Study On Active Power Filter Based On Instantaneous Reactive Power

With the wide use of non-linear loads in industry and daily life, grid current wave form distortion is becoming more and more serious, and the harm harmonics do to the grid has become increasingly evident. Passive filter (PF), which is used as a traditional controlling device, has characteristics of simple structure, low cost, high operational reliability, so it is widely used. Active Power Filter (APF), compared with the PF, has several advantages:1) APF is resistant to system impedance;2) in APF, equipments will not be damaged because of overload;3) the APF’s compensation effect is resistant to changing load;4) it is able to compensate reactive power, adjust the load balance and reduce voltage flicker when APF is in harmonics governance at the same time.Based on the structure of active power filter which is widely used currently, a three-phase three-wire voltage active power filter is chose to suppress harmonic current in the grid in this paper.(1) Through analysis the working principle of active filter and the mathematical model of its topology structure, the main circuit parameters are designed, and the overall model of the active filter is given in this article.(2) harmonic detection algorithm based on instantaneous reactive power theory is a harmonic current detection method most studied and most widely used at present, in which, the p-q detection method and ip-iq detection method are the most representative methods. After a detailed analysis of their algorithm principle, the MATLAB simulation software is used to verify the two methods, as a result, the simulation results obtained is consistent with the theoretical analysis. It is demonstrated that the ip-iq detection method is superior to p-q detection method, but there are still some shortcomings.(3) As the instantaneous reactive power theory(ip-iq) is insufficient in harmonic detection under grid voltage unbalanced and distortion circumstances, a new three-phase looked loop based on double synchronous coordinate transform and cross decoupling is proposed in this paper. This method eliminates the second harmonic components; it improves the phase lock precision, and increases the effectiveness of ripple elimination. Compared with harmonic detection simulation result of traditional phase locked loop (SRF-PLL) used in ip-iq method, it shows that the fundamental current distortion can be extracted more by the new phase lock loop (IDDSRF-PLL) has reduced by1.18%and1.42%under grid voltage unbalanced and distortion circumstances, so the loop has better harmonic detection performance.(4) the three-phase three-wire voltage type APF is adopted to control, by analyzing the current tracking control method and the DC side voltage control method, the triangle wave comparison method and the PI regulator are both selected at last. The APF system model is built and researched in MATLAB2011b, and the simulation results proved the real-time characteristic and feasibility of the triangle wave comparison control method and the PI parameter adjustment method. The APF designed in this paper can well suppress harmonics not only when the power grid voltage is sine voltage, but also when there is imbalance, distortion and dynamic load changes in the grid voltage.