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Method of DC Grid Voltage Transient Stability Restoration Control Based on Additional Power

A DC power grid, DC voltage technology, applied in electrical digital data processing, data processing applications, instruments, etc., can solve the problems of continuous oscillation, DC bus voltage fluctuation, etc., to delay the action time, and prolong the time to drop to the limit point. Effect

Active Publication Date: 2022-05-27
NORTH CHINA ELECTRIC POWER UNIV (BAODING)
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Since the load-side converter adopts constant power control, it will exhibit negative impedance characteristics during the dynamic process. If a load power mutation or line fault occurs, this characteristic will cause large fluctuations and continuous oscillations in the DC bus voltage.

Method used

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  • Method of DC Grid Voltage Transient Stability Restoration Control Based on Additional Power
  • Method of DC Grid Voltage Transient Stability Restoration Control Based on Additional Power
  • Method of DC Grid Voltage Transient Stability Restoration Control Based on Additional Power

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0108] The present invention builds the following in the Matlab / Simulink environment. Figure 7 The multi-terminal flexible DC grid simulation model shown. The AC grid side uses the power frequency three-phase AC power supply to connect to the VSC after filtering and transforming. 1 The converter is connected to the DC grid, and the capacitor C is connected in parallel dc The voltage across both ends represents the DC bus voltage. The load side is connected to the inverter VSC with constant power control 2 , to ensure that the connected load exhibits constant power characteristics. During the simulation, the wind power generation system is regarded as an equivalent unit. The basic parameters of the simulation model are shown in Table 1.

[0109] Table 1 Basic parameters of the flexible DC grid simulation model

[0110]

[0111] Combined with the basic parameters of the flexible DC grid simulation in Table 1, according to the theoretical formulas (2) and (3), the theor...

Embodiment 2

[0113] To verify the voltage operating limit of the DC grid, by changing the VSC 1 The voltage droop in the DC voltage reference value in the controller, so that the system is in different degrees of step-down operation. The four step-down operation calculations are as follows: at 0.02s, the DC voltage droop control reference values ​​are set to 485V, 470V, 455V, and 430V respectively, and the initial value is restored at 0.03s. The system dynamic response is as follows Figure 8 shown.

[0114] like Figure 8 As shown in the figure, as the DC voltage reference value decreases, the capacitor discharges, and the DC voltage drops rapidly from 498V in a stable operating state. After the disturbance is eliminated, the system can resume stable operation in the first two cases. In Example 3, the system runs stably around 235V, slightly exceeding the theoretically calculated operating limit of 224V. At this time, the system cannot return to the initial operating state. In calcula...

Embodiment 3

[0116] In order to further analyze the limit time of DC voltage fault removal, at the moment of 0.02s, a bipolar short-circuit fault is set at the DC bus. Under the traditional droop control, the fault is removed at different times, and the dynamic response of the system is as follows Figure 9 shown. In the five fault examples, the removal time is set to 0.025s, 0.0265s, 0.028s, 0.030s, and 0.031s, respectively.

[0117] In the first three examples, after the short-circuit fault was removed at different times, the DC bus voltage dropped to 480V, 420V, and 315V, respectively, which did not exceed the theoretical calculation limit of 224V. As shown in the figure, after the fault is cleared, the system returns to the initial stable operation state. When the fault duration is extended to 0.030s, in example 4, during the fault period, the system voltage drops to the limit voltage. Even if the fault is cleared, the system cannot return to the initial operating state. In example ...

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Abstract

The invention discloses a method for recovering and controlling DC power grid voltage transient stability based on additional power, which comprises the following steps: A. Calculate the system limit voltage value C according to the basic restriction conditions when the flexible DC power grid system ensures stable operation 0 and voltage safety margin ΔU dcm ; B. Detect the instantaneous value U of the DC grid bus voltage dc ; C. Judging whether the DC voltage drop exceeds the allowable voltage safety margin at this time; if not, there is no need to adjust the droop coefficient, and the coefficient k for stable system operation is still used dc , still has the ability to restore stability; if the voltage safety margin is exceeded, the droop controller adjusts the coefficient k in real time dc A safe voltage margin will be added to the system until the current limit is reached and the maximum additional charge is obtained. The invention can improve the deficiencies of the prior art, further ensure that the system still has the ability to establish stable operation after disturbance or fault recovery, and enhance the transient stability of the direct current system.

Description

technical field [0001] The invention relates to the technical field of fault analysis and protection of flexible direct current power grids, in particular to a method for transient stability recovery control of direct current power grid voltage based on additional power. Background technique [0002] Compared with the AC grid, the distributed generation is connected to the DC grid, the conversion device is simplified, the DC-AC inverter link is omitted, and there is no need to pay attention to the frequency fluctuation, reactive power compensation and power angle swing, and the system operation is more stable. Not only that, the increasing demand for DC loads has also promoted the development of flexible DC power grids, and the system operation control technology is being gradually improved. Since the load-side converter adopts constant power control, it will show a negative impedance characteristic in the dynamic process. If a sudden change of load power or a line fault occ...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G06Q10/00G06Q50/06G06F30/20G06F113/04
CPCG06Q10/20G06Q50/06Y02E60/60
Inventor 张祥宇江国文付媛朱正振
Owner NORTH CHINA ELECTRIC POWER UNIV (BAODING)
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