A power measurement method for elevator balance coefficient inspection

Abstract

A power measurement method for elevator balance coefficient inspection includes: signal feature identification and analysis: actually measuring the up and down signals of the elevator under no-load condition, analyzing the signal results for features, and demodulating and filtering the output voltage and load current; power measurement: selecting one signal as the reference signal, performing frequency characteristic filtering on the reference signal to obtain the fundamental frequency and zero-crossing information of the reference signal; using the fundamental frequency and zero-crossing information of the reference signal as the trigger signal for resampling, and performing resampling on the original sampling sequence to achieve full-cycle transformation; the signal after full-cycle transformation contains all the information of the original sampling signal, and it is also necessary to perform line filtering processing on the resampled signal, including demodulating the output voltage of the frequency converter and filtering out high-frequency harmonics, and then calculating the voltage, current, and power parameters; finally, automatic compensation of the parameters is performed. The present invention ensures that the power measurement meets the technical index requirements of the power measurement instrument for elevator balance coefficient inspection.

Description

Technical Field

[0001] The present invention belongs to the technical field of measurement, and specifically refers to a power measurement method for elevator balance coefficient inspection. Background Art

[0002] The elevator balance coefficient is one of the important performance indicators of elevators, which is related to the safety, comfort and economy of elevator operation, and is also an important factor for energy-saving operation of elevators. The Special Equipment Inspection Association recommends the "secondary current method" and the "no-load power method" as quick detection methods for elevator balance coefficients. Among them, the "no-load power method" has the advantages of greatly shortening the on-site detection time and eliminating the need to carry weights, etc., and has been greatly improved in terms of labor intensity and operation safety, and is widely used in the on-site inspection of elevator balance coefficients.

[0003] The "T / CASEI T101-2015 Quick Detection Method for Elevator Balance Coefficient" stipulates the inspection process of the "no-load power method". Connect the power measurement instrument to the incoming line terminal of the elevator drive motor, measure the active power of the drive motor in real time, and use the speed measurement instrument to measure the running speed of the elevator car in real time. Record the active power (Ns, Nx) and speed (Vs, Vx) of the drive motor when the elevator is running no-load upward and downward with the condition that the car and the counterweight are at the same horizontal position, and then calculate the balance coefficient according to the formula q = (Nx×Vs + Ns×Vx) / 2QgVxVs (q is the balance coefficient, and Q is the rated load of the elevator).

[0004] The measurement principle of the "no-load power method" for elevator balance coefficient is to measure the power of the drive motor and the speed of the car when the elevator is running upward and downward under the no-load condition respectively, and solve the elevator balance coefficient based on the functional relationship between power, speed and load. When measuring the power of the drive motor, due to the different electrical signal waveform characteristics at the front end and the rear end of the frequency converter, and the electrical parameters during elevator operation are time-varying signals, the general universal power measurement instrument cannot meet the measurement requirements. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a power measurement method for elevator balance coefficient inspection to accurately measure the power of the drive motor under the elevator operating conditions.

[0006] The present invention is implemented as follows:

[0007] A power measurement method for elevator balance coefficient inspection includes the following steps:

[0008] Step 1: Signal feature identification and analysis:

[0009] Measure the up and down signals of the elevator under no-load condition, and conduct feature analysis on the signal results. There are significant distortions in the grid-side current, resulting in a reduction in power factor, and reactive power compensation is required. The output voltage on the load side is a modulated pulse wave that varies sinusoidally. Since only the fundamental wave of the driving motor does work, in order to correctly measure the power, it is necessary to measure the output voltage and load current after demodulation and filtering;

[0010] Step 2: Power measurement:

[0011] Select one path of the signal as the reference signal, perform frequency characteristic filtering on the reference signal to obtain the fundamental frequency and zero-crossing information of the reference signal;

[0012] Use the fundamental frequency and zero-crossing information of the reference signal as the trigger signal for resampling, and resample the original sampling sequence to achieve integral cycle transformation; the signal after integral cycle transformation contains all the information of the original sampling signal. It is also necessary to perform line filtering processing on the resampled signal, including demodulation of the output voltage of the frequency converter and filtering of high-frequency harmonics, and then calculate the voltage, current, and power parameters, and finally perform automatic compensation of the parameters;

[0013] Among them, the frequency characteristic filtering is used to process the reference signal and serve as the synchronization source for other channels. Its basic function is to obtain zero-crossing and fundamental frequency information for integral cycle transformation and resampling of the sampling sequences of other channels. Specifically, it includes:

[0014] (1) Design filter parameters: Downsample the sampling sequence of the reference signal to obtain the downsampling factor and downsampling decimation frequency; when performing frequency characteristic measurement, use a FIR windowed filter for filtering, and the designed frequency characteristic filter uses a Kaiser window as the smoothing window. The smoothing window can reduce the ripple in the filter passband and improve the attenuation of the filter for frequency components in the stopband;

[0015] (2) Filter the reference signal: Perform low-pass filtering, downsampling, and band-pass filtering on the input reference signal by the obtained FIR windowed filter coefficients; there is a phase shift between the filtered reference signal and the original signal, that is, the group delay of the filtering link;

[0016] (3) Calculate the fundamental frequency and zero-crossing information: According to the filter parameters, including the forward coefficient, reverse coefficient, periodic sampling number, downsampling factor, and downsampling decimation frequency, calculate the number of zero-crossings and the corresponding zero-crossing times of the filtered signal, and calculate the average fundamental frequency according to the sampling interval and the periodic sampling number.

[0017] Furthermore, the full-cycle transformation is to perform a full-cycle transformation on the sampling sequence to eliminate the analysis error caused by asynchronous sampling. The zero-crossing information of the reference signal and the fundamental frequency are used as the new sampling trigger signal. According to the sampling trigger moment and the number of sampling triggers per cycle, the original sampling sequence is resampled, and the resampled samples need to meet the Nyquist criterion.

[0018] Furthermore, the line filtering is to filter the high-frequency harmonics and noise of the front-end loop current, the output voltage at the back end, and the load current. The specific operation is to set appropriate high / low cut-off frequencies, filter lengths, and select the window function form according to the characteristics and bandwidth characteristics of the on-site signal. Then, according to the sampling frequency, the filter coefficients required for implementing the FIR windowed filter are solved (i.e., the unit impulse response of the filter), and then the frequency response and forward coefficients of the filter are obtained. Finally, the input sampling sequence is filtered by the direct-form IIR filter specified by the forward coefficients.

[0019] Furthermore, the power parameter calculation is for the calculation of the basic parameters of U, I, and P. The waveform sampling data after line filtering is subjected to FFT to obtain the effective values, initial phases, and fundamental frequencies of the phase voltages and currents. For the convenience of calculation, the two components in polar coordinates are converted into complex numbers to obtain the three-phase active power.

[0020] Furthermore, the parameter automatic compensation, also known as "frequency dynamic compensation", is to calibrate the entire power measurement system with a standard signal and establish an error compensation model without changing the hardware configuration after the power measurement system is established. Its basic functions include "amplitude-frequency" dynamic correction and "phase-frequency" dynamic correction.

[0021] Furthermore, it also includes: power measurement performance experiment: Extract the voltage and current signals of the power supply end and the motor end respectively from the elevator operation site. Based on the analysis of the signals, synthetic test signals are synthesized using laboratory standard equipment, and the power measurement performance experiment is carried out using the synthetic test signals to obtain the comprehensive measurement error of the power. It can be used only when it meets the inspection requirements of the elevator balance coefficient.

[0022] The advantages of the present invention are as follows:

[0023] 1. Based on the analysis of the signal characteristics, a processing method for the reference signal is proposed, which is more in line with the actual operation conditions of the elevator, with strong pertinence, strong practicability, and high accuracy.

[0024] 2. Filter the frequency characteristics of the reference signal to obtain the fundamental frequency and zero-crossing information of the reference signal, which are used as the trigger signal for resampling. Then, perform an integer-period transformation on the sampling sequence. The resampled samples should meet the Nyquist criterion, contain the characteristics of the original sampling signal without distortion, eliminate the synchronization analysis error, and further improve the accuracy of the analysis process.

[0025] 3. Perform line filtering on the high-frequency harmonics and noise contained in the current of the front-end circuit of the frequency converter, the output voltage of the back-end, and the load current, and automatically compensate the amplitude-frequency and phase-frequency responses of the primary parameter sensing unit to ensure the accuracy of the measurement.

[0026] 4. Use laboratory standard equipment to synthesize test signals for power measurement performance experiments to ensure that the power measurement meets the technical index requirements of the power measurement instrument for elevator balance coefficient inspection. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below with reference to the accompanying drawings in conjunction with embodiments.

[0028] Figure 1 It is a schematic diagram of a three-phase AC variable-frequency power supply for supplying power to the AC motor of the elevator.

[0029] Figure 2 It is a waveform diagram of the grid-side AC voltage.

[0030] Figure 3 It is a waveform diagram of the grid-side AC current.

[0031] Figure 4 It is a frequency spectrum diagram of the grid-side AC current.

[0032] Figure 5 It is a waveform diagram of the load-side AC voltage.

[0033] Figure 6 It is a waveform diagram of the load-side AC current.

[0034] Figure 7 It is a waveform diagram of the output voltage of the inverter after filtering.

[0035] Figure 8 It is a waveform diagram of the load current after filtering.

[0036] Figure 9 It is a flow chart of the sampling sequence processing of the present invention.

[0037] Figure 10 It is a schematic diagram of downsampling of the present invention.

[0038] Figure 11 It is a schematic diagram of the reference signal and the filtered signal of the present invention.

[0039] Figure 12It is the reference signal and the full-cycle transformation signal diagram of the present invention.

[0040] Figure 13 It is the schematic diagram of the parameter automatic compensation module in the present invention.

[0041] Figure 14 It is the waveform diagram of the test signal at the power supply end of the power measurement experiment of the present invention.

[0042] Figure 15 It is the waveform diagram of the test signal at the motor end of the power measurement experiment of the present invention. Specific embodiments

[0043] A power measurement method for elevator balance coefficient inspection includes the following steps:

[0044] Step 1: Signal feature identification and analysis:

[0045] The elevator drive motor is usually an AC motor with variable speed operation. The supply voltage changes with the frequency of the power supply. The power supply for the AC motor should be a variable frequency and variable voltage AC power supply with coordinated control of the output voltage and frequency, that is, a VVVF (Variable Voltage Variable Frequency) AC power supply. Common technical solutions are as Figure 1 shown. A two-stage conversion circuit is adopted. The first stage is an AC / DC rectification conversion circuit, and the second stage is a DC / AC inversion circuit.

[0046] The rectification circuit is usually composed of diode switching devices, semi-controlled switching thyristors, and self-turn-off switching devices to form rectifiers with different structures, and the conversion of AC electrical energy to DC electrical energy is achieved by controlling the on and off of semiconductor switching devices. The extensive use of these semiconductor devices and the change of the load cause distortion of the grid-side AC voltage and loop current. Figures 2 to 4 It is the measured signal of the elevator running no-load downward. According to the signal analysis result, the total harmonic distortion of the AC voltage is 2%, the total harmonic distortion of the AC current is 128%, the odd harmonic content of the AC current is large, and it mainly contains the 5th, 7th, 11th, and 13th harmonics. The harmonic content of the grid-side input AC current is large, resulting in a reduction in the power factor. When the active power of the load is constant, it is required that the power supply outputs a larger effective value current, thus reducing the use efficiency of the power supply. Therefore, it is necessary to perform power measurement and signal feature analysis on the grid side to provide a basis for power factor compensation.

[0047] The DC voltage VD output after rectification is converted into AC through inversion and used as the power supply for the drive motor. The inversion link commonly uses SPWM (Sinusoidal Pulse Width Modulation) technology. By controlling the on and off states of the switching devices in real time, a multi-pulse voltage with a rectangular pulse width varying according to the sine law is obtained. The output voltage after inversion contains high-order harmonics that are multiples of the switching frequency in addition to the fundamental wave. The low-order harmonics are well suppressed. The higher the switching frequency, the more pulse numbers there are, the more low-order harmonics are eliminated, and the closer the output voltage waveform is to a sine wave. For a three-phase inverter, the multi-pulse PWM control or SPWM control method of a single-phase inverter can be adopted. In each cycle of the output voltage, the switching devices are turned on and off multiple times, enabling the control of the magnitude and waveform of the output voltage and the elimination of specific-order harmonics as needed. Figure 5 and Figure 6 The original sampled waveforms of the voltage and current output by the inverter when the elevator is running empty upward are shown. It can be seen that the pulse-width modulation wave voltage and the load current output by the inverter need to be demodulated and filtered before power measurement. The processed voltage and current waveforms are as shown in Figure 7 and Figure 8 After analysis, the total harmonic distortion rate of the output voltage after inversion is 37%, and the total harmonic distortion of the load current is 3.5%.

[0048] Step 2: Power measurement:

[0049] From the above signal characteristic analysis, it can be seen that there are large distortions in the grid-side current, and the output voltage on the load side belongs to a modulated pulse wave that changes according to the sine law. In addition to the need to process the signal, with the fluctuations of the grid voltage and the changes of the load, the amplitudes and frequencies of the electrical parameters on both sides of the frequency converter are not stable and constant. Based on the sampling measurement method, in order to ensure the accuracy of the analysis, when processing the sampling sequence, the synchronization of sampling should be ensured. Since the frequency of the signal to be measured fluctuates with time, when a fixed sampling rate is used for sampling, it is difficult for the discrete sequence to achieve an integer-cycle truncation, resulting in a synchronization analysis error. A commonly used method is to adopt a software synchronization method, that is, select a path of signal as the reference signal, first perform frequency characteristic filtering on the reference signal to obtain the fundamental frequency and zero-crossing information of the reference signal, use it as the trigger signal for resampling, and resample the original sampling sequence, so as to achieve integer-cycle sampling. The signal after integer-cycle transformation contains all the information of the original sampling signal, and the resampled signal still needs to be further processed, including the demodulation of the output voltage of the frequency converter and the filtering of high-frequency harmonics, and then the voltage, current, and power parameter calculations are performed, and finally the automatic compensation of the parameters is carried out. The signal processing flow is as shown in Figure 9 shown.

[0050] The frequency characteristic filtering is used to process the reference signal and serve as the synchronization source for other channels. Its basic function is to obtain the zero-crossing point and fundamental frequency information for the full-cycle transformation and resampling of the sampling sequence of other channels. Specifically, it includes:

[0051] (1) Waveform inspection: Check the reference signal sampling rate f s =1 / dt, fundamental frequency limit (fundamental frequency range: f max 、f min ), frequency measurement filter parameters (including: passband ripple δ p , stopband attenuation δ s , passband edge frequency f pb and the stopband edge frequency f sb ), the waveform formed by the sampling sequence during waveform inspection must satisfy formula (1). The passband edge frequency is greater than or equal to the upper limit of the fundamental frequency, and the stopband edge frequency is less than or equal to 2 times the lower limit of the fundamental frequency.

[0052]

[0053] (2) Design filter parameters:

[0054] To calculate the parameters of the windowed FIR filter, it is necessary to downsample the reference signal sampling sequence to obtain the downsampling factor and downsampling decimation frequency. The downsampling function is as follows: Figure 10 As shown. Based on the upper limit of the fundamental frequency f of the reference signal max and the stopband edge frequency f set in the filter design specification sb , select 40f max and 2f sb The maximum value f of the two e . Sampling rate f s Divide by f e The quotient is rounded down as the downsampling factor K df , divide the original sampling rate by the downsampling factor to obtain the decimation frequency after downsampling, denoted as f ds ;f ds The Nyquist criterion should be satisfied.

[0055] Let y be the filtered sampling sequence X, N b is the number of FIR coefficients, b j is the FIR coefficient. Then:

[0056]

[0057] The designed frequency characteristic filter uses the Kaiser window as the smoothing window. The Kaiser window is a flexible smoothing window, whose shape can be modified by adjusting the input, thereby controlling the magnitude of spectral leakage. For small beta values, the shape is close to that of a rectangular window. The FIR filter with a Kaiser window has a linear phase response, which only delays the input without distorting the signal. Therefore, its output is similar to the waveform of the input signal, but there is delay and attenuation. When calculating the zero-crossing information, this filter should be used to correct for the delay, and the attenuation of the amplitude does not affect the calculation of the zero-crossing. The mathematical expression of the Kaiser window is shown in Equation (3).

[0058]

[0059] Where \(I_0{}\) is the zero-order Bessel function of the first kind. β is a parameter for adjusting the shape of the window function. If β = 0, the Kaiser window becomes a rectangular window.

[0060] (3) Reference signal filtering:

[0061] Perform low-pass filtering, downsampling, and band-pass filtering on the input reference signal using the obtained FIR windowed filter coefficients. Figure 11 The effect of performing frequency characteristic filtering on the analog reference signal is given. It can be seen from the figure that there is a phase shift between the filtered reference signal and the original signal, that is, the group delay of the filtering section.

[0062] (4) Calculate the fundamental frequency and zero-crossing information:

[0063] From Figure 11 The filtered signal shown is used as the data sample for calculating the zero-crossing and fundamental frequency. According to the filter parameters (including forward coefficients, reverse coefficients, number of periodic samples, downsampling factor, and downsampling decimation frequency, etc.), the number of zero-crossings of the filtered signal and the corresponding zero-crossing times can be calculated, and the average fundamental frequency can be calculated based on the sampling interval and the number of periodic samples.

[0064] Full-cycle transformation:

[0065] One of the methods to eliminate the analysis error caused by sampling asynchrony is to perform a full-cycle transformation on the sampling sequence. The zero-crossing information and fundamental frequency of the obtained reference signal can be used as the new sampling trigger signal. According to the sampling trigger moment and the number of sampling triggers per cycle, resample the original sampling sequence. The resampled samples need to satisfy the Nyquist criterion, so that they can contain the characteristics of the original sampling signal without distortion, and at the same time, the synchronous analysis error is eliminated. The effect of the full-cycle transformation is as Figure 12 shown.

[0066] Line filtering:

[0067] When the elevator is in operation, the current in the front-end circuit, the output voltage at the back-end, and the load current of the frequency converter all contain high-frequency harmonics and noise. To ensure the accuracy of power measurement, pre-filtering is required. Figure 5 and Figure 7 The differences in the output voltage of the frequency converter before and after filtering were compared. Figure 6 and Figure 8 The differences in the load current before and after filtering were compared. The FIR filter has its own prominent advantages. First, the system is always stable. Second, it is easy to achieve linear phase. Third, it allows the design of multi-bandpass filters. When designing a windowed FIR filter, the appropriate high / low cut-off frequencies, filter length, window function form should be set according to the characteristics and bandwidth characteristics of the on-site signal, and the filter coefficients (i.e., the unit impulse response of the filter) required for implementing the windowed FIR filter should be solved according to the sampling frequency, and then the frequency response and forward coefficients of the filter are obtained. Then, the input sampling sequence is filtered by the direct-form IIR filter specified by the forward coefficients. In the present invention, 5 forms of window functions (Flat Top window, Kaiser-Bessel window, Blackman-Harris window, ExactBlackman window, Hamming window) in the "LabVIEW Help Document" were selected for performance comparison, and a suitable window function was selected for windowed FIR filtering.

[0068] There is no unified evaluation standard for the performance of window functions, and selection needs to be based on signal characteristics. According to its working principle and circuit structure, the frequency converter for elevators mainly considers harmonics below the 21st order. To evaluate the amplitude measurement performance index of the window function, the standard signal source superposition harmonic method is used for assessment.

[0069] To further verify the performance of the window function, a terminal voltage waveform of the drive motor was recorded from the elevator operation site and signal analysis was performed on it. A standard test signal was synthesized using the standard signal source according to the data in the analysis results, and the performance test experiment of the above 5 window functions was carried out again. The experimental results show that the application of the Blackman-Harris window has a smaller amplitude measurement error.

[0070] Basic parameter calculation:

[0071] In a three-phase system, the expressions of the three-phase voltage and three-phase current are shown in Equations (4) and (5). For a three-wire system, i a +i b +i c = 0, and the instantaneous power is p, and the expression is as shown in Equation (6). For a four-wire system, the expression is as shown in Equation (7).

[0072]

[0073]

[0074] p = v ab i a + v cb i c = v ba i b + v ca i c = v ac i a + v bc i b (6)

[0075] p = v a i a + v b i b + v c i c (7)

[0076] Wherein v ab , v bc , v ca are the instantaneous line voltages, v a , v b , v c are the instantaneous phase voltages, V a , V b , V c are the effective values of the phase voltages, I a , I b , I c are the effective values of the currents. When the load is connected in delta, the calculation method of the active power P is as shown in Equation (8), and when it is connected in star, the calculation method of the active power P is as shown in Equation (9).

[0077] P = V ab I a cos(α a - α b - β a ) + V cb I c cos(α c - α b - β c ) (8)

[0078] P = V a I a cos(α a - β a ) + V b I b cos(α b - β b ) + V c I c cos(αc -β c ) (9)

[0079] The waveform sampling data after line filtering is subjected to FFT to obtain the effective values, initial phases and fundamental frequencies of the phase voltages and currents shown in Equations (4) and (5). For the convenience of calculation, the two components of the polar coordinates are subjected to complex conversion to obtain Equations (8) and (9), and then the three-phase active power can be obtained.

[0080] Automatic parameter compensation:

[0081] Also known as "frequency dynamic compensation", it is an error compensation model established by calibrating the entire power measurement system with a standard signal without changing the hardware configuration after the power measurement system is established; Figure 13 The program block diagram of the automatic parameter compensation module in the delta connection is shown. The input on the left is the calculation result of the basic parameters, and the calculation result is corrected for errors according to the analysis frequency. The output on the right is the result after error compensation of each parameter. For unified expression, the core module (the dotted box in the figure) of the automatic parameter compensation module is called "frequency dynamic compensation", and its basic functions include two aspects: "amplitude-frequency" dynamic correction and "phase-frequency" dynamic correction. Amplitude compensation principle: High-accuracy and high-stability signal sources (Fluke5720A, 52120A) are used to provide sine wave voltages and currents of different frequencies, which are input into the power acquisition system to obtain the amplitude measurement results of the voltage and current at each frequency point. The relative error of the amplitude measurement is calculated, and a mathematical model of the relationship between the error and the frequency is obtained by polynomial fitting. Phase compensation principle: A high-stability current source is provided, and a precision coaxial shunt (Fluke A40B) with a known angular difference is connected in series in the current loop of the power acquisition system. The output signal of the shunt is used as the phase reference to obtain the phase difference measurement results of the current channel at each frequency point, and a mathematical model of the relationship between the angular difference and the frequency is obtained by piecewise polynomial fitting.

[0082] Power measurement performance experiment:

[0083] There are two main monitoring positions for power measurement under the elevator operating conditions, namely the power supply end and the motor end. It can be seen from the foregoing characteristic analysis that the current distortion in the power supply end loop is serious and the signal frequency is the power frequency; at the motor end, the motor voltage is a pulse width modulation waveform and the signal frequency changes with the elevator operation process. According to the voltage and current signals at the two monitoring positions extracted from the elevator operation site, test signals are synthesized using laboratory standard equipment based on the analysis of the signals. The test signal waveforms at the power supply end and the motor end are as shown in Figure 14 and Figure 15 shown. The results of the power measurement performance experiment are shown in Table 1. The data in Table 1 show that the comprehensive measurement error of the power is better than ±1%. It meets the inspection requirements of the elevator balance coefficient.

[0084] Table 1 Experimental Results of Power Measurement Performance

[0085]

[0086] Based on the analysis of signal characteristics, the present invention proposes a processing method for reference signals, which is more in line with the actual operating conditions of elevators, with strong pertinence, practicability and high accuracy. The frequency characteristics of the reference signal are filtered to obtain the fundamental frequency and zero-crossing information of the reference signal, which are used as the trigger signal for resampling. Then, the sampling sequence is subjected to a full-cycle transformation. The resampled samples need to meet the Nyquist criterion, that is, they contain the characteristics of the original sampling signal without distortion, eliminating the synchronous analysis error and further improving the accuracy of the analysis process. Line filtering is performed on the high-frequency harmonics and noise contained in the current of the front-end circuit of the frequency converter, the output voltage of the rear-end, and the load current, and automatic parameter compensation is performed on the amplitude-frequency and phase-frequency responses of the primary parameter sensing unit to ensure the accuracy of the measurement. The power measurement performance experiment is carried out by synthesizing test signals using laboratory standard equipment to ensure that the power measurement meets the technical index requirements of the power measurement instrument for elevator balance coefficient inspection.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A power measurement method for elevator balance coefficient inspection, characterized in that: It includes the following steps: Step 1: Signal feature identification and analysis: Measure the up and down signals of the elevator under no-load conditions, and conduct feature analysis on the signal results. There are significant distortions in the grid-side current, resulting in a decrease in power factor, and reactive power compensation is required. The output voltage on the load side shows a modulated pulse wave that changes in a sine wave pattern. Since only the fundamental wave of the drive motor does work, in order to correctly measure the power, it is necessary to measure the output voltage and load current after demodulation and filtering. Step 2: Power measurement: Select one path of the signal as the reference signal, perform frequency characteristic filtering on the reference signal to obtain the fundamental frequency and zero-crossing information of the reference signal. Use the fundamental frequency and zero-crossing information of the reference signal as the trigger signal for resampling, and resample the original sampling sequence to achieve an integer-cycle transformation. The signal after the integer-cycle transformation contains all the information of the original sampling signal. It is also necessary to perform line filtering on the resampled signal, including demodulation of the output voltage of the frequency converter and filtering of high-frequency harmonics, and then calculate the voltage, current, and power parameters. Finally, automatic compensation of the parameters is performed. Among them, the frequency characteristic filtering, its basic function is to obtain zero-crossing and fundamental frequency information. The filtered signal is used to process the reference signal and serve as the synchronization source for other channels, for the integer-cycle transformation and resampling of the sampling sequences of other channels. Specifically, it includes: (1) Design filter parameters: Downsample the sampling sequence of the reference signal to obtain the downsampling factor and the downsampling decimation frequency, and the designed frequency characteristic filter uses the Kaiser window as the smoothing window. (2) Filter the reference signal: Perform low-pass filtering, downsampling, and band-pass filtering on the input reference signal by the obtained FIR windowed filter coefficients. There is a phase shift between the filtered reference signal and the original signal, that is, the group delay of the filtering link. (3) Calculate the fundamental frequency and zero-crossing information: According to the filter parameters, including the forward coefficient, backward coefficient, number of periodic samples, downsampling factor, and downsampling decimation frequency, calculate the number of zero-crossings and the corresponding zero-crossing times of the filtered signal, and calculate the average fundamental frequency according to the sampling interval and the number of periodic samples.

2. A power measurement method for elevator balance coefficient inspection according to claim 1, characterized in that: The integer-cycle transformation is to perform an integer-cycle transformation on the sampling sequence to eliminate the analysis error caused by sampling asynchronization. Use the zero-crossing information and fundamental frequency of the reference signal as the new sampling trigger signal, and resample the original sampling sequence according to the sampling trigger moment and the number of sampling triggers per cycle. The resampled samples need to meet the Nyquist criterion.

3. A power measurement method for elevator balance coefficient inspection according to claim 1, characterized in that: The line filtering process is to filter the high-order harmonics or noise of the front-end loop current and the output voltage and load current at the back end. The specific operation is to set appropriate high and low cut-off frequencies, filter length, select the form of the window function according to the characteristics and bandwidth characteristics of the on-site signal, and solve the filter coefficients required for the implementation of the FIR windowed filter according to the sampling frequency, that is, the unit impulse response of the filter, and then obtain the frequency response and forward coefficient of the filter. Then, use the direct-form IIR filter specified by the forward coefficient to filter the input sampling sequence.

4. A power measurement method for elevator balance coefficient inspection according to claim 1, characterized in that: The automatic compensation of the parameters, also known as "frequency dynamic compensation", is an error compensation model established by calibrating the entire power measurement system with a standard signal without changing the hardware configuration after the power measurement system is established; its basic functions include "amplitude-frequency" dynamic correction and "phase-frequency" dynamic correction.

5. A power measurement method for elevator balance coefficient inspection according to claim 1, characterized in that: It further includes: Power measurement performance experiment: Extract the voltage and current signals at the power supply end and the motor end monitoring positions from the elevator operation site respectively. On the basis of analyzing the signals, synthesize test signals using laboratory standard equipment, and use the synthesized test signals to conduct power measurement performance experiments to obtain the comprehensive measurement error of power. It can be used only when the inspection requirements of the elevator balance coefficient are met.

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