String Inverter

A string inverter is a type of solar inverter that connects multiple series-connected photovoltaic panels (a string) to a single DC input and injects the converted power into the grid in a centralized manner. Designed for medium to large systems (typically 10 kW to 100 kW and above), these inverters usually feature multiple independent MPPT inputs to optimize performance under partial shading conditions. Internally they include input circuits with fuse and SPD protection, multiple booster converters, a three-phase inverter bridge with high-power IGBTs, advanced output filters, and active cooling systems. Common issues include efficiency loss due to string mismatch, burnt MPPT inputs caused by overvoltage or arcing, cooling fan failures, communication errors with monitoring systems, and faults in grid disconnection relays. Expert diagnostics and repair involve IV curve testing of each string, temperature and current measurements at hot spots, replacement of power modules and control boards, software updates, and comprehensive performance testing under variable load conditions while verifying compliance with grid injection standards.