Research On Control Strategy Of Photovoltaic Off-grid Power System

Nowadays countries among the world are vigorously developing new energy sources because of the increasingly serious energy crisis, among which the photovoltaic(PV) solar energy attaches great attention for its inexhaustible characteristics to all countries. The PV inverter is one of the most important parts in the development of solar energy, which is separated into off-grid inverter and grid-connected inverter. PV off-grid inverter play an irreplaceable role in storing energy and reverse into AC power supply,which is suitable for outdoor, remote areas and small independent PV power generation.Mature technology, low cost and high output voltage are the reason that this paper chooses lead-acid battery as a PV solar energy storage device. Then inverter the low DC voltage of battery into common use AC power supply. This system consists of the battery charging and off-grid inverter.In view of the designed low battery capacity and small PV solar panels power, so we choose pluses type multi-stage intelligent charging technology to charge the battery, and it can also charge through appropriate size external constant current adapter. The off-grid inverter consist of push-pull booster and full bridge inverter, the working principle of the main circuit has been discussed in detail, and so do the steps of designing the transformers and other key power devices, Different design conditions will how to impact on system performance is also been analyzed, The sampling circuit, driver circuit and protection circuit design is also been mentioned.The system adopts double MCU control mode, one is mainly control battery charging and the other is AC inverter function. The charging software flow chart is established to realize the management of multi-stage intelligent battery charging, and can quickly achieve protection function when system get fault. There are two methods are being discussed to design the full bridge inverter software, one is single polarity modulation and the other is frequency doubling single polarity modulation. A detailed analysis of the principle and control strategy of the two different modulation mode has been given and the method of how to generated SPWM ware, the flow chart of software are also been given in detail.A stand-alone off-grid PV power system test platform is build, and detailed test has been carried on for three aspects: the basic function test, the temperature rise efficiency test and the EMC test. This test shows that: the system charging function is perfect, the output AC sine ware and key nodes ware are good, perfect protect function can be achieved, and strong output load capacity, proves the validity of the software control strategy. By continuously improving design, the machine performs well in temperature rise test for a long time, the highest efficiency can reach 90%, electromagnetic compatibility is improved to a certain extent, proves the hardware and software of the system is reasonable and reliable.