Simple PWM Technique of Capacitor Voltage Balance for Three-Level Inverter with DC-link Voltage Sensor Only

This paper presents a simple PWM technique of capacitor voltage balance for three-level inverters. For the presented PWM technique only DC-link voltage sensor is required. As compared to previous methods, current sensor is not required for the presented technique. Moreover, number of sectors per sextant is divided into six sectors rather than four. The presented PWM technique slightly modifies conventional space vector modulation technique by adding a control factor which is used to adjust the distribution of vector times of middle voltage vector according to the voltage of DC-link capacitors. The presented PWM technique is realized using a digital signal processor and experimental results show that the voltage balance of the DC-link capacitors can be achieved even the voltage difference is up to 100 V for a 300 V DC-link system. The harmonic contents of the presented PWM technique and the effect of control factor on the voltage balance are also investigated in this paper. Experimental results derived from a three-phase induction motor drive system are presented to confirm the presented techniques.