Research And Implementation Of Grid Connected/independent Dual Mode Inverter In Distributed Photovoltaic Power Generation System

With the increasingly serious problem of traditional fossil energy crisis and environmental pollution,photovoltaic technology with the characteristics of energy saving and environmental protection has attracted worldwide attention.Grid-connected/independent dual-mode inverters in distributed photovoltaic power generation systems have become an important research direction for photovoltaic power generation,because of the flexibility of the inbound and outbound power grids,which can improve the reliability of power supply and improve the load balance of power systems.The circuit topology of the grid-connected/independent dual-mode inverter was studied,and the DC-DC-AC two-stage dual-mode inverter conversion structure was selected.A pre-stage DC/DC boost circuit with spike voltage and current suppression function is proposed to solve the problem of excessive voltage and current spikes when the circuit is started,and to reduce the voltage and current stress of the power device.The effects of different inverter topologies and modulation methods on common-mode leakage current were analyzed and studied.A non-isolated Heric inverter with good leakage current suppression effect was selected as the circuit topology of the rear-end inverter.The grid-connected current control technology of the dual-mode inverter is studied,and the high-order harmonic compensation is added on the basis of the quasi-PR control algorithm to form a multi-resonant PR controller to eliminate the static error of the grid-connected current and the fundamental voltage of the grid voltage.The effect of higher harmonics.On this basis,a method of grid-connected current control combining multi-resonant PR and PI is further proposed.The added PI control is used to further eliminate the grid-connected current DC component and obtain high quality grid-connected electrical energy.The switching control technology of grid-connected/independent dual-mode inverter was studied,and the optimal switching control mode with small impact on local load voltage and grid current was designed.The dual-mode inverter off-grid and grid-connected controllers were designed separately.The reasons for the current zero-crossing distortion in the off-grid/grid-connected operation of the Heric inverter were analyzed.A current zero-crossing region determination method and zero-crossings were proposed.The mixed modulation scheme solves the problem of current zero-crossing distortion and improves the power generation quality of the inverter.The hardware and software design process of grid-connected/independent dual-mode inverter based on TI's DSP TMS320F28335 as control core was introduced in detail.Theprototype of dual-mode inverter was successfully developed.