Shi Zhao

Observability Analysis and State Estimation of Lithium-Ion Batteries in the Presence of Sensor Biases

This brief investigates the observability of one of the most commonly used equivalent circuit models (ECMs) for lithium-ion batteries and presents a method to estimate the state of charge in the presence of sensor biases, highlighting the importance of observability analysis for choosing appropriate state estimation algorithms. Using a differential geometric approach, necessary and sufficient conditions for the nonlinear ECM to be observable are derived and are shown to be different from the conditions for the observability of the linearized model. It is then demonstrated that biases in the measurements, due to sensor aging or calibration errors, can be estimated by applying a nonlinear Kalman filter to an augmented model where the biases are incorporated into the state vector. Experiments are carried out on a lithium-ion pouch cell and three types of nonlinear filters, the first-order extended Kalman filter (EKF), the second-order EKF, and the unscented Kalman filter, are applied using experimental data. The different performances of the filters are explained from the point of view of observability.

Circuit synthesis of electrochemical supercapacitor models

This paper is concerned with the synthesis of RC electrical circuits from physics-based supercapacitor models describing conservation and diffusion relationships. The proposed synthesis procedure uses model discretisation, linearisation, balanced model order reduction and passive network synthesis to form the circuits. Circuits with different topologies are synthesized from several physical models. This work will give greater understanding to the physical interpretation of electrical circuits and will enable the development of more generalised circuits, since the synthesized impedance functions are generated by considering the physics, not from experimental fitting which may ignore certain dynamics.

Global Sensitivity Analysis of Battery Equivalent Circuit Model Parameters

This paper considers one of the most commonly used equivalent circuit models (ECMs) for lithium-ion batteries and investigates the sensitivity of the model output to changes of model parameters using the Morris method. Experiments are carried out on a lithium- ion cell with nickel manganese cobalt oxide (NMC) electrode and parameters of the model are identified in the state of charge (SOC) range [100%,10%]. Although all the model parameters do vary with SOC, global sensitivity analysis reveals that the uncertainties of some of the parameters generate very little uncertainty in the voltage output, implying that those parameters can be taken as constants without compromising the accuracy of the model. This is further confirmed by experimental validation.

Performance Evaluation of an Extended Kalman Filter for State Estimation of a Pseudo-2D Thermal-Electrochemical Lithium-Ion Battery Model

Fast and accurate state estimation is one of the major challenges for designing an advanced battery management system based on high-fidelity physics-based model. This paper evaluates the performance of a modified extended Kalman filter (EKF) for on-line state estimation of a pseudo-2D thermal-electrochemical model of a lithium-ion battery under a highly dynamic load with 16C peak current. The EKF estimation on the full model is shown to be significantly more accurate (< 1% error on SOC) than that on the single-particle model (10% error on SOC). The efficiency of the EKF can be improved by reducing the order of the discretised model while maintaining a high level of accuracy. It is also shown that low noise level in the voltage measurement is critical for accurate state estimation.Copyright

Energy amplification of poiseuilleflow in a pipe lined with riblets

Using as a passive method for drag reduction, riblets are structures that run parallel to one another and are aligned longitudinally to fluid flows. While the benefits of riblets have been well known, the mechanism of drag reduction is not fully understood. This paper analyses the effects of riblet structures on energy amplification in streamwise constant Poiseuille flow in a circular pipe. The linearised governing equations of the flow are written into the two-dimensional/three-component form. Through a change of coordinates, the rough domain is transformed into a smooth one. The equations are discretised using spectral methods and the finite-dimensional approximation of the system is represented by a state space model. The transient growth in the flow without external forcing and H2 norm of the system subject to stochastic noise are calculated. Our computation shows that the presence of riblets can reduce the transient growth and H2 norm in pipe flow.

Energy Amplification of Streamwise Constant Channel Flow over Riblets

Abstract Riblets have been used as a passive method of reducing the drag of a fluid flowing over an airfoil. Riblets are structures that run parallel to one another that are positioned longitudinally to the flow. It has been shown experimentally that the drag coefficients over the surface can be reduced by up to 10% when the shape, spacing and height of the riblets are optimized. However, the mechanism of drag reduction is not fully understood. This paper investigates the effects of riblets on energy amplification in streamwise constant channel flow. The linearized Navier-Stokes equations are described by the two-dimensional/three-component model. The irregular domain is converted into a uniform one through a change of coordinates. Spectral methods are used to discretize these equations, leading to a finite-dimensional state space model. The transient growth and ℋ 2 norm of the flow system are calculated, which shows that the presence of riblets can reduce the transient growth and ℋ 2 norm of channel flow.

Passivity of plane Poiseuille flow

This paper considers the passivity of plane Poiseuille flow, which is the incompressible flow observed between two parallel plates that are assumed to be of infinite extent. A model in which the flow is considered as the feedback connection between a linear time-invariant system and a static, memoryless nonlinear system is used. It is well known that the nonlinearity of plane Poiseuille flow is not only passive but lossless, which means that it does not generate or consume energy and the only effect of the nonlinearity is to move energy from one flow mode to another. However, little has been addressed about the passivity of the entire flow system. The primary aim of this paper is to find a subcritical Reynolds number below which the linearized flow is always strictly passive, which means that the origin of the full nonlinear system is globally asymptotically stable when the Reynolds number does not exceed the subcritical number. Our results show that the subcritical Reynolds number obtained by the passivity approach is equal to the energy Reynolds number, which is derived by the classical energy approach. This result indicates that the passivity approach is closely related to the energy approach and is a valuable tool to study the stability of fluid flows.