space vectors of motor variables, such as the voltage and flux. They are employed known direct torque control (DTC) method described in the. Field Oriented Control: FOC has two types: Direct vector control (DVC) and Indirect flux . A Modified Direct Torque Control for Induction Motor Sensorless Drive. View Test Prep - Sensorless Vector and Direct Torque Control (OCR)- P. Vas_1. pdf from ELECTRICAL at caite.info University of Technology. Monographs.
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Serzsorless uector arid direct torqrre coiifrol () Peter Vas. Sensorless Vector and Direct. Torque Control. Peter Vas. Professor oJJ'Efec~ricnl E~lgilleerfi~g. Peter Vas - Sensor Less Vector and Direct Torque Control - Ebook download as PDF File .pdf), Text File .txt) or read book online. PDF | This paper presents the application of a sensorless direct torque control ( DTC) for an flux vector and all the voltage vectors in the level inverter.
Tlie block diajgam of the rotor-oriented controlled permanent-magnet synchronous macliine using Cartesian coordinates is shown in Fig. It follows that i. Many industrial companies have marketed various forms of induction. If the machine has a so-called double-cage pMs. New scheme for speed control is called combined vector control and DTC is employed by Boulghasoul et al.
This is the reason for the terminology 'vector control'. Because of the high cost of efficient. Owing to their excellent control capabilities. Variable-speed a. In particular. The cage motor is simple and rugged and is one of the cheapest machines available at all power ratings. As for d. I General introduction In the past. These problems can be overcome by the application of alternating-current motors.
The hook also covers savings. At present direct. In addition. In this drive. In tlie case of d. With vector control of a. Many industrial companies have marketed various forms of induction. They have established a sub- torque-controlled induction-motor drive. Due to the increasing importance of switched reluctance motors technique when. Vector-controlled drives torque-controlled drives are receiving great attention worldwide.
The book contains a step-by-step. Basic torque control schemes. Direct-torque-controlled In tlie present book the very wide field of torque control of smooth-air-gap and es were introduced in Japan by Takahashi and also in Germany by Depenbrock salient-pole a. It is the primary aim of the present permanent-magnet synchronous motors. Great emphasis is laid on presenting a xpected that other manufacturers will soon follow.
Vector-controlled drives are one particular type mathematical and physical details of numerous direct torque control DTC of torque-controlled drive. In the absence of this control.
In recent years. They have achieved a high degree of maturity and have become ago. Presently only one large manufacturer is marketing one form of direct. For this drive is the so-called direct-torque-controlled drive. The other type of high-performance torque-controlled schemes of synchronous motors and induction motors are also discussed. The theory developed also covers tlie opera- and yield unwanted oscillating dynamic response. The details of a very large number of d.
Following the early works of Blaschke and Hasse. It is possible to contribute to tlie energy savings by the application of some drive applications using artificial intelligence fuzzy logic.
Four types of vector control are considered: The formulae given in many well-known textbooks on machine theory understanding of these drives and also to recognize the main difTerences between which d o not discuss space-vector theory have also implied that.
This physical picture.. This will help the reader to have a good earlier. The field flux can be - established either by a stationary d. The derivation is not given fact that the rotor currents or rotor flux of a squirrel-cage induction motor cannot here.
Hence the terminology: It follows from eqn 1. Equations 1. Unfortunately this similarity was not emphasized before the s. At present. The torque- 1. Conventional d In these three cases the instantaneous electromagnetic torque can be expressed as follows: In eqn 1.
In a ing reference rrame. The required knowledge of space- monitoring of the instantaneous electromagnetic torque of an induction machine. In this case.. Details of all the vector drives and direct-torque-controlled drives instantaneous electromagnetic lorque have not been simplified.
The application of eqn 1. Even in will be kept to a minimum. Torque control can be achieved by varying the armature current. This principle can also be used for the - instantaneous torque control of ax.
It should be noted that in the pre- various manufacturers. There are in general three possibilities for the selection of the flux-linkage proportional to the product of the field current. It is a common feature of all vector. The direct implementation relies on tlie direct measurement consideration by using a thermal model of tlie machine.
Tlie components of the hese have relatively simpler hardware and better overall performance at low stator flux-linkage space vector can also be used to obtain the rotor speed signal frequencies.
The monitoring of tlie stator voltages can irect vector control scliemes use searcli coils. Details of various sensorless drive very small and the ohmic voltage drops become dominant. The indirect method uses a machine model. Drifts and otisets can r estimation of the rotor-. Thus an accurate knowledge equation is utilized in tlie vector control implementations of smooth-air-gap of the machine inductances is required and tliis is a difficult problem.
Hall angle of the Rux-linkage space vector e. At low frequencies more sophisticated techniques must be e indirect methods are liiglily dependent on macliine parameters.
These include self-tuning controller applications. The overall accuracy of the estim. They are also temperature- real axis of the stationary reference frame. It should be noted that for simplicity. As shown below in magnetizing flux-linkage vector is obtained by using monitored values of the Section 1. In contrast to direct metliods. When the selected flux-linkage space vector is the rotor Hux-linkage vector IR. Schemes using tlie flux angle and also the flux-linkage modulus. Some of these models also use tlie rotor speed or rotor reference frame must be transformed into the stator current components in the position.
Traditional used to obtain the stator flux-linkages. This introduces limitations due to machine struc- structed by using the monitored value of the d. In principle.. The stator There are basically two dilferent types of vector control techniques: Many applications use indirect scliemes. When the selected flux-linltage is the magnetizing flux-linkage space vector. F G is a function generator. Such a model can be obtained by considering the rotor space-vector voltage equation of the induction motor see Section 4.
For this purpose is. When the conventional field-weakening technique is used. In the simple case shown.. In Fig. Dirccl rotor-flux-oriented control or induclion motor with impressed stator currcnb. This yields the modulus and angle of the rotor flux-linkage space vector hence the name flux model. It can be seen that the sclieme shown in Fig.. For this purpose the relationship between the stator current space vector expressed in the rotor-flux-oriented reference frame Ti and the stator current space vector expressed in the stationary ference frame is is considered.
In the drive scheme of Fig. This can he a ntional PI controller.. For illustration purposes Fig.. To obtain a solution.. The flux. This can be used for feld- cening purposes. Low frequency response. A synchronous reluctance machine is a salient-pole machine which produces i There are basically three types of permanent magnet machines with buried magnets. The transformation of i These obtained. In and their inferior performance combined with their relatively high price have Fig.
In the SYRM with modulus li. If the synchronous machine is supplied by a current- controlled voltage-source PWM inverter The With this structure it is possible to produce vesy high saliency ratios. Such synchronous Figure In the permanent-magnet synchronous macliiue with inset magnets.
This also leads to fast torque responses I [see eqns For high-performance drives it is possible Lo use various rotor configura- tions: The expressions used for the estimation or i..
By using multiple segmental structures In earlier constructions In the permanent- magnet synchronous machine with buried magnets interior magnets. If the reference value of the slip angle O. The rotor position There are basically three types of permanent-magnet synchronous machine tlie permanent magnets are on the rotor. As stated above. Since changed rapidly e.. In contrast to this. It follows from stator current components is..
I cannot exceed its maximum value i.. The torque expres.. If the magnet flux is constant. Equation 1. This follows from the fact that the magnet flux is Iixed to the direct axis of the rotor In tlie past. It can be seen that the electromagnetic torque is proportional to the is 90" and maximum torquelampere is obtained..
It also follows that maximum torque per expression also follows directly from the fact that for all singly salient electrical stator current is obtained when the torque angle is 90". It would permanent-magnet synchronous motor is simple. Figure 1.
It can also be seen that the electromag.. The vector control scheme for the these permanent magnets can be restrictive for many applications. This bas opened up new possibilities for a larger-scale rotor-flux-oriented control is performed. Below base speed. In this expression the rect- In a permanent-magnet synchronous motor witli surface-mounted magnets.. The stator current components in the stationary reference frame i..
Although such a salient machine similarly to the stator of an induction machine.. It should be noted that the i.. The synchronous reluctance motor SYRM is a greatly robust singly- of change of the angle of the stator flux-linkage space vector.. In a synchronous machine with surface-mounted magnets..
In permanent-magnet synchronous motors using these materials. This position p. This effect must he considered when design- ing the motor. In general. The demagnetization of tlie permanent magnet is non-reversible when a large d-axis current is applied. These types of motors were developed in is. In a high-performance synchronous reluctance motor the rotor is axially. It is expected that permanent-magnet machines will carrying balanced three-phase currents..
This last equation magncts supplied by a currcnt-controlled PWM inverter. It should be noted that tliis scheme is similar to that shown weakening capability. Thus there is no demagnetization effect caused by tlie torque-producing stator current.. In an electrically excited synchronous machine. On the inputs of these the difference the synchronous reluctance machine shown in Fig. This is why in general the rotor position is required e..
Equation The subscripts d and q denote the direct. In a vector-controlled synchronous reluctance motor different constant-angle control strategies: By considering that the electromagnetic torque is developed by the interaction of the stator flux-linkage space vector and stator current space vector.. The electromagnetic torque of a synchronous reluctance motor can also be expressed similarly to that or the induction motor or the permanent-magnet synchronous motor.
It should he noted that the rotor-oriented control scheme of the output of hysteresis current controllers. Rotor-oricntcd control of synchronous reluclance motor supplied by a current-controlled the measured stator currents i. The eqn 1. This estimation block can be implemented in various permanent-magnet synchronous motor with surface magnets.
Due to the absence of rotor currents. In general there are three 1. It will be proved in where rotor-oriented control is performed. It follows that It is important to note that in eqn 1. These reference values are obtained in the dependent.
Reluctance torque is created by the alignment of the minimum reluctance path of the rotor with the rotating magnetizing m. This constant phase current. The required current profile is a non-linear function of the rotor position and also of the electromagnetic torque. Calculatiou of the phase current references For constant torque.
The direction of the torque is always towards the nearest. When a stator pole-pair is energized. To obtain negative braking torque.
In a 'sensorless' drive the position information is obtained witliout rotation. In the SRM the direction of rotation is current in a stator phase should be switched on during the constant inductance region so it can build up before the region of increasing inductance starts. In contrast to other types of a. If tlie fundamental switching frequency is f.. The rotor is of the reluctance type the electromagnetic torque as a product of the flux.
When designing stator-current-rererence waveforms for constant torque opera- is the angular rotor speed and N. Thus positive torque can only be produced if the rotor is between conventional SRM drive. The operation of tlie SRM is zero when the stator inductance is maximum. For example.. The concentrated stator windings on diametrically opposite poles teeth tion curve. Thus to produce constant torque. The speed of the SRM drive can be changed by varying tlie stator using a position sensor e.
Due to the unidirectional stator where L. In contrast to a variable reluctance stepper motor. When the In the SRM In a aligned position. It follows that to obtain positive motoring torque. In a controlled by the stator phase excitation sequence. In an idealized SRM where saturation and fringing effects are neglected..
This corresponds to the aligned is also simple: It should be noted that the tlie maximum rate of change of the stator flux linkage with respect to rotor general expression for the electromagnetic torque in an SRM is t. It follows that the electromapetic torque currents the topology of tlie power converter is simple. The maximum rate of change of the stator current is a dB.
Thus the stator currents are unidirectional currents and one stator phase conducts at a time. The non-uniform tion. Since the torque is not zero in the unaligned positions.
The current references are inputs to the current controller e. The gradient of each flux ramp determines the maximum speed esearchers Talcaliashi and Noguchi The first solution uses profiled stator currents. Drives with at which it is possible to track tlie constant torque-flux characteristic for a given irect torque control DTC are being shown great interest. Torque-controlled SRM drive. It is expected that in the future SRMs will be more widely used. The torque-controlled SRM is an ideal candidate for a flux contrallcr.
By using linear flux-linkage ramps. Depenbrock The d. Tor the determination of the stator current references. It is shown that tlie second scheme is simpler to implement. This is used together with the rotor position 0. It is. Tlie torque-controlled SRM can operate in a wide speed-range. The actual Aux linkages can he obtained from the stator currents and the rotor position.
This is a very significant industrial planned over the cycle as a whole. Tlie flux-linkage controller also requires the actual stator flux linkages. When such a scheme is used. If the constant-torque operation has to be extended to the tly introduced a direct-torque-controlled induction motor drive. The current controller outputs tlie required switching signals for an IGBT converter.
The main advantages of DTC are: The motor moder used by ABB is a conventional type of mathematical model using various machine parameters. For this purpose various predictive schemes stator-flux-based DTC induction motor drive. It has also been claimed by ABB that the new a.
The the macliine the outputs of which can be used for accurate stator resistance selection is made to restrict the flux-linkage and electromagnetic torque errors estimation. Thus it will be referred to as a switching-voltage vector estimation. The outputs of minimal. A simplified predictive scheme will also be flux-linkage and electromagnetic torque errors are restricted within their respect. The required required to estimate the 'hot' value of the stator resistance. Schematic of n stator-flux-based DTC induction motor drive.
Similarly as is done in one form of a which are required in most of the vector-controlled drive implementations. It should be noted that for stator flux-linkage estimation it is not necessary switching-voltage vector look-up table.
For this purpose a two-level flux liysteresis comparator and linkage. This can be obtained by simple physical to monitor the stator voltages since they can be reconstructed by using the considerations involving tlie position of tlie stator flux-linkage space vector. It should be noted that it is not the actual flux-linkage stator fluxes and stator currents. Therefore instead of using open-loop the drive contains a speed loop.
For example. It can be seen that the drive scheme requires stator flux-linkage bands. DTC of synchronous motor ently by d. Scheme 1: Drive with non-predictive switching-vector selection in wliicli the motor. It is also possible to use other types of solutions. Sensorless vector drives have become the norm for industry and almost every large manufacturer Control Techniques plc.
Both the voltage-source and current-source inverter-fed drives VSI. DTC of induction motor would appear that. Direct control of the electromagnetic torque and stator flux using incremental or absolute encoders.
In a low-power torque-controlled drive the cost of such a d DTC of CSI-fed electrically excited synchronous motor sensor can he almost equal to the other costs. In summary the main objectives of sensorless drive control are: These drives are usually referred to as 'sensorless' drives. Optical encoders are one of the most using optimal voltage switching look-up table widely-used position sensors. Only one large Other types of DTC drives utilize principles similar to those discussed above.
Direct control of the electromagnetic torque and reactive first derivative of the position can be estimated directly from the position. It also increases the maintenance requirements. As real-time predictive-algorithm-based DTC schemes will he more widely used. Electromagnetic resolvers are popular for measuring Scheme 2 Direct control of the electromagnetic torque and rl-axis the rotor position because of their rugged construction and higher operating stator current using optimal voltage switching look-up table temperature.
In very small motors it is impossible to use elec- c DTC of VSI-fed electrically excited synchronous motor tromechanical sensors. In drives operating in hostile environ- It is expected that in the future DTC drives kill have an increased role and ments. Drive with predictive switching-vector selection by the same manufacturer. In such a case special techniques are also possible.
In the past few years great efforts have been made to introduce speed. Direct torque control using a predictive algorithm for switch. Direct control of the electromagnetic torque and stator flux is desirable to eliminate these sensors in vector-controlled and direct-torque- Scheme 2: Direct control of tlie electromagnetic torque and stator controlled drives.
In and direct-torque-controlled electrically excited synclironous motor drives are also general.
Thus the eleven types of DTC drives discussed in this book wliicli deliberately introduce asymmetries in tlie machine. Obviously if the rotor position is monitored. The main techniques for sensorless control of switched reluctance motors are: Tlie ACS ance motors are: Luenberger position estimators. Estimators using saliency geometrical. Estimators using stator voltages and currents. Estimators using spatial saturation tliird-harmonic voltage component.
Stator-phase third liarmonic voltage-based position estimators. The main techniques for sensorless control of synchronous reluct. Observers Kalman. Artificial-intelligence-based position estimation. For the The details of these will be discussed in Sections 3.
Observer-based Icalman. Estimators using spatial saturation stator-phase third harmonic voltages. Unidrive in the world. Estimators based on inductance variation due to geometrical and saturation Unidrive is available in five frame sizes from 0.
Universal drives offer distinct advantages to tlie user in that the systems. The inverter switcliings directly applications. Position estimation from the monitored stator currents. It can be directly erects. Model reference adaptive systems MRAS. Estimators using artificial intelligence neural network. Open-loop estimators using monitored stator voltageslcurrents. Open-loop estimators using monitored stator voltageslcurrents and improved schemes. At present there exist several integrated drives.
Unidrive is a radically new drive. Position estimation using an observer extended Kalman filter. Estimators using observers e. Estimators based on inductance variation due to geometrical erects: It is believed that the most The main techniques of sensorless control of permanent-magnet synchronous significant recent industrial contributions to variable-speed drives are due to motor drives are: Control Techniques plc.
These techniques are discussed in detail in Chapter 5. It is expected that in the future further sensorless universal and direct-torque- 3. Luenberger observer. Basic torqlre control schernes. Back e.
Tlie details of these techniques will be discussed in Sections 4. The development of switched reluctance motor applications. Two-speed operation of salient-pole reluctance machines. IEE Proc. Comparison of speed sensorless DTC drives. B Torque control or switched reluctance motor drives.
Drehzahlregelverfahren fiir schnelle Umkehrantriebe mit stromrichter- gespeisten Asynchron-Kurzschlusslaufermotoren. Unidrive Courtesy of Control Techniques plc. Electroirrcs Clarendon Press. Elecrrical Maclrines Electric driues urrrl tlreir conrrols.. Stator-flux-based vector control of induction machines in mapetic saturation.
A class of fast and robust torque-speed and position digital controllers for electric drives. IEE PI. Field-oriented asynchronous pulse-width modulation for high-performance a. DSP-controlled sensorless a. The principle of field-orientation as applied to the new Transvektor closed-loop control system for rotating machines..
ETZ A 7. Design and application of extended observers for joint state and parameter estimation in high-performance a. Digital simulation of a vector controlled axially laminated anisotropic ALA rotor synchronous motor servo-drive. A review of the integral horsepower switched reluctance drive.
PCIM Elrrope 7. A novel vector control scheme for transistor PWM inverter-fed induction motor drives. Control strategies for direct torque control using discrete pulse modulation. A reluctance motor drive for high dynamic performance applications. Torque vector control W C. PCIhf considerations. Parurnerer e. I E E Proc. I E E Prac.. For Nrzrnberg.
Oxford University Press. Application of space-vector techniques to electrical machines and variable. Such a model. P C I M Serlrirmr. Variable-speed drives incorporating multi-loop adaptive controllers. D Applicaliurrs IA Efficiency-optimisedflux trajectories for closed-cycle the production of electroniagnetic torque in d.. Implementation of intelligenl self-orgimising levels e. For simplicity. Magna Physics Publishing and Clarendon Press.
Quick torque response control of an induction motor This is because every control scheme must absorb the changes of the plant par- using a new concept.
As discussed in Chapter 1. I t is also assumed that the permeability of tlie iron parts is infinite and Vas. Meetirrg or? Rorutirrg AfcrcIzirre. Artificial intelligence in drives. Conrrol of electrical driues. Figure 2. The next generation motor control method. For the purpose of understanding and designing Lorque controlled drives.
Clarendon involved in vector-controlled and direct-torque-controlled machines. New pole reluctance motor. A new quick response and liigh efficiencycontrol model of the electrical machine which is adequate for designing the control system strategy of an induction motor.
Application of artificial-intelligence-based speed machine models which are needed to design control loops are very different to estimators in iligli-performance electromecllanical drives. Nonlinear theory of tlie switched reluctance motor for rapid computer-aided design.
Erlergio Elertricn Application of conventional and ity is radial in the air-gap. With the help of these. E P E trrlurial. The elfects of iron losses and end-elfects. First the space-phasor quantities voltages. Converter volt-ampere requirements of the switched reluctance ations. Full Cuny control of a DSP-based liigh machine under consideration. The Stronacli. Variable speed reluctance motors. Electric 2 The space-phasor model of a.
Future developments and trends in electrical machines and o-axis equations will be emphasized throughout the book. Artificial intelligence. Machine designers must have tolerance Stronach. Developments in tlie performance and theory of segmented-rotor reluctance machines. From this point of view.. Cross-section of an elementary symmetrical thrcc-phasc machine historically they have been introduced by using the same notation.
In the symmetrical steady state In eqn 2. Direct-axis of the stator. In this case the space phasor of the. It should be noted that.. It follows from eqn 2. Thus the locus of the respectively of a stator winding. Then the currents are sinusoidal and form a three-phase balanced system.
The real axis of the stator is denoted by sD. The phase windings the currents vary in time. Thus the space pliasor of the showli in Fig. Projeclions or tile atator-current space phasor. The stantaneous values of the phase variables of the same quantity. In symmetrical three-phase machines. In a quadrature-phase machine is. In the transient state the space-phasor locus must he utilized..
Mathematically this means that. For the so-called classical. If the currents form an It should be emphasized that the space phasor does not contain the zero-sequence asymmetrical system.. This is shown space phasor of the stator currents can he defined as a phasor whose real part is Fig. I1 follows from the definition of the space phasor of the stator currents eqn 2. B-4i 2. Here i. The rotor-current D and sQ respectively and the reference frame fixed to the rotor.
This definition is similar to that of the stator-current space ference frame fixed to the stator whose direct and quadrature axes are denoted phasor expressed in the stationary reference frame eqn 2. Substitution of eqn 2. This angle is also shown in Fig.
The The fact that i. For a machine with quadrature-phase rotor 0. Thus let i. The relationship between the shown in Fig. It can be seen that the phase-variable flux is ohtained. By a special selection of the turns here L. The rotor magnetizing-current space phasor lere are two flux-linkage space phasor components. The second component. Substitution of eqns Thus in the stationary reference frame fixed to tlie stator.
Tlte space-phasor illode1 of a. When i: In eqn The stator flux-linkage space phasor describes the modulus and phase angle of current space pliasor expressed in the stationary reference frame.
The relationship between the stationary and rolating reference frames.. The first component. A considerable simplification is achieved if eqns 2. In this case L. The rotor currents tween two rotor phases. Instead of defining the rotor flux-linkage space phasor in terms of the rotor in contrast to the matrix forms used in generalized machine theory. Bby eqn 2. It can be seen that all three rotor flux-linkage com- i. Thus it is also valid when chine theory can be obtained [Vas It is important to note that eqn 2.
Thus it or currents. The space phasor of the rotor flux linkages expressed in its own natural reference frame.. In the equations above. In terms of the instant- and the quadrature-axis stator flux-linkage component is given by aneous values of the stator and rotor currents they can be expressed as The relationship between the instantaneous values of the direct.
It is also an advantage of the application of the space phasors that. This will he discussed 2. Thus the stator currents in tlie station.. In eqns 2. Thus the following equation holds frame. The trans- sin 8. Transformation of the stator-current space pirasor. The relationship of the stator current components is Thus and the rotor-voltage space phasor in the reference frame fixed to the moving rotor is G: Thus if there are zero-sequence voltages.
Thus ately follows from these equations. By resolving into real form. A similar transrormation matrix applies for the rotor voltages. These are denoted by if. The currents in the compensating winding and the field winding flux with the currents in the armature winding and compensating winding pro- produce an electromagnetic torque which acts against the armature.
The current in the field winding i. Re it Vr sD c and on the rotor there is the armature winding a. On the stator of the machine there are the field 0 and compensating windings. T o enhance the analogy between the mechanism of torque production in d. Since the excita- tion flux linkage is in space quadrature to the armature current.
The space phasors in a d. Electromagnelic torque produclion in a d. If current i. Thus the resultant field will be reference frame fixed to the stator of the machine. This proof will be based on It will be shown in later sections e.. IiJ are the moduli of the stator flux-linkage and rotor-current space in the field W. Section 2. I and. If the excitation flux is maintained constant Tliere will also be a discussion on how they can be three-phase or quadrature-phase smooth-air-gap a.
Tlie search for simple control schemes. Thus the electromagnetic torque is the latter is equal to the product of the instantaneous rotor speed and electromag- tlie cross product of a flux linlcage and a current space phasor. It is a further complication that in machines with a squirrel-cage tlie instantaneous values of the excitation flux-linkage and armature current rotor..
It is possible to wliere under linear magnetic conditions r is a constant and q3 and i: For completeness. Since the two where. Of course. It will be shown tliat in general. It is the purpose of but these are only suitable for laboratory work or under very special conditions. For this purpose. It can be put into the more familiar Thus a rotational voltage. Equation 2. The induced stator e. In general Equations which is the physically expected result Tlte space-plmsor rtiodel of a. See also Section 2.
The losses are due to heat dissipation across the stator and rotor winding resistances Tlie schematic of the magnetizing inductance L.
From eqns 2. Thus the stator voltage currents L. Expanding eqn 2. It would be possible to define harmonic space pliasors which correspond to non-sinusoidal flux density For a machine with P pole pairs this has to be multiplied by P for a two-pole and current density distributions. Thus eqn 2. It should be noted that in eqn are incorporated only in the parameters of the machine under consideration and 2.
The application of space-phasor theory results in a drastic simplification of is the self-inductance of a rotor winding. Tlie tlrree-plmse rzlodel: Here the symmetrical three-phase two-pole smooth-air- gap machine with sinusoidally distributed windings. It is assumed that the stator and rotor and eqn 2. To acquire superiority in speed control the modern industries are revolutionized and alternately several advancements were originated in the control areas.
More complex control logics being implemented due to the availability of fast acting computers and digital signal processors since a digital computer comprise the ability to control more than four hundred parameters efficiently. In this study an over view of control structures empowered in the industrial drives are conversed. Control Structure: Normally feedback control mechanism was employed because it is difficult to predict and measure the disturbance.
The control structure implemented in the plants to achieve stable operation is shown in Fig. It is the basic control structure put in practice for both AC and DC drives. Corresponding Author: Saravanan and K. Where as in AC machines simplicity in control is not like DC machines, which requires a coordinated control of stator current magnitudes, frequencies and their phases making complex in control. Field Oriented Control: FOC has two types: Direct vector control DVC and Indirect flux vector orientation.
In DVC, the flux vector is obtained by measuring stator terminal quantities, whereas in indirect control, the slip frequency of the motor is used to achieve the field orientation Boulghasoul et al. FOC algorithm consent good dynamic control of torque and provides better performance over a wide speed ranges by field weakening Aengus Murray et al. It makes independent control of flux and torque Jannati and Fallah, like in DC machines, by supplying variable stator voltage to the induction motor IM to provide the desired motor torque and flux.
Seeing that, the rotor flux is a function of the d - axis current and motor torque is the products of rotor flux and q-axis current. R, The phase current control loops may use either pulse width modulation or hysteresis or space vector modulation techniques for the switching.
The function of FOC greatly depends on the machine parameters, in order to reduce the dependency and to improve the dynamic response the DTC was introduced Yongchang Zhang et al. Direct Torque Control: The functional block diagram of the DTC is shown in Fig. The DTC concepts are easy to implement in the real time and it does not entail the coordinate transformations.
Here the torque and the flux are estimated based on the measurement of stator current and Vdc as feedback, they are compared with theirs set values. The torque and flux errors are compared with the flux and torque hysteresis controllers.
Even though it has several benefits, it has some drawbacks. They are, the use of high speeds modified switching table leads losing of flux control in a wide area, results inefficient operation, variable switching frequency operation, difficult to implement in digital control, difficult to control the torque at reduced speeds and the variation of stator resistance due to temperature rise degrades the performance over its control.
Study of Dtc: To obtain fast torque response a switching table is employed to select optimum inverter voltage vector Malik Elbuluk, For a given speed, to change the electromagnetic torque at a faster rate the magnitude of stator flux linkage is kept unvarying and the sector angle is to be changed rapidly.
Based on position of the stator flux, an optimum switching table is designed for picking up the suitable voltage vector to control the torque and flux. The stator flux linkage is related with the applied voltage 7 , thus required flux is obtained by choosing the appropriate inverter switching state because the changes in flux and torque are the functions of applied voltage and switching time of the inverter.
Case 1. Malik Elbuluk presented the fuzzy logic based duty ratio control scheme to reduce the torque ripples, proven that an improved steady state torque response is achieved by this method. Instead of applying voltage vector continuously for the entire switching period a zero switching state vector is applied for some period to minimize the torque ripples.
New scheme for speed control is called combined vector control and DTC is employed by Boulghasoul et al. It has the current vector control and switching table. Using this combination the PI controller is replaced with hysteresis controller and the pulse width modulation PWM signals by switching table.
The objective of FOC is independent control of flux and torque as like in DC machines, this is achieved by using d - q reference frame rotating synchronously with rotor flux space vector.
The torque and flux are controlled by using hysteresis loops. Case 3. Cristian Lascu et al. It preserves the robustness of DTC with lower torque ripples and provides constant switching frequency operation.
The estimator calculates the fluxes, torque and speed based on the IM equations with respect to the stationary reference frame. The full order flux estimator contains two modes: The SVM unit generates the inverter command signal based on these control signals.
Case 4. Emre Ozkop and Halil I. Okumus presented the SVM — DTC, many advantages of this method were discussed such as, SVM provide better DC bus utilization, lower switching loss, reduced total harmonic distortion, ease of implementation in digital systems, reduced torque ripples etc. Use of high number of voltage vector gives more accurate switching table, which provides tight control over the flux and torque in conventional DTC.
In SVM - DTC method the exact voltage space vector is estimated depends on the flux and torque errors using predictive technique and the vector is generated using SVM at every sampling period. In the conventional DTC, a single voltage vector is applied for the entire sampling period. Where as in SVM instead of using one vector in a sampling period more than one vector is used and the slip frequency were controlled by applying zero state vectors with constant switching frequency. It is shown in Fig.
Equations 15 to 17 are holds good for the calculation of switching times and one transient state occurs in every switching state as shown in Fig. The switching time Tz is for both the zero state vectors V0 and V7. Simulation result illustrates on employment of this method, it maintains the benefits of DTC with reduced torque ripples. Case 5. Brahmananda Reddy et al. Here, for every sampling period, voltage vectors are generated to minimize the ripples.
Whereas here, it is subdivided into seven switching zones, the number of switching state in each sub — cycle is three or lesser as like in conventional SVPWM. The switching sequences are given bellow.
Case 6. The appropriate sequence of voltage vectors are used instead of using single voltage vector over a sampling period. Selection of appropriate sequence of voltage vector at every sampling instant is done by the minimization of cost functions that minimizes the torque and flux errors over the specified prediction horizon. MPC computes the optimal control input to be applied based on the current state of the plant and future states predicted over the specified prediction horizon using the plant model.
The objective of MPC is to replace the switching table by some optimization algorithms, which uses the predicted output of the plant model over the specified time. By appropriate creation of voltage vector sequence over the specified horizon with constant duration provides controls having SVM property, which is the constant frequency operation of the inverter. The general pattern of the control action sequence is as shown in Fig.
It uses the null voltage vector V7 in the middle, V0 at both the ends. Active vectors are used in the remaining part left to the V7 and the same are used its right side in the reverse order. It gives switching similar to Fig. A low speed switching strategy is proposed, which selects an optimum voltage vector based on the machine speed.
In this study the 32 states V1 to V32 are distributed in the d1 — q1 and d3 — q3 planes as long 0. This feature provides decrease and cancellation of d3 — q3 stator flux.