A standby power supply system is provided for supplying normal AC power to a critical load from an AC power source during normal operating conditions, and for supplying emergency AC power to the load during failure of the AC power source. During normal operation, the standby power supply system actively neutralizes undesirable harmonic components in the input current drawn by the load. The standby power supply system includes a power conversion device having a DC side coupled to a back-up power source and an AC side in parallel with the load and the AC source. A harmonic distortion sensor senses a harmonic distortion current component of a load current drawn by the load during normal operating conditions. A controller is responsive to the harmonic distortion sensor for causing the power conversion device to produce a harmonics neutralizing current to substantially neutralize the harmonic distortion current component produced by the load. A method is also provided for supplying AC power to a load during normal and emergency operating conditions.

Standby power supply with load-current harmonics neutralizer

An unified constant-frequency integration (UCI) control method based on one-cycle control employs an integrator with reset as its core component along with a few logic and linear components to control the pulse width of a three-phase recitifier, active power filter, or grid-connected inverter so that the all three phase current draw from or the current output to the utility line is sinusoidal. No multipliers and reference calculation circuitry are needed for controlling active power filters. The UCI control employs constant switching frequency and operates in continuous conduction mode (CCM). If in some cases a DSP is desired for some other purposes, the Unified Constant-frequency Control function can be realized by a low cost DSP with a high reliability, because no high speed calcutation, high speed A/D converter, and mutipliers are required.

Unified constant-frequency integration control of three-phase power factor corrected rectifiers, active power filters, and grid-connected inverters

A series impedance compensation system for a set of transmission lines which are used for electrical power transmission, with these parallel lines being protected from the transient faults and dynamic subsynchronous oscillation problems. These problems can become aggravated by the introduction of capacitor banks which thus serve as only a partial solution to the disturbances of transient faults during conventional recovery modes of operation. The impedance compensation system is coupled in series to each transmission line to dynamically balance the inductor impedance on the transmission line, responsive to demand, by injecting a voltage component determined to be optimized substantially at quadrature leading or lagging phase angles (±90°) with respect to the transmission line voltage and current components. The impedance compensation system includes a circuit based solid-state switching power converter with self-commutating thyristor or GTO semiconductor switches connected in a parallel shunting arrangement with reverse poled or freewheeling diodes. This is done in order to provide either an absorptive component or a generated component of output pole voltage carrying a 90° segment of the output current in each cycle, as this provides dynamic stability without fostering subsynchronous resonance.

Transmission line dynamic impedance compensation system

A power line conditioner includes an active filter coupled, in series, and a passive filter coupled, in parallel, to a three-phase power distribution network The three-phase power distribution network includes a voltage source that induces three-phase input currents at a first end of the three-phase power distribution network A load, circulating three-phase load currents, is positioned at a second end of the three-phase power distribution network The active filter controller of the invention uses synchronous transformations to identify selected harmonic reference components corresponding to individual harmonics of the three-phase load currents The selected harmonic reference components are multiplied by a predetermined factor corresponding to a permissible percentage of the individual harmonics that may be injected into the supply voltage This results in active filter reference signal components that are applied to the active filter In response to the active filter reference signal components, the active filter injects a permissible percentage of harmonics into the supply voltage so as to reduce the voltage distortion at the passive filter By reducing voltage distortion, the controlled injection of harmonics into the supply allows for a simplified passive filter design Consequently, the passive filter may be implemented as a power factor correction capacitor

Hybrid series active/parallel passive power line conditioner with controlled harmonic injection

An apparatus to be used with a PWM VSI which is linked by voltage supply cables to either a passive or a dynamic load, the VSI providing voltages on the cables which have at least one primary harmonic component, the apparatus linked to the output terminals of the VSI and including a line inductor between each output terminal and the load and, for each cable, at least one resonant filter branch including an inductor and a capacitor linked to each of the supply lines and to a common node wherein the line inductors are chosen so as to limit filter current and the branch elements are chosen such that a resonant frequency thereof is essentially equal to the frequency of the primary harmonic component.

Series resonant sinewave output filter and design methodology

A harmonic suppressing device provided in a power system such as, for example, a transmission and distribution system or a power generating system, to filter higher harmonic currents generated by a higher harmonic current source of the power system such as, for example, a cycloconverter. The harmonic suppressing device comprises, as the principal components thereof, a passive filter serving as a high-order higher harmonic filtering unit for filtering higher harmonic currents of comparatively high order among those generated by the higher harmonic current source, and an active filter serving as low-order higher harmonic filtering unit for filtering higher harmonic currents of comparatively low orders among those generated by the higher harmonic current source. The active filter comprises: a main active filtering circuit comprising a plurality of switching transistors, rectifying diodes combined with the switching transistors, respectively, a capacitor, and a reactor; an operating circuit which calculates controlling data for controlling the commutating action of the main active filtering circuit on the basis of the detected values of the higher harmonic currents that flows into the power source side of the power system and the detected values of the output voltage of the higher harmonic current source; and a control circuit which gives control signals such as, for example, pulse width modulating signals to the main active filtering circuit. The harmonic suppressing device is capable of filtering higher harmonic currents in a wide frequency band.

Kazuo Mitsubishi Denki K.K. Ikeda

Papers

Harmonic suppressing device