Research On Current Deadbeat Control Of The Five-level Converter

Multilevel inverters have been widely used in medium-voltage high powerapplications such as high power drive, active filter and flexible AC transmission.Compared with the traditional two levels, multilevel inverters have many advantages:low output voltage harmonic content, low switching frequency, small switch loss andelectromagnetic interference. In this paper the SVPWM algorithm and current controlstrategy of diode-clamped five-level inverter are studied in details. The main researchcontents are as follows:Firstly, the working principle of diode-clamed five-level inverter is presented.This paper presents the basic principle of SVPWM and analyzes the traditionalSVPWM algorithm implementation steps based on two-level inverter. Then the spacevector pulse width modulation strategy of five-level inverter based on g-h coordinatesystem is analyzed. Compared with the traditional SVPWM modulation method thisalgorithm simplifies vectors selecting and functional time calculation as well asavoiding trigonometric function calculations. The simulation and experimental resultsverified the feasibility of the algorithm.Secondly, the current control strategy of vector control system with a five-levelinverter with a permanent magnet synchronous motor (PMSM) load is analyzed. Thealgorithm theory, parameters’ design and the performance of control of twoalgorithms: current PI control and current deadbeat control are analyzed in this paper.The theoretical analysis and simulation results show that the bandwidth of current PIcontrol is restricted and there is a contradiction on its steady-state accuracy andrapidity. Deadbeat control algorithm has fast dynamic response and can achieve nostatic error. However, it high depends on the system parameters, which become itshighest disadvantage. In order to improve this disadvantage, this paper adopts animproved dead beat control algorithm so that the system’s robustness is improved.Besides, the motor torque ripple is reduced.Based on the theoretical analysis of the current control strategy, MATLABsimulation research on the current PI control and current deadbeat control is applied.This paper established a five-level vector control system simulation model, whichtakes the PMSM as load and applies PI control to the speed loop. As for the currentloop, applies PI control strategy and improved deadbeat control strategy respectively.Simulation results show that compared to current PI control strategy, deadbeat control strategy gets smaller torque ripple of the motor as well as ensures a fast response andno static error.Finally, the experimental platform of five-level inverter was completed, and thecontrol system based on TMS320F28335DSP and XC3S400FPGA was designed andthe design parameters of each module were presented. The experimental researches ofcurrent PI control algorithm and current deadbeat control algorithm have beencompleted on the experiment platform. The experiment results and simulation resultsare accordance and this lay a theoretical foundation for applying the deadbeat controlstrategy to the five-level inverter and in practical using.