CN113740651B - Quality detection method suitable for three-phase frequency converter input power grid - Google Patents
Quality detection method suitable for three-phase frequency converter input power grid Download PDFInfo
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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Abstract
The invention relates to a quality detection method suitable for a three-phase frequency converter input power grid, which is used for rectifying three-phase power grid input voltage, obtaining a voltage characteristic signal, sampling the voltage characteristic signal, carrying out Fourier analysis, and evaluating the quality of the input power grid signal by combining an analysis result. The invention can realize quantitative analysis on the quality of the input power grid through Fourier analysis, can accurately judge the input open phase of the frequency converter, or realize real-time monitoring of the quality of the power grid due to the negative sequence and zero sequence introduced by the self quality of the power grid.
Description
Technical Field
The invention relates to a state discrimination and quality detection method related to a power grid, in particular to a quality detection method suitable for a three-phase frequency converter input power grid.
Background
Today, for three-phase frequency converters, only three-phase inputs can be operated when they are normal, otherwise the driving capability is insufficient. Therefore, protection is needed in time to avoid abnormality caused by insufficient driving capability.
Currently, for input grid quality detection, it is mainly used to detect input open-phase, which requires RS, RT (or any other two-phase input combination) on the input side to increase input voltage sampling during implementation. And then, combining the three-phase circuit theorem to obtain a third phase line voltage sampling value. Then, the three-phase input line voltage effective value is calculated according to the effective value definition. And finally, comparing every two to judge which phase of power grid is abnormal.
In addition, there is another scheme, which mainly adds an uncontrolled rectifying circuit on the input side. During implementation, the three-phase input voltage is rectified into a direct-current voltage, and the rectified direct-current voltage signal is shaped into a square wave through a Schmitt trigger or a comparator. Then, the square wave is counted for a certain time by edge capturing, and converted into a frequency. Taking domestic 50Hz power grid as an example, if the square wave frequency is 300Hz, the three-phase input is considered to be normal. If the square wave frequency is 100Hz, the input open-phase is judged.
However, the conventional method at present mainly locates whether the input is out of phase or not, and does not monitor the quality of the realized power grid.
Specifically, for input open-phase detection, the first solution requires solving the effective value of the three-phase line voltage. The voltage signal of a complete period needs to be acquired when the effective value is calculated, and then the calculation is performed according to the definition formula of the effective value. For this reason, the calculation pressure applied is large and the calculation period is long. Taking a 50Hz power grid as an example, at least 20ms is required to obtain the result of the effective value, at least 20ms is required to judge the input open phase, and the minimum time for judging the abnormality is limited.
For the second scheme, although the frequency of the detected signal is increased to 300Hz, the corresponding detection time can be reduced to 3.3ms, so that the scheme can accurately detect the abnormal problem of open-phase input of the power grid. However, the rectified voltage is shaped into square waves, so that the amplitude information of the input power grid is lost, and the full utilization of the information is not realized.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a quality detection method suitable for a three-phase frequency converter input power grid.
The quality detection method suitable for the three-phase frequency converter input power grid comprises the following steps: rectifying input voltage of a three-phase power grid to obtain a voltage characteristic signal; step two, sampling the voltage characteristic signals and carrying out Fourier analysis; and thirdly, evaluating the quality of the input power grid signal by combining the result of Fourier analysis.
In the first step, the input voltage signal of the three-phase power grid is sent to a three-phase uncontrolled rectifying circuit for rectification, and a rectified input voltage characteristic signal is obtained.
Furthermore, the quality detection method suitable for the three-phase frequency converter input power grid is characterized in that the Fourier analysis mode and the evaluation method are as follows,
If the harmonic distribution in the rectified voltage signal exists in a frequency multiplication relation by taking a preset Hertz parameter, the preset Hertz parameter is the largest in duty ratio, and the frequency multiplication harmonic duty ratio is reduced along with the increase of the harmonic frequency, the input phase failure is estimated;
If the frequency multiplication harmonic of the preset Hertz parameter exists in the rectified voltage signal, and the preset Hertz parameter and the fundamental wave parameter occupy a larger proportion in the rectified voltage signal, carrying out harmonic analysis on the rectified voltage signal, and evaluating that the power grid has zero sequence after the preset Hertz parameter occupies a zero sequence duty preset value;
If the frequency multiplication harmonic of the preset Hertz parameter exists in the rectified voltage signal, and the preset Hertz parameter and the fundamental wave parameter occupy a larger proportion in the rectified voltage signal, harmonic analysis is carried out on the rectified voltage signal, and when the preset Hertz parameter occupy a negative sequence occupying ratio preset value, the negative sequence of the power grid is estimated.
Still further, the quality detection method suitable for the three-phase frequency converter input power grid is described above, wherein the zero sequence duty ratio preset value is 10% to 50%, and the negative sequence duty ratio preset value is 50% to 99%.
Taking a domestic 50Hz power grid as an example, the fundamental wave is 300Hz, the preset Hz parameter is 100Hz, and if the power grid frequency is 60Hz, the fundamental wave frequency needs to be adjusted to 360Hz, and the preset Hz parameter is adjusted to 120Hz. The zero sequence duty ratio preset value is 10 to 50 percent, and the negative sequence duty ratio preset value is 50 to 99 percent. In other words, the actual values of the fundamental wave and the preset hertz parameter need to be matched with the current power grid quality and the harmonic waves caused by the zero sequence and the negative sequence of the power grid which can be tolerated by the system.
By means of the scheme, the invention has at least the following advantages:
1. The invention can realize quantitative analysis on the quality of the input power grid through Fourier analysis, and can accurately judge the input open-phase of the frequency converter or the zero sequence influence due to the negative sequence introduced by the self quality of the power grid.
2. According to the invention, the quantitative analysis result is realized on the quality of the input power grid through Fourier analysis, so that the quality of the power grid can be monitored in real time, thereby realizing early warning and reminding of abnormal occurrence of the driver and facilitating the protection of equipment by a back-end personnel.
3. The method is convenient to realize, and can be conveniently connected into the existing power grid to carry out effective detection and supervision.
The foregoing description is only an overview of the present invention, and is intended to provide a better understanding of the present invention, as it is embodied in the following description, with reference to the preferred embodiments of the present invention and the accompanying drawings.
Drawings
Fig. 1 is a schematic diagram of a power grid quality detection circuit constructed using the principles of the present invention.
Fig. 2 is a schematic diagram of a detection flow according to the present invention.
Fig. 3 is a schematic diagram of a fourier analysis of the input grid as normal (for example, a domestic 50Hz grid).
Fig. 4 is a schematic diagram of fourier analysis of input open phase (for example, a domestic 50Hz grid).
Fig. 5 is a schematic diagram of fourier analysis of 5% zero sequence input (for example, a domestic 50Hz grid).
Fig. 6 is a schematic diagram of fourier analysis of an input 5% negative sequence (for example, a domestic 50Hz grid).
Detailed Description
The following describes in further detail the embodiments of the present invention with reference to the drawings and examples. The following examples are illustrative of the invention and are not intended to limit the scope of the invention. Only domestic 50Hz power grid is taken as an example at present.
The quality detection method for the input power grid of the three-phase frequency converter according to fig. 1 to 6 is distinguished by comprising the following steps:
step one, sending a three-phase power grid input voltage signal into a three-phase uncontrolled rectifying circuit for rectification to obtain a rectified input voltage characteristic signal;
sampling the voltage characteristic signal and performing Fourier analysis (FFT analysis);
and thirdly, evaluating the quality of the input power grid signal by combining the result of Fourier analysis.
In connection with practical implementation, the evaluation results obtained after the fourier analysis are as follows:
in the mode 1, if the harmonic distribution in the rectified voltage signal exists in a frequency multiplication relation by taking the preset Hertz parameter as the frequency multiplication relation, and the preset Hertz parameter is the largest in duty ratio, the frequency multiplication harmonic duty ratio is reduced along with the increase of the harmonic frequency, and the input phase failure is estimated.
And 2, if the frequency multiplication harmonic of the preset Hertz parameter exists in the rectified voltage signal, the preset Hertz parameter and the fundamental wave parameter occupy a larger proportion in the rectified voltage signal, carrying out harmonic analysis on the rectified voltage signal, and evaluating that the zero sequence exists in the power grid after the preset Hertz parameter occupy a preset zero sequence occupying ratio value.
And 3, if the frequency multiplication harmonic of the preset Hertz parameter exists in the rectified voltage signal, and the preset Hertz parameter and the fundamental wave parameter occupy a larger proportion in the rectified voltage signal, carrying out harmonic analysis on the rectified voltage signal, and evaluating that the power grid has a negative sequence after the preset Hertz parameter occupy a preset negative sequence occupy value.
Considering the convenience of embodiment expression, in view of domestic conventional grid parameters, for the currently adopted 50Hz grid, the fundamental wave can be set to 300Hz, and the preset Hz parameter can be set to 100Hz. In addition, in order to obtain more visual values, the judgment is convenient, the adopted zero sequence ratio preset value is 10-50%, and the negative sequence ratio preset value is 50-99%. Taking a domestic 50Hz power grid as an example, referring to fig. 2, the harmonic amplitudes of 100Hz and 300Hz can be compared by using a Fourier algorithm to obtain the current running state of the power grid. If the grid frequency is 60Hz, the corresponding extracted harmonic frequencies are 120Hz and 360Hz.
Specifically, for a typical 50Hz power grid in China, the result of Fourier analysis and analysis at the time of normal input is shown in FIG. 3. In order to realize unified standard, the invention can take 300Hz as fundamental wave in analysis. From this, it is found from the analysis result that only 300Hz fundamental wave signal exists in the voltage rectification signal when the power grid is normal.
Referring to fig. 4 again, the harmonic distribution in the rectified signal is characterized by the presence of 100Hz as a frequency multiplication, such as 100Hz,200Hz,300Hz,400Hz, etc. Wherein the 100Hz duty cycle is maximum, and the frequency multiplication harmonic duty cycle is reduced as the harmonic frequency increases. Thus, the result of inputting the open phase can be obtained.
Meanwhile, if the zero sequence exists in the power grid, 100Hz frequency multiplication harmonic exists in the rectified voltage signal, and the preset Hz parameter and the fundamental wave parameter occupy a larger proportion in the rectified voltage signal, as shown in fig. 5, wherein 100Hz and 300Hz occupy a larger proportion, so that the two parameters are taken as analysis objects.
Under the condition, under the condition that 5% of zero sequence exists in the power grid, harmonic waves of the rectified voltage signal are analyzed, and the graph 5 is obtained. At this time, it can be seen that the 100Hz harmonic accounts for about 30% of the fundamental wave of about 300 Hz. Specifically, taking domestic 50Hz power grid as an example, the characteristics of signals under different frequencies under 5% zero sequence influence are obvious. For this reason, the 5% is taken as an illustration only for the sake of convenience in acquiring signal characteristics, and the characteristics under the zero sequence with any ratio are similar to those of the illustration 5, except that the amplitude ratio of each subharmonic is different, which is not described in detail.
Still further, if the power grid has a negative sequence, harmonics of the 100Hz frequency multiplication relationship can be analyzed in the rectified voltage signal. It can be found that the preset hertz parameter and the fundamental wave parameter occupy larger proportion in the rectified voltage signal similar to the zero sequence condition, and as shown in fig. 6, the largest proportion is the harmonic wave of 100Hz and 300Hz, so that the two parameters are taken as analysis objects.
In the above case, the grid may have 5% negative sequence, and the result obtained by analyzing the rectified voltage harmonic is shown in fig. 6. At this time, the harmonic of 100Hz is relatively large, and can reach about 88% of the fundamental wave. Therefore, the negative sequence influence of the power grid is more serious than that of the zero sequence under the interference of the same amplitude. As can be seen in connection with fig. 6, the characteristics of the signal at different frequencies are evident under the influence of 5% negative sequence. It should be noted that this embodiment selects 5% of the description, which is merely convenient to better describe how to express the interface graphically shown in fig. 6 in the case that the grid has a negative sequence. In practice, the features of any duty cycle under the negative sequence are similar to those of the schematic diagram 6, and the difference is mainly that the amplitude duty cycle of each subharmonic is different, which is not described in detail.
Furthermore, in order to better implement the present invention, the power grid quality detection circuit shown in fig. 1 may be used, and the power grid quality detection circuit may be connected to the power grid. The circuit mainly comprises an uncontrolled rectifying circuit, an isolated amplifying circuit and an ADC sampling module.
It should be noted that the hertz parameters and the ratio data adopted in the present embodiment are only for better describing the implementation process of the present invention, and are not parameters for setting the conditions required during the implementation of the present invention.
As can be seen from the above text expressions and the accompanying drawings, the invention has the following advantages:
1. the quality of the input power grid can be quantitatively analyzed through Fourier analysis, and input open-phase of the frequency converter can be accurately judged, or the influence of the zero sequence due to the negative sequence introduced by the quality of the power grid can be accurately judged.
2. According to the invention, the quantitative analysis result is realized on the quality of the input power grid through Fourier analysis, so that the quality of the power grid can be monitored in real time, thereby realizing early warning and reminding of abnormal occurrence of the driver and facilitating the protection of equipment by a back-end personnel.
3. The method is convenient to realize, and can be conveniently connected into the existing power grid to carry out effective detection and supervision.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, and it should be noted that it is possible for those skilled in the art to make several improvements and modifications without departing from the technical principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.
Claims (1)
1. The quality detection method suitable for the three-phase frequency converter input power grid is characterized in that,
The method comprises the following steps:
rectifying input voltage of a three-phase power grid to obtain a voltage characteristic signal;
Step two, sampling the voltage characteristic signals and carrying out Fourier analysis;
thirdly, evaluating the quality of the input power grid signal by combining the result of Fourier analysis;
In the first step, an input voltage signal of a three-phase power grid is sent into a three-phase uncontrolled rectifying circuit for rectification, and an input voltage characteristic signal is obtained;
the fourier analysis method and the evaluation method are that,
If the harmonic distribution in the rectified voltage signal exists in a frequency multiplication relation by taking a preset Hertz parameter, the preset Hertz parameter is the largest in duty ratio, and the frequency multiplication harmonic duty ratio is reduced along with the increase of the harmonic frequency, the input phase failure is estimated;
If the frequency multiplication harmonic of the preset Hertz parameter exists in the rectified voltage signal, and the preset Hertz parameter and the fundamental wave parameter occupy more than the rectified voltage signal, carrying out harmonic analysis on the rectified voltage signal, and evaluating that the zero sequence exists in the power grid after the preset Hertz parameter occupies more than 10-50% of the zero sequence ratio preset value;
if the frequency multiplication harmonic of the preset Hertz parameter exists in the rectified voltage signal, and the preset Hertz parameter and the fundamental wave parameter occupy more than more in the rectified voltage signal, harmonic analysis is carried out on the rectified voltage signal, and when the preset Hertz parameter occupy more than 50% to 99% of a negative sequence occupying ratio preset value, the existence of the negative sequence of the power grid is estimated.
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