۱- Introduction

۲- Bi-level control architecture

۳- Consensus-based distributed active power and reactive power dispatch for WFC

۴- Centralized MPC-based active and reactive power control of wind farm

۵- Case study

۶- Conclusion

References

Abstract

This paper proposes a bi-level decentralized active and reactive power control (DARPC) for the large-scale wind farm cluster (WFC) composed of several wind farms. The WFC tracks the active power reference from the transmission system operator (TSO) while controlling the bus voltage of the point of connection (POC), and maintaining the wind turbine (WT) terminal voltages stable in each wind farm. In the upper level, a distributed active and reactive power control scheme based on the consensus protocol is designed for the WFC, which can achieve fair active and reactive power sharing among multiple wind farms, and generates active and reactive power references for each wind farm. In the lower level, a centralized control scheme based on Model Predictive Control (MPC) is proposed, which can effectively regulates active and reactive power outputs of all WTs within the wind farm. The proposed centralized control scheme can maintain WTs terminal voltage close to the rated voltage while tracking the power reference from the upper level control. The DARPC can effectively reduce the computation burden of the WFC controller by distributing the computation and monitoring tasks to several wind farm controllers. Moreover, the communication cost is reduced. A WFC with 8 wind farms and totally 128 WTs was used to validate the proposed DARPC scheme.

Introduction

Renewable energy, especially wind energy, is developing rapidly over the world because of the pressure of reducing carbon emission and dependence on fossil fuels. The European Wind Energy Association (EWEA) estimates that the installed capacity of wind power could expand to 320 GW by 2030 [1]. In Denmark, the target is to achieve 50% electricity from wind by 2020 and become 100% fossil fuel free by 2050 [2]. As wind power penetration increases, the large-scale wind farm cluster (WFC) is required to have the same level of performance as conventional generation plants [3]. Due to the intermittency of wind power, the increasing wind power penetration has introduced various challenges to the power system operation [4]. Such challenges include power reference tracking, voltage regulation, ancillary services for power systems, etc. [5]. Usually, the short circuit ratio at the point of connection (POC) is small because large-scale wind farms are mainly located in areas far from load centers [6], and the grid at the POC is weak. The voltage fluctuation caused by the wind power variation is quite large. Voltage support at the POC has been specified in several grid codes around the world. The WFC controller receives the power dispatch command and specific technical requirement from the transmission system operator (TSO), such as the POC voltage requirement and reactive power dispatch command [7]. For active power control of the large-scale wind farms, the main control objective is power tracking, and the control strategy can be classified into proportional distribution (PD) control [8,9], proportional-integral (PI) control [10] and optimal active power control [11,12]. Among these, the PD strategy is widely adopted in modern wind farms due to its simple implementation, and considers the available power and Var capability of wind turbines (WTs) [13,14]. The voltage and reactive power control of wind farms, as one of the major topics of wind power integration, have motivated a great number of studies.