DC-link Capacitor Voltage Balancing Control without Auxiliary Circuits for Five-level Hybrid T-type Neural-Point Clamped Inverters

In this paper, the DC-link balancing control for five-level hybrid T-type (HTNPC) inverters has been proposed. The 5L-HTNPC structure is comprised of two half-bridge cells one TNPC cell, and four DC-link capacitors. The latter components require an auxiliary voltage balancing circuit which consists of one diode, two inductors and two IGBTs. These components incur additional cost and converter volume. In this paper, a balancing control is proposed to regulate the DC-link capacitor voltages without any auxiliary circuit. Multireference of carrier-overlapped PWM (COPWM) is generated by adjusting the amount of duty ratio through PI controllers according to the polarity of the output current and voltage difference between two capacitors. Finally, simulation results have verified the validity of DC-link capacitor voltages balancing control under various conditions.