The flywheel generator in use as a power source for fusion experimental device is enough large to generate the electric power to make it suitable for application in wide range of industries. The authors propose an AC-excited variable speed flywheel generator for short-period load leveling device and utility line power stabilizing device such as power factor, unbalanced load, flicker etc. In this paper, the validity of the flywheel for this purpose are described. And the new control method which applies the voltage control of Vector Control scheme are proposed. Compared to a conventional generator withflywheel, the following advantages are offered: (1) The necessary converter capacity is small; (2) It is possible to accumulate and yield electricity rapidly with large power; (3) Reactive power can be supplied through phase-modified operation of generater, making it possible to reduce in capacity of static power factor compensator. The experiments using the M-G set simulator with 4kW wound type induction motor with flywheel are carried out to demonstrate the control ability. It is reported that the system proposed here controls the active and reactive power with so fast step response of less than 5ms that the power-input attains the perfect leveling of even in unbalanced loads.
Reduction of seek-time (the time for the magnetic head to start to move and settle on the desired track) is an important R & D item for a hard disk drive together with increase of memory density. In an usual hard disk drive, position control of the head is divided in three modes, velocity control, transient control and track-following control modes. The reduction of the seek-time in the transient control mode depends directly on control method and it is most important to develop a control method to reduce the time for the head to settle on the track in this mode. A conventional hard disk drive uses analog control servo method but the reduction of the seek time by analog servo method is limited. We digitize the head position control and apply dead-beat control method to reduce the settling time of the head. The dead-beat control is sensitive to the fluctuation of the system constants, therefore, we use the adaptive control scheme to the system. In the paper, characteristics of the proposed system are studied by a numerical simulation and an experiment. It is demonstrated that the settling time of the head on the track is reduced by a factor of more than two comparing with conventional analog servo method.
FDRV (Fuel Diverter and Return Valve) is one of the hydraulic servo valves used in V 2500 turbofun engines in order to control fuel temperature. FDRV, currently in production, is manufactured to meet its specification which allows appropriate tolerance. Hence, there are some performance variation of FDRV. Also, performance of FDRV may significantly vary with operating conditions. In order to meet engine control objectives, performance of the FDRV control system is also specified, which includes response time, overshoot, offset, and sensor noise. To satisfy the above requirements, a compensator, which is part of FADEC(Full Authority Digital Engine Control) software, is used. Single compensator which can accommodate specified performance variation of FDRV is required since it is not practical to adjust parameters in the compensator for each FDRV. In this paper, we design a compensator based on H∞ control theory and evaluate its performance by experiments on bench test stand. Here, we do not use adaptive compensator. We consider performance variation due to the manufacturing tolerance as uncertainty of nominal model and variation due to the operating condition as distarbance to nominal model. Then, we synthesize a robust compensator that satisfies the system performance specification under existence of the uncertainty and the disturbance.
As superconducting generators have a number of advantages, the investigations for such machine have been actively carried out throughout the world. In the superconducting generator, it is very important to support the field winding and to protect it from quenching. On the other side, as the armature winding is of air core, the evaluation of eddy current loss in the winding and the way of its support are inevitable. Thus, we should know the magnetic fields and the electromagnetic forces acting on both the field and the armature windings at the early stages of the machine design. We have partially discussed in previous papers the transient behavior of magnetic fields and electromagnetic forces acting on the windings of a superconducting generator based on a computer simulation for a sudden 3-phase fault. However, the behavior of magnetic fields and electromagnetic forces during transient period is very complicated and many calculations are required in order to find their maximum values. In this paper, for practical use at the early stages of the machine design, we derived approximate expressions to calculate the maximum values of the magnetic fields and electromagnetic forces on the windings in the case of a 3-phase fault. In order to numerically check these expressions, we conceptually designed a 1, 000 MVA superconducting generator. The numerical results obtained by using these expressions agree well with the computer simulation results.
Pole-changing is a simple method for changing the speed of a cage induction motor. However, excessive currents and torques appear during deceleration of the motor by pole-changing. These characteristics are unfavorable for shafts and couplings of the motor system. And further, these cause the sudden voltage drop of the supply. From user's viewpoint, it is desirable to control these currents and torques as low as possible. In order to decelerate the speed by pole-changing, first, the supply is removed from the delta connected high speed terminals. Next, the supply is connected to low speed terminals, and finally, the winding is changed to the parallel _??_ connection. From the simulation results, the authors discuss the effects of the supply removal period, impressed voltage phase and the period between the supply impression and the changing to the parallel _??_ on the motor. This discussion gives the conclusion that the transient current and torque can not sufficiently controlled even when the above conditions are appropriately selected. In order to reduce these transient current and torque sufficiently, this paper proposes a method in which external resistors are inserted in series with the three-phase primary winding. From the simulation results, it is found that the inserted resistance of 1.55 times the locked rotor impedance of the induction motor, can sufficiently reduce the excessive transients.
The field harmonics produce a radial electromagnetic force in a squirrel-cage induction motor with a particular number of rotor slots corresponding the number of poles. The radial force causes vibration and acoustic noise. In this paper, a simplified equation for the radial force at no-load is introduced and the relation between the width of the stator slot opening and the radial force is discussed quantitatively. The field harmonic component produced by the interaction between the fundamental magnetomotive force due to the stator current and the pulsation of air gap permeance dominates for the radial force. Furthermore, the vibration of the stator core due to the radial force is calculated under a simple assumption. The calculated results are verified by experiments.
This paper describes the improvements in launching stability and launching velocity of the linear accelerator (LAC). The authors have designed and produced a railgun using the LAC for weaving loom shuttles. The LAC is an electromagnetic launcher which enable a projectile to be launched at a speed of more than 50m/s. It basically consists of an uni-pole linear DC motor and operates the same principle as DC rotary motors, the most difficult problem in this system being the stabilization of the current collection on the projectile. Then we have conducted the various launch experiments. As a result, we have achieved that the carbon projectile was launched at a speed of 73m/s using double-stage type LAC.
Direct drive motors have come to be used as actuators in various motion control systems, since they provide fast and smooth motion precisely. However, direct drive systems without reduction gears require the motors for high torque at low speed. The vernier motor developed as a high torque motor at low speed has not been used because of its poor power factor and various problems. Recently, “The low speed high torque drive system applying vernier motor torque” was developed by Dr. Ishizaki. However, the characteristics of the vernier motor are not clear yet. Authers have found that the vernier motors are analyezed as a 3-phase reluctance motors which have the different number of salient poles from poles, and have obtained the voltage equations on γ-δ axis and the general expression of the torque. The torque expression at the steady state condition is obtained in consideration of the stator winding resistance. The tests were performed on the trial motor. The calculated pull-out torques have agreed very well with the mesured values. The voltage equation and the torque expression of the vernier motor are very usefull for the optimum design of the motor and the design of the motion control system.