Power system inertia evaluation method and system without frequency differential

Abstract

The invention provides a power system inertia evaluation method and system without frequency differential, and belongs to the technical field of power system inertia evaluation, and the method comprises the steps: carrying out the frequency slope test of a converter when a power supply or a load which takes the converter as a grid-connected interface operates in a grid-connected manner, enabling the frequency of a power grid to generate slope change, and carrying out the frequency slope test; recording converter power data measured in the frequency slope test process; the method comprises the following steps: preprocessing converter power data measured in a frequency slope test process, and then separating a constant component from the converter power data; and evaluating the inertia of the power system according to the separated constant component. According to the method, the existing power step test is replaced by the frequency slope test, so that frequency differential and differential operation which is susceptible to interference in the prior art is avoided, and the inertia evaluation precision is obviously improved; the established inertia evaluation model can reflect the influence of the speed regulator of the synchronous machine in the power system, and the inertia evaluation precision is further improved; and a special inertia evaluation device does not need to be additionally invested, so that the method has a relatively high economic advantage.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system inertia evaluation, and particularly relates to a power system inertia evaluation method and system without frequency differentiation. Background Art

[0002] With the gradual advancement of the dual-carbon goal, the power system is undergoing a profound transformation from being dominated by synchronous machines to being dominated by converter equipment. Specifically, the proportion of power grids or loads with converters as grid connection interfaces in the power grid is increasing. However, different from traditional generators / motors, converter equipment lacks physical rotating masses that are dynamically coupled with the grid frequency, resulting in a rapid decline in the inertia level of the power system. Research shows that if the system inertia level is too low, the power system will face serious stability problems such as frequency instability and system oscillation when suffering from disturbances. Therefore, accurately evaluating the inertia of the power system is of great significance for analyzing and improving the stability of the power system.

[0003] Most existing power system inertia evaluations adopt the power step test method. Its basic principle is to inject a step disturbance power into the power system and record the frequency data at the inertia detection node, and obtain the frequency change rate through differential operation or similar difference operation (hereinafter collectively referred to as differential operation) on the measured frequency, and evaluate the power system inertia using the maximum value of the frequency change rate.

[0004] However, frequency differential operation will reduce the evaluation accuracy of the power system inertia. The specific reasons are as follows: (1) The maximum value of the frequency change rate usually occurs at the moment when the step disturbance is injected. At this time, the power system is undergoing a complex electromagnetic transient process, and the credibility of the measured values of the grid frequency and its maximum change rate is low; (2) Frequency differential operation is easily interfered by measurement noise, which has a great impact on the inertia evaluation accuracy. Summary of the Invention

[0005] In order to solve the problem of low evaluation accuracy of the existing power system inertia, the present invention provides a power system inertia evaluation method without frequency differentiation. This method innovatively uses a frequency ramp test to replace the existing power step test scheme, thus eliminating the need for frequency differential operation and being able to solve the technical problem that the existing inertia evaluation method has poor evaluation accuracy due to frequency differential operation; at the same time, the present invention has strong versatility and can be widely applied to various power sources or loads with converters as grid connection interfaces, such as flexible DC transmission, energy storage power stations, wind farms, photovoltaic power stations, hydrogen production stations, etc.

[0006] To achieve the above object, the present invention provides the following technical solutions: A power system inertia evaluation method without frequency differentiation, comprising: When a power source or load with a converter as the grid connection interface is operating in parallel with the grid, a frequency ramp test is carried out on the converter to make the grid frequency ramp change, and the power data of the converter measured during the frequency ramp test is recorded; Preprocess the power data of the converter measured during the frequency ramp test, and then separate the constant component therein; evaluate the power system inertia according to the separated constant component.

[0007] Preferably, during the period of carrying out the frequency ramp test on the converter, the reference frequency adopted by the converter is: ; Wherein, f ref is the reference frequency of the converter, f 0 is the grid frequency before the frequency ramp test, k f is the change rate of the reference frequency, t is time, and the start time of the ramp test t = 0, T is the duration of the frequency ramp test.

[0008] Preferably, during the period of the grid frequency ramp change, the power data of the converter is as follows: If the change rate of the set reference frequency makes the reference frequency during the frequency ramp test within the dead zone of primary frequency regulation of the grid and the primary frequency regulation of the grid does not act, the power of the converter during the frequency ramp change includes a constant component and a ramp component, specifically as follows: ; If the change rate of the set reference frequency makes the reference frequency during the frequency ramp test exceed the dead zone of primary frequency regulation of the grid and the effect of primary frequency regulation of the grid needs to be considered, the power of the converter during the frequency ramp change includes a constant component, a ramp component and an exponential component, specifically as follows: ; Wherein, P VSC,t is the power of the converter at the time t during the frequency ramp test, P VSC0 is the power of the converter before the frequency ramp test, k f is the change rate of the reference frequency, H g is the power system inertia, D g is the damping parameter of the power system, t is time, f 1 is the reference frequency at the end of the frequency ramp test, fN is the rated grid frequency, ε is the dead band of primary frequency regulation of the grid, k m and R g and F H and T RH are coefficients related to the primary frequency regulation of the grid, which are respectively the coefficients related to the generator power factor and the reserve power, the governor coefficient, the high-pressure cylinder coefficient, and the equivalent time constant of the reheater steam volume.

[0009] Preferably, the power system inertia is evaluated according to the separated constant component, specifically, the power system inertia is evaluated through a power system inertia evaluation model without frequency differentiation, and the power system inertia evaluation model without frequency differentiation is as follows: ; wherein, H g is the power system inertia, α const is the constant component in the converter power, α ramp is the coefficient of the ramp component in the converter power, α exp1 and α exp2 are the coefficients of the exponential component in the converter power, k f is the rate of change of the reference frequency, is the converter power actually measured before the frequency ramp test, is during the frequency ramp test t is the converter power actually measured at time t is time, f 1 is the reference frequency at the end of the frequency ramp test, f N is the rated grid frequency, ε is the dead band of primary frequency regulation of the grid.

[0010] Preferably, the converter power data measured during the frequency ramp test is preprocessed, and then the constant component therein is separated, and the power system inertia is evaluated according to the separated constant component, which specifically includes the following steps: Filter the converter power data measured during the frequency ramp test; Use the converter power data and obtain the constant component in the converter power through the data fitting method α const , and evaluate the power system inertia according to the power system inertia evaluation model without frequency differentiation; Alternatively, first obtain the coefficient of the ramp component in the converter power α ramp , then deduct the ramp component in the converter power during the frequency ramp test, and evaluate the power system inertia using the remaining converter power after deducting the ramp component according to the power system inertia evaluation model without frequency differentiation.

[0011] Preferably, the process of obtaining the ramp component in the converter power and the process of evaluating the power system inertia using the remaining converter power after deducting the ramp component are as follows: When the frequency ramp test is completed, the converter continues to operate while maintaining the reference frequency at the end of the ramp test unchanged, and records the power data of the converter ; Perform filtering processing on the two segments of converter power data measured during the frequency ramp test and during the period when the reference frequency remains unchanged after the frequency ramp test is completed; Using the power data of the converter during the second period when the grid frequency remains unchanged, estimate the coefficient of the ramp component in the converter power α ramp ; Using the estimated coefficient of the ramp component in the converter power and the measured grid frequency, calculate the ramp component in the converter power during the first frequency ramp test period; Deduct the ramp component in the converter power during the first frequency ramp test period, and then estimate the power system inertia using the remaining converter power.

[0012] Preferably, the coefficient of the ramp component in the converter power estimated using the power data of the converter during the second period when the grid frequency remains unchanged is as follows: ; Where α ramp is the coefficient of the ramp component in the converter power, and are the actually measured converter power and grid frequency before the frequency ramp test respectively, and are the actually measured converter power and grid frequency during the period when the reference frequency remains unchanged after the frequency ramp test is completed respectively, k f is the change rate of the reference frequency.

[0013] Preferably, the process of deducting the ramp component in the converter power during the first frequency ramp test period and estimating the power system inertia using the remaining converter power is as follows: If the reference frequency during the frequency ramp test is within the dead band of the power grid's primary frequency regulation, after deducting the ramp component in the converter power during the first-stage frequency ramp test, only the constant component remains. α const , evaluate the power system inertia according to the power system inertia evaluation model without frequency differentiation. If the reference frequency during the frequency ramp test exceeds the dead band of the power grid's primary frequency regulation, after deducting the ramp component in the converter power during the first-stage frequency ramp test, the remaining constant component and exponential component are obtained. By using the data fitting method, the constant component is acquired. α const , and then evaluate the power system inertia according to the power system inertia evaluation model without frequency differentiation.

[0014] Preferably, the power source or load with the converter as the grid connection interface is: various power sources or loads with the converter as the grid connection interface in flexible DC transmission, energy storage, photovoltaic power station, wind farm, hydrogen production station, electric vehicle charging station.

[0015] The present invention also provides a power system inertia evaluation system without frequency differentiation, including: A frequency ramp test module, which is used to conduct a frequency ramp test on the converter when the power source or load with the converter as the grid connection interface is connected to the grid, causing the grid frequency to ramp and recording the converter power data measured during the frequency ramp test; An inertia evaluation module, which is used to preprocess the converter power data measured during the frequency ramp test, and then separate the constant component therefrom; evaluate the power system inertia according to the separated constant component.

[0016] The power system inertia evaluation method provided by the present invention improves the evaluation accuracy of the power system inertia and realizes the accurate evaluation of the power system inertia, which is specifically reflected as follows: 1) Using the given frequency change rate to replace the differential and difference operations on the frequency measurement value, avoiding the frequency differential and difference operations that are vulnerable to interference in the prior art, and significantly improving the inertia evaluation accuracy; 2) Replacing the existing power step test with a frequency ramp test, avoiding the complex electromagnetic transient interference problem during the power step; 3) The established power system inertia evaluation model without frequency differentiation can reflect the influence of the synchronous generator speed governor in the power system, further improving the inertia evaluation accuracy.

[0017] In addition, the present invention also has strong universality and economic advantages: it can be applied to various existing power sources and loads with the converter as the grid connection interface in the power system, and there is no need to invest in a dedicated inertia evaluation device additionally, having relatively practical engineering application value. Description of the Drawings

[0018] To more clearly illustrate the embodiments of the present invention and their design solutions, the following will briefly introduce the drawings required for this embodiment. The drawings in the following description are only partial embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0019] Figure 1 It is a flowchart of the power system inertia evaluation method without frequency differentiation in Embodiment 1; Figure 2 It is the circuit topology of the power supply and load with the converter as the grid connection interface in Embodiment 1; Figure 3 It is a schematic diagram of the power components of the converter under the frequency ramp test in Embodiment 1; Figure 4 It is a flowchart of evaluating the power system inertia using the converter power data in Embodiment 1; Figure 5 It is the control block diagram of the converter under the frequency ramp test in Embodiment 1; Figure 6 It is the grid frequency and converter power during the evaluation process of the traditional power system inertia evaluation method in Embodiment 1; where, Figure 6 (a) is the measured grid frequency before and after filtering the measurement noise; Figure 6 (b) is the measured converter power before and after filtering the measurement noise; Figure 7 It is the grid frequency change rate of the traditional power system inertia evaluation method in Embodiment 1 under different differential step sizes; where, Figure 7 (a) is the calculation result of the frequency change rate under ideal differentiation; Figure 7 (b) is the calculation result of the frequency change rate under the common differential step size; Figure 8 It is the grid frequency and converter power during the evaluation process of the method proposed in the present invention in Embodiment 1; where, Figure 8 (a) is the grid frequency during the evaluation process; Figure 8 (b) is the converter power during the evaluation process; Figure 9 It is the structural block diagram of the power system inertia evaluation system without frequency differentiation provided in Embodiment 2; Figure 10 It is the structural block diagram of the electronic device provided in Embodiment 3. Detailed Embodiments

[0020] To enable those skilled in the art to better understand the technical solution of the present invention and be able to implement it, the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and cannot be used to limit the protection scope of the present invention.

[0021] Embodiment 1 The present invention provides a method for evaluating the inertia of a power system without frequency differentiation, specifically as Figure 1 shown, including the following steps: S1. When a power source or load with a converter as the grid connection interface is operating in parallel with the grid, a frequency ramp test is carried out on the converter to cause the grid frequency to change rampantly, and the power data of the converter during the frequency ramp test is recorded.

[0022] As shown in the Figure 2 accompanying drawings, the power source or load with a converter as the grid connection interface can be: various power sources or loads with a converter as the grid connection interface such as flexible DC transmission, energy storage, photovoltaic power station, wind farm, hydrogen production station, electric vehicle charging station, etc.

[0023] The reference frequency of the converter during the grid frequency ramp change is: (1) Wherein, f ref is the reference frequency of the converter, f 0 is the grid frequency before the frequency ramp test, k f is the change rate of the reference frequency, t is the time, and the start time of the ramp test t = 0, T is the duration of the frequency ramp test.

[0024] S2. Construct a power response model of the converter under the frequency ramp test.

[0025] The power system frequency response model is: (2) (3) Wherein, H g is the inertia of the power system, s is the complex frequency, f is the grid frequency, f 0 is the grid frequency before the frequency ramp test, P g is the grid power, P VSC is the converter power, P L is the load power,P g0 is the grid power before the frequency ramp test, D g is the damping parameter of the power system, k m , R g , F H , T RH are the coefficients related to the primary frequency regulation of the grid, which are the coefficients related to the generator power factor and reserve power, the governor coefficient, the high-pressure cylinder coefficient, and the equivalent time constant of the reheater steam volume respectively.

[0026] Substituting the frequency under the frequency ramp test into the power system frequency response model, the power response model of the converter under the frequency ramp test can be constructed as: (4) where, P VSC0 is the converter power before the frequency ramp test.

[0027] S3. Analyze the component components of the converter power under the frequency ramp test.

[0028] According to the power response model of the converter under the frequency ramp test, it can be known that: If the change rate of the set reference frequency is small, so that the reference frequency during the frequency ramp test is within the dead zone of the grid primary frequency regulation and the grid primary frequency regulation does not act, the power of the converter during the frequency ramp change includes a constant component and a ramp component, specifically as follows: (5) If the change rate of the set reference frequency is large, so that the reference frequency during the frequency ramp test exceeds the dead zone of the grid primary frequency regulation and the effect of the grid primary frequency regulation needs to be considered, the power of the converter during the frequency ramp change includes a constant component, a ramp component and an exponential component, specifically as follows: (6) where, P VSC,t is the power of the converter at time t during the frequency ramp test, P VSC0 is the power of the converter before the frequency ramp test, k f is the change rate of the reference frequency, H g is the inertia of the power system, D g is the damping parameter of the power system, tis time, f 1 is the reference frequency at the end of the frequency ramp test, f N is the rated grid frequency, ε is the dead band of primary frequency regulation of the grid, k m and R g and F H and T RH are coefficients related to the primary frequency regulation of the grid, which are the coefficients related to the generator power factor and the reserve power, the governor coefficient, the high-pressure cylinder coefficient, and the equivalent time constant of the reheater steam volume respectively.

[0029] In the first embodiment, the converter power composition under the frequency ramp test is as shown in the appendix Figure 3 As shown; in the frequency ramp test, if the change rate of the set reference frequency is small, so that the reference frequency during the frequency ramp test is within the dead band of the primary frequency regulation of the grid and the primary frequency regulation of the grid does not act, the power of the converter during the frequency ramp change consists of two components, including a constant component and a ramp component; if the change rate of the set reference frequency is large, so that the reference frequency during the frequency ramp test exceeds the dead band of the primary frequency regulation of the grid and the effect of the primary frequency regulation of the grid needs to be considered, the power of the converter during the frequency ramp change consists of three components, including a constant component, a ramp component, and an exponential component; among them, the constant component in the converter power in both cases uniquely characterizes the power system inertia, specifically the product of the power system inertia and the set frequency change rate. Therefore, only the constant component in the converter power needs to be used to evaluate the power system inertia.

[0030] Compared with the complex coupling characteristics of the power system inertia and the converter power under the power step test, in the power system inertia evaluation scheme without frequency differentiation under the frequency ramp test disclosed by the present invention, the relationship between the power system inertia and the converter power is a linear multiplication relationship, and its magnitude is a constant component during the frequency ramp test, which significantly reduces the difficulty of realizing accurate inertia evaluation.

[0031] S4. Construct a power system inertia evaluation model without frequency differentiation.

[0032] According to the expressions (5) and (6) of the converter power under the frequency ramp test in S3, it can be seen that the constant component therein uniquely characterizes the power system inertia, specifically the product of the power system inertia and the set frequency change rate. Therefore, only the constant component in the converter power needs to be used to evaluate the power system inertia. The power system inertia evaluation model without frequency differentiation is constructed as follows:

[0033] (7) Among them, the differential-free feature is: using a given rate of change of frequency k f to replace the differentiation of the frequency measurement value, without the need for frequency differentiation or frequency difference operation.

[0034] Among them, H g is the inertia of the power system, α const is the constant component in the converter power, α ramp is the coefficient of the ramp component in the converter power, α exp1 and α exp2 are the coefficients of the exponential component in the converter power, k f is the rate of change of the reference frequency, is the converter power actually measured before the frequency ramp test, is during the frequency ramp test t the converter power actually measured at time t is time, f 1 is the reference frequency at the end of the frequency ramp test, f N is the rated grid frequency, ε is the dead zone of the primary frequency regulation of the power grid.

[0035] S5. Evaluate the inertia of the power system using the converter power data.

[0036] The process of evaluating the inertia of the power system using the converter power data under the frequency ramp test is as follows: S5.1. Filter the converter power data measured during the frequency ramp test to reduce measurement noise; then there are two optional methods for evaluating the inertia of the power system using the converter power data, as shown in steps S5.2 and S5.3 respectively. Embodiment 1 of the present invention provides a flowchart for evaluating the inertia of the power system using the converter power data, as shown in the appendix Figure 4 as shown, and the detailed description is as follows.

[0037] S5.2. Use the converter power data and obtain the constant component α const in the converter power through the data fitting method, and then use the power system inertia evaluation model without frequency differentiation in step S4 to evaluate the inertia of the power system.

[0038] S5.3. Or, first obtain the coefficient α ramp, then deduct the ramp component in the converter power during the frequency ramp test, and then use the power system inertia evaluation model without frequency differentiation in step S4 to evaluate the power system inertia using the remaining converter power after deducting the ramp component.

[0039] Furthermore, the process of obtaining the ramp component in the converter power and the process of evaluating the power system inertia using the remaining converter power after deducting the ramp component are as follows: When the frequency ramp test is completed, the converter continues to operate while maintaining the reference frequency at the end of the ramp test unchanged, and records the power data of the converter.

[0040] Filter the two segments of converter power data measured during the frequency ramp test and during the period when the reference frequency remains unchanged after the frequency ramp test is completed to reduce measurement noise.

[0041] Use the power data of the converter during the second period when the grid frequency remains unchanged to estimate the coefficient of the ramp component in the converter power. α ramp .

[0042] Use the estimated coefficient of the ramp component in the converter power and the measured grid frequency to calculate the ramp component in the converter power during the first period of the frequency ramp test.

[0043] Deduct the ramp component in the converter power during the first period of the frequency ramp test, and use the remaining converter power to estimate the power system inertia.

[0044] Furthermore, the coefficient of the ramp component in the converter power estimated using the power data of the converter during the second period when the grid frequency remains unchanged is as follows: (8) Where, α ramp is the coefficient of the ramp component in the converter power, and are the actually measured converter power and grid frequency before the frequency ramp test respectively, and are the actually measured converter power and grid frequency during the period when the reference frequency remains unchanged after the frequency ramp test is completed respectively, k f is the change rate of the reference frequency.

[0045] Furthermore, the process of deducting the ramp component in the converter power during the first period of the frequency ramp test and using the remaining converter power to estimate the power system inertia is as follows: If the reference frequency during the frequency ramp test is within the dead zone of the power grid's primary frequency regulation, after deducting the ramp component in the converter power during the first-stage frequency ramp test, only the constant component remains. α const , the inertia of the power system is evaluated using the power system inertia evaluation model without frequency differentiation in step S4.

[0046] If the reference frequency during the frequency ramp test exceeds the dead zone of the power grid's primary frequency regulation, after deducting the ramp component in the converter power during the first-stage frequency ramp test, the remaining constant component and exponential component are obtained. By means of the data fitting method, the constant component is acquired. α const , and then the inertia of the power system is evaluated using the power system inertia evaluation model without frequency differentiation in step S4.

[0047] Embodiment 1 of the present invention also provides a control block diagram of the converter under the frequency ramp test, as shown in the appendix Figure 5 shown. In the figure i abc and u abc are respectively the voltage and current on the grid-connected side of the converter, f and θ are respectively the measured grid frequency and phase, P ref and Q ref are respectively the active reference power and reactive reference power, and are respectively the active power and reactive power of the converter actually measured at the moment t during the frequency ramp test. During inertia evaluation, a frequency outer loop is connected to the power loop of the existing converter control, and its frequency control target is the reference power for the ramp change of the converter in step S1. Specifically, during the frequency ramp test, according to the given rate of change of the reference frequency and the duration of the frequency ramp test, a ramp-changing reference frequency can be generated. Then, the power adjustment amount generated by the frequency loop controller is superimposed on the reference power of the power loop. Among them, the frequency loop controller can select the existing controller type, and the type of the controller is not limited.

[0048] Compared with the prior art, the present invention improves the evaluation accuracy of the inertia of the power system and realizes the accurate evaluation of the inertia of the power system, which is specifically reflected as follows: 1) Using the given rate of change of frequency to replace the differential and difference operations on the frequency measurement value, avoiding the frequency differential and difference operations that are vulnerable to interference in the prior art, and significantly improving the inertia evaluation accuracy.

[0049] 2) Replacing the existing power step test with a frequency ramp test, avoiding the complex electromagnetic transient interference problem during power step.

[0050] 3) The established power system inertia evaluation model without frequency differentiation can reflect the influence of the synchronous generator governor in the power system, further improving the inertia evaluation accuracy.

[0051] In addition, the present invention also has strong generality and economic advantages: it can be applied to various existing power sources and loads in the power system with converters as the grid connection interface, such as: flexible DC transmission, energy storage power stations, photovoltaic power stations, wind farms, hydrogen production stations, etc.; and there is no need to invest in additional dedicated inertia evaluation devices, having relatively practical engineering application value.

[0052] Effectiveness verification test: The following is to verify the effectiveness of the power system inertia evaluation method without frequency differentiation in Embodiment 1 by building a converter grid-connected test system; among them, the circuit topology of the converter grid-connected test system is as shown in the appendix. Figure 5 as shown.

[0053] Based on the built converter grid-connected test system, this embodiment compares the existing grid inertia evaluation method based on power step test and the power system inertia evaluation method without frequency differentiation proposed by the present invention.

[0054] As shown in the appendix Figure 6 shown, the appendix Figure 6 shows the grid frequency and converter power diagram during the execution of the existing grid inertia evaluation method based on power step test, where the blue line and the red line respectively represent the measured grid frequency and converter power before and after filtering the measurement noise; the appendix Figure 7 shows the rate of change of frequency (RoCoF) obtained by differentiating the measured grid frequency. It can be seen from the appendix Figure 7 that the frequency differentiation operation is extremely vulnerable to noise, and the ideal differentiation is greatly affected, and its result cannot be used for inertia evaluation. Therefore, a certain differential step size needs to be set T d . Referring to domestic and foreign standards, the appendix Figure 7 also shows the calculation results of the rate of change of frequency under common differential step sizes, as shown in the appendix Figure 7 shown; obviously, the calculation of the rate of change of frequency varies greatly under different differential step sizes, which will affect the subsequent evaluation accuracy of the power system inertia.

[0055] As shown in the appendix Figure 8 shown, the appendix Figure 8 shows the grid frequency and converter power diagram during the execution of the power system inertia evaluation method without frequency differentiation in Embodiment 1; it can be seen from the appendix Figure 8 that under the proposed scheme, the grid frequency shows a ramp change characteristic, that is, it changes according to the given ramp reference frequency.

[0056] The comparison results of the existing power grid inertia evaluation method based on power step test and the inertia evaluation method proposed by the present invention are shown in Table 1, where the true value of the power system inertia is set to 5 s. It can be seen from Table 1 that since the method proposed by the present invention avoids the frequency differential operation vulnerable to interference, its estimation error is significantly smaller than that of the existing power grid inertia evaluation method based on power step test. Moreover, the estimation error of the existing power grid inertia evaluation method based on power step test is greatly affected by the differential step size. Too small or too large differential step size will lead to large estimation errors. On the contrary, the method proposed by the present invention shows good evaluation effects at different frequency change rates, indicating that the estimation error of the method proposed by the present invention is not affected by the ramp test parameters.

[0057] Table 1 Comparison results of different power system inertia evaluation methods Example 2 As shown in the Figure 9 appendix, this Example 2 provides a power system inertia evaluation system without frequency differentiation, including: A frequency ramp test module, which is used to conduct a frequency ramp test on the converter when a power supply or load with the converter as the grid connection interface is connected to the grid, so that the grid frequency changes in a ramp manner, and record the converter power data measured during the frequency ramp test.

[0058] An inertia evaluation module, which is used to preprocess the converter power data measured during the frequency ramp test and separate the constant component therein; evaluate the power system inertia according to the separated constant component.

[0059] Each module in the above power system inertia evaluation system without frequency differentiation can be implemented in whole or in part by software, hardware and their combination. The above modules can be embedded in the processor in the computer device in the form of hardware or independent of it, or stored in the memory in the computer device in the form of software, so as to facilitate the processor to call and execute the operations corresponding to the above modules.

[0060] In summary, the power system inertia evaluation method and system without frequency differentiation of the present invention avoid the frequency differential operation vulnerable to interference, can significantly improve the inertia evaluation accuracy, and achieve the accurate evaluation of the power system inertia. In addition, the present invention also has strong universality and economic advantages, can be applied to various existing power supplies and loads with converters as grid connection interfaces in the power system, and does not require additional investment in special inertia evaluation devices, having relatively practical engineering application value.

[0061] Example 3 As shown in the Figure 10As shown in the figure, Embodiment 3 of the present invention provides an electronic device, including: a memory for storing a computer program; a processor for implementing the steps of a power system inertia evaluation method without frequency differentiation when executing the computer program; or, when the processor executes the computer program, implementing the functions of each module in the above-mentioned power system inertia evaluation system without frequency differentiation.

[0062] Exemplarily, the computer program can be divided into one or more modules / units, and the one or more modules / units are stored in the memory and executed by the processor to complete the present invention. The one or more modules / units can be a series of computer program instruction segments capable of completing preset functions, and the instruction segments are used to describe the execution process of the computer program in the electronic device.

[0063] The electronic device can be a computing device such as a desktop computer, a notebook, a palm computer, and a cloud server. The electronic device may include, but is not limited to, a processor and a memory.

[0064] The so-called processor may be a central processing unit, or may also be other general-purpose processors, digital signal processors, application-specific integrated circuits, off-the-shelf programmable gate arrays, or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor, or the processor may also be any conventional processor, etc.

[0065] The memory can be used to store the computer program and / or module. The processor realizes various functions of the electronic device by running or executing the computer program and / or module stored in the memory, and calling the data stored in the memory. The memory mainly includes a program storage area and a data storage area. Among them, the program storage area can store an operating system, application programs required for at least one function (such as functions of data measurement and processing, parameter calculation, etc.).

[0066] Those skilled in the art should understand that the embodiments of the present invention can provide a method, a system, or a computer program product. Therefore, the present invention can be implemented in the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can be implemented in the form of a computer program product implemented on one or more computer-usable storage media containing computer-usable program code.

[0067] The present invention is described with reference to the flowcharts and / or block diagrams of methods, systems (devices), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, as well as the combination of flows and / or blocks in the flowchart and / or block diagram. These computer program instructions can be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including an instruction device that implements the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or multiple blocks specified in the function.

[0068] It should be noted that the above specific embodiments can enable those skilled in the art to more comprehensively understand the present invention, but do not limit the present invention in any way. Therefore, although the present specification and embodiments have described the present invention in detail, those skilled in the art should understand that the present invention can still be modified or equivalently replaced; and all technical solutions and improvements that do not depart from the spirit and scope of the present invention are covered by the protection scope of the patent of the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved. Any simple changes or equivalent replacements of technical solutions that can be obviously obtained by any person skilled in the art within the technical scope disclosed by the present invention belong to the protection scope of the present invention.

Claims

1. A method for evaluating the inertia of a power system without frequency differentiation, characterized in that Including: When a power source or load with a converter as the grid connection interface is connected to the grid and operating, a frequency ramp test is carried out on the converter to cause the grid frequency to ramp and change, and the power data of the converter measured during the frequency ramp test is recorded; The power data of the converter measured during the frequency ramp test is preprocessed, and then the constant component therein is separated; the power system inertia is evaluated according to the separated constant component.

2. The inertia evaluation method of the power system without frequency differentiation according to claim 1, wherein During the period of carrying out the frequency ramp test on the converter, the reference frequency adopted by the converter is: ； Among them, f ref is the reference frequency of the converter, f 0 is the grid frequency before the frequency ramp test, k f is the change rate of the reference frequency, t is time, and the start time of the ramp test t = 0, T is the duration of the frequency ramp test.

3. The method for evaluating the inertia of a power system without frequency differentiation according to claim 2, wherein During the period of the grid frequency ramp change, the power data of the converter is as follows: If the change rate of the set reference frequency causes the reference frequency during the frequency ramp test to be within the dead zone of the grid primary frequency regulation and the grid primary frequency regulation does not act, the power of the converter during the frequency ramp change includes a constant component and a ramp component, specifically as follows: ； In the formula, is the constant component, is the ramp component; If the change rate of the set reference frequency causes the reference frequency during the frequency ramp test to exceed the dead zone of the grid primary frequency regulation and the effect of the grid primary frequency regulation needs to be considered, the power of the converter during the frequency ramp change includes a constant component, a ramp component and an exponential component, specifically as follows: ； In the formula, is the constant component, is the ramp component, is the exponential component; Wherein, P VSC,t is the power of the converter during the frequency ramp test t at a certain moment, P VSC0 is the power of the converter before the frequency ramp test, k f is the change rate of the reference frequency, H g is the inertia of the power system, D g is the damping parameter of the power system, t is time, f 1 is the reference frequency at the end of the frequency ramp test, f N is the rated grid frequency, ε is the dead zone of the primary frequency regulation of the power grid, k m and R g and F H and T RH are coefficients related to the primary frequency regulation of the power grid, which are respectively coefficients related to the generator power factor and reserve power, governor coefficient, high-pressure cylinder coefficient, and reheater steam volume equivalent time constant.

4. The method for evaluating the inertia of a power system without frequency differentiation according to claim 3, characterized in that, The evaluation of the power system inertia according to the separated constant component is specifically to evaluate the power system inertia through a power system inertia evaluation model without frequency differentiation. The power system inertia evaluation model without frequency differentiation is as follows: ； Among them, H g is the inertia of the power system, α const is the constant component in the converter power, α ramp is the coefficient of the ramp component in the converter power, α exp1 and α exp2 are the coefficients of the exponential component in the converter power, k f is the change rate of the reference frequency, is the converter power actually measured before the frequency ramp test, is during the frequency ramp test t is the converter power actually measured at time t is time, f 1 is the reference frequency at the end of the frequency ramp test, f N is the rated grid frequency, ε is the dead band of primary frequency regulation of the grid.

5. The method for evaluating the inertia of a power system without frequency differentiation according to claim 4, characterized in that The preprocessing of the power data of the converter measured during the frequency ramp test, then separating the constant component therein, and evaluating the power system inertia according to the separated constant component specifically includes the following steps: Filter the power data of the converter measured during the frequency ramp test; Using the converter power data, obtain the constant component in the converter power through the data fitting method α const , and evaluate the power system inertia according to the power system inertia evaluation model without frequency differentiation Alternatively, first obtain the coefficient of the ramp component in the converter power α ramp , then deduct the ramp component in the converter power during the frequency ramp test, and evaluate the power system inertia using the remaining converter power after deducting the ramp component according to the power system inertia evaluation model without frequency differentiation.

6. The method for evaluating the inertia of a power system without frequency differentiation according to claim 5, wherein The process of obtaining the ramp component in the converter power and the process of evaluating the power system inertia by using the remaining converter power after deducting the ramp component are as follows: When the frequency ramp test is completed, the converter continues to operate while maintaining the reference frequency at the end of the ramp test unchanged, and records the power data of the converter ; Filter the two segments of converter power data measured during the frequency ramp test period and during the period when the reference frequency remains unchanged after the frequency ramp test is completed respectively; Estimate the coefficient of the ramp component in the converter power using the power data of the converter during the period when the second-stage grid frequency remains unchanged α ramp ; Calculate the ramp component in the converter power during the first frequency ramp test period by using the coefficient of the ramp component estimated in the converter power and the measured grid frequency; Deduct the ramp component in the converter power during the first frequency ramp test period, and then estimate the power system inertia by using the remaining converter power.

7. The power system inertia evaluation method without frequency differentiation according to claim 6, wherein The coefficient of the ramp component estimated in the converter power by using the power data of the converter during the second period when the grid frequency remains unchanged is as follows: ； Among them, α ramp is the coefficient of the ramp component in the converter power, and are respectively the converter power and the grid frequency actually measured before the frequency ramp test, and are respectively the converter power and the grid frequency actually measured during the period when the reference frequency remains unchanged after the frequency ramp test is completed, k f is the change rate of the reference frequency.

8. The power system inertia evaluation method without frequency differentiation according to claim 6, characterized in that The process of deducting the ramp component in the converter power during the first frequency ramp test period and estimating the power system inertia by using the remaining converter power is as follows: If the reference frequency during the frequency ramp test is within the dead zone of the primary frequency regulation of the power grid, after the ramp component in the converter power is deducted during the first-stage frequency ramp test, only the constant component remains. α const , evaluate the power system inertia according to the power system inertia evaluation model without frequency differentiation. If the reference frequency during the frequency ramp test exceeds the dead zone of the power grid's primary frequency regulation, after deducting the ramp component in the converter power during the first-stage frequency ramp test, the remaining constant component and exponential component are obtained through data fitting to acquire the constant component, and then the power system inertia is evaluated according to the power system inertia evaluation model without frequency differentiation. α const , and then the power system inertia is evaluated according to the power system inertia evaluation model without frequency differentiation.

9. The power system inertia evaluation method without frequency differentiation according to claim 1, wherein The power source or load with a converter as the grid connection interface is: various power sources or loads with a converter as the grid connection interface in flexible DC transmission, energy storage, photovoltaic power stations, wind farms, hydrogen production stations, and electric vehicle charging stations.

10. A power system inertia evaluation system without frequency differentiation, characterized in that, Including: A frequency ramp test module, configured to carry out a frequency ramp test on a converter when a power source or load with a converter as the grid connection interface is connected to the grid and operating, cause the grid frequency to ramp and change, and record the power data of the converter measured during the frequency ramp test; An inertia evaluation module is used to preprocess the converter power data measured during the frequency ramp test, and then isolate the constant component therein; the power system inertia is evaluated based on the isolated constant component.

Images