Permanent Magnet Brushless AC Motor Research Articles

Optimization of surface-mounted permanent magnet brushless AC motor using analytical model and differential evolution algorithm

Abstract This paper discusses the optimization of surface-mounted permanent magnet brushless AC (PMBLAC) motor using Analytical Sub-domain model with Differential Evolution Algorithm (ASDEA). Only two regions were considered in this analytical sub-domain model, ie magnet and airgap regions, with assistance of Complex Relative Permeance Function (CRPF) to account for the stator slotting effect. Five machine parameters were chosen to be optimized, namely the magnet arc-pole-pitch ratio, slot opening width, magnet thickness, airgap length and stator inner radius. The optimization process has four objectives, ie minimum torque ripple, low cogging torque, high efficiency, and high output torque. The results from the optimized ASDEA were compared with the Analytical Sub-domain Genetic Algorithm (ASGA) and further validated against 2-D finite element model (FEM). Results show a good agreement between analytically optimized models and finite element model. The ASDEA has faster computational time compared to ASGA, and this provides benefit in terms of reducing the machine design parameterization time and less redundancy work required to achieve motor design specifications.

Static Characteristics Analysis and Experimental Study of a Novel Axial Field Flux-Switching Permanent Magnet Generator

A novel axial field flux-switching permanent magnet (AFFSPM) machine with a doubly-salient structure is developed as a wind power generator. The electromagnetic characteristics of a 0.6 kW, 3-phase 12/10-pole AFFSPM machine, including the air-gap flux density distribution, open-circuit flux linkage, EMF, and winding inductances, etc., are investigated based on 3-D finite element (FE) analysis. A prototype is built to test the characteristics under both open-circuit and load conditions. The theoretical analysis is validated experimentally. It shows that the phase EMF is essentially sinusoidal, and the machine can not only be used as a wind power generator, but also as a permanent magnet brushless AC motor.

Sensor-less pseudo-sinusoidal drive for a permanent-magnet brushless ac motor

The precise rotor-position information is required for a permanent-magnet brushless ac motor (BLACM) drive. In the conventional sinusoidal drive method, either an encoder or a resolver is usually employed. For position sensor-less vector control schemes, the rotor flux estimation and torque components are obtained by complicated coordinate transformations. These computational intensive methods are susceptible to current distortions and parameter variations. To simplify the method complexity, this work presents a sensor-less pseudo-sinusoidal drive scheme with speed control for a three-phase BLACM. Based on the sinusoidal drive scheme, a floating period of each phase current is inserted for back electromotive force detection. The zero-crossing point is determined directly by the proposed scheme, and the rotor magnetic position and rotor speed can be estimated simultaneously. Several experiments for various active angle periods are undertaken. Furthermore, a current feedback control is included to minimize and compensate the torque fluctuation. The experimental results show that the proposed method has a competitive performance compared with the conventional drive manners for BLACM. The proposed scheme is straightforward, bringing the benefits of sensor-less drive and negating the need for coordinate transformations in the operating process.

DTC of Three-Phase PM BLAC Motor Having One Phase Open-Circuit Fault with Current Model Flux Estimator

Direct torque control (DTC) of three-phase permanent magnet brushless AC (PM BLAC) motor having one phase open-circuit fault (OPOF) is presented. Torque and flux linkages of the faulty motor are estimated by proposed estimators. Control topology, voltage vectors and design procedure are described. Simulated results show that the proposed topology can be operated under fault situation at rated torque and speed operation. Performances of the system are validated by the measured data.

Investigation of Effectiveness of Sensorless Operation in Carrier-Signal-Injection-Based Sensorless-Control Methods

This paper investigates the effectiveness of sensorless operation in carrier-signal-injection-based sensorless-control methods for permanent-magnet brushless ac motors. The sensorless safety operation area (SSOA) is introduced with due account for the quantization error in the analog to digital conversion. The SSOA defines a working area in the d-q plane in which the motor can operate in sensorless mode with a guaranteed performance in steady state. With the aid of SSOA, a proper injected carrier signal can be selected for the specific prototype machine and current-measurement resolution. Experimental results confirm that the performance of sensorless operation can be guaranteed when the machine operates inside the SSOA with cross-saturation compensation.

A General Magnetic-Energy-Based Torque Estimator: Validation via a Permanent-Magnet Motor Drive

This paper describes the use of the current-flux-linkage (i-psi) diagram to validate the performance of a general magnetic-energy-based torque estimator. An early step in the torque estimation is the use of controller duty cycles to reconstruct the average phase-voltage waveform during each pulsewidth-modulation (PWM) switching period. Samples over the fundamental period are recorded for the estimation of the average torque. The fundamental period may not be an exact multiple of the sample time. For low speed, the reconstructed voltage requires additional compensation for inverter-device losses. Experimental validation of this reconstructed waveform with the actual PWM phase-voltage waveform is impossible due to the fact that one is PWM in nature and the other is the average value during the PWM period. A solution to this is to determine the phase flux-linkage using each waveform and then plot the resultant i-psi loops. The torque estimation is based on instantaneous measurements and can therefore be applied to any electrical machine. This paper includes test results for a three-phase interior permanent-magnet brushless AC motor operating with both sinusoidal and nonsinusoidal current waveforms.

Improved sensorless operation of interior PM BLAC motor drives with reduced-order EKF

It is a challenge to realise an EKF-based sensorless controller for an Interior Permanent Magnet (IPM) brushless ac motor drive due to the influence of non-linearities and rotor saliency. An improved reduced-order EKF method is presented, reducing the rotor position estimation error of an IPM motor, as evident in [1] due to the neglect of saliency. The effectiveness of the proposed method is verified experimentally.

Application of full-order and simplified EKFs to sensorless PM brushless AC machines

This paper employs an extended Kalman filter (EKF) to estimate the rotor position and speed of a vector controlled surface-mounted permanent magnet (PM) brushless AC (BLAC) motor from measured terminal voltages and currents only. Both full-order and simplified EKFs are employed and their simulated performance capabilities are compared. Excellent agreement is achieved between estimated and commanded results. The EKF is also employed to identify the stator flux-linkage due to the PMs, which is influenced by temperature variation and magnetic saturation.

Design of a novel phase-decoupling permanent magnet brushless ac motor

This paper presents a phase-decoupling permanent magnet brushless ac motor which can offer better controllability, faster response, and smoother torque than its counterparts. The key is due to its different motor configuration and simple scalar control. The motor configuration is so unique that it inherently offers the features of phase decoupling, flux focusing, and flux shaping, hence achieving independent phase control, fast response, and smooth torque. The scalar control is fundamentally different from the complicated vector control. It can achieve direct torque control through independent control of the phase currents. The proposed motor is prototyped and experimentally verified.

Improved speed estimation in sensorless PM brushless AC drives

The application of flux-observer-based sensorless control to permanent-magnet brushless AC motor drives is described. Current methods of speed estimation are assessed, both theoretically and experimentally, and an improved method, which combines the best features of methods in which speed is derived from the differential of rotor position and from the ratio of the electromotive force to excitation flux linkage, is proposed. Its performance is verified experimentally.