Magnesense PapersMagnesense Papers
Magnetic
Analysis by a Flux-Centered Approach, Part 1:
Choosing Flux Linkage As An Independent Variable
In most analyses of solenoid dynamics, the three primary or state variables are armature position, armature velocity, and electric current. The choice of these three determines that values of a number of dependent variables: momentum, inductance, flux linkage, etc. Other choices for the three state variables are possible, leading to different dependent variables. This paper argues that it is advantageous to pick position, velocity, and flux linkage as the state variables, making electric current a dependent variable. From a measurement standpoint, flux is less accessible than current, but the solenoid governing equations are greatly simplified. More important, thinking in terms of flux rather than current leads to a different approach to engineering. This thinking is evident in the Magnesense papers and in the patents that relate to sensorless measurement and state space control.
Magnetic
Analysis by a Flux-Centered Approach, Part 2:
Basic Equations for Solenoids with Ideal Ferromagnetic Conductors
The content of this paper can be gleaned from physics and engineering texts, but this paper puts it together in one place. From fundamental physics it derives the basic equations for solenoids, ignoring magnetic saturation, hysteresis, and eddy currents. Anyone wishing to examine these effects of non-ideal iron properties needs to have mastered the basics of this paper.
B
vs H Narrative
This paper presents Magnesense research into the non-ideal iron properties of the cores used in the valve rocker solenoid. While the results are particular, they are representative of the important realm of engine valve solenoids constructed from transformer lamination material. Departures of real behavior from the idealized behavior of the “Part 2: Basic Equations…” paper are quantified, indicating the kinds of first-order correction formulas in actual use in Magnesense real-time control software.
Taming the Electromagnetic Solenoid: Building a System that Achieves a Soft Landing,
presented Gary Bergstrom at the SAE TOPTEC Conference, 9/12/2000:
In applying servo control to the motion of a solenoid, one starts with a basic control loop for driving the solenoid, then layers on feedback corrections. The drive control loop can regulate the winding current, the voltage, or the flux linkage. A choice that leads to a nearly stable system is preferable to one that is going to require a great deal of additional compensation. How do these three choices rank? Current control is the least stable solution and may be plagued by voltage overload problems, but it has the advantage of immunity to current runaway if the solenoid enters magnetic saturation. Voltage control leads to more stable dynamics but runs into trouble with magnetic saturation: the current spikes up rapidly. Flux linkage control means control of the time integral of inductive voltage. Applied voltage must be corrected for resistive voltage loss in order to compute inductive voltage, after which a time integration is needed. This effort pays off, however, as it is shown that the flux-controlled electromechanical system is relatively stable and less vulnerable to saturation problems.
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