Composite Switch Circuit
The composite switch circuit simplifies configuration by using a current transformer and control circuit to transfer current, allowing the use of smaller capacity switches, reducing conduction losses and preventing power outages.
Patent Information
- Application Number
- JP2021162719
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2021-10-01
- Publication Date
- 2025-07-23
- Estimated Expiration
- 2041-10-01
AI Technical Summary
Composite switch circuits often require complex configurations due to the unavailability of low-voltage MOSFETs with large current capacity, making it difficult to achieve simplified designs.
A composite switch circuit configuration using a first switch connected in series with a current transformer, a secondary switch, a current path, and a control circuit that transfers current from the series circuit to the current path, simplifying the design by allowing the use of smaller current capacity switches.
The configuration is simplified, reducing conduction losses and enabling the use of easily obtainable switches with smaller current capacity, while preventing power outages and minimizing conduction losses.
Smart Images
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Abstract
Description
Technical Field
[0001] The present disclosure relates to a composite switch circuit.
Background Art
[0002] FIG. 1 is a circuit diagram of a composite semiconductor switch disclosed in Patent Documents 1 and 2. The composite semiconductor switch 10 shown in FIG. 1 includes a main conduction part 11 which is a current conduction part between an input terminal IN and an output terminal OUT, and an auxiliary conduction part 12 connected in parallel with the main conduction part 11. The main conduction part 11 has a thyristor 1 having no self-extinguishing function, and a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) 2 connected in series with the thyristor 1. The auxiliary conduction part 12 has an IGBT (Insulated Gate Bipolar Transistor) 3 which is a self-extinguishing element.
[0003] When the composite semiconductor switch 10 conducts, the main conduction part 11 including the thyristor 1 with a small voltage drop conducts electricity. When turning off, the MOSFET 2 is cut off and the current is diverted to the IGBT 3 side, and the IGBT 3 performs the cut-off. Thereby, reduction of conduction loss and speeding up of current interruption are achieved. At the timing of turning off the MOSFET 2, since the IGBT 3 is in the on state, only a voltage of about several volts is applied to the MOSFET 2. Therefore, a low breakdown voltage product can be adopted for the MOSFET 2, and even when connected in series with the thyristor 1, an increase in conduction loss can be suppressed.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Patent Document 2
Summary of the Invention
Problems to be Solved by the Invention
[0005] Composite switch circuits such as the above-described composite semiconductor switch 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, so they are not easily obtainable. For this reason, if a plurality of MOSFETs with a small current capacity are connected in parallel to secure the current capacity, the configuration of the composite switch circuit may become complicated.
[0006] The present disclosure provides a composite switch circuit that can simplify the configuration.
Means for Solving the Problems
[0007] In one aspect of the present disclosure, a first switch, a current transformer having a primary winding connected in series to the first switch and a secondary winding having more turns than the primary winding, a second switch connected to the secondary winding, a current path connected in parallel to the series circuit of the first switch and the primary winding, a control circuit that opens the first switch and the current path after current has transferred from the series circuit to the current path due to the opening of the second switch, is provided. A composite switch circuit is provided.
Advantages of the Invention
[0008] According to the technology of the present disclosure, the configuration of the composite switch circuit can be simplified.
Brief Description of the Drawings
[0009]
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Embodiments for Carrying Out the Invention
[0010] Hereinafter, embodiments will be described.
[0011] FIG. 2 is a diagram showing a configuration example 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 energization and non-energization of the electric circuit 21, and when switching the electric circuit 21 to non-energization, it cuts off the current I flowing through the electric circuit 21. 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, a cutoff circuit 31, and a control circuit 50.
[0012] The thyristor Th is an example of a first switch and is connected in series to the electric circuit 21 through which a direct current I flows. The thyristor Th is an example of a semiconductor switching element having no self-extinguishing function and has a gate which is a control electrode, an anode which is a current input terminal, and a cathode which is a current output terminal.
[0013] The current transformer CT has a primary winding 41 connected in series to the thyristor Th and a secondary winding 42 having more turns than the primary winding 41. One end of the primary winding 41 is connected to the cathode side of the thyristor Th. Assuming that the turn 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.
[0014] The switching element Q1 is an example of the second switch and is connected to the secondary winding 42. The switching 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 switching 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 switching 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 anti-parallel.
[0015] 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 limiting voltage. For example, the voltage limiting circuit 43 has a varistor Z1 that limits the increasing secondary voltage V2 to a predetermined limiting voltage.
[0016] The current path 22 is a bypass circuit 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).
[0017] The cutoff circuit 31 is provided in the current path 22 and cuts off the current flowing through the current path 22. In this example, the cutoff circuit 31 has a switching element Q2 inserted in series with the current path 22. The current flowing through the current path 22 is cut off by the opening (off) of the switching element Q2. The switching element Q2 is an example of the third switch and is, for example, a semiconductor switching element such as an IGBT or a MOSFET having a first main electrode, a second main electrode, and a control electrode. In the example shown in FIG. 2, the switching 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 anti-parallel.
[0018] The control circuit 50 controls the timing of applying a voltage to each gate of the thyristor Th, the switch element Q1, and the switch element Q2.
[0019] Next, the operation of the composite switch circuit 101 will be described.
[0020] First, with the thyristor Th, the switch element Q1, and the switch element Q2 in the off state, the control circuit 50 applies a voltage to the gate of the switch element Q2 to turn on only the switch element Q2. Since the switch element Q2 is a semiconductor switching element capable of switching operation relatively fast, it quickly turns on. By first turning on the switch element Q2 capable of high-speed switching operation, the startup operation of the entire composite switch circuit 101 can be accelerated. In this case, since only the switch element Q2 is on, the series circuit 23 of the thyristor Th and the primary winding 41 is not conductive, and only the current path 22 is conductive. Therefore, the current I does not flow through the series circuit 23 but flows through the current path 22.
[0021] Next, after a delay time tdon from when the control circuit 50 applies a voltage to the gate of the switch element Q2, the control circuit 50 applies a voltage to each gate 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 compared to the switch element Q2. Also, when the switch element Q1 is turned on, the secondary voltage V2 generated across both ends of the secondary winding 42 becomes substantially zero, so the primary voltage V1 generated across both ends of the primary winding 41 also becomes substantially zero. Therefore, most of the current I from the circuit 21 flows through the thyristor Th and the primary winding 41 on the side with higher conductivity, that is, through the series circuit 23.
[0022] The delay time tdon only needs to ensure the time required for the turn-on of the switch element Q2, that is, the time until the turn-on operation is completed and a steady-state current flows. Specifically, the delay time tdon is about 1 microsecond to 2 microseconds, but it is not limited to this. In this way, by turning on the switch element Q2 first, the occurrence of turn-on loss of the thyristor Th can be suppressed.
[0023] Note that the control circuit 50 may or may not apply the gate drive voltages for turning on the thyristor Th and the switch element Q1 to both gates simultaneously at the timing after the delay time tdon. For example, the control circuit 50 may apply the gate drive voltage for turning on the switch element Q1 at the timing after the delay time tdon and then apply the gate drive voltage for turning on the thyristor Th. Alternatively, the control circuit 50 may apply the gate drive voltage for turning on the thyristor Th at the timing after the delay time tdon and then apply the gate drive voltage for turning on the switch element Q1.
[0024] Next, the current interruption operation will be described.
[0025] To interrupt the current I flowing through the circuit 21, first, a control signal for opening the switch element Q1 is supplied from the control circuit 50 to the control electrode (in this case, the gate) of the switch element Q1, and the switch element Q1 opens (turns off). Due to the turn-off of the switch element Q1, the secondary voltage V2 increases. The secondary voltage V2 increases to the avalanche breakdown voltage of the switch element Q1 or the limiting voltage of the varistor Z1 connected in parallel with the switch element Q1 and is clamped. As the secondary voltage V2 increases, the primary voltage V1 also increases. When 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].
[0026] Since the primary voltage V1 is higher than the voltage drop of the ON-state switch element Q2, the current I flowing through the circuit 21 transfers from the series circuit 23 to the current path 22. When the transfer causes the current I to stop flowing through the thyristor Th, the thyristor Th extinguishes the arc. After the thyristor Th extinguishes the arc (for example, after a predetermined delay time Tdoff from turning off the switch element Q1), the control circuit 50 turns off the gate of the thyristor Th and turns off the switch element Q2. The thyristor Th is opened by turning off the gate of the thyristor Th. When the switch element Q2 of the cutoff circuit 31 is turned off (opened), the current path 22 is opened, and the current flowing through the current path 22 after the transfer is cut off. As a result, the operation of cutting off the current I by the entire composite switch circuit 101 is completed.
[0027] The forward voltage drop (secondary voltage V2) of the switch element Q1 when the thyristor Th is conducting is about 2 volts. When N = 50, the primary voltage V1 is as low as about 0.04 volts (V1 = V2 / N), so the increase in loss in the primary side winding 41 is suppressed. Also, the current capacity of the switch element Q1 may be about (1 / N) of the current I.
[0028] Therefore, according to the first embodiment shown in FIG. 2, a switch with a relatively small current capacity that is easier to obtain compared to a low-voltage MOSFET with a relatively large current capacity can be adopted as the switch element Q1. Therefore, the switch element Q1 can be simplified, and thus the composite switch circuit 101 can be simplified.
[0029] Also, according to the first embodiment, when the switch element Q1 has an open-circuit fault during the energization of the series circuit 23, the current transformer CT saturates and becomes conductive in a short period of time, so a power outage of the load connected to the circuit 21 can be prevented.
[0030] Note that the composite switch circuit 101 according to the first embodiment may include a reverse current blocking circuit 24 that blocks the reverse current flowing through the current path 22 in the direction opposite 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 the 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 type composite switch circuit 101 can be realized.
[0031] The composite switch circuit 101 may include a capacitor C connected in parallel with the switch element Q2. By providing the capacitor C, the current flowing through the current path 22 due to commutation can flow through both the switch element Q2 and the capacitor C, so that the conduction loss of the switch element Q2 can be reduced.
[0032] Also, by providing a capacitor C connected in parallel with the switch element Q2, an element with a relatively narrow reverse bias safe operating area (RBSOA) can be adopted as the switch element Q2. In the conducting state of the composite switch circuit 101, the switching element Q2 is continuously on, so at the timing 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 with soft switching.
[0033] FIG. 3 is a diagram illustrating the reverse bias safe operating area of an IGBT that can be adopted as the switching element Q2. The relationship between the collector-emitter voltage and the collector current that can operate safely when the IGBT turns off is known as the reverse bias safe operating area (RBSOA). The general safe operating area has a rectangular characteristic indicated by a dotted line. That is, many commercially available IGBTs are designed to withstand even if the voltage-current locus at turn-off passes through points of the rated voltage and the rated current or several times thereof. In the present embodiment, when soft switching is performed by the action of the capacitor C connected in parallel with the switching element Q2, if it is guaranteed that the maximum voltage and the maximum current are not applied simultaneously, the voltage and current ratings of the element can be relaxed. That is, since the current is shunted to the capacitor C, the current flowing through the switching element Q2 decreases. Therefore, as shown in FIG. 3, a low-cost element with a narrow reverse bias safe operating area can be used as the switching element Q2. This characteristic is particularly advantageous when using a high breakdown voltage switching element.
[0034] In FIG. 2, the composite switch circuit 101 may include a resistor R connected in parallel with 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 reduced. After the switching element Q2 is turned off and then turned on again, the charge of the capacitor C is discharged by the resistor R. Thereby, it is possible to ensure the ability of the capacitor C to accept the commutation current generated by the next turn-off operation of the switching element Q1.
[0035] The switch element Q2 may be configured such that, for example, as shown in FIG. 4, a plurality of switch elements having a breakdown voltage lower than the maximum circuit voltage generated across both ends of 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. And the capacitor C connected in parallel with the switch element Q2 is a voltage dividing circuit having a plurality of capacitor elements connected in series. In the example shown in FIG. 4, the capacitor elements Ca, Cb, Cc, Cd having all the same capacitance are respectively connected between the main electrodes of the corresponding switch elements among the plurality of switch elements Q2a, Q2b, Q2c, Q2d (in this example, between the collector and the emitter). Thereby, the voltage applied between the main electrodes of each of the plurality of switch elements Q2a, Q2b, Q2c, Q2d can be equalized.
[0036] Also, the thyristor Th may be replaced with a mechanical contact (also referred to as a relay). The mechanical contact does not have, for example, a current interruption ability exceeding 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, in the same manner as the above-described gate turn-off of the thyristor Th.
[0037] FIG. 5 is a diagram showing a configuration example of a composite switch circuit according to the second embodiment. In the second embodiment, the description of the same configuration and effects as those in the first embodiment is omitted by referring to 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, a cutoff circuit 32, and a control circuit 50. The composite switch circuit 102 according to the second embodiment is different from the composite switch circuit 101 according to the first embodiment in the configuration of the cutoff circuit.
[0038] The cutoff circuit 32 is provided in the current path 22 and cuts off the current flowing through the current path 22. In this example, the cutoff circuit 32 has a capacitor C inserted in series in the current path 22 and a resistor R connected in parallel with the capacitor C.
[0039] Next, the operation of the composite switch circuit 102 will be described.
[0040] First, with the thyristor Th and the switch element Q1 in the off state, the control circuit 50 applies a voltage to the gates of the thyristor Th and the switch element Q1 respectively to turn on the thyristor Th and the switch element Q1. Since the secondary voltage V2 generated across both ends of the secondary winding 42 becomes substantially zero due to the turn-on of the switch element Q1, the primary voltage V1 generated across both ends of the primary winding 41 also becomes substantially zero. Therefore, most of the current I from the circuit 21 flows through the thyristor Th and the primary winding 41 on the side with high conductivity, that is, into the series circuit 23.
[0041] Note that the control circuit 50 may or may not apply the gate drive voltages for turning on the thyristor Th and the switch element Q1 simultaneously to both gates.
[0042] Next, the current interruption operation will be described.
[0043] To interrupt the current I flowing through the circuit 21, first, a control signal for opening the switch element Q1 is supplied from the control circuit 50 to the control electrode (in this case, the gate) of the switch element Q1, and the switch element Q1 opens (turns off). Due to the turn-off of the switch element Q1, 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 with the switch element Q1 and is clamped. As the secondary voltage V2 rises, the primary voltage V1 also rises. When 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].
[0044] Since the primary voltage V1 is higher than the voltage across the capacitor C, the current I flowing through the circuit 21 transfers from the series circuit 23 to the current path 22. When the transfer of current I causes it not to flow through the thyristor Th, the thyristor Th extinguishes the arc. The control circuit 50 turns off the gate of the thyristor Th after the thyristor Th extinguishes the arc (for example, after a predetermined delay time Tdoff from turning off the switching element Q1). The thyristor Th is opened by turning off the gate of the thyristor Th.
[0045] When the current transfers to the current path 22, the capacitor C is charged by the transferred current. Due to the charging of the capacitor C, the voltage of the capacitor C rises. When the capacitor C is fully charged, the current path 22 is opened and the current flowing through the current path 22 after the transfer is interrupted. As a result, the operation of interrupting the current I by the entire composite switch circuit 101 is completed.
[0046] The diode D1 of the reverse current prevention circuit 24 prevents the discharge from the capacitor C to the anode side of the thyristor Th. Therefore, the circuit voltage generated across both ends of the series circuit 23 or the current path 22 disappears, and the off state of the composite switch circuit 102 is maintained until the capacitor C starts to discharge due to the resistor R.
[0047] 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, so that the occurrence of conduction loss in the composite switch circuit 102 can be suppressed.
[0048] Also, similar to the first embodiment, the thyristor Th may be replaced with a mechanical contact (also referred to as a relay). The mechanical contact does not have a current interruption ability 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 the transfer, in the same manner as the above-described gate off of the thyristor Th.
[0049] In addition, since the mechanical contact is operated by an electromagnet, there is a delay time (for example, several tens of milliseconds) from when the off command is received until the contact actually starts to open. The control circuit 50 may start to open (turn off) the switch element Q1 after the elapse of the delay time until the contact starts to open, or when detecting the start of the opening of the contact. Thereby, the product of the voltage applied to the current transformer CT and time can be minimized, and the current transformer CT can be miniaturized.
[0050] As described above, the embodiments have been explained, but the technology of the present disclosure is not limited to the above embodiments. Various modifications and improvements such as combinations or substitutions of some or all of other embodiments are possible.
Explanation of Reference Numerals
[0051] 1 Thyristor 2 MOSFET 3 IGBT 10 Composite semiconductor switch 11 Main conduction part 12 Auxiliary conduction part 21 Circuit 22 Current path 23 Series circuit 24 Backflow prevention circuit 31, 32 Cutoff 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
1. A first switch, a current transformer having a primary winding connected in series to the first switch, and a secondary winding having more turns than the primary winding, a second switch connected to the secondary winding, a current path connected in parallel to the series circuit of the first switch and the primary winding, a control circuit that opens the first switch and the current path after current has transferred from the series circuit to the current path due to the opening of the second switch. A composite switch circuit comprising.
2. Comprising a cutoff circuit provided in the current path, The current flowing through the current path after transfer is cut off by the cutoff circuit. The composite switch circuit according to claim 1.
3. The cutoff circuit has a third switch inserted in series in the current path, The current flowing through the current path after transfer is cut off by the opening of the third switch. The composite switch circuit according to claim 2.
4. Comprising a capacitor connected in parallel to the third switch. The composite switch circuit according to claim 3.
5. The cutoff circuit has a capacitor inserted in series in the current path, The current flowing through the current path after transfer is cut off by charging the capacitor. The composite switch circuit according to claim 2.
6. Comprising a resistor connected in parallel to the capacitor. The composite switch circuit according to claim 4 or 5.
7. Comprising a backflow prevention circuit that prevents current flowing in the opposite direction to the current flowing through the current path after transfer from flowing through the current path. The composite switch circuit according to any one of claims 2 to 6.
8. The first switch is a semiconductor switching element. The composite switch circuit according to any one of claims 1 to 7.
9. The semiconductor switching element is an element without a self-extinguishing function. The composite switch circuit according to claim 8.
10. The semiconductor switching element is a thyristor. The composite switch circuit according to claim 9.
11. The first switch is a mechanical contact. The composite switch circuit according to any one of claims 1 to 7.
12. Comprising a voltage limiting circuit that limits the secondary voltage generated in the secondary winding. The composite switch circuit according to any one of claims 1 to 11.
13. The voltage limiting circuit has a varistor that limits the secondary voltage. The composite switch circuit according to claim 12.
Citation Information
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