Reactive Power Planning of Distribution Network Considering Time Series Characteristics of Grid-connected Photovoltaic Power Supply
College of Electrical and Mechanical Engineering, Agricultural University of Hebei, School of Electrical and Electronic Engineering, North China Electric Power University, Chen Li, Zhang Jinguo, etc., wrote an article in the 12th issue of the “Journal of Electrotechnics†in 2014 to improve the acceptance of distributed power sources and make distribution networks The economic and efficient operation of equipment is one of the basic requirements of smart distribution networks. This paper analyzes the probability distribution of active power and reactive power of grid-connected photovoltaic power sources. After ensuring the maximum active power output of grid-connected photovoltaic power sources and making full use of its reactive power output, a full life-cycle net income of reactive power compensation scheme is established. The reactive power planning model of the distribution network with the present value as the objective function realizes the reactive power demand of the distribution network with less reactive compensation investment. A chaotic multi-particle swarm optimization algorithm is proposed to solve the above model. This algorithm overcomes the "premature" problem of the basic particle swarm optimization algorithm. Through the example of reactive power planning of distribution network with grid-connected photovoltaic power supply, the correctness and effectiveness of the above-mentioned reactive power planning model and algorithm are verified.
In recent years, distributed generation (DG) technology has attracted more and more attention due to its unique environmental protection and economy. After years of development, solar photovoltaic power generation has become a more mature new energy power generation technology [1]. On October 27, 2012, the State Grid Corporation of China formally issued the "Opinions on the Implementation of Distributed Photovoltaic Power Grid-connected Services," which clearly stipulates the full acquisition of surplus power generated by distributed generation.
After the distributed photovoltaic power supply is connected to the distribution network, the traditional single-power radiation distribution network becomes a multi-power supply structure, which has an impact on the node voltage of the distribution network, branch current and network loss. In this paper, based on the analysis of the timing characteristics of active output and reactive power of grid-connected photovoltaic power supplies, the reactive power planning of distribution networks with grid-connected photovoltaic power supplies is studied.
There have been studies on reactive power planning of distribution networks with distributed power sources. The literature [2,3] analyzed the reactive power output characteristics of distributed grid-connected power generation systems, and proposed that the reactive power compensation capability of DG be fully utilized in reactive power planning. Literature [4] takes distributed power access planning into consideration on the basis of distributed power reactive power output characteristics. Literature [5] studied the influence of DG on distribution network voltage and network loss after accessing distribution network with different capacities and locations, and established a reactive power planning model for distribution network.
Literature [6] studied the reactive power planning of distribution networks containing multiple distributed power sources. Literature [7] studied the reactive power planning of distribution networks with distributed generation systems based on the consideration of distributed power sources active and reactive power independent regulation capabilities.
The above literature analyses the active and reactive power of various distributed power sources. The literature [4-7] studies the reactive power planning of distribution networks with the premise of constant active and reactive power distributed power. Due to the intermittent and time-series nature of distributed power output, the accuracy of planning results is poor.
The grid-connected photovoltaic inverter converts the direct current output from the photovoltaic cell into alternating current and transmits it to the grid, and at the same time selectively compensates the grid for a certain amount of reactive current. Its main circuit generally adopts the voltage type full bridge structure, this structure is identical with the main circuit of the regular Static Var Generator (SVG). In general, PV inverters have a minimum operating voltage (450V for conventional inverters), and enter sleep or off-grid mode when the illuminance is insufficient (eg, cloudy, night, etc.) when the input voltage is below its minimum operating voltage.
In this case, if the control strategy is changed, a power regulation system having both grid-connected power generation and reactive power compensation functions or only reactive power compensation functions can be realized. Making full use of the reactive power of PV inverters can not only save the investment of traditional reactive power compensation equipment, but also have good characteristics of quick response of reactive power compensation, and it plays an important role in improving the power supply capacity and power quality of the distribution network.
In recent years, the literature has studied the use of photovoltaic grid-connected inverters for excess capacity to perform reactive power compensation [3,8–11] and active filtering [12,13]. The literature [3] carried out the simulation and experimental prototype development for the unified control of photovoltaic grid-connected power generation and reactive power compensation. Literature [8] proposed a two-phase three-phase photovoltaic grid-connected system that combines reactive power compensation, voltage fluctuation compensation and photovoltaic grid-connected power generation with strong low voltage ride-through capability. Literature [9] proposed a single-stage three-phase photovoltaic grid-connected system with reactive power compensation function. This system can realize real-time compensation of local load reactive current while realizing the maximum power point tracking of solar cells.
Literature [10] proposed a cascaded multi-level inverter for single-phase PV combined with a segmented energy storage system to achieve reactive power compensation for the grid. Literature [11] proposed the idea of ​​integrating photovoltaic grid-connected power generation with reactive power compensation and active filtering. The new system structure and control strategy enabled photovoltaic grid-connected power generation systems to simultaneously realize photovoltaic grid-connected generation and reactive power and harmonics. Compensation.
The simulation results and practical application of the above-mentioned literature prove that, through a reasonable control strategy, the photovoltaic grid-connected inverter can simultaneously realize reactive power compensation to the grid while ensuring the maximum active output. Therefore, the intermittent and time-series characteristics of active and reactive power output of grid-connected photovoltaic power sources are studied. Reactive power planning of distribution networks can be carried out by making full use of active and reactive power of grid-connected photovoltaic power sources, and less reactive power can be used. The compensation investment enables the distribution network to operate safely, stably, economically, and efficiently.
in conclusion
This paper considers intermittent generation of grid-connected photovoltaic power sources to establish its output timing model. Based on the full utilization of active and reactive power of grid-connected photovoltaic power sources, a reactive power planning model and solving method for distribution network are proposed. Examples of reactive power planning are given. Analysis, draw the following conclusions:
(1) The grid-connected photovoltaic power source has a strong reactive power output characteristic, and it should be used rationally when the reactive power distribution network is planned.
(2) Considering the intermittent and time-dependent output model of grid-connected photovoltaic power supply will make the reactive power planning of the distribution network closer to reality and reflect the economic and technical indicators of the distribution network planning more truly.
(3) Using the characteristics of ergodicity, randomness and regularity of chaotic motion, combined with the solving characteristics of reactive power planning in distribution networks, the multi-population particle swarm optimization algorithm is improved, but it can help at the same time without increasing the amount of computation. The local optimal particle escapes from the local extreme point and quickly searches for the optimal solution.
Distribution network load output also has obvious timing characteristics. At the same time, reactive power planning of distribution network considering load and grid timing of photovoltaic power supply output can better improve the rationality of reactive power planning results. This paper only considers the grid-connected photovoltaic power supply, and its model and method can also be applied to the reactive power planning of distribution network with other distributed power sources or multiple distributed power sources.
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