The Research Of Shunt Three-phase Four-wire APF Harmonic Detection And Control

With advances in power electronics technology, a variety of non-linear loads andpower electronic devices appear in people’s daily lives. However, the use of non-linearloads and power electronic devices produce harmonic and reactive current. Once theseharmonic currents and reactive current inject into the grid, and this situationendangers the safety operation of the power system. With the extensive application ofelectrical installations, the pollution from the utility grid is also increasinglyintensified. Therefore, inhibited harmonics in the grid, and improved the quality of theutility grid become the primary task of the current governance harmonic pollutionproblem.Active power filter is a new type of harmonic compensation device. It not onlycan quickly compensate harmonics caused by electronic devices, but also be able toquickly compensate the real-time changing reactive current. Its developmentprospects are very bright.The study object in this paper is a three-phase four-leg active power filter. Thispaper focuses on the analysis about harmonic current detection and current trackingcontrol. In harmonic-current detection part, the three-phase instantaneous reactivepower theory is firstly introduced in detail, and then, the instantaneous reactive powertheory based d-q-0harmonic detection method is designed. The simulativeexperiments on the symmetry and asymmetry of the three-phase voltage source wereconducted, followed by the comparisons. The simulation results show that the d-q-0detection method is able to quickly and accurately detect the harmonic and reactivecomponent of the load current, and not affected by the change of grid voltage. Inaddition, based on sliding window iterative method, a low-pass filter is designed andsimulation results indicated that has the good performance. In the part of currenttracking control, this paper first analyses the conventional integral PI control method.The simulative experiments show that the control method can efficiently suppress theharmonic. However, the control effect is not satisfied. Therefore, in this paper wedesign another control method based on the fuzzy recursive integral PI control. In thiscontrol method, the grid current after compensation has been significantly improved,and grid current harmonic content is markedly reduced. The purpose of harmonicsuppression is achieved ant the power quality is improved.