This article deals with nonlinear model‐based control design for wind turbines. By systematically integrating several mechanical degrees of freedom in the control design model, the load mitigation potential from the proposed multivariable control framework is demonstrated. The application of the linear matrix inequality (LMI)‐based control design is discussed in detail. Apart from the commonly considered power production mode, an extended operating range to provide stabilization of the electrical grid through power tracking is considered. This control functionality allows for an evaluation of the resulting fatigue and ultimate loads for power tracking at different dynamic requirements. The results indicate that under the impact of a dedicated control scheme, this functionality is feasible with respect to the occurring loads and operational behavior of the wind turbine.
SummaryA proportional multi‐integral (PMI) observer scheme is used to reconstruct actuator and sensor faults in large‐scale wind turbines. For the nonlinear full‐load region, a PMI observer in Takagi‐Sugeno form is used. Two different methods are proposed for the observer design: a Lyapunov‐based and a modified linear quadratic regulator approach, where the stability is ensured by a negative derivative of the Lyapunov function candidate. The actuator and sensor faults are directly reconstructed from an augmented state‐space vector. The control inputs and measurement signal are then modified with the reconstructed fault signals to achieve fault‐tolerant control in the presence of faults with a similar behavior to the fault‐free case. It is shown by extensive simulation studies that the PMI observer is able the reconstruct offset and ramp‐shaped faults with high accuracy. The performance of the fault reconstruction and fault‐tolerant control scheme based on a 4‐degree‐of‐freedom observer model is tested in simulations by a high‐order 24‐degree‐of‐freedom model with the aeroelastic code FAST by the National Renewable Energy Laboratory. The new results are also compared with those of the previously published fault reconstruction scheme using Takagi‐Sugeno sliding‐mode observers.
The doubly fed induction generator is widely used in wind power applications. For stand-alone operation of this machine, the control of the stator flux with fixed voltage and frequency has been proposed. This paper extends the stator flux control of the doubly fed induction machine by droop mechanisms, which vary the setpoint of flux magnitude and frequency depending on active and reactive power. This gives the doubly fed induction generator system unknown grid supporting and grid forming performance. The validation of the proposed control scheme has been conducted on a 10kVA testbed system. The closed-loop behavior of the system has been proven to enable grid-tied and islanded operation with the same control structure. The system response to load changes and islanding events show no disruptive transients in both conditions.
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