CN110389251B - Instantaneous voltage dq decomposition method for power grid voltage drop detection - Google Patents
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Abstract
The invention discloses an instantaneous voltage dq decomposition method for power grid voltage drop detection, which relates to the field of voltage drop detection. Compared with the 3.33ms of an instantaneous voltage dq decomposition method, the theoretical delay time of the method is 0.83ms, the actual delay time is only 0.9375ms, and the real-time performance is greatly improved. The invention adopts single-phase voltage signals to virtually construct a multi-phase system, reduces the number of alternating-current voltage sensors and reduces the cost. The method has the advantages of simple algorithm, practicality, good dynamic performance and stronger engineering practice effect.
Description
Technical Field
The invention relates to the field of voltage drop detection, in particular to an instantaneous voltage dq decomposition method for power grid voltage drop detection.
Background
With the rapid development of global economy, the problems of energy shortage and environmental pollution are increasingly aggravated, and renewable energy sources such as photovoltaic power generation and wind power generation, which have the significance of energy conservation, emission reduction, green and low-carbon functions, are increasingly valued and developed. However, the inherent randomness and volatility of renewable energy sources make the problem of electric energy quality more prominent, especially the problem of voltage stability at high permeability.
Meanwhile, among the power quality problems, voltage sag is one of the most serious power quality problems, which may account for more than 80% of the entire power quality problem, but cannot be solved due to harmonics, switching operation overvoltage, and the like. In recent years, with the development of modern science and technology, computer and microprocessor based electric devices and various high-power electronic devices have been widely used. The requirements of the electric equipment on the electric energy quality are more severe, the voltage sag is considered to be a main electric energy quality problem influencing the normal and safe operation of many electric equipment, and the power supply of the equipment is interrupted due to the voltage interruption or voltage sag of only a few cycles, so that serious economic loss is caused. It is necessary to take appropriate compensation measures to avoid the large losses caused by voltage sags.
The real-time and accurate detection of the voltage sag characteristic quantity is the premise of quickly and effectively compensating the voltage sag. At present, most of voltage sag occurring in a power system is a single-phase event, and a commonly used detection method is to perform voltage sag parameter detection by adopting dq transformation through a fictitious three-phase system, and is generally called as an instantaneous voltage dq decomposition method. Due to the phase shift operation, when the voltage signal is temporarily dropped, the fictitious voltage amplitude change can be detected only by delaying 1/6 power frequency cycles, the theoretical delay is 3.33ms, and adverse effects are brought to real-time control.
Disclosure of Invention
Aiming at the defects of the prior art, the method improves and processes the current commonly used instantaneous voltage dq decomposition method by performing imaginary construction on a single-phase system voltage signal and using a space vector superposition principle, so that the time delay time of the method is further shortened.
The invention adopts the technical scheme that the instantaneous voltage dq decomposition method for detecting the voltage drop of the power grid comprises the following steps:
step S1, acquiring a one-phase voltage signal in a power grid voltage signal system;
step S2, selecting an instantaneous voltage dq decomposition method, and improving the instantaneous voltage dq decomposition method according to the space vector superposition principle;
and step S3, carrying out amplitude characteristic detection on the single-phase power grid voltage signal by using an improved instantaneous voltage dq decomposition method.
Further, the specific steps of step S2 are as follows:
step S21, the collected single-phase voltage signal is uoWill uoLag by 15 degrees, to obtain u15A space voltage vector uoIn space voltage vector u15The projection on is denoted as u2Let u stand for2Modulus of (d) divided by uoThe modulus of (a) is given as a;
step S22, according to the calculation result of step S21, u2By u15Expressed by the formula (1) while u1、u2And uoThree voltage vectors form a triangle u1Is u2And uoSpace voltage vector obtained by subtracting space voltage vector:
u2＝au15 (1)；
step S23, according to the calculation result of step S22, u1By uoAnd u15Expressed by equation (2):
u1＝uo-au15 (2)；
step S24, according to the calculation result of step S23, uoVoltage vector u with 30 degree lag30By uoAnd u15Expressed by equation (3):
u30＝2au15-uo (3)；
step S25, converting the space voltage vector uoIn space voltage vector u30The projection on is denoted as u4Let u stand for4Modulus of (d) divided by uoThe modulus of (a) and the result of (b);
step S26, according to the calculation result of step S25, u4Can be composed of30Expressed by equation (4):
u4＝bu30 (4)；
step S27, according to the calculation result of step S26, u0、u3And u4Three voltage vectors form a triangle u3Is uoAnd u4Space voltage vector obtained by subtracting space voltage vector, and u3Expressed by equation (5):
u3＝uo-u4 (5)；
step S28, according to the calculation result of step S27, uoVoltage vector u with a lag of 60 degrees60By uoAnd u15Expressed by equation (6):
u60＝4abu15-2(2+b)uo (6)；
step S29, using the result obtained in step S28, calculating the voltage signal u according to the formula (7) based on the three-phase voltage signal symmetry principlea，ub，uc；
Step S210, using the result obtained in step S29, converting the three-phase voltage signal u according to CLACKa，ub，ucConverting to a two-phase u and u static coordinate system according to a formula (8);
step S211, using the result obtained in step S210, calculates a u-phase voltage in-phase sine signal sin θ and a cosine signal cos θ according to equation (9):
step S212, obtained using step S210 and step S211As a result, u in the two-phase stationary coordinate system is transformed to u in the dq rotation coordinate system according to equation (10)d，uq；
Step S213, using u in dq rotation coordinate system obtained in step S212d，uqThe amplitude information of the fundamental voltage is obtained according to equation (11):
the invention has the beneficial effects that:
1. compared with the delay time of an instantaneous voltage dq decomposition method, the delay time of the method is 3.33ms under the power frequency condition, the theoretical delay time of the algorithm is only 0.83ms, the actual delay time is only 0.9375ms, and the real-time performance is greatly improved.
2. And a single-phase voltage signal fictitious multi-phase system is adopted, so that the number of alternating-current voltage sensors is reduced, and the cost is reduced.
3. The algorithm is simple and practical, has good dynamic performance and has strong engineering practice effect.
Drawings
FIG. 1 is a flow chart of the system of the present invention.
FIG. 2 is a schematic diagram of the transient voltage dq decomposition method according to the present invention, which is improved by the spatial vector superposition principle.
FIG. 3 is an experimental diagram of a conventional transient voltage dq decomposition method.
FIG. 4 is an experimental diagram of the improved transient voltage dq decomposition method of the present invention.
Detailed Description
The foregoing embodiments and description have been presented only to illustrate the principles and preferred embodiments of the invention, and various changes and modifications may be made therein without departing from the spirit and scope of the invention as hereinafter claimed.
The invention is described in further detail below with reference to the figures and the specific embodiments.
The experimental conditions are as follows: the mathematical analysis expression of the detected voltage signal is as follows:
voltage uaJumping of 50% of amplitude sag occurs within 0.04-0.12 s, and the duration is 4 power frequency periods. The sampling frequency of the signal is 3.2kHz, i.e. 64 data samples per signal period. FIG. 1 shows a flow chart of the whole system; the specific implementation steps are as follows:
step S1, collecting u in the power grid voltage signal systemaA phase voltage signal;
and step S2, selecting an instantaneous voltage dq decomposition method, and improving the instantaneous voltage dq decomposition method according to the space vector superposition principle. The method comprises the following specific steps:
step S21, the collected single-phase voltage signal is uoWill uoLag by 15 degrees, to obtain u15A space voltage vector uoIn space voltage vector u15The projection on is denoted as u2Let u stand for2Modulus of (d) divided by uoThe modulus of (a) is given as a;
step S22, according to the calculation result of step S21, u2By u15Expressed by the formula (1) while u1、u2And uoThree voltage vectors form a triangle u1Is u2And uoSpace voltage vector obtained by subtracting space voltage vector:
u2＝au15 (1)；
step S23, according to the calculation result of step S22, u1By uoAnd u15Expressed by equation (2):
u1＝uo-au15 (2)；
step S24, according to the calculation result of step S23, uoVoltage vector u with 30 degree lag30By uoAnd u15Expressed by equation (3):
u30＝2au15-uo (3)；
step S25, converting the space voltage vector uoIn space voltage vector u30The projection on is denoted as u4Let u stand for4Modulus of (d) divided by uoThe modulus of (a) and the result of (b);
step S26, according to the calculation result of step S25, u4By u30Expressed by equation (4):
u4＝bu30 (4)；
step S27, according to the calculation result of step S26, u0、u3And u4Three voltage vectors form a triangle u3Is uoAnd u4Space voltage vector obtained by subtracting space voltage vector, and u3Expressed by equation (5):
u3＝uo-u4 (5)；
step S28, according to the calculation result of step S27, uoVoltage vector u with a lag of 60 degrees60By uoAnd u15Expressed by equation (6):
u60＝4abu15-2(2+b)uo (6)；
step S29, using the result obtained in step S28, calculating the voltage signal u according to the formula (7) based on the three-phase voltage signal symmetry principlea，ub，uc；
Step S210, using the result obtained in step S29, converting the three-phase voltage signal u according to CLACKa，ub，ucConverting to a two-phase u and u static coordinate system according to a formula (8);
step S211, using the result obtained in step S210, calculates a u-phase voltage in-phase sine signal sin θ and a cosine signal cos θ according to equation (9):
step S212, using the results obtained in step S210 and step S211, transforms u, u in the two-phase stationary coordinate system to u in the dq rotation coordinate system according to equation (10)d，uq；
Step S213, using u in dq rotation coordinate system obtained in step S212d，uqThe amplitude information of the fundamental voltage is obtained according to equation (11):
and step S3, carrying out amplitude characteristic detection on the single-phase power grid voltage signal by using an improved instantaneous voltage dq decomposition method.
The initial sampling point serial numbers are arranged from 0, and because the initial sampling points are power frequency alternating current signals, when voltage signals are collected by using a 3.2kHz sampling frequency, 64 data are sampled in each signal period, 512 data are sampled in 8 periods, and the serial numbers are 0 to 511. Data of a period from the beginning of the sag to the detection of the sag amplitude is focused, and actual collected data is shown in table 1.
Because the voltage signal generates a jump of 50% of the temporary reduction of the amplitude, when the collected voltage data is half of the amplitude of the voltage, the algorithm detection is considered to be limited. Table 1 shows voltage data tables detected by the conventional instantaneous voltage dq decomposition method and the improved instantaneous voltage dq decomposition method, and the conventional instantaneous voltage dq decomposition method needs 12 sampling points to perform effective detection. The improved instantaneous voltage dq decomposition method only needs to detect 3 sampling points, and the effective detection can be realized. As can be seen from the comparison table 2 of the delay times of different detection algorithms under the sampling frequency of 3.2kHz, the delay time obtained by calculating actual sampling data is consistent with the theoretical analysis result, and only the calculation error of one sampling point exists.
TABLE 1 Voltage data sheet detected by conventional instantaneous voltage dq decomposition method and improved instantaneous voltage dq decomposition method
| Data sample sequence number | Instantaneous voltage dq decomposition method | Improved instantaneous voltage dq decomposition method |
| 126 | 310.7025 | 310.5346 |
| 127 | 311.2683 | 256.5623 |
| 128 | 301.5047 | 197.8321 |
| 129 | 289.6628 | 157.8916 |
| 130 | 275.9623 | 155.5006 |
| 131 | 260.6808 | 155.5534 |
| 132 | 244.1664 | 155.5998 |
| 133 | 226.8558 | 155.6380 |
| 134 | 209.2998 | 155.6665 |
| 135 | 192.1973 | 155.6843 |
| 136 | 176.4294 | 155.6906 |
| 137 | 162.8372 | 155.6852 |
| 138 | 155.5214 | 155.6684 |
| 139 | 155.5368 | 155.6407 |
| 140 | 155.5491 | 155.6032 |
| 141 | 155.5578 | 155.5574 |
| 142 | 155.5627 | 155.5050 |
| 143 | 155.5636 | 155.4480 |
| 144 | 155.5603 | 155.3886 |
TABLE 23.2 kHz delay time comparison table for different detection algorithms under sampling frequency
| Detection algorithm | Time delay point | Actual delay (ms) | Theoretical time delay (ms) |
| Instantaneous voltage dq decomposition method | 12 sampling points | 3.4375 | T/6(3.33) |
| Improved instantaneous voltage dq decomposition method | 3 sampling points | 0.9375 | T/24(0.83) |
The comparison result of the voltage drop experiments in the prior art and the invention shows that the two detection methods can effectively detect the amplitude of the voltage sag, as shown in fig. 3, the theoretical delay time is 3.33ms by adopting an instantaneous voltage dq decomposition method, and as shown in fig. 4, the theoretical delay time is 0.83ms and the actual delay time is only 0.9375ms by adopting the improved detection method provided by the invention, so that the real-time property is greatly improved.
The present invention is not limited to the above-described embodiments, which are merely preferred embodiments of the present invention, and the present invention is not limited thereto, and any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (1)
1. An instantaneous voltage dq decomposition method for grid voltage sag detection is characterized by comprising the following steps:
step S1, acquiring a one-phase voltage signal in a power grid voltage signal system;
step S2, selecting an instantaneous voltage dq decomposition method, and improving the instantaneous voltage dq decomposition method according to the space vector superposition principle;
the method specifically comprises the following substeps:
step S21, the collected single-phase voltage signal is uoWill uoLag by 15 degrees, to obtain u15A space voltage vector uoIn space voltage vector u15The projection on is denoted as u2Let u stand for2Modulus of (d) divided by uoThe modulus of (a) is given as a;
step S22, according to the calculation result of step S21, u2By u15Expressed by the formula (1) while u1、u2And uoThree voltage vectors form a triangle u1Is u2And uoSpace voltage vector obtained by subtracting space voltage vector:
u2＝au15 (1)；
step S23, according to the calculation result of step S22, u1By uoAnd u15Expressed by equation (2):
u1＝uo-au15 (2)；
step S24, according to the calculation result of step S23, uoVoltage vector u with 30 degree lag30By uoAnd u15Expressed by equation (3):
u30＝2au15-uo (3)；
step S25, converting the space voltage vector uoIn space voltage vector u30The projection on is denoted as u4Let u stand for4Modulus of (d) divided by uoThe modulus of (a) and the result of (b);
step S26, according to the calculation result of step S25, u4By u30Expressed by equation (4):
u4＝bu30 (4)；
step S27, according to the calculation result of step S26, u0、u3And u4Three voltage vectors form a triangle u3Is uoAnd u4Space voltage vector obtained by subtracting space voltage vector, and u3Expressed by equation (5):
u3＝uo-u4 (5)；
step S28, according to the calculation result of step S27, uoVoltage vector u with a lag of 60 degrees60By uoAnd u15Expressed by equation (6):
u60＝4abu15-2(2+b)uo (6)；
step S29, using the result obtained in step S28, calculating the voltage signal u according to the formula (7) based on the three-phase voltage signal symmetry principlea，ub，uc；
Step S210, using the result obtained in step S29, converting the three-phase voltage signal u according to CLACKa，ub，ucConversion to two phases u according to equation (8)α，uβUnder a static coordinate system;
step S211, using the result obtained in step S210, calculates u according to equation (9)αPhase voltage in-phase sine signal sin θ, cosine signal cos θ:
step S212, using the results obtained in step S210 and step S211, makes u in the two-phase stationary coordinate system according to equation (10)α，uβU transformed to dq rotation coordinate systemd，uq；
Step S213, using u in dq rotation coordinate system obtained in step S212d，uqThe amplitude information of the fundamental voltage is obtained according to equation (11):
and step S3, carrying out amplitude characteristic detection on the single-phase power grid voltage signal by using an improved instantaneous voltage dq decomposition method.
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