A low penetration optimization method and device for flexible direct current

Abstract

The application provides a low penetration optimization method and device for flexible direct current, which comprises the following steps: firstly, calculating energy loss, combining system inertia, energy loss and preset minimum frequency ratio to determine the minimum system frequency and maximum energy deficiency, and then determining the penetration power and low penetration active power control value; secondly, determining the reactive current range according to voltage stiffness, combining active loss and rotor kinetic energy to determine the active current range, and taking the intersection; finally, dynamically or preset adjusting the recovery rate according to the bus phase change amount and the critical value. The lowest active current and the highest reactive current in the intersection which meet the low penetration active power control value and the adaptive recovery rate are selected to perform the flexible direct current low penetration. Through dynamic energy balance, adaptive recovery rate and active / reactive current collaborative optimization, the stability and control accuracy of the flexible direct current system under low penetration fault are significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flexible direct current control, and particularly relates to a low penetration optimization method and device for flexible direct current. BACKGROUND

[0002] With large-scale access of new energy and wide application of power electronic equipment, the flexible direct current transmission system plays an important role in the power grid due to its fast response capability and flexible control characteristics. When voltage sag occurs at the grid connection point, the flexible direct current converter needs to adopt a low penetration (LVRT) strategy to ensure continuous on-grid operation by dynamically adjusting active power and reactive power. However, an unreasonable low voltage penetration strategy may worsen the stability of the system. SUMMARY

[0003] The purpose of the present application is to overcome the defects in the prior art, and to provide a low penetration optimization method and device for flexible direct current.

[0004] The present application provides a low penetration optimization method for flexible direct current, comprising:

[0005] determining a low penetration active power control value: calculating an energy loss value caused by flexible direct current low penetration; determining a kinetic energy value released by the rotor according to the system inertia; combining the system inertia, the energy loss value and a preset minimum system frequency ratio to determine the minimum system frequency value through engineering experience or simulation data; calculating the maximum energy that can be missed corresponding to the minimum system frequency value according to a preset coefficient; determining the penetration power during flexible direct current low penetration according to the maximum energy that can be missed and the predetermined flexible direct current low penetration time; determining the low penetration active power control value according to the penetration power;

[0006] determining the proportion range of active current and reactive current: determining the reactive current proportion range according to the relationship between voltage stiffness and non-triggering overvoltage protection; determining the maximum active power loss based on the actual active power consumed during the fault, and determining the active current proportion range according to the maximum active power loss and the total amount of rotor kinetic energy; selecting the intersection of the active current proportion range and the reactive current proportion range;

[0007] determining an adaptive recovery rate: obtaining the change amount of the bus phase of the flexible direct current compared to the initial value and the critical phase change amount; if the change amount does not exceed the critical phase change amount, dynamically adjusting the recovery rate according to the phase change rate: the faster the phase drops, the greater the recovery rate increases; if the change amount exceeds the critical phase change amount, a preset maximum recovery rate is adopted;

[0008] selecting the lowest active current and the highest reactive current in the intersection that meet the low penetration active power control value and the adaptive recovery rate for low penetration of the flexible direct current.

[0009] Optionally, the preset coefficient is a ratio between the maximum energy loss and the rotor kinetic energy of the system.

[0010] Optionally, the range of the reactive current proportion is determined according to a predetermined relationship between the voltage stiffness and the non-triggering of the overvoltage protection.

[0011] In a small system, the maximum range of the reactive current proportion of the non-synchronous power supply without overvoltage is determined for different voltage stiffness levels.

[0012] Optionally, the energy loss value caused by the low penetration of the flexible DC is calculated, and the expression is:

[0013] E sag = (P0-P sag )t sag

[0014] wherein E sag is the energy loss value, P0 is the power of the flexible DC in normal operation, P sag is the power of the flexible DC during the low penetration, and t sag is the duration of the low penetration.

[0015] Optionally, when the intersection is selected, the active current is first reduced to improve the output capability of the reactive current.

[0016] The application also provides a low penetration optimization device of a flexible DC, comprising:

[0017] The low penetration active power control value module: calculates an energy loss value caused by the low penetration of the flexible DC; determines a kinetic energy value released by the rotor according to the system inertia; combines the system inertia, the energy loss value, and a preset minimum frequency proportion allowed by the system to determine a minimum frequency value of the system through engineering experience or simulation data; calculates a maximum energy that can be lacked corresponding to the minimum frequency value of the system according to a preset coefficient; determines a penetration power during the low penetration of the flexible DC according to the maximum energy that can be lacked and a predetermined low penetration time of the flexible DC; and determines a low penetration active power control value according to the penetration power.

[0018] The range module of the proportion of the active current and the reactive current: determines a range of the reactive current proportion according to a relationship between the voltage stiffness and the non-triggering of the overvoltage protection; determines a maximum active loss amount based on the actual consumed active power during the fault, and determines a range of the active current proportion according to the total amount of the rotor kinetic energy; and selects an intersection of the range of the active current proportion and the range of the reactive current proportion.

[0019] The adaptive recovery rate module: obtains the change amount of the bus phase of the flexible DC compared to the initial value and the critical phase change amount; if the change amount does not exceed the critical phase change amount, the recovery rate is dynamically adjusted according to the phase change rate: the faster the phase drop speed, the greater the recovery rate increase; if the change amount exceeds the critical phase change amount, the preset maximum recovery rate is adopted.

[0020] The execution module selects the lowest active current and the highest reactive current in the intersection that meets the low-pass active power control value and the adaptive recovery rate, and performs low-pass of the flexible DC.

[0021] Optionally, the preset coefficient is a ratio between the maximum energy loss of the flexible DC and the rotor kinetic energy of the system.

[0022] Optionally, the reactive current proportion range is determined according to the relationship between the predetermined voltage stiffness and the non-triggering of the overvoltage protection, and includes:

[0023] In a small system, for different voltage stiffness levels, the maximum reactive current proportion range of the non-synchronous generator that does not cause overvoltage is determined.

[0024] Optionally, the energy loss value caused by the low-pass of the flexible DC is calculated, and the expression is:

[0025] E sag = (P0-P sag )t sag

[0026] Wherein, E sag is the energy loss value, P0 is the power of the flexible DC during normal operation, P sag is the power of the flexible DC during low-pass, and t sag is the low-pass duration.

[0027] Optionally, when selecting the intersection, the active current is first reduced to improve the reactive current output capability.

[0028] The beneficial effects of the present application are:

[0029] The application provides a low penetration optimization method of flexible direct current, comprising the following steps: determining a low penetration active power control value; calculating an energy loss value caused by flexible direct current low penetration; determining a kinetic energy value released by a rotor according to system inertia; combining the system inertia, the energy loss value and a preset system minimum frequency ratio to determine a system minimum frequency value through engineering experience or simulation data; calculating a maximum missing energy corresponding to the system minimum frequency value according to a preset coefficient; determining a penetration power during flexible direct current low penetration according to the maximum missing energy and a predetermined flexible direct current low penetration time; determining the low penetration active power control value according to the penetration power; determining a proportion range of active current and reactive current; determining a reactive current proportion range according to the relationship between voltage stiffness and non-triggering overvoltage protection; determining a maximum active loss amount based on actual active power consumed during a fault, and determining an active current proportion range according to the maximum active loss amount and the total amount of rotor kinetic energy; selecting an intersection of the active current proportion range and the reactive current proportion range; determining an adaptive recovery rate: obtaining a change amount of a bus phase of flexible direct current compared with an initial value and a critical phase change amount; if the change amount does not exceed the critical phase change amount, dynamically adjusting the recovery rate according to a phase change rate: the faster the phase drop speed, the greater the recovery rate improvement amplitude; if the change amount exceeds the critical phase change amount, a preset maximum recovery rate is adopted; selecting the lowest active current and the highest reactive current in the intersection that meet the low penetration active power control value and the adaptive recovery rate to perform low penetration of the flexible direct current. Through dynamic energy balance analysis, adaptive adjustment of the recovery rate and coordinated optimization of active current and reactive current, the application significantly improves the stability and control accuracy of the flexible direct current system under low penetration fault. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a low penetration optimization schematic diagram of flexible direct current in the application;

[0031] Figure 2 is a whole process curve schematic diagram of the low penetration and recovery process of flexible direct current in the application;

[0032] Figure 3 is a reactive current control schematic diagram during low penetration of flexible direct current in the application;

[0033] Figure 4 is a single-machine infinite system schematic diagram in the application;

[0034] Figure 5 is a maximum reactive current schematic diagram of a non-synchronous power supply under different voltage stiffness levels in the application;

[0035] Figure 6 is a synchronous machine power angle characteristic curve schematic diagram considering the influence of flexible direct current in the application;

[0036] Figure 7 Fig. 1 is a schematic diagram of a two-machine infinite system in the present application;

[0037] Figure 8 Fig. 2 is a schematic diagram of a two-terminal system in the present application. DETAILED DESCRIPTION

[0038] Exemplary embodiments of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it is understood that the present disclosure should not be limited to the embodiments set forth herein and can be carried out in various forms. Instead, the embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0039] The current flexible DC low penetration (LVRT) configuration scheme (as shown in Table 1) aims to maintain constant active current and maximize reactive support.

[0040] Table 1

[0041]

[0042]

[0043] Synchronous stability and voltage stability require to reduce active current and increase reactive current, while frequency stability requires to maintain or increase active power. If the flexible DC reduces active power output, it will exacerbate energy shortage and further deteriorate frequency stability.

[0044] Based on the above analysis, the following dynamic coordination optimization principles are proposed:

[0045] Principle 1: During the fault, preferentially reduce the active current to suppress the power angle swing, while increasing the reactive current; after the fault is cleared, gradually restore the active power to balance the energy shortage.

[0046] Principle 2: Ensure that the active power is not lower than the critical value to maintain frequency stability;

[0047] Principle 3: Limit the upper limit of the reactive current to prevent equipment overvoltage damage.

[0048] Referring to Figure 1 Based on the above principles, the present application provides a low penetration optimization method for flexible DC, which includes:

[0049] S101, determining a low-pass active power control value: calculating an energy loss value caused by flexible DC low-pass; determining a kinetic energy value released by a rotor according to system inertia; combining the system inertia, the energy loss value, and a preset system allowed minimum frequency ratio, determining a system minimum frequency value through engineering experience or simulation data; calculating a maximum energy that can be lacked corresponding to the system minimum frequency value according to a preset coefficient; determining a low-pass power during flexible DC low-pass according to the maximum energy that can be lacked and a predetermined flexible DC low-pass time; determining the low-pass active power control value according to the low-pass power.

[0050] Please refer to Figure 2 When the flexible DC port bus voltage drops, its power will decrease to a very small value P sag , and after a time t sag , it will start to recover, and the recovery process will last t rc .

[0051] The core goal of low-pass strategy optimization is to determine parameters P sag , t sag and recovery rate to achieve multi-dimensional stability balance. Specifically, during low-pass, the lower P sag is, the more conducive to suppressing power angle oscillation and maintaining voltage level. The reduction of P sag will lead to system energy shortage, which needs to be combined with the duration t sag to evaluate its impact on frequency.

[0052] Energy loss within time t sag :

[0053] E sag = (P0-P sag ) t sag

[0054] Where E sag is energy loss, P0 is normal operating power, and P sag is low-pass power.

[0055] Kinetic energy release of the generator rotor:

[0056]

[0057] Where E k is rotor kinetic energy, H sys is system inertia, ω is real-time speed, and ω0 is initial speed.

[0058] The relationship between system frequency and energy loss is:

[0059]

[0060] Let the system allowed minimum frequency be Kf The maximum energy shortage that the system can withstand when the flexible DC is immediately restored to active power after low penetration is:

[0061]

[0062] wherein K f is the minimum frequency ratio allowed by the system.

[0063] In actual engineering, an empirical coefficient K s is introduced to correct the theoretical energy shortage:

[0064] E max = K s H sys ω0 2

[0065] wherein E max is the maximum energy loss allowed during low penetration of the flexible DC.

[0066] t sag is actually the time during which the power angle difference of the system continues to increase, and the specific method for calculating t sag is to scan various faults through simulation, find the unit with the longest power angle increase duration among all faults, and take this time as t sag .

[0067] After obtaining t sag , the low penetration power P sag can be directly calculated as:

[0068]

[0069] The penetration power is the active power control value.

[0070] S102, determine the proportion range of active current and reactive current: according to the relationship between voltage stiffness and non-triggering overvoltage protection, determine the reactive current proportion range; determine the maximum active loss based on the actual active power consumed during the fault, and determine the active current proportion range according to the maximum active loss and the total amount of rotor kinetic energy; select the intersection of the active current proportion range and the reactive current proportion range.

[0071] When the low penetration duration t sag is known, the residual power during the low penetration of the flexible DC is calculated by the following formula:

[0072] E max = K s H sys ω0 2

[0073]

[0074] Among them, E max H is the maximum allowable energy deficit for the system. sys Let K be the system's equivalent inertia, ω0 be the rotor angular velocity corresponding to the grid's rated frequency, and K be the angular velocity. s This is an engineering experience coefficient. Residual power refers to the remaining power that the flexible DC transmission can output during low-voltage testing, that is, the power output after reducing the active power to P. sag Afterwards, the portion of power that can be used to output reactive power can also be used.

[0075] Please refer to Figure 3 As shown, flexible DC reduces active power output to P during low-voltage ride-through. sag This frees up capacity to output reactive power to support the grid voltage. Its dynamic reactive current command is calculated using the following formula:

[0076] △I t =K1*(0.9-U t *I N ), 0.2≤U t ≤0.9

[0077] Among them, △I t U represents the dynamic reactive current increment, K1 is the dynamic reactive current proportional coefficient (typically ranging from [1.5, 3]), and U... t This is the per-unit value of the flexible DC grid connection point voltage; I N This is the rated voltage per unit value (usually 1.0 pu).

[0078] In the traditional scheme, K1 is fixed at 1.5, which does not fully utilize the voltage support capability of flexible DC.

[0079] To fully utilize the voltage support capability of flexible DC transmission, the maximum output reactive current is calculated based on the active current setting and is used as the upper limit of reactive current. When the system voltage level is low, K1 is set to a larger value, allowing the flexible DC transmission to directly release all reactive capacity to improve voltage stability.

[0080] Based on the above, the next step is to determine the range of key parameters.

[0081] Reactive current under overvoltage constraint:

[0082] To ensure that overvoltage protection is not triggered, the reactive current ratio range is determined by considering the relationship between system voltage stiffness and reactive current. Voltage stiffness is calculated using the following formula:

[0083]

[0084] Among them, K vtg For voltage stiffness, U sysThe voltage amplitude of the port for the flexible DC system to access the power grid, U sys0 The no-load voltage amplitude of the access point, The system Thevenin equivalent impedance, The impedance of the flexible DC system, λ SCR The short-circuit ratio.

[0085] For example: please refer to Figure 4 The transient maximum current of the non-synchronous machine power supply is 1.2pu. When the voltage stiffness is lower than 0.89pu, the reactive power priority output of the non-synchronous machine power supply will cause 1.2 times overvoltage.

[0086] Please refer to Figure 5 To ensure that the grid-connected point voltage does not exceed 1.1pu, the reactive current needs to be limited to 0.6pu (based on the no-load voltage of 1.05pu).

[0087] Active current under frequency constraint:

[0088] Determine the active current proportion range by combining the maximum active loss and the total rotor kinetic energy of the partition;

[0089] Determine the parameters by adjusting the recovery rate multiple times through t sag , H sys and K s as the criterion that does not cause the unit power angle to accelerate twice.

[0090] The same region flexible DC uses unified low penetration parameters, and different regions are set respectively.

[0091] Determine the intersection of the active current proportion range and the reactive current proportion range, and preferentially reduce the active current within the intersection range to improve the reactive current output capability, while meeting the low penetration power control demand.

[0092] S103, determine the adaptive recovery rate: obtain the change amount of the bus phase of the flexible DC compared to the initial value and the critical phase change amount; if the change amount does not exceed the critical phase change amount, dynamically adjust the recovery rate according to the phase change rate: the faster the phase drops, the greater the recovery rate increases; if the change amount exceeds the critical phase change amount, the maximum recovery rate is used.

[0093] Please refer to Figure 6 In the recovery stage of the flexible DC low voltage ride through (LVRT), if the power recovery speed is too fast, it may cause the synchronous machine power angle to accelerate again until instability. To reveal this mechanism, the synchronous machine power angle characteristic curve considering the influence of the flexible DC is as shown in Figure 6 The curve is established by the following formula:

[0094]

[0095] Among them, P g For the synchronous machine output, U g θ g These represent the amplitude and phase of the synchronous machine bus voltage, E sys X is the amplitude of the infinite bus voltage. sys P is the equivalent impedance of the system. n This is the rated transmission power for flexible DC.

[0096] Please continue to refer to this. Figure 6 As shown, the initial operating point A: If a three-phase metallic short-circuit fault occurs at the port, the synchronous machine operating point will jump to point I, and then rapidly accelerate to point H due to power deficit.

[0097] Two scenarios after fault clearance:

[0098] Flexible DC instantaneous full power recovery: The synchronous machine's operating point changes abruptly from point H to point D, and decelerates along curve 1.

[0099] Flexible DC power reduction operation: The synchronous machine's operating point changes abruptly from point H to point C, and decelerates along curve 2.

[0100] Stability Comparison: When operating at reduced power, the synchronous machine has a larger deceleration area and better stability; however, if the flexible DC power is restored before the power angle returns to the stable region, it may cause the power angle to accelerate and become unstable again. For example, if the synchronous machine decelerates from point C to point F along curve 2 and then restores full power, its power angle characteristics will switch to curve 1, and it may abruptly change from point F to point G and accelerate again.

[0101] Please refer to Figure 7 As shown, to ensure that the synchronous machine does not accelerate twice during deceleration, the following conditions must be met:

[0102] P g >P m

[0103] Substituting the above equation into the power angle characteristic curve, we can obtain the limit requirement for flexible DC power recovery:

[0104]

[0105] Adaptive recovery strategy for power systems at both ends:

[0106] Please refer to Figure 8 As shown, the recovery speed of the flexible DC system at both ends can be adaptively adjusted through cross-sectional power flow. Taking flexible DC i as an example, its recovery speed v ni (t) satisfies:

[0107]

[0108] wherein, v ni (t) represents the power recovery speed of the flexible DC i at time t, v maxi is the maximum power recovery speed that the flexible DC i can withstand, θ i is the bus phase of the flexible DC i, △θ i is the change amount of the bus phase of the flexible DC i compared with the initial value, θ c is the critical phase change amount.

[0109] The expression of the h function is as follows:

[0110]

[0111] wherein, a is a constant.

[0112] S104, selecting the lowest active current and the highest reactive current in the intersection that meet the low penetration active power control value and the adaptive recovery rate, and setting the low penetration strategy of the flexible DC.

[0113] The application significantly improves the stability and control accuracy of the flexible DC system under low penetration fault through dynamic energy balance analysis, adaptive adjustment of recovery rate, and active / reactive current collaborative optimization.

[0114] According to Table 1, the low penetration configuration scheme of the application is provided according to the above embodiment:

[0115] Table 2

[0116]

[0117] The application also provides a low penetration optimization device of a flexible DC, comprising:

[0118] The low penetration active power control value module: calculates the energy loss value caused by the low penetration of the flexible DC; determines the kinetic energy value released by the rotor according to the system inertia; combines the system inertia, the energy loss value, and the preset minimum frequency ratio allowed by the system, and determines the minimum frequency value of the system through engineering experience or simulation data; calculates the maximum energy that can be missed corresponding to the minimum frequency value of the system according to the preset coefficient; determines the penetration power during the low penetration of the flexible DC according to the maximum energy that can be missed and the low penetration time of the flexible DC determined in advance; determines the low penetration active power control value according to the penetration power;

[0119] The active current and reactive current proportion range module: determines the reactive current proportion range according to the relationship between voltage stiffness and non-triggering of overvoltage protection; determines the maximum active power loss based on the actual active power consumed during the fault, and determines the active current proportion range according to the maximum active power loss and the total amount of rotor kinetic energy; selects the intersection of the active current proportion range and the reactive current proportion range;

[0120] The adaptive recovery rate module obtains a change amount of the bus phase of the flexible DC compared to an initial value and a critical phase change amount; if the change amount does not exceed the critical phase change amount, a recovery rate is dynamically adjusted according to a phase change rate; the faster the phase drop speed, the greater the recovery rate increase amplitude; if the change amount exceeds the critical phase change amount, a preset maximum recovery rate is adopted;

[0121] The execution module selects the lowest active current and the highest reactive current in the intersection that meet the low-pass active power control value and the adaptive recovery rate, and performs low-pass of the flexible DC.

[0122] The preset coefficient is a ratio between the maximum energy loss of the flexible DC and the rotor kinetic energy of the system. According to a predetermined relationship between the voltage stiffness and the non-triggering overvoltage protection, the reactive current proportion range is determined, including: in a small system, for different voltage stiffness levels, the maximum reactive current proportion range of the non-synchronous generator is determined without overvoltage.

[0123] Further, the energy loss value caused by the low-pass of the flexible DC is calculated, and the expression is:

[0124] E sag =(P0-P sag )t sag

[0125] wherein E sag is the energy loss value, P0 is the power of the flexible DC in normal operation, P sag is the power of the flexible DC during the low-pass, and t sag is the low-pass duration.

[0126] Further, when selecting the intersection, the active current is first reduced to improve the reactive current output capability.

[0127] The above description of the embodiments is for the convenience of the general technical personnel in the art to understand and apply the present application. Those skilled in the art can easily make various modifications to the above embodiments, and apply the general principles described herein to other embodiments without having to go through creative labor. Therefore, the present application is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art to the present application according to the disclosure of the present application should be within the scope of protection of the present application.

Claims

1. A method for low penetration optimization of flexible DC, characterized in that, The method comprises the following steps: determining a low-pass active power control value: calculating an energy loss value caused by flexible DC low-pass; determining a kinetic energy value released by a rotor according to system inertia; combining the system inertia, the energy loss value and a preset minimum frequency ratio allowed by the system to determine a minimum system frequency value through engineering experience or simulation data; calculating a maximum energy that can be lost corresponding to the minimum system frequency value according to a preset coefficient; determining a low-pass power during flexible DC low-pass according to the maximum energy that can be lost and a predetermined flexible DC low-pass time; and determining the low-pass active power control value according to the low-pass power; determining a proportional range of active current and reactive current: determining a reactive current proportional range according to the relationship between voltage stiffness and non-triggering of overvoltage protection; determining a maximum active loss amount based on actual active power consumed during a fault; and determining an active current proportional range according to the maximum active loss amount and the total amount of rotor kinetic energy; selecting an intersection of the active current proportional range and the reactive current proportional range; determining an adaptive recovery rate: obtaining a change amount of a bus phase of flexible DC compared to an initial value and a critical phase change amount; if the change amount does not exceed the critical phase change amount, dynamically adjusting the recovery rate according to a phase change rate: the faster the phase drops, the greater the recovery rate increases; if the change amount exceeds the critical phase change amount, using a preset maximum recovery rate; selecting the lowest active current and the highest reactive current in the intersection that meet the low-pass active power control value and the adaptive recovery rate to perform low-pass of the flexible DC.

2. The method of low penetration optimization for flexible DC of claim 1, wherein, The preset coefficient is a ratio between maximum energy loss of the flexible DC and rotor kinetic energy of the system.

3. The method of low penetration optimization for flexible DC of claim 1, wherein, According to a predetermined relationship between voltage stiffness and non-triggering of overvoltage protection, the reactive current proportional range is determined, which comprises: In a small system, for different voltage stiffness levels, the maximum reactive current proportional range of a non-synchronous generator is determined without overvoltage.

4. The method of low penetration optimization for flexible DC of claim 1, wherein, The energy loss value caused by flexible DC low-pass is calculated, and the expression is: ； wherein, is the energy loss value, is the power of the flexible DC during normal operation, is the power of the flexible DC during low penetration, is the low penetration duration.

5. The method of low penetration optimization for flexible DC of claim 1, wherein, When selecting the intersection, the active current is first reduced to improve the reactive current output capability.

6. A low penetration optimization device for flexible DC, characterized in that The method comprises the following steps: a low-pass active power control value module: calculating an energy loss value caused by flexible DC low-pass; determining a kinetic energy value released by a rotor according to system inertia; combining the system inertia, the energy loss value and a preset minimum frequency ratio allowed by the system to determine a minimum system frequency value through engineering experience or simulation data; calculating a maximum energy that can be lost corresponding to the minimum system frequency value according to a preset coefficient; determining a low-pass power during flexible DC low-pass according to the maximum energy that can be lost and a predetermined flexible DC low-pass time; and determining the low-pass active power control value according to the low-pass power; an active current and reactive current proportional range module: determining a reactive current proportional range according to the relationship between voltage stiffness and non-triggering of overvoltage protection; determining a maximum active loss amount based on actual active power consumed during a fault; and determining an active current proportional range according to the maximum active loss amount and the total amount of rotor kinetic energy; selecting an intersection of the active current proportional range and the reactive current proportional range; The adaptive recovery rate module: obtain the change amount of the bus phase of the flexible DC compared to the initial value and the critical phase change amount; if the change amount does not exceed the critical phase change amount, the recovery rate is dynamically adjusted according to the phase change rate: the faster the phase drop speed, the greater the recovery rate increase; if the change amount exceeds the critical phase change amount, the preset maximum recovery rate is adopted; The execution module selects the lowest active current and the highest reactive current in the intersection that meets the low-pass active power control value and the adaptive recovery rate, and performs low-pass of the flexible DC.

7. The device for low penetration optimization of flexible DC of claim 6, wherein, The preset coefficient is a ratio between the maximum energy loss of the flexible DC and the system rotor kinetic energy.

8. The device for low penetration optimization of flexible DC of claim 6, wherein, According to the relationship between the predetermined voltage stiffness and the non-triggering overvoltage protection, the reactive current proportion range is determined, including: In a small system, for different voltage stiffness levels, the maximum reactive current proportion range of the non-synchronous generator is determined without overvoltage.

9. The device for low penetration optimization of flexible DC of claim 6, wherein, The energy loss value caused by the low-pass of the flexible DC is calculated, and the expression is: ； wherein, is the energy loss value, is the power of the flexible DC during normal operation, is the power of the flexible DC during low penetration, is the low penetration duration.

10. The device for low penetration optimization of flexible DC of claim 6, wherein, When selecting the intersection, the active current is first reduced to improve the reactive current output capability.

Images