Medium Voltage String Inverter for Future Utility-Scale PV Power Plants

State of the art utility-scale PV power plants use AC-Voltages up to 880 VAC. This voltage increased steadily in the past, because with higher system voltage the currents decrease. Due to the smaller currents, cable crosssections can also be decreased. At the same time the subsystem power in a PV plant can be increased. This results in a reduced number of transformers for the same power plant size. These points lead to significant savings at cost for materials as well as for installation. In present there is no further increase in the system voltage despite further increasing output powers of the string inverters. The reasons can be found in the now necessary step beyond the low voltage range. At Fraunhofer ISE a new system concept for future utility-scale power plants was developed that is based on this step beyond the low voltage range with VAC ≥ 1,000 V. Further a medium voltage string inverter was developed that perfectly fits into the new concept. It has a line to line output voltage of 1,500 V and a output power of 250 kVA. The new concept and the developed inverter are shown in this paper.