Abstract
The Modular Multilevel Converters (MMC) have been a spotlight for the high voltage and high power transmission systems. In the VSC-HVDC (High Voltage Direct Current based on Voltage Source Converter) transmission system, the energy of DC link is stored in the distributed capacitors, and the difference of capacitors in parameters and charge rates causes capacitor voltage balance which affects the safety and stability of HVDC system. A method of MMC based on the expert system for reducing the frequency of the submodules (SMs) of the IGBT switching frequency is proposed. Firstly, MMC with 51 levels for HVDC is designed. Secondly, the nearest level control (NLC) for 51-level MMC is introduced. Thirdly, a modified capacitor voltage balancing method based on expert system for MMC-based HVDC transmission system is proposed. Finally, a simulation platform for 51-level Modular Multilevel Converter is constructed by using MATLAB/SIMULINK. The results indicate that the strategy proposed reduces the switching frequency on the premise of keeping submodule voltage basically identical, which greatly reduces the power losses for MMC-HVDC system.
Highlights
The results indicate that the strategy proposed reduces the switching frequency on the premise of keeping submodule voltage basically identical, which greatly reduces the power losses for Modular Multilevel Converters (MMC)-HVDC system
In High Voltage Direct Current applications, high voltage long distance transmission is often constrained by the fact that the components of power electronics are limited in terms of rated voltage
To validate the effectiveness of the voltage balancing method proposed in this paper, the 51-level MMC-HVDC transmission system simulation platform in MATLAB/SIMULINK is taken, and specific parameters are as follows: the number of submodule N is 50; the converter rating for the openloop simulation is considered as 1000 MVA with the total dc voltage Vdc being 400 kV
Summary
In High Voltage Direct Current applications, high voltage long distance transmission is often constrained by the fact that the components of power electronics are limited in terms of rated voltage. Compared with two-level VSC, MMC has much lower switching frequency and switching losses, which makes the MMC suitable for applications in HVDC. There are many topologies of MMC, modulation, capacitor voltage balancing, circulation suppression, the research results of the fault tolerant technique, and so forth [1,2,3,4,5]; there still exist challenges in the field of control, such as capacitor voltage balancing and circulating current control [6]. A method for each module, respectively, for closed-loop control voltage balancing strategies is proposed in [7]. A modified CPS-SPWM method with the reduced-switching frequency (RSF) voltage balancing algorithm is proposed in [9]; the modulation strategy of it requires massive calculation. An intelligent distributed control of MMC is adopted in [10]; “The Tortoise and the Hare” sorting method shows the fast response for HVDC system
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
