Integrated on-board battery chargers for EVs based on multiphase machines and power electronics

The concept of integration of an electric vehicle (EV) drivetrain’s components into the charging process is not novel. It has been considered over the years in both industry and academia, which resulted in a number of published papers and patents in this area. Possibilities of charging from single-phase and three-phase mains were both considered. In the former group the charging power rating cannot exceed the limit set by the single-phase mains. Therefore, the topologies are characterised with low charging powers, leading to a long duration of the charging process. Although the topologies supplied form three-phase mains are capable of achieving fast charging, they were considered to a much lesser extent. The main reason is the undesirable torque production in machines integrated into the charging process during the battery charging, which is unavoidable when a three-phase machine of either synchronous or induction type is used. The thesis investigates integrated on-board battery chargers for electric vehicles (EVs) based on multiphase machines and multiphase power electronics. At present, EVs rely on three-phase systems for machine propulsion. However, recent advances in multiphase drive technology have firmly established their potential advantages over their three-phase counterparts for this application. One of the most notable features of multiphase drive systems is their excellent fault tolerance, which is highly desirable in EVs since it enables realisation of the requirement for “limp-home” operation in the propulsion mode, in case of a fault. The thesis demonstrates that multiphase drives have an additional major advantage over three-phase systems in vehicular applications, which is related to the aspect of battery charging. It shows a clear superiority of multiphase over three-phase systems in designing integrated charging topologies for EVs. In order to support the statement, the thesis provides a multitude of novel charging solutions that incorporate multiphase machines and multiphase power electronics into the charging process. The developed solutions could contribute to achieve significantly faster and cost-free (or at a minimum additional cost) on-board chargers in the near future. The thesis demonstrates how additional degrees of freedom that exist in multiphase systems can be conveniently utilised to achieve torque-free charging operation. Therefore, although three-phase currents flow through machines’ stator windings, they are not capable of producing a torque; thus the machines do not have to be mechanically locked. The principal advantage is that either very few or no new elements are required in order to realise the charging process. Thus savings are made with regard to cost and weight, and available spare space in the vehicle is increased. The novel integrated charging solutions, developed in the thesis, are based on primarily five-phase, asymmetrical and symmetrical six-phase, and asymmetrical and symmetrical nine-phase systems. Solutions with other phase numbers are also considered. Thus, in essence, all the possible phase numbers are encompassed by the research and the solutions are valid for both induction and synchronous machines. A common attribute of all discussed topologies is that they do not require a charger as a separate device since the charging function is performed by the drivetrain elements, predominantly a multiphase machine and an inverter. Further, each topology is capable of operating in both charging and vehicle-to-grid (V2G) mode. Three types of voltage sources are considered as a power supply for the charging process, namely single-phase, three-phase, and multiphase. For each supply type, and each phase number, viability of torque-free charging operation is theoretically assessed. Mathematical models of multiphase rectifiers are developed. For each topology equivalent scheme in the charging/V2G mode of operation is constructed. A control scheme, which aims at achieving unity power factor operation and complete suppression of the low order grid current harmonics, is designed for each solution. Finally, the validity of theoretical considerations and control algorithms for the developed solutions is experimentally assessed in charging, V2G, and propulsion mode of operation. Experimental performances of all discussed topologies are compared, and advantages and shortcomings of each solution are identified and discussed

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

Induction Motors

AC motors play a major role in modern industrial applications. Squirrel-cage induction motors (SCIMs) are probably the most frequently used when compared to other AC motors because of their low cost, ruggedness, and low maintenance. The material presented in this book is organized into four sections, covering the applications and structural properties of induction motors (IMs), fault detection and diagnostics, control strategies, and the more recently developed topology based on the multiphase (more than three phases) induction motors. This material should be of specific interest to engineers and researchers who are engaged in the modeling, design, and implementation of control algorithms applied to induction motors and, more generally, to readers broadly interested in nonlinear control, health condition monitoring, and fault diagnosis

Improving energy capture and power quality of power electronic connected generation

Power electronic converter is a significant intermediate media for electric renewable energy systems when integrated into the utility grid. Renewable energy systems such as wind, solar and wave energy systems usually operate with irregular natural energy sources. Advanced energy conversion interfaces are therefore highly desirable for stable power supply, good system reliability and high energy extraction efficiency. This thesis investigates the power generation and conversion systems, with the concentrations on the long-term operation cost, full-power-range efficiency and power quality of power electronic converters, for wind, solar and wave energy applications. The story starts with a hybrid wind-solar energy system design targeting at improving energy yield and system reliability. Wind energy and solar energy, as two complementary energy resources, are combined in a single energy system that features improved energy supply stability and reduced energy storage requirement. Special adaptive energy extraction maximisation algorithms are developed for energy generators in order to increase the energy extraction efficiency. The overall energy cogeneration system can offer high productivity and robustness under varying weather conditions. In the second part of this thesis, a bidirectional DC-AC converter based on the well-established Silicon (Si) based two-level circuit and the emerging Silicon Carbide (SiC) based three-level circuit is investigated, with the motivation to enhance the full-power-range efficiency in renewable energy generation and conversion systems. The SiC based circuit is advantageous especially under low-power conditions due to its low switching losses. The costs of power electronics, especially the power semiconductor devices, are taken into account. The Si based circuit provides a more cost-effective option and lower conduction losses under high-power conditions to further improve the overall energy conversion efficiency. All these benefits are integrated in a single converter called hybrid level-matching (HLM) converter, which is comprised of parallel-connected SiC and Si based circuits. A model predictive control (MPC) algorithm is developed to assist the switching state selection for minimised power losses across the full power range. The proposed HLM converter shows similar power control quality and better full-power-range efficiency compared to its conventional counterparts. The operation of the HLM converter under the proposed MPC controller is experimentally verified by a lab-scale demonstrator. The final part of this thesis focuses on the control of an existing flying capacitor based multilevel converter known as stacked multicell converter (SMC). Considered as a superior DC-AC converter candidate in renewable energy standalone load applications, SMC can be controlled under different capacitor voltage ratios to increase the output voltage resolution. This is studied to explore the potential to improve power control quality within the same SMC circuit by applying different capacitor voltage set-points. The capacitor voltage balancing and the basic three-phase current control are achieved by means of a space vector based MPC algorithm. A method to reduce the computational burden by shrinking the space vector candidate size is proposed. The trade-off between capacitor voltage balancing and current reference tracking poses a major challenge to the SMC in its flexibility in capacitor voltage ratio choice. This is investigated in detail to verify the feasibility to reduce load harmonic distortion by modifying the traditional capacitor voltage ratio in a SMC with three stacked cells