Small Signal Model for Current Mode Control of Coupled Inductor SIDO Buck Converter

Single-input multiple-output (SIMO) dc-dc converter is a cost-effective solution compared to multiple parallel converters in the field of electric vehicles (EVs). This paper focuses on the coupled inductor single-input dual-output (CISIDO) buck converter. The current-mode control scheme is widely used in the dc-dc converter. It has advantages of current limiting capability, simple controller with fast dynamic response and noise immunity. In CI-SIDO, coupling in inductor currents leads to cross-coupling problems, which affects the dynamic performance.To understand the dynamics of the converter, the open-loop small-signal model (SSM) relevant for current-mode control is essential. However, no equivalent SSM for current-mode control of CI-SIDO is available in the literature. This paper provides the SSM for current-mode control of CI-SIDO buck converter in continuous conduction mode (CCM). The model is developed by deriving the transfer functions from duty cycles to inductor currents, the input voltage to inductor currents and load currents to inductor currents. The transfer function is calculated using the state-space averaging technique. It is observed that low-frequency gain of cross-coupling transfer functions is less. Also, cross-coupling affects only the transient performance. The developed SSM finds useful in designing closed-loop current mode control of CI-SIDO buck converter. The small-signal model is verified in MATLAB/SIMULINK.