A method for flexible HVDC transmission AC side fault ride-through coupled with active AC system

Abstract

The application provides a flexible HVDC transmission AC side fault ride-through method of a coupled active AC system, determines an amplitude limiting value basic value reference value based on the line voltage effective value of the AC system, and determines an amplitude limiting value basic value reference value change rate based on the amplitude limiting value basic value reference value; determines a real-time amplitude limiting control upper limit and a lower limit based on the amplitude limiting value basic value reference value and the amplitude limiting value basic value reference value change rate; determines an inner loop current reference value based on the real-time amplitude limiting control upper limit and the lower limit, avoids the protection misoperation of the converter station caused by the temporary fault, greatly shortens the time for recovering the flexible HVDC transmission power transmission; during the recovery process of the flexible HVDC transmission after the temporary fault of the two-end active AC system and the elimination of the fault, no great impact, serious overvoltage and overcurrent are generated on the flexible HVDC transmission system, the flexible HVDC transmission system can quickly recover the power transmission, and the whole flexible HVDC transmission system has the AC side fault ride-through capability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible DC power transmission, in particular to a method for fault ride-through of a flexible DC power transmission AC side connected to an active AC system. BACKGROUND

[0002] Currently, in a two-terminal flexible DC power transmission system, if the AC systems connected to the two converter stations are both active AC systems, the one-terminal converter station is usually controlled to be a constant DC voltage, and the other-terminal converter station is controlled to be a constant active power, so as to realize power transmission between the two active AC systems through the DC line. During the recovery process of the two-terminal flexible DC power transmission system after temporary faults occur in the two active AC systems and are eliminated, the transient process will have a huge impact on the power transmission of the two-terminal flexible DC power transmission system, causing serious overvoltage and overcurrent, thereby triggering the protection of the converter station, causing the converter valve to be blocked, the AC circuit breaker to be tripped, and even causing the entire converter station to be shut down. Once the protection of the converter station is triggered (blocked, tripped, and shut down), it will take a long time to realize the recovery of the flexible DC power transmission power transmission after the fault is eliminated.

[0003] In the existing technology, in the constant active double-loop control of the flexible DC power transmission, the difference between the reference value and the real-time sampling value of the DC voltage / active power of the outer loop is subjected to PI operation, and finally the current reference value of the inner loop current controller is output after being subjected to constant value limiting. The existing technology will cause the protection of the converter station to be misoperated due to temporary faults, and it will take a long time to recover the flexible DC power transmission power transmission. SUMMARY

[0004] In order to overcome the deficiencies of the existing technology that the protection of the converter station is misoperated and it takes a long time to recover the flexible DC power transmission power transmission, the present application provides a method for fault ride-through of a flexible DC power transmission AC side connected to an active AC system. The limit value base reference value is determined based on the line voltage effective value of the AC system, and the limit value base reference value change rate is determined based on the limit value base reference value. The real-time limit control upper limit and lower limit are determined based on the limit value base reference value and the limit value base reference value change rate. The inner loop current reference value is determined based on the real-time limit control upper limit and lower limit, which avoids the misoperation of the protection of the converter station due to temporary faults, and greatly shortens the time to recover the flexible DC power transmission power transmission.

[0005] In order to achieve the above-mentioned application purposes, the present application adopts the following technical solutions:

[0006] On the one hand, the present application provides a method for fault ride-through of a flexible DC power transmission AC side connected to an active AC system, comprising:

[0007] The limit value base reference value is determined based on the line voltage effective value of the AC system, and the limit value base reference value change rate is determined based on the limit value base reference value.

[0008] determine the upper limit and the lower limit of the real-time limiting control based on the limiting value base reference value and a change rate of the limiting value base reference value;

[0009] determine the inner loop current reference value based on the upper limit and the lower limit of the real-time limiting control.

[0010] The limiting value base reference value is determined based on the line voltage effective value of the alternating current system, comprising:

[0011] obtain the line voltage effective value of the local alternating current system and the line voltage effective value of the opposite end alternating current system;

[0012] multiply the line voltage effective value of the local alternating current system by a gain coefficient and perform limiting processing to obtain a first limiting value base reference value MIN_U;

[0013] determine the smaller one of the line voltage effective value of the local alternating current system and the line voltage effective value of the opposite end alternating current system, multiply the smaller one by a gain coefficient and perform limiting processing to obtain a second limiting value base reference value MIN_P.

[0014] The change rate of the limiting value base reference value is determined based on the limiting value base reference value, comprising:

[0015] perform derivative operation on the first limiting value base reference value MIN_U after a first-order inertia link to obtain a first derivative result, and perform derivative operation on the second limiting value base reference value MIN_P after a first-order inertia link to obtain a second derivative result;

[0016] determine a first limiting value base reference value change rate rateD1 according to the first derivative result, and determine a second limiting value base reference value change rate rateD2 according to the second derivative result.

[0017] The upper limit and the lower limit of the real-time limiting control are determined based on the limiting value base reference value and the change rate of the limiting value base reference value, comprising:

[0018] perform first-order inertia link processing on the first limiting value base reference value MIN_U with a time constant being the first limiting value base reference value change rate rateD1 to obtain a real-time limiting control upper limit lim_HD_U and a real-time limiting control lower limit lim_LD_U;

[0019] perform first-order inertia link processing on the second limiting value base reference value MIN_P with a time constant being the second limiting value base reference value change rate rateD2 to obtain a real-time limiting control upper limit lim_HD_P and a real-time limiting control lower limit lim_LD_P.

[0020] When the flexible HVDC power transmission system is in the constant DC voltage control mode, the inner loop current reference value is determined based on the real-time hysteresis control upper limit and lower limit, and the method comprises the following steps:

[0021] The obtained DC voltage reference value is subtracted from the real-time DC voltage to obtain a DC voltage change value;

[0022] The DC voltage change value is passed through a proportional integral element to obtain a PI-controlled DC voltage change value;

[0023] The PI-controlled DC voltage change value is limited by the real-time hysteresis control upper limit lim_HD_P and the real-time hysteresis control lower limit lim_LD_P to obtain the inner loop current reference value of the flexible HVDC power transmission system in the constant DC voltage control mode.

[0024] When the flexible HVDC power transmission system is in the constant DC voltage control mode, the inner loop current reference value is determined based on the real-time hysteresis control upper limit and lower limit, and the method comprises the following steps:

[0025] The obtained DC voltage reference value is multiplied by a low margin gain coefficient, and then subtracted from the obtained real-time DC voltage to obtain a DC voltage change value;

[0026] The DC voltage change value is passed through a proportional integral element to obtain a PI-controlled DC voltage change value;

[0027] The PI-controlled DC voltage change value is limited by the real-time hysteresis control upper limit lim_HD_U and the real-time hysteresis control lower limit lim_U1 to obtain the inner loop current reference value of the flexible HVDC power transmission system in the constant DC voltage control mode.

[0028] The determination of the real-time hysteresis control lower limit lim_U1 comprises:

[0029] The obtained DC voltage reference value is multiplied by a high margin gain coefficient, and then subtracted from the obtained real-time DC voltage to obtain a DC voltage change value;

[0030] The DC voltage change value is passed through a proportional integral element to obtain a PI-controlled DC voltage change value;

[0031] The PI-controlled DC voltage change value is limited by the real-time hysteresis control upper limit lim_U2 and the real-time hysteresis control lower limit lim_LD_U to obtain the real-time hysteresis control lower limit lim_U1.

[0032] The determination of the real-time hysteresis control upper limit lim_U2 comprises:

[0033] The obtained active power reference value is subtracted from the real-time active power to obtain an active power change value;

[0034] The active power change value is passed through a proportional integral element to obtain a PI-controlled active power change value;

[0035] The PI-controlled active power change value is limited by a real-time limiting control upper limit lim_HD_P and a real-time limiting control lower limit lim_LD_P to obtain a real-time limiting control upper limit lim_U2.

[0036] Compared with the closest prior art, the technical solution provided by the present application has the following beneficial effects:

[0037] In the flexible DC power transmission AC side fault ride-through method provided by the present application, the amplitude limiting value base reference value is determined based on the line voltage effective value of the AC system, and the amplitude limiting value base reference value change rate is determined based on the amplitude limiting value base reference value; the real-time limiting control upper limit and lower limit are determined based on the amplitude limiting value base reference value and the amplitude limiting value base reference value change rate; and the inner loop current reference value is determined based on the real-time limiting control upper limit and lower limit, thereby avoiding the false operation of the converter station protection caused by temporary faults and greatly shortening the time for restoring the flexible DC power transmission;

[0038] The technical solution provided by the present application is suitable for the flexible DC power transmission connected to the active AC system, and during the temporary fault and fault elimination of the two-end active AC system and the flexible DC power transmission recovery process, no great impact, serious overvoltage and overcurrent are generated on the flexible DC power transmission system, and the flexible DC power transmission system can quickly restore power transmission;

[0039] The technical solution provided by the present application can ensure that the flexible DC power transmission system has the AC side fault ride-through capability;

[0040] In the present application, the AC side fault ride-through voltage margin of the flexible DC power transmission can be adjusted to zero according to the specific working conditions. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is the flow chart of the flexible DC power transmission AC side fault ride-through method connected to the active AC system in the embodiment of the present application;

[0042] Figure 2 is the first amplitude limiting value base reference value MIN_U determination block diagram in the embodiment of the present application;

[0043] Figure 3 is the second amplitude limiting value base reference value MIN_P determination block diagram in the embodiment of the present application;

[0044] Figure 4 is the first amplitude limiting value base reference value change rate rateD1 determination block diagram in the embodiment of the present application;

[0045] Figure 5is a second limiting value base value reference value change rate rateD2 determination block diagram in the embodiment of the application;

[0046] Figure 6 is a real-time limiting control upper limit lim_LD_U determination block diagram in the embodiment of the application;

[0047] Figure 7 is a real-time limiting control upper limit lim_LD_P determination block diagram in the embodiment of the application;

[0048] Figure 8 is a flexible DC power transmission system in a constant DC voltage control mode based on real-time limiting control upper limit and lower limit determination of inner loop current reference value block diagram in the embodiment of the application;

[0049] Figure 9 is a flexible DC power transmission in a constant active power control mode based on real-time limiting control upper limit and lower limit determination of inner loop current reference value block diagram in the embodiment of the application;

[0050] Figure 10 is a constant DC voltage control system block diagram in the embodiment of the application;

[0051] Figure 11 is a constant active power control system block diagram in the embodiment of the application;

[0052] Figure 12 is a flexible DC power transmission control system block diagram in the embodiment of the application. DETAILED DESCRIPTION

[0053] The application will be further described below in conjunction with the drawings.

[0054] The embodiment of the application provides a flexible DC power transmission AC side fault ride-through method for connecting an active AC system, and a specific flow chart is as shown in Figure 1 The specific process is as follows:

[0055] S101: determining a limiting value base value reference value based on the line voltage effective value of the AC system, and determining a limiting value base value reference value change rate based on the limiting value base value reference value;

[0056] S102: determining a real-time limiting control upper limit and a lower limit based on the limiting value base value reference value and the limiting value base value reference value change rate;

[0057] S103: determining an inner loop current reference value based on the real-time limiting control upper limit and the lower limit.

[0058] In S101, the limiting value base value reference value is determined based on the line voltage effective value of the AC system, and the limiting value base value reference value change rate is determined based on the limiting value base value reference value, and the limiting value base value reference value change rate is determined based on the limiting value base value reference value.

[0059] obtaining line voltage effective values of the local AC system and the opposite end AC system respectively;

[0060] multiplying the line voltage effective value of the local AC system by a gain coefficient and performing amplitude limiting processing to obtain a first amplitude limiting value base reference value MIN_U, as shown in Figure 2 Figure 2 In the formula, V1 is the line voltage effective value of the local AC system, k2 is the gain coefficient, k3 and k4 are upper and lower limits in the amplitude limiting processing respectively, and MIN_U is the first amplitude limiting value base reference value.

[0061] determining a smaller one of the line voltage effective value of the local AC system and the line voltage effective value of the opposite end AC system, multiplying the smaller one by a gain coefficient and performing amplitude limiting processing to obtain a second amplitude limiting value base reference value MIN_P, as shown in Figure 3 Figure 3 In the formula, V remote is the line voltage effective value of the opposite end AC system, k5 is the gain coefficient, k6 and k7 are upper and lower limits in the amplitude limiting processing respectively, MIN_P is the second amplitude limiting value base reference value, and e is the smaller one of the line voltage effective value of the local AC system and the line voltage effective value of the opposite end AC system.

[0062] In S101, a rate of change of the amplitude limiting value base reference value is determined based on the amplitude limiting value base reference value, including:

[0063] deriving the first amplitude limiting value base reference value MIN_U after a first-order inertia link to obtain a first derivation result, and deriving the second amplitude limiting value base reference value MIN_P after a first-order inertia link to obtain a second derivation result;

[0064] determining a first amplitude limiting value base reference value change rate rateD1 based on the first derivation result (as shown in Figure 4 ), and determining a second amplitude limiting value base reference value change rate rateD2 based on the second derivation result (as shown in Figure 5 ), Figure 4 In the formula, rateD1 is the first amplitude limiting value base reference value change rate, T is a time constant of the first-order inertia link, and du / dt is the derivation result. Figure 5 In the formula, rateD2 is the second amplitude limiting value base reference value change rate, T is a time constant of the first-order inertia link, and du / dt is the derivation result.

[0065] In S102, a real-time amplitude limiting control upper limit and a real-time amplitude limiting control lower limit are determined based on the amplitude limiting value base reference value and the rate of change of the amplitude limiting value base reference value, including:

[0066] ​​The first clipping value base reference value MIN_U is processed through a first-order inertia link with a time constant of a first clipping value base reference value change rate rateD1 to obtain a real-time clipping control upper limit lim_HD_U and a real-time clipping control lower limit lim_LD_U, as shown in Figure 6 . Figure 6 In the formula, T1 is the time constant of the first-order inertia link, and rateD1 is taken.

[0067] The second clipping value base reference value MIN_P is processed through a first-order inertia link with a time constant of a second clipping value base reference value change rate rateD2 to obtain a real-time clipping control upper limit lim_HD_P and a real-time clipping control lower limit lim_LD_P, as shown in Figure 7 . Figure 7 In the formula, T2 is the time constant of the first-order inertia link, and rateD2 is taken.

[0068] The flexible DC power transmission system has two working modes: a constant DC voltage control mode and a constant active power control mode.

[0069] As shown in Figure 8 , when the flexible DC power transmission system is in the constant DC voltage control mode, S103 determines the inner loop current reference value based on the real-time clipping control upper limit and lower limit, including:

[0070] The obtained DC voltage reference value U dcref_pu and the real-time DC voltage U dc_pu are subtracted to obtain a DC voltage change value;

[0071] The DC voltage change value is processed through a proportional integral link (i.e., a PI link) to obtain a PI-controlled DC voltage change value;

[0072] After the PI-controlled DC voltage change value is limited by the real-time clipping control upper limit lim_HD_P and the real-time clipping control lower limit lim_LD_P, an inner loop current reference value I ref of the flexible DC power transmission system in the constant DC voltage control mode is obtained.

[0073] The inner loop current reference value of the flexible DC power transmission system in the constant DC voltage control mode is input into an inner loop current controller, and then dq inverse transformation is performed to obtain a constant DC voltage control system as shown in 10.

[0074] As shown in Figure 9 , when the flexible DC power transmission system is in the constant active power control mode, S103 determines the inner loop current reference value based on the real-time clipping control upper limit and lower limit, including:

[0075] The obtained DC voltage reference value U dcref_pumultiplied by a low margin gain coefficient k13, and then subtracted from the acquired real-time DC voltage U dc_pu to obtain a DC voltage change value;

[0076] The DC voltage change value is passed through a proportional integral link (i.e., a PI link) to obtain a PI-controlled DC voltage change value;

[0077] The PI-controlled DC voltage change value is limited by a real-time limiting control upper limit lim_HD_U and a real-time limiting control lower limit lim_LD_U to obtain an inner loop current reference value I ref .

[0078] The determination of the real-time limiting control lower limit lim_LD_U includes:

[0079] The acquired DC voltage reference value U dcref_pu is multiplied by a high margin gain coefficient k12, and then subtracted from the acquired real-time DC voltage to obtain a DC voltage change value;

[0080] The DC voltage change value is passed through a proportional integral link (i.e., a PI link) to obtain a PI-controlled DC voltage change value;

[0081] The PI-controlled DC voltage change value is limited by a real-time limiting control upper limit lim_U2 and a real-time limiting control lower limit lim_LD_U to obtain the real-time limiting control lower limit lim_LD_U.

[0082] The determination of the real-time limiting control upper limit lim_U2 includes:

[0083] The acquired active power reference value P ref_pu is subtracted from the real-time active power P pu to obtain an active power change value;

[0084] The active power change value is passed through a proportional integral link (i.e., a PI link) to obtain a PI-controlled active power change value;

[0085] The PI-controlled active power change value is limited by a real-time limiting control upper limit lim_HD_P and a real-time limiting control lower limit lim_LD_P to obtain the real-time limiting control upper limit lim_U2.

[0086] The inner loop current reference value I of the flexible DC power transmission system in the constant active power control mode is input into an inner loop current controller, and then passed through dq inverse transformation to obtain a constant active power control system as shown in 11.

[0087] The control system corresponding to the flexible DC power transmission system connected with the active AC system is as shown in Figure 12 , and the inner loop current reference value Iref The input inner loop current controller, after dq inverse transformation, obtains the flexible DC power transmission system connected with the active AC system.

[0088] For ease of description, the parts of the above apparatus are described as various modules or units in function. Of course, the functions of the modules or units can be implemented in one or more software or hardware in implementing the present application.

[0089] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage, etc.) containing computer-usable program code.

[0090] The present application is described with reference to flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing apparatus to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing apparatus generate a means for implementing the functions specified in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 an apparatus that carries out the functions specified in one or more blocks.

[0091] These computer program instructions can also be stored in a computer-readable memory that can direct the computer or other programmable data processing apparatus to work in a specific manner, so that the instructions stored in the computer-readable memory produce a manufactured product including instruction apparatus, which implements the functions specified in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 an apparatus that carries out the functions specified in one or more blocks.

[0092] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, so that a series of operation steps are performed on the computer or other programmable data processing apparatus to produce a computer-implemented process, so that the instructions executed on the computer or other programmable data processing apparatus provide a means for implementing the functions specified in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 an apparatus that carries out the functions specified in one or more blocks.

[0093] It should be pointed out finally that the above examples are only used to illustrate the technical solutions of the present application but not to limit it, and the ordinary skilled in the art can still modify or equivalently replace the specific embodiments of the present application according to the above examples, and any modification or equivalent replacement which does not depart from the spirit and scope of the present application is within the protection scope of the claims of the present application.

Claims

1. A method for flexible HVDC transmission AC side fault ride through coupled with active AC system, characterized in that, The method comprises the steps of: determining a limiting value base reference value based on the effective value of the line voltage of the alternating current system, and determining a limiting value base reference value change rate based on the limiting value base reference value; determining a real-time limiting control upper limit and a real-time limiting control lower limit based on the limiting value base reference value and the limiting value base reference value change rate; determining an inner loop current reference value based on the real-time limiting control upper limit and the real-time limiting control lower limit; the step of determining the limiting value base reference value based on the effective value of the line voltage of the alternating current system comprises the steps of: obtaining the effective value of the line voltage of the local alternating current system and the effective value of the line voltage of the opposite end alternating current system; multiplying the effective value of the line voltage of the local alternating current system by a gain coefficient and performing limiting processing to obtain a first limiting value base reference value MIN_U; determining the smaller one of the effective value of the line voltage of the local alternating current system and the effective value of the line voltage of the opposite end alternating current system, and multiplying the smaller one by a gain coefficient and performing limiting processing to obtain a second limiting value base reference value MIN_P; the step of determining the limiting value base reference value change rate based on the limiting value base reference value comprises the steps of: deriving the first limiting value base reference value MIN_U after a first-order inertia link to obtain a first derivative result, and deriving the second limiting value base reference value MIN_P after a first-order inertia link to obtain a second derivative result; determining a first limiting value base reference value change rate rateD1 according to the first derivative result, and determining a second limiting value base reference value change rate rateD2 according to the second derivative result; the step of determining the real-time limiting control upper limit and the real-time limiting control lower limit based on the limiting value base reference value and the limiting value base reference value change rate comprises the steps of: processing the first limiting value base reference value MIN_U through a first-order inertia link with a time constant being the first limiting value base reference value change rate rateD1 to obtain a real-time limiting control upper limit lim_HD_U and a real-time limiting control lower limit lim_LD_U; processing the second limiting value base reference value MIN_P through a first-order inertia link with a time constant being the second limiting value base reference value change rate rateD2 to obtain a real-time limiting control upper limit lim_HD_P and a real-time limiting control lower limit lim_LD_P.

2. The method for coupled active AC system flexible HVDC transmission AC side fault ride through as claimed in claim 1, wherein, when the flexible direct current power transmission system is in a constant direct current voltage control mode, the step of determining the inner loop current reference value based on the real-time limiting control upper limit and the real-time limiting control lower limit comprises the steps of: obtaining a direct current voltage change value by subtracting the obtained real-time direct current voltage from the obtained direct current voltage reference value; obtaining a PI-controlled direct current voltage change value by processing the direct current voltage change value through a proportional integral link; obtaining an inner loop current reference value of the flexible direct current power transmission system in the constant direct current voltage control mode by limiting the PI-controlled direct current voltage change value through the real-time limiting control upper limit lim_HD_P and the real-time limiting control lower limit lim_LD_P.

3. The method of claim 1, wherein, when the flexible direct current power transmission is in a constant active power control mode, the step of determining the inner loop current reference value based on the real-time limiting control upper limit and the real-time limiting control lower limit comprises the steps of: obtaining a direct current voltage change value by multiplying the obtained direct current voltage reference value by a low margin gain coefficient and then subtracting the obtained real-time direct current voltage; The DC voltage change value is input into a proportional integral link to obtain a PI-controlled DC voltage change value; The PI-controlled DC voltage change value is limited by a real-time upper limit lim_HD_U and a real-time lower limit lim_U1 to obtain an inner loop current reference value of the flexible DC power transmission in a constant active power control mode.

4. The method of claim 2, wherein, The determination of the real-time lower limit lim_U1 includes: The DC voltage change value is obtained by multiplying the obtained DC voltage reference value by a high margin gain coefficient and then subtracting the obtained real-time DC voltage; The DC voltage change value is input into a proportional integral link to obtain a PI-controlled DC voltage change value; The PI-controlled DC voltage change value is limited by a real-time upper limit lim_U2 and a real-time lower limit lim_LD_U to obtain the real-time lower limit lim_U1.

5. The method of claim 3, wherein, The determination of the real-time upper limit lim_U2 includes: The active power change value is obtained by subtracting the real-time active power from the obtained active power reference value; The active power change value is input into a proportional integral link to obtain a PI-controlled active power change value; The PI-controlled active power change value is limited by a real-time upper limit lim_HD_P and a real-time lower limit lim_LD_P to obtain the real-time upper limit lim_U2.

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