Method and system for testing inertia of network-forming converter in full-power electronic power system

Abstract

The invention belongs to the technical field of new energy power electronics, and relates to a method and system for testing inertia of a network-forming converter in a full power electronic power system, and the method comprises the steps: 1, controlling the network-forming converter to work in a no-load state; 2, controlling an active loop of a VSG control system of the network-forming converter to only keep an inertia simulation link to operate; 3, taking an active power value which is actually fed back as an active power instruction of the network construction type converter; 4, after the active power is stabilized, setting the step increase of the active power instruction of the network construction type converter, and monitoring the frequency value increase amount of the output voltage of the network construction type converter; 5, recording the time required for the frequency value increment of the output voltage of the network-forming converter to reach a specified target value; 6, calculating the inertia of the network construction type converter based on the relationship between the inertia and the frequency change rate; according to the method, the inertia of the network-building type converter can be quickly and accurately determined in a full-power electronic power system, so that the inertia supporting effect provided by the network-building type converter for a power grid is quantified, and stable operation of the power grid is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of new energy power electronics technology, specifically relating to a method and system for testing the inertia of a medium-sized grid converter in a fully power electronic power system. Background Technology

[0002] Against the backdrop of accelerated global energy transition, the penetration rate of new energy power generation technologies such as wind power and photovoltaics continues to rise, and the high proportion of renewable energy connected to the grid has become an inevitable trend in the development of new power systems. However, wind power and photovoltaics are mainly connected to the grid through power electronic converters. These devices generally adopt grid-following control strategies, exhibiting controlled current source characteristics. Compared with traditional synchronous generators, they lack rotational inertia and damping characteristics, and cannot provide the necessary voltage and frequency support to the grid. As the penetration rate of distributed renewable energy grids continues to increase, the rotational inertia and damping components in the entire power system will inevitably decrease relatively. This will lead to increased grid frequency fluctuations, decreased power quality, and in severe cases, may even jeopardize grid frequency stability, posing a potential threat to the safe and stable operation of the power system.

[0003] To achieve a high proportion of new energy integration into the power system and ensure its safe and stable operation, grid-connected converter technology has emerged. Traditional grid-connected converters employ a current-source control strategy, relying on the grid to provide stable voltage and frequency references for synchronization. Unlike synchronous generators, they cannot provide voltage and frequency support to the grid. In contrast, grid-connected converters use a voltage-source control strategy, simulating the operating characteristics of synchronous generators, actively constructing grid voltage and frequency, and providing inertia and damping support. By introducing strategies such as active power-frequency droop control and reactive power-voltage droop control into the converter control, the converter possesses the ability to autonomously respond to system frequency fluctuations and voltage changes, thereby effectively improving grid stability.

[0004] However, the inertia provided by grid-connected converters in the power system cannot be quickly obtained through rotor parameters like that of synchronous generators. This makes it difficult to quantify their supporting role in the power grid, hindering the construction of a fully power electronic system within the grid. Therefore, designing an inertia testing method for grid-connected converters to accurately obtain their inertia supporting role in the power grid is of great significance.

[0005] Currently, although some studies have proposed inertia testing methods that induce power response changes in grid-connected converters by manipulating grid frequencies, significant drawbacks remain in practical applications. These studies, based on the principle of manipulating grid frequency changes and monitoring the converter's output active power response, are essentially more similar to the pseudo-grid effect of grid-connected converters, contradicting the fundamental principles of grid-connected converters. Therefore, the converter inertia response time measured in this way cannot accurately reflect the true inertial time constant, and thus cannot accurately measure the performance of grid-connected converters.

[0006] Especially in all-power-electronic power systems where all power sources are power-electronic converters, the voltage and frequency are maintained entirely by the output voltage frequency of the grid-connected converters. The significance of inertia in all-power-electronic power systems lies in maintaining a low rate of change in the output frequency of the grid-connected converters and suppressing rapid frequency fluctuations. Therefore, if existing inertia testing methods based on grid-following thinking are used to test grid-connected converters in all-power-electronic power systems, it may result in converters that pass the test not possessing the true ability to build frequency, but rather remaining pseudo-grid-connected converters that only simulate the power support effect corresponding to inertia. Such converters, when truly applied to all-power-electronic power systems, will be unable to maintain system frequency stability.

[0007] Therefore, a method and system that can truly test the inertia support capability of grid-type converters is needed to solve the above-mentioned technical problems. Summary of the Invention

[0008] This invention aims to achieve accurate measurement of the inertia of grid-connected converters in all-power electronic power systems. It addresses the problems of traditional methods, which rely on measuring converter response power based on simulated grid frequency changes, failing to accurately reflect the true inertial time constant and unable to identify pseudo-grid-connected converters. This allows for quantitative analysis of the inertial support effect of grid-connected converters simulating synchronous generator operation, promoting stable operation of all-power electronic power systems.

[0009] This invention provides the following technical solution: a method for testing the inertia of a grid-type converter in a fully power electronic power system. The grid-type converter includes a main circuit and a VSG control system. The method for testing the inertia of the grid-type converter includes the following steps: S1. Control the grid-type converter to operate under no-load conditions.

[0010] S2. The active power loop of the VSG control system for the grid-type converter only retains the inertia simulation element.

[0011] S3. The actual active power value fed back in this state is used as the active power command for the grid-type converter.

[0012] S4. After the active power stabilizes, set the active power command of the grid-type converter to increase stepwise, and monitor the increase in the frequency value of the output voltage of the grid-type converter.

[0013] S5. Record the time required for the frequency value of the grid-type converter output voltage to increase to the specified target value.

[0014] S6. Calculate the inertia of the grid converter based on the relationship between inertia and frequency change rate.

[0015] Preferably, in step S1, a single grid-type converter operates independently without parallel connection; no load is applied to the grid-type converter, and the grid-type converter operates independently without power exchange with the external power grid.

[0016] Preferably, in step S2, the active-frequency droop link in the active loop of the grid-type converter VSG control system is closed, and the active damping link in the active loop of the grid-type converter VSG control system is closed, ensuring that the frequency response is only related to the inertia of the grid-type converter.

[0017] More preferably, the active-frequency droop link in the active loop of the closed grid-type converter VSG control system specifically includes: setting the active frequency droop coefficient kp to 0.

[0018] More preferably, the active power damping element in the active power loop of the closed grid-type converter VSG control system specifically includes: setting the feedback coefficient D of the active power damping element to 0.

[0019] Preferably, in step S3, under no-load conditions, the output voltage and output current of the grid converter port are collected, dq transformation is performed and filtered to obtain the dq axis components of voltage and current; the actual active power of the grid converter circuit under no-load conditions is calculated based on the obtained dq axis components of voltage and current; the obtained actual active power of the circuit under no-load conditions is used as the active power command of the grid converter to offset its no-load loss.

[0020] Preferably, in step S4, from t At time 1, the active power command of the grid-type converter is increased by 1 p.u., causing a change in the frequency of the converter output voltage; the increase in the frequency of the grid-type converter output voltage caused by the active power step is monitored.

[0021] Preferably, in step S5, to avoid measurement errors caused by the delay of the monitoring module itself, the frequency value generated by inertia simulation in the VSG control system of the grid converter can be directly measured to obtain the accurate time required for the frequency value increase to reach the specified target value. Simultaneously, the frequency of the output port voltage of the grid converter is monitored to confirm that the frequency value generated by the inertia simulation in the control system is consistent with the frequency value output to the grid converter port.

[0022] Preferably, in step S6, the frequency change rate is calculated by dividing the frequency change of the obtained grid-type converter output voltage by the specified target value and the time required to reach the target value. The inertial time constant is calculated by dividing 0.5 by the frequency change rate. The inertial time constant is multiplied by twice the rated power of the converter and then divided by the square of the rated angular frequency to calculate the inertia of the grid-type converter.

[0023] This invention also discloses an inertia testing system for a grid-type converter in a fully power electronic power system, which is used to implement the above-described testing method; the testing system includes: Acquisition module: Used to acquire the port output voltage and output current of the grid-type converter during operation; Power measurement module: used to perform dq transformation on the acquired output voltage and current to obtain the dq axis components of voltage and current and to calculate the output power of the converter; Active power command module: used to provide no-load loss power command when no-load and active power command step during measurement; First frequency measurement module: used to acquire the frequency value generated after inertia simulation in the VSG control system of the grid converter; Second frequency measurement module: used to obtain the voltage frequency value at the output port of the grid converter; Time measurement module: used to obtain the time required for the frequency to rise to a specified value after a change in active power command; Calculation module: Used to calculate the inertia of the grid-type converter based on the acquired frequency and the required time.

[0024] The beneficial effects of this invention are: 1. This invention controls the grid-type converter to operate under no-load conditions, facilitating the analysis of the frequency response of a single grid-type converter under varying power commands, thus providing a basis for inertia testing. Furthermore, by disabling the active-frequency droop and active-damping components in the active loop of the grid-type converter's VSG control system, the frequency response of the grid-type converter becomes solely dependent on its inertia.

[0025] 2. This invention uses the actual active power at the output port under no-load operation as the active power command for the grid-type converter, thereby offsetting the no-load loss of the converter and making the frequency response measurement results more accurate. A step increase in the converter's active power command is set, causing the converter's output voltage frequency to rise under the influence of system inertia. The time required for the converter's output voltage frequency to reach the target value is recorded. During testing, the frequency generated by the VSG control system and the frequency at the output port of the grid-type converter are monitored simultaneously, making the measurement results more accurate and ensuring that the frequency value generated by the inertia simulation is consistent with the frequency value output to the grid-type converter port. Using the time data obtained from the test, the inertia time constant of the grid-type converter is calculated according to the relationship between the converter's inertia time constant and the frequency response time, realizing the quantitative analysis of the converter's inertia.

[0026] 3. The inertia testing process in this invention is more in line with the basic principles of grid-type converters. It effectively solves the problems of existing inertia testing methods, which rely on creating grid frequency changes and monitoring the converter's output active power response, resulting in inaccurate reflection of the true inertia time constant and the inability to identify pseudo-grid-type converters. It meets the inertia testing requirements of grid-type converters and can quickly and accurately determine the inertia of grid-type converters in a full power electronic system. This quantifies the inertia support provided by grid-type converters to the power grid, which is beneficial to promoting the stable operation of the full power electronic power system. Attached Figure Description

[0027] Figure 1 This is a flowchart of the method and system for testing the inertia of a medium-sized grid converter in a fully power electronic power system according to the present invention. Figure 2 This is a schematic diagram of the operating structure of the VSG control system in an embodiment of the present invention, where only the inertia simulation stage is retained in the active loop. Figure 3 This is a schematic diagram of the active power command curve of the VSG control system of the grid-type converter according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the output voltage frequency response curve of a grid-type converter according to an example of the present invention; Figure 5 This is a schematic diagram of the inertia testing system for a mid-mounted grid converter in a fully power electronic power system according to an embodiment of the present invention.

[0028] In the diagram, 210 is the active power loop channel; 220 is the active power-frequency droop unit; 230 is the active power damping unit; 240 is the inertia simulation unit; 310 is the power measurement module; 320 is the acquisition module; 330 is the active power command module; 340 is the first frequency measurement module; 350 is the second frequency measurement module; 360 is the time measurement module; and 370 is the calculation module. Detailed Implementation

[0029] The related technologies of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] like Figures 1-5As shown, this embodiment is applicable to grid-connected converters in all-power electronic power systems. Specifically, a grid-connected converter may include a DC energy storage unit, a converter main circuit, and a VSG control system. The DC energy storage unit may include components for storing DC energy, such as DC battery packs, or DC power generation components, such as photovoltaic arrays. The converter main circuit is used to achieve bidirectional conversion and energy conversion between DC power and standard AC power from the grid. The VSG control system is used to implement the grid-connected converter's grid-connected operating mode, ensuring that the grid-connected converter can meet the active / reactive power requirements of the grid, guaranteeing stable output voltage and current, and providing reliable voltage and frequency support to the grid by simulating the stator and rotor characteristics of a synchronous generator, which is beneficial to the stable operation of the all-power electronic system.

[0031] The inertia testing method for grid-type converters provided in this embodiment can be executed by a grid-type converter inertia testing system. For example... Figure 1 As shown, the inertia testing method for this grid-type converter includes: S1. Control the grid-type converter to operate under no-load conditions; The test employed a single grid-connected converter. The DC side of the grid-connected converter remained connected to the DC energy storage unit, using a DC power supply as its operating power source. The AC side of the grid-connected converter did not draw load from the grid; its output port was disconnected from the grid. The VSG control system within the converter operated normally, actively constructing an AC voltage, generating voltage amplitude, frequency, and phase, and producing a main circuit trigger pulse through a modulation circuit to control the converter to operate under no-load conditions. Under the action of the trigger pulse, the main circuit inverted and filtered the energy in the DC energy storage unit to generate a standard AC voltage. The output port voltage remained at the rated voltage, and the frequency remained at 50Hz. At this time, a certain no-load current existed in the converter's main circuit. Measuring elements were present at the grid-connected converter ports to acquire the converter's output voltage and current, which were then fed back to the VSG control system.

[0032] S2, The active power loop of the VSG control system for the grid-type converter only retains the inertia simulation link for operation; The complete VSG control system includes an active-frequency droop loop based on the active power frequency regulation function of a synchronous generator, a reactive-voltage droop loop based on the reactive power voltage regulation function of a synchronous generator, a rotor simulation loop simulating the inertia and damping of a synchronous generator, a virtual impedance loop simulating the stator characteristics of a synchronous generator, and a voltage-current dual closed-loop loop tracking voltage and current commands. In inertia testing, the response of the grid-type converter's output voltage frequency to changes in active power commands needs to be monitored to test the grid-type converter's inertia. To ensure that the frequency response is only related to the converter's inertia, the active-frequency droop loop in the active power loop of the VSG control system must first be closed, setting the active-frequency droop coefficient to 0. Then, the active damping coefficient in the rotor simulation loop is set to 0, so that the difference between electromagnetic power and actual active power only affects the converter's frequency response under the influence of system inertia, while system droop control and active damping do not participate. Therefore, the inertia of the grid-type converter can be accurately tested by monitoring the converter's output voltage frequency response.

[0033] The VSG control system's active loop retains only the inertia simulation stage, as shown in the schematic diagram below. Figure 2 As shown, by adjusting the droop and damping coefficients, the active-frequency droop unit 220 and the active-frequency damping unit 230 are shut down, leaving only the inertia simulation unit 240 in the active-frequency loop channel 210. At this time, the active-frequency loop channel 210 receives the system's active power command. The difference between the equal electromagnetic power and the actual active power of the converter is used to generate the system output frequency increment after passing through the inertia simulation unit 240 and the integrator, thereby obtaining the new system frequency. After integration again, the system output phase is obtained.

[0034] S3. The actual active power value fed back in this state is used as the active power command of the grid-type converter. When a grid-type converter operates under no-load conditions, the inductive and capacitive elements in the internal filter circuit will generate no-load current, causing no-load losses in the converter's internal impedance. To ensure the accuracy of frequency response measurements after applying active power commands, the impact of no-load power losses on the converter's output active power needs to be eliminated beforehand. The converter's output voltage and current under no-load conditions are obtained using measuring elements at the output port of the grid-type converter. The voltage and current are then transformed using a dq transformation to obtain their dq-axis components, and the active power output under no-load conditions is calculated. This calculated active power output under no-load conditions is used as the active power command for the VSG control system. It serves as an active power reference in the active power loop for electromagnetic power calculations, thus offsetting the impact of no-load losses in the grid-type converter and providing the basis for applying active power commands and testing the frequency response.

[0035] S4. After the active power stabilizes, set the active power command of the grid-type converter to increase stepwise, and monitor the increase in the frequency value of the output voltage of the grid-type converter. In grid-type converters, when only the inertia simulation element is retained in the active power loop, the output voltage frequency will respond to changes in active power command under the influence of system inertia. The response speed reflects the magnitude of the grid-type converter's inertia. t At time 1, an active power command step is applied to the grid-type converter, increasing the active power command by 1.pu based on the original active power command in the active loop of the converter's VSG control system, causing the grid-type converter to switch to rated active power operation. At this time, the output voltage frequency of the grid-type converter will gradually increase, and the increase in output voltage frequency over time is monitored using measuring elements.

[0036] S5. Record the time required for the frequency increase of the grid-type converter output voltage to reach the specified target value; Specifically, after the active power command step is applied, the output voltage frequency begins to rise. The time required for the frequency increase from time t1 to reach 0.05 pu is recorded as the time. In actual measurements, due to the inherent delay in the monitoring module, the measurement time exceeds the actual time required for the frequency to rise to the target value, resulting in measurement errors. To avoid the impact of time measurement errors on the inertia test results of the grid-type converter, the frequency value generated after inertia simulation can be monitored in the VSG control system of the grid-type converter, thereby obtaining the accurate time required for the frequency to rise. Simultaneously, to ensure that the frequency value generated after inertia simulation matches the frequency value output to the grid converter port, the frequency value of the grid converter output port voltage should also be monitored. The rate of increase of the converter output voltage frequency value by 0.05 pu reflects the magnitude of the grid converter's inertia, and the measured frequency rise time... This will serve as the basis for calculating the converter's inertia.

[0037] S6. Calculate the inertia of the grid-type converter based on the relationship between inertia and frequency change rate.

[0038] When the grid-type converter operates with only the inertia simulation element retained in the active power loop of the VSG control system, the frequency change and the active power command change satisfy a linear relationship with the grid-type converter's inertia as the only parameter. Let the frequency change be... The change in active power command is The inertia of the grid-type converter is The system's rated operating frequency is The relation satisfies: (1) In engineering, the inertial time constant is often used. To replace the inertia of grid-type converters The inertial time constant is the time constant after inertia has been normalized, which makes it easier to compare and coordinate between different types and capacities of power generation units. In the calculation process, the inertial time constant... With inertia The relationship between them satisfies: (2) After a step change in active power command is applied to the system, the output voltage frequency begins to rise, indicating that the rate of increase in its change is only related to the inertial time constant of the grid-type converter. Related, can be deduced from t Applying an increment at time 1 equals S N The active power command step start begins, and the rate of increase of the per-unit value of the output voltage frequency of the grid converter is: (3) That is, from t From moment 1, at Within a few seconds, the per-unit value of the output voltage frequency of the grid-connected converter will increase by 0.5 pu. Considering that the frequency variation range should not be too large during actual operation of the converter, the frequency variation can be reduced by shortening the test duration. The time required for the test frequency to increase by 0.05 pu is recorded. The inertial time constant of the grid-type converter is calculated based on this, where the inertial time constant is... With frequency rise time The relationship between them satisfies: (4) Therefore, the inertial time constant of the grid-type converter can be tested, that is, its inertia can be quantitatively analyzed.

[0039] For example, Figure 3 This embodiment provides a schematic diagram of the active power command curve of a grid-type converter VSG control system, where the horizontal axis represents time and the vertical axis represents the per-unit value of active power. Figure 4 This embodiment provides an output voltage frequency response curve for a grid-type converter, where the horizontal axis represents time and the vertical axis represents frequency. Figures 3 to 4As shown, after the system starts running, the grid-type converter initially operates in no-load mode. At this time, the active power command of the VSG control system is close to 0 and fluctuates continuously. The no-load converter output power is used as the active power command to offset no-load losses. After one second of system operation, the VSG control system issues a step-up active power command, with the step value being the converter's rated power. The total active power command is then the sum of the step command and the no-load power command, and the system operates under this active power command. Before the step-up active power command is issued, the converter output voltage frequency remains at 50Hz. After the step-up, the converter output voltage frequency begins to respond to power changes, rising linearly. The slope of this rise represents the magnitude of the grid-type converter's inertial time constant. The time it takes for the system frequency per unit value to rise to 0.05 pu is recorded. Based on the relationship between the frequency rise time and the inertial time constant, the inertial time constant of this grid-type converter can be derived. .

[0040] This embodiment also provides an inertia testing system for mid-grid converters in a fully power electronic power system. Figure 5 This is a schematic diagram of the structure of the inertia testing system for a mid-grid converter in a fully power electronic power system provided in this embodiment. Figure 5 As shown, the inertia testing system includes: Acquisition module 310: used to acquire the port output voltage and output current of the grid-type converter during operation.

[0041] Power measurement module 320: used to perform dq transformation on the acquired output voltage and current to obtain the dq axis components of voltage and current and to calculate the output power of the converter.

[0042] Active power command module 330: used to give no-load loss power command when no load is applied and to give active power command step when measured.

[0043] First frequency measurement module 340: used to acquire the frequency value generated after inertia simulation in the VSG control system of the grid converter and to monitor the voltage frequency of the output port of the grid converter.

[0044] Second frequency measurement module 350: used to obtain the voltage frequency value of the output port of the grid converter.

[0045] Time measurement module 360: Used to obtain the time required for the frequency to rise to a specified value after a change in active power command.

[0046] Calculation module 370: Used to calculate the inertia of the grid-type converter based on the acquired frequency and the required time.

[0047] The technical solution of this embodiment controls the grid-type converter to operate under no-load conditions, facilitating the analysis of the frequency response of a single grid-type converter when the power command changes, thus providing a basis for inertia testing. Based on this, the active-frequency droop and active-damping components in the active loop of the grid-type converter's VSG control system are disabled, making the frequency response of the grid-type converter only related to its inertia. The actual active power at the output port under no-load operation is used as the active power command of the grid-type converter, thereby offsetting the converter's no-load losses and making the frequency response measurement results more accurate. A step increase in the converter's active power command is set, causing the converter's output voltage frequency to rise under the action of system inertia. The time required for the converter's output voltage frequency to reach the target value is recorded. During testing, the frequency generated by the VSG control system and the frequency at the grid-type converter's output port are monitored simultaneously, making the measurement results more accurate and ensuring that the frequency value generated by the inertia simulation is consistent with the frequency value output to the grid-type converter port. Using the time data obtained from the test, the inertial time constant of the grid-type converter is calculated based on the relationship between the converter's inertial time constant and frequency response time, thus achieving a quantitative analysis of the converter's inertia. In this embodiment, the inertia testing process is more consistent with the basic principles of grid-type converters. It effectively solves the problems of existing inertia testing methods, which rely on artificially creating grid frequency changes and monitoring the converter's output active power response, resulting in inaccurate reflection of the true inertial time constant and the inability to identify pseudo-grid-type converters. This meets the inertia testing requirements for grid-type converters and can quickly and accurately determine the inertia of grid-type converters in projects with a high proportion of new energy integration. This quantifies the grid-type converter, providing sufficient inertia support for the power grid and promoting the stable operation of the entire power electronic system.

[0048] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for testing the inertia of a grid-type converter in a fully power electronic power system, characterized in that, The grid-type converter includes a main circuit and a VSG control system. The inertia testing method for the grid-type converter includes the following steps: S1. Control the grid-type converter to operate under no-load conditions; S2. The active power loop of the VSG control system for the grid-type converter only retains the inertia simulation element for operation; S3. The actual active power value fed back in this state is used as the active power command for the grid-type converter; S4. After the active power stabilizes, set the active power command of the grid-type converter to increase stepwise, and monitor the increase in the frequency value of the output voltage of the grid-type converter. S5. Record the time required for the frequency increase of the grid-type converter output voltage to reach the specified target value; S6. Calculate the inertia of the grid converter based on the relationship between inertia and frequency change rate.

2. The method for testing the inertia of a grid-type converter in a fully power electronic power system according to claim 1, characterized in that, In step S1, a single grid-type converter operates independently without parallel connection; no load is applied to the grid-type converter, and the grid-type converter operates independently without power exchange with the external power grid.

3. The method for testing the inertia of a grid-type converter in a fully power electronic power system according to claim 1, characterized in that, In step S2, the active-frequency droop link in the active loop of the grid-type converter VSG control system is closed, and the active damping link in the active loop of the grid-type converter VSG control system is closed, ensuring that the frequency response is only related to the inertia of the grid-type converter.

4. The method for testing the inertia of a grid-type converter in a fully power electronic power system according to claim 3, characterized in that, The active-frequency droop link in the active loop of the closed-grid converter VSG control system specifically includes setting the active frequency droop coefficient kp to 0.

5. The method for testing the inertia of a grid-type converter in a fully power electronic power system according to claim 3, characterized in that, The active power damping element in the closed-loop VSG control system of the grid-connected converter specifically includes setting the feedback coefficient D of the active power damping element to 0.

6. The method for testing the inertia of a grid-type converter in a fully power electronic power system according to claim 1, characterized in that, In step S3, under no-load conditions, the output voltage and output current of the grid converter port are collected, dq transformation is performed and filtered to obtain the dq axis components of voltage and current; the actual active power of the grid converter circuit under no-load conditions is calculated based on the obtained dq axis components of voltage and current; the obtained actual active power of the circuit under no-load conditions is used as the active power command of the grid converter to offset its no-load loss.

7. The method for testing the inertia of a grid-type converter in a fully power electronic power system according to claim 1, characterized in that, In step S4, from t At time 1, the active power command of the grid-type converter is increased by 1 p.u., causing a change in the frequency of the converter output voltage; the increase in the frequency of the grid-type converter output voltage caused by the active power step is monitored.

8. The method for testing the inertia of a grid-type converter in a fully power electronic power system according to claim 1, characterized in that, In step S5, to avoid measurement errors caused by the delay of the monitoring module itself, the frequency value generated by inertia simulation in the VSG control system of the grid converter can be directly measured to obtain the accurate time required for the frequency value increase to reach the specified target value. Simultaneously, the frequency of the output port voltage of the grid converter is monitored to confirm that the frequency value generated by the inertia simulation in the control system is consistent with the frequency value output to the grid converter port.

9. The method for testing the inertia of a grid-type converter in a fully power electronic power system according to claim 1, characterized in that, In step S6, the frequency change rate is calculated by dividing the frequency change of the obtained grid-type converter output voltage by the specified target value and the time required to reach the target value. The inertial time constant is calculated by dividing 0.5 by the frequency change rate. The inertial time constant is multiplied by twice the rated power of the converter and then divided by the square of the rated angular frequency to calculate the inertia of the grid-type converter.

10. A system for testing the inertia of a grid-type converter in a fully power electronic power system, characterized in that, The testing system is used to implement the testing method according to any one of claims 1 to 9; the testing system includes: Acquisition module: Used to acquire the port output voltage and output current of the grid-type converter during operation; Power measurement module: used to perform dq transformation on the acquired output voltage and current to obtain the dq axis components of voltage and current and to calculate the output power of the converter; Active power command module: used to provide no-load loss power command when no-load and active power command step during measurement; First frequency measurement module: used to acquire the frequency value generated after inertia simulation in the VSG control system of the grid converter; Second frequency measurement module: used to obtain the voltage frequency value at the output port of the grid converter; Time measurement module: used to obtain the time required for the frequency to rise to a specified value after a change in active power command; Calculation module: Used to calculate the inertia of the grid-type converter based on the acquired frequency and the required time.

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