Load Reduction for Wind Turbines: an Output Constrained, Subspace Predictive Repetitive Control Approach

Abstract

Abstract. Individual Pitch Control (IPC) is a well-known approach to reduce blade loads on wind turbines. Although very effective, IPC usually requires high levels of actuator activities, which significantly increases the pitch Actuator Duty Cycle (ADC). This will subsequently result in an increase of the wear on the bearings of the blades and make the current IPC design not economical viable. An alternative approach to this issue is to reduce the actuator activities by incorporating the output constraints in IPC. In this paper, a fully data driven IPC approach, which is called constrained Subspace Predictive Repetitive Control (cSPRC) is introduced. The output constraints can be explicitly considered in the control problem formulation via a Model Predictive Control (MPC) approach. The cSPRC approach will actively produce the IPC action for the necessary load reduction when the blade loads violate the output constraints. In this way, actuator activities can be significantly reduced. Two kinds of scenarios are simulated to illustrate the unique applications of the proposed method: wake-rotor overlap and turbulent wind conditions. Simulation results show that the developed cSPRC is able to account for the output constraints into the control problem formulation. Since the IPC action from cSPRC is only triggered to prevent violating the output constraints, the actuator activities are significantly reduced. This will help to reduce the pitch ADC, thus leading to an economical viable load control strategy. In addition, this approach allows the wind farm operator to design conservative bounds to guarantee the safety of the wind turbine control system.

Reply on CC1

“…Based on the wind turbine model, the implementation of the case study is illustrated in Figure 1. The aero-structural dynamic part of the wind turbine is simulated in the FAST model (Jonkman and Buhl, 2005) while the turbine control part is implemented in Simulink (Mulders et al, 2019). The developed the cSPRC approach, which is encompassed by a light grey block, will be described in Section 3.…”

“…The baseline control is based on a Linear Time Invariant (LTI) dynamical system (Bak et al, 2013). The MBC-based IPC is implemented following the work of Multders et al (Mulders et al, 2019). On the other hand, the proposed cSPRC approach, will be introduced in Section 3 to show the capability of output constraints and its application to the load control of wake overlapping and turbulent wind flow scenarios.…”

“…This makes it possible to use simple linear Single-Input Single-Output (SISO) control approaches for IPC, such as Proportional-Integral (PI) controllers (Bossanyi, 2005;van Solingen et al, 2014). More recently, other advanced IPC approaches, such as fixed-structure H ∞ feedback-feedforward IPC (Ungurán et al, 2019) and multivariable robust IPC (Yuan et al, 2020), were developed to mitigate the blade loads on the wind turbine. On the other hand, the application of IPC to wake load control is receiving increasing attention.…”

Comment on wes-2021-2

“…vital importance to guarantee the reliability of the turbine system and to reduce the O&M costs (Njiri and Söffker, 2016). In general, the majority of the loads on wind turbine rotors shows a periodic nature (Yuan et al, 2020). Individual Pitch Control (IPC) has demonstrated its effectiveness in reduction of these periodic loads (Bossanyi, 2003).…”

“…Block diagram of the wind turbine model and of the control loop. The aero-hydro-structural dynamic part is simulated in FAST code while the turbine control part including a baseline CPC(Jonkman and Buhl, 2005), an MBC-IPC(Mulders et al, 2019) and the proposed cSPRC, are implemented in Simulink. The two IPC controllers can be selectively enabled in order to compare their performances against each other and against the baseline controller alone.…”