Redundancy control method of MMC for HVDC
The present invention provides a method of MMC for HVDC. According to the present invention, there is provided a redundancy control method of an MMC for HVDC, wherein the MMC includes multiple converter arms each has multiple submodules in operation and redundancy modules for spares, the method including: checking whether a breakdown of a submodule in operation of a first converter arm among the multiple converter arms occurs in a case where the all redundancy modules of the first converter arm are applied in operation; and lowering an output voltage of each submodule of other converter arms in such a manner that a DC link voltage of each of the other converter arms is controlled to be equal to a DC link voltage of the first converter arm when the breakdown of the submodule of the first converter arm occurs.
1. A redundancy control method of a modular multilevel converter (MMC) for high voltage direct current (HVDC), wherein the MMC has multiple converter arms each including multiple submodules and redundancy submodules, the method comprising:
checking whether a breakdown of a submodule in operation of a first converter arm among the multiple converter arms occurs in a case where all of the redundancy submodules of the first converter arm are applied and in operation; and
controlling a DC link voltage supplied to the multiple converter arms to be equal to a sum of output voltages of the submodules of the first converter arm except for the submodule which has broken down and lowering an output voltage of each submodule of the other converter arms according to the DC link voltage when the breakdown of the submodule in operation of the first converter arm occurs,
wherein a number of submodules operable in the first converter arm except for the submodule which has broken down is different from a number of submodules operable in each of the other converter arms, and
wherein each of the output voltages of the operable submodules of the first converter arm is different from each of the output voltages of the operable submodules of each of the other converter arms.
2. The method of claim 1 , wherein the submodules of the first converter arm except for the submodule which has broken down are controlled to output a rated output voltage.
3. The method of claim 1 , wherein the output voltage of each submodule of the other converter arms is equal to a value obtained by multiplying an original rated output voltage of each submodule and a value obtained by dividing the DC link voltage by a rated DC link voltage of the other converter arms.
4. The method of claim 1 , wherein the multiple submodules in operation included in each of the converter arms output same voltages, respectively.