Three-phase input power supply input open-phase detection method and application

Abstract

The invention provides an input open-phase detection method for a three-phase input power supply, which relates to the technical field of open-phase detection, and comprises the following steps of: sampling three-phase input voltage, and calculating to obtain an absolute value of three-phase voltage to ground; setting three variables to store the comparison value of each phase voltage; at each sampling moment, comparing the absolute value of each phase voltage with the corresponding storage variable: if the absolute value of the voltage is greater than the value of the storage variable, updating the absolute value of the voltage to the corresponding storage variable, and if the absolute value of the voltage is less than the value of the storage variable, calculating a new value of the storage variable according to the attenuation characteristic of the RC circuit; and after a preset period, comparing each storage variable value with a preset open-phase threshold value, and if the storage variable value is smaller than the open-phase threshold value, judging that the corresponding phase is open-phase. The attenuation characteristic of the RC circuit is introduced into a software algorithm, reliable open-phase detection can be achieved without an additional hardware circuit, the method does not depend on accurate sampling time, and the method has the advantages of being easy to achieve and small in calculation amount.

Description

Technical Field

[0001] The present invention relates to the technical field of phase loss detection, and in particular to a method for detecting phase loss of a three-phase input power supply. Background Art

[0002] Three-phase loss is a common fault phenomenon in industrial and power systems. In three-phase AC applications, three-phase balance is the key to ensuring the normal operation of the system. However, in actual applications, due to external environmental influences, equipment line aging and other issues, one or more phases of the three-phase power supply may lose power, that is, input phase loss occurs.

[0003] Phase failure can have a serious impact on system operation. In industrial rectifiers, inverters and other systems, phase failure can cause the output power quality to decline, causing voltage fluctuations and reducing the system life; in electric traction systems, phase failure can cause unbalanced motor operation, causing motor overheating and performance degradation, and even damage the motor in severe cases. Therefore, timely and accurate detection of input phase failure is crucial to the safe operation of three-phase AC equipment.

[0004] At present, phase loss detection mainly adopts two methods: hardware detection and software detection. In hardware detection, it is necessary to design a specific detection circuit and use comparators, triggers and other components to monitor the voltage signal, phase difference signal or frequency signal of the three-phase input in real time to determine whether there is a phase loss. This method not only has complex hardware circuit implementation and increases system cost, but also its poor anti-interference ability makes it difficult to ensure the reliability and accuracy of phase loss detection under harsh electromagnetic environment conditions.

[0005] In the software detection method, the traditional approach is to sample the input voltage, use the coordinate transformation of the two-phase voltage to obtain the DC component and make a judgment with the threshold. However, when a phase is missing, for a three-phase input with a base frequency of 50Hz, the DC component obtained by coordinate transformation is actually an AC signal with a frequency fluctuation of 100Hz. The AC signal increases from zero to the maximum value according to the sine law, then decays to zero according to the sine law, and so on. This method not only has strict requirements on the judgment time and low reliability, but also the coordinate transformation involves multiple square root operations, which will consume additional limited computing resources.

[0006] In addition, there are some improved software detection methods. For example, the Chinese patent with announcement number CN117233484A samples the output bus voltage at multiple points, and compares the reversal of the bus voltage waveform with the preset state to make a phase loss judgment; the announcement number CN102323491A samples the rectified bus voltage at the carrier frequency, and calculates the bus voltage head fluctuation frequency according to the number of times the bus voltage is sampled in a fluctuation cycle. When the wave head fluctuation frequency is between 50-150Hz, it is determined that there is a phase loss. However, these software detection algorithms are complex to implement, and the reliability of their detection strongly depends on the precise selection of the sampling point time. More importantly, when a phase is missing and the system is running at no load, the output bus voltage fluctuation is not obvious. At this time, it is difficult to ensure the accuracy of the phase loss detection by applying the above software detection algorithm. Summary of the invention

[0007] The purpose of the present invention is to provide a method for detecting phase loss of a three-phase input power supply, which realizes a simple, reliable, computationally small and independent phase loss detection method without increasing hardware costs.

[0008] To achieve the above object, the present invention is implemented through the following technical solutions:

[0009] A method for detecting a phase loss of a three-phase input power supply comprises the following steps:

[0010] S1: Sample the three-phase input voltage and calculate the absolute value of the three-phase voltage to ground;

[0011] S2: Set three variables to store the comparison value of each phase voltage respectively;

[0012] S3: Preset a sampling period, and at each sampling moment in the sampling period, compare the absolute value of each phase voltage with the corresponding storage variable:

[0013] If the absolute value of the voltage is greater than the value of the storage variable, the absolute value of the voltage is updated to the corresponding storage variable;

[0014] If the absolute value of the voltage is less than the stored variable value, a new stored variable value is calculated based on the attenuation characteristics of the RC circuit;

[0015] S4: After a preset period, compare each stored variable value with the preset phase loss threshold. If the stored variable value is less than the phase loss threshold, the corresponding phase is determined to be phase lost; if the stored variable value is greater than the phase loss threshold, repeat S1-S3 for the next detection.

[0016] Furthermore, the sampling of the three-phase input voltage in step S1 includes: sampling the three-phase voltage to ground, or sampling the line voltage between any two phases and calculating the line voltage of the third phase according to the line voltage.

[0017] Further: in step S3, the step of calculating a new storage variable value according to the attenuation characteristic of the RC circuit includes:

[0018] The new storage variable value is calculated according to the following formula:

[0019]

[0020] Wherein, V0 is the current storage variable value, t is the accumulated time since the storage variable was last updated, R is the preset resistance value, and C is the preset capacitance value.

[0021] Furthermore: the preset resistance value is 400Ω~1000Ω, and the preset capacitance value is 50μF~500μF.

[0022] Further: in step S3, the preset sampling period includes 20-40 sampling moments.

[0023] Furthermore: in step S4, the preset phase loss threshold is 5% to 10% of the maximum phase voltage.

[0024] The present invention also provides an application of a three-phase input power input phase loss detection method, which is applied to input phase loss detection of a three-phase rectifier or a three-phase inverter.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention introduces the attenuation characteristics of the RC circuit into the software algorithm and adopts the storage value comparison and attenuation update mechanism to realize phase loss detection. There is no need to design a specific hardware detection circuit. Reliable phase loss detection can be achieved only through the software algorithm, thus avoiding the hardware circuit cost. At the same time, it also overcomes the disadvantage that the hardware detection has poor anti-interference ability in harsh electromagnetic environments.

[0027] Second, the present invention adopts a simple storage value comparison and RC attenuation calculation method, without the need for complex coordinate transformation operations, which greatly reduces the occupation of computing resources. Compared with the method of obtaining the DC component by coordinate transformation in the prior art, the present invention has higher computing efficiency.

[0028] 3. The present invention introduces the attenuation characteristics of the RC circuit to update the stored value, so that the phase loss detection is no longer dependent on the precise sampling time, which overcomes the shortcoming of the existing technology that the sampling time is strictly required when detecting based on the bus voltage waveform, and improves the reliability of the detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A method for detecting a phase loss in a three-phase input power supply in an embodiment of the present invention;

[0030] Figure 2It is a schematic diagram of the three-phase rectifier topology;

[0031] Figure 3 It is a schematic diagram of the absolute value and comparison value of the phase voltage when there is no phase loss;

[0032] Figure 4 It is a schematic diagram of phase voltage and comparison value when phase failure occurs at a certain moment;

[0033] Figure 5 This is a schematic diagram of the voltage attenuation characteristics across the resistor in the RC circuit;

[0034] Figure 6 This is the A phase missing judgment flow chart;

[0035] Figure 7 This is a comparison result diagram of phase A failure detection in a specific implementation case;

[0036] Figure 8 This is a comparison result diagram of phase B missing detection in a specific implementation case;

[0037] Fig. 9 This is a comparison diagram of the C phase missing detection results in a specific implementation case. DETAILED DESCRIPTION

[0038] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only 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] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0040] like Figure 1 As shown: In some embodiments, a method for detecting a phase loss in a three-phase input power supply includes the following steps:

[0041] S1: Sample the three-phase input voltage and calculate the absolute value of the three-phase voltage to ground;

[0042] In some other embodiments, the sampling of the three-phase input voltage in step S1 includes: sampling the three-phase voltage to ground, or sampling the line voltage between any two phases and calculating the line voltage of the third phase according to the line voltage.

[0043] S2: Set three variables to store the comparison value of each phase voltage respectively;

[0044] S3: Preset a sampling period, and at each sampling moment in the sampling period, compare the absolute value of each phase voltage with the corresponding storage variable:

[0045] If the absolute value of the voltage is greater than the value of the storage variable, the absolute value of the voltage is updated to the corresponding storage variable;

[0046] If the absolute value of the voltage is less than the stored variable value, a new stored variable value is calculated based on the attenuation characteristics of the RC circuit;

[0047] In one embodiment, the step of calculating a new storage variable value according to the attenuation characteristic of the RC circuit includes:

[0048] The new storage variable value is calculated according to the following formula:

[0049]

[0050] Among them, V0 is the current storage variable value, t is the cumulative time since the storage variable was last updated, R is the preset resistance value, and C is the preset capacitance value. The preset resistance value can be 500Ω, and the preset capacitance value can be 100μF.

[0051] Furthermore, in another embodiment, the preset sampling period includes 20-40 sampling moments.

[0052] S4: After a preset period, compare each stored variable value with the preset phase loss threshold. If the stored variable value is less than the phase loss threshold, the corresponding phase is determined to be phase lost; if the stored variable value is greater than the phase loss threshold, repeat S1-S3 for the next detection. The preset phase loss threshold is 10% of the maximum phase voltage.

[0053] In another example, the present invention further provides an application of a three-phase input power input phase loss detection method, which is applied to input phase loss detection of a three-phase rectifier or a three-phase inverter.

[0054] In order to clearly, in detail and intuitively describe the technical solution of the present invention, the following takes a three-phase rectifier as an example to specifically illustrate the three-phase input power input phase loss detection method:

[0055] Taking a three-phase rectifier as an example, its typical topology diagram is as follows: Figure 2 As shown, firstly, the phase voltage or line voltage of the three-phase input is sampled. If it is the phase voltage sampled, the three-phase voltage VA ,V B ,V C If the line voltage is sampled, the A to B phase line voltage V ll_AB ,B to C phase line voltage V ll_BC Then use the following formula to get the line voltage V ll_CA :

[0056] Line Voltage:

[0057] Use the following formula to convert line voltage to V A ,V B ,V C Phase voltage:

[0058] Phase voltage:

[0059] Phase voltage:

[0060] Phase voltage:

[0061] The above-mentioned line voltage to phase voltage conversion relationship is applicable when the input three-phase is balanced or when one phase of the input is missing. After obtaining the three-phase voltage, three variables Max are pre-set in the software. a ,Max b ,Max c To store each comparison value, the above three variables are initialized to 0. Here, in order to combine the case description, a three-phase alternating current with a base frequency of 50 Hz is selected, and the phase voltage sampling frequency is selected as 1 kHz, that is, one point is sampled every 1 ms, and 20 points are fully sampled in one cycle of 50 Hz alternating current.

[0062] When the three-phase equipment is in high voltage operation, the voltage of each phase is obtained at the first point V A1 , V B1 , V C1 After taking the absolute value, they are compared with Max a , Max b , Max c By comparison, we take phase A as an example to describe in detail. When the first sampling time t1 is completed, if |V A1 |>Max a When |V A1 |Update to Max a and set the decay time T to 0; if |V A1 | <Max a When , the decay time T is added with a sampling time interval Δt, and T+Δt is assigned to T, then Max a Calculate according to the following formula:

[0063]

[0064] The R and C in the formula can be calibrated according to the actual situation. The attenuation principle will be described in detail later. The attenuated value is updated to Max a At this point, the comparison of the first sampling moment is completed; when the second sampling moment t2 is completed, the above comparison process is repeated. For 50Hz AC, after n signal cycles, 20*n samplings and 20*n comparisons are completed. If there is no phase loss, Max a The absolute value of the phase voltage will be updated at regular intervals. If there is a phase loss, the Max a It will continue to decay according to the above decay law. a Compared with the phase loss threshold, if it is greater than the threshold, there is no phase loss, and the subsequent sampling comparison is continued and judged again every n cycles; if it is less than the threshold, it means that the phase is missing, and phase loss protection is implemented. The selection of n here is related to the capacitor C and the resistor R. The phase loss detection process of phase B and phase C is the same as that of phase A, so it will not be repeated.

[0065] For auxiliary explanation, when there is no phase loss, the absolute value of phase A voltage |V A1 | and Max a The value changes over time as Figure 3 As shown, the black line is the absolute value of voltage |V A1 |, the red line is Max a Value, when there is no phase loss Max a The value will be updated by the absolute value of the voltage at regular intervals and will not decay continuously. Absolute value of phase A voltage when there is a phase loss |V A1 | and Max a The value changes over time as Figure 4 As shown, the black line is the absolute value of voltage |V A1 |, the red line is Max a Value, after phase failure occurs, Max a The value will continue to decay towards 0.

[0066] The above attenuation law uses the attenuation characteristics of the resistor voltage in the RC circuit over time. The capacitor C in the RC circuit has an initial voltage U0, that is, the initial voltage across the resistor is U0, the resistor value is R, and the capacitor current discharge formula is:

[0067]

[0068] Where e is a natural constant and t is the decay time, then the voltage U(t) across the resistor is:

[0069]

[0070] The circuit and the voltage attenuation diagram of the resistor are as follows: Figure 5 shown.

[0071] The phase failure judgment flow chart executed according to the above method is as follows Figure 6 The application of the phase loss detection method does not require the addition of additional hardware circuits. The hardware circuit principle is implemented through software. The algorithm is simple to implement and has strong reliability. The algorithm calculation does not involve complex operations required for coordinate transformation, which saves computing resources to a certain extent.

[0072] In addition, the present invention also provides an implementation example of a method for detecting a phase loss of a three-phase input power supply based on a three-phase rectifier to further illustrate the technical effect of the method of the present invention.

[0073] In this case, the phase voltage of the three-phase input is 220Vrms, the base frequency is 50Hz, the phase loss detection threshold is set to 10% of the maximum phase voltage, i.e. 31V, the sampling frequency is 1ms, the attenuation capacitor parameter is 100uF, the attenuation resistor parameter is 500Ω, and the phase loss judgment cycle n is selected as 2, and three phase losses are simulated respectively. The first time, the phase loss of phase A is simulated at 0.5s in the system, the second time, the phase loss of phase B is simulated at 0.5s in the system, and the third time, the phase loss of phase C is simulated at 0.5s in the system. Each time the phase is lost, the system can report the corresponding phase loss fault in real time, and the phase loss fault position is 1, which verifies that the software phase loss algorithm of the present invention is effective and reliable.

[0074] like Figure 7 The figure shows the comparison result of phase A missing detection. Figure 8 The figure shows the comparison result of phase B missing detection. Fig. 9 The figure shows the comparison results of phase loss detection of phase C.

[0075] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting a phase loss of a three-phase input power supply, characterized in that: The following steps are involved: S1: Sample the three-phase input voltage and calculate the absolute value of the three-phase voltage to ground; S2: Set three variables to store the comparison value of each phase voltage respectively; S3: Preset a sampling period, and at each sampling moment in the sampling period, compare the absolute value of each phase voltage with the corresponding storage variable: If the absolute value of the voltage is greater than the value of the storage variable, the absolute value of the voltage is updated to the corresponding storage variable; If the absolute value of the voltage is less than the stored variable value, a new stored variable value is calculated based on the attenuation characteristics of the RC circuit; S4: After a preset period, compare each stored variable value with the preset phase loss threshold. If the stored variable value is less than the phase loss threshold, the corresponding phase is determined to be phase lost; if the stored variable value is greater than the phase loss threshold, repeat S1-S3 for the next detection.

2. A three-phase input power supply input phase loss detection method according to claim 1, characterized in that: The sampling of the three-phase input voltage in step S1 includes: sampling the three-phase voltage to ground, or sampling the line voltage between any two phases and calculating the line voltage of the third phase according to the line voltage.

3. A three-phase input power input missing phase detection method according to claim 2, characterized in that: In step S3, the step of calculating a new storage variable value according to the attenuation characteristic of the RC circuit includes: The new storage variable value is calculated according to the following formula: Wherein, V0 is the current storage variable value, t is the accumulated time since the storage variable was last updated, R is the preset resistance value, and C is the preset capacitance value.

4. A three-phase input power input missing phase detection method according to claim 3, characterized in that: The preset resistance value is 400Ω to 1000Ω, and the preset capacitance value is 50μF to 500μF.

5. A three-phase input power input missing phase detection method according to claim 1, characterized in that: In step S3, the preset sampling period includes 20-40 sampling moments.

6. A three-phase input power input missing phase detection method according to claim 1, characterized in that: In step S4, the preset phase loss threshold is 5% to 10% of the maximum phase voltage.

7. A three-phase input power input missing phase detection method according to claim 1, characterized in that: Applicable to input phase loss detection of three-phase rectifier or three-phase inverter.

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