Generalized Harmonic Injection Strategy for Dynamic Pole Reconfiguration of a Multiphase Induction Machine

QC 20250513

Abstract

The rapid evolution of electrification across industries demands electric machines that combine high efficiency, adaptability, and a large operating range. Traditional induction machine (IM), constrained by fixed winding configurations and static operating characteristics, struggle to meet these dynamic requirements over the wider operational range demanded by the application. This thesis addresses these limitations by pioneering dynamic pole reconfiguration of multiphase IMs, leveraging control frameworks and modeling techniques to unlock flexibility and performance.

Central to this thesis is the vector space decomposition (VSD) mathematical framework, which decomposes the electrical variables of machines into orthogonal vector spaces, allowing for the separation of space harmonics. These independent vector spaces enable the dynamic control of magnetic pole pairs through magnetic pole pair transition (MPT) theory. This capability allows a single machine to emulate a ”virtual gearbox,” transforming its torque-speed profile from one pole pair configuration to another in real-time without requiring physical winding reconfiguration. For instance, a 9-phase multiphase IM can transition from a 1-pole pair configuration for high-speed operation to a 3-pole pair configuration for high-torque demands, expanding the torque-speed operational range to suit diverse applications.

A critical contribution of this work is its robust approach to parameter identification. Traditional methods rely on time-consuming finite element analysis (FEA) and static laboratory tests. The thesis introduces a methodology for translating equivalent circuit parameters of the multiphase IM in a known pole pair winding configuration to any target pole pair winding configuration. Additionally, the research addresses practical challenges such as converter non-linearities, proposing converter parameter identification and compensation algorithm that reduces voltage drop errors, ensuring reliable control under practical operating conditions.

One of the cornerstones of this thesis is generalized harmonic injection (GHI), a groundbreaking control strategy developed in this work. GHI optimizes torque density by strategically injecting harmonic currents into multiple subspaces while synchronizing their stator frequencies to mitigate the adverse effects of inter-plane cross-coupling (IPXC), which otherwise could cause beat-frequency oscillations resulting in large torque ripple. This enables the possibility of loss reduction by minimizing the stator current for any given operating point of the multiphase IM. Furthermore, smooth reference frame transition (SRFT) extends the GHI to achieve ripple-free pole pair transition (RFPT). The synchronization strategy proposed in this thesis suppresses these beat-frequency oscillations and torque ripples, thereby improving the performance of the multiphase IM during pole pair transitions. Experimental validation on a 9-phase test bench demonstrated the efficacy of GHI, and results show a significant reduction in measured torque ripples.

The findings of this research have far-reaching effects in various industries. In electric mobility, RFPT enables vehicles to seamlessly switch between high torque urban driving and high-efficiency highway cruising, thereby improving the vehicle’s energy efficiency. Renewable energy systems, such as wind turbines, leverage adaptive pole pair numbers to optimize power generation across fluctuating wind speeds. As industries worldwide transition to greener technologies, the methodologies and insights presented here can serve as a cornerstone for the electric machines of tomorrow.

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