Performance comparison of DC and AC controllers for a two-stage power converter in energy storage application

This paper presents a procedure for modelling and controlling a single-phase, two-stage, bidirectional DC-AC converter for application of energy storage system (ESS) in autonomous microgrids, in addition to experimental verification of its uninterruptible power supply (UPS) functionality. Average theory and frequency analysis are utilized to model the power converters and design the controllers in a generic fashion. Performance comparison of different controllers (type-2 and type-3 Venable compensators, Proportional Integral, Resonant-PI and multiple-RPI) is realised through simulations and tests. To tune the controllers, parameter values of crossover frequency and phase margin are adjusted by comparing simulation responses of the converters. A 5-kW ESS is evaluated through simulations during normal operation (grid-connected or stand-alone mode), as well as under transition events such as disconnection and recovery of the main grid. Besides that, a 100-W system was implemented, in which grid-connected mode was evaluated by measuring the power factor (about 0.998 in simulation and 0.993 in test at rated power), while stand-alone mode was evaluated by the total harmonic distortion of the output voltage (about 1.57% in simulation and 2.35% in test at rated power). The presented procedure can also be used to design higher power systems.