H_∞Robust Control Study On The Water Level Of Steam Generator Of Nuclear Power Station With Uncertainty

The steam generator (SG) as a key equipment of heat exchange in nuclear power plants(NPP), its water level control is of great importance to stable operation of NPP.The challengesposed to the water level control of steam generators (SG) in nuclear power station come notfrom nonlinearity and large delay of the control object, uncertainties and noises, but theinherent instability caused by given parameters at different operation points, which make itdifficult for SG systems to meet qualified safety and economic operation demand.In this paper, based on SG traditional linear model, SG control model was built withparametric uncertainty, during which modeling error, parameter variation and thermodynamicsystem noises were taken into accout. The performances of different H∞robust controlstrategies were studied and a pointed prioritization scheme was presented to provide atheoretical basis for SG watel level control strategy in reality conditions.The performance of H∞robust state-feedback control (HIRC) strategy was studiedbased on five SG steady operating points. The results indicated that actual height of waterlevel had reverse fluctuation of200~400mm from#1to#5when the set value of water levelchanged. From#3, the specified value perturbation of steam flow rate had an increasingimpact on water level with the load rising, raising the water level from500mm to around800mm at#5, though the water level got steady on set value around3800s with overshootsand oscillations. The feedwater flow rate had large perturbation from#1to#5when set valueof water level changed and its variation decreased gradually with load rising, from around600kg/s at#1to around400kg/s at#5.The performance of H∞pole placement control (PPHIC) strategy and H∞trackingcontrol (HITC) strategy were studied at the same condition. The results indecated that PPHICachived better stability from#1to#5, and it achived faster response at low operating points(#1to#3), stabilizing the water level at specified value at around3000s. Although fluctuationof water level of around300mm was brought by specified value perturbation at#5, PPHICachived better stability with stabilizing the water level at specified value at around3500s.HITC failed to keep stable when tracking the set value of water level at medium/highoperating points (#3to#5), but its fluctuation of u was surppressed within100kg/s. In general, the performance of water level control of PPHIC had certain promotion comparedwith HIRC.The performance of H∞pole placement tracking control (HIPT) strategy was studied inthe case of increment of system paramatric uncertainty and inducing noises. The resultsindicated that HIPT achived better performance on control stability and response velocity,stabilizing the water level at specified value at around4000s at#1~#4, around5000s at#5.HIPT also achived better performance on suppressing the perturbation of feedwater flow rateat medium/high operating points (#3to#5). A minimum of5kg/s was obtained at#3.Although the specified value perturbation of steam flow rate brought large variation onwater level, it hardly had an impact on the control stability of system, which was determinedby its inherent characteristics. The poles of system moved away gradually from zero oncomplex plane when load rising, which made it easy to achive better performance for controlstrategy.