their cathodes are located on the DC side. While FIG. 1 illustrates a case where the semiconductor elements Q1 to Q6 are IGBTs (insulated gate bipolar transistors), MOSFETs (metal oxide semiconductor field effect transistors) may be used instead of IGBTs. Note that, because MOSFETs have a built-in parasitic diode due to their structure, a configuration in which the diodes D1 to D6 are not connected in parallel may also be employed.

[0022] The inverter 9 converts direct current into alternating current. More specifically, the inverter 9 converts the output voltage of the power conversion device 50 into an alternating current voltage and applies it to a motor 120 provided in the load 130. An example of an apparatus equipped with the motor 120 is a blower or compressor in an air conditioner. The air conditioner is an example of an apparatus that applies a refrigeration cycle.

[0023] The current detection unit 12 detects the inverter current I2, which is a second current flowing between the inverter 9 and the terminal N of the capacitor 4. In the configuration of FIG. 1, the inverter current I2 flows through the shunt resistor 8, and is detected. The current detection unit 12 converts the voltage value generated when the inverter current I2 flows through the shunt resistor 8 into a current value and outputs it to the control unit 15. In this document, the shunt resistor 8 and the current detection unit 12 will be collectively referred to as the "second current detector" where appropriate.

[0024] The inverter 9 includes six semiconductor elements Q21 to Q26 that are connected in a three-phase bridge configuration. The semiconductor elements Q21 and Q22 are connected in series in this order, with a connection point 9a between the semiconductor elements Q21 and Q22 electrically connected to the U-phase of the motor 120. The semiconductor elements Q23 and Q24 are connected in series in this order, with a connection point 9b between the semiconductor elements Q23 and Q24 electrically connected to the V-phase of the motor 120. The semiconductor elements Q25 and Q26 are connected in series in this order, with a connection point 9c between the semiconductor elements Q25 and Q26 electrically connected to the W-phase of the motor 120. Note that, from the perspective of the inverter 9, the side of the converter 3 is the DC side, and the side of the motor 120 where the connection points 9a to 9c are located is the AC side. In this paper, in order to distinguish between the semiconductor elements Q1 to Q6 provided in the converter 3 and the semiconductor elements Q21 to Q26 provided in the inverter 9 without using symbols, the former may be referred to as the "first semiconductor elements" and the latter as the "second semiconductor elements."

[0025] The semiconductor elements Q21 to Q26 each include a diode D21 to D26 connected in parallel. The diodes D21 to D26 are connected so that their cathodes are on the DC side and their anodes are on the AC side. While FIG. 1 shows a case where the semiconductor elements Q21 to Q26 are IGBTs, MOSFETs may be used instead of the IGBTs. Note that, in the case of MOSFETs, a parasitic diode is built into the structure, so a configuration in which the diodes D21 to D26 are not connected in parallel may also be employed. Furthermore, an IGCT (Integrated Gate Commutated Thyristor) may be used instead of the IGBTs.

[0026] Current detectors 18a and 18b detect three-phase motor currents flowing between inverter 9 and motor 120 and output the detected motor current values ​​to control unit 15. An example of current detectors 18a and 18b is an ACCT. Note that while FIG. 1 shows an example in which current detector 18a detects U-phase motor current Iu and current detector 18b detects W-phase motor current Iw, this example is not limiting. Current detectors 18a and 18b only need to detect currents in any two of the three phases, and the currents in the remaining phases can be calculated by utilizing the fact that motor currents are three-phase balanced.

[0027] The control unit 14 controls the operation of the converter 3. Specifically, the control unit 14 generates control signals S1 to S6 for controlling the bus voltage to a desired voltage while controlling the power supply current to a sinusoidal waveform based on the detection values ​​of the current detectors 5a and 5b, the detection value of the phase voltage detection unit 6, the detection value of the current detection unit 10, and the detection value of the voltage detection unit 11. The control signals S1 to S6 are control signals for controlling the semiconductor elements Q1 to Q6 of the converter 3, respectively. The control signals S1 to S6 generated by the control unit 14 are input to the drive circuit 16.

[0028] Furthermore, the control unit 15 controls the operation of the inverter 9. Specifically, the control unit 15 generates control signals S21 to S26 for rotating the motor 120 at a desired rotation speed based on the detection values ​​of the voltage detection unit 11, the current detection unit 12, and the current detectors 18a and 18b. The control signals S21 to S26 are control signals for controlling the semiconductor elements Q21 to Q26 of the inverter 9, respectively. The control signals S21 to S26 generated by the control unit 15 are input to the drive circuit 17.

[0029] Drive circuit 16 generates drive pulses G1 to G6 based on control signals S1 to S6. Semiconductor elements Q1 to Q6 of converter 3 perform switching operations in response to the drive pulses G1 to G6. Drive circuit 17 generates drive pulses G21 to G26 based on control signals S21 to S26. Semiconductor elements Q21 to Q26 of inverter 9 perform switching operations in response to the drive pulses G21 to G26.

[0030] 1, the control units 14 and 15 are provided inside the motor drive device 100, but this configuration is not limiting. The control unit 14 may be provided inside the power conversion device 50, and the control unit 15 may be provided inside the load 130. Also, in FIG. 1, the control units 14 and 15 are configured as separate control units, but this configuration is not limiting. The control units 14 and 15 may be integrated into a common control unit that controls both the converter 3 and the inverter 9.

[0031] Next, the configuration and key points of operation of the power conversion device 50 according to the first embodiment will be described. Fig. 2 is a diagram showing the operational waveforms of the main parts of the power conversion device 50 according to the first embodiment. Fig. 2 shows, from top to bottom, the waveforms of the phase voltages of each of the three phases, the phase currents of each of the three phases, and the bus voltage Vdc. The horizontal axis of Fig. 2 represents time.

[0032] The upper part of FIG. 2 shows the waveforms of the R-phase voltage Vr, the S-phase voltage Vs, and the T-phase voltage Vt, which are sinusoidal voltage waveforms. The meaning of period T1 will be described later. The middle part of FIG. 2 shows the waveforms of the R-phase current Ir, the S-phase current Is, and the T-phase current It, which are sinusoidal current waveforms. These sinusoidal current waveforms are obtained by PWM control of the semiconductor elements Q1 to Q6 of the converter 3. By making the R-phase current Ir, the S-phase current Is, and the T-phase current It sinusoidal, power supply harmonics are suppressed. The lower part of FIG. 2 shows the waveform of the bus voltage Vdc, which is controlled to be approximately constant. By controlling the bus voltage Vdc to be constant, it is possible to stably drive the load 130. Note that in the first embodiment, the bus voltage Vdc does not necessarily have to be controlled to be constant.

[0033] Fig. 3 is a diagram illustrating the essential configuration of the power conversion device 50 according to embodiment 1. Fig. 3 shows the three-phase power supply 110, the reactor 2, the converter 3, the capacitor 4, and the shunt resistor 7 extracted from Fig. 1.

[0034] As explained in the section [Problem to be Solved by the Invention], converter 3 may experience a phenomenon known as an upper / lower arm short circuit, in which both semiconductor elements in the upper and lower arms are accidentally turned on simultaneously. FIG. 3 shows an example in which semiconductor elements Q5 and Q6 short circuit the upper and lower arms. When semiconductor elements Q5 and Q6 short circuit the upper and lower arms, a short-circuit current flows through the path indicated by the thick dashed arrow. Because the resistance value of shunt resistor 7 is small, the short-circuit current is large. Therefore, if the amount of current flowing through semiconductor elements Q5 and Q6 exceeds the short-circuit resistance of semiconductor elements Q5 and Q6, semiconductor elements Q5 and Q6 will be damaged.

[0035] Therefore, the power conversion device 50 according to the first embodiment first detects that an upper or lower arm short circuit has occurred. The upper or lower arm short circuit is detected based on the polarity of the converter current I1 flowing through the shunt resistor 7. In Fig. 3, the direction of the current flowing during power running is indicated by a thick solid arrow, but this direction is opposite to that of the upper or lower arm short-circuit current. Therefore, the polarity of the voltage generated across the shunt resistor 7 is opposite between the current during power running and the upper or lower arm short-circuit current, and this phenomenon is utilized.

[0036] Furthermore, in the power conversion device 50 according to the first embodiment, relays for breaking electrical connections are disposed at key points in the circuit section. In FIG. 3 , circles indicate the locations of the relays. First, the relays are disposed at either one of positions B1 or B2. Position B1 is an arbitrary position on the electrical wiring 72a, and position B2 is an arbitrary position on the electrical wiring 72b. When the detection value of the current detection unit 10 is significant and has a polarity opposite to that of the current detected during powering, the control unit 14 of the power conversion device 50 determines that an upper or lower arm short circuit may have occurred in one of the semiconductor elements Q1 to Q6. When the control unit 14 determines that an upper or lower arm short circuit may have occurred, the control unit 14 performs control to open the relay disposed at either position B1 or B2 as a protective operation for the converter 3. A significant detection value means that the detection value is at or above a level at which it can be determined that an upper or lower arm short circuit may have occurred. This control quickly cuts off the short-circuit current that has been flowing due to the short circuit between the upper and lower arms, making it possible to protect the semiconductor element through which the short-circuit current has been flowing.

[0037] The relay may be located at either position B3 or B4 instead of position B1 or B2. Position B3 is an arbitrary position on electrical wiring 74a, and position B4 is an arbitrary position on electrical wiring 74b. Even in this case, the short-circuit current can be quickly interrupted by opening the relay located at either position B3 or B4.

[0038] Furthermore, instead of positions B1 and B2 or positions B3 and B4, the relays may be placed at any two of positions B5 to B7. Position B5 is any position on the electrical wiring 70a, position B6 is any position on the electrical wiring 70b, and position B7 is any position on the electrical wiring 70c. Opening each of the relays placed at any two of positions B5 to B7 cuts off the power supply to the capacitor 4. Therefore, since there is no power supply source that serves as the source of the short-circuit current, it is possible to quickly cut off the short-circuit current that was flowing due to the short circuit between the upper and lower arms.

[0039] Furthermore, in the power conversion device 50 according to the first embodiment, instead of the method using the relays described above, control may be performed to turn off the semiconductor elements Q1 to Q6. By turning off the semiconductor elements Q1 to Q6, the power supply to the capacitor 4 is cut off, and it becomes possible to cut off the short-circuit current that has been flowing due to the short circuit between the upper and lower arms.

[0040] Next, a description will be given of a hardware configuration for realizing the functions of the control units 14 and 15 according to embodiment 1. Fig. 4 is a block diagram showing an example of a hardware configuration for realizing the functions of the control units 14 and 15 according to embodiment 1.

[0041] To realize some or all of the functions of the control units 14 and 15, a configuration including a processor 201 that performs calculations and a memory 202 that stores programs read by the processor 201 can be used, as shown in FIG.

[0042] The processor 201 is an example of a computing unit. The processor 201 may be a computing unit called a microprocessor, a microcomputer, a central processing unit (CPU), or a digital signal processor (DSP). Examples of the memory 202 include non-volatile or volatile semiconductor memory such as random access memory (RAM), read-only memory (ROM), flash memory, erasable programmable read-only memory (EPROM), and electrically programmable programmable read-only memory (EEPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, and a digital versatile disk (DVD).

[0043] The memory 202 holds programs that execute the functions of the control units 14 and 15. The processor 201 exchanges necessary information and stores it in the memory 202, and the processor 201 executes the programs held in the memory 202 and refers to the data and tables stored in the memory 202, thereby executing the above-mentioned processing. The calculation results by the processor 201 can be stored in the memory 202.

[0044] As described above, the power conversion device according to the first embodiment includes a converter that converts AC to DC and outputs the converted DC to a load, a capacitor that smooths the output voltage of the converter, a first current detector that detects a first current flowing between the converter and the low-potential side of the capacitor, and a first controller that controls the operation of the converter. The first controller performs a protective operation on the converter based on the polarity of the detected value of the first current. With this power conversion device configured as described above, even if an upper or lower arm short circuit occurs in semiconductor elements of the upper or lower arms of the converter, the current flowing through the semiconductor elements can be interrupted before the amount of current flowing through the semiconductor elements exceeds the short-circuit resistance of the semiconductor elements. Therefore, the power conversion device according to the first embodiment makes it possible to quickly detect an upper or lower arm short circuit and protect the semiconductor elements.

[0045] In the power conversion device according to the first embodiment, the protection operation for the converter can be performed by turning off all of the first semiconductor elements.

[0046] Furthermore, in the power conversion device according to embodiment 1, a relay may be inserted in the first electrical wiring for electrically connecting the AC power supply and the converter, the second electrical wiring for electrically connecting the converter and the capacitor, or the third electrical wiring for electrically connecting the capacitor to the second electrical wiring. In the power conversion device configured in this manner, a protection operation for the converter can be performed by opening any of the relays inserted in the first, second, or third electrical wiring.

[0047] Embodiment 2 Fig. 5 is a diagram showing an example of the configuration of a converter 3 provided in a power conversion device 50 according to embodiment 2. Components that are the same as or equivalent to those in Fig. 3 are denoted by the same reference numerals, and duplicated explanations will be omitted.

[0048] In converter 3 according to the second embodiment, semiconductor elements Q2, Q4, and Q6, which are lower arm elements, are provided with sense terminals St. In semiconductor element Q2, sense terminal St is configured so that a minute current that is correlated with the emitter current flowing through semiconductor element Q2 flows through it. The same is true for sense terminals St of semiconductor elements Q4 and Q6. In semiconductor elements Q2, Q4, and Q6, when a path through which the emitter current flows is defined as a main path and a path through which a minute current that is correlated with the emitter current flows is defined as a sub-path, the magnitude of the current flowing through the sub-path is approximately one hundredth to one thousandth of the current flowing through the main path.

[0049] One end of resistor 7a is connected to sense terminal St. The other end of resistor 7a is connected to terminal N. Resistor 7a may be a resistive element formed inside semiconductor elements Q2, Q4, and Q6, or may be a resistive element or resistor provided outside semiconductor elements Q2, Q4, and Q6.

[0050] In the second embodiment, the current detection unit 10 detects a voltage generated by the current flowing through the resistor 7a. The current detection unit 10 converts the voltage generated across the resistor 7a into a collector current and transmits the collector current to the control unit 14. As in the first embodiment, the control unit 14 detects an upper or lower arm short circuit based on the polarity of the value detected by the current detection unit 10. In this way, in the second embodiment, the current flowing between the sense terminal St and the low-potential side terminal N of the capacitor 4 can be used as the first current to perform a protection operation for the converter 3.

[0051] As described above, in the power conversion device according to the second embodiment, the converter includes a plurality of first semiconductor elements connected in a three-phase bridge configuration, and the lower arm elements of the first semiconductor elements have sense terminals. In the second embodiment, the first current detector detects, as the first current, a current flowing between the sense terminal and the low-potential terminal of the capacitor, and the first control unit performs a protection operation for the converter based on the polarity of the detected value of the first current. The power conversion device according to the second embodiment configured in this manner can quickly detect a short circuit in the upper and lower arms and protect the semiconductor elements, as in the first embodiment.

[0052] Third Embodiment In a third embodiment, a description will be given of the main points of the operation of motor drive device 100 shown in Fig. 1. Fig. 6 is a diagram illustrating the main points of the operation of motor drive device 100 according to the third embodiment.

[0053] The upper and lower arm short circuit described in the first embodiment can also occur in the semiconductor elements Q21 to Q26 of the inverter 9. FIG. 6 shows an example in which the semiconductor elements Q21 and Q22 short circuit the upper and lower arms. When the semiconductor elements Q21 and Q22 short circuit the upper and lower arms, a short-circuit current flows through the path indicated by the thick dashed arrow. Because the resistance value of the shunt resistor 8 is small, the short-circuit current is large. Therefore, if the amount of current flowing through the semiconductor elements Q21 and Q22 exceeds the short-circuit withstand capability of the semiconductor elements Q21 and Q22, the semiconductor elements Q21 and Q22 will be damaged.

[0054] Therefore, motor drive device 100 according to the third embodiment detects the occurrence of an upper / lower arm short circuit based on inverter current I2 flowing through shunt resistor 8. However, unlike converter 3, the direction of the upper / lower arm short-circuit currents is the same as the direction of the current flowing during powering, as indicated by the thick solid arrow. For this reason, motor drive device 100 according to the third embodiment compares the detected value of inverter current I2 with a threshold value, and performs a protective operation on inverter 9 when the detected value of inverter current I2 exceeds the threshold value.

[0055] In motor drive device 100 according to embodiment 3, when the detected value of inverter current I2 exceeds a threshold value, the protective operation for inverter 9 is performed by performing the protective operation according to embodiment 1 or 2 and then controlling semiconductor elements Q21 to Q26 to be turned off. By turning off semiconductor elements Q21 to Q26, the short-circuit current flowing due to the short circuit in the upper and lower arms is quickly interrupted, thereby protecting the semiconductor elements through which the short-circuit current was flowing. Furthermore, by performing the protective operation according to embodiment 1 or 2, the power supply to capacitor 4 is cut off, and as a result, the power supply source that is the source of the short-circuit current is eliminated, allowing the short-circuit current flowing due to the short circuit in the upper and lower arms to be quickly interrupted.

[0056] 6 illustrates the inverter 9 having the configuration shown in FIG. 1, but is not limited to this configuration. In the inverter 9 shown in FIG. 6, the semiconductor elements Q22, Q24, and Q26, which are lower arm elements, may have sense terminals St, as with the semiconductor elements Q2, Q4, and Q6 shown in FIG. 5. In this case, the sense terminals St of the semiconductor elements Q22, Q24, and Q26 may be configured to be electrically connected to the low-potential side terminal N of the capacitor 4 via a resistor, as shown in FIG. 5. Even with this configuration, the protection operation according to the third embodiment can be performed.

[0057] As described above, the motor drive device according to the third embodiment includes the power conversion device according to the first or second embodiment, an inverter that converts the output voltage of the power conversion device into an AC voltage and applies the AC voltage to a motor provided in a load, and a second control unit that controls the operation of the inverter. The second control unit performs a protective operation on the inverter when the detected value of the second current exceeds a threshold. With this motor drive device configured in this manner, even if an upper or lower arm short circuit occurs in the semiconductor elements of the upper or lower arms of the inverter, the current flowing through the semiconductor elements can be cut off before the amount of current flowing through the semiconductor elements exceeds the short-circuit resistance of the semiconductor elements. Therefore, the motor drive device according to the third embodiment makes it possible to quickly detect an upper or lower arm short circuit and protect the semiconductor elements.

[0058] In the motor drive device of embodiment 3, the protection operation for the inverter can be performed by performing the protection operation of embodiment 1 or embodiment 2 and then turning off all of the second semiconductor elements.

[0059] 7 is a diagram showing an example of the configuration of an air conditioner 300 according to embodiment 4. The air conditioner 300 according to embodiment 4 is an example of a refrigeration cycle-applied device, and includes a motor 120 as well as the motor drive device 100 described in embodiment 1. The air conditioner 300 also includes a compressor 81, a four-way valve 82, an outdoor heat exchanger 83, an expansion valve 84, an indoor heat exchanger 85, and refrigerant piping 86.

[0060] The air conditioner 300 may be a separate type air conditioner in which the outdoor unit is separated from the indoor unit, or an integrated type air conditioner in which the compressor 81, indoor heat exchanger 85, and outdoor heat exchanger 83 are provided within a single housing.

[0061] The compressor 81 contains a compression mechanism 87 that compresses the refrigerant and a motor 120 that operates the compression mechanism 87. The motor 120 is driven by a motor drive device 100. In the air conditioner 300, a refrigeration cycle is formed by circulating the refrigerant through the compressor 81, the four-way valve 82, the outdoor heat exchanger 83, the expansion valve 84, the indoor heat exchanger 85, and the refrigerant piping 86.

[0062] The components of the air conditioner 300 can also be applied to appliances such as refrigerators or freezers equipped with a refrigeration cycle. In addition, in the fourth embodiment, the motor 120 is used as the drive source for the compressor 81, but the motor 120 may also be used as the drive source for an indoor unit blower and an outdoor unit blower (not shown) instead of the compressor 81. Alternatively, the motor 120 may be used as the drive source for each of the indoor unit blower, the outdoor unit blower, and the compressor 81, and these three motors 120 may be driven by the motor drive device 100.

[0063] Although the air conditioner 300 according to the fourth embodiment has been described as including the motor drive device 100 described in the first embodiment, the present invention is not limited to this. The converter 3 included in the motor drive device 100 may be configured as shown in Fig. 5. Furthermore, the inverter 9 included in the motor drive device 100 may be configured as shown in Fig. 6.

[0064] The air conditioner 300 according to embodiment 4 is equipped with a motor drive device 100 according to any one of embodiments 1 to 3, and is therefore able to enjoy the effects obtained in each embodiment.

[0065] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, and parts of the configurations may be omitted or modified without departing from the spirit of the invention.

[0066] 1 noise filter, 2 reactor, 3 converter, 3a to 3c, 9a to 9c connection points, 4 capacitor, 5a, 5b, 18a, 18b current detector, 6 phase voltage detection unit, 7, 8 shunt resistor, 7a resistor, 9 inverter, 10, 12 current detection unit, 11 voltage detection unit, 14, 15 control unit, 16, 17 drive circuit, 50 power conversion device, 70a, 70b, 70c, 72a, 72b, 74a, 74b electrical wiring, 81 compressor, 82 four-way valve, 83 outdoor heat exchanger, 84 expansion valve, 85 indoor heat exchanger, 86 refrigerant piping, 87 compression mechanism, 100 motor drive device, 110 three-phase power supply, 120 motor, 130 load, 201 processor, 202 memory, 300 air conditioner, B1 to B7 Position, D1 to D6, D21 to D26 diodes, N, P terminals, Q1 to Q6, Q21 to Q26 semiconductor elements, St sense terminal.

Claims

1. A converter that converts AC to DC and outputs it to the load, A capacitor for smoothing the output voltage of the converter, A first current detector for detecting a first current flowing between the converter and the low-potential side of the capacitor, A first control unit that controls the operation of the converter, Equipped with, The first control unit performs a protection operation for the converter based on the polarity of the detected value of the first current. Power converter.

2. The converter has a plurality of first semiconductor elements connected in a three-phase bridge configuration. The lower arm element of the first semiconductor element has a sense terminal, The first current is the current that flows between the sense terminal and the low-potential terminal of the capacitor. The power conversion device according to claim 1.

3. The protection operation for the converter is performed by turning off all of the first semiconductor elements. The power conversion device according to claim 2.

4. A relay is inserted in the first electrical wiring for electrically connecting the AC power supply and the converter, the second electrical wiring for electrically connecting the converter and the capacitor, or the third electrical wiring for electrically connecting the capacitor to the second electrical wiring. The protection operation for the converter is performed by opening one of the relays inserted into the first, second, or third electrical wiring. A power conversion device according to any one of claims 1 to 3.

5. A power conversion device according to any one of claims 1 to 3, An inverter that converts the output voltage of the power converter into an AC voltage and applies it to a motor provided in the load, A second current detector for detecting a second current flowing between the inverter and the low-potential side of the capacitor, A second control unit that controls the operation of the inverter, Equipped with, The second control unit performs a protective operation on the inverter if the detected value of the second current exceeds a threshold. Motor drive device.

6. The inverter has a plurality of second semiconductor elements connected in a three-phase bridge configuration. The lower arm element of the second semiconductor element has a sense terminal, The second current is the current that flows between the sense terminal and the low-potential terminal of the capacitor. The motor drive device according to claim 5.

7. The protection operation for the inverter is performed by turning off all of the second semiconductor elements. The motor drive device according to claim 6.

8. A refrigeration cycle application device comprising the motor drive device described in claim 5.