Multilevel CHB inverter balancing capacitor technique

Recent research on converter topologies and modulation strategies has advanced considerably. Cascaded H-bridge multilevel inverters are an alternative for medium and high-power systems; however, several topologies depend on having DC voltage sources of different levels to synthesize the multilevel AC waveform. This article describes the control of a 15-level non-modular cascaded H-bridge multilevel inverter. The topology includes six IGBTs and six complementary switching devices, a single DC voltage source, and two electrolytic capacitors. The power switch activation control technique is carried out through a hysteresis control based on monitoring the reference signal and balancing the voltages of the asymmetric capacitors. Using the output voltage and the voltages of two capacitors, the voltage levels are generated, according to a combinational logic that establishes which operating mode is the most appropriate to comply with the regulation of the reference signal and the voltage balance of the capacitors.