System modeling method considering participation of new energy in frequency modulation and deep peak regulation of thermal power generating unit

Abstract

The invention discloses a system modeling method considering participation of new energy in frequency modulation and deep peak regulation of a thermal power generating unit, and belongs to the technical field of power system frequency control. Comprising the steps of introducing a coefficient alpha to obtain a new energy system frequency response model; introducing a coefficient A to ensure that the proportion of the new energy in the system is 1-alpha, and obtaining a new energy system frequency response simplified model; a fixed parameter turbine model is improved into a variable parameter turbine model changing along with the depth peak regulation degree, and steam volume influence parameters of a communicating pipe between a medium-pressure cylinder and a low-pressure cylinder are ignored to obtain a turbine simplified model; and replacing the fixed parameter turbine model with the turbine simplified model to obtain a system frequency response model considering participation of new energy in frequency modulation and deep peak regulation of the thermal power generating unit. According to the method, the adaptive capacity of the system to frequency fluctuation is improved, and the frequency control performance of the power system under the deep peak regulation working condition can be evaluated more accurately.

Description

Technical Field

[0001] The present invention relates to the technical field of power system frequency control, and in particular to a system modeling method considering the participation of new energy in frequency regulation and deep peak regulation of thermal power units. Background Art

[0002] With the large-scale access and wide distribution of high-proportion renewable energy, in order to balance the total power generation of the system generator set and the total demand of the power load, it is necessary to introduce load frequency control LFC (load frequency control). After the frequency response modeling of the speed governor, turbine, generator and load is carried out, the actual output power of the generator set is controlled to respond to the system frequency change within the planned range. The existing technology mainly explores the system frequency evolution characteristics after the access of renewable energy and the identification of the speed regulation system parameters of thermal power units after flexibility transformation. However, when constructing the frequency response model of the power system, renewable energy generation is generally regarded as a disturbance, and renewable energy is rarely considered to participate in frequency regulation. In addition, the changes in turbine parameters under different operating conditions during deep peak regulation of thermal power units are ignored. Therefore, the traditional system frequency response modeling method cannot correctly reflect the actual regulation characteristics.

[0003] Frequency control is a key link in the operation of power systems. When load disturbances occur in power systems, the system frequency increases or decreases. After the speed regulator of the prime mover of the thermal power unit detects the change in rotor speed, it increases or decreases the steam or water intake accordingly, so that the mechanical power output of the prime mover can keep up with the load change, re-achieve active power balance, and stabilize the system frequency. However, with the increase in the penetration rate of renewable energy, the total system inertia and frequency regulation reserve capacity continue to decrease, the frequency support capacity of the power grid continues to decline, and the operation practice of some deep peaking thermal power units after flexibility transformation shows that deep peaking leads to a decrease in the primary frequency regulation capacity of thermal power units. The traditional frequency response modeling method can no longer describe the frequency regulation characteristics of thermal power units under deep peaking conditions. The access of a high proportion of new energy and inaccurate frequency response modeling of deep peaking thermal power units will cause the frequency security of the power grid to be seriously threatened.

[0004] Therefore, a system modeling method that considers the participation of new energy in frequency regulation and deep peak regulation of thermal power units is needed to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to propose a system modeling method considering the participation of new energy in frequency regulation and deep peak regulation of thermal power units, comprising the following steps:

[0006] Based on the system frequency response model of synchronous generators, the coefficient α representing the proportion of new energy replacing thermal power is introduced to obtain the new energy system frequency response model;

[0007] Based on the frequency response model of the new energy system, the coefficient A representing the participation of new energy power generation in frequency regulation is introduced to ensure that the proportion of new energy in the system is 1-α, and a simplified frequency response model of the new energy system is obtained;

[0008] The fixed parameter turbine model in the simplified frequency response model of the new energy system is improved into a variable parameter turbine model that changes with the depth of peak regulation, and the steam volume influencing parameters of the connecting pipe between the medium and low pressure cylinders are ignored to obtain a simplified turbine model.

[0009] The simplified turbine model replaces the fixed parameter turbine model to obtain the system frequency response model that takes into account the participation of new energy in frequency regulation and deep peak regulation of thermal power units.

[0010] Furthermore, the system frequency response model of the synchronous generator is:

[0011] ΔP m (s)-ΔP L (s)=2Hs+DΔf(s)

[0012] Where Δf is the frequency deviation, ΔP m is the mechanical power change, ΔP L is the load disturbance change, H is the inertia constant, and D is the load damping coefficient.

[0013] Furthermore, the speed regulator model in the simplified frequency response model of the new energy system is:

[0014] 1 / R'

[0015] in, R is the regulation coefficient of the generator.

[0016] Furthermore, the fixed parameter turbine model is:

[0017]

[0018] in, T is the equivalent inertia time constant of the turbine, and a is the characteristic coefficient of the turbine.

[0019] Furthermore, the simplified model of the turbine is:

[0020]

[0021] Where: T SC 、T RH are the time constants of steam chamber and primary reheat respectively; F HP is the power coefficient of the high-pressure cylinder, λ is the natural over-modulation coefficient of the high-pressure cylinder power, ΔP g is the steam power input to the turbine; ΔP t is the mechanical power output of the turbine.

[0022] Furthermore, considering the system frequency response model of the frequency regulation of new energy and the deep peak regulation of thermal power units, the output ΔP of thermal power units under different deep peak regulation conditions is m 'for:

[0023]

[0024] The beneficial effects of the present invention are:

[0025] 1. The present invention fully considers the participation of new energy in frequency control. Compared with traditional methods, it models the load-frequency characteristics of new power systems more accurately. Traditional methods usually regard new energy as an external disturbance of the system, while the present invention makes the frequency response model of the power system more realistic and comprehensive by fully considering the response characteristics of new energy. This helps to better understand and utilize the role of new energy in the power system and improves the system's adaptability to frequency fluctuations.

[0026] 2. The present invention takes into account the impact of changes in turbine parameters on frequency control under deep peak-shaving conditions. Compared with the traditional fixed parameter modeling method, the present invention better adapts to the actual changes in turbine regulation system parameters under deep peak-shaving conditions by establishing a turbine variable parameter model, making the frequency response model more accurate and practical, and helping to more accurately evaluate the frequency control performance of the power system under deep peak-shaving conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of a system modeling method considering the participation of new energy in frequency regulation and deep peak regulation of thermal power units in the present invention;

[0028] Figure 2 is the frequency response block diagram of the synchronous generator;

[0029] Figure 3 is a simplified frequency response model of a synchronous generator;

[0030] Figure 4 Simplified frequency response models for systems with renewable energy generation;

[0031] Figure 5 LFC model for systems where new energy sources participate in frequency regulation;

[0032] Figure 6 This is the block diagram of the improved turbine model;

[0033] Figure 7 For a simplified turbine model;

[0034] Figure 8 A system frequency response model that takes into account thermal power deep regulation and new energy frequency regulation;

[0035] Fig. 9 It is the frequency response curve of thermal power unit under different working conditions;

[0036] Fig.10 It is the turbine output variation curve under different working conditions;

[0037] Fig.11 For different K r This is the frequency modulation effect diagram when new energy participates in frequency modulation. DETAILED DESCRIPTION

[0038] The present invention proposes a system modeling method that considers the participation of new energy in frequency regulation and deep peak regulation of thermal power units. The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0039] Figure 1 This is a flow chart of the system modeling method considering the participation of new energy in frequency regulation and deep peak regulation of thermal power units in the present invention; the details are as follows:

[0040] (1) Based on the system frequency response model of synchronous generators, the coefficient α representing the proportion of renewable energy replacing thermal power is introduced to obtain the new energy system frequency response model.

[0041] like Figure 2 As shown in the figure, the power system frequency model is a closed-loop control system with highly nonlinear and time-varying characteristics, mainly including synchronous generators and loads, turbines and their speed regulators. In order to study the overall frequency characteristics of the power system under load disturbances, the model ignores the specific nonlinear links such as speed regulator control, turbine model, amplitude limiting and secondary frequency regulation.

[0042] The frequency deviation is Δf, and the mechanical power change is ΔP m , the load disturbance change is ΔP L , H is the inertia constant, D is the load damping coefficient, and the dynamic relationship between the entire generator and the load can be expressed as formula (1-1);

[0043]

[0044] After Laplace transform, we can rewrite the above formula into formula (1-2);

[0045] ΔP m (s)-ΔP L (s)=2Hs+DΔf(s) (1-2)

[0046] Equation (1-2) can be expressed as a transfer function block diagram: Figure 3 Indicates that, where ω refis the reference value of the system electrical angular frequency, Δf is the change value of the system frequency after the disturbance, which is numerically equal to the change value of the electrical angular frequency after the disturbance after normalization. T is the equivalent inertia time constant of the turbine, a is the characteristic coefficient of the turbine, a=-2 for the turbine, and 0<a<1 for the turbine. The speed governor is used for primary frequency regulation, which is simplified by pure gain 1 / R, and R is the regulation coefficient of the generator.

[0047] In order to reduce the phenomenon of energy abandonment, thermal power is gradually transformed from a power source to a regulating resource to absorb the volatility of renewable energy. Renewable energy is connected to the grid in the form of replacing thermal power units. Therefore, a coefficient α is needed to characterize the proportion of renewable energy replacing thermal power. The system frequency response model considering renewable energy generation is as follows: Figure 4 shown.

[0048] (2) Based on the frequency response model of the new energy system, the coefficient A representing the participation of new energy power generation in frequency regulation is introduced to ensure that the proportion of new energy in the system is 1-α, and a simplified frequency response model of the new energy system is obtained.

[0049] The above model equates power electronic converters such as new energy to power sources without inertia and frequency modulation characteristics, but existing technologies show that wind power and photovoltaic units can provide frequency modulation capabilities through virtual inertia and droop control, so that they have the ability to respond to system frequency. With the increase of dual uncertainty of source and load, the method of only considering the spare capacity of synchronous units in the traditional planning mode can no longer meet the requirements of grid frequency stability. Therefore, it is urgent to carry out frequency control capacity planning research for new energy power generation and form a frequency modulation capacity supply and demand balance analysis method that adapts to the new power system.

[0050] exist Figure 4 On the basis of , we introduce the coefficient A that represents the participation of renewable energy generation in frequency regulation, and at this time, the proportion of renewable energy in the system is 1-α. The obtained model is simplified as follows: Figure 5 shown.

[0051] Among them are:

[0052]

[0053] (3) The fixed parameter turbine model in the simplified frequency response model of the new energy system is improved into a variable parameter turbine model that changes with the degree of deep peak regulation. The steam volume in the connecting pipe between the intermediate and low pressure cylinders is ignored to obtain a simplified turbine model.

[0054] In order to support energy transformation and improve the large-scale grid connection and consumption of new energy, coal-fired thermal power units are actively carrying out flexibility transformation to reduce their minimum technical output and grid connection operation space. The operation practice of thermal power units shows that the primary frequency regulation capability of the units will change significantly under deep peak regulation conditions, the frequency regulation amplitude will decrease, the response speed will slow down, and the frequency regulation margin will decrease. The active power regulation characteristics on the power supply side will change, resulting in a threat to the frequency security of the power grid. Therefore, it is necessary to improve the traditional fixed parameter turbine model to a variable parameter turbine model that changes with the degree of deep regulation. The improved turbine model is as follows: Figure 6 shown.

[0055] Among them, T SC 、T RH and T CO are the time constants of steam chamber, primary reheat and connecting pipe respectively. HP 、F IP and F LP is the power coefficient of the high-pressure cylinder, the medium-pressure cylinder and the low-pressure cylinder, λ is the natural overmodulation coefficient of the high-pressure cylinder power, ΔP g is the steam power input to the turbine, ΔP t is the mechanical power output by the turbine. To reduce the number of parameters, the steam volume in the connecting pipe between the medium and low pressure cylinders is ignored, and the model can be derived as follows:

[0056]

[0057] The simplified turbine model is as follows: Figure 7 shown.

[0058] (4) The simplified turbine model replaces the fixed parameter turbine model to obtain a system frequency response model that takes into account the participation of new energy in frequency regulation and deep peak regulation of thermal power units.

[0059] like Figure 8 As shown in the figure, the improved turbine model replaces the original model. At this time, by modifying the turbine parameters λ, T SC 、T RH 、F HP The value of can be used to obtain the output of thermal power units under different depth peak regulation conditions, that is, the system frequency response model considering the participation of new energy in frequency regulation and deep peak regulation of thermal power units.

[0060] against Figure 8 The block diagram shown in the figure shows that the output ΔP of the thermal power unit under different depth peak load conditions is m 'for:

[0061]

[0062] Considering the deep peak load regulation of thermal power units, a turbine model of a 600MW pure condensing gas thermal power unit under different load depths was selected for simulation experiments. The load depths were 100%, 75%, 50%, 40%, and 30%, respectively. Fig. 9 and Fig.10 Frequency response and turbine output variation curve.

[0063] Fig. 9 The frequency regulation characteristics of thermal power units under different peak load conditions show that when the system is disturbed, as the load depth of the thermal power units decreases from 100%Pe to 30%Pe, the lowest frequency point of the system deteriorates, and the steady-state deviation of the system frequency increases, requiring a longer frequency recovery time. Fig.10 It can be seen that the lower the operating point, the slower the climbing rate of the thermal power unit.

[0064] Use MATLAB / SIMULINK simulation platform to Figure 8 The model shown in the figure is simulated after being disturbed to study the frequency response characteristics when the new energy unit does not participate in frequency regulation and when the new energy unit participates in frequency regulation. The results are as follows Fig.11 Only the inertia response and primary frequency regulation are considered, where the turbine part is represented by the simplified synchronous machine transfer function G(s) = 1 / (0.15s+1), Tg = 0.3s, the speed regulator gain R' is 0.04, and the synchronous machine power generation ratio coefficient α is set to 0.7. The national standard GB / T 19963-2011 "Technical Regulations for Wind Farm Access to Power System" requires that the virtual inertia coefficient is generally set to 8s~12s, and the droop control coefficient is generally set to 10~50. For the new energy frequency regulation gain K r , set to 0, 20, 30, 40.

[0065] Depend on Fig.11 It can be seen that the frequency of the system is very different when new energy participates in frequency modulation and when it does not participate in frequency modulation. After new energy participates in frequency modulation, the system frequency is at its lowest point and the steady-state frequency increases. At the same time, the new energy frequency modulation gain K r The larger it is, the better the frequency response of the system will be.

[0066] In summary, the present invention helps to better understand and utilize the role of renewable energy in the power system and improves the system's adaptability to frequency fluctuations. At the same time, it makes the frequency response model more accurate and practical, and can more accurately evaluate the frequency control performance of the power system under deep peak-shaving conditions.

Claims

1. A system modeling method considering the participation of new energy in frequency regulation and deep peak regulation of thermal power units, characterized in that: The following steps are involved: Based on the system frequency response model of synchronous generators, the coefficient α representing the proportion of new energy replacing thermal power is introduced to obtain the new energy system frequency response model; Based on the frequency response model of the new energy system, the coefficient A representing the participation of new energy power generation in frequency regulation is introduced to ensure that the proportion of new energy in the system is 1-α, and a simplified frequency response model of the new energy system is obtained; The fixed parameter turbine model in the simplified frequency response model of the new energy system is improved into a variable parameter turbine model that changes with the depth of peak regulation, and the steam volume in the connecting pipe between the medium and low pressure cylinders is ignored to obtain a simplified turbine model. The simplified turbine model replaces the fixed parameter turbine model to obtain the system frequency response model that takes into account the participation of new energy in frequency regulation and deep peak regulation of thermal power units.

2. The system modeling method considering the participation of new energy in frequency regulation and deep peak regulation of thermal power units according to claim 1 is characterized in that: The system frequency response model of the synchronous generator is: ΔP m (s)-ΔP L (s)=2Hs+DΔf(s) Where Δf is the frequency deviation, ΔP m is the mechanical power change, ΔP L is the load disturbance change, H is the inertia constant, and D is the load damping coefficient.

3. The system modeling method considering the participation of new energy in frequency regulation and deep peak regulation of thermal power units according to claim 2 is characterized in that: The speed regulator model in the simplified frequency response model of the new energy system is: 1 / R' in, R is the regulation coefficient of the generator.

4. The system modeling method considering the participation of new energy in frequency regulation and deep peak regulation of thermal power units according to claim 3 is characterized in that: The fixed parameter turbine model is: in, T is the equivalent inertia time constant of the turbine, and a is the characteristic coefficient of the turbine.

5. The system modeling method considering the participation of new energy in frequency regulation and deep peak regulation of thermal power units according to claim 4 is characterized in that: The simplified model of the turbine is: Where: T SC , T RH are the time constants of steam chamber and primary reheat respectively; F HP is the power coefficient of the high-pressure cylinder, λ is the natural over-modulation coefficient of the high-pressure cylinder power, ΔP g is the steam power input to the turbine; ΔP t is the mechanical power output of the turbine.

6. The system modeling method considering the participation of new energy in frequency regulation and deep peak regulation of thermal power units according to claim 5 is characterized in that: The output ΔP of thermal power units under different deep peak regulation conditions in the system frequency response model considering the participation of new energy in frequency regulation and deep peak regulation of thermal power units m 'for:

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