A multiphase induction machine model using vector space decomposition provides insights into many space harmonics through decoupled reference frames. In order to utilize this potential of the multiphase machine, the parameters of each vector space must be identified. These parameters are usually identified using standard no-load and locked rotor tests of each torque-producing vector space. However, these tests do not provide a method for identifying stator leakage inductances, which have comparable magnitudes to the magnetizing inductances for higher-order vector spaces. Thus, the magnetizing current cannot be neglected during the locked-rotor test. This paper proposes an accurate method for identifying the T-model parameters of a multiphase induction machine, which can be conveniently translated into the model of choice. The proposed method use harmonic relations to segregate the stator leakage inductance from the total stator inductance, enabling accurate locked-rotor and partial-load tests for the measurement of rotor side parameters. Lastly, a 9-phase induction machine is used for the evaluation of the proposed parameter measurement method. These measured parameters are used for the field-oriented control of each torque-producing vector space, whose performances are analyzed by quantifying the measured output torque error and linearity.

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.

Den snabba utvecklingen av elektrifiering inom olika industrier kräver elektriska maskiner som kombinerar hög effektivitet, anpassningsförmåga och ett stort driftområde. Traditionella (IM), begränsade av fasta lindningskonfigurationer och statiska driftkarakteristiker, har svårt att möta dessa dynamiska krav över det bredare driftområde som applikationen kräver. Denna avhandling tar itu med dessa begränsningar genom att introducera dynamic pole reconfiguration i multiphase induction machine (IM), och utnyttjar styrningsramverk och modelleringsmetoder för att frigöra flexibilitet och prestanda. 

Centralt i denna avhandling är den matematiska vector space decomposition (VSD), som delar upp maskiners elektriska variabler i ortogonala vektorrum, vilket möjliggör separering av rymdharmoniska komponenter. Dessa oberoende vektorrum möjliggör dynamisk kontroll av magnetiska polpar genom teorin om magnetic pole pair transition (MPT). Denna kapabilitet gör att en enda maskin kan fungera som en ”virtuell växellåda och omvandla sitt moment-hastighetsförhållande från en polparskonfiguration till en annan i realtid utan att kräva fysisk lindningsomkonfiguration. Till exempel kan en nio-fasig flerfasig IM växla från en enpolsparskonfiguration för hög hastighet till en trepolsparskonfiguration för hög momentkrav, vilket utökar moment-hastighetsområdet för att passa olika applikationer. 

En kritisk insats i detta arbete är dess robusta metod för parameteridentifiering. Traditionella metoder är beroende av tidskrävande finite element analysis (FEA) och statiska laboratorietester. Avhandlingen introducerar en metodologi för att övers ätta ekvivalenta kretsparametrar hos den multiphase IM i en känd polparslindningskonfiguration till en målad polparskonfiguration. Dessutom tar forskningen itu med praktiska utmaningar såsom omvandlarnonlineariteter, och föreslår en identifieringsoch kompensationsalgoritm för omvandlarparametrar som minskar spänningsfallfel, vilket s äkerställer tillförlitlig kontroll under praktiska driftförhållanden. 

En av hörnstenarna i denna avhandling är generalized harmonic injection (GHI), en banbrytande styrningsstrategi utvecklad inom detta arbete. GHI optimerar momenttäthet genom att strategiskt injicera harmoniska strömmar i flera delrum samtidigt som deras statorfrekvenser synkroniseras för att mildra de negativa effekterna av inter-plane cross-coupling (IPXC), vilket annars skulle kunna orsaka svängningar med slagfrekvens och därigenom stora momentvariationer. Detta möjliggör även förlustreducering genom att minimera statorströmmen vid varje givet driftläge för den multiphase IM. Dessutom utvidgar smooth reference frame transition (SRFT) GHI för att uppnå ripple-free pole pair transition (RFPT). Synkroniseringsstrategin som föreslås i denna avhandling undertrycker dessa slagfrekvenssvängningar och momentvariationer, vilket förbättrar prestandan hos den multiphase IM under polparstransition. Experimentell validering på en nio-fasig testbänk visade effekten av GHI, och resultaten visar en betydande minskning av uppmätta momentvariationer. 

Resultaten av denna forskning har långtgående effekter inom olika industrier. Inom elektrisk mobilitet möjliggör RFPT att fordon sömlöst kan växla mellan högt moment för stadskörning och hög effektivitet för motorvägskörning, vilket förbättrar fordonets energieffektivitet. Förnybara energisystem, såsom vindkraftverk, utnyttjar anpassningsbara polparsnivåer för att optimera elproduktionen över varierande vindhastigheter. När industrier över hela världen övergår till grönare teknologier kan de metoder och insikter som presenteras här utgöra en grundsten för framtidens elektriska maskiner. 

Induction machine-based multiphase electrical machines combine the robustness and reliability of well-known induction machines with the benefits of additional degrees of freedom, such as potential higher torque density and true fault tolerance. The subcategory of variable phase-pole machines allows extending the operational torque and speed range with the same voltage and current limits by changing the number of magnetic poles through control without hardware reconfiguration. Maintaining the torque throughout the operation is vital for many applications. The question of maintaining torque during a pole transition still needs to be answered, especially concerning the electric limitations. This paper's proposed pole transition strategy minimizes the torque dip during the pole transition. Field weakening is added to the control scheme to accommodate the voltage limitation. Experimentally controlled, loaded, and scheduled pole transitions demonstrate the capabilities of the proposed strategy with and without voltage limitation.

A multiphase induction machine (MPIM) modeled using vector space decomposition (VSD) provides insight into space harmonics which are segregated into vector spaces. Depending on the winding configuration of the MPIM, some vector spaces can produce torque in addition to the fundamental vector space, and they can be represented by a standard equivalent circuit (EC) of an induction machine (IM). This paper evaluates multiple EC parameters identification methods (IDMs) and proposes a robust IDM routine for their accurate estimation. Furthermore, the proposed IDM routine shows reduced sensitivity to errors in known parameters compared to the standard IDMs, which is validated with the help of a detailed simulation model of a 9-phase IM.

Magnet-free variable phase-pole machines are competitive alternatives in electric vehicles where torque-speed operating region, reliability, cost, and energy efficiency are key metrics. However, their modeling and control have so far relied on existing fixed-phase and pole-symmetrical models, limiting their drive capabilities especially when switching the number of poles on the fly. This paper establishes the harmonic plane decomposition theory as a space-discrete Fourier transformation interpretation of the Clarke transformation, decomposing all pole-pair fields into a fixed number of orthogonal subspaces with invariant parameters. The model remains unaltered for all phase-pole configurations, guaranteeing continuity even under phase-pole transitions. Relations of the state and input space vectors, and model parameters to those of the vector space decomposition theory used for multiphase machines are established via the use of the complex winding factor. Experiments confirm the modeling theory and demonstrate its practical usefulness by performing a field-oriented-controlled phase-pole transition. Non-trivial configurations with more than one slot/pole/phase and a fractional phase number are also demonstrated.

A multiphase induction machine model using vector space decomposition provides insights into many space harmonics through decoupled reference frames. These decoupled reference frames host specific space vectors related to particular space harmonics. Based on the physical winding configuration, these vector spaces can be excited independently and simultaneously for the production of torque. However, this approach may result in beat oscillations due to interference between excited vector spaces if proper synchronization of vector spaces is not maintained. This paper describes this phenomenon through experimental tests. Furthermore, a solution eliminating the beat oscillations is proposed while optimizing the stator current or rotor flux linkage peaks. The effectiveness of the solution is experimentally verified on a 9-phase  induction machine. 

Multiphase converters are usually composed of several standard 3-phase converters containing Intelligent Power Modules (IPMs). These 3-phase IPM have 6 sets of IGBT-diode pairs having similar switching properties. However, switching properties and/or forward voltage drops of different IPMs can vary significantly, causing an asymmetry in the converter's output. This paper proposes a generic method for identifying these converter asymmetries and estimates an average non-linear voltage drop across each converter leg. These identified voltage drops are experimentally evaluated on a 9-phase multiphase electrical machine (MPEM) supplied from three 3-phase converters, decomposed into four vector spaces and a zero component. With non-linearity correction, the fundamental components of vector spaces 1 and 3 are improved significantly while reducing the rest of the harmonic components.

A multiphase induction machine model using vector space decomposition provides insights into many space harmonics through decoupled reference frames. These decoupled reference frames host specific space vectors related to particular space harmonics. Based on the physical winding configuration, these vector spaces can be excited independently or simultaneously for the production of torque. Each torque-producing vector space generates a unique number of magnetic pole pairs and has independent torque-slip characteristics. In most literature, the transition between these magnetic pole pairs is achieved by magnetizing a desired vector space and then performing the torque transition. This approach results in beat oscillations due to interference between magnetized vector spaces. This paper proposes a solution that eliminates these beat oscillations during magnetic pole-pair transition while optimizing the stator current peaks. The effectiveness of this synchronized phase- pole modulation solution is experimentally verified on a 9-phase induction machine in comparison to the standard magnetic pole-pair transition methods.

A multiphase induction machine model using vector space decomposition provides insights into many space harmonics through decoupled reference frames. These decoupled reference frames host specific space vectors related to particular space harmonics. Based on the physical winding configuration, these vector spaces can be excited independently or simultaneously for the production of torque. Each torque-producing vector space generates a unique number of magnetic pole pairs and has independent torque-slip characteristics. In most literature, the transition between these magnetic pole pairs is achieved by magnetizing a desired vector space and then performing the torque transition. This approach results in beat oscillations due to interference between magnetized vector spaces. This paper proposes a solution that eliminates these beat oscillations during magnetic pole-pair transition while optimizing the stator current peaks. The effectiveness of this synchronized phase-pole modulation solution is experimentally verified on a 9-phase induction machine in comparison to the standard magnetic pole-pair transition methods. 

A multiphase induction machine model using vector space decomposition or harmonic plane decomposition provides insights into many space harmonics through decoupled reference frames, each hosting specific space vectors related to particular harmonics. The dynamics of each voltage and current space vector are described by an equivalent circuit, whose parameters must be obtained either by finite-element analysis or laboratory measurements. This paper presents and experimentally verifies a methodology for calculating these parameters from a single configuration, with minimal knowledge of the geometrical dimensions of the machine.