Improved Disturbance Rejection Ability for Speed Control of PMSM Drives Using a Modified Cascaded Extended State Observer

As the demand for high precision in permanent magnet synchronous motors (PMSMs) increases, achieving superior disturbance rejection in PMSM speed regulation becomes essential. In this context, active disturbance rejection control (ADRC) has emerged as a widely employed method. To enhance disturbance rejection, researchers have explored higher order extended state observers (ESOs) and cascaded ESO (CESO). However, the unclear relationship between these approaches leads to redundant efforts, and the fixed ESO structure used in constructing CESO often limits its potential improvement. Additionally, the impact of individual observer bandwidth within CESO on the overall system is poorly understood. To address these gaps, this article analyzes various ESO structures for constructing CESO and identifies two promising CESO configurations with improved disturbance rejection. Subsequently, a comparative analysis of different observer bandwidths is conducted to optimize performance. Furthermore, this article establishes the equivalence between CESO and higher order ESO (HESO). The results are validated through theoretical analysis and experimental tests using dSPACE DS1202 MicroLabBox.