A Two-Degree-of-Freedom Structure-Based Backstepping Observer for DC Error Suppression in Sensorless PMSM Drives

The back-electromotive force (BEMF) model-based observer is an attractive sensorless control strategy for permanent magnet synchronous motor (PMSM) drives. However, the accuracy of BEMF observer is deteriorated due to the dc offsets caused by current measurement and inverter nonlinearity. To address this problem, the article proposed a two-degree-of-freedom structure-based backstepping observer (TSBO) for sensorless PMSM drives. First, a two-degree-of-freedom structure is presented to improve the frequency-domain response of the BEMF observer. Second, a second-order complex vector transfer function is inversely introduced into the studied structure to achieve bandpass characteristics. Compared with the conventional BEMF observer, the studied TSBO can achieve dc error suppression without introducing the extra bandpass filter. The studied algorithm is verified by the experimental results on a 4.4 kW PMSM platform.