M.F. Rahman

Analysis of direct torque control in permanent magnet synchronous motor drives

This paper describes an investigation of direct torque control (DTC) for permanent magnet synchronous motor (PMSM) drives. It is mathematically proven that the increase of electromagnetic torque in a permanent magnet motor is proportional to the increase of the angle between the stator and rotor flux linkages, and, therefore, the fast torque response can be obtained by adjusting the rotating speed of the stator flux linkage as fast as possible. It is also shown that the zero voltage vectors should not be used, and stator flux linkage should be kept moving with respect to the rotor flux linkage all the time. The implementation of DTC in the permanent magnet motor is discussed, and it is found that for DTC using available digital signal processors (DSPs), it is advantageous to have a motor with a high ratio of the rated stator flux linkage to stator voltage. The simulation results verify the proposed control and also show that the torque response under DTC is much faster than the one under current control.

A novel direct torque controlled interior permanent magnet synchronous machine drive with low ripple in flux and torque and fixed switching frequency

A modified direct torque control (DTC) scheme for interior permanent magnet synchronous machine (IPMSM) is investigated in this paper, which features in very low flux and torque ripple and almost fixed switching frequency. It is based on the compensation of the error flux linkage vector by means of space vector modulation. Modeling and experimental results show that the flux and torque ripples are greatly reduced when compared with those of the basic DTC. With the new scheme, very short sampling time is not essential. All the advantages of the basic DTC are still retained. In addition, fixed switching frequency at different operating conditions becomes possible. The field-weakening control of this drive is also studied; an IPM DTC drive with a wider operation range and lower flux and torque ripple has been achieved experimentally.

A direct torque controlled interior permanent magnet synchronous motor drive incorporating field weakening

This paper presents a new control scheme for the wide speed range operation of interior permanent magnet synchronous motor (PMSM) drives, where both torque and stator flux linkage are directly controlled. The proposed scheme possesses some attractive features when compared to conventional current controlled drives. Current controllers followed by PWM or hysteresis comparators and coordinate transformation are not used. This eliminates the delays through these networks and offers the possibility of dispensing with the rotor position sensor for the electronic commutator, if the initial rotor position is known only approximately. The scheme incorporates all the usual control regimes such as the maximum torque per ampere operation in constant torque region, the flux weakening region, and operates the drive within the voltage and current limits of the motor/inverter. The control scheme has been verified by simulation and experimental tests with a prototype interior magnet motor. This paper describes the scheme in detail, followed by results of its implementation.

Sensorless Sliding-Mode MTPA Control of an IPM Synchronous Motor Drive Using a Sliding-Mode Observer and HF Signal Injection

This paper proposes a nonlinear sliding-mode speed-control scheme for interior permanent-magnet synchronous motor (IPMSM) drives incorporating the maximum-torque-per-ampere trajectory. The drive uses an adaptive sliding-mode observer (SMO) for rotor-speed estimation. The global asymptotic stabilities of both the controller and observer are guaranteed by Lyapunov stability analysis. The very low speed and standstill performance of the drive is further enhanced by combining high-frequency signal injection with the SMO. Hence, the sensorless drive is capable of exhibiting high dynamic and steady-state performances over a wide speed range. Experimental results confirm the effectiveness of the proposed method.

Online Stator and Rotor Resistance Estimation Scheme Using Artificial Neural Networks for Vector Controlled Speed Sensorless Induction Motor Drive

This paper presents a new method of online estimation for the stator and rotor resistances of the induction motor for speed sensorless indirect vector controlled drives, using artificial neural networks. The error between the rotor flux linkages based on a neural network model and a voltage model is back propagated to adjust the weights of the neural network model for the rotor resistance estimation. For the stator resistance estimation, the error between the measured stator current and the estimated stator current using neural network is back propagated to adjust the weights of the neural network. The rotor speed is synthesized from the induction motor state equations. The performance of the stator and rotor resistance estimators and torque and flux responses of the drive, together with these estimators, are investigated with the help of simulations for variations in the stator and rotor resistances from their nominal values. Both resistances are estimated experimentally, using the proposed neural network in a vector controlled induction motor drive. Data on tracking performances of these estimators are presented. With this speed sensorless approach, the rotor resistance estimation was made insensitive to the stator resistance variations both in simulation and experiment. The accuracy of the estimated speed achieved experimentally, without the speed sensor clearly demonstrates the reliable and high-performance operation of the drive

A direct torque controller for permanent magnet synchronous motor drives

This paper describes an investigation of direct torque control (DTC) for permanent magnet synchronous motor (PMSM) drives. The analysis of PMSMs shows that the increase of electromagnetic torque is proportional to the increase of the angle between the stator and rotor flux linkages and therefore fast torque response can be obtained by increasing the rotating speed of the stator flux linkage as fast as possible. The implementation of DTC in PMSM drives is discussed and the switching table specific for an interior PMSM is derived. The proposed control is implemented on a prototype PMSM, which has a standard induction motor stator, and the experimental results show that the torque response is extremely fast. It is also demonstrated that the position sensor is not essential for the inner torque control loop of PMSM drives with DTC.

A novel direct torque control for interior permanent-magnet synchronous machine drive with low ripple in torque and flux-a speed-sensorless approach

A novel direct torque control (DTC) scheme for interior permanent magnet synchronous machine is proposed in this paper, which features low torque and flux ripple and almost fixed switching frequency. The torque and flux ripples have been significantly reduced if compared with those of the basic DTC reported in the literature. A speed estimation scheme is integrated with the proposed DTC scheme.

The dynamic characteristics of an isolated self-excited induction generator driven by a wind turbine

The analysis of self-excited induction generator (SEIG) starts from its magnetizing inductance. The value of magnetizing inductance at very low terminal voltage is one of the key factors for self excitation. This paper presents the effect of magnetizing inductance on self-excitation and describes the loading analysis of an isolated induction generator. It also describes how the operating frequency and generated voltage are affected by the change in operating slip value. Wind powered self-excited induction generators (SEIG) have an input wind which is not controllable, but they can be set to operate within a given variation of speed. The experimental and simulated results for a dynamic generated voltage, frequency, stator current and power are presented.

A direct torque-controlled interior permanent-magnet synchronous motor drive without a speed sensor

This paper reports results of further investigation of the so-called direct torque control (DTC) technique to an interior permanent magnet (1PM) synchronous motor drive. This torque control technique for IPM motors requires no dq-axes current controllers and coordinate transformnation networks. A completely sensorless 1PM motor drive with DTC, which uses a new speed estimator from the stator flux linkage vector and the torque angle, is presented. It is shown that including the torque angle in the estimation process results in a far more accurate transient speed estimator than what is reported in the existing literature.

Problems associated with the direct torque control of an interior permanent-magnet synchronous motor drive and their remedies

This paper investigates problems associated with the implementation of a direct torque control (DTC) strategy for an interior permanent-magnet synchronous motor drive. The DTC technique is increasingly drawing attention because of elimination of current controllers and, hence, their inherent delays, and elimination of the rotor position sensor. The latter advantage perhaps is the main impetus for considering this new approach of torque control. Problems associated with this controller, namely, the offset in the current measurements, the stator resistance variation, and the requirement of initial rotor position are addressed in this paper. Ways of mitigating of these problems are also investigated in this paper. These are evaluated with modeling and experimental studies, results of which are also presented.