A general relation for the instantaneous torque developed by a convertor-fed synchronous motor for known phase current waveform and the field flux distribution is formulated. The influence of these quantities, together with other parameters such as phase number, on torque ripple is discussed with the aid of tabulated predictions for a number of typical cases. Techniques for the achievement of low values of torque ripple are outlined.

Influence of motor design and feed-current waveform on torque ripple in brushless DC drives

Brushless permanent magnet (BLPM) motor drives based on Hall sensors have received extensive attention in the literature and are widely used in many applications. However, most of the available and published controllers assume that the Hall signals are always available, which is not true if any of the sensors are faulted. In this paper, several fault-tolerant control schemes for BLPM motor drives are proposed. The methodology is based on fault diagnosis and its classification, and subsequent signal reconstruction. Simulation and experimental results demonstrate the effectiveness and advantages of the proposed fault-tolerant schemes in restoring the motor operation when failures occur in up to two Hall sensors. The proposed fault-tolerant schemes can be easily and flexibly realized for conventional drive systems, either by adding the code in the existing driver or by adding a simple auxiliary circuit between the Hall sensors and the driver.

Fault Diagnosis and Signal Reconstruction of Hall Sensors in Brushless Permanent Magnet Motor Drives

This paper focuses on the start-up strategy of a high-speed 100-kW brushless dc motor with small inductance using a voltage comparator. This paper includes three key technique contributions: 1) determining zero-speed positioning, 2) removing high-frequency disturbances, and 3) optimizing the controller parameters. The sensorless low-current start-up strategy is based on an amplification circuit: a low-pass filter circuit and a signal modulate circuit. The amplification circuit is used to amplify the amplitude of back electromotive force for detecting the rotor position at low speed, the low-pass filter circuit is used to remove high-frequency disturbances, and the signal modulate circuit is used to obtain the rotor position signal. A hysteresis control strategy is proposed against the load disturbance in the start-up stage. Experimental results show that the proposed sensorless start-up strategy can realize a low-current start-up.

Sensorless Low-Current Start-Up Strategy of 100-kW BLDC Motor With Small Inductance

This paper proposes a Power factor Corrected (PFC) Bridgeless Buck-Boost converter fed BLDC motor drive. The Bridgeless configuration eliminates the Diode Bridge Rectifier in order to reduce the number of components and the conduction loss. The position sensors used in BLDC drives have drawbacks of additional cost, mechanical alignment problems. These bottle necks results in sensorless technique. The Sensorless technique mostly relies on measurement of Back EMF to determine relative positions of stator and rotor for the correct coil energising sequence can be implemented. This paper introduces the offline Finite Element method for sensorless operation. The proposed sensorless scheme estimates the motor position at standstill and running condition. The obtained Power Factor is within the acceptable limits IEC 61000-3-2. The proposed drive is simulated in MATLAB/Simulink the obtained results are validated experimentally on a developed prototype of the drive.

A Novel Approach of Position Estimation and Power Factor Corrector Converter Fed BLDC Motor

By predicting future phase-current commutation instants of brushless dc (BLDC) machines, self-sensing control is achieved. Detection of the back electromotive force (EMF) zero-crossing moments is one of the methods used to predict the phase-current commutation instants. Most of the techniques based on back-EMF zero-crossing detection have the inherit disadvantage of an indirect prediction of commutation instants. This is the result of the commutation instant occurring at the $30^{\circ}$ electrical position after zero-crossing of the induced back-EMF in the unexcited phase. Often, the time difference between the zero-crossing of the back-EMF and the current commutation instant is assumed constant. This assumption can be valid for steady-state operation; however, a different time span should be taken into account during transient operation of the BLDC machine. To overcome this problem, an enhancement is proposed here, which improves the performance while keeping the simplicity of the back-EMF zero-crossing detection method.

A Back-EMF Threshold Self-Sensing Method to Detect the Commutation Instants in BLDC Drives

This paper discusses a commutation control method aimed at reducing the commutation torque ripple in sensorless drive of brushless direct current motors. These motors are generally used for low-cost applications because of relatively high efficiency and low manufacturing cost. On the other hand, they show a high torque ripple characteristic caused by nonideal commutation currents. This limits their application area, especially for low-voltage applications. In order to minimize torque ripple for the entire speed range, a comprehensive analysis of commutation torque ripple was made according to three commutation control methods whereupon an optimal current vector trajectory for low torque ripple was devised. The effectiveness of the proposed method was verified through simulation and experimental results.

Sang-Yong Jung

Papers

Commutation Control for the Low-Commutation Torque Ripple in the Position Sensorless Drive of the Low-Voltage Brushless DC Motor