Cost-Effective Scheme for a Brushless Wound Rotor Synchronous Machine

This paper proposes a new scheme for a brushless wound rotor synchronous machine (WRSM) by generating an additional, two-pole component of magneto-motive force (MMF) with a series-connected additional three-phase winding with the armature three-phase winding. Unlike existing brushless excitation schemes, which use the inverter to inject harmonic currents in the stator windings, the proposed scheme uses series-connected additional winding on the stator with the armature winding in a two-pole configuration. Consequently, as the current flows in the armature winding, it creates a fundamental rotating air gap flux to interact with the field flux. At the same time, additional rotating flux is created from the additional three-phase winding, which cannot synchronize with the field winding. This additional flux can cause the induction of a voltage in a winding with exactly the same number of poles. For this purpose, a harmonic winding is installed in the rotor along with the field winding connected through a diode bridge rectifier, in order to feed the direct current (DC) to the field winding for rotor excitation without an input current from the brush-slip-ring assembly. The 2D finite-element analysis (FEA) was performed to validate the brushless operation of the proposed machine system.

Study of Tunnel-Face to Borehole ERI (TBERI) Measurement Configurations and Its Optimization

Most of the existing electrical-resistivity-based ahead prospecting methods in tunnel use only the tunnel cavity and tunnel face space to locate the water-bearing structures in front of the tunnel. However, due to the limitation of the narrow available space for arranging electrodes in tunnel, this kind of method is difficult to achieve more accurate image for water-bearing structures. The cross-hole electrical resistivity tomography (CHERT) and borehole-to-surface electrical resistivity tomography (BSERT) methods using borehole space have been proved effective means to achieve better images of deep anomalies on the surface. In this paper, the tunnel-face and borehole ERI (TBERI) method in tunnels was studied. To less affect the construction progress, the pole-pole configuration using a single borehole was studied in this paper. Moreover, the configuration is optimized based on the block weighted CR optimization strategy. After considering the data combination, an effective measurement configuration suitable for TBERI detection was formed. To accelerate calculation, some redundant data are removed from the obtained data after proposed block weighted optimization is conducted. By adopting the proposed configuration, the abnormal objects in the target area in the inversion are more accurate. The effectiveness of proposed configuration is verified by numerical simulation.

Active Loading Control Design for a Wearable Exoskeleton with a Bowden Cable for Transmission

Exoskeletons with a Bowden cable for power transmission have the advantages of a concentrated mass and flexible movement. However, their integrated motor is disturbed by the Bowden cable’s friction, which limits the performance of the force loading response. In this paper, we solve this problem by designing an outer-loop feedforward-feedback proportion-differentiation controller based on an inner loop disturbance observer. Firstly, the inner loop’s dynamic performance is equivalent to the designed nominal model using the proposed disturbance observer, which effectively compensates for the parameter perturbation and friction disturbance. Secondly, based on an analysis of the stability of the inner loop controller, we obtain the stability condition and discuss the influence of modeling errors on the inner loop’s dynamic performance. Thirdly, to avoid excessive noise from the force sensors being introduced into the designed disturbance observer, we propose the feedforward-feedback proportion-differentiation controller based on the nominal model and pole configuration, which improves the outer loop’s force loading performance. Experiments are conducted, which verify the effectiveness of the proposed methods.

Groundwater aquifer detection using the electrical resistivity method at Ito Campus, Kyushu University (Fukuoka, Japan)

An electrical resistivity survey was carried out using the pole–pole configuration around the Sayanokami spring area in the northern part of Ito Campus (Kyushu University, Fukuoka, Japan) to study the groundwater aquifer and its electrical characteristics. A Code Division Multiple Transmission (CDMT) system was used. The CDMT system transmits 24 currents simultaneously and measures 24 potential responses with monitoring of actual current waveforms. The system can inject current from multiple electrodes into the underground environment simultaneously using different individual current waveforms. The two-dimensional (2-D) inversion results of the electrical resistivity data indicate three layers from top to bottom, as follows: (a) a thin layer with a thickness of 3 m and a low resistivity (< 50 Ω m) representing topsoil; (b) a groundwater aquifer layer with an average resistivity between 50 and 170 Ω m and with a thickness ranging from 7 to 10 m, and (c) a highly resistive bedrock layer with resistivities higher than 200 Ω m and occupying depths from 15 m to the base of the model.

Performance Analysis of Brushless Motors with Segmented Cores considering Manufacturing Constraints

Brushless servomotors are widely used in industry and in all domains that require precise and easy position/speed/torque control. To further improve the performance of these motors, the segmentation of the stator core is taken into account. This approach to core construction provides a high slot fill factor, compact design, and efficient use of materials. This paper aims to present that the manufacturing constraints and tolerances of this particular core construction can increase unwanted effects in brushless motors, like cogging torque, torque ripple and their influence regarding the back-EMF. Two models for a 12slots-10 pole configuration, one with segmented core and one with standard laminated core are compared and analysed using the FEA (Finite Element Analysis) method. The influence of the additional air gaps that occur in such constructions is investigated to provide an overview for the design of segmented motors. Various lengths for air gaps between the segments of the core are taken into consideration and non-uniform distribution of such gaps. The paper also provides further steps that must be taken in order to verify/validate the studied model’s impact on motor design.

An Improvement of Output Power in Doubly Salient Permanent Magnet Generator Using Pole Configuration Adjustment

The doubly salient permanent magnet (DSPM) machines are very attractive for low-speed power generation. In this work, we propose a design technique to improve the output power of the DSPM generator by an adjustment of pole configuration. The number of stator and rotor poles, split ratio, as well as the stator pole arc of the generator, were proposedly adjusted and optimized. The output characteristics of the generator including the magnetic flux linkage, electromotive force, harmonic, cogging torque, electromagnetic torque, output voltage and output power were analyzed through finite element analysis. The symmetrical magnetic field distribution of all generators was firstly verified. Then, the results indicated that this particular generator was optimized at 18 stator poles and 12 rotor poles, while the split ratio and the stator pole arc should be set as 0.78 and 6.15 degrees, respectively. The proposed optimal generator could provide a significant improvement in the output voltage and the output power compared to the conventional structure. The output power of 1.28 kW can be reached by the optimal structure, which was two times higher than that of the conventional structure. The physical explanation regarding to the structural modification was also given. The proposed design technique can be applied for improving the output power of the DSPM machines.