Insulation coordination for a modular multilevel converter prototype

Abstract

This paper provides a detailed overview of the dielectric design and insulation coordination applied to a medium voltage modular multilevel converter prototype. The complete system has ratings of 0.5 MVA and is designed for connection to a 10 kV dc supply with a system voltage of 6.6 kV ac . The choice of air as insulating and cooling medium requires careful considerations regarding the clearance and creepage distances with respect to the selected materials. The design considerations from the submodule to the cabinet level are presented in the paper, considering safety standards and their requirements for a selected over-voltage category and pollution degree. The final dielectric design is verified experimentally with dielectric ac withstand test and partial discharge measurements.

Condition Health Monitoring of Modular Multilevel Converter Submodule Capacitors

“…1 and the already existing SM design presented in Fig. 2, which has already been detailed in previous publications of the authors [39], [6], [40]. The method is deployed in each SM so that each dc-link capacitance is estimated locally using the available dc-link voltage and terminal current measurements to reconstruct the SM dc-link current.…”

Review of Standards on Insulation Coordination for Medium Voltage Power Converters

“…The first parameter that is needed to be determined is the OVC that defines impulse voltage level required to determine the clearance distance. IEC-61800-5-1 states that it is sufficient for some converters to have OVC I due to no direct connection [43]. However, in the same standard, section "Insulation to the Surroundings", the OVC definitions are classified from OVC II to OVC IV depending on parameters such as whether the device is directly connected to the supply mains or connected directly to the origin of the installation supply mains and the connection type.…”

“…To the authors' knowledge, the approaches to MV insulation coordination on emerging power electronic systems have not been fully discussed and covered in the literature. There are only a limited number of studies, which have focused on insulation coordination of specific MV power conversion systems [1], [43], [44].…”

Virtual Submodule Concept for Fast Semi-Numerical Modular Multilevel Converter Loss Estimation

“…The MMC prototype, currently under development, has the following rating: 10 kV DC bus, 0.5 MVA apparent power and uses 96 SMs with low-voltage insulated gate bipolar transistor (IGBT) semiconductors (Semikron, SK 100 GH 12T4 T) that can be configured into unipolar or bipolar SM [6], [7]. The targeted application is the interconnection of the widely deployed 400 V low voltage AC (LVAC) grid, or corresponding microgrid, with the emerging medium voltage DC (MVDC) grids (10 kV is considered in our case) [8].…”