Research on loss reduction of dual active bridge converter over wide load range for solid state transformer application

Abstract

This paper presents the design of new high frequency transformer isolated bidirectional dc-dc converter modules connected in module-cascaded solid state transformer (SST). A phase-shift dual active bridge (DAB) converter is employed to achieve high-frequency galvanic isolation, bidirectional power flow, and zero voltage switching (ZVS) of all switching devices, which leads to low switching losses even with high-frequency operation. Bidirectional DC-DC converter is crucial to the power transmission in SST. The proposed DAB converter consists of two three-leg bridges and a high-frequency transformer with winding shunting taps. Furthermore, the commutation inductance connected in series with the transformer in the conventional DAB converter is integrated into the transformer windings, thus, enjoying smaller volume and higher power density. By changing the number of primary winding turns, leakage inductance, which is the key parameter in the energy transfer process of DAB converter, can be adjusted on a large scale, enabling the possibility of reducing loss over wide load range. Additionally, time-sharing circuit topology and operation mode are adopted to adapt to the output power by detecting the output current as the feedback. As a result, the efficiency at both light and heavy load can be significantly improved compared with the conventional DAB converter, and, therefore, high efficiency over wide load range and high power density can be achieved. Besides, the additional bridge arm structure along with a flexible control scheme provides possible high-level fault tolerance. Finally, the simulation results on a 2-kW DAB converter module switching at 10kHz are presented to validate the theoretical analysis. Keywords-solid state transformer (SST); dual active bridge (DAB); circulating energy; zero voltage switching (ZVS); high efficiency. 978-1-5090-2464-3/16/$31.00 ©2016 IEEE I. INTRODUCTION Fig.I. The Energy Internet diagram.Sustainable energy distributed generation is paid tremendous attention in the last decade due to energy shortage and environmental pollution issues. However, the inherent intermittence and randomness in renewable energy sources pose stiff challenges for the traditional power management system. In order to achieve optimization control of the entire grid, many promising schemes of the smart grid concept have been put forward by experts until the present time. The Energy Internet is a representative one which provides intelligent energy management (IEM) ports for the plug-and-play integration of the distributed renewable energy resources (DRER), the distributed energy storage devices (DESD), and ac/dc loads, as shown in Fig. l. The intelligent fault management (IFM) is responsible for fault isolation, used for protecting the system. In order to enable intelligent management and remote monitoring, the distributed grid intelligence (DGI) unit, which integrates both advanced control and communication functions, is embedded into the IEM and IFM for fulfilling the needs of the smart grid concept. What's...

Power Losses Calculation for Medium Voltage DC/DC Current-Fed Solid State Transformer for Battery Grid-Connected

“…Numerous publications proposed techniques to calculate power losses based on the power electronics parameters and core losses equations [11][12][13][14][15][16]. They can be divided into three categories.…”