“Sensor Less Direct Field Oriented Control(DFOC) Of Induction Motor Drive

– MRAS Estimator” 

Presented by… Guided by…Himanshu Paghdal (232825) Prof. dr hab. inż. Grzegorz TarchałaNileshkumar Solanki (239587) Politechnika Wrocławska

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Outline

• Introduction•Advantages•Theory for MRAS•Block Diagram•Simulink Model•Output Results•Conclusion•References

2016-2017Sensor Less Direct Field Oriented Control(DFOC) Of Induction Motor Drive

– MRAS Estimator

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Introduction• The study of speed sensor less control of the IM has undergone through

maturing years when new techniques came into introduction to improve the previous techniques. The motivation is to find one method that can cater the entire problem related to speed sensor less IM. Among them, MRAS based techniques have been proven to be one of the best methods being proposed by the researchers due to its good high performance ability and straight-forward stability approach. The method was first proposed in followed by which consists of a reference model (RM), an adjustable model (AM) and an adaptation mechanism. RM is independent of the rotor speed whereas AM requires the rotor speed information. Through Landau‘s idea of comparing the outputs of RM and of AM, the error between the two models can be minimized using the adaptation mechanism.

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Advantages•The sensor less control of drive system which is different from

conventional methods because it doesn‘t require speed or position sensors.

•Removing these sensors gives a number of advantages such as increased reliability, lower production costs, reduced size and removal of excess cabling. Sensor less drives require less maintenance and are also more suitable for harsh inaccessible environments.

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Adjustment of the PI current controllers in the DFOCstructure (voltage source)

• Based on the block scheme, the identical transfer functions for the current is x and is y control circuits are obtained,

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Adjustment of the PI speed controllerin the DFOC structure (voltage source)

• The open-loop transfer function of the speed control is,

• Parameters of the rotor speed controller Rw should be calculated according to the Symmetry Criterion,

• S the transfer function of the PI peed controller is,

• And the oen-loop transfer function of the rotor speed control path will be,

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• The closed-loop transfer function of the rotor speed control path will be,

• After filter application in the speed reference unit we have,

• So ,the dynamics of the rotor speed is determined by the minimal time constant of this control path – substitute time constant of the stator current component.

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Adjustment of the PI current, flux and speed controllersin the DFOC structure (voltage source)

• The proposed parameters of PI controllers enable the initial adjustment of the rotor field and speed control loops in the DFOC structure of IM drive.

•We have 2 independent control paths (rotor flux and rotor speed), the dynamics of which is determined by the inverter time constant Tv.

•Current PI controllers (adjusted acc. Modulus Criterion) compensate the influence of the stator winding time constant Tss (inertial block).

•Rotor flux PI controller (adjusted acc. Modulus Criterion) compensates the influence of the rotor winding time constant Tr .

•Rotor speed PI controller (adjusted acc. Symmetry Criterion) compensates the influence of the mechanical time constant TM.

• The analogy to the cascade control structure of the DC drive is visible.

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Block diagram of an induction motor in synchronous frame

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Speed Estimation in system with reference model (MRAS)

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Simulink Model

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MRAS Simulation Model

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Estimated and reference speed of the motor with step changes in load torque

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Error of the motor for changes in speed and load torque

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Generated torque of the motor with step changes in load torque

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 Phase voltage and 3-ph currents of the motor with step changes in load torque

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Conclusion

•Direct Field Oriented Control and sensor less vector control with MRAS observer technique for the control of induction machine are presented. First, generalized dynamic mathematical model of the induction motor is studied.

•The principle of Sensor less control of induction motor is given elaborately. The mathematical model of the drive system has been developed and results have been simulated.

•Simulation results of Sensor less Control of induction motor using AFPO technique were carried out by using Mat lab/Simulink. The simulation results of the proposed scheme have been presented.

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Reference

•Model Reference Adaptive System (MRAS) Based Speed Sensorless Vector Control of Induction Motor Drive,P N H Phanindra Kumar•State Estimation Techniques For Speed Sensorless Field Oriented Control Of Induction Motors, B_Lal Akin•Speed Control of Induction Motor Using APFO Technique, T. Raghu, J.

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Acknowledgement

Special thanks and guidance - prof. dr hab. inż. Grzegorz Tarchała•My classmates - Mr. Himanshu Paghdal