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1. AN EXTENDED LYAPUNOV-FUNCTION-BASED CONTROL STRATEGY FOR
SINGLE-PHASE UPS INVERTERS
ABSTRACT
In this study, an extended Lyapunov-function-based control strategy that assures global
asymptotic stability is proposed for single-phase UPS inverters. The Lyapunov function is
formed from the energy stored in the inductor and capacitor due to the fact that the system states
converge to the equilibrium point if the total energy is continuously dissipated. It is shown
analytically that the classical Lyapunov-function-based control leads to a globally asymptotically
stable system at the expense of steady-state errors in the output voltage, which exist due to the
lack of outer voltage loop in the control input. Therefore, an extended Lyapunov function based
control strategy is proposed, which eliminates the steady-state error without destroying the
global stability of the closed-loop system. The steady state and dynamic performance of the
proposed control strategy has been tested by simulations and experiments under resistive and
diode bridge rectifier loads. The results obtained from a 1-kW inverter demonstrate that the
developed control strategy not only offers global stability, but also leads to good quality
sinusoidal voltage with a reasonably low THD, almost zero steady-state error in the output
voltage, and fast dynamic response under linear and nonlinear loads.