Showing papers by "James S. Freudenberg published in 2009"

Author's Reply to Comments on Feedback Stabilization Over Signal-to-Noise Ratio Constrained Channels

Abstract: There has recently been significant interest in feedback stabilization problems over communication channels, including several with bit rate limited feedback. Motivated by considering one source of such bit rate limits, we study the problem of stabilization over a signal-to-noise ratio (SNR) constrained channel. We discuss both continuous and discrete time cases, and show that for either state feedback, or for output feedback delay-free, minimum phase plants, there are limitations on the ability to stabilize an unstable plant over an SNR constrained channel. These limitations in fact match precisely those that might have been inferred by considering the associated ideal Shannon capacity bit rate over the same channel.

Implicit Model Predictive Control of a Full Bridge DC–DC Converter

Abstract: This paper presents a model predictive control (MPC)-based approach for a full bridge dc-dc converter of a fuel cell power system. The objective of the proposed control algorithm is to regulate the output voltage without violating the peak current constraint. We first develop a large signal dynamic model for the full bridge dc-dc converter. The peak current protection requirement is then formulated as a mixed input and state constraint for the MPC scheme. We next introduce the integrated perturbation analysis and sequential quadratic programming (InPA-SQP) method to solve the constrained optimal control problem with sub-millisecond level sampling time. The InPA-SQP solver can meet the computational efficiency demand, thereby enabling implementation of an implicit MPC for power electronics system with fast dynamics. The effectiveness of the proposed control algorithm in the peak current protection and the output voltage regulation has been verified with experimental results.

Feedback Stabilization Over a First Order Moving Average Gaussian Noise Channel

Abstract: Recent developments in information theory by Y.-H. Kim have established the feedback capacity of a first order moving average additive Gaussian noise channel. Separate developments in control theory have examined linear time invariant feedback control stabilization under signal to noise ratio (SNR) constraints, including colored noise channels. This note considers the particular case of a minimum phase plant with relative degree one and a single unstable pole at z=phi (with |phi| > 1) over a first order moving average Gaussian channel. SNR constrained stabilization in this case is possible precisely when the feedback capacity of the channel satisfies CFB ges log2 |phi|. Furthermore, using the results of Kim we show that there exist linear encoding and decoding schemes that achieve stabilization within the SNR constraint precisely when CFB ges log2 |phi|.

Practical observers for unmeasured states in turbocharged gasoline engines

Abstract: Turbocharged gasoline engines are becoming more common in production vehicles as consumers demand improved fuel economy with uncompromised performance. Controlling this complex system to meet these and other competing objectives is a challenging task. Knowledge of exhaust manifold pressure and turbocharger speed can be important to success. Physical conditions of the system, however, make measurement impractical and costly, compelling manufacturers to implement some form of on-line estimation. Additional constraints imposed by computational resources and calibration processes limit application of a traditional state observer. In this paper, singular perturbation concepts are employed in concert with the reduced order observer to develop more practical estimates of exhaust manifold pressure and turbocharger speed. Simulation results show excellent observer performance with a significant reduction in calibration complexity.

Stabilization and performance over a Gaussian communication channel for a plant with time delay

Abstract: Two problems that have received much attention are those of finding the minimum channel signal to noise ratio compatible with closed loop stability, and of finding the optimal performance, in terms of disturbance attenuation, for a channel with specified signal to noise ratio. In this paper, we study these problems for the case in which the plant has relative degree greater than one, and thus introduces a delay greater than one time step. We show that, unlike the relative degree one case, for the problem of stabilization linear time varying control and communication strategies may have advantages over linear time invariant strategies. We derive a lower bound on optimal disturbance response at a fixed terminal time. If the encoder has access to the state of the plant, then this bound is achievable using linear time varying communication and control.