**6. Conclusions**

The paper proposed a market clearance and safety checking method for multi-type units that considers flexible loads. A market clearance model that considers the convertible loads and a safety checking model that considers the reducible loads were established. The safety checking can further eliminate the out-of-limit flow of the branches and sections and ensure the safety of the market clearing. A case study of a 220 kV and above power grid was used to analyze the results. The results show that the convertible loads participating in the market clearing can reduce the node's marginal

electricity price and reduce the peak and valley electricity price. Reducible loads participate in the safety checking, compared with the single adjustment of the power of the generator set, the power adjustment amount of the generator set is reduced; at the same time, the cost of safety checking is reduced. However, in engineering applications, the establishment of a reasonable incentive/price mechanism is the prerequisite for guiding flexible loads to participate in market clearing and safety checking. In the next study, in-depth research will be conducted on this issue.

**Author Contributions:** Conceptualization, D.H.; Data curation, C.Z.; Formal analysis, C.Z.; Funding acquisition, D.H.; Investigation, W.C.; Methodology, C.Z.; Project administration, D.H.; Resources, D.H.; Software, C.Z.; Supervision, W.C.; Validation, D.H.; Visualization, W.C.; Writing—original draft, W.C.; Writing—review & editing, W.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Key Research and Development Program of China [2016YFB0900100].

**Conflicts of Interest:** The authors declare no conflict of interest.
