Analysis and calculation of the power device switching frequency of modular multilevel converters

Abstract

In order to analyze and calculate the switching frequency of power switches in modular multilevel converter (MMC) quantitatively, a mathematical model for sinusoidal pulse width modulation (SPWM) and nearest level modulation (NLM) is proposed in this paper. The factors influencing the switching frequency are summarized, and the superior and inferior limits in extreme cases of operation are analyzed which infer the range of switching frequency. And then, the theoretical formulae for calculating the switching frequency are presented, which is helpful for designing the parameters of the power switches and the control system. Finally, the correctness of the calculation formulae and the feasibility of the analysis are well validated by simulation results.

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

“…It not only has the fixed SM capacitor voltage deviation, but also reduces the cost of processing time for sorting the SMs. These modified voltage‐balancing algorithms allow proper SM capacitor voltage deviations to reduce the switching frequency and losses, and the switching frequency and losses need to be evaluated under this condition. The upper and lower limits of switching frequency under the identical capacitor voltage are investigated in [25]. The number of switching transitions is analysed in staircase modulated MMCs, and switching frequency under the restricted voltage‐balancing algorithm is derived in [26].…”

Research on an Auto-Optimized Capacitor Voltage Balancing Control Strategy of MMC SM for Renewable Energy HVDC Transmission System

“…In order to guarantee the stable operation of MMC at various operating points (e.g., currents and voltages), it is important to evenly distribute the voltage of multiple floating capacitors among each SM. Many capacitor voltage balancing approaches have been proposed in the literature [18][19][20][21][22][23][24]. The simplest way to balance the capacitor voltage is through the periodic rotation [15] of the gated mode based on the phase voltage switching state redundancy.…”

“…In References [22][23][24][25][26], if the SM capacitor voltage deviation is within the acceptable range of the system, the SM switching frequency is reduced by different methods. In References [22,23], the SM operating state is determined according to the direction of the bridge arm current and change trend of the reference voltage.…”

“…In References [22,23], the SM operating state is determined according to the direction of the bridge arm current and change trend of the reference voltage. In Reference [24], a method of fixing the switching frequency is proposed. By using a fixed module rotation number in each control cycle, the frequent switching issue of the SMs is avoided.…”