CN115333139A

CN115333139A - Flexible direct current transmission control method, electronic equipment and medium

Info

Publication number: CN115333139A
Application number: CN202211066374.4A
Authority: CN
Inventors: 王一凡; 吕敬; 武文; 尹嘉豪; 邹祖冰; 蔡旭
Original assignee: China Three Gorges Corp
Current assignee: China Three Gorges Corp
Priority date: 2022-07-07
Filing date: 2022-07-07
Publication date: 2022-11-11
Also published as: CN114865684A; CN114865684B

Abstract

The invention discloses a flexible direct current transmission control method, electronic equipment and a medium, wherein the method is applied to a flexible direct current transmission system, the system comprises a flexible direct current converter, a transformer and an equivalent circuit, the control circuit comprises a detection module and a control module, and the method comprises the following steps: the control module receives the resonance dominant frequency and the resonance amplitude value output by the detection module, and adjusts filter parameters of a first filter, a second filter and a third filter according to the resonance dominant frequency; when the adjusted filter parameters are matched with the resonance dominant frequency and the resonance amplitude is larger than or equal to a preset value, a first control signal is generated and sent to the flexible direct current converter, and the first control signal is used for controlling at least one filter to work according to the matched filter parameters.

Description

Flexible direct current transmission control method, electronic equipment and medium

This application is a divisional application, filed on even 202210795192.4, filed on 7/2022, and incorporated by reference herein in its entirety.

Technical Field

The invention relates to the field of flexible direct current transmission, in particular to a flexible direct current transmission control method, electronic equipment and a medium.

Background

Under the development background of 'double high' of a power system, a Modular Multilevel Converter (MMC) has the advantages of low switching frequency, high waveform quality, good controllability, easiness in expansion and the like, is widely applied to occasions such as offshore wind power direct current output and alternating current power grid interconnection and is an important development direction of a medium-high voltage high-power transmission technology. The flexible direct-current transmission technology based on the MMC is also developed rapidly due to the advantages of strong fault ride-through capability of the system, convenience in pressurization and expansion and the like. However, in practical engineering, due to the interaction between the compliance-dc converter and the power grid, high frequency resonance with a frequency of several hundred hertz (Hz) to kilohertz (khz) may occur, which may cause problems such as harmonic overvoltage, overcurrent, converter station trip, power surplus or shortage, and may seriously affect the quality of electric energy and the stability of the system, so that it is necessary to suppress the high frequency resonance.

At present, a method for suppressing high frequency resonance of a flexible direct system has been proposed, which adds a filter, such as a low pass filter, a band stop filter, etc., to a voltage feed-forward channel in a circuit to suppress the generation of high frequency resonance by limiting the transmission of a high frequency signal through the feed-forward channel. In addition, passive damping is added, such as connecting a passive impedance adapter in parallel at a Point of Common Coupling (PCC), subdividing bridge arm inductances, connecting the passive damping in parallel at the same time, adding a passive filter at the PCC, and the like, so that the impedance characteristic of a high-frequency band is changed by adding an actual physical element, and thus, the condition generated by resonance is avoided.

The method also comprises the steps of changing the structure of the controller, such as superposing a feedforward voltage with a current loop reference current through a high-frequency resonance damping controller, connecting a virtual impedance active damping control and a nonlinear voltage feedforward control in series in a current inner loop, connecting a low-pass filter in series in a current inner loop proportion link, adding a first-order high-pass filtering link and a virtual resistance adjusting link modulation channel, adopting an open-loop control method and the like, improving the impedance characteristic of a high-frequency band by adjusting a control strategy, and improving the phase margin in a specific frequency band so as to inhibit high-frequency resonance.

However, the resonance suppression methods proposed by the above methods are all adapted to specific operating conditions under specific parameters after obtaining the impedance characteristics in a specific frequency band through off-line analysis, and cannot effectively suppress the high-frequency resonance phenomenon of different frequencies under different operating conditions. In addition, the partial suppression method requires a passive device or a large number of filters to be previously arranged in the control system, resulting in high investment cost.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a control circuit and a control method of a flexible direct current transmission system, which can adapt to different power grid operation conditions and realize the inhibition of high-frequency resonance phenomena in different frequency bands. In order to solve the above technical problems, embodiments of the present invention specifically provide the following technical solutions:

in a first aspect, an embodiment of the present invention provides a control circuit of a flexible dc power transmission system, where the system includes a flexible dc converter, a transformer and an equivalent circuit, a PCC is located between the transformer and the equivalent circuit, and the control circuit is connected between the flexible dc converter and the PCC, and the control circuit includes: the device comprises a detection module and a control module;

the detection module is used for acquiring a voltage signal of the PCC point and outputting a resonant dominant frequency and a harmonic amplitude value according to the voltage signal;

the control module is configured to receive the resonant dominant frequency and the harmonic amplitude value output by the detection module, adjust at least one filter parameter in the flexible dc converter according to the resonant dominant frequency, so that the at least one filter parameter matches the resonant dominant frequency, and detect that when the resonant amplitude value meets a preset condition, a first control signal is generated and sent to the flexible dc converter, where the first control signal is used to control the at least one filter to operate according to the matched filter parameter.

With reference to the first aspect, in a possible implementation manner of the first aspect, the flexible dc converter includes: the device comprises a PI controller, a delayer, a main circuit equivalent module, a first filter, a second filter and a third filter, wherein the first filter is a voltage feedforward channel filter, the second filter is a voltage feedforward additional reference current channel filter, and the third filter is a current feedback additional modulation channel filter;

the control module is specifically configured to adjust the gain and the cutoff frequency of the first filter, the second filter, and the third filter according to the resonant dominant frequency.

With reference to the first aspect, in another possible implementation manner of the first aspect, the control module is specifically configured to adjust a cutoff frequency of a first-order low-pass filter in the second filter to be equal to the resonance dominant frequency, where the resonance dominant frequency is a frequency component with a largest ratio of an amplitude to a fundamental frequency amplitude.

With reference to the first aspect, in yet another possible implementation manner of the first aspect, the control module is specifically configured to obtain a system delay, calculate a frequency corresponding to a reciprocal of the system delay, perform a modulus operation on the frequency by using the resonant dominant frequency to obtain a modulus result, determine a gain function where the modulus result is located, and adjust a gain of the third filter to a function value corresponding to the gain function.

In a second aspect, an embodiment of the present invention provides a control method for a flexible direct current power transmission system, where the method is applied to a control circuit in the foregoing first aspect and in various implementation manners of the first aspect, and the method includes:

collecting a voltage signal of a PCC point of the flexible direct current power transmission system;

outputting a harmonic dominant frequency and amplitude value of resonance according to the voltage signal;

adjusting at least one filter parameter in a flexible direct current converter according to the resonance dominant frequency to enable the at least one filter parameter to be matched with the resonance dominant frequency;

when the resonance amplitude is detected to meet a preset condition, generating a first control signal;

and sending the first control signal to the flexible direct current converter, wherein the first control signal is used for controlling the at least one filter to work according to matched filtering parameters.

With reference to the second aspect, in a possible implementation manner of the second aspect, the outputting a resonant dominant frequency and a harmonic amplitude value according to the voltage signal includes:

processing the voltage signal by using fast Fourier transform to obtain at least one amplitude, wherein each amplitude corresponds to a frequency component; calculating the ratio of each amplitude to the fundamental frequency amplitude, and determining a frequency component with the maximum ratio; and determining the main resonance frequency as the frequency component with the maximum ratio, and determining the harmonic amplitude value as the amplitude corresponding to the frequency component with the maximum ratio.

With reference to the second aspect, in another possible implementation manner of the second aspect, the flexible dc converter includes: the main circuit comprises a PI controller, a delayer, a main circuit equivalent module, a first filter, a second filter and a third filter, wherein the first filter is a voltage feedforward channel filter, the second filter is a voltage feedforward additional reference current channel filter, and the third filter is a current feedback additional modulation channel filter;

adjusting at least one filter parameter in the flexible DC converter according to the main resonant frequency, including: adjusting the gain and cut-off frequency of the first filter, the second filter, and the third filter, respectively, according to the resonance dominant frequency.

With reference to the second aspect, in yet another possible implementation manner of the second aspect, the adjusting the gain of the third filter according to the main resonant frequency includes: obtaining system delay; calculating the frequency corresponding to the system delay reciprocal; performing a modulus operation on the frequency by the resonance dominant frequency to obtain a modulus result; and determining a gain function where the modulus-taking result is located, and adjusting the gain of the third filter to be a function value corresponding to the gain function.

With reference to the second aspect, in a further possible implementation manner of the second aspect, when it is detected that the resonance amplitude satisfies a preset condition, generating a first control signal includes: and when the resonance amplitude is detected to be larger than or equal to a preset value, generating the first control signal.

With reference to the second aspect, in yet another possible implementation manner of the second aspect, the method further includes: when the resonance amplitude value corresponding to the voltage signal is detected to be smaller than the preset value, generating a second control signal; and sending the second control signal to the flexible direct current converter, wherein the second control signal is used for controlling a first filter, a second filter and a third filter in the flexible direct current converter to stop working.

In a third aspect, an embodiment of the present invention further provides an electronic device, including: a processor and a memory, the memory to store computer-executable instructions; the processor is configured to read the instructions from the memory and execute the instructions to implement the methods according to the second aspect and the various implementation manners of the second aspect.

In a fourth aspect, an embodiment of the present invention further provides a computer-readable storage medium, where the storage medium stores computer program instructions, and when the computer reads the instructions, the method described in the foregoing second aspect and various implementation manners of the second aspect is performed.

Furthermore, the present invention also provides a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium, the computer program including program instructions that, when executed by a computer, cause the computer to perform the method in the foregoing second aspect or various implementations of the second aspect.

The control circuit and the control method provided by the embodiment of the invention are suitable for different power grid operation conditions, can effectively inhibit high-frequency resonance phenomena of different frequency bands, and have stronger robustness.

In addition, in the control circuit provided by the above embodiment, the first, second and third filters to be controlled are all active digital filtering devices, so that it is not necessary to configure a large number of filters in advance, and it is not necessary to configure passive capacitance and inductance devices, thereby reducing investment cost and saving overhead.

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, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 is a schematic diagram of a flexible dc power transmission system according to an embodiment of the present invention;

fig. 2 is a schematic diagram of another flexible dc power transmission system according to an embodiment of the present invention;

fig. 3 is a block diagram of a flexible dc converter according to an embodiment of the present invention;

fig. 4 is a block diagram of another flexible dc converter according to an embodiment of the present invention;

fig. 5 is a flowchart of a control method of a flexible dc power transmission system according to an embodiment of the present invention;

fig. 6 is a flowchart of another method for controlling a flexible dc power transmission system according to an embodiment of the present invention;

fig. 7 is a flowchart of a control method of a flexible direct-current power transmission system according to another embodiment of the present invention;

FIG. 8 is a graph of a linear function of a dominant resonant frequency and a gain according to an embodiment of the present invention;

FIG. 9a is a diagram illustrating simulation results according to an embodiment of the present invention;

fig. 9b is a schematic diagram of another simulation result according to the embodiment of the present invention.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1 to fig. 4, the flexible dc power transmission system and the adaptive high-frequency resonance suppression circuit of the present invention are described in detail in this embodiment.

Fig. 1 is a schematic diagram of a flexible dc power transmission system according to an embodiment of the present invention. This flexible direct current transmission system includes: the system comprises a modular multilevel converter MMC, a transformer, a pi-type equivalent circuit and an alternating current power grid. And these elements/components are serially linked, where PCC is the point of common connection, v _g Representing the AC mains voltage v _dc Indicates the DC side voltage v _pcc Representing the PCC point voltage signal, i _g Representing the grid current, i _dc The pi-type equivalent circuit is formed by series-parallel connection of a resistance inductor and a capacitor. The pi-type equivalent circuit comprises one or more circuit elements such as a resistor, a capacitor, an inductor and the like.

The MMC is connected with a high-voltage direct-current transmission line on the direct-current side, and the alternating-current side is connected with an alternating-current power grid through a transformer and a pi-type equivalent circuit. Based on the system, the embodiment provides the adaptive high-frequency resonance suppression circuit of the flexible direct-current power transmission system, which is used for suppressing the high-frequency resonance phenomenon.

Optionally, the MMC is a flexible dc Converter, and in addition, the MMC may be replaced with another Converter, such as a Voltage Source Converter (VSC). In this embodiment, a flexible dc converter is taken as an MMC for example.

Referring to fig. 2, a schematic diagram of another flexible dc power transmission system according to an embodiment of the present invention is shown. The system comprises: the system comprises a flexible direct current converter, a transformer and an equivalent circuit, wherein a common connection point PCC of the system is positioned between the transformer and the equivalent circuit, the equivalent circuit can be a pi-type equivalent circuit, and a control circuit is added on the basis of the structure shown in figure 1 and is connected between the flexible direct current converter and the PCC, as shown by a dashed box in figure 2.

The control circuit includes: the device comprises a detection module and a control module. Further, the air conditioner is provided with a fan,

the detection module is used for acquiring a voltage signal v of the PCC point _pcc And outputting the resonant dominant frequency and harmonic amplitude value according to the voltage signal.

Optionally, the dominant resonant frequency output by the detection module is f _HFR Harmonic amplitude value of A _HFR 。

And the control module is used for receiving the resonance dominant frequency and the harmonic amplitude value output by the detection module, and adjusting at least one filter parameter in the flexible direct current converter according to the resonance dominant frequency so as to enable the at least one filter parameter to be matched with the resonance dominant frequency. And detecting that a first control signal is generated when the resonance amplitude meets a preset condition, and sending the first control signal to the flexible direct current converter, wherein the first control signal is used for controlling at least one filter to work according to matched filtering parameters.

Wherein at least one filter coefficient is associated with a dominant resonance frequency f _HFR Matching means that the dominant frequency f is based on the resonance _HFR And the gain and the cut-off frequency of each filter are adaptively adjusted, so that the adjusted parameters of the filter, such as the gain, the cut-off frequency and the like, play a role in inhibiting high-frequency resonance on the whole system.

When the detection module detects that the system generates high-frequency resonance, that is, meets a preset condition, for example, the harmonic amplitude value is A _HFR And when the current gain and the cut-off frequency are larger than or equal to the preset value, generating a first control signal, and sending the first control signal to the MMC, so that each filter in the MMC works according to the currently adjusted gain and cut-off frequency, and high-frequency resonance is restrained.

Furthermore, if it is detected that the currently obtained resonance amplitude does not satisfy a preset condition, such as A _HFR And when the frequency of the input signal is less than the preset value, the system does not generate high-frequency resonance, and at the moment, the control module generates other control signals and sends the control signals to the flexible direct current converter so that at least one filter in the flexible direct current converter does not work. The control module generates a control signal in real time according to the resonance dominant frequency and the harmonic amplitude value output by the detection module to control whether at least one filter in the MMC is put into operation or not, and when the filters are controlled to be put into operation, the high-frequency resonance of the system can be inhibited.

Referring to fig. 3 and fig. 4, a structure of a flexible dc converter is provided for the present embodiment, where a basic portion of the flexible dc converter related to a control structure includes: PI controller, delayer, main circuit equivalent module. Wherein, the PI controller is also called as current PI controller (H) _i ) The delayer can be a control delay link (G) _d ) The main circuit equivalent module is (1/(sL) _eq +R _eq ))。

In addition, a first filter (filter 1), a second filter (filter 2) and a third filter (filter 3) are added to the basic part, wherein the first filter is a voltage feedforward channel filter and can be expressed as F _lpf (ii) a The second filter is a voltage feedforward additional reference current path filter, which may be denoted as F _damp1 (ii) a The third filter is a current feedback additional modulation channel filter, which may be denoted as F _damp2 . Optionally, the first, second and third filters are active digital filter devices.

Further, F _lpf A second-order low-pass filter; f _damp1 Including a gain K _damp1 Two first-order low-pass filters, respectively denoted as F _lpf1 、F _lpf2 And additionally a first order high pass filter, which may be writtenIs H _hpf ；F _damp2 Including a gain K _damp2 First order high pass filter H _hpf And a current controller H _i 。

The control module is specifically configured to adjust the gain and the cutoff frequency of the first filter, the second filter, and the third filter, respectively, according to the main resonant frequency. In this embodiment, the control module mainly adjusts two parameters, one is low-pass filtering F _lpf2 Another is the gain K _damp2 The remaining parameters may be obtained as preset.

The two parameters to be adjusted are both in accordance with the dominant frequency f of the system resonance _HFR And (4) correlating. The following will specifically describe the design scheme of the adaptive control architecture:

one specific implementation is according to a simplified high-frequency impedance model, which is shown in expression (1):

in the expression (1), Z _p Indicating the positive sequence impedance, L, of the soft DC converter in the high frequency range _eq And R _eq Respectively representing the equivalent inductance and resistance of the AC side, H _i Indicating current inner loop PI controller, G _d The delay is controlled for the system.

In the specific regulation process, the time delay G is controlled for counteracting the numerator denominator term _d The influence brought by the feed-forward voltage is reduced, and a control structure filter F is respectively added on a voltage feed-forward channel, a voltage feed-forward additional reference current channel and a current feedback additional modulation channel _lpf 、F _damp1 、F _damp2 And these filters are arranged to satisfy the following relational expressions (2) to (4):

F _damp1 ＝K _damp1 F _lpf1 F _lpf2 H _hpf (3)

F _damp2 ＝K _damp2 H _i H _hpf (4)

wherein f is _cr Representing the cut-off frequency, ω, of the low-pass filter _cr Representing the cut-off angular frequency, ξ representing the damping ratio (selectable between 0.5 and 1), K _f For voltage feedforward coefficient, default K is used in system analysis _f ＝1；K _damp1 The gain factor can be taken as the inverse of the current loop scaling factor.

Further, F _lpf1 Low pass filter representing a lower cut-off frequency, the cut-off frequency being in accordance with a feed-forward path low pass filter F _lpf Same, F _lpf2 A low-pass filter representing a higher cut-off frequency, the cut-off frequency of which is related to the resonance frequency, H _hpf A first order high pass filter with a cut-off frequency higher than 50Hz and lower than 200Hz to pass high frequency components and block fundamental frequency components; k is _damp2 Is a gain factor, related to the resonant frequency and system delay, and can be considered as a virtual impedance, H _i And the current inner loop PI control link is shown. In this embodiment, when f _cr When 65Hz is taken, xi is 0.707, K _damp1 Is 5,H _hpf The cut-off frequency of (2) is 100Hz.

In addition, optionally, at least one filter parameter in the flexible dc converter is matched with the main resonant frequency, and the method includes: adjusting the cut-off frequency of a first-order low-pass filter in the second filter to be equal to the dominant resonant frequency f by means of a control module _HFR The dominant frequency f of resonance _HFR The frequency component with the maximum ratio of the amplitude to the fundamental frequency amplitude is obtained, and the gain of the third filter is adjusted to be a function value corresponding to the gain function.

Further, the control module is specifically configured to obtain a system delay, calculate a frequency corresponding to a reciprocal of the system delay, perform a modulo operation on the frequency by using the resonant dominant frequency to obtain a modulo result, determine a gain function where the modulo result is located, and adjust a gain of the third filter to a function value corresponding to the gain function.

The control module determines a first order low pass filter F _lpf2 Cut-off frequency and gain factor K of _damp2 The procedure for this is described in detail in the method examples which follow.

It should be noted that the detection module and the control module of the control circuit provided in this embodiment may be integrated into one module, or may be respectively disposed on two or more functional modules. In addition, the control module may also be disposed inside the MMC, and the structure, position, and form of the detection module and the control module are not particularly limited in this embodiment.

The control circuit provided by the embodiment is suitable for different power grid operation conditions, can effectively inhibit high-frequency resonance phenomena of different frequency bands, and has stronger robustness.

In addition, in the control circuit, the first filter, the second filter and the third filter which are controlled are all active digital filter devices, so that a large number of filters do not need to be arranged in advance, and a passive capacitance and inductance device does not need to be arranged, thereby reducing the investment cost.

The method for suppressing high frequency resonance provided by the present embodiment will be discussed in detail below.

The embodiment provides a control method of a flexible direct current power transmission system, the method is applied to the control circuit shown in fig. 2, and on the basis of the control circuit, the embodiment provides a control method, and an execution subject of the method can be the control circuit in the foregoing circuit embodiment, such as the detection module and the control module. As shown in fig. 5, the control method includes the steps of:

step 101: and acquiring a voltage signal of a PCC point of the flexible direct current power transmission system.

Step 102: and outputting a resonance dominant frequency and a harmonic amplitude value according to the voltage signal.

Step 103: and adjusting at least one filter parameter in the flexible direct current converter according to the resonance dominant frequency to enable the at least one filter parameter to be matched with the resonance dominant frequency.

Wherein the at least one filter comprises a first, a second and a third filter, and the filteringThe parameters of the device include the low-pass filtering F _lpf2 Cut-off frequency, gain K _damp2 And other parameters K _damp1 Voltage feedforward coefficient K _f And the matching means that the relations (2) to (4) are satisfied, and specific reference is made to the description of the circuit device part, which is not described herein again.

Step 104: and generating a first control signal when the resonance amplitude is detected to meet a preset condition.

Step 105: and sending the first control signal to the flexible direct current converter, wherein the first control signal is used for controlling the at least one filter to work according to matched filtering parameters.

Specifically, the first control signal is sent to the MMC, so that a first filter, a second filter and a third filter in the MMC are all put into operation, and after the filters adjust parameters such as cut-off frequency, gain and the like according to the resonance dominant frequency, the voltage feedforward is added to a reference current channel F _damp1 And current feedback additional modulation path F _damp2 Are all turned on, so that high frequency resonance can be effectively suppressed.

According to the control method provided by the embodiment, the voltage signal of the PCC point is collected, the resonance dominant frequency and the harmonic amplitude value of the system are output, and the control signal is generated according to the output results so as to adjust the relevant parameters of each filter in the MMC, so that the adjusted filters work to effectively inhibit the high-frequency resonance of the system.

In addition, the method can be suitable for different power grid operation conditions, for example, the method is suitable for occasions considering negative sequence current control, and therefore the method has stronger robustness.

Optionally, in a specific implementation manner, as shown in fig. 6, the step 102 specifically includes:

step 102-1: and processing the voltage signal by using fast Fourier transform to obtain at least one amplitude, wherein each amplitude corresponds to one frequency component.

Specifically, the detection module utilizes Fast Fourier Transform (FFT) to detect the voltage signal v acquired at the current time _pcc To perform treatmentAnd obtaining a plurality of voltage amplitudes, wherein each amplitude corresponds to one frequency component.

Step 102-2: the ratio of each of said amplitudes to the amplitude of the fundamental frequency is calculated and the frequency component with the largest ratio is determined.

The fundamental frequency amplitude may be a preset value/fixed value, each amplitude obtained in step 102-1 is subjected to quotient calculation with the fundamental frequency amplitude, all ratio results are compared, and one amplitude with the largest ratio is selected.

Step 102-3: and determining the main resonance frequency as the frequency component with the maximum ratio, and determining the harmonic amplitude value as the amplitude corresponding to the frequency component with the maximum ratio.

Taking the amplitude with the maximum ratio determined in the previous step as the harmonic amplitude value A _HFR . Correspondingly, the frequency component with the largest ratio is taken as the main resonance frequency f _HFR 。

In a specific example, assume every t _s Acquiring a voltage signal at the PCC point once in every 100 mu s seconds with a sampling rate f _s ＝1/t _s =10kHz, and if the FFT is performed on the acquired signal at N =2000 points, the frequency resolution of the signal is f _s The detection method has the advantages that the calculation speed and the detection precision are simultaneously considered, and the method is suitable for high-frequency resonance occasions.

According to the result obtained by FFT calculation, each frequency component f can be obtained _i Amplitude A of _i Where f is _i Is 5n Hz, N =0,1, \ 8230, N-1. For example, when n =0, fi =0hz; when n =1, fi =5hz; when n =2, fi =10hz; since the high-frequency resonant frequency is generally in the range of 200-3000 Hz, only the range of n = 40-600 needs to be paid attention to, and the frequency component with the maximum amplitude is found in the range, namely the main resonant frequency f _HFR The corresponding amplitude is the harmonic amplitude value A _HFR . Subsequently, a low-pass filter F is applied _lpf2 Is set to f _HFR 。

Optionally, in another specific implementation manner, the flexible dc converter, such as an MMC, includes: the device comprises a PI controller, a delayer, a main circuit equivalent module, a first filter, a second filter and a third filter. The first filter is a voltage feedforward channel filter, the second filter is a voltage feedforward additional reference current channel filter, and the third filter is a current feedback additional modulation channel filter.

The foregoing step 103: adjusting at least one filter parameter in the flexible direct current converter according to the main resonant frequency, specifically comprising: according to the dominant frequency f of resonance _HFR Adjusting gains K of the first filter, the second filter and the third filter, respectively _damp2 And a low-pass filter F _lpf2 The cut-off frequency. In addition, other parameters may be preset.

Further, the control module is utilized to conduct the frequency f according to the resonance dominant frequency _HFR Adjusting the gain K of the third filter _damp2 As shown in fig. 7, the specific process includes:

step 201: and obtaining system delay.

The delay element (G) can be controlled as shown in FIG. 3 or FIG. 4 _d ) The delay of the system is obtained, which can be denoted as T _d And reports to the control circuit. Delay T of the system _d May be collected and reported periodically.

Step 202: and calculating the frequency corresponding to the system delay reciprocal.

In particular, the system delay T can be calculated _d Frequency f corresponding to reciprocal _T 。

Step 203: and carrying out modulus operation on the frequency by the resonance dominant frequency to obtain a modulus result.

In particular, the dominant frequency f of resonance _HFR For frequency f _T Taking the mode, the operation of taking the mode is to make the main resonant frequency f _HFR Limited to one frequency period 1/f _T And (4) the following steps. Judging whether the obtained fruiting falls into (0, f) _T /2) or (f) _T /2,f _T ) Wherein (0, f) _T /2)、(f _T /2,f _T ) As a two-piece linear function, as shown in FIG. 8, (0, f) _T Per 2) is an increasing function, (f) _T /2,f _T ) Is a decreasing function.

Step 204: and determining a gain function where the modulus-taking result is located, and adjusting the gain of the third filter to be a function value corresponding to the gain function.

Wherein the gain function can be illustrated by the curve of fig. 8, representing the dominant resonant frequency f _HFR And a gain F _damp2 Corresponding relation between the frequency bands, 1/f in one frequency cycle _T Internal, known resonant dominant frequency f _HFR Corresponding gains F can be obtained _damp2 。

In this embodiment, if the system control delay is 500 μ s, f _T At 2000Hz, e.g. when the system resonance frequency f _HFR At 725Hz, the corresponding frequency is 725f _T /2000, function value g (f) _HFR ) Is located at (0, f) _T /2), the gain K can be obtained by the function corresponding relation of FIG. 8 _damp2 0.225, at which time F is adjusted _damp2 Gain K _damp2 Is 0.225. When the resonant frequency f _HFR At 410Hz, the corresponding frequency is 410f _T /2000, function value g (f) _HFR ) Is located at (0,f) _T /2) adjustable F based on the above function correspondence _damp2 Gain K of _damp2 It was-0.09.

Optionally, in step 104, generating a first control signal according to the resonance amplitude includes: judging harmonic amplitude value A _HFR Whether the amplitude is larger than a preset value epsilon (or a preset amplitude epsilon); if so, a first control signal is generated.

Otherwise, if NO, namely A _HFR And if the voltage signal is smaller than the preset value, generating and sending a third control signal, wherein the first filter, the second filter and the third filter of the third control signal are not in work, and the detection module continues to monitor and acquire the voltage signal of the PCC.

Optionally, the preset value ε is 5% of the fundamental frequency amplitude, i.e. when A _HFR When the preset value is more than or equal to the preset value epsilon, the first filter, the second filter and the third filter are controlled to work under the condition of the adjusted filter parameters so as to inhibit high-frequency resonance.

In addition, the method of the above embodiment further includes: acquiring a voltage signal of the PCC point in real time; according to the voltage signal collected in real time; when the resonance amplitude output based on the voltage signal is detected to be smaller than a preset value, generating a second control signal; sending the second control signal to the flexible direct current converter, such as MMC, so as to stop the first, the second and the third filters in the flexible direct current converter.

The embodiment utilizes the control signal to adjust whether the first, second and third filters in the MMC are put into operation, when the control module sends the first control signal to the MMC, the adjusted first, second and third filters are indicated to operate, and at this time, the channel of the MMC plays a role in inhibiting high-frequency resonance; when the control module sends a second control signal to the MMC, these filters are instructed not to be put into operation because the condition for suppressing high frequency resonance is not reached, i.e., high frequency resonance does not occur.

The method comprises continuously collecting PCC voltage signal by control circuit, and measuring f in real time _HFR And A _HFR Adjusting two adjustable parameters in real time, low-pass filtering F _lpf2 Cut-off frequency and gain K of _damp2 If f in the inhibition process _HFR Change to f _HFR ', then according to f _HFR ' repeating the aforementioned steps 101 to 105, updating the low pass filter F in real time _lpf2 Cut-off frequency and gain K _damp2 Up to A _HFR And stopping adjustment when the frequency is smaller than the preset value epsilon, and further eliminating high-frequency resonance.

In the simulation test, as shown in fig. 9a and 9b, the simulation results of the adaptive control circuit suppression method are given for 120km and 180km of the ac line, respectively. The ac line length was changed when the interval 1s was simulated. As shown in fig. 9a, as a result of the simulation of suppressing the high-frequency resonance in the 120km ac line, the control circuit controls each filter in the MMC to operate in the 1 st s and the 1.1 st s, and after the 1.1 st s, the high-frequency resonance is eliminated to reach a stable state, where the voltage signals collected at the PCC point are three-phase voltages corresponding to Vpcca, vpcb, and Vpccc, respectively. Similarly, after 1.2s in a 180km ac line, as shown in fig. 9b, the high frequency resonance was eliminated.

By observing the voltage waveform of the PCC point, the high-frequency resonance phenomena of 725Hz and 410Hz are effectively inhibited under the two working conditions of 120km and 180km, and therefore the effectiveness of inhibiting the high-frequency resonance under different scenes is verified by the control method of the embodiment.

In a hardware implementation level, an embodiment of the present invention further provides an electronic device, including: a processor and a memory, the memory to store computer-executable instructions; the processor is configured to read the instruction from the memory and execute the instruction to implement the control method according to the foregoing embodiment.

Optionally, an embodiment of the present invention further provides a computer-readable storage medium, where the storage medium stores computer program instructions, and when a computer reads the instructions, the control method described in the foregoing embodiment is executed.

In addition, an embodiment of the present invention also provides a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium, the computer program including program instructions that, when executed by a computer, cause the computer to execute the control method described in the foregoing embodiment.

In addition, in the description of the present application, "a plurality" means two or more than two unless otherwise specified. In addition, for the convenience of clearly describing the technical solutions of the embodiments of the present application, in the embodiments of the present application, words such as "first", "second", "third", and the like are used to distinguish the same items or similar items with substantially the same functions and actions. Those skilled in the art will appreciate that the terms "first," "second," "third," and the like do not denote any order or quantity, nor do the terms "first," "second," "third," and the like denote any order or importance.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.

Claims

1. A flexible dc power transmission control method applied to a flexible dc power transmission system including a flexible dc converter, a transformer and an equivalent circuit, a point of common coupling PCC of the system being located between the transformer and the equivalent circuit, and a control circuit connected between the flexible dc converter and the PCC, the control circuit including: detection module and control module, including in the flexible direct current converter: the filter comprises a first filter, a second filter and a third filter, wherein the first filter is a voltage feedforward channel filter, the second filter is a voltage feedforward additional reference current channel filter, and the third filter is a current feedback additional modulation channel filter;

the method comprises the following steps:

the control module receives the resonance dominant frequency and the resonance amplitude value output by the detection module;

the control module adjusts filter parameters of the first filter, the second filter and the third filter according to the resonance dominant frequency;

when the adjusted filter parameter is matched with the resonance dominant frequency and the resonance amplitude is larger than or equal to a preset value, generating a first control signal, wherein the first control signal is used for controlling at least one filter to work according to the matched filtering parameter;

the control module sends the first control signal to the flexible direct current converter.

2. The method of claim 1, wherein the control module adjusts filter parameters of the first, second, and third filters based on the resonant dominant frequency, comprising:

the control module adjusts the gain and cut-off frequency of the first filter, the second filter and the third filter, respectively, according to the resonant dominant frequency.

3. The method of claim 2, wherein the control module adjusts the gain of the third filter according to the resonant dominant frequency, comprising:

the control module acquires system delay;

the control module calculates frequency according to the system delay, wherein the frequency is the reciprocal of the system delay;

the control module performs modulus operation on the frequency to obtain a modulus result;

and the control module adjusts the gain of the third filter into a function value corresponding to the gain function according to the gain function where the modulus-taking result is located.

4. The method according to claim 2 or 3, wherein the flexible DC converter further comprises: the PI controller, the delayer and the main circuit equivalent module;

the adjusted filter parameters are matched with the resonant dominant frequency, including:

the parameters of the first filter, the second filter and the third filter after adjustment satisfy the following relations:

ω _cr ＝2πf _cr

F _damp1 ＝K _damp1 F _lpf1 F _lpf2 H _hpf

F _damp2 ＝K _damp2 H _i H _hpf

wherein f is _cr Representing the cut-off frequency, ω, of the low-pass filter _cr Representing cut-off angle frequency, [ xi ] representing damping ratio, K _f Is a voltage feedforward coefficient, s is a variable, K _damp1 And K _damp2 As a gain factor, F _lpf Representing said first filter, F _damp1 Representing said second filter, F _damp2 Represents the third filter, F _lpf1 Low pass filtering representing lower cut-off frequenciesWave filter, F _lpf2 Low-pass filter, H, representing a higher cut-off frequency _hpf Is a first order high pass filter, H _i And the current inner loop PI control link is shown.

5. The method of claim 1, further comprising:

when detecting that the harmonic amplitude value is smaller than the preset value, the control module generates a second control signal, wherein the second control signal is used for controlling a first filter, a second filter and a third filter in the flexible direct current converter to stop working;

the control module sends the second control signal to the flexible direct current converter.

6. A flexible dc power transmission control method applied to a flexible dc power transmission system including a flexible dc converter, a transformer and an equivalent circuit, a point of common coupling PCC of the system being located between the transformer and the equivalent circuit, and a control circuit connected between the flexible dc converter and the PCC, the control circuit including: detection module and control module, including in the flexible direct current converter: the filter comprises a first filter, a second filter and a third filter, wherein the first filter is a voltage feedforward channel filter, the second filter is a voltage feedforward additional reference current channel filter, and the third filter is a current feedback additional modulation channel filter;

the method comprises the following steps:

the detection module acquires a voltage signal of the PCC point;

the detection module determines a harmonic dominant frequency and an amplitude value of resonance according to the voltage signal;

the detection module sends the resonance dominant frequency and the resonance amplitude to the control module, so that the control module adjusts filter parameters of the first filter, the second filter and the third filter according to the resonance dominant frequency and the resonance amplitude.

7. The method of claim 6, wherein the detection module determines a resonant dominant frequency and harmonic amplitude value from the voltage signal, comprising:

processing the voltage signal by using fast Fourier transform to obtain at least one amplitude, wherein each amplitude corresponds to a frequency component;

calculating the ratio of each amplitude to the fundamental frequency amplitude, and determining a frequency component with the maximum ratio;

and determining the main resonance frequency as the frequency component with the maximum ratio, and determining the harmonic amplitude value as the amplitude corresponding to the frequency component with the maximum ratio.

8. An electronic device comprising a processor and a memory, the processor and the memory coupled,

the memory to store computer-executable instructions;

the processor is configured to read the instructions from the memory and execute the instructions to implement the flexible direct current power transmission control method according to any one of claims 1 to 5 or 6 or 7.

9. The electronic device of claim 8, wherein the electronic device is a control module or a detection module.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that,

the computer program when executed by a processor implements a flexible direct current power transmission control method as claimed in any one of claims 1 to 5, or claims 6 or 7.