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Simulation Study of Indirect Current Control Technique for Shunt Active Filter

Solid state control of ac power using thyristors and other semiconductor devices are used extensively in number of applications such as adjustable speed drives (ASD’s), furnaces, computers power supplies and asynchronous ac– dc–ac links. These power converters behave as nonlinear loads to ac supply system and cause harmonic injection, lower power-factor, poor voltage regulation, and utilization of ac network. There is a great need to mitigate these harmonic and reactive current components. Active Power Filters are a viable solution to these problems. In this project work a three-phase shunt active filter is used to eliminate supply current harmonics, correct supply power-factor, and balance the nonlinear/linear loads. A three-phase insulated gate bipolar transistor based current controlled voltage source inverter with a dc bus capacitor is used as an active filter. The firing pulses to the shunt active filter will be generated by using Indirect current control technique. In the indirect control algorithm of the Active filter, the three-phase reference supply currents are obtained using a closed loop PI controller. A Hysterisis PWM current controller is employed over the reference and sensed supply currents to generate gating pulses of IGBT's of the Active filter. But Hysterisis current control having disadvantage like the switching frequency varied during fundamental period, this may be results in increased switching losses and phase angle errors. To overcome problems in the Hysterisis current control, a Ramp-comparator current controller is used. Results of both Hysterisis current control method and Ramp comparator current control method are compared, which shows the Ramp-comparator current control method is better than Hysterisis current control method for harmonic reductions.