Preventing transformer saturation in bi-directional dual active bridge buck-boost DC/DC converters

In switch-mode power electronic converters, DC offset of the magnetizing flux in the isolation transformer can cause saturation. In typical single-ended dc/dc converters, this is handled using a current loop which ensures that the average current in the winding is zero. For bi-directional dc/dc converters with active bridges on both sides, there exists a danger of impressing dc offsets from both sides, creating significant issues in terms of preventing transformer saturation. This paper demonstrates the issue for the Dual Active Bridge Buck Boost converter (DAB³). The paper also presents a control strategy for avoiding such saturation, eliminating DC currents on both sides, while realizing full converter control. The paper presents simulation results to prove the proposed control technique.