Research On Low Voltage Control Method And Experiment In Low Voltage Distribution Network

The low-voltage(LV)distribution network is located at the end of the whole power network.As the last network for the majority of residential users,it is responsible for directly supplying power to users,and its network construction and operation status will have a direct impact on the power quality of users.Different from the mature and well-developed transmission lines,the LV distribution network in China usually have problems such as old and aging electrical equipment,small cross-section of conductor,large power supply radius,which resulting in the phenomenon of low voltage at the end of line.At present,the power department often uses the line rebuild method with high cost and long construction time,while the parallel reactive power compensation method has poor effect on voltage rising.In order to solve the problem of voltage deviation in LV distribution network,this thesis studies the applicability of series compensation technology in LV distribution network,then compares the lifting effect of series and parallel compensation in the process of low voltage improvement.Next,studies the thyristor controlled series compensation(TCSC)technology and puts forward the TCSC structure and control algorithm which suits for LV distribution network.On the basis of the above theoretical analysis,the TCSC experimental prototype for LV distribution network is developed,and be tested in the laboratory environment,which verifies the feasibility of the method and device in this thesis in dealing with the voltage deviation.It provides a new reference method and engineering value for solving the low voltage problem in the actual LV distribution network.The main work of the thesis is as follows:(1)The working principle of series capacitor compensation in power system is studied.According to the circuit model of single point load,the influence of series compensation on power transmission and voltage loss is analyzed.Then,the calculation formula of the required capacitance reactance for target voltage is derived,and the optimal installation position of the series compensation is analyzed.In addition,the principle and effects of series compensation and parallel compensation on low voltage improvement are compared: the compensation capacity formulas of the two for the same target voltage are derived,and the calculation and comparison are carried out under the single point and multi-point LV distribution line model respectively,which verifies that the series capacitor compensation has advantages in low voltage improvement in LV distribution network than the parallel one.(2)The basic structure,working principle,fundamental impedance,characteristic curve,harmonic and loss characteristics,and layered control strategy of traditional TCSC are analyzed.In view of the problems faced by TCSC running in LV distribution network,such as short circuit distance and large number of capacitors,an optimized TCSC structure with additional series inductance is proposed,which can reduce the number of capacitors required by the device.By analyzing the characteristics of the new structure,it is found that proper inductance configuration can also increase the adjustable range of capacitive reactance.For the current look-up table control method commonly used in TCSC engineering,the mathematical idea of function approximation is proposed to better control the fundamental impedance of TCSC in LV distribution network.(3)According to the typical LV line model in China,the method of central point voltage management is proposed,and the calculation process of TCSC compensation reactance is analyzed.Then,an actual LV line in Zhejiang Province is analyzed,and the compensation reactance and position of TCSC are determined.Combined with the engineering practice,the control scheme and process of TCSC for voltage control are put forward,and the functional design of the device control system is introduced.In addition,the model and parameters of the main circuit components of the device are selected,and the physical device and its overall layout design is shown.Finally,a set of TCSC experimental device prototype for low voltage control in LV distribution network is formed.(4)The experimental verification of the research content and the device prototype is carried out.First of all,The TCSC simulation model is established in the model of actual line given above,and the simulation results show that TCSC can enhance the low voltage and produce little harmonic effects.Then,the experimental platform is built in the laboratory.Firstly,the characteristics and functions of the thyristor module are tested,and then the functions of TCSC device are tested in the environment of low load and small current.The results show that the experimental device developed in this thesis has good control effect for low voltage phenomenon.