Research And Design Of Inject Signal Source In Distribution Network

In the 10 KV medium voltage distribution network,the distribution equipment will generally be grounded with an arc suppression coil at the neutral point to avoid ground faults caused by excessive capacitor current.Grid staff can accurately and effectively detect the distributed capacitance of the distribution network to the ground to achieve the best effect of current compensation.Among many measurement methods,the signal injection method is better than other existing methods for measuring the capacitive current of the distribution network,and its measurement accuracy can meet the actual application requirements.The injection signal source is the core part of the injection signal method to measure the capacitance current.The injection signal source that meets the specific requirements is also a prerequisite for the application of the injection signal method.This paper mainly studies the hardware structure and algorithm control strategy of the injected signal source,and designs an LCL type adjustable frequency constant current signal source:(1)Considering the characteristics of frequency conversion and amplitude modulation of the injected signal source,this paper designs a basic circuit topology of the signal source and a method of frequency conversion modulation.Through the analysis of the circuit structure,this paper establishes the mathematical model of the injected signal source;(2)By discussing the actual application scenario of the signal source,this paper explains the reason for using the current output method in the injection signal source.On this basis,this paper designs a closed-loop control method based on current output,and simulates and analyzes various indicators of the system control loop;(3)This paper details the design and implementation of the actual injection signal source.The main content is the composition of the hardware of the injection signal source and the implementation of the software algorithm,including the working principle of the hardware module,the selection of device parameters,and the generation and adjustment of the SPWM wave;(4)By establishing an experimental platform of 10 KV medium-voltage power grid,this paper experimentally debugs the designed signal source system,and verifies the correctness of related functions such as drive waveform,control strategy,output current accuracy,and output protection.The LCL type variable frequency constant current signal source designed in this thesis meets the requirement of using the signal injection method to measure the grid capacitance current.The experimental results show that the technical specifications such as high frequency accuracy of the injected signal source,fault handling,and inverter efficiency all meet the requirements of the design standards,the system is stable and reliable,and the expected design goals have been achieved.