Harmonic based analysis of DAB converters for ZVS operation and reactive power minimization

The dual active bridge (DAB) converter is topologically considered as a preferred energy conversion system for applications that require bidirectional power flow between energy sources. To achieve maximum conversion efficiency, this converter needs to ensure zero voltage switching (ZVS) operation over a wide range of voltage variation. It also needs to maintain minimum reactive current. This paper adopts 3-level square wave modulation to control the active and reactive power of the DAB converter. However, the analytical solution of DAB converters is very difficult using the time domain analysis approach and requires a multiple mode analysis process based on different operational states. This increases the complexity for proper identification of the ZVS operating area. In this paper, a detailed universal expression of a DAB converter has been developed using the harmonic analysis method for ZVS region identification. This paper also proposes a method to reduce the reactive current of the DAB converter to ensure minimum reactive power. Simulation models have been developed to show the performance of the DAB converters under 2-level and 3-level square wave modulation methods. These simulation results have been validated by an experimental prototype. A comparative study shows that the proposed reactive power minimization method with 3-level modulation improves the conversion efficiency.