1：Experimental Design and Method Selection:

The paper presents a novel AC coupled solution that transforms an existing grid following PV system to a grid forming one without any hardware and software modification of the PV inverter. The resulting system, the Photovoltaic Synchronous Generator (PVSG), is achieved by an AC coupled supercapacitor-based energy storage system (ESS). The novel control of the PVSG is implemented in the ESS side. The novel control scheme includes a fast and slow instantaneous power controls. The fast-instantaneous power flow control is fulfilled by the DC-link voltage control and AC voltage control. The cascaded voltage source controls enable the fast-instantaneous power balance, while a slow instantaneous power control is used to implement the inertia and grid synchronization.

2：Sample Selection and Data Sources:

The correctness and effectiveness of the proposed PVSG is validated experimentally in a 480V PVSG prototype with TMS320F28379D DSP controller.

3：List of Experimental Equipment and Materials:

The experimental setup includes a PVSG experimental setup with DC-DC and DA-AC converters employing Applied Power System (APS) IAP 100T120 IGBT power modules. A 32-bit floating-point dual-core TMS320LF28377D DSP is used to realize all the control algorithms in the experiment.

4：Experimental Procedures and Operational Workflow:

The DC voltage loop is first experimentally verified. The damping oscillation frequency of the SC current loop is selected as 2000 Hz with critical damping factor, while the DC link voltage loop is designed with damping oscillation frequency of 200 Hz which is one-tenth of the current loop.

5：Data Analysis Methods:

The proposed power controller is experimentally compared with the PI-based power control with the power reference step.