SINGLE-PHASE ACTIVE POWER FILTERS FOR MULTIPLE NONLINEAR LOADS

This paper presents active power filters for single-phase systems which are comprised of multiple nonlinear loads, This work is motivated by industrial systems which may include triac-based sc controllers (heaters) and uncontrolled bridge rectifiers (dc equipment) within the same piece of apparatus, The active filter is based on a single-phase inverter with four controllable switches, a standard H-bridge inverter, The ac side of the inverter is connected in parallel with the other nonlinear loads through a filter inductance, The dc side of the inverter is connected to a filter capacitor, The inverter switches are controlled to shape the current through the filter inductor such that the line current is in phase with, and of the same shape as, the input voltage, The controller is based on a conceptually simple sliding-mode control law. The paper provides background on the operation of the filter, the details of the power circuit, the details of the control design, representative waveforms, and spectral performance for a filter which supports a 384 W ac controller and a 900 W uncontrolled bridge rectifier, Experimental data indicate that the active filter typically consumes 3% or less of the average load power, suggesting that a parallel filter is an efficient compensation approach, The spectral performance shows that the active filter brings the system into compliance with IEC-555 for decision frequencies in excess of 30 kHz, A discussion is presented outlining an alternative single-phase active filter which uses two controllable switches and is based on a half-bridge topology.