Browsing by Author "Khan, Mohamed"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Open Access
    AI-based hybrid optimisation of multi-megawatt scale permanent magnet synchronous generators for offshore wind energy capture
    (2019) Lilla, Abdurahman Daleel; Khan, Mohamed; Barendse, Paul
    The finite nature of earth’s natural resources has become a post-industrial reality. Despite their alarming depletion, fossil fuels still dominated the global final energy landscape. Technological advances and rapid deployment of various renewable energy technologies have demonstrated their potential at reducing the worlds dependency on fossil fuels and their negative impacts. Presently, wind energy is the most cost-effective means of renewable energy conversion in the developed world and has currently has a price point that is in direct competition with fossil fuel. Coupled with the low price, the adoption of wind power has seen capacity increases in excess of 650% over the last ten years. Permanent Magnet Synchronous Generators (PMSGs) have become prominent in large wind energy system applications. The Radial Flux machine topology has become particularly attractive. In order to improve the competitiveness of large wind energy systems, the main focal point of current research is toward reducing the Levelised Cost of Energy (LCOE) of the systems. A proven method of reducing the LCOE of wind power generation is by upscaling RF-PMSGs to the multi mega-watt (MW) range. For the much wider adoption of wind power generation, the cost of energy (price/MWh) needs to be driven down further, by the development of more efficient and cost-effective ways to harvest the vast amounts of energy. The main objective of this dissertation is the drive-train selection, detailed design, sizing and optimisation of a 10.8 MW permanent magnet radial flux synchronous generator (RF-PMSG) to be used in the next generation of offshore wind farms. From an analytical viewpoint, the results suggested the use of a medium speed RF-PMSG utilizing a single-stage geared drivetrain, together with a MV voltage rating (3.3kV) for the 10.8 MW RF-PMSG designed in the thesis. Finally, this dissertation proposes a promising hybrid, analytical-numerical optimisation of a 10.8 MW RF-PMSG to be used for offshore Wind Energy Conversion. The hybrid optimisation utilises a two-stage optimisation strategy that incorporates both an analytical and a numerical (FEA) optimisation; using the DE algorithm and the Taguchi method respectively. Although the permanent magnet losses are neglected in the analytical loss calculations, they are included in the numerical FE portion of the hybrid optimisation. The initial stage (STAGE I) of the hybrid optimisation utilised the DE algorithm. The objective function was set to reduce the initial cost (!"#"$%&) of the RF-PMSG, by reducing the active material mass ('()$"*+) in the generator, i.e. NdFeB PM mass (',-), copper mass (').), and active steel in the stator lamination and rotor core ('/0$%&1$++&), while maintaining a pmsg efficiency (23456 ≥ 97%). The initial stage saw a reduction in initial cost by 25.5%, while maintaining an efficiency of 23456 = 97.8%. The final stage (STAGE II) of the hybrid optimisation utilising the Taguchi method, to make improvements on the performance of the machine, by optimising the Torque and back EMF characteristics while further reducing the NdFeB PM mass. The Magnet Fill Factor (APM), the Slot opening (bs0), the thickness of the permanent magnet poles (ℎ34) and the equivalent length of the air gap (?6) were used as optimisation variables. The final stage saw a decrease in cogging torque (@)06) by 53.4%, an increase in average torque (@%*) by 1.1%, a reduction in the total harmonic distortion of the back EMF (@AB) by 8.0%, a reduction in the required mass of the NdFeB permanent magnet material by 12.43%, while maintaining a torque ripple (@C"3) < 10%. The RF-PMSG characteristics optimised using the hybrid analytical-numerical optimisation were hypothesised to contribute in a reduction of the LCOE of offshore wind energy both in terms of Operational expenditure (OPEX) and Capital expenditure (CAPEX).
  • Thumbnail Image
    Item
    Open Access
    Development of a power conditioner for a PMSG-based wind energy system integrated into a weak grid
    (2020) Khan, Akrama; Khan, Mohamed; Malengret Michel
    With the growing use of non-linear loads and due to their ever changing nature, electricity networks experience power imbalance continually. These non-linear asymmetrical loads draw distorted unbalanced currents and voltages at the point of common coupling (PCC) which propagate into the distribution network. Power quality has therefore become an important issue, which has resulted in the development of numerous control strategies and other interventions to maintain the integrity of the electric network. Recent advancements in power electronics have provided new ways to optimize power systems by regulating the active power transfer. These developments lead to opportunities for renewable energy systems to harness energy and at the same time inject optimized currents into the network by means of distributed units. An emerging problem with most such units is that they are located far from the PCC and are usually designed for the small linear loads. Moreover, the problem is exacerbated during overload conditions when the voltage level drops below the allowed minimum level due to the high network impedance which characterizes a weak grid. This thesis aims to study similar scenarios where a permanent magnet synchronous generator (PMSG) based wind energy conversion system (WECS) is integrated into a weak AC grid. The system comprises of a machine-side (MSC) and a grid-side (GSC) converter, which provides available ancillary services and is envisaged to augment existing power quality conditioners such as STATCOM devices. To represent a weak grid, a Thevenin equivalent model of the electric network is considered with unbalanced loads. The main objective of this project is to transform the traditional converter topology into a versatile system that can perform as a power conditioner. In particular, it monitors a distribution line, sense changes in the load, detects faults and redistributes the currents to ensure maximized power transfer into the network. The system under consideration possesses the capability of independent injection of active and reactive currents within the defined limits. Since the system under consideration is integrated v into a weak grid, the perceived load is always considered to be unbalanced. Under the specified condition, if a fault occurs at one or two phases, unbalanced voltages are observed at the PCC. Two scenarios are created to perform the case study. Firstly, a no-fault case is considered with symmetrical voltages at the PCC. To ensure maximum power transfer into the network with least losses, a set of currents is injected according to the optimal current injection technique. Secondly, asymmetrical faults are considered at the PCC and currents are injected according to the coordinated sequence current injection technique. This technique defines a new current injection limit which not only improves the power transfer but also enhances the power factor. Furthermore, the peak magnitude of the three phase currents is also kept within the rated current limit. For both scenarios described above, the MSC regulates the DC link voltage so as to limit the active power coming from the generator according to the grid condition. The GSC however performs two important functions. It implements small active/reactive power perturbations for the impedance estimation, and once the impedances are determined, magnitudes of the required currents are calculated and injected based on the proposed techniques. Validation of the analysis is done experimentally on a 3.3kW PMSG connected to a programmable regenerative power supply which emulates a weak grid. The MSC and GSC utilized in this project are conventional two-level converters which are controlled by means of a FPGA based controller.