Abstract
Small grid-tied wind turbines based on permanent magnet generators often use a cost-effective power converter topology consisting of a passive rectifier, a boost converter, and an H-bridge inverter. Speed or position sensors are rarely used due to cost issues. Model-based estimators relying on electrical magnitudes are used instead. However, such estimators are parameter sensitive, which limit their accuracy. Further concerns arise if these parameters change with the operating condition of the machine, mainly due to temperature. Speed sensorless control using the rectifier voltage ripple is analyzed in this paper. This technique provides good dynamic response and does not depend on machine parameters. Simulations are provided for speed and power tracking comparison with an accurate model-based speed estimation method operating at non-rated parameters. They show the speed accuracy and power tracking capability of the proposed method are similar to that provided by a speed sensor. This is translated into a 0.9% power increase when the model-based speed estimator shows 9% of error. Experimental results are carried out to test the effect of current and temperature in the estimation, showing temperature insensitivity and some distortion due to fast current transients. A speed estimation accuracy of zero mean error and 1.7% standard error is experimentally obtained in the regular operation of the wind turbine.
Highlights
In the last years, cost and sustainability concerns have raised the interest in the use of low-power renewable resources for self-generation due to cost issues
Controllers and estimation blocks discussed in previous sections have been discretized using bilinear (Tustin) approximation with a sampling frequency of 20 kHz, which is the switching frequency of the boost converter
Rotor speed is controlled by the generator while the load drive emulates the wind turbine behavior, including inertia [10]
Summary
Cost and sustainability concerns have raised the interest in the use of low-power renewable resources for self-generation due to cost issues. The frequency of the voltage ripple components is a function of the generator speed and does not depend on machine parameters or load conditions. The rotor speed is accurately estimated using a polynomial approximation function using boost current and rectifier voltage (2) in [10] Coefficients of this function are obtained in a commissioning stage and stored in a table, which is later accessed during normal operation of the turbine. They are not completely removed due to the low value of the capacitor. Some additional comments are made below regarding some blocks due to their importance for a correct implementation
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