A semiconductor switching circuit, for use in a HVDC power converter, comprising: a main semiconductor switching element, including first and second connection terminals between which current flows from the first connection terminal to the second connection terminal and an auxiliary semiconductor switching element electrically connected between the first and second connection terminals thereof, and a control unit, operatively connected to auxiliary semiconductor switching element and programmed to control the switching element to create an alternative current path between the first and second connection terminals by at least two of: a fully-on mode in which the switching element is operated at its maximum rated base current or gate voltage; a pulsed switched mode in which the switching element is turned on and off; and an active mode in which the switching element is operated with a continuously variable base current or gate voltage.

A static transfer switch is provided for supplying power to a load alternately from two different power sources. Switching between the two power sources may occur within a fraction of one electrical cycle. In response to sensing degraded performance in the power source supplying the load, a main circuit is turned off with a resonant turn off circuit. The resonant turn off circuit is shared between the main circuits of two different power sources such that the resonant turn off circuit is connected to the main circuit of whichever power source is currently supply power to the load.

A fault detector for an anti-parallel thyristor includes: a power supply unit configured to supply power to the first and second thyristors; a first current sensor configured to output a first current measurement value that flows through the first thyristor; a second current sensor configured to output a second current measurement value that flows through the second thyristor; and a detector which notifies a fault of a thyristor when the first and second current measurement values satisfy a set fault condition,

A semiconductor switching string includes a plurality of series-connected semiconductor switching assemblies, each having a main semiconductor switching element that includes first and second connection terminals. The main semiconductor switching element also has an auxiliary semiconductor switching element electrically connected between the first and second connection terminals. Each semiconductor switching assembly also includes a control unit configured to switch on a respective auxiliary semiconductor switching element to selectively create an alternative current path between the first and second connection terminals whereby current is diverted to flow through the alternative current path to reduce the voltage across the corresponding main semiconductor switching element. The or each control unit is further configured to switch on the auxiliary semiconductor switching element when the voltage across the corresponding main semiconductor switching element differs from a voltage reference derived from the voltage across all of the main semiconductor switching elements.

Within a direct current hybrid circuit breaker (DC HCB), a commutation unit (CU) is provided in a semiconductor switch path in series with a semiconductor switch to facilitate opening the DC HCB. The semiconductor switch path is connected in parallel with a mechanical switch path that includes a mechanical switch. The CU is a controlled voltage source which applies a reverse biased voltage on the semiconductor switch path. The CU causes the current through the mechanical switch to ramp down while the current through the semiconductor switch ramps up to a supply current. The CU maintains the current through the mechanical switch to remain at a zero vale by compensating for the voltage drop across the semiconductor switch and the self-inductance of the semiconductor switch path. The mechanical switch can open without current and against no recovery voltage.

Unique systems, methods, techniques and apparatuses of solid state circuit breaker protection are disclosed. One exemplary embodiment is a solid state circuit breaker comprising a primary switching device including a first terminal and a second terminal and a voltage clamping circuit coupled in parallel with the primary switching device. The voltage clamping circuit includes a metal-oxide varistor (MOV) coupled in series between the first terminal and an auxiliary semiconductor device, the auxiliary semiconductor device being arranged so as to selectively couple the MOV with the second terminal, and a bypass circuit coupled between the first terminal and the auxiliary semiconductor device.

Within a direct current hybrid circuit breaker (DC HCB), a commutation unit (CU) is provided in a semiconductor switch path in series with a semiconductor switch to facilitate opening the DC HCB. The semiconductor switch path is connected in parallel with a mechanical switch path that includes a mechanical switch. The CU is a controlled voltage source which applies a reverse biased voltage on the semiconductor switch path. The CU causes the current through the mechanical switch to ramp down while the current through the semiconductor switch ramps up to a supply current. The CU maintains the current through the mechanical switch to remain at a zero vale by compensating for the voltage drop across the semiconductor switch and the self-inductance of the semiconductor switch path. The mechanical switch can open without current and against no recovery voltage.

A fault detector for an anti-parallel thyristor includes: a power supply unit configured to supply power to the first and second thyristors; a first current sensor configured to output a first current measurement value that flows through the first thyristor; a second current sensor configured to output a second current measurement value that flows through the second thyristor; and a detector which notifies a fault of a thyristor when the first and second current measurement values satisfy a set fault condition.

A semiconductor switching circuit, for use in a HVDC power converter, comprising: a main semiconductor switching element, including first and second connection terminals between which current flows from the first connection terminal to the second connection terminal and an auxiliary semiconductor switching element electrically connected between the first and second connection terminals thereof, and a control unit, operatively connected to auxiliary semiconductor switching element and programmed to control the switching element to create an alternative current path between the first and second connection terminals by at least two of: a fully-on mode in which the switching element is operated at its maximum rated base current or gate voltage; a pulsed switched mode in which the switching element is turned on and off; and an active mode in which the switching element is operated with a continuously variable base current or gate voltage.

A semiconductor switching string including a series-connected switching assemblies. Each assembly has a main switching element including first and second connection terminals which current flows between when the main switching element is on. The main element has an auxiliary element between the connection terminals. The string includes a local control unit connected with each auxiliary element which are programmed to switch an auxiliary element to create an alternative current path between the connection terminals that diverts current through to reduce the voltage across the corresponding main switching element. The local unit is programmed to control switching an auxiliary element to a fully-on mode in which the auxiliary element is at maximum rated base current, a pulsed mode which turns the auxiliary element on and off and/or an active mode operating the auxiliary element with a continuously variable base current. The string includes a higher level control unit programmed to implement the modes.