Research On Cascade H-bridge Multilevel PV Power System

In traditional PV power generation system,several PV arrays are in series or parallel to produce enough DC voltage.Through a centralized inverter,DC voltage is transformed into AC voltage and integrated into the grid for people to use.However,in the real environment,the effect of shadow,dust,light intensity and other external conditions causes every PV array to fail to reach the maximum power point.As a result,the power generation of the whole system dramatically declines.Cascaded H-bridge inverter can independently control every PV array to make it reach the maximum power point,thereby making the whole system reach the maximum power output.At the same time,cascaded H-bridge inverter easily realizes modular extension and its control strategy is relatively easy,without the problem of voltage imbalance.Direct high voltage and grid can be realized,without needing an inverter.While improving power generation efficiency,it greatly saves PV power generation costs.This paper studies and designs the single-phase PV power generation system based on cascaded H-bridge multilevel inverter.Careful analysis and simulation is conducted on a series of core problems,including the principle,modulation mode and control strategy of cascaded H-bridge inverter.The main research content of the paper is as follows:First,according to the characteristics and working principles,the mathematical model is constructed.Based on the model,PV array's MATLAB engineering model is constructed as well.By changing light intensity,temperature and other parameters,the research studies the changes of the output of the simulation model.Thereby,the output characteristics of PV array is obtained,which lays a foundation for the design and research of the whole PV system.Second,detailed theoretical analysis is conducted on the topological structure,working principle and modulation mode of cascaded H-bridge multilevel inverter.Carrier phase shifting CPS-PWM control technology is utilized for simulation study and output waveform analysis of single-phase cascaded three-level,five-level and seven-level inverters.With the example of single-phase seven-level inverter,it studies the relation between modulation level and the number of output levels.Finally,it focuses on control strategy of cascaded H-bridge multilevel PV power generation system.Deep research is conducted in control modules such as MPPT control,inverter double closed loop control and modulation degree compensation.Through simulation experiment,the research compares and analyzes two kinds of MPPT control algorithm and proposes band-pass PR control technology for the drawbacks of steady-state error arising from proportional integral regulator's tracking AC.Then,three loop control strategies are put up with voltage outer loop PI control,current inner loop PR control and MPPT control,besides,modulation compensation module of H-bridge unit is designed.Based onMATLAB/Simulink platform,the research erects the simulation model of the whole cascaded H-bridge multilevel PV power generation system.Through the simulation and data analysis of the model,it verifies the correctness and practicability of the proposed theory.