Control of static transfer switch system for volt-second balance transfer

A power system comprising a controller to control a switch to apply normal voltages or alternate voltages to a load as load voltages to power the load, the controller configured to perform:

• causing the switch to apply the normal voltages to the load as the load voltages;
• first volt-second balance the normal voltages against the load voltages;
• upon detecting a power fault that necessitates applying the alternate voltages to the load in place of the normal voltages, causing the switch to disconnect the normal voltages from the load;
• while waiting to detect a volt-second balance between the alternate voltages and the load voltages, determining one or more qualified voltages among the alternate voltages that will not saturate the load, applying the one or more qualified voltages to the load as the load voltages, computing alternate volt-seconds of the alternate voltages and load volt-seconds of the load voltages, and comparing the alternate volt-seconds against the load volt-seconds;
• upon detecting the volt-second balance, causing the switch to also apply to the load each alternate voltage that is not the one or more qualified voltages;
• and
• after causing the switch to also apply to the load each alternate voltage that is not a qualified voltage, second volt-second balance the alternate voltages with the load voltages.