A network-based new energy adaptive virtual inertia synchronization control method and system

Abstract

The present invention provides a method and system for adaptive virtual inertia synchronization control of grid-forming new energy, which belongs to the field of new energy power generation technology and control technology. It includes: collecting grid-forming new energy grid-connected voltage and current, calculating the instantaneous active power and reactive power injected into the grid by the grid-forming new energy; obtaining a voltage reference value through virtual synchronous machine control calculation according to the instantaneous active power, reactive power and active power reference value, reactive power reference value; obtaining a PWM modulation voltage according to the voltage reference value by using voltage and current double closed-loop control; obtaining a PWM control signal of the inverter according to the modulation voltage, and driving the inverter to operate. The present invention adaptively adjusts the virtual inertia according to the degree of grid-connected voltage fluctuation, so as to achieve synchronous stability of the grid-forming new energy when the voltage drops.

Description

Technical Field

[0001] The present application relates to the field of new energy power generation technology and control technology, and relates to a network-building new energy adaptive virtual inertia synchronization control method and system. Background Art

[0002] At present, with the large-scale grid connection of new energy, my country's power system is transforming into a new power system dominated by new energy. In order to solve the problem of inertia reduction caused by the grid connection of new energy, grid-connected new energy power generation technology has emerged. However, when the voltage of the point of common coupling (PCC) is disturbed, the grid-connected new energy is very prone to synchronous instability. Solving the problem of synchronous instability is of great significance for the large-scale safe and stable grid connection of new energy.

[0003] In view of the synchronous instability problem of grid-connected new energy, it is necessary to design corresponding control strategies. The existing methods are: ① Enhance transient stability by reducing virtual inertia. However, this will increase the frequency deviation and change rate between the voltage frequency of the grid-connected point of new energy and the rated frequency. ② After the fault occurs, the control mode switches from the VSG control mode to the vector current control mode in the PLL control coordinate system. It uses VSG to support the voltage amplitude and frequency of the grid during normal operation, and uses the phase-locked loop to synchronize with the grid during faults. This method has challenges in mode switching and parameter adjustment. ③ Improve the synchronous stability of the grid-connected inverter by reducing the active power reference value or increasing the reactive power reference value. However, this method will lead to a reduction in transmission power. ④ Use Lyapunov's second method for research. By constructing the Lyapunov function, the stability problem is transformed into the relationship between the comparison function value and the critical value, and then the stability of the system is judged. However, due to the complexity of numerical calculations, this method is difficult to obtain an analytical solution for general power systems.

[0004] In summary, the synchronous control method of grid-connected new energy is not yet mature and needs further design. This is of great significance to improving the penetration rate of new energy and realizing safe and reliable grid connection of new energy.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present application, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] In order to provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. The summary is not an extensive review, nor is it intended to identify key / critical elements or delineate the scope of protection of these embodiments, but rather serves as a prelude to the detailed description that follows.

[0007] The disclosed embodiments provide a method and system for adaptive virtual inertia synchronization control of a grid-connected new energy, which is mainly used to solve the risk of synchronization instability when the grid-connected new energy is disturbed. The virtual inertia is adaptively adjusted according to the PCC voltage fluctuation amplitude to achieve rapid response under small frequency deviation and suppress synchronization instability.

[0008] In some embodiments, the method comprises:

[0009] Collect the grid-connected voltage and current of the grid-forming new energy, and calculate the instantaneous active power and reactive power injected into the grid by the grid-forming new energy;

[0010] The voltage reference value is obtained by VSG control calculation according to the instantaneous active power, reactive power, active power reference value, and reactive power reference value;

[0011] According to the voltage reference value, the PWM modulation voltage is obtained by using the voltage and current double closed loop control;

[0012] The PWM control signal of the inverter is obtained according to the PWM modulation voltage to drive the inverter to operate.

[0013] Preferably, the VSG control adds an adaptive virtual inertia calculation module, which calculates the virtual inertia of the VSG control according to the PCC voltage fluctuation; the input end of the adaptive virtual inertia calculation module is connected to the PCC voltage, and the difference between the PCC voltage and the rated voltage is multiplied by the adjustment coefficient Get virtual inertia;

[0014] Virtual inertia The calculation formula is as follows:

[0015] ,

[0016] In the formula, is the initial value of virtual inertia, is the adjustment coefficient, , is the PCC voltage, is the rated voltage.

[0017] Preferably, the adjustment coefficient The calculation is as follows:

[0018] Set the system parameter active power reference value , transmission line impedance 、PCC voltage and grid voltage Input to the VSG control loop to calculate the power angle value at the unstable equilibrium point Steady-state value of power angle ;

[0019] According to the stability domain Steady-state value of power angle Calculate the maximum value of power angle overshoot and minimum damping ;

[0020] According to the minimum damping Calculate the maximum virtual inertia ;

[0021] Calculate the adjustment coefficient based on the maximum value of virtual inertia , the calculation formula is as follows:

[0022] ,

[0023] In the formula, is the maximum value of virtual inertia, is the initial value of virtual inertia.

[0024] Preferably, the maximum value of virtual inertia is calculated as follows:

[0025] ,

[0026] ,

[0027] In the formula, is the VSG damping coefficient, is the VSG angular velocity, is the equivalent inductance of the transmission line between PCC and the grid, is the grid voltage, is the minimum damping value.

[0028] Preferably, The specific calculation formula is as follows:

[0029] ,

[0030] ,

[0031] In the formula, To maintain the maximum value of the power angle overshoot allowed when the synchronization is stable, To consider the angle subtracted from the critical value of the stable power angle, Steady-state value of power angle.

[0032] Preferably, consider the stability domain The value range is .

[0033] Preferably, the voltage and current dual closed-loop control adopts a PI controller with feedforward decoupling.

[0034] A networked new energy adaptive virtual inertia synchronous control system, comprising:

[0035] Voltage and current acquisition module: collects grid-connected voltage and current of new energy sources;

[0036] Power calculation module: configured to calculate the instantaneous active power and reactive power injected into the power grid by the grid-forming new energy according to the grid-forming new energy grid-connected voltage and current;

[0037] A virtual synchronous machine control module: configured to calculate a voltage reference value according to instantaneous active power, reactive power and reference values ​​thereof;

[0038] Voltage and current dual closed-loop control module: configured to obtain PWM modulation voltage by voltage and current dual closed-loop control according to a voltage reference value;

[0039] Pulse width modulation module: configured to obtain a PWM control signal of an inverter according to a PWM modulation voltage.

[0040] In some embodiments, the device includes: a processor and a memory storing program instructions, and the processor is configured to execute the networked new energy adaptive virtual inertia synchronization control method when running the program instructions.

[0041] The embodiments of the present disclosure provide a network-based new energy adaptive virtual inertia synchronization control method and system, which can achieve the following technical effects:

[0042] The present invention adaptively adjusts the virtual inertia according to the PCC voltage fluctuation degree, so as to achieve the synchronization stability of the grid-building new energy when the voltage drops. The method enhances the frequency stability under the premise of ensuring the synchronization stability of the grid-building new energy by adaptively adjusting the virtual inertia. At the same time, the adjustment of the virtual inertia makes the system damping ratio equal to 0.707 (optimal damping ratio) as much as possible, thereby improving the dynamic response characteristics of the grid-building inverter.

[0043] The above general description and the following description are exemplary and explanatory only and are not intended to limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] One or more embodiments are exemplarily described by corresponding drawings, which do not limit the embodiments. Elements with the same reference numerals in the drawings are shown as similar elements, and the drawings do not constitute a scale limitation, and wherein:

[0045] Figure 1 This is a traditional grid-type new energy structure diagram;

[0046] Figure 2 It is the power angle characteristic curve of grid-type new energy;

[0047] Figure 3This is the block diagram of the adaptive virtual inertia synchronous control structure proposed in this patent;

[0048] Figure 4 The adjustment coefficient Calculation flow chart of

[0049] Figure 5 Output waveform diagram of new energy grid-type using traditional control strategy;

[0050] Figure 6 This is the waveform diagram of the grid-type new energy output when the voltage drops by 20% using the control strategy proposed in this patent;

[0051] Figure 7 This is the waveform diagram of the grid-type new energy output when the voltage drops by 30% using the control strategy proposed in this patent. DETAILED DESCRIPTION

[0052] In order to be able to understand the features and technical contents of the embodiments of the present disclosure in more detail, the implementation of the embodiments of the present disclosure is described in detail below in conjunction with the accompanying drawings. The attached drawings are for reference only and are not used to limit the embodiments of the present disclosure. In the following technical description, for the convenience of explanation, a full understanding of the disclosed embodiments is provided through multiple details. However, one or more embodiments can still be implemented without these details. In other cases, to simplify the drawings, well-known structures and devices can be simplified for display.

[0053] Example 1

[0054] Traditional grid-based new energy structures such as Figure 1 As shown in the figure, is the DC side voltage, , , is the three-phase voltage at PCC, , , is the inverter three-phase output current, , , It is the three-phase grid-connected current. and They are the inductance and capacitance of the inverter output side filter respectively. and are the equivalent resistance and inductance of the transmission line between PCC and the grid, respectively.

[0055] The network control algorithm used in this patent generates the reference voltage amplitude and phase through the virtual synchronous generator (VSG), then generates the three-phase modulation voltage through the voltage and current inner loop controller, and finally generates the drive signal through PWM to drive the inverter. The active control loop equation of the virtual synchronous generator control is:

[0056] ,

[0057] Where: is the virtual inertia; is the virtual rotor damping coefficient; and are VSG angular velocity and angular velocity reference value, respectively. ; and They are active power reference value and grid-building new energy output active power respectively; is the power angle, which is the phase difference between the voltage at the PCC and the grid voltage.

[0058] The adaptive virtual inertia synchronous control structure of this embodiment is as follows: Figure 3 As shown in the figure, by introducing the virtual inertia calculation module, the virtual inertia is adaptively adjusted according to the PCC voltage fluctuation, and the frequency stability is maximized under the premise of ensuring the synchronous stability of the grid-forming inverter. At the same time, the system damping is made as equal to 0.707 (optimal damping ratio) as possible to improve the dynamic response characteristics of the grid-forming inverter.

[0059] A network-based new energy adaptive virtual inertia synchronization control method, such as Figure 3 As shown, the specific steps include:

[0060] S1: Collect the output voltage and current of the grid-forming renewable energy, and calculate the instantaneous active power and reactive power injected into the grid by the grid-forming renewable energy.

[0061] S2: The voltage reference value is obtained by VSG control calculation according to the instantaneous active power, reactive power, active power reference value and reactive power reference value.

[0062] S3: Obtain PWM modulation voltage by using voltage and current double closed-loop control according to the voltage reference value.

[0063] S4: Obtain a PWM control signal of the inverter according to the PWM modulation voltage, and drive the inverter to operate.

[0064] As a refinement of the above steps, after the grid-building new energy source is connected to the grid in step S1, the instantaneous active power delivered to the grid is:

[0065] ,

[0066] In the formula, , is the equivalent inductance of the transmission line between PCC and the grid, is the grid voltage.

[0067] As a refinement of the above steps, in step S2, the VSG control adds an adaptive virtual inertia calculation module, which calculates the virtual inertia of the VSG control according to the PCC voltage fluctuation; the input end of the adaptive virtual inertia calculation module is connected to the PCC voltage, and the difference between the PCC voltage and the rated voltage is multiplied by the adjustment coefficient Obtain virtual inertia; calculate a voltage reference value according to the adjusted virtual inertia, wherein the voltage reference value includes a voltage amplitude , voltage phase angle , the specific formula is as follows:

[0068] ,

[0069] ,

[0070] In the formula, represents the proportional controller gain of the reactive power control loop, Output reactive power for grid-connected new energy. is the reactive power reference value, is the voltage rating.

[0071] Virtual inertia The calculation formula is as follows:

[0072] ,

[0073] In the formula, is the initial value of virtual inertia, is the adjustment coefficient, , is the PCC voltage.

[0074] Normally, , When the voltage drops, ,but , the virtual rotor moment of inertia (virtual inertia) is reduced, thereby increasing the system damping and reducing the peak value of the power angle in the transient process.

[0075] Control parameters The setting is as follows: In practical application, It's not that the smaller the better. Too small will result in excessive damping, which will slow down the system response time and deteriorate the frequency stability. The optimal damping ratio of the system is 0.707, at which the system can be adjusted quickly and stably. Therefore, the virtual inertia should be as large as possible while ensuring that the system remains synchronous and stable. At the same time, in order to ensure that the system has a certain degree of stability, the maximum value of the grid-connected inverter power angle peak should be less than .

[0076] Based on the above considerations, if Figure 4 As shown, the adjustment coefficient The calculation process is as follows:

[0077] S2-1: Set the system parameter active power reference value , Line impedance 、PCC voltage and grid voltage Input VSG control and calculate the power angle value at the stable or unstable equilibrium point Steady-state value of power angle , the calculation formula is as follows:

[0078] ,

[0079] S2-2: According to the stability domain Steady-state value of power angle Calculate the maximum value of the power angle overshoot allowed to maintain synchronous stability and minimum damping , the specific calculation formula is as follows:

[0080] ,

[0081] ,

[0082] In the formula, is the maximum value of the power angle overshoot, is the critical value of power angle, Steady-state value of power angle, The angle is the angle subtracted from the critical value of the power angle in the stable domain. The value range is .

[0083] S2-3: Calculate the maximum value of virtual inertia , the calculation formula is as follows:

[0084] ,

[0085] ,

[0086] In the formula, is the VSG damping coefficient, is the VSG angular velocity, is the equivalent inductance of the transmission line between PCC and the grid, is the grid voltage, The minimum damping allowed to maintain synchronous stability.

[0087] S2-4: Calculate the adjustment coefficient based on the maximum value of virtual inertia , the calculation formula is as follows:

[0088] ,

[0089] In the formula, is the maximum value of virtual inertia, is the initial value of virtual inertia.

[0090] As a refinement of the above steps, the voltage and current dual closed-loop control in step S3 adopts a PI controller with feedforward decoupling. The specific PI controller obtains the voltage amplitude of the VSG control output , voltage phase angle , after abc-dq coordinate transformation, it becomes a two-phase DC voltage and current output PWM modulation voltage.

[0091] Combine the following Figure 3 The rationality of the technical solution of this embodiment is analyzed as follows:

[0092] Under normal circumstances, grid-connected new energy operates at Figure 3 In After the PCC voltage fluctuates, the system transmission power decreases, and the power angle curve switches from the normal operation curve in the figure to the disturbance curve. , the power angle curve moves in the direction of increasing power angle. If during the transient process, the peak power angle Less than , then the system returns to the equilibrium point in steady state, such as Figure 2 At points b and c in the figure, the grid-connected inverter can maintain synchronous stability. Otherwise, synchronous instability occurs.

[0093] In summary, when the system is disturbed, in order to ensure that the grid-connected renewable energy source keeps pace with the power grid, the peak value of the power angle Should be less than , the system returns to the equilibrium point in steady state.

[0094] The small signal model of grid-connected new energy can be obtained by linearizing the active control loop equation of the virtual synchronous machine control and the instantaneous active power calculation equation transmitted to the power grid, as follows:

[0095] ,

[0096] In the formula, Power angle change, is the virtual inertia, is the Laplace operator representing the differential, is the damping coefficient, Active power disturbance, is the transmission line impedance

[0097] It can be seen that the grid-building new energy is a second-order system, which can be transformed into a typical second-order system as follows:

[0098] ,

[0099] In the formula, is a constant coefficient, For damping, is the natural oscillation angular frequency, calculated as follows:

[0100] ,

[0101] In a second-order system, the overshoot is calculated as follows:

[0102] ,

[0103] In the formula, is the power angle overshoot, is the peak power angle, is the steady-state value of the power angle.

[0104] From the above formula, we can see that small virtual inertia can reduce the power angle peak by increasing system damping.

[0105] Combine the following Figures 5 to 7 The effect of this embodiment is described as follows:

[0106] use Figure 3 The adaptive virtual inertia synchronization control strategy proposed in this patent is shown in Figure 1. Taking a 50kW new energy grid-connected system under typical parameters as an example, a fault is set at 2s. The grid-connected new energy output waveform is as follows: Figures 5 to 7 As shown, from top to bottom in the figure are grid-connected voltage, grid-connected current, active power, and power angle. Figure 5 When the voltage drops by 20%, the traditional synchronous control strategy is adopted, and the grid-forming new energy will experience synchronous instability after the fault occurs. The output results of the grid-forming new energy are as follows: Figure 6 As shown in the figure, after a fault occurs, the grid-connected new energy adaptively adjusts the virtual inertia to keep in sync with the grid. The voltage drop is further set to 30%, and the output result is as follows: Figure 7 As shown in Figure 2, grid-connected renewable energy can still keep pace with the power grid. Figure 6 and Figure 7From the results shown, it can be seen that the new method effectively ensures the synchronization stability of grid-connected new energy.

[0107] Example 2

[0108] A networked new energy adaptive virtual inertia synchronous control system, comprising:

[0109] Voltage and current acquisition module: collects grid-connected voltage and current of new energy sources.

[0110] Power calculation module: configured to calculate the instantaneous active power and reactive power injected into the power grid by the grid-connected new energy according to the grid-connected new energy voltage and current.

[0111] The virtual synchronous machine control module is configured to calculate a voltage reference value according to instantaneous active power, reactive power and reference values ​​thereof.

[0112] Voltage-current dual closed-loop control module: configured to obtain PWM modulation voltage based on voltage reference value by utilizing voltage-current dual closed-loop control.

[0113] Pulse width modulation module: configured to obtain a PWM control signal of an inverter according to a PWM modulation voltage.

[0114] The disclosed embodiment also provides a network-based new energy adaptive virtual inertia synchronous control device, including a processor and a memory. Optionally, the device may also include a communication interface and a bus. The processor, the communication interface, and the memory may communicate with each other through the bus. The communication interface may be used for information transmission. The processor may call the logic instructions in the memory to execute the network-based new energy adaptive virtual inertia synchronous control method of the above embodiment.

[0115] In addition, the logic instructions in the above-mentioned memory can be implemented in the form of software functional units and can be stored in a computer-readable storage medium when sold or used as an independent product.

[0116] The memory, as a computer-readable storage medium, can be used to store software programs and computer executable programs, such as program instructions / modules corresponding to the method in the embodiment of the present disclosure. The processor executes the functional application and data processing by running the program instructions / modules stored in the memory, that is, the network-based new energy adaptive virtual inertia synchronous control method in the above embodiment is realized.

[0117] The memory may include a program storage area and a data storage area, wherein the program storage area may store an operating system and an application required for at least one function; the data storage area may store data created according to the use of the terminal device, etc. In addition, the memory may include a high-speed random access memory and may also include a non-volatile memory.

[0118] An embodiment of the present disclosure provides a computer-readable storage medium storing computer-executable instructions, wherein the computer-executable instructions are configured to execute the above-mentioned networked new energy adaptive virtual inertia synchronous control method.

[0119] The computer-readable storage medium mentioned above may be a transient computer-readable storage medium or a non-transitory computer-readable storage medium.

[0120] The technical solution of the embodiment of the present disclosure can be embodied in the form of a software product, which is stored in a storage medium and includes one or more instructions for enabling a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in the embodiment of the present disclosure. The aforementioned storage medium may be a non-transient storage medium, including: a USB flash drive, a mobile hard disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a disk or an optical disk, and other media that can store program codes, or a transient storage medium.

[0121] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A network-based new energy adaptive virtual inertia synchronous control method, characterized in that: include: Collect the grid-connected voltage and current of the grid-forming new energy, and calculate the instantaneous active power and reactive power injected into the grid by the grid-forming new energy; The voltage reference value is obtained by VSG control calculation according to the instantaneous active power, reactive power, active power reference value, and reactive power reference value; According to the voltage reference value, the PWM modulation voltage is obtained by using the voltage and current double closed loop control; The PWM control signal of the inverter is obtained according to the PWM modulation voltage to drive the inverter to operate; The VSG control adds an adaptive virtual inertia calculation module, which calculates the virtual inertia of the VSG control according to the PCC voltage fluctuation; the input end of the adaptive virtual inertia calculation module is connected to the PCC voltage, and the difference between the PCC voltage and the rated voltage is multiplied by the adjustment coefficient Get virtual inertia; Virtual inertia The calculation formula is as follows: ， In the formula, is the initial value of virtual inertia, is the adjustment coefficient, , is the PCC voltage, is the rated voltage; The adjustment factor The calculation is as follows: Set the system parameter active power reference value , transmission line impedance 、PCC voltage and grid voltage Input to the VSG control loop to calculate the power angle value at the unstable equilibrium point Steady-state value of power angle ; According to the stability domain Steady-state value of power angle Calculate the maximum value of power angle overshoot and minimum damping ; According to the minimum damping Calculate the maximum virtual inertia ; Calculate the adjustment coefficient based on the maximum value of virtual inertia , the calculation formula is as follows: ， In the formula, is the maximum value of virtual inertia, is the initial value of virtual inertia; The calculation formula for the maximum virtual inertia is as follows: ， ， In the formula, is the VSG damping coefficient, is the VSG angular velocity, is the equivalent inductance of the transmission line between PCC and the grid, is the grid voltage, is the minimum damping value; The specific calculation formula is as follows: ， ， In the formula, To maintain the maximum value of the power angle overshoot allowed when the synchronization is stable, To consider the angle subtracted from the critical value of the stable power angle, Steady-state value of power angle.

2. The network-based new energy adaptive virtual inertia synchronous control method according to claim 1 is characterized in that: Consider the stability domain The value range is .

3. The network-based new energy adaptive virtual inertia synchronous control method according to any one of claims 1-2 is characterized in that: The voltage and current dual closed-loop control adopts a PI controller with feedforward decoupling.

4. A networked new energy adaptive virtual inertia synchronous control system for executing any of the methods described in claims 1-3, characterized in that: include: Voltage and current acquisition module: collects grid-connected voltage and current of new energy sources; Power calculation module: configured to calculate the instantaneous active power and reactive power injected into the power grid by the grid-forming new energy according to the grid-forming new energy grid-connected voltage and current; A virtual synchronous machine control module: configured to calculate a voltage reference value according to instantaneous active power, reactive power and reference values ​​thereof; Voltage and current dual closed-loop control module: configured to obtain PWM modulation voltage by voltage and current dual closed-loop control according to a voltage reference value; Pulse width modulation module: configured to obtain a PWM control signal of an inverter according to a PWM modulation voltage.

5. A network-based new energy adaptive virtual inertia synchronous control device, comprising a processor and a memory storing program instructions, characterized in that: The processor is configured to execute the networked new energy adaptive virtual inertia synchronization control method as described in any one of claims 1 to 3 when running the program instructions.

6. A storage medium storing program instructions, characterized in that: When the program instructions are run, they execute the networked new energy adaptive virtual inertia synchronization control method as described in any one of claims 1 to 3.

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