A novel discretized closed-loop full-order rotor flux observer for induction motor based on re-organization of state space

The flux observer with 1st-order forward Euler discretization approach shows large discretization error and divergent result, under the low switching-frequency range of traction converter. This paper presents a novel discretized closed-loop full-order rotor flux observer, which is based on the re-organization of state space and models according to the asynchronous motor itself. In the observer, the coefficient array is constructed between a dynamic coefficient array, which is related to synchronous frequency and slip frequency array, and a constant coefficient array, which is merely derived out of the motor parameters. The coefficient array is then applied into the re-organization of state space. With locally accurate discretization approach, a novel discretized observer is derived, whose output is stator current, taking the error between actual and observed currents as a value for feedback compensation. By designing carefully the feedback compensation array, an accurate observation of the rotor flux is achieved. Simulated and experimental results testify the validity of the approach and model proposed, which shows excellent stability through the overall velocity range, with less discretized observation error and higher convergence rate.