Control method for improving transient power angle stability of power system containing grid-type wind turbines

Abstract

The present invention discloses a control method for improving the transient power angle stability of a grid-type wind turbine power system. The method comprises: employing an active power control loop under improved virtual synchronous control when the fault voltage drops beyond an allowable value; compensating for the imbalance between the initial active power command value and the active power output during the fault period; dynamically correcting the active power command value during the fault period; and significantly reducing the deviation between the active power command value and the active power output during the fault period. The present invention can improve the transient power angle stability of a grid-type wind turbine power system, resolving the issues of focusing solely on the transient stability of grid-type units incorporated into a single-machine infinite system and the lack of transient stability control methods applicable to grid-type wind turbine power systems.

Description

Technical Field

[0001] The present invention relates to a control method for improving the transient power angle stability of a power system containing a grid-type wind turbine, and belongs to the field of transient stability of new energy grid connection. Background Art

[0002] As the proportion of wind power generation in the power system continues to increase, the randomness, intermittency and output fluctuation of wind power generation have caused the access of wind farms to have a great impact on the original transient stability of the power system. The transient power angle stability analysis between traditional synchronous machines is not sufficient to reflect the synchronous stability problem of the power system containing wind turbines. Therefore, it is very necessary to study the power angle stability of the power system containing wind turbines.

[0003] Wind turbines are generally categorized into two control modes, grid-following and grid-forming, depending on the synchronization mechanism. Grid-following wind turbines utilize a phase-locked loop (PLL) to synchronize with the grid, and their external characteristics generally exhibit current source characteristics. Research on the transient power angle stability of grid-following wind farms connected to the power system is currently relatively mature. However, grid-following wind turbines lack grid-forming capabilities and suffer from low inertial damping. As the proportion of wind turbines connected to the grid increases, it is necessary to promote the application of grid-forming wind turbines in the grid.

[0004] Grid-type wind turbines generally use virtual synchronous generator technology, which simulates the operating characteristics of synchronous generators through active power control loops and reactive power control loops, so that wind turbines have frequency and voltage regulation characteristics similar to conventional synchronous units. They actively respond to grid disturbances, have different control strategies and external characteristics, and have quite different interaction mechanisms with the grid, facing the problem of transient stability. Therefore, it is very necessary to study the transient power angle stability of power systems containing grid-type wind turbines.

[0005] Since the grid-type wind turbine simulates the rotor motion equation of the synchronous machine, compared with the traditional grid-type unit, the virtual power angle δ is introduced. vsg and the rotor angular velocity ω vsg The two new state variables have power angle stability problems similar to those of synchronous machines, and their transient instability mechanisms are also similar to those of synchronous generators. Therefore, when studying the transient power angle stability of power systems containing grid-type wind turbines, in addition to considering the power angle stability between synchronous machines, it is also necessary to consider the power angle stability between grid-type wind turbines and synchronous machines.

[0006] Among the current related technologies, the large disturbance stability control technology for grid-type units is still in its infancy, and only focuses on the transient stability improvement control strategy for grid-type units connected to infinite systems. There is a lack of transient stability control strategies suitable for grid-type new energy units connected to the power system, and it still needs to be improved. Summary of the Invention

[0007] The present invention aims to address the deficiencies of the above-mentioned prior art and proposes a control method for improving the transient power angle stability of a power system containing grid-type wind turbines, so as to reduce the relative power angle between the grid-type wind turbines and the synchronous machines by dynamically changing the active power command value during a fault, thereby improving the transient power angle stability of the power system containing grid-type wind turbines.

[0008] The present invention solves the technical problem by adopting the following technical solutions:

[0009] A control method for improving the transient power angle stability of a power system containing grid-type wind turbines according to the present invention is characterized by comprising the following steps:

[0010] Step 1: Assume that the power system includes a single grid-type wind farm and a synchronous group; perform single-machine equivalent calculation on the single grid-type wind farm to obtain a grid-type wind turbine;

[0011] Assuming that the synchronous generator group is in a two-group swing instability mode, the severely disturbed synchronous generators are called the leading group, and the remaining synchronous generators are called the remaining group. The leading group and the remaining group are respectively equal to a leading group equivalent synchronous generator SG1 and a remaining group equivalent synchronous generator SG2, and the rotor angle of SG2 is selected as the system reference power angle;

[0012] Step 2: Collect the grid connection point voltage, grid connection point current and system reference power angle of the grid-connected wind turbine;

[0013] Step 3: Calculate the output active power P of the grid-connected wind turbine based on the grid connection point voltage and grid connection point current. e ;

[0014] Step 4: Use formula (1) to construct the active power control loop of the grid-type wind turbine under virtual synchronous control:

[0015] (1)

[0016] In formula (1), d represents differential, t represents time; P ref is the active power command value of the grid-type wind turbine; ω vsg , ω0 are the output rotor angular velocity and rated value of angular velocity of the grid-type fan, J and D are the rotor inertia coefficient and damping coefficient of the grid-type fan, respectively; δ vsg is the power angle of the grid-type fan;

[0017] Step 5: When a fault occurs and the grid connection point voltage of the grid-connected wind turbine drops beyond the maximum allowable fluctuation value, use equation (2) to construct the improved active power control loop equation of the grid-connected wind turbine during the fault period:

[0018] (2)

[0019] In formula (2): P refF 、P F are the active power command value and output active power of the grid-type wind turbine during the fault period; ω vsg is the output rotor angular velocity of the grid-type wind turbine during the fault period; δ vsgF is the power angle of the grid-type wind turbine during the fault period; δ g is the system reference power angle during the fault period; δ N , δ F are the relative power angles between the grid-type wind turbine and the reference synchronous machine during fault and steady-state periods, respectively;

[0020] Step 6: According to the active power command value P of the grid-type wind turbine ref and the output active power P during the fault F The unbalanced amount is used to dynamically correct the active power command value P of the grid-type wind turbine during the fault period. refF , to reduce the deviation between the active power command value and the active power output during the fault period;

[0021] Step 7: Use formula (6) to calculate the improved active power command value of the grid-type wind turbine :

[0022] (6)

[0023] In formula (6): U N0 is the initial value of the grid connection point voltage of the grid-connected wind turbine; is the maximum allowable voltage fluctuation;

[0024] Step 8: Substituting into the active power control loop shown in formula (1), the power angle δ of the grid-type wind turbine is obtained: vsg , and is used to control the grid-type wind turbine to achieve transient power angle stability.

[0025] The control method for improving the transient power angle stability of a grid-type wind turbine power system according to the present invention is also characterized in that step 6 comprises the following steps:

[0026] Step 6.1: Calculate the active power command value P of the grid-type wind turbine using formula (3): ref and the output active power P during the fault F :

[0027] (3)

[0028] In formula (3): P N is the output active power of the grid-type wind turbine during steady state; U N 、U N1 、U N2are the grid-connected point voltage amplitudes of the grid-connected wind turbine, SG1, and SG2 during the steady state period, U F 、U F1 、U F2 are the grid connection point voltage amplitudes of the grid-connected wind turbine, SG1, and SG2 during the fault period; G 33 G is the self-conductance of the grid-type wind turbine; 21 , G 31 are the conductances between the grid-type wind turbine and SG1 and SG2 respectively; B 31 is the susceptance between the grid-type wind turbine and SG1;

[0029] Step 6.2: Use formula (4) to calculate the active power command value P of the grid-type wind turbine during the fault period. refF :

[0030] (4)

[0031] In formula (4), M is the active power command adjustment coefficient of the grid-type wind turbine, and:

[0032] (5).

[0033] An electronic device of the present invention includes a memory and a processor, wherein the memory is used to store a program that supports the processor to execute the control method, and the processor is configured to execute the program stored in the memory.

[0034] The present invention provides a computer-readable storage medium, wherein a computer program is stored on the computer-readable storage medium, and the computer program executes the steps of the control method when executed by a processor.

[0035] Compared with the existing technology, the beneficial effects of the present invention are embodied in:

[0036] 1. The present invention reduces the relative power angle between the grid-type wind turbine and the synchronous machine by dynamically changing the active power command value during the fault period, thereby improving the transient power angle stability of the power system containing the grid-type wind turbine.

[0037] 2. The present invention is no longer limited to a single-machine infinite system. For power systems containing grid-type wind turbines, an improved active power control loop under virtual synchronous control is proposed, which has a wider scope of application.

[0038] 3. When analyzing the transient power angle stability of the power system containing new energy units, the present invention is no longer limited to the power angle stability between synchronous units, but also considers the power angle stability between grid-type wind turbines and synchronous units, and proposes an improved active power control loop under virtual synchronous control, thereby improving the transient power angle stability of the power system containing grid-type wind turbines. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a structural diagram of the active power control loop under the virtual synchronous control of the improved grid-type wind turbine according to the present invention;

[0040] Figure 2 This is a basic control structure diagram of the grid-type direct-drive fan of the present invention;

[0041] Figure 3 Expand the dual-machine system model topology diagram for the present invention;

[0042] Figure 4 This is a waveform diagram showing the impact of different control strategies on transient power angle stability adopted by the present invention. DETAILED DESCRIPTION

[0043] In this embodiment, a control method for improving the transient power angle stability of a power system including grid-type wind turbines includes the following steps:

[0044] Step 1. Assume that the power system containing grid-type wind turbines includes a single wind farm and multiple synchronous units; make a single-unit equivalent for the wind farm; and assume that the synchronous group is in a two-group swing instability mode, and the several synchronous units that are severely disturbed are called the leading group, and the remaining synchronous units are called the remaining groups. The groups on both sides are respectively equivalent to a synchronous generator, SG1 represents the leading group equivalent synchronous unit, SG2 represents the remaining group equivalent synchronous unit, and the rotor angle of SG2 is selected as the system reference power angle; when performing transient power angle stability analysis of the power system containing grid-type wind turbines, consider the transient power angle stability between the synchronous machines SG1 and SG2, and the transient power angle stability of SG1 and SG2 between the grid-type wind turbine and the synchronous machine.

[0045] Step 2: Collect the grid connection point voltage, grid connection point current and system reference power angle of the grid-connected wind turbine;

[0046] Step 3: Calculate the output active power P of the grid-connected wind turbine based on the grid connection point voltage and grid connection point current. e ;

[0047] Step 4: Use equation (1) to construct the active power control loop of the grid-type wind turbine under virtual synchronous control, which simulates the synchronous machine rotor motion equation to adjust the output active power and provide the synchronous phase:

[0048] (1)

[0049] In formula (1), d represents differential, t represents time; P ref is the active power command value of the grid-type wind turbine; ω vsg, ω0 are the output rotor angular velocity and rated value of angular velocity of the grid-type fan, J and D are the rotor inertia coefficient and damping coefficient of the grid-type fan, respectively; δ vsg is the power angle of the grid-type fan.

[0050] Step 5: When a fault occurs and the grid connection point voltage of the grid-connected wind turbine drops beyond the maximum allowable fluctuation value, use equation (2) to construct the improved active power control loop equation of the grid-connected wind turbine during the fault period:

[0051] (2)

[0052] In formula (2): P refF 、P F are the active power command value and output active power of the grid-type wind turbine during the fault period; ω vsg is the output rotor angular velocity of the grid-type wind turbine during the fault period; δ vsgF is the power angle of the grid-type wind turbine during the fault period; δ g is the system reference power angle during the fault period; δ N , δ F are the relative power angles between the grid-type wind turbine and the reference synchronous machine during the fault period and the steady state period, respectively. Assuming that during the fault period, the proposed transient control strategy can enable the grid-type wind turbine to achieve better synchronous operation, that is, δ F is controlled near the rated value, it is approximately considered that δ F =δ N =δ vsgF -δ g .

[0053] Step 6: According to the active power command value P of the grid-type wind turbine ref and the output active power P during the fault F The unbalanced amount is based on the system reference power angle, and after an integral control link and a proportional integral control link, the active power instruction value of the grid-type wind turbine during the fault period is dynamically corrected to P refF , in order to reduce the deviation between the active power command value and the active power output during the fault period:

[0054] Step 6.1: Calculate the active power command value P of the grid-type wind turbine using formula (3): ref and the output active power P during the fault F :

[0055] (3)

[0056] In formula (3): P N is the output active power of the grid-type wind turbine during steady state; U N 、U N1 、U N2are the grid-connected point voltage amplitudes of the grid-connected wind turbine, SG1, and SG2 during the steady state period, U F 、U F1 、U F2 are the grid connection point voltage amplitudes of the grid-connected wind turbine, SG1, and SG2 during the fault period; G 33 G is the self-conductance of the grid-type wind turbine; 21 , G 31 are the conductances between the grid-type wind turbine and SG1 and SG2 respectively; B 31 are the susceptances between the grid-type wind turbine and SG1 respectively.

[0057] Step 6.2: Use formula (4) to calculate the active power command value P of the grid-type wind turbine during the fault period. refF :

[0058] (4)

[0059] In formula (4), M is the active power command adjustment coefficient of the grid-type wind turbine, and:

[0060] (5)

[0061] Step 7: Use formula (6) to calculate the active power command value under the improved control method :

[0062] (6)

[0063] In formula (6): U N0 is the initial voltage value of the grid connection point of the grid-connected wind turbine; The maximum voltage fluctuation allowed can be set by default. The improved active frequency control loop is as follows: Figure 1 shown.

[0064] Step 8. Exploit Substituting the active power control loop under the improved virtual synchronous control shown in formula (1) into the grid-type wind turbine power angle δ can be calculated: vsg ; Using the reactive power control loop under typical virtual synchronous control, the internal potential U of the grid-type wind turbine can be calculated vsg δ vsg and U vsg After the inner loop control, it acts on the grid-side converter of the grid-type wind turbine, thereby realizing the control of the grid-type wind turbine to achieve the stability of the transient power angle. The detailed control block diagram is as follows Figure 1 and Figure 2 shown.

[0065] In this embodiment, an electronic device includes a memory and a processor, wherein the memory is used to store a program that supports the processor to execute the above method, and the processor is configured to execute the program stored in the memory.

[0066] In this embodiment, a computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the above method are executed.

[0067] Example:

[0068] Taking the grid-type direct-drive wind turbine GFM-PMSG into a dual-machine system as an example, the following simulation software is used to build Figure 3 The extended two-machine system model shown here includes a GFM-PMSG and two synchronous generators. Its basic parameters are shown in Table 1. Synchronous generator SG1 is unit 1, representing the leading group, with a rated power of 120 MW; synchronous generator SG2 is unit 2, representing the remaining group, with a rated power of 75 MW. The GFM-PMSG is represented by an equivalent model, with a single unit rated power of 5 MW, connected to the system at node 5. The transmission line between nodes 6 and 7 is a double-circuit line L. A three-phase symmetrical short-circuit fault is assumed on one of the loops of line L.

[0069] Table 1 Parameters of the extended dual-machine system

[0070]

[0071] The GFM-PMSG access ratio was set to approximately 20%. After the connected wind turbine system stabilized, a three-phase short-circuit fault was set to start at 30 seconds and last for 0.3 seconds. Furthermore, this example used the first swing amplitude of the power angle difference curves of the two units during the fault phase as the system transient power angle stability criterion to verify the effectiveness of the control method proposed in this invention.

[0072] Table 2 Maximum power angle difference of the first swing using different control methods

[0073]

[0074] Figure 4 Table 2 and Table 3 show the transient power angle characteristics of the system when using the transient control method before improvement and the improved control method proposed in this invention. As shown in the simulation results, when the control method of this invention is not used, the relative power angle deviation between the GFM-PMSG and the synchronous generator is large. In this case, the transient power angle stability of the power system containing grid-type wind turbines is poor, and power angle instability is prone to occur. When the transient control strategy improved in this paper is used, the power angle stability between the GFM-PMSG and SG1 and SG2 is significantly improved, and the power angle stability between the synchronous generators SG1 and SG2 is also improved to a certain extent.

Claims

1. A control method for improving the transient power angle stability of a grid-type wind turbine power system, characterized in that: The steps include: Step 1: Assume that the power system includes a single grid-type wind farm and a synchronous group; perform single-machine equivalent calculation on the single grid-type wind farm to obtain a grid-type wind turbine; Assuming that the synchronous generator group is in a two-group swing instability mode, the severely disturbed synchronous generators are called the leading group, and the remaining synchronous generators are called the remaining group. The leading group and the remaining group are respectively equal to a leading group equivalent synchronous generator SG1 and a remaining group equivalent synchronous generator SG2, and the rotor angle of SG2 is selected as the system reference power angle; Step 2: Collect the grid connection point voltage, grid connection point current and system reference power angle of the grid-connected wind turbine; Step 3: Calculate the output active power P of the grid-connected wind turbine based on the grid connection point voltage and grid connection point current. e ; Step 4: Use formula (1) to construct the active power control loop of the grid-type wind turbine under virtual synchronous control: (1) In formula (1), d represents differential, t represents time; P ref is the active power command value of the grid-type wind turbine; ω vsg , ω0 are the output rotor angular velocity and rated value of angular velocity of the grid-type fan, J and D are the rotor inertia coefficient and damping coefficient of the grid-type fan, respectively; δ vsg is the power angle of the grid-type fan; Step 5: When a fault occurs and the grid connection point voltage of the grid-connected wind turbine drops beyond the maximum allowable fluctuation value, use equation (2) to construct the improved active power control loop equation of the grid-connected wind turbine during the fault period: (2) In formula (2): P refF 、P F are the active power command value and output active power of the grid-type wind turbine during the fault period; ω vsg is the output rotor angular velocity of the grid-type wind turbine during the fault period; δ vsgF is the power angle of the grid-type wind turbine during the fault period; δ g is the system reference power angle during the fault period; δ N , δ F are the relative power angles between the grid-type wind turbine and the reference synchronous machine during fault and steady-state periods, respectively; Step 6: According to the active power command value P of the grid-type wind turbine ref and the output active power P during the fault F The unbalanced amount is used to dynamically correct the active power command value P of the grid-type wind turbine during the fault period. refF , to reduce the deviation between the active power command value and the active power output during the fault period; Step 7: Use formula (6) to calculate the improved active power command value of the grid-type wind turbine : (6) In formula (6): U N0 is the initial value of the grid connection point voltage of the grid-connected wind turbine; is the maximum allowable voltage fluctuation; Step 8: Substituting into the active power control loop shown in formula (1), the power angle δ of the grid-type wind turbine is obtained: vsg , and is used to control the grid-type wind turbine to achieve transient power angle stability.

2. A control method for improving transient power angle stability of a grid-type wind turbine power system according to claim 1, characterized in that: The step 6 comprises the following steps: Step 6.1: Calculate the active power command value P of the grid-type wind turbine using formula (3): ref and the output active power P during the fault F : (3) In formula (3): P N is the output active power of the grid-type wind turbine during steady state; U N 、U N1 、U N2 are the grid-connected point voltage amplitudes of the grid-connected wind turbine, SG1, and SG2 during the steady state period, U F 、U F1 、U F2 are the grid connection point voltage amplitudes of the grid-connected wind turbine, SG1, and SG2 during the fault period; G 33 G is the self-conductance of the grid-type wind turbine; 21 , G 31 are the conductances between the grid-type wind turbine and SG1 and SG2 respectively; B 31 is the susceptance between the grid-type wind turbine and SG1; Step 6.2: Use formula (4) to calculate the active power command value P of the grid-type wind turbine during the fault period. refF : (4) In formula (4), M is the active power command adjustment coefficient of the grid-type wind turbine, and: (5)。 3. An electronic device comprising a memory and a processor, characterized in that: The memory is used to store a program that supports the processor to execute the control method according to claim 1 or 2, and the processor is configured to execute the program stored in the memory.

4. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the control method according to claim 1 or 2 are executed.

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