Study On The Integrated Compensation Of Harmonic, Reactive And Negative Sequence Currents In Power Systems

Active power filter is an advanced power electronic device, which can be used for integrated compensating harmonic, reactive and negative sequence currents. Compared with some conventional measures, active power filter has many advantages and favorable prospects. Because of the characteristics, real time and accurate compensation, it is possible to take full advantage of digital signal processing, artificial intelligence control and many other technologies. If so, not only can the functions of active power filters be optimized, but also the performances of active power filters can be improved significantly. The principle of power energy flows among active power filter, AC source and nonlinear load is discussed. The factors, which are related with the time delay in the real thne compensation of active power filters, are analyzed systematically. The influences of the delay time on active power filters are investigated in detail. Adaptive linear neural network is used for detecting the distortion currents of nonlinear loads. A detecting method of distortion currents, which is based on adaptive linear neural network for active power filters, under the condition of unbalance and nonlinear loads is proposed, and the analog circuits to realize the method are given. The proposed method, which can be used under the conditions of single-phase and three-phase balanced and nonlinear loads, can be applicable to detect harmonic, reactive and negative sequence currents respectively or the sum of ones. Besides, the proposed method also can be used under the distorted or unbalanced source voltages. On the base of theoretical analysis, some computer simulations and experiments are developed, and the results show that the method has some advantages, such as real time, high accuracy, adaptability to load currents, etc. Many studies on the current control techniques for active power filters are carried out. On the basis of theoretical analysis for the direct current control technique, a new current control technique, the indirect current control technique, is presented. Compared with the direct control technique, the indirect current control technique can make the distortion current detecting circuits simpler and offer better performances. Many studies on the DC link voltage control techniques for the PWM converter circuits of active power filter are developed. On the basis of theoretical analysis for the P1 control technique, fuzzy control is proposed and used for controlling the DC link voltage. The results of computer simulations show that the fuzzy control technique offers better performances, compared with the P1 control technique. Studies on the main circuit, the PWM converter circuit, of active power filter are developed and the calculating methods for the parameters of the power electronic elements and their peripheral circuits are given. The protection measures are also discussed for active power filters. An experimental active power filter with capacity 1 OOkVA is developed, and some experiments of the active power filter are carried out under several conditions. The results of the experiments show that the active power filter has excellent performances and can be used for compensating the harmonic, reactive and negative sequence currents.