Abstract：The DC-DC converter plays a pivotal role in renewable energy systems by serving as an interface converter connecting the DC bus and energy storage devices. The application demands a fast dynamic response to accommodate load fluctuations, voltage drops, or other external disturbances. Therefore, a multi-stage discrete extended-phase-shift (MD-EPS) control method is proposed for DAB DC-DC converters, considering peak-to-peak value current optimization during the control design. Thus, the proposed MD-EPS control can achieve both a fast dynamic response and high efficiency across a wide load range. Firstly, this paper provides a comprehensive introduction to the principle of MD-EPS control. Different from conventional linear control methods, the proposed MD-EPS controller has (m-1) level output voltage references Uref, j (j=1,···, m-1, and m is an even number), dividing the output voltage into m output voltage intervals [Uref, j-1,Uref, j]. Each interval corresponds to preset fixed inner/outer phase-shift duty ratio signals D1, j and D2, j. At the beginning of each switching cycle, the output voltage Uo is sampled and compared with m-1 level Uref, j to determine the instantaneous output voltage's corresponding interval when Uo∈[Uref, j-1,Uref, j], D1 (D1=D1, j) and D2 (D2=D2, j) are selected as the active phase-shift duty ratio signals for the current switching cycle. Secondly, the control parameter design method is presented using the 4-level discrete extended-phase-shift (4LD-EPS) controlled DAB DC-DC converter as an example. The rated power range, output voltage ripple, and peak current optimization are considered during the parameter design. Thirdly, the steady-state performance, dynamic performance, and interference immunity of the 4LD-EPS controlled DAB DC-DC converter are explored by theoretical analysis and simulation verification. Finally, the control performance of the proposed converter is verified by a 160W low-power test prototype. The experimental results highlight a remarkable improvement in the dynamic response of the converter system, with a 99.95% reduction in recovery time and a maximum efficiency of 94.54%. The following conclusions can be drawn through the theoretical and experimental analysis: (1) The proposed MD-EPS control offers a simple control principle, ease of implementation, fast dynamic performance, and high reliability. Moreover, compared with conventional PWM-EPS control, the proposed MD-EPS control eliminates the need for an error amplifier and corresponding compensation circuits. (2) The proposed MD-EPS controlled DAB DC-DC converter effectively minimizes current peak values, thereby achieving high efficiency.
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2024, Vol. 39 
