Parameter Identification Method And Performance Research Of Thermoelectric Current Measurement System

The rapid development of Smart Grid indicates that it is an inevitable trend to realize intelligent control of circuit breakers in low-voltage distribution appliances.In the huge team of low-voltage circuit breakers,the universal circuit breaker（ACB）and the molded case circuit breaker（MCCB）have achieved intelligent control and occupy a certain position in the lowvoltage market,while the intelligence of the small circuit breaker（MCB）has been in the bud.In the process of realizing intelligent control of low-voltage circuit breakers,the current measurement and overload protection technology of the system are important links.However,the performance of the tripping device completely affects the performance of the circuit breaker.Nowadays,most of the intelligent circuit breaker releases use the electronic tripping method.The core technology is to measure the current through the current transformer,but the current market The current transformers on the LV circuit breaker are large in size and take up a lot of space to install in the low-voltage circuit breaker.The internal structure of the miniature circuit breaker system is compact and the space is limited,so the installation of the current transformer cannot be realized at all,so the realization of the intelligentization of the miniature circuit breaker has become a difficult problem.This paper aims to solve the current measurement problem of small circuit breakers.Therefore,a thermoelectric current measurement method based on the thermal effect of current is proposed to overcome the problem that the current small circuit breakers cannot be intelligent due to their internal volume defects.This topic comes from the National Natural Science Foundation of China: Research on New Thermo-electromagnetic Hybrid Intelligent Miniature Circuit Breakers and Intelligent Low-Voltage Power Distribution Microsystems（Project Number: 51777129）.Firstly,the basic working principle of thermoelectric current measurement method is briefly analyzed,and the reason why the electrothermal system of small circuit breaker and the measuring cavity can be replaced equivalently is expounded.Based on the conservation of energy,the basic mathematical model for parameter identification of small circuit breaker system is deduced,and the thermoelectric current measurement method using temperature rise to measure current is realized.Secondly,master the basic process of system identification and choose the parameter identification method suitable for the system.Finally,the recursive least square algorithm which can realize online identification is selected,and its formula is mathematically deduced based on the least square algorithm.Thirdly,build a simulation model based on the deduced identification mathematical model,write the identification program of the recursive least squares algorithm,study whether there is noise in the system,analyze the final parameter identification results,and verify the identification mathematical model.On the basis of the original mathematical model,a new mathematical model and a simulation model are improved by changing the positions of the input and output,and the parameter identification conditions of the two different models are compared,and the mathematical model that is more suitable for the requirements is selected.Finally,in order to solve the current situation that the small circuit breaker can only complete the system identification before leaving the factory,a new idea is proposed.A resistance and an inductance are connected in series to the heating element in the small circuit breaker system,and a switch is used to control the resistance and inductance.In this way,the on-site parameter identification of the system is realized.The performance of on-site identification of the system is studied through simulation,and the most suitable resistance and inductance values for series connection in the system are selected.