SRC as a Reliable Methodology to Evaluate Flux Observer Estimation Accuracy

Accurate flux linkage estimation is essential for Direct Torque and Flux Control (DTFC) of interior permanent magnet synchronous machines (IPMSMs). For this, a discrete-time Gopinath flux observer is used by combining the current and voltage models of the IPMSM. The factors affecting the flux estimation accuracy such as inverter nonlinearities, iron loss, discretization errors, and encoder offset-angle are analyzed in this paper with simulation and experimental results. Usually, the accuracy of the flux observer is evaluated by comparing the estimated and measured torques. However, this method is unreliable. Hence, this paper presents the Square-Root-Condition (SRC) as a more reliable and precise methodology to tune the flux observer and determine the flux estimation accuracy without measuring the flux or the voltage. SRC is an extension to Deadbeat-Direct Torque and Flux Control (DB-DTFC) that calculates the Maximum Torque per Flux (MTPF) solution based on the estimated flux. SRC does not rely on pre-calculated data or solving the parameter-dependent MTPF equation. Moreover, it has a minimum sensitivity to machine parameters.