Three-phase Imbalance Of Power Quality Problems

With the increasingly diversified of the unbalanced three-phase load, the power system of three-phase unbalance phenomenon gets more and more serious, resulting in an extremely adverse impact on the quality of electricity. In view of this situation, the paper combines compensation algorithm and TCR+FC type static var compensator, phase separation control SVC to compensate the umbalance system. Thus this algorithm could improve the three-phase unbalance condition and enhance system power factor.The paper introduces the harm of three-phase unbalance and formulas of asymmetrie degree of three-phase, and then analyzes the structure and the working principle of TCR-SVC. According to the theory of balance, discusses the three phase of the compensation principle. For different conditions of three-phase three-wire system and three-phase four-wire system, the paper designs the corresponding compensation algorithms.Under the condition of the three-phase three-wire system, proposes the compensation methods based on symmetrical component method and the theory of instantaneous power. According to the proposed algorithm to calculate the three-phase compensating admittance, use the method of rational interpolation to calculate the angle of the trigger delay,and triggered TCR conduction to compensate system. The article respectively uses open-loop and combination of open-loop and closed-loop to control the SVC, which in the closed-loop control using the fuzzy PID controller in order to achieve better compensation effect.Under the conditions of the three-phase four-wire system, through the transformation, the unbalanced load decomposes for asymmetric star-shaped connection forms and triangular connection forms. According to the different loads, put forword to corresponding compensation algorithm, and use the superposition theorem to compensate the system, improving the overall system performance.On the basis of theoretical analysis, builds model simulation with Matlab/Simulik software, to compare these compensation algorithms and two kinds of control mode. The simulik result shows,the designed algorithms and the control modes, could improve the three-phase unbalance condition and enhance system power factor.