Balanced Conduction Loss Distribution among SMs in Modular Multilevel Converters

Abstract

Due to the parameter mismatch, the unbalanced power loss distribution among SMs in the modular multilevel converter (MMC) can be introduced and further deteriorated by the low-frequency asynchronous switching transients related to no-carrier modulation techniques. The unbalanced thermal stress can reduce the reliability of the MMC and increase the complexity of cooling system design. Nevertheless, an internal balance mechanism exists in the MMC thanks to the capacitor voltage balancing. It contributes to an even conduction loss dissipation among SMs, which is studied and revealed in this paper. Moreover, a computationally light conduction loss estimation method is proposed correspondingly relying on the characteristics of semiconductors and the arm current only. Simulations and experiments are conducted to verify the effectiveness the proposed method.

Comprehensive Analysis and Design of Current-Balance Loop in Constant On-Time Controlled Multi-Phase Buck Converter

“…The output voltage can be written as (23) After adding the current-balance loop, the per-phase duty cycles is deviated from D voltage and is represented below using the same procedure when deriving (10) and (11).…”

Submodule power balancing control of modular multilevel converters under capacitor degradation

“…To attain equal SM loss in the arm, various loss equalisation control techniques for the MMCs are proposed in [32–36]. A power loss distribution scheme based on CCs at dc voltage offset, fundamental frequency, and second‐harmonic components of the output waveform, which maintains equal losses between the upper and lower switches is introduced in [32].…”

“…In these schemes, switching losses balancing distribution for each power semiconductor in SM is not considered. In [34], a balanced control scheme is presented that evenly distributes conduction losses among SMs. However, the effect of switching loss and performance of the system under capacitor degradation is ignored.…”

“…The performance and effectiveness of the proposed SM PB approach are validated through PLECS simulations and a laboratory MMC prototype based on the OPAL‐RT/OP4510 control platform. The proposed approach prevents the determination of total losses (conduction and switching) in each power unit, thus simplifying the control algorithm compared to the methods in [33–35]. Finally, the superiority of the proposed strategy is evaluated through a number of cycles to failure by acquiring the junction temperature fluctuations on power semiconductor devices.…”

Submodule Level Power Loss Balancing Control for Modular Multilevel Converters

“…Besides the temperature, regulating power losses is also an alternative for thermal balancing control [14]. However, as revealed in [15], the submodule-level conduction losses among SMs are well balanced regardless of the operation condition, the modulation techniques and the parameter mismatch under the circumstance of balanced SM capacitor voltages. It can be readily achieved by various voltage balancing control (VBC) strategies.…”