Consequent-pole Permanent Magnet Research Articles

A Spoke-Type IPM Machine With Novel Alternate Airspace Barriers and Reduction of Unipolar Leakage Flux by Step-Staggered Rotor

This paper proposes a spoke-type interior permanent magnet (IPM) machine with novel alternate airspace barriers, through which higher torque capability and better manufacturability can be obtained, without remarkable deterioration in mechanical strength. Further, the influence of end leakage flux in the novel IPM design is investigated by three-dimensional finite element method, including the leakage flux characteristics and torque capability. Furthermore, a step-staggered rotor is proposed to reduce the unipolar leakage flux and magnetization of the end shaft. As an extension, unipolar leakage flux is further investigated in consequent-pole PM machines, as well as the validity of step-staggered method. Finally, prototypes are fabricated and tested to verify the foregoing analyses, including the magnetic field at the end shaft and the output capability.

Comparative Analysis of End Effect in Partitioned Stator Flux Reversal Machines Having Surface-Mounted and Consequent Pole Permanent Magnets

In this paper, the end effects of a partitioned stator flux reversal permanent magnet (PM) machine with a surface-mounted PM (SPM) inner stator and a consequent pole PM (CPM) inner stator are comparatively analyzed. It is found that due to higher saturated inner stator steel in a CPM machine, it suffers from larger end effect than the SPM machine. Influence of armature reaction on end effect is investigated by a finite-element (FE) analysis, together with that of aspect ratio, i.e., axial stack length to stator outer diameter. Furthermore, it is found that in the CPM machine, the optimal PM arcs for the highest average electromagnetic torque predicted by 2-D and 3-D FE are different due to the variation of end effect with PM arc. Prototypes with both SPM and CPM inner stators are built and tested to verify the FE analysis.

Power Factor Improvement of a Linear Vernier Permanent-Magnet Machine Using Auxiliary DC Field Excitation

Vernier permanent-magnet (VPM) machines attract more and more attention recently because of the high-torque density and low-speed operation features. Due to the vernier structure for field modulation, its power factor (PF) usually is lower than that of the conventional PM machines. In this paper, a new linear VPM machine for improving the PF is proposed. By using an auxiliary dc field winding to provide an additional excitation, the air-gap flux excited by PMs is compensated. The proposed machine has a similar structure to the split-pole VPM machines with surface-mounted PMs. For implementing the auxiliary dc field winding, a parallel-hybrid excitation topology and consequent-pole PM machine structure are adopted. The machine topology, modeling, and operating principle are discussed. Both simulation and experimentation show that the PF of the machine can be improved by the auxiliary dc field excitation.

Rotor Position Detection of CPPM Belt Starter Generator with Trapezoidal Back EMF using Six Hall Sensors

Six-step commutation control widely used in brushless DC (BLDC) motor can be applied to consequent pole permanent magnet (CPPM) belt starter generator (BSG) with trapezoidal back electromotive force (EMF) in the starter state. However, rotor position detection with three Hall sensors in BLDC motor can hardly be employed in CPPM BSG due to asymmetric flux distribution in each pole side of CPPM BSG. This paper presents a low-cost rotor position detection method for CPPM BSG in which six Hall sensors are proposed to be used based on the analysis of flux distribution by 3D FEA. In the method, the six Hall sensors are divided into three groups and two signals in each group are combined through performing logic operations. In addition, offset angle between back EMF and the related Hall signal can be compensated by moving the Hall sensors. Experiments of a 2 kW CPPM BSG prototype have also been performed to verify the proposed method.

2-D Analytical Magnetic Field Prediction for Consequent-Pole Permanent Magnet Synchronous Machines

Consequent-pole permanent magnet (PM) synchronous machines (PMSMs) provide especial features by the use of alternate PM and ferromagnetic poles. The design of these types of electric machines requires an accurate model due to the asymmetrical flux distribution in the air gap under adjacent poles. The equivalent magnetic circuit technique can hardly offer an accurate model for consequent-pole PMSMs. To this end, a 2-D analytical model is presented for consequent-pole slotted stator PMSMs to accurately compute the magnetic field distribution due to PMs and armature reaction. The slotting effects and the tooth-tip effects are taken into consideration by using the subdomain technique. The proposed model is used to calculate the magnetic flux density distributions of three consequent-pole PMSMs: an 8-pole, 9-slot machine with a non-overlapping winding; a 4-pole, 15-slot machine with an overlapping winding; and a 10-pole, 12-slot machine with a non-overlapping winding, each with three different magnetization patterns, i.e., radial, parallel, and Halbach. Based on the magnetic flux distribution, the electromagnetic torque, the self- and mutual-inductances, and the unbalanced magnetic forces have been analytically calculated. The analytical results are compared with those obtained from the finite-element method to show the accuracy and efficacy of the proposed 2-D analytical model.

Partitioned Stator Flux Reversal Machine With Consequent-Pole PM Stator

In this paper, partitioned stator flux reversal permanent magnet (PS-FRPM) machines having different stator/rotor pole combinations with consequent-pole PM (CPM) stator are proposed and analyzed. Compared with the conventional 12-stator-pole PS-FRPM machines having 10-, 11-, 13-, and 14-rotor-pole rotors and surface-mounted PM (SPM) stator, the PM volume in the proposed PS-FRPM machines with CPM stator can be saved by 28.33%, 30%, 30%, and 33.33%, respectively, while the torque density are similar, i.e., 98.59%, 96.69%, 95.50%, and 97.15%, respectively. Besides, the proposed PS-FRPM machines with CPM stator can exhibit only <1% smaller efficiency compared with the existing PS-FRPM machines with SPM inner stator.

A Speed Sensor Fault-Tolerant Control of the CPPM Machine for Electric Vehicle

A speed sensor fault-tolerant control (FTC) strategy for electric vehicle is proposed in electric vehicles using a consequent-pole permanent-magnet (CPPM) machine. In order to obtain good FTC performance at low speed region, a HF voltage injection method is proposed to detect the rotor position from the magnetic saliency. This magnetic saliency of a CPPM machine is analysed by the finite-element analysis (FEA), and the high-frequency (HF) impedances are measured to confirm the saliency. At high speed range, the extended-electromotive force (EMF) method is applied when the failure of the speed sensor is detected. The speed sensor FTC strategy is verified effective by experimental results on a 25kW CPPM machine at different operating conditions. The reliability is enhanced and smooth transition to the fault-tolerant operation is realized. DOI: http://dx.doi.org/10.5755/j01.eee.20.7.5087

Flux Control of a CPPM Machine for Both a Wide Speed Range and High Efficiency

This paper proposes a flux control strategy for a consequent-pole permanent-magnet (CPPM) machine that increases torque capability over a wide speed range and enhances efficiency with a fast convergence. After a brief analysis of the parameters of the CPPM machine, a new flux-weakening algorithm is proposed to achieve maximum torque output over the entire speed range. The optimal flux reference is determined by the preset output flux generated by the 1/ω method and compensated by the voltage closed-loop controller to improve dynamics response. A variable structure voltage controller incorporated with a limiter is designed to generate the antiwindup control. Furthermore, the loss model of the CPPM machine is derived to demonstrate that a 1-D search is suitable for optimizing the machine's efficiency. Then, an adaptive flux step search algorithm, which calculates the flux step proportional to the derivative of the input power with respect to the q-axis voltage, is proposed to minimize the power losses online. The experimental results are compared with the traditional flux control strategy on a CPPM prototype machine, which confirmed the robustness of the presented flux control strategy to obtain the maximum torque output over the entire flux-weakening speed range. The convergence speed is also increased in the efficiency optimization process.

Voltage Characteristics of a Consequent-Pole Bearingless PM Motor With Concentrated Windings

A bearingless permanent magnet (PM) motor combines functions of non-contact magnetic suspension and torque generation together, thus it can drive without mechanical contact. Unlike conventional bearingless PM motors, such as a surface-mounted PM motor, a consequent-pole type of bearingless PM motor has inherent advantages. It can regulate the radial rotor positions independently of the motor drive and has no tradeoff between radial suspension force and torque. In the consequent-pole bearingless PM motors, distributed or concentrated windings can be employed to the motor winding structure. However, relationship between voltage characteristics and the winding design has not yet been revealed. In this paper, the induced electromotive force (EMF) of the consequent-pole bearingless PM motor is numerically calculated on the basis of the magnetic flux distribution in the airgap around the rotor. It is found that the EMF is distorted by the second harmonic at a specific slot number in a consequent-pole rotor. The calculated EMFs are confirmed with the experimental results in the fabricated test machines.