Carrier Based PWM Methods of Dual Cascaded Inverter for Solar Power Plant Solid State Transformer

A new structure of solid state transformer (SST) for grid connected solar power plant is introduced in this paper. The SST utilizes dual cascaded multi-level inverter configuration. This paper investigates the performance of various PWM methods for the proposed SST. The dual cascaded inverter is controlled by using carrier based PWM methods, i.e Phase Shifted PWM, Level Shifted PWM and its variations. Simulation results show that the Overlapping Carrier (OC)-PWM method generates the highest fundamental component in the output. The Phase Disposition (DP)-PWM produces the best quality output voltage with the lowest value of THD (16,92%) among the PWM methods while the PS-PWM method provides the worst THD (39,41%). However, after filtering, the PS-PWM method generates the most sinusoidal waveform that indicates by significant improvement in the value of THD (0.029%). The PS-PWM is able to remove the low order harmonics better and send them into the around 4 kHz and it side band which is twice of the applied switching frequency (2 kHz).