Research And Design Of Off-grid Photovoltaic Inverter

With the excessive consumption of energy and environmental contamination getting seriously in contemporary, there is no doubt that solar energy is one of the most valuable renewable energy to ease energy crisis, and the inverter plays an important role in the photovoltaic power generation system. This paper in-depth study of the Off-grid photovoltaic inverter key technologies, designed an accurate algorithm and high performance Off-grid photovoltaic inverter prototype.The inverter is divided tow parts, the hardware circuit and software control system, and the hardware circuit is mainly used in the structure of “push-pull inverter+filter rectifier+full-bridge inverter”, and the software control algorithm is achieved by digital signal processor. Around the switching device of the push-pull inverter circuit designed a Zener snubber to solve the problem that with the existence of the transformer leakage inductance and parasitical inductance of the wire in the PCB, producing the over-voltage damages the switching device, when the power switch fast turning-on or turning-off, So enhance the reliability of power devices; designed a loop compensation circuit in the pre-stage circuit, when the load mutation or the DC-power fluctuation, loop compensation circuit can quickly stabilize the output voltage, improving the stability and dynamic performance of the inverter. RCD snubber is designed in the full-bridge inverter circuit to reduce the stress of the power device and EMI, when the moment of the switch turning-on or tuning-off, simultaneously it also plays the soft switching effect, decreasing the loss of power switch and improving the efficiency of the inverter. By digital control mode to generate Bipolar SPWM wave drive signal, the advantages of this method make the control signal more precision, gain higher performance algorithm, and simplify the complexity of the circuit structure, improving the overall power density of the inverter. Research and design the algorithm of generation SPWM wave, what’s more, writing the software code.The rated power of off-grid photovoltaic inverter is 500 W, and the RMS value of the output AC voltage is 225 V, and the total harmonic distortion less than 5%. When the load is 300 W, the overall efficiency of inverter reaches 85%. Snubber circuit can efficiently restain the overshoot voltage, enhancing the power switching device reliable. When the surface case temperature of switch devices in the full-bridge inverter reach50℃, temperature-controlled fan automatically turns on, providing a good protection performance, and all of the tested results meet the expected design specifications.