A high-precision power frequency phase angle synchronous measurement method under an undetermined frequency sampling condition

Abstract

The application discloses a high-precision power frequency phase angle synchronous measurement method under an undefined frequency sampling condition, and the method comprises the following steps: cyclically recording a current sampling completion time t clk_k and a current sampling code value x k ; recording a pulse trigger time t clk_pulse when a synchronous pulse is triggered, and recording sampling values and sampling completion times of a certain number of cycles from the current time backward to form a sampling time-sampling code value record table; and performing fixed frequency correction on the sampling code values in the record table through high-order interpolation according to the current electrical quantity frequency. Since the application does not require very accurate sampling intervals and is not affected by context switching, interruption preemption and other problems, it is unnecessary to use a chip with higher performance of a bare core to process, chip cost is reduced, and therefore the application can be applied to low-voltage secondary devices which are more sensitive to cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of power system automation, and particularly relates to a high-precision power frequency phase angle synchronous measurement method under an undefined frequency sampling condition. BACKGROUND

[0002] In a power system, in order to better obtain the state of the current power grid, facilitate real-time detection, power flow calculation, state estimation and other goals, the voltage and current amplitude and phase angle at the current time often need to be obtained. In a high-voltage network, a synchronous phasor measurement device (PMU) emerges as the times require. The device uses GPS synchronization time + high-performance processing chips to complete the accurate measurement of the amplitude and phase angle of a certain time section. This scheme uses high-performance processing chips, which is costly and not suitable for low-voltage networks. In a low-voltage network, if the accurate voltage amplitude and phase angle of each installed node at the current time can be obtained, it provides a solid foundation for advanced applications such as topology analysis and impedance analysis. The devices installed in each node of the low-voltage network often use low-performance processing chips due to cost sensitivity, and the devices integrate communication, sampling, protection, measurement and metering into one, with heavy processing tasks and are often affected by various factors, so the sampling frequency cannot be accurately controlled. Therefore, a method is needed to accurately calculate the phase angle of the electrical quantity at the current time section under the condition of undefined frequency sampling. SUMMARY

[0003] To achieve the above purpose, the present application provides a high-precision power frequency phase angle synchronous measurement method under an undefined frequency sampling condition. The phase angle measurement accuracy is high, and under the condition of 12-bit ad and sampling period error of 50us, the phase angle synchronization error between devices is reduced from 2 degrees to 0.4 degrees; the influence of inter-harmonic and signal frequency deviation is small, signal frequency following and windowing are used to reduce the frequency spectrum leakage caused by inter-harmonic or frequency deviation; the cost is low, since the present application does not require very accurate sampling interval and is not affected by context switching, interrupt preemption and other problems, therefore it does not need to use a higher-performance chip with a bare core for processing, reducing the chip cost, and therefore it can be applied to low-voltage secondary devices which are more sensitive to cost. The technical scheme of the present application is as follows: a high-precision power frequency phase angle synchronous measurement method under an undefined frequency sampling condition, the method comprising:

[0004] recording the current sampling completion time t clk_k and the current sampling code value x k ;

[0005] when a synchronization pulse is triggered, recording the pulse triggering time t clk_pulse , and recording a certain number of cycles of sampling values and sampling completion times from the current time, forming a sampling time-sampling code value record table;

[0006] According to the current electrical quantity frequency, the sampling code value in the record table is corrected by high order interpolation;

[0007] As an improvement of the present application, according to the current sampling completion time t clk_k The sampling rate is interpolated and corrected, and in order to prevent the frequency spectrum leakage effect caused by the power grid frequency deviation, the signal is interpolated and corrected according to the power grid frequency, and the formula is as follows:

[0008]

[0009] In the above formula (1), T sam_clk represents the set sampling period, f now represents the current electrical quantity frequency, f base represents the electrical quantity reference frequency.

[0010] As an improvement of the present application, the fixed frequency sampling time after the electrical quantity frequency correction is as follows:

[0011] t cps_k = kdT (2)

[0012] In the above formula (2), k represents the current calculation sampling point number, and dT is the calculation value of the fixed frequency correction in formula (1).

[0013] As an improvement of the present application, the three upper and lower index numbers of the k-th correction point in the tclk_k array at the current sampling completion time are as follows:

[0014]

[0015]

[0016]

[0017] In the above formulas (3), (4) and (5), k represents the current calculation sampling point number, dT is the calculation value of the fixed frequency correction in formula (1), T sam_clk represents the set sampling period, and the symbol <> represents rounding down.

[0018] As an improvement of the present application, the fixed frequency sampling value after correction following the electrical quantity frequency is as follows:

[0019]

[0020] In the above formula (4), the symbol [] represents taking value according to index in array, t clk [] represents taking value in t clk array, and x[] represents taking value in x array.

[0021] As an improvement of the present application, the frequency of the corrected following electrical quantity is recorded as the following table:

[0022] <![CDATA[t cps_0 ]]> [cat cps_1 ]]> [CAT cps_2 ]] [CAT cps_3 ]]> [cat cps_(10*M-1) ]]> [y0] [cdta] [ y2 ] [cdta] … [[ y (10*M-1) ]]>

[0023] wherein t cps_k represents the time of the fixed frequency sampling after correction of the frequency of the following electrical quantity, and M represents the number of sampling points of one power frequency cycle.

[0024] As an improvement of the present application, the time of the sampling completion is recorded by using a timer counter or an internal systick counter of the MCU, and the frequency of the electrical quantity is obtained by a frequency measuring circuit.

[0025] As an improvement of the present application, the record table of the time of the sampling and the sampling code value is formed as the following table:

[0026] t clk_0 ]]>

[00002] clk_1 ]] t clk_2 ]]> <![CDATA[t clk_3 ]]> [cat cl_k(10*M-1) ]]> x0 x1 x2 x3 … x (10*M-1) ]]>

[0027] wherein x represents the sampling code value, and t clk represents the time of the current sampling completion, and M represents the number of sampling points of one power frequency cycle.

[0028] As an improvement of the present application, the amplitude and the phase angle of the electrical quantity are calculated by using the windowed DFT according to the corrected data.

[0029] The Fourier real and imaginary part coefficients after windowing:

[0030]

[0031] In the above formula, coe_real i represents the windowed DFT real part coefficient of the i-th point, and M represents the number of sampling points of one power frequency cycle;

[0032]

[0033] In the above formula, coe_imag i represents the windowed DFT imaginary part coefficient of the i-th point;

[0034] As an improvement of the present application, the time t clk_pulse of the trigger of the synchronous pulse is used to calculate the actual power frequency electrical quantity phase angle at the trigger time:

[0035]

[0036] In the above formula (5), ang_pulse represents the power frequency electrical quantity phase angle at the trigger time of the synchronous pulse, ang represents the vector phase angle, T sam_clk represents the set sampling period, t clk_pulse is the trigger time, and f nowrepresents the current electrical quantity frequency, f base represents the electrical quantity reference frequency.

[0037] The beneficial effects of the present application relative to the prior art are: the innovation of the present application is that under the condition of non-fixed frequency sampling, the sampling signal is corrected at each sampling time, and the sampling signal is followed by the real-time frequency of the electrical quantity, the phase angle amplitude is calculated through the Fourier coefficient of the window, and the phase angle is compensated according to the synchronization pulse trigger time, so as to obtain high-precision phase angle synchronization measurement under the condition of non-fixed frequency sampling; Since the present application does not require very accurate sampling interval, it is not affected by context switching, interrupt preemption and other problems, so it does not need to use a chip with higher performance of bare core for processing, thereby reducing the chip cost, and therefore it can be applied to low-voltage secondary equipment which is more sensitive to cost. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a flowchart of the measurement method in the embodiment.

[0039] Figure 2 It is a timing diagram of non-fixed frequency sampling in the embodiment. DETAILED DESCRIPTION

[0040] The present application will be further illustrated in conjunction with the drawings and specific embodiments, and it should be understood that the following specific embodiments are only used to illustrate the present application and not to limit the scope of the present application.

[0041] Embodiment: In a multi-task MCU, the sampling frequency of ADC is not completely fixed due to the influence of operating system context switching or different priority interrupt preemption, which will cause a random error of about 2 degrees in the calculation of the phase angle of the electrical quantity. The present application records the completion time of each ADC conversion to form a sampling time-sampling code value record table; and according to the current electrical quantity (voltage and current) frequency, the sampling time-sampling code value record table is reconstructed through high-order interpolation to compensate for the randomness of the sampling frequency, forming a fixed frequency sampling time-sampling code value record table following the electrical quantity frequency; and the actual phase angle and amplitude of the power frequency electrical quantity at the synchronization pulse trigger time are calculated according to the synchronization pulse trigger time.

[0042] As shown in Figure 1 , the specific non-fixed frequency sampling high-precision power frequency phase angle synchronization measurement method is as follows:

[0043] Record the current sampling completion time t clk_k and the current sampling code value x k . The sampling completion time t clk_k is recorded using a timer counter or an internal systick counter of the MCU,

[0044] At the synchronization pulse trigger time, record the pulse trigger time tclk_pulse And record 10 cycles or more sampling values and sampling completion time from the current time, form a sampling time-sampling code value record table, sampling time sequence diagram as shown in Figure 2

[0045] [cat clk_0 ]]> <![CDATA[t clk_1 ]]> <![CDATA[t clk_2 ]]> t clk_3 ]]> t clk_(10*M-1) ]]> x0 x1 x2 x3 … x (10*M-1) ]]>

[0046] Wherein, x represents the sampling code value, t clk represents the sampling completion time, M represents a power frequency cycle sampling point number.

[0047] According to the current electrical quantity frequency, by high order interpolation, the sampling code value in the record table is corrected. Wherein, the electrical quantity frequency can be obtained by frequency measurement circuit,

[0048] The method for following the electrical quantity frequency correction is:

[0049] Taking ideal sampling rate 1000Hz as an example. Due to the influence of multi-task mcu, the actual sampling rate may not be 1000Hz, may be randomly fluctuated between 995-1005Hz, that is, t clk_k May not be a constant. Therefore, the sampling rate needs to be interpolated and corrected according to the t clk_k Value, so that the corrected sampling rate is 1000Hz. At the same time, in order to prevent the frequency spectrum leakage effect caused by the power grid frequency deviation, the signal also needs to be interpolated according to the power grid frequency.

[0050] The frequency correction algorithm is:

[0051]

[0052] In the above formula (1), wherein, T sam_clk Indicates the set sampling period, f now Indicates the current electrical quantity frequency, f base Indicates the electrical quantity reference frequency.

[0053] The frequency sampling time after following the electrical quantity frequency correction is as follows:

[0054] t cps_k = kdT (2)

[0055] In the above formula (2), k represents the current calculation of sampling point number, dT is the calculation value of frequency correction in formula (1).

[0056] In the current sampling completion time t clk_k The three upper and lower index numbers of the kth correction point in the array are as follows:

[0057]

[0058] ​

[0059]

[0060] In the above formulas (3), (4), and (5), k represents the number of sampling points currently calculated, dT is the calculated value of the fixed-frequency correction in formula (1), T sam_clk represents the set sampling period, and the symbol < > represents rounding down.

[0061] The fixed-frequency sampling value of the corrected following electrical quantity frequency is as follows:

[0062]

[0063] In the above formula (4), the symbol [ ] represents taking a value according to an index in an array, t clk represents taking a value in the t clk array, and x[ ] represents taking a value in the x array.

[0064] The corrected fixed-frequency sampling record of the following electrical quantity frequency is as shown in the following table:

[0065] [CAT cps_0 ]]> [CAT cps_1 ]]> t cps_2 ]]> [CAT cps_3 ]]> <![CDATA[t cps_(10*M-1) ]]> [y0] [cdta] [ y2 ] [cdta] … [[ y (10*M-1) ]]>

[0066] where cps represents, and M represents the number of sampling points of one power frequency cycle.

[0067] The sampling completion time is recorded using a timer counter or an internal systick counter of the MCU, and the electrical quantity frequency is obtained through a frequency measurement circuit.

[0068] According to the corrected data, the electrical quantity amplitude and phase angle are calculated using windowed DFT.

[0069] The Fourier real and imaginary part coefficients after windowing:

[0070]

[0071] In the above formula (5), coe_real i represents the windowed DFT real part coefficient of the i-th point;

[0072]

[0073] In the above formula (6), coe_imag i represents the windowed DFT imaginary part coefficient of the i-th point;

[0074] According to the synchronization pulse trigger time t clk_pulse the vector real part, the actual power frequency electrical quantity phase angle at the trigger time is calculated through the following formula:

[0075]

[0076] In the above equation (7), ang_pulse represents the phase angle of the power frequency electrical quantity at the synchronization pulse trigger time, ang represents the vector phase angle, T sam_clk represents the set sampling period, t clk_pulse is the pulse trigger time, f now represents the current electrical quantity frequency, f base represents the electrical quantity reference frequency.

[0077] It should be noted that the above content only illustrates the technical idea of the present application, and cannot limit the protection scope of the present application. For ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which fall within the scope of the claims of the present application.

Claims

1. A method for high-precision synchronous measurement of power frequency phase angle under variable frequency sampling conditions, characterized in that, The method includes: Loop through and record the current sampling completion time t clk_k and the current sampled code value x k ; When the synchronization pulse is triggered, record the pulse trigger time t. clk_pulse And record a certain number of sampling values ​​above the current time and the sampling completion time from the current time backward, forming a sampling time-sampling code value record table; Based on the current electrical quantity frequency, the sampling code values ​​in the record table are corrected for fixed frequency through high-order interpolation. Based on the corrected data, the amplitude and phase angle of the electrical quantities are calculated using windowed DFT; Based on the synchronization pulse trigger time The real part of the vector is used to calculate the phase angle of the actual power frequency electrical quantity at the triggering moment using the following formula: （7） In the above formula (7), The phase angle of the power frequency electrical quantity at the moment of synchronous pulse triggering. Represents the phase angle of a vector. This indicates the setting of the sampling period. Pulse trigger time, Indicates the current electrical quantity frequency. Indicates the reference frequency for electrical quantities.

2. The method for high-precision power frequency phase angle synchronous measurement under variable frequency sampling conditions according to claim 1, characterized in that, Based on the current sampling completion time t clk_k The numerical value is interpolated to correct the sampling rate. The fixed-frequency correction formula is as follows: （1） In the above formula (1), where, This indicates the setting of the sampling period. Indicates the current electrical quantity frequency. Indicates the reference frequency for electrical quantities.

3. The method for high-precision power frequency phase angle synchronous measurement under variable frequency sampling conditions according to claim 2, characterized in that, The fixed-frequency sampling time after frequency correction following the electrical quantity is as follows: （2） In the above formula (2), dT represents the number of sampling points currently being calculated, and dT is the calculated value of the fixed-frequency correction in formula (1).

4. The method for high-precision power frequency phase angle synchronous measurement under variable frequency sampling conditions according to claim 3, characterized in that, At the current sampling completion time t clk_k The three upper and lower bound indices of the k-th correction point in the array are as follows: （3） （4） （5） In the above formulas (3), (4), and (5), This represents the number of sampling points currently being calculated, and dT is the calculated value of the fixed-frequency correction in formula (1). Indicates the setting of the sampling period, symbol This indicates rounding down to the nearest integer.

5. The method for high-precision power frequency phase angle synchronization measurement under variable frequency sampling conditions according to claim 4, characterized in that, The corrected frequency sampling value of the following electrical quantity is given by the following formula: （6） In the above formula (6), the symbol This indicates retrieving values ​​by index in the array. Indicates in Retrieving values ​​from an array Indicates in Retrieves a value from an array.

6. The method for high-precision power frequency phase angle synchronization measurement under variable frequency sampling conditions according to claim 5, characterized in that, Corrected fixed-frequency sampling record sequence for following electrical quantities: < , > in, This indicates the fixed-frequency sampling time after frequency correction following the electrical quantity. This represents the corrected sampled value, M represents the number of sampling points for one power frequency cycle, and k takes values ​​of 0, 1, ..., 10*M-2, 10*M-1.

7. The method for high-precision power frequency phase angle synchronous measurement under variable frequency sampling conditions according to claim 1, characterized in that, The sampling completion time is recorded using a timer / counter or the MCU's internal Systick counter, and the electrical frequency is obtained through a frequency measurement circuit.

8. The method for high-precision power frequency phase angle synchronous measurement under variable frequency sampling conditions according to claim 6, characterized in that, This forms the sampling time-sampling code value record sequence: <t clk_k ,x k > Where, x k Represents the sampled code value, t clk_k This indicates the current sampling completion time, M represents the number of sampling points for one power frequency cycle, and k takes values ​​of 0, 1, ..., 10*M-2, 10*M-1.

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