The Study Of Diode Clamp Three-level Active Power Filter Based On PR-controller

With the development of modern industry, various non-linear loads are widely used to bring convenience to production and life, but large scale introduction of harmonic current sources caused a very serious impact to power quality. As a power electronic device, parallel active power filter can be used to eliminate harmonic currents and compensating reactive power. In particular, active power filter based on multi-level technology, which has advantages of low switching frequency and be fit for high-voltage large-capacity venues, etc., is becoming a research focus.Several key technical of diode clamped three-level active power filter including the switching device modulation strategy, harmonic detection algorithm, PLL technology and current tracking control are analyzed in this thesis.The basic operating principle and debugging strategies of diode clamped three-level active power filter are introduced at first, then neutral voltage unbalance cause is analyzed through topology and switch phasor combination in detail, two elimination of neutral voltage unbalanced approach are given after analysis.Two active power filter harmonic detection methods based on the analysis of instantaneous reactive power theory are introduced, p-q method is applied only under condition that grid voltage is under balanced, and ip-iq method can be applied to the case of the grid voltage distortion. Two software phase-locked loop method of SSRF-SPLL and DDSRF-SPLL are elaborated, their mathematical models are established, the simulation results show that DDSRF-SPLL has a strong adaptability to grid voltage unbalance.Finally, a three-level APF mathematical model is established, and the PI control strategy and PR control strategy are analyzed to show that PR controller can not only track the current without error, but also avoids disturbance from the grid voltage, simulation results of dual-loop control system proved its effectiveness.