Abstract
This paper develops a robust regulator design approach to maximum power point tracking (MPPT) of a variable-speed wind energy conversion system (WECS) under the concept of perturbation and observation. The proposed perturb and observe regulators (PORs) rooted on the sliding mode method employs the optimal power curve (OPC) to realize MPPT operations by continuously adjusting rotor speeds and the duty cycles, which can ensure control performance against system parameter variations. The proposed PORs can detect sudden wind speed changes indirectly through the mechanical power coefficient, which is used to acquire the rotor speed reference by comparing it with the optimal power constant. For the speed and duty cycle regulation, two novel controllers based on the proposed POR, i.e., an MPPT controller and a speed controller, are devised in this research. Moreover, by applying the small-signal analysis on a nonlinear wind turbine system, the convergence of the proposed speed controller is proven for the first time based on the Lyapunov theory, and meanwhile, a single-pole transfer function, to describe the effect of duty cycle variations on rotor speeds, is designed to ensure its stability. The proposed strategy is verified by simulation cases operated in MATLAB/Simulink and experimental results performed from a 0.5-kW wind turbine generator simulator.
Highlights
Wind energy conversion systems (WECSs) are widely used to convert wind energy into different forms of electrical energy through a wind turbine and a power conversion system [1]
The current maximum power point tracking (MPPT) methods can be classified into three major types: power signal feedback (PSF) control, tip speed ratio (TSR)
The control block diagram of the proposed MPPT strategy presented in Figure 1 is composed of three parts, where Block A is the estimator for calculating k ωt defined as the mechanical power coefficient [4], Block B is the perturb and observe regulators (PORs)-based MPPT controller used to track the optimal power constant kopt and Block C is the POR-based speed controller applied to track the estimated rotor speed reference ωref
Summary
Wind energy conversion systems (WECSs) are widely used to convert wind energy into different forms of electrical energy through a wind turbine and a power conversion system [1]. In [11], a traditional HCS algorithm required measurements of the output power and checking dP/dω in real time, which was difficult to track the reference signal at fast-varying wind speeds To overcome this problem, an optimal power coefficient (OPC) curve is for the first time proposed, which includes a fixed optimal power coefficient fitted for all of the wind speeds and the rotor speeds. For the sake of the proposed OPC curve, the control system has been integrated, from one side, with the proposed POR-based MPPT controller, so as to improve the efficiency and energy extraction just by tracking the OPC at all of the winds; from the other side, with techniques for estimating the mechanical power coefficient and reducing current sensors.
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