Research On Flyback-type Photovoltaic Grid-connected Micro-inverter And Its Control Strategy

In the21st century, the energy shortages and environmental pollution problems have made thedevelopment and utilization of new energy sources to draw more and more attention. Solar energy isclean, non-polluting energy with features like wide distribution and infinite stock. As an importantpart of distributed generation, traditional photovoltaic power generation has many disadvantagescaused by partial shade structure, such as low utilization of solar energy, photovoltaic modulemismatch leading to hot spots and the overall low efficiency. The photovoltaic grid-connectedmicro-inverters integrated with PV modules have been studied. Each micro-inverter’s power is within500W, and each module can be guaranteed to run at the maximum power point because of theindependent control. And the utilization of solar power generation systems is increased even themodules are covered by partial shade.This paper researched on an interleaved active-clamp flyback-type micro-inverter. The formerstage as active-clamp flyback converters uses non-complementary drive to absord and transfer theleakage energy. The voltage spikes are effectively limited when the main switch is turned off. Theefficiency of the inverter can be greatly optimized. The interleaved structure decreases the stress ofthe switch and the harmonics of the input and output current. The operating principle of theactive-clamp flyback converters is provided. The main power losses of the inverter are analyzed. Thedesign reference of key parameters is presented. Then, this paper presented the small signal model ofthe micro-inverter and designed the close-loop control of the current to meet the demands of dynamicproperty and the stability and the quality of the current. The MPPT control with voltage loop wasdesigned to track the MPP quickly and precisely and to solve the DC voltage breakdown problem. Theload balance control guarnteed the power equal and increased the reliability and life of the inverter.Finally, detailed design of the entire grid-connected micro-inverter system is presented. A PVgrid-connected micro-inverter experimental platform based on the DSP TMS320F2812is designed.On this platform, the basic functions and various protection functions are achieved. The experimentalresults verify the feasibility of circuit theory, control strategies and the system designs.