• Due to the increased abnormality in supply voltage, Adjustable Speed Drive (ASD) connected to grid are required to be protected from adverse effects of poor power quality.
• Based on the field Power Quality (PQ) data study, distortion in the supply voltage is found to be the dominant disturbance followed by unbalance. These mainly affect the DC bus capacitor and may lead to a failure. But, there is no solution to increase the ASD immunity under distorted and unbalanced grid conditions.

In order to save the ASD from such grid disturbances, a cost-effective auxiliary circuit is introduced in this patent that will make ASD immune to supply voltage distortion and unbalance.

• The present patent discloses a Grid Disturbance Compensation Module (GDCM), operated based on the stress level of the DC bus capacitor.
• The GDCM connected between the rectifier & the DC Bus capacitor in a Main conversion unit.
• The GDCM comprises an AC source, a converter including a first rectification unit, a filter connected to the output terminal of the first rectification unit and including an inductor Ldc, a DC bus capacitor (Cdc) and one or more loads.
• Further the GDCM module comprises a compensator DC bus including one or more capacitors and a DC to AC converter having one or more controllable switches connected to the compensator DC bus.
• Said compensator DC bus and the DC to AC Converter are interfaced to a DC side of the Main Conversion Unit.
• The DC to AC converter is a H-bridge having controllable semiconductor switches.
• The GDCM is interfaced at an output terminal of the first rectification unit in the main conversion unit through a step-down transformer and a relay.
• The GDCM is designed to inject a voltage in the DC side of the Main Conversion Unit.
• Thereby, the GDCM is configured to reduce the effect of power quality disturbances on the DC bus capacitors.
• Fig. 1 illustrates the GDCM in an AC to DC converter feeding multiple loads with a common DC bus.