Research And Application Of Diode Clamped Three-level APF

With the development of the increasing scale of distribution network and industrial technology,The types of load in the low voltage distribution network are becoming more and more complex and the application of high-power nonlinear loads becomes more and more popular,which leads to the problem of voltage and current fluctuations and distortion which effects the quality of electric energy.Active power filter(APF),as an important harmonic compensation device,has been widely studied and applied at home and abroad.In order to improve the withstand voltage level and compensation capability of APF to be applied to high voltage and high power applications,the diode clamped three level power converter is used as the main circuit structure of APF.Firstly,the main circuit structure of diode clamped three level APF is analyzed.The APF mathematical model is set up in the three-phase static coordinate,and through coordinate transformation the mathematical model is also set up in dq synchronous rotating coordinate.Secondly,the harmonic detection method based on the theory of FBD are studied.The influence of voltage distortion and LPF on FBD is introduced,and the shortcomings of traditional FBD harmonic detection method are pointed out.An improved method of SRFPLL+ mean filter is studied.Finally,the simulation model is built based on the Matlab simulation tool,and the two FBD harmonic detection methods are compared and analyzed to verify the correctness of the improved method.The principle of the three-level SVPWM control strategy is analyzed.The three level SVPWM control strategy is converted into two-level SVPWM control strategy by coordinate transformation.And the simplified two level SVPWM algorithm is applied to the three level SVPWM,which greatly simplifies the operation process.And the influence of different vectors on neutral point is analyzed,and then the neutral point voltage is controlled by adjusting the effect time of small vectors.Finally,the simulation model is build,which proves the correctness of the control strategy of the neutral point potential.Then,the design methods of main circuit parameters such as APF DC side voltage,DC side capacitor and grid connected reactor are analyzed and then set up a simulation platform of diode clamped three level APF to verify the compensation effect of APF.A diode clamped three-level APF test platform is built based on the DSP+FPGA main control circuit.to verify compensation effect of three level APF by experiment.Finally,the three level APF is applied in engineering practice,and its application effect is analyzed.