Security apparatus for power converter

Claim 1

A security apparatus for a power converter, comprising: power converting means including a DC power source and at least one power converter for converting DC power from said DC power source into an AC power output applied to an AC system; and security means for stopping operation of said power converter in the event of an abnormal state of said AC system, comprising, disturbance generator means for periodically generating a disturbance signal; phase detector means for detecting the phase of a voltage or current of said AC system, and providing a phase detection signal based on the detected phase of the voltage or current of said AC system and on said disturbance signal; control means for controlling an output of said power converting means in accordance with said phase detection signal, and state detector means for detecting whether or not the phase or frequency of the output of said power converting means deviates from a predetermined value, for detecting an abnormal state of said AC system if the phase or frequency of the output of said power converting means deviates from said predetermined value, and for stopping the operation of said control means when said abnormal state is detected; wherein said disturbance signal produces deviations in the phase or frequency of the power converting means, said deviations being detected by said state detector means in the event that the phase or frequency of said AC system is in said abnormal state; wherein said phase detector of said security means includes: a phase locked loop including, a comparator for comparing an output of a voltage controlled oscillator with a phase reference which corresponds to the voltage or current phase of said AC system, means for generating timing pulses having a frequency corresponding to an output of said comparator and said disturbance signal, and signal converter means including said voltage controlled oscillator for converting said timing pulses into said phase detection signal; and means for feeding said disturbance signal into said phase locked loop; wherein said disturbance signal has the effect of breaking synchronization of said detected phase of the voltage or current of said AC system and the output of said comparator, said phase reference restoring synchronization when the phase or frequency of said phase reference is within predetermined values and said phase reference otherwise not restoring said synchronization such that said phase locked loop is desynchronized when said phase or frequency of said phase reference is outside said predetermined values.