Robust nonlinear controller for single ended primary inductor converter supplying shared load from multiple sources with asymmetrical dynamics

Abstract

This work proposes a systematic approach to design a novel Integral Sliding Mode Controller (ISMC) for a Single-Ended Primary-Inductor converter (SEPIC) with dynamic load sharing. The designed sliding surface is used to connect and control two different input-energy sources via two SEPICs to drive a parallel-connected load with a fixed or dynamic autotuned sharing ratio. This structure enables to maintain battery health and extend its life. This proposal provides a solution that is scalable to the power system industry where there is a need to integrate other energy sources to the main power network; the proposed controller can function with sources having different dynamics and varying voltage levels with respect to the main network. Furthermore, the work also contributes to the field of control theory by deriving and designing a SMC for a SEPIC converter with only one parameter to tune where the upper and lower bounds are derived. The designed surface results in a minimal chattering behaviour at the output voltage as well as at the duty cycle level and allows for operating the SEPIC at a fixed switching frequency. The proposed controller can withstand up to a 75% variation in the input voltage, 100% variation on the load side in addition to providing a superior cold start performance. The proposed controller is nonlinear and has a variable structure; these features suit the SEPIC converter which is based on switching behaviour. The controller’s ability to reject input voltage disturbances which vary over a wide range is a key to integrating alternative energy sources (such as an ultracapacitor) to the main power network. Finally, the work demonstrates how the proposed sliding surface can be modified to drive two parallel converters to dynamically share load current where the current shared ratio is autotuned during the transient period while at steady-state it follows a pre-set shared ratio.