A method for detecting voltage sag

Abstract

The present invention discloses a voltage sag detection method, comprising: step 1, detecting the instantaneous value of the three-phase line voltage within the three-phase line voltage cycle T; step 2, calculating the actual value of the three-phase line voltage; step 3, judging whether the voltage is in a sag state according to the actual value and 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, if it does not exceed the duration threshold, the three-phase voltage changes from the sag state to the normal state, then clearing the duration timing; if it exceeds the duration threshold, alarming and outputting the sag state information. The present invention realizes rapid grid sag detection and can quickly respond to grid anomalies; the key parameters of the voltage anomaly threshold and the voltage sag time counting threshold in the implementation method can be flexibly set according to needs to meet different application requirements.

Description

Technical Field

[0001] The present invention relates to the field of voltage sag detection, and in particular to a voltage sag detection method. Background Art

[0002] With the rapid development of power electronics technology and computer control technology, AC speed control systems consisting of servo drives and servo motors have been widely used in CNC machine tools. However, CNC machine tools are subject to grid voltage fluctuations to varying degrees during operation. The prior art does not take into account the normal fluctuations in grid voltage. Once the grid voltage fluctuates, an alarm is immediately issued to stop the machine, affecting the normal operation and stability of the equipment itself, and bringing the risk of damage to the workpiece being processed. Summary of the invention

[0003] The present invention provides a method to overcome the above problems.

[0004] The present invention comprises the following steps:

[0005] Step 1: Detect the instantaneous value of the three-phase line voltage within the three-phase line voltage cycle T; the three-phase line voltage cycle is the inverse of the three-phase line voltage frequency;

[0006] Step 2: Calculate the actual value of the three-phase line voltage according to the instantaneous value of the three-phase line voltage;

[0007] Step 3: According to the actual value of the three-phase line voltage and the rated value of the three-phase line voltage, determine whether the three-phase line voltage is in a sag state. If the actual value of the three-phase line voltage is less than 80% of the rated value of the three-phase line voltage, it is determined that the three-phase line voltage is in a sag state, and proceed to the next step; otherwise, it is determined that the three-phase line voltage is not in a sag state, that is, the three-phase line voltage is in a normal state, and step 1 is executed for the next three-phase line voltage cycle T;

[0008] Step 4: determine the type of sag of the three-phase line voltage according to the actual value of the three-phase line voltage; set a different duration threshold for each type of sag state; the time threshold is set based on experience;

[0009] Step 5: According to the type of three-phase line voltage sag, the duration of the three-phase line voltage sag is timed.

[0010] If the duration does not exceed the duration threshold of the type to which it belongs, the three-phase voltage changes from the temporary sag state to the normal state, then the duration timer is reset to zero, and step 1 is executed for the next three-phase line voltage cycle T;

[0011] If the duration exceeds the duration threshold of the corresponding sag type, an alarm is triggered and sag status information is output. The sag status information includes: sag type and sag status duration.

[0012] Preferably, step 2 comprises:

[0013] Step 21, calculating the absolute value of the instantaneous value of the three-phase line voltage;

[0014] Step 22: In the three-phase line voltage cycle, multiple sampling cycles t are set. The sampling cycle t is set based on experience. Each sampling cycle t is integrated, that is, the unit integration:

[0015]

[0016] Among them, U x|t is the absolute value of the instantaneous value of the three-phase line voltage sampled in the tth sampling period, U x|t-1 The absolute value of the instantaneous value of the three-phase line voltage sampled in the t-1th sampling period, U x|t and U x|t-1 is the absolute value of the instantaneous value of the three-phase line voltage in adjacent sampling periods, and t is the sampling period;

[0017] Step 23: perform integral calculation on the three-phase line voltage half cycle T / 2 according to the unit integral value:

[0018]

[0019] Wherein, N = T / 2t is the number of unit integral values ​​in a half cycle, and T is the three-phase line voltage cycle;

[0020] Step 24: Calculate the actual value of the three-phase line voltage according to the half-cycle integral value of the three-phase line voltage:

[0021]

[0022] Among them, U R is the actual value of the three-phase line voltage, U N is the rated voltage of the three-phase line voltage, f N is the rated frequency of the three-phase line voltage, f K is the sampling frequency, which is the reciprocal of the sampling period t.

[0023] Preferably, in step 4, the type of the temporary sag state of the three-phase line voltage, i.e., the temporary sag type, is determined based on the following strategy:

[0024] If 70%U N <U R <80%U N , then the type of the temporary sag state of the three-phase line voltage is determined to be Flag_80;

[0025] If 40%U N <U R <70%U N, then the type of the temporary sag state of the three-phase line voltage is determined to be Flag_70;

[0026] If 10%U N <U R <40%U N , then the type of the temporary sag state of the three-phase line voltage is determined to be Flag_40;

[0027] If 0%U N <U R <10%U N , then the type of the temporary sag state of the three-phase line voltage is determined to be Flag_0;

[0028] Among them, U R is the actual value of the three-phase line voltage, U N is the rated voltage of the three-phase line voltage.

[0029] Preferably, in step 6, if the duration does not exceed the duration threshold of the corresponding type, the sag state of the three-phase voltage changes to a different type, and the duration is re-timed according to the new sag type of the three-phase voltage, i.e., the second sag type.

[0030] Preferably, before re-timing the duration, 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;

[0031] If the duration does not exceed the duration threshold of the corresponding type, the sag state of the three-phase voltage changes from the second sag type to the first sag type, and the timing of the first sag type is obtained, and the timing is continued based on the timing of the first sag type.

[0032] The present invention realizes rapid grid sag detection without adding hardware circuits, does not increase costs, and improves reliability; the minimum detection time is only half a grid voltage cycle, and can quickly respond to grid anomalies; the key parameters of the implementation method, the voltage anomaly threshold and the voltage sag detection time counting threshold, can be flexibly set as needed to meet different application requirements; the method includes an integration link and time counting filtering, and has higher reliability and detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0034] Figure 1 is a flow chart of the steps of the present invention;

[0035] Figure 2 It is the overall flow chart of the present invention;

[0036] Figure 3 is a flow chart of the present invention;

[0037] Figure 4 This is a voltage sag diagram of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] like Figure 1-Figure 3 As shown, the present invention comprises the following steps:

[0040] Step 1: Detect the instantaneous value of the three-phase line voltage within the three-phase line voltage cycle T; the three-phase line voltage cycle is the inverse of the three-phase line voltage frequency;

[0041] Step 2: Calculate the actual value of the three-phase line voltage according to the instantaneous value of the three-phase line voltage;

[0042] Step 3: According to the actual value of the three-phase line voltage and the rated value of the three-phase line voltage, determine whether the three-phase line voltage is in a sag state. If the actual value of the three-phase line voltage is less than 80% of the rated value of the three-phase line voltage, it is determined that the three-phase line voltage is in a sag state, and proceed to the next step; otherwise, it is determined that the three-phase line voltage is not in a sag state, that is, the three-phase line voltage is in a normal state, and the above steps are repeated for the next three-phase line voltage cycle T;

[0043] Specifically, the grid line voltage is usually expressed in the form of sine and cosine, such as E = cosθ. It is known that the sine and cosine functions are continuous periodic functions. When the zero bias is ignored, the amplitude and period in the positive and negative directions are consistent. Therefore, the absolute value of the instantaneous value of the grid voltage is calculated by half a period to obtain a fixed value. The instantaneous value of the grid voltage at adjacent sampling times is set as U x|t-1 and U x|t , set the sampling period to t, set the grid voltage period to T, then the grid voltage half period is T / 2, and set the grid voltage half period integral to:

[0044]

[0045] In digital control systems, the continuous grid voltage needs to be discretized. Since a grid voltage cycle T is much longer than the sampling cycle t, the instantaneous value of the grid voltage U can be used. x As the discrete data of the grid voltage. Take each sampling period t as the unit integration unit, take the absolute value of the instantaneous value of the adjacent sampling time as the voltage amplitude reference, and perform trapezoidal integration, that is, the unit integration can be expressed as:

[0046]

[0047] For the half-cycle integration of the grid voltage, all unit integral values ​​within the half-cycle T / 2 are accumulated, and the number of unit integral values ​​within the half-cycle is set to N = T / 2t. The half-cycle integral of the grid voltage is expressed as The grid voltage half-cycle integral is mathematically related to the actual grid voltage value. According to the Newton-Leibniz formula for sine-cosine integral calculation, the actual grid voltage value is set to U R , assuming the rated voltage of the grid is U N , assuming the rated frequency of the grid voltage is f N , let the sampling frequency be f K , the conversion relationship between the actual value of the grid voltage and the half-cycle integral value of the grid voltage can be expressed by the following formula:

[0048] The actual value of the grid voltage can be calculated in real time. The half-cycle integration of the grid voltage can ensure the accurate calculation of the actual value of the sine and cosine signals, and the calculation time is shorter than that of the full-cycle integration.

[0049] Step 4: determine the type of sag of the three-phase line voltage according to the actual value of the three-phase line voltage; set a different duration threshold for each type of sag state; the time threshold is set based on experience;

[0050] Specifically, the time threshold is set according to the IEC61000-4-11 standard, the SEMIF047 standard, or the equipment requirement.

[0051] Specifically, according to the calculated effective value of the line voltage and the preset voltage abnormal amplitude threshold, it is judged whether the line voltage meets the abnormal state. According to the requirements of the three types of equipment in the IEC61000-4-11 temporary sag, short interruption and voltage change immunity test standard, the three-phase or single-phase voltage is required to be temporarily dropped to 0%, 40%, 70% and 80% of the rated value respectively. Considering that 0% voltage is difficult to accurately measure in the actual detection system, the 0% voltage detection threshold is set to 10%, that is, the preset voltage abnormal amplitude threshold is set to 10%, 40%, 70%, 80% of the rated voltage. When the actual calculated value of the line voltage is lower than the above-mentioned preset voltage abnormal threshold, the corresponding voltage sag flag will be set, and the voltage sag flag will be set to Flag_0, Flag_40, Flag_70, Flag_80, that is, when U R <80%·U N When the voltage drops to 80% of the rated voltage, the flag Flag_80 is set to 1; when U R <70%·U N When the voltage drops to 70% of the rated voltage, the flag Flag_70 is set to 1; when U R <40%·U N When the voltage drops to 40% of the rated voltage, the flag Flag_40 is set to 1; when U R <10%·U N When the voltage drops to 0% of the rated voltage, the flag Flag_0 is set to 1. When the actual calculated value of the grid voltage is not lower than the above-mentioned preset voltage abnormality threshold, the corresponding voltage sag flag will be cleared, that is, when U R ≥80%·U N When the voltage drops to 80% of the rated voltage, the flag Flag_80 is set to 0; when U R ≥70%·U N When the voltage drops to 70% of the rated voltage, the flag Flag_70 is set to 0; when U R ≥40%·U N When the voltage drops to 40% of the rated voltage, the flag Flag_40 is set to 0; when U R ≥10%·U N When the voltage drops to 0% of the rated voltage, the flag Flag_0 is set to 0. The above scheme is designed according to the IEC61000 standard, and can also be based on the SEMIF047 standard or other standards, or customized according to the characteristics of the electrical equipment to preset the abnormal voltage amplitude threshold, and the processing scheme is consistent with the above scheme.

[0052] Step 5: According to the type of three-phase line voltage sag, the duration of the three-phase line voltage sag is timed.

[0053] If the duration does not exceed the duration threshold of the type to which it belongs, the three-phase voltage changes from the temporary sag state to the normal state, and the duration timer is reset to zero, and the above steps are repeated for the next three-phase line voltage cycle T;

[0054] If the duration exceeds the duration threshold of the corresponding sag type, an alarm is triggered and sag status information is output. The sag status information includes: sag type and sag status duration.

[0055] Specifically, the voltage sag time counter is set to Count_0, Count_40, Count_70, and Count_80. When the voltage sag flag is in the set state, the independent counter is accumulated by 1, that is, when Flag_0=1, Count_0=Count_0+1; when Flag_40=1, Count_40=Count_40+1; when Flag_70=1, Count_70=Count_70+1; when Flag_80=1, Count_80=Count_80+1. When the voltage sag flag is in the cleared state, the independent counter is cleared, that is, when Flag_0=0, Count_0=0; when Flag_40=0, Count_40=0; when Flag_70=0, Count_70=0; when Flag_80=0, Count_80=0. The above calculation cycle is a half cycle of the grid voltage, that is, the line voltage abnormal time calculation is performed once the actual value calculation of the grid voltage is completed. Different intervals are judged and counted independently, and the independent counter value of each interval represents the duration of the voltage sag in each interval.

[0056] Specifically, if the counting time is greater than the corresponding preset time threshold, it can be determined that the voltage sag occurs in this interval, and the associated voltage sag information is output. The preset voltage sag or interruption detection time threshold is T_0, T_40, T_70, T_80, and the voltage sag or interruption alarm status is set to Err_0, Err_40, Err_70, Err_80, that is, when Count_0>T_0, Err_0; when Count_40>T_40, Err_40; when Count_70>T_70, Err_70; when Count_80>T_80, Err_80. Each interval is judged independently, and independent voltage sag or interruption alarm status information is output. According to the requirements of the three types of equipment in the IEC61000-4-11 sag, short interruption and voltage variation immunity test standard, the time (50Hz) for the three-phase or single-phase voltage to temporarily drop to 0%, 40%, 70%, and 80% of the rated value is required to be 1 cycle, 10 cycles, 25 cycles, and 250 cycles respectively. The preset voltage sag or interruption detection time count threshold can be set to 2, 20, 50, and 500 respectively. It is also possible to customize the preset voltage sag or interruption detection time count threshold according to the SEMIF047 standard or other standards, or according to the characteristics of the electrical equipment.

[0057] Preferably, step 2 comprises:

[0058] Step 21, calculating the absolute value of the instantaneous value of the three-phase line voltage;

[0059] Step 22: In the three-phase line voltage cycle, multiple sampling cycles t are set. The sampling cycle t is set based on experience. Each sampling cycle t is integrated, that is, the unit integration:

[0060]

[0061] Among them, U x| t is the absolute value of the instantaneous value of the three-phase line voltage sampled in the tth sampling period, U x|t-1 The absolute value of the instantaneous value of the three-phase line voltage sampled in the t-1th sampling period, U x|t and U x|t-1 is the absolute value of the instantaneous value of the three-phase line voltage in adjacent sampling periods, and t is the sampling period;

[0062] Specifically, the sampling period is usually very small. In the following examples of this article, the period corresponding to the sampling frequency of 8KHz is 125us, and the period corresponding to the grid voltage frequency of 50Hz is 20ms. It can be considered that the sampling period is much smaller than the grid voltage period.

[0063] Specifically, the grid voltage sampling is performed according to the sampling period, that is, sampling is performed once every sampling period t. The instantaneous value of adjacent sampling times is 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 times; the sampling value of 1000us and the sampling value of 1125us are the values ​​of adjacent sampling times.

[0064] Step 23: perform integral calculation on the three-phase line voltage half cycle T / 2 according to the unit integral value:

[0065]

[0066] Wherein, N = T / 2t is the number of unit integral values ​​in a half cycle, and T is the three-phase line voltage cycle;

[0067] Specifically, the grid voltage (three-phase line voltage is the same) has a regular sine and cosine signal. China stipulates that the rated grid frequency is 50Hz, and the corresponding period (that is, the inverse of the frequency) is 20ms.

[0068] Step 24: Calculate the actual value of the three-phase line voltage according to the half-cycle integral value of the three-phase line voltage:

[0069]

[0070] Among them, U R is the actual value of the three-phase line voltage, U N is the rated voltage of the three-phase line voltage, f N is the rated frequency of the three-phase line voltage, f K is the sampling frequency, which is the reciprocal of the sampling period t.

[0071] Specifically, the sampling frequency refers to how fast the data is sampled. It is usually expressed in terms of frequency, and the units are usually Hz, KHz, MHz, GHz, etc. The sampling frequency is usually the optimal frequency that the control system can achieve, which is determined by the hardware and system characteristics. The sampling frequency is set based on experience.

[0072] Preferably, in step 5, the type of the temporary sag state of the three-phase line voltage is determined based on the following strategy:

[0073] If 70%U N <U R <80%U N , then the type of the temporary sag state of the three-phase line voltage is determined to be Flag_80;

[0074] If 40%U N <U R <70%U N, then the type of the temporary sag state of the three-phase line voltage is determined to be Flag_70;

[0075] If 10%U N <U R <40%U N , then the type of the temporary sag state of the three-phase line voltage is determined to be Flag_40;

[0076] If 0%U N <U R <10%U N , then the type of the temporary sag state of the three-phase line voltage is determined to be Flag_0;

[0077] Among them, U R is the actual value of the three-phase line voltage, U N is the rated voltage of the three-phase line voltage.

[0078] Preferably, in step 6, if the duration does not exceed the duration threshold of the type to which it belongs, the sag state of the three-phase voltage changes to a different type, and the duration is retimed according to the second sag type, i.e., the second sag type.

[0079] Preferably, before re-timing the duration, 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;

[0080] If the duration does not exceed the duration threshold of the corresponding type, the sag state of the three-phase voltage changes from the second sag type to the first sag type, and the timing of the first sag type is obtained, and the timing is continued based on the timing of the first sag type.

[0081] like Figure 4 As shown, this embodiment is based on the rated input three-phase AC line voltage of 380V, the rated frequency of 50Hz (half cycle 10ms), and the sampling period of 8KHz (the minimum sampling time unit is 125us), and the absolute value of the instantaneous value of the line voltage is integrated and calculated with the half cycle of the power grid (10ms) as the time period. According to the conversion formula of the actual effective value and the integral value of the power grid voltage,

[0082]

[0083] Taking PI = 3.142, we can get:

[0084]

[0085] Based on the IEC61000-4-11 standard and according to the characteristics of the equipment itself, the voltage abnormal amplitude threshold is set to 30%, 50%, 70%, and 80% of the rated voltage, respectively, and the actual corresponding line voltage is 114V, 190V, 266V, and 304V. The voltage sag or interruption detection time threshold corresponding to each voltage interval is 100ms, 400ms, 2000ms, and 8000ms, and the corresponding abnormal counter threshold is 10, 40, 200, and 800. That is, when the counter value corresponding to the actual line voltage is lower than 114V and is greater than 10, the output voltage sag or interruption alarm information is output; when the counter value corresponding to the actual line voltage is lower than 190V and is greater than 40, the output voltage sag or interruption alarm information is output; when the counter value corresponding to the actual line voltage is lower than 266V and is greater than 200, the output voltage sag or interruption alarm information is output; when the counter value corresponding to the actual line voltage is lower than 304V and is greater than 800, the output voltage sag or interruption alarm information is output.

[0086] Beneficial effects:

[0087] The present invention realizes rapid grid sag detection without adding hardware circuits, does not increase costs, and improves reliability; the minimum detection time is only half a grid voltage cycle, and can quickly respond to grid anomalies; the key parameters of the implementation method, the voltage anomaly threshold and the voltage sag detection time counting threshold, can be flexibly set as needed to meet different application requirements; the method includes an integration link and time counting filtering, and has higher reliability and detection accuracy.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A voltage sag detection method, characterized in that: The following steps are involved: Step 1: Detect the instantaneous value of the three-phase line voltage within the three-phase line voltage cycle T; the three-phase line voltage cycle is the inverse of the three-phase line voltage frequency; Step 2: Calculate the actual value of the three-phase line voltage according to the instantaneous value of the three-phase line voltage; Step 3: According to the actual value of the three-phase line voltage and the rated value of the three-phase line voltage, determine whether the three-phase line voltage is in a sag state. If the actual value of the three-phase line voltage is less than 80% of the rated value of the three-phase line voltage, it is determined that the three-phase line voltage is in a sag state, and proceed to the next step; otherwise, it is determined that the three-phase line voltage is not in a sag state, that is, the three-phase line voltage is in a normal state, and step 1 is executed for the next three-phase line voltage cycle T; Step 4: determine the type of sag of the three-phase line voltage according to the actual value of the three-phase line voltage; set a different duration threshold for each type of sag state; the time threshold is set based on experience; Step 5: According to the type of three-phase line voltage sag, the duration of the three-phase line voltage sag is timed. If the duration does not exceed the duration threshold of the type to which it belongs, the three-phase line voltage changes from the temporary sag state to the normal state, then the duration timer is reset to zero, and step 1 is executed for the next three-phase line voltage cycle T; If the duration exceeds the duration threshold of the corresponding sag type, an alarm is triggered and sag status information is output. The sag status information includes: sag type and sag status duration.

2. A voltage sag detection method according to claim 1, characterized in that: The step 2 comprises: Step 21, calculating the absolute value of the instantaneous value of the three-phase line voltage; Step 22: In the three-phase line voltage cycle, multiple sampling cycles t are set. The sampling cycle t is set based on experience. Each sampling cycle t is integrated, that is, the unit integration: Among them, U x|t is the absolute value of the instantaneous value of the three-phase line voltage sampled in the tth sampling period, U x|t-1 The absolute value of the instantaneous value of the three-phase line voltage sampled in the t-1th sampling period, U x|t and U x|t-1 is the absolute value of the instantaneous value of the three-phase line voltage in adjacent sampling periods, and t is the sampling period; Step 23: perform integral calculation on the three-phase line voltage half cycle T / 2 according to the unit integral value: Wherein, N = T / 2t is the number of unit integral values ​​in a half cycle, and T is the three-phase line voltage cycle; Step 24: Calculate the actual value of the three-phase line voltage according to the half-cycle integral value of the three-phase line voltage: Among them, U R is the actual value of the three-phase line voltage, U N is the rated voltage of the three-phase line voltage, f N is the rated frequency of the three-phase line voltage, f K is the sampling frequency, which is the reciprocal of the sampling period t.

3. A voltage sag detection method according to claim 1, characterized in that: In step 4, the type of the temporary sag state of the three-phase line voltage, i.e., the temporary sag type, is determined based on the following strategy: If 70%U N <U R <80%U N , then the type of the temporary sag state of the three-phase line voltage is determined to be Flag_80; If 40%U N <U R <70%U N , then the type of the temporary sag state of the three-phase line voltage is determined to be Flag_70; If 10%U N <U R <40%U N , then the type of the temporary sag state of the three-phase line voltage is determined to be Flag_40; If 0%U N <U R <10%U N , then the type of the temporary sag state of the three-phase line voltage is determined to be Flag_0; Among them, U R is the actual value of the three-phase line voltage, U N is the rated voltage of the three-phase line voltage.

4. A voltage sag detection method according to claim 1, characterized in that: In step 5, if the duration does not exceed the duration threshold of the corresponding type, the sag state of the three-phase voltage changes to a different type, and the duration is re-timed according to the new sag type of the three-phase voltage, that is, the second sag type.

5. A voltage sag detection method according to claim 4, characterized in that: Before re-timing the duration, the timing of the sag type before the transition of the three-phase line voltage is stored, and the sag type before the transition is the first sag type; If the duration does not exceed the duration threshold of the corresponding type, the sag state of the three-phase line voltage changes from the second sag type to the first sag type, and the timing of the first sag type is obtained, and the timing is continued based on the timing of the first sag type.

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