Berker Bilgin

Design Considerations for Switched Reluctance Machines With a Higher Number of Rotor Poles

Switched-reluctance-machine (SRM) technology is a potential candidate for the propulsion systems of hybrid and plug-in hybrid electric vehicles. They are robust in harsh operational conditions and have a wide constant power speed range. Conventional SRM configurations have a higher number of stator poles than rotor poles. This paper presents the advantages of a novel SRM configuration with the number of rotor poles greater than the number of stator poles. It also investigates different design challenges toward the traction applications. The proposed SRM configuration is based on a pole-design formula. Geometrical design equations and related challenges are introduced, and their applicability has been verified on a three-phase 6/10 SRM using finite-element-analysis simulations.

Comprehensive Evaluation of the Dynamic Performance of a 6/10 SRM for Traction Application in PHEVs

Switched reluctance machine (SRM) has been viewed as a low-cost machine with concentrated windings on the stator and no magnetic source on the rotor. Owing to the higher torque-production capability with lower ripple, an SRM with a higher number of rotor poles is a potential candidate for traction applications in hybrid and plug-in hybrid electric vehicles. However, since external phase commutation and rotor-position detection are necessary to run the SRM, its control can be challenging. In case of an SRM with a higher number of rotor poles, each phase is energized more frequently in one revolution, and the current conduction time is shorter due to the smaller interpolar gap between rotor poles. This paper investigates potential control complexity owing to the higher number of rotor poles, self-starting, and fault tolerance of the machine. A 5-hp drivetrain with a three-phase 6/10 SRM has been developed for traction application. Conventional current and speed controls have been implemented to experimentally evaluate the dynamic performance of the new family of SRMs. It has been shown that the 6/10 SRM is capable of operating even if two of its phases develop a fault. Moreover, the 6/10 SRM is capable of starting by itself with an initial hard alignment when only two phases are operating.

Making the Case for Electrified Transportation

In order to achieve lower fuel consumption and less greenhouse gas (GHG) emissions, we need higher efficiency vehicles with improved performance. Electrification is the most promising solution to enable a more sustainable and environmentally friendly transportation system. Electrified transportation vision includes utilizing more electrical energy to power traction and nontraction loads in the vehicle. In electrified powertrain applications, the efficiency of the electrical path, and the power and energy density of the components play important roles to improve the electric range of the vehicle to run the engine close to its peak efficiency point and to maintain lower energy consumption with less emissions. In general, the electrified powertrain architecture, design and control of the powertrain components, and software development are coupled to facilitate an efficient, high-performance, and reliable powertrain. In this paper, enabling technologies and solutions for the electrified transportation are discussed in terms of power electronics, electric machines, electrified powertrain architectures, energy storage systems (ESSs), and controls and software.

An Offline Torque Sharing Function for Torque Ripple Reduction in Switched Reluctance Motor Drives

In this paper, an offline torque sharing function (TSF) for torque ripple reduction in switched reluctance motor (SRM) drives over a wide speed range is proposed. The objective function of an offline TSF is composed of two secondary objectives with a Tikhonov factor to minimize the square of the phase current (copper loss) and derivatives of current references (rate of change of flux linkage). The proposed TSFs with different Tikhonov factors are compared with the conventional TSFs including linear, cubic, and exponential TSFs in terms of efficiency and torque-speed performance while operating in both magnetic linear and saturation regions. Then, the Tikhonov factor is selected based on a tradeoff between the copper loss and torque-speed performance. The maximum torque-ripple-free speed of the selected offline TSF is validated to be seven times as high as the best case in these conventional TSFs. The performance of the offline TSF is verified by simulations and experiments with a 2.3-kW, three-phase 12/8 SRM. Results show that the proposed offline TSF can significantly reduce the torque ripple of SRM without increasing copper loss over a wide speed range.

Loss and Efficiency Analysis of Switched Reluctance Machines Using a New Calculation Method

In this paper, a fast and accurate analytical method is proposed to analyze the loss and efficiency of switched reluctance machines (SRMs) under various operating conditions. The analyses are applied on a four-phase 16/12 SRM with high power density and wide speed range, which was designed for traction application. A direct method is proposed to calculate hysteresis and eddy current loss without empirical equations. The machine is discretized into a limited number of elements according to the magnetic flux density distribution using an analytical magnetic circuit method. Variable loss coefficients are used for each element to improve the accuracy. The developed method has been validated with simulation and experimental results.

Electric Motors in Electrified Transportation: A step toward achieving a sustainable and highly efficient transportation system

The transportation sector is one of the largest energy users, and the main source of energy in our transportation system is still fossil fuels. As an example, in the United States, 98% of transportation energy comes from oil, but most of it is wasted due to the low efficiency of con-ventional internal combustion engine (ICE) vehicles. To-days low fuel efficiencies make the automotive industry one of largest sources of greenhouse gas emissions. In this article, the multidisciplinary nature of electric traction motors is investigated and related design issues are presented for interior permanent magnet (PM), induction, and switched reluctance machines (SRMs). These are the commonly considered machine types for traction applications, although the PM machine is the most widely used type in currently available electrified vehicles. The operating principles of these machines were also be explained.

Elimination of Mutual Flux Effect on Rotor Position Estimation of Switched Reluctance Motor Drives

An approach to eliminate mutual flux effect on rotor position estimation of switched reluctance motor drives at rotating shaft conditions without a prior knowledge of mutual flux is proposed in this paper. Neglecting the magnetic saturation, the operation of conventional self-inductance estimation using phase current slope difference method can be classified into three modes: Mode I, II, and III. At positive-current-slope and negative-current-slope sampling point of one phase, the sign of current slope of the other phase changes in Mode I and II, but does not change in Mode III. Theoretically, based on characteristics of a 2.3 kW, 6000 rpm, three-phase 12/8 SRM, mutual flux introduces a maximum ±7% self-inductance estimation error in Mode I and II, while, in Mode III, mutual flux effect does not exist. Therefore, in order to ensure that self-inductance estimation is working in Mode III exclusively, two methods are proposed: variable-hysteresis-band current control for the incoming phase and variable-sampling self-inductance estimation for the outgoing phase. Compared with the conventional method which neglects mutual flux effect, the proposed position estimation method demonstrates an improvement in position estimation accuracy by 2°. The simulations and experiments with the studied motor validate the effectiveness of the proposed method.

Design considerations for a universal input battery charger circuit for PHEV applications

Requirements of the battery charger circuit for plugin hybrid electric vehicle applications are defined and a PWM boost rectifier cascaded with a bidirectional DC/DC converter has been proposed in this paper. Operation of the circuit has been analyzed and its mathematical model has been derived to investigate the design consideration of the circuit parameters. Feedback controller requirements to control the input and output current and DC bus voltage have been studied. Major points to be considered in parameter selection of the voltage and current controllers are explained in terms of the universal input operation. Finally, the mathematical model of the system is implemented in Simulink and its performance for steady-state power factor correction and response to load disturbance have been tested for a 3kW, 90–250Vrms, 50–60Hz input and 48V DC output battery charger circuit.

Universal input battery charger circuit for PHEV applications with simplified controller

Plug-in hybrid electric vehicles (PHEVs) are equipped with a high energy density battery pack, which should be externally charged form the grid. This requires a high power battery charger circuit which can operate at universal input voltage and be capable of maintaining the required output voltage and current with low ripple. The topology composed of PWM boost rectifier cascaded with a bidirectional DC/DC converter is a simple and low cost solution for this application. However, when individual average mode current controllers are used for each converter, the controller parameters have significant effect on the circuit performance. Moreover, feedforward compensator is necessary at the AC/DC conversion stage, if the circuit is working with universal input voltage. In this paper, to make the design and implementation process easier, a simplified controller is proposed in the battery charger circuit which produces pulses according to the sign of the error of the feedback and which does not require any parameter. Since it is the most critical and restrictive case, charging mode of operation is addressed for the controller design. The simplified control is compared with conventional PI control in terms of performance, stability and robustness for universal input operation and the simulation results are supported with experimental verification.

A topological evaluation of isolated DC/DC converters for Auxiliary Power Modules in Electrified Vehicle applications

This paper presents a comparative evaluation of the suitable isolated DC-DC converters for the Auxiliary Power Module (APM) in Electrified Vehicle applications. The basic Single-Input-Single-Output (SISO) DC-DC converter topologies are reviewed. Different configurations of Single-Input-Multiple-Output (SIMO) and Multiple-Input-Multiple-Output (MIMO) topologies and their control strategies are presented. By applying full bridge current doubler as the base topology, different multiple topology configurations are compared from a MOSFET switch efficiency drop and cost aspect. Results of the study show that the Input-Series-Output-Parallel (ISOP) topology configuration presents better performance for the APM application in terms of switch efficiency and cost.