Frequency dynamic support capability evaluation method for grid-connected converters

Abstract

The present invention discloses a method for evaluating the frequency dynamic support capability of a grid-type converter. The method measures the reactance from the grid-type converter to the grid connection point and the voltage amplitude of the grid connection point and the grid-type converter immediately before the disturbance in real time, obtains the active outer loop control parameters of the grid-type converter, obtains the formula for evaluating the frequency dynamic support capability of the grid-type converter, obtains the amplitude characteristic curve of the frequency dynamic support capability evaluation index, and obtains the frequency dynamic support capability of the grid-type converter during the dynamic process after the disturbance occurs by comparing the amplitudes. Compared with traditional indicators for measuring frequency stability, the frequency dynamic support capability evaluation index proposed in the present invention can evaluate the frequency support capability of the grid-type converter during the dynamic process of the disturbance, and the index reflects the influence of the active outer loop control parameters of the grid-type converter on the frequency support capability. This method is of great significance for improving the frequency support capability of the grid-type converter and ensuring the safe and stable operation of the power system.

Description

Technical Field

[0001] The present invention belongs to the technical field of equipment evaluation for use with a power supply or a similar power supply system, and in particular relates to a method for evaluating the frequency dynamic support capability of a grid-type converter. Background Art

[0002] With economic development and improved living standards, my country's demand for electricity is increasing. Fossil fuels such as coal, oil, and natural gas, the primary sources of electricity, are non-renewable resources and face energy depletion. Furthermore, the combustion of coal and other fossil fuels causes severe ecological damage, incompatible with the concept of sustainable development. To address this issue and build a green power environment, new energy sources, primarily wind and solar, have been developed and utilized on a large scale and are gradually becoming a vital component of the power system. Traditional power systems, dominated by synchronous generators, are transitioning to new power systems based on power electronics.

[0003] Currently, grid-side converters for a large number of renewable energy generators, such as wind and photovoltaic power plants, and energy storage devices in power systems employ grid-following control. These converters often lack active support, inertial response, and frequency control capabilities. As the proportion of renewable energy in the power system continues to rise, grid strength is declining, posing significant challenges to the grid's frequency stability and reliability.

[0004] At the same time, with the large-scale integration of power electronic equipment into the grid, problems such as insufficient grid inertia have become increasingly prominent. The emergence of grid-connected converters offers a new approach to addressing these issues. By simulating the characteristics of synchronous motors, grid-connected converters can act as an equivalent voltage source when connected to the grid, enhancing the grid's inertia and damping characteristics, providing effective frequency support for the power system and thus improving grid stability.

[0005] In engineering, metrics such as maximum frequency change rate and maximum frequency deviation are often used to measure power system frequency security. However, there is a lack of analysis of the frequency support capabilities of equipment, particularly emerging grid-connected converters. Therefore, it is necessary to study frequency support capability evaluation methods for renewable energy grid-connected systems that include grid-connected converters. Based on these evaluation metrics, the control parameters of the grid-connected converters can be adjusted to improve the power system's frequency stability margin, thereby promoting the construction of a more stable, reliable, and sustainable power system. Summary of the Invention

[0006] In order to solve the current problem of lack of frequency support capability evaluation indicators for grid-type converters, the purpose of the present invention is to propose a frequency dynamic support capability evaluation method suitable for grid-type converters. The present invention is based on the control logic inside the grid-type converter, and analyzes the impact of control parameter changes on the stability of the power system through the amplitude characteristic curve, thereby improving the frequency support capability of the grid-type converter and solving the problem of lack of indicators for measuring the frequency support capability of new energy equipment.

[0007] In order to achieve the above object, the technical solution adopted in the present invention is:

[0008] A method for evaluating the frequency dynamic support capability of a grid-type converter includes the following steps:

[0009] Step 1: In a power system containing a grid-type converter, the reactance from the grid-type converter to the grid connection point, the voltage amplitude of the grid connection point immediately before the disturbance, and the voltage amplitude of the grid-type converter are measured in real time to obtain the active power outer loop control parameters of the grid-type converter.

[0010] Step 2: Based on the active power output equation of the grid-connected converter , Active power outer loop control equation of grid-connected converter The relationship equation between the angle and angular frequency of the grid-connected converter , and obtain the evaluation index of the dynamic frequency support capability of the grid-type converter for:

[0011]

[0012] Where, P s is the active power output of the grid-type converter, U PCC 、 are the voltage amplitude and phase angle of the grid connection point, E, are the voltage amplitude and phase angle of the grid-connected converter, respectively; x2 is the reactance from the grid-connected converter to the grid connection point; is the inertia time constant of the active outer loop of the grid-type converter, is the per-unit value of the angular frequency of the grid-type converter, P ref The active power reference value output by the grid-connected converter is is the reference value of angular frequency, is the per-unit value of the grid-connected point angular frequency, D is the damping coefficient of the active outer loop of the grid-connected converter, and s is the Laplace operator. is the output active power difference of the grid-type converter, is the per-unit difference of the angular frequency at the grid connection point. 、 are the voltage amplitude of the grid connection point and the voltage amplitude of the grid-connected converter at the moment before the disturbance respectively;

[0013] Substituting the real-time measured data and the obtained control parameters in step 1 into the frequency dynamic support capability evaluation index of the grid-type converter to obtain the frequency dynamic support capability of the grid-type converter;

[0014] Step 3: Measure multiple parameters in real time through step 1 to obtain the frequency dynamic support capability evaluation index during the entire disturbance process, draw the amplitude characteristic curve of the frequency dynamic support capability evaluation index, and obtain the frequency dynamic support capability of the grid-type converter in the dynamic process after the disturbance occurs by comparing the amplitudes of the amplitude characteristic curve of the frequency dynamic support capability evaluation index; the larger the amplitude of the amplitude characteristic curve, the stronger the frequency dynamic support capability of the grid-type converter; by comparing the amplitude characteristic curve of the change in the value of the active outer loop control parameter of the grid-type converter, the support stage of the active outer loop control parameter of the grid-type converter on the frequency dynamic support capability can be reflected.

[0015] Through simulation verification, the inertia time constant of the active outer loop of the grid-type converter is The impact on the frequency dynamic support capability is mainly reflected in the mid-frequency band, that is, the dynamic development process of the disturbance; when When the frequency increases, the mid-frequency As the amplitude increases, the frequency support capability is enhanced; the influence of the damping coefficient D of the active outer loop of the grid-type converter on the dynamic frequency support capability is mainly reflected in the medium and low frequency bands, that is, the steady-state and dynamic recovery processes. The larger the damping coefficient, the stronger the frequency support capability.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The method of the present invention can calculate the frequency dynamic support capability of the grid-type converter during the entire disturbance process based on the power system operating parameters and the active outer loop control parameters of the grid-type converter. Compared with traditional frequency stability measurement indicators, the present invention effectively solves the problem that most traditional indicators focus on the frequency stability of the entire power system, and can measure the frequency support capability of the grid-type converter during the dynamic interference process. The present invention evaluates the frequency support capability of the grid-type converter by combining the active outer loop control strategy of the grid-type converter. The proposed indicator can reflect the influence of controllable parameters on the frequency support capability of the grid-type converter, and is of great significance in guiding the parameter design of the grid-type converter and ensuring the safe and stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flow chart of the method of the present invention.

[0019] Figure 2 It is a new energy transmission system topology containing grid-type converters.

[0020] Figure 3It is the active outer loop control of the grid-type converter.

[0021] Figure 4 It is a comparison of frequency dynamic support capacity evaluation indicators under different inertia time constants.

[0022] Figure 5 It is a comparison of frequency dynamic support capabilities under different inertia time constants.

[0023] Figure 6 It is a comparison of frequency dynamic support capacity evaluation indicators under different damping coefficients.

[0024] Figure 7 It is a comparison of frequency dynamic support capabilities under different damping coefficients. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0026] like Figure 1 As shown, the present invention is a method for evaluating the frequency dynamic support capability of a grid-type converter, comprising the following steps:

[0027] Step 1: In a power system containing a grid-type converter, the reactance from the grid-type converter to the grid connection point, the voltage amplitude of the grid connection point immediately before the disturbance, and the voltage amplitude of the grid-type converter are measured in real time to obtain the active power outer loop control parameters of the grid-type converter.

[0028] Step 2: Based on the active power output equation of the grid-connected converter , Active power outer loop control equation of grid-connected converter The relationship equation between the angle and angular frequency of the grid-connected converter , and obtain the evaluation index of the dynamic frequency support capability of the grid-type converter for:

[0029]

[0030] Where, P s is the active power output of the grid-type converter, U PCC 、 are the voltage amplitude and phase angle of the grid connection point, E, are the voltage amplitude and phase angle of the grid-connected converter, respectively; x2 is the reactance from the grid-connected converter to the grid connection point; is the inertia time constant of the active outer loop of the grid-type converter, is the per-unit value of the angular frequency of the grid-type converter, P ref The active power reference value output by the grid-connected converter is is the reference value of angular frequency, is the per-unit value of the grid-connected point angular frequency, D is the damping coefficient of the active outer loop of the grid-connected converter, and s is the Laplace operator; is the output active power difference of the grid-type converter, is the per-unit difference of the angular frequency at the grid connection point. 、 are the voltage amplitude of the grid connection point and the voltage amplitude of the grid-connected converter at the moment before the disturbance respectively;

[0031] Active power output equation based on grid-connected converter , Active power outer loop control equation of grid-connected converter The relationship equation between the angle and angular frequency of the grid-connected converter , we get the evaluation index of the dynamic frequency support capability of the grid-type converter, specifically: it is considered that the grid-type converter does not output active power in steady state, so ; Linearize and Laplace transform the three equations: 、 、 , eliminate and , and obtain the evaluation index of the dynamic frequency support capability of the grid-type converter This indicator can reflect the support stage of the active outer loop control parameters of the grid-type converter for the dynamic support capability of frequency.

[0032] Substituting the real-time measured data and the obtained control parameters in step 1 into the frequency dynamic support capability evaluation index of the grid-type converter to obtain the frequency dynamic support capability of the grid-type converter;

[0033] Step 3: Measure multiple parameters in real time through step 1 to obtain the frequency dynamic support capability evaluation index during the entire disturbance process, draw the amplitude characteristic curve of the frequency dynamic support capability evaluation index, and obtain the frequency dynamic support capability of the grid-type converter in the dynamic process after the disturbance occurs by comparing the amplitudes of the amplitude characteristic curve of the frequency dynamic support capability evaluation index; the larger the amplitude of the amplitude characteristic curve, the stronger the frequency dynamic support capability of the grid-type converter; by comparing the amplitude characteristic curve of the change in the value of the active outer loop control parameter of the grid-type converter, the support stage of the active outer loop control parameter of the grid-type converter on the frequency dynamic support capability can be reflected.

[0034] Example:

[0035] In order to verify the correctness of the frequency support capability evaluation method for grid-type converters proposed in this invention, a simulation platform is built as follows: Figure 2 The power system model with grid-connected converter shown in the figure was simulated and verified according to the following parameters:

[0036] The actual output of the grid-connected converter is 7MW; the receiving end is an infinite power grid. The power system frequency drops by 0.05Hz during a disturbance of 4-4.15s.

[0037] Figure 3 The active outer loop control of the grid-connected converter is shown, which can be expressed in the form of equations: .

[0038] In order to verify the influence of the inertia time constant of the active outer loop of the grid-type converter on the frequency dynamic support capability, simulation analysis is carried out for the cases where the inertia time constant is 2s, 5s and 10s. The influence of the inertia time constant on the frequency dynamic support capability is as follows: Figure 4 and Figure 5 shown. Figure 4 It is a comparison of frequency dynamic support capacity evaluation indicators under different inertia time constants. Figure 5 This is a comparison of frequency dynamic support capabilities under different inertia time constants. Figure 4 It can be seen that the influence of the inertia time constant of the active outer loop of the grid-type converter on the frequency support capability is mainly reflected in the mid-frequency band, that is, the dynamic development process of the disturbance. When the frequency increases, the mid-frequency As the amplitude increases, the frequency support capability is enhanced. Figure 5 The simulation results show that Increases, the active power output of the grid-type converter increases during the disturbance process, and the frequency support capability of the grid-type converter is enhanced, which proves the rationality of the frequency dynamic support capability index proposed in the present invention.

[0039] In order to verify the influence of the damping coefficient of the active outer loop of the grid-type converter on the frequency dynamic support capability, a simulation analysis is carried out for the cases where the damping coefficient D of the active outer loop of the grid-type converter is 100, 150 and 200. The influence of the damping coefficient on the frequency dynamic support capability is as follows: Figure 6 and Figure 7 shown. Figure 6 It is a comparison of frequency dynamic support capacity evaluation indicators under different damping coefficients. Figure 7 This is a comparison of the frequency dynamic support capabilities under different damping coefficients. Figure 6 It can be seen that the influence of the damping coefficient of the active outer loop of the grid-type converter on the frequency support capability is mainly reflected in the medium and low frequency bands, that is, the steady state and dynamic recovery process. The larger the damping coefficient, the stronger the frequency support capability. Figure 7 It can be seen from the simulation results that with the increase of the damping coefficient, the active power output of the grid-type converter increases, and the frequency dynamic support capability of the grid-type converter is enhanced.

[0040] Through analysis Figure 4 and Figure 5 , Figure 6 and Figure 7 , which proves that the frequency dynamic support capability evaluation method proposed in the present invention can evaluate the frequency support capability of the grid-type converter during the whole disturbance process, and can serve as a supporting basis for the design of the active outer loop parameters of the grid-type converter.

Claims

1. A method for evaluating the frequency dynamic support capability of a grid-type converter, characterized by: The following steps are involved: Step 1: In a power system containing a grid-type converter, the reactance from the grid-type converter to the grid connection point, the voltage amplitude of the grid connection point immediately before the disturbance, and the voltage amplitude of the grid-type converter are measured in real time to obtain the active power outer loop control parameters of the grid-type converter. Step 2: Based on the active power output equation of the grid-connected converter , Active power outer loop control equation of grid-connected converter The relationship equation between the angle and angular frequency of the grid-connected converter , and obtain the evaluation index of the dynamic frequency support capability of the grid-type converter for: Where, P s is the active power output of the grid-type converter, U PCC 、 are the voltage amplitude and phase angle of the grid connection point, E, are the voltage amplitude and phase angle of the grid-connected converter, respectively; x2 is the reactance from the grid-connected converter to the grid connection point; is the inertia time constant of the active outer loop of the grid-type converter, is the per-unit value of the angular frequency of the grid-type converter, P ref The active power reference value output by the grid-connected converter is is the reference value of angular frequency, is the per-unit value of the grid-connected point angular frequency, D is the damping coefficient of the active outer loop of the grid-connected converter, and s is the Laplace operator; is the output active power difference of the grid-type converter, is the per-unit difference of the angular frequency at the grid connection point; 、 are the voltage amplitude of the grid connection point and the voltage amplitude of the grid-connected converter at the moment before the disturbance respectively; Substituting the real-time measured data and the obtained control parameters in step 1 into the frequency dynamic support capability evaluation index of the grid-type converter to obtain the frequency dynamic support capability of the grid-type converter; Step 3: Measure multiple parameters in real time through step 1 to obtain the frequency dynamic support capability evaluation index during the entire disturbance process, draw the amplitude characteristic curve of the frequency dynamic support capability evaluation index, and obtain the frequency dynamic support capability of the grid-type converter in the dynamic process after the disturbance occurs by comparing the amplitudes of the amplitude characteristic curve of the frequency dynamic support capability evaluation index; the larger the amplitude of the amplitude characteristic curve, the stronger the frequency dynamic support capability of the grid-type converter; by comparing the amplitude characteristic curve of the change in the value of the active outer loop control parameter of the grid-type converter, the support stage of the active outer loop control parameter of the grid-type converter on the frequency dynamic support capability can be reflected.

2. A method for evaluating the frequency dynamic support capability of a grid-type converter according to claim 1, characterized in that: Inertia time constant of active outer loop of grid-connected converter The impact on the frequency dynamic support capability is mainly reflected in the mid-frequency band, that is, the dynamic development process of the disturbance; when When the frequency increases, the mid-frequency As the amplitude increases, the frequency support capability is enhanced; the influence of the damping coefficient D of the active outer loop of the grid-type converter on the dynamic frequency support capability is mainly reflected in the medium and low frequency bands, that is, the steady-state and dynamic recovery processes. The larger the damping coefficient, the stronger the frequency support capability.

3. The method for evaluating the frequency dynamic support capability of a grid-connected converter according to claim 1, wherein: In the step 2, based on the active power output equation of the grid-type converter , Active power outer loop control equation of grid-connected converter The relationship equation between the angle and angular frequency of the grid-connected converter , it is considered that the grid-type converter does not output active power in steady state, so ; Linearize and Laplace transform the three equations: 、 、 , eliminate and , and obtain the evaluation index of the dynamic frequency support capability of the grid-type converter This indicator can reflect the support stage of the active outer loop control parameters of the grid-type converter for the dynamic support capability of frequency.

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