Frequency response analysis method for doubly-fed fan through MMC-HVDC grid-connected system

Abstract

The invention relates to a frequency response analysis method for a wind power grid-connected system through MMC-HVDC (modular multilevel converter-high voltage direct current) based on H2 and H infinity norms. The method comprises the following steps: firstly, based on a small signal linearization theory, deducing a power frequency transfer function between active power variations of DFIG, MMC-HVDC and frequency modulation units of a synchronous generator containing a control system detailed model and frequency variations of a receiving end power grid, and establishing a system detailed frequency response model; obtaining a transfer function between the system frequency variation and the load disturbance quantity; secondly, analyzing the influence of the comprehensive inertia control parameters Kp and Kd, the virtual inertia time constant Hmmc of the converter station and the difference adjustment parameter R of the synchronous machine on the system frequency response characteristic of the detailed frequency response model of the established system based on the H2 and H infinity norm theory;

Description

Technical Field

[0001] The present invention relates to the technical field of flexible DC power transmission, and particularly to a method for constructing a frequency response model and theoretical analysis of a wind power grid-connected system via MMC-HVDC. Background Art

[0002] In recent years, due to the characteristics of new energy power generation such as sustainability, renewability, and pollution-free, and with the rapid development of new energy power generation technology, the proportion of new energy power generation in the power supply structure of the power system is increasing rapidly. The stator winding of a doubly-fed induction generator (DFIG) is directly connected to the power grid, and the rotor winding is connected to the power grid through a back-to-back converter. The capacity of the converter is about 1 / 3 of the rated capacity of the wind turbine. The initial investment cost of the power electronic device is relatively low, and the DFIG technology is mature, making it the preferred solution for balancing efficiency and economy in the domestic wind power market at the present stage. The doubly-fed wind turbine is grid-connected through modular multilevel converter-based high voltage direct current (MMC-HVDC). With the increase in the new energy penetration rate, the inertia support capacity of the system decreases, and the existence of the DC system makes the wind turbine side unable to perceive the frequency fluctuation of the receiving-end power grid side. When the power generation and load do not match, resulting in frequency fluctuation of the receiving-end system, it is difficult for the DFIG to actively respond to the frequency regulation demand.

[0003] The existing frequency response analysis methods for wind power grid-connected systems via MMC-HVDC can be divided into the following categories:

[0004] 1. Frequency domain analysis method. The frequency domain analysis method reveals the frequency dynamic mechanism through small-signal modeling, establishes a linearized model of the system, and derives the system frequency response (SFR) model, which can effectively characterize the active power output of each frequency regulation unit in the system after load disturbance. However, most of the existing studies do not consider the detailed model of the control system, and construct a reduced-order frequency response model of the system in the form of the actual power value tracking the reference value through an inertia link, resulting in a deviation from the actual system frequency response characteristics and being difficult to accurately reflect the frequency dynamic response characteristics of the actual system.

[0005] 2. System fitting method. Fitting methods such as support vector machines, deep learning, parameter identification, and data-driven are applicable to scenarios where the parameters of the power system are unknown. By using the parameter identification method, a reasonable mapping relationship between the system frequency change and load disturbance is established according to the data characteristics of the system, but it is difficult to effectively characterize the active power coordination and distribution relationship between each frequency regulation unit in the system like the small-signal model.

[0006] 3. Time-domain analysis method. A detailed state model of the equipment is established in the simulation system, which can completely and accurately present the non-linear dynamic process of the system frequency response, but the calculation efficiency is relatively low, and it can be used as a reference for the frequency-domain analysis method and the system fitting method.

[0007] In view of the defects of the existing analysis methods, the present invention proposes a frequency response analysis method for a doubly-fed wind power generation unit connected to the grid via MMC-HVDC based on the H2 and H ∞ norms. This method improves the reduced-order SFR model by considering the detailed model of the control system, and studies the roles of the doubly-fed wind farm, the converter station, and the synchronous generator in the frequency response through the H2 and H ∞ norms of the transfer function between the frequency change amount of the doubly-fed wind power generation unit connected to the grid via MMC-HVDC and the load disturbance amount, which is of great significance for the setting of control parameters and the optimal coordinated distribution of frequency modulation active power in the frequency modulation strategy of the wind power grid-connected system. Summary of the Invention

[0008] The present invention proposes a frequency response analysis method for a wind power grid-connected system via MMC-HVDC based on the H2 and H ∞ norms. The technical solution of the present invention is as follows:

[0009] A frequency response analysis method for a wind power grid-connected system via MMC-HVDC based on the H2 and H ∞ norms, characterized in that, firstly, based on the small-signal linearization theory, the power-frequency transfer function between the active power change amount of each frequency modulation unit of the doubly-fed induction generator (DFIG), MMC-HVDC and the synchronous generator including the detailed model of the control system and the frequency change amount of the receiving-end power grid is deduced, and a detailed system frequency response model is established to obtain the transfer function between the system frequency change amount and the load disturbance amount; secondly, based on the H2 and H ∞ norm theory, the influences of the comprehensive inertia control parameters K p , K d , the virtual inertia time constant H of the converter station mmc and the synchronous machine droop parameter R on the system frequency response characteristics of the established detailed system frequency response model are analyzed.

[0010] Furthermore, it includes the following steps:

[0011] (1) The frequency deviation Δf and the frequency change rate df / dt are introduced into the active power reference value of the rotor-side converter (RSC) by adopting comprehensive inertia control. Considering the detailed model of the RSC double closed-loop PI control system, the power-frequency transfer function between the additional active power change amount ΔP we of the DFIG and the frequency change amount Δf of the receiving-end power grid is deduced as:

[0012]

[0013] wherein, G0(s) = K pr_P + K ir_P / s; G1(s) = (K pr_in + K ir_in / s) / (R r + sσL r / ω0 + K pr_in + K ir_in / s); G2(s) = (L m u sd0 (3kω r0 3 G0(s)G1(s) + i rd0 ) / [(ω0L s )(k wm - T J_DFIG ω r0 s)]; u sd0 is the steady-state value of the d-axis component of the DFIG stator voltage; K pr_P , K ir_P , K pr_Q and K ir_Q are the proportional and integral coefficients of the d and q axes in the RSC outer-loop controller respectively; R r is the rotor equivalent resistance; σ is the leakage magnetic coefficient, satisfying σ = 1 - L m 2 / (L s L r ); L s , L r are the self-inductances of the equivalent two-phase windings of the stator and rotor in the dq rotating coordinate system respectively; L m is the mutual inductance between the coaxial equivalent windings of the stator and rotor in the dq rotating coordinate system; K pr_in , K ir_in are the proportional and integral coefficients of the d and q axes in the RSC inner-loop current controller respectively; ω0 is the fundamental angular frequency; T J_DFIG is the inertia time constant of the doubly-fed wind turbine; K p , K d are the droop and inertia coefficients of the synthetic inertia control respectively; ω r0 is the steady-state value of the rotor speed; k is the maximum power tracking coefficient; i rd0 is the steady-state value of the rotor d-axis current; k wm is the coefficient between the input mechanical power of the wind turbine and the change in speed; Denote Equation (1) as ΔP we (s) = G DFIG (s)Δf. When the wind farm side senses the change Δf of the receiving-end AC system frequency, it can be known that the electromagnetic power ΔP we increased by the DFIG under the synthetic inertia control;

[0014] (2) The frequency deviation Δf is introduced into the DC voltage control of the grid-side converter station GSMMC by using virtual inertia control. Considering the detailed model of the GSMMC control system, the change in the additional active power ΔP of the GSMMC is derived. mmc The power-frequency transfer function between the change in the additional active power ΔP and the change in the frequency of the receiving-end power grid Δf is:

[0015]

[0016] In the formula, G mmc0 (s) = K Udc_p + K Udc_i / s; G mmc1 (s) = (K pind + K iind / s) / (R + sL eq + K pind + K iind / s); u gsd0 is the steady-state operating point value of the GSMMC modulation point voltage; H mmc is the virtual inertia time constant of the converter station; K Udc_p , K Udc_i , K Q_p and K Q_i are the proportional and integral coefficients of the d-axis and q-axis in the outer-loop controller of the GSMMC respectively; K pind , K iind are the proportional and integral coefficients of the inner-loop controller of the GSMMC respectively; R is the equivalent resistance of the connecting transformer; L eq = L T2 + L arm / 2 is the equivalent inductance, L T2 is the inductance of the connecting transformer T2; L arm is the arm inductance of the MMC converter; U dc0 is the steady-state value of the DC voltage of the converter station; P mmc0 is the steady-state value of the active power of the converter station; C eq is the equivalent DC capacitance of the converter station; Denote Equation (2) as ΔP mmc (s) = G mmc (s)Δf. When the converter station senses the change in the frequency of the receiving-end AC system Δf, it can be known that under the virtual inertia control with a fixed coefficient H mmc , the additional electromagnetic power ΔP mmc of the converter station;

[0017] (3) Derive the power-frequency transfer function between the change in the active power ΔP GM of the prime mover and governor of the synchronous generator and the change in the frequency of the receiving-end power grid Δf:

[0018]

[0019] In the formula, TSM is the valve servo time constant; T SR is the inertia time coefficient of the governor; R is the droop parameter; k G is the compensation value of the governor droop parameter; G T (s) is the transfer function between the turbine output mechanical power and the turbine valve power; Denote Equation (3) as ΔP GM (s) = G GM (s)Δf, that is, when the synchronous generator set senses the change Δf of the receiving-end AC system frequency, it can be known that under the action of the governor, the synchronous generator increases the electromagnetic power ΔP GM ;

[0020] (4) Establish a detailed frequency response model of the DFIG-MMC-HVDC grid-connected system, and the transfer function between the system frequency change and the load disturbance amount from the frequency domain perspective is:

[0021]

[0022] In the formula, T J and D are the equivalent inertia time constant and damping coefficient of the synchronous generator respectively; Equation (4) indicates that when there is an active load disturbance of ΔP L in the DFIG-MMC-HVDC grid-connected system, it can be known the frequency change amount Δf under the coordinated frequency regulation of the doubly-fed wind turbine with comprehensive inertia control, the converter station with virtual inertia control and the synchronous generator set;

[0023] (5) Among the indicators measuring the output-input gain ratio of the DFIG-MMC-HVDC grid-connected system, use the H2 and H ∞ norms to quantitatively measure the ability of the system to suppress the disturbance input signal. The transfer function G sys (s) characterizes the dynamic relationship between the frequency change amount of the doubly-fed wind farm-MMC-HVDC grid-connected system and the active load disturbance; For the detailed frequency response model of the system, the H2 norm of the transfer function between the system frequency change amount and the active load disturbance reflects the average frequency response of the DFIG-MMC-HVDC grid-connected system under the load disturbance input; H ∞ norm reflects the most serious frequency response situation of the DFIG-MMC-HVDC grid-connected system under the load disturbance input, and is used to evaluate the maximum frequency deviation of the system after being disturbed.

[0024] Furthermore, for the DFIG-MMC-HVDC grid-connected system, the calculation formulas of the H2 and H ∞ norms of its transfer function matrix G(s) are respectively:

[0025]

[0026] where tr is the trace of the matrix; the superscript H represents the conjugate transpose; supσ max is the maximum singular value of the system transfer function matrix.

[0027] The beneficial results of the present invention are as follows:

[0028] (1) Based on the small-signal linearization theory, the present invention derives the power-frequency transfer function between the active power change of each frequency modulation unit of the doubly-fed wind turbine, MMC-HVDC, and synchronous generator and the frequency change of the receiving-end power grid. The physical meaning is clear and can be used to analyze the roles of the doubly-fed wind farm, converter station, and synchronous generator in the frequency response.

[0029] (2) The present invention considers the detailed dynamic characteristics of the control system to derive the system frequency response model, solves the problem that there is a deviation between the reduced-order frequency response model constructed in the form of tracking the reference value through the inertia link with the actual power value and the actual frequency response characteristics, and avoids the deviation between the reduced-order SFR model for analyzing the system frequency response characteristics and tuning the frequency modulation control strategy parameter values and the actual frequency dynamic response of the system, which may lead to the inability to provide an accurate basis for the optimal allocation of the active power of each frequency modulation unit of DFIG, MMC-HVDC, and synchronous machine.

[0030] (3) Based on the H2 and H ∞ norm theory, compared with the traditional means of analyzing the system's ability to suppress frequency disturbances, it has significant advantages. It can quantify the system's ability to suppress frequency disturbances, and the H2 and H ∞ norms are negatively correlated with the system's ability to suppress frequency disturbances. The smaller the value, the better the system's frequency regulation performance. Therefore, the H2 and H sys norms of the transfer function G ∞ (s) of the wind power integrated into the grid through MMC-HVDC can be used as the theoretical basis for the multi-dimensional collaborative optimization configuration of the frequency modulation resources of the wind power integrated into the grid through MMC-HVDC, thereby ensuring the system frequency stability. Quantitatively studying the influence of the change of system control parameters on the system frequency support ability from the frequency domain perspective provides a theoretical basis for the optimization configuration of the frequency modulation resources of multi-source collaboration. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the topology diagram of the doubly-fed wind turbine integrated into the grid through MMC-HVDC

[0032] Figure 2 is the control block diagram of the rotor-side converter of the doubly-fed wind turbine

[0033] Figure 3 is the control block diagram of the receiving-end converter station of MMC-HVDC

[0034] Figure 4 is the block diagram of the frequency response model of the doubly-fed wind turbine integrated into the grid through MMC-HVDC Detailed implementation manners

[0035] The present invention proposes a frequency response analysis method for a wind power grid-connected system via MMC-HVDC based on the H2 and H ∞ norm. The detailed implementation manners of the present invention will be described below with reference to the accompanying drawings:

[0036] (1) Comprehensive inertia control is adopted to introduce the frequency deviation Δf and the frequency change rate df / dt into the active power reference value of the rotor side converter (RSC). Considering the detailed model of the RSC double closed-loop PI control system, the change in the additional active power ΔP we of the DFIG and the power-frequency transfer function between the change in the frequency of the receiving-end power grid Δf are as follows:

[0037]

[0038] In the formula, G0(s) = K pr_P + K ir_P / s; G1(s) = (K pr_in + K ir_in / s) / (R r + sσL r / ω0 + K pr_in + K ir_in / s); G2(s) = (L m u sd0 (3kω r0 3 G0(s)G1(s) + i rd0 ) / [(ω0L s )(k wm - T J_DFIG ω r0 s)]; u sd0 is the steady-state value of the d-axis component of the DFIG stator voltage; K pr_P , K ir_P , K pr_Q and K ir_Q are the proportional and integral coefficients of the d and q axes in the outer loop controller of the RSC, respectively; R r is the rotor equivalent resistance; σ is the leakage magnetic coefficient, satisfying σ = 1 - L m 2 / (L s L r ); L s , L r are the self-inductances of the stator and rotor equivalent two-phase windings in the dq rotating coordinate system, respectively; L m is the mutual inductance between the stator and rotor coaxial equivalent windings in the dq rotating coordinate system; K pr_in , K ir_inare the proportional and integral coefficients of the d-axis and q-axis in the RSC inner-loop current controller respectively; ω0 is the fundamental angular frequency; T J_DFIG is the inertia time constant of the doubly-fed wind turbine; K p , K d are the droop and inertia coefficients of the synthetic inertia control respectively; ω r0 is the steady-state value of the rotor speed; k is the maximum power tracking coefficient; i rd0 is the steady-state value of the rotor d-axis current; k wm is the coefficient between the input mechanical power of the wind turbine and the change in speed. Denote Equation (1) as ΔP we (s) = G DFIG (s)Δf. When the wind farm side senses the change in the receiving-end AC system frequency Δf, it can be known that the electromagnetic power ΔP we increased by the DFIG under the synthetic inertia control.

[0039] (2) Introduce the frequency deviation Δf into the DC voltage control of the grid-side converter station (GSMMC) by using virtual inertia control. Considering the detailed model of the GSMMC control system, deduce the power-frequency transfer function between the increased active power change ΔP mmc of the GSMMC and the receiving-end grid frequency change Δf as:

[0040]

[0041] In the formula, G mmc0 (s) = K Udc_p + K Udc_i / s; G mmc1 (s) = (K pind + K iind / s) / (R + sL eq + K pind + K iind / s); u gsd0 is the steady-state operating point value of the GSMMC modulation point voltage; H mmc is the virtual inertia time constant of the converter station; K Udc_p , K Udc_i , K Q_p and K Q_i are the proportional and integral coefficients of the d-axis and q-axis in the outer-loop controller of the GSMMC respectively; K pind , K iind are the proportional and integral coefficients of the inner-loop controller of the GSMMC respectively; R is the equivalent resistance of the connecting transformer; L eq = L T2 + L arm / 2 is the equivalent inductance, L T2 is the inductance of the connecting transformer T2; L arm is the arm inductance of the MMC converter; U dc0is the DC voltage steady-state value of the converter station; P mmc0 is the active power steady-state value of the converter station; C eq is the equivalent DC capacitance of the converter station. Denote Equation (2) as ΔP mmc (s) = G mmc (s)Δf. When the converter station senses the change in the receiving-end AC system frequency Δf, it can be known that the electromagnetic power ΔP mmc increased by the converter station under virtual inertia control mmc .

[0042] (3) Derive the power-frequency transfer function between the change in active power ΔP GM of the synchronous generator prime mover and governor and the change in receiving-end grid frequency Δf as:

[0043]

[0044] In the formula, T SM is the valve servo time constant; T SR is the inertia time constant of the governor; R is the droop parameter; k G is the compensation value of the governor droop parameter; G T (s) is the transfer function between the output mechanical power of the steam turbine and the valve power of the steam turbine. Denote Equation (3) as ΔP GM (s) = G GM (s)Δf, that is, when the synchronous generator set senses the change in the receiving-end AC system frequency Δf, it can be known that the synchronous generator increases the electromagnetic power ΔP GM .

[0045] (4) The rotor motion equation on the receiving-end grid side satisfies:

[0046] ΔP we -ΔP mmc +ΔP GM -ΔP L = T J sΔf + DΔf (4)

[0047] Establish a detailed frequency response model of the DFIG grid-connected system via MMC-HVDC. Substitute Equations (1), (2), and (3) into Equation (4), and the transfer function between the system frequency deviation and the load disturbance quantity from the frequency domain perspective can be obtained as:

[0048]

[0049] In the formula, T J and D are the equivalent inertia time constant and damping coefficient of the synchronous generator respectively. Equation (5) indicates that when a ΔP LWhen there is an active power load disturbance, the frequency change Δf under the coordinated frequency regulation of the doubly-fed wind turbine with comprehensive inertia control, the converter station with virtual inertia control, and the synchronous generator set can be known.

[0050] (5) Among the indicators for measuring the ratio of the system output to the input gain, H2 and H ∞ The norm can quantitatively measure the ability of the DFIG grid-connected system via MMC-HVDC to suppress the disturbance input signal. Therefore, the transfer function G sys (s) characterizes the dynamic relationship between the frequency change of the DFIG grid-connected system via MMC-HVDC and the active power load disturbance.

[0051] (6) For the DFIG grid-connected system via MMC-HVDC, the calculation formulas for the H2 and H ∞ norms of its transfer function matrix G(s) are respectively:

[0052]

[0053] In the formula, tr is the trace of the matrix; the superscript H represents the conjugate transpose; supσ max is the maximum singular value of the system transfer function matrix.

[0054] For the detailed frequency response model of the system, the H2 norm of the transfer function between the frequency change of the DFIG grid-connected system via MMC-HVDC and the active power load disturbance reflects the average frequency response of the DFIG grid-connected system via MMC-HVDC under the load disturbance input; the H ∞ norm reflects the most severe frequency response of the DFIG grid-connected system via MMC-HVDC under the load disturbance input, and can be used to evaluate the maximum frequency deviation of the system after being disturbed.

Claims

1. A frequency response analysis method for a wind power integrated into the MMC-HVDC grid-connected system based on the H2 and H ∞ norm, characterized in that, First, based on the small-signal linearization theory, the power-frequency transfer functions between the active power change of each frequency regulation unit of the doubly-fed induction generator (DFIG), modular multilevel converter high-voltage direct current (MMC-HVDC), and synchronous generator with a detailed control system model and the change in the receiving-end grid frequency are derived. A detailed system frequency response model is established to obtain the transfer function between the system frequency change and the load disturbance. Secondly, based on the H2 and H ∞ norm theory, the comprehensive inertia control parameters K p , K d , the virtual inertia time constant H of the converter station mmc , and the synchronous machine droop parameter R on the system frequency response characteristics of the established detailed system frequency response model are analyzed.

2. The frequency response analysis method of a wind power integrated into the MMC-HVDC grid-connected system based on the H2 and H ∞ norm, characterized in that including the following steps: (1) The comprehensive inertia control is adopted to introduce the frequency deviation Δf and the frequency change rate df / dt into the active power reference value of the rotor side converter (RSC). Considering the detailed model of the RSC double closed-loop PI control system, the change in the additional active power ΔP of the DFIG is derived. we The power-frequency transfer function between the change in the additional active power ΔP and the change in the receiving-end grid frequency Δf is as follows: where \(G_0(s)=K\) pr_P +K ir_P / s; \(G_1(s)=\frac{K\) pr_in +K ir_in / s}{R r +s\sigma L r / \omega_0+K pr_in +K ir_in / s}; \(G_2(s)=\frac{L m u sd0 (3k\omega r0 3 G_0(s)G_1(s)+i rd0 )}{(\omega_0L s )(k wm -T J_DFIG \omega r0 s)}; u sd0 is the steady-state value of the d-axis component of the DFIG stator voltage; K pr_P , K ir_P , K pr_Q and K ir_Q are the proportional and integral coefficients of the d- and q-axes in the RSC outer-loop controller respectively; R r is the rotor equivalent resistance; \(\sigma\) is the leakage magnetic coefficient, satisfying \(\sigma = 1 - L m 2 / (L s L r ); L s , L r are the self-inductances of the stator and rotor equivalent two-phase windings in the dq rotating coordinate system respectively; L m is the mutual inductance between the stator and rotor coaxial equivalent windings in the dq rotating coordinate system; K pr_in , K ir_in are the proportional and integral coefficients of the d- and q-axes in the RSC inner-loop current controller respectively; \(\omega_0\) is the fundamental angular frequency; T J_DFIG is the inertia time constant of the doubly-fed wind turbine; K p , K d are the droop and inertia coefficients of the synthetic inertia control respectively; \(\omega r0 is the steady-state value of the rotor speed; k is the maximum power tracking coefficient; i rd0 is the steady-state value of the rotor d-axis current; k wm is the coefficient between the input mechanical power of the wind turbine and the change in speed; Denote Equation (1) as \(\Delta P we (s)=G DFIG (s)\Delta f. When the wind farm side senses the change \(\Delta f\) in the frequency of the receiving-end AC system, it can be known that the additional electromagnetic power \(\Delta P we of the DFIG under synthetic inertia control; (2) The virtual inertia control is adopted to introduce the frequency deviation Δf into the DC voltage control of the grid-side converter station GSMMC. Considering the detailed model of the GSMMC control system, the change in the additional active power ΔP of the GSMMC is deduced. mmc The power-frequency transfer function between the additional active power change ΔP of the GSMMC and the change in the frequency of the receiving-end power grid Δf is as follows: where G mmc0 (s) = K Udc_p + K Udc_i / s; G mmc1 (s) = (K pind + K iind / s) / (R + sL eq + K pind + K iind / s); u gsd0 is the steady - state operating point value of the GSMMC modulation point voltage; H mmc is the virtual inertia time constant of the converter station; K Udc_p , K Udc_i , K Q_p and K Q_i are the proportional and integral coefficients of the d - axis and q - axis in the outer - loop controller of GSMMC respectively; K pind , K iind are the proportional and integral coefficients of the inner - loop controller of GSMMC respectively; R is the equivalent resistance of the connecting transformer; L eq = L T2 + L arm / 2 is the equivalent inductance, L T2 is the inductance of the connecting transformer T2; L arm is the arm inductance of the MMC converter; U dc0 is the steady - state value of the DC voltage of the converter station; P mmc0 is the steady - state value of the active power of the converter station; C eq is the equivalent DC capacitance of the converter station; Denote Equation (2) as ΔP mmc (s) = G mmc (s)Δf. When the converter station senses the change in the receiving - end AC system frequency Δf, it can be known that with the virtual inertia control coefficient H mmc the additional electromagnetic power ΔP mmc generated by the converter station; (3) Derive the active power change ΔP of the prime mover and governor of the synchronous generator GM The power-frequency transfer function between the change in the frequency Δf of the receiving-end power grid is as follows: Where, T SM is the valve servo time constant; T SR is the inertia time coefficient of the governor; R is the droop parameter; k G is the compensation value of the governor droop parameter; G T (s) is the transfer function between the output mechanical power of the steam turbine and the valve power of the steam turbine; Denote Equation (3) as ΔP GM (s) = G GM (s)Δf, that is, when the synchronous generator set senses the change Δf of the receiving-end AC system frequency, it can be known that under the action of the governor, the synchronous generator increases the electromagnetic power ΔP GM . (4) Establish a detailed frequency response model of the DFIG-MMC-HVDC grid-connected system, and obtain the transfer function between the system frequency change and the load disturbance quantity from the frequency domain perspective as: where T J and D are the equivalent inertia time constant and damping coefficient of the synchronous generator respectively; Equation (4) indicates that when there is an active power load disturbance of ΔP L in the DFIG integrated with the MMC-HVDC grid-connected system, the frequency change Δf under the coordinated frequency regulation of the doubly-fed wind turbine with comprehensive inertia control, the converter station with virtual inertia control and the synchronous generator set can be obtained. (5) In the index of measuring the ratio of the output to the input gain of the DFIG through the MMC-HVDC grid-connected system, the H2 and H ∞ norm are used to quantitatively measure the ability of the system to suppress the disturbance input signal. The transfer function G sys (s) characterizes the dynamic relationship between the frequency change of the DFIG wind farm through the MMC-HVDC grid-connected system and the active power load disturbance; for the detailed frequency response model of the system, the H2 norm of the transfer function between the system frequency change and the active power load disturbance reflects the average frequency response of the DFIG through the MMC-HVDC grid-connected system under the load disturbance input; H ∞ norm reflects the most severe frequency response of the DFIG through the MMC-HVDC grid-connected system under the load disturbance input and is used to evaluate the maximum frequency deviation of the system after being disturbed.

3. The frequency response analysis method of a wind power integrated into the grid system via MMC-HVDC based on the H2 and H ∞ norm as claimed in claim 1, characterized in that For the DFIG grid-connected system via MMC-HVDC, the calculation formulas for the H2 and H ∞ norms of its transfer function matrix G(s) are respectively as follows: where tr is the trace of the matrix; the superscript H represents the conjugate transpose; and max supσ is the maximum singular value of the system transfer function matrix.

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