Research On Improved Capacitor Voltage Control Strategy For Five Level ANPC Inverter

Compared with the traditional NPC five level topology,ANPC five level inverter topology has the advantages of small switching device stress,small number of capacitors,simple structure and flexible control strategy,so it has been widely concerned in the field of wind power,photovoltaic and other high-power equipment.The difficulty of ANPC five level inverter control strategy is to control the balance between neutral point voltage and suspended capacitor voltage.At the same time,the three-phase isolation measurement circuit of capacitor voltage not only increases the complexity of control strategy,but also increases the cost of inverter.To solve these problems,the main work of this paper is as follows:1.The development history,research significance,topology types and modulation methods of multilevel inverter are introduced,then the research status and key problems of ANPC five level inverter are analyzed.2.The working principle of ANPC five level inverter topology is introduced,the basic principle and implementation of carrier modulation and space vector modulation are introduced.3.Aiming at the problems of large volume,high cost and complex conditioning circuit in ANPC five-level inverter,a control strategy of no-suspension capacitor voltage sensor is proposed.This control strategy is based on the carrier comparison PWM,according to the dc bus capacitor voltage and output phase voltage to calculate the voltage value of the suspended capacitor,control the balance of the suspended capacitor voltage,reduce the number of voltage sensors in the three-phase circuit,simplify the circuit design,reduce the system cost.4.Aiming at the problem of neutral point voltage balance,a SVPWM control strategy based on virtual space vector of specific area is proposed in this paper to balance the neutral point voltage.At the same time,it can estimate and balance the voltage of suspended capacitance under SVPWM.The neutral current of each vector under different switching states is analyzed,the vector which can’t adjust the neutral point voltage through its own redundant state is recombined,some cells are redefined to eliminate the influence of the neutral point current generated by the vector on the neutral point voltage.In order to verify the feasibility and effectiveness of the above algorithm,this paper is based on Matlab/Simulink computer simulation platform and five level ANPC inverter low power experimental platform,the control strategy is verified by experiments.