# Patent

## Title
Matrix-stages solid state ultrafast switch

## Abstract

A semiconductor switching device for switching high voltage and high current. The semiconductor switching device includes a control-triggered stage and one or more auto-triggered stages. The control-triggered stage includes a plurality of semiconductor switches, a breakover switch, a control switch, a turn-off circuit, and a capacitor. The control-triggered stage is connected in series to the one or more auto-triggered stages. Each auto-triggered stage includes a plurality of semiconductor switches connected in parallel, a breakover switch, and a capacitor. The control switch provides for selective turn-on of the control-triggered stage. When the control-triggered stage turns on, the capacitor of the control-triggered stage discharges into the gates of the plurality of semiconductor switches of the next highest stage to turn it on. Each auto-triggered stage turns on in a cascade fashion as the capacitor of the adjacent lower stage discharges or as the breakover switches of the auto-triggered stages turn on.

## Background
RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 13/273,767, filed on Oct. 14, 2011, now U.S. Pat. No. 8,575,990, which issued Nov. 5, 2013, the entire contents of which are hereby incorporated by reference.


FIELD OF THE INVENTION
The present invention relates to a solid state switch and, more specifically, to a solid state switch having a plurality of switch levels connected in series, each level having a plurality of semiconductors connected in parallel and to a method of triggering the solid state switch.
BACKGROUND OF THE INVENTION
Switching high current and high voltage is required in some applications in military, medical, and commercial devices and systems. Depending upon on the application, a switching device may be required to switch tens of kilovolts and tens of kiloamperes. Devices for switching such high current and high voltage have been proposed to include a plurality of levels connected in series, each level having a plurality of high-power semiconductor switching devices connected in parallel. Each semiconductor includes a gate and a driver of the gate. To control these devices, the gate driver has special requirements such as high voltage isolation between levels, minimum delay time in gate pulses from one level to another, overvoltage protection, and sharing voltage protection.
Many drive circuits use pulse transformers in the gate circuitry to isolate one level of the switch from another. Because the switch comprises many semiconductors in series and in parallel, these pulse transformers become very large, costly, and impractical. In addition pulse transformers must be shielded to avoid external magnetic field pick up which could create unwanted low level gate pulses and, as a result, cause misfiring, which may destroy devices connected to the switch.
In response, methods have been developed using power stored in a capacitor floating with the device for the trigger energy. These methods use low-power triggers for a low-power solid state device that discharges the capacitor into the gate of the high-power semiconductor switching device. While still requiring a pulse transformer, because of the lower energy requirements in the gate circuitry, the switching device can be smaller. General examples of these switching devices are described in U.S. Pat. Nos. 5,444,610 and 5,646,833.
Other methods for switching the high-power semiconductor switching devices have been proposed. U.S. Pat. Nos. 6,396,672 and 6,710,994 describe a power electronic switch circuit that includes a silicon-controlled rectifier and a gate trigger circuit coupled to the gate of the silicon-controlled rectifier (SCR). A snubber capacitor is coupled to the anode and cathode of the SCR. Energy stored in the snubber capacitor provides the necessary energy to power the gate trigger circuit to trigger the SCR.
U.S. Pat. No. 6,624,684 describes a compact method for triggering thyristors connected in series using energy stored in a pulse forming network coupled to the gate of each thyristor. Each pulse forming network is coupled to a snubber circuit that, together with the pulse forming network, acts as a snubber capacitor to limit the dv/dt imposed on the thyristor, thereby preventing spurious turn-on of the thyristor. The pulse forming network provides current to the gate of the thyristor through a gate switch to turn on the thyristor while the snubber circuit provides a source of fast rising current to the anode of the thyristor to speed up turn-on as it discharges through the anode of the thyristor. Either a low-power electrical signal through a pulse transformer or an optical signal can be used to trigger the gate switch.
U.S. Pat. Nos. 5,933,335 and 5,180,963 provide examples of an optically triggered switch. In U.S. Pat. No. 5,180,963, there is described an optically triggered solid state switch. The switch uses an optical signal for each set of two high power solid state devices. The optical signal triggers a phototransistor, which in turn triggers a low power solid state device. The low power solid state device then discharge a capacitor through a pulse transformer, producing signals in the gates of two high power solid state devices to turn on the devices.
U.S. Pat. No. 7,072,196 describes a method of turning on a high voltage solid state switch that comprises a set of solid state devices, such as thyristors, connected in series. The switch comprises a snubber circuit coupled to the anode and cathode of each solid state device to speed up turn-on.
SUMMARY OF THE INVENTION
According to an exemplary aspect of the present invention there is provided a semiconductor switching device having a control-triggered stage and one or more auto-triggered stages connected in series. The control-triggered stage includes one or more semiconductor switches connected in parallel, a breakover switch comprising a first end and a second end, and a control switch connected across the breakover switch. Each semiconductor switch includes a power input, a power output, and a control input. The first end of the breakover switch is coupled to the power input of each semiconductor switch, and the second end of the breakover switch is coupled to the control input of each semiconductor switch. Each auto-triggered stage includes one or more semiconductor switches connected in parallel and a breakover switch comprising a first end and a second end. Each semiconductor switch of each auto-triggered stage includes a power input, a power output, and a control input. The first end of the breakover switch of the each auto-triggered stage is coupled to the power input of each semiconductor switch of the each auto-triggered stage, and the second end of the breakover switch of the each auto-triggered stage is coupled to the control input of each semiconductor switch of the each auto-triggered stage. The control-triggered stage is connected in series with the one or more auto-triggered stages.
According to another exemplary aspect of the present invention there is provided a high voltage circuit having an energy storage device, a load, a power supply coupled across the energy storage device, and a semiconductor switching device for coupling the energy storage device across the load. The semiconductor switching device includes a control-triggered stage and one or more auto-triggered stages connected in series. The control-triggered stage includes one or more semiconductor switches connected in parallel, a breakover switch comprising a first end and a second end, and a control switch connected across the breakover switch. Each of the semiconductor switches includes a power input, a power output, and a control input. The first end of the breakover switch is coupled to the power input of each semiconductor switch, and the second end of the breakover switch is coupled to the control input of each semiconductor switch. Each auto-triggered stage includes one or more semiconductor switches connected in parallel and a breakover switch comprising a first end and a second end. Each semiconductor switch of each auto-triggered stage includes a power input, a power output, and a control input. The first end of the breakover switch of the each auto-triggered stage is coupled to the power input of each semiconductor switch of the each auto-triggered stage, and the second end of the breakover switch of the each auto-triggered stage is coupled to the control input of each semiconductor switch of the each auto-triggered stage. The control-triggered stage is connected in series with the one or more auto-triggered stages.



BRIEF DESCRIPTION OF THE DRAWINGS
For the purpose of illustration, there are shown in the drawings certain embodiments of the present invention. In the drawings, like numerals indicate like elements throughout. It should be understood, however, that the invention is not limited to the precise arrangements, dimensions, and instruments shown. In the drawings:
FIG. 1 illustrates an exemplary embodiment of a system for providing pulsed power to a load, the system comprising a power source, an energy storage device, and a semiconductor switching device, in accordance with an exemplary embodiment of the present invention;
FIG. 2 illustrates an exemplary embodiment of the semiconductor switching device of FIG. 1, in accordance with an exemplary embodiment of the present invention;
FIG. 3 illustrates exemplary waveforms for voltage and current provided by the energy storage device of FIG. 1 during turn-on of the semiconductor switching device, in accordance with an exemplary embodiment of the present invention; and
FIG. 4 illustrates exemplary waveforms for voltage and current provided by the energy storage device of FIG. 1 during turn-off of the semiconductor switching device, in accordance with an exemplary embodiment of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
As described above, various conventional high voltage, high current solid state switches have been proposed. Some of the conventional high voltage, high current solid state switches comprise one or more solid state devices, such as thyristors, across which a snubber circuit is coupled. The snubber circuit facilitates turn-on of the solid state device but limits using an insulated-gate bipolar transistor (IGBT) or a metal oxide field effects transistor (MOSFET) as the solid state devices because IGBTs and MOSFETs are normally used in snubberless circuits.
Other conventional high voltage, high current solid state switches use pulse transformers to drive the one or more solid state devices. Pulse transformers, however, are not desirable as they increase the inductance of the solid state switches. Further, the primary winding wire of the trigger transformer conducts the same current that the one or more solid state devices conduct. With wide pulse duration and high load current, the primary winding wire becomes very thick, and the trigger transformer becomes very big and insufficient.
The conventional solid state switches which use snubber circuits or pulse transformers are disadvantageous for additional reasons. Typically, a solid state switch operates in a very narrow range of voltage, usually between Vswitch−Vswitch/Nlevels and Vswitch. The value of the snubber parameters and the design of the trigger transformer must be selected to avoid auto triggering of the switch during the charging phase. Unwanted turn-on may happen if any unexpected voltage spikes in initial dv/dt occur.
In all of the above-mentioned switches, pulse transformers, multiple phototransistors, and other components are required for each high power solid state device being triggered. With many semiconductors in series and in parallel, the multitude of triggering devices required become very large, thereby increasing the cost, size, and expense of the solid state switch. The size and expense may become impractical if the number of solid state devices is large. Furthermore, if pulse transformers are use, the pulse transformers must be shielded to avoid external magnetic field pick-up, which could create unwanted low-level gate pulses and, as a result, cause misfiring and destroy the solid state devices. Shielding further increases the size and expense of the solid state switch.
Referring now to FIG. 1, there is illustrated a system 100 for use in a pulsed power application, in accordance with an exemplary embodiment of the present invention. The system 100 comprises a power source 110, an energy storage device 120, a load 130, and a switch 200. The power source 110 is coupled to the energy storage device 120 and to ground 140. The switch 200 is coupled to the energy storage device 120 and to ground 140. The load is coupled to the energy storage device 120 and to ground 140.
During use of the system 100, the switch 200 is initially open, and the power source 110 charges the energy storage device 120. When the energy storage device 120 has been charged to a desired level, the power source 110 may be disabled or disconnected from the device 120.
When power is desired to be delivered to the load 130, the switch 200 is closed, and the charge stored in the energy storage device 120 discharges into the load 130. The charging time of the energy storage device 120 may be two or more orders of magnitude greater than the discharge time thereof. Thus, the current supplied to the load via the switch 200 may be many times that of the current supplied to the energy storage device 120 during charge up by the power source 110. Exemplary embodiments of the energy storage device 120 include one or more capacitors, one or more transmission lines, or a pulse forming network. Exemplary values of the voltage and current provided by the energy storage device 120 during discharge are, respectively, tens of kilovolts and ten of kiloamperes, making the system 100 a high voltage, high current circuit.
In the system 100, each of the power source 110, the switch 200, and the load 130 is connected to ground 140. It is to be understood from FIG. 1 that alternative embodiments of the system 100 are contemplated. For example, in an exemplary alternative embodiment, the positions of the switch 200 and the energy storage device 120 are switched.
Illustrated in FIG. 2 is a circuit diagram for the switch 200 of FIG. 1, in accordance with an exemplary embodiment of the present invention. The switch 200 is used for switching a current IS provided by the energy storage device 120 at a voltage VS. As noted above, the current IS may be tens of kiloamperes, and the voltage VS may be tens of kilovolts.
The switch 200 comprises a plurality of levels or stages, respectively designated as 2101, 2102, . . . 210n, connected in series. In the exemplary embodiment of the switch 200 illustrated in FIG. 2, there are n stages 2101 through 210n. By using a plurality of stages 2101 through 210n, the switch 200 divides the source voltage VS over n stages so that VS/n is less than the maximum permissible voltage across any of the stages 2101 through 210n. Thus, the switch 200 has a higher voltage hold-off capability than it would have had it had only one stage, and each stage is protected from overvoltage.
Each stage comprises a plurality of solid state semiconductor switches or devices, respectively designated as Sx,y, connected in parallel, where x refers to any of stages 2101 through 210n and y refers to the semiconductor devices in each stage. In the exemplary embodiment of the switch 200 illustrated in FIG. 2, the first stage 2101 comprises m semiconductor devices S1,1 through S1,m connected in parallel (herein, “S1” is used as shorthand to refer to the plurality of semiconductor devices S1,1 through S1,m in the stage 2101); the second stage 2102 comprises m semiconductor devices S2,1 through S2,m connected in parallel (herein, “S2” is used as shorthand to refer to the plurality of semiconductor devices S2,1 through S2,m in the stage 2101); and the nth stage 210n comprises m semiconductor devices Sn,1 through Sn,m connected in parallel (herein, “Sn” is used as shorthand to refer to the plurality of semiconductor devices Sn,1 through Sn,m in the stage 210n). By using a plurality of m semiconductor devices in each stage, the switch 200 divides the input current IS by m. Thus, each stage 2101 through 210n and, specifically, each semiconductor device Sx,y is protected from overcurrent.
In the exemplary embodiment illustrated in FIG. 2, the first stage 2101 is a control-triggered stage used to control the turn-on and turn-off of the stages 2102 through 210n and thereby of the switch 200. FIG. 2 illustrates that the control-triggered stage 2101 is the first or bottommost stage and connected to ground 140. It is to be understood that the control-triggered stage 2101 need not be so located and could be positioned in the place of any of the other stages 2102 through 210n in the switch 200.
The control-triggered stage 2101 comprises the semiconductor devices S1,1 through S1,m having respective control inputs CI1,1 through CI1,m power inputs PI1,1 through PI1,m, and power outputs PO1,1 through PO1,m. The power outputs PO1,1 through PO1,m are connected to an output 2111 of the control-triggered stage 2101 which is at ground 140. The control-triggered stage 2101 further comprises a capacitor C1, a turn-off circuit 215, and a suppressor Z1. A first side or end of the suppressor Z1 is connected to the output 2111, as is a first side or end of the capacitor C1 and a first end 215A of the turn-off circuit 215. A second side or end of the capacitor C1 is connected to the control inputs CI2,1 through CI2,m of the semiconductor devices S2,1 through S2,m of the second stage. A second side or end of the suppressor Z1 is connected to the control inputs CI1,1 through CI1,m of the semiconductor devices S1,1 through S1,m, as is a second end 215B of the turn-off circuit 215.
The control-triggered stage 2101 further comprises a breakover switch BOS1, a second side or end of which is coupled to the second side of the suppressor Z1. A first side or end of the breakover switch BOS1 is coupled to the power inputs PI1,1 through PI1,m of the semiconductor devices S1,1 through S1,m via a resistor R1. The power inputs PI1,1 through PI1,m of the semiconductor devices S1,1 through S1,m are connected to an input 2121 of the control-triggered stage 2101. A switch SW1 is disposed in the control-triggered stage 2101 across the breakover switch BOS1.
In an exemplary embodiment, the suppressor Z1 is a Zener diode, the breakover switch BOS1 is a breakover diode, the switch SW1 is a MOSFET, and the turn-off circuit 215 is a MOSFET. The first side of the Zener diode Z1, its anode, is connected to the output 2111 of the stage 2101, and the second side of the Zener diode Z1, its cathode, is connected to the control inputs CI1,1 through CI1,m of the semiconductor devices S1,1 through S1,m. The first side of the breakover switch BOS1, its anode, is connected to the resistor R1, and the second side of the breakover switch BOS1, its cathode, is connected to the control inputs CI1,1 through CI1,m of the semiconductor devices S1,1 through S1,m.
In this exemplary embodiment, the collector of the MOSFET SW1 is connected to the anode of the breakover diode BOS1, and the emitter is connected to the cathode of the breakover diode BOS1. The gate of the MOSFET SW1 serves as a control input to selectively turn on the switch 200. The collector of the MOSFET 215 is connected to the control inputs CI1,1 through CI1,m of the semiconductor devices S1,1 through S1,m, and the emitter is connected to the output 2111 of the control-triggered stage 2101. The gate of the MOSFET 215 serves as a control input to selectively turn off the switch 200. The control inputs into the MOSFETS SW1 and 215 are low-power inputs, which allows for low-power control of the switch 200.
Still referring to FIG. 2, the second through nth stages, 2102 through 210n, are auto-triggered stages triggered by the control-triggered stage 2101. The stages 2102 through 210n are constructed similarly to the stage 2101 but differ in that they do not include the switch SW1 or the turn-off circuit 215.
The second stage 2102 comprises the semiconductor devices S2,1 through S2,m having respective control inputs CI2,1 through CI2,m, power inputs PI2,1 through PI2,m, and power outputs PO2,1 through PO2,m. The second stage 2102 further comprises a capacitor C2, a suppressor Z2, a breakover switch BOS2, and a resistor R2. The power outputs PO2,1 through PO2,m of the semiconductor devices S2,1 through S2,m are connected to an output 2121 of the second stage 2102. The output 2112 of the second stage 2102 is the input 2121 of the first stage 2101. Thus, the second stage 2102 is connected in series to the first stage 2101.
A first side or end of the suppressor Z2 is connected to the output 2112 of the second stage 2102, as is a first side or end of the capacitor C2. A second side or end of the suppressor Z2 is connected to the control inputs CI2,1 through CI2,m of the semiconductor devices S2,1 through S2,m and to a second side or end of the breakover switch BOS2. A first side or end of the breakover switch BOS2 is coupled to the power inputs PI2,1 through PI2,m of the semiconductor devices S2,1 through S2,m via the resistor R2. A second side or end of the capacitor C2 is connected to the control input of the semiconductor devices of the next higher stage. The power inputs PI2,1 through PI2,m of the semiconductor devices S2,1 through S2,m are connected to the input 2122 of the auto-triggered stage 2102, which input 2122 is an output 2113 of the next higher stage.
Each next higher stage through to stage n−1 is configured the same as the stage 2102 (stage 2). The last stage, stage 201n comprises the semiconductor devices Sn,1 through Sn,m having respective control inputs CIn,1 through CIn,m, power inputs PIn,1 through PIn,m, and power outputs POn,1 through POn,m. The stage 201n further comprises a capacitor Cn, a suppressor Zn, a breakover switch BOSn, and a resistor Rn. These components are connected in the same manner as those in the auto-triggered stage 2102, except that the second side or end of the capacitor Cn is not connected to the control input of the semiconductor devices of the next higher stage as there is no next higher stage. Rather, the second side or end of the capacitor Cn is connected to the input 212n of the auto-triggered stage 210n. This input 212n is connected to an input 220 of the switch 200. As with the other auto-triggered stages, the output 211n of the auto-triggered stage 201n is connected to the input of the next lowest stage, in this case an input 212n-1 of the auto-triggered stage 210n-1 (not illustrated).
In an exemplary embodiment, for each of the stages 2102 through 210n, the suppressors Z2 through Zn are Zener diodes, and the breakover switches BOS2 through BOSn are breakover diodes. The first side of each of the Zener diodes Z2 through Zn, its anode, is connected to the respective output 2112 through 211n of the respective stage 2102 through 210n, and the second side of each of the Zener diodes Z2 through Zn, its cathode, is connected to the respective control inputs of the respective semiconductor devices S2 through Sn. The first side of each of the breakover diodes BOS2 through BOSn, its anode, is connected to the respective resistor R2 through Rn, and the second side of each of the breakover diodes BOS2 through BOSn, its cathode, is connected to the respective control inputs of the respective semiconductor devices S2 through Sn.
As further shown in FIG. 2, the breakover switches BOS1 through BOSn are identical, as are the respective components among the stages 2101 through 210n. The breakover switches BOS1 through BOSn have a breakover voltage equal to VS/n+ΔV, where VS is the maximum voltage seen across the switch 200, n is the number of stages, and ΔV is a minimum acceptable difference in blocking voltage between a stage and its breakover switches. The breakover voltage of each of the breakover switches BOS1 through BOSn is desirably ΔV greater than VS/n, so that the switch 200 does not automatically turn on when VS is applied at its input 220. For example, if the switch 200 comprises 5 levels, and VS is 5,000V, the maximum voltage across each stage is 1,000V, and each breakover switches BOS1 through BOSn desirably has a breakover voltage greater than 1,000V. For example, the breakover voltage may be 1,007V so that ΔV=7V.
Turn-on and turn-off of the control-triggered stage 2101 is now described. In its initial state, the switch 200 is open and a voltage VS is present at its input 220 by the energy storage device 120. The voltage drop across each stage is equal to VS/n, and each capacitor C1 through Cn is fully charged. Each breakover diode BOS1 through BOSn desirably has a breakover voltage greater than VS/n but less than VS/(n−1), so that once one stage turns on, all stages turn on. The voltage drop VS/n across each stage is distributed over the suppressor, the breakover switch, and the resistor of each respective stage.
Turn-on of the control-triggered stage 2101 and the auto-triggered stages 2102 through 210n is now described. In the description below, the voltage across each stage 2101 through 210n is, respectively, ΔVS1 through ΔVSn, each of which is equal to VS/n when the switch 200 is off. Current IS is then zero because the switch 200 is off because the stages 2101 through 210n are in a non-conducting (off) state. The voltage ΔVS1 through ΔVSn across each stage 2101 through 210n when the switch 200 is turned on is, respectively VSaturation-1 through VSaturation-n, the voltages across each of the semiconductor devices S1 through Sn while in saturation. Current IS is then non-zero because the switch 200 is on because all of the stages 2101 through 210n are conducting, i.e., in an on state. The switch 200 is not turned on until each stage 2101 through 210n is conducting (turned on).
Turn-on of the control-triggered stage 2101 begins with each of the semiconductor devices S1,1 through S1,m in a non-conducting (off) state such that the stage 2101 is in a non-conducting (off) state. The control-triggered stage 2101 operates as follows during turn-on:
a) In response to a control signal, for example supplied to the switch SW1, the switch SW1 across the breakover switch BOS1 is closed, thereby shorting the first side of the breakover switch BOS1 to its second side.
b) The voltage drop ΔVS1 across the stage 2101 instantaneously decreases slightly and is redistributed over the resistor R1 and the suppressor Z1.
c) The voltage at the control inputs CI1,1 through CI1,m of the semiconductor devices S1,1 through S1,m instantaneously increases, i.e., a positive voltage pulse is provided to control inputs CI1,1 through CI1,m of the semiconductor devices S1,1 through S1,m.
d) The positive voltage pulse at the control inputs CI1,1 through CI1,m of the semiconductor devices S1,1 through S1,m turns on the semiconductor devices S1,1 through S1,m and places them into saturation. The control-triggered stage 2101 is thereby turned on.
Because the semiconductor devices S1,1 through S1,m turn on and go into saturation, the voltage at the power inputs PI1,1 through PI1,m of the semiconductor devices S1,1 through S1,m decreases, thereby pulling down the voltage at the input 2121 of the control-triggered stage 2101 and at the output 2112 of the auto-triggered stage 2102. The voltage ΔVS1 across the stage 2101 is VSaturation-1 after turn-on. Because the remaining stages 2102 through 210n are still in the off state and the total voltage VS across the switch 200 remains the same, the voltages ΔVS2 through ΔVSn across respective stages 2102 through 210n increase after the switch SW1 closes and the semiconductor devices S1,1 through S1,m turn on.
After the stage 2101 is turned on, the voltage ΔVS2 through ΔVSn across each respective stage 2102 through 210n is (VS−VSaturation-1)/(n−1). In other words, the voltage ΔVS2 through ΔVSn across each respective stage 2102 through 210n increases to (VS−VSaturation-1)/(n−1), where (VS−VSaturation-1)/(n−1)>VS/n because VSaturation-1<VS/n. This increase in voltage ΔVS2 through ΔVSn across each respective stage 2102 through 210n causes the stages 2102 through 210n to turn on by one of two ways: via turn-on of the breakover switches BOS2 through BOSn or via the capacitors C2 through Cn discharging into the control inputs of their respective semiconductor devices.
Following turn-on of the control-triggered stage 2101, if the voltage ΔVS2 through ΔVSn across each of the respective stages 2102 through 210n causes the voltage ΔVBOS2 through ΔVBOSn across each respective breakover switch BOS2 through BOSn to exceed the breakover voltage (VS/n+ΔV) of each of the breakover switches BOS2 through BOSn, turn-on of the auto-triggered stages 2102 through 210n proceeds as follows (“the first auto turn-on procedure”):
a) Each of the breakover switches BOS2 through BOSn begins conducting at the same time.
b) ΔVBOS2 through ΔVBOSn decreases because breakover switches BOS2 through BOSn begin conducting.
c) The voltage drops ΔVS2 through ΔVSn across the respective stages 2102 through 210n instantaneously redistribute over the respective resistors R2 through Rn and the suppressors Z2 through Zn.
d) The voltages at the control inputs of the semiconductor devices S2 through Sn instantaneously increase, i.e., positive voltage pulses are provided to control inputs of the semiconductor devices S2 through Sn.
e) The positive voltage pulses at the control inputs CI2,1 through CI2,m of the semiconductor devices S2 through Sn turn on the semiconductor devices S2 through Sn and place them into saturation.
f) Because the semiconductor devices S2 through Sn turn on and go into saturation, the voltages at the power inputs of the semiconductor devices S2 through Sn decrease, thereby pulling down the respective voltages at the respective inputs 2122 through 212n of the respective stages 2102 through 210n. The voltages ΔVS2 through ΔVSn across the respective stages 2101 through 210n are, respectively, VSaturation-2 through VSaturation-n after turn-on.
g) The voltage ΔVS across the switch 200 decreases to VSaturation-1+VSaturation-2+ . . . +VSaturation-n and IS increases from zero.
Following turn-on of the control-triggered stage 2101, if the voltage ΔVS2 through ΔVSn across each of the respective stages 2102 through 210n does not cause the voltage ΔVBOS2 through ΔVBOSn across each respective breakover switch BOS2 through BOSn to exceed the breakover voltage (VS/n+ΔV) of each of the breakover switches BOS2 through BOSn, turn-on of the auto-triggered stage 2102 proceeds as follows (“the second auto turn-on procedure”):
a) After the control-input stage 2101 turns on, the voltage ΔVS1 decreases to VSaturation-1 and the voltages ΔVS2 through ΔVSn across the remaining stages increase to (VS−VSaturation-1)/(n−1).
b) The voltages across the resistor R2, the breakover switch BOS2, and the suppressor Z2 increase.
c) The capacitor C2 discharges into the control inputs CI2,1 through CI2,m of the semiconductor devices S2,1 through S2,m.
d) The semiconductor devices S2,1 through S2,m turn on and go into saturation. The auto-triggered stage 2102 is thereby turned on.
Because the semiconductor devices S2,1 through S2,m turn on and go into saturation, the voltage at the power inputs PI2,1 through PI2,m of the semiconductor devices S2,1 through S2,m, decrease, thereby pulling down the voltage at the input 2122 of the auto-triggered stage 2102 and at the output 2113 of the auto-triggered stage 2103. The voltage ΔVS2 across the stage 2102 is VSaturation-2 after turn-on. Because the remaining stages 2103 through 210n are still in the off state and the total voltage VS across the switch 200 remains the same, the voltages ΔVS3 through ΔVSn across respective stages 2103 through 210n increase after the auto-triggered stage 2102 turns on.
After the auto-triggered stage 2102 turns on according to the second auto turn-on procedure, the capacitor C3 begins to discharge into the control inputs CI3,1 through CI3,m of the semiconductor devices S3,1 through S3,m. The auto-triggered stages 2103 through 210n start to cascade on according to the second auto turn-on procedure. However, turn-on of any of the auto-triggered stages 2103 through 210n progresses according to the first turn-on procedure if the voltages across the remaining breakover switches are exceeded. Thus, cascading turn-on may shift to simultaneous turn-on once the breakover voltages of the remaining breakover switches are exceeded.
The suppressors Z1 through Zn provide protection for the control-input-to-power-output junctions of the semiconductor devices S1 through Sn against overcurrent and overvoltage during switching of the switch 200 on and off. The breakover switches BOS1 through BOSn also provide protection for each of the levels 2101 through 210n from overvoltage when the switch 200 is off and while it is being turned on. Protection from overvoltage during turn-on is desirable as the voltages across levels that are not on increase as other levels are turned on. Thus, the switch 200 is able to handle voltages VS in the level of 10 s of kilovolts.
As noted above, the semiconductor devices S1 through Sn are desirably distributed m per stage, although differing numbers of semiconductor devices per stage are contemplated. Thus, the current IS is divided across in semiconductors in each of stages 2101 through 210n. Accordingly, the switch 200 is able to handle currents IS in the level of 10 s of kiloamps.
Turn-off of the switch 200 proceeds as follows:
a) In response to a control signal, for example supplied to the turn-off circuit 215, the turn-off circuit 215 provides a negative-voltage signal to the control inputs CI1,1 through CI1,m of the semiconductor devices S1,1 through S1,m, for example by pulling the control inputs to ground 140.
b) The negative voltage pulse at the control inputs CI1,1 through CI1,m of the semiconductor devices S1,1 through S1,m turns of the semiconductor devices S1,1 through S1,m.
c) Because the semiconductor devices S1,1 through S1,m turn off, the voltage at the power inputs PI1,1 through PI1,m of the semiconductor devices S1,1 through S1,m increases, thereby causing the voltage at the input 2121 of the control-triggered stage 2101 and at the output 2112 of the auto-triggered stage 2102 to rise. The voltage ΔVS1 across the stage 2101 increases, and the voltage ΔVS2 across the stage 2102 decreases.
d) Negative current from the control inputs CI2,1 through CI2,m of the semiconductor devices S2,1 through S2,m charges the capacitor C1 providing a negative-voltage signal to the control inputs CI2,1 through CI2,m of the semiconductor devices S2,1 through S2,m.
e) The semiconductor devices S2,1 through S2,m turn off.
f) Steps (c) through (e) repeat for each next higher stage, so that the stages 2103 through 210n cascade off until all of the stages of the switch 200 are turned off.
Turn-on and turn-off of the switch 200 does not require the use of a pulse transformer for each stage 2101 through 210n. As noted above, pulse transformers are bulky and require isolation from one another, increasing the size and complexity of the switch. Further, pulse transformers have non-negligible inductance, which is not desirable for high voltage, high current switches. Finally, pulse transformers provide pulses of short time periods, which may not be long enough to turn on the semiconductor devices S1 through Sn.
By using breakover switches BOS1 through BOSn and capacitors connecting the output of one level to the control inputs of the semiconductor devices of another lover, the switch 200 provides for very fast turn-on and turn-off and avoids the use of pulse transformers. Inductance in the switch 200 is reduced and the control inputs of the semiconductor devices S1 through Sn may be kept at a negative voltage for as long as is needed to turn them on. For a six level device, turn-on time may be 200 nanoseconds.
Various types of semiconductor devices are contemplated for the semiconductor devices S1 through Sn. For example, in an exemplary embodiment, the semiconductor devices S1 through Sn are IGBTs. In another embodiment, they are MOSFETs. In yet another embodiment, they are SCRs. In still another embodiment, they are gate turn-off thyristors (GTOs). In a further embodiment, they are MOS controlled thyristors or light-controlled thyristors. It is to be understood that the anodes or collectors of such devices are the power inputs, as that term is used herein, the cathodes or emitters of such devices are the power outputs, as that term is used herein, and the gates of such devices are the control inputs, as that term is used herein.
The semiconductor devices S1 through Sn desirably have low output impedances when on. For example, in an exemplary embodiment, the semiconductor devices S1 through Sn desirably have output impedances in the milliohm region, and, when off, they desirably have output impedances greater than 5,000 ohms. The input impedances of the semiconductor devices S1 through Sn depend on the type of semiconductor device employed. If the semiconductor devices S1 through Sn are MOSFETs, then the input impedances are in the megohm region. If they are thyristors, then the input impedances are in the milliohm region.
In the embodiments of the switch 200 described herein, the switch 200 may include the suppressors Z1 through Zn to protect the semiconductor devices S1 through Sn against overcurrent and overvoltage during turn-on and turn-off. In an exemplary embodiment, the semiconductor devices S1 through Sn include gate-to-cathode junctions, and the suppressors Z1 through Zn provide protection for these gate-to-cathode junctions against overcurrent and overvoltage during switching of the switch 200 on and off. It is to be understood that other embodiments of the switch 200 are contemplated in which the suppressors Z1 through Zn are not included.
It is further to be understood that the breakover switches BOS1 through BOSn also provide protection for each of the levels 2101 through 210n from overvoltage when the switch 200 is off and while it is being turned on. Protection from overvoltage during turn-on is desirable as the voltages across levels that are not on increase as other levels are turned on. Thus, the switch 200 is able to handle voltages VS in the level of 10 s of kilovolts.
In an exemplary embodiment, the energy storage device 120 is a capacitor. FIG. 3 illustrates the waves for the voltage VS across an exemplary embodiment of the energy storage device 120 and the current IS supplied by the exemplary energy storage device 120 as an exemplary embodiment of the switch 200 is turned on, in accordance with an exemplary embodiment of the present invention. For the example illustrated in FIG. 3, the energy storage device 120 is a 0.15 μF capacitor.
Referring to FIG. 3, prior to the exemplary switch 200 closing, VS is 4.92 kV and IS is 0 A. At time t0, corresponding to 0 seconds, a command signal is sent to the switch SW1 to close, beginning the turn-on process of the exemplary switch 200. At time t1, corresponding to 40 ns, the exemplary switch 200 is fully turned on, and the exemplary energy storage device 120 begins discharging. IS increases to a maximum of 2.04 kA at time t2, corresponding to 48 ns. VS and IS then oscillate until settling at zero.
FIG. 4 illustrates the waves for the voltage VS across another exemplary embodiment of the energy storage device 120 and the current IS supplied by the exemplary energy storage device 120 as another exemplary embodiment of the switch 200 is turned on and then turned off, in accordance with an exemplary embodiment of the present invention. In FIG. 4, prior to the exemplary switch 200 closing, VS is about 1.4 kV and IS is 0 A. At time t1, the exemplary switch 200 is fully turned on, and the exemplary energy storage device 120 begins discharging. IS increases to a maximum of 100 A at time t2, at which time the exemplary switch 200 is provided with a turn-off signal via the turn-off circuit 215. The exemplary switch 200 turns off, as described above. As the exemplary switch 200 turns off, IS decreases, and VS spikes to 5.4 kV at time t3 before returning to 1.4 kV when the exemplary switch 200 is fully closed.
These and other advantages of the present invention will be apparent to those skilled in the art from the foregoing specification. Accordingly, it is to be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It is to be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention.

## Claims

1. A semiconductor switching device comprising:
a control-triggered stage comprising:
a plurality of semiconductor devices connected in parallel, each semiconductor device comprising a power input, a power output, and a control input; and
a control switch coupled to the control input of each semiconductor device, the control switch configured for turning on each semiconductor device; and

one or more auto-triggered stages, each respective auto-triggered stage comprising:
a plurality of semiconductor devices connected in parallel, each semiconductor device of the respective auto-triggered stage comprising a power input, a power output, and a control input; and
a breakover switch comprising a first end and a second end, the first end of the breakover switch of the respective auto-triggered stage coupled to the power input of each semiconductor device of the respective auto-triggered stage, the second end of the breakover switch of the respective auto-triggered stage coupled to the control input of each semiconductor device of the respective auto-triggered stage,

wherein the control-triggered stage is connected in series with one of the one or more auto-triggered stages and the one or more auto-triggered stages are connected in series, and
wherein the one or more auto-triggered stages are configured to turn on when the control-triggered stage turns on.

2. The semiconductor switching device of claim 1, wherein the control-triggered stage further comprises:
a breakover switch comprising a first end and a second end, the first end of the breakover switch coupled to the power input of each semiconductor device of the control-triggered stage, the second end of the breakover switch coupled to the control input of each semiconductor device of the control-triggered stage; and
a suppressor comprising a first end and a second end, the first end of the suppressor coupled to the power output of each semiconductor device of the control-triggered stage, the second end of the suppressor coupled to the control input of each semiconductor device of the control-triggered stage.

3. The semiconductor switching device of claim 2, wherein:
the control-triggered stage further comprises a resistor; and
the first end of the breakover switch of the control-triggered stage is coupled to the power input of each semiconductor device of the control-triggered stage via the resistor of the control-triggered stage.

4. The semiconductor switching device of claim 2, wherein the control-triggered stage further comprises a turn-off circuit connected across the suppressor.

5. The semiconductor switching device of claim 2, wherein each breakover switch is a breakover diode.

6. The semiconductor switching device of claim 1, wherein each respective auto-triggered stage further comprises:
a suppressor comprising a first end and a second end, the first end of the suppressor coupled to the power output of each semiconductor device of the respective auto-triggered stage, the second end of the suppressor coupled to the control input of each semiconductor device of the respective auto-triggered stage.

7. The semiconductor switching device of claim 1, wherein:
each respective auto-triggered stage comprises a respective resistor; and
the first end of the breakover switch of each respective auto-triggered stage is coupled to the power input of each semiconductor device of the respective auto-triggered stage via the respective resistor of the respective auto-triggered stage.

8. The semiconductor switching device of claim 1, wherein each breakover switch is a breakover diode.

9. The semiconductor switching device of claim 1, wherein the control-triggered stage further comprises a capacitor having a first end and a second end, the first end of the capacitor coupled to the power output of each semiconductor device of the control-triggered stage and the second end of the capacitor coupled to the control input of each semiconductor device of the one of the one or more auto-triggered stages, the capacitor configured to discharge into the control input of the each semiconductor device of the one of the one or more auto-triggered stages to turn on the each semiconductor device of the one of the one or more auto-triggered stages in response to the control switch closing.

10. The semiconductor switching device of claim 9,
wherein the one or more auto-triggered stages comprise a plurality of the auto-triggered stages;
wherein for each respective auto-triggered stage except a highest one of the plurality of auto-triggered stages:
the respective auto-triggered stage comprises a respective capacitor having a first end and a second end;
the first end of the respective capacitor of the respective auto-triggered stage is coupled to the power output of each semiconductor device of the respective auto-triggered stage;
the second end of the respective capacitor of the respective auto-triggered stage is coupled to the control input of each semiconductor device of a next higher one of the plurality of auto-triggered stages; and

wherein the second end of the respective capacitor of the highest one of the plurality of auto-triggered stages is coupled to the power input of each semiconductor device of the highest one of the plurality of auto-triggered stages.

11. The semiconductor switching device of claim 1, wherein each semiconductor device has a low output impedance.

12. A semiconductor switching device comprising:
a control-triggered stage comprising:
a plurality of semiconductor devices connected in parallel, each semiconductor device comprising a power input, a power output, and a control input;
a breakover switch comprising a first end and a second end, the first end of the breakover switch coupled to the power input of each semiconductor device, the second end of the breakover switch coupled to the control input of each semiconductor device; and
a control switch connected across the breakover switch, the control switch configured for turning on each semiconductor device; and

a plurality of auto-triggered stages, each comprising:
a plurality of semiconductor devices connected in parallel, each semiconductor device of each auto-triggered stage comprising a power input, a power output, and a control input; and
a breakover switch comprising a first end and a second end, the first end of the breakover switch of the each auto-triggered stage coupled to the power input of each semiconductor device of the each auto-triggered stage, the second end of the breakover switch of the each auto-triggered stage coupled to the control input of each semiconductor device of the each auto-triggered stage,

wherein the control-triggered stage is connected in series with one of the auto-triggered stages and the auto-triggered stages are connected in series, and
wherein the auto-triggered stages are configured to turn on when the control-triggered stage turns on.

13. The semiconductor switching device of claim 12, wherein the control-triggered stage further comprises:
a suppressor comprising a first end and a second end, the first end of the suppressor coupled to the power output of each semiconductor device of the control-triggered stage, the second end of the suppressor coupled to the control input of each semiconductor device of the control-triggered stage.

14. The semiconductor switching device of claim 13, wherein:
the control-triggered stage further comprises a resistor; and
the first end of the breakover switch of the control-triggered stage is coupled to the power input of each semiconductor device of the control-triggered stage via the resistor of the control-triggered stage.

15. The semiconductor switching device of claim 13, wherein the control-triggered stage further comprises a turn-off circuit connected across the suppressor.

16. The semiconductor switching device of claim 12, wherein each breakover switch is a breakover diode.

17. The semiconductor switching device of claim 12, wherein the each auto-triggered stage further comprises:
a suppressor comprising a first end and a second end, the first end of the suppressor coupled to the power output of each semiconductor device of the each auto-triggered stage, the second end of the suppressor coupled to the control input of each semiconductor device of the each auto-triggered stage.

18. The semiconductor switching device of claim 17, wherein:
the each auto-triggered stage comprises a respective resistor; and
the first end of the breakover switch of the each auto-triggered stage is coupled to the power input of each semiconductor device of the each auto-triggered stage via the respective resistor of the each auto-triggered stage.

19. The semiconductor switching device of claim 12, wherein each breakover switch is a breakover diode.

20. The semiconductor switching device of claim 12, wherein the control-triggered stage further comprises a capacitor having a first end and a second end, the first end of the capacitor coupled to the power output of each semiconductor device of the control-triggered stage and the second end of the capacitor coupled to the control input of each semiconductor device of the one of the auto-triggered stages, the capacitor configured to discharge into the control input of the each semiconductor device of the one of the auto-triggered stages to turn on the each semiconductor device of the one of the auto-triggered stages in response to the control switch closing.

21. The semiconductor switching device of claim 20, wherein:
the each auto-triggered stage comprises a respective capacitor having a first end and a second end;
the first end of the respective capacitor of the each auto-triggered stage is coupled to the power output of each semiconductor device of the each auto-triggered stage;
the second end of the respective capacitor of the each auto-triggered stage except a highest one of the auto-triggered stages is coupled to the control input of each semiconductor device of a next higher one of the auto-triggered stages; and
the second end of the respective capacitor of the highest auto-triggered stage is coupled to the power input of each semiconductor device of the highest auto-triggered stage.

22. A semiconductor switching device comprising:
a device input;
a device output;
a control-triggered stage comprising:
an input;
an output;
a resistor;
a plurality of semiconductor devices connected in parallel, each semiconductor device comprising a power input connected to the input of the control-triggered stage, a power output connected to the output of the control triggered stage, and a control input;
a breakover switch comprising a first end and a second end, the first end of the breakover switch coupled to the power input of each semiconductor device of the control-triggered stage via the resistor, the second end of the breakover switch coupled to the control input of each semiconductor device of the control-triggered stage; and
a control switch connected across the breakover switch, the control switch configured for turning on each semiconductor device; and
a turn-off circuit coupled to the control input of each semiconductor device, the turn-off circuit configured for turning off each semiconductor device; and

a plurality of auto-triggered stages, each comprising:
an input;
an output;
a resistor;
a plurality of semiconductor devices connected in parallel, each semiconductor device of each auto-triggered stage comprising a power input connected to the input of the each auto-triggered stage, a power output connected to the output of the auto-triggered stage, and a control input; and
a breakover switch comprising a first end and a second end, the first end of the breakover switch of the each auto-triggered stage coupled to the power input of each semiconductor device of the each auto-triggered stage via the resistor of the each auto-triggered stage, the second end of the breakover switch of the each auto-triggered stage coupled to the control input of each semiconductor device of the each auto-triggered stage;

wherein the input of the control-triggered stage is connected to the output of one of the auto-triggered stages,
wherein the output of the control-triggered stage is connected to the device output,
wherein the input of each auto-triggered stage except for a highest one of the auto-triggered stages is connect to the output of a next higher one of the auto-triggered stages,
wherein the input of the highest auto-triggered stage is connect to the device input, and
wherein the auto-triggered stages are configured to turn on when the control-triggered stage turns on.

23. The semiconductor switching device of claim 22, wherein each breakover switch is a breakover diode.

24. The semiconductor switching device of claim 22, wherein:
the control-triggered stage further comprises a suppressor comprising a first end and a second end, the first end of the suppressor coupled to the power output of each semiconductor device of the control-triggered stage, the second end of the suppressor coupled to the control input of each semiconductor device of the control-triggered stage, and
the each auto-triggered stage further comprises a suppressor comprising a first end and a second end, the first end of the suppressor coupled to the power output of each semiconductor device of the each auto-triggered stage, the second end of the suppressor coupled to the control input of each semiconductor device of the each auto-triggered stage.

25. The semiconductor switching device of claim 22, wherein the control-triggered stage further comprises a capacitor having a first end and a second end, the first end of the capacitor coupled to the power output of each semiconductor device of the control-triggered stage and the second end of the capacitor coupled to the control input of each semiconductor device of the one of the auto-triggered stages, the capacitor configured to discharge into the control input of the each semiconductor device of the one of the auto-triggered stages to turn on the each semiconductor device of the one of the auto-triggered stages in response to the control switch closing.

26. The semiconductor switching device of claim 25, wherein:
the each auto-triggered stage comprises a respective capacitor having a first end and a second end;
the first end of the respective capacitor of the each auto-triggered stage is coupled to the power output of each semiconductor device of the each auto-triggered stage;
the second end of the respective capacitor of the each auto-triggered stage except the highest auto-triggered stage is coupled to the control input of each semiconductor device of the next higher one of the auto-triggered stages connected in series with the each auto-triggered stage; and
the second end of the capacitor of the highest auto-triggered stage is coupled to the power input of each semiconductor device of the highest auto-triggered stage.