Natee Limsuwan

Design and Evaluation of a Variable-Flux Flux-Intensifying Interior Permanent-Magnet Machine

This paper presents a design approach for interior permanent magnet (IPM) machines with variable-flux characteristics using low coercive force magnet material for improved efficiency and extended operating speed range. A flux-intensifying interior permanent (FI-IPM) type having Ld >; Lq is used in the design due to positive Id operation and reduced load Iq effects. Design consideration of machine structures and variable-flux machine attributes are discussed. In addition, leakage flux in a rotor is specially designed to obtain another degree-of-freedom in variable-flux control as well. Evaluation of the designed machine is provided using FEA simulations and experimental evaluation of a proof-of-principle prototype machine. The designed machine shows benefits in improving efficiency and extending the range of the torque-speed map when magnetization level of the low coercive force magnet is operated at the optimal levels.

Rare Earth Reduction Using a Novel Variable Magnetomotive Force Flux-Intensified IPM Machine

This paper presents a novel variable magnetomotive force flux-intensifying interior permanent-magnet (IPM) (VFI-IPM) machine, which uses only low-coercive force magnets to reduce usage of rare earth metals. The VFI-IPM machine is designed with a characteristic of

Novel Design of Flux-Intensifying Interior Permanent Magnet Synchronous Machine Suitable for Self-Sensing Control at Very Low Speed and Power Conversion

L_{d} > L_{q}

Design and evaluation of a variable-flux flux-intensifying interior permanent magnet machine

, which is typical for FI-IPM machines and uses low-coercive force magnets with magnetization level control. A theoretical magnet operating point analysis was conducted to investigate the design methodology. A proof-of-principle prototype machine was then designed based on these principles. Simulation and experimental results show that the VFI-IPM prototype can achieve a wide torque–speed envelope and variable torque–speed characteristics while not requiring high-coercive force magnets that would include far more expensive rare earth materials, such as dysprosium.

Efficiency contours and loss minimization over a driving cycle of a variable-flux flux-intensifying interior permanent magnet machine

This paper proposes a new rotor design for flux-intensifying interior permanent magnet synchronous machine (FI-IPM SM) that is more suitable for self-sensing control at zero/very low speed based on saliency-tracking methods and retains acceptable power conversion capability as compared to a traditional flux-weakening IPM SM (FW-IPM SM). Design steps for the rotor structure of the new machine are laid out and discussed to emphasize key design challenges. The proposed FI-IPM SM and a conventional FW-IPM SM with similar torque-speed capability are made to evaluate performances in power conversion as well as self-sensing capability at very low speed. Finite-element analysis (FEA) is used to evaluate each machines performance. The proposed FI-IPM SM shows less variation in the saliency when the machine is loaded, leading to a possibility of better self-sensing performance at very low speed as compared to the traditional FW-IPM SM. Experimental results on the efficiency and self-sensing performance of these two machines are presented to verify the design methodology.

Efficiency Contours and Loss Minimization Over a Driving Cycle of a Variable Flux-Intensifying Machine

This paper presents a design approach for interior permanent magnet (IPM) machines with variable-flux characteristics using low coercive force magnet material for improved efficiency and extended operating speed range. A flux-intensifying interior permanent (FI-IPM) type having L d > L q is used in the design due to positive I d operation and reduced load I q effects. Design consideration of machine structures and variable-flux machine attributes are discussed. In addition, leakage flux in a rotor is specially designed to obtain another degree-of-freedom in variable-flux control as well. Evaluation of the designed machine is provided using FEA simulations and experimental evaluation of a proof-of-principle prototype machine. The designed machine shows benefits in improving efficiency and extending the range of the torque-speed map when magnetization level of the low coercive force magnet is operated at the optimal levels.

Variable-Flux Machine Torque Estimation and Pulsating Torque Mitigation During Magnetization State Manipulation

In this paper, experimental evaluations for the efficiency of a novel interior permanent magnet (IPM) machine with variable-flux characteristics using low coercive force magnets is presented. The variable-flux characteristics allow improving the efficiency of machine and also reducing the usage of rare-earth material in the high-coercive magnets, which are currently used for the IPM machines in electrified vehicles. A flux-intensifying interior permanent magnet (FI-IPM) type having positive saliency is employed for a positive d-axis current to mitigate a demagnetizing field in the magnet due to a q-axis current. A proof-of-principle machine is designed, fabricated and evaluated. A series of experiments are conducted to capture the efficiency contours with different magnetization states of the low coercive force magnets. The designed machine shows benefits in improving efficiency when the magnetization state is optimally operated. With these results, the loss over a driving cycle is then simulated and the benefits of changing the magnetization state are quantified.

Secondary resistive losses with high-frequency injection-based self-sensing in IPM machines

In this paper, experimental evaluations for the efficiency of a novel interior permanent-magnet (IPM) machine with variable-flux characteristics using low-coercive-force magnets are presented. The variable-flux characteristics allow improving the efficiency of a machine. A flux-intensifying IPM type having positive saliency is employed for a positive d-axis current to mitigate a demagnetizing field in the magnet due to a q-axis current. A proof-of-principle machine is designed, fabricated, and evaluated. A series of experiments are conducted to capture the magnetization and demagnetization properties of the low-coercive-force magnets by applying control d-axis current pulse. The efficiency contours with different magnetization states (MSs) of the magnets are then experimentally obtained. The designed machine shows benefits in improving efficiency when the MS is optimally operated. With these results, the loss over a driving cycle is then simulated, and the benefits of changing the MS are quantified.

Self-Sensing Comparison of Fractional Slot Pitch Winding Versus Distributed Winding for FW- and FI-IPMSMs Based on Carrier Signal Injection at Very Low Speed

This paper focuses on dynamic control, under loaded conditions, of the magnetization state of suitably designed variable-flux (VF) permanent-magnet (PM) machines. Such VF-PM machines have been shown to achieve low loss operation over a wide range of load and speed. For this type of machine, the PM flux linkage varies during the magnetization manipulation process. Published magnetization techniques have occurred at zero load conditions and thus did not generate torque pulsations. However, under loaded conditions, the existing methods would produce unwanted torque pulsation. This paper proposes a parameter insensitive method to solve this issue. This method generates a decoupling current command that is calculated from accurately estimated stator flux linkage. Accurate flux estimation, i.e., insensitive to inductance saturation and PM flux linkage variation (e.g., temperature or magnetization level) is achieved by using the voltage disturbance estimated by a closed-loop stator current vector observer. In both simulations and experiments, it is shown that even during magnetization processes under loaded conditions, the flux can be estimated correctly, and smooth torque output can be achieved.

Design methodology for variable-flux, flux-intensifying interior permanent magnet machines for an electric-vehicle-class inverter rating

This paper investigates the impact of high-frequency injection-based self-sensing on secondary resistive losses associated with the high-frequency carrier component in interior permanent magnet (IPM) machines. Two types of salient machines, the flux-weakening IPM (FW-IPM, Lq > Ld) and the flux-intensifying IPM (FI-IPM, Lq < Ld) are investigated. Simulation with 3D finite-element analysis (FEA) is used to analyze loss characteristics of the machines. Iron losses and eddy-current losses in permanent magnets dominate during high-frequency carrier signal injection. The magnet eddy-current loss is found to be dependent on the magnet locations and sensitive to loading, while the iron loss is dependent on stator and rotor structural designs and less sensitive to loading. This characteristic can be used to improve position and magnet temperature sensing. Experimental evaluation of losses on a built FI-IPM machine is used to evaluate the simulation results.