Reconstruction of Phase Current of Induction Motor Drive based on DC Link Measurement

The aim of this paper is the study of speed sensorless control of IM drive by using dc link quantities. The sensorless control method is to determined the appropriate moment when the motor winding should be commutated. This moment is determined by the rotor position. In this type of drive, the limitations of using various sensors for the measurement of rotor speed, stator current & voltages are minimized by estimating these quantities with the help of algorithms. The aim of reconstruction is to achieve the required motor output without exceeding either the short-term or the long-term motor and inverter ratings. These restraints inevitably mean that a number of working currents within the drive must be monitored. All these currents are difficult to measure accurately in the presence of high di/dt and dv/dt switching transients. In a three-phase motor, at-least two motor phase currents must be measured. It is difficult to get current sensors with equal gain over a wide range of frequencies, voltages and currents used in a practical inverter. Therefore we are using the stator current reconstruction method to reduce the physical sensors. The input current and voltage signals to the speed estimation algorithm are the reconstructed waveforms of stator current & voltages obtained from the dc link & not directly on the stator side. In this paper, the focus is given on study of DTC and compare its performance with other speed controlling techniques such as scalar and vector control. A current sensor is usually present in the dc link of most drives that is employed for the over current protection. To reconstruct the three phase currents from the dc link, information regarding the inverter switching states is required. The whole studies has been performed in MATLAB/Simulink environment.