Improved Adaptive Augmentation Control for a Flexible Launch Vehicle with Elastic Vibration

The continuous development of spacecraft with large flexible structures has resulted in an increase in the mass and aspect ratio of launch vehicles, while the wide application of lightweight materials in the aerospace field has increased the flexible modes of launch vehicles. In order to solve the problem of deviation from the nominal control or even destabilization of the system caused by uncertainties such as unknown or unmodelled dynamics, frequency perturbation of the flexible mode, changes in its own parameters, and external environmental disturbances during the flight of such large-scale flexible launch vehicles with simultaneous structural deformation, rigid-elastic coupling and multimodal vibrations, an improved adaptive augmentation control method based on model reference adaption, and spectral damping is proposed in this paper, including a basic PD controller, a reference model, and an adaptive gain adjustment based on spectral damping. The baseline PD controller was used for flight attitude control in the nominal state. In the non-nominal state, the spectral dampers in the adaptive gain adjustment law extracted and processed the high-frequency signal from the tracking error and control-command error between the reference model and the actual system to generate the adaptive gain. The adjustment gain was multiplied by the baseline controller gain to increase/decrease the overall gain of the system to improve the system’s performance and robust stability, so that the system had the ability to return to the nominal state when it was affected by various uncertainties and deviated from the nominal state, or even destabilized.

Comparative analysis of Direct and Indirect Model Reference Adaptive Control by Extended Kalman Filter

Considerations about the increasing complexity of technological systems have stimulated the interest in hybrid systems that can successfully manage switching behaviour or approach nonlinearity. Hybrid systems are made up of two parts: a constant dynamics component and a switching mechanism. This article investigates the effectiveness of direct and indirect model adaptive control approaches for any common tool for hybrid modelling and approximation nonlinear systems. A reference model may be linear or partially refined, specifies the desired loop system behavior that the adaptive controllers are capable of achieving in the face of unknown system dynamics regardless of the system dynamics. Individual control gains are obtained for each subsystem and it is also carefully tuned to the altered behavior of each system. Through the application of dynamic gain adjustment, singularities in the principle of certainty equivalence are avoided indirectly. The state of the reference model is asymptotically monitored for both techniques by assuming that a shared Lyapunov feature is available for the switched reference model.

Efficient hearing aid algorithm using DCT with uniformly re-sampled and recursively modified audiogram values

People with the hearing problems have different listening preferences and characteristics in hearing loss. So, hearing aids need algorithms that provide amplification based on frequency, so that the hearing-impaired persons can use hearing aids comfortably for a long duration. In this paper, a new algorithm is proposed for hearing aids in order to compensate for sensorineural and conductive hearing loss using discrete cosine transform (DCT). DCT coefficients of the input audio signal are multiplied with uniformly resampled and recursively modified audiogram values to compensate for hearing loss. This algorithm comprised of 4 stages namely precomputation to calculate gain values from audiogram, DCT, gain adjustment, and inverse DCT. In the above stated stages except precomputation, each stage requires only one matrix multiplication, which makes the proposed algorithm computational efficient. Performance of the proposed algorithm is compared with uniform filter banks, non-uniform filter banks, variable filter bank and reconfigurable filter banks. The algorithm is tested using audiograms with four different hearing loss cases. It is proved that the proposed algorithm provides less complexity, minimized delay and better matching with all types of audiograms, further, it also avoids degradation of audio signal due to sampling rate conversions in variable and reconfigurable filter banks.

The effect of stimulus duration on preferences for gain adjustments in speech

ObjectivesIn the personalisation of hearing aid fittings, gain is often clinically adjusted to patient preferences using live speech. When using brief sentences as stimuli, the minimum gain adjustments necessary to elicit preferences (‘preference thresholds’) were previously found to be much greater than typical adjustments in current practice. The current study examined the role of duration on preference thresholds.DesignParticipants heard 2, 4 and 6-s segments of a continuous monologue presented in pairs. Participants judged whether the second stimulus of each pair, with a ±0-12 dB gain adjustment in one of three frequency bands, was “better”, “worse” or “no different” from the first at their individual real-ear or prescribed gain.Study SampleTwenty-nine adults, all with hearing-aid experience.ResultsThe minimum gain adjustments to elicit “better” or “worse” judgments decreased with increasing duration for most adjustments. Inter-participant agreement and intra-participant reliability increased with increasing duration. The effect of duration, however, decreased with increasing duration, with no increase in agreement or reliability for 6-s vs. 4-s segments.ConclusionsProviding longer stimuli improves the likelihood of patients providing reliable judgments of hearing-aid gain adjustments, but the effect is limited, and alternative fitting methods may be more viable for effective hearing-aid personalisation.

Full Digital Control of an All-Si On-Board Charger Operating in Discontinuous Conduction Mode

This paper deals with the design, tuning and implementation of a digital controller for an all-Si electric vehicle (EV) on-board battery charger operated in discontinuous conduction mode (DCM). This charger consists of two cascaded conversion stages: a front-end power factor corrector (PFC) with two interleaved legs and an isolated phase-shifted full bridge DC/DC converter. Both stages operate in DCM over the complete battery charging power range, allowing lower inductance values for both the PFC and the DC/DC filtering elements. Moreover, DCM operation ensures a large reduction of the reverse-recovery losses in the power diodes, enabling the adoption of relatively cheap Si devices. The main goal of the work is to address the well-known DCM control challenges, leveraging a novel control strategy for both converter stages. This control scheme counteracts the DCM system non-linearities with a proper feed-forward contribution and an open-loop gain adjustment, ensuring consistent dynamical performance over the complete operating range. The designed controllers are tuned analytically, taking into account the delay components related to the digital implementation. Finally, the proposed control strategy is implemented on a single general purpose microcontroller unit (MCU) and its performance is experimentally validated on a 3.3 kW battery charger prototype.