Direct Control of Capacitors Voltage using Backstepping Technique for Bidirectional Compact Multilevel Converters

Abstract

Although compact multilevel converters provide the most cost-effective bidirectional structures (BCMCs), they have sort of stability problems due to using several floating capacitors with unequal voltage levels. Model Predictive Control (MPC) is the only reported advanced technique that engages the dynamical model of capacitors in control equations to regulate the dc-links voltages. MPC however causes variable switching frequency that escalates dv/dt as well as power losses. Variable switching frequency also distributes the harmonic content of the converter current that is a serious challenge to design passive filters. This paper proposes a simple low frequency control technique based on backstepping theory to apply direct voltages control to dc-link capacitors in a promising grid-connected BCMC namely nine-level Packed E-Cell (PEC9) converter. Simulation and experimental results validate the success of the proposed backstepping-based nonlinear technique in fulfilling the desired control objectives including accurate reference current tracking, low THD, standard dc voltage ripple and minimum steady state error and transient effects under stable and unstable conditions.