A method for rapid sampling of harmonic current

Abstract

The present invention discloses a method for rapid sampling of harmonic current, including: A1. Conducting six current samplings on the resonant branch current of an electrical appliance within one working cycle, with a sampling interval phase of 1 / 12, to obtain the current sampling values of six sampling points; A2. Determining the relationships between the current sampling values of the six sampling points and the amplitudes of the fundamental wave, second harmonic, and third harmonic, as well as the relative phase between the harmonic and the fundamental wave; A3. According to the relationships between the current sampling values of the six sampling points and the amplitudes of the fundamental wave, second harmonic, and third harmonic, as well as the relative phase between the harmonic and the fundamental wave, using the current sampling values of the six sampling points to calculate the amplitudes of the fundamental wave and the harmonic, and the relative phase between the harmonic and the fundamental wave. The present invention does not need to ensure the same initial phase for each sampling, and can meet the accuracy and real-time requirements of harmonic current decomposition under high sampling frequency conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of control sampling, and particularly to a method for rapidly sampling harmonic current. Background Art

[0002] A piezoelectric transformer is a new type of electronic transformer, which has a small volume, a high output voltage, and a small power, but the control method of the piezoelectric transformer is complex.

[0003] Conventional harmonic current detection methods include the following: analog band-pass filter detection method, Fryze time-domain analysis method, and instantaneous reactive power theory detection method based on the Japanese scholar H. Akagi, etc. Among them, the analog band-pass filter detection method has poor sensitivity, large measurement error, and high design difficulty, and it is difficult to meet the requirements of harmonic current detection for accuracy and real-time performance; the Fryze time-domain analysis method has a slow dynamic response and a large amount of calculation, and cannot meet the requirements of real-time and rapid detection; the instantaneous reactive power theory detection method based on Akagi has good real-time performance, but there is still room for optimization in the rapidity of harmonic detection under finite harmonic conditions. In recent years, some scholars have proposed other detection methods: wavelet transform detection method, harmonic current detection method based on neural network theory, etc. However, whether these new harmonic detection methods can be applied in engineering practice still needs to be further verified. The main difficulties faced by existing methods are as follows: ① The sampling frequency is too high to ensure the initial phase of the sampling points. ② It is impossible to ensure the accuracy and real-time performance of harmonic current detection. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems that the sampling frequency is too high to ensure the initial phase of the sampling points, and that the accuracy and real-time performance of harmonic current decomposition cannot be guaranteed, and to provide a method for rapidly sampling harmonic current.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for rapidly sampling harmonic current includes the following steps:

[0007] A1. Perform six current samplings on the resonant branch current of the electrical appliance within one working cycle, with a sampling interval phase of 1 / 12, to obtain the current sampling values of six sampling points; A2. Determine the relationships between the current sampling values of the six sampling points and the amplitudes of the fundamental wave, second harmonic, and third harmonic, as well as the relative phases between the harmonics and the fundamental wave; A3. According to the relationships between the current sampling values of the six sampling points and the amplitudes of the fundamental wave, second harmonic, and third harmonic, as well as the relative phases between the harmonics and the fundamental wave, use the current sampling values of the six sampling points to calculate the amplitudes of the fundamental wave and harmonics, and the relative phases between the harmonics and the fundamental wave.

[0008] In some embodiments of the present invention, the relationship between the current sampling values of the six sampling points and the amplitudes of the fundamental wave, second harmonic, and third harmonic, as well as the relative phase between the harmonic and the fundamental wave, is as follows:

[0009]

[0010] where S n is the sampling value of the six sampling points, n = 1, 2, 3, 4, 5, 6, M1, M2, and M3 are the amplitudes of the fundamental wave, second harmonic, and third harmonic, θ is the initial phase of the sampling point, is the relative phase between the harmonic and the fundamental wave, Samplinginterval is the sampling interval phase, ω is the angular frequency of the fundamental wave, and t is the time.

[0011] In some embodiments of the present invention, step A3 includes: simplifying the relationship between the sampling point values and the amplitudes and phases in the form of a matrix.

[0012] In some embodiments of the present invention, the matrix is:

[0013]

[0014] where

[0015]

[0016] where X1, X2, Y1, Y2, Z1, and Z2 are intermediate quantities.

[0017] In some embodiments of the present invention, step A3 further includes: finding the inverse of the matrix:

[0018]

[0019] Calculating X1, X2, Y1, Y2, Z1, and Z2 through the sampling values S1, S2, S3, S4, S5, and S6 to obtain the amplitudes of the fundamental wave, second harmonic, and third harmonic:

[0020]

[0021] In some embodiments of the present invention, step A3 further includes: determining the relative phase between the harmonic and the fundamental wave of the resonant current according to the following formula:

[0022]

[0023] In some embodiments of the present invention, the electrical appliance is a piezoelectric transformer.

[0024] In some embodiments of the present invention, in step A1, an input sampling circuit is used to collect the resonant branch current of the piezoelectric transformer input thereto. The input sampling circuit includes a sampling capacitor (C x ), a sampling resistor (R x ), and an operational amplifier circuit. The sampling capacitor (C x ) is connected in parallel at the input end of the piezoelectric transformer. The sampling capacitor (C x ) << piezoelectric transformer input capacitance (C in ), and the loop time constant formed by the sampling resistor (R x ) and the sampling capacitor (C x ) is much smaller than the period T of the circuit operating frequency. An electrical circuit proportional adder is formed through the operational amplifier circuit to calculate the resonant branch current of the piezoelectric transformer.

[0025] In some embodiments of the present invention, the operational amplifier circuit includes an operational amplifier, analog transformer ground resistors (R1, R5), an inverting input resistor (R2), a feedback resistor (R3), and a balancing resistor (R4). One end of the sampling capacitor (C x ) is connected to one input end of the piezoelectric transformer. One end of the inverting input resistor (R2) is connected between the other end of the sampling capacitor (C x ) and the sampling resistor R x . The other end of the inverting input resistor (R2) is connected to the inverting input end of the operational amplifier. The feedback resistor (R3) is connected between the inverting input end and the output end of the operational amplifier. One end of the sampling resistor (R x ) is connected to the other end of the sampling capacitor (C x ). The other end of the sampling resistor (R x ) is grounded. One end of the analog transformer ground resistors (R1, R5) is grounded. The other end of the analog transformer ground resistors (R1, R5) is connected to the non-inverting input end of the operational amplifier through the balancing resistor (R4). The other input end of the piezoelectric transformer is connected between the balancing resistor (R4) and the analog transformer ground resistors (R1, R5).

[0026] In some embodiments of the present invention, the analog transformer ground resistors (R1, R5) include two resistors connected in parallel between the balancing resistor (R4) and the ground.

[0027] The invention has the following beneficial effects:

[0028] The harmonic current fast sampling method proposed by the present invention obtains current sampling values of six sampling points with a phase interval of 1 / 12π from the resonant branch current containing resonant currents of different frequencies obtained by sampling through the method of six samplings with a phase interval of 1 / 12π per cycle. According to the relationship between the current sampling values of the six sampling points and the amplitudes of the fundamental wave, second harmonic, and third harmonic, as well as the relative phase between the harmonic and the fundamental wave, the amplitudes of the fundamental wave and the harmonic, and the relative phase between the harmonic and the fundamental wave can be obtained through simple operations. Therefore, the harmonic current fast sampling method of the present invention does not need to ensure that the initial phase of each sampling is the same, and can meet the accuracy and real-time requirements of harmonic current decomposition under high sampling frequency conditions. The harmonic current sampling method of the present invention has been verified to be fast and accurate.

[0029] Other beneficial effects in the embodiments of the present invention will be further described below. Brief Description of the Drawings

[0030] Figure 1 is a schematic diagram of the step flow in the embodiment of the present invention;

[0031] Figure 2 is a schematic diagram of the input sampling circuit in the embodiment of the present invention;

[0032] Figure 3 is a physical diagram of the experimental platform built in the embodiment of the present invention;

[0033] Figure 4 is a test waveform diagram output in the embodiment of the present invention;

[0034] Figure 5 is a physical diagram of the pulse power supply of the piezoelectric transformer built in the embodiment of the present invention;

[0035] Figure 6 is a typical waveform diagram of the output of the pulse power supply of the piezoelectric transformer built in the embodiment of the present invention.

[0036] The reference numerals are as follows:

[0037] C x is the sampling capacitor, R x is the sampling resistor, R1 is the analog transformer grounding resistor, R2 is the inverting input terminal resistor, R3 is the feedback resistor, R4 is the balancing resistor, R5 is the analog transformer grounding resistor,

[0038] 1 is the oscilloscope, 2 is the DC power supply, 3 is the inverter, 4 is the single-chip microcomputer, 5 is the load. Detailed Embodiments

[0039] The present invention will be further described below with reference to the accompanying drawings and in conjunction with preferred embodiments. It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other.

[0040] It should be noted that the orientation terms such as left, right, up, down, top, bottom, etc. in this embodiment are only relative concepts to each other or are referenced based on the normal use state of the product, and should not be considered restrictive.

[0041] Aiming at the problem that the sampling frequency is too high to ensure the initial phase of the sampling points, the embodiment of the present invention innovatively proposes a fast harmonic current sampling method that does not require the initial phase of each sampling to be the same, meeting the accuracy and real-time requirements of harmonic current decomposition under high sampling frequency conditions.

[0042] As Figure 1 shown, the fast harmonic current sampling method proposed in the following embodiments of the present invention includes the following steps:

[0043] A1. Perform six current samplings on the resonant branch current of the electrical appliance device within one working cycle, with a sampling interval phase of 1 / 12, to obtain the current sampling values of six sampling points; A2. Determine the relationships between the current sampling values of the six sampling points and the amplitudes of the fundamental wave, second harmonic, and third harmonic, as well as the relative phase between the harmonic and the fundamental wave; A3. According to the relationships between the current sampling values of the six sampling points and the amplitudes of the fundamental wave, second harmonic, and third harmonic, as well as the relative phase between the harmonic and the fundamental wave, use the current sampling values of the six sampling points to calculate the amplitudes of the fundamental wave and the harmonic, as well as the relative phase between the harmonic and the fundamental wave.

[0044] In a specific embodiment, for the sampling of the resonant branch current of the piezoelectric transformer, in step A1, an input sampling circuit is used to collect the resonant branch current of the input piezoelectric transformer. The input sampling circuit includes a sampling capacitor C x , a sampling resistor R x and an operational amplifier circuit. The sampling capacitor C x is connected in parallel at the input end of the piezoelectric transformer. The sampling capacitor C x << the input capacitance C in of the piezoelectric transformer, and the loop time constant formed by the sampling resistor R x and the sampling capacitor C x is much smaller than the period T of the circuit operating frequency. An operational amplifier circuit is used to form a circuit proportional adder to calculate the resonant branch current of the piezoelectric transformer.

[0045] The above operational amplifier circuit includes an operational amplifier, analog transformer ground resistors R1 and R5, an inverting input terminal resistor R2, a feedback resistor R3, and a balancing resistor R4. The sampling capacitor C xOne end of it is connected to an input terminal of a piezoelectric transformer, and one end of the inverting input resistor R2 is connected to the sampling capacitor C x The other end of it is between the sampling resistor R x The other end of the inverting input resistor R2 is connected to the inverting input terminal of the operational amplifier. The feedback resistor R3 is connected between the inverting input terminal and the output terminal of the operational amplifier. One end of the sampling resistor R x is connected to the other end of the sampling capacitor C x The other end of the sampling resistor R x is grounded. One ends of the analog transformer grounding resistors R1 and R5 are grounded, and the other ends of the analog transformer grounding resistors R1 and R5 are connected to the non-inverting input terminal of the operational amplifier through the balancing resistor R4. The other input terminal of the piezoelectric transformer is connected between the balancing resistor R4 and the analog transformer grounding resistors R1 and R5.

[0046] In addition, the analog transformer grounding resistors R1 and R5 include two resistors connected in parallel between the balancing resistor R4 and the ground.

[0047] The main function of the input sampling circuit is to collect the current of the resonant branch of the input piezoelectric transformer and input it to the single-chip microcomputer for processing. Since the Q value of the piezoelectric transformer resonant branch is very high, it can be considered that only the currents of specific resonant frequencies can pass through the resonant branch and participate in power transmission. In this embodiment, the current input to the piezoelectric transformer resonant branch is considered to be composed only of the fundamental wave, the second harmonic, and the third harmonic, without other high-frequency components. The topological structure of the sampling input circuit is as Figure 2 .

[0048] The input current of the power supply system is divided into two parts. One part passes through the input capacitor of the piezoelectric transformer, and the other part passes through the resonant branch and outputs to the output terminal of the piezoelectric transformer. The first part of the current does not pass through the resonant branch of the piezoelectric transformer and cannot affect the working state of the piezoelectric transformer. In order to accurately detect the current of the piezoelectric transformer resonant branch, it is necessary to design the circuit to detect and eliminate the input capacitor current. The specific design idea is as follows. By connecting a capacitor C x in parallel at the input terminal of the piezoelectric transformer. If C x << C in (the input capacitor of the piezoelectric transformer), and the time constant of the loop formed by the sampling resistor R x and C x is much smaller than the period T of the circuit operating frequency, then the current of this branch can be considered to be in a proportional relationship with the current passing through the input capacitor of the piezoelectric transformer. On this basis, by using an operational amplifier circuit to form a circuit proportional adder, the current of the resonant branch of the piezoelectric transformer can be calculated.

[0049] In this embodiment, six samplings are performed within each working cycle, and the sampling interval phase is 1 / 12, that is, Samplinginterval = 1 / 12. Therefore, the range covered by sampling per cycle is 2 / . Preferably, due to the high sampling frequency, the single-chip microcomputer adopts an alternating sampling mode. On the premise that the current input to the resonant branch of the piezoelectric transformer is considered to be composed only of the fundamental wave and the second and third harmonics, let the sampling values of the six sampling points be S1, S2, S3, S4, S5, and S6. The resonant branch current obtained by sampling contains resonant currents of different frequencies. In this embodiment, according to the sampling values of these six sampling points, the amplitudes and phases of the resonant currents of different frequencies are calculated through the following calculation process. Preferably, in this embodiment, the initial phase of the sampling point is set as θ, and the relative phase between the harmonic and the fundamental wave is Then the sampling point values can be expressed as:

[0050]

[0051] Among them, ω is the angular frequency of the current fundamental wave, ω = 2πf, f = 1 / T, t is time, in seconds, n is the subscript of the six sampling values S n (the range is 1-6), M1, M2, and M3 are the amplitudes of the fundamental wave, the second harmonic, and the third harmonic, Samplinginterval is the sampling interval phase, and let:

[0052]

[0053] Therefore, Equation (2) can be rewritten as:

[0054]

[0055] Substitute Samplinginterval = 1 / 12 and n = 1, 2, 3, 4, 5, 6 into it:

[0056]

[0057] Inverse the matrix:

[0058]

[0059] Thus, through the sampling values S1, S2, S3, S4, S5, and S6, X1, X2, Y1, Y2, Z1, and Z2 can be calculated. Further, the amplitudes of the fundamental wave, the second harmonic, and the third harmonic can be calculated as:

[0060]

[0061] Known:

[0062]

[0063] Further, from the trigonometric function transformation formula:

[0064]

[0065]

[0066] and

[0067]

[0068] Equation (9) is a mathematical formula for double angle and triple angle.

[0069] Substituting Equation (7) into Equations (8) and (9), we can get:

[0070]

[0071] Up to this point, the amplitude and relative phase relationship of harmonics can be quickly calculated by sampling six times per period. The amplitudes of the fundamental wave and harmonics can be obtained only through a matrix operation and a square root operation, while the relative phase relationship can be obtained only through simple multiplication and division operations. This embodiment can quickly calculate the amplitude and relative phase of the resonant current according to the sampling results.

[0072] Based on this embodiment, an experimental platform is built as Figure 3 shown. This experimental platform includes an oscilloscope 1, a DC power supply 2, an inverter 3, a single-chip microcomputer 4, and a load 5. Some test waveforms are as Figure 4 shown, and the results show that this embodiment can quickly and accurately achieve harmonic current decomposition.

[0073] The physical diagram of the pulse power supply of the piezoelectric transformer built based on this embodiment is as Figure 5 shown, and the typical output waveform is as Figure 6 shown. The results show that this embodiment can well meet the accuracy and real-time performance of harmonic current decomposition under high sampling frequency conditions.

[0074] In the embodiment of the present invention, from the resonant branch current containing resonant currents of different frequencies obtained by sampling, under the condition of a limited sampling frequency, a fast sampling method is designed to obtain the harmonic amplitude and relative phase relationship, without the need to ensure that the initial phase of each sampling is the same, and it meets the accuracy and real-time performance of harmonic current decomposition under high sampling frequency conditions.

[0075] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those skilled in the technical field to which the present invention belongs, without departing from the concept of the present invention, several equivalent substitutions or obvious variations can be made, and if the performance or use is the same, they should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for rapid sampling of harmonic current, characterized in that, It includes the following steps: A1. Conduct six current samplings on the resonant branch current of the electrical device within one working cycle, with a sampling interval phase of 1 / 12π, to obtain the current sampling values at six sampling points; A2. Determine the relationships between the current sampling values at the six sampling points and the amplitudes of the fundamental wave, second harmonic, and third harmonic, as well as the relative phases between the harmonics and the fundamental wave; A3. According to the relationships between the current sampling values at the six sampling points and the amplitudes of the fundamental wave, second harmonic, and third harmonic, as well as the relative phases between the harmonics and the fundamental wave, use the current sampling values at the six sampling points to calculate the amplitudes of the fundamental wave and the harmonics, and the relative phases between the harmonics and the fundamental wave; The relationships between the current sampling values at the six sampling points and the amplitudes of the fundamental wave, second harmonic, and third harmonic, as well as the relative phases between the harmonics and the fundamental wave are as follows: where S n is the sampling value of the six sampling points, n = 1, 2, 3, 4, 5, 6, M1, M2, and M3 are the amplitudes of the fundamental wave, second harmonic, and third harmonic, θ is the initial phase of the sampling point, is the relative phase between the harmonic and the fundamental wave, Samplinginterval is the sampling interval phase, ω is the angular frequency of the fundamental wave, and t is the time; Step A3 includes: simplifying the relationship between the sampling point values and the amplitudes and phases in the form of a matrix; The matrix is: Wherein, wherein, X1, X2, Y1, Y2, Z1, Z2 are intermediate quantities; Wherein, by sampling six times per cycle, the relationship between the amplitudes and relative phases of the harmonics is quickly calculated, and the amplitudes of the fundamental wave and the harmonics are obtained through a matrix operation and a square root operation.

2. The method for rapid sampling of harmonic current according to claim 1, characterized in that, Step A3 further includes: inverting the matrix; Calculate X1, X2, Y1, Y2, Z1, Z2 through the sampling values S1, S2, S3, S4, S5, S6 to obtain the amplitudes of the fundamental wave, second harmonic, and third harmonic; 3. The method for rapid sampling of harmonic current according to claim 2, characterized in that, Step A3 further includes: determining the relative phase between the harmonics and the fundamental wave of the resonant current according to the following formula:

4. The method for rapid sampling of harmonic current according to any one of claims 1 to 3, characterized in that, The electrical device is a piezoelectric transformer.

5. The method for rapid sampling of harmonic current according to claim 4, characterized in that, In step A1, an input sampling circuit is used to collect the resonant branch current input to the piezoelectric transformer. The input sampling circuit includes a sampling capacitor (C x ), a sampling resistor (R x ), and an operational amplifier circuit. The sampling capacitor (C x ) is connected in parallel at the input end of the piezoelectric transformer. The sampling capacitor (C x ) << the input capacitance of the piezoelectric transformer (C in ), and the loop time constant formed by the sampling resistor (R x ) and the sampling capacitor (C x ) is much smaller than the working period T of the circuit. An in-circuit proportional adder is formed through the operational amplifier circuit to calculate the resonant branch current of the piezoelectric transformer.

6. The method for rapid sampling of harmonic current according to claim 5, characterized in that, The operational amplifier circuit includes an operational amplifier, analog transformer grounding resistors (R1, R5), an inverting input terminal resistor (R2), a feedback resistor (R3), and a balancing resistor (R4). One end of the sampling capacitor (C x ) is connected to one input terminal of the piezoelectric transformer. One end of the inverting input terminal resistor (R2) is connected between the other end of the sampling capacitor (C x ) and the sampling resistor (R x ). The other end of the inverting input terminal resistor (R2) is connected to the inverting input terminal of the operational amplifier. The feedback resistor (R3) is connected between the inverting input terminal and the output terminal of the operational amplifier. One end of the sampling resistor (R x ) is connected to the other end of the sampling capacitor (C x ). The other end of the sampling resistor (R x ) is grounded. One end of the analog transformer grounding resistors (R1, R5) is grounded. The other end of the analog transformer grounding resistors (R1, R5) is connected to the non-inverting input terminal of the operational amplifier through the balancing resistor (R4). The other input terminal of the piezoelectric transformer is connected between the balancing resistor (R4) and the analog transformer grounding resistors (R1, R5).

7. The method for rapid sampling of harmonic current according to claim 6, characterized in that, The grounding resistors (R1, R5) of the analog transformer include two resistors connected in parallel between the balancing resistor (R4) and the ground.

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