Stator Flux Vector Control Research Articles

Fault-Tolerant Predictive Torque Control Design for Induction Motor Drives Based on Discrete Space Vector Modulation

Four-switch three-phase inverters (FSTPIs) are generally applied as fault-tolerant topologies or cost-effective topologies for induction motor (IM) drives. However, conventional predictive torque control (PTC) for FSTPI-fed IM suffers from poor steady-state performance and tedious weighting factor assignment. In this article, a PTC based on discrete space vector modulation (PTC-DSVM) for an FSTPI-fed IM drive is proposed. First, the relationship between the dc-link capacitor voltage offset (CVO) and the load current is derived, and a stator voltage compensation strategy is proposed to suppress the CVO. Meanwhile, a reference-voltage-vector-error-based cost function that combines the reference stator flux vector control, the stator voltage compensation strategy, and the deadbeat control is designed to fully eliminate the weighting factors in the cost function of the conventional PTC. In addition, a DSVM scheme is developed to increase the number of admissible voltage vectors and improve the steady-state performance of IM drives. A preselection algorithm based on the offset voltage vector and sector division is designed to reduce the number of candidate voltage vectors. Extensive simulations and experimental results with a 2.2-kW IM are demonstrated to validate the effectiveness of the proposed control strategy.

Dual direct torque control of doubly fed induction machine using second order sliding mode control

In this paper a dual direct torque control (DDTC) strategy with second-order sliding mode control (SOSMC) controller of the doubly fed Induction motor (DFIM) is presented in order to overcome some drawback such as ripples in torque, flux and to improve dual direct torque control (DDTC) performance toward the electrical parameters variations. This control strategy used in the doubly fed induction machine supplied, coupled by two voltage source inverters in rotor and stator sides witches are linked to two switching tables in order to determined the rotor and stator flux vector control. This controller based on super-twisting algorithm (STA). Comparative results between a classical controller (PI) and the proposed controller can prove the very satisfactory performance and robustness of this new controller.

Direct Stator Flux Vector Control Strategy for IPMSM using a Full-order State Observer

A direct stator flux vector control scheme in discrete-time domain is proposed in this paper for the interior permanent magnet synchronous motor (IPMSM) drive to remove the proportional-integral (PI) controller from the direct torque control (DTC) scheme applied to IPMSM and to obtain faster dynamic response and lower torque ripple output. The output of speed outer loop is used as the desired torque angle instead of the desired torque in the proposed scheme. The desired stator flux vector in dq coordinate is calculated with a given amplitude. The state-space equations in discrete-time for IPMSM are established, the actual stator flux vector is estimated in deadbeat manner by a full-order state observer, and then the closed-loop control is achieved by the pole placement. The stator flux error vector is utilized to calculate the reference stator voltage vector. Extracting the angle position and amplitude from the estimated stator flux vector and estimating the output torque are eliminated for the direct feedback control of the stator flux vector. The proposed scheme is comparatively investigated with a PI-SVM DTC scheme by experiment results. Experimental results show the feasibility and advantages of the proposed control scheme.

Indirect Control of a Doubly-Fed Induction Machine for Wind Energy Conversion

In this paper, a grid connected wind power generation scheme using a doubly fed induction generator ( DFIG) is studied. The aims of this paper are: The modelling and simulation of the operating in two quadrants (torque-speed ) of a DFIG, the analysis employs a stator flux vector control algorithm to control rotor current, the system enables optimal speed tracking for maximum energy capture from the wind and high performance active and reactive power regulation using the PI regulator. The simulation calculations were achieved using MATLAB ® -SIMULINK ® package. Lastly, the obtained results are presented, for different operating points, illustrating the good control performances of the system

A Novel Dynamic Overmodulation Strategy of Direct Torque Control

The direct torque control-space vector modulation (DTC-SVM) is well-known for achieving excellent dynamic overmodulation. However, the method uses complicated predictive stator flux vector control and requires high precision stator flux vector to define overmodulation mode. This paper proposes a straightforward dynamic overmodulation method and constant switching frequency controller without SVM to obtain a faster dynamic torque response in DTC for induction machines. To perform this method, the flux error status produced from the flux hysteresis comparator during dynamic condition is modified slightly before being fed to the look-up table. The verification of proposed method was performed using MATLAB/Simulink simulation package. The effects of different switching and operating condition on dynamic torque performance are analyzed. The result shows that a faster torque response is achieved in proposed dynamic overmodulation DTC method. The main benefit of the proposed method is its simplicity since only minor modification is made to the basic DTC hysteresis-based structure.

Qualitative performance evaluation of torque control methods for industrial applications

AbstractRobust control of torque has been a motivation for research in the servo and electric drives industry. For industrial drives and servo applications AC machine drives are gaining prominence over the conventional DC‐motor drives. Two methods, (a) field oriented control (FOC) and (b) the direct torque control (DTC) have been proposed to control an AC motor. FOC is a current control method and needs co‐ordinated transformation. Torque dynamic depends upon the modulator, which also decides the steady state performance. DTC on the other hand is more robust and has physically the fastest torque dynamic. These methods have succeeded in achieving a fast and dynamically decoupled torque control but at what expense? Problems of FOC are saturation of current controllers, current control in the overmodulation region, and parameter sensitivity. Problems with DTC are variable switching frequency and sampling period dependence of hysteresis controllers, during digital implementation. This paper highlights the problems and explains a method of achieving direct control of torque using a method of stator flux vector control. The analysis carried out here is backed with appropriate simulation results. Copyright © 2009 John Wiley & Sons, Ltd.

Stator Flux Vector Control of Induction Motor Drive in the Field Weakening Region

A torque control scheme that utilizes the stator flux components as control variables, applied to a speed-sensorless induction motor drive, is presented. The proposed scheme allows the motor to exploit the maximum torque capability in the whole speed range, and shows a reduced dependence from the motor parameters. It is based on a control algorithm that decreases the d-component of the stator flux as soon as the voltage corresponding to the maximum torque exceeds the available voltage. The control scheme produces a smooth transition into and out of the field weakening region and preserves the torque dynamic. The feasibility of the field weakening technique is confirmed by computer simulations and experimental tests.

Dual Direct Torque Control of Doubly Fed Induction Machine

The main idea developed in this paper is a novel biconverter structure to supply a doubly fed induction machine (DFIM). Two voltage source inverters (VSIs) feed the stator and rotor windings. The outputs of the two VSIs are combined electromechanically in the machine, and as a result, novel features can be obtained. For example, for high power drive applications, this configuration uses two inverters dimensioned for a half of the DFIM power. A new dual direct torque control is developed with flux model of DFIM. Two switching tables linked to VSI are defined for stator and rotor flux vector control. The satisfactory experimental and simulation results are shown, and they confirm good dynamic behavior in four quadrants of the speed-torque plane. Moreover, experimental results show the correct flux vector control behavior and speed tracking performances.

Direct Method of Overmodulation With Integrated Closed Loop Stator Flux Vector Control

Overmodulation achieves full utilization of installed dc link voltage, by modifying the magnitude and the phase of reference voltage vector. Due to the nonlinear behavior in this region, closed loop vector control becomes difficult. A simple method of overmodulation with closed loop control of stator flux vector is proposed in this paper. Instead of modifying the voltage reference by nonlinear equations or look up table, we propose a direct method to generate the switching times. In so doing, the average angular velocity of the stator flux vector is controlled linearly throughout the modulation range. The proposed method shows lower harmonic distortion compared with existing methods. It greatly reduces the complexity and cost of achieving overmodulation over existing schemes.

Induction motor drive based on the stator flux vector control

This paper presents a new torque control algorithm for induction motors, based on the stator flux vector control. For each sampling period, the value of the stator voltage is calculated to keep the stator flux equal to the reference vector, while the stator flux reference vector is calculated to keep the rotor flux amplitude constant at all operating conditions. An improved stator and rotor flux estimation algorithm is proposed, enabling robust and stable operation of the drive, even at low speeds. The induction motor torque is manipulated by variations of the flux angular velocity, enabling drive operation with fixed switching frequency and ripple-free torque in the steady state. The performance of the proposed algorithm is tested through various experimental runs, proving good behavior of the drive in both transient and steady-state operating conditions.

Decoupled direct control for PWM inverter-fed induction motor drives

A new direct torque and stator flux control method is presented for pulsewidth modulation (PWM) inverter-fed induction motors. This new strategy, called decoupled direct control (DDC), is based on a decoupling matrix that allows for the separate control of the stator flux and the torque. This method is compared to the well-known direct field-oriented control (FOC) and stator flux vector control (SFVC) methods. Two DDC-based methods are presented. The first determines the stator voltage vector such that the torque and the flux track their respective reference trajectories in one sampling time. The second sets separately the dynamic behavior of the torque and stator flux errors by the use of proportional-plus integral (PI)-type controllers. These methods take into account the full motor dynamics without the need of a coordinate transformation and reduce significantly computation requirements compared to FOC and SFVC. The two proposed strategies have been implemented experimentally and comparisons with FOC and SFVC were carried out. The obtained results show the effectiveness of the proposed PI-DDC strategy.

Improved direct torque and flux vector control of PWM inverter-fed induction motor drives

In this paper, a direct torque and stator flux vector control system is presented. The principle of this method was proposed by Takahashi and Noguchi in 1985. In contrast to the field oriented control, no coordinate transformation and current control loop is required. In practical application, however, problems occur with starting and operation in the zero speed region. This paper shows how, by introducing an additional carrier signal to the torque controller input, a robust start and improved operation in the low speed region can be achieved. The simulation and experimental results which illustrate the performances of the proposed system are presented. Also, nomograms for controller design are given. >

Torque Vector Control (TVC)-A Class of Fast and Robust Torque-Speed and Position Digital Controllers for Electric Drives

ABSTRACT This paper presents the fundamentals of a new class of torque speed and position controllers for electric drives, characterized by the association of a modified sliding mode position (speed) controller and stator flux control through a unique table of optimal conduction sequence to fire directly the static power converter SCR switches. Robustness is provided by the sliding mode controller and stator (instead of rotor) flux vector estimation while control precision is secured by the torque pulsation controller. Fast response is obtained through the table of optimal conduction sequence which leads to the fastest response available through a stator flux vector (or stator accelerating field) control obtained without the transformation of coordinates or special techniques. The control computation time (costs) is drastically reduced in comparison with PWM transvector (or field accelerating) methods while the performance in terms of precision, response and robustness are better.