CN115360757B

CN115360757B - Single-machine equivalent modeling method for multi-converter grid-connected flexible interconnection system

Info

Publication number: CN115360757B
Application number: CN202211062901.4A
Authority: CN
Inventors: 徐旖旎; 季宇; 熊雄; 张颖; 孙丽敬; 刘海涛; 吕广宪; 吴鸣
Original assignee: China Online Shanghai Energy Internet Research Institute Co ltd
Current assignee: China Online Shanghai Energy Internet Research Institute Co ltd
Priority date: 2022-08-31
Filing date: 2022-08-31
Publication date: 2023-04-25
Anticipated expiration: 2042-08-31
Also published as: CN115360757A

Abstract

The invention discloses a single-machine equivalent modeling method and system for a multi-converter grid-connected flexible interconnection system. Wherein the method comprises the following steps: comprising the following steps: determining a network equivalent model of a low-voltage transformer area flexible interconnection system of the multi-converter grid connection and a single-converter grid connection target single-machine equivalent model; determining a filter inductance relation between a network equivalent model and a target single machine equivalent model; determining transfer functions and control parameters of each control link of the target single machine equivalent model; determining transfer functions and control parameters of each link of each converter of the actual multi-converter grid-connected system, and establishing a relation between the control parameters of the target single-machine equivalent model and the control parameters of each converter of the actual multi-converter grid-connected system; and obtaining control parameters of each control link of each converter. The stability analysis and control parameter selection difficulty of the interconnection system is effectively reduced.

Description

Single-machine equivalent modeling method for multi-converter grid-connected flexible interconnection system

Technical Field

The invention relates to the technical field of low-voltage alternating current-direct current hybrid power distribution, in particular to a single-machine equivalent modeling method and system for a multi-converter grid-connected flexible interconnection system.

Background

The interconnection and mutual supply of the plurality of load space-time characteristic complementary transformer areas are implemented between the low-voltage distribution transformer areas through a flexible direct current technology, and the method is a brand new scheme for coping with challenges of urgent need of improving the power supply capacity and the power supply quality of the low-voltage alternating current distribution network. However, the current scene and engineering which adopt flexible direct current technology interconnection to realize the load balance and supply-demand interaction of the distribution transformer area are not promoted in a large area, and a complete stability modeling analysis method is not formed yet.

When the converters are operated on the same direct current bus in parallel, a large amount of constant power load with negative resistance is connected to the direct current side of the interconnection system due to the mutual coupling action between the converters, so that the stability problem of the interconnection system can be caused. Most of the existing research results refer to high-voltage direct-current transmission and medium-voltage direct-current distribution, and are developed aiming at a coordination control strategy of a multi-terminal converter station and a medium-voltage multi-port energy router. Because of the mutual coupling effect between the multiple converters, only the control parameters of a single converter are adjusted, and the dynamic control characteristics of other converters can be influenced, so that the stability of an interconnection system is influenced, and the problems to be solved are urgent at present in formulating reasonable stable control parameters and coordination control strategies for effectively simplifying a low-voltage flexible interconnection system model of the grid connection of the multiple converters and deeply analyzing the stability of the system based on the model.

Disclosure of Invention

According to the invention, a single-machine equivalent modeling method and a single-machine equivalent modeling system for a multi-converter grid-connected flexible interconnection system are provided, so that the technical problem that the stability of the interconnection system is influenced by only adjusting the control parameters of a single converter and possibly affecting the dynamic control characteristics of other converters due to the mutual coupling effect between the multi-converters in the prior art is solved.

According to a first aspect of the invention, a single machine equivalent modeling method for a multi-converter grid-connected flexible interconnection system is provided, comprising the following steps:

determining a network equivalent model of a low-voltage transformer area flexible interconnection system of the multi-converter grid connection and a single-converter grid connection target single-machine equivalent model;

determining a filter inductance relation between the network equivalent model and the target single machine equivalent model;

determining transfer functions and control parameters of each control link of the single-machine equivalent model based on the filter inductance relation between the network equivalent model and the single-machine equivalent model;

determining transfer functions and control parameters of each converter link of the actual multi-converter grid-connected system, and establishing a connection between the control parameters of each control link of the target single machine equivalent model and the control parameters of each converter link of the actual multi-converter grid-connected system;

In the actual model analysis, the equivalent converter control parameters meeting the stability requirement are obtained based on the target single-machine equivalent model, and the control parameters of each control link of each converter are obtained according to the relation between the control parameters of each control link of the target single-machine equivalent model and the control parameters of each control link of each converter of the actual multi-converter grid-connected system.

According to another aspect of the present invention, there is also provided a single machine equivalent modeling system for a multi-converter grid-connected flexible interconnection system, including:

the module for determining the equivalent model of the single target machine is used for determining the network equivalent model of the flexible interconnection system of the low-voltage transformer area of the multi-converter grid connection and the equivalent model of the single target machine of the single converter grid connection;

the filter inductance relation determining module is used for determining the filter inductance relation between the network equivalent model and the target single machine equivalent model;

the single-machine equivalent transfer function determining module is used for determining transfer functions and control parameters of each control link of the single-machine equivalent model based on the filter inductance relation between the network equivalent model and the single-machine equivalent model;

determining transfer function modules of each converter, which are used for determining transfer functions and control parameters of each converter link of the actual multi-converter grid-connected system, and establishing a connection between the control parameters of each control link of the target single machine equivalent model and the control parameters of each converter link of the actual multi-converter grid-connected system;

And the control parameter module is used for obtaining the equivalent converter control parameters meeting the stability requirement based on the target single-machine equivalent model in the actual model analysis, and obtaining the control parameters of each control link of each converter according to the connection between the control parameters of each control link of the single-machine equivalent model obtained in the steps and the control parameters of each control link of each converter of the actual multi-converter grid-connected system. Therefore, the control capability and characteristics of a plurality of grid-connected AC/DC converters and direct current grid-connected constant power loads are fully considered through the single-machine equivalent model, the influence of a certain link on stability is not weakened or ignored, and all dynamic characteristics of the low-voltage flexible interconnection system can be comprehensively reflected by the obtained conclusion. The method solves the complex modeling problem of the low-voltage area flexible interconnection system of the multi-converter grid connection, can synchronously perform small-signal stability and large-signal stability analysis by combining an automatic control theory, simplifies the stability modeling analysis difficulty of the system, and further supports the control parameter formulation and coordinated control research of the low-voltage area flexible interconnection system.

Drawings

Exemplary embodiments of the present invention may be more completely understood in consideration of the following drawings:

Fig. 1 is a schematic flow chart of a single-machine equivalent modeling method for a multi-converter grid-connected flexible interconnection system according to the embodiment;

fig. 2 is a schematic diagram of a typical structure of a flexible interconnection system of a grid-connected transformer area of the multi-converter according to the present embodiment;

fig. 3a and fig. 3b are detailed control topology and stand-alone equivalent topology diagrams of the flexible interconnection system for grid connection of multiple converters according to the present embodiment;

fig. 4a and fig. 4b are schematic diagrams of an L-type detailed control topology and a single machine equivalent topology of the multi-converter grid-connected interconnection system according to the present embodiment;

fig. 5 is a block diagram of a dc bus voltage closed-loop control structure of a single-machine equivalent system according to the present embodiment;

fig. 6 is a block diagram of a dc bus voltage closed-loop control structure of a multi-converter parallel-grid low-voltage transformer area interconnection system according to the present embodiment;

fig. 7 is a schematic diagram of a stand-alone equivalent topology of the multi-converter grid-connected flexible interconnection system according to the present embodiment;

fig. 8 is a schematic diagram of dc bus voltage of the interconnection system and the single-unit equivalent system under the parameter set 1 set in this embodiment;

fig. 9 is a schematic diagram of the dc bus voltage of the interconnection system and the stand-alone equivalent system under the setting of the parameter set 2 according to the present embodiment.

Fig. 10 is a schematic diagram of a single-machine equivalent modeling system for a multi-converter grid-connected flexible interconnection system according to the embodiment.

Detailed Description

The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the examples described herein, which are provided to fully and completely disclose the present invention and fully convey the scope of the invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like elements/components are referred to by like reference numerals.

Unless otherwise indicated, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, it will be understood that terms defined in commonly used dictionaries should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.

According to a first aspect of the present invention, there is provided a single machine equivalent modeling method 100 for a multi-converter grid-connected flexible interconnection system, as shown with reference to fig. 1, the method 100 comprising:

S101, determining a network equivalent model of a low-voltage transformer area flexible interconnection system of multi-converter grid connection and a single-converter grid connection target single-machine equivalent model;

s102, determining a filter inductance relation between the network equivalent model and the target single machine equivalent model;

s103, determining transfer functions and control parameters of each control link of the single-machine equivalent model based on the filter inductance relation between the network equivalent model and the single-machine equivalent model;

s104, determining transfer functions and control parameters of all links of each converter of the actual multi-converter grid-connected system, and establishing a connection between the control parameters of all control links of the target single machine equivalent model and the control parameters of all control links of each converter of the actual multi-converter grid-connected system;

s105, in the actual model analysis, obtaining equivalent converter control parameters meeting the stability requirement based on the target single machine equivalent model, and obtaining the control parameters of each control link of each converter according to the relation between the control parameters of each control link of the target single machine equivalent model and the control parameters of each control link of each converter of the actual multi-converter grid-connected system.

Specifically, the single-machine equivalent modeling method is mainly applied to a flexible interconnection system of a low-voltage transformer area of a multi-converter grid connection, and takes a flexible interconnection typical topological structure shown in fig. 1 as an example, wherein the system comprises a typical low-voltage distribution transformer area, a bidirectional AC/DC converter, a direct-current bus, a direct-current side analog load, a photovoltaic source and a load power unit, and the steps and the effectiveness of the method are described by taking a system topology shown in fig. 2 as an example.

In the present invention, the "inverter" is a "converter".

Step one: and determining a network equivalent model of the low-voltage transformer area interconnection system of the multi-converter grid connection.

The converter is equivalent to the LCL filter, the detailed control topology of the flexible interconnection system of the multi-converter grid connection shown in fig. 2 and the equivalent topology of the target single machine are shown in fig. 3a and 3b, the characteristics of the LCL filter in a low frequency range are considered to be basically matched with the L filter, and the control bandwidth of a current loop is set to be smaller than the resonant frequency of the LCL filter in order to ensure the stability of the system, so that the high-frequency characteristics of the controller in design, namely the filter capacitor branch, are ignored. Based on the method, the LCL model can be approximately equivalent to a pure inductance model, a network equivalent model diagram 4a of a low-voltage transformer area interconnection system of the multi-converter grid connection is determined, and an L-shaped detailed control topology and a target single machine equivalent topology of the multi-converter grid connection interconnection system are shown in diagrams 4a and b. Fig. 3b is an equivalent model diagram of fig. 3a, fig. 4b is an equivalent control model diagram of fig. 4a, and fig. 4a is a network model equivalent diagram of fig. 3a omitting filter capacitor branches. Step two: the filter inductance of the alternating current side of the multi-converter is equivalent to the filter inductance of single machine.

In dq coordinate system (two-phase synchronous rotation coordinate system (d, q)), the mathematical model of the AC/DC converter in the target equivalent model of fig. 4b can be expressed as:

wherein: e, e _d And e _q D-axis and q-axis components of the equivalent single-machine fundamental voltage respectively; u (u) _d And u _q D-axis and q-axis components of the equivalent single-machine grid-connected point voltage respectively; i.e _d And i _q D-axis and q-axis components of the equivalent single-machine input alternating current are respectively; l and R are filter inductance of equivalent single machine and additional resistance; ω is the rotational angular frequency.

Ignoring the q-axis dependent variable and the resistor R, one can obtain

In the frequency domain:

e _d ＝u _d +Li _d s＝u _d +Li _d s (3)

from this, the output current i of the single-machine equivalent converter to the DC bus is calculated _d The method comprises the following steps:

i of the x-th converter _dx The method comprises the following steps:

in the formula e _dx And e _qx D-axis and q-axis components of the fundamental voltage of the x-th converter; l (L) _x Is the filter inductance of the x-th converter.

Thus, i of equivalent stand-alone model _d I with x converters _dx Is equivalent to

Wherein p is _x To consider the current average coefficient of the x-th converter of droop control, thereby obtaining i of equivalent single machine model _d ：

Namely, the filter inductance relation between the single machine equivalent model and the network equivalent model of the low-voltage station area interconnection system is as follows:

wherein: l is the equivalent inductance of the system, lx is the filter inductance of the xth converter, and n is the number of grid-connected converters.

Step three: calculating transfer functions of a current inner loop control link, a voltage outer loop control link and a sagging control link of an objective single machine equivalent model

1) Considering current inner loop control, the AC/DC converter mathematical model (single machine equivalent model) can be expressed as:

e _d ＝u _d +Li _d s＝u _d +p _md (9)

wherein: wherein p is _md And p _mq The d-axis and q-axis components of the equivalent stand-alone current control loop output signal, respectively.

Open loop transfer function G of current inner loop of single machine equivalent model _id (s) is:

the current PI controller of the single machine equivalent model can be expressed as:

the loop gain of the current inner loop from which the single machine equivalence can be obtained can be expressed as:

the closed loop transfer function of the current inner loop of the single machine equivalent model is deduced as follows:

wherein: i.e _d I is the output current of the grid-connected converter to a direct current bus _dref For the current reference value, K _ipx And K _iix The current inner loop proportion coefficient and integral coefficient of the x-th converter, K _ipe And K _iie The current inner loop proportional coefficient and the integral coefficient of the target single machine equivalent model are respectively, L is the equivalent inductance of the system, and s is the Laplacian.

2) Frequency domain expression taking into account the voltage outer loop control on the direct current side:

wherein: i.e _dc And u _dc Respectively equivalent single machine direct current output current and direct current output voltage; c (C) _eq A direct current filter capacitor which is an equivalent single machine; r is R _eq Is a direct current load resistor. I.e.

Neglecting the loss of the converter, the power of the alternating current transformer area injected into the direct current bus through the AC/DC converter is as follows:

P＝1.5u _d i _d ＝u _dc i _dc (16)

at steady state operating points are:

wherein i is _dc0 And u _dc0 The values of the equivalent single machine direct current output current and the voltage at a certain steady-state operating point are respectively; u (u) _d0 The d-axis component of the equivalent single-machine fundamental voltage is the value of the d-axis component at a certain steady-state operating point; i.e _d0 The d-axis component of the input ac current is the value of the equivalent single machine at some steady state operating point.

The simultaneous equations (15), (16) and (17) can be obtained:

/>

the open loop transfer function of the voltage outer loop control link is:

open loop transfer function G of voltage outer loop after taking into account current inner loop _iude (s) is:

the voltage PI controller of the stand-alone equivalence model can be expressed as:

the loop gain of the voltage outer loop, taking into account the current inner loop, can be described as:

T _uude (s)＝G _iude (s)G _vcde (s) (22)

the closed loop transfer function of the voltage outer loop after the current inner loop is obtained is as follows:

wherein u is _dcref Is the direct current output voltage reference value of the equivalent single machine.

I.e.

The closed loop transfer function of the voltage outer loop after the current inner loop is considered is as follows:

3) Considering a transfer function of a droop control link of a single machine equivalent model:

the same principle can be obtained:

based on the theoretical derivation formula, the equivalent detailed control block diagram is combined with fig. 4b, and the direct current bus voltage closed-loop control structure block diagram of the target single machine equivalent can be obtained as shown in fig. 5. Equation 27 corresponds to fig. 5.

Step four: and calculating transfer functions of a current inner ring, a voltage outer ring and a sagging control link of an x-th converter of the actual multi-converter grid-connected system, and establishing connection with control parameters of a target equivalent model.

1) Current inner loop transfer function derivation for x-th converter

E of x-th converter _dx The method comprises the following steps:

e _dx ＝u _d +(L _x s+R _x )i _dx ＝u _d +p _mdx (28)

wherein p is _mdx And p _mqx D-axis and q-axis components of the x-th inverter current control loop output signal, respectively.

The corresponding open loop transfer function is:

L _x i _dx s＝p _mdx (29)

namely G _idx (s) is:

the current PI controller of the x-th inverter can be expressed as:

the closed loop transfer function of the current inner loop of the x-th converter is as follows:

wherein i is _dref And inputting a d-axis component reference value of the alternating current for the x-th converter.

The equivalent transfer function of the current inner loop thus pushed to each inverter is:

u _d +L _x i _dx s＝u _d +p _mdx (33)

i.e.

After accumulation, can obtain

Namely:

the equivalent closed loop transfer function of the current inner loop of each converter is:

/>

i.e.

Namely, the relation between the control parameters of the current inner loop of the x-th converter of the multi-converter grid-connected system and the control parameters of the current inner loop of the single machine equivalent model is as follows:

2) Voltage outer loop control of the x-th converter:

the voltage outer loop transfer function of the x-th converter is:

the following relationship exists:

Further, the voltage outer loop transfer function of the x-th inverter is:

i.e.

The voltage PI controller of the x-th inverter can be expressed as:

the loop gain of the voltage outer loop of the x-th inverter can be described as:

T _uudx (s)＝G _iudx (s)G _vcdx (s) (45)

the voltage outer ring equivalent transfer function of each converter is deduced as follows:

namely, can obtain

The closed loop transfer function of the voltage outer loop of the x-th inverter is:

after mutual accumulation, the closed loop transfer function of the system can be obtained as follows:

the closed loop transfer function of the voltage outer loop of the equivalent single machine model is as follows:

simultaneous availability of

Wherein: k (K) _vpx And K _vix The voltage outer ring proportion coefficient and the integral coefficient of the x-th converter are respectively K _vpe And K _vie The voltage outer loop proportional coefficient and the integral coefficient of the target single machine equivalent model are respectively.

Namely, the relation between the control parameters of the voltage outer ring of the x-th converter of the multi-converter grid-connected system and the control parameters of the voltage outer ring of the single machine equivalent model is as follows:

3) After the droop control of the x-th converter is considered, the equivalent relation of the currents is as follows:

the closed loop transfer function of the x-th converter is:

that is, 39, 52, 54 are cumulatively available, considering the closed loop transfer function of the droop control loop of the x-th inverter as:

due to the formula (27)

Then equation 55 is derived using equation 27 to obtain

Wherein: p is p _x Is the droop average coefficient K of the x-th converter _dx Is the sagging control coefficient of the x-th converter, K _d And the droop control coefficient is the droop control coefficient of the target single machine equivalent model.

Therefore, the relation between the control parameters of the droop control of the x-th converter of the multi-converter grid-connected system and the control parameters of the droop control of the single-machine equivalent model is as follows:

k _d ＝k _dx p _x (58)

based on the theoretical derivation formula, in combination with fig. 4a, a block diagram of a direct current bus voltage closed-loop control structure of the multi-converter parallel network low-voltage transformer area interconnection system is shown in fig. 6.

Step five: in the actual model analysis, the large-signal equivalent modeling of the flexible interconnected system of the low-voltage transformer area is carried out to obtain a single-machine equivalent model of the grid-connected flexible interconnected system of the multi-converter.

1) Circuit model equivalent

The detailed topology of the multiple converters grid-connected flexible interconnection system and the equivalent single machine can be known that the relationship between the direct-current side output filter capacitor of the equivalent single machine and the direct-current side output filter capacitor of the x-th AC/DC converter is as follows:

wherein C is _x And C _eq The output filter capacitors are respectively the x-th AC/DC converter and the direct-current side of the equivalent single machine.

The relation between the output filter inductance of the alternating current side of the equivalent single machine and the output filter inductance of the alternating current side of the x-th AC/DC converter is as follows:

Wherein L is _x And L is the output filter inductance of the alternating current side of the x-th AC/DC converter and the equivalent single machine respectively.

2) Equivalent modeling of sagging control link

The relationship between the output current of the DC side of each AC/DC converter in the interconnection system and the output current of the DC side of the equivalent single machine is as follows:

wherein i is _dcx And i _dc The output currents are respectively the direct current side of the x-th AC/DC converter and the equivalent single machine.

After the sagging control link is considered, the relationship between the output current of the direct current side of each AC/DC converter and the control parameter of the equivalent single machine is as follows:

3) Equivalent modeling of voltage control link

The relationship of the voltage outer loop PI control parameters of each AC/DC converter is as follows:

the current equivalence relation of droop control and voltage control is considered after single machine equivalence:

i _dref ＝G _uc (s)(u _dcref -u _dc -k _d ·i _dc ) (64)

the x-th AC/DC converter considers the current equivalence relation of droop control and voltage control:

i _drefx ＝G _vcdx (s)(u _dcrefx -u _dcx- k _ix ·i _dcx ) (65)

64 and 65 are available in parallel,

the voltage PI controller of single machine equivalence can be expressed as:

the voltage PI controller of the x-th AC/DC converter can be expressed as:

then the relation between the voltage control parameters of the x-th AC/DC converter and the equivalent single machine is shown in the following formula

4) Equivalent modeling of current control link

If the relation of the current inner loop PI control parameters of each converter is as follows:

after the single machine is equivalent, the voltage equivalent relation of the sagging control loop, the voltage control loop and the current control loop is considered:

e _d ＝u _d +G _icde (s)(i _dref -i _d )+ωL _f i _q (71)

The x-th AC/DC converter considers the voltage equivalence relation of the droop control loop, the voltage control loop and the current control loop:

e _dx ＝u _dx +G _icdx (s)(i _drefx -i _dx )+ωL _fx i _qx ＝u _dx +L _x i _dx s+ωL _fx i _qx (72)

71 and 72 are available simultaneously:

i.e.

After the summation and accumulation of 74, the method can obtain

Due to formula (76)

I.e. 75 and 76 are equal

The current PI controller of single machine equivalence can be expressed as:

the current controller of the x-th AC/DC converter can be expressed as:

then, the relation between the current control parameters of the x-th AC/DC converter and the equivalent single machine is shown as follows:

so far, an equivalent single machine model of the multi-converter grid-connected flexible interconnection system is established.

In order to verify the effectiveness of the single machine equivalent modeling method provided by the invention, a multi-converter grid-connected flexible interconnection system with a topological structure shown in figure 1 is built, wherein a transformer area 1 and a transformer area 2 come from the same 10kV interval or branch line; the station area 3, the station area 4 comes from the other two paths of 10kV branch lines; the variable capacity of the transformer is 400kVA, the capacity of the AC/DC converter is 400kVA, the alternating current side is three-phase four-bridge arm, and the direct current side is pseudo bipolar +/-375V; the system is of a common bus topological structure, four converters are all operated in a sagging control mode, the energy storage system is operated in a fixed power mode, the photovoltaic is operated in an MPPT mode, and the load equivalent of a direct current system can be combined to be a constant power load. In connection with the equivalent single machine model of fig. 4a, the system can be simplified into a topology structure as shown in fig. 7.

The initial output power of the 4 grid-connected converters is respectively divided equally according to the sagging coefficient, and the initial power of the constant power load is 50kW; the 1 st second constant power load power is changed from 50kW to 450kW. The control parameters of the two groups of outer voltage rings and inner current control rings meeting the stability control requirement are drawn by combining the automatic control theory of the single machine equivalent modeling method provided by the invention, and the control parameters of each controller are obtained by combining the invention and are shown in a table 1.

Table 1 parameter settings for small disturbance stabilization of the system

Under the setting of the parameter set 1, waveforms and oscillation frequencies of the direct current bus voltages of the interconnection system and the single-machine equivalent system are shown in figure 8, and the simulation oscillation frequencies are 46Hz; under parameter set 2 settings: the waveform and the oscillation frequency of the direct current bus voltage of the interconnection system and the single-machine equivalent system are shown in figure 9, and the simulation oscillation frequency is 14Hz; therefore, the effectiveness of the bill of lading machine equivalent modeling method is verified.

Therefore, the control capability and characteristics of a plurality of grid-connected AC/DC converters and direct current grid-connected constant power loads are fully considered through the single-machine equivalent model, the influence of a certain link on stability is not weakened or ignored, and all dynamic characteristics of the low-voltage flexible interconnection system can be comprehensively reflected by the obtained conclusion. The method solves the complex modeling problem of the low-voltage area flexible interconnection system of the multi-converter grid connection, can synchronously perform small-signal stability and large-signal stability analysis by combining an automatic control theory, simplifies the stability modeling analysis difficulty of the system, and further supports the control parameter formulation and coordinated control research of the low-voltage area flexible interconnection system.

Optionally, determining a network equivalent model of the low-voltage transformer area flexible interconnection system of the multi-converter grid connection and a target single machine equivalent model of the single-converter grid connection includes:

the method comprises the steps of performing equivalence on a plurality of grid-connected converters of a low-voltage transformer area interconnection system through LCL-type filters, setting a current loop control bandwidth smaller than the resonant frequency of the LCL filters, performing approximate equivalence on the LCL-type filters to be a pure inductance model, namely, an L-type filter, and determining a network equivalent model of the multi-converter grid-connected low-voltage transformer area interconnection system;

and determining an object single machine equivalent model corresponding to the network equivalent model.

Optionally, the step of equivalently converting the filter inductance of the ac side of the multi-converter into a filter inductance with equivalent value of a single machine, and the step of determining the filter inductance relation between the network equivalent model and the target single machine equivalent model includes:

the filter inductance relation between the network equivalent model and the target single machine equivalent model is determined as follows:

wherein: l is the equivalent inductance of the system, L _x The filter inductance of the x-th converter is the number of grid-connected converters.

Optionally, determining the transfer function and the control parameter of each control link of the single-unit equivalent model based on the filter inductance relation between the network equivalent model and the single-unit equivalent model includes:

Determining a closed loop transfer function of a control link of a current inner loop of the single-machine equivalent model based on the filter inductance relation between the network equivalent model and the single-machine equivalent model:

wherein: i.e _d I is the output current of the grid-connected converter to a direct current bus _dref For the current reference value, K _ipe And K _iie The current inner loop proportional coefficient and the integral coefficient of the target single machine equivalent model are respectively, L is the equivalent inductance of the system, and s is the Laplacian;

the closed loop transfer function of the control link of the voltage outer loop of the target single machine equivalent model considering the current inner loop control is determined as follows:

wherein: u (u) _dc Is the direct current voltage of the grid-connected converter, u _dcref For DC output voltage reference value, K _ipe And K _iie The current inner loop proportional coefficient and the integral coefficient are respectively the target single machine equivalent model, K _vpe And K _vie Respectively the voltage outer loop proportional coefficient and integral coefficient of the target single machine equivalent model, L is the equivalent inductance of the system, C _eq And R is _eq The direct current filter capacitor and the direct current load resistor of the system are respectively, u _dc0 And u _d0 The values of the d-axis component of the equivalent single-machine direct-current output voltage and the fundamental voltage at a certain steady-state operating point are respectively shown, and s is a Laplacian operator;

the closed loop transfer function of the droop control link of the target single machine equivalent model is determined as follows:

Wherein: k (k) _d Is the sag factor of the inverter.

Optionally, the transfer function of each control link includes a transfer function of a current inner loop control link, a transfer function of a voltage outer loop control link, and a transfer function of a droop control link;

the control parameters comprise control parameters of a current inner loop control link, control parameters of a voltage outer loop control link and control parameters of a sagging control link.

Optionally, determining transfer functions and control parameters of each link of each converter of the actual multi-converter grid-connected system, and establishing a connection between the control parameters of each control link of the target single machine equivalent model and the control parameters of each control link of each converter of the actual multi-converter grid-connected system, including:

the current inner loop control link of a plurality of converters in an actual multi-converter grid-connected system is equivalent to the current inner loop control link of a target single-converter grid-connected system, and the closed loop transfer function of the current inner loop of the target single-converter grid-connected system is as follows:

wherein: i.e _d I is the output current of the grid-connected converter to a direct current bus _dref For the current reference value, K _ipx K _iix The current inner loop proportion coefficient and integral coefficient of the x-th converter, K _ipe And K _iie The current inner loop proportional coefficient and the integral coefficient of the target single machine equivalent model are respectively;

the relation between the current inner loop control parameter of the target single converter and the current inner loop control parameter of the target single equivalent model is determined as follows:

wherein: l is the equivalent inductance of the system, L _x The filter inductance of the x-th converter is n the number of grid-connected converters, K _ipx K _iix The current inner loop proportion coefficient and integral coefficient of the x-th converter, K _ipe And K _iie The current inner loop proportional coefficient and the integral coefficient of the target single machine equivalent model are respectively.

Optionally, determining transfer functions and control parameters of each link of each converter of the actual multi-converter grid-connected system, and establishing a connection between the control parameters of each control link of the target single machine equivalent model and the control parameters of each control link of each converter of the actual multi-converter grid-connected system, and further including:

the method comprises the steps of enabling a voltage outer ring control link of a plurality of converters in an actual multi-converter grid-connected system to be equivalent to a voltage outer ring control link of a target single-converter grid-connected voltage outer ring, wherein a closed loop transfer function of the target single-converter grid-connected voltage outer ring is as follows:

wherein: k (K) _vpx 、K _vix The voltage outer ring proportion coefficient and the integral coefficient of the x-th converter are respectively K _vpe And K _vie Respectively a voltage outer loop proportional coefficient and an integral coefficient of the target single machine equivalent model;

the relation between the control parameters of the voltage outer ring of the target single converter and the control parameters of the voltage outer ring of the target single equivalent model is determined as follows:

wherein: l is the equivalent inductance of the system, L _x The filter inductance of the x-th converter is n the number of grid-connected converters, K _vpx 、K _vix The voltage outer ring proportion coefficient and the integral coefficient of the x-th converter are respectively K _vpe And K _vie The voltage outer loop proportional coefficient and the integral coefficient of the target single machine equivalent model are respectively.

the droop control link of a plurality of converters in an actual multi-converter grid-connected system is equivalent to the droop control link of a target single-converter grid-connected system, and the closed loop transfer function of the droop control of the target single-converter grid-connected system is as follows:

the relation between the droop control parameters of the target single converter and the droop control parameters of the equivalent model of the target single converter is determined as follows:

k _d ＝k _dx p _x

Wherein: p is p _x Is the droop average coefficient K of the x-th converter _dx Is the sagging control coefficient of the x-th converter, K _d And the droop control coefficients are respectively the droop control coefficients of the equivalent model of the target single machine.

Optionally, obtaining the equivalent current converter control parameter meeting the stability requirement based on the target single machine equivalent model, and obtaining the control parameter of each control link of each current converter according to the relation between the control parameter of each control link of the target single machine equivalent model and the control parameter of each control link of each current converter of the actual multi-current converter grid-connected system, including: the control parameters of each control link of each converter are obtained as follows:

wherein: l is the equivalent inductance of the system, L _x The filter inductance of the x-th converter is n the number of grid-connected converters, K _ipx 、K _iix 、K _vpx 、K _vix The current inner loop proportional coefficient, the current inner loop integral coefficient, the voltage outer loop proportional coefficient and the voltage outer loop integral coefficient of the x-th converter are respectively; k (K) _ipe 、K _iie 、K _vp 、K _vi The current inner loop proportional coefficient, the current inner loop integral coefficient, the voltage outer loop proportional coefficient and the voltage outer loop integral coefficient of the target single machine equivalent model are respectively obtained. P is p _x Is the droop average coefficient K of the x-th converter _dx Is the sagging control coefficient of the x-th converter, K _d Droop control coefficients i of the equivalent models of the target single machine respectively _dc Is equivalent single machine direct current output current, i _dcx The direct current output current of the x-th converter.

According to another aspect of the present invention, there is also provided a stand-alone equivalent modeling system 1000 for a multi-converter grid-connected flexible interconnection system, referring to fig. 10, the system 1000 includes:

the module 1010 for determining the equivalent model of the single machine is used for determining the network equivalent model of the flexible interconnection system of the low-voltage transformer area of the multi-converter grid connection and the equivalent model of the single machine of the single converter grid connection;

The filter inductance relation determining module 1020 is configured to determine a filter inductance relation between the network equivalent model and the target single machine equivalent model;

the single-machine equivalent transfer function determining module 1030 is configured to determine transfer functions and control parameters of each control link of the single-machine equivalent model based on a filter inductance relationship between the network equivalent model and the single-machine equivalent model;

the transfer function module 1040 is used for determining transfer functions and control parameters of each link of each converter of the actual multi-converter grid-connected system, and establishing a connection between the control parameters of each control link of the target single machine equivalent model and the control parameters of each control link of each converter of the actual multi-converter grid-connected system;

and the control parameter acquisition module 1050 is used for acquiring the equivalent converter control parameters meeting the stability requirement based on the target single-machine equivalent model in the actual model analysis, and acquiring the control parameters of each control link of each converter according to the connection between the control parameters of each control link of the single-machine equivalent model and the control parameters of each control link of each converter of the actual multi-converter grid-connected system. Optionally, determining the target single machine equivalent model module includes:

The network equivalent model determining sub-module is used for enabling a plurality of grid-connected converters of the low-voltage transformer area interconnection system to be equivalent by using LCL-type filters, setting the control bandwidth of a current loop to be smaller than the resonant frequency of the LCL filters, enabling the LCL-type filters to be approximately equivalent to a pure inductance model, namely an L-type filter control topology model, and determining a network equivalent model of the low-voltage transformer area interconnection system with the grid-connected converters;

and the target single machine equivalent model determining sub-module is used for determining a target single machine equivalent model corresponding to the network equivalent model.

Optionally, the determining a filtering inductance relation module includes:

the sub-module for determining the filter inductance relationship is used for determining the filter inductance relationship between the network equivalent model and the target single machine equivalent model as follows:

Optionally, determining a stand-alone equivalent transfer function module includes:

the sub-module for determining the single-machine equivalent current inner loop transfer function is used for determining the closed loop transfer function of the control link of the current inner loop of the target single-machine equivalent model based on the filter inductance relation between the network equivalent model and the target single-machine equivalent model:

the sub-module for determining the single-machine equivalent voltage outer ring transfer function is used for determining the closed loop transfer function of the control link of the voltage outer ring of the target single-machine equivalent model considering the current inner ring control, wherein the closed loop transfer function is as follows:

the sub-module for determining the single-machine equivalent droop control transfer function is used for determining the closed loop transfer function of the droop control link of the target single-machine equivalent model as follows:

wherein: k (k) _d Is the sag factor of the inverter.

Optionally, determining each converter transfer function module includes:

the current inner loop sub-module of the target single converter is used for equivalently converting the current inner loop control links of a plurality of converters in an actual multi-converter grid-connected system into the current inner loop control links of the target single converter grid-connected, and the closed loop transfer function of the current inner loop of the target single converter grid-connected is as follows:

the sub-module for determining the relationship between the current inner loop control parameters of the target single converter and the current inner loop control parameters of the target single equivalent model is as follows:

Optionally, determining each converter transfer function module further includes:

the method comprises the steps of determining a target single-converter voltage outer ring sub-module, wherein the target single-converter voltage outer ring sub-module is used for equivalently converting a voltage outer ring control link of a plurality of converters in an actual multi-converter grid-connected system into a voltage outer ring control link of a target single-converter grid-connected, and the closed loop transfer function of the voltage outer ring of the target single-converter grid-connected is as follows:

wherein: k (K) _vpx 、K _vix The voltage outer ring proportion coefficient and the integral coefficient of the x-th converter are respectively K _vp And K _vi Respectively a voltage outer loop proportional coefficient and an integral coefficient of the target single machine equivalent model;

the sub-module for determining the relation between the control parameters of the voltage outer ring of the target single converter and the control parameters of the voltage outer ring of the target single equivalent model is used for determining the relation between the control parameters of the voltage outer ring of the target single converter and the control parameters of the voltage outer ring of the target single equivalent model as follows:

wherein: l is the equivalent inductance of the system, L _x The filter inductance of the x-th converter is n the number of grid-connected converters, K _vpx 、K _vix The voltage outer ring proportion coefficient and the integral coefficient of the x-th converter are respectively K _vp And K _vi The voltage outer loop proportional coefficient and the integral coefficient of the target single machine equivalent model are respectively.

the method comprises the steps of determining a sagging control submodule of a target single current converter, wherein the sagging control submodule is used for equivalently enabling sagging control links of a plurality of current converters in an actual multi-current converter grid-connected system to be sagging control links of the target single current converter grid-connected, and the closed loop transfer function of sagging control of the target single current converter grid-connected is as follows:

the sub-module for determining the sagging control parameter relation determines that the relation between the sagging control parameter of the target single-unit converter and the sagging control parameter of the target single-unit equivalent model is as follows:

k _d ＝k _dx p _x

Optionally, the obtaining each converter control parameter module 1050 includes:

the sub-module for acquiring the control parameters of each converter is used for acquiring the control parameters of each control link of each converter as follows:

/>

the single-machine equivalent modeling system 1000 for a multi-converter grid-connected flexible interconnection system according to the embodiment of the present invention corresponds to the single-machine equivalent modeling method 100 for a multi-converter grid-connected flexible interconnection system according to another embodiment of the present invention, and is not described herein.

It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein. The solutions in the embodiments of the present application may be implemented in various computer languages, for example, object-oriented programming language Java, and an transliterated scripting language JavaScript, etc.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

While preferred embodiments of the present application have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the application.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present application without departing from the spirit or scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims and the equivalents thereof, the present application is intended to cover such modifications and variations.

Claims

1. A single-machine equivalent modeling method for a multi-converter grid-connected flexible interconnection system is characterized by comprising the following steps of:

In the actual model analysis, obtaining equivalent current converter control parameters meeting the stability requirement based on the target single machine equivalent model, and obtaining the control parameters of each current converter control link according to the relation between the control parameters of each control link of the target single machine equivalent model and the control parameters of each current converter of an actual multi-current converter grid-connected system;

the method for determining the network equivalent model of the low-voltage transformer area flexible interconnection system of the multi-converter grid connection and the target single machine equivalent model of the single-converter grid connection comprises the following steps:

the method comprises the steps of performing equivalence on a plurality of grid-connected converters of a low-voltage transformer area interconnection system through LCL-type filters, setting a current loop control bandwidth smaller than the resonant frequency of the LCL filters, performing approximate equivalence on the LCL-type filters to be a pure inductance model, namely an L-type filter control topology model, and determining a network equivalent model of the multi-converter grid-connected low-voltage transformer area interconnection system;

determining an objective single machine equivalent model corresponding to the network equivalent model;

the method for determining the filter inductance relation between the network equivalent model and the target single-machine equivalent model comprises the following steps of:

wherein: l is the equivalent inductance of the system, L _x The filter inductance of the x-th converter is the number of grid-connected converters;

based on the filter inductance relation between the network equivalent model and the target single machine equivalent model, determining transfer functions and control parameters of each control link of the target single machine equivalent model, wherein the method comprises the following steps:

wherein: i.e _d I is the output current of the grid-connected converter to a direct current bus _dref For the current reference value, K _ipe And K _iie The current inner loop proportional coefficient and the integral coefficient of the target single machine equivalent model are respectively, L is the equivalent inductance of the system, s is the Laplacian, T _ide (s) loop gain for a single equivalent current loop；

wherein: k (k) _d Is the sag factor of the inverter.

2. The method of claim 1, wherein the step of determining the position of the substrate comprises,

the transfer functions of the control links comprise a transfer function of a current inner loop control link, a transfer function of a voltage outer loop control link and a transfer function of a sagging control link;

3. The method according to claim 1, wherein determining transfer functions and control parameters of each converter link of the actual multi-converter grid-connected system, and associating the control parameters of each control link of the target single machine equivalent model with the control parameters of each control link of each converter of the actual multi-converter grid-connected system, comprises:

wherein: i.e _d I is the output current of the grid-connected converter to a direct current bus _dref For the current reference value, K _ipx K _iix The current inner loop proportion coefficient and integral coefficient of the x-th converter, K _ipe And K _iie The current inner loop proportional coefficient and integral coefficient, p of the target single machine equivalent model are respectively _x Is the droop average coefficient of the x-th converter;

wherein: l is the equivalent inductance of the system, L _x The filter inductance of the x-th converter is n the number of grid-connected converters, K _ipx And K _iix The current inner loop proportion coefficient and integral coefficient of the x-th converter, K _ipe And K _iie The current inner loop proportional coefficient and the integral coefficient of the target single machine equivalent model are respectively.

4. The method according to claim 1, wherein determining transfer functions and control parameters of each converter link of the actual multi-converter grid-connected system, and associating the control parameters of each control link of the target single machine equivalent model with the control parameters of each control link of each converter of the actual multi-converter grid-connected system, further comprises:

wherein: k (K) _vpx 、K _vix The voltage outer ring proportion coefficient and the integral coefficient of the x-th converter are respectively K _vpe And K _vie Respectively the voltage outer ring proportion coefficient and the integration coefficient of the target single machine equivalent model, K _ipx And K _iix The current inner loop proportion coefficient and integral coefficient of the x-th converter, K _ipe And K _iie The current inner loop proportional coefficient and the integral coefficient of the target single machine equivalent model are respectively;

wherein: l is the equivalent inductance of the system, lx is the filter inductance of the xth converter, n is the number of grid-connected converters, K _vpx 、K _vix The voltage outer ring proportion coefficient and the integral coefficient of the x-th converter are respectively K _vpe And K _vie The voltage outer loop proportional coefficient and the integral coefficient of the target single machine equivalent model are respectively.

5. The method according to claim 1, wherein determining transfer functions and control parameters of each converter link of the actual multi-converter grid-connected system, and associating the control parameters of each control link of the target single machine equivalent model with the control parameters of each control link of each converter of the actual multi-converter grid-connected system, further comprises:

wherein K is _ipx And K _iix The current inner loop proportion coefficient and integral coefficient of the x-th converter, K _vpx 、K _vix The ratio coefficient and the integral coefficient of the voltage outer ring of the xth converter are respectively, L is the equivalent inductance of the system, lx is the filter inductance of the xth converter, C _eq Is a direct current filter capacitor of an equivalent single machine, R _eq The resistor is a direct current load resistor;

k _d ＝k _dx p _x

6. The method according to claim 1, wherein obtaining the equivalent converter control parameters satisfying the stability requirement based on the target single machine equivalent model, and obtaining the control parameters of each control link of each converter according to the relation between the control parameters of each control link of the target single machine equivalent model and the control parameters of each control link of each converter of the actual multi-converter grid-connected system, comprises: the control parameters of each control link of each converter are obtained as follows:

Wherein: l is the equivalent inductance of the system, lx is the filter inductance of the xth converter, n is the number of grid-connected converters, K _ipx 、K _iix 、K _vpx 、K _vix The current inner loop proportional coefficient, the current inner loop integral coefficient, the voltage outer loop proportional coefficient and the voltage outer loop integral coefficient of the x-th converter are respectively; k (K) _ipe 、K _iie 、K _vpe 、K _vie The current inner loop proportional coefficient, the current inner loop integral coefficient, the voltage outer loop proportional coefficient and the voltage outer loop integral coefficient of the target single machine equivalent model are respectively p _x Is the droop average coefficient K of the x-th converter _dx Is the sagging control coefficient of the x-th converter, K _d Droop control coefficient i of target single machine equivalent model _dc Is equivalent single machine direct current output current, i _dcx The direct current output current of the x-th converter.

7. A single-machine equivalent modeling system for a multi-converter grid-connected flexible interconnection system is characterized by comprising:

the control parameter module is used for obtaining equivalent converter control parameters meeting the stability requirement based on the target single-machine equivalent model in the actual model analysis, and obtaining the control parameters of each control link of each converter according to the connection between the control parameters of each control link of the single-machine equivalent model obtained in the steps and the control parameters of each control link of each converter of the actual multi-converter grid-connected system;

Wherein: i.e _d I is the output current of the grid-connected converter to a direct current bus _dref For the current reference value, K _ipe And K _iie The current inner loop proportional coefficient and the integral coefficient of the target single machine equivalent model are respectively, L is the equivalent inductance of the system, s is the Laplacian, T _ide (s) is the loop gain of the current inner loop of the single machine equivalent;

/>

wherein: u (u) _dc For grid-connected conversionDC voltage of current transformer, u _dcref For DC output voltage reference value, K _ipe And K _iie The current inner loop proportional coefficient and the integral coefficient are respectively the target single machine equivalent model, K _vpe And K _vie Respectively the voltage outer loop proportional coefficient and integral coefficient of the target single machine equivalent model, L is the equivalent inductance of the system, C _eq And R is _eq The direct current filter capacitor and the direct current load resistor of the system are respectively, u _dc0 And u _d0 The values of the d-axis component of the equivalent single-machine direct-current output voltage and the fundamental voltage at a certain steady-state operating point are respectively shown, and s is a Laplacian operator;

wherein: k (k) _d Is the sag factor of the inverter.