Design And Research Of Residual Current Integtated Device Under Complicated Waveform Conditions

With the increasing of electrical equipments, when power electronic equipments fail, thegenerated residual currents are not only including sinusoidal current component, but alsoincluding pulsating DC current component, or even smooth DC current component. Currently,type AC residual current devices are widely used in China. However, they can not meet the newrequirements of the low-voltage distribution power system because they can only detectsinusoidal residual current and their functions are so simply. Therefore, it is very important tostudy on the residual current device under complicated waveform conditions.Firstly, three non-contacted current detecting methods, which are electromagnetic currenttransformer, Hall current sensor transformer and magnetic modulation-based current transformer,are introduced in this paper. The principles and technical features of the three methods areanalyzed. And the results show that the magnetic modulation-based current transformer is moresuitable to detect the complicated residual current.Secondly, the hardware circuits are designed, including magnetic modulation-based residualcurrent detecting circuit, current and voltage detecting circuit, driving circuits for motor andtripper and RS485communication circuit. So that the functions such as residual currentprotection under complicated waveform conditions, over-current protection and short-circuitprotection, over-voltage or under-voltage protection, automatic reclosing function and RS485communication can be implemented. And a type of switch mode power supply is designed forthe device.Thirdly, the software is designed based on the floating-point DSP TMS320F28335. And anIIR digital filter is designed to filter complicated residual current. It is verified by experimentsthat the software can meet the requirement of the relevant standard.Finally, refined measures are presented based on the principle of EMI andanti-electromagnetic interference tests are conducted. It is verified that the prototype can meetthe requirement.