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A Method for Determining Transient Stability Criterion of Flexible DC Grid Under Disturbance Fault

A flexible DC and transient stability technology, applied in the direction of automatic disconnection emergency protection devices, electrical components, circuit devices, etc., can solve problems such as low inertia of flexible DC grids, system safety hazards, large fluctuations in DC bus voltage, etc., to achieve Safe and stable voltage drop margin, lower action speed requirements, and enhanced transient stability effects

Active Publication Date: 2021-02-19
NORTH CHINA ELECTRIC POWER UNIV (BAODING)
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, the inertia of the flexible DC grid is low. After a bipolar short-circuit fault occurs, large fluctuations or continuous oscillations of the DC bus voltage will cause serious safety hazards to the system.

Method used

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  • A Method for Determining Transient Stability Criterion of Flexible DC Grid Under Disturbance Fault
  • A Method for Determining Transient Stability Criterion of Flexible DC Grid Under Disturbance Fault
  • A Method for Determining Transient Stability Criterion of Flexible DC Grid Under Disturbance Fault

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0124] The present invention builds such as in Matlab / Simulink environment Figure 8 The simulation model of the two-terminal flexible DC grid is shown. On the power supply side, the power frequency three-phase AC power supply is filtered and transformed, and then connected to the VSC1 converter to connect to the DC power grid. The voltage at both ends of the parallel capacitor C represents the DC bus voltage. On the load side, the duty ratio of the converter VSC2 is adjusted to ensure that the connected load exhibits constant power characteristics. The basic parameters of the simulation model are shown in Table 1.

[0125] Table 1 Basic parameters of flexible DC grid

[0126]

[0127] Combined with the basic parameters of the flexible DC grid in Table 1, according to the theoretical formulas (7) and (8), the theoretical stable operating parameters of the system in this example are shown in Table 2.

[0128] It can be seen from Table 2 that the stable operating voltage o...

Embodiment 2

[0136] When the present invention operates stably with an initial load of 20kW under the drooping control of the DC bus voltage, the stable operating voltage is 498V. When the load changes suddenly at 0.05s, the response result is as follows Figure 10 shown.

[0137] When the load increases from 20kW to 25kW in 0.05s, the load characteristic curve shifts upwards, resulting in a change in the stable operating point of the system, and a new stable operating state is established after the DC bus voltage drops to 486V. After the load drops from 25kW to 10kW in 0.15s, the DC bus voltage rises to 506V to re-establish a stable operating state, as shown in Figure 10 In (b) DC system bus voltage is shown. It can be seen that when the system load power changes and the DC bus voltage fluctuates within the allowable range, it can still run stably at the new voltage operating point in the end. Figure 10 (a) is the DC system load power.

[0138]In 0.05s, the load increased from 20kW ...

Embodiment 3

[0140] The initial operating state of this example is the same as that of Example 2. The power supply voltage drops from 730V to varying degrees at 0.05 seconds. After the power supply is restored, the response results are as follows Figure 11 shown.

[0141] When the power supply suffers from four different levels of voltage drops in 0.05s, the power supply disturbance is recovered in 0.06s, and the response results of the system are as follows: Figure 11 shown. The power supply voltage drops, the capacitor discharges, and the DC bus voltage drops rapidly from 498V. Figure 11 From the curves 1, 2 and 3, it can be seen that the bus voltage of the system dropped to 420V, 343V and 338V respectively in 0.06s. With the elimination of the disturbance, the systems in curves 1 and 2 resumed stable operation, and the system in curve 3 operated stably at 350V. 4. After the power supply voltage drops, the DC bus voltage drops below 338V in 0.06s, and finally shows a trend of instab...

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Abstract

The invention discloses a method for determining transient stability criteria of a flexible direct current power network under a disturbance fault. The method comprises the steps of determining basiclimit conditions of a flexible direct current power network system during stable operation; calculating an accumulated electric quantity of a fault current and a change quantity of charge of a capacitor caused by charging and discharging of a bus voltage; calculating the maximum change quantity of the charge of the capacitor during the fault period; and according to an "equal electric quantity principle" and in combination with the basic limit conditions of the flexible direct current power network system during stable operation, obtaining the voltage transient stability criteria of the flexible direct current power network system. According to the method for determining the transient stability criteria of the flexible direct current power network under the disturbance fault, the direct current power network can have safer and more stable bus voltage drop margin by designing system parameters according to necessary conditions required for meeting the transient stability criteria; it isfurther guaranteed that the system still has the capability of establishing stable operation after disturbance or fault recovery; and the transient stability of the direct current system is enhanced.

Description

technical field [0001] The invention relates to the technical field of fault analysis and protection of a flexible DC power grid, in particular to a method for determining a transient stability criterion of a flexible DC power grid under a disturbance fault. Background technique [0002] With the widespread application of distributed energy and constant power loads, the flexible DC grid has become the focus of research and application at home and abroad relying on its advantages. Compared with the AC distribution network, the flexible DC grid has the advantages of simple conversion device and low cost, and there is no need to pay attention to the impact of frequency mutation and power angle swing on power quality. At present, the measures to improve the voltage stability of the flexible DC grid include adding controllers, and analyzing the fault characteristics of the system and quickly and effectively isolating faults. However, the inertia of the flexible DC grid is low. A...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): H02H3/00H02H3/093
CPCH02H3/006H02H3/093
Inventor 付媛江国文张祥宇
Owner NORTH CHINA ELECTRIC POWER UNIV (BAODING)
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