Research Of The Photovoltaic Three Level Inverter On Efficiency Optimization Control Strategy

With the rapid development of economy and technology, all countries’ demandfor energy is gradually growing. The shortage of traditional energy and environmentpollution which was caused by it has become a hot topic all over the world. Thedevelopment and application of environment protection and renewable energy is takenmore seriously, so is the improvement of utilization efficiency of the existing energy.The photovoltaic power generation system obtained rapid development because of itscleaning, environmental protection, inexhaustible and so on. This paper is researchedthe control strategies which could reduce photovoltaic three level inverter switchinglosses and improve the efficiency.Firstly，the topology and space vector pulse width modulation (SVPWM) ofthree level neutral point clamped (NPC) inverter was introduced. Then this papermakes the research the control strategy to reducing switching losses for three-levelNPC inverter, and a hysteresis controller was proposed. This controller combined thevectors into two vector sequence modes by neutral point voltage opposite effect, andswitching the modes to control neutral point voltage balance. In addition, a noveldiscontinuous SVPWM strategy was proposed to avoid switching losses at peak valueof unity power factor load current. The strategy can reduce switching losses at largeand control neutral point voltage balance.Secondly, as for controlling of neutral point voltage, the influence of mediumand short vectors was analyzed, and the limitation of neutral point potential balancingproblem for all power-factor conditions is explored. Then this paper propose a noveldiscontinuous SVPWM strategy which can control neutral point voltage and reduceswitching losses by switching the vector sequence mode in all power-factor, and makethe switching losses comparison between novel strategy and traditional modulationstrategy.And then, this paper made the analysis and comparison for kinds of maximumpower point tracking (MPPT) method, and optimized the perturbation and observationmethod to faster and more accurate. In addition, a photovoltaic on-grid inverterclose-loop controller was introduced.Finally, this paper makes the simulation by Matlab, and does the experiment in a 10kva photovoltaic three level on grid inverter. The simulation and experimentalresults show the feasibility and effectiveness of the novel modulation strategy.