Researching the primary frequency control ability of large-capacity thermal power units is the main purpose of this article. The coupling model of digital electro-hydraulic(DEH) control system and coordinated control system(CCS) was established to analyze the dynamic process of primary frequency modulation.Moreover

several operation modes were introduced to improve the lack of primary frequency control ability on sliding pressure operation. Furthermore

through the primary frequency control experiment in a 1 000 MW unit

the sliding pressure enhancement

small feed water bypass and mixed frequency modulation were tested. The results show that

using the DEH and CCS together to carry out the primary frequency modulation has the best modulation effect. Increasing the sliding pressure by rising the main steam control valve throttling is the most direct and effective method for improving the unit's primary frequency control ability. The initial response is slow for small feed water bypass and the modulation characteristics are better at high loads. It can be regarded as the effective complement to adjust the frequency for main steam regulating valve. The regulating effect is similar with that by increasing the main steam control value throttling.