HYBRID SOLUTIONS FOR IMPROVING PASSIVE FILTER PERFORMANCE IN HIGH-POWER APPLICATIONS

This paper presents a new control scheme for a parallel hybrid active filter system intended for harmonic compensation of large nonlinear lo ads up to 50 MVA, to meet IEEE 519 recommended harmonic standards, The active filter is small rated, 2%-3% of load kilovoltampere rating, Th e control scheme is based on the concept of synthesizing a dynamically variable inductance, and its usefulness is demonstrated for an active filtering application, A synchronous reference frame (SRF) controller implements the dynamically varying negative or positive inductance by generating active filter inverter voltage commands, This variable ind uctance controller parallel hybrid active filter system can selectivel y synthesize multiple ''active inductances'' at dominant harmonic freq uencies without affecting passive filter impedances at all other frequ encies, This controller also provides a ''current limiting'' function to prevent passive filter overloading under ambient harmonic loads and /or supply voltage distortions, Three implementation variations of a p arallel hybrid active filter system are presented, This paper also pro poses the use of power factor correction capacitors as low cost passiv e filters for a parallel hybrid active filter system, which are contro lled to provide either single or multiple tuned harmonic sinks and to increase cost effectiveness for high power applications, Simulation re sults with small rated pulsewidth modulated (PWM) and square-wave acti ve filter inverters validate the proposed variable inductance controll er operation for mistuned passive filters, to provide single and multi ple frequency tuning to achieve harmonic compensation of a 325 kVA har monic load under supply voltage harmonics and ambient harmonic loads.