Flexible voltage controller and tuning method for robust operation of standalone grid forming converters

The grid forming inverter plays a key role in standalone power systems, where it must generate a stable and stiff voltage for the elements connected to the grid. One of the most common control structures to achieve the voltage source behavior is the cascaded voltage–current controller in synchronous reference frame. However, conventional tuning strategies do not ensure a robust performance of the voltage controller when delays and bandwidth separation are not negligible. To solve this problem, this work proposes a design and optimization methodology based on bilinear matrix inequalities optimization. This approach ensures the robustness of the voltage control on a wide operational range, while meeting different constraints, such as the bandwidth or the decay rate of the system response. The proposed methodology is not limited to conventional control structures, based on decoupled PI regulators and feedforward terms on each of the axes of the synchronous reference frame. Instead, additional terms or degrees of freedom can be added to boost the performance without increasing the tuning complexity. Simulations show that the proposed controller, along with the tuning methodology, can enhance system robustness with minimal impact on the dynamic response.