Study And Design On Single-phase Two-stage 5L-ANPC PV Inverter

As the voltage and power level of photovoltaic inverter systems increase,multilevel inverter gains more and more study and application for its advantages of less switch stress,higher efficiency and lower output voltage distortion.As a kind of novel multilevel inverter,five-level active neutral point clamped(ANPC)converter has drawn a lot concerns in academia since its introduction.In recent years,the research on the five-level ANPC circuit is mainly focused on driving of three-phase motor and rarely related with PV generation,which is selected as research object in this paper.The main contents are as below:Based on the background of low power residential PV grid-connected generation system,a single-phase two-stage 5L-ANPC PV inverter is introduced,which guarantees the elimination of common-mode leakage current.The input-stage DC/DC circuits and the output stage with a 5L-ANPC inverter are analysed respectively.Principle and MPPT of input-stage interleaved Boost circuits are introduced.Then,the topology,principle and modulation strategy of the 5L-ANPC inverter are introduced.Finally,control strategies for both stages are described.A floating capacitor voltage balancing method is proposed aiming at the capacitor voltage balance and switching loss distribution in this converter.Two redundant output states are arranged alternately at carrier frequency and voltage hysteresis control is utilized by real time detecting the floating capacitor voltage,achieving the balance of floating capacitor voltage.This method reduces the capacitance and volume of floating capacitor and realizes an even distribution of switching losses among the power devices.This method is easy to design and its feasibility is validated in Simulink.Hardware circuits and main electrical parameters of the inverter are designed in this paper.The calculation results of losses are given,especially the conduction and switching losses of each switch in the 5L-ANPC inverter.A simulation model in Simulink and a 3.3kW prototype were built to validate the theoretical analysis and design.The design and control strategy are verified by simulation and experiment.