Improved passivity-based control method and its robustness analysis for single-phase uninterruptible power supply inverters

An improved passivity-based control (IPBC) method is proposed for single-phase uninterruptible power supply inverters. The proposed IPBC method is based on energy shaping and damping injection idea which is performed for regulating the energy flow of inverter to a desired level and assure global asymptotic stability, respectively. It is shown that the control of output voltage can be accomplished indirectly provided that the inductor current tracks its reference. Since the estimated parameters do not match with the actual parameters in practice, a perfect tracking without any output voltage error is not possible. To reduce the influence of parameter mismatch on the output voltage, an outer voltage loop is added into the feedback path of conventional passivity-based control (PBC) method. The robustness of both PBC methods has been investigated and analytical expressions in terms of estimated and actual parameters are derived for the output voltage. The effectiveness of the IPBC method in terms of both robustness and harmonic distortion is verified by the simulations and experiments under resistive and diode rectifier loads. The results demonstrate that the IPBC method not only leads to good quality output voltage with a reasonably low harmonic distortion, but also offers a global asymptotic stable operation with a strong robustness to wide range of parameter mismatch.