Saad Sayeef

Low-Speed and Standstill Operation of a Sensorless Direct Torque and Flux Controlled IPM Synchronous Motor Drive

This paper investigates a sensorless direct torque and flux control scheme for interior permanent magnet synchronous motor drives at low speeds, including standstill. Closed-loop control of both torque and stator flux linkage are achieved by using two proportional-integral controllers. The reference voltage vectors are generated by a space vector modulation unit. A high-frequency signal injection technique is adopted at low speeds to obtain the rotor position information. A hybrid current-voltage model flux observer with a smooth handover algorithm estimates the stator flux linkage over the whole speed range. Experimental results confirm the effectiveness of the proposed method.

Cogging Torque Analysis of a Segmented Interior Permanent Magnet Machine

This paper investigates the reduced cogging torque seen in a prototype Segmented Interior Permanent Magnet (SIPM) machine. The Interior Permanent Magnet (IPM) machine in which the rotor pole magnets are segmented to provide an improved flux-weakening capability are called in this paper as the Segmented IPM (SIPM) machine. It has been seen that the cogging torque of the segmented IPM machine is much lower than that of a conventional, non-segmented IPM machine of similar ratings and dimensions. The cogging torques of both the segmented IPM machine and the conventional IPM machine were first calculated using finite element analysis and the results were later verified by the experimental measurements. The same stator was used for both the machine during calculation and measurements. The paper attempts to analyse the reasons behind the reduced cogging torque seen in the prototype SIPM machine.

Improved low speed performance of a PI-DTC interior PM machine with compensations of dead-time effects and forward voltage drops

The performance of direct torque control (DTC) interior permanent magnet (IPM) machines at low speed is poor due to a few reasons, namely limited accuracy of stator voltage acquisition and the presence of offset and drift components in the acquired signals. Due to factors such as forward voltage drop across devices in the three phase inverter and dead-time of switching devices, the voltage across the machine terminals differ from the reference voltage vector used to estimate stator flux and electromagnetic torque. This can lead to instability of the IPM drive during low speed operation. Compensation schemes for forward voltage drops and dead-time are implemented, resulting in better performance of the PI DTC IPM drive.

Comparison of Proportional+Integral Control and Variable Structure Control of Interior Permanent Magnet Synchronous Motor Drives

A comparison of the performance of an interior permanent synchronous motor drive, when driven by two different types of direct torque controllers, is presented in this paper. Both these controllers utilize space vector modulation (SVM) to generate switching signals for the inverter. The first of these control strategies uses a Proportional and Integral (PI) controller and reference flux vector calculator (RFVC) to determine the reference stator flux linkage vector, instead of a switching table and hysteresis controllers employed by the basic DTC. The other control strategy, namely variable structure control scheme, is based on the design of discontinuous control signal that drives the system states towards special manifolds in the state-space. The switching surfaces are chosen in a way that the system will have the desired behaviour as the states converge to the manifolds. Both these control strategies have had positive impacts on improving the performance of the interior permanent magnet (IPM) synchronous motor drive during transient, steady state and dynamic operations. However, they each have their own drawbacks.

Wide speed sensorless SVM direct torque controlled interior permanent magnet synchronous motor drive

This paper investigates a sensorless direct torque control (DTC) scheme based on space vector modulation (SVM) for interior permanent magnet synchronous motor (IPMSM) drives over a wide speed range. Closed-loop control of both the torque and stator flux linkage are achieved by using two proportional-integral (PI) controllers. The reference voltage vectors are generated by a SVM unit. A high frequency signal injection technique is adopted at low speeds to obtain the rotor position information. The hybrid current-voltage model flux observer with a smooth handover algorithm estimates the stator flux linkage over the whole speed range. The operating range of the sensorless DTC drive is extended into the high speed region by incorporating field weakening. Experimental results confirm the effectiveness of the proposed method.

An Extended Kalman filter for sensorless direct torque controlled IPM synchronous motor drive

This paper investigates the application of an extended Kalman filter (EKF) for closed-loop flux, torque and speed estimation of a direct torque controlled (DTC) IPMSM drive over a wide speed range. The EKF provides a recursive optimum state estimation for IPMSMs using terminal signals that may be polluted by noise. Furthermore, the EKF has robustness to parameter variations, disturbance rejection capabilities and accurate estimation abilities. Experimental results verify the effectiveness of the proposed EKF observer for DTC of IPMSMs.This paper investigates the application of an Extended Kalman Filter (EKF) for closed-loop flux, torque and speed estimation of a direct torque controlled (DTC) IPMSM drive over a wide speed range. The EKF provides a recursive optimum state estimation for IPMSMs using terminal signals that may be polluted by noise. Furthermore, the EKF has robustness to parameter variations, disturbance rejection capabilities and accurate estimation abilities. Experimental results verify the effectiveness of the proposed EKF observer for DTC of IPMSMs.

Analysis of Cogging Torque and its Effect on Direct Torque Control (DTC) in a Segmented Interior Permanent Magnet Machine

This paper investigates reduced cogging torque seen in the Segmented Interior Permanent Magnet (SIPM) machine and explores the effects of cogging torque on direct torque control (DTC) performance. In the segmented IPM machine, the pole magnets are segmented to provide an improved flux-weakening capability to the rotor. The cogging torque of the segmented IPM machine is found to be significantly lower than that of a conventional, non-segmented IPM machine of similar ratings and dimensions. The cogging torque of the segmented IPM machine was first calculated using finite element analysis which was verified later by experimental measurements. The cogging torque of the conventional IPM rotor, using the same stator, was also calculated and measured. The DTC was implemented on both the segmented and conventional IPM machines to observe the effects of cogging torque on the speed, torque and flux performance of the controller. This paper presents results of cogging torque comparison and its effects on DTC performance between the two machines, and a detailed analysis of the reduced cogging torque seen in the Segmented IPM machine.

Sensorless SVM direct torque controlled interior permanent magnet synchronous drive

This paper presents a sensorless SVM direct torque control (DTC) scheme for interior permanent magnet (IPM) synchronous motors. A speed observer based on the stator flux linkage is investigated in this paper. In addition, an initial rotor position estimator is also introduced. By using high frequency signal injection and exploiting the saliency property of an IPM motor, the initial rotor position can be found. Both the position and speed estimators are simple, software-based and irrespective to machine parameters. Hence, the basic advantages of a DTC controller are retained. The sensorless DTC scheme is simulated in MATLAB and tested experimentally.

Very low speed operation of a variable structure direct torque controlled IPM synchronous motor drive using combined HF signal injection and sliding observer

The performance of a speed sensorless variable structure direct torque controlled interior permanent magnet synchronous motor drive is investigated in this paper. The speed is estimated using position information extracted using high frequency signal injection at low speeds and a sliding observer at high speeds. The changeover between these two algorithms is performed using a weighting function which smoothly hands over position information used for speed, torque and flux estimation. Experiments were performed to test the effectiveness of the proposed algorithm and results show that the sensorless drive is capable of accurately estimating position and speed at very low speeds including zero speed.

Sensorless direct torque and flux control of an IPM synchronous motor drive at low speed and standstill

Abstract This paper investigates a sensorless direct torque and flux control (DTFC) scheme for interior permanent magnet synchronous motor (IPMSM) drives at low speed and standstill. Closed-loop control of both the torque and stator flux linkage are achieved using two proportional-integral (PI) controllers. A high frequency signal injection technique is utilised at low speeds to obtain the rotor position information. The hybrid current-voltage model flux observer with a smooth handover algorithm estimates the stator flux linkage over the whole speed range. The sensorless method is capable of zero-speed full load operation. Experimental results confirm the effectiveness of the proposed sensorless space vector modulation-DTFC system.