PhD Oral Exam - Bigyan Basnet, Electrical and Computer Engineering
Modeling, Analysis and Control of a Variable Flux Machine
This event is free
School of Graduate Studies
When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
Electric motors are the key elements in electric propulsion systems. The performance of Electric vehicles (EVs) significantly depends on the electric motors. Permanent magnet synchronous machines (PMSMs) with rare-earth magnets are widely used in EV applications because they fulfill most requirements of EV motors. However, low efficiency at high speed, limited resources and fluctuating prices of rare-earth permanent magnets (PMs) have forced industries to develop alternatives to rare-earth machine technologies. Recently, Variable-Flux PMSMs (VF-PMSMs) also known as memory motors have been introduced to overcome the drawbacks of PMSMs. This thesis focuses on the modeling, analysis and control of the Aluminum-Nickel-Cobalt (AlNiCo) magnet-based VF-PMSMs.
This thesis presents the effect of different magnetization pulse widths and methods on the magnetization level, back-EMF and no-load losses of the VF-PMSM. The injection of the magnetization or de-magnetization current pulse will change the magnet flux linkage and back-EMF harmonics. An adaptive nonlinear filter is used to estimate the back-EMF during the motoring mode. The harmonics present in the machine back-EMF due to different magnetization and de-magnetization current pulse widths and magnetization methods are analyzed. Besides, the quality of the back-EMF for different speeds and machine no-load losses are presented for different magnetization states (MSs).
During de-magnetization and re-magnetization, a d-axis current pulse is injected to change the MS. However, the injected d-axis current abruptly changes the magnet flux linkage changing the magnet torque as well as reluctance torque and results in a pulsating torque. To solve this pulsating torque issue, a q-axis current reference during the re-magnetization is determined by two different methods: voltage limit method and load torque method. The derived q-axis current reduces the torque pulsation during the re-magnetization.
A closed-loop current controller-based parameter measurement of VF-PMSMs for different MSs is presented. Automated machine parameters such as flux linkage, inductance and resistance are generated in real-time by the real-time processor.
A co-simulation-based VF-PMSM drive system and loss analysis due to pulse-width modulation (PWM) inverter drive is presented. An integrative simulation approach gives higher fidelity results since it includes magnetic saturation (inductance nonlinearities), machine geometry (torque ripple and spatial harmonics) effects. Besides, the comparative effect of the sinusoidal current and PWM inverter fed VF-PMSM’s losses have been studied. The co-simulation results are validated with the conventional simulation (dq-mathematical model) model, finite element model and experimental results.