Circuit and method for controlling reactive load currents of a three-phase system
First Claim
1. Circuit assembly for compensating and balancing rapidly variable reactive currents of loads connected to a three-phase network, the circuit assembly having compensation control element in the form of three converters with forced commutation connected in parallel with the loads of the three-phase network, at least one energy accumulator connected to the d-c side of the converter, and a closed control loop having measuring transformers for the actual values of the currents (iR, iS, iT) of the compensation control elements, measuring transformers for the actual values of the load currents (iRO, iSO, iTO) and measuring transformers for determining the actual values of the voltages (uRS, uST, uTR) between the conductors of the three-phase network, and evaluator means for calculating reference values for the active currents (iWR, iWS, iWT) from the actual values of the voltages (uRS, uST, uTR) and the load currents (iRO, iSO, iTO), said evaluator means including three summers of first current components (iVR, iVS, i.sub. VT) determined instantaneously and means for determining the reference values for the control element currents (iR, iS, iT) from the difference of said current components (iVR, iVS, iVT), and for determining reference values for active currents (iWR, iWS, iWT) from the difference of the reference values and the actual values of the control element currents (iR, iS, iT) which control deviations (xR, xS, xT) for controlling firing pulse formers for the compensation control elements to adjust the waveform of the currents on the three-phase side, comprising(a) said evaluator means being in the form of a conductance measuring converter having an output connected to a fourth summer and an active-current reference value generator connected to said fourth summer for determining, continuously in time, the reference values for the active currents (iWR, iWS, iWT), said conductance measuring transformer being acted upon on the input side thereof by the first current components (iVR, iVS, iVT) and the linked load voltages (uRS, uST, uTR), the active-current reference value generator being additionally acted upon by the linked load voltages (uRS, uST, uTR) and by the output signal of the conductance measuring transformer,(b) capacitors shunted across the loads in all three phases,(c) said energy accumulator being in the form of an additional capacitor and a resonant circuit, said resonant circuit being tuned to twice the network frequency,(d) said control loop comprising means for regulating the mean voltage (Uc) on the d-c side of the compensation control element as well as said evaluator means for controlling the wave-shape of the currents on the three-phase side,(e) said regulating means having an output connected to said fourth summer.
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Abstract
Circuit for controlling reactive currents of a three-phase network, having three converters with forced commutation connected in parallel with the loads of the three-phase network, at least one energy accumulator connected to the d-c side of the converter, and a closed control loop having measuring transformers for input currents of the converter, for the load currents and for the conductor voltages of the network, means for evaluating required compensation currents and means for controlling firing pulse formers for the converters to adjust the waveform of the currents on the three-phase side, including capacitors shunted across the loads in three phases, the compensation control element being a three-phase four-quadrant control element, the energy accumulator being an additional capacitor and a resonant circuit tuned to twice the network frequency, the resonant circuit being connected in parallel to the additional capacitor, the control loop including means for controlling the mean voltage on the d-c side of the four-quadrant control device, a conductance measuring converter connected to the measuring transformers for the load currents and an active-current reference-value generator connected to the conductance measuring converter.
9 Citations
12 Claims
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1. Circuit assembly for compensating and balancing rapidly variable reactive currents of loads connected to a three-phase network, the circuit assembly having compensation control element in the form of three converters with forced commutation connected in parallel with the loads of the three-phase network, at least one energy accumulator connected to the d-c side of the converter, and a closed control loop having measuring transformers for the actual values of the currents (iR, iS, iT) of the compensation control elements, measuring transformers for the actual values of the load currents (iRO, iSO, iTO) and measuring transformers for determining the actual values of the voltages (uRS, uST, uTR) between the conductors of the three-phase network, and evaluator means for calculating reference values for the active currents (iWR, iWS, iWT) from the actual values of the voltages (uRS, uST, uTR) and the load currents (iRO, iSO, iTO), said evaluator means including three summers of first current components (iVR, iVS, i.sub. VT) determined instantaneously and means for determining the reference values for the control element currents (iR, iS, iT) from the difference of said current components (iVR, iVS, iVT), and for determining reference values for active currents (iWR, iWS, iWT) from the difference of the reference values and the actual values of the control element currents (iR, iS, iT) which control deviations (xR, xS, xT) for controlling firing pulse formers for the compensation control elements to adjust the waveform of the currents on the three-phase side, comprising
(a) said evaluator means being in the form of a conductance measuring converter having an output connected to a fourth summer and an active-current reference value generator connected to said fourth summer for determining, continuously in time, the reference values for the active currents (iWR, iWS, iWT), said conductance measuring transformer being acted upon on the input side thereof by the first current components (iVR, iVS, iVT) and the linked load voltages (uRS, uST, uTR), the active-current reference value generator being additionally acted upon by the linked load voltages (uRS, uST, uTR) and by the output signal of the conductance measuring transformer, (b) capacitors shunted across the loads in all three phases, (c) said energy accumulator being in the form of an additional capacitor and a resonant circuit, said resonant circuit being tuned to twice the network frequency, (d) said control loop comprising means for regulating the mean voltage (Uc) on the d-c side of the compensation control element as well as said evaluator means for controlling the wave-shape of the currents on the three-phase side, (e) said regulating means having an output connected to said fourth summer.
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6. Measured-value converter for a circuit arrangement for compensating and balancing rapidly variable reactive currents of loads connected to three-phase system for determining a component of, or a component proportional to a periodically oscillating electrical reference quantity, and a component from the group of a voltage and a cuurent (i) in accordance with the equation:
- ##EQU19## where iw =active component of the current,
T=period of the reference quantity, of the voltages U=r.m.s. value of the voltage, t=time, and having at least one multiplier on the input side for forming the product of the current and the reference quantity, a dead time member with a signal propogation time equal to the period (T), and at least one integrator, comprising said integrator having controlled resettability, the input of said integrator being connected to the output of said multiplier, so as to sum the output variables, said integrator being resettable after each period (T) to a defined value, a sample-and-hold member operating with the same period (T), the inputs of said dead time member and said sample-and-hold member being jointly connected to the output of said integrator, said sample-and-hold member storing the output variable of said integrator before said integrator is reset, and including at least one summer and another multiplier having first and second inputs, the outputs of said sample-and-hold member, said integrator and the inverted output of said dead time member, are jointly connected to the inputs of said summer, the output of said summer being connected to a first input of said other multiplier the periodic reference quantity being connected to the second input of said multiplier. - View Dependent Claims (7, 8, 9, 10, 11, 12)
- ##EQU19## where iw =active component of the current,
Specification