In this paper, a distributed optimal reactive power control (DORPC) scheme is proposed for minimizing the total losses of doubly fed induction generator (DFIG)-based wind farms (WFs), including the losses of generators, converters, filters, and networks. The DORPC minimizes total WF losses by optimally coordinating reactive power outputs of the DFIG stator and the grid-side converter. The optimal control problem is solved in a distributed manner by using the consensus alternating direction method of multipliers (ADMM). With the consensus ADMM, the total WF loss optimization problem is transformed into a distributed optimal power flow problem considered with DFIGs’ optimal operation. The optimization problem with local constraints considers the reactive power limit of DFIG-based wind turbines (WTs) and the voltage limits at all WT terminal buses inside the WF. In the DORPC, the optimal control problem is solved by the collector bus station controller and WT controllers in parallel, only with the information exchange between immediate neighbors. It eliminates the need of a central controller and centralized communication, implying better robustness and plug-and-play capability. A WF with 20 DFIG-based WTs was used to validate the proposed DORPC scheme.

Introduction

Wind power has become a widely used renewable energy source (RES) with substantial potential and mature technology. With wind power generation expanding, the intermittency of wind power and the interaction between wind farms (WFs) and power systems introduce challenges [1]. The doubly fed induction generator (DFIG)-based wind turbine (WT) has been widely used in modern WFs due to high controllability and small converter rating [2]. With power electronic converters, DFIG-based WFs can regulate reactive power independently and provide reactive power support for power systems [3]. Voltage and reactive power control of WFs has motivated numerous studies. The WF is required to maintain the power factor within the limit at the point of connection (POC) [4,5] or provide reactive power support for power systems while tracking the dispatch command from the transmission system operator (TSO) [6]. Dynamic power electronic devices, such as static var compensators (SVC) and static synchronous compensators (STATCOM), are used in WFs for providing rapid reactive compensation and voltage control [7,8]. In DFIG-based WFs, each DFIG-based WT is equipped with power electronic converters. The DFIG-based WF can utilize the capabilities of the DFIG-based WTs for providing reactive power support to meet grid code requirements. The most widely used reactive power control scheme in WFs is the proportional dispatch (PD) scheme, which is simple, easy to implement, and considers the reactive power margin of each DFIG-based WT [9,10]. However, without the optimizing reactive power references for individual WTs, the WF controller cannot achieve WF optimal operation. In [11], the particle swarm optimization (PSO) was adopted to dispatch reactive power of WTs by minimizing total active power losses along the cables and the transformers of WTs.