Analysis for magnetic field disturbance of modular multilevel converter based high voltage direct current (MMC-HVDC) converter valve

The standardised design and operational reliability enhancement of the flexible DC converter valve are impending with the construction of high shares of renewables and power electronics power system. A power frequency magnetic field calculation model able to obtain the electromagnetic disturbance at the submodule (SM) drive board during normal operation of a flexible DC converter valve is presented. Hundreds of SMs with complex structures in a converter valve tower are simplified by the equivalent to the line current to fulfil calculation accuracy requirements. In addition, a random function is employed to simulate the non-sequential switching process of the SMs. By comparing the calculated results with the measured data obtained from the SM equivalent operation experiment of 2200 V/2150 A, the validity of the calculation model is confirmed. According to the final calculations, the influence of non-sequential switching cannot be ignored when recognising the time-domain distribution features of the power frequency magnetic field of the drive board. However, engineering design can be guided only by the power frequency magnetic field intensity of the drive board calculated based on SM’s full removal in the valve tower.