Abstract:The fluctuations of wind power impact the stable operation of a power system as its penetration grows high. Energy storage may be a potential solution to suppress these fluctuations and has drawn much attention in recent years. As the time scale of wind power fluctuations is in a range of seconds to hours, multi-type energy storage with complementary characteristics, such as the combination of energy-type storage devices (ESD) and power-type storage device (PSD), may be technically and economically feasible to suppress multi-time-scale wind power fluctuations. Therefore, system control is very important when the power allocation among each of the energy storage units is considered. In this paper, a novel coordinated control strategy based on model predictive control (MPC) was proposed for wind power fluctuation suppression, which employs MPC for the total power required for the whole energy storage system and then allocates it between ESD and PSD with the low-pass filter algorithm (LFA) method. Due to the predictive feature of MPC, the power requirement of the energy storage system can be obtained with little time delay, which means less energy is needed. The effectiveness of the proposed control strategy was verified in a time-domain simulation system. The influence of wind speed conditions and LFA time constant on the wind/storage system were further discussed.

Abstract:The impact of the rapid development of large-scale centralized wind power farms on the power system is drawing more and more attention. Some topics about grid-connected wind power are discussed from the view of complex network theory in this paper. Firstly, a complex network cascading failure model is established, combined with dynamic AC power flow (DACPF). Then, the IEEE 30 bus system is used to analyze its validity using the simulations of nodes removal, wind power integration, as well as the change of current and voltage boundaries. Furthermore, the influences of wind power before and after smoothing are investigated. Also, different wind power coupling locations are studied. Finally, some significant conclusions are obtained to provide references for large-scale wind power integration.

No abstract

Controlled islanding has been proposed as a last resort action to stop blackouts from happening when all standard methods have failed. Successful controlled islanding has to deal with three important issues: when, and where to island, and the evaluation of the dynamic stability in each island after islanding. This paper provides a framework for preventing wide-area blackouts using wide area measurement systems (WAMS), which consists of three stages to execute a successful islanding strategy. Normally, power system collapses and blackouts occur shortly after a cascading outage stage. Using such circumstances, an adapted single machine equivalent (SIME) method was used online to determine transient stability before blackout was imminent, and was then employed to determine when to island based on transient instability. In addition, SIME was adopted to assess the dynamic stability in each island after islanding, and to confirm that the chosen candidate island cutsets were stable before controlled islanding was undertaken. To decide where to island, all possible islanding cutsets were provided using the power flow (PF) tracing method. SIME helped to find the best candidate islanding cutset with the minimal PF imbalance, which is also a transiently stable islanding strategy. In case no possible island cutset existed, corresponding corrective actions such as load shedding and critical generator tripping, were performed in each formed island. Finally, an IEEE 39-bus power system with 10 units was employed to test this framework for a three-stage controlled islanding strategy to prevent imminent blackouts.