Power Quality Enhancement using Predictive Controlled Multilevel Converters

Abstract

Electrical power is one of the factors that most influences the economic development of our society. Since the beginning of the use of electricity the continuous improvement of generation, distribution and use of electricity tries to satisfy the ever increasing quality and performance needs of most sectors of human activity. The power quality of the electrical network is mainly related to the technical characteristics of the voltage waveform at a given point of the electrical power network. The quality of the AC voltage can be evaluated, considering that electrical power networks should provide constant frequency constant amplitude pure sinusoidal voltages, with 120° phase shift between phases. Voltage deviations from these characteristics of the sinusoidal waveforms, imply a loss of power quality (Moreno-Munoz, 2007), (Tan et al., 2005). To mitigate some power quality issues, dynamic adjustable solutions based on electronic power converters have been developed. These power converters must use fully controlled (turn-on and turn-off) power semiconductor switching devices to reduce the harmonic content of currents in the electrical power network. These converters can perform as active power filters (APF) (Singh et al., 1999), to cancel disturbing current or voltage harmonics, or Unity Power Factor Rectifiers (UPFR) to obtain almost sinusoidal and in phase AC currents. The dynamic voltage restorer (DVR) is an advantageous solution to mitigate power quality problems such as sags, ripple, flicker, transients or swells, and to reduce the susceptibility of loads (or people) sensitive to them. This chapter presents the optimal predictive control of power converters applied to power quality enhancement procedures. A three-level, three-phase neutral point clamped multilevel (NPC) converter, useful in medium voltage applications, is considered. The predictive optimal controllers and fundamental frequency synchronizers are designed, and applied to control the NPC converter AC currents and to balance the DC capacitor voltages in applications such as: 1. Active Power Filters (APF) 2. Unity Power Factor Rectifiers (UPFR) 3. High Quality Dynamic Voltage Restorers (DVR) Simulation and experimental results show that the AC currents and voltages are almost sinusoidal (THD less than 1%) in steady state operation, but also when facing balanced and