Data-driven online temperature compensation for robust field-oriented torque-controlled induction machines

Squirrel-cage induction machines (IMs) with indirect field-oriented control are widely used in industry and are frequently chosen for their accurate and dynamic torque control. During operation, however, temperature rises leading to changes in machine parameters. The rotor resistance, in particular, alters, affecting the accuracy of the torque control. The authors investigated the effect of a rotor resistance parameter mismatch in the control algorithm on the angular rotor flux misalignment and the subsequent deviation of stator currents and motor torque from their setpoints. Hence, an online, data-driven torque compensation to eliminate the temperature effect is proposed to enable robust torque-controlled IMs. A model-based analysis and experimental mapping of the temperature effect on motor torque is presented. A temperature-torque lookup-table is subsequently implemented within the control algorithm demonstrating the ability to reduce the detrimental effect of temperature on torque control. Experimental results on a 5.5 kW squirrel-cage induction motor show that the proposed data-driven online temperature compensation method is able to reduce torque mismatch when compared to having no temperature compensation. Up to 17% torque mismatch is reduced at nominal torque and even up to 23% at torque setpoints that are lower than 20% of the nominal torque. A limited torque error of <1% remains in a broad operating range

Direct torque control for dual three-phase induction motor drives

A direct torque control (DTC) strategy for dual three-phase induction motor drives is discussed in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The DTC strategy is based on a predictive algorithm and is implemented in a synchronous reference frame aligned with the machine stator flux vector. The advantages of the discussed control strategy are constant inverter switching frequency, good transient and steady-state performance, and low distortion of machine currents with respect to direct self-control (DSC) and other DTC schemes with variable switching frequency. Experimental results are presented for a 10-kW DTC dual three-phase induction motor drive prototype

Self-Commissioning Algorithm for Inverter Non-Linearity Compensation in Sensorless Induction Motor Drives

In many sensorless field-oriented control schemes for induction motor (IM) drives, flux is estimated by means of measured motor currents and control reference voltages. In most cases, flux estimation is based on the integral of back-electromotive-force (EMF) voltages. Inverter nonlinear errors (dead-time and on-state voltage drops) introduce a distortion in the estimated voltage that reduces the accuracy of the flux estimation, particularly at low speed. In the literature, most of the compensation techniques of such errors require the offline identification of the inverter model and offline postprocessing. This paper presents a simple and accurate method for the identification of inverter parameters at the drive startup. The method is integrated into the control code of the IM drive, and it is based on the information contained in the feedback signal of the flux observer. The procedure applies, more in general, to all those sensorless ac drives where the flux is estimated using the back-EMF integration, not only for IM drives but also for permanent-magnet synchronous motor drives (surface-mounted permanent magnet and interior permanent magnet). A self-commissioning algorithm is presented and tested for the sensorless control of an IM drive, implemented on a fixed-point DSP. The feasibility and effectiveness of the method are demonstrated by experimental result

Stability Analysis and Robust Controller Design of Indirect Vector Controlled Induction Motor

The thesis considers stability analysis and controller design through different performance measures for indirect vector controlled induction motor (IVCIM).These problems are known to be complex due to nonlinearity, large order and multi-loop scenario. Some new approaches and results on IVCIM are proposed in this work. IVCIM dynamics is well known for having different bifurcation behavior, viz., saddle-node, Hopf, Bogdanov–Takens and Zero–Hopf bifurcations due to rotor resistance variation. These bifurcations affect the control performance and may lead to stalling or permanent damage of motor. A numerical analysis of these bifurcations for proportional integral (PI) controlled IVCIM is made in this thesis using full-order induction motor model (stator dynamics is included). This analysis aids to determine the allowable bifurcation parameter variation range as well as suitable choice of speed-loop gains to avoid these. Some new observations on the bifurcation behavior are made. Simulation and experimental results are presented validating the bifurcation behaviors. For improving dynamic performance in the presence of load torque and rotor resistance variation, a new method for designing PI gains is proposed for IVCIM. The inner-loop current PI controllers are tuned simultaneously along with the speed controller. This method is implemented using a static output feedback scheme in which iterative linear matrix inequality (ILMI) based∞control technique is employed. Such a design makes stator currents and speed response to be robust against rotor resistance and load variations. A comparison between proposed design and a conventional one is shown using simulation and experimental results that validate the superiority of the proposed approach. Owing to multi-loop and nonlinear system behavior, IVCIM dynamics is known to have coupling in between the two inner-loop stator current components (flux and torque). Such coupling affects the dynamic torque output of the motor. Decoupling of the stator currents are important for smoother torque response of IVCIM. Conventionally, additional feedforward decoupler is used to take care of the coupling that requires exact knowledge of the motor parameters and additional circuitry or signal processing. A method is proposed to design the regulating PI gains while minimizing coupling without any requirement of additional decoupler. The variation of the coupling terms for change in load torque is considered as the performance measure. The same ILMI based∞control design approach is used to obtain the controller gains. A comparison between the conventional feedforward decoupling and proposed decoupling scheme is presented through simulation and experimental results that establish the effectiveness of the proposed method riding over its simplicity. Finally, since the PI controller can yield limited performance, a dynamic controller is designed for the IVCIM drive system. In the design process, iron-loss dynamics are incorporated into induction motor model to fetch benefit through better performance. A sequential design method is used for the controller design in which, first, the inner-loop controllers are designed. The designed inner-loop controllers is then used for designing the outer speed-loop controller. The proposed design employs ILMI based∞control design for dynamic output feedback controller that makes stator currents and speed response to be robust against disturbances. A comparison among proposed dynamic controller design, PI controller and compensator design is shown using simulation and experimental results demonstrate enhanced performance of the proposed controller and suitability for industrial purpose

Sensored and sensorless speed control methods for brushless doubly fed reluctance motors

The study considers aspects of scalar V/f control, vector control and direct torque (and flux) control (DTC) of the brushless doubly fed reluctance machine (BDFRM) as a promising cost-effective alternative to the existing technological solutions for applications with restricted variable speed capability such as large pumps and wind turbine generators. Apart from providing a comprehensive literature review and analysis of these control methods, the development and results of experimental verification, of an angular velocity observerbased DTC scheme for sensorless speed control of the BDFRM which, unlike most of the other DTC-concept applications, can perform well down to zero supply frequency of the inverter-fed winding, have also been presented in the study

Performance Analysis of Induction Motor For Sudden Load Disturbance Using PI And FUZZY Controller

This paper presents the improved performance in speed of an induction motor by applying vector control techniques which transforms the induction motor from nonlinear to linear plant system and fuzzy control system provides the better running performance of the induction motor at various disturbances in load by tracking the waves to reach the steady state response earlier than PI controller. The benefits of squirrel-cage induction motors are high robustness and low maintenance which make it widely used through various industrial modem processes, with growing economical and demands. In conventional FOC, PI controller is used to control the speed response of the induction motor drive. The use of PI controller induces many problems like high overshoot, oscillation of speed and torque due to sudden changes in load and external disturbances. This behavior of the controller causes deterioration of drive performance. To overcome this disadvantages an intelligent controller based on fuzzy logic is employed in the place of the conventional PI controller. DOI: 10.17762/ijritcc2321-8169.15061

A Comparative Analysis of Field Oriented Control and Direct Torque Control of Induction Motor Drive

Electric Motor Drive System is employed in the various industrial applications such as pumping, air blowing, cooling and compression refrigeration. The motor drive speed control can be achieved by variety of techniques, but an emerging one is Variable Frequency Drive System (VFDS). The motor driven equipment on a typical industrial site accounts for approximately two thirds of the electricity consumption. Now-a-days induction motor is the main work-horse of the industries. So controlling of performance of induction motor is most precisely required in many high performance applications. Scalar control method gives good steady state response but poor dynamic response. While vector control method gives good steady state as well as dynamic response. But it is complicated in structure so to overcome this difficulty, direct torque control introduced. This paper discusses the comparative analysis of Field Oriented Control (FOC) and Direct Torque Control (DTC) methods of Polyphase Induction Motor (PIM) according to their working principle, structure complexity, performance, merits and demerits

Unified Direct-Flux Vector Control for AC Motor Drives

The paper introduces a Unified Direct-Flux Vector Control scheme suitable for sinusoidal AC motor drives. The AC drives considered here are Induction Motor, Synchronous Reluctance and synchronous Permanent Magnet motor drives, including Interior and Surface-mounted Permanent Magnet types. The proposed controller operates in stator flux coordinates: the stator flux amplitude is directly controlled by the direct voltage component, while the torque is controlled by regulating the quadrature current component. The unified direct-flux control is particularly convenient when flux-weakening is required, since it easily guarantees maximum torque production under current and voltage limitations. The hardware for control is standard and the control firmware is the same for all the motors under test with the only exception of the magnetic model used for flux estimation at low speed. Experimental results on four different drives are provided, showing the validity of the proposed unified control approac

Performance Comparison of Different Speed Estimation Techniques in Sensorless Vector Controlled Induction Motor Drives

Field-oriented control and direct torque control are fast becoming necessities of modern industrial setups for induction motor drive control. Induction motors are considered as the beginning part to create any electrical drive system to be subsequently utilized for several industrial requirements. So now a day due to its high application the need to control the performance of the induction motor is gaining importance. In modern control system, IM is analyzed by different mathematical models mainly depending on its applications. Vector control method is suitably applied to induction machine in 3-phase symmetrical or in 2-phase unsymmetrical version. For vector control IM is realized as DC motor having its characteristics. This dissertation work is aimed to give a detailed idea about the speed control and variations in an induction motor through vector control technique thereby showing its advantage over the conventional scalar method of speed control. It also focusses on the speed estimation techniques for sensorless closed loop speed control of an IM relying on the direct field-oriented control technique. The study is completed through simulations with use of MATLAB/Simulink block sets allowing overall representation of the whole control system arrangement of the Induction motor. The performance of different sensorless schemes and comparison between them on several parameters like at low speed, high speed etc. is also provided emphasizing its advantages and disadvantages. The analysis has been carried out on the results obtained by simulations, where secondary effects introduced by the hardware implementations have not been considered. The simulations and the evaluations of different control techniques are executed using parameters of a 50 HP, 60 Hz induction motor which is fed by an inverter