Vernier control system for subsynchronous resonance mitigation

A subsynchronous resonance mitigation system for damping subsynchronous resonance oscillations occurring in a generator from a transmission line coupled to the generator, comprising:

• a coupling apparatus for coupling to the transmission line, the coupling apparatus responsive to a firing command to introduce subsynchronous resonance mitigating currents into the transmission line;
• a higher-level controller for synthesizing the generator speed based on a rotating reference frame, and producing in response thereto a voltage command;
• and
• a firing time controller responsive to the voltage command for providing the firing command to the coupling apparatus.

A method of damping subsynchronous resonance oscillations occurring in a generator from a coupling apparatus coupled to the generator by a transmission line, the coupling apparatus responsive to a firing command, the method comprising the steps of:

• determining a speed of the generator;
• generating a voltage command in response to the determined generator speed;
• generating a firing command signal in response to the voltage command and the monitored parameter of power flowing through the transmission line;
• and
• introducing subsynchronous resonance mitigating currents into the transmission line through the coupling apparatus in response to the firing command.

A vernier firing time controller for driving a coupling apparatus of a subsynchronous resonance mitigation system for remotely damping subsynchronous resonance oscillations occurring in a generator coupled thereto by a transmission line, the coupling apparatus responsive to a firing command, a transmission line sensor monitoring a parameter of the power flowing through the transmission line, and a higher-level controller having a generator speed monitoring device and producing in response thereto a voltage command, the vernier firing time controller comprising:

• a coupling apparatus predictor responsive to the transmission line sensor for predicting an initial voltage;
• a limiter for limiting the initial voltage and the voltage command received from the higher-level controller to provide a limited final voltage;
• a storage device for determining a predicted firing angle from the limited final voltage and the predicted initial voltage;
• a synchronizer for generating a first timing signal in response to the monitored line current;
• and
• a firing time computer responsive to the first timing signal and the predicted firing angle for generating the firing command to introduce subsynchronous resonance mitigating currents into the transmission line through the coupling apparatus.