Abstract:The classical direct torque control (DTC) strategy-controlled dual three-phase permanent-magnet machine usually suffers from high harmonic current, flux ripple and torque ripple. To improve the steady state performance of DTC, a duty ratio modulation direct torque control (DRM-DTC) strategy based on virtual voltage vector set is proposed in this paper. Firstly, the voltage vector set is extended from 12 basic voltage vectors to 24 virtual voltage vectors. The harmonic plane is controlled by the virtual voltage vector, and the harmonic current is suppressed. By increasing the number of voltage vectors, the control of the flux is more accurate and the flux ripple can be reduced. Moreover, the switching table and duty cycle calculation method for dynamic and steady state conditions are defined. Subsequently, the torque ripple in steady state can be reduced, and the dynamic performance can be ensured, respectively. Experiments on the prototype machine are carried out to verify the feasibility of the proposed DRM-DTC strategy.
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