Westinghouse Electric Corporation

Electric Power Research Institute Incorporated

Siemens Westinghouse Power Corporation

Siemens Power Transmission & Distribution, Inc.

Charles W Edwards

Laszlo Gyugyi

Colin D Schauder

Derek Albert Paice

Miklos Sarkozi

Nicholas C Abi-Samra

Apparatus for injection voltage compensation in series into an electric power line includes an inverter or other controlled voltage source which wye connects the secondary windings of a three-phase transformer to the load end of the electric power line. The transformer, which could already be present for meeting load requirements, has its primary winding connected to the source end of the electric power line and sustains the saturation currents rather than the inverter in response to faults on the source side of the transformer. Preferably, a three-phase inverter with a common dc link is used. For active power line conditioner (APLC) action, a second, also preferably a three-phase, inverter is connected in parallel to the load end of the electric power line and to the common dc link. This parallel inverter provides harmonic and reactive power compensation and also supplies the real power requirements of the wye connection inverter.

Neutral point connected apparatus providing compensation to an AC power

DVRs and APLCs utilize a single transformer for injection of compensating voltages into an ac power line and for drawing power from or exchanging power with the ac power line. The poles of an inverter are connected in series with the wye connected transformer primary winding which is also connected to the source end of the power line. A first secondary winding is connected to the load end of the power line. A rectifier circuit or a power interface inverter in the DVR and APLC, respectively, is connected to a second secondary winding on the transformer. For high pulse numbers, the rectifier circuit or interface inverter can have additional rectifier bridges or inverter poles connected to additional transformer secondary windings phase shifted with respect to each other. The single transformer can be a load transformer already provided in the power line, thereby further reducing the cost of the arrangement.

Line powered, primary side connected apparatus injecting voltage

A power switching apparatus includes a positive-sequence fundamental signal magnitude detector. The positive-sequence fundamental signal magnitude detector derives a positive-sequence fundamental signal from a three-phase voltage signal carried by a power line; it also generates a switch firing command when the positive-sequence fundamental signal exceeds a predetermined threshold value indicative of a fault condition on the power line. The power switching apparatus also includes a solid state switch connected to the power line and the positive-sequence fundamental signal magnitude detector. The solid state switch bloch power on the power line in response to the switch firing command.

Power system switch incorporating a positive-sequence fundamental signal

An apparatus and method of constructing a sinusoidal output signal corresponding to a predetermined harmonic component of a sinusoidal input signal is described. The input signal is multiplied by a specified harmonic component of cosine and sine reference signals to divide it into direct and quadrature signals. The direct and quadrature signals are proportional to the amplitude of the specified harmonic component of the reference signals at the specified phase. Each cycle of the direct and quadrature signals is sampled a number of times to form direct and quadrature signal segments. The direct and quadrature signal segments are respectively placed in direct and quadrature circular buffers. Each circular buffer includes a number of formerly sampled segments. Before adding a new segment, the oldest segment in the buffer is dropped. Direct and quadrature amplitude sums, corresponding to the sum of all sampled segments within the respective circular buffers, are maintained. The buffers act as an averaging or integrating filter for the segment amplitude values. The instantaneous direct and quadrature amplitude sums are respectively re-multiplied by the same specified harmonic component of the cosine and sine reference signals to produce in-phase direct and quadrature fundamental signal components. These signals are then added to form a vector sum constituting a one-cycle delayed output signal which corresponds, in phase and amplitude, to the specified harmonic component of the input signal.

Load current fundamental filter with one cycle response

An apparatus and method of constructing a sinusoidal output signal corresponding to a selected harmonic of a sinusoidal input signal is described. The input signal is deconstructed into direct and quadrature components by respectively multiplying it with a selected harmonic of cosine and sine reference signals. The direct and quadrature components contain orthogonal dc components corresponding to the direct and quadrature magnitudes of the input signal at the selected harmonic frequency. The generated direct and quadrature magnitude values are respectively applied to error amplifiers in accordance with the invention. The outputs of the error amplifiers are respectively multiplied by the selected harmonic component of the sine and cosine reference signals. This provides the proper phase values for the respective quadrature and direct processed signals at the selected harmonic frequency. The processed quadrature and direct signals are then summed to yield an output signal which corresponds to the magnitude and phase values of the selected harmonic of the input signal.

Harmonic controller for an active power line conditioner

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.

Apparatus and method for dynamic voltage restoration of utility

A circuit for producing an output signal representative of the phase angle of a single phase input signal includes a phase shift generator for receiving a single phase input signal and for generating a quadrature signal and a direct signal in response to the single phase input signal, and a phase locked loop coupled to the phase shift generator for generating an output signal in response to the quadrature and direct signals such that the output signal is phase locked with the single phase input signal. A method is also provided for producing an output signal representative of the phase angle of a single phase input signal, comprising the steps of: receiving a single phase input signal; generating a quadrature signal and a direct signal in response to the single phase input signal; and generating an output signal in response to the direct and quadrature signals, such that the output signal is phase locked with the single phase input signal.

Low jitter phase locked loop for single phase applications

A single quadrant chopper timing control circuit is used with unidirectional power flow chopper arrangements in a power inverter to maintain current oscillation between positive and negative threshold levels of a hysteresis controller. The single quadrant chopper timing control circuit creates a mimic current when the current in the power inverter becomes zero or less. The mimic current allows the unidirectional power arrangement to continue oscillating so that there is little or no discontinuity in the timing. The device will continue to operate and provide a high bandwidth to ensure that the device will function during an overload or load dump condition.

Single quadrant chopper timing control circuit for discontinuous current

A two-phase bang-bang current control synchronizer for synchronizing two current streams which pass within a hysteresis controller. Synchronization occurs by summing a fixed hysteresis threshold voltage from a master chopper and a sawtooth wave voltage corresponding to a synchronization and outputting a summed signal to an integrator controller which integrated the summed signal and outputs an intergrates signal. A synchronization circuit receives the integrated signal and generates a sawtooth waveform corresponding to an average value of the fixed hysteresis threshold voltage. The sawtooth waveform is fed to the slave chopper and synchronizes the master chopper and the slave chopper.

Two-phase bang-bang current control synchronizer

In an AC/DC converter, the dissipation voltage sharing resistors commonly placed in parallel with the series capacitors are replaced by a resistor balancing path derived from the capacitor junction point to a symmetrically disposed voltage reference point belonging to the AC input vectorial system.

Low dissipation capacitor voltage sharing circuit for a static AC/DC

Low voltage GTO inverter modules are combined to form a high-voltage multi-inverter system by connecting standard modules in a string with isolated DC links. Modular construction is arranged for building multiphase systems. Voltage control is effected by controlling selected modules on the DC sides, or by pulse-width modulation of the inverter of a selected module.

High voltage modular inverter and control system thereof

In a multi-inverter system, inverters in series are swapped around in order to eliminate regenerative power due to phase difference between consecutive inverters in series.

Multi-inverter control apparatus

Transistors or GTO's of an inverter are switched ON/OFF with a delay circuit which has a capacitor first charged at a forcing rate, then, held at an intermediary level, and which is first discharged at a forcing rate, then held at an intermediary level, thereby to provide underlap, minimum ON and OFF time control and noise filtering with a high precision.

Delay circuit for inverter switches

Motor control apparatus for controlling the speed of a motor as a function of a variable frequency square wave and chopping pulses. The chopping pulses are cut off at some value greater than zero pulse width which causes motor voltage to increase in a step manner thus causing a feed forward voltage signal which is related to a DC rectified voltage which cooperates with the square wave production system to increase accordingly. A hysteresis circuit is provided within the pulse generating means to guarantee that once the pulse generation has stopped it will not increase again as a result of the aforementioned motor voltage rise.

Inverter system with hysteresis transition between pulse width

A pulse-width-modulated motor drive includes means for the derivation of a signal representative of the torque by sensing the DC-link current directly, or indirectly, and by dividing the sensed signal by the modulation index of the motor drive to obtain proportionality through the duty-cycle long range succession.

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Monroeville, PA, United States of America

Charles W Edwards