Research On A Novel PV Grid-connected Inverter

Renewable energy has become increasingly irreplaceable in easing the global energycrisis and improving the corresponding environmental issues. Photovoltaic power generationis also increasingly playing a role in it, but the high cost, low efficiency, and which cannotadapt to a wider range of DC input voltage and other issues are major problems with whichconventional buck-frequency inverters now face.In order to meet the adaptability to a wide range of DC input voltage, DC-DC converterand conventional buck inverter are mostly used in cascaded structure in inverter, but thedisadvantages are higher cost and switching losses. Different single-phase inverter topologieswere reviewed and discussed in this paper. Single-stage inverter which has the advantages ofhigh efficiency, low cost, compact structure, has become one hotspot of research ongrid-connected inverter, and single-stage grid-connected inverter was further studied in thisthesis. A novel three-switch fly-back buck-boost inverter was analyzed, and the inverter usesa buck-boost converter in which DC input voltage was raised or lowered, and a single-stagecircuit to transmit power to the grid.PV grid connected inverter connects photovoltaic arrays and the grid, and to achieveeffective control of the inverter is particularly important. Due to the advantages of which canbe easily implemented and directly demodulated by the low-pass filter, PWM control methodhas been widely used. Closed-loop SPWM control method, has fast dynamic response, goodtracking performance, as well as strong adaptation to DC input voltage change, but theparameters of PID in control system have to adjust to different operating pointscorrespondingly, thus increases the difficulty of controller design.On the basis of PWM control strategy, a new control strategy which was based on thebalance of energy was proposed in this paper，named as pulse energy modulation (PEM).That was in one switching cycle, the pulse width was calculated in accordance with theprinciple of energy balance between the energy stored in fly-back inductor and energydemanded in the output.First of all, A detailed analysis of the inverter inductor current operating in discontinuousconduction mode (DCM) and continuous current mode (CCM) were expanded in this paper toderive the calculation method of pulse width.Then, SPWM and PEM control strategies were used to simulate for three-switch inverter,the simulation results show that power factor can be close to1, THD less than5%,and theinput voltage from50V to300V in PEM, and it indicates that the three-switch inverter basedon PEM method has advantages of unit power factor operation, lower THD of output currentand adaptability to a wide range of DC input voltage. Finally, in order to verify the validity of the three-switch inverter and PEM controlstrategy, an experimental platform of500W was built, and a control system based ondsPIC33FJ64MC506was designed.