A frequency conversion drive access system and control method suitable for a coal mine high-voltage power grid

Abstract

The application discloses a variable frequency drive access system and control method suitable for a coal mine high-voltage power grid, and particularly relates to the technical field of coal mine power system access control. Firstly, the voltage grade, power grid topology structure, grounding mode, system impedance, power grid load change curve and bus transient stability coefficient of the coal mine high-voltage power grid are acquired to construct a dynamic stability model; then the output voltage, current harmonic component, impact current, voltage change rate and carrier frequency of the variable frequency drive equipment are acquired as disturbance input for multi-scene simulation to extract bus response indexes; the polynomial regression model is used to predict the interference level coefficient, and the interference level coefficient is compared with a safety threshold value to screen a target access parameter group, determine an access path and a buffer modulation strategy, generate a control instruction and transmit the control instruction to a main control unit to realize stable access of the equipment in the high-voltage power grid; and the application improves the adaptability and safety of the variable frequency equipment access and is suitable for dynamic control requirements in a complex power grid environment.

Description

Technical Field

[0001] This invention relates to the field of coal mine power system access control technology, specifically to a frequency converter drive access system and control method suitable for coal mine high-voltage power grids. Background Technology

[0002] Large-scale electrical equipment in coal mines (such as scraper conveyors, belt conveyors, and hoists) commonly employs variable frequency drive (VFD) technology to improve operating efficiency and energy saving. However, coal mine main power supply systems often use high-voltage power (e.g., 10kV and above) and are characterized by complex grounding methods, large short-circuit currents, low system impedance, and unbalanced loads. When VFD-driven equipment is connected to such high-voltage power grids, it is highly susceptible to instability phenomena such as high-frequency harmonic injection, bus voltage drops, increased system voltage fluctuations, and grounding current disturbances. These instabilities are further amplified in the confined and humid underground environment, potentially leading to frequent tripping of the VFD equipment and operational interruptions. Furthermore, it can also cause grid resonance, resulting in widespread harmonic pollution.

[0003] Especially in coal mines where frequency converters are densely distributed at the working face, the traditional centralized access or direct series connection method often ignores the dynamic response capability of the high-voltage bus under transient overload, and cannot accurately match the dynamic change characteristics of various frequency converter loads, resulting in difficulties in voltage stability control. Summary of the Invention

[0004] The purpose of this invention is to provide a frequency converter drive access system and control method suitable for high-voltage power grids in coal mines, so as to solve the shortcomings in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a frequency converter drive access system and control method suitable for high-voltage power grids in coal mines, comprising:

[0006] Obtain the set of high-voltage power grid characteristic parameters P of the target coal mine power supply system, including voltage level, power grid topology, grounding method, system impedance Z, power grid load variation curve L, and bus transient stability coefficient T;

[0007] Based on the parameter set P, a dynamic stability model M of the target power grid is constructed to reflect the dynamic response capability of the power grid bus to the access disturbance under different disturbance scenarios.

[0008] Obtain the set of device parameters V of the variable frequency drive device to be connected, including output voltage, current harmonic components, inrush current I, voltage change rate du / dt and carrier frequency f;

[0009] Input the set of equipment parameters V into the dynamic stability model M, and obtain the set of bus response indicators R under each access scheme based on multi-scenario disturbance simulation;

[0010] Based on the bus response index set R, the access interference level coefficient D is calculated and compared with the preset safety threshold value Ds to select the target access parameter group V′ that meets the Ds condition.

[0011] Based on the access parameter group V′, determine the dynamic access path and buffer modulation strategy of the target frequency converter drive device, and generate the corresponding control commands;

[0012] The control commands are transmitted to the high-voltage power grid main control unit to complete the stable connection of the target frequency converter in the high-voltage power grid.

[0013] Preferably, the dynamic stability model M of the target power grid is constructed, including:

[0014] Based on the power grid topology, a node-branch graph is constructed, and the main power supply path and key node set are extracted using graph theory analytical methods.

[0015] By combining the system impedance and grounding method, an equivalent RLC branch is introduced into the busbar of each node to construct a set of time-domain state equations;

[0016] By introducing the power grid load change curve and the bus transient stability coefficient as disturbance inputs, and using multi-scenario disturbance simulation, the voltage response sequence of each bus is solved.

[0017] Based on the voltage response sequence, the offset rate and stabilization time are used as criteria to output the stability evaluation results under various disturbance conditions, forming the dynamic stability model M of the target power grid.

[0018] Preferably, the set of equipment parameters V is input into the dynamic stability model M, including:

[0019] The current harmonic components and voltage change rate in the equipment parameter set are used as disturbance source signals and injected into the corresponding positions of key nodes in the dynamic stability model M.

[0020] By combining load change curves and inrush current, multiple typical disturbance scenarios are constructed to form a disturbance simulation input matrix;

[0021] The state equations are solved step by step using the time-domain numerical integration method to obtain the bus voltage response data of key nodes under various disturbance scenarios;

[0022] For each set of simulation results, the voltage offset rate, stabilization time deviation value, and waveform distortion rate fluctuation value are extracted to generate the corresponding bus response index set R.

[0023] Preferably, for each set of simulation results, the voltage offset rate, stabilization time deviation value, and waveform distortion rate fluctuation value are extracted, including:

[0024] The bus voltage response data output from the disturbance simulation is normalized to establish a standard voltage reference curve;

[0025] Calculate the ratio of the maximum deviation between the actual voltage offset value and the standard voltage in each set of response curves, and extract the voltage offset rate.

[0026] Identify the time required for the bus voltage to recover from the maximum deviation to the set stable threshold, calculate the difference between the time and the rated stabilization time, and extract the stabilization time deviation value;

[0027] The fluctuation amplitude of harmonic components in the bus voltage is extracted using the spectrum analysis method, and the waveform distortion rate fluctuation value is generated.

[0028] Preferably, the interference level coefficient D is calculated based on the bus response index set R, including: converting the voltage offset rate, stabilization time deviation value and waveform distortion rate fluctuation value into a comprehensive feature vector; using the comprehensive feature vector as the input of a machine learning model; the machine learning model uses the prediction of the interference level coefficient value label for each set of comprehensive feature vectors as the prediction objective; and uses minimizing the sum of prediction errors for all interference level coefficient value labels as the training objective. The machine learning model is trained until the sum of prediction errors converges, at which point the model training stops. The interference level coefficient D is determined based on the model output results. The machine learning model is a multinomial regression model.

[0029] Preferably, the interference level coefficient D is normalized; the normalized interference level coefficient is compared with the preset safety threshold value Ds one by one, and the access parameter group with the interference level coefficient less than or equal to the safety threshold value is selected to generate the target access parameter group V′.

[0030] Preferably, based on the access parameter group V′, the dynamic access path and buffer modulation strategy of the target frequency converter drive device are determined, and corresponding control commands are generated, including:

[0031] Based on the equipment parameters and power grid characteristics in the target access parameter group V′, analyze and determine the optimal access path for the frequency converter drive equipment, and select the optimal power grid node and branch as the access point.

[0032] Based on the access path, voltage fluctuations are smoothed and instantaneous current surges are reduced by adjusting the start-up frequency and voltage step mode of the frequency converter drive equipment.

[0033] The buffer modulation strategy and dynamic access path information are converted into control commands to generate precise access commands for variable frequency drive equipment, which are used to control the equipment's startup timing and power regulation.

[0034] Control commands are sent to the frequency converter drive device via the communication interface.

[0035] The technical effects and advantages provided by the present invention in the above technical solution are as follows:

[0036] 1. This invention analyzes the access parameters of variable frequency drive equipment and grid characteristics, combines machine learning models to predict interference level coefficients, and smoothly controls the equipment startup process according to the access path and buffer modulation strategy, significantly improving the stability and safety of equipment connected to the high-voltage grid. By optimizing the access path, startup frequency, and voltage regulation mode, it can effectively reduce grid load fluctuations, avoid sudden voltage rises or falls, and reduce the risk of mutual interference between the grid and the equipment.

[0037] 2. This invention ensures the dynamic adaptability of variable frequency drive equipment during the grid connection process through real-time monitoring and intelligent adjustment, enabling the equipment to flexibly adjust under different load and grid conditions, thus optimizing the utilization efficiency of grid resources. This technical solution can significantly improve the stability and safety of high-voltage grids in coal mines, while reducing the risk of equipment failure, providing a reliable solution for high-voltage grid connection in complex industrial environments such as coal mines. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0039] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] For examples, please refer to Figure 1 As shown in this embodiment, a frequency converter drive access system and control method suitable for high-voltage power grids in coal mines includes:

[0042] Obtain the set of high-voltage power grid characteristic parameters P of the target coal mine power supply system, including voltage level, power grid topology, grounding method, system impedance Z, power grid load change curve L, and bus transient stability coefficient T.

[0043] First, the core electrical characteristics of the target coal mine's power supply network need to be comprehensively acquired and parameterized to form a complete set of high-voltage power grid characteristic parameters P. This parameter set P consists of the following six categories of parameters: voltage level, power grid topology, grounding method, system impedance, power grid load variation curve, and bus transient stability coefficient. In this embodiment, the definition and acquisition methods of each parameter are as follows:

[0044] The voltage level refers to the line voltage value of the target coal mine power supply network bus under rated operating conditions. This value can be collected through sampling data from on-site voltage transformers and verified in conjunction with the primary electrical drawings. If there are multiple bus levels, their nominal voltage and operating voltage range should be calibrated one by one, and the recorded values ​​should be in kilovolts (kV).

[0045] The power grid topology reflects the connection relationships and topological form between substations, busbars, feeders, and load units in the high-voltage power supply network of a coal mine. Using a graph modeling approach, each transformer, circuit breaker, and cable node is defined as a node in the graph, and their electrical connections are defined as edges, forming a topology graph Tg=(N,E), where N is the set of nodes and E is the set of edges.

[0046] By analyzing the electrical schematic diagram and on-site wiring data of the target power supply area, a topology identification algorithm is used to perform network analysis and output graph structure data for subsequent modeling.

[0047] Grounding method refers to the grounding form of the neutral point or protective conductor in a coal mine's high-voltage power supply network under normal operation and fault conditions. According to the national standard GB 50059 and coal mine design drawings, common grounding methods are divided into: direct grounding, grounding through a resistor, grounding through an arc suppression coil, and no grounding.

[0048] The calibration results are recorded using type codes (such as G1, G2, G3, G4) by measuring the voltage variation characteristics from the neutral point to ground and combining the results with the zero-sequence current detection.

[0049] System impedance is defined as the combined equivalent reactance and resistance of the target high-voltage power supply network from the main power supply node to the frequency converter drive access point under power frequency conditions, and the unit is ohms (Ω).

[0050] The impedance method was used for actual measurement. The specific operation was as follows: a stable load was applied during the selected test period, and the three-phase bus voltage U and feeder current I were collected. The system impedance Z was calculated using the vector ratio method. The calculation formula is: System Impedance Where U and I are both effective values ​​in complex form, and are represented by phasors during calculation. The resistance and reactance components are extracted for calibration.

[0051] The power grid load change curve L is the active power change trend curve of the target power supply network in different operating periods, in kilowatts (kW), with a time interval of 5 minutes.

[0052] Real-time active power data P(t) is collected continuously for 72 hours by smart energy meters and recorders installed at the bus end. The data is plotted with time t on the horizontal axis and power P on the vertical axis to form a function L(t), which is used to represent the load change trend on a typical operating day.

[0053] The load change curve is used to evaluate the load superposition response when the variable frequency drive is connected, and is used as the input for transient calculation in subsequent modeling.

[0054] The bus transient stability coefficient T is defined as the bus's ability to maintain voltage stability under short-time disturbance conditions, and its unit is per second. The larger the value, the stronger the busbar's ability to absorb disturbances.

[0055] The disturbance response test method is adopted. By applying a standard disturbance (such as the connection or disconnection of frequency converter equipment) within the control time window, the bus voltage response U(t) is recorded, and the maximum voltage deviation ΔU and the settling time τ are calculated to establish the following mathematical relationship: Bus transient stability coefficient This coefficient reflects the speed at which the power grid recovers from voltage disturbances caused by the connection of frequency converter loads, and is a key fundamental parameter for constructing dynamic simulation models.

[0056] In summary, the set of high-voltage power grid characteristic parameters P={U,Tg,Gx,Z,L(t),T} constructed by the above method is as follows: U is the voltage level, Tg is the topology diagram, Gx is the grounding mode code, Z is the system impedance, L(t) is the load curve function, and T is the bus transient stability coefficient.

[0057] Based on the parameter set P, a dynamic stability model M of the target power grid is constructed to reflect the dynamic response capability of the power grid bus to the access disturbance under different disturbance scenarios.

[0058] Based on the power grid topology in parameter set P, a node-branch diagram is established by defining each busbar, transformer, and feeder connection point as a node, and defining the electrical connections between different nodes as branches. The node set of the diagram is denoted as N, and the branch set is denoted as E. Each branch records its impedance parameters, voltage level, and connection direction.

[0059] Based on the node-branch graph, a graph theory analytical method is used for path analysis. All power supply paths from the main power supply node to each load node are extracted through a depth-first search. The path with the shortest electrical distance and the highest power flow density is identified as the main power supply path.

[0060] Based on the main power supply path, the node with the highest sensitivity to power flow changes is identified as the critical node, forming a critical node set Nkey. This set will be used as the basis for node selection in the subsequent construction of the time-domain equations.

[0061] Based on the system impedance and grounding method in parameter set P, equivalent resistance, inductance, and capacitance structures are established for each branch in the node-branch diagram, forming an equivalent RLC branch. The resistance component of the equivalent RLC branch is determined by the real part of the ratio of the measured phase voltage to the phase current, the inductance component is calculated by combining the imaginary part of the above ratio with the power frequency angular velocity, and the capacitance component is determined based on the measured value of the node-to-ground capacitance.

[0062] The equivalent RLC branches are combined according to the node-branch topology, and a set of time-domain state equations relating node voltages and branch currents is established using Kirchhoff's current law and voltage law. Each node voltage is used as a state variable, and each branch current is used as a constraint variable, forming a set of first-order differential equations that constitute the mathematical basis of the dynamic stability model M.

[0063] The number of equations is determined by the number of nodes. For each key node, a corresponding node voltage equation must be established to ensure that the model can accurately reflect the bus voltage change under local disturbance conditions.

[0064] The power grid load variation curve in the parameter set P is used as an external power disturbance input and applied as a time function to the load node position corresponding to the critical node, so that the equation system can simulate the dynamic disturbance caused by the actual coal mine load changing with time during the solution process.

[0065] Meanwhile, the bus transient stability coefficient is used as a disturbance suppression factor in the model. By introducing this coefficient into the state equations, the equations can adjust the voltage recovery rate according to the bus transient stability coefficient when a disturbance occurs, thus reflecting the true transient recovery capability of the bus.

[0066] Based on the aforementioned disturbance input, the time-domain state equations are solved step-by-step using a numerical integration method to obtain the voltage response sequence of each key node within a preset simulation period. This sequence is output at intervals of 0.01 seconds to reflect the transient voltage variation trend of the bus under different disturbance conditions.

[0067] By analyzing the voltage response sequence, two stability criteria were calculated: bus voltage deviation rate and stabilization time. The voltage deviation rate is defined as the ratio of the maximum voltage deviation to the rated voltage, and the stabilization time is defined as the time required for the voltage to recover to a deviation rate of less than 5%.

[0068] Using the two criteria mentioned above as evaluation standards, the response sequences under different disturbance conditions are scored to form a stability evaluation result set. This result set is used to characterize the steady-state maintenance capability of the target power grid under different disturbance scenarios.

[0069] Finally, the node-branch diagram, time-domain state equations, voltage response sequences, and stability evaluation results are combined in a unified structure to form a complete dynamic stability model M of the target power grid. Model M can reflect the bus dynamic response capability of the target high-voltage power grid in the face of different disturbances during actual operation.

[0070] Obtain the set of device parameters V of the variable frequency drive device to be connected, including output voltage, current harmonic components, inrush current I, voltage change rate du / dt and carrier frequency f.

[0071] The output voltage is the effective value of the three-phase AC line voltage from the output terminal to the load terminal of the frequency converter drive equipment under stable operating conditions, expressed in volts (V). The measurement method is as follows: using a metrology-certified three-phase digital voltmeter or sampling transmitter, voltage data is collected continuously for 30 seconds at the output terminal under the equipment's rated operating conditions, and the average value during the stable phase is selected as the final output voltage. This parameter is used to evaluate the equipment's adaptability to bus voltage levels.

[0072] Harmonic current components refer to the high-frequency harmonic current amplitude and frequency characteristics other than the fundamental frequency contained in the output current of variable frequency drive equipment during operation. They are usually expressed as harmonic order and total harmonic distortion rate, with units of percentage (%) or amplitude / frequency pairs.

[0073] A high-precision power quality analyzer is used to collect the output current signal under rated load conditions. The frequency domain is decomposed by the fast Fourier transform algorithm to extract the amplitude and corresponding frequency of the first 15 harmonic currents and calculate the total harmonic distortion rate (THDi). This value is used to assess the degree of impact of the equipment on the harmonic pollution of the power grid.

[0074] The inrush current is the maximum instantaneous peak value of the output current during the startup or switching of operating modes of a variable frequency drive device, measured in amperes (A). The measurement method is as follows: In a simulated startup scenario, a current transformer with a high sampling frequency (not less than 10 kHz) and a data acquisition instrument are installed on the output side to continuously monitor the current waveform, capture the peak current at the moment of startup, and extract and record the maximum value as the inrush current. This parameter is used to simulate transient impacts on the power grid in disturbance simulations.

[0075] The voltage change rate du / dt refers to the rate of change of the output voltage of a frequency converter drive device per unit time, usually expressed in volts per microsecond (V / μs). It is an important indicator reflecting the device's ability to withstand impacts on the insulation system and sensitive loads.

[0076] A high-frequency oscilloscope was used to sample the voltage waveform at the inverter output, recording the rise and fall slopes of the voltage waveform during the switching cycle. The maximum rate of change was calculated and used as the du / dt index input to the model. Excessively high du / dt values ​​may lead to bus insulation aging or resonant triggering.

[0077] The carrier frequency is the carrier signal frequency set during the pulse width modulation control process inside the frequency converter drive equipment. The unit is Hertz (Hz), and it is usually between 2 kHz and 20 kHz.

[0078] The carrier frequency setting can be read directly from the device panel parameter menu or obtained by retrieving the configuration file through the communication interface. This frequency directly affects the harmonic distribution characteristics and interference propagation path, and is an important input factor for harmonic disturbance modeling in simulation.

[0079] Finally, the above five parameters—output voltage, current harmonic components, inrush current, voltage change rate, and electrical carrier frequency—are combined to form a complete parameter set V for the variable frequency drive equipment, as shown below:

[0080] The device parameter set V = {output voltage U_out, current harmonic characteristics H_i, inrush current I_peak, voltage change rate du / dt, carrier frequency f_c}

[0081] The parameter set V will be loaded as an input variable into the dynamic stability model M to simulate the disturbance effect of the target variable frequency drive equipment on the high voltage power grid bus of the coal mine under different operating conditions, providing a basis for the calculation of the disturbance level coefficient and the formulation of control strategies.

[0082] Input the set of equipment parameters V into the dynamic stability model M, and obtain the set of bus response indicators R for each access scheme based on multi-scenario disturbance simulation.

[0083] The key disturbance factors in the equipment parameter set V, namely the current harmonic components and the voltage change rate, are used as the main disturbance source signals to simulate the transient impact and continuous disturbance behavior on the target bus voltage characteristics when the frequency converter drive equipment is connected.

[0084] The current harmonic components are multiple harmonic components obtained through frequency domain decomposition, represented as a spectrum vector consisting of the harmonic order and its corresponding amplitude, denoted as... , where n represents the harmonic order, A represents the amplitude, and k is the total number of harmonic components. This vector will be used as a periodic current disturbance function, injected into the key node branch connected to the frequency converter in the model, affecting the branch current variable and introducing a high-frequency dynamic response.

[0085] The voltage change rate du / dt represents the slope of the output voltage change per unit time. Its physical meaning is the steepness of the voltage edge at the inverter output terminal, and its unit is volts per microsecond. This value is modeled using the first derivative of the input voltage change function u(t) and constructed as a time-domain impulse function. In the simulation, it directly acts on the initial conditions of the bus voltage state variable to simulate the voltage disturbance effect at the moment of connection.

[0086] To comprehensively reflect the equipment disturbance behavior under different operating conditions, a disturbance scenario set needs to be constructed based on two additional dynamic variables in the equipment parameter set V: the inrush current and the grid load change curve. Each scenario is a specific combination of disturbance inputs, forming a disturbance input matrix denoted as S={s1,s2,…,sm}, where m is the total number of disturbance scenarios. Each si group includes: a set of current harmonic spectra Hi; the corresponding voltage change rate du / dt; the inrush current value I_peak at startup; and a certain segment of the grid load change curve Li(t). By combining the above four types of disturbance source parameters, no fewer than 10 typical disturbance scenarios are set, covering typical operating conditions such as light load, high load, frequent start-stop, and high-frequency harmonic excitation. This input matrix will be loaded as an external input variable into the solution process of the state equation system of the simulation model.

[0087] The constructed disturbance input matrices are loaded one by one into the time-domain state equations established in the dynamic stability model M. The state equations are a set of first-order differential equations based on bus node voltages and branch currents, and their structure satisfies the following mathematical relationship: In the formula, This represents the voltage at node i, in volts (V). The equivalent capacitance of the grounded branch at node i is expressed in farads (F). This represents the resistance of the branch between node i and its adjacent node j, expressed in ohms (Ω). The inductance of the branch between node i and node j is expressed in Henry (H). This represents the current in the branch between nodes i and j, expressed in amperes (A). This represents the time function of the input disturbance current source, such as current harmonic injection or impulse current, and is expressed in amperes (A). The voltage of adjacent node j is expressed in volts (V); n: the number of all adjacent nodes connected to node i.

[0088] To solve the above system of equations, a time-domain numerical integration method is introduced. The fourth-order Runge-Kutta method is used to advance the state variables step by step over time, with a time step size set to 0.01 seconds and a total simulation duration of 30 seconds, ensuring complete coverage of the disturbance occurrence and stabilization process.

[0089] Each set of disturbance inputs will output a set of bus voltage response curves as a function of time, denoted as U_i(t), where i represents the i-th disturbance scenario, t represents the simulation time axis, and U is the amplitude sequence of the bus voltage.

[0090] To quantitatively analyze the impact of frequency converter drive equipment disturbance behavior on bus voltage stability, three key indicators are extracted from each set of response curves U_i(t): voltage deviation rate, voltage stabilization time deviation value, and waveform distortion rate fluctuation value, forming a complete set of bus response indicators R_i.

[0091] The calculation method for voltage deviation rate includes: first, normalizing the response data U_i(t), and using the rated bus voltage value U_ref as a reference to form a standard voltage reference curve U_ref(t). Voltage deviation rate is defined as the ratio of the maximum deviation of the bus voltage relative to the reference voltage curve during the response process, expressed as: Voltage deviation rate E_dev = maximum value |U_i(t) – U_ref(t)| ÷ U_ref; this value represents the degree of maximum instantaneous voltage deviation caused by the disturbance and is an important characteristic parameter for judging the intensity of the disturbance.

[0092] The method for extracting the stabilization time deviation value includes: monitoring the time period during which the bus voltage recovers from its maximum deviation state to the allowable stable range after a deviation occurs. The voltage stability tolerance threshold is set to ±5%, meaning that voltage stabilization is determined when U_i(t) recovers to within ±5% of U_ref(t) and remains unchanged for more than 5 seconds. The stabilization time deviation value is the difference between the actual stabilization time τ_i and the rated stabilization time τ_ref: Stabilization Time Deviation Value Where τ_ref is the preset bus design stabilization time (e.g., 3 seconds). This indicator is used to measure the degree of matching between disturbance elimination speed and bus recovery capability.

[0093] The method for extracting waveform distortion rate fluctuation values ​​includes: performing a Fourier transform on the simulated output voltage waveform U_i(t) over the entire simulation period to extract the spectral signal and identify harmonic components higher than the fundamental frequency (50 Hz). The waveform distortion rate fluctuation value is defined as the maximum amplitude fluctuation of the total harmonic content during the simulation period, expressed as: Waveform distortion rate fluctuation value D_dev = Maximum value THD_i(t) – Minimum value THD_i(t); where THD_i(t) represents the total harmonic distortion rate at simulation time t. A larger value indicates a more severe impact of disturbances on the integrity of the voltage waveform, necessitating restrictions on the access of such devices.

[0094] Finally, the three indicators extracted from the simulation results of each disturbance scenario are summarized into a bus response indicator set, which is represented as: Bus response indicator set R_i={voltage offset rate E_dev, stabilization time deviation value T_dev, waveform distortion rate fluctuation value D_dev}. R_i under all disturbance scenarios are uniformly archived for subsequent calculation of interference level coefficient and determination of whether the access threshold condition is met.

[0095] Based on the bus response index set R, the access interference level coefficient D is calculated and compared with the preset safety threshold value Ds to select the target access parameter group V′ that meets the condition Ds.

[0096] The voltage offset rate, stabilization time deviation value, and waveform distortion rate fluctuation value are converted into a comprehensive feature vector. The comprehensive feature vector is used as the input of the machine learning model. The machine learning model uses the prediction of the interference level coefficient value label of each set of comprehensive feature vectors as the prediction objective and the minimization of the sum of prediction errors for all interference level coefficient value labels as the training objective. The machine learning model is trained until the sum of prediction errors converges and the model training stops. The interference level coefficient D is determined based on the model output. The machine learning model is a multinomial regression model.

[0097] The normalized interference level coefficients are compared one by one with the preset safety threshold value Ds. Access parameter sets V′ with interference level coefficients less than or equal to Ds are selected. These access parameter sets V′ are used as target access parameter sets for subsequent control strategy formulation and execution. The target access parameter set V′ includes parameter combinations of frequency converter drives that ensure grid stability and safety when connected to the coal mine's high-voltage power grid.

[0098] Based on the access parameter group V′, the dynamic access path and buffer modulation strategy of the target frequency converter drive device are determined, and the corresponding control commands are generated.

[0099] Based on the variable frequency drive equipment parameters (such as rated voltage, power requirements, and starting inrush current) contained in the target access parameter group V′, and the grid characteristics (such as voltage level, grounding method, impedance distribution, and bus voltage stability), a grid load and power flow analysis is first performed to determine the grid node at the access point. This step is implemented in the following specific way:

[0100] Grid node selection: Based on the grid topology and the power requirements of the target frequency converter drive equipment, select the grid bus node that is closest to and can meet the equipment's power requirements. This node should have the minimum voltage drop, the minimum current load variation, and ensure that the connection of the equipment has no significant impact on the stability of the grid.

[0101] Branch selection: Analyze the current carrying capacity and voltage fluctuation characteristics of each power grid branch, and select a branch with high stability as the equipment access path to ensure that the equipment will not cause significant power grid fluctuations or impacts during startup.

[0102] The optimal access path is determined by using power flow optimization algorithms and node selection strategies.

[0103] Once the access path is determined, the next step is to design a buffer modulation strategy suitable for that path. The core objective of this strategy is to smooth out voltage fluctuations and instantaneous current surges that may occur during the startup process of the frequency converter drive by controlling the startup frequency and voltage stepping mode. The specific implementation is as follows:

[0104] Startup frequency control: During equipment startup, the instantaneous current surge in the system is reduced by gradually increasing the operating frequency of the variable frequency drive. Specifically, starting from zero frequency, the frequency is slowly increased according to a set frequency step rule (such as increasing by 1 Hz or 5% per step) until the equipment reaches its rated operating frequency. The frequency increase process should comply with the grid's carrying capacity to avoid large voltage fluctuations.

[0105] Voltage Stepping Mode: Sets a voltage stepping curve to ensure the output voltage of the variable frequency drive equipment increases gradually. The voltage stepping mode setting can be adjusted according to the characteristics of the power grid connected to the circuit to avoid sudden voltage changes. For example, the voltage starts from 0V and gradually increases according to the set voltage step size (such as increasing the rated voltage by 5% per step) until the rated voltage of the equipment is reached.

[0106] By using a smooth voltage fluctuation algorithm and a current surge optimization model, a buffer modulation strategy suitable for this grid access path is designed.

[0107] The buffer modulation strategy is combined with the determined access path information and transformed into control commands for the variable frequency drive equipment. The control command generation process includes the following steps:

[0108] Startup timing control: Based on the access path information and buffer modulation strategy, the specific startup timing of the device is set. The control command ensures that the startup voltage and current of the device at each stage do not exceed the load capacity of the power grid by precisely scheduling the startup time of each step.

[0109] Power regulation control: Based on a buffer modulation strategy, the power demand at each stage is calculated to ensure a smooth transition in power output of the frequency converter drive at each frequency and voltage step, avoiding grid overload or voltage drop. Control commands include power regulation parameters to ensure that current and voltage changes are linear and smooth.

[0110] The generated control commands are sent to the frequency converter drive equipment via the communication interface to achieve precise control of the equipment. The communication interface can use industrial standard communication protocols (such as Modbus, CAN, etc.) to transmit control commands from the power grid main control system to the control unit of the frequency converter equipment.

[0111] The specific transmission process includes:

[0112] Control commands are encoded in the form of data packets to ensure that all control parameters (start-up frequency, voltage step mode, power regulation, etc.) can be accurately transmitted to the frequency converter.

[0113] After receiving the instruction, the device executes the startup process step by step according to the instruction content to ensure that voltage fluctuations and current surges are minimized when the device is connected to the power grid.

[0114] The control commands are transmitted to the high-voltage power grid main control unit to complete the stable connection of the target frequency converter in the high-voltage power grid.

[0115] In the preceding steps, through detailed analysis and scheduling, precise control commands for the variable frequency drive equipment were generated. These commands contain the following key information:

[0116] Equipment start-up frequency: Specifies the frequency stepping mode required for the variable frequency drive equipment to go from startup to stable operation;

[0117] Voltage regulation step mode: Sets a gradual voltage increase mode according to power grid characteristics and equipment requirements;

[0118] Power regulation control parameters: Set a gradual power output adjustment scheme based on the access path and equipment power requirements;

[0119] Start-up sequence and timing: Ensure that the variable frequency drive equipment can execute according to the specified sequence at each stage to avoid grid fluctuations.

[0120] Control commands will be encoded using a standardized data format. The encoding format converts the command content into data packets, including but not limited to the following:

[0121] Control command header: includes command type, timestamp, device identifier, command version number, etc.;

[0122] Control command text: includes specific control parameters such as equipment start-up frequency, voltage regulation step, current limit, and power regulation;

[0123] Verification information: Used to ensure the integrity and correctness of instructions.

[0124] This encoding format ensures the reliability and recognizability of instructions, facilitating transmission via communication protocols.

[0125] The generated and encoded control commands are transmitted to the main control unit of the coal mine high-voltage power grid through a reliable communication interface. The specific operation is as follows:

[0126] Communication protocol selection: Based on the compatibility between the power grid management system and the frequency converter drive equipment, industry-standard communication protocols such as Modbus RTU / TCP, CAN, and Ethernet / IP are adopted to ensure efficient and stable data transmission. Each control command data packet is packaged into a frame format that conforms to the protocol requirements;

[0127] Data transmission: Control commands are transmitted from the control terminal to the frequency converter drive equipment via wired or wireless networks. Common data transmission media include Ethernet connections, fiber optic links, and wireless transmission. During transmission, packet segmentation and acknowledgment mechanisms are employed to ensure that each command accurately reaches the target device without data loss or corruption.

[0128] After the control command is transmitted to the power grid main control unit, the system will confirm receipt, including but not limited to:

[0129] CRC check: Checks whether data packets have been corrupted or lost during transmission;

[0130] Confirmation feedback received: The device returns confirmation information to ensure that the instruction has been successfully received.

[0131] After receiving the instruction, the main control unit controls the access behavior of the frequency converter according to the instruction content to ensure that the equipment starts smoothly according to the preset timing sequence.

[0132] After receiving the control command, the power grid main control unit begins to execute the specific connection operation. The specific steps are as follows:

[0133] Variable frequency drive equipment startup: According to the startup frequency and voltage stepping mode set in the control command, the variable frequency drive equipment gradually increases the frequency and voltage according to the specified frequency to avoid large current surges and voltage fluctuations.

[0134] Power regulation and output stability: During startup, the equipment gradually adjusts its output power according to control commands to ensure that the power of the frequency converter drive is balanced with the grid load and does not exceed the grid's load capacity.

[0135] Real-time monitoring during the connection process: The power grid main control unit continuously monitors the operating status of the frequency converter drive equipment and makes adjustments based on real-time data feedback (such as current, voltage, power, etc.) to ensure the stability of the power grid during the equipment connection process.

[0136] After the equipment is stably connected, the power grid control unit continues to monitor its operating status and ensure its stability and safety in subsequent operation. The real-time data feedback system regularly updates the equipment status and optimizes and adjusts the operation process after connection.

[0137] After the variable frequency drive equipment is connected to the power grid, the power grid control unit will continuously monitor the equipment's operating status, including power output, bus voltage fluctuations, and load conditions. Once an abnormality is detected (such as overcurrent, abnormal voltage fluctuations, or equipment failure), the system will automatically trigger the protection mechanism and take the following actions:

[0138] Early warning notification: Sends early warning signals to power grid monitoring personnel to alert them to potential abnormal risks in the equipment;

[0139] Automatic shutdown protection: In extreme cases, the connection between the variable frequency drive equipment and the power grid is automatically disconnected to prevent the spread of equipment failure or power grid failure.

[0140] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A control method for a variable frequency drive equipment access system suitable for high-voltage power grids in coal mines, characterized in that: include: Obtain the set of high-voltage power grid characteristic parameters P of the target coal mine power supply system, including voltage level, power grid topology, grounding method, system impedance Z, power grid load variation curve L, and bus transient stability coefficient T; Based on the set of characteristic parameters P of the high-voltage power grid, a dynamic stability model M of the target power grid is constructed to reflect the dynamic response capability of the power grid bus to the access disturbance under different disturbance scenarios. The dynamic stability model M of the target power grid is constructed as follows: Based on the power grid topology, a node-branch graph is constructed, and the main power supply path and key node set are extracted using graph theory analytical methods. By combining the system impedance Z and the grounding method, an equivalent RLC branch is introduced into the busbar of each node to construct a set of time-domain state equations; The power grid load change curve L and the bus transient stability coefficient T are introduced as disturbance inputs. Multi-scenario disturbance simulation is adopted to solve the voltage response sequence of each bus. Based on the voltage response sequence, the offset rate and stabilization time are used as criteria to output the stability evaluation results under each disturbance condition, forming the dynamic stability model M of the target power grid. Obtain the set of device parameters V of the variable frequency drive device to be connected, including output voltage, current harmonic components, inrush current I, voltage change rate du / dt and carrier frequency f; Input the set of equipment parameters V into the dynamic stability model M, and based on multi-scenario disturbance simulation, obtain the set of bus response indicators R for each access scheme, including: The current harmonic components and voltage change rate du / dt in the equipment parameter set are used as disturbance source signals and injected into the corresponding positions of key nodes in the dynamic stability model M. By combining the power grid load change curve L and the inrush current I, multiple typical disturbance scenarios are constructed to form a disturbance simulation input matrix; The state equations are solved step by step using the time-domain numerical integration method to obtain the bus voltage response data of key nodes under various disturbance scenarios; For each set of simulation results, the voltage offset rate, stabilization time deviation value, and waveform distortion rate fluctuation value are extracted to generate the corresponding bus response index set R; Based on the bus response index set R, the access interference level coefficient D is calculated and compared with the preset safety threshold value Ds to select the target access parameter group V′ that meets the preset safety threshold value Ds condition; Based on the access parameter group V′, the dynamic access path and buffer modulation strategy of the target variable frequency drive device are determined, and corresponding control commands are generated, including: Based on the equipment parameters and power grid characteristics in the target access parameter group V′, analyze and determine the optimal access path for the frequency converter drive equipment, and select the optimal power grid node and branch as the access point. Based on the access path, voltage fluctuations are smoothed and instantaneous current surges are reduced by adjusting the start-up frequency and voltage step mode of the frequency converter drive equipment. The buffer modulation strategy and dynamic access path information are converted into control commands to generate precise access commands for variable frequency drive equipment, which are used to control the equipment's startup timing and power regulation. Control commands are sent to the frequency converter drive device via the communication interface; The control commands are transmitted to the main control unit of the high-voltage power grid to complete the stable connection of the target frequency converter drive equipment in the high-voltage power grid.

2. The control method for a variable frequency drive equipment access system suitable for high-voltage power grids in coal mines according to claim 1, characterized in that: For each set of simulation results, the voltage offset rate, stabilization time deviation value, and waveform distortion rate fluctuation value are extracted, including: The bus voltage response data output from the disturbance simulation is normalized to establish a standard voltage reference curve; Calculate the ratio of the maximum deviation between the actual voltage offset value and the standard voltage in each set of response curves, and extract the voltage offset rate. Identify the time required for the bus voltage to recover from the maximum deviation to the set stable threshold, calculate the difference between the required time and the rated stabilization time, and extract the stabilization time deviation value; The fluctuation amplitude of harmonic components in the bus voltage is extracted using the spectrum analysis method, and the waveform distortion rate fluctuation value is generated.

3. The control method for a variable frequency drive equipment access system suitable for high-voltage power grids in coal mines according to claim 1, characterized in that: Based on the bus response index set R, the access interference level coefficient D is calculated, including: converting the voltage offset rate, stabilization time deviation value, and waveform distortion rate fluctuation value into a comprehensive feature vector; using the comprehensive feature vector as the input of the machine learning model; the machine learning model uses the prediction of the interference level coefficient value label for each set of comprehensive feature vectors as the prediction objective; and uses minimizing the sum of prediction errors for all interference level coefficient value labels as the training objective. The machine learning model is trained until the sum of prediction errors converges, at which point the model training stops. The access interference level coefficient D is determined based on the model output. The machine learning model is a multinomial regression model.

4. The control method for a variable frequency drive equipment access system suitable for high-voltage power grids in coal mines according to claim 3, characterized in that: The access interference level coefficient D is normalized; the normalized access interference level coefficient D is compared with the preset safety threshold value Ds one by one, and the access parameter group with access interference level coefficient D less than or equal to the preset safety threshold value Ds is selected to generate the target access parameter group V′.

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