A network-configuration type doubly-fed wind turbine fault ride-through method based on instantaneous flux linkage compensation

Abstract

A network type doubly-fed wind turbine fault ride-through method based on instantaneous flux linkage compensation belongs to the technical field of doubly-fed wind power generation system control, establishes full-order mathematical model of doubly-fed induction generator in d-q rotating coordinate system, analyzes the influence of dynamic change of stator flux linkage on system in fault transient state, transforms active-frequency loop and reactive-voltage loop of rotor side converter, constructs adaptive virtual synchronous generator control, adds instantaneous flux linkage compensation strategy in inner loop of rotor side converter, suppresses disturbance term and coupling term of stator flux linkage caused by transient offset of stator flux linkage, sets active-reactive coordinated control strategy in combination with actual power instruction, and dynamically adjusts active and reactive reference values.The application can consider rotor overcurrent suppression, power angle stability and dynamic voltage support under serious grid voltage drop, improve transient response characteristics of network type doubly-fed wind turbine, and improve low voltage ride-through capability and network support performance.

Description

Technical Field

[0001] This invention belongs to the field of control technology for doubly-fed wind power generation systems, specifically a fault ride-through method for grid-type doubly-fed wind turbines based on instantaneous flux compensation. Background Technology

[0002] Doubly fed induction generators (DFIGs) are one of the mainstream technologies in the global wind turbine market due to their advantages such as low converter capacity and wide operating speed range. However, for wind power to become the dominant power source, it needs to transform from the traditional "grid-following" (GFL) to "grid-forming" (GFM) power source. In addition, more and more countries require wind farms to have a certain low voltage ride-through (LVRT) capability, actively undertaking the important task of supporting the grid's dynamic voltage and regulating the overall energy balance.

[0003] Due to the direct grid connection of the stator to the grid in doubly-fed induction generator (DFIG) wind turbines, grid-connected DFIGs face a more severe electromagnetic transient challenge during low-voltage ride-through (LDR). The stator flux linkage cannot keep pace with the grid voltage fluctuations, and the transient flux linkage components are cross-coupled through the air gap, inducing a large transient back electromotive force on the rotor side. This presents a more severe electromagnetic transient challenge than that of full-power wind turbines. Currently, most fault current limiting protection schemes for grid-connected DFIG wind power systems adopt grid-connected LRD control methods, which may weaken the voltage source characteristics of grid control. Therefore, to overcome the limitations of traditional current limiting protection that sacrifices voltage source characteristics, advanced control strategies are needed to improve the system's LRD transient stability and grid support performance. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention proposes a fault ride-through method for grid-type doubly-fed induction generators based on instantaneous flux compensation. This method is used for the power outer loop and voltage and current inner loop control of the rotor-side converter of the doubly-fed induction generator. It can simultaneously suppress rotor overcurrent, stabilize power angle, and provide dynamic voltage support under severe grid voltage dips, thereby improving the transient response characteristics of grid-type doubly-fed induction generators and enhancing their low-voltage ride-through capability and grid support performance.

[0005] The technical solution adopted by this invention to solve its technical problem is: A fault ride-through method for grid-type doubly-fed induction generators based on instantaneous flux compensation is proposed, establishing a method for doubly-fed induction generators in... dqA full-order mathematical model in a rotating coordinate system is used to analyze the impact of dynamic changes in stator flux linkage on the system during fault transients. The active-frequency loop and reactive-voltage loop of the rotor-side converter are modified to construct an adaptive virtual synchronous generator control. An instantaneous flux linkage compensation strategy is added to the inner loop of the rotor-side converter to suppress stator flux linkage disturbance and coupling terms caused by stator flux linkage transient offset. Based on the actual power command, an active-reactive coordinated control strategy is set to dynamically adjust the active and reactive power reference values.

[0006] The method includes the following steps: Step S10: Based on the stator voltage oriented control (SVO) method of the rotor-side converter, construct a doubly-fed induction generator in... dq Full-order mathematical model in a rotating coordinate system; Step S20: Modify the active-frequency loop and reactive-voltage loop of the traditional virtual synchronous generator (VSG) control, design the adaptive virtual synchronous generator (AVSG) control, and apply it to the outer loop control of the rotor-side converter of the doubly-fed wind turbine. Step S30: Based on the stator flux disturbance and coupling terms caused by the stator flux transient offset analyzed in S10, an instantaneous flux-linkage compensation (IFC) control strategy is proposed and applied to the inner loop control of the doubly-fed wind turbine rotor converter. Step S40: In the AVSG control strategy of step S20, the active-reactive power coordinated control (ARPCC) strategy is added in combination with the power reference of the maximum power point control.

[0007] Preferably, the stator and rotor three-phase voltage and current signals of the doubly-fed induction generator are acquired in a three-phase stationary coordinate system. u sabc , i sabc , u rabc , i rabc and rotor mechanical angular velocity signal oh r Constructing a doubly-fed induction generator in dq Full-order mathematical model in a rotating coordinate system: (1); In the formula, u sd ，u sq and u rd ，u rq for dq Stator and rotor voltages in the coordinate system; i rd ，i rq for dq Rotor current in the coordinate system; R s ，R r and L s ，L r These are the equivalent resistance and self-inductance of the stator and rotor windings, respectively; oh s Oh, oh r Let be the angular velocities of the stator and rotor, and define the slip angle as . oh sl = oh s - oh r ; L m This refers to the mutual inductance between the stator and rotor windings; The leakage flux coefficient; i ms This is the equivalent current for stator excitation; ψ sd and ψ sq express dq Stator flux linkage in the coordinate system.

[0008] By comparing the SVO control under the simplified model, we can conclude that the dynamic changes in stator flux not only introduce disturbance terms but also affect the coupling within the system.

[0009] The technical concept of this invention is as follows: The outer loop of the rotor-side converter control combines adaptive VSG and active-reactive power coordination control to improve the dynamics of the power angle and voltage support capability. The adaptive VSG control includes modifications to the active-frequency and reactive-voltage links of the traditional virtual synchronous control VSG. The inner loop introduces instantaneous flux compensation to suppress stator flux transient disturbances. The instantaneous flux compensation control strategy includes a state feedback flux disturbance compensation method and a feasible domain constraint for the compensation coefficient.

[0010] Compared with the prior art, the beneficial effects of the present invention are: the introduction of instantaneous flux compensation in the inner loop to suppress stator flux transient disturbances, and the combination of adaptive VSG and active-reactive power coordinated control in the outer loop to improve power angle dynamics and voltage support capability; the wind turbine control of the present invention can not only achieve autonomous fault ride-through and self-protection in severe grid voltage drop faults, but also provide high-quality voltage support capability without sacrificing system damping performance. Attached Figure Description

[0011] Figure 1 This is the main circuit topology of the grid-type doubly fed wind power generation system of the present invention; Figure 2 This is a block diagram of low voltage ride-through control for a grid-type doubly-fed wind turbine provided by the present invention; Figure 3 This is a block diagram of the active-frequency loop adaptive parameter control of the present invention; Figure 4 This is a block diagram of the adaptive virtual synchronous generator control of the present invention; Figure 5 To compare the dynamic response waveforms of the wind turbine when the grid voltage drops to 0.2 pu and the ARPCC method is applied, the dynamic response waveforms of the system using three different grid configuration control strategies are compared: traditional VSG, AVSG+VI (the proposed active loop adaptive parameter control strategy + virtual impedance current limiting), and AVSG+IFC. Detailed Implementation

[0012] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0013] Figure 1 This invention illustrates the main circuit topology of a grid-connected doubly-fed induction generator (DFIG) wind power system. The generator stator is directly connected to the grid, while the rotor is connected via two back-to-back converters. Stable power generation is achieved by controlling the converters on both the rotor and grid sides. Each of the rotor-side converter (RSC) and grid-side converter (GSC) has an independent control system. This invention proposes a transient flux linkage compensation low-voltage ride-through control strategy for the RSC control, considering grid characteristics. The GSC employs DC bus voltage control and grid-connected current control to maintain DC bus stability and achieve grid-side power exchange.

[0014] like Figure 2 The diagram shown is a control block diagram of the rotor-side converter RSC of the present invention. A fault ride-through method for a grid-type doubly-fed wind turbine based on instantaneous flux compensation includes the following steps: Step S10: Based on the stator voltage oriented control (SVO) method of the rotor-side converter, construct a doubly-fed induction generator in... dq Full-order mathematical model in a rotating coordinate system; Acquire the stator and rotor three-phase voltage and current signals of the doubly-fed induction generator in a three-phase stationary coordinate system. u sabc , i sabc , u rabc , i rabc and rotor mechanical angular velocity signal oh r Constructing a doubly-fed induction generator in dq Full-order mathematical model in a rotating coordinate system: (1); In the formula, u sd ，u sq and u rd ，u rq for dq Stator and rotor voltages in the coordinate system; i rd ，i rq for dq Rotor current in the coordinate system; R s ，R r and L s ，L r These are the equivalent resistance and self-inductance of the stator and rotor windings, respectively; oh s Oh, oh r Let be the angular velocities of the stator and rotor, and define the slip angle as . oh sl = oh s - oh r ; L m This refers to the mutual inductance between the stator and rotor windings; The leakage flux coefficient; i ms This is the equivalent current for stator excitation; ψ sd and ψ sq express dq Stator flux linkage in the coordinate system.

[0015] By comparing the SVO control under the simplified model, we can conclude that the dynamic changes in stator flux not only introduce disturbance terms but also affect the coupling within the system.

[0016] Step S20: Modify the active-frequency loop and reactive-voltage loop of the traditional virtual synchronous generator (VSG) control, design the adaptive virtual synchronous generator (AVSG) control, and apply it to the outer loop control of the rotor-side converter of the doubly-fed wind turbine. In this embodiment, the outer loop control of the rotor-side converter adopts the proposed adaptive virtual synchronous motor control strategy, namely step S20: using the actual stator active power of the doubly-fed wind turbine. P s reactive power Q s The reference power obtained from the proposed Active-Reactive Coordinated Control (ARPCC) P ref As input, the output angular velocity of the virtual synchronization control oh vsg Rotor current reference value i rabc,ref Then generate through coordinate transformation dq Shaft rotor current reference value , .

[0017] Specifically, step S20 includes the following sub-steps: Sub-step S201: To improve the attenuation rate of stator flux linkage offset and the stability of power angle during a fault, the active-frequency link of the traditional virtual synchronous control VSG is modified, and an adaptive adjustment of virtual inertia is proposed. J and damping coefficient D The calculation formula is designed as follows: (2); (3); In the formula, J 0 and D 0 These are the initial moment of inertia and initial damping coefficient of the VSG, respectively. K j1 , K j2 respectively accelerate d ω / dtReduce and suppress dω / dt Increased adjustment coefficient, oh For VSG virtual angular velocity; K d To suppress Give Increased adjustment coefficient; c 1 and c 2 They are respectively J and D The index adjustment coefficient; T j and T d They are respectively J and D The threshold for change. Based on (2) and (3), the adaptive parameter control strategy is as follows: Figure 3 .

[0018] Virtual inertia is limited by the active power loop cutoff frequency. J and damping coefficient D The range of values ​​can be determined by substituting the cutoff frequency into the open-loop transfer function of the active power loop. f c have to: (4); In the formula: L f It is a low-pass filter inductor; U s This refers to the stator voltage amplitude. E The equivalent internal potential amplitude of the VSG reactive power-voltage loop output; oh 0 For the grid synchronization angular velocity, oh vsg The instantaneous virtual angular velocity generated by VSG.

[0019] For equation (4) to hold true, the value under the square root must be greater than 0, thus we can obtain: (5); In the formula: f c,pmax It is the maximum cutoff frequency of the open-loop transfer function of the active power loop, and is generally taken within 10% margin of twice the power frequency.

[0020] The range of values ​​for adaptive moment of inertia and adaptive damping coefficient are determined by (4) and (5).

[0021] Sub-step S202: Modify the reactive power-voltage link of the traditional virtual synchronous control VSG, based on the stator voltage disturbance increment term caused by stator flux displacement in equation (1) of step S10. , The proposal is to convert the voltage output of the reactive power-voltage loop. E With stator voltage U s The difference is calculated, and its error voltage passes through a virtual impedance. Z v = sL v + R v The virtual reference current is then output: (6); In the formula, i ref To generate a virtual reference current for output through a virtual impedance circuit; L v For virtual inductance, R v For virtual resistance; s For the Laplace operator; when a fault occurs, EU s When the current increases rapidly, a surge occurs, but this introduces a virtual inductance. L v , making yes rd / dt Physical constraints limit the rate of increase of the rotor current, and at this time... E It is still generated by the VSG outer loop, ensuring that the converter always follows the characteristics of a controlled voltage source that drives the current by the voltage difference in its external characteristics.

[0022] Figure 4 To create an adaptive virtual synchronous generator control block diagram, the AVSG control strategy is applied to the outer loop control of the rotor-side converter RSC of a doubly-fed wind turbine.

[0023] Step S30: Based on the stator flux disturbance and coupling terms caused by the stator flux transient offset analyzed in S10, an instantaneous flux-linkage compensation (IFC) control strategy is proposed and applied to the inner loop control of the doubly-fed wind turbine rotor converter. In this embodiment, the stator flux disturbance term caused by the stator flux transient offset in step S10 (1) is used. , and coupling terms , A transient flux compensation control strategy is proposed and applied to the inner loop control of the doubly-fed wind turbine rotor converter, namely step S30: , and reality dq Shaft rotor current i rd、i rq As the input signal to the current loop controller, the output rotor voltage reference value , Then, the voltage cross-decoupling term Δ u sd Δ u sq and the designed instantaneous flux compensation term Δ ψ sd Δ ψ sq As the input for voltage loop compensation, the output voltage reference value u rd 、u rq Then, coordinate transformation is performed and SPWM signal is output using space pulse vector modulation technology to control the operation of RSC.

[0024] In this embodiment, step S30 specifically includes the following sub-steps: Sub-step S301: If the magnetic flux coupling disturbance term in equation (1) of step S10 is directly compensated using a feedforward method, and d- q Correcting the free flux coupling components caused by the shaft cross-coupling term leads to system complexity. Furthermore, since the stator flux linkage is directly affected by grid voltage fluctuations, it... U s The system is sensitive to changes and will be superimposed with the stator voltage disturbance increment term in (1), leading to overcompensation. Therefore, this invention adopts a flux linkage disturbance compensation method based on state feedback and designs compensation coefficients. k This suppresses the free component of the stator flux linkage, thereby reducing the impact of coupled disturbances on the transient current on the rotor side.

[0025] In the traditional voltage command value equation, for and Further adjustments were made, and the output voltage reference value is now output as follows: (7); In the formula, , and , They are respectively dq Reference values ​​for rotor voltage and rotor current in the coordinate system; K p , K i These are the proportional and integral coefficients of the inner-loop PI regulator for the rotor current, respectively; Δ ψ sd and Δ ψ sq Indicates the introduction of a voltage loop d-q Instantaneous stator flux compensation term; Sub-step S302: Let the compensation term Δ ψ The matrix equation is: (8); To ensure the closed-loop system remains intact after compensation Hurwitz Stable, it can be constrained by the real part of the eigenvalues ​​of the flux linkage compensation matrix. k The feasible region. Considering the physical meaning, when oh s At higher levels, k 2 It can be negative, so it needs to be restricted. k 2 >0 ,but k The feasible region is [ , ].

[0026] Step S40: In the AVSG control strategy of step S20, the active-reactive power coordinated control (ARPCC) strategy is added in combination with the power reference of the maximum power point control.

[0027] In this embodiment, based on the requirements for reactive current injection during low voltage ride-through, the reactive power command value injected by the converter into the grid is... Q ref The drop depth of the stator voltage amplitude should be considered. Perform segmented real-time calculations: (9); In the formula, S N This is expressed as the rated apparent power of a doubly-fed wind turbine generator set; Available capacity boundary of active power P lim Constraints must be met: (10); In the formula, the maximum apparent power of the converter is... S max Subject to maximum fault current Restrictions.

[0028] To ensure that the converter does not experience destructive overcurrent under any transient conditions, the system ultimately issues an active power reference command. P ref The active power setpoint must be the value before the fault. Pref0 With dynamic limit value P lim The smaller values ​​between these ranges ultimately form the active power control law: (11).

[0029] In this embodiment, K j1 =1.0, K j2 =0.5, K d =0.5, c 1 =0.1, c 2 =2.0, T j , =0.05, T d =0.1. Set at t At 0.5s, a symmetrical voltage drop occurs in the power grid, with the grid voltage dropping to 0.2pu, and the duration is 1s.

[0030] Figure 5 This paper compares the system dynamic response waveforms of four different grid-type control strategies—traditional VSG, AVSG+VI (the proposed active power loop adaptive parameter control strategy + virtual impedance current limiting), and AVSG+IFC—when the grid voltage drops to 0.2 pu after implementing the ARPCC mechanism. It can be seen that compared to other grid-type LVRT control strategies, the proposed AVSG+IFC strategy suppresses the rotor-side transient electromotive force with zero delay at the initial moment of voltage drop, limiting the peak rotor current to within 1.05 pu, avoiding RSC overmodulation, and controlling DC voltage fluctuations within 8% of the rated value. The AVSG adaptively widens the bandwidth, allowing for deep active power drop matching fault grids within 15ms, and outputting 0.24 pu reactive power within 20ms under ARPCC. The high-damping mechanism during the recovery period limits active power overshoot to within 0.05 pu, and the power angle quickly returns to steady state with minimal overshoot, eliminating secondary oscillations.

[0031] The embodiments described in this specification are merely examples of implementations of the inventive concept and are for illustrative purposes only. The scope of protection of this invention should not be considered limited to the specific forms described in these embodiments; rather, it extends to equivalent technical means conceived by those skilled in the art based on the inventive concept.

Claims

1. A fault ride-through method for grid-type doubly-fed wind turbines based on instantaneous flux compensation, characterized in that, Establish a doubly fed induction generator in dq A full-order mathematical model in a rotating coordinate system is used to analyze the impact of dynamic changes in stator flux linkage on the system during fault transients. The active-frequency loop and reactive-voltage loop of the rotor-side converter are modified to construct an adaptive virtual synchronous generator control. An instantaneous flux linkage compensation strategy is added to the inner loop of the rotor-side converter to suppress stator flux linkage disturbance and coupling terms caused by stator flux linkage transient offset. Based on the actual power command, an active-reactive coordinated control strategy is set to dynamically adjust the active and reactive power reference values.

2. The fault ride-through method for a grid-type doubly-fed wind turbine based on instantaneous flux compensation as described in claim 1, characterized in that, The method includes the following steps: Step S10: Based on the stator voltage-oriented SVO control method of the rotor-side converter, construct a doubly-fed induction generator. dq Full-order mathematical model in a rotating coordinate system; Step S20: Modify the active-frequency loop and reactive-voltage loop of the virtual synchronous control VSG, design the adaptive virtual synchronous generator control AVSG, and apply it to the outer loop control of the rotor-side converter of the doubly fed wind turbine. Step S30: Based on the stator flux disturbance and coupling terms caused by the stator flux transient offset analyzed in S10, an instantaneous flux compensation control strategy is proposed and applied to the inner loop control of the doubly fed wind turbine rotor converter. In step S40, the active-reactive coordinated control (ARPCC) strategy is added to the AVSG control strategy of step S20, incorporating the power reference of maximum power point tracking control.

3. The fault ride-through method for a grid-type doubly-fed wind turbine based on instantaneous flux compensation as described in claim 2, characterized in that, In step S10, the doubly-fed induction generator is dq The full-order mathematical model in the rotating coordinate system is: (1)； In the formula, u sd ，u sq and u rd ，u rq for dq Stator and rotor voltages in the coordinate system; i rd ，i rq for dq Rotor current in the coordinate system; R s ，R r and L s ，L r These are the equivalent resistance and self-inductance of the stator and rotor windings, respectively; ω s ω r Let be the angular velocities of the stator and rotor, and define the slip angle as . ω sl = ω s - ω r ; L m This refers to the mutual inductance between the stator and rotor windings; The leakage flux coefficient; i ms This is the equivalent current for stator excitation; ψ sd and ψ sq for dq Stator flux linkage in the coordinate system.

4. A fault ride-through method for a grid-type doubly-fed wind turbine based on instantaneous flux compensation as described in claim 2 or 3, characterized in that, In step S20, the outer loop control of the rotor-side converter adopts the proposed Adaptive Virtual Synchronous Motor (AVSG) control strategy, which includes the following sub-steps: S201, Proposes adaptive adjustment of virtual inertia J and damping coefficient D The calculation formula is designed as follows: (2)； (3)； In the formula, J 0 and D 0 These are the initial moment of inertia and initial damping coefficient of the VSG, respectively. K j1 , K j2 respectively accelerate dω / dt Reduce and suppress dω / dt Increased adjustment coefficient, ω For VSG virtual angular velocity; K d To suppress Δω Increase the adjustment coefficient; c 1 and c 2 They are respectively J and D The index adjustment coefficient; T j and T d They are respectively J and D Change threshold Virtual inertia is limited by the active power loop cutoff frequency. J and damping coefficient D The range of values ​​can be determined by substituting the cutoff frequency into the open-loop transfer function of the active power loop. f c have to: (4)； In the formula, L f It is a low-pass filter inductor; U s This refers to the stator voltage amplitude. E The equivalent internal potential amplitude of the VSG reactive power-voltage loop output; ω 0 For the grid synchronization angular velocity, ω vsg The instantaneous virtual angular velocity generated by the VSG; For equation (4) to hold true, the value under the square root must be greater than 0, thus: (5)； In the formula, f c,pmax The maximum cutoff frequency of the open-loop transfer function of the active power loop; The range of values ​​for adaptive moment of inertia and adaptive damping coefficient are determined by equations (4) and (5).

5. The fault ride-through method for a grid-type doubly-fed wind turbine based on instantaneous flux compensation as described in claim 4, characterized in that, Step S20 further includes the following sub-steps: Sub-step S202: Stator voltage disturbance increment term caused by stator flux displacement in step S10 (1) , The proposal is to convert the voltage output of the reactive power-voltage loop. E With stator voltage U s The difference is calculated, and its error voltage passes through a virtual impedance. Z v = sL v + R v The virtual reference current is then output: (6)； In the formula, i ref To generate a virtual reference current for output through a virtual impedance circuit; L v For virtual inductance, R v For virtual resistance; s For the Laplace operator; When the fault occurs, EU s When the current increases rapidly, a surge occurs, but this introduces a virtual inductance. L v , making di rd / dt Physical constraints limit the rate of increase of the rotor current, and at this time... E It is still generated by the VSG outer loop, ensuring that the converter always follows the characteristics of a controlled voltage source that drives the current by the voltage difference in its external characteristics. The AVSG control strategy is applied to the outer loop control of the rotor-side converter RSC of a doubly-fed wind turbine.

6. The fault ride-through method for a grid-type doubly-fed wind turbine based on instantaneous flux compensation as described in claim 5, characterized in that, In step S30, the stator flux disturbance term caused by the stator flux transient offset in equation (1) of step S10 is used. , and coupling terms , A transient flux compensation control strategy is proposed and applied to the inner loop control of the rotor converter of a doubly fed wind turbine. Includes the following sub-steps: Sub-step S301: Using a state feedback-based flux disturbance compensation method, design the compensation coefficient. k Suppress the free components of the stator flux linkage; In the voltage command value equation, for and Further adjustments were made, and the output voltage reference value is now output as follows: (7)； In the formula, , and , They are respectively dq Reference values ​​for rotor voltage and rotor current in the coordinate system; K p , K i These are the proportional and integral coefficients of the inner-loop PI regulator for the rotor current, respectively; Δ ψ sd and Δ ψ sq Indicates the introduction of a voltage loop dq Instantaneous stator flux compensation term; Sub-step S302, let the compensation term Δ ψ The matrix equation is: (8)； Constraints by the real part of the eigenvalues ​​of the flux linkage compensation matrix k feasible domain, k The feasible region is [ , ].

7. The fault ride-through method for a grid-type doubly-fed wind turbine based on instantaneous flux compensation as described in claim 6, characterized in that, In step S40, based on the requirements for reactive current injection during low-voltage ride-through, the reactive power command value injected by the converter into the grid is determined. Q ref Based on the drop depth of stator voltage amplitude Perform segmented real-time calculations: (9)； In the formula, S N This is expressed as the rated apparent power of a doubly-fed wind turbine generator set; Available capacity boundary of active power P lim Constraints must be met: (10)； In the formula, the maximum apparent power of the converter is... S max Subject to maximum fault current Restrictions; To ensure that the converter does not experience destructive overcurrent under any transient conditions, the system ultimately issues an active power reference command. P ref Active power setpoint before the fault P ref0 With dynamic limit value P lim The smaller values ​​between these ranges ultimately form the active power control law: (11)。

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