Photovoltaic DC system series arc detection method based on voltage harmonic characteristics

Abstract

The invention discloses a photovoltaic DC system series arc detection method based on voltage harmonic characteristics. A harmonic expression of a DC transformer switching current is obtained based on the working characteristics of a one-way isolation type DC transformer in a photovoltaic DC system under the effect of inverter circuit cascade and an outlet filter capacitor; a large-current arc model numerical equation is utilized, switching current harmonics serve as current excitation of an arc, arc voltage response is obtained, and an arc fault detection criterion is constructed according to the arc voltage response; in order to solve the problem of misjudgment during load switching, opening and closing and current converter locking of the photovoltaic direct current system, disturbance detection auxiliary criteria are added; and the arc fault type of the photovoltaic direct current system is detected according to the obtained arc fault detection criterion, and corresponding protection measures are taken. The method is not influenced by switching noise of the system, does not need communication, is small in data storage and calculation amount, and can be reliable without misjudgment under normal disturbance of the system.

Description

technical field [0001] The invention relates to the technical field of grid connection of new energy power generation, in particular to a method for detecting series arcs in a photovoltaic DC system based on voltage harmonic characteristics. Background technique [0002] In order to solve the problems of limited transmission capacity and small transmission radius of traditional AC photovoltaic grid-connected systems, flexible DC collection and transmission systems are mostly used in the development and utilization of large-scale photovoltaic resources. Since photovoltaic power stations are mostly built in deserts, mountains and other remote inland areas, it is difficult to erect overhead lines, and cable transmission is the main method. In large-scale photovoltaic power stations, cables are affected by factors such as insulation aging, mechanical strain, and loose joints, resulting in DC arcing. Under the suppression of the constant voltage and constant current control strat...

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Problems solved by technology

Since photovoltaic power stations are mostly built in deserts, mountains and other remote inland areas, it is difficult to erect overhead lines, and cable transmission is the main method. In large-scale photovoltaic power stations, cables are affected by factors such as insulation aging, mechanical strain, and loose joints, resulting in DC arcing. Under the suppression of the constant voltage and constant current control strategy of the converter, coupled with the low resistance characteristics of the arc, the characteristics of the series arc fault are weak, the fluctuation of the line voltage and current is small, the traditional overcurrent and low voltage protection will not operate, and the fault will evolve into a continuous ignition. If the arc fault is not detected and dealt with in time, it will cause serious hazards such as fire and joint explosion, which will seriously affect the safe and stable operation of the system

[0003] Most of the detection methods for DC arc faults in the prior art use the time-frequency characteristics of arc current and voltage. When a single time-frequency characteristic criterion is used, it is inevitable that misjudgments and missed judgments will occur.

However, the arc fault detection method using multi-dimensional time-frequency characteristic criterion has high reliability, but the operation is cumbersome and requires a large amount of measured data as support.

These methods are also subject to system structure, load fluctuation and switching noise, and simulate arc faults in the laboratory. Although they can approximate the real arc characteristics to the greatest extent, the electrical circuit of the test system is relatively simple, the voltage level is low, and the load change is small. , which is quite different from the actual photovoltaic system, and it is impossible to verify the influence of the converter control strategy on the detection method

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