Current Traveling Wave Based Protection Scheme For Medium-voltage Microgrids Using Morphological Gradient Algorithm

A microgrid is a low-to-medium voltage energy network which contains distributed generators,loads and storage devices.It provides an effective channel to use renewable energy,like solar and wind,as well as environmentally friendly energy such as natural gas and hydrogen.However,flexible changeful operation modes,various network topologies and control strategies of DGs bring challenges to microgrid protection.The fault characteristics of microgrids are significantly different from those of macrogrids,so protection design of microgrids is facing difficulties.Research on protection of microgrids is one of the most popular research subjects.Firstly,this paper introduces a wide variety of methods of microgrid protection at home and abroad.Because of various DGs of microgirds,many traditional protection methods are not suitable for microgrids.While,the traveling wave based protection method has outstanding advantages in microgrids.Secondly,this paper introduces the basic structure of microgrids and the mathematical model,control strategies and output characteristics of DGs.And this paper analyzes whether current protection,differential protection and,distance protection applies to microgrids.Finally,compared with discrete wavelet transform algorithm and morphological gradient algorithm,it is found that morphological gradient algorithm can extract traveling wave signals more clearly.A complete current traveling wave based protection scheme using morphological gradient algorithm is proposed,which can use three-phase current traveling waves and modulus components to realize fault line and phase selection.Solutions to power fluctuation and dead zone problem are proposed.The current traveling wave based protection scheme proposed is suitable for microgrids with flexible changeful operation modes and currents which are difficult to calculate.Furthermore,in general,this scheme dispenses with potential transformers.However,current traveling wave based protection have a relatively high requirement for hardware equipment like high-frequency current transformers and high-speed communication devices.