With the ever widening application of power electronic based residential loads and new energy devices in distribution systems

very considerable collective harmonics that have non-negligible impacts on the power systems have been generated. Therefore

a collective harmonic assessment method based on the cloud theory for residential loads is presented. The fundamental theory of the cloud model and cloud transform is introduced briefly firstly. And then the procedure of the collective harmonic assessment of residential loads is illustrated in details. The analysis results of practical cases prove that the cloud transform is capable of fitting the harmonic current distribution curves in high precision

and presenting the multi-modal characteristics of the distribution curves well. The 95% maximum probability calculated with the cloud transform is much more accurate than the normal distribution method does. The research results are meaningful to analyze the residential harmonic sources and determine the harmonic control and supervision measures. This work is supported by National Natural Science Foundation of China(No. 51207088)and Shanghai Key Supported Research Program(No. 14DZ1201602)

and State Grid Corporation of China(No. SGRI-DL-71-14-004).