Micro-grid on-grid and off-grid all-condition simulation circuit and systematic checking method

Abstract

The invention provides a micro-grid on-grid and off-grid all-condition simulation circuit, which comprises a data processing unit, a power grid architecture model, an energy storage unit model, a load unit model and a power supply unit model, and is characterized in that the power grid architecture model comprises a section I bus, a section II bus and a power transmission line; the energy storage unit model, the load unit model and the power supply unit model are configured in the range of the I-section bus and the II-section bus in a high-voltage direct hanging mode, and loads in the range of the I-section bus and the II-section bus are unequal. According to the invention, the source, the network, the load and the operation mode of the micro-grid are used as a whole for systematic testing for the first time, and the limitation of traditional single fault simulation is avoided. Potential risks such as grid-connected and off-grid switching failure and voltage collapse can be exposed in advance, and passive-to-active conversion is realized. A simulation result is directly used for guiding energy storage capacity configuration, protection constant value setting, control strategy optimization and equipment type selection, and the success rate and reliability of actual engineering are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of power system simulation and operation control technology, and in particular to a microgrid full-condition simulation circuit and system verification method for both on-grid and off-grid operation. Background Technology

[0002] Microgrids are small-scale power generation and distribution systems that integrate distributed renewable energy sources, energy storage, and loads. One of their core capabilities is the ability to operate stably and smoothly switch between grid-connected (connected to the main grid) and off-grid (islanded) modes. However, the random fluctuations in renewable energy output and the drastic changes in load power (especially impact loads such as electric arc furnaces) within microgrids pose significant challenges to their stable operation. Traditional power system simulations mostly focus on single operating conditions or single faults, lacking a complete and standardized testing system to comprehensively evaluate the integrated performance of microgrids under multiple disturbances from the source-grid-load system. This leads to potential blind spots in microgrid control strategies during actual engineering projects, which are exposed in real faults, causing system instability or even collapse. Summary of the Invention

[0003] In this section, as well as in the abstract and title of this application, some simplifications or omissions may be made to avoid obscuring the purpose of this section, the abstract, and the title of this application, and such simplifications or omissions shall not be used to limit the scope of the invention.

[0004] To address the shortcomings of existing technologies, one objective of this invention is to provide a simulation circuit that can comprehensively and realistically reflect the dynamic characteristics of a microgrid, enabling the early detection and resolution of potential safety and stability risks before system commissioning.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a microgrid parallel and off-grid full-condition simulation circuit, comprising: The power grid architecture model, stored in the data processing unit, includes a 35kV Section I busbar and a 35kV Section II busbar connected by a bus tie, and 220kV transmission lines connected to Section I and Section II busbars respectively by transformers; the power grid architecture model is stored in the data processing unit, which is used to perform simulation calculations and disturbance injection machine data acquisition and analysis; The I-section busbar and the II-section busbar are respectively connected in a high-voltage direct connection manner to an energy storage unit model simulating charging, a load unit model simulating power consumption, and several power supply unit models simulating power generation. The energy storage unit model adopts a virtual synchronous generator control strategy, with a frequency adjustment range of 49.5Hz to 50.5Hz and 1.5 times overcurrent limiting protection, which is used to provide voltage and frequency support for the power grid architecture model; among them, the I section bus is equipped with two 45MW energy storage units and the II section bus is equipped with one 30MW energy storage unit. The loads within the range of bus section I and bus section II are unequal.

[0006] As a preferred embodiment of the microgrid on-grid and off-grid full-condition simulation circuit of the present invention, the load unit model includes an impact load model and a sensitive load model respectively set within the range of bus section I and bus section II; The first busbar is configured with a 120MW impact load model, which is a composite model of 70% constant current and 30% constant power. It includes three electric boiler sub-models to simulate the composite characteristics of constant current and constant power, and supports a maximum power impact simulation of 120MW. The electric boiler sub-models include the Kangsi electric furnace sub-model and the LF refining furnace model. The Kangsi electric furnace model supports the simulation of the 80MW power impact curve of the first smelting furnace, and the LF refining furnace model supports the simulation of the 25MW power supply heating power curve. All three can be set to start, run, or be shut down simultaneously. The II section bus is configured with a 25MW sensitive load model, which is a composite model of 60% asynchronous motors and 40% frequency converters, used to simulate the load characteristics of motors and frequency converters. The motor voltage withstand threshold is set to 0.87pu and the frequency converter trip setting is set to 0.9pu.

[0007] As a preferred embodiment of the microgrid on-grid and off-grid full-condition simulation circuit of the present invention, the power supply unit model includes: A wind power generation model, configured to output constant power; A photovoltaic power generation model, wherein the reactive power output of the photovoltaic power generation model is configured to a fixed value or linearly adjustable according to the voltage.

[0008] As a preferred embodiment of the microgrid on-grid and off-grid full-condition simulation circuit of the present invention, the wind power generation model includes: a newly built wind power electronic model of 12.5MW connected within the range of bus section I, and an existing wind power electronic model of 16.8MW connected within the range of bus section II. The wind power generation model adopts an induction generator model and is equipped with phase-locked loop constant power control.

[0009] As a preferred embodiment of the microgrid on-grid and off-grid full-condition simulation circuit of the present invention, the photovoltaic power generation model includes: a newly built photovoltaic sub-model of 28.8MW connected within the range of bus section I, and an existing photovoltaic sub-model of 25.7MW connected within the range of bus section II; The photovoltaic power generation model adopts MPPT control mode, and realizes reasonable distribution of reactive power through closed-loop control of voltage outer loop and current inner loop.

[0010] To address the shortcomings of existing technologies, another objective of this invention is to provide a systematic verification method for a full-condition simulation circuit of a microgrid, both on and off-grid.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: a systematic verification method for a microgrid parallel and off-grid full-condition simulation circuit, which operates according to the following steps: S1: Define multiple basic operating modes, which include at least grid-connected mode and off-grid mode, as well as power surplus condition, power deficit condition and power balance condition under different modes; S2: For each of the basic operating modes, set up a standardized set of disturbance test cases; S3: Apply the disturbance test set sequentially to the microgrid and off-grid full-condition simulation circuit to perform dynamic simulation; S4: Acquire and analyze simulation results data, and verify the safety and stability of the microgrid system based on preset stability criteria.

[0012] As a preferred embodiment of the systematic verification method for the full-condition simulation circuit of the microgrid connected and disconnected from the grid described in this invention, wherein: the standardized disturbance test set in step S2 includes at least three of the following disturbance types: Source-side power perturbation is used to simulate abrupt changes in light intensity or wind speed. Load-side power disturbance is used to simulate the sudden addition or removal of large-capacity impact loads; Short circuit faults are used to simulate transient or permanent short circuit faults occurring at different locations in the power grid. The off-grid switching disturbance is used to simulate the dynamic process of a microgrid being forced to switch to off-grid operation due to a serious fault on the main grid side.

[0013] Step S2 involves matching three standardized test items for each basic operating mode: "source-side power disturbance, load-side power disturbance, and fault disturbance (including grid connection / off-grid switching disturbance)". This clarifies the disturbance amplitude, triggering timing, and duration, ensuring that the disturbance scenarios are repeatable and comparable, and covering the extreme operating conditions that the actual system may face.

[0014] As a preferred embodiment of the systematic verification method for the microgrid on-grid and off-grid full-condition simulation circuit described in this invention, step S3 is as follows: a microgrid on-grid and off-grid simulation circuit (including a data processing unit, a grid architecture model, and a power supply-energy storage-load unit) is built based on DIgSILENT software, and dynamic simulation is performed according to the process of "basic mode loading → disturbance sequence application → real-time data acquisition".

[0015] As a preferred embodiment of the systematic verification method for the microgrid on-grid and off-grid full-condition simulation circuit of the present invention, the stability criterion in step S4 includes: The system voltage is maintained within the range of 0.9 to 1.1 per unit. The system frequency was maintained within the range of 49.5Hz to 50.5Hz; The current of critical equipment shall not exceed its preset short-time overcurrent multiple.

[0016] As a preferred embodiment of the systematic verification method for the microgrid on-grid and off-grid full-condition simulation circuit of the present invention, the method further includes step S5: Based on the verification results of step S4, optimization suggestions for control and protection strategies and / or equipment selection suggestions for microgrids are generated; wherein, the optimization suggestions for control and protection strategies include configuring and off-grid switching stability control load shedding strategies; and the equipment selection suggestions include overcurrent capacity selection suggestions for grid-type energy storage devices.

[0017] As a preferred embodiment of the systematic verification method for the full-condition simulation circuit of the microgrid parallel and off-grid operation described in this invention, wherein: when the disturbance type is a parallel / off-grid switching disturbance, the verification method includes: The simulation shows a serious fault and line tripping on the main grid side, causing the microgrid to switch to off-grid operation; Verify whether the grid-type energy storage unit can independently support the voltage and frequency stability of the off-grid system; If the system is stable but the grid-type energy storage unit experiences steady-state overload, then the effectiveness of the corresponding stability control and load shedding strategy needs to be verified.

[0018] The beneficial effects of this invention are as follows: Comprehensiveness: For the first time, the source, grid, load and operation mode of a microgrid are tested as a whole, avoiding the limitations of traditional single fault simulation.

[0019] Foresight and risk prevention: It can expose and prevent potential risks such as grid switching failure and voltage collapse in advance, realizing the transformation from "passively responding to faults" to "proactively designing safety".

[0020] Strong engineering guidance: Simulation results can be directly used to guide energy storage capacity configuration, protection setting, control strategy optimization and equipment selection, significantly improving the success rate and reliability of actual projects. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic diagram of the simulation circuit structure for microgrid parallel and off-grid connections; Figure 2 A graph showing the electricity consumption curve for smelting in the Constadt electric furnace; Figure 3 This is a graph showing the electricity consumption curve for smelting in refining furnace No. 1. Figure 4 This is a graph showing the electricity consumption curve for smelting in refining furnace No. 2. Figure 5 This is a diagram of the outer loop control model for the constant power source control in the control module. Figure 6 This is a diagram of the inner loop control model for the constant power source control in the control module. Figure 7 This is a schematic diagram of photovoltaic voltage control. Figure 8 This is a graph showing the static characteristic curve of photovoltaic reactive current-voltage. Figure 9 This is a schematic diagram of the photovoltaic MPPT control principle. Figure 10 This is a block diagram of the outer loop control for photovoltaic power generation. Figure 11 This is a flowchart of the systematic verification method of the present invention; Figure 12 This is the power flow diagram of the power grid when a fault occurs in Example 1; Figure 13 This is a simulated waveform diagram of the active power of the grid-connected energy storage system during a sudden drop in light intensity in Example 1. Figure 14 The simulated waveform of the system frequency during a sudden drop in illumination is shown in Example 1. Figure 15 This is the power flow diagram when a fault occurs in Example 2; Figure 16 This is a simulation waveform diagram of the grid energy storage power when the electric boiler load suddenly drops in Example 2; Figure 17 This is a simulation waveform diagram of the grid-connected energy storage current when the electric boiler load suddenly drops in Example 2; Figure 18 This is the power flow diagram when a fault occurs in Example 3; Figure 19 This is a simulated waveform diagram of the bus voltage during the grid-connected / off-grid switching process in Example 3; Figure 20 The simulated waveform of the bus frequency during the grid-connected / off-grid switching process in Example 3 is shown. Figure 21 This is the power flow diagram when a fault occurs in Example 4; Figure 22 The simulated waveform diagram of the active power of the grid energy storage when a transient nonmetallic short-circuit fault occurs on the 35kV bus in Example 4 is shown. Figure 23 This is a simulation waveform diagram of the instantaneous overcurrent of the grid energy storage when a transient non-metallic short-circuit fault occurs on the 35kV bus in Example 4. Detailed Implementation

[0023] To make the objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0025] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0026] Please refer to Figures 1-2 This invention provides a full-condition simulation circuit for microgrid parallel and off-grid operation, comprising: The data processing unit 100 is used to perform simulation calculations, disturbance injection, and data acquisition and analysis.

[0027] The power grid architecture model 200, stored in the data processing unit 100, includes a first-section bus 201 and a second-section bus 202 connected by a bus tie switch, and a transmission line 203 connected to the first-section bus 201 and the second-section bus 202 by a transformer. The loads within the range of the first-section bus and the second-section bus are different. The voltage level of the first-section bus 201 and the second-section bus 202 is 35kV, and the voltage level of the transmission line 203 is 220kV.

[0028] On busbar I 201 and busbar II 202, there are energy storage unit models 300 simulating charging, load unit models 400 simulating power consumption, and several power supply unit models 500 simulating power generation, respectively connected in a high-voltage direct connection manner.

[0029] It should be noted that the energy storage unit model 300 adopts a virtual synchronous generator control strategy, with a frequency adjustment range of 49.5Hz to 50.5Hz and 1.5 times overcurrent limiting protection, which is used to provide voltage and frequency support for the grid architecture model 200.

[0030] To further explain, the load unit model 400 includes an impact load model 401 and a sensitive load model 402, respectively located within the range of bus section I 201 and bus section II 202. Specifically: Section 1 busbar 201 is equipped with a 120MW impact load model 401. The impact load model 401 is a composite model of 70% constant current + 30% constant power, which includes 3 electric boiler sub-models to simulate the composite characteristics of constant current and constant power. It supports the simulation of a maximum power impact of 120MW. Among them, the electric boiler sub-models include 1 Kangsi electric furnace and 2 LF refining furnaces. The Kangsi electric furnace supports the simulation of the 80MW power impact curve of the first smelting, and the LF refining furnace supports the simulation of the 25MW power supply heating power curve. All three can be set to start, run or stop simultaneously.

[0031] Impact load model 401 is connected to the main transformer at 35kV, combined with Figures 2-4 ( Figure 2 In the graph, the horizontal axis represents the time progression of the steel smelting process, with the unit being min (minutes); the vertical axis represents the power level, with the unit being MW (megawatts). Figure 3 In the graph, the horizontal axis represents the time progression of the smelting process, with the unit being min (minutes); the vertical axis represents the power magnitude, with the unit being MV (megavolts). Figure 4 In the diagram, the horizontal axis represents the time progression of the smelting process, in minutes (min); the vertical axis represents the power magnitude, in megavolts (MV). The load curves of the three electric boilers shown indicate that the load is relatively stable during normal operation. However, the commissioning and decommissioning of the electric boilers both have power impacts on the microgrid. Based on the worst-case scenario for the safe and stable operation of the microgrid, and considering a certain margin, the load types and proportions are as follows: The 20MW load on busbar 201 (Section I) is all steelmaking load, while the related auxiliary equipment is configured on busbar 202 (Section II). Therefore, the 120MW electric boiler load on busbar 201 (Section I) is designed to be primarily constant current load with constant power load as a secondary type, with constant current load accounting for 70% and constant power load accounting for 30%. The maximum limit for simultaneous shutdown of electric boiler loads is 120MW. The load on busbar 202 (Section II) is mostly electric motor load connected via frequency converters. Frequency converter loads are sensitive loads, and voltage fluctuations can easily cause them to disconnect from the grid. Therefore, the 25MW load on busbar 202 (Section II) is designed with electric motor load accounting for 60% and constant current load accounting for 40%. In the simulation, the frequency converter load protection trip setting is 0.90 pu.

[0032] Section II bus 202 is equipped with a 25MW sensitive load model 402. Sensitive load model 402 is a composite model of 60% asynchronous motor + 40% frequency converter, used to simulate the load characteristics of motors and frequency converters. It is set with a motor voltage withstand threshold of 0.87pu and a frequency converter trip setting of 0.9pu.

[0033] To further explain, the power unit model 500 includes: wind power generation model 501 and photovoltaic power generation model 502; specifically: The wind power generation model 501 includes: a newly built 12.5MW wind power electronic model 501a connected within the range of bus section I 201, and an existing 16.8MW wind power electronic model 501b connected within the range of bus section II 202. The wind power generation model 501 adopts an induction generator model and is configured with phase-locked loop constant power control. It simulates the change in wind turbine output when the wind speed changes by changing the power setpoint (Pref).

[0034] Figure 5 This is a diagram of the outer loop control model for a constant power source; where the active power control branch: Pref represents the target active power; The low-pass filter stage (Tp is the filtering time constant) represents the active power and is used to smooth the fluctuation of active power; Pme represents the actual value of active power after filtering; Pset represents the feedback value of active power output from the energy storage, and ∆P=Pme-Pset represents the active power deviation (the difference between the reference value and the actual output). This indicates a PI controller (proportional + integral) for active-frequency regulation, used to convert power deviation into current command; iref represents the final output active current reference value.

[0035] The active power-frequency transfer process is as follows: the externally given target active power Pref is filtered by a low-pass filter to obtain a smooth Pme, which is compared with the actual active power output Pset of the energy storage to obtain the active power deviation ∆P. The active power deviation ∆P is input to the PI controller, and after proportional-integral regulation, the corresponding current reference value iref is output.

[0036] Reactive power control branch: Qref represents the target reactive power; The low-pass filter (Tq is the filtering time constant) represents reactive power and is used to smooth reactive power fluctuations; Qme represents the actual reactive power value after filtering; Qset represents the reactive power feedback value of the actual output of energy storage, and ∆Q=Qme-Qset represents the reactive power deviation (the difference between the reference value and the actual output). This indicates a PI controller (proportional + integral) for reactive power-voltage regulation, used to convert power deviation into current command; iref represents the final output active current reference value.

[0037] The reactive power-voltage transfer process is as follows: the target reactive power Qref is given externally, and a smooth Qme is obtained after low-pass filtering. This is compared with the actual reactive power output Qset of the energy storage to obtain the reactive power deviation ∆Q. The reactive power deviation ∆Q is input to the PI controller, and after proportional-integral regulation, the corresponding current reference value iref is output.

[0038] Figure 6 This is a diagram of the inner loop control model for a constant power source. In the diagram, in the upper power loop section: irefd represents the current reference command, corresponding to the d-axis; The low-pass filter stage (Tdf is the filtering time constant) of the current signal is used to eliminate high-frequency noise in the current sampling and output a smoothed reference current irefdf; iactd represents the actual current feedback value; Δid=irefdf-iactd represents the current deviation (the difference between the smoothed reference current and the actual current). The current loop PI controller (proportional + integral) uses Kpid as the proportional coefficient and Kiid as the integral coefficient to convert current deviation into an initial power regulation signal Pcd; Pcd_out represents the final output power limited to a safe range on the d-axis. In the lower power loop section: irefq represents the current reference command, corresponding to the q-axis. The low-pass filter stage (Tqf is the filtering time constant) represents the current signal and is used to eliminate high-frequency noise in the current sampling, outputting a smoothed reference current irefqf; iactq represents the actual current feedback value; Δiq=irefqf-iactq represents the current deviation (the difference between the smoothed reference current and the actual current). The PI controller (proportional + integral) in the current loop converts the current deviation into a preliminary power regulation signal Pcq; Pcq_out represents the final output power limited to the safe range on the q-axis.

[0039] Taking the d-axis as an example, the current-power transfer process of the d-axis branch is as follows: the current reference command irefd is smoothed by a low-pass filter to obtain the filtered reference current irefdf. The difference between irefdf and the actual feedback current iacdt is calculated to obtain the current deviation Δid. The current deviation Δid is then input to the PI controller. After proportional-integral regulation, the initial power regulation signal Pcd is output; the power regulation signal Pcd enters the limiter, and the final output power Pcd_out is limited to a safe range.

[0040] The photovoltaic power generation model 502 includes: a newly built photovoltaic sub-model 502a with a capacity of 28.8MW connected within the range of bus section I 201, and an existing photovoltaic sub-model 502b with a capacity of 25.7MW connected within the range of bus section II 202. The photovoltaic power generation model 502 participates in system voltage control. The voltage control module monitors the low-voltage bus voltage in real time and achieves closed-loop control through an outer voltage loop and an inner current loop. The outer voltage loop uses voltage feedback to achieve droop characteristics, and the voltage at the micro-source terminal is linearly related to the reactive current. By setting the droop coefficient, the reactive power of micro-sources connected to the same low-voltage bus can be rationally allocated. Its control model schematic diagram and static control characteristics are shown below. Figure 7, Figure 8 As shown; Figure 7 In this context, uref represents the target output voltage, u represents the output voltage detected during actual operation, the comparator is used for the deviation value, and the deviation signal Δu is transmitted to the control loop; where the deviation signal Δu = uref - u; Figure 8 In the diagram, the horizontal axis Iq represents the reactive current, reflecting the magnitude of reactive power; the vertical axis U represents the actual operating voltage of the system, which is the per-unit value or actual value of the voltage; U0 represents the no-load voltage (or rated voltage), that is, the reference value of the output voltage of the grid-connected equipment when the reactive current (Iq=0); U1 represents the actual operating voltage of the system when the reactive current is Iq1; Iq1 represents the specific value of the reactive current output by the grid-connected equipment under a certain operating condition; ΔIq represents the change in reactive current from no-load (Iq=0) to Iq1.

[0041] The active power output of photovoltaic (PV) systems is significantly affected by external environmental factors. To maximize the absorption of renewable energy sources such as PV, PV systems do not participate in system frequency regulation during normal operation and adopt MPPT control mode. Figure 9 As shown in the figure; E represents light intensity (or irradiance), which is the core environmental parameter affecting photovoltaic output; theta represents ambient temperature, and temperature changes affect the output characteristics of photovoltaics; P represents power control command (or power setpoint), used to adjust the output power of photovoltaics; Iarray represents the output DC current; Udc represents the actual DC voltage across the DC capacitor, which is the DC side voltage feedback value; and Uderef represents the DC side voltage reference value / setpoint.

[0042] For photovoltaic power generation, its detailed outer loop control is as follows: Figure 10 As shown in the figure; Udc represents the actual DC-side voltage (feedback value); 600 represents low-pass filter one (time constant is T), which filters the DC voltage Udc to eliminate high-frequency noise and outputs the filtered DC voltage Udefilt; Uderef represents the DC-side voltage reference value (setpoint); ΔUdc represents the voltage deviation, ΔUdc=Uderef-Udefilt; 700 represents PI controller one (proportional-integral controller); Umax / Umin represents the limiting circuit, used to limit the output range of PI controller one to avoid the active current reference value i dref Exceeding the safe operating range of the equipment; drefThe output active current reference value is used to control the active power output of the equipment; Qmea represents the actual measured reactive power value (feedback value); 800 represents low-pass filter two (time constant is TQ), which filters the measured reactive power Qmea and outputs the filtered reactive power Qfilt; Qref represents the reactive power reference value (setpoint); ΔQ represents the reactive power deviation, ΔQ=Qref-Qfilt; 900 represents the second PI controller (proportional-integral controller); Qmax / Qmin represents the limiting circuit, used to limit the output range of the second PI controller to avoid the reactive current reference value i qref Exceeding the safe operating range of the equipment; qref This represents the reference value of the final output reactive current, used to control the reactive power output of the equipment.

[0043] DC voltage-d-axis current command: Sample the DC side voltage Udc, and obtain Udefilt after filtering by module 600; calculate the DC voltage deviation ΔUdc = Uderef - Udefilt (if Udc is lower than the reference value, ΔUdc is positive, otherwise it is negative); module 700 converts ΔUdc into d-axis current reference i. dref If Udc is too low, increase i dref (Increase active power output and supplement DC side energy); at the same time, Umax / Umin limit i dref Within a certain range, avoid overcurrent.

[0044] Reactive power-q-axis current command: Sample reactive power Qmea, filter it through module 800 to obtain Qfilt; calculate reactive power deviation ΔQ = Qref - Qfilt (if the actual reactive power is lower than the reference value, ΔQ is positive; otherwise, it is negative); module 900 converts ΔQ into q-axis current reference i. qref (q-axis current corresponds to reactive power): If the actual reactive power is too low, increase i. qref (Increase reactive power output); if the actual reactive power is too high, decrease i. qref (jiangdi0 reactive output); simultaneously Qmax / Qmin limit i qref Within the range, avoid reactive power overload.

[0045] Active power control uses constant DC voltage control, with the DC voltage reference value calculated by the photovoltaic module based on sunlight intensity and module temperature. Reactive power control uses constant reactive power control; under normal circumstances, photovoltaic power generation operates at unity power factor.

[0046] Please refer to Figure 11 This invention provides a systematic verification method for a microgrid parallel and off-grid full-condition simulation circuit, which is operated according to the following steps: S1: Define multiple basic operating modes; the basic operating modes include at least grid-connected mode and off-grid mode, as well as power surplus condition, power deficit condition and power balance condition under different modes.

[0047] S2: For each basic operating mode, set up a standardized perturbation test set; the standardized perturbation test set includes at least three of the following perturbation types: Source-side power perturbation is used to simulate abrupt changes in light intensity or wind speed. Load-side power disturbance is used to simulate the sudden addition or removal of large-capacity impact loads; Short circuit faults are used to simulate transient or permanent short circuit faults occurring at different locations in the power grid. The off-grid switching disturbance is used to simulate the dynamic process of a microgrid being forced to switch to off-grid operation due to a serious fault on the main grid side.

[0048] S3: Apply the disturbance test set sequentially to the microgrid and off-grid full-condition simulation circuit to perform dynamic simulation.

[0049] S4: Acquire and analyze simulation results data, and verify the safety and stability of the microgrid system based on preset stability criteria; wherein, the stability criteria include: The system voltage is maintained within the range of 0.9 to 1.1 per unit. The system frequency was maintained within the range of 49.5Hz to 50.5Hz; The current of critical equipment shall not exceed its preset short-time overcurrent multiple.

[0050] S5: Based on the verification results of step S4, generate optimization suggestions for control and protection strategies and / or equipment selection suggestions for microgrids; wherein, the optimization suggestions for control and protection strategies include configuring and off-grid switching stability control load shedding strategies; the equipment selection suggestions include overcurrent capacity selection suggestions for grid-type energy storage devices.

[0051] When the disturbance type is a grid-connection / offline handover disturbance, the corresponding verification methods include: The simulation shows a serious fault and line tripping on the main grid side, causing the microgrid to switch to off-grid operation; Verify whether the grid-type energy storage unit can independently support the voltage and frequency stability of the off-grid system; If the system is stable but the grid-type energy storage unit experiences steady-state overload, then the effectiveness of the corresponding stability control and load shedding strategy needs to be verified.

[0052] To further explain, step S2 matches three standardized test items for each basic operating mode: "source-side power disturbance - load-side power disturbance - fault disturbance (including grid connection / off-grid switching disturbance)," clarifying the disturbance amplitude, triggering time and duration, ensuring that the disturbance scenarios are repeatable and comparable, and covering the extreme operating conditions that the actual system may face.

[0053] To further explain, step S3 involves building a microgrid on-grid and off-grid simulation circuit (including a data processing unit, a grid architecture model, and a power source-energy storage-load unit) based on the DIgSILENT software, and performing dynamic simulation according to the process of "basic mode loading → disturbance sequence application → real-time data acquisition".

[0054] Example 1

[0055] Source-side power disturbance test: The first basic approach is adopted: grid connection and full-scale generation of new energy. The microgrid is connected to the main grid, and photovoltaic and wind turbines are operating at full capacity.

[0056] Test procedure: In the first second of the simulation, the light intensity suddenly dropped to 50% of its original value, and the photovoltaic output plummeted accordingly. At this time, the power flow diagram of the power grid is as follows. Figure 12 As shown.

[0057] Working Principle and Effect: A sudden decrease in photovoltaic output causes a power deficit in the system. At this time, the grid-connected microgrid mainly relies on the main grid to balance this power deficit, such as... Figure 13 As shown, the grid-connected energy storage in this system responds instantaneously, utilizing the inertia of its VSG control to increase active power output without delay, thus making up for part of the power gap. For example... Figure 14 As shown, this action significantly suppressed the fluctuation amplitude of the system frequency, allowing it to quickly return to the normal range. This example verifies the technical effectiveness of grid-connected energy storage in smoothing out renewable energy fluctuations and improving power quality.

[0058] Example 2

[0059] Load-side power disturbance test: The same basic approach is adopted: grid connection and large-scale generation of new energy.

[0060] Test procedure: In the first second of the simulation, the 120MW electric boiler load suddenly stopped working completely. At this time, the power flow diagram of the power grid is as follows. Figure 15 As shown.

[0061] Working principle and effects: A sudden loss of load leads to a momentary power surplus in the system. Without grid-connected energy storage, all excess power will flow to the main grid, causing a reversal of power transmission on the tie lines (from receiving power to transmitting power), potentially triggering grid performance issues. For example... Figure 16 As shown, in this invention, grid-connected energy storage, leveraging its voltage source characteristics, immediately senses changes in the system's power angle and instantaneously absorbs a large amount of active power. For example... Figure 17 As shown, the result is that the power surge in the tie line was suppressed from as high as 60MW to a level close to 0MW, and recovered quickly. This example highlights the technical effectiveness of grid-connected energy storage in reducing the impact of large load commissioning and decommissioning on the main grid, and avoids the risk of power backflow assessment.

[0062] Example 3

[0063] And offline handover disturbance test: Using basic approach two: grid connection and small-scale renewable energy generation. In this case, the microgrid heavily relies on the main grid for power supply, representing the most dangerous scenario for off-grid switching. The power flow diagram at this time is as follows: Figure 18 As shown.

[0064] Test process: In the first second of the simulation, a serious short-circuit fault was simulated on the 220kV main grid side; at 1.1 seconds, the protection system activated, tripping all switches connected to the main grid, and the microgrid was forced to switch to off-grid operation.

[0065] Working Principle and Effects: This is the ultimate test of system stability. Upon disconnection from the grid, the microgrid loses the support of the main grid, resulting in severe power imbalance. At this moment, the grid-connected energy storage, as the sole voltage source, rapidly transitions from a "follower" mode during grid connection to a "dominant" mode during disconnection, re-establishing the voltage and frequency of the entire microgrid through its VSG control. For example... Figure 19 , Figure 20 As shown, after a brief and limited dip, the voltage and frequency are quickly pulled back and stabilized within acceptable ranges. This example verifies the survivability of the microgrid design under worst-case conditions and can be used to determine the necessary "stabilization load shedding" amount to ensure system safety.

[0066] Example 4

[0067] Short-circuit fault disturbance test: The third basic approach is adopted: off-grid, high-energy renewable energy generation. In this scenario, the microgrid is disconnected from the main grid, and wind and solar power operate at full capacity (output factor 1.0). The power balance between source and load relies entirely on grid-connected energy storage for regulation. Short-circuit faults can easily trigger voltage drops and power surges, making this an extreme scenario for verifying the transient support capabilities of grid-connected energy storage. The power flow diagram in this situation is as follows: Figure 21 As shown.

[0068] Test process: In the first second of the simulation, a transient nonmetallic short-circuit fault occurred on the 35kV bus; after 1.1 seconds, the fault disappeared automatically.

[0069] Working principle and effects: At this time, the microgrid is disconnected from the main grid, and wind and solar power operate at full capacity (output coefficient 1.0). The power balance between source and load relies entirely on the regulation of grid-connected energy storage. Short-circuit faults can easily cause voltage drops and power surges, making it an extreme scenario for verifying the transient support capability of grid-connected energy storage. Figure 22As shown, during a 35kV bus short circuit, the grid-connected energy storage system provides instantaneous, delay-free active power output to maintain overall system power balance and limit system frequency fluctuations to a reasonable range. Simultaneously, the grid-connected energy storage system provides instantaneous reactive power output to maintain system voltage, ultimately restoring the system to stable operation. In off-grid mode, both system voltage and frequency are supported by the grid-connected energy storage system, as shown below. Figure 23 As shown, the grid-connected energy storage system has a high instantaneous overcurrent requirement at the moment of failure, and the current is quickly limited to 1.5 pu after the failure, with a deep transient voltage drop, which meets the system's safety and stability requirements.

[0070] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A microgrid parallel and off-grid full-condition simulation circuit, characterized in that: include: The power grid architecture model (200) includes a bus section I (201) and a bus section II (202) connected by a bus tie, and a transmission line (203) connected to the bus section I (201) and the bus section II (202) respectively by a transformer; The I-section busbar (201) and II-section busbar (202) are respectively connected in a high-voltage direct connection manner to an energy storage unit model (300) simulating charging, a load unit model simulating power consumption, and several power supply unit models simulating power generation. The energy storage unit model (300) adopts a virtual synchronous generator control strategy to provide voltage and frequency support for the power grid architecture model (200); The loads within the range of the I section busbar (201) and the II section busbar (202) are unequal.

2. The microgrid parallel and off-grid full-condition simulation circuit as described in claim 1, characterized in that: The load unit model (400) includes an impact load model (401) and a sensitive load model (402) located within the range of bus section I (201) and bus section II (202). The impact load model (401) is used to simulate the combined characteristics of constant current and constant power; Includes three electric boiler sub-models (401a); The sensitive load model (402) is used to simulate the load characteristics of motors and frequency converters.

3. The microgrid parallel and off-grid full-condition simulation circuit as described in claim 1 or 2, characterized in that: The power supply unit model (500) includes: Wind power generation model (501) is configured to output constant power; A photovoltaic power generation model (502) is configured to have a fixed reactive output or to be linearly adjustable according to voltage.

4. The microgrid parallel and off-grid full-condition simulation circuit as described in claim 3, characterized in that: The wind power generation model (501) includes: a newly built wind power electronic model (501a) connected within the range of bus section I (201), and an existing wind power electronic model (501b) connected within the range of bus section II (202). The wind power generation model (501) adopts an induction generator model and is configured with phase-locked loop constant power control.

5. The microgrid parallel and off-grid full-condition simulation circuit as described in claim 3, characterized in that: The photovoltaic power generation model (502) includes: a newly built photovoltaic sub-model (502a) connected within the range of bus section I (201), and an existing photovoltaic sub-model (502b) connected within the range of bus section II (202). The photovoltaic power generation model (502) adopts MPPT control mode, and performs reasonable distribution of reactive power through closed-loop control of voltage outer loop and current inner loop.

6. A systematic verification method for a microgrid parallel and off-grid full-condition simulation circuit, characterized in that: Follow these steps: S1: Define multiple basic operating modes, which include at least grid-connected mode and off-grid mode, as well as power surplus and power deficit conditions under different modes; S2: For each of the basic operating modes, set up a standardized set of disturbance test cases; S3: Apply the disturbance test set sequentially to the microgrid and off-grid full-condition simulation circuit to perform dynamic simulation; S4: Acquire and analyze simulation results data, and verify the safety and stability of the microgrid system based on preset stability criteria.

7. The systematic verification method for the full-condition simulation circuit of microgrid parallel and off-grid operation as described in claim 6, characterized in that: The standardized perturbation test set in step S2 includes at least three of the following perturbation types: Source-side power perturbation is used to simulate abrupt changes in light intensity or wind speed. Load-side power disturbance is used to simulate the sudden addition or removal of large-capacity impact loads; Short circuit faults are used to simulate transient or permanent short circuit faults occurring at different locations in the power grid. The off-grid switching disturbance is used to simulate the dynamic process of a microgrid being forced to switch to off-grid operation due to a serious fault on the main grid side.

8. The systematic verification method for the full-condition simulation circuit of microgrid parallel and off-grid operation as described in claim 6, characterized in that: The stability criteria in step S4 include: The system voltage is maintained within the range of 0.9 to 1.1 per unit. The system frequency was maintained within the range of 49.5Hz to 50.5Hz; The current of critical equipment shall not exceed its preset short-time overcurrent multiple.

9. The systematic verification method for the full-condition simulation circuit of microgrid parallel and off-grid operation as described in claim 6, characterized in that: The method further includes step S5: Based on the verification results of step S4, optimization suggestions for control and protection strategies and / or equipment selection suggestions for microgrids are generated. The control and protection strategy optimization suggestions include configuring and off-grid switching stability control load shedding strategies; the equipment selection suggestions include overcurrent capacity selection suggestions for grid-type energy storage devices.

10. The systematic verification method for the full-condition simulation circuit of microgrid parallel and off-grid operation as described in claim 6, characterized in that: When the disturbance type is a grid-connection / offline handover disturbance, the verification method includes: The simulation shows a serious fault and line tripping on the main grid side, causing the microgrid to switch to off-grid operation; Verify whether the grid-type energy storage unit can independently support the voltage and frequency stability of the off-grid system; If the system is stable but the grid-type energy storage unit experiences steady-state overload, then the effectiveness of the corresponding stability control and load shedding strategy needs to be verified.

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