A Frequency Feedforward Strategy for the Grid-Forming Inverter

In the 100% renewable energy penetration power system, due to the absence of the conventional giant synchronous generator, the grid-forming inverter is required to offer more inertia power. The grid-forming converter can be seen as a typical second-order dynamic system, it is hardly to balance multiple control objectives. The inertia time constant usually contradicts with the dynamic response indices, such as the response speed and overshoot suppression ability under the step response of the positive power. To solve these problems, the frequency at the PCC (Point of Common Coupling) is estimated by the SOGI-FLL (Second Order General Integrator Frequency Locked Loop) and filtered for the feedforward control of the positive power control loop in this paper. With this strategy, both the dynamic response and the inertia power support can be improved. Finally, experiments are conducted on a 228 kW PV string inverter to validate the effectiveness of the proposed strategy.