Voltage Inertia Control Method for Improving the Transient Voltage Stability of a Grid-Forming Converter

Abstract

The present invention relates to a voltage inertia control method for improving the transient voltage stability of a network-forming converter. A voltage control architecture is set up, and the voltage control architecture includes an outer reactive power loop, a middle voltage loop, and an inner current loop; the outer reactive power loop includes a low-pass filter with a proportional coefficient, and the proportional coefficient is set according to the ratio of the voltage disturbance amount to the maximum adjustable reactive power; the reactive power on the grid side is input to obtain a feedforward term for reactive power loop control, and the outer reactive power loop is feedforward adjusted according to the feedforward term for reactive power loop control; the voltage control architecture is calculated based on the outer reactive power loop after feedforward adjustment, so as to control the converter.

Description

Technical Field

[0001] The present invention belongs to the technical field of converter control, and particularly relates to a voltage inertia control method for improving the transient voltage stability of a grid-forming converter. Background Art

[0002] Currently, the global penetration rate of renewable energy is increasing rapidly. At the same time, the number of energy storage devices and electric vehicles connected to the grid through power converters is also increasing significantly. With the continuous advancement of the global energy transition, the modern power grid is gradually transforming from a traditional power system to a power system centered on electronic devices, and may ultimately evolve into a purely power-electronic system. In this process, the control method of grid-connected power converters plays a crucial role in ensuring the safe and stable operation of the electronic power system.

[0003] Among them, the grid-forming converter is considered to be an ideal technical solution for the scenario of high-proportion power electronic devices connected to the grid in the future due to its ability to support the grid voltage and frequency. However, the power electronic devices used in the grid-forming converter itself have relatively weak overcurrent capabilities and cannot withstand large current shocks like traditional rotating machines. This characteristic leads to a current-priority strategy during its operation, and further makes its voltage control present an indirect control mode. Compared with existing synchronous generators, the voltage support ability of the grid-forming converter is relatively weak.

[0004] In order to improve the voltage control ability of the grid-forming converter in the future power-electronic system and ensure the stability of the grid voltage, it is urgent to improve the voltage control structure of the grid-forming converter. At the same time, optimize its control parameters to enhance its response ability in the face of grid fluctuations. This will help to ensure the reliability and stable operation of the grid in the case of high-proportion power electronic device access and provide technical support for the construction of future electronic power systems. Summary of the Invention

[0005] One of the objectives of the present invention is to at least solve one or more of the above problems in the prior art. In other words, one of the objectives of the present invention is to provide a voltage inertia control method for improving the transient voltage stability of a grid-forming converter that meets one or more of the aforementioned requirements.

[0006] To achieve the above-mentioned invention objective, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a voltage inertia control method for improving the transient voltage stability of a grid-forming converter, including:

[0008] Set up a voltage control architecture, which includes an outer reactive power loop, a middle voltage loop, and an inner current loop;

[0009] Set a low - pass filter for reactive power;

[0010] Obtain the voltage disturbance amount and the maximum adjustable reactive power on the grid side, and set the proportional coefficient according to the ratio of the voltage disturbance amount to the maximum adjustable reactive power;

[0011] Input the reactive power on the grid side into the low - pass filter to calculate the voltage inertia, and multiply the proportional coefficient by the voltage inertia to obtain the feed - forward term for reactive power loop control;

[0012] Perform feed - forward regulation on the outer - layer reactive power loop according to the feed - forward term for reactive power loop control;

[0013] Calculate the voltage control architecture according to the outer - layer reactive power loop after feed - forward regulation, so as to control the converter.

[0014] As a preferred implementation manner, the lower bound of the cut - off frequency of the low - pass filter is calculated according to the time - domain analytical solution of the step response, and the upper bound of the cut - off frequency of the low - pass filter is calculated according to the gain of the open - loop transfer function at twice the power frequency.

[0015] As a further preferred implementation manner, the specific calculation method of the lower bound of the cut - off frequency of the low - pass filter is as follows:

[0016] Calculate the reactive power steady - state value and the time - domain response of the outer - layer reactive power loop, and calculate the lower bound of the cut - off frequency according to the ratio of the reactive power steady - state value to the time - domain response.

[0017] As a further preferred implementation manner, it is characterized in that

[0018] As a preferred implementation manner, the converter responds to the control of the voltage control architecture and modulates the output voltage of the converter using the pulse - width modulation method.

[0019] As a preferred implementation manner, the output current frequency of the converter is calculated by substituting the inertia coefficient and the damping coefficient into the difference between the active power and the active power control command through the virtual synchronous control link.

[0020] On the other hand, the present invention provides a voltage inertia control system for improving the transient voltage stability of a grid - forming converter, including a voltage inertia calculation unit, a voltage control architecture generation unit, and a control unit;

[0021] The voltage inertia calculation unit is used to set a low - pass filter with a proportional coefficient according to the voltage disturbance amount and the maximum adjustable reactive power of the grid, calculate the voltage inertia according to the low - pass filter, and the proportional coefficient is calculated according to the ratio of the voltage disturbance amount to the maximum adjustable reactive power;

[0022] The voltage control architecture generation unit is used to generate a voltage control architecture, which includes an outer reactive power loop, a middle voltage loop, and an inner current loop. The outer reactive power loop uses voltage inertia for feedforward regulation;

[0023] The control unit is used to control the converter according to the three-level voltage control architecture.

[0024] As a preferred embodiment, the voltage inertia calculation unit calculates the lower bound of the cut-off frequency of the low-pass filter according to the time-domain analytical solution of the step response, and calculates the upper bound of the cut-off frequency of the low-pass filter according to the gain of the open-loop transfer function at twice the power frequency.

[0025] As a preferred embodiment, the specific method for the voltage inertia calculation unit to calculate the lower bound of the cut-off frequency of the low-pass filter is as follows:

[0026] Calculate the reactive power steady-state value and time-domain response of the outer reactive power loop, and calculate the lower bound of the cut-off frequency according to the ratio of the reactive power steady-state value to the time-domain response.

[0027] As a preferred embodiment, the converter responds to the control of the voltage control architecture and uses the pulse width modulation method to modulate the output voltage of the converter.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] The method and system of the present invention calculate the proportional coefficient in the voltage inertia control and the cut-off frequency of the low-pass filter, and substitute them into the reactive power loop in the three-level voltage control architecture, so that the voltage inertia control has a larger feasible region of the stable equilibrium point, and enhances the anti-interference ability in the transient process of the reactive power control link, enabling the system to operate safely and stably. Description of the Drawings

[0030] Figure 1 It is a schematic diagram of the feasible region of the stable equilibrium point of the embodiment of the present application;

[0031] Figure 2 It is a schematic diagram of the time-domain simulation of the comparative method in the embodiment of the present application under a fault;

[0032] Figure 3 It is a schematic diagram of the time-domain simulation of the method of the embodiment of the present application under a fault. Detailed Embodiments

[0033] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the drawings in the embodiments of the present application.

[0034] The following description provides examples and does not limit the scope, applicability, or examples set forth in the claims. Changes may be made to the function and arrangement of the elements described without departing from the scope of the content of this application. Various processes or components may be appropriately omitted, substituted, or added to each example. For example, the methods described may be performed in a different order than the described order, and various steps may be added, omitted, or combined. In addition, the features described for some examples may be combined into other examples.

[0035] This embodiment provides a voltage inertia control method for improving the transient voltage stability of a network-forming converter, including:

[0036] S1. Preset a voltage control architecture for the voltage inertia control of the network-forming converter. This voltage control architecture includes three levels, namely, an outer reactive power loop, a middle voltage loop, and an inner current loop.

[0037] Among them, the outer reactive power loop adopts a voltage inertia control structure, and a low-pass filter with a proportional coefficient is set to filter the voltage inertia transmitted to the reactive power loop.

[0038] Specifically, the expression of the above low-pass filter is:

[0039] ;

[0040] Among them, k is the proportional coefficient, is the cut-off frequency of the low-pass filter.

[0041] The lower bound of the above cut-off frequency is determined by the gain of the open-loop transfer function at twice the power frequency, and the upper bound is determined by the time-domain analytical solution of the step response.

[0042] Specifically, the calculation formula for the lower bound of the cut-off frequency is:

[0043] Among them, ln is the logarithmic function, is the controller d-axis voltage, E is the equivalent voltage of the external power grid, is the phase angle difference between the converter connection point voltage and the equivalent voltage of the external power grid, is the equivalent reactance of the external power grid, t represents time, with the unit of second, is the reactive power steady-state value, is the time-domain response of the outer reactive power loop.

[0044] The calculation formula of

[0045]

[0046] The calculation formula of

[0047] 。

[0048] The reactive power outer loop constructed by the above low-pass filter enables the grid-forming converter to exhibit characteristics similar to those of a synchronous machine in terms of reactive power regulation. When the system voltage is disturbed, the outer reactive power layer enables the converter to suppress voltage fluctuations by adjusting the reactive power output like a synchronous generator. This response can quickly stabilize the voltage and improve the anti-disturbance ability of the system.

[0049] S2. Receive the grid operation data, obtain the voltage disturbance amount and the maximum adjustable reactive power on the grid side, and set the proportional coefficient according to the ratio of the voltage disturbance amount to the maximum adjustable reactive power.

[0050] The proportional coefficient is specifically set by the following formula:

[0051] ;

[0052] where is the disturbance amount of the grid-connected voltage of the grid-forming converter, is the maximum adjustable reactive power allowed by the grid-forming converter.

[0053] After calculating the proportional coefficient, use the reactive power outer loop with a low-pass filter set in step S1 to calculate the voltage inertia.

[0054] During the control process, input the reactive power on the grid side at each moment into the low-pass filter, output the voltage inertia from the low-pass filter, and then multiply the proportional coefficient by the voltage inertia at this moment to obtain the feedforward term of the reactive power loop control for the next moment.

[0055] S4. Perform feedforward adjustment on the outer reactive power loop according to the feedforward term of the reactive power loop control, and then execute step S5. Calculate the voltage control architecture according to the outer reactive power loop after feedforward adjustment, so as to control the converter.

[0056] The method of this embodiment calculates the proportional coefficient in the voltage inertia control and the cut-off frequency of the low-pass filter, and substitutes them into the reactive power loop in the three-level voltage control architecture, so that the voltage inertia control has a large feasible region of stable equilibrium points and enhances the anti-interference ability during the transient process of the reactive power control link, enabling the system to operate safely and stably.

[0057] As an example, when performing feedforward adjustment on the outer reactive power loop, the transfer function of the reactive power outer loop is: , where is the control command value, and Q is the reactive power output by the converter.

[0058] The reactive power Q on the grid side is specifically: , is the inductive impedance. After combining the above two formulas, we get:

[0059]

[0060] Let the above formula be equal to 0, and we can find two values, that is, two equilibrium points. One of them is less than 0. Therefore, the feasible region of the stable equilibrium point is from 0 to the other value, specifically as shown in Figure 1 .

[0061] After taking t = 1s and setting the proportional coefficient and cut-off frequency according to this embodiment, the time-domain simulation comparison of the grid-forming converter controlled by the method of this embodiment and the conventional method under faults is shown in Figure 2 and Figure 3 . Figure 2 shows the transient stability of the reactive power PI control under faults, Figure 3 shows the transient stability of the voltage inertia control strategy of this embodiment under faults. As shown in the figure, compared with the reactive power PI control, the control method based on voltage inertia of this embodiment expands the stability region. Therefore, when the power grid fails, the grid-forming equipment controlled by the method of this embodiment can operate more stably and is less likely to make the transient voltage unstable.

[0062] On the other hand, the present invention provides a voltage inertia control system for improving the transient voltage stability of a grid-forming converter, including a voltage inertia calculation unit, a voltage control architecture generation unit, and a control unit;

[0063] Among them, the voltage inertia calculation unit is used to execute steps S1 - S3 of the method in the above embodiment, set a low-pass filter with a proportional coefficient according to the voltage disturbance amount of the power grid and the maximum adjustable reactive power, and calculate the voltage inertia according to the low-pass filter.

[0064] The voltage control architecture generation unit is used to generate the voltage control architecture of the method in the above embodiment. The voltage control architecture includes an outer reactive power loop, a middle voltage loop, and an inner current loop.

[0065] The control unit is used to calculate the control instruction according to the three-level voltage control architecture generated by the voltage control architecture, so as to control the converter.

[0066] Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of this application.

[0067] The above are only exemplary embodiments of the present disclosure and should not be used to limit the scope of the present disclosure. That is, any equivalent changes and modifications made in accordance with the teachings of the present disclosure still fall within the scope covered by the present disclosure. Those skilled in the art will readily conceive of other implementations of the present disclosure after considering the specification and practicing the disclosure herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include known common general knowledge or conventional technical means in the technical field not recorded in the present disclosure. The specification and examples are only to be regarded as exemplary, and the scope and spirit of the present disclosure are defined by the claims.

Claims

1. A voltage inertia control method for improving the transient voltage stability of a grid-forming converter, characterized in that, Including: A voltage control architecture is provided, which includes an outer reactive power loop, a middle voltage loop, and an inner current loop; A low-pass filter for reactive power is provided; The lower bound of the cut-off frequency of the low-pass filter is calculated based on the time-domain analytical solution of the step response, specifically by calculating the reactive power steady-state value and the time-domain response of the outer reactive power loop, and calculating the lower bound of the cut-off frequency according to the ratio of the reactive power steady-state value and the time-domain response; the upper bound of the cut-off frequency of the low-pass filter is calculated based on the gain of the open-loop transfer function at twice the power frequency; The voltage disturbance amount and the maximum adjustable reactive power on the grid side are obtained, and a proportional coefficient is set according to the ratio of the voltage disturbance amount and the maximum adjustable reactive power; The reactive power on the grid side is input into the low-pass filter to calculate the voltage inertia, and the proportional coefficient is multiplied by the voltage inertia to obtain the feedforward term for reactive power loop control; The outer reactive power loop is feedforward adjusted according to the feedforward term for reactive power loop control; The voltage control architecture is calculated based on the outer reactive power loop after feedforward adjustment, so as to control the converter.

2. The voltage inertia control method for improving the transient voltage stability of a grid-forming converter according to claim 1, characterized in that, The converter responds to the control of the voltage control architecture and modulates the output voltage of the converter using the pulse width modulation method.

3. A voltage inertia control method for improving the transient voltage stability of a grid-forming converter according to claim 1, characterized in that, The calculation of the output current frequency of the converter is obtained by substituting the inertia coefficient and the damping coefficient into the difference between the active power and the active power control command through the virtual synchronous control link.

4. A voltage inertia control system for improving the transient voltage stability of a grid-forming converter, characterized in that, Including a voltage inertia calculation unit, a voltage control architecture generation unit, and a control unit; The voltage inertia calculation unit is used to set a low-pass filter with a proportional coefficient according to the voltage disturbance amount and the maximum adjustable reactive power on the grid, calculate the voltage inertia according to the low-pass filter, and the proportional coefficient is calculated according to the ratio of the voltage disturbance amount and the maximum adjustable reactive power; the lower bound of the cut-off frequency of the low-pass filter is calculated based on the time-domain analytical solution of the step response, specifically by calculating the reactive power steady-state value and the time-domain response of the outer reactive power loop, and calculating the lower bound of the cut-off frequency according to the ratio of the reactive power steady-state value and the time-domain response; the upper bound of the cut-off frequency of the low-pass filter is calculated based on the gain of the open-loop transfer function at twice the power frequency; The voltage control architecture generation unit is used to generate a voltage control architecture, which includes an outer reactive power loop, a middle voltage loop, and an inner current loop, and the outer reactive power loop is feedforward adjusted using the voltage inertia; The control unit is used to control the converter according to the voltage control architecture.

5. The voltage inertia control system for improving the transient voltage stability of a grid-forming converter according to claim 4, characterized in that, The converter responds to the control of the voltage control architecture and modulates the output voltage of the converter using the pulse width modulation method.

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