Design And Control Algorithm Study On Diode-Clamped Multilevel Converter-Based Shunt Active Power Filter

As the application of power electronic technology becomes more and more widely. Various power converters generate large amount of harmonics to the power grid while operating. The harmonics seriously affect the power quality of modern power grid. In order to solve the problem of harmonic pollution in power grid, passive LC filter was mainly adopted to suppress the harmonics in the early period. Due to its poor real-time compensation ability when current changes, the passive filter and is gradually replaced by active power filter (APF). For the issue of control algorithms and topologies of diode-clamped multilevel APF, the following work is carried on in this paper.At first, the topology, compensation effect and applicable occasion of different types of APF are introduced. On the basis of reactive power theory, p/q-based and ip/iq-based detection algorithms are expounded. Detection accuracy and harmonic compensation effect for reactive and harmonic current of the two comparison algorithms are theoretically analyzed when the power grid voltage is fluctuated. On the basis of ip/iq-based detection algorithm, two-level APF model using hysteresis current control method is built, so as to verify its effectiveness for filtering the harmonics.Secondly, the circuit topology and operating principle of three-level APF are discussed. The predictive current control method is adapted. The neutral voltage imbalance problem in three-level converter is analyzed and the auxiliary equalizing circuit is used. Two-level and three-level APF prototypes based on predictive current control method are constructed respectively, in order to the feasibility of predictive current control algorithm.All control algorithms are coded by Verilog HDL programming language and are realized on FPGA. A small prototypes of two-level APF based on hysteresis current control, two-level APF based on predictive current control method and three-level APF based on predictive current control method are built. The experimental results of harmonic filtering are proposed to verify the static and dynamic performances of the proposed APF system.