CN113890054B - Wind-fire coupling system stability judging and compensating method based on equivalent open loop process - Google Patents

Abstract

The invention discloses a wind-fire coupling system stability judging and compensating method based on an equivalent open loop process, which belongs to the technical field of stability analysis and control of new energy grid-connected systems and comprises the following steps: decoupling the wind-fire coupling system through an equivalent open loop process to obtain a fan taking virtual inertia and sagging control into account and a residual subsystem after the fan is removed; respectively establishing a multivariable open-loop frequency domain model for the fan and the residual subsystem which account for virtual inertia and sagging control, and converting the multivariable open-loop frequency domain model into a univariable closed-loop transfer function; and taking the inverse of the closed loop transfer function as a characteristic transfer function, and judging the stability of the wind-fire coupling system through the characteristic transfer function. And when the wind-fire coupling system is unstable, performing phase compensation on a phase-locked loop of the wind-fire coupling system. The stability judgment result is accurate, and satisfactory frequency modulation effect can be achieved on the premise of ensuring the stability of the coupling system by performing subsynchronous oscillation suppression through phase compensation.

Description

Stability Judgment and Compensation Method of Wind-fire Coupled System Based on Equivalent Open-loop Process

technical field

The invention belongs to the technical field of stability analysis and control of new energy grid-connected systems, and more specifically relates to a method for determining and compensating the stability of a wind-fire coupling system based on an equivalent open-loop process.

Background technique

With the rapid development of renewable energy, on the one hand, power electronic equipment is widely connected to the power grid, and its non-linearity leads to more power system oscillation problems, especially the subsynchronous oscillation problem; on the other hand, the interaction between renewable energy and local thermal power units Mutual coupling is becoming more and more obvious. The coupling and integration at the same grid-connected point is a unified control object. This scenario is common in the northern power grid of my country. Therefore, a method that can accurately analyze the oscillation stability of the wind-fire coupling system is urgently needed.

Renewable energy sources such as wind and solar work in the maximum power point tracking mode during normal operation, which cannot provide sufficient inertial response and primary frequency regulation capabilities to the grid. After a large number of them are connected to the grid, they will have a significant impact on the stable operation of the system. In order to meet the needs of large-scale grid-connection of renewable energy and build a "grid-friendly" renewable energy station, a number of national standards have put forward requirements for the active frequency support control of renewable energy. For the typical operation scenarios of the wind-fire coupled system, it is necessary to study the multi-characteristic parameter stability criterion of the wind-fire coupled system considering the virtual inertia and droop control, and determine the stability and safety boundary conditions of the coupled system. However, there are few related studies.

It can be seen that the existing wind-fire coupling system has the technical problem of inaccurate stability determination results.

Contents of the invention

Aiming at the above defects or improvement needs of the prior art, the present invention provides a method for determining and compensating the stability of the wind-fire coupling system based on an equivalent open-loop process. Accurate technical questions.

In order to achieve the above object, according to one aspect of the present invention, a method for determining the stability of a wind-fire coupling system based on an equivalent open-loop process is provided, including the following steps:

(1) The wind-fire coupling system is decoupled through an equivalent open-loop process, and the fan and the remaining subsystem after removing the fan are obtained considering the virtual inertia and droop control;

(2) Establish a multivariable open-loop frequency-domain model for the fan and the remaining subsystems considering virtual inertia and droop control, and convert the multivariate open-loop frequency-domain model into a single-variable closed-loop transfer function;

(3) The reciprocal of the closed-loop transfer function is used as the characteristic transfer function, and the stability of the wind-fire coupling system is judged by the characteristic transfer function.

Further, the specific way of determining the stability is as follows:

Divide the characteristic transfer function into real and imaginary parts;

When the slope of the curve of the imaginary part is negative at the zero-crossing point, if the real part is less than zero, the wind-fire coupled system is stable; if the real part is greater than zero, the wind-fire coupled system is unstable;

When the slope of the imaginary part curve at the zero crossing point is positive, if the real part is greater than zero, the wind-fire coupled system is stable, and if the real part is less than zero, the wind-fire coupled system is unstable.

Further, the specific way of determining the stability is as follows:

Draw a Bode plot of the characteristic transfer function;

In the Bode diagram, the phase angle rotates counterclockwise through the real axis in the subsynchronous oscillation frequency range, and the angle increases, and the wind-fire coupling system in the corresponding frequency band is stable;

In the Bode diagram, the phase angle rotates clockwise through the real axis in the subsynchronous oscillation frequency range, the angle decreases, and the wind-fire coupling system in the corresponding frequency band is unstable.

Further, the characteristic transfer function has a pair of conjugate zeros close to the imaginary axis within the subsynchronous frequency range, and the oscillation frequency of the wind-fire coupling system is greater than the attenuation coefficient.

Further, the step (2) includes:

Considering the virtual inertia and droop control, the fans form an open-loop subsystem, and its state equation is In the formula, ΔU _g and ΔI _g represent the voltage vector and current vector of the fan port in the synchronous rotating coordinate system, respectively. A _g , B _g , D _g and D _g are the fan-side state matrix, input matrix, output matrix and direct transmission matrix respectively, ΔX _g is the state variable of the fan, and the subscript g represents the fan-side parameter;

The ring frequency domain model of the fan is derived from the state equation of the fan:

In the formula, I _w is the identity matrix of the fan, s is the Laplacian operator, g _g11 (s), g _g12 (s), g _g21 (s) and g _g22 (s) are the open-loop frequency of the fan, respectively Elements in the matrix after the domain model transfer function C _g (s) is transformed into a matrix;

The state equations of the remaining subsystems are In the formula, ΔX _s is the state variable of the remaining subsystem; A _s , B _s , C _s and D _s are the state matrix, input matrix, output matrix and direct transfer matrix of the remaining subsystem respectively; the subscript s represents the parameter of the remaining subsystem ;

The open-loop frequency domain model of the remaining subsystems is as follows:

In the formula, I _s is the identity matrix in the remaining subsystem, and g _s11 (s), g _s12 (s), g _s21 (s) and g _s22 (s) are the open-loop frequency domain model transfer functions of the remaining subsystem G _s (s) is converted to an element in the matrix after matrix;

Finally, the closed-loop transfer function is:

in,

D(s)＝g _g11 (s)g _s11 (s)+g _g12 (s)g _s21 (s)+G _i (s)[g _g11 (s)g _s12 (s)+g _g12 (s)g _s22 (s)]

in,

According to another aspect of the present invention, a kind of compensation method of wind-fire coupling system based on equivalent open-loop process is provided, it is characterized in that, comprises:

When a wind-fire coupling system stability determination method based on an equivalent open-loop process determines that the wind-fire coupling system is unstable, the phase compensation is performed on the phase-locked loop of the wind-fire coupling system.

Further, the compensation phase angle in the phase compensation process in, For the maximum compensation phase angle obtained at frequency f _p , ω represents the oscillation frequency.

Generally speaking, compared with the prior art, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

(1) Based on the theory of equivalent open-loop process, the present invention equivalently considers the wind-fire coupling system of virtual inertia and droop control as a single-variable closed-loop transfer function, which can effectively judge the Oscillation characteristics determine the stable and safe boundary conditions of the coupling system, and the method of the invention is used for stability judgment, and the result is accurate, simple and intuitive.

(2) An improved stability criterion suitable for analyzing system subsynchronous oscillation proposed by the present invention is simple to deduce and easy to verify. The stability of the wind-fire coupling system can be judged only by the phase-frequency characteristics of the characteristic transfer function. The proposed method has the advantages of The potential of quantitative stability analysis for the actual complex new energy grid-connected system. The present invention also provides a stability judgment method, drawing the Bode diagram of the characteristic transfer function, and by observing the direction in which the phase passes through the real axis in the subsynchronous oscillation frequency range, the stability of the coupling system can be judged, the judgment method is simple and effective, High accuracy.

(3) For the wind-fire coupling system that takes virtual inertia and droop control into account, the present invention also proposes a subsynchronous oscillation suppression measure based on phase reshaping control, and the phase of the subsynchronous oscillation mode is dominated by the phase compensation phase-locked loop In order to improve its damping characteristics, the stability margin of the coupling system considering the active frequency support control in the sub-synchronous frequency range is improved, and a satisfactory frequency modulation effect can be achieved on the premise of ensuring the stability of the wind-fire coupling system.

Description of drawings

Fig. 1 is a schematic diagram of the topological structure of the wind-fire coupling system provided by the embodiment of the present invention;

Fig. 2 is a schematic diagram of virtual inertia and droop control provided by an embodiment of the present invention;

Fig. 3 is a schematic diagram of the closed-loop structure of the wind-fire coupling system provided by the embodiment of the present invention;

(a) in Fig. 4 is a circuit structure diagram of a fire coupling system provided by an embodiment of the present invention;

(b) in Fig. 4 is the equivalent structural diagram of a loop of the fire coupling system provided by the embodiment of the present invention;

Among Fig. 5 (a) is the first kind of stability criterion schematic diagram of the proposed single variable system provided by the embodiment of the present invention;

(b) in Fig. 5 is the second kind of stability criterion schematic diagram of the proposed single variable system provided by the embodiment of the present invention;

(a) in Figure 6 is a schematic diagram of the equivalent stability criterion provided by the embodiment of the present invention;

(b) in Fig. 6 is the equivalent characteristic transfer function Bode figure provided by the embodiment of the present invention;

Fig. 7 is the Bode diagram of the characteristic transfer function of the equivalent univariate system provided by the embodiment of the present invention;

Among Fig. 8 (a) is the output schematic diagram of thermal power unit provided by the embodiment of the present invention;

(b) in Fig. 8 is the enlarged schematic diagram of the output of thermal power unit provided by the embodiment of the present invention;

(c) in FIG. 8 is a schematic diagram of the wind turbine output provided by the embodiment of the present invention;

(d) in FIG. 8 is a schematic diagram of wind turbine output amplification provided by an embodiment of the present invention;

Fig. 9 is a characteristic transfer function Bode diagram of an equivalent univariate system provided by an embodiment of the present invention;

(a) in Figure 10 is a schematic diagram of the system frequency and the output of wind power and thermal power units when the frequency modulation link is not added according to the embodiment of the present invention;

(b) in Figure 10 is a schematic diagram of the system frequency and the output of wind power and thermal power units when the frequency modulation link is added according to the embodiment of the present invention;

(c) in Fig. 10 is a schematic diagram of the system frequency and the output of wind power and thermal power units when the phase compensation link is added on the basis of the frequency modulation link provided by the embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

The present invention provides a wind-fire coupled system stability judgment and compensation method based on an equivalent open-loop process, comprising the following steps:

(1) Establish the frequency-domain equivalent model of the wind-fire coupling system based on the effective open-loop process theorem (EOP) and taking active frequency support control into account. Use EOP to decouple the loops of the wind-fire coupling system that takes virtual inertia and droop control into account, and convert the multivariable system loop equation into a single-variable system loop equation, thereby establishing a single-input and single-output wind-fire coupling system in the frequency domain, etc. effective model. The model mainly includes:

(11) Determine the topology of the wind-fire coupling system. The topological structure of the wind-fire coupling system is shown in FIG. 1 . In the figure, the synchronous generator G1 represents thermal power, and P _e and P _D are the output electromagnetic power of the synchronous generator and DFIG (double-fed asynchronous wind generator) respectively. E∠δ and U∠θ represent the internal potential of the synchronous generator and the voltage of the DFIG access point, respectively. U _s ∠0° represents infinite grid voltage. X ₁ is the line reactance between synchronous generator and PCC point, X ₂ is the line reactance between DFIG and PCC point, X ₃ is the line reactance between PCC point and infinite grid.

(12) Determine the wind power topology considering the virtual inertia and droop control. The structure is shown in Figure 2. In the figure, ω is the system frequency value measured by the phase-locked loop; PWM is pulse width modulation; P _sref and Q _sref are the active power reference value and reactive power reference value output by DFIG respectively; P _s and Q _s are DFIG Actual active output and reactive output; U _pcc is the PCC point voltage; U _d and U _q are the d-axis and q-axis voltage components of the PCC point voltage respectively; θ _pll is the phase angle of the PCC point voltage measured by the phase-locked loop; K _p and K _i are the proportional parameters and integral parameters of the phase-locked loop PI controller, respectively; K _df and K _pf are the virtual inertia coefficient and droop coefficient, respectively; T _df and T _pf are the virtual inertia control response time and droop control response time, respectively.

(13) Split the wind-fire coupling system. The wind-fire coupling system is divided into two parts: the fan considering the virtual inertia and droop control and the remaining subsystem after removing the fan. In the wind-fire coupling system, the fan considering virtual inertia and droop control can constitute an open-loop subsystem, and its state equation in the synchronous rotating coordinate system is In the formula, ΔU _g and ΔI _g represent the voltage vector and current vector of the DFIG port in the synchronous rotating coordinate system, respectively, and are the input vector and the output vector, respectively. A _g , B _g , C _g and D _g are the DFIG side state matrix, input matrix, output matrix and direct transfer matrix, respectively. ΔX _g is the state variable of DFIG. The subscript g represents the fan side parameters.

The open-loop frequency domain model on the DFIG side can be derived from the above formula:

In the formula, I _w is the identity matrix, and s is the Laplacian operator. g _g11 (s), g _g12 (s), g _g21 (s) and g _g22 (s) are elements in the transfer function G _g (s) of the open-loop frequency domain model on the DFIG side, respectively.

In the wind-fire coupling system, the remaining subsystems except the grid-connected fan also constitute an open-loop subsystem, and its state equation is In the formula, ΔX _s is all the state variables of the remaining subsystem after removing the fan; A _s , B _s , C _s and D _s are the state matrix, input matrix, output matrix and direct transmission matrix of the remaining subsystem respectively; the subscript s indicates Parameters of the remaining subsystems in the wind-fire coupled system after removing the fan.

According to the above formula, the open-loop frequency domain model of the remaining subsystem is as follows:

In the formula, I _s is the identity matrix. g _s11 (s), g _s12 (s), g _s21 (s) and g _s22 (s) are elements in the transfer function G _s (s) of the remaining subsystem open-loop frequency domain model after removing the fan, respectively.

Considering the virtual inertia and droop control fan and the remaining subsystems after removing the fan can form an interconnected closed-loop system, as shown in Figure 3.

(14) Equivalent simplification of a single-input single-output system. The interconnected closed-loop system shown in Figure 3 is equivalent to a single-input single-output system, as shown in (a) and (b) in Figure 4. Based on (b) in Figure 4, the closed-loop transfer function of the single-input and single-output system can be obtained:

in,

D(s)＝g _g11 (s)g _s11 (s)+g _g12 (s)g _s21 (s)+G _i (s)[g _g11 (s)g _s12 (s)+g _g12 (s)g _s22 (s)]

In the formula,

(2) It is suitable for analyzing the stability criterion of subsynchronous oscillation of wind-fire coupled system. The criterion is based on a simplified single-input-single-output wind-fire coupled system equivalent model, which can effectively judge the oscillation characteristics in the subsynchronous frequency range and determine the stability and safety boundary conditions of the coupled system. The criterion mainly includes:

As shown in (b) in Figure 4, its characteristic transfer function is T(s)=1/D(s)-1, if the characteristic transfer function has a pair of conjugate zeros λ close to the imaginary axis within the subsynchronous frequency range _{1, 2} =σ _o ±jω _o , and satisfy |σ _o |<<|ω _o |, then the characteristic transfer function of the system can be transformed into the following form:

T(s)=(s-λ ₁ )(s-λ ₂ )G(s)

In the formula, G(s) is the remaining part after removing the two conjugate zero-point polynomials in T(s), let s=jω, when ω is in the small neighborhood of λ _{1, 2} , the above formula can be expressed as follows form:

T(jω)＝(jω-λ ₁ )(jω-λ ₂ )G(jω)

Obviously G(jω) is a rational polynomial, so the real part and imaginary part can be separated, that is, G(jω)=a(ω)+jb(ω), it is obvious that a(ω) and b(ω) are related to ω The real function of , then the above formula can be expressed as the following form:

T(jω)＝[-σ _o +j(ω-ω _o )][-σ _o +j(ω+ω _o )][a(ω)+jb(ω)]

The real part and imaginary part of T(jω) can be separated to get the following expression:

Let the imaginary part of the characteristic transfer function Im[T(jω)]=0, the following expression can be obtained:

Obviously, when |σ _o |<<|ω _o |, σ _o /ω _o ≈0, it can be found that ω _r ≈ω _o . Therefore, the dominant oscillation frequency ω _o of the system can be approximated according to the fact that the imaginary part of the characteristic transfer function is equal to zero. Bringing the frequency ω _r of this zero-crossing point into the real part Re[T(jω)] of the characteristic transfer function, the following expression can be obtained:

It can also be known that the slope of the imaginary part at the zero crossing point is as follows:

The positive or negative of b can be determined by the slope of the zero-crossing point of the imaginary part. Further, the positive or negative of the attenuation coefficient σ ₀ can be judged according to Re[T(jω _r )].

When b>0, the slope of the imaginary part of the characteristic transfer function at the zero-crossing point is negative, that is, the curve crosses from positive to negative at the zero-crossing point; when b<0, the imaginary part of the characteristic transfer function is at the zero-crossing point The slope of is positive, that is, the curve crosses from negative to positive at the zero-crossing point; combined with the previous formula, the stability criterion of the system can be obtained as follows:

① When the imaginary part of the characteristic transfer function, that is, the curve of Im[T(jω _r )] has a negative slope at the zero-crossing point, if Re[T(jω _r )]<0, then σ ₀ <0, the system is stable; On the contrary, if Re[T(jω _r )]>0, then σ ₀ >0, the system is unstable.

②When the imaginary part of the characteristic transfer function, that is, the slope of the curve of Im[T(jω _r )] at the zero-crossing point is positive, if Re[T(jω _r )]>0, then σ ₀ <0, the system is stable; On the contrary, if Re[T(jω _r )]<0, then σ ₀ >0, and the system is unstable.

The above expression can be expressed in (a) and (b) in Figure 5. It can be further expressed as shown in (a) in Figure 6. The direction of the arrow is the direction of frequency increase. As shown in (b) in Figure 6, the phase angle in the Bode diagram of the characteristic transfer function rotates counterclockwise through the real axis (0° or 180°), the angle increases, and the corresponding frequency band is stable; the phase angle rotates clockwise through the real axis, and the angle Decrease, the corresponding frequency band is unstable. Based on this conclusion, the Bode diagram of the characteristic transfer function can be drawn, and the stability of the coupled system can be judged by observing the direction in which the phase passes through the real axis (0° or 180°) within the subsynchronous oscillation frequency range.

(3) Subsynchronous oscillation suppression measures based on phase reshaping control. The phase of the dominant subsynchronous oscillation mode of the PLL is compensated by the phase reshaping controller to improve its damping characteristics, and the stability margin of the coupled system in the subsynchronous frequency range is improved considering the active frequency support control. The control strategy mainly includes:

In order to realize the compensation of the system phase margin, a phase compensation link is added in the system control loop to make up for the insufficient system phase margin caused by the active frequency support control link. For this reason, the present invention selects the phase compensation link H(s) in series after the active frequency support control link, as shown in Figure 2, the corresponding expression is The compensation phase angle of the phase compensation link H(s) can be obtained from the above formula The expression is /> Assuming that the phase compensation link obtains the maximum compensation phase angle at the frequency f _p , then according to the above formula, it can be known that If the maximum compensation phase angle is set to /> Then according to the above two formulas, the expression of _τ1 can be obtained as />

In the present invention, f _p = 10 Hz is selected as a compromise, Thus, τ ₁ =0.0190; τ ₂ =07041 are obtained.

The present invention provides a wind-fire coupling system stability judgment and compensation method based on an equivalent open-loop process. Based on the wind-fire coupling system taking into account virtual inertia and droop control, the following two sets of embodiments are set up. Firstly, different frequency modulation parameters are compared. The stability of the wind-fire coupling system is investigated, and the effectiveness of the proposed criterion is verified. Then, the additional controller is used to compensate the phase of the dominant mode of the phase-locked loop in the subsynchronous oscillation frequency range to improve its damping characteristics. It is verified that the phase reshaping control proposed by this method can achieve Satisfactory FM effect.

Example 1: Validation of the validity of the proposed stability criterion.

Figure 7 shows the Bode diagram of the characteristic transfer function of the equivalent single-input single-output system under different frequency modulation parameters. (a)-(d) in Fig. 8 show the time-domain simulation results of the wind-fire coupling system under the same working conditions as Fig. 7. It can be seen from Figure 7 that the phase-frequency characteristic curves in the Bode diagram of the characteristic transfer function corresponding to Case 1 and Case3 pass the imaginary axis clockwise (the angle decreases) in the subsynchronous frequency range, and the phase-frequency characteristic curves in the Bode diagram of the characteristic transfer function corresponding to Case 2 The frequency characteristic curve passes through the imaginary axis counterclockwise (angle increases) in the subsynchronous frequency range. According to the proposed criterion, the wind-fire coupling system under Case 1 and Case 3 will oscillate and lose stability, while the wind-fire coupling system under Case 2 will maintain Stablize. The time-domain simulation results of (a)-(d) in Figure 8 show that the wind-fire coupling system corresponding to Case 1 and Case 3 does oscillate and become unstable under load disturbance, while the wind-fire coupling system corresponding to Case 2 does remain stable. The time-domain simulation results The effectiveness of the proposed criterion is verified.

Example 2: Validation of the effectiveness of the phase reshaping control strategy based on the proposed criterion.

Figure 9 shows the Bode diagram of the characteristic transfer function of the equivalent single-input single-output system under different frequency modulation parameters. (a)-(c) in Figure 10 show the time-domain simulation results of the wind-fire coupling system under the same working conditions as in Figure 9. Case 1 is the simulation condition of the wind-fire coupling system without frequency modulation; Case 2 is the simulation condition of wind-fire coupling system without phase compensation; Case 3 is the simulation condition of frequency modulation and phase compensation The simulation working conditions of the wind-fire coupling system corresponding to the compensation link. It can be seen from Fig. 9 that the phase-frequency characteristic curves in the Bode diagram of the characteristic transfer function corresponding to Case 1 and Case 3 pass the imaginary axis counterclockwise (the angle increases) in the subsynchronous frequency range, and the phase-frequency characteristic curves in the Bode diagram corresponding to the characteristic transfer function of Case 2 The frequency characteristic curve passes through the imaginary axis clockwise in the subsynchronous frequency range (the angle decreases). According to the proposed criterion results, the wind-fire coupling system under Case 1 and Case 3 will remain stable, while the wind-fire coupling system under Case 2 will oscillate Unsteady. The time-domain simulation results of (a)-(c) in Figure 10 show that when the frequency modulation link is not added, the wind-fire coupling system corresponding to Case 1 is indeed stable under load disturbance. After adding the frequency modulation link, the wind-fire coupling system corresponding to Case 2 under the load disturbance does respond to the frequency change and achieve a certain frequency modulation effect, but at the same time, due to the addition of the frequency modulation link, the dominant characteristic root of the phase-locked loop moves to the right half of the polar coordinate system plane, the system oscillates and becomes unstable. Further, on the basis of adding the frequency modulation link, a phase compensation link (Case3) is added to reshape the phase near the dominant oscillation frequency of the phase-locked loop of the wind-fire coupling system, ensuring the stability of the wind-fire coupling system under the same frequency modulation parameters as Case 2 to achieve a satisfactory FM effect. Simulation results in time domain verify the effectiveness of the phase reshaping control strategy based on the proposed criterion.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (6)

1. A wind-fire coupling system stability determination method based on equivalent open-loop process, is characterized in that, comprises the steps: (1) The wind-fire coupling system is decoupled through an equivalent open-loop process, and the fan and the remaining subsystem after removing the fan are obtained considering the virtual inertia and droop control; (2) Establish a multivariable open-loop frequency-domain model for the fan and the remaining subsystems considering virtual inertia and droop control, and convert the multivariate open-loop frequency-domain model into a single-variable closed-loop transfer function; (3) The reciprocal of the closed-loop transfer function is used as the characteristic transfer function, and the stability of the wind-fire coupling system is judged by the characteristic transfer function; Described step (2) comprises: Considering the virtual inertia and droop control, the fans form an open-loop subsystem, and its state equation is In the formula, ΔU _g and ΔI _g represent the voltage vector and current vector of the fan port in the synchronous rotating coordinate system, respectively; A _g , B _g , C _g and D _g are the state matrix, input matrix, output matrix and direct transmission matrix of the fan side, respectively , ΔX _g is the state variable of the fan, and the subscript g represents the parameter of the fan side; The ring frequency domain model of the fan is derived from the state equation of the fan: In the formula, I _w is the identity matrix of the fan, s is the Laplacian operator, g _g11 (s), g _g12 (s), g _g21 (s) and g _g22 (s) are the open-loop frequency of the fan, respectively Elements in the matrix after the domain model transfer function G _g (s) is transformed into a matrix; The state equations of the remaining subsystems are In the formula, ΔX _s is the state variable of the remaining subsystem; A _s , B _s , C _s and D _s are the state matrix, input matrix, output matrix and direct transfer matrix of the remaining subsystem respectively; the subscript s represents the parameter of the remaining subsystem ; The open-loop frequency domain model of the remaining subsystems is as follows: In the formula, I _s is the identity matrix in the remaining subsystem, and g _s11 (s), g _s12 (s), g _s21 (s) and g _s22 (s) are the open-loop frequency domain model transfer functions of the remaining subsystem G _s (s) is converted to an element in the matrix after matrix; Finally, the closed-loop transfer function is: in, D(s)＝g _g11 (s)g _s11 (s)+g _g12 (s)g _s21 (s)+G _i (s)[g _g11 (s)g _s12 (s)+g _g12 (s)g _s22 (s)] in, 2. a kind of wind-fire coupling system stability judgment method based on equivalent open-loop process as claimed in claim 1, is characterized in that, the specific mode of described stability judgment is: Divide the characteristic transfer function into real and imaginary parts; When the slope of the curve of the imaginary part is negative at the zero-crossing point, if the real part is less than zero, the wind-fire coupled system is stable; if the real part is greater than zero, the wind-fire coupled system is unstable; When the slope of the imaginary part curve at the zero crossing point is positive, if the real part is greater than zero, the wind-fire coupled system is stable, and if the real part is less than zero, the wind-fire coupled system is unstable. 3. a kind of wind-fire coupling system stability judgment method based on equivalent open-loop process as claimed in claim 1, is characterized in that, the specific mode of described stability judgment is: Draw a Bode plot of the characteristic transfer function; In the Bode diagram, the phase angle rotates counterclockwise through the real axis in the subsynchronous oscillation frequency range, and the angle increases, and the wind-fire coupling system in the corresponding frequency band is stable; In the Bode diagram, the phase angle rotates clockwise through the real axis in the subsynchronous oscillation frequency range, the angle decreases, and the wind-fire coupling system in the corresponding frequency band is unstable. 4. a kind of wind-fire coupling system stability judgment method based on equivalent open-loop process as claimed in claim 2 or 3, it is characterized in that, described characteristic transfer function exists a pair of near imaginary axis in the scope of synchronous frequency The conjugate zero point, and the oscillation frequency of the wind-fire coupling system is greater than the attenuation coefficient. 5. A compensation method based on the wind-fire coupling system of equivalent open-loop process, is characterized in that, comprises: When the wind-fire coupling system stability determination method based on the equivalent open-loop process described in any one of claims 1-4 determines that the wind-fire coupling system is unstable, phase compensation is performed on the phase-locked loop of the wind-fire coupling system . 6. a kind of compensation method based on the wind-fire coupling system of equivalent open-loop process as claimed in claim 5, is characterized in that, the compensation phase angle in the phase compensation process in, For the maximum compensation phase angle obtained at frequency f _p , ω represents the oscillation frequency.