JP6608441B2 - Power converter, harmonic current compensator, and air conditioner - Google Patents

Description

  The present invention relates to a power converter, a harmonic current compensator, and an air conditioner.

  Conventionally, in order to convert AC power, switching elements: IGBTs (Insulated Gate Bipolar Transistors) are connected in series to form an arm, and this arm is further connected in parallel and connected to both ends with a smoothing capacitor. Conversion circuits are known. As a device including this power conversion circuit, for example, a harmonic current suppressing device (active filter) is known. The harmonic current suppression device is connected in parallel with a load such as a motor connected to an AC power source, and suppresses harmonic current generated on the load side (Patent Document 1).

  Further, a rush resistance is provided on the DC side of the power conversion circuit to prevent an excessive rush current from flowing through the smoothing capacitor when the power is turned on (Patent Document 2). Thereby, the load arrange | positioned in a back | latter stage can also be protected.

JP2012-143094 JP-A-5-15170

  However, according to experiments conducted by the inventors, a phenomenon occurs in which the switching element connected to the AC power supply is damaged when the power is turned on depending on conditions. As a result of examining this problem, the inventors have found that the breakdown voltage of the switching element is lowered due to the fluctuation of the gate voltage when the power is turned on. As a result of further investigation on this, it was found that the breakdown voltage of the switching element depends on the dv / dt of the collector voltage, and decreasing the dv / dt reduced the fluctuation of the gate voltage and improved the breakdown voltage of the switching element. .

  An object of the present invention is to provide a power converter, a harmonic current compensator, and an air conditioner in which damage to a switching element is suppressed and reliability is improved.

In order to solve the above-described problems, the present invention provides a power conversion device that is connected to an AC power source and converts electric power, and includes an arm in which an upper switching element that is an IGBT and a lower switching element that is an IGBT are connected in series. A plurality of power converters configured to be connected in parallel, and provided for each of the upper switching element and the lower switching element, and when the power is turned on, the rate of change of the collector voltage of the upper switching element or the lower switching element is A plurality of drive circuits configured to reduce the withstand voltage of the upper switching element or the lower switching element, a smoothing capacitor connected to both ends of the arm, the upper switching element, and the lower Provided between the midpoint of the switching element and the AC power supply And an inrush resistance for suppressing an inrush current.

  ADVANTAGE OF THE INVENTION According to this invention, the power converter device, harmonic current compensation apparatus, and air conditioner which suppressed the damage of the switching element and improved reliability can be provided.

Circuit diagram of IGBT and driver output stage The figure which shows the relationship between IGBT collector voltage change rate and IGBT breakdown voltage A diagram showing the relationship between inrush resistance and surge voltage A diagram showing the relationship between rush resistance and voltage change rate Diagram showing the relationship between inrush resistance and inrush current 1 is a circuit diagram of a harmonic current compensator according to a first embodiment of the present invention. Circuit diagram of harmonic current compensator of second embodiment of the present invention Circuit diagram of harmonic current compensator of third embodiment of the present invention The circuit diagram of the power converter device of 4th Example of this invention The circuit diagram of the air conditioner provided with the harmonic current compensation apparatus of 5th Example of this invention The side view of the outdoor unit of the air conditioner which implemented at least one among 1st Example to 5th Example of this invention The front view of the outdoor unit of the air conditioner which implemented at least one among 1st Example to 5th Example of this invention

  Embodiments of the present invention will be described below with reference to the drawings.

  First, a phenomenon in which the IGBT that is a switching element is destroyed will be described. FIG. 1 shows an IGBT and a driver circuit. 1 shows an output stage 25 of a driver circuit for driving the IGBT 5 and the diode 6 and the IGBT 5, a P-type MOSFET 21, an N-type MOSFET 22, a gate resistor 20, a positive terminal 24 of the driver power supply, and a positive terminal of the main circuit power supply. 23 is described. The gate terminal of the IGBT 5 is connected to the emitter terminal of the IGBT 5 through the gate resistor 20 and the N-type MOSFET 22. Since no voltage is supplied to the positive terminal 24 of the driver power supply when the breaker is turned on, the impedance of the N-type MOSFET 22 becomes indefinite.

  In this case, the gate of the IGBT 5 is not floating with respect to the emitter, and is not short-circuited because the N-type MOSFET 22 is not turned on. In other words, it can be said that the gate and emitter of the IGBT are in an intermediate state between floating and short. When the IGBT gate and emitter are not short-circuited, that is, when the IGBT gate and emitter are in an intermediate state between floating and short-circuit, the breakdown voltage between the IGBT collector and emitter decreases.

  FIG. 2 shows the relationship between the IGBT collector voltage change rate and the breakdown voltage. The reason why the breakdown voltage on the vertical axis is BVcez is that the gate and emitter of the IGBT are connected via the impedance Z. The components of the impedance Z are a gate resistor 20, a parasitic resistance Rs caused by the N-type MOSFET 22, a parasitic inductance Ls, a parasitic resistance Rs caused by the substrate wiring pattern and the pins of the power semiconductor package, and a parasitic inductance Ls. The breakdown voltage when the gate and the emitter are short-circuited is described as BVces, and the breakdown voltage when the gate and the emitter are open is described as BVceo. As the IGBT collector voltage change rate dv / dt increases, the breakdown voltage of the IGBT decreases. In addition, as the parasitic resistance Rs and the parasitic inductance Ls between the gate and the emitter are larger, the breakdown voltage is significantly reduced.

  The reason why the breakdown voltage of the IGBT decreases as the change rate dv / dt of the IGBT collector voltage increases is that the change in the collector voltage becomes higher in frequency, and the fluctuation of the gate voltage via the parasitic capacitance between the collector and the gate of the IGBT. This is because the frequency becomes higher and the impedance Z between the gate and the emitter of the IGBT increases. As the impedance Z increases, the voltage of the IGBT gate tends to fluctuate with respect to the emitter, and the breakdown voltage of the IGBT decreases.

  Regardless of the parasitic resistance Rs between the gate and the emitter and the magnitude of the parasitic inductance Ls, the withstand voltage when dv / dt is low is converged to 700V. This indicates that when dv / dt is sufficiently small, the breakdown voltage of the IGBT matches BVces, that is, the breakdown voltage when the gate and the emitter are short-circuited. In the state where the gate of the IGBT is connected to the emitter via the driver output stage as described above, “the IGBT breakdown voltage decreases as the IGBT collector voltage change rate dv / dt increases”, “the parasitic between the IGBT gate and the emitter The invention shows that the greater the resistance Rs and the parasitic inductance Ls, the more the IGBT withstand voltage decreases, and “if dv / dt is sufficiently small, the IGBT withstand voltage matches BVces (withstand voltage when the gate and emitter are short-circuited)”. They found out. Furthermore, the inventors of the present invention have found that these phenomena appear when the breaker of the AC power source of the active filter is turned on.

  FIG. 3 shows the relationship between the resistance value of the bump resistance and the surge voltage of the IGBT collector when the bump resistance is provided on the positive terminal or the negative terminal of the smoothing capacitor. The surge voltage decreases as the resistance value of the rush resistance decreases. This is because the surge voltage suppression effect of the smoothing capacitor becomes significant by reducing the rush resistance. FIG. 4 shows the relationship between the resistance value of the rush resistance and the IGBT collector voltage change rate dv / dt. The dv / dt decreases as the resistance value of the rush resistance decreases. A region below the dotted line in the figure is a range of dv / dt in which a withstand voltage of 700 V obtained from FIG. 2 can be secured. As can be seen from FIG. 4, even if the rush resistance is reduced, a withstand voltage of 700 V cannot be secured.

  FIG. 5 shows the relationship between the resistance value of the inrush resistance and the inrush current of the smoothing capacitor. If the inrush resistance is reduced, the inrush current of the smoothing capacitor increases, and the target range of the inrush current is not satisfied. That is, reducing the inrush resistance does not fulfill the function of compensating for the inrush current, which is the original role of the inrush resistance. Therefore, the method of providing the inrush resistance at the positive electrode terminal or the negative electrode terminal of the smoothing capacitor cannot achieve both the IGBT breakdown voltage and the smoothing capacitor inrush current target.

Example 1 (active filter)
A first embodiment of the present invention will be described with reference to FIG. FIG. 6 is a circuit block diagram showing an example of the configuration of a harmonic current compensation system including the harmonic current compensation apparatus of this embodiment. This harmonic current compensation system is connected to an AC power source 1, an AC power source 1 through a breaker 2, a diode bridge 13 for converting AC power into DC power, a smoothing capacitor 14 connected to an output terminal of the diode bridge 13, and a motor. A power conversion device 15 such as an inverter that supplies AC power to a load 42 such as an inverter and the diode bridge 13 are connected to the AC power source 1 in parallel to compensate for harmonic current generated in the diode bridge 13 and the power conversion device 15. A harmonic current compensator 70 that is an active filter is provided. In addition, below, the structural example in case AC power supply 1 is mainly three-phase is demonstrated.

  Upper switching elements 5a to 5c such as IGBTs and lower switching elements 5d to 5f are connected in series to form an arm. This arm is further connected in parallel to constitute a power converter. Diodes 6a-6c connected in antiparallel with upper switching elements 5a-5c and diodes 6d-6f connected in antiparallel with lower switching elements 5d-5f are connected in series, respectively. The midpoints of the upper switching elements 5 a to 5 c and the lower switching elements 5 d to 5 f are connected to the AC power source 1 through the breaker 2. Driving circuits 4a to 4f for driving switching elements 5a to 5f, smoothing capacitors 3 connected to collector terminals of upper switching elements 5a to 5c and emitter terminals of lower switching elements 5d to 5f are provided. A DC / DC converter 12 is provided that steps down the voltage across the smoothing capacitor 3 and supplies the voltage to the harmonic current compensation controller 11 and the drive circuits 4a to 4f. While the AC power source 1 is connected to the middle point of the upper switching element and the lower switching element, the anti-resistance resistors 8a and 8b and the relays 7a and 7b connected in parallel to the anti-resistance resistors 8a and 8b, respectively Is provided. The harmonic current compensator 70 is configured as described above. In addition, as shown in FIG. 6, the inrush resistances 8a and 8b are preferably provided in at least two phases of the three-phase alternating current in order to protect all the switching elements from the inrush current.

  When the breaker is turned on, the relays 7a and 7b are turned off, and the charging current of the smoothing capacitor 3 flows via the anti-resistance resistors 8a and 8b. Thereby, since an inrush current is suppressed and it flows into the smoothing capacitor 3, damage to the smoothing capacitor 3 is suppressed. Furthermore, since the anti-resistance resistors 8a and 8b are connected to the alternating current side of the switching elements 5a to 5f, the rate of change dv / dt of the voltage applied to the switching elements 5a to 5f can be greatly reduced. Thereby, damage to switching elements 5a-5f can be controlled.

  After the smoothing capacitor 3 is charged, the relays 7a and 7b connected in parallel to the anti-resistance resistors 8a and 8b are turned on. Then, the current flow is switched from the resistances 8a and 8b to the relays 7a and 7b, and power loss due to the resistances 8a and 8b does not occur during normal operation.

  The value of the current flowing through the diode bridge 13 is detected by the current detectors 80a and 80b and input to the harmonic current compensation control unit 11. Using the current values detected by the current detectors 80 a and 80 b, the active filter 70 outputs a current that compensates for the harmonic current included in the current of the diode bridge 13.

  As described above, by providing the resistances 8a and 8b on the AC side of the switching elements 5a to 5f, the rate of change dv / dt of the voltage between the collector and the emitter of the switching elements 5a to 5f when the breaker 2 is turned on. Is reduced, and the breakdown voltage of the switching elements 5a to 5f is improved. Therefore, destruction of the switching elements 5a to 5f is suppressed, and a highly reliable harmonic current compensation device and a harmonic current compensation system can be provided.

(Example 2) (AC L and noise filter are added)
A second embodiment of the present invention will be described with reference to FIG. FIG. 7 differs from FIG. 6 of the first embodiment in that AC reactors 30 a to 30 c and a noise filter 31 are provided after the AC power source 1 branches to the diode bridge 3 and the active filter 70.

  The noise filter 31 includes a common mode coil 32, an X capacitor 33, and a Y capacitor 34. AC reactors 30a to 30c compensate for harmonics generated by active filter 70. The noise filter 31 suppresses noise such as a noise terminal voltage.

  Similar to the first embodiment, by providing the anti-resistance resistors 8a and 8b on the AC side, the rate of change dv / dt of the voltage between the collector and emitter of the switching elements 5a to 5f when the breaker 2 is turned on is reduced. The breakdown voltage of the switching element is improved. Further, the AC reactors 30a to 30c and the noise filter 31 are provided with anti-resistance resistors 8a and 8b at the subsequent stage in order to suppress fluctuations in current, so that the anti-resistance resistors 8a and 8b themselves protecting the switching elements 5a to 5f. Can also be protected. Therefore, the destruction of the switching elements 5a to 5f and the collision resistances 8a and 8b can be suppressed, and the reliability can be improved.

Example 3 (single phase)
A third embodiment of the present invention will be described with reference to FIG. FIG. 7 differs from FIG. 6 of the first embodiment in that the AC power source 1 is a single phase. In the single phase, at least one pair of the rush resistance 8a and the relay 7a is provided.

  In the case of a single phase, all the switching elements can be protected by providing an anti-impact resistor 8a on one of the connection lines connecting the AC power source 1 and the midpoint of the switching element. Compared to the case of a power supply, the cost can be reduced and the breakdown voltage of the switching element can be improved.

  Also in the present embodiment, the provision of the resistance resistor 8a on the AC side reduces the rate of change dv / dt of the voltage between the collector and emitter of the switching elements 5a to 5f when the breaker 2 is turned on, and the switching element The breakdown voltage is improved. Therefore, the destruction of the switching element is suppressed, and a highly reliable harmonic current compensation device and harmonic current compensation system can be provided.

(Example 4) (Converter)
A fourth embodiment of the present invention will be described with reference to FIG. 9 differs from FIG. 6 of the first embodiment in that a converter 71 is provided instead of the diode bridge 13. When the current is rectified by the diode bridge 13 to be a direct current, the diode current is distorted in waveform as compared with the sine wave, and therefore an active filter for compensating the harmonic current is required.

  On the other hand, the converter 71 switches the switching elements 5a to 5f at a carrier frequency of about several kHz to 20 kHz, thereby making the current waveform of the smoothing capacitor 3 close to a sine wave and suppressing the harmonic current. The inverter 72 converts the direct current of the smoothing capacitor 3 into alternating current and drives the motor 42 serving as a load. The inverter 72 includes switching elements 40a to 40f and diodes 41a to 41f connected in antiparallel with the switching elements.

  Also in this embodiment, by providing the anti-resistance resistors 8a and 8b on the AC side, the rate of change dv / dt of the voltage between the collector and emitter of the switching elements 5a to 5f when the breaker 2 is turned on is reduced, and switching is performed. The breakdown voltage of the element is improved. Therefore, destruction of a switching element is suppressed and a highly reliable power converter and power conversion system can be provided.

(Example 5) (Air conditioner)
A fifth embodiment of the present invention will be described with reference to FIGS. FIG. 10 is an overall configuration diagram in which the harmonic current compensator according to the first to third embodiments of the present invention is applied to an air conditioner. FIG. 11 is a side view of the outdoor unit of the air conditioner. FIG. 12 is a front view of the outdoor unit of the air conditioner.

  As shown in FIG. 10, an inverter 15 and a compressor 61 driven by the inverter 15 are connected. From this compressor 61, a condenser 62, an expansion device 63, and an evaporator 64 are connected in this order by refrigerant piping to constitute a refrigeration cycle.

  The air conditioner according to the present embodiment includes the harmonic current compensator according to the first to third embodiments as a constituent element. The gas refrigerant compressed to high temperature and high pressure by the compressor 61 in the refrigeration cycle undergoes heat exchange in the condenser 62, dissipates heat and condenses. The condensed refrigerant is depressurized and expanded by the expansion device 63, heat exchange is performed by the evaporator 64, and the heat is absorbed and vaporized. The vaporized gas refrigerant is compressed again by the compressor 61.

  The outdoor unit of the air conditioner of FIG. 11 includes a fan guard 51, a propeller fan 53, a fan motor 54, an electric component box 55, a compressor 56, an accumulator 57, and a heat exchanger 58. There is a service opening in the front 52 of the outdoor unit. The compressor 56 sucks and compresses the refrigerant, and discharges the compressed refrigerant. Various compressors such as a scroll compressor can be adopted as the compressor 56. The heat exchanger 58 is an air heat exchanger for exchanging heat between the refrigerant and outdoor air, and a cross fin type fin-and-tube heat exchanger or the like can be adopted. The propeller fan 53 blows outdoor air to the heat exchanger 58. The accumulator 57 gas-liquid separates the incoming refrigerant and sends the separated gas refrigerant to the compressor 56. FIG. 12 shows a front view of FIG. When the service opening on the front side of the outdoor unit of the air conditioner is opened, the electric component box 55 is arranged on the front side, and the active filters 60 of the first to fourth embodiments are arranged beside the electric box 55.

  Also in this embodiment, by providing the anti-resistance resistors 8a and 8b on the AC side, the rate of change dv / dt of the voltage between the collector and emitter of the switching elements 5a to 5f when the breaker 2 is turned on is reduced, and switching is performed. The breakdown voltage of the element is improved. Therefore, destruction of a switching element is suppressed and a highly reliable air conditioner and air conditioning system can be provided.

  In the harmonic compensator according to the first to third embodiments and the power converter according to the fourth embodiment, power is obtained by using a wide gap semiconductor such as SiC (silicon carbide), GaN (gallium nitride), or diamond for the switching element or the diode. Loss is reduced, and the harmonic current compensator can be miniaturized and mounted inside the outdoor unit as shown in FIG.

  In the present invention, several embodiments have been described in order to solve the problems of the present application, but the present invention is not limited to this. As long as there is no contradiction, it cannot be overemphasized that it can change and implement by the change implementation according to the meaning of a claim, for example, the combination between Examples, the combination of the characteristic in an Example, etc.

DESCRIPTION OF SYMBOLS 1 AC power source 2 Breaker 3, 14 Smoothing capacitor 42 Load 4 Drive circuit 5, 40 Switching element 6, 41 Diode 7 Relay 8 Anti-shock resistance 11 Harmonic current compensation control part 12 DC / DC converter 13 Diode bridge 15, 71 Device 20 Gate resistance 21 P-type MOSFET
22 N-type MOSFET
23 Positive terminal of main circuit power supply 24 Positive terminal of driver power supply 25 Output stage 30 of driver circuit 31 AC reactor 31 Noise filter 55 Electrical component box 56, 61 Compressor 60, 70 Harmonic current compensator (active filter)
70 Converter 80 Current detector

Claims (6)

A power conversion device that is connected to an AC power source and converts power,
A power converter configured by connecting in parallel a plurality of arms in which an upper switching element that is an IGBT and a lower switching element that is an IGBT are connected in series;
The upper switching element or the lower switching element is provided for each of the upper switching element and the lower switching element, and the higher the change rate of the collector voltage of the upper switching element or the lower switching element when the power is turned on, A plurality of drive circuits configured to reduce the breakdown voltage of
Smoothing capacitors connected to both ends of the arm;
A power converter comprising: a rush resistance provided between a middle point of the upper switching element and the lower switching element and the AC power supply connected to suppress an inrush current. The power conversion unit is configured by connecting the three arms in parallel,
The AC power supply is a three-phase AC power supply,
Each phase of the AC power supply is connected to each middle point of the upper switching element and the lower switching element, respectively.
Each of the plurality of drive circuits includes a P-type MOSFET, an N-type MOSFET connected to the P-type MOSFET, a connection point of the P-type MOSFET and the N-type MOSFET, and the upper switching element or the lower switching element. A gate resistor connected to the gate terminal of
The power conversion device according to claim 1, wherein the rush resistance is provided at at least two locations between each phase and each midpoint. An AC reactor is provided between the middle point of the upper switching element and the lower switching element and the AC power source is connected,
The power conversion device according to claim 1, wherein the collision prevention resistance is provided between the AC reactor and the midpoint. A noise filter is provided between the middle point of the upper switching element and the lower switching element and the AC power supply,
The power converter according to claim 1, wherein the rush resistance is provided between the noise filter and the midpoint. A harmonic current compensator comprising the power converter of claim 1,
A load current detector for detecting a current supplied to a load connected in parallel with the power converter to the AC power source;
A harmonic current compensator comprising: a compensation control unit that drives the power converter based on a load current detected by the load current detector and suppresses harmonics generated in the load. A refrigeration cycle configured by connecting a compressor for compressing a refrigerant, an expansion device, and a heat exchanger;
An air conditioner comprising: a harmonic current compensator according to claim 5 that suppresses harmonics generated by an inverter that drives the compressor.

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