Reactive angular frequency deviation feedforward control-based network construction type converter control method and system

Abstract

The invention discloses a grid-forming converter control method and system based on reactive angular frequency deviation feedforward control, and the method specifically comprises the steps: firstly building a simplified model of a grid-forming converter and a droop control strategy of the grid-forming converter, and obtaining a power transfer function and a droop control function of the grid-forming converter; updating a transmission power function of the network-forming converter according to the influence of the power grid resistance on the transient stability, and establishing a large-signal model in which only an active power loop contains inertia; and finally, according to the influence of the system damping ratio on overshoot, in a droop control strategy, performing feedforward control by using the reactive angular frequency deviation, amplifying and feedforward the angular frequency deviation generated by an active power loop to a reactive power loop, and controlling the grid-forming converter. According to the invention, no extra power supply circuit assembly needs to be connected, the frequency stability and the dynamic stability of the network construction type converter system can be improved through a simple control method, and the control cost of the network construction type converter is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a control method for a grid-connected converter based on reactive angular frequency deviation feedforward control. Background Art

[0002] With the continuous increase of clean energy such as wind power generation and photovoltaic power generation, power conversion equipment has been widely used in social production, transportation and consumption, playing an important role in the process of energy development. Although power electronic equipment has the advantages of fast response speed and flexible control method, it lacks the inertia and damping characteristics of traditional synchronous machines, and has poor anti-interference ability. When disturbances occur, the system's ability to maintain voltage and frequency stability is weak, and its stability problem will face huge challenges.

[0003] In order to improve the stability of the "double high" grid frequency and voltage, the concept of "grid-type converter" has begun to be proposed. The grid-type converter simulates the characteristics of a synchronous generator, making the power electronic device appear as a voltage source externally, thereby providing voltage and frequency support and enhancing the stability of the power system. This type of converter allows power electronic devices to operate both on and off the grid. Grid-type converters have been widely used in new energy power generation systems, and can effectively solve the problems of insufficient inertia support and poor voltage and frequency stability.

[0004] A typical representative of grid-type converters is a voltage source converter that uses amplitude and phase control or power synchronization control. In a power system lacking a synchronous machine, the lack of inertia causes large fluctuations in system frequency and voltage. Therefore, the frequency and voltage stability of the grid-type converter must be guaranteed to ensure the stability of the power system when disturbances occur. Summary of the invention

[0005] The object of the present invention is to provide a control method for a grid-type converter with strong frequency stability and transient stability, strong anti-disturbance capability and strong voltage stability capability.

[0006] The technical solution to achieve the purpose of the present invention is: a grid-connected converter control method based on reactive angular frequency deviation feedforward control, comprising the following steps:

[0007] Step 1: Establish a simplified model of a grid-type converter and a droop control strategy of the grid-type converter to obtain a power transfer function and a droop control function of the grid-type converter;

[0008] Step 2: According to the influence of grid resistance on transient stability, the transmission power function of the grid-connected converter is updated, and a large signal model with inertia of only the active power loop is established;

[0009] Step 3: According to the influence of the system damping ratio on the overshoot, in the droop control strategy, the reactive angular frequency deviation is used for feedforward control. The angular frequency deviation generated by the active power circuit is amplified and fed forward to the reactive power circuit to control the grid-type converter.

[0010] A grid-type converter control system based on reactive angular frequency deviation feedforward control, the system is used to implement the grid-type converter control method based on reactive angular frequency deviation feedforward control, the system includes a droop control strategy building module, a large signal model building module and a feedforward control module, wherein:

[0011] A droop control strategy building module is used to establish a simplified model of a grid-connected converter and a droop control strategy of the grid-connected converter, and obtain a power transfer function and a droop control function of the grid-connected converter;

[0012] A large signal model building module is used to update the transmission power function of the grid-type converter according to the influence of the grid resistance on transient stability, and to build a large signal model with inertia only for the active power loop;

[0013] The feedforward control module is used to perform feedforward control using reactive angular frequency deviation in the droop control strategy according to the influence of the system damping ratio on the overshoot. The angular frequency deviation generated by the active power circuit is amplified and fed forward to the reactive power circuit to control the grid-type converter.

[0014] A mobile terminal comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the program, the control method of a grid-connected converter based on reactive angular frequency deviation feedforward control is implemented.

[0015] Compared with the prior art, the present invention has the following significant advantages: (1) the present invention reduces the overshoot of the system output by increasing the damping ratio of the system, increases the damping ratio of the power loop, reduces the overshoot of the frequency of the grid-type converter system, and enhances the frequency stability of the grid-type converter system; (2) the present invention uses droop control to generate a power angle and a reference voltage, uses a voltage-current loop control structure, and the inner loop uses inductor current feedback to better suppress the output LC filter resonance and the inherent overcurrent protection implementation capability, thereby improving the dynamic stability of the system; (3) angular frequency deviation feedforward is used in front of the reactive power control loop to improve the damping ratio of the grid-type converter system, thereby improving the frequency stability of the grid-type converter system; (4) the frequency stability of the grid-type converter system can be improved by a simple control method without connecting any additional power circuit components, thereby reducing the control cost of the grid-type converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1It is a flow chart of a control method of a grid-type converter based on reactive angular frequency deviation feedforward control of the present invention.

[0017] Figure 2 It is a system principle diagram of the grid-type converter in the present invention.

[0018] Figure 3 It is a simplified model diagram of the grid-type converter in the present invention.

[0019] Figure 4 is the different grid resistance R in the embodiments of the present invention gs The P–δ curve below.

[0020] Figure 5 It is a schematic diagram of the principle of reactive angular frequency deviation feedforward control in an embodiment of the present invention.

[0021] Figure 6 Schematic diagram of the structure of a small signal model with an angular frequency deviation feedforward path in an embodiment of the present invention.

[0022] Figure 7 It is a simulation waveform diagram of grid voltage sag when K=0 in an embodiment of the present invention.

[0023] Figure 8 It is a simulation waveform diagram of grid voltage sag when K=2000 in an embodiment of the present invention.

[0024] Fig. 9 It is a simulation waveform diagram of grid voltage sag when K=4000 in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention provides a control method for a grid-connected converter based on reactive angular frequency deviation feedforward control, comprising the following steps:

[0026] Step 1: Establish a simplified model of a grid-type converter and a droop control strategy of the grid-type converter to obtain a power transfer function and a droop control function of the grid-type converter;

[0027] Step 2: According to the influence of grid resistance on transient stability, the transmission power function of the grid-connected converter is updated, and a large signal model with inertia of only the active power loop is established;

[0028] Step 3: According to the influence of the system damping ratio on the overshoot, in the droop control strategy, the reactive angular frequency deviation is used for feedforward control. The angular frequency deviation generated by the active power circuit is amplified and fed forward to the reactive power circuit to control the grid-type converter.

[0029] As a specific example, the simplified model of the grid-type converter and the droop control strategy of the grid-type converter described in step 1 are established to obtain the power transfer function and droop control function of the grid-type converter, which are specifically as follows:

[0030] Step 1.1, establish a simplified model of the grid-type converter, and obtain the active power transfer function P and reactive power transfer function Q of the grid-type converter according to the simplified model of the grid-type converter:

[0031]

[0032] Among them, V g is the voltage amplitude of the grid-connected converter, V s is the grid voltage, δ is the phase difference between the grid-connected converter and the grid, i.e., the power angle; R gs is the grid resistance, X gs is the grid reactance;

[0033] Step 1.2: Based on the droop control strategy, obtain the droop control function:

[0034] dω / dt=K pf (P ref -P)-ω p (ω-ω0)

[0035] V mref =V0+K qv (Q ref -Q)

[0036] Among them, ω0 is the rated angular frequency of the grid-type converter, ω is the active power loop output angular frequency, ω p is the active power loop low-pass filter cut-off frequency, K pf is the droop gain of active power control, P ref is the reference active power of the grid-type converter, V0 is the system reference voltage, V mref is the reference voltage of the grid-connected converter, K qv is the droop gain of reactive power control, Q ref is the reference reactive power of the grid-connected converter.

[0037] As a specific example, in step 2, according to the influence of the grid resistance on transient stability, the transmission power function of the grid-connected converter is updated as follows:

[0038] According to the active power transfer function P, reactive power transfer function Q and droop control function, the P-δ relationship is obtained:

[0039]

[0040] in, B=1.5k1K qv V g cosδ+1.5k2K qv V g sinδ-1;

[0041] According to the P-δ relationship, the maximum power P that the grid-type converter can transmit is max With grid resistance R gs increases, and the grid resistance R gs The larger the value, the wider the allowable variation range of the power angle δ, which is more conducive to the synchronization stability during grid failure. Therefore, the grid resistance R is set gs =0, update the active power transfer function P and reactive power transfer function Q as follows:

[0042]

[0043] As a specific example, in step 2, a large signal model containing inertia of only the active power loop is established, as follows:

[0044] According to the power transfer function and the droop control function, since V g =V mref , so the second-order differential equation about δ is:

[0045]

[0046] Let x = [x1, x2] T =[δ,Δω], Δω is the angular frequency deviation, and the superscript T represents the transpose of the matrix or vector. The reduced-order state space model of the grid-type converter, i.e., the large signal model, is obtained as follows:

[0047]

[0048] As a specific example, in step 3, according to the influence of the system damping ratio on the overshoot, in the droop control strategy, the reactive angular frequency deviation is used for feedforward control, the angular frequency deviation generated by the active power circuit is amplified and fed forward to the reactive power circuit, and the grid-type converter is controlled as follows:

[0049] Step 3.1, since the power loop of the grid-type converter is an under-damped power loop, increasing the damping ratio of the system can reduce the overshoot of the system output, so a reactive angular frequency deviation feedforward control method is adopted to increase the damping ratio of the power loop, thereby reducing the overshoot of the grid-type converter system frequency;

[0050] Step 3.2: Determine a small signal model with a frequency feedforward path, amplify the angular frequency deviation generated by the active power loop, feed forward to the reactive power loop, and control the grid-type converter.

[0051] As a specific example, in step 3.1, the reactive power loop function is:

[0052] V mref =V0+K qv (Q ref +Q)+KK qv Δω

[0053] Among them, Δω is the angular frequency deviation, and K is the amplification factor.

[0054] As a specific example, in step 3.2, a small signal model with a frequency feedforward path is determined as follows:

[0055] Combining the power transfer function, we get the second-order differential equation about δ:

[0056]

[0057] Where f(δ,Δω)=V g sinδ;

[0058] but

[0059]

[0060] Where V pccs Indicates the system output voltage after the fault, δ s is the power angle of the equilibrium point after the fault;

[0061] In order to obtain a specific small signal model of the frequency feedforward path, let

[0062]

[0063] Therefore, a small signal model with a frequency feedforward path is obtained, resulting in a small signal transfer function between Δδ and Δω:

[0064]

[0065] As a specific example, step 3 also includes:

[0066] Step 3.3: Analyze the influence of reactive angular frequency deviation feedforward control method on frequency stability and transient stability, as follows:

[0067] The small signal transfer function is rearranged to:

[0068]

[0069] Among them, ω n is the undamped oscillation frequency, and ζ is the damping ratio:

[0070]

[0071] Therefore, the response of the power angle and frequency changes in the time domain is:

[0072]

[0073] When the derivative of Δδ(t) with respect to time t is equal to 0, Δδ(t) takes the maximum value Δδ max ,at this time:

[0074]

[0075] Δδ max It is related to the damping ratio ζ, and Δδ max Taking the derivative of ζ, we get:

[0076]

[0077] δ max It decreases monotonically with the increase of ζ, which means that increasing the damping ratio ζ can enhance the transient stability of the system;

[0078] When the derivative of Δω(t) with respect to time t is equal to 0, Δω(t) reaches its maximum value, and we get:

[0079]

[0080] Maximum frequency deviation Δω max It is inversely proportional to the damping ratio ζ, so increasing the damping ratio ζ can increase the frequency stability of the grid-type converter;

[0081] System voltage V at fault pccs =V s , so f'(Δω)>0; with the increase of K, f'(Δω) increases, G2 also increases, so the damping ratio ζ increases with the increase of K; therefore, adding an additional frequency feedforward path with a larger K, thereby producing a larger damping ratio, enhances the synchronous stability and is beneficial to the frequency stability during grid faults.

[0082] The present invention provides a grid-type converter control system based on reactive angular frequency deviation feedforward control, the system is used to implement the grid-type converter control method based on reactive angular frequency deviation feedforward control, the system includes a droop control strategy building module, a large signal model building module and a feedforward control module, wherein:

[0083] A droop control strategy building module is used to establish a simplified model of a grid-connected converter and a droop control strategy of the grid-connected converter, and obtain a power transfer function and a droop control function of the grid-connected converter;

[0084] A large signal model building module is used to update the transmission power function of the grid-type converter according to the influence of the grid resistance on transient stability, and to build a large signal model with inertia only for the active power loop;

[0085] The feedforward control module is used to perform feedforward control using reactive angular frequency deviation in the droop control strategy according to the influence of the system damping ratio on the overshoot. The angular frequency deviation generated by the active power circuit is amplified and fed forward to the reactive power circuit to control the grid-type converter.

[0086] The present invention provides a mobile terminal, comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the grid-type converter control method based on reactive angular frequency deviation feedforward control as described in any one of claims 1 to 8 when executing the program.

[0087] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0088] Example

[0089] like Figure 1 As shown, the present invention provides a control method for a grid-connected converter based on reactive angular frequency deviation feedforward control, comprising the following steps:

[0090] Step 1: Establish a simplified model of a grid-type converter and a droop control strategy of the grid-type converter, and obtain a power transfer function and a droop control function of the grid-type converter, as follows:

[0091] The schematic diagram of the grid-type converter system is as follows: Figure 2 Its equivalent circuit is shown as Figure 3 As shown in FIG. 1 , the control structure of the grid-type converter includes a multi-loop control structure of an active power loop, a reactive power loop, an inner current loop, and an outer voltage loop. The active power loop can obtain the phase angle of the system, the reactive power loop can obtain the reference voltage of the system, and the active power loop and the reactive power loop can adopt droop control, wherein the active power loop has inertia. The voltage loop and the current loop can use traditional proportional integral PI controllers respectively.

[0092] Step 1.1, establish a simplified model of the grid-type converter, and obtain the active power transfer function P and reactive power transfer function Q of the grid-type converter according to the simplified model of the grid-type converter:

[0093]

[0094] Among them, V g is the voltage amplitude of the grid-connected converter, V s is the grid voltage, δ is the phase difference between the grid-connected converter and the grid, i.e., the power angle; Rgs is the grid resistance, X gs is the grid reactance;

[0095] Step 1.2: Based on the droop control strategy, obtain the droop control function:

[0096]

[0097] Where ω0 is the rated angular frequency of the grid-connected converter, ω is the active power loop output angular frequency, K pf is the droop gain of active power control, P ref is the reference active power of the grid-type converter, V0 is the system reference voltage, V mref is the reference voltage of the grid-connected converter, K qv is the droop gain of reactive power control, Q ref is the reference reactive power of the grid-connected converter.

[0098] Step 2: According to the influence of grid resistance on transient stability, update the transmission power function of the grid-connected converter and establish a large signal model with only active power loop and inertia, as follows:

[0099] Step 2.1: According to the active power transfer function P, the reactive power transfer function Q and the droop control function, the P-δ relationship is obtained:

[0100]

[0101] in, B=1.5k1K qv V g cosδ+1.5k2K qv V g sinδ-1;

[0102] According to the P-δ relationship, we can get Figure 4 ,Depend on Figure 4 It can be seen that the maximum power P that can be transmitted by the grid-type converter is max With grid resistance R gs increases, and the grid resistance R gs The larger the grid resistance R is, the wider the allowable variation range of the power angle δ is, and the more conducive it is to the synchronization stability during grid failure. gs =0, update the active power transfer function P and reactive power transfer function Q as follows:

[0103]

[0104] Step 2.2: According to the power transfer function and the droop control function, since V g =V mref, so the second-order differential equation about δ can be obtained as:

[0105]

[0106] Let x = [x1, x2] T =[δ, Δω], the reduced-order state space model of the grid-connected converter, i.e., the large signal model, can be obtained as:

[0107]

[0108] Step 3: According to the influence of the system damping ratio on the overshoot, in the droop control strategy, the reactive angular frequency deviation is used for feedforward control. The angular frequency deviation generated by the active power circuit is amplified and fed forward to the reactive power circuit to control the grid-type converter. The details are as follows:

[0109] Step 3.1: Since the power loop of the grid-type converter is an under-damped power loop, increasing the damping ratio of the system can reduce the overshoot of the system output. Therefore, the reactive angular frequency deviation feedforward control method can be used to increase the damping ratio of the power loop, thereby reducing the overshoot of the grid-type converter system frequency, such as Figure 5 As shown, the reactive power loop function is:

[0110] V mref =V0+K qv (Q ref +Q)+KK qv Δω

[0111] Among them, Δω is the angular frequency deviation, K is the amplification factor;

[0112] Step 3.2: Determine the small signal model with the frequency feedforward path as follows:

[0113] Combined with the power transfer function, the second-order differential equation for δ can be obtained:

[0114]

[0115] Where f(δ,Δω)=V g sinδ;

[0116] but

[0117]

[0118] In order to obtain a specific small signal model of the frequency feedforward path, let

[0119]

[0120] Therefore, a small signal model with a frequency feedforward path can be obtained, such as Figure 6As shown by Figure 6 The small signal transfer function between Δδ and Δω can be obtained:

[0121]

[0122] Step 3.3: Analyze the influence of reactive angular frequency deviation feedforward control method on frequency stability and transient stability, as follows:

[0123] Arranging the small signal transfer function yields:

[0124]

[0125] Among them, ω n is the undamped oscillation frequency, and ζ is the damping ratio:

[0126]

[0127] Therefore, the response of the power angle and frequency changes in the time domain is:

[0128]

[0129] When the derivative of Δδ(t) with respect to time t is equal to 0, Δδ(t) takes the maximum value Δδ max ,at this time:

[0130]

[0131] It can be seen that Δδ max It is related to the damping ratio ζ, and Δδ max Taking the derivative of ζ, we get:

[0132]

[0133] It can be seen that δ max It decreases monotonically with the increase of ζ, which means that increasing the damping ratio ζ can enhance the transient stability of the system;

[0134] When the derivative of Δω(t) with respect to time t is equal to 0, Δω(t) reaches its maximum value, and we can obtain:

[0135]

[0136] Maximum frequency deviation Δω max It is inversely proportional to the damping ratio ζ, so increasing the damping ratio ζ can increase the frequency stability of the grid-type converter;

[0137] System voltage V at fault pccs =V s, so f'(Δω)>0; with the increase of K, f'(Δω) increases, G2 also increases, so the damping ratio ζ increases with the increase of K; therefore, adding an additional frequency feedforward path with a larger K, thereby producing a larger damping ratio, enhances the synchronous stability and is beneficial to the frequency stability during grid faults.

[0138] In order to verify the superiority of the control method provided by the present invention, this embodiment is simulated and analyzed in MATLAB / simulink, and the system parameters are shown in Table 1.

[0139] Table 1 System parameters

[0140] parameter Value <![CDATA[V0]]> 100V <![CDATA[V s ]]> 100V <![CDATA[V g_ref ]]> 100V f 50Hz <![CDATA[L gs ]]> 2.5mH <![CDATA[K pf ]]> 0.00628 <![CDATA[K qv ]]> 0.005

[0141] The simulation results are as follows Figure 7 , Figure 8 , Fig. 9 As shown, Figure 7 It is the simulation waveform of the grid voltage sag when K=0. When the angular frequency deviation coefficient K is 0, when there is no voltage sag in the grid-type converter, the grid-type converter can work normally, and Vg, Pg and ωg remain unchanged as expected. When the grid voltage drops, the grid voltage Vs drops from 100V to 30V, the first type of fault occurs in the grid-type converter, ωg fluctuates, and stabilizes again after the fluctuation. According to Figure 7 It can be found that the maximum value of the frequency change Δωmax is 5.7rad / s. At this time, the frequency change rate is large and the frequency stability is poor. In order to ensure the frequency stability of the grid-type converter, it is necessary to increase the angular frequency deviation coefficient K, thereby increasing the damping ratio ζ, and then increasing the frequency stability and transient stability of the grid-type converter;

[0142] Figure 8 This is the simulation waveform of the grid voltage sag when K=2000. When the angular frequency deviation coefficient K is 2000, when there is no voltage sag in the grid-type converter, the grid-type converter can work normally, and Vg, Pg and ωg remain unchanged as expected. When the grid voltage drops, the grid voltage Vs drops from 100V to 30V, the first type of fault occurs in the grid-type converter, ωg fluctuates, and stabilizes again after the fluctuation. According to Figure 8 It can be found that the maximum value of the frequency change Δωmax is 3.4rad / s. At this time, the frequency change rate is reduced compared with no reactive angular frequency deviation feedforward, but the frequency stability is still poor. However, compared with K=0, the frequency stability has been enhanced.

[0143] Fig. 9This is the simulation waveform of the grid voltage sag when K=4000. When the angular frequency deviation coefficient K is 4000, when the grid-type converter does not experience a voltage sag, the grid-type converter can work normally, and Vg, Pg and ωg remain unchanged as expected. When the grid voltage drops, the grid-type converter has a first-class fault, ωg fluctuates, and stabilizes again after the fluctuation. Fig. 9 It can be found that the maximum value of the frequency change Δωmax is 1.5rad / s, at which point the frequency change rate is further reduced, the frequency stability is stronger, and the frequency stability is further enhanced;

[0144] It can be seen that when a grid fault occurs, adding an additional frequency feed-forward path with a larger K, resulting in a larger damping ratio, enhances the synchronization stability and is beneficial to the frequency stability during the grid fault.

[0145] The above are only preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A grid-connected converter control method based on reactive angular frequency deviation feedforward control, characterized in that: The following steps are involved: Step 1: Establish a simplified model of a grid-type converter and a droop control strategy of the grid-type converter to obtain a power transfer function and a droop control function of the grid-type converter; Step 2: According to the influence of grid resistance on transient stability, the transmission power function of the grid-connected converter is updated, and a large signal model with inertia of only the active power loop is established; Step 3: According to the influence of the system damping ratio on the overshoot, in the droop control strategy, the reactive angular frequency deviation is used for feedforward control. The angular frequency deviation generated by the active power circuit is amplified and fed forward to the reactive power circuit to control the grid-type converter.

2. The grid-connected converter control method based on reactive angular frequency deviation feedforward control according to claim 1 is characterized in that: The simplified model of the grid-type converter and the droop control strategy of the grid-type converter described in step 1 are established to obtain the power transfer function and droop control function of the grid-type converter, which are specifically as follows: Step 1.1, establish a simplified model of the grid-type converter, and obtain the active power transfer function P and reactive power transfer function Q of the grid-type converter according to the simplified model of the grid-type converter: Among them, V g is the voltage amplitude of the grid-connected converter, V s is the grid voltage, δ is the phase difference between the grid-connected converter and the grid, i.e., the power angle; R gs is the grid resistance, X gs is the grid reactance; Step 1.2: Based on the droop control strategy, obtain the droop control function: dωdt=K pf (P ref -P)-ω p (oh-oh0) V mref =V0+K qv (Q ref -Q) Among them, ω0 is the rated angular frequency of the grid-type converter, ω is the active power loop output angular frequency, ω p is the active power loop low-pass filter cut-off frequency, K pf is the droop gain of active power control, P ref is the reference active power of the grid-type converter, V0 is the system reference voltage, V mref is the reference voltage of the grid-connected converter, K qv is the droop gain of reactive power control, Q ref is the reference reactive power of the grid-connected converter.

3. The grid-connected converter control method based on reactive angular frequency deviation feedforward control according to claim 2 is characterized in that: In step 2, according to the influence of grid resistance on transient stability, the transmission power function of the grid-connected converter is updated as follows: According to the active power transfer function P, reactive power transfer function Q and droop control function, the P-δ relationship is obtained: in, B=1.5k1K qv V g cosδ+1.5k2K qv V g sinδ-1; According to the P-δ relationship, the maximum power P that the grid-connected converter can transmit is max With grid resistance R gs increases, and the grid resistance R gs The larger the value, the wider the allowable variation range of the power angle δ, which is more conducive to the synchronization stability during grid failure. Therefore, the grid resistance R is set gs =0, update the active power transfer function P and reactive power transfer function Q as follows:

4. The grid-connected converter control method based on reactive angular frequency deviation feedforward control according to claim 3 is characterized in that: In step 2, a large signal model containing inertia of only the active power loop is established, as follows: According to the power transfer function and the droop control function, since V g =V mref , so the second-order differential equation about δ is: Let x = [x1, x2] T =[δ,Δω], Δω is the angular frequency deviation, and the superscript T represents the transpose of the matrix or vector. The reduced-order state space model of the grid-type converter, i.e., the large signal model, is obtained as follows:

5. The grid-connected converter control method based on reactive angular frequency deviation feedforward control according to claim 4 is characterized in that: In step 3, according to the influence of the system damping ratio on the overshoot, in the droop control strategy, the reactive angular frequency deviation is used for feedforward control, the angular frequency deviation generated by the active power circuit is amplified and fed forward to the reactive power circuit to control the grid-type converter, as follows: Step 3.1, since the power loop of the grid-type converter is an under-damped power loop, increasing the damping ratio of the system can reduce the overshoot of the system output, so a reactive angular frequency deviation feedforward control method is adopted to increase the damping ratio of the power loop, thereby reducing the overshoot of the grid-type converter system frequency; Step 3.2: Determine a small signal model with a frequency feedforward path, amplify the angular frequency deviation generated by the active power loop, feed forward to the reactive power loop, and control the grid-type converter.

6. The grid-connected converter control method based on reactive angular frequency deviation feedforward control according to claim 5 is characterized in that: In step 3.1, the reactive power loop function is: V mref =V0+K qv (Q ref +Q)+KK qv Δω Among them, Δω is the angular frequency deviation, and K is the amplification factor.

7. The grid-connected converter control method based on reactive angular frequency deviation feedforward control according to claim 6 is characterized in that: In step 3.2, the small signal model with the frequency feedforward path is determined as follows: Combining the power transfer function, we get the second-order differential equation about δ: Where f(δ,Δω)=V g sinδ; but Where V pccs Indicates the system output voltage after the fault, δ s is the power angle of the equilibrium point after the fault; In order to obtain a specific small signal model of the frequency feedforward path, let Therefore, a small signal model with a frequency feedforward path is obtained, resulting in a small signal transfer function between Δδ and Δω:

8. The grid-connected converter control method based on reactive angular frequency deviation feedforward control according to claim 7 is characterized in that: Step 3 also includes: Step 3.3: Analyze the influence of reactive angular frequency deviation feedforward control method on frequency stability and transient stability, as follows: The small signal transfer function is rearranged to: Among them, ω n is the undamped oscillation frequency, and ζ is the damping ratio: Therefore, the response of the power angle and frequency changes in the time domain is: When the derivative of Δδ(t) with respect to time t is equal to 0, Δδ(t) takes the maximum value Δδ max ,at this time: Δδ max It is related to the damping ratio ζ, and Δδ max Taking the derivative of ζ, we get: δ max It decreases monotonically with the increase of ζ, which means that increasing the damping ratio ζ can enhance the transient stability of the system; When the derivative of Δω(t) with respect to time t is equal to 0, Δω(t) reaches its maximum value, and we get: Maximum frequency deviation Δω max It is inversely proportional to the damping ratio ζ, so increasing the damping ratio ζ can increase the frequency stability of the grid-type converter; System voltage V at fault pccs =V s , so f'(Δω)>0; as K increases, f'(Δω) increases, G2 also increases, so the damping ratio ζ increases with the increase of K.

9. A grid-connected converter control system based on reactive angular frequency deviation feedforward control, characterized in that: The system is used to implement the grid-connected converter control method based on reactive angular frequency deviation feedforward control according to any one of claims 1 to 8, and the system includes a droop control strategy building module, a large signal model building module and a feedforward control module, wherein: A droop control strategy building module is used to establish a simplified model of a grid-connected converter and a droop control strategy of the grid-connected converter, and obtain a power transfer function and a droop control function of the grid-connected converter; A large signal model building module is used to update the transmission power function of the grid-type converter according to the influence of the grid resistance on transient stability, and to build a large signal model with inertia only for the active power loop; The feedforward control module is used to perform feedforward control using reactive angular frequency deviation in the droop control strategy according to the influence of the system damping ratio on the overshoot. The angular frequency deviation generated by the active power circuit is amplified and fed forward to the reactive power circuit to control the grid-type converter.

10. A mobile terminal comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the grid-connected converter control method based on reactive angular frequency deviation feedforward control as described in any one of claims 1 to 8 is implemented.

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