Utilizing ultra-capacitor energy storage in motor drives with cascaded multilevel inverters

This paper proposes two cascaded multilevel inverter topologies and corresponding control strategies applied to motor drive that interfaces single DC source and ultra-capacitor (UC) energy storage elements. In the first topology, a dynamic control method is developed, which allows the UC to provide reactive power to cancel lower order harmonics through a conditioning inverter both in steady state and transient state. Therefore, the bulk inverter supplied by the DC source can provide real power with reduced switching loss, improved efficiency, and better electromagnetic interference (EMI). In the second topology, the UC energy storage can be controlled not only to provide reactive power compensation, but to also provide real power to compensate for peak power demands such as braking and acceleration. The control scheme for this topology includes decoupled current control for independent active/reactive power compensation between DC source and energy storage, and voltage balancing control of energy storage elements. In order to analyze and verify the proposed control algorithms, co-simulation using Simulink and PSIM is used to formulate a detail system simulation platform, while utilizing a circuit model of a Maxwell Technologies UC pack. Experimental results will be presented in the final paper.