A mid-point self-balancing three-level grid-connected converter topology

Abstract

The invention belongs to the technical field of power electronics and is used for a distributed generation system, and particularly relates to a three-level grid-connected converter midpoint self-balancing topology comprises a three-level converter, inductors La, Lb, Lc, Lga, Lgb and Lgc, a capacitor Ca, a capacitor Cb, a capacitor Cc, a capacitor Cr and a capacitor C1 and a capacitor C2 which arearranged on the DC side. According to the topology, fast and equal voltage distribution of the DC side can be realized when the voltage distribution of the DC side capacitors C1 and C2 is uneven, andthe equal voltage distribution of the DC side can be maintained. The topology can realize self-balancing of the DC side midpoint potential without increasing the switching device and the DC side voltage sensor so that the unequal voltage stress of the switching tube can be avoided and the grid-connected current quality and the service life of the converter can be enhanced.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and in particular relates to a midpoint self-balancing three-level grid-connected converter topology, which is used in a distributed power grid-connected system. Background technique [0002] With the rapid development of distributed power, grid-connected converters have played a pivotal role as the interactive interface between distributed power and the grid. Three-level neutral-point clamped NPC and T-NPC structure converters are widely used in high-power systems due to their low output harmonic content. Ideally, the DC side of the three-level converter is composed of two voltage-dividing capacitors with the same parameters in series, and the voltage of the capacitor is half of the DC bus voltage. There are factors such as even harmonics and unbalanced operation of three-phase loads, and there is a problem of midpoint potential drift. The midpoint potential drift will deteriorate th...

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Problems solved by technology

When the circuit uses the SVPWM modulation method, the midpoint potential is adjusted by changing the action time of the redundant vector by measuring the capacitance potential difference, but this method suffers from increased harmonic distortion, complex control strategies and more voltage sensors. Cost; by introducing the coefficient of the relationship between the midpoint current and the midpoint potential of the capacitor, the value of the injected midline current is calculated according to the midpoint voltage difference, but this method does not take into account the deviation of the DC side capacitance value. This algorithm is not well applicable; the concept of self-balancing can naturally stabilize the neutral point at the midpoint of the DC side. Due to the self-adjustment of the traditional circuit, the transient time for the midpoint potential to recover is relatively long. In order to make the circuit quickly reach equilibrium , by connecting the RLC regulator circuit in parallel with the load, the circuit transient recovery time can be shortened

However, this circuit is mainly used for the converter connected to the load, the load affects each other on the self-balancing effect, and the RLC branch increases the loss of the circuit, and the mid-point self-balancing mechanism of the grid-connected converter is not clear

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