Power converter

Abstract

To provide a power conversion device capable of shortening the time required from stop of a three-phase AC voltage to stop of operation of the power conversion device.SOLUTION: A power conversion device 1 comprises: an AC / DC conversion circuit 3 which converts a three-phase AC voltage supplied from a power supply unit 2 into a DC voltage; a voltage detection circuit 6 which detects a voltage value Vu of a U-phase voltage, a voltage value Vv of a V-phase voltage, and a voltage value Vw of a W-phase voltage; and a control circuit 10 for outputting a drive signal which drives the AC / DC conversion circuit 3. In a case where a total value of an absolute value of the voltage value Vu, an absolute value of the voltage value Vv, and an absolute value of the voltage value Vw is less than a predetermined threshold, the control circuit 10 determines that the three-phase AC voltage is stopped, and stops the output of the drive signal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a power conversion device.

Background Art

[0002] Techniques for determining the stop of a three-phase AC power source are known. For example, Patent Document 1 describes a technique of stopping an inverter when a deviation between an instantaneous value of a voltage of an intermediate capacitor provided downstream of a rectifier that converts a three-phase AC voltage into a DC voltage and an average value of the instantaneous values falls below a reference value.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of Invention

Problem to be Solved by the Invention

[0004] In the technique described in Patent Document 1, the stop of a three-phase AC voltage is determined using the voltage of the intermediate capacitor. However, even if the three-phase AC voltage stops, this stop is not immediately reflected in the voltage of the intermediate capacitor, so it takes time from when the three-phase AC voltage stops to when the inverter is stopped. As a result, current is regenerated to the three-phase AC power source, which may cause component failure due to overcurrent.

[0005] The present disclosure describes a power conversion device capable of reducing the time required from when a three-phase AC voltage stops to when the operation of the power conversion device is stopped.

Means for Solving the Problem

[0006] A power conversion device relating to one aspect of this disclosure includes an AC / DC conversion circuit that converts a three-phase AC voltage supplied from a power supply device, which includes a first-phase voltage, a second-phase voltage, and a third-phase voltage, into a DC voltage; a detection circuit that detects a first voltage value of the first-phase voltage, a second voltage value of the second-phase voltage, and a third voltage value of the third-phase voltage; and a control circuit that outputs a drive signal to drive the AC / DC conversion circuit. The control circuit determines that the three-phase AC voltage has stopped when the sum of the absolute values ​​of the first voltage value, the second voltage value, and the third voltage value falls below a predetermined threshold, and stops outputting the drive signal.

[0007] In this power converter, when the sum of the absolute values ​​of the first voltage of the first phase voltage, the second voltage of the second phase voltage, and the third voltage of the third phase voltage falls below a threshold, it is determined that the three-phase AC voltage has stopped, and the output of the drive signal is stopped. In the case of a momentary power outage, or when the waveform of the three-phase AC voltage is an abnormal waveform such as a square wave or half-wave waveform, the above sum will have a certain magnitude. Therefore, by appropriately setting the threshold, it is possible to distinguish between momentary power outages and abnormal waveforms and the stop of the three-phase AC voltage. Furthermore, since the voltage values ​​of each phase voltage are used, the stop of the three-phase AC voltage is immediately determined, and the output of the drive signal is immediately stopped. Therefore, it is possible to shorten the time required from the stop of the three-phase AC voltage until the operation of the power converter is stopped.

[0008] In some embodiments, the control circuit may determine that the three-phase AC voltage has recovered if the total value remains above a threshold for a specified period of time, and may resume outputting the drive signal. The total value may fluctuate near the threshold. In such cases, if the drive signal output is resumed only when the total value exceeds the threshold, the drive signal output may repeatedly stop and restart, potentially causing chattering. In contrast, by resuming outputting the drive signal only when the total value remains above the threshold for a specified period of time, the possibility of chattering can be reduced. [Effects of the Invention]

[0009] According to this disclosure, the time required from the cessation of the three-phase AC voltage until the operation of the power converter is stopped can be reduced. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram of a power conversion device according to one embodiment. [Figure 2] Figure 2 is a flowchart showing an example of a method for determining the stop of three-phase AC voltage performed by the control circuit shown in Figure 1. [Figure 3] Figure 3 shows the waveforms of the normal three-phase AC voltage and total value. [Figure 4] Figure 4 shows the waveforms of the three-phase AC voltage and total value, including momentary power outages. [Figure 5] Figure 5 shows the waveforms of the three-phase AC voltage and its total value in a rectangular wave. [Modes for carrying out the invention]

[0011] A power conversion device according to one embodiment will be described in detail below with reference to the attached drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and redundant explanations are omitted.

[0012] The configuration of a power converter according to one embodiment will be described with reference to Figure 1. Figure 1 is a schematic diagram of the power converter according to one embodiment. The power converter 1 shown in Figure 1 is a device that converts a three-phase AC voltage supplied from a power supply 2 into a DC voltage. The power converter 1 is applied, for example, to a charger.

[0013] Power supply unit 2 is a three-phase AC power supply. Power supply unit 2 supplies a three-phase AC voltage including U-phase voltage (first phase voltage), V-phase voltage (second phase voltage), and W-phase voltage (third phase voltage). The phases of the U-phase voltage, V-phase voltage, and W-phase voltage are shifted by 120° from each other.

[0014] The power converter 1 has input terminals 1a, 1b, 1c, and 1d. The power converter 1 is connected to the power supply 2 via input terminals 1a, 1b, 1c, and 1d. Specifically, input terminal 1a receives the U-phase voltage, input terminal 1b receives the V-phase voltage, and input terminal 1c receives the W-phase voltage. Input terminal 1d is connected to the neutral point of the power supply 2.

[0015] The power converter 1 has output terminals 1e and 1f. Output terminals 1e and 1f output DC voltage. Output terminal 1f is grounded.

[0016] The power converter 1 includes an AC / DC conversion circuit 3, a filter circuit 4, a filter circuit 5, a voltage detection circuit 6 (detection circuit), a current detection circuit 7, a control circuit 10, and smoothing capacitors C1 and C2.

[0017] The AC / DC conversion circuit 3 is a circuit that converts the three-phase AC voltage supplied from the power supply unit 2 into a DC voltage. The AC / DC conversion circuit 3 includes a plurality of switching elements (switching element SW1, switching element SW2, switching element SW3, switching element SW4, switching element SW5, and switching element SW6).

[0018] Each switching element is a circuit element capable of switching the electrical connection state between both ends thereof between a conducting state (on-state) and a cut-off state (off-state). Each switching element is constituted of, for example, a metal oxide semiconductor field effect transistor (MOSFET) with a freewheeling diode connected in parallel, or an insulated gate bipolar transistor (IGBT) with a freewheeling diode connected in parallel. The state of the switching element is switched between the on-state and the off-state by a drive signal being supplied from the control circuit 10 to each switching element. In the present embodiment, an n-channel MOSFET having a freewheeling diode connected in parallel is exemplified as the switching element.

[0019] The switching element SW1 and the switching element SW4 are connected in series between the output terminal 1e and the output terminal 1f. Specifically, the drain of the switching element SW1 is connected to the output terminal 1e. The source of the switching element SW1 and the drain of the switching element SW4 are connected to each other, and are connected to the input terminal 1a via a reactor 51 and a filter circuit 4 which will be described later. The source of the switching element SW4 is connected to the output terminal 1f.

[0020] The switching element SW2 and the switching element SW5 are connected in series between the output terminal 1e and the output terminal 1f. Specifically, the drain of the switching element SW2 is connected to the output terminal 1e. The source of the switching element SW2 and the drain of the switching element SW5 are connected to each other, and are connected to the input terminal 1b via a reactor 52 and the filter circuit 4 which will be described later. The source of the switching element SW5 is connected to the output terminal 1f.

[0021] Switching element SW3 and switching element SW6 are connected in series between output terminal 1e and output terminal 1f. Specifically, the drain of switching element SW3 is connected to output terminal 1e. The source of switching element SW3 and the drain of switching element SW6 are connected to each other, and are connected to input terminal 1c via reactor 53 and filter circuit 4 described later. The source of switching element SW6 is connected to output terminal 1f.

[0022] Smoothing capacitor C1 and smoothing capacitor C2 smooth the DC voltage output from the AC / DC conversion circuit 3. Smoothing capacitor C1 and smoothing capacitor C2 are connected in series between output terminal 1e and output terminal 1f.

[0023] Filter circuit 4 and filter circuit 5 are circuits that suppress harmonic components generated by switching of the AC / DC conversion circuit 3. Filter circuit 4 and filter circuit 5 are provided between input terminal 1a, input terminal 1b, input terminal 1c, and the AC / DC conversion circuit 3. Filter circuit 5 includes reactor 51, reactor 52, and reactor 53.

[0024] One end of reactor 51 is connected to input terminal 1a via filter circuit 4, and the other end of reactor 51 is connected to the connection point between switching element SW1 and switching element SW4. One end of reactor 52 is connected to input terminal 1b via filter circuit 4, and the other end of reactor 52 is connected to the connection point between switching element SW2 and switching element SW5. One end of reactor 53 is connected to input terminal 1c via filter circuit 4, and the other end of reactor 53 is connected to the connection point between switching element SW3 and switching element SW6.

[0025] The voltage detection circuit 6 is a circuit that detects the voltage value Vu (first voltage value) of the U-phase voltage, the voltage value Vv (second voltage value) of the V-phase voltage, and the voltage value Vw (third voltage value) of the W-phase voltage. The voltage value Vu is the instantaneous value of the U-phase voltage. The voltage value Vv is the instantaneous value of the V-phase voltage. The voltage detection circuit 6 includes voltage sensors 61, 62, and 63. Voltage sensor 61 detects the voltage value Vu and outputs the voltage value Vu to the control circuit 10. Voltage sensor 62 detects the voltage value Vv and outputs the voltage value Vv to the control circuit 10. Voltage sensor 63 detects the voltage value Vw and outputs the voltage value Vw to the control circuit 10.

[0026] The current detection circuit 7 is a circuit that detects the current value Iu of the U-phase current, the current value Iv of the V-phase current, and the current value Iw of the W-phase current. The current value Iu is the instantaneous value of the U-phase current. The current value Iv is the instantaneous value of the V-phase current. The current value Iw is the instantaneous value of the W-phase current. The current detection circuit 7 includes current sensors 71, 72, and 73. Current sensor 71 detects the current value Iu and outputs the current value Iu to the control circuit 10. Current sensor 72 detects the current value Iv and outputs the current value Iv to the control circuit 10. Current sensor 73 detects the current value Iw and outputs the current value Iw to the control circuit 10.

[0027] The control circuit 10 is a circuit that outputs a drive signal to drive the AC / DC conversion circuit 3. The control circuit 10 generates a drive signal by PWM (Pulse Width Modulation) control and outputs the drive signal to the AC / DC conversion circuit 3, thereby switching the on and off states of each switching element included in the AC / DC conversion circuit 3. The control circuit 10 is an electronic control unit composed of a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). For example, a program stored in ROM is loaded onto RAM and executed by the CPU, thereby realizing various functions of the control circuit 10.

[0028] Next, the method for determining the stop of the three-phase AC voltage performed by the control circuit 10 will be explained with further reference to Figures 2 to 5. Figure 2 is a flowchart showing an example of the method for determining the stop of the three-phase AC voltage performed by the control circuit shown in Figure 1. Figure 3 shows the waveforms of the normal three-phase AC voltage and its total value. Figure 4 shows the waveforms of the three-phase AC voltage and its total value, including momentary power interruptions. Figure 5 shows the waveforms of the three-phase AC voltage and its total value as a rectangular wave.

[0029] The series of processes shown in Figure 2 are repeated, for example, at predetermined time intervals. The voltage detection circuit 6 continuously detects the voltage values ​​Vu, Vv, and Vw. The control circuit 10 generates a drive signal by PWM control and outputs the drive signal to the AC / DC conversion circuit 3.

[0030] As shown in Figure 2, first, the control circuit 10 obtains the voltage values ​​Vu, Vv, and Vw from the voltage detection circuit 6 (step S1). Then, the control circuit 10 calculates the total value Va based on the voltage values ​​Vu, Vv, and Vw (step S2). Specifically, as shown in equation (1), the control circuit 10 calculates the total value Va as the sum of the absolute values ​​of the voltage values ​​Vu, Vv, and Vw.

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[0031] Next, the control circuit 10 compares the total value Va with the threshold value Vth to determine whether the total value Va is less than or equal to the threshold value Vth (step S3). The threshold value Vth is a value that can distinguish between momentary power interruptions and abnormal waveforms of the three-phase AC voltage and the complete shutdown of the three-phase AC voltage, and is preset.

[0032] As shown in Figure 3, when a normal three-phase AC voltage is supplied from power supply unit 2, the total value Va fluctuates, for example, between 300V and 400V. As shown in Figure 4, if a momentary power interruption occurs in the three-phase AC voltage, the voltage value of one of the phase voltages (voltage value Vu in the example shown in Figure 4) temporarily becomes 0V. In this case, the total value Va fluctuates, for example, between 100V and 400V. As shown in Figure 5, when each phase voltage is a square wave, the total value Va fluctuates, for example, between 180V and 400V.

[0033] Thus, even when a momentary power outage occurs, or when the waveform of the three-phase AC voltage is an abnormal waveform such as a square wave, the total value Va will have a certain magnitude. On the other hand, when the three-phase AC voltage stops, the total value Va becomes 0V. Therefore, the threshold Vth is set to a value between 0V and the smallest of the following: the minimum value of the total value Va when the three-phase AC voltage is normal, the minimum value of the total value Va when a momentary power outage occurs, and the minimum value of the total value Va when the waveform of the three-phase AC voltage is an abnormal waveform such as a square wave or half-wave waveform. In other words, the threshold Vth is set to a value that is smaller than the smallest of the minimum values ​​of the total value Va in all cases where the three-phase AC voltage is not stopped, and greater than 0V.

[0034] In step S3, if it is determined that the total value Va is greater than or equal to the threshold Vth (step S3: NO), the control circuit 10 determines that the three-phase AC voltage has not stopped and terminates the series of processes shown in Figure 2. On the other hand, in step S3, if it is determined that the total value Va is less than the threshold Vth (step S3: YES), the control circuit 10 determines that the three-phase AC voltage has stopped and stops outputting the drive signal (step S4).

[0035] Next, the control circuit 10 obtains the voltage values ​​Vu, Vv, and Vw from the voltage detection circuit 6 (step S5), and calculates the total value Va based on the voltage values ​​Vu, Vv, and Vw (step S6). Steps S5 and S6 are the same as steps S1 and S2, respectively, so a detailed explanation of them is omitted here.

[0036] Next, the control circuit 10 compares the total value Va with the threshold Vth to determine whether the total value Va is greater than or equal to the threshold Vth (step S7). If, in step S7, it is determined that the total value Va is less than or equal to the threshold Vth (step S7: NO), the control circuit 10 repeats the process in steps S5 to S7 until the total value Va exceeds the threshold Vth. On the other hand, if, in step S7, it is determined that the total value Va is greater than the threshold Vth (step S7: YES), the control circuit 10 activates a timer (not shown) to measure the duration for which the total value Va remains above the threshold Vth.

[0037] Then, the control circuit 10 determines whether the state in which the total value Va exceeds the threshold Vth continues for a specified time (step S8). The specified time is a time to prevent chattering and is set in advance. If, in step S8, it is determined that the state in which the total value Va exceeds the threshold Vth has not continued for the specified time (step S8: NO), the control circuit 10 determines that the three-phase AC voltage has not recovered and repeats the process in steps S5 to S8 until the state in which the total value Va exceeds the threshold Vth continues for the specified time.

[0038] On the other hand, in step S8, if it is determined that the total value Va has remained above the threshold Vth for a specified period of time (step S8: YES), the control circuit 10 determines that the three-phase AC voltage has been restored and resumes outputting the drive signal (step S9). With this, the series of processes shown in Figure 2 is completed.

[0039] In the power converter 1 described above, when the sum of the absolute values ​​of voltage Vu, voltage Vv, and voltage Vw, Va, falls below the threshold Vth, it is determined that the three-phase AC voltage has stopped, and the output of the drive signal is stopped. When a momentary power outage occurs (see Figure 4), or when the waveform of the three-phase AC voltage is an abnormal waveform such as a square wave or half-wave waveform (see Figure 5), the sum Va will have a certain magnitude. Therefore, by appropriately setting the threshold Vth, it is possible to distinguish between momentary power outages and abnormal waveforms and the stopping of the three-phase AC voltage. Furthermore, since the voltage values ​​of each phase voltage are used, the stopping of the three-phase AC voltage is immediately determined, and the output of the drive signal is immediately stopped. Therefore, it is possible to shorten the time required from the stopping of the three-phase AC voltage until the operation of the power converter 1 is stopped.

[0040] The total value Va may fluctuate near the threshold Vth. In such cases, if the drive signal output is restarted only when the total value Va exceeds the threshold Vth, the drive signal output will repeatedly stop and restart, potentially causing chattering. In contrast, by restarting the drive signal output only when the state in which the total value Va exceeds the threshold Vth continues for a specified period of time, the possibility of chattering can be reduced.

[0041] Although one embodiment of the present disclosure has been described in detail above, the power conversion device according to the present disclosure is not limited to the above embodiment.

[0042] The control circuit 10 may resume outputting the drive signal when the total value Va exceeds the threshold Vth. In this case, step S8 is omitted.

[0043] In the above embodiment, the control circuit 10 stops outputting the drive signal and then restarts outputting the drive signal, but the configuration for stopping and restarting the output of the drive signal is not limited to this configuration. For example, the control circuit 10 may output a drive signal and also output a detection signal indicating the stop of the three-phase AC voltage. In this case, a logic circuit provided outside the control circuit 10 may stop outputting the drive signal and restart outputting the drive signal based on the detection signal.

[0044] In this case, the hardware stops the output of the drive signal, further reducing the time required from the time the three-phase AC voltage stops until the operation of the power converter 1 stops. Similarly, the hardware restarts the output of the drive signal, further reducing the time required from the time the three-phase AC voltage recovers until the operation of the power converter 1 restarts. [Explanation of Symbols]

[0045] 1...Power converter, 2...Power supply unit, 3...AC / DC conversion circuit, 6...Voltage detection circuit (detection circuit), 10...Control circuit, Va...Total value, Vu...Voltage value (1st voltage value), Vv...Voltage value (2nd voltage value), Vw...Voltage value (3rd voltage value).

Claims

1. An AC / DC conversion circuit that converts a three-phase AC voltage supplied from a power supply device, which includes a first-phase voltage, a second-phase voltage, and a third-phase voltage, into a DC voltage, A detection circuit for detecting a first voltage value which is the instantaneous value of the first phase voltage, a second voltage value which is the instantaneous value of the second phase voltage, and a third voltage value which is the instantaneous value of the third phase voltage, A control circuit that outputs a drive signal to drive the AC / DC conversion circuit, Equipped with, The control circuit is a power converter that stops outputting the drive signal only when it determines that the three-phase AC voltage has stopped because the sum of the absolute values ​​of the first voltage, the second voltage, and the third voltage falls below a predetermined threshold.

2. The power conversion device according to claim 1, wherein the control circuit determines that the three-phase AC voltage has recovered when the total value exceeds the threshold for a specified period of time, and restarts the output of the drive signal.

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