Abstract : Based on the analysis of the operation of the AC-AC variable frequency speed control system of synchronous motor, this paper proposes an analysis method that decomposes the variables of the d and q axes of the synchronous motor into low-frequency components (including aperiodic components) and high-frequency components for separate processing, neglecting the resistance of the rotor circuit to the high-frequency components and the effect of the damping winding on the low-frequency components. Furthermore, an equivalent circuit model of the synchronous motor suitable for steady-state and quasi-steady-state analysis is established. Using this model, a new method for designing the current controller of the speed control system is proposed. Operational tests and simulation results show that the established equivalent circuit model is correct and the proposed regulator design method is effective. Keywords : Synchronous motor; AC-AC variable frequency converter; Equivalent circuit model; Current regulator 1 Introduction Establishing a mathematical model of the AC-AC variable frequency synchronous motor speed control system is the theoretical basis for analyzing the dynamic and steady-state operating performance of this type of system. Because analytical analysis of such strongly nonlinear systems is extremely difficult, digital simulation is typically employed. However, digital simulation methods struggle to reveal underlying patterns, particularly in designing corresponding control laws for the system. Previous literature, when designing the stator current regulator, neglected the resistance of the synchronous motor's damping winding and employed simplification techniques to obtain a simplified model of the synchronous motor's stator winding; however, this method introduces significant errors. This paper, based on the analysis of the operating characteristics of this type of system, decomposes the d-axis and q-axis variables of the synchronous motor connected to the AC-AC inverter into low-frequency and high-frequency components for separate processing. It establishes an equivalent circuit model and a small-disturbance analytical model suitable for the steady-state and quasi-steady-state process analysis of the synchronous motor powered by the AC-AC inverter. Applying this model, this paper proposes a new method for stator current regulator design. [b][align=center]For more details, please click: Equivalent Circuit Model and Current Regulator Design of AC-AC Inverter-Synchronous Motor System[/align][/b]