Tripolar VSC-HVDC transmission system and method
First Claim
1. A tripolar VSC-HVDC control method for controlling a tripolar VSC-HVDC system adopting three conductors to transmit DC power,the system comprising:
- a rectifier and an inverter formed by a three phase six-bridge arms modular multilevel converter (MMC) respectively, midpoints of 1, 2, 3 phase units of the rectifier and inverter are connected with a secondary side of a converter transformer, andtwo converter valves of fully controlled semiconductor devices are arranged between poles 1 and 2 on the DC side of the rectifier and inverter respectively, positive poles of the rectifier and inverter are connected with a pole 1 DC line by a smoothing reactor, negative poles of the rectifier and inverter are connected with a pole 2 DC line by a smoothing reactor, and connecting points of the upper and lower converter valves of the rectifier and inverter are connected with a pole 3 DC line by a smoothing reactor,the method comprising;
controlling current directions of the poles 1 and 2 to be constant without change;
periodically modulating a current fixed value between a maximum and a minimum, wherein a ratio of the maximum to the minimum of the current fixed value is 2, the pole 3 current is a difference value between the pole 1 and pole 2, and the fixed value of the direct current of the pole 3 is the minimum of the fixed values of the direct current of the poles 1 and 2;
periodically changing a current direction of the pole 3, wherein DC voltage polarity of the poles 1 and 2 is constant without change;
controlling triggering of the upper and lower converter valves of the rectifier and the inverter to cause a pole 3 line to operate in parallel with a pole 1 line or a pole 2 line periodically, thereby changing the DC voltage polarity of the pole 3 periodically and ensuring unchanged DC power direction of the pole 3.
1 Assignment
0 Petitions
Accused Products
Abstract
A tripolar VSC-HVDC system and method include a rectifier and an inverter formed by a three-phase six-bridge arms modular multilevel converter (MMC) respectively, and two converter valves are arranged on the DC side of the rectifier and inverter respectively. The midpoint of upper and lower converter valves of the rectifier and inverter are connected with a pole 3 DC line by a smoothing reactor. Triggering of the upper and lower converter valves is controlled to change the DC voltage polarity of the pole 3 periodically, and tripolar DC transmission is realized by modulating current orders of the three poles.
-
Citations
4 Claims
-
1. A tripolar VSC-HVDC control method for controlling a tripolar VSC-HVDC system adopting three conductors to transmit DC power,
the system comprising: -
a rectifier and an inverter formed by a three phase six-bridge arms modular multilevel converter (MMC) respectively, midpoints of 1, 2, 3 phase units of the rectifier and inverter are connected with a secondary side of a converter transformer, and two converter valves of fully controlled semiconductor devices are arranged between poles 1 and 2 on the DC side of the rectifier and inverter respectively, positive poles of the rectifier and inverter are connected with a pole 1 DC line by a smoothing reactor, negative poles of the rectifier and inverter are connected with a pole 2 DC line by a smoothing reactor, and connecting points of the upper and lower converter valves of the rectifier and inverter are connected with a pole 3 DC line by a smoothing reactor, the method comprising; controlling current directions of the poles 1 and 2 to be constant without change; periodically modulating a current fixed value between a maximum and a minimum, wherein a ratio of the maximum to the minimum of the current fixed value is 2, the pole 3 current is a difference value between the pole 1 and pole 2, and the fixed value of the direct current of the pole 3 is the minimum of the fixed values of the direct current of the poles 1 and 2; periodically changing a current direction of the pole 3, wherein DC voltage polarity of the poles 1 and 2 is constant without change; controlling triggering of the upper and lower converter valves of the rectifier and the inverter to cause a pole 3 line to operate in parallel with a pole 1 line or a pole 2 line periodically, thereby changing the DC voltage polarity of the pole 3 periodically and ensuring unchanged DC power direction of the pole 3. - View Dependent Claims (2, 3, 4)
-
Specification