Power distribution strategy method and system for virtual synchronous generator parallel system

Abstract

The invention belongs to the technical field of virtual synchronous generator parallel system power distribution control, and discloses a virtual synchronous generator parallel system power distribution strategy method, which can realize proportional power distribution of each VSG through a traditional virtual impedance control method. By introducing the power distribution coefficient, when the source side is disturbed, each VSG parameter can still be set in proportion. The self-adaptive virtual impedance control method is provided based on the combination of the power distribution coefficient and the virtual impedance, so that each VSG can still distribute power according to the proportion when the output power of the source side changes, and the overall stability of the system is improved.

Description

Technical Field

[0001] This invention belongs to the field of power distribution control technology for virtual synchronous generator parallel systems, and particularly relates to a power distribution strategy method and system for virtual synchronous generator parallel systems. Background Technology

[0002] With the continuous increase in the installed capacity and proportion of renewable energy, the degree of power electronics in power systems is constantly improving. For new power electronic systems, a series of new control strategies are constantly being proposed. In view of the characteristics of low inertia and low damping of power electronic devices, the Virtual Synchronous Generator (VSG) control technology has emerged.

[0003] Since the capacity of a single VSG is limited, multiple VSGs are typically connected in parallel to increase system capacity. To improve the power distribution accuracy of parallel VSG systems, virtual impedance and dynamically adjusted power distribution coefficients are generally used. While the traditional fixed-value virtual impedance method can improve power distribution accuracy, it does not consider the reduced stability of the parallel VSG system when the power supply output power changes, making it unsuitable for complex and variable external environments. When the proportion of source-side output power changes, a fixed virtual impedance will lead to increased power distribution errors. Although dynamically adjusting the power distribution coefficient can reduce the impact of power supply disturbances on the system, the mutual influence between the VSGs can still reduce system stability.

[0004] Existing technology solution

[0005] In the research on the control strategy for parallel operation of VSGs, the virtual negative impedance method is used to improve the power distribution accuracy when multiple VSGs are connected in parallel. Each VSG can distribute power proportionally, but it cannot adapt to the situation of power supply disturbance.

[0006] In the paper "Power Allocation Strategy for Inverter Parallel Systems Based on Virtual Synchronous Motor Control", the power allocation coefficient between each VSG is dynamically adjusted according to the change of the output power at the power supply end, which reduces the impact of power supply disturbances on system stability, but ignores the coupling effect between VSGs.

[0007] Based on the above analysis, the problems and shortcomings of the existing technology are as follows:

[0008] (1) The virtual impedance is set to a fixed value, which cannot cope with the output power disturbance of each parallel VSG power supply terminal.

[0009] (2) Only the dynamic change of the power allocation coefficient is realized, and there will still be coupling effects between each VSG. Summary of the Invention

[0010] To address the problems existing in the prior art, this invention provides a power allocation strategy method for a virtual synchronous generator parallel system.

[0011] This invention is implemented as follows: a power allocation strategy method for a virtual synchronous generator parallel system includes:

[0012] Step 1: Design the VSG control structure;

[0013] The active frequency loop of the VSG, where ω0, ω, and ωpcc are the reference angular frequency, the VSG output angular frequency, and the common coupling point angular frequency, respectively; Kp is the active droop coefficient; Pref and Pe are the reference active power and the VSG output active power, respectively; J and D are the moment of inertia and damping coefficient, respectively; referring to the synchronous generator rotor motion equation, we can obtain:

[0014] (1)

[0015] Step 2: Design an adaptive virtual impedance control strategy.

[0016] Furthermore, the VSG control structure is designed as follows:

[0017] The reactive voltage loop of the VSG, where Qref and Qe are the reference reactive power and the VSG output reactive power, respectively; Kq is the reactive droop factor; E0 and E are the reference voltage and the VSG output voltage, respectively;

[0018] The following relationship can be obtained from the control loop:

[0019] (2)

[0020] Equivalent circuit of VSG parallel system, where E is the VSG output voltage, δ is the VSG output power angle, R is the sum of line resistance and equivalent output resistance, L is the sum of line inductance and equivalent output inductance, and Upcc is the voltage of the common connection line; current expression, impedance expression, active power expression, and reactive power expression:

[0021] The sum of the line impedance and the equivalent output impedance Z can be expressed as:

[0022] (3)

[0023] The expression for the apparent power output of the VSG is:

[0024] (4)

[0025] This leads to the expressions for the active and reactive power output of the VSG:

[0026] (5)

[0027] Because voltage-type control is used, the output voltage of the VSG will remain constant at all times. Therefore, when the power is proportional, the output current must also be proportional. In order to ensure that the power can be distributed according to the set ratio when the VSGs are connected in parallel, it is necessary to discuss the power distribution strategy of the parallel system under different capacities.

[0028] Furthermore, the design incorporates an adaptive virtual impedance control strategy:

[0029] With the addition of a virtual impedance, the equivalent output impedance of the VSG can be expressed as follows:

[0030] (6)

[0031] The equivalent star circuit model of two VSGs connected in parallel; the output voltage amplitudes of the two VSGs are defined as E1 and E2, respectively, and δ1 and δ2 are the phase angles of the two modules; the equivalent sums of the output impedance and line impedance are Z1 and Z2, respectively, where Z1=R1+jX1, Z2=R2+jX2; U represents the load terminal voltage, its phase angle is set to 0, and the load impedance is ZL, ZL=RL+jXL;

[0032] Let N be the ratio of the rated capacities of the two VSGs. The following conditions must be met for the VSG power to be distributed proportionally, derived using the formula:

[0033] (7)

[0034] Introducing a power allocation coefficient μi during the dynamic process, the following relationship can be obtained when multiple VSGs are running in parallel:

[0035] (8)

[0036] When the above conditions are met, each VSG can achieve a proportional power distribution in steady state. However, each VSG is usually connected to a different new energy power generation platform, and the output characteristics of each platform are different. Affected by the external environment, the output power of the new energy power generation platform will also change continuously. At this time, the power ratio of each VSG will also change, that is, μi is dynamically changing. The virtual impedance control method mentioned above is no longer applicable at this time. Therefore, an adaptive virtual impedance control method suitable for the dynamic change of VSG power ratio is proposed by combining formula (6) and formula (8).

[0037] (9)

[0038] Wherein, KR and KL are the virtual inductance coefficient and virtual resistance coefficient, respectively; it can be seen that when the power output changes, the increased virtual impedance will be dynamically adjusted with the change of μi, and the equivalent output impedance ratio of each VSG will always be the same as the power distribution ratio, thus achieving stable power distribution of the VSG parallel system.

[0039] Another object of the present invention is to provide a power distribution strategy system for a virtual synchronous generator parallel system, comprising:

[0040] The VSG design module is used to design VSG control structures.

[0041] The adaptive design module is used to design adaptive virtual impedance control strategies.

[0042] Another object of the present invention is to provide a computer device including a memory and a processor, the memory storing a computer program, which, when executed by the processor, causes the processor to perform the steps of the power allocation strategy method for the virtual synchronous generator parallel system.

[0043] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the power allocation strategy method for the virtual synchronous generator parallel system.

[0044] Another objective of this invention is to provide an information data processing terminal for implementing the power distribution strategy system of the virtual synchronous generator parallel system.

[0045] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows:

[0046] This invention proposes an adaptive virtual impedance control method from the perspective of line impedance, dynamically adjusting the virtual impedance based on changes in source-side output power. Simulation verification shows that the proposed method can effectively cope with changes in source-side output power and improve power distribution accuracy, maintaining stable output voltage even during sudden external changes. To address the voltage sag issue caused by the proposed method, this invention employs bus voltage compensation to reduce voltage sag, and simulations further verify the effectiveness of the proposed control method.

[0047] Improve the power distribution accuracy of VSG parallel systems and achieve proportional power distribution among VSGs.

[0048] When the output power at the power supply terminal changes, the power can still be distributed among the VSGs according to the power supply terminal power ratio.

[0049] It improves the power distribution accuracy of VSG parallel systems.

[0050] It ensures that the VSG power can still be distributed proportionally when there is a disturbance in the source-side output power.

[0051] To address the issue that traditional virtual impedance control cannot adapt to changes in source-side output power, an adaptive virtual impedance control is proposed. When the source side is subjected to external environmental disturbances, it can effectively improve the power distribution accuracy and bus voltage stability of the VSG networking system, providing a feasible control scheme for enhancing the overall stability of the VSG networking system.

[0052] Traditional virtual impedance control methods can achieve proportional power distribution among VSGs. By introducing a power allocation coefficient, the parameters of each VSG can still be set proportionally when the source side is disturbed. Based on the combination of power allocation coefficient and virtual impedance, an adaptive virtual impedance control method is proposed to ensure that each VSG still distributes power proportionally when the source-side output power changes, thereby improving the overall stability of the system. Attached Figure Description

[0053] Figure 1 This is a flowchart of the power allocation strategy method for a virtual synchronous generator parallel system provided in an embodiment of the present invention.

[0054] Figure 2 This is a system structure block diagram of the power allocation strategy method for a virtual synchronous generator parallel system provided in an embodiment of the present invention.

[0055] Figure 3 This is a diagram of the virtual synchronous generator network operation structure provided in an embodiment of the present invention.

[0056] Figure 4 This is a block diagram of the VSG active frequency loop control provided in an embodiment of the present invention.

[0057] Figure 5 This is a block diagram of the VSG reactive voltage loop control provided in an embodiment of the present invention.

[0058] Figure 6 This is the equivalent circuit diagram of the VSG parallel system provided in the embodiment of the present invention.

[0059] Figure 7 This is a virtual impedance structure diagram provided in an embodiment of the present invention.

[0060] Figure 8 This is a diagram of the equivalent star circuit model of the parallel VSG provided in the embodiment of the present invention.

[0061] Figure 9 This is a diagram illustrating the expected control effect provided by an embodiment of the present invention. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0063] like Figure 1 As shown, the power allocation strategy method for a virtual synchronous generator parallel system provided by this embodiment of the invention includes the following steps:

[0064] S101, Design the VSG control structure;

[0065] The active frequency loop of the VSG, where ω0, ω, and ωpcc are the reference angular frequency, the VSG output angular frequency, and the common coupling point angular frequency, respectively; Kp is the active droop coefficient; Pref and Pe are the reference active power and the VSG output active power, respectively; J and D are the moment of inertia and damping coefficient, respectively; referring to the synchronous generator rotor motion equation, we can obtain:

[0066] (1)

[0067] S102, design an adaptive virtual impedance control strategy.

[0068] The VSG control structure provided in this embodiment of the invention is as follows:

[0069] The reactive voltage loop of the VSG, where Qref and Qe are the reference reactive power and the VSG output reactive power, respectively; Kq is the reactive droop factor; E0 and E are the reference voltage and the VSG output voltage, respectively;

[0070] The following relationship can be obtained from the control loop:

[0071] (2)

[0072] Equivalent circuit of VSG parallel system, where E is the VSG output voltage, δ is the VSG output power angle, R is the sum of line resistance and equivalent output resistance, L is the sum of line inductance and equivalent output inductance, and Upcc is the voltage of the common connection line; current expression, impedance expression, active power expression, and reactive power expression:

[0073] The sum of the line impedance and the equivalent output impedance Z can be expressed as:

[0074] (3)

[0075] The expression for the apparent power output of the VSG is:

[0076] (4)

[0077] This leads to the expressions for the active and reactive power output of the VSG:

[0078] (5)

[0079] Because voltage-type control is used, the output voltage of the VSG will remain constant at all times. Therefore, when the power is proportional, the output current must also be proportional. In order to ensure that the power can be distributed according to the set ratio when the VSGs are connected in parallel, it is necessary to discuss the power distribution strategy of the parallel system under different capacities.

[0080] The design adaptive virtual impedance control strategy provided by the embodiments of the present invention:

[0081] With the addition of a virtual impedance, the equivalent output impedance of the VSG can be expressed as follows:

[0082] (6)

[0083] The equivalent star circuit model of two VSGs connected in parallel; the output voltage amplitudes of the two VSGs are defined as E1 and E2, respectively, and δ1 and δ2 are the phase angles of the two modules; the equivalent sums of the output impedance and line impedance are Z1 and Z2, respectively, where Z1=R1+jX1, Z2=R2+jX2; U represents the load terminal voltage, its phase angle is set to 0, and the load impedance is ZL, ZL=RL+jXL;

[0084] Let N be the ratio of the rated capacities of the two VSGs. The following conditions must be met for the VSG power to be distributed proportionally, derived using the formula:

[0085] (7)

[0086] Introducing a power allocation coefficient μi during the dynamic process, the following relationship can be obtained when multiple VSGs are running in parallel:

[0087] (8)

[0088] When the above conditions are met, each VSG can achieve a proportional power distribution in steady state. However, each VSG is usually connected to a different new energy power generation platform, and the output characteristics of each platform are different. Affected by the external environment, the output power of the new energy power generation platform will also change continuously. At this time, the power ratio of each VSG will also change, that is, μi is dynamically changing. The virtual impedance control method mentioned above is no longer applicable at this time. Therefore, an adaptive virtual impedance control method suitable for the dynamic change of VSG power ratio is proposed by combining formula (6) and formula (8).

[0089] (9)

[0090] Wherein, KR and KL are the virtual inductance coefficient and virtual resistance coefficient, respectively; it can be seen that when the power output changes, the increased virtual impedance will be dynamically adjusted with the change of μi, and the equivalent output impedance ratio of each VSG will always be the same as the power distribution ratio, thus achieving stable power distribution of the VSG parallel system.

[0091] like Figure 2 As shown, the power allocation strategy system for a virtual synchronous generator parallel system provided in this embodiment of the invention includes:

[0092] The VSG design module is used to design VSG control structures.

[0093] The adaptive design module is used to design adaptive virtual impedance control strategies.

[0094] Another object of the present invention is to provide a computer device including a memory and a processor, the memory storing a computer program, which, when executed by the processor, causes the processor to perform the steps of the power allocation strategy method for the virtual synchronous generator parallel system.

[0095] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the power allocation strategy method for the virtual synchronous generator parallel system.

[0096] Another objective of this invention is to provide an information data processing terminal for implementing the power distribution strategy system of the virtual synchronous generator parallel system.

[0097] Specific implementation of the present invention:

[0098] like Figure 3 The diagram shows the virtual synchronous generator network operation structure. Each VSG connects to a separate new energy power generation platform, and all VSGs are connected in parallel to the AC bus to share the external load. The VSG control loop mainly consists of two parts: the active frequency loop and the reactive voltage loop.

[0099] Step 1: Design the VSG control structure

[0100] Figure 4 The diagram shows the active frequency loop of the VSG, where ω0, ω, and ωpcc are the reference angular frequency, VSG output angular frequency, and common coupling point angular frequency, respectively; Kp is the active droop coefficient; Pref and Pe are the reference active power and VSG output active power, respectively; J and D are the moment of inertia and damping coefficient, respectively; referring to the synchronous generator rotor motion equation, we can obtain:

[0101] (1)

[0102] Figure 5 The diagram shows the reactive voltage loop of the VSG, where Qref and Qe are the reference reactive power and the VSG output reactive power, respectively; Kq is the reactive droop factor; and E0 and E are the reference voltage and the VSG output voltage, respectively.

[0103] The following relationship can be obtained from the control loop:

[0104] (2)

[0105] Figure 6 The diagram shows the equivalent circuit of a VSG parallel system, where E is the VSG output voltage, δ is the VSG output power angle, R is the sum of the line resistance and the equivalent output resistance, L is the sum of the line inductance and the equivalent output inductance, and Upcc is the voltage across the common connection. Current, impedance, active power, and reactive power are expressed as follows:

[0106] The sum of the line impedance and the equivalent output impedance Z can be expressed as:

[0107] (3)

[0108] The expression for the apparent power output of the VSG is:

[0109] (4)

[0110] This leads to the expressions for the active and reactive power output of the VSG:

[0111] (5)

[0112] Because voltage-type control is used, the output voltage of the VSG will remain constant at all times. Therefore, when the power is proportional, the output current must also be proportional. In order to ensure that the power is distributed according to the set ratio when VSGs are connected in parallel, it is necessary to discuss the power distribution strategy for parallel systems with different capacities.

[0113] Step 2: Design an adaptive virtual impedance control strategy

[0114] Traditional virtual impedance control structures, such as Figure 7 As shown:

[0115] With the addition of a virtual impedance, the equivalent output impedance of the VSG can be expressed as follows:

[0116] (6)

[0117] Taking two VSG units connected in parallel as an example, Figure 8This is the equivalent star circuit model for two VSGs connected in parallel. The output voltage amplitudes of the two VSGs are defined as E1 and E2, respectively, and δ1 and δ2 are the phase angles of the two modules. The equivalent sums of the output impedance and line impedance are Z1 and Z2, respectively, where Z1 = R1 + jX1 and Z2 = R2 + jX2. U represents the load terminal voltage, with its phase angle set to 0, and the load impedance is ZL, ZL = RL + jXL.

[0118] Let N be the ratio of the rated capacities of the two VSGs. The following conditions must be met for the VSG power to be distributed proportionally, derived using the formula:

[0119] (7)

[0120] Introducing a power allocation coefficient μi during the dynamic process, the following relationship can be obtained when multiple VSGs are running in parallel:

[0121] (8)

[0122] When the above conditions are met, each VSG can achieve a proportional power distribution in steady state. However, each VSG is usually connected to a different new energy power generation platform, and the output characteristics of each platform are different. Affected by the external environment, the output power of the new energy power generation platform will also change continuously. At this time, the power ratio of each VSG will also change, that is, μi is dynamically changing. The virtual impedance control method mentioned above is no longer applicable at this time. Therefore, an adaptive virtual impedance control method suitable for the dynamic change of VSG power ratio is proposed by combining formula (6) and formula (8).

[0123] (9)

[0124] Where KR and KL are the virtual inductance and virtual resistance coefficients, respectively. It can be seen that when the power output changes, the increased virtual impedance dynamically adjusts with the change in μi, and always maintains the same ratio of the equivalent output impedance of each VSG to the power distribution ratio, ultimately achieving stable power distribution in the VSG parallel system.

[0125] Expected control effect such as Figure 9 As shown.

[0126] It should be noted that embodiments of the present invention can be implemented in hardware, software, or a combination of both. The hardware portion can be implemented using dedicated logic; the software portion can be stored in memory and executed by a suitable instruction execution system, such as a microprocessor or dedicated-design hardware. Those skilled in the art will understand that the above-described devices and methods can be implemented using computer-executable instructions and / or included in processor control code, for example, such code provided on a carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and modules of the present invention can be implemented by hardware circuitry such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, or programmable hardware devices such as field-programmable gate arrays, programmable logic devices, etc., or by software executed by various types of processors, or by a combination of the above-described hardware circuitry and software, such as firmware.

[0127] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A power distribution method for a virtual synchronous generator parallel system, characterized in that, Includes the following steps: An active power and frequency control loop is established. The rotor motion equation is solved in real time by a digital controller. The product of the moment of inertia parameter and the rate of change of angular frequency plus the product of the damping coefficient parameter and the difference between the output angular frequency of the virtual synchronous generator and the angular frequency of the point of common coupling is equal to the difference between the reference active power and the actual output active power. The output angular frequency of the virtual synchronous generator is adjusted accordingly. Establish a reactive power and voltage control loop so that the output voltage of the virtual synchronous generator is equal to the reference voltage minus the product of the reactive power droop coefficient and the difference between the actual reactive power and the reference reactive power. The apparent output power is calculated based on the sum of the line impedance and the equivalent output impedance, and the target output current of each virtual synchronous generator is set according to a preset ratio. A virtual impedance consisting of a virtual resistance coefficient and a virtual inductance coefficient is set at the output of each virtual synchronous generator. A power allocation coefficient is introduced, and the virtual impedance is dynamically adjusted based on this coefficient to ensure that the equivalent output impedance ratio of each virtual synchronous generator is consistent with the power allocation ratio, thereby achieving stable proportional power allocation when the power on the power supply side changes.

2. The method according to claim 1, wherein the power allocation coefficient is determined by the ratio of the reference active power of each virtual synchronous generator to the sum of the reference active power of all virtual synchronous generators.

3. The method according to claim 1, wherein the virtual resistance coefficient and the virtual inductance coefficient are adjusted in real time proportionally to the power distribution coefficient.

4. The method according to claim 1, wherein the angular frequency of the common connection point is measured by a phase-locked loop, and the measurement period is less than a set sampling period threshold.

5. The method according to claim 1, wherein when the active power of the system undergoes a step change, the time for the system to recover to a steady state does not exceed a preset recovery time threshold.

6. A power distribution system for a virtual synchronous generator parallel system, characterized in that, include: Multiple virtual synchronous generator modules, each containing a power converter, a measurement unit, and a local controller; The communication bus is used to transmit power distribution coefficients and synchronization signals between the virtual synchronous generator modules; A centralized control unit is used to coordinate the dynamic updating of virtual resistance coefficients and virtual inductance coefficients by each local controller according to the method of any one of claims 1 to 5.

7. The system according to claim 6, wherein the measurement unit acquires the output voltage and output current at a sampling frequency higher than a set reference sampling frequency.

8. A computer device comprising a memory and a processor, the memory storing a program that, when executed by the processor, causes the processor to perform the method of any one of claims 1 to 5.

9. A computer-readable storage medium having instructions stored thereon that, when executed by a processor, cause the processor to perform the method of any one of claims 1 to 5.

10. An information data processing terminal for implementing the system of claim 6, and providing power setting, operation status display and human-computer interaction functions.

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