MMC sub-module open-circuit fault diagnosis and positioning method based on improved observer

Abstract

The invention discloses an MMC sub-module open-circuit fault diagnosis and positioning method based on an improved observer, and the method comprises the steps: obtaining a bridge arm current observation value after a fault based on a constructed novel sliding-mode observer, and judging whether the residual error between the bridge arm current observation value and an actual bridge arm current measurement value is greater than a threshold value or not. The diagnosis of the open-circuit fault of the sub-module of a certain phase of bridge arm is realized by continuing for a certain time, and whether the open-circuit fault of the upper tube or the open-circuit fault of the lower tube of a certain sub-module occurs is judged according to whether the residual error is greater than 0; according to the invention, not only can the open-circuit faults of the upper and lower tubes of the single-phase modular multi-level converter be accurately diagnosed and positioned, but also the open-circuit faults of the upper and lower tubes of the three-phase modular multi-level converter can be accurately diagnosed and positioned; the method also solves the problem that the change of the capacitor voltage of a normal sub-module and the change of the capacitor voltage of a fault sub-module are consistent and cannot be identified under the condition that the open-circuit fault of the upper tube of the sub-module occurs in a sorting voltage-sharing algorithm.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and in particular relates to a method for diagnosing and locating an open-circuit fault of an MMC submodule based on an improved observer. Background technique [0002] Modular multilevel converter (MMC) topology, since the German scholar Rainer Marquardt proposed in 2001, because each bridge arm has multiple sets of identical power supply units or sub-modules in series, no phase-shifting transformer is needed, which simplifies Topological structure, compared with traditional multilevel converters, MMC has many advantages such as good scalability, simple sub-module structure, rich application scenarios, and high power density, and its technical and economic advantages are obvious. MMC has emerged as the most promising topology for medium to high power applications such as HVDC flexible transmission, medium voltage variable speed drives, and power quality improvement. [0003] Since the...

AI Technical Summary

Problems solved by technology

For the method based on hardware detection, it is necessary to add additional hardware circuits for fault diagnosis. The principle is relatively simple and the diagnosis speed is fast, but this method increases the cost of hardware, and the existence of the new hardware itself will also constitute a potential fault. point

For the detection method based on artificial intelligence algorithm, although the detection speed is fast, it requires a large number of training samples and the accuracy is limited.

Taking the machine learning method as an example, when using this method to diagnose sub-module faults, it is necessary to analyze the data characteristics of normal operation and after a fault occurs. It is only necessary to evaluate the data characteristics of the measured values ​​of characteristic parameters to determine whether a fault has occurred. This method requires a large number of samples to complete the determination of the data characteristics before diagnosis, and the failure of the module is an abnormal state, and the relevant sample data is less, which has caused many difficulties in practical applications.

For the method based on the system model, the algorithm is simple and easy to implement, but the robustness is poor, and there may be a problem of model mismatch

Images