FPGA DESIGN APPROACH OF DIGITAL CONTROL OF THREE-PHASE INDUCTION MOTOR By: Prof Dr. Cesar da Costa

OBJECTIVE Variable speed control of three phase induction motor using a six switch inverter by Direct Torque Control (DTC).

Variable speed control

Variable speed control

Variable speed control

DISADVANTAGES OF EXISTING METHOD Harmonic content in motor current increase at low speed; The machine saturates at light loads due high V/f ratio; These effects overheat the machine at low speed; Smooth speed control of induction motor is not possible; The cost of the method is high but less efficient.

PROPOSED METHOD The speed control of induction motor is done using Direct Torque Control (DTC) with six switch three phase inverter; The switching technique used is space vector modulation technique; The two phases are connected to the two legs of the inverter, while the third phase is connected to the mid point of the dc-bus voltage.

Project Methodology

Design flow with the MATLAB/Simulink and DSP Builder

BLOCK DIAGRAM Structure of direct torque control proposed.

Direct Torque Control Stator flux linkage is estimated by integrating the stator voltages; Torque is estimated as a cross product of estimated stator flux linkage vector and measured motor current vector; The estimated flux magnitude and torque are then compared with their reference values.

INVERTER (VSI) Scheme of Voltage Source Inverter (VSI).

SPACE VECTOR MODULATION . SPACE VECTOR MODULATION The space sector N is obtained from the angle between the stacionary reference and the stator flux.

DTC Strategy Simulation

DTC Strategy Simulation DSP Builder

Simulation Results (a) (b) Stator flux estimated (a), and Electromagnetic torque estimated by the proposed DTC (b).

Simulation Results (a) (b) Three-phase stator currents (a), and Motor Speed by the proposed DTC algorithm (b).

CONCLUSIONS The implementation, which proved that the DTC strategy, was accomplished using the combination of a MATLAB/Simulink and DSP Builder software. This project addressed a way of structuring and simulating a DTC algorithm. The target technology was FPGAs, which have been growing steadily and has been taking up space in the industrial market worldwide.

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