Small Signal Stability Analysis And Control For Power Systems With Large-Scale Concentrated Solar Photovoltaic Plant

The energy system dominated by fossil energy has been unable to meet the need of the energy development of the world today.As a result,with major changes emerging in large numbers in the global energy structure,the field of renewable is full of vitality at present.In recent years,the installed capacity of photovoltaic in China has ranked first in the world,and continues to grow at a very high rate each year.Longyangxia photovoltaic plant with 850 MW,which was completed and put into operation in 2017,has become the world's largest photovoltaic plant.However,the energy distribution in our country is uneven.A large number of renewables are located in the western region which is far from the load center.Thus,the renewable energy needs to be transported over long distances,which poses a serious threat to the security and stability of the power system in our country.Small signal stability is related to a wide range and a large number of equipments in the power system.Hence,it is crucial to effectiveness of the resource allocation in the power system.In conclusion,the study of the impact of the large-scale concentrated photovoltaic plant on the power system small signal stability,and measures to improve its small signal stability performance are critical to improving the ability of the power system to accommodate photovoltation power.In this paper,the concentrated photovoltaic plant model was built,which enabled the simulation analysis and small signal stability computation of the power system integrated by the concentrated photovoltaic plant.The damping torque model and analysis method for the power system with the concentrated photovoltaic plant were studied,and the impact of multiple factors was analyzed.The photovoltaic wide-area damping controller(PWADC)was designed based on gain scheduling method to prevent small signal instability happening in power systems integrated by the large-scale concentrated photovoltaic plant.The risk assessment and the emergency control of small signal instability was proposed based on stochastic response surface method to protect the power system integrated by the large-scale concentrated photovoltaic plant against small signal instability.The main contents in this paper are as follows.The detailed model of the concentrated photovoltaic plant was built.The main circuits in this model contains the photovoltaic array,the DC/DC boost,the DC link,the inverter and the filter.And the control part of this model includes the phase locked loop,the current control of the inverter,the control of the boost,and the active and reactive power control of the inverter.The active power control consists of the maximum power point tracking control and the constant active output power control.The reactive power control is made up of the constant reactive power control,the constant power factor control,and the control of constant voltage at the point of common coupling.The proposed model was realized in the power system toolbox(PST),and further analysis by the simulation and the small signal stability calculation were carried out.Also,the proposed model was verified in different test systems which adopt different control modes of the concentrated photovoltaic plant.The damping torque analysis method for the concentrated photovoltaic plant was studied.Base on the proposed detailed photovoltaic planlt model,the damping torque analysis model was built in the single machine infinite bus test system.The impact of different control parameters,irradiance,control modes and photovoltaic proportions brought on the power system damping was studied.A photovoltaic wide-area damping controller was proposed based on gain scheduling control.Considering the feature of the power system integrated by the large scale concentrated photovoltaic plant,the linear parameter varying power system was modeled by the tensor analysis method to deal with the uncertainty of the photovoltaic output power.And a Lyapunov stability criterion with low conservatism was proposed to handel the delay of the networked control system for the design of the scheduled gain of the controller.The gains of the gain scheduling controller was computed offline based on the expected scenarios generated by the day-ahead scheduling plan.Then the gain of the controller was scheduled in real-time based on the monitored system status.Hence the controller can be realized by offline computation and online application.The performance of the proposed gain scheduling photovoltaic wide-area damping was tested by a 16-machine 68-bus system.A small signal probilistic stability analysis method and an emergency control strategy were proposed based on the stochastic response surface method for the power system with uncertain photovoltaic output.In terms of the small signal probabilistic stability analysis,the cumulative density function of the critical mode damping ratio was computed by the stochastic response surface method,and then the probability of instabilty can be obtained.As for the emergency control,the system status can be captured by the model built by the stochastic response surface method,and then the emergency control strategy can be provided in several milliseconds through the optimization of the rescheduling.The proposed method was tested by a 2-area 4-machine system and a 10-machine 39-bus system.