Predictive Current Control for an Active Power Filter With LCL-Filter

Voltage source inverter based active power filters are widely used for the compensation of harmonic currents, especially in industrial environments. Loads such as three-phase diode rectifiers, thyristor-based rectifiers or variable-speed drives can cause relevant harmonics up to the 50th order or even higher, depending on the line filter. Usually, the control of the harmonics is either done in multiple rotating frames, where the harmonics appear as dc values, or by resonant controllers in a stationary frame. At this, the calculation effort is rising with the number of harmonics to compensate. In this paper, a predictive current control scheme is presented. It is implemented in addition to common PI current control and used for a three-phase four-wire LCL-filter-based active power filter. Inaccuracies in the model caused by parameter variations are compensated by an additional control structure. Both structures are related only with low computational effort and are not depending on the desired number of the harmonics to compensate. Experimental tests are demonstrating, that both structures individually, and especially the combination of both, are offering a very good behavior in the steady state and in the case of load changes.