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Hysteretic Control Technology in New Flexible HVDC

The nearest level modulation (NLM) is commonly used in the multi-level multi-module converter (MMC), which need to convert the fractional part of the input sine wave to the digital signal (DPWM). However, the narrow pulse width of digital signal , the frequent change of the digital signal and the frequent instability of output are caused by the sensitive fractional portion of the input, which push Multilevel converter into the position where it has to operate in high frequency and be unstable. In order to solve the problem mentioned above, this paper provides a way called hysteresis comparison to meet the control requirements of precision, adopting the comparison between the fractional part and triangular carrier wave. The approach this study provides is called hysteresis comparison which not only can ensure the stability of the output of the digital signal but also can be able to obtain better digital pulse width by adjusting hysteresis threshold trigger. At the same time, it could ensure the stability and pulse width of the output by means of reducing the frequency of the digital output. The feasibility of this approach has been certified by the simulation of field-programmable gate array (FPGA). Apparently, the actual results show that this method can optimize the control of HVDC Flexible.