Reactive-power compensator for compensating a reactive-current component in an alternating-voltage system

A reactive-power compensator for compensating a reactive-current component in an alternating-voltage system, comprising:

• at least one current converter bridge circuit having an alternating-voltage input which is to be connected to each branch of the alternating-voltage system and a direct-current output, including plural forced-commutation current converter rectifiers coupled to each of the branches of the alternating-voltage system and arranged such that a defined current direction is produced at the direct-current output;
• a capacitor connected in parallel at the alternating-voltage input;
• a smoothing choke connected to the direct current output;
• and
• compensation means for driving the forced-commutation current converter rectifiers such that the current converter bridge circuit accepts at its alternating-voltage input a compensation current (.DELTA.I) in the form of approximately rectangular current pulses having a pulse frequency (f) which is greater than the frequency of the alternating-voltage system, said current pulses having a polarity and a width modulated in accordance with a sine function so that a fundamental frequency component of the compensation current (.DELTA.I) is identical in frequency and amplitude with respect to a reactive-current component at said alternating-voltage input but shifted in phase by 180.degree.;
• wherein said compensation means comprises,
• a drive unit for applying control pulses to said rectifiers, and
• a pulse-width modulator connected to said drive unit for applying thereto width-modulated pulses at the pulse frequency (f) in accordance with a control voltage (U.sub.S) dependent on the magnitude and phase of the reactive-current component (I.sub.B);
• and
• means for generating the control voltage (U.sub.S), including a first multiplier which multiplies a reference voltage (U.sub.R) which is shifted in phase by an angle of 90.degree. with respect to a system voltage (U.sub.N) of the alternating-voltage system by a multiplication factor (M), the magnitude of which is proportional to the magnitude of the reactive-current component (I.sub.B) and which changes its sign when the reactive-current component (I.sub.B) changes between an inductive and a capacitive range.