Power grid impedance simulation device, design method and use method

Abstract

The invention belongs to the technical field of power systems, and particularly relates to a power grid impedance simulation device, a design method and a use method.The design of the device comprises the steps that the types of needed components are determined, and the number of the components and electrical parameter values are obtained according to the actual national standard in combination with the minimum component number criterion; all components are connected according to needs, and a controller is adopted to realize corresponding control so as to support working condition simulation and switching of different short circuit ratios and series compensation degrees; a switch logic control program is set in the controller, so that when the controller receives a power grid working condition switching instruction, switching of working conditions corresponding to the power grid short-circuit ratio and the series compensation degree is achieved by executing the preset switch logic control program. According to the technical scheme, through the integrated design of parameter calculation, hardware topology and logic control, the problems of low test efficiency, poor simulation precision and high cost in the prior art are solved, and an efficient, accurate and economical solution is provided for the adaptability test of the new energy converter under a double-high power system.

Description

Technical Field

[0001] The present invention belongs to the technical field of power systems, and in particular relates to a power grid impedance simulation device, a design method and a use method. Background Art

[0002] With the global push for clean energy, the use of new energy sources such as wind and solar power is becoming increasingly widespread in power systems. The large-scale integration of new energy sources has significantly changed the structure and characteristics of the power system, gradually transforming the power grid from a traditional system dominated by synchronous generators to a "double-high" power system characterized by a high proportion of new energy sources and a high level of power electronics. During this transformation, the system's short-circuit ratio has gradually decreased, and weak grid characteristics have become increasingly apparent, posing severe challenges to the stable operation of the power system. To ensure the stable operation of the "dual-high" power system, it is crucial to test the adaptability of new energy converters under low short-circuit ratio, variable short-circuit ratio, and variable string compensation conditions. However, current experimental testing methods have obvious flaws. After completing one set of short-circuit ratio tests, the existing testing method must shut down the system and rearrange the grid impedance before testing another set of short-circuit ratio conditions. This method is not only time-consuming and labor-intensive, but also fundamentally unable to simulate conditions where the grid short-circuit ratio changes in real time or suddenly, seriously affecting the efficiency of the test and the accurate simulation of actual grid operation. Although related invention patents have proposed online switchable grid impedance simulation devices, these devices still face numerous challenges in practical application. For one thing, existing devices only consider grid impedances composed of inductors. However, in actual testing, the actual grid impedance provided by power grid companies is often composed of resistance (R), inductance (L), and capacitance (C). This results in existing devices being unable to simulate variations in LC series compensation and the characteristics of RLC grid impedance, leading to significant deviations between test results and actual grid operation. Furthermore, existing technologies only provide switchable grid impedance combinations, focusing on variable or switchable inductance, but offer no guidance on component parameter selection or calculation methods for the simulation device. In field testing, simulation of specific grid short-circuit ratios (SCRs)—such as those required by grid connection permits or national standards (SCRs = 1.8, 2.5, 4, and 10)—is more important than the number of impedance combinations the device can accommodate. If the parameters of the grid short-circuit ratio simulation device are not properly selected during design, multiple impedance simulators and other external RLC systems will need to be connected in series and parallel to achieve the desired grid short-circuit ratio during actual testing. This will undoubtedly significantly increase testing costs and make the testing process more time-consuming, seriously hindering the efficient testing of new energy converters. In summary, the existing technology has obvious deficiencies in simulating grid series compensation and short-circuit ratio, and cannot meet the needs of adaptability testing of new energy converters under the "double-high" power system. Summary of the Invention

[0003] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and propose a grid impedance simulation device, design method and usage method. Through the integrated design of "parameter calculation-hardware topology-logic control", the problems of low testing efficiency, poor simulation accuracy and high cost in the prior art are solved, providing an efficient, accurate and economical solution for the adaptability test of new energy converters under the "dual-high" power system.

[0004] Specifically, the above objectives are achieved through the following technical solutions: A method for designing a power grid impedance simulation device is provided, wherein the power grid impedance simulation device is obtained by sequentially implementing component parameter calculation and selection, device hardware connection topology, and setting a switch logic control program.

[0005] Component parameter calculation and selection: Based on the simulation test requirements of the short-circuit ratio and series compensation corresponding working conditions, the required components including automatic sliding resistors, inductors, capacitors and contactors are determined; based on the actual national standard for the short-circuit ratio corresponding working conditions for converter testing, the minimum number of components criterion is used to obtain the number of components and the values ​​of electrical parameters.

[0006] Device hardware connection topology: The selected components are connected on demand, that is, the controller is used to control the on and off of the contactor and the adjustment of the automatic sliding resistor, so that the automatic sliding resistor can be coordinated with different inductors to realize the simulation of working conditions corresponding to different short-circuit ratios, and different capacitor combinations can realize the simulation of working conditions corresponding to series compensation degrees. The opening and closing coordination of different contactors can realize the switching 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.

[0007] Set the switch logic control program: Set the switch logic control program in the controller so that when the controller receives the grid operating condition switching instruction, it can realize the switching between the operating conditions corresponding to different short-circuit ratios, between the operating conditions corresponding to different series compensation degrees, and between the operating conditions corresponding to the short-circuit ratio and the operating conditions corresponding to the series compensation degree by executing the preset switch logic control program.

[0008] Preferably, in the calculation and selection of component parameters, the number of automatic sliding resistors is 1, represented by R, and the resistance range is [0, 40]Ω.

[0009] Preferably, in the component parameter calculation and selection, obtaining the inductance quantity includes the following steps: S11-11, obtain the test requirements of the national standard for the grid short-circuit ratio of the converter, that is, the short-circuit ratio Four typical working condition tests are conducted at 1.8, 2.5, 4 and 10 hours; S11-12, it is preset that two groups of inductors are used to form the grid impedance. The two groups of inductors are inductors and inductance ;inductance and inductance When connected in series, the grid impedance is the largest, and the short-circuit ratio is 1.8; and inductance When connected in parallel, the grid impedance is minimum and the short-circuit ratio is 10; S11-13, take the inductance Achieve the simulation of the working condition with a short-circuit ratio of 2.5 independently; S11-14, for the simulation of the working condition with a short circuit ratio of 4, give the inductor Adding a parallel inductor .

[0010] Preferably, in the component parameter calculation and selection, obtaining the electrical parameter values ​​of the inductor includes the following steps: S11-21, obtain the grid inductance value The calculation formula is ;in: Indicates the grid voltage; Indicates the grid-connected capacity of new energy; Indicates frequency; Indicates short-circuit ratio; Indicates the short-circuit ratio condition, that is ; S11-22, inductor-based If the short-circuit ratio is 2.5, the grid inductance value is , calculate the inductance Inductance value ; S11-23, based on the inductance and inductance The series connection of the grid inductance is obtained ; Based on inductance and inductance The parallel connection of the grid inductance is obtained ; S11-23, combined with the grid inductance calculation formula under the maximum and minimum grid impedance conditions, derive the inductance value With inductor The product of ; Substitute the inductor Inductance value , then the inductance is obtained Inductance value ; S11-24, inductor-based With inductor The parallel connection of the grid inductance is obtained , transform to obtain ; Substitute the inductor Inductance value , then the inductance is obtained Inductance value .

[0011] Preferably, in the component parameter calculation and selection, obtaining the number of capacitors includes the following steps: S12-11, select the working condition when the short circuit ratio SCR=1.8 and give the simulation requirements of three states with series compensation TCR of 10%, 40% and 60% respectively; S12-12, it is preset that two groups of capacitors are used to meet the three state simulation requirements; the two groups of capacitors are capacitors and capacitors ; Capacitor Achieve the simulation of the working condition with a series compensation TCR of 40% independently; capacitance and capacitors When connected in series, the maximum simulated series compensation TCR of the capacitive reactance is 60%; capacitance and capacitors When connected in parallel, the minimum simulated series compensation TCR of the capacitive reactance is 10%.

[0012] Preferably, in the component parameter calculation and selection, the electrical parameter determination of the capacitor includes the following steps: S12-21, capacitor-based To simulate the working condition of 40% series compensation TCR separately, the formula Calculate the capacitance Capacitance ;in Inductance Inductance value; Indicates frequency; S12-22, capacitor-based With capacitor The series working condition has the capacitance calculation formula ; Based on capacitance With capacitor The capacitance calculation formula is: ; S12-23, combined with capacitor With capacitor The capacitance calculation formula under series and parallel conditions is derived to obtain the capacitance With capacitor The product of the capacitance, that is ; Substitute the capacitor Capacitance , then the capacitance is obtained Capacitance .

[0013] Preferably, in the calculation and selection of component parameters, the number of contactors is indeed based on the automatic sliding resistor R, inductor ,inductance ,inductance ,capacitance and capacitors To meet the series and parallel requirements, 8 groups of contactors are preset, namely KM1, KM2, KM3, KM4, KM5, KM6, KM7 and KM8.

[0014] Preferably, in the hardware connection topology of the device, the on-demand connection of the selected components includes: the automatic sliding resistor R and the contactors KM1-KM8 are connected to the controller respectively; the A end and the B end represent the left and right ends of each component, then: the A end of the automatic sliding resistor R is the device acquisition input end, and the B end of the automatic sliding resistor R is connected to the inductor. The A end of the inductor is connected; The A end of the contactor KM1 and the inductor The A terminal of the inductor is connected The B terminal and the inductor The B terminal of the inductor is connected; The A end of the contactor KM2 and the inductor The A terminal of the inductor is connected The B terminal and the inductor The B terminal of the capacitor is connected; The A end of the contactor KM3 and the inductor The A terminal is connected to the capacitor The B end of the contactor KM4 and the inductor The B terminal of the capacitor is connected; The A end of the contactor KM5 is connected to the capacitor The A terminal is connected to the output terminal of the device through the contactor KM8; the capacitor The B end of the contactor KM6 is connected to the capacitor The B end is connected to the output end of the device through the contactor KM7.

[0015] Preferably, the setting of the switch logic control program includes editing the contactor switch code for different short-circuit ratios and series compensation corresponding working conditions, that is, using 0 and 1 flag bits to represent the opening and closing of the contactor respectively, and encoding 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.

[0016] Preferably, the setting of the switch logic control program also includes designing the delayed switching action logic sequence of the corresponding contactor for switching of working conditions corresponding to different short-circuit ratios and series compensation degrees, so that when a power grid working condition switching instruction is received, the closing instruction in the switch code corresponding to the working condition to be switched is executed first, and after executing the closing instruction, the opening instruction in the switch code corresponding to the working condition to be switched is executed after a delay of 1-2 seconds.

[0017] This technical solution proposes a power grid impedance simulation device, which is obtained through the above-mentioned design method.

[0018] The method for using the above-mentioned power grid impedance simulation device comprises the following steps: Step 1: Connect the device acquisition input of the grid impedance simulation device to the converter to be tested, connect the device output of the simulation test device to the grid, and set a table of correspondence between simulated working conditions and switch combination states; Step 2: Connect the controller of the grid impedance simulation device to the host computer, start the grid impedance simulation device, and initialize the grid impedance simulation device; Step 3: When the converter is connected to the grid and started, query the corresponding relationship table between the simulated working condition and the switch combination according to the simulated working condition required by the test target, obtain the switch combination state corresponding to the required simulated working condition, and use the host computer to issue the power grid working condition switching instruction according to the corresponding switch combination state; Step 4: The controller determines whether it has received a grid operating mode switching instruction; if so, it proceeds to step 5; if not, it directly proceeds to step 6; Step 5: The controller controls the opening or closing of the corresponding contactor and adjusts the automatic sliding resistor according to the received grid operating condition switching instruction, thereby completing the switching of the simulated operating condition required by the test target; Step 6: Determine whether the current test work is completed according to the test requirements; if so, proceed to step 7; if not, return to step 3; Step 7: The converter is shut down, the corresponding contactor is reset, and the grid impedance simulation device returns to the initialization state.

[0019] Preferably, in step 5, controlling the corresponding contactor to open or close includes the following steps: Step 5.1: Under the condition of maintaining the current switch states of all contactors, the controller reads the switch combination state corresponding to the simulated working condition required by the test target in the grid working condition switching instruction; Step 5.2, matching the switch code according to the switch combination state corresponding to the simulated working condition required by the test target; Step 5.3, execute the contactor closing action with switch code 1; Step 5.4, delay 1s-2s; Step 5.5, execute the contactor disconnection action with the switch code as 0; Step 5.6, determine whether the contactor closing and opening actions corresponding to the simulated working conditions required by the current test target are completed; if not, return to step 5.2; if so, the current switching task is completed.

[0020] Beneficial effects of the present invention: 1. Solve the inefficiency problem of existing test methods in stopping and changing working conditions, and realize dynamic real-time switching Switching between short-circuit ratio and series compensation conditions without downtime: This device utilizes a controller to control contactor switching and automatic sliding rheostat adjustment, enabling online switching between different short-circuit ratio and series compensation conditions. For example, through pre-set contactor switching codes and delay logic, the controller automatically switches impedance upon receiving a command, eliminating time-consuming downtime and significantly improving testing efficiency.

[0021] Dynamic simulation of grid parameter mutation conditions: The present invention can achieve rapid switching of working conditions (such as 1-2s delayed switching) through the switch logic control program, and can reproduce the working conditions of short-circuit ratio mutation in the actual power grid, making the test closer to the real operation scenario.

[0022] 2. Considering both RLC impedance characteristics and series compensation corresponding working condition simulation to improve test accuracy Complete simulation of the RLC impedance characteristics of actual power grids: This invention uses a combination of an automatic sliding resistor, an inductor, and a capacitor to accurately simulate RLC series or parallel impedance. For example, by combining capacitors and inductors in series and parallel, it simulates changes in series compensation. This overcomes the limitation of existing technologies that cannot simulate LC series compensation, making test results more accurate than actual power grid operation.

[0023] Covering typical short-circuit ratio and series compensation conditions required by national standards: This invention, based on national standards for converter testing (e.g., SCR = 1.8, 2.5, 4, 10), combined with RLC parameter calculation methods, accurately replicates grid weakness (short-circuit ratio) and compensation levels (series compensation). For example, different short-circuit ratios can be achieved by combining three inductors in series and parallel, and different series compensation levels can be achieved by combining two capacitors in series and parallel, avoiding test deviations caused by improper parameter selection in existing technologies.

[0024] 3. Optimize component parameter selection to reduce testing costs and complexity Parameter calculation method based on the minimum number of components: Compared to existing devices that lack a parameter selection method, requiring multiple impedance simulators and resulting in high costs, this presents a scientific parameter calculation logic: For inductor selection, a single set of inductors is used to achieve an SCR of 2.4. Two sets of inductors are connected in series and parallel to achieve SCRs of 1.8 and 10, and an additional set of inductors is added in parallel to achieve an SCR of 4, covering four short-circuit ratio conditions with only three sets of inductors. For capacitor selection, two sets of capacitors are connected in series and parallel to achieve TCRs of 10%, 40%, and 60%, meeting the series compensation requirements with only two sets of capacitors. For resistor selection, a single automatic sliding 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.

[0025] Eliminates the tedious 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 uses precise parameter calculation to enable the device to automatically combine the required impedance, eliminating the need for external components and simplifying the testing process.

[0026] 4. Automated control and logic design to improve operational convenience and safety Contactor coding and delay logic enable automated switching: This invention utilizes contactor switch coding and delayed action logic to avoid momentary short circuits during switching, improving device reliability. For example, when switching between operating conditions, the controller first executes the close command and then the open command after the circuit stabilizes, preventing component damage.

[0027] Host computer communication and one-touch operating mode switching: In operation, commands are sent from the host computer, and the controller automatically matches the switch code and executes the switch switching, without manual intervention. For example, the tester only needs to query the "Simulated Operating Condition-Switch Combination Table" and send a command from the host computer, and the device automatically completes the impedance reconstruction, reducing operational complexity and human error.

[0028] 5. Standardized design adapts to national standard testing requirements and has strong scalability The design method of this invention is based on typical short-circuit ratio operating conditions for converter testing as specified in national standards. The parameter calculation process can be flexibly adjusted based on actual grid requirements. For example, if a new operating condition is required, only a few components need to be added to the existing topology or the switch coding needs to be modified, without requiring a complete hardware redesign. This provides superior adaptability and scalability compared to existing fixed-circuit devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a diagram showing the structure of a power grid impedance simulation device and its operating principle; Figure 2 A flowchart for the use of a power grid impedance simulation device structure; Figure 3 This is the action flow chart for switching simulation working conditions. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0031] Therefore, the following detailed description of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0032] Example 1 This embodiment discloses a power grid impedance simulation device, a design method, and a method of use. As a preferred implementation scheme of the present invention, its design method is to obtain a power grid impedance simulation device by sequentially implementing component parameter calculation and selection, device hardware connection topology, and setting a switch logic control program.

[0033] Component parameter calculation and selection: Determine the required component types based on the simulation test requirements of the short-circuit ratio and series compensation corresponding working conditions; based on the short-circuit ratio working conditions required by the actual national standard for converter testing, combine the minimum number of components criterion to obtain the number of components and electrical parameter values.

[0034] The short-circuit ratio (SCR) of the power grid is essentially the ratio of the short-circuit capacity of the AC busbar of the power grid to the rated capacity of the connected converter. Its mathematical expression is: ( is the short-circuit capacity, is the rated capacity of the converter). When the grid impedance increases, the short-circuit capacity decreases, the SCR value decreases, and the system stability decreases accordingly. The series compensation ratio (TCR) is the ratio of the compensation capacity of the series capacitor to the line transmission capacity, and the expression is ( is the capacitive 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.

[0035] The automatic sliding resistor continuously adjusts the resistance value by changing the length of the resistance wire connected to the circuit. Its principle is based on Ohm's law, that is, ( is the resistivity, is the resistance wire length, The inductor component generates inductive reactance in the circuit based on the principle of electromagnetic induction. ( Indicates frequency, Indicates the inductance value) and is used to simulate the inductive impedance of the power grid. Capacitor components generate capacitive reactance according to the capacitance characteristics. ( (where is the capacitance value) is used to offset some inductive impedance in the simulation of the series compensation operating condition. Contactors use electromagnetic mechanisms to control the opening and closing of contacts. The principle is that energizing the electromagnetic coil generates a magnetic field, which attracts the armature and drives the contacts, thus switching the circuit.

[0036] In summary, this technical solution determines that the required component types include automatic sliding resistors, inductors, capacitors and contactors based on the power grid short-circuit ratio and series compensation corresponding working condition simulation test requirements.

[0037] The short-circuit ratio conditions required by the actual national standard for converter testing are typical scenarios based on the actual degree of grid weakness. ( is the rated voltage, The calculation logic of the equivalent impedance of the power grid is to select the model by the principle of minimum number of components, which is to apply the circuit equivalent transformation principle (such as star-delta transformation and impedance series-parallel formula) to meet the requirements of ( is the error impedance, Optimize the component combination under the accuracy of (target impedance).

[0038] Device hardware connection topology: The selected components are connected on demand, and the controller is used to control the on and off of the contactor and the adjustment of the automatic sliding resistor, so that the automatic sliding resistor can be coordinated with different inductors to realize the simulation of working conditions corresponding to different short-circuit ratios, and different capacitor combinations can realize the simulation of working conditions corresponding to series compensation degrees. The opening and closing coordination of different contactors can realize switching 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.

[0039] The controller can be a PLC (Programmable Logic Controller) or MCU (Micro Control Unit), which controls the contactor coil voltage through the digital output port (DO), and uses the on and off of the contactor main contacts to build different impedance circuits. The automatic sliding resistor can be driven by a servo motor to move the slider. The servo motor pulse number and resistance value follow ( is the maximum resistance, The number of pulses =Total pulse number) linear relationship, combined with the controller's PWM (pulse width modulation) signal for continuous regulation. The capacitors and inductors adopt a modular parallel structure, with contactor switches combining capacitance and inductance values ​​to simulate operating conditions with varying short-circuit ratios and series compensation.

[0040] Set the switch logic control program: Set the switch logic control program in the controller so that when the controller receives the grid operating condition switching instruction, it can realize the switching between the operating conditions corresponding to different short-circuit ratios, between the operating conditions corresponding to different series compensation degrees, and between the operating conditions corresponding to the short-circuit ratio and the operating conditions corresponding to the series compensation degree by executing the preset switch logic control program.

[0041] The switch logic control program can be designed based on a state machine model, defining state nodes such as the initial state, standby state, switching state, and operating state. State transition conditions include command reception, component state feedback (such as the DI input of the contactor auxiliary contact), time delay (such as waiting for stabilization after a preset time interval after switching), etc. Furthermore, the logic can be written in 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 switch logic control program calculates the required component combination through a table lookup method, generates a contactor action sequence, and prevents short circuits through hardware interlocking logic (for example, two contactors in the same branch cannot be closed at the same time).

[0042] According to the above design method, a grid impedance simulation device is obtained, and the grid impedance simulation device is applied to practice, that is, a method for using the grid impedance simulation device is provided, such as Figure 2 As shown, the following steps are included: Step 1, such as Figure 1 As shown, connect the grid impedance simulation device's acquisition input to the converter under test, connect the simulation test device's output to the grid, and create a table that maps simulated operating conditions to switch combination states. This mapping relationship between physical connections and electrical parameters ensures the device accurately senses the converter's operating status and outputs simulated grid impedance. This pre-configured mapping table allows for quick recall of operating conditions, significantly reducing manual configuration time and improving testing efficiency.

[0043] The table of correspondence between simulated working conditions and switch combination states is a mapping table of simulated working conditions and contactor switch codes shown in Table 1 below:

[0044] Step 2: Communicate with the host computer via Ethernet (IEEE 802.3 standard) or RS485 (Modbus-RTU protocol), using the communication protocol compliant with DL / T634.5104-2009, to implement command transmission and data exchange. The grid impedance simulator is activated and initialized. This initialization process may include: ① Contactor status verification (reading the auxiliary contact status via the DI port to ensure that all contactors are in the preset state); ② Component parameter self-test (such as detecting the initial position of a rheostat and testing the capacitor withstand voltage); and ③ Controller register reset (such as resetting PID control parameters). This process follows the PLC's scan cycle mechanism to ensure synchronization of module states.

[0045] In step three, with the converter connected to the grid and started, the system queries the table that maps simulated operating conditions to switch combinations based on the desired simulated operating conditions (corresponding to the grid's vulnerability and compensation level). The corresponding switch combination state is retrieved, and the host computer issues switching instructions based on the power grid operating conditions under the corresponding switch combination state. The goal is to enable the grid impedance simulator to replicate typical operating conditions of the actual grid, providing standardized grid conditions for converter testing. Digital command transmission enables precise control of operating conditions, avoiding errors associated with manual adjustment of component parameters.

[0046] In step 4, the controller uses a scanning cycle mechanism (such as scanning the DO port once every 10ms) to detect the instruction reception status and determine whether the grid operating condition switching instruction has been received; if so, it proceeds to step 5; if not, it directly proceeds to step 6.

[0047] In step 5, the controller controls the opening or closing of the corresponding contactor and adjusts the automatic sliding resistor according to the received grid operating condition switching instruction, thereby completing the switching of the simulated operating condition required by the test target.

[0048] Step 6: Determine whether the current test work is completed based on the test requirements; if so, proceed to step 7; if not, return to step 3.

[0049] Step 7: The converter is shut down, the corresponding contactor is reset, and the grid impedance simulation device returns to the initialization state.

[0050] Example 2 This embodiment discloses a power grid impedance simulation device, design method and use method. As a preferred implementation scheme of the present invention, based on Example 1, the automatic sliding resistor selects high power, the number is 1, and it is represented by R. It is only necessary to design the upper limit of the resistance value. Considering that the equivalent resistance of most power grids in actual tests is within 8-22Ω, in order to ensure design redundancy, the resistance range of the automatic sliding resistor is [0, 40]Ω.

[0051] Example 3 This embodiment discloses a power grid impedance simulation device, design method, and use method. As a preferred embodiment of the present invention, based on Example 1 or Example 2, in the calculation and selection of component parameters, the inductance quantity and electrical parameter values ​​are obtained as follows: Obtain the test requirements for the short-circuit ratio of the power grid in the national standard of the converter grid access standard, that is, the short-circuit ratio Four typical operating conditions were tested when the short circuit ratio (SCR) was 1.8, 2.5, 4 and 10. Based on the test requirements of the national standard for wind power converters for grid access with a short circuit ratio (SCR) of 1.8, 2.5, 4 and 10, and substituted into the grid impedance calculation formula, the grid inductance value can be obtained. On this basis, the grid inductance value is deduced based on the inductance configuration principle of the mapping relationship between electromagnetic induction and short circuit ratio. The calculation formula , the grid inductance value The calculation formula is Converted to get. Among them: Indicates short-circuit ratio; Indicates the short-circuit ratio condition, that is ; Indicates the grid voltage; Indicates the grid-connected capacity of new energy; is the reference value of the grid impedance, denoted as ; is the inductor impedance, , Indicates frequency.

[0052] To achieve the simulation of four working conditions, at least two groups of inductance units are required to be connected in series and parallel. This technical solution takes economic optimization into consideration and aims to achieve the simulation of four typical working conditions with SCR of 1.8, 2.5, 4 and 10 with the least inductance. That is, it is preset to first use two groups of inductances to form the grid impedance. The two groups of inductances are inductances. and inductance .inductance and inductance When connected in series, the grid impedance is the largest, and the short-circuit ratio is 1.8; and inductance When connected in parallel, the grid impedance is minimum and the short-circuit ratio is 10. This allows the simulation of the corresponding operating conditions with SCRs of 1.8 and 10, respectively, and .

[0053] Combined with the above grid inductance calculation formula under the maximum and minimum grid impedance conditions, the inductance value is derived and inductance value The product of . Take the inductance To simulate the working condition with a short circuit ratio of 2.5, the grid inductance value Calculate the inductance Inductance value . Inductance value Substitute the inductance value and inductance value The inductance can be calculated by multiplying the formula Inductance value .

[0054] After actual testing, when only the inductor is used When SCR=7.2, the corresponding working condition simulation of SCR=4 cannot be achieved. Adding a parallel inductor , and In the case of parallel connection, the corresponding working condition simulation of SCR=4 is realized, so the grid inductance value is , transform to obtain ; Substitute the inductor Inductance value , then the inductance is obtained Inductance value .

[0055] In summary, in this technical solution, the number of inductors is 3, which are inductors ,inductance and inductance , the corresponding electrical parameters are inductance , inductance value and inductance value .

[0056] Example 4 This embodiment discloses a power grid impedance simulation device, design method, and use method. As a preferred embodiment of the present invention, based on Example 3, in the calculation and selection of component parameters, the number of capacitors and the values ​​of electrical parameters are obtained as follows: The purpose of connecting capacitors is to simulate different series compensation TCRs of the power grid. Considering that series compensation is generally installed when the power grid is relatively weak to reduce the grid impedance, the grid impedance simulation device of this technical solution selects the working condition when SCR=1.8 to give three state simulation requirements of series compensation of 10%, 40%, and 60%, respectively, and then implements the electrical parameter value of the capacitor. Considering the economy, it is preset to use two groups of capacitors to meet the three state simulation requirements; the two groups of capacitors are capacitors and capacitors .capacitance and capacitors When connected in series, the maximum simulated series compensation TCR of the capacitive reactance is 60%, and the capacitance and capacitors When connected in parallel, the minimum simulated series compensation of the capacitive reactance TCR is 10%, when connected in series, the maximum simulated series compensation of the capacitive reactance is 60%, and when connected in parallel, the minimum simulated series compensation of the capacitive reactance is 10%. .

[0057] Combined Capacitor With capacitor The capacitance calculation formula under series and parallel conditions is derived to obtain the capacitance With capacitor The product of the capacitance, that is . Take the capacitor To simulate the working condition of 40% series compensation TCR separately, the formula Calculate the capacitance Capacitance . The capacitor Capacitance Bring in capacitors With capacitor The capacitance can be calculated by multiplying the capacitance value by Capacitance .

[0058] In summary, in this technical solution, the number of capacitors is 2, which are capacitors and capacitors , the corresponding electrical parameters are capacitance and capacitance .

[0059] Example 5 This embodiment discloses a grid impedance simulation device, design method and use method. As a preferred embodiment of the present invention, based on Example 4, in the calculation and selection of component parameters, the number of contactors is indeed based on the automatic sliding resistor R, the inductor ,inductance ,inductance ,capacitance and capacitors To meet the series and parallel requirements, 8 groups of contactors are preset, namely KM1, KM2, KM3, KM4, KM5, KM6, KM7 and KM8.

[0060] On this basis, in the device hardware connection topology, the selected components are connected on demand, including: connecting the automatic sliding resistor R and contactors KM1-KM8 to the controller respectively; using the A end and the B end to represent the left and right ends of each component, then: the A end of the automatic sliding resistor R is the device acquisition input end, which is used to connect to the converter; the B end of the automatic sliding resistor R is connected to the inductor The A terminal of the inductor is connected. The A end of the contactor KM1 and the inductor The A terminal of the inductor is connected The B terminal and the inductor The B terminal of the inductor is connected. The A end of the contactor KM2 and the inductor The A terminal of the inductor is connected The B terminal and the inductor The B terminal of the capacitor is connected. The A end of the contactor KM3 and the inductor The A terminal is connected to the capacitor The B end of the contactor KM4 and the inductor The B terminal of the capacitor is connected. The A end of the contactor KM5 is connected to the capacitor The A terminal is connected to the output terminal of the device through the contactor KM8; the capacitor The B end of the contactor KM6 is connected to the capacitor The output terminal of the device is used to connect to the power grid or voltage source.

[0061] Example 6 This embodiment discloses a grid impedance simulation device, design method, and use method. As a preferred embodiment of the present invention, based on Example 5, in setting the switch logic control program, the contactor switch coding is edited according to the corresponding working conditions of different short-circuit ratios and series compensation degrees. That is, the flag bits 0 and 1 are used to represent the opening and closing of the contactor, respectively, and the coding is performed in the order of KM1-KM8. Then: When SCR=1.8, the switch code is 00101001, indicating that KM1, KM2, KM4, KM6 and KM7 are disconnected, and KM3, KM5 and KM8 are closed.

[0062] When SCR=2.5, the switch code is 00010110, indicating that KM1, KM2, KM3, KM5 and KM8 are disconnected, and KM4, KM6 and KM7 are closed.

[0063] When SCR=4, the switch code is 10010110, indicating that KM2, KM3, KM5 and KM8 are disconnected, and KM1, KM4, KM6 and KM7 are closed.

[0064] When SCR=10, the switch code is 01010110, indicating that KM1, KM3, KM5 and KM8 are disconnected, and KM2, KM4, KM6 and KM7 are closed.

[0065] When TCR=10%, the switch code is 00011101, indicating that KM1, KM2, KM3 and KM7 are disconnected, and KM4, KM5, KM6 and KM8 are closed.

[0066] When TCR=40%, the switch code is 00011001, indicating that KM1, KM2, KM3, KM6 and KM7 are disconnected, and KM4, KM5 and KM8 are closed.

[0067] When TCR=60%, the switch code is 00011010, indicating that KM1, KM2, KM3, KM6 and KM8 are disconnected, and KM4, KM5 and KM7 are closed.

[0068] Example 7 This embodiment discloses a grid impedance simulation device, design method, and use method. As a preferred implementation scheme of the present invention, based on Example 6, in setting the switch logic control program, in order to avoid instantaneous short circuit caused by simultaneous operation of switches, it also includes designing a delayed switching action logic sequence of the corresponding contactors for switching of working conditions corresponding to different short-circuit ratios and series compensation degrees, so that when a grid working condition switching instruction is received, the closing instruction in the switch code corresponding to the working condition to be switched is executed first, and after executing the closing instruction, the opening instruction in the switch code corresponding to the working condition to be switched is executed after a delay of 1-2 seconds.

[0069] Based on this, in step 5 of the method for using the grid impedance simulation device, if Figure 3 As shown, controlling the corresponding contactor to open or close includes the following steps: Step 5.1: Under the condition of maintaining the current switch states of all contactors, the controller reads the switch combination state corresponding to the simulated working condition required by the test target in the grid working condition switching instruction; Step 5.2, matching the switch code according to the switch combination state corresponding to the simulated working condition required by the test target; Step 5.3, execute the contactor closing action with switch code 1; Step 5.4: Delay for 1s-2s to reduce the risk of instantaneous short circuit caused by switching action and improve the reliability of the grid impedance simulation device; Step 5.5, execute the contactor disconnection action with the switch code as 0; Step 5.6, determine whether the contactor closing and opening actions corresponding to the simulated working conditions required by the current test target are completed; if not, return to step 5.2; if so, the current switching task is completed.

[0070] Example 8 This embodiment discloses a grid impedance simulation device, design method, and usage method. As a preferred embodiment of the present invention, based on Example 7, taking a wind power converter test as an example, the following component parameter calculations are performed: Read the wind farm capacity and voltage data, such as the high-voltage side of the wind power transformer is 37kV and the unit capacity is 7MW, and get the grid impedance base value .

[0071] Using inductors Achieve the corresponding working condition simulation of short circuit ratio 2.5 and calculate the inductance value as follows: .

[0072] According to the inductance With inductor The series and parallel connections simulate the corresponding working conditions of short-circuit ratios of 1.8 and 10 respectively, and substitute the inductance value Then convert it to inductance The value of , the process is as follows: .

[0073] inductance and inductance After parallel connection, the corresponding working condition simulation with a short-circuit ratio of 4 is realized, and the inductance value is substituted Then convert it to inductance The value of , the process is as follows: .

[0074] The calculation of series compensation is as follows: Capacitor To achieve the corresponding working condition simulation of 40% series compensation, the capacitor Capacitance The calculation is as follows: .

[0075] According to the capacitance With capacitor The series and parallel connections simulate the corresponding working conditions of 10 and 60 series compensation respectively, and substitute the capacitance value The capacitance can be calculated Capacitance : .

[0076] According to the design content of the present invention, the short-circuit ratio and series compensation that can be composed are not limited to the combinations listed above. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. For ordinary technicians in this technical field, several improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A design method for a power grid impedance simulation device, characterized in that: The grid impedance simulation device is obtained by sequentially implementing the calculation and selection of component parameters, the device hardware connection topology and the setting of the switch logic control program; Component parameter calculation and selection: Based on the simulation test requirements of the short-circuit ratio and series compensation corresponding working conditions, the required components, including automatic sliding resistors, inductors, capacitors, and contactors, are determined. Based on the actual national standard for converter testing requirements corresponding to the short-circuit ratio working conditions, the minimum component quantity principle is used to determine the number of components and electrical parameter values. Device hardware connection topology: Implementation of on-demand connection of selected components, i.e., using a controller to control the on / off of the contactor and the adjustment of the automatic sliding resistor, so that the automatic sliding resistor can be coordinated with different inductors to simulate working conditions corresponding to different short-circuit ratios, and different capacitor combinations can simulate working conditions corresponding to series compensation degrees. The on / off coordination of different contactors can realize switching 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. Set the switch logic control program: Set the switch logic control program in the controller so that when the controller receives the grid operating condition switching instruction, it can realize the switching between the operating conditions corresponding to different short-circuit ratios, between the operating conditions corresponding to different series compensation degrees, and between the operating conditions corresponding to the short-circuit ratio and the operating conditions corresponding to the series compensation degree by executing the preset switch logic control program.

2. The method for designing a grid impedance simulation device according to claim 1, wherein: In the component parameter calculation and selection, the number of automatic sliding resistors is 1, represented by R, and the resistance range is [0, 40]Ω.

3. The design method of a power grid impedance simulation device according to claim 1, characterized in that: In the component parameter calculation and selection, obtaining the inductance quantity includes the following steps: S11-11, obtain the test requirements of the national standard for the grid short-circuit ratio of the converter, that is, the short-circuit ratio Four typical working condition tests are conducted at 1.8, 2.5, 4 and 10 hours; S11-12, it is preset that two groups of inductors are used to form the grid impedance. The two groups of inductors are inductors and inductance ;inductance and inductance When connected in series, the grid impedance is the largest, and the short-circuit ratio is 1.8; and inductance When connected in parallel, the grid impedance is minimum and the short-circuit ratio is 10; S11-13, take the inductance Achieve the simulation of the working condition with a short-circuit ratio of 2.5 independently; S11-14, for the simulation of the working condition with a short circuit ratio of 4, give the inductor Adding a parallel inductor .

4. The design method of a power grid impedance simulation device according to claim 3, characterized in that: In the component parameter calculation and selection, the electrical parameter values ​​of the inductor include the following steps: S11-21, obtain the grid inductance value The calculation formula is ;in: Indicates the grid voltage; Indicates the grid-connected capacity of new energy; Indicates frequency; Indicates short-circuit ratio; Indicates the short-circuit ratio condition, that is ; S11-22, inductor-based If the short-circuit ratio is 2.5, the grid inductance value is , calculate the inductance Inductance value ; S11-23, based on the inductance and inductance The series connection of the grid inductance is obtained ; Based on inductance and inductance The parallel connection of the grid inductance is obtained ; S11-23, combined with the grid inductance calculation formula under the maximum and minimum grid impedance conditions, derive the inductance value and inductance value The product of ; Substitute the inductor Inductance value , then the inductance is obtained Inductance value ; S11-24, inductor-based With inductor The parallel connection of the grid inductance is obtained , transform to obtain ; Substitute the inductor Inductance value , then the inductance is obtained Inductance value .

5. The design method of a power grid impedance simulation device according to claim 3, characterized in that: In the component parameter calculation and selection, obtaining the number of capacitors includes the following steps: S12-11, select the working condition when the short circuit ratio SCR=1.8 and give the simulation requirements of three states with series compensation TCR of 10%, 40% and 60% respectively; S12-12, it is preset that two groups of capacitors are used to meet the three state simulation requirements; the two groups of capacitors are capacitors and capacitors ; Capacitor Achieve the simulation of the working condition with a series compensation TCR of 40% independently; capacitance and capacitors When connected in series, the maximum simulated series compensation TCR of the capacitive reactance is 60%; capacitance and capacitors When connected in parallel, the minimum simulated series compensation TCR of the capacitive reactance is 10%.

6. A method for designing a grid impedance simulation device according to claim 5, characterized in that: In the component parameter calculation and selection, the electrical parameter values ​​of the capacitor include the following steps: S12-21, capacitor-based To simulate the working condition of 40% series compensation TCR separately, the formula Calculate the capacitance Capacitance ;in Inductance Inductance value; Indicates frequency; S12-22, capacitor-based With capacitor The series working condition has the capacitance calculation formula ; Based on capacitance With capacitor The capacitance calculation formula is: ; S12-23, combined with capacitor With capacitor The capacitance calculation formula under series and parallel conditions is derived to obtain the capacitance With capacitor The product of the capacitance, that is ; Substitute the capacitor Capacitance , then the capacitance is obtained Capacitance .

7. The method for designing a grid impedance simulation device according to claim 5, wherein: In the calculation and selection of component parameters, the number of contactors is indeed based on the automatic sliding resistor R, inductor ,inductance ,inductance ,capacitance and capacitors To meet the series and parallel requirements, 8 groups of contactors are preset, namely KM1, KM2, KM3, KM4, KM5, KM6, KM7 and KM8.

8. A method for designing a grid impedance simulation device according to claim 7, characterized in that: In the device hardware connection topology, the selected components are connected on demand, including: the automatic sliding resistor R and contactors KM1-KM8 are connected to the controller respectively; using the A and B terminals to represent the left and right ends of each component, we have: The A end of the automatic sliding resistor R is the device collection input end, and the B end of the automatic sliding resistor R is connected to the inductor The A end of the connection; inductance The A end of the contactor KM1 and the inductor The A terminal of the inductor is connected The B terminal and the inductor The B end of the connection; inductance The A end of the contactor KM2 and the inductor The A terminal of the inductor is connected The B terminal and the inductor The B end of the connection; capacitance The A end of the contactor KM3 and the inductor The A terminal is connected to the capacitor The B end of the contactor KM4 and the inductor The B end of the connection; capacitance The A end of the contactor KM5 is connected to the capacitor The A terminal is connected to the output terminal of the device through the contactor KM8; the capacitor The B end of the contactor KM6 is connected to the capacitor The B end is connected to the output end of the device through the contactor KM7.

9. A method for designing a grid impedance simulation device according to claim 8, characterized in that: The switch logic control program is set up, including editing the contactor switch code for different short-circuit ratios and series compensation degrees corresponding to the working conditions, that is, using 0 and 1 flags to represent the opening and closing of the contactor respectively, and coding 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.

10. The method for designing a grid impedance simulation device according to claim 9, wherein: The setting of the switch logic control program also includes designing the delayed switching action logic sequence of the corresponding contactor for switching of working conditions corresponding to different short-circuit ratios and series compensation degrees, so that when a grid working condition switching instruction is received, the closing instruction in the switch code corresponding to the working condition to be switched is executed first, and after executing the closing instruction, the opening instruction in the switch code corresponding to the working condition to be switched is executed after a delay of 1-2 seconds.

11. A power grid impedance simulation device, characterized in that: The method is obtained by the design method as claimed in any one of claims 1 to 10.

12. A method for using a power grid impedance simulation device, characterized in that: The grid impedance simulation device is a grid impedance simulation device according to claim 11, and the method of using the device comprises the following steps: Step 1: Connect the device acquisition input of the grid impedance simulation device to the converter to be tested, connect the device output of the simulation test device to the grid, and set a table of correspondence between simulated working conditions and switch combination states; Step 2: Connect the controller of the grid impedance simulation device to the host computer, start the grid impedance simulation device, and initialize the grid impedance simulation device; Step 3: When the converter is connected to the grid and started, query the corresponding relationship table between the simulated working condition and the switch combination according to the simulated working condition required by the test target, obtain the switch combination state corresponding to the required simulated working condition, and use the host computer to issue the power grid working condition switching instruction according to the corresponding switch combination state; Step 4: The controller determines whether it has received a grid operating mode switching instruction; if so, it proceeds to step 5; if not, it directly proceeds to step 6; Step 5: The controller controls the opening or closing of the corresponding contactor and adjusts the automatic sliding resistor according to the received grid operating condition switching instruction, thereby completing the switching of the simulated operating condition required by the test target; Step 6: Determine whether the current test work is completed according to the test requirements; if so, proceed to step 7; if not, return to step 3; Step 7: The converter is shut down, the corresponding contactor is reset, and the grid impedance simulation device returns to the initialization state.

13. A method for using a grid impedance simulation device according to claim 12, characterized in that: In step 5, controlling the corresponding contactor to open or close includes the following steps: Step 5.1: Under the condition of maintaining the current switch states of all contactors, the controller reads the switch combination state corresponding to the simulated working condition required by the test target in the grid working condition switching instruction; Step 5.2, matching the switch code according to the switch combination state corresponding to the simulated working condition required by the test target; Step 5.3, execute the contactor closing action with switch code 1; Step 5.4, delay 1s-2s; Step 5.5, execute the contactor disconnection action with the switch code as 0; Step 5.6, determine whether the contactor closing and opening actions corresponding to the simulated working conditions required by the current test target are completed; if not, return to step 5.2; if so, the current switching task is completed.

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