Research On Photovoltaic Grid-connected Inverter For Soft Fault Diagnosis Method

Due to the rapid development of social production and growing energy demand, the energy shortage of worldwide becomes increasingly severe. Fossil fuels are non-renewable resources of the earth and it will run out one day. The price increases with the declining of fossil fuels, which brings serious constraints of social development and the level of people’s living standards. As a consequence, renewable energy source plays an important role in the global energy demands, especially in such a large population of our country. Solar energy resources are very abundant, and with good prospects for developmentGrid-connected PV power system refers to the solar panels produce DC electricity converted into AC power through grid-connected inverter which meets the requirement of city power grid, and then is directly connected to the public power grid. When is sunny, the city power grid is rest and the solar energy of electricity can be used; but when the sun is not sufficient or PV power generation can’t meet the standards, the control part of grid-connected PV system can switch to city power grid which gives supplement automatically.Grid-connected inverter is the core part of the grid-connected P V system. The security of grid-connected inverters and power grid depends on the reliable operation of the inverter. The main circuit of grid-connected inverter is made up of a number of switches, inductor and capacitor combination Removing switch short circuit and structural open circuit faults in the working of inverter circuit process, soft fault also has a great effect on the reliability, and the failure of filter capacitor is more prominent Due to the extraction electrode of capacitor is subjected to the charging and discharging of large currents for long time, which performs various degree of oxidation phenomena. The storage capacity of capacitor is reduced with the decrease of capacitance transient current value’s charging and discharging, and the equivalent capacitance is reduced significantly. When the capacity of capacitor is decrease, it shows with a poor load capacity lightly; but usually is reflected undervoltage fault in the DC circuit with a heavy bad. The further damage of capacitor also makes the DC circuit produce voltage oscillation possibly, which causes serious damage to inverter module.Such faults are often more subtle and are different from the element open circuit and short circuit, which is easier to cause attentioa When measured, the phenomenon of charging and discharging is obvious with a multimeter and the resistance of reverse leakage current is in the permitted range, so the check is sometimes a struggle and brings troubles to the maintenance department.This paper analyses soft fault characteristic quantity of electrolytic capacitor under different tolerance. According to the features of photovoltaic grid-connected inverter, the soft fault diagnosis method of three-phase grid-connected photovoltaic inverter electrolytic capacitor is proposed. Due to the electrolytic capacitors of inverter performs aging phenomenon with working time, leading to its tolerance increases and capacitance decreases, which namely soft failure of the circuit As a result, the output line voltage of power grid is different from the voltage in normal operation, and takes the voltage as a characteristic quantity. Combined with the features of grid-connected unity power factor of photovoltaic grid-connected inverter, and made voltage vector angles as the reference, so the soft fault of electrolytic capacitors is diagnosed. Simulation and hardware test results show that the method can determine the specific capacitance and value of capacitance with soft fault in a current cycle.