Mixed type three-pole direct current power transmission system and control method thereof

Abstract

The invention discloses a mixed type three-pole direct current power transmission system and a control method thereof. The system comprises a rectifying converter station and an inverting converter station, wherein the rectifying converter station and the inverting converter station respectively comprise an alternating current bus and a three-pole converting system, each alternating current bus is connected with a corresponding alternating current power grid, each three-pole converting system is hung on each alternating current bus through a converting transformer, and a converting unit H3 of each three-pole converting system adopts an MMC (modular multilevel converter). The system and the method have the advantages that the decoupling control capability of the active and inactive parts is realized, the power can be transmitted to an inactive network, the number of inactive compensation equipment is greatly reduced, the balance of the direct current among the three poles is maintained by introducing the MCC (modified current control), the current of a grounding pole is inhibited, the service life of the grounding pole is effectively prolonged, the on-site balance of the inactive power is realized by introducing the AVC (alternating voltage control), and the voltage of the connected AC (alternating current) system is maintained to solve the overvoltage or undervoltage problem.

Description

technical field [0001] The invention belongs to the technical field of power electronic systems, and in particular relates to a hybrid three-pole direct current transmission system and a control method thereof. Background technique [0002] The overall policy of my country's electric power planning is "power transmission from west to east, mutual supply between north and south, and national networking". However, with the increasing scale and complex structure of the power grid, and the interest disputes involving land acquisition issues have gradually emerged in recent years, it is more difficult to open up new line corridors on the basis of the original lines. Therefore, using the original high-voltage AC station and line grid to transform and convert it into a DC transmission project has become an idea worth exploring to solve this problem. Furthermore, for a very large-scale power grid, using DC engineering to separate it into several asynchronous subsystems can effectiv...

AI Technical Summary

Problems solved by technology

[0007] 1. It cannot supply power to passive networks, and is not suitable for power transmission to long-distance isolated loads;

[0008] 2. There is a problem of commutation failure, which causes a large capacity shortage of DC transmission power, causes deterioration of AC and DC response characteristics, and seriously affects the stable operation of the connected AC system;

[0009] 3. There are reactive power compensation and harmonic problems, and reactive power compensation equipment and filtering equipment need to be installed, which not only increases the cost of the equipment, but also causes excess reactive power during load shedding, which easily leads to overvoltage;

[0010] 4. Under its current modulation strategy, the transition phase of current modulation is accompanied by reactive power changes. Due to the slow adjustment of reactive power equipment, it will cause surplus or insufficient reactive power in the AC system, resulting in overvoltage and other phenomena;

[0011] 5. Under its current modulation strategy, in the current modulation transition stage of the converter unit H3, its DC current needs to be reversed, and there is a zero-crossing phenomenon, while the traditional DC has a minimum DC power (current) requirement, generally 10 of the rated value %, therefore, the transition stage is likely to cause problems such as overvoltage

At the same time, the transition stage H3 needs to perform locking and unlocking actions, which is relatively cumbersome

Images