MMC converter modulation method and system capable of shutting direct current fault current

A DC fault and converter technology, applied in electrical components, emergency protection circuit devices, etc., can solve the problems of system reliability impact, cut off fault short-circuit current, high cost, etc., to achieve stable operation and suppress fluctuations.

Pending Publication Date: 2019-04-09
CHINA ELECTRIC POWER RES INST +2
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0003] The DC power grid is a "low inertia" system. If a DC fault occurs, a large short-circuit current may be generated, and it will instantly affect the entire DC power grid. It requires a high response time for the protection system. The traditional AC system protection method , such as overcurrent protection, distance protection and differential protection, etc., are not suitable for direct application to the DC power grid; and the DC power grid has a large scale, complex structure, diverse operation modes, and a large number of equipment, so it is not possible to simply use the two-terminal DC transmission system The protection method of cutting off the entire DC system from the AC side; at the same time, in the DC power transmission and distribution system, the development of large-capacity DC circuit breakers is relatively difficult, and the DC converter is usually required to have fault protection and isolation functions to prevent fault transmission from

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  • MMC converter modulation method and system capable of shutting direct current fault current
  • MMC converter modulation method and system capable of shutting direct current fault current
  • MMC converter modulation method and system capable of shutting direct current fault current

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Experimental program
Comparison scheme
Effect test

Embodiment 1

[0068] 1. Multi-level modulation at the bridge arm level:

[0069] Currently, commonly used multi-level modulation strategies are mainly divided into two types: pulse width modulation (PWM) and stepped wave modulation (SWM). The switching frequency of pulse width modulation is high, and the switching loss is relatively large; while the principle of step wave modulation is simple, the harmonic content is low, and the pulse width does not need to be controlled, so it is relatively simple to implement. Therefore, considering the economy and practicability, step wave modulation has more advantages than pulse width modulation.

[0070] Pulse width modulation includes carrier phase shift modulation SPWM (carrier phase shifted SPWM, CPS-SPWM), space vector pulse width modulation (space vector PWM, SVPWM), pulse phase shift modulation SPWM (pulse phase shifted SPWM, PPS-SPWM), specific Harmonic pulse width modulation (selected harmonic elimination PWM, SHE-PWM) and other control meth...

Embodiment 2

[0111] In order to verify the reliability of the MMC-type DC-DC transformer modulation strategy proposed in the present invention for blocking DC fault current, taking the DRB-MMC system as an example, an MMC-based DC-DC transformer was built under MATLAB / Simulink to complete the experiment. Due to limiting factors such as simulation speed and accuracy, this DC-DC transformer simulation model is applied to the double-terminal DC transmission network. The high-voltage side adopts a 9-level DRB-MMC structure, and each bridge arm contains 4 sub-modules. Three-phase full-bridge structure, such as Figure 6 shown. The high-voltage side adopts the nearest level approach modulation strategy and the equalization control algorithm of capacitor voltage sorting. The specific simulation parameters are shown in Table 1.

[0112] Table 1 Simulation system parameter design

[0113]

[0114] The fault type selection affects the serious bipolar short-circuit fault. When the system is runn...

Embodiment 3

[0117] Based on the same inventive concept, the present invention also provides an MMC converter modulation system capable of blocking DC fault current, including:

[0118] The first determination module is used to determine the switching state of the bridge arm sub-module of the modular multilevel converter according to the input modulation signal;

[0119] The second determination module is used to determine the steady-state voltage of the DC-DC converter according to the DC-DC converter equivalent circuit model constructed by the capacitor voltage of the bridge arm sub-module in the switching state;

[0120] A calculation module, configured to calculate the number of sub-modules input by the lower bridge arm under the steady-state voltage;

[0121] The adjustment module is used to define the DC-DC converter transfer function according to the number of input sub-modules and determine the switching sequence according to the preset method, and adjust the capacitor voltage of t...

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PUM

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Abstract

The invention relates to an MMC converter modulation method and system capable of shutting direct current fault current. A switching state of a modular multilevel converter bridge arm submodule is determined according to an input modulation signal; steady-state voltage of a DC-DC converter is determined according to an equivalent circuit model of the DC-DC converter constructed by the bridge arm submodule capacitor voltage in the switching state; the number of the submodules input by a lower bridge arm under the steady-state voltage is calculated; according to the number of the input submodules, a DC-DC converter transfer function is defined, and the switching sequence is determined according to a preset manner to adjust the capacitor voltage of the modular multilevel converter bridge armsubmodule to be in a voltage stabilization state. The scheme can effectively provide safe, stable and reliable control protection for the DC-DC converter capable of shutting the direct current fault current.

Description

technical field [0001] The invention belongs to the field of power electronic device control, in particular to an MMC converter modulation method and system capable of blocking DC fault current. Background technique [0002] The development of DC grids is still limited by the lag of key equipment such as DC circuit breakers and DC converters, among which DC converters are of great significance for connecting different DC lines to form a DC grid. Compared with the traditional AC grid, it can be found that there are multiple different voltage levels in the AC grid, among which the higher voltage level is used for long-distance power transmission, while the lower voltage level is used for power distribution and power consumption. Similarly, in order to reduce the transmission loss in the DC power grid, a higher DC voltage level is required from the power generation center to the load center, while a lower voltage level should be used in the distribution network and the user sid...

Claims

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Application Information

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IPC IPC(8): H02H7/12
CPCH02H7/1213
Inventor 李丹李官军陶以彬杨波胡安平
Owner CHINA ELECTRIC POWER RES INST
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