Bernhard Burkhart

The effect of excitation angles in single-pulse controlled switched reluctance machines on acoustics and efficiency

To make the development process of electric machines more efficient, it is very important to assess the characteristics of a given machine design early in the design process. In the case of a Switched Reluctance Machine in single-pulse operation, the efficiency is mainly determined by the turn-on and turn-off angle. These parameters on the other hand have a significant impact on the acoustic behavior of the drive system. This paper compares different sets of excitation angles and investigates the validity of a late-single-pulse strategy for Switched Reluctance Machines in generator mode. Measurements confirm partly this control strategy and the underlying simplified simulation approach for the examined machine.

Fully digital FPGA-based current controller for switched reluctance machines

A novel fully digital FPGA-based current controller for switched reluctance machines is presented in this paper. The digital current controller provides PWM and hysteresis band modulation in a seamless way and allows complex rotor position based shaping of the phase currents to optimize torque ripple and acoustic behavior. Arbitrary phase current waveforms can be stored in a position-addressed memory. The FPGA based implementation ensures flexible scaling and adaptation to various machine designs and inverter topologies. Experimental results prove the feasibility and performance of the chosen approach.

Design of a switched reluctance traction drive for Electric Vehicles

The cost of an electric traction drive has a strong impact on the overall price of small electric cars. Therefore, a cost effective design of such a drive train is essential. This paper investigates the design of a switched reluctance machine for application in electric vehicles from a system perspective. The goal of the paper is to propose a design procedure, which takes into account machine, inverter, battery and mechanical system. First, relevant components of the system as well as the basic requirements are defined. Special attention is paid to the modeling of the battery and dc-link behavior, which often was neglected in previous studies. Afterwards, the machine design considerations and machine characteristics are presented. The analysis clearly shows that the entire propulsion system has to be optimized in closed form to optimize the overall efficiency. In addition, it is essential to minimize the size of the dc-link capacitor of the inverter, while reducing the influence of ripple current on the high-voltage battery.

Technology, research and applications of switched reluctance drives

Electrical drives are one of the major consumers of electrical energy and their penetration in the market is still growing. Hence, for many drive applications efficient, reliable and cost effective solutions have to be found. Switched reluctance drives (SRD) offer a potential solution when focus is mainly on cost and robustness. However, to benefit from the unique advantages of this machine type a deep understanding of its strongly non-linear behavior is required. After discussing some major differences to classic rotating field machines, this paper presents a broad overview of the state of the art of SRD taking into consideration all aspects relevant to machine modeling, design and control development process. Finally, applications on the market utilizing SRDs and the focus of current research is presented. After reading this paper the reader will be able to assess if this modern drive technology could be advantagous in a given application.

Impact of smooth torque control on the efficiency of a high-speed automotive SRM drive

Switched reluctance motors are an alternative to conventional rotating field machines due to their robust mechanical design and low-cost production. In automotive drives the application of a dedicated algorithm for torque ripple reduction is indispensable as otherwise mechanical resonances in the drive train are excited. In this paper an automotive-sized high-speed SRM drive is investigated for two different control schemes - hysteresis current control and pwm-based direct instantaneous torque control. The main focus of the study lies on the evaluation of both algorithms in terms of efficiency. An analytic loss analysis in selected operating points is carried out and confirmed by simulation. Furthermore a comparison of experimentally derived efficiency maps is presented.

Impact of Smooth Torque Control on the Efficiency of a High-Speed Automotive Switched Reluctance Drive

This paper examines the efficiency performance of an automotive-size high-speed switched reluctance drive. It investigates the impact of a smooth torque control algorithm on the efficiency and losses in the drive. In automotive drives, the application of a dedicated algorithm for torque ripple reduction at low to medium speed is indispensable to avoid excitation of mechanical resonances in the drive train. The predictive direct instantaneous torque control method is compared with efficiency optimized hysteresis current control in terms of efficiency. Dynamic finite-element loss analysis is employed to investigate the source of the efficiency deviation and the results are verified by measurements. The study shows that the requirement for smooth torque leads to a decrease in the drives efficiency and altered loss distribution. The efficiency map comparison reveals that the efficiency degradation amounts to 4–9% for this particular drive.

Active source current filtering to minimize the DC-link capacitor in switched reluctance drives

Switched reluctance machines receive increased attention by the automotive industry because of their cost efficiency. However, the comparatively larger inverter is a disadvantage of this machine type. This paper evaluates the effects of the usage of a dc-dc converter to reduce the size of the dc-link capacitor by active filtering of the source current. The active filter is compared to a passive filter. Besides, the influence of a variable dc-link voltage level on the machine efficiency is investigated.