Multi-converter alternating current bus loop closing operation control method and system

Abstract

The invention relates to a multi-converter alternating current bus closed loop operation control method and system, and belongs to the technical field of power electronic conversion. According to the method, when a bus tie switch closing instruction is received, a main guide electrode converter and a non-main guide electrode converter respectively lock current alternating current active power actual values as corresponding active power reference values, and a reference phase generator of the main guide electrode converter is superposed with a frequency difference value on the basis of an alternating current reference frequency; the generation of the phase angle of the non-main-electrode converter is kept unchanged, and when the alternating-current bus voltages on the two sides of the alternating-current bus tie switch are detected to cross zero points in the same direction and the phase difference is smaller than a set threshold value, the alternating-current bus tie switch is closed to prevent impact current from being generated in the loop closing process, so that the direct-current bus tie switch can be prevented from being damaged, and the service life of the alternating-current bus tie switch is prolonged. On the basis of not adding extra equipment, the problem of closed-loop operation of the segmented alternating-current bus of the flexible direct-current power transmission system of the new energy station is solved, the construction cost of the new energy station is reduced, and the occupied area is saved.

Description

Technical Field

[0001] The invention relates to a multi-converter AC bus closed-loop operation control method and system, belonging to the technical field of power electronic conversion. Background Art

[0002] The existing flexible DC transmission system topology diagram is as follows: Figure 1 As shown in the figure, the topology mainly consists of a sending-end renewable energy source, a sending-end converter station, a DC line, a receiving-end converter station, and a receiving-end power grid. The sending-end renewable energy source station is connected to the AC segmented busbar of the sending-end converter station. The AC segmented busbar is connected through a bus tie switch. The segmented AC busbar is connected to two converters GFMMC1 and GFMMC2 respectively, and is connected to the corresponding converters GSMMC1 and GSMMC2 of the receiving-end converter station through the pole 1 line and the pole 2 line, as well as the metal return line. The output ends of the receiving-end converters are connected to different AC power grids.

[0003] Independent control of the two converters GFMMC1 and GFMMC2 can be achieved through fixed V / F control. According to the requirements of the power dispatching department, the AC voltage and AC frequency controlled by the two converters GFMMC1 and GFMMC2 at the sending end are usually consistent. However, due to the different commissioning times of the two converters, there are differences in the phases of the AC bus generated by the control of converters GFMMC1 and GFMMC2. This difference will cause impact current in the closing process, which will have a huge impact on the closing operation of the AC bus at the sending end.

[0004] Therefore, the Chinese patent application publication document with publication number CN114094576A discloses a flexible closed-loop switch, power supply network and control method, which realizes closed-loop operation of different AC buses by adding closed-loop equipment such as a commutation chain, a first disconnect switch, a first bypass switch, a second bypass switch and a main control unit, etc., and compensating the phase and amplitude of the AC bus at both ends through the operation of the knife switch. Although this solution can also overcome the phase difference and realize the closed-loop operation control of multi-converter AC buses, this solution requires additional equipment, which not only increases the construction cost, but also increases the floor space, resulting in poor adaptability. Summary of the invention

[0005] The purpose of the present invention is to provide a multi-converter AC bus closed-loop operation control method and system to solve the problems of high construction cost, limited site and poor adaptability caused by the need to add additional equipment to support AC bus closed-loop operation in the prior art.

[0006] To achieve the above object, the solution of the present invention includes:

[0007] A multi-converter AC bus closed-loop operation control method of the present invention comprises:

[0008] 1) When receiving the closing instruction of the bus tie switch, select one pole converter as the main pole converter and the other pole converter as the non-dominant pole converter, respectively lock the current AC active power actual values ​​of the main pole converter and the non-dominant pole converter as their corresponding active power reference values; control the reference phase generator of the main pole converter to superimpose the first frequency difference on the basis of the AC reference frequency to generate the phase angle of the main pole converter, and control the main pole converter according to the phase angle; the first frequency difference is obtained by performing P / F droop control on the active power reference value, the actual active power value and the active power change value of the main pole converter;

[0009] 2) When it is detected that the AC bus voltages on both sides of the AC bus tie switch cross zero in the same direction and the phase difference of the AC buses on both sides is less than the set threshold, the AC bus tie switch is closed.

[0010] Furthermore, when the AC bus tie switch is closed, both the dominant pole converter and the non-dominant pole converter adopt dual V / F droop control, and the active power reference value of the dominant pole converter and the non-dominant pole converter during dual V / F droop control is the active power reference value determined in step 1).

[0011] Furthermore, the first frequency difference is obtained by the following formula:

[0012] Δf1=k pf ((P ref +ΔP)-P)

[0013] Wherein, Δf1 represents the first frequency difference, in Hz; P ref represents the active power reference value of the converter, P represents the actual value of the AC active power of the converter, in MW; ΔP represents the active power change value; k pf Indicates the droop coefficient of the P / F droop controller in Hz / MW.

[0014] Furthermore, the dual V / F droop control includes an outer loop controller, a current inner loop controller and a reference phase generator; the outer loop controller is used to generate the d-axis and q-axis component current command values ​​required by the current inner loop controller. When generating the d-axis component current command value, the AC bus voltage command value is superimposed with the reactive power differential adjustment amount and then subtracted from the actual value of the AC bus voltage, and then the reactive power droop control result is superimposed; the current inner loop controller is used to combine the generated d-axis and q-axis component voltage command values ​​with the phase angle generated by the reference phase generator to generate a three-phase voltage command value for the converter; when generating the phase angle for controlling the converter, the reference phase generator superimposes a second frequency difference on the basis of the AC reference frequency, and the second frequency difference is obtained by performing P / F droop control on the active power reference value and the actual active power value of the converter.

[0015] Furthermore, the d-axis component current command value i of the dual V / F droop control dref Obtained by the following formula:

[0016]

[0017] Among them, i dref Indicates the d-axis component current command value of the current inner loop controller, in KA; U sref Indicates the AC bus voltage command value, U d It represents the d-axis component of the AC bus voltage after Parker transformation, in KV; Q represents the actual value of the reactive power of the converter, Q op Indicates the actual value of the reactive power of the converter, in Mvar; Q ref is the reactive power reference value; k0 represents the reactive power differential adjustment coefficient, k qv Indicates reactive power droop control coefficient, unit is kV / Mvar; kp d Indicates the proportional coefficient of the PI control link of the outer ring d-axis controller, ki d It represents the integral coefficient of the PI control link of the outer ring d-axis controller, dimensionless.

[0018] Furthermore, the q-axis component current command value i of the dual V / F droop control is qref Obtained by the following formula:

[0019]

[0020] Among them, i qref It represents the q-axis component current command value of the current inner loop controller, in KA; Uq represents the q-axis component of the AC bus voltage after Park transformation, in KV; kp q represents the proportional coefficient of the PI control link of the outer loop q-axis controller, ki q It represents the integral coefficient of the PI control link of the outer loop q-axis controller, dimensionless.

[0021] Furthermore, the second frequency difference of the reference phase generator of the dual V / F droop control is obtained by the following formula:

[0022] Δf2=k pf (P ref -P)

[0023] Wherein, Δf2 represents the second frequency difference, in Hz; P ref represents the active power reference value of the converter, P represents the actual value of the AC active power of the converter, in MW; k pf Indicates the droop coefficient of the P / F droop controller in Hz / MW.

[0024] Furthermore, the active power variation value is 5% to 10% of the active power rated value.

[0025] A multi-converter AC bus closed-loop operation control system of the present invention comprises a processor, and the processor is used to execute a computer program to implement the steps of any one of the above multi-converter AC bus closed-loop operation control methods.

[0026] The beneficial effects of the present invention are as follows: as an improved invention, when receiving the bus tie switch closing instruction, the main pole converter and the non-dominant pole converter respectively lock the current AC active power actual value as the corresponding active power reference value, the reference phase generator of the main pole converter superimposes the frequency difference on the basis of the AC reference frequency, thereby generating the phase angle of the main pole converter, and the generation of the phase angle of the non-dominant pole converter remains unchanged, the frequency difference is obtained by performing P / F droop control on the active power reference value, the active power actual value and the active power change value of the main pole converter, thereby gradually reducing the AC bus voltage phase difference on both sides of the AC bus tie switch, when the phase selection closing device of the AC bus tie switch detects that the AC bus voltage on both sides of the AC bus tie switch crosses the zero point in the same direction, and the phase difference is less than the set threshold value, the AC bus tie switch is closed again to prevent the generation of impact current during the closing process, therefore, the present invention solves the problem of segmented AC bus closing operation of the flexible DC transmission system of the new energy station without adding additional equipment, reduces the construction cost of the new energy station, and saves space. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a topological block diagram of the flexible DC transmission system;

[0028] Figure 2 This is the fixed V / F control block diagram of the sending-end converter;

[0029] Figure 3 It is the frequency switching logic block diagram;

[0030] Figure 4 This is the converter dual V / F droop control block diagram;

[0031] Figure 5 It is the waveform of the closed-loop operation of the segmented AC bus at the sending end. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail in a clear and complete manner in conjunction with the accompanying drawings and embodiments.

[0033] The idea of ​​the present invention is that, when a main-pole switch closing command is received, the current actual values ​​of the AC active power of the main-pole converter and the non-dominant-pole converter are locked as their corresponding active power reference values, and the reference phase generator of the main-pole converter superimposes the frequency difference on the basis of the AC reference frequency to generate the phase angle of the main-pole converter; when the phase selection and closing device of the AC main-pole switch detects that the AC bus voltages on both sides of the AC main-pole switch pass through zero points in the same direction and the phase difference is less than the set threshold value, the AC main-pole switch is closed.

[0034] Method Example:

[0035] Below Figure 1 The flexible DC transmission system in the example is used to illustrate that the two converters in the sending-end converter station both use fixed V / F control to control the AC voltage and frequency of the connected segmented bus. The control block diagram is as follows Figure 2 As shown, the d-axis and q-axis current command values ​​i required by the current inner loop controller are generated by the outer loop controller. dref and i qref ; Then the d and q axis voltage command value components v of the converter are obtained through the inner loop current controller d and v q ; Finally, the three-phase voltage command value v of the converter is obtained by combining the phase angle θ output by the reference phase generator a 、v b and v c .

[0036] Specifically, the outer loop controller generates the d-axis and q-axis current command values ​​i required by the inner loop controller. dref and i qref The formula is as follows:

[0037]

[0038] In the formula, i dref Indicates the current d-axis component command value of the current inner loop controller, in units of KA; i qref Indicates the current q-axis component command value of the current inner loop controller, in KA; U sref Indicates the AC bus voltage command value, in KV; U d It represents the d-axis component of the AC bus voltage after Park transformation, in KV; U q Indicates the q-axis component of the AC bus voltage after Parker transformation, in KV; kp d Indicates the proportional coefficient of the PI control link of the outer ring d-axis controller, ki d kp represents the integral coefficient of the PI control link of the outer ring d-axis controller, dimensionless; q represents the proportional coefficient of the PI control link of the outer loop q-axis controller, ki qIt represents the integral coefficient of the PI control link of the outer loop q-axis controller, dimensionless. (U sref 、kp d ,ki d 、kp q ,ki q Keep the parameters consistent.)

[0039] The d-axis control link of the inner loop current controller is decoupled and the d-axis component of the AC bus voltage after Park transformation is used as the feedforward and q-axis current coupling term to obtain the d-axis component v of the converter voltage command value. d , the formula is as follows:

[0040]

[0041] In the formula, v d Represents the d-axis component of the converter voltage command value, in KV; i d represents the d-axis component of the valve-side AC current after Parker transformation, i q It represents the q-axis component of the valve-side AC current after Parker transformation, and the unit is KA; kp1 represents the proportional coefficient of the PI control link of the inner loop current d-axis controller, and ki1 represents the integral coefficient of the PI control link of the inner loop current d-axis controller, which is dimensionless. (The parameters such as kp1 and ki1 of the two converters are consistent.)

[0042] The q-axis control link of the inner loop current controller is decoupled and the q-axis component of the AC bus voltage after Park transformation is used as the feedforward and d-axis current coupling term to obtain the q-axis component v of the converter voltage command value. q , the formula is as follows:

[0043]

[0044] In the formula, v q Represents the q-axis component of the converter voltage command value, in KV; i q represents the q-axis component of the valve-side AC current after Parker transformation, i d It represents the d-axis component of the valve-side AC current after Parker transformation, in units of KA; kp2 represents the proportional coefficient of the PI control link of the inner loop current d-axis controller, and ki2 represents the integral coefficient of the PI control link of the inner loop current q-axis controller, dimensionless. (The parameters such as kp2 and ki2 of the two converters are consistent.)

[0045] The inner loop current controller then uses the generated voltage command value d-axis component v d and the q-axis component v q The three-phase voltage command value of the converter is obtained through Parker inverse transformation, and the formula is as follows:

[0046]

[0047] In the formula, v a 、v b 、v c They represent the voltage command values ​​of the converter phase a, phase b, and phase c respectively, in KV. The phase angle θ is generated by a reference phase generator, which sets the AC reference frequency f0 to 50 Hz. The reference phase generator realizes a cycle between 0 and 2π through an integral link, and finally outputs the phase angle θ of the converter.

[0048] In order to solve the problem of difference in the phase of the segmented AC bus mentioned in the background technology, the present invention selects converter GFMMC1 as the dominant pole and GFMMC2 as the non-dominant pole (as another implementation method, GFMMC2 can also be selected as the dominant pole and GFMMC1 as the non-dominant pole); after the instruction of the segmented AC bus closing operation at the sending end is issued, the current actual values ​​of the AC active power of the dominant pole converter and the non-dominant pole converter are locked respectively as their corresponding active power reference values; the reference phase generator of the dominant pole converter superimposes the frequency difference on the basis of the AC reference frequency to generate the phase angle of the dominant pole converter, and the generation of the non-dominant pole phase angle remains unchanged; as the dominant pole converter controls the change of the AC frequency, the AC bus voltage phase difference on both sides of the AC bus tie switch is gradually reduced. When the phase selection and closing device of the AC bus tie switch detects that the AC bus voltages on both sides of the AC bus tie switch cross zero in the same direction and the phase difference is less than the set threshold, the AC bus tie switch is closed to prevent the generation of impact current during the closing process.

[0049] Specifically, upon receiving the issued bus tie switch closing command, the dominant pole converter GFMMC1 and the non-dominant pole converter GFMMC2 respectively lock the current converter AC active power actual value P as their corresponding active power reference value P ref The reference phase generator of the main pole converter GFMMC1 is superimposed on the AC reference frequency f0 and then on the first frequency difference output by the P / F droop controller, such as Figure 3 As shown in the figure, the active power reference value of the P / F droop controller is P ref becomes (P ref +△P), the input is (P ref +△P) and P, where P ref is the active power reference value of the converter, △P is the active power change value, and the value range is 5% to 10% of the rated power; the first frequency difference of the main pole converter is obtained by the following formula:

[0050] Δf1=k pf ((P ref +ΔP)-P)

[0051] Wherein, Δf1 represents the first frequency difference of the control system obtained by P / F droop control, in Hz; P ref represents the active power reference value of the converter, P represents the actual value of the AC active power of the converter, in MW; ΔP represents the active power change value; k pf Indicates the droop coefficient of the P / F droop controller in Hz / MW.

[0052] The non-dominant pole converter GFMMC2 still adopts constant V / F control, and the AC voltage command value U sref The reference frequency f0 remains unchanged, and the active power reference value remains P ref (Locked AC active power actual value); as the main pole converter GFMMC1 controls the change of AC frequency, the phase difference of the AC bus voltage on both sides of the AC bus tie switch is gradually reduced. When the phase selection and closing device of the AC bus tie switch detects that the AC bus voltage on both sides of the AC bus tie switch passes through the zero point in the same direction and the phase difference is less than 5°, the AC bus tie switch is closed.

[0053] When the AC bus tie switch is closed, the main pole converter GFMMC1 and the non-dominant pole converter GFMMC2 both adopt dual V / F droop control, and the active power reference value of the main pole converter GFMMC1 is determined by the switch closing gate command (P ref +△P) changes to P ref (locked AC active power actual value); the active power reference value of the non-dominant pole converter GFMMC2 is still P ref (locked AC active power actual value), its control block diagram is as follows Figure 4 shown.

[0054] Specifically, in the reference phase generator part of the dual V / F droop control, the main pole converter GFMMC1 and the non-dominant pole converter GFMMC2 both use the active power command value P ref The actual value of active power P is used to obtain the second frequency difference Δf2 of the control system through P / F droop control. Δf2 is superimposed on the reference frequency f0, and the cycle between 0 and 2π is realized through the integral link, and the phase angle θ of the converter is finally output. The formula is as follows:

[0055] Δf2=k pf (P ref -P)

[0056] Where △f2 represents the second frequency difference of the control system obtained by P / F droop control, in Hz; P ref represents the active power reference value of the converter, P represents the actual value of the AC active power of the converter, in MW; k pfIndicates the droop coefficient of the P / F droop controller in Hz / MW. (k pf Keep the parameters consistent.)

[0057] In the outer loop controller part of the dual V / F droop control, the d-axis control link of the outer loop controller of the two converters adopts the AC voltage mode, using the AC bus voltage command value U sref The reactive power difference adjustment is added and then the difference is made with the actual value of the AC bus voltage. Finally, the output of the reactive power droop controller is added and then passed through the PI control link to obtain the d-axis component current command value i of the current inner loop controller. dref , the formula is as follows:

[0058]

[0059] In the formula, i dref Indicates the d-axis component current command value of the current inner loop controller, in KA; U sref Indicates the AC bus voltage command value, U d It represents the d-axis component of the AC bus voltage after Parker transformation, in KV; Q represents the actual value of the reactive power of the converter, Q op Indicates the actual value of the reactive power of the converter, in Mvar; Q ref is the reactive power reference value; k0 represents the reactive power differential adjustment coefficient, k qv Indicates reactive power droop control coefficient, unit is kV / Mvar; kp d Indicates the proportional coefficient of the PI control link of the outer ring d-axis controller, ki d It represents the integral coefficient of the PI control link of the outer ring d-axis controller, dimensionless. (U sref , k0, k qv 、kp d ,ki d Keep the parameters consistent.)

[0060] The q-axis control link of the outer loop controller of the two converters suppresses the negative sequence current during AC unbalanced fault by controlling the q-axis component of the AC bus voltage after Park transformation to 0. The formula is as follows:

[0061]

[0062] In the formula, i qref Indicates the q-axis component current command value of the current inner loop controller, in KA; U q It represents the q-axis component of the AC bus voltage after Parker transformation, in kV; kp q represents the proportional coefficient of the PI control link of the outer loop q-axis controller, ki qIt represents the integral coefficient of the PI control link of the outer loop q-axis controller, dimensionless. (kp of the two converters q ,ki q Keep the parameters consistent.)

[0063] In the inner loop current controller part of the dual V / F droop control, the control strategy of the inner loop current controller part of the two converters is consistent with the control strategy of the inner loop current controller part of the fixed V / F control, which will not be repeated here.

[0064] The beneficial effects of this embodiment are as follows: Figure 5 As shown in the figure, after the bus tie switch closing command is issued, both poles (dominant pole converter and non-dominant pole converter) lock the current active power actual value of 750MW as the active power reference value Pref, the frequency of pole 1 (dominant pole converter) is switched to 50Hz superimposed on the output of the P / F controller, and pole 2 (non-dominant pole converter) remains at 50Hz unchanged. At the same time, pole 1 changes the active power reference value from 750MW to 825MW, and the frequency of pole 1 is gradually adjusted from 50Hz to 50.1Hz.

[0065] It can be seen from the waveform that before 0.2s, after the adjustment of pole 1, the difference between the AC bus voltage phase Uac1_Phase of pole 1 and the AC bus voltage phase Uac2_Phase of pole 2 gradually decreases, as shown in the small figure in the figure. When the phase selection closing device detects that the AC bus A phase voltage Uac1_A of pole 1 and the AC bus A phase voltage Uac2_A of pole 2 pass through the zero point in the same direction, and the phase difference is less than 5°, the closing bus tie switch operation is executed; after pole 1 receives the closed state of the bus tie switch, the active power reference value of 825MW is changed to the original 750MW. The bipolar adopts dual V / F droop control to operate stably, realize the self-adaptation of segmented / closed loop operation mode, and improve the reliability of the symmetrical bipolar new energy DC grid-connected system.

[0066] System Example:

[0067] A multi-converter AC bus closed-loop operation control system of the present invention includes a processor, and the processor is used to execute computer program instructions to implement a multi-converter AC bus closed-loop operation control method introduced in the method embodiment. The method has been introduced clearly enough in the method embodiment and will not be repeated here.

Claims

1. A multi-converter AC bus closed-loop operation control method, characterized in that: The method includes: 1) When receiving a bus tie switch closing command, select one pole converter as the main pole converter and the other pole converter as the non-dominant pole converter, respectively lock the current AC active power actual values ​​of the main pole converter and the non-dominant pole converter as their corresponding active power reference values; control the reference phase generator of the main pole converter to superimpose a first frequency difference on the basis of the AC reference frequency to generate a phase angle of the main pole converter, and control the main pole converter according to the phase angle; the first frequency difference is obtained by performing P / F droop control on the active power reference value, the actual active power value and the active power change value of the main pole converter; 2) When it is detected that the AC bus voltages on both sides of the AC bus tie switch cross zero in the same direction and the phase difference of the AC buses on both sides is less than the set threshold, the AC bus tie switch is closed.

2. The multi-converter AC bus closed-loop operation control method according to claim 1, characterized in that: When the AC bus tie switch is closed, both the dominant pole converter and the non-dominant pole converter adopt dual V / F droop control, and the active power reference value of the dominant pole converter and the non-dominant pole converter during dual V / F droop control is the active power reference value determined in step 1).

3. The multi-converter AC bus closed-loop operation control method according to claim 1, characterized in that: The first frequency difference is obtained by the following formula: Δf1=k pf ((P ref +ΔP)-P) Wherein, Δf1 represents the first frequency difference, in Hz; P ref represents the active power reference value of the converter, P represents the actual value of the AC active power of the converter, in MW; ΔP represents the active power change value; k pf Indicates the droop coefficient of the P / F droop controller in Hz / MW.

4. The multi-converter AC bus closed-loop operation control method according to claim 2, characterized in that: The dual V / F droop control includes an outer loop controller, a current inner loop controller and a reference phase generator; the outer loop controller is used to generate the d-axis and q-axis component current command values ​​required by the current inner loop controller. When generating the d-axis component current command value, the AC bus voltage command value is added with the reactive power differential adjustment amount, and then the difference is made with the actual value of the AC bus voltage, and then the reactive power droop control result is added; the current inner loop controller is used to combine the generated d-axis and q-axis component voltage command values ​​with the phase angle generated by the reference phase generator to generate the three-phase voltage command value of the converter; When generating the phase angle for controlling the converter, the reference phase generator superimposes a second frequency difference on the basis of the AC reference frequency, and the second frequency difference is obtained by performing P / F droop control on the active power reference value and the actual active power value of the converter.

5. The multi-converter AC bus closed-loop operation control method according to claim 4, characterized in that: The d-axis component current command value i of the dual V / F droop control dref Obtained by the following formula: Among them, i dref Indicates the d-axis component current command value of the current inner loop controller, in KA; U sref Indicates the AC bus voltage command value, U d It represents the d-axis component of the AC bus voltage after Parker transformation, in KV; Q represents the actual value of the reactive power of the converter, Q op Indicates the actual value of the reactive power of the converter, in Mvar; Q ref is the reactive power reference value; k0 represents the reactive power differential adjustment coefficient, k qv Indicates reactive power droop control coefficient, unit is kV / Mvar; kp d Indicates the proportional coefficient of the PI control link of the outer ring d-axis controller, ki d It represents the integral coefficient of the PI control link of the outer ring d-axis controller, dimensionless.

6. The multi-converter AC bus closed-loop operation control method according to claim 4, characterized in that: The q-axis component current command value i of the dual V / F droop control qref Obtained by the following formula: Among them, i qref It represents the q-axis component current command value of the current inner loop controller, in KA; Uq represents the q-axis component of the AC bus voltage after Park transformation, in KV; kp q represents the proportional coefficient of the PI control link of the outer loop q-axis controller, ki q It represents the integral coefficient of the PI control link of the outer loop q-axis controller, dimensionless.

7. The multi-converter AC bus closed-loop operation control method according to claim 4, characterized in that: The second frequency difference of the reference phase generator of the dual V / F droop control is obtained by the following formula: Δf2=k pf (P ref -P) Wherein, Δf2 represents the second frequency difference, in Hz; P ref represents the active power reference value of the converter, P represents the actual value of the AC active power of the converter, in MW; k pf Indicates the droop coefficient of the P / F droop controller in Hz / MW.

8. The multi-converter AC bus closed-loop operation control method according to claim 3, characterized in that: The active power variation value is 5% to 10% of the active power rated value.

9. A multi-converter AC bus closed-loop operation control system, comprising a processor, characterized in that: The processor is used to execute a computer program to implement the steps of a multi-converter AC bus closed-loop operation control method as described in any one of claims 1 to 8.

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