Research On Power Grid Adaptability And Countermeasures To Grid-connected Photovoltaic Power Station

Photovoltaic power stations are not affected by the shortage of coal, oil and other primary energy. And they are eco-friendly and have flexible control mode. Besides, they are not bound to external factors, such as traffic and so on. So the photovoltaic power station is a good complement and replacement to the city electric power system and will become important power generation in the future. Although its construction cost is relatively high, the cost has shown the trend of rapidly decline with the development of correlative technology. As the phovoltaic power generation does not need the raw material input, its cost is close to the cost of fire power in the long-range economic term. According to the domestic and foreign authorities forecast, the proportion of photovoltaic power generation presents the trend of accelerated growth, and in the future electric power system, photovoltaic power generation will occupy an increasingly important position.At present, due to the lack of in-depth research of large capacity PV power plant characteristics, control strategy, influence on power grids and countermeasures and so on, the development of photovoltaic power generation has been seriously hindere. Under this backdrop, this paper has made a thorough research, and the three main innovations as follows:(1) to build large-scale photovoltaic power plant overall mathematical model and implementation of grid simulation calculation:At present, the models of a single photovoltaic cell model, single chopper and a inverter and maximum power point tracking (MPPT) algorithms have been established, but the large-scale PV power station is lack of the overall modelling. This paper provides in-depth theoretical study and experimental analysis of photovoltaic power plant, and has established the MW PV power station static and dynamic overall model. And based on the model, a real distribution network containing10MW PV power station is simulated and analyzed. This model lays a good foundation for the research of photovoltaic power station electric power system related to analysis of security, stability, trend, voltage, short circuit, a protection configuration scheme and plan of distribution network. (2) The dynamic behavior of grid-connected PV power station is described with the differential and algebraic equations. Secondly, the power system stability-criterion is proposed when the grid-connected PV power stations are under the maximum power point tracking (MPPT) control mode and fixed power control(FPC) mode respectively. According to this criterion, the stability of the PV power system can be fully determined by using the the PV array voltage and power measured; in the meanwhile, this criterion provides theoretical basis for the implementation of stability’s detection and control. Lastly, the validity and the feasibility of the dynamic model of the PV power station and the stability criterion established here are all verified by the simulation results on a real grid-connected PV power station in Jinan City.(3) With the interconnection of PV power stations, the fundamental functions of traditional protection devices are seriously affected or even complete failure, such as protective scope, selectivity, sensitivity, reliability. Furthermore, the operating characteristic parameters of distribution generations can be easily affected by natural conditions, such as light intensity, temperature, wind speed and other uncontrollable factors. Consequently, fault current of distribution network with grid-connected PV power stations is difficult to forecast. In this situation, this paper proposes a suitable protection scheme for distribution network with grid-connected PV power stations. It is based on the distribution system network structure and the fault currents contribution characters of every power source and specially takes into account the random characteristics of grid-connected PV power stations. And in the last part of this paper, the scheme is verified to be feasible and effective by the example of distribution network with the1.6MW total grid-connected PV power stations capacity in some area of Jinan City.In the end, this paper uses some10MW grid-connected PV power station project located in Shandong province Ji’nan city as an example combined with the PV power station network technical requirements and design, and through the in-depth impact analysis and research of station access system trend, network loss, voltage, relay protection, system stability and so on, puts forward corresponding countermeasures and photovoltaic power station network access scheme, which shows that the theory and the method of this paper is correct and effective.