Journal
IEEE TRANSACTIONS ON POWER ELECTRONICS
Volume 36, Issue 5, Pages 5262-5277Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TPEL.2020.3025976
Keywords
Capacitors; Voltage control; Switches; Topology; Support vector machines; Stress; Pulse width modulation; Multilevel converter; nested neutral point piloted (NNPP) convertor; space vector modulation (SVM); voltage balance control (VBC)
Categories
Funding
- National Natural Science Foundation of China [51577187]
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An improved SVM and VBC function are proposed in this article to address the voltage balance issues in 5L-NNPP converters, achieving decoupling of voltage control. The performance of the improved SVM is investigated and validated through simulation and experimental results.
In this article, a novel control method is proposed to control capacitor voltages for the T-type five-level nested neutral point piloted (5L-NNPP) converter. Due to the diversity of switching states for NNPP topology, there is no guarantee that the redundant vectors have the opposite effect on the dc bus neutral voltage. Meanwhile, the voltage balance controls between the dc bus neutral voltage and three-phase flying capacitor voltage are coupled and interacted with each other in the 5L-NNPP converter. This has severe voltage balance problems with the conventional space vector modulation (SVM), which limits its wide applications, especially under low output frequency. To solve the voltage balance problems, an improved SVM and voltage balance control (VBC) function are proposed to balance dc bus capacitor voltages and flying capacitor voltages, which realizes decoupling of voltage control. The switching states, switching principle, and dwell time calculation are developed, and the flowchart of VBC function is also elaborated on. The performance of the proposed improved SVM is investigated and compared with conventional SVM. The effectiveness and validity of the improved SVM with a VBC function is verified by simulation and experimental results of the 5L-NNPP converter.
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