CN110007145B - Resonance point detection method based on constant voltage source converter and voltage current phase difference - Google Patents
Resonance point detection method based on constant voltage source converter and voltage current phase difference Download PDFInfo
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Abstract
The invention discloses a resonance point detection method based on a constant voltage source converter and a voltage current phase difference, which comprises the following steps of firstly, injecting carrier voltage signals with equal amplitude and different frequencies to a low-voltage side of a transformer by using the designed constant voltage source converter; detecting a voltage signal U (t) and a current signal I (t) of the low-voltage side of the transformer; extracting voltage and current harmonic phase differences of different frequencies at the low-voltage side of the transformer according to a sliding DFT algorithm; and step four, detecting the resonance point according to the calculated voltage and current harmonic phase difference under different frequencies. According to the method, only low-frequency carrier voltage signals with different frequencies are injected to the low-voltage side of the transformer, and simultaneously, voltage and current signals of the low-voltage side of the transformer are detected, so that the resonance point can be automatically detected, repeated measurement is not needed, and the operation is simple. In addition, the algorithm has small calculation amount, completely meets the requirement of real-time online detection on low power consumption, and is applied to actual engineering.
Description
Technical Field
The invention relates to the field of distribution network automation systems, in particular to a resonance point detection method based on a constant voltage source converter and a voltage-current phase difference.
Background
In the field of power systems, the excellent quality factor of a system is a precondition for ensuring the safe, stable and economic operation of the system, and therefore, in order to improve the quality factor of a power grid system and reduce the system loss, reactive compensation is generally performed by switching a capacitor bank into the power grid system. However, due to the use of some electric welding machines and household appliances, a large number of harmonic sources exist in a power grid system, when a capacitor bank is switched, parallel resonance may occur between the system and a capacitor, and an excessive resonant current is generated, so that the capacitor bank is burnt, and even other devices in the power grid are damaged, thereby causing a serious power accident. Therefore, the resonance point of the system can be detected in advance, and a basis is provided for governing a harmonic source and switching a capacitor bank.
The resonance point detection tool that uses commonly at present is mostly professional equipment, and the cost is higher, detects voltage electric current data back, still need carry on harmonic analysis with the host computer of uploading to data to can not realize real-time on-line measuring to detection speed is slower, and the testing process is complicated, and the flexibility is relatively poor. Therefore, there is an urgent need to develop a method capable of detecting the resonance point on line in real time.
Disclosure of Invention
The invention aims at the problems and overcomes the defects of the prior art, and provides a resonance point detection method based on a constant voltage source converter and a voltage-current phase difference. The method is simple to realize, the resonance point can be automatically detected only by injecting a low-frequency carrier voltage signal to the low-voltage side of the transformer by using the constant-voltage source converter and detecting a voltage current signal of the low-voltage side of the transformer, and the real-time online detection of the resonance point can be realized. The method does not need repeated tests, is simple to operate, is applied to an actual power system, and achieves good effects.
The invention detects the resonance point by injecting low-frequency carrier voltage signals with different frequencies and detecting the voltage current harmonic phase difference through the constant voltage source converter. The method comprises the steps of firstly, injecting carrier voltage signals with equal amplitude and different frequencies to a low-voltage side of a transformer by using a designed constant-voltage source converter, simultaneously detecting voltage and current signals of the low-voltage side of the transformer, then extracting voltage and current harmonic phase differences of different frequencies according to a sliding DFT algorithm, and finally detecting a resonance point according to the extracted voltage and current harmonic phase differences of different frequencies.
In order to achieve the purpose of the invention, the invention adopts the following technical scheme:
a resonance point detection method based on a constant voltage source converter and a voltage-current phase difference comprises the following steps,
step one, injecting carrier voltage signals with equal amplitude and different frequencies to a low-voltage side of a transformer by using a designed constant-voltage source converter.
Step two, detecting a voltage signal U (t) and a current signal I (t) of the low-voltage side of the transformer.
And step three, extracting voltage and current harmonic phase differences of different frequencies at the low-voltage side of the transformer according to a sliding DFT algorithm.
And step four, detecting the resonance point according to the calculated voltage and current harmonic phase difference under different frequencies.
Further, the transfer function of the resonance controller in the constant voltage source converter in the step one is,
wherein n is the frequency of the carrier voltage signal, ω is the fundamental angular frequency, KrIs the resonance term coefficient.
Furthermore, the calculation formula of the sliding DFT algorithm in step three for extracting the voltage and current harmonic phase difference is as follows,
wherein the content of the first and second substances,
for the phase difference of the extracted kth voltage current harmonic,
respectively the real parts of the extracted kth voltage harmonic and the extracted current harmonic,
respectively is the imaginary part of the extracted kth voltage harmonic and the current harmonic, and k is the extracted harmonic frequency. In the above formula ak、bkThe calculation formulas of (a) and (b) are respectively,
wherein x is a detection signal, T0For the initial moment of the detection signal, i is the sampling point of the ith detection signal, N represents the number of data points in the power frequency period, k represents the number of harmonic frequencies, and T is the time of the power frequency period.
Further, the principle of detecting the resonance point according to the calculated voltage and current harmonic phase difference at different frequencies in the fourth step is that
When the phase of the k harmonic wave of the voltage leads the phase of the k harmonic wave of the current, the frequency corresponding to the k harmonic wave is positioned in front of the resonance point when
When the phase of the voltage k-th harmonic is in the same direction as that of the current k-th harmonic, the frequency corresponding to the k-th harmonic is a resonance point, when
When the temperature of the water is higher than the set temperature,the phase of the k-th harmonic of the voltage lags the phase of the k-th harmonic of the current, and the frequency corresponding to the k-th harmonic is positioned behind the resonance point. The principle of the detection is determined that when the system generates parallel resonance, the system presents pure resistance, the impedance R reaches the maximum, when k is smaller than the frequency of the resonance point, the capacitive reactance of the system is larger than the inductive reactance, the system presents inductive, voltage phase leads current, when k is larger than the frequency of the resonance point, the capacitive reactance of the system is smaller than the inductive reactance, the system presents capacitive, and voltage phase lags current.
Further, in the first step, the frequency range is between 1K and 5 KHz.
Further, in the step one, the amplitude range is between 5 and 15V.
Further, a constant voltage source converter structure adopts a three-level structure, the SVPWM modulation algorithm is utilized to generate driving signals of switching tubes of all phases, and the switching driving signals S of all phases are driven by driving IGBTs of all phasesxn(where x is a, b, c, n is 1,2,3,4) regulating the converter output voltage UAO、UBOAnd UCOThereby realizing the voltage UAB UBC UCAAnd (4) controlling.
The invention has the beneficial effects that: the invention relates to a resonance point detection method based on a constant voltage source converter and a voltage-current phase difference. According to the method, only low-frequency carrier voltage signals with different frequencies are injected to the low-voltage side of the transformer, and simultaneously, voltage and current signals of the low-voltage side of the transformer are detected, so that the resonance point can be automatically detected, repeated measurement is not needed, and the operation is simple. In addition, the algorithm has small calculation amount, completely meets the requirement of real-time online detection on low power consumption, and is applied to actual engineering.
Drawings
Fig. 1 is a general flow chart of a resonant point detection method based on a constant voltage source converter and a voltage-current phase difference according to the present invention.
Fig. 2 is a general block diagram of the constant voltage source inverter system of the present invention.
FIG. 3 is a waveform of a voltage-current measurement signal at the low-voltage side of a transformer when a 550Hz low-frequency carrier voltage signal is injected according to the present invention.
FIG. 4 is a waveform of a voltage-current measurement signal at the low-voltage side of a transformer when a 1100Hz low-frequency carrier voltage signal is injected according to the present invention.
FIG. 5 is a waveform of a voltage-current measurement signal at the low-voltage side of a transformer when injecting a 1250Hz low-frequency carrier voltage signal according to the present invention.
FIG. 6 is a voltage-current phase difference waveform of 11 th harmonic in the voltage-current signal of the low-voltage side of the transformer extracted by the present invention.
FIG. 7 is a waveform of voltage-current phase difference of 22 th harmonic in the voltage-current signal of the low-voltage side of the transformer extracted by the present invention.
FIG. 8 is a voltage-current phase difference waveform of 25 th harmonic in the voltage-current signal of the low-voltage side of the transformer extracted by the present invention.
FIG. 9 shows the waveform of 11 th harmonic current generated by the compensation capacitor when injecting a 550Hz low frequency carrier voltage signal.
FIG. 10 shows the waveform of the 22 th harmonic current generated by the compensation capacitor when injecting the 1100Hz low frequency carrier voltage signal extracted by the present invention.
FIG. 11 is a waveform of 25 th harmonic current generated by the compensation capacitor when injecting a 1250Hz low frequency carrier voltage signal extracted by the present invention.
In fig. 3-5, the abscissa represents the number of sampling points, and the ordinate represents the magnitude of the voltage and current, respectively in V, A units. In fig. 6-8, the abscissa represents the extracted harmonic voltage current phase difference in degrees, respectively; in fig. 9-11, the abscissa represents the number of sampling points, and the ordinate represents the magnitude of the harmonic current generated by the capacitor compensation, in a.
Detailed Description
The present invention will be further described with reference to the accompanying drawings 1-11 and examples to illustrate the technical solutions of the present invention. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
Referring to fig. 1, the resonance point detection method based on the constant voltage source converter and the voltage-current phase difference of the present invention includes the following steps,
step one, injecting low-frequency carrier current signals with amplitude of 10V and frequencies of 550Hz, 1100Hz and 1250Hz respectively into the low-voltage side of the transformer by using the constant-voltage source converter designed in the figure 2.
The constant voltage source converter structure adopts a three-level structure, the driving signals of the switching tubes of all phases are generated by utilizing an SVPWM (space Vector Pulse Width modulation) modulation algorithm, and the switching driving signals S of all phases are driven by driving the IGBTs of all phasesxn(where x is a, b, c, n is 1,2,3,4) regulating the converter output voltage UAO、UBOAnd UCOThereby realizing the voltage UABUBC UCAAnd (4) controlling.
Step two, waveforms of the voltage signal u (t) and the current signal i (t) at the low-voltage side of the detection transformer are shown in fig. 3 to 5.
Step three, respectively extracting phase differences of 11, 22 and 25 times of low-frequency carrier wave voltage and current in the low-voltage side measuring signal of the transformer according to a sliding DFT algorithm, wherein the waveforms of the phase differences are respectively shown in figures 6 to 8, a calculation formula for extracting voltage and current harmonic phase differences by the sliding DFT algorithm is as follows,
wherein the content of the first and second substances,
for the phase difference of the extracted kth voltage current harmonic,
respectively the real parts of the extracted kth voltage harmonic and the extracted current harmonic,
respectively the imaginary parts of the extracted kth voltage harmonic and the extracted current harmonic, k is the extracted harmonic frequency,
k＝11,22,25。
in the above formula ak、bkThe calculation formulas of (a) and (b) are respectively,
wherein x is a detection signal, T0For the initial moment of the detection signal, i is the sampling point of the ith detection signal, N represents the number of data points in the power frequency period, k represents the number of harmonics, T is the time of the power frequency period, and T is 20 ms.
Step five, detecting a resonance point according to the calculated voltage and current harmonic phase difference, and extracting 11 times of voltage and current harmonic phase difference when injecting a 550Hz low-frequency carrier voltage signal
The 11 th harmonic wave is positioned in front of the resonance point, and when a low-frequency carrier voltage signal of 1100Hz is injected, the extracted 22-th harmonic wave phase difference of the voltage and the current is obtained
The 22 nd harmonic is located before the resonance point, and when injecting a low-frequency carrier voltage signal of 1250Hz, the phase difference of the extracted 25 th harmonic of the voltage and the current is equal to
The 25 th harmonic is located after the resonance point, and therefore, it can be determined that the resonance point is located in a frequency range between the 22 th harmonic and the 25 th harmonic.
In this embodiment: and verifying the resonance point detection method by using actual field test data. According to the invention, the resonance point between the frequency of the 22 th harmonic and the frequency of the 25 th harmonic is determined according to the phase difference of the voltage and the current, meanwhile, as can be seen from the graphs in fig. 9-10, the harmonic current generated by the compensation capacitor when the low-frequency carrier voltage signals of 1100Hz and 1250Hz are injected is much larger than the current generated by the compensation capacitor when the low-frequency carrier voltage signal of 550Hz is injected, which shows that the system is in resonance around the 22 th harmonic and the 25 th harmonic, and further verifies that the method provided by the invention is feasible. Because the actual detection equipment adopts the mode of injecting the low-frequency carrier voltage signal into the power grid for detection, when the fast approaching resonance point is detected, the vicinity of the resonance point can be skipped, the resonance of the system is avoided, finally, the method can detect that the resonance point is in a certain frequency range, a certain theoretical basis is provided for the governance of the harmonic source, and a new implementation mode is provided for the detection of the resonance point.
In the first step of the present invention, the frequency range is between 1K and 5KHz, and may be any value between 1KHz, 5KHz or 1K and 5KHz, and is not limited to the values given in the embodiments. In the first step, the range of the amplitude is between 5 and 15V, and the amplitude can be any value between 5V, 15V or 5 to 15V, and is not limited to the values given in the embodiments.
In summary, the invention provides a resonance point detection method based on a constant voltage source converter and a voltage-current phase difference, which injects carrier voltage signals with equal amplitude and different frequencies to a low-voltage side of a transformer by using the designed constant voltage source converter, detects voltage-current signals at the low-voltage side of the transformer at the same time, extracts voltage-current harmonic phase differences with different frequencies according to a sliding DFT algorithm, and finally detects a resonance point according to the extracted voltage-current harmonic phase differences with different frequencies. According to the method, the resonance point of the system can be automatically detected only by injecting low-frequency carrier voltage signals with different frequencies into the low-voltage side of the transformer by using the designed constant-voltage source converter and detecting the voltage and current signals of the injection side, the operation is simple, and the resonance point can be accurately detected in a certain frequency range in real time on line.
The above embodiments are illustrative of specific embodiments of the present invention, and are not restrictive of the present invention, and those skilled in the relevant art can make various changes and modifications without departing from the spirit and scope of the present invention to obtain corresponding equivalent technical solutions, and therefore all equivalent technical solutions should be included in the scope of the present invention.
Claims (4)
1. A resonance point detection method based on a constant voltage source converter and a voltage current phase difference is characterized in that: comprises the following steps of (a) carrying out,
injecting carrier voltage signals with equal amplitude and different frequencies to a low-voltage side of a transformer by using a designed constant-voltage source converter, wherein the frequency range is between 1K and 5KHz, and the amplitude range is between 5 and 15V;
detecting a voltage signal U (t) and a current signal I (t) of the low-voltage side of the transformer;
extracting voltage and current harmonic phase differences of different frequencies at the low-voltage side of the transformer according to a sliding DFT algorithm;
detecting a resonance point according to the calculated voltage and current harmonic phase difference under different frequencies, wherein the resonance point detected by the method is in a certain frequency range;
in the third step, the voltage and current harmonic phase difference of different frequencies at the low voltage side of the transformer is extracted according to the sliding DFT algorithm, wherein the calculation formula for extracting the voltage and current harmonic phase difference by the sliding DFT algorithm is as follows,
wherein the content of the first and second substances,
for the phase difference of the extracted kth voltage current harmonic,
respectively the real parts of the extracted kth voltage harmonic and the extracted current harmonic,
respectively extracting the imaginary parts of the kth voltage harmonic and the current harmonic, wherein k is the extracted harmonic frequency;
in the above formula ak、bkThe calculation formulas of (a) and (b) are respectively,
wherein x is a detection signal, T0For the initial moment of the detection signal, i is the sampling point of the ith detection signal, N represents the number of data points in the power frequency period, k represents the number of harmonic frequencies, and T is the time of the power frequency period.
2. The method according to claim 1, wherein the method comprises the following steps: in the first step, a designed constant voltage source converter is used for injecting low-frequency pulsating voltage signals with equal amplitude and different frequencies to the low-voltage side of a transformer, wherein the transfer function of a resonance controller in the constant voltage source converter is as follows,
wherein n is the number of times of pulsating voltage, ω is the fundamental angular frequency, KrIs the resonance term coefficient.
3. The method according to claim 1, wherein the method comprises the following steps: the principle of detecting the resonance point according to the calculated voltage and current harmonic phase difference under different frequencies in the fourth step is that
When the phase of the k harmonic wave of the voltage leads the phase of the k harmonic wave of the current, the frequency corresponding to the k harmonic wave is positioned in front of the resonance point when
When the phase of the voltage k-th harmonic is in the same direction as that of the current k-th harmonic, the frequency corresponding to the k-th harmonic is a resonance point, when
When the voltage k-th harmonic lags behind the phase of the current k-th harmonic, the frequency corresponding to the k-th harmonic is behind the resonance point.
4. The method according to claim 1, wherein the method comprises the following steps: the constant voltage source converter structure adopts a three-level structure, a SVPWM (space vector pulse width modulation) algorithm is utilized to generate driving signals of switching tubes of all phases, and the switching driving signals Sxn (x is a, b, c, n is 1,2,3,4) of all phases are driven by driving IGBTs of all phases to adjust the output voltage U of the converterAO、UBOAnd UCOThereby realizing the voltage UAB、UBC、UCAAnd (4) controlling.
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