CN114256854A - Fault ride-through method and control system for flexible direct current transmission system - Google Patents
Fault ride-through method and control system for flexible direct current transmission system Download PDFInfo
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- H—ELECTRICITY
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Abstract
The invention discloses a fault ride-through method and a control system of a flexible direct current transmission system, wherein the flexible direct current transmission control protection system mostly adopts a method of delaying 1/4 fundamental frequency cycles to obtain positive and negative sequence voltage and current components, then inhibits negative sequence current at fault moments by methods of negative sequence current inner loop control and the like to ensure that the flexible direct current transmission system realizes alternating current fault ride-through, and due to the inherent characteristics of a method of delaying 1/4 fundamental frequency cycle positive and negative sequence decomposition, periodic fluctuation of impedance of the flexible direct current transmission system is caused, especially at high frequency, the risk that the flexible direct current impedance exceeds 90 degrees is increased, so that the flexible direct current transmission system has unstable possibility when being connected with other systems. According to the invention, by adopting inner ring full-sequence current control, the periodic fluctuation of the flexible direct current transmission system is avoided in a steady state, the risk that the flexible direct current resistance exceeds 90 degrees is reduced, and meanwhile, negative sequence current control is superposed in a fault period, so that alternating current fault ride-through of the flexible direct current transmission system is realized.
Description
Technical Field
The invention belongs to the field of flexible direct current power transmission and distribution, and particularly relates to a fault ride-through method and a control system of a flexible direct current power transmission system.
Background
The flexible direct current power transmission and distribution system adopts a voltage source type current converter, and active power and reactive power of the system can be independently and rapidly controlled, so that the stability of the system is improved, the fluctuation of system frequency and voltage is inhibited, and the steady-state performance of an alternating current system is improved.
With the development of flexible direct current transmission technology, more and more flexible direct current transmission projects are built and put into operation at home and abroad. By 7 months in 2020, domestic flexible direct-current transmission projects have been put into operation: the fields of low-frequency and high-frequency oscillation and the like of a flexible direct current transmission system, an alternating current power grid, a new energy system and the like are more and more prominent. The phenomenon is studied in detail in domestic and foreign universities, scientific research institutions, enterprises and the like, and the small disturbance stability of the flexible direct current transmission is researched by adopting an impedance stability analysis method.
In the operation process of the flexible-direct current converter, due to the rapid control characteristic of power electronic equipment, inductive or capacitive negative resistance is easy to present near the harmonic frequency of a system, so that the flexible-direct current converter interacts with other impedance equipment of the system to cause the harmonic current of the system to be dispersed. The oscillation mechanism of the flexible-straight system can be initially divided into the following two categories: the current transformer presents the oscillation caused by the oscillation circuit formed by the inductive/capacitive impedance and the capacitive/inductive equipment at the source end, and the current transformer presents the oscillation caused by the amplification effect of the negative resistance on the harmonic wave of the receiving-end power grid.
Meanwhile, in order to realize the ride-through of the flexible direct-current power transmission system when the alternating-current system fails, the flexible direct-current power transmission system mostly adopts negative sequence current loop control to realize the suppression of fault negative sequence current, and the common positive and negative sequence decomposition link of the delay 1/4 cycle introduces the periodic fluctuation of the flexible direct-current impedance, so that the flexible direct-current system is easier to have the phase exceeding 90 degrees on the medium-high frequency impedance characteristic, an inductive negative resistance is presented, and the instability phenomenon between the flexible direct-current system and the alternating-current system or new energy equipment is caused.
Disclosure of Invention
The invention aims to provide a fault ride-through method and a control system of a flexible direct current transmission system aiming at the defects of the prior art, and the problem of impedance periodic fluctuation caused by a positive and negative sequence decomposition link in flexible direct current control is solved, so that the reliable and stable operation of the system is ensured.
On one hand, the application provides a fault ride-through method for a flexible direct current transmission system, wherein inner loop current control of the flexible direct current transmission control system comprises a full-sequence control link and a negative-sequence control link;
the full-sequence control link is characterized in that a full-sequence sampling current d-axis component and a full-sequence sampling current q-axis component which are obtained after full-sequence sampling current which does not undergo delayed 1/4 fundamental frequency cycle positive and negative sequence decomposition processing is subjected to DQ conversion are used as input of the full-sequence control link, difference is respectively made between a full-sequence d-axis current reference value and a full-sequence q-axis current reference value, then PI control is carried out, a full-sequence sampling current DQ-axis component cross decoupling link and a positive-sequence voltage feedforward link are superposed to obtain a full-sequence DQ-axis voltage control quantity, and then the full-sequence DQ-axis voltage control quantity is converted into a full-sequence alpha beta voltage control quantity;
in the negative sequence control link, the negative sequence dq axis voltage control quantity is obtained only through negative sequence voltage feedforward during normal fault-free operation; when an alternating current side fault occurs, putting negative sequence current control into the system, superposing the negative sequence current control on negative sequence voltage feedforward to obtain negative sequence dq axis voltage control quantity; then converting the negative sequence dq axis voltage control quantity into a negative sequence alpha beta voltage control quantity;
and superposing the full-sequence alpha beta voltage control quantity on the negative-sequence alpha beta voltage control quantity to obtain a final alpha beta voltage reference value.
Preferably, the negative sequence current control is implemented by taking a negative sequence sampling current d-axis component and a negative sequence sampling current q-axis component, which are obtained by performing positive and negative sequence decomposition and DQ conversion on a full sequence sampling current, as negative sequence current control input, performing PI control after difference is respectively made between the negative sequence sampling current d-axis component and the negative sequence sampling current q-axis component, and overlapping a negative sequence sampling current DQ-axis component cross decoupling link to obtain negative sequence current control output.
Preferably, the flexible direct current transmission control system adopts double closed-loop control, and the double closed-loop control comprises an inner loop current control link and an outer loop control link; the outer ring control link comprises one or a combination of several control methods of constant direct current voltage control, constant active power control, constant alternating current voltage control, constant reactive power control and constant frequency control.
Preferably, the positive sequence voltage feedforward in the full sequence control link is subjected to first-order low-pass filtering, second-order low-pass filtering or nonlinear filter, and the cut-off frequency f of the first-order low-pass or second-order low-pass filtercLess than or equal to 200 Hz; the negative sequence voltage feedforward in the negative sequence control link is subjected to first-order low-pass filtering or second-order low-pass filtering, and the cut-off frequency f of the filterc≤200Hz。
Preferably, the judgment criterion of the ac side fault is as follows:
1) voltage positive sequence component per unit amplitude Umpos≤kposWherein k ispos≤0.85p.u.；
2) Voltage negative sequence component per unit amplitude Umneg≥knegWherein k ispos≥0.1p.u.；
3) Voltage zero sequence component per unit amplitude Um0≥k0Wherein k is0≥0.1p.u.；
And if the 3 criteria meet one of the criteria, judging that the alternating current side fault of the flexible direct current transmission system occurs.
On the other hand, the application provides a control system for fault ride-through of a flexible direct current transmission system, wherein the control system adopts double closed-loop control and comprises an outer loop control unit, an inner loop control unit, a positive and negative sequence decomposition unit and an alternating current fault judgment unit:
the outer ring control unit is used for outer ring control of the flexible direct current power transmission control system, and the output of the outer ring control unit is the reference value input of the inner ring control unit;
the inner ring control unit is used for inner ring control of the flexible direct current power transmission control system and comprises a full sequence control module and a negative sequence control module;
the positive and negative sequence decomposition unit is used for performing positive and negative sequence decomposition on the voltage and the current obtained by sampling and outputting a positive sequence quantity, a negative sequence quantity and a zero sequence quantity;
the alternating current fault judging unit judges whether the current power transmission system has an alternating current side fault or not according to the voltage and current states of the alternating current system;
the full-sequence control module directly uses the full-sequence sampling current after DQ conversion as the input of the full-sequence control module, respectively makes differences with a full-sequence d-axis current reference value and a full-sequence q-axis current reference value, then performs PI control, and superposes a full-sequence sampling current DQ-axis component cross decoupling link and a positive-sequence voltage feedforward link to obtain a full-sequence DQ-axis voltage control quantity, and then converts the full-sequence DQ-axis voltage control quantity into a full-sequence alpha beta voltage control quantity to be used as the output of the full-sequence control module;
the negative sequence control module receives the judgment result of the alternating current fault judgment unit, and when the alternating current fault judgment unit judges the alternating current fault, the negative sequence current control is put into, the negative sequence current control is superposed with the negative sequence voltage feedforward to obtain a negative sequence dq axis voltage control quantity which is converted into a negative sequence alpha beta voltage control quantity to be used as the output of the negative sequence control module; otherwise, the output of the negative sequence control module is only determined by the negative sequence voltage feedforward.
Preferably, the negative sequence current control is implemented by taking a negative sequence sampling current d-axis component and a negative sequence sampling current q-axis component, which are obtained by performing positive and negative sequence decomposition and DQ conversion on a full sequence sampling current, as negative sequence current control input, performing PI control after difference is respectively made between the negative sequence sampling current d-axis component and the negative sequence sampling current q-axis component, and overlapping a negative sequence sampling current DQ-axis component cross decoupling link to obtain negative sequence current control output.
Preferably, the outer ring control unit includes one or a combination of several control modules of a constant direct current voltage control module, a constant active power control module, a constant alternating current voltage control module, a constant reactive power control module and a constant frequency control module.
Preferably, the positive sequence voltage feedforward in the full sequence control module is subjected to first-order low-pass filtering or second-order low-pass filtering, and the cut-off frequency f of the filtercLess than or equal to 200 Hz; the negative sequence voltage feedforward in the negative sequence control module is subjected to first-order low-pass filtering or second-order low-pass filtering, and the cut-off frequency f of the filterc≤200Hz。
Preferably, the alternating current fault determination unit has the following determination criteria:
1) voltage positive sequence component per unit amplitude Umpos≤kposWherein k ispos≤0.85p.u.；
2) Voltage negative sequence component per unit amplitude Umneg≥knegWherein k ispos≥0.1p.u.；
3) Voltage zero sequence component per unit amplitude Um0≥k0Wherein k is0≥0.1p.u.；
And if one of the 3 criteria is met, judging that the alternating current side fault of the flexible direct current transmission system occurs.
After the scheme is adopted, the invention has the beneficial effects that:
(1) according to the fault ride-through method and device for the flexible direct current transmission system, the problem of periodic fluctuation of impedance when the flexible direct current transmission system normally operates is solved, and the resonance risk of the flexible direct current transmission system, an alternating current system, new energy equipment and the like is reduced;
(2) the method and the device for fault ride-through of the flexible direct current transmission system solve fault judgment and fault current suppression during alternating current system fault and avoid lockout outage during the fault period of the flexible direct current system.
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Fig. 1 is a block diagram of inner loop control of a flexible direct current power transmission system.
Detailed Description
The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The application provides an embodiment of a fault ride-through method of a flexible direct current transmission system.
The full-sequence control link is characterized in that a full-sequence sampling current d-axis component and a full-sequence sampling current q-axis component which are obtained after full-sequence sampling current which does not undergo delayed 1/4 fundamental frequency cycle positive and negative sequence decomposition processing is subjected to DQ conversion are used as input of the full-sequence control link, difference is respectively made between a full-sequence d-axis current reference value and a full-sequence q-axis current reference value, then PI control is carried out, a full-sequence sampling current DQ-axis component cross decoupling link and a positive-sequence voltage feedforward link are superposed to obtain a full-sequence DQ-axis voltage control quantity, and then the full-sequence DQ-axis voltage control quantity is converted into a full-sequence alpha beta voltage control quantity.
In the negative sequence control link, the negative sequence dq axis voltage control quantity is obtained only through negative sequence voltage feedforward during normal fault-free operation; when an alternating current side fault occurs, putting negative sequence current control into the system, superposing the negative sequence current control on negative sequence voltage feedforward to obtain negative sequence dq axis voltage control quantity; and then the negative sequence dq-axis voltage controlled quantity is converted into a negative sequence α β voltage controlled quantity. And superposing the full-sequence alpha beta voltage control quantity on the negative-sequence alpha beta voltage control quantity to obtain a final alpha beta voltage reference value.
In a preferred embodiment, the negative sequence current control is implemented by taking a negative sequence sampling current d-axis component and a negative sequence sampling current q-axis component, which are obtained by performing positive and negative sequence decomposition and DQ conversion on a full sequence sampling current, as negative sequence current control input, performing PI control after difference is respectively made between the negative sequence sampling current d-axis component and the negative sequence sampling current q-axis component, and overlapping a negative sequence sampling current DQ-axis component cross decoupling link to obtain negative sequence current control output.
In a preferred embodiment, the flexible direct current transmission control system adopts double closed-loop control, and the double closed-loop control comprises an inner loop current control link and an outer loop control link; the outer ring control link comprises one or a combination of several control methods of constant direct current voltage control, constant active power control, constant alternating current voltage control, constant reactive power control and constant frequency control.
In a preferred embodiment, the positive sequence voltage feed-forward in the full sequence control element is subjected to first-order low-pass filtering, second-order low-pass filtering or nonlinear filter, and the cut-off frequency f of the first-order low-pass or second-order low-pass filtercLess than or equal to 200 Hz; the negative sequence voltage feedforward in the negative sequence control link is subjected to first-order low-pass filtering or second-order low-pass filtering, and the cut-off frequency f of the filterc≤200Hz。
In a preferred embodiment, the judgment criteria of the ac side fault are as follows:
1) voltage positive sequence component per unit amplitude Umpos≤kposWherein k ispos≤0.85p.u.；
2) Voltage negative sequence component per unit amplitude Umneg≥knegWherein k ispos≥0.1p.u.；
3) Voltage zero sequence component per unit amplitude Um0≥k0Wherein k is0≥0.1p.u.；
And if the 3 criteria meet one of the criteria, judging that the alternating current side fault of the flexible direct current transmission system occurs.
As shown in fig. 1, in an embodiment of a method for fault ride-through of a flexible direct current transmission system, double closed-loop control is adopted, wherein inner-loop current control includes a full-sequence control link 1 and a negative-sequence control link 2. The full-sequence sampling current required by the full-sequence control link is not subjected to delayed 1/4 fundamental frequency period positive and negative sequence decomposition processing, and the full-sequence d-axis current reference value idref_allAnd full-sequence d-axis current input id_allDifference, full-sequence q-axis current reference value iqref_allAnd full-sequence q-axis current input iq_allThe difference of the positive sequence dq axis voltage control quantity is obtained after PI control, a decoupling link and a positive sequence voltage feedforward link 3 are superposed; then converting the full-sequence dq axis voltage control quantity into a full-sequence alpha beta voltage control quantity uαβref_allAs the output of the full sequence control link 1.
And the negative sequence control link 2 only obtains the negative sequence dq axis voltage control quantity through negative sequence voltage feedforward when in normal fault-free operation. When the AC side occursWhen the FAULT occurs, the alternating current FAULT judgment mark position AC _ FAULT of the flexible direct current transmission control system is 1, and at the moment, the negative sequence control link 2 is put into the negative sequence current control link 5. In the negative sequence current control link 5, the reference value i of the negative sequence d-axis currentdref_negAnd negative sequence d-axis current input id_negNegative sequence q-axis current reference value iqref_negAnd negative sequence q-axis current input iq_negThe difference of (3) is respectively subjected to PI control, and a decoupling link is superposed to obtain the output of the negative sequence current control link 5. The output of the negative sequence current control link 5 is simultaneously superposed with the negative sequence voltage feedforward link 4 to obtain the negative sequence dq axis voltage control quantity. Conversion of negative sequence dq-axis voltage controlled variable into negative sequence alpha beta voltage controlled variable uαβref_negAs the output of the negative sequence control element 2. Finally, the output u of the full sequence control link 1αβref_allAnd the output u of the negative sequence control element 2αβref_negSuperposing to generate a reference wave uαβref。
The application also provides an embodiment of a fault ride-through control system of the flexible direct current transmission system. The control system adopts double closed-loop control and comprises an outer loop control unit, an inner loop control unit, a positive and negative sequence decomposition unit and an alternating current fault judgment unit:
the outer ring control unit is used for outer ring control of the flexible direct current power transmission control system, and the output of the outer ring control unit is the reference value input of the inner ring control unit;
the inner ring control unit is used for inner ring control of the flexible direct current power transmission control system and comprises a full sequence control module and a negative sequence control module;
the positive and negative sequence decomposition unit is used for performing positive and negative sequence decomposition on the voltage and the current obtained by sampling and outputting a positive sequence quantity, a negative sequence quantity and a zero sequence quantity;
the alternating current fault judging unit judges whether the current power transmission system has an alternating current side fault or not according to the voltage and current states of the alternating current system;
the full-sequence control module directly uses the full-sequence sampling current after DQ conversion as the input of the full-sequence control module, respectively makes differences with a full-sequence d-axis current reference value and a full-sequence q-axis current reference value, then performs PI control, and superposes a full-sequence sampling current DQ-axis component cross decoupling link and a positive-sequence voltage feedforward link to obtain a full-sequence DQ-axis voltage control quantity, and then converts the full-sequence DQ-axis voltage control quantity into a full-sequence alpha beta voltage control quantity to be used as the output of the full-sequence control module;
the negative sequence control module receives the judgment result of the alternating current fault judgment unit, and when the alternating current fault judgment unit judges the alternating current fault, the negative sequence current control is put into, the negative sequence current control is superposed with the negative sequence voltage feedforward to obtain a negative sequence dq axis voltage control quantity which is converted into a negative sequence alpha beta voltage control quantity to be used as the output of the negative sequence control module; otherwise, the output of the negative sequence control module is only determined by the negative sequence voltage feedforward.
In a preferred embodiment, the negative sequence current control is implemented by taking a negative sequence sampling current d-axis component and a negative sequence sampling current q-axis component, which are obtained by performing positive and negative sequence decomposition and DQ conversion on a full sequence sampling current, as negative sequence current control input, performing PI control after difference is respectively made between the negative sequence sampling current d-axis component and the negative sequence sampling current q-axis component, and overlapping a negative sequence sampling current DQ-axis component cross decoupling link to obtain negative sequence current control output.
In a preferred embodiment, the outer loop control unit includes one or a combination of several control modules, namely a constant direct current voltage control module, a constant active power control module, a constant alternating current voltage control module, a constant reactive power control module and a constant frequency control module.
In a preferred embodiment, the positive sequence voltage feedforward in the full sequence control module is subjected to first-order low-pass filtering or second-order low-pass filtering, and the cut-off frequency f of the filtercLess than or equal to 200 Hz; the negative sequence voltage feedforward in the negative sequence control module is subjected to first-order low-pass filtering or second-order low-pass filtering, and the cut-off frequency f of the filterc≤200Hz。
In a preferred embodiment, the alternating current fault determining unit has the following determination criteria:
1) voltage positive sequence component per unit amplitude Umpos≤kposWherein k ispos≤0.85p.u.；
2) Voltage negative sequence component per unit amplitude Umneg≥knegWherein k ispos≥0.1p.u.；
3) Voltage zero sequence component per unit amplitude Um0≥k0Wherein k is0≥0.1p.u.；
And if one of the 3 criteria is met, judging that the alternating current side fault of the flexible direct current transmission system occurs.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.
Claims (10)
1. A method for fault ride-through of a flexible direct current transmission system is characterized in that inner loop current control of the flexible direct current transmission control system comprises a full sequence control link and a negative sequence control link;
the full-sequence control link is characterized in that a full-sequence sampling current d-axis component and a full-sequence sampling current q-axis component which are obtained after full-sequence sampling current which does not undergo delayed 1/4 fundamental frequency cycle positive and negative sequence decomposition processing is subjected to DQ conversion are used as input of the full-sequence control link, difference is respectively made between a full-sequence d-axis current reference value and a full-sequence q-axis current reference value, then PI control is carried out, a full-sequence sampling current DQ-axis component cross decoupling link and a positive-sequence voltage feedforward link are superposed to obtain a full-sequence DQ-axis voltage control quantity, and then the full-sequence DQ-axis voltage control quantity is converted into a full-sequence alpha beta voltage control quantity;
in the negative sequence control link, the negative sequence dq axis voltage control quantity is obtained only through negative sequence voltage feedforward during normal fault-free operation; when an alternating current side fault occurs, putting negative sequence current control into the system, superposing the negative sequence current control on negative sequence voltage feedforward to obtain negative sequence dq axis voltage control quantity; then converting the negative sequence dq axis voltage control quantity into a negative sequence alpha beta voltage control quantity;
and superposing the full-sequence alpha beta voltage control quantity on the negative-sequence alpha beta voltage control quantity to obtain a final alpha beta voltage reference value.
2. The method for fault ride-through of the flexible direct-current transmission system according to claim 1, wherein in the negative sequence current control, a negative sequence sampling current d-axis component and a negative sequence sampling current q-axis component, which are obtained by performing positive and negative sequence decomposition and DQ conversion on a full sequence sampling current, are used as inputs of the negative sequence current control, are subjected to PI control after being respectively subtracted from a negative sequence d-axis current reference value and a negative sequence q-axis current reference value, and a negative sequence sampling current DQ-axis component cross decoupling link is superposed to obtain an output of the negative sequence current control.
3. The method according to claim 1, wherein the flexible direct current transmission control system adopts double closed-loop control, and the double closed-loop control comprises an inner loop current control link and an outer loop control link; the outer ring control link comprises one or a combination of several control methods of constant direct current voltage control, constant active power control, constant alternating current voltage control, constant reactive power control and constant frequency control.
4. The method according to claim 1, wherein the positive sequence voltage feed-forward in the full sequence control element is subjected to first-order low-pass filtering, second-order low-pass filtering or nonlinear filter, and the cut-off frequency f of the first-order low-pass or second-order low-pass filtercLess than or equal to 200 Hz; the negative sequence voltage feedforward in the negative sequence control link is subjected to first-order low-pass filtering or second-order low-pass filtering, and the cut-off frequency f of the filterc≤200Hz。
5. The method according to claim 1, wherein the criteria for determining the ac side fault are as follows:
1) voltage positive sequence component per unit amplitude Umpos≤kposWherein k ispos≤0.85p.u.；
2) Voltage negative sequence component per unit amplitude Umneg≥knegWherein k ispos≥0.1p.u.；
3) Voltage zero sequence component per unit amplitude Um0≥k0Wherein k is0≥0.1p.u.；
And if the 3 criteria meet one of the criteria, judging that the alternating current side fault of the flexible direct current transmission system occurs.
6. The control system for fault ride-through of the flexible direct current transmission system is characterized in that the control system adopts double closed-loop control and comprises an outer loop control unit, an inner loop control unit, a positive and negative sequence decomposition unit and an alternating current fault judgment unit:
the outer ring control unit is used for outer ring control of the flexible direct current power transmission control system, and the output of the outer ring control unit is the reference value input of the inner ring control unit;
the inner ring control unit is used for inner ring control of the flexible direct current power transmission control system and comprises a full sequence control module and a negative sequence control module;
the positive and negative sequence decomposition unit is used for performing positive and negative sequence decomposition on the voltage and the current obtained by sampling and outputting a positive sequence quantity, a negative sequence quantity and a zero sequence quantity;
the alternating current fault judging unit judges whether the current power transmission system has an alternating current side fault or not according to the voltage and current states of the alternating current system;
the full-sequence control module directly uses the full-sequence sampling current after DQ conversion as the input of the full-sequence control module, respectively makes differences with a full-sequence d-axis current reference value and a full-sequence q-axis current reference value, then performs PI control, and superposes a full-sequence sampling current DQ-axis component cross decoupling link and a positive-sequence voltage feedforward link to obtain a full-sequence DQ-axis voltage control quantity, and then converts the full-sequence DQ-axis voltage control quantity into a full-sequence alpha beta voltage control quantity to be used as the output of the full-sequence control module;
the negative sequence control module receives the judgment result of the alternating current fault judgment unit, and when the alternating current fault judgment unit judges the alternating current fault, the negative sequence current control is put into, the negative sequence current control is superposed with the negative sequence voltage feedforward to obtain a negative sequence dq axis voltage control quantity which is converted into a negative sequence alpha beta voltage control quantity to be used as the output of the negative sequence control module; otherwise, the output of the negative sequence control module is only determined by the negative sequence voltage feedforward.
7. The system according to claim 6, wherein the negative sequence current control is performed by taking a negative sequence sampling current d-axis component and a negative sequence sampling current q-axis component, which are obtained by performing positive and negative sequence decomposition and DQ conversion on a full sequence sampling current, as inputs of the negative sequence current control, performing PI control after performing differences with a negative sequence d-axis current reference value and a negative sequence q-axis current reference value respectively, and performing overlapping negative sequence sampling current DQ-axis component cross-coupling to obtain an output of the negative sequence current control.
8. The system according to claim 6, wherein the outer loop control unit comprises one or a combination of a constant DC voltage control module, a constant active power control module, a constant AC voltage control module, a constant reactive power control module and a constant frequency control module.
9. The fault ride-through control system for the flexible direct current power transmission system according to claim 6, wherein the positive sequence voltage feedforward in the full sequence control module is subjected to first-order low-pass filtering or second-order low-pass filtering, and the cut-off frequency f of the filter iscLess than or equal to 200 Hz; the negative sequence voltage feedforward in the negative sequence control module is subjected to first-order low-pass filtering or second-order low-pass filtering, and the cut-off frequency f of the filterc≤200Hz。
10. The system according to claim 6, wherein the ac fault determining unit determines the following criteria:
1) voltage positive sequence component per unit amplitude Umpos≤kposWherein k ispos≤0.85p.u.；
2) Voltage negative sequence component per unit amplitude Umneg≥knegWherein k ispos≥0.1p.u.；
3) Voltage zero sequence component per unit amplitude Um0≥k0Wherein k is0≥0.1p.u.；
And if one of the 3 criteria is met, judging that the alternating current side fault of the flexible direct current transmission system occurs.
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| CN115954923A (en) * | 2023-02-22 | 2023-04-11 | 中国华能集团清洁能源技术研究院有限公司 | Fault ride-through method and device for offshore wind power flexible direct current transmission system |
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