Research On Control Strategy Of Multi - Level ANPC Converter

With the development of power electric technology, applications of active netrual point clamped multilevel converter in the field of high voltage and large capacity have drawn the attention of the scholars in the world.This paper studies the three-level active netrual point clamped(ANPC) converter and the five-level active netrual point clamped converter converter topology, and deeply analised their structure characteristics, working principle and control algorithm.The traditional three-level netrual point clamped converter has the fault of unbalanced loss, which seriously limits the enhancement of converter’s capacity.Three level active netrual clamped inverter can realize the loss of balance, beneficial to the improvement of the system capacity. Based on the working principle of the three level active netrual clamped inverter, this article analised converter characteristic and built the model of power loss of the swich devices.Comparing of the loss of power devices under the two kinds of PWM modulation methods, a control method of balanced loss is also put forward in this paper. At last, verified the feasibility by the matlab simulation.Five level active netrual clamped converter is a kind of new topology which can realize the multilevel and high voltage output without transformer. Firstly the paper analyzes the five-level active netrual point inverter’s working principle, and finds out the relationship between the output voltage and switch function, and based on this, changes the traditional five-level PWM modulation method based on phase disposition into three-level PWM modulation based on phase-shifting carrier.Using the redundant swich states of the output voltage to charge or discharge the float capacitor when out put same voltage to control float capacitance voltage. In order to solve the neutral voltage fluctuation problem, this paper finds out the connection of the neutral voltage, the average current of netrual point and the zero sequence voltage, and two kinds of control methods which are search optimization and optimal zero sequence are studied in this paper. Search optimization method the limits zero sequence voltage range and then uses the method of exhaustion, calculates the zero sequence need to be injected within the scope of the zero sequence voltage and compares it with the neutral current neutral current, finally find out the zero sequence voltage which can minimize the neutral current as the optimal zero sequence voltage. The optimal zero sequence method is obtained by analyzing the average relationship between average netrual current and zero sequence voltage to calculate the optimal zero sequence voltage by interpolation method. This paper aimed at solve the charging problem of floating capacitance. Based on the analysis of the structure characteristics, this paper finds two different charging circuits, put forward a new pre-charge method after the analysis of the simulation and comparison to achieve the goal of charging the three-phase bridge arm floating capacitance at the same time.Finally, To validating the methods and software, an experimental platform of five-level active netrual clamped inverter is built.