Application of Superconducting Magnetic Energy Storage to Compensate the Pitch System Delay in Output Power Smoothing of Wind Turbines

Wind power is one of the most widely available renewable energy sources (RES). However, due to the intermittent nature of wind, the output power of wind turbines (WTs) is always variable. In WTs, at speeds lower than the rated wind speed, the goal is to maximise the power extracted from the wind. At higher wind speeds, the goal is to keep the WT's power constant at rated value; that is typically done by the WT's pitch control system. The operation of the pitch system has a delay due to WT's blades and rotor inertia and limited pitch rate, which may lead to output power fluctuations. Superconducting magnetic energy storage (SMES) has fast response and high efficiency. This paper explores the application of SMES to compensate for the pitch system delay in output power smoothing of a permanent magnet synchronous generator (PMSG)-based WT. It is verified that the SMES properly compensates for the pitch lag by absorbing the surplus power and releasing it at power shortage intervals, particularly when pitch control returns the blades to their initial position. In the meantime, the pitch system reduces the SMES coil current and prevents it from saturation, which allows selecting an optimal/practical coil size for the SMES.