The Design Of A 1000 Watt Offline Photovoltaic Inverter

With the growing energy crisis all around the world, utilization and development of the renewable energy are gradually being valued by the world. Meanwhile, people put forward higher requests of voltage stability, decreasing harmonics, etc. The thesis focuses on the analysis of the current domestic and foreign status quo on inverter power. Finally design an offline photovoltaic inverter with 1000 W power output.The thesis provides an overall block diagram of the PV inverter system, and analysis the basic principles of photovoltaic inverters for necessity. Through the research of five kinds of DC-DC topology, we ultimately adopt push-pull topology for the pre-boost circuit. The analysis of the poststage inverter circuit mainly focuses on the full-bridge topology and the sampling of SPWM modulation.The thesis analysis the working principle and waveform of push-pull inverter circuit topology.Explanation the specific system circuit design from power devices. Use SG3525 as the control chip of push-pull topology. The chip’s peripheral circuit concludes RC oscillating circuit, dead time circuit, feedback circuit, etc. 12 volt auxiliary power is controlled by chip UC3842 and have a capability of 1A output.The post DC-AC inverter circuit introduces the work principle of bipolar PWM modulation,giving an explanation of how the filter inductance and capacitor design. The main control chip is TDS2285. The frequency of carry wave is 20 kHz, and the modulation wave 50 Hz. Chip’s peripheral circuits is composed of battery detection circuit, AC feedback adjustment circuit,dead time circuit, optocoupler isolation and so on.The thesis designs OCP circuit, OVP and UVP circuit, OTP circuit. The prototype inverter’s input source adopts the tandem style of four 12 V lead-acid batteries with capacity of 100 Ah. The permissible AC output voltage ranges from 214-226 V, and the output 49.5 to 50.5 Hz. The design satisfies the requirement of 1000 W output. Average efficiency approaches to 88%, and the peak efficiency is 90.5%.