阅读说明：本技术 一种vsc/lcc并联混合多馈系统换相失败后的恢复方法及系统 (Recovery method and system after commutation failure of VSC/LCC parallel hybrid multi-feed system ) 是由 杨尚瑾 雷霄 夏勇军 李新年 陈堃 王薇薇 张侃君 刘琳 张隆恩 贺郁文 庞广恒 于 2021-07-28 设计创作，主要内容包括：本发明公开了一种VSC/LCC并联混合多馈系统换相失败后的恢复方法及系统,属于高压直流输电技术领域。本发明方法,包括：当检测到LCC发生换相失败之后,发出VSC/LCC功率频率协调控制指令；当VSC和LCC在接收到VSC/LCC功率频率协调控制指令后,控制VSC和LCC进入功率补偿模式；功率补偿模式持续预设时间后,控制VSC和LCC将功率补偿模式切换为频率调制模式；在检测到交流电网频率振荡结束之后,控制VSC和LCC退出功率频率协调控制指令,和频率调制模式,并恢复VSC和LCC正常运行。本发明可对LCC换相失败后的交流系统频率波动进行抑制。(The invention discloses a recovery method and a recovery system after commutation failure of a VSC/LCC parallel hybrid multi-feed system, and belongs to the technical field of high-voltage direct-current power transmission. The method comprises the following steps: when the LCC is detected to have phase commutation failure, sending a VSC/LCC power frequency coordination control instruction; after receiving a power frequency coordination control command of the VSC/LCC, the VSC and the LCC are controlled to enter a power compensation mode; after the power compensation mode lasts for the preset time, controlling the VSC and the LCC to switch the power compensation mode into a frequency modulation mode; and after the frequency oscillation of the alternating current power grid is detected to be finished, the VSC and the LCC are controlled to exit a power frequency coordination control instruction and a frequency modulation mode, and the normal operation of the VSC and the LCC is recovered. The invention can restrain the frequency fluctuation of the alternating current system after LCC commutation failure.)

1. A recovery method after commutation failure of a VSC/LCC parallel hybrid multi-feed system, the method comprising:

when the LCC is detected to have phase commutation failure, sending a VSC/LCC power frequency coordination control instruction;

after receiving a power frequency coordination control command of the VSC/LCC, the VSC and the LCC are controlled to enter a power compensation mode;

after the power compensation mode lasts for the preset time, controlling the VSC and the LCC to switch the power compensation mode into a frequency modulation mode;

and after the frequency oscillation of the alternating current power grid is detected to be finished, the VSC and the LCC are controlled to exit a power frequency coordination control instruction and a frequency modulation mode, and the normal operation of the VSC and the LCC is recovered.

2. The method of claim 1, wherein the delay time for issuing the VSC/LCC power frequency coordination control command is no more than 50ms after detecting that the LCC has failed to commutate.

3. The method according to claim 1, wherein the entering into the power compensation mode specifically comprises:

controlling the VSC to perform power back-down operation by modifying an active power reference value of the VSC in a power compensation mode;

the back-down power is a smaller value between a set value and the LCC power down due to commutation failure;

the power reduction caused by the commutation failure is the difference value between the active power reference value before the LCC has commutation failure and the LCC active power measured value;

and controlling the LCC to perform power boosting operation in the power compensation mode by modifying the LCC active power reference value, wherein the boosted power cannot exceed the LCC active power upper limit.

4. The method according to claim 1, wherein the frequency modulation mode is specifically:

and controlling the VSC and the LCC to stop power lifting, controlling the output quantity of the active power reference value superposed frequency modulation link, and inhibiting the frequency oscillation of the alternating current power grid.

5. The method of claim 1, wherein the predetermined time is required to limit a first oscillation peak value of the frequency without causing exacerbation of subsequent frequency oscillations.

6. A recovery system after commutation failure of a VSC/LCC parallel hybrid multi-feed system, the system comprising:

the detection module is used for detecting whether the VSC/LCC parallel hybrid multi-feed system fails in commutation or not, and sending a VSC/LCC power frequency coordination control instruction after detecting that the LCC fails in commutation;

the first mode switching module is used for controlling the VSC and the LCC to enter a power compensation mode after receiving a VSC/LCC power frequency coordination control instruction;

the second mode switching module controls the VSC and the LCC to switch the power compensation mode into a frequency modulation mode after the power compensation mode lasts for a preset time;

and the quitting module is used for controlling the VSC and the LCC to quit the power frequency coordination control instruction and the frequency modulation mode and recovering the normal operation of the VSC and the LCC after detecting that the frequency oscillation of the alternating current power grid is finished.

7. The system of claim 6, wherein the delay time for issuing the VSC/LCC power frequency coordination control command is no more than 50ms after detecting that the LCC has failed to commutate.

8. The system of claim 6, wherein the entering the power compensation mode specifically comprises:

controlling the VSC to perform power back-down operation by modifying an active power reference value of the VSC in a power compensation mode;

the back-down power is a smaller value between a set value and the LCC power down due to commutation failure;

the power reduction caused by the commutation failure is the difference value between the active power reference value before the LCC has commutation failure and the LCC active power measured value;

and controlling the LCC to perform power boosting operation in the power compensation mode by modifying the LCC active power reference value, wherein the boosted power cannot exceed the LCC active power upper limit.

9. The system of claim 6, wherein the frequency modulation mode is specifically:

and controlling the VSC and the LCC to stop power lifting, controlling the output quantity of the active power reference value superposed frequency modulation link, and inhibiting the frequency oscillation of the alternating current power grid.

10. The system of claim 6, wherein the predetermined time is required to limit a first oscillation peak value of the frequency without causing exacerbation of subsequent frequency oscillations.

Technical Field

The invention relates to the technical field of high-voltage direct-current transmission, in particular to a recovery method and a recovery system after commutation failure of a VSC/LCC parallel hybrid multi-feed system.

Background

In China, an objective condition that energy resources and load requirements are reversely distributed exists, so that conventional high voltage direct current (LCC-HVDC) transmission is rapidly developed in recent years to meet practical requirements in the aspects of long-distance and large-capacity transmission, asynchronous networking and the like.

Meanwhile, in the aspect of flexible direct current transmission (VSC-HVDC), multiple flexible direct current projects such as five ends of the navi and the hill, the true bipolar of the building door, the back-to-back of the Yubei and the like are built in China, and direct current transmission systems of two technical routes are widely applied, so that a brand new system structure of VSC/LCC direct current parallel hybrid multi-feed (a plurality of direct currents share a common alternating current bus or an alternating current bus with a relatively short electrical distance) appears in a power grid of China, which is a necessary result for vigorously developing a high-voltage direct current transmission technology in China and is also necessary to be increased increasingly under the large background that energy resources and load requirements of China are reversely distributed in the future. The structure enables new research requirements to appear in the aspect of coordination control of a near-region alternating current and direct current power grid, for example, reactive power control between flexible direct current and near-region conventional direct current is coordinated to optimize reactive power coordination between the flexible direct current and the near-region conventional direct current, the transient stability of the near-region alternating current and direct current power grid is optimized by utilizing the flexible controllability of the flexible direct current, and the like.

By combining the objective fact that the structural engineering application of the VSC/LCC direct-current parallel hybrid multi-feed system is increased day by day, and starting from dynamic power coordination control, a coordination technical scheme and a control strategy between flexible direct current and nearby conventional direct current and alternating current networks are provided, and the method has very important practical significance for constructing a strong smart power grid with high utilization rate and strong stability.

As commutation failure is the most common fault type of LCC-HVDC, the power frequency coordination control method after commutation failure in the VSC/LCC direct current parallel hybrid multi-feed system becomes an important research subject.

Disclosure of Invention

Aiming at the problem of commutation failure in the VSC/LCC direct current parallel hybrid multi-feed system, the invention provides a recovery method after commutation failure of the VSC/LCC parallel hybrid multi-feed system, which comprises the following steps:

when the LCC is detected to have phase commutation failure, sending a VSC/LCC power frequency coordination control instruction;

after receiving a power frequency coordination control command of the VSC/LCC, the VSC and the LCC are controlled to enter a power compensation mode;

after the power compensation mode lasts for the preset time, controlling the VSC and the LCC to switch the power compensation mode into a frequency modulation mode;

and after the frequency oscillation of the alternating current power grid is detected to be finished, the VSC and the LCC are controlled to exit a power frequency coordination control instruction and a frequency modulation mode, and the normal operation of the VSC and the LCC is recovered.

Optionally, after detecting that the LCC has failed in commutation, the delay time for issuing the VSC/LCC power frequency coordination control instruction does not exceed 50 ms.

Optionally, entering a power compensation mode, specifically:

controlling the VSC to perform power back-down operation by modifying an active power reference value of the VSC in a power compensation mode;

the back-down power is a smaller value between a set value and the LCC power down due to commutation failure;

the power reduction caused by the commutation failure is the difference value between the active power reference value before the LCC has commutation failure and the LCC active power measured value;

and controlling the LCC to perform power boosting operation in the power compensation mode by modifying the LCC active power reference value, wherein the boosted power cannot exceed the LCC active power upper limit.

Optionally, the frequency modulation mode specifically includes:

and controlling the VSC and the LCC to stop power lifting, controlling the output quantity of the active power reference value superposed frequency modulation link, and inhibiting the frequency oscillation of the alternating current power grid.

Optionally, the preset time is required to limit the first oscillation peak value of the frequency, and the subsequent frequency oscillation is not aggravated.

The invention also provides a recovery system after the commutation failure of the VSC/LCC parallel hybrid multi-feed system, which comprises the following steps:

the detection module is used for detecting whether the VSC/LCC parallel hybrid multi-feed system fails in commutation or not, and sending a VSC/LCC power frequency coordination control instruction after detecting that the LCC fails in commutation;

the first mode switching module is used for controlling the VSC and the LCC to enter a power compensation mode after receiving a VSC/LCC power frequency coordination control instruction;

the second mode switching module controls the VSC and the LCC to switch the power compensation mode into a frequency modulation mode after the power compensation mode lasts for a preset time;

and the quitting module is used for controlling the VSC and the LCC to quit the power frequency coordination control instruction and the frequency modulation mode and recovering the normal operation of the VSC and the LCC after detecting that the frequency oscillation of the alternating current power grid is finished.

Optionally, after detecting that the LCC has failed in commutation, the delay time for issuing the VSC/LCC power frequency coordination control instruction does not exceed 50 ms.

Optionally, entering a power compensation mode, specifically:

controlling the VSC to perform power back-down operation by modifying an active power reference value of the VSC in a power compensation mode;

the back-down power is a smaller value between a set value and the LCC power down due to commutation failure;

the power reduction caused by the commutation failure is the difference value between the active power reference value before the LCC has commutation failure and the LCC active power measured value;

and controlling the LCC to perform power boosting operation in the power compensation mode by modifying the LCC active power reference value, wherein the boosted power cannot exceed the LCC active power upper limit.

Optionally, the frequency modulation mode specifically includes:

and controlling the VSC and the LCC to stop power lifting, controlling the output quantity of the active power reference value superposed frequency modulation link, and inhibiting the frequency oscillation of the alternating current power grid.

Optionally, the preset time is required to limit the first oscillation peak value of the frequency, and the subsequent frequency oscillation is not aggravated.

The invention can restrain the frequency fluctuation of the alternating current system after LCC commutation failure.

Drawings

FIG. 1 is a structural diagram of a VSC/LCC parallel hybrid multi-feed system in an embodiment of the present invention;

FIG. 2 is a flow chart of the method of the present invention;

FIG. 3 is a logic diagram of a frequency modulation link according to an embodiment of the present invention;

fig. 4 is a power frequency coordination control block diagram after a commutation failure of the VSC/LCC parallel hybrid multi-feed system in the embodiment of the present invention;

FIG. 5 is a diagram illustrating the effect of the VSC/LCC power frequency coordination control method on suppressing frequency fluctuation after a commutation failure in the embodiment of the present invention;

FIG. 6 is a VSC active power graph according to an embodiment of the present invention;

FIG. 7 is a LCC active power curve diagram in an embodiment of the present invention;

fig. 8 is a block diagram of the system of the present invention.

Detailed Description

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

Unless otherwise defined, terms (including 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. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.

The invention is further illustrated by the following examples:

as shown in FIG. 1, FIG. 1 is a typical VSC/LCC parallel hybrid multi-feed system, the VSC is connected with an AC A system and an AC B system, power is sent from A to B, the LCC is connected with the AC B system and the AC C system, power is sent from B to C, and the B system is simultaneously connected with the VSC and the LCC. The system B is simultaneously connected with conventional direct current and flexible direct current, faults or operation mode changes of the two direct currents can affect the system B, and meanwhile, the two direct currents can adjust the operation mode through a certain control strategy to affect the operation voltage, frequency, power and the like of the system B, so that the operation stability of the system B is improved.

After a short-circuit fault occurs to the LCC receiving end C system, a commutation failure of the LCC receiving end converter can be caused, the active power of the LCC rapidly decreases in a short time, the power of the B system is excessive, frequency fluctuation is caused, and the transient stability of the B system is even influenced. Therefore, the VSC and the LCC are required to exert the regulation capability together to compensate the power variation of the B system and to smooth the frequency fluctuation.

The invention provides a recovery method after commutation failure of a VSC/LCC parallel hybrid multi-feed system, as shown in FIG. 2, comprising the following steps:

(1) after detecting that the LCC has failed in commutation, the control system immediately sends a VSC/LCC power frequency coordination control instruction, generally from the failed commutation to the sending of the control instruction, and the delay time is not more than 50 ms.

(2) And after receiving the VSC/LCC coordination control instruction, the VSC and the LCC enter a power compensation mode.

The VSC needs to perform power back-down in the power compensation mode, and the power to be reduced is a set value delta P_downAnd LCC power reduction Δ P due to commutation failure_LCCAnd the smaller value of the interval is realized by modifying the VSC active power reference value. Wherein, Δ P_downNeeds to be determined according to the power grid structure in a simulation mode, and the determination principle is that the active power change of the B system can be compensated to a certain degree, the first peak value of the frequency oscillation of the B system is limited, the stable operation of the A system is not influenced, and the delta P_LCCCalculated by the following formula;

wherein the content of the first and second substances,is the reference value of active power before phase commutation failure of LCC, P_LCCIs an LCC active power measurement value.

The LCC needs to carry out power boosting in a power compensation mode, and the boosted power is a set value delta P_upAnd modifying the LCC active power reference value. Delta P_upThe active power change of the B system can be compensated to a certain extent, the first peak value of the frequency oscillation of the B system is limited, the stable operation of the C system is not influenced, and the upper limit of the active power of the LCC system cannot be exceeded.

(3) Power compensation mode duration t_sAnd then, the VSC and the LCC are both switched to a frequency modulation mode, specifically, the VSC and the LCC stop power lifting, and the active power reference value is superposed with the output quantity of the frequency modulation link so as to inhibit the frequency oscillation of the alternating current power grid. t is t_sSimulation determination is carried out according to system requirements, and the fact that subsequent frequency oscillation is aggravated is prevented while the first oscillation peak value of the limiting frequency is guaranteed. The frequency modulation link is shown in fig. 3, and the transfer function is shown in equation (2).

Where f is the measured value of the frequency of the AC network, f₀Is the system power frequency, delta f is the frequency and power frequency deviation of the LCC transmitting end power grid, T is the inertia link time constant, K_PIs a proportional element coefficient, T_HIIs the integral element time constant, K_TIs a feedback coefficient, and K_T<<1，ΔP_fAnd finally adding the frequency modulation output quantity to the VSC/LCC active power reference value. Parameters of frequency modulation links adopted by the VSC and the LCC are determined according to system simulation so as to ensure the rapid suppression of frequency oscillation.

(4) After the frequency oscillation of the alternating current power grid is finished, the VSC/LCC coordinated control instruction exits, the VSC and the LCC exit the frequency modulation mode, and normal operation is recovered.

According to the steps of the above coordination control method, a VSC and LCC control block diagram is obtained, as shown in fig. 4.

In the context of figure 4, it is shown,andis an active power reference value when the VSC and the LCC run in a steady state,andthe final active power reference value is obtained after coordinated control of the VSC and the LCC power frequency, and the final output active power reference value needs to pass through an amplitude limiting link.

Based on the method, the frequency fluctuation of the alternating current system after LCC commutation failure is suppressed, and simulation verification is carried out by taking a certain power grid as an example, wherein the structure of the power grid is the same as that of the power grid shown in the figure 1. A single-phase instantaneous ground fault occurs on the receiving-end bus of the LCC, then the LCC fails to change phase, and the comparison between the VSC/LCC not performing control and the adoption of the power frequency coordination control method is shown in FIG. 5;

as can be seen from fig. 5, after the coordination control method is adopted, the first swing peak value of the frequency of the alternating current power grid is reduced, and then the oscillation is quickly subsided.

Fig. 6 shows VSC active power reference values and measured values, and fig. 7 shows LCC active power reference values and measured values.

The present invention further provides a recovery system 200 after a commutation failure of a VSC/LCC parallel hybrid multi-feed system, as shown in fig. 8, including:

the detection module 201 detects whether a VSC/LCC parallel hybrid multi-feed system fails to change phase, and sends a VSC/LCC power frequency coordination control instruction after detecting that the LCC fails to change phase;

the first mode switching module 202 controls the VSC and the LCC to enter a power compensation mode after receiving the VSC/LCC power frequency coordination control instruction;

the second mode switching module 203 controls the VSC and the LCC to switch the power compensation mode to the frequency modulation mode after the power compensation mode lasts for the preset time;

and the quitting module 204 is used for controlling the VSC and the LCC to quit the power frequency coordination control instruction and the frequency modulation mode and recovering the normal operation of the VSC and the LCC after detecting that the frequency oscillation of the alternating current power grid is finished.

And when the LCC is detected to have phase commutation failure, the delay time for sending the VSC/LCC power frequency coordination control instruction does not exceed 50 ms.

Wherein, entering a power compensation mode specifically comprises:

controlling the VSC to perform power back-down operation by modifying an active power reference value of the VSC in a power compensation mode;

the back-down power is a smaller value between a set value and the LCC power down due to commutation failure;

the power reduction caused by the commutation failure is the difference value between the active power reference value before the LCC has commutation failure and the LCC active power measured value;

and controlling the LCC to perform power boosting operation in the power compensation mode by modifying the LCC active power reference value, wherein the boosted power cannot exceed the LCC active power upper limit.

The frequency modulation mode specifically includes:

and controlling the VSC and the LCC to stop power lifting, controlling the output quantity of the active power reference value superposed frequency modulation link, and inhibiting the frequency oscillation of the alternating current power grid.

The preset time needs to limit the first oscillation peak value of the frequency, and meanwhile, the subsequent frequency oscillation is not aggravated.

The invention can restrain the frequency fluctuation of the alternating current system after LCC commutation failure.

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

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

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

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

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

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.