Yong-jun Zhang

Study on Reactive Power and Voltage Control in Large Grid Based on Sensitivity Analysis

Following the large development of grid, the emerging problem of reactive power and voltage mismatch is given an in-depth analysis in this paper, and the ideal control state and mismatch control state are distinguished. Then for the problem of reactive power and voltage mismatch, this paper presents a method of power Jacobian matrix and level of sensitivity to analyze the problem qualitatively in order to acquire the regulation strategy and direction. Finally, the Example of 14- bus system shows it is an effective method in the analysis.

A joint day-ahead scheduling for photovoltaic-storage systems based on extended QV bus-type power flow

This paper focuses on voltage fluctuation and the mismatch between generation and load demand caused by photovoltaic access to distribution network, using energy storage to solve negative effects brought by photovoltaic. According to the characteristics of point of common coupling (PCC) photovoltaic and energy storage accessed to, extended QV bus-type is put forward in order to describe the feature of PCC more reasonably. The solution of power flow calculation with QV bus-type is also shown in this paper. Furthermore, a joint day-ahead scheduling of photovoltaic-storage is put forward in core view of voltage control at PCC. The two scenarios where whether the power output of energy storage system is beyond the limit are considered. When the power output beyond its limit, the bus-type is transformed. As a consequence, node voltage curve and joint power curves of photovoltaic-storage are thus gained. The result is comprehensively compared with the case where photovoltaic and energy storage operate with constant power. It shows that the strategy this paper proposed has a significant effect on suppressing voltage fluctuation, improving power flow, peak load shifting and so on.

Influence of distributed photovoltaic system on the voltage of distribution networks with probabilistic model

The grid-connected photovoltaic (PV) system makes a great influence on reactive-voltage characteristics of distribution networks. Based on the β-distribution of solar irradiance, the probabilistic distribution model of PV power system is established in the paper. Considering the probabilistic impact of solar radiation on the output of PV power system, the simulation of voltage profile in distribution networks including PV in three typical weather conditions is provided. The law of voltage distribution and fluctuation in PV grid-connected distribution networks is demonstrated. The result also shows that the probabilistic model of PV can reflect the randomness and volatility of PV output and power quality issues such as over-limit voltage that PV power brings.

Application of power circle to reactive power optimization

Reactive power optimization has been a hard problem for years. However, the existed optimization algorithms are usually complex in calculation and not obvious in physical meaning. To study a simple and effective method for reactive power optimization, this paper puts forward a concept of optimal reactive load, and proposes a method called power circle method. With power circles, this paper presents a geometric explanation of minimization of active power loss and obtains the analytic expression of the optimal reactive load. And a simulation is carried out to verify the effectiveness of power circle method on reactive power optimization. The results show that power circle method has a good effect on loss reduction. Those conclusions provide theoretical basis for reactive power optimization of transmission line.

Energy storage demand of distribution network with photovoltaic based on voltage quality

Photovoltaic generation access to distribution network will cause voltage disturbance even beyond limits because of its variability and intermittency. Energy storage can effectively suppress the influence of PV on voltage and improve voltage quality. Voltage quality, the intuitive and practical indicator, is proposed in this paper to analyze the energy storage demand of distribution network with photovoltaic at the situation of different PV generation capacity, different partial load location and different gird parameters. Also, the result of voltage regulation is given after put into energy storage. Modeling and simulation shows that the energy storage demand is greater when photovoltaic with a larger capacity, partial load is closer to PV access point, or the node of PV access is farther away from balance node. Furthermore, the specific energy storage capacity and deploying recommendations are given according to using Matlab/Simulink to calculate.

Research on optimization setting of reactive power interval based on nine-area figure strategy

Focused on the current problems which exist in nine-area control strategy, such as frequent operation of control equipment and low qualified rate of voltage, the theory of nine-area method is deeply analyzed, and a new optimal setting method of reactive power interval in nine-area figure is proposed. A math model of evaluation function based on one-day energy loss of network, one-day adjusting times of transformer tap and capacitor switch and voltage quality is applied and improved to get proper upper and lower limit of reactive power. Simulation research of consecutive sections of nine-area strategy is conducted by programming with C# language. Simulation results show that the method is effective and the math model is accurate, and it has the guiding significance for setting reactive power parameters in voltage/ reactive power control over substation.

Automatic reactive power control in distribution network based on Feeder Power Factor Assessment

Based upon the analysis of the mechanism of power loss and voltage drop in distribution system, a new automatic control method of reactive compensation, namely, Feeder Power Factor Assessment (FPFA) is proposed in this paper. Promising that the voltage of all nodes is qualified, the proposed method aims at keeping the power factor of feeders between 0.98 and 1.0 in lagging, so that the reactive power of feeders can balance themselves as possible. A continuous power flow simulation method is put forward and programmed. The result shows that the proposed method performs excellently in reducing power loss, improving the voltage qualification rate and avoiding the frequent operation of devices.

Voltage curve developing of 220kV power plant based on the optimal voltage difference method

Based on the optimal allocation of reactive power load between a 220kV power plant and power systems to minimize the active power loss, this paper shows some key factors affecting the optimal reactive power of power plant. An evaluation index is proposed to reflect the relationship between the voltage magnitude of power plant and the reactive power flow of the system, i.e., the voltage difference between the high-voltage bus of power plant and the hinge bus. Then, by controlling the value of variables that affect the voltage difference, the paper adopts an optimal mathematical model to obtain the optimal voltage difference under different operation modes of power grids. After differently and uniformly dealing with the optimal voltage difference, the daily voltage control curve of power plant is optimally developed with rounding the predictive voltage curve of the hinge bus. The effectiveness of the method is verified by example results.