A parallel three-terminal DC transmission system FLC power coordination method and device

Abstract

The present invention relates to a FLC power coordination method and device for a parallel three-terminal direct current transmission system. The method converts, limits, and coordinates the current regulation amount generated by the FLC operating end, and distinguishes between situations where both ends transmit power and one end receives power, and situations where one end transmits power and both ends receive power. This method solves the power coordination problem after the FLC is activated in the parallel three-terminal direct current transmission system, meets the requirements of modulation functions such as FLC in the parallel three-terminal direct current transmission system, prevents overmodulation, increases the stability of the direct current system, improves the correctness of the direct current system's response, and can stabilize the frequency of the alternating current system to which it is connected, thus playing a certain regulatory role on the alternating current system.

Description

Technical Field

[0001] The present invention relates to the technical field related to direct current (DC) transmission systems, and in particular to a FLC power coordination method and device for a parallel three-terminal DC transmission system. Background Art

[0002] Frequency Limit Control (FLC) regulates the active power of the DC transmission system to influence the frequency of the connected AC system, thereby stabilizing the AC system frequency. After FLC is activated in the DC transmission system, the resulting adjustment is added to the DC current reference value to regulate the DC power of the DC transmission system.

[0003] In the prior art, the FLC power coordination method for a two-terminal DC transmission system is usually as follows:

[0004] The power regulation amount P generated by the FLC action of this station ref_FLC Divide by the DC line voltage to get the current regulation amount I generated by the FLC action of this station ref_FLC ;

[0005] The current regulation value of this station I ref_FLC Transmitted to another station via inter-station communication of the DC system;

[0006] The current regulation value of this station I ref_FLC and the current regulation value I of the opposite station ref_FLC_OS Add up to get I ref_AC , and then added to the DC current reference value I ref_DC The DC current reference value I is obtained ref_AC+DC , and participate in the subsequent DC current reference value calculation.

[0007] A parallel three-terminal DC transmission system is a DC transmission system consisting of three converter stations connected in parallel. Figure 1 、 Figure 2 As shown, it can be operated at two ends or three ends. The three-terminal operation state includes the two-to-one mode, that is, in a three-terminal DC transmission system, two ends transmit power and one end receives power, as shown in Figure 1 As shown, and the one-to-two mode, that is, in a three-terminal DC transmission system, one end transmits power and the other two receive power, as shown Figure 2 However, the above-mentioned FLC power coordination method for the two-terminal DC transmission system is only applicable to the two-terminal operation condition. For the three-terminal operation condition, a special power coordination method is required to solve the power distribution problem after the FLC is activated. Summary of the Invention

[0008] Based on the above-mentioned situation of the prior art, the purpose of the present invention is to provide a parallel three-terminal DC transmission system FLC power coordination method and device to solve the power coordination problem after the parallel three-terminal DC transmission system FLC is activated, ensure the correct response of the DC system, and play a certain regulatory role on the AC system.

[0009] To achieve the above object, according to one aspect of the present invention, a method for FLC power coordination of a parallel three-terminal direct current transmission system is provided, comprising the steps of:

[0010] Obtain the current regulation amount generated by the FLC action at the FLC action end;

[0011] Limiting the current regulation amount to obtain a current upper limit value and a current lower limit value of the limited current;

[0012] Based on the current upper limit value and the current lower limit value, obtaining the current regulation amount of each of the three terminals of the direct current transmission system according to the coordination strategy;

[0013] The current adjustment amounts of the three terminals obtained after adjustment are respectively added to the preset DC current reference values ​​of the three terminals to obtain the final current reference value.

[0014] Furthermore, the current regulation amount I generated by the FLC action at this end ref_FLC Calculated by the following formula:

[0015] I ref_FLC =P ref_FLC / U dc

[0016] Among them, P ref_FLC is the power regulation amount generated by the FLC action at this end, U dc is the DC line voltage.

[0017] Furthermore, the parallel three-terminal DC power transmission system includes three terminals A, B, and C; by adjusting the power at terminals A and B, the power at terminal C is automatically distributed to achieve power coordination.

[0018] Furthermore, when the parallel three-terminal DC transmission system operates in a mode where terminals A and B transmit power and terminal C receives power, the upper and lower current limits of each terminal are:

[0019] U _Lim_A =min{(I max_A -I ref_A ),(I max_C -I ref_C )}

[0020] D _Lim_A =0.1-I ref_A

[0021] U _Lim_B =min{(I max_C -I ref_C ),(I max_B -I ref_B )}

[0022] D _Lim_B =0.1-I ref_B

[0023] U _Lim_C =min{(I max_C -I ref_C ),(I max_A -I ref_A )+(I max_B -I ref_B )}

[0024] D _Lim_C =0.2-I ref_C

[0025] Among them, U _Lim_A 、U _Lim_B 、U _Lim_C The upper limit of the current of the three terminals A, B, and C, respectively, _Lim_A 、D _Lim_B 、D _Lim_C are the lower current limits of terminals A, B, and C, respectively. max_A , I max_B , I max_C are the maximum DC currents at terminals A, B, and C, respectively. ref_A , I ref_B , I ref_C They are the DC current reference values ​​of terminals A, B and C respectively.

[0026] Furthermore, the current regulation amount of each of the three terminals of the DC transmission system is obtained according to the coordination strategy based on the current upper limit value and the current lower limit value, including:

[0027] When satisfied

[0028] I ref_FLC_C >0, or

[0029] I ref_FLC_C <0 and I act_B <0.12,

[0030] I ref_AC_A =I ref_FLC_C +(I ref_B -0.1);

[0031] otherwise,

[0032] I ref_AC_A =0

[0033] Among them, I ref_FLC_C is the current regulation amount generated by the FLC action at the C terminal, I act_B is the actual value of the DC current at terminal B, I ref_AC_A is the current regulation value at terminal A.

[0034] Furthermore, the current regulation amount of each of the three terminals of the DC transmission system is obtained according to the coordination strategy based on the current upper limit value and the current lower limit value, including:

[0035] When satisfied

[0036] I ref_FLC_C >0 and I max_A act_A hour,

[0037] I ref_AC_B =I ref_FLC_C -(I max_A -I ref_A );

[0038] When satisfied

[0039] I ref_FLC_C <0,

[0040] I ref_AC_B =I ref_FLC_C ;

[0041] In other cases,

[0042] I ref_AC_B =0

[0043] Among them, I ref_FLC_C is the current regulation amount generated by the FLC action at the C terminal, I act_A is the actual value of the DC current at terminal A, I ref_AC_B is the current regulation value at terminal B.

[0044] Furthermore, when the parallel three-terminal DC transmission system operates in a mode where terminal A transmits power and terminals B and C receive power, the upper and lower current limits of each terminal are:

[0045] U _Lim_A =min{(I max_A -I ref_A ),(I max_B -I ref_B )+(I max_C -I ref_C )}

[0046] D _Lim_A =0.2-I ref_A

[0047] U​_Lim_B =min{(I max_A -I ref_A ),(I max_B -I ref_B )}

[0048] D _Lim_B =0.1-I ref_B

[0049] U _Lim_C =min{(I max_A -I ref_A ),(I max_C -I ref_C )}

[0050] D _Lim_C =0.1-I ref_C

[0051] Among them, U _Lim_A 、U _Lim_B 、U _Lim_C The upper limit of the current of the three terminals A, B, and C, respectively, _Lim_A 、D _Lim_B 、D _Lim_C are the lower current limits of terminals A, B, and C, respectively. max_A , I max_B , I max_C are the maximum DC currents at terminals A, B, and C, respectively. ref_A , I ref_B , I ref_C They are the DC current reference values ​​of terminals A, B and C respectively.

[0052] Furthermore, the current regulation amount of each of the three terminals of the DC transmission system is obtained according to the coordination strategy based on the current upper limit value and the current lower limit value, including:

[0053] I ref_AC_A =I ref_FLC_B +I ref_FLC_C ;

[0054] Among them, I ref_FLC_B , I ref_FLC_C is the current regulation amount generated by the FLC action at the B and C terminals, I ref_AC_A is the current regulation value at terminal A.

[0055] Furthermore, the current regulation amount of each of the three terminals of the DC transmission system is obtained according to the coordination strategy based on the current upper limit value and the current lower limit value, including:

[0056] When satisfied

[0057] I max_A >0 and I act_A -Iref_B >I max_C hour,

[0058] I ref_AC_B =I ref_FLC_A -(I max_C -I ref_C );

[0059] When satisfied

[0060] I ref_FLC_A <0,

[0061] I ref_AC_B =I ref_FLC_A ;

[0062] In other cases,

[0063] I ref_AC_B =0;

[0064] Among them, I ref_FLC_A is the current regulation amount generated by the FLC action at terminal A, I act_A is the actual value of the DC current at terminal A, I ref_AC_B is the current regulation value at terminal B.

[0065] According to another aspect of the present invention, a parallel three-terminal direct current transmission system FLC power coordination device is provided, comprising a conversion module, a limiting module, a current regulation amount acquisition module, and a coordination module; wherein,

[0066] The conversion module obtains the current regulation amount generated by the FLC action at the FLC action end;

[0067] The limiting module limits the current regulation amount to obtain a current upper limit value and a current lower limit value of the limiting current;

[0068] The current regulation value acquisition module acquires the current regulation values ​​of the three terminals of the DC power transmission system according to the coordination strategy based on the current upper limit value and the current lower limit value;

[0069] The coordination module adds the current adjustment amounts of the three terminals obtained after adjustment to the preset DC current reference values ​​of the three terminals to obtain the final current reference value.

[0070] In summary, the present invention provides a method and apparatus for FLC power coordination in a parallel three-terminal DC transmission system. The method converts, limits, and coordinates the current regulation amount generated by the FLC operating end, and differentiates between situations where power is transmitted at both ends and received at one end, and where power is transmitted at one end and received at both ends. This method solves the power coordination problem after FLC operation in the parallel three-terminal DC transmission system, improves the accuracy of the DC system response, and can stabilize the frequency of the AC system to which it is connected, thereby playing a certain regulatory role in the AC system. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 This is a schematic diagram of a parallel three-terminal DC transmission system in a two-terminal power transmission and one-terminal power receiving mode;

[0072] Figure 2 This is a schematic diagram of a parallel three-terminal DC transmission system in a one-terminal power transmission and two-terminal power receiving mode;

[0073] Figure 3 is a block diagram of the FLC power coordination process of the parallel three-terminal DC transmission system of the present invention;

[0074] Figure 4 is a flow chart of the FLC power coordination method for a parallel three-terminal DC transmission system of the present invention;

[0075] Figure 5 This is a block diagram of the FLC power coordination device of the parallel three-terminal DC transmission system of the present invention. DETAILED DESCRIPTION

[0076] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0077] The technical solution of the present invention is described in detail below with reference to the accompanying drawings. According to one embodiment of the present invention, a FLC power coordination method for a parallel three-terminal DC transmission system is provided. The method implements FLC power coordination for the parallel three-terminal DC transmission system through a conversion link, a limit link, and a coordination link. The block diagram of the coordination process is shown in FIG. Figure 3 The flow chart of the coordination method is shown in Figure 4 As shown, the steps include:

[0078] Get the current regulation value I generated by the FLC action at the FLC action end ref_FLC , the current regulation value I ref_FLC It can be calculated by the following formula:

[0079] I ref_FLC =P ref_FLC / U dc

[0080] The parallel three-terminal DC transmission system may include terminals A, B, and C. By adjusting the power at terminals A and B, the power at terminal C is automatically distributed to achieve power coordination.

[0081] According to the above calculation, the current regulation value I ref_FLC The steps are as follows: in the conversion link, the power regulation amount P generated by the FLC action of each of the three ends ref_FLC_A 、P ref_FLC_B 、P ref_FLC_C , divided by the DC line voltage, the current regulation amount I generated by the FLC action at each of the three terminals can be obtained. ref_FLC_A , I ref_FLC_B , I ref_FLC_C .

[0082] In order to ensure that there will be no over-regulation after the FLC is activated, the current regulation amount generated by the FLC action of each of the three terminals needs to pass through the limiting link. The limiting link can be implemented by the following steps: ref_FLC The current is limited to obtain the upper and lower current limits. ref_FLC When the current regulation value I does not exceed the range of the upper limit and the lower limit, the current regulation value I ref_FLC If the current exceeds the range, the current regulation amount is adjusted to the current upper limit or the current lower limit. This step can be divided into two cases:

[0083] When the parallel three-terminal DC transmission system operates in a mode where terminals A and B transmit power and terminal C receives power, the upper and lower current limits of each terminal are:

[0084] U _Lim_A =min{(I max_A -I ref_A ),(I max_C -I ref_C )}

[0085] D _Lim_A =0.1-I ref_A

[0086] U _Lim_B =min{(I max_C -I ref_C ),(I max_B -I ref_B )}

[0087] D _Lim_B =0.1-I ref_B

[0088] U _Lim_C =min{(I max_C -I ref_C ),(I max_A -I ref_A )+(I max_B -I ref_B )}

[0089] D _Lim_C =0.2-I ref_C

[0090] When the parallel three-terminal DC transmission system operates in the mode where terminal A transmits power and terminals B and C receive power, the upper and lower current limits of each terminal are:

[0091] U _Lim_A =min{(I max_A -I ref_A ),(I max_B -I ref_B )+(I max_C -I ref_C )}

[0092] D _Lim_A =0.2-I ref_A

[0093] U _Lim_B =min{(I max_A -I ref_A ),(I max_B -I ref_B )}

[0094] D _Lim_B =0.1-I ref_B

[0095] U _Lim_C =min{(I max_A -I ref_A ),(I max_C -I ref_C )}

[0096] D _Lim_C =0.1-I ref_C .

[0097] In order to regulate the power between the three terminals, the coordination link needs to follow certain coordination principles.

[0098] In a scenario where both ends A and B transmit power, and end C receives power: when the FLC at one transmitting end activates, end C adjusts accordingly without affecting the power of the other transmitting end. When the FLC at the sole receiving end, end C, activates, the FLC prioritizes increasing the power at end A when increasing power, and then increases the power at end B if it's insufficient. When the FLC decreases power, it prioritizes decreasing the power at end B, and then decreases the power at end A if it's insufficient.

[0099] In a mode where end A is transmitting power and end B is receiving power, when the FLC at end A, the only transmitting end, activates. When the FLC increases power, it prioritizes increasing power at end C, and if it's insufficient, it then increases power at end B. When the FLC decreases power, it prioritizes decreasing power at end B, and if it's insufficient, it then decreases power at end C. When the FLC at one receiving end activates, end A coordinates the adjustment without affecting the power at the other receiving end.

[0100] Regardless of the two-end power transmission and one-end power reception mode or the one-end power transmission and two-end power reception mode, terminals A and B always control the power (current), while terminal C controls the voltage. When coordinating the power of the three terminals, only the power of terminals A and B needs to be adjusted, and the power of terminal C will be automatically distributed. The specific implementation of the coordination link can be carried out according to the following steps:

[0101] Based on the current upper limit value and the current lower limit value, obtaining the current regulation amount of each of the three terminals of the direct current transmission system according to the coordination strategy includes:

[0102] When the parallel three-terminal DC transmission system operates in the mode of power transmission at terminals A and B and power reception at terminal C,

[0103] I ref_FLC_C >0, or

[0104] I ref_FLC_C <0 and I act_B <0.12,

[0105] I ref_AC_A =I ref_FLC_C +(I ref_B -0.1);

[0106] otherwise,

[0107] I ref_AC_A =0.

[0108] When satisfied

[0109] I ref_FLC_C >0 and I max_A act_A hour,

[0110] I ref_AC_B =I ref_FLC_C -(I max_A -I ref_A );

[0111] When satisfied

[0112] I ref_FLC_C <0,

[0113] I ref_AC_B =I ref_FLC_C ; ​

[0114] In other cases,

[0115] I ref_AC_B =0.

[0116] When the parallel three-terminal DC transmission system operates in the mode where terminal A transmits power and terminals B and C receive power,

[0117] I ref_AC_A =I ref_FLC_B +I ref_FLC_C ;

[0118] When satisfied

[0119] I max_A >0 and I act_A -I ref_B >I max_C hour,

[0120] I ref_AC_B =I ref_FLC_A -(I max_C -I ref_C );

[0121] When satisfied

[0122] I ref_FLC_A <0,

[0123] I ref_AC_B =I ref_FLC_A ;

[0124] In other cases,

[0125] I ref_AC_B =0.

[0126] The current adjustment amount of each of the three terminals after adjustment is added to the preset DC current reference value of each of the three terminals. The preset DC current reference value can usually be the DC current reference value issued by the operator. That is to say, after the power coordination link, the I ref_AC Superimpose on the three terminals of the I ref_DC It participates in the subsequent calculation of the current reference value.

[0127] In the formulas involved in the above steps,

[0128] P ref_FLC The power regulation amount generated by the FLC action at this end;

[0129] U dc is the DC line voltage;

[0130] U _Lim_A 、U _Lim_B 、U _Lim_CThey are the upper limit of current for the three terminals A, B and C respectively;

[0131] D _Lim_A 、D _Lim_B 、D _Lim_C They are the lower current limits of the three terminals A, B and C respectively;

[0132] I max_A , I max_B , I max_C are the maximum DC currents at terminals A, B, and C respectively;

[0133] I ref_A , I ref_B , I ref_C They are the DC current reference values ​​of terminals A, B and C respectively;

[0134] I ref_FLC_A , I ref_FLC_B , I ref_FLC_C They are the current regulation amounts generated by the FLC action at terminals A, B, and C respectively;

[0135] I act_A , I act_B , I act_C are the actual values ​​of DC current at terminals A, B, and C respectively;

[0136] I ref_AC_A , I ref_AC_B , I ref_AC_C They are the current regulation amounts at terminals A, B, and C respectively;

[0137] When the method provided in this embodiment is used for power coordination, when operating in a mode of transmitting power at both ends and receiving power at one end, the FLC action results of ends A and B are consistent; when operating in a mode of transmitting power at one end and receiving power at both ends, the FLC action results of ends B and C are consistent. The following uses the FLC action of ends A and C as an example to illustrate the power coordination results of the method described in this embodiment. Table 1 shows the power coordination results of the FLC action at end A in the mode of transmitting power at both ends and receiving power at one end; Table 2 shows the power coordination results of the FLC action at end C in the mode of transmitting power at both ends and receiving power at one end; Table 3 shows the power coordination results of the FLC action at end A in the mode of transmitting power at one end and receiving power at both ends; Table 4 shows the power coordination results of the FLC action at end C in the mode of transmitting power at one end and receiving power at both ends.

[0138] Table 1 Power coordination results of FLC operation at end A in the two-end power transmission and one-end power reception mode

[0139] A-side B-side C-end Initial state 0.4pu 0.4pu 0.8pu A-end power increase 0.2pu 0.6pu 0.4pu 1.0pu A-side power reduction 0.2pu 0.2pu 0.4pu 0.6pu

[0140] Table 2 Power coordination results of FLC operation at end C in the two-end power transmission and one-end power receiving mode

[0141] A-side B-side C-end Initial state 0.4pu 0.4pu 0.8pu C-end power increase 0.2pu 0.6pu 0.4pu 1.0pu C-end power reduction 0.2pu 0.4pu 0.2pu 0.6pu C-end power reduction 0.5pu 0.2pu 0.1pu 0.3pu

[0142] Table 3 Power coordination results of FLC operation at end A in the one-end power transmission and two-end power reception mode

[0143] A-side B-side C-end Initial state 0.8pu 0.4pu 0.4pu A-end power increase 0.2pu 1.0pu 0.4pu 0.6pu A-side power reduction 0.2pu 0.6pu 0.2pu 0.4pu A-side power reduction 0.5pu 0.3pu 0.1pu 0.2pu

[0144] Table 4 Power coordination results of FLC operation at end C in one-end power transmission and two-end power reception mode

[0145] A-side B-side C-end Initial state 0.8pu 0.4pu 0.4pu C-end power increase 0.2pu 1.0pu 0.4pu 0.6pu C-end power reduction 0.2pu 0.6pu 0.4pu 0.2pu

[0146] As can be seen from the power coordination results in Tables 1 to 4, the method provided in this embodiment can effectively solve the DC power coordination problem between the three terminals of a parallel three-terminal DC transmission system after the FLC at each terminal is activated, thereby improving the stability of the DC system and the AC system.

[0147] According to another embodiment of the present invention, a parallel three-terminal DC transmission system FLC power coordination device is provided. The block diagram of the device is as follows: Figure 5 As shown, the device includes a conversion module, a limiting module, a current regulation amount acquisition module, and a coordination module.

[0148] The conversion module obtains the current regulation value I generated by the FLC action at the FLC action end. ref_FLC ;

[0149] The limiting module adjusts the current I ref_FLC Performing amplitude limiting to obtain an upper current limit value and a lower current limit value of the amplitude limiting;

[0150] a current regulation value acquisition module, which acquires the current regulation values ​​of the three terminals of the DC transmission system according to the coordination strategy based on the current upper limit value and the current lower limit value;

[0151] The coordination module adds the current adjustment amounts of the three terminals obtained after adjustment to the preset DC current reference values ​​of the three terminals to obtain the final current reference value.

[0152] The implementation of each function in each module is the same as the steps of the power coordination method provided in the first embodiment of the present invention, and will not be repeated here.

[0153] In summary, the present invention relates to a FLC power coordination method and apparatus for a parallel three-terminal DC transmission system. The method converts, limits, and coordinates the current regulation amount generated by the FLC operating end, and differentiates between situations where both ends transmit power and one end receives power, and where one end transmits power and both ends receive power. This method solves the power coordination problem after FLC operation in the parallel three-terminal DC transmission system, meets the requirements of modulation functions such as FLC in the parallel three-terminal DC transmission system, prevents overmodulation, increases the stability of the DC system, improves the accuracy of the DC system response, and stabilizes the frequency of the AC system to which it is connected, thereby playing a certain regulatory role in the AC system.

[0154] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

Claims

1. A parallel three-terminal direct current transmission system FLC power coordination method, characterized in that: The parallel three-terminal DC power transmission system includes three terminals A, B, and C. The method includes the following steps: Obtain the current regulation amount generated by the FLC action at the FLC action end; The current regulation amount is limited by calculating the current upper limit and lower limit. When the parallel three-terminal DC transmission system operates in a mode where terminals A and B transmit power and terminal C receives power, the current regulation amount of each of the three terminals of the DC transmission system is obtained according to a coordination strategy based on the current regulation amount after limiting, including: When satisfied I ref_FLC_C >0, or I ref_FLC_C <0 and I act_B <0.12 hours, I ref_AC_A = I ref_FLC_C +(I ref_B - 0.1); otherwise, I ref_AC_A =0 Among them, I ref_FLC_C is the current regulation amount generated by the FLC action at the C terminal, I act_B is the actual value of the DC current at terminal B, I ref_AC_A is the current regulation value at terminal A; I ref_B is the DC current reference value at terminal B; When the parallel three-terminal DC transmission system operates in a mode where one terminal A transmits power and the other terminals B and C receive power, the current regulation values ​​of the three terminals of the DC transmission system are obtained according to a coordination strategy based on the current regulation value after limiting, including: I ref_AC_A =I ref_FLC_B + I ref_FLC_C ; Among them, I ref_FLC_B , I ref_FLC_C is the current regulation amount generated by the FLC action at the B and C terminals, I ref_AC_A is the current regulation value at terminal A; The current adjustment amounts of the three terminals obtained after adjustment are respectively added to the preset DC current reference values ​​of the three terminals to obtain the final current reference value.

2. The method according to claim 1, characterized in that The current regulation amount I generated by the FLC action at this end ref_FLC Calculated by the following formula: AND ref_FLC =P ref_FLC / IN dc Among them, P ref_FLC is the power regulation amount generated by the FLC action at this end, U dc is the DC line voltage.

3. The method according to claim 2, characterized in that By adjusting the power at ends A and B, the power at end C is automatically distributed to achieve power coordination.

4. The method according to claim 3, characterized in that When the parallel three-terminal DC transmission system operates in a mode where terminals A and B transmit power and terminal C receives power, the upper and lower current limits of each terminal are: U _Lim_A = min{(I max_A -I ref_A ) , (I max_C -I ref_C )} D _Lim_A = 0.1 - I ref_A U _Lim_B = min{(I max_C -I ref_C ) , (I max_B -I ref_B )} D _Lim_B = 0.1 - I ref_B U _Lim_C = min{(I max_C -I ref_C ) , (I max_A -I ref_A )+(I max_B -I ref_B )} D _Lim_C = 0.2 - I ref_C Among them, U _Lim_A 、U _Lim_B 、U _Lim_C The upper limit of the current of the three terminals A, B, and C, respectively, _Lim_A 、D _Lim_B 、D _Lim_C are the lower current limits of terminals A, B, and C, respectively. max_A , I max_B , I max_C are the maximum DC currents at terminals A, B, and C, respectively. ref_A , I ref_B , I ref_C They are the DC current reference values ​​of terminals A, B and C respectively.

5. The method according to claim 4, characterized in that Based on the current upper limit value and the current lower limit value, the current regulation amount of each of the three terminals of the DC transmission system is obtained according to the coordination strategy, which also includes: when the current upper limit value and the current lower limit value are satisfied, I ref_FLC_C >0 and I max_A act_A Time,​ I ref_AC_B =I ref_FLC_C -(I max_A - I ref_A ); When satisfied I ref_FLC_C <0, I ref_AC_B =I ref_FLC_C ; In other cases, I ref_AC_B =0 Among them, I ref_FLC_C is the current regulation amount generated by the FLC action at the C terminal, I act_A is the actual value of the DC current at terminal A, I ref_AC_B is the current regulation value at terminal B.

6. The method according to claim 3, characterized in that When the parallel three-terminal DC transmission system operates in a mode where terminal A transmits power and terminals B and C receive power, the upper and lower current limits of each terminal are: U _Lim_A = min{(I max_A -I ref_A ) , (I max_B -I ref_B )+(I max_C -I ref_C )} D _Lim_A = 0.2 - I ref_A U _Lim_B = min{(I max_A -I ref_A ) , (I max_B -I ref_B )} D _Lim_B = 0.1 - I ref_B U _Lim_C = min{(I max_A -I ref_A ) , (I max_C -I ref_C )} D _Lim_C = 0.1 - I ref_C Among them, U _Lim_A 、U _Lim_B 、U _Lim_C The upper limit of the current of the three terminals A, B, and C, respectively, _Lim_A 、D _Lim_B 、D _Lim_C are the lower current limits of terminals A, B, and C, respectively. max_A , I max_B , I max_C are the maximum DC currents at terminals A, B, and C, respectively. ref_A , I ref_B , I ref_C They are the DC current reference values ​​of terminals A, B and C respectively.

7. The method according to claim 6, characterized in that Based on the current upper limit value and the current lower limit value, the current regulation amount of each of the three terminals of the DC transmission system is obtained according to the coordination strategy, which also includes: when the current upper limit value and the current lower limit value are satisfied, I max_A >0 and I act_A -I ref_B >I max_C Time, I ref_AC_B =I ref_FLC_A -(I max_C - I ref_C ); When satisfied I ref_FLC_A <0, I ref_AC_B =I ref_FLC_A ; In other cases, I ref_AC_B =0； Among them, I ref_FLC_A is the current regulation amount generated by the FLC action at terminal A, I act_A is the actual value of the DC current at terminal A, I ref_AC_B is the current regulation value at terminal B.

8. A parallel three-terminal DC transmission system FLC power coordination device, characterized in that: The parallel three-terminal DC transmission system includes three terminals A, B, and C. The device includes a conversion module, a limiting module, a current regulation amount acquisition module, and a coordination module; wherein, The conversion module obtains the current regulation amount generated by the FLC action at the FLC action end; The limiting module limits the current regulation amount by calculating the upper limit value and the lower limit value of the current; The current regulation amount acquisition module acquires the current regulation amount of each of the three terminals of the DC transmission system according to the coordination strategy based on the current regulation amount after limiting; wherein, When the parallel three-terminal DC transmission system operates in a mode where terminals A and B transmit power and terminal C receives power, the current regulation values ​​of the three terminals of the DC transmission system are obtained according to a coordination strategy based on the current regulation value after limiting, including: When satisfied I ref_FLC_C >0, or I ref_FLC_C <0 and I act_B <0.12 hours, I ref_AC_A = I ref_FLC_C +(I ref_B - 0.1); otherwise, I ref_AC_A =0 Among them, I ref_FLC_C is the current regulation amount generated by the FLC action at the C terminal, I act_B is the actual value of the DC current at terminal B, I ref_AC_A is the current regulation value at terminal A, I ref_B is the DC current reference value at terminal B; When the parallel three-terminal DC transmission system operates in a mode where one terminal A transmits power and the other terminals B and C receive power, the current regulation values ​​of the three terminals of the DC transmission system are obtained according to a coordination strategy based on the current regulation value after limiting, including: I ref_AC_A =I ref_FLC_B + I ref_FLC_C ; Among them, I ref_FLC_B , I ref_FLC_C is the current regulation amount generated by the FLC action at the B and C terminals, I ref_AC_A is the current regulation value at terminal A; The coordination module adds the current adjustment amounts of the three terminals obtained after adjustment to the preset DC current reference values ​​of the three terminals to obtain the final current reference value.

Images