Research On Three-phase Voltage-source Three-level PWM Rectifier

In recent years, with the rapid development of electric vehicle industry, the performance of high power off-board charger becomes the key restricting the development of electric vehicles. Rectifying equipments are used during the electric vehicle charging, however, general rectifier equipment will produce a lot of harmonic pollution to the power grid, based on this background, this paper compares the advantages and disadvantages of the switching devices MOSFET and IGBT, design a diode clamped PWM rectifier based on MOSFET as the front end of the charger. In the premise of satisfying the voltage level, high MOSFET switching frequency can make the PWM rectifier to obtain a better performance. Then by comparing and analyzing the control method of PWM rectifier and pulse modulation strategy, the double-closed-loop control method and the space vector modulation technique are selected, which makes the high power off-board charger has the advantages of high power factor and low harmonic content, high efficiency and low noise when the equipment is running.Firstly, based on diode clamped PWM rectifier as the research object, analyzed the working principle of the main circuit topology, established the mathematical model of three-phase static coordinate by defining the switch function, and then deduced the mathematical model in rotating coordinates. The double-closed-loop control method based on feedforward decoupling is designed, which the voltage loop is used to make the DC voltage tracking command voltage and the current loop is used to realize unity power factor sinusoidal current control. Parameters of the current loop and voltage loop control system are designed by deducing the transfer function.Then, the space vector modulation algorithm based on Vα and Vβ is described in detail, which contains the division of the region, region judgment of the reference vector located, reasonable arrangement of vector sequence, the calculation of each vector function time. The problem of narrow pulse width and dead zone time setting which cannot be ignored in reality are also analysised. Aiming at the inherent neutial poingt unbalance problem, a precise control method based on variable ratio factor is selected. The simulation model in the Matlab/Simulink environment is established and the results show that the AC current phase can follow the voltage phase and performs good sinusoidal, DC voltage tracking the instruction voltage stabilized, neutral point potential can be controlled very well.Finally, the hardware and software system of three level PWM rectifier are designed, where the hardware system consists of parameters selection of AC inductance and DC capacitor, design of sampling circuit, conditioning circuit, drive circuit and protection circuit. Software system consists of program writing and debugging. In the end, the experimental prototype is builded, the experiments are carried out. The results showed that the proposed control strategy was feasible and effective.