Energy saving control is desirable for magnetically levitated (MAGLEV) vehicles. Hybrid magnets controlled with a zero power control system can reduce the exciting power. However, this conventional system requires a feed bipolar current, and the excitation system becomes complicated. To achieve a simple excitation system, a hybrid magnet with permanent magnets and divided cores was developed. The magnet was a salient-pole type magnet, and the poles were placed in two rows. Each iron core pole was equipped with a coil to control both the levitation force and lateral damping force. The coils of one side of the divided core were excited with a direct current driver to produce the same polarity as the permanent magnet the others were excited the opposite polarity. The two sets of the coils were excited with direct current drivers, each of which had one IGBT. The system needed only two IGBTs per magnet, whereas the conventional zero power systems needed four IGBTs per magnet. According to our test results, the energy consumption was very small and the levitation part could start levitating from both upper and lower touch-down positions. In this paper, the characteristics of the proposed excitation system are presented.
With the increase in the use of three-phase squirrel-cage induction motors (IMs), there is a need for not only increasing the efficiency but also reducing the cost of the IMs. The stator winding structure of typical IMs is the distributed winding, and the length of coil end on the IMs relatively increases as the output and number of poles decrease. If a concentrated winding (CW) structure is used, the cost will reduce owing to shorter coil ends. However, the characteristics of CW-IM worsen because of the influence of magnetomotive force harmonics. In this study, we investigated the CW-IM, and determined that CW is effective in two-pole small IMs, and thus developed a trial CW-IM. This paper discusses about the effects of the stator core shapes on the characteristics of the CW-IM and describe the characteristics of trial CW-IM. The results show that the stator teeth and yoke width must be appropriately sized, the amount of copper and axial length could be reduced with CW, and an abnormal torque is occurred. With regard to abnormal torque, the use of a rotor with appropriate skewed slots is propose to be effective.
This paper proposes a DAB converter using two transformers as a method to improve the efficiency in the light-load region when the output voltage fluctuates. In the proposed circuit, in addition to the operation mode of the conventional DAB converter, there exist three other operation modes initiated by switching the connection of these transformers as series or parallel. In the proposed circuit, the transformer-applied voltage can be changed and efficiency can be improved by switching between series-parallel, conventional, and parallel operations according to the input/output voltage ratio. The experimental results confirmed that for the input/output voltage ratios of 1.9 and 0.25, the conversion efficiencies were 96%, and 90%, respectively, the phase difference of 30° as the light-load condition.
Extended electromotive force (EEMF) estimation method is a representative method used for position sensorless control of PMSM in the middle/high speed range. EEMF enables position estimation by utilizing back-EMF and the saliency of inductance. The amplitude of EEMF is adjusted to maintain it above a certain voltage by using a signal injection, regardless of the rotor speed. Thus, EEMF can be used as a single position estimator to estimate overall speed range. Based on the validation of a EEMF control performance and a parameter sensitivity analysis, this paper presents a position sensorless control system configured with a single position estimator from startup to middle/high speed. The necessary adjustment parameter and control performance of the actual machine are also presented.
This paper proposes a model predictive current control method for independent double three-phase interior permanent magnet synchronous motors (IPMSMs). The switching pattern selected by the model predictive control is determined, and the current of each winding is controlled considering of the voltage output of the inverter of the own group for each sampling and the voltage disturbance due to the inverter of the other winding. The effectiveness of the proposed control method is validated by the experimental results of dynamic and static performances. The proposed control method is also experimentally compared with a PI controller. The proposed model predictive current control can achieve a high torque response under dynamic characteristics.
This paper proposes a method to determine the fuel cell voltage of hybrid powered railway vehicles for reducing traction circuit weight. The fuel cell voltage affects traction circuit weight because the number of fuel cell and the required cooling performance of power converters depend on the voltage. Therefore, the voltage should be determined such that it reduces the weight of the entire traction circuit. We propose a method to determine the fuel cell voltage by evaluating traction circuit loss considering the deterioration of fuel cell.
The current limit of the traction inverters has been relaxed by using silicon carbide devices. The integrated design of the traction circuit system is required. In this paper, the relationship between the speed-torque characteristics of the railway vehicle and the energy saving effect is presented. We considered a model for calculating the mass of induction motors and inverters. The relationship between the V/f characteristics of induction motors and the reduction size and weight of the traction circuit system are discussed. An integrated design method to maximize the output power density of traction circuit systems for electric railway vehicles is revealed.
This paper proposes an input current control method to eliminate the DC current ripple component that distorts input current. In the proposed method, the effect of the DC current ripple is cancelled to change the order of the voltage vector generated by a traditional space vector modulation. The experimental results show that the input current distortion is reduced to 5.0% from 12.9% with the ripple cancel method.