Comparison of Plant-Level and Unit-Level Virtual Inertia for BESS Power Converters

Distributed energy resources, such as, re-newable energies and energy storage systems are usually connected to the power system through some power electronics converters, which -unlike the traditional synchronous generators- lack the inertia feature. Thus, there are stability concerns over the modern ‘low-inertia’ power grids and microgrids. In literature, this issue has been successfully tackled by adding the ‘virtual inertia’ feature to the control of power conversion systems. For off-the-shelf devices whose internal control schemes and logics cannot be accessed nor reprogrammed, adding virtual inertia inside the power converter controller is challenging. Therefore, it is desirable to have a top level controller with virtual inertia capabilities. For this reason, this paper adds the virtual inertia implementation to the plant controller of a group of power converters that are used for a battery energy storage plant and compares it to the virtual inertia implemented inside the power converter controller. The idea is validated in a hardware-in-the-loop environment by including the BESS plant controller which sends commands to the individual power converters via Modbus TCP protocol. Results show that the communication delay may influence the plant-level virtual inertia performance, compared to the conventional way of implementing virtual inertia inside the power converter controller. The studies are performed through simulations on electrical networks with slow and fast frequency response dynamics.