K.J. Tseng

Design of a Robust Grid Interface System for PMSG-Based Wind Turbine Generators

A robust and reliable grid power interface system for wind turbines using a permanent-magnet synchronous generator (PMSG) is proposed in this paper, where an integration of a generator-side three-switch buck-type rectifier and a grid-side Z-source inverter is employed as a bridge between the generator and the grid. The modulation strategy for the proposed topology is developed from space-vector modulation and Z-source network operation principles. Two PMSG control methods, namely, unity-power-factor control and rotor-flux-orientation control (Id = 0), are studied to establish an optimized control scheme for the generator-side three-switch buck-type rectifier. The system control scheme decouples active- and reactive-power control through voltage-oriented control and optimizes PMSG control for the grid- and generator-side converters independently. Maximum power point tracking is implemented by adjusting the shoot-through duty cycles of the Z-source network. The design considerations of the passive components are also provided. The performances and practicalities of the designed architecture have been verified by simulations and experiments.

A Novel Axial Flux Permanent-Magnet Machine for Flywheel Energy Storage System: Design and Analysis

This paper presents the design and analysis of a novel axial flux permanent-magnet (AFPM) machine for a flywheel energy storage system (FESS). Its design and control facilitate significant reduction in axial bearing stress and losses. Due to the unconventional flux distribution in this machine, a 3-D finite element method was employed for its design and analysis, including its electromagnetic torque and axial force performances. The effects of the rotor PM skew angle on the cogging torque and the axial force have been studied. It is found that an optimum skew angle is effective in reducing the overall cogging torque with negligible effect on the static axial force. The latter is crucial as it can be utilized to minimize the axial bearing stress in FESS application. The concept, design, and analysis methodology have been validated by experimental results from an experimental AFPM machine prototype.

An experimentally verified hybrid Cassie-Mayr electric arc model for power electronics simulations

This paper presents an electric arc model that can approximately represent both the static and dynamic characteristics of an arc load controlled by a power electronic circuit. The proposed model was developed from the combination and modifications of the classical Cassie and Mayr equations. The model equations have been expressed in a form suitable for incorporation into circuit simulators employing the nodal analysis method of equation solving. The model has been test-implemented in the Saber circuit simulator. Simulated and experimental results appear to be in good agreement.

A Statistical Approach to the Design of a Dispatchable Wind Power-Battery Energy Storage System

A scheme that allows the dispatch of steady and controllable level of power from a wind power generating station is proposed in this paper. The scheme utilizes two battery energy storage systems (BESSs) in which the generated wind power is used to charge one BESS, while the second BESS is used to discharge constant power into grid. The role of the two BESS interchanges when the discharging BESS reaches specified operating limit. With this scheme in mind and based on given wind speed statistics, charging characteristics of the BESS are studied, and a method to determine the expected charging time of the BESS to reach stipulated battery state of charge is developed. The expected BESS charging time, in turn, dictates the constant power level that can be dispatched to the grid through the discharging BESS. The corresponding discharge time is also determined using the developed method, the accuracy of which is validated experimentally. The proposed design procedure is then used to determine the minimum BESS capacity based on the expected wind power. Statistical likelihood of dispatchable power delivery achievable from the scheme is also obtained.

Analyses and compensation of rotor position detection error in sensorless PM brushless DC motor drives

In a permanent-magnet (PM) brushless DC motor, the waveform of back electromotive force (EMF) is related to the rotor position; hence, the back EMF can be used for position sensorless control. However, in practical implementation, the terminal voltage or phase voltage is used instead, as the back EMF is difficult to be sensed directly. Thus, detection error of the rotor position can occur. This paper documents the calculations and analyses on the detection error and the motor commutation angle, and presents an error compensation circuit to ensure proper commutation. Finite-element field simulation and experimental results are also given to verify the calculations as well as the compensation circuit.

Robust adaptive control of a three-axis motion Simulator with state observers

The development of a nonlinear robust adaptive tracking control system for a three-axis motion simulator is presented in this paper. The motion simulator is used to test and calibrate certain spacecraft instruments within a hardware-in-the-loop environment. Permanent magnet synchronous motor (PMSM) drives are used as simulator actuators. The control system is developed based on Lyapunov stability theory for which only rotor position and stator current signals are required. By using mechanical and electrical state observers, the measurement of acceleration and load torque which is usually required when motor dynamics are considered, is avoided. The control system can be made adaptable to constant unknown motor parameters and load inertia and robust to unknown but bounded fast varying disturbances. Simulation and experimental results are presented to verify the stability and efficacy of the proposed control system.

Generalized Optimal Trajectory Control for Closed Loop Control of Series-Parallel Resonant Converter

The series parallel resonant converter (SPRC) is known to have combined the merits of the series resonant converter (SRC) and the parallel resonant converter (PRC). However, the series PRC (SPRC) has a three-element LCC structure with complex transient dynamics and without control of the resonant circuits dynamics, the converters closed loop bandwidth to switching frequency ratio will be much reduced compared to that of pulsewidth modulation converters. In this paper, the generalized optimal trajectory control (GOTC) for the SPRC is presented. It allows the nonlinear resonant circuit of the SPRC having an arbitrary starting state to reach a desired steady state in one cycle with two optimally controlled switching instances. It is a generalized form of optimal trajectory control (OTC) which is restricted to transitions between steady states. Based on GOTC, a traditional controller with inner current and outer voltage state-feedback is designed for an SPRC based dc-dc converter. The GOTC based feedback controller allows use of higher feedback gains compared with one using OTC or frequency control and gives higher closed loop bandwidth. This results in either better disturbance rejection for the converter or the possibility of reducing output filter sizing. Experimental results confirm the theoretical claims

A PSpice model for the electrical characteristics of fluorescent lamps

This paper presents a PSpice circuit model for the simulation of both static and dynamic characteristics of fluorescent lamps. The proposed model was developed from the combination and modifications of classical Cassie and Mayr equations. It is helpful for a preliminary design of high frequency electronic ballasts. Experimental results on fluorescent lamps at different conditions are presented and they appear to be in good agreement with simulation results.

Computer-aided design and analysis of direct-driven wheel motor drive

This paper presents the computer-aided design (CAD) and performance analysis of a novel direct-driven wheel brushless DC motor drive for electric vehicles (EVs). The proposed motor is a permanent magnet square-wave motor, whose rotor with rare earth magnets forms the exterior of the motor, which can be fitted with a wheel tire to realize the direct drive for each wheel of an EV. The interior stator with its windings is rigidly mounted onto the suspension and frame structure of the vehicle. In order to achieve the direct drive without any mechanical transmission for EVs, the wheel motor has been designed as a low-speed high-torque motor. The design and optimization of the motor geometry was achieved with the aid of finite-element electromagnetic field analysis. Simulation studies on the transient performance of the motor drive were also carried out. This involved the creation of the motor transient model and formulation of a motor control strategy to ensure the wheel motor drive runs efficiently in the entire permitted speed and load range. The application of CAD techniques in the design of this very unconventional drive is described in this paper.

Observer-based robust adaptive control of PMSM with initial rotor position uncertainty

In this paper, a mathematical model and control methodology for permanent magnet synchronous motor (PMSM) with initial rotor position uncertainty is proposed. Based on Lyapunov stability theory, an observer-based robust adaptive position and speed tracking control system for the PMSM is developed given that all parameters including load inertia and motor parameters are unknown, acceleration is not measurable and friction and external disturbances are bounded. An incremental encoder providing relative position of the rotor is used along with stator current signals to achieve stable control. The simulation and experimental results have proven the stability and efficacy of the proposed control law.