A method and system for collecting multiple parameters of an operating state of an electric power device

Abstract

The application discloses a kind of power equipment operating state multi-parameter acquisition method and system, belong to electric power system monitoring technical field.Method includes: sensor array acquires multiple original analog signals, integrates after being conditioned synchronous sampling, and obtains digital stream by analog-digital conversion;Using orthogonal frequency division multiplexing technology is mapped to preset subcarrier, and composite modulation signal is generated;Coupling circuit formed by high-voltage capacitor, high-frequency transformer and low-voltage capacitor is superimposed on power supply line;After receiving end separates signal, FFT demodulation and frequency division demultiplexing are carried out, and the digital signal of each sensor is recovered.The application uses power line as medium, reduces wiring and cost, is strong and flexible in expansion.

Description

Technical Field

[0001] This application belongs to the field of power systems, specifically relating to a method and system for acquiring multiple parameters of the operating status of power equipment. Background Technology

[0002] Condition monitoring of power equipment is crucial for ensuring the safe operation of power systems. By collecting and analyzing various operating parameters such as temperature, vibration, current, and voltage in real time, potential equipment hazards can be detected promptly. Among these, multi-parameter collaborative acquisition technology has become an important development direction in the field of intelligent operation and maintenance due to its ability to comprehensively assess equipment operating status.

[0003] Existing multi-parameter acquisition systems mostly adopt the following solutions: First, independent wiring, which configures a dedicated transmission cable for each sensor, and the number of cables increases exponentially with the increase of monitored parameters; second, centralized bus method, which aggregates multiple signals through a communication bus, but still requires additional deployment of dedicated communication cables; third, wireless transmission method, which eliminates the need for cables, but the signal reliability is insufficient in strong electromagnetic environments, and the sensor nodes need to be powered independently, resulting in high maintenance costs.

[0004] The common core drawback of the above solutions is that they all require establishing a dedicated transmission path for signal transmission, independent of the power supply line of the electrical equipment itself. This results in a large amount of wiring work, high installation costs, and difficulty in guaranteeing the anti-interference capability of signal transmission in the strong electromagnetic environment near high-voltage power equipment. Therefore, there is an urgent need for a multi-parameter acquisition solution that can utilize existing power lines to transmit multiple sensor signals, reduce the amount of wiring, and has strong anti-interference capabilities. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for acquiring multiple parameters of the operating status of power equipment, which can effectively solve the problems in the background art such as the large number of wiring, high installation cost, susceptibility to electromagnetic interference, and limited transmission bandwidth in acquiring multiple parameters of power equipment.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for acquiring multiple parameters of the operating status of power equipment includes the following specific steps: At the transmitting end, a sensor array deployed on the power equipment side collects multiple raw analog signals corresponding to various operating parameters. After signal conditioning, the multiplexer synchronously samples the signals according to a unified sampling clock and integrates them into a set of multiple analog signals. The set of multiple analog signals is converted from analog to digital to obtain a set of multiple digital signal streams in a unified format. Orthogonal frequency division multiplexing technology is used to map the multiple digital signal streams to a preset subcarrier frequency band to generate a composite modulation signal. The composite modulation signal is superimposed onto the power supply line of the power equipment through a coupling circuit. The coupling circuit consists of a high-voltage capacitor, a high-frequency transformer, and a low-voltage capacitor connected in series. The high-voltage capacitor is connected in series between the power supply line and the primary side of the high-frequency transformer. The secondary side of the high-frequency transformer is connected to the output terminal of the orthogonal frequency division multiplexing modulation unit through the low-voltage capacitor, so as to achieve isolated coupling between the composite modulation signal and the power frequency power supply. At the receiving end, the composite modulation signal is separated from the power supply line through a coupling circuit, and after analog-to-digital conversion, fast Fourier transform demodulation and frequency demultiplexing are performed sequentially. The digital signals corresponding to each sensor are separated from the frequency domain signal according to the preset subcarrier frequency band.

[0007] Furthermore, the sensor array deployed on the power equipment side collects multiple raw analog signals corresponding to various operating parameters, specifically including: deploying temperature sensors to collect temperature signals of the power equipment, deploying vibration sensors to collect vibration signals of the power equipment, deploying current sensors to collect current signals of the power equipment, and deploying voltage sensors to collect voltage signals of the power equipment; wherein, The temperature sensor is a PT100 resistance temperature detector (RTD) sensor or a thermocouple sensor, connected through a three-wire or four-wire temperature measurement circuit, with a measurement range of -50℃ to 200℃ and a measurement accuracy of ±0.5℃. The vibration sensor is a piezoelectric accelerometer or MEMS accelerometer with a sensitivity of 100mV / g, a frequency response range of 0.5Hz to 10kHz, and a maximum range of 50g. The current sensor is a sampling sensor on the secondary side of a current transformer or a Hall current sensor, with a transformation ratio of 1000:1 and a measurement accuracy of 0.5 class. The voltage sensor is a resistive voltage divider network sensor or a secondary side sampling sensor of a voltage transformer, with a voltage division ratio of 1000:1 and a measurement accuracy of 0.5%.

[0008] Furthermore, the step of using orthogonal frequency division multiplexing (OFDM) technology to map the multiple digital signal streams to a preset subcarrier frequency band to generate a composite modulation signal specifically includes: In a system containing 256 subcarriers, the subcarriers are numbered from 0 to 255, of which subcarriers numbered from 0 to 10 are reserved for transmitting pilot symbols, which use a preset PN sequence. Subcarriers numbered 11 to 30 are allocated to the temperature sensor signal, subcarriers numbered 31 to 80 are allocated to the vibration sensor signal, subcarriers numbered 81 to 120 are allocated to the current sensor signal, subcarriers numbered 121 to 180 are allocated to the voltage sensor signal, and subcarriers numbered 181 to 255 are reserved as backup resources. After subcarrier allocation, serial-to-parallel conversion and QAM constellation mapping are performed on each signal, and the frequency domain signals distributed in parallel on N subcarriers are converted into time domain OFDM symbol sequences through inverse fast Fourier transform. The number of points N in the inverse fast Fourier transform is 256. A cyclic prefix is ​​added to the head of the time-domain OFDM symbol sequence. The length of the cyclic prefix is ​​64 sampling points, which is 1 / 4 of the length of the effective data portion of the OFDM symbol.

[0009] Furthermore, the coupling circuit consists of a high-voltage capacitor, a high-frequency transformer, and a low-voltage capacitor connected in series, specifically: The high-voltage capacitor has a capacitance of 0.1 microfarads and a withstand voltage of not less than 1000V. One end of the capacitor is connected to the power supply line, and the other end is connected to the primary side of the high-frequency transformer. The high-frequency transformer has a turns ratio of 1:1, an operating frequency range of 1MHz to 100MHz, and a magnetic core made of high-frequency manganese-zinc ferrite material or nanocrystalline material. It provides an electrical isolation withstand voltage of not less than 2000V between the primary and secondary sides. The low-voltage capacitor has a capacitance of 0.1 microfarads and a withstand voltage of not less than 100V, and is connected in series between the secondary side of the high-frequency transformer and the output terminal of the orthogonal frequency division multiplexing modulation unit. The coupling circuit must meet the performance requirements of coupling insertion loss not exceeding 3dB and isolation not less than 60dB.

[0010] Furthermore, the step of performing analog-to-digital conversion on the set of multiple analog signals to obtain a multi-channel digital signal stream in a unified format specifically includes: Independent analog-to-digital converter (ADC) channels are configured for different types of sensors. The temperature signal channel uses a 24-bit high-precision ADC with a sampling rate of 1kHz and performs 16 average filtering operations per sample. The vibration signal channel uses a 16-bit high-speed ADC with a sampling rate of 20kHz. The current signal channel and voltage signal channel each use a 16-bit ADC with a sampling rate of 1kHz. The signals from each analog-to-digital converter channel are quantized and encoded, and then uniformly converted into a digital signal stream in IEEE 754 standard 32-bit floating-point format.

[0011] Furthermore, before performing QAM constellation mapping, channel coding is performed on the digital signal streams of each sensor. The channel coding uses convolutional codes or LDPC codes, and the coding rate is dynamically adjusted between 1 / 2 and 7 / 8 according to the real-time power line channel conditions. The coding rate is reduced when the channel conditions deteriorate and increased when the channel conditions improve.

[0012] Furthermore, the receiving end sequentially performs Fast Fourier Transform demodulation and frequency demultiplexing to separate the digital signals corresponding to each sensor from the frequency domain signal according to the preset subcarrier frequency band, specifically including: After frame synchronization is locked and the cyclic prefix is ​​removed, a 256-point fast Fourier transform operation is performed on the 256-point time-domain sequence to obtain the frequency-domain signal. The received signal at the pilot subcarrier position is extracted, compared with the preset PN sequence, the channel frequency response at the pilot subcarrier position is calculated, and the channel frequency response at all subcarrier positions is estimated by interpolation algorithm; Single-tap frequency domain equalization is used, and each subcarrier symbol is multiplied by the corresponding equalization coefficient to compensate for channel fading. The equalization coefficient is the reciprocal of the estimated channel frequency response value of the subcarrier. According to the preset subcarrier frequency band division, the complex symbols corresponding to each sensor are extracted from the equalized frequency domain signal according to the subcarrier number range. After parallel-to-serial conversion and QAM demapping, they are reassembled into a sequence of sensor sampling values ​​corresponding to the sampling time of the transmitting end.

[0013] Furthermore, after separating the digital signals corresponding to each sensor, a multi-parameter joint analysis step is also included, specifically: Perform over-temperature alarm, temperature rise calculation, and temperature trend prediction on the temperature signal; Perform time-domain waveform display, spectrum analysis, and vibration intensity calculation on vibration signals; Perform RMS value calculation, active power calculation, reactive power calculation, apparent power calculation, power factor calculation, and harmonic analysis on current and voltage signals; Perform cross-parameter joint analysis, including correlation analysis of temperature data and load current data to assess whether the transformer is in an overloaded operating state; and comparative analysis of vibration signal spectrum and load current spectrum to detect transformer core or winding faults.

[0014] Furthermore, the QAM constellation mapping specifically involves: when the channel conditions are poor, QPSK modulation is used to map every 2 bits to a complex symbol; when the channel conditions are good, 16QAM modulation is used to map every 4 bits to a complex symbol.

[0015] A multi-parameter acquisition system for the operating status of power equipment, comprising: Includes the sender, the transmission channel, and the receiver; The transmitting end is located on the power equipment side and includes: Sensor array unit, used to deploy multiple sensors to collect various operating parameters of power equipment and output multiple raw analog signals; The multiplexer unit is used to condition and synchronously sample the multiple original analog signals and integrate them into a set of multiple analog signals; The OFDM modulation unit is used to perform analog-to-digital conversion on the set of multiple analog signals to obtain multiple digital signal streams in a unified format, and to map the multiple digital signal streams to a preset subcarrier frequency band using orthogonal frequency division multiplexing technology to generate a composite modulation signal. A coupling circuit unit is used to superimpose the composite modulation signal onto the power supply line of the power equipment. The coupling circuit consists of a high-voltage capacitor, a high-frequency transformer, and a low-voltage capacitor connected in series. The high-voltage capacitor is connected in series between the power supply line and the primary side of the high-frequency transformer. The secondary side of the high-frequency transformer is connected to the output terminal of the OFDM modulation unit through the low-voltage capacitor to achieve isolated coupling between the composite modulation signal and the power frequency power supply. The transmission channel is the power supply line of the power equipment itself, used to simultaneously carry the power frequency power and the superimposed composite modulation signal; The receiving end is located on the monitoring terminal side and includes: A coupling circuit unit is used to separate the composite modulation signal from the power supply line and perform analog-to-digital conversion; The FFT demodulation unit is used to perform fast Fourier transform demodulation on the digitized time-domain signal to obtain the frequency-domain signal. The frequency demultiplexer unit is used to separate the digital signals corresponding to each sensor from the frequency domain signal according to the preset subcarrier frequency band.

[0016] In summary, this application includes at least one of the following beneficial technical effects: 1. This invention utilizes the power supply line of the power equipment itself as a communication medium to transmit multiple sensor signals, eliminating the need for additional signal transmission cables, significantly reducing the number of cables, and effectively reducing the complexity and material costs of cable laying.

[0017] 2. The present invention eliminates the need for conduit wiring, and the sensor signal multiplexing and transmission utilizes existing power lines, significantly shortening the installation cycle and greatly reducing the investment of construction manpower and time.

[0018] 3. This invention uses OFDM multi-carrier modulation technology. The orthogonal distribution of each subcarrier has good anti-multipath fading capability. Furthermore, the high-voltage capacitor and high-frequency transformer in the coupling circuit realize the isolation coupling between the modulation signal and the power frequency power supply, effectively blocking power frequency interference and grid noise.

[0019] 4. This invention can easily increase the number of monitoring parameters by allocating additional subcarriers. The spare subcarrier resources can be used to expand other types of sensors besides temperature, vibration, current, and voltage, making system upgrades flexible and convenient. Attached Figure Description

[0020] Figure 1 A schematic diagram of the overall technical solution for a method of acquiring multiple parameters of power equipment operating status; Figure 2 This is a schematic diagram illustrating the core principle of OFDM (Orthogonal Frequency Division Multiplexing) and power line coupled transmission. Figure 3 A logic flowchart for multi-channel sensor signal acquisition and composite modulation signal generation; Figure 4 This diagram illustrates the multi-level interaction and data flow between the sending end and the monitoring terminal. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the following description is provided in conjunction with the appendix. Figure 1 To be continued Figure 4 The present invention will be further described in detail below with reference to specific embodiments.

[0022] Firstly, the multi-parameter signal multiplexing transmission method based on power line carrier disclosed in this application comprises three functional module groups at the hardware architecture level: a transmitter, a transmission channel, and a receiver. The transmitter is located on the power equipment side, and its core functional modules sequentially include a sensor array unit, a multiplexer unit, an OFDM modulation unit, and a coupling circuit unit.

[0023] The sensor array unit contains various types of sensor nodes, which are physically connected to the monitoring points of the power equipment to collect various operating parameters of the power equipment. The sensor array unit outputs multiple raw analog signals to the multiplexer unit, which performs preprocessing, signal conditioning, and timing integration on each analog signal to form a set of multiple analog signals in a unified format.

[0024] The OFDM modulation unit receives multiple analog signals output from the multiplexer unit, first performs analog-to-digital conversion to obtain multiple digital signal streams, and then uses OFDM orthogonal frequency division multiplexing technology to map the multiple digital signal streams to different subcarrier frequency bands to form a composite modulation signal.

[0025] The coupling circuit unit superimposes the composite modulation signal output from the OFDM modulation unit onto the power supply line of the power equipment through capacitive coupling and transformer isolation, achieving isolated coupling between the modulation signal and the power frequency power supply. The transmission channel is the power supply line of the power equipment itself, including the 220V / 50Hz power frequency power supply and the high-frequency modulation signal superimposed on it. The modulation signal is transmitted to the monitoring terminal along with the power frequency power supply through the power line.

[0026] The receiver is located on the monitoring terminal side, and its core functional modules include, in sequence, a coupling circuit unit, an ADC sampling unit, an FFT demodulation unit, and a frequency demultiplexer unit. The coupling circuit unit separates the composite modulated signal from the power line in the reverse manner. The ADC sampling unit samples and digitizes the separated analog signal. The FFT demodulation unit performs a Fast Fourier Transform demodulation on the digitized time-domain signal to obtain the frequency-domain signal.

[0027] The frequency demultiplexer unit separates the signal components corresponding to each subcarrier from the frequency domain signal according to the preset subcarrier allocation scheme, and recovers the original sensor digital signals of each channel.

[0028] The multi-parameter signal multiplexing transmission method based on power line carrier in this application is implemented according to the following steps: The first step is S1, the multi-channel sensor signal acquisition stage. In this stage, the sensor array set on the power equipment side will synchronously acquire various physical quantities reflecting the operating status of the equipment, and process each original analog signal into a set of analog signals with matched amplitude and consistent timing for subsequent analog-to-digital conversion and OFDM modulation unit processing. Specifically, it includes the following steps.

[0029] Step S101: Deploy multiple sensors and establish sensing connections with the power equipment. At least two types of sensors should be deployed at the monitored parts of the power equipment to collect relevant operating parameters. The specific deployment and configuration methods are as follows: The temperature sensor uses a PT100 resistance temperature detector (RTD) or thermocouple sensor, connected through a three-wire or four-wire temperature measurement circuit. The measurement range covers -50℃ to 200℃, with a measurement accuracy of ±0.5℃ and a response time of less than 1 second. It is used to collect the surface temperature of power equipment or the oil temperature of oil-immersed transformers.

[0030] The vibration sensor is a piezoelectric accelerometer or MEMS accelerometer with a sensitivity of 100mV / g, a frequency response range of 0.5Hz to 10kHz, a maximum range of 50g, and a lateral sensitivity of less than 5%. It is used to collect mechanical vibration signals from power equipment.

[0031] The current sensor uses sampling from the secondary side of a current transformer or a Hall current sensor, with a transformation ratio of 1000:1, a measurement accuracy of 0.5 class, and a bandwidth of DC to 10kHz. It is used to collect the load current or leakage current of power equipment.

[0032] The voltage sensor uses a resistive voltage divider network or the secondary side of a voltage transformer for sampling, with a voltage division ratio of 1000:1 and a measurement accuracy of 0.5 class. It is used to collect the phase voltage or line voltage of power equipment.

[0033] Step S102 involves independently conditioning each sensor signal. The raw analog signal output from each sensor is processed through its own independent signal conditioning channel. Each channel performs the following operations sequentially: first, a low-pass filter removes high-frequency noise components from the signal; then, an instrumentation amplifier effectively amplifies the signal amplitude; and finally, a level conversion circuit linearly adjusts the signal amplitude to a voltage range that matches the input range of the subsequent analog-to-digital converter, such as 0-5V or ±5V. This step ensures that sensor signals with different dynamic ranges and amplitude characteristics can be processed uniformly and effectively by the subsequent acquisition circuit.

[0034] In step S103, a multiplexer performs synchronous sampling and timing integration. The analog signals from each channel, conditioned in step S102, are input to the multiplexer in parallel. The multiplexer is configured with an independent sample-and-hold circuit for each input channel and is triggered by a unified sampling clock. Instantaneous values ​​of the signals from all channels are acquired at the same time, achieving strict synchronous sampling of the multiple signals. Subsequently, these held analog quantities are arranged according to a preset timing sequence and integrated into a set of multiple analog signals. This set completely preserves the synchronization time correspondence between the sensor signals, laying the foundation for subsequent multi-parameter joint analysis.

[0035] In summary, step S1 completes the entire process of acquiring multiple types of operating parameters from the power equipment, adaptively conditioning the signals, and synchronizing them. The multi-channel analog signal set output by this process has high synchronization accuracy and amplitude consistency, fully mapping the real-time changes in the equipment's operating status, and providing high-quality raw signals for the analog-to-digital conversion, quantization encoding, and frequency division multiplexing transmission based on OFDM technology in the subsequent step S2.

[0036] The next step is step S2, the analog-to-digital conversion and signal quantization encoding stage. After obtaining the set of multiple analog signals in step S1, this stage uses the analog-to-digital conversion module to convert the analog signals of each channel into digital signal streams that can be used for OFDM modulation. During the conversion process, the sampling rate, quantization accuracy, and output format are configured according to the type of each parameter to ensure that the time domain resolution and amplitude accuracy of each signal meet the requirements of subsequent analysis. The specific steps include the following.

[0037] Step S201: Configure independent analog-to-digital converter (ADC) channels and parameters for different types of sensors. The ADC module has multiple independent ADC channels built-in. Temperature signals, vibration signals, current signals, and voltage signals each occupy a dedicated channel, ensuring they do not interfere with each other. The sampling rate and quantization accuracy of each channel are dynamically configured based on the bandwidth and resolution requirements of that signal, as detailed below: The temperature signal channel employs a 24-bit high-precision analog-to-digital converter, supporting a temperature resolution of ±0.1℃. The sampling rate is configured at 1kHz, and the sampling period is 1 millisecond. Each sample undergoes 16 average filters to reduce quantization noise interference with the temperature readings.

[0038] The vibration signal channel employs a 16-bit high-speed analog-to-digital converter with a sampling rate configured at 20kHz and a sampling period of 50 microseconds. This channel supports continuous sampling mode, with a single continuous sampling length set to 1024 points, corresponding to a sampling window of 51.2 milliseconds, which meets the requirements of subsequent vibration signal spectrum analysis for frequency resolution and time domain truncation length.

[0039] Both the current signal channel and the voltage signal channel use a 16-bit analog-to-digital converter, with a sampling rate of 1kHz and a sampling period of 1 millisecond, maintaining the same sampling rhythm as the temperature signal channel. This facilitates direct multi-parameter timing alignment in subsequent data processing without the need for additional interpolation or timestamp correction operations.

[0040] The above configuration of each channel together defines the two key parameters of sampling rate and quantization bits for the acquisition of multiple types of signals, so that the signals of different types of sensors can complete parameter matching with their own physical characteristics before entering the digital domain.

[0041] Step S202: Perform sample-and-hold and quantization encoding on each channel signal. Under the parameters determined in step S201, each analog-to-digital converter channel sequentially performs sample-and-hold and quantization encoding operations on the analog signal input to its channel.

[0042] The sample-and-hold circuit captures the instantaneous value of the current analog signal at the trigger edge of the sampling clock and maintains it stable on the holding capacitor for subsequent quantization circuitry to read. The quantization encoding circuit converts the held analog voltage value into a digital code. The quantization precision is no less than 12 bits, and the quantization encoding uses binary two's complement format. 12 bits of quantization precision corresponds to 4096 quantization levels, and the quantization noise is approximately -72dB.

[0043] The temperature signal channel has a quantization accuracy higher than 12 bits, and a 24-bit analog-to-digital converter ensures that its temperature resolution reaches the required ±0.1℃. The vibration signal channel and the current and voltage signal channels all meet the requirement of a quantization accuracy of not less than 12 bits, which can preserve the main dynamic characteristics of the signal.

[0044] Through a sample-and-hold circuit, the analog-to-digital converter ensures that the input voltage for each quantization operation is strictly consistent with the instantaneous value of the analog signal at the time of sampling. Quantization encoding then converts this instantaneous value into a digital code that can be processed by subsequent circuits.

[0045] Step S203: Unify the output format of each digital signal stream. After quantization encoding is completed, the digital signal streams output by each channel analog-to-digital converter are represented and transmitted using the unified IEEE 754 standard 32-bit floating-point format.

[0046] Regardless of whether the original data comes from a 24-bit temperature channel or a 16-bit vibration, current, or voltage channel, it is converted to floating-point numbers in the same format before leaving the analog-to-digital conversion module. This process allows the subsequent OFDM modulation unit to receive and process data from each channel directly through a unified interface without worrying about the differences in the number of quantization bits between channels when processing multiple signals, thus simplifying the input interface design and data scheduling logic of the OFDM modulation unit.

[0047] Step S2 completes the conversion process from analog to digital signals. The analog-to-digital conversion module configures the channel parameters according to the bandwidth and accuracy requirements of the four types of signals: temperature, vibration, current, and voltage. It obtains digital codes that accurately reflect the instantaneous values ​​of the signals through sample-and-hold and quantization encoding, and finally outputs them as a digital signal stream in standard floating-point format.

[0048] These four digital signal streams are synchronized at the sampling time and retain the accuracy characteristics of their respective physical ranges in terms of values, providing a digital signal source with a unified format and capable of direct parallel processing for OFDM-based subcarrier allocation, constellation mapping, and IFFT modulation in step S3.

[0049] The next step is step S3, the OFDM frequency division multiplexing and composite modulation signal generation stage. After converting the multiple sensor signals into a unified format digital signal stream in step S2, this stage involves the OFDM modulation unit performing frequency division multiplexing and orthogonal modulation processing on these digital signal streams. Using OFDM technology, each data stream is allocated to different subcarriers. Through constellation mapping, IFFT transformation, cyclic prefix addition, and up-conversion, a composite modulation signal that can be transmitted over power lines is finally generated.

[0050] Step S301: Divide and allocate subcarrier resources. The OFDM modulation unit first dynamically allocates subcarrier resources within the total number of subcarriers preset by the system according to the bandwidth requirements of each sensor signal.

[0051] For an OFDM system containing 256 subcarriers, the subcarriers are numbered sequentially from 0 to 255. The subcarrier allocation scheme is as follows: Eleven subcarriers, numbered 0 to 10, are reserved for transmitting pilot symbols. The pilot symbols use a pre-defined PN sequence, which the receiver uses for channel estimation and carrier synchronization.

[0052] Twenty subcarriers, numbered 11 to 30, are allocated to the temperature sensor signal. The temperature sensor has a sampling rate of 100Hz and a bandwidth requirement of approximately 2kHz. Each subcarrier carries a symbol rate of 1k symbols / second.

[0053] Fifty subcarriers, numbered 31 to 80, are allocated to the vibration sensor signal. The vibration sensor has a sampling rate of 10 kHz and a bandwidth requirement of approximately 50 kHz. Each subcarrier carries a symbol rate of 10 k symbols / second.

[0054] Forty subcarriers, numbered 81 to 120, are allocated to the current sensor signal. The current sensor has a sampling rate of 1 kHz and a bandwidth requirement of approximately 40 kHz.

[0055] Sixty subcarriers, numbered 121 to 180, are allocated to the voltage sensor signal. The voltage sensor has a sampling rate of 1 kHz and a bandwidth requirement of approximately 60 kHz.

[0056] Seventy-five subcarriers, numbered 181 to 255, are reserved as spare resources. These spare subcarriers can be used for future expansion to include more types of sensors, or for transmitting redundant information from error correction codes.

[0057] The frequency spacing between each subcarrier is configured within the range of 1kHz to 10kHz to ensure orthogonality between subcarriers and eliminate inter-carrier interference. After the subcarrier allocation is completed, each sensor digital signal stream is assigned to its respective subcarrier group according to the above division, and subsequent processing will be based on this allocation scheme.

[0058] Step S302: Perform QAM constellation mapping and channel coding. After the subcarrier allocation is determined, each digital signal stream enters the QAM constellation mapping stage. This stage maps the bit stream to be transmitted on each subcarrier to constellation points on the complex plane.

[0059] In practice, the digital signal streams from each sensor are first converted from serial to parallel based on the subcarrier allocation results, distributing each serial bit stream to its corresponding multiple subcarriers. The data on each subcarrier is grouped according to the selected modulation order. For QPSK modulation, every two bits are grouped and mapped to a complex symbol, with constellation points located at four positions on the unit circle at 90-degree intervals. This method is suitable for situations with poor channel conditions or high transmission reliability requirements. For 16QAM modulation, every four bits are grouped and mapped to a complex symbol, with constellation points distributed across 16 positions in a 4×4 grid. This method is suitable for situations with good channel conditions and high spectral efficiency requirements.

[0060] Before constellation mapping, the digital signal stream undergoes channel coding. Channel coding employs convolutional codes or LDPC codes, and the coding rate can be dynamically adjusted between 1 / 2 and 7 / 8 based on real-time power line channel conditions. When channel conditions deteriorate, the coding rate is reduced to increase redundancy and improve noise immunity; when channel conditions improve, the coding rate is increased to enhance effective data throughput.

[0061] The aforementioned subcarrier allocation and constellation mapping operations together organize multiple sensor data with different bandwidth requirements into the frequency domain resources of the OFDM system, and adapt to the transmission characteristics of the power line channel with appropriate modulation order and coding protection.

[0062] Step S303: A time-domain signal is generated using an N-point inverse fast Fourier transform (IFFT). The complex symbols of each subcarrier frequency domain output from the constellation mapping are fed into the IFFT operation module. The IFFT converts the frequency-domain signals distributed in parallel on the N subcarriers into a time-domain sampling sequence.

[0063] The number of points N in IFFT is the total number of subcarriers. In a system with 256 subcarriers, N equals 256. The IFFT operation transforms the frequency domain complex symbols on subcarriers 0 to 255 simultaneously into a time domain complex sequence of length 256, which contains both real and imaginary parts.

[0064] The mathematical expression for the IFFT operation is in standard form: ; In this formula, uppercase X[k] represents the complex number symbol in the frequency domain after constellation mapping on the k-th subcarrier, where k is the subcarrier index, ranging from 0 to N-1; lowercase x[n] represents the complex value of the n-th time-domain sampling point after IFFT transformation, where n is the sampling point index, also ranging from 0 to N-1; N is the number of IFFT points, i.e., the total number of subcarriers; j is the imaginary unit; e is the base of the natural logarithm; and π is pi.

[0065] IFFT operations are implemented in digital signal processors or FPGAs, using fast radix-2 or radix-4 algorithms to keep the computational complexity of complex multiplication and addition within an engineering-feasible range. After IFFT transformation, multiple data streams that were originally transmitted in parallel via subcarriers in the frequency domain are merged into a unified time-domain OFDM symbol sequence.

[0066] Step S304: Add a cyclic prefix to the header of the time-domain signal. Before the time-domain sequence output by IFFT is output as a complete OFDM symbol, a cyclic prefix needs to be added to the header of the symbol.

[0067] The cyclic prefix is ​​generated by copying a segment of samples from the end of the IFFT output sequence and inserting it into the beginning of the sequence. The length of the cyclic prefix is ​​denoted as Ncp samples. In a 256-subcarrier system, Ncp is typically 64 samples, approximately one-quarter of the length of the effective data portion of the OFDM symbol. After adding the cyclic prefix, a complete OFDM symbol consists of 64 cyclic prefix samples and 256 effective data samples.

[0068] The direct purpose of adding a cyclic prefix is ​​to transform the linear convolution effect of power line multipath channels on OFDM symbols into a cyclic convolution effect. This avoids inter-symbol interference, allowing the receiver to compensate for channel fading using only a single-tap frequency domain equalizer after FFT demodulation, eliminating the need for complex time-domain equalization algorithms.

[0069] Step S305 involves performing digital-to-analog conversion and up-conversion processing. The digital OFDM time-domain sequence after cyclic prefix addition is sent to the digital-to-analog converter (DAC) to be converted into an analog voltage signal. The sampling rate of the DAC is set to the product of the subcarrier interval and the number of IFFT points N to meet the requirements of the Nyquist sampling theorem for signal reconstruction.

[0070] Subsequently, the upconversion module modulates the baseband OFDM analog signal onto a high-frequency carrier band. The carrier frequency is selected based on the actual transmission characteristics of the power line channel and local radio management regulations, typically set in the range of 1MHz to 100MHz. The upconversion modulation method can be either double-sideband modulation or single-sideband modulation, striking a trade-off between spectrum utilization efficiency and implementation complexity.

[0071] Step S3 integrates the originally independent multi-channel sensor digital signal streams into a composite modulated signal with resistance to power line multipath fading through five sub-steps: subcarrier allocation, QAM constellation mapping and channel coding, IFFT transformation, cyclic prefix addition, and digital-to-analog conversion and up-conversion.

[0072] The center frequency, subcarrier distribution, and symbol structure of the composite modulation signal have been adapted to the characteristics of the power line channel and can be directly provided to the coupling circuit in step S4 for efficient and isolated superposition of the signal onto the power line for transmission.

[0073] Then, in step S4, the power line coupling stage, the composite modulation signal generated in step S3 is safely and efficiently superimposed onto the existing power supply line of the power equipment through the coupling circuit, so as to realize the co-cable transmission of high-frequency signals and power frequency power on the same line.

[0074] Step S401: Construct a three-stage isolation coupling circuit consisting of a high-voltage capacitor, a high-frequency transformer, and a low-voltage capacitor connected in series. The coupling circuit is composed of a high-voltage capacitor, a high-frequency transformer, and a low-voltage capacitor connected in series to form a three-stage cascaded isolation structure.

[0075] The first stage consists of a high-voltage capacitor C1, with one end connected to the power line and the other end connected to the primary side of the high-frequency transformer. The capacitance of the high-voltage capacitor is selected to be 0.1 microfarads, and its withstand voltage rating is not less than 1000V. The main function of the high-voltage capacitor is to block the 50Hz power frequency current from flowing into the subsequent signal processing circuit, while simultaneously allowing the high-frequency modulation signal to pass through with almost no attenuation due to its extremely low impedance in the modulation signal frequency band.

[0076] The ability of a high-voltage capacitor to pass high-frequency signals can be quantitatively described by its capacitive reactance. The calculation of capacitive reactance follows the formula: ; In this formula, Capacitive reactance represents the capacitance, and its unit is ohms; Pi; This represents the frequency of the signal passing through the capacitor, measured in Hertz (Hz). This represents the capacitance value, measured in farads. For example, when using capacitance values... The capacitor is 0.1 microfarads and operates at the carrier frequency. The calculated capacitive reactance at 10MHz It is approximately 0.16 ohms, a value far lower than the characteristic impedance of the power line, so high-frequency modulation signals can pass through smoothly.

[0077] The second stage is a high-frequency transformer T, with a high-voltage capacitor C1 connected to its primary side and a low-voltage capacitor C2 connected to its secondary side. The transformer's turns ratio is set to 1:1, and its operating frequency range is selected between 1MHz and 100MHz. Its magnetic core uses high-frequency manganese-zinc ferrite material or nanocrystalline material. The high-frequency transformer enables signal transmission from the power line to the signal processing circuit, while providing an electrical isolation withstand voltage of not less than 2000V between the primary and secondary sides, effectively blocking the DC component and low-frequency AC component from the power line side from entering the signal processing circuit.

[0078] The third stage involves a low-voltage capacitor, C2, connected in series between the secondary side of the high-frequency transformer T and the output of the OFDM modulation unit. The capacitance of this low-voltage capacitor is 0.1 microfarads, and its withstand voltage is no less than 100V. The function of this low-voltage capacitor is to further isolate any residual power frequency components that may leak from the transformer's secondary side, and it also acts as a DC blocking capacitor at the signal output.

[0079] Step S402 involves performing signal superposition and ensuring that the circuit performance indicators meet the standards. The coupling circuit constructed in step S401 uses a combined working method of capacitive coupling and transformer isolation to superimpose the OFDM time-domain signal onto the power line. The result of the superposition is that the high-frequency modulated signal and the power frequency waveform coexist on the power line and are transmitted together to the remote monitoring terminal.

[0080] For this coupling process to be effective and safe, the coupling circuit needs to meet the following key performance requirements.

[0081] The coupling insertion loss does not exceed 3dB. This specification ensures that the power attenuation of the modulated signal is limited to an acceptable range when it passes through the coupling circuit, and that the signal-to-noise ratio of the signal reaching the receiver will not deteriorate sharply due to excessive attenuation.

[0082] The isolation level is no less than 60dB. This specification ensures that the strong electrical signal on the 50Hz power supply side can be effectively blocked and will not leak to the signal processing circuit side, thereby avoiding physical damage to the low-voltage signal circuit or introducing power frequency measurement errors.

[0083] The coupling circuit also needs to have good impedance matching characteristics. Specifically, the input impedance of the coupling circuit should match the characteristic impedance of the power line, and its output impedance should match the characteristic impedance of the OFDM modulation unit output or the signal processing circuit. By reducing impedance discontinuities, signal reflection can be suppressed and the standing wave ratio on the line can be reduced.

[0084] Step S4 provides a complete technical means for safely injecting high-frequency signals into high-voltage lines by specifically defining the three-level structure, component parameters, and key performance indicators of the coupling circuit.

[0085] After this stage of processing, the composite modulated signal carrying multi-channel sensor data is loaded onto the power supply line without damage, providing a physical basis for long-distance signal transmission using existing power lines in step S5.

[0086] Regarding step S5, the signal transmission stage, in this stage, the composite modulated signal already superimposed on the power supply line is transmitted towards the monitoring terminal using the existing power supply line of the power equipment as the physical transmission medium. The entire transmission process does not require the laying of any additional dedicated signal cables, and specifically includes the following steps.

[0087] In step S501, a signal transmission channel is established based on the power supply line. The signal output from the transmitting end coupling circuit directly enters the existing power supply line of the power equipment. This power supply line simultaneously carries the 50Hz power frequency and the high-frequency modulation signal injected in step S4. The two signals propagate in parallel on the same copper or aluminum conductor, without occupying independent physical lines.

[0088] The conductors of a power line themselves constitute the signal transmission medium. Modulated signals utilize the conductivity of these metallic conductors to propagate along the line as electromagnetic waves. The transmission distance is affected by the line's own conditions, including the material of the power line, the cross-sectional area of ​​the conductors, the joints and branches along the line, as well as the carrier frequency selected for the modulated signal and the output power of the transmitting end. Under the combined influence of these factors, the actual transmission distance can reach hundreds of meters to several kilometers.

[0089] Step S502: Maintain stable signal superposition on the power frequency power supply. During transmission, the high-frequency modulation signal is always superimposed on the power frequency power supply voltage waveform. Taking a typical application scenario of this invention as an example, the transmitting end on the power equipment side couples the OFDM modulated signal to a 220V / 50Hz power line through a coupling circuit. At this time, the amplitude of the modulated signal is approximately 1 volt RMS, while the peak voltage of the power frequency power supply reaches approximately 311 volts. The amplitudes differ by more than two orders of magnitude, and the modulated signal is attached to the surface of the power frequency power supply waveform in the form of a small signal.

[0090] The signal transmission delay from the transmitting end to the monitoring terminal is no more than 10 milliseconds. This delay level is acceptable for applications with high real-time requirements, such as power equipment condition monitoring, and ensures the temporal correspondence between the sensor data received by the monitoring terminal and the actual operating status of the equipment.

[0091] Step S503 addresses the complex transmission characteristics of power line channels. As a signal transmission channel, the impedance characteristics of power lines are not constant. The line impedance varies with factors such as the frequency of the transmitted signal, the type and size of the load connected to the line, and the line length. This varying impedance can cause the modulated signal to experience different degrees of attenuation during transmission, and reflections can occur at impedance discontinuities, resulting in multipath propagation effects.

[0092] Multipath propagation causes the receiver to receive multiple copies of the same signal, with different arrival times and phases, resulting in inter-symbol interference in the time domain. This is where the OFDM multicarrier modulation technique used in step S3 of this scheme demonstrates its inherent advantages.

[0093] OFDM symbols themselves consist of multiple mutually orthogonal subcarriers, have a relatively long symbol period, and are supplemented with a cyclic prefix, making them inherently robust to delay spread caused by multipath propagation. Therefore, even if the power line channel exhibits frequency-selective fading under multipath conditions, OFDM signals can still ensure reliable transmission of multipath sensor data.

[0094] Step S5 describes the entire process of the composite modulated signal originating from the coupling point at the transmitting end, passing through the existing power supply lines of the power equipment, and finally arriving at the monitoring terminal. The transmission capacity of this stage is based on the adaptability of the OFDM signal format to power line channel multipath and frequency-selective fading. After the signal arrives at the monitoring terminal, it enters the signal demodulation stage in step S6.

[0095] The next step is step S6, the signal demodulation stage. This stage is performed on the monitoring terminal side and is used to recover multiple digital signal streams from the mixed signals received from the power line. Specifically, it includes the following steps.

[0096] Step S601: The composite modulation signal is separated and digitized from the power line. The coupling circuit unit on the monitoring terminal side processes the mixed signal on the power line. The structure of this coupling circuit is symmetrical to that of the transmitting coupling circuit, but the signal flow is opposite. The coupling circuit unit extracts the high-frequency modulation signal component from the line voltage, which simultaneously contains power frequency power and high-frequency modulation signal, while suppressing the 50Hz power frequency power and low-frequency noise components on the line.

[0097] The separated analog modulated signal is fed into the ADC sampling unit for digitization. The sampling rate of the ADC sampling unit is set to be no less than twice the carrier frequency of the modulated signal to satisfy the Nyquist sampling theorem. In engineering implementations, the sampling rate is usually configured to four times the carrier frequency for oversampling to obtain a higher signal-to-noise ratio and improve anti-aliasing performance.

[0098] In step S602, the digitized time-domain signal is frame-synchronized and the cyclic prefix is ​​removed. The time-domain sampling sequence output by the ADC sampling unit enters the frame synchronization stage. The receiver uses the pilot symbols or training sequences embedded in the OFDM symbols by the transmitter to perform correlation operations with the locally known reference sequence, and determines the starting boundary of each OFDM symbol by detecting the position of the correlation peak.

[0099] After frame synchronization is locked, the receiver discards the cyclic prefix portion of the OFDM symbol header according to the preset cyclic prefix length Ncp of the transmitter. In a 256-subcarrier system, Ncp takes 64 sampling points. The receiver cuts off the first 64 sampling points from each complete OFDM symbol, retaining only the subsequent 256 valid data sampling points for FFT operation.

[0100] After the cyclic prefix is ​​removed, inter-symbol interference caused by power line multipath channels is eliminated. The residual effects of the previous symbol that were diffused into the cyclic prefix due to multipath delay spread are discarded along with the cyclic prefix, and the effective data portion of the current symbol is no longer affected by crosstalk from adjacent symbols.

[0101] In step S603, the time-domain signal is converted back to the frequency-domain signal using FFT transformation. The 256-point time-domain sequence retained after cyclic prefix removal is sent to the FFT demodulation unit. The FFT demodulation unit performs an N-point FFT operation. In a 256-subcarrier system, N equals 256, which is consistent with the number of points in the IFFT at the transmitting end.

[0102] The FFT operation transforms the time-domain sampled sequence into complex symbols on each subcarrier in the frequency domain. Its mathematical expression is: ; In this formula, The number obtained after removing the cyclic prefix at the receiving end. Complex values ​​of each time-domain sampling point The sampling point number ranges from 0 to... ; Represents the FFT transformation of the th The frequency domain complex values ​​recovered on each subcarrier The subcarrier index is also from 0 to... ; The number of points in the FFT is equal to the total number of subcarriers; The imaginary unit; is the base of the natural logarithm; Pi is the mathematical constant of a circle.

[0103] The FFT operation is implemented in a digital signal processor or FPGA, using a fast radix-2 or radix-4 algorithm. After the FFT transformation, the receiver obtains the frequency domain complex symbols carried on each subcarrier. The amplitude and phase of these symbols have been offset relative to the original values ​​when the constellation was mapped at the transmitter due to the influence of channel fading.

[0104] Step S604: Perform channel estimation and single-tap frequency domain equalization. After the FFT operation, the receiver performs channel estimation and frequency domain equalization to compensate for the amplitude and phase distortion introduced by the channel.

[0105] Channel estimation relies on pilot symbols transmitted by the transmitter on specific subcarriers. The receiver extracts the received signals at the pilot subcarrier positions and compares these received values ​​with the PN sequence pilot symbols preset by the transmitter. By calculating the complex ratio of the received pilot to the transmitted pilot, the channel frequency response sample value at the pilot subcarrier position is obtained. Subsequently, the receiver estimates the channel frequency response at all subcarrier positions using an interpolation algorithm. The interpolation algorithm can employ linear interpolation, spline interpolation, or an interpolation method based on the discrete Fourier transform.

[0106] After obtaining the channel frequency response estimates for each subcarrier, frequency domain equalization employs a single-tap structure. For each subcarrier, the equalization coefficient is taken as the reciprocal of the estimated channel frequency response for that subcarrier. The equalization operation is a complex multiplication, multiplying each subcarrier symbol output by the corresponding equalization coefficient to compensate for the channel fading experienced by that subcarrier.

[0107] After single-tap frequency domain equalization, the signal amplitude and phase on each subcarrier are restored to a state close to that of the transmitting end constellation mapping.

[0108] Step S605: Perform QAM demapping and channel decoding. The equalized complex symbols of each subcarrier enter the QAM demapping stage. QAM demapping is the reverse process of QAM constellation mapping in step S302, which determines the received complex symbols as the corresponding bit stream.

[0109] The specific demapping operation is as follows: For each equalized complex symbol, calculate its Euclidean distance to each standard constellation point in the QAM constellation diagram, select the constellation point with the closest distance, and use the bit sequence corresponding to that constellation point as the decision output. This decision method is hard-decision demapping. When the system adopts a soft-decision method, the demapping module outputs the log-likelihood ratio of each bit as soft information for use by the subsequent channel decoder.

[0110] The demapped bitstream passes through a channel decoding stage. The channel decoder employs a decoding algorithm matched to that of the transmitter: when the transmitter uses convolutional coding, the receiver uses Viterbi decoding; when the transmitter uses LDPC coding, the receiver uses belief propagation decoding. The decoder utilizes the redundant information added during encoding to detect and correct bit errors caused by channel noise and interference during transmission, thus recovering the original digital signal stream.

[0111] In step S6, the monitoring terminal extracts the high-frequency modulation component from the power line mixed signal, and obtains the digital signal corresponding to each subcarrier through digitization, frame synchronization, cyclic prefix removal, FFT demodulation, channel equalization and QAM demapping and decoding. This signal is then used for frequency demultiplexing in step S7 to separate the independent data streams of each sensor.

[0112] Finally, in step S7, the signal separation and data processing stage, the frequency demultiplexing module separates the digital signals corresponding to each sensor from the frequency domain signal demodulated in step S6 according to the preset subcarrier allocation scheme, and then hands them over to the data processing module for status analysis and fault diagnosis.

[0113] In step S701, the frequency domain signal components corresponding to each sensor are extracted according to the subcarrier allocation scheme. The frequency demultiplexing module determines the subcarrier range occupied by each sensor signal according to the subcarrier allocation scheme determined in step S301. The temperature sensor signal corresponds to subcarrier numbers 11 to 30, the vibration sensor signal corresponds to subcarrier numbers 31 to 80, the current sensor signal corresponds to subcarrier numbers 81 to 120, and the voltage sensor signal corresponds to subcarrier numbers 121 to 180.

[0114] The frequency demultiplexing module extracts complex symbols at corresponding positions from the frequency domain signal obtained after FFT operation in step S603 and channel equalization in step S604, according to the above subcarrier number range, and sends each group of extracted complex symbols to its corresponding demodulation channel.

[0115] Step S702: Perform parallel-to-serial conversion on each channel signal and reassemble the sensor sample value sequence. Each demodulation channel performs parallel-to-serial conversion on the complex symbols of the assigned subcarriers, converting the complex symbols distributed in parallel on multiple subcarriers into a serial bit stream.

[0116] The serial bitstream is then reassembled according to the sampling rate and data format of each sensor. The reassembly is based on the sampling rate parameter configured in step S201 and the IEEE 754 standard 32-bit floating-point format determined in step S203. The reassembled data forms a sequence of sensor sample values ​​that corresponds one-to-one with the sampling time at the transmitting end. The temperature sensor channel outputs a temperature sample value sequence, the vibration sensor channel outputs a vibration sample value sequence, the current sensor channel outputs a current sample value sequence, and the voltage sensor channel outputs a voltage sample value sequence.

[0117] The sampled value sequences of each sensor channel are output to the data processing module of the monitoring terminal.

[0118] Step S703 involves performing over-temperature alarm, temperature rise calculation, and temperature trend prediction on the temperature signal. The data processing module processes the sequence of sampled values ​​input from the temperature sensor channel. The processing includes: comparing the sampled temperature values ​​with a preset alarm threshold; triggering an over-temperature alarm when the sampled value exceeds the threshold; calculating the temperature rise rate per unit time based on continuously sampled temperature values; and performing trend analysis on historical temperature data sequences to predict future temperature trends, providing a criterion for early detection of potential equipment overheating.

[0119] Step S704 involves performing time-domain waveform display, spectrum analysis, and vibration intensity calculation on the vibration signal. The data processing module processes the sampled value sequence input from the vibration sensor channel. The processing includes: plotting the time-domain waveform of vibration acceleration over time to visually display the transient characteristics of the equipment vibration; performing spectrum analysis on the vibration sampled data, identifying characteristic frequency components in the vibration signal through Fourier transform, and determining whether the equipment has typical faults such as mechanical loosening or bearing wear; and calculating the vibration intensity based on the root mean square value of the vibration velocity to quantitatively assess the overall vibration level of the equipment.

[0120] Step S705 involves performing RMS value calculation, power calculation, harmonic analysis, and power quality assessment on the current and voltage signals. The data processing module performs joint processing on the sampled value sequences input from the current sensor channel and the voltage sensor channel. The processing includes: calculating the RMS values ​​of current and voltage; calculating active power, reactive power, apparent power, and power factor from the instantaneous sampled values ​​of current and voltage; performing harmonic analysis on the current and voltage waveforms, calculating the content of each harmonic and the total harmonic distortion rate, and assessing power quality accordingly.

[0121] Step S706: Perform multi-channel signal joint analysis to achieve equipment status assessment and fault diagnosis. The data processing module performs cross-parameter joint analysis on the multi-channel sensor data processed in steps S703 to S705. One joint analysis method is to correlate temperature data with load current data to assess whether the transformer is currently operating under overload conditions. Another joint analysis method is to compare the vibration signal spectrum with the load current spectrum to detect faults such as loosening of the transformer core or deformation of the windings.

[0122] Step S7 completes the entire receiver processing flow from frequency domain demultiplexing and data reconstruction to multi-parameter comprehensive analysis. The frequency demultiplexing module separates the composite signal into independent sensor data streams according to the subcarrier allocation scheme preset by the transmitter. The data processing module performs feature extraction and status discrimination of each data stream in the time domain, frequency domain, and joint domain, and finally outputs the monitoring results and diagnostic information of the power equipment operating status.

[0123] This embodiment uses a comprehensive monitoring system for power transformers as an example to describe the specific application of the present invention in detail. In this application example, the monitored object is a 10kV oil-immersed power transformer, and the monitored parameters include the transformer top oil temperature, bottom oil temperature, winding temperature, mechanical vibration, load current, and bus voltage, totaling six sensor signals.

[0124] In terms of sensor configuration, the top and bottom oil temperature sensors are PT100 resistance temperature detectors (RTDs), installed on the top and bottom of the transformer tank respectively, and connected to the transmitter via a three-wire connection. The measurement range is -40°C to 150°C, with an accuracy of ±0.5°C. The winding temperature sensor is a fiber optic grating temperature sensor, installed near the transformer windings and connected to the demodulator via fiber optic cable. Its measurement range is -40°C to 200°C, with an accuracy of ±1°C. The vibration sensor is a triaxial piezoelectric accelerometer, installed on the transformer tank casing, with a sensitivity of 100 mV / g and a frequency response range of 0.5 Hz to 5 kHz. The current sensor uses sampling from the secondary side of a current transformer with a transformation ratio of 600:5 and an accuracy of 0.5 class. The voltage sensor uses sampling from the secondary side of a voltage transformer with a transformation ratio of 10000:100 and an accuracy of 0.5 class.

[0125] For signal acquisition, a multiplexer synchronously samples six sensor signals. The temperature sensor signal has a sampling rate of 100Hz, meaning it is sampled once every 10 milliseconds, and each sample is averaged 10 times to reduce quantization noise. The vibration sensor signal has a sampling rate of 20kHz, meaning it is sampled once every 50 microseconds, and each continuous sample contains 1024 points for analysis. The current and voltage sensor signals have a sampling rate of 1kHz, meaning they are sampled once every 1 millisecond, and the effective value is calculated for each sample.

[0126] For OFDM modulation, a 128-subcarrier OFDM system is used, numbered 0 to 127. Subcarriers 0 to 9 are used to transmit pilot symbols, employing a known PN sequence in QPSK modulation, for channel estimation and synchronization at the receiver. Subcarriers 10 to 29 (20 subcarriers in total) are allocated to the top-level oil temperature sensor, using 16QAM modulation, with each subcarrier carrying 1k symbols per second. Subcarriers 30 to 49 (20 subcarriers in total) are allocated to the bottom-level oil temperature sensor, also using 16QAM modulation. Subcarriers 50 to 69 (20 subcarriers in total) are allocated to the winding temperature sensor, also using 16QAM modulation. Subcarriers 70 to 109 (40 subcarriers in total) are allocated to the vibration sensor, using 16QAM modulation, with each subcarrier carrying 10k symbols per second. Subcarriers 110 to 124 (15 subcarriers in total) are allocated to the current sensor, also using 16QAM modulation. Subcarriers 125 to 127 (3 subcarriers in total) are reserved as backup resources. The subcarrier spacing is configured to 4 kHz, or 4 kilohertz. The OFDM symbol period is 256 microseconds, the cyclic prefix length is 64 microseconds, and the total symbol period is 320 microseconds.

[0127] In terms of the coupling circuit, the high-voltage capacitor C1 is a 0.1 microfarad, 1500V ceramic capacitor, connected in series between the power line on the transformer side and the high-frequency transformer. The high-frequency transformer uses a nanocrystalline magnetic core, has a 1:1 turns ratio, operates from 1MHz to 50MHz, and has an isolation withstand voltage of 2000V. The low-voltage capacitor C2 is a 0.1 microfarad, 100V ceramic capacitor, connected in series between the secondary side of the high-frequency transformer and the OFDM modulation unit. The coupling insertion loss is approximately 2.5dB, and the isolation is approximately 65dB.

[0128] In terms of signal transmission, the high-frequency modulated signal output by the OFDM modulation unit is superimposed onto the high-voltage busbar of the 10kV power transformer through a coupling circuit, with a modulation signal amplitude of approximately 0.8 volts RMS. The signal is transmitted to the substation integrated monitoring terminal via the busbar over a distance of approximately 50 meters, with a transmission delay of approximately 3 milliseconds. The power line channel exhibits a relatively flat frequency response in this frequency band, with relatively weak multipath effects, which is beneficial for the reliable transmission of OFDM signals.

[0129] For signal demodulation, the coupling circuit of the monitoring terminal separates the OFDM modulated signal from the power line. The ADC sampling unit digitizes the analog signal at a sampling rate of 128kHz, which is four times the carrier frequency. After frame synchronization and cyclic prefix removal, the digitized time-domain signal undergoes a 128-point FFT transform to obtain the frequency-domain signal. Channel equalization utilizes pilot subcarriers for frequency-domain interpolation estimation to compensate for the effects of channel fading. The signals on each subcarrier undergo 16QAM demapping and parallel-to-serial conversion to recover the bitstream data from each sensor.

[0130] For signal separation, the frequency demultiplexer separates the subcarrier signals corresponding to the six sensors from the frequency domain signal according to the subcarrier allocation scheme, and sends them to the corresponding demodulation channels. Each channel undergoes parallel-to-serial conversion and format parsing to recover the sequence of six sensor sampling values ​​synchronized with the transmitter. The top oil temperature and bottom oil temperature sampling values ​​are updated at a rate of 100Hz, the winding temperature sampling value is updated at a rate of 100Hz, the vibration signal sampling value is continuously output at a rate of 20kHz, and the current and voltage sampling values ​​are updated at a rate of 1kHz.

[0131] In terms of data processing, the monitoring terminal's data processing module comprehensively analyzes data from six sensors. Temperature data is used to calculate oil temperature rise, assess transformer load capacity, and trigger over-temperature alarms. Vibration data is used for spectrum analysis to identify characteristic frequency components and determine if faults such as mechanical loosening or bearing wear exist. Current and voltage data are used to calculate electrical parameters such as active power, reactive power, apparent power, and power factor, and to perform harmonic analysis to assess power quality. Multi-parameter joint analysis can be used for transformer condition assessment and fault diagnosis. For example, correlation analysis between temperature and load current can be used to assess whether the transformer is under overload, and joint analysis of vibration spectrum and load current spectrum can detect faults such as loose transformer core or winding deformation.

[0132] On the other hand, the multi-parameter acquisition system for the operating status of power equipment disclosed in this application includes: Includes the sender, the transmission channel, and the receiver; The transmitter is located on the power equipment side and includes: Sensor array unit, used to deploy multiple sensors to collect various operating parameters of power equipment and output multiple raw analog signals; The multiplexer unit is used to condition and synchronously sample multiple raw analog signals and integrate them into a set of multiple analog signals; The OFDM modulation unit is used to perform analog-to-digital conversion on a collection of multiple analog signals to obtain a multi-channel digital signal stream in a unified format, and to use orthogonal frequency division multiplexing technology to map the multi-channel digital signal stream to a preset subcarrier frequency band to generate a composite modulation signal. The coupling circuit unit is used to superimpose the composite modulation signal onto the power supply line of the power equipment. The coupling circuit consists of a high-voltage capacitor, a high-frequency transformer and a low-voltage capacitor connected in series. The high-voltage capacitor is connected in series between the power supply line and the primary side of the high-frequency transformer. The secondary side of the high-frequency transformer is connected to the output terminal of the OFDM modulation unit through the low-voltage capacitor to achieve isolation coupling between the composite modulation signal and the power frequency power supply. The transmission channel is the power supply line of the power equipment itself, used to simultaneously carry power frequency power and superimposed composite modulation signals; The receiving end is set on the monitoring terminal side, including: The coupling circuit unit is used to separate the composite modulated signal from the power supply line and perform analog-to-digital conversion; The FFT demodulation unit is used to perform fast Fourier transform demodulation on the digitized time-domain signal to obtain the frequency-domain signal. The frequency demultiplexer unit is used to separate the digital signals corresponding to each sensor from the frequency domain signal according to the preset subcarrier frequency band.

[0133] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects.

[0134] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for acquiring multiple parameters of the operating status of power equipment, characterized in that, Includes the following steps: At the transmitting end, a sensor array deployed on the power equipment side collects multiple raw analog signals corresponding to various operating parameters. After signal conditioning, the multiplexer synchronously samples the signals according to a unified sampling clock and integrates them into a set of multiple analog signals. The set of multiple analog signals is converted from analog to digital to obtain a set of multiple digital signal streams in a unified format. Orthogonal frequency division multiplexing technology is used to map the multiple digital signal streams to a preset subcarrier frequency band to generate a composite modulation signal. The composite modulation signal is superimposed onto the power supply line of the power equipment through a coupling circuit. The coupling circuit consists of a high-voltage capacitor, a high-frequency transformer, and a low-voltage capacitor connected in series. The high-voltage capacitor is connected in series between the power supply line and the primary side of the high-frequency transformer. The secondary side of the high-frequency transformer is connected to the output terminal of the orthogonal frequency division multiplexing modulation unit through the low-voltage capacitor, so as to achieve isolated coupling between the composite modulation signal and the power frequency power supply. At the receiving end, the composite modulation signal is separated from the power supply line through a coupling circuit, and after analog-to-digital conversion, fast Fourier transform demodulation and frequency demultiplexing are performed sequentially. The digital signals corresponding to each sensor are separated from the frequency domain signal according to the preset subcarrier frequency band.

2. The method for acquiring multiple parameters of power equipment operating status according to claim 1, characterized in that, The sensor array deployed on the power equipment side collects multiple raw analog signals corresponding to various operating parameters, specifically including: deploying temperature sensors to collect temperature signals from the power equipment, deploying vibration sensors to collect vibration signals from the power equipment, deploying current sensors to collect current signals from the power equipment, and deploying voltage sensors to collect voltage signals from the power equipment; wherein... The temperature sensor is a PT100 resistance temperature detector (RTD) sensor or a thermocouple sensor, connected through a three-wire or four-wire temperature measurement circuit, with a measurement range of -50℃ to 200℃ and a measurement accuracy of ±0.5℃. The vibration sensor is a piezoelectric accelerometer or MEMS accelerometer with a sensitivity of 100mV / g, a frequency response range of 0.5Hz to 10kHz, and a maximum range of 50g. The current sensor is a sampling sensor on the secondary side of a current transformer or a Hall current sensor, with a transformation ratio of 1000:1 and a measurement accuracy of 0.5 class. The voltage sensor is a resistive voltage divider network sensor or a secondary side sampling sensor of a voltage transformer, with a voltage division ratio of 1000:1 and a measurement accuracy of 0.5%.

3. The method for acquiring multiple parameters of power equipment operating status according to claim 1, characterized in that, The step of using orthogonal frequency division multiplexing (OFDM) technology to map the multiple digital signal streams to a preset subcarrier frequency band to generate a composite modulation signal specifically includes: In a system containing 256 subcarriers, the subcarriers are numbered from 0 to 255, of which subcarriers numbered from 0 to 10 are reserved for transmitting pilot symbols, which use a preset PN sequence. Subcarriers numbered 11 to 30 are allocated to the temperature sensor signal, subcarriers numbered 31 to 80 are allocated to the vibration sensor signal, subcarriers numbered 81 to 120 are allocated to the current sensor signal, subcarriers numbered 121 to 180 are allocated to the voltage sensor signal, and subcarriers numbered 181 to 255 are reserved as backup resources. After subcarrier allocation, serial-to-parallel conversion and QAM constellation mapping are performed on each signal, and the frequency domain signals distributed in parallel on N subcarriers are converted into time domain OFDM symbol sequences through inverse fast Fourier transform. The number of points N in the inverse fast Fourier transform is 256. A cyclic prefix is ​​added to the head of the time-domain OFDM symbol sequence. The length of the cyclic prefix is ​​64 sampling points, which is 1 / 4 of the length of the effective data portion of the OFDM symbol.

4. The method for acquiring multiple parameters of power equipment operating status according to claim 1, characterized in that, The coupling circuit consists of a high-voltage capacitor, a high-frequency transformer, and a low-voltage capacitor connected in series, specifically: The high-voltage capacitor has a capacitance of 0.1 microfarads and a withstand voltage of not less than 1000V. One end of the capacitor is connected to the power supply line, and the other end is connected to the primary side of the high-frequency transformer. The high-frequency transformer has a turns ratio of 1:1, an operating frequency range of 1MHz to 100MHz, and a magnetic core made of high-frequency manganese-zinc ferrite material or nanocrystalline material. It provides an electrical isolation withstand voltage of not less than 2000V between the primary and secondary sides. The low-voltage capacitor has a capacitance of 0.1 microfarads and a withstand voltage of not less than 100V, and is connected in series between the secondary side of the high-frequency transformer and the output terminal of the orthogonal frequency division multiplexing modulation unit. The coupling circuit must meet the performance requirements of coupling insertion loss not exceeding 3dB and isolation not less than 60dB.

5. The method for acquiring multiple parameters of power equipment operating status according to claim 1, characterized in that, The step of performing analog-to-digital conversion on the set of multiple analog signals to obtain a multi-channel digital signal stream in a unified format specifically includes: Independent analog-to-digital converter (ADC) channels are configured for different types of sensors. The temperature signal channel uses a 24-bit high-precision ADC with a sampling rate of 1kHz and performs 16 average filtering operations per sample. The vibration signal channel uses a 16-bit high-speed ADC with a sampling rate of 20kHz. The current signal channel and voltage signal channel each use a 16-bit ADC with a sampling rate of 1kHz. The signals from each analog-to-digital converter channel are quantized and encoded, and then uniformly converted into a digital signal stream in IEEE 754 standard 32-bit floating-point format.

6. The method for acquiring multiple parameters of power equipment operating status according to claim 1, characterized in that, Before performing QAM constellation mapping, channel coding is performed on the digital signal streams of each sensor. The channel coding uses convolutional codes or LDPC codes, and the coding rate is dynamically adjusted between 1 / 2 and 7 / 8 according to the real-time power line channel conditions. Reduce the coding rate when channel conditions deteriorate, and increase the coding rate when channel conditions improve.

7. The method for acquiring multiple parameters of power equipment operating status according to claim 1, characterized in that, The receiving end sequentially performs Fast Fourier Transform demodulation and frequency demultiplexing, separating the digital signals corresponding to each sensor from the frequency domain signal according to the preset subcarrier frequency band, specifically including: After frame synchronization is locked and the cyclic prefix is ​​removed, a 256-point fast Fourier transform operation is performed on the 256-point time-domain sequence to obtain the frequency-domain signal. The received signal at the pilot subcarrier position is extracted, compared with the preset PN sequence, the channel frequency response at the pilot subcarrier position is calculated, and the channel frequency response at all subcarrier positions is estimated by interpolation algorithm; Single-tap frequency domain equalization is used, and each subcarrier symbol is multiplied by the corresponding equalization coefficient to compensate for channel fading. The equalization coefficient is the reciprocal of the estimated channel frequency response value of the subcarrier. According to the preset subcarrier frequency band division, the complex symbols corresponding to each sensor are extracted from the equalized frequency domain signal according to the subcarrier number range. After parallel-to-serial conversion and QAM demapping, they are reassembled into a sequence of sensor sampling values ​​corresponding to the sampling time of the transmitting end.

8. The method for acquiring multiple parameters of power equipment operating status according to claim 7, characterized in that, After separating the digital signals corresponding to each sensor, the process also includes a multi-parameter joint analysis step, specifically including: Perform over-temperature alarm, temperature rise calculation, and temperature trend prediction on the temperature signal; Perform time-domain waveform display, spectrum analysis, and vibration intensity calculation on vibration signals; Perform RMS calculation, active power calculation, reactive power calculation, apparent power calculation, power factor calculation, and harmonic analysis on current and voltage signals; Perform cross-parameter joint analysis, including correlation analysis of temperature data and load current data to assess whether the transformer is in an overloaded operating state; and comparative analysis of vibration signal spectrum and load current spectrum to detect transformer core or winding faults.

9. The method for acquiring multiple parameters of power equipment operating status according to claim 3, characterized in that, The QAM constellation mapping is specifically as follows: when the channel conditions are poor, QPSK modulation is used to map every 2 bits to a complex symbol; when the channel conditions are good, 16QAM modulation is used to map every 4 bits to a complex symbol.

10. A multi-parameter acquisition system for the operating status of power equipment, characterized in that, Includes the sender, the transmission channel, and the receiver; The transmitting end is located on the power equipment side and includes: Sensor array unit, used to deploy multiple sensors to collect various operating parameters of power equipment and output multiple raw analog signals; The multiplexer unit is used to condition and synchronously sample the multiple original analog signals and integrate them into a set of multiple analog signals; The OFDM modulation unit is used to perform analog-to-digital conversion on the set of multiple analog signals to obtain multiple digital signal streams in a unified format, and to map the multiple digital signal streams to a preset subcarrier frequency band using orthogonal frequency division multiplexing technology to generate a composite modulation signal. A coupling circuit unit is used to superimpose the composite modulation signal onto the power supply line of the power equipment. The coupling circuit consists of a high-voltage capacitor, a high-frequency transformer, and a low-voltage capacitor connected in series. The high-voltage capacitor is connected in series between the power supply line and the primary side of the high-frequency transformer. The secondary side of the high-frequency transformer is connected to the output terminal of the OFDM modulation unit through the low-voltage capacitor to achieve isolated coupling between the composite modulation signal and the power frequency power supply. The transmission channel is the power supply line of the power equipment itself, used to simultaneously carry the power frequency power and the superimposed composite modulation signal; The receiving end is located on the monitoring terminal side and includes: A coupling circuit unit is used to separate the composite modulation signal from the power supply line and perform analog-to-digital conversion; The FFT demodulation unit is used to perform fast Fourier transform demodulation on the digitized time-domain signal to obtain the frequency-domain signal. The frequency demultiplexer unit is used to separate the digital signals corresponding to each sensor from the frequency domain signal according to the preset subcarrier frequency band.

Images