An Algorithm Of Instantaneous Harmonic Detection In Three-phase Circuit

With the rapid development of non-linear loads, the voltage and the current waveform is seriously distorted as a mass of harmonic and inter-harmonics poured in the power system. The active power filter (APF) is an important equipment to compensate harmonic and reactive power in power system and it is a key component of APF to detect the harmonic. The purpose of harmonic detection is compensation for the reactive power and harmonic currents as well as the diagnosis of default and protection. The former needs to detect the fundamental active, reactive current and the whole of harmonic current or voltage accurately,the latter need to detect the random harmonic current or voltage.Methods based in instantaneous reactive power are the most continual and successful. But the methods are only used for harmonic current detection, such as: the detection for fundamental active, reactive current and the whole of harmonic current. When it comes to random harmonic and voltage detection, the method seems useless. This paper discusses the instantaneous reactive power theory in three-phase, single-phase and three phase four wire system respectively. At the basis of analyzing present methods about harmonic voltage detection, a novel method for random harmonic voltage detection based on double d-q transformation and triangle transformation is presented, in which the unit of phase-lock loop is substituted by presetting the frequency of the double d-q transformation matrix. A forecasting algorithm in the detecting method is added for compensating the delays caused by the digital controller and inverter. The proposed method is not affected by such factors as the disequilibrium of both amplitudes and initial phase of three-phase voltages, voltage distortion.