Design and Experimental Verification of DC Autotransformer Prototype

Abstract

To interconnect HVDC systems with different voltage levels, DC transformers are the most important devices. Among different topologies of DC transformers, DC autotransformer (DC AUTO) is one of the most promising technologies. This paper develops a DC-DC autotransformer prototype constructed with two-level voltage source converters (VSC). By blocking specific VSC converter, a bidirectional DC AUTO can be reconfigured to a unidirectional DC AUTO. Main circuit configuration of an experimental prototype is designed. Control strategies and control system architecture of each VSC for different operation modes are presented. And a dual-loop controller with current protection is proposed. The startup method and operating characteristics are analyzed. Feasibility of different topologies for DC AUTO is verified in experimental conditions, such as DC power step and reversal. Experiment results show that the prototypes have excellent static and dynamic performance under DC power step and DC power flow reversal.