# The Optimal Dispatch of a Power System Containing Virtual Power Plants under Fog and Haze Weather
###### Abstract
The concept of the virtual power plant (VPP) is employed in this paper to solve the above problems [6; 7; 8; 9; 10; 11]. There is no universally-accepted definition for VPPs, and recent theoretical studies and applications have mainly been reported in the European and American regions, such as flexible electricity network to integrate expected energy solution project (FENIX) and electric vehicles in distributed and integrated market using sustainable energy and open networks (EDISON). The VPP, which comprises controllable energy units (generations, consumers and prosumers) and can be controlled (centralized or decentralized) in order to alter the electricity production (like any other conventional units), is not a real power plant. In this paper, the VPP is defined as a special virtual unit that logically aggregates diverse DERs distributed in the generation and consumption sides, based on information and communication technology, increasing the visibility and enhancing the controllability of DERs in the power grid. The external performance of the VPP is the overall characteristic of DERs, and the VPP center internally controls the operation of all DERs. The operation control of the VPP mainly concentrates on two points: On the one hand, previous studies have researched the strategies that power systems integrally control VPPs at the grid level to make plans for power generating and purchasing according to optimal power flow and maximum economic benefits of VPPs or other conventional power plants, the objectives of which contain the profit of electricity sale, power purchase cost, ancillary service profit of the spinning reserve, generation cost of DERs, charge-discharge cost of electrical energy storage, compensatory payment for demand response resources, _etc._[6; 7; 8]. For instance, research on VPPs that contain electric vehicles (EVs) have focused on operating plans considering generating and start-up (shut-down) costs of distributed generations (DGs), fees of battery aging and system power balance constraints [9; 10]. On the other hand, the methods by which the VPP internally controls the aggregated DERs, based on a mathematical programming model and a multi-agent system, have been researched, as well [6; 11]. The internal control of the VPP has three different structures: centralized structure (all of the information of the power generation and consumption is available to the VPP center), centralized-decentralized structure (there are several subordinate control units of the VPP center) and decentralized structure (the information transformation relies on the multi-agent system). In conclusion, previous studies emphatically researched measures for capacity allocation, coordinated operation, operation control and market bidding participation to maximize the benefits of VPPs or power systems from the perspective of VPPs. In this paper, the VPP dispatch strategies at the grid level that consider the impacts of F-H weather are discussed. F-H weather would still exist in vast areas of China, and strategies of the operation, maintenance, prediction and dispatch control of power systems under F-H weather need improving. As for the predictions, the early studies about photovoltaic output and load forecasts only consider traditional meteorological factors, such as temperature, humidness and all kinds of weather types, rarely focusing on F-H [12; 13]. The literature [14] has proven that illumination intensity is directly blocked by F-H, and the instantaneous output and effective operating time of photovoltaic panels (PV panels) are greatly restricted. Residents' modes of production and life are affected by F-H, as well. People would stay indoors for health reasons, and industries with high energy consumption and high emission would be shut down by the government's contingency plan to reduce pollutant emission when the air is seriously polluted [15]. Therefore, a suitable prediction model that considers the F-H factor is urgently needed, which would increase the reliability of photovoltaic output and load forecasts.