Research On Harmonic Current Detection Algorithm And Control Technology In Shunt Active Power Filter

Being the fast, potent, and economical control means to industrial devices, extensive use of power electronics technology, however, have also deteriorated power quality by injecting the non-negligible harmonics and reactive current to the network. Active Power Filter (APF) is an efficient, stable and flexible advanced mean for optimizing power's quality, its application will play a significant role in improving the quality of power grid.This paper presents an introduction to the cause and perniciousness of the harmonic current, the harmonic current standard at home and abroad,the ways to-suppress the harmonic current, the classification of APF, and the basic principle of work.The familiar main circuits of shunt APF are three phase three wire APF, split-Capacitor three phase four wire APF, and three phase four leg APF. The mathematical model is the basis of any researches. This paper builds three mathematical models for three main circuits of shunt APF at synchronization rotational coordinate. Although there are coupled currents between d axes and q axes in these models, that the positive sequence component of the fundamental wave is transformed DC is a strong point for control strategy.Double closed-loop control strategies of three main circuits are similar at synchronization rotational coordinate. Three phase three wire APF use Space Vector Pulse Width Modulation (SVPWM) strategy. Split-Capacitor three phase four wire APF use Sinusoidal Pulse Width Modulation (SPWM) strategy. Three phase four leg APF use three-dimensional SVPWM strategy. The difference of the modulation strategy make different DC link voltage usage, that means APF have different compensate ability when DC link voltage is same. What follows is the shortcoming of Split-Capacitor three phase four wire APF in comparison with three phase four leg APF. The distortion of output wave is bigger and DC link voltage usage is lower because of SPWM strategy. Because of the midpoint of capacitor link with zero curve, the compensate current pass through capacitor when APF compensate unbalance current, that will make useful time of capacitor reduce. The strong point of Split-Capacitor three phase four wire APF is this main circuit saves IGBT and output inductance of a leg, and it has same main circuit and control circuit with three phase three wire APF. So it can be applicable three phase three wire system and three phase four wire system by using different software. DC link voltage control is a key technology of shunt APF. DC link voltage reference is designed according to operating space of the Grid voltage, DC link capacitor value, rating output current, output inductance value, current regulator, voltage regulator, and modulation strategy etc. parameters. That will bring the higher designed value of DC link voltage. The higher value will bring the bigger losses of APF. So the value of DC link voltage effects on power losses and compensative ability of APF. This paper introduces a control strategy which uses a drop regulator to regulate the reference value of DC link voltage. When Grid voltage increase, DC link voltage increase by the drop regulator for ensuring compensative ability of APF. When Grid voltage decrease, DC link voltage decrease by the drop regulator for decrease power losses of APF. The drop regulator can realize comprehensive optimization between power losses and compensative ability of APF.Harmonic detection algorithm is an important part of shunt active power filter and significantly affects its filtering characteristics. When the load current is fluctuating, all of harmonic detection algorithms need dynamic response time to track the varied load current and compute the real time harmonic current value. In the dynamic response time, there is error between the computed harmonic current value and the actual harmonic current value. For the different types of harmonic detection algorithms, the error is different. The previous publications are mainly focused on the dynamic response speed and dynamic response time of harmonic detection algorithms and do not analyze the error which will affect the APF system in the dynamic response time. This paper will analyze the error which is caused by computing with the different types of harmonic detection algorithms when the load current is fluctuating and the APF system is working in transient state. Then it moves on to discuss whether the error will affect DC link voltage control.To improve the compensation characteristic and dynamic response of three-phase shunt active power filter (APF), a novel control strategy based on multiple synchronous rotating reference coordinates is proposed. Positive-sequence and negative-sequence harmonic current are both transformed into DC components by respective harmonic synchronous rotating transformation, which are then controlled by proportion-integral (PI) regulators in order to implement zero steady-state error compensation. The complete harmonic current control is realized as the superposition of all individual harmonic controllers. Mathematical model is built based on the harmonic synchronous rotating frame and the combined decoupling control strategy is proposed. Theoretical analysis of harmonic current controller proves that the compensation accuracy is improved compared to the traditional current control of APF. The proposed controller is designed based on the pole-zero cancellation technique. The superiority of the control architecture proposed is verified completely by experimental results.Finally, based on all research above, three prototypes which use three main circuits respectively were realized. On the basis of these prototypes, this paper did a plentiful research on the modulation strategy, harmonic detection algorithm, DC link voltage control, and current regulator. The theories and strategies proposed in this paper are verified completely by experimental results.