This paper presents an indirect vector control scheme with an improved flux pattern using third harmonic injection. The control objective is to independently control both flux and torque and to ...generate a nearly rectangular air-gap flux, resulting in improved machine power density. If there is a proportional relation between the third harmonic and fundamental plane currents, variable misalignment between fundamental and third air-gap flux components occurs with varying mechanical loading. Due to this misalignment, saturation may take place. Accordingly, the total flux is saturated and iron loss increases. Hence, coupling results between different sequence planes. Instead of a proportional relation between the current components, direct and quadrature current components of the injected third harmonic current reference are a function of the fundamental direct and quadrature reference current components, respectively. These functions ensure that the air-gap flux is near rectangular with a maximum value of 1 p.u. from no load to full load. Moreover, this controller guarantees complete decoupling between the sequence planes. An eleven-phase induction machine is used to validate the proposed controller experimentally, while supporting simulation results and theoretical analysis use both MATLAB and finite element platforms.
This article presents the operation of onboard integrated battery chargers tied to a nine-phase EV-drive train, shedding light on the charging performance during the postfault operation, when one or ...more faulty inverter legs are disconnected. The objective in that case is to ensure balanced grid currents, while maintaining minimum machine losses at zero average torque production. The proposed concept requires a minimalistic change from a control structure perspective to switch between the pre- and postfault cases. Limitations and fault cases are discussed and corroborated with experimental tests on a 1.5-kW prototype.The derived concept is parameter independent and applicable to nine-phase drives, irrespective of the type of rotor used.
This paper presents the steady-state mathematical model of a five-phase induction machine with a combined star/pentagon connection. The connection splits the stator winding into two five-phase ...windings displaced in space by <inline-formula> <tex-math notation="LaTeX">\pi</tex-math></inline-formula>/10 and connected in a combined star/pentagon configuration. Recent work limited to an experimental investigation demonstrated that the connection possesses improved fault tolerance when compared to a conventional star-connected stator, as well as avoids the pentagon connection problems. Although the machine has five-phase terminals, it is intrinsically an asymmetrical ten-phase machine, which introduces additional subspaces in the machine's mathematical model. In order to theoretically investigate and thoroughly assess this connection against conventional connections, this paper introduces the steady-state mathematical model based on vector space decomposition and symmetrical component theory. Finite-element analysis is first used to investigate the different harmonic current components induced in the cage rotor circuit, upon which the effect of different subspaces can be clarified and the required transformation matrix from phase variables to their sequence components can be derived. The model is verified using a 1-kW prototype five-phase induction machine.
Fractional slot concentrated windings (FSCWs), or modular windings, have shown promise with permanent magnet machines. However, their inability to produce high quality travelling fields has limited ...their application from spreading to induction machines. This paper presents the design considerations and tradeoffs involved in applying FSCWs to five-phase induction machines using the conventional three-phase lap wound machine as a reference. Previous work has touched upon the application of modular windings to three-phase induction machines, concluding that a conventional distributed winding is superior in terms of torque production and rotor bar losses. In applications such as high frequency induction machines and manually wound electrical submersible pump motors, the proposed machine topology provides advantages that may warrant its application despite an apparent power density penalty. In this paper, a prototype five-phase modular winding induction machine designed to significantly reduce the effect of space harmonics is investigated through simulations and experimentally.
Permanent magnet (PM) machines equipped with fractional slot concentrated windings (FSCW) offer a compelling solution for electric vehicles (EVs), boasting high torque and power density, high ...efficiency, a wide operational range, and several other advantageous features. However, faults can impair the magnets' performance, leading to significant issues that negatively affect the EVs' performance and worsen motor reliability. Although fault tolerance can be maintained through innovative control schemes to meet specific performance criteria, these solutions often introduce side issues, such as torque ripple. While extensive studies have focused on mitigating these side issues through control techniques, incorporating solutions at the design stage remains underexplored. This paper presents the design and optimization of a 12-slot / 10-pole permanent magnet synchronous motor (PMSM) aimed at achieving high-quality operation in both healthy conditions and post fault operation under an open-phase fault. A finite element-based multi-objective optimization using a genetic algorithm is proposed to optimize the machine by maximizing average torque and minimizing torque ripple during both healthy operation and in the case of an open phase fault. Embarking on an exploration of diverse rotor topologies and their implications, this study engages in comprehensive theoretical and simulation analyses. The research initiative involves the design and simulation of a 15-kW Interior Permanent Magnet (IPM) motor, crafted to emulate the characteristics of a practical light-duty Electric Vehicle (EV). To validate the conceptual framework, empirical testing is conducted using a 2-kW laboratory-scale Surface-Mounted Permanent Magnet (SPM) motor.
The multiphase induction motor is considered to be the promising alternative to the conventional three-phase induction motor, especially in safety-critical applications because of its inherent ...fault-tolerant feature. Therefore, the attention of many researchers has been paid to develop different techniques for detecting various fault types of multiphase induction motors, to securely switch the control mode of the multiphase drive system to its post-fault operation mode. Therefore, several fault detection methods have been researched and adapted; one of these methods is the indices-based fault detection technique. This technique was firstly introduced to detect open-phase fault of multiphase induction motors. The main advantage of this technique is that its mathematical formulation is straightforward and can easily be understood and implemented. In this paper, the study of the indices-based fault detection technique has been extended to test its applicability in detecting some other stator and rotor fault types of multiphase induction motors, namely, open-phase, open-switch, bad connection and broken rotor bar faults. Experimental and simulation validations of this technique are also introduced using a 1 kW prototype symmetrical six-phase induction motor.
For contemporary variable-speed electric drives, the accuracy of the machine's mathematical model is critical for optimal control performance. Basically, phase variables of multiphase machines are ...preferably decomposed into multiple orthogonal subspaces based on vector space decomposition (VSD). In the available literature, identifying the correlation between states governed by the dynamic equations and the parameter estimate of different subspaces of multiphase IM remains scarce, especially under unbalanced conditions, where the effect of secondary subspaces sounds influential. Most available literature has relied on simple RL circuit representation to model these secondary subspaces. To this end, this paper presents an effective data-driven-based space harmonic model for n-phase IMs using sparsity-promoting techniques and machine learning with nonlinear dynamical systems to discover the IM governing equations. Moreover, the proposed approach is computationally efficient, and it precisely identifies both the electrical and mechanical dynamics of all subspaces of an IM using a single transient startup run. Additionally, the derived model can be reformulated into the standard canonical form of the induction machine model to easily extract the parameters of all subspaces based on online measurements. Eventually, the proposed modeling approach is experimentally validated using a 1.5 Hp asymmetrical six-phase induction machine.
The most recent literature on multiphase machine drives is based on voltage-source converter (VSC) systems utilizing different modulation techniques. Very little attention is given to the multiphase ...current-source converters (CSCs). Applying CSCs in high-power multiphase drive systems is promising and can effectively solve many technical problems associated with conventional VSC-based systems. This paper proposes a space vector pulsewidth-modulation (SVPWM) scheme suitable for a five-phase CSC. Generally, in SVPWM-CSCs, a current path should be provided for the dc-link current by ensuring that one pair of upper and lower switches is always on . Applying this constraint yields 25 different space vectors, which are mapped into two concentric decagons with ten equal sectors in the <inline-formula> <tex-math notation="LaTeX">\alpha\beta</tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">xy</tex-math></inline-formula> sequence planes. Each sector has two active-large vectors, two active-small vectors, and a null vector. Moreover, the active-large vectors in the <inline-formula> <tex-math notation="LaTeX">\alpha\beta</tex-math></inline-formula> plane are active-small vectors in the <inline-formula> <tex-math notation="LaTeX">xy</tex-math></inline-formula> plane, and vice versa. In the proposed scheme, the ampere-second concept is utilized to determine the ratio between the dwelling times of the large and small vectors such that the <inline-formula> <tex-math notation="LaTeX">xy</tex-math></inline-formula> current components are nullified, the utilization of the input dc-current is maximized, and the switching transitions are minimized, which, in turn, minimizes the CSC switching losses. The proposed scheme can effectively provide sinusoidal converter currents, which is suitable for motor drives and energy conversion applications. The proposed scheme is verified using a 1-kW prototype five-phase induction motor fed by a five-phase CSC.
Multi-terminal high voltage DC transmission currently represents a leading technology in long-distance power transmission systems. Among the main technical challenges facing such technology, DC fault ...isolation, permitting different grounding schemes, providing interoperability, and high DC voltage stepping between different HVDC networks, and allowing high-speed power reversal without power interruption especially when connecting the pre-existing voltage source converters (VSC) and line commutated converters (LCC)-based HVDC networks. This paper introduces a new modular multilevel converter (MMC) based front-to-front DC-DC converter to interconnect two different types (LCC/VSC) of HVDC networks. The proposed topology comprises a voltage source MMC (VS-MMC) and a current source MMC (CS-MMC), while both are coupled via an AC link including the isolating transformer. The proposed topology can successfully provide an uninterruptible bi-directional power flow, high DC voltage stepping with a DC fault blocking capability, and low number of semiconductors due to the usage of only half-bridge SMs. The system design is provided with a detailed mathematical analysis. Furthermore, two active power control methodologies are proposed and compared. The first control technique is simpler and entails lower passive elements, while the second technique ensures a zero reactive power over the full range of active power flow. Furthermore, Losses analysis and comparison are provided between the two proposed control techniques. Finally, Control-Hardware-in-the-Loop (CHiL) test validation is employed to confirm the validity of the proposed system under healthy as well as different fault scenarios.
Proper operation of the grid-tie transformerless converters under unbalanced and distorted conditions entails a precise detection of the frequency and fundamental component of the grid voltage. One ...of the main problems that could arise during the estimation of grid parameters is the existence of a DC offset generated from measurement and A/D conversion. This undesirable induced DC offset could appear as a part of the reference sinusoidal current of grid-tie converters. Although literature has proposed the use of an extended complex Kalman filter (ECKF) for the estimation of positive and negative sequence voltage components as a promising competitor to phase locked loops, mitigating the effect of possible DC offsets when a Kalman filter is employed remains scarce. This paper proposes a new extended complex Kalman filter to improve the filter stability for estimating the frequency and the fundamental positive and negative symmetrical components of the grid voltages, where DC offset, scaling error, and noise can successfully be rejected. The theoretical findings are experimentally validated.
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