Power converter

Abstract

To provide a power conversion device that can suppress undercharging of capacitors. [Solution] The power converter A1 comprises a DC terminal T1 to which a DC power supply B1 is connected, an AC terminal T2 to which an AC power supply B2 is connected, an inverter 1, a DC-side switch 31, an AC-side switch 32, a DC capacitor 4, a current-limiting resistor 5, an inverter control unit 62, and a switch control unit 61. In the first state, when the capacitor voltage of the DC capacitor 4 is less than a threshold corresponding to the AC power supply voltage of the AC power supply B2, the switch control unit 61 turns off both the DC-side switch 31 and the AC-side switch 32. In the second state, when the capacitor voltage is above the threshold, the DC-side switch 31 is turned off while the AC-side switch 32 is turned on. The inverter control unit 62 stops the inverter 1 in the first state and controls the inverter 1 in a capacitor charging mode in the second state, charging the DC capacitor 4 from the AC power supply B2.

Description

Technical Field

[0001] The present disclosure relates to a power conversion device that converts direct current and alternating current.

Background Art

[0002] Conventionally, there is a power conversion device that converts at least one of direct current to alternating current and alternating current to direct current. For example, Patent Document 1 discloses an example of a conventional power conversion device. The power conversion device described in Patent Document 1 includes an inverter. The inverter converts direct current power input from a direct current power source such as a battery into alternating current power and outputs it to a load. The inverter includes a power conversion unit, a capacitor, and an initial charging circuit. The power conversion unit converts direct current power into alternating current power. The capacitor is connected in parallel with the power conversion unit on the input side (direct current side) of the power conversion unit. The initial charging circuit includes a resistor and is provided to initially charge the capacitor via the resistor. In the power conversion device of Patent Document 1, during charging of the capacitor by this initial charging circuit, a current flows from the direct current power source through the resistor to the capacitor. Thereby, it is possible to prevent an inrush current from flowing through the capacitor when the direct current power source is connected. After that, when the charging of the capacitor is completed (when the voltage of the capacitor becomes greater than a threshold value based on the input voltage from the direct current power source), the direct current power source and the capacitor are electrically connected without passing through the resistor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the power conversion device described in Patent Document 1, a discharge resistor is connected in parallel with the capacitor. In this configuration, even when attempting to charge the capacitor of the power conversion device from a DC power supply via the resistor, current may flow through the discharge resistor. As a result, the capacitor voltage may not exceed a threshold value based on the input voltage from the DC power supply, and the capacitor may not be fully charged. Consequently, the connection between the DC power supply and the capacitor remains unchanged, without the resistor. Alternatively, if the DC power supply and the capacitor are electrically connected without the resistor, there is a risk of an inrush current flowing through the capacitor. These issues are also true when a load is connected to the DC capacitor, even without a discharge resistor.

[0005] This disclosure was conceived in view of the above circumstances, and its purpose is to provide a power conversion device that can suppress undercharging of a capacitor. [Means for solving the problem]

[0006] The power converter provided by this disclosure comprises a DC terminal to which a DC power supply is connected, an AC terminal to which an AC power supply is connected, an inverter connected between the DC terminal and the AC terminal, a DC-side switch connected between the DC terminal and the inverter, an AC-side switch connected between the AC terminal and the inverter, a DC capacitor connected between the DC-side switch and the inverter, a current-limiting resistor connected in series with the DC capacitor and in parallel with the DC-side switch, an inverter control unit for controlling the inverter, and a switch control unit for controlling the on and off states of the DC-side switch and the AC-side switch, respectively. The inverter control unit, in connection processing to electrically connect the DC power supply and the DC capacitor via the DC-side switch, in a first state where the capacitor voltage of the DC capacitor is less than a threshold corresponding to the AC power supply voltage of the AC power supply, turns off both the DC-side switch and the AC-side switch; in a second state where the capacitor voltage is equal to or greater than the threshold, turns off the DC-side switch while turning on the AC-side switch; and in the first state, stops the inverter; and in the second state, operates the inverter in a capacitor charging mode in which the DC capacitor is charged from the AC power supply.

[0007] In a preferred embodiment of the power conversion device, the switch control unit turns on both the DC-side switch and the AC-side switch when the difference between the capacitor voltage and the DC power supply voltage of the DC power supply is within a predetermined range in the connection process, and the inverter control unit operates the inverter in a power conversion mode corresponding to the DC power supply and the AC power supply when the third state is reached.

[0008] In a preferred embodiment of the power conversion device, the DC power source is a storage battery, and the inverter control unit controls the charging and discharging of the storage battery in the power conversion mode.

[0009] In a preferred embodiment of the power conversion device, the device includes a first voltage sensor for detecting the capacitor voltage and a second voltage sensor for detecting the terminal voltage of the AC terminal, wherein the threshold value is the peak value of the AC power supply voltage, and the switch control unit determines whether the device is in the first state or the second state by comparing the value detected by the first voltage sensor with the peak value calculated from the value detected by the second voltage sensor. [Effects of the Invention]

[0010] In the power converter of this disclosure, when the DC capacitor is in the first state, it is charged by the DC power supply via a current-limiting resistor, thereby suppressing the inrush current to the DC capacitor that may occur when the DC power supply is connected. Furthermore, in the power converter of this disclosure, when the DC capacitor is in the second state, it is charged by the current output from the AC power supply, thereby suppressing undercharging of the DC capacitor. Therefore, according to the power converter of this disclosure, undercharging of the DC capacitor can be suppressed while suppressing the inrush current from the DC power supply during the charging of the DC capacitor. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows an example configuration of a power conversion device according to one embodiment. [Figure 2] This diagram illustrates the charge states (first to third states) of a DC capacitor. [Figure 3] This flowchart shows the connection process between DC and AC power supplies performed by the control circuit of the power converter shown in Figure 1. [Figure 4] This figure shows the current flow when the DC capacitor in the power converter shown in Figure 1 is in the first state and when it is in the third state. [Figure 5] This figure shows the current flow (the AC current flow is the opposite of that in Figure 6) when the DC capacitor of the power converter shown in Figure 1 is in the second state of charge. [Figure 6]This figure shows the current flow (the AC current flow is the opposite of that in Figure 5) when the DC capacitor of the power converter shown in Figure 1 is in the second state of charge. [Modes for carrying out the invention]

[0012] Preferred embodiments of the power converter of this disclosure will be described below with reference to the drawings. Hereafter, identical or similar components will be denoted by the same reference numerals, and redundant descriptions will be omitted. The terms "first," "second," "third," etc., in this disclosure are used merely as labels and are not necessarily intended to assign a sequence to the objects.

[0013] Figure 1 shows a power converter A1 according to one embodiment of the present disclosure. As shown in the figure, the power converter A1 comprises a DC terminal T1, an AC terminal T2, an inverter 1, a filter circuit 2, a DC-side switch 31, an AC-side switch 32, a DC capacitor 4, a current-limiting resistor 5, a control circuit 6, and a plurality of voltage sensors 71 to 73. The control circuit 6 includes a switch control unit 61 and an inverter control unit 62. The power converter A1 may also be equipped with a discharge resistor, similar to the power converter described in Patent Document 1, or a load may be connected to the DC power supply B1 side (DC capacitor 4) of the inverter 1.

[0014] Power converter A1 is connected between DC power source B1 and AC power source B2. Power converter A1 converts the DC power input from DC power source B1 into AC power and outputs it to AC power source B2. It also converts the AC power input from AC power source B2 into DC power and outputs it to DC power source B1. For example, DC power source B1 is a battery, and AC power source B2 is a grid power source. In this example, power converter A1 is, for example, a grid-connected inverter device (a power conditioner for a battery). Note that DC power source B1 is not limited to a battery, but may be an electric vehicle (more specifically, a battery installed in an electric vehicle), a solar cell, or a device that generates AC power and converts it to DC power for output. AC power source B2 is not limited to a grid power source, but may be, for example, an inverter device capable of converting DC power to AC power.

[0015] DC terminal T1 is an external terminal of power converter A1. DC power supply B1 is connected to DC terminal T1. AC terminal T2 is an external terminal of power converter A1. AC power supply B2 is connected to AC terminal T2.

[0016] Inverter 1 is connected between DC terminal T1 and AC terminal T2. In this embodiment, inverter 1 is connected between DC capacitor 4 and filter circuit 2. Inverter 1 converts DC power to AC power. Inverter 1 is, for example, a PWM controlled inverter. In the illustrated example, inverter 1 is a full-bridge circuit including four switching elements SW1 to SW4. In the illustrated example, the four switching elements SW1 to SW4 are each IGBTs (Insulated-Gate Bipolar Transistors), but other transistors such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) and bipolar transistors may also be used. In inverter 1, multiple diodes D1 to D4 are individually connected in antiparallel to each of the four switching elements SW1 to SW4. The configuration of inverter 1 is not limited to a full-bridge circuit; for example, it may be a half-bridge circuit, or any circuit capable of converting DC to AC.

[0017] In inverter 1, a drive signal (e.g., a PWM signal) is input from the inverter control unit 62 to each switching element SW1 to SW4, and each switching element SW1 to SW4 is switched on and off according to the input drive signal. Inverter 1 converts the DC power input from the DC terminal T1 (DC power supply B1) into AC power by switching each switching element SW1 to SW4 on and off (switching operation). Inverter 1 rectifies the AC power (AC power supply B2) input from the AC terminal T2 using diodes D1 to D4 and converts it into DC power.

[0018] The filter circuit 2 is connected between the inverter 1 and the AC side switch 32. In the illustrated example, the filter circuit 2 is an LC circuit including an inductor L and a capacitor C.

[0019] The DC side switch 31 is connected between the DC terminal T1 and the inverter 1. When the DC side switch 31 is on, it connects the current path between the DC terminal T1 and the inverter 1, and when it is off, it cuts off the current path (without passing through the current-limiting resistor 5) between the DC terminal T1 and the inverter 1.

[0020] The AC side switch 32 is connected between the AC terminal T2 and the inverter 1. When the AC side switch 32 is on, it connects the current path between the AC terminal T2 and the inverter 1, and when it is off, it cuts off the current path between the AC terminal T2 and the inverter 1.

[0021] The DC capacitor 4 is connected between the DC side switch 31 and the inverter 1. The DC capacitor 4 is connected in parallel with the DC terminal T1 and also in parallel between the terminals on the DC power supply B1 side of the inverter 1. The type and capacitance of the DC capacitor 4 can be appropriately changed according to the specifications of the power conversion device A1.

[0022] The current-limiting resistor 5 is connected in series with the DC capacitor 4. The current-limiting resistor 5 is connected in parallel with the DC side switch 31 between the DC terminal T1 and the DC capacitor 4. The type and resistance value of the current-limiting resistor 5 can be appropriately changed according to the specifications of the power conversion device A1.

[0023] Voltage sensor 71 detects the terminal voltage of DC terminal T1. Since the terminal voltage of DC terminal T1 corresponds to the power supply voltage of DC power supply B1 (hereinafter referred to as "DC power supply voltage"), voltage sensor 71 detects the DC power supply voltage of DC power supply B1. Voltage sensor 72 detects the capacitor voltage, which is the terminal voltage of DC capacitor 4. Voltage sensor 73 detects the terminal voltage of AC terminal T2. Since the terminal voltage of AC terminal T2 corresponds to the power supply voltage of AC power supply B2 (hereinafter referred to as "AC power supply voltage"), voltage sensor 73 detects the AC power supply voltage of AC power supply B2. The detected values ​​of voltage sensor 71 (DC terminal voltage), voltage sensor 72 (capacitor voltage), and voltage sensor 73 (AC terminal voltage) are each input to the control circuit 6 (at least the switch control unit 61).

[0024] The control circuit 6 performs various controls in the power converter A1. The control circuit 6 is implemented by, for example, a microcomputer, but may also be implemented by one or more analog circuits, one or more digital circuits, or both. As mentioned above, the control circuit 6 includes a switch control unit 61 and an inverter control unit 62. The switch control unit 61 and the inverter control unit 62 may be implemented on a common microcomputer, or they may be implemented on different microcomputers.

[0025] The switch control unit 61 controls the on and off states of the DC side switch 31 and the AC side switch 32, respectively. The switch control unit 61 uses the detected values ​​of the voltage sensors 71 to 73 to determine which of the following first to third states the charge state of the DC capacitor 4 is in, and switches the on and off states of the DC side switch 31 and the AC side switch 32, respectively.

[0026] Figure 2 is a diagram illustrating the charging states (first to third states) of the DC capacitor 4, showing which of the first to third states is being reached when the DC capacitor 4 is being gradually charged. The first state is when the capacitor voltage of the DC capacitor 4 is less than a threshold value corresponding to the AC power supply voltage of the AC power supply B2. When the charging state of the DC capacitor 4 is this first state, the switch control unit 61 turns off both the DC side switch 31 and the AC side switch 32. In this embodiment, the following rectified voltage value is used as the threshold value corresponding to the AC power supply voltage. This is the voltage (rectified voltage) when the AC voltage is input from the AC power supply B2 to the inverter 1, and this AC voltage is rectified by each of the diodes D1 to D4 of the inverter 1. This rectified voltage is, for example, the peak value of the AC power supply voltage (a voltage that is √2 times the effective value of the AC power supply voltage). Therefore, in this embodiment, the threshold value is a value corresponding to the AC power supply voltage. The third state is when the difference between the capacitor voltage of the DC capacitor 4 and the DC power supply voltage of the DC power supply B1 is within a predetermined range. When the charge state of the DC capacitor 4 is in this third state, the switch control unit 61 turns on both the DC side switch 31 and the AC side switch 32. The second state is when the capacitor voltage of the DC capacitor 4 is greater than or equal to the threshold (rectified voltage in this embodiment), and the difference between the capacitor voltage of the DC capacitor 4 and the DC power supply voltage of the DC power supply B1 is not within a predetermined range. In other words, as shown in Figure 2, the second state is between the range in which the capacitor voltage of the DC capacitor 4 satisfies the first state (when it is less than the threshold) and the range in which it satisfies the third state (when the difference between the capacitor voltage and the DC power supply voltage is within a predetermined range). When the charge state of the DC capacitor 4 is in this second state, the switch control unit 61 turns off the DC side switch 31 while turning on the AC side switch 32.

[0027] The switch control unit 61 determines whether the system is in the first or second state by comparing the value detected by the voltage sensor 72 (capacitor voltage) with the peak value (rectified voltage) calculated from the value detected by the voltage sensor 73 (AC power supply voltage). The switch control unit 61 also determines whether the system is in the third state by comparing the value detected by the voltage sensor 72 (capacitor voltage) with the value detected by the voltage sensor 71 (DC power supply voltage). The threshold value corresponding to the AC power supply voltage of AC power supply B2 is not limited to the example described above. For example, the threshold value may be a fixed value based on the rated voltage of AC power supply B2.

[0028] The inverter control unit 62 controls the inverter 1. The inverter control unit 62 generates drive signals (e.g., PWM signals) to control the driving (switching operation) of each switching element SW1 to SW4 of the inverter 1 and outputs them to each switching element SW1 to SW4. The inverter control unit 62 switches the control mode of the inverter 1 according to the charge state of the DC capacitor 4 (the first to third states described above) and controls the inverter 1 according to the control mode. The inverter control unit 62 may determine which of the first to third states is in place, for example, based on the judgment result of the switch control unit 61, or it may determine it using the detection values ​​of each voltage sensor 71 to 73, similar to the switch control unit 61.

[0029] When in the first state described above, the inverter control unit 62 sets the control mode to stop mode. In stop mode, the inverter control unit 62 does not output a drive signal (PWM signal) to the inverter 1. In other words, in stop mode, the inverter control unit 62 stops the inverter 1. When in the second state described above, the inverter control unit 62 sets the control mode to capacitor charging mode. In capacitor charging mode, the inverter control unit 62 controls the inverter 1 with DC voltage control to charge the DC capacitor 4. With DC voltage control, the inverter 1 is controlled by generating a drive signal (PWM signal) based on the difference between the detected value of the terminal voltage (DC voltage) on the DC power supply B1 side of the inverter 1 and the target value of the said terminal voltage. When in the third state described above, the inverter control unit 62 sets the control mode to a power conversion mode corresponding to the DC power supply B1 and the AC power supply B2. In power conversion mode, the inverter control unit 62 controls the inverter 1 with output power control, and in the example where the DC power supply B1 is a storage battery and the AC power supply B2 is a grid power supply, it controls the charging and discharging of the storage battery. In output power control, a drive signal (PWM signal) is generated based on the difference between the detected output power value of the AC power supply B2 side of inverter 1 and the target value of that output power (in battery charge / discharge control, this is a positive value during discharge and a negative value during charging) to control inverter 1.

[0030] Figure 3 is a flowchart showing the connection process between DC power supply B1 and AC power supply B2, which is performed by the control circuit 6 in power converter A1. At the start of the flowchart, the DC side switch 31 and the AC side switch 32 are both off, and the inverter 1 is in a stopped state.

[0031] First, the DC power supply B1 is physically connected to the DC terminal T1, and the AC power supply B2 is physically connected to the AC terminal T2 (S101). The order in which the DC power supply B1 and the AC power supply B2 are connected is not limited. At this time, since the DC side switch 31 and the AC side switch 32 are both off, when the DC power supply B1 is connected to the DC terminal T1, the DC capacitor 4 is charged from the DC power supply B1 via the current limiting resistor 5. In other words, the capacitor voltage of the DC capacitor 4 rises.

[0032] Next, the switch control unit 61 determines whether the capacitor voltage is equal to or greater than the threshold (rectified voltage) (S102). If, in step S102, the capacitor voltage is less than the threshold (rectified voltage) (S102: NO), the switch control unit 61 determines that it is in the first state and continues to keep the DC side switch 31 and the AC side switch 32 in the OFF state. On the other hand, if, in step S102, the capacitor voltage is equal to or greater than the threshold (rectified voltage) (S102: YES), the switch control unit 61 determines that it is in the second state and keeps the DC side switch 31 OFF and turns on the AC side switch 32 (S103). As a result, the AC power supply B2 is electrically connected to the power converter A1. The inverter control unit 62 also operates the inverter 1 in capacitor charging mode (S104). As a result, the DC capacitor 4 is charged from the AC power supply B2 via the inverter 1. In other words, the capacitor voltage of the DC capacitor 4 rises further.

[0033] Next, the switch control unit 61 determines whether the difference between the capacitor voltage and the DC power supply voltage is within a predetermined range (S105). If, in step S105, the difference between the capacitor voltage and the DC power supply voltage is not within the predetermined range (S105: NO), the switch control unit 61 determines that the system remains in the second state and keeps the DC-side switch 31 off and the AC-side switch 32 on, while the inverter control unit 62 operates the inverter 1 in capacitor charging mode. On the other hand, if, in step S105, the difference between the capacitor voltage and the DC power supply voltage is within the predetermined range (S105: YES), the switch control unit 61 determines that the system is in the third state and turns on both the DC-side switch 31 and the AC-side switch 32 (S106). As a result, the DC power supply B1 is electrically connected to the power converter A1. The inverter control unit 62 also operates the inverter 1 in power conversion mode (S107). As a result, power control according to the DC power supply B1 and the AC power supply B2 is initiated.

[0034] The connection process for the DC power supply B1 and AC power supply B2 shown in Figure 3 is an example and is not limited thereto. For example, in step S105, the switch control unit 61 determined whether the difference between the capacitor voltage and the DC power supply voltage was within a predetermined range, but instead, it could determine whether the capacitor voltage was above a threshold corresponding to the DC power supply voltage (for example, a value of about 95% of the DC power supply voltage). In this example, if the capacitor voltage was above the threshold corresponding to the DC power supply voltage, it would be sufficient to determine that it was in the third state.

[0035] Figures 4 to 6 show the current flow in the power converter A1 when the DC capacitor 4 is in the first to third charge states. Figure 4(a) shows the current path in the first state, Figures 5 and 6 show the current path in the second state, and Figure 4(b) shows the current path in the third state. In Figure 4(b), the power conversion mode shown is when current flows from the DC power supply B1 to the AC power supply B2 (if the DC power supply B1 is a battery, the battery is being discharged). In Figures 4(b), 5, and 6, the current paths (AC current paths) when the high potential side and low potential side of the AC power supply B2 are opposite to each other are shown with solid and dashed lines, respectively. In Figures 4 to 6, for simplification, the DC terminal T1, AC terminal T2, control circuit 6, and voltage sensors 71 to 73 are omitted from the illustration. Furthermore, in Figures 5 and 6, an "×" is written next to each switching element SW1 to SW4 that is in the "off" state to indicate whether it is on or off.

[0036] In the first state, as mentioned above, both the DC-side switch 31 and the AC-side switch 32 are off, and the inverter 1 is stopped. In the first state, as shown in Figure 4(a), the current generated by the DC power supply voltage of the DC power supply B1 flows to the DC capacitor 4 through the current-limiting resistor 5. As a result, charge accumulates in the DC capacitor 4, and the capacitor voltage rises. In other words, in the first state, the DC capacitor 4 is charged from the DC power supply B1 through the current-limiting resistor 5. Also, since the inverter 1 is stopped, the current from the DC power supply B1 does not flow to the AC terminal T2 side, i.e., to the inverter 1, rather than to the DC capacitor 4. Furthermore, since the AC-side switch 32 is off, the current from the AC power supply B2 to the inverter 1 is also cut off.

[0037] In the second state, as mentioned above, the DC-side switch 31 is off and the AC-side switch 32 is on, and the inverter 1 operates in capacitor charging mode. In the second state, as shown in Figures 5 and 6, since the AC-side switch 32 is on, the current generated by the AC power supply voltage of the AC power supply B2 flows to the inverter 1 via the filter circuit 2. The current input to the inverter 1 is then rectified and boosted by each switching element SW1 to SW4 (and each diode D1 to D4) and flows to the DC capacitor 4. Specifically, when the upper terminal of the AC power supply B2 in Figure 5 is on the high-potential side, the switching elements SW1 to SW4 are switched on and off in the order of "Figure 5(a) → Figure 5(b) → Figure 5(c) → Figure 5(b) → Figure 5(a) → Figure 5(b) → ... (repeating)", causing the current (solid lines) shown in Figures 5(a) to (c) to flow. Here, in Figures 5(a) and (c), energy is stored in the inductor L, and in Figure 5(b), the energy stored in the inductor L is released. As a result, even if the AC power supply voltage of the AC power supply B2 is lower than the capacitor voltage of the DC capacitor 4, voltage is supplied from the AC power supply B2 to the DC capacitor 4. On the other hand, when the lower terminal of the AC power supply B2 in Figure 6 is on the high potential side, the switching elements SW1 to SW4 are switched on and off in the order of "Figure 6(a) → Figure 6(b) → Figure 6(c) → Figure 6(b) → Figure 6(a) → Figure 6(b) → ... (repeating), causing the current (dashed line) shown in Figures 6(a) to (c) to flow. Here, in Figures 6(a) and (c), energy is stored in the inductor L, and in Figure 6(b), the energy stored in the inductor L is released. As a result, even if the AC power supply voltage of AC power supply B2 is lower than the capacitor voltage of DC capacitor 4, voltage is supplied from AC power supply B2 to DC capacitor 4. In this way, charge is accumulated in DC capacitor 4, and the capacitor voltage rises further. In other words, in the second state, DC capacitor 4 is charged from AC power supply B2 via inverter 1.

[0038] In the third state, as described above, both the DC-side switch 31 and the AC-side switch 32 are on, and the inverter 1 operates in power conversion mode. In the third state, as shown in Figure 4(b), since the DC-side switch 31 is on, the current between the DC power supply B1 and the DC capacitor 4 flows through the DC-side switch 31 and does not flow through the current-limiting resistor 5. Then, current flows from the DC power supply B1 (DC capacitor 4) to the inverter 1, which converts it into AC current and outputs it to the AC power supply B2.

[0039] The operation and effects of the power converter A1 according to this embodiment are as follows.

[0040] In power converter A1, in the first state where the capacitor voltage of the DC capacitor 4 is below a threshold corresponding to the AC power supply voltage of the AC power supply B2, the switch control unit 61 turns off both the DC-side switch 31 and the AC-side switch 32, and the inverter control unit 62 stops the inverter 1. In this configuration, the DC capacitor 4 can be charged from the DC power supply B1 via the current-limiting resistor 5, so the inrush current to the DC capacitor 4 that may occur when the DC power supply B1 is connected can be suppressed. Furthermore, in power converter A1, in the second state where the capacitor voltage of the DC capacitor 4 is above the threshold, the switch control unit 61 turns off the DC-side switch 31 while turning on the AC-side switch 32, and the inverter control unit 62 operates the inverter 1 in a capacitor charging mode in which the DC capacitor 4 is charged from the AC power supply B2. In this configuration, the DC capacitor 4 can be charged by the current output from the AC power supply B2, so the capacitor voltage of the DC capacitor 4 can be further increased. As a result, power converter A1 can suppress insufficient charging of the DC capacitor 4 even when a discharge resistor or load is connected to the DC power supply B1 side (DC capacitor 4) of inverter 1. Therefore, power converter A1 can suppress inrush current from the DC power supply B1 while simultaneously suppressing insufficient charging of the DC capacitor 4 during charging. Furthermore, in power converter A1, when the switch control unit 61 determines that it is in the second state and turns on the AC side switch 32 (when electrically connecting the AC power supply B2), the capacitor voltage of the DC capacitor 4 is above the above threshold. Therefore, the inrush current from the AC power supply B2 to the DC capacitor 4 is also suppressed.

[0041] In the power converter A1, when the difference between the capacitor voltage of the DC capacitor 4 and the DC power supply voltage of the DC power supply B1 is within a predetermined range, the switch control unit 61 turns on both the DC-side switch 31 and the AC-side switch 32, and the inverter control unit 62 operates the inverter 1 in a power conversion mode corresponding to the DC power supply B1 and the AC power supply B2 when the third state is reached. With this configuration, when the difference between the DC power supply voltage of the DC power supply B1 and the capacitor voltage of the DC capacitor 4 becomes small, the DC power supply B1 and the DC capacitor 4 can be electrically connected without the current-limiting resistor 5. Therefore, the power converter A1 can suppress the inrush current from the DC power supply B1 to the DC capacitor 4 that may occur when the DC power supply B1 is electrically connected.

[0042] As described above, power converter A1 suppresses inrush currents that may arise from DC power supply B1 and AC power supply B2 by controlling the DC-side switch 31 and AC-side switch 32 and the inverter 1. The AC-side switch 32 may be required to be installed according to grid connection regulations, etc. Also, the DC-side switch 31 may have been installed conventionally for the safety of users of power converter A1. Therefore, power converter A1 can be implemented by changing the software of the control circuit 6 without changing the hardware configuration in any way. In other words, power converter A1 can be easily implemented without adding any special circuits.

[0043] In the power converter A1, the DC power source B1 is a battery, and the inverter control unit 62 controls the charging and discharging of the battery in power conversion mode. With this configuration, when connecting the battery as the DC power source B1, the inrush current flowing into the battery can be suppressed, thereby preventing damage to the battery. Furthermore, the charging and discharging of the battery can be controlled after the DC power source B1 and AC power source B2 are connected. Therefore, the power converter of this disclosure can be applied to a grid-connected inverter device for batteries (a power conditioner for batteries).

[0044] In power converter A1, the switch control unit 61 determines whether the device is in the first or second state by comparing the peak value of the AC power supply voltage calculated from the detection value of the voltage sensor 72 (detection value of the capacitor voltage) as the first voltage sensor and the detection value of the AC power supply voltage calculated from the detection value of the voltage sensor 73 (detection value of the AC power supply voltage) as the second voltage sensor. In the AC power supply B2, the output (AC power supply voltage) may fluctuate. For example, the grid voltage of the grid power supply may fluctuate by about 10% relative to the basic voltage. Therefore, in power converter A1, by using the peak value of the AC power supply voltage calculated from the detection value of the voltage sensor 73 (the rectified voltage, which is √2 times the effective value of the AC power supply voltage) as a threshold value corresponding to the AC power supply voltage, the threshold value corresponding to the AC power supply voltage can be changed according to the fluctuation of the AC power supply voltage. As a result, even when the AC power supply voltage fluctuates, power converter A1 can appropriately determine whether the charging of the DC capacitor 4 is in the first or second state. Therefore, the power converter A1 can appropriately increase the capacitor voltage of the DC capacitor 4 even when there are fluctuations in the AC power supply voltage. Specifically, when electrically connecting the AC power supply B2 to the power converter A1, the capacitor voltage of the DC capacitor 4 can be increased to the extent that no inrush current occurs from the AC power supply B2 to the DC capacitor 4.

[0045] In the above embodiment, an example was shown in which the rectified voltage (the peak value of the AC power supply voltage, which is √2 times the effective value of the AC power supply voltage) calculated from the detection value of the voltage sensor 73 was used as the threshold value corresponding to the AC power supply voltage of the AC power supply B2 when the switch control unit 61 determines whether it is in the first state or the second state. In a configuration different from this example, the threshold value corresponding to the AC power supply voltage may be a fixed value such as the rated value or maximum value of the AC power supply voltage of the AC power supply B2, or the rectified voltage calculated from either of these. In an example in which the AC power supply B2 is a 100V AC grid power supply, the threshold value may be 141V, and in an example in which the AC power supply B2 is a 200V AC grid power supply, the threshold value may be 282V. However, if there is a fluctuation in the AC power supply voltage of the AC power supply B2, it is preferable to use the rectified voltage as the threshold value, as in the power converter A1.

[0046] The power conversion device relating to this disclosure is not limited to the embodiments described above. The specific configuration of each part of the power conversion device relating to this disclosure can be modified in various ways. [Explanation of Symbols]

[0047] A1: Power converter, B1: DC power supply, B2: AC power supply, T1: DC terminal, T2: AC terminal, 1: Inverter, 31: DC side switch, 32: AC side switch, 4: DC capacitor, 5: Current limiting resistor, 61: Switch control unit, 62: Inverter control unit, 72, 73: Voltage sensors

Claims

1. DC terminals to which a DC power supply is connected, AC terminals to which AC power is connected, An inverter connected between the DC terminal and the AC terminal, A DC-side switch connected between the DC terminal and the inverter, An AC-side switch connected between the AC terminal and the inverter, A DC capacitor connected between the DC-side switch and the inverter, A current-limiting resistor is connected in series with the DC capacitor and in parallel with the DC switch, An inverter control unit that controls the inverter, A switch control unit that controls the on and off states of the DC-side switch and the AC-side switch, Equipped with, In the connection process of electrically connecting the DC power supply and the DC capacitor via the DC-side switch, the switch control unit turns off both the DC-side switch and the AC-side switch when the capacitor voltage of the DC capacitor is less than a threshold corresponding to the AC power supply voltage of the AC power supply (first state), and turns off the DC-side switch while turning on the AC-side switch when the capacitor voltage is equal to or greater than the threshold (second state). The inverter control unit is a power conversion device that, in the first state, stops the inverter, and in the second state, operates the inverter in a capacitor charging mode in which the DC capacitor is charged from the AC power supply.

2. In the connection process, the switch control unit turns on both the DC-side switch and the AC-side switch when the difference between the capacitor voltage and the DC power supply voltage of the DC power supply is within a predetermined range (third state). The power conversion device according to claim 1, wherein the inverter control unit operates the inverter in a power conversion mode corresponding to the DC power supply and the AC power supply when in the third state.

3. The DC power source is a storage battery, The power conversion device according to claim 2, wherein the inverter control unit controls the charging and discharging of the storage battery in the power conversion mode.

4. A first voltage sensor for detecting the capacitor voltage, The system includes a second voltage sensor for detecting the terminal voltage of the aforementioned AC terminals, The threshold is the peak value of the AC power supply voltage. The power conversion device according to any one of claims 1 to 3, wherein the switch control unit determines whether the state is the first state or the second state by comparing the detected value of the first voltage sensor with the peak value calculated from the detected value of the second voltage sensor.

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