Gain Scheduled Torque Compensation of PMSG-Based Wind Turbine for Frequency Regulation in an Isolated Grid

Abstract

Frequency stability in an isolated grid can be easily impacted by sudden load or wind speed changes. Many frequency regulation techniques are utilized to solve this problem. However, there are only few studies designing torque compensation controllers based on power performances in different Speed Parts. It is a major challenge for a wind turbine generator (WTG) to achieve the satisfactory compensation performance in different Speed Parts. To tackle this challenge, this paper proposes a gain scheduled torque compensation strategy for permanent magnet synchronous generator (PMSG) based wind turbines. Our main idea is to improve the anti-disturbance ability for frequency regulation by compensating torque based on WTG speed Parts. To achieve higher power reserve in each Speed Part, an enhanced deloading method of WTG is proposed. We develop a new small-signal dynamic model through analyzing the steady-state performances of deloaded WTG in the whole range of wind speed. Subsequently, H ∞ theory is leveraged in designing the gain scheduled torque compensation controller to effectively suppress frequency fluctuation. Moreover, since torque compensation brings about untimely power adjustment in overrated wind speed condition, the conventional speed reference of pitch control system is improved. Our simulation and experimental results demonstrate that the proposed strategy can significantly improve frequency stability and smoothen power fluctuation resulting from wind speed variations. The minimum of frequency deviation with the proposed strategy is improved by up to 0.16 Hz at overrated wind speed. Our technique can also improve anti-disturbance ability in frequency domain and achieve power balance.

Multiple Adaptive Model Predictive Controllers for Frequency Regulation in Wind Farms

“…Since the rotor speed is stabilized by pitch control system at its nominal speed in speed section 3, the state variables and state-space matrices are different from the other two speed sections. Thus, two ARX models corresponding to different speed sections are established as shown in (11) and (12), respectively. Their orders of A(z) and B(z) are selected by Akaike's Information Criterion.…”

“…WTG cannot fully rely on the pitch system to regulate frequency due to its delay characteristic [9]. 3) Deloading control [10]- [11]. In this case, WTG will not operate in the MPPT mode, and the power reserve can be achieved by over-speeding control.…”

Fast Power Reserve Emulation Strategy for VSWT Supporting Frequency Control in Multi-Area Power Systems

“…With regard to de-loading control methods, they are based on operating VSWTs below their optimal generation point. A certain amount of active power reserve is thus available to supply additional generation under a contingency [48]. It can be implemented by regulating the pitch angle from β min to a maximum value or by increasing the rotational speed above the Maximum Power Point Tracking (MPPT) speed (over-speeding) [49].…”

HVDC Transmission Technology of Wind Power System with Multi-Phase PMSG

“…where, k p5 and k i5 are the proportional and integral coefficients, respectively. Finally, the required DC transmission voltage U HVDC is realized by nearest level control (NLC) with voltage sorting [31].…”