Conversor Full-Bridge cascata baseado na técnica de entrelaçamento para aplicações de alta tensão e alta corrente

Abstract

The energy challenges in high-power applications require the use of voltage source converters (VSCs) capable of handling high power levels. Technical barriers may limit the utilization of traditional solutions in high-voltage, high-current applications. Traditional solutions often rely on two approaches: i) multilevel topologies to enhance voltage capability; and ii) parallel connection of discrete semiconductors and power sub-modules (SM) to enhance the current capability. In order to obtain a flexible solution, this work proposes and analyses the generalized cascaded full-bridge (GCFB) converter, which allows increasing the power levels of the derived topologies while providing voltage and current sharing. The systhesis principle of the GCFB converter uses the single-phase full-brigde (FB) converter as a basic SM. Moreover, it takes advantage of cascading techniques and incorporates the interleaved configuration to build a multi-branched, multilayer structure with reduced current and voltage stresses on the FB-SMs and semiconductors. This work focuses on topologies that use asymmetrical dc-link voltages with balanced power processing among the FB-SMs. The study also provides an in-depth analysis regarding the system modeling and design, circulating currents, and modulation strategy. Despite the aforementioned advantages, the multilevel GCFB converter requires a complex control system. In this sense, this work proposes the study of the overall circuit model of the GCFB converter. A generalized mathematical approach is derived to obtain the main differential equations that define the dynamics of common-mode (CM) and differential-mode (DM) currents, as well as the voltage waveforms synthesized by the converter. A novel and generalized control strategy based on the Lunze’s similarity transformation is also analyzed in detail. The main concept associated with the voltage balancing method of the control system relies on using the DM currents. The exchange of energy stored in the dc-link capacitors occurs through the DM currents, whereas proper current sharing is ensured. Compared with conventional topologies and solutions, the proposed solution is quite competitive in terms of power losses in the semicondutors and lower component count. A small-scale laboratory prototype of a static synchronous compensator (STATCOM) rated at 2.2 kVA/311 V is implemented to validate the theoretical assumptions about the GCFB converter, considering the behavior of the structure in steadystate and transient conditions.