Abstract: An AC/DC converter has an auxiliary control system which attenuates or suppresses an unwanted or non-characteristic harmonic component (such as a 3rd harmonic component) of voltage in an AC power system caused by operation of the converter. The converter comprises thyristors and is connected via transformer to the AC power system which comprises an AC or Thevenin e.m.f. source, an impedance, and busbars. The auxiliary control system is connected to a main control system of the AC/DC converter providing firing pulses for the converter.

Abstract: An AC/DC converter has an auxiliary control system which attenuates or suppresses an unwanted or non-characteristic harmonic component (such as a 3rd harmonic component) of voltage in an AC power system caused by operation of the converter. The converter comprises thyristors and is connected via transformer to the AC power system which comprises an AC or Thevenin e.m.f. source, an impedance, and busbars. The auxiliary control system is connected to a main control system of the AC/DC converter providing firing pulses for the converter.

Abstract: A tuned filter for connection to a busbar in a high voltage electric power system. The filter incorporates a variable inductor comprising a main winding, auxiliary windings and switching circuitry associated with each auxiliary winding. The auxiliary windings are arranged to act in inductive series with respect to the main winding, and the switching circuitry is used to selectively connect the auxiliary windings in electrical series with the main winding, so allowing the inductance of the inductor to be varied. To achieve enhanced variability of the inductance, each auxiliary winding has a number of turns substantially equal to x2(n−1), where n is a positive integer corresponding to the position of each auxiliary winding in the inductive series of auxiliary windings and x is also a positive integer.

Abstract: A control system to control at least one of the thyristor converters (1) or (2) of an ac system (7,8) or (9,10) connected by busbars (5,6) and transformers (3,4) to the converters (1,2) which have their dc sides connected by a dc link, for example inductor (11). Each thyristor converter receives firing pulses from a firing control (12) or (13), including a firing angle control (18) and a summing junction (16) receiving a control current signal input (17) and a current signal (14) which is a function of converter operation. An electrical power measurement is made of one of the ac systems, for example the ac system (7,8,5) and in accordance with that power measurement a signal which is a function thereof is produced as an output (19) from an integral two-axis ac servo control having demodulator, integrator and modulator circuit receiving the power measurement signal as input. Signal (19) is a function of the cross-modulation noise component caused by interaction of electrical noise from the two converters.

Abstract: A tuned filter for connection to a busbar in a high voltage electric power system. The filter incorporates a variable inductor comprising a main winding, auxiliary windings and switching circuitry associated with each auxiliary winding. The auxiliary windings are arranged to act in inductive series with respect to the main winding, and the switching circuitry is used to selectively connect the auxiliary windings in electrical series with the main winding, so allowing the inductance of the inductor to be varied. To achieve enhanced variability of the inductance, each auxiliary winding has a number of turns substantially equal to x2(n−1) where n is a positive integer corresponding to the position of each auxiliary winding in the inductive series of auxiliary windings and x is also a positive integer.

Abstract: A control system to control at least one of the thyristor converters (1) or (2) of an ac system (7,8) or (9,10) connected by busbars (5,6) and transformers (3,4) to the converters (1,2) which have their dc sides connected by a dc link, for example inductor (11). Each thyristor converter receives firing pulses from a firing control (12) or (13), including a firing angle control (18) and a summing junction (16) receiving a control current signal input (17) and a current signal (14) which is a function of converter operation. An electrical power measurement is made of one of the ac systems, for example the ac system (7,8,5) and in accordance with that power measurement a signal which is a function thereof is produced as an output (19) from an integral two-axis ac servo control having demodulator, integrator and modulator means receiving the power measurement signal as input. Signal (19) is a function of the cross-modulation noise component caused by interaction of electrical noise from the two converters.

Abstract: A switching control arrangement for a multilevel convertor minimizes the harmonic content of the converter voltage or current by an open-loop and/or a closed-loop control of the timing of the switching of the GTOs associated with the energy-storage components (e.g. capacitors) in the convertor. In a first open-loop arrangement the convertor current is quantized over its working range and different threshold values are provided in dependence on the quantization values of the current. In a second open-loop arrangement a continuous, non-quantized control is provided based on at least a quadratic approximation to the desired current-dependent behavior of the GTO switching angles. In a third, closed-loop arrangement, different GTO-switching threshold levels are provided as controlled by a Fourier integration process involving the nulling of those harmonics desired to be nulled.