Power conversion device, motor drive device, and air conditioner

Abstract

The power conversion device comprises: a bridge arm circuit (3) which converts an AC voltage output from an AC power source (1) into a DC voltage and has at least one bridge arm formed by connecting a switching element connected in parallel with a diode in series; and a reactor (2) having one end connected to the AC power source (1) and the other end connected to a connection point of two switching elements of the bridge arm. When the bridge arm circuit (3) is short-circuited, the short-circuit current flowing therethrough flows in the order from the reactor (2) to the switching element of the bridge arm that causes the current to flow in the direction opposite to the forward direction of the diode connected in parallel, or from the switching element of the bridge arm that causes the current to flow in the direction opposite to the forward direction of the diode connected in parallel to the reactor (2), depending on the polarity of the AC power source (1).

Description

Technical Field

[0001] The present invention relates to a power conversion device, a motor drive device and an air conditioner for converting AC power into DC power. Background Art

[0002] Conventionally, there is a power conversion device that uses a bridge arm circuit composed of switching elements to convert supplied AC power into DC power and output it. The power conversion device can perform a voltage-boosting operation to boost the voltage of the AC power and a synchronous rectification operation to rectify the AC power by turning the switching elements on and off.

[0003] Patent document 1 discloses a technology in which a power conversion device controls two of four switching elements according to the polarity of the voltage of AC power supplied from an AC power source and the current flowing to the AC power source, and controls the other two switching elements according to the polarity of the current.

[0004] Prior Art Literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-7326 Summary of the invention

[0007] Problems to be solved by the invention

[0008] In a power conversion device, generally speaking, when a switching element with a low switching speed is used, the switching frequency is low, so the reactor connected between the converter and the AC power supply will be large. The power conversion device can miniaturize the reactor by using a switching element with a high switching speed. However, when a power conversion device uses a switching element with a high switching speed, the switching frequency becomes high, so there is a problem that noise such as radiation noise and conduction noise increases.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to obtain a power conversion device capable of reducing the size of a reactor and reducing noise.

[0010] Solutions to Solve Problems

[0011] In order to solve the above problems and achieve the purpose, the power conversion device of the present invention comprises: a bridge arm circuit, which converts the AC voltage output from the AC power supply into a DC voltage, and has at least one bridge arm, which is formed by connecting in series the switching elements connected in parallel with the diodes; and a reactor, one end of which is connected to the AC power supply, and the other end of which is connected to the connection point of the two switching elements of the bridge arm. In the power conversion device, the short-circuit current flowing when the bridge arm circuit is short-circuited flows in the order from the reactor to the switching element of the bridge arm that makes the current flow in the direction opposite to the forward direction of the diode connected in parallel, or in the order from the switching element of the bridge arm that makes the current flow in the direction opposite to the forward direction of the diode connected in parallel to the reactor, depending on the polarity of the AC power supply.

[0012] Effects of the Invention

[0013] The power conversion device according to the present invention has the effect of reducing the size of the reactor and reducing noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a diagram showing a configuration example of a power conversion device according to the first embodiment.

[0015] Figure 2 It is a schematic cross-sectional view showing a schematic structure of a MOSFET.

[0016] Figure 3 This is a first diagram showing the path of the current flowing through the power conversion device according to the first embodiment when the absolute value of the power supply current is larger than the current threshold value and the polarity of the power supply voltage is positive.

[0017] Figure 4 The first diagram shows the path of the current flowing through the power conversion device according to the first embodiment when the absolute value of the power supply current is larger than the current threshold value and the polarity of the power supply voltage is negative.

[0018] Figure 5 The second diagram shows the path of the current flowing through the power conversion device according to the first embodiment when the absolute value of the power supply current is larger than the current threshold value and the polarity of the power supply voltage is positive.

[0019] Figure 6 The second diagram shows the path of the current flowing through the power conversion device according to the first embodiment when the absolute value of the power supply current is larger than the current threshold value and the polarity of the power supply voltage is negative.

[0020] Figure 7 This is a diagram showing a first configuration example of a gate driving unit included in the arm circuit of the power conversion device according to the first embodiment.

[0021] Figure 8 This is a diagram showing a second configuration example of a gate driving unit included in the arm circuit of the power conversion device according to the first embodiment.

[0022] Fig. 9 This is a diagram showing a third configuration example of the gate driving unit included in the arm circuit of the power conversion device according to the first embodiment.

[0023] Fig.10 This is a diagram showing a fourth configuration example of the gate driving unit included in the arm circuit of the power conversion device according to the first embodiment.

[0024] Fig.11 This is a diagram showing an example of a hardware configuration for realizing a control unit included in the power conversion device according to the first embodiment.

[0025] Fig.12 This is a diagram showing a configuration example of a motor drive device according to the second embodiment.

[0026] Fig.13 This is a diagram showing a configuration example of an air conditioner according to Embodiment 3.

[0027] Fig.14 This is a diagram showing a configuration example of a power conversion device according to a fourth embodiment. DETAILED DESCRIPTION

[0028] Hereinafter, a power conversion device, a motor drive device, and an air conditioner according to an embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the embodiment.

[0029] Implementation method 1.

[0030] Figure 1 1 is a diagram showing a configuration example of a power conversion device 100 according to Embodiment 1 of the present invention. The power conversion device 100 is a power supply device having an AC-DC conversion function that converts AC power supplied from an AC power source 1 into DC power using a bridge arm circuit 3 and applies the DC power to a load 50. Figure 1 As shown, the power conversion device 100 includes a reactor 2 , an arm circuit 3 , a smoothing capacitor 4 , a power supply voltage detection unit 5 , a power supply current detection unit 6 , a bus voltage detection unit 7 , and a control unit 10 .

[0031] The bridge arm circuit 3 is a circuit that includes two arms connected in parallel, the arms are connected in series with two switching elements connected in parallel with diodes, and the two arms are connected in parallel. The bridge arm circuit 3 converts the AC voltage output from the AC power supply 1 into a DC voltage. Specifically, the bridge arm circuit 3 includes a first arm 31 as a first circuit and a second arm 32 as a second circuit. The first arm 31 includes a switching element 311 and a switching element 312 connected in series. A parasitic diode 311a is formed in the switching element 311. The parasitic diode 311a is connected in parallel between the drain and source of the switching element 311. A parasitic diode 312a is formed in the switching element 312. The parasitic diodes 311a and 312a are diodes used as freewheeling diodes, respectively. In addition, the first arm 31 is sometimes referred to as a bridge arm.

[0032] The second arm 32 includes a switch element 321 and a switch element 322 connected in series. The second arm 32 is connected in parallel with the first arm 31. A parasitic diode 321a is formed in the switch element 321. The parasitic diode 321a is connected in parallel between the drain and source of the switch element 321. A parasitic diode 322a is formed in the switch element 322. The parasitic diodes 321a and 322a are respectively used as freewheeling diodes. In addition, the second arm 32 is sometimes referred to as a bridge arm.

[0033] Specifically, the power conversion device 100 includes: a first wiring 501 and a second wiring 502 respectively connected to the AC power source 1; and a reactor 2 arranged on the first wiring 501. In addition, the first arm 31 includes: a switching element 311 as a first switching element; a switching element 312 as a second switching element; and a third wiring 503 having a first connection point 506. The switching element 311 and the switching element 312 are connected in series by the third wiring 503. The first wiring 501 is connected to the first connection point 506. The first connection point 506 is connected to the AC power source 1 via the first wiring 501 and the reactor 2. It can also be said that for the reactor 2, one end is connected to the AC power source 1, and the other end is connected to the connection point of the switching element 311 and the switching element 312.

[0034] The second arm 32 includes a switch element 321 as a third switch element, a switch element 322 as a fourth switch element, and a fourth wiring 504 having a second connection point 508. The switch element 321 and the switch element 322 are connected in series by the fourth wiring 504. The second wiring 502 is connected to the second connection point 508. The second connection point 508 is connected to the AC power source 1 via the second wiring 502.

[0035] In addition, the bridge arm circuit 3 includes: a gate driving unit 33 for driving the switching element 311; a gate driving unit 34 for driving the switching element 312; a gate driving unit 35 for driving the switching element 321; and a gate driving unit 36 ​​for driving the switching element 322. The gate driving unit 33 is a first driving unit that turns on or off the switching element 311 based on a control signal generated by the control unit 10. The gate driving unit 34 is a second driving unit that turns on or off the switching element 312 based on a control signal generated by the control unit 10. The gate driving unit 35 is a third driving unit that turns on or off the switching element 321 based on a control signal generated by the control unit 10. The gate driving unit 36 ​​is a fourth driving unit that turns on or off the switching element 322 based on a control signal generated by the control unit 10.

[0036] The gate drive units 33 to 36 control the switching speed of the connected switching elements by means of gate resistors provided therein. In the present embodiment, the gate drive unit 33 uses gate resistors with different resistance values ​​when turning on the switching element 311 and when turning off the switching element 311. Similarly, the gate drive unit 34 uses gate resistors with different resistance values ​​when turning on the switching element 312 and when turning off the switching element 312. The specific configuration of the gate drive units 33 and 34 will be described later. The gate drive units 35 and 36 have one gate resistor inside, and use the same resistor as the gate resistor when turning on and when turning off. In the following description, turning on is sometimes referred to as turning on, and turning off is sometimes referred to as turning off. In addition, the gate drive units are not limited to Figure 1 For example, the switching elements 311 and 312 may be turned on or off by one gate driving unit, and the switching elements 321 and 322 may be turned on or off by one gate driving unit.

[0037] The smoothing capacitor 4 is a capacitor connected in parallel with the bridge arm circuit 3, specifically the second arm 32. In the bridge arm circuit 3, one end of the switch element 311 is connected to the positive side of the smoothing capacitor 4, the other end of the switch element 311 is connected to one end of the switch element 312, and the other end of the switch element 312 is connected to the negative side of the smoothing capacitor 4.

[0038] The switching elements 311, 312, 321, and 322 are composed of MOSFETs. MOSFETs composed of wide band gap (WBG) semiconductors such as gallium nitride (GaN), gallium oxide (Ga2O3), silicon carbide (SiC), diamond, or aluminum nitride can be used in the switching elements 311, 312, 321, and 322. By using WBG semiconductors in the switching elements 311, 312, 321, and 322, the voltage resistance is improved and the allowable current density is also increased, so the module can be miniaturized. Since WBG semiconductors also have high heat resistance, the heat dissipation fins of the heat dissipation part can also be miniaturized. In this embodiment, the switching speed of the switching elements 311 and 312 is set to be faster than the switching speed of the switching elements 321 and 322.

[0039] The control unit 10 generates a control signal for operating the gate drive units 33 to 36 of the bridge arm circuit 3 based on the signals respectively output from the power supply voltage detection unit 5, the power supply current detection unit 6, and the bus voltage detection unit 7. The power supply voltage detection unit 5 is a voltage detection unit that detects the voltage value of the output voltage of the AC power supply 1, that is, the power supply voltage Vs, and outputs an electrical signal indicating the detection result to the control unit 10. The power supply current detection unit 6 is a current detection unit that detects the current value of the current output from the AC power supply 1, that is, the power supply current Is, and outputs an electrical signal indicating the detection result to the control unit 10. The power supply current Is is the current value of the current flowing between the AC power supply 1 and the bridge arm circuit 3. The bus voltage detection unit 7 is a voltage detection unit that detects the bus voltage Vdc and outputs an electrical signal indicating the detection result to the control unit 10. The bus voltage Vdc is a voltage obtained by smoothing the output voltage of the bridge arm circuit 3 by the smoothing capacitor 4. The control unit 10 generates a control signal based on the power supply voltage Vs, the power supply current Is, and the bus voltage Vdc to operate the gate drive units 33 to 36 and control the on and off of the switching elements 311, 312, 321, and 322. In addition, the control unit 10 may control the on and off of the switching elements 311, 312, 321, and 322 using at least one of the power supply voltage Vs, the power supply current Is, and the bus voltage Vdc.

[0040] Next, the basic operation of the power conversion device 100 according to Embodiment 1 is described. Hereinafter, the switching elements 311 and 321 connected to the positive side of the AC power source 1, that is, the positive terminal of the AC power source 1, are sometimes referred to as upper switching elements. In addition, the switching elements 312 and 322 connected to the negative side of the AC power source 1, that is, the negative terminal of the AC power source 1, are sometimes referred to as lower switching elements.

[0041] In the first arm 31, the upper switching element and the lower switching element work complementarily. That is, when one of the upper switching element and the lower switching element is turned on, the other is turned off. The switching elements 311 and 312 constituting the first arm 31 are driven by the drive signals, i.e., PWM (Pulse Width Modulation) signals, generated by the gate drive units 33 and 34, respectively. Hereinafter, the operation of turning on or off the switching elements 311 and 312 according to the PWM signal will also be referred to as switching operation. In order to prevent the short circuit of the smoothing capacitor 4 via the AC power supply 1 and the reactor 2, when the absolute value of the power supply current Is output from the AC power supply 1 is below the current threshold, the switching element 311 and the switching element 312 are both turned off. Hereinafter, the short circuit of the smoothing capacitor 4 is referred to as capacitor short circuit. Capacitor short circuit is a state in which the energy stored in the smoothing capacitor 4 is released and current is regenerated in the AC power supply 1.

[0042] The switch elements 321 and 322 constituting the second arm 32 are turned on or off by the drive signals generated by the gate drive units 35 and 36, respectively. The switch elements 321 and 322 are basically turned on or off according to the polarity of the voltage output from the AC power supply 1, that is, the polarity of the power supply voltage. Specifically, when the polarity of the power supply voltage is positive, the switch element 322 is turned on and the switch element 321 is turned off. When the polarity of the power supply voltage is negative, the switch element 321 is turned on and the switch element 322 is turned off. In addition, Figure 1 In FIG. 1 , control signals to the gate driving units 33 to 36 are indicated by arrows from the control unit 10 toward the arm circuit 3 .

[0043] Next, the relationship between the state of the switching element in the first embodiment and the path of the current flowing in the power conversion device 100 according to the first embodiment will be described. Figure 2 The structure of MOSFET is described.

[0044] Figure 2 is a schematic cross-sectional view showing the schematic structure of a MOSFET. Figure 2 In the case of an n-type MOSFET, as shown in FIG. Figure 2 As shown in FIG. 1 , a p-type semiconductor substrate 600 is used. On the semiconductor substrate 600, a source electrode S, a drain electrode D, and a gate electrode G are formed. In the portion in contact with the source electrode S and the drain electrode D, ion implantation of high-concentration impurities is performed to form an n-type region 601. In addition, in the semiconductor substrate 600, an oxide insulating film 602 is formed between the portion where the n-type region 601 is not formed and the gate electrode G. That is, the oxide insulating film 602 is interposed between the gate electrode G and the p-type region 603 in the semiconductor substrate 600.

[0045] When a positive voltage is applied to the gate electrode G, electrons are attracted to the interface between the p-type region 603 and the oxide insulating film 602 in the semiconductor substrate 600, and the interface becomes negatively charged. In the area where electrons gather, the electron density is higher than the hole density, and the n-type is formed. The n-type portion becomes a channel for current and is called a channel 604. The channel 604 is Figure 2 In the example of , the n-type channel is used. By controlling the MOSFET to be turned on, more current flows into the channel 604 than the parasitic diode formed in the p-type region 603 .

[0046] Figure 3 1 is a first diagram showing the path of the current flowing through the power conversion device 100 according to the first embodiment when the absolute value of the power supply current Is is greater than the current threshold value and the polarity of the power supply voltage is positive. Figure 3 In the embodiment 1, the power supply voltage polarity is positive, the switch element 311 and the switch element 322 are turned on, and the switch element 312 and the switch element 321 are turned off. In this state, the current flows in the order of the AC power supply 1, the reactor 2, the switch element 311, the smoothing capacitor 4, the switch element 322, and the AC power supply 1. Thus, in the first embodiment, the current does not flow to the parasitic diode 311a and the parasitic diode 322a, but flows to the respective channels of the switch element 311 and the switch element 322, thereby performing synchronous rectification. In addition, in Figure 3 In the figure, the switched-on switching element is indicated by a circular mark. The same is true in the subsequent figures.

[0047] Figure 4 1 is a first diagram showing the path of the current flowing through the power conversion device 100 according to the first embodiment when the absolute value of the power supply current Is is greater than the current threshold value and the polarity of the power supply voltage is negative. Figure 4 In the embodiment 1, the power supply voltage polarity is negative, the switch element 312 and the switch element 321 are turned on, and the switch element 311 and the switch element 322 are turned off. In this state, the current flows in the order of the AC power supply 1, the switch element 321, the smoothing capacitor 4, the switch element 312, the reactor 2, and the AC power supply 1. In this way, in the first embodiment, the current does not flow to the parasitic diode 321a and the parasitic diode 312a, but the current flows to the respective channels of the switch element 321 and the switch element 312, thereby performing synchronous rectification operation.

[0048] Figure 5 FIG. 2 is a second diagram showing the path of the current flowing through the power conversion device 100 according to the first embodiment when the absolute value of the power supply current Is is greater than the current threshold value and the polarity of the power supply voltage is positive. Figure 5In the embodiment 1, the power supply voltage polarity is positive, the switch elements 312 and 322 are turned on, and the switch elements 311 and 321 are turned off. In this state, the current flows in the order of the AC power supply 1, the reactor 2, the switch element 312, the switch element 322, and the AC power supply 1, forming a power supply short-circuit path that does not pass through the smoothing capacitor 4. In this way, in the first embodiment, the current flows to the channels of the switch elements 312 and 322 instead of the parasitic diodes 312a and 322a, thereby forming a power supply short-circuit path.

[0049] Figure 6 FIG2 is a second diagram showing the path of the current flowing through the power conversion device 100 according to the first embodiment when the absolute value of the power supply current Is is greater than the current threshold value and the polarity of the power supply voltage is negative. Figure 6 In the embodiment 1, the power supply voltage polarity is negative, the switch element 311 and the switch element 321 are turned on, and the switch element 312 and the switch element 322 are turned off. In this state, the current flows in the order of the AC power supply 1, the switch element 321, the switch element 311, the reactor 2, and the AC power supply 1, forming a power supply short-circuit path that does not pass through the smoothing capacitor 4. In this way, in the first embodiment, the current flows to the channels of the switch element 321 and the switch element 311 instead of the parasitic diode 321a and the parasitic diode 311a, thereby forming a power supply short-circuit path.

[0050] exist Figure 5 as well as Figure 6 In the example of , the switch elements 311 and 312 function as switches for controlling the flow of short-circuit current. Figure 5 as well as Figure 6 In the example, the switching elements 321 and 322 function as rectifiers. In the power conversion device 100, when the bridge arm circuit 3 is short-circuited, the short-circuit current flows from the inductor 2 to the switching element 312 that causes the current to flow in the direction opposite to the forward direction of the parasitic diode 312a, or from the switching element 311 that causes the current to flow in the direction opposite to the forward direction of the parasitic diode 311a to the inductor 2, depending on the polarity of the AC power supply 1. Specifically, Figure 5 As shown in the example, when the positive electrode of the AC power source 1 is on the reactor 2 side, in the power conversion device 100, since the reactor 2 and the switching element 312 are connected in series, the short-circuit current flows through the reactor 2 and then flows to the switching element 312. Figure 6As shown in the example, when the negative electrode of the AC power source 1 is on the reactor 2 side, in the power conversion device 100, since the switching element 311 is connected in series with the reactor 2, the short-circuit current flows to the reactor 2 after flowing through the switching element 311. With such a configuration, it is expected that the noise generated in the switching elements 311 and 312 during switching will be attenuated due to the influence of the impedance of the reactor 2.

[0051] Here, in Figure 3 When the synchronous rectification is in operation, current may flow through the parasitic diode 311a of the switching element 311 depending on the timing of switching on and off. Figure 5 When the power supply shown in FIG. 1 is short-circuited, the load side voltage (DC voltage) is applied to the parasitic diode 311a via the switch element 312a. Therefore, although a recovery current formed by the reverse operation flows in the parasitic diode 311a, this current also causes noise (recovery noise) to be generated. This recovery noise is transmitted along the wiring and conducted to the AC power supply 1 side, but by Figure 5 The power supply short-circuit operation is performed along the path shown, and the noise outflow to the AC power supply 1 side can be suppressed due to the existence of the impedance of the reactor 2. That is, with respect to the diode connected in parallel with the switching element of the bridge arm connected to the reactor side, by controlling the switching element so that a short-circuit current flows in the direction opposite to the forward direction, the outflow of the power supply side of the recovery noise can be suppressed.

[0052] The control unit 10 can control the values ​​of the power supply current Is and the bus voltage Vdc by controlling the switching of the current path described above. The power conversion device 100 continuously switches when the power supply voltage polarity is positive. Figure 3 The load power supply mode and Figure 5 The power supply short-circuit mode shown here switches continuously when the supply voltage polarity is negative. Figure 4 The load power supply mode and Figure 6 The power supply short-circuit mode shown in the figure is used to realize the operation such as the rise of the bus voltage Vdc and the synchronous rectification of the power supply current Is. Specifically, the control unit 10 sets the switching frequency of the switching elements 311 and 312 that perform the switching operation based on PWM to be higher than the switching frequency of the switching elements 321 and 322 that perform the switching operation corresponding to the polarity of the power supply voltage Vs, and controls the switching elements 311, 312, 321, and 322 to be turned on and off. In the following description, the switching elements 311, 312, 321, and 322 are sometimes referred to as switching elements when they are not distinguished. Similarly, the parasitic diodes 311a, 312a, 321a, and 322a are sometimes referred to as parasitic diodes when they are not distinguished.

[0053] Next, the configuration of the gate drive units 33 and 34 included in the arm circuit 3 will be described. In the arm circuit 3, by connecting the reactor 2, the noise caused by the switching elements 311 and 312 of the first arm 31 can be reduced, and the shaking of the ground line of the arm circuit 3 can be suppressed. In the arm circuit 3, since the noise caused by the switching elements 311 and 312 can be reduced, the resistance value of the gate resistor included in the gate drive units 33 and 34 connected to the switching elements 311 and 312 can be reduced. As a result, as described above, the switching speed of the switching elements 311 and 312 can be set to a higher speed than the switching speed of the switching elements 321 and 322. In addition, in the power conversion device 100, the size of the reactor 2 can be reduced, that is, the reactor 2 can be miniaturized, compared with the case where the switching speed of the switching elements 311 and 312 is the same as the switching speed of the switching elements 321 and 322.

[0054] The bridge arm circuit 3 can increase the switching speed of the switching elements 311 and 312 by reducing the resistance value of the gate resistor of the gate drive unit 33 and 34. On the other hand, even if the bridge arm circuit 3 makes the switching speed of the switching elements 311 and 312 too fast, the noise such as the radiation noise caused by the switching, the conduction noise returned from the load 50 or the structure connected to the load 50 through the ground impedance, etc. will also increase. In addition, in the switching elements 311 and 312, the noise generation conditions may be different when they are turned on and when they are turned off. Therefore, in this embodiment, in the gate drive units 33 and 34 that turn the switching elements 311 and 312 on and off, gate resistors with different resistance values ​​are used when they are turned on and when they are turned off. Specifically, the gate drive units 33 and 34 set the resistance value of the gate resistor used in the operation with less noise generated when turning on or off in the switching elements 311 and 312 to be smaller than the resistance value of the gate resistor used in the operation with greater noise. By changing the resistance value of the gate resistor used in the gate driving units 33 and 34 at the time of opening and closing, the arm circuit 3 can suppress the generation of noise and increase the switching speed of the switching element.

[0055] Specifically, the configuration of the gate drive units 33 and 34 will be described when the noise generated when the switching elements 311 and 312 are turned on is greater than when they are turned off. In addition, since the gate drive units 33 and 34 have the same configuration, the gate drive unit 33 will be described. Figure 71 is a diagram showing a first configuration example of a gate drive unit 33 included in the bridge arm circuit 3 of the power conversion device 100 according to Embodiment 1. The gate drive unit 33 includes a resistor 331, a diode 332, and a resistor 333. The resistor 331 is a gate resistor and is a first resistor used when the switch element 311 is turned off. The diode 332 is a first diode through which current flows when the switch element 311 is turned off. The cathode of the diode 332 is connected to the resistor 331, and the anode is connected to the switch element 311. In addition, Figure 7 The arrangement of the diode 332 shown is an example, but is not limited thereto. The cathode of the diode 332 may be connected to the control unit 10, and the anode may be connected to the resistor 331. The resistor 333 is a gate resistor, and is a second resistor used when the switch element 311 is turned on. Figure 7 In the embodiment, a series circuit of a resistor 331 and a diode 332 is connected in parallel with a resistor 333 . Figure 7 The circuit shown is a speed changing mechanism that changes the switching speed when the switching element 311 is turned on and off. The same applies to the circuit included in the gate drive unit described below. The gate drive unit 33 changes the switching speed when turning on and off according to the resistance value of the gate resistor.

[0056] Here, the resistance value of the resistor 331 is set to be less than or equal to the resistance value of the resistor 333. Figure 7 In the case where the difference between the resistance value of the resistor 331 and the resistance value of the resistor 333 is large, for example, when the difference is 10 times or more, the current from the switch element 311 to the control unit 10 flows mostly to the resistor 331 and hardly flows to the resistor 333. In this case, the resistance value of the gate resistor when the gate driver 33 turns off the switch element 311 is substantially the resistance value of the resistor 331. In addition, when the resistance value of the resistor 331 and the resistance value of the resistor 333 are the same or not much different, the current from the switch element 311 to the control unit 10 also flows to the resistor 333. In this case, the resistance value of the gate resistor when the gate driver 33 turns off the switch element 311 is the resistance value of the combined resistor connected in parallel with the resistor 331 and the resistor 333. However, since the resistance value of the resistor 331 is ≤ the resistance value of the resistor 333, the resistance value of the combined resistor is smaller than the resistance value of the resistor 333.

[0057] When the gate driving unit 33 turns on the switching element 311, since the diode 332 is reversely connected in the gate driving unit 33, current does not flow to the resistor 331, but current flows from the control unit 10 to the switching element 311 via the resistor 333. At this time, the gate driving unit 33 turns on the switching element 311 so that the resistance value of the gate resistor becomes the resistance value of the resistor 333.

[0058] In this way, the gate driver 33 can use the resistor 333 as a gate resistor when the gate driver 33 is turned on with a large noise, and can use the resistor 331 or a combined resistor of the resistor 331 and the resistor 333 as a gate resistor when the gate driver 33 is turned off with a small noise.

[0059] Next, the configuration of the gate drive units 33 and 34 will be described when the noise generated when the switching elements 311 and 312 are turned off is greater than when they are turned on. In addition, since the gate drive units 33 and 34 have the same configuration, the gate drive unit 33 will be described. Figure 8 1 is a diagram showing a second configuration example of the gate drive unit 33 included in the bridge arm circuit 3 of the power conversion device 100 according to the first embodiment. The gate drive unit 33 includes a resistor 331, a resistor 333, and a diode 334. The diode 334 is a second diode through which current flows when the switch element 311 is turned on. The anode of the diode 334 is connected to the resistor 333, and the cathode is connected to the switch element 311. Figure 8 The arrangement of the diode 334 shown is an example and is not limited thereto. The anode of the diode 334 may be connected to the control unit 10, and the cathode may be connected to the resistor 333. Figure 8 In the embodiment, the resistor 331 is connected in parallel with a series circuit of a resistor 333 and a diode 334 .

[0060] Here, the resistance value of the resistor 331 is set to be greater than or equal to the resistance value of the resistor 333. Figure 8 In the case where the difference between the resistance value of the resistor 331 and the resistance value of the resistor 333 is large, for example, when the difference is 10 times or more, the current from the control unit 10 to the switch element 311 flows mostly to the resistor 333 and hardly flows to the resistor 331. In this case, the resistance value of the gate resistor when the gate driving unit 33 turns on the switch element 311 is substantially the resistance value of the resistor 333. In addition, when the resistance value of the resistor 331 is the same as or not much different from the resistance value of the resistor 333, the current from the control unit 10 to the switch element 311 also flows to the resistor 331. In this case, the resistance value of the gate resistor when the gate driving unit 33 turns on the switch element 311 is the resistance value of the combined resistance connected in parallel with the resistor 333 and the resistor 331. However, since the resistance value of the resistor 331 is ≥ the resistance value of the resistor 333, the resistance value of the combined resistance is smaller than the resistance value of the resistor 331.

[0061] When the gate driving unit 33 turns off the switching element 311, since the diode 334 is reversely connected in the gate driving unit 33, the current does not flow to the resistor 333, but the current flows from the switching element 311 to the control unit 10 via the resistor 331. At this time, the gate driving unit 33 makes the resistance value of the gate resistor when the switching element 311 is turned off become the resistance value of the resistor 331.

[0062] In this way, the gate driver 33 can use the resistor 331 as a gate resistor when the gate driver 33 is turned off with a large noise, and can use the resistor 333 or a combined resistor of the resistor 333 and the resistor 331 as a gate resistor when the gate driver 33 is turned on with a small noise.

[0063] Next, the configuration of gate drive units 33 and 34 will be described when the noise generated when the switching elements 311 and 312 are turned on is slightly larger than when they are turned off. In addition, since gate drive units 33 and 34 have the same configuration, gate drive unit 33 will be used for the description. Fig. 9 3 is a diagram showing a third configuration example of the gate driver 33 included in the bridge arm circuit 3 of the power conversion device 100 according to the first embodiment. The gate driver 33 includes a resistor 331, a diode 332, a resistor 333, and a diode 334. Fig. 9 In the embodiment, a series circuit of a resistor 331 and a diode 332 is connected in parallel with a series circuit of a resistor 333 and a diode 334 .

[0064] Here, the resistance value of the resistor 331 is set to be less than the resistance value of the resistor 333. When the gate driving unit 33 turns on the switching element 311, since the diode 332 is reversely connected in the gate driving unit 33, the current does not flow to the resistor 331, but flows from the control unit 10 to the switching element 311 via the resistor 333 forwardly connected via the diode 334. At this time, the resistance value of the gate resistor when the gate driving unit 33 turns on the switching element 311 becomes the resistance value of the resistor 333.

[0065] When the gate driver 33 turns off the switch element 311, the diode 334 is reversely connected in the gate driver 33, so the current does not flow to the resistor 333, but the current flows from the switch element 311 to the control unit 10 via the resistor 331 connected in the forward direction via the diode 332. At this time, the gate driver 33 makes the resistance value of the gate resistor when the switch element 311 is turned off become the resistance value of the resistor 331. In addition, when the noise when the switch elements 311 and 312 are turned off is slightly larger than when they are turned on, the resistance value of the resistor 331 is set to be greater than the resistance value of the resistor 333.

[0066] When there is no significant difference between the noise generated when the switch element 311 is turned on and the noise generated when it is turned off, the user can use the resistors 331 and 333 of appropriate resistance values ​​in the gate driver 33 according to the noise generated. The gate driver 33 uses two diodes 332 and 334, so that the resistor 331 with a resistance value that takes into account the noise when it is turned off can be used as a gate resistor, and the resistor 333 with a resistance value that takes into account the noise when it is turned on can be used as a gate resistor.

[0067] In addition, although the gate drive units 33 and 34 are described as having the same structure, this is only an example and is not limited to this. Figure 7 In the case of the structure shown in FIG. 1 , the gate driver 34 can also be configured as Figure 8 or Fig. 9 The composition shown.

[0068] Furthermore, when the gate driving units 33 and 34 have the same configuration, gate resistors having different resistance values ​​may be used in the gate driving units 33 and 34 . Fig.10 3 is a diagram showing a fourth configuration example of gate drive units 33 and 34 included in the bridge arm circuit 3 of the power conversion device 100 according to the first embodiment. The gate drive unit 33 includes a resistor 331, a diode 332, and a resistor 333. In addition, the gate drive unit 34 includes a resistor 341, a diode 342, and a resistor 343. The resistor 341 is a gate resistor, and is a third resistor used when the switch element 312 is turned off. The diode 342 is a third diode through which current flows when the switch element 312 is turned off. The cathode of the diode 342 is connected to the resistor 341, and the anode is connected to the switch element 312. In addition, Fig.10 The arrangement of the diode 342 shown is an example and is not limited thereto. The cathode of the diode 342 may be connected to the control unit 10, and the anode may be connected to the resistor 341. The resistor 343 is a gate resistor and is a fourth resistor used when the switch element 312 is turned on. Fig.10 In the embodiment, a series circuit of a resistor 341 and a diode 342 is connected in parallel with a resistor 343.

[0069] For example, when the noise of the switching element 312 is larger than the noise of the switching element 311 during opening, the resistance value of the resistor 343 of the gate driving unit 34 is set to be larger than the resistance value of the resistor 333 of the gate driving unit 33. Similarly, when the noise of the switching element 312 is larger than the noise of the switching element 311 during closing, the resistance value of the resistor 341 of the gate driving unit 34 is set to be larger than the resistance value of the resistor 331 of the gate driving unit 33. Thus, the arm circuit 3 can use a gate resistor having an appropriate resistance value according to the magnitude of the noise generated in each switching element.

[0070] That is, the resistance value of the gate resistor when the gate drive unit 33 turns on the switching element 311 may be different from the resistance value of the gate resistor when the gate drive unit 34 turns on the switching element 312. Similarly, the resistance value of the gate resistor when the gate drive unit 33 turns off the switching element 311 may be different from the resistance value of the gate resistor when the gate drive unit 34 turns off the switching element 312. The power conversion device 100 can suppress the generation of noise without changing the control content of the control unit 10 by using the gate resistance of the gate drive units 33 and 34 set according to the magnitude of the noise generated in the switching elements 311 and 312. In addition, in Fig.10 In the embodiment of the present invention, as the configuration of the gate drive units 33 and 34, the gate drive units 33 and 34 are described as follows. Figure 7 Although the gate drive unit 33 of FIG. 1 is similar in structure to the gate drive unit 33 of FIG. 2 , this is only an example and is not limited to this. As the structure of the gate drive unit 33 and 34, the same Figure 8 or Fig. 9 The gate driving unit 33 has the same structure.

[0071] Here, the configuration of the switching element is described. In the power conversion device 100, as one of the methods for increasing the switching speed of the switching element, a method of reducing the gate resistance of the switching element can be cited. The smaller the gate resistance, the shorter the charging and discharging time relative to the gate input capacity, the shorter the opening period and the closing period, and thus the faster the switching speed.

[0072] However, there are limitations when reducing switching conversion losses by reducing gate resistance. Therefore, by forming the switching element with a WBG semiconductor such as GaN or SiC, the loss of each conversion can be further suppressed, the efficiency is further improved, and high-frequency switching can be performed. In addition, since high-frequency switching can be performed, the reactor 2 can be miniaturized, and the power conversion device 100 can be miniaturized and lightweight. In addition, by using WBG semiconductors in the switching element, the switching speed is increased, the switching conversion loss can be suppressed, and thus the heat dissipation countermeasures that enable the switching element to continue to operate normally can be simplified. In addition, by using WBG semiconductors in the switching element, the switching frequency can be set to a sufficiently high value, such as above 16kHz, so the noise caused by switching can be suppressed.

[0073] In addition, GaN semiconductors generate a two-dimensional electron gas at the interface between the GaN layer and the aluminum gallium nitride layer. Due to the two-dimensional electron gas, the carrier mobility is high. Therefore, the switching element using GaN semiconductors can achieve high-speed switching. Here, when the AC power supply 1 is a commercial power supply of 50Hz / 60Hz, the audible frequency becomes a range of 16kHz to 20kHz, that is, a range of 266 times to 400 times the frequency of the commercial power supply. GaN semiconductors are suitable for switching at frequencies higher than the audible frequency. When the switching elements 311, 312, 321, and 322 composed of silicon (Si), which is the mainstream semiconductor material, are driven at a switching frequency of more than tens of kHz, the ratio of the switching conversion loss becomes large, and heat dissipation measures are required. In contrast, the switching elements 311, 312, 321, and 322 composed of GaN semiconductors have very small switching conversion losses even when they are driven at a switching frequency of more than tens of kHz, specifically a switching frequency higher than 20kHz. Therefore, heat dissipation measures are not required, or the size of the heat dissipation component used for heat dissipation measures can be reduced, and the power conversion device 100 can be miniaturized and lightweight. In addition, since high-frequency switching can be performed, the reactor 2 can be miniaturized. In addition, in order to prevent the primary component of the switching frequency from entering the measurement range of the noise terminal voltage specification, it is preferable that the switching frequency is 150 kHz or less.

[0074] In addition, since the electrostatic capacitance of a WBG semiconductor is smaller than that of a Si semiconductor, the generation of a recovery current due to switching is small, and the loss and noise caused by the recovery current can be suppressed, so it is suitable for high-frequency switching.

[0075] In addition, since the on-resistance of SiC semiconductor is smaller than that of GaN semiconductor, the switch elements 311 and 312 of the first arm 31 having more switching times than the second arm 32 can be formed of GaN semiconductor, and the switch elements 321 and 322 of the second arm 32 having fewer switching times can be formed of SiC semiconductor. Thus, the respective characteristics of SiC semiconductor and GaN semiconductor can be utilized to the maximum extent. In addition, by using SiC semiconductor in the switch elements 321 and 322 of the second arm 32 having fewer switching times than the first arm 31, the proportion of conduction loss in the loss of the switch elements 321 and 322 increases, and the opening loss and closing loss become smaller. Therefore, the increase of heat generation accompanying the switching conversion of the switch elements 321 and 322 can be suppressed, the inner core area of ​​the switch elements 321 and 322 constituting the second arm 32 can be relatively reduced, and the SiC semiconductor with low productivity during the manufacture of the inner core can be effectively utilized.

[0076] In addition, super junction (SJ)-MOSFETs may be used in the switching elements 321 and 322 of the second arm 32 having a small number of switching times. By using SJ-MOSFETs, the advantage of SJ-MOSFETs, i.e., low on-resistance, can be utilized, and the disadvantage of high electrostatic capacitance and easy recovery can be suppressed. In addition, by using SJ-MOSFETs, the manufacturing cost of the second arm 32 can be reduced compared to the case of using WBG semiconductors.

[0077] In addition, WBG semiconductors have higher heat resistance than Si semiconductors and can operate even when the junction temperature is high. Therefore, by using WBG semiconductors, the first arm 31 and the second arm 32 can be formed even in a small inner core with high thermal resistance. In particular, SiC semiconductors, which have low productivity during the manufacture of inner cores, can achieve low costs when used in small inner cores.

[0078] Furthermore, the WBG semiconductor can suppress the increase in loss generated in the switching element even when driven at a high frequency of about 100 kHz, so the loss reduction effect obtained by miniaturizing the inductor 2 becomes greater, and a high-efficiency converter can be realized in a wide output band, that is, a wide load condition.

[0079] Furthermore, since WBG semiconductors have higher heat resistance than Si semiconductors and a high heat tolerance level for switching depending on the bias of losses between arms, they are suitable for the first arm 31 that generates switching losses due to high-frequency driving.

[0080] Next, the hardware configuration of the control unit 10 included in the power conversion device 100 will be described. Fig.11 1 is a diagram showing an example of a hardware configuration for realizing the control unit 10 included in the power conversion device 100 according to Embodiment 1. The control unit 10 is realized by a processor 201 and a memory 202 .

[0081] The processor 201 is a CPU (Central Processing Unit, also known as a central processing device, a processing device, an arithmetic device, a microprocessor, a microcomputer, a processor, a DSP (Digital Signal Processor)), or a system LSI (Large Scale Integration). The memory 202 may be exemplified by a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Only Memory), or an EEPROM (registered trademark) (Electrically Erasable Programmable Read-Only Memory). In addition, the memory 202 is not limited thereto, and may also be a magnetic disk, an optical disk, a compact disk, a mini optical disk, or a DVD (Digital Versatile Disc).

[0082] As described above, according to the present embodiment, in the power conversion device 100, the following circuit configuration is formed: when the bridge arm circuit 3 is short-circuited, the reactor 2 is connected in series with the switching element 312 functioning as a switch and the reactor 2, or the switching element 311 functioning as a switch is connected in series with the reactor 2, depending on the polarity of the AC power supply 1. Thus, the power conversion device 100 can attenuate the noise generated in the switching elements 311 and 312 during switching due to the influence of the impedance of the reactor 2, so that the reactor 2 can be miniaturized and the noise can be reduced.

[0083] In the power conversion device 100, in the bridge arm circuit 3, the switching speed of the switching elements 311 and 312 is made faster than the switching speed of the switching elements 321 and 322. In addition, in the bridge arm circuit 3, the gate driving unit 33 driving the switching element 311 uses gate resistors of different resistance values ​​when the switching element 311 is turned on and when it is turned off, and the switching speed can be changed by turning on and off. The gate driving unit 34 driving the switching element 312 uses gate resistors of different resistance values ​​when the switching element 312 is turned on and when it is turned off, and the switching speed can be changed by turning on and off. As a result, the power conversion device 100 can miniaturize the reactor 2 and reduce noise.

[0084] In the power conversion device 100, the gate driver 33 uses a gate resistor set according to the magnitude of the noise generated in the switching element 311, and the gate driver 34 uses a gate resistor set according to the magnitude of the noise generated in the switching element 312. That is, the gate driver 33 and the gate driver 34 use gate resistors with different resistance values ​​when turning on the switching element, and use gate resistors with different resistance values ​​when turning off the switching element. Thus, the power conversion device 100 can use gate resistors with different resistance values ​​in the gate driver 33 and 34, and can reduce noise according to the actual noise generation situation without changing the control content of the control unit 10.

[0085] Implementation method 2.

[0086] In the second embodiment, a motor drive device including the power conversion device 100 described in the first embodiment will be described.

[0087] Fig.12 1 is a diagram showing a configuration example of a motor drive device 101 according to Embodiment 2. The motor drive device 101 drives a motor 42 as a load. The motor drive device 101 includes the power conversion device 100 according to Embodiment 1, an inverter 41, a motor current detection unit 44, and an inverter control unit 43. The inverter 41 converts the DC power supplied from the power conversion device 100 into AC power and outputs it to the motor 42, thereby driving the motor 42. In addition, although an example is described in which the load of the motor drive device 101 is the motor 42, this is only an example, and as long as the device connected to the inverter 41 is a device that inputs AC power, it may also be a device other than the motor 42.

[0088] The inverter 41 is a circuit that forms a 3-phase bridge arm structure or a 2-phase bridge arm structure with a switching element headed by an IGBT (Insulated Gate Bipolar Transistor). The switching element used in the inverter 41 is not limited to an IGBT, and may also be a switching element composed of a WBG semiconductor, an IGCT (Integrated Gate Commutated Thyristor), a FET (Field Effect Transistor) or a MOSFET.

[0089] The motor current detection unit 44 detects the current flowing between the inverter 41 and the motor 42. The inverter control unit 43 generates a PWM signal for driving the switching element in the inverter 41 so that the motor 42 rotates at a desired speed using the current detected by the motor current detection unit 44, and applies the PWM signal to the inverter 41. The inverter control unit 43 is implemented by a processor and a memory in the same manner as the control unit 10. In addition, the inverter control unit 43 of the motor drive device 101 and the control unit 10 of the power conversion device 100 can also be implemented by one circuit.

[0090] When the power conversion device 100 is used in the motor drive device 101, the bus voltage Vdc required for the control of the bridge arm circuit 3 changes according to the operating state of the motor 42. Generally speaking, the higher the rotation speed of the motor 42, the more it is necessary to increase the output voltage of the inverter 41. The upper limit of the output voltage of the inverter 41 is limited by the input voltage to the inverter 41, that is, the bus voltage Vdc as the output of the power conversion device 100. The area where the output voltage from the inverter 41 exceeds the upper limit limited by the bus voltage Vdc and is saturated is called an overmodulation area.

[0091] In such a motor drive device 101, it is not necessary to increase the bus voltage Vdc in the range where the motor 42 rotates at a low speed, that is, in the range where the overmodulation region has not been reached. On the other hand, when the motor 42 rotates at a high speed, by increasing the bus voltage Vdc, the overmodulation region can be brought closer to the high speed side. Thus, the operating range of the motor 42 can be expanded to the high speed side.

[0092] In addition, if it is not necessary to expand the operating range of the motor 42, the number of turns of the winding of the motor 42 wound around the stator can be increased accordingly. By increasing the number of turns of the winding, the motor voltage generated at both ends of the winding in the low speed region becomes higher, and the current flowing to the winding is reduced accordingly, so that the loss generated in the switching operation of the switching element in the inverter 41 can be reduced. In the case of obtaining both the effects of expanding the operating range of the motor 42 and improving the loss in the low speed region, the number of turns of the winding of the motor 42 is set to an appropriate value.

[0093] As described above, according to the present embodiment, by using the power conversion device 100 , it is possible to reduce the bias of heat generation between the arms, and to realize the motor drive device 101 with high reliability and high output.

[0094] Implementation method 3.

[0095] In Embodiment 3, an air conditioner including the motor drive device 101 described in Embodiment 2 will be described.

[0096] Fig.131 is a diagram showing a configuration example of an air conditioner 700 according to Embodiment 3. The air conditioner 700 is an example of a refrigeration cycle device, and includes the motor drive device 101 and the motor 42 according to Embodiment 2. The air conditioner 700 includes a compressor 81 having a compression mechanism 87 and the motor 42 built therein, a four-way valve 82, an outdoor heat exchanger 83, an expansion valve 84, an indoor heat exchanger 85, and a refrigerant pipe 86. The air conditioner 700 is not limited to a split-type air conditioner in which an outdoor unit and an indoor unit are separated, and may be an integrated air conditioner in which the compressor 81, the indoor heat exchanger 85, and the outdoor heat exchanger 83 are provided in one frame. The motor 42 is driven by the motor drive device 101.

[0097] A compression mechanism 87 for compressing the refrigerant and a motor 42 for operating the compression mechanism 87 are provided inside the compressor 81. 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 pipe 86. In addition, the components of the air conditioner 700 can also be applied to equipment such as a refrigerator or a freezer having a refrigeration cycle.

[0098] In addition, in Embodiment 3, a configuration example is described in which the motor 42 is used as the driving source of the compressor 81 and the motor 42 is driven by the motor driving device 101. However, the motor 42 may be applied to the driving source for driving the indoor air blower and the outdoor air blower (not shown) of the air conditioner 700, and the motor 42 may be driven by the motor driving device 101. In addition, the motor 42 may be applied to the driving source of the indoor air blower, the outdoor air blower, and the compressor 81, and the motor 42 may be driven by the motor driving device 101.

[0099] In addition, in the air conditioner 700, since the operation under the intermediate condition, that is, the low output condition, where the output is less than half of the rated output, is dominant throughout the year, the contribution to the annual power consumption under the intermediate condition becomes high. In addition, in the air conditioner 700, the rotation speed of the motor 42 is low, and there is a tendency that the bus voltage Vdc required for driving the motor 42 is low. Therefore, from the perspective of system efficiency, it is effective to operate the switching element used in the air conditioner 700 in a passive state. Therefore, the power conversion device 100 that can reduce the loss in the large-scale operation mode from the passive state to the high-frequency switching state is useful for the air conditioner 700. As described above, the reactor 2 can be miniaturized in the interleave mode, but in the air conditioner 700, since there are many operations under the intermediate conditions, it is not necessary to miniaturize the reactor 2, and the structure and operation of the power conversion device 100 are effective in suppressing high-order harmonics and power factor of the power supply.

[0100] In addition, since the power conversion device 100 can suppress switching loss, the temperature rise of the power conversion device 100 can be suppressed, and even if the size of the outdoor air blower (not shown) is miniaturized, the cooling capacity of the substrate mounted on the power conversion device 100 can be ensured. Therefore, the power conversion device 100 is highly efficient and suitable for a high-output air conditioner 700 of 4.0 kW or more.

[0101] In addition, according to the present embodiment, since the bias of heat generation between arms is reduced by using the power conversion device 100, the reactor 2 relying on high-frequency driving of the switching element can be miniaturized, and the increase in weight of the air conditioner 700 can be suppressed. In addition, according to the present embodiment, the switching conversion loss is reduced by high-frequency driving of the switching element, the energy consumption rate is reduced, and a high-efficiency air conditioner 700 can be realized.

[0102] Implementation method 4.

[0103] In the first embodiment, the arm circuit 3 of the power conversion device 100 includes two arms each having two switching elements connected in series. However, the switching element in one arm may be replaced with a diode.

[0104] Fig.14 It is a diagram showing a configuration example of a power conversion device 100a according to the fourth embodiment. Fig.14 The power conversion device 100a shown in FIG. Figure 1 The bridge arm circuit 3 of the power conversion device 100 shown is replaced by the bridge arm circuit 3a. The bridge arm circuit 3a is formed by reducing the gate drive units 35 and 36 from the bridge arm circuit 3 and replacing the second arm 32 with the second arm 32a. When only the boost operation is considered, the power conversion device 100a can set the second arm 32a as two diodes 323 and 324. The power conversion device 100a can reduce the switching elements 321 and 322 and the gate drive units 35 and 36 compared with the power conversion device 100 by setting the second arm 32a as two diodes 323 and 324, so that the circuit cost can be reduced. In this way, in the power conversion device 100a, the bridge arm circuit 3a only needs to have at least one bridge arm formed by connecting the switching elements connected in parallel with the diodes in series.

[0105] The configuration described in the above embodiment is an example of the content of the present invention, and may be combined with other known technologies, or part of the configuration may be omitted or modified without departing from the scope of the present invention.

[0106] Description of Reference Numerals

[0107] 1 AC power supply; 2 reactor; 3, 3a bridge arm circuit; 4 smoothing capacitor; 5 power supply voltage detection unit; 6 power supply current detection unit; 7 bus voltage detection unit; 10 control unit; 31 first arm; 32, 32a second arm; 33-36 gate drive unit; 41 inverter; 42 motor; 43 inverter control unit; 44 motor current detection unit; 50 load; 81 compressor; 82 four-way valve; 83 outdoor heat exchanger; 84 expansion valve; 85 indoor heat exchanger; 86 refrigerant pipe; 87 compression mechanism; 100, 100a power conversion device; 101 motor drive driving device; 201 processor; 202 memory; 311, 312, 321, 322 switching elements; 311a, 312a, 321a, 322a parasitic diodes; 331, 333, 341, 343 resistors; 323, 324, 332, 334, 342 diodes; 501 first wiring; 502 second wiring; 503 third wiring; 504 fourth wiring; 506 first connection point; 508 second connection point; 600 semiconductor substrate; 601, 603 regions; 602 oxide insulating film; 604 channel; 700 air conditioner.

Claims

1. A power conversion device, wherein: The power conversion device has: an arm circuit that converts an AC voltage output from an AC power source into a DC voltage, and includes a first arm and a second arm, the first arm being formed by connecting in series a first switching element and a second switching element to which a diode is connected in parallel, and the second arm being formed by connecting in series a third switching element and a fourth switching element to which a diode is connected in parallel; and a reactor, one end of which is connected to the AC power supply, and the other end of which is connected to a connection point between the first switching element and the second switching element of the first bridge arm, The bridge arm circuit includes a driving unit for driving the first bridge arm and the second bridge arm. The driving unit includes a speed changing mechanism for changing a switching speed when the first switching element or the second switching element is turned on or off. The speed changing mechanism changes the switching speed by using a gate resistor for connection, a gate resistor for disconnection, and a diode connected in series with each gate resistor. The resistance value of the gate resistor used in an operation in which the noise generated when turning on or off is small is set smaller than the resistance value of the gate resistor used in an operation in which the noise is large. The switching speeds of the first switching element and the second switching element of the first bridge arm, which are switching elements for reducing switching noise and can change the switching speed when connected and disconnected, are faster than the switching speeds of the third switching element and the fourth switching element of the second bridge arm, which are switching elements not for reducing switching noise and whose switching speeds do not change when connected and disconnected.

2. The power conversion device according to claim 1, wherein: The resistance value of the gate resistor when the driving unit turns on the first switching element is different from the resistance value of the gate resistor when the driving unit turns on the second switching element. A resistance value of the gate resistor when the driving unit turns off the first switching element is different from a resistance value of the gate resistor when the driving unit turns off the second switching element.

3. A motor drive device, the motor drive device drives a motor, wherein: The motor drive device has: The power conversion device according to claim 1 or 2; and An inverter converts the DC power output from the power conversion device into AC power and outputs the AC power to the motor.

4. An air conditioner, wherein: The air conditioner has: Motors; and The motor drive device as claimed in claim 3.

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