Control of Asymmetric Permanent Magnet Synchronous Generator Systems

The thesis focuses on the control of asymmetric permanent magnet synchronous generator (PMSG) system, with particular reference to the suppression of its second harmonic (2h) power, DC bus voltage and torque ripples. The asymmetries include the unbalanced resistances, unbalanced inductances, and unbalanced 3-phase back-electromotive forces (EMFs). The mathematical model of the general asymmetries in the PMSG system is firstly presented. The power ripple and torque ripple due to the asymmetries without/with negative-(N-) sequence currents are then analysed in detail. It shows that there are 2h impedances in the synchronous dq-axis frame. Consequently, the N-sequence currents emerge under the conventional current proportional and integral (PI) control, which will result in undesired 2h power, DC bus voltage and torque ripples. To suppress the 2h torque resulted from the N-sequence currents, three typical methods aiming for balanced currents without N-sequence currents are reviewed, evaluated and their relationship is revealed. It shows that all these three methods are capable of suppressing the N-sequence currents as verified by experiments. However, the 2h power and DC bus voltage cannot be suppressed. To suppress the undesired 2h power and DC bus voltage, an improved power control without any sequential component decomposers under general unbalanced conditions is proposed. Its effectiveness is validated by elaborated experiments on a prototype PMSG with inherent asymmetry and deliberately introduced asymmetries. However, the 2h torque is compromised. To solve the 2h torque, power and DC bus voltage simultaneously, the compensation in parallel with the DC bus is investigated in the PMSG system with asymmetric impedances. The undesired 2h power from the PMSG is compensated by the 2h power from the compensation unit. Two topologies of the compensation unit and corresponding control methods are investigated, while the compensation effectiveness is validated by experiments. Furthermore, the compensation unit with external circuits in series with the asymmetric PMSG is investigated. By the compensation in series, the original unbalanced system is modified to a balanced system in theory. Therefore, the N-sequence currents, 2h power, DC bus voltage, and torque ripple can be naturally suppressed. The feasibility of this compensation method is verified by experiments at different speeds and load conditions, although the effectiveness may be slightly affected by the non-linearity of the compensation inductors in practice. Finally, the research of suppressing the 2h DC bus voltage and torque ripple is extended to the dual 3-phase PMSG system with one channel failed. By utilizing the windings, rectifier or inverter in the faulty channel which are still functional, three methods designated as two sets in parallel, two DC buses in parallel and N-sequence currents compensation are investigated, which require minimum extra hardware investment compared with the compensation in parallel and in series

Advances in Rotating Electric Machines

It is difficult to imagine a modern society without rotating electric machines. Their use has been increasing not only in the traditional fields of application but also in more contemporary fields, including renewable energy conversion systems, electric aircraft, aerospace, electric vehicles, unmanned propulsion systems, robotics, etc. This has contributed to advances in the materials, design methodologies, modeling tools, and manufacturing processes of current electric machines, which are characterized by high compactness, low weight, high power density, high torque density, and high reliability. On the other hand, the growing use of electric machines and drives in more critical applications has pushed forward the research in the area of condition monitoring and fault tolerance, leading to the development of more reliable diagnostic techniques and more fault-tolerant machines. This book presents and disseminates the most recent advances related to the theory, design, modeling, application, control, and condition monitoring of all types of rotating electric machines

Magnetic Material Modelling of Electrical Machines

The need for electromechanical energy conversion that takes place in electric motors, generators, and actuators is an important aspect associated with current development. The efficiency and effectiveness of the conversion process depends on both the design of the devices and the materials used in those devices. In this context, this book addresses important aspects of electrical machines, namely their materials, design, and optimization. It is essential for the design process of electrical machines to be carried out through extensive numerical field computations. Thus, the reprint also focuses on the accuracy of these computations, as well as the quality of the material models that are adopted. Another aspect of interest is the modeling of properties such as hysteresis, alternating and rotating losses and demagnetization. In addition, the characterization of materials and their dependence on mechanical quantities such as stresses and temperature are also considered. The reprint also addresses another aspect that needs to be considered for the development of the optimal global system in some applications, which is the case of drives that are associated with electrical machines

Investigation of performance improvement of doubly salient synchronous reluctance machine with current harmonic injection

This thesis investigates some novel current harmonic injection methods to improve the electromagnetic performance of doubly salient synchronous reluctance machines (DS-SRMs). These machines will have different winding configurations, slot/pole number combinations and phase numbers. The theoretical analyses (both static and dynamic) are carried out based on Fourier Series analysis, and validated by 2-dimensional finite element method and also experiments using several prototype machines. Based on the analytical torque model in abc-axis frame, a powerful insight into the mechanism of torque generation of the DS-SRMs with pure sinewave current supply can be achieved. The electromagnetic torque (both magnitude and phase angle) produced by each order of inductance harmonic can be predicted, which allows us to obtain the dominant torque ripple components for such machines. Therefore, the appropriate current harmonic (3rd, 5th and 7th) can be injected to generate torque ripple components in order to compensate that produced by the fundamental current, and hence to achieve an overall reduced torque ripple. On the other hand, the average torque of the DS-SRMs can also be improved by properly selecting the current harmonics in terms of harmonic order, amplitude and phase angle. However, it is found that the current harmonics, although can improve torque performance, will often cause extra losses (both copper and iron losses) and undesirable distortion in the phase voltages, which could lead to negative impact on the machine efficiency and dynamic performance. Therefore, in order to fully evaluate the potential of the proposed harmonic current injection method, comprehensive studies about losses, efficiency and dynamic performances such as torque-speed curves of 3-phase and multi-phase DS-SRMs have been carried out. In order to simplify the investigation of dynamic performance analyses such as the torque speed curves and efficiency maps, novel analytical torque model in dq0-axis frame has also been proposed. The findings in this thesis can provide some useful guidelines for torque performance improvement of DS-SRMs using harmonic current injections

Advances in the Field of Electrical Machines and Drives

Electrical machines and drives dominate our everyday lives. This is due to their numerous applications in industry, power production, home appliances, and transportation systems such as electric and hybrid electric vehicles, ships, and aircrafts. Their development follows rapid advances in science, engineering, and technology. Researchers around the world are extensively investigating electrical machines and drives because of their reliability, efficiency, performance, and fault-tolerant structure. In particular, there is a focus on the importance of utilizing these new trends in technology for energy saving and reducing greenhouse gas emissions. This Special Issue will provide the platform for researchers to present their recent work on advances in the field of electrical machines and drives, including special machines and their applications; new materials, including the insulation of electrical machines; new trends in diagnostics and condition monitoring; power electronics, control schemes, and algorithms for electrical drives; new topologies; and innovative applications

Power Converters in Power Electronics

In recent years, power converters have played an important role in power electronics technology for different applications, such as renewable energy systems, electric vehicles, pulsed power generation, and biomedical sciences. Power converters, in the realm of power electronics, are becoming essential for generating electrical power energy in various ways. This Special Issue focuses on the development of novel power converter topologies in power electronics. The topics of interest include, but are not limited to: Z-source converters; multilevel power converter topologies; switched-capacitor-based power converters; power converters for battery management systems; power converters in wireless power transfer techniques; the reliability of power conversion systems; and modulation techniques for advanced power converters

Power quality improvement of electrical power systems within more electric aircraft

The application of more-electric aircraft concept will see a significant increase of electrical power demands with newly developed electrical loads. This will make it essential to extract electrical power from both high-pressure and low-pressure shafts of an aircraft engine for future aircraft. With each shaft driving one electrical generation subsystem, an advanced dual-channel power generation system can be formed. The dual-generation architecture can significantly reduce the fuel assumption of aircraft engines through power transfer between different engine shafts. In such a system, two permanent magnet synchronisation generators (PMSGs) will supply a common DC bus through their dedicated AC-DC converters. On the load side, a significant penetration of power electronics is foreseen as they are essential elements to interface load and the DC bus. With an increased number of power electronic converters, harmonics from these converters will impose significant power quality challenges to the electric grid. A capacitor is required to filter the switching harmonics in the DC bus to ensure that its voltage is within the required range. However, due to a high current rating, this capacitor will be bulky and heavy. This thesis aims to address the power quality issues for the common DC bus electrical power system architecture considering a dual-channel power generation system. To improve the power quality on the DC bus, switching harmonic component cancellation schemes are proposed for different cases. In the first case, two PMSGs are considered to supply the DC bus through AC/DC converters. In this case, the modulation scheme (either SPWM or SVPWM) of one AC-DC converter is controlled to actively cancel one specific harmonic component on the DC bus. After the first case study, the use of a bidirectional buck-boost DC-DC converter as a harmonic absorber with the proposed equal-gate-width (EGW) modulation scheme is considered. The proposed method allows for the active control of the magnitude and phase angle of some specific harmonic component and thus can be used to suppress the required harmonic component on the DC bus. Simulation and experimental results have demonstrated the high robustness and effectiveness of the proposed methods