Unbalanced voltage effects on a single phase multilevel inverter due to control strategies

This work presents two control strategies for a single phase multilevel inverter to demonstrate how affects the natural balance on the flying capacitors to the output voltage. The analyzed topology is based on a stacked multicell converter (SMC), which uses stacks and columns in a matrix configuration to minimize the voltage stress on all semiconductor components. Due to the array is built with p-series commutation cells disposed on n stacks; the circuit has more elements, allowing to divide the voltage in all the semiconductors. Then, the control strategy becomes too complex, for that reason we proposed the use of a fixed control and later on a PWM strategy to evaluate the output voltage and the natural balancing on the flying capacitors. The first control strategy was implemented with simple switching signals to the commutation cells generated by FPGA technology. The second control strategy was generated by horizontally phase shifted carrier PWM strategy. The physical setup uses a DSP card, to generate the switching signals, and FPGA to shift signals between cells. Both control strategies where based on a SMC prototype of two cells and two stacks. The paper shows a detailed theoretical background as well as the simulation and experimental results obtained on a low power-high voltage circuit.