King Jet Tseng

Determination of Short-Term Power Dispatch Schedule for a Wind Farm Incorporated With Dual-Battery Energy Storage Scheme

A battery energy storage scheme to enable short-term dispatch commitment from a grid-connected wind-turbine generating power station is considered. Among the various types of energy storage medium, technical factors leading to the selection of battery are explained. The scheme utilizes two battery energy storage systems (BESS) in which the generated wind power charges one BESS while concurrently, the second BESS is to discharge power into the grid. The role of the two BESS interchanges when the BESS reaches specified state of charge/discharge. Furthermore, based on forecasted charging wind power and the monitored states of charge of the two BESS, the discharge power level from the generating station is determined and scheduled a few hours ahead. The dispatch scheme maximizes wind energy harnessed, achieved with the minimum number of the BESS switch-overs. The design thus prolongs the service life of the BESS. Numerical examples to demonstrate the performance of the scheme are also included.

Advanced Control of Series Voltage Compensation to Enhance Wind Turbine Ride Through

Due to increasing wind power penetration into utility grids, system operators have instituted stringent standards for ride-through compliance of grid-connected wind turbines. Series voltage compensation can be an effective solution to meet the new standards, especially if a low-cost system can be developed. This paper first presents the characteristics of ride-through behavior of doubly fed induction generator (DFIG) using phasor analysis. The analysis is extended to include the effects of generic series voltage compensation. A new control scheme is then described and analyzed, which allows relatively low-energy ratings in the series compensator, thereby significantly lowering the overall system cost. The new controller enables the DFIG with the compensator to provide the reactive power required for system voltage recovery during grid fault, in compliance with the new grid codes. Simulation and experimental results have demonstrated the enhanced performances resulting from the application of the control scheme.

Modeling of Lithium-Ion Battery for Energy Storage System Simulation

Batteries are the power providers for almost all portable computing devices. They can also be used to build energy storage systems for large-scale power applications. In order to design battery systems for energy-optimal architectures and applications with maximized battery lifetime, system designers require computer aided design tools that can implement mathematical battery models, predict the battery behavior and thus help the designers search for the optimal schemes. This paper presents a lithium-ion battery model which can be used on SIMPLORER software to simulate the behavior of the battery under dynamic conditions. Based on measured battery data, a mathematical model of the battery is developed which takes into account battery operating temperature and the rates of the battery charge/discharge currents. In addition, thermal characteristics of the battery are also studied.

Using power diode models for circuit simulations-a comprehensive review

In recent years, a number of new models for the power diode have been proposed. The objectives of this paper are to provide the power electronics community with a comprehensive review and summary of recent power diode models. The models have been categorized systematically according to their modeling concepts with objective comparison of their status pertaining to the various modeling issues. A summary table has been created to aid power circuit design engineers and power rectifier device engineers in selecting appropriate models for their applications.

High-power, multioutput piezoelectric transformers operating at the thickness-shear vibration mode

In this study, a piezoelectric transformer operating at the thickness shear vibration mode and with dual or triple outputs is proposed. It consists of a lead zirconate titanate (PZT) ceramic plate with a high mechanical quality factor Qm and a size of 120 x 20 x 4 mm3. The PZT ceramic plate is poled along the width direction. The electrodes of input and output parts are on the top and bottom surfaces of the ceramic plate and separated by narrow gaps. A new construction of support and lead wire connection is used for the transformer. At a temperature rise less than 20 degrees C and efficiency of 90%, the piezoelectric transformer with dual outputs has a maximum total output power of 169.8 W, with a power of 129.5 W in one output and 40.3 W in another. The one with triple outputs has a maximum total output power of 163.1 W, with a power of 36.9 W in the first output, 13.0 W in the second output and 113.2 W in the third output. The maximum efficiency of the piezoelectric transformer with dual outputs and triple outputs is 98% and 95.7%, respectively. The voltage gains of the transformers are less than one, and different outputs have different gains. Also, there is a driving frequency range in which the load resistance of one output has little effect on the voltage gain of another output.

Reducing dielectric losses in MnZn ferrites by adding TiO/sub 2/ and MoO/sub 3/

We investigated the complementary effects of TiO/sub 2/ and MoO/sub 3/ additives on the magnetic properties, the core loss, and the dielectric properties of MnZn ferrites. We analyzed the composition factors influencing the permeability of MnZn ferrites. A high initial permeability base ZnO-MnO-Fe/sub 2/O/sub 3/ composition ratio was selected. Electrical and dielectric analyses indicated that the introduction of TiO/sub 2/ can improve the high-frequency loss properties of MnZn ferrite cores, but such introduction will also have a negative effect on the magnetic properties of the sintered samples. Introduction of MoO/sub 3/ can alleviate the negative influence of TiO/sub 2/ and also reduce the internal polarization intensity. As a result, the dielectric constant and corresponding dielectric loss may be reduced. We give experimental results in the paper.

A Novel Flywheel Energy Storage System With Partially-Self-Bearing Flywheel-Rotor

A compact and efficient flywheel energy storage system is proposed in this paper. The system is assisted by integrated mechanical and magnetic bearings, the flywheel acts as the rotor of the drive system and is sandwiched between two disk type stators to save space. The combined use of active magnetic bearings, mechanical bearings and axial flux permanent magnet (PM) synchronous machine assists the rotor-flywheel to spin and remain in magnetic levitation in the vertical orientation, while constrains the other four degrees of freedom in radial directions mechanically. The mathematical model of the proposed system has been derived. Three-dimensional finite element method (3D FEM) is applied for studying the performances and verifying the mathematical model of the system. The analysis results support the feasibility of the system.

Effects of multi-segment structure on core losses in MnZn ferrites at high frequencies

Multi-segment cores have been developed by cutting standard MnZn ferrite cores into thin segments and then re-assembling the segments together. All the segments were separated by a thin film of air or insulation materials of microscopic dimensions. The core loss properties of these experimental samples have been investigated between the frequencies of 200 kHz to 2 MHz. The real and imaginary parts of the effective permeability have been determined from these measurements. Experiment results show that the multi-segment ferrite cores are effective in reducing the core loss by possible mechanisms of reduction in the internal electromagnetic field strength and of reduction in the influence of the magnetic skin effect.

On the modeling and control of a novel flywheel energy storage system

The concept of a novel axial flux permanent magnet machine for flywheel energy storage system is presented. Modeling and control of this novel flywheel energy storage system are given. This flywheel energy storage system is designed to work as a fast-response energy storage device which is planned for use in ride-through applications in wind power. Therefore the flywheel has to store and release energy at high power rating in short period of time to meet such requirements. Motoring torque and axial force of this flywheel are well controlled by a simple control technique. The flywheel is driven by a single power converter. Mathematical model of the proposed flywheel is presented and verified by Matlab simulations. In order to evaluate this novel machine concept, an experimental test-rig was fabricated and tested. Experimental and simulation results are presented and compared.

A new structure transcutaneous transformer for artificial heart system

A new geometrical design of a transcutaneous transformer for an artificial heart system is presented in this paper. The primary and secondary cores are made of ferrite and amorphous magnetic materials respectively. The experimental results indicate that it is possible to transmit an electrical power of 20 W which is sufficient to drive the heart pump. With a gap of 5 mm between the coils, its transmission efficiency with the inverter can be up to 90% with a switching frequency 102.5 kHz. Some characteristics of the proposed transformer are also shown and discussed in this paper.