Grid‐forming inverter control design for PV sources considering DC‐link dynamics
Ishita Ray, Leon M. Tolbert
Abstract
Abstract A grid‐forming inverter in an inverter‐dominated grid should operate as a dispatchable voltage source, which is difficult to achieve when the inverter is interfaced with nonlinear dc sources such as photovoltaic (PV) arrays. This paper presents a new grid‐forming controller which considers the PV source dynamics and limitations and maintains dc‐link stability under transient and overload conditions. A single‐loop voltage controller without ac current feedback is used, and the synchronization is achieved using dc voltage‐frequency droop. Additional dc current‐virtual impedance feedforward compensation is included to improve the ac output passivity. The controller limits the operation of the PV source inverter in the linear portion of its characteristic by regulating its modulation index, thus preventing dc voltage collapse. The proposed controller is implemented and tested on a controller‐in‐the‐loop simulation platform. The simulation results show that the controller shares power in proportion to the dc source capacities of parallel inverters, effectively limits the output current during faults, and limits dc‐link voltage drop when the inverter is overloaded. The controller is also validated on a hardware testbed.