Levitation-guidance stabilization of superconducting maglev through LSM currents
This paper presents a modeling and simulation of a superconducting maglev vehicle with a levitation and guidance assist method we have proposed. The assist system stabilizes and assists the vehicle operation so that the vehicle does not need to depend on the mechanical wheels as much as possible at low speeds. By controlling the LSM armature currents, the auxiliary levitation and guidance forces are provided. The results show that the assist system produces appropriate levitation and guidance forces, establishing the reference levitation height and a sufficient guidance at low speeds even against the disturbance force of lateral wind.
Investigation of superconducting linear synchronous motor propulsion control via an exact mathematical model
This paper describes the performance of the superconducting linear synchronous motor control system used for a transportation vehicle by using an exact dq0-axis mathematical model. The paper first shows the detailed block diagram of the speed control system, which includes the blocks of propulsion force and speed emf computations. A detailed discussion is devoted to the design of the control system. A cascade control system with PI controllers is designed as a numerical demonstration. It is also pointed out that the cascade control structure is a natural form for the power feeding method with three inverters. Performance simulations are shown for severe track conditions such as tunnel and track gradients as well as in a normal case. It is demonstrated that integrator windup of the speed controller can occur in the case of a severe condition in which one of the inverters is disabled. We present a design with more robustly stable performance by designing an antiwindup controller. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 45–52, 1999
The Vascular Theory of Migraine‐Resuscitated or More Moribund?
Your decision to publish an important paper on cerebral blood flow (CBF) in migraine1 as the first in Headache for 1989 is to be applauded. But does it clarify or cloud the issue? After 20 years of CBF studies in migraine the results show 1) a reduction of at least 25 30% in classical migraine1, 2) an average increase of 31% in common and classical migraine2, 3) or no change in common migraine3. Now we learn that the measurements need modifying by 40% to allow for scattering of radiation the Compton scatter effect which has led to "an unbalanced interpretation of the data"1 So the results are as contradictory as they can be, the measurements require adjustment, and the interpretation is therefore doubly doubtful. From the clinical point of view the neurological aura, the enlarging scotoma, the scintillations, the migration of the paraesthesiae up the arm or visual disturbances across the visual field, have not been seen in cerebrovascular disease.4 The headache is throbbing in only 47% of 750 patients questioned during a migraine5; but even when the pain is pulsatlie, it throbs for only a portion of the time at the maximum of the headache (Blau unpublished observations). The evidence for a neurological aetiology has been examined6: the most potent argument against a vascular cause is that the common triggers stress, light and hunger go direct to the nervous system, not via blood vessels. No one denies that vascular changes occur in migraine but are they primary or secondary to a neurological disturbance? Sokoloff7 concluded that the stimulated rat and monkey cortex showed increased glucose uptake, and that the increased local blood flow occurred "in response (my italics) to changes in local functional activity". The evidence, therefore, points to an underlying neurological basis with secondary vascular responses. The vascular theory may need resuscitation but who is going to give it the kiss of life?