A Powerful Control Strategy for High Power Hybrid Active Power Filters to Extraction and Compensation of Dominate Harmonics in HVDC Links

摘要

The HVDC systems that use the highest power nonlinear converters, use the 12-pulse converters in which the 11th and 13th harmonics are the dominate harmonics. In the conventional links, these harmonics are compensated by tuned passive filters. For nonlinear loads beyond 10 MW, the hybrid active power filters are not cost effective due to high bandwidth, high ratting and low efficiency; therefore, the passive filters are typically used for harmonic filtering of high power nonlinear loads. However, the hybrid active power filters that can inject the certain components, don't need to have high bandwidth and have acceptable efficiency. On the other hand, the passive filters compensation characteristics are affected by utility system impedance variations. This paper presents a new control scheme for a shunt hybrid parallel active power filter (HPAF) intended for high power application to meet IEEE 519 recommended harmonic standards. The instantaneous value of those harmonics are extracted separately by abc to dq transformation (SRF) and the active inductor reference voltage which have to be applied to voltage source inverter of hybrid active power filter, are made by active inductance concept. In addition, it controls the dc voltage of the capacitor in the dc side of HPAF. 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 parallel hybrid active filter system are presented. The resultant vectors, which is obtained from control unit, is applied to produce the gating signals of the HAPF converter by space vector modulation (SVM) method.