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Modulation and design for high-efficiency sic-based motor drive systems

Yunus, Suleman ORCID: 2023. Modulation and design for high-efficiency sic-based motor drive systems. PhD Thesis, Cardiff University.
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The need for inverters with ever increasing power density, efficiency and reliability has recently become the driving factor for research in motor drives. Silicon carbide MOSFETs (SiC MOSFETs), a class of wide bandgap semiconductors, mark a substantial leap towards fulfilling this demand. These devices not only reduce the size and weight of passive components but also enhance thermal performance through their capacity for high switching frequencies. However, the adoption of SiC MOSFETs is not without its difficulties; it necessitates the management of increased losses at higher frequencies and the control of overvoltage due to their high voltage slew rate (dv/dt) characteristics. Addressing these challenges, this thesis presents innovative solutions for optimising SiC MOSFET switching frequency and minimising operational impediments due to high dv/dt. This thesis first investigates the enhancement of SiC-based motor drive efficiency via variable switching frequency pulse-width modulation (VSF-PWM). By leveraging accurate motor drive loss modelling, a VSF-PWM method is proposed that determines the optimal switching frequency providing the lowest system losses, contingent on motor speed and torque. Adopting this loss modelling approach to vary the switching frequency leads to a system efficiency improvement of up to 0.3%, which is a notable gain compared to a fixed high-frequency operation. However, the technique also leaves potential for limiting peak current ripple. To address this, an additional VSF-PWM modulation control scheme is subsequently introduced, which adaptively varies the switching frequency in response to both the current ripple magnitude and the established loss model technique. This approach is especially relevant in industries where stringent standards mandate limitations on peak current ripple. In SiC-based cable-fed motor drives, the high dv/dt and impedance mismatches can trigger the reflected wave phenomenon, increasing the risk of motor overvoltage. Such a scenario can hasten the deterioration of the motor stator winding insulation due to partial discharges, jeopardising the system’s longevity and reliability. In response to this, the second part of the thesis presents the use of a zero-voltage switching (ZVS) inverter, designed to actively modulate voltage rise and fall times. Comprehensive guidelines on the selection of inductor and capacitor parameters, aiming for ZVS and overvoltage mitigation, are detailed. Results indicate that the ZVS inverter provides up to a 1% efficiency gain and a 30% volume reduction when compared with alternative solutions. The research work documented in this thesis is underpinned by comprehensive simulations, further validated through experimental results.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: 1).Motor Drives 2).Silicon Carbide 3).MOSFET 4).Permanent Magnet Motors 5).Overvoltage 6).Switching Frequency
Date of First Compliant Deposit: 14 June 2024
Last Modified: 14 Jun 2024 12:44

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