A Positive Position Feedback controller for vibration control of wind turbines

Positive position feedback (PPF) control is widely used in active vibration control offlexible structures. To ensure quick vibration suppression, a large PPF scalar gain is oftenapplied. However, PPF control with a large scalar gain causes initial overshoot, which isundesirable in many situations. In this paper, a fuzzy gain tuner is proposed to tune thegain in the positive position feedback control to reduce the initial overshoot while stillmaintaining quick vibration suppression. The fuzzy system is trained by a batch leastsquares algorithm based on desired input–output data so that the trained fuzzysystem can behave like the training data. A 3.35 m long composite I-beam withpiezoceramic patch sensors and actuators is used to demonstrate the fuzzy PPFcontrol. For comparison purposes, three types of control methods are used in theexperiment: a standard PPF control, a standard PPF control with traditionalfuzzy gain tuning, and a PPF control with batch least squares fuzzy gain tuning.Experimental results clearly demonstrate that PPF control with batch least squares fuzzygain tuning behaves much better than the other two control methods in terms ofsuccessfully reducing the initial overshoot and quickly suppressing vibration.

: POSITIVE position feedback (PPF) control was introduced by Goh and Caughey in 1985 to control vibrations of large exible space structures. A PPF controller has several distinguished advantagesas compared to then widely used velocity feedbackcontrol laws. It is insensitive to spillover, where contributions from unmodeled modes affect the control of the modes of interest. As a second-order low-pass lter, a PPF controller rolls off quickly at high frequencies and is well suited to controlling the lower modes of a structure with well separated modes. Because of these advantages, PPF controller along with smart materials, in particular PZT (lead zirconatetitanate) type of piezoelectricmaterial, has been applied to many exible systems to achieve active damping. The design of a PPF controller requires the natural frequency of a structure. In practice, the structuralnatural frequencymay not be known exactlyor itmay varywith time.When the frequencyused in thePPF controller is different from that of the structure, the performance of the PPF control will adversely affected. Despite that PPF control is widely researched in literature, robustness study of PPF control when natural frequency is inexactly known is not reported. This motivates the authors to conduct experimental study of robustness of PPF control in active vibration suppression of a smart exible structure.

This paper presents a new method of active vibration control (AVC) of flexible composite cantilever beams. A recursive least mean squares (LMS) based filter is used to perform on-line system identification, updating a positive position feedback (PPF) controller in real-time. With conventional time-invariant PPF control the damping ratio and natural frequency are selected based on the structural response, with the feedback path taking the form of a second-order filter; therefore having performed an off-line system identification of the plant dynamics, this controller is relatively straightforward to implement. Some structures undergo parameter changes over time and actuation in the control sequence can contribute to this change in the system dynamics. PPF control is optimized when an accurate estimation of the natural frequency is available. It is demonstrated that the recursive LMS algorithm can be used to provide a continual on-line estimation of the plant dynamics, for robust control of a slender glass fiber beam. The result is an increase in vibration attenuation, which is robust to variations in the beam properties. It is shown that this controller delivers a high performance settling time when compared with the standard PPF controller for free vibration in the first mode. Robustness of the technique is further demonstrated by altering the fundamental frequency of the beam, via the addition of a lumped mass. The adaptive controller re-tunes itself to this parameter variation, ensuring a high level of vibration suppression is upheld.

In this study, the Genetic Algorithm (GA) was used to search the 4 modes filter frequencies to be applied to the multiple Positive Position Feedback (PPF) controller. The PPF technique, which makes use of generalized displacement measurements to maximize damping in a specific mode effectively and accomplish vibration suppression was employed as control scheme. However it is necessary to tune the filter frequency of the controller to the structural resonance prior to compensator design. Another disadvantage in the multi mode PPF control is that the lower mode natural frequency is shifted to the low-ward as the effect of the higher mode control by PPF controller. To minimize the effect of frequency shift and search the optimal filter frequencies for the multiple modes PPF controller, the GA was applied. The generally used fitness function of the GA in low modes PPF control, the square sum of sensor voltage output hardly distinguishes the definite difference in higher modes. Instead of it, in this study, the GA with the fitness function as the power spectrum information was performed. As a result of GA algorithm with this fitness function, the optimal filter frequencies of higher modes were found successfully.

This paper presents experimental results of vibration suppression of a flexible structure using a miniaturized digital controller, called modular control patch (MCP). The MCP employs a TI-C30 digital signal processor and was developed by TRW for the United States Air Force for future space vibration control. In this research, the MCP is used to implement different control algorithms for vibration suppression of a cantilevered aluminum beam with piezoceramic sensors and actuators. Positive position feedback (PPF) control, strain rate feedback (SRF) control, and their combinations were implemented. Experiments found that PPF control is most effective for single-mode vibration suppression, and two PPF filters in parallel are most effective for multi-mode vibration suppression. Further experiments demonstrated the robustness of PPF control. PPF can achieve effective vibration suppression when there is a 20% error in modal frequency.

This paper presents performance comparison of a novel hybrid control algorithm and a Positive Position Feedback (PPF) control law for vibration suppression with low energy consumption. The proposed hybrid control method combines a bang-bang active controller with a PPF control law and results in a significant reduction of actuation energy requirement due to its ability to switch the actuation voltage source between external power supply and PPF feedback controller. Experimental results show that a single mode vibration control system using this proposed hybrid controller consumes 46% less power compared to the traditional PPF control system to give the same settling time. Experiments also reveal that substantial nonlinearity exists in the piezoelectric constant of the transducer, especially under high voltage actuation. The voltage dependent behavior of electromechanical coupling coefficient is identified empirically and represented by a curve fit expression. A real time adaptive control algorithm is developed to account for the voltage dependent behavior of the coupling coefficient and the simulation results are validated experimentally.

This paper is concerned with the implementation of the active vibration suppression controller using analog circuit and microprocessor. The target active vibration controller is the positive position feedback(PPF) controller since it provides a simple algorithm suitable for both analog circuit and digital controllers. In this study, the analog PPF controller is realized using an operational amplifier and the digital PPF controller is realized using a low-cost micro-controller. The circuit diagrams are explained in detail. We then discuss the advantages and disadvantages of both methods from the view of practical implementation. Experimental results show that both implementation methods can be effectively used for the active vibration control but need to be chosen based on the mission objective.

A Compact Piezoelectric Stack Actuator and Its Simulation in Vibration Control

In this article, active vibration control of a micro-actuator for hard disk drives using self-sensing actuation is presented. The micro-actuators used in this article are a slider type and a suspension type. The self-sensing performance of the installing position is compared and evaluated. An assembly including these micro-actuators may not be able to sense some vibration of suspension modes. Feedback control results of direct velocity feedback and positive position feedback are presented. The feasibility of these self-sensing approaches as a vibration suppression control on the micro-actuator was verified. Using the slider type micro-actuator, the sway mode spike signal in power spectrum density was suppressed by 76% using the direct velocity feedback control, and by 60% using the positive position feedback control. Using the suspension type micro-actuator, the suspension second bending mode spike signal in power spectrum density was reduced by 74% using the direct velocity feedback control, and by 96% using the positive position feedback control. The control scheme using self-sensing signals can partially dampen the suspension modes.

PurposeTo provide an approach to active vibration reduction of flexible spacecraft actuated by on‐off thrusters during attitude control for spacecraft designers, which can help them analysis and design the attitude control system.Design/methodology/approachThe new approach includes attitude controller acting on the rigid hub, designed by using pulse‐width pulse‐frequency modulation integrated with component command technique, and the piezoelectric material elements as sensors/actuators bonded on the surface of the beam appendages for active vibration suppression of flexible appendages, designed by optimal positive position feedback (OPPF) control technique. The OPPF compensator is devised by setting up a cost function to be minimized by feedback gains, which are subject to the stability criterion at the same time, and an extension to the conventional positive position feedback control design approach is investigated.FindingsNumerical simulations for the flexible spacecraft show that the precise attitude control and vibration suppression can be accomplished using the derived vibration attenuator and attitude control controller.Research limitations/implicationsStudies on how to control the on‐off actuated system under impulse disturbances are left for future work.Practical implicationsAn effective method is proposed for the spacecraft engineers planning to design attitude control system for actively suppressing the vibration and at the same time quickly and precisely responding to the attitude control command.Originality/valueThe advantage in this scheme is that the controllers are designed separately, allowing the two objectives to be satisfied independently of one another. It fulfils a useful source of theoretical analysis for the attitude control system design and offers practical help for the spacecraft designers.

The paper discusses some of the recent developments in vibration control strategies for wind turbines, and in this context proposes a new dual control strategy based on the combination and modification of two recently proposed control schemes. Emerging trends in the vibration control of both onshore and offshore wind turbines are presented. Passive, active and semi-active structural vibration control algorithms have been reviewed. Of the existing controllers, two control schemes, active pitch control and active tendon control, have been discussed in detail. The proposed new control scheme is a merger of active tendon control with passive pitch control, and is designed using a Pareto-optimal problem formulation. This combination of controllers is the cornerstone of a dual strategy with the feature of decoupling vibration control from optimal power control as one of its main advantages, in addition to reducing the burden on the pitch demand. This dual control strategy will bring in major benefits to the design of modern wind turbines and is expected to play a significant role in the advancement of offshore wind turbine technologies.

An experimental approach to multi-input multi-output nonlinear active vibration control of a clamped sandwich beam

This paper is concerned with the determination of multiple positive position feedback controller gains using genetic algorithms. The genetic algorithms have proven its effectiveness in searching optical design parameters without falling into local minima thus rendering globally optimal solutions. The use of genetic algorithms to the controller design have been investigated by many researchers but limited to the PID control, and optimal controls. In this paper, the genetic algorithm is applied to the positive position feedback control which has been successfully used for the active vibration suppression of smart structures. The advantage of the positive position feedback controller is that it can be easily implemented in analog circuits and each mode can be tackled independently. However, the disadvantage is that the natural vibration characteristics should be accurately determined a priori either theoretically or experimentally. In this paper, we develop a new algorithm for the determination of controller gains based on the genetic algorithm. Hence, the traditional positive position feedback controller can be used in adaptive fashion. Experimental results will prove its effectiveness.

The control of flexible structures is often very tough because modal frequencies may vary in operation and are difficult to obtain accurately in advance. The variation in the modal dynamics may cause degradation in performance. This paper presents an adaptive positive position feedback method for controlling the vibration of a flexible beam with bonded piezoelectric sensors and actuators. Dynamics of an experimental flexible beam is modeled via finite element method. The proposed vibration controller combines the positive position feedback (PPF) with an online adaptive parameter estimator based on the gradient algorithm with parameter projection and a dead zone. Since the online estimator is able to identify the modal frequencies, the PPF controller is able to damp out the target modes quickly. Simulation results are presented to illustrate the effectiveness of the proposed control method.

Modulated–demodulated control: Q control of an AFM microcantilever