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This paper describes the design of a power conditioning unit (PCU) for photovoltaic power system to be interconnected with the utility grid (UG). The proposed PCU employs six-pulse three-phase inverter with modified-sinusoidal-pulse- width-modulation (MSPWM) switching technique, a parallel and series filters and an efficient control of dc to ac power conversion. The parallel and series filters are designed for both harmonics reduction and power factor correction. The efficient control of dc to ac power conversion makes the inverter output voltage immune to the variation in the dc voltage. The proposed PCU has been studied with both equation solving and extensive simulations. A 5 MW PCU has been designed and its performance has been investigated in detail.

A novel switching strategy for conducted-noise level reduction has been proposed in this paper. The proposed strategy uses three randomized parameters for generating the switching signals. These parameters are carrier frequency, duty-ratio, and the pulse position. This triple-hybrid switching strategy has been designed and implemented using field-programmable gate array (FPGA) technology. Moreover, the effect of using the proposed controller on commonmode and differential-mode noise, total conducted-noise, and radiated-noise characteristics of the dc-dc converter has been experimentally investigated. Furthermore, sweeping of the three randomization parameters has been carried-out for identifying the values which achieve the best conducted-noise level reduction. Numerous cases have been studied. All the studied cases have been designed, implemented and experimentally investigated. Then, the conducted-noise spectra have been compared. The experimental results show that using the proposed technique, with the identified randomization parameter values, significantly improves the conducted-noise spectrum and effectively reduces the noise peaks in both high- and low-frequency ranges. Moreover, the radiated-noise spectrum has been improved.