Research On The Digital Control Algorithm Of The Current Loop Based The Three Level Active Power Filter

With the wide use of all kinds of nonlinear loads, power quality problems is urgent and need to be solved instantly. The Neutral-Point Clamped active power filter(APF) with 3-phase 4-wire structure, because of the dynamic harmonic current compensation, reactive current compensation, adjusting unbalanced currents and other functions, has became one of the ideal solutions to solve the problem of power quality. In this paper, regard the Neutral-Point Clamped active power filter with 3-phase 4-wire structure as the research object, this paper focuses on the current loop digital control technology, and mainly completed the following work:First of all, the introduction of the working principle of the Neutral-Point Clamped active power filter with 3-phase 4-wire structure, is conducted in this paper. The mathematical models for the continuous domain of the APF current loop are built respectively based on single inductor topology, LCL topology with resonant circuit. The influence of digital process on continuous domain model of the controlled object, has been carried on the analysis.Then, this paper introduces the basic principle of the deadbeat control, and introduces the design method of the deadbeat control based on repetitive current prediction applyed to the APF current loop control. In order to solve the problem of bad performance of the traditional deadbeat control algorithm in the one step delay control system, this paper put forward a new deadbeat control algorithm based on repetitive current prediction and State observer. The simulation results show that the new deadbeat control algorithm can still maintain good control effect in the one step delay control system.Then, this paper introduces the basic principle of resonant control, and introduces in detail the resonant controller design method applied to APF current loop. According to the bad performance of the traditional resonant control while the grid frequency widely fluctuated, this paper put forward a new resonant control algorithm with wide range adaptability on power grid frequency fluctuation. The simulation results show that the new resonant control algorithm can still maintain good control effect while the grid frequency widely fluctuated.Finally, this paper introduces the basic principle of repetitive control, and introduces in detail the repetitive controller design method applied to APF current loop. According to the bad performance of the traditional repetitive control while the grid frequency widely fluctuated, this paper put forward a new repetitive control algorithm with wide range adaptability on power grid frequency fluctuation. The simulation results show that the new repetitive control algorithm can still maintain good control effect while the grid frequency widely fluctuated.