Abstract: A system and method for determining non-linear load harmonics impact on the voltage distortion at the point of common coupling is disclosed. Briefly described, one embodiment is a method comprising metering voltage on an electric power system; metering current on the electric power system; determining a predicted voltage based upon the metered current; comparing the predicted voltage with the metered voltage; and determining a harmonic voltage component using a plurality of weights determined when the predicted voltage converges with the metered voltage.

Abstract: Voltage synthesis using virtual quadrature sources may be provided. First, a quadrature wave form may be created. The quadrature wave form may have the same frequency as an input voltage and may be ninety degrees out of phase with the input voltage. Next, a harmonic wave form may be created. The harmonic wave form may be based upon an even harmonic of the input voltage and may comprise a triplen wave form. Then, the quadrature wave form and the harmonic wave form may be added to create a resultant wave form. The resultant wave form may be contained within an envelope defined by the input voltage. Next, duty cycle control may be applied to the resultant wave form to create an output voltage. The duty cycle control may be applied without using an energy storage device.

Abstract: Disclosed are various embodiments of voltage protectors that include a first voltage clamping device configured to clamp a voltage of an input power applied to an electrical load, and a second voltage clamping device configured to clamp the voltage applied to the electrical load. A series inductance separates the first and second voltage clamping devices. Also, a switching element is employed to selectively establish a direct coupling of the input power to the electrical load, where a circuit is employed to control the operation of the switching element.

Abstract: Dual feed power supply system provides high reliability of a dual utility feed, with minimal interruptions in power supplied to critical loads during switching, and compensation for voltage sags occurring on the primary power feed. AC input buses are connected through a transfer switching apparatus to phase lines of a distribution bus. The transfer switching apparatus has a first input terminal connected to one of the phase lines of the first input bus and a second input terminal connected to one of the phase lines of the second input bus, and an output terminal connected to one of the phase lines of the distribution bus. Input switches allow switching from one or the other of the AC input buses to the distribution bus, with a fast transfer switch used to interrupt the supply of power from the input buses to the distribution bus during switching of the input switches.

Abstract: Floating electrically isolated active impedance modules are formed to attach to power transmission lines without breaking the lines such that the power line forms a secondary of the main transformer of the module. Each module includes an electrical energy storage device and a switching circuit, such as a single phase inverter, connected to the storage device and to the main transformer primary winding. The inverter can be controlled to couple a selected voltage to the transmission line through the main transformer primary winding which can provide effective positive impedance, negative impedance, or a voltage at or near phase quadrature with the line current. Many active impedance modules may be distributed over a power system grid to allow control of the impedance of the power lines in the grid and to steer power through the grid, with each module electrically isolated from ground and from other phase lines of the transmission system.

Abstract: A dual feed power supply system provides the high reliability of a dual utility feed, with minimization of interruptions in the power supplied to critical loads during switching, and compensation for voltage sags occurring on the primary power feed. First and second AC input buses are connected through a transfer switching apparatus to each of the phase lines of a distribution bus. The transfer switching apparatus has a first input terminal connected to one of the phase lines of the first input bus and a second input terminal connected to one of the phase lines of the second input bus, and an output terminal connected to one of the phase lines of the distribution bus. Input switches allow switching from one or the other of the AC input buses to the distribution bus, with a fast transfer switch used to interrupt the supply of power from the input buses to the distribution bus during switching of the input switches.

Abstract: A low cost, small size, light weight, and highly effective system and method for providing dynamic power line voltage sag correction is provided. A dynamic voltage sag corrector includes a static bypass switch and a regulator/storage module connected together in parallel between input terminals and output terminals. Under normal operating conditions, the static bypass switch is closed, and a normal line voltage level is provided directly from the input terminals to the output terminals via the static bypass switch. When a voltage sag condition is indicated, the static bypass switch is opened, and the regulator/storage module is controlled to provide a near normal output voltage signal to the output terminals. The regulator/storage module includes a power conversion circuit which is controlled to provide the desired output voltage signal by adding a voltage level on storage capacitors to the available input line voltage signal.

Abstract: A coaxial winding transformer is cooled by having heat transfer members connected to an outer conductor of the transformer to receive heat therefrom. The heat transfer members form a heat transfer conducting path from the outer conductor of the transformer to a surface of a heat sink. The heat sink may have fins to maximize transfer of the heat from the heat sink to the ambient air. The outer conductor can include a metal strap member in contact with the surface of extending sections of tubular straight leg sections to electrically connect the tubular sections and transfer heat therefrom. Heat is then transferred from the strap of the outer conductor through the heat transfer members to an available surface of the heat sink.

Abstract: A converter for providing three phase power to a three phase load from a single phase supply includes an inverter connected to single phase input power lines and a bi-directional switch connected in series with one of the input power lines. The converter has three output lines, one connected to the inverter output, another connected to an input power line between the bi-directional switch and the inverter, and the third connected directly to the other input power line. The inverter switching devices are controlled to provide a signal on the output of the inverter to provide balanced three phase power on the converter output lines. This is preferably accomplished by pulse width modulation of an inverter output voltage reference signal derived by phase shifting the single phase input voltage signal by 60.degree.. The inverter is preferably also controlled to phase shift the inverter output signal when necessary to ensure that the net power flow into the inverter is zero under light load conditions.

Abstract: A method and apparatus is provided for restoring a sagging voltage signal on a power transmission line, caused by a remote fault in the utility power system, to a balanced three-phase condition at the pre-fault voltage level. Voltage restoration is provided by injecting a voltage signal in series with the power transmission line which restores the load voltage vectors to the pre-fault condition. The restored load voltage vectors are rotated by a selected phase angle such that zero real power flow is associated with the voltage restoration. The voltage compensation signal may be injected into the power transmission line by connecting a voltage compensator inverter in series with the transmission line. The voltage compensator inverter may be controlled to provide the desired injected voltage signal using a synchronous reference frame based controller.

Abstract: Multi-phase power is provided to a load via the use of an inverter which has an even number of inverter legs. DC source voltage, such as from an AC-to-DC converter receiving power from a main AC power supply or from an independent DC power source such as a battery, is provided to the inverter. The DC source voltage is provided on DC bus lines of the inverter so as to be symmetric about ground. Switching devices in the inverter legs are controlled using a modulation strategy to synthesize desired output voltage waveforms on the inverter leg outputs from the voltage on the DC bus lines. The modulation strategy is subject to a modulation constraint such that, at any one time, half of the inverter legs provide a positive output voltage signal with respect to ground, and the other half of the inverter legs provide a negative output voltage signal, of equal magnitude, with respect to ground.

Abstract: A DC-to-DC converter topology is provided having switching devices that are switched under zero voltage switching conditions to minimize switching losses. The converter of the present invention includes two input side converter bridges, each based on a two switch forward converter topology. The input side converter bridges may be connected in series for high input voltage levels and in parallel for low voltage levels. The switching devices of each input side converter bridge are coupled together by coupling inductors. The turning-off of a switching device in one bridge causes part of the energy stored in the corresponding coupled inductor to discharge an output capacitance of an incoming switching device in the other bridge, causing an anti-parallel connected diode to conduct. The incoming switch can thus be turned on under zero voltage switching conditions. Zero voltage switching can be achieved over a wide load range by properly sizing the coupled inductors.

Abstract: A parallel hybrid active filter system for harmonic compensation of large non-linear loads is provided. The hybrid filter includes a passive filter connected in series with an inverter that is controlled to produce a dynamically variable inductance at selected harmonic frequencies. The passive filter may include passive capacitive and inductive elements, or may include a power factor correction capacitor alone, with all the inductance for the hybrid filter provided by the active filter inverter. The active filter inverter is controlled to provide the dynamically variable inductance by a synchronous reference frame (SRF) based controller that generates active filter inverter voltage commands that are fed to a PWM or square wave modulated voltage source inverter (VSI).

Abstract: A hybrid parallel active/passive filter system is provided which provides line power harmonic isolation and compensation for power systems connected to high power non-linear loads. The hybrid filter includes a passive filter connected in series with an active filter inverter. The active filter inverter is controlled to generate inverter voltages such that the filter terminal voltage tracks the supply voltage harmonics at a selected dominant harmonic frequency to regulate the supply current harmonics to zero. A synchronous reference frame (SRF) based controller is used to generate harmonic inverter voltage commands based on measured supply current values. A feed forward command signal generator may be used to improve the response of the control system. The active filter inverter is preferably implemented as a square-wave inverter. The active filter inverter DC bus is controlled to achieve power balancing and to provide real power to compensate for losses of the inverter.

Abstract: A DC-to-DC converter for high current outputs is provided having an input side circuit, including two converter bridges, and an output side circuit, including two diode rectifier configurations. The input and output circuits are preferably connected by a co-axial winding transformer (CWT). Switches in the input side bridges alternately connect and disconnect a DC input voltage to and from the primary side of the transformer. The waveform appearing on the secondary of the transformer is rectified by the output side rectifier configurations. A switched-in bias voltage in each input side converter bridge provides for reversal of the current in the bridge after the bridge is switched off, and before the other bridge is switched on. This current reversal allows a current in one of the rectifier configurations of the output side circuit to be brought softly to zero before being reversed biased by the switching on of the other converter bridge. Thus, a reverse recovery spike in the output circuit is avoided.

Abstract: A simple, low-cost technique for charge equalization of a series connected string of battery cells is provided. The secondary windings of a transformer having a single primary winding and multiple secondary windings are connected across each battery cell to be equalized. A single power converter applies a charging signal to the primary of the transformer, inducing a charging current in each secondary which is inversely related to the charge on the battery cells to be equalized. The transformer is preferably implemented as a coaxial winding transformer having low secondary-to-secondary winding coupling. The power converter is preferably implemented as a forward converter supplied with DC power from an adjustable DC power source. A source voltage provided by the DC source may preferably be adjusted during the course of charge equalization to preferentially direct charge to weaker cells.

Abstract: A modulator for resonant DC link and other power converters is provided having superior performance and general applicability to multi-phase converters. The modulator includes three major components: (1) a multi-input, multi-output linear system, (2) a quantizer, and (3) a latch. The linear system receives multiple reference signal waveforms and multiple feedback signal waveforms representative of the modulator output as input signals and produces multiple linear output signals derived from the difference between the reference and feedback waveforms as outputs. The linear system is preferably a second order system. The quantizer assigns the continuous output of the linear system to one of a finite set of discrete output vectors. The output of the quantizer is latched at a sampling rate synchronized with the times of zero voltage or current on the DC bus of the converter.

Abstract: An Uninterruptible Power Supply (UPS) for de-centralized operation in a distributed UPS system is described. The UPS system includes a number of UPS units that do not have communication links between them and therefore operate in a de-centralized manner. Coordinated operation in the UPS system is achieved through a controller associated with each UPS unit. The controller identifies when the operating power signal frequency on the UPS system does not correspond to a nominal operating frequency. In response to this condition, the controller generates a frequency reference signal that is used to control the inverter of the UPS unit. The controller continuously estimates the fractional loading of the distributed system by gauging the system response to disturbances, and sets its own operating point accordingly. The controller also ensures that the system operates at its nominal frequency independent of loading.

Abstract: The apparatus includes an active filter, coupled in series, and a passive filter, coupled in parallel, to a power distribution network. The power distribution network includes a voltage source that induces input currents at a first end of the power distribution network. Nonlinear loads and other conditions on the power distribution network cause unbalanced power signals. The active filter controller of the invention uses synchronous transformations on the input currents to identify a negative sequence fundamental signal and a positive sequence fundamental signal, while filtering all harmonic components within the input currents. The negative sequence fundamental signal and the positive sequence fundamental signal are combined to form an active filter reference signal which is applied to the active filter. In response to the active filter reference signal, the active filter operates as a current controlled harmonic voltage source, carrying only the fundamental current, while only injecting harmonic voltages.

Abstract: A power conversion system for driving a three phase synchronous or induction motor receives power from AC power lines and rectifies the power to provide DC current on DC link lines through a link inductor. An inverter connected to the DC link lines is composed of three sets of two thyristors connected in series across the DC link lines. Three output lines extend from connections between each of the three sets of thyristors to the motor. Capacitors are connected across each of the three phase output lines. A controller controls the switching of the thyristors in two modes. In a first mode, used from start-up to low speed operation, a high frequency switching cycle is produced in three steps during which pairs of thyristors in different ones of the three sets are triggered. The relative length of time spent in each one of the three periods during the switching cycle is varied to obtain a desired change in the average output voltage on the three phase output lines at a fundamental frequency.