| Ferroalloy submerged arc furnace load has nonlinear characteristics and it often run in a short circuit way so that harmonics are caused. In order to reduce the harm caused by harmonic problem, harmonic suppression is necessary. Harmonic suppression can be carried out only when the harmonic is accurately and real-time detected. Various harmonic detection methods, including analog filtering algorithm, FFT transform, adaptive filter algorithm, instantaneous reactive power method and so on, are analyzed, and those harmonic detecting methods are compared. Through analyzing harmonic characteristics in ferroalloy submerged arc furnace power supply network, a ip-iq method based on instantaneous reactive power theory is proposed for the detection of harmonic in ferroalloy submerged arc furnace power supply network, and several improvements are proposed. In the new algorithm, a multiplier is added in the detecting circuit so thant any sub-harmonic can be detected, while a new variable step-size adaptive filter is used as the low-pass filter in the harmonics detection circuit instead of traditional Butterworth low-pass filter so that the dynamic response speed and accuracy of the harmonic detection are both improved. Through detecting the positive and negative sequence component, harmonic in network with three-phase asymmetric load can be detected. Simulations prove that the proposed harmonic current detection method is correct and effective.The harmonic suppression techniques are also described, and characteristics of the the passive filter and active filter are analyzed. Current control methods of parallel active power filter are researched, and the Hysteresis Current Control mode is chosen as the controlling strategy. At last, based on the above harmonic detection approach and current control method, a three-phase three-line parallel active power filter is developed, and simulation results verify the good compensation characteristics and performance of the method. |
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