Fault detection method for phase-to-ground faults in three-phase inverter applications

A method to detect phase-to-ground faults in a three-phase four wire networks is presented. Lately, the interest has grown towards the low voltage DC networks to be used as distribution networks or in-house networks. In these networks the protection against different faults must currently be realized using off-the-shelf components meant to be used in AC networks. It means that in short circuit operation, the DC/AC inverter is used to inject the fault current to the AC network in order to enable the proper operation of protection devices. To ensure the reliable operation in fault situations a method is needed to detect these faults and when the fault has been recognized the references are assigned accordingly. The study indicates that by using this type of fault detection, the accurate statictics of the faults in the customer-end AC networks can be obtained.