Equal Resistance Control - A control methodology for line-connected converters that offers balanced resistive load under unbalanced input voltage conditions

The result of several control schemes, applied to three-phase line-connected PWM converters under unbalanced input voltage conditions, is to further reduce the utility supply voltages due to the drawn currents. The proposed method, named Equal Resistance Control (ERC), considers the health of the phases during unbalanced conditions in order to minimize the effects of the drawn power on the network voltages. The control philosophy is to make the current drawn from a particular phase proportional to the amplitude of remaining voltage on that phase and in-synchronism with its phase angle. The power transfer to the load is therefore optimal since no reactive power is drawn from the network. The ERC philosophy uses a feed-forward per-phase control structure, where the voltage drop across the input impedance is estimated. An application example is included where this scheme is applied to a power quality device designed to mitigate voltage disturbances. Theoretical analysis, computer simulations and experimental measurements are included.