A lcc-hvdc topology and its controllable sub-module charging initial voltage determination method

Abstract

The invention discloses an LCC-HVDC topological structure internally provided with controllable sub-modules in series. The topological structure is characterized in that six valve arms of a six-pulse converter are connected with the controllable sub-modules in series. The invention further provides an optimal charging initial voltage determining method for the controllable sub-modules of the LCC-HVDC topological structure internally provided with the controllable sub-modules in series, the method is used for preventing the capacitor voltage of the controllable sub-modules from being out of control, ensuring normal work and operation of the controllable sub-modules and enhancing the function of preventing LCC-HVDC topology swapping phase failures.

Description

technical field [0001] The invention relates to a device in the technical field of power transmission and distribution, in particular to an LCC-HVDC topology structure connected in series with controllable sub-modules and a method for determining the initial charging voltage of the controllable sub-modules. Background technique [0002] Since the 1950s, the line-commutated-converter high-voltage direct current (LCC-HVDC) of the traditional power grid has gained rapid popularity worldwide due to its large-capacity long-distance power transmission and fast controllable active power. develop. However, since it uses a thyristor that cannot be turned off automatically as a commutation device, it needs a certain strength of the AC system to provide the commutation voltage, which has certain limitations, especially the problem of commutation failure. The occurrence of commutation failure severely limits the transmission power of the DC system, causing the transmission power to sud...

AI Technical Summary

Problems solved by technology

However, CCC has the following problems: when the voltages on the three commutation capacitors are unbalanced, the commutation performance of the inverter will deteriorate [1]; in the event of a commutation fault, the capacitors continue to charge to overvoltage, and the inverter will Loss of self-recovery ability; the introduction of capacitors causes current harmonic pollution problems in DC transmission systems [12]

[0005] However, in this improved LCC-HVDC topology, when the capacitor is switched on, the capacitor will be charged or discharged, and its voltage value will increase or decrease as the commutation process proceeds

If the capacitor voltage is not controlled, then when the capacitor voltage is too high, the voltage borne by each switching device in the sub-module is too high, threatening the normal operation of the sub-module; when the capacitor voltage is too low, the output voltage of the sub-module is also Low, limited assistance to the commutation process

[0006] In summary, the improved LCC-HVDC topology has a certain effect on improving the ability of the original LCC-HVDC topology to resist commutation failure, but if the capacitor voltage of its controllable sub-module is not controlled, it may threaten the normal operation of the controllable sub-module operation, or reduce the defense effect of the improved LCC-HVDC topology on commutation failure

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