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The interaction between controllers of doubly fed induction generators (DFIGs) and fixed series compensations may cause a new type of subsynchronous resonance (SSR), namely subsynchronous control interaction. To mitigate this emerging issue, a novel suppression method, embedding subsynchronous notch filters (SNFs) into DFIG converter controllers, is proposed in this study. By using the impedance‐model‐based analysis and a quantitative location‐dependent performance index, the best location is identified to insert SNFs into the controllers of both rotor‐side and grid‐side converters. Two specific SNF schemes are recommended for practical use, and a design procedure is developed to tune their parameters. As a case study, they are then applied to a practical series‐compensated wind‐farm system that suffered from SSR. Both impedance analysis and time‐domain simulations have been conducted to investigate their performance. The results verified that they can defuse the interaction between DFIG controllers and series compensation; therefore, successfully eliminating the risk of unstable SSR under all possible operating conditions. The proposed SNF schemes are easy to design and implement, robust to changeable operating conditions and would not affect the normal dynamics of DFIGs. So, they are of great potential in addressing practical SSR issues. [ABSTRACT FROM AUTHOR]

Practical subsynchronous instability events have been observed in doubly fed induction generator‐based wind farms, which are radially connected to fixed series compensated transmission lines. As a special type of subsynchronous resonance, this phenomenon is described here as subsynchronous control interaction (SSCI). This study proposes a centralised SSCI mitigation scheme named as subsynchronous damper (SSD). In this scheme, an additional high‐power electronic voltage‐sourced converter is added to the collection bus of wind farms. It is designed to dissipate the electrical resonance power of SSCI. Thus, SSD provides positive damping for SSCI. Its basic principle is explained with equivalent electric circuit and the sufficient conditions for stabilisation are obtained mathematically. Controller design guidelines are given and have been verified first by eigenvalue analysis. Then a method to choose the capacity of power electronic converter is proposed. The effectiveness of SSD is finally demonstrated by extensive time‐domain simulations on a target system. [ABSTRACT FROM AUTHOR]

Torsional damping controllers, such as supplementary excitation damping controllers (SEDCs), are widely used to stabilise subsynchronous resonance (SSR) induced by torsional interactions (TIs) between turbo‐generators and series‐compensated power systems. However, because of the changeable operating situations of a power system, it is a great challenge to design them to guarantee torsional stability under all possible operating conditions. This study proposes a global optimal control‐design procedure for tuning SEDCs to accommodate the variation of system conditions. Considering TI is a small‐signal stability issue, the non‐linear power system is converted into a family of linear parameter varying models and the parameter‐tuning task for multiple SEDCs is formulated into a multi‐model constrained non‐linear optimisation problem. A global optimisation procedure based on genetic algorithm and simulated annealing is designed to efficiently solve this problem and obtain a set of robust or several sets of gain‐scheduling SEDCs. The proposed method is applied to a multi‐machine series‐compensated power system. The results of both eigenvalue analysis and time‐domain simulation have fully demonstrated the effectiveness of the optimised SEDCs in stabilising SSR under all possible operating conditions. [ABSTRACT FROM AUTHOR]