Application of Type 3 Wind Turbines for System Restoration

Back-To-back voltage-source converters enable Type 3 wind turbines (WTs) to operate with zero-power transfer, and this allows them to restore the system both in black-starting and stand-Alone loaded stages. Therefore, this paper first identifies the prerequisites for Type 3 WTs to act as voltage-source interfaces in the case of bulk system outage and reveals their inherent deficiency for system restoration from the voltage/frequency and output power ( P-f and Q-V) relationships. These analyses provide the basic guidance for subsequent control updating. Afterwards, to allow Type 3 WTs to provide black-starting capacity, a concomitant control strategy and a restoration sequence are proposed. The uncovered P-f relationship is reinforced by self-maintained frequency control for the subsequent stand-Alone loaded stage. The mechanism of frequency matching among multiple WTs is also discussed. Furthermore, a mathematical analysis for the impacts of controller parameters on the frequency characteristics of a Type 3 WTs-based stand-Alone system is developed, thereby providing the guidance for control design. Eventually, a specific islanded system, merely consisting of Type 3 WTs and some passive local loads, is constructed to verify the feasibility of Type 3 WTs for system restoration and to validate the analytical results.