Subharmonic detection method suitable for APF (Active Power Filter) under load unbalance system
A technology of unbalanced load and sub-harmonics, applied in measurement devices, spectrum analysis, measurement of electrical variables, etc., can solve the problems of unbalanced load active power filter compensation and inaccurate detection results, etc. Achieve the effects of advanced prediction, accurate detection results, and diverse detection data
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specific Embodiment approach 1
[0023] Specific implementation mode 1. Combination figure 1 Describe this specific implementation mode, a sub-harmonic detection method applicable to APF under a load unbalanced system described in this specific implementation mode includes the following steps:
[0024] Step 1. The three-phase voltage e of the common points A, B and C of the APF output terminal a 、e b 、e c Phase-locked by the phase-locked loop PLL to obtain the fundamental phase ωt of the A-phase voltage, so as to obtain the unit sine signal sinωt and unit cosine signal cosωt in the same phase as the A-phase voltage of the three-phase AC grid voltage, and at the same time, form any h-order harmonic The reference phase hωt of the wave, and the sine signal sinhωt and cosine signal coshωt of any h harmonic;
[0025] Step 2. Input current i of phase A of the three-phase nonlinear load La , Phase B input current i Lb and C-phase input current i Lc The load three-phase current i in the αβ coordinates is obtain...
specific Embodiment approach 2
[0034] Embodiment 2. The difference between this embodiment and the sub-harmonic detection method applicable to APF under a load unbalanced system described in Embodiment 1 is that, among any h-th harmonics, for positive sequence harmonics wave, h=3k+1; for negative sequence harmonics, h=3k-1, where k is a natural number.
specific Embodiment approach 3
[0035] Specific Embodiment 3. The difference between this specific embodiment and the sub-harmonic detection method applicable to APF under a load unbalanced system described in specific embodiment 1 is that the A-phase input current i of the three-phase nonlinear load La , Phase B input current i Lb and C-phase input current i Lc The expressions are respectively:
[0036]
[0037] When h=3k+1, the sequence of the three-phase harmonic phase sequence is 120° lagging behind ABC in sequence, which is the positive sequence harmonic; when h=3k-1, the phase sequence sequence of the three-phase harmonics is 120° lagging behind ACB in sequence , which is the negative sequence harmonic; when h=3k, the amplitude and phase of the three-phase harmonic are equal, that is, the zero sequence harmonic, is the initial phase of the hth harmonic, I h is the current amplitude of the hth harmonic.
[0038] In a three-phase unbalanced system, the current can be expressed as the sum of the c...
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