Q8Power System - I
Question
Q.8. What are the two basic requirements for the firing pulse generation of HVDC values?
Answer
The two basic requirements for HVDC valve firing pulse generation are: precise synchronization of the firing instant with the AC system voltage (phase reference), and sufficient pulse power/amplitude with adequate duration to reliably trigger the thyristor valve into conduction.
In HVDC converters using thyristor (SCR) valves, firing pulses must satisfy two basic requirements: first, accurate synchronization with the AC supply voltage waveform through a phase-locked loop, so that the firing angle (α) is measured correctly from the natural commutation point (zero crossing) of the respective phase voltage, ensuring proper and consistent control of DC output voltage/power; second, the pulse must have sufficient amplitude, energy and duration (or be a train of pulses) to guarantee reliable triggering of the thyristor into full conduction under all operating conditions, since a weak or too-short pulse could leave the thyristor in an unlatched state, causing a valve misfire and converter maloperation.