The ''Phase-Hopping'' AC-AC frequency conversion technology proposed on the basis of traditional technology has the advantages of no circulating current, no dead zone and output frequency that can be improved to close to the power frequency. However, the research on this technology at present is still limited to the low voltage level, and problems such as low system capacity and high harmonic wave still exist, which cannot be applied in practice. To this end, a three-phase series-connected six-fold ''phasehopping'' AC-AC frequency conversion main circuit is designed on the basis of traditional series-connected multiple technology, which addresses the voltage withstanding problem of thyristors, reduces harmonic content and enlarges system capacity, and the circuit is simulated by MATLAB. Furthermore, a singlephase series-connected six-fold ''phase-hopping'' AC-AC frequency conversion experiment platform is set up, which includes the key main circuit and the trigger circuit and improves its synchronous detection circuit. The simulation and experimental results are consistent with the theoretical analysis. In view of the technical transformation of ''phase-hopping'' AC-AC frequency conversion of common high-voltage and large-capacity pump station motors, the main circuit is designed, the model selection of thyristor is conducted, and the cost estimation of frequency converter is carried out. The analysis shows that the system has a high cost performance, thus it can be seen that this technology has a broad practical application prospect. INDEX TERMS AC-AC frequency conversion, high voltage, large capacity, MATLAB.

Frequency converter is a kind of important energy-saving device. As a kind of improved cycloconverter, the "phase hopping" AC-AC frequency converter can increase the output frequency to close to the line frequency and has the advantages of no circulation current and no dead zone. By combining multiple-stage AC-AC frequency conversion technology, the "phase hopping" AC-AC frequency conversion can regulate the output voltage and the output frequency at the same time. Relative to current frequency converters, it has the advantages of large capacity, high voltage level, and low cost. Taking a six-fold circuit as an example, all the voltage results are analyzed according to the voltage vector superposition method. Three groups of parameters are chosen as instances and performed a simulation with MATLAB in the condition of constant voltage to frequency ratio. Then an experimental platform is set up and the experimental analysis has been carried on. The experimental results are in good agreement with theory and simulation studies.

Background: The output voltage frequency for the previously proposed "phase hopping" AC-AC frequency conversion technology is determined by the law that the number of output voltage cycles is reduced by one relative to the power frequency in a large cycle containing six jumps. According to the law, only a limited number of output frequencies such as 37.5 Hz, 42.86 Hz and 45 Hz are found. Due to the large spacing between the output frequencies, the "phase hopping" frequency conversion technology is difficult to put into practical use. Methods: In this paper, the law of the output frequency control is generalized so that the number of output cycles in a large cycle is reduced by n relative to the power frequency. The analysis shows that the appropriate selection of large cycles including the number of power frequency cycles and the value of n can find more frequencies to be used. Objective: Thereby reducing the interval between the output frequencies to within 1Hz. Results: The analysis results were verified in simulation by MATLAB, and the harmonics and the feasibility of the actual application were analyzed. Conclusion: Finally, an experimental platform was built and an experimental analysis was carried out. The experimental results show that the theoretical and simulation analysis are correct.

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