Managing Inrush Current in A Variable Speed Drive Short Term Power Interruption Ride-Through Module

This paper proposes and compares transient currents limiting techniques for a variable speed drive short term power interruption ride-through improvement module. The module comprises of an additional capacitor that is switched onto the dc link during a short-term power interruption. The switching on of the additional capacitor to the dc-link results in high inrush currents which if not mitigated could damage the variable speed drive components and cause nuisance tripping of incoming supply breakers. Proposed inrush current limiting techniques are investigated which include the use of a fixed resistor, inductor, variable resistor and the equipotential voltage switching. Experimental results indicate that the variable resistor technique results in the least torque pulsations of 12% and 9% at the start and end of dc-link compensation. The inductor technique produced the greatest disturbance at the start of compensation with a torque pulsation of 15%. The equipotential voltage switching technique produced torque pulsations of 6.8% and 9.8% at start and end of compensation respectively. It also produced the least drops in torque and speed of 9.9% and 3.2% respectively.