Conference Paper

# Analysis of DC-Link capacitor losses in three-level neutral point clamped and cascaded H-Bridge voltage source inverters

Univ. of Southampton, Southampton, UK

DOI: 10.1109/ISIE.2010.5637820 Conference: Industrial Electronics (ISIE), 2010 IEEE International Symposium on Source: IEEE Xplore

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**ABSTRACT:**The DC capacitor is an important component in a voltage source inverter. The RMS current flowing through the capacitor determines the capacitor size and losses. The losses, in turn, influence the capacitor life. This paper proposes a space vector based modulation strategy for reducing the capacitor RMS current in a three-level diode-clamped inverter. An analytical closed-form expression is derived for the DC capacitor RMS current with the proposed PWM strategy. The analytical expression is validated through simulations and also experimentally. Theoretical and experimental results are presented, comparing the proposed strategy with conventional space vector PWM (CSVPWM). It is shown that the proposed strategy reduces the capacitor RMS current significantly at high modulation indices and high power factors.Electric Power Systems Research 12/2014; 117:1–13. · 1.60 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Cascaded H-bridge (CHB) inverters used in high-voltage variable frequency drives are usually composed of several power cells. Each power cell consists of a three-phase uncontrolled rectifier as its input stage and a single-phase inverter as its output stage. It is difficult to obtain the analytical expression of the dc-link capacitor current because of both the nonlinear characteristics of the uncontrolled rectifier and the low-frequency harmonics caused by the single-phase inverter. On the other hand, exact analysis of the capacitor current is important for dc-link capacitor selection. This paper proposes an analytical method for calculating the capacitor current. Considering both the input current of the inverter and the output current of the rectifier, an approximately linear equivalent circuit model is established. According to the proposed equivalent circuit model, the analytical expressions of the harmonic spectrum and the root mean square value of the capacitor current are derived. The capacitor ripple voltage is further estimated. Applicable conditions of the proposed method are also presented. This method may be useful when designing dc-link capacitors of power cells in CHB inverters. Simulation and experimental results show that the proposed method can achieve good accuracy in the continuous conduction mode.IEEE Transactions on Power Electronics 12/2014; 29(12):6281-6292. · 5.73 Impact Factor

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