CN115864415A - Stable control method for flexible AC/DC power distribution system in weak network interconnection scene - Google Patents

Stable control method for flexible AC/DC power distribution system in weak network interconnection scene Download PDF

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CN115864415A
CN115864415A CN202310119769.4A CN202310119769A CN115864415A CN 115864415 A CN115864415 A CN 115864415A CN 202310119769 A CN202310119769 A CN 202310119769A CN 115864415 A CN115864415 A CN 115864415A
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weak
network
alternating current
active power
droop
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CN115864415B (en
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邓卫
刘颜滔
裴玮
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Institute of Electrical Engineering of CAS
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Abstract

The invention provides a stable control method of a flexible alternating current and direct current power distribution system in a weak network interconnection scene, which is a variable droop control method. The method is limited by the characteristics of small capacity and low anti-interference capability of an alternating current distribution network, and the situation that the voltage of a direct current network cannot be freely adjusted due to frequency fluctuation of the alternating current distribution network can possibly occur in the traditional droop control in the construction of an alternating current and direct current distribution system. The invention provides variable active power on the basis of conventional direct current active power-voltage droop control
Figure ZY_1
And variable sag factor
Figure ZY_2
The novel control method can flexibly adjust the droop control under different working conditions.

Description

Stable control method for flexible AC/DC power distribution system in weak network interconnection scene
Technical Field
The invention belongs to the field of power control, and particularly relates to a stable control method for a flexible alternating current-direct current power distribution system in a weak network interconnection scene.
Background
Under the big background of global energy crisis and increasingly serious environmental pollution, distributed energy such as wind power, photovoltaic and the like develops rapidly, the capacity of connecting the distributed energy into an alternating current distribution network is increased continuously, and an alternating current and direct current distribution system develops rapidly. The direct current droop control is one of wide control modes in the new energy grid-connected technology, the implementation mode is simple, the power can be distributed in proportion according to a specific droop coefficient under the ideal condition without communication, and for a long-distance line, the construction cost of a communication line is reduced, and the reliability is further improved; the plug and play is convenient for the expansion of the system, and the complexity of the system is reduced.
Fig. 1 depicts a flexible ac/dc distribution system configuration in which an ac power grid is connected to a dc power grid through a voltage source type converter station. In fig. 1, the weak ac grids 1, 2, 3, and n represent the 1 st, 2 nd, 3 rd, and nth weak ac grids, respectively. The AC/DC module is a voltage-source converter (VSC), the Load is a DC network Load, the DG is a Distributed power Generation unit (Distributed Generation), and the ES is an Energy Storage system (Energy Storage).
In the actual operation process, when the frequency of the weak alternating-current power grid is lower, the active power absorbed by the weak alternating-current power grid to the direct-current network can be increased, or the active power injected into the direct-current network can be reduced. The alternating current power grid connected in the system is a weak alternating current power grid, when the frequency fluctuates in a normal range, the traditional direct current droop control strategy is used for adjusting, the active power required to be provided by the weak alternating current power grid is less, and the influence on the weak alternating current power grid is less. However, when the frequency of the weak ac grid is reduced to a certain range, the active power provided by the ac weak grid is difficult to maintain the stability of the dc network according to the curve given by the conventional droop control strategy. Therefore, in a weak grid interconnection scene, a conventional droop control strategy can enable a weak alternating current grid to bear huge pressure, and system instability is easily induced.
Disclosure of Invention
In order to solve the technical problem, the invention provides a stable control method of a flexible alternating current-direct current power distribution system in a weak network interconnection scene, which is a variable droop control method. Limited by the characteristics of small capacity and low anti-interference capability of a weak alternating current power gridIn the construction of a current distribution system, the traditional droop control may cause the situation that the direct current network voltage cannot be freely adjusted due to the frequency fluctuation of a weak alternating current power grid. The invention provides variable active power on the basis of a conventional direct current active power-voltage droop control strategy
Figure SMS_1
And a variable droop factor>
Figure SMS_2
The novel control method can flexibly adjust the droop control under different working conditions.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for stably controlling a flexible alternating current-direct current power distribution system in a weak network interconnection scene specifically comprises the following steps:
for a weak AC network n, the nominal frequency is
Figure SMS_3
The droop control formula is:
Figure SMS_4
；
wherein ,
Figure SMS_5
for DC bus voltage, in conjunction with a voltage regulation circuit>
Figure SMS_6
For a reference value of the DC bus voltage, for>
Figure SMS_7
Is a droop factor>
Figure SMS_8
Injecting active power of a direct current network into a weak alternating current power grid n through a corresponding AC/DC converter station n; in actual operation, the following working conditions occur in the alternating current weak grid n, and the control method comprises the following steps:
working condition 1. Frequency of weak AC network n
Figure SMS_9
In the normal range, the AC/DC converter station n active power->
Figure SMS_10
And a droop factor>
Figure SMS_11
The change is not changed;
working condition 2. Frequency of weak AC network n
Figure SMS_12
Figure SMS_13
Rated frequency->
Figure SMS_14
The variable active power injected into the DC network by the AC/DC converter station n is:
Figure SMS_15
, wherein />
Figure SMS_16
Is a scale factor;
according to the formula
Figure SMS_17
And formula->
Figure SMS_18
Simultaneous determination of a variable droop factor>
Figure SMS_19
And then the variable active power is used
Figure SMS_20
Substituting to further deduce
Figure SMS_21
Thereby adjusting the droop control.
Has the advantages that:
the variable droop control method provided by the invention can solve the problem that the voltage of a direct current network cannot be maintained because a weak alternating current power grid cannot provide enough active power under the condition of weak grid interconnection. Compared with the traditional droop control method, the method not only ensures the stability of the voltage control of the direct current network, but also reduces the active power pressure on the weak alternating current power grid. The invention is beneficial to maintaining the stability of the voltage of the direct current network, improving the power supply quality, reducing the active power pressure on the weak alternating current power grid when the voltage of the alternating current and direct current network is adjusted, making up the defect of the traditional droop control, providing important support for the construction of the grid connection of distributed energy and the alternating current and direct current power distribution system and having wide market prospect.
Drawings
FIG. 1 is a block diagram of a flexible AC/DC system;
FIG. 2 is a graph of active-voltage droop;
fig. 3 is a graph of improved flexible droop control.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The method for stably controlling the flexible alternating current-direct current power distribution system in the weak network interconnection scene specifically comprises the following steps:
defining a variable droop factor
Figure SMS_22
And variable active power>
Figure SMS_23
The voltage droop control curve for the dc network is shown in fig. 2.
The droop control formula is:
Figure SMS_24
；
wherein ,
Figure SMS_25
is the DC bus voltage>
Figure SMS_26
Is a DC bus voltage reference value>
Figure SMS_27
Is a droop factor>
Figure SMS_28
The active power of the direct current network is injected into the weak alternating current power grid n through the corresponding AC/DC converter station n. The curve shows that the DC bus voltage->
Figure SMS_29
And the AC/DC converter station n active power ∑ is ∑ stored in the AC/DC converter station>
Figure SMS_30
Is linearly related.
For a weak AC network n, the nominal frequency is
Figure SMS_31
In actual operation, the following conditions may occur:
working condition 1. Frequency of weak AC network n
Figure SMS_32
Is in the normal range, i.e. < >>
Figure SMS_33
Not very small, the weak alternating current grid n provides active power ≥ to the direct current network via the corresponding AC/DC converter station>
Figure SMS_34
Very small, weak ac grids n can normally provide the required active power. In this case, the original droop control strategy is maintained, i.e. the AC/DC converter station n active power->
Figure SMS_35
And a droop factor>
Figure SMS_36
And is not changed. At this time, the AC/DC system can stably operate.
Working condition 2. Frequency of weak AC network n
Figure SMS_37
Figure SMS_38
Rated frequency->
Figure SMS_39
At the moment, the active power which is required to be provided by the weak alternating current power grid to the direct current network through the corresponding AC/DC converter station is->
Figure SMS_40
If the voltage is too large, the weak ac power grid n cannot provide sufficient active power, which corresponds to fig. 2, that is, the voltage adjustment range becomes small. Variable active power is introduced at this time
Figure SMS_41
, wherein />
Figure SMS_42
Is a scale factor.
Can be based on formula
Figure SMS_43
And formula
Figure SMS_44
Simultaneous determination of a variable droop factor>
Figure SMS_45
The variable active power is selected>
Figure SMS_46
Substituted into this, a further deduction can be made>
Figure SMS_47
At this time, the dc active-voltage droop control curve is shown in fig. 3.
It can be seen from the above control strategy that when the dc network voltage is desired to be maintained at
Figure SMS_48
At this constant value, the active power it is required to provide from the weak ac grid can always be maintained at a lower level. By dynamically adjusting the droop factor in sections, the control method can not only ensure the stability of the voltage of the direct current network, but also reduce the active power pressure on the weak alternating current power grid.
In summary, the present invention: put forward a variable active power
Figure SMS_50
And a specific calculation method, i.e. formula
Figure SMS_53
, wherein />
Figure SMS_55
Is a scale factor; at the same time by the formula
Figure SMS_51
And formula->
Figure SMS_52
In conjunction therewith, it can be further deduced that a variable droop factor->
Figure SMS_54
The specific numerical values of (A): />
Figure SMS_56
Will be selected as described above>
Figure SMS_49
The expression is substituted into the expression, and a further evaluation can be made>
Figure SMS_57
Can realize the variable droop factor>
Figure SMS_58
And further, the droop control can be flexibly adjusted under different working conditions.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (1)

1. A method for stably controlling a flexible AC/DC power distribution system in a weak network interconnection scene is characterized by comprising the following steps:
for a weak AC network n, its rated frequency is set to
Figure QLYQS_1
The droop control formula is:
Figure QLYQS_2
；
wherein ,
Figure QLYQS_3
is the DC bus voltage>
Figure QLYQS_4
Is a DC bus voltage reference value>
Figure QLYQS_5
Is a droop factor>
Figure QLYQS_6
Injecting active power of a direct current network into a weak alternating current power grid n through a corresponding AC/DC converter station n;
in actual operation, the weak alternating current power grid n has the following working conditions, and the control method comprises the following steps:
working condition 1. Frequency of weak AC network n
Figure QLYQS_7
Is in the normal range and has active power>
Figure QLYQS_8
And a droop factor>
Figure QLYQS_9
The change is not changed;
working condition 2. Frequency of weak AC network n
Figure QLYQS_10
Figure QLYQS_11
Rated frequency->
Figure QLYQS_12
The variable active power injected into the DC network by the AC/DC converter station n is:
Figure QLYQS_13
, wherein />
Figure QLYQS_14
Is a scale factor;
according to the formula
Figure QLYQS_15
And formula->
Figure QLYQS_16
Simultaneous determination of a variable droop factor>
Figure QLYQS_17
And then the variable active power is->
Figure QLYQS_18
Substituting it further deduces->
Figure QLYQS_19
Thereby flexibly adjusting the droop control. />
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Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106300342A (en) * 2016-08-30 2017-01-04 上海交通大学 A kind of isolated island micro-capacitance sensor operation method based on fuzzy PI hybrid control
CN109861265A (en) * 2018-12-28 2019-06-07 四川大学 A kind of virtual inertia control method of the wind power plant through MMC-HVDC access weak grid
CN110649643A (en) * 2019-09-23 2020-01-03 上海交通大学 Wind field multi-end flexible-direct control method and system capable of actively supporting power grid frequency
CN110808602A (en) * 2019-11-15 2020-02-18 华北电力大学 Improved additional frequency control method and system for multi-terminal flexible direct current power transmission system
CN112542849A (en) * 2020-11-12 2021-03-23 华北电力大学（保定） Self-adaptive virtual inertia frequency modulation control method for flexible direct current power transmission system
CN113067357A (en) * 2021-03-18 2021-07-02 华中科技大学 Direct-current voltage self-adaptive droop control method and system for alternating-current and direct-current hybrid power distribution network
CN113206516A (en) * 2021-05-14 2021-08-03 华北电力大学（保定） VSC-MTDC system self-adaptive combination control method considering DC voltage stability
WO2022041366A1 (en) * 2020-08-26 2022-03-03 东南大学溧阳研究院 Multi-terminal flexible direct current transmission system-based power grid frequency modulation method

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106300342A (en) * 2016-08-30 2017-01-04 上海交通大学 A kind of isolated island micro-capacitance sensor operation method based on fuzzy PI hybrid control
CN109861265A (en) * 2018-12-28 2019-06-07 四川大学 A kind of virtual inertia control method of the wind power plant through MMC-HVDC access weak grid
CN110649643A (en) * 2019-09-23 2020-01-03 上海交通大学 Wind field multi-end flexible-direct control method and system capable of actively supporting power grid frequency
CN110808602A (en) * 2019-11-15 2020-02-18 华北电力大学 Improved additional frequency control method and system for multi-terminal flexible direct current power transmission system
WO2022041366A1 (en) * 2020-08-26 2022-03-03 东南大学溧阳研究院 Multi-terminal flexible direct current transmission system-based power grid frequency modulation method
CN112542849A (en) * 2020-11-12 2021-03-23 华北电力大学（保定） Self-adaptive virtual inertia frequency modulation control method for flexible direct current power transmission system
CN113067357A (en) * 2021-03-18 2021-07-02 华中科技大学 Direct-current voltage self-adaptive droop control method and system for alternating-current and direct-current hybrid power distribution network
CN113206516A (en) * 2021-05-14 2021-08-03 华北电力大学（保定） VSC-MTDC system self-adaptive combination control method considering DC voltage stability

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