Linear Parameter-Varying Control of A Power-Synchronized Grid-Following PLL-Less Inverter

This paper proposes a Linear Parameter-Varying loop-shaping controller for a power-synchronized Phase-locked Loop (PLL)-less grid-following inverter (GFLI). This control strategy regulates the inverter's output active and reactive powers at the terminal instead of the point of connection and does not require a PLL for extracting the voltage phase angle. Hence, the prevalent stability issues exhibited when GFLIs are connected to weak grids are not present, and the proposed GFLI control strategy can work under both very weak and strong grid conditions without being prone to instability. In this approach, the controller parameters are functions of the operating point and changed during the real-time operation such that the closed-loop performance is preserved in all operating points. Furthermore, since the grid impedance is a factor in the design process, a robustness analysis against grid impedance estimation error is conducted, and it is shown that discrepancies in estimated and real grid impedances are unlikely to make the system unstable. The performance of the proposed control design is validated in Matlab/PLECS and experiment for both strong and weak grids.