Impedance modelling and stability assessment for grid‐connected dual‐PWM adjustable speed drives with motor torque oscillations

The grid-connected dual-PWM adjustable speed drives (ASDs) modulate the energy of motor torque oscillation and inject it into power system, potentially causing low-frequency (LFO) in grid. In this study, considering harmonic common-modulation both-side converters, precise sequence impedance models are derived for ASDs using linearisation method. Based on ASD, oscillation, which is equivalent to time-varying impedance, causes a series discontinuities at torque-oscillation-related frequencies its amplitude-frequency curve. Moreover, these discontinuous drops make more likely intersect with curve grid may lead LFO Then, by applying proposed model Bode plot, stability grid-ASD cascade system assessed. conclusions analysis demonstrate exact mechanism that mechanical oscillations grid-converter instability through coupling ASD. Finally, experimental results 3 kW ASD laboratory measured distribution Shanghai Yangshan Deepwater Port area verify correctness effectiveness assessment.