A method and device for judging and controlling reactive power overload of a flexible direct-current island converter station

Abstract

The application discloses an island converter station reactive power overload judgment control method, and belongs to the field of flexible direct current power transmission. The method comprises the following steps: an island AC voltage control is adopted by an island converter station; actual active power and actual reactive power of the island converter station are calculated in real time; according to a PQ operation interval of the island converter station, a reactive power operation interval corresponding to the current actual active power is calculated; the actual reactive power is compared with the reactive power operation interval, and if the actual reactive power is not in the reactive power operation interval, the AC voltage instruction value is changed to adjust the system reactive power by adjusting the AC voltage, so that the system reactive power returns to the power interval range. The technical scheme can avoid the harm of long-term reactive power of the island station exceeding the PQ operation range to the system, and ensure the safe and stable operation of the system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flexible HVDC transmission technology of power system, and particularly relates to a reactive power overload judgment and control method and device for island converter station. BACKGROUND

[0002] Flexible HVDC transmission technology is a new generation of HVDC transmission technology, which has the characteristics of independent control of active power and reactive power, and does not require short-circuit capacity of AC power grid to support commutation, thereby solving the problem of clean energy such as wind power and photovoltaic power connected to the power grid, and having a good development prospect. Due to the limitation of the converter and the converter transformer capacity, the active power and the reactive power must be limited in a specific range on the PQ plane in the same converter station, otherwise the device capacity limit may be exceeded, thereby damaging the device and threatening the safe operation of the system.

[0003] The offshore converter station of offshore wind power flexible HVDC transmission project is a sending-end converter station, which generally adopts an island AC voltage control strategy, taking the AC voltage on the grid side of the converter station as the control target, and the active power of the offshore converter station is provided by the wind farm. When the reactive power generated by the wind farm is excessive or there is a large reactive power load in the flexible HVDC system, the reactive power of the converter station is large, which may exceed the PQ range of the system, thereby threatening the safe and stable operation of the system. At this time, a certain overload control strategy needs to be used to reduce the reactive power of the system. The current overload control strategy of the flexible HVDC converter station mainly aims at the active power overload of the system, and considers adjusting the generator output and cutting off the load to correct the active power overload. The adjustment capacity of these control strategies for the reactive power of the system is limited.

[0004] At present, there are few control strategies for reactive power overload of island system in the literature, and the stable operation of the island converter station is an important prerequisite for renewable energy on-grid and consumption. Therefore, it is necessary to find an overload control strategy suitable for island station to actively adjust when the reactive power overload of the island station occurs, so as to make it return to the PQ operation range, thereby ensuring the safe and stable operation of the system, which has great practical demand. SUMMARY

[0005] The purpose of the present application is to provide an overload control method and device for flexible HVDC transmission system island station, which can avoid the harm to the system caused by long-term reactive power of the island station exceeding the PQ operation range, and ensure the safe and stable operation of the system.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is:

[0007] On the one hand, the present application provides a reactive power overload judgment and control method for island converter station, comprising:

[0008] The island converter station adopts island AC voltage control;

[0009] calculating actual active power and actual reactive power of the island converter station in real time;

[0010] calculating a reactive power operation interval corresponding to the current actual active power according to the PQ operation interval of the island converter station;

[0011] comparing the actual reactive power with the reactive power operation interval, and if the actual reactive power is not within the reactive power operation interval, changing the AC voltage instruction value to adjust the system reactive power by adjusting the AC voltage so as to return to the power interval range.

[0012] In the preferred scheme, if the actual reactive power is not within the reactive power operation interval, the method of changing the AC voltage instruction value to adjust the system reactive power by adjusting the AC voltage is specifically: if the positive direction of the reactive power is positive and the reactive power is inductive, if the actual reactive power is higher than the upper limit of the reactive power operation interval, the AC voltage instruction value is increased to reduce the reactive power by increasing the AC voltage; if the actual reactive power is lower than the lower limit of the reactive power operation interval, the AC voltage instruction value is decreased to increase the reactive power by decreasing the AC voltage; when the actual reactive power is within the reactive power operation interval, the increase of the AC voltage is stopped, and the AC voltage instruction value is kept as the current value. If the positive direction of the reactive power is opposite, the direction of the voltage adjustment is also opposite.

[0013] In the preferred scheme, the change of the AC voltage instruction value can only adjust the voltage within the upper and lower limits of the AC voltage, and the AC voltage will not continue to increase or decrease when reaching the upper and lower limits.

[0014] In the preferred scheme, when the AC voltage is adjusted to the upper and lower limits of the voltage and the actual reactive power is still not within the reactive power operation interval, the system stops adjusting the AC voltage, and the system judges the reactive power out of limit and processes it.

[0015] In the preferred scheme, the processing method of the system includes: locking the converter after a preset time delay, and tripping the AC line switch.

[0016] In the preferred scheme, the processing method of the system includes: requesting the wind turbine to trip to reduce the reactive power load, or only reminding the operator to process through background alarm.

[0017] In the preferred scheme, the method of changing the AC voltage instruction value includes: adjusting the AC voltage instruction value at a preset rate, or adjusting the AC voltage instruction value in sections and at different rates, or calculating the voltage deviation amount by the deviation between the reactive power limit target value and the actual reactive power and superimposing it on the AC voltage instruction value.

[0018] In a preferred solution, the island converter station adopts island AC voltage control, i.e. an outer ring control generates active current command, reactive current command and reference phase command according to the deviation between AC voltage command and actual AC voltage; and an inner ring adopts current control to obtain a modulated voltage reference value.

[0019] In a preferred solution, the PQ operation interval of the island converter station is provided by complete design of the converter station.

[0020] In another aspect, the application provides a reactive power overload judgment and control device for an island converter station, comprising a connected power calculation module, a reactive power operation interval calculation module, a reactive power adjustment module and a closed-loop control module; wherein:

[0021] The power calculation module is configured to calculate actual active power and actual reactive power of the island converter station in real time.

[0022] The reactive power operation interval calculation module is configured to calculate the reactive power operation interval corresponding to the current actual active power according to the PQ operation interval of the island converter station.

[0023] The reactive power adjustment module is configured to compare the actual reactive power with the reactive power operation interval, and if the actual reactive power is not within the reactive power operation interval, change the AC voltage command value of the closed-loop control module to adjust the system reactive power by adjusting the AC voltage so as to return to the power interval range.

[0024] The closed-loop control module is configured to control the island converter station by using island AC voltage control method.

[0025] In a preferred solution, in the reactive power adjustment module: when the positive direction of the reactive power is positive for absorbing inductive reactive power, if the actual reactive power is higher than the upper limit of the reactive power operation interval, the AC voltage command value is increased to reduce the reactive power by increasing the AC voltage; if the actual reactive power is lower than the lower limit of the reactive power operation interval, the AC voltage command value is decreased to increase the reactive power by decreasing the AC voltage; when the actual reactive power returns to the reactive power operation interval, the increase of the AC voltage is stopped, and the AC voltage command value is kept as the current value. If the positive direction of the reactive power is defined reversely, the voltage adjustment direction is also reversed.

[0026] In a preferred solution, in the reactive power adjustment module, the change of the AC voltage command value can only adjust the voltage within the upper and lower limits of the AC voltage, and when the AC voltage reaches the allowed upper and lower limits, the AC voltage is no longer increased or decreased.

[0027] In the preferred solution, the over-load judging and controlling device of the island converter station further comprises a reactive power over-limit processing module. When the actual reactive power is still not within the reactive power operation range after the AC voltage is regulated to the upper and lower limits, the AC voltage is stopped from being regulated, the over-limit of the reactive power is judged, and the reactive power over-limit processing module is triggered. The reactive power over-limit processing module is used to process the over-limit of the reactive power of the system.

[0028] In the preferred solution, the reactive power over-limit processing module is used to lock the converter after a preset delay time, and trip the AC line switch.

[0029] In the preferred solution, the reactive power over-limit processing module is used to request the wind turbine to cut off the machine to reduce the reactive load.

[0030] In the preferred solution, the reactive power over-limit processing module is used to trigger a background alarm to remind the operator to process.

[0031] In the preferred solution, the method for changing the AC voltage command value in the reactive power regulating module comprises: regulating the AC voltage command value at a preset rate, or regulating the AC voltage command value in sections and at different rates, or regulating the AC voltage command value in steps, or calculating the voltage deviation amount by the deviation between the reactive power limit target value and the actual reactive power and superimposing the voltage deviation amount on the AC voltage command value.

[0032] In the preferred solution, the closed-loop control module comprises outer loop control and inner loop control. The outer loop control generates active current command, reactive current command and reference phase command according to the deviation between the AC voltage command and the actual AC voltage. The inner loop uses current control to obtain a modulated voltage reference value.

[0033] The beneficial effects of the present application are:

[0034] (1) The technical solution of the present application actively controls the size of the reactive power, and the AC voltage changes smoothly, which not only avoids the harm to the safe operation of the system caused by the long-term over-load of the island station exceeding the PQ operation range, but also achieves good AC control characteristics.

[0035] (2) When the over-limit of the PQ operation range cannot be avoided by regulating the voltage, the system actively trips or requests the wind turbine to cut off the machine, which avoids the harm to the system caused by the long-term over-load of the island station. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 Schematic diagram of a flexible HVDC power transmission system;

[0037] Figure 2 Closed-loop control block diagram of an island station;

[0038] Figure 3A flowchart of a reactive power overload judgment and control method for an islanded converter station provided in one embodiment of this application;

[0039] Figure 4 Block diagram of reactive power overload control for isolated station;

[0040] Figure 5 Schematic diagram of the PQ operating section of the isolated station;

[0041] Figure 6 The flowchart of a reactive power overload judgment and control method for an islanded converter station is provided in another embodiment of this application. Detailed Implementation

[0042] To make the technical solution of this application clearer, the technical solution of this application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] A schematic diagram of a flexible DC transmission system at both ends is shown below. Figure 1 As shown, it mainly includes islanded converter stations and constant DC voltage converter stations. Figure 2 As shown, after the island station is unlocked, island AC voltage control is adopted. The outer loop control generates active current command Idref, reactive current command Iqref, and reference phase command θ based on the deviation between the AC voltage command and the actual AC voltage. The inner loop uses current control to obtain the modulation voltage reference values ​​Udref and Uqref, and then obtains the three-phase modulation voltage reference values ​​through dq / abc transformation.

[0044] like Figure 3 As shown in the figure, an embodiment of the reactive power overload judgment and control method for an islanded converter station according to this application includes the following steps:

[0045] S101: The islanded converter station adopts islanded AC voltage control.

[0046] S102: Real-time calculation of the actual active power and actual reactive power of the islanded converter station.

[0047] S103: Based on the PQ operating range of the islanded converter station, calculate the corresponding reactive power operating range under the current actual active power. The PQ operating range of the islanded converter station can be provided by the complete converter station design.

[0048] S104: Compare the actual reactive power with the reactive power operating range. If the actual reactive power is not within the reactive power operating range, change the AC voltage command value to adjust the system reactive power and bring it back within the power range. For example... Figure 4 The block diagram for reactive power overload control of the isolated station is shown below.

[0049] Specifically, when the positive direction of the reactive power is positive for absorbing inductive reactive power, if the actual reactive power is higher than the upper limit of the reactive power operating range, the AC voltage command value is increased to reduce the reactive power by increasing the AC voltage; if the actual reactive power is lower than the lower limit of the reactive power operating range, the AC voltage command value is decreased to increase the reactive power by decreasing the AC voltage, and when the actual reactive power returns to the reactive power operating range, the increase of the AC voltage is stopped, and the AC voltage command value is kept as the current value. If the positive direction of the reactive power is defined reversely, the voltage regulation direction is also reversed.

[0050] In the preferred embodiment, the change of the AC voltage command value can only regulate the voltage within the upper and lower limits of the AC voltage, and when the AC voltage reaches the upper and lower limits, the increase or decrease of the AC voltage is stopped.

[0051] In the preferred embodiment, based on the first embodiment, when the AC voltage is regulated to the upper and lower limits of the voltage and the actual reactive power is still not within the reactive power operating range, the system stops regulating the AC voltage, and at this time, the system judges the reactive power over-limit and processes it. The processing method of the system can include locking the converter after a delay of a preset time, or tripping the AC line switch. The processing method of the system can also include requesting the wind turbine to trip to reduce the reactive load, or only sending a background alarm to remind the operator to process it.

[0052] In the preferred embodiment, the method of changing the AC voltage command value includes regulating the AC voltage command value at a preset rate, or regulating it in sections and at different rates, or regulating it in steps, or calculating the voltage deviation amount by the deviation of the reactive power limit target value and the actual reactive power and adding it to the AC voltage command value.

[0053] As shown in Figure 6 Another island converter station reactive power overload judgment and control method embodiment of the application is shown. As known from the basic characteristics of the power grid, the size of the reactive power absorbed or generated by the converter station can be controlled by regulating the AC voltage of the flexible AC transmission system (FACTS) converter station. For absorbing inductive reactive power, decreasing the AC voltage can increase the reactive power, and increasing the AC voltage can decrease the reactive power. The following takes the island AC voltage controlled converter station as an example to explain the specific implementation process of the method.

[0054] (1) Collect the actual values of the three-phase AC voltage Usa, Usb, Usc and the three-phase current Isa, Isb, Isc of the island station, and obtain the synchronous rotation angle θ through the phase-locked loop.

[0055] (2) Obtain the d, q axis components of the AC voltage Usd, Usq and the d, q axis components of the AC current Isd, Isq through dq coordinate transformation.

[0056] (3) Calculate the real-time value of active power Ps and reactive power Qs by the d, q axis components of alternating voltage Usd, Usq and the d, q axis components of alternating current Isd, Isq.

[0057]

[0058] (4) The PQ operation interval of island station is shown in the figure as Figure 5 The horizontal axis is active power and the vertical axis is reactive power. According to the real-time value of active power Ps of the island converter station, the operation range of reactive power is calculated, and the maximum value Qs_max and the minimum value Qs_min of the system allowed reactive power can be obtained according to the PQ operation interval.

[0059] (5) According to the actual operation requirement, set the alternating voltage operation range as Us_min ~ Us_max, and the alternating voltage command value as Us * .

[0060] (6) Compare the real-time value of reactive power Qs calculated in step (3) with the reactive power operation range obtained in step (4), if Qs_min ≤ Qs ≤ Qs_max, that is, the reactive power falls within the PQ operation interval, then the alternating voltage adjustment process is ended, otherwise, go to step (7).

[0061] (7) Compare the real-time value of reactive power Qs calculated in step (3) with the reactive power operation range obtained in step (4), if Qs > Qs_max, that is, the reactive power exceeds the upper limit value of the PQ operation interval, then go to step (8); if Qs < Qs_min, that is, the reactive power is less than the lower limit value of the PQ operation interval, then go to step (11).

[0062] (8) Increase the alternating voltage command value at the speed of α kV / s, reduce the reactive power by increasing the alternating voltage, specifically, the alternating voltage adjustment amount ΔUs starts from 0 and increases at the speed of α kV / s, and then is superimposed with the alternating voltage command value Us * .

[0063] (9) Real-time detect the value of the reactive power of the current converter station, if the reactive power returns to the PQ operation interval, stop increasing the alternating voltage, and the alternating voltage command value remains the current value.

[0064] (10) When the alternating voltage is increased to Us_max, the alternating voltage is no longer increased, and if the reactive power is still out of limit, the system is tripped after a time delay, and the action result is

[0065] a, lock the converter

[0066] b, trip the alternating current line switch;

[0067] The reactive power overload regulation ends.

[0068] (11) Reduce the AC voltage command value at a rate of akV / s, and increase the reactive power by reducing the AC voltage. Specifically, the AC voltage regulation amount ΔUs is reduced at a rate of akV / s from 0, and then is reduced in proportion to the AC voltage command value Us * superimposed.

[0069] (12) Real-time detect the value Qs of the current converter station reactive power, if the reactive power Qs returns to the PQ operation interval, i.e. Qs_min≤Qs≤Qs_max, stop reducing the AC voltage, and the AC voltage command value is kept as the current value.

[0070] (13) When the AC voltage is reduced to Us_min, the AC voltage is no longer reduced, and if the reactive power is still out of limit, the system is delayed for a period of time and tripped, and the action result is

[0071] a, lock the converter

[0072] b, trip the AC line switch;

[0073] The reactive power overload regulation ends.

[0074] The application provides a kind of island converter station reactive power overload judgment control device embodiment, including the power calculation module of connection, reactive power operation interval calculation module, reactive power regulation module and closed loop control module;Wherein:

[0075] Power calculation module, for real-time calculation of actual active power and actual reactive power of island converter station;

[0076] Reactive power operation interval calculation module, for calculating the corresponding reactive power operation interval under the current actual active power according to the PQ operation interval of island converter station;

[0077] Reactive power regulation module, for comparing actual reactive power and reactive power operation interval, if actual reactive power is not in reactive power operation interval, then change the AC voltage command value of closed loop control module to adjust the reactive power of system by adjusting AC voltage, so that it returns to power interval range;

[0078] Closed loop control module, for using island AC voltage control method to control island converter station.

[0079] In the preferred embodiment, in the reactive power adjustment module, when the positive direction of the reactive power is positive and the reactive power is inductive, if the actual reactive power is higher than the upper limit of the reactive power operating range, the AC voltage command value is increased to reduce the reactive power by increasing the AC voltage; if the actual reactive power is lower than the lower limit of the reactive power operating range, the AC voltage command value is decreased to increase the reactive power by decreasing the AC voltage; when the actual reactive power returns to the reactive power operating range, the increase of the AC voltage is stopped, and the AC voltage command value remains the current value. If the positive direction of the reactive power is opposite, the voltage adjustment direction is also opposite.

[0080] In the preferred embodiment, in the reactive power adjustment module, the change of the AC voltage command value can only adjust the voltage within the upper and lower limits of the AC voltage. When the AC voltage reaches the upper and lower limits, the increase or decrease of the AC voltage is stopped.

[0081] In the preferred embodiment, the over-load judgment and control device of the isolated converter station further comprises a reactive power over-limit processing module. In the reactive power adjustment module, when the AC voltage is adjusted to the upper and lower limits of the voltage and the actual reactive power is still not within the reactive power operating range, the adjustment of the AC voltage is stopped, the over-limit of the reactive power is judged, and the reactive power over-limit processing module is triggered. The reactive power over-limit processing module is used to process the over-limit of the reactive power of the system.

[0082] In the preferred embodiment, the reactive power over-limit processing module is used to lock the converter after a delay of a preset time and trip the AC line switch.

[0083] In the preferred embodiment, the reactive power over-limit processing module is used to request the wind turbine to trip to reduce the reactive load.

[0084] In the preferred embodiment, the reactive power over-limit processing module is used to trigger a background alarm to remind the operator to process.

[0085] In the preferred embodiment, the method for changing the AC voltage command value in the reactive power adjustment module comprises: adjusting the AC voltage command value at a preset rate, or adjusting the AC voltage command value in sections and at different rates, or adjusting the AC voltage command value in steps, or calculating the voltage deviation amount by the deviation of the reactive power limit target value and the actual reactive power and superimposing it on the AC voltage command value.

[0086] In the preferred embodiment, the closed-loop control module comprises outer loop control and inner loop control. The outer loop control generates active current command, reactive current command and reference phase command according to the deviation of the AC voltage command and the actual AC voltage. The inner loop uses current control to obtain a modulated voltage reference value.

[0087] The above examples only illustrate the technical idea of the present application, and cannot be used to define the protection scope of the present application. Any modification made on the basis of the technical idea of the present application and technical solutions falls within the protection scope of the present application.

Claims

1. A method for judging and controlling reactive power overload in an islanded converter station, characterized in that, The islanded converter station adopts islanded AC voltage control; the islanded converter station adopts islanded AC voltage control, that is: the outer loop control generates active current command and reactive current command based on the deviation between the AC voltage command and the actual AC voltage, and the active current command, reactive current command and reference phase command are used as inputs for the inner loop control; the inner loop uses current control to obtain the modulation voltage reference value; Real-time calculation of the actual active power and actual reactive power of the isolated converter station; Based on the PQ operating range of the isolated converter station, calculate the corresponding reactive power operating range under the current actual active power. Compare the actual reactive power with the reactive power operating range. If the actual reactive power is outside the operating range, adjust the AC voltage command value to regulate the system's reactive power and bring it back within the operating range. Specifically: When the positive direction of reactive power absorption is positive, if the actual reactive power is higher than the upper limit of the reactive power operating range, the AC voltage command value is increased to reduce reactive power; if the actual reactive power is lower than the lower limit of the reactive power operating range, the AC voltage command value is decreased to increase reactive power; when the actual reactive power returns to the reactive power operating range, the increase of AC voltage stops, and the AC voltage command value remains at the current value. If the positive direction of reactive power is defined in the opposite way, then the direction of voltage regulation is also in the opposite way.

2. The reactive power overload judgment and control method for an islanded converter station as described in claim 1, characterized in that, The AC voltage change command value can only be adjusted within the upper and lower limits of the AC voltage. When the AC voltage reaches the allowable upper and lower limits, the AC voltage will no longer be increased or decreased.

3. The reactive power overload judgment and control method for an islanded converter station as described in claim 2, characterized in that, When the AC voltage is adjusted to the upper or lower limit, and the actual reactive power is still not within the reactive power operating range, the system stops adjusting the AC voltage. At this time, the system judges that the reactive power exceeds the limit and takes action.

4. The reactive power overload judgment and control method for an islanded converter station as described in claim 3, characterized in that, The system's processing methods include: locking the converter after a preset delay and tripping the AC incoming line switch.

5. The reactive power overload judgment and control method for an islanded converter station as described in claim 3, characterized in that, The system can handle this by either requesting the wind turbines to be shut down to reduce reactive load, or simply issuing an alarm in the background to alert operators to take action.

6. The reactive power overload judgment and control method for an islanded converter station as described in claim 1, characterized in that, The method for changing the AC voltage command value includes: adjusting the AC voltage command value at a preset rate, or adjusting it in segments and at different rates, or adjusting the AC voltage command value in a step manner, or calculating the voltage deviation by superimposing it onto the AC voltage command value based on the deviation between the reactive power limit target value and the actual reactive power.

7. The reactive power overload judgment and control method for an islanded converter station as described in claim 1, characterized in that, The PQ operating range of the isolated converter station is provided by the complete converter station design.

8. A reactive power overload judgment and control device for an islanded converter station, characterized in that, It includes a power calculation module, a reactive power operating range calculation module, a reactive power adjustment module, and a closed-loop control module connected to it. The power calculation module is used to calculate the actual active power and actual reactive power of the islanded converter station in real time. The reactive power operating range calculation module is used to calculate the reactive power operating range corresponding to the current actual active power based on the PQ operating range of the islanded converter station. The reactive power regulation module compares the actual reactive power with the reactive power operating range. If the actual reactive power is outside the operating range, the AC voltage command value of the closed-loop control module is changed to regulate the system's reactive power by adjusting the AC voltage, bringing it back within the operating range. Specifically, in the reactive power regulation module: when the positive direction of reactive power is the absorption of inductive reactive power, if the actual reactive power is higher than the upper limit of the reactive power operating range, the AC voltage command value is increased to reduce reactive power; if the actual reactive power is lower than the lower limit of the reactive power operating range, the AC voltage command value is decreased to increase reactive power; when the actual reactive power returns to the operating range, the increase in AC voltage stops, and the AC voltage command value remains at its current value. If the positive direction of reactive power is defined in the opposite direction, the voltage regulation direction is also reversed. The closed-loop control module is used to control the islanded converter station using the islanded AC voltage control method. The closed-loop control module includes an outer loop control and an inner loop control. The outer loop control generates active current commands and reactive current commands based on the deviation between the AC voltage command and the actual AC voltage. The active current commands, reactive current commands, and reference phase commands serve as inputs to the inner loop control. The inner loop uses current control to obtain the modulation voltage reference value.

9. The reactive power overload judgment and control device for an islanded converter station as described in claim 8, characterized in that, The reactive power regulation module can only adjust the AC voltage within the upper and lower limits of the AC voltage. When the AC voltage reaches the allowable upper or lower limits, it will no longer increase or decrease the AC voltage.

10. The reactive power overload judgment and control device for an islanded converter station as described in claim 9, characterized in that, It also includes a reactive power limit handling module. In the reactive power regulation module, when the AC voltage is adjusted to the upper and lower limits of the voltage, and the actual reactive power is still not within the reactive power operating range, the AC voltage adjustment is stopped, the reactive power over-limit is judged, and the reactive power over-limit processing module is triggered. The reactive power limit exceeding processing module is used to process the reactive power limit exceeding situation of the system.

11. The reactive power overload judgment and control device for an islanded converter station as described in claim 10, characterized in that, The reactive power over-limit processing module is used to lock the converter and trip the AC incoming line switch after a preset delay time.

12. The reactive power overload judgment and control device for an islanded converter station as described in claim 10, characterized in that, The reactive power over-limit processing module is used to request the wind turbine to be shut down to reduce reactive power load.

13. The reactive power overload judgment and control device for an islanded converter station as described in claim 10, characterized in that, The reactive power over-limit processing module is used to trigger a background alarm to remind operators to handle the issue.

14. The reactive power overload judgment and control device for an islanded converter station as described in claim 8, characterized in that, The methods for changing the AC voltage command value in the reactive power regulation module include: adjusting the AC voltage command value at a preset rate, or adjusting it in segments and at different rates, or adjusting the AC voltage command value in a step manner, or calculating the voltage deviation by superimposing it onto the AC voltage command value based on the deviation between the reactive power limit target value and the actual reactive power.

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