Safe-triggering-region control scheme for suppressing cross current in static transfer switch

• The cross current phenomenon in static transfer switch (STS) system has been studied theoretically, experimentally and by simulation.
• A “safe triggering region” (STR) control scheme is proposed to enhance the traditional make before transfer (MBB) transfer strategy, which can limit cross current to a safe level when it happens.
• The STR method doesn’t rely on the current measurement.
• By using STR method, the time costs of transfer will be smaller than one system cycle in all cases.
• The proposed control strategy proved to be reliable and insensitive to line impedance and sensor accuracy.

This paper presents a safe-triggering-region control strategy suitable for operating a static transfer switch. The suggested approach is helpful in limiting the cross current surge and enhances system's reliability. The maximum transfer time of the suggested control scheme is analyzed and found to be shorter than one cycle in all cases. The proposed approach does not require any additional components in the system. The theoretical expectations are validated by simulations and experimental results.