Research And Design Of Two-Stage Photovoltaic Grid-Connected Micro Inverter

Nowadays,PV generation systems are the key breakthrough in the development of new energy technologies,and have become a hot topic around the world,as they can provide technical support for solving the two elusive problems including energy shortage and environmental pollution.Among the systems,Micro-grid inverter system has been a vital branch in PV generation systems as its convenience and rapidity.And the Micro-inverter,the core of the Micro-grid power generation system,also gains more attention due to its small size,high efficiency and flexible installation.Hence,it is of great practical significance to study a new and efficient Micro-grid inverter.And in the paper,taking the photovoltaic micro-inverter as the research object,the research focuses on the MPPT control and power decoupling control from the angles of topology and control strategy.Specific tasks are as follows:(1)By analyzing and comparing several main circuit structures of the grid-connected photovoltaic inverters,it is determined that the single-phase photovoltaic grid-connected inverter studied in this paper adopts two-stage unisolated grid-connected structure.Then,discussing the operating principle and control strategy of the front and rear stages respectively.(2)Referring to the DC conversion in the front stage,the mathematical model and characteristics of output in the photovoltaic cell are analyzed firstly.And combining the shortcomings of the existing control technology of MPPT,the second-order sliding-mode control idea of Super-Twisting is proposed,and its sliding mode MPPT controller is designed.Meanwhile,based on the Boost converter,the second-order sliding mode control introduced in this paper is compared with the traditional sliding mode control aiming at the intermittent perturbation problem in PV generation,which verifies that the second-order sliding-mode controller has great advantages in reducing chattering and enhancing robustness.(3)Regarding to the AC grid connection of the inverter,firstly,the causes of the secondary power disturbance occurring in the two-stage grid-connected system are analyzed in the paper,and the principle of the electrolytic capacitor absorbs the ripple power in the traditional decoupling scheme are expounded.Secondly,the power decoupling converter circuit is introduced on the short-lived defects of traditional electrolytic capacitors,revealing the method of reducing the capacitance of decoupling capacitors in theory.Then,the electroless capacitor technology will berealized.Thirdly,a buck-boost decoupling circuit is proposed based on analyzing several usual decoupling circuits,and its working process is discussed in detail.At last,building the simulation model to verify the feasibility and effectiveness of the decoupling circuit.(4)Based on the theoretical analysis,the digital processing chip TMS320F28335 is used as the main control chip.And the micro-grid inverter is designed in a complete way,then a 500 W experimental platform is built.Through the experiment and analysis of the maximum power tracking in front stages and the power decoupling of the rear stage,the topology and control algorithm proposed in the paper can be proved to improve the MPPT and the grid-connected current quality effectively,meeting the technical requirements of the micro-inverter.