Multi-level Inverter And Its Application In Photovoltaic Grid Connected System

In renewable energy power generation system, the application of multi-level inverter isgetting more and more scientific interests because it can realize high voltage power convertwith low voltage switch devices. Multi-level inverter has the advantages of low totalharmonic distortion of output voltage and low voltage stress of power switches, and it canimprove the efficiency of grid connected system and reduce the cost. This paper analyzesthe working principle of the traditional inverter circuit, and proposes a new type of highefficiency2H-bridge cascaded multi-level inverter circuit. This circuit is controlled withladder wave modulation strategy and a simple method of trigger angel calculation. Thequality of the output waveforms can be improved by adjusting the size of the trigger angle.The correlative protective circuit is proposed in order to let the designed circuit apply tophotovoltaic (PV) grid connected system. Through analysis of simulation experiment modelthat is built based on MATLAB/Simulink platform verify correctness of the designedcircuit and feasibility of the application in PV system. The designed circuit not only canimprove the utilization of the DC source, but also can output high quality waveforms, andimprove the efficiency of grid connected inverter and grid quality effectively. The specificresearch work is as follows:1. The analysis and comparison of the basic multi-level inverter circuit and workingprinciple is carried out by researching multi-level inverter circuit’s structure and itsoperating principle.2. The improved design of the main circuit of the2H-bridge cascade inverter iscompleted, and the analysis of circuit working principle and the improving effects is carriedout.3. The comparative analysis of the merits and drawbacks of triangle carrier modulation,space vector modulation, carrier phase shift SPWM modulation and ladder wavemodulation is carried out based on the research of multi-level inverter modulation strategy.Ladder wave modulation is selected as the modulation strategy of the designed circuit, andcorrelation analysis is carried out.4. A simulation experiment is carried out based on the simulation model that is built inthis chapter. Comparative analysis of the traditional H-bridge cascaded seven-level single-phase inverter and efficient2H-bridge cascaded single-phase inverter simulations iscarried out to analyze the performance of the inverter.5. Modulation strategy algorithms and hardware control circuit of cascaded multi-levelinverter is designed based on DSP and FPGA. DSP is used for the main controller, andFPGA is used for DSP I/O port expansion.6. The designed circuit is applied to PV grid-connected model system. The topologyand control strategy of the PV grid-connected system is researched.