Sliding mode observer design for universal flexible power management (Uniflex-PM) structure

In this paper a sliding mode observer is designed and applied to the Uniflex-PM structure in order to observe the capacitor voltages. The objective of the Uniflex-PM project is to develop advanced power conversion technique to meet future needs of electricity networks. Uniflex-PM can provide optimized connection of distributed energy resources, integration and management of energy storage, optimized utilization of the transmission/distribution infrastructure, a high quality of supply and coordinated control across the network. The strategic objectives are to secure a clean, sustainable & economic energy supply for the EU and a new modular power conversion architecture for universal applications. The main characteristics that make Uniflex-PM a unique choice for power system applications is the modular structure and the interleaved connection between phases at different ports. Each module comprises two H-bridges connected as an AC/DC converter and a DC/DC converter with a medium frequency transformer isolation. By having interleaved connection between phases, Uniflex-PM is able to operate under unbalanced conditions. In a two-port Uniflex-PM there are nine capacitors whose voltages, are needed in feedback loops of the system controller, which includes the voltage control loop and balancer. This means that nine voltage transducers are required. The use of so many transducers can make the system unreliable, thus it is desirable to observe the capacitor voltages instead of measuring them. The sliding mode observer (SMO) via equivalent control approach has been selected to be applied to the Uniflex-PM because of its robustness against a class of uncertainties in system equations. Simulation results from SABER are used to demonstrate the use of this observer technique.