Indirect Sliding Mode Control of a MIMO Modular Converter for DC Microgrids: a ROV Case Study

This paper deals with sliding mode control of a DC microgrid consisting of n sources and m loads connected to the same DC bus through a Multi-Input Multi-Output (MIMO) converter based on bidirectional half-bridge modules. The mi-crogrid model is nonlinear and differential-type. In the proposed control method, the output voltages and DC bus voltage are indirectly controlled by managing suitably the current flowing in the n + m converters branches, whose reference signals are deduced by computing the equilibrium state corresponding to the desired output variables. This allows the design of n + m decoupled current control loops using the sliding mode control method. Since the model is of order higher than the number of the controlled variables, internal dynamics of order m+1 exist, which are unobservable from the output. Such dynamics can be suitably allocated to achieve secondary tasks (i.e., maintaining constant current in some branches). Robustness against parameter, load, and supply voltage variations is gained through an outer control loop by a PI-type controller. The onboard DC microgrid of a small marine remotely operated vehicle (ROV) was considered as a case study with two sources and two loads. A 200 W laboratory prototype of the microgrid converter was built, and experimental tests were performed to validate the proposed control approach.