Modelling and Design of Virtual Synchronous Generator Control for Back-to-Back Inverter Testing in Renewable Energy Systems

This paper presents a Virtual Synchronous Generator (VSG) based control method for back-to-back (B2B) inverters testing configuration in renewable energy applications. The test configuration includes two inverters (both are 3-leg inverters) which are B2B connected through an LCL filter, where one inverter acts as a Grid-Forming (GFM) mode and the other operates as a Grid-Following (GFL) mode. In the proposed control method, active power controller (APC) is designed based on VSG concept which forms the frequency at the point of connection (POC), and the reactive power controller (RPC) establishes the voltage magnitude at the POC. On the other hand, the GFL inverter utilizes an input current control method and maintains synchronization with the POC which is formed by the GFM inverter through the use of a Phase-Locked Loop (PLL). This B2B inverters configuration enables power to recirculate through the GFL inverter back to the common DC-link, allowing continuous power flow. A key feature of this B2B configuration is that it eliminates the need for high-power DC supplies and AC loads to test high-power inverters, requiring only a low-power DC supply to offset minor losses in the system. The concept is validated through MATLAB simulations and experimental results.