Mechanism analysis and optimum control of negative airgap eccentricity effect for in-wheel switched reluctance motor driving system

Abstract

In this paper, the generation mechanism of the negative airgap eccentricity effect for the in-wheel switched reluctance motor (SRM) driving system is analyzed. An independent current chopping control strategy is proposed to achieve optimum control between the response characteristic of the in-wheel motor driving system and the dynamic performance of electric vehicle (EV). Firstly, the electromagnetic characteristic of the studied SRM under airgap eccentricity is studied based on electromagnetic coupling model and circuit driving equation, and the radial electromagnetic force under different airgap eccentricity is verified by adopting the built experiment device. Then, combined with the excitation characteristics of the radial electromagnetic force, the negative dynamic effect of the in-wheel motor driving system is analyzed in the time–frequency domain. Finally, an independent current chopping control strategy for the in-wheel SRM driving system based on vehicle vibration feedback is proposed. The controller parameters including the turn-off angle and chopping current threshold are optimized by data interpolation. Results show that the proposed control strategy can achieve the optimum control between the response characteristics of the in-wheel motor driving system and the vehicle dynamic performance, especially to suppress the vehicle sprung mass acceleration and tire bounce while starting EV.

Appendices

Appendix A: Structure parameters about the studied SRM and EV

The SRM
Parameter	Value	Unit	Meaning
D r	382	mm	Outer diameter of rotor
D s	266	mm	Outer diameter of stator
β r	23	deg	Rotor pole arc angle
β s	22	deg	Stator pole arc angle
L g	0.5	mm	Airgap length
L s	46	mm	Thickness of stator back iron
L r	32	mm	Thickness of rotor back iron
H	74	mm	Motor axial length
N	136	/	Number of turns per phase
The EV
Parameter	Value	Unit	Meaning
m b	337.5	kg	Sprung mass of vehicle
m s	37.5	kg	Total mass of stator and shell
m r	65	kg	Total mass of rotor and tire
c s	1450	Ns/m	Suspension damping
k s	23500	N/m	Suspension stiffness
k t	250000	N/m	Tire stiffness
k r	3850000	N/m	Total motor and hub bearing stiffness

Appendix B: State-space equation system matrices

$$ \begin{aligned} A & = \left[ {\begin{array}{*{20}c} 0 & 1 & 0 & 0 & 0 & 0 \\ { - k_{s} m_{{_{b} }}^{ - 1} } & { - c_{s} m_{{_{b} }}^{ - 1} } & {k_{s} m_{{_{b} }}^{ - 1} } & {c_{s} m_{{_{b} }}^{ - 1} } & 0 & 0 \\ 0 & 0 & 0 & 1 & 0 & 0 \\ {k_{s} m_{{_{s} }}^{ - 1} } & {c_{s} m_{{_{s} }}^{ - 1} } & { - (k_{r} + k_{s} )m_{{_{s} }}^{ - 1} } & { - c_{s} m_{{_{s} }}^{ - 1} } & {k_{r} m_{{_{s} }}^{ - 1} } & 0 \\ 0 & 0 & 0 & 0 & 0 & 1 \\ 0 & 0 & {k_{r} m_{{_{r} }}^{ - 1} } & 0 & { - (k_{t} + k_{r} )m_{{_{r} }}^{ - 1} } & { - c_{t} m_{{_{r} }}^{ - 1} } \\ \end{array} } \right]; \\ B & = \left[ {\begin{array}{*{20}c} {0_{3*3} } & {0_{3*3} } \\ {0_{3*3} } & {\begin{array}{*{20}c} { - m_{{_{s} }}^{ - 1} } & 0 & 0 \\ 0 & 0 & 0 \\ {m_{{_{r} }}^{ - 1} } & {k_{t} m_{{_{r} }}^{ - 1} } & {c_{t} m_{{_{r} }}^{ - 1} } \\ \end{array} } \\ \end{array} } \right]; \\ C & = \left[ {\begin{array}{*{20}c} {\begin{array}{*{20}c} { - k_{s} m_{b}^{ - 1} } & { - c_{s} m_{b}^{ - 1} } & {k_{s} m_{b}^{ - 1} } & {c_{s} m_{b}^{ - 1} } & 0 & 0 \\ 1 & 0 & { - 1} & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 0 & 1 & 0 \\ \end{array} } \\ {0_{2*6} } \\ \end{array} } \right]; \\ D & = \left[ {\begin{array}{*{20}c} {0_{3*6} } \\ {\begin{array}{*{20}c} 0 & 0 & 0 & 0 & { - 1} & 0 \\ \end{array} } \\ {0_{2*6} } \\ \end{array} } \right]. \\ \end{aligned} $$