This work investigates the performances of DirectTorqueControl (DTC) of DualStatorInductionMotor (DSIM) powered by two types of MatrixConverter (MC), namely the direct and indirect MC. To this end, the design of DTC with conventional DirectMatrixConverter (DMC) is firstly presented. Then, in order to illustrate the main feature of IndirectMatrixConverter (IMC) in terms of the output voltages and input currents waveforms, the full steps of IMC are well explained. To discuss the performance of each scheme, both techniques are simulated in the Matlab / Simulink environment for a 4.5 kW DSIM at different operating conditions. The obtained results show that the IMC provides high performance in torque and flux at different conditions and while minimization the Total Harmonic Distortion (THD) in the input current compared by the conventional DMC.
DirectTorqueControl (DTC) is one of the active researched control schemes which is based on the decoupled control of flux and toque. This method was first proposed for three-phase induction machines and then was implemented on three- phase permanent magnet synchronous motors (PMSMs) [6,7]. DTC provides a very quick and precise torque response and also has very simple instruction, i.e., no need of rotary coordinate transformation, inner current regulator, or pulse width modulation (PWM) block. The basic principle of DTC is to directly select stator voltage vectors according to the differences between the reference and actual torque and statorflux linkage. Also, this method was presented for the first time in five and six-phase induction motors in [8,9]. L. Parsa, et al. investigated the DTC algorithm for a five-phase PMSM in .
Abstract: This paper presents a comparative study on the Predictive DirectTorqueControl method and the Indirect Space Vector Modulation DirectTorqueControl method for a Doubly-Fed Induction Machine (DFIM) which its rotor is fed by an IndirectMatrixConverter (IMC). In Conventional DTC technique, good transient and steady-state performances are achieved but it presents a non constant switching frequency behavior and non desirable torque ripples. However, in this paper by using the proposed methods, a fixed switching frequency is obtained. In this model Doubly-Fed Induction Machine is connected to the grid by the stator and the rotor is fed by an IndirectMatrixConverter. Functionally this converter is very similar to the DirectMatrixConverter, but it has separate line and load bridges. In the inverter stage, the Predictive method and ISVM method are employed. In the rectifier stage, in order to reduce losses caused by snubber circuits, the rectifier four- step commutation method is employed. A comparative study between the Predictive DTC and ISVM-DTC is performed by simulating these control systems in MATLAB/SIMULINK software environments and the obtained results are presented and verified.
The results show the graph of rotor speed, electromagnetic torque and stator currents. Initially the speed is set at 500 rpm at time t=0 sec. We can observe that the speed is increasing in ramp fashion from initial position. After some time the speed sets at 500 rpm. After the application of load torque the speed of motor still ramps to its final value for short time. The speed is set zero at t= 1 sec. Though the value of torque varies the speed remain constant.
The basic principles of flux and torquecontrol and the switching table are firstly presented in order to accomplish the DTC concept. The switching strategies as well as the influence of the torque and flux hysteresis band amplitude on the drive behaviour are then shown. A particular attention has been made on the analytical
In early 1970s, the appearance of the Field oriented control (FOC) allowed a considerable increase of dynamic performance of the induction motors . Theoretically, FOC that based on Fleming's law  makes the control performance of inductionmotor as good as the DC motor’s where torque and flux are decoupled and hence could be controlled independently. However, during the practical practice of engineering application, the actual performance of vector control will be worse than predicted due to the effect of factors such as inaccurate control model and variable motor parameters . Several methods are investigated to inquire into this problem and some improved techniques such as flux observer, rotor resistance identification are adopted in order to reduce the effect of this variation so that the control performance of FOC can be satisfied in most of applications , . The DirectTorqueControl was first introduced by Takahashi around the mid-1980s has found great success with the notion to reduce the dependence on parameters of inductionmotor and increase the precision and the dynamic of flux and torque response .
detrimentally affects the switching operations in the comparators. It is much cleared that by decreasing the hysteresis band of torque and flux comparators, the switching frequency of the inverter can be increased and hence the torque and the flux ripple can be reduced. But even decreasing in hysteresis band for both the comparators does not increase the switching frequency of the inverter and hence does not reduce the flux and the torque ripple if the delay exists in obtaining the feedback signal. The relation between the hysteresis band of both the torque and the flux comparators and the switching frequency of the inverter is presented for DTC of three-phase inductionmotor. The percentage of the hysteresis band for both the comparators is compared with their rated values. For example 1% of the torque comparator hysteresis band reflects the magnitude of the band which is 0.13, if the rated torque of the three-phase induction machine is 13 Nm. These relations are obtained by considering the delay of 10µs and 20 µs. It is cleared from these figs that the maximum switching frequency of 20 kHz can be obtained with no delay with both the hysteresis band reduced to sufficiently low levels. In case of 10 µs delay, the maximum switching frequency of 16 kHz can be obtained whereas in case of 20 µs delay, the maximum switching frequency of 9 kHz can be obtained. In order to get the maximum possible switching frequency there should not be any delay in obtaining the feedback signal but practically it is not possible because the isolation amplifiers, Hall-effect transducer, and other related components easily bring these levels of the delay to the system in estimating the statorflux and the torque which makes the situation worse. Even by using broad frequency bands components, the delay cannot be avoided. These delay effect can be compensated by introducing the triangular dither signal of very high frequency may be double or triple (according to DSP limitation) the sampling frequency of the control scheme. This dither signal after adding to torque and flux error, increases the average switching frequency of the inverter and hence effectively reduces the torque and the flux ripple. In order to find out the first instant of switching after adding dither signal, the slope time instant relation is used. The slope time instant relation can be written as, when the dither of doubled the frequency of sampling frequency of the control scheme is added to the torque error.
In this paper a modification of the switching table is presented and it is compared to the classic DTC. The present paper is organized as follows: Section 2 is reserved to describe the model of dual three phase multi-phase drive systems. A presentation of the DTC of dual three phase induction machines is given
Pabitra kumar behra, et.al, proposed a scalar control strategy to control the speed of inductionmotor by varying supply frequency and applied voltage by keeping (v/f) ratio as  constant and also presented open loop and closed loop v/f control of an inductionmotor. Madhavi L.mhaisgawali, et.al, proposed speed control of an inductionmotor by means of PID controller by using vector control technique and analyzed performance curves without controller and with PID controller. G.Kohlrusz, et.al, distinguished scalar control strategy from vector control strategy  of an inductionmotor. And also stated that vector control is a complex technique, but it is commonly used in industries since scalar control cannot be applied to systems with dynamic behavior. Srujana dabbeti, et.al, proposed speed control strategy of an inductionmotor with predictive torque  and current controllers and without using sensors. Sandeep Goyat, et.al, suggested field orient control (FOC) strategy to control the speed  of an inductionmotor and developed FOC algorithm. D.H Choi, et.al, implemented vector control scheme of inductionmotor to control speed in field waning region by tuning mutual inductance  and rotor time constant.
The indirectmatrixconverter (IMC) has received considerable attention as it provides a good alternative to double-sided PWM voltage source rectifier-inverter having advantage of being a two stage converter with six bidirectional switches and six unidirectional switches for three phase to three phase conversion and inherent bidirectional power flow, sinusoidal input/output waveforms with modulate switching frequency, the possibility of compact design due to the absence of dc-link reactive components and controllable input power factor independent of output load current. The main disadvantages of matrixconverter are the inherent restriction of the voltage transfer ratio (0.866), more complex control and protection strategy.
This paper presents an improved DirectTorqueControl (DTC) of inductionmotor. DTC drive gives the high torque ripple. In DTC inductionmotor drive there are torque and flux ripples because none of the VSI states is able to generate the exact voltage value required to make zero both the torque electromagnetic error and the statorflux error. To overcome this problem a torque hysteresis band with variable amplitude is proposed based on fuzzy logic. The fuzzy logic controller is used to reducing the torque and flux ripples and it improve performance DTC especially at low speed.
Directtorquecontrol (DTC) is one of the control strategies of the Torquecontrol of Induction machine. Sliding Mode Control (SMC) is known for its capability to cope with bounded disturbance as well as model imprecision which makes it ideal for the robust nonlinear control of IM drives. In this Paper Directtorquecontrol (DTC) of the inductionmotor controlled by two fuzzy logic based sliding modecontrollers.The aim is to control effectively the torque and flux. Torquecontrol of an induction machine based on DTC strategy has been developed using Ziegler-Nichols (ZN), fuzzy sliding mode1(FSM1) and fuzzy sliding mode2 (FSM2) speed controllers and a comprehensive study is presented in this paper. The model is constructed and simulated by using Matlab/Simulink for different operating conditions such as reference speed. Several numerical simulations have been carried out in a steady state and transient operation on a speed control mode. The results shows that the FSM2 gives better performance with less ITAE
Directtorquecontrol combines the benefit of directflux and torquecontrol into sensor less variable frequency drive that does not require a PWM modulator. Recent advances in digital signal processor and application specific integrated circuit and the theoretical concepts developed so far for direct self control makes this possible. The objective of the present work was to make a model of directtorquecontrol of three phase inductionmotor .Various speed control schemes were studied and extensive literature survey was carried out for understanding the directtorquecontrol technique. MATLAB/SIMULINK was chosen as modeling and simulation tool because of its versatility. Model for directtorque controlled inductionmotor was developed using MATLAB/SIMULINK and performance of the system for different operating condition like starting, load changes, speed reversal, effect of changing the values of Kp and Ki on the performance characteristics, was studied. The model was validated by comparing the plots of various performance parameters with those available
estimator differs from the actual value. The effect of stator resistance variation on the instantaneous fluxes, flux angle, torque is studied. For the study, 50% step change in the stator resistance is applied at 1sec. The investigation is carried out at a low frequency under the load torque of 1Nm as the stator resistance variation is more significant at low frequency. The d and q-axis fluxes, flux angle, torque obtained are presented in Fig. 2, Fig. 3, Fig.4 and Fig.5 respectively. From the results obtained, it is observed that as soon as the step change in stator resistance is applied at 1 sec, the d-axis flux, q-axis flux, flux angle and electromagnetic torque deviates from the actual. This in turn leads the drive system become unstable. This necessitates the need for stator resistance estimator.
In the conventional DTC a voltage vector applies for the entire switching period, and this causes the stator current and electromagnetic torque to increase over the whole switching period. For small errors, the electromagnetic torque exceeds its reference value early during the switching period, and continues to increase, causing a high torque ripple. This is then followed by switching cycles in which the zero switching vectors are applied in order to reduce the electromagnetic torque to its reference value. The ripple in the torque and flux can be reduced by applying the selected inverter vector not for the entire switching period, as in the conventional DTC inductionmotor drive, but only for part of the switching period. The time for which a non-zero voltage vector has to be applied is chosen just to increase the electromagnetic torque to its reference value and the zero voltage vector is applied to the rest of the increase in the number of semiconductor switches in the inverter. During the application of the zero voltage vector no power is absorbed by the machine, and thus the electromagnetic flux is almost constant; it only decreases slightly. Fig. 4 shows a DTC inductionmotor drive with a duty ratio fuzzy logic controller. The average input DC voltage to the motor during the application of each switching vector is δV dc . By varying the duty ratio between zero and one, it is possible to apply
ABSTRACT - Vector control, also called field- oriented control (FOC), is a Variable frequency Drive (VFD) control method in which the stator currents of a 3 phase inductionmotor are identified as two orthogonal components that can be visualized with a vector. The vector control of induction motors is one of the most suitable and popular speed control technique presently used. The vector control technique decouples the two components of stator current space vector: one providing the control of flux and the other providing the control of torque. The two components are defined in the synchronously rotating reference frame. With the help of this control technique the inductionmotor can replace a separately excited dc motor. The scalar control technique is simple to implement but have the coupling effect ultimately responsible for the sluggish response, which leads to instability due to higher order system effect. The DC motor needs time to time maintenance of commutator, brushes and brush holders. The main effort is to replace DC motor by an inductionmotor and merge the advantages of both the motors together into variable speed brushless motor drive and eliminate the associated problems. The squirrel cage inductionmotor being simple, rugged, and cheap and requiring less maintenance, has been widely used motor for fixed speed application. The inductionmotor is transformed from a non-linear to linear control plant. It is expected that with increasing computational power of the DSP controllers, it will eventually nearly universally displace scalar volts -per-Hertz (V/f) control. In this paper we will come to know the concept of vector control and different types of vector control techniques available. And finally we will be able to compare them.
This paper describes a mix of directtorquecontrol (DTC) and space vector modulation (SVM) for a customizable speed sensor less inductionmotor (IM) drive. The motor drive is provided by a two-level SVPWM inverter. The inverter reference voltage is gotten in view of information output criticism linearization control, utilizing the IM display in the stator – axes reference frame with stator current further more flux vectors segments as state factors. Additionally, a powerful full-arrange versatile statorflux observer is intended for a speed sensor less DTC-SVM system and another speed-versatile law is given. By outlining the observer pick up matrix in view of state criticism H_∞ control hypothesis, the strength and robustness of the observer systems is guaranteed. At last, the viability and validity of the proposed control approach is verified by simulation results. Keywords : DirectTorqueControl (DTC), Speed Sensor less InductionMotor (IM) Drive, Space Vector
The directtorque controlled inductionmotor drive has decoupled control of statorflux and torque and has the feature of precise and quick torque response and reduction of the complexity of field oriented control (FOC) algorithms. In DTC, the generation of inverter switching state is made to restrict the statorflux and electromagnetic torque errors with in the respective flux and torque hysteresis bands so as to obtain the fastest torque response and highest efficiency at every instant. But in conventional DTC, the common mode voltage is very high because of the switching of zero voltage vectors.
Three no-load inductionmotor tests were made. The first one was the response to a torque step of 12.2 Nm which is shown in Figure 7. The response of the DTC with complex controller presented a slightly better per- formance in transient and steady state when such re- sponse is compared with the response of DTC with PI controller. It can be observed that the response time is 25 ms and the reference is followed with a small oscilla- tion. This oscillation occurs due to the natural lack of accuracy in the measurements of currents and voltages. In the second test the speed varies in forward and re- versal operation and the result is presented in Figure 8. The speed changes from 13 rad/s to -13 rad/s in 1 s and the complex gain is not changed during the test. This result confirms the satisfactory performance and the ro- bustness of the controller due to the fact that the the speed reaches the reference in several conditions. The responses of the DTC with complex controller and of the DTC with PI controller have the same performance in transient and steady state. The small error occurs due the natural lack of accuracy in the measurement of the speed.