A low switching frequency voltage balancing strategy of modular multilevel converter

MMC-HVDC: Simulation and control system

“…In the figure, v c refers to the vector consisting of all the SM capacitor voltages, r arm refers to the vector consisting of R y,j , and i refers to the vector containing all the arm currents. The SM capacitor voltage system calculations are based on (6) and the arm current system calculations are based on (14). Parallel computation of the SM capacitor voltages is feasible in the SM capacitor voltage system if a multi-core CPU is used.…”

“…The operation of the proposed control system under various operating conditions and a comparison of the proposed control system with the existing ones are considered in this section. The comparison is performed only with control systems that consider an O(N ) SM capacitor voltage balancing algorithm like the ones in [13], [14]. These control systems impose much lower computational burden when compared to the ones that [18].…”

Analysis and calculation on switching frequency and switching losses of modular multilevel converter with maximum sub‐module capacitor voltage deviation

“…5a. It can be seen that the maximum SM capacitor voltage deviation changes according to (19) under ɛ = 0, and the average value of maximum SM capacitor voltage deviation is 5 V under ɛ = 0.833%. The SM capacitor voltage deviation exceeds 5 V which is caused by the SM capacitor voltage variation in one control cycle.…”

“…To solve these problems, various modified voltage-balancing algorithms have been proposed to reduce the switching frequency in MMC [17,[19][20][21][22][23][24]. These methods can be divided into three categories:…”

“…(a) The state of SMs in the previous sample period is taken into consideration. Voltage-balancing control works only when the numbers of on-state SMs are changed [19][20][21]. The switching transitions can be significantly reduced, but the SMs capacitor voltage deviation is related with the operating state.…”