Responsive and Resilient Vector Current Control for Variable Grids

Abstract

This article presents a set of control enhancements for standard vector current control (VCC) that improves its stability and dynamic performance in an extended range of SCRs. Increasingly, the local SCR as seen by the converter fluctuates, making it difficult to tune the control algorithms. Usually, stability is prioritised over performance and converters become less responsive. The modifications proposed in this article allow VCC to maintain high dynamic performance and stability, optimised to the real-time grid conditions. These modifications do not alter the standard operation of the outer loops, the current controller or the phase-locked loop. Instead, a Pre-emptive Voltage Decoupler (PVD) is introduced to compensate reactive current for changes in active current, thus decoupling the local voltage from active power. The PVD is optimised to the grid conditions by an impedance estimator. Further, an instability detector is proposed, anticipating instability and triggering preventive action, improving the resiliency of the converter. Supervisory control is employed to coordinate instability detection, prevention, impedance estimation and PVD optimisation. As a result, VCC is more responsive and adaptable to variable grid conditions. It is also more resilient to grid events, such as the loss of a transmission line.

Keywords

• Active power
• voltage decoupling
• impedance estimation
• instability detection
• vector control
• weak grid