An Active Damping Scheme With Energy Saving Feature for Use with Regenerative Converters

Abstract

Regenerative drives, also known as four-quadrant drives are an integral part of many industrial applications ranging from wind power generation, elevators, escalators, centrifuges, pump jacks in oil fields, etc. All regenerative converters need passive LCL filters to filter out pulsewidth modulation frequency components. One disadvantage of using an input LCL filter in front of regenerative converters is that they are also a major source of power loss in the power system as their configuration allows for the flow of capacitive circulating currents even when the power converter is off . The associated power loss in the power system can significantly affect the overall system efficiency when there are large numbers of large power regenerative units in the power system. The filter capacitors also interact with pre-existing voltage distortion in the power system. Multiple regenerative units of various sizes have been shown in this paper to cause undesirable voltage ripple, which in turn causes current oscillations especially in smaller sized regenerative converters. A new active damping scheme is proposed, which also includes actively opening the neutral point of the filter capacitor to eliminate standby power loss associated with regenerative converters with LCL filters. Two ideas are proposed. In the first, only one damping resistor is used, whereas in the other two, damping resistors are used in parallel, where one resistor acts as the fixed damping resistor whereas the other is modulated depending on the amount of system distortion. Test results are given to demonstrate the fundamental concept.