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

This paper proposes a low-complexity control strategy for a DC microgrid composed of n sources and m loads, all interfaced to a common DC bus through a modular Multi-Input Multi-Output (MIMO) converter. The onboard DC microgrid of a small marine Remotely Operated Vehicle (ROV), comprising two sources and two loads, was considered as a case study. The DC microgrid has been modeled as a nonlinear differential system. In the proposed control strategy, the DC bus and output voltages are controlled indirectly by appropriately regulating the currents in the n + m converter branches through sliding mode control. The reference currents are obtained by computing the equilibrium state associated with the desired output variables, which enables the design of n + m decoupled current control loops. Robustness to parameter variations, load changes, and supply voltage fluctuations is ensured by external PI -type control loops that adjust the equilibrium state. Since the system order exceeds the number of controlled variables, internal dynamics of order m + 1 arise, which are unobservable from the outputs. These dynamics can be suitably allocated to achieve secondary objectives, such as maintaining constant current in selected branches. A laboratory prototype of the MIMO converter has been developed, and experimental results validated the proposed control method.