Power conversion device and air conditioner

Abstract

The power conversion device includes: a power conversion section in which at least two switching elements are connected in series; and a gate drive circuit that drives the switching elements based on a control signal output pulse signal from a control section provided externally, the gate drive circuit having: a first drive circuit that drives a switching element connected to a reference potential side with power supplied from a control power supply; a second drive circuit that drives a switching element connected to a power supply potential side; and a power supply section that includes a limit resistor, a bootstrap diode, and a bootstrap capacitor connected in series between the control power supply and an output terminal, generates a power supply voltage supplied to the second drive circuit, charges the bootstrap capacitor by switching the switching element connected to the reference potential side, and the charging period of the bootstrap capacitor includes at least a first period and a second period, in the first period, the switching element connected to the reference potential side is driven by a pulse signal having a first pulse width, in the second period, the switching element connected to the reference potential side is driven by a pulse signal having a second pulse width that is larger than the first pulse width, and the first pulse width of the first period is determined based on the magnitude of a voltage drop of the control power supply allowed in the first period.

Description

Technical Field

[0001] This disclosure relates to a power conversion device that converts electricity from a power source into an arbitrary frequency and voltage and supplies it to a load such as a motor, and an air conditioner equipped with the power conversion device. Background Technology

[0002] Due to increasing demands for energy conservation, most air conditioners in recent years have adopted inverter technology. An inverter is a device that can arbitrarily adjust voltage and frequency and output power. When an air conditioner is equipped with an inverter, by adjusting the output of the motor driving the compressor according to the load of the conditioned space, it is possible to prevent over-cooling or over-heating of the conditioned space, thereby saving energy.

[0003] Furthermore, the voltage and frequency of the power supplied to loads such as motors are adjusted by switching on and off the switching devices mounted on the inverter board. The control method for this switching operation is generally PWM (Pulse Width Modulation).

[0004] As inverters used in air conditioners, most of them use power modules that integrate transistors as switching devices and transistor gate drive circuits.

[0005] In this case, a power supply is needed to power the gate drive circuit in order to drive the power module. In the inverter, the transistor on the upper arm (high side) of the high-potential side is connected in series with the transistor on the lower arm (low side). Hereinafter, the circuit driving the transistor on the lower arm will be called the low-side circuit, and the circuit driving the transistor on the upper arm will be called the high-side circuit. Furthermore, the connection point between the transistor on the upper arm and the transistor on the lower arm will be called the midpoint.

[0006] Because the reference potential of the low-side circuit is grounded, a normal power supply can be used as the control power supply. On the other hand, because the reference potential of the high-side circuit is the midpoint potential, a normal power supply grounded as the reference potential cannot be used as the control power supply.

[0007] Therefore, a floating power supply or a bootstrap method is used to supply power to the high-side circuit. In the bootstrap method, a bootstrap capacitor is connected to the power input of the high-side circuit. Then, by switching the transistor in the lower arm, a current path is created towards the gate drive circuit of the upper arm, thereby charging the bootstrap capacitor. After charging, the charge stored in the bootstrap capacitor is used as a power source to drive the transistor in the upper arm. This charging of the bootstrap capacitor is called the bootstrap operation, and the charging period is called the bootstrap period.

[0008] The bootstrap method eliminates the need for costly components such as transformers or dedicated power supplies in the high-side circuit drive, but it does present the following challenge: When charging the bootstrap capacitor, a large instantaneous current flows through the low-side circuit power supply circuit, which can sometimes cause a voltage drop in the control power supply of the low-side circuit due to the internal impedance of the low-side circuit power supply circuit.

[0009] For example, Patent Document 1 describes that during the initial charging of a bootstrap capacitor, due to the large current flowing in the bootstrap circuit, a large allowable current is required to withstand the initial charging current. Patent Document 1, as a prior art issue, lists the problems of increasing the size of the bootstrap circuit to ensure this allowable current, as well as the power loss and heat generated by the limiting resistor of the bootstrap circuit.

[0010] Furthermore, in Patent Document 1, as a conventional solution to the aforementioned problem, a scheme is proposed to set a first period and a second period as the charging period for the bootstrap capacitor. During the first period, the low-side circuit suppresses current by intermittent charging, while during the second period, continuous power is applied to complete the charging.

[0011] Patent Document 1: Japanese Patent Application Publication No. 2011-67029

[0012] By employing the method described in Patent Document 1, the aforementioned problems of increasing the size of the bootstrap circuit, as well as power loss and heat generation caused by the limiting resistor of the bootstrap circuit, can be solved.

[0013] However, Patent Document 1 does not consider the voltage drop of the control power supply. Therefore, depending on the pulse width, duty cycle, duration of the first period, and internal impedance of the control power supply, the voltage drop can increase, potentially putting significant stress on the power supply circuit of the low-side circuit. Furthermore, in Patent Document 1, as a countermeasure against the voltage drop of the control power supply, if a protection circuit for detecting the voltage drop is assumed to be installed in the low-side circuit, then in this case, the activation of the protection circuit could potentially cause an abnormal shutdown of the power conversion device. Summary of the Invention

[0014] This disclosure was made to solve the above-mentioned problems, and its purpose is to provide a power conversion device that can charge a bootstrap capacitor while suppressing the voltage drop of the control power supply during the charging of the bootstrap capacitor, and an air conditioner equipped with the power conversion device.

[0015] The power conversion device disclosed herein includes: a power conversion section comprising at least two switching elements connected in series to form a series circuit, one end of the series circuit being connected to a power supply potential side, the other end of the series circuit being connected to a reference potential side, and the midpoint of the series circuit being connected to an output terminal; and a gate drive circuit that drives the switching elements by outputting a pulse signal based on a control signal from an externally provided control unit, the gate drive circuit comprising: a first drive circuit that receives power from a control power supply and drives the switching element connected to the reference potential side; a second drive circuit that drives the switching element connected to the power supply potential side; and a power supply section including a limiting device connected in series between the control power supply and the output terminal. A resistor, a bootstrap diode, and a bootstrap capacitor generate a power supply voltage to be supplied to the second drive circuit. The bootstrap capacitor is charged by switching the switching element connected to the reference potential side. The charging period of the bootstrap capacitor includes at least a first period and a second period. In the first period, the switching element connected to the reference potential side is driven by a pulse signal having a first pulse width. In the second period, the switching element connected to the reference potential side is driven by a pulse signal having a second pulse width that is larger than the first pulse width. The first pulse width of the first period is determined based on the magnitude of the voltage drop of the control power supply allowed in the first period.

[0016] The air conditioner disclosed herein includes: a refrigeration cycle device comprising the aforementioned power conversion device, a compressor driven by an electric motor serving as a load of the aforementioned power conversion device, a condenser for condensing refrigerant discharged from the aforementioned compressor, an expansion valve for depressurizing the condensed refrigerant, and an evaporator for evaporating the depressurized refrigerant; and a blower for supplying air to at least one of the aforementioned condenser and the aforementioned evaporator of the aforementioned refrigeration cycle device.

[0017] According to the power conversion device and air conditioner disclosed herein, the bootstrap capacitor can be charged while suppressing the voltage drop of the control power supply during charging. Attached Figure Description

[0018] Figure 1 This is a structural diagram showing an example of the structure of the power conversion device 100 according to Embodiment 1.

[0019] Figure 2 It means Figure 1 Enlarged view of a portion of the structure of the gate drive circuit 130 and the structure of the inverter 120.

[0020] Figure 3This is a schematic diagram showing the gate waveform for charging the bootstrap capacitor 133 in the power conversion device 100 according to Embodiment 1.

[0021] Figure 4 This is a schematic diagram showing the gate waveform for charging the bootstrap capacitor 133 in the power conversion device 100 according to Embodiment 2.

[0022] Figure 5 This is a structural diagram illustrating an example of the structure of the power conversion device 100 according to Embodiment 3.

[0023] Figure 6 It means Figure 5 Enlarged view of a portion of the structure of the gate drive circuit 130 and the structure of the inverter 120.

[0024] Figure 7 This is a structural diagram illustrating an example of the structure of the air conditioner 400 according to Embodiment 4.

[0025] Figure 8 (a) and (b) are diagrams illustrating examples of the case where the converter 110 installed in the power conversion device 100 according to Embodiment 1 is an active converter. Detailed Implementation

[0026] Hereinafter, embodiments of the power conversion device and air conditioner involved in this disclosure will be described with reference to the accompanying drawings. This disclosure is not limited to the following embodiments, and various modifications can be made without departing from the spirit of this disclosure. Furthermore, this disclosure includes all combinations of structures that can be combined in the structures shown in the following embodiments and their modifications. Additionally, in each drawing, parts labeled with the same reference numerals correspond to the same or equivalent parts, and these are generally used throughout the specification. Furthermore, in the following embodiments and their modifications, electrical connections are simply referred to as "connections". Moreover, in each drawing, the relative dimensional relationships or shapes of the constituent components may sometimes differ from the actual figures.

[0027] Implementation Method 1

[0028] Figure 1 This is a structural diagram showing an example of the structure of the power conversion device 100 according to Embodiment 1. Figure 2 It means Figure 1 Enlarged view of a portion of the structure of the gate drive circuit 130 and the structure of the inverter 120.

[0029] like Figure 1As shown, the power conversion device 100 according to Embodiment 1 includes a power conversion section 150 composed of a converter 110 and an inverter 120, and a gate drive circuit 130. The gate drive circuit 130 is controlled by an external control unit 140. An AC power supply 1 as a power source and a motor 2 as a load are connected to the power conversion device 100. The AC power supply 1 is, for example, a three-phase commercial power supply having U phase, V phase, and W phase. The motor 2 is, for example, a three-phase permanent magnet synchronous motor having U phase, V phase, and W phase. Furthermore, in the power conversion section 150, the converter 110 can be provided as needed and is not necessarily required. Hereinafter, the case where the converter 110 is provided will be described as an example.

[0030] The inverter 120 is composed of semiconductor switches 121. The semiconductor switches 121 are, for example, IGBTs (Insulated Gate Bipolar Transistors), MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), HEMTs (High Electron Mobility Transistors), and other switching elements. The inverter 120 controls the path of current flowing in the motor 2 and drives the motor 2 by controlling the on / off state of the semiconductor switches 121. In the inverter 120, each phase is formed by connecting at least two semiconductor switches 121 in series. One end of this series connection is connected to the power supply potential side (high potential side), and the other end is connected to the reference potential side (low potential side). Furthermore, the midpoint 125 of this series connection is connected to the output terminal 126 of the power conversion device 100 (see reference). Figure 2 )connect.

[0031] exist Figure 1 In this example, inverter 120 is connected to the positive bus 151 and negative bus 152, which are the output terminals of converter 110. Inverter 120 converts the DC voltage rectified by the rectifier circuit 111 of converter 110 into AC voltage and outputs it to motor 2. By operating inverter 120, the voltage value and frequency of the AC voltage supplied to motor 2 can be changed. Furthermore, although motor 2 has been described here as the load of power conversion device 100, the load of power conversion device 100 can also be other devices. Inverter 120 is, for example, constructed from a full-bridge circuit with six semiconductor switches 121. Figure 2The following is a detailed explanation. As the upper arm semiconductor switch 121 connected to the positive bus 151, three semiconductor switches 121Hu, 121Hv, and 121Hw are respectively provided for each phase U, V, and W of the motor 2. Similarly, as the lower arm semiconductor switch 121 connected to the negative bus 152, three semiconductor switches 121Lu, 121Lv, and 121Lw are respectively provided for each phase U, V, and W of the motor 2. Each phase is formed by connecting the upper arm semiconductor switches 121Hu, 121Hv, and 121Hw in series with the lower arm semiconductor switches 121Lu, 121Lv, and 121Lw. These three series switches are then connected in parallel to form a full-bridge circuit. Hereinafter, the upper arm semiconductor switch 121H will be referred to as the high-side semiconductor switch 121H, and the lower arm semiconductor switch 121L will be referred to as the low-side semiconductor switch 121L. Furthermore, although the inverter 120 is listed here as an example with 3 phases, the number of phases can be 2 or less, or it can be 4 or more.

[0032] like Figure 1 as well as Figure 2 As shown, the freewheeling diode 122 is connected to each semiconductor switch 121 in reverse parallel. Each semiconductor switch 121 independently switches on and off according to the drive switching signal output by the gate drive circuit 130. Through this switching action, the DC voltage is converted into an AC voltage.

[0033] like Figure 1 As shown, the converter 110 includes a rectifier circuit 111, a DC reactor 112, and a smoothing capacitor 113. The rectifier circuit 111 rectifies the AC voltage of the AC power supply 1 into a DC voltage. The smoothing capacitor 113 is connected in parallel with the output side of the rectifier circuit 111 via the DC reactor 112. The smoothing capacitor 113 smooths the DC voltage input from the rectifier circuit 111 via the DC reactor 112.

[0034] The rectifier circuit 111 is, for example, a full-bridge circuit comprising six rectifier diodes 114. Specifically, two rectifier diodes 114 are connected in series to form a series circuit. Furthermore, three such series circuits are prepared and connected in parallel to form a full-bridge circuit. Alternatively, switching elements such as transistors can be used instead of the rectifier diodes 114 in the rectifier circuit 111. The output terminal of the rectifier circuit 111 is connected to the positive bus 151 and the negative bus 152.

[0035] Generally speaking, converters can be classified into passive converters that convert AC to DC using passive components such as rectifier diodes 114, and active converters that are composed of switching elements such as IGBTs, MOSFETs, and HEMTs, similar to inverters 120. Figure 1 The converter 110 shown is a passive converter. However, the converter 110 according to Embodiment 1 is not limited to a passive converter and may also be an active converter. Figure 8 Figures (a) and (b) are examples illustrating the case where the converter 110 installed in the power conversion device 100 according to Embodiment 1 is an active converter. Figure 8 In example (a), a switching element 115 is connected in parallel to the rectifier circuit 111. Additionally, in Figure 8 In example (b), the switching element 116 is connected in parallel to each of the rectifier diodes 114 in the rectifier circuit 111. In an active converter, such as Figure 8 As shown in (b), sometimes passive components such as rectifier diode 114 and switching element 116 are used in combination. In either passive or active converters, such as Figure 1 and Figure 8 As shown in (a) and (b), the components of the rectifier circuit 111 are used in a bridge configuration. Furthermore, the converter 110 in Embodiment 1 is not limited to... Figure 1 , Figure 8 (a) or Figure 8 The structure of (b) is not limited. Furthermore, the number of phases of converter 110, the combination of components used, and the connection order are not limited to... Figure 1 , Figure 8 (a) or Figure 8 The structure of (b).

[0036] The control unit 140 is located outside the power conversion device 100. Operating commands such as speed commands and torque commands are input to the control unit 140 from the outside. The control unit 140 generates control signals based on these operating commands and outputs the control signals to the gate drive circuit 130. Alternatively, the control unit 140 may be located inside the power conversion device 100.

[0037] Gate drive circuit 130 will drive pulse signal 10 (reference) Figure 3 The gate drive circuit 130 outputs a drive switch signal to the semiconductor switch 121 of the inverter 120. Thus, the semiconductor switches 121 can independently turn on and off. Alternatively, if the converter 110 is an active converter using active components, the gate drive circuit 130 can also drive the converter 110. The gate drive circuit 130 drives the converter 110 or the inverter 120, or both, according to the control signal from the control unit 140.

[0038] Furthermore, the converter 110, inverter 120, and gate drive circuit 130 can be configured within the same module or separately in two or more modules. For example, the converter 110 and gate drive circuit 130 can be configured together in the same module, while the inverter 120 can be configured in another module. Alternatively, the inverter 120 and gate drive circuit 130 can be configured together in the same module, while the converter 110 can be configured in another module. Thus, while multiple combinations are considered, Embodiment 1 is not limited to any single combination.

[0039] In addition, such as Figure 1 As shown, multiple gate drive circuits 130u, 130v, and 130w are provided in the gate drive circuit 130 and in each phase U, V, and W of the motor 2 respectively. Figure 2 For the sake of simplicity, only [the diagram] is shown. Figure 1 The gate drive circuit 130u is the U-phase gate drive circuit in the gate drive circuit 130. Since the gate drive circuits 130u, 130v, and 130w have the same structure, only the gate drive circuit 130u will be described here, and the descriptions of the other gate drive circuits 130v and 130w will be omitted.

[0040] like Figure 2 As shown, the gate drive circuit 130u includes a limiting resistor 131, a bootstrap diode 132, a bootstrap capacitor 133, a second drive circuit 134H, a first drive circuit 134L, and a control power supply 135. The limiting resistor 131, the bootstrap diode 132, and the bootstrap capacitor 133 are connected in series between the control power supply 135 and the output terminal 126 to form a power supply section 137. The power supply section 137 generates a power supply voltage supplied to the second drive circuit 134H. Furthermore, Figure 2 For the sake of simplicity, only one phase (U phase) is shown. However, in the case of multiple phases, the power supply unit 137 can be provided separately for each phase, or a single power supply unit 137 can be shared by all phases. In addition, components other than those mentioned above, such as filter circuits or protection circuits, can also be provided in the gate drive circuit 130u.

[0041] The control power supply 135 is connected to both ends of the first drive circuit 134L. The control power supply 135 supplies power to the first drive circuit 134L.

[0042] One end of the limiting resistor 131 is connected to the control power supply 135, and the other end is connected to the anode of the bootstrap diode 132.

[0043] The cathode of the bootstrap diode 132 is connected to the positive electrode of the bootstrap capacitor 133.

[0044] The negative electrode of the bootstrap capacitor 133 is connected to the midpoint 125u, which is the connection point between semiconductor switches 121Hu and 121Lu. The bootstrap capacitor 133 is connected to both ends of the second drive circuit 134H. The bootstrap capacitor 133 supplies power to the second drive circuit 134H.

[0045] The low-side semiconductor switch 121L of the inverter 120 is driven by a first drive circuit 134L that receives a control signal from the control unit 140. When the low-side semiconductor switch 121L is turned on, a current path is generated, and current flows to the low-side semiconductor switch 121L. That is, in this current path, current flows to the low-side semiconductor switch 121L through the control power supply 135, the limiting resistor 131, the bootstrap diode 132, and the bootstrap capacitor 133. As a result, the bootstrap capacitor 133 is charged. In this state, when the low-side semiconductor switch 121L is turned off, the bootstrap capacitor 133 can replace the floating power supply to drive the high-side semiconductor switch 121H. In this way, by switching at least one of the low-side semiconductor switches 121L, the bootstrap capacitor 133 is charged.

[0046] Figure 3 This is a schematic diagram showing the gate waveform for charging the bootstrap capacitor 133 in the power conversion device 100 according to Embodiment 1. Figure 3 In the diagram, the horizontal axis represents time, and the vertical axis, from top to bottom, represents the gate waveforms of the U phase, V phase, and W phase, respectively.

[0047] When the bootstrap capacitor 133 is charging, the control unit 140 outputs commands to the first drive circuits 134L of the gate drive circuits 130u, 130v, and 130w, respectively, to intermittently power on the low-side semiconductor switch 121L. Figure 3 In the gate waveform, when the pulse signal 10 is on, the semiconductor switch 121L is on (powered state), and when the pulse signal 10 is off, the semiconductor switch 121L is off (cut-off state).

[0048] like Figure 3As shown, the charging period of the bootstrap capacitor 133 includes at least two periods. In Embodiment 1, the case where the charging period of the bootstrap capacitor 133 has two periods is described as an example. In these two periods, the period from time 0 to time t1 is called the first period, and the period from time t1 to time t2 is called the second period. The switching mode of the low-side semiconductor switch 121L is different in each period. In the first period, the low-side semiconductor switch 121L is driven by a pulse signal having a first pulse width w1, and in the second period, the low-side semiconductor switch 121L is driven by a pulse signal 10 having a second pulse width w3 that is larger than the first pulse width w1. In addition, the duration T1 of the first period is determined based on the resistance value R of the limiting resistor 131 and the capacitance C of the bootstrap capacitor 133. This will be explained in detail below.

[0049] <First Period>

[0050] During the first period, the low-side semiconductor switches 121Lu, 121Lv, and 121Lw are intermittently energized (hereinafter referred to as pulse charging). Specifically, as follows... Figure 3 As shown, during the first period, in each phase, a pulse signal 10 with a pulse width w1 (first pulse width) is output at a constant pulse interval w2. The "pulse interval" is sometimes also referred to as the carrier period or switching carrier. Thus, the pulse interval w2 is the pulse interval or carrier period within the bootstrapping period of each phase.

[0051] The duty cycle (Duty) of each phase in the first period is given by the following formula (1). The duty cycle (Duty) is the ratio of the pulse width (W1) to the pulse interval (W2), that is, the ratio of the energizing time to the pulse interval (W2).

[0052] Duty=w1 / w2···(1)

[0053] The pulse width w1 is a value that is larger than the minimum pulse limit value determined by the performance of the processor constituting the control unit 140 or the protection circuit protecting the control power supply 135, and smaller than the pulse interval w2. That is, the pulse width w1 is determined based on the magnitude of the voltage drop (allowed voltage fluctuation range) of the control power supply 135 allowed during the first period. As a result, it is possible to prevent a large voltage drop that would cause the protection circuit to operate.

[0054] Additionally, if inverter 120 is a three-phase inverter, such as Figure 3As shown, the pulse signals 10 of each phase are output with their phases shifted by 120°. That is, the pulse signal 10 of phase V is output with a phase delay of D1 (=120°) relative to the pulse signal 10 of phase U. Similarly, the pulse signal 10 of phase W is output with a phase delay of D1 (=120°) relative to the pulse signal 10 of phase V. Therefore, the pulse signal 10 of phase W is output with a phase delay of twice the phase delay D1, D2 (=240°), relative to the pulse signal 10 of phase U. Thus, the pulse signals are output with phase shifts of D1 in the order of phase U, phase V, and phase W. However, the number of phases in the inverter 120 is not limited. Therefore, if the number of phases is set to p, the pulse signals 10 of each phase are output with their phases shifted by 360° divided by the number of phases p (360° ÷ p).

[0055] The duration T1 of the first period of pulse charging is determined according to... Figure 2 The time constant τ is determined by the capacitance C of the bootstrap capacitor 133 and the resistance R of the limiting resistor 131.

[0056] The time constant τ is given by equation (2), for example, based on the capacitance C, the resistance R, and the duty cycle (Duty) of equation (1) above.

[0057] τ=C×R / Duty···(2)

[0058] In addition, the duration T1 of the first period is set as shown in equation (3).

[0059] T1>τ···(3)

[0060] Alternatively, when setting the duration T1 of the first period, equation (3) can also be based on the magnitude of the voltage drop of the control power supply 135 allowed in the second period, by multiplying any coefficient A by the time constant τ. In this case, using equations (2) and (3), the duration T1 is represented by equation (4). Wherein, the coefficient A is any value greater than or equal to 1.

[0061] T1>A×C×R / Duty···(4)

[0062] When A=1, at the end of the first period of time T1, the voltage of the bootstrap capacitor 133 reaches approximately 63% of the input voltage from the control power supply 135. When A=2, the time period T1 can be longer than that of A=1, so at the end of the first period, the voltage of the bootstrap capacitor 133 reaches approximately 86% of the input voltage from the control power supply 135. Furthermore, when A=3, at the end of the first period, the voltage of the bootstrap capacitor 133 reaches approximately 95% of the input voltage from the control power supply 135. After the end of the first period, the second period begins, and the charging of the bootstrap capacitor 133 is completed. The smaller the difference between the voltage of the bootstrap capacitor 133 and the input voltage, the smaller the charging current. Therefore, to reduce the voltage drop in the second period, the coefficient A is increased, thereby increasing the voltage of the bootstrap capacitor 133. As a result, the difference between the voltage of the bootstrap capacitor 133 and the input voltage in the second period can be reduced, thus suppressing the voltage drop in the second period. Thus, coefficient A can also be determined based on the magnitude of the voltage drop (allowed voltage fluctuation range) of the control power supply 135 during the second period. In this case, coefficient A is preferably any value of 2 or higher. As described above, the value of coefficient A can be appropriately determined as any value depending on the purpose. Furthermore, as examples of the value of coefficient A, the above description illustrates the case of integers such as 1, 2, 3, etc., but it is not limited to this case; coefficient A can be any real number of 1 or higher.

[0063] <Second Period>

[0064] exist Figure 3 In this process, the period from time t1 to time t2 is the second period. Time t2 is the time when the bootstrap action ends. Thus, during the bootstrap action, after the first period has elapsed, the process moves to the second period. During the second period, the timing of the switches of each phase (U, V, and W) is set to be the same, and the switches are operated by a pulse signal 10 with a pulse width w3 (the second pulse width), thereby charging the bootstrap capacitor 133. The pulse width w3 is longer than the pulse interval w2 of the first period, and is less than or equal to the duration T2 of the second period. Therefore, the pulse width w3 is within the range of the following equation (4).

[0065] w2<w3≤T2···(5)

[0066] As can be seen from equation (5) above, the pulse width w3 can also be consistent with the duration T2 of the second period. In this case, w3 = T2. When w3 = T2, the pulse signal 10 is continuously on during the second period. At time t2 after the second period has elapsed, the bootstrap capacitor 133 has completed charging.

[0067] As described above, in Embodiment 1, the bootstrap capacitor 133 is charged by switching at least one of the low-side semiconductor switches 121 connected to the reference potential side. The charging period of the bootstrap capacitor 133 includes at least a first period and a second period. During the first period, the low-side semiconductor switch 121 is driven by a pulse signal 10 having a first pulse width w1. During the second period, the low-side semiconductor switch 121 is driven by a pulse signal 10 having a second pulse width w3 that is larger than the first pulse width w1. During the first period, the first pulse width w1 is determined based on the magnitude of the voltage drop allowed in the first period to prevent the generation of a voltage drop sufficient to activate the protection circuit.

[0068] Thus, in Embodiment 1, the first pulse width w1 is determined during the first period in a way that suppresses the voltage drop of the control power supply 135. Furthermore, in Embodiment 1, the duration T1 of the first period is set based on the resistance value R of the limiting resistor 131 and the capacitance C of the bootstrap capacitor 133. Therefore, the bootstrap capacitor 133 can be charged while suppressing the voltage drop of the control power supply 135 during charging. Thus, according to Embodiment 1, by suppressing the voltage drop of the supply source that supplies voltage to the bootstrap capacitor 133, i.e., the control power supply 135, the stress on the power supply unit 137 caused by rapid voltage changes can be suppressed. Furthermore, even when a protection circuit for detecting the voltage drop of the control power supply 135 is provided, since the voltage drop of the control power supply 135 is suppressed, abnormal shutdown due to the protection circuit can be prevented.

[0069] Furthermore, the voltage of the control power supply 135 decreases due to the charging current during the initial charging period, i.e., the first period, when the voltage of the bootstrap capacitor 133 has not yet risen. Therefore, in Embodiment 1, during the first period, the pulse width w1, pulse interval w2, and duration T1 of the first period are set to specifically suppress the voltage drop of the control power supply 135. Additionally, after the voltage of the bootstrap capacitor 133 rises to a certain extent through pulse charging during the first period, the voltage of the control power supply 135 becomes difficult to decrease. Therefore, in Embodiment 1, during the second period, the low-side semiconductor switch 121 is driven by a pulse signal 10 having a second pulse width w3 larger than the first pulse width w1. This allows for a shorter charging period.

[0070] Furthermore, in Embodiment 1, a first drive circuit 134L for driving the low-side semiconductor switch 121L, a second drive circuit 134H for driving the high-side semiconductor switch 121H, and a power supply unit 137 are provided. The power supply unit 137 includes a limiting resistor 131, a bootstrap diode 132, and a bootstrap capacitor 133, and generates a power supply voltage supplied to the second drive circuit 134H. Additionally, in each phase, switching is performed with a phase difference equal to the value obtained by dividing 360° by the number of phases p. In Patent Document 1, switching of each phase is performed at the same timing without a phase difference. Therefore, it is difficult to suppress the voltage drop of the control power supply, and a voltage drop in the control voltage is easily caused. In contrast, in Embodiment 1, since switching is performed with a phase difference in each phase during the first period, the voltage drop of the control voltage can be effectively suppressed.

[0071] Implementation Method 2

[0072] Figure 4 This is a schematic diagram showing the gate waveform for charging the bootstrap capacitor 133 in the power conversion device 100 according to Embodiment 2. Figure 4 In the diagram, the horizontal axis represents time, and the vertical axis, from top to bottom, represents the gate waveforms of the U phase, V phase, and W phase, respectively.

[0073] In Embodiment 1 described above, the pulse width w1 of the pulse signal 10 during the first period is a fixed value. In contrast, in Embodiment 2, the pulse width w1 of the pulse signal 10 during the first period is variable. That is, in Embodiment 2, the pulse width w1 of the pulse signal 10 is not fixed during the first period, and the switching of the low-side semiconductor switch 121L is performed. Other structures and operations are the same as in Embodiment 1, so their description is omitted here.

[0074] In implementation method 2, such as Figure 4 As shown, the pulse width w1 of the pulse signal 10 output in the first carrier cycle of the first period is set to w1-1. Furthermore, the pulse width w1 of the pulse signal 10 output in the last (hereinafter, the nth) carrier cycle of the first period is set to w1-n. At this time, the pulse width w1 is changed in a manner consistent with the following equation (6).

[0075] (w1-n)>(w1-1)···(6)

[0076] That is, the pulse width w1-n is greater than the pulse width w1-1. In embodiment 2, the pulse width w1 is increased at a predetermined increase rate according to the interval of each carrier cycle. As an increase method, for example, there are the following methods (1) and (2). However, it is not limited to these, and other methods may also be used. In addition, (1) and (2) may be combined.

[0077] (1) From the interval of the first carrier cycle to the interval of the nth carrier cycle, the pulse width w1 is increased at a constant rate (linear change) for each interval. That is, when the pulse width w1 of the pulse signal 10 output in the interval of the kth carrier cycle in the first period is set to w1-k, the relationship (w1-n)>(w1-k)>(w1-1) holds. Here, k is any natural number from 1 to n. Therefore, the pulse width w1 of the pulse signal 10 output in the interval of the (k+1)th carrier cycle is a constant value larger than the pulse width w1 of the pulse signal 10 output in the interval of the kth carrier cycle.

[0078] (2) From the interval of the first carrier period to the interval of the kth carrier period, the pulse width w1 is always the same with a increment of w1-1. Here, k is any natural number from 1 to n. Furthermore, from the interval of the (k+1)th carrier period to the interval of the nth carrier period, the pulse width w1 is always the same with a increment of w1-n. In (1) above, the pulse width w1 increases linearly, but in (2), the pulse width w1 increases in a stepwise manner. The rate of increase can be constant or variable. Moreover, although an example of variation in two stages is given here, variation in three or more stages is also possible.

[0079] In Implementation 2, similarly to Implementation 1, the duration T1 of the first period is defined by the above formula (4). However, in Implementation 2, the average value of the duty cycle of the first period is substituted into the Duty of the above formula (4). That is, in the interval of each carrier period from the 1st to the nth, the above formula (1) is used to calculate Duty = w1 / w2, and the average value of these Duties is calculated.

[0080] The above description illustrates the pulse width of a single phase, but in the case of multiple phases, the pulse widths of each phase during the same carrier period are the same.

[0081] During the second period from the time t1 to the time t2 when the bootstrap action ends, the timing of the switching of each phase is made the same, and the switching is performed with a pulse width w3. The pulse width w3 is within the range of the following formula (7). Here, w2 is the pulse interval of the first period, and T2 is the time length of the second period.

[0082] w2<w3≤T2···(7)

[0083] In Embodiment 2, similarly to Embodiment 1, the pulse width w3 can also be the same as the duration T2 of the second period. In this case, w3 = T2, which is also included in the above equation (7). When w3 = T2, the pulse signal 10 is continuously on during the second period. At time t2 after the second period has elapsed, the bootstrap capacitor 133 has completed charging.

[0084] As described above, in Embodiment 2, since the structure is essentially the same as in Embodiment 1, the same effects as in Embodiment 1 can be obtained. Furthermore, in Embodiment 2, the pulse width w1 of the pulse signal 10 during the first period is variable, gradually increasing linearly or in a stepped manner. As mentioned above, the voltage of the control power supply 135 decreases due to the charging current during the initial charging phase before the voltage of the bootstrap capacitor 133 rises. Therefore, in Embodiment 2, the pulse width w1 of the pulse signal 10 gradually increases as the voltage of the bootstrap capacitor 133 increases. The larger the pulse width w1, the faster the charging speed of the bootstrap capacitor 133 and the shorter the charging time. On the other hand, if the pulse width w1 of the pulse signal 10 is excessively increased, the voltage drop of the control power supply 135 cannot be sufficiently suppressed. Therefore, in Embodiment 2, a method is adopted to gradually increase the pulse width w1 of the pulse signal 10 as the voltage of the bootstrap capacitor 133 increases, so as not to generate a voltage drop in the control power supply 135. This allows for the suppression of voltage drop in the control power supply 135 and a reduction in the charging time of the bootstrap capacitor 133.

[0085] Implementation Method 3

[0086] Figure 5 This is a structural diagram illustrating an example of the structure of the power conversion device 100 according to Embodiment 3. Figure 6 It means Figure 5 A partial view of the structure of the gate drive circuit 130 and the structure of the inverter 120 are shown. In Embodiment 3, a voltage detection unit 136 is added to the structure of the power conversion device 100 of Embodiment 1. The voltage detection unit 136 detects the voltage of the control power supply 135. During the charging of the bootstrap capacitor 133, the control unit 140 determines the timing of turning the semiconductor switch 121 on and off based on the voltage of the control power supply 135 detected by the voltage detection unit 136. Other structures are the same as in Embodiment 1, so they will be briefly described below; for details, please refer to the description of Embodiment 1.

[0087] like Figure 5As shown, the power conversion device 100, like in Embodiment 1, includes a power conversion section 150 having a converter 110 and an inverter 120, and a gate drive circuit 130. The gate drive circuit 130 applies a voltage to the gate of the semiconductor switch 121 provided in the inverter 120 to drive the semiconductor switch 121. Furthermore, if the converter 110 is an active converter using active elements, the gate drive circuit 130 can also drive the converter 110.

[0088] Furthermore, the converter 110, inverter 120, and gate drive circuit 130 can be configured in the same module or separately in two or more modules. When separately configured in two or more modules, the combination of their partitioning methods is not limited to Embodiment 3.

[0089] The gate drive circuit 130 drives the converter 110 or the inverter 120, or both, through a control signal from the control unit 140.

[0090] like Figure 6 As shown, the power supply section 137 of the gate drive circuit 130u is composed of a limiting resistor 131, a bootstrap diode 132, and a bootstrap capacitor 133. Figure 6 This refers to only one phase (U phase), but in the case of multiple phases, the power supply unit 137 can be provided for each phase, or a single power supply unit 137 can be shared by all phases. In addition, other components such as filter circuits and protection circuits can also be assembled into the gate drive circuit and the power supply unit 137.

[0091] Furthermore, in Embodiment 3, as described above, a voltage detection unit 136 is provided to detect the voltage of the control power supply 135 of the gate drive circuit 130. The voltage detection unit 136 sends a voltage detection signal to the control unit 140.

[0092] When the bootstrap operation begins, the control unit 140, similar to embodiments 1 and 2, outputs a pulse signal 10 from the gate drive circuit 130 to turn on the low-side semiconductor switch 121L. During the bootstrap operation, the control unit 140 calculates the voltage fluctuation amplitude ΔVreal, which is the actual voltage fluctuation amplitude, based on the voltage detection signal from the voltage detection unit 136. ΔVreal is the difference between the voltage of the control power supply 135 before the bootstrap operation begins and the current voltage of the control power supply 135.

[0093] In addition, the control unit 140 stores a preset allowable voltage fluctuation range ΔV (first threshold) in its memory. The control unit 140 compares the voltage fluctuation range ΔVreal with the allowable voltage fluctuation range ΔV.

[0094] Based on the comparison, when ΔVreal > ΔV, the control unit 140 determines that a voltage drop has occurred in the control power supply 135, and disconnects the currently on semiconductor switch 121. Specifically, the control unit 140 disconnects the pulse signal 10 output from the gate drive circuit 130. When the semiconductor switch 121 becomes off, the voltage of the control power supply 135 recovers. Therefore, when ΔVreal ≤ ΔV, the control unit 140 outputs the pulse signal 10, reconnecting the semiconductor switch 121 and restarting the bootstrap operation. The control unit 140 repeats this operation, charging the bootstrap capacitor 133.

[0095] Furthermore, in the above description, ΔVreal is the difference between the voltage of the control power supply 135 before the start of the bootstrap operation and the current voltage of the control power supply 135, but it is not limited to this case. That is, as long as the same operation can be achieved, ΔVreal can also be set as the voltage difference between the turn-on and turn-on of a semiconductor switch 121, such as the U-phase semiconductor switch 121Lu, or other methods. In this case, the voltage detection unit 136 is configured for the low-side semiconductor switch 121L.

[0096] Alternatively, if the minimum value of the pulse width w1 is determined, the control can be performed as follows: If the time from the moment a semiconductor switch 121 is turned on until the condition ΔVreal > ΔV is satisfied is less than the minimum value of the pulse width w1, the semiconductor switch 121 may not be immediately turned off. Alternatively, the semiconductor switch 121 may remain on until its on-time exceeds the minimum value of the pulse width w1, after which the semiconductor switch 121 may be turned off.

[0097] Additionally, during the charging of the bootstrap capacitor 133, the control unit 140 can also determine whether charging is complete based on the power supply voltage detected by the voltage detection unit 136. In this case, the control unit 140 calculates the voltage fluctuation amplitude ΔVreal before and after the low-side semiconductor switch 121 is turned on using the same process as described above. If the low-side semiconductor switch 121 is in the on state but the voltage fluctuation amplitude ΔVreal is 0 or below a preset second threshold, the control unit 140 determines that the charging of the bootstrap capacitor 133 is complete. In this case, the control unit 140 keeps the semiconductor switch 121 turned on and remains in standby mode until the end of the bootstrap operation, i.e., time t2.

[0098] Furthermore, in Embodiment 3, the operation of a single phasor was described, but in the case of multiple phases, the semiconductor switch 121 switches based on the phase difference obtained by dividing 360° by the number of phases p.

[0099] As described above, in Embodiment 3, a voltage detection unit 136 is provided to detect the power supply voltage of the control power supply 135 of the gate drive circuit 130. During the charging period of the bootstrap capacitor 133, the control unit 140 determines the timing of turning the semiconductor switch 121 on and off based on the voltage of the control power supply 135 detected by the voltage detection unit 136. Therefore, in Embodiment 3, the first period and the second period shown in Embodiments 1 and 2 may not be provided. Alternatively, the control unit 140 may determine the timing of turning the semiconductor switch 121 on and off based on the voltage of the control power supply 135 detected by the voltage detection unit 136 during at least one of the first and second periods. Thus, in Embodiment 3, by providing the voltage detection unit 136, a pulse signal 10 is output according to the voltage drop of the control power supply 135, thereby making the duty cycle variable.

[0100] Furthermore, in Embodiment 3, during the charging of the bootstrap capacitor 133, the control unit 140 calculates the voltage fluctuation amplitude ΔVreal of the low-side semiconductor switch 121 before and after it is turned on, based on the voltage of the control power supply 135 detected by the voltage detection unit 136. Then, when the voltage fluctuation amplitude ΔVreal becomes greater than a first threshold, the low-side semiconductor switch 121 is turned off. As a result, the control power supply 135 gradually recovers. When the voltage fluctuation amplitude ΔVreal becomes below the first threshold, the control unit 140 determines that the control power supply 135 has recovered to a rechargeable state and turns the low-side semiconductor switch 121 back on. Thus, the bootstrap capacitor 133 is charged only during the period when the voltage drop of the control power supply 135 is within the allowable range, thereby preventing the voltage drop of the control power supply 135 from putting pressure on the power supply unit 137.

[0101] Furthermore, in Embodiment 3, during the charging of the bootstrap capacitor 133, the control unit 140 calculates the voltage fluctuation amplitude ΔVreal of the low-side semiconductor switch 121 before and after it is turned on, based on the voltage of the control power supply 135 detected by the voltage detection unit 136. If the low-side semiconductor switch 121 is in the on state but the voltage fluctuation amplitude ΔVreal is 0 or below the second threshold, the control unit 140 determines that the charging of the bootstrap capacitor 133 is complete. In this case, the control unit 140 maintains the semiconductor switch 121 in the on state and remains in standby mode until time t2. Therefore, the charging of the bootstrap capacitor 133 can be reliably performed, and the pressure on the power supply unit 137 caused by the voltage drop of the control power supply 135 is prevented.

[0102] Furthermore, the hardware structure of the control unit 140 in the power conversion device 100 according to embodiments 1 to 3 described above will be explained here. The control unit 140 can implement the above-described operations in software, such as a microcomputer, or in hardware, such as an analog circuit. Alternatively, it can be implemented in combination.

[0103] The hardware structure of the control unit 140 will be described in more detail below. The control unit 140 is composed of processing circuitry. The processing circuitry is composed of dedicated hardware or a processor. Dedicated hardware may be, for example, an ASIC (Application Specific Integrated Circuit) or a FPGA (Field Programmable Gate Array). The processor executes a program stored in memory. The control unit 140 has memory. The memory may be non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, or EPROM (Erasable Programmable ROM), or a disk such as a hard disk, floppy disk, or optical disk.

[0104] Furthermore, in the embodiments 1 to 3 described above, AC power supply 1 was used as an example of the power source connected to the power conversion device 100, but this is not a limitation. That is, the power source connected to the power conversion device 100 can also be DC power supply. In this case, Figure 1 as well as Figure 5 In the illustrated configuration example, the converter 110 may also be omitted. Additionally, Figure 1 as well as Figure 5 The diagram shows the AC power supply 1 as a three-phase three-wire system, but the AC power supply 1 can be single-phase or three-phase four-wire.

[0105] Furthermore, in the power conversion device 100 described in embodiments 1 to 3 above, the components used in the converter 110 and inverter 120 may also be made of wide-bandgap semiconductors with a larger bandgap than silicon (Si). Specifically, the semiconductor switch 121 and switching elements such as 115 and 116, the rectifier diode 114 and freewheeling diode 122, and other components may also be made of wide-bandgap semiconductors. Examples of wide-bandgap semiconductors include silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), or diamond.

[0106] Switching elements and diodes formed from such wide-bandgap semiconductors exhibit high voltage withstand capability and allow for high current density. Therefore, miniaturization of individual components such as switching elements and diodes is possible. Furthermore, by using these miniaturized components, miniaturization of semiconductor modules in which these components are assembled is also possible.

[0107] In addition, wide-bandgap semiconductors have high heat resistance, which enables the miniaturization of heat sinks. Furthermore, since they can enable air cooling in water-cooled sections, they can further miniaturize semiconductor modules.

[0108] Furthermore, wide-bandgap semiconductors, due to their low power loss, enable high efficiency in switching elements and diodes, thereby achieving high efficiency in semiconductor modules.

[0109] Furthermore, it is preferred that all components, including the switching elements and diodes, are formed of wide-bandgap semiconductors. However, this is not a limitation; any one of them may also be formed of a wide-bandgap semiconductor. In this case, the aforementioned effects can also be achieved.

[0110] Implementation Method 4

[0111] Embodiment 4 describes the application of the power conversion device 100 described in Embodiment 1 to the air conditioner 400.

[0112] Figure 7 This is a structural diagram illustrating an example of the structure of the air conditioner 400 according to Embodiment 4. For example... Figure 7 As shown, the air conditioner 400 includes a refrigeration cycle unit 300 and a blower 401. The refrigeration cycle unit 300 includes a refrigerant compressor 200, a condenser 301, an expansion valve 302, and an evaporator 303. The refrigerant compressor 200 includes a compressor 201 and a power conversion unit 100.

[0113] like Figure 7 As shown, compressor 201 and condenser 301 are connected via refrigerant piping 304. Similarly, condenser 301 is also connected to expansion valve 302, expansion valve 302 to evaporator 303, and evaporator 303 to compressor 201 via refrigerant piping 304. Thus, compressor 201, condenser 301, expansion valve 302, and evaporator 303 constitute a refrigerant circuit for refrigerant circulation.

[0114] Compressor 201 draws in refrigerant through the suction port. It compresses the drawn-in refrigerant, transforming it into a high-temperature, high-pressure gaseous refrigerant, which is then discharged through the discharge port. Compressor 201 has an electric motor 2 whose speed is variablely controlled by a power conversion device 100. Compressor 201 is, for example, a variable frequency compressor. The operating frequency of compressor 201 can be arbitrarily changed via the inverter 120 of the power conversion device 100. Therefore, the amount of refrigerant delivered by compressor 201 per unit time can be varied. The refrigerant discharged from compressor 201 flows into condenser 301.

[0115] The condenser 301 facilitates heat exchange between the refrigerant flowing inside and the air. The condenser 301 condenses the high-temperature, high-pressure refrigerant flowing in from the compressor 201, transforming it into a high-pressure liquid refrigerant (single-phase). The condenser 301 is, for example, a finned-tube heat exchanger.

[0116] Expansion valve 302 is a pressure-reducing device that depressurizes the liquid refrigerant flowing from condenser 301, causing it to expand. Expansion valve 302 is, for example, an electronic expansion valve. When expansion valve 302 is an electronic expansion valve, its opening is adjusted based on instructions from a control device (not shown). Expansion valve 302 is located between condenser 301 and evaporator 303. Expansion valve 302 depressurizes the liquid refrigerant flowing from condenser 301, causing it to become a two-phase refrigerant in a low-pressure gaseous and liquid state.

[0117] Evaporator 303 facilitates heat exchange between the refrigerant flowing inside and the air. Evaporator 303 causes the liquid refrigerant portion of the two-phase refrigerant flowing in from expansion valve 302 to evaporate, transforming it into a low-pressure gaseous refrigerant (single-phase). Evaporator 303 is, for example, a finned tube heat exchanger.

[0118] In addition, the blower 401 blows air to at least one of the condenser 301 and the evaporator 303.

[0119] In the refrigeration cycle unit 300, the processes of evaporation, compression, condensation, and expansion of the refrigerant are repeatedly performed. The refrigerant changes from liquid to gas and then from gas to liquid, thereby exchanging heat between the refrigerant and the outside air. Therefore, an air conditioner 400 can be constructed by combining the refrigeration cycle unit 300 and the blower 401 that circulates outside air.

[0120] Furthermore, in the above description, an example of applying the power conversion device 100 according to Embodiment 1 to the air conditioner 400 was described, but it is not limited to this case. The power conversion device 100 according to Embodiment 2 or 3 can also be applied to the air conditioner 400.

[0121] Industrial availability

[0122] In the above embodiments 1 to 4, an air conditioner 400 was described as an application example of the power conversion device 100, but the power conversion device 100 can of course also be used in other equipment. For example, the power conversion device 100 can be widely used in air conditioning heating and cooling equipment that uses an inverter, or in equipment that drives loads such as compressors or motors.

[0123] Explanation of reference numerals in the attached figures

[0124] 1... AC power supply; 2... Motor; 10... Pulse signal; 100... Power conversion device; 110... Converter; 111... Rectifier circuit; 112... DC reactor; 113... Smoothing capacitor; 114... Rectifier diode; 115... Switching element; 116... Switching element; 120... Inverter; 121... Semiconductor switch; 121H... Semiconductor switch; 121Hu... Semiconductor switch; 121Hv... Semiconductor switch; 121Hw... Semiconductor... Conductor switch; 121L... Semiconductor switch; 121Lu... Semiconductor switch; 121Lv... Semiconductor switch; 121Lw... Semiconductor switch; 122... Freewheeling diode; 125... Midpoint; 125u... Midpoint; 126... Output terminal; 130... Gate drive circuit; 130u... Gate drive circuit; 130v... Gate drive circuit; 130w... Gate drive circuit; 131... Limiting resistor; 132... Bootstrap diode; 133... Bootstrap capacitor ; 134H...Second drive circuit; 134L...First drive circuit; 135...Control power supply; 136...Voltage detection unit; 137...Power supply unit; 140...Control unit; 150...Power conversion unit; 151...Positive busbar; 152...Negative busbar; 200...Refrigerant compression unit; 201...Compressor; 300...Refrigeration cycle unit; 301...Condenser; 302...Expansion valve; 303...Evaporator; 304...Refrigerant piping; 400...Air Adjustment; 401... Blower; A... Coefficient; C... Capacitor; D1... Phase difference; D2... Phase difference; Duty... Duty cycle; R... Resistance value; T1... Time length; T2... Time length; p... Number of phases; t1... Time; t2... Time; w1... Pulse width (first pulse width); w2... Pulse interval; w3... Pulse width (second pulse width); ΔV... Allowable voltage variation range; ΔVreal... Voltage variation range; τ... Time constant.

Claims

1. A power conversion device, wherein, The power conversion device includes: The power conversion unit connects at least two switching elements in series to form a series circuit. One end of the series circuit is connected to the power supply potential side, the other end of the series circuit is connected to the reference potential side, and the midpoint of the series circuit is connected to the output terminal. and The gate drive circuit drives the switching element by outputting pulse signals based on control signals from an externally located control unit. The gate drive circuit has: The first drive circuit is powered by a control power supply and drives the switching element connected to the reference potential side. The second driving circuit drives the switching element connected to the power supply potential side; as well as The power supply section includes a limiting resistor, a bootstrap diode, and a bootstrap capacitor connected in series between the control power supply and the output terminal, generating a power supply voltage to be supplied to the second drive circuit. The bootstrap capacitor is charged by switching the switching element connected to the reference potential side. The charging period of the bootstrap capacitor includes at least a first period and a second period. During the first period, the switching element connected to the reference potential side is driven by a pulse signal having a first pulse width. During the second period, the switching element connected to the reference potential side is driven by a pulse signal having a second pulse width that is larger than the first pulse width. The first pulse width during the first period is determined based on the magnitude of the voltage drop of the control power supply allowed during the first period.

2. The power conversion device according to claim 1, wherein, The power conversion unit has multiple phases, and each phase has the series connection. When the number of phases of the power conversion unit is set to p, During the first period, the switching elements of each phase connected to the reference potential side switch by the phase difference, which is the value obtained by dividing 360° by the number of phases p.

3. The power conversion device according to claim 1 or 2, wherein, When the value obtained by dividing the on-time of the switching element on the reference potential side by the carrier period is set as Duty, The duration T1 of the first period, relative to the Duty, the capacitance C of the bootstrap capacitor, and the resistance R of the limiting resistor within the first period, satisfies the following relationship: T1>A×C×R / Duty Here, coefficient A is a value greater than or equal to 1.

4. The power conversion device according to claim 3, wherein, The coefficient A is a value greater than 2, and is determined based on the magnitude of the voltage drop of the control power supply allowed during the second period.

5. The power conversion device according to any one of claims 1, 2, and 4, wherein, The second pulse width during the second period is greater than the carrier period of the pulse signal during the first period.

6. The power conversion device according to any one of claims 1, 2, and 4, wherein, The first pulse width of the pulse signal during the first period is variable. When the first period is divided into n intervals based on the carrier period The first pulse width of the pulse signal in the nth interval of the first period is greater than the first pulse width of the pulse signal in the 1st interval of the first period.

7. The power conversion device according to claim 6, wherein, When the value obtained by dividing the on-time of the switching element on the reference potential side by the carrier period is set as Duty, The Duty in the first period is calculated using the average of the first pulse widths of the pulse signals in each interval from the first to the nth.

8. The power conversion device according to any one of claims 1, 2, 4, and 7, wherein, The system includes a voltage detection unit that detects the power supply voltage of the control power supply for the gate drive circuit. During the charging of the bootstrap capacitor, the control unit determines the timing for turning the switching element connected to the reference potential side on and off based on the power supply voltage detected by the voltage detection unit.

9. The power conversion device according to claim 8, wherein, During the charging of the bootstrap capacitor, Based on the power supply voltage detected by the voltage detection unit, the control unit calculates the voltage fluctuation range of the switching element connected to the reference potential side before and after it is turned on. When the voltage fluctuation amplitude becomes greater than a first threshold, the switching element connected to the reference potential side is disconnected. When the voltage fluctuation amplitude falls below the first threshold, the switching element connected to the reference potential side is switched on.

10. The power conversion device according to claim 8, wherein, During the charging of the bootstrap capacitor, Based on the power supply voltage detected by the voltage detection unit, the control unit calculates the voltage fluctuation range of the switching element connected to the reference potential side before and after it is turned on. When the switching element connected to the reference potential side is in the ON state, the ON state of the switching element is maintained when the voltage fluctuation amplitude is 0 or below the second threshold.

11. The power conversion device according to any one of claims 1, 2, 4, 7, 9, and 10, wherein, The switching element is formed of a wide-bandgap semiconductor. The wide bandgap semiconductor is silicon carbide, gallium nitride, gallium oxide, or diamond.

12. An air conditioner, wherein, The air conditioner has the following features: A refrigeration cycle device includes a power conversion device according to any one of claims 1 to 11, a compressor driven by an electric motor as a load of the power conversion device, a condenser for condensing refrigerant discharged from the compressor, an expansion valve for depressurizing the condensed refrigerant, and an evaporator for evaporating the depressurized refrigerant. and A blower supplies air to at least one of the condenser and the evaporator of the refrigeration cycle device.

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