Abstract: A unified power flow controller has a dc-to-dc converter which uses the dc voltage produced by a first static inverter, connected in shunt with a transmission line and providing parallel reactive compensation, to establish the magnitude of a series compensation voltage injected into the transmission line by a second static inverter. The second static inverter then only has to regulate the phase angle of the series injected voltage. With the dc-to-dc converter turned off, the two inverters are decoupled and can be operated independently even if the other inverter is not operational.

Abstract: A transmission line power controller for controlling the flow of electric power in an alternating current three-phase transmission system is described. The power line controller includes a parallel inverter connected to a series inverter through a dc link. The parallel inverter is connected in shunt to the transmission system through a shunt transformer. The series inverter is connected in series with the transmission system through a series transformer. A transmission line power control circuit is used to specify a desired real power demand and reactive power demand for the transmission system. The power control circuit processes this information along with a transmission line voltage vector and a transmission line current vector to produce a voltage source reference signal that is applied to the series inverter. In response to the voltage source reference signal, the series inverter produces an injected voltage vector into the transmission system.

Abstract: An apparatus and method are disclosed for controlling the power flow in an electric transmission system including at least two transmission lines, each transmission line having two ends and carrying alternating current at a selected transmission line voltage and fundamental frequency between the ends. At least two alternating voltages at the fundamental frequency of the alternating currents flowing in the transmission lines, with variable magnitude and controllable phase angle relative to the transmission line current, are generated and coupled in series with the transmission lines. The magnitude and phase of each generated voltage are controlled selectively and individually to adjust the effective reactive and real impedance of each transmission line, to control the real power transmitted between the two ends of the transmission line and, concurrently, to control the amount of real power individually transferred between the transmission lines.

Abstract: A series compensator for damping power oscillations in an electric power transmission system includes a switching power converter which injects a voltage into the transmission line having a phase angle relative to transmission line current which is controlled to provide reactive compensation and to inject virtual real impedance into the line. The switching power converter is a dc to ac converter which is capable of injecting virtual real impedance into the transmission line by virtue of the fact that it has a power exchange device connected to its dc terminals. Where the power exchange device is a resistor, the switching power converter is capable of absorbing real power during surges in power on the line. Alternatively, the power exchange device is a storage device such as a battery bank or a super conducting magnet, in which case the switching power converter can provide both virtual positive and negative real impedance.

Abstract: A solid-state circuit breaker with fault current conduction is described. The circuit includes a power sensor connected to a power line having an up-stream side and a down-stream side. The output of the power sensor is conveyed to a switch selection circuit that identifies a line disturbance on the power line. In response to a line disturbance, the switch selection circuit generates a set of output signals. The output signals force the opening of a fault current interruption circuit including a set of turn-off thyristors. The turn-off thyristors respond to the line disturbance within a fraction of a power signal cycle to provide isolation between the up-stream side and downstream side of the power line. An alternate power source may then be applied to the down-stream side of the power line. If the line disturbance exists on the down-stream side of the power line, the output signals force the closing of a fault current conduction circuit including a set of thyristors connected in series with a reactor.

Abstract: A bias voltage vectorially added to the controllable voltage injected in series with the line voltage of a transmission line reduces the required MVA rating for a unified power flow controller (UPFC) in applications where the power in the transmission line only flows in a single direction, or where the range of the transmission angle is otherwise unequal about zero.

Abstract: A novel active power line conditioner is disclosed. The apparatus includes a parallel inverter, with a dc-link, coupled to an output line. The parallel inverter is controlled by a parallel inverter controller which forces the parallel inverter to act as a variable capacitor or inductor. The parallel inverter controller identifies and feeds-forward a desired phase shift value between an active power line conditioner voltage output signal and an active power line conditioner voltage input signal. Utilization of the desired phase shift value results in voltage control of the dc-link of the parallel inverter. The parallel inverter controller also produces a tuning capacitance current reference signal which reduces voltage magnitude errors of the output voltage.

Abstract: First and second dc linked, preferably voltage sourced, inverters are connected to an electric power transmission line in shunt and in series, respectively, by coupling transformers. Firing of the GTO-thyristors of the first inverter is controlled to regulate reactive power on the transmission line and to supply real power requirements of the second inverter. The second inverter is controlled to inject into the transmission line in series a voltage which can be adjusted in magnitude and from zero through 360 degrees in phase with respect to the transmission line voltage to selectively adjust any one or more of transmission line voltage magnitude, transmission line impedance and transmission line voltage phase angle.

Abstract: A system and method is provided compensating utility distribution line transients such as voltage sags in a dynamic manner, by inserting a voltage signal in series with the distribution signal having a magnitude and phase to effectively cancel out the voltage deviation caused by a network disturbance. An energy storage device such as a storage capacitor is used to provide energy to an inverter circuit which is controlled to generate the series-inserted signal. Preferably a converter such as a chopper is utilized between the storage element and the inverter, to provide a constant dc input to the inverter. A controller generates a corrective error signal based upon the deviation between the utility supply voltage as affected by the disturbance, and the nominal ideal voltage signal, and adjusts the insertion voltage so as to optimize real power delivery to the utility distribution line.

Abstract: A fault current surge bypassing and transitional impedance compensation system for preventing subsynchronous currents on electrical power lines, with parallel lines being protected from the clearing of transient faults. Capacitor banks serve as only a partial solution to the disturbances with transient faults during conventional recovery modes of operation. The fault current bypassing and impedance compensation system, coupled in series to each transmission line, clears a transmission line fault current and dynamically balances the inductor impedance on the transmission line after the fault mode clears when a return is made to the normal mode of operation. A circuit based solid-state switching power converter or "voltage-sourced inverter" with self-commutating GTO semiconductor switches is used, having all GTOs switched-on and maintained in this condition for the fault current to pass.

Abstract: 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.degree.) with respect to the transmission line voltage and current components.

Abstract: An apparatus and method for reducing certain harmonics in the output of static inverters. Static inverters which employ a switching device arranged in a bridge circuit to convert direct current power to alternating current power produce undesired harmonics in the output of the inverter. Harmonic neutralization techniques are further improved by the invention utilizing selective notching of the inverter pole voltage and a coordinate phase shift between the set of pole voltages produced by the individual inverters. The notch angles in the individual pole voltage outputs are chosen to minimize or eliminate specific undesired harmonics.

Abstract: A current fed unrestricted frequency converter (UFC) for supplying power with balanced voltages to a three-phase unbalanced load generates two sets of existence functions for controlling the switching matrices of the UFC to generate positive and negative sequence current components in the load. Existence function generators generating the positive and negative sequence existence functions are phase locked, respectively, to a positive sequence reference signal generated by a clock and a negative sequence reference signal derived by circuits which monitor the negative sequence voltage in the load. Select circuits alternately gate the positive and negative sequence existence functions to the UFC switching matrices in proportion to the detected magnitude of the negative sequence voltage in a sense to drive the negative sequence voltage in the load to zero.

Abstract: In a current-source GTO converter, protection against a DC fault or a commutation fault condition is provided by immediately interrupting the conduction of a GTO device which is ON and by turning ON another GTO device to allow fault current to bypass the bridge or safely pass through the bridge. As a result, protective action is immediate and an early recovery is made possible. Bypassing of the bridge is done by freewheeling, with an auxiliary GTO switch or with one of the main GTO switches. Diversionary action is done through the bridge by changing the mode of operation of the bridge from rectifier to inversion, or conversely.

Abstract: To a static VAR generator of the split reactor type, a scaled down model is associated to be controlled concurrently with the static switches of the split reactor and to generate under proportional line voltage a simulated reactive current which is matched with the actual reactive current to detect a flashover across one of the two halves of the split reactor.

Abstract: In a static VAR generator for providing reactive power compensation to an ac network and including a thyristor-switched capacitor bank having the series combination of a capacitor, a bidirectional thyristor switch having gate drive, and a current limiting inductor with an applied voltage appearing across the combination with a current being conducted therethrough, a damping circuit and method for switching the thyristor switch to achieve damping of oscillatory transients generated by the switching of the capacitor in the network, comprising:determining the magnitude and polarity of a voltage difference .DELTA.

Abstract: In a pulse-width modulated unrestricted frequency changer (UFC) the harmonic contents of the input current are minimized by splitting the active time intervals within the fundamental time frame into at least two pulses which are located within such time frame and controlled in width as if individual PWM single-pulse UFC's were controlled having a phase shift between each other so as to eliminate or reduce undesired frequency components. Such elimination or minimization of selected frequency components is used to reduce the size of the lowpass filter at the input of the UFC, namely by allowing a higher cut-off resonance limit.

Abstract: In a static frequency changer controlled by adjusting the time of conduction of the bilateral switching units forming static converters, the time of conduction is split into n time intervals of respective subdurations adding up to be equivalent to the effective time of conduction of the controlled switching unit, and such subdurations are spread and distributed throughout the time period of control of the switching unit both within the original switching pattern of each converter and between the effective times of conduction of the respective converters, thereby to minimize harmonic distortion of the input supply current of the frequency changer.

Abstract: A device is taught for controlling the residual charge on a thyristor switched capacitor. A capacitor is in series circuit relationship with at least two bidirectional back-to-back thyristor switches which are then connected across an AC network. Each back-to-back thyristor combination is shunted by a non-linear clamping device which exhibits a very high resistance below a specified voltage level and a very low resistance above that voltage level. A pulse stretcher and a sequential firing circuit arrangement is used to prolong the conduction of one of the thyristor switches at a time to allow the shunting of its associated clamping device. During an overvoltage condition in the AC network, the residual charge on the capacitor will be limited to the breakdown voltage of the conducting clamping device. A plurality of capacitor, thyristor switch, non-linear clamping device combinations may be utilized in parallel with the AC network.

Abstract: There is provided a static VAR generator employing a bank of series-connected inductors, each inductor being supplied by different secondary taps of a step-down transformer. The voltage rating of each inductor is appropriately decreased so as to make their sum correspond to the supply voltage. All but one of the inductors are controlled by thyristors in an on-off fashion to supply reactive power to the network in incremental steps. One of the thyristors is continuously phase-angle fired in combination with the incremental insertion of the other inductors to vary the VAR output over the full range, but generating harmonics that are proportional only to the continuously controlled inductor.