Sensor-less based direct vector control techniques are widely used for three-phase induction motor drive. Whereas in case of multiple motor control, it becomes intensively complicated and found very few research articles support to industrial applications. A straight forward direct vector control with sensor-less operation for parallel connected two similar rated induction motors driven by single three-phase inverter is proposed and verified numerically by simulation software test under balanced and unbalanced conditions. The proposed control algorithm adapts the nature observer to estimate the rotor speed, rotor flux and load torque of both motors. Simulation results along with theoretical background provided in this article confirm the feasibility of operation of the ac motors and proves reliability for industrial applications. Padmanaban Sanjeevikumar (M'12, SM'15) received B.E., M.Tech. (with distinction), and Ph.D degree in electrical engineering

This paper directed the speed-sensorless vector control of induction motor drive with PI and fuzzy controllers. Natural observer with fourth order state space model is employed to estimate the speed and rotor fluxes of the induction motor. The formation of the natural observer is similar to and as well as its attribute is identical to the induction motor. Load torque adaptation is provided to estimate the torque and rotor speed is estimated from the load torque, rotor fluxes and stator currents. There is no direct feedback in natural observer and also observer gain matrix is absent. Both the induction motor and the observer are characterized by state space model. Simple fuzzy logic controller and conventional PI controllers are used to control the speed of the induction motor in closed loop. MATLAB simulations are made with PI and fuzzy controllers and the performance of fuzzy controller is better than PI controller in view of torque ripples. The simulation results are obtained for various running conditions to exhibit the suitability of this method for sensorless vector control. Experimental results are provided for natual observer based sensorless vector control with conventional PI controller. Keyword:Fuzzy INTRODUCTIONInduction motors are preferred for most of the industry applications because of the limitations of commutation and rotor speed in DC drives. The induction motor is in fact 'brushless' and can operate with simple control methods not requiring a shaft position transducer. With no shaft position feedback, the motor remains stable only as long as the load torque does not exceed the breakdown torque. At low speeds it is possible for oscillatory instabilities to develop. To overcome these limitations 'field-oriented' or 'vector' control has been developed in which the phase and magnitude of the stator currents are regulated so as to maintain the optimum angle between stator mmf and rotor flux. This control is based on transforming a three phase time and frequency dependent system into a two co-ordinate (d and q axes) time invariant system. These projections lead to a structure similar to that of a separately excited DC motor control. Field orientation, however, requires either a shaft position encoder or an in-built control model whose parameters are specific to the motor.Generally, two types of field oriented control schemes are available. 1. Direct field oriented control 2. Indirect field oriented control. In the direct scheme, the instantaneous position of rotor flux (θ e ) has to be measured using flux sensors. This adds to the cost and complexity of the drive system. In the indirect scheme, a model of the induction motor is required to calculate the reference angular slip frequency that has to be added to the measured rotor speed. The sum is integrated to calculate the instantaneous position of the

Original scientific paperThis paper describes a speed sensorless vector control method of the torque for cost-effective parallel-connected dual induction motor fed by a single inverter. A natural observer with load torque adaptation is employed to estimate the speeds of the same rating induction motors connected in parallel and fed by a single inverter. The speed difference between the two induction motors for unbalanced load conditions is less in natural observer than the conventional adaptive rotor flux observer. Direct field oriented control is used to calculate the rotor angle from the estimated rotor fluxes and the mean rotor flux is kept constant by rotor flux feedback control. The simulation and experimental results of studies are demonstrated for various running conditions to prove the effectiveness of the proposed method. The closed loop speed control operation with inner current control was performed by TMS320F2812 processor.Key words: Field oriented control, Induction motor, Natural observer, Sensorless vector control Vektorsko upravljanje momentom bez korištenja senzora brzine za paralelno spojeni pogon s dva motora. U ovom radu opisano je vektorsko upravljanje momentom bez korištenja senzora brzine za paralelno spojeni dualni asinkroni motor napajan jednim inverterom. Prirodni observer s adaptacijom momenta tereta koristi se za estimaciju brzina jednakih asinkronih motora spojenih u paralelu i napajanih jednim inverterom. Razlika u brzinama izmeu dva asinkrona motora pri asimetričnim teretima je manja kod prirodnog observera, nego kod konvencionalnog adaptivnog observera toka u rotoru. Izravno vektorsko upravljanje koristi se za računanje kuta rotora iz estimiranih tokova rotora, a srednja vrijednost toka rotora održava se konstantnom korištenjem upravljanja u povratnoj vezi. Simulacijski i eksperimentalmni rezultati prikazani su za različite pogonske uvjete kako bi se pokazala učinkovitost predložene metode. Upravljanje brzinom u zatvorenoj petlji s unutanjim krugom za upravljanje strujom izvodi se u TMS320F2812 procesoru.Ključne riječi: vektorsko upravljanje, asinkroni motor, prirodni observer, vektorsko upravljanje bez senzora

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The key objective of wind turbine development is to ensure that output power is continuously increased. It is authenticated that wind turbines (WTs) supply the necessary reactive power to the grid at the time of fault and after fault to aid the flowing grid voltage. At this juncture, this paper introduces a novel heuristic based controller module employing differential evolution and neural network architecture to improve the low-voltage ride-through rate of grid-connected wind turbines, which are connected along with doubly fed induction generators (DFIGs). The traditional crowbar-based systems were basically applied to secure the rotor-side converter during the occurrence of grid faults. This traditional controller is found not to satisfy the desired requirement, since DFIG during the connection of crowbar acts like a squirrel cage module and absorbs the reactive power from the grid. This limitation is taken care of in this paper by introducing heuristic controllers that remove the usage of crowbar and ensure that wind turbines supply necessary reactive power to the grid during faults. The controller is designed in this paper to enhance the DFIG converter during the grid fault and this controller takes care of the ride-through fault without employing any other hardware modules. The paper introduces a double wavelet neural network controller which is appropriately tuned employing differential evolution. To validate the proposed controller module, a case study of wind farm with 1.5 MW wind turbines connected to a 25 kV distribution system exporting power to a 120 kV grid through a 30 km 25 kV feeder is carried out by simulation.

This paper presents a hybrid wavelet-fuzzy based multiresolution (MR) controller for robust speed control of induction motor. The discrete wavelet transform (DWT) is used to decompose the error between the actual speed and command speed of the induction motor drive in to different frequency components. A self-tuning fuzzy logic is used for online tuning of the controller parameters. The proposed controller has the ability of meeting the speed tracking requirements in the closed loop system. The complete indirect field oriented control scheme incorporating the proposed wavelet-fuzzy based MR controller is investigated theoretically and simulated under various dynamic operating conditions. Simulation results are compared with that of conventional PI controller and fuzzy based PI controller. The speed control scheme incorporating the proposed controller is implemented in real time using the digital processor (DSP) control board. Simulation and experimental results validates the effectiveness of the proposed controller over conventional controllers and proves to be more suitable for high performance applications.

IS that i t dminrtds si!;iiificant ai:tount of re;ictii. 2 p a t e r froill eurJM,shhHd in r,wmt , e J I~ i n counlr). uril,tr ix fadng the grid Hcrice. tlic power Eictot I . > low e q x~i d l l~ :it 11: : 111 Abstncx -With large number of w n d enera con\ersion systems =\ere problmi of p w r p o w t factor at low w n d speeds. 1 his is because load conjlrlon. 1 e, 'it reduced wlilcj s p e d 'T1115 of the reactive pcwer tahrti by tht induction generator from the grid. The use of an ac r d t~g e controller. ss in the o s e of an induction motor, undesirable cliarxtei istic plnccs ;in undue bttrderl oii tllc pouer nat\:urk and i n tiii II 011 otlwr uttI1s connrcted 13 I t Wherr a fev, induct1011 generators arc conilcctd to tilt. grid, the iiiipact of the supply of reaciibe power froni the gild ma> not be felt vorq niuch However, wltcn a ciost?r of ~t i i i d suggwsloll oJ o, ,,,ethods tf, in,pro,e powrr ,sctor. ,', thi5 paper. d d e d inv-tiptions a r e cnrried out on a grid connected inducttan generator wth voltage conlrd. The generator perfomiance w s determined theoretird-ally under different operating conditions. Expenmcntsl in\es~gatiuns carried out using autotransfotnier a3 voltas controller confirm the thtwreticai results. Further, the fe3sibifity 01 uzinq a three phJse thyribtnrised 3c vdta?e cnnlrctller. u d in wind energy conversion system for the soft s t m t of rnduaion nischine ns U motor, for the power factor itiiprovement of the s y s t~i IS studird. Here farins \ilth illore 1 l t n C h l n C S are SOlltlilg Up. t h l S prOblt.111 14111 be s e \ m the p w U e m is that the \oitage applied to the indocoon generator cnn not SeLeral attempts have been niade to inlpro.i:! the powx factor of the grid corinected induction gencrators The most popular method IS the use of fixed capacitors But, III app'i:atioiIs such as wild energy conversion s>stmls be reduced M o w a pnrfjcular value.sndjsed in this paper 2nd a solution suggest&.

This paper presents a wavelet-fuzzy based controller for indirect field oriented control of three-phase induction motor drives. The discrete wavelet transform is used to decompose the error between the actual speed and the command speed of the induction motor drive into different frequency components. The transformed error coefficients along with the scaling gains are used for generating the control component of the motor. Self-tuning fuzzy logic is used for online tuning of the scaling gains of the controller. The proposed controller has the ability to meet the speed tracking requirements in the closed loop system. The complete indirect field oriented control scheme incorporating the proposed wavelet-fuzzy based controller is investigated theoretically and simulated under various dynamic operating conditions. The simulation results are compared with a conventional proportional integral controller and a fuzzy based controller. The speed control scheme incorporating the proposed controller is implemented in real time using a digital processor control board. Simulation and experimental results validate the effectiveness of the proposed controller.