This paper proposes a new type of high frequency DC/AC converter developed for flexible, compact and high efficiency uninterruptible power supply (UPS) systems. The proposed DC/AC converter consists of a high frequency inverter, a high frequency transformer and a cycloconverter with a new voltage clamper. This cycloconverter is capable of being operated by both sourcecommutation and self-commutation (commutation by turning off the switching device). Consequently, by choosing between the two commutating methods, based on consideration and the internal voltage drop caused by commutating reactance, a commpact and efficient UPS can be realized. The voltage clamper effectively reduces power loss of the conversion system. Fabrication of a 10 kVA high frequency link type DC/AC converter is described and its loss reduction effect is demonstrated.
The introduction of a multiple PWM inverter to the power supply system for LSM drive is examined. The author are examining about the output harmonics of the inverter which is composed of a Half Bridge (HB) unit and Full Bridge (FB) ones. The PWM inverter generates the lowest frequency harmonics of fc (Hz), which is the carrier wave frequency of HB unit. To improve the characteristics of the output harmonics, the author have proposed “the balanced carrier phase method”, which assignes balanced phase angles to the carrier waves of units with HB connection. In this paper, the principle of the proposed method is described. Then the author derive the analytic expression of the output voltage, and examine quantitatively about the characteristics of output harmonics. Moreover, the author show that the new method shifts the lowest frequency of the harmonics to higher region and reduces whole quantity of harmonics in comparison with conventional method.
The paper describes a workspace force controller of the multi-degrees-of-freedom manipulator. First, the disturbance observer is applied to each joint to improve the robustness against the disturbance effect and the joint acceleration controller is realized in the joint space. Secondly, the workspace motion equation is derived and the workspace force controller is constructed based on its motion equation. In the proposed force controller, the equivalent mass matrix of the workspace is defined clearly and the impedance of the manipulator is selected arbitrary. This is a remarkable point of the proposed method. Several experimental results are shown to verify the proposed controller.
There is a levitation method which uses 8-shape levitation coils arranged on the vertical surface of the guideway. These coils can act as a guidance means as well as the levitation means. The characteristics of this system is examined using numerical examples and experimental data. The cables connecting right and left coils are not connected to a high voltage power source unlike the usual guidance system which is combined with propulsion. Thus the electric insulation of the cables is now not a problem. Numerical examples show that the levitation characteristics of the combined levitation and guidance system is almost the same as in the system without the guidance function, and that it atains reduced running resistance with necessary guidance stiffness obtained. Test run was done at Miyazaki Test Line equipped with coils of this type arranged about 120m, and the results show stable running and balanced displacement which agrees with calculated value.
Determination of field current of a synchronous generator at a specified load is an important problem from the practical point of view. Two methods are now recognized as the most accurate ones. They are the method using Potier diagram (Clause 31 of IEC Publication 34-4) and the method using ASA diagram (Clause 32 of IEC Publication 34-4). However, the results obtained by these methods are sometimes not accurate enough for practical purposes. In this paper, a new accurate method of determination of the field current is proposed. In the case when the rated power factor is unity, the field current at rated load can be determined, in principle, from the measurements of field current in the low-speed short-circuit test carried out at an appropriate speed. In practice, it is convenient to determine the field current by the interpolation of the results of low-speed short-circuit tests carried out at two slightly different speeds. In the case when the rated power factor is not unity, the field current at rated load can be determined as the sum of two components, that is, the measured field current for a fictitious unity-power-factor rated load and the field current component which is necessary for compensating the difference of direct-axis armature magnetomotive force at the true rated load and that at the fictitious rated load. Method for determining field current of a synchronous motor is also treated herein. It has been proved experimentally that the new method gives fairly accurate results compared with those obtained by the other methods.
Magnetically-levitated (MAGLEV) railway is being studied intensively in many countries for the purpose of its' large scaled realization. In fact, some plans have already started in Japan. Now, the standard of ride-quality called UTACV is indicated by the power spectrum density of vertical acceleration described in the frequency domain. To satisfy this standard, we have to design a suspension system by using some effective control theory. But optimum control theory which deals with the integration of errors in the time domain is not always effective for the problem of ride-quality. In this paper, in order to solve this problem, H∞ control theory is applied to an active suspension system of a MAGLEV vehicle by adoping a suitable weighting function to be effective for the special frequency band at which high ride-quality is required. Then we have to pay attention to two points, namely keeping suitable clearance for safe running and ride-comfort. As for the former point, it is achieved by optimum control theory which is applied to the MAGLEV system, and the latter is improved by H∞ control theory which is applied to the suspension system.
Recently a demand for small-capacity generators is increasing as electric sources in small ships and automobiles or as portable electric sources driven by engines. It is desired that the structure of small-capacity generators is simple and robust, and that the generators are highly reliable, easily maintained and controlled. This paper describes an analysis of the original brushless synchronous generator without exciter. The output voltage can be adjusted in the wide range by controlling the stator DC current. To analyze the characteristics of this generator, the finite element method is applied. It is found that the results of theoretical analysis agree well with the experimntal results.
This paper describes a finite element analysis of hybrid type permanent-magnet synchronous motors at asynchronous speed. In this analysis, any instantaneous operating point of permanentmagnet, eddy current and magnetic saturation in the rotor are considered. First, the authors propose a simple analytical model in which the rotational motion of the rotor is considered. Secondly, asynchronous operating characteristics are analysed by using this analytical model and the finite element analysis when the terminal voltage is given. In order to explore the effect of the magnet magnetization on asynchronous performance, the motor characteristics of the case that no magnetization exists in permanent-magnets, are considered. In this case, an agreement between calculated and measured values of input currents for experimental motor is good. Therefore, it is made clear that this analysis is reasonable. Lastly, the average and pulsating torques, and the braking torque caused by the permanent-magnets at asynchronous speed, are determined quantitatively.