JP2022117623A - Power conversion device - Google Patents

Abstract

To provide a power conversion device in which a semiconductor element included in a power converter can be protected against occurrence of a short circuit on an output side without using a DC breaker.SOLUTION: A power converter 10 includes at least one semiconductor switching element Q, and at least one reflux diode D that is connected in reversely parallel with the at least one semiconductor switching element Q so that DC power is generated. A capacitor C1 is connected between a first output terminal T3 and a second output terminal T4. Reactors L1, L2 are connected between the first output terminal T3 and the second output terminal T4 so as to be in series with the capacitor C1. A first switch SW1 is connected in parallel with the capacitor C1. A control device 16 maintains the off state of the first switch SW1 when the power converter 10 is operating, and turns on the first switch SW1 when a short circuit occurs between the first output terminal T3 and the second output terminal T4.SELECTED DRAWING: Figure 1

Description

The present invention relates to power converters.

Japanese Unexamined Patent Application Publication No. 2020-68621 (Patent Document 1) discloses a DC power transmission system that converts power in an AC system into DC power with an AC/DC converter and transmits the DC power. In the above system, a DC circuit breaker and a DC reactor are connected in series between the AC/DC converter and the DC line. The AC/DC converter is constructed using a self-extinguishing element and a capacitor. A DC circuit breaker has a DC line protection function including a measuring section and a protection control section in addition to a breaking section. The protection control unit opens the DC circuit breaker based on an opening command transmitted from a host device when a short-circuit accident occurs in the DC line.

Japanese Patent Application Laid-Open No. 2020-68621

However, when the voltage class of the target voltage system is a high voltage of several kV or more, there may be no DC circuit breaker that can be applied. In such a case, since a DC circuit breaker cannot be installed on the DC line, power converters such as AC/DC converters or DC/DC converters cannot be isolated from the accident point in the event of a ground fault or short circuit accident on the DC line. First, the short-circuit current may damage the semiconductor elements forming the power converter.

SUMMARY OF THE INVENTION The present invention was made to solve such problems, and its object is to protect a semiconductor device included in a power converter when a short circuit occurs on the output side without using a DC circuit breaker. An object of the present invention is to provide a power converter that can

A power conversion device according to the present invention includes at least one semiconductor switching element and at least one freewheeling diode connected in antiparallel to each of the at least one semiconductor switching element, and is configured to generate DC power. a power converter connected between a first output terminal and a second output terminal for outputting DC power generated by the power converter; a capacitor, a reactor connected in series with the capacitor between the first output terminal and the second output terminal, a first switch connected in parallel with the capacitor, and a control device for controlling the power converter; Prepare. The control device keeps the first switch off during operation of the power converter, and turns on the first switch when a short circuit between the first output terminal and the second output terminal occurs.

ADVANTAGE OF THE INVENTION According to this invention, the power converter device which can protect the semiconductor element contained in a power converter at the time of short circuit occurrence on an output side can be provided, without using a DC circuit breaker.

1 is a circuit block diagram showing a configuration of a power converter according to Embodiment 1; FIG. 4 is a diagram showing operation waveforms of the power converter according to Embodiment 1. FIG. 2 is a circuit block diagram showing a first configuration example of a switch; FIG. FIG. 4 is a circuit block diagram showing a second configuration example of a switch; 2 is a circuit block diagram showing the configuration of a power conversion device according to Embodiment 2; FIG. FIG. 10 is a diagram showing operation waveforms of the power conversion device according to Embodiment 2; FIG. 4 is a circuit block diagram showing the configuration of a power conversion device according to a comparative example; It is a circuit diagram which shows the structural example of a power converter. FIG. 4 is a circuit block diagram showing operation of a power conversion device according to a comparative example;

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated in principle.

[Power conversion device according to comparative example and problem thereof]
First, a power converter according to a comparative example and problems thereof will be described with reference to FIGS. 7 to 9. FIG. Next, the power converter according to this embodiment will be described.

FIG. 7 is a circuit block diagram showing the configuration of a power converter according to a comparative example. The power conversion device 200 according to the comparative example is a power conversion device configured to receive supply of power and generate DC power, and includes input terminals T1 and T2, output terminals T3 and T4, and a power converter. 10, reactors L1 and L2, a capacitor C1, and a controller 12.

Input terminals T1 and T2 receive power from a power source (not shown). When the power source is an AC power source, the input terminals T1 and T2 receive AC power, and when the power source is a DC power source, the input terminals T1 and T2 receive DC power. The AC power supply may include an inverter that converts DC power to AC power, and the DC power supply may include a converter that converts AC power to DC power.

The output terminals T3 and T4 are connected to a DC load or a DC transmission line (not shown). The output terminal T3 is a positive DC terminal and corresponds to an embodiment of the "first output terminal". The output terminal T4 is a negative DC terminal and corresponds to an embodiment of the "second output terminal".

Power converter 10 generates DC power based on power (AC power or DC power) applied to input terminals T1 and T2. The DC power generated by power converter 10 is supplied to a load or a DC transmission line via output terminals T3 and T4.

The power converter 10 has at least one semiconductor switching element Q and at least one diode D. FIG. 8 is a circuit diagram showing a configuration example of the power converter 10. As shown in FIG. In the example of FIG. 8, power converter 10 is configured to convert AC voltage V1 applied between input nodes 10a and 10b into DC voltage V2 and output DC voltage V2 between output nodes 10c and 10d. be.

Specifically, power converter 10 is a full bridge inverter and includes semiconductor switching elements Q1-Q4 and diodes D1-D4. The semiconductor switching elements Q1 to Q4 are, for example, IGBTs (Insulated Gate Bipolar Transistors). Any self-extinguishing switching element can be applied to the semiconductor switching elements Q1 to Q4.

The collectors of IGBTs Q1 and Q3 are both connected to output node 10c, and their emitters are connected to input nodes 10a and 10b, respectively. The collectors of IGBTs Q2 and Q4 are connected to input nodes 10a and 10b, respectively, and their emitters are both connected to output node 10d.

Diodes D1-D4 are freewheeling diodes (FWD) and are connected in anti-parallel with IGBTs Q1-Q4, respectively. That is, each diode D has an anode connected to the emitter of the corresponding IGBT and a cathode connected to the collector of the corresponding IGBT. If the semiconductor switching elements Q1-Q4 are MOSFETs (Metal-Oxide-Semiconductor Field-Effect-Transistors), the diodes D1-D4 can be formed by parasitic diodes (body diodes) of the MOSFETs.

The gates of IGBTs Q1-Q4 receive gate signals G1-G4 from controller 12, respectively. When the gate signals G1 to G4 become H (logic high) level, the IGBTs Q1 to Q4 turn on (conduct) respectively, and when the gate signals G1 to G4 become L (logic low) level, the IGBTs Q1 to Q4 turn off (nonconducting) respectively. )do. The IGBTs Q1 to Q4 are PWM (Pulse Width Modulation) controlled by the controller 12 and turned on/off at predetermined timings in synchronization with the AC voltage V1.

Returning to FIG. 7, reactor L1 is connected between output node 10c and output terminal T3. Reactor L2 is connected between output node 10d and output terminal T4. Capacitor C1 is connected between a node between output node 10c and reactor L1 and a node between output node 10d and reactor L2. That is, reactor L1, capacitor C1 and reactor L2 are connected in series between output terminal T3 and output terminal T4.

Reactors L1, L2 and capacitor C3 form an output filter. The output filter is connected between the output nodes 10c, 10d of the power converter 10 and the output terminals T3, T4, and allows the DC power generated by the power converter 10 to pass through the output terminals T3, T4 so that the power converter 10 is prevented from passing to the output terminals T3 and T4.

In the example of FIG. 7, the reactors L1 and L2 are connected to the output terminal T3 that receives the positive voltage and the output terminal T4 that receives the negative voltage, respectively. good too.

Here, it is assumed that a short-circuit failure occurs in the load or the DC transmission line to which the power converter 200 according to the comparative example is connected. In this case, since output terminal T3 and output terminal T4 are electrically short-circuited, a parallel resonant circuit of reactors L1 and L2 and capacitor C1 is formed on the output side of power converter 10 . When the capacitor C1 starts to discharge in this parallel resonance circuit, a short-circuit current flows through the reactor L2, the capacitor C1 and the reactor L1 in order, as indicated by an arrow A1 in FIG. Reactors L1 and L2 store the short-circuit current as magnetic field energy. The voltage Vc across the terminals of the capacitor C1 gradually decreases, and current continues to flow through the reactors L1 and L2 even after the discharge of the capacitor C1 is completed. By accumulating this current in the capacitor C1, a voltage of opposite polarity (negative voltage) is applied across the terminals of the capacitor C1.

When the terminal voltage Vc of the capacitor C1 becomes a negative voltage, a forward voltage is applied to the diode D (freewheeling diode) connected between the output nodes 10c and 10d of the power converter 10. FIG. When this voltage exceeds the forward voltage of diode D, diode D is turned on and forward current If begins to flow. As a result, the short-circuit current is commutated from the capacitor C1 to the diode D, as indicated by the arrow A2 in FIG.

After commutation, the short-circuit current continues to flow sequentially through reactor L2, diode D and reactor L1. The short-circuit current continues to flow through the diode D although it is moderately attenuated by the parasitic resistance component included in the current path. As a result, there is a risk that the semiconductor elements forming the power converter 10 will be damaged.

[Embodiment 1]
FIG. 1 is a circuit block diagram showing the configuration of a power converter according to Embodiment 1. FIG.

Referring to FIG. 1, power conversion device 100 according to Embodiment 1 is different from power conversion device 200 according to the comparative example shown in FIG. different. The description of the parts that overlap with FIG. 7 will be omitted.

The switch SW1 is connected in parallel with the capacitor C1. The on/off of the switch SW1 is controlled by the controller 16. FIG. When switch SW1 is turned on, output nodes 10c and 10d of power converter 10 are short-circuited. That is, the switch SW1 functions as a bypass switch capable of short-circuiting the output nodes 10c and 10d of the power converter 10. FIG.

Voltage sensor 14 detects terminal voltage Vc of capacitor C1 and outputs a signal indicating the detected value to controller 16 . Based on the inter-terminal voltage Vc detected by the voltage sensor 14, the controller 16 controls on/off of the semiconductor switching elements forming the power converter 10, and also controls on/off of the switch SW1.

Next, the operation of the power conversion device 100 when a short-circuit fault occurs in the load or the DC transmission line to which the power conversion device 100 is connected according to the first embodiment will be described with reference to FIG.

FIG. 2 is a diagram showing current IL flowing through reactors L1 and L2, voltage Vc across terminals of capacitor C1, forward current If of freewheeling diode D of power converter 10, and operating waveforms of switch SW1.

As shown in FIG. 2, when output terminals T3 and T4 are electrically short-circuited due to a short-circuit fault occurring in the load or DC transmission line at time t0, a parallel resonant circuit of reactors L1 and L2 and capacitor C1 is formed. , the discharge of the capacitor C1 is started. After time t0, voltage Vc between terminals of capacitor C1 gradually decreases, while current IL flowing through reactors L1 and L2 gradually increases. Magnetic field energy is accumulated in the reactors L1 and L2 by the current IL. Even after the discharge of capacitor C1 ends at time t1, current continues to flow through reactors L1 and L2.

2, when the voltage Vc across the terminals of the capacitor C1 becomes the opposite polarity (negative voltage) by receiving the currents of the reactors L1 and L2, in the comparative example (FIG. 7), from the capacitor C1 A commutation of the short-circuit current occurs to the diode D, and the forward current If of the diode D starts to flow. Due to the forward current If continuing to flow, there is a risk that the semiconductor elements forming power converter 10 will be damaged at time t3 after time t1.

On the other hand, in the first embodiment, when controller 16 determines that terminal voltage Vc detected by voltage sensor 14 has become equal to or lower than a preset threshold voltage, controller 16 turns on switch SW1 (time t2). By turning on the switch SW1, a new path is formed through which a short-circuit current flows through the reactor L2, the switch SW1, and the reactor L1 in order, as indicated by an arrow A3 in FIG. As a result, commutation to diode D is suppressed.

The threshold voltage is set to zero voltage or a voltage near zero voltage. When setting the threshold voltage to a negative voltage, the absolute value of the threshold voltage is preferably smaller than the sum of the forward voltages of the diodes D connected in series between the output nodes 10c and 10d of the power converter 10. FIG. For example, when power converter 10 has the configuration of FIG. 8, the absolute value of the threshold voltage is preferably smaller than the sum of the forward voltages of diodes D1 and D2 (or diodes D3 and D4). By doing so, the switch SW1 can be turned on before the commutation to the diode D starts. A similar effect can be obtained when the threshold voltage is set to zero voltage or positive voltage. However, if the threshold voltage is set to a positive voltage, the capacitor C1 may be short-circuited when the switch SW1 is turned on. Therefore, the threshold voltage is set based on the terminal voltage Vc at which the short-circuit failure of the capacitor C1 does not occur. There is a need.

In order to form the path of the short-circuit current shown in FIG. 1, the switch SW1 is required to have a conduction resistance value (also referred to as an on-resistance value) smaller than that of the freewheeling diode D in the power converter 10. . For example, when power converter 10 is a full bridge inverter shown in FIG. 8, the conduction resistance value of switch SW1 is higher than the conduction resistance value of a full bridge circuit of diodes D1 to D4 connected between output nodes 10c and 10d. is also required to be small.

(Configuration example of switch SW1)
The switch SW1 shown in FIG. 1 can be composed of a mechanical switch M1 such as a relay as shown in FIG. The mechanical switch M1 is turned on when an electrical signal is output from the controller 16, and is turned off when no electrical signal is output. A mechanical switch capable of high-speed operation is applied to the mechanical switch M1.

Alternatively, the switch SW1 can be composed of a normally-off semiconductor switch, as shown in FIG. In the example of FIG. 4, the switch SW1 is the thyristor Th1. The thyristor Th1 has an anode electrically connected to the output terminal T4 and a cathode electrically connected to the output terminal T3. The thyristor Th1 is turned on according to a signal supplied from the controller 16 to the gate terminal while a forward voltage is applied between the anode and the cathode. Normally, when the output terminals T3 and T4 are not short-circuited, a reverse voltage is applied between the anode and the cathode, so the thyristor Th1 is turned off.

In the configuration example of FIG. 3, the controller 16 gives a signal to the gate terminal of the thyristor Th1 when determining that the voltage Vc between the terminals of the capacitor C1 has become equal to or less than zero voltage. When the terminal voltage Vc of the capacitor C1 becomes a negative voltage, a forward voltage is applied across the anode and cathode of the thyristor Th1, so that the gate terminal receives a signal to turn on the thyristor Th1. As a result, as shown in FIG. 4, the commutation to the diode D is suppressed by the short-circuit current flowing through the ON-state thyristor Th1.

In general, semiconductor switches are capable of high-speed operation compared to mechanical switches, but have the disadvantage of being easily destroyed when the voltage or current exceeds the rated value. Therefore, an element having a rated value higher than the short-circuit current is applied to the thyristor Th1.

As described above, the power converter according to Embodiment 1 has the configuration in which the reactors L1 and L2 and the capacitor C1 are connected in series between the output terminals T3 and T4 of the power converter, and the switch SW1 is connected to the capacitor C1. are connected in parallel, and when the output terminals T3 and T4 are short-circuited, the switch SW1 is turned on. More specifically, the switch SW1 is turned on when the voltage Vc across the terminals of the capacitor C1 becomes equal to or lower than zero voltage due to the currents flowing through the reactors L1 and L2. According to this, it is possible to suppress the commutation of the short-circuit current to the free wheel diode D in the power converter 10, so that the semiconductor element included in the power converter 10 can be protected when a short circuit occurs on the output side.

[Embodiment 2]
FIG. 5 is a circuit block diagram showing the configuration of the power converter according to the second embodiment.

Referring to FIG. 5, power converter 100 according to the second embodiment is obtained by adding switch SW2 to power converter 100 according to the first embodiment shown in FIG. The description of the parts overlapping with FIG. 1 will be omitted.

Switch SW2 is connected in parallel to a series circuit of reactor L1, switch SW1 and reactor L2 between output terminals T3 and T4. The on/off of the switch SW2 is controlled by the controller 16. FIG. Like the switch SW1, the switch SW2 can be composed of a mechanical switch such as a relay or a normally-off semiconductor switch. For example, both switches SW1 and SW2 may be composed of mechanical switches or semiconductor switches. Alternatively, the switch SW1 may be composed of a normally-off semiconductor switch, and the switch SW2 may be composed of a mechanical switch.

Next, the operation of the power converter 100 when a short-circuit fault occurs in the load or the DC transmission line to which the power converter 100 is connected according to the second embodiment will be described with reference to FIG.

FIG. 6 is a diagram showing current IL flowing through reactors L1 and L2, voltage Vc between terminals of capacitor C1, forward current If of freewheeling diode D of power converter 10, and operating waveforms of switches SW1 and SW2.

As shown in FIG. 6, when output terminals T3 and T4 are electrically short-circuited at time t0, a parallel resonant circuit of reactors L1 and L2 and capacitor C1 is formed, and capacitor C1 starts to discharge. After time t0, voltage Vc between terminals of capacitor C1 gradually decreases, while current IL flowing through reactors L1 and L2 gradually increases. Magnetic field energy is accumulated in the reactors L1 and L2 by the current IL. Even after the discharge of capacitor C1 ends at time t1, current continues to flow through reactors L1 and L2.

When the controller 16 determines that the terminal voltage Vc detected by the voltage sensor 14 has become equal to or less than zero voltage, the controller 16 turns on the switches SW1 and SW2 (time t2). Specifically, the controller 16 simultaneously turns on the switches SW1 and SW2. Alternatively, the controller 16 turns on the switch SW2 after turning on the switch SW1.

When the switch SW1 is composed of a normally-off semiconductor switch and the switch SW2 is composed of a mechanical switch, when the controller 16 simultaneously outputs signals to the switches SW1 and SW2 at time t2, the switch SW1 ( semiconductor switch) is turned on, and then the switch SW2 (mechanical switch) is turned on.

By turning on the switch SW1, commutation to the freewheeling diode D in the power converter 10 is suppressed. Further, when SW2 is turned on, a closed circuit consisting of reactor L1, switch SW1, reactor L2 and switch SW2 is formed as indicated by arrow A4 in FIG. 5, and a short-circuit current flows through this closed circuit. This short-circuit current is gradually attenuated by the parasitic resistance component included in the closed circuit. In addition, since the short-circuit current does not flow through the output terminals T3 and T4, the output terminals T3 and T4 can be isolated from the load or the fault point of the DC transmission line.

It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above description, and is intended to include all modifications within the meaning and range of equivalents of the scope of the claims.

10 power converter, 12, 16 controller, 14 voltage sensor, 100, 200 power converter, L1, L2 reactor, C1 capacitor, SW1, SW2 switch, M1 mechanical switch, Th1 thyristor (semiconductor switch), Q, Q1 ~ Q4 semiconductor switching element, D, D1 to D4 diodes (freewheeling diodes), T1, T2 input terminals, T3, T4 output terminals.

Claims (11)

a power converter having at least one semiconductor switching element and at least one freewheeling diode connected in anti-parallel to each of the at least one semiconductor switching elements and configured to generate DC power;
a first output terminal and a second output terminal for outputting the DC power generated by the power converter;
a capacitor connected between the first output terminal and the second output terminal;
a reactor connected in series with the capacitor between the first output terminal and the second output terminal;
a first switch connected in parallel with the capacitor;
A control device that controls the power converter,
The control device maintains the first switch in an OFF state during operation of the power converter, and when a short circuit between the first output terminal and the second output terminal occurs, the first switch is turned off. A power conversion device that switches on the Further comprising a voltage sensor that detects the voltage between the terminals of the capacitor,
The power converter according to claim 1, wherein said control device turns on said first switch when the detected value of said voltage sensor becomes equal to or less than a threshold voltage. The threshold voltage is less than or equal to zero voltage, and the absolute value of the threshold voltage is less than the sum of forward voltages of freewheeling diodes connected in series between the first output terminal and the second output terminal. 3. The power conversion device according to claim 2. 4. A conduction resistance value of said first switch is less than a conduction resistance value between said first output terminal and said second output terminal by said at least one freewheeling diode. The power conversion device according to . 5. The power converter according to claim 4, wherein said first switch is a mechanical switch. 5. The power converter according to claim 4, wherein said first switch is configured by a normally-off semiconductor switch. further comprising a second switch connected in parallel to the series circuit of the reactor and the first switch between the first output terminal and the second output terminal;
The control device maintains the first switch and the second switch in an off state during operation of the power converter, while a short circuit between the first output terminal and the second output terminal occurs. 7. The power converter according to any one of claims 1 to 6, wherein said first switch and said second switch are turned on when said second switch is turned on. When a short circuit between the first output terminal and the second output terminal occurs, the control device controls the second output terminal when turning on the first switch or after turning on the first switch. 8. The power converter according to claim 7, wherein the switch of is turned on. The first switch is composed of a normally-off semiconductor switch,
9. The power converter according to claim 7, wherein said second switch is a mechanical switch. 9. The power converter according to claim 7, wherein said first switch and said second switch are mechanical switches. 9. The power converter according to claim 7, wherein said first switch and said second switch are configured by normally-off semiconductor switches.

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