RT23 | Interaction between Grid-Forming converter and synchronous machine - PHIL validation

The increasing penetration of power-electronics interfaced resources brings new challenges regarding the stability of power systems. To improve their stability, grid-forming controlled converters have been proposed as an alternative to their conventional grid-following counterparts. However, their interactions with classical electrical production have to be studied. The objective of this presentation is to deeply analyze the interactions between synchronous machines and converters. At first, a brief recall on the synchronous machine and Grid-Forming converter modelling will be presented. Different test cases will be illustrated: 2 synchronous machines connected together, 1 synchronous machine with a converter, etc. Then, different simple models will be derived from these test cases: A first simplified model to obtain the dominant pole and the other one to obtain the first oscillating poles. This approach is similar to the classical approach with 2 synchronous machines, but as indicated during the presentation with a higher damping. Moreover, we will show that a frequency droop applied to a Grid-Forming converter has a significant effect on the damping of the overall system. To validate this study, a lab-scale test-bench composed of: 1- a 12 kVA synchronous machine mock-up which emulates a classical production, 2- a 7.5 kVA 2-level inverter with an output LCL filter mock-up which is totally open and can be controlled in Grid-Following or Grid-Forming mode, 3- a real-time simulated power system on RT-LAB which can be connected to the remaining components using Power-Hardware-In-the-Loop principle through a 20kVA power amplifier. This test bench will be used to illustrate the interaction mechanisms between synchronous-based and power electronics-based generations.