Actvie Power Filter Based On Multi-Level Diode-Clamped Circuits And Controls

Active power filter (APF) is one equipment of flexible alternative current transmission systems, which can filter harmonics and reactive power of the loads in real-time. Its dynamic performance is distinctive to suppress the current irush and overvoltage on other electrical devices. Therefore, APF becomes an effective compensator for harmonics filtering and reactive compensating to improve the power quality of the grids.Hoever, the current and voltage capacities of current technology about power electronic devices are limited. The APF appling in high voltage and high capacity is difficult. Nowdays, the multilevel APF has not been widely researched. One solution is adopting diode-clamped multilevel converter (DCMC). This kind of multilevel converter can operated in times higher voltage and capacity than traditional two-level converter, which make it be one focus of power electronics applications. To solve the problems existed in the research field, this thesis will discuss the configuration, operation, and control algorithm of the DCMC-based APF as list below:(1) Firstly the circuit configuration of multilevel APF is gived. Then its mathematical model is setup to analyzed the circuits operation. Moreover, the equivalent circuits in three-phase and dq coordinates are discussed. Based on active/reactive decoupling control, the detection and control algorithm of active, reactive and harmonic current is proposed for a DCMC-based APF. The simulation results validate the discussed circuit model and control algorithm.(2) One kind of indirect harmonic current control in voltage vector space domain is proposed. This algorithm predeterminate the output harmonic and transfer the current reference to the voltage reference. Meanwhile, it is independent of active and reactive power control and can output voltage reference to multilevel space vector pulse-width modulation (SVPWM) directly.(3) A fast algorithm of SVPWM with equalization of dc-link capacitors’voltages is proposed. This algorithm is suiable for fix-point ditigal controller with simplify calculation in αβ coordinate with dc-link voltage balancing in reactive power compensation and harmonic filtering. One kind of inductor-based auxiliary circuits for the voltages equalization of dc-link capacitors is proposed and discussed. The circuits can provide the exchange circuits between dc-link capacitor and auxiliary inducitor.(4) A small-scale experimental five-level DCMC-based APF is built and tested. The full digital controller is coded and designed. Finally, the experimental results show the steady-state and dynamic performance of the multilevel APF in voltage equalization, reactive compensation and harmonic filtering.