Hybrid Clamped Four-Level T-Type Inverter With Capacitor Voltage Balancing Algorithm

A new three-phase four-level (4L) hybrid clamped T-type inverter (4L-HCT²I) topology and its capacitor voltage balancing algorithm (CVBA) is investigated in this paper. The topology consists only a common half-bridge (CmHB) module and any existing three-phase three-level (3L) T-type inverter or neutral point clamped inverter (NPCI). In comparison with 4L-NPCI topologies which require eighteen active switches, the proposed 4L-HCT²I topology requires only fourteen active switches. Therefore, a significant reduction in the cost and complexity of the proposed converter has been achieved. The voltage balancing of the three DC-link capacitors in the proposed 4L-HCT²I is accomplished by employing the virtual three-level operation concept to cancel out the effect of neutral currents flowing through the clamping points during operation. Therefore, the proposed 4L-HCT²I does not require any additional circuitry for balancing the capacitor voltages. The duty ratios of the voltage vectors are adjusted online using a dynamically calculated multiplication factor and duty ratio perturbations. The voltage total harmonic distortion (THD) and the power losses of the proposed 4L-HCT²I are compared with that of the existing four-level and three-level topologies incorporating different capacitor voltage balancing approaches. MATLAB/SIMULINK and a downscale experimental prototype are used to validate the proposed 4L-HCT²I and its CVBA.