A kind of step-down operation method of hvdc system based on hybrid mmc

An operation method and hybrid technology, which are applied to output power conversion devices, electrical components, and AC power input to DC power output, etc., can solve the problems affecting the safe and stable operation of the AC power grid and the reduction of the output AC voltage of the converter. , to achieve good pressure equalization effect, improve conveying capacity, and solve the effect of pressure equalization problem

Active Publication Date: 2018-06-26
ECONOMIC TECH RES INST STATE GRID QIANGHAI ELECTRIC POWER +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

[0004] In view of the above defects, the present invention provides a step-down operation method of a hybrid MMC-based HVDC system, aiming to solve the problem of the existing flexible DC transmission due to the lack of decoupling of the DC side voltage and the AC side voltage in the existing converter. When the system is in step-down operation, the output AC voltage of the converter is also reduced, which makes the flexible DC transmission system absorb a large amount of reactive power from the grid, which affects the safe and stable operation of the AC grid.

Method used

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  • A kind of step-down operation method of hvdc system based on hybrid mmc
  • A kind of step-down operation method of hvdc system based on hybrid mmc
  • A kind of step-down operation method of hvdc system based on hybrid mmc

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Embodiment 1

[0056] After the step-down operation, the DC voltage requirement becomes 15kV, the transmitted active power is 15MW, and the reactive power is adjusted from 4MVar to 6MVar during the step-down operation. Such as image 3 As shown, by changing the number of full-bridge sub-modules and half-bridge sub-modules in the upper bridge arm and the lower bridge arm, the sum of the output voltage of the upper bridge arm and the output voltage of the lower bridge arm is changed, and the DC output of the hybrid MMC is changed. Voltage, Figure 4 In (a), the DC voltage is reduced from 20kV to 15kV, and then by changing the number of full-bridge sub-modules and half-bridge sub-modules in the upper bridge arm and the lower bridge arm again, the output voltage of the upper bridge arm and the output voltage of the lower bridge arm The voltage difference remains unchanged, so that the output voltage of the AC side of the hybrid MMC does not change, that is, the AC output of the hybrid MMC is as...

Embodiment 2

[0058] After step-down operation, the DC voltage requirement becomes 5kV, the transmission reactive power remains unchanged, the reactive power is 4MVar, and the transmission active power is reduced to 5MW. By changing the number of full-bridge sub-modules and half-bridge sub-modules that are turned on in the upper bridge arm and the lower bridge arm, changing the sum of the output voltage of the upper bridge arm and the output voltage of the lower bridge arm, and changing the output voltage of the DC side of the hybrid MMC, by 20kV becomes 5kV, and the voltage drop is large at this time. By changing the number of full-bridge sub-modules and half-bridge sub-modules in the upper bridge arm and the lower bridge arm again, the output voltage of the upper bridge arm and the output voltage of the lower bridge arm The difference remains unchanged, so that the output voltage of the hybrid MMC AC side remains unchanged, such as Figure 5 (a), the active power P changes from 20MW to 5M...

Embodiment 3

[0060] After step-down operation, the DC voltage requirement becomes 5kV, the transmitted reactive power remains unchanged, the reactive power is 4MVar, and the transmitted active power is 5MW. By changing the number of full-bridge sub-modules and half-bridge sub-modules that are turned on in the upper bridge arm and the lower bridge arm, changing the sum of the output voltage of the upper bridge arm and the output voltage of the lower bridge arm, and changing the output voltage of the DC side of the hybrid MMC, by 20kV becomes 5kV. By changing the number of full-bridge sub-modules and half-bridge sub-modules in the upper bridge arm and the lower bridge arm again, the difference between the output voltage of the upper bridge arm and the output voltage of the lower bridge arm remains unchanged, so that Hybrid MMC AC side output voltage remains unchanged, such as Figure 6 (a), the active power P changes from 20MW to 5MW, and the reactive power remains unchanged. By injecting lo...

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Abstract

The invention discloses a step-down operation method of an HVDC system based on a hybrid MMC. Due to the existence of a full-bridge sub-module in the hybrid MMC, the bridge arm can output negative voltage, thereby realizing the flexible and controllable voltage of the AC side of the hybrid MMC. By adjusting the sum of the output voltages of the upper and lower bridge arms, the output voltage of the DC side of the hybrid MMC can be adjusted, and the difference between the output voltages of the upper and lower bridge arms can be adjusted to realize the adjustment of the AC internal potential output by the hybrid MMC, that is, the output voltage of the AC side of the hybrid MMC can be adjusted. Realize the adjustment of the active power transmitted by the hybrid MMC and the reactive power exchanged to the AC grid to ensure the safe and stable operation of the AC and DC system. The problem that the sub-modules cannot equalize the voltage when outputting a large active power at a low DC voltage expands the operating range of the hybrid MMC at a low DC voltage, enabling it to transmit more active power.

Description

technical field [0001] The invention belongs to the technical field of multilevel power electronic converters, and more specifically relates to a method for step-down operation of a hybrid MMC-based HVDC system. Background technique [0002] In extreme weather conditions, such as thunderstorms, rainstorms, snowstorms, etc., the DC transmission system needs to reduce the DC side voltage to reduce the probability of line failure. However, due to the restriction of the voltage modulation ratio, the reduction of the DC side voltage will lead to the reduction of the output AC voltage of the converter, which will cause the converter to absorb a large amount of reactive power from the connected grid, which will cause serious damage to the safe and stable operation of the AC-DC system. influences. At the same time, the reduction of the DC voltage will lead to a reduction in the transmission power of the DC system, an increase in the loss of the system line, and a reduction in the o...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): H02M7/483
CPCH02M7/483H02M1/007H02M7/4835
Inventor 徐克成路茂增苗淼张祥成田旭白左霞靳宝宝
Owner ECONOMIC TECH RES INST STATE GRID QIANGHAI ELECTRIC POWER
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