Research On Rapid Load Response Of Supercritical Unit Coordinated Control System

Aiming at the problem that the load response of supercritical unit is slow due to the large delay at the furnace side and the small available heat storage,a new coordinated control system involving condensate throttling is proposed,and the technology of condensate throttling for 350 MW supercritical unit with small installed capacity is analyzed and discussed in detail.Understanding the working mechanism of condensate throttling technology,the steam-water distribution equation of steam turbine regeneration system is established.Combining with the steam turbine work equation,the static analysis of condensate throttling capacity is carried out.The upper limit of throttling output of condensate water is mainly limited by the minimum flow of condensate water.It is concluded that the upper limit of throttling output of condensate water and the output coefficient are positively related to the unit load.The throttling output time of condensate water is mainly affected by the low limit of deaerator water level.The theoretical calculation shows that the throttling output time of condensate water is negatively correlated with the unit load on the premise of ensuring the maximum throttling flow of condensate water.Condensate throttling test was carried out,and the variation trend of operation parameters such as unit output,deaerator water level,condenser water level,condenser vacuum and low pressure heater water level caused by condensate throttling was reasonably analyzed and explained.The test results show that condensate throttling has little effect on condenser water level,condenser vacuum and low-pressure heater water level.It will not cause alarm or other protective actions in a short time,but deaerator water level will drop rapidly,which needs to be monitored and analyzed emphatically.A non-linear dynamic model of condensate throttling is established by using a composite modeling method combining mechanism analysis with intelligent identification algorithm of particle swarm optimization.The mathematical model of transfer function at each working point is obtained by using small deviation linearization method.The characteristics of the coordinated control system of supercriti cal thermal power unit are analyzed.The difficulties and key points of the control are pointed out that compared with the subcritical unit,the furnace side delay is larger,the available heat storage is less,and the response speed is slower at the initi al stage of variable load.It is also pointed out that most units adopt coordinating mode based on furnace follow-up in order to improve the response speed of load instructions,but the throttling loss of steam turbine regulating valve exists for a long time,which leads to the decrease of economic benefits.The model of coordinated control system for supercritical units is obtained by closed-loop identification,and a new coordinated control system with condensate throttling is designed.The load-varying simulation experiment of units is carried out based on MATLAB platform.The simulation results show that the new coordinated control system with condensate throttling is more negative than the original coordinated control system.In the initial stage of loa d changing,the inert dead zone is quickly stepped out,and the change of load instructions is tracked.It has the advantages of small overshoot and short adjustment time.At the same time,it can relieve the dependence of the unit on the heat storage at the furnace side in the initial stage of load changing,reduce the opening margin of the turbine regulating valve,reduce the throttling loss and improve the economic benefit.In order to ensure the global adaptability of the control system,a fuzzy gain scheduling global controller is designed.The simulation results show that the fuzzy gain scheduling global controller can better adapt to a wide range of operating conditions.