A method for monitoring a protective device, which has a series circuit of a multiplicity of thyristors. The protective device has a series circuit of N>1 thyristors. The series circuit is connected in a parallel circuit with an electrical device to be protected. A snubber branch is connected in parallel with each thyristor. For the purpose of testing a firing capacity, n<N thyristors in a first thyristor group are fired when a positive voltage is present across the series circuit and a negative snubber current is flowing through the snubber branches of the thyristors in the first thyristor group.

The present invention discloses a DC converter valve state detection method based on temporal features of converter terminal currents, including the following steps: collecting three-phase AC currents on a converter valve-side of a DC transmission system; defining a current when the currents of two commutating valves are equal as a base value, greater than the base value as a valve conducting current, and less than the base value as a valve blocking current; constructing a valve conducting state by a relative relationship among amplitudes of the three-phase AC currents, and calculating a time interval of each valve conducting state; comparing time intervals of 6 valve conducting states with a time interval of a valve conducting state in normal operation, and determining whether the 6 valve states are normal according to the result of comparison and locating all abnormal valves. The present invention can reliably detect valve states and locate abnormal valves through sequence detection. This method can be applied to actual fault phase judgment and commutation failure judgment, providing a good support for accurate judgment of DC control and protection.

A method analyzes an operation of a power semiconductor device. The method includes: providing a set of reference voltages of the device and a set of corresponding reference currents; measuring, within a predetermined time-interval, Nframe on-state voltages and Nframe corresponding on-state currents of the device to obtain Nframe measurement points, Nframe being an integer number equal to or greater than 2; adapting the set of reference voltages by carrying out a least squares fit to the Nframe measurement points; and using the adapted set of reference voltages to analyze the operation of the power semiconductor device.

A method of detecting a failure of an antiparallel thyristor, wherein the antiparallel thyristor includes a first thyristor and a second thyristor connected in parallel and in opposite directions, and is configured to control power supplied from an alternating current power supply to a load, the method including: detecting, as a first detection value, a voltage or a current supplied to the load when ceasing an output command for the second thyristor and issuing an output command for the first thyristor; detecting, as a second detection value, the voltage or the current supplied to the load when ceasing the output command for the first thyristor and issuing the output command for the second thyristor; and determining the failure of the antiparallel thyristor based on a difference between the first detection value and the second detection value.

A method analyzes an operation of a power semiconductor device. The method includes: providing a set of reference voltages of the power semiconductor device and a set of corresponding reference currents; measuring an on-state voltage and a corresponding on-state current of the power semiconductor device to obtain a measurement point; adapting the set of reference voltages by adapting two of the set of reference voltages lying closest to the measurement point by extrapolating the measurement point; and using the adapted set of reference voltages to analyze the operation of the power semiconductor device. The extrapolation is based on a predefined reference increment current and a predefined reference increment voltage.

A thyristor circuit comprising at least one series circuit in which two or more thyristors are connected in series. Each thyristor is parallel-connected to an RC member. A control device can energize the thyristors individually and independently of each other by a control signal, so that each thyristor can be individually switched into its conducting condition. During a test sequence, the thyristors are switched successively into their conducting condition, wherein, in a series circuit and/or in the thyristor circuit, respectively only one thyristor is in its conducting condition. While a thyristor is conducting, the capacitor of the associate RC member discharges and produces a thyristor current. As a result, the conducting condition is maintained until the thyristor current falls below the holding current. The control device can use the thyristor voltage and/or the thyristor current to evaluate the function or the switching behavior of the thyristor.

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 system for monitoring polarization and conduction of a thyristor includes a transformer configured to generate a secondary current from a triggering current waveform applied to a gate of the thyristor; a converter configured to convert the secondary current into a monitored voltage; a first hysteresis comparator configured to generate a first voltage pulse based on the monitored voltage when the triggering current waveform includes a first current pulse; a second hysteresis comparator configured to generate one or more second voltage pulses based on the monitored voltage when the triggering current waveform includes one or more second current pulses; a monitoring unit configured to receive the first and the one or more second voltage pulses, and determine whether the triggering current waveform satisfies pre-defined characteristics, and to determine whether a current flowing between the anode and cathode of the thyristor satisfies additional pre-defined characteristics.

A system for monitoring polarization and conduction of a thyristor includes a transformer configured to generate a secondary current from a triggering current waveform applied to a gate of the thyristor; a converter configured to convert the secondary current into a monitored voltage; a first hysteresis comparator configured to generate a first voltage pulse based on the monitored voltage when the triggering current waveform includes a first current pulse; a second hysteresis comparator configured to generate one or more second voltage pulses based on the monitored voltage when the triggering current waveform includes one or more second current pulses; a monitoring unit configured to receive the first and the one or more second voltage pulses, and determine whether the triggering current waveform satisfies pre-defined characteristics, and to determine whether a current flowing between the anode and cathode of the thyristor satisfies additional pre-defined characteristics.

A method analyzes an operation of a power semiconductor device. The method includes: providing a set of reference voltages of the power semiconductor device and a set of corresponding reference currents; measuring an on-state voltage and a corresponding on-state current of the power semiconductor device to obtain a measurement point; adapting the set of reference voltages by adapting two of the set of reference voltages lying closest to the measurement point by extrapolating the measurement point; and using the adapted set of reference voltages to analyze the operation of the power semiconductor device. The extrapolation is based on a predefined reference increment current and a predefined reference increment voltage.