FPGA-based implementation of the back-EMF symmetric-threshold-tracking sensorless commutation method for brushless DC-machines

The operation of brushless DC permanent-magnet machines requires information of the rotor position to steer the semiconductor switches of the power-supply module which is commonly referred to as Brushless Commutation. Different sensorless techniques have been proposed to estimate the rotor position using current and voltage measurements of the machine. Detection of the back-electromotive force (EMF) zero-crossing moments is one of the methods most used to achieve sensorless control by predicting the commutation moments. Most of the techniques based on this phenomenon have the inherit disadvantage of an indirect detection of commutation moments. This is the result of the commutation moment occurring 30 electrical degrees after the 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 optimal current commutation is assumed constant. This assumption can be valid for steady-state operation, however a varying time difference should be taken into account during transient operation of the BLDC machine. This uncertainty degrades the performance of the drive during transients. To overcome this problem which improves the performance while keeping the simplicity of the back-emf zero-crossing detection method an enhancement is proposed. The proposed sensorless method operates parameterless in a way it uses none of the brushless dc-machine parameters. In this paper different aspects of experimental implementation of the new method as well as various aspects of the FPGA programming are discussed. Proposed control method is implemented within a Xilinx Spartan 3E XC3S500E board

Fault analysis and remedial strategies on a fault-tolerant motor drive with redundancy

Copyright © 2007 IEEEFault-tolerant motor drives are required in a range of safety-critical applications. Using a special motor design and an appropriate inverter topology, brushless permanent magnet AC motor drives can have an effective fault-tolerant capability. Although a single motor fault-tolerant drive system may be sufficient in many critical applications, a higher degree of fault tolerance requires redundancy in the motor system as considered in this paper. This is achieved by using a dual motor module on a common shaft. The simulation model of the entire drive system and the analysis of the various faults are presented in this paper. The effects of fault(s) on the phase current and output torque are provided. Three remedial operating modes are proposed and their features are compared. In addition, an experimental setup was introduced, which is based on dual electrically and magnetically isolated brushless AC motor modules, H-bridge inverters for individual phases and dsPICDEM MCU motor controller. © 2007 IEEE

Detection and remediation of switch faults on a fault tolerant permanent magnet motor drive with reduncancy

Copyright © 2007 IEEE. All Rights Reserved.Fault-tolerant motor drives are becoming more important in safety critical applications. Using a special motor design and an appropriate inverter topology, brushless permanent magnet AC motor drives can have a fault-tolerant capability. This paper considers a dual motor drive system on a common shaft to introduce redundancy. The paper provides a systematic classification for the potential electrical faults which may occur in a real motor drive. In the paper, the switch and winding short circuit fault detection and identification methods are studied and experimental results are presented. In addition, the effects of switch faults on the phase currents and output torque are discussed, and remedial strategies for these faults are proposed. Furthermore, it was also demonstrated using simulation results that the proposed remedial strategies can compensate for the loss of torque due to the switch faults and can keep the peak-to-peak torque ripple factor comparable to healthy operation of the drive.Jingwei Zhu; Ertugrul, N.; Wen Liang Soon

Quantifying the commutation error of a BLDC machine using sensorless load angle estimation

BLDC motors are often used for high speed applications, for example in pumps, ventilators and refrigerators. For commutation discrete position information is necessary. This feedback is often provided by Hall sensors instead of more expensive encoders. However, even small misalignment of the Hall sensors in low cost BLDC motors can lead to unwanted torque ripples or reduced performance of BLDC motors. This misplacement leads not only to noise and vibrations caused by the torque ripples but also to lower efficiency. In this paper, a self-sensing technique to assess the misalignment is introduced. The objective is to obtain knowledge of the quality of the commutation by quantifying the misalignment. The method used in this paper is based on the fundamental components of voltage and current measurements and only needs the available current and voltage signals and electrical parameters such as resistance and inductance to estimate the misalignment

Implementation,Simulation of Four Switch Converter Permanent Magnet Brushless DC Motor Drive for Industrial Applications

This Research paper proposes a low cost four switch three phase inverter (FSTPI) fed brushless DC (BLDC) motor drive for Active power factor correction for residential applicationswith out environmental issues. This proposed system is simplified the topological structure of the conventional six switch three phase inverter (SSTPI) and includes an active power factor correction in front end rectifier which results in sinusoidal input current and it closed to unity power factor. In this project a new structure of four switch three phase inverter with reduced number of switches for system is introduced. This system consists of single phase rectifier and four switch three phase inverter. This proposed inverter fed BLDC motor used in Sensorless control schemes. To improve sensorless control performance, six commutation modes based on direct current controlled PWM scheme is implemented to produced the desire Torque-Speed characteristics. This four switch three phase inverter is achieved by the reduction of switches, low cost control and saving of hall sensor. The design and implementation of low cost four switch inverter for Brushless motor drive with active power factor correction  have been conducted successfully and valediction  of the proposed sensorless control for four switch three phase inverter fed BLDC motor drive is developed and analysed using both  MATLAB/SIMULINK and hardware results  are verified out successfully

Direct torque control of brushless DC drives with reduced torque ripple

The application of direct torque control (DTC) to brushless ac drives has been investigated extensively. This paper describes its application to brushless dc drives, and highlights the essential differences in its implementation, as regards torque estimation and the representation of the inverter voltage space vectors. Simulated and experimental results are presented, and it is shown that, compared with conventional current control, DTC results in reduced torque ripple and a faster dynamic response

An optimized design modelling of PV integrated SEPIC-based four-switch inverter for sensorless PMBLDC motor control

The design of PV-based high gain SEPIC converter integrated with four-switch strategy, which has been used to achieve sensorless speed control of Permanent magnet Brushless DC motor (PMBLDC) is analysed in this work. Hence SEPIC converter coupled with Fuzzy Logic, MPPT Algorithm is employed to retain voltage. SEPIC converter is chosen as it has a continuous current operation with high gain; Fuzzy MPPT algorithm is used as it provides accurate results faster while the classical MPPT techniques provide the results with fluctuations in attaining the maximum power. Regarding the sensorless control of PMBLDC motor, the conventional six-switch strategy is replaced by four-switch strategy and the sensors are replaced by back EMF method. Four-switch strategy has the capability of reducing the losses, size, cost and complexity of control. For achieving the nominal speed, a closed-loop control is implemented with PI controller, which is tuned by GWO technique. The proposed methodology is more efficient as the motor speed remains unchanged even under the full load condition. The end result of traditional PI algorithm and PI algorithm, which have been tuned by GWO algorithm, is compared and simulated through MATLAB. This is also implemented and validated in hardware by FPGA Spartan 6E controller

Modelling of sensored speed control of BLDC motor using MATLAB/SIMULINK

Recent developments in the field of magnetic materials and power electronics, along with the availability of cheap powerful processors, have increased the adoption of brushless direct current (BLDC) motors for various applications, such as in home appliances as well as in automotive, aerospace, and medical industries. The wide adoption of this motor is due to its many advantages over other types of motors, such as high efficiency, high dynamic response, long operating life, relatively quiet operation, and higher speed ranges. This paper presents a simulation of digital sensor control of permanent magnet BLDC motor speed using the MATLAB/SIMULINK environment. A closed loop speed control was developed, and different tests were conducted to evaluate the validity of the control algorithms. Results confirm the satisfactory operation of the proposed control algorithms

Torque Controlled Drive for Permanent Magnet Direct Current Brushless Motors

This thesis describes the design and implementation of a simple variable speed drive (VSD) based on a brushless direct current (BLDC) machine and discrete logic circuits. A practical VSD was built, capable of operating a BLDC machine in two quadrants, motoring and regenerative braking. The intended applications are electric scooters and electric bicycles, where the recovered energy from braking extends the range of the vehicle. A conceptual four quadrant VSD, suitable for three and four wheelers requiring reverse operation, was designed and tested in simulation. Simplicity was emphasized in this design to help achieve a robust, easy to analyse system. The versatility of multi-function gate integrated circuits (ICs) made them ideal for implementing the commutation logic and keeping the system simple. The BLDC machine has sensors with a resolution of 60 ed to determine rotor position. An electronic commutator or phase switcher module interprets the position signals and produces a switching pattern. This effectively transforms the BLDC machine into a direct current (DC) brushed machine. A synchronous step down converter controls the BLDC machine current with a tolerance band scheme. This module treats the BLDC machine as if it was a DC machine. The leakage inductance of the electric machine is used as the inductive filter element. The unipolar switching scheme used ensures that current flows out of the battery only for motoring operation and into the battery only during regeneration. The current and torque are directly related in a DC brushed machine. The action of an electronic commutator or phase switcher creates that same relationship between torque and current in a BLDC machine. Torque control is achieved in the BLDC machine using a single channel current controller. The phase switcher current is monitored and used to control the duty ratio of the synchronous converter switches. Successful operation of the practical VSD was achieved in two quadrants: forwards motoring and forwards regenerating. The maximum tested power outputs were 236W in motoring mode and 158W in regenerating mode. The output torque could be smoothly controlled from a positive to a negative value. iv v Simulation of the conceptual four quadrant design was successful in all the motoring, generating and active braking zones. The required manipulation of logic signals to achieve this type of operation was done automatically while the machine was running. The resulting output torque is smoothly controlled in all of the operating zones. Commutation at certain speeds and torques are handled better by some topologies than others. Some current sensing strategies adversely affect instantaneous phase currents under certain conditions. The final design chose the method where phase currents experience no overshoot, minimizing component stress. The battery, or energy storage system, used in verifying the operation of the VSD in the practical electric bicycle was found to be the most limiting component. In regenerating mode, the low charge acceptance rate of the battery reduced the maximum retarding torque and energy recovery rate