Araz Darba

Sensorless commutation and speed control of Brushless DC-machine drives based on the back-EMF symmetric threshold-tracking

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 and higher speed. In this paper a new method is proposed to overcome this problem which improves the performance while keeping the simplicity of the back-emf zero-crossing detection method. The proposed sensorless method operates parameterless in a way it uses none of the brushless dc-machine parameters.

Improved Dynamic Behavior in BLDC Drives Using Model Predictive Speed and Current Control

Model-based predictive control is a powerful control strategy to drive electrical machines. Conventional cascade proportional-integral (derivative) [PI(D)] controllers are often used to control speed, torque, and current. However, for low-inertia machines, achieving a high-performance and wide speed range is far beyond the application conditions for which these controllers are designed for. Using two cascaded PI(D) controllers for the speed/current control of a low-inertia machine, changes in the speed set point should be slowly applied in order to avoid stability problems. In this paper, a model predictive control algorithm that is able to control the speed of a low-inertia brushless direct-current machine with a high bandwidth and good disturbance rejection properties is proposed. The algorithm is implemented on a SPARTAN 3E 1600 field-programmable gate-array board, and experimental results verify the performance of the proposed algorithm.

Evaluation of a dual-T-type converter supplying an open-end winding induction machine

The multilevel inverter is a promising technology compared to two-level inverters in the applications of ac-drives and smart-grid applications. In this paper, a dual-T-type three-level inverters is used to drive an open-end winding induction machine. The Space-Vector Pulse-Width Modulation is selected as a good-performing control strategy to control the dual-inverter. Furthermore, an optimized method is used to select the proper switching state for the new configuration to decrease the converter losses. A comparison between the proposed configuration and the conventional diode clamped converter is made. The proposed drive system is designed and modelled by using Matlab/Simulink. It is shown that the converter can give the same hexagon, wave forms and harmonic spectrum of the five level converter. An optimized switching state selection is used to reduce the converter losses. The advantages and drawbacks of the dual-T-type configuration are discussed. In addition, the harmonic analysis and the loss calculations of the dual-T-type converter are provided and compared to the T-type three-level converter and the conventional five-level diode-clamped-converter.

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

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° 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.

Improving the Dynamic Stiffness in a Self-Sensing BLDC Machine Drive Using Estimated Load Torque Feedforward

This paper presents a load torque estimation method for self-sensing brushless dc drives. Torque ripples in brushless dc machines can be reduced using load torque information. This method uses the terminal voltage, the virtual neutral point voltage, and the dc bus current of the machine. The algorithm uses the variation of successive back electromotive force (back EMF) samples to estimate the rotor speed. The rotor position is estimated by defining an intermediate function of estimated speed and back EMF samples. An estimate of acceleration is used to estimate load torque. The load torque information is used for increasing the dynamic stiffness of the drive. The mathematical background is given and discussed, and the simulations and the experimental results prove the performance of the proposed method.

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.

FPGA-based real-time simulation of sensorless control of PMSM drive at standstill

This paper presents a real-time simulation of a sensorless control method for IPMSM drives based on Park Transformation with a reference frame fixed to the rotor and assuming a sinusoidal flux (sinusoidal back-emf). The objective of this paper is to Hardware In Loop (HIL) evaluation of a sensorless position estimation of the Permanent Magnet Synchronous Motor (PMSM) drive at standstill as well as the current controller. An anti-windup method is integrated within the controller to ensure a good dynamic performance during transients. Test voltages vectors are injected in such a manner the current samples are not affected. An asymmetric Pulse Width Modulation (PWM) allows to apply these test vectors each PWM period.

Rotor speed, position and load torque estimation using back-emf sampling for self-sensing brushless DC machine drives

This paper presents a load torque estimation method for self-sensing brushless DC drives. Torque ripples in brushless DC machines can be reduced using load torque information. This method uses the terminal voltage, the virtual neutral point voltage and the DC-bus current of the machine. The algorithm uses the variation of successive back-emf samples to estimate the rotor speed. The rotor position is estimated by defining an intermediate function of estimated speed and back-emf samples. An estimate of acceleration is used to estimate load torque. The mathematical background is given and discussed and the simulation results prove the performance of the proposed method.

Digitally current controlled three-phase machines: enhancements in dynamic analysis and antiwind-up scheme

Many electrical machines are nowadays controlled using digital controllers resulting in variable-speed drives. To enhance control engineers want to deal with the switching behaviour of the power converters or pulse-width modulation in more detail. To help them, in this paper, a previously proposed enhanced discrete-time model in the z-domain is applied to machine drives. Additionally, the application of a discrete-time anti-windup method for three-phase machines is presented.

Improving the torque generation in self-sensing BLDC drives by shaping the current waveform

Brushless DC drives are widely used in different fields of application because of their high efficiency and power density. Torque ripple can be considered one of the drawbacks of these drives. This paper proposes a method to reduce the torque ripple in BLDC drives. For this reason, the current amplitude is adapted to the rotor position rather than to be kept constant as done in a conventional commutation method. This is done by computing an optimum reference current based on the phase back-EMF waveform. The proposed approach is implemented in a self-sensing drive so its applicability to self-sensing BLDC motor drives is verified. Simulation and experimental results are given and discussed to show that the proposed method actually is able to improve torque production.