Composite Current Synchronous Control Method, Device and Computer Readable Storage Medium for Grid-Forming Inverters

Abstract

The present application discloses a composite current synchronization control method, device and computer-readable storage medium for a network-forming inverter, belonging to the technical field of inverter control. In the synchronization control loop, the d-axis and q-axis grid-connected current components are symmetrically introduced, respectively subtracted from the reference values and passed through inertia and droop links to output double angular frequency adjustment amounts, which are combined to generate a synchronization angular frequency adjustment amount, and further passed through an integration link to obtain the required synchronization phase angle θ. The present application omits the instantaneous power calculator in the traditional network-forming control, and uses the d-axis and q-axis grid current components of the system to realize the synchronization of the network-forming inverter and the grid voltage, which can effectively enhance the robustness of the network-forming inverter to grid impedance changes and also has better synchronization stability under a strong grid.

Description

Technical Field

[0001] The present application relates to the field of inverter control, and particularly to a composite current synchronization control method, device, and computer-readable storage medium for a grid-forming inverter. Background Art

[0002] As the connection interface between new energy distributed generation systems and the power grid, grid-connected inverters play a crucial role in the new power system. With the increasing penetration rate of new energy, some grid-connected inverters need to switch from the traditional current source control mode to the voltage source control mode. Such inverters are called grid-forming inverters, and their main function is to construct the grid voltage and frequency, providing basic support for the stable operation of the power system.

[0003] Relevant research results show that grid-forming inverters exhibit good stability under weak grid conditions and can effectively maintain system operation. However, under strong grid conditions, their synchronization performance is relatively weak, and sub- / supra-synchronous oscillation problems are likely to occur. In addition, due to the intermittent, random, and volatile characteristics of high-proportion new energy generation, the grid impedance will undergo dynamic changes in strength properties, which undoubtedly poses a severe challenge to the safe, stable, and high-quality operation of grid-forming inverters connected to the grid. Existing improvement strategies usually enhance synchronization stability by introducing additional damping links or virtual impedance control based on traditional power synchronization control. However, existing strategies still have certain limitations and urgently need further innovation and optimization to meet the growing new energy grid connection requirements. Summary of the Invention

[0004] The present application aims to provide a composite current synchronization control method, device, and computer-readable storage medium for a grid-forming inverter with strong robustness.

[0005] To achieve the above object, the technical solution of the present application is as follows:

[0006] A composite current synchronization control method for a grid-forming inverter includes the following steps:

[0007] Step S1, detecting the inductor current i L_x , and performing a coordinate transformation to obtain the inductor current dq in the i L_n coordinate system; detecting the grid current i g_x , and performing a coordinate transformation to obtain the grid current dq in the i g_n coordinate system; detecting the output voltage v o_x , and performing a coordinate transformation to obtain the output voltage dq in thev o_n ; Among them, the subscript x represents a , b , c , the subscript n represents d, q ;

[0008] Step S2, according to d the shaft grid current reference value i gref_d and d the shaft grid current i g_d , calculate d the shaft angular frequency adjustment amount Δ ω d ;

[0009] Step S3, according to q the shaft grid current reference value i gref_q and q the shaft grid current i g_q , calculate q the shaft angular frequency adjustment amount Δ ω q ;

[0010] Step S4, according to d the shaft angular frequency adjustment amount Δ ω d , q the shaft angular frequency adjustment amount Δ ω q and the rated angular frequency ω n , calculate the output voltage phase angle of the grid-forming inverter θ ;

[0011] Step S5, according to q the shaft grid current reference value i gref_q , the grid-connected rated voltage amplitude V n and q the shaft grid current i g_q , calculate the output voltage amplitude reference of the grid-forming inverter V ref ;

[0012] Step S6, according to the output voltage phase angle of the grid-forming inverter θ and the output voltage amplitude reference of the grid-forming inverter V ref , use the voltage reference calculation formula to obtain the output voltage reference value voref_n ; The output voltage reference value v oref_n includes: d The output voltage reference value in the axial direction v oref_d and q The output voltage reference value in the axial direction v oref_q ;

[0013] Step S7, sending the error between the output voltage reference value v oref_n and the output voltage v o_n to the voltage controller G v , obtaining the inductor current reference value i Lref_n ; Sending the error between the inductor current reference value i Lref_n and the inductor current i L_n to the current controller G i , obtaining the modulation wave v m_n ; Converting the modulation wave v m_n to the three-phase stationary coordinate system to obtain v m_x , and generating a PWM control signal through sinusoidal pulse width modulation.

[0014] Optionally, step S2 includes subtracting the d axis grid current reference value i gref_d from the d axis grid current i g_d , and then multiplying by the inertia link m d ω d / ( s + ω d ) to generate the d axis angular frequency adjustment amount Δ ω d ; where m d is the d axis grid-connected current-frequency droop coefficient, ω d is the corner frequency of the inertia link, s is the Laplace coefficient.

[0015] Optionally, in step S3, the qAxis grid current reference value i gref_q and q Axis grid current i g_q take the difference, and then multiply by the high-pass filter section m q s / ( s + ω c ) to generate q Axis angular frequency adjustment amount Δ ω q ; where m q is q Axis grid-connected current - frequency droop coefficient, ω c is the corner frequency of the high-pass filter.

[0016] Optionally, in step S4, add d Axis angular frequency adjustment amount Δ ω d 、 q Axis angular frequency adjustment amount Δ ω q and the rated angular frequency ω n and pass through the integral link 1 / s to obtain the phase angle θ of the output voltage of the network-forming inverter.

[0017] Optionally, in step S5, take the difference between q Axis grid current reference value i gref_q and q Axis grid current i g_q multiply by the inertia link n q ω q / ( s + ω q ) to generate the voltage change amount ΔV, and add the voltage change amount ΔV to the rated grid-connected voltage amplitude V n to obtain the amplitude reference V ref of the output voltage of the network-forming inverter, where n q is q Axis grid-connected current - voltage droop coefficient, ω q is the corner frequency of the inertia link.

[0018] Optionally, in step S6, the voltage reference calculation formula is:

[0019] ,

[0020] .

[0021] Optionally, the voltage controller G v is a PI regulator.

[0022] Optionally, the current controller G i is a proportional-integral controller.

[0023] A device, comprising: one or more processors; a memory for storing one or more programs, which when executed by the one or more processors cause the one or more processors to execute a method for composite current synchronization control of a network-forming inverter as described in any one of the above.

[0024] A computer-readable storage medium storing a computer program, which when executed by a processor implements a method for composite current synchronization control of a network-forming inverter as described in any one of the above.

[0025] The method for composite current synchronization control of a network-forming inverter provided by this application utilizes the d axis and q axis grid current components to achieve synchronization between the network-forming inverter and the grid voltage, omitting the instantaneous power calculation link in the traditional control of the network-forming inverter, enabling the network-forming inverter to operate reliably and stably, effectively improving the robustness of the network-forming inverter to grid impedance changes and its stability under strong grid conditions, thereby achieving plug-and-play in the grid.

[0026] To make the above features and advantages of the application more obvious and understandable, specific embodiments are hereinafter given and detailed descriptions are provided in conjunction with the accompanying drawings as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of the system structure of a network-forming inverter under a traditional control method.

[0028] Figure 2 is a flowchart of the method for composite current synchronization control of a network-forming inverter provided by this application.

[0029] Figure 3 is a circuit block diagram of a network-forming inverter under the method for composite current synchronization control of a network-forming inverter provided by this application.

[0030] Figure 4The simulation waveform diagrams of the active power P and reactive power Q output by the network-forming inverter using the network-forming inverter composite current synchronization control method provided in this application and the traditional control method respectively under strong grid conditions.

[0031] Figure 5 The simulation waveform diagram of the voltage output by the network-forming inverter using the network-forming inverter composite current synchronization control method provided in this application and the traditional control method respectively under strong grid conditions.

[0032] Figure 6 The simulation waveform diagram of the current output by the network-forming inverter using the network-forming inverter composite current synchronization control method provided in this application and the traditional control method respectively under strong grid conditions. Detailed implementation manners

[0033] To make the objectives and technical solutions of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this application. Obviously, the described embodiments are some but not all of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of this application without creative efforts shall fall within the scope of protection of this application.

[0034] Please refer to Figure 1 , Figure 1 The control block diagram of the network-forming inverter under the traditional control mode. The network-forming inverter 1 includes: a three-phase inverter bridge 111, an LC filter 112, and a common power grid 113, which are connected in sequence. Among them, the three-phase inverter bridge 111 includes a DC power supply V dc , a capacitor C dc1 , a capacitor C dc2 , and a switching unit 1111; the LC filter 112 includes three groups of filter inductors L f and a filter capacitor C f ; the common power grid 113 includes a three-phase voltage source v g and an equivalent grid impedance Z g .

[0035] Furthermore, Figure 1It also includes: an active - frequency synchronization controller 12, a reactive - voltage synchronization controller 13, a network - forming inverter controller 14, and an instantaneous power calculator 15. The instantaneous power calculator 15 is respectively connected to the first ends of the active - frequency synchronization controller 12 and the reactive - voltage synchronization controller 13, and the second ends of the active - frequency synchronization controller 12 and the reactive - voltage synchronization controller 13 are respectively connected to the network - forming inverter controller 14.

[0036] Among them, the network - forming inverter controller 14 includes: abc / dq a coordinate transformer 141, a voltage - current double - closed - loop controller 142, and an SPWM controller 143; abc / dq The first end of the coordinate transformer 141 is connected to the active - frequency synchronization controller 12, abc / dq the second end of the coordinate transformer 141 is connected to the LC filter 112, the first end of the voltage - current double - closed - loop controller 142 is connected to the second ends of the active - frequency synchronization controller 12 and the reactive - voltage synchronization controller 13, the second end of the voltage - current double - closed - loop controller 142 is connected to the first end of the SPWM controller 143, and the second end of the SPWM controller 143 is connected to the three - phase inverter bridge 111.

[0037] In Figure 1 this structure, the traditional control method is to first input the output voltage dq in the v o_n coordinate system and the grid - connected current i g_n to the instantaneous power calculator 15, obtaining the active power P and the reactive power Q . The active power P obtains the phase angle of the output voltage of the network - forming inverter through the active - frequency synchronization controller 12, and the reactive power Q obtains the reference value V ref of the output voltage of the network - forming inverter through the reactive - voltage synchronization controller 13. Then, through the voltage - current double - closed - loop controller 142, the tracking of the command value is realized, thus playing a role in voltage support. Finally, the SPWM controller 143 modulates and outputs a PWM wave. Among them, the output voltage v o_n and the grid - connected current i g_n are sampled by abc / dq the coordinate transformer 141, and the subscript n represents d, q .

[0038] Please refer to Figure 2 and Figure 3 as Figure 3 shown, adjust the active - frequency synchronization controller 12 in Figure 1 to the grid - connected current - frequency synchronization controller 32 in Figure 3 , where the d - axis grid - connected current - frequency synchronization controller 321 and d the q - axis grid - connected current - frequency synchronization controller 322 are combined; adjust the reactive - voltage synchronization controller 13 in Figure 1 to the q - axis grid - connected current - amplitude synchronization controller 33 in Figure 3 ; q The first ends of the d - axis grid - connected current - frequency synchronization controller 321 and d the q - axis grid - connected current - frequency synchronization controller 322 are connected and then connected to the first ends of the q / abc coordinate converter 341 and the voltage - current double - closed - loop controller 342; dq The second end of the q - axis grid - connected current - frequency synchronization controller 322 is connected to the first end of the q q - axis grid - connected current - amplitude synchronization controller 33; q The second end of the q - axis grid - connected current - amplitude synchronization controller 33 is connected to the first end of the voltage - current double - closed - loop controller 342. Compared with q , the instantaneous power calculator 15 in the traditional network - forming control is omitted. Figure 1

[0039] Please continue to refer to Figure 2 Figure 3 and Figure 2 , the control method provided by the present invention includes the following steps: Figure 3

[0040] i Step S1, detect the inductor current dq L_x , and perform a coordinate transformation to obtain the inductor current in the i coordinate system i L_n ; detect the grid current dq g_x , and perform a coordinate transformation to obtain the grid current in the i coordinate system v g_n ; detect the output voltage dq o_x , and perform a coordinate transformation to obtain the output voltage in the v coordinate system x o_n ; where the subscript a represents b , c , n, subscript n indicates d, q .

[0041] Step S2, in d the d-axis grid-connected current-frequency synchronization controller 321, receive d the d-axis grid current i g_d , according to d the d-axis grid current reference value i gref_d and d the d-axis grid current i g_d , calculate d the d-axis angular frequency adjustment amount Δ ω d .

[0042] As an example, subtract d the d-axis grid current reference value i gref_d from d the d-axis grid current i g_d , then multiply by the inertia link m d ω d / (s + ω d ) to generate d the d-axis angular frequency adjustment amount Δ ω d . Wherein, m d is d the d-axis grid-connected current-frequency droop coefficient, ω d is the corner frequency of the inertia link, s is the Laplace coefficient.

[0043] Step S3, in q the q-axis grid-connected current-frequency synchronization controller 322, receive q the q-axis grid current i g_q , according to q the q-axis grid current reference value i gref_q and q the q-axis grid current i g_q , calculate q the q-axis angular frequency adjustment amount Δ ω q .

[0044] As an example, subtract q the q-axis grid current reference value igref_q Subtract from q the grid current of the i g_q axis, then multiply by the high-pass filter section m q s / ( s + ω c ) to generate q the angular frequency regulation amount Δ ω q . Among them, m q is q the angular frequency droop coefficient of the grid-connected current of the ω c axis, and

[0045] Step S4, according to d the angular frequency regulation amount Δ ω d , q the angular frequency regulation amount Δ ω q and the rated angular frequency ω n , calculate the output voltage phase angle θ of the grid-forming inverter.

[0046] As an example, add d the angular frequency regulation amount Δ ω d , q the angular frequency regulation amount Δ ω q and the rated angular frequency ω n and pass through the integral link 1 / s to obtain the output voltage phase angle θ of the grid-forming inverter.

[0047] Step S5, in the grid-connected current-amplitude synchronization controller 33 of the q axis, receive q the grid current of the i g_q , according to q the reference value of the grid current of the i gref_q , the rated grid-connected voltage amplitude V n and q the grid current of the i g_q , calculate the reference value of the output voltage amplitude V ref of the grid-forming inverter.

[0048] As an example, q the reference value of the d-axis grid current i gref_q is subtracted from q the d-axis grid current i g_q and multiplied by an inertia link n q ω q / ( s + ω q ) to generate a voltage change ΔV. The voltage change ΔV is added to the rated grid-connected voltage amplitude V n to obtain the reference value of the output voltage amplitude of the grid-forming inverter V ref . Among them, n q is q the d-axis grid-connected current-voltage droop coefficient, ω q is the corner frequency of the inertia link.

[0049] Step S6. In the grid-forming inverter controller 34, according to the phase angle of the output voltage of the grid-forming inverter θ and the reference value of the output voltage amplitude of the grid-forming inverter V ref , the reference value of the output voltage v oref_n is calculated using the voltage reference calculation formulas (Equation I and Equation II); including d the reference value of the output voltage in the d-axis direction v oref_d and q the reference value of the output voltage in the q-axis direction v oref_q . d The calculation formula of the reference value of the output voltage in the d-axis direction v oref_d (Equation I) and q the calculation formula of the reference value of the output voltage in the q-axis direction v oref_q (Equation II) are as follows:

[0050] (Equation I)

[0051] (Equation II).

[0052] Step S7. The error between the reference value of the output voltage v oref_n and the output voltage v o_n is fed into the voltage controllerG v , obtain the reference value of the inductor current i Lref_n ; Feed the reference value of the inductor current i Lref_n and the inductor current i L_n error into the proportional-integral current controller G i , obtain the modulation wave v m_n ; Convert the modulation wave v m_n to the three-phase stationary coordinate system to obtain the modulation wave v m_x , and generate the PWM control signal through sinusoidal pulse width modulation.

[0053] In an embodiment of the present application, the voltage controller G v is a PI regulator.

[0054] In an embodiment of the present application, the current controller G i is a proportional-integral controller.

[0055] As an example, please refer to Figure 4 , Figure 5 and Figure 6 . Under the grid conditions (Lg = 0.01mH, Rg = 0.001Ω), for the grid-forming inverter adopting the traditional control method and the control method proposed in the present application respectively, through the PLECS simulation software for simulation comparison, to verify the superiority of the grid-forming inverter composite current synchronization control method provided by the present application. At t = 8s, the control mode is switched from the grid-forming inverter composite current synchronization control method provided by the present application to the traditional control method, and the comparison diagrams of the simulation results as shown in Figure 4 , Figure 5 and Figure 6 are obtained. Figure 4 is the simulation waveform diagram of the active power P and reactive power Q output by the grid-forming inverter adopting the grid-forming inverter composite current synchronization control method and the traditional control method provided by the present application respectively under strong grid conditions, Figure 5 is the simulation waveform diagram of the voltage output by the grid-forming inverter adopting the grid-forming inverter composite current synchronization control method and the traditional control method provided by the present application respectively under strong grid conditions, Figure 6 is the simulation waveform diagram of the current output by the grid-forming inverter adopting the grid-forming inverter composite current synchronization control method and the traditional control method provided by the present application respectively under strong grid conditions. From Figure 4 , Figure 5 and 6It can be seen that when the grid-forming inverter composite current synchronization control method provided by this application is adopted, the output power, voltage and current waveforms of the grid-forming inverter are stable and smooth, while when switching to the traditional control method, the grid-forming inverter cannot ensure the stability of the system under a strong power grid.

[0056] In another embodiment of this application, a device is further provided. The device includes: one or more processors; a memory for storing one or more programs. When the one or more programs are executed by the one or more processors, the one or more processors are caused to execute a grid-forming inverter composite current synchronization control method as described in any one of the above.

[0057] In another embodiment of this application, a computer-readable storage medium is further provided, storing a computer program. When the computer program is executed by a processor, it implements a grid-forming inverter composite current synchronization control method as described in any one of the above.

[0058] In summary, for the grid-forming inverter composite current synchronization control method, device and computer-readable storage medium provided by this application, in the synchronization control loop, the d-axis grid-connected current component is symmetrically introduced, dq which is respectively subtracted from the reference value and passes through the inertia and droop links to output a double angular frequency adjustment amount, and the two are combined to generate a synchronous angular frequency adjustment amount , and further passes through an integration link to obtain the output voltage phase angle of the grid-forming inverter required for synchronization θ . By adopting the grid-forming inverter composite current synchronization control method provided by this application, the d-axis and q-axis grid current components of the system are used to achieve the synchronization of the grid-forming inverter and the grid voltage, omitting the instantaneous power calculation link in the traditional grid-forming inverter control, enabling the grid-forming inverter to operate reliably and stably, effectively improving the robustness of the grid-forming inverter to grid impedance changes and the stability under strong grid conditions, so as to achieve plug-and-play in the power grid. d d q axis and the q-axis grid current components of the system are used to achieve the synchronization of the grid-forming inverter and the grid voltage, omitting the instantaneous power calculation link in the traditional grid-forming inverter control, enabling the grid-forming inverter to operate reliably and stably, effectively improving the robustness of the grid-forming inverter to grid impedance changes and the stability under strong grid conditions, so as to achieve plug-and-play in the power grid.

[0059] Although this application has been disclosed as above with embodiments, it is not intended to limit this application. Any person with ordinary knowledge in the technical field to which this application pertains can make some modifications and refinements without departing from the spirit and scope of this application. Therefore, the protection scope of this application shall be subject to that defined by the appended patent application scope.

Claims

1. A composite current synchronous control method for a grid-connected inverter, characterized in that: The following steps are involved: Step S1, detecting the inductor current i L_x , and perform coordinate transformation to obtain dq Inductor current in coordinate system i L_n ; Detect grid current i g_x , and perform coordinate transformation to obtain dq Grid current in coordinate system i g_n ; Detect output voltage v o_x , and perform coordinate transformation to obtain dq Output voltage in coordinate system v o_n ; Among them, the subscript x express a , b , c , subscript n express d, q ; Step S2, according to d Axis grid current reference value i gref_d and d Axis grid current i g_d , calculate d Shaft angular frequency adjustment Δ ω d ; Step S3, according to q Axis grid current reference value i gref_q and q Axis grid current i g_q , calculate q Shaft angular frequency adjustment Δ ω q ; Step S4, according to d Shaft angular frequency adjustment Δ ω d , q Shaft angular frequency adjustment Δ ω q and angular frequency ratings ω n , calculate the output voltage phase angle of the grid-type inverter θ ; Step S5, according to q Axis grid current reference value i gref_q , Grid-connected rated voltage amplitude V n and q Axis grid current i g_q , calculate the output voltage amplitude reference of the grid-type inverter V ref ; Step S6: According to the grid-type inverter output voltage phase angle θ Reference to the output voltage amplitude of the grid-connected inverter V ref , use the voltage reference calculation formula to get the output voltage reference value v oref_n ; The output voltage reference value v oref_n include: d Output voltage reference value in the axis direction v oref_d and q Output voltage reference value in the axis direction v oref_q ; Step S7, output voltage reference value v oref_n With output voltage v o_n The error is fed into the voltage controller G v , get the inductor current reference value i Lref_n ; Set the inductor current reference value i Lref_n and the inductor current i L_n The error is fed into the current controller G i , and get the modulated wave v m_n ; Modulate the wave v m_n Converted to the three-phase stationary coordinate system, we get v m_x , PWM control signal is generated by sinusoidal pulse width modulation.

2. The grid-type inverter composite current synchronous control method according to claim 1, characterized in that: The step S2 comprises: d Axis grid current reference value i gref_d and d Axis grid current i g_d Make the difference, then multiply by the inertia link m d ω d / ( s + ω d )produce d Shaft angular frequency adjustment Δ ω d ; in, m d for d Shaft grid-connected current-frequency droop coefficient, ω d is the turning angular frequency of the inertia link, s is the Laplace coefficient.

3. The grid-type inverter composite current synchronous control method according to claim 2, characterized in that: In step S3, q Axis grid current reference value i gref_q and q Axis grid current i g_q Make a difference and then multiply it by the high-pass filter link m q s / ( s + ω c ) q Shaft angular frequency adjustment Δ ω q ; in, m q for q Shaft grid-connected current-frequency droop coefficient, ω c is the corner frequency of the high-pass filter.

4. The grid-type inverter composite current synchronous control method according to claim 3, characterized in that: In step S4, d Shaft angular frequency adjustment Δ ω d , q Shaft angular frequency adjustment Δ ω q and angular frequency ratings ω n Add and pass the integration phase 1 / s Get the phase angle of the grid inverter output voltage θ .

5. The grid-type inverter composite current synchronous control method according to claim 4, characterized in that: In step S5, q Axis grid current reference value i gref_q and q Axis grid current i g_q Make a difference, multiply by the inertia link n q ω q / ( s + ω q ) generates a voltage variation ΔV, which is proportional to the grid-connected rated voltage amplitude V n Add together to get the amplitude reference of the grid inverter output voltage V ref ,in, n q for q Axis grid-connected current-voltage droop coefficient, ω q is the turning angular frequency of the inertia link.

6. The grid-type inverter composite current synchronous control method according to claim 5, characterized in that: In step S6, the voltage reference calculation formula is: ， 。 7. The grid-type inverter composite current synchronous control method according to claim 1, characterized in that: The voltage controller G v It is a PI regulator.

8. The grid-connected inverter composite current synchronous control method according to claim 1, characterized in that: The current controller G i It is a proportional-integral controller.

9. A device, characterized in that: The device includes: one or more processors; a memory for storing one or more programs, and when the one or more programs are executed by the one or more processors, the one or more processors execute a grid-type inverter composite current synchronization control method as described in any one of claims 1-8.

10. A computer-readable storage medium, characterized in that: A computer program is stored, and when the computer program is executed by a processor, a grid-type inverter composite current synchronization control method as described in any one of claims 1 to 8 is implemented.

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