Bus residual voltage detection method, motor loss of voltage protection method, storage device and terminal

Abstract

The application provides a bus residual voltage detection method, a motor loss of voltage protection method, a storage device and a terminal. The bus residual voltage detection method comprises the following steps: constructing a mathematical model of motor counter electromotive force and a mathematical model of bus residual voltage initial value; based on the mathematical model, analyzing the change rule of the phase angle of the bus voltage to obtain a relationship expression between the differential quantity of the bus voltage space phase angle with respect to time and the rotor angular velocity; establishing a relationship expression between the motor speed and the motor rotor angular velocity; analyzing the motor speed and the rotor speed to obtain a relationship expression between the speed detection setting value and the motor speed during normal operation; and comparing the real-time collected rotor speed of the motor with the speed detection setting value to determine whether the bus voltage is the counter electromotive force of the motor. The application has the beneficial effect of achieving the motor loss of voltage protection according to the bus residual voltage characteristic quantity change and is suitable for the field of bus residual voltage detection.

Description

Technical Field

[0001] This invention relates to the technical field of busbar residual voltage detection, specifically to busbar residual voltage detection methods, motor undervoltage protection methods, storage devices, and terminals. Background Technology

[0002] In industrial production, when a large-capacity high-voltage motor suddenly encounters a power outage, a residual voltage (hereinafter referred to as "residual voltage") will temporarily exist on the bus side of the motor due to the generation of back electromotive force. This residual voltage value can usually reach a very high value.

[0003] Depending on the specific industrial production requirements, some electric motors are equipped with automatic transfer switch (ATS) backup power supplies. These systems utilize the residual voltage on the busbar generated by the back electromotive force (EMF) after the motor stops for grid connection detection, enabling rapid switching of the power supply after a power outage and preventing the risk of motor shutdown during production. However, for motors that do not require power switching, residual voltage on the busbar side can lead to backfeeding of voltage to the power supply system during shutdown after a power outage. When the residual voltage reaches a significant value, it can pose a potential risk to the user side. For example, the residual voltage on the busbar generated by the back EMF of an electric motor in a coal mine could trigger a gas and coal dust explosion or cause electric shock injuries. When the busbar voltage is fed back to the power supply system via a transformer, it can affect the automatic transfer switch's operation, potentially causing transformer protection to malfunction and resulting in a large-scale power outage.

[0004] Electric motors are typically equipped with undervoltage protection. Undervoltage protection ensures that the motor will not start automatically when the supply voltage is lower than the required restart voltage, thus avoiding damage to the motor caused by forced restart.

[0005] When the motor loses power, if the voltage value of the bus residual voltage generated by the back electromotive force is low, the undervoltage protection can detect and disconnect it, thereby eliminating the impact of the back electromotive force on the user and the system. However, when the voltage value of the bus residual voltage is high, such as when the voltage value of the bus residual voltage is greater than the setting range of the undervoltage protection, the undervoltage protection cannot detect and disconnect the back electromotive force, resulting in the traditional undervoltage protection being unable to accurately detect and disconnect the back electromotive force of the motor.

[0006] In summary, studying the busbar residual voltage generated by the back electromotive force of the motor to achieve the purpose of back electromotive force detection, and then improving the traditional undervoltage protection by adding the function of back electromotive force isolation, is particularly important for protecting the safe production of users and the safe operation of the power supply system. Summary of the Invention

[0007] To address the shortcomings of related technologies, the technical problem to be solved by this invention is to provide a method for detecting busbar residual voltage, a method for protecting motors from undervoltage, a storage device, and a terminal for detecting busbar residual voltage, a method for protecting motors from undervoltage, and a method for eliminating back electromotive force after motor power failure, based on mathematical modeling and analysis of busbar residual voltage characteristic quantities and changes in busbar residual voltage.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] The method for detecting residual voltage on a motor busbar is characterized by the following steps:

[0010] S10, Construct a mathematical model of the back electromotive force of the motor and a mathematical model of the initial value of the bus residual voltage;

[0011] S20, based on the mathematical model of the motor back electromotive force and the mathematical model of the initial value of the bus residual voltage, analyzes the variation law of the phase angle in the bus voltage, and obtains the expression for the relationship between the differential component of the bus voltage spatial phase angle with respect to time and the rotor angular velocity, which is:

[0012]

[0013] in: ω is the differential component of the spatial phase angle of the bus voltage with respect to time. r This represents the rotor angular velocity of the electric motor.

[0014] S30, establish the expression relating the motor speed and the motor rotor angular velocity as follows:

[0015]

[0016] Where: n r To collect the rotor speed of the motor in real time, kr is the conversion coefficient;

[0017] S40 analyzes the motor speed and rotor speed to obtain the expression relating the speed detection setpoint to the motor speed during normal operation:

[0018] n set =n s -Δn Equation (3)

[0019] Where: n set n is the speed detection setpoint. s Δn represents the motor speed during normal operation, and Δn represents the empirical error.

[0020] S50, n r With n set Comparison, when n r ≤n setWhen the bus voltage reaches the level of the motor's back electromotive force, it is determined that the bus voltage has reached the level of the motor's back electromotive force.

[0021] Preferably, in step S10, constructing a mathematical model of the back electromotive force of the motor and a mathematical model of the initial value of the bus residual voltage includes:

[0022] S101, establish the stator flux linkage equation, the rotor winding flux linkage equation, and the stator current mathematical model of the motor:

[0023] The stator flux linkage equation of the electric motor is:

[0024]

[0025] In equation (10), the coefficient K s1 K s2 K s3 T s '、T r The expression for ' is:

[0026]

[0027] T s '=(L s -L m 2 / L r ) / R s Equation (10-2)

[0028] T r '=(L r -L m 2 / L s ) / R r Equation (10-3)

[0029] The flux linkage equation of the rotor winding is:

[0030]

[0031] In equation (11), the coefficient K r1 K r2 K r3 The expression is:

[0032]

[0033] The mathematical model for stator current is:

[0034]

[0035] in: Let ω be the bus voltage vector of the motor. S M is the frequency of the power grid. mThe mutual inductance between the stator and rotor windings of the electric motor; R r R is the rotor resistance. s For the stator resistance, ω r This represents the rotor angular velocity of the electric motor.

[0036] L S For stator inductance, L m For the magnetizing inductor, L r For rotor inductance;

[0037] ψ s0 ψ r0 This represents the initial values ​​of the stator and rotor circuit flux linkages, i.e., the flux linkages of the stator and rotor windings during steady-state operation of the motor.

[0038] S102, based on the current zero-crossing time calculated using the stator current equation, determine the stator flux linkage at the moment the motor is de-energized:

[0039]

[0040] The equations for solving parameters s1, s2, and s3 are as follows:

[0041]

[0042] T r =L r / R r

[0043] S103, based on the flux linkage equation and voltage equation at the moment the motor is de-energized, the initial value of the voltage is obtained as follows in spatial vector coordinates:

[0044]

[0045] Equation (15) is the mathematical model for the initial value of the busbar residual pressure.

[0046] Preferably, step S101, establishing the stator flux linkage equation, the rotor winding flux linkage equation, and the stator current mathematical model of the motor, specifically includes:

[0047] S1011, The vector expression of the initial voltage of the motor during normal operation in space is established as follows:

[0048]

[0049] When the motor is running stably, the relationship between the stator flux linkage and the bus voltage is as follows:

[0050]

[0051] S1012, Construct the flux linkage equations of the rotor and stator of the electric motor in the dq rotating coordinate system:

[0052] The flux linkage equation of the rotor is:

[0053]

[0054] The flux linkage equation of the stator is:

[0055]

[0056] Where: ψ dr ψ qr ψ represents the components of the stator flux linkage along the d-axis and q-axis, respectively. ds ψ qs These are the components of the rotor flux linkage on the d-axis and q-axis, respectively; σ is the leakage flux coefficient, and its value is: σ = 1 - L m 2 / L r L s i ds i qs These are the components of the stator current on the d-axis and q-axis, respectively; u ds u qs These are the components of the stator voltage along the d-axis and q-axis, respectively;

[0057] S1013, establish the voltage equations for the stator and rotor as follows:

[0058]

[0059] Where: u dr u qr These represent the components of the rotor voltage along the d-axis and q-axis, respectively; i dr andi qr These are the components of the rotor current on the d-axis and q-axis;

[0060] S1014, based on the rotor flux linkage equation, the stator flux linkage equation, the stator voltage equation, and the rotor voltage equation, the steady-state flux linkage equation of the rotor during normal motor operation is obtained as follows:

[0061]

[0062] S1015, when the voltage starts to drop, the stator flux linkage equation of the motor is:

[0063]

[0064] S1016, Establish the flux linkage equation of the rotor winding during voltage dip:

[0065]

[0066] S1017, the formula for calculating the stator current during voltage dips is:

[0067]

[0068] S1018, the time when the stator crosses zero is denoted as: t = t m And establish the equation:

[0069]

[0070] Solving equation (13) yields the stator flux linkage at the moment the motor loses power, which is:

[0071]

[0072] S1019, based on the flux linkage equation and the voltage equation, the initial value of the voltage is obtained as follows in spatial vector coordinates:

[0073]

[0074] Preferably, according to equation (15), the expressions for the magnitude and phase angle of the initial value of the busbar residual voltage are:

[0075]

[0076] According to equation (15-2), the phase angle varies in space as follows:

[0077]

[0078] Wherein: T r =L r / R r In the above expression, u s (t) represents the initial value of the busbar residual voltage; U s (t) represents the magnitude of the initial value of the busbar residual load, θ us (t) is the phase angle of the initial value of the busbar residual voltage, ω r Let ψ be the rotor angular velocity of the electric motor. s0 Let t be the initial value of the stator winding flux linkage, and t be time.

[0079] Accordingly, the motor undervoltage protection method based on busbar residual voltage detection includes the following steps:

[0080] A10 monitors the bus voltage and extracts the bus voltage phase angle;

[0081] A20, Calculate the differential component of the bus voltage spatial phase angle with respect to time.

[0082] A30, Calculate the motor speed.

[0083] A40, determine if the back electromotive force has been reached. If so, proceed to step A50; otherwise, proceed to step A60.

[0084] A50 issues an action signal based on the undervoltage protection setting value and time limit value;

[0085] A60, locked.

[0086] Preferably, the determination of whether a back electromotive force has been reached specifically involves:

[0087] The rotor speed n of the motor is collected in real time. r With the speed detection set value n set Comparison, when n r ≤n set When the bus voltage reaches the point where the back electromotive force of the motor is at that point, it is determined that the bus voltage has reached the point where the back electromotive force of the motor ... is at that point.

[0088] The n set =n s -Δn;

[0089] The n s Let Δn be the motor speed when the motor is running normally, and Δn be the empirical error.

[0090] Preferably, step A50 includes: issuing an action signal based on the undervoltage protection setting value and the time limit value, specifically including:

[0091] A501, determine if |U res |≤U op If satisfied, output the time limit value t. op ;

[0092] The U op The setting value for undervoltage protection based on busbar residual voltage detection is expressed as follows:

[0093]

[0094] Among them: U N.min k is the minimum allowable voltage for normal operation of the motor. r k is the return coefficient of the relay. rel The reliability coefficient;

[0095] A502, obtain the setting value U of traditional undervoltage protection. op.1 and time limit t op.1 ;

[0096] A503, determine whether the time limit value t is met. op.1 Or time limit value t op If one of these conditions is met, an action signal is issued.

[0097] Preferably, in step A50, the time limit value t op.1 And the time limit value is t op The relationship between them is:

[0098] t op =t op.1 +Δt Equation (17)

[0099] Where: Δt is the time margin.

[0100] Accordingly, a storage device stores multiple instructions adapted for loading and execution by a processor of the motor bus residual voltage detection method as described above.

[0101] Accordingly, the terminal is characterized by comprising:

[0102] Processor, adapted to implement instructions; and

[0103] A storage device is adapted to store multiple instructions, which are adapted to be loaded by a processor and executed as described above for the motor bus residual voltage detection method.

[0104] The beneficial technical effects of this invention are as follows:

[0105] 1. The method for detecting residual voltage of motor busbar provided by the present invention constructs a mathematical model of motor back electromotive force and a mathematical model of initial value of busbar residual voltage, and uses the differential component of phase angle of initial value of motor back electromotive force as a parameter for identifying back electromotive force, effectively detects and identifies back electromotive force, and improves the sensitivity of back electromotive force identification.

[0106] 2. This invention proposes a motor undervoltage protection method based on busbar residual voltage detection. It proposes an undervoltage protection method based on the detection of the phase angle of the initial value of the busbar residual voltage, which achieves effective isolation of back electromotive force and reduces the harm to users and the power grid.

[0107] 3. This invention adds back EMF identification and detection to the traditional undervoltage protection, which improves the reliability and selectivity of undervoltage protection and ensures the reliable operation of the motor. Attached Figure Description

[0108] Figure 1 This is a flowchart illustrating the method for detecting residual voltage on the motor busbar provided by the present invention.

[0109] Figure 2 This is a schematic diagram of the equivalent circuit model of the electric motor in this invention;

[0110] Figure 3 This is a schematic diagram illustrating the variation law of the reaction potential in this invention;

[0111] Figure 4This is a flowchart illustrating the motor undervoltage protection method based on busbar residual voltage detection provided by the present invention.

[0112] Figure 5 This is a schematic diagram of the action module of the motor undervoltage protection method in this invention. Detailed Implementation

[0113] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0114] Secondly, the present invention will be described in detail with reference to the schematic diagrams. When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure will be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0115] An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[0116] Example 1

[0117] like Figure 1 As shown, the method for detecting residual voltage on the motor busbar includes the following steps:

[0118] S10, Construct a mathematical model of the back electromotive force of the motor and a mathematical model of the initial value of the bus residual voltage;

[0119] S20, based on the mathematical model of the motor back electromotive force and the mathematical model of the initial value of the bus residual voltage, analyzes the variation law of the phase angle in the bus voltage, and obtains the expression for the relationship between the differential component of the bus voltage spatial phase angle with respect to time and the rotor angular velocity, which is:

[0120]

[0121] S30, establish the expression relating the motor speed and the motor rotor angular velocity as follows:

[0122]

[0123] Where: n r To collect the rotor speed of the motor in real time, kr is the conversion coefficient;

[0124] S40 analyzes the motor speed and rotor speed to obtain the expression relating the speed detection setpoint to the motor speed during normal operation:

[0125] n set =n s -Δn Equation (3)

[0126] Where: n s Δn represents the motor speed during normal operation, and Δn represents the empirical error.

[0127] S50, n r With n set Comparison, when n r ≤n set When the bus voltage reaches the level of the motor's back electromotive force, it is determined that the bus voltage has reached the level of the motor's back electromotive force.

[0128] The method for detecting residual voltage on the busbar of a motor provided by this invention constructs a mathematical model of the back electromotive force (EMF) of the motor and a mathematical model of the initial value of the residual voltage on the busbar. It uses the differential phase angle of the initial value of the back EMF as a parameter for identifying the back EMF, effectively detecting and identifying the back EMF and improving the sensitivity of back EMF identification.

[0129] Example 2

[0130] Figure 2 This is a schematic diagram of the equivalent circuit model of the electric motor in this invention; Figure 2 In this context, u is the motor bus voltage, ω is the power grid frequency, S is the motor slip, and R... r R is the rotor resistance. s R is the stator resistance. m For excitation resistor; L S For stator inductance, L m For the magnetizing inductor, L r For rotor inductance; ω r ω is the rotor angular velocity of the electric motor; when the motor is running normally, ω r =(1-s)ω s ;

[0131] In this application, ω s This refers to the stator voltage frequency of the motor during normal operation. It is the grid frequency and is equal to ω.

[0132] like Figure 3 As shown, based on Embodiment 1, step S10 involves constructing a mathematical model of the motor's back electromotive force and a mathematical model of the initial value of the busbar residual voltage, including:

[0133] S101, Establish the stator flux linkage equation, rotor winding flux linkage equation, and stator current mathematical model of the electric motor: specifically including:

[0134] S1011, The vector expression of the initial voltage of the motor during normal operation in space is established as follows:

[0135]

[0136] When the motor is running stably, the relationship between the stator flux linkage and the bus voltage is as follows:

[0137]

[0138] S1012, Construct the flux linkage equations of the rotor and stator of the electric motor in the dq rotating coordinate system:

[0139] The flux linkage equation of the rotor is:

[0140]

[0141] The flux linkage equation of the stator is:

[0142]

[0143] Where: ψ dr ψ qr ψ represents the components of the stator flux linkage along the d-axis and q-axis, respectively. ds ψ qs These are the components of the rotor flux linkage on the d-axis and q-axis, respectively; σ is the leakage flux coefficient, and its value is: σ = 1 - L m 2 / L r L s i ds i qs These are the components of the stator current on the d-axis and q-axis, respectively; u ds u qs These are the components of the stator voltage along the d-axis and q-axis, respectively;

[0144] S1013, establish the voltage equations for the stator and rotor as follows:

[0145]

[0146] Where: u dr u qr These represent the components of the rotor voltage along the d-axis and q-axis, respectively; i dr andi qr These are the components of the rotor current on the d-axis and q-axis;

[0147] S1014, based on the rotor flux linkage equation, the stator flux linkage equation, the stator voltage equation, and the rotor voltage equation, the steady-state flux linkage equation of the rotor during normal motor operation is obtained as follows:

[0148]

[0149] Generally, when a motor is running normally, if a sudden power outage occurs, the stator current will suddenly drop to zero. However, the magnetic field generated by the stator current will not drop to zero instantaneously. Since the magnetic flux of the stator winding cannot change abruptly, a DC current component is induced in the stator winding and decays in the stator winding. Therefore, its decay time constant is related to the stator winding parameters.

[0150] Due to the disappearance of the stator current, the magnetic flux linkage within the motor is conserved, resulting in an instantaneous induced current in the rotor windings. This current counteracts the change in magnetic flux caused by the sudden disappearance of the stator current, preventing abrupt changes in magnetic flux. The magnetic field generated by the rotor winding current is relatively stationary with respect to the rotor. Due to the rotor's inertial motion, this magnetic field cuts through the stator windings at a rate of ω. r As the rotor rotates at a certain speed (the rotor speed), this current decays according to the rotor winding time constant and is a slowly changing current component.

[0151] Therefore, when the external power supply suddenly disappears, the magnetic flux of the motor consists of three parts:

[0152] One part is the magnetic flux generated by the DC current component induced by the change in the magnetic field of the stator winding;

[0153] The second part is the magnetic flux induced by the conservation of magnetic flux in the stator winding; it is the magnetic flux generated by the magnetic field of the induced current in the rotor winding cutting the stator.

[0154] The third part is that the initial magnetic flux in the stator winding will not change abruptly, and the stator winding will still be interleaved.

[0155] Therefore, based on the above theory, we can conclude that:

[0156] S1015, when the voltage starts to drop, the stator flux linkage equation of the motor is:

[0157]

[0158] In equation (10), the coefficient K s1 K s2 K s3 T s '、T r The expression for ' is:

[0159]

[0160] T s '=(L s -L m 2 / L r ) / R sEquation (10-2)

[0161] T r '=(L r -L m 2 / L s ) / R r Equation (10-3)

[0162] S1016, Establish the flux linkage equation of the rotor winding during voltage dip:

[0163]

[0164] In equation (11), the coefficient K r1 K r2 K r3 The expression is:

[0165]

[0166] S1017, the formula for calculating the stator current during voltage dips is:

[0167]

[0168] Where: M m The mutual inductance between the stator and rotor windings of the electric motor; ψ s0 ψ r0 This represents the initial values ​​of the stator and rotor circuit flux linkages, i.e., the flux linkages of the stator and rotor windings during steady-state operation of the motor.

[0169] In this embodiment, the initial value of the back electromotive force is calculated using the current in equation (12):

[0170] When the stator current drops to zero, the back electromotive force takes an initial value. Therefore, the zero-crossing time of the stator current can be obtained through the expression of the stator current, the initial value of the flux linkage can be obtained through the zero-crossing time, and the initial value of the voltage, i.e. the initial value of the back electromotive force, can be obtained according to the flux linkage equation.

[0171] S1018, the time when the stator crosses zero is denoted as: t = t m And establish the equation:

[0172]

[0173] Solving equation (13) yields the stator flux linkage at the moment the motor loses power, which is:

[0174]

[0175] The equations for solving parameters s1, s2, and s3 are as follows:

[0176]

[0177] T r =L r / R r

[0178] S1019, based on the flux linkage equation and the voltage equation, the initial value of the voltage is obtained as follows in spatial vector coordinates:

[0179]

[0180] Equation (15) is the mathematical model for the initial value of the busbar residual pressure.

[0181] In this embodiment, a mathematical model for the initial value of the busbar residual voltage is established by deriving the initial value of the back electromotive force. This model can be analyzed in two parts.

[0182] According to equation (15), the expressions for the magnitude and phase angle of the initial value of the busbar residual voltage are:

[0183]

[0184]

[0185] Wherein: T r =L r / R r In the above expression, u s (t) represents the initial value of the busbar residual voltage; U s (t) represents the magnitude of the initial value of the busbar residual load, θ us (t) is the phase angle of the initial value of the busbar residual voltage, ψ s0 Let t be the initial value of the stator winding flux linkage, and t be time.

[0186] like Figure 3 As shown, the variation law of the reaction electromotive force is as follows: with the rotor angular frequency ω r As the time constant T of the rotor gradually decreases, the amplitude of the back electromotive force also gradually decreases; simultaneously, as the time constant T of the rotor decreases... r It exhibits an exponential decay; the phase angle decreases gradually as the rotor angular frequency decreases.

[0187] Therefore, according to equation (15-2), the variation law of the phase angle in space is as follows:

[0188]

[0189] Then, the expression for the relationship between the differential component of the bus voltage spatial phase angle with respect to time and the rotor angular velocity is:

[0190]

[0191] in: ω is the differential component of the spatial phase angle of the bus voltage with respect to time. r This represents the rotor angular velocity of the electric motor.

[0192] As can be seen from equation (1), the differential component of the phase angle of the back electromotive force is the rotor angular velocity after the motor loses power. Therefore, the back electromotive force can be identified by detecting the change of this characteristic quantity.

[0193] By detecting the rotor's angular velocity, it is converted into rotational speed, because:

[0194]

[0195] ω=2πf

[0196] Where: n is the rotational speed, f is the frequency, and p is the number of pole pairs of the motor;

[0197] Therefore, we can conclude that:

[0198] Based on the above theory, the relationship between the motor speed and the motor rotor angular velocity can be established as follows:

[0199]

[0200] Generally, when the motor is running stably, ω r If the speed remains constant, the motor speed is: n s =(1-s)n N ; where n N s is the rotational speed of the magnetic field generated by the stator of the motor at the rated frequency, and s is the slip, which is usually between 0.02 and 0.05. Therefore, the rotational speed of the motor is slightly lower than the magnetic field speed, generally (0.95 to 0.97)n. N between.

[0201] When the external power to the motor is suddenly lost, the motor speed begins to decrease. At the initial moment, due to the inertia of the rotor's high-speed motion, the rotor speed is still very high, resulting in a large back electromotive force that is fed back to the busbar, causing the busbar to have a high residual voltage. Based on the phase angle of the detected busbar residual voltage, the change in back electromotive force is reflected by the infinitesimal change in the phase angle at the initial moment.

[0202] Typically, at the initial moment, the motor speed remains constant due to inertia. Therefore, at the initial moment, the differential detection quantity of the phase angle is the initial rotor speed, i.e., (0.95~0.97)n. N However, considering the impact of acquisition errors and the resistance consumption of the motor, therefore, n should be appropriately adjusted. s Adjustments are made by increasing the empirical error Δn based on operational experience. Therefore, the concept of a speed detection setpoint is introduced, whereby the differential component of the phase angle is set to n. s -Δn;

[0203] The expression relating the speed detection setpoint to the motor speed is:

[0204] n set =n s -Δn Equation (3)

[0205] Where: n set The rotational speed detection setpoint is Δn, which is the empirical error.

[0206] Therefore, the identification of the reaction potential is represented as: real-time acquisition of the rotor speed n of the motor. r and n r With n set Comparison, when n r ≤n set When the bus voltage reaches the level of the motor's back electromotive force, it is determined that the bus voltage has reached the level of the motor's back electromotive force.

[0207] That is: when the motor is running normally, n r =n set When the motor loses power, its speed begins to decrease; therefore, n r ≤n set .

[0208] In addition, the present invention also provides a method for motor undervoltage protection based on busbar residual voltage detection.

[0209] The main function of motor undervoltage protection is to enable the motor to start automatically or cut off automatically when the voltage disappears for a short time or the voltage drops due to a short circuit in the power grid, so as to protect the load and production process from loss. Undervoltage protection is usually achieved by low voltage protection that trips. Therefore, the low voltage setting value is set differently according to the operating requirements of the motor.

[0210] When a motor loses power, if it is allowed to start automatically, the back electromotive force (EMF) generates a large residual voltage on the bus, allowing for a rapid power switch and automatic restart. However, when the motor is not allowed to start automatically, the presence of the back EMF poses a potential hazard, especially affecting the stable operation of the power grid. If the back EMF is very high, the resulting residual voltage on the bus will be large. If it does not reach the setting value of the undervoltage protection, the bus voltage will be fed back to the high-voltage side through the transformer in the substation, affecting the operation of the automatic grid devices and even causing malfunctions in the protection system, leading to a power outage within the substation. Therefore, detecting and disconnecting the back EMF of the motor on the user side protects the motor and reduces the harm to the power grid.

[0211] like Figure 4 As shown, the motor undervoltage protection method based on busbar residual voltage detection includes the following steps:

[0212] A10 monitors the bus voltage and extracts the bus voltage phase angle;

[0213] A20, Calculate the differential component of the bus voltage spatial phase angle with respect to time.

[0214] A30, Calculate the motor speed.

[0215] A40, determine if the back electromotive force has been reached. If so, proceed to step A50; otherwise, proceed to step A60.

[0216] A50 issues an action signal based on the undervoltage protection setting value and time limit value;

[0217] A60, locked.

[0218] This invention proposes a motor undervoltage protection method based on busbar residual voltage detection. It proposes an undervoltage protection method based on the detection of the phase angle of the initial value of the busbar residual voltage, which achieves effective isolation of back electromotive force and reduces the harm to users and the power grid.

[0219] Specifically, the determination of whether a back electromotive force has been reached is as follows:

[0220] The rotor speed n of the motor is collected in real time. r With the speed detection set value n set Comparison, when n r ≤n set When the bus voltage reaches the point where the back electromotive force of the motor is at that point, it is determined that the bus voltage has reached the point where the back electromotive force of the motor ... is at that point.

[0221] The n set =n s -Δn;

[0222] The n s Let Δn be the motor speed when the motor is running normally, and Δn be the empirical error.

[0223] Further, step A50 includes: issuing an action signal based on the undervoltage protection setting value and the time limit value, specifically including:

[0224] A501, determine if |U res |≤U op If satisfied, output the time limit value t. op ;

[0225] The U op The setting value for undervoltage protection based on busbar residual voltage detection is expressed as follows:

[0226]

[0227] Among them: UN.min k is the minimum allowable voltage for normal operation of the motor. r k is the return coefficient of the relay. rel The reliability coefficient;

[0228] A502, obtain the setting value U of traditional undervoltage protection. op.1 and time limit t op.1 ;

[0229] A503, determine whether the time limit value t is met. op.1 Or time limit value t op If one of these conditions is met, an action signal is issued.

[0230] Furthermore, in step A50, the time limit value t op.1 And the time limit value is t op The relationship between them is:

[0231] t op =t op.1 +Δt Equation (17)

[0232] Where: Δt is the time margin.

[0233] In this embodiment, a back electromotive force logic criterion is added to the traditional motor undervoltage protection to improve the reliability of detecting and cutting off motor power loss based solely on voltage as a single criterion.

[0234] Traditional undervoltage protection is set according to the condition that a self-starting motor is not allowed to be disconnected, and the voltage is usually:

[0235] U op =0.6~0.7U N ;

[0236] The protection action is set to 0.5s to avoid false tripping caused by instantaneous overcurrent protection and voltage circuit disconnection.

[0237] When the motor is running normally, the allowable voltage range is generally (0.95~1.10)U. N Therefore, upon detecting the back electromotive force, a signal is sent to the low-voltage detection module, which then makes a judgment. Its setpoint is:

[0238]

[0239] Among them: U N.min This is the minimum allowable voltage for normal operation of the motor, typically taken as 0.95U. N ;

[0240] k r This is the return coefficient of the relay, typically taken as 0.85; krel The reliability coefficient is typically set to 1.2; therefore, in this embodiment, U op ≈0.8U N

[0241] The operating time limit should be coordinated with the undervoltage protection:

[0242] t op =t op.1 +Δt

[0243] Where: t op.1 For the undervoltage protection to function, Δt is the time margin, which is generally taken as 0.5s, so the action time limit is taken as 1s.

[0244] like Figure 5 As shown, the implementation process of the action module is as follows:

[0245] First, the voltage U of the motor bus. res The data is collected for ∠θ, including the voltage amplitude |U. res | and phase angle θ(t);

[0246] Secondly, differential calculations are performed on the phase angle. The corresponding rotational speed n is calculated using the coefficient kr. r Compare with the setpoint; if n r ≤n set Then, the differential component of the phase angle detects that the bus voltage has reached the back electromotive force of the motor, and at the same time, the voltage amplitude |U res |≤U op When both conditions are met, the protection will activate.

[0247] Furthermore, in this embodiment, the undervoltage protection based on phase angle differential detection needs to be coordinated with traditional undervoltage protection. When the voltage amplitude |U res |≤U op.1 When the voltage drops, the undervoltage protection will activate. In terms of coordination between the two types of protection, the undervoltage protection has a shorter time limit and a lower threshold value, so it takes priority over the traditional undervoltage protection for judgment and action. Generally, the initial value of the back electromotive force of large-capacity motors is relatively high. If the undervoltage protection cannot clear the circuit, the phase angle micro-component can be detected. If the undervoltage protection cannot judge and clear the circuit, it can be activated to clear the circuit, thus making up for the shortcomings of the traditional undervoltage protection. At the same time, the detection of the phase angle micro-component enables the triggering and blocking of non-back electromotive force signals.

[0248] In summary, this invention adds back EMF identification and detection to the traditional undervoltage protection, which improves the reliability and selectivity of undervoltage protection and ensures the reliable operation of the motor.

[0249] The present invention also provides a storage device storing a plurality of instructions adapted for loading and execution by a processor of the motor bus residual voltage detection method as described above.

[0250] The present invention also provides a terminal, which may include:

[0251] Processor, adapted to implement instructions; and

[0252] A storage device suitable for storing multiple instructions, which are adapted to be loaded and executed by a processor, such as the motor bus residual voltage detection method described by the flower-sprinkling girl.

[0253] The storage device may be a computer-readable storage medium, including ROM, RAM, disk, or optical disk, etc.

[0254] The terminal can be any device capable of implementing the method for detecting residual voltage on the motor busbar. This device can be various terminal equipment, such as desktop computers, laptops, etc., and can be implemented through software and / or hardware.

[0255] In the description of this invention, it should be understood that the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly defined. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0256] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0257] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0258] The algorithms and displays provided herein are not inherently related to any particular computer, virtual system, or other device. Various general-purpose systems can also be used in conjunction with the teachings herein. The required structure for constructing such devices is apparent from the above description. Furthermore, this invention is not directed to any particular programming language. It should be understood that the contents of the invention described herein can be implemented using various programming languages, and the above description of specific languages ​​is for the purpose of disclosing the best mode of implementation of the invention.

[0259] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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 method of detecting a residual voltage of a motor bus, characterized by: The method comprises the following steps: S10, constructing a mathematical model of back electromotive force of the motor and a mathematical model of an initial value of the bus residual voltage; S20, based on the mathematical model of the back electromotive force of the motor and the mathematical model of the initial value of the bus residual voltage, analyzing a variation law of a phase angle of the bus voltage to obtain a relationship expression between a differential quantity of the bus voltage space phase angle with respect to time and a rotor angular velocity, and the relationship expression is specifically: The mathematical model of the initial value of the bus residual voltage is: Equation (15); The mathematical model of the initial value of the bus residual voltage can be analyzed in two parts; according to equation (15), the expression of the amplitude and phase angle of the initial value of the bus residual voltage is: Equation (15-1); Equation (15-2); wherein: ; in the above expressions, is the initial value of the bus residual voltage; is the amplitude of the initial value of the bus residual voltage, is the phase angle of the initial value of the bus residual voltage; is the initial value of the stator winding flux linkage, is the time; is the rotor angular velocity of the motor; is the rotor resistance; is the rotor inductance; The change rule of the back EMF is that the back EMF gradually decreases with the decrease of the angular frequency of the rotor , and the amplitude of the back EMF also gradually decreases; at the same time, the time constant of the rotor exponentially decays; the change rule of the phase angle is that the phase angle gradually decreases with the decrease of the angular frequency of the rotor; therefore, according to formula (15-2), the change rule of the phase angle in space is that Equation (15-3); Then, the relationship expression between the differential of the bus voltage space phase angle with respect to time and the rotor angular velocity is: Equation (1); wherein: is the differential of the bus voltage space phase angle with respect to time; S30, establishing a relationship expression between the motor speed and the motor rotor angular velocity, and the relationship expression is: Equation (2); wherein: to collect the rotor speed of the motor in real time, is a conversion factor; S40, analyzing the motor speed and the rotor speed to obtain a relationship expression between the speed detection setting value and the motor speed during normal operation, and the relationship expression is: Equation (3); wherein: is the rotational speed detection setting value, is the rotational speed of the electric motor when the electric motor is operating normally, is the empirical error quantity; S50, when with comparison, when the bus voltage is determined to be the back electromotive force of the motor.

2. The motor bus voltage residue detection method of claim 1, wherein: In the step S10, the mathematical model of the back electromotive force of the motor and the mathematical model of the initial value of the bus residual voltage are constructed, and the construction comprises: S101, establishing a motor stator flux linkage equation, a rotor winding flux linkage equation and a stator current mathematical model: The motor stator flux linkage equation is: Equation (10); In formula (10), the coefficients , , , , are expressed by the following formulae: Equation (10-1); Equation (10-2); Equation (10-3); The rotor winding flux linkage equation is: Equation (11); In formula (11), the coefficient , , is expressed by Equation (11-1); The stator current mathematical model is: Equation (12); wherein: is the bus voltage vector of the electric motor, is the frequency of the power grid, is the mutual inductance of the stator winding and the rotor winding of the electric motor; is the rotor resistance, is the stator resistance, is the rotor angular velocity of the electric motor; Ls for the stator inductance, Lm for the magnet inductance, Lr for the rotor inductance; , the initial value of the stator and rotor flux linkage, i.e. the stator and rotor winding flux linkage at steady state operation of the motor; S102, calculating the stator flux linkage at the motor power failure moment according to the current zero-crossing time calculated by the stator current equation: Equation (14); Wherein: the solving equation of parameters s1, s2 and s3 is: ； S103, according to the flux linkage equation and the voltage equation at the motor power failure moment, the initial value of the voltage is obtained in the space vector coordinates as: Equation (15); The equation (15) is the mathematical model of the initial value of the bus residual voltage.

3. The motor bus voltage residue detection method of claim 2, wherein: The S101, the motor stator flux linkage equation, the rotor winding flux linkage equation and the stator current mathematical model are established, and specifically comprising: S1011, establishing a vector expression of the initial voltage of the motor during normal operation in space as: ； When the motor is stably operated, the relationship between the stator flux linkage and the bus voltage is: ； S1012, constructing a rotor flux linkage equation and a stator flux linkage equation of the motor in the dq rotating coordinate system: The rotor flux linkage equation is: Equation (5); The stator flux linkage equation is: Equation (6); wherein: , are the components of the stator flux linkage on the d-axis and q-axis, respectively, , are the components of the rotor flux linkage on the d-axis and q-axis, respectively; is the leakage coefficient and has the value: ; , are the components of the stator current on the d-axis and q-axis, respectively; , are the components of the stator voltage on the d-axis and q-axis, respectively. S1013, establishing a stator voltage equation and a rotor voltage equation: Equation (7); Equation (8); wherein: , are the components of the rotor voltage on the d- and q-axes, respectively; and are the components of the rotor current on the d- and q-axes, respectively. S1014, according to the rotor flux linkage equation, the stator flux linkage equation, the stator voltage equation and the rotor voltage equation, obtaining a steady-state rotor flux linkage equation of the motor during normal operation as: Equation (9); S1015, establishing a motor stator flux linkage equation when the voltage begins to drop: Equation (10); S1016, establishing a rotor winding flux linkage equation when the voltage drops: Equation (11); S1017, establishing a calculation expression of the stator current when the voltage drops: Equation (12); S1018, the stator zero crossing time, recorded as: ; and the equation is established: Equation (13); Solving equation (13) can obtain: the stator flux linkage at the motor power failure moment is: Equation (14); S1019, according to the flux linkage equation and the voltage equation, the initial value of the voltage is obtained in the space vector coordinates as: Equation (15).

4. The method for motor loss of voltage protection based on bus residual voltage detection, characterized in that: The method comprises the following steps: A10, monitoring the bus voltage and extracting the bus voltage phase angle; A20, the differential of the bus voltage space phase angle with respect to time ; A30, calculating the rotational speed of the electric motor ; A40, judging whether the back electromotive force reaches, if yes, executing step A50, otherwise, executing step A60; A50, according to the loss of pressure protection setting value and time limit value, sends out an action signal; A60, locking; In the A40, it is judged whether the counter electromotive force arrives, specifically: First, the voltage quantity of the motor bus is acquired The acquisition part includes the voltage amplitude part and the phase angle ; Secondly, differential calculations are performed on the phase angle. Through coefficients Calculate the rotor speed of the motor ; The rotor rotational speed of the motor is collected in real time The rotational speed detection setting value is compared, and if , the differential of the phase angle detects that the bus voltage reaches the back electromotive force of the motor wherein , ; The ; the is the rotational speed of the electric motor when the electric motor is operating normally, is the empirical error quantity; In the A50, according to the loss of pressure protection setting value and time limit value, sends out an action signal, specifically including: A501, judges whether or not If satisfied, outputs the time limit value ; The The voltage loss protection setting value based on bus residual voltage detection is expressed as: Equation (16); wherein: Vmin is the minimum voltage for the proper operation of the electric motor, Kret is the return coefficient of the relay; Kreli is the reliability coefficient; a voltage amplitude part of a motor bus; AS502, acquires the setting value of the conventional loss of voltage protection and the time limit value ; A503, determines whether the time limit value is satisfied or the time limit value If one of them is satisfied, the action signal is issued.

5. The bus voltage residual detection based motor loss of voltage protection method according to claim 4, characterized in that: In the step A50, the time limit value and the time limit value is the relationship is: Equation (17); wherein: is the time limit margin.

6. A storage device having stored therein a plurality of instructions, the method comprising: The instructions are adapted to be loaded and executed by the processor to implement the motor bus residual voltage detection method according to any one of claims 1 to 3.

7. A terminal, characterized by: Including: The processor is adapted to implement the instructions; And The storage device is adapted to store a plurality of instructions, and the instructions are adapted to be loaded and executed by the processor to implement the motor bus residual voltage detection method according to any one of claims 1 to 3.

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