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Studies on Multi-objective Secondary Voltage Control

Author: ZuoZhiZuo
Tutor: LiuYuTian
School: Shandong University
Course: Proceedings of the
Keywords: Secondary Voltage Control Linear Goal Programming Multi-objective Control
CLC: TM761
Type: PhD thesis
Year: 2008
Downloads: 339
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Abstract


Secondary Voltage Control is a very important part of hierarchical voltage control. It links tertiary voltage control and primary voltage control and can coordinate reactive power resources of the control region. Its performance directly affects voltage and reactive power control effect. With the development of power system and its technology, the number of secondary voltage control goals has been gradually increased. For example, due to the closer coupling among different voltage level and control zones, it is necessary to consider the voltages at important and critical nodes, and the optimal coordinate control of generator and other reactive power compensation devices such as shunt capacitors and reactors, as well as the traditional control of pilot node voltages and the reactive power outputs from generators. Therefore, the study of multi-objective control method and control system is very important to secondary voltage control. Using the linear goal programming, which is a powerful tool of multi-objective optimization, the secondary voltage multi-objective control method is proposed in this paper and the multi-objective control system is developed. The main contributions of the thesis include the following parts:1、A secondary voltage multi-objective control model based on linear goal programming is established and solved by simplex algorithm which can fulfill the real time control requirements in confinement characteristics and memory space. According to the practical principle, the coordinate control method of generator and other reactive power compensation devices is proposed to achieve secondary voltage multi-objective control. Linear goal programming which has been extensive used among multiple objective programming is introduced into secondary voltage control and three goals are selected as control objectives. The first is pilot node voltage, the second is important node voltage and the third is to keep the reactive power output of the generators by a ratio of the rate reactive power capacity. Only generator as control measure, linear goals and constraints of secondary voltage control can be described by sensitivity analysis. By introducing deviation variables and defining priority of each goal, these linear goals and constraints can be transformed into linear goal programming model. Then the optimization solution can be obtained by simplex algorithm which satisfies the real-time control requirement in confinement characteristics and memory space. Simulation results of Zouxian power plant show that multi-objective control effect according to the priority order is satisfied. Coordinate control of generator and other reactive power compensation devices is very important for secondary voltage control. To deal with this problem, secondary voltage multi-objective control model based on the mixed-integer linear goal programming is established through sensitivity analysis, but the computation speed and reliability of branch bound algorithm is difficult to meet the real-time online control requirement. Therefore, according to the practical principle, reactive power compensation devices are used firstly and generators can be used for dynamic voltage support if the discrete control equipments could not be controlled. The discrete control equipments do not have control capability involving two reasons: one is no control measures, for example, all shunt capacitors have been used when need extra reactive power; the other is either voltage or power factor maybe go beyond the limit if using the discrete control equipments. After determining the values of discrete control variables, by revising constraints and goals of the mixed-integer linear goal programming model, the problem can be transformed into linear goal programming model which only includes generators and can be solved by simplex algorithm. Simulation results show that this coordination method is feasible and effective for secondary voltage multi-objective control.2、Considering influence of each regulation, multi-objective multi-stage optimization decision model based on dynamic programming and linear goal programming of secondary voltage control is established and solved by simplex algorithm. According to practical principle, multi-stage coordinate control method of generator and reactive power compensation devices is proposed to achieve secondary voltage multi-objective multi-stage optimal control. Practical secondary voltage control is a continuous operation system. Each regulation will influence the contol procedure. The effect of multi-objective control should be evaluated by control procedure not by single regulation. Based on this point, the multi-objective control procedure should be optimized by using dynamic programming and linear goal programming to solve the optimal decision series and fulfill the multi-objective optimization. To optimize the multiple objectives of control procedure, the procedure is divided into some stage firstly. The state variables, decision variables, and state transition equation of each stage and multi-stage control goals are determined. Then the multi-objective and multi-stage optimization decision model of secondary voltage control can be established by sensitivity analysis on the condition of only generator as control measures. Each stage decision variables of this linear goal programming model including can be solved by simplex algorithm. Simulation results show that the control effect of the procedure is better than the method ignoring the influence of each stage. To deal with the problem of coordinate control of generators and reactive power compensation devices, establish the mixed-integer multi-objective and multi-stage optimization decision model of secondary voltage control by sensitivity analysis. According the practical principle, the value of discrete variables of each stage can be determined. Revising the constraints and the goals of each stage of the mixed-integer model, the problem can be transformed into multi-objective and multi-stage optimization decision model in which the control measure only includes generators. This model can be solved by simplex algorithm and avoid using branch bound method to fulfill the multi-objective optimal control procedure with coordinate control of generators and reactive power compensation devices.3、The secondary voltage multi-objective control system which can be suitable for all kinds of control zones is developed based on structure variety of control zone being taken into account in control method and control system configuration. The operation results of Zouxian power plant show that the multi-objective control system is stable and reliable, and the control effect is satisfied. In the system design, goals and constraints expansion method of secondary voltage multi-objective model is proposed at first. Based on this method, the secondary voltage multi-objective control model can be applied in all kinds of control zones. The configuration of this control system is composed of high performance industrial control computer, control devices and fibre-opticalcommunication. The real-time multi-objective optimization is performed by theindustrial control computer based on the sample data from all control devicesthrough fibre-optical communication. The control device based on advancedembedded software and hardware design is used for data sampling, data processing,data saving, and generators and other reactive power compensation devices control.The configuration of control devices is flexible and the number can be determinedaccording to the number of generators and reactive power compensation devices ofthe control zone. The fibre-optical communication of this control system canensure data transmission speed and reliability at long distance. Based on thisdesign, this multi-objective secondary voltage control system is stable, reliable andpowerful, and can be suitable for all kinds of control zone. According torequirements of automatic voltage control system of Shandong power system, asecondary voltage multi-objective control system which have a industrial controlcomputer, six control devices and special fibre-optical communication net isdeveloped and installed in Zouxian power plant which has two 600MW and four300MW control generators to keep the voltages of 500kV and 220kV bus in thesetting value updated by tertiary voltage control of Shandong power systemdispatch center and the reactive power output of the controlled generator by a ratioof the rate reactive power capacity. The function of this multi-objective controlsystem includes accurate data sampling, parameters and control model setting,multi-objective control deciding, beyond limits alarming, data saving andexploring, chart displaying and database querying. The comparison of results withand without the secondary voltage control system of high, low and mean loadshows that the control effect is remarkable and system operation is safe, stable andreliable.

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