Modelling and Dynamic Analysis of FCS-MPC for Inverter-based Generation in AC Microgrids

Abstract

Microgrids (MGs) have been introduced as a paradigm to the traditional grid to enable better the inclusion of a more diverse mix of energy resources, mainly renewables, into the previously coal and gas dominated electric grid. One of the main challenges of shifting to a renewable energy distribution system is the management of power and the maintenance of high-quality power despite numerous intermittent energy sources and the presence of a large amount of power electronics. Therefore, the hierarchical control structure was adopted to improve power system control capabilities, active consumer participation in the market, plug-and-play capabilities and increase the scalability of the MG. It consists of the zero, primary, secondary, and tertiary levels of control to ensure accurate tracking of frequency, voltage and power sharing between generation units.

Cascaded linear controllers have been widely used in the implementation of the hierarchical control levels. However, they have a slow transient response, high volatility to MG parameter changes and require high tuning efforts for their administration. Contrarily, model predictive controllers (MPC) use a comprehensive mathematical model of the system to optimize predicted future control variables to achieve accurate control. They are non-linear control techniques increasingly being adopted to overcome the drawbacks of cascaded linear controllers. MPC provides more flexibility and can include several control objectives while providing fast dynamic control. The advancement of computational power in micro-controllers has enabled the use of MPC in power electronic applications.

The principal objective of the proposed methodology is to achieve distributed control in AC microgrids with accurate power sharing, stabilized frequency & voltage and grid synchronization and de-synchronization for the seamless transition between the islanded and grid connected modes of operation by excluding cascaded control and using purely predictive control for the primary and secondary hierarchical control layers. The control is developed and discussed for solar integrated renewable energy sources. Proposed control concepts are investigated on a microgrid testbed with multiple parallel connected inverters for both modes of operation.