Abstract
With the increasing penetration of renewable power, its reliability and cost-effective production are becoming more important. A filter is inserted between the grid-connected inverter and the power grid to reduce the PWM switching harmonics, which may become a fragile part seen from the power electronics converter perspective. As the grid-connected inverter is typically designed with additional reactive power capability, this paper tries to investigate the additional stresses of the filter capacitor introduced by the reactive power injection. According to an electro-thermal stress evaluation, the time-to-failure distribution of a single LCL filter capacitor is investigated in detail. Moreover, the increasing equivalent series resistance along with the operational period is taken into account. Aiming towards a system-level reliability analysis, a Weibull distribution based reliability of an individual capacitor can be linked to the reliability of a capacitor bank by using a reliability block diagram. A case study of a 2 MW wind power converter shows that the lifetime is significantly reduced from the individual capacitor to the capacitor bank. Besides, over-excited reactive power injection further reduces the lifetime of the LCL filter capacitors.
Highlights
With the increased adoption of renewable energy for the power generation, the three-phase voltage source inverter has become an important interface to convert clean energy to the utility grid [1]
Both the fundamental and harmonic components of the converter voltage totally agree with the theoretical analysis, where the harmonic components are mostly dominated by sidebands of the Pulse Width Modulation (PWM) switching
It can be seen that the lifetime is significantly over-estimated by the ignorance of the parameter shifting of the equivalent series resistance (ESR) due to degradation
Summary
With the increased adoption of renewable energy for the power generation, the three-phase voltage source inverter has become an important interface to convert clean energy to the utility grid [1]. ZHOU ET AL.: REACTIVE POWER IMPACTS ON LCL FILTER CAPACITOR LIFETIME IN GRID-CONNECTED INVERTER drives [8], [9]. These electrolytic capacitors commonly form passive DC-links, which are one of the highest failure rate components and contribute to more than 20% of failure in certain applications [11]. The influence of the reactive power is taken into account, along with the produced real power from the wind conditions It is a physics-of-failure approach from the component-level [13]– [16] to system-level reliability, which considers the parameter shifts of ESR and capacitance due to degradation.
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