Lyapunov-based control of unbalanced pulse-width modulation boost type rectifiers

The three-phase pulse-width modulation (PWM) Boost Type Rectifier under balanced operating conditions exhibits instability as the resistance of the input line decreases. Under unbalanced operating conditions the PWM Boost Type Rectifier is subject to instability and severe disturbance such as distortion in the input line current, significant increase in output capacitor voltage and current ripple, generation of sub-harmonic components in the rectifier's output voltage and input current.; The objective of this research was to develop a Lyapunov based controller that could be used to improve the performance of the PWM Boost Type Rectifier under unbalanced operating conditions. By selecting the switching function as the control variable, and by utilizing Lyapunov's stability theory (direct method), a control strategy that not only eliminates sub-harmonics, but also guarantees stability, was developed. The objective of this new control strategy is to cancel harmonics at the input and output of the converter and bring the system to stability while provide unity power factor with near sinusoidal input line current.; The study involves numerous computer simulations to ascertain the feasibility of the Lyapunov based controller. The models used for the verification process include: unbalanced input voltage and balanced input line impedance; balanced input voltage and unbalanced input line impedance. The results of the simulations show that the Lyapunov based controller indeed provides system stability and cancellation of harmonics at the output and at the input of the converter at the same time. The dynamic response of the system is excellent and the input line currents are nearly sinusoidal.