CN114355026A - Voltage sag detection method - Google Patents
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Abstract
The invention discloses a voltage sag detection method, which comprises the following steps: step 1, detecting an instantaneous value of a three-phase line voltage in a three-phase line voltage period T; step 2, calculating an actual value of the three-phase line voltage; step 3, judging whether the voltage is in a sag state or not according to the actual value and the rated value of the three-phase line voltage; step 4, judging the voltage sag type according to the actual value of the three-phase line voltage; step 5, timing the duration of the sag state of the three-phase line voltage, and resetting the duration for timing if the three-phase line voltage is converted from the sag state to the normal state when the duration threshold is not exceeded; and if the time duration exceeds the time duration threshold, alarming and outputting the sag state information. The method and the device realize rapid detection of the sag of the power grid, and can rapidly respond to the abnormity of the power grid; the key parameter voltage abnormity threshold and the voltage sag time counting threshold in the implementation method can be flexibly set according to the requirement, and different application requirements are met.
Description
Technical Field
The invention relates to the field of voltage sag detection, in particular to a voltage sag detection method.
Background
With the rapid development of power electronic technology and computer control technology, an alternating current speed regulating system consisting of a servo driver and a servo motor is widely applied to a numerical control machine tool. However, numerically controlled machine tools are subject to varying grid voltage fluctuations during operation. The normal fluctuation condition of the power grid voltage is not considered in the prior art, once the power grid voltage fluctuates, the alarm shutdown is immediately carried out, the normal work and the stability of the equipment are influenced, and the risk of damage to the machined workpiece is brought.
Disclosure of Invention
The present invention provides a solution to overcome the above problems.
The invention comprises the following steps:
step 1, detecting an instantaneous value of a three-phase line voltage in a three-phase line voltage period T; the three-phase line voltage period is the reciprocal of the three-phase line voltage frequency;
step 2, calculating an actual value of the three-phase line voltage according to the instantaneous value of the three-phase line voltage;
step 3, judging whether the three-phase voltage is in a sag state or not according to the actual value of the three-phase line voltage and the rated value of the three-phase line voltage, and if the actual value of the three-phase line voltage is smaller than 80% of the rated value of the three-phase line voltage, judging that the three-phase line voltage is in the sag state, and performing the next step; otherwise, judging that the three-phase line voltage is not in a sag state, namely the three-phase line voltage is in a normal state, and executing the step 1 for the next three-phase line voltage period T;
step 4, judging the sag type of the three-phase line voltage according to the actual value of the three-phase line voltage; setting different duration threshold values for the types of each sag state; the time threshold is set according to experience;
step 5, timing the duration of the sag state of the three-phase line voltage according to the three-phase line voltage sag type,
if the duration time does not exceed the duration time threshold of the type, the three-phase voltage is converted from the sag state to the normal state, the timing of the duration time is cleared, and the step 1 is executed for the next three-phase line voltage period T;
if the duration time exceeds the duration time threshold value of the sag type, alarming and outputting sag state information, wherein the sag state information comprises: dip type, dip state duration.
Preferably, step 2 comprises:
step 21, calculating the absolute value of the instantaneous value of the voltage of the three-phase line;
step 22, in the three-phase line voltage period, setting a plurality of sampling periods t, wherein the sampling periods t are set according to experience, and integrating each sampling period t, namely unit integration:
wherein, Ux|tAbsolute value, U, of instantaneous value of voltage of three-phase line sampled for the t-th sampling periodx|t-1Absolute value, U, of instantaneous value of voltage of three-phase line sampled in the t-1 th sampling periodx|tAnd Ux|t-1The absolute value of the instantaneous value of the voltage of the three-phase line in the adjacent sampling period is shown, and t is the sampling period;
step 23, according to the unit integral value, carrying out integral calculation on the three-phase line voltage half cycle T/2:
wherein, N is T/2T is the number of unit integral values in a half period, and T is a three-phase line voltage period;
step 24, calculating the actual value of the three-phase line voltage according to the integrated value of the voltage half period of the three-phase line:
wherein, URIs the actual value of the voltage of the three-phase line, UNRated voltage of three-phase line voltage, fNRated frequency of three-phase line voltage, fKIs the sampling frequency, which is the inverse of the sampling period t.
Preferably, in step 4, the type of the sag state of the three-phase line voltage, i.e. the sag type, is determined based on the following strategy:
if 70% UN＜UR＜80％UNJudging that the type of the sag state of the three-phase line voltage is Flag _ 80;
if 40% UN＜UR＜70％UNJudging that the type of the sag state of the three-phase line voltage is Flag _ 70;
if 10% UN＜UR＜40％UNJudging the type of the sag state of the three-phase line voltage to be Flag _ 40;
if 0% UN＜UR＜10％UNJudging that the type of the sag state of the three-phase line voltage is Flag _ 0;
wherein, URIs the actual value of the voltage of the three-phase line, UNIs rated for three-phase line voltage.
Preferably, in step 6, if the duration time does not exceed the duration time threshold of the corresponding type, and the three-phase voltage sag state is changed to the type, the duration time is counted again according to a new sag type of the three-phase voltage, that is, the second sag type.
Preferably, before the duration is re-timed, the timing of the sag type before the transition of the three-phase voltage is stored, and the sag type before the transition is the first sag type;
and if the duration time does not exceed the duration time threshold of the type, the sag state of the three-phase voltage is changed from the second sag type to the first sag type, the timing of the first sag type is acquired, and the timing is continued on the basis of the timing of the first sag type.
The method realizes rapid power grid sag detection, does not need to add a hardware circuit, does not increase cost, and improves reliability; the minimum detection time is only a half period of the voltage of the power grid, and the power grid abnormity can be quickly responded; the key parameter voltage abnormity threshold and the voltage sag detection time counting threshold in the implementation method can be flexibly set according to the requirement, and different application requirements are met; the method comprises an integration link, has time for counting and filtering, and is higher in reliability and detection accuracy.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a flow chart of the steps of the present invention;
FIG. 2 is an overall flow chart of the present invention;
FIG. 3 is a flow chart of the present invention;
FIG. 4 is a graph of voltage sag according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1 to 3, the present invention includes the following steps:
step 1, detecting an instantaneous value of a three-phase line voltage in a three-phase line voltage period T; the three-phase line voltage period is the reciprocal of the three-phase line voltage frequency;
step 2, calculating an actual value of the three-phase line voltage according to the instantaneous value of the three-phase line voltage;
step 3, judging whether the three-phase voltage is in a sag state or not according to the actual value of the three-phase line voltage and the rated value of the three-phase line voltage, and if the actual value of the three-phase line voltage is smaller than 80% of the rated value of the three-phase line voltage, judging that the three-phase line voltage is in the sag state, and performing the next step; otherwise, judging that the three-phase line voltage is not in a sag state, namely the three-phase line voltage is in a normal state, and repeating the steps for the next three-phase line voltage period T;
specifically, the grid line voltage is usually expressed in a form of sine and cosine, for example, E ═ cos θ, the sine and cosine function is known as a continuous periodic function, and when zero offset is neglected, the positive and negative direction amplitudes and periods are consistent, so that half-cycle is performed on the absolute value of the instantaneous value of the grid voltage, and a fixed value is obtained. Setting the instantaneous value of the adjacent sampling time of the network voltage as Ux|t-1And Ux|tSetting the sampling period as T and the grid voltage period as T, setting the grid voltage half period as T/2, and setting the grid voltage half period integral as:
in a digital control system, continuous power grid voltage needs to be discretized, and because one power grid voltage period T is far larger than a sampling period T, a power grid voltage instantaneous value U can be usedxAs discretized data of the grid voltage. Every sampling periodt is taken as a unit integration unit, and the absolute value of the instantaneous value of the adjacent sampling time is taken as a voltage amplitude reference to perform trapezoidal integration, that is, the unit integration can be expressed as:
and integrating the half cycle of the grid voltage, accumulating all unit integral values in the time of T/2 of the half cycle, and expressing the half cycle of the grid voltage as T/2T if the number of the unit integral values in the half cycle is N
The half-cycle integral of the power grid voltage is mathematically related to the actual value of the power grid voltage, and the actual value of the power grid voltage is set to be U according to a Newton-Lei-Bluenitz formula calculated by sine and cosine integralRSetting rated voltage of power grid as UNLet the rated frequency of the grid voltage be fNLet the sampling frequency be fKThe conversion relation between the actual value of the grid voltage and the integral value of the half period of the grid voltage can be expressed by the following formula:
the actual value of the grid voltage can be calculated in real time. The half-period integral of the power grid voltage can ensure the accurate calculation of the actual value of the sine and cosine signal, and the calculation time is shorter than that of the full-period integral.
Step 4, judging the sag type of the three-phase line voltage according to the actual value of the three-phase line voltage; setting different duration threshold values for the types of each sag state; the time threshold is set according to experience;
specifically, the time threshold is set according to the IEC61000-4-11 standard, or the SEMIF047 standard, or the equipment requirements.
Specifically, whether the line voltage meets an abnormal state or not is judged according to the calculated line voltage effective value and a preset voltage abnormal amplitude threshold value. Sag, short interruption and Voltage Change noise immunity test according to IEC61000-4-11Three types of devices in the standard respectively require three-phase or single-phase voltage to dip to 0%, 40%, 70% and 80% of the rated voltage, and considering that the 0% voltage is difficult to be accurately measured in an actual detection system, the 0% voltage detection threshold is set to 10%, that is, the preset voltage abnormal amplitude threshold is correspondingly set to 10%, 40%, 70% and 80% of the rated voltage. When the actual calculated value of the line voltage is lower than the preset voltage abnormal threshold value, the corresponding voltage sag identifier is set, and the voltage sag identifiers are set to Flag _0, Flag _40, Flag _70 and Flag _80, namely when U is detectedR＜80％·UNWhen the voltage is temporarily reduced to 80% of the rated voltage, the Flag _80 is marked to be 1; when U is turnedR＜70％·UNWhen the voltage is temporarily reduced to 70% of the rated voltage, the Flag _70 is set to 1; when U is turnedR＜40％·UNWhen the voltage is temporarily reduced to 40% of the rated voltage, the Flag _40 is set to 1; when U is turnedR＜10％·UNWhen the voltage drops temporarily to the rated voltage 0%, the Flag _0 is set to 1. When the actual calculated value of the grid voltage is not lower than the preset voltage abnormal threshold, the corresponding voltage sag identifier is cleared, namely when the U is not lower than the preset voltage abnormal thresholdR≥80％·UNWhen the voltage is temporarily reduced to 80% of the rated voltage, the Flag _80 is marked to be 0; when U is turnedR≥70％·UNWhen the voltage temporarily drops to the rated voltage 70%, the Flag _70 is set to 0; when U is turnedR≥40％·UNWhen the voltage is temporarily reduced to 40% of the rated voltage, the Flag _40 is set to 0; when U is turnedR≥10％·UNWhen the voltage drops temporarily to the rated voltage 0%, the Flag _0 is set to 0. The scheme is designed according to IEC61000 standard, and can also be designed according to SEMIF047 standard or other standards, or according to the characteristics of the electric equipment, the preset voltage abnormal amplitude threshold value is customized, and the processing scheme is consistent with the scheme.
Step 5, timing the duration of the sag state of the three-phase line voltage according to the three-phase line voltage sag type,
if the duration time does not exceed the duration time threshold of the type, the three-phase voltage is converted from the sag state to the normal state, the timing of the duration time is cleared, and the steps are repeated for the next three-phase line voltage period T;
if the duration time exceeds the duration time threshold value of the sag type, alarming and outputting sag state information, wherein the sag state information comprises: dip type, dip state duration.
Specifically, the voltage sag time counters are set as Count _0, Count _40, Count _70, and Count _80, and when the voltage sag Flag is in the set state, the independent counters add up to 1, that is, when Flag _0 is equal to 1, Count _0 is equal to Count _0+ 1; when Flag _40 is 1, Count _40 is Count _40+ 1; when Flag _70 is 1, Count _70 is Count _70+ 1; when Flag _80 is equal to 1, Count _80 is equal to Count _80+ 1. When the voltage sag Flag is in a zero clearing state, the independent counter is cleared, namely when Flag _0 is 0, Count _0 is 0; when Flag _40 is 0, Count _40 is 0; when Flag _70 is 0, Count _70 is 0; when Flag _80 is equal to 0, Count _80 is equal to 0. The calculation period is a power grid voltage half period, namely, the line voltage abnormal time is calculated once the calculation of the actual value of the power grid voltage is completed. And (4) independently judging and counting in different intervals, wherein the value of the independent counter in each interval represents the duration of voltage sag in each interval.
Specifically, if the Count time is greater than the corresponding preset time threshold, it may be determined that a voltage sag occurs in this interval, and output associated voltage sag information, where the preset voltage sag or interrupt detection time threshold is T _0, T _40, T _70, and T _80, and the voltage sag or interrupt alarm state is set to Err _0, Err _40, Err _70, and Err _80, that is, Err _0 is set when Count _0> T _ 0; when Count _40> T _40, Err _ 40; when Count _70> T _70, Err _ 70; when Count _80> T _80, Err _ 80. And each interval is independently judged, and independent voltage sag or interruption alarm state information is output. According to the requirements of three types of equipment in IEC61000-4-11 sag, short interruption and voltage change immunity test standards, three-phase or single-phase voltage sag to rated values of 0%, 40%, 70% and 80% is respectively required to be 1 cycle, 10 cycles, 25 cycles and 250 cycles. The preset voltage sag or interruption detection time count threshold may be set to 2, 20, 50, 500, respectively. The preset voltage sag or interruption detection time counting threshold value can also be customized according to the SEMIF047 standard or other standards and according to the characteristics of the electric equipment.
Preferably, step 2 comprises:
step 21, calculating the absolute value of the instantaneous value of the voltage of the three-phase line;
step 22, in the three-phase line voltage period, setting a plurality of sampling periods t, wherein the sampling periods t are set according to experience, and integrating each sampling period t, namely unit integration:
wherein, Ux|t is the absolute value of the instantaneous value of the voltage of the three-phase line sampled in the t-th sampling period, Ux|t-1Absolute value, U, of instantaneous value of voltage of three-phase line sampled in the t-1 th sampling periodx|tAnd Ux|t-1The absolute value of the instantaneous value of the voltage of the three-phase line in the adjacent sampling period is shown, and t is the sampling period;
specifically, the sampling period is usually very small, in the following examples, the period corresponding to the sampling frequency of 8KHz is 125us, and the period corresponding to the grid voltage frequency of 50Hz in china is 20 ms. The sampling period can be considered to be much shorter than the grid voltage period.
Specifically, the grid voltage is sampled according to a sampling period, that is, once every sampling period t. The instantaneous value of the adjacent sampling time, i.e. the voltage value sampled at two consecutive sampling times. If t is set to 125us, the sampling value of 0us and the sampling value of 125us are the values of adjacent sampling time; the 1000us samples and the 1125us samples are the values of adjacent sample times.
Step 23, according to the unit integral value, carrying out integral calculation on the three-phase line voltage half cycle T/2:
wherein, N is T/2T is the number of unit integral values in a half period, and T is a three-phase line voltage period;
in particular, the grid voltage (and the three-phase line voltage is the same) and the signal is in the form of a regular sine and cosine. Where china specifies a nominal grid frequency of 50Hz, the corresponding period (i.e. the reciprocal of the frequency) is 20 ms.
Step 24, calculating the actual value of the three-phase line voltage according to the integrated value of the voltage half period of the three-phase line:
wherein, URIs the actual value of the voltage of the three-phase line, UNRated voltage of three-phase line voltage, fNRated frequency of three-phase line voltage, fKIs the sampling frequency, which is the inverse of the sampling period t.
In particular, the sampling frequency, i.e. how fast the data is sampled. Usually expressed in terms of frequency, typically in Hz, KHz, MHz, GHz, etc. The sampling frequency is usually an optimal frequency that can be achieved by the control system, and is determined by hardware and system characteristics. The sampling frequency is set empirically.
Preferably, in step 5, the type of the sag state of the three-phase line voltage is judged based on the following strategy:
if 70% UN＜UR＜80％UNJudging that the type of the sag state of the three-phase line voltage is Flag _ 80;
if 40% UN＜UR＜70％UNJudging that the type of the sag state of the three-phase line voltage is Flag _ 70;
if 10% UN＜UR＜40％UNJudging the type of the sag state of the three-phase line voltage to be Flag _ 40;
if 0% UN＜UR＜10％UNJudging that the type of the sag state of the three-phase line voltage is Flag _ 0;
wherein, URIs the actual value of the voltage of the three-phase line, UNIs rated for three-phase line voltage.
Preferably, in step 6, if the duration time does not exceed the duration time threshold of the corresponding type, and the three-phase voltage is switched from the sag state to the sag state, the duration time is counted again according to a second sag type, that is, a second sag type.
Preferably, before the duration is re-timed, the timing of the sag type before the transition of the three-phase voltage is stored, and the sag type before the transition is the first sag type;
and if the duration time does not exceed the duration time threshold of the type, the sag state of the three-phase voltage is changed from the second sag type to the first sag type, the timing of the first sag type is acquired, and the timing is continued on the basis of the timing of the first sag type.
As shown in fig. 4, in this embodiment, the nominal input three-phase ac line voltage is 380V, the nominal frequency is 50Hz (half cycle is 10ms), and the absolute value of the instantaneous value of the line voltage is respectively integrated and calculated by taking the half cycle of the power grid (10ms) as a time cycle based on the sampling cycle of 8KHz (the minimum sampling time unit is 125 us). According to the conversion formula of the actual effective value and the integral value of the power grid voltage,
the PI is taken to be 3.142,
based on the IEC61000-4-11 standard and according to the characteristics of the equipment, the voltage abnormity amplitude threshold values are respectively set to be 30%, 50%, 70% and 80% of the rated voltage, and the actual corresponding line voltages are 114V, 190V, 266V and 304V. The voltage sag or interruption detection time thresholds corresponding to the voltage intervals are 100ms, 400ms, 2000ms, 8000ms, and the abnormality counter thresholds are 10, 40, 200, 800. When the actual line voltage is lower than 114V and the corresponding counter value is larger than 10, outputting voltage sag or interruption alarm information; when the actual line voltage is lower than 190V and the corresponding counter value is larger than 40, outputting voltage sag or interruption alarm information; when the actual line voltage is lower than 266V, the corresponding counter value is greater than 200, and voltage sag or interruption alarm information is output; and when the actual line voltage is lower than 304V and the corresponding counter value is larger than 800V, outputting voltage sag or interrupt alarm information.
Has the advantages that:
the method realizes rapid power grid sag detection, does not need to add a hardware circuit, does not increase cost, and improves reliability; the minimum detection time is only a half period of the voltage of the power grid, and the power grid abnormity can be quickly responded; the key parameter voltage abnormity threshold and the voltage sag detection time counting threshold in the implementation method can be flexibly set according to the requirement, and different application requirements are met; the method comprises an integration link, has time for counting and filtering, and is higher in reliability and detection accuracy.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (5)
1. A voltage sag detection method is characterized by comprising the following steps:
step 1, detecting an instantaneous value of a three-phase line voltage in a three-phase line voltage period T; the three-phase line voltage period is the reciprocal of the three-phase line voltage frequency;
step 2, calculating an actual value of the three-phase line voltage according to the instantaneous value of the three-phase line voltage;
step 3, judging whether the three-phase line voltage is in a sag state or not according to the actual value of the three-phase line voltage and the rated value of the three-phase line voltage, and if the actual value of the three-phase line voltage is smaller than 80% of the rated value of the three-phase line voltage, judging that the three-phase line voltage is in the sag state, and performing the next step; otherwise, judging that the three-phase line voltage is not in a sag state, namely the three-phase line voltage is in a normal state, and executing the step 1 for the next three-phase line voltage period T;
step 4, judging the sag type of the three-phase line voltage according to the actual value of the three-phase line voltage; setting different duration threshold values for the types of each sag state; the time threshold is set according to experience;
step 5, timing the duration of the sag state of the three-phase line voltage according to the three-phase line voltage sag type,
if the duration time does not exceed the duration time threshold of the type, the three-phase line voltage is converted from the sag state to the normal state, the timing of the duration time is cleared, and the step 1 is executed for the next three-phase line voltage period T;
if the duration time exceeds the duration time threshold value of the sag type, alarming and outputting sag state information, wherein the sag state information comprises: dip type, dip state duration.
2. The method according to claim 1, wherein the step 2 comprises:
step 21, calculating the absolute value of the instantaneous value of the voltage of the three-phase line;
step 22, in the three-phase line voltage period, setting a plurality of sampling periods t, wherein the sampling periods t are set according to experience, and integrating each sampling period t, namely unit integration:
wherein, Ux|tAbsolute value, U, of instantaneous value of voltage of three-phase line sampled for the t-th sampling periodx|t-1Absolute value, U, of instantaneous value of voltage of three-phase line sampled in the t-1 th sampling periodx|tAnd Ux|t-1The absolute value of the instantaneous value of the voltage of the three-phase line in the adjacent sampling period is shown, and t is the sampling period;
step 23, according to the unit integral value, carrying out integral calculation on the three-phase line voltage half cycle T/2:
wherein, N is T/2T is the number of unit integral values in a half period, and T is a three-phase line voltage period;
step 24, calculating the actual value of the three-phase line voltage according to the integrated value of the voltage half period of the three-phase line:
wherein, URIs the actual value of the voltage of the three-phase line, UNRated voltage of three-phase line voltage, fNRated frequency of three-phase line voltage, fKIs the sampling frequency, which is the inverse of the sampling period t.
3. The method according to claim 1, wherein in the step 4, the type of sag state of the three-phase line voltage is determined based on the following strategy:
if 70% UN＜UR＜80％UNJudging that the type of the sag state of the three-phase line voltage is Flag _ 80;
if 40% UN＜UR＜70％UNJudging that the type of the sag state of the three-phase line voltage is Flag _ 70;
if 10% UN＜UR＜40％UNJudging the type of the sag state of the three-phase line voltage to be Flag _ 40;
if 0% UN＜UR＜10％UNJudging that the type of the sag state of the three-phase line voltage is Flag _ 0;
wherein, URIs the actual value of the voltage of the three-phase line, UNIs rated for three-phase line voltage.
4. The method according to claim 1, wherein in step 6, if the duration time does not exceed the duration time threshold of the type, the three-phase voltage is switched from the sag state to the sag state, and the duration time is counted again according to a new sag type of the three-phase voltage, i.e. the second sag type.
5. A voltage sag detection method according to claim 4, wherein the timing of a pre-transition sag type of the three-phase line voltage, the first sag type, is stored before the duration is re-timed;
and if the duration time does not exceed the duration time threshold of the type, the sag state of the three-phase line voltage is changed from the second sag type to the first sag type, the timing of the first sag type is acquired, and the timing is continued on the basis of the timing of the first sag type.
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| CN115219953A (en) * | 2022-08-01 | 2022-10-21 | 江苏方天电力技术有限公司 | Low-voltage transformer area line abnormity detection system and method based on voltage drop |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115219953A (en) * | 2022-08-01 | 2022-10-21 | 江苏方天电力技术有限公司 | Low-voltage transformer area line abnormity detection system and method based on voltage drop |
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