Study On Firing-pulse Generator Used In HVDC Control And Protection System

HVDC (High Voltage Direct Current) has many merits, and it will take an important role in national grid. For a long time, the equipment of HVDC was totally imported from foreign companies, such as ABB and SIEMENS. The equipment imported is very expensive and brings troubles in installing of the equipment, daily operation and maintenance. It is obviously necessary to product the equipment by ourselves. The heart of HVDC link is its control and protect system, and my work is focused on firing-pulse generator―an important part in the control and protect system .A conventional control system for timing the firing pulse contains six or twelve independent delay circuits. This kind of firing-pulse generator may leads to uncharacteristic harmonics due to unbalance of impedance or ac line voltages, or timing errors in the control system. Another kind of firing-pulse generator that greatly reduces uncharacteristic harmonics is based on the phase-locked oscillator. But it also has shortcomings: the firing angle delay of firing-pulses is not very accurate, and the respond speed is not very fast.In this paper, a firing-pulse generator based on measuring ac system frequency is presented. A modern programmable ASIC―FPGA is used to build logical circuits. The whole generator and its every part are designed by VHDL and illustrated by logical graphics.At the end, the shortcomings of the generator are discussed, and the tendency of technology on firing-pulse generator is predicted.