Converter-Switching Surges: Railroad Vehicle Power Converter Impact Studies

The application of new power electronics equipment to the rolling stocks of electrified railroad vehicles in recent years brought about the benefits of smooth acceleration and braking, higher efficient of propulsion systems, improved power quality, easy-and-simple maintenance of propulsion motor, and even lower procurement and service costs. Hence, they are generally regarded as a blessing and progress for the rail industry. The switching techniques and new power modules with fast response times are key components to make the above functions possible. If a railroad system is built with vehicles and traction power substations are designed for new equipment, then all power components should be designed to withstand the transient dynamic behavior, especially, the switching surge voltage and current. This is usually the responsibility of the general consultant or the turn-key contractor. Unfortunately, the situation in most electrified railroad systems is new, and renovated trains equipped with new converters and new IGBT power modules join service together with old trains and existing traction networks designed and commissioned decades ago. The impact of the switching surge voltage and current will become an issue of great concern, as illustrated by the two cases presented in this article. The problems presented in the two cases were eventually solved by some sort of soft-switching schemes as a remedy or correction solution. Yet, this problem should be addressed and examined in front of the commission phase to avoid impacts. In conclusion, clear specification of surge transients or permissible impacts need to be included in the procurement documents, and field tests are recommended to verify the compatibility of new power converters with the existing equipment in the entire system.