PWM inverter active filters for industrial drive systems under unbalanced ac supply conditions

The performance curves for a wide range of pwm inverter harmonic correction topologies are examined that draw sinusoidal supply currents and that can be attached to the input stage of standard industrial drive systems. The pwm inverter cells examined can operate with current ratings as low as 0.3 pu. When the pwm inverter harmonic correction cell is separated from the drive rectifier, its rms currents increases significantly as the drive filter inductance is lowered and the more unbalanced the ac supply becomes. This is due to the pwm inverter cell compensating for large harmonics and harmonic imbalances between phases. PWM inverter harmonic correction topologies that are integrated with the drive input stage can lower these adverse effects, and can be divided into two classes: (a) zero power flow, (b) positive power flow.