In general, the cycloconverter is adopted as VVVF power source to drive large scale motors and linear motors. However, it is necessary to improve its input power factor because the input power factor is low. This paper describes a method to reduce the input reactive power by using a non-symmetrical gate triggering control for the cycloconverter. In this method, some converters which are connected in series are separated into two groups. One group generates maximum voltage, and the other controls output voltage. For both circulating current and non-circulating current type cycloconverters, the input current waveforms are analyzed in this control method, and the relationship between the maximum voltage of converter and the reduction effect on input reactive power is made clear. Further, the characteristic harmonic components in input current are investigated. They are confirmed by digital simulation and the examination using a large scale cycloconverter at Miyazaki Maglev Test Track.
Maglev vehicle HSST-05 had been operated in Yokohama Exhibition through the period by HSST Corp., which had taken the first licence of the railway service in Japan from Ministry of Transport. This paper describes the linear motor thrust control method, thrust characteristics, the new PWM method for HSST-05 and the successful results. (1) HSST uses single sided linear induction motors (LIM) driven by the voltage source type PWM inverter mounted on the vehicle. The thrust force is controlled in accordance with inverter output voltage with constant slip frequency. The slip frequency is fixed at 12.5 Hz. Such larger slip frequency is effective to get better dynamic thrust performance in case of the variation of LIM air gap. The result of the running test showed the adequate performance to the designed scheme. However the end effect for higher speed range should be investigated in the near future. (2) A new PWM method based on the instantaneous spatial vector theory has been applied for improving acoustic noise of the HSST. The zerovector control modulated by a constant carrier frequency are adopted and digitalized by DSP (TMS 32010). The cycling time is 20 ms and the carrier frequency is 400 Hz. This method is very effective to improve the feeling of PWM acoustic noise and to reduce the thrust force variation at various transient conditions.
The two-axis theory is now recognized as the most important theory of analysis of synchronous machines. However, some problematic points have been left in its basic theory. The first point of them is that the physical meaning of dq-transformation is not clarified sufficiently. The second point is that the transformation of rotor windings caused by dq-transformation of armature winding is not discussed at all. The third point is the problem of base values of rotor quantities in per-unit system. A. W. Rankin recommended the use of the armature-reaction-based base values of rotor quantities as an improvement of Park's base values. However, the derivation of the formulae of them is not so simple, and besides, his theory is not completely obvious. The first point has already been resolved by the author's previous paper. The second and the third points are resolved in this paper using the results of the previous paper. The resolution of the second point can be obtained by the application of the ratio of change of air-gap magnetomotive force and that of air-gap flux which are caused by dq-transformation of the armature winding to the rotor windings. The resolution of the third point can easily be obtained by the use of the results of the resolution of the second point. From the point of view of theoretical transformation, the correction factor for field magnetomotive force is separated into winding-factor component and non-uniform air-gap component. From the results of comparison of existing formulae of base values with those obtained in this paper, it is proved that all the existing formulae for the base value of field current are correct, but the existing formulae for the base values of field voltage and field winding resistance are not reasonable in the case of salient-pole machine.
In the single-phase AC railroad electrification, the voltage unbalance of three-phase electric power system has to be reduced. For this purpose, three-phase power is converted to two-phase power by the Scott-connected transformer, and the electric power is received from a powerful or high-tension source. Recently, regenerative braking has come to be applied to electric rolling-stocks, but occasionally the regenerative brake increases the voltage unbalance in the three-phase electric power source with the ordinary two-phase feeding system. So, in some cases unbalance power compensation may be found more profitable than the Scott-connected transformer. This paper describes a theoretical study and results of a test on a mini-model which uses a scalene Scott-connected transformer, switched reactors and capacitors for the purpose of reducing the voltage unbalance in the three-phase electric power source. By this method, main phase (M) and teaser transformer (T) voltages of scalene Scott-connected transformer secondary side are decided by a single load power factor, and the sum of the capacities of the reactors and the capacitors is equal to the apparent power of single-phase load. For example in SCR switched control of the reactors/capacitors which has four steps in power running and two steps in regenerative braking, the voltage unbalance in the three-phase electric power source can be reduced satisfactorily.
The authors have developed a rotary inchworm-type actuator which has a rotor directly driven by a stator, and can operate both clockwise and counterclockwise with potential good repeatability for highly precise positioning. The stator comprises a torsional-movement multilayered piez-oelectric actuator (TMPA) and two sets of longitudinal-movement multilayered piezoelectric actuators (LMPA). The two sets of the LMPA act as a clutch mechanism and transfer the torque from the TMPA to the rotor. As a result of the experiment with the actuator made experimentally, it has been proved that the rotor moves as expected. It has also been found that the rotational speed of the rotor can be controlled in the range from 10-7 to 10-4 rad/s by changing the applied voltage to the TMPA and the driving frequency and that the maximum torque of 2.0kg•cm can be realized when the voltage reaches 800Vp-p. Using the bending and torsional movement of the stator, we explained the torque characteristics that the rotational speed of the rotor decreased with the increase of load.
The characteristics by the changing scale of size in annular linear induction motors are not clear so far. In this paper, therefore, the thrust/input power ratios by the changing scale of pole pitch and radius of the annular linear induction motor are clarified theoretically and experimentally under the conditions of constant voltage source and of constant current source. The theoretical analysis is given by the electromagnetic field equations in analytical model and the circuit equation in equivalent circuit. In experiment, the thrust/input power ratios at slip 1.0 are given by changing length of size in three test prototypes. The thrust/input power ratio in constant input voltage is inversely proportional to the length of pole pitch (one-dimensional change of size). In the two-dimensional change of size, it is little changed by the length of radius. In the three-dimensional change of size (pole pitch and radius), it shows almost the same as the characteristic of the one-dimensional change of size. In the case of constant input current, the thrust/input power ratios show the same tendency as the case of constant input voltage by influence of annular type structure. As a result, the thrust/input power ratios depend nearly on the length of pole pitch.
A simulation model for induction heating problems in pipe benders is proposed. This model, which is valid for cylindrical geometries, treats a coupling problem between electromagnetic fields and temperature fields. In order to effectively deal with a movement of a pipe during heating process, the electromagnetic field has been solved by Finite-Boundary Element Method. The transient temperature field which is caused by eddy current losses at each time step has been analyzed by Finite Element Method. The influence of temperature on electromagnetic and material properties have been taken into account. In addition, the results of the experiments in the pipe bender for stainless steel pipe, whose diameter is 267mm, are described. The accuracy of the calculation has been confirmed by comparisons with the experimental measurements.
V/f ratio constant control has been widely utilized for induction motor drives as a general purpose inverter. Then, notwithstanding that the inverter is required to meet the load drive of various styles of which torque characteristics or inertias are largely different, it does not always satisfy all sorts of the specification required from the load sides. Particularly, in the low speed range, generation of large torque, stable operation at light loads and excellent dynamic response have hardly been achieved yet. As a countermeasure to solve these problems, this paper proposes equivalently realize the idealized induction motor which has no stator winding resistance and leakage inductance. This is done by introducing such a kind of vectorial feedback control focussing our attention on the resultant rotating vector by three phase instantaneous voltage over the equivalent magnetizing inductance. The proposed control is that the ratio obtained by dividing the magnitude of the vector by the instantaneous frequency is kept constant in any instant. As a result, the electromagnetic torque is almost precisely proportional to the slip frequency and the torque slip characteristics are given as a group of parallel straight lines which have no breakdown torque. Torque generation over 150% is feasible even at the frequency 1.5Hz. Moreover, the torque response is quite fast to the change of stator frequency and rotor speed compared with the conventional V/f constant control. Therefore, the system is exactly stabilized. There often occurs the problem on wave distortions in stator voltage and current, which are caused by the dead time accompanied by the switching, as an inherent phenomenon in the conventional PWM type voltage controlled inverter and its suppressing control has to be additionally equipped. However, the proposed control does not need such a equipment. Nevertheless, the waveform of the stator voltage and current is kept sinusoidal in any states.