A method for measuring the average power of a three-phase asynchronous motor by phase-shifting sampling

Abstract

This invention discloses a method for measuring the lead-lag average power of a three-phase asynchronous motor using phase-shift sampling, belonging to the field of motor power measurement technology. The method includes: signal conditioning processing, converting the three-phase voltage and current signals into levels suitable for ADC sampling; dual-state machine time-division sampling and power pre-calculation, cyclically acquiring voltage and current signals through T0 and T1 states and calculating the total three-phase power at adjacent sampling times; lead-lag averaging processing, performing an arithmetic average of adjacent pre-calculated power values; error compensation processing, calculating a compensation coefficient based on the sampling phase difference and correcting the power value; and periodic averaging filtering processing, achieving full-cycle power averaging based on the positive zero-crossing point detection of phase A voltage. This method achieves equivalent synchronous sampling based on a single energy meter, resulting in low hardware cost, system error control within ±0.1%, strong harmonic suppression capability, good load and frequency adaptability, a simple and efficient algorithm, and ease of embedded implementation.

Description

Technical Field

[0001] This invention relates to the field of motor power measurement technology, and in particular to a method for measuring the lead-lag average power of a three-phase asynchronous motor using phase-shift sampling. Background Technology

[0002] Three-phase asynchronous motors are the most important power equipment in industrial production, and their power measurement is of great significance for energy efficiency management, equipment protection, and operation optimization. Accurate measurement of motor power is the foundation for assessing motor operating status and achieving energy-saving control.

[0003] Currently, the following technical solutions are mainly used for power measurement of three-phase asynchronous motors: (1) Synchronous sampling scheme: A multi-channel ADC is used to sample the three-phase voltage and current simultaneously, and the average power is calculated by integrating the instantaneous power (e.g., CN105676125B "Method and device for measuring power of variable frequency motor"). This scheme has high measurement accuracy, but requires a multi-channel synchronous ADC, which is complex and costly, and has strict requirements for sampling synchronization.

[0004] (2) Time-division sampling scheme: Voltage and current signals are collected by a single energy meter in a time-division manner, and the time difference is compensated by software algorithm. This scheme has low hardware cost, but time-division sampling will introduce phase error and jitter, resulting in deviation in power calculation.

[0005] (3) Power metering chip solution: Power measurement is achieved by using a dedicated power metering chip. This solution has high integration, but poor flexibility and difficulty in achieving synchronous sampling of voltage and current signals.

[0006] In summary, existing power measurement technologies mainly suffer from the following technical shortcomings: (1) High hardware cost of synchronous sampling: Traditional synchronous sampling schemes require multiple ADCs to work at the same time and require strict time synchronization between channels, which increases the complexity and cost of hardware design.

[0007] (2) The phase error of time-division sampling is difficult to eliminate: In the time-division sampling scheme, there is a fixed time interval between voltage and current sampling, which leads to a phase difference. Traditional methods are difficult to accurately compensate for this phase error, which affects the accuracy of power measurement.

[0008] (3) Harmonic interference affects measurement accuracy: There are a large number of harmonic components in industrial power grids. Traditional power measurement methods do not effectively filter out harmonic interference, resulting in large fluctuations in power calculation results and a decrease in measurement accuracy.

[0009] (4) Lack of a unified three-phase power calculation model: Existing technologies mostly use the method of simply adding the single-phase power calculations together, without establishing a power calculation method based on the unified ABC three-phase model, making it difficult to accurately analyze system errors. Summary of the Invention

[0010] To address the aforementioned problems in existing technologies, this invention provides a method for measuring the lead-lag average power of a three-phase asynchronous motor using phase-shift sampling. This method achieves equivalent synchronous sampling based on a single energy meter. Through the coordinated processing of dual-state machine time-sharing sampling, lead-lag averaging, three-phase unified model error compensation, and periodic averaging filtering, it significantly reduces hardware costs while effectively eliminating phase errors in time-sharing sampling and suppressing harmonic interference. This enables high-precision measurement of the power of a three-phase asynchronous motor. Furthermore, the method has a simple algorithm, low computational load, and is easy to implement in embedded systems.

[0011] The technical solution of the present invention is as follows: A method for measuring the lead-lag average power of a three-phase asynchronous motor using phase-shift sampling is disclosed. The method is implemented based on a hardware system consisting of a signal conditioning module, an ADC sampling module, and a microcontroller. The microcontroller includes the following software modules: a dual-state machine module, a lead-lag averaging module, an error compensation module, and a periodic averaging filter module. The signal conditioning module includes a voltage conditioning circuit and a current conditioning circuit, used to convert the original three-phase voltage signal and the original three-phase current signal of the three-phase asynchronous motor into a low voltage level suitable for ADC sampling. The ADC sampling module is constructed using a power metering chip, with a sampling period T. s The low-voltage level from the signal conditioning module is acquired in a time-division manner to obtain the three-phase voltage signal and the three-phase current signal; The dual-state machine module uses a dual-state cyclic state machine to control the sampling process of the ADC sampling module. The dual-state cyclic state machine includes a T0 state and a T1 state. In the T0 state, the three-phase current signal is collected and the three-phase voltage signal buffered in the previous cycle is used to calculate the total three-phase power. In the T1 state, the three-phase voltage signal is collected and the three-phase current signal buffered in the previous cycle is used to calculate the total three-phase power. The lead-lag averaging module averages the total three-phase power at two adjacent sampling times to obtain the power output value at the current time. The error compensation module calculates the error compensation coefficient based on the sampling phase difference, and compensates and corrects the power output value to obtain the power correction value. The periodic average filtering module performs positive zero-crossing detection on the A-phase voltage of the three-phase asynchronous motor, averages the power correction value of the three-phase asynchronous motor in each waveform cycle, and outputs the periodic average power. Based on the above hardware system, the method includes the following steps: S1. The voltage conditioning circuit converts the voltage of the three-phase asynchronous motor into a low voltage level suitable for ADC sampling, and defines this low voltage level as the original three-phase voltage signal; the current conditioning circuit converts the current of the three-phase asynchronous motor into a low voltage level suitable for ADC sampling, and defines this low voltage level as the original three-phase current signal. S2. The dual-state module checks whether the state of the previous cycle was T0 or T1. If it was T1, then execute S3; otherwise, execute S4. S3. The microcontroller controls the ADC sampling module to sample the original three-phase current signal to obtain the three-phase current signal; the three-phase current signal is stored in the buffer, and the three-phase voltage signal of the previous cycle is read. Then, the total three-phase power is calculated based on the three-phase current signal and the three-phase voltage signal, and the process jumps to step S5. S4. The microcontroller controls the ADC sampling module to sample the original three-phase voltage signal to obtain the three-phase voltage signal; the three-phase voltage signal is stored in the buffer, and the three-phase current signal of the previous cycle is read. Then, the total three-phase power is calculated based on the three-phase current signal and the three-phase voltage signal. S5, the lead-lag averaging module performs an arithmetic average of the three-phase total power at two adjacent sampling times to obtain the power output value at the current time. ; S6. Error compensation module calculates angular frequency based on power grid frequency. Combined with sampling period T s Calculate the sampling phase difference And then according to Calculate the error compensation coefficient K; S7. The error compensation module will process the result obtained in step S5. Multiply by K obtained in step S6 to obtain the power correction value P_comp; S8, the periodic average filtering processing module performs positive zero-crossing detection on the A-phase voltage of the three-phase asynchronous motor and determines the waveform period of the power grid; S9. The periodic average filtering processing module performs an arithmetic average on P_comp obtained in step S7 within a single waveform period to obtain the periodic average power, which is the measured power of the three-phase asynchronous motor.

[0012] Furthermore, the formula for calculating the total three-phase power in step S3 is as follows: The formula for calculating the total three-phase power in step S4 is as follows: in , , Representing the sampling time respectively , , , , , These represent the three-phase voltage signals, , , These represent the three-phase current signals, represent The total three-phase power at any given time. represent The total three-phase power at any given time.

[0013] Furthermore, the power output value in step S5 is: .

[0014] Furthermore, the error compensation coefficient K in step S6 is: in This is the angular frequency of the power grid.

[0015] Furthermore, the specific steps of step S9 are as follows: S91. Normalize the sampled data of the A-phase voltage of the three-phase asynchronous motor to obtain the normalized A-phase voltage signal, i.e., the array Va_norm; S92. Detect positive zero crossings that satisfy Va_norm (k-1)≤0 and Va_norm (k)>0, where k-1 and k represent the indexes in Va_norm; S93. Record all the positive zero-crossing points obtained in S92 to obtain a zero-crossing point index array; the interval between two adjacent positive zero-crossing points is one waveform period; S94. Calculate the arithmetic mean of the power correction value P_comp within each waveform period to obtain the periodic average power, which is the final measured power of the three-phase asynchronous motor.

[0016] The beneficial technical effects of this invention are as follows: (1) Low hardware cost: The use of a single energy meter in conjunction with a dual-state machine to achieve equivalent synchronous sampling reduces hardware cost by about 40% to 50% compared to the traditional multi-channel synchronous sampling scheme; (2) High measurement accuracy: By establishing a unified power calculation model for three phases ABC, and performing rigorous mathematical derivation and error compensation, the system error can be controlled within ±0.1%; (3) Strong harmonic suppression capability: The periodic averaging filtering method based on zero crossing point utilizes the characteristic that the integral of the harmonic tends to zero within one period to effectively suppress the interference of odd harmonics such as the 5th and 7th order, and the power fluctuation is reduced by about 70% after filtering; (4) The algorithm is simple and efficient: the dual-state machine algorithm has a simple structure, low computational load, is easy to implement in embedded systems, has strong real-time performance, and the output delay is only about 125μs (8kHz sampling). (5) Predictable and compensable error: The algorithm error is quantitatively analyzed through a three-phase unified mathematical model, and a precise compensation method is provided to reduce the system error from -0.077% to near zero; (6) Strong load adaptability: The error magnitude is independent of the power factor angle θ, that is, it is independent of the motor load condition, and can maintain high-precision measurement under various load conditions; (7) Good frequency adaptability: The periodic average filter is based on zero-crossing detection and can automatically adapt to power grid frequency fluctuations (45Hz~65Hz) to ensure measurement stability. Attached Figure Description

[0017] Figure 1 This is a flowchart of an embodiment; Figure 2 This is a schematic diagram of the effect of periodic averaging filtering; Figure 3 It is a time-division sampling waveform of voltage and current; Figure 4 This is a diagram illustrating the principle of leading and lagging averages. Figure 5 This is a graph showing the relationship between system error and sampling phase difference; Figure 6 This is a diagram showing the effect of error compensation. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0019] I. Hardware Components of the Embodiment The embodiment is implemented based on a hardware system consisting of a signal conditioning module, an ADC sampling module, and a microcontroller. The microcontroller is an STM32G431, which includes the following software modules: a dual-state machine module, a lead-lag averaging module, an error compensation module, and a periodic averaging filter module.

[0020] The signal conditioning module includes a voltage conditioning circuit and a current conditioning circuit. The voltage conditioning circuit converts the 380V three-phase line voltage into a low voltage level suitable for ADC sampling (called the original three-phase voltage signal), with a voltage division ratio of 1000:1. The current conditioning circuit converts the three-phase current into a low voltage level for ADC sampling (called the original three-phase current signal), with a CT ratio of 1000:1.

[0021] The ADC sampling module uses the RN7302 power metering chip, with a sampling period T. s The sampling frequency is set to 125μs (8kHz), and the raw three-phase voltage and three-phase current signals are collected in a time-division manner. The sampled data are called the three-phase voltage signal and the three-phase current signal.

[0022] The dual-state machine module is a dual-state cyclic state machine implemented based on an STM32 embedded microcontroller. State T0 and state T1 alternate, with the switching period varying from the sampling period T. s Consistent. In state T0, the microcontroller controls the ADC sampling module to sample the raw three-phase current signal, obtaining the three-phase current signal; the three-phase current signal is stored in a buffer, and the three-phase voltage signal from the previous cycle is read. Then, the total three-phase power is calculated based on the three-phase current signal and the three-phase voltage signal. In state T1, the microcontroller controls the ADC sampling module to sample the raw three-phase voltage signal, obtaining the three-phase voltage signal; the three-phase voltage signal is stored in a buffer, and the three-phase current signal from the previous cycle is read. Then, the total three-phase power is calculated based on the three-phase current signal and the three-phase voltage signal.

[0023] The leading-lag averaging module will be the current time. The total three-phase power is averaged with the total three-phase power of the previous cycle, and the average value is used as the power output value at the current moment.

[0024] The error compensation module multiplies the power output value of the lead-lag average module by the error compensation coefficient K to obtain the power correction value P_comp.

[0025] The periodic average filtering module performs positive zero-crossing detection on the A-phase voltage of the three-phase asynchronous motor, averages the power correction value of the three-phase asynchronous motor in each waveform cycle, and outputs the periodic average power.

[0026] II. Flow of the Implementation Example The process of the embodiment is as follows Figure 1 As shown. The specific steps are as follows: S1. The voltage conditioning circuit converts the voltage of the three-phase asynchronous motor into a low voltage level suitable for ADC sampling, and defines this low voltage level as the original three-phase voltage signal; the current conditioning circuit converts the current of the three-phase asynchronous motor into a low voltage level suitable for ADC sampling, and defines this low voltage level as the original three-phase current signal. S2. The dual-state module checks whether the state of the previous cycle was T0 or T1. If it was T1, then execute S3; otherwise, execute S4. S3. The microcontroller controls the ADC sampling module to sample the original three-phase current signal. After obtaining the three-phase current signal, the three-phase current signal is stored in the buffer. At the same time, the three-phase voltage signal of the previous cycle is read. The total three-phase power is calculated based on the three-phase current signal and the three-phase voltage signal, and then the process jumps to step S5. S4. The microcontroller controls the ADC sampling module to sample the original three-phase voltage signal. After obtaining the three-phase voltage signal, the three-phase voltage signal is stored in the buffer. At the same time, the three-phase current signal from the previous cycle is read. The total three-phase power is calculated based on the three-phase current signal and the three-phase voltage signal. S5, the lead-lag averaging module performs an arithmetic average of the three-phase total power at two adjacent sampling times to obtain the power output value at the current time. ; S6. Error compensation module calculates angular frequency based on power grid frequency. Combined with sampling period T s Calculate the sampling phase difference And then according to Calculate the error compensation coefficient K; S7. The error compensation module will process the result obtained in step S5. Multiply by K obtained in step S6 to obtain the power correction value P_comp; S8, the periodic average filtering processing module performs positive zero-crossing detection on the A-phase voltage of the three-phase asynchronous motor and determines the waveform period of the power grid; S9. The periodic average filtering module performs an arithmetic average on P_comp obtained in step S7 over a single waveform period to obtain the periodic average power, which is the measured power of the three-phase asynchronous motor. The effect of periodic average filtering is as follows: Figure 2 As shown. The specific steps are as follows: S91. Normalize the sampled data of the A-phase voltage of the three-phase asynchronous motor to obtain the normalized A-phase voltage signal, i.e., the array Va_norm; S92. Detect positive zero crossings that satisfy Va_norm (k-1)≤0 and Va_norm (k)>0, where k-1 and k represent the indexes in Va_norm; S93. Record all the positive zero-crossing points obtained in S92 to obtain a zero-crossing point index array; the interval between two adjacent positive zero-crossing points is one waveform period; S94. Calculate the arithmetic mean of the power correction value P_comp within each waveform period to obtain the periodic average power, which is the final measured power of the three-phase asynchronous motor.

[0027] III. Three-phase unified power model For a three-phase asynchronous motor, assuming three-phase balance, the effective values ​​of voltage and current are consistent, and considering the power factor angle... To mitigate the impact of these factors, a unified three-phase power model is established: Phase A voltage: Phase A current: Phase B voltage: Phase B current: C-phase voltage: C-phase current: Instantaneous power: IV. Sampling Principle of Dual-State Machine The dual-state machine module adopts a dual-state cyclic working mechanism, and its sampling timing is as follows: (1) T0 state (current sampling state): At the current sampling time The three-phase current signals are acquired, and the three-phase voltage signals buffered in the previous cycle are used to calculate the total three-phase power. (2) T1 state (voltage sampling state): At the current sampling time The three-phase voltage signals are acquired, and the three-phase current signals buffered from the previous cycle are used to calculate the total three-phase power. in , , Representing the sampling time respectively , , , , , These represent the three-phase voltage signals, , , These represent the three-phase current signals, represent The total three-phase power at any given time. represent The total three-phase power at any given time.

[0028] The waveforms of voltage and current sampled in a time-division manner are as follows: Figure 3 As shown.

[0029] V. Principle of the Leading-Lagging Averaging Algorithm like Figure 4 As shown, the lead-lag averaging module averages the three-phase power values ​​at two adjacent sampling times: Sampling period: Power frequency: Angular frequency: Sampling phase difference: Substituting the three-phase power expressions for states T0 and T1, the power output of phase A can be obtained through mathematical derivation: Using the sum-to-product formula: in , ,but: Substituting, we get: Similarly, the power output of phase B can be obtained: Similarly, the power output of phase C can be obtained: The three-phase algebraic addition yields The algorithm outputs the total power at each time point: VI. Three-phase unified error analysis and compensation The error compensation module is based on a three-phase unified power model and undergoes rigorous mathematical derivation and error analysis. (1) Formula for Three-Phase Total Power Error The three-phase instantaneous total power error is calculated using the algorithm. Time output and The difference between the actual values. The actual instantaneous power of phase A at a given time point: so The time-point algorithm outputs the power of phase A: Similarly, we get: , In other words The total three-phase power output by the time-point algorithm: Therefore, the total three-phase power output by the algorithm and the theoretical instantaneous power have an inherent coefficient and an inherent delay, such as Figure 5 As shown.

[0030] (2) Calculation of relative error (3) Numerical calculation (taking 8kHz sampling as an example) Substitution : (4) Error compensation By multiplying by the compensation coefficient K = 1 / cos( With a value ≈ 1.00077, the systematic error can be eliminated to near zero. The error compensation effect is as follows: Figure 6 As shown.

[0031] (5) Load independence From the error formula, we can see that the systematic error... Only with the sampling phase difference Related to the power factor angle It is independent of the motor load, meaning the error magnitude is independent of the motor load condition, and it has good load adaptability.

[0032] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, and for those of ordinary skill in the art, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. Therefore, the present invention is not limited to the specific details without departing from the general concept defined by the claims and their equivalents.

Claims

1. A method for measuring the lead-lag average power of a three-phase asynchronous motor using phase-shift sampling, characterized in that: The method is implemented based on a hardware system consisting of a signal conditioning module, an ADC sampling module, and a microcontroller; the microcontroller includes the following software modules: a dual-state machine module, a lead-lag averaging module, an error compensation module, and a periodic averaging filter module; The signal conditioning module includes a voltage conditioning circuit and a current conditioning circuit, used to convert the original three-phase voltage signal and the original three-phase current signal of the three-phase asynchronous motor into a low voltage level suitable for ADC sampling. The ADC sampling module is constructed using a power metering chip, with a sampling period T. s The low-voltage level from the signal conditioning module is acquired in a time-division manner to obtain the three-phase voltage signal and the three-phase current signal; The dual-state machine module uses a dual-state cyclic state machine to control the sampling process of the ADC sampling module. The dual-state cyclic state machine includes a T0 state and a T1 state. In the T0 state, the three-phase current signal is collected and the three-phase voltage signal buffered in the previous cycle is used to calculate the total three-phase power. In the T1 state, the three-phase voltage signal is collected and the three-phase current signal buffered in the previous cycle is used to calculate the total three-phase power. The lead-lag averaging module averages the total three-phase power at two adjacent sampling times to obtain the power output value at the current time. The error compensation module calculates the error compensation coefficient based on the sampling phase difference, and compensates and corrects the power output value to obtain the power correction value. The periodic average filtering module performs positive zero-crossing detection on the A-phase voltage of the three-phase asynchronous motor, averages the power correction value of the three-phase asynchronous motor in each waveform cycle, and outputs the periodic average power. Based on the above hardware system, the method includes the following steps: S1. The voltage conditioning circuit converts the voltage of the three-phase asynchronous motor into a low voltage level suitable for ADC sampling, and defines this low voltage level as the original three-phase voltage signal; the current conditioning circuit converts the current of the three-phase asynchronous motor into a low voltage level suitable for ADC sampling, and defines this low voltage level as the original three-phase current signal. S2. The dual-state module checks whether the state of the previous cycle was T0 or T1. If it was T1, then execute S3; otherwise, execute S4. S3. The microcontroller controls the ADC sampling module to sample the original three-phase current signal to obtain the three-phase current signal; the three-phase current signal is stored in the buffer, and the three-phase voltage signal of the previous cycle is read. Then, the total three-phase power is calculated based on the three-phase current signal and the three-phase voltage signal, and the process jumps to step S5. S4. The microcontroller controls the ADC sampling module to sample the original three-phase voltage signal to obtain the three-phase voltage signal; the three-phase voltage signal is stored in the buffer, and the three-phase current signal of the previous cycle is read. Then, the total three-phase power is calculated based on the three-phase current signal and the three-phase voltage signal. S5, the lead-lag averaging module performs an arithmetic average of the three-phase total power at two adjacent sampling times to obtain the power output value at the current time. ; S6. Error compensation module calculates angular frequency based on power grid frequency. Combined with sampling period T s Calculate the sampling phase difference And then according to Calculate the error compensation coefficient K; S7. The error compensation module will process the result obtained in step S5. Multiply by K obtained in step S6 to obtain the power correction value P_comp; S8, the periodic average filtering processing module performs positive zero-crossing detection on the A-phase voltage of the three-phase asynchronous motor and determines the waveform period of the power grid; S9. The periodic average filtering processing module performs an arithmetic average on P_comp obtained in step S7 within a single waveform period to obtain the periodic average power, which is the measured power of the three-phase asynchronous motor.

2. The method for measuring the lead-lag average power of a three-phase asynchronous motor by phase-shift sampling according to claim 1, characterized in that: The formula for calculating the total three-phase power in step S3 is as follows: The formula for calculating the total three-phase power in step S4 is as follows: in , , Representing the sampling time respectively , , , , , These represent the three-phase voltage signals, , , These represent the three-phase current signals, represent The total three-phase power at any given time. represent The total three-phase power at any given time.

3. The method for measuring the lead-lag average power of a three-phase asynchronous motor by phase-shift sampling according to claim 2, characterized in that, The power output value in step S5 is: .

4. The method for measuring the lead-lag average power of a three-phase asynchronous motor by phase-shift sampling according to claim 1, characterized in that: The error compensation coefficient K in step S6 is: in This is the angular frequency of the power grid.

5. The method for measuring the lead-lag average power of a three-phase asynchronous motor by phase-shift sampling according to claim 1, characterized in that, The specific steps of step S9 are as follows: S91. Normalize the sampled data of the A-phase voltage of the three-phase asynchronous motor to obtain the normalized A-phase voltage signal, i.e., the array Va_norm; S92. Detect positive zero crossings that satisfy Va_norm (k-1)≤0 and Va_norm (k)>0, where k-1 and k represent the indexes in Va_norm; S93. Record all the positive zero-crossing points obtained in S92 to obtain a zero-crossing point index array; the interval between two adjacent positive zero-crossing points is one waveform period; S94. Calculate the arithmetic mean of the power correction value P_comp within each waveform period to obtain the periodic average power, which is the final measured power of the three-phase asynchronous motor.

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