The parallel operation of two UPS by the coupled-inductor method

For expanding uninterruptible power supply (UPS) capacity, the coupled-inductor method is proposed for the parallel operation of two UPSs in this paper. Because of the use of the magnetic coupling concept, the circulating current flowing through the respective inverters can be avoided, and the load can be automatically shared between the two UPSs. In parallel operation with the coupled-inductor method, a little error of phase angle between the UPSs can be allowed, so the control circuit is simple to implement in the practical application