Study with magnetic property measurement of soft magnetic composite material and its application in electrical machines

This paper reports our study with the magnetic property measurements of soft magnetic composite (SMC) materials under both alternating and rotational magnetic excitations, and development of different electrical machines with SMC cores and three-dimensional magnetic field, such as claw pole and transverse flux motors. Three-dimensional finite element electromagnetic field analysis is conducted for determining some important parameters and optimizing the machine structures. The analysis methods are validated by the experimental results on two SMC motor prototypes

Improved single-ended traveling-wave fault- location algorithm based on experience with conventional substation transducers

Single-ended unsynchronized traveling-wave fault-location algorithms have been around for several years. They avoid the costs and complexities associated with remote-end synchronization. Nevertheless, there is a corresponding increase in required signal processing as each reflection must be identified and then related in time to the signal wavefront. The current signal processing techniques include a combination of modal and wavelet analysis, where the resulting vectors are often squared. However, the performance of this process degrades dramatically with the filtering associated with the substation transducers and secondary circuits. Furthermore, the variation in observed reflection patterns demonstrates that these methods cannot adequately distinguish between faults on the near, or far half of the transmission line. This paper considers the traveling-wave data observed on a 330-kV transmission system and presents a new signal processing methodology to cater for the observations. This is based on the continuous wavelet transform that is calculated at a suitably large scale. The polarities of the resulting coefficients are used to confirm the nature of the fault and to infer the true fault location. © 2006 IEEE

A general method for designing the transformer of flyback converters based on nonlinear FEA of electromagnetic field coupled with external circuit

This paper presents a general method for designing the transformer of flyback switching AC-DC converters based on nonlinear finite element analysis (FEA) of electromagnetic field coupled with external circuit. For that, the variation patterns of the PWM duty ratio and the current flowing through the windings of transformer versus the input voltage are introduced first, and then several important principles for the design of the transformer are given by using analytical method. As the magnetic saturation and control delay possess heavy influence on the safety of the operation, a MATLAB/Simulink based simulation model, in which both the nonlinear differential inductance and the control delay are included, is built to predict the converter transient performance. The nonlinear differential inductance is calculated by a general program of nonlinear 2-D FEA in Matlab/Simulink surrounding. By running the model, the performances of the converter with different loads and input voltages are obtained. Simulation results are in good agreement with theoretical analysis

Initial rotor position estimation and sensorless direct torque control of surface-mounted permanent magnet synchronous motors considering saturation saliency

For a practical direct torque-controlled (DTC) permanent magnet synchronous motor (PMSM) drive system, the information of the initial rotor position, which is usually obtained by a mechanical position sensor, is essential for starting under the full load. To avoid the disadvantages of using mechanical position sensors, great efforts have been made on the development of sensorless control schemes. An initial rotor position estimation strategy is presented for a DTC PMSM drive based on a nonlinear model of PMSM incorporating both structural and saturation saliencies. In the new scheme, specially designed high-voltage pulses are applied to amplify the saturation saliencies. The peak currents corresponding to the voltage pulses are used, in combination with the inductance patterns, to determine the d-axis position and the polarity of the rotor. The presented initial rotor position identification strategy has been implemented in a sensorless DTC drive for a surface-mounted PMSM. Experiments are conducted to confirm the effectiveness of the method and the performance of the drive system. © The Institution of Engineering and Technology 2008

Transformer-less local grid based 11 kV SCHB multilevel converter for renewable energy systems

Due to the variable nature of renewable energy resources and power demand by the consumers, it is difficult to operate a power system installed with only one type of renewable energy resource. The local grid based renewable generation may be the only solution to overcome this problem. In this regard, an 11 kV Series Connected H-Bridge (SCHB) multilevel Voltage Source Converter (VSC) is proposed, which is the transformer less, cost effective solution to interface the renewable generation system to the local grid directly. This paper presents the design, simulation and analysis of a Five Level (5L)-SCHB and an Eleven Level (11L)-SCHB VSC for an 11 kV local grid based renewable energy systems. The performance, cost, modulation scheme and harmonic spectra of the converter are the bases for analysis. © 2011 IEEE

Performance and cost comparison of NPC, FC and SCHB multilevel converter topologies for high-voltage applications

The rapid increase in global energy consumption and the impact of greenhouse gas emissions have accelerated the renewable energy technology into a more competitive area. Due to the variable nature of renewable energy resources and power demand by the consumers, grid based renewable generation has gained significant popularity in the world. High-voltage converter can interconnect the renewable systems to the grid directly without introducing a lossy, costly and bulky transformer. Three popular multilevel converter topologies: Neutral Point Clamped (NPC), Flying Capacitor (FC) and Series Connected H-Bridge (SCHB) have successfully made their way into the industry and therefore can be considered a mature and proven technology for low and medium voltage applications. But most of them are not suitable for high-voltage applications. This paper presents the comparison of a Five-Level (5L)-NPC, a 5L-FC, a 5L-SCHB, an Eleven-Level (11L)-NPC, an 11L-FC and an 11L-SCHB topologies for an 11 kV Voltage Source Converter (VSC). The comparison is made in terms of number of semiconductors, semiconductor cost, Total Harmonic Distortion (THD), filter size and control complexity. © 2011 IEEE

Effects of armature reaction on the performance of a claw pole motor with soft magnetic composite stator by finite-element analysis

We investigated the effects of armature reaction on the performance of a three-phase three-stack claw pole motor with soft magnetic composite stator core by using three-dimensional finite-element analysis (FEA), which is an effective approach to accurately compute the parameters and performance such as the back electromotive force (EMF), core losses, and winding inductance at various saturation levels. The motor is rated as 500 W at 1800 rpm when the stator current is 4.1 A, driven by a sensorless brushless DC scheme. Because of the armature reaction, the back EMF produced by the rotor permanent magnets and the developed torque is reduced by about 3.3% at the rated load, and the core losses increase drastically by 41% from no-load to full-load. The winding inductance is computed with different loads at different rotor angles. © 2007 IEEE

Intelligent coordination steering control of automated guided vehicle

In this paper, based on the neural network, fuzzy control and bang-bang control, an intelligent coordination control strategy for automated guided vehicle (AGV) steering system is presented. The dynamic steering model of distance error and orientation angle error for AGV is expressed. With least square method of system identification, the model of AGV is identified. Because a toy type of AGV is employed, its structure is simple, but AGV model parameters are variable according to the operating conditions and environment. In order to improve the dynamic performances of AGV, the intelligent coordinated control strategy is used to design the AGV controller in the AGV steering control system. Simulation and experimental results show the effectiveness of the proposed control strategy. © 2011 IEEE

Accurate determination of parameters of a claw-pole motor with SMC stator core by finite-element magnetic-field analysis

Effective and accurate prediction of key motor parameters, such as winding flux, back electromotive force, inductance and core losses, is crucial for design of high-performance motors. Particularly, for electrical machines with new materials and nonconventional topology, traditional design approaches based on the equivalent magnetic circuit, empirical formulas and previous experiences cannot provide correct computation. The paper presents accurate determination of major parameters of a three-phase three-stack claw-pole permanent-magnet motor with a soft magnetic composite (SMC) stator core by finite-element analysis of the magnetic field. The effects of magnetic saturation and armature reaction are considered. The theoretical results by numerical analysis are validated by the experiments on the claw-pole SMC-motor prototype

Modelling and optimization of direct expansion air conditioning system for commercial building energy saving

This paper presents a comprehensive refinement of system modeling and optimization study of air-cooled direct expansion (DX) refrigeration systems for commercial buildings to address the energy saving problem. An actual DX rooftop package of a commercial building in the hot and dry climate condition is used for experimentation and data collection. Both inputs and outputs are known and measured from the field monitoring. The optimal supply air temperature and refrigerant flow rate are calculated based on the cooling load and ambient dry-bulb temperature profiles in one typical week in the summer. Optimization is performed by using empirically-based models of the refrigeration system components for energy savings. The results are promising as approximately 9% saving of the average power consumption can be achieved subject to a predetermined comfort constraint on the ambient temperature. The proposed approach will make an attractive contribution to residential and commercial building HVAC applications in moving towards green automation