Virtual voltage control method for suppressing overcurrent under voltage disturbance in virtual synchronous generator

Abstract

The invention provides a virtual voltage control method for suppressing overcurrent under voltage disturbance in a virtual synchronous generator, which comprises the following steps: two virtual voltages are introduced as reference output voltages of the virtual synchronous generator, one virtual voltage is equal to a power grid voltage, and the other virtual voltage replaces the power grid voltage to help to stabilize the current. Under the condition that extra hardware is not added, the two virtual voltages are used as reference voltages, the output voltage of the virtual synchronous machine is adjusted, and therefore overcurrent suppression in the voltage disturbance period is achieved, and the synchronous stability of the virtual synchronous machine is kept. According to the method, the current fluctuation can be remarkably reduced, the overcurrent phenomenon is avoided, the low-voltage ride-through capability of the virtual synchronous machine under the voltage disturbance condition is improved, and the reliability and stability of a power system are ensured. The method has the advantages of simple control structure and no need of complex current regulation and current limiters, and is widely applicable to virtual synchronous generator control of distributed power generation systems such as wind power generation, photovoltaic power generation and the like.

Description

Technical Field

[0001] The present invention generally relates to the technical field of converter control, and in particular to a virtual voltage control method for suppressing overcurrent under voltage disturbance in a virtual synchronous generator. Background Art

[0002] With the rapid development of renewable energy technology, especially the large-scale access of wind power and photovoltaic power generation, traditional power systems are facing unprecedented challenges. Traditional power systems are composed of a large number of synchronous generators, which have rotational inertia, damping effect and synchronization capability, and can effectively enhance the stability of the power system. However, distributed generation units, such as wind power and photovoltaic power generation, are usually connected to the grid through voltage source inverters. These distributed generation units lack the rotational inertia and synchronization capability of traditional synchronous generators, so the synchronization stability of the power system will be affected.

[0003] Especially when voltage disturbance occurs in the power grid, the voltage source inverter system is susceptible to overcurrent. Since the voltage source inverter is composed of semiconductor devices, it cannot effectively suppress overcurrent caused by voltage disturbance compared with traditional synchronous generators, which may cause equipment damage or even system disconnection from the grid. In order to improve the stability of distributed generation units in power grid disturbances, virtual synchronous generators came into being. Virtual synchronous machines enhance the stability of power systems by simulating the inertia characteristics of synchronous generators.

[0004] There are two main control methods for virtual synchronous machines: current-controlled virtual synchronous machines and voltage-controlled virtual synchronous machines. The current-controlled virtual synchronous machine effectively suppresses overcurrent caused by voltage disturbances through a current limiter. Although its control effect is good, its structure is complex and difficult to implement. In contrast, the voltage-controlled virtual synchronous machine has a simpler control structure, fewer design parameters, and is easy to implement. However, due to the lack of current control loops and current limiters in the voltage-controlled virtual synchronous machine system, it is difficult to effectively suppress overcurrent problems under voltage disturbances, especially in the case of symmetrical and asymmetrical voltage sags. Summary of the invention

[0005] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a virtual voltage control method for suppressing overcurrent under voltage disturbance in a virtual synchronous generator.

[0006] The present invention provides a virtual voltage control method for suppressing overcurrent under voltage disturbance in a virtual synchronous generator, comprising:

[0007] S1, introduces virtual voltage v v1 、v v2 As the reference output voltage of the virtual synchronous machine, v v1 Equal to the grid voltage v g, v v2 Replace grid voltage and help stabilize current;

[0008] S2, set the reference output voltage v of the virtual synchronous machine i ref v vsg +v v1 -v v2 , where v vsg is the output voltage of the virtual synchronous machine;

[0009] S3, suppresses overcurrent caused by voltage sag or recovery through a virtual voltage control method.

[0010] According to the technical solution provided by the embodiment of the present invention, the virtual voltage v v1 The calculation method is:

[0011]

[0012] Where V g is the effective value of the grid voltage, θ g is the phase angle of the power grid, [·] T Represents the transpose of a matrix.

[0013] According to the technical solution provided by the embodiment of the present invention, the virtual voltage v v2 The calculation method is:

[0014]

[0015] Where V g n is the nominal voltage effective value of the power grid.

[0016] According to the technical solution provided by the embodiment of the present invention, the virtual synchronous machine voltage v vsg The calculation method is:

[0017]

[0018] Where V vsg is the effective value of the virtual synchronous machine output voltage, θ m Output phase angle for virtual synchronous machine.

[0019] According to the technical solution provided by the embodiment of the present invention, the reference output voltage v of the virtual synchronous machine i ref for:

[0020]

[0021] The beneficial effects of the present invention are:

[0022] First, the control method of the present invention does not require complex current control algorithms or current limiters, and the control structure is simple and easy to implement. By introducing a virtual voltage control method, the trouble of complex current analysis and current regulation required in traditional current-controlled virtual synchronous machines is avoided, and the control process is greatly simplified. Secondly, the method does not require the addition of additional hardware equipment such as fault current limiters, thereby effectively reducing system costs and avoiding additional investment in hardware. In addition, the present invention can adapt to a variety of voltage disturbances, whether it is symmetrical or asymmetrical voltage sag, it can effectively suppress overcurrent and ensure that the system still operates stably under grid voltage disturbances. Most importantly, during voltage disturbances, the present invention can effectively maintain the synchronization stability of the virtual synchronous machine, ensuring that the system does not suffer from synchronization instability, thereby improving the reliability and stability of the power system in a disturbed environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0024] Figure 1 Configure diagram for virtual synchronous generator;

[0025] Figure 2 This is the proposed virtual voltage control framework diagram;

[0026] Figure 3 is the proposed virtual voltage control equivalent circuit. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It should also be noted that, for ease of description, only the parts related to the invention are shown in the accompanying drawings.

[0028] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0029] The virtual synchronous machine system is connected to the grid via a voltage source inverter, e.g. Figure 1 As shown, DGU is a distributed generation unit; ESS is an energy storage module; VSG controller is a virtual synchronous machine controller; VSI is a voltage source inverter; PWM is a PMW wave generator; TRS is an inverter; Bus is a bus; Filter is a filter; P ipu ref is the reference power of the virtual synchronous machine; P i is the DC side input power; P gFor AC output power measurement; v i is the inverter output voltage; v g 、i g is the grid voltage and current; v b is the bus voltage; E dc is the DC side voltage of the inverter; L is the filter inductance; L g is the grid inductance; the voltage source inverter is connected to the grid through a filter. The output voltage of the voltage source inverter is regulated by the virtual synchronous machine controller to maintain the stability of the power system.

[0030] The proposed virtual synchronous machine controller framework is as follows Figure 2 As shown, PLL is a phase-locked loop, and the virtual voltage control module calculates the virtual voltage v v1 and v v2 , adjust the output voltage v of the virtual synchronous machine i ref The design of the virtual synchronous machine controller uses this module to ensure that the virtual synchronous machine can effectively maintain the stability of the power grid during voltage disturbances and avoid overcurrent. Under the regulation of the virtual synchronous machine controller, the output voltage v i ref The calculation combines the virtual voltage v v1 and v v2 , where v v1 Equal to the grid voltage v g .

[0031] The present invention provides a virtual voltage control method for suppressing overcurrent under voltage disturbance in a virtual synchronous generator, comprising:

[0032] S1, introduces virtual voltage v v1 、v v2 As the reference output voltage of the virtual synchronous machine, v v1 Equal to the grid voltage v g , v v2 Replace grid voltage and help stabilize current;

[0033] S2, set the reference output voltage v of the virtual synchronous machine i ref v vsg +v v1 -v v2 , where v vsg is the output voltage of the virtual synchronous machine;

[0034] S3, suppresses overcurrent caused by voltage sag or recovery through a virtual voltage control method.

[0035] Specifically, the virtual voltage v v1 The calculation method is:

[0036]

[0037] Where V g is the effective value of the grid voltage, θ g is the phase angle of the power grid, [·] T Represents the transpose of a matrix.

[0038] Virtual voltage v v2 The calculation method is:

[0039]

[0040] Where V g n is the nominal voltage effective value of the power grid.

[0041] Virtual synchronous machine voltage v vsg The calculation method is:

[0042]

[0043] Where V vsg is the effective value of the virtual synchronous machine output voltage, θ m Output phase angle for virtual synchronous machine.

[0044] The reference output voltage v of the virtual synchronous machine i ref for:

[0045]

[0046] The proposed virtual voltage control equivalent circuit is shown in Figure 3 As shown, the arrow direction represents the direction of electromotive force. v1 The output is the measured grid voltage v g , so when the grid voltage v g When a symmetrical or asymmetrical fault occurs, v v1 Can be used with v g The short-circuit current is suppressed by offsetting the phase. The normal working grid voltage is simulated, so that the virtual synchronous machine maintains the stability of the angle of attack and does not lose stability when the grid fails. This method enables the virtual synchronous machine to flexibly adjust the output voltage according to the change of the grid voltage and effectively suppress the overcurrent caused by the grid voltage disturbance. The virtual synchronous machine controller adjusts the output voltage through the virtual voltage control method, while maintaining the synchronization stability of the virtual synchronous machine and the grid, suppressing excessive current.

[0047] Traditional virtual synchronous machine control methods may cause overcurrent during voltage disturbances, especially when the voltage sags or recovers, thereby threatening the stability of the power system. The present invention introduces a virtual voltage control method to enable the virtual synchronous machine to effectively suppress overcurrent under voltage disturbance conditions while maintaining the synchronization stability of the system.

[0048] The above description is only a preferred embodiment of the present invention and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present invention is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with the technical features with similar functions disclosed in the present invention (but not limited to) to form a technical solution.

Claims

1. A virtual voltage control method for suppressing overcurrent under voltage disturbance in a virtual synchronous generator, characterized in that: The following steps are involved: S1, introduces virtual voltage v v1 、v v2 As the reference output voltage of the virtual synchronous machine, v v1 Equal to the grid voltage v g , v v2 Replace grid voltage and help stabilize current; S2, set the reference output voltage v of the virtual synchronous machine i ref v vsg +v v1 -v v2 , where v vsg is the output voltage of the virtual synchronous machine; S3, suppresses overcurrent caused by voltage sag or recovery through a virtual voltage control method.

2. A virtual voltage control method for suppressing overcurrent under voltage disturbance in a virtual synchronous generator according to claim 1, characterized in that: In step S1, the virtual voltage v v1 The calculation method is: Where V g is the effective value of the grid voltage, θ g is the phase angle of the power grid, [·] T Represents the transpose of a matrix.

3. A virtual voltage control method for suppressing overcurrent under voltage disturbance in a virtual synchronous generator according to claim 1, characterized in that: In step S1, the virtual voltage v v2 The calculation method is: Where V g n is the nominal voltage effective value of the power grid.

4. A virtual voltage control method for suppressing overcurrent under voltage disturbance in a virtual synchronous generator according to claim 1, characterized in that: In step S2, the virtual synchronous machine voltage v vsg The calculation method is: Where V vsg is the effective value of the virtual synchronous machine output voltage, θ m Output phase angle for virtual synchronous machine.

5. A virtual voltage control method for suppressing overcurrent under voltage disturbance in a virtual synchronous generator according to claim 1, characterized in that: In step S2, the reference output voltage v of the virtual synchronous machine is i ref for:

Images