Field upgradeable transformer: A fractionally-rated voltage regulator for the distribution system

The distribution system voltage volatility caused by changing load conditions and penetration of renewable resources presents an increasing challenge in the grid integration of renewables. This paper presents a novel voltage regulator, or field upgradeable transformer (FUT), for the distribution system, targeting at direct voltage regulation at the customer side with a fast dynamic response. Proposed system consists of a conventional medium voltage (MV) distribution transformer interfaced with a fractionally-rated power converter. Compared to other power electronics solutions for grid applications, the proposed device has advantages of low cost, high reliability, and high efficiency. The paper presents the FUT topology, principle of operation, control and protection scheme verified through simulation studies. Experimental results at 7.2 kV, 50 kVA, demonstrating FUT technology are also presented.