Alternating-current side cascaded hybrid MMC topology resistant to alternating-current and direct-current faults and control method thereof

Abstract

The invention discloses an alternating-current side cascaded hybrid MMC topology resistant to alternating-current and direct-current faults and a control method thereof, and belongs to the field of power transmission and distribution of power systems. The alternating-current side cascaded hybrid MMC topology is composed of a direct-current side main branch and an alternating-current side auxiliarybranch, and the main branch is composed of half-bridge type sub-modules and used for power transmission during normal operation of a system; and the auxiliary branch is formed by cascading full-bridge sub-modules on the alternating current side, and is used for operation optimization in a steady state of the system and voltage support in alternating current and direct current fault ride-through.During steady-state operation, the auxiliary branch outputs the finer voltage to smooth the step wave voltage output by the main branch of the low sub-module, so that the grid-connected point voltageis closer to sine waveform; when a DC fault occurs, the main branch bypasses part of the half-bridge sub-modules in the bridge arm to suppress a DC fault current, and the auxiliary branch supports a grid-connected point AC voltage. When an alternating-current fault occurs, the auxiliary branch outputs an alternating-current voltage with a certain phase and amplitude so as to reduce the voltage ofa grid-connected point and suppress an alternating-current fault current.

Description

technical field [0001] The invention belongs to the field of power transmission and distribution of power systems, and more specifically relates to an AC-side cascaded hybrid MMC topology and a control method thereof that are resistant to AC-DC faults. Background technique [0002] Flexible DC transmission technology based on Modular Multilevel Converters (MMC) has technical advantages such as decoupling control of active power and reactive power, and no commutation failure. Effective means for network and long-distance transportation problems. Due to the distribution characteristics of renewable energy in my country, the construction of flexible DC power grids based on overhead lines is an inevitable trend in future development. However, the traditional modular multilevel converter topology and its control method are difficult to cope with the complex and changeable AC characteristics of new energy and the rapidly rising fault current of the DC grid. The new topology and c...

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Problems solved by technology

[0004] Aiming at the above defects or improvement needs of the prior art, the present invention provides an AC-side cascaded hybrid MMC topology and its control method that are resistant to AC-DC faults. It solves the problem that the existing flexible DC transmission system is difficult to deal with AC and DC faults, and reduces the cost and volume of MMC

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