CN113612263A - Low-frequency oscillation suppression method and system for multi-port alternating current-direct current hybrid power distribution network - Google Patents
Low-frequency oscillation suppression method and system for multi-port alternating current-direct current hybrid power distribution network Download PDFInfo
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J4/00—Circuit arrangements for mains or distribution networks not specified as ac or dc
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H—ELECTRICITY
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- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
- H02J2003/365—Reducing harmonics or oscillations in HVDC
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
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Abstract
The invention relates to the technical field of power system stability, in particular to a low-frequency oscillation suppression method and a low-frequency oscillation suppression system for a multi-port alternating current-direct current hybrid power distribution network, wherein an oscillation suppression additional controller is configured on a controller of a three-phase Buck circuit link of the alternating current-direct current power distribution network; determining configuration parameters of a phase compensation link; determining a time constant of a signal filtering link and determining a gain coefficient of a signal; compared with the prior art, the method has the advantages that additional equipment is not needed, the operation is convenient, the damping of the AC/DC power distribution network can be effectively improved, the low-frequency oscillation is inhibited, the stability of the system is improved, and the method can be widely applied to the inhibition of the low-frequency oscillation in the AC/DC power distribution network containing the power electronic transformer.
Description
Technical Field
The invention relates to the technical field of power system stability, in particular to a low-frequency oscillation suppression method and system for a multi-port alternating current-direct current hybrid power distribution network.
Background
The distribution network, as an important component of the power system, plays a key role in distributing electric energy to a large number of power consumers. The traditional alternating current power distribution system has a series of problems of high line loss, power quality disturbance, voltage drop and the like, and is difficult to meet the increasing power requirements of power users; the direct current part in the alternating current-direct current hybrid power distribution network has no synchronization problem, can effectively isolate alternating current side disturbance and faults, and ensures high-reliability power supply. The AC-DC hybrid power distribution network is a development trend of the future power distribution network on the basis of the AC power distribution network.
However, the existing ac/dc hybrid power distribution network is still in the development transition stage, some low-frequency oscillation problems may occur, and in the operation test of some existing ac/dc power distribution networks, the phenomenon of low-frequency oscillation of the voltage at the dc side occurs, and the grid structure of the ac/dc hybrid power distribution network in the actual operation process will be more complex and will also contain more electric energy conversion devices, and if the oscillation problem occurs, the serious system safety problem will be caused, and adverse consequences are caused to the production and life of power users. Therefore, an additional control link is required to be added to suppress low-frequency oscillation on the basis of the existing controller of the alternating current/direct current distribution network.
The main reason for the low frequency oscillations is due to the weak and negative damping of the system, and the additional controller added to these low frequency oscillations is often used to boost the positive damping of the system. Currently, there are primary system control methods and secondary system control methods as additional control methods for low frequency oscillation. The primary system control method comprises a grid structure for enhancing the system and an energy storage device, but the grid structure of the physical part needs to be added or modified, and the actual implementation process is complex. The secondary system control method comprises FACTS devices based on the flexible alternating current transmission system, such as a static var compensator, a static synchronous series compensator and the like. However, these methods are often used for suppressing inter-regional low-frequency oscillation methods for large-scale interconnected power systems, but the suppression methods based on the low-frequency oscillation of the multi-port alternating-current/direct-current hybrid power distribution network are few, the multi-port alternating-current/direct-current hybrid power distribution network system is complex in structure and numerous in equipment, the multi-port alternating-current/direct-current hybrid power distribution network system comprises various equipment such as a power electronic transformer, an inverter and a DC-DC converter, the control methods are various, the input and output selection is difficult when an additional controller is designed, and the determination of the form of the additional controller is challenging.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method and the system for inhibiting the low-frequency oscillation of the multi-port alternating current and direct current hybrid power distribution network are provided, the damping of the alternating current and direct current power distribution network is improved, the low-frequency oscillation is inhibited, and therefore the stability of the system is improved.
In order to achieve the purpose, the invention adopts the technical scheme that: a low-frequency oscillation suppression method for a multi-port alternating current-direct current hybrid power distribution network comprises the following steps:
s1, configuring an additional oscillation suppression controller G (S) on a controller of a three-phase Buck circuit link of an alternating current-direct current distribution network H (S);
s2, determining the configuration parameter alpha of the phase compensation element in the additional controller G (S)1And T1Time constant T of signal filtering linkwA gain coefficient K of the signal;
and S3, superposing the oscillation signal on the current inner ring of the Buck controller through an additional controller G (S).
Further, in step S1, the additional controller g (S) includes a gain element, a signal filtering element and a phase compensation element, and the transfer function can be expressed as:
in the formula, K is the gain coefficient of the gain element, which determines the damping provided for the system,
for the signal filtering stage, TwIs the time constant of the high-pass filter,
for the phase compensation stage, α1Indicating the strength of a single-stage lead link, T1Is the time constant of a single-stage lead link.
Further, the signal filtering element is a high-pass filter for filtering unnecessary low-frequency signals, and the phase compensation element adopts multi-stage phase lead compensation (the stage number m is 1,2, …) for compensating the phase lag brought by the controller.
Further, in step S2, the configuration parameter α of the phase compensation element is determined1And T1Determining the time constant T of the signal filtering elementwDetermining a gain coefficient K of the signal, which comprises the following steps:
the characteristic equation of the system is as follows:
1-G(s)H(s)＝0(2)
wherein H(s) is a transfer function of the multi-port AC/DC distribution network, if s ═ s1Is the root of the above characteristic equation, the following two conditions should be satisfied:
amplitude condition
Phase angle condition
As can be seen from formulas (3) and (4), when s ═ s1When is, H(s)1)G(s1) Has a phase angle of zero, i.e.
θp＝-θh(5)
In the formula (5), θpTo the phase angle of the additional controller, thetahThe phase angle of the multi-port AC/DC hybrid power distribution network, namely the lead phase angle of the additional controller is equal to the lag phase angle of the multi-port AC/DC hybrid power distribution network;
if thetahIf m-stage lead links are adopted for compensation, the compensation phase angle is thetahAnd m, the parameters can be obtained by the basic formula of the lead link:
in the formula (7), ωdThe parameters of the single-stage phase lead link can be calculated by the formulas (6) and (7) for the imaginary part of the characteristic root of the system equation, and the time constant T of the high-pass filtering linkwUsually, 3-5 is taken, so that the transfer function g(s) of the stabilizer is known except for the gain link, the known parameters are substituted into formula (1) to obtain the transfer function of the stabilizer containing gain K, and then the value of K can be calculated by the amplitude condition (3) as follows:
in the formula (8), KhThe amplitude of the transfer function H(s) of the multi-port AC/DC hybrid power distribution network is obtained, so that all parameters of the additional controller G(s) can be obtained.
Further, in step 2, parameters of two-stage phase lead compensation links in the additional controller g(s) are calculated, and the specific steps are as follows:
the phase of the closed-loop transfer function of the system is seen from the ports of the additional controllers G(s), and the root of the system equation is calculated to be approximate to s1＝0.1+j25.5；
The phase position of the port alternating current and direct current hybrid power distribution network system is-97.9 degrees, namely the phase angle needing to be compensated by the additional controller is 97.9 degrees;
if two stages of phase compensation links are adopted, the phase angle compensated by each stage of compensation link is equal, namely, the compensation links compensate 49-degree phase angles, and the parameters of the compensation links at each stage are as follows:
therefore, the additional controller phase compensation element is expressed as
The signal filtering unit is a high-pass filter with time constant TwCan be arbitrarily selected from 3 to 5, in this example, the time constant is 3, and the expression of the high-pass filter is
The gain link of the additional controller is calculated by the formula (8), and the amplitude K of the transfer function of the original multi-port alternating current-direct current hybrid power distribution network modelh3.56, so the additional controller gain factor is calculated as follows:
the gain link coefficient can be obtained by the formula (10);
the expression for the additional controller in this example is given by the above calculation:
further, in step 3, an oscillation signal is superimposed on the current inner ring of the Buck controller through the additional controller G(s), and the voltage waveform of the direct current side is restored to be stable again through a short dynamic process.
The invention also provides a low-frequency oscillation suppression system of the multi-port alternating current and direct current hybrid power distribution network, which adopts the low-frequency oscillation suppression method of the multi-port alternating current and direct current hybrid power distribution network according to any one of claims 1 to 6;
the suppression system comprises an AC/DC distribution network H(s) and an additional controller G(s);
the multi-port AC/DC distribution network H(s) comprises a CHB controller, a DAB controller, a three-phase Buck circuit and a VSC controller, wherein an oscillation suppression additional controller G(s) is configured on a controller of a three-phase Buck circuit link of the AC/DC distribution network H(s), and oscillation signals are superposed on a current inner ring of the three-phase Buck circuit through the additional controller G(s).
Further, the CHB controller is an H-bridge cascaded rectifier that rectifies 10kV ac input voltage to 2200V dc voltage;
the DAB controller is an isolated DC-DC converter and is used for reducing the 2200V direct-current voltage to 750V direct-current voltage;
the three-phase Buck circuit is used for reducing the 750V direct-current voltage to 375V direct-current voltage;
the VSC controller is a three-phase inverter that is grid-connected after converting a 375V dc voltage to a 380V ac, where low frequency oscillations occur on the 375V dc side.
Furthermore, the three-phase Buck circuit adopts a voltage outer ring and current inner ring control mode, acquires the oscillation voltage at the direct current side as an input source, and obtains an additional control signal delta i through an additional controller G(s)sThe additional control signal is added to the current comparison stage of the Buck circuit controller.
Compared with the prior art, the invention has the beneficial effects that: according to the invention, an additional oscillation suppression controller is configured on a controller of a three-phase Buck circuit link of an AC/DC power distribution network; determining configuration parameters of a phase compensation link; determining a time constant of a signal filtering link; determining a gain factor of the signal; the method has the advantages that additional equipment is not needed, the operation is convenient, the damping of the AC/DC distribution network can be effectively improved, the low-frequency oscillation is inhibited, the stability of the system is improved, and the method can be widely applied to the inhibition of the low-frequency oscillation in the AC/DC distribution network containing the power electronic transformer.
The low-frequency oscillation suppression method based on the Buck additional control link of the multi-port alternating current-direct current hybrid power distribution network does not need other engineering changes or reconstruction, does not need additional mechanical equipment, and is convenient to operate, low in engineering implementation cost, simple to implement and wide in applicability.
The invention realizes the compensation of the phase lag of the multi-port AC/DC hybrid power distribution network and has comprehensive inhibiting function.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a flow chart of a low-frequency oscillation suppression method for a multi-port alternating current-direct current hybrid power distribution network in an embodiment of the invention;
FIG. 2 is a schematic diagram of a low-frequency oscillation suppression system of a Buck additional control link according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an example model of a multi-port AC/DC hybrid power distribution network according to an embodiment of the invention;
fig. 4 is a schematic diagram illustrating a comparison of low-frequency oscillation waveforms before and after the additional controller is connected in the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only and do not represent the only embodiments.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The method for suppressing the low-frequency oscillation of the multi-port alternating current-direct current hybrid power distribution network shown in fig. 1 comprises the following steps:
s1, configuring an additional oscillation suppression controller G (S) on a controller of a three-phase Buck circuit link of an alternating current-direct current distribution network H (S);
s2, determining the configuration parameter alpha of the phase compensation element in the additional controller G (S)1And T1Time constant T of signal filtering linkwA gain coefficient K of the signal;
and S3, superposing the oscillation signal on the current inner ring of the Buck controller through an additional controller G (S).
In the embodiment of the present invention, the general structure of the additional controller, in step S1, the additional controller g (S) includes a gain element, a signal filtering element, and a phase compensation element, and the transfer function can be expressed as:
in the formula, K is the gain coefficient of the gain element, which determines the damping provided for the system,
the signal filtering link is a high-pass filter for filtering unnecessary low-frequency signals TwIs the time constant of the high pass filter.
For the phase compensation link, the phase compensation link of the invention adopts multi-stage phase lead compensation (the stage number m is 1,2, …) for compensating the phase lag brought by the controller, wherein, alpha1Indicating the strength of a single-stage lead link, T1Is the time constant of a single-stage lead link.
Additional controlThe phase lead link parameter design in the link is crucial, and in step S2 of the embodiment of the present invention, the configuration parameter α of the phase compensation link is determined1And T1Determining the time constant T of the signal filtering elementwDetermining a gain coefficient K of the signal, which comprises the following steps:
the characteristic equation of the system is as follows:
1-G(s)H(s)＝0 (2)
wherein H(s) is a transfer function of the multi-port AC/DC distribution network, if s ═ s1Is the root of the above characteristic equation, the following two conditions should be satisfied:
amplitude condition
Phase angle condition
As can be seen from formulas (3) and (4), when s ═ s1When is, H(s)1)G(s1) Has a phase angle of zero, i.e.
θp＝-θh(5)
In the formula (5), θpTo the phase angle of the additional controller, thetahThe phase angle of the multi-port AC/DC hybrid power distribution network, namely the lead phase angle of the additional controller is equal to the lag phase angle of the multi-port AC/DC hybrid power distribution network.
If thetahIf m-stage lead links are adopted for compensation, the compensation phase angle is thetahAnd m, the parameters can be obtained by the basic formula of the lead link:
in the formula (7), ωdThe parameters of the single-stage phase lead link can be calculated by the formulas (6) and (7) for the imaginary part of the characteristic root of the system equation, and the time constant T of the high-pass filtering linkwUsually, 3-5 is taken, so that the transfer function g(s) of the stabilizer is known except for the gain link, the known parameters are substituted into formula (1) to obtain the transfer function of the stabilizer containing gain K, and then the value of K can be calculated by the amplitude condition (3) as follows:
in the formula (8), KhThe amplitude of the transfer function H(s) of the multi-port AC/DC hybrid power distribution network is obtained, so that all parameters of the additional controller G(s) can be obtained.
In the preferred embodiment of the present invention, the parameters of the two-stage phase lead compensation link in the additional controller g(s) are calculated in step 2, and the specific steps are as follows:
as can be seen from equation (5), to determine the phase angle to be compensated by the additional controller, the phase of the original multiport AC/DC hybrid power distribution network model is first calculated, as shown in FIG. 3, the phase of the closed-loop transfer function of the outward-looking system at the port of the additional controller G(s) is calculated, and the root of the system equation is approximated to s1The phase of the port ac/dc hybrid power distribution network system is-97.9 °, i.e., the phase angle that the additional controller needs to compensate is 97.9 °;
if two stages of phase compensation links are adopted, the phase angle compensated by each stage of compensation link is equal, namely, the compensation links compensate 49-degree phase angles, and the parameters of the compensation links at each stage are as follows:
therefore, the additional controller phase compensation element is expressed as
The signal filtering unit is a high-pass filter with time constant TwCan be arbitrarily selected from 3 to 5, in this example, the time constant is 3, and the expression of the high-pass filter is
The gain link of the additional controller is calculated by the formula (8), and the amplitude K of the transfer function of the original multi-port alternating current-direct current hybrid power distribution network modelh3.56, so the additional controller gain factor is calculated as follows:
the gain element coefficient can be obtained from equation (10).
The expression for the additional controller in this example is given by the above calculation:
in step 3 of the preferred embodiment of the present invention, the oscillation signal is superimposed on the current inner loop of the Buck controller through the additional controller g(s), and the voltage waveform of the dc side is restored to be stable again through a short dynamic process.
The invention also provides an alternating current and direct current mixed low-frequency oscillation suppression system, referring to fig. 3, the specific implementation manner of the additional controller is that the suppression system comprises an alternating current and direct current distribution network H(s) and an additional controller G(s), and the additional controller G(s) adopts the alternating current and direct current mixed low-frequency oscillation suppression method;
the invention discloses a low-frequency oscillation suppression system based on a Buck additional control link of a multi-port alternating current-direct current hybrid power distribution network, wherein four types of equipment are arranged in the multi-port alternating current-direct current hybrid power distribution network, the multi-port alternating current-direct current power distribution network H(s) comprises a CHB controller, a DAB controller, a three-phase Buck circuit and a VSC controller, an oscillation suppression additional controller G(s) is configured on the controller of the three-phase Buck circuit link of the alternating current-direct current power distribution network H(s), and oscillation signals are superposed on a current inner ring of the three-phase Buck circuit through the additional controller G(s).
As shown in fig. 4, before the additional controller g(s) is connected, the system operates stably until t is 2s, the dc-side voltage waveform has no oscillation, the oscillation is excited at the time t is 2s, the dc-side voltage waveform shows low-frequency oscillation, and when the additional controller is connected at the time t is 3s, the dc-side voltage waveform resumes to be stable again through a short dynamic process. Therefore, the low-frequency oscillation suppression method based on the Buck additional control link of the multi-port alternating current-direct current hybrid power distribution network is correct, and can play a role in increasing damping and suppressing low-frequency oscillation when applied to an actual system.
On the basis of the above embodiment, the CHB controller is an H-bridge cascade rectifier that rectifies 10kV ac input voltage to 2200V dc voltage; the DAB controller is an isolated DC-DC converter and is used for reducing the 2200V direct-current voltage to 750V direct-current voltage; the three-phase Buck circuit is used for reducing the 750V direct-current voltage to 375V direct-current voltage; the VSC controller is a three-phase inverter that is grid-connected after converting a 375V dc voltage to a 380V ac, where low frequency oscillations occur on the 375V dc side.
The three-phase Buck circuit adopts a voltage outer ring and current inner ring control mode, acquires the oscillation voltage at the direct current side as an input source, and obtains an additional control signal delta i through an additional controller G(s)sThe additional control signal is added to a current comparison link of the Buck circuit controller, so that the damping of the whole alternating current-direct current distribution network can be increased, and the oscillation is restrained.
It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (9)
1. A low-frequency oscillation suppression method for a multi-port alternating current-direct current hybrid power distribution network is characterized by comprising the following steps:
s1, configuring an additional oscillation suppression controller G (S) on a controller of a three-phase Buck circuit link of an alternating current-direct current distribution network H (S);
s2, determining the configuration parameter alpha of the phase compensation element in the additional controller G (S)1And T1Time constant T of signal filtering linkwA gain coefficient K of the signal;
and S3, superposing the oscillation signal on the current inner ring of the Buck controller through an additional controller G (S).
2. The method for suppressing low frequency oscillation in a multiport ac/dc hybrid power distribution network according to claim 1, wherein in step S1, the additional controller g (S) includes a gain element, a signal filtering element and a phase compensation element, and the transfer function can be expressed as:
in the formula, K is the gain coefficient of the gain element, which determines the damping provided for the system,
for the signal filtering stage, TwIs the time constant of the high-pass filter,
for the phase compensation stage, α1Indicating the strength of a single-stage lead link, T1Is the time constant of a single-stage lead link.
3. The method for suppressing the low-frequency oscillation of the multiport alternating current-direct current hybrid power distribution network according to claim 2, wherein the signal filtering unit is a high-pass filter for filtering unnecessary low-frequency signals, and the phase compensation unit adopts multi-stage phase lead compensation (the stage number m is 1,2, …) for compensating the phase lag brought by the controller.
4. The method for suppressing the low-frequency oscillation of the multi-port AC/DC hybrid power distribution network according to claim 2, wherein in step S2, the configuration parameter α of the phase compensation element is determined1And T1Determining the time constant T of the signal filtering elementwDetermining a gain coefficient K of the signal, which comprises the following steps:
the characteristic equation of the system is as follows:
1-G(s)H(s)＝0 (2)
wherein H(s) is a transfer function of the multi-port AC/DC distribution network, if s ═ s1Is the root of the above characteristic equation, the following two conditions should be satisfied:
amplitude condition
Phase angle condition
As can be seen from formulas (3) and (4), when s ═ s1When is, H(s)1)G(s1) Has a phase angle of zero, i.e.
θp＝-θh (5)
In the formula (5), θpTo the phase angle of the additional controller, thetahThe phase angle of the multi-port AC/DC hybrid power distribution network, namely the lead phase angle of the additional controller is equal to the lag phase angle of the multi-port AC/DC hybrid power distribution network;
if thetahIf m-stage lead links are adopted for compensation, the compensation phase angle is thetahAnd m, the parameters can be obtained by the basic formula of the lead link:
in the formula (7), ωdThe parameters of the single-stage phase lead link can be calculated by the formulas (6) and (7) for the imaginary part of the characteristic root of the system equation, and the time constant T of the high-pass filtering linkwUsually, 3-5 is taken, so that the transfer function g(s) of the stabilizer is known except for the gain link, the known parameters are substituted into formula (1) to obtain the transfer function of the stabilizer containing gain K, and then the value of K can be calculated by the amplitude condition (3) as follows:
in the formula (8), KhThe amplitude of the transfer function H(s) of the multi-port AC/DC hybrid power distribution network is obtained, so that all parameters of the additional controller G(s) can be obtained.
5. The method for suppressing the low-frequency oscillation of the multi-port alternating current-direct current hybrid power distribution network according to claim 4, wherein in the step 2, parameters of a two-stage phase lead compensation link in an additional controller G(s) are calculated, and the specific steps are as follows:
the phase of the closed-loop transfer function of the system is seen from the ports of the additional controllers G(s), and the root of the system equation is calculated to be approximate to s1＝0.1+j25.5；
The phase position of the port alternating current and direct current hybrid power distribution network system is-97.9 degrees, namely the phase angle needing to be compensated by the additional controller is 97.9 degrees;
if two stages of phase compensation links are adopted, the phase angle compensated by each stage of compensation link is equal, namely, the compensation links compensate 49-degree phase angles, and the parameters of the compensation links at each stage are as follows:
therefore, the additional controller phase compensation element is expressed as
The signal filtering unit is a high-pass filter with time constant TwCan be arbitrarily selected from 3 to 5, in this example, the time constant is 3, and the expression of the high-pass filter is
The gain link of the additional controller is calculated by the formula (8), and the amplitude K of the transfer function of the original multi-port alternating current-direct current hybrid power distribution network modelh3.56, so the additional controller gain factor is calculated as follows:
the gain link coefficient can be obtained by the formula (10);
the expression for the additional controller in this example is given by the above calculation:
6. the method for suppressing the low-frequency oscillation of the multi-port AC/DC hybrid power distribution network according to claim 1, wherein in the step 3, the oscillation signal is superimposed on the current inner ring of the Buck controller through an additional controller G(s), and the DC side voltage waveform is restored to be stable again through a short dynamic process.
7. The system for suppressing low frequency oscillation of a multi-port AC/DC hybrid power distribution network according to claim 1, wherein the suppression system adopts the method for suppressing low frequency oscillation of a multi-port AC/DC hybrid power distribution network according to any one of claims 1 to 6;
the suppression system comprises an AC/DC distribution network H(s) and an additional controller G(s);
the multi-port AC/DC distribution network H(s) comprises a CHB controller, a DAB controller, a three-phase Buck circuit and a VSC controller, wherein an oscillation suppression additional controller G(s) is configured on a controller of a three-phase Buck circuit link of the AC/DC distribution network H(s), and oscillation signals are superposed on a current inner ring of the three-phase Buck circuit through the additional controller G(s).
8. The system for suppressing low frequency oscillations in a multiport AC/DC hybrid power distribution network according to claim 7, wherein said CHB controller is an H-bridge cascaded rectifier rectifying a 10kV AC input voltage to a 2200V DC voltage;
the DAB controller is an isolated DC-DC converter and is used for reducing the 2200V direct-current voltage to 750V direct-current voltage;
the three-phase Buck circuit is used for reducing the 750V direct-current voltage to 375V direct-current voltage;
the VSC controller is a three-phase inverter that is grid-connected after converting a 375V dc voltage to a 380V ac, where low frequency oscillations occur on the 375V dc side.
9. The system for suppressing low-frequency oscillation of the multi-port AC/DC hybrid power distribution network according to claim 7, wherein the three-phase Buck circuit adopts a voltage outer loop and current inner loop control mode, collects the oscillation voltage at the DC side as an input source, and obtains an additional control signal Δ i through an additional controller G(s)sThe additional control signal is added to the current comparison stage of the Buck circuit controller.
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