Patent ID: 9444322
Filing Date: 2016-09-13
CPC Classification: H02J,H02M,Y02B,Y02E

Claim Text:
1. A method for suppressing circulating currents of a, b, c phases in a modular multi-level converter for a high voltage direction-current (HVDC) transmission system converting an alternating current (AC) into a direct current (DC) and vice versa, transmitting energy using a DC cable, and having the modular multilevel converter generating a high voltage source by stacking a plurality of sub-modules in series, the method comprising: receiving circulating currents in each of a phase, b phase, and c phase in an 3 phase stationary reference frame, a DC current i controlling AC components of the circulating currents in each of a phase, b phase, and c phase to become zero; and outputting a compensation value V* wherein the controlling of AC components of the circulating currents comprises: calculating the current reference value i* extracting a current i* controlling the current i wherein the controlling of AC components of the circulating currents further comprises: calculating AC components i removing the AC components i wherein the removing of the AC components i here, a, b, c: division factors for dividing 3-phase system voltage into a-phase, b-phase, c-phase P V i* V K s: d( )/dt in Laplace transform.