Two Level State Estimation Of AC/DC Systems With PV Plants Considering Irradiance Distribution

With the increasing penetration of the photovoltaic(PV)power generation,real-time monitoring of the operating state of PV plants using heterogeneous sensors becomes inevitable for achieving grid-wise situational awareness and decision-making capabilities of the AC/DC power system with PV plants.This paper presents a systematic methodology for the comprehensive state estimation of the "sources"(PV plants)and "network"(AC/DC grid)in the AC/DC power system with PV plants,which provides a new idea for the situational awareness of power systems with the renewable energy generation.The main research works are as follows:1)Aiming at the problem that the situation awareness of the AC/DC grid needs to be enhanced due to the integration of the large-scale intermittent and random renewable energy generations,a high-precision multi-voltage level AC/DC grid state estimation model is developed.Firstly,in order to improve the accuracy of the state estimation model of the AC/DC grid,loss models which can accurately describe the operating states of the bidirectional isolated DC/DC voltage source converters(VSCs)and bidirectional DC/AC VSCs are developed,respectively;Then,a selection scheme of the state variables and measurements of the DC grid is proposed,and the state estimation model of the DC grid with the multi-voltage level and "mesh" structure is developed;Finally,combined with the state estimation model of the traditional AC transmission grid,a high-precision multi-voltage level AC/DC grid state estimation model is developed.2)A state estimation model of the AC/DC power system with PV plants is developed.The model has the following advantages: the PV arrays adopt the explicit fitting function model,and the converters adopt the accurate and tractable loss models,which improves the accuracy of the state estimation model of the AC/DC power system with PV plants and maintains high computation efficiency;Considering the measurement information of non-electrical quantities such as the irradiance and temperature in detail,the state estimation model of the AC/DC power system with PV plants is developed,and the state estimation range of the AC/DC power system is extended from the "network" to the "source",which improves the measurement redundancy,the accuracy,and the bad data processing ability of the state estimation model of the AC/DC power system with PV plants;The parameter estimation method of PV plants based on the multiple measurement scans is used to accurately estimate the missing parameters of converter circuits,which improves the usability of the proposed method in the engineering practice.3)Aiming at the problem of the limited situational awareness of the single-unit equivalent model of the PV plants caused by different irradiance of each PV array and different operation states of the same components in each confluence area in PV plants,a state estimation model of AC/DC power systems with multi-string PV plants considering the irradiance distribution is developed.A state estimation model of AC/DC power systems with multi-string PV plants considering the irradiance distribution is developed.Firstly,in order to improve the accuracy of the state estimation model of the AC/DC grid with PV plants,the multi-string PV plants are modeled in detail based on the component models of PV plants and the topology of multi-string PV plants,and the different operation states of the same components in each confluence area are considered;Then,based on the historical sky image and the corresponding irradiance datasets,the irradiance in each confluence area of PV plants at the state estimation time is forecasted,which improves the measurement redundancy and the accuracy of the state estimation model of the AC/DC power system.Finally,a state variable selection scheme that can characterize the operation state of the multi-string PV plant is proposed,and the measurement equations and Jacobian matrix are derived.Combined with the state estimation model of the AC/DC grid,the state estimation model of the AC/DC power system with multi-string PV plants considering the irradiance distribution is developed.4)Aiming at the problem that the computational efficiency of the centralized state estimation method of the AC/DC power system is reduced due to the detailed modeling of PV plants,a two-level distributed state estimation method for the multi-string PV plants and AC/DC grid is proposed.In the PV plants,based on the detailed model of the multi-string PV plants,and the measurement redundancy provided by the irradiance forecast data and the sensor,the state estimation model of the multi-string PV plants is developed to realize the real-time monitoring of the operation state of the PV plants.In the AC/DC grid,the state estimation model of the AC/DC power system with the multi-unit equivalent model of multi-string PV plants is developed to provide basic data for the response of PV plants at the point of the common coupling(PCC)when the AC/DC power system operates normally or fails.On the basis of ensuring the accuracy,the computational burden of the AC/DC power system state estimation caused by the modeling multi-string PV plants is reduced.