Study of Dual Active Bridge With Modified Modulation Techniques for Reduced Link Current Peak Stress and Harmonics Losses in Magnetics

High-frequency-link power-conversion is gaining popularity in recent days due to reduction of the size and weight of the converters for various applications. The performance of the dual active bridge heavily depends on the nature of modulation strategy used and on the loading conditions. Look-up table (LUT) based output power and output voltage dependent modulation strategies to investigate the peak current stress and harmonics in high-frequency link current is proposed in this article. The modulator is, thus, simple to implement. The peak stress, the harmonics (total demand distortion) in link current, and associated losses due to the proposed techniques are compared in four main cases, namely, first, single-phase shift, second, dual-phase shift, third, triple phase shift, and, fourth, modified phase shift (MPS)-I, -II, and -III. In MPS-I, weighted aggregate of harmonic currents minimization including fundamental component is carried out to achieve the minimum conduction losses in the magnetic elements. The same method is extended for minimizing the peak-to-peak ripple in the link current as MPS-II. In MPS-III, the desired total demand distortion in the ac-link current is enforced. The variation of voltage transfer ratio between input and output is taken into consideration using two-dimensional (2-D) LUT. Moreover, the requirement of 2-D LUTs are eliminated by using suitable curve-fitting exercise for the output load voltage variation and 1-D LUTs of coefficients. A detailed simulation study, associated mathematical analysis of the methods adopted and experimental verification are presented from 1 kW prototype.