Abstract: In the case of a method for feeding reactive power into an AC grid system, in the case of which method at least one line (10) of the grid system has a compensation voltage (U.sub.comp) produced for it, which compensation voltage (U.sub.comp) is phase-shifted with respect to the current in the line (10) and is injected into the line (10), simplified compensation is achieved in that the compensation voltage (U.sub.comp) is produced from a DC voltage by means of an inverter (11), which is formed by gate turn-off power semiconductors in a bridge circuit, and in that the compensation voltage (U.sub.comp) is injected in series directly into the line (10).

Abstract: A method and apparatus for the low noise operation of a electrical machine driven by a pulse inverter computes the amplitudes and frequencies of the harmonics of the inverter output voltages. Through targeted setting of the modulation parameters, the frequency spectrum or the noise spectrum can be fanned out and harmonics, which would excite stator resonances, can be eliminated. Due to the independence of the modulation parameters from the modulation index (a.sub.0) and the fundamental oscillation frequency (f.sub.1), the fanning-out and the elimination has no influence on the fundamental oscillation (u.sub.GS) or on the operating point of the machine. The inverter is controlled through sinusoidal pulse width modulation (PWM) and sinusoidal pulse frequency modulation (PFM) of a triangular carrier signal (U.sub.H). By this method, the main groups of the harmonics with two ordinate numbers (n, v) are fanned out into subgroups with three ordinate numbers (n, m, v).

Abstract: A converter circuit arrangement is specified which is constructed to have a particularly low inductance. This is achieved by the circuit area of the commutation circuit being kept as small as possible. A circuit area which is as small as possible is achieved by the branch modules and switch modules of a phase module being arranged either in a U-shape or in a meandering shape. The branch modules can be arranged either parallel to or at right angles to a main direction, between the positive and negative connections and the load connection. In addition, it is advantageous if the power semiconductor switches and the reverse-connected parallel diodes and freewheeling diodes are arranged in separate stacks which are held together by means of a clamping-in device.

Abstract: An a.c. machine (7) with, connected in parallel thereto, a capacitor bank (CR, CS, CT), which are fed by a converter (1-4) with a d.c. intermediate circuit, form a resonant system which is excited by the rectangular current of an inverter (4) of the converter. In this case, there is superimposition of the fundamentals and the normal harmonics in the machine voltage and in the machine current of an additional harmonic with the frequency of the resonance point. In the lower speed range of the a.c. machine (7), this excitation is eliminated by an optimum operating sequence of current gaps, which are generated inside a current block by means of a quenching circuit (3). Current gaps are generated at the start and end of each current block for the purpose of damping the 11th and 13th harmonic, and in the middle of the current block for the purpose of damping the 7th harmonic. A turn-on angle basic value signal (.alpha..sub.M) is modified by a turn-on angle differential signal (.DELTA..alpha..sub.

Abstract: With respect to their connection to snubber capacitors (C1, C2), a discharge resistor (12) connecting these snubber capacitors, and a link capacitor bank (3), inverter circuits with GTO thyristors (T1, T2) connected in series have parasitic leakage inductances which limit the level of the permissible link direct voltage. In order to reduce the leakage inductances, the snubber capacitors (C1, C2) are surrounded by effectively conducting capacitor covers (17). Sheet-metal shielding covers are fitted over the two ends of the discharge resistor (12). Parallel and series connected capacitors of the link capacitor bank (3) are connected to the positive/negative terminals (23, 24) of the GTO thyristors (T1, T2) in the middle of a heat sink connecting strainer (33), the supply leads being guided essentially parallel and the capacitors being arranged in opposite planes.

Abstract: Inverters (5.1, 5.2) for feeding a three-phase load such as, for example, an asynchronous machine (6), are controlled by pulse width modulation, in such a manner that they supply output voltages (U.sub.5.1R, U.sub.5.2R) which are as closely sinusoidal as possible, having few harmonics per alternating-current phase (R, S, T). To achieve the pulse width modulation, a first auxiliary alternating voltage (U.sub.H1) of a sawtooth generator (1.1), on the one hand, and a second auxiliary alternating voltage (U.sub.H2) of a sawtooth generator (1.2), which is phase-shifted by 180.degree. with respect to the first one, on the other hand, is superimposed by a control signal transmitter (2) on a sinusoidal first superimposition alternating voltage (U.sub.StR, U.sub.StS, U.sub.StT) with the required frequency and phase angle in logic circuits (3.1, 3.2). Separate inverter groups (5.1, 5.2), the outputs of which are connected via a reactor coil (7), the center tab of which is connected to a stator winding (W.sub.

Abstract: A method for attenuating at least one unwanted harmonic, particularly the second harmonic, with respect to the system frequency in a multi-phase alternating current system, wherein an additional stabilizing circuit is installed into a conventional current/voltage controller including a current/voltage controller and a three-phase firing pulse generator in a reactive-power compensator connected via a reactive-power transformer and a current transformer to a 50 Hz three-phase system. The reactive power compensator has for each phase of the three-phase current at least one air choke, which is connected via a current transformer and via an alternating-current switch via another sum-current transformer to a secondary winding of the reactive-power transformer. In addition, the reactive-power compensator has for each phase of the three-phase current at least one capacitor bank or a capacitor, which is connected via a current transformer and an alternating-current switch (13) to the sum-current transformer (20).

Abstract: A reactive-power compensator for compensating a reactive current component in an alternating-voltage system, including a reactive-current converter formed by forced-commutation current converter rectifiers arranged in a current converter bridge circuit, and a smoothing choke used as a termination at the direct-current side of the bridge circuit. The compensator attains constant compensation of both inductive and capactive reactive-current components with clearly reduced system reaction by driving the rectifiers such that the bridge circuit accepts at its input a compensation current in the form of approximately rectangular current pulses having a pulse frequency greater than that of the alternating voltage system. The polarity and width of these current pulses are modulated in accordance with a sine function so that the compensation current is identical in frequency and amplitude with respect to the reactive current component at the system voltage input, but shifted in phase by 180.degree..

Abstract: To reduce unwanted current oscillations such as, for example, of the second harmonic of the system frequency (f.sub.o), the firing angles (.alpha.1, .alpha.2) of a link-circuit rectifier (1) and of a link-circuit inverter (2) are compensatingly acted on in push-pull mode. For this purpose, a direct-current link-circuit current signal (S5, S5'), which contains the instability or the current oscillation to be compensated, is fed by means of a current detector (5, 5') to a bandpass filter (16, 16', 16") which is tuned to the frequency (f.sub.o, f.sub.x) of the respective current oscillation. The phase of a bandpass filter output signal (S16) is shifted by 90.degree. trailing in a 90.degree. phase-shifting section (15, 15', 15"). A compensating signal (S15,S15', S15") obtained in this manner is fed to first and second function generators (13, 13', 13"; 14, 14', 14").

Abstract: A power converter typically used for operating electrical machines and provided with protective measures to protect against overvoltages which can otherwise occur in the process of switching off the inductive loads represented by the electrical machines. To that end, the converter includes plural bridge circuits having a.c. voltage terminals and d.c. voltage terminals, wherein the a.c. voltage terminals are phasewise parallel-connected and coupled to each other via at least one capacitor and wherein the d.c. voltage terminals are coupled to each other via at least one intermediate circuit reactor. The bridge circuits include bridge arms having GTO thyristors that can be switched off, and the plural bridges are driven out of phase with respect to one another. In this way, the converter supplies an alternating current which is relatively near-sinusoidal and exhibits a low harmonics content to the electrical machine.

Abstract: A method of amplifying an analog low-frequency signal, and a switching amplifier implementing the method, wherein the maximum amplifiable voltage of the analog input signal is divided up into as many voltage bands as there are switching stages provided in the switching amplifier, and one switching stage is associated with each voltage band. Thereby the number of switching stages actuated and their switched-on period may be modulated in dependence upon the amplitude. In this way it is possible to reduce considerably the total number of switching processes during one period of the low-frequency input signal and the losses connected with each switching process.

Abstract: A variable phase-shifting transformer network including at least one pair of multi-phase transformers, wherein the network transformation ratio and phase shift is step wise adjustable as a result of the provision of plural auxiliary windings located on the core of a preselected secondary winding, each auxiliary winding having plural taps, which are not initially interconnected. Each transformer phase includes an AC semiconductor switch connected across selected tappings of the respective auxiliary windings via selected watt-less isolating switches. The voltage vector appearing across a selected secondary winding is varied by connecting an non-ignited semiconductor switch, via the isolating switches associated therewith, to desired tappings of the respective auxiliary windings while the rectifier is non-current conducting. Thereupon this AC semiconductor switch is ignited and ignition pulses are removed from the previously conducting semiconductor switch.