Search

This paper presents a uniform optimal power sharing strategy to coordinate the wind turbines (WTs) in a wind farm (WF) to provide occasional and continuous frequency response (FR). The coordination of WTs is formulated as an optimisation problem that takes into account the WT dynamics and tries to reduce the long term loss of energy yield caused by the provision of FR. This is achieved by maximising the total kinetic energy of the WF over time while reducing wear and tear of WTs. The proposed optimal power sharing strategy relies on periodic communication between each WT and a WF controller. Local linear approximations are employed to predict the system behaviour and the solution of the optimisation problem is obtained using the proposed centralised and/or distributed algorithm. The distributed algorithm only requires one‐way communication between the WF controller and local WTs, reducing the communication overheads. Simulation studies are carried out on a WF model to demonstrate the effectiveness of the proposed strategy. The results show the strategy enables reduction of yield loss over previous methods while avoiding over torque operation during FR provision.

Power system stabiliser (PSS) widely used to enhance the stability of power systems is based on the feedback of rotor speed error with respect to the rated value. However in many occasions, after the disturbances, it is desirable to re-synchronise all generators first rather than to make all generators back to the rated 50/60 Hz immediately. This study proposed a distributed power system stabiliser (DPSS) that aims to synchronise generators by the feedback of relative rotor speed errors of each generator with respect to its neighbouring generators. The proposed DPSS is analysed on a double machine infinite bus system, and shows that the proposed DPSS can enhance the stability of power systems by increasing the synchronising torque. To evaluate the efficiency of proposed method, the proposed DPSS is tested on three benchmark systems. The simulation results verify the efficacy of theoretical analysis, show the outperformance of DPSS over other PSSs, and demonstrate the superiority of re-synchronising generators over making them back to rated value in the post-fault. Communication issues have also been evaluated, which demonstrates the robustness of DPSS against both communication failures and random delays.

Utility-scale energy storage systems (ESSs) have been widely used in power system to facilitate its secure and economic operation. This paper investigates the transient influence of ESSs on bulk power systems. ESSs are treated as a controllable current source, whose dynamic response is represented by a first order transfer function. The influence of ESSs on the system dynamics is analyzed on a single machine infinite bus (SMIB) system with a ESS connected at its transmission line. The analytical result indicates that the deviated electrical power of synchronous machine (SG) caused by ESS is linear to both the d-axis and q-axis current of ESS. Based on this result, a control strategy of ESS’s reference current is proposed to improve the system damping. Case studies are performed on both SMIB system and the 2-Area 4-Generator system to validate the correctness of the analysis and the effectiveness of proposed ESS control strategy.

Constant-Power Load (CPL) introduces destabilizing effect to dc-dc converters, which may lead to voltage oscillation or collapse. To mitigate the destabilizing problem brought by CPL, a nonlinear boundary controller is proposed in this paper, which has a nonlinear switching line. The converters' dynamics on the state space plane is analyzed through phase portrait. The proposed controller is verified by simulation tests in MATLAB/Simulink for controlling the output voltage of a buck converter with CPL.

Static synchronous compensator (STATCOM) and battery energy storage (BES) have been increasingly employed in power systems for the reliable and economic operation of power transmission. However, the transient interaction between the electrical power of synchronous generator (SG) and the active power of STATCOM with/without BES is still misunderstood and treated incorrectly. This paper presents an analysis of this interaction and investigates the control and optimal placement of STATCOM with/without BES for the purpose of improving SG&rsquo, s damping, and thus enhancing system&rsquo, s oscillation damping performance. The results show that (1) the deviated electrical power of SG is not equal to the active power of STATCOM. Instead, it is related to STATCOM&rsquo, s current, placement and SG&rsquo, s electrical states, (2) with the increased damping as the index, the optimal location for STATCOM with BES is at the terminal of SG, while it is at the electrical mid-point of the transmission line for STATCOM without BES. Non-linear simulations and eigenvalue analysis are performed to validate the correctness of the above results.