Detuning minimization for alternative energy vehicular drive system

Abstract

An Indirect Field Oriented (IFO) induction motor is one of the most commonly used drive system for the alternative energy vehicles. The variation in the rotor time constant due to change in the motor temperature so called the detuning is one of the major problem for such a drive system. This paper proposes an offline and an online technique and compares them for overcoming the detuning problem. The offline technique suggests a slip gain scheduler while the online technique is designed using Model Reference Adaptive System (MRAS) for the rotor resistance adaptation. The offline scheme sets the slip gain at various operating conditions based on the fact that if the rotor resistance is set properly and field orientation is achieved, then there should be a linear relationship between the torque current and the output torque. The online rotor resistance adaptation technique is based on current model flux observer and it utilizes the fact that the rotor flux along q-axis for an ideal field oriented drive system should be zero. This condition acts as a reference model for the proposed MRAS scheme whiles the current model flux observer is selected as an adjustable model. The rotor resistance in the adjustable model is tuned such that the flux along the q-axis becomes zero thus setting the rotor resistance to its accurate value. The effectiveness of the proposed offline and online schemes for overcoming the detuning problem is analyzed and verified through the experimental results.