Operating Point Selected Flux-Weakening Control of Induction Motor for Torque-Improved High-Speed Operation Under Multiple Working Conditions

Due to the requirements of multiple working conditions for induction motor in high-speed flux-weakening operation, conventional “maximum torque oriented” flux-weakening controller reveals its own limitations. This paper focuses on holistic torque performance optimization for multi-condition operation. Torque ripple and dynamic response under two kinds of specific working conditions (high-speed braking and load step change) are explicitly analyzed. The theoretically precise maximum torque point is derived to extract the possible output torque for deep flux-weakening operation. Further, an operating point selected flux-weakening controller (OPS-FC) is proposed. It retains the maximum output torque capability for step acceleration and full-load conditions, as well as holding other novel features for the changing working conditions. First, the selected operating point is automatically manipulated for torque ripple alleviation under non-maximum torque condition. Second, since the voltage reference in proposed OPS-FC is directly constructed, the system robustness is enhanced. Finally, speed range is extended to the deep flux-weakening operation, and the complex vector decoupling part of d-axis current regulator is first applied and shared as a flux-weakening path for closed-loop control. Hence, the complicated PI regulator tuning is averted. The proposed scheme is experimentally verified on a 3.7 kW commercial platform.

Nomenclature

Stator and rotor resistances.

Stator and rotor self-inductances, mutual inductance.

Rotor and excitation angular frequency.

Rotor flux in synchronous reference.

Leakage coefficient.

DC-link voltage.

Nominal value of dc-link voltage.

Number of pole pairs.

Electromagnetic torque.

d-axis and q-axis stator voltages.

d-axis and q-axis stator currents.

Maximum current and voltage.

Value of d-axis current for rated flux.

Weaken item generated from the flux-weakening controller.

Item processed by a low-pass filter.

Coefficient of the voltage reference in flux-weakening controller.

Angle between the input voltage vector and the rotor flux vector in d-q frame.

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Reference quantities.

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Command voltage quantities from current regulator.

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Quantities on the synchronous rotating d-q reference frame.

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Quantities on the stationary α-β reference frame.