An active filtration system is described which may be particularly useful for filtering undesired harmonics of the fundamental AC frequency produced by AC to DC or DC to AC conversion. The filtration system of the invention produces currents of a phase, frequency and magnitude for injection into the AC system such that the undesired harmonic currents to be filtered sum with the injected currents giving a net zero current at the undesired harmonic frequency. The system can incorporate existing passive filtration elements and provides a high-impedance parallel-filtration network to prevent the filteration system from acting as a "sink" for the ambient harmonics generated elsewhere in the AC system. Because the frequency, phase and magnitude of the injected currents are controlled, the filter of the invention remains highly effective even when these quantities and the filter component values vary.
For reducing the amount of circuitry and losses in double highpasses for filter arrangements in networks with a high voltage level, the two resonance frequencies and Q-factors of the double highpass are tuned so that in a critical harmonic range, at most a harmless slight resonance peak can occur, for which purpose a series capacitor together with a series choke are connected in series with a shunt circuit grounded, in the case of high voltage and ungrounded in the case of medium voltage, of ohmic, inductive and capacitive circuit elements connected to the network.
A superconduction power storage apparatus includes a superconduction coil for storage and release of electrical energy, and a separately excited thyristor conversion unit having d.c. terminals connected to the said superconduction coil and a.c. terminals connected to an a.c. power source. The conversion unit is arranged so as to convert the electrical energy from a d.c. form to an a.c. form and vice versa between the superconduction coil and the a.c. power source. An on-load voltage regulator is connected between the a.c. side terminals of the thyristor conversion unit and the a.c. power source, and is arranged for adjusting the voltage appearing at the a.c. terminals of the thyristor conversion unit.
A better filtering effect for disturbing harmonic currents in a high-tension direct current transmission installation is described. A balancing winding is provided between a primary winding as an outer winding and a secondary winding in a 3-winding transformer with a transformer core. The distances between the balancing winding and the primary winding and the secondary winding, respectively, are selected such that the equivalent reactance of this balancing winding is equal to or less than zero. A second balancing winding can be provided as the inner winding in a series with the first balancing winding. In the case of a 4-winding transformer, two winding arrangements are provided with two parallel-connected primary windings as the outer windings, with a separate secondary winding for each and a balancing winding for each between the primary and secondary windings, the two balancing windings being connected in series.
A system and method for providing harmonic currents to a harmonic generating load connected to a multiphase alternating current power system includes a zig-zag transformer and a current generator. The zig-zag transformer is electrically connected to the multiphase alternating current power system. The current generator is electrically connected between a neutral of the zig-zag transformer and a neutral return path of the multiphase alternating current power system. The current generator injects a harmonic current into the neutral of the zig-zag transformer which in turn, reduces the harmonic currents provided to the load from the multiphase alternating current power system.
A power source system, which comprises a converter for converting AC power on an AC bus into DC power, a damped filter connected between the AC bus and ground and including a capacitor and an inductor, a diode-rectifying circuit for taking out and rectifying fundamental and harmonic waves produced across the inductor in the damped filter and a circuit for connecting a DC output circuit in the diode-rectifying circuit in series with a DC output circuit in said converter, and in which the rectified output is regeneratively added to the output of the converter.
