Damping Local Oscillations of a Direct- Drive PMSG Wind Turbine

Abstract

Abstract-Damping local oscillations is vital in the operation of a direct-drive permanent magnet synchronous generator wind turbine as well as its integration into a grid. Currently, these oscillations are controlled by proportional-integral controllers. This paper proposes the inclusion of virtual resistors to improve the performance of the wind turbine further. Simulation results show that virtual resistors, connected in series to stator windings, have a positive impact on the damping of local oscillations. They significantly reduce the rise and settling times of the rotor speed, electromagnetic torque, active power and reactive power and increase the corresponding damping ratios. In contrast, the ones, connected in parallel to stator windings, have a negative impact on the damping of local oscillations. This indicates that an appropriate selection and connection of virtual resistors improves the dynamic and small-signal performances of a PMSG wind turbine.Keyword-Damping local oscillations, permanent magnet synchronous generator, wind turbine, dynamic performance, small-signal stability, virtual resistors I. INTRODUCTION For the past two centuries, rapidly growing populations and modernization trends have accelerated the demand for energy. Today, the world heavily depends on fossil fuels such as oil, coal, and natural gas for its increasing energy requirements. However, this fossil-fuelled economy is facing challenges including depletion of reserves, global warming, security concerns, and rising cost [1]. In tackling these challenges, much attention is given to the development of renewable energy, among which harnessing wind energy is the cheapest alternative [2,3].Three types of wind energy technologies-squirrel-cage induction generator (SCIG), doubly fed induction generator (DFIG) and permanent magnet synchronous generator (PMSG) wind turbines-are widely adopted in the wind industry. Compared to SCIG, DFIG and PMSG are popular for two reasons [4]. Firstly, they offer the opportunity to operate the machine at maximum power for various wind speeds, and secondly, they have less mechanical stress on their shafts. These days, the popular variable-speed wind turbines employed in large-scale wind parks are DFIG wind turbines [5]. Nevertheless, recently, direct-drive PMSG wind turbines are gaining momentum among researchers, engineers and turbine manufacturers for their high efficiency, low power loss and smaller size [6 -11].The integration of wind power into grids is rapidly growing. In some European countries, the level of penetration has reached as high as 21% [12]. However, due to this high penetration and the intermittent nature of the wind, there are concerns such as generation reserve, power system stability and reliability [13]. Furthermore, wind turbines themselves have stability problems, which surely challenge transmission system operators. In large grids, the ability of both local and system-wide power system oscillation damping plays a crucial role [14].A range of efforts have been made to damp local ...

Model predictive control of a doubly fed induction generator

“…In (3)(4)(5)(6)(7)(8)(9)(10), it is seen that if the stator resistance is neglected, the stator active power is dependent on the rotor quadrature current. In (3)(4)(5)(6)(7)(8)(9)(10)(11), it is seen that the stator reactive power is dependent on the rotor direct current. The last terms in (3.7) and (3.8) are known as the coupling terms and are added at the output of the proportional-integral controllers.…”

“…𝛷 𝑞𝑠 = −𝛷 𝑠 = 𝐿 𝑠 𝐼 𝑞𝑠 + 𝐿 𝑚 𝐼 𝑞𝑟 (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) Rewriting these, making the stator currents the subject of the formula yields:…”

“…Equations (3-18) - (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) form the basis for indirect FOC using SVOC. In (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21), it is seen that if the stator resistance is neglected, the stator active power is dependent on the rotor direct current.…”

“…Equations (3-18) - (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) form the basis for indirect FOC using SVOC. In (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21), it is seen that if the stator resistance is neglected, the stator active power is dependent on the rotor direct current. In (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)<...>…”

“…WECS deploy the use of highpowered electronic switches to regulate the output of the system [8]. Both synchronous and asynchronous generators are used in WECS [9]. The derivation of electrical energy from WECS is rapidly gaining widespread popularity and seems and attractive option to coal based power generation [10].…”