# Smart Inverters for Microgrid Applications: A Review
## Discussion  
In order to define a device as smart, it has to represent several qualities and characteristics mostly depending on its application and implementation. In this study, these characteristics have been described for inverters, which are used as interfaces for DGs in microgrids:  
* Plug-and-play capability has been the first concept discussed. Regardless of how much effort has been expended to omit the communication requirement, in order to achieve a stable and functional microgrid, especially in the context of accurate active, reactive and harmonic current sharing, this requirement still exists. In contrast to other smartness indicators that evaluate the smartness based on how less it relies on communication for normal operation, plug-and-play is mainly related to communication compatibility. Different relevant communication technologies have been introduced and investigated in detail with tabular information. The fact that the DGs can be spread over a large area, maybe several kilometers apart, will emphasize the infeasibility of using conventional communication protocols mostly according to economic considerations. One practical and attractive solution can be the use of the Internet. However, in accordance with M2M communication and the Internet of things concept, it is not practical to connect every node of a system directly to the web. A long range, low implementation and operating cost, protocol that is reliable enough at the same time, such as LoRa or ZigBee, can be used to communicate each of the inverters to internet gateways. It is understood, further research and thorough experimental work are required to end up with a conclusion and chose one communication protocol over another. * Self-awareness is another smartness indicator. In this section, the concept of fault diagnosis, condition monitoring and prognosis have been explained. In addition, fault detection methods have been briefly reviewed since all three-health indicators of inverters require fault detection at some point in their control structure. According to various methods proposed for open-circuit fault detection, it can be observed that, no matter how complicated the detection algorithm could be, there are still based on local measurements with the aim of avoiding the further requirement of communication. Short-circuit fault detection can be effectively conducted by use of hardware and local current measurements. * Another studied characteristic of smart inverters has been their adaptability. This is related to the change of parameters of the grid, the loads and the working mode of the inverter itself. Here smartness is the ability to sense and identify some fluctuations in the parameters readings that can be an indication for faults. Then, effectively self-adjust to be able to continue to function regardless of the mode change or the fault as it is not always possible to shut down the system immediately even if a serious problem has been detected. This is called fault tolerance, and the different methods have been introduced and compared. Some of them require extra, redundant, hardware and others provide redundancy by manipulating the modulation process. Unintended islanding for microgrids due to grid failure is another issue, and if the system cannot self-adapt itself with this phenomenon, the results can be catastrophic. Methods for islanding detection are different, and they have been briefly introduced and compared. It is understood, same as the fault detection methods, in islanding detection methods the aim of reducing communication requirements and self-adapting in the procedure is a major consideration nowadays. * The other important characteristic is autonomy, which intends to reduce the requirements for communications among inverters installed far away from each other even more. In microgrids, depending on if it is islanded or grid-connected, the inverters are controlled as VSCs or CSCs connected in parallel.