Electric Power Research Institute Incorporated

Westinghouse Electric Corporation

Eaton Corporation

Steven A Moran

Michael B Brennen

Laszlo Gyugyi

Colin D Schauder

Scott K Suko

A digital network protector relay samples the polyphase current, network voltage and phasing voltage at 16, and preferably 32, times per cycle so that up to the seventh and fifteenth harmonics, respectively, are eliminated from the sequence calculation used to make trip and close decisions. The relay also provides metering, forward overcurrent protection, and an anti-pumping feature, the latter of which locks the circuit breaker out if a selected number of breaker operations is exceeded during a given time interval. Sequential sampling of the polyphase current and voltages by a single analog to digital converter reduces the cost of the relay. In order to accommodate metering and extraction of the fundamental components of the current and voltages for the sequence calculations, the polyphase current and network voltage are sampled sequentially in a first order for a given number of cycles and then in a second reverse order for the same given number of cycles.

Sequence based network protector relay with forward overcurrent

An improved active power line conditioner is disclosed. A series inverter is controlled by a series filter controller which performs synchronous transformations on a load current to generate a series filter feedforward signal corresponding to the fundamental components of the load current. The series filter controller also generates a series filter reference signal corresponding to a negative sequence fundamental output voltage. The series filter feedforward signal and the series filter reference signal are combined to form a series filter compensation signal. The series filter compensation signal is applied to the series inverter to generate sinusoidal input currents, with negative sequence fundamental output voltage compensation, for a non-linear load. A parallel inverter is controlled by a parallel filter controller which performs synchronous transformations to generate a parallel filter feedforward signal corresponding to the harmonic ripple components of the load current. The parallel filter controller also generates a parallel filter reference signal corresponding to a negative sequence fundamental source current. The parallel filter feedforward signal and the parallel filter reference signal are combined to form a parallel filter compensation signal. The parallel filter compensation signal is applied to the parallel inverter to generate sinusoidal voltages, with source current negative sequence fundamental compensation, for the non-linear load.

Active power line conditioner with fundamental negative sequence

An improved active power line conditioner is disclosed. The active power line conditioner includes a series inverter coupled to an energy input source, and a parallel inverter coupled to a non-linear load. The non-linear load is powered by a three phase load current which includes fundamental components and harmonic components. An energy storage element is electrically connected between the series inverter and the parallel inverter. The series inverter is controlled by a series filter controller which performs synchronous transformations on the load current to generate a series filter feedforward signal corresponding to the fundamental components of the load current. The series filter feedforward signal is applied to the series inverter to generate sinusoidal input currents for the non-linear load. The parallel inverter is controlled by a parallel filter controller which performs synchronous transformations on the load current or series inverter input voltages to generate a parallel filter signal corresponding to the harmonic ripple components of the load current. The parallel filter signal is applied to the parallel inverter to generate sinusoidal voltages for the non-linear load.

Active power line conditioner with synchronous transformation control

An improved active power line conditioner with fast dynamic response is disclosed. The active power line conditioner includes a series inverter coupled to an energy input source, and a parallel inverter coupled to a non-linear load. The non-linear load is powered by a three phase load current which includes fundamental components and harmonic components. An energy storage element is electrically connected between the series inverter and the parallel inverter. The load current fundamental signal is derived and is multiplied by a derived voltage output/input ratio to render a current reference product. The current reference product may be further modified by a user-set displacement power factor correction ratio. The current reference product is applied to the series inverter for fast dynamic response within the active power line conditioner.

Active power line conditioner with a derived load current fundamental

An improved active power line conditioner is disclosed. The active power line conditioner includes a series inverter coupled to an energy input source, and a parallel inverter coupled to a non-linear load. The non-linear load is powered by a load current which includes fundamental components and harmonic components. An energy storage element is electrically connected between the series inverter and the parallel inverter. The parallel inverter is used for current control functions, while the series inverter is used for instantaneous output voltage regulation. In one embodiment of the invention, a parallel current limiter is used for the parallel inverter. The parallel current limiter is fixed to satisfy specified output voltage total harmonic distortion requirements or peak to rms output current ratios in the active power line conditioner. A series current limiter may be used for the series inverter. The series current limiter is set slightly above the peak of the active power line conditioner input current fundamental. This allows the onset of a small intentional peak output voltage distortion that in turn limits excessive nonlinear load peak currents without back feeding of current harmonics into the input supply of the active power line conditioner.

Highly fault tolerant active power line conditioner

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.

Low cost active power line conditioner

A three-phase active filter for connection into a three-phase power distribution system to compensate undesirable harmonic deviations. A converter is electrically connected between the power distribution system and a DC energy storage element. The converter is selectively controlled by control means to effectuate a flow of energy between the system and the storage element to offset the harmonic deviations. To improve the dynamic response of the filter, the control means utilize vector control principles. Specifically, a synchronous fundamental vector of AC energy waveforms in the power distribution system is derived in a rotating reference frame. Fundamental reference signals are then produced in a stationary reference frame which are compared with corresponding actual condition signals. Error signals thus produced are then utilized to operate the converter. To compensate losses in the storage element and inverter, the control means preferably further comprise loss compensation means also utilizing vector control principles.

Three-phase active filter utilizing rotating axis transformation

An electrical control system includes multiple frames of reference in the error path of a controller. In each such frame, a particular chosen component of the error vector appears as a constant vector and is passed through a pure integrator thus acquiring infinite gain. In the steady state, the net error vector can then be forced to have zero content at each of the targeted frequencies (as set by the rotational velocity of the frames of reference). Both parallel and series configuration of the controller are provided, as well as the control methods used by the controllers.

Multiple reference frame controller for active filters and power line

These and other objects are achieved by an improved active power line conditioner in accordance with the invention. The active power line conditioner includes series inverter coupled to an energy input source, and a parallel inverter coupled to a non-linear load. The non-linear load is powered by a load current which includes fundamental components and harmonic components. An energy storage element is electrically connected between the series inverter and the parallel inverter. A fault condition shorting circuit is supplied in accordance with the invention. The fault condition shorting circuit is coupled to a secondary transformer winding within the series inverter. The fault condition shorting circuit includes a diode bridge which conveys diode bridge current only in the presence of an overvoltage or overcurrent condition. A threshold device is connected to the diode bridge and conducts threshold device current in response to the diode bridge current. The circuit also includes a thyristor with its gate coupled to the threshold device. The thyristor is fired by the first threshold device current so as to short the secondary transformer winding in the presence of an overvoltage or overcurrent condition.

Active power line conditioner with low cost surge protection and fast

The present invention pertains to a line voltage regulator for a cable which is electrically connected to at least one load. The line voltage regulator includes a device for producing a cable voltage drop signal that corresponds to a voltage drop across the cable which separates the line voltage regulator and the load. The line voltage regulator also includes a sensor circuit for determining distortion voltage across the cable which separates the power supply and the line voltage regulator and the fundamental frequency signal required for regulation. The sensor circuit produces a drive signal that corresponds to the distortion voltage and the fundamental frequency signal required for regulation. Additionally, there is a device for providing voltage to the cable such that the voltage is regulated and distortion voltage across the cable is essentially eliminated as applied to the load. The device for providing voltage is electrically connected to the sensor circuit and controlled by the drive signal therefrom. The cable voltage drop signal producing device provides the cable voltage drop signal to the sensor circuit. The sensor circuit adds a cable voltage drop signal to the distortion voltage and the fundamental voltage that the sensor circuit has identified and produces the drive signal that is used to control the device for providing voltage to the cable. The voltage providing device provides voltage to the cable such that the voltage in the cable is regulated and distortion voltage in the cable is essentially eliminated as applied to the load.

Line voltage regulator

A circuit for controlling the power dissipated by an electrical resistance coupled to a supply voltage which varies, includes a feedback circuit, coupled to the electrical resistance, for producing a feedback current corresponding to the current flowing through the heater. A correction circuit produces a correction current corresponding to variations in the supply voltage. An integrator receives the correction current and the feedback current and amplifies the error indicated by the correction current and the feedback current. A pulse width modulator receives the amplified error and controls the ON time of a switching device to control the flow of current through the electrical resistance. The flow of current through the electrical resistance is controlled to maintain the power dissipated by the resistance constant.

Circuit for controlling power dissipated by an electrical resistance

The present invention pertains to an AC electrical distribution system. The AC distribution system includes at least one nonlinear load. The nonlinear load causes distortion voltage in the AC distribution system. The AC distribution system also includes a zone filter which provides voltage to the AC distribution system. The AC distribution system can have a first zone which includes a nonlinear load and can have a second zone which includes at least one sensitive load. The zone filter regulates the voltage in the first zone as applied to the second zone and essentially eliminates the distortion voltage in the first zone as applied to the second zone. The zone filter can include a transformer device which provides a voltage to the AC distribution system. There is also a device for supplying power to the transformer device. Additionally, there is a sensor circuit for determining the distortion voltage and a fundamental voltage in the AC distribution system and providing a distortion and fundamental voltage correcting signal to the transformer device. The distortion and fundamental voltage correcting signal controls the transformer device such that the voltage in the first zone is regulated and voltage opposite to the distortion voltage is added to the first zone as applied to or subtracted from the second zone of the AC distribution system.

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Pittsburgh, PA, United States of America

Steven A Moran