Control method for improving low voltage ride through capability and transient stability margin of wind turbine generator

Abstract

The invention discloses a control method for improving low-voltage ride-through capability and transient stability margin of a wind turbine generator, which belongs to the technical field of wind power generation grid connection and comprises the following steps of: S1, calculating grid-connected point voltage in real time, calculating a grid-connected point voltage drop deviation value, judging that the grid-connected point voltage drop deviation value exceeds a set dead zone, if so, executing step S2; executing the step S2; if not, repeating the step S1; s2, when the power system is disturbed, a droop control module of the wind generating set is started; s3, calculating a droop control coefficient of the wind generating set by taking an absolute value of the voltage deviation of the grid-connected point at the current moment and a real-time power angle output by the grid-forming converter; and S4, calculating the reactive compensation amount of the wind generating set participating in the system voltage support based on the grid-connected point voltage drop deviation value and the wind generating set droop control coefficient. It is guaranteed that the power angle changes within a stable range, and the transient power angle instability phenomenon is avoided.

Description

Technical Field

[0001] This invention relates to the field of wind power grid connection technology, specifically to a control method for improving the low voltage ride-through capability and transient stability margin of wind turbine generators. Background Technology

[0002] New energy power generation equipment needs to transmit electrical energy to the grid through converters. Currently, large-scale grid connection of new energy uses conventional grid-following (GFL) converters to complete energy conversion and transmission. However, GFL converters achieve synchronization with the grid by following the voltage phase through phase-locked loops. In scenarios with a high proportion of new energy, this can easily lead to instability. At the same time, GFL converters themselves do not have inertia and damping characteristics, and connecting them to the grid will cause the grid to exhibit low inertia and weak damping characteristics.

[0003] Furthermore, due to the limitations of power semiconductor devices' overload capacity, converters have relatively weak overload capabilities. These differences pose new challenges to the stable operation of power systems. Addressing the inherent shortcomings of GFL converters, some scholars have proposed a Virtual Synchronous Generator (VSG) technology with inertia and damping characteristics by simulating the operating characteristics of synchronous generators. By simulating the rotor motion characteristics of a synchronous generator, the VSG exhibits voltage source characteristics similar to traditional synchronous generators in grid-connected performance. It can achieve autonomous synchronization with the grid, avoiding the negative impact of PLLs that could exacerbate system instability risks. It can operate stably in scenarios with ultra-high proportions of renewable energy (extremely weak short-circuit ratios), gradually becoming a feasible solution to alleviate the "high-voltage and high-stress" power system. Power systems are susceptible to fault disturbances during operation. Existing literature mainly focuses on the steady-state operation of VSGs, but under fault conditions, the voltage drop at the VSG grid connection point causes the VSG operation to deviate from the stable operating range under small disturbances. Because VSGs possess the inertia characteristics of synchronous generators, their internal potential cannot change abruptly during a fault, which can easily trigger a large inrush current and increase the power angle, posing a significant threat to the stable operation of the power grid.

[0004] Based on this, the present invention designs a control method to improve the low voltage ride-through capability and transient stability margin of wind turbine units in order to solve the above problems. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a control method to improve the low voltage ride-through capability and transient stability margin of wind turbine units.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A control method for improving the low-voltage ride-through capability and transient stability margin of wind turbine generators includes the following steps:

[0008] Step S1: Calculate the grid connection point voltage in real time, calculate the grid connection point voltage drop deviation value, and determine whether the grid connection point voltage drop deviation value exceeds the set dead zone. If the determination is yes, proceed to step S2; if the determination is no, repeat step S1.

[0009] Step S2: When a disturbance occurs in the power system, the droop control module of the wind turbine generator is activated;

[0010] Step S3: Take the absolute value of the voltage deviation at the grid connection point at the current moment and the real-time power angle output of the grid-connected converter to calculate the droop control coefficient of the wind turbine generator set;

[0011] Step S4: Based on the voltage drop deviation at the grid connection point and the droop control coefficient of the wind turbine generator set, calculate the reactive power compensation amount of the wind turbine generator set participating in the system voltage support.

[0012] Step S5: Input the calculated active power change into the grid-side controller to obtain the reactive power reference value of the wind turbine generator.

[0013] Furthermore, step S1 is performed as follows:

[0014] Step S11: Real-time acquisition of the instantaneous values ​​of the three-phase voltage at the grid connection point using voltage transformers and analog-to-digital converters. , and ;

[0015] Step S12: Instantaneous values ​​of the three-phase voltage at the grid connection point , and Perform low-pass filtering, filter voltage ;

[0016] Remove high-frequency noise and interference signals to avoid voltage calculation deviations caused by noise;

[0017] Step S13: Filter the voltage Calculate periodic voltage ;

[0018] Step S14: Through the rated voltage and periodic voltage Calculate voltage drop deviation value ;

[0019] Step S15: Determine if the voltage drop deviation at the grid connection point exceeds the set dead zone. If the determination is yes, proceed to step S2; if the determination is no, repeat step S11.

[0020] Furthermore, periodic voltage signals The calculation formula is as follows:

[0021]

[0022] This is the fundamental frequency period of the power grid.

[0023] Furthermore, voltage sag deviation value The specific calculations are as follows:

[0024] .

[0025] Furthermore, the voltage droop coefficient of wind turbine generators The calculation formula is as follows:

[0026]

[0027] The real-time power angle output by the grid-type converter. This represents the initial power angle of the grid-type converter during steady-state operation. This is the critical value of the output power angle of the grid-type converter.

[0028] Furthermore, the reactive power compensation of wind turbine generators participating in system voltage support The calculation formula is as follows:

[0029]

[0030] This is the voltage droop factor for wind turbine generator sets. This refers to the voltage deviation at the grid connection point.

[0031] Furthermore, the real-time power angle output of the grid-type converter... The logical discriminant is as follows:

[0032]

[0033] To distinguish the signal, , These are virtual resistance and virtual reactance, respectively.

[0034] Furthermore, the reference value of reactive power of wind turbine generators The specific calculations are as follows:

[0035]

[0036] It outputs reactive power to the converter.

[0037] Beneficial effects: During the voltage dip phase of the power system, this invention constructs a tuning formula for the voltage droop control coefficient of the wind turbine generator using an exponential function. During the grid voltage dip phase, the exponential function couples the droop control coefficient of the wind turbine generator with the grid connection point voltage deviation, effectively improving the reactive power support capability of the wind turbine generator itself. This enables the wind turbine generator to fully utilize reactive power to help the grid achieve fault ride-through under large disturbance scenarios. Secondly, during the voltage dip of the wind turbine generator, by adding power angle information to the custom gain function, the power angle is ensured to change within a stable range, avoiding transient power angle instability. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0039] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0041] The present invention will be further described below with reference to embodiments.

[0042] Example 1: Please refer to Figure 1 The control method for improving the low-voltage ride-through capability and transient stability margin of wind turbine units includes the following steps:

[0043] Step S1: Calculate the grid connection point voltage in real time, calculate the grid connection point voltage drop deviation value, and determine whether the grid connection point voltage drop deviation value exceeds the set dead zone. If the determination is yes, proceed to step S2; if the determination is no, repeat step S1.

[0044] Step S2: When a disturbance occurs in the power system, the droop control module of the wind turbine generator is activated;

[0045] Step S3: Take the absolute value of the voltage deviation at the grid connection point at the current moment and the real-time power angle output of the grid-connected converter to calculate the droop control coefficient of the wind turbine generator set;

[0046] Step S4: Based on the voltage drop deviation at the grid connection point and the droop control coefficient of the wind turbine generator set, calculate the reactive power compensation amount of the wind turbine generator set participating in the system voltage support.

[0047] Step S5: Input the calculated active power change into the grid-side controller to obtain the reactive power reference value of the wind turbine generator.

[0048] The specific steps for step S1 are as follows:

[0049] Step S11: Real-time acquisition of the instantaneous values ​​of the three-phase voltage at the grid connection point using voltage transformers and analog-to-digital converters. , and ;

[0050] Step S12: Instantaneous values ​​of the three-phase voltage at the grid connection point , and Perform low-pass filtering, filter voltage ;

[0051] Remove high-frequency noise and interference signals to avoid voltage calculation deviations caused by noise;

[0052] Step S13: Filter the voltage Calculate periodic voltage ;

[0053] Step S14: Through the rated voltage and periodic voltage Calculate voltage drop deviation value ;

[0054] Step S15: Determine if the voltage drop deviation at the grid connection point exceeds the set dead zone. If the determination is yes, proceed to step S2; if the determination is no, repeat step S11.

[0055] Periodic voltage signal The calculation formula is as follows:

[0056]

[0057] This is the fundamental frequency period of the power grid.

[0058] Voltage sag deviation The specific calculations are as follows:

[0059] .

[0060] Voltage droop coefficient of wind turbine generator set The calculation formula is as follows:

[0061]

[0062] The real-time power angle output by the grid-type converter. This represents the initial power angle of the grid-type converter during steady-state operation. This is the critical value of the output power angle of the grid-type converter.

[0063] As the voltage deviation at the grid connection point gradually increases, the droop coefficient increases with the increase of the voltage deviation at the grid connection point, thereby realizing the grid-connected converter's function of actively compensating reactive power to raise the voltage at the grid connection point under large disturbance scenarios.

[0064] Reactive power compensation of wind turbine generators in system voltage support The calculation formula is as follows:

[0065]

[0066] This is the voltage droop factor for wind turbine generator sets. This refers to the voltage deviation at the grid connection point.

[0067] Real-time power angle of grid converter output The logical discriminant is as follows:

[0068]

[0069] To distinguish the signal, , These are virtual resistance and virtual reactance, respectively.

[0070] During grid fault operation, the voltage at the grid-connected converter terminal is affected by the grid connection point voltage. When the grid connection point voltage drops, the voltage at the grid-connected converter terminal also decreases, leading to a decrease in the active power output of the wind turbine. This causes the deceleration area of ​​the power angle curve to be smaller than the acceleration area, resulting in transient power angle instability in the system. To improve the transient stability of the system, a voltage droop coefficient for the wind turbine generator set containing power angle information is defined. Simultaneously, a discrimination device judges based on the critical power angle value; when the power angle exceeds the critical value, the system is determined to be in a power angle instability state.

[0071] Reference value of reactive power of wind turbine generator set The specific calculations are as follows:

[0072]

[0073] It outputs reactive power to the converter.

[0074] During the voltage dip phase of the power system, an exponential function is used to construct the tuning formula for the voltage droop control coefficient of the wind turbine generator. During the voltage dip phase of the grid, an exponential function is used to couple the droop control coefficient of the wind turbine generator with the voltage deviation at the grid connection point, effectively improving the reactive power support capability of the wind turbine generator itself. This enables the wind turbine generator to fully utilize reactive power to help the grid achieve fault ride-through under large disturbance scenarios. Secondly, during the voltage dip phase of the wind turbine generator, power angle information is added to the custom gain function to ensure that the power angle changes within a stable range, avoiding transient power angle instability.

[0075] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for improving the low-voltage ride-through capability and transient stability margin of wind turbine generators, characterized in that: Includes the following steps: Step S1: Calculate the grid connection point voltage in real time, calculate the grid connection point voltage drop deviation value, and determine whether the grid connection point voltage drop deviation value exceeds the set dead zone. If the determination is yes, proceed to step S2; if the determination is no, repeat step S1. Step S2: When a disturbance occurs in the power system, the droop control module of the wind turbine generator is activated; Step S3: Take the absolute value of the voltage deviation at the grid connection point at the current moment and the real-time power angle output of the grid-connected converter to calculate the droop control coefficient of the wind turbine generator set; Step S4: Based on the voltage drop deviation at the grid connection point and the droop control coefficient of the wind turbine generator set, calculate the reactive power compensation amount of the wind turbine generator set participating in the system voltage support. Step S5: Input the calculated active power change into the grid-side controller to obtain the reactive power reference value of the wind turbine generator.

2. The control method according to claim 1, characterized in that, The specific steps for step S1 are as follows: Step S11: Real-time acquisition of the instantaneous values ​​of the three-phase voltage at the grid connection point using voltage transformers and analog-to-digital converters. , and ; Step S12: Instantaneous values ​​of the three-phase voltage at the grid connection point , and Perform low-pass filtering, filter voltage ; Remove high-frequency noise and interference signals to avoid voltage calculation deviations caused by noise; Step S13: Filter the voltage Calculate periodic voltage ; Step S14: Through the rated voltage and periodic voltage Calculate voltage drop deviation value ; Step S15: Determine if the voltage drop deviation at the grid connection point exceeds the set dead zone. If the determination is yes, proceed to step S2; if the determination is no, repeat step S11.

3. The control method according to claim 2, characterized in that, Periodic voltage signal The calculation formula is as follows: ； This is the fundamental frequency period of the power grid.

4. The control method according to claim 3, characterized in that, Voltage sag deviation The specific calculations are as follows: 。 5. The control method according to claim 4, characterized in that, Voltage droop coefficient of wind turbine generator set The calculation formula is as follows: ； The real-time power angle output by the grid-type converter. This represents the initial power angle of the grid-type converter during steady-state operation. This is the critical value of the output power angle of the grid-type converter.

6. The control method according to claim 5, characterized in that, Reactive power compensation of wind turbine generators in system voltage support The calculation formula is as follows: ； This refers to the voltage droop factor of the wind turbine generator set. This refers to the voltage deviation at the grid connection point.

7. The control method according to claim 6, characterized in that, Real-time power angle of grid converter output The logical discriminant is as follows: ； To distinguish the signal, , These are virtual resistance and virtual reactance, respectively.

8. The control method according to claim 7, characterized in that, Reference value of reactive power of wind turbine generator set The specific calculations are as follows: ； It outputs reactive power to the converter.

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