Research On Large-Capacity APF Based On A New Root-Mean-Square Harmonic Detection Method

Active power filter is generally recognized as a kind of advanced powerelectronic equipment that dynamically suppresses harmonic and reactive power. Thedetection of harmonic current, follow-up control of compensating current, and theimprovement of APF’s capacity are the three key technologies. This paper studied thekey technologies of APF.Accurate detection of harmonic is the prerequisite to implement compensation.The ip-iq method is widely used. However, its design of low pass filter affects thetransient response. A method of constructing approximately equivalent fundamentalcurrent to extract the harmonic current is proposed. The utilization of load current rootmean square instead its fundamental wave and using phase-locked loop to achieve thefundamental wave phase of load current or grid voltage. In addition, this paper putsforward a relevant DC-link voltage control strategy and analyzes its compensation oferror and real-time effects. Simulation and experiment verified these algorithms.Meanwhile, the compensation current tracking control directly determines theAPF compensation result. Hysteresis has the advantage of simple principle, fastdynamic response, high reliability, and good robustness. Nevertheless, it cannot getsteady switching frequency. This paper applied a new hysteresis current control basedon space-vector-modulation technique, which remains the traditional advantageswhile stabilize switching frequency to some extent. Compared with simulation of thetraditional way, the superiority of the method is confirmed.The under-capacity of APF is another key factor that inhibits APF application inlarge-capacity occasions.Through analysis the advantages and disadvantages oftwo-level and multi-level APF, this study utilizes the method of two-levelmulti-module APF in parallel connection. Through its current sharing, not onlyenlarge its capacity and improve individual efficacy of APF, and facilitating inputinductance type selection. Besides, theoretical analysis is carried out to examine theexistence of circulation between parallel modules. Using MATLAB confirmed theeffectiveness and correctness of the proposed method.Finally, a three parallel-module APF test platform is set up for experimentconfirmation and a part of result is achieved.