Equalizing Aerodynamic Blade Loads Through Individual Pitch Control Via Multiblade Multilag Transformation

Abstract

Control algorithms for rotor load mitigation are today generally adopted by industry. Most of them are based on the Coleman transformation, which is easy to implement and bears satisfactory results when the rotor is balanced. A multitude of causes, e.g., blade erosion, dirt, and especially pitch misalignment, may create significant imbalances. This gives birth to undesirable vibrations and reduced control performance in terms of load mitigation. In this paper, an alternative transformation is introduced, able to detect and quantify the rotor load harmonics due to aerodynamic imbalance. Next, a control algorithm, capable of targeting rotor imbalance itself and simultaneously lowering rotor loads, is presented. The effectiveness of the proposed solution is confirmed through simulations in virtual environment.

Monitoring rotor aerodynamic and mass imbalances through a self-balancing control

“…(4) and previously demonstrated in [6,7]. In fact, a generic pitch misalignment may entail also an alteration of the value of the collective pitch.…”

“…The final MBML transformation aimed at extracting simultaneously the 1× and 2×Rev cyclic loads and the imbalanced induced loads (cf. [6,7]) results to be…”

“…In order to simultaneously extract the 1×Rev and 2×Rev harmonic amplitudes, named respectively a 1 = {a 1c , a 1s } T and a 2 = {a 2c , a 2s } T , and the biases of the three blades, b = {b 1 , b 2 , b 3 } T from blade moments, it is possible to employ an ad hoc transformation based on the Multiblade Multilag (MBML) concept, as reported in [6,7]. The concept behind the MBML transformation is to exploit multiple samples, at different azimuthal lagged angles, of the multiple blade signals.…”

“…In general, aerodynamic and mass imbalances have a similar impact on rotor loads and differentiating automatically between the two is a very difficult task, which requires more sophisticated approaches [3,4,5]. In case the sole pitch misalignment is of concern, the opportunity to cope with this issue using automatic control has gained the attention of researchers, as witnessed by some recent publications [6,7,8,9,10]. The scope of this paper is twofold.…”

“…The scope of this paper is twofold. First, the formulation of the self-balancing control developed in [6] and [7] is extended in order to make it able to target not only pitch misalignmentinduced but also mass imbalance-induced loads. In practice, the the self-balancing control will generate an artificial aerodynamic imbalance which compensates the inertial one, if present, and a pre-existent aerodynamic imbalance due to pitch misalignment or blade aerodynamic inequality.…”