Dissertations / Theses on the topic 'Induction motor drive; Vector control scheme'

High dynamic performance, which is obtained from dc motors, became achievable from induction motors with the recent advances in power semiconductors, digital signal processors and development in control techniques. By using field oriented control, torque and flux of the induction motors can be controlled independently as in dc motors. The control performance of field oriented induction motor drive greatly depends on the correct stator flux estimation. In this thesis voltage model is used for the flux estimation. Stator winding resistance is used in the voltage model. Also leakage inductance, mutual inductance and referred rotor resistance values are used in vector control calculations. Motor control algorithms use motor models, which depend on motor parameters, so motor parameters should be measured accurately. Induction motor parameters may be measured by conventional no load and locked rotor test. However, an intelligent induction motor drive should be capable of identifying motor parameters itself. In this study parameter estimation algorithms are implemented and motor parameters are calculated. Then these parameters are used and rotor flux oriented vector control is implemented. Test results are presented.

Thesis (Ph. D.)--Michigan State University. Dept. of Electrical Engineering, 2007.
Title from PDF t.p. (viewed on Apr. 16, 2009) Includes bibliographical references (p. 113-114). Also issued in print.

This work focuses on speed estimation techniques for sensorless closed-loop speed control of an induction machine based on direct field-oriented control technique. Details of theories behind the algorithms are stated and their performances are verified by the help of simulations and experiments. The field-oriented control as the vector control technique is mainly implemented in two ways: indirect field oriented control and direct field oriented control. The field to be oriented may be rotor, stator, or airgap flux-linkage. In the indirect field-oriented control no flux estimation exists. The angular slip velocity estimation based on the measured or estimated rotor speed is required, to compute the synchronous speed of the motor. In the direct field oriented control the synchronous speed is computed with the aid of a flux estimator. Field Oriented Control is based on projections which transform a three phase time and speed dependent system into a two co-ordinate time invariant system. These projections lead to a structure similar to that of a DC machine control. The flux observer used has an adaptive structure which makes use of both the voltage model and the current model of the machine. The rotor speed is estimated via Kalman filter technique which has a recursive state estimation feature. The flux angle estimated by flux observer is processed taking the angular slip velocity into account for speed estimation. For closed-loop speed control of system, torque, flux and speed producing control loops are tuned by the help of PI regulators. The performance of the closed-loop speed control is investigated by simulations and experiments. TMS320F2812 DSP controller card and the Embedded Target for the TI C2000 DSP tool of Matlab are utilized for the real-time experiments.

Vector control technique is being widely used in ac motors drives for precise dynamic control of torque, speed and position. The application of vector control scheme to the induction motor drive and the complete modeling, analysis and simulation of the drive system are presented in this thesis. State space models of the motor and the speed controller and the real time models of the inverter switches and the vector controller are integrated to model the drive. Performance differences due to the use of PWM and hysteresis current controllers are examined. Simulation results of the torque and speed drive systems are given. The drive system is linearised around an operating point and the small signal response is evaluated.
Master of Science

In this thesis, a practical vector controlled elevator drive is presented. Indirect vector control of induction machine is investigated in theory and then implemented. Control technique is compared with scalar control and induction machine is compared with dc motor. The operation of the system depends on induction machine parameters, so how to accurately and automatically obtaining of the parameters is also presented. Finally, the elevator system is introduced, the application of this control system to the elevator system is described and a basic elevator control system is simulated.

This thesis is about the development and performance enhancement of an induction motor electric vehicle drive system. The fundamental operation of the induction motor drive hardware and control software are introduced, and the different modulation techniques tested are described. A software simulation package is developed to assist in the control design and analysis of the drive system. Next, to establish the efficiency gains obtained by using space vector modulation in the improved drive system, an inverter with hysteresis current control is compared to the same inverter with space vector modulation in steady state and on separate driving profiles. A method for determining induction motor harmonic losses is introduced and is based on obtaining the phase current harmonics from sampled induction motor stator phase currents obtained. Using a semi-empirical loss model, the induction motor losses are compared between different pulse width modulation control strategies throughout the torque versus speed operating region. Next, several issues related to the robustness of the control design are addressed. To obtain good performance in the actual vehicle, a new method for driveline resonance compensation is developed and proven to work well through simulation and experiment. Lastly, this thesis discusses the development of a new method to compensate for the gain and phase error obtained in the feedback of the d-axis and q-axis stator flux linkages. Improved accuracy of the measured stator flux linkages will be shown to improve the field oriented controller by obtaining a more accurate measurement of the feedback electromagnetic torque.
Master of Science

Baigiamajame darbe sudarytas uždarosios asinchroninės bejutiklės vektoriškai valdomos pavaros imitacinis modelis ir ištirtos charakteristikos. Teorinėje darbo dalyje yra aptariami asinchroninių elektros pavarų privalumai bei šiose pavarose naudojami greičio jutikliai. Aprašomi stebiklių privalumai bei trūkumai, pagrindžiamas jų naudojimas asinchroninėse pavarose. Nagrinėjami bejutiklių elektros pavarų ypatumai, aprašomi vektorinio valdymo bendrieji principai bei aprašomi bejutiklėse vektoriškai valdomose pavarose naudojamų stebiklių modeliai. Pateikiami du skirtingi asinchroninių variklių matematiniai modeliai. Tiriamojoje dalyje parenkamas asinchroninio variklio modelis, tiriant abiejų imitacinių modelių dinamines greičio charakteristikas. Sudaromas stebiklio imitacinis modelis. Tiriamos stebiklio greičio dinaminės charakteristikos, sudaroma uždaroji greičio reguliavimo sistema su stebikliu. Analizuojamos uždarosios greičio reguliavimo sistemos greičio charakteristikos be apkrovos, su šuoline apkrova ir harmoniškai kintančia apkrova. Nagrinėjama sistemos stiprinimo koeficiento įtaka uždarosios greičio reguliavimo sistemos greičio charakteristikų pereinamiesiams procesams. Magistro darbas baigiamas tyrimo išvadomis, kuriose aptariamas darbo rezultatų realaus pritaikymo galimybės. Darbą sudaro 8 dalys: įvadas, žymėjimai, literatūros šaltinių analizė, tyrimo tikslas ir uždaviniai, teorinė dalis, tiriamoji dalis išvados ir pasiūlymai, literatūros šaltiniai.
The final master degree thesis presents sensorless vector controlled induction motor drive simulation model and characteristics. In the analytic part of master thesis advantages of induction motor drives and speed sensors are described. Advantages and disadvantages of speed estimators are presented and purpose of using them are proved. Peculiarities of sensorless motor drives, principles of vector control and models of speed estimators are analyzed. Two simulation models of induction motor are proposed. In the research part characteristics of induction motors are compared and motor model is chosen. Characteristics of open loop induction motor drive are investigated and simulation model of closed loop induction motor drive with speed estimator is designed. Characteristics of closed loop control system at no load, constant load and harmonic load are analyzed and influence of speed controller gain is considered. Thesis is closed with conclusions about designed system application in real projects. Structure: introduction, list of symbols, literature review, the study aims and objectives, the theoretical part, research part, conclusions and proposals, references.

碩士
崑山科技大學
電機工程研究所
97
A speed sensorless system is proposed for indirect vector control of induction motor drive. The synchronous flux angle used in indirect vector control are often sensitive to the motor parameters. In this thesis, a rotor time constant online tuner and a robust to parameters variations sliding mode observer are adopted. The former tuning scheme consists of a magnetic current observer and a rotor time constant observer. The estimated rotor time constant will approach to the actual rotor time constant when the estimated current error approaches zero. The proposed flux observer is based on a sliding mode stator current observer. Rotor flux is merely integrated from the control input of the current observer when the estimated current error approaches zero. In other words, the sliding mode observer is insensitive to motor parameters variations. Then, the aforementioned rotor time constant online tuning scheme and sliding mode rotor flux observer are combined with the sliding mode current controller proposed in [18] and apply to a speed sensorless induction motor drives. First, the proposed control scheme has simulated by MATLAB/Simulink toolbox to verify the feasibility of the proposed strategy. Finally, a PC-based experimental system is constructed to test the performances of the drive system.

碩士
中華科技大學
機電光工程研究所碩士班
101
Abstract The traditional six-switch three-phase (6S3Ph) inverter is used to variable speed drive for AC motors and uninterruptible power systems over the years. However, The current control method in power electronic circuits play an important role, especially the PWM(Pulse Width Modulation) converter is widely used in AC motor drives and continuous AC power supply. The conventional methods including triangular wave or space-vector-based chopper control or hysteresis control, rather the former is a fixed switching frequency, the latter is a variables witching frequency. This thesis presents an adjustable hysteresis current control. The scheme is consisting of two single-phase switching voltage source to supply the three-phase induction machine drive. The technology is based on single-phase four-switch inverter hysteresis current controlled that can reduce the switching frequency and obtain lower harmonic performance to improved third-level phase variable voltage source with hysteresis of inverter. In this research, the output load torque and THD are used to adjust value of current waveform and hysteresis, respectively. The method could reduce the switching frequency and lose under the limit maximum THD value.ThePSimsofeware simulation and verified that the method is simple and effective.

碩士
正修科技大學
電機工程研究所
96
The advantage of the conventional direct torque control (DTC) method is that both torque and flux linkage can be controlled rapidly to get a better and faster speed response. Because of using only 8 fundamental voltage space-vectors, DTC easily induces the large ripple problems of the controlled torque and flux responses. Therefore, this thesis proposes a proportional-integral controller (PIC) for induction motor drive based on DTC and space-vector pulsewidth modulation, to solve these ripple problems. However, since PIC is sensitive to parameter uncertainties and load disturbances, a hybrid sliding mode controller (SMC), involving a flux SMC and speed SMC, is then provided to improve the robustness of the controlled system for the parameter uncertainties and load disturbances. Based on field-oriented control principle and space-vector modulation technology, a flux SMC is firstly developed to achieve fast direct flux control and a speed SMC is, then, presented to enhance speed control response by direct torque control approach. Finally, simulation results, compared among DTC, PIC and Hybrid SMC, verify that the proposed hybrid SMC can achieve a better robust control performance, even though under the influence of parameter variations, load disturbance etc.

碩士
國立虎尾科技大學
電機工程研究所
101
In the thesis, a kind of hybrid vector control is implemented for three-phase induction motor drive. In order to achieve maximum torque control which based on estimating the flux magnitude and phase by motor parameters for indirect vector control, the hybrid vector control uses the voltage sensor to correct the variation of motor parameters, just like the effect of direct vector control with a flux estimator to measure the flux magnitude and phase. The three-phase induction motor drive consists of two dc power supplies, three power switches and three power diodes. Each of the induction motor windings can be controlled independently by three-switch inverter, which is driven by special current waveform. Therefore, when one of the windings of induction motor is used to detect induced voltage, it corrects variation of motor parameters to enhance robustness of the system. In the control circuit, both VisSim simulation and DSP TMS320F2812 are employed to finish digital control. Finally, some experimental results are presented to verify the feasibility of the hybrid vector control in the motor drive.

碩士
國立虎尾科技大學
電機工程研究所
99
In this thesis, hybrid vector control is used for three-phase induction motor drive to implement the torque control of motor. The three-phase induction driver combines a buck converter with a three-phase full-bridge converter. The three-phase full-bridge converter is composed of three diodes in upper arm and three power switches in lower arm. Indirect vector control of induction motor needs some motor parameters to control torque, but temperature affects the parameters and correct control. In addition, direct vector method controls the torque directly using a flux estimator, but the flux estimator is expensive and not easily to install. Therefore, a hybrid vector control method for three-phase induction motor drive is proposed. The method applies voltage sensor to control flux phase, then to control the torque. Finally, VisSim software is employed to simulate hybrid vector control for the motor drive. Simulation results are presented to verify the feasibility of the proposed hybrid vector control method.

碩士
中原大學
電機工程研究所
84
In the past, the induction motor was difficult to control due to its highly nonlinear and high-order dynamic. Recently, the technologies of microprocessors, power electronics and control theories have been rapidly developed. Using the advanced technologies, an induction motor can be controlled like a separately excited dc motor. The most popular way to control the induction motor is the indirect field-oriented control using voltage source inverter (VSI); and the control of VSI are implemented by the current control or the space vector control. In this thesis, the current control methods (hysteresis, predict and ramp comparison PWM), and the space vector control methods (average voltage and current control space vector) of the VSI will be discussed and implemented. Current control have the following merits: (1) simple control circuit; (2) combining the advantage of VSI and current source inverter (CSI); (3) high switching frequency; (4) small peak values of voltage and current during switching. On the other hand, the ramp comparison current co ntrolled PWM method needs addition analog control circuit, which results increasing of circuit cost and reducing the flexibility of the system. The space vector methods have the merits of short switching interval, reducing harmonic component and the carrier modulation is not need. So most fully digitized induction motor drive systems are implemented with space vector control. In this thesis, the theoretic principles of the current control and space vector control methods are described first. Next, the simul ation using Matlab are carrier out. Then the current and space vector control methods are implemented by a computed-based induction motor drive. The hardware circuits of the motor drive are mainly composed of three parts, one is the power circuit, another is the lockout and driving circuit, and the other is the ramp comparison

Variable-speed Induction motor drives are nowadays used for various kinds of industrial processes, transportation systems, wind turbines and household appliances in the world. The majority of drives are for general purpose speed control applications where accurate speed control is not required for entire speed range. But for high dynamic drive application, very precise and fast control of induction motor drive is essential. For such applications, sophisticated and well-performing control design is a key issue. Precise and accurate torque control of the Induction Motor (IM) can only be accomplished by vector control and direct torque control. In terms of space vector theory, vector control implies that the instantaneous torque is controlled by way of the stator current vector that is orthogonal to the rotor flux vector. Precise knowledge of the rotor flux angle is therefore essential for a vector controlled IM. IMs do not allow the flux position to be easily measured, so most modern vector controlled IM drives rely on flux estimation. This means that the flux angle is derived from a flux estimator, using the dynamic model of the IM. Given that the rotor speed of the IM is measured by a mechanical shaft sensor. Flux estimation is a fairly easy task. However, vector control of IM without mechanical shaft speed sensor is of current interest in industrial environment. The driving motivations behind the development in sensorless control are lower cost, improved reliability and operating environment. In this thesis, a sensorless vector control scheme for rotor flux estimation using current error space phasor based hysteresis controller is proposed including the method for estimation of leakage inductance, Ls. For frequencies of operation less than 25 Hz, the rotor voltage and hence the rotor flux position is computed during the inverter zero voltage space vector using steady state model of IM. For above 25 Hz, active vector period and steady state model of IM is used. The whole rotor flux estimation scheme is dependent on current error space phasor and the steady state motor model, with rotor flux as a reference vector. Since no terminal voltage sensing is involved, dead time effects will not create problem in rotor flux sensing at low frequencies of operation. But appropriate device on-state drop are compensated at low frequencies (below 5 Hz) of operation to achieve a steady state operation up to less than 1 Hz. A constant switching frequency hysteresis current controller is used in inner current control loop for the PWM regulation, with smooth transition of operation to six-step mode operation. A simple Ls estimation based on current error space phasor is also proposed to nullify the deteriorating effect on rotor flux estimation. The parameter sensitivity of the control scheme to changes in the stator resistance Rs is also investigated. The drive scheme is tested up to a low frequency operation less than 1 Hz. The extensive simulation and experiment results are presented to show the proposed scheme’s good dynamic performance extending up to six-step operation. In contrast to vector control, direct torque control (DTC) method requires the knowledge of stator resistance only and thereby decreasing the associated sensitivity to parameters variation and the elimination of speed information. DTC as compared to vector control does not require co-ordinate transformation and PI controller. DTC is easy to implement because it needs only two hysteresis comparators and a lookup table for both flux and torque control. This thesis also investigates the possibilities in improvement of direct torque control scheme for high performance induction motor drive applications. Here, two schemes are proposed based on the direct torque control scheme for IM drive using 12-sided polygonal voltage space vectors for fast torque control. The torque control scheme based on DTC algorithm is proposed using 12-sided polygonal voltage space vector. The basic DTC scheme is used to control the torque. But the IM drive is open-end type. For torque control, the voltage space vectors orthogonal to stator flux vector in 12-sided polygonal space vector structure are used as hexagonal space vector based DTC scheme. The advantages achieved due to 12-sided polygonal space vector are mainly fast torque control and small torque ripple. The fast transient of torque with precise control is achieved using voltage space vector placed with a resolution of ±15. The torque ripple will be less as 6n±1 (n=odd) harmonic torque is totally eliminated from the whole range of PWM modulation. The comparative analysis of proposed 12-sided polygonal voltage space vector based DTC and conventional hexagonal space vector based DTC is also presented. Extensive simulation and experiment results are also presented to show the fast torque control at speeds of operation ranging from 5 Hz to the rated speed. The concept of 12-sided polygonal space vector based DTC is further extended for a variable speed control scheme using estimated fundamental stator voltage for sector identification. The conventional DTC scheme uses stator flux vector for identification of the sector and the switching vector are selected based on this sector information to control stator flux and torque. However, the proposed DTC scheme selects switching vectors based on the sector information of the estimated fundamental stator voltage vector and its relative position with respect to the stator flux vector. The fundamental stator voltage estimation is based on the steady state model of IM and information of synchronous frequency which is derived from computed stator flux using a low pass filter technique. The proposed DTC scheme utilizes the exact position of fundamental stator voltage vector and stator flux vector position to select optimal switching vector for fast control of torque with small variation of stator flux within hysteresis band. The present DTC scheme allows the full load torque control with fast transient response to very low speeds of operation below 5 Hz. The extensive simulation and experiment results are presented to show the fast torque control for speed of operation from zero speed to rated speed. However, the present scheme will have all the advantages of DTC scheme using stator flux vector for sector identification. All the above propositions are first simulated by MATLAB/Simulink and subsequently verified by an experimental laboratory prototype. The proposed control schemes are experimentally verified on a 3.7 kW IM drive. The control algorithms of the sensorless vector control using current error space phasor as well as DTC using 12-sided polygonal voltage space vector are completely implemented on a TI TMS320LF2812 DSP controller platform. These are some of the constituents for chapters 2, 3 and 4 in this thesis. Additionally, the first chapter also covers a brief survey on some of the recent progresses made in the field of sensorless vector control, direct torque control and current hysteresis controller. The thesis concludes with suggestion for further exploration.

For low and medium power applications, conventional two-level inverters are widely used in industrial applications including electric vehicle drives, traction drives, distributed generation, power management and grid connected renewable energy systems. To filter out the harmonic currents from the load, passive line filters are used. These filters are designed to pass the fundamental phase current and suppress higher harmonic currents, making the filters bulky. To get a nearly sinusoidal current waveform, these two level inverters are switched at high frequency to shift the harmonic components in the phase current to high frequencies to reduce size and cost of the filter. But higher switching frequencies have some drawbacks like large dV /dt stresses on the motor terminals and switching devices, leading to electro-magnetic interference (EMI) problems and higher switching losses. For full DC bus utilization to enhance the power output from the two level inverter, the inverter has to operate in overmodulation region up to the six-step operation. Considerable fifth and seventh order (6n ± 1, n = odd) harmonics are produced when the inverter operates in overmodulation region. These include some low order harmonics like fifth and seventh, which are currently suppressed by using bulky passive line filters. Different high frequency modulation schemes are uniquely used in overmodulation region to suppress these harmonics. Another well accepted method of harmonic suppression is the selective harmonic elimination (SHE) techniques. SHE introduces notches at specific angles in a fundamental period of the inverter pole voltage to eliminate a particular harmonic component from the pole voltage. But, SHE involves extensive offline computation and requirement for higher memory for implementation of huge lookup tables. dodecagonal voltage space vectors have been reported in literature. Dodecagonal voltage space vector structures inherently eliminate fifth and seventh order (6n ± 1, n = odd) harmonics from the phase voltage. However, these require multiple isolated and unequal DC supplies (like VDC and 0.366VDC ). Generating DC voltage supplies at particular ratio to the main DC supply, requires additional circuitry. This increases the size of the converter and four quadrant back to back operation is not possible for the converter. To overcome the problems mentioned above, a novel switched capacitive filtering technique is proposed in this work for low and medium power drives applications. The filtering is done by an inverter fed by capacitor. A novel method to ensure zero power contribution by an inverter is shown, enabling the inverter to be fed by a capacitor. Thus, the capacitor fed inverter is shown to operate as a switched capacitive filter, which generates harmonic voltages that gets eliminated from the phase voltage of conventional two level inverters. With the proposed switched capacitive filtering technique, the following benefits are achieved. • Fifth and seventh order (6n ± 1, n = odd) harmonics are eliminated from the phase voltage, for the full modulation range of the two level inverters even while operating in overmodulation region and six-step mode. Thus, bulky passive line filters are avoided. • Since, the capacitive filter does not contribute any active power to the load, single DC supply operation is possible. Hence, four quadrant back to back operations is possible with the proposed filtering technique. • Dodecagonal voltage space vector structures are realized using single DC supply for the first time. • Modulation techniques for different power circuit topologies have been proposed which inherently controls the capacitor voltage at specific voltage levels for the full modulation range of the inverter including six-step operation. Hence, no additional pre-charging circuitry is required. • High frequency switching is shifted to the capacitive filter which is at a low voltage compared to the DC supply fed power contributing inverter. Thus, the main inverter need not be switched at high switching frequency for harmonic suppression. This reduces the switching loss as compared to conventional inverters, to achieve harmonic suppression of comparable order. • Reduced voltage stress on the switches of the switched capacitive filter. Hence, low voltage devices can be used to implement the switched capacitive filter, reducing the cost and size drastically as compared to conventional passive line filters. The proposed switched capacitive filtering scheme has been realized for open-end winding induction motor drive and three phase star connected three terminal induction motor drive where conventional two level inverter is used as the power contributing inverter. Additionally, extension of the capacitive filtering scheme to multilevel inverter fed drives is also shown, where the main power contributing inverter is a three level flying capacitor (FC) inverter. The power circuit implementations are briefly described as following. (i) In open-end winding three phase induction motors, the two terminals of each of the three phase windings are accessed. The main DC bus connected two level inverter feeds power from one end of the motor terminals. A capacitor fed two level inverter eliminates the fifth and seventh order harmonics from the other end for the full modulation range including overmodulation and six-step operation of DC bus fed inverter. The voltage space vectors from both the inverters connected at opposite ends of the motor forms dodecagonal voltage space vectors. An uniform pulse width modulation (PWM), for the full modulation range is proposed which switches from the dodecagonal voltage space vectors while inherently maintaining the capacitor voltage at 0.289VDC . (ii) In conventional star connection of three phase induction motors, all three terminals of the three phase windings are shorted from one end, leaving access to just three terminals. Such three terminal induction motor fed to conventional two level inverter is commonly used in many drives applications. Capacitor fed H-bridges are cascaded to such two-level inverters, to eliminate the fifth and seventh order harmonics from the phase voltage for the full modulation range including overmodulation and six-step operation of DC fed inverter. The voltage space vectors from capacitor fed H-bridges get added to the voltage space vectors from the two level inverter to form dodecagonal voltage space vectors. A PWM technique for the full modulation range is proposed to switch from the dodecagonal voltage space vector while inherently maintaining the three H-bridge connected capacitor voltages at 0.1445VDC . (iii) Advantages of dodecagonal space vector switching and multilevel inverters are achieved with a single DC supply. A DC supply fed three level flying capacitor (FC) inverter feeds active power to one end of the induction motor winding terminals and H-bridge connected capacitors eliminate fifth and seventh order harmonics from the other end of the motor winding terminals. The voltage space vectors from the three level FC inverter and the H-bridge inverter forms a three level dodecagonal voltage space vectors with symmetric triangular sectors. A PWM technique is developed to switch the three level dodecagonal space vectors and simultaneously control the H-bridge connected capacitors at 0.1445VDC . The fifth and seventh order harmonics are eliminated for the full modulation range of the three level FC inverter, including the extreme six-step operation. Additionally, the proposed inverter has also been shown to operate for rotor field oriented vector control of the open-end winding induction motor drive. For all the power circuit implementation of the switched capacitive filter, an increase of 7.8% in the linear modulation range (up to 48.8Hz) is achieved, implying better DC bus utilization as compared to conventional inverter topologies switching from hexagonal voltage space vectors. With advantages like fifth and seventh order (6n ± 1, n = odd) harmonic elimination throughout the modulation range, reduced dv/dt stress, lower switching frequency in high voltage devices, single DC supply requirement, dodecagonal voltage space vector switching, PWM technique with inherent capacitor balancing, increased linear modulation range and reduced voltage stress on high frequency switches, the proposed switched capacitive filtering scheme is well suited for low and medium power drives application with requirements for high dynamic performance and precise speed control.