This article introduces a sensorless control strategy for a seven-phase induction motor drive, leveraging the inherent degrees of freedom in multiphase systems. The proposed approach relies on injecting a low-frequency current to excite the third spatial harmonic of the magnetic field in the air gap. This excitation facilitates the estimation of the third spatial harmonic component of the flux linkage. The injection of a low-frequency current enables the estimation of the rotor flux position at zero and very low speeds without torque ripple, which is an essential requirement for the reliable operation of sensorless drives. The experimental tests conducted under different operating conditions confirm the robustness of the proposed solution, as well as its dynamic response and stable behavior at zero and low speeds.

DC-link current harmonics and common mode voltage (CMV) are key design challenges for inverter-based power electronic systems. Addressing them collectively without additional hardware and/or complexity has promising advantages. This article investigates the interleaved utilization of modified space vector PWM schemes for parallel-inverter systems, targeting a combined and simultaneous reduction of these quality concerns. A time-domain analytical dc-link current formulation and a new application of sequence-based interleaving are combined in an offline numerical optimization algorithm that locates optimal interleaving shifts synced with the PWM sequence. With simulation and experimental validation, the corresponding numerical results ascertain an effective suppression of dc-link current harmonics alongside CMV reduction. In addition, this article extends the proposed idea to a special application for 3x multiphase machines through experimental validation.

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.

Variable phase-pole machines possess the capability to expand their operational range by employing magnetic pole change while adhering to the same electrical voltage and current limits. This article proposes a strategy to achieve a pole change with constant torque while simultaneously optimizing current distributions for stator copper loss minimization. The overall outcome is the ability to facilitate smooth $dq0$ current transitions while reducing the energy consumption of variable phase-pole machine drives. Experimental results affirm the efficacy of this approach during the pole change process.

This work proposes a variable switching frequency scheme for a flying capacitor multilevel (FCML) converter in dc-ac operation to better utilize the output inductor for its rated peak-to-peak current ripple and substantially reduce converter losses over the ac line cycle. The proposed technique holds the inductor current ripple constant by leveraging the duty-cycle dependent inductor current ripple, and variably changes the switching frequency to hold this constant at its rated design value. Practical lower switching limits are taken into consideration in developing this approach, and experimental results validate the feasibility in a common micro-controller framework. Hardware results are provided for a 400 Vdc to 240 Vrms 6-level FCML inverter and showcase loss reductions on the order of 10 − 35% across the measured power range, compared to conventional control with fixed frequency operation.

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. 

With falling semiconductor prices, multiphase electrical machines are gaining more attention from academic and industrial research. So-called variable-pole machines are multiphase induction machines with squirrel cage rotors with the ability to be excited with a different number of magnetic pole pairs. Using this kind of machines can reduce the total cost of ownership of an electrical drive, mainly through reduction of the cost of running and the cost of NOT running. The omission or reduction of the mechanical gear has the potential to increase the overall system efficiency. Moreover, the additional degrees of freedom allow for true fault tolerance.

This work first introduces the harmonic plane decomposition theory for a unified machine model independent of the excitation of the variable-pole machine. This allows continuous modeling in any condition without model discontinuity. Based on the harmonic plane decomposition, this work presents vector control schemes. Subsequently, it presents pole transition strategies generating the control references for minimum torque dip pole transitions. Moreover, flux weakening during the pole transition maintains the voltage within the drive’s limits.

Next, this work presents the harmonic-plane-decomposition fault detection, a fast, non-invasive, and computational lean fault detection for variable pole machines. By leveraging the additional degrees of freedom due to the increased amount of independent currents, the fault detection shifts partially from information over time to information over space. It continues by demonstrating a pole transition under faulty conditions by adapting a minimum stator copper losses current injection post fault control such that it can carry out a pole transition. In this way, true fault tolerance is achieved.

Lastly, this work also shows a sensorless operation of a multiphase electrical machine capable of operation at low and zero speeds. This is achieved by separating the torque generation and the sensorless observer in different harmonic planes as well as introducing feedback for all estimated state variables.

This work shows technical solutions to take advantage of all independent currents in a variable-pole machines. Applying these techniques in a drive system poses electrical drives with such machines as a viable option for industrial and traction applications.

Med sjunkande priser på halvledare får flerfasiga elektriska maskiner mer uppmärksamhet inom akademisk och industriell forskning. Så kallade variabelpoliga maskiner är flerfasiga induktionsmaskiner med burrotorer som kan exciteras med olika antal av magnetiska polpar. Användning av denna typ av maskiner kan minska den totala ägandekostnaden för en elektrisk drivenhet, främst genom minskning av kostnaden för att köra och kostnaden för att INTE köra. Utelämnandet eller minskningen av den mekaniska växeln har potential att öka den totala systemeffektiviteten. Dessutom möjliggör de ytterligare frihetsgrader en sann feltolerans.

Detta arbete introducerar först teorin om harmonisk planedekomposition för en enhetlig maskinmodell oberoende av variabel-polmaskinens excitation. Detta möjliggör en kontinuerlig modellering under alla förhållanden utan modelldiskontinuitet. Baserat på harmonisk planedekomposition presenterar detta arbete vektorstyrningsmetoder. Därefter presenteras strategier för polövergång som genererar styrreferenser för minimala momentdipolövergångar. Dessutom bibehåller fältsförsvagning under polövergången spänningen inom driftens gränser.

Därefter presenterar detta arbete feldetektering med harmonisk plan dekomposition feldetektering, en snabb, icke-invasiv och beräkningsmässigt enkel feldetektering för variabelpoliga maskiner. Genom att utnyttja de ytterligare frihetsgraderna på grund av den ökade antalet oberoende strömmar, skiftar feldetekteringen delvis från information över tid till information över rum. Arbetet fortsätter med att demonstrera en polövergång under felaktiga förhållanden genom att anpassa en ströminjektion för minimala kopparförluster i statorn, så att den kan utföra en polövergång. På så sätt uppnås sann feltolerans.

Slutligen visar detta arbete också en sensorlös drift av en flerfasig elektrisk maskin som kan arbeta vid låga hastigheter och nollhastigheter. Detta uppnås genom att separera momentgenereringen och den sensorlösa observatören i olika harmoniska plan samt genom att införa återkoppling för alla uppskattade tillståndsvariabler.

Detta arbete presenterar tekniska lösningar för att dra nytta av alla oberoende strömmar i variabel-polmaskiner. Att tillämpa dessa tekniker i ett drivsystem gör elektriska drivsystem med sådana maskiner till ett livskraftigt alternativ för industriella och dragapplikationer.

The Clarke transformation is mathematically a Vandermonde matrix of a discrete Fourier transformation. Its purpose is to transform space-vector quantities in the space domain. One necessary condition is that the base function forms an n-th root of unity. This condition translates into requiring all sampling points to be equally spaced. However, manufacturing constraints and imperfections in electric machines may result in non-equally spaced magnetic axes, especially in the case of multiphase electrical machines, making the conventional inverse Clarke transformation used in classic vector control inaccurate. The mathematical inverse Clarke transformation solves this issue, and the existence of this matrix is always ensured. This avoids additional control action and for model predictive controllers, an accurate model is crucial. Analytical results and a simple experimental validation on a multiphase induction machine show the improvements introduced by changing the transformation matrix.

The Clarke transformation is mathematically a Vandermonde matrix of a discrete Fourier transformation. Its purpose is to transform space-vector quantities in the space domain. One necessary condition is that the base function forms an n-th root of unity. This condition translates into requiring all sampling points to be equally spaced. However, manufacturing constraints and imperfections in electric machines may result in non-equally spaced magnetic axes, especially in the case of multiphase electrical machines, making the conventional inverse Clarke transformation used in classic vector control inaccurate. The mathematical inverse Clarke transformation solves this issue, and the existence of this matrix is always ensured. This avoids additional control action and for model predictive controllers, an accurate model is crucial. Analytical results and a simple experimental validation on a multiphase induction machine show the improvements introduced by changing the transformation matrix.