Digital control of load commutated inverters for starting equipment of gas turbine power stations

Gas turbines need starting equipment to accelerate from standstill and follow a preset speed-time profile as required by the ignition and start-up procedure. The authors describe a new-design power electronic equipment based on digitally controlled LCI thyristor converter that supplies the synchronous generator with variable-amplitude/variable-frequency AC voltage so that it can be utilized as a variable speed electric motor to start the gas turbine. The digital control, besides performing all regulator functions, such as feedback control of DC current and rotor speed, thyristor firing and converter protection, includes extensive monitoring and diagnostic functions. An operator interface is also available that shows on a CRT-display all tuning and configuration parameters as well as the actual values of the main quantities acquired or calculated by the digital regulators. When any pre-selected event, e.g. a fault, occurs, the data stored in a dedicated register buffer can be used to trace the behaviour of the main converter variables, before and after such an event