Transient stability enhancing method for net-forming type double-fed fan

Abstract

The invention provides a method for enhancing transient stability of a grid-forming type doubly-fed fan. The method comprises the following steps: acquiring a current actual power grid voltage and a current actual stator voltage; determining a first theoretical curve based on the current actual power grid voltage; determining a current theoretical stator voltage corresponding to the current actual power grid voltage based on the current actual power grid voltage and the first theoretical curve; determining a given stator voltage based on the current theoretical stator voltage and the current actual stator voltage; determining an active power reference value based on the current theoretical stator voltage; and determining a compensation phase angle based on the current theoretical stator voltage and the current actual power grid voltage. Through the ways of dynamically adjusting the stator voltage and the active power reference value, directly compensating the phase angle and the like, power angle stability, fault current suppression and reactive support can be comprehensively considered, and the safe and stable operation capability of the grid-forming type double-fed fan under the working conditions of power grid voltage amplitude drop and phase jump is effectively improved.

Description

Technical Field

[0001] The present application relates to the field of research on transient stability of grid-type doubly-fed wind turbines, and specifically to a method for enhancing transient stability of grid-type doubly-fed wind turbines. Background Art

[0002] As the proportion of renewable energy sources like wind power connected to the grid continues to rise annually, the "dual-high" characteristics of new power systems are becoming increasingly prominent, weakening the grid's voltage and frequency stability capabilities. Therefore, the transition from "grid-following" to "grid-forming" renewable energy grid-connected generators has become an inherent requirement and a key path for the construction of new power systems. Doubly-fed wind turbines, with their low cost and high operating efficiency, have become the mainstream model for onshore wind power. Research on grid-forming doubly-fed induction generators (GFM-DFIGs) has garnered widespread attention. However, when a grid fault condition such as a short circuit occurs, GFM-DFIGs face transient stability issues similar to synchronous generators, such as transient power angle instability. Furthermore, the power electronic converters built into GFM-DFIGs can also face fault overcurrent issues under fault conditions. Furthermore, as the scale of renewable energy sources like wind power connected to the grid increases, existing grid-connection standards require that renewable energy sources provide necessary reactive power support during grid faults. Therefore, considering these multiple constraints, conducting transient performance analysis and stability control research on GFM-DFIGs is of great practical significance.

[0003] However, existing research on grid-connected wind power systems has two major shortcomings. Regarding fault scenarios, most studies focus solely on grid voltage dips, while fewer consider phase jumps. Regarding control strategies, most often only consider one or two of the following: transient power angle constraints, fault current constraints, and reactive power support constraints. Few consider transient stability issues under multiple constraints. Summary of the Invention

[0004] In order to overcome the above technical defects, the present application provides a method for enhancing transient stability of a grid-type doubly-fed wind turbine. To achieve the above objectives, the present application is implemented according to the following technical solutions:

[0005] The present application provides a method for enhancing transient stability of a grid-type doubly-fed wind turbine, comprising:

[0006] Collect the current actual grid voltage and the current actual stator voltage;

[0007] Determining a first theoretical curve based on the current actual grid voltage; the first theoretical curve is a curve showing stator voltage varying with grid voltage, and points on the first theoretical curve satisfy fault current suppression and reactive power support requirements;

[0008] Determining a current theoretical stator voltage corresponding to the current actual grid voltage based on the current actual grid voltage and the first theoretical curve;

[0009] Determining a given stator voltage based on the current theoretical stator voltage and the current actual stator voltage;

[0010] determining an active power reference value based on the current theoretical stator voltage;

[0011] A compensation phase angle is determined based on the current theoretical stator voltage and the current actual grid voltage.

[0012] Optionally, determining a first theoretical curve based on the current actual grid voltage includes:

[0013] Determining an upper limit and a lower limit of a theoretical stator voltage adjustment value based on the current actual grid voltage;

[0014] Based on the upper limit value and the lower limit value, a first theoretical curve is designed.

[0015] Optionally, the determining a given stator voltage based on the current theoretical stator voltage and the current actual stator voltage includes:

[0016] The given stator voltage is obtained by subtracting the current theoretical stator voltage from the current actual stator voltage q-axis component.

[0017] Optionally, determining an active power reference value based on the current theoretical stator voltage includes:

[0018] determining a reactive current based on the current theoretical stator voltage;

[0019] determining an active current based on the current theoretical stator voltage and the reactive current;

[0020] An active power reference value is determined based on the active current and the current theoretical stator voltage.

[0021] Optionally, after the step of determining the active power reference value, the method further includes:

[0022] Subtracting the active power reference value from the actual output active power to obtain an active power deviation value;

[0023] The active power deviation value is input into the active power loop.

[0024] Optionally, the determining the compensation phase angle based on the current theoretical stator voltage and the current actual grid voltage includes:

[0025] Determining a power angle based on the current actual grid voltage and the active current;

[0026] A compensation phase angle is determined based on the current actual grid voltage and the power angle.

[0027] Optionally, determining the compensation phase angle based on the actual grid voltage and the power angle includes:

[0028] Based on the current actual grid voltage, determining a grid voltage phase angle of the current actual grid voltage offset coordinate system q axis;

[0029] The phase compensation angle is obtained by subtracting the grid voltage phase angle from the power angle.

[0030] This application has the following beneficial effects:

[0031] The method proposed in this application can achieve comprehensive consideration of power angle stability, fault current suppression and reactive power support by dynamically adjusting the stator voltage, active power reference value and directly compensating the phase angle, effectively improving the safe and stable operation capability of the grid-type doubly fed wind turbine under the conditions of grid voltage amplitude drop and phase jump.

[0032] In addition to the above-described purposes, features and advantages, the present application has other purposes, features and advantages. The present application will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0034] Figure 1 This is a control block diagram of a grid-type doubly-fed wind turbine transient stability enhancement method provided by an embodiment of the present application;

[0035] Figure 2 1 is a flow chart of a method for enhancing transient stability of a grid-type doubly-fed wind turbine provided in an embodiment of the present application;

[0036] Figure 3 is a schematic diagram of a first theoretical curve taking into account multiple constraints during the experimental simulation provided in an embodiment of the present application;

[0037] Figure 4 This is a comparison diagram of the simulated waveforms when the grid voltage amplitude drops to 0.6 pu and the phase jumps negatively by 30 degrees during the experimental simulation provided by the embodiment of the present application. Figure 4 (a) is the simulation waveform diagram of the traditional control method. Figure 4 (b) is a simulation waveform diagram of the method proposed in this application;

[0038] Figure 5This is a comparison diagram of the simulated waveforms when the grid voltage amplitude drops to 0.4 pu and the phase jumps negatively by 30 degrees during the experimental simulation provided by the embodiment of the present application. Figure 5 (a) is the simulation waveform diagram of the traditional control method. Figure 5 (b) is a simulation waveform diagram of the method proposed in this application. DETAILED DESCRIPTION

[0039] The embodiments of the present application are described in detail below with reference to the accompanying drawings, but the present application can be implemented in many different ways as defined and covered by the claims.

[0040] Figure 1 This is a control block diagram of a method for enhancing transient stability of a grid-type doubly fed wind turbine described in this application. Under normal grid conditions, switches S1, S2, and S3 are all in position 1; and under grid voltage amplitude drop and phase jump conditions, switches S1, S2, and S3 are all switched to position 2, where P rated is the rated power; U ref is the rated voltage.

[0041] In order to solve the problems raised by the background technology, such as Figure 2 As shown, the present application provides a method for enhancing transient stability of a grid-type doubly-fed wind turbine, comprising:

[0042] Step S201: Collect the current actual grid voltage U gF And the current actual stator voltage U hF ;

[0043] During the fault period, the actual grid voltage U gF It refers to the actual voltage value in the power grid when a fault occurs. It varies depending on many factors, including the type of fault, fault location, system operation mode, and the action of protective devices.

[0044] During the operation of the motor, the actual stator voltage U hF Refers to the actual voltage applied to the motor stator winding.

[0045] It should be noted that the present application does not specifically limit the method of collecting the current actual grid voltage and the current actual stator voltage.

[0046] Step S202: determining a first theoretical curve based on the current actual grid voltage; the first theoretical curve is a curve showing stator voltage changing with grid voltage, and points on the first theoretical curve meet fault current suppression and reactive power support requirements;

[0047] After collecting the current actual grid voltage U gF Then, the theoretical stator voltage U can be obtained according to the current actual grid voltage.sF Adjust the upper and lower limits of the value; the specific process is as follows:

[0048] According to the rotor current stress constraint, determine the theoretical stator voltage U sF Adjust the upper limit of the value as follows:

[0049] U sF ≤U gF +1.5I sN X g (1)

[0050] Among them: U sF is the theoretical stator voltage at fault; I sN is the rated stator current; X g is the line impedance.

[0051] The grid-connected doubly-fed wind turbine needs to provide the necessary reactive power to the grid during a fault. According to the grid connection guidelines, the lower limit of the theoretical stator voltage adjustment value is determined:

[0052]

[0053] Where: s is the angular velocity of the grid fundamental voltage; L s 、L m are the stator self-inductance and the mutual inductance between stator and rotor respectively; L g is the line inductance; I rmax is the maximum allowable rotor current.

[0054] Then, according to the upper and lower limits of the theoretical stator voltage, a first theoretical curve can be designed. The first theoretical curve is a curve showing the stator voltage changing with the grid, and the points on the curve can meet the requirements of fault current suppression and reactive power support.

[0055] Step S203: determining a current theoretical stator voltage corresponding to the current actual grid voltage based on the current actual grid voltage and the first theoretical curve;

[0056] Since the stator voltage and the grid voltage are in one-to-one correspondence on the first theoretical curve, when the actual grid voltage U gF Later, the first theoretical curve can be used to find the voltage that matches the actual grid voltage U gF , the corresponding current theoretical stator voltage U sF .

[0057] Step S204: determining a given stator voltage based on the current theoretical stator voltage and the current actual stator voltage;

[0058] Then, the current theoretical stator voltage is compared with the current actual stator voltage UhF The q-axis component U sq The given stator voltage is obtained by making a difference, and then the given stator voltage is input into the proportional integral PI controller of the voltage outer loop to adjust the value of the stator voltage during the fault period.

[0059] Step S205: determining an active power reference value based on the current theoretical stator voltage;

[0060] After determining the current theoretical stator voltage U sF After that, the current theoretical stator voltage U sF , determine the reactive current I sFd ,Right now:

[0061]

[0062] Then according to the current theoretical stator voltage U sF and reactive current I sFd , obtain the active current I sFq .Right now:

[0063]

[0064] According to the current theoretical stator voltage U sF and active current I sFq , obtain the active power reference value P′ during the fault period ref ,Right now:

[0065] P′ ref =1.5U sF I sFq (6)

[0066] Then the active power reference value P′ ref and the actual output active power P e The active power deviation value is input into the active loop to adjust the active power reference value.

[0067] Step S206: Determine a compensation phase angle based on the current theoretical stator voltage and the current actual grid voltage.

[0068] After obtaining the actual grid voltage and active current, the power angle δ during the fault period can be determined. F ,Right now:

[0069]

[0070] According to the current actual grid voltage, the grid voltage phase angle θ of the current actual grid voltage offset coordinate system q axis is determined. g ;Right now:

[0071]

[0072] Among them: U gF_d and U gF_q are the current actual grid voltage U gF The dq-axis components in the dq rotating coordinate system.

[0073] The grid voltage phase angle θ g and power angle δ F After the compensation phase angle is obtained, it is added to the output angle of the active loop for subsequent adjustment, so that the stator voltage can quickly respond to changes in the grid voltage.

[0074] Experimental simulation

[0075] This application takes a grid-type doubly fed wind turbine with a capacity of 5.5kW and a rated voltage of 380V under the conditions of grid voltage amplitude drop and phase jump as an example. The key parameters of the grid-type doubly fed wind turbine are shown in Table 1.

[0076] Table 1 Key parameters of grid-type doubly fed wind turbine

[0077]

[0078] Figure 3 To account for the multi-constrained stator voltage curve, the theoretical upper and lower limits of the stator voltage are obtained based on the fault current constraint and the reactive power support constraint according to equations (1) and (2), as shown by the blue and red solid lines in the figure. The first theoretical curve, which accounts for the fault current constraint and the reactive power support constraint, is obtained by fitting between the upper and lower limits, as shown by the pink curve. As the depth of the fault voltage drop changes, the stator voltage is adaptively adjusted to ensure that the fault current safety is met while providing the necessary reactive power support to the grid in accordance with the grid connection guidelines.

[0079] Figure 4 The comparison diagram of the simulated waveforms of the grid-type doubly fed wind turbine using the traditional control method and the control method proposed in this invention when the grid voltage amplitude drops to 0.6pu and the phase jumps negatively by 30° is shown. rabc is the rotor three-phase current; I sFd is the reactive current; δ is the power angle; P e and Q e are the actual output active power and reactive power respectively. Figure 4(a) It can be seen that when the traditional control method is applied, the GFM-DFIG is transiently stable after the fault and meets the power angle stability constraint; the stator current d-axis component is 0.76pu (capacitive), which meets the reactive power support constraint; but the rotor current amplitude reaches 1.67pu, which does not meet the fault current constraint, and due to the phase jump of the grid voltage, the rotor current peak value rises rapidly at the beginning of the fault, seriously threatening the safe and stable operation of the system. Figure 4 (b) When the control method proposed in the present invention is applied, the d-axis component of the stator current is 0.88 pu (capacitive), which meets the reactive support constraint; the system transient power angle is stable, which meets the power angle stability constraint; the rotor current is controlled at 1.5 pu, which meets the fault current constraint, and the system's safe and stable operation capability is effectively improved.

[0080] Figure 5 The following is a comparison of the simulated waveforms of the grid-type doubly fed wind turbine using the traditional control method and the control method proposed in this invention when the grid voltage amplitude drops to 0.4pu and the phase jumps negatively by 30°. Figure 5 (a) It can be seen that when the traditional control method is applied, the output current, power and power angle periodically oscillate, and the system suffers from transient instability and fault overcurrent problems. Figure 5 (b) It can be seen that when the control method proposed in this invention is applied, the system power angle increases slightly, the d-axis component of the stator current is 1.1 pu (capacitive), and the rotor current is controlled at 1.5 pu. The GFM-DFIG can simultaneously meet the power angle stability constraint, fault current constraint, and reactive power support constraint.

[0081] Figure 4 、 Figure 5 The results of the example verify the effectiveness and feasibility of the transient stability enhancement method of the grid-type doubly fed wind turbine described in this application.

[0082] To sum up, it can be seen that the method proposed in this application can achieve comprehensive consideration of power angle stability, fault current suppression and reactive power support by dynamically adjusting the stator voltage, active power reference value and directly compensating the phase angle, and effectively improves the safe and stable operation capability of the grid-type doubly fed wind turbine under the conditions of grid voltage amplitude drop and phase jump.

[0083] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for enhancing transient stability of a grid-type doubly-fed wind turbine, characterized in that: include: Collect the current actual grid voltage and the current actual stator voltage; Determining a first theoretical curve based on the current actual grid voltage; The first theoretical curve is a curve showing the stator voltage changing with the grid voltage, and the points on the first theoretical curve meet the requirements of fault current suppression and reactive power support; Determining a current theoretical stator voltage corresponding to the current actual grid voltage based on the current actual grid voltage and the first theoretical curve; Determining a given stator voltage based on the current theoretical stator voltage and the current actual stator voltage; determining an active power reference value based on the current theoretical stator voltage; A compensation phase angle is determined based on the current theoretical stator voltage and the current actual grid voltage.

2. The method according to claim 1, characterized in that The determining of a first theoretical curve based on the current actual grid voltage includes: Determining an upper limit and a lower limit of a theoretical stator voltage adjustment value based on the current actual grid voltage; Based on the upper limit value and the lower limit value, a first theoretical curve is designed.

3. The method according to claim 1, characterized in that The determining of a given stator voltage based on the current theoretical stator voltage and the current actual stator voltage includes: The given stator voltage is obtained by subtracting the current theoretical stator voltage from the current actual stator voltage q-axis component.

4. The method according to claim 1, wherein Determining an active power reference value based on the current theoretical stator voltage includes: determining a reactive current based on the current theoretical stator voltage; determining an active current based on the current theoretical stator voltage and the reactive current; An active power reference value is determined based on the active current and the current theoretical stator voltage.

5. The method according to claim 4, characterized in that After the step of determining the active power reference value, the following steps are further included: Subtracting the active power reference value from the actual output active power to obtain an active power deviation value; The active power deviation value is input into the active power loop.

6. The method according to claim 4, characterized in that The determining of the compensation phase angle based on the current theoretical stator voltage and the current actual grid voltage includes: Determining a power angle based on the current actual grid voltage and the active current; A compensation phase angle is determined based on the current actual grid voltage and the power angle.

7. The method according to claim 6, characterized in that The determining of the compensation phase angle based on the actual grid voltage and the power angle includes: Based on the current actual grid voltage, determining a grid voltage phase angle of the current actual grid voltage offset coordinate system q axis; The phase compensation angle is obtained by subtracting the grid voltage phase angle from the power angle.

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