A method and device for mode switching of a converter, the converter, a medium and a product

Abstract

The present invention discloses a method, device, converter, medium and product for mode switching of a converter, relating to the field of power electronics technology. The method includes: in the grid-forming mode, outputting a grid-forming mode modulation voltage based on a second control loop and controlling the operation of the converter; backing up and operating in the grid-following mode, and processing an integrator of a first control loop in the grid-following mode based on a first state parameter of the converter. In the grid-following mode, outputting a grid-following mode modulation voltage based on a first control loop and controlling the operation of the converter; backing up and operating in the grid-forming mode, and processing an integrator of a second control loop in the grid-forming mode based on a second state parameter of the converter. This method can achieve seamless and smooth switching of the converter between the grid-forming mode and the grid-following mode, effectively cope with the dynamic changes of the power grid, and improve the stability of the power system.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular, to a method, device, converter, medium, and product for mode switching of a converter. Background Art

[0002] With the rapid development of new energy power generation technology, as one of the core devices of a new energy power generation system, the flexibility and adaptability of the control mode of a converter are crucial for the stable operation of the system. The converter usually adopts two main control modes: grid-following mode and grid-forming mode. The grid-following mode is suitable for a strong grid environment and can achieve efficient power transmission and system synchronization; while the grid-forming mode shows stronger grid support ability in a weak grid environment.

[0003] In actual operation, the strong and weak characteristics of the grid will change dynamically due to factors such as load changes and network topology adjustments. Therefore, it is necessary for new energy power generation equipment to be able to flexibly switch between the grid-following mode and the grid-forming mode. However, the existing technology has deficiencies in the switching between the grid-following mode and the grid-forming mode of the converter, mainly manifested as a long time required to adjust control parameters and system states during the switching process, resulting in a slow switching speed and inability to adapt to the rapid changes in the grid state in a timely manner. Summary of the Invention

[0004] The present invention provides a method, device, converter, medium, and product for mode switching of a converter to solve the problem of slow switching speed between the grid-following mode and the grid-forming mode of the existing converter connected to the grid.

[0005] In a first aspect, an embodiment of the present invention provides a method for mode switching of a converter, which is applied to a converter connected to the grid. The operating modes of the converter include a grid-following mode and a grid-forming mode. The method includes:

[0006] When the converter operates in the grid-forming mode, based on the second control loop in the grid-forming mode, output a grid-forming mode modulation voltage and control the operation of the converter;

[0007] Back up and operate the grid-following mode, and process the integrator of the first control loop in the grid-following mode based on the first state parameter of the converter;

[0008] When the converter switches from the grid-forming mode to the grid-following mode, based on the processed first control loop, output a grid-following mode modulation voltage and control the operation of the converter.

[0009] In a second aspect, an embodiment of the present invention provides a method for mode switching of a converter, which is applied to a converter connected to the grid. The operating modes of the converter include a grid-following mode and a grid-forming mode. The method includes:

[0010] When the converter operates in the grid-following mode, a grid-following mode modulation voltage is output based on a first control loop and the operation of the converter is controlled;

[0011] The grid-forming mode is backed up and an integrator of a second control loop in the grid-forming mode is processed based on a second state parameter of the converter;

[0012] When the converter switches from the grid-following mode to the grid-forming mode, a grid-forming mode modulation voltage is output based on the processed second control loop and the operation of the converter is controlled.

[0013] In a third aspect, an embodiment of the present invention provides a mode switching device for a converter, which is applied to a converter connected to a power grid. The operation modes of the converter include a grid-following mode and a grid-forming mode. The device includes:

[0014] A grid-forming mode operation module, configured to output a grid-forming mode modulation voltage based on a second control loop in the grid-forming mode and control the operation of the converter when the converter operates in the grid-forming mode;

[0015] A grid-following mode backup module, configured to back up and operate the grid-following mode, and process an integrator of a first control loop in the grid-following mode based on a first state parameter of the converter;

[0016] A grid-following mode switching module, configured to output a grid-following mode modulation voltage based on the processed first control loop and control the operation of the converter when the converter switches from the grid-forming mode to the grid-following mode.

[0017] In a fourth aspect, an embodiment of the present invention provides a mode switching device for a converter, which is applied to a converter connected to a power grid. The operation modes of the converter include a grid-following mode and a grid-forming mode. The device includes:

[0018] A grid-following mode operation module, configured to output a grid-following mode modulation voltage based on a first control loop and control the operation of the converter when the converter operates in the grid-following mode;

[0019] A grid-forming mode backup module, configured to back up and operate the grid-forming mode, and process an integrator of a second control loop in the grid-forming mode based on a second state parameter of the converter;

[0020] A grid-forming mode switching module, configured to output a grid-forming mode modulation voltage based on the processed second control loop and control the operation of the converter when the converter switches from the grid-following mode to the grid-forming mode.

[0021] In a fifth aspect, an embodiment of the present invention provides a converter, which includes:

[0022] at least one processor;

[0023] and a memory communicatively connected to the at least one processor;

[0024] wherein, the memory stores a computer program executable by the at least one processor, and when the computer program is executed by the at least one processor, the at least one processor is enabled to execute the mode switching method of the converter according to any embodiment of the present invention.

[0025] In a sixth aspect, an embodiment of the present invention provides a computer-readable storage medium storing computer instructions for causing a processor to implement the mode switching method of the converter according to any embodiment of the present invention when executed.

[0026] In a seventh aspect, an embodiment of the present invention provides a computer program product including a computer program, which implements the mode switching method of the converter according to any embodiment of the present invention when executed by a processor.

[0027] In the technical solution of the embodiment of the present invention, when the converter operates in the grid-forming mode, the grid-forming mode modulation voltage is output based on the second control loop in the grid-forming mode and the operation of the converter is controlled; the grid-following mode is backed up and run, and the integrator of the first control loop in the grid-following mode is processed based on the first state parameter of the converter; when the converter switches from the grid-forming mode to the grid-following mode, the grid-following mode modulation voltage is output based on the processed first control loop and the operation of the converter is controlled. When the converter operates in the grid-following mode, the grid-following mode modulation voltage is output based on the first control loop and the operation of the converter is controlled; the grid-forming mode is backed up and run, and the integrator of the second control loop in the grid-forming mode is processed based on the second state parameter of the converter; when the converter switches from the grid-following mode to the grid-forming mode, the operation of the converter is controlled based on the processed second control loop. By backing up and running the grid-following mode when the converter operates in the grid-forming mode and processing the integrator of the first control loop based on the state parameter of the converter during the backup operation, seamless and smooth switching of the converter from the grid-forming mode to the grid-following mode can be achieved. By backing up and running the grid-forming mode when the converter operates in the grid-following mode and processing the integrator of the second control loop based on the state parameter of the converter during the backup operation, seamless and smooth switching of the converter from the grid-following mode to the grid-forming mode can be achieved. The problem that the existing converters connected to the power grid have a slow switching speed between the grid-following mode and the grid-forming mode is solved, and the technical effect of effectively coping with the dynamic changes of the power grid and improving the stability of the power system is achieved.

[0028] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0030] Figure 1 It is a flowchart of a method for mode switching of an inverter provided in Embodiment 1 of the present invention;

[0031] Figure 2 It is a schematic diagram of the system topology of a three-phase inverter incorporated into the power grid;

[0032] Figure 3 It is a flowchart of a method for mode switching of an inverter provided in Embodiment 2 of the present invention;

[0033] Figure 4 It is a control logic diagram of the phase-locked loop control in the active and reactive power control loops in the grid-following mode provided in Embodiment 2 of the present invention;

[0034] Figure 5 It is a control logic diagram of the current loop control in the active and reactive power control loops in the backup operation grid-following mode provided in Embodiment 2 of the present invention;

[0035] Figure 6 It is a flowchart of a method for mode switching of an inverter provided in Embodiment 3 of the present invention;

[0036] Figure 7 It is a control logic diagram of the active power loop control in the virtual synchronous generator control loop in the currently operating grid-forming mode provided in Embodiment 3 of the present invention;

[0037] Figure 8 It is a control logic diagram of the reactive power loop control in the virtual synchronous generator control loop in the currently operating grid-forming mode provided in Embodiment 3 of the present invention;

[0038] Figure 9 It is a control logic diagram of the virtual impedance control and voltage-current loop control in the virtual synchronous generator control loop in the currently operating grid-forming mode provided in Embodiment 3 of the present invention;

[0039] Figure 10 It is a flowchart of a method for mode switching of an inverter provided in Embodiment 4 of the present invention;

[0040] Figure 11 Flow chart of a mode switching method for an inverter provided in Embodiment 5 of the present invention;

[0041] Figure 12 Control logic diagram of virtual impedance control and voltage-current loop control in the virtual synchronous generator control loop under the backup operation grid-forming mode provided in Embodiment 5 of the present invention;

[0042] Figure 13 Control logic diagram of active power loop control in the virtual synchronous generator control loop under the backup operation grid-forming mode provided in Embodiment 5 of the present invention;

[0043] Figure 14 Control logic diagram of reactive power loop control in the virtual synchronous generator control loop under the backup operation grid-forming mode provided in Embodiment 5 of the present invention;

[0044] Figure 15 Flow chart of a mode switching method for an inverter provided in Embodiment 6 of the present invention;

[0045] Figure 16 Control logic diagram of current loop control in the active and reactive power control loop under the current operation grid-following mode provided in Embodiment 6 of the present invention;

[0046] Figure 17 Flow chart of a mode switching method for an example inverter provided in Embodiment 7 of the present invention;

[0047] Figure 18 Switching waveform diagram of grid-forming mode - grid-following mode - grid-forming mode under the condition of the same active power and reactive power provided in Embodiment 7 of the present invention;

[0048] Figure 19 Switching waveform diagram of grid-forming mode - grid-following mode - grid-forming mode when the active power changes provided in Embodiment 7 of the present invention;

[0049] Figure 20 Structural schematic diagram of a mode switching device for an inverter provided in Embodiment 8 of the present invention;

[0050] Figure 21 Structural schematic diagram of a mode switching device for an inverter provided in Embodiment 9 of the present invention;

[0051] Figure 22 Structural schematic diagram of an inverter for implementing the mode switching method of the inverter in the embodiments of the present invention. Detailed implementation manners

[0052] To enable those skilled in the art to better understand the solution of the present invention, the following will clearly and completely describe the technical solution in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0053] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned accompanying drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0054] Embodiment 1

[0055] Figure 1 It is a flowchart of a method for switching the mode of a converter provided in Embodiment 1 of the present invention. This embodiment is applicable to the situation of switching the operating mode of a converter connected to the power grid from the grid-forming mode to the grid-following mode. This method can be executed by a mode switching device of the converter. The mode switching device of the converter can be implemented in the form of hardware and / or software, and the mode switching device of the converter can be configured in the converter. A converter generally refers to a device that can convert electrical energy in one form into electrical energy in another form. For example, it can convert alternating current into direct current, or convert direct current into alternating current. In a new energy power system, the converters connected to the power grid are usually three-phase converters, which can include photovoltaic inverters and energy storage converters, etc. A photovoltaic inverter converts the direct current generated by photovoltaic modules into alternating current; an energy storage converter is used to achieve bidirectional conversion between direct current and alternating current and control the charging and discharging process of energy storage batteries.

[0056] As Figure 1 shown, the method includes:

[0057] S110. When the converter is operating in the grid-forming mode, output a grid-forming mode modulation voltage based on the second control loop in the grid-forming mode and control the operation of the converter.

[0058] Exemplarily, Figure 2 is a schematic diagram of the system topology of a three-phase converter connected to the power grid. AsFigure 2 As shown, the converter adopts an LC filter, where L is the filtering inductor and C is the filtering capacitor, and it is connected to the power grid through the Point of Common Coupling (PCC). VSI represents the converter as a voltage source. is the port voltage of the converter. is the power grid voltage. is the equivalent resistance of the power grid line impedance. is the equivalent inductive reactance resistance of the power grid line. The converter can operate in the grid-connected mode or the grid-forming mode.

[0059] Among them, the converter in the grid-forming mode is essentially a voltage source. By simulating the characteristics of a traditional synchronous generator, the power converter can actively support the frequency, voltage, and inertia of the power grid, enhancing the stability and reliability of the power grid. The second control loop can be understood as the control loop of the converter in the grid-forming mode. The grid-forming mode modulation voltage can be understood as the modulation voltage signal output by the converter in the grid-forming mode.

[0060] Specifically, when the converter operates in the grid-forming mode, the second control loop is used to output the grid-forming mode modulation voltage; the grid-forming mode modulation voltage is converted into a high-frequency pulse PWM signal through Pulse Width Modulation (PWM) technology to control the on and off of the switching devices of the converter; the converter outputs stable voltage and current according to the PWM signal to achieve the support for the frequency and voltage of the power grid.

[0061] Exemplarily, the second control loop can adopt a virtual synchronous generator control loop. The Virtual Synchronous Generator (VSG) control loop is a control method that provides damping and inertia for the power grid and participates in the regulation process of the power grid by simulating the internal mechanism and external characteristics of a synchronous generator. The virtual synchronous generator control loop can include: power loop control, virtual impedance control, and voltage-current loop control. Power loop control is the core of VSG, responsible for regulating the active power and reactive power to achieve the stability of frequency and voltage; virtual impedance control improves the dynamic response and stability of the system by simulating the line impedance characteristics. By introducing virtual impedance, VSG can provide better voltage support under weak grid conditions. The voltage-current loop control is the execution link of the VSG control strategy, responsible for converting the voltage reference value generated by the power loop into the actual voltage and current output.

[0062] S120, backup operation in the grid-connected mode, processes the integrator of the first control loop in the grid-connected mode based on the first state parameter of the converter.

[0063] Among them, the converter in the grid-following mode is essentially a current source, and its operation depends on the voltage and frequency of the power grid. By capturing the phase information of the power grid, it ensures synchronization with the power grid. The first control loop can be understood as the control loop of the converter in the grid-following mode, and the first control loop includes an integrator. The first state parameter can be understood as a parameter related to the state of the converter. For example, it can include the port voltage of the converter, the port current, and the grid-forming mode modulation voltage output in the grid-forming mode.

[0064] Specifically, while the converter is operating in the grid-forming mode and outputting the grid-forming mode modulation voltage, the grid-following mode of the backup operating converter is run. In the grid-following mode of the backup operation, the integrator of the first control loop is processed based on the current first state parameter of the converter.

[0065] Exemplarily, the first control loop can be an active and reactive power control loop. The active and reactive power control loop includes an active power control loop and a reactive power control loop, abbreviated as PQ control. The core goal is to precisely control the active power (P) and reactive power (Q) output by the converter to meet the requirements of power grid dispatching or system operation. The active and reactive power control loop in the grid-following mode can include: phase-locked loop control and current loop control; the main function of the phase-locked loop control is to ensure that the output current of the energy storage system or converter is synchronized with the grid voltage by measuring the voltage phase of the point of common coupling (PCC); the current loop control is the core link to achieve active and reactive power regulation. Its main function is to adjust the output current of the converter according to the power command, so as to achieve precise power control. The current loop control usually can adopt a proportional integral (PI) controller.

[0066] S130. When the converter switches from the grid-forming mode to the grid-following mode, based on the processed first control loop, output the grid-following mode modulation voltage and control the operation of the converter.

[0067] Among them, the grid-following mode modulation voltage can be understood as the modulation voltage signal output by the converter in the grid-following mode.

[0068] Specifically, when the converter switches from the grid-forming mode to the grid-following mode, based on the first control loop processed during the backup operation, output the grid-following mode modulation voltage, and convert the grid-forming mode modulation voltage output in the grid-following mode of the backup operation into a high-frequency pulse PWM signal through Pulse Width Modulation (PWM) technology, control the output current of the converter, and perform precise power control. Thus, the converter can quickly achieve seamless and smooth switching from the grid-forming mode to the grid-following mode by backing up and running the grid-following mode in the grid-forming mode and processing the integrator of the first control loop based on the state parameters of the converter during the backup operation, reducing the power fluctuation and current fluctuation during the mode switching process.

[0069] It can be understood that when the converter switches from the grid-forming mode to the grid-following mode, based on the processed first control loop, the converter can quickly output the grid-following mode modulation voltage in the grid-following mode and control the operation of the converter; subsequently, the converter operates normally in the grid-following mode, and in the grid-following mode, the grid-following mode modulation voltage is output based on the first control loop and the operation of the converter is controlled.

[0070] In the technical solution of the embodiment of the present invention, when the converter operates in the grid-forming mode, the grid-forming mode modulation voltage is output based on the second control loop in the grid-forming mode and the operation of the converter is controlled; the grid-following mode is backed up and run, and the integrator of the first control loop in the grid-following mode is processed based on the first state parameter of the converter; when the converter switches from the grid-forming mode to the grid-following mode, the grid-following mode modulation voltage is output based on the processed first control loop and the operation of the converter is controlled. By backing up and running the grid-following mode when the converter operates in the grid-forming mode and processing the integrator of the first control loop based on the state parameter of the converter during the backup operation, seamless and smooth switching of the converter from the grid-forming mode to the grid-following mode can be achieved, effectively coping with the dynamic changes of the power grid and improving the stability of the power system.

[0071] Embodiment 2

[0072] Figure 3 It is a flowchart of a method for switching the mode of a converter provided in Embodiment 2 of the present invention. In this embodiment, the control process of backing up and running the grid-following mode of the converter is further refined on the basis of the above embodiment.

[0073] As Figure 3 shown, the method includes: [[ID=!9]]

[0074] S210. When the converter operates in the grid-forming mode, output the grid-forming mode modulation voltage based on the second control loop in the grid-forming mode and control the operation of the converter.

[0075] S220. Back up and run the grid-following mode.

[0076] Specifically, in the backed-up and run grid-following mode, the integrator in the first control loop is processed based on the first state parameter of the converter. The specific steps include S230 to S260. The first state parameter includes the port voltage of the converter and the grid-forming mode modulation voltage output in the grid-forming mode. The first control loop is an active and reactive power control loop, and the active and reactive power control loop includes phase-locked loop control and current loop control; the integrator of the first control loop includes the integrator of the current loop control.

[0077] S230. Perform phase-locked loop control on the port voltage of the converter and output the phase-locked angle.

[0078] Among them, a phase-locked loop (PLL) is a system that uses feedback control principles to achieve frequency and phase control. Its core function is to synchronize the frequency and phase of the output signal with the input reference signal.

[0079] Specifically, Figure 4 This is a control logic diagram of a phase-locked loop control in an active and reactive power control loop in a grid-following mode provided by the second embodiment of the present invention. Figure 4 As shown, in the backup operation mode, the port voltage Perform Clarke transformation to obtain the two-phase stationary coordinate system Shaft port voltage and Shaft port voltage ;Use the phase-locked angle of output feedback For the two-phase stationary coordinate system Shaft port voltage Perform Park transformation to obtain the port voltage of the d-axis in the two-phase rotating coordinate system and the q-axis port voltage ; Based on the phase-locked loop controller, the port voltage of the q axis in the two-phase rotating coordinate system Perform phase-locked loop control and output the phase-locked loop angular frequency change , the angular frequency change of the phase-locked loop and rated angular frequency The sum is integrated and the phase-locked angle is output. Among them, the phase-locked loop controller can adopt a phase-locked loop proportional integral controller (abbreviated as phase-locked loop PI controller), based on the phase-locked loop control output of the phase-locked loop controller. It can be expressed as:

[0080] ;

[0081] in, is the proportional coefficient of the phase-locked loop PI controller, is the integral coefficient of the phase-locked loop PI controller.

[0082] S240 , performing coordinate transformation on the port voltage based on the phase-locked angle to obtain a first port voltage in a two-phase rotating coordinate system.

[0083] The first port voltage is the result of transforming the port voltage in the grid-following mode to the two-phase rotating coordinate system based on the phase-locked angle, including: the first port voltage of the d-axis and the first port voltage of the q-axis .

[0084] Specifically, in the backup grid mode, the phase-locked angle Perform a Park transformation on the port voltage of the converter to obtain the first port voltage on the d-axis and the first port voltage on the q-axis in the two-phase rotating coordinate system. Perform a Park transformation on the port voltage of the converter to obtain the first port voltage on the d-axis and the first port voltage on the q-axis in the two-phase rotating coordinate system. and the first port voltage on the q-axis .

[0085] S250. Perform a coordinate transformation on the grid-forming mode modulation voltage in the two-phase stationary coordinate system based on the phase-locked angle to obtain the grid-forming mode modulation voltage in the two-phase rotating coordinate system.

[0086] Specifically, Figure 5 This is the control logic diagram of the current loop control in the active and reactive power control loop in the backup operation and grid-following mode provided in the second embodiment of the present invention. As shown, use the phase-locked angle Figure 5 to perform a Park transformation on the grid-forming mode modulation voltage on the axis in the two-phase stationary coordinate system output in the grid-forming mode to obtain the grid-forming mode modulation voltage on the d-axis in the two-phase rotating coordinate system , and perform a Park transformation on the grid-forming mode modulation voltage on the axis in the two-phase stationary coordinate system output in the grid-forming mode to obtain the grid-forming mode modulation voltage on the q-axis in the two-phase rotating coordinate system . axis in the two-phase stationary coordinate system output in the grid-forming mode to obtain the grid-forming mode modulation voltage on the q-axis in the two-phase rotating coordinate system , and perform a Park transformation on the grid-forming mode modulation voltage on the .

[0087] S260. Assign the difference between the grid-forming mode modulation voltage in the two-phase rotating coordinate system and the first port voltage in the two-phase rotating coordinate system to the integrator in the current loop control.

[0088] Specifically, as shown, the current loop control adopts current loop proportional-integral control, including the current loop proportional-integral control on the d-axis and the current loop proportional-integral control on the q-axis; assign the difference between the grid-forming mode modulation voltage on the d-axis in the two-phase rotating coordinate system Figure 5 and the first port voltage on the d-axis in the two-phase rotating coordinate system to the integrator in the current loop proportional-integral control on the d-axis, that is, the integral term output by the integrator in the current loop proportional-integral control on the d-axis is ; assign the difference between the grid-forming mode modulation voltage on the q-axis in the two-phase rotating coordinate system and the first port voltage on the q-axis in the two-phase rotating coordinate system to the integrator in the current loop proportional-integral control on the q-axis, that is, the integrator output by the integrator in the current loop proportional-integral control on the q-axis is .

[0089] ​In this embodiment, by assigning values to the integrator of the current loop control in the network-following mode of backup operation, an initial value for the operation of the control loop in the network-following mode of backup operation can be provided, enabling the converter to operate quickly and stably when switching to the network-following mode.

[0090] In an alternative embodiment, it further includes:

[0091] A1. Perform coordinate transformation on the port current of the converter to obtain the first port current in the two-phase rotating coordinate system.

[0092] Among them, the first port current is the result of transforming the port voltage in the network-following mode to the two-phase rotating coordinate system based on the phase-locked angle, including the first port current on the d-axis and the first port current on the q-axis.

[0093] Specifically, using the phase-locked angle , perform Park transformation on the port current of the converter to obtain the first port current on the d-axis and the first port current on the q-axis in the two-phase rotating coordinate system.

[0094] A2. Calculate the current reference value on the direct axis in the two-phase rotating coordinate system according to the first port voltage in the two-phase rotating coordinate system, the first port current on the quadrature axis in the two-phase rotating coordinate system, and the active power reference value; the current reference value on the direct axis in the two-phase rotating coordinate system is input into the current loop control on the direct axis in the second control loop.

[0095] Specifically, as Figure 5 shown, the calculation formula for the current reference value on the d-axis in the two-phase rotating coordinate system is:

[0096] ;

[0097] Among them, is the current reference value on the direct axis in the two-phase rotating coordinate system, is the active power reference value, is the first port voltage on the q-axis in the two-phase rotating coordinate system, is the first port voltage on the d-axis in the two-phase rotating coordinate system, is the first port current on the q-axis in the two-phase rotating coordinate system.

[0098] A3. Assign the first port current on the quadrature axis in the two-phase rotating coordinate system to the current reference value on the quadrature axis in the two-phase rotating coordinate system; the current reference value on the quadrature axis in the two-phase rotating coordinate system is input into the current loop control on the quadrature axis in the second control loop.

[0099] Specifically, assign the first port current on the quadrature axis in the two-phase rotating coordinate system to the current reference value on the quadrature axis in the two-phase rotating coordinate system, that is 。

[0100] S270. When the converter switches from the grid-forming mode to the grid-following mode, based on the processed first control loop, output the grid-following mode modulation voltage and control the operation of the converter.

[0101] As an alternative implementation of this embodiment, S270. When the converter switches from the grid-forming mode to the grid-following mode, based on the processed first control loop, output the grid-following mode modulation voltage and control the operation of the converter, including:

[0102] S271. When the converter switches from the grid-forming mode to the grid-following mode, based on the processed current loop control, control the difference between the current reference value in the two-phase rotating coordinate system and the first port current in the two-phase rotating coordinate system to obtain the grid-following mode modulation voltage in the two-phase rotating coordinate system.

[0103] Specifically, as Figure 5 shown, after processing the integrators in the d-axis and q-axis current loop controls in the grid-following mode, the current reference value on the d-axis in the two-phase rotating coordinate system and the first port current on the d-axis in the two-phase rotating coordinate system The difference is used as the current loop error on the d-axis, and after proportional-integral control and voltage feedforward control, the grid-following mode modulation voltage on the d-axis in the two-phase rotating coordinate system is obtained ; the difference between the current reference value on the q-axis in the two-phase rotating coordinate system and the first port current on the q-axis in the two-phase rotating coordinate system The difference is used as the current loop error, and after proportional-integral control and voltage feedforward control, the grid-following mode modulation voltage on the q-axis in the two-phase rotating coordinate system is obtained . In the grid-following mode, the grid-following mode modulation voltage on the d-axis in the two-phase rotating coordinate system and the grid-following mode modulation voltage on the q-axis can be expressed as:

[0104]

[0105] Further simplified, it can be expressed as:

[0106]

[0107] S272. Based on the phase-locked angle, perform coordinate transformation on the first grid-following mode modulation voltage in the two-phase rotating coordinate system to obtain the grid-following mode modulation voltage in the two-phase stationary coordinate system.

[0108] Among them, the first grid-connected mode modulation voltage can be understood as the grid-connected mode modulation voltage in the two-phase rotating coordinate system output in the grid-connected mode. The grid-connected mode modulation voltage on the d-axis can be expressed as , and the first grid-connected mode modulation voltage on the q-axis can be expressed as .

[0109] Specifically, based on the phase-locked angle , the inverse Park transformation is performed on the first grid-connected mode modulation voltage on the d-axis in the two-phase rotating coordinate system to obtain the grid-connected mode modulation voltage on the axis in the two-phase stationary coordinate system. The inverse Park transformation is performed on the first grid-connected mode modulation voltage on the q-axis in the two-phase rotating coordinate system to obtain the grid-connected mode modulation voltage on the axis in the two-phase stationary coordinate system.

[0110] S273. Pulse width modulation is performed on the grid-connected mode modulation voltage in the two-phase stationary coordinate system to obtain the grid-connected mode pulse width modulation voltage; the converter is controlled to operate based on the grid-connected mode pulse width modulation voltage.

[0111] Specifically, the grid-connected mode modulation voltage on the axis and the grid-connected mode modulation voltage on the axis in the two-phase stationary coordinate system are sent to the pulse width modulation link for pulse width modulation to obtain the grid-connected mode pulse width modulation voltage, and the converter is controlled to operate based on the grid-connected mode pulse width modulation voltage.

[0112] In the technical solution of the embodiment of the present invention, when the converter operates in the grid-forming mode, the grid-forming mode modulation voltage is output based on the second control loop in the grid-forming mode, and the operation of the converter is controlled; the backup operation follows the grid mode, the phase-locked loop control is performed on the port voltage of the converter, and the phase-locked angle is output; the coordinate transformation is performed on the port voltage based on the phase-locked angle to obtain the first port voltage in the two-phase rotating coordinate system; the coordinate transformation is performed on the grid-forming mode modulation voltage in the two-phase stationary coordinate system based on the phase-locked angle to obtain the grid-forming mode modulation voltage in the two-phase rotating coordinate system; the difference between the grid-forming mode modulation voltage in the two-phase rotating coordinate system and the first port voltage in the two-phase rotating coordinate system is assigned to the integrator in the current loop control; when the converter switches from the grid-forming mode to the following grid mode, the following grid mode modulation voltage is output based on the processed first control loop and the operation of the converter is controlled. By using the assignment method in the backup operation following grid mode to quickly determine the initial value of the integrator in the first control loop, the calculation of the following grid mode modulation voltage in the backup operation following grid mode is simplified, the output speed of the following grid mode modulation voltage is increased, thereby further improving the smoothness of the converter switching from the grid-forming mode to the following grid mode, being able to effectively cope with the dynamic changes of the power grid, and improving the stability of the power system.

[0113] Embodiment III

[0114] Figure 6 The flowchart of a method for mode switching of a converter provided in Embodiment III of the present invention. In this embodiment, the control process of the converter in the grid-forming mode is further defined on the basis of the above embodiment. Specifically, when the converter operates in the grid-forming mode, the grid-forming mode modulation voltage is output based on the second control loop; the second control loop is a virtual synchronous generator control loop, and the virtual synchronous generator control loop includes: power loop control, virtual impedance control, and voltage-current loop control. When the converter operates in the grid-forming mode, outputting the grid-forming mode modulation voltage based on the second control loop in the grid-forming mode and controlling the operation of the converter includes: when the converter operates in the grid-forming mode, outputting the self-synchronizing angle and no-load electromotive force based on the power loop control in the virtual synchronous generator control loop; performing virtual impedance control on the port current according to the self-synchronizing angle and no-load electromotive force to obtain the voltage reference value; performing voltage-current loop control on the voltage reference value according to the self-synchronizing angle and no-load electromotive force to obtain the grid-forming mode modulation voltage; performing pulse width modulation on the grid-forming mode modulation voltage and controlling the operation of the converter.

[0115] As Figure 6 shown, the method includes:

[0116] S310. When the converter operates in the grid-forming mode, output the self-synchronizing angle and no-load electromotive force based on the power loop control in the virtual synchronous generator control loop.

[0117] Among them, the self-synchronization angle can be understood as a certain predetermined angle to which the phase difference of the currents or voltages of each phase in a polyphase system is automatically adjusted. The no-load electromotive force can be understood as a parameter used to describe the voltage output characteristics of a generator or motor when operating without load.

[0118] Specifically, when the converter operates in the grid-forming mode, the grid-forming mode outputs the grid-forming mode modulation voltage based on the virtual synchronous generator control loop. In the virtual synchronous generator control loop, the power loop control adjusts the active power and reactive power output by the converter to meet the system requirements and maintain the stable operation of the power grid. The power loop control includes the active loop control and the reactive loop control. The active loop control maintains the balance of active power by adjusting the frequency, and the reactive power loop control can adjust the voltage to the rated value, thereby realizing the stable output of reactive power. The active loop control and the reactive loop control can be implemented using a PI controller (Proportional-Integral controller) or a PID controller (Proportional-Integral-Derivative controller).

[0119] As an optional implementation manner of this embodiment, outputting the self-synchronization angle and the no-load electromotive force based on the power loop control includes:

[0120] Taking the active power reference value, the actual active power value, and the rated angular frequency as input parameters, outputting a virtual angular frequency based on the active loop control, and integrating the virtual angular frequency to obtain the self-synchronization angle;

[0121] Taking the reactive power reference value, the actual reactive power value, the rated voltage, and the terminal voltage as input parameters, outputting an adjustment amount of the no-load electromotive force based on the reactive loop control, and determining the sum of the adjustment amount of the no-load electromotive force and the rated no-load electromotive force as the no-load electromotive force.

[0122] Exemplarily, Figure 7 FIG. is a control logic diagram of the active loop control in the virtual synchronous generator control loop under the current operating grid-forming mode provided in Embodiment 3 of the present invention. As Figure 7 shown, the active loop control of the converter in the grid-forming mode includes an active-frequency droop link, a virtual inertia link, and a damping link. Taking the active power reference value 、the actual active power value [[ID=2,2]] and the rated angular frequency as input parameters and inputting them into the active loop control of the converter, the self-synchronization angle of the VSG is obtained through the active loop control. The self-synchronization angle can be expressed as:

[0123] ;

[0124] ;

[0125] Therefore, it can be deduced that: 。

[0126] Among them, is the self - synchronization angle, is the rated angular frequency, is the virtual angular frequency, is the change amount of the virtual angular frequency, is the active - frequency droop coefficient, is the virtual inertia, is the damping coefficient, is the differential operator ( is the integral operator). is the reference value of the active power, is the actual value of the active power.

[0127] Figure 8 This is the control logic diagram of the reactive power loop control in the virtual synchronous generator control loop under the current operating network - forming mode provided by the third embodiment of the present invention. As Figure 8 shown, in the network - forming mode, the reactive power loop control of the converter includes a reactive - voltage droop link and an integral link. Taking the reference value of the reactive power , the actual value of the reactive power , the rated voltage and the port voltage as input parameters, input them into the reactive power loop control, and obtain the no - load electromotive force E through the reactive power loop control. The no - load electromotive force E can be expressed as:

[0128] ;

[0129] Among them, E is the no - load electromotive force, is the rated no - load electromotive force, is the reactive - voltage droop coefficient, is the integral coefficient.

[0130] S320. Perform virtual impedance control on the port current according to the self - synchronization angle and the no - load electromotive force to obtain the voltage reference value.

[0131] Among them, the virtual impedance control simulates the impedance characteristics in the traditional power grid by introducing a virtual inductor or resistor at the output end of the converter.

[0132] Specifically, in the network - forming mode, according to the self - synchronization angle output by the active power loop control, for the port current Perform coordinate transformation, and perform virtual impedance control on the port current of the converter after coordinate transformation according to the no-load electromotive force E output by the reactive power loop control to obtain a voltage reference value. By adjusting the virtual impedance, reasonable distribution of active power and reactive power between parallel converters can be achieved, and the stability of the converter under island operation or weak grid conditions can be improved. The virtual impedance control can be achieved by calculating the derivative of the current and multiplying it by the value of the virtual inductor, or by extracting the orthogonal components of the current through SOGI-FLL. The embodiments of the present invention do not limit this.

[0133] As an optional implementation manner of this embodiment, performing virtual impedance control on the port current according to the self-synchronization angle and the no-load electromotive force to obtain a voltage reference value includes:

[0134] Perform coordinate transformation on the port current of the converter according to the self-synchronization angle to obtain the second port current in the two-phase rotating coordinate system;

[0135] Perform virtual impedance control on the second port current in the two-phase rotating coordinate system according to the no-load electromotive force to obtain the voltage reference value in the two-phase rotating coordinate system.

[0136] Among them, the two-phase rotating coordinate system (i.e., the dq coordinate system) is a coordinate system used for motor analysis and control, and simplifies the operation by decomposing complex rotating vectors into a synchronously rotating coordinate system. The two-phase rotating coordinate system includes a direct axis (also called the d-axis) and a quadrature axis (also called the q-axis). The d-axis coincides with the direction of the permanent magnet N pole of the motor rotor, and the q-axis leads the d-axis by 90 degrees and rotates with the rotor.

[0137] Among them, the second port current is the result of transforming the port current in the grid-forming mode to the two-phase rotating coordinate system based on the self-synchronization angle, including: the second port current of the d-axis and the second port current of the q-axis.

[0138] Specifically, in the grid-forming mode, according to the self-synchronization angle Perform coordinate transformation on the port current of the converter Perform virtual impedance control on the port current of the converter after coordinate transformation according to the no-load electromotive force E to obtain a voltage reference value.

[0139] Exemplarily, Figure 9 This is a control logic diagram of virtual impedance control and voltage-current loop control in a virtual synchronous generator control loop in a current operating grid-forming mode provided by Embodiment 3 of the present invention. As Figure 9 shown, in the running grid-forming mode, based on the self-synchronization angle Perform Park transformation on the port current of the converter in the three-phase stationary coordinate system to obtain the second port current of the d-axis in the two-phase rotating coordinate system and the second - port current of the q - axis . According to the no - load electromotive force E, the second - port current of the d - axis in the two - phase rotating coordinate system is subjected to virtual impedance control to obtain the voltage reference value of the d - axis in the two - phase rotating coordinate system , the first - port current of the q - axis is subjected to virtual impedance control to obtain the voltage reference value of the quadrature axis in the two - phase rotating coordinate system , the voltage reference value of the d - axis and the voltage reference value of the q - axis can be calculated as follows:

[0140]

[0141] wherein, is the virtual resistance, is the virtual inductive reactance.

[0142] S330. According to the self - synchronization angle and the no - load electromotive force, perform voltage - current loop control on the voltage reference value to obtain the grid - forming mode modulation voltage.

[0143] Among them, the voltage - current loop control may include voltage - loop (Voltage Loop) control and current - loop (Current Loop) control. The voltage - loop control can use a voltage - loop proportional - integral controller, that is, a voltage - loop PI controller, and the current - loop control can use a current - loop proportional - integral controller, that is, a current - loop PI controller.

[0144] Specifically, in the grid - forming mode, perform voltage - loop control on the voltage reference value output by the virtual impedance control respectively to obtain the current - loop reference value; perform current - loop control on the current - loop reference value to obtain the grid - forming mode modulation voltage.

[0145] As an optional implementation manner of this embodiment, the performing voltage - current loop control on the voltage reference value according to the self - synchronization angle and the no - load electromotive force to obtain the grid - forming mode modulation voltage includes: performing coordinate transformation on the port voltage of the converter according to the self - synchronization angle to obtain the second - port voltage in the two - phase rotating coordinate system; performing voltage - loop control according to the voltage reference value in the two - phase rotating coordinate system and the second - port voltage in the two - phase rotating coordinate system to obtain the current - loop reference value in the two - phase rotating coordinate system; performing current - loop control on the current - loop reference value in the two - phase rotating coordinate system and the second - port current in the two - phase rotating coordinate system to obtain the grid - forming mode modulation voltage in the two - phase rotating coordinate system; performing coordinate transformation on the grid - forming mode modulation voltage in the two - phase rotating coordinate system based on the self - synchronization angle to obtain the grid - forming mode modulation voltage in the two - phase stationary coordinate system.

[0146] wherein, the port voltage of the converter Generally, it is represented in the ABC three-phase stationary coordinate system. The second-port voltage is the result of transforming the port voltage in the grid-forming mode based on the self-synchronization angle to the two-phase rotating coordinate system, including: the second-port voltage on the d-axis and the second-port voltage on the q-axis.

[0147] Exemplarily, as Figure 9 shown, in the grid-forming mode, based on the self-synchronization angle the port voltage of the converter in the three-phase stationary coordinate system is subjected to Park transformation to obtain the second-port voltage on the d-axis in the two-phase rotating coordinate system and the second-port voltage on the q-axis . In the two-phase rotating coordinate system, based on the voltage-loop proportional-integral controller the voltage reference value on the d-axis and the second-port voltage on the d-axis are subjected to voltage-loop control to obtain the current-loop reference value on the d-axis ; and the voltage reference value on the q-axis and the second-port voltage on the q-axis are subjected to voltage-loop control to obtain the current-loop reference value on the q-axis . The calculation methods of the current-loop reference value on the d-axis and the current-loop reference value on the q-axis can be:

[0148]

[0149] where is the proportional coefficient of the voltage-loop PI controller, is the integral coefficient of the current-loop PI controller.

[0150] In the two-phase rotating coordinate system, based on the current-loop proportional-integral controller the current-loop reference value on the d-axis and the second-port current on the d-axis are subjected to current-loop control to obtain the grid-forming mode modulation voltage on the d-axis ; and the current-loop reference value on the q-axis and the second-port current on the q-axis are subjected to current-loop control to obtain the grid-forming mode modulation voltage on the q-axis . The calculation methods of the grid-forming mode modulation voltage on the d-axis and the grid-forming mode modulation voltage on the q-axis can be:

[0151]

[0152] where is the proportional coefficient of the current loop PI controller, is the integral coefficient of the current loop PI controller.

[0153] S340. Perform pulse width modulation on the grid-forming mode modulation voltage and control the operation of the converter.

[0154] Specifically, perform pulse width modulation on the grid-forming mode modulation voltage output based on the virtual synchronous generator control loop and then control the operation of the converter.

[0155] As an optional implementation manner of this embodiment, performing pulse width modulation on the grid-forming mode modulation voltage and controlling the operation of the converter includes: performing pulse width modulation on the grid-forming mode modulation voltage in the two-phase stationary coordinate system to obtain the grid-forming mode pulse width modulation voltage; controlling the operation of the converter based on the grid-forming mode pulse width modulation voltage.

[0156] Among them, the grid-forming mode modulation voltage can be understood as the modulation voltage output in the grid-forming mode; the grid-forming mode pulse width modulation voltage can be understood as the voltage obtained by performing pulse width modulation on the grid-forming mode modulation voltage.

[0157] Specifically, as Figure 9 shown, based on the self-synchronization angle perform inverse Park transformation on the grid-forming mode modulation voltage on the d-axis in the two-phase rotating coordinate system to obtain the grid-forming mode modulation voltage on the axis in the two-phase stationary coordinate system ; perform inverse Park transformation on the grid-forming mode modulation voltage on the q-axis in the two-phase rotating coordinate system to obtain the grid-forming mode modulation voltage on the axis in the two-phase stationary coordinate system . Send the grid-forming mode modulation voltage on the [[ID=3*]]axis in the two-phase stationary coordinate system and axis grid-forming mode modulation voltage to the pulse width modulation link for pulse width modulation to obtain the grid-forming mode pulse width modulation voltage. Control the operation of the converter based on the grid-forming mode pulse width modulation voltage.

[0158] S350. Back up the operation of the grid-following mode, and process the integrator of the first control loop in the grid-following mode based on the first state parameter of the converter.

[0159] S360. When the converter switches from the grid-forming mode to the grid-following mode, output the grid-following mode modulation voltage based on the processed first control loop and control the operation of the converter.

[0160] The technical solution of the embodiment of the present invention outputs a grid-forming mode modulation voltage when the converter operates in the grid-forming mode, which is used to control the operation of the converter and output state parameters, and is used to process the integrator of the first control loop in the grid-following mode of backup operation. It can realize seamless and smooth switching of the converter from the grid-forming mode to the grid-following mode, effectively cope with the dynamic changes of the power grid, and improve the stability of the power system.

[0161] Embodiment 4

[0162] Figure 10 FIG. is a flowchart of a method for switching the mode of a converter provided in Embodiment 4 of the present invention. This embodiment is applicable to the situation where the operation mode of a converter connected to the power grid is switched from the grid-following mode to the grid-forming mode. This method can be executed by a mode switching device of the converter. The mode switching device of the converter can be implemented in the form of hardware and / or software, and the mode switching device of the converter can be configured in the converter.

[0163] As Figure 10 shown, the method includes:

[0164] S410. When the converter operates in the grid-following mode, output a grid-following mode modulation voltage based on the first control loop and control the operation of the converter.

[0165] Specifically, when the converter operates in the grid-following mode, control the port voltage of the converter based on the first control loop, and output a grid-following mode modulation voltage. The grid-following mode modulation voltage is converted into a PWM signal of high-frequency pulses through Pulse Width Modulation (PWM) technology to control the on / off of the switching devices of the converter; the converter outputs stable voltage and current according to the PWM signal to achieve frequency and voltage support for the power grid.

[0166] Exemplarily, the first control loop in the grid-following mode can be an active and reactive power control loop. The active and reactive power control loop can include: phase-locked loop control and current loop control; the main function of the phase-locked loop control is to ensure that the output current of the energy storage system or the converter is synchronized with the grid voltage by measuring the voltage phase of the point of common coupling (PCC); the current loop control is the core link to realize active and reactive power regulation. Its main function is to adjust the output current of the converter according to the power command to achieve precise power control. The current loop control usually can adopt a proportional integral (PI) controller.

[0167] S420. Back up and operate the grid-forming mode, and process the integrator of the second control loop in the grid-forming mode based on the second state parameter of the converter.

[0168] Among them, the second state parameter can be understood as a parameter related to the state of the converter. For example, it may include the current reference value output in the grid-following mode, the phase-locked angle, and the grid-following mode modulation voltage.

[0169] Specifically, while the converter is operating in the grid-following mode and outputting the grid-following mode modulation voltage, the grid-forming mode of the backup operating converter is configured. In the configured grid-forming mode of the backup operation, the integrator of the second control loop is processed based on the current second state parameter of the converter.

[0170] S430. In the case where the converter switches from the grid-following mode to the grid-forming mode, it operates based on the processed second control loop and controls the converter.

[0171] Specifically, when the converter switches from the grid-following mode to the grid-forming mode, it controls the converter to output the grid-forming mode modulation voltage based on the second control loop processed during the backup operation, and converts the grid-following mode modulation voltage output in the configured grid-forming mode of the backup operation into a PWM signal of high-frequency pulses through Pulse Width Modulation (PWM) technology, controls the output current of the converter, and performs precise power control. Thus, the converter can achieve seamless and smooth switching from the grid-following mode to the grid-forming mode by backing up and operating the grid-forming mode in the grid-following mode, and processing the integrator of the second control loop based on the state parameter of the converter during the backup operation, reducing the power fluctuation and current fluctuation during the mode switching process.

[0172] The technical solution of the embodiment of the present invention outputs the grid-following mode modulation voltage and controls the operation of the converter based on the first control loop when the converter is operating in the grid-following mode; configures and operates the grid-forming mode in backup, and processes the integrator of the second control loop in the grid-forming mode based on the second state parameter of the converter; in the case where the converter switches from the grid-following mode to the grid-forming mode, it operates based on the processed second control loop and controls the converter. By backing up and operating the grid-forming mode when the converter is operating in the grid-following mode, and processing the integrator of the second control loop based on the state parameter of the converter during the backup operation, seamless and smooth switching of the converter from the grid-following mode to the grid-forming mode can be achieved, effectively coping with the dynamic changes of the power grid and improving the stability of the power system.

[0173] Embodiment Five

[0174] Figure 11 It is a flowchart of a mode switching method for a converter provided by Embodiment Five of the present invention. This embodiment further defines the control process of the converter for backing up and operating the grid-forming mode on the basis of any of the above embodiments.

[0175] As Figure 11 shown, the method includes:

[0176] S510. When the converter operates in the grid - following mode, output the grid - following mode modulation voltage based on the first control loop and control the operation of the converter.

[0177] S520. Backup and operate in the grid - forming mode.

[0178] Specifically, in the backup grid - following operation mode, process the integrator in the second control loop based on the second state parameters of the converter. The specific steps include S530 to S540. The second state parameters include the current reference value, the phase - locked angle, and the grid - following mode modulation voltage output in the grid - following mode. The second control loop is a virtual synchronous generator control loop. The virtual synchronous generator control loop includes power - loop control, virtual impedance control, and voltage - current loop control; the voltage - loop integrator and / or current - loop integrator of the voltage - current loop control.

[0179] S530. In the grid - forming mode, output the self - synchronization angle and no - load electromotive force based on the power - loop control in the virtual synchronous generator control loop.

[0180] Among them, the power - loop control includes active - power loop control and reactive - power loop control.

[0181] Specifically, in the grid - forming mode, output the self - synchronization angle based on the active - power loop control in the virtual synchronous generator control loop, and output the no - load electromotive force based on the reactive - power loop control in the virtual synchronous generator control loop.

[0182] S540. Process the voltage - loop integrator of the voltage - current loop control in the virtual synchronous generator control loop according to the self - synchronization angle, the current reference value output in the grid - following mode, and the phase - locked angle; and / or process the current - loop integrator of the voltage - current loop control in the virtual synchronous generator control loop according to the self - synchronization angle and the grid - following mode modulation voltage output in the grid - following mode.

[0183] Among them, the voltage - current loop control can include voltage - loop (Voltage Loop) control and current - loop (Current Loop) control. The voltage - loop control uses a voltage - loop proportional - integral controller, that is, a voltage - loop PI controller; then the voltage - loop integrator can be considered as the integrator in the voltage - loop control. The current - loop control can use a current - loop proportional - integral controller, that is, a current - loop PI controller; then the current - loop integrator can be considered as the integrator in the current - loop control.

[0184] Specifically, assign values to the voltage - loop integrator in the voltage - current loop control according to the self - synchronization angle, the phase - locked angle output in the grid - following mode, and the current reference value in the two - phase rotating coordinate system. of the voltage - loop integrator Assign values to the current - loop integrator in the current - loop control of the voltage - current loop control according to the self - synchronization angle and the grid - following mode modulation voltage in the two - phase stationary coordinate system. of the current - loop integrator Perform assignment.

[0185] As an alternative implementation of this embodiment, processing the voltage loop integrator of the voltage-current loop control in the virtual synchronous generator control loop according to the self-synchronization angle, the current reference value output in the grid-following mode, and the phase-locked angle includes: performing coordinate transformation on the current reference value in the two-phase rotating coordinate system output in the grid-following mode based on the phase-locked angle to obtain the current reference value in the two-phase stationary coordinate system; performing coordinate transformation on the current reference value in the two-phase stationary coordinate system based on the self-synchronization angle to obtain the current loop current reference value in the two-phase rotating coordinate system;

[0186] Assign the current loop current reference value in the two-phase rotating coordinate system to the voltage loop integrator of the voltage-current loop control.

[0187] Specifically, Figure 12 This is a control logic diagram of virtual impedance control and voltage-current loop control in the virtual synchronous generator control loop in a backup operation grid-forming mode provided by Embodiment 5 of the present invention. As Figure 12 shown, based on the phase-locked angle perform inverse Park transformation on the d-axis current reference value in the two-phase rotating coordinate system output in the grid-following mode to obtain the -axis current reference value in the two-phase stationary coordinate system, and perform inverse Park transformation on the q-axis current reference value in the two-phase rotating coordinate system output in the grid-following mode to obtain the -axis current reference value in the two-phase stationary coordinate system. Based on the self-synchronization angle perform Park transformation on the -axis current reference value in the two-phase stationary coordinate system to obtain the d-axis current loop current reference value in the two-phase rotating coordinate system, and perform Park transformation on the -axis current reference value in the two-phase stationary coordinate system to obtain the q-axis current loop current reference value in the two-phase rotating coordinate system.

[0188] Assign the d-axis current loop current reference value in the two-phase rotating coordinate system to the voltage loop integrator of the d-axis voltage-current loop control , and assign the q-axis current loop current reference value in the two-phase rotating coordinate system to the voltage loop integrator of the voltage loop control in the q-axis voltage-current loop control .

[0189] After assigning values to the voltage loop integrators of the d-axis and q-axis in the voltage-current loop control, the current loop current reference value in the two-phase rotating coordinate system obtained through the voltage loop control can be expressed as:

[0190]

[0191] As another optional implementation manner of this embodiment, processing the current loop integrator of the voltage-current loop control in the virtual synchronous generator control loop according to the self-synchronization angle and the grid-following mode modulation voltage output in the grid-following mode includes: performing coordinate transformation on the grid-following mode modulation voltage in the two-phase stationary coordinate system based on the self-synchronization angle to obtain a second grid-following mode modulation voltage in the two-phase rotating coordinate system; assigning the second grid-following mode modulation voltage to the current loop integrator of the voltage-current loop control.

[0192] Among them, the second grid-following mode modulation voltage in the two-phase rotating coordinate system can be understood as the grid-following mode modulation voltage converted from the two-phase stationary coordinate system based on the self-synchronization angle. The second grid-following mode modulation voltage of the d-axis can be expressed as and the second grid-following mode modulation voltage of the q-axis can be expressed as .

[0193] Specifically, as Figure 12 shown, based on the self-synchronization angle perform Park transformation on the grid-following mode modulation voltage of the axis in the two-phase stationary coordinate system to obtain the second grid-following mode modulation voltage of the d-axis in the two-phase rotating coordinate system ; perform Park transformation on the grid-following mode modulation voltage of the axis in the two-phase stationary coordinate system to obtain the second grid-following mode modulation voltage of the q-axis in the two-phase rotating coordinate system . Assign the second grid-following mode modulation voltage of the d-axis to the current loop integrator of the current loop control in the voltage-current loop control of the d-axis; assign the grid-following mode modulation voltage of the q-axis to the current loop integrator of the current loop control in the voltage-current loop control of the q-axis.

[0194] In an optional embodiment, it further includes at least one of the following;

[0195] Assign the integrator of the virtual inertia link in the active power loop control in the virtual synchronous generator control loop to a preset phase-locked loop adjustment amount;

[0196] Assign the integrator of the integral link in the active loop control to the sum of the preset angle deviation value and the phase-locked angle; the preset angle deviation value is the angle deviation value between the phase-locked angle and the self-synchronization angle;

[0197] Calculate the target no-load electromotive force adjustment amount according to the preset angle deviation value and the second-port current in the two-phase rotating coordinate system output in the grid-following mode, and assign the integrator of the integral link in the reactive loop control in the virtual synchronous generator control loop to the target no-load electromotive force adjustment amount.

[0198] Specifically, Figure 13 This is the control logic diagram of the active loop control in the virtual synchronous generator control loop in the grid-forming mode with backup operation provided in Embodiment 5 of the present invention. As Figure 13 shown, in the active loop control of the virtual synchronous generator control loop, assign the preset phase-locked loop adjustment amount to the integrator of the virtual inertia link in the active loop control , that is, .

[0199] Calculate the phase-locked angle and the self-synchronization angle The angle deviation value between them, and assign the sum of the preset angle deviation value and the phase-locked angle to the integrator of the integral link in the active loop control ; Since the output of the integrator of the active loop control is , that is, . Based on the assigned active loop control, the self-synchronization angle can be output.

[0200] Exemplarily, the calculation formula of the angle deviation value can be derived from the state quantity of the grid-following mode. For example, it can be:

[0201] ;

[0202] Among them, is the virtual resistance, is the virtual inductive reactance; is the second-port current of the d-axis output in the grid-following mode, is the second-port current of the q-axis output in the grid-following mode, is the peak value of the phase voltage of the port voltage.

[0203] It should be noted that in the grid-forming mode of backup operation, by assigning values to the integrators of the virtual inertia link and the integration link in the active power loop control, accurate initial values are provided for the integrators of the virtual inertia link and the integration link in the active power loop control, thereby saving computational effort and time, increasing the speed of outputting the grid-following mode modulation voltage in the grid-forming mode of backup operation, and reducing the switching time from the grid-following mode to the grid-forming mode.

[0204] Figure 14 This is the control logic diagram of the reactive power loop control in the virtual synchronous generator control loop in the grid-forming mode of backup operation provided by the fifth embodiment of the present invention. As Figure 14 shown, in the reactive power loop control of the virtual synchronous generator control loop, according to the preset angle deviation value and the second port current in the two-phase rotating coordinate system output in the grid-following mode, the target no-load electromotive force adjustment amount is calculated, and the target no-load electromotive force adjustment amount is assigned to the integration link in the reactive power loop control. Exemplarily, The calculation formula of is:

[0205] ;

[0206] where is the rated no-load electromotive force.

[0207] S550. When the converter switches from the grid-following mode to the grid-forming mode, based on the processed output of the second control loop, the grid-forming mode modulation voltage is output and the operation of the converter is controlled.

[0208] As an alternative implementation of this embodiment, when the converter switches from the grid-following mode to the grid-forming mode, based on the processed output of the second control loop, the grid-forming mode modulation voltage is output and the operation of the converter is controlled, including:

[0209] S551. When the converter switches from the grid-following mode to the grid-forming mode, based on the reactive power loop control in the processed second control loop, the no-load electromotive force is output.

[0210] Specifically, as Figure 14 shown, the target no-load electromotive force adjustment amount is assigned to the integrator in the reactive power loop control, and the integrator of the reactive power loop control outputs the no-load electromotive force adjustment amount .

[0211] S552. According to the self-synchronization angle and the no-load electromotive force, based on the virtual impedance control in the processed second control loop, the port current is controlled to obtain the voltage reference value.

[0212] Specifically, according to the self-synchronization angle Port current of the converter The coordinate system is transformed, and virtual impedance control is performed on the port current of the converter after the coordinate system transformation according to the no-load electromotive force E to obtain a voltage reference value.

[0213] For example, Figure 12 As shown, in the backup operation network mode, based on the self-synchronization angle Port current of the converter Perform Park transformation to obtain the first port current of the d-axis in the two-phase rotating coordinate system and the first port current of the q axis According to the no-load electromotive force E, the first port current of the direct axis in the two-phase rotating coordinate system is Perform virtual impedance control to obtain the voltage reference value of the d-axis in the two-phase rotating coordinate system , the first port current on the q axis Perform virtual impedance control to obtain the voltage reference value of the quadrature axis in the two-phase rotating coordinate system , voltage reference value of d-axis and the voltage reference value of the q axis The calculation method can be:

[0214]

[0215] S553. Based on the pressure-current loop control in the processed second control loop, the voltage reference value is controlled according to the self-synchronization angle and the no-load electromotive force to obtain a meshing mode modulation voltage; the meshing mode modulation voltage is pulse-width modulated and the operation of the converter is controlled.

[0216] Specifically, the port voltage is transformed based on the self-synchronization angle to obtain the second port voltage in the two-phase rotating coordinate system. The port current is transformed based on the self-synchronization angle to obtain the first port current in the two-phase rotating coordinate system. Voltage loop control is performed on the difference between the voltage reference value in the two-phase rotating coordinate system and the second port voltage in the two-phase rotating coordinate system to obtain the current loop current reference value in the two-phase rotating coordinate system. Current loop control is performed on the difference between the current loop current reference value in the two-phase rotating coordinate system and the first port current in the two-phase rotating coordinate system to obtain the meshing mode modulation voltage in the two-phase rotating coordinate system.

[0217] For example, Figure 12 As shown, in the backup operation network mode, based on the self-synchronization angle The terminal voltage of the converter in the three-phase stationary coordinate system Perform Park transformation to obtain the first port voltage on the d-axis in the two-phase rotating coordinate system and the first port voltage on the q-axis . Based on the self-synchronization angle perform Park transformation on the port current of the converter in the three-phase stationary coordinate system to obtain the first port current on the d-axis in the two-phase rotating coordinate system and the first port current on the q-axis .

[0218] In the two-phase rotating coordinate system, based on the voltage loop PI controller perform voltage loop control on the voltage reference value on the d-axis and the first port voltage on the d-axis to obtain the current reference value of the current loop on the d-axis ; and perform voltage loop control on the voltage reference value on the q-axis and the first port voltage on the q-axis to obtain the current reference value of the current loop on the q-axis . The calculation methods of the current loop reference value on the d-axis and the current loop reference value on the q-axis can be:

[0219]

[0220] wherein, is the proportional coefficient of the voltage loop PI controller, is the integral coefficient of the current loop PI controller.

[0221] In the two-phase rotating coordinate system, based on the current loop proportional-integral controller perform current loop control on the current loop reference value on the d-axis and the first port current on the d-axis to obtain the network-forming mode modulation voltage on the d-axis ; and perform current loop control on the current loop reference value on the q-axis and the first port current on the q-axis to obtain the network-forming mode modulation voltage on the q-axis . The calculation methods of the network-forming mode modulation voltage on the d-axis and the network-forming mode modulation voltage on the q-axis can be:

[0222]

[0223] wherein, is the proportional coefficient of the current loop PI controller, is the integral coefficient of the current loop PI controller.

[0224] After assigning values to the current-loop integrators of the d-axis and q-axis in the control of the voltage-fed current loop, the grid-forming mode modulation voltage of the d-axis in the two-phase rotating coordinate system obtained through the current-loop control and the grid-forming mode modulation voltage of the q-axis can be expressed as:

[0225]

[0226] The grid-forming mode modulation voltage of the d-axis in the two-phase rotating coordinate system is and the grid-forming mode modulation voltage of the q-axis converted into a PWM signal of high-frequency pulses through pulse-width modulation to control the output current of the converter and perform precise power control.

[0227] The technical solution of the embodiment of the present invention is as follows: when the converter operates in the grid-following mode, based on the output of the first control loop, the grid-following mode modulation voltage is output and the operation of the converter is controlled, and the grid-forming mode is backed up; in the grid-forming mode, the self-synchronization angle and no-load electromotive force are output based on the power loop control in the virtual synchronous generator control loop; the voltage-loop integrator of the voltage-fed current loop control in the virtual synchronous generator control loop is processed according to the self-synchronization angle, the current reference value output in the grid-following mode, and the phase-locked angle; and / or the current-loop integrator of the voltage-fed current loop control in the virtual synchronous generator control loop is processed according to the self-synchronization angle and the grid-following mode modulation voltage output in the grid-following mode; when the converter switches from the grid-following mode to the grid-forming mode, the grid-forming mode modulation voltage is output based on the processed second control loop and the operation of the converter is controlled. By using the assignment method in the backed-up grid-forming mode to quickly determine the initial values of the integrators in the second control loop, the calculation of the grid-forming mode modulation voltage in the backed-up grid-forming mode is simplified, the output speed of the grid-forming mode modulation voltage is increased, and thus the smoothness of the converter switching from the grid-following mode to the grid-forming mode is further improved, which can effectively cope with the dynamic changes of the power grid and improve the stability of the power system.

[0228] Embodiment Six

[0229] Figure 15The flowchart of a mode switching method for a converter provided in Embodiment 6 of the present invention. In this embodiment, the control process of the converter in the grid-following mode is further refined on the basis of the above embodiment. Specifically, when the converter operates in the grid-following mode, the grid-following mode modulation voltage is output based on the active and reactive power control loop. The active and reactive power control loop includes: phase-locked loop control and current loop control. When the converter operates in the grid-following mode, outputting the grid-following mode modulation voltage based on the first control loop and controlling the operation of the converter includes: when the converter operates in the grid-following mode, performing phase-locked loop control on the port voltage of the converter to output a phase-locked angle; performing coordinate transformation on the port voltage based on the phase-locked angle to obtain the first port voltage in the two-phase rotating coordinate system, and performing coordinate transformation on the port current of the converter to obtain the first port current in the two-phase rotating coordinate system; determining the current reference value in the two-phase rotating coordinate system, and performing current loop control on the difference between the current reference value in the two-phase rotating coordinate system and the first port current in the two-phase rotating coordinate system to obtain the grid-following mode modulation voltage; performing pulse width modulation on the grid-following mode modulation voltage and controlling the operation of the converter. As Figure 15 shown, the method includes:

[0230] S610. When the converter operates in the grid-following mode, perform phase-locked loop control on the port voltage of the converter to output a phase-locked angle.

[0231] Specifically, as Figure 4 shown, a control logic of phase-locked loop control in the grid-following mode. In the grid-following mode, the port voltage of the converter in the three-phase stationary coordinate system is subjected to Clarke transformation to obtain the port voltage on the axis in the two-phase stationary coordinate system and the port voltage on the axis; using the output feedback phase-locked angle to perform Park transformation on the port voltage on the axis in the two-phase stationary coordinate system to obtain the port voltage on the d axis and the port voltage on the q axis in the two-phase rotating coordinate system. Based on the phase-locked loop controller, perform phase-locked loop control on the port voltage on the q axis in the two-phase rotating coordinate system to output the phase-locked loop angular frequency variation , and perform integral operation on the sum of the phase-locked loop angular frequency variation and the rated angular frequency to output the phase-locked angle . Among them, the phase-locked loop controller can adopt a phase-locked loop proportional integral controller (abbreviated as phase-locked loop PI controller), and the phase-locked angle output based on the phase-locked loop control of the phase-locked loop controller can be expressed as:

[0232] ;

[0233] Among them, is the proportional coefficient of the phase-locked loop PI controller, is the integral coefficient of the phase-locked loop PI controller.

[0234] S620. Perform coordinate transformation on the port voltage based on the phase-locked angle to obtain the first port voltage in the two-phase rotating coordinate system, and perform coordinate transformation on the port current of the converter to obtain the first port current in the two-phase rotating coordinate system.

[0235] Among them, the first port voltage is the result of transforming the port voltage in the grid-following mode to the two-phase rotating coordinate system based on the phase-locked angle, including: the second port voltage on the d-axis and the first port voltage on the q-axis . The second port current is the result of transforming the port voltage in the grid-following mode to the two-phase rotating coordinate system based on the phase-locked angle, including: the first port current on the d-axis and the first port current on the q-axis .

[0236] Specifically, in the grid-following mode of the converter, using the phase-locked angle , perform Park transformation on the port voltage of the converter to obtain the second port voltage on the d-axis and the first port voltage on the q-axis in the two-phase rotating coordinate system; using the phase-locked angle , perform Park transformation on the port current of the converter to obtain the first port current on the d-axis and the first port current on the q-axis in the two-phase rotating coordinate system.

[0237] S630. Determine the current reference value in the two-phase rotating coordinate system, and perform current loop control on the difference between the current reference value in the two-phase rotating coordinate system and the first port current in the two-phase rotating coordinate system to obtain the grid-following mode modulation voltage.

[0238] Specifically, Figure 16 is the control logic diagram of the current loop control in the active and reactive power control loop in the current grid-following mode provided by the sixth embodiment of the present invention. As Figure 16 shown, when the converter is operating in the grid-following mode, determine the current reference value on the d-axis and the current reference value on the q-axis in the two-phase rotating coordinate system. The current reference value The difference between the first port current on the d-axis in the two-phase rotating coordinate system is used as the current loop error on the d-axis, and through proportional-integral control and voltage feed-forward control, the first grid-following mode modulation voltage on the d-axis in the two-phase rotating coordinate system is obtained ; the current reference value on the q-axis in the two-phase rotating coordinate system and the first port current on the q-axis in the two-phase rotating coordinate system The difference is used as the current loop error, and through proportional-integral control and voltage feed-forward control, the first grid-following mode modulation voltage on the q-axis in the two-phase rotating coordinate system is obtained . In the grid-following mode, the first grid-following mode modulation voltage on the d-axis in the two-phase rotating coordinate system and the first grid-following mode modulation voltage on the q-axis can be expressed as:

[0239] [[ID=I7]]

[0240] Based on the phase-locked angle, the first grid-following mode modulation voltage on the d-axis in the two-phase rotating coordinate system is subjected to coordinate transformation to obtain the grid-following mode modulation voltage on the axis in the two-phase stationary coordinate system ; the first grid-following mode modulation voltage on the q-axis in the two-phase rotating coordinate system is subjected to coordinate transformation to obtain the grid-following mode modulation voltage on the axis in the two-phase stationary coordinate system.

[0241] As an alternative implementation of this embodiment, the determination of the current reference value in the two-phase rotating coordinate system includes: calculating the current reference value on the direct axis in the two-phase rotating coordinate system according to the second port voltage in the two-phase rotating coordinate system, the first port current on the quadrature axis in the two-phase rotating coordinate system, and the active power reference value; assigning a pre-configured current reference value to the current reference value on the quadrature axis in the two-phase rotating coordinate system.

[0242] Specifically, as Figure 16 shown, the calculation formula for the current reference value on the d-axis in the two-phase rotating coordinate system is:

[0243] ;

[0244] where is the current reference value on the direct axis in the two-phase rotating coordinate system, is the active power reference value, is the second port voltage on the q-axis in the two-phase rotating coordinate system, is the second port voltage on the d-axis in the two-phase rotating coordinate system, is the second port current on the q-axis in the two-phase rotating coordinate system.

[0245] It is understandable that the current reference value of the q-axis under the two-phase rotating coordinate system can be obtained by assigning a pre-configured current reference value, and the pre-configured current reference value can be set according to requirements, and the embodiments of the present invention do not limit this.

[0246] S640. Perform pulse width modulation on the grid-following mode modulation voltage and control the operation of the converter.

[0247] Specifically, after performing pulse width modulation on the grid-following mode modulation voltage output based on the active and reactive power control loop, control the operation of the converter.

[0248] As an optional implementation manner of this embodiment, the performing pulse width modulation on the grid-following mode modulation voltage and controlling the operation of the converter includes: performing pulse width modulation on the grid-following mode modulation voltage under the two-phase stationary coordinate system to obtain a grid-following mode pulse width modulation voltage; controlling the operation of the converter based on the grid-following mode pulse width modulation voltage.

[0249] Among them, the grid-following mode pulse width modulation voltage can be understood as the voltage obtained by performing pulse width modulation on the grid-following mode modulation voltage.

[0250] Specifically, as Figure 16 shown, based on the phase-locked angle perform an inverse Park transformation on the grid-following mode modulation voltage of the d-axis under the two-phase rotating coordinate system to obtain the grid-following mode modulation voltage of the axis under the two-phase stationary coordinate system ; perform an inverse Park transformation on the grid-following mode modulation voltage of the q-axis under the two-phase rotating coordinate system to obtain the grid-following mode modulation voltage of the axis under the two-phase stationary coordinate system . Send the grid-following mode modulation voltage of the axis and the grid-following mode modulation voltage of the axis and axis to the pulse width modulation link for pulse width modulation to obtain a grid-following mode pulse width modulation voltage, and control the operation of the converter based on the grid-following mode pulse width modulation voltage.

[0251] S650. Backup the operation of the grid-forming mode, and process the integrator of the second control loop in the grid-forming mode based on the second state parameter of the converter.

[0252] S660. When the converter switches from the grid-following mode to the grid-forming mode, output a grid-forming mode modulation voltage based on the processed second control loop and control the operation of the converter.

[0253] In the technical solution of the embodiment of the present invention, when the converter operates in the grid-following mode, the phase-locked loop control is performed on the port voltage of the converter to output the phase-locked angle; based on the phase-locked angle, the coordinate transformation is performed on the port voltage to obtain the first port voltage in the two-phase rotating coordinate system, and the coordinate transformation is performed on the port current of the converter to obtain the first port current in the two-phase rotating coordinate system; the current reference value in the two-phase rotating coordinate system is determined, and the current loop control is performed on the difference between the current reference value in the two-phase rotating coordinate system and the first port current in the two-phase rotating coordinate system to obtain the grid-following mode modulation voltage; the pulse width modulation is performed on the grid-following mode modulation voltage and the operation of the converter is controlled; the grid-forming mode is backed up and the integrator of the second control loop in the grid-forming mode is processed based on the second state parameter of the converter; when the converter switches from the grid-following mode to the grid-forming mode, the grid-forming mode modulation voltage is output based on the processed second control loop and the operation of the converter is controlled. By outputting the grid-following mode modulation voltage when the converter operates in the grid-following mode, which is used to control the operation of the converter and participate in the output of the second control loop in the backed-up grid-forming mode, seamless and smooth switching of the converter from the grid-following mode to the grid-forming mode can be achieved, effectively coping with the dynamic changes of the power grid and improving the stability of the power system.

[0254] Embodiment Seven

[0255] In an actual power grid, the converter connected to the power grid can operate in two working modes: the grid-forming mode or the grid-following mode. The two modes operate in mutual backup and can be smoothly and instantaneously switched between the grid-forming mode and the grid-following mode at any state. In a specific embodiment, Figure 17 is a flowchart of a method for switching the mode of an exemplary converter provided in Embodiment Seven of the present invention. As Figure 17 shown, the method includes: when the converter operates in the grid-forming mode, the grid-forming mode modulation voltage is output based on the second control loop in the grid-forming mode to control the operation of the converter; the grid-following mode is backed up and the integrator of the first control loop in the grid-following mode is processed based on the first state parameter of the converter. When the converter operates in the grid-following mode, the grid-following mode modulation voltage is output based on the first control loop and the operation of the converter is controlled; the grid-forming mode is backed up and the integrator of the second control loop in the grid-forming mode is processed based on the second state parameter of the converter. By repeating this process, seamless and smooth switching between the grid-following mode and the grid-forming mode of the operation mode of the converter can be achieved, effectively coping with the dynamic changes of the power grid and improving the stability of the power system.

[0256] Exemplarily, taking a power conversion system (PCS) as an example, a method for verifying the switching between a grid-forming mode and a grid-following mode provided by this proposal is carried out. Keeping the active power P = 0.5 p.u. and the reactive power Q = 0 p.u. unchanged, the PCS directly switches from the grid-forming mode to the grid-following mode and then to the grid-forming mode. Figure 18 It is a switching waveform diagram of the grid-forming mode - grid-following mode - grid-forming mode under the condition of the same active power and reactive power provided in the seventh embodiment of the present invention. As Figure 18 shown, there are almost no power fluctuations and current fluctuations during the grid-forming to grid-following switching process, while the power fluctuation is less than 3% and the current fluctuation is small during the grid-following to grid-forming switching process.

[0257] Keeping the reactive power Q = 0 p.u. unchanged, in the grid-following mode, when the active power P suddenly increases from 0.5 p.u. to 0.75 p.u., the PCS directly switches from the grid-forming mode to the grid-following mode and then to the grid-forming mode. Figure 19 It is a switching waveform diagram of the grid-forming mode - grid-following mode - grid-forming mode when the active power changes provided in the seventh embodiment of the present invention. As Figure 19 shown, there are almost no power fluctuations and current fluctuations during the grid-forming to grid-following switching process, while the power fluctuation is less than 10% and the current fluctuation is also small during the grid-following to grid-forming switching process. The above verifies that this method can ensure seamless and smooth switching of the converter in any state, and the switching effect is good.

[0258] Embodiment Eight

[0259] Figure 20 It is a schematic structural diagram of a mode switching device of a converter provided in the eighth embodiment of the present invention. This mode switching device is applied to a converter incorporated into the power grid, and the operating modes of the converter include a grid-following mode and a grid-forming mode. As Figure 20 shown, this device includes: a grid-forming mode operation module 810, a grid-following mode backup module 820, and a grid-following mode switching module 830;

[0260] The grid-forming mode operation module 810 is used to output a grid-forming mode modulation voltage based on a second control loop in the grid-forming mode and control the operation of the converter when the converter operates in the grid-forming mode;

[0261] The grid-following mode backup module 820 is used to backup and operate the grid-following mode and process the integrator of the first control loop in the grid-following mode based on the first state parameter of the converter;

[0262] The grid-following mode switching module 830 is used to output a grid-following mode modulation voltage based on the processed first control loop and control the operation of the converter when the converter switches from the grid-forming mode to the grid-following mode.

[0263] An embodiment of the present invention provides a mode switching device for an inverter. When the inverter operates in the grid-forming mode, a grid-forming mode modulation voltage is output based on the second control loop in the grid-forming mode to control the operation of the inverter; the follow-the-grid mode is backed up and run, and the integrator of the first control loop in the follow-the-grid mode is processed based on the first state parameter of the inverter; when the inverter switches from the grid-forming mode to the follow-the-grid mode, a follow-the-grid mode modulation voltage is output based on the processed first control loop to control the operation of the inverter. By backing up and running the follow-the-grid mode when the inverter operates in the grid-forming mode and processing the integrator of the first control loop based on the state parameter of the inverter during the backup operation, seamless and smooth switching of the inverter from the grid-forming mode to the follow-the-grid mode can be achieved, effectively coping with the dynamic changes of the power grid and improving the stability of the power system.

[0264] Optionally, the first state parameter includes the port voltage of the inverter and the grid-forming mode modulation voltage; the integrator of the first control loop includes the integrator for current loop control in the active and reactive power control loop; the follow-the-grid mode backup module 820 includes:

[0265] A first phase-locked loop control unit for performing phase-locked loop control on the port voltage of the inverter and outputting a phase-locked angle;

[0266] A first coordinate transformation unit for performing coordinate transformation on the port voltage based on the phase-locked angle to obtain a first port voltage in the two-phase rotating coordinate system;

[0267] A second coordinate transformation unit for performing coordinate transformation on the grid-forming mode modulation voltage in the two-phase stationary coordinate system based on the phase-locked angle to obtain a grid-forming mode modulation voltage in the two-phase rotating coordinate system;

[0268] An assignment unit for assigning the difference between the grid-forming mode modulation voltage in the two-phase rotating coordinate system and the first port voltage in the two-phase rotating coordinate system to the integrator in the current loop control.

[0269] Optionally, it further includes:

[0270] A first coordinate transformation module for performing coordinate transformation on the port current of the inverter to obtain a first port current in the two-phase rotating coordinate system;

[0271] A direct-axis current reference value calculation module for calculating a direct-axis current reference value in the two-phase rotating coordinate system according to the first port voltage in the two-phase rotating coordinate system, the first port current on the quadrature axis in the two-phase rotating coordinate system, and the active power reference value; the direct-axis current reference value in the two-phase rotating coordinate system is input into the direct-axis current loop control in the second control loop;

[0272] The quadrature-axis current reference value assignment module assigns the first-port current of the quadrature axis in the two-phase rotating coordinate system to the current reference value of the quadrature axis in the two-phase rotating coordinate system; the current reference value of the quadrature axis in the two-phase rotating coordinate system is input into the current loop control of the quadrature axis in the second control loop.

[0273] Optionally, the grid-following mode switching module 830 includes:

[0274] The first current loop control unit is used to, when the converter switches from the grid-forming mode to the grid-following mode, control the difference between the current reference value in the two-phase rotating coordinate system and the first-port current in the two-phase rotating coordinate system based on the processed current loop control to obtain the first grid-following mode modulation voltage in the two-phase rotating coordinate system;

[0275] The third coordinate transformation unit is used to perform coordinate transformation on the first grid-following mode modulation voltage in the two-phase rotating coordinate system based on the phase-locked angle to obtain the grid-following mode modulation voltage in the two-phase stationary coordinate system;

[0276] The first pulse width modulation unit is used to perform pulse width modulation on the grid-following mode modulation voltage in the two-phase stationary coordinate system to obtain the grid-following mode pulse width modulation voltage;

[0277] The first grid-following mode control unit is used to control the operation of the converter based on the grid-following mode pulse width modulation voltage.

[0278] Optionally, the grid-forming mode operation module 810 includes:

[0279] The parameter output unit is used to output the self-synchronization angle and the no-load electromotive force based on the power loop control in the virtual synchronous generator control loop when the converter operates in the grid-forming mode;

[0280] The first virtual impedance control unit is used to perform virtual impedance control on the port current according to the self-synchronization angle and the no-load electromotive force to obtain the voltage reference value;

[0281] The first voltage-current loop control unit is used to perform voltage-current loop control on the voltage reference value according to the self-synchronization angle and the no-load electromotive force to obtain the grid-forming mode modulation voltage;

[0282] The first grid-forming mode control unit is used to perform pulse width modulation on the grid-forming mode modulation voltage and control the operation of the converter.

[0283] Optionally, the first virtual impedance control unit is specifically used for:

[0284] Performing coordinate transformation on the port current of the converter according to the self-synchronization angle to obtain the second port current in the two-phase rotating coordinate system;

[0285] Perform virtual impedance control on the second port current in the two-phase rotating coordinate system according to the no-load electromotive force to obtain the voltage reference value in the two-phase rotating coordinate system.

[0286] Optionally, the first voltage-current loop control unit is specifically configured to:

[0287] Perform coordinate transformation on the port voltage of the converter according to the self-synchronization angle to obtain the second port voltage in the two-phase rotating coordinate system;

[0288] Perform voltage loop control according to the voltage reference value in the two-phase rotating coordinate system and the second port voltage in the two-phase rotating coordinate system to obtain the current loop reference value in the two-phase rotating coordinate system;

[0289] Perform current loop control on the current loop reference value in the two-phase rotating coordinate system and the second port current in the two-phase rotating coordinate system to obtain the grid-forming mode modulation voltage in the two-phase rotating coordinate system;

[0290] Perform coordinate transformation on the grid-forming mode modulation voltage in the two-phase rotating coordinate system based on the self-synchronization angle to obtain the grid-forming mode modulation voltage in the two-phase stationary coordinate system.

[0291] Optionally, the first grid-forming mode control unit is specifically configured to:

[0292] Perform pulse width modulation on the grid-forming mode modulation voltage in the two-phase stationary coordinate system to obtain the grid-forming mode pulse width modulation voltage;

[0293] Control the operation of the converter based on the grid-forming mode pulse width modulation voltage.

[0294] The mode switching device of the converter provided by the embodiments of the present invention can execute the mode switching method of the converter provided by any embodiment of the present invention, and has the corresponding functional modules and beneficial effects for executing the method.

[0295] Embodiment Nine

[0296] Figure 21 It is a schematic structural diagram of a mode switching device of a converter provided by Embodiment Nine of the present invention. This mode switching device is applied to a converter connected to the power grid, and the operating modes of the converter include a grid-following mode and a grid-forming mode. As Figure 21 shown, the device includes: a grid-following mode operation module 910, a grid-forming mode backup module 920, and a grid-forming mode switching module 930;

[0297] The grid-following mode operation module 910 is configured to output a grid-following mode modulation voltage based on the first control loop and control the operation of the converter when the converter operates in the grid-following mode; <##

[0298] The grid-forming mode backup module 920 is used to back up the operation of the grid-forming mode and process the integrator of the second control loop in the grid-forming mode based on the second state parameter of the converter.

[0299] The grid-forming mode switching module 930 is used to output the grid-forming mode modulation voltage based on the processed second control loop and control the operation of the converter when the converter switches from the grid-following mode to the grid-forming mode.

[0300] An embodiment of the present invention provides a mode switching device for a converter. When the converter operates in the grid-following mode, it outputs the grid-following mode modulation voltage based on the first control loop and controls the operation of the converter; it backs up and operates the grid-forming mode, and processes the integrator of the second control loop in the grid-forming mode based on the second state parameter of the converter; when the converter switches from the grid-following mode to the grid-forming mode, it controls the operation of the converter based on the processed second control loop. By backing up and operating the grid-forming mode when the converter operates in the grid-following mode and processing the integrator of the second control loop based on the state parameter of the converter during the backup operation, seamless and smooth switching of the converter from the grid-following mode to the grid-forming mode can be achieved, effectively coping with the dynamic changes of the power grid and improving the stability of the power system.

[0301] Optionally, the second state parameter of the converter includes: the current reference value, the phase-locked angle, and the grid-following mode modulation voltage output in the grid-following mode; the integrator of the second control loop includes: the voltage loop integrator and / or the current loop integrator of the voltage-current loop control in the virtual synchronous generator control loop.

[0302] The grid-forming mode backup module 920 includes:

[0303] The self-synchronization angle output unit is used to output the self-synchronization angle based on the active power loop control in the virtual synchronous generator control loop in the grid-forming mode.

[0304] The integrator processing unit is used to process the voltage loop integrator of the voltage-current loop control in the virtual synchronous generator control loop according to the self-synchronization angle, the current reference value output in the grid-following mode, and the phase-locked angle; and / or process the current loop integrator of the voltage-current loop control in the virtual synchronous generator control loop according to the self-synchronization angle and the grid-following mode modulation voltage output in the grid-following mode.

[0305] Optionally, the integrator processing unit is specifically used for:

[0306] Perform coordinate transformation on the current reference value in the two-phase rotating coordinate system output in the grid-following mode based on the phase-locked angle to obtain the current reference value in the two-phase stationary coordinate system.

[0307] Perform coordinate transformation on the current reference value in the two-phase stationary coordinate system based on the self-synchronization angle to obtain the current loop current reference value in the two-phase rotating coordinate system;

[0308] Assign the current loop current reference value in the two-phase rotating coordinate system to the voltage loop integrator controlled by the current-voltage loop.

[0309] Optionally, the integrator processing unit is further configured to:

[0310] Perform coordinate transformation on the grid-following mode modulation voltage in the two-phase stationary coordinate system output in the grid-following mode based on the self-synchronization angle to obtain the second grid-following mode modulation voltage in the two-phase rotating coordinate system;

[0311] Assign the second grid-following mode modulation voltage to the current loop integrator controlled by the current-voltage loop.

[0312] Optionally, the integrator of the second control loop further includes: the integrator of the virtual inertia link and the integrator of the integral link in the active power loop control in the virtual synchronous generator control loop, and the integrator of the integral link in the reactive power loop control. The device further includes at least one of the following modules;

[0313] The first integrator assignment module is configured to assign the integrator of the virtual inertia link in the active power loop control in the virtual synchronous generator control loop to a preset phase-locked loop adjustment amount;

[0314] The second integrator assignment module is configured to assign the integrator of the integral link in the active power loop control to the sum of a preset angle deviation value and the phase-locked angle; the preset angle deviation value is the angle deviation value between the phase-locked angle and the self-synchronization angle;

[0315] The third integrator assignment module is configured to calculate a target no-load electromotive force adjustment amount according to the preset angle deviation value and the second port current in the two-phase rotating coordinate system output in the grid-following mode, and assign the integrator of the integral link in the reactive power loop control in the virtual synchronous generator control loop to the target no-load electromotive force adjustment amount.

[0316] Optionally, the calculation formula of the preset angle deviation value is:

[0317] ;

[0318] The calculation formula of the target no-load electromotive force adjustment amount is:

[0319] ;

[0320] Wherein, is the preset angle deviation value, is the second port current of the direct axis output in the grid-following mode, The second port current on the quadrature axis in the two-phase rotating coordinate system output in the grid-following mode; is the virtual inductive reactance, is the virtual resistance; is the peak value of the phase voltage of the port voltage; is the target no-load electromotive force adjustment amount, is the rated no-load electromotive force.

[0321] Optionally, the grid-forming mode switching module 930 includes:

[0322] The no-load electromotive force output unit is configured to, when the converter switches from the grid-following mode to the grid-forming mode, control the output of the no-load electromotive force based on the reactive power loop control in the processed second control loop;

[0323] The second virtual impedance control unit is configured to control the port current based on the virtual impedance control in the processed second control loop according to the self-synchronization angle and the no-load electromotive force to obtain a voltage reference value;

[0324] The second voltage-current loop control unit is configured to control the voltage reference value according to the self-synchronization angle and the no-load electromotive force based on the voltage-current loop control in the processed second control loop to obtain a grid-forming mode modulation voltage;

[0325] The second grid-forming control unit is configured to perform pulse width modulation on the grid-forming mode modulation voltage and control the operation of the converter.

[0326] Optionally, the grid-following mode operation module 910 includes:

[0327] The second phase-locked loop control unit is configured to perform phase-locked loop control on the port voltage of the converter and output a phase-locked angle when the converter operates in the grid-following mode;

[0328] The fourth coordinate transformation unit is configured to perform coordinate transformation on the port voltage based on the phase-locked angle to obtain the first port voltage in the two-phase rotating coordinate system, and perform coordinate transformation on the port current of the converter to obtain the first port current in the two-phase rotating coordinate system;

[0329] The second current loop control unit is configured to determine the current reference value in the two-phase rotating coordinate system and perform current loop control on the difference between the current reference value in the two-phase rotating coordinate system and the first port current in the two-phase rotating coordinate system to obtain a grid-following mode modulation voltage;

[0330] The second grid-following mode control unit is configured to perform pulse width modulation on the grid-following mode modulation voltage and control the operation of the converter.

[0331] Optionally, the second current loop control unit is specifically configured to:

[0332] Calculate the current reference value of the direct axis in the two-phase rotating coordinate system according to the second port voltage in the two-phase rotating coordinate system, the first port current of the quadrature axis in the two-phase rotating coordinate system, and the reference value of the active power.

[0333] Assign the pre-configured current reference value to the current reference value of the quadrature axis in the two-phase rotating coordinate system.

[0334] Optionally, the second grid-following mode control unit is specifically configured to:

[0335] Perform pulse width modulation on the grid-following mode modulation voltage in the two-phase stationary coordinate system to obtain the grid-following mode pulse width modulation voltage; and control the operation of the converter based on the grid-following mode pulse width modulation voltage.

[0336] The converter mode switching device provided by the embodiments of the present invention can execute the converter mode switching method provided by any embodiment of the present invention, and has the corresponding functional modules and beneficial effects for executing the method.

[0337] Embodiment Ten

[0338] Figure 22 FIG. shows a schematic structural diagram of a converter 10 that can be used to implement the embodiments of the present invention. The components shown herein, their connections and relationships, and their functions are merely illustrative and are not intended to limit the implementation of the present invention described and / or claimed herein.

[0339] As Figure 22 shown, the converter 10 includes at least one processor 11 and a memory communicatively connected to the at least one processor 11, such as a read-only memory (ROM) 12, a random access memory (RAM) 13, etc. Among them, the memory stores a computer program executable by the at least one processor. The processor 11 can execute various appropriate actions and processes according to the computer program stored in the read-only memory (ROM) 12 or the computer program loaded from the storage unit 18 into the random access memory (RAM) 13. In the RAM 13, various programs and data required for the operation of the converter 10 can also be stored. The processor 11, the ROM 12, and the RAM 13 are connected to each other through a bus 14. The input / output (I / O) interface 15 is also connected to the bus 14.

[0340] Multiple components in the converter 10 are connected to the I / O interface 15, including: an input unit 16, a data input interface; an output unit 17, such as a data output interface, etc.; a storage unit 18, such as a disk, an optical disc, etc.; and a communication unit 19, such as a network card, a modem, a wireless communication transceiver, etc. The communication unit 19 allows the converter 10 to exchange information / data with other devices through a computer network such as the Internet and / or various telecommunication networks.

[0341] The processor 11 may be various general-purpose and / or special-purpose processing components with processing and computing capabilities. Some examples of the processor 11 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various dedicated artificial intelligence (AI) computing chips, various processors running machine learning model algorithms, a digital signal processor (DSP), and any suitable processor, controller, microcontroller, etc. The processor 11 executes the various methods and processes described above, such as the mode switching method of the converter.

[0342] In some embodiments, the mode switching method of the converter may be implemented as a computer program, which is tangibly contained in a computer-readable storage medium, such as the storage unit 18. In some embodiments, part or all of the computer program may be loaded and / or installed onto the converter 10 via the ROM 12 and / or the communication unit 19. When the computer program is loaded into the RAM 13 and executed by the processor 11, one or more steps of the mode switching method of the converter described above may be executed. Alternatively, in other embodiments, the processor 11 may be configured to execute the mode switching method of the converter in any other suitable manner (e.g., by means of firmware).

[0343] Various embodiments of the systems and techniques described above in this document may be implemented in digital electronic circuit systems, integrated circuit systems, field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), systems-on-a-chip (SOCs), complex programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various embodiments may include: being implemented in one or more computer programs, which may be executed and / or interpreted on a programmable system including at least one programmable processor, which may be a special-purpose or general-purpose programmable processor, and which may receive data and instructions from a storage system, at least one input device, and at least one output device, and transmit the data and instructions to the storage system, the at least one input device, and the at least one output device.

[0344] In some embodiments, the method for mode switching of the converter can be implemented as a computer program, which is invisibly included in a computer program product. When the computer program is executed by a processor, it implements the method for mode switching of the converter of the present invention. The computer program product can be understood as a software product that mainly implements its solution through a computer program. The computer program for implementing the method of the present invention can be written in any combination of one or more programming languages. These computer programs can be provided to the processor of a general-purpose computer, a special-purpose computer, or other programmable data processing devices, so that when the computer program is executed by the processor, the functions / operations specified in the flowchart and / or block diagram are implemented. The computer program can be executed entirely on the machine, partially on the machine, executed partially on the machine as an independent software package and partially on a remote machine, or executed entirely on a remote machine or server.

[0345] In the context of the present invention, a computer-readable storage medium can be a tangible medium that can contain or store a computer program for use by or in connection with an instruction execution system, apparatus, or device. The computer-readable storage medium can include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. Alternatively, the computer-readable storage medium can be a machine-readable signal medium. More specific examples of the machine-readable storage medium would include an electrical connection based on one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0346] It should be understood that various forms of the flow shown above can be used, with steps reordered, added, or deleted. For example, the steps recited in the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of the present invention can be achieved, and no limitations are imposed herein.

[0347] The above specific embodiments do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for mode switching of an inverter, characterized in that, Applied to an inverter connected to the grid, the operating modes of the inverter include a grid-following mode and a grid-forming mode, and the method includes: When the inverter operates in the grid-forming mode, output a grid-forming mode modulation voltage based on the second control loop in the grid-forming mode and control the operation of the inverter; Back up and operate the grid-following mode, and process the integrator of the first control loop in the grid-following mode based on the first state parameter of the inverter; When the inverter switches from the grid-forming mode to the grid-following mode, output a grid-following mode modulation voltage based on the processed first control loop and control the operation of the inverter; The first state parameter includes the port voltage of the inverter and the grid-forming mode modulation voltage; the integrator of the first control loop includes the integrator of the current loop control in the active and reactive power control loop; the processing of the integrator of the first control loop in the grid-following mode based on the first state parameter of the inverter includes: Perform phase-locked loop control on the port voltage of the inverter to output a phase-locked angle; Perform coordinate transformation on the port voltage based on the phase-locked angle to obtain the first port voltage in the two-phase rotating coordinate system; Perform coordinate transformation on the grid-forming mode modulation voltage in the two-phase stationary coordinate system based on the phase-locked angle to obtain the grid-forming mode modulation voltage in the two-phase rotating coordinate system; Assign the difference between the grid-forming mode modulation voltage in the two-phase rotating coordinate system and the first port voltage in the two-phase rotating coordinate system to the integrator in the current loop control.

2. The method according to claim 1, characterized in that, It also includes: Perform coordinate transformation on the port current of the inverter to obtain the first port current in the two-phase rotating coordinate system; Calculate the current reference value of the direct axis in the two-phase rotating coordinate system according to the first port voltage in the two-phase rotating coordinate system, the first port current of the quadrature axis in the two-phase rotating coordinate system, and the active power reference value; Input the current reference value of the direct axis in the two-phase rotating coordinate system into the direct axis current loop control in the second control loop; Assign the first port current of the quadrature axis in the two-phase rotating coordinate system to the current reference value of the quadrature axis in the two-phase rotating coordinate system; Input the current reference value of the quadrature axis in the two-phase rotating coordinate system into the quadrature axis current loop control in the second control loop.

3. The method according to any one of claims 1-2, characterized in that, The step of when the inverter switches from the grid-forming mode to the grid-following mode, output a grid-following mode modulation voltage based on the processed first control loop and control the operation of the inverter includes: When the inverter switches from the grid-forming mode to the grid-following mode, control the difference between the current reference value in the two-phase rotating coordinate system and the first port current in the two-phase rotating coordinate system based on the processed current loop control to obtain the first grid-following mode modulation voltage in the two-phase rotating coordinate system; Perform coordinate transformation on the first grid-following mode modulation voltage in the two-phase rotating coordinate system based on the phase-locked angle to obtain the grid-following mode modulation voltage in the two-phase stationary coordinate system; Perform pulse width modulation on the grid-following mode modulation voltage in the two-phase stationary coordinate system to obtain the grid-following mode pulse width modulation voltage; Control the operation of the inverter based on the grid-following mode pulse width modulation voltage.

4. A method for mode switching of an inverter, characterized in that Applied to a converter connected to the grid, the operating modes of the converter include a grid-following mode and a grid-forming mode, and the method includes: When the converter operates in the grid-following mode, output a grid-following mode modulation voltage based on a first control loop and control the operation of the converter; Back up and operate the grid-forming mode, and process the integrator of the second control loop in the grid-forming mode based on the second state parameter of the converter; the second state parameter of the converter includes: the phase-locked angle output in the grid-following mode; the integrator of the second control loop includes: the integrator of the virtual inertia link and the integrator of the integral link in the active power loop control of the virtual synchronous generator control loop, and the integrator of the integral link in the reactive power loop control; when the converter switches from the grid-following mode to the grid-forming mode, output a grid-forming mode modulation voltage based on the processed second control loop and control the operation of the converter; The method further includes at least one of the following: Assign the integrator of the virtual inertia link in the active power loop control of the virtual synchronous generator control loop to a preset phase-locked loop adjustment amount; Assign the integrator of the integral link in the active power loop control to the sum of a preset angle deviation value and the phase-locked angle; the preset angle deviation value is the angle deviation value between the phase-locked angle and the self-synchronization angle; the self-synchronization angle is output based on the active power loop control in the virtual synchronous generator control loop in the grid-forming mode; Calculate a target no-load electromotive force adjustment amount according to the preset angle deviation value and the second-port current in the two-phase rotating coordinate system output in the grid-following mode, and assign the integrator of the integral link in the reactive power loop control of the virtual synchronous generator control loop to the target no-load electromotive force adjustment amount.

5. The method according to claim 4, characterized in that, The second state parameter of the converter includes: the current reference value and the grid-following mode modulation voltage output in the grid-following mode; the integrator of the second control loop includes: the voltage loop integrator and / or the current loop integrator of the voltage-current loop control in the virtual synchronous generator control loop; the processing of the integrator of the second control loop in the grid-forming mode based on the second state parameter of the converter includes: In the grid-forming mode, output a self-synchronization angle based on the active power loop control in the virtual synchronous generator control loop; Process the voltage loop integrator of the voltage-current loop control in the virtual synchronous generator control loop according to the self-synchronization angle, the current reference value output in the grid-following mode, and the phase-locked angle; and / or process the current loop integrator of the voltage-current loop control in the virtual synchronous generator control loop according to the self-synchronization angle and the grid-following mode modulation voltage output in the grid-following mode.

6. The method according to claim 5, characterized in that The processing of the voltage loop integrator of the voltage-current loop control in the virtual synchronous generator control loop according to the self-synchronization angle, the current reference value output in the grid-following mode, and the phase-locked angle includes: Perform coordinate transformation on the current reference value output in the two-phase rotating coordinate system in the grid-following mode based on the phase-locked angle to obtain a current reference value in the two-phase stationary coordinate system; Based on the self - synchronization angle, perform coordinate transformation on the current reference value in the two - phase stationary coordinate system to obtain the current - loop current reference value in the two - phase rotating coordinate system; Assign the current - loop current reference value in the two - phase rotating coordinate system to the voltage - loop integrator of the voltage - current loop control.

7. The method according to claim 5, characterized in that The processing of the current - loop integrator of the voltage - current loop control in the virtual synchronous generator control loop according to the self - synchronization angle and the grid - following mode modulation voltage output in the grid - following mode includes: Based on the self - synchronization angle, perform coordinate transformation on the grid - following mode modulation voltage in the two - phase stationary coordinate system output in the grid - following mode to obtain the second grid - following mode modulation voltage in the two - phase rotating coordinate system; Assign the second grid - following mode modulation voltage to the current - loop integrator of the voltage - current loop control.

8. The method according to claim 4, characterized in that, The calculation formula for the preset angle deviation value is: ； The calculation formula for the target no - load electromotive force adjustment amount is: ； wherein, is a preset angular deviation value, is the second port current of the direct axis output in the grid-following mode, is the second port current of the quadrature axis in the two-phase rotating coordinate system output in the grid-following mode; is a virtual inductive reactance, is a virtual resistance; is the peak value of the phase voltage of the port voltage; is the target no-load electromotive force adjustment amount, is the rated no-load electromotive force.

9. The method according to claim 5, characterized in that, When the converter switches from the grid - following mode to the grid - forming mode, based on the processed second control loop, output the grid - forming mode modulation voltage and control the operation of the converter, including: When the converter switches from the grid - following mode to the grid - forming mode, based on the reactive - power loop control in the processed second control loop, output the no - load electromotive force; According to the self - synchronization angle and the no - load electromotive force, based on the virtual impedance control in the processed second control loop, control the port current to obtain the voltage reference value; Based on the voltage - current loop control in the processed second control loop, according to the self - synchronization angle and the no - load electromotive force, control the voltage reference value to obtain the grid - forming mode modulation voltage; Perform pulse - width modulation on the grid - forming mode modulation voltage and control the operation of the converter.

10. A mode switching device for an inverter, characterized in that Applied to a converter connected to the power grid, the operation modes of the converter include the grid - following mode and the grid - forming mode. The device includes: A grid - forming mode operation module, used for when the converter operates in the grid - forming mode, based on the second control loop in the grid - forming mode, output the grid - forming mode modulation voltage and control the operation of the converter; A grid - following mode backup module, used for backing up and operating the grid - following mode, and processing the integrator of the first control loop in the grid - following mode based on the first state parameters of the converter; A grid - following mode switching module, used for when the converter switches from the grid - forming mode to the grid - following mode, based on the processed first control loop, output the grid - following mode modulation voltage and control the operation of the converter; The first state parameters include the port voltage of the converter and the grid - forming mode modulation voltage; the integrator of the first control loop includes the integrator of the current - loop control in the active - reactive power control loop. The grid - following mode backup module includes: A first phase - locked loop control unit, used for performing phase - locked loop control on the port voltage of the converter and outputting the phase - locked angle; A first coordinate transformation unit, used for based on the phase - locked angle, performing coordinate transformation on the port voltage to obtain the first port voltage in the two - phase rotating coordinate system; A second coordinate transformation unit, configured to perform coordinate transformation on the network-forming mode modulation voltage in the two-phase stationary coordinate system based on the phase-locked angle to obtain the network-forming mode modulation voltage in the two-phase rotating coordinate system; An assignment unit, configured to assign the difference between the network-forming mode modulation voltage in the two-phase rotating coordinate system and the first port voltage in the two-phase rotating coordinate system to the integrator in the current loop control.

11. A mode switching device for an inverter, characterized in that Applied to a converter connected to the grid, the operating modes of the converter include a grid-following mode and a network-forming mode, and the device includes: A grid-following mode operation module, configured to output a grid-following mode modulation voltage based on a first control loop and control the operation of the converter when the converter operates in the grid-following mode; A network-forming mode backup module, configured to back up and operate the network-forming mode, and process the integrator of the second control loop in the network-forming mode based on the second state parameter of the converter; the second state parameter of the converter includes: the phase-locked angle output in the grid-following mode; the integrator of the second control loop includes: the integrator of the virtual inertia link and the integrator of the integral link in the active power loop control of the virtual synchronous generator control loop, and the integrator of the integral link in the reactive power loop control; A network-forming mode switching module, configured to output a network-forming mode modulation voltage based on the processed second control loop and control the operation of the converter when the converter switches from the grid-following mode to the network-forming mode; The device further includes at least one of the following modules; A first integrator assignment module, configured to assign the integrator of the virtual inertia link in the active power loop control of the virtual synchronous generator control loop to a preset phase-locked loop adjustment amount; A second integrator assignment module, configured to assign the integrator of the integral link in the active power loop control to the sum of a preset angle deviation value and the phase-locked angle; the preset angle deviation value is the angle deviation value between the phase-locked angle and the self-synchronization angle; the self-synchronization angle is output based on the active power loop control in the virtual synchronous generator control loop in the network-forming mode; A third integrator assignment module, configured to calculate a target no-load electromotive force adjustment amount according to the preset angle deviation value and the second port current in the two-phase rotating coordinate system output in the grid-following mode, and assign the integrator of the integral link in the reactive power loop control of the virtual synchronous generator control loop to the target no-load electromotive force adjustment amount.

12. A current converter, characterized in that, The converter includes: At least one processor; And a memory communicatively connected to the at least one processor; Wherein, the memory stores a computer program executable by the at least one processor, and the computer program is executed by the at least one processor so that the at least one processor can execute the mode switching method of the converter according to any one of claims 1-9.

13. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions, and the computer instructions are used to implement the mode switching method of the converter according to any one of claims 1-9 when executed by a processor.

14. A computer program product, characterized in that, The computer program product includes a computer program, and the computer program implements the mode switching method of the converter according to any one of claims 1-9 when executed by a processor.

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