| The rapid development of the power grid has made traditional low-voltage power distribution equipments no longer meet all the demands of customers,the intelligent development of the LV power distribution system has become an inevitable trend.As an important node in the grid,to meet the development needs of the smart grid,electrical appliance should also have the basic characteristics of digitization,informationization,automation and interaction in addition to the traditional functions.With the popularization of the concept of the smart grid,the research on the intelligentization of LV circuit breakers has received more and more attention.In this thesis,a centralized power supply system that can realize carrier communication is proposed for the intelligent LV power distribution microsystem(circuit breakers used in it are miniature circuit breakers).The centralized power supply system consists of two parts,power module and carrier comminication module.The tripping of the circuit breaker needs to be powered by 24 V DC supply,traditional method is to integrate the power module into the circuit breaker shell,but this microsystem adopts a mode of centralized power supply outside the shell that can reduce the volume of breaker to some extent.While the power supply provides power for circuit breaker,it also provides a channel for information transmission that can replace the original field bus and reduce the cabling in the microsystem.This topic comes from the National Natural Science Foundation of China: Research on a new type of thermal electromagnetic hybrid intelligent miniature circuit breaker and intelligent low-voltage power distribution microsystem(Project Number: 51777129).The main research contents are as follows:The main power supply is designed based on transformer.Its design of hardware circuit is based on STC89C52 and MOSFET driver.Its software circuit uses incremental PI algorithm to adjust the duty cycle of the PWM signal.The main power supply is simulated on Proteus,and the stability of power supply is verified when the input disturbance is added.The actual test is carried out to verify the correctness of the design.In order to still have stable and sufficient power supply when a short circuit fault occurs,an auxiliary power supply is designed based on current transformer.Its hardware circuit is based on pulse width control chip TL494 and triodes driver.The auxiliary power supply is simulated on Proteus,and the correctness of the design is verified.The power of the main supply and the power of the auxiliary supply are both 48 W.Considering the requirements of communication for real-time and rapidity,a carrier communication scheme based on FPGA data processing chip and RS485 link standard is proposed according to the characteristics of DC channel.The FPGA model is EP4C6E22C8 which has phase-locked loop(PLL).The whole hardware circuit is designed,including coupling circuit,RS485 carrier interface circuit and so on.The parameter selection of related component such as coupling transformer is given.In order to solve the problem such as carrier signal has DC component,the differential Manchester coding is finally adopted after analyzing the modulation mode of signal.The coding and decoding and CRC verification are simulated on Quartus II.A test platform is built to test the communication system,the digital carrier communication on 60 m power line is realized and the transmission rate is 10 Mbps,the correctness and feasibility of the design are verified. |
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