The low air pressure at high altitude will reduce the space of the protective layer inside the converter valve equipment and reduce the current transmission capacity

so it is necessary to complete the switching action in a very short time to achieve the conversion between alternating current and direct current

while it will lead to the voltage and current change faster during operation

resulting in a variety of frequencies of harmonics. Then

the accuracy of harmonic detection is affected. The frequencies of these harmonics are usually distributed in higher frequency bands

and it is very difficult to extract their sequence. Therefore

a high frequency harmonic detection method of direct current side converter valve load in insulated overhead ground wires transmission in high-altitude environment is studied. The frequency harmonic current changes with time when the converter valve is loaded

and the transfer function of the load signal in the high frequency range is determined by the power flow theory to extract the frequency harmonic sequence of the converter valve load. According to the operating principle of low arm passive clamp

the instantaneous voltage of the converter valve load is determined

and the total number of bridge arm inputs is controlled to be a fixed value

achieving approximate modulation of the direct current side of insulated overhead ground wire transmission and correcting the squeezing interference caused by the instantaneous frequency of high-frequency harmonics. A window function is set to suppress the spectral leakage caused by the attenuation of high-frequency harmonics

convert the main lobe width to other high-frequency harmonics

and ultimately achieve full detection of high-frequency harmonics. After setting up a harmonic detection environment

it can be concluded through full detection of high-frequency harmonics that the designed harmonic detection method produces the smallest amplitude error and the best detection performance.