Research On Improved CPS Standard And Its Control Strategy

Electric power system frequency is an important indicator of power quality and is one of the most important parameters of power system operation.It has a very significant impact on safety and efficiency of power system equipments and users' electrical equipments.The basic task of power system operation is to maintain frequency to its scheduled value and guarantee frequency error is in a limited range.National Standard of power quality and Operation Specification of power system in China have set a certain limit on frequency error and present minimum requirement on eligibility rate of frequency.With the rapid development of China's power system industry,the interconnection among regional grids has been strengthened and the modern Electric power systems have become interconnected systems comprised of multi-control areas.Automatic Generation Control(AGC) is one of the most important techniques to maintain the tie-line flows and frequency to their scheduled values.In order to keep the balance of active power,each control area is required to maneuver the turbine governor setpoints of generators so that the generated power follows the load fluctuations,which is implemented automatically by AGC.In the actual operation of power system,the regulating target of frequency is to maintain frequency to its scheduled value.In this case,most frequency deviation from scheduled value may lead to regulate even if the frequency is in eligible region.So regulation service is required frequently to track load fluctuations.Besides,this regulating target leads to a large number of regulating and huge regulating magnitude of generators even if CPS standard is taken.Continuously tracking load fluctuations definitely causes wear and tear on governor's equipments,shortens their lifetime,which can be very costly.By analyzing the frequency datum of several grids,it's found that actual frequency control effect is much better than requirement.In fact,the perfect eligibility rate of frequency is unnecessary and extravagant for exceeding the requirement deeply.That's because electrical equipments can also work well under a certain frequency offset and the limit of eligibility rate of frequency prescribed by Nation standard has assured the dependable working of user's electrical equipments. Besides,frequency measurement error can't make sure the regulating target of frequency is true rated frequency and System frequency is on the true rated value even if frequency is controlled to scheduled value accurately.So it's no need to ordain scheduled value as the regulating target of frequency.Considering about changing the regulating target of frequency is necessary in order to reduce the amount of regulation and the regulating burden and to minimize the operating cost.This paper first introduces the basic theory of load frequency control and AGC and analysis the cooperating effects of AGC control mode between two-area interconnected power systems.The control performance criteria A and CPS have been introduced and compared detailedly.In order to reduce the amount of regulation and the regulating burden and to minimize the operating cost,this paper presents the regulating target of frequency should be extend to frequency band from scheduled value,then improves the CPS standard.A CPS standard oriented AGC control strategy which consists of CPS1 control module,CPS2 control module and coordination output module has been designed.The control effects of A control strategy,CPS control strategy,improved CPS control strategy have been compared.The simulation results indicate that the improving CPS criteria considering frequency band has the greatest help to reduce the amount of regulation and mitigate the regulating burden under the precondition of keeping an eligible eligibility rate of frequency.