Circulating Current Control Enabling Parallel Grid Tied Inverter Operation for EV Fast Charging Stations

A new method of controlling parallel grid tied inverters is introduced, enabled by the use of an additional connection between the star point of the LCL filter and the DC negative point of each inverter. This connection provides a path for the zero sequence current to flow, allowing for direct and symmetric control in the dqz frame of both the zero sequence voltage and current in the same manner as the d and q components. A model is created for N + 1 inverter "workers" operating in parallel, with one designated as a leader and the remaining N as followers. Analysis of the system is provided in state space form and through transfer functions between specific inputs and outputs. The control is achieved through compartmentalized layers, each of which operates at a different level of abstraction. The highest application layer sets the tasks, they are then distributed by the link layer, and executed by physical layers. The system is demonstrated experimentally with two converters in a leader-follower configuration.