Three Phase, Steady-State Static Var generator Filter Design for Power Systems

Abstract

In power systems, the harmonics originating from thyristor switching are usually eliminated by filtering. Exact solutions of voltages and currents for Static VAR Generators (SVG) used in power systems are found using a state variable formulation with time-domain convolution. Each conduction period of delta-connected thyristor- controlled-reactors is a linear circuit. The initial conditions for each piece-wise linear circuit depend on the prior firing sequence of the thyristors. An additional condition is zero initial current through the thyristor when turning on. There are six possible thyristor conduction sequences for every half cycle of the periodic system voltage. An iterative method is used to determine the initial conditions for the first of the six conduction sequences in order to force the system response into periodic operation at the line frequency. State variable transition matrices and initial conditions are then used to calculate circuit, voltages and currents at any instant of time. It is thus possible to obtain peaks or determine harmonic distributions. Unbalanced three phase voltages and component unbalances may be introduced in the circuit using this analysis. Filters, which are capacitive compensation at the line frequency, are then sized to limit harmonic content in the voltage supply.