A power grid inertia online measurement method, system, device and medium

Abstract

The application discloses a kind of power grid inertia online measurement method, system, equipment and medium, by injecting the active power excitation signal under characteristic frequency into power grid through flexible HVDC transmission system, active power and frequency information of power grid feedback are collected, and the real-time inertia of power grid is calculated.This method is an online measurement method, which can measure the inertia of power grid in real time, and has the advantages of small noise interference and high accuracy of measurement results.Thereby, the problem that the prior art is easily disturbed and cannot measure the inertia of power grid in real time and accurately is solved.

Description

Technical Field

[0001] This application relates to the field of power grid inertia assessment technology, and in particular to a method, system, device and medium for online measurement of power grid inertia. Background Technology

[0002] The operating characteristics of new power systems based on new energy sources are undergoing profound changes. Power systems are facing the problem of decreasing inertia levels, posing challenges to system safety and stability, and urgently requiring research on online inertia measurement technology.

[0003] In the power industry, inertia assessment methods mainly include: 1) large disturbance-based assessment methods, which assess grid inertia using information after a large disturbance event occurs in the grid. This method has the advantages of easy data processing and high accuracy, but the inertia assessment results are not real-time; 2) obtaining the inertia of all units through generator status monitoring in the SCADA system. This method ignores the inertia provided by power electronic equipment and the load side, resulting in a large error; 3) quasi-steady-state assessment methods, which use noise-like signals or frequency changes caused by some events during real-time system operation to assess the equivalent inertia of the system online. This method is highly susceptible to noise interference and has low measurement accuracy. Therefore, there is an urgent need to design a grid inertia measurement method that can measure grid inertia in real time, has low susceptibility to noise interference, and provides high measurement accuracy. Summary of the Invention

[0004] This application provides a method, system, device, and medium for online measurement of power grid inertia, which addresses the problems of existing technologies being susceptible to interference and unable to measure power grid inertia accurately and in real time.

[0005] In view of this, the first aspect of this application provides a method for online measurement of power grid inertia, the method comprising:

[0006] S1. Set the active power reference value P at the base frequency according to scheduling requirements. ref and reactive power reference value Q ref Start the flexible DC transmission system and maintain its operation;

[0007] S2. Based on the operating parameters of the power grid under test, determine the amplitude P of the active power excitation signal to be injected into the power grid under test. href and frequency f h The operating parameters include: load level, primary frequency regulation dead zone, frequency change rate protection setting, and voltage and current measurement equipment accuracy.

[0008] S3, Judgment Does it exceed the rated capacity of the flexible DC transmission system? If not, proceed to step S4; otherwise, adjust the active power reference value P. ref Once the conditions are met, proceed to step S4.

[0009] S4, injecting an active power excitation signal at a characteristic frequency into the measured power grid through the flexible HVDC system based on a preset characteristic power control function;

[0010] S5, collecting active power and frequency information of the power grid, so as to calculate real-time inertia of the measured power grid according to the active power and frequency information.

[0011] Optionally, step S4 specifically comprises:

[0012] S41, collecting three-phase voltage U ABC at the grid side of the flexible HVDC system; ABC obtaining grid frequency f0 and voltage phase angle θ0 through a phase-locked loop; setting amplitude P href and characteristic frequency f h of the injected active power excitation signal, and constructing phase angle θ1 and phase angle θ2;

[0013] S42, collecting three-phase current I ABC at the valve side, and transforming to obtain d-axis and q-axis currents in a rotating coordinate system, and then extracting direct current components of the d-axis and q-axis currents through a decoupling control algorithm to obtain d-axis current direct current component and q-axis current direct current component at reference phase angle θ0, d-axis current direct current component and q-axis current direct current component at reference phase angle θ1, and d-axis current direct current component and q-axis current direct current component at reference phase angle θ2;

[0014] S43, controlling active power and reactive power at the fundamental frequency through a double-loop vector control link based on the d-axis current direct current component and the q-axis current direct current component at the reference phase angle θ0;

[0015] S44, controlling active power at the characteristic frequency through a characteristic power control link based on the d-axis current direct current component and the q-axis current direct current component at the reference phase angle θ1, and the d-axis current direct current component and the q-axis current direct current component at the reference phase angle θ2;

[0016] S45, performing dq0 / abc coordinate transformation on parameters output after steps S43 and S44 are controlled to obtain three-phase voltage reference values V cAref , V cBref , and V cCref at the valve side, and then obtaining switching signals through a modulation link to control IGBT.

[0017] Optionally, the expression of the decoupling control algorithm is:

[0018]

[0019] In the formula, I d0 , and I q0respectively, are the d-axis current direct current component and the q-axis current direct current component at the reference phase angle θ0; I d1 q1 respectively, are the d-axis current direct current component and the q-axis current direct current component at the reference phase angle θ1; I d2 q2 respectively, are the d-axis current direct current component and the q-axis current direct current component at the reference phase angle θ2.

[0020] Optionally, the real-time inertia of the measured power grid is calculated according to the active power and frequency information, and specifically includes:

[0021] The real-time inertia of the measured power grid is calculated according to the active power and frequency information based on an inertia calculation formula.

[0022] The inertia calculation formula is as follows:

[0023]

[0024] In the formula, ΔP is the active power change, and df / dt is the frequency change rate.

[0025] The second aspect of the present application provides a power grid inertia online measurement system, and the system includes:

[0026] A starting unit is configured to set the active power reference value P ref and the reactive power reference value Q ref under the base frequency according to the scheduling demand, start the flexible HVDC system, and maintain the operation.

[0027] A setting unit is configured to determine the amplitude P href and the frequency f h of the active power excitation signal injected into the measured power grid in combination with the working parameters of the measured power grid, wherein the working parameters include the load level, the primary frequency modulation dead zone, the frequency change rate protection setting value, and the voltage and current measurement device accuracy.

[0028] An analysis unit is configured to determine whether the rated capacity of the flexible HVDC system is exceeded, and if not, trigger a control unit, and if so, adjust the active power reference value P ref , and trigger the control unit after the condition is met.

[0029] A control unit is configured to inject the active power excitation signal at the characteristic frequency into the measured power grid through the flexible HVDC system based on the preset characteristic power control function.

[0030] A calculation unit is configured to collect the active power and frequency information of the power grid, and calculate the real-time inertia of the measured power grid according to the active power and frequency information.

[0031] ​​Optionally, the control unit is specifically used for:

[0032] S41, collecting three-phase voltage U of the grid side of the flexible HVDC system ABC ABC The grid frequency f0 and the voltage phase angle θ0 are obtained through a phase-locked loop; the amplitude P of the injected active power excitation signal and the characteristic frequency f are set href h , and the phase angles θ1 and θ2 are constructed;

[0033] S42, collecting three-phase current I of the valve side ABC The d-axis and q-axis currents in the rotating coordinate system are obtained through transformation, and the direct current components of the d-axis and q-axis currents are extracted through a decoupling control algorithm to obtain the d-axis current direct current component and the q-axis current direct current component under the reference phase angle θ0, the d-axis current direct current component and the q-axis current direct current component under the reference phase angle θ1, and the d-axis current direct current component and the q-axis current direct current component under the reference phase angle θ2;

[0034] S43, controlling the active power and the reactive power under the fundamental frequency through a double-loop vector control link based on the d-axis current direct current component and the q-axis current direct current component under the reference phase angle θ0;

[0035] S44, controlling the active power under the characteristic frequency through a characteristic power control link based on the d-axis current direct current component and the q-axis current direct current component under the reference phase angle θ1 and the d-axis current direct current component and the q-axis current direct current component under the reference phase angle θ2;

[0036] S45, the parameters output after the control of steps S43 and S44 are subjected to dq0 / abc coordinate transformation to obtain the valve side three-phase voltage reference value V cAref cBref cCref , and then the switching signal is obtained after the modulation link to control the IGBT.

[0037] Optionally, the expression of the decoupling control algorithm is:

[0038]

[0039] In the formula, I d0 , I q0 are the d-axis current direct current component and the q-axis current direct current component under the reference phase angle θ0; I d1 , I q1 are the d-axis current direct current component and the q-axis current direct current component under the reference phase angle θ1; I d2 , I q2 are the d-axis current direct current component and the q-axis current direct current component under the reference phase angle θ2. ​​​​

[0040] Optionally, the computing unit is specifically configured to:

[0041] collect active power and frequency information of the power grid;

[0042] calculate real-time inertia of the measured power grid according to the active power and frequency information based on an inertia calculation formula;

[0043] wherein the inertia calculation formula is:

[0044]

[0045] wherein, ΔP is the active power variation, and df / dt is the frequency change rate.

[0046] The third aspect of the present application provides a power grid inertia online measurement device, the device comprising a processor and a memory:

[0047] The memory is configured to store program code and transmit the program code to the processor;

[0048] The processor is configured to execute the steps of the power grid inertia online measurement method according to the instructions in the program code.

[0049] The fourth aspect of the present application provides a computer readable storage medium for storing program code, the program code being used to execute the power grid inertia online measurement method of the first aspect.

[0050] From the above technical solutions, the present application has the following advantages:

[0051] The present application provides a power grid inertia online measurement method based on flexible DC signal injection. The method injects an active power excitation signal at a characteristic frequency into the power grid through a flexible DC transmission system, collects the active power and frequency information fed back by the power grid, and calculates the real-time inertia of the power grid. The method is an online measurement method, which can measure the power grid inertia in real time, and has the advantages of small noise interference and high accuracy of measurement results.

[0052] Compared with the prior art:

[0053] ①The power grid inertia online measurement of the present application is an online measurement method, which can measure the power grid inertia in real time;

[0054] ②Compared with the method of obtaining the inertia of all units through the state of the generator in the SCADA monitoring system in the prior art, the method provided by the present application can take into account the inertia provided by the power electronic equipment and the load side in the power grid, and has higher accuracy;

[0055] ③ Compared with the existing technology based on quasi-steady-state evaluation methods, the method provided in this application injects active power signals at characteristic frequencies into the power grid, resulting in measurement results that are less affected by noise interference and have higher accuracy. Attached Figure Description

[0056] Figure 1 This is a flowchart illustrating an online power grid inertia measurement method provided in an embodiment of this application.

[0057] Figure 2 This is a schematic diagram of the dual closed-loop vector control topology provided in the embodiments of this application;

[0058] Figure 3 This is a schematic diagram of the characteristic power control topology provided in the embodiments of this application;

[0059] Figure 4 This is an example of characteristic power signal injection provided in the embodiments of this application;

[0060] Figure 5 This is a second example of characteristic power signal injection provided in the embodiments of this application;

[0061] Figure 6 This is a schematic diagram of the structure of an online power grid inertia measurement system provided in an embodiment of this application. Detailed Implementation

[0062] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0063] Please see Figure 1 The online measurement method for power grid inertia provided in this application embodiment includes:

[0064] Step 101: Set the active power reference value P at the base frequency according to the scheduling requirements. ref and reactive power reference value Q ref The flexible DC transmission system was started and maintained in operation.

[0065] Step 102: Based on the operating parameters of the power grid under test, determine the amplitude P of the active power excitation signal to be injected into the power grid under test. href and frequency f h The operating parameters include: load level, primary frequency regulation dead zone, frequency change rate protection setting, and voltage and current measurement equipment accuracy.

[0066] Step 103, judging whether the rated capacity of the flexible HVDC power transmission system is exceeded, if not, executing step 104, if yes, adjusting the active power reference value P ref , and executing step 104 after the condition is met.

[0067] Step 104, based on the preset characteristic power control function, injecting an active power excitation signal at a characteristic frequency into the measured power grid through the flexible HVDC power transmission system.

[0068] Step 105, collecting the active power and frequency information of the power grid, so as to calculate the real-time inertia of the measured power grid according to the active power and frequency information.

[0069] In one embodiment, step 104 specifically comprises:

[0070] Step 1041, collecting the three-phase voltage U ABC at the grid side of the flexible HVDC power transmission system ABC , obtaining the grid frequency f0and the voltage phase angle θ0through a phase-locked loop; setting the amplitude P href and the characteristic frequency f h of the injected active power excitation signal, and constructing the phase angle θ1and the phase angle θ2.

[0071] It should be noted that the phase angle θ1and the phase angle θ2are constructed as formula (1):

[0072]

[0073] Step 1042, collecting the three-phase current I ABC at the valve side, and transforming to obtain the d-axis and q-axis currents in the rotating coordinate system, and then extracting the direct current components of the d-axis and q-axis currents through a decoupling control algorithm to obtain the direct current components of the d-axis and q-axis currents at the reference phase angle θ0, the direct current components of the d-axis and q-axis currents at the reference phase angle θ1, and the direct current components of the d-axis and q-axis currents at the reference phase angle θ2.

[0074] It should be noted that the IABC is transformed to obtain the d-axis and q-axis currents in the rotating coordinate system through formula (2).

[0075]

[0076] Then, the direct current components of the d-axis and q-axis currents are extracted through the decoupling control algorithm of formula (3) as follows:

[0077]

[0078] In the formula, I d0 , I q0respectively are the d-axis current DC component and the q-axis current DC component at the reference phase angle θ0; I d1 , I q1 respectively are the d-axis current DC component and the q-axis current DC component at the reference phase angle θ1; I d2 , I q2 respectively are the d-axis current DC component and the q-axis current DC component at the reference phase angle θ2.

[0079] Step 1043, based on the d-axis current DC component and the q-axis current DC component at the reference phase angle θ0, the active power and the reactive power at the fundamental frequency are controlled by a double closed-loop vector control link.

[0080] It should be noted that, based on the d-axis current DC component and the q-axis current DC component at the reference phase angle θ0, the active power and the reactive power at the fundamental frequency are controlled by a double closed-loop vector control link of Figure 2 , the control topology is consistent with the traditional control method of the flexible DC power transmission system.

[0081] Figure 2 P ref , Q ref respectively are the active power reference value and the reactive power reference value at the fundamental frequency, U d , U q respectively are the d-axis voltage and the q-axis voltage at the reference phase angle θ0, I dref , I qref respectively are the d-axis current reference value and the q-axis current reference value at the fundamental frequency, ω0 is the rated angular velocity, L is the equivalent inductance on the valve side of the flexible, V cd0 , V cq0 respectively are the d-axis valve side voltage reference value and the q-axis valve side voltage reference value at the fundamental frequency, PI is a proportional integral control link.

[0082] Step 1044, based on the d-axis current DC component and the q-axis current DC component at the reference phase angle θ1, the d-axis current DC component and the q-axis current DC component at the reference phase angle θ2, the active power at the characteristic frequency is controlled by a characteristic power control link.

[0083] It should be noted that, based on the d-axis current DC component and the q-axis current DC component at the reference phase angle θ1, the d-axis current DC component and the q-axis current DC component at the reference phase angle θ2, the active power at the characteristic frequency is controlled by a characteristic power control link of Figure 3 .

[0084] Figure 3 I href is the current amplitude reference value at the characteristic frequency, V cd1 , V cq1Vd0 and Vq0 are respectively the d-axis and q-axis voltage reference values at the characteristic frequency (f0+f h ) and (f0-f cd2 ) respectively. cq2 h Vd0 and Vq0 are respectively the d-axis and q-axis voltage reference values at the characteristic frequency (f0+f h ) and (f0-f cd2 ) respectively.

[0085] The parameters outputted after step 1045, step 1043 and step 1044 are subjected to dq0 / abc coordinate transformation to obtain valve-side three-phase voltage reference values V cAref , V cBref , V cCref , which are then subjected to a modulation link to obtain switching signals for controlling IGBT.

[0086] It should be noted that the parameters outputted after step 1043 and step 1044 are subjected to dq0 / abc coordinate transformation of formula (4) to obtain valve-side three-phase voltage reference values V cAref , V cBref , V cCref as follows:

[0087]

[0088] The valve-side voltage reference values are subjected to a modulation link to obtain switching signals for controlling IGBT, which is consistent with the conventional method.

[0089] Further, through the actions of Figure 2 and Figure 3 control links, the system can obtain I d0 = I dref , I q0 = I qref , I d1 = I d2 = I href in steady state, and the actual output active power P and reactive power Q of the system are as follows:

[0090]

[0091] In one embodiment, the real-time inertia of the measured power grid is calculated according to the active power and frequency information in step 105, which specifically includes:

[0092] The real-time inertia of the measured power grid is calculated according to the active power and frequency information based on the inertia calculation formula.

[0093] The inertia calculation formula is as follows:

[0094]

[0095] Wherein, ΔP is the active power change, and df / dt is the frequency change rate.

[0096] The method for injecting the active power excitation signal at the characteristic frequency into the power grid by the flexible HVDC system is shown in the following example Figure 4 and Figure 5 .

[0097] The above is the online measurement method of the power grid inertia provided in the embodiments of the present application, and the following is an online measurement system of the power grid inertia provided in the embodiments of the present application.

[0098] Referring to Figure 6 , the online measurement system of the power grid inertia provided in the embodiments of the present application comprises:

[0099] The starting unit 201 is configured to set the active power reference value P ref and the reactive power reference value Q ref at the base frequency according to the scheduling demand, start the flexible HVDC system, and maintain the operation.

[0100] The setting unit 202 is configured to determine the amplitude P href and the frequency f h of the active power excitation signal for injection into the measured power grid in combination with the working parameters of the measured power grid, wherein the working parameters comprise the load level, the primary frequency modulation dead zone, the frequency change rate protection setting value, and the accuracy of the voltage and current measurement device.

[0101] The analysis unit 203 is configured to determine whether the rated capacity of the flexible HVDC system is exceeded, and if not, trigger the control unit, and if so, adjust the active power reference value P ref , and trigger the control unit after the condition is met.

[0102] The control unit 204 is configured to inject the active power excitation signal at the characteristic frequency into the measured power grid through the flexible HVDC system based on the preset characteristic power control function.

[0103] The calculation unit 205 is configured to collect the active power and frequency information of the power grid, so as to calculate the real-time inertia of the measured power grid according to the active power and frequency information.

[0104] Further, the embodiments of the present application further provide an online measurement device of the power grid inertia, which comprises a processor and a memory:

[0105] The memory is configured to store program codes and transmit the program codes to the processor.

[0106] The processor is configured to execute the steps of the method for online measurement of power grid inertia according to the instructions in the program code.

[0107] Further, the embodiments of the present application also provide a computer readable storage medium for storing program code, the program code being used for executing the method for online measurement of power grid inertia.

[0108] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described system and unit can refer to the corresponding processes in the foregoing method embodiments, which will not be described here.

[0109] The terms "first", "second", "third", "fourth" and the like used in the description of the present application and the above drawings, if any, are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented, for example, in an order other than that illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0110] It should be understood that in the present application, "at least one" means one or more, and "multiple" means two or more. "And / or" is used to describe the association relationship between the associated objects, which means that there can be three relationships, for example, "A and / or B" can represent three cases: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the front and rear associated objects. "At least one of the following" or similar expressions means any combination of these items, including any combination of single or multiple items. For example, at least one of a, b or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0111] In several embodiments provided in the present application, it should be understood that the disclosed system, device and method can be implemented in other manners. For example, the described device embodiments are merely schematic. The division of the units is merely a logical function division. There can be another division manner for the actual implementation, for example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections can be indirect couplings or communication connections through some interfaces, devices or units, and can be in electrical, mechanical or other forms.

[0112] The units described as separated components can or can not be physically separated, and the components displayed as units can or can not be physical units, i.e., can be located in one place, or can be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purposes of the embodiments of the present application.

[0113] In addition, each functional unit in the embodiments of the present application can be integrated in one processing unit, or each unit can exist physically, or two or more units can be integrated in one unit. The integrated unit can be implemented in the form of hardware, or in the form of software functional units.

[0114] When the integrated unit is implemented in the form of software functional units and sold or used as an independent product, it can be stored in a computer readable storage medium. Based on such an understanding, the technical solutions of the present application essentially, or the part that contributes to the prior art, or all or a part of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium, and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the embodiments of the present application. The foregoing storage medium includes: U disk, mobile hard disk, read-only memory (English full name: Read-Only Memory, English abbreviation: ROM), random access memory (English full name: Random Access Memory, English abbreviation: RAM), magnetic disk or optical disk, and various program codes that can be stored in the medium.

[0115] The above-described embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for online measurement of grid inertia, characterized in that, Comprising: S1, set active power reference value P under base frequency according to scheduling requirement ref and reactive power reference value Q ref , start and maintain operation of the flexible HVDC power transmission system S2, in combination with the operating parameters of the measured power grid, determine the amplitude P of the active power excitation signal for injection into the measured power grid href and the frequency f h , the operating parameters including: load level, primary frequency regulation dead zone, frequency rate of change protection setting, voltage and current measurement device accuracy; S3, judging whether the rated capacity of the flexible HVDC power transmission system is exceeded, if not, executing step S4, if yes, adjusting the active power reference value P ref , after the condition is met, executing step S4; S4, based on the preset characteristic power control function, injecting an active power excitation signal at a characteristic frequency into the measured power grid through the flexible DC power transmission system; S5, collecting active power and frequency information of the power grid, so as to calculate the real-time inertia of the measured power grid according to the active power and frequency information; Wherein, the expression for constructing the phase angle θ1 and the phase angle θ2 is: S41, collect flexible HVDC transmission system grid side three-phase voltage U ABC , ABC Through the phase-locked loop to get the grid frequency f0and voltage phase angle θ0; set the amplitude P href and characteristic frequency f h of the injected active power excitation signal, and construct the phase angle θ1and phase angle θ2; S43, based on the d-axis current DC component and the q-axis current DC component at the reference phase angle θ0, controlling the active power and the reactive power at the fundamental frequency through a double closed loop vector control link; ； S42, collect valve side three-phase current I ABC And get d-axis and q-axis current in rotating coordinate system through transformation, then extract direct current component of d-axis and q-axis current through decoupling control algorithm, get d-axis current direct current component and q-axis current direct current component under reference phase angle θ0, d-axis current direct current component and q-axis current direct current component under reference phase angle θ1, d-axis current direct current component and q-axis current direct current component under reference phase angle θ2. S44, based on the d-axis current DC component and the q-axis current DC component at the reference phase angle θ1, the d-axis current DC component and the q-axis current DC component at the reference phase angle θ2, controlling the active power at the characteristic frequency through a characteristic power control link; The expression of the decoupling control algorithm is: S45, the parameters outputted after step S43 and S44 are subjected to dq0 / abc coordinate transformation to obtain valve-side three-phase voltage reference value V cAref cBref cCref , and then after a modulation link, a switching signal pair is obtained to control the IGBT.​​ 2. The method of online measurement of grid inertia according to claim 1, characterized in that, The expression of the decoupling control algorithm is: ； where I d0 , I q0 are the d-axis current DC component and the q-axis current DC component at the reference phase angle θ0, respectively; I d1 , I q1 are the d-axis current DC component and the q-axis current DC component at the reference phase angle θ1, respectively; I d2 , I q2 are the d-axis current DC component and the q-axis current DC component at the reference phase angle θ2, respectively.

3. The method of online measurement of grid inertia according to claim 1, characterized in that, S5, collecting active power and frequency information of the power grid, so as to calculate the real-time inertia of the measured power grid according to the active power and frequency information; Based on the inertia calculation formula, the real-time inertia of the measured power grid is calculated according to the active power and frequency information; Wherein, the inertia calculation formula is: ； In the formula, ΔP is the active power change, and df / dt is the frequency change rate.

4. An online measurement system of grid inertia, characterized in that, Comprising: A starting unit is configured to set active power reference value P and reactive power reference value Q at base frequency according to scheduling requirements ref and maintain operation of the flexible HVDC power transmission system ref ​ The setting unit is configured to determine an amplitude P of an active power excitation signal for injection into the measured power grid in combination with operating parameters of the measured power grid href and a frequency f h , the operating parameters including: a load level, a primary frequency regulation dead zone, a frequency rate of change protection setting value, voltage and current measurement device accuracy; an analysis unit for determining whether the rated capacity of the flexible HVDC power transmission system is exceeded, and if not, triggering the control unit, and if so, adjusting the active power reference value P ref , and after the condition is met, triggering the control unit; A control unit configured to inject an active power excitation signal at a characteristic frequency into the measured power grid through the flexible DC power transmission system based on a preset characteristic power control function; A calculation unit configured to collect active power and frequency information of the power grid, so as to calculate the real-time inertia of the measured power grid according to the active power and frequency information; Wherein, the control unit is specifically configured to: S41, collect flexible HVDC transmission system grid side three-phase voltage U ABC , ABC Through the phase-locked loop to get the grid frequency f0and voltage phase angle θ0; set the amplitude P href and the characteristic frequency f h of the injected active power excitation signal, and construct the phase angle θ1and the phase angle θ2; Wherein, the expression for constructing the phase angle θ1 and the phase angle θ2 is: ； S42, collect valve side three-phase current I ABC And get d-axis and q-axis current in rotating coordinate system through transformation, then extract direct current component of d-axis and q-axis current through decoupling control algorithm, get d-axis current direct current component and q-axis current direct current component under reference phase angle θ0, d-axis current direct current component and q-axis current direct current component under reference phase angle θ1, d-axis current direct current component and q-axis current direct current component under reference phase angle θ2. S43, based on the d-axis current DC component and the q-axis current DC component at the reference phase angle θ0, controlling the active power and the reactive power at the fundamental frequency through a double closed loop vector control link; S44, based on the d-axis current DC component and the q-axis current DC component at the reference phase angle θ1, the d-axis current DC component and the q-axis current DC component at the reference phase angle θ2, controlling the active power at the characteristic frequency through a characteristic power control link; S45, the parameters outputted after step S43 and S44 are subjected to dq0 / abc coordinate transformation to obtain valve-side three-phase voltage reference value V cAref cBref cCref , and then the switch signal pair IGBT is controlled after passing through a modulation link.​​ 5. The on-line measurement system of grid inertia according to claim 4, characterized in that, The expression of the decoupling control algorithm is: ； where I d0 , I q0 are the d-axis current DC component and the q-axis current DC component at the reference phase angle θ0, respectively; I d1 , I q1 are the d-axis current DC component and the q-axis current DC component at the reference phase angle θ1, respectively; I d2 , I q2 are the d-axis current DC component and the q-axis current DC component at the reference phase angle θ2, respectively.

6. The online measurement system of grid inertia as claimed in claim 4, wherein, The calculation unit is specifically configured to: Collecting active power and frequency information of the power grid; Based on the inertia calculation formula, the real-time inertia of the measured power grid is calculated according to the active power and frequency information; Wherein, the inertia calculation formula is: ； In the formula, ΔP is the active power change, and df / dt is the frequency change rate.

7. An online measurement device of grid inertia, characterized in that, The device comprises a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the power grid inertia online measurement method according to the instructions in the program code.

8. A computer-readable storage medium, characterized in that, The computer readable storage medium is used to store program code, and the program code is used to execute the power grid inertia online measurement method. The device comprises a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the power grid inertia online measurement method according to the instructions in the program code. The computer readable storage medium is used to store program code, and the program code is used to execute the power grid inertia online measurement method.

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