Innovation: A control scheme for grid-connected three-phase five-level multistring inverter with isolated PV sources was developed. The conventional modulation schemes for CHB multilevel inverter do not apply to this multistring inverter. The developed modulation schemes were successfully used to meet the set objectives of simultaneous regulating the dc voltage control and providing compensation for disturbance due to power mismatch in the PV strings. As such, the level of the multistring inverter can be increased for other power applications such as applicable to transformer-less inverters, which are lighter in weight.

Sector/Industry Application: ENERGY/POWER

Description: A control scheme of a three-phase multi-level multi-string inverter for grid integration of photovoltaic (PV) power systems is developed. The three-phase inverter synthesizes a five level output voltage from six isolated PV sources using reduced number of power switches when compared to conventional multi-level inverter topologies. Only eighteen power semiconductor switches are required to synthesize the five level ac output, six of which are operated at line frequency. This reduces the switching losses and also the overall cost of the system. The inverter uses a new modulation scheme in its control for handling power imbalance between the PV sources in each phase and amongst the three phases.

Problem: Renewable energy penetration into Nigerian grid