This paper proposes an approach for distribution system load forecasting, which aims to provide highly accurate short-term load forecasting with high resolution utilizing a support vector regression (SVR) based forecaster and a two-step hybrid parameters optimization method. Specifically, because the load profiles in distribution systems contain abrupt deviations, a data normalization is designed as the pretreatment for the collected historical load data. Then an SVR model is trained by the load data to forecast the future load. For better performance of SVR, a two-step hybrid optimization algorithm is proposed to determine the best parameters. In the first step of the hybrid optimization algorithm, a designed grid traverse algorithm (GTA) is used to narrow the parameters searching area from a global to local space. In the second step, based on the result of the GTA, particle swarm optimization is used to determine the best parameters in the local parameter space. After the best parameters are determined, the SVR model is used to forecast the short-term load deviation in the distribution system. The performance of the proposed approach is compared to some classic methods in later sections of this paper.

This paper proposes a temporary frequency-support scheme of a doubly fed induction generator (DFIG) that can improve the frequency nadir while ensuring rapid frequency stabilization, particularly for high wind power penetration levels (WPPLs). Upon detecting a disturbance, the power reference is increased by the incremental power and maintained for a preset period. The proposed incremental power varies with the rotor speed and WPPL. Then, to force the rotor speed to converge to a stable operating range, the reference decreases with the rotor speed. During the deceleration period, the proposed scheme releases less kinetic energy, which helps in the rapid recovery of the rotor speed. During the acceleration period, to accelerate the rotor speed recovery, the reference smoothly decreases with time and rotor speed until it reaches the maximum power point tracking curve. The test results, which are based on the IEEE 14-bus system, demonstrate that even though less kinetic energy is released, the proposed scheme can improve the frequency nadir while rapidly recovering the rotor speed under various wind conditions and penetration levels, but it is particularly effective for higher penetration levels. The scheme helps providing a promising solution to the ancillary services of a DFIG in a power system with high WPPLs.

This paper introduces the concept of constant volt/hertz operation of offshore wind power plants (WPPs). The deployment of offshore WPPs requires power transmission from the plant to the load center inland. Because this power transmission requires submarine cables, there is a need to use high-voltage direct current (HVDC) transmission, which is economical for distances greater than 50 km. In the concept presented here, the onshore substation was operated at 60 Hz synced with the grid, and the offshore substation was operated at variable frequency and voltage, allowing the WPP to be operated at constant volt/hertz. In this paper, a variable frequency at rated volt/hertz operation was applied to a Type 3 doubly fed induction generator (DFIG) wind turbine generator. The size of the power converter at the turbine can be significantly reduced from 30 % of the rated power output in a conventional Type 3 turbine to 5 % of the rated power. The DFIG allows each turbine to vary its operating speed with respect to the other turbines. Thus, small wind diversity within the WPP can be accommodated by the DFIG, and the collector system frequency can be controlled by HVDC to follow large variations in average wind speed.