Annegret Klein-Hessling

Direct instantaneous torque and force control: A novel control approach for switched reluctance machines

Switched-reluctance technology is appealing to the automotive industry due to its cost efficiency. Conventional research focuses on the two main issues torque ripple and acoustic noise. However, control schemes usually only address one of these two issues at a time. This paper unifies the approaches of direct instantaneous torque control and direct instantaneous force control to simultaneously tackle the two central drawbacks of the switched reluctance machine. A searching algorithm was used to determine appropriate reference values for each phase to keep torque and overall radial force smooth at any time. Simulation and measurement results confirmed that the control objectives were met so that the torque ripple was reduced and the acoustic behavior of the investigated automotive traction drive was improved. The new control approach thus provides future engineers with a powerful tool for adapting the switched reluctance machine to the requirements of the automotive sector.

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.

Is acoustically oriented control always inefficient for an automotive switched reluctance machine

Recent publications have shown that the adverse acoustic behavior of automotive-size switched reluctance machines can be tackled by aid of Direct Instantaneous Force Control. The former work mainly focused on the functionality regarding acoustics. This paper, however, compares the drive losses between standard Hysteresis Current Control and Direct Instantaneous Force Control. Iron loss, copper loss and losses of the inverter were investigated by simulation. It turned out that iron loss decreases when applying Direct Instantaneous Force Control. Ohmic losses inevitably increase, though. Therefore, it depends on the load-cycle of the vehicle whether Direct Instantaneous Force Control or standard control is preferable.

Measuring SRM profiles including radial force on a standard drives test bench

Switched reluctance machines exhibit highly nonlinear characteristics which must be known to accurately model and control this machine type. These profiles are typically derived by finite-element analysis or measured on dedicated test benches. The aim of this paper is to propose a measurement procedure that requires only standard laboratory equipment. Moreover, a method is presented that allows the reconstruction of the radial-force characteristic, which has never been mentioned before in literature. A standard current source and a differential voltage probe were used to measure flux linkage. Afterwards torque was derived from the flux-linkage profile. Radial force was reconstructed by the aid of vibration excited under particular test circumstances. At the end the three fingerprint characteristics of the machine, i.e., flux linkage, torque and radial force, are known. The results are robust against measurement noise since they are obtained by averaging numerous electrical cycles.

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.

Acoustic optimization using vibration sensor feedback to the controller

Switched reluctance machines have the drawback of a high acoustic excitation. This paper presents an acoustic optimization method that analyzes the signal of a vibration sensor in the control loop and is able to eliminate mode-0 borne vibrations. A search algorithm which determines the optimized control parameters is proposed. The potential of the control concept is described including measurement results.

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.

Adopting a SOGI filter for flux-linkage based rotor position sensing of switched reluctance machines

Position sensorless control of switched reluctance motors reduces the system cost and increases the drives overall reliability. The flux-linkage method is a commonly applied technique when sensorless control of switched reluctance motors is pursued. The sensing quality, though being sensitive to model errors and further effects, can be sufficient for a number of applications. However, sophisticated control algorithms like predictive direct instantaneous torque control and direct instantaneous force control require highly accurate rotor position estimation. Current profiling methods rely on accurate position sensing as well. The main objective of the present paper is the improvement of the conventional flux-linkage method by adopting a band pass filter and a self-characterization routine. As a result the estimation error can be crucially reduced and the operation area of the flux-linkage method can be expanded. The paper includes simulative and experimental validation of the algorithm.

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.