JP7711540B2 - Composite Switch Circuit - Google Patents

Description

This disclosure relates to a composite switch circuit.

Figure 1 is a circuit diagram of the composite semiconductor switch disclosed in Patent Documents 1 and 2. The composite semiconductor switch 10 shown in Figure 1 includes a main conducting part 11, which is a current conducting part, between an input terminal IN and an output terminal OUT, and an auxiliary conducting part 12 connected in parallel to the main conducting part 11. The main conducting part 11 has a thyristor 1 that does not have a self-extinguishing function, and a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) 2 connected in series to the thyristor 1. The auxiliary conducting part 12 has an IGBT (Insulated Gate Bipolar Transistor) 3, which is a self-extinguishing element.

When the composite semiconductor switch 10 is conductive, the main conducting section 11, which includes the thyristor 1 with a small voltage drop, is energized, and when it is turned off, the MOSFET 2 is cut off and the current is diverted to the IGBT 3 side, and the cutoff is performed by the IGBT 3. This reduces conduction loss and speeds up current cutoff. When the MOSFET 2 is cut off, the IGBT 3 is on, so only a voltage of a few volts is applied to the MOSFET 2. Therefore, a low-voltage product can be used for the MOSFET 2, and even when it is connected in series with the thyristor 1, an increase in conduction loss can be suppressed.

JP 2019-115030 A JP 2020-014045 A

Composite switch circuits such as the composite semiconductor switch described above are often used in circuits with a relatively large current capacity. However, low-voltage MOSFETs with a relatively large current capacity are rarely commercially available and are therefore not easy to obtain. For this reason, if multiple MOSFETs with small current capacities are connected in parallel to ensure a certain current capacity, the configuration of the composite switch circuit may become complicated.

This disclosure provides a composite switch circuit that can be simplified in configuration.

In one aspect of the present disclosure,
A first switch;
a current transformer having a primary winding connected in series with the first switch and a secondary winding having a greater number of turns than the primary winding;
A second switch connected to the secondary winding;
a current path connected in parallel to a series circuit of the first switch and the primary winding;
a control circuit that opens the first switch and the current path after current is diverted from the series circuit to the current path by opening the second switch.

The technology disclosed herein can simplify the configuration of a composite switch circuit.

FIG. 1 is a circuit diagram of a switch circuit disclosed in Patent Documents 1 and 2. FIG. 2 is a diagram illustrating a configuration example of a composite switch circuit according to the first embodiment. FIG. 2 is a diagram illustrating a reverse bias safe operating area of an IGBT. FIG. 1 is a diagram showing a configuration in which a plurality of switch elements are connected in series. FIG. 13 is a diagram illustrating a configuration example of a composite switch circuit according to a second embodiment.

The following describes the embodiment.

Fig. 2 is a diagram showing an example of the configuration of a composite switch circuit according to the first embodiment. The composite switch circuit 101 shown in Fig. 2 is a circuit that switches between energized and de-energized states of the electric circuit 21, and when the electric circuit 21 is switched to de-energized state, the current I flowing through the electric circuit 21 is interrupted. The composite switch circuit 101 is, for example, a current breaker used in a switchboard in a factory or the like. The composite switch circuit 101 includes a thyristor Th, a current transformer CT, a switch element Q1, a current path 22, an interruption circuit 31, and a control circuit 50.

Thyristor Th is an example of a first switch, and is connected in series to an electric circuit 21 through which a direct current I flows. Thyristor Th is an example of a semiconductor switching element that does not have a self-extinguishing function, and has a gate that is a control electrode, an anode that is a current input terminal, and a cathode that is a current output terminal.

The current transformer CT has a primary winding 41 connected in series to the thyristor Th, and a secondary winding 42 having a larger number of turns than the primary winding 41. One end of the primary winding 41 is connected to the cathode side of the thyristor Th. If the winding ratio of the current transformer CT is 1:N (N is a number greater than 1), when the number of turns of the primary winding 41 is 1, the number of turns of the secondary winding 42 is N. The number of turns of the primary winding 41 may be greater than 1.

The switch element Q1 is an example of a second switch and is connected to the secondary winding 42. The switch element Q1 is, for example, a semiconductor switching element having a first main electrode, a second main electrode, and a control electrode. Specific examples of the switch element Q1 include an IGBT having a collector, an emitter, and a gate, and a MOSFET having a drain, a source, and a gate. In the example shown in FIG. 2, the switch element Q1 is an IGBT having a collector connected to one end of the secondary winding 42, an emitter connected to the other end of the secondary winding 42, and a gate connected to the control circuit 50, and a diode is connected in inverse parallel.

The composite switch circuit 101 may include a voltage limiting circuit 43 that limits the secondary voltage V2 generated in the secondary winding 42 to a predetermined limit voltage. For example, the voltage limiting circuit 43 has a varistor Z1 that limits the increasing secondary voltage V2 to a predetermined limit voltage.

The current path 22 is a bypass path connected in parallel to the series circuit 23 of the thyristor Th and the primary winding 41. One end of the current path 22 is connected to the anode side of the thyristor Th, and the other end of the current path 22 is connected to the other end of the primary winding 41 (the end opposite to the end to which the cathode of the thyristor Th is connected).

The interrupter circuit 31 is provided in the current path 22 and interrupts the current flowing through the current path 22. In this example, the interrupter circuit 31 has a switch element Q2 inserted in series with the current path 22. The current flowing through the current path 22 is interrupted by opening (turning off) the switch element Q2. The switch element Q2 is an example of a third switch, and is, for example, a semiconductor switching element such as an IGBT or MOSFET having a first main electrode, a second main electrode, and a control electrode. In the example shown in FIG. 2, the switch element Q2 is an IGBT having a collector connected to the anode side of the thyristor Th, an emitter connected to the other end side of the primary winding 41, and a gate connected to the control circuit 50, and a diode is connected in inverse parallel.

The control circuit 50 controls the timing of applying voltage to the gates of the thyristor Th, the switch element Q1, and the switch element Q2.

Next, the operation of the composite switch circuit 101 will be described.

First, with the thyristor Th, the switching element Q1, and the switching element Q2 in an off state, the control circuit 50 applies a voltage to the gate of the switching element Q2 to turn on only the switching element Q2. The switching element Q2 is a semiconductor switching element capable of relatively high-speed switching operation, and therefore quickly turns on. By turning on the switching element Q2 capable of high-speed switching operation first, the startup operation of the entire composite switching circuit 101 is accelerated. In this case, since only the switching element Q2 is on, the series circuit 23 between the thyristor Th and the primary winding 41 is not conductive, and only the current path 22 is conductive. Therefore, the current I flows through the current path 22 without flowing through the series circuit 23.

Next, the control circuit 50 applies a voltage to the gate of the switch element Q2, and then, after a delay time tdon, applies a voltage to the gates of the thyristor Th and the switch element Q1 to turn on the thyristor Th and the switch element Q1. In this case, the thyristor Th has a lower on-resistance and higher conductivity than the switch element Q2. Furthermore, when the switch element Q1 is turned on, the secondary voltage V2 generated across both ends of the secondary winding 42 becomes approximately zero, and the primary voltage V1 generated across both ends of the primary winding 41 also becomes approximately zero. Therefore, most of the current I from the electric circuit 21 flows through the thyristor Th and primary winding 41 with higher conductivity, that is, the series circuit 23.

The delay time tdon is the time required to turn on the switch element Q2, i.e., the time required for the turn-on operation to be completed and for steady-state current to flow. The delay time tdon is specifically, but is not limited to, about 1 microsecond to 2 microseconds. In this way, by turning on the switch element Q2 first, the occurrence of turn-on loss in the thyristor Th can be suppressed.

The control circuit 50 may apply gate drive voltages to turn on the thyristor Th and the switch element Q1 at the same time to both gates at a timing after the delay time tdon, or may not apply the gate drive voltages to both gates at the same time. For example, the control circuit 50 may apply a gate drive voltage to turn on the switch element Q1 at a timing after the delay time tdon, and then apply a gate drive voltage to turn on the thyristor Th. Alternatively, the control circuit 50 may apply a gate drive voltage to turn on the thyristor Th at a timing after the delay time tdon, and then apply a gate drive voltage to turn on the switch element Q1.

Next, we will explain the current interruption operation.

To cut off the current I flowing through the electric circuit 21, first, a control signal for opening the switch element Q1 is supplied from the control circuit 50 to the control electrode (gate in this case) of the switch element Q1, and the switch element Q1 is opened (turned off). When the switch element Q1 is turned off, the secondary voltage V2 rises. The secondary voltage V2 rises to the avalanche breakdown voltage of the switch element Q1 or the limiting voltage of the varistor Z1 connected in parallel to the switch element Q1 and is then clamped. As the secondary voltage V2 rises, the primary voltage V1 also rises. If the turns ratio of the current transformer CT is 1:N, the primary voltage V1 is V2/N. For example, when V2=1000 [V] and N=50, V1=V2/N=20 [V].

Because the primary voltage V1 is higher than the voltage drop of the switch element Q2 in the on state, the current I flowing through the electric circuit 21 is commutated from the series circuit 23 to the current path 22. When the current I stops flowing through the thyristor Th due to the commutation, the thyristor Th is extinguished. After the thyristor Th is extinguished (for example, after a predetermined delay time Tdoff after the switch element Q1 is turned off), the control circuit 50 turns off the gate of the thyristor Th and also turns off the switch element Q2. Turning off the gate of the thyristor Th opens the thyristor Th. Turning off (opening) the switch element Q2 of the cutoff circuit 31 opens the current path 22, and the current flowing through the current path 22 after the commutation is cut off. As a result, the operation of cutting off the current I by the entire composite switch circuit 101 is completed.

When thyristor Th is conductive, the forward voltage drop (secondary voltage V2) of switch element Q1 is approximately 2 volts, and when N=50, the primary voltage V1 is low at approximately 0.04 volts (V1=V2/N), so the increase in loss in the primary winding 41 is suppressed. In addition, the current capacity of switch element Q1 can be approximately (1/N) of the current I.

Therefore, according to the first embodiment shown in FIG. 2, a switch with a relatively small current capacity, which is easier to obtain than a low-voltage MOSFET with a relatively large current capacity, can be used as the switch element Q1. Therefore, the switch element Q1 can be simplified, and the composite switch circuit 101 can be simplified.

In addition, according to the first embodiment, when an open circuit fault occurs in the switch element Q1 while the series circuit 23 is energized, the current transformer CT saturates in a short period of time and becomes conductive, thereby preventing a power outage in the load connected to the electric circuit 21.

The composite switch circuit 101 according to the first embodiment may include a reverse current blocking circuit 24 that blocks a current (reverse current) flowing through the current path 22 in the opposite direction to the current I flowing through the current path 22 after commutation. The reverse current blocking circuit 24 shown in FIG. 2 has a diode D1 inserted in series with the current path 22, and blocks reverse current with the diode D1. The anode of the diode D1 is connected to the anode side of the thyristor Th. By providing the reverse current blocking circuit 24, a reverse current blocking composite switch circuit 101 can be realized.

The composite switch circuit 101 may include a capacitor C connected in parallel to the switch element Q2. By including the capacitor C, the current flowing through the current path 22 due to commutation can be made to flow through both the switch element Q2 and the capacitor C, thereby reducing the conduction loss of the switch element Q2.

In addition, by providing a capacitor C connected in parallel to the switch element Q2, an element with a relatively narrow reverse bias safe operating area (RBSOA) can be used for the switch element Q2. When the composite switch circuit 101 is in a conductive state, the switching element Q2 is continuously on, so when the control circuit 50 turns off the switch element Q2, the capacitor C is sufficiently discharged and the voltage across the capacitor C (switch element Q2) is relatively low. Therefore, the control circuit 50 can turn off the switch element Q2 by soft switching.

Figure 3 is a diagram illustrating the reverse bias safe operating area of an IGBT that can be used as the switch element Q2. The relationship between the collector-emitter voltage and the collector current that allows safe operation when the IGBT is turned off is known as the reverse bias safe operating area (RBSOA). A typical safe operating area is a rectangular characteristic shown by the dotted line. That is, many commercially available IGBTs are designed to withstand even if the voltage-current trajectory at turn-off passes through the rated voltage and rated current or a point several times the rated voltage and current. In this embodiment, when soft switching is performed by the action of the capacitor C connected in parallel to the switch element Q2, if it is guaranteed that the maximum voltage and maximum current are not applied simultaneously, the voltage and current tolerance of the element can be relaxed. In other words, since the current is shunted to the capacitor C, the current flowing through the switch element Q2 is reduced, so that a low-cost element with a narrow reverse bias safe operating area can be used for the switch element Q2, as shown in Figure 3. This characteristic is particularly advantageous when using a high-voltage switch element.

In FIG. 2, the composite switch circuit 101 may include a resistor R connected in parallel to the capacitor C2. The resistor R discharges the charge of the capacitor C2. The resistor R has a relatively high resistance value so that the loss when the rated voltage of the composite switch circuit 101 is applied is small. After the switch element Q2 is turned off and then turned on again, the charge of the capacitor C is discharged by the resistor R. This ensures that the capacitor C has the ability to accept the commutation current generated by the next opening (turning off) operation of the switch element Q1.

The switch element Q2 may be configured as shown in FIG. 4, for example, in which multiple switch elements with a lower breakdown voltage than the maximum circuit voltage generated across the series circuit 23 or the current path 22 are connected in series. In this example, four IGBTs (switch elements Q2a, Q2b, Q2c, Q2d) connected in series are shown. The capacitor C connected in parallel to the switch element Q2 is a voltage divider circuit having multiple capacitor elements connected in series. In the example shown in FIG. 4, the capacitor elements Ca, Cb, Cc, and Cd, all of which have the same capacitance, are connected between the main electrodes (between the collector and emitter in this example) of the corresponding switch elements among the multiple switch elements Q2a, Q2b, Q2c, and Q2d. This allows the voltages applied between the main electrodes of the multiple switch elements Q2a, Q2b, Q2c, and Q2d to be equalized.

The thyristor Th may also be replaced with a mechanical contact (also called a relay). The mechanical contact does not have the ability to interrupt a current that exceeds, for example, the rated value of the composite switch circuit 101. The control circuit 50 turns off (opens) the mechanical contact after the current flowing through the mechanical contact becomes zero after commutation, similar to the above-mentioned gate-off of the thyristor Th.

Fig. 5 is a diagram showing an example of the configuration of a composite switch circuit according to the second embodiment. In the second embodiment, the description of the configuration and effects similar to those of the first embodiment will be omitted by invoking the above description. The composite switch circuit 102 shown in Fig. 5 includes a thyristor Th, a current transformer CT, a switch element Q1, a current path 22, an interrupter circuit 32, and a control circuit 50. The composite switch circuit 102 according to the second embodiment differs from the composite switch circuit 101 according to the first embodiment in the configuration of the interrupter circuit.

The interruption circuit 32 is provided in the current path 22 and interrupts the current flowing through the current path 22. In this example, the interruption circuit 32 has a capacitor C inserted in series in the current path 22 and a resistor R connected in parallel to the capacitor C.

Next, the operation of the composite switch circuit 102 will be described.

First, with the thyristor Th and the switch element Q1 in an off state, the control circuit 50 applies a voltage to the gates of the thyristor Th and the switch element Q1 to turn on the thyristor Th and the switch element Q1. When the switch element Q1 is turned on, the secondary voltage V2 generated across the secondary winding 42 becomes approximately zero, and the primary voltage V1 generated across the primary winding 41 also becomes approximately zero. Therefore, most of the current I from the electric circuit 21 flows through the thyristor Th and the primary winding 41 with higher conductivity, that is, the series circuit 23.

The control circuit 50 may or may not apply the gate drive voltages that turn on the thyristor Th and the switch element Q1 to both gates simultaneously.

Next, we will explain the current interruption operation.

To cut off the current I flowing through the electric circuit 21, first, a control signal for opening the switch element Q1 is supplied from the control circuit 50 to the control electrode (gate in this case) of the switch element Q1, and the switch element Q1 is opened (turned off). When the switch element Q1 is turned off, the secondary voltage V2 rises. The secondary voltage V2 rises to the avalanche breakdown voltage of the switch element Q1 or the limiting voltage of the varistor Z1 connected in parallel to the switch element Q1 and is then clamped. As the secondary voltage V2 rises, the primary voltage V1 also rises. If the turns ratio of the current transformer CT is 1:N, the primary voltage V1 is V2/N. For example, when V2=1000 [V] and N=50, V1=V2/N=20 [V].

Because the primary voltage V1 is higher than the voltage across the capacitor C, the current I flowing in the current path 21 is commutated from the series circuit 23 to the current path 22. When the current I stops flowing through the thyristor Th due to the commutation, the thyristor Th is extinguished. After the thyristor Th is extinguished (for example, a predetermined delay time Tdoff after the switch element Q1 is turned off), the control circuit 50 turns off the gate of the thyristor Th. Turning off the gate of the thyristor Th opens the thyristor Th.

When the current is diverted to current path 22, capacitor C is charged with the diverted current. As capacitor C is charged, the voltage of capacitor C rises, and when capacitor C is fully charged, current path 22 is opened and the current flowing through current path 22 after diverting is cut off. As a result, the operation of cutting off current I by the entire composite switch circuit 101 is completed.

The diode D1 of the reverse current blocking circuit 24 prevents the capacitor C from discharging to the anode side of the thyristor Th. Therefore, the off state of the composite switch circuit 102 is maintained until the circuit voltage generated across the series circuit 23 or the current path 22 disappears and the capacitor C starts discharging through the resistor R.

According to the second embodiment, in addition to the effects of the first embodiment, the current flowing through the current path 22 during the energization operation of the composite switch circuit 102 is suppressed, thereby suppressing the occurrence of conduction loss in the composite switch circuit 102.

Furthermore, as in the first embodiment, the thyristor Th may be replaced with a mechanical contact (also called a relay). The mechanical contact does not have the current interruption capability exceeding, for example, the rated value of the composite switch circuit 102. The control circuit 50 turns off (opens) the mechanical contact after the current flowing through the mechanical contact becomes zero after commutation, similar to the above-mentioned gate-off of the thyristor Th.

In addition, because the mechanical contacts are operated by electromagnets, there is a delay time (e.g., several tens of milliseconds) between receiving an OFF command and the contacts actually starting to open. The control circuit 50 may start opening (OFF) the switch element Q1 after the delay time until the contacts start to open has elapsed, or upon detecting that the contacts have started to open. This makes it possible to minimize the product of the voltage and time applied to the current transformer CT, making it possible to miniaturize the current transformer CT.

Although the embodiments have been described above, the technology of the present disclosure is not limited to the above-described embodiments. Various modifications and improvements are possible, such as combinations or substitutions with part or all of other embodiments.

1 Thyristor 2 MOSFET
3. IGBT
REFERENCE SIGNS LIST 10 composite semiconductor switch 11 main conducting portion 12 auxiliary conducting portion 21 current path 22 current path 23 series circuit 24 reverse current blocking circuit 31, 32 interrupting circuit 41 primary winding 42 secondary winding 43 voltage limiting circuit 50 control circuit 101, 102 composite switch circuit C capacitor R resistor CT current transformer D1 diode Q1, Q2 switch element Th thyristor Z1 varistor

Claims (13)

A first switch;
a current transformer having a primary winding connected in series with the first switch and a secondary winding having a greater number of turns than the primary winding;
A second switch connected to the secondary winding;
a current path connected in parallel to a series circuit of the first switch and the primary winding;
a control circuit that opens the first switch and the current path after current is diverted from the series circuit to the current path by opening the second switch. An interruption circuit is provided in the current path,
2. The composite switch circuit according to claim 1, wherein the current flowing through the current path after commutation is interrupted by the interruption circuit. the interruption circuit includes a third switch inserted in series in the current path,
3. The composite switch circuit according to claim 2, wherein the current flowing through the current path after commutation is interrupted by opening the third switch. The composite switch circuit of claim 3, further comprising a capacitor connected in parallel to the third switch. the interruption circuit includes a capacitor inserted in series in the current path,
3. The composite switch circuit according to claim 2, wherein the current flowing through the current path after commutation is interrupted by charging the capacitor. The composite switch circuit according to claim 4 or 5, further comprising a resistor connected in parallel to the capacitor. The composite switch circuit according to any one of claims 2 to 6, further comprising a reverse current blocking circuit that blocks a current flowing through the current path in a direction opposite to the direction of the current flowing through the current path after commutation. The composite switch circuit according to any one of claims 1 to 7, wherein the first switch is a semiconductor switching element. The composite switch circuit according to claim 8, wherein the semiconductor switching element is an element that does not have a self-extinguishing function. The composite switch circuit according to claim 9, wherein the semiconductor switching element is a thyristor. The composite switch circuit according to any one of claims 1 to 7, wherein the first switch is a mechanical contact. The composite switch circuit according to any one of claims 1 to 11, further comprising a voltage limiting circuit that limits a secondary voltage generated in the secondary winding. The composite switch circuit of claim 12, wherein the voltage limiting circuit includes a varistor that limits the secondary voltage.