Improvement of power decoupling for grid-forming control: An output voltage compensation approach

Grid-forming control is an effective method for enhancing the stability of power systems dominated by power electronic devices. The ability to independently control active power (P) and reactive power (Q) depends on the characteristics of the line impedance. In high-voltage systems, the line impedance is equivalent to pure inductance, allowing independent control of P and Q. However, in medium and low-voltage grids with distributed renewable energy integration, the resistive component of the line cannot be neglected, resulting in significant coupling between P and Q. Power coupling reduces the accuracy of reactive power control and can even lead to system instability. To address this issue, the influencing factors of power coupling are first analyzed through a power coupling model. Then, the comparison between output voltage and the degree of power coupling indicates that the ability to compensate the converter's output voltage determines the effectiveness of power decoupling. Based on these observations, an improved decoupling approach is proposed. By directly compensating the output voltage using apparent power feedforward (APPFF), power coupling is effectively eliminated. Compared to existing virtual impedance decoupling methods, the APPFF method can eliminate power coupling in situations with a large R/X ratio without slowing down the response speed of the converter. The effectiveness of this method is validated through both simulations and experimental results.