Derivative-Free Decoupling Method for Asymmetric Six-Phase PMSMs Based on the Dual dq Reference Frame

This paper presents the modeling, control, and hardware-in-the-loop (HIL) evaluation of an asymmetric six-phase Permanent Magnet Synchronous Motor (6ϕ-PMSM) supplied by two three-phase Voltage Source Inverters (VSIs). The machine is modeled as two coupled three-phase subsystems using a dual dq representation. Based on this model, a cascade control structure composed of two parallel inner current loops and an outer speed loop is designed. A frequency-domain tuning methodology is also proposed, requiring only the selection of the inner closed-loop time constant and the desired phase margin of the outer loop, allowing all controller gains to be analytically obtained. To mitigate coupling effects between coordinates and subsystems and enable a single-input single-output (SISO) design approach, a decoupling strategy is proposed and comparatively analyzed. The proposed approach is directly derived from the state-space model and eliminates the need for state-variable derivatives, reducing sensitivity to switching noise and simplifying digital implementation. The control strategy is verified through HIL test bench, in which the plant is implemented in the HIL platform while the control algorithm is executed in a digital signal processor. Experimental results demonstrate accurate dynamic behavior, fast current response, reduced coupling effects, and low current harmonic distortion under different operating conditions.