• Proceedings of the KIEE Conference
• /
• 2000.07b
• /
• pp.693-695
• /
• 2000

Wide operating range and speed control is needed for wind power generating and a Doubly Fed Induction Generator(DFIG) has good adaptivity for that purpose. This paper deals with power and power factor control using the Grid connected DFIG in the wide speed regions, by controlling frequency and voltage fed to the rotor. Power flow of the DFIG and steady-state algebraic equations of the equivalent circuit are analyzed. For a normal operating region, in which the generator ratings were not exceeded, the rotor current was either less than or equal to the rated value. Accordingly, the optimal power factor can be selected relative to the permissible rated current at the rotor coil which controls the magnitude of the injected rotor voltage to the rotor according to a given rotor frequency.

• Tribology and Lubricants
• /
• v.30 no.3
• /
• pp.131-138
• /
• 2014

This study investigates the effects of the slopes of the rotational axis and bearing preloads on the natural frequencies and onset speeds of the instability of a rotor supported on gas foil bearings (GFBs). The predictive model for the rotating system consists of a rigid rotor supported on two gas foil journal bearings (GFJBs) and a pair of gas foil thrust bearings (GFTBs). Each GFJB supports approximately half the rotor weight. As the slope of the rotational axis increases from $0^{\circ}$(horizontal rotor operation) to $90^{\circ}$(vertical rotor operation), the applied load on the GFJB owing to the rotor weight decreases. The predictions show that the natural frequency and onset speed of instability decrease significantly with an increase in the slope of the rotational axis. In a parametric study, the nominal radial clearance and preload for the GFJB were changed. In general, a decrease in the nominal radial clearance lead to an increase in the natural frequency and onset speed of instability. For constant assembly clearance, the decrease in the preload changed the natural frequency and onset speed of instability with insignificant improvements in the rotordynamic stability. The present predictions can be used as design guidelines for GFBs for oil-free high-speed rotating machinery with improved rotordynamic performance.

• Proceedings of the KIEE Conference
• /
• 1995.07a
• /
• pp.321-324
• /
• 1995

Switched reluctance motors and drives are increasingly used in high speed applications due to their robust mechanical structures, low inertia, and reduction in the rotor losses. The turn-on angle has to be advanced as the motor speed increases, but it may cause the starting problem in some rotor positions. In this paper, the characteristics of the maximum speed and input voltage with the advance angle at high speeds is investigated. To overcome the starting problem and reduce the torque ripple, conduction overlapping is added in adjacent phases. The effectiveness of conduction overlapping is verified through the simulation and experiments.

• Tribology and Lubricants
• /
• v.35 no.2
• /
• pp.123-131
• /
• 2019

This study characterizes the coastdown performances of two small electric motors supported on high-speed ball bearings (BBs) and gas foil bearings (GFBs), and it predicts their acceleration performances. The two motors have identical permanent magnetic rotors and mating stators. However, the shaft of the GFBs has a larger mass and polar/transverse moments of inertia than that of the BBs. Motor coastdown tests demonstrate that the rotor speed decreases linearly with the BBs and nonlinearly with the GFBs. A simple model for the BBs predicts a constant drag torque and linear decay of speed with time. The test data validate the model predictions. For the GFBs, the hydrodynamic lubrication model predictions reveal that the drag torque increases linearly with speed, and the speed decreases exponentially with time. The predictions agree very well with the test data in the speed range of 100-30 krpm. The boundary lubrication model predicts a constant drag torque and linear decay of speed with time. The predictions agree well with the test data below 15 krpm. Mixed lubrication occurs in the speed range of 30-15 krpm. Rotor acceleration performances are predicted based on the characteristics of deceleration performances. The GFBs require more time to reach 100,000 krpm than the BBs because of their larger shaft polar moment of inertia. However, predictions for the assumed identical polar moment of inertia reveal that the GFBs have a nearly identical acceleration performance to that of the BBs with a motor torque greater than $0.03N{\cdot}m$.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2002.04a
• /
• pp.190-198
• /
• 2002

In switched reluctance motor(SRM) drive, it is necessary to synchronize the stator phase excitation with the rotor position. Therefore the rotor position information is an essential. Usually optical encoders or resolvers are used to provide the rotor position information. These sensors are expensive and are not suitable for high speed operation. In general, the accuracy of the switching angles is dependent upon the resolution of the encoder and the sampling period of the microprocessor. But the region of high speed, switching angles are fluctuated back and forth from the preset values, witch are cause by the sampling period of the microprocessor. Therefore, the low cost linear encoder suitable for the practical and stable SRM drive is proposed and the control algorithm to provide the switching signals using the simple digital logic circuit is also presented in this paper It is verified from the experiments that the proposed encoder and logic controller can be a powerful candidate for the practical low cost SRM drive.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.12 no.1
• /
• pp.65-71
• /
• 2003

In a high speed spindle system it is very important to monitor the state of rotating rotor. Particularly in active control spindle system the position sensor must provide feedback to the control system on the exact position of the rotor. In order to monitor the state of a high speed spindle exactly, high accuracy and wide frequency bandwidth of sensors are important. The focus in this paper is to make a fiber optic sensor for monitoring rotor of magnetic bearing, to design the circuit for detecting optical signal, and to evaluation static and dynamic characteristics of fiber optic sensor.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2002.10a
• /
• pp.411-416
• /
• 2002

In a high speed spindle system, it is very important to monitor the state of rotating rotor. Particularly in active control spindle system, the position sensor must provide feedback to the control system on the exact position of the rotor. In order to monitor the state of a high speed spindle exactly, high accuracy and wide frequency bandwidth of sensors are important. The focus in this paper is to make a fiber optic sensor for monitoring rotor of magnetic bearing, to design the circuit for detecting optical signal, and to evaluation static and dynamic characteristics of fiber optic sensor.

• Journal of Electrical Engineering and Technology
• /
• v.11 no.3
• /
• pp.769-774
• /
• 2016

In the design of sensorless control system for induction motor, high-precision speed estimation is one of the most difficult problems. To solve this problem, the common method is model reference adaptive method (MRAS). MRAS requires accurate motor parameters to estimate rotor speed precisely. However, when motor is running, the variety of temperature and magnetic saturation will lead to the change of motor parameters such as stator resistance and rotor resistance, which will lower the accuracy of the speed estimation. To improve the accuracy and rapidity of speed estimation, this paper analyses the mutual MRAS speed identification based on rotor flux linkage, and proposes an improved mutual MRAS speed identification based on back-EMF. The improved method is verified by Simulink simulation and motor experimental platform based on DSP2812. The results of simulation and experiment indicate that the method proposed by this paper can significantly improve the accuracy of speed identification, and speed up the response of identification.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1995.10a
• /
• pp.30-36
• /
• 1995

This paper proposed on the effective cutting conditions of cage motor rotor by turning. If you want to introduce automatic manufacturing system into the cutting process of cage motor rotor, the selections of effective cutting conditions are necessary. The cutting process of cage motor rotor requires the precision and the out of roundness of cage motor rotor. The surface roughness of cutting face. it is very important factor with effect on the magnetic flux density of cage motor rotor. The purpose of this study is to find out the effects of cutting condition. upon adapting this results, we will improve the production rate in the cutting process of cage motor rotor. As a result, the selection of cutting conditions are important factors to production rate. And these are chosen by the investigations of cutting characters and surface roughness. The experimental result, showed that the increase of cutting speed caused the decrease of cutting force and the high surface integrity. The increase of feed rate and increase of depth of cut caused the increase of cutting force and surface roughness. Thus, the effective cutting conditions of cage motor rotor by turing are cutting speed 291m/min, feed rate 0.10mm/rev, depth of cut 0.05mm.

• The KSFM Journal of Fluid Machinery
• /
• v.16 no.3
• /
• pp.32-38
• /
• 2013

This paper deals with the study on the rotordynamic and experimental analysis of turbine-generator system connected with a magnetic coupling. Although magnetic coupling has been used to torque transmission of chemical processing pump rotating at under 3,600rpm, magnetic coupling in this study is applied to high-speed turbine-generator system using a working fluid that is refrigerant such as ammonia or R-124a. Results of rotordynamic design analysis are as follows. The first, shaft diameter nearest to outer hub of magnetic coupling has a big effect on the $1^{st}$ critical speed of generator rotor. The second, if the $1^{st}$ critical speeds of turbine rotor and generator rotor have enough to separation margin in comparison to rated speed, the $1^{st}$ critical speed of turbine-magnetic coupling-generator rotor train has enough to separation margin regardless of connection stiffness of magnetic coupling. The analytical FE model is guaranteed by impact test on the prototype and condition monitoring such as measurements of vibration and bearing temperature is also performed.