Yuang-Shung Lee

Intelligent control battery equalization for series connected lithium-ion battery strings

An intelligent battery equalization scheme based on fuzzy logic control is presented to adaptively control the equalizing process of series-connected lithium-ion batteries. The proposed battery equalization scheme is a bidirectional dc-dc converter with energy transferring capacitor that can be used to design the bidirectional nondissipative equalizer for a battery balancing system. Furthermore, it can be designed as a ripple-free converter for improving the input current distortion of the battery charge supply power system. A fuzzy-logic-controlled strategy is constructed with a set of membership functions to prescribe the cells equalizing behavior within a safe equalizing region for rapid cell voltage balancing. The simulation and experimental results show the advantage of the predicted equalizing performance of the lithium-ion battery stacks. The proposed fuzzy logic control battery equalization controller can abridge the equalization time about 32%. The proposed method maintains safe operation during the charge/discharge state in each lithium-ion cell of the battery strings.

Design of Parallel Inverters for Smooth Mode Transfer Microgrid Applications

In this paper, a microgrid architecture comprised of parallel inverters, critical loads, and CAN communication is studied. The controller designs in both grid-tie and islanding modes for the designed MG system are described. How to distribute the currents among paralleled inverters with CAN bus as communication interface is addressed. The mode transfer tests are conducted with an inverter-simulated grid to define the proper transfer procedures. Experimental results show that the inverter can work properly in different basic microgrid operation modes. With current sharing scheme, the output current is equally shared among different inverters without noticeable circulating current. Both the simulation and experimental results of mode transfer show that the inverter can switch between grid-tie and islanding modes smoothly, which indicates that the proposed mode transfer procedure is capable of minimizing the transients during mode transfer.

Soft Computing for Battery State-of-Charge (BSOC) Estimation in Battery String Systems

In this paper, a soft computing technique for estimating battery state-of-charge of individual batteries in a battery string is proposed. The soft computing approach uses a fusion of a fuzzy neural network (FNN) with B-spline membership functions (BMFs) and a reduced-form genetic algorithm (RGA). The algorithm is employed to tune both control points of the BMFs and the weights of the FNNs. The traditional multiple-input multiple-output FNN (MIMOFNN) cannot directly be used in this paper. The main reason is that there are too many free parameters in the MIMOFNN to be trained if many inputs are required. In this paper, a merged multiple-input single-output (MISO) FNN is proposed and can be trained by the RGA optimization approach. The merged MISO FNN with RGA (FNNRGA) can achieve faster convergence and lower estimation error than neural networks with the back propagation method. From experimental results, the proposed merged MISO FNNRGA is superior, more robust than the traditional method, and the overfitting suppression features are significantly improved.

A Merged Fuzzy Neural Network and Its Applications in Battery State-of-Charge Estimation

To solve learning problems with vast number of inputs, this paper proposes a novel learning structure merging a number of small fuzzy neural networks (FNNs) into a hierarchical learning structure called a merged-FNN. In this paper, the merged-FNN is proved to be a universal approximator. This computing approach uses a fusion of FNNs using B-spline membership functions (BMFs) with a reduced-form genetic algorithm (RGA). RGA is employed to tune all free parameters of the merged-FNN, including both the control points of the BMFs and the weights of the small FNNs. The merged-FNN can approximate a continuous nonlinear function to any desired degree of accuracy. For a practical application, a battery state-of-charge (BSOC) estimator, which is a twelve input, one output system, in a lithium-ion battery string is proposed to verify the effectiveness of the merged-FNN. From experimental results, the learning ability of the newly proposed merged-FNN with RGA is superior to that of the traditional neural networks with back-propagation learning.

Application of superconducting magnetic energy storage unit to improve the damping of synchronous generator

A systematic approach to the design of a controller for superconducting magnetic energy storage (SMES) units to improve the dynamic stability of a power system is presented. The scheme employs a proportional-integral (PI) controller to enhance the damping of the electromechanical mode oscillation of synchronous generators. The parameters of the PI controller are determined by the pole assignment method based on modal control theory. Eigenvalue analysis and nonlinear computer simulations show that SMES with the PI controller can greatly improve the damping of the system under various operating conditions. Although the PI controller is designed for a special load condition, it can also provide good damping under other load conditions. >

Individual Cell Equalization for Series Connected Lithium-Ion Batteries

A systematic approach to the analysis and design of a bi-directional Cuk converter for the cell voltage balancing control of a series-connected lithium-ion battery string is presented in this paper. The proposed individual cell equalizers (ICE) are designed to operate at discontinuous-capacitor-voltage mode (DCVM) to achieve the zero-voltage switching (ZVS) for reducing the switching loss of the bi-directional DC/DC converters. Simulation and experimental results show that the proposed battery equalization scheme can not only enhance the bi-directional battery equalization performance, but also can reduce the switching loss during the equalization period. Two designed examples are demonstrated, the switch power losses are significantly reduced by 52.8% from the MOSFETs and the equalization efficiency can be improved by 68-86.9% using the proposed DCVM ZVS battery equalizer under the specified cell equalization process. The charged/discharged capacity of the lithium-ion battery string is increased by using the proposed ICEs equipped in the battery string.

Multiphase Zero-Current Switching Bidirectional Converters and Battery Energy Storage Application

A multiphase quasi-resonant (QR) zero-current switching (ZCS) switched capacitor (SC) bidirectional dc-dc converter structure is proposed to reduce current ripple and switching loss, and significantly increase converter efficiency and power density. This approach provides a more precise output voltage to obtain voltage conversion ratios from the double-mode versus half-mode to n-mode versus 1/n mode. This is accomplished by adding a different number of switched capacitors and power MOSFET switches with a small series connected resonant inductor for forward and reverse schemes. The size and cost can be reduced when the proposed converter is designed with coupled inductors. Simulation and experimental results demonstrate four-phase with and without coupled inductor interleaved QR ZCS SC converter performance for bidirectional power flow control applications. A battery energy storage system for a bidirectional power flow control application is demonstrated.

Fuzzy controlled lithium-ion battery equalization with state-of-charge estimator

A fuzzy controlled method for the equalization of series connected lithium-ion batteries is presented. The state-space representation of bi-directional dc-to-dc equalizer that modified from Cuk-converter is derived for design the battery equalization controller. A PWM switching control and equalization with the intelligent state-of-charge (SOC) estimator is employed to balance the cell voltage of the battery strings. An intelligent SOC estimator is designed based on a fuzzy logic control (FLC) with a set of membership function, it can predict the complex cell equalizing dynamics with an accurate state determination of batteries. A designed procedure is presented for constructing the FLC SOC estimator for the battery equalizer of the battery strings. The validity of the controller design method is further verified by using computer simulation and experiment. The numerical results indicate that the battery equalizer with the FLC SOC estimator can improve the equalization performance under the safe operating region of lithium-ion batteries.

ZCS switched-capacitor bidirectional converters with secondary output power amplifier for biomedical applications

This paper proposes a zero-current-switching (ZCS) quasi-resonant (QR) bidirectional converter with secondary output power amplifier. For implantable biomedical devices applications, the proposed device could be regarded as a power regulator with power amplifier. The bidirectional converter could provide voltage conversion ratio double-mode/half-mode and also be employed as a secondary output power amplifier. The forward and reverse power conversion modes and power amplifier operating principles are described. Simulations and experiments are carried out to verify the concept and performance for the bidirectional power conversions and secondary output power amplifier. This device can be applied to wireless energy transfer for a battery management system (BMS) in an implantable electronics system.

State-space modeling, analysis, and implementation of paralleled inverters for microgrid applications

The state-space model and implementation results of a power conditioning system are presented in this paper. Eigenvalues with different controller gains and load conditions for grid-tie mode and standalone mode are utilized to analyze the system stability. For standalone mode, higher controller gain and higher load resistance tend to make system more unstable. In grid-tie mode, higher controller gain is also found to make the system more unstable but load variation will not change the system stability much. Experimental and simulation results also verify the model. The state-space model is extended to a parallel-inverter system for investigation of the load variation and current-sharing controller effects to the system stability. A timedomain current ripple criterion is also suggested for light-load operation of the parallel-inverter microgrid system.