Six-phase Permanent Magnet Synchronous Machine Research Articles

Influence of Gear Ratio on the Performance of Fractional Slot Concentrated Winding Permanent Magnet Machines

Fractional slot concentrated winding (FSCW) permanent magnet synchronous machines (PMSMs) have been a research hotspot over the past few decades. Recently, the magnetic gearing effect in FSCW PMSMs is revealed along with its gear ratio, which is a function of slot/pole number combination. At the design stage of FSCW PMSMs, one of the key issues is the selection of the slot/pole number combination. This paper shows that the gear ratio can contribute to a proper slot/pole number selection in any multiphase FSCW PMSMs by acting as a unified index for a quick overall performance comparison. In this paper, first, the magnetic gearing effect in FSCW PMSMs is explained and the gear ratio is further discussed. The advantages of adopting gear ratio as the overall performance index over other indices are revealed. The influence of the gear ratio on the winding factor, torque output, cogging torque, inductance, and rotor losses of three- and six-phase FSCW PMSMs is analyzed and validated by experiments, thus proving the analyses.

An Effective Charging-Torque Elimination Method for Six-Phase Integrated On-Board EV Chargers

This paper proposes an effective charging-torque elimination method for six-phase integrated on-board electric vehicle (EV) chargers. The integrated EV charger is derived from the power inverter, motor windings, sensors, and microchips, which can significantly reduce the system cost and volume. In fact, the charging electromagnetic torque is inevitable to produce, since the alternating currents flow through the motor windings. This is due to the motor windings serving as the filtering inductors of the rectifier for the on-board charger. In order to keep the vehicle standstill during the charging process, a universal expression of charging torque is derived and analyzed, which is according to magnetic co-energy approach. All possible charging torque elimination positions are presented with a numerical method. Moreover, the unity power factor and zero sequence current control are executed during the EV charging process. Finally, the proposed charging torque elimination method is verified by both simulation and experimentation. The results prove the validity of the proposed charging-torque elimination method for six-phase permanent magnet synchronous machine.

A Flux Constrained Predictive Control for a Six-Phase PMSM Motor With Lower Complexity

This paper proposes a low-complexity model predictive flux control (MPFC) with current harmonics and torque ripple reduced for a six-phase permanent magnet synchronous machine (PMSM) motor. First, the virtual vectors in two different magnitudes are adopted for the sake of harmonic currents and torque ripple reduction, as well as simplifying the predictive model by eliminating the z 1– z 2 variables from the cost function. Then, a look-up table is developed to exclude the useless voltage vectors in advance. In this way, the number of prediction vectors is reduced and heavy computation burden is alleviated. Moreover, to avoid the tedious tuning work of the weighting factor in the cost function, the torque and flux amplitude are transformed into an equivalent reference flux vector. Thus, the complexity of the cost function is significantly reduced. Meanwhile, the current and torque performance are highly improved using the proposed method. Also, the fast dynamic response of predictive control is retained. Finally, simulation and experimental results are offered to verify the effectiveness of the proposed MPFC method.

Fault-Tolerant Predictive Control of Six-Phase PMSM Drives Based on Pulsewidth Modulation

Multiphase machines are famous for their fault-tolerant capability. Conventional fault-tolerant model predictive current control (FT-CMPC) of multiphase machines suffers from high computational burden, low switching frequency, and relatively high current harmonics. This paper proposes a fault-tolerant PWM predictive control (FT-PWMPC) to enhance the performance of fault-tolerant predictive control strategy without using complex enumeration method. The reference phase voltages are generated by a postfault mathematical model in stationary reference frame and transformed to duty cycles with a properly set common-mode voltage. Then, a comparative study of fault-tolerant predictive control strategies is presented, including FT-CMPC, FT-two-vector-based-predictive control, and the proposed FT-PWMPC. The control strategies are implemented with the same sampling frequency or switching frequency on a six-phase permanent magnet synchronous machine test bench. Experimental results of dynamic response, steady-state currents, vibration, and parameter sensitivities are given to identify the advantages and limitations of each control strategy.

Elimination of Harmonic Currents Using a Reference Voltage Vector Based-Model Predictive Control for a Six-Phase PMSM Motor

This paper proposes a novel deadbeat current control (DBCC)-based model predictive control for an asymmetrical six-phase permanent magnet synchronous machine. First, the solution of DBCC is adopted to obtain the expected reference voltage vector (RVV). Then, two groups of virtual vectors, in the total number of 24 with different magnitudes, are defined for the sake of current harmonics suppression. Subsequently, two in-phase virtual vectors which are closest to the RVV are selected as the prediction vectors. The next step is to define a cost function which is composed of the error between the RVV and the available prediction vectors. Then, the selected two virtual vectors are evaluated and the one that minimizes the cost function will be applied in the next instant. In this way, only two prediction vectors need to be evaluated and the computation burden is highly alleviated. In the meantime, the weighting factor involved in predictive torque control is avoided. In addition, to achieve the readily implementation with standard pulsewidth modulation switching sequence, 18 virtual vectors are artfully replaced by their corresponding equivalent virtual vectors. Finally, the proposed method is comparatively studied and compared with other benchmark methods. Simulation and experimental results are offered to confirm the effectiveness of the proposed method.

Bi‐subspace predictive current control of six‐phase PMSM drives based on virtual vectors with optimal amplitude

Owing to the low equivalent impedance of six-phase machines in the secondary subspace, in which currents do not contribute to torque production, low-order current harmonics with high amplitude are likely to appear in the stator currents, increasing the harmonic distortion and the losses in the machine. In the case of permanent magnet synchronous machines (PMSMs), the main causes of these harmonics are machine asymmetries, non-linearities of the power converters and back-electromotive force harmonics. The existing predictive control strategies based on virtual vectors for six-phase machines only regulate the currents mapped into the fundamental subspace, responsible for flux/torque production and leave the currents mapped into the secondary subspace uncontrolled. This study proposes a novel bi-subspace predictive control strategy for six-phase PMSMs with optimal amplitude virtual vectors, which is able to effectively regulate the currents in both subspaces simultaneously, leading to a significant minimisation of the current harmonic distortion. Moreover, the proposed control strategy also allows operating the six-phase PMSM with a current unbalance between the two sets of windings. Both simulation and experimental results confirm the much better performance of the proposed strategy in comparison with other state-of-the-art predictive control strategies found in the literature.

Model Predictive Control for a Six-Phase PMSM Motor With a Reduced-Dimension Cost Function

This paper presents a model predictive control for a six-phase permanent magnet synchronous machine (PMSM) with a reduced-dimension cost function. Only the variables in the harmonic subspace are included into the cost function, while the energy conversion related variables are excluded. This is achieved by using the deadbeat direct torque and flux control method to obtain a reference voltage vector and then to track the torque and stator flux properly in the energy conversion related subspace. Then, according to the position of the reference vector, the appropriate prediction vectors can be determined. Subsequently, a reduced-dimension cost function including only the harmonic constraints is defined to evaluate the feasible prediction vectors. In this way, the predictive model and the cost function are simplified without redundant constraints. Meanwhile, the torque and flux can be regulated satisfactorily, and the harmonic currents are suppressed effectively. Finally, experimental results of the proposed method and the conventional model predictive torque control are presented in this paper to verify the validity of the proposed method.

Efficient Modeling of Six-Phase PM Synchronous Machine-Rectifier Systems in State-Variable-Based Simulation Programs

Many advanced energy conversion systems utilize multiphase (e.g., six or more phases) electrical machines that feed high-count-pulse (e.g., 12 or more pulses) rectifiers for supplying dc power. Efficient simulation of such power systems in commonly-used state-variable-based programs requires fast and accurate models of electrical machines and power electronic converters with compatible interfaces. As an alternative to the existing $qd$ and voltage-behind-reactance (VBR) machine models, this paper develops a constant-parameter VBR model for six-phase permanent magnet synchronous machines to offer computationally efficient interface. For system-level studies where the switching details of rectifiers can be neglected, a multiple-reference-frame parametric-average-value model is developed for the 12-pulse rectifiers that provides fast simulation and preserves the dominant ac harmonics of interest. The accuracy and numerical efficiency of the proposed machine-converter models are verified using the detailed and alternative existing models.

Torque Cancelation of Integrated Battery Charger Based on Six-Phase Permanent Magnet Synchronous Motor Drives for Electric Vehicles

This paper proposes a torque cancelation strategy for a nonisolated three-phase integrated battery charger topology for light and medium duty electric vehicle drives based on six-phase permanent magnet (PM) synchronous machines. The charger requires a three-phase grid interface and utilizes the machine windings as the input filter inductances after minor reconfiguration. The drive power electronics are used to control the currents drawn from the three-phase grid. The current flowing through the machine windings induces a torque on the PM machine rotor which is eliminated by the proposed torque cancelation strategy in battery charging mode. The torque cancelation strategy is general and works with both symmetric and asymmetrically wound six-phase PM machines. The strategy is also capable of eliminating the torque when the rotor is displaced from the stator $d$ -axis. The linear quadratic regulator with the integral action control scheme is used to accommodate for the asymmetry caused by the dependence of winding inductance on the rotor position. Co-simulation results with Finite-Element Analysis and hardware experiments show the topology based on six-phase PM machines can be used to charge or discharge the battery for grid support functions while the torque on the machine shaft remains canceled.

Investigation of a Novel 24-Slot/14-Pole Six-Phase Fault-Tolerant Modular Permanent-Magnet In-Wheel Motor for Electric Vehicles

In this paper, a six-phase fault-tolerant modular permanent magnet synchronous machine (PMSM) with a novel 24-slot/14-pole combination is proposed as a high-performance actuator for wheel-driving electric vehicle (EV) applications. Feasible slot/pole combinations of the fractional-slot concentrated winding six-phase PMSM are elicited and analyzed for scheme selection. The novel 24-slot/14-pole combination is derived from the analysis and suppression of the magnetomotive force (MMF) harmonics. By making use of alternate-teeth-wound concentrated winding configuration, two adjacent coils per phase and unequal teeth widths, the phase windings of the proposed machine is magnetically, thermally isolated, which offers potentials of modular design and fault tolerant capability. Taking advantage of the leakage component of winding inductance, 1.0 per unit short-circuit current is achieved endowing the machine with short-circuit proof capability. Optimal design of essential parameters aiming at low eddy current losses, high winding factor and short-circuit-proof ability are presented to pave the way for a high-quality system implementation.

Analysis, Design and Prototyping of a Low-Speed High-Torque Six-Phase Fault-Tolerant Permanent Magnet Synchronous Machine for EVs

This paper deals with a low-speed high-torque six-phase fault-tolerant permanent magnet synchronous machine (PMSM) for wheel-driving electric vehicle (EV) applications. In machine design, winding arrangements and feasible slot/pole combinations are discussed and compared; a 24-slot/22-pole alternate-teeth-wound scheme is analyzed and designed. With reinforced slot-leakage component, the inductance of the machine is increased to restrain the one-phase short-circuit current to nearly 1.0 per unit preventing the machine from deteriorations in condition of that fault. The 24-slot/22-pole alternate-teeth-wound prototype machine is manufactured and the experimental verification is provided.

MULTI-PHASE SYNCHRONOUS MOTOR SOLUTION FOR STEERING APPLICATIONS

This paper presents the analysis of a six-phase permanent magnet synchronous machine (PMSM6) dedicated for electrical power steering system applications. The motor design is brie∞y described, as well as the construction of the studied motor. The study is validated by flnite element method and via experimental results. Some simulated results prove the machine's capability to work even in faulty conditions. The operation of the machine was evaluated in generator and motor operation. In motor operation, the PMSM6 was fed based on scalar control.