## 4 Discussion and Conclusions  
This paper provides a systematic review of 3743 articles published in renewable energy fields of electrical and electronic disciplines from 1992 to 2018, including evolution, topic distribution, and dynamic prediction. The results show that this field is technology-oriented, improving the efficiency of renewable energy production and utilization through the establishment of multiple energy systems. In the next few years, research on renewable energy technologies will continue to grow substantially, with a growth rate of 16.74%. It entered the preliminary research stage in 1995 and has continued to grow since 2005. Twenty one topics have been added since 2005, indicating that the renewable energy field has developed rapidly in the past 15 years. This article examined 29 topics. The topics related to the stability of renewable energy are \"Optimal dispatch and manage for power systems\" (topic 12), \"Study on power system stability\" (topic 21) and \"Power quality control\" (topic 24), etc., and the topics on the economics of renewable energy are \"Bidding and development strategies for the electricity market\" (topic 10) and topic 12. Additionally, the topics related to the availability of renewable energy are \"Hybrid energy generation system\" (topic 2), \"Photovoltaic power generation system\" (topic 4), and \"Wind power generation system\" (topic 13). Most of the topics have a large or stable growth trend in the future, which shows that as a field with a short research period (relative to the economic and financial fields), renewable energy has significant deficiencies in the above three aspects, and future research on these aspects also has growth potential.  
We found that the development in this field is not balanced. For example, research on new energy sources has made breakthrough progress in tidal energy and wave energy [104], but there are few articles in this field and the research enthusiasm in the future is cold, so more researchers should be called on to pay more attention to this topic. Similarly, the topics of \"Power system in teaching\", \"Research on dc circuit breaker and fault current limiter\", and \"Control technology and some systems\" need to be addressed. In addition, each country has a set of specific standards for the conductor temperature and current carrying value of transmission lines. The smaller examination of the transmission potential of transmission lines will not change the national standards, which may be the reason why the topic of \"Transmission line and transmission congestion control\" will become cold in the future.  
In summary, this paper describes the renewable energy field in the electrical and electronic disciplines at a more detailed level. For readers, it can help them gain a deeper understanding of the field and obtain the relative saliency of the topics of interest. For researchers, it can help them to summarize studies. For students and teachers, it can provide teachers with information for targeted teaching and help students choose course design themes. For editors, it provides important results for them to appreciate and apply.  
Our research may have some limitations. First, we analyzed only nine of 56 fields per article. In the future, we will focus on using these fields as much as possible to learn more about potential information. Second, we classified each article into a single topic, without considering the correlation between topics. Some articles may belong to multiple topics. Future research may focus on multi-label source text classification research.  
Conceptualization, L.L. and L.G.; methodology and data, W.X.; writing--original draft preparation, W.X.; writing--review and editing, L.L. and L.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Science and Technology Development Project of Weihai City, grant number 2018.  
The authors declare no conflicts of interest.