Abstract: A method and apparatus for controlling a battery energy storage system of the type in which an inverter is coupled to convert direct current power from a DC source to a controlled frequency AC power suitable for supplementing utility power or for replacing utility power includes a control mechanism for operating the system and either a supplemental or replacement mode in parallel with a utility power system. The system favors frequency control over power control and maintains constant monitoring of frequency output with adjustment of power in response to any frequency shift of the inverter output. The system also includes apparatus for determining a power error signal based upon commanded power output in which the power error signal is applied as a phase shift control signal in the frequency control circuit for regulating the real component of power supplied by the inverter.

Abstract: A hydroelectric power generation system (20) generates electrical power for an electrical utilization system (72). A controller (42) obtains a requested output electrical power level from a hydro-turbine unit (70) by using a signal indicative of water head (h.sub.meas) to control speed of an asynchronous rotary converter (50) coupled to the hydro-turbine unit and to control gate position of the hydro-turbine unit. The requested output electrical power level is applied from the hydro-turbine unit via the rotary converter to the electrical utilization system. In one embodiment, the controller (42B) accesses an updatable memory wherein Hydraulic Hill Chart information is stored. In another embodiment, the controller (42C) also includes a real-time automatic governor which uses a signal indicative of ac transmission frequency to the electrical utilization system to control the output electrical power level of the rotary converter.

Abstract: A hybrid active power filter having programmed impedance characteristics is presented. In accordance with which, a passive device comprising a capacitor C.sub.F is connected in series with an active device which are together connected in shunt with a power source and a load at transmission lines of a power system. Capacitor C.sub.F substantially supports the full-line voltage V.sub.H of the power source, whereby the active filter is exposed to a substantially lower voltage than the line voltage V.sub.H. The active device includes an active filter, i.e., an inverter current regulator with a programmable controller for executing a control algorithm. The controller of the active device receives signals corresponding to a voltage V.sub.M, at the low side of filter capacitor C.sub.F. Voltage V.sub.M is at a substantially lower voltage than the line voltage V.sub.H, whereby the cost of sensing voltage V.sub.M is significantly less than sensing the high line voltage V.sub.H.

Abstract: An active power line conditioner circuit having a series compensation system arrangement utilizes a transformer-coupled three-phase voltage-source inverter. A conventional metal oxide varistor (MOV) and bypass breaker combination are provided on the line side of the coupling transformer. A solid-state thyristor shorting ("crowbar") switch is provided on the secondary side of the coupling transformer across the outputs of the three-phase voltage-source inverter (VSI). The crowbar switch circuitry utilizes a diode bridge with a thyristor on the dc side of the bridge resulting in the simplification that only one active device need be gated. Crowbar switching logic activates the crowbar switch based on the exceeding of a threshold voltage measured at the dc power source link to the voltage-source inverter. A direct measure of dc source link voltage is employed to determine when to trigger the conduction of the crowbar thyristor switch.

Abstract: A metal oxide varistor in series with a semiconductor switch forms a protection circuit that reduces the steady-state voltage across the metal oxide varistor during normal operation, During an overvoltage transient condition, the semiconductor switch is gated on and the metal oxide varistor is placed in the voltage clamping mode.

Abstract: An overload management system is provided, including a method and an apparatus, for controlling the operation of electrical equipment in a short-term overload region above the equipment's continuous capability operation curve, without suffering significant loss of equipment life. This overload management system is particularly beneficial for use with equipment having load management capability, such as a modular thyristor controlled series capacitor (TCSC) system using phase controlled firing based on monitored capacitor voltage and line current. For vernier operation, the system predicts an upcoming firing angle for switching a switching device to govern the current received by the electrical device, such as to bypass line current around a series capacitor of the TCSC system. The overload management system may serve as one of several higher-level controllers providing input to a vernier controller for accommodating competing objectives of various system demands.

Abstract: A voltage regulator regulates the voltage a static VAR compensator (SVC) supplies to a power supply network. An SVC status detector detects the conducting status of the SVC thyristors and generates the measured SVC susceptance in accordance with that conduction status. A calculator calculates a representative voltage, (i.e. the Thevenin equivalent), of the power supply network based on the measured SVC susceptance, measured SVC voltage, and an estimate of the power supply network's equivalent reactance. An ordered susceptance to be provided by the SVC to maintain the SVC voltage at a desired level is predicted based on the calculated voltage. A firing control unit receives the predicted susceptance value and calculates drive signals for controlling thyristors in the SVC. The equivalent reactance is initially estimated, and thereafter, it is modified automatically to track and compensate for large disturbances in the power transmission network.

Abstract: A firing controlled scheme including a method and apparatus for vernier operation of a shunt-connected thyristor-controlled capacitor (STCC) uses phase controlled firing of the thyristors based on monitored line voltage, monitored thyristor current, and a thyristor current command to vary the effective reactance of the capacitor. The STCC includes a capacitor and surge inductor connected in shunt across a power transmission line via a thyristor switch. A vernier controller predicts an upcoming firing angle based on the above parameters and switches the thyristor circuit to partially conduct pulses of thyristor current at different amplitude levels depending upon the commanded firing angle. By varying the firing angle, variable inductive and capacitive reactive power can be selectively delivered to the transmission line.

Abstract: A modular thyristor controlled series capacitor (TCSC) system, including a method and apparatus, uses phase controlled firing based on monitored capacitor voltage and line current. For vernier operation, the TCSC system predicts an upcoming firing angle for switching a thyristor controlled commutating circuit to bypass line current around a series capacitor. Each bypass current pulse changes the capacitor voltage proportionally to the integrated value of the current pulse. The TCSC system promptly responds to an offset command from a higher-level controller to control bypass thyristor duty to minimize thyristor damage, and to prevent capacitor voltage drift during line current disturbances. In a multi-module TCSC system, the higher level controller accommodates competing objectives of various system demands, including minimizing losses in scheduling control, stabilizing transients, damping subsynchronous resonance (SSR) oscillations, damping direct current (DC) offset, and damping power-swings.

Abstract: A static VAR compensator (11) is connected across a power transmission line (10) and includes a capacitor (12) connected to transmission line (10). The static VAR compensator (11) includes a capacitor (12) connected to the AC transmission line (10) and thyristor switches (18, 22) for controllably switching the capacitor (12) across the transmission line (10). The thyristors (18, 22) are fired based on signals generated by control circuitry (26, 28, 30). A substantially constant or DC voltage exists across the capacitor (12) after the thyristor switches have been turned-off. Discharge control circuitry (30) generates firing pulses to activate the thyristor switches (18, 22) in order to discharge the capacitor (12) and reduce the voltage across the capacitor (12) to zero. In one embodiment, the capacitor (12) is discharged gradually using a series of discharge pulses.

Abstract: A thyristor controlled series capacitor (TCSC) system, including a method and apparatus, uses phase controlled firing based on monitored capacitor voltage and line current. For vernier operation, the TCSC system predicts an upcoming firing angle for switching a thyristor controlled commutating circuit to bypass line current around a series capacitor. Each bypass current pulse changes the capacitor voltage proportionally to the integrated value of the current pulse. To damp the natural oscillatory response of the inductive commutating circuit and the capacitor, a bypass mode firing angle is introduced to create a nonlinear response. The harmonic distortion on the commutating circuit current waveform is determined from the capacitor voltage, which is then used to determine the magnitude of the firing angle. Preferably the firing angle magnitude decreases in response to decreasing capacitor voltage, eventually returning to steady-state conditions.

Abstract: A subsynchronous resonance mitigation system, including a method and apparatus, for damping undesirable subsynchronous resonance oscillations in a generator, which, if left unchecked, may damage the shafts of a turbine-generator set. A remote coupling apparatus, such as a thyristor controlled series capacitor (TCSC) system, a sourced inverter device, or a static phase shifter, is coupled to the generator by a transmission line. In response to a firing command, the coupling apparatus introduces subsynchronous resonance mitigating currents into the transmission line. Sensors monitor power line parameters and/or the generator speed, and in response thereto, a higher-level controller generates a voltage command. A vernier controller responds to the monitored power line parameters and the voltage command to provide the firing command to the coupling apparatus.

Abstract: A firing control scheme, including a method and apparatus, for secure vernier operation of a thyristor controlled series capacitor (TCSC) in series with a transmission line uses phase controlled firing based on monitored capacitor voltage and line current. The TCSC system has a thyristor switched inductive commutating circuit in parallel with the series capacitor. Vernier operation of the TCSC system is provided by predicting an upcoming firing angle for switching the commutating circuit to conduct a thyristor bypass current pulse therethrough. The current pulse causes an alternating offset component of voltage to appear across the series capacitor, in addition to the normal voltage component. Each current pulse changes the capacitor voltage proportionally to the integrated value of the current pulse.

Abstract: A dynamic braking system resistor for stabilizing a power system during power system disturbances includes a braking resistor for coupling with a power system bus. A controller monitors a power system parameter, such as the speed of a generator coupled with the power system bus, and determine therefrom a thyristor control signal. The controller uses the power system parameter to establish a desired modulation and then provides a bias to the desired modulation. The controller conditions the biased desired modulation signal to provide the thyristor control signal. A thyristor valve responsive to the thyristor control signal couples the braking resistor with a ground potential. A method is also provided of damping subsequent oscillations on a power system following a power system disturbance using the dynamic braking resistor.

Abstract: A faster, more controllable phase-shifting transformer system is provided, along with a method of retrofitting and upgrading a preexisting system for faster operation, and a method of applying a desired phase shift to the voltage on a polyphase transmission line. A phase-shifting transformer set has series and regulating transformers coupled together by a switching network, An optional modulator modulates the phase shift voltage about a nominal level established by the switching network. The modulator may be a variable susceptance switched inductor or a switched capacitor, or a variable source device, such as a voltage source inverter device or a synchronous condenser. A thyristor augmented switching network may have a pair of thyristor valves augmenting a reversing switch, or a thyristor augmented load tap changer for varying the phase shift discreet step magnitude.

Abstract: An improved control system for static volt ampere reactance compensator provides for a transformation of the three phases into a two-variable system which thus isolates any common mode in the associated delta. Improved control is provided by utilizing the flux change as an advance indication of a disturbance. Lastly, the two-variable system, as it is inverse transformed into a three variable system, has its phasors rotated to prevent oscillation.

Abstract: A negative sequence occurring in a polyphase power system control including a continuous wave frequency transducer causes a second harmonic to be generated which for a 60 Hz system comprises a 120 Hz signal. In a preferred embodiment of the invention, the continuous wave frequency transducer includes an active 120 Hz notch filter having one stage which provides a component of the 120 Hz second harmonic. This signal is coupled to a second harmonic detector implemented by a semiconductor diode connected to the output of an operational amplifier. The detector diode is coupled to one input of a comparator circuit whose other input is coupled to a selectable DC reference signal. The comparator operates to generate a fault indicating signal indicative of a negative sequence when the output from the second harmonic detector exceeds the reference.

Abstract: A voltage source is connected in series with the neutral secondary winding on a generator step-up transformer through an electrical reactance. A control circuit and a pair of thyristor banks are employed to apply the voltage source to the transformer winding to dampen sybsynchronous resonance currents and to prevent torsional mode vibrations from occurring within the generator.