Design of Increasing Dielectric Constant of Metallized Film Capacitor to Reduce Its Volume in MMC

Metallized polypropylene film capacitors (MPPFC) are usually used in modular multilevel converters (MMC) in HVDC transmission due to their good self-healing, strong current capacity, high energy density, and high reliability. However, due to the low dielectric constant of polypropylene film material (only 2.2), the capacitance value of polypropylene film capacitors is constrained, so the volume, weight, and cost of metallized film capacitors occupy a large part of the MMC system. For this reason, this paper considers reducing the volume of metallized film capacitors by increasing the dielectric constant of polypropylene film and analyzes a feasible range for the increased dielectric constant. Through the Comsol finite element simulation calculation, it is found that the volume can be reduced by 26.7%. Although the ESR of the capacitor increases, the capacitor temperature drops by 3.5 ℃ when the capacitor temperature is close to the steady-state due to the reduced diameter of the capacitor and better heat dissipation. This result can provide a reference for the optimal design of film capacitors in MMC applications.