A current source inverter-fed constant air gap flux controlled squirrel cage induction motor drive

Project Abstract

This research project focuses on the design and implementation of a constant air gap flux controlled squirrel cage induction motor drive using a current source inverter (CSI) as the power electronic converter. The constant air gap flux control strategy aims to improve the performance of the induction motor drive by regulating the air gap flux at a desired level regardless of the motor speed and load variations. The use of a current source inverter provides several advantages such as reduced dv/dt stress on the motor windings, simplified motor protection requirements, and improved performance under unbalanced and distorted supply voltages. The proposed drive system consists of a three-phase squirrel cage induction motor, a CSI, a controller unit, and sensing devices for feedback signals. The CSI is responsible for converting the DC input power to a variable frequency and magnitude AC output current to control the speed and torque of the induction motor. The controller unit implements the constant air gap flux control algorithm, which regulates the motor current components to achieve the desired air gap flux reference value. The feedback signals from the motor and load conditions are used to adjust the control algorithm parameters in real-time, ensuring smooth operation under various operating conditions. Simulation studies of the constant air gap flux controlled squirrel cage induction motor drive system are conducted using software tools like MATLAB/Simulink. The performance of the drive system is evaluated in terms of steady-state and dynamic responses, efficiency, and robustness to parameter variations. The simulation results demonstrate that the proposed control strategy effectively maintains the air gap flux at the desired level, resulting in improved motor efficiency and dynamic response compared to traditional control methods. Furthermore, experimental validation of the drive system is carried out on a prototype setup to verify the simulation results and assess the practical feasibility of the proposed solution. The experimental tests confirm the effectiveness of the constant air gap flux control strategy in regulating the motor performance under different operating conditions. The prototype tests also validate the advantages of using a CSI in terms of motor protection, efficiency, and performance. Overall, the research project establishes the feasibility and benefits of implementing a constant air gap flux controlled squirrel cage induction motor drive using a current source inverter. The proposed drive system offers improved motor performance, efficiency, and robustness, making it a promising solution for various industrial applications requiring precise speed and torque control.

Project Overview

<p> In this thesis, a current source inverter fed squirrel cage induction motor drive at constant air gap flux is presented. The drive scheme is conceived to take advantage of the short circuit withstand capability of the current source inverter and the ruggedness (even under harsh conditions) of the squirrel cage induction motor. The variable inverter input dc link current is derivable from either a controlled ac to dc converter or a controlled dc to dc converter. The constant motor air gap flux control drive scheme has inner dc link current control loop and an outer motor speed control loop that maintains the motor slip frequency constant for a given motor load torque. The closed loop control parameters are selected such that negligible torque pulsation and relatively fast motor speed response are obtained without the need for an inverter output capacitor filter. A 400V, 10hp, 1440rpm, 50Hz squirrel cage induction motor is used to simulate the motor drive scheme in Matlab-Simulink environment. For step changes in demand (reference) speed at no load torque and at load torque equals to or less than the motor rated torque, the drive response has relatively fast settling time and acceptably low overshoot/undershoot over the motor speeds not exceeding the rated value. <br></p>