Modified grid forming converter controller with fault ride through capability without PLL or current loop

The electrical power system is facing several challenges as the penetration of converter based renewable power increases, including a reduction of the synchronous based inertia, loss of converter synchronism and weakened grids. Grid forming converter controllers, especially the socalled Virtual Synchronous Machines (VSMs), are seen as a potential solution for some of these issues. VSM controllers mimic the behaviour of a synchronous machine to different degrees of detail. Of these implementations, those that do not use Phase Locked Loops (PLLs) or current loops have been shown to be advantageous. This paper presents several proposals for a Fault Ride Through controller for a VSM controlled converter without a PLL or vector current control loop, which are imposing limitations on the stability of the inverter in low Short Circuit Ratio grids. Also, a method to limit the power and voltage/reactive power references, considering the converter maximum current, is presented. This paper validates and shows the advantages and limitations for the proposed control structures through extensive simulations using MATLAB Simulink for different grid conditions applied to a wind turbine.