Sizing of wind powered axial flux permanent magnet alternator using analytical approach

The demand for a more sustainable energy supply worldwide is constantly growing hence, leading to the exploration of various renewable energy sources in energy generation systems especially in the demand for power in homes, industrial sectors and other utilities. Hydro power, wave power, solar energy, biomass and wind power are only a few that are being harnessed in various capacities. With new advances in wind energy technologies and energy conversion systems, a perfect fit is found in the utilization of wind in developing direct drive energy conversion systems. In this work, a wind-powered, single-phase, permanent magnet alternator utilizing an axial flux distribution system is developed. Using analytical calculations, the design parameters of the alternator’s main dimensions were obtained in a similar procedure for conventional electrical machines. To prove the feasibility of the concept, a prototype was built and tested. The alternator was built using Neodymium Iron Boron (NdFeB), a permanent magnet, with high concentration of flux around its periphery. The stator is slot-less and carries a concentrated air-cored type of winding. The procedures leading to either the selections and/or calculations for the machine parameters were carried out from first principle and fundamental assumptions in electrical machines design were made accordingly. Tests were conducted to determine its voltage output and were found optimal giving the abound limitations as stated. http://dx.doi.org/10.4314/njt.v35i4.2

Electric Power Systems and Components for Electric Aircraft

Electric aircraft have gained increasing attention in recent years due to their potential for environmental and economic benefits over conventional airplanes. In order to offer competitive flight times and payload capabilities, electric aircraft power systems (EAPS) must exhibit extremely high efficiencies and power densities. While advancements in enabling technologies have progressed the development of high performance EAPS, further research is required. One challenge in the design of EAPS is determining the best topology to be employed. This work proposes a new graph theory based method for the optimal design of EAPS. This method takes into account data surveyed from a large set of references on commonly seen components including electric machines, power electronics and jet engines. Thousands of design candidates are analyzed based on performance metrics such as end-to-end system efficiency, overall mass, and survivability. It is also shown that sensitivity analysis may be used to systematically evaluate the impact of components and their parameters on various aspects of the architecture design. Once an EAPS architecture has been selected, further, detailed, validation of the power system is required. In these EAPS, many subsystems exist with timescales varying from minutes to hours when considering the aerodynamics, to nanosecond dynamics in the power electronics. This dissertation presents a multiphysics co-simulation framework for the evaluation of EAPS with a unique decoupling method to reduce simulation time without sacrificing detail. The framework has been exemplified on a case study of a 500kW all-electric aircraft, including models for aerodynamics, energy storage, electric motors and power electronics. Electric machines for aviation propulsion must meet several performance requirements, including a constant power speed range (CPSR) of approximately thirty percent above rated speed. This operation is traditionally achieved through the flux weakening technique with an injection of negative d-axis current. However, the degree of CPSR achievable through flux weakening is a strong function of the back emf and d-axis inductance. This dissertation reviews alternative methods for CPSR operation in machines with low inductance. A new method of current weakening has been proposed to address this challenge, involving reducing the machine\u27s current inversely proportional to the operating speed, maintaining constant power through the extended speed range. One benefit of the proposed method is that all current is maintained in the q-axis, maintaining maximum torque per ampere operation. Coreless axial flux permanent magnet (AFPM) machines have recently gained significant attention due to their specific form factor, potentially higher power density and lower losses. Coreless machine designs promise high efficiency particularly at higher speeds, due to the absence of a ferromagnetic core. In this dissertation, coreless AFPM machines with PCB stators are investigated as candidates for propulsion in electric aircraft applications. Two PCB stator design variations are presented with both simulation and experimental results

Investigations of LC Filter Unbalance in an Inverter-Fed Permanent Magnet Synchronous Motor Drives

Permanent magnet synchronous machines (PMSMs) are usually controlled using two-level inverters. The output voltage of the inverter is in the form of the switching pulses between the positive DC-bus voltage and the negative DC-bus voltage. Such voltage waveforms have several adverse effects on the motor. These include, higher stress on winding insulation, higher eddy current losses and acoustic noise. Thus, to overcome these problems, different types of filters, typically LC-filters are used between the inverter and motor terminals to smooth the pulse width modulation (PWM) output voltages of the motor drives. Theoretically, the inductance and capacitance used for the filters are considered identical in each phase. However, in a practical scenario, it is difficult to have identical filter elements for all three phases. This non-ideal condition of filter elements amongst the three phases is considered as filter unbalance. This thesis investigates the impacts of filter unbalance on the PMSM drive system. Specifically, a comprehensive model of the motor drive system considering filter unbalance is proposed and developed at first. With the developed model, conventional field oriented control (FOC) is implemented to investigate the impact of this filter unbalance. A range of filter parameter variation and the corresponding impact on the motor drive including the motor current, torque and speed ripples is then studied in detail. Thereafter, the results obtained from the proposed model are validated through both circuit simulations and experimental tests. Based on the investigation results, this thesis will discuss the allowable parameter variation in the LC filters to limit the motor performance deterioration within the required bounds, which will be beneficial to engineering practice in motor drive area. In addition, this investigation shows that a conventional FOC with proportional integral (PI) controller might not be capable of mitigating the negative impact on the motor due to filter unbalance, for example, the negative sequence current. Therefore, this thesis implemented an adaptive proportional resonant (PR) controller to address negative sequence current and the corresponding impacts. A detailed mathematical framework to develop this proposed controller will also be presented in the thesis. Finally, the proposed adaptive PR controller is extensively evaluated on a laboratory PMSM drive system under different operating conditions

An Assessment of Integrated Flywheel System Technology

The current state of the technology in flywheel storage systems and ancillary components, the technology in light of future requirements, and technology development needs to rectify these shortfalls were identified. Technology efforts conducted in Europe and in the United States were reviewed. Results of developments in composite material rotors, magnetic suspension systems, motor/generators and electronics, and system dynamics and control were presented. The technology issues for the various disciplines and technology enhancement scenarios are discussed. A summary of the workshop, and conclusions and recommendations are presented

Power conversion for a modular lightweight direct-drive wind turbine generator

A power conversion system for a modular lightweight direct-drive wind turbine generator has been proposed, based on a modular cascaded multilevel voltage-source inverter. Each module of the inverter is connected to two generator coils, which eliminates the problem of DC-link voltage balancing found in multilevel inverters with a large number of levels.The slotless design of the generator, and modular inverter, means that a high output voltage can be achieved from the inverter, while using standard components in the modules. Analysis of the high voltage issues shows that isolating the modules to a high voltage is easily possible, but insulating the generator coils could result in a signicant increase in the airgap size, reducing the generator effciency. A boost rectier input to the modules was calculated to have the highest electrical effciency of all the rectier systems tested, as well as the highest annual power extraction, while having a competitive cost. A rectier control system, based on estimating the generator EMF from the coil current and drawing a sinusoidal current in phase with the EMF, was developed. The control system can mitigate the problem of airgap eccentricity, likely to be present in a lightweight generator. A laboratory test rig was developed, based on two 2.5kW generators, with 12 coils each. A single phase of the inverter, with 12 power modules, was implemented, with each module featuring it's own microcontroller. The system is able to produce a good quality AC voltage waveform, and is able to tolerate the fault of a single module during operation. A decentralised inverter control system was developed, based on all modules estimating the grid voltage position and synchronising their estimates. Distributed output current limiting was also implemented, and the system is capable of riding through grid faults

Magnetic Guidance for Linear Drives

Linear drives provide many new attractive solutions for the material transportation and processing in the manufacturing industry. With no mechanical transmission elements, they enable high dynamics and rigidity as well as low installation- and low maintenance-costs. That performance can give the linear motor system a better precision, a higher acceleration and a higher speed of the moving part. Therefore, the material transportation and processing using linear motors is studied and applied increasingly in manufacturing industry. For these applications, the linear motor is typically with stationary long primary and a short moving secondary. As the secondary part is passive, no energy transmission is required between the moving and stationary part, avoiding the use of brushes or inductive transmission. The motor type best suited for the mentioned applications is the synchronous one with permanent magnets, because of its higher efficiency, compactness, but most important because it allows a higher air-gap. In the usual approach, the linear motor is only used for thrust force production. The guidance is usually implemented by a mechanical assembly. The guidance constrains the movement to the longitudinal displacement, fixing the lateral and vertical displacement: yaw, roll and pitch. To achieve the necessary precision of the movement, accurate mechanical guidance is required. Such the mechanical assembly can be complex and source of high friction. In this dissertation, a research of an active guiding system is presented. The purpose of this research is finding out a solution for the material transportation and processing applications. The target is a linear drive system, which can reduce the complicated mechanical structure. In additions, the passive vehicle is also necessary. The result of the research is PM-synchronous linear motors with long and double-sided primaries. In the system, the lateral displacement and the yaw angle are controlled while a simple wheel-rail system fixes the vertical displacement. This combination of the magnetic and mechanical guidance offers a good trade-off among the complexity of the control, actuators and mechanics, when considering industrial applications. To allow multiple vehicles traveling simultaneously and independently on the guide-way (each vehicle is controlled by an individual part of the guide-way), the double side primary is separated into segments. With that structure, flexible-operating methods can be implemented. That is very useful in process-integrated material handling where different speeds of material carriers in each processing station are necessary. Another advantage of segmented structure is the energy saving. The power is supplied only to the segment or the two consecutive segments in which the vehicle runs over. In one segment, each side of the primary is supplied by its own inverter, allowing the necessary degree of freedom to control the lateral position and the yaw angle in addition to the thrust control. In order to make the vehicle completely passive, a capacitive sensor is proposed and implemented to measure the lateral position and the yaw angle. The sensor has active parts installed on the guide-way and passive parts on the vehicle. The mathematical analysis and the finite element method (FEM) are used to analysis the proposed system. With the analysed results, the control for the system is investigated in detail. Hardware and software for the experimental system is developed and implemented. The analysed results and the experimental results validate the proposed system. That gives a new solution for the material transportation and processing application using linear synchronous motors

High Speed flywheel and test rig design for rural energy storage

There is considerable growth in the renewable energy sector to contribute to sustainable development, environmental conservation and most importantly to provide affordable energy to isolated rural communities of sub-Saharan Africa. Renewable energy sources such as solar and wind require energy storage since the source of energy is intermittent. Electrochemical batteries especially from lead acid are commonly used to store energy in Solar Home Systems (SHS) for rural electrification in sub-Saharan Africa. Disadvantages such as low efficiencies, low life cycle costs, high maintenance, comparatively short life and serious environmental and human toxicity effects exist. Since recycling is not widespread, replacement costs are high, as are the resultant environmental damage and health hazards from lead and sulphuric acid. In this thesis, an electromechanical flywheel energy storage device is proposed as an alternative to a lead acid battery in order to increase efficiency, life expectancy, increased high depth of discharge, low life cycle cost and elimination of adverse environmental effects. Due to income and service skill constraints in rural areas, the proposed, high speed flywheel systems (for long time energy storage) will require the use of low cost configurations and topologies, special considerations on the flywheel rotor profile design, robust electrical machines, simple power electronics and a low cost bearing set. Low loss magnetic bearings are also possible but were limited by time while also making their maintenance complex especially in rural areas. Conventional high strength composite materials used in flywheel rotor manufacture for high speed operation are expensive. Therefore there is a need to develop techniques to profile the rotor shape so as to improve on material usage and exhibit lower mechanical stresses. A robust electrical machine topology for high speed operation and a simple drive system are investigated to ensure simple assembly, low cost and low maintenance. vii The various flywheel components were designed using analytical and numerical methods. Two techniques were used to develop two optimal profiles for the flywheel rotor structure. Partial differential equations and analytical solutions were employed to develop the profiles. Analytical equations were used to design the electrical machine, drive, bearing system and other accessories. The final electromechanical battery prototype consisted of a composite flywheel rotor made from E-glass fibre materials, double rotor Axial Flux Permanent Magnet (AFPM) machine and a drive system using Brushless DC (BLDC) mode of operation. The system was designed for 300Wh of energy storage for the delivery of 100W and 500W of power and an operating speed range of 8,000 rpm-25,000 rpm. The design and development of the flywheel energy storage system and test rig using locally available materials was investigated. Experiments were conducted for speeds up to 6,000 rpm. The electromechanical battery was able to store a maximum of 77Wh of energy. The shortfall of the system to meet its design specifications was investigated and found to have been caused by vibrations resulting from prototyping issues. A thermal model was developed to predict the temperature rise in the system which showed a good correlation with the experimental results

A novel linear motor for a linear refrigeration compressor: modelling, measurement and sensor-less stroke detection

With the increasing global awareness of the environmental conservation, linear compressors have attracted growing attention with their applications in domestic and cryogenic refrigeration systems. A linear compressor is driven directly by a linear motor and the free-piston design allows piston stroke to be variable. An active control of stroke prevents piston-cylinder collision and enables efficient cooling capacity modulation. This thesis introduces the performance of a novel moving magnet type linear compressor/motor and investigates the approaches to sensor-less stroke detection. An experimental test facility incorporating the linear compressors into a vapour compression refrigeration system was introduced, in which piston displacement was measured with a displacement sensor. The piston stroke and offset were controlled with PID controllers implemented in LabVIEW. To investigate the characteristics of the moving magnet linear motor, a finite element analysis (FEA) model was built in ANSYS Maxwell 19.2. Simulations were validated through static force measurements. Force constant was given by the static shaft force against current. Saturation can be observed with the increase of current. A smaller saturation current was shown for a larger armature displacement. For the purpose of increasing cooling capacity of the linear compressor, operations with small axial clearance volumes were considered. Refrigeration performance using R1234yf as refrigerant with various clearance volumes and with an offset of 0 mm were experimentally compared. The cooling capacity for a pressure ratio of 2.5 and a stroke of 13 mm increases by 12% as the clearance decreases from 1.07 mm to 0.4 mm. Piston stroke detection without a displacement sensor reduces the cost and facilitates the stroke control especially in miniature linear compressors. An artificial neural network (ANN) based stroke detection was presented. Fast Fourier transform (FFT) analysis was performed on current and voltage signals to extract harmonic terms as inputs of the neural network model to predict the stroke. The ANN technique can achieve a good accuracy for most of the cases, but reliability remains a problem. A more reliable sensor-less stroke detection technique based on flux linkage variation using inductive coils was proposed. The technique requires resonant operation. A 1D (One-Dimensional) electromagnetic model and a 3D (Three-Dimensional) FEA model were built to compute the flux linkage variations. The open-circuit flux linkage in each core produced by NdFebB magnets varies linearly with the piston displacement. Flux linkage difference at two zero-crossing points of current was used to infer stroke. The proposed low-cost sensor-less stroke detection technique can achieve error of only 4%. The adoption of this novel technique is crucial to the commercialization of free-piston machines for high efficiency