Strategy Power Three-level PWM Rectifier

The research of power electronic converter such as PWM rectifier, reactive power compensator and active electric power filter is of great significance for power grid harmonic control and reactive power compensation. The neutral point clamped three-level PWM rectifier is wildly researched and application because it has many advantages such as large capacity, high voltage grade, high equivalent frequency, etc. This paper through researched revolves around the key technology of three-level PWM rectifier.The mathematic model is the basis of analysis of dynamic and steady state performance of three-level PWM rectifier. This paper analyzes the working principle of three-level PWM rectifier, briefly describes the switch state and switching function and the corresponding relation of three-level voltage vector of the neutral point clamped three-level PWM rectifier, set up the average mathematical model of three-level PWM rectifier described by duty ratio, get the DC steady-state model and AC small signal dynamic model of the system through the way of small signal distuibance near the DC working point, and gives out the design instance of system DC working point and the design principle of filter inductance parameters.The three-level neutral-point voltage balance is the basis of the stable operation of three-level PWM rectifier. Aim to the inherent neutral-point fluctuations problem of three-level inverter, this paper proposes a hybrid control strategy of three-level neutral-point voltage balance based on simplified three-level SVPWM. The control strategy clearly clarifies sector selection principle based on the neutral-point voltage offset and three phrase current under low modulation index condition, to overcome the voltage offset caused by non-redundant small vector; in high modulation index condition, it fully considers the impact of the medium vector on the neutral-point voltage offset, sets a different time controlling element for every small triangle, to achieve meticulous control of neutral-point.The effective control of PWM rectifier of grid current is the key technologies to improve the power quality. This paper combined the neutral-point voltage control, researches the voltage and current double circle control strategy based on current feedforward decoupling, studies three-level rectifier grid current control strategy when three-phase power grid is unbalance, proposes a fully digital power electronic simulation method based on MATLAB, uses S-fuction write control program, and implements three-level PWM rectifier of all-digital simulation, and verified the control algorithm. This paper does double circle control experiment of PWM rectifier experiment when the three-phase voltage of grid is balance or unbalance, and compared the waveform transformation before and after the neutral voltage balance control algorithm joined, and analysis the harmonic of the grid current waveform. Finally, this paper designed the control panel of three-level PWM rectifier based on DSP and FPGA, and established three-level PWM rectifier platform, briefly analyze the principle and the circuit structure and basic principle of the control panel. Then this paper experimentally verified the neutral-point voltage balance control strategy based on the500kW verified inverter with three-phase inductor, motor with and without load, and verified the current forward feed decoupling control algorithm of three-level PWM rectifier based on the100kW NPC three-level PWM rectifier experiment platform. The results of experiments indicated that the neutral point control strategy is effective and the control system of PWM rectifier can work stably and can get good dynamic performance.