Research On Power System Static Voltage Stability Considering AGC And AVC Control System

Modern power system has developed to a large capacity and long-distancetransmission system quickly to improve economic performance and protect theenvironment. This causes voltage stability problem looms large and threatens the wholesystem’s security[1]. AGC (Automatic Generation Control system) and AVC (AutomaticVoltage Control system) have a remarkable effect on power system’s voltagestability[5].Thus, this paper studied the issue further and has do some research asfollows:Firstly, this paper proposed a network partitioning algorithm considering regionalgenerators’ effect reactive power reserve. Whether network partitioning results isreasonable or not was key for AVC applied in actual system well. The existing researchdivided network just base on bus nodes’ electrical distance. To improve it, this paperhas considered regional reactive power reserve and built an optimization partitioningmodel. The objective function in this model was minimizing the sum of square of eacharea’s radius and maximizing the least area in regional reactive power reserve. Theconstraint was that all generators’ output reactive power must be greater than loads ineach area. Evolutionary programming algorithm and objective relative dominantstrategy was used to solve the problem afterwards. Finally, Simulation results on IEEE39-bus system and comparison with other network partitioning methods showed that theproposed method was reasonable and effective.Secondly, this paper proposed an improved power flow model which consideredgenerator’s static regulating character and secondary voltage control. Static voltagestability analysis and CPF are all based on power flow calculation model. Therefore,only when the power flow model is meeting to the real system, the load margin can beused to guide the security preventive control. Although the normal power flow model issimple and efficient, its solution condition is too fixed and is added too much humanfactors which cause its results different from operating conditions. For those reason, thispaper analyze the AVC and AGC system’s specialty and built the model. System’sunbalanced power is distribute to all generators based on its frequency regulatingcharacter. And it considers the secondary voltage control by modeling for pilot bus andcontrolled generators. The simulation result shows that this model is more close toactual power flow than normal model. Finally, based on above research this paper improved traditional continuationpower flow model, because it make some assumption on load variation and generators’reactive power dispatch which does not match the actual system. This paper proposed anew model considering AGC and AVC simultaneously. It adopts linear least squares fitbased on ultra-short-term load forecast data to determine load variation coefficient. Itdeals with the generators’ active power dispatch problem by considering generator’sstatic regulating character and AGC strategy. It also takes into account the plant andsubstation’s AVC control when load is increasing. To testify this model, this paper useIEEE39-bus system to simulation. The result shows that the static voltage stabilitymargin is different under different load variation and generator’s reactive powerdispatch pattern. It also indicates that the AVC control can enhance system’s voltagestability level. In short the static voltage stability analysis model can be used to guidethe security preventive control better than normal CPF.