scholarly journals Pareto Frontier of the Arm Energy Ripple and the Conduction Losses of a Modular Multilevel Converter

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 392
Author(s):  
Mario Lopez ◽  
Hendrik Fehr ◽  
Marcelo A. Perez ◽  
Albrecht Gensior
Keyword(s):  
Pareto Frontier ◽  
Good Alternative ◽  
Operating Conditions ◽  
Modular Multilevel Converter ◽  
Multilevel Converter ◽  
High Voltage Direct Current ◽  
Circulating Current ◽  
Voltage Ripple ◽  
Capacitor Voltage ◽  
The Impact

Modular multilevel converters can achieve high power quality and voltage ratings, becoming a good alternative for high-voltage direct-current applications. However, the circulating current and capacitor voltage ripple remain significant drawbacks, mainly due to the impact on efficiency and power density. In this work, a stationary operation of a modular multilevel converter is optimized by calculating the Pareto frontier of the arm energy ripple and the conduction losses for different operating conditions. From the set of optimal solutions, the best trade-off between energy ripple and power losses can be chosen depending on the application requirements. Therefore, an optimal operating point regarding capacitor voltage ripple and circulating current was found, optimizing efficiency and allowing a reduction of capacitance, hence size and cost. The theoretical analysis and results are validated experimentally on a prototype test-bench.

scholarly journals Circulating Current Suppression Control in Surrogate Network of MMC- HVDC System

2020 ◽  
Vol 8 (6S) ◽  
pp. 29-34
Keyword(s):  
Output Voltage ◽  
Electromagnetic Transients ◽  
Modular Multilevel Converter ◽  
Multilevel Converter ◽  
Voltage Balancing ◽  
Hvdc System ◽  
Circulating Current ◽  
Capacitor Voltage ◽  
Circulating Currents ◽  
Three Phases

Modular multilevel converter consists of hundreds of submodules (SMs) like half bridge and full bridge converters etc. These hundreds of SMs and electrical nodes poses challenges while computing electromagnetic transients (EMTs). This problem becomes more complex while computed in real-time. To overcome this, an equivalent topology to model MMC arm/valve called surrogate network is utilized. But, the major ambiguity integrated with surrogate network model is SM capacitor voltage balancing. This leads to variation in voltage among the three phases which are parallel and produces circulating current between the three phases. A control circuitry is proposed in this paper to suppress/minimize circulating currents between the phases. Apart from circulating current suppression, the ‘ac’ output voltage is also enhanced at the converter with this proposed controller. Simulation is carried out in RSCAD software using RTDS simulator.

scholarly journals A Novel Z-Type Self-Balancing Modular Multilevel Converter for Flywheel Driving Applications

2021 ◽  
Vol 271 ◽  
pp. 01025
Author(s):  
Shuoqi Cheng ◽  
Tong Zheng ◽  
Congzhe Gao ◽  
Jingliang Lv ◽  
Xinjian Jiang
Keyword(s):  
Wide Frequency Range ◽  
Modular Multilevel Converter ◽  
Multilevel Converter ◽  
Variable Frequency Drive ◽  
Medium Voltage ◽  
Circulating Current ◽  
Capacitor Voltage ◽  
Voltage Balance ◽  
Current Characteristics ◽  
Capacitor Voltage Balance

With the development of flywheel technology, the speed and the voltage level of flywheel continue to increase. The Z-type self-balancing modular multilevel converter can have a wide frequency range at medium voltage and is suitable for flywheel driving application. However, the voltage and current characteristics of the flywheel and the variable frequency drive still affect capacitor voltage balance in each phase-leg. The new balance of capacitor voltage can be achieved by controlling the circulating current. This paper proposed a control algorithm of the novel Z-type self-balancing modular multilevel converter for flywheel driving applications. Simulation results are presented to validate the theoretical analysis.

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