A power grid impedance simulation device, design method and use method

Abstract

This invention belongs to the field of power system technology, and particularly relates to a power grid impedance simulation device, its design method, and its usage method. The device design includes determining the required component types, obtaining the quantity and electrical parameter values ​​of each component based on actual national standards and the minimum component quantity criterion; implementing on-demand connection of each component, and using a controller to achieve corresponding control to support the simulation and switching of operating conditions with different short-circuit ratios and series complement degrees; setting a switching logic control program in the controller so that when the controller receives a power grid operating condition switching command, it executes the pre-set switching logic control program to achieve the switching of the operating condition corresponding to the power grid short-circuit ratio and series complement degree. This technical solution, through the integrated design of "parameter calculation - hardware topology - logic control," solves the problems of low testing efficiency, poor simulation accuracy, and high cost in existing technologies, providing an efficient, accurate, and economical solution for the adaptability testing of new energy converters under "high-voltage and high-efficiency" power systems.

Description

Technical Field

[0001] This invention belongs to the field of power system technology, and in particular relates to a power grid impedance simulation device, its design method, and its usage method. Background Technology

[0002] With the vigorous promotion of clean energy globally, new energy sources such as wind power and solar power are increasingly being used in power systems. The large-scale integration of new energy sources has significantly changed the structure and characteristics of power systems, gradually transforming the power grid from a traditional system dominated by synchronous machines to a "dual-high" power system characterized by a high proportion of new energy and high levels of power electronics. During this transformation, the system short-circuit ratio is gradually decreasing, and the characteristics of a weak power grid are becoming increasingly apparent, posing a severe challenge to the stable operation of the power system.

[0003] To ensure the stable operation of high-voltage and high-efficiency power systems, it is crucial to test the adaptability of renewable energy converters under low short-circuit ratio, variable short-circuit ratio, and variable series compensation conditions. However, current experimental testing methods have significant drawbacks. Existing testing methods require shutdown and rearrangement of grid impedance after completing one set of short-circuit ratio tests before another set of short-circuit ratio tests can be performed. This method is not only time-consuming and labor-intensive but also fundamentally unable to simulate real-time changes or abrupt changes in the grid short-circuit ratio, severely impacting testing efficiency and the accuracy of simulating actual grid operation.

[0004] Although existing invention patents have proposed online switching grid impedance simulation devices, these devices still have many problems in practical applications. Firstly, existing devices only consider grid impedance composed of inductors. However, in actual testing, the real grid impedance provided by power grid companies is often composed of resistors (R), inductors (L), and capacitors (C). This means that existing devices cannot simulate changes in LC series complement and the characteristics of RLC grid impedance, resulting in significant deviations between test results and actual grid operation. Secondly, existing technologies only provide switchable grid impedance combinations, focusing on variable or switchable inductance, but completely neglecting to provide selection or calculation methods for the components of the simulation device. In field testing, the focus is more on simulating specific grid short-circuit ratios, such as the typical short-circuit ratios required by grid connection permits or national standards (SCR=1.8, 2.5, 4, 10), rather than pursuing a large number of impedance combinations in the device. If the parameters of the grid short-circuit ratio simulation device are not selected reasonably during the design phase, then multiple impedance simulators and other external RLCs will need to be connected in series and parallel during actual testing to achieve the required grid short-circuit ratio. This will undoubtedly lead to a significant increase in testing costs and a more time-consuming testing process, severely hindering the efficient implementation of testing work for new energy converters.

[0005] In summary, existing technologies have significant shortcomings in simulating grid series compensation and short-circuit ratio, and cannot meet the requirements for adaptability testing of new energy converters under "high-voltage and high-efficiency" power systems. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the existing technology by proposing a power grid impedance simulation device, design method, and usage method. Through the integrated design of "parameter calculation - hardware topology - logic control", it solves the problems of low testing efficiency, poor simulation accuracy, and high cost in the existing technology, and provides an efficient, accurate, and economical solution for the adaptability testing of new energy converters under the "high-voltage and high-efficiency" power system.

[0007] The above objectives are achieved through the following technical solutions:

[0008] A design method for a power grid impedance simulation device is provided, which obtains the power grid impedance simulation device by sequentially performing component parameter calculation and selection, device hardware connection topology, and setting switch logic control program.

[0009] Component parameter calculation and selection: Based on the simulation test requirements corresponding to the short-circuit ratio and series compensation degree, the required components are determined, including automatic slide wire rheostats, inductors, capacitors and contactors; based on the actual national standard for the short-circuit ratio corresponding to the converter test requirements, the quantity of each component and the value of electrical parameters are obtained by combining the principle of using the minimum number of components.

[0010] Device hardware connection topology: Selected components are connected on demand, that is, the controller controls the on and off of the contactors and the adjustment of the automatic slide wire rheostat, so that the automatic slide wire rheostat, in combination with different inductors, can simulate the working conditions corresponding to different short-circuit ratios, different capacitor combinations can simulate the working conditions corresponding to different series compensation degrees, and the on and off of different contactors can switch between working conditions corresponding to different short-circuit ratios, between working conditions corresponding to different series compensation degrees, and between working conditions corresponding to short-circuit ratios and working conditions corresponding to series compensation degrees.

[0011] Configure the switching logic control program: Configure the switching logic control program in the controller so that when the controller receives the power grid operating condition switching command, it can realize the switching between different short-circuit ratio corresponding operating conditions, different series complement degree corresponding operating conditions, and the switching between the short-circuit ratio corresponding operating condition and the series complement degree corresponding operating condition by executing the pre-set switching logic control program.

[0012] Preferably, in the component parameter calculation and selection, the number of automatic slide wire rheostats is 1, represented by R, and its resistance range is [0, 40]Ω.

[0013] Preferably, in the component parameter calculation and selection, obtaining the number of inductors includes the following steps:

[0014] S11-11, Obtain the test requirements for the grid short-circuit ratio of the converter according to the national standard grid connection criteria, i.e., the short-circuit ratio... Tests were conducted under four typical operating conditions at 1.8, 2.5, 4, and 10.

[0015] S11-12, the preset method first uses two sets of inductors to form the mains impedance, the two sets of inductors being inductance... and inductor ;inductance and inductor When connected in series, the mains impedance is at its maximum, and the short-circuit ratio is 1.8; inductance and inductor When connected in parallel, the grid impedance is at its minimum, and the short-circuit ratio is 10.

[0016] S11-13, Take the inductor Simulate the operating condition with a short-circuit ratio of 2.5 independently;

[0017] S11-14, for simulation of operating conditions with a short-circuit ratio of 4, provides inductors Add parallel inductor .

[0018] Preferably, in the component parameter calculation and selection, the electrical parameter values ​​of the inductor include the following steps;

[0019] S11-21, Obtain the grid inductance value The calculation formula, namely ;in: Indicates the mains voltage; Indicates the grid-connected capacity of new energy sources; Indicates frequency; Indicates the short-circuit ratio; Indicates the short-circuit ratio condition, i.e. ;

[0020] S11-22, based on inductance If a simulation of the operating condition with a short-circuit ratio of 2.5 is performed independently, then the grid inductance value is obtained. Calculate the inductance inductance value ;

[0021] S11-23, based on the inductance and inductor By connecting them in series, the inductance value of the power grid can be obtained. Based on inductance and inductor Parallel connection to obtain the grid inductance value ;

[0022] S11-23, combining the formulas for calculating the grid inductance under the conditions of maximum and minimum grid impedance, derive the inductance value. With inductance The product of, i.e. Substitute inductance inductance value Then an inductance is obtained. inductance value ;

[0023] S11-24, based on inductance With inductance Parallel connection to obtain the grid inductance value Transformation to obtain Substitute inductance inductance value Then an inductance is obtained. inductance value .

[0024] Preferably, in the component parameter calculation and selection, obtaining the number of capacitors includes the following steps:

[0025] S12-11, select the working condition with short-circuit ratio SCR=1.8 and give the simulation requirements for three states with series complement TCR of 10%, 40% and 60% respectively;

[0026] S12-12, Two sets of capacitors are pre-configured to meet the simulation requirements of the three states; wherein the two sets of capacitors are capacitors... and capacitor ;

[0027] Take capacitor Achieve simulation of a working condition with a series complement ratio (TCR) of 40% independently;

[0028] capacitance and capacitor The maximum analog series complement (TCR) of the capacitive reactance in series is 60%.

[0029] capacitance and capacitor The minimum analog series complement (TCR) of the capacitive reactance in parallel is 10%.

[0030] Preferably, in the component parameter calculation and selection, the electrical parameter values ​​of the capacitor include the following steps;

[0031] S12-21, based on capacitor To simulate a working condition with a series complement ratio (TCR) of 40% independently, the formula is used. Calculate the capacitance The capacitance value ;in Inductance The inductance value; Indicates frequency;

[0032] S12-22, based on capacitor With capacitor For series operation, there is a formula for calculating the capacitance. Based on capacitance With capacitor For parallel operation, there is a formula for calculating the capacitance. ;

[0033] S12-23, combined with capacitor With capacitor Formulas for calculating capacitance under series and parallel operating conditions are derived to obtain the capacitance value. With capacitor The product of the tolerance values, i.e. Substitute capacitor The capacitance value Then the capacitance is obtained. The capacitance value .

[0034] Preferably, in the component parameter calculation and selection, the number of contactors is indeed based on the automatic slide wire rheostat R and the inductor. ,inductance ,inductance ,capacitance and capacitors To meet the series and parallel connection requirements, 8 sets of contactors are preset, namely KM1, KM2, KM3, KM4, KM5, KM6, KM7 and KM8.

[0035] Preferably, in the hardware connection topology of the device, the on-demand connection of the selected components includes: the automatic slide wire rheostat R and contactors KM1-KM8 are respectively connected to the controller; using terminals A and B to represent the left and right ends of each component, then: terminal A of the automatic slide wire rheostat R is the device's data acquisition input terminal, and terminal B of the automatic slide wire rheostat R is connected to the inductor... Terminal A is connected; inductor Terminal A is connected to the inductor via contactor KM1. Terminal A is connected, inductor B-terminal and inductor B-end connection; inductor Terminal A is connected to the inductor via contactor KM2. Terminal A is connected, inductor B-terminal and inductor The B terminal is connected; capacitor Terminal A is connected to the inductor via contactor KM3. Terminal A is connected to the capacitor. Terminal B is connected to the inductor via contactor KM4. The B terminal is connected; capacitor Terminal A is connected to capacitor via contactor KM5. Terminal A is connected, and the device output is also connected via contactor KM8; capacitor Terminal B is connected to the capacitor via contactor KM6. The B terminal is connected, and the output terminal of the device is connected via contactor KM7.

[0036] Preferably, the setting switch logic control program includes editing the contactor switch code for different short-circuit ratios and series complement degrees corresponding to different operating conditions. That is, 0 and 1 flag bits are used to represent the contactor's opening and closing respectively, and the code is performed in the order of KM1-KM8. Then: when SCR=1.8, the switch code is 00101001; when SCR=2.5, the switch code is 00010110; when SCR=4, the switch code is 10010110; when SCR=10, the switch code is 01010110; when TCR=10%, the switch code is 00011101; when TCR=40%, the switch code is 00011001; when TCR=60%, the switch code is 00011010.

[0037] Preferably, the setting switch logic control program also includes designing a delayed switch action logic sequence for the switching of different short-circuit ratios and series complement degrees corresponding to different operating conditions. This ensures that when a power grid operating condition switching command is received, the closing command in the switch code corresponding to the operating condition to be switched is executed first, and after executing the closing command, the opening command in the switch code corresponding to the operating condition to be switched is executed after a delay of 1-2 seconds.

[0038] This technical solution proposes a power grid impedance simulation device, which is obtained through the above-mentioned design method.

[0039] The method of using the above-mentioned power grid impedance simulation device includes the following steps:

[0040] Step 1: Connect the input terminal of the power grid impedance simulation device to the converter under test, connect the output terminal of the simulation test device to the power grid, and set up a table showing the correspondence between simulated operating conditions and switch combination states.

[0041] Step 2: Connect the controller of the power grid impedance simulation device to the host computer and start the power grid impedance simulation device to initialize it.

[0042] Step 3: With the converter connected to the grid and started, according to the simulated operating conditions required by the test target, query the correspondence table between the simulated operating conditions and the switch combination, obtain the switch combination status corresponding to the required simulated operating conditions, and then use the host computer to switch the power grid operating conditions according to the corresponding switch combination status.

[0043] Step 4: The controller determines whether it has received a power grid operating condition switching command; if yes, proceed to step 5; if no, proceed directly to step 6.

[0044] Step 5: The controller controls the corresponding contactor to open or close and adjusts the automatic sliding rheostat according to the received power grid operating condition switching command, thereby completing the switching of the simulated operating conditions required for the test target.

[0045] Step 6: Determine whether the current testing work is complete based on the testing requirements; if yes, proceed to Step 7; if no, return to Step 3.

[0046] Step 7: The converter stops, the corresponding contactor is reset, and the grid impedance simulation device returns to the initialization state.

[0047] Preferably, step five, controlling the corresponding contactor to open or close, includes the following steps:

[0048] Step 5.1: While maintaining the current switching state of all contactors, the controller reads the switching combination state corresponding to the simulated operating condition required for the test target from the power grid operating condition switching instruction;

[0049] Step 5.2: Match the switch codes according to the switch combination states corresponding to the simulated working conditions required by the test target;

[0050] Step 5.3: Execute the contactor closing action with the switch code set to 1;

[0051] Step 5.4, delay for 1-2 seconds;

[0052] Step 5.5: Perform the contactor disconnection action if the switch code is 0;

[0053] Step 5.6: Determine whether the contactor closing and opening actions corresponding to the simulated working conditions required by the current test target have been completed; if not, return to step 5.2; if yes, the current switching task ends.

[0054] The beneficial effects of this invention are:

[0055] I. Solve the inefficiency of existing testing methods that require downtime to change operating conditions, and achieve dynamic real-time switching.

[0056] Switching between short-circuit ratio and series compensation conditions without system downtime: This invention uses a controller to control the on / off state of the contactor and automatically adjusts the slide wire rheostat, enabling online switching between different short-circuit ratios and series compensation conditions. For example, through preset contactor switch coding and delay logic, the controller can automatically complete impedance switching upon receiving a command, avoiding downtime and significantly improving testing efficiency.

[0057] Dynamic simulation of sudden changes in power grid parameters: This invention can achieve rapid switching of operating conditions (such as 1-2s delay switching) through a switch logic control program, which can reproduce the operating conditions of sudden changes in short-circuit ratio in the actual power grid, making the test closer to the real operating scenario.

[0058] II. Simulating operating conditions that take into account both RLC impedance characteristics and series compensation degree to improve test accuracy

[0059] Complete Simulation of RLC Impedance Characteristics in Actual Power Grids: This invention accurately simulates RLC series or parallel impedance through a combination of automatic slide wire rheostats, inductors, and capacitors. For example, by utilizing the series and parallel connection of capacitors and inductors, the variation in series complement is simulated, overcoming the limitation of existing technologies in simulating LC series complement, and making the test results closer to the actual operation of the power grid.

[0060] Covering typical short-circuit ratio and series compensation conditions required by national standards: Based on the national standard requirements for converter testing (e.g., SCR=1.8, 2.5, 4, 10), and combined with RLC parameter calculation methods, this invention can accurately reproduce the grid weakness (short-circuit ratio) and compensation level (series compensation). For example, different short-circuit ratios are achieved through the series-parallel combination of three sets of inductors, and different series compensations are achieved through the series-parallel combination of two capacitors, avoiding test deviations caused by unreasonable parameter selection in existing technologies.

[0061] III. Optimize component parameter selection to reduce testing costs and complexity.

[0062] A parameter calculation method based on the principle of minimum component count: Compared to existing devices that lack a parameter selection method, leading to the need for multiple impedance simulators and high costs, this invention proposes a scientific parameter calculation logic: For inductor selection, a single inductor group achieves an SCR of 2.4; two inductor groups connected in series and parallel achieve SCRs of 1.8 and 10; adding another inductor in parallel achieves an SCR of 4, covering four short-circuit ratio conditions with only three inductor groups; for capacitor selection, two capacitor groups connected in series and parallel achieve three TCR states: 10%, 40%, and 60%, satisfying the series compensation requirement with only two capacitor groups; for resistor selection, a single automatic slide wire rheostat (R=0~40Ω) is used to adjust the resistance component. This method achieves multi-condition simulation with a minimum number of components, avoiding the investment in multiple sets of equipment and significantly reducing testing costs.

[0063] Avoiding the cumbersome operation of connecting external RLC components in series and parallel: Compared to existing technologies that require additional external RLC components to meet testing requirements due to unreasonable parameter selection, which is time-consuming and labor-intensive, this invention enables the device itself to generate the required impedance through precise parameter calculation, eliminating the need for external components and simplifying the testing process.

[0064] IV. Automated control and logic design to improve ease of operation and safety.

[0065] Automated switching is achieved through contactor coding and delay logic: This invention avoids momentary short circuits during switching by using contactor switch coding and delay logic, thus improving device reliability. For example, when switching operating conditions, the controller first executes a closing command, and then executes a closing command after the circuit stabilizes, preventing damage to components.

[0066] Host computer communication and one-click operating condition switching: In operation, commands are sent via a host computer, and the controller automatically matches the switch code and executes the switching without manual intervention. For example, testers only need to query the "Simulated Operating Conditions - Switch Combination Table" and send commands via the host computer; the device can then automatically complete impedance reconstruction, reducing operational complexity and minimizing human error.

[0067] V. Standardized design adapts to national standard testing requirements and has strong scalability.

[0068] The design method of this invention is based on the national standard for testing typical short-circuit ratio conditions of converters, and the parameter calculation process can be flexibly adjusted according to actual power grid needs. For example, if a new operating condition is required, only a few components need to be added or the switch code needs to be modified based on the existing topology, without the need to redesign the hardware. Its adaptability and scalability are superior to those of fixed devices in the prior art. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of the structure and operating principle of a power grid impedance simulation device.

[0070] Figure 2 A flowchart illustrating the use of a power grid impedance simulation device.

[0071] Figure 3 This is a flowchart simulating the switching action of operating conditions. Detailed Implementation

[0072] To make the purpose, technical solution and advantages of the invention clearer, the technical solution of the invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the invention, but not all embodiments.

[0073] Therefore, the following detailed description of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0074] Example 1

[0075] This embodiment discloses a power grid impedance simulation device, its design method, and its usage method. As a preferred embodiment of the present invention, the design method is to obtain the power grid impedance simulation device by sequentially performing component parameter calculation and selection, device hardware connection topology, and setting switch logic control program.

[0076] Component parameter calculation and selection: Based on the simulation test requirements corresponding to the short-circuit ratio and series compensation degree, determine the required component types; based on the short-circuit ratio requirements of the actual national standard for converter testing, combine the principle of using the minimum number of components to obtain the quantity of each component and the values ​​of electrical parameters.

[0077] The short-circuit ratio (SCR) is essentially the ratio of the short-circuit capacity of the AC bus of the power grid to the rated capacity of the connected converters. Its mathematical expression is: ( For short-circuit capacity, (This refers to the rated capacity of the converter). When the grid impedance increases, the short-circuit capacity decreases, the SCR value decreases, and the system stability will decline accordingly. The series compensation ratio (TCR) is the ratio of the series capacitor compensation capacity to the line transmission capacity, expressed as: ( For capacitor reactance, (For inductive reactance). Based on this, this technical solution accurately selects components that can simulate the impedance characteristics of the power grid according to the electrical characteristics of the short-circuit ratio and series compensation degree.

[0078] An automatic slide wire rheostat continuously adjusts its resistance by changing the length of the resistance wire connected to the circuit. Its principle is based on Ohm's law, i.e. ( Resistivity The length of the resistance wire. (This refers to the cross-sectional area) thus enabling fine adjustment of the circuit impedance. Inductive components, based on the principle of electromagnetic induction, generate inductive reactance in the circuit. ( Indicates frequency, This represents the inductance value, used to simulate the inductive impedance of the power grid. Capacitive components, based on their capacitance characteristics, generate capacitive reactance. ( (This refers to the capacitance value), which partially cancels out the inductive impedance in the simulation of the corresponding operating conditions. The contactor uses an electromagnetic mechanism to control the opening and closing of the contacts. Its principle is that the electromagnetic coil is energized to generate a magnetic field, which attracts the armature and drives the contacts to move, thereby realizing the switching of the circuit.

[0079] In summary, based on the simulation test requirements of the power grid short-circuit ratio and series compensation degree, this technical solution determines the required component types, including automatic slide wire rheostats, inductors, capacitors, and contactors.

[0080] The actual national standard for converter testing requires short-circuit ratio conditions based on typical scenarios categorized by the actual weaknesses of the power grid, following... ( Rated voltage, The calculation logic for the equivalent impedance of the power grid is as follows. Selection is based on the minimum number of components criterion, utilizing the principles of circuit equivalent transformation (such as star-delta transformation and impedance series-parallel formulas) to meet the requirements. ( For error impedance, Optimize the component combination to achieve the target impedance accuracy.

[0081] Device hardware connection topology: Selected components are connected as needed. A controller is used to control the on / off state of the contactors and the adjustment of the automatic slide wire rheostat. The automatic slide wire rheostat, in combination with different inductors, simulates the operating conditions corresponding to different short-circuit ratios. Different capacitor combinations simulate the operating conditions corresponding to different series compensation degrees. The switching between different contactors is achieved by coordinating their opening and closing to switch between operating conditions corresponding to different short-circuit ratios, operating conditions corresponding to different series compensation degrees, and operating conditions corresponding to both short-circuit ratios and series compensation degrees.

[0082] The controller can be a PLC (Programmable Logic Controller) or an MCU (Microcontroller Unit), controlling the contactor coil voltage via a digital output port (DO), and constructing different impedance circuits by opening and closing the contactor's main contacts. The automatic slide wire rheostat can be driven by a servo motor to move the slider; the number of servo motor pulses and the resistance value follow a specific relationship. ( For the maximum resistance, pulse number The linear relationship between the total number of pulses and the controller's PWM (Pulse Width Modulation) signal enables continuous adjustment. The capacitors and inductors employ a modular parallel structure, with combinations of capacitor and inductor values ​​achieved through contactor switches to simulate operating conditions with varying short-circuit ratios and series compensation degrees.

[0083] Configure the switching logic control program: Configure the switching logic control program in the controller so that when the controller receives the power grid operating condition switching command, it can realize the switching between different short-circuit ratio corresponding operating conditions, different series complement degree corresponding operating conditions, and the switching between the short-circuit ratio corresponding operating condition and the series complement degree corresponding operating condition by executing the pre-set switching logic control program.

[0084] The switching logic control program can be designed based on a state machine model, defining state nodes such as initial state, standby state, switching state, and running state. State transition conditions include command reception, component state feedback (such as DI input of contactor auxiliary contacts), and time delay (such as stabilization after a preset time interval following switching). Furthermore, the logic can be written using ladder diagrams or ST (structured text) language. The core algorithm is as follows: when a working condition switching command (including target SCR and TCR values) is received, the switching logic control program calculates the required component combination using a lookup table method, generates a contactor action sequence, and prevents short circuits through hardware interlocking logic (two contactors on the same branch cannot close simultaneously).

[0085] Based on the above design method, a power grid impedance simulation device is obtained. The device is then applied in practice, i.e., a method for using the power grid impedance simulation device is described below. Figure 2 As shown, it includes the following steps:

[0086] Step 1, as follows Figure 1 As shown, the input terminal of the power grid impedance simulation device is connected to the converter under test, and the output terminal of the simulation test device is connected to the power grid. A mapping table between simulated operating conditions and switch combination states is set up. A mapping relationship between physical connections and electrical parameters is established to ensure that the device can accurately sense the converter's operating status and output simulated power grid impedance. The pre-made mapping table enables rapid recall of operating conditions, greatly reducing manual configuration time and improving testing efficiency.

[0087] The table showing the correspondence between simulated operating conditions and switch combination states is as follows: Table 1 below shows the mapping table between simulated operating conditions and contactor switch codes.

[0088]

[0089] Step two involves communicating with the host computer via Ethernet (IEEE 802.3 standard) or RS485 (Modbus-RTU protocol), following the communication protocol DL / T634.5104-2009, to achieve command transmission and data interaction. The power grid impedance simulation device is then started and initialized. The initialization process may include: ① Contactor status verification (reading the auxiliary contact status through the DI port to ensure all contactors are in the preset state); ② Component parameter self-test (such as rheostat initial position detection and capacitor withstand voltage test); ③ Controller register clearing (such as PID control parameter reset), following the PLC's scan cycle mechanism to ensure synchronization of module states.

[0090] Step three: With the converter connected to and started by the grid, based on the simulated operating conditions required for the test target (corresponding to the grid's weakness and compensation level), consult the correspondence table between simulated operating conditions and switch combinations to obtain the corresponding switch combination status. Then, use the host computer to send a switching command to the power grid operating conditions according to the corresponding switch combination status. The purpose is to enable the grid impedance simulation device to reproduce typical operating conditions of the actual power grid, providing standardized grid conditions for converter testing. Precise control of operating conditions is achieved through digital command transmission, avoiding errors caused by manual adjustment of component parameters.

[0091] Step 4: The controller uses a scanning cycle mechanism (e.g., scanning the DO port once every 10ms) to detect the command reception status and determine whether a power grid operating condition switching command has been received; if yes, proceed to step 5; if no, proceed directly to step 6.

[0092] Step 5: Based on the received power grid operating condition switching command, the controller controls the corresponding contactor to open or close, and adjusts the automatic sliding rheostat, thereby completing the switching of the simulated operating conditions required for the test target.

[0093] Step 6: Determine whether the current testing work is complete based on the testing requirements; if yes, proceed to Step 7; otherwise, return to Step 3.

[0094] Step 7: The converter stops, the corresponding contactor is reset, and the grid impedance simulation device returns to the initialization state.

[0095] Example 2

[0096] This embodiment discloses a power grid impedance simulation device, design method, and usage method. As a preferred embodiment of the present invention, based on embodiment 1, a high-power automatic slide wire rheostat is selected, with a quantity of 1, denoted by R. Only the upper limit of the resistance value needs to be designed. Considering that the equivalent resistance of most power grids in actual tests is within 8-22Ω, in order to ensure design redundancy, the resistance value range of the automatic slide wire rheostat is [0, 40]Ω.

[0097] Example 3

[0098] This embodiment discloses a power grid impedance simulation device, its design method, and its usage method. As a preferred embodiment of the present invention, based on Embodiment 1 or Embodiment 2, the specific details of obtaining the number of inductors and the values ​​of electrical parameters in the component parameter calculation and selection are as follows:

[0099] Obtain the national standard grid connection criteria for converters regarding the test requirements for the grid short-circuit ratio, i.e., the short-circuit ratio... Four typical operating conditions (SCR) of 1.8, 2.5, 4, and 10 were tested. Based on the national standard for wind power converter grid connection requirements for SCRs of 1.8, 2.5, 4, and 10, the grid inductance value was derived by substituting these values ​​into the grid impedance calculation formula. Furthermore, the grid inductance value was derived based on the inductance configuration principle derived from the mapping relationship between electromagnetic induction and SCR. Calculation formula The inductance value of the power grid The calculation formula is through Obtained through conversion. Wherein: Indicates the short-circuit ratio; Indicates the short-circuit ratio condition, i.e. ; Indicates the mains voltage; Indicates the grid-connected capacity of new energy sources; The reference value for the power grid impedance is denoted as . ; For inductive impedance, we have , Indicates frequency.

[0100] To simulate the four operating conditions, at least two sets of inductor units are required in series and parallel. This technical solution prioritizes economic efficiency, aiming to simulate four typical operating conditions with SCRs of 1.8, 2.5, 4, and 10 using the fewest possible inductors. Specifically, it pre-determines that two sets of inductors are used to form the grid impedance, with each set being an inductor... and inductor .inductance and inductor When connected in series, the mains impedance is at its maximum, and the short-circuit ratio is 1.8; inductance and inductor When connected in parallel, the grid impedance is at its minimum, and the short-circuit ratio is 10. This allows for simulation of operating conditions with SCRs of 1.8 and 10, respectively. .

[0101] Based on the above formulas for calculating the grid inductance under the conditions of maximum and minimum grid impedance, the inductance value is derived. With inductance value The product of, i.e. Take an inductor To simulate a short-circuit ratio of 2.5 independently, the grid inductance value is used. Calculate the inductance inductance value Inductor inductance value Inductance value With inductance value The product formula can be used to calculate the inductance. inductance value .

[0102] After actual testing, when using only the inductor... At that time, SCR=7.2, which cannot simulate the corresponding operating condition of SCR=4. Therefore, the inductor... Add parallel inductor , and Simulate the operating condition with SCR=4 under parallel connection, thus obtaining the grid inductance value. Transformation to obtain Substitute inductance inductance value Then an inductance is obtained. inductance value .

[0103] In summary, in this technical solution, the number of inductors is 3, which are inductors... ,inductance and inductor The corresponding electrical parameters are the inductance value. Inductance value and inductance value .

[0104] Example 4

[0105] This embodiment discloses a power grid impedance simulation device, its design method, and its usage method. As a preferred embodiment of the present invention, based on embodiment 3, the specific details of obtaining the number of capacitors and the values ​​of electrical parameters in the component parameter calculation and selection are as follows:

[0106] The capacitor is connected to simulate different series compensation ratios (TCR) of the power grid. Considering that series compensation is generally added when the power grid is relatively weak to reduce the grid impedance, the power grid impedance simulation device in this technical solution selects the operating condition with SCR=1.8 to simulate three states with series compensation ratios of 10%, 40%, and 60%, and then implements the selection of the electrical parameters of the capacitor. Considering economic factors, two sets of capacitors are preset to meet the simulation requirements of the three states; wherein the two sets of capacitors are capacitors. and capacitor .capacitance and capacitor When connected in series, the maximum analog series complement (TCR) of the capacitive reactance is 60%, and the capacitance... and capacitor When connected in parallel, the minimum analog series complement (TCR) of the capacitive reactance is 10%; when connected in series, the maximum analog series complement of the capacitive reactance is 60%; and when connected in parallel, the minimum analog series complement of the capacitive reactance is 10%. Thus, we have... .

[0107] Combined with capacitor With capacitor Formulas for calculating capacitance under series and parallel operating conditions are derived to obtain the capacitance value. With capacitor The product of the tolerance values, i.e. Take a capacitor. To simulate a working condition with a series complement ratio (TCR) of 40% independently, the formula is used. Calculate the capacitance The capacitance value . Capacitor The capacitance value Capacitor With capacitor The capacitance value can be calculated using the formula for the product of capacitance values. The capacitance value .

[0108] In summary, in this technical solution, the number of capacitors is 2, namely capacitors... and capacitor The corresponding electrical parameters are capacitance values. and capacitance .

[0109] Example 5

[0110] This embodiment discloses a power grid impedance simulation device, its design method, and its usage method. As a preferred embodiment of the present invention, based on embodiment 4, in the component parameter calculation and selection, the exact number of contactors is based on the automatic sliding rheostat R and the inductor. ,inductance ,inductance ,capacitance and capacitors To meet the series and parallel connection requirements, 8 sets of contactors are preset, namely KM1, KM2, KM3, KM4, KM5, KM6, KM7 and KM8.

[0111] Based on this, in the device hardware connection topology, the on-demand connection of the selected components includes: connecting the automatic slide wire rheostat R and contactors KM1-KM8 to the controller respectively; using terminals A and B to represent the left and right ends of each component, then: terminal A of the automatic slide wire rheostat R is the device's data acquisition input terminal, used to connect to the converter; terminal B of the automatic slide wire rheostat R is connected to the inductor... Connect terminal A. Inductor. Terminal A is connected to the inductor via contactor KM1. Terminal A is connected, inductor B-terminal and inductor The B-terminal connection. Inductor. Terminal A is connected to the inductor via contactor KM2. Terminal A is connected, inductor B-terminal and inductor The B terminal is connected. Capacitor. Terminal A is connected to the inductor via contactor KM3. Terminal A is connected to the capacitor. Terminal B is connected to the inductor via contactor KM4. The B terminal is connected. Capacitor. Terminal A is connected to capacitor via contactor KM5. Terminal A is connected, and the device output is also connected via contactor KM8; capacitor Terminal B is connected to the capacitor via contactor KM6. The B terminal is connected, and the device output terminal is also connected via contactor KM7. The device output terminal is used to connect to the power grid or voltage source.

[0112] Example 6

[0113] This embodiment discloses a power grid impedance simulation device, its design method, and its usage method. As a preferred embodiment of the present invention, based on embodiment 5, the switch logic control program includes editing the contactor switch code for different short-circuit ratios and series complement degrees corresponding to different operating conditions. Specifically, 0 and 1 flag bits are used to represent the contactor's opening and closing, respectively, and the coding is performed in the order of KM1-KM8. Then:

[0114] When SCR=1.8, the switch code is 00101001, which means that KM1, KM2, KM4, KM6 and KM7 are open, and KM3, KM5 and KM8 are closed.

[0115] When SCR=2.5, the switch code is 00010110, which means that KM1, KM2, KM3, KM5 and KM8 are open, and KM4, KM6 and KM7 are closed.

[0116] When SCR=4, the switch code is 10010110, which means that KM2, KM3, KM5 and KM8 are open, and KM1, KM4, KM6 and KM7 are closed.

[0117] When SCR=10, the switch code is 01010110, which means that KM1, KM3, KM5 and KM8 are open, and KM2, KM4, KM6 and KM7 are closed.

[0118] When TCR=10%, the switch code is 00011101, indicating that KM1, KM2, KM3 and KM7 are open, and KM4, KM5, KM6 and KM8 are closed.

[0119] When TCR=40%, the switch code is 00011001, indicating that KM1, KM2, KM3, KM6 and KM7 are open, and KM4, KM5 and KM8 are closed.

[0120] When TCR=60%, the switch code is 00011010, indicating that KM1, KM2, KM3, KM6 and KM8 are open, and KM4, KM5 and KM7 are closed.

[0121] Example 7

[0122] This embodiment discloses a power grid impedance simulation device, design method, and usage method. As a preferred embodiment of the present invention, based on embodiment 6, in setting the switch logic control program, in order to avoid instantaneous short circuits caused by simultaneous operation of switches, it also includes designing the delayed switch operation logic sequence of the corresponding contactor for switching of different short-circuit ratios and series complement degrees, so that when a power grid operating condition switching command is received, the closing command in the switch code corresponding to the operating condition to be switched is executed first, and after executing the closing command, the opening command in the switch code corresponding to the operating condition to be switched is executed after a delay of 1-2 seconds.

[0123] Based on this, in step five of the method for using the power grid impedance simulation device, such as Figure 3 As shown, controlling the corresponding contactor to open or close includes the following steps:

[0124] Step 5.1: While maintaining the current switching state of all contactors, the controller reads the switching combination state corresponding to the simulated operating condition required for the test target from the power grid operating condition switching instruction;

[0125] Step 5.2: Match the switch codes according to the switch combination states corresponding to the simulated working conditions required by the test target;

[0126] Step 5.3: Execute the contactor closing action with the switch code set to 1;

[0127] Step 5.4, delay for 1-2 seconds to reduce the risk of instantaneous short circuit caused by switching action and improve the reliability of the power grid impedance simulation device;

[0128] Step 5.5: Perform the contactor disconnection action if the switch code is 0;

[0129] Step 5.6: Determine whether the contactor closing and opening actions corresponding to the simulated working conditions required by the current test target have been completed; if not, return to step 5.2; if yes, the current switching task ends.

[0130] Example 8

[0131] This embodiment discloses a power grid impedance simulation device, its design method, and its usage method. As a preferred embodiment of the present invention, based on Embodiment 7, taking the testing of a wind power converter as an example, the following component parameter calculations are performed:

[0132] Read the wind farm capacity and voltage data, such as the high-voltage side of the wind turbine transformer substation being 37kV and the unit capacity being 7MW, to obtain the basic value of the grid impedance. .

[0133] Using inductors Simulate the operating condition with a short-circuit ratio of 2.5 and calculate the inductance value. as follows:

[0134] .

[0135] According to inductance With inductance The series and parallel connections simulate the corresponding operating conditions with short-circuit ratios of 1.8 and 10, respectively, and the inductance values ​​are substituted. The inductance was then calculated. The value of The process is as follows:

[0136] .

[0137] inductance and inductor After parallel connection, the simulation of the corresponding operating condition with a short-circuit ratio of 4 is achieved by substituting the inductance value. The inductance was then calculated. The value of The process is as follows:

[0138] .

[0139] The calculations related to string complement are as follows:

[0140] With capacitor To simulate the corresponding operating condition with a series compensation of 40%, the capacitor... The capacitance value The calculation is as follows:

[0141] .

[0142] According to capacitance With capacitor The series and parallel connections simulate the corresponding operating conditions with series complement of 10 and 60 respectively, and the capacitance values ​​are substituted. The capacitance can then be calculated. The capacitance value :

[0143] .

[0144] According to the design of this invention, the short-circuit ratio and series compensation degree that can be formed are not limited to the combinations listed above. All technical solutions that fall within the scope of this invention are protected by this invention. For those skilled in the art, any improvements and modifications made without departing from the principle of this invention should also be considered within the scope of this invention.

Claims

1. A design method for a power grid impedance simulation device, characterized in that, A power grid impedance simulation device is obtained by sequentially performing component parameter calculation and selection, device hardware connection topology, and setting switch logic control program. Component parameter calculation and selection: Based on the simulation test requirements corresponding to the short-circuit ratio and series compensation degree, the required components are determined, including automatic slide wire rheostats, inductors, capacitors and contactors; based on the actual national standard for the short-circuit ratio corresponding to the converter test requirements, the quantity of each component and the value of electrical parameters are obtained by combining the principle of using the minimum number of components. Device hardware connection topology: The selected components are connected on demand. That is, the controller controls the on and off of the contactors and the adjustment of the automatic slide wire rheostat, so that the automatic slide wire rheostat and different inductors can simulate the working conditions corresponding to different short circuit ratios, different capacitor combinations can simulate the working conditions corresponding to series compensation degree, and the on and off of different contactors can switch between the working conditions corresponding to different short circuit ratios, between the working conditions corresponding to different series compensation degree, and between the working conditions corresponding to short circuit ratios and the working conditions corresponding to series compensation degree. Configure the switch logic control program: Configure the switch logic control program in the controller so that when the controller receives the power grid operating condition switching command, it can realize the switching between different short-circuit ratio corresponding operating conditions, different series complement corresponding operating conditions, and the switching between the short-circuit ratio corresponding operating condition and the series complement corresponding operating condition by executing the pre-set switch logic control program; For the switching of different short-circuit ratio and series complement corresponding operating conditions, design the corresponding contactor delay switch action logic sequence so that when the power grid operating condition switching command is received, the closing command in the switch code corresponding to the operating condition to be switched is executed first, and after executing the closing command, the opening command in the switch code corresponding to the operating condition to be switched is executed after a delay of 1-2 seconds.

2. The design method of the power grid impedance simulation device as described in claim 1, characterized in that, In the component parameter calculation and selection, the number of automatic slide wire rheostats is 1, represented by R, and its resistance range is [0, 40]Ω.

3. The design method of the power grid impedance simulation device as described in claim 1, characterized in that, In the calculation and selection of component parameters, obtaining the number of inductors includes the following steps: S11-11, Obtain the test requirements for the grid short-circuit ratio of the converter according to the national standard grid connection criteria, i.e., the short-circuit ratio... Tests were conducted under four typical operating conditions at 1.8, 2.5, 4, and 10. S11-12, the preset method first uses two sets of inductors to form the mains impedance, the two sets of inductors being inductance... and inductor ;inductance and inductor When connected in series, the mains impedance is at its maximum, and the short-circuit ratio is 1.8; inductance and inductor When connected in parallel, the grid impedance is at its minimum, and the short-circuit ratio is 10. S11-13, Take the inductor Simulate the operating condition with a short-circuit ratio of 2.5 independently; S11-14, for simulation of operating conditions with a short-circuit ratio of 4, provides inductors Add parallel inductor .

4. The design method of the power grid impedance simulation device as described in claim 3, characterized in that, In the calculation and selection of component parameters, the electrical parameters of the inductor are determined by the following steps; S11-21, Obtain the grid inductance value The calculation formula, namely ;in: Indicates the mains voltage; Indicates the grid-connected capacity of new energy sources; Indicates frequency; Indicates the short-circuit ratio; Indicates the short-circuit ratio condition, i.e. ; S11-22, based on inductance If a simulation of the operating condition with a short-circuit ratio of 2.5 is performed independently, then the grid inductance value is obtained. Calculate the inductance inductance value ; S11-23, based on the inductance and inductor By connecting them in series, the grid inductance value can be obtained. Based on inductance and inductor Parallel connection to obtain the grid inductance value ; S11-23, combining the formulas for calculating the grid inductance under the conditions of maximum and minimum grid impedance, derive the inductance value. With inductance value The product of, i.e. Substitute inductance inductance value Then an inductance is obtained. inductance value ; S11-24, based on inductance With inductance Parallel connection to obtain the grid inductance value Transformation to obtain Substitute inductance inductance value Then an inductance is obtained. inductance value .

5. The design method of the power grid impedance simulation device as described in claim 3, characterized in that, In the calculation and selection of component parameters, obtaining the number of capacitors includes the following steps: S12-11, select the working condition with short-circuit ratio SCR=1.8 and give the simulation requirements for three states with series complement TCR of 10%, 40% and 60% respectively; S12-12, Two sets of capacitors are pre-configured to meet the simulation requirements of the three states; wherein the two sets of capacitors are capacitors... and capacitor ; Take capacitor Achieve simulation of a working condition with a series complement ratio (TCR) of 40% independently; capacitance and capacitor The maximum analog series complement (TCR) of the capacitive reactance in series is 60%. capacitance and capacitor The minimum analog series complement (TCR) of the capacitive reactance in parallel is 10%.

6. The design method of the power grid impedance simulation device as described in claim 5, characterized in that, In the calculation and selection of component parameters, the electrical parameter values ​​of the capacitor include the following steps; S12-21, based on capacitor To simulate a working condition with a series complement ratio (TCR) of 40% independently, the formula is used. Calculate the capacitance The capacitance ;in Inductance The inductance value; Indicates frequency; S12-22, based on capacitor With capacitor For series operation, there is a formula for calculating the capacitance. Based on capacitance With capacitor For parallel operation, there is a formula for calculating the capacitance. ; S12-23, combined with capacitor With capacitor Formulas for calculating capacitance under series and parallel operating conditions are derived to obtain the capacitance value. With capacitor The product of the tolerance values, i.e. Substitute capacitor The capacitance Then the capacitance is obtained. The capacitance .

7. The design method of the power grid impedance simulation device as described in claim 5, characterized in that, In the calculation and selection of component parameters, the number of contactors is indeed based on the automatic sliding rheostat R and the inductor. ,inductance ,inductance ,capacitance and capacitors To meet the series and parallel connection requirements, 8 sets of contactors are preset, namely KM1, KM2, KM3, KM4, KM5, KM6, KM7, and KM8.

8. The design method of the power grid impedance simulation device as described in claim 7, characterized in that, In the hardware connection topology of the device, the on-demand connection of the selected components includes: the automatic slide wire rheostat R and contactors KM1-KM8 are respectively connected to the controller; using terminals A and B to represent the left and right ends of each component, then: Terminal A of the automatic slide wire rheostat R is the input terminal for the device, and terminal B of the automatic slide wire rheostat R is connected to the inductor. Connect to end A; inductance Terminal A is connected to the inductor via contactor KM1. Terminal A is connected, inductor B-terminal and inductor B-end connection; inductance Terminal A is connected to the inductor via contactor KM2. Terminal A is connected, inductor B-terminal and inductor B-end connection; capacitance Terminal A is connected to the inductor via contactor KM3. Terminal A is connected to the capacitor. Terminal B is connected to the inductor via contactor KM4. B-end connection; capacitance Terminal A is connected to capacitor via contactor KM5. Terminal A is connected, and the device output is also connected via contactor KM8; capacitor Terminal B is connected to the capacitor via contactor KM6. The B terminal is connected, and the output terminal of the device is connected via contactor KM7.

9. The design method of the power grid impedance simulation device as described in claim 8, characterized in that, The aforementioned switch logic control program includes editing the contactor switch code for different short-circuit ratios and series complement degrees corresponding to different operating conditions. Specifically, it uses 0 and 1 flag bits to represent the contactor's open and closed states, respectively, and encodes the switches in the order KM1-KM8. When SCR=1.8, the switch code is 00101001; When SCR=2.5, the switch code is 00010110; When SCR=4, the switch code is 10010110; When SCR=10, the switch code is 01010110; When TCR=10%, the switch code is 00011101; When TCR=40%, the switch code is 00011001; When TCR=60%, the switch code is 00011010.

10. A power grid impedance simulation device, characterized in that: Obtained by the design method described in any one of claims 1-9.

11. A method of using a power grid impedance simulation device, characterized in that, The power grid impedance simulation device is the power grid impedance simulation device as described in claim 10, and the method of using it includes the following steps: Step 1: Connect the input terminal of the power grid impedance simulation device to the converter under test, connect the output terminal of the simulation test device to the power grid, and set up a table showing the correspondence between simulated operating conditions and switch combination states. Step 2: Connect the controller of the power grid impedance simulation device to the host computer and start the power grid impedance simulation device to initialize it. Step 3: With the converter connected to the grid and started, according to the simulated operating conditions required by the test target, query the correspondence table between the simulated operating conditions and the switch combination, obtain the switch combination status corresponding to the required simulated operating conditions, and then use the host computer to switch the power grid operating conditions according to the corresponding switch combination status. Step 4: The controller determines whether it has received a power grid operating condition switching command; if yes, proceed to step 5; if no, proceed directly to step 6. Step 5: The controller controls the corresponding contactor to open or close and adjusts the automatic sliding rheostat according to the received power grid operating condition switching command, thereby completing the switching of the simulated operating conditions required for the test target. Step 6: Determine whether the current testing work is complete based on the testing requirements; if yes, proceed to Step 7; if no, return to Step 3. Step 7: The converter stops, the corresponding contactor is reset, and the grid impedance simulation device returns to the initialization state.

12. The method of using the power grid impedance simulation device as described in claim 11, characterized in that, Step five, controlling the corresponding contactor to open or close, includes the following steps: Step 5.1: While maintaining the current switching state of all contactors, the controller reads the switching combination state corresponding to the simulated operating condition required by the test target from the power grid operating condition switching instruction; Step 5.2: Match the switch codes according to the switch combination states corresponding to the simulated working conditions required by the test target; Step 5.3: Execute the contactor closing action with the switch code set to 1; Step 5.4, delay for 1-2 seconds; Step 5.5: Perform the contactor disconnection action if the switch code is 0; Step 5.6: Determine whether the contactor closing and opening actions corresponding to the simulated working conditions required by the current test target have been completed; if not, return to step 5.2; if yes, the current switching task ends.

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