An Improved Discretization Method for IM Full-order Flux Observer under Low Sampling Frequency

Full-order flux observer is widely used in high-performance control of induction motor (IM) drives due to its good parameter robustness and easy implementation of speed sensorless control. In practical application, the observer may be unstable if the fist-order forward Euler (FE) discretization method is applied under low sampling frequency. Though high-order discretization methods could achieve satisfactory performance, they are usually complex for implementation. In this paper, an improved discretization method is developed, which takes dynamic model of the rotor flux as an independent first-order differential equation. Assuming that the inverter voltage is constant during one sampling interval and that the estimated states are rotating vectors, the discrete observer equations can be easily obtained by solving a differential equation without calculating matrix exponential. Theoretical analysis and simulation tests confirm that the proposed presents good stability and estimation accuracy under low sampling frequency.