Search

Stability of multi-converter power systems, which exist in advanced more electric vehicles, is of great importance. The stability issue is investigated in this paper, and design considerations and limitations of the methods that stabilize the open-loop converters are presented. By stabilizing the open-loop converter, it is shown that the feedback loop design is usually translated into a conventional feedback design task. The behavior of the unstable converter is also discussed, and a method for decreasing the amplitude of the output voltage oscillations is proposed. The model of a tightly regulated practical converter is presented. This model is used to decide how much damping should be added to make the feeder converter stable. Furthermore, because we have this information about the load converter, the feeder converter can be redesigned so that it does not see the load converter as a constant power load. Index Terms--Constant power loads (CPLs), continuous-conduction mode (CCM), damping methods, DC/DC converters, feedback, loop gain and bandwidth, multi-converter power systems, stability, vehicular power systems.

A highly efficient and novel control strategy for improving the transients in the output voltage of a dc-dc positive buck--boost converter, required for low-power portable electronic applications, is presented in this paper. The proposed control technique can regulate the output voltage for variable input voltage, which is higher, lower, or equal to the output voltage. There are several existing solutions to these problems, and selecting the best approach involves a tradeoff among cost, efficiency, and output noise or ripple. In the proposed method, instead of instantaneous transition from buck to boost mode, intermediate combination modes consisting of several buck modes followed by several boost modes are utilized to distribute the voltage transients. This is unique of its kind from the point of view of improving the efficiency and ripple content in the output voltage. Theoretical considerations are presented. Simulation and experimental results are shown to prove the proposed theory. Index Terms--Control, efficiency, Li-ion battery, positive buck--boost converter, transients.

Multi-converter power electronic systems exist in land, sea, air, and space vehicles. In these systems, load converters exhibit constant power load (CPL) behavior for the feeder converters and tend to destabilize the system. In this paper, the implementation of novel active-damping techniques on dc/dc converters has been shown. Moreover, the proposed active-damping method is used to overcome the negative impedance instability problem caused by the CPLs. The effectiveness of the new proposed approach has been verified by PSpice simulations and experimental results. Index Terms--Active damping, constant power loads (CPLs), continuous conduction mode (CCM), dc/dc converters, feedback control, multi-converter power systems, negative impedance, stability.

With the advent of battery-powered portable devices and mandatory adoption of power factor correction, noninverting buck-boost converters are garnering lots of attention. Conventional two-switch or four-switch noninverting buck-boost converters choose their operation modes by measuring input and output voltage magnitude. The criterion for the selection of the operation mode can cause higher output voltage transients in the neighborhood, where input and output are close to each other. For the mode selection, due to the voltage drops raised by the parasitic components, it is not enough just to compare the magnitude of input and output voltages. In addition, the difference in the minimum and maximum effective duty cycles between controller output and switching device yields discontinuity at the instant of mode change. Moreover, the different properties of output voltage versus a given duty cycle of buck and boost operating modes contribute to the output voltage transients. In this paper, the effect of the discontinuity due to the effective duty cycle derived from the device switching time at the mode change is analyzed. A technique to compensate the output voltage transient due to this discontinuity is proposed. In order to attain additional mitigation of output transients and a linear input/output voltage characteristic in buck and boost modes, the linearization of dc gain of the large-signal model in boost operation is analyzed as well. Analytical, simulation, and experimental results are presented to validate the proposed theory. Index Terms--Discontinuity, duty cycle, noninverting buck-boost converter, nonlinearity, transition.

The fuel efficiency and performance of novel vehicles with electric propulsion capability arc largely limited by the performance of the energy storage system (ESS). This paper reviews state-of-the-art ESSs in automotive applications. Battery technology options are considered in detail, with emphasis on methods of battery monitoring, managing, protecting, and balancing. Furthermore, other ESS candidates such as ultracapacitors, flywheels and fuel cells are also discussed. Finally, hybrid power sources are considered as a method of combining two or more energy storage devices to create a superior power source. Index Terms--Capacitors, energy storage, flywheels, fuel cells (FC), land vehicle, transportation.

With the requirements for reducing emissions and improving fuel economy, automotive companies are developing electric, hybrid electric, and plug-in hybrid electric vehicles. Power electronics is an enabling technology for the development of these environmentally friendlier vehicles and implementing the advanced electrical architectures to meet the demands for increased electric loads. In this paper, a brief review of the current trends and future vehicle strategies and the function of power electronic subsystems are described. The requirements of power electronic components and electric motor drives for the successful development of these vehicles are also presented. Index Terms--Electric machines, electric vehicles, fuel-cell vehicles, hybrid vehicles, motor drive, plug-in hybrid vehicles, power electronics, propulsion systems, vehicle strategy.

Efficiency, fuel economy, federal mandates, and global socio-political scenarios are the issues that are forcing the vehicular industry to seek more electrification. As land, sea/undersea, air, and space vehicles become more electric and less mechanical, vehicular industry is emerging as a leading application area for power electronics. Electrical architectures of power electronic based vehicular systems are in the form of multi-converter configurations. In multi-converter vehicular systems power electronic converters are mostly utilized in generating, distributing, and utilizing electrical energy in the vehicle. Power electronic converters, when tightly regulated, act as constant power loads. Constant power loads have a destabilizing effect on multi-converter systems. In order to mitigate this instability problem, which is also known as negative impedance instability, this paper introduces pulse adjustment, a novel digital control technique, to control dc/dc converters. This method applies predefined duty cycles, instead of conventional pulsewidth modulation (PWM) techniques, to regulate the output voltage. It is simple, cost-effective, and needs few logic gates and comparators to implement, thus, making it extremely simple and easy to develop using a low-cost application-specific integrated circuit (ASIC). Experimental results as well as simulation results are presented to describe and verify the proposed technique.

Multiconverter-distributed dc architectures have been utilized for power distribution in many applications such as telecommunication systems, sea and undersea vehicles, an international space station, aircraft, electric vehicles, hybridelectric vehicles, and fuel-cell vehicles, where reliability is of prime concern. The number of power-electronic converters (ac/dc, dc/dc, dc/ac, and ac/ac) in these multiconverter electrical power systems varies from a few converters in a conventional land vehicle, to tens of converters in an advanced aircraft, and to hundreds of converters in the international space station. In these advanced applications, power-electronic converters might need to have a tight output-voltage regulation. From the output perspective, this property is highly desirable. However, since power-electronic converters are efficient, tight regulation of the output makes the converter appear as a constant-power load (CPL) at its input side. Dynamic behavior of CPLs is equivalent to negative impedance and, therefore, can result in instability of the interconnected power system. In order to mitigate the instability of the power converters loaded by CPLs, this paper presents the pulse-adjustment digital control technique. It is simple and easy to implement in application-specific integrated circuits, digital-signal processors, or field-programmable gate arrays. Moreover, its dynamic response is fast and robust. Line and load regulations are simply achievable using this technique. Analytical, as well as simulation and experimental results of applying the proposed method to a dc/dc buck-boost converter confirm the validity of the presented technique. Index Terms--Automotive, buck-boost converter, constantpower loads (CPLs), control, electric vehicles, line regulation, modeling and analysis, multiconverter, negative-impedance instability, power converters.

This paper presents the design consideration and performance analysis of an on-line, low-cost, high performance, and single-phase uninterruptible power supply (UPS) system based on a boost integrated flyback rectifier/energy storage dc/dc (BIFRED) converter. The system consists of an isolated ac/dc BIFRED converter, a bidirectional dc/dc converter, and a dc/ac inverter. It provides input power factor correction, electric isolation of the input from the output, low battery voltage, and control simplicity. Unlike conventional UPS topologies, the electrical isolation is provided using a high frequency transformer that results in a smaller size and lower cost. Detailed circuit operation, analysis, as well as simulation and experiment results are presented. A novel digital control technique is also presented for UPS inverter control. This controller follows the reference current and voltage of the inverter with a delay of two and four sampling periods, respectively. Index Terms--Battery charger, digital control, integrated converters, inverters, modeling and analysis, power electronic converters, rectifiers, uninterruptible power supplies (UPSs).

Brushless dc (BLDC) motor drives are continually gaining popularity in motion control applications. Therefore, it is necessary to have a low cost, but effective BLDC motor speed/torque regulator. This paper introduces a novel concept for digital control of trapezoidal BLDC motors. The digital controller was implemented via two different methods, namely conduction-angle control and current-mode control. Motor operation is allowed only at two operating points or states. Alternating between the two operating points results in an average operating point that produces an average operating speed. The controller design equations are derived from Newton's second Jaw. The novel controller is verified via computer simulations and an experimental demonstration is carried out with the rapid prototyping and real-time interface system dSPACE. Index Terms--Brushless dc (BLDC) motor drives, digital control, electric motor drives, inverters, modeling and analysis, motion control, permanent-magnet machines, power electronic converters.

Multiconverter power-electronics-based power systems are being increasingly used in advanced vehicles. Stability of these power electronics-intensive systems is a significant design consideration because of the potential for negative impedance instability. In this paper, in order to mitigate the problem of negative impedance instability, pulse adjustment, which is a novel fixed frequency digital control technique for converters operating with constant power loads (CPLs), is presented. This novel digital control approach treats the converter as a digital system and achieves output voltage regulation by choosing high- and low-power pulses instead of using conventional pulsewidth modulation scheme. A comparator compares the actual output voltage with the reference voltage and then switches between the appropriate states. Therefore, the digital control task is to deliver the right amount of energy to the converter by right numbers of state operations so that the average power delivery matches the required power. It needs few logic gates and comparators to implement this digital control, thus making it extremely simple and easy to develop using low-cost application specific integrated circuits. It is simple, cost effective, and dynamically fast. In this paper, a model to analyze the dc/dc buck-boost converter that is controlled by the pulse adjustment approach in the discontinuous conduction mode is derived. Stability of the buck-boost converter driving CPLs is analyzed using the introduced model. Furthermore, comprehensive sensitivity analyses of applying the pulse adjustment method to control dc/dc converters that are loaded by CPLs are presented. In addition, this paper gives design considerations to assess performance and stability robustness of the pulse adjustment method to control buck-boost converters that are loaded by CPLs. Analytical, simulation, and experimental results are presented to describe and verify the proposed technique. Index Terms--Constant power loads (CPLs), control, modeling and analysis, multiconverter, negative impedance instability, power converters, stability, state-space averaging (SSA), vehicular systems.

Although hybrid-electric vehicles have been studied mainly with the aim of increasing fuel economy, little has been done in order to improve both fuel economy and performance. However, vehicular-dynamic-performance characteristics such as acceleration and climbing ability are of prime importance in military vehicles such as the high-mobility multipurpose wheeled vehicle (HMMWV). This paper concentrates on the models that describe hybridized HMMWV vehicles and the simulation results of those models. Parallel and series configurations have been modeled using the advanced-vehicle-simulator software developed by the National Renewable Energy Laboratory. Both a retrofit approach and a constant-power approach have been tested, and the results are compared to the conventional model results. In addition, the effects of using smaller engines than the existing ones in hybrid HMMWV drive trains have been studied, and the results are compared to the data collected from an actual implementation of such a vehicle. Moreover, the integrated-starter/alternator (ISA) configuration has been considered, and the results were encouraging. Index Terms--Diesel engine, electric drives, electric propulsion, hybrid-electric vehicles (HEVs), military vehicles, power-electronic converters, sport-utility vehicles (SUVs), vehicle simulation.

Power electronic converters and electric motor drives are being put into use at an increasingly rapid rate in advanced automobiles. However, the new advanced automotive electrical systems employ multivoltage level hybrid ac and dc as well as electromechanical systems that have unique characteristics, dynamics, and stability problems that are not well understood due to the nonlinearity and time dependency of converters and because of their constant power characteristics. The purpose of this paper is to present an assessment of the negative impedance instability concept of the constant power loads (CPLs) in automotive power systems. The main focus of this paper is to analyze and propose design criteria of controllers for automotive converters/systems operating with CPLs. The proposed method is to devise a new comprehensive approach to the applications of power electronic converters and motor drives in advanced automotive systems. Sliding-mode and feedback linearization techniques along with large-signal phase plane analysis are presented as methods to analyze, control, and stabilize automotive converters/systems with CPLs. Index Terms--Constant power loads (CPLs), control, electric vehicles (EVs), fuel cell vehicles (FCVs), hybrid electric vehicles (HEVs), modeling, modeling and analysis, motor drives, negative impedance instability, power converters, stability, state-space averaging.

From the point of view of overall hybrid electric vehicle (HEV) and fuel cell vehicle (FCV) drive train efficiency, the research focus is mainly on the efficiency analysis of the power train components, which prove to be an integral part of modern HEV and FCV drive trains. The critical portion of any HEV electrical system consists of a power electronic converter (inverter) and a suitable traction motor. Thus, the efficiency analysis of the inverter/motor is of prime importance for the calculation of the overall efficiency of the drive trains. This paper aims at modeling the efficiencies of the traction motor/controller through efficiency maps. Efficiency maps are a convenient way to represent motor drive systems of large and complex systems, like that of a HEV. The paper uses the advanced vehicle simulator (ADVISOR) software for the simulations of a large-sized car, similar to a Chevy Lumina, over the urban dynamometer-driving schedule and highway fuel economy test drive cycles. Furthermore, the paper investigates the traction motor efficiency maps and consequent overall drive train efficiencies of commercially available Honda Insight and Toyota Prius HEVs. In all the case studies, the aim is to analyze the overall drive train efficiency over the city and highway drive cycles based on the inverter/motor efficiency maps. Index Terms--Electric propulsion, hybrid electric vehicles (HEV), internal combustion engines (ICE), inverters, road vehicles, traction motors.

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. Index Terms--Acoustic noice, switched reluctance machines (SRM), vibration.

There is a clear trend in the automotive industry to use more electrical systems in order to satisfy the ever-growing vehicular load demands. Thus, it is imperative that automotive electrical power systems will obviously undergo a drastic change in the next 10-20 years. Currently, the situation in the automotive industry is such that the demands for higher fuel economy and more electric power are driving advanced vehicular power system voltages to higher levels. For example, the projected increase in total power demand is estimated to be about three to four times that of the current value. This means that the total future power demand of a typical advanced vehicle could roughly reach a value as high as 10 kW. In order to satisfy this huge vehicular load, the approach is to integrate power electronics intensive solutions within advanced vehicular power systems. In view of this fact, this paper aims at reviewing the present situation as well as projected future research and development work of advanced vehicular electrical power systems including those of electric, hybrid electric, and fuel cell vehicles (EVs, HEVs, and FCVs). The paper will first introduce the proposed power system architectures for HEVs and FCVs and will then go on to exhaustively discuss the specific applications of dc/dc and dc/ac power electronic converters in advanced automotive power systems. Index Terms--Electric propulsion, electric vehicles (EVs), fuel cell vehicles (FCVs), hybrid electric vehicles (HEVs), internal combustion engines, motor drives, power converters, semiconductor devices.

Pulse regulation, a fixed frequency control technique, is introduced and applied to flyback converter operating in discontinuous conduction mode (DCM). The control parameters are designed in a way that the converter operates as close as possible to the critical conduction mode. In contrast to the conventional pulsewidth modulation control scheme, the principal idea of pulse regulation is to achieve output voltage regulation using high and low-power pulses. Pulse regulation is simple, cost effective, and enjoys a fast dynamic response. The proposed technique is applicable to any converter operating in DCM. However, this work mainly focuses on flyback topology. In this paper, the main mathematical concept of the new control algorithm is introduced and simulations as well as experimental results are presented. Index Terms--Critical conduction mode (CCM), dc-dc power converters, discontinuous conduction mode (DCM), flyback converter, switch mode power supplies.

One of the major issues surrounding the research and development work involving hybrid electric and fuel cell vehicles (HEVs and FCVs) is their overall efficiency of converting the input fuel into actual work at the wheels of the vehicle. The main idea behind efficiency comparisons between HEVs and FCVs is the analysis of their respective well-to-tank (WTT) and tank-to-wheels (TTW) efficiencies, the product of which reveals the well-to-wheels (WTW) efficiency, which is one of the deciding factors for technology acceptance. This paper primarily aims at presenting critical comparative issues with regards to the overall efficiencies of the most popularly proposed HEV and FCV topologies. Finally, the overall efficiency analysis performed in this paper will lay down the foundation for a concrete conclusive comparison between advanced vehicular topologies of the future. Index Terms--Diesel engines, electric propulsion, fuel cells, hybrid electric vehicles (HEVs), internal combustion engines, road vehicles, vehicle simulation.

This paper discusses the operational characteristics of the topologies for hybrid electric vehicles (HEV), fuel cell vehicles (FCV), and more electric vehicles (MEV). A brief description of series hybrid, parallel hybrid, and fuel cell-based propulsion systems are presented. The paper also presents fuel cell propulsion applications, more specific to light-duty passenger cars as well as heavy-duty buses. Finally, some of the major fundamental issues that currently face these advanced vehicular technologies including the challenges for market penetration are highlighted. Index Terms--Electric drives, electric propulsion, electric vehicles, fuel cells, hybrid electric vehicles (HEVs), internal combustion engines, power electronic converters, road vehicles.

The Pulse Regulation control scheme is presented and applied to the boost integrated flyback rectifier/energy storage dc/dc (BIFRED) converter as the most popular member of the integrated high-quality rectifier-regulators (IHQRR). In contrast to the conventional control techniques, the principal idea of Pulse Regulation is to regulate the output voltage using a series of high- and low-power pulses generated by the current of the input inductor, which is operating in discontinuous conduction mode (DCM). In this paper, analysis of the BIFRED converter operating in DCM is presented. Fundamentals of Pulse Regulation as well as its stability analysis and the estimation of the output voltage ripple are introduced. Experimental results on a prototype converter are also presented to validate the analytical and simulation results. Index Terms--AC/DC power converters, boost integrated flyback rectifier/energy storage dc/dc (BIFRED) converter, dc/dc power converters, digital control, discontinuous conduction mode (DCM), integrated high-quality rectifier-regulators, simulation, stability, switch-mode prower supplies, voltage regulation.

Pulse Train[TM] control scheme is presented and applied to a boost integrated flyback rectifier/energy storage dc-dc (BIFRED) converter operating in discontinuous conduction mode (DCM), which avoids the light-load high-voltage stress problem. In contrast to the conventional control techniques, the principal idea of Pulse Train technique is to regulate the output voltage using a series of high and low energy pulses generated by the current of the inductor. The applicability of the proposed technique to both the input and magnetizing inductances of BIFRED converter is investigated. Analysis of BIFRED converter operating in DCM as well as the output voltage ripple estimation are given. Experimental results on a prototype converter are also presented.

Proper synchronization of the excitation with respect to the rotor position is essential in optimal control of switched reluctance motor (SRM) drives. To avoid additional cost, size, and unreliability caused by the external position sensors, magnetic status of the SRM can be directly monitored to detect commutation instants. A one-to-one correspondence between magnetic status of the SRM and rotor position removes the need for an explicit access to the rotor position. In order to obtain a good precision over the entire speed range, educated modifications on the structure of the sensorless strategy is necessary. This is due to the impact of the operational regions on dynamic behavior of the SRM. In addition, introduction of SRM technology to industrial and domestic applications has raised the need for four-quadrant operation of the SRM drives. The present paper introduces a range of strategies that are necessary to accommodate this requirement in a sensorless format. Our experimental findings indicate that high-grade sensorless operation in a four-quadrant SRM drive is possible and can be integrated in a variety of applications. Index Terms--Rotor position, switched reluctance motor (SRM) drives.

Most of the loads in ac distribution systems have positive incremental impedance characteristic. However, power electronic loads, when tightly regulated, sink constant power from the system. Therefore, they have negative incremental impedance characteristic. This can cause negative impedance instability. Power electronic loads usually have a controlled or uncontrolled rectifier at the front end. In this paper, these loads are modeled using the generalized state-space averaging method. An assessment of their effects in ac distribution systems is also presented. Experimental results are presented to verify the proposed analysis. Index Terms--Analysis, constant power loads, dc/dc power converters, generalized state-space averaging, modeling, simulation, stability, state-space averaging.

Drive-train hybridization improves the fuel economy and emissions of vehicles. This is the concept of hybrid electric vehicles (HEVs). Application of this concept in sport utility vehicles (SUVs), which consume more fuel as compared to passenger cars, will positively have a great impact. However, dynamic performances such as acceleration and gradeability also are of great importance in SUVs. Therefore, the optimum choice of the system hybridization level includes complex tradeoffs between the engine and electric propulsion motor on the one hand and fuel economy, performance, and cost on the other. In this paper, we classify SUVs as small, medium, and large vehicles. Effects of hybridization on the fuel economy and dynamic performances of each class of SUVs are investigated. Different hybridization levels, from mild to full hybrid electric traction systems, are examined. Index Terms--Electric drives, electric propulsion, hybrid electric vehicles (HEVs), power electronic converters, sport utility vehicles (SUVs), vehicle simulation.

Increasing use of electrical power to drive automobile subsystems, which historically have been driven by a combination of mechanical and hydraulic power transfer systems, is seen as a dominant trend in advanced automotive power systems. This trend manifests itself through the more-electric-cars (MEC) concept, which requires highly reliable, fault-tolerant, and cost-effective electrical systems. This paper introduces the Illinois Institute of Technology (IIT) Interprofessional Projects (IPRO) Program and a series of multidisciplinary student team projects focused on applications of electrical systems in advanced automobiles. IIT's interprofessional course engages multidisciplinary teams of students in semester-long projects. It delivers a team-oriented project-based requirement within the undergraduate curriculum. Among its many benefits, the interprofessional course offers the opportunity to integrate the education and research environment of the university and, in this case, introduces students to the role of electrical systems in emerging automotive platforms that offer numerous research and technology application opportunities for electrical engineers. Index Terms--Automotive power systems, hybrid electric vehicles, interprofessional projects, modeling, muitidisciplinary team projects, real-world design, student experiments.

This paper presents the concept of hybrid electric vehicles (HEVs) applied to sport utility vehicles (SUVs) with diesel engines. Two SUVs currently available in the U.S. market have been selected as the representative vehicles used in this study, which consists of the modeling and simulation of the vehicles as close as possible to the manufacturer's specifications and then running the models through the Advance Vehicle Simulator (ADVISOR). Effects of hybridization on the fuel economy and dynamic performances of the two representative SUVs are investigated. Different hybridization levels from mild to full hybrid electric drive trains are studied through comprehensive simulations. Index Terms--Diesel engine, electric propulsion, hybrid electric vehicles (HEVs), sport utility vehicles (SUVs), vehicle simulation.

This paper presents a modular approach for the modeling and simulation of multiconverter dc power electronic systems based on the generalized state-space averaging method. These systems may consist of many individual converters connected together to form large and complex systems. In addition to simplifying the analysis procedure, by using the proposed method, time step for analysis of the system can be increased. Therefore, required computation time and computer memory for complex systems can be reduced considerably. In this paper, after introducing the proposed approach, results of applying the method to a representative system are presented. Index Terms--Analysis, dc/dc power converters, generalized state-space averaging, inverters, modeling, simulation, state-space averaging.

High power density is the main advantage of the axial flux motors compared to the conventional radial flux motors. Therefore, they are suitable candidates for the power train of hybrid electric vehicles. In addition, operating speed range and efficiency of axial flux motors can be improved by changing the air gap of the machine. In this paper, for each operating point, the optimal air gap is estimated based on the measured efficiency at different air gaps. The motor model is developed using the estimated optimal air gap and efficiency. Vehicle performance with the axial flux motor is also simulated based on the developed motor/controller model. Furthermore, the actual motor performance in a typical vehicle environment is analyzed with a vehicle simulator by applying the concept of hardware in the loop without installing the motor in the vehicle. Actual motor performance is compared with the simulation results as well. Motor performance in different drive cycles is also tested. The test motor can be used for the drivetrain of a series hybrid electric vehicle. Index Terms--Axial flux-variable gap motor, electric drives, electric propulsion, hardware in the loop (HIL), hybrid electric vehicles (HEVs), power electronic converters, vehicle simulation.

Pulse Train[TM] control technique is introduced and applied to Flyback converter operating in discontinuous conduction mode (DCM). In contrast to the conventional pulse width modulation (PWM) control scheme, the principal idea of Pulse Train is to achieve output voltage regulation using high and low power pulses. The proposed technique is applicable to any converter operating in DCM. However, this work mainly focuses on Flyback topology. In this paper, the main mathematical concept of the new control algorithm is introduced and simulations as well as experimental results are presented. Index Terms--Critical conduction mode, dc--dc power converters, discontinuous conduction mode, flyback converter, near-zero-voltage switching, switch mode power supplies.

Hybrid electric vehicles have proved to be the most practical solution in reaching very high fuel economy as well as very low emissions. However, there is no standard solution for the optimal size or ratio of the internal combustion engine and the electric system. The optimum choice includes complex tradeoffs between the heat engine and electric propulsion system on one hand and cost, fuel economy, and performance on the other. Each component, as well as the overall system, have to be optimized to give optimal performance and durability at a low price. In this paper, we look at the effects of hybridization on fuel economy and dynamic performances of vehicles. Different hybridization levels from mild to full hybrid electric traction systems are examined. We also present the optimum level of hybridization for typical passenger cars. This study shows that low hybridization levels provide an acceptable fuel economy benefit at a low price, while the optimal level of hybridization ranges between 0.3 and 0.5, depending on the total vehicle power. Index Terms--Control systems, hybrid electric vehicles (HEVs), internal combustion engines, road vehicle electric propulsion, vehicle simulation.

Automotive manufacturers have been taking advantage of simulation tools for modeling and analyzing various types of vehicles, such as conventional, electric, and hybrid electric vehicles. These simulation tools are of great assistance to engineers and researchers to reduce product-development cycle time, improve the quality of the design, and simplify the analysis without costly and time-consuming experiments. In this paper, a modeling tool that has been developed to study automotive systems using the power electronics simulator (PSIM) software is presented. PSIM was originally made for simulating power electronic converters and motor drives. This user-friendly simulation package is able to simulate electric/electronic circuits; however, it has no capability for simulating the entire system of an automobile. This paper discusses the PSIM validity as an automotive simulation tool by creating module boxes for not only the electrical systems, but also the mechanical, energy-storage, and thermal systems of the vehicles. These modules include internal combustion engines, fuel converters, transmissions, torque couplers, and batteries. Once these modules are made and stored in the library, the user can make the car model either a conventional, an electric, or a hybrid vehicle at will, just by dragging and dropping onto a schematic blank page. Index Terms--Electric drives, electric propulsion, electric vehicles, hybrid electric vehicles, power electronic converters, vehicle simulation.

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. Index Terms--Closed-loop control, more electric cars, position sensorless, signature detection, switched reluctance generators, switched reluctance motors.

An energy source is the heart of a hybrid electric vehicle. If it is capable of supplying enough power at all times, then it is an adequate source. Major problems presently facing the industry include the size, cost, and efficiency of the energy source. The primary energy source presently used in automotive systems is a battery. In order to reduce the cost of the battery, the current needs to be decreased and stabilized so it is not very erratic. The purpose of this paper is to introduce and justify the use of a new model for an energy source: a battery in parallel with an ultra-capacitor. The ultra-capacitor can supply a large burst of current, but cannot store much energy. Conversely, the battery can store mass amounts of energy; however, without expensive and inefficient units, a battery cannot provide the current that the ultra-capacitor can. By combining the two energy sources in parallel, the storage and peak current characteristics desired can be achieved. The standards of the vehicle are not degraded, allowing this to be a promising technique to incorporate into hybrid electric vehicles to reduce their cost and increase the efficiency of their energy-source system. Index Terms--Electric drives, electric propulsion, energy source, hybrid electric vehicles, power electronic converters, ultra-capacitor, vehicle simulation.