Dr. Espinosa-Neira, Eduardo

Cascaded H-bridge multilevel (CHB-ML) inverters are an attractive alternative for supplying power to ac grids as they have high reliability and offer an acceptable quality of voltage at their output terminals. In order to achieve efficient operation in these CHB-ML inverters, they must work at low switching frequencies. The finite-control set model predictive control (FCS-MPC) scheme is a very intuitive strategy for controlling this type of converter, but traditional FCS-MPC algorithms generally have a steady-state error when operating at low sampling frequencies and/or if there are parameters mismatch in the prediction model, regarding those of the real system. In this article, a grid-connected CHB-ML inverter that uses an improved FCS-MPC scheme is proposed. The proposed strategy eliminates the steady-state error in an MPC operating at low sampling frequencies and maintains correct operation when a change in the control reference occurs. Experimental results from a grid-connected CHB-ML inverter with three units (seven levels) demonstrate the feasibility of the proposal.

This work proposes a multicell topology based on current-source cells in order to inherit the advantages of current-source topologies such as reduced load dv/dt voltage and natural bidirectional power flow and to adopt a similar behavior of the multicell topology based on a voltage source converter such as voltage controlled behavior where n C cells are connected in series to feed one load phase. In order to check the technical feasibility and performance of the proposed topology, a mathematical model is introduced and studied and key design guidelines of passive components are defined. The analysis shows the possibility of using components with a lower voltage rating than that of the classic multilevel current source topologies and allows the use of low switching frequencies in both rectifier and inverter stages while at the same time obtaining a high-quality waveform in both load voltage and converter input currents. A case of example is used to corroborate the theoretical analysis and the component design methodology, as well as the performance of the topology using a low-power prototype.