Improving the energy efficiency and increasing the power density of indirectly hydrogen-cooled turbine generators used in high efficiency combined-cycle power plants is important due to global warming and increasing power demands. When the output current is increased for achieving high power density, the stray load loss at the stator end region increases due to leakage flux from the armature and field coils. Therefore, it is necessary to evaluate the temperature of the stator end region under the condition of leading power factor load. In this paper, we analyzed the loss density distributions at the end region structures using large-scale 3D electromagnetic field analysis to establish the temperature reliability of an 870 MVA indirectly hydrogen cooled machine, which is the largest class capacity in the world. Thermal analysis was then performed using the loss density distribution obtained from the 3D analysis. The analysis results show good agreement with the measured values.
In this paper, the impact of the DC bus voltage on the iron losses of a permanent magnet synchronous motor (PMSM) fed by a pulse-width modulation inverter is evaluated. Under constant speed operation, the modulation index decreases when the DC bus voltage increases. This modifies the harmonic content of the PMSM input voltage and then affects the motor iron losses. The experimental measurements results show that, for the conditions considered in this paper, the total iron losses are 1.8 times larger at the lowest modulation index than at the highest one.
In this paper, a synchronous frame control for a voltage sag/swell compensator utilizing single-phase matrix converter is proposed. First, the configuration of the proposed system and its operation are described. Next, the effects of the degree of voltage sag and load variation on the system stability are analyzed using the transfer function. Finally, the experimental waveforms of the system with the proposed synchronous frame control are compared with those of the system with a stationary frame control. The results demonstrate that the proposed synchronous frame control can suppress the steady state error and pulsation caused by the LC filter resonance better than the stationary frame control.
In this study, we investigate the characteristics of claw-pole alternators for automobiles from the results of both calculation and experiments. Nonlinear 3-D finite element analysis is employed to take the claw-pole shape into account. The calculated characteristics are compared with the experimental results in order to confirm the validity of the analysis. Then, the magnetic field is decomposed according to the field sources in order to understand the effect of armature reaction. It is clarified that the large armature reaction in the claw-pole alternator causes saturation of the electrical output and an increase in the harmonic losses in the machine. The possibility of improving the characteristics by reducing the armature reaction is also clarified.
The simple and robust construction of reluctance machines and the fact that they need an unsophisticated control have reignited interest in these machines. The constructional modifications and new configurations such as brushless doubly fed reluctance machines (BDFRM) show superior performance compared to their traditional counterparts, especially in variable speed applications such as pumps and wind generators. The design of BDFRM is different from other machines, as there are unusual pole combinations of stator and rotor besides the absence of a winding on the rotor. The operation and performance of the machine greatly depends on the mutual interaction between the stator windings. This interaction is modulated by the rotor with increased saliency. This paper examines a few critical issues in the design of BDFRM. Design optimization is performed using the gradient method from non-linear programming for 6-4-2 pole and 8-6-4 pole configurations of BDFRM. The performance of these optimized machines is examined through finite element analysis employing MAXWELL 16 software and then compared with 2kW prototypes constructed for laboratory use. A comparative analysis of the two configurations are presented and experimental results show that the BDFRM with the 8-6-4 ducted rotor is superior to BDFRM with the 6-4-2 reluctance and ducted rotor configurations.
Recently, interior permanent magnet motors (IPMs) or motors with field winding have been investigated from a viewpoint of magnetic field control. IPMs have an advantage of field weakening; however, their overall flux passing the stator core is not sufficiently suppressed. On the other hand, motors with field winding can control a wide range; however, they need the field windings and are the complicated shape and heavy. In this paper, a new structure of hybrid field motor without a field winding is proposed, whose rotor has regular salient poles arranged with interpolar gap and permanent magnet. In addition, this interpolar gap and permanent magnet motor (IGPM) is investigated along with its characteristics. By means of some basic equations related to flux, torque, and FEA, it is clarified that IGPM is more appropriate for field weakening control than IPM. In addition, we found that the proposed IGPM has yielded successful FEA and experimental results by preliminary prototype.
High-power converter applications are usually realized using the hard-switching technology under a low-switching frequency condition; moreover, the isolation transformer size must be larger. To reduce transformer size, the switching frequency must be increased; however, this increase directly results in the increase of switching loss. This paper proposes a high-voltage(HV) and high-power supply by using a thyristors-controlled rectifier and LCC series parallel resonant converter (LCC-SPRC). The introduced dc-dc converters are connected in parallel at the input side and in series at the output side, and soft-switching technology is applied to reduce the switching loss by using the frequency control mode. In addition, an equivalent mathematical model of LCC-SPRC with discontinuous current mode1 (DCM1) was analyzed in detail. For obtaining accurate parameters of LCC-SPRC, the Matlab/Simulink software was employed to calculate the system parameters, and provide the system with dynamic simulating curves. The simulation and experimental results verify that the LCC-SPRC design scheme of for supplying furnace power during the electron beam melting (EBM) is feasible in applications.
A model reduction method for finite element analysis such as the zooming analysis is conducted to calculate the AC copper loss of high speed electric machines. In this paper, the accuracy of the zooming method is validated by comparison with thorough analysis and the calculation speed in the zooming analysis is found to increase by 7.8 times that of thorough analysis.
Moreover, the zooming method is applied to the analysis of the copper loss of a litz wire with respect to an interior permanent magnet motor rotating at high speed. The copper loss of the litz wire could be calculated within a practical computation time.
Nowadays, interior permanent magnet synchronous motors (IPMSMs) are widely utilized as traction motors. The permanent magnets used in IPMSMs are an important factor; thus, high-coercivity permanent magnets with lesser rare-earth elements are in development. This study investigated the performance of IPMSMs typically used in automotive applications modified to contain a strong magnet model (SMM). Rotor models with two permanent magnet arrangements, that is, a V-shaped single-layered permanent magnet structure (Type 1V) and a double-layered permanent magnet structure (Type 2D), were considered in this study. This paper discusses the characteristics of the analysis models based on the results of a two-dimensional finite element analysis. The maximum torques of Types 1V and 2D with the SMMs were approximately the same. In addition, the loss of Type 2D with the SMM was lower than that of Type 1V with the SMM at two evaluation points and under two driving schedules. Therefore, Type 2D was proved to be suitable for use with the SMM.
Permanent magnet synchronous motors (PMSMs) possess many good characteristics, such as high efficiency and high torque density. In this study, a design assist system is proposed for PMSMs. This system uses motor parameters and a magnetic equivalent circuit to design a PMSM that satisfies the demanded output characteristics. This paper describes the outline of the design assist system. The system is applied to the design of surface permanent magnet synchronous motors (SPMSMs) and the effectiveness of the proposed system is confirmed.
We propose a topology optimization method that incorporates the concept of the cluster and cleaning method in a genetic algorithm. This method can be used to design a rotor structure with high output power and low permanent magnet volume from an empty space. In this study, the effect of the level of the cleaning method on the obtained rotor structure is investigated. A permanent magnet synchronous generator is designed using the optimal level of the cleaning method. This generator has higher output power characteristic with low permanent magnet volume than a generator used in Prius, which is a general hybrid vehicle.
This work investigates the impact of thin electrical steel laminations on the performance of interior permanent magnet (IPM) motors for electric vehicle tractions. Three different electrical steel grades are used in IPM motor designs and the performance is evaluated by simulation. It is found that thin laminations can improve the efficiency of the IPM motor, but the output torque could be slightly reduced due to low saturation flux density. Therefore, direct replacement of core materials for the same motor design may not be suitable. This paper presents the considerations for the design of IPM motors using thin laminations. The motor performance, including torque, efficiency, and constant power speed range is evaluated. A process is developed for the design of high performance IPM motors using thin laminations. Experimental studies are conducted to validate the simulations and designs.
This paper proposes a transformation matrix to generate two phase reference voltage signals for Four Switch Three Phase Inverter (FSTPI) using vector control. The feasibility of the control strategy is verified by proving the power invariance before and after the transformation. Simulation and experimental results have verified the validity and effectiveness of the proposed method to obtain instantaneous response in different operating conditions and provide fast speed response.
This paper adopts the modularity principle to completely model the transmission-connected photovoltaic plant. With more and more power electronics being integrated into the power system, modeling based on the modularity principle will increase the generality of the model of each module, for example, allowing the power electronic module for the PV plant to be used in other elements such as the wind plant. Moreover, we still lack complete PV plant models that express all components of the PV plant, such as changing irradiance, common control modes, and even the signal transmission model. The objective of this paper is to solve these problems. An overall structure using the modularity principle to model the PV plant is provided. Then each module is described, which is followed by the algorithm that how all modules work in conjunction. Finally, applications of the provided models in the power system small signal stability study are presented, where the characteristics of the PV plant can be closely simulated. A 2-area 4-machine system is used to test the applications of the models.
This paper presents a new pole-zero-assignment-based design method of a two-degree-of-freedom (TDOF) PID controller, which is applicable to both positioning and tracking drives of linear servo motors. This design method involves easy determination of five PID control parameters from six items: mover mass, maximum load mass, thrust constant, cutoff frequency of the position control system, crossover frequency of sensitivity and complementary sensitivity functions, and pole-angle in the s-plane. Consequently, it is possible to design a suitable TDOF PID controller for both positioning and tracking drives by changing the pole-angle in the s-plane. Simulation and experimental results validate the proposed design method.
Stator coils of large rotating machines are divided into strands, which are transposed to reduce the inter-strand circulating current loss. Circulating current analysis is required to evaluate the effect of transposition, but full 3D analysis is difficult because of the complicated configuration of the transposed coils. In this paper, magnetic field analysis model using 3D multi-layer finite element method is proposed to calculate the inter-strand circulating current in the stator coil with both transposed and non-transposed parts in the coil end region. Then circulating currents are analyzed considering the magnetic flux in the end region and some transposition patterns are compared.
This paper presents the energy-saving effect of a single-drive bearingless motor. In the single-drive bearingless motor, only the axial direction is actively positioned. The other radial and tilting directions are passively stabilized by repulsive passive magnetic bearings. Therefore, it has the advantages of low cost, absence of contact, maintenance-free and a long lifetime. In this paper, an additional advantage, an energy-saving effect, is verified. In experiments, the input power is measured with and without mechanical ball bearings. The bearingless motor can reduce the input power because the magnetic suspension power is low compared with the mechanical bearing loss. In addition, it is found that the efficiency can be improved.
Interleaved dc-dc converters with integrated magnetic components are popular as converters capable to achieve high efficiency with less of volume and mass. There are three methods for integrated magnetic components: loosely-coupled inductors, closed-coupled inductors and integrated-winding-coupled inductors. This paper presents a method to calculate the allowable power in various circuit topologies. It is useful for measuring the allowable power without magnetic saturation of an inductor based on its size. Following the analysis of allowable power for each coupled inductor, the allowable power of the integrated magnetic components is compared to that of the conventional interleaved converter. This comparison is realized under the same conditions. As a result, the interleaved converter with loosely-coupled and integrated winding coupled inductors were found to be effective for the downsizing of the magnetic components under continuous conduction mode operation. On the other hand, the interleaved converter with close-coupled inductors is effective for the downsizing of the magnetic components under critical conduction mode operation. This comparative data is discussed from both theoretical and experimental points of view.
In recent years, wireless power transfer has been a popular research topic because it allows both static and dynamic charging without using cables, thus easing the process for the user. However, achieving high efficiency and desired power corresponding to the load at any time is important. Communication between sides is often used, but sometimes its operation is not guaranteed because of harsh environmental conditions or malfunctioning. This paper addresses this problem by proposing a novel yet simple control strategy. It consists of simultaneous regulation of both power and efficiency by the secondary side alone, without communication with the primary side. When the primary side is not manipulated, the power is controlled by an AC/DC converter by using a two-mode control. On the other hand, the efficiency is controlled by a DC/DC converter by adjusting the DC link voltage to a reference value related to the maximum wireless transmitting efficiency. In this paper, the control concept as well as the design are provided. The proposed control shows a good trade-off by achieving power regulation capability at the cost of slight reduction in efficiency when compared to the currently existing state-of-the-art control.
It is important for railway companies to reduce the power consumption of substations in order to reduce the contract power cost and facilities. This study proposes a decentralized control system for controlling the train power demand. Each train calculates its own power allocation independently and in parallel using the information broadcasted by the substations in this control scheme. This control system is very advantageous from the view point of communication load, plug & play' and capital investment because it does not need a server. This work investigates the effect of train power control using the decentralized control scheme via simple and precise numerical simulations' which demonstrate that several trains run on the railroad and are powered by a substation.