Reactive power compensation and harmonic suppression method and device for underground coal mine mobile substation

Abstract

A method and apparatus for reactive power compensation and harmonic suppression in a mobile substation in a coal mine includes: acquiring operating condition signals of the load-side electrical equipment, voltage signals and current signals at the input terminals of the reactive power compensation and harmonic suppression device; determining, based on the voltage and current signals, the reactive power deficit value on the low-voltage side of the mobile substation and the contribution weight of harmonics of each preset frequency to the temperature rise of the low-voltage side cable of the mobile substation; and generating coordinated control commands based on the operating condition signals, the reactive power deficit value, and the temperature rise contribution weights. These coordinated control commands include switching control commands for the reactive power compensation module in the reactive power compensation and harmonic suppression device and filtering control commands for the harmonic suppression module in the reactive power compensation and harmonic suppression device, to perform reactive power compensation and harmonic suppression on the low-voltage side of the mobile substation. This application improves the accuracy and precision of reactive power compensation and harmonic suppression in mobile substations in coal mines to meet the high-quality and stable power supply requirements of the underground power grid.

Description

Technical Field

[0001] This application relates to the technical field of underground power system equipment in coal mines, specifically to a method and device for reactive power compensation and harmonic suppression in a mobile substation in an underground coal mine. Background Technology

[0002] As a core infrastructure ensuring coal production, the underground power system in coal mines operates in harsh environments with complex load characteristics. On the low-voltage load side of mobile substations in coal mines, high-power inductive loads such as coal mining machines, scraper conveyors, and crushers, as well as variable frequency speed control equipment, are widely connected. These nonlinear devices generate reactive power fluctuations and multi-frequency harmonic pollution during operation, affecting the power supply quality and safety stability of the underground power grid. Therefore, reactive power compensation and harmonic suppression are necessary for mobile substations in coal mines.

[0003] In related technologies, the control logic for reactive power compensation and harmonic suppression in mobile substations in coal mines is usually quite rudimentary, making it difficult to meet the stringent requirements of underground power grids for high-quality and stable power supply. Summary of the Invention

[0004] This application provides a method and apparatus for reactive power compensation and harmonic suppression in a mobile substation in an underground coal mine, aiming to improve the accuracy and precision of reactive power compensation and harmonic suppression in the mobile substation in an underground coal mine, so as to meet the high-quality and stable power supply requirements of the underground power grid.

[0005] In a first aspect, this application provides a method for reactive power compensation and harmonic suppression in a mobile substation underground in a coal mine. The method is applied to a reactive power compensation and harmonic suppression device connected between the mobile substation and the load-side electrical equipment. The method includes:

[0006] Acquire the operating status signals of the load-side electrical equipment, as well as the voltage and current signals at the input terminals of the reactive power compensation and harmonic suppression devices;

[0007] Based on voltage and current signals, the reactive power deficit value on the low-voltage side of the mobile substation and the contribution weight of harmonics of each preset frequency to the temperature rise of the low-voltage side cable of the mobile substation are determined.

[0008] Based on the operating condition signal, reactive power deficit value, and temperature rise contribution weight, a coordinated control command is generated. The coordinated control command includes switching control command for the reactive power compensation module in the reactive power compensation and harmonic suppression device, and filtering control command for the harmonic suppression module in the reactive power compensation and harmonic suppression device.

[0009] According to the coordinated control instructions, the reactive power compensation module and harmonic suppression module in the reactive power compensation and harmonic suppression device are adjusted to perform reactive power compensation and harmonic suppression on the low-voltage side of the mobile substation.

[0010] In the above embodiments, the feedforward signal of the load condition, the real-time reactive power gap, and the contribution weight of cable temperature rise based on the skin effect are integrated to ensure the thermal safety of underground cables. By giving higher priority to suppressing high-frequency harmonics, the power factor is improved while reducing the additional cable losses caused by high-frequency harmonics. This effectively prevents mine safety accidents caused by cable overheating and improves the accuracy and precision of reactive power compensation and harmonic suppression of mobile substations in coal mines, so as to meet the high-quality and stable power supply requirements of the underground power grid.

[0011] In some embodiments, the reactive power deficit value is determined by the following steps:

[0012] Based on voltage signals, current signals, and actual power factor angle, determine the actual reactive power and actual active power on the low-voltage side of the mobile substation;

[0013] Based on the actual active power and the target power factor angle, determine the target reactive power on the low-voltage side of the mobile substation;

[0014] The reactive power deficit value is determined based on the power difference between the target reactive power and the actual reactive power.

[0015] In the above embodiments, by accurately quantifying the fundamental reactive power demand by stripping away harmonic interference, the reactive power deficit value is accurately calculated.

[0016] In some embodiments, the contribution weight of temperature rise is determined through the following steps:

[0017] Spectral analysis of the current signal is performed to obtain the harmonic amplitudes at each preset frequency;

[0018] Based on the harmonic amplitude of each preset frequency, determine the effective value of the harmonics at each preset frequency;

[0019] Based on each preset frequency and its effective harmonic value, determine the contribution weight of each preset frequency harmonic to the temperature rise of the low-voltage side cable of the mobile substation.

[0020] In the above embodiments, a harmonic evaluation system based on the physical thermal characteristics of cables is established, which converts the current amplitude into a contribution weight that can reflect the actual heating risk, so that reactive power compensation and harmonic suppression strategies can accurately locate the "hot spot" frequency that causes cable temperature rise.

[0021] In some embodiments, the contribution weight of each preset frequency harmonic to the temperature rise of the low-voltage side cable of the mobile substation is determined based on each preset frequency and the effective value of each preset frequency harmonic, including:

[0022] Using each preset frequency, the effective harmonic values ​​of the corresponding preset frequencies are weighted to obtain the weighted effective harmonic values;

[0023] The weighted effective values ​​of all preset frequencies are summed to obtain the total effective values ​​of the harmonics.

[0024] The contribution weight of each preset frequency harmonic to the temperature rise of the low-voltage side cable of the mobile substation is determined based on the ratio between the weighted effective value of each preset frequency harmonic and the sum of the effective values ​​of each harmonic.

[0025] In the above embodiments, a preset frequency is introduced as a weighting factor. The actual contribution of each harmonic to cable heating is quantified by calculating the weighted proportion, and the temperature rise contribution weight is obtained. This enables the reactive power compensation and harmonic suppression device to identify and prioritize the suppression of those hidden harmonics that have "low amplitude but high frequency and significant thermal effect", so as to improve the thermal stability of the underground power supply system in coal mines and the service life of cables.

[0026] In some embodiments, based on operating condition signals, reactive power deficit values, and temperature rise contribution weights, coordinated control commands are generated, including:

[0027] Based on operating condition signals, the predicted change value of reactive power deficit on the low-voltage side of the mobile substation is determined.

[0028] Based on the predicted change value of reactive power deficit and the reactive power deficit value, the total value of reactive power deficit is determined;

[0029] Based on the total reactive power deficit, switching control commands are generated.

[0030] In the above embodiments, by introducing a feedforward prediction mechanism based on operating condition signals, a composite control strategy of "feedforward prediction + feedback correction" is constructed. The total compensation value is included and the switching command is generated before the reactive power impact occurs, which effectively solves the problem of voltage fluctuation lag compensation caused by impact load in coal mines and realizes rapid response and smoothing of large reactive power fluctuations.

[0031] In some embodiments, a switching control command is generated based on the total reactive power deficit, including:

[0032] Obtain the preset reactive power deficit threshold;

[0033] If the total reactive power deficit is less than the reactive power deficit threshold, a switching control command is generated to adjust the static var generator in the reactive power compensation module.

[0034] If the total reactive power deficit is greater than or equal to the reactive power deficit threshold, a switching control command is generated to simultaneously adjust the static var generator and the graded capacitor bank in the reactive power compensation module.

[0035] In the above embodiments, the compensation subject is intelligently selected according to the scale of the reactive power gap: small gaps are handled by the SVG alone to ensure accuracy and speed, while large gaps are handled by the capacitor bank as the base load and the SVG as the finisher. This avoids small load oscillations of the capacitors and reduces the capacity requirements of expensive power electronic equipment, thereby improving the economy and regulation quality of the reactive power compensation and harmonic suppression device.

[0036] In some embodiments, generating control commands for simultaneously adjusting the switching of the static var generator and the tiered capacitor bank in the reactive power compensation module includes:

[0037] Based on the total reactive power deficit and the rated capacity of each capacitor bank in the tiered capacitor bank, determine the target number of capacitor banks to be put into operation.

[0038] Generate the first switching instruction for controlling the deployment of a target number of capacitor banks;

[0039] Determine the power gap difference between the total reactive power deficit and the total rated capacity of the target number of capacitor banks;

[0040] Based on the power gap difference, a second switching command is generated to adjust the reactive power output of the static var generator;

[0041] The switching control instructions include a first switching instruction and a second switching instruction.

[0042] In the above embodiments, the reactive power deficit is decomposed into an "integer step part" and a "fractional residual part", which are processed by the capacitor bank and SVG respectively. The SVG is used to compensate for the quantization error of the capacitor, thereby eliminating the step effect of graded compensation without increasing the high equipment cost, and realizing the unity power factor operation of the reactive power compensation and harmonic suppression device in coal mine underground power supply across the entire range.

[0043] In some embodiments, based on operating condition signals, reactive power deficit values, and temperature rise contribution weights, coordinated control commands are generated, including:

[0044] Based on the operating condition signal, the frequency of the harmonics that will be generated on the low-voltage side of the mobile substation is predicted to obtain the predicted frequency, which is included in multiple preset frequencies.

[0045] The corrected temperature rise contribution weights are obtained by adjusting the harmonics of the predicted frequency to the temperature rise contribution weights of the low-voltage side cables of the mobile substation.

[0046] Based on the corrected temperature rise contribution weight, the target frequency is determined from multiple preset frequencies;

[0047] Based on the target frequency, filter control commands are generated.

[0048] In the above embodiments, the temperature rise contribution weight of harmonics is corrected by using operating condition signals, thereby identifying and locking high-risk frequencies before harmonic outbreaks for priority treatment, thus achieving proactive protection of the thermal life of underground cables in coal mines.

[0049] In some embodiments, after adjusting the reactive power compensation module and harmonic suppression module in the reactive power compensation and harmonic suppression device according to the coordinated control command, the method further includes:

[0050] Obtain at least one of the following: the first temperature of the reactive power compensation module, the second temperature of the harmonic suppression module, and the internal ambient temperature of the reactive power compensation and harmonic suppression device;

[0051] If at least one of the first temperature, the second temperature, and the internal ambient temperature exceeds the corresponding preset temperature protection threshold, a blocking command is triggered. The blocking command is used to cut off the power supply to the reactive power compensation module and the harmonic suppression module, and to switch to the bypass operation mode on the low-voltage side of the mobile substation. The bypass operation mode is used to ensure that the power supply from the mobile substation to the load-side electrical equipment does not pass through the reactive power compensation and harmonic suppression devices.

[0052] In the above embodiments, the thermal safety of the reactive power compensation and harmonic suppression device is placed above its operational function. Once the temperature of any part is detected to exceed the limit, the power supply of the reactive power compensation and harmonic suppression device is immediately cut off and automatically bypassed, thereby eliminating the potential for electrical fires underground while maximizing the continuity and reliability of power supply for coal mine production.

[0053] Secondly, the embodiments of this application provide a reactive power compensation and harmonic suppression device, which is used in any of the reactive power compensation and harmonic suppression methods for mobile substations in coal mines.

[0054] One or more technical solutions provided in this application have at least the following technical effects or advantages: by integrating the feedforward signal of the load condition, the real-time reactive power gap, and the contribution weight of cable temperature rise based on the skin effect, with the priority of ensuring the thermal safety of underground cables, and by giving higher suppression priority to high-frequency harmonics, the power factor is improved while the additional cable loss caused by high-frequency harmonics is reduced, effectively preventing mine safety accidents caused by cable overheating. Furthermore, the accuracy and precision of reactive power compensation and harmonic suppression of mobile substations in coal mines are improved to meet the high-quality and stable power supply requirements of underground power grids. Attached Figure Description

[0055] Figure 1 This is a flowchart illustrating a method for reactive power compensation and harmonic suppression in a mobile substation underground in a coal mine, as described in this application. Detailed Implementation

[0056] The terminology used in the following embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. As used in the specification of this application, the singular expressions “a,” “an,” “the,” “the,” and “this” are intended to include the plural expressions as well, unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this application refers to any or all possible combinations including one or more of the listed items.

[0057] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as implying or suggesting relative importance or implicitly indicating the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature, and in the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more.

[0058] In a first aspect, embodiments of this application provide a method for reactive power compensation and harmonic suppression of a mobile substation in a coal mine.

[0059] This method is applied to a reactive power compensation and harmonic suppression device, which is connected between the mobile substation and the load-side electrical equipment. In other words, the reactive power compensation and harmonic suppression device is used to compensate for reactive power and suppress harmonics in the power supply from the mobile substation to the load-side electrical equipment, thereby meeting the high-quality and stable power supply requirements of the underground power grid. The mobile substation in the coal mine is not a typical surface substation facility, but a compact combined device integrating high-voltage switches, dry-type transformers, and low-voltage protection boxes, typically moving with the advancement of the mining face. Both the load-side electrical equipment and the reactive power compensation and harmonic suppression device are located on the low-voltage side of the mobile substation.

[0060] Reference Figure 1 The reactive power compensation and harmonic suppression method for mobile substations in coal mines may include the following steps:

[0061] S101. Obtain the operating condition signal of the load-side electrical equipment, as well as the voltage and current signals at the input terminal of the reactive power compensation and harmonic suppression device.

[0062] In this embodiment, the operating condition signals of the load-side electrical equipment refer to information that characterizes the operating status or intention of load-side electrical equipment such as coal mining machines, scraper conveyors, and tunneling machines. These operating condition signals include not only the equipment's start / stop status (logic switching quantities), but also analog quantities or digital communication messages characterizing the load dynamics of the load-side electrical equipment, such as changes in cutting resistance, traction speed adjustment, and coal seam hardness prediction. The voltage and current signals at the incoming line refer to the real-time electrical parameters at the low-voltage busbar of the mobile substation where the reactive power compensation and harmonic suppression device is connected.

[0063] The significance of acquiring operating condition signals lies in introducing a feedforward control mechanism, so that reactive power compensation and harmonic suppression devices no longer rely solely on the delayed response after changes in electrical parameters, but can predict the drastic fluctuations that are about to occur in the load, thereby providing a time margin for subsequent rapid compensation.

[0064] S102. Based on voltage and current signals, determine the reactive power deficit value on the low-voltage side of the mobile substation and the contribution weight of harmonics of each preset frequency to the temperature rise of the low-voltage side cable of the mobile substation.

[0065] In this embodiment, the reactive power deficit value refers to the amount of reactive power required to bring the power factor of the low-voltage side of the mobile substation to a preset target value (e.g., above 0.95). The contribution weight of each preset frequency harmonic to the temperature rise of the low-voltage side cable of the mobile substation is a coefficient reflecting the difference in the thermal effect generated by harmonic currents of different frequencies flowing through a specific type of power cable. Due to the skin effect and proximity effect, the effective cross-sectional area of ​​high-frequency current flowing in the conductor decreases, resulting in a significant increase in the equivalent AC resistance as the frequency increases. Therefore, for the same amplitude current, the higher the frequency, the more Joule heat is generated on the cable.

[0066] S103. Based on the operating condition signal, reactive power deficit value, and temperature rise contribution weight, generate coordinated control instructions. The coordinated control instructions include switching control instructions for the reactive power compensation module in the reactive power compensation and harmonic suppression device, and filtering control instructions for the harmonic suppression module in the reactive power compensation and harmonic suppression device.

[0067] In this embodiment, the coordinated control command is the core decision-making tool for the reactive power compensation and harmonic suppression device. It integrates feedforward information (operating condition signal), steady-state demand (reactive power deficit value), and safety constraints (temperature rise contribution weight). Coordinated control refers to simultaneously performing multi-objective optimization on reactive power and calculated thermal risks. The switching control command for the reactive power compensation module is mainly used to compensate for the reactive power deficit, typically controlling capacitor banks or discrete reactor banks. The filtering control command for the harmonic suppression module is used for dynamic harmonic elimination.

[0068] In some embodiments of this application, a weighted priority allocation strategy is employed when generating filter control commands. When the compensation capacity of the reactive power compensation and harmonic suppression devices is limited and cannot simultaneously and completely eliminate all subharmonics, suppression commands for harmonic frequencies with significant temperature rise contribution weights (i.e., those with a large impact on cable heating) can be prioritized based on the temperature rise contribution weight, even if the amplitudes of these harmonics may not be the highest. For example, although the 5th harmonic has the largest amplitude, if the combined thermal effect risk of the 11th and 13th harmonics is higher, resources are prioritized for suppressing the 11th and 13th harmonics. This strategy ensures the maximum thermal stability of the power supply system with limited resources. Filter control commands are typically converted into pulse width modulation (PWM) signals to drive power electronic devices (such as insulated gate bipolar transistors, IGBTs).

[0069] S104. According to the coordinated control command, adjust the reactive power compensation module and harmonic suppression module in the reactive power compensation and harmonic suppression device to perform reactive power compensation and harmonic suppression on the low-voltage side of the mobile substation.

[0070] In this embodiment, adjusting the reactive power compensation and harmonic suppression device refers to performing physical-level switching actions and waveform output. The reactive power compensation module can be composed of a thyristor-switched capacitor (TSC), which, upon receiving a switching control command, is switched on at the voltage zero-crossing point or switched off at the current zero-crossing point to provide stepped capacitive reactive power support. The harmonic suppression module can be composed of an active power filter (APF) or a static var generator (SVG), which, upon receiving a filtering control command, generates a compensation current with the same amplitude but opposite phase to the grid harmonic current and injects it into the grid.

[0071] As can be seen, the embodiments of this application integrate the feedforward signal of the load condition, the real-time reactive power gap, and the contribution weight of cable temperature rise based on the skin effect, with the priority of ensuring the thermal safety of underground cables. By giving higher suppression priority to high-frequency harmonics, the power factor is improved while the additional cable loss caused by high-frequency harmonics is reduced, effectively preventing mine safety accidents caused by cable overheating. Furthermore, it improves the accuracy and precision of reactive power compensation and harmonic suppression of mobile substations in coal mines, so as to meet the high-quality and stable power supply requirements of underground power grids.

[0072] In some embodiments of this application, the reactive power deficit value can be determined through the following steps:

[0073] S201. Based on voltage signal, current signal, and actual power factor angle, determine the actual reactive power and actual active power on the low-voltage side of the mobile substation.

[0074] In this embodiment, the actual power factor angle refers to the phase difference between the fundamental voltage and fundamental current on the low-voltage side of the mobile substation. Due to the presence of numerous harmonics caused by nonlinear loads (such as frequency converters) in underground coal mines, direct zero-crossing detection may introduce errors. Therefore, the fundamental phase difference can be extracted through spectrum analysis or coordinate transformation to obtain the actual power factor angle. Actual reactive power refers to the power component actually present on the low-voltage side of the mobile substation at the current moment, used to establish the magnetic field but not consumed; it primarily refers to the fundamental reactive power. Actual active power refers to the power component actually performing work on the low-voltage side of the mobile substation at the current moment. Determining these two parameters is the basis for quantifying the current load state of the low-voltage side of the mobile substation.

[0075] In some embodiments of this application, the actual reactive power It can be calculated using the following formula:

[0076] in, This refers to the three-phase line voltages in the voltage signal. This refers to the three-phase line current in the current signal. This is the actual power factor angle.

[0077] In some embodiments of this application, the actual active power It can be calculated using the following formula:

[0078] S202. Based on the actual active power and the target power factor angle, determine the target reactive power on the low-voltage side of the mobile substation.

[0079] In this embodiment, the target power factor angle is a phase angle value calculated based on a preset desired power factor (e.g., 0.96 or 0.98), and this value is typically stored in a relevant register. The target reactive power refers to the ideal reactive power level that the low-voltage side of the mobile substation should possess in order to achieve the desired power factor while keeping the current actual active power constant.

[0080] In some embodiments of this application, the target reactive power It can be calculated using the following formula:

[0081] in, The target power factor angle.

[0082] S203. Determine the reactive power deficit value based on the power difference between the target reactive power and the actual reactive power.

[0083] In this embodiment, the reactive power deficit value is a signed numerical value representing the deviation of the current low-voltage side of the mobile substation from the ideal operating state. This deficit value directly determines the amount of energy that the reactive power compensation and harmonic suppression devices need to output or absorb during subsequent reactive power compensation. If the deficit value is positive, it usually indicates that the low-voltage side of the mobile substation lacks capacitive reactive power, requiring the reactive power compensation and harmonic suppression devices to generate capacitive reactive power; if the deficit value is negative, it indicates that the reactive power compensation and harmonic suppression devices may be overcompensated, requiring the capacitor to be disconnected or the generator to generate inductive reactive power.

[0084] In some embodiments of this application, the reactive power deficit value It can be calculated using the following formula:

[0085] As can be seen, the embodiments of this application accurately quantify the fundamental reactive power demand by stripping away harmonic interference, thereby achieving accurate calculation of the reactive power deficit value.

[0086] In some embodiments of this application, the temperature rise contribution weight can be determined through the following steps:

[0087] S301. Perform spectrum analysis on the current signal to obtain the harmonic amplitude of each preset frequency.

[0088] In the embodiments of this application, the preset frequency refers to the characteristic harmonic frequency points that are defined and focused on during the design stage of the reactive power compensation and harmonic suppression device. These typically include, but are not limited to, the 5th (250Hz), 7th (350Hz), 11th (550Hz), and 13th (650Hz) odd harmonics that dominate in three-phase rectified loads. The harmonic amplitude refers to the maximum amplitude of the current signal at that specific frequency component after decomposition. Spectrum analysis is a digital signal processing procedure that converts a discrete sampling sequence in the time domain into frequency domain information. Spectrum analysis can be implemented, for example, using an algorithm based on the Fast Fourier Transform (FFT).

[0089] In some embodiments of this application, the harmonic amplitude of a preset frequency is... It can be calculated using the following formula:

[0090]

[0091]

[0092] Where k is the preset frequency. For the complex current of the harmonic with a preset frequency of k, This represents the modulo operation, where N is the number of sampling points in the Fast Fourier Transform. Let be the current value at the nth discrete sampling time.

[0093] This is the twiddle factor in the Fast Fourier Transform algorithm. It is the base of the natural logarithm. The imaginary unit, The square of is equal to -1. Let π be the mathematical constant pi. k is the preset frequency mentioned above, and n is the nth discrete sampling time mentioned above.

[0094] S302. Based on the harmonic amplitude of each preset frequency, determine the effective value of the harmonics at each preset frequency.

[0095] In the embodiments of this application, the effective value of a harmonic refers to the value of a direct current equivalent to the Joule heating effect produced by alternating current at that frequency. Under a sinusoidal waveform, its value is mathematically equal to the harmonic amplitude divided by the square root of 2. For some non-stationary signals, the effective value is calculated by integral averaging over a period of time.

[0096] In some embodiments of this application, the effective value of harmonics at a preset frequency is... It can be calculated using the following formula:

[0097] S303. Based on each preset frequency and the effective value of each preset frequency harmonic, determine the contribution weight of each preset frequency harmonic to the temperature rise of the low-voltage side cable of the mobile substation.

[0098] In this embodiment, the temperature rise contribution weight is a dimensionless or relatively physically meaningful evaluation coefficient used to quantify the proportion or degree of harmonic damage of specific frequency harmonics during cable heating. The temperature rise contribution weight depends not only on the magnitude (RMS) of the current but also nonlinearly on the frequency (preset frequency) of the current. This is because under high-frequency conditions, the skin effect inside the conductor and the proximity effect between conductors lead to a significant increase in AC resistance, making the heat loss generated by the high-frequency current much greater than that of the power frequency current of the same amplitude.

[0099] In some embodiments of this application, the contribution weight of harmonics of a preset frequency to the temperature rise of the low-voltage side cable of the mobile substation is specified. It can be calculated using the following formula:

[0100] Where m is the preset frequency involved in the calculation, and M is the maximum value of m.

[0101] This application establishes a harmonic evaluation system based on the physical thermal characteristics of cables, which converts the current amplitude into a contribution weight that can reflect the actual heating risk, so that reactive power compensation and harmonic suppression strategies can accurately locate the "hot spots" frequencies that cause cable temperature rise.

[0102] In some embodiments of this application, determining the contribution weight of each preset frequency harmonic to the temperature rise of the low-voltage side cable of the mobile substation based on each preset frequency and its effective harmonic value may include:

[0103] S401. Using each preset frequency, the effective harmonic values ​​of the corresponding preset frequencies are weighted to obtain the weighted effective harmonic values.

[0104] In this embodiment, the preset frequency serves as a key variable for distinguishing the physical characteristics of different harmonics. It not only represents the rate of current change but also directly corresponds to the differences in the electromagnetic field distribution within the conductor. The weighted effective harmonic value is a virtual current index characterizing the "equivalent thermal damage capability," rather than a simple electrical measurement. Due to the skin effect and proximity effect, the higher the current frequency, the more electrons tend to flow towards the conductor surface, resulting in a decrease in the effective conductive cross-sectional area and an increase in AC resistance. The weighting process uses mathematical methods to map this physical resistance increment onto the current value, ensuring that the weighted value reflects the true potential of the harmonic at that frequency to cause heat generation in the cable.

[0105] S402. Sum the weighted effective values ​​of all preset frequencies to obtain the total effective values ​​of harmonics.

[0106] In this embodiment, the sum of the effective harmonic values ​​is not equivalent to the total effective harmonic current value (i.e., the square root of the sum of the squares of each harmonic) in the traditional definition of power quality, but rather a cumulative "total thermal risk" indicator. It represents the total thermal stress level exerted on the cable by all detected characteristic harmonics as a whole at the current moment.

[0107] S403. Based on the ratio between the weighted effective value of each preset frequency harmonic and the sum of the effective values ​​of harmonics, determine the contribution weight of each preset frequency harmonic to the temperature rise of the low-voltage side cable of the mobile substation.

[0108] In this embodiment, this step is crucial for generating the final decision-making basis. This ratio is the temperature rise contribution weight, a value between 0 and 1 (or a percentage between 0% and 100%), describing the degree of influence of harmonics of the corresponding preset frequency on cable heating.

[0109] Accordingly, the reactive power compensation and harmonic suppression device can generate a dynamic weighted vector table. For example, the calculation results may show that although the original current amplitude of the 5th harmonic is the largest, after weighted calculation, its temperature rise contribution weight is 0.3, while the 11th harmonic, although smaller in amplitude, has a high AC resistance due to its high frequency, resulting in a temperature rise contribution weight of 0.5. Based on the temperature rise contribution weight, the specific frequency gain of the harmonic suppression module (such as SVG) can be dynamically adjusted, prioritizing the allocation of 50% of the computing power and current capacity to eliminate the 11th harmonic, rather than applying equal effort. Thus, given the limited capacity of the reactive power compensation and harmonic suppression device, it prioritizes the elimination of high-frequency components that pose the greatest threat to cable insulation life.

[0110] As can be seen, the embodiments of this application introduce a preset frequency as a weighting factor, and quantify the actual contribution of each harmonic to the heating of the cable by calculating the weighted proportion, so as to obtain the temperature rise contribution weight, enabling the reactive power compensation and harmonic suppression device to identify and prioritize the suppression of those hidden harmonics that are "low in amplitude but high in frequency and have significant thermal effects", so as to improve the thermal stability of the underground power supply system in coal mines and the service life of cables.

[0111] In some embodiments of this application, generating coordinated control commands based on operating condition signals, reactive power deficit values, and temperature rise contribution weights may include:

[0112] S501. Based on the operating condition signal, determine the predicted change value of the reactive power gap on the low-voltage side of the mobile substation.

[0113] In this embodiment, the operating condition signal not only reflects the current operating status but also includes the upcoming load change trend, such as the instant the coal mining machine drum cuts into the coal face, the heavy-load start command of the scraper conveyor, or the pushing signal of the hydraulic support. The predicted change value of reactive power deficit refers to the estimated amount of additional or reduced reactive power demand that the low-voltage side load of the mobile substation will generate within a very short time window (e.g., tens to hundreds of milliseconds) based on the operating condition signal. This value represents a dynamic feedforward quantity used to compensate for the lag caused by relying solely on feedback control.

[0114] In some embodiments of this application, the predicted change value is determined by consulting a pre-defined database of electromechanical coupling load characteristics. This database stores mapping models between different operating condition signals and electrical characteristics. For example, when a signal indicating that the traction speed of a coal mining machine increases from 0 to 2 meters per minute is received, the reactive power compensation and harmonic suppression device calculates the inductive reactive power surge curve caused by this acceleration process based on the electrical model in the database, and extracts the peak or average value of the curve as the predicted change value. Furthermore, the reactive power compensation and harmonic suppression device can also utilize machine learning algorithms such as Long Short-Term Memory (LSTM) networks to extrapolate the reactive power fluctuations at the next moment in real time based on historical operating condition sequences, thereby sensing demand in advance before drastic changes in electrical parameters occur.

[0115] S502. Based on the predicted change value of reactive power deficit and the reactive power deficit value, determine the total value of reactive power deficit.

[0116] In this embodiment, the reactive power deficit value is calculated based on the steady-state error (feedback quantity) derived from the real-time sampled voltage and current, while the predicted change value of the reactive power deficit is based on the dynamic increment (feedforward quantity) predicted by the operating conditions. Therefore, the total reactive power deficit is a composite control target that integrates the current steady-state compensation demand and the future dynamic impact suppression demand. The total reactive power deficit determines the overall energy throughput scale that the reactive power compensation and harmonic suppression devices will execute.

[0117] In some embodiments of this application, the process of determining the total reactive power deficit employs a weighted synthesis strategy. Considering the potential uncertainty in the predicted change value, the reactive power compensation and harmonic suppression device assigns a confidence coefficient to the predicted change value. The calculation formula can be expressed as: Total reactive power deficit = Reactive power deficit value + (Confidence coefficient × Predicted change value). For example, if the operating condition signal indicates that a high-power motor direct on-line (DOL) is imminent, the confidence coefficient is set to a preset high value, causing the total value to increase rapidly. This allows the reactive power compensation and harmonic suppression device to mobilize sufficient reactive power reserves to support the bus voltage and prevent voltage dips caused by motor starting current. This synthesis mechanism ensures that the reactive power compensation and harmonic suppression device can both correct the current power factor deviation and readily cope with upcoming load surges.

[0118] In some further embodiments, a confidence coefficient calculation scheme is provided that can effectively identify real load surges and filter out false interference. This scheme utilizes the high impedance physical characteristics of the weak power grid in underground coal mines, namely, "a large current start-up inevitably leads to a voltage drop," and specifically includes the following steps:

[0119] Step 1: Signal acquisition and differential calculation;

[0120] The bus voltage u(t) and load current i(t) are synchronously acquired at a high frequency (e.g., 10kHz). To obtain the trend of change, the differential value (rate of change) of the current time t relative to the previous time t-1 is calculated:

[0121] du / dt = u(t) - u(t-1)

[0122] di / dt = i(t) - i(t-1)

[0123] Step 2: Calculate the reverse linkage characteristic value (K);

[0124] Whether a true heavy-load start-up event has occurred is determined by calculating the product of the current rise rate and the voltage fall rate. The calculation formula is: K = (di / dt) × (-du / dt)

[0125] In this step, the following operating logic conditions exist:

[0126] Operating Condition A (Real Motor Start-up): At the moment of starting a high-power motor, the current rises sharply (i.e., di / dt is a very large positive number), while at the same time, due to the voltage division caused by the line impedance, the bus voltage drops sharply (i.e., du / dt is a very large negative number). At this time, (-du / dt) is a positive number, and the product of the two, K, is a large positive value.

[0127] Condition B (sensor high-frequency interference): If only the current signal is affected by electromagnetic interference and spikes occur, but the bus voltage remains stable (i.e., du / dt≈0), then the calculated K≈0.

[0128] Operating condition C (external power grid fluctuation): If the voltage of the upstream substation increases, it leads to an increase in the underground voltage, and the current passively increases slightly accordingly. At this time, du / dt>0 and di / dt>0. Since (-du / dt) becomes negative, the calculated result K<0.

[0129] Step 3: Mapping output of confidence coefficient (γ);

[0130] Based on the magnitude of the eigenvalue K, the confidence coefficient γ is dynamically output:

[0131] When K≤0: It is determined to be a non-load impact (such as interference or grid fluctuation), and γ is forced to be 0. At this time, the reactive power compensation and harmonic suppression device does not compensate for the predicted change in reactive power deficit to avoid misjudging the upcoming load impact.

[0132] When K > 0: This is considered a genuine load shock. The confidence coefficient is calculated using the "normalized saturation function": γ = K / (K + β). Here, β is a sensitivity adjustment constant, for example, 5000. If the shock is extremely strong (K value is large), the result of K / (K + β) approaches 1, indicating a very high confidence coefficient. The predicted change in reactive power deficit will be fully accepted for compensation. If the shock is relatively mild (K value is small), the confidence coefficient will be between 0 and 1, and the predicted change in reactive power deficit will be accepted proportionally for compensation.

[0133] It can be seen that the above solution can effectively solve the problem of malfunction of reactive power compensation and harmonic suppression devices in the complex electromagnetic environment of coal mines.

[0134] S503. Generate switching control commands based on the total reactive power deficit.

[0135] In this embodiment, the switching control command is a discrete control signal specifically for the reactive power compensation module (typically including tiered capacitor banks). These commands are used to control the opening and closing of thyristor switches or contactors in the capacitor bank, corresponding to coarse-grained, high-capacity reactive power throughput. Since the capacitor bank can only be switched in stages and cannot be continuously adjusted like power electronic devices, generating this command requires quantization and logical judgment.

[0136] As can be seen, the embodiments of this application introduce a feedforward prediction mechanism based on operating condition signals to construct a composite control strategy of "feedforward prediction + feedback correction". The total compensation value is included and the switching command is generated before the reactive power impact occurs, which effectively solves the problem of voltage fluctuation lag compensation caused by impact load in coal mines and realizes rapid response and suppression of large reactive power fluctuations.

[0137] In some embodiments of this application, generating switching control commands based on the total reactive power deficit may include:

[0138] S601. Obtain the preset reactive power deficit threshold.

[0139] In the embodiments of this application, the reactive power gap threshold is a pre-set critical value used to divide the compensation strategy mode. Its physical meaning is to define whether the reactive power demand is within a small range that can be precisely adjusted by power electronic devices alone, or has reached a large range that requires the investment of large-capacity passive components for support.

[0140] In some embodiments of this application, the threshold is set in relation to the rated capacity of the smallest capacitor in the tiered capacitor bank. Specifically, the reactive power compensation and harmonic suppression device sets the reactive power deficit threshold to be equal to or slightly less than the nominal reactive power of the smallest capacitor bank (e.g., 50 kVar (Kilo Volt Amps Reactive)). This setting prevents ineffective switching of large-capacity capacitors under low load demand due to control logic malfunctions, while also preserving the excellent regulation characteristics of the SVG in the low current range.

[0141] S602. If the total reactive power deficit is less than the reactive power deficit threshold, generate a switching control command for adjusting the static var generator in the reactive power compensation module.

[0142] In this embodiment, when the total reactive power deficit is less than the reactive power deficit threshold, it indicates that the current reactive power demand is within a relatively small and potentially fluctuating range, suitable for equipment with rapid and continuous adjustment capabilities to handle. The switching control command generated at this time is essentially a modulation signal or current reference command for the SVG, and does not include a signal to trigger capacitor operation.

[0143] S603. If the total reactive power deficit is greater than or equal to the reactive power deficit threshold, generate a switching control command for simultaneously adjusting the static var generator and the graded capacitor bank in the reactive power compensation module.

[0144] In this embodiment, when the total reactive power deficit is greater than or equal to the reactive power deficit threshold, it indicates that the reactive power compensation and harmonic suppression device is facing a large reactive power deficit. Relying solely on the SVG may result in insufficient capacity or poor economic efficiency, thus requiring the activation of the collaborative compensation mode. The generated instruction at this time includes two parts: one part is a discrete switching signal for the graded capacitor bank (corresponding to "coarse adjustment"), and the other part is a continuous adjustment signal for the SVG (corresponding to "fine adjustment").

[0145] As can be seen, the embodiments of this application intelligently select the compensation subject based on the scale of the reactive power gap: small gaps are independently handled by the SVG to ensure accuracy and speed, while large gaps are handled by the capacitor bank as the base load and the SVG as the finisher. This avoids small load oscillations of the capacitors and reduces the capacity requirements of expensive power electronic equipment, thereby improving the economy and regulation quality of the reactive power compensation and harmonic suppression device.

[0146] In some embodiments of this application, generating switching control commands for simultaneously adjusting the static var generator and the tiered capacitor bank in the reactive power compensation module may include:

[0147] S701. Based on the total reactive power deficit and the rated capacity of each capacitor bank in the graded capacitor bank, determine the target number of capacitor banks to be put into operation.

[0148] In this embodiment, the graded capacitor bank consists of several capacitor branches connected in parallel with fixed reactive power capacity. The rated capacity of a single capacitor bank refers to the nominal reactive power of the smallest switching unit. The target number is an integer value representing the number of capacitor branches that should be put into operation on the grid to approximate the total reactive power deficit.

[0149] In some embodiments of this application, the target number of capacitor banks to be deployed can be determined using a floor function algorithm. Specifically, the reactive power compensation and harmonic suppression device calculates the total reactive power deficit by dividing it by the rated capacity of a single capacitor bank, and takes the integer part of the quotient as the target number. For example, if the total deficit is 230 kVar and the capacity of a single capacitor bank is 50 kVar, the calculation result is 4.6, and the target number is determined to be 4 banks. The advantage of using a floor function instead of rounding is that it always keeps the reactive power provided by the capacitor banks slightly less than or equal to the actual demand, thus ensuring that the remaining deficit is positive (inductive reactive power deficit), which is left for the static var generator with bidirectional adjustment capability to fill, avoiding the risk of voltage rise caused by the reactive power compensation and harmonic suppression device becoming capacitive due to over-deployment of capacitors.

[0150] S702, Generate the first switching instruction for controlling the use of a target number of capacitor banks.

[0151] In this embodiment, the first switching command is a discrete control signal that directly drives the capacitor switching switch (such as a thyristor switch or contactor). This command contains specific physical address information and operational logic, used to instruct the selected groups of capacitors to be closed and connected to the bus.

[0152] S703. Determine the power gap difference between the total reactive power deficit and the total rated capacity of the target number of capacitor banks.

[0153] In this embodiment, the power gap difference refers to the quantification error caused by the graded (discontinuous) characteristics of the capacitor bank. Numerically, it equals the total demand minus the total capacity that the capacitor bank can actually provide. This difference is typically less than the rated capacity of a single capacitor bank and falls under the category of a "minor residual gap."

[0154] S704. Based on the power gap difference, generate a second switching command to adjust the reactive power output of the static var generator.

[0155] In this embodiment, the second switching command is a dynamic modulation reference command for the Static Var Generator (SVG). It instructs the SVG how much precise reactive current it needs to output to fill the aforementioned power gap difference. Specifically, the reactive power compensation and harmonic suppression device converts the power gap difference into a corresponding current value and generates a corresponding second switching command, which is input to the SVG's pulse width modulation (PWM) controller. Based on this command, the SVG controls the switching timing of its internal IGBTs, outputting reactive power equal in magnitude and direction to the power gap difference. This utilizes the SVG's stepless adjustment characteristics to completely eliminate the compensation dead zone caused by the capacitor bank quantization step, achieving smoothing and linearization of the overall compensation effect, ensuring that the final reactive power injected into the grid perfectly matches the actual demand.

[0156] The switching control command is a composite control package, which includes a first switching command and a second switching command. The reactive power compensation and harmonic suppression device sends these two types of commands in parallel through different I / O ports or communication buses.

[0157] As can be seen, the embodiments of this application decompose the reactive power deficit into an "integer step part" and a "decimal residual part", which are processed by the capacitor bank and SVG respectively. The SVG is used to compensate for the quantization error of the capacitor, thereby eliminating the step effect of graded compensation without increasing the high equipment cost, and realizing the unity power factor operation of the reactive power compensation and harmonic suppression device in coal mine underground power supply across the entire range.

[0158] In some embodiments of this application, generating coordinated control commands based on operating condition signals, reactive power deficit values, and temperature rise contribution weights may include:

[0159] S801. Based on the operating condition signal, predict the frequency of the harmonics that will be generated on the low-voltage side of the mobile substation to obtain the predicted frequency, which is included in multiple preset frequencies.

[0160] In this embodiment, the predicted frequency refers to a specific order harmonic that is about to appear in the power grid, inferred from prior knowledge based on the specific equipment or operating mode currently triggered by the operating condition signal. The significance of this step is that it advances the timeline of harmonic mitigation from "post-detection mitigation" to "pre-generation preparation".

[0161] In the embodiments of this application, the generation of the operating condition signal is not a simple external switching input, but rather based on real-time characteristic analysis of the total load current on the low-voltage side of the mobile substation. The specific data processing logic and flow are as follows:

[0162] First, current data from the low-voltage side of the mobile substation is collected at a sampling frequency of 20kHz, and the effective value change rate and waveform distortion rate of the current are calculated using a 20-millisecond (i.e., one power frequency cycle) sliding window. Second, the reactive power compensation and harmonic suppression device has several preset feature vector templates for typical operating conditions. For example, the feature vector for the "heavy-load start-up of the variable frequency scraper conveyor" condition is defined as follows: the effective value of the current rises from 0 to twice the rated current within 200 milliseconds, and the waveform distortion rate exceeds 15% during this period.

[0163] Next, the real-time calculated feature data is matched with a preset feature vector template. If the Euclidean distance obtained from the matching calculation is less than a preset matching threshold, it is determined that the current working condition is in that specific condition, and a corresponding working condition signal code is generated.

[0164] Finally, based on the operating condition signal code, the reactive power compensation and harmonic suppression device can not only look up the predicted harmonic frequencies (such as the 5th and 7th harmonics) but also obtain the expected duration of the operating condition (such as 30 seconds). For example, when the operating condition of "frequent start-stop of emulsion pump station" is identified, the reactive power compensation and harmonic suppression device predicts that the 5th and 11th harmonics with drastic amplitude fluctuations will occur within the next 10 seconds, thus locking in these frequencies in advance and using them as the predicted frequencies.

[0165] In some embodiments of this application, the reactive power compensation and harmonic suppression device internally maintains a working condition-spectrum mapping table. For example, when the working condition signal is identified as "heavy load start of the variable frequency scraper conveyor," the reactive power compensation and harmonic suppression device predicts the harmonics that will mainly be generated at predicted frequencies (e.g., 5th, 7th, 11th, and 13th) based on the number of pulses of the frequency converter (e.g., 6 pulses or 12 pulses). If the working condition signal is identified as "dim mode of the lighting integrated protection system," the predicted frequency may mainly focus on the 3rd harmonic, and the predicted frequency is 3rd. It can be seen that this step, by utilizing the indication function of the working condition signal, enables the reactive power compensation and harmonic suppression device to adjust the control parameters in advance for specific frequency harmonics that are about to occur, eliminating the sampling and calculation delay required for FFT (Fast Fourier Transform) detection.

[0166] S802. Correct the contribution weight of the predicted frequency harmonics to the temperature rise of the low-voltage side cable of the mobile substation to obtain the corrected temperature rise contribution weight.

[0167] In this embodiment, the correction process refers to introducing a "predictive gain factor" to adjust the importance of harmonics that are about to be generated but have not yet been detected. This is because the real-time calculated temperature rise contribution weight reflects the "past" thermal effects, while the corrected temperature rise contribution weight incorporates the "future" thermal risk expectations.

[0168] In some embodiments of this application, the correction algorithm employs a weighted synthesis method. The reactive power compensation and harmonic suppression device assigns a risk factor greater than 1 (e.g., 1.5) to the predicted frequency, multiplying it by the current temperature rise contribution weight of that frequency. This gives the reactive power compensation and harmonic suppression device a forward-looking perspective, ensuring that it can prioritize resource allocation to address frequency components that are about to cause severe thermal shock to cable insulation.

[0169] S803. Based on the corrected temperature rise contribution weight, determine the target frequency from multiple preset frequencies.

[0170] In the embodiments of this application, the target frequency refers to the harmonic order that the reactive power compensation and harmonic suppression device needs to focus on eliminating in the current and short future period.

[0171] In some embodiments of this application, the target frequency can be determined using a sorting and truncation strategy. The reactive power compensation and harmonic suppression device sorts all preset frequencies from largest to smallest according to their corrected temperature rise contribution weights, and selects the top N frequencies (e.g., the top 3) with the largest temperature rise contribution weights as target frequencies. Alternatively, a weight threshold is set, and all preset frequencies with corrected temperature rise contribution weights exceeding this weight threshold are marked as target frequencies.

[0172] S804: Generate filter control instructions based on the target frequency.

[0173] In the embodiments of this application, the filter control command is a signal that instructs the reactive power compensation and harmonic suppression device to perform specific current injection actions. Unlike full-band compensation, the filter control command is an instruction for selective compensation based on a selected frequency, which typically corresponds to the activation of a specific resonant controller within the harmonic suppression module or the synthesis of a reference current for a specific frequency band.

[0174] As can be seen, the embodiments of this application utilize operating condition signals to correct the temperature rise contribution weight of harmonics, thereby identifying and locking high-risk frequencies before harmonic outbreaks for priority treatment, thus achieving proactive protection of the thermal life of underground cables in coal mines.

[0175] In some embodiments of this application, after adjusting the reactive power compensation module and harmonic suppression module in the reactive power compensation and harmonic suppression device according to the coordinated control command, it may further include:

[0176] S901, Obtain at least one of the following: the first temperature of the reactive power compensation module, the second temperature of the harmonic suppression module, and the internal ambient temperature of the reactive power compensation and harmonic suppression device.

[0177] In this embodiment, the first temperature refers to the real-time surface or core temperature of key heat-generating components in the reactive power compensation module. These components typically include staged switching power capacitors, series reactors, and thyristor switches or contactor contacts used for switching. The second temperature refers to the temperature of power semiconductor devices (such as insulated-gate bipolar transistors, IGBTs) and their heat sinks and DC bus capacitors in the harmonic suppression module (i.e., the active part, such as a static var generator). The internal ambient temperature refers to the average temperature of the air inside the explosion-proof housing or cabinet of the reactive power compensation and harmonic suppression device.

[0178] S902. If at least one of the first temperature, the second temperature, and the internal ambient temperature is greater than the corresponding preset temperature protection threshold, a blocking command is triggered. The blocking command is used to cut off the power supply to the reactive power compensation module and the harmonic suppression module, and to switch to the bypass operation mode on the low-voltage side of the mobile substation. The bypass operation mode is used to ensure that the power supply from the mobile substation to the load-side electrical equipment does not pass through the reactive power compensation and harmonic suppression devices.

[0179] In this embodiment, the preset temperature protection threshold is the lower limit of the limit safety value set according to the insulation heat resistance level of each component and the coal mine safety regulations (e.g., 70℃ for capacitors, 90℃ for IGBTs, and 55℃ for the chassis environment). The interlock command is a high-priority fault interruption signal; it not only includes software-level logic blocking but also typically links to hardware-level tripping mechanisms. The bypass operation mode is a fault-oriented safe operating state. When an overheating hazard occurs inside the reactive power compensation and harmonic suppression device, the circuit topology is changed to completely isolate the reactive power compensation module and harmonic suppression module from the main circuit. Power is then supplied directly to the load-side equipment such as the coal mining machine and conveyor by the mobile substation transformer, ensuring that critical underground production equipment can still receive continuous power even when the reactive power compensation and harmonic suppression device experiences an overheating hazard.

[0180] As can be seen, the embodiments of this application prioritize the thermal safety of the reactive power compensation and harmonic suppression device over its operational function. Once any part of the temperature exceeds the limit, the power supply to the reactive power compensation and harmonic suppression device is immediately cut off and automatically bypassed, thereby eliminating the potential for electrical fires underground while maximizing the continuity and reliability of power supply for coal mine production.

[0181] Secondly, embodiments of this application provide a reactive power compensation and harmonic suppression device, which is used to perform the reactive power compensation and harmonic suppression method for a mobile substation in a coal mine as described in any embodiment.

[0182] In some embodiments, the reactive power compensation and harmonic suppression device adopts an independent explosion-proof integrated design, comprising the following seven units: Ex d I (Ex refers to the general designation of explosion-proof electrical equipment, d refers to the explosion-proof type, and I refers to Class I (i.e., coal mine use) explosion-proof housing), load-side data acquisition unit, intelligent decision control unit, reactive power compensation module, harmonic suppression module, load linkage-remote communication unit, and explosion-proof power supply module. The composition, key parameters, and functions of each unit are as follows:

[0183] (1) Ex d Class I explosion-proof enclosure: The Ex d Class I explosion-proof enclosure is welded from metal plates and has three independent compartments: the main functional compartment is used to house the reactive power compensation module and harmonic suppression module; the control compartment is used to house the load-side data acquisition unit, intelligent decision control unit, and load linkage-remote communication unit; and the power protection compartment is used to house the explosion-proof power supply module. The compartments are equipped with heat dissipation ducts and auxiliary cooling fans, and the starting temperature threshold of the fans is set to 45℃. Its main function is to provide explosion protection in underground gas and dust environments, and to achieve fault zoning of each unit and / or module through physical isolation, so as to ensure the overall operational safety of the reactive power compensation and harmonic suppression device.

[0184] (2) Load-side data acquisition unit: The load-side data acquisition unit consists of two high-precision voltage transformers (adapted to 660V / 100V and 1140V / 100V ratios respectively) and two current transformers (adapted to 500A / 5A and 800A / 5A ratios respectively). In addition, the load-side data acquisition unit also includes three platinum resistance temperature sensors for detecting the temperature of the reactive power compensation module, harmonic suppression module, and explosion-proof power supply module, as well as a load status acquisition unit supporting a digital input (DI) interface for acquiring operating condition signals (e.g., start / stop and operation mode signals) of load-side electrical equipment such as coal mining machines or scraper conveyors. Its main function is to acquire real-time data such as voltage signals, current signals, harmonic components, and temperature on the load side, providing raw data support for intelligent decision-making.

[0185] (3) Intelligent Decision Control Unit: The intelligent decision control unit includes an industrial-grade Advanced RISC Machines (ARM) processor, a Field Programmable Gate Array (FPGA) logic chip for auxiliary harmonic calculation, storage devices, and a human-machine interface consisting of a display screen and three physical buttons. Its main functions are to receive data from the load-side data acquisition unit, run reactive power calculation and harmonic spectrum analysis algorithms, generate switching control commands for the reactive power compensation module and filtering control commands for the harmonic suppression module, and simultaneously perform self-diagnosis and fault logic judgment of the reactive power compensation and harmonic suppression devices.

[0186] (4) Reactive Power Compensation Module: The reactive power compensation module consists of four sets of Insulated Gate Bipolar Transistor (IGBT) power units, four sets of thin-film capacitor banks, four reactors, and four sets of drive circuits. Its main function is to receive switching control commands from the intelligent decision control unit, quickly control the switching of capacitor banks through IGBTs, dynamically compensate the reactive power on the load side, avoid overcompensation or undercompensation, and stabilize the power factor of the power grid.

[0187] (5) Harmonic Suppression Module: The harmonic suppression module includes four sets of passive inductor-capacitor (LC) filter branches corresponding to the 5th, 7th, 11th, and 13th harmonics, respectively. Each branch includes a reactor, a capacitor, and a damping resistor; and an active power filter (APF) unit using a three-phase three-level IGBT topology. Its main function is to suppress harmonics of the target frequency and avoid overheating and insulation aging on the low-voltage side of the mobile substation caused by harmonics.

[0188] (6) Load Linkage - Remote Communication Unit: The load linkage - remote communication unit includes an explosion-proof Ethernet device and communication device that support Transmission Control Protocol / Internet Protocol (TCP / IP), and a load linkage interface with two digital inputs / digital outputs (DI / DO) for linkage with load-side electrical equipment. Its main functions are, on the one hand, to realize data interaction with the ground monitoring center, upload operating parameters and receive remote commands; on the other hand, to establish linkage control with load-side equipment.

[0189] (7) Explosion-proof power supply module: The explosion-proof power supply module consists of an explosion-proof AC / DC (Alternating Current / Direct Current) converter, a backup lithium battery pack, and a power monitoring circuit. Its main function is to provide a stable DC power supply for the load-side data acquisition unit, intelligent decision control unit, and load linkage-remote communication unit, and to ensure the short-term operation of the reactive power compensation and harmonic suppression device through the backup battery pack when the main power supply of the reactive power compensation and harmonic suppression device is interrupted, ensuring the timely uploading of fault information.

[0190] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for reactive power compensation and harmonic suppression in a mobile substation underground in a coal mine, characterized in that, An application to a reactive power compensation and harmonic suppression device, wherein the reactive power compensation and harmonic suppression device is connected between a mobile substation and the load-side electrical equipment, the method includes: Acquire the operating status signals of the load-side electrical equipment, as well as the voltage and current signals at the input terminals of the reactive power compensation and harmonic suppression devices; Based on the voltage signal and the current signal, the reactive power deficit value of the low-voltage side of the mobile substation and the contribution weight of each preset frequency harmonic to the temperature rise of the low-voltage side cable of the mobile substation are determined. Based on the operating condition signal, the reactive power deficit value, and the temperature rise contribution weight, a coordinated control instruction is generated. The coordinated control instruction includes a switching control instruction for the reactive power compensation module in the reactive power compensation and harmonic suppression device, and a filtering control instruction for the harmonic suppression module in the reactive power compensation and harmonic suppression device. According to the coordinated control command, the reactive power compensation module and harmonic suppression module in the reactive power compensation and harmonic suppression device are adjusted to perform reactive power compensation and harmonic suppression on the low-voltage side of the mobile substation. The acquisition of the operating condition signal of the load-side electrical equipment includes: acquiring the current on the low-voltage side of the mobile substation at a sampling frequency of 20kHz, calculating the effective value change rate and the distortion rate of the current waveform with a sliding window of 20 milliseconds, and using these as feature data; matching the real-time calculated feature data with a preset feature vector template, wherein the reactive power compensation and harmonic suppression device has preset feature vector templates for several typical operating conditions; if the Euclidean distance obtained by the matching calculation is less than a preset matching threshold, it is determined that the current condition is a typical operating condition of the corresponding feature vector template, and a corresponding operating condition signal code is generated to obtain the operating condition signal; The step of generating coordinated control commands based on the operating condition signal, the reactive power deficit value, and the temperature rise contribution weight includes: determining the predicted change value of the reactive power deficit on the low-voltage side of the mobile substation based on the operating condition signal; calculating the differential value du / dt of the bus voltage and the differential value di / dt of the load current at the current time t relative to the previous time t-1; and obtaining the characteristic value K by calculating the product of the differential value of the load current and the negative of the differential value of the bus voltage, K=(di / dt)×(-du / dt); Based on the magnitude of the characteristic value K, determine the corresponding confidence coefficient γ: when K≤0, it is determined to be a non-load impact, let γ=0; when K>0, it is determined to be a real load impact, and calculate the confidence coefficient γ using the formula γ=K / (K+β), where β is the sensitivity adjustment constant; determine the total reactive power gap, the total reactive power gap = the reactive power gap value + (the confidence coefficient γ × the predicted change value of the reactive power gap); based on the total reactive power gap, generate the switching control command.

2. The reactive power compensation and harmonic suppression method for a mobile substation in a coal mine as described in claim 1, characterized in that, The reactive power deficit value is determined through the following steps: Based on the voltage signal, the current signal, and the actual power factor angle, the actual reactive power and actual active power on the low-voltage side of the mobile substation are determined. Based on the actual active power and the target power factor angle, the target reactive power on the low-voltage side of the mobile substation is determined. The reactive power deficit value is determined based on the power difference between the target reactive power and the actual reactive power.

3. The reactive power compensation and harmonic suppression method for a mobile substation in a coal mine as described in claim 1, characterized in that, The temperature rise contribution weight is determined through the following steps: The current signal is subjected to spectral analysis to obtain the harmonic amplitude values ​​of each preset frequency; Based on the harmonic amplitude of each preset frequency, determine the effective value of the harmonics at each preset frequency; Based on each preset frequency and its effective harmonic value, the contribution weight of each preset frequency harmonic to the temperature rise of the low-voltage side cable of the mobile substation is determined.

4. The reactive power compensation and harmonic suppression method for a mobile substation in a coal mine as described in claim 3, characterized in that, The determination of the contribution weight of each preset frequency harmonic to the temperature rise of the low-voltage side cable of the mobile substation based on each preset frequency and its effective harmonic value includes: Using each preset frequency, the effective harmonic values ​​of the corresponding preset frequencies are weighted to obtain the weighted effective harmonic values; The weighted effective values ​​of all preset frequencies are summed to obtain the total effective values ​​of the harmonics. The contribution weight of each preset frequency harmonic to the temperature rise of the low-voltage side cable of the mobile substation is determined based on the ratio between the weighted effective value of each preset frequency harmonic and the sum of the effective values ​​of the harmonics.

5. The reactive power compensation and harmonic suppression method for a mobile substation in a coal mine as described in claim 1, characterized in that, The step of generating the switching control command based on the total reactive power deficit includes: Obtain the preset reactive power deficit threshold; If the total reactive power deficit is less than the reactive power deficit threshold, a switching control command is generated to adjust the static var generator in the reactive power compensation module. If the total reactive power deficit is greater than or equal to the reactive power deficit threshold, a switching control command is generated to simultaneously adjust the static var generator and the graded capacitor bank in the reactive power compensation module.

6. The reactive power compensation and harmonic suppression method for a mobile substation in a coal mine as described in claim 5, characterized in that, The generation of the switching control command for simultaneously adjusting the static var generator and the tiered capacitor bank in the reactive power compensation module includes: Based on the total reactive power deficit and the rated capacity of a single capacitor bank in the tiered capacitor bank, determine the target number of capacitor banks to be put into operation. Generate a first switching command for controlling the deployment of the target number of capacitor banks; Determine the power gap difference between the total reactive power deficit and the total rated capacity of the target number of capacitor banks; Based on the power gap difference, a second switching command is generated to adjust the reactive power output of the static var generator; The switching control command includes the first switching command and the second switching command.

7. The reactive power compensation and harmonic suppression method for a mobile substation in an underground coal mine as described in claim 1, characterized in that, The generation of coordinated control commands based on the operating condition signal, the reactive power deficit value, and the temperature rise contribution weight includes: Based on the operating condition signal, the frequency of the harmonics that will be generated on the low-voltage side of the mobile substation is predicted to obtain the predicted frequency, which is included among multiple preset frequencies. The contribution weight of the predicted frequency harmonics to the temperature rise of the low-voltage side cable of the mobile substation is corrected to obtain the corrected temperature rise contribution weight. Based on the corrected temperature rise contribution weight, the target frequency is determined from multiple preset frequencies; The filter control command is generated based on the target frequency.

8. The reactive power compensation and harmonic suppression method for a mobile substation in a coal mine as described in claim 1, characterized in that, After adjusting the reactive power compensation module and harmonic suppression module in the reactive power compensation and harmonic suppression device according to the coordinated control command, the method further includes: Obtain at least one of the following: the first temperature of the reactive power compensation module, the second temperature of the harmonic suppression module, and the internal ambient temperature of the reactive power compensation and harmonic suppression device; If at least one of the first temperature, the second temperature, and the internal ambient temperature is greater than the corresponding preset temperature protection threshold, a lockout command is triggered. The lockout command is used to cut off the power supply to the reactive power compensation module and the harmonic suppression module, and to switch to the bypass operation mode of the low-voltage side of the mobile substation. The bypass operation mode is used to ensure that the power supply from the mobile substation to the load-side electrical equipment does not pass through the reactive power compensation and harmonic suppression devices.

9. A reactive power compensation and harmonic suppression device, characterized in that, The reactive power compensation and harmonic suppression device is used to perform the reactive power compensation and harmonic suppression method for the underground mobile substation in coal mines as described in any one of claims 1 to 8.

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