Online Harmonic Resonance Monitoring for Adaptive Control of HVDC System

Integration of these active systems brings new challenges and opportunities to have a more resilient operation of transmission system. Harmonic resonance issues have always been a challenge and are traditionally dealt with by using harmonic filters or damping devices. The control function/flexibility of HVDC converters open new doors for suppression of harmonics and providing additional damping if necessary. This can be performed using different active control methods, e.g., digital filtering. To control the harmonics/damping adaptively, it is crucial to detect them properly, so that damping can be reshaped locally. In this study, a comparative analysis among different harmonic detection methods, time domain (SOGI-FLL) and frequency domain (SWDFT and SWIFT), has been analyzed in terms of speed, accuracy and computational effort. In the ideal testing environment, SOGI-FLL performs faster, more accurately, and with less computational effort. However, it can impose some instability under an actual transient event that contains varying and complex harmonic content. This can be avoided by additional filters and logic. On the other hand, time domain-based methods perform stable frequency information in actual complex situations, while causing more computational effort. All methods provide a fast response, <5 ms, and enough accuracy to be processed in the control action depending on the parameter settings. Integration of these methods into control functions shall be studied further considering different aspects given in Section 3.5, safety logic, threshold design and digital filtering. To analyze further how they perform, it is recommended to experiment the resonance detection methods on a site, without control function integration.

In the case of an event, the records can be analyzed as a pre-control integration stage. Together with resonance detection and control actions, so called adaptive control, can avoid harmonic stability issues and provide more damping when necessary.