Field Weakening Performance Research Articles

Influence of Flux Barrier Shape and Mechanical Constraints on Field-Weakening Performance in Double-Layer Interior Permanent Magnet Machines

Influence of Flux Barrier Shape and Mechanical Constraints on Field-Weakening Performance in Double-Layer Interior Permanent Magnet Machines

Integration of FOC With DFVC for Interior Permanent Magnet Synchronous Machine Drives

In this paper, the drawbacks of the conventional f-t frame based maximum torque per ampere (MTPA) control schemes are analyzed and mathematically proved. In order to inherit the merits of both the direct flux vector control (DFVC) in field weakening region and field orientated control (FOC) in constant torque region while avoiding their disadvantages, an integrated control scheme is proposed. The proposed control scheme integrates the FOC into f-t reference frame at low speeds to achieve a relatively accurate and robust MTPA control, while at high speeds, the DFVC is adopted to utilize the advantages of f-t frame based control scheme in field weakening region. A shape function is utilized by the proposed control scheme to achieve a smooth transition between the two control schemes. The proposed control scheme is verified by experiments under various operation conditions on a prototype IPMSM drive. The simulation and experimental results illustrate that the proposed control scheme could achieve a better MTPA control accuracy in constant torque region and a better field weakening performance in the constant power region. Meanwhile the complex look-up tables for FOC in field weakening region and the difficulties in observing flux vector at low speed are avoided.

A Robust Field-Weakening Approach for Direct Torque and Flux Controlled Reluctance Synchronous Motors With Extended Constant Power Speed Region

This paper proposes a new robust field-weakening approach for reluctance synchronous motors regulated by direct torque and flux control. Compared to the existing direct torque and flux control based field-weakening methods that cannot achieve maximized DC-link voltage utilization and are parameter dependent, the proposed approach contributes to improve the field-weakening performance of reluctance synchronous motor in two aspects. First, it extends the constant power speed range through autonomous stator flux reference adjustment, which maximizes the dc-link voltage utilization. Smooth transition between the maximum torque per ampere trajectory and field-weakening trajectory is also realized. Second, it enhances the parameter robustness of drives in very high-speed region by employing a torque reference adjustment scheme. This effectively avoids the instability of drives caused by machine parameter variations. The proposed approach is verified experimentally on a laboratory setup.

On Field Weakening Performance of a Brushless Direct Current Motor with Higher Winding Inductance: Why Does Design Matter?

This paper comprises the design, analysis, experimental verification and field weakening performance study of a brushless direct current (BLDC) motor for a light electric vehicle. The main objective is to design a BLDC motor having a higher value d-axis inductance, which implies an improved performance of field weakening and a higher constant power speed ratio (CPSR) operation. Field weakening operation of surface-mounted permanent magnet (SMPM) BLDC motors requires a large d-axis inductance, which is characteristically low for those motors due to large air gap and PM features. The design phases of the sub-fractional slot-concentrated winding structure with unequal tooth widths include the motivation and the computer aided study which is based on Finite Element Analysis using ANSYS Maxwell. A 24/20 slot–pole SMPM BLDC motor is chosen for prototyping. The designed motor is manufactured and performed at different phase-advanced currents in the field weakening region controlled by a TMS320F28335 digital signal processor. As a result of the experimental work, the feasibility and effectiveness of field weakening for BLDC motors are discussed thoroughly and the contribution of higher winding inductance is verified.

Investigation of Losses for a Concentrated Winding High-Speed Permanent Magnet-Assisted Synchronous Reluctance Motor for Washing Machine Application

In this paper, improvement of torque quality and magnetic losses of a concentrated winding high-speed permanent magnet (PM)-assisted synchronous reluctance motor (PMaSRM) that can operate in the wide speed range are investigated. Optimization studies have been carried out to enhance the torque quality. In addition, ac copper losses in the stator coils and iron losses in laminations at high frequencies have been investigated. Since the PMaSRM can operate in a wide constant power-speed range, the field weakening performance has also been investigated. The motor performance results of the PMaSRM at both no-load and on-load conditions are examined by using Flux 2-D FEA software. A prototype motor based on the simulations has been built and validated in order to show the feasibility of such technology for white good applications.

Field-Weakening Capability of Interior Permanent-Magnet Machines With Salient Pole Shoe Rotors

Brushless permanent-magnet (BLPM) machines, with inherent advantages of high-power density and high efficiency, have been widely employed to achieve traction characteristics for traction applications. Generally, traction characteristics require high torque at low speed and wide field-weakening region keeping constant power. However, both conventional interior permanent-magnet (IPM) and surface-mounted permanent-magnet (SPM) machines suffer from high-speed issues in the field-weakening region. A different BLPM machine topology, the pole shoe topology, is proposed in this paper. Although the pole shoe machine is common in industrial variable speed drives employing constant torque regimes, it has not been previously considered for machines designed for a wide field-weakening region. For analysis and comparison, a conventional IPM machine, which is employed as the Nissan Leaf vehicle traction machine, is studied as a reference benchmark machine. Experimental results from this machine are used to validate the analysis presented in this paper. The design results show that the proposed pole shoe machine achieves better field-weakening performance, compared with the conventional IPM and SPM machine topologies.

Field-Weakening Performance Improvement of the Yokeless and Segmented Armature Axial Flux Motor for Electric Vehicles

In order to avoid the unsafe operation and raise efficiency of yokeless and segmented armature axial flux motors at high speed, the control current of air gap flux is expected to be as small as possible with the same field-weakening effect. To reduce the control complexity, a new structure of module poles with a combination of permanent magnet and soft magnetic material is proposed, which has the characteristics of lower d-axis reluctance and a higher performance of yokeless and segmented armature axial flux motor with surface mounted permanent magnet. According to finite element analysis (FEA), the flux distributions of a rotor pole in no-load and demagnetization condition are contrasted, and under this new configuration, the derivative analytical models of back electromotive-force (EMF), electromagnetic torque, and air gap flux are validated, moreover, the influence of soft magnetic material of rotor poles on controlling the air gap flux is investigated in different load. Based on a particular objective function, the combination of permanent magnet and soft magnetic material is optimized. The results show that optimal solution of field-weakening performance of yokeless and segmented armature axial flux motors can be improved effectively and legitimately.

A novel stator and rotor dual PM flux modulated machine

A novel structure of Veriner permanent magnet (VPM) machine is presented as an effective option for high torque density direct-driven applications. The key is to locate PMs on both sides of rotor and stator, and design the stator PMs as a cylinder shape, the rotation of which can be controlled by an external driven system. With this design, magnetic field in the airgap can be directly regulated by the rotation of stator PMs. The structure and operation principle are introduced and the performance is analyzed with time-stepping finite element method (FEM). Analysis results show that the novel structure has really high torque density and good field weakening performance.

Effect of open stator slots on the performance of an interior permanent magnet automotive alternator

This work describes a study of the effect of using open stator slots in an interior permanent magnet automotive alternator to increase its effective air gap and thus reduce its iron losses under field-weakening conditions. Analytical, finite-element and experimental results are compared for the back-electromotive waveforms, inductance saturation/torque curves, iron loss and field-weakening performance characteristics for the alternator with both semi-closed and with open slots. It is shown for the highly saturated machine considered, that using open stator slots can reduce the field-weakening iron loss without significantly affecting the machine performance.

IPM Traction Machine With Single Layer Non-Overlapping Concentrated Windings

In this paper, an interior permanent-magnet traction drive machine with single layer non-overlapping concentrated stator winding is analyzed. In the single layer winding design, the number of stator slots and a winding factor are specifically considered. Moreover, the effect of varying the coil pitch on the winding factor and torque pulsations is investigated. A new calculation method is proposed, whereby the constant torque and field-weakening speed characteristics of the machine drive can be predicted using torque and flux linkage functions. The measured and predicted field-weakening performance of a 150-kW direct traction drive machine is presented.

Improvement in the field-weakening performance of switched reluctance machine with continuous mode

A new operation mode for switched reluctance motors (SRMs), called 'continuous mode', is described. By using this mode, the torque and then power in field-weakening mode can be considerably increased without any hardware modifications. Consequently, power and torque densities of SRMs become comparable to other technologies (synchronous and induction motors) and with a field weakening operation over a large speed range. This new degree of freedom makes it possible to improve the motor design, by modifying the rotor pole arc size or the windings turns per pole. Only simulation results are presented here, for a 12/8 SRM. Results confirm that the maximum power is improved (constant power on a very large speed range) and with a higher efficiency than that in the classical discontinuous mode.

Field-weakening performance of interior permanent-magnet motors

This paper compares the field-weakening performance under rated and overload conditions of synchronous reluctance and interior permanent-magnet motors against that of a baseline 2.2-kW induction machine. Four prototype rotors based on axially laminated and multiple-barrier designs were built and tested in the same induction machine stator. Field-weakening performance was estimated based on 50-Hz load tests at reduced voltage. It was found that the performance of the axially laminated synchronous reluctance machine was comparable with the induction machine while the interior permanent-magnet motors offered significantly better output power above rated speed. The multiple-barrier interior permanent-magnet motor design gave the most promising field-weakening performance.

Maximum power limits of small single-phase permanent magnet drives

The authors deal with the theoretical limitations on the field-weakening performance of small single-phase nonsalient permanent-magnet motors when driven from an inverter with limited volt–ampere rating. A specific normalisation is introduced to obtain advantageous normalised parameters. It is shown that a theoretical infinite constant power speed range can be achieved, even with the ohmic voltage drop, by properly choosing the armature flux linkage. The effect of normalised parameters on the output characteristics is analysed and presented in the normalised parameter plane. The number of turns of the winding is computed and applied to an existing single-phase hybrid motor. A wide range of normalised parameter values exists for this structure.

Design and field-weakening performance of a synchronous reluctance motor with axially laminated rotor

Axially laminated reluctance motors can be designed to have high saliency and so offer very good performance in terms of torque capacity, power factor and efficiency. This paper presents the design and performance of a 7.5 kW four-pole machine, using thin rotor laminations, which achieved an unsaturated saliency ratio of 12.5. Finite-element analysis is used to predict machine parameters, paying special attention to modeling of the thin rotor elements and to saturation effect on the d axis. Computed parameters are compared with test measurements, showing good agreement. Load tests with 50Hz supply confirm the expected performance characteristics, but also show the occurrence of additional losses associated with the axially laminated rotor construction. A design modification to reduce the extra losses is demonstrated. A detailed investigation of field-weakening performance is reported, showing constant-power characteristics and good agreement between predicted and measured performance over a speed range of 2.25:1 above base speed.

Design and field-weakening performance of permanent-magnet/reluctance motor with two-part rotor

A synchronous motor with two-part rotor is described whose rotor comprises a surface-magnet part and a reluctance part mounted adjacent to each other on the same axis. An axially laminated construction is used in the reluctance part to achieve a high saliency ratio. Machine parameters and physical design details are selected to obtain constant-power characteristics over a 3:1 speed range by field-weakening. Test results demonstrate the achievement of the desired characteristics, in good agreement with computed predictions. The two-part rotor construction is thus a candidate for applications such as electric vehicles.

Field weakening performance of a linear brushless AC machine

The use of field weakening in the control of linear brushless AC machines is investigated using finite element modelling and is shown to be viable. The results are validated using a practical machine.

Design of a new axially-laminated interior permanent magnet motor

The design of a new type of axially-laminated interior permanent magnet motor drive showing an extremely wide constant-power speed range which exceeds 7.5:1 is described. The effect on the field-weakening performance of the number of poles, the pole-piece material, the rotor bolt holes, the airgap size, the rotor insulation ratio, and the magnet type are analyzed using analytical and finite-element techniques. A 7.5-kW synchronous reluctance and a 7.5-kW interior permanent magnet axially-laminated rotor were built for a commercial induction motor stator and experimental low-speed and field-weakening results are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Field-weakening performance of brushless synchronous AC motor drives

The paper examines the theoretical and practical limitations to the field-weakening performance of surface permanent magnet, synchronous reluctance and interior permanent magnet motors when driven from an inverter with a limited volt-ampere rating. It is shown that the &apos;optimal&apos; field-weakening performance consists of an infinite constant-power speed range but is limited to an inverter utilisation of about 0.7. The new concept of the interior permanent magnet parameter plane is introduced. This graphically illustrates the effect of varying the drive parameters on the shape of the field-weakening characteristic. The interior permanent magnet parameter plane is used to show that there are three types of optimal field-weakening designs. When practical factors and considerations are taken into account, the optimal high-saliency interior permanent magnet motor design is the most promising for applications requiring a wide field-weakening range. A 7.5 kW design was built and a constant-power speed range exceeding 7.5:1 was demonstrated.