On the Modeling, Analysis and Development of PMSM: For Traction and Charging Application

Permanent magnet synchronous machines (PMSMs) are widely implemented commercially available traction motors owing to their high torque production capability and wide operating speed range. However, to achieve significant electric vehicle (EV) global market infiltration in the coming years, the technological gaps in the technical targets of the traction motor must be addressed towards further improvement of driving range per charge of the vehicle and reduced motor weight and cost. Thus, this thesis focuses on the design and development of a novel high speed traction PMSM with improved torque density, maximized efficiency, reduced torque ripple and increased driving range suitable for both traction and integrated charging applications. First, the required performance targets are determined using a drive cycle based vehicle dynamic model, existing literature and roadmaps for future EVs. An unconventional fractional–slot distributed winding configuration with a coil pitch of 2 is selected for analysis due to their short end–winding length, reduced winding losses and improved torque density. For the chosen baseline topology, a non–dominated sorting genetic algorithm based selection of optimal odd slot numbers is performed for higher torque production and reduced torque ripple. Further, for the selected odd slot–pole combination, a novel star–delta winding configuration is modeled and analyzed using winding function theory for higher torque density, reduced spatial harmonics, reduced torque ripple and machine losses. Thereafter, to analyze the motor performance with control and making critical decisions on inter–dependent design parameter variations for machine optimization, a parametric design approach using a novel coupled magnetic equivalent circuit model and thermal model incorporating current harmonics for fractional–slot wound PMSMs was developed and verified. The developed magnetic circuit model incorporates all machine non–linearities including effects of temperature and induced inverter harmonics as well as the space harmonics in the winding inductances of a fractional–slot winding configuration. Using the proposed model with a pareto ant colony optimization algorithm, an optimal rotor design is obtained to reduce the magnet utilization and obtain maximized torque density and extended operating range. Further, the developed machine structure is also analyzed and verified for integrated charging operation where the machine’s winding inductances are used as line inductors for charging the battery thereby eliminating the requirement of an on–board charger in the powertrain and hence resulting in reduced weight, cost and extended driving range. Finally, a scaled–down prototype of the proposed PMSM is developed and validated with experimental results in terms of machine inductances, torque ripple, torque–power–speed curves and efficiency maps over the operating speed range. Subsequently, understanding the capabilities and challenges of the developed scaled–down prototype, a full–scale design with commercial traction level ratings, will be developed and analyzed using finite element analysis. Further recommendations for design improvement, future work and analysis will also be summarized towards the end of the dissertation

Control of a nine-phase symmetrical PMSM with reduced rare earth material

The rising demand for high-power fault-tolerant applications such as wind generators and electric vehicles, alongside the desire to achieve better performance, have directed the interests of many research centres around the world towards electric drive configurations comprising AC machines with more than three stator phases. These so-called multiphase machines have become well recognized as an attractive alternative to the conventional three-phase machines and are used when the three-phase counterpart cannot provide a drive system with the desired performance. The Thesis examines advanced control possibilities for multiphase surface-mounted permanent magnet synchronous machines (PMSMs). Although it is well-known that permanent magnet machines are today the first choice in many applications and that their market is anticipated to catch up with the induction machines market in the near future, the main drawbacks of this machine type are the relatively high capital costs, the security of magnet supply and the environmental costs associated with the rear-earth magnet materials used in the rotor construction. This has motivated researchers to investigate methods to reduce the amount of rare earth material used in the construction of these machines. If the amount of permanent magnet material is reduced, this will inevitably result in a machine which produces lower electromagnetic tor que. On the other hand, the additional degrees of freedom, present in multiphase systems, can be exploited to inject, into the stator windings, harmonic current(s) to enhance the developed torque. This work analyses a new nine-phase symmetrical PMSM with two surface mounted magnet poles on the rotor with a shortened span. This simple design produces a highly non-sinusoidal back-electromotive force (back-EMF) comprising high third and fifth harmonic components. It is shown that these harmonic components can be utilised to boost the torque to near the value obtainable with full span magnets, provided a suitable control system is developed. The developed control algorithm is based on the well-known vector space decomposition (VSD) and classic field-oriented control methods. To test the developed control algorithm, phase domain machine model is presented first, for both sinusoidal and non-sinusoidal back-EMF distributions. To transform variables from one reference frame to another, the VSD and rotational transformations are used. The optimal ratios between fundamental and other harmonic current components are derived using the maximal torque-per-Ampere (MTPA) theory. It is shown that, by using optimal current injection, the electromagnetic torque can be improved by 36% with third harmonic only, and, up to 45% with a combination of the fundamental, the third and the fifth harmonics. Simulation results are validated in finite element method software and afterwards verified experimentally using an experimental prototype. Control of the PMSM is next expanded with position sensor fault-tolerant capability. For this purpose, the same EMF spectrum is used. When harmonic current elimination is performed in x-y subspace, remaining hth harmonic order back-EMF can be efficiently used for position angle and speed estimation. For the estimation purpose, phase-locked-loop method is employed. With estimated position/speed, a new control algorithm is devised, which combines control in two auxiliary subspaces with the control of the first plane. The third harmonic is, in combination with the fifth, used for the torque boost prior to the fault, while afterwards, the fifth EMF harmonic enables position estimation for position-sensorless control. Hence, previously stated maximal torque improvement is preserved until position sensor fault is detected, while afterwards machine continues to operate in position-sensorless mode still with partial enhancement of the torque. Control is verified experimentally. Finally, operation in the flux-weakening region is investigated. Because finding sets of multiple harmonic current references which maximize torque by taking into account voltage and current limits leads to a difficult problem to formulate, which is often impossible to solve analytically, the work presented here builds on (offline) numerical optimisation procedure. To obtain best performance, harmonics up to the (and including) fifth are considered. Limitation of voltage is achieved by comparing measured phase-to-phase voltage with maximal dc-link voltage, while thermal (RMS) constraint and inverter switch (peak) current constraint are taken into account by limiting the current. In such scenario, maximal reachable speed is much higher than the base speed, while respecting at the same time both machine and inverter constraints

General Torque Enhancement Approach for a Nine-Phase Surface PMSM with Built-in Fault Tolerance

The paper investigates maximum possible torque improvement in a two-pole surface permanent magnet synchronous machine (PMSM) with a reduced magnet span, which causes production of highly non-sinusoidal back-EMF. It contains a high third and fifth harmonics, which can be used for the torque enhancement, using stator current harmonic injection. Optimal magnet span is studied first and it is shown that with such a value the machine would be able to develop an insignificantly lower maximum torque than with the full magnet span. Next, field-oriented control (FOC) algorithm, which considers all non-fundamental EMF components lower than the machine phase number, is devised. Using maximum-torque per Ampere (MTPA) principles, optimal ratios between fundamental and all other injected components are calculated and then used in the drive control. The output torque can be in this way increased up to 45% with respect to the one obtainable with fundamental current only. Alternatively, for the same load torque, stator current RMS value can be reduced by 45%. Last but not least, a method for position sensor fault mitigation is introduced. It is based on the alternative use of a back-EMF harmonic for rotor position estimation, instead of the torque enhancement. Experimental verification is provided throughout for all the relevant aspects

Optimal Third-Harmonic Current Injection for Asymmetrical Multiphase Permanent Magnet Synchronous Machines

This article proposes a modeling approach and an optimization strategy to exploit a third-harmonic current injection for the torque enhancement in multiphase isotropic permanent magnet synchronous machines with nonsinusoidal back electromotive forces. The modeling approach is based on a proper vector space decomposition and on the associated rotational transformation, aimed to properly select a set of stator current space vectors to be controlled. It is presented for a generic (i.e., asymmetrical, with an arbitrary angular shift) winding configuration. The injection strategy is related to the choice of a constant synchronous current set aimed at minimizing the average stator winding losses for a given reference torque by using the first and the third spatial harmonics of the air-gap flux density. The optimal solution has been found analytically and has been developed in detail for a selected set of asymmetrical winding configurations. Both the numerical and experimental results are in good agreement with the theoretical analysis

Optimal Third-Harmonic Current Injection for Asymmetrical Multiphase PMSMs

The paper proposes a modelling approach and an optimization strategy to exploit a third harmonic current injection for the torque enhancement in multiphase isotropic PMSMs with non-sinusoidal back-EMFs. The modelling approach is based on a proper vector space decomposition and on the associated rotational transformation, aimed to properly select a set of stator current space vectors to be controlled. It is presented for a generic (i.e. asymmetrical, with an arbitrary angular shift) winding configuration. The injection strategy is related to the choice of a constant synchronous current set, aimed at minimizing the average stator winding losses for a given reference torque by using the 1st and the 3rd spatial harmonics of the air-gap flux density. The optimal solution has been found analytically and has been developed in detail for a selected set of asymmetrical winding configurations. Both the numerical and experimental results are in good agreement with the theoretical analysis

General Torque Enhancement Approach for a Nine-Phase Surface PMSM with Built-in Fault Tolerance

The paper investigates maximum possible torque improvement in a two-pole surface permanent magnet synchronous machine (PMSM) with a reduced magnet span, which causes production of highly non-sinusoidal back-EMF. It contains a high third and fifth harmonics, which can be used for the torque enhancement, using stator current harmonic injection. Optimal magnet span is studied first and it is shown that with such a value the machine would be able to develop an insignificantly lower maximum torque than with the full magnet span. Next, field-oriented control (FOC) algorithm, which considers all non-fundamental EMF components lower than the machine phase number, is devised. Using maximum-torque per Ampere (MTPA) principles, optimal ratios between fundamental and all other injected components are calculated and then used in the drive control. The output torque can be in this way increased up to 45% with respect to the one obtainable with fundamental current only. Alternatively, for the same load torque, stator current RMS value can be reduced by 45%. Last but not least, a method for position sensor fault mitigation is introduced. It is based on the alternative use of a back-EMF harmonic for rotor position estimation, instead of the torque enhancement. Experimental verification is provided throughout for all the relevant aspects

Modeling And Analysis Of Multi–Phase Permanent Magnet Synchronous Machines: Direct–Drive Electric Vehicle Application

In commercially existing electric vehicles (EVs), power is transferred from the motor to the wheels through a fixed gear mechanical transmission system. However, such a transmission system contributes to a power loss between 2% to 20% of output power of the motor depending on the operating speed and torque of the motor. Therefore, by removing the transmission, a direct–drive EV configuration is obtained with lower component count, improved motor to wheel efficiency and frequency dependent losses. However, challenges in developing a single on–board permanent magnet synchronous machine (PMSM) for such a configuration include high torque density, low torque ripple and high torque per permanent magnet (PM) volume. Therefore, this dissertation proposes a novel PMSM addressing the aforementioned challenges for a direct–drive application. Initially, the design targets, stator and rotor configuration and phase numbers of the PMSM are chosen to satisfy the requirements of a direct drive application. A novel torque and torque ripple model based on multiple reference frames is proposed, in which the torque ripple from spatial harmonics of flux, inductances and the time harmonics of stator currents are included. Using the analytical model, optimal slot–pole combination of the machine is selected based on adaptive gradient descent algorithm. A new consequent pole rotor topology is proposed to improve the torque density and torque per PM volume thereby reducing the usage of expensive rare earth magnets. The proposed PMSM with novel rotor is further improved in terms of torque density, losses and cost by performing an intensive structural optimization based on novel hybrid analytical model, finite element analysis and supervised learning. The optimized PMSM is then analyzed for various drive cycles and performance in terms of torque, speed and efficiency are discussed. A scaled–down prototype of the proposed PMSM is developed and comprehensive experimental analysis in terms of torque ripple, torque–speed characteristics and efficiency are performed under different speeds and load conditions and are compared with the results obtained from proposed analytical model

Optimal Design of a Five-phase External Rotor Permanent Magnet Machine for Convey Application

This paper proposes the design and development of a five-phase external rotor permanent magnet synchronous machine (PMSM) which is used for direct drive convey application. Firstly, the slot/pole combination of fraction slot concentrated winding (FSCW) is selected according to four criteria, which are the least common multiple (LCM) and the greatest common divisor (GCD), the winding factor and the MMF distribution; secondly, based on the design requirement, an analytical model of the proposed machine topology is built, and the initial machine parameters are then obtained; thirdly, the machine is optimized by combing the finite element model and the Kriging model, and the final optimal results are compared to the initial one. Detail design principles and performance characteristics of the proposed machine topology are presented and validated with finite element models

Integrated drive and reliabilities: fault tolerant architectures and supply

One major challenge of e-aerospace motor is high densities (kW/kg, Nm/kg) keeping a high functional reliability. With high switching frequency Voltage Source Inverter (VSI) using Wide-Band Gap (WBG) components, the DC-bus capacitor mass can be reduced. On contrary, because of very short commutation time (<50ns), the requirements for the connexion between VSI and machine terminals are higher. For a better proficiency, the integration of VSI inside the machine is then desirable. Besides, with WBG components, the temperature limit of the VSI is becoming higher than 150°C and consequently close to those of machines, favouring a common cooling and so, mass reduction. Finally, in integrated drive, the major drawback of fault-tolerant multiphase machines due to numerous external cables is alleviated. In order to benefit of this evolution, new topologies of integrated drive can be imagined. The paper examines different candidates of multiphase machines for integration and proposes an original topology taking into account simultaneously different constraints and opportunities

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