Babak Fahimi

Advantages of switched reluctance motor applications to EV and HEV: design and control issues

The purpose of this paper is to investigate the capabilities of switched reluctance motors (SRMs) for EV and HEV applications. This investigation is carried out in two steps. The first step involves the machine design and the finite element analysis to obtain the static characteristic of the motor. In the second step, the finite element field solutions are used in the development of a nonlinear model to investigate the dynamic performance of the designed motor. Several 8-6 and 6-4 SRM geometries are investigated. The effects of different stator and rotor pole widths and pole heights on the steady state as well as on the dynamic performance of the motor are studied. Simulation results of the designed SRM are presented for vehicle acceleration. To demonstrate the SRMs capability in producing an extended constant power range, experimental results are presented; however, for a reduced size motor available commercially.

A switched reluctance machine-based starter/alternator for more electric cars

Switched reluctance machines (SRMs) are considered as serious candidates for starter/alternator (S/A) systems in more electric cars. Robust performance in the presence of high temperature, safe operation, offering high efficiency, and a very long constant power region, along with a rugged structure contribute to their suitability for this high impact application. To enhance these qualities, we have developed key technologies including sensorless operation over the entire speed range and closed-loop torque and speed regulation. The present paper offers an in-depth analysis of the drive dynamics during motoring and generating modes of operation. These findings will be used to explain our control strategies in the context of the S/A application. Experimental and simulation results are also demonstrated to validate the practicality of our claims.

Making the case for applications of switched reluctance motor technology in automotive products

Switched reluctance machines (SRM) offer attractive attributes for automotive applications. These include robustness to harsh operational conditions, rugged structure, fault resilient performance, and a wide range of speed. The main debate over the adequacy of switched reluctance drives in automotive applications has often focused on efficiency and position sensorless control over the entire speed range, adaptation of control algorithms in the presence of parameter variations, and high levels of acoustic noise and vibration. The present paper demonstrates three key technologies developed over the past few years that have resulted in tangible improvements in the performance of SRM/generators (SRM/G) as related to the above areas of interest. This paper intends to illustrate the new possibilities and remaining challenges in applications of SRM in automotive industry. The proposed technologies have been validated by simulation and experimental results

Active Current Sharing and Source Management in Fuel Cell–Battery Hybrid Power System

Fuel cells (FCs) are being considered as a potential alternative in long term to replace diesel/gasoline combustion engines in vehicles and emergency power sources. However, high cost and slow dynamic response of FC still persist as the main hurdles for wider applications. To remedy this problem, an energy storage system with adequate power capacity has to be incorporated. This paper presents a novel control design for FC-battery hybrid power system which enables both active current sharing and power source management control in such hybrid systems. Different hybrid power system structures are investigated and evaluated; dual-converter structure and four modes of operation are defined to provide efficient and sustainable solution to such a hybrid power system. A novel integrated control system with inherent current sharing and generation mode swapping capability is proposed; based on system component status, the control system is able to regulate the output power from each source under different scenarios. The dedicated control system is implemented in a TMS320F2812 DSP, and experimental results for an FC-battery-based uninterruptible power supply are provided to demonstrate the static and dynamic performance of the control system.

Elimination of position sensors in switched reluctance motor drives: state of the art and future trends

This paper covers the range of topics related to sensorless control of switched reluctance motor (SRM) drives from their fundamentals to their limitations and state of the art and future trends. This should help the reader to develop a systematic understanding of the sensorless techniques that have been developed over the past two decades. The inherent vulnerability to mechanical failures, extra cost, and size associated with external position sensors such as optical encoders, resolvers, and custom-designed Hall-effect sensors has motivated many researchers to develop sensorless control techniques for SRM drives. Ideally, it is desirable to have a sensorless scheme, which uses only terminal measurements and does not require additional hardware or memory while maintaining a reliable operation over the entire speed and torque range with high resolution and accuracy. Advances in the development of low-cost digital-signal-processor-based microcontrollers have paved the way for the fulfillment of this objective. It is, furthermore, our view that the existing trends in the development of more powerful processors will ultimately replace the concept of sensorless controls with the concept of eliminating the need for position sensing, a concept that will further revolutionize the motor drive technology.

Multiport Power Electronic Interface—Concept, Modeling, and Design

The continuous effort to improve efficiency, reduce particle, and greenhouse gase emissions leads to the emergence of the concept “more electric.” This concept helps to boost the performance as well as the flexibility of the domestic and vehicular applications; however, on the other hand, it excessively burdens current power networks (including vehicle power systems). In order to remedy this problem, simultaneous usage of renewable sources and energy storages is encouraged. A multiconverter system is commonly adopted to process the renewable power in form of distributed generation. However, due to the discrete structure of such systems, power flow and load regulation are coordinated via communication channel, which inevitably reduces the reliability and dynamic response of the system. This paper presents the concept of multiport power electronic interface (MPEI) for renewable energy sources and storages. With a unified modular topology and highly integrated digital control system, controlled quasi-current source is achieved for each input port in both steady-state and transient power-sharing modes. MPEI analysis, modeling, design, and system operation are treated in a systematic manner in this paper. Both power stages and digital control system are implemented for a five-port MPEI. Experiments are conducted under meaningful operation scenarios. The results are presented to prove the feasibility of MPEI concept and system design methodology.

Double-Stator Switched Reluctance Machines (DSSRM): Fundamentals and Magnetic Force Analysis

In this paper, a new switched reluctance machine with a double-stator configuration (DSSRM) is introduced. The proposed design is based on optimization of the motional forces, which leads to a high-grade electromechanical energy conversion process. A local examination of the force densities within and throughout a conventional switched reluctance machine (SRM) shows that the majority of the force produced is in the radial direction and does not contribute to motion. If the normal forces happen to be in the direction of motion, a larger motional force profile for SRM is yield. Based on these guidelines, a new SRM (DSSRM) is proposed. To compare energy conversion efficiency of DSSRM with that of the conventional SRM, a finite element model is constructed. An experimental prototype of the proposed machine is developed, and the phase inductance is measured. The results of our investigations indicate that the proposed geometry offers superior performance in terms of higher power density and higher percentage of the motional forces.

A field reconstruction method for optimal excitation of permanent magnet synchronous machines

Vibration caused by torque ripple and radial force harmonics is a concern in many applications of permanent magnet synchronous machines (PMSMs). Alternative methods of machine design and/or stator excitation to minimize torque ripple have received considerable attention in recent years. Comparatively, methods to minimize radial force harmonics have received less attention. In this paper, a field reconstruction (FR) method is derived that provides a designer with the capability to rapidly determine the radial and tangential components of force under arbitrary stator excitation. Using the field reconstruction method, stator current waveforms that minimize the ripple of both torque and radial force are derived subject to the constraint of maintaining a satisfactory level of torque density.

On the Concept of Negative Impedance Instability in the More Electric Aircraft Power Systems with Constant Power Loads

The purpose of this paper is to present an assessment of the negative impedance instability concept of the constant power loads in the More Electric Aircraft (MEA) power systems. We address the fundamental problems faced in the stability studies of these multi-converter power electronic systems. An approach to the design of sliding-mode controllers for PWM DC/DC converters with constant power loads is presented. Because of the negative impedance destabilizing characteristics of constant power loads, conventional linear control methods have stability limitations around the operating points. However, the proposed controllers improve large-signal stability and dynamic responses. The proposed controllers are simulated and their responses under different operations are discussed. Finally, we verify the stability of the controllers using the second theorem of Lyapunov.

A new approach to model switched reluctance motor drive application to dynamic performance prediction, control and design

In this paper a new model for the switched reluctance motor (SRM) based on phase currents as state variables is presented. Position dependency of the phase inductance is represented by a limited number of Fourier series terms and the nonlinear variation of the inductance with phase current is expressed by means of polynomial functions. The coefficients of the terms in the Fourier series are determined by the aligned position inductance, the unaligned position inductance and the inductance at the midway point from the aligned position. The main advantage of the proposed model is that it requires minimum amount of measurements and predicts the complete dynamic performance of the drive system, viz., constant torque, constant power and natural mode regions. Any type of control strategy can be incorporated in the simulation. A low-voltage, high current SRM drive has been simulated and the results are validated by comparing with finite element and experimental results.