A method for detecting three-phase overvoltage and undervoltage

Abstract

The present invention provides a method for detecting overvoltage and undervoltage in three-phase electricity. The three phases are connected to the same sampling circuit for unified sampling, and the sampled signals are transmitted to an MCU for processing. The detection method comprises the following steps: first, sampling the voltage n times within a single cycle, and finding the maximum value of the first phase voltage based on the sampled data; then, calculating the maximum values ​​of the second and third phase voltages based on the maximum value of the first phase voltage; then, calculating the actual voltage value of each phase; and finally, comparing the actual voltage value of each phase with an overvoltage threshold and an undervoltage threshold to determine whether overvoltage or undervoltage is present. The overall detection is simple and convenient, reducing the amount of calculation, and can achieve overvoltage and undervoltage detection in a small electrical appliance space. It also reduces the use of electrical components and saves costs.

Description

Technical Field

[0001] The present invention relates to the detection of three-phase electricity in the field of low-voltage electricity, and in particular to a method for detecting overvoltage and undervoltage of three-phase electricity. Background Art

[0002] In the field of low-voltage electrical appliances, grid voltage over- and under-voltage detection is a function that must be possessed by many products. For example, in the self-resetting over- and under-voltage protector, the grid voltage must be detected in real time. When the grid voltage is detected to be lower than the set under-voltage threshold, the circuit breaker must be disconnected; when the grid voltage is detected to be higher than the set over-voltage threshold, the circuit breaker must also be disconnected; the load electrical appliances will not be damaged due to over- and under-voltage power supply. When the grid voltage returns to normal, the circuit breaker can be automatically connected to ensure normal power supply to the load. For example, in the photovoltaic automatic grid-connected system, grid voltage over- and under-voltage detection is also required. When the grid voltage is lower than or higher than the set value, the circuit breaker can be disconnected, and when the voltage is normal, the circuit breaker can be automatically closed. Especially when the grid is out of power, the circuit breaker must be disconnected to cut off the connection between the load and the grid, isolating the photovoltaic system from the grid system. Figure 1 The circuit shown in Figure 1 illustrates a commonly used three-phase voltage detection method. The three-phase input voltages VA, VB, and VC are rectified, divided by resistors, and fed into the three A / D sampling terminals of an MCU. The MCU's A / D sampling generates digital values, which are then calculated to determine the voltage values ​​of the input voltages VA, VB, and VC. Overvoltage and undervoltage detection is then performed based on these values. This circuit utilizes independent sampling and calculation of the three phases, requiring a large number of components and A / D sampling terminals. This requires significant MCU resources, making it impractical for applications requiring a compact footprint. Furthermore, the high number of components increases costs. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a three-phase power overvoltage and undervoltage detection method suitable for small-volume electrical appliance spaces.

[0004] The technical solution adopted by the present invention to solve the technical problem is: a method for detecting overvoltage and undervoltage of three-phase electricity, wherein the three-phase electricity is connected to the same sampling circuit for unified sampling, and the sampled signals are transmitted to the MCU for processing. The steps of the detection method are as follows:

[0005] S1. Sample the voltage value once every t time. The number of samples in a single cycle is n times, where: f is the frequency of three-phase electricity, and n is an integer;

[0006] S2. Compare the voltage values ​​obtained by sampling n times to obtain the maximum value Vamax in the n times of sampling, and record the sampling position maxaid of the maximum value to obtain the maximum value Vamax and the sampling position maxaid of the first phase of the three-phase electricity;

[0007] S3. Take the sampling position maxaid of the maximum value of the first phase and calculate the sampling position bid of the second phase = maxaid + n / 3. Then the sampling position maxbid of the second phase = maxaid + n / 3. The voltage value corresponding to this sampling position is the maximum value Vbmax of the second phase.

[0008] S4. Take the sampling position maxaid of the maximum value of the first phase and calculate the sampling position cid of the third phase = maxaid + 2n / 3. Then the sampling position maxcid of the maximum value of the third phase = maxaid + 2n / 3. The voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase.

[0009] S5. Calculate the actual voltages Va, Vb, and Vc based on Vamax, Vbmax, and Vcmax;

[0010] S6. Compare the actual voltages Va, Vb, and Vc with the overvoltage threshold and undervoltage threshold built into the MCU. If any actual voltage is higher than the overvoltage threshold, it is determined to be an overvoltage. If any actual voltage is lower than the undervoltage threshold, it is determined to be an undervoltage.

[0011] More specifically, the frequency of the three-phase power in step S1 is 50 Hz, the interval time t=0.667 ms, and the calculated sampling number n=30.

[0012] Further specifically, the sampling circuit includes a first diode connected to the first phase, a second diode connected to the second phase, and a third diode connected to the third phase. The first diode, the second diode, and the third diode are all connected to one end of the first resistor. The other end of the first resistor is divided into three paths. The first path is connected to the neutral line after passing through the second resistor, the second path is connected to the neutral line after passing through the first capacitor, and the third path is connected to the MCU.

[0013] More specifically, the actual voltage of the three-phase electricity in step S5 is calculated by the following formula:

[0014]

[0015] Wherein, V is the actual voltage, 0.7 is the forward voltage drop of the diode, 1.414 is the relationship coefficient between the actual voltage and the maximum voltage, R1 is the resistance value of the first resistor, and R2 is the resistance value of the second resistor.

[0016] More specifically, in step S3, after calculating the sampling position bid=maxaid+n / 3 of the second phase, the sampling position bid of the second phase is judged. If bid≤n, the sampling position of the second phase maximum value maxbid=maxaid+n / 3, and the voltage value corresponding to this sampling position is the maximum value Vbmax of the second phase; if bid>n, the sampling position of the second phase maximum value maxbid=maxaid+n / 3-n, and the voltage value corresponding to this sampling position is the maximum value Vbmax of the second phase.

[0017] More specifically, in step S4, after calculating the sampling position cid of the third phase = maxaid + 2n / 3, the sampling position cid of the third phase is judged. If cid ≤ n, the sampling position of the third phase maximum value maxcid = maxaid + 2n / 3, and the voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase; if cid > n, the sampling position of the third phase maximum value maxcid = maxaid + 2n / 3 - n, and the voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase.

[0018] Further specifically, step S4 can be replaced by taking the sampling position maxbid of the maximum value of the second phase and calculating the sampling position cid of the third phase = maxbid + n / 3. Then the sampling position maxcid of the maximum value of the third phase = maxbid + n / 3, and the voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase.

[0019] More specifically, the method for comparing the sampled data in step S2 is to set the maximum value as the variable Vamax, initially assign it to 0, compare Vamax with the sampled data one by one, and if Vamax is less than a certain sampled data, assign the sampled data to Vamax, and then continue to compare it with the remaining sampled data one by one until the end.

[0020] The beneficial effects of the present invention are: through the above-mentioned detection method, three-phase electrical sampling can be achieved through a sampling circuit, and the maximum voltage values ​​and actual voltage values ​​of the first phase, the second phase and the third phase can be obtained through the designed calculation method, and whether there is overvoltage or undervoltage can be determined by comparing the actual voltage with the overvoltage threshold and the undervoltage threshold. The overall detection is simple and convenient, and overvoltage and undervoltage detection can be achieved in a small electrical space, while reducing the use of electrical components and saving expenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a sampling circuit diagram of the prior art;

[0022] Figure 2 is a sampling circuit diagram of the present invention;

[0023] Figure 3-Figure 6 It is a schematic diagram of four variations of the three-phase electricity in the present invention in which the first phase is the maximum value;

[0024] Figure 7 It is a schematic flow chart of the detection method of the present invention;

[0025] Figure 8 This is a logic diagram of the present invention when the cycle is 1. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0027] based on Figure 1 The sampling scheme of the prior art shown in FIG. 1 samples the first phase, the second phase, and the third phase of the three-phase electricity respectively, and then determines the overvoltage and undervoltage of the three-phase electricity; Figure 2 The scheme shown uses the same sampling circuit for unified sampling. The sampled data here also contains data of the first phase, the second phase, and the third phase. After analyzing and processing the data of these three phases, the actual voltage value of the first phase, the actual voltage value of the second phase, and the actual voltage value of the third phase are obtained. The sampling circuit includes a first diode D1 connected to the first phase, a second diode D2 connected to the second phase, and a third diode D3 connected to the third phase. The first diode D1, the second diode D2, and the third diode D3 are all connected to one end of the first resistor R1. The other end of the first resistor R1 is divided into three paths. The first path passes through the second resistor R2 and is connected to the neutral line. The second path passes through the first capacitor C1 and is connected to the neutral line. The third path is connected to the MCU for analysis and processing by the MCU.

[0028] based on Figure 2The sampling circuit shown is used for sampling. Within one cycle of the three-phase electricity, there are four forms of changes in the first phase, the second phase, and the third phase. The first form is that the first phase, the second phase, and the third phase are all equal. The second form is that the first phase is the largest, and the second phase and the third phase are both smaller than the first phase. The third form is that the second phase is the largest, and the first phase and the third phase are both smaller than the second phase. The fourth form is that the third phase is the largest, and the first phase and the second phase are both smaller than the third phase. Since random sampling is performed, the positions of the first phase, the second phase, and the third phase in the situation encountered are different from the above four forms. However, when making an overvoltage or undervoltage judgment, it is only necessary to find the maximum values ​​of the first phase, the second phase, and the third phase respectively. Since the phase difference between the first phase, the second phase, and the third phase is 120°, it is only necessary to find the maximum values ​​of the first phase, the second phase, and the third phase to obtain the maximum values ​​of the other two phases.

[0029] The following is a detailed explanation using the first phase as an example. The maximum value of the first phase can appear as follows Figure 3-6 When the second and third phases are at their maximum values, the detection method is the same as when the first phase is at its maximum value.

[0030] like Figure 7 and Figure 8 The steps of a three-phase power over-voltage and under-voltage detection method are as follows:

[0031] S1. Sample the voltage value once every t time. The number of samples in a single cycle is n times, where: f is the frequency of three-phase electricity, n is an integer, and the frequency of three-phase electricity f = 50 Hz is usually used. Therefore, the time of a single cycle is 20 ms, and the sampling time interval t = 0.667 ms, thereby calculating the number of sampling times n = 29.98. After rounding, the number of sampling times n = 30. In a single cycle, the maximum values ​​of the first phase, the second phase, and the third phase can be sampled. Since the phase difference between the three phases is the same, 1≤n≤10 corresponds to one of the multiple phases of the three-phase electricity, 11≤n≤20 corresponds to one of the remaining two phases of the three-phase electricity, and 21≤n≤30 corresponds to the last remaining phase of the three-phase electricity.

[0032] S2. Compare the voltage values ​​obtained from 30 samplings to obtain the maximum value Vamax among the 30 samplings, and record the sampling position maxaid of the maximum value, where the sampling position is a sampling in the 30 samplings, to obtain the maximum value Vamax and the sampling position maxaid of the first phase of the three-phase electricity;

[0033] The above comparison method is as follows: first, the voltage values ​​obtained by 30 samplings are stored in the RAM array variable voltagevalue[n-1] of the MCU, and the maximum value is found in voltagevalue[0] to voltagevalue

[29] ; secondly, the variable of the maximum value is set as Vamax in the MCU, and the initial value is assigned to 0, and Vamax is compared with the sampling data in voltagevalue[0] to voltagevalue

[29] one by one. If Vamax is less than a certain sampling data, the sampling data is assigned to Vamax. If Vamax is greater than or equal to a certain sampling data, no replacement is performed; then continue to compare with the remaining sampling data one by one and repeat the steps after comparison until the end. After 30 comparisons are completed, the maximum value of the 30 sampling data can be obtained, and the sampling position of the maximum value is recorded at the same time, thereby obtaining the maximum value Vamax and sampling position maxaid of the first phase.

[0034] S3. Sampling is performed according to the cycle. When the sampling cycle is greater than 1, the calculation method of the second phase is as follows:

[0035] Take the sampling position maxaid of the maximum value of the first phase, and calculate the sampling position bid of the second phase = maxaid + 10. Then the sampling position maxbid of the maximum value of the second phase = maxaid + 10. The voltage value corresponding to this sampling position is the maximum value Vbmax of the second phase.

[0036] When the sampling period is 1, the second phase is calculated as follows:

[0037] Take the sampling position maxaid of the maximum value of the first phase, calculate the sampling position bid = maxaid + 10 of the second phase, and judge the sampling position bid of the second phase. If bid ≤ 30, then the sampling position maxbid = maxaid + 10 of the maximum value of the second phase, and the voltage value corresponding to this sampling position is the maximum value Vbmax of the second phase; if bid > 30, then the sampling position maxbid = maxaid + 10 - 30 of the maximum value of the second phase, and the voltage value corresponding to this sampling position is the maximum value Vbmax of the second phase.

[0038] S4. There are two ways to calculate the maximum value of the third phase voltage. The first method is based on the first phase. The calculation method is as follows:

[0039] Here, it can also be divided into when the sampling period is greater than 1 time,

[0040] Take the sampling position maxaid of the maximum value of the first phase, and calculate the sampling position cid of the third phase = maxaid + 20. Then the sampling position maxcid of the maximum value of the third phase = maxaid + 20. The voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase.

[0041] When the sampling period is 1,

[0042] Take the sampling position maxaid of the maximum value of the first phase, calculate the sampling position cid of the third phase = maxaid + 20, and judge the sampling position cid of the third phase. If cid ≤ 30, then the sampling position maxcid of the maximum value of the third phase = maxaid + 20, and the voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase; if cid > 30, then the sampling position maxcid of the maximum value of the third phase = maxaid + 20 - 30, and the voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase.

[0043] The second method is to calculate based on the second phase, and the calculation method is as follows:

[0044] When the cycle is greater than 1,

[0045] Take the sampling position maxbid of the maximum value of the second phase, and calculate the sampling position cid of the third phase = maxbid + 10. Then the sampling position maxcid of the maximum value of the third phase is maxbid + 10, and the voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase;

[0046] When the sampling period is 1,

[0047] Take the sampling position maxbid of the maximum value of the second phase, calculate the sampling position cid of the third phase = maxbid + 10, and judge the sampling position cid of the third phase. If cid ≤ 30, then the sampling position maxcid of the maximum value of the third phase = maxbid + 10, and the voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase; if cid > 30, then the sampling position maxcid of the maximum value of the third phase = maxbid + 10 - 30, and the voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase.

[0048] S5. Calculate the actual voltages Va, Vb, and Vc based on Vamax, Vbmax, and Vcmax. The calculation formula is:

[0049]

[0050] Transforming the formula we get:

[0051]

[0052] Wherein, V is the actual voltage, 0.7 is the forward voltage drop of the diode, 1.414 is the relationship coefficient between the actual voltage and the maximum voltage, R1 is the resistance value of the first resistor, and R2 is the resistance value of the second resistor.

[0053] S6. Compare the actual voltages Va, Vb, and Vc with the overvoltage threshold Vm and undervoltage threshold Vn built into the MCU. If any actual voltage is higher than the overvoltage threshold Vm, it is determined to be an overvoltage. If any actual voltage is lower than the undervoltage threshold Vn, it is determined to be an undervoltage.

[0054] In summary, first, the voltages of the first phase, second phase and third phase of the three-phase electricity are uniformly collected through an acquisition circuit, and the maximum value of the collected voltage data is first found. The maximum value is one of the three-phase electricity. Then, according to the relationship that the phase difference of the three-phase electricity is 120°, the maximum value of a certain phase is also the maximum value of the corresponding phase voltage after rotating 120° and 240°. Therefore, the sampling positions of the maximum values ​​of the other two phases are obtained by calculation, and the maximum voltages of the other two phases are obtained according to the sampling positions; then the actual voltage is calculated by the corresponding formula, and finally the actual voltage is compared with the overvoltage threshold Vm and the undervoltage threshold Vn to determine whether it is overvoltage or undervoltage; this detection method only needs to find one maximum value in the three-phase electricity to obtain the maximum values ​​of the other phases. There is no need to sample separately, which reduces the MCU's data processing time and simplifies the processing method. At the same time, it can also simplify the sampling circuit, which is suitable for use in electrical appliances with small volume and reduces costs.

[0055] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for detecting three-phase overvoltage and undervoltage, characterized in that: The three-phase electricity is connected to the same sampling circuit for unified sampling, and the sampled signal is transmitted to the MCU for processing. The steps of the detection method are as follows: S1. Sample the voltage value once every t time. The number of samples in a single cycle is n times, where: , f is the frequency of three-phase electricity, n is an integer; S2. Compare the voltage values ​​obtained by sampling n times to obtain the maximum value Vamax in the n times of sampling, and record the sampling position maxaid of the maximum value to obtain the maximum value Vamax and the sampling position maxaid of the first phase of the three-phase electricity; S3. Take the sampling position maxaid of the maximum value of the first phase and calculate the sampling position bid of the second phase = maxaid + n / 3. Then the sampling position maxbid of the second phase = maxaid + n / 3. The voltage value corresponding to this sampling position is the maximum value Vbmax of the second phase. S4. Take the sampling position maxaid of the maximum value of the first phase and calculate the sampling position cid of the third phase = maxaid + 2n / 3. Then the sampling position maxcid of the maximum value of the third phase = maxaid + 2n / 3. The voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase. S5. Calculate the actual voltages Va, Vb, and Vc based on Vamax, Vbmax, and Vcmax; S6. Compare the actual voltages Va, Vb, and Vc with the overvoltage threshold and undervoltage threshold built into the MCU. If any actual voltage is higher than the overvoltage threshold, it is determined to be an overvoltage. If any actual voltage is lower than the undervoltage threshold, it is determined to be an undervoltage.

2. The method for detecting three-phase overvoltage and undervoltage according to claim 1, characterized in that: In step S1 , the frequency of the three-phase power is 50 Hz, the interval time t is 0.667 ms, and the calculated sampling number n is 30.

3. The method for detecting three-phase overvoltage and undervoltage according to claim 1, characterized in that: The sampling circuit includes a first diode connected to the first phase, a second diode connected to the second phase, and a third diode connected to the third phase. The first diode, the second diode, and the third diode are all connected to one end of the first resistor. The other end of the first resistor is divided into three paths. The first path is connected to the neutral line after passing through the second resistor, the second path is connected to the neutral line after passing through the first capacitor, and the third path is connected to the MCU.

4. The method for detecting three-phase overvoltage and undervoltage according to claim 3, characterized in that: The actual voltage of the three-phase electricity in step S5 is calculated by the following formula: ； Wherein, V is the actual voltage, 0.7 is the forward voltage drop of the diode, 1.414 is the relationship coefficient between the actual voltage and the maximum voltage, R1 is the resistance value of the first resistor, and R2 is the resistance value of the second resistor.

5. The method for detecting three-phase overvoltage and undervoltage according to claim 1, characterized in that: When the sampling period is 1, in step S3, after calculating the sampling position bid=maxaid+n / 3 of the second phase, the sampling position bid of the second phase is judged. If bid≤n, the sampling position maxbid=maxaid+n / 3 of the maximum value of the second phase, and the voltage value corresponding to this sampling position is the maximum value Vbmax of the second phase; if bid>n, the sampling position maxbid=maxaid+n / 3-n of the maximum value of the second phase, and the voltage value corresponding to this sampling position is the maximum value Vbmax of the second phase.

6. The method for detecting three-phase overvoltage and undervoltage according to claim 1, characterized in that: When the sampling period is 1, in step S4, after calculating the sampling position cid=maxaid+2n / 3 of the third phase, the sampling position cid of the third phase is judged. If cid≤n, the sampling position of the third phase maximum value maxcid=maxaid+2n / 3, and the voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase; if cid>n, the sampling position of the third phase maximum value maxcid=maxaid+2n / 3-n, and the voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase.

7. The method for detecting three-phase overvoltage and undervoltage according to claim 1, characterized in that: When the cycle is greater than 1, step S4 can be replaced by taking the sampling position maxbid of the maximum value of the second phase and calculating the sampling position cid=maxbid+n / 3 of the third phase. Then the sampling position maxcid=maxbid+n / 3 of the maximum value of the third phase, and the voltage value corresponding to this sampling position is the maximum value Vcmax of the third phase.

8. The method for detecting three-phase overvoltage and undervoltage according to claim 1, characterized in that: The method for comparing the sampled data in step S2 is to set the maximum value as the variable Vamax, initially assign it to 0, compare Vamax with the sampled data one by one, and if Vamax is less than a certain sampled data, assign the sampled data to Vamax, and then continue to compare it with the remaining sampled data one by one until the end.

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