Method and system for determining short-circuit fault protection strategy of permanent magnet motor considering load characteristics

Abstract

The present invention provides a method and system for determining a short-circuit fault protection strategy for a permanent magnet motor considering load characteristics. The method includes constructing a finite element model of the permanent magnet motor; determining the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit; determining the short-circuit peak current ratio of the finite element model under the potential constant torque load as the first short-circuit peak current ratio; determining the short-circuit peak current ratio of the finite element model under the counteractive constant torque load as the second short-circuit peak current ratio; and determining the short-circuit fault protection strategy of the permanent magnet motor in different load torque and inertia intervals according to the first short-circuit peak current ratio and the second short-circuit peak current ratio. The present invention considers the influence of load characteristics on short-circuit current, obtains the variation characteristics of single-phase short circuit and three-phase short circuit of the permanent magnet motor under different load characteristics, and selects the protection strategy according to the ratio of peak current and short-circuit characteristics, avoiding the situation of misselecting the protection strategy.

Description

Technical Field

[0001] The present invention belongs to the technical field of motor fault diagnosis, and particularly relates to a method and system for determining a short - circuit fault protection strategy for a permanent - magnet motor considering load characteristics. Background Art

[0002] Permanent - magnet motors are widely used in various industrial fields due to their high efficiency and high torque density. The application of permanent - magnet materials brings the risk of irreversible demagnetization to permanent - magnet motors, which may lead to a decline in motor performance. To achieve the output torque before demagnetization, the motor requires a larger winding current, which may cause the winding temperature to rise and damage the insulation.

[0003] During the operation of a permanent - magnet motor, irreversible demagnetization may occur for various reasons. Among them, the short - circuit fault caused by the drive is a major reason. It will generate a short - circuit current much larger than the rated current, thus generating a huge magnetic field and causing demagnetization of the permanent magnet. The short - circuit fault caused by the drive means that when a switch of the inverter short - circuits, the remaining switches receive control signals normally. For the short - circuit fault caused by the drive, forced transition to single - phase short - circuit and three - phase short - circuit are two commonly used short - circuit protection strategies. The traditional protection strategy preferentially selects three - phase short - circuit because the peak current of single - phase short - circuit is greater than that of three - phase short - circuit at a constant speed, which will cause more serious demagnetization.

[0004] However, the above conclusion is based on the assumption of infinite inertia. In practical applications, the rotor speed usually cannot remain constant, and load characteristics including load torque and inertia will affect the short - circuit current. If the traditional protection strategy determination method is still used, that is, only comparing the peak currents of single - phase short - circuit and three - phase short - circuit at a constant speed, the wrong protection strategy may be selected, leading to serious demagnetization of the permanent magnet. Summary of the Invention

[0005] The present invention provides a method and system for determining a short - circuit fault protection strategy for a permanent - magnet motor considering load characteristics to solve the problem that if only comparing the peak currents of single - phase short - circuit and three - phase short - circuit at a constant speed, the wrong protection strategy may be selected, leading to serious demagnetization of the permanent magnet.

[0006] In a first aspect, the present invention provides a method for determining a short - circuit fault protection strategy for a permanent - magnet motor considering load characteristics, including:

[0007] Performing finite - element simulation modeling on the permanent - magnet motor to obtain a finite - element model of the permanent - magnet motor; wherein, the load torque and inertia considering load characteristics are used as variables of the finite - element model;

[0008] Obtaining a first load - torque interval and a first inertia interval of the finite - element model;

[0009] Determine the critical torque of the finite element model considering the constant potential torque load under single-phase short circuit according to the first load torque interval and the three-phase short circuit critical torque of the finite element model;

[0010] Determine the short-circuit peak current ratio of the finite element model under the constant potential torque load according to the critical torque of the finite element model considering the constant potential torque load under single-phase short circuit, so as to be used as the first short-circuit peak current ratio;

[0011] Determine the short-circuit peak current ratio of the finite element model under the constant reverse torque load, so as to be used as the second short-circuit peak current ratio;

[0012] Determine the short-circuit fault protection strategy of the permanent magnet motor under different load torque and inertia intervals according to the first short-circuit peak current ratio and the second short-circuit peak current ratio.

[0013] Optionally, the determining the critical torque of the finite element model considering the constant potential torque load under single-phase short circuit according to the first load torque interval and the three-phase short circuit critical torque of the finite element model includes:

[0014] Calculate the three-phase short circuit critical torque T of the finite element model according to the following formula 3PSC :

[0015]

[0016] where p is the number of pole pairs of the permanent magnet motor; ψ f is the permanent magnet flux linkage; L d is the d-axis inductance;

[0017] Replace the maximum value in the first load torque interval with the three-phase short circuit critical torque of the finite element model to obtain the second load torque interval;

[0018] Use the average value of the maximum and minimum values in the current load torque interval as the load torque of the finite element model, and judge whether the speed of the finite element model is stable;

[0019] If it is not stable, replace the maximum value in the current load torque interval with the average value of the maximum and minimum values in the current load torque interval to obtain a new load torque interval;

[0020] If it is stable, replace the minimum value in the current load torque interval with the average value of the maximum and minimum values in the current load torque interval to obtain a new load torque interval;

[0021] Judge whether the difference between the maximum and minimum values in the new load torque interval is greater than the preset difference;

[0022] If it is greater than the preset difference, return to execute the operation of "using the average value of the maximum and minimum values in the current load torque interval as the load torque of the finite element model, and determining whether the rotational speed of the finite element model is stable".

[0023] If it is not greater than the preset difference, use the average value of the maximum and minimum values in the new load torque interval as the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit.

[0024] Optionally, the determining the short-circuit peak current ratio of the finite element model under the potential constant torque load based on the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit to be used as the first short-circuit peak current ratio includes:

[0025] Divide the load torque interval [0, T SPSC into multiple equal-spaced load torque sub-intervals; T SPSC is the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit;

[0026] Divide the first inertia interval into multiple equal-spaced inertia sub-intervals;

[0027] Use the average value of the maximum and minimum values in the target load torque sub-interval as the load torque of the finite element model to be used as the first load torque;

[0028] Calculate the single-phase short-circuit peak current I under the target load torque sub-interval and the target inertia sub-interval according to the following formula SPSC_max1 :

[0029]

[0030] where, x 1 is the minimum value in the target load torque sub-interval; y 1 is the maximum value in the target load torque sub-interval; x 2 is the minimum value in the target inertia sub-interval; y 2 is the maximum value in the target inertia sub-interval; represents the single-phase short-circuit peak current corresponding to the load torque being the first load torque and the inertia being x 2 ; represents the single-phase short-circuit peak current corresponding to the load torque being the first load torque and the inertia being y 2 ;

[0031] Calculate the three-phase short-circuit peak current I under the target load torque sub-interval and the target inertia sub-interval according to the following formula 3PSC_max1 :

[0032]

[0033] Among them, represents the three-phase short-circuit peak current corresponding to the first load torque and the inertia of x 2 when; represents the three-phase short-circuit peak current corresponding to the first load torque and the inertia of y 2 when;

[0034] Take as the short-circuit peak current ratio of the finite element model under the potential constant torque load.

[0035] Optionally, the determination of the short-circuit peak current ratio of the finite element model under the counteractive constant torque load as the second short-circuit peak current ratio includes:

[0036] Equally divide the first load torque interval into multiple load torque sub-intervals;

[0037] Equally divide the first inertia interval into multiple inertia sub-intervals;

[0038] Take the average of the maximum and minimum values in the target load torque sub-interval as the load torque of the finite element model as the second load torque;

[0039] Calculate the single-phase short-circuit peak current I totalmax -nT, J totalmax -(n - 1)T] under the target load torque sub-interval and the inertia sub-interval [J SPSC_max2 :

[0040]

[0041] where J totalmax is the maximum inertia; T is the interval length of a single inertia sub-interval; n = 1, 2, 3,..., N; the initial value of n is 1; N is the total number of inertia sub-intervals; x 3 is the minimum value in the target load torque sub-interval; y 3 is the maximum value in the target load torque sub-interval; x 4 is the minimum value in the interval [J totalmax -nT, J totalmax -(n - 1)T]; y 4 is the maximum value in the interval [J totalmax -nT, J totalmax -(n - 1)T]; represents the single-phase short-circuit peak current corresponding to the second load torque and the inertia of x 4 when; represents the single-phase short-circuit peak current corresponding to the second load torque and the inertia of y 4 when;

[0042] Calculate the target load torque sub - interval and inertia sub - interval [J totalmax -nT, J totalmax -(n - 1)T] of the three - phase short - circuit peak current I 3PSC_max2 :

[0043]

[0044] wherein, represents the three - phase short - circuit peak current corresponding to when the load torque is the second load torque and the inertia is x 4 ; represents the three - phase short - circuit peak current corresponding to when the load torque is the second load torque and the inertia is y 4 ;

[0045] Take as the short - circuit peak current ratio of the finite - element model under the counter - electromotive force constant - torque load. Among them, when stop calculating the short - circuit peak current ratio of the remaining inertia sub - intervals within the target load torque sub - interval.

[0046] Optionally, the determining the short - circuit fault protection strategy of the permanent - magnet motor under different load torques and inertia intervals according to the first short - circuit peak current ratio and the second short - circuit peak current ratio includes:

[0047] When considering the potential - energy constant - torque load, when the load torque of the finite - element model is greater than the single - phase short - circuit critical torque, determine to transition to three - phase short - circuit; when the load torque of the finite - element model is less than or equal to the single - phase short - circuit critical torque and the short - circuit peak current ratio within the corresponding load torque interval and inertia interval is less than 1, determine to transition to single - phase short - circuit; when the load torque of the finite - element model is less than or equal to the single - phase short - circuit critical torque and the short - circuit peak current ratio within the corresponding load torque interval and inertia interval is greater than or equal to 1, determine to transition to three - phase short - circuit;

[0048] When considering the counter - electromotive force constant - torque load, when the short - circuit peak current ratio within the corresponding load torque interval and inertia interval is less than 1, determine to transition to single - phase short - circuit; when the short - circuit peak current ratio within the corresponding load torque interval and inertia interval is greater than or equal to 1, determine to transition to three - phase short - circuit; among them, the inertia interval that does not need to be calculated is determined to transition to single - phase short - circuit.

[0049] In a second aspect, the present invention provides a system for determining a short - circuit fault protection strategy of a permanent - magnet motor considering load characteristics, including:

[0050] A modeling module for performing finite - element simulation modeling on the permanent - magnet motor to obtain a finite - element model of the permanent - magnet motor; wherein, the load torque and inertia considering load characteristics are used as variables of the finite - element model;

[0051] An acquisition module, configured to acquire a first load torque interval and a first inertia interval of a finite element model;

[0052] A first determination module, configured to determine a critical torque of the finite element model under single-phase short circuit considering a potential constant torque load according to the first load torque interval and the three-phase short circuit critical torque of the finite element model;

[0053] A second determination module, configured to determine a short-circuit peak current ratio of the finite element model under a potential constant torque load based on the critical torque of the finite element model under single-phase short circuit considering a potential constant torque load, so as to be used as a first short-circuit peak current ratio;

[0054] A third determination module, configured to determine a short-circuit peak current ratio of the finite element model under a counteractive constant torque load, so as to be used as a second short-circuit peak current ratio;

[0055] A fourth determination module, configured to determine a short-circuit fault protection strategy of the permanent magnet motor under different load torque and inertia intervals according to the first short-circuit peak current ratio and the second short-circuit peak current ratio.

[0056] Optionally, the first determination module includes:

[0057] A first calculation unit, configured to calculate the three-phase short circuit critical torque T of the finite element model according to the following formula 3PSC :

[0058]

[0059] where p is the number of pole pairs of the permanent magnet motor; ψ f is the permanent magnet flux linkage; L d is the d-axis inductance;

[0060] A first replacement unit, configured to replace the maximum value in the first load torque interval with the three-phase short circuit critical torque of the finite element model to obtain a second load torque interval;

[0061] A first judgment unit, configured to use the average value of the maximum value and the minimum value in the current load torque interval as the load torque of the finite element model to judge whether the speed of the finite element model is stable;

[0062] A second replacement unit, configured to, when the first judgment unit determines that the speed of the finite element model is unstable, replace the maximum value in the current load torque interval with the average value of the maximum value and the minimum value in the current load torque interval to obtain a new load torque interval;

[0063] A third replacement unit, configured to, when the first determination unit determines that the rotational speed of the finite element model is stable, replace the minimum value in the current load torque range with the average value of the maximum value and the minimum value in the current load torque range, so as to obtain a new load torque range;

[0064] A second determination unit, configured to determine whether the difference between the maximum value and the minimum value in the new load torque range is greater than a preset difference;

[0065] A first determination unit, configured to, when the second determination unit determines that the difference between the maximum value and the minimum value in the new load torque range is greater than the preset difference, determine to return to execute the operation of the first determination unit;

[0066] A second determination unit, configured to, when the second determination unit determines that the difference between the maximum value and the minimum value in the new load torque range is not greater than the preset difference, determine to use the average value of the maximum value and the minimum value in the new load torque range as the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit.

[0067] Optionally, the second determination module includes:

[0068] A first division unit, configured to equally divide the load torque range [0, T SPSC into a plurality of load torque sub-ranges at equal intervals; T SPSC is the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit;

[0069] A second division unit, configured to equally divide the first inertia range into a plurality of inertia sub-ranges at equal intervals;

[0070] A third determination unit, configured to use the average value of the maximum value and the minimum value in the target load torque sub-range as the load torque of the finite element model, so as to be used as the first load torque;

[0071] A second calculation unit, configured to calculate the single-phase short-circuit peak current I SPSC_max1 under the target load torque sub-range and the target inertia sub-range according to the following formula:

[0072]

[0073] wherein, x 1 is the minimum value in the target load torque sub-range; y 1 is the maximum value in the target load torque sub-range; x 2 is the minimum value in the target inertia sub-range; y 2 is the maximum value in the target inertia sub-range; represents the single-phase short-circuit peak current corresponding to the case where the load torque is the first load torque and the inertia is x 2 ; Indicates that the load torque is the first load torque and the inertia is y 2 The corresponding single-phase short-circuit peak current when

[0074] A third calculation unit for calculating the three-phase short-circuit peak current I under the target load torque sub-interval and the target inertia sub-interval according to the following formula 3PSC_max1 :

[0075]

[0076] Wherein, Indicates that when the load torque is the first load torque and the inertia is x 2 The corresponding three-phase short-circuit peak current when Indicates that when the load torque is the first load torque and the inertia is y 2 The corresponding three-phase short-circuit peak current when

[0077] A fourth determination unit for using As the short-circuit peak current ratio of the finite element model under the potential constant torque load.

[0078] Optionally, the third determination module includes:

[0079] A third division unit for equally spacing the first load torque interval into multiple load torque sub-intervals;

[0080] A fourth division unit for equally spacing the first inertia interval into multiple inertia sub-intervals;

[0081] A fifth determination unit for using the average of the maximum and minimum values in the target load torque sub-interval as the load torque of the finite element model to be the second load torque;

[0082] A fourth calculation unit for calculating the single-phase short-circuit peak current I under the target load torque sub-interval and the inertia sub-interval [J totalmax -nT, J totalmax -(n - 1)T] according to the following formula SPSC_max2 :

[0083]

[0084] Wherein, J totalmax Is the maximum inertia; T is the interval length of a single inertia sub-interval; n = 1, 2, 3,..., N; the initial value of n is 1; N is the total number of inertia sub-intervals; x 3 Is the minimum value in the target load torque sub-interval; y 3 Is the maximum value in the target load torque sub-interval; x 4 Is the interval [J totalmax -nT, J totalmaxThe minimum value in [-(n - 1)T]; y 4 is the interval [J totalmax -nT, J totalmax The maximum value in [-(n - 1)T]; represents the single-phase short-circuit peak current corresponding to the second load torque and the inertia of x 4 when; represents the single-phase short-circuit peak current corresponding to the second load torque and the inertia of y 4 when;

[0085] The fifth calculation unit is used to calculate the target load torque sub-interval and the inertia sub-interval [J totalmax -nT, J totalmax The three-phase short-circuit peak current I under [-(n - 1)T] is as follows: 3PSC_max2 :

[0086]

[0087] where, represents the three-phase short-circuit peak current corresponding to the second load torque and the inertia of x 4 when; represents the three-phase short-circuit peak current corresponding to the second load torque and the inertia of y 4 when;

[0088] The sixth determination unit is used to take as the short-circuit peak current ratio of the finite element model under the counteractive constant torque load. Wherein, when stop calculating the short-circuit peak current ratio of the remaining inertia sub-intervals within the target load torque sub-interval.

[0089] Optionally, the fourth determination module includes:

[0090] The seventh determination unit is used to, when considering the potential constant torque load, determine to transition to three-phase short circuit when the load torque of the finite element model is greater than the single-phase short-circuit critical torque; determine to transition to single-phase short circuit when the load torque of the finite element model is less than or equal to the single-phase short-circuit critical torque and the short-circuit peak current ratio within the corresponding load torque interval and inertia interval is less than 1; determine to transition to three-phase short circuit when the load torque of the finite element model is less than or equal to the single-phase short-circuit critical torque and the short-circuit peak current ratio within the corresponding load torque interval and inertia interval is greater than or equal to 1;

[0091] An eighth determination unit, configured to determine to transition to single-phase short circuit when the ratio of the short-circuit peak current within the corresponding load torque range and inertia range is less than 1 considering a resistive constant-torque load; and determine to transition to three-phase short circuit when the ratio of the short-circuit peak current within the corresponding load torque range and inertia range is greater than or equal to 1; wherein, for the inertia range that does not require calculation, it is determined to transition to single-phase short circuit.

[0092] The present invention provides a method and system for determining a short-circuit fault protection strategy for a permanent magnet motor considering load characteristics. The method takes into account the influence of load characteristics on short-circuit current, obtains the variation characteristics of single-phase short circuit and three-phase short circuit of the permanent magnet motor under different load characteristics, eliminates unnecessary calculations, saves calculation time, and selects a protection strategy based on the ratio of peak current and short-circuit characteristics, avoiding the situation of misselecting a protection strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0094] Figure 1 It is a schematic flowchart of a method for determining a short-circuit fault protection strategy for a permanent magnet motor considering load characteristics provided by an embodiment of the present invention;

[0095] Figure 2 It is a comparison diagram of single-phase short-circuit and three-phase short-circuit currents at a rotational speed of 500 rpm provided by an embodiment of the present invention;

[0096] Figure 3 It is a comparison diagram of single-phase short-circuit and three-phase short-circuit currents at a rotational speed of 5000 rpm provided by an embodiment of the present invention;

[0097] Figure 4 It is a torque-speed curve diagram of a potential constant-torque load provided by an embodiment of the present invention;

[0098] Figure 5 It is a torque-speed curve diagram of a resistive constant-torque load provided by an embodiment of the present invention;

[0099] Figure 6 It is a schematic diagram of a finite element model of a permanent magnet motor provided by an embodiment of the present invention;

[0100] Figure 7 It is a schematic diagram of a single-phase short-circuit circuit structure of a permanent magnet motor provided by an embodiment of the present invention;

[0101] Figure 8Schematic diagram of the three-phase short-circuit circuit structure of the permanent magnet motor provided by the embodiment of the present invention;

[0102] Figure 9 Schematic diagram of the loss of steady state of the rotational speed provided by the embodiment of the present invention;

[0103] Figure 10 Schematic diagram of the rotational speed in a steady state provided by the embodiment of the present invention;

[0104] Figure 11 Schematic diagram of the structure of a system for determining a short-circuit fault protection strategy for a permanent magnet motor considering load characteristics provided by the embodiment of the present invention. Detailed implementation manners

[0105] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0106] As Figure 2 shown, a short circuit of a permanent magnet motor occurs when the rotor speed is 500 rpm. At this time, the peak current of single-phase short circuit is 28.44 A, the peak current of three-phase short circuit is 25.86 A, and the difference between the peak current of single-phase short circuit and the peak current of three-phase short circuit is 2.58 A. This difference will be larger at high speeds. As Figure 3 shown, when the rotor speed is 5000 rpm, the peak current of single-phase short circuit is 51.42 A, the peak current of three-phase short circuit is 25.86 A, the difference between the peak current of single-phase short circuit and the peak current of three-phase short circuit is 36.42 A, the difference between the peak current of single-phase short circuit and the peak current of three-phase short circuit is 25.56 A, and the peak current of single-phase short circuit is almost twice that of the peak current of three-phase short circuit, which will cause much more serious demagnetization than three-phase short circuit. Therefore, the existing technical solution selects to forcibly transition to three-phase short circuit as the protection strategy for short-circuit faults caused by driving, which can effectively reduce the demagnetization risk.

[0107] However, the protection method proposed by this existing technical solution is determined at a constant rotational speed, based on the assumption of infinite inertia, which actually does not exist. In practical applications, the current distortion during the short-circuit process causes the electromagnetic torque distortion, which often causes the rotational speed of the permanent magnet motor to change, and the change in rotational speed will in turn affect the short-circuit current. At this time, the short-circuit current is very different from the short-circuit current at a constant rotational speed. In this case, the rotational speed and current of the motor during the short-circuit process largely depend on the load characteristics. The common load types of permanent magnet synchronous motors are potential constant-torque loads and counteractive constant-torque loads, and their torque-speed curves are respectively as Figure 4 andFigure 5 as shown

[0108] The torque of the potential constant torque load remains constant at different motor speeds. Generally, the potential constant torque load is generated by gravity. For example, an elevator is a typical potential constant torque load. For the counteractive constant torque load, the amplitude of its load torque remains unchanged, but the direction changes with the change of the motor speed direction, and it usually appears in applications such as gears, couplings, and brakes.

[0109] Therefore, to solve the above problems, the present invention considers the influence of load characteristics on the short-circuit current, obtains the variation characteristics of single-phase short-circuit and three-phase short-circuit of the permanent magnet motor under different load characteristics, omits unnecessary calculations, saves calculation time, and selects a protection strategy according to the ratio of the peak current and the short-circuit characteristics, avoiding the situation of misselecting the protection strategy.

[0110] Embodiment 1

[0111] As Figure 1 shown, this embodiment provides a method for determining a short-circuit fault protection strategy for a permanent magnet motor considering load characteristics, including:

[0112] Step S1, perform finite element simulation modeling on the permanent magnet motor to obtain a finite element model of the permanent magnet motor; wherein, the load torque and inertia considering load characteristics are used as variables of the finite element model.

[0113] As Figure 6 shown, use finite element simulation software to model the permanent magnet motor.

[0114] Step S2, obtain the first load torque interval and the first inertia interval of the finite element model.

[0115] In this embodiment, the minimum value of the first load torque interval is 0. Exemplarily, the first load torque interval is [0 Nm, 10 Nm]; the minimum value of the first inertia interval is J r , and the maximum value is 40J r , where J r is the rotor inertia. The maximum value of the first load torque interval is the maximum load torque that ensures that the angular acceleration of the permanent magnet motor does not exceed the threshold. Among them, the threshold of the angular acceleration is a safety value that the permanent magnet motor cannot exceed in commercial applications. For example, the angular acceleration of a permanent magnet motor used in precision control applications such as robots and numerical control machine tools generally does not exceed 10000 rad / s2, the angular acceleration of a permanent magnet motor used to drive equipment with a large load inertia such as conveyor belts and cranes generally does not exceed 5000 rad / s2, and the angular acceleration of a permanent magnet motor used to drive large loads such as wind turbines or electric vehicles generally does not exceed 2000 rad / s2. Determine the maximum load torque according to the motion equation:

[0116] Tmax = α max J totalmax .

[0117] Among them, T max is the maximum load torque; α max is the maximum angular acceleration; J totalmax is the maximum inertia.

[0118] Step S3, determine the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit according to the first load torque interval and the three-phase short circuit critical torque of the finite element model.

[0119] In this step, the bisection method is used to determine the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit.

[0120] Exemplarily, construct a three-phase short circuit equation to obtain the magnitude of the three-phase short circuit critical torque of the finite element model considering the potential constant torque load; the three-phase short circuit equation includes a three-phase short circuit voltage equation and a motion equation; the critical torque refers to the maximum electromagnetic torque that can be generated when the speed of the permanent magnet motor is in a steady state.

[0121] Construct an expression for the three-phase short circuit voltage equation:

[0122]

[0123] Among them, R is the phase resistance; i d is the d-axis current; i q is the q-axis current; L d is the d-axis inductance; L q is the q-axis inductance; Ψ f is the permanent magnet flux linkage; ω is the angular velocity; t is the time; represents the derivative of the d-axis current with respect to time; represents the derivative of the q-axis current with respect to time.

[0124] When the three-phase short circuit is in a steady state, the d-axis current and the q-axis current no longer change, and the voltage equation becomes:

[0125]

[0126] Construct an expression for the motion equation of the motor:

[0127]

[0128] Among them, T em is the electromagnetic torque; p is the number of pole pairs of the permanent magnet motor; T load is the load torque; k is the damping coefficient; J total is the total inertia; represents the derivative of the angular velocity with respect to time.

[0129] To simplify the calculation, assume that the damping coefficient is 0 and the rotational speed remains unchanged when the motor is in a steady state. The motion equation then becomes:

[0130]

[0131] Combining the three-phase short-circuit steady-state voltage equation and the motion equation, the three-phase short-circuit steady-state angular velocity ω is obtained steady :

[0132]

[0133] The condition for the existence of the steady-state angular velocity is that the part under the square root is greater than 0.

[0134] Exemplarily, this step includes:

[0135] S31, calculate the three-phase short-circuit critical torque T of the finite element model according to the following formula 3PSC :

[0136]

[0137] S32, replace the maximum value in the first load torque interval with the three-phase short-circuit critical torque of the finite element model to obtain the second load torque interval.

[0138] S33, use the average value of the maximum and minimum values in the current load torque interval as the load torque of the finite element model, and judge whether the rotational speed of the finite element model is stable; from S32 to S33, the current load torque interval is the second load torque interval.

[0139] S34, if it is unstable, replace the maximum value in the current load torque interval with the average value of the maximum and minimum values in the current load torque interval to obtain a new load torque interval; in S32 to S34, the new load torque interval is the third load torque interval.

[0140] S35, if it is stable, replace the minimum value in the current load torque interval with the average value of the maximum and minimum values in the current load torque interval to obtain a new load torque interval; in S32, S33 and S35, the new load torque interval is the third load torque interval.

[0141] S36, judge whether the difference between the maximum and minimum values in the new load torque interval is greater than the preset difference;

[0142] S37, if it is greater than the preset difference, return to execute the operation of S33; when returning to S33, the new load torque interval is used as the current load torque interval.

[0143] S38. If it is not greater than the preset difference, then take the average of the maximum value and the minimum value in the new load torque range as the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit.

[0144] To make the solutions of S31 - S38 clearer, this embodiment further discloses specific examples:

[0145] Use the bisection method to determine the critical torque of single-phase short circuit. The inertia of the finite element model is set to the maximum value J in the first inertia range totalmax ; In the bisection method, when calculating the rotational speed of the finite element model for the first time, the load torque is set to the average of the maximum value and the minimum value in the second load torque range (the first average value). At this time, if the rotational speed is unstable, then use this average value (the first average value) to replace the maximum value in the second load torque range to form the third load torque range. If the rotational speed is stable, then use this average value (the first average value) to replace the minimum value in the second load torque range to form the third load torque range. Subsequently, calculate the rotational speed of the finite element model again, set the load torque to the average of the maximum value and the minimum value in the third load torque range, observe the rotational speed, and form a new load torque range until the preset conditions are met.

[0146] When considering the potential constant torque load, switch the finite element model to single-phase short circuit operation, and set the inertia to 40J r , and use the bisection method to find the critical torque of the finite element model. The circuit structures of single-phase short circuit and three-phase short circuit are respectively as Figure 7 and Figure 8 shown. Take the finite element model of a 10-pole / 12-slot permanent magnet synchronous motor as shown in Figure 6 shown. First, determine the critical torque of three-phase short circuit as 9 Nm according to the formula. Therefore, the new load torque range is [0 Nm, 9 Nm]. Set the load torque to 4.5 Nm, and the rotational speed is as shown in Figure 9 shown. The rotational speed loses balance. Therefore, replace the maximum value of the load torque range with 4.5 Nm to form a new range [0 Nm, 4.5 Nm]. Then set the load torque to 2.25 Nm, and the rotational speed is as shown in Figure 10 shown. The rotational speed is in a steady state. Therefore, replace the minimum value of the load torque range with 2.25 Nm to form a new range [2.25 Nm, 4.5 Nm]. Then set the load torque to 3.375 Nm, and continue to observe whether the rotational speed is in a steady state, continuously forming new load torque ranges. Repeat this process until the difference between the maximum value and the minimum value of the load torque range is less than or equal to 0.05 Nm. Then take the average of the maximum value and the minimum value of this range. In this embodiment, the critical torque of single-phase short circuit is determined to be 4 Nm.

[0147] Step S4: Determine the short - circuit peak - current ratio of the finite - element model under a potential - energy constant - torque load based on the critical torque of the finite - element model considering a potential - energy constant - torque load under single - phase short - circuit, as the first short - circuit peak - current ratio.

[0148] Exemplarily, this step includes:

[0149] Equally divide the load - torque interval [0, T SPSC into multiple load - torque sub - intervals; T SPSC is the critical torque of the finite - element model considering a potential - energy constant - torque load under single - phase short - circuit.

[0150] Equally divide the first inertia interval into multiple inertia sub - intervals. The larger the number of load - torque sub - intervals and inertia sub - intervals, the more accurate the subsequent calculation of the peak current.

[0151] Take the average of the maximum and minimum values in the target load - torque sub - interval as the load torque of the finite - element model, as the first load torque. At the first load torque, set the inertia of the finite - element model to x 2 , use finite - element software to calculate the single - phase short - circuit peak current of the finite - element model under this condition, and then set the inertia of the finite - element model to y 2 , and calculate the single - phase short - circuit peak current of the finite - element model under this condition.

[0152] Calculate the single - phase short - circuit peak current I in the target load - torque sub - interval and target inertia sub - interval according to the following formula SPSC_max1 :

[0153]

[0154] where, x 1 is the minimum value in the target load - torque sub - interval; y 1 is the maximum value in the target load - torque sub - interval; x 2 is the minimum value in the target inertia sub - interval; y 2 is the maximum value in the target inertia sub - interval; represents the single - phase short - circuit peak current corresponding to a load torque of the first load torque and an inertia of x 2 ; represents the single - phase short - circuit peak current corresponding to a load torque of the first load torque and an inertia of y 2 ;

[0155] Single - phase short - circuit and three - phase short - circuit are set in the finite - element model by modifying the circuit settings; calculate the three - phase short - circuit peak current I in the target load - torque sub - interval and target inertia sub - interval according to the following formula 3PSC_max1 :

[0156]

[0157] Among them, represents the three-phase short-circuit peak current corresponding to the case where the load torque is the first load torque and the inertia is x 2 when. represents the three-phase short-circuit peak current corresponding to the case where the load torque is the first load torque and the inertia is y 2 when.

[0158] Take as the short-circuit peak current ratio of the finite element model under the potential constant torque load.

[0159] To make the solution of this step clearer, this embodiment further discloses a specific example:

[0160] When considering the potential constant torque load, the load torque range is [0 Nm, 4 Nm], and the inertia range is [J r , 40J r . In this embodiment, the load torque is divided into 4 intervals, as shown in Table 1, where T load is the load torque. Optionally, more intervals can be divided according to the accuracy requirements. The finite element model is switched to single-phase short-circuit and three-phase short-circuit operations respectively, and the short-circuit peak current ratios in different load torque and inertia intervals are calculated.

[0161] Table 1 Load torque interval division table considering potential constant torque load

[0162] <![CDATA[0 Nm ≤ T Load <1 Nm]]> <![CDATA[1 Nm ≤ T Load <2 Nm]]> <![CDATA[2 Nm ≤ T Load <3 Nm]]> <![CDATA[3 Nm ≤ T Load ≤ 4 Nm]]>

[0163] In a certain load torque and inertia interval, the load torque is set to the average value of the maximum and minimum values in this interval, and its corresponding relationship is shown in Table 2. Then, the peak currents when the inertia is the maximum and minimum values in the interval are calculated respectively, and their average value is taken.

[0164] Table 2 Corresponding relationship table between load torque interval and load torque setting value considering potential constant torque load

[0165] <![CDATA[0 Nm ≤ T Load <1 Nm]]> <![CDATA[1 Nm ≤ T Load <2 Nm]]> <![CDATA[2 Nm ≤ T Load <3 Nm]]> <![CDATA[3 Nm ≤ T Load ≤ 4 Nm]]> <![CDATA[T Load = 0.5 Nm]]> <![CDATA[T Load = 1.5 Nm]]> <![CDATA[T Load = 2.5 Nm]]> <![CDATA[T Load = 3.5 Nm]]>

[0166] The single-phase short-circuit and three-phase short-circuit peak currents are shown in Table 3 and Table 4 respectively. For example, the second row and the second column in Table 3 correspond to the single-phase short-circuit peak current in the interval 0 Nm ≤ T Load <1 Nm and J r ≤ J total <10J r under, and this peak current is the peak current when the load torque is 0.5 Nm and the total inertia is J r and the peak current when the load torque is 0.5 Nm and the total inertia is 10J rThe average value of the peak current under

[0167] Table 3 Peak current table for single-phase short circuit in different load torque and inertia ranges considering potential constant torque load

[0168]

[0169] Table 4 Peak current table for three-phase short circuit in different load torque and inertia ranges considering potential constant torque load

[0170]

[0171] Finally, calculate the ratio of the peak currents in the corresponding ranges, that is, the ratio of the peak currents of single-phase short circuit and three-phase short circuit, as shown in Table 5.

[0172] Table 5 Ratio table of short-circuit peak currents in different load torque and inertia ranges considering potential constant torque load

[0173]

[0174] Step S5, determine the ratio of the short-circuit peak currents of the finite element model under the counteractive constant torque load as the second short-circuit peak current ratio.

[0175] Exemplarily, this step includes:

[0176] Equally divide the first load torque range into multiple load torque sub-ranges.

[0177] Equally divide the first inertia range into multiple inertia sub-ranges.

[0178] Take the average of the maximum and minimum values in the target load torque sub-range as the load torque of the finite element model as the second load torque.

[0179] Calculate the single-phase short-circuit peak current I in the target load torque sub-range and the inertia sub-range [J totalmax -nT, J totalmax -(n - 1)T] according to the following formula SPSC_max2 :

[0180]

[0181] where J totalmax is the maximum inertia; T is the interval length of a single inertia sub-range; n = 1, 2, 3,..., N; the initial value of n is 1; N represents the total number of inertia sub-ranges (when the interval length of a single inertia sub-range is T); x 3 is the minimum value in the target load torque sub-range; y 3 is the maximum value in the target load torque sub-range; x 4 is the interval [Jtotalmax -nT, J totalmax - (n - 1)T], the minimum value; y 4 is the interval [J totalmax -nT, J totalmax - (n - 1)T]; represents the single - phase short - circuit peak current corresponding to the second load torque and inertia x 4 when; represents the single - phase short - circuit peak current corresponding to the second load torque and inertia y 4 when.

[0182] Calculate the target load torque sub - interval and the three - phase short - circuit peak current I under the inertia sub - interval [J totalmax -nT, J totalmax - (n - 1)T] according to the following formula: 3PSC_max2 :

[0183]

[0184] wherein, represents the three - phase short - circuit peak current corresponding to the second load torque and inertia x 4 when; represents the three - phase short - circuit peak current corresponding to the second load torque and inertia y 4 when;

[0185] Take as the short - circuit peak current ratio of the finite - element model under the counter - electromotive force constant - torque load. Among them, when stop calculating the short - circuit peak current ratio of the remaining inertia sub - intervals within the target load torque sub - interval.

[0186] To make the solution of this step clearer, this embodiment further discloses a specific example:

[0187] Consider the counter - electromotive force constant - torque load and set it in the finite - element model by modifying the motion force condition. The calculation method is to set the load torque of the finite - element model within the corresponding load torque interval [x 3 , y 3 as:

[0188]

[0189] Start calculating from the largest inertia sub - interval. Assume that the length of each inertia sub - interval is T. Then start calculating from the inertia sub - interval [J totalmax -T, J totalmax , that is, first calculate within the load torque interval [x 3 , y 3 and the inertia interval [Jtotalmax -T, J totalmax The short - circuit peak current ratio under [x 3 , y 3 and inertia range [J totalmax -2T, J totalmax -T] is calculated in the same way as the formula and steps in S4, except that the force - motion conditions of the finite - element model are different. If this ratio is less than 1, the peak current ratios of other inertia sub - ranges within this load - torque sub - range do not need to be calculated. If this ratio is greater than or equal to 1, continue to calculate the short - circuit peak current ratios in the load - torque sub - range [x

[0190] Set the load - torque range as [0 Nm, 10 Nm] and the inertia range as [Jr, 40Jr]. Calculate the peak current under different sub - ranges according to the calculation method in step S4. The difference is that in this step, the ratio needs to be calculated first, and within a certain load - torque sub - range, calculate the short - circuit peak current ratio in the corresponding range in the order from the maximum - inertia sub - range to the minimum - inertia sub - range (which can be understood as sorting in descending order according to the maximum value of the sub - range). When the short - circuit peak current ratio is less than 1, stop the calculation, and the ratios of other inertia sub - ranges do not need to be calculated. Then calculate the short - circuit peak current ratios in other load - torque sub - ranges. Within a certain load - torque sub - range and inertia sub - range, the load torque is set as the average value of the maximum and minimum values within this sub - range. The corresponding relationship is shown in Table 6, and the short - circuit peak current ratios in the corresponding ranges are shown in Table 7. Among them, "\ " represents the range that does not need to be calculated.

[0191] Table 6 Corresponding relationship table of torque range and load - torque setting values considering a constant - torque load with counter - electromotive force

[0192]

[0193] Table 7 Short - circuit peak current ratio table in different load - torque and inertia ranges considering a constant - torque load with counter - electromotive force

[0194]

[0195] Step S6: Determine the short - circuit fault protection strategy of the permanent - magnet motor under different load torques and inertia ranges according to the first short - circuit peak current ratio and the second short - circuit peak current ratio.

[0196] When considering the potential energy constant torque load, when the load torque of the finite element model is greater than the single-phase short-circuit critical torque, it is determined to transition to a three-phase short circuit; when the load torque of the finite element model is less than or equal to the single-phase short-circuit critical torque and the ratio of the short-circuit peak current in the corresponding load torque range and inertia range is less than 1, it is determined to transition to a single-phase short circuit; when the load torque of the finite element model is less than or equal to the single-phase short-circuit critical torque and the ratio of the short-circuit peak current in the corresponding load torque range and inertia range is greater than or equal to 1, it is determined to transition to a three-phase short circuit.

[0197] When considering the counteractive constant torque load, when the ratio of the short-circuit peak current in the corresponding load torque range and inertia range is less than 1, it is determined to transition to a single-phase short circuit; when the ratio of the short-circuit peak current in the corresponding load torque range and inertia range is greater than or equal to 1, it is determined to transition to a three-phase short circuit; among them, the inertia range that does not need to be calculated is determined to transition to a single-phase short circuit.

[0198] In summary, the method for determining the short-circuit fault protection strategy of a permanent magnet motor considering load characteristics provided in this embodiment determines a reasonable range of load torque and inertia, meets the needs of the permanent magnet motor in practical applications, and avoids meaningless range calculations; when determining the critical torque under the potential energy constant torque load, the maximum value in the inertia range is selected to calculate the minimum critical torque; the key point for determining the critical torque is to judge whether the speed is stable; under the counteractive constant torque load, in a certain load torque range, the ratio of the peak current is calculated in the order from the maximum inertia range to the minimum inertia range to reduce the calculation amount; under the potential energy constant torque load, when the load torque is greater than the critical torque, directly select to transition to a three-phase short circuit as the protection strategy, and under the counteractive constant torque load, directly select to transition to a single-phase short circuit as the protection strategy for the range that has not been calculated. In addition, in all other cases, the protection strategy is selected to transition to the short circuit with the smaller peak current according to the ratio of the peak current.

[0199] Embodiment 2

[0200] Based on the same inventive concept as Embodiment 1, this embodiment provides a system for determining a short-circuit fault protection strategy of a permanent magnet motor considering load characteristics. Since the principle of this system for solving problems is similar to the method for determining the short-circuit fault protection strategy of a permanent magnet motor considering load characteristics provided in the foregoing Embodiment 1, the implementation of this system can refer to the implementation of the method for determining the short-circuit fault protection strategy of a permanent magnet motor considering load characteristics provided in Embodiment 1.

[0201] As Figure 11 shown, the system for determining a short-circuit fault protection strategy of a permanent magnet motor considering load characteristics includes:

[0202] The modeling module 10 is used to perform finite element simulation modeling on the permanent magnet motor to obtain a finite element model of the permanent magnet motor; among them, the load torque and inertia considering the load characteristics are used as variables of the finite element model.

[0203] The obtaining module 20 is used to obtain the first load torque interval and the first inertia interval of the finite element model.

[0204] The first determination module 30 is used to determine the critical torque of the finite element model under single-phase short circuit considering the potential constant torque load according to the first load torque interval and the three-phase short circuit critical torque of the finite element model.

[0205] The second determination module 40 is used to determine the short-circuit peak current ratio of the finite element model under the potential constant torque load according to the critical torque of the finite element model under single-phase short circuit considering the potential constant torque load, so as to be used as the first short-circuit peak current ratio.

[0206] The third determination module 50 is used to determine the short-circuit peak current ratio of the finite element model under the counteractive constant torque load, so as to be used as the second short-circuit peak current ratio.

[0207] The fourth determination module 60 is used to determine the short-circuit fault protection strategy of the permanent magnet motor under different load torque and inertia intervals according to the first short-circuit peak current ratio and the second short-circuit peak current ratio.

[0208] Exemplarily, the first determination module includes:

[0209] The first calculation unit is used to calculate the three-phase short circuit critical torque T of the finite element model according to the following formula 3PSC :

[0210]

[0211] where p is the number of pole pairs of the permanent magnet motor; ψ f is the permanent magnet flux linkage; L d is the d-axis inductance.

[0212] The first replacement unit is used to replace the maximum value in the first load torque interval with the three-phase short circuit critical torque of the finite element model to obtain a second load torque interval.

[0213] The first judgment unit is used to judge whether the speed of the finite element model is stable by taking the average value of the maximum value and the minimum value in the current load torque interval as the load torque of the finite element model.

[0214] The second replacement unit is used to replace the maximum value in the current load torque interval with the average value of the maximum value and the minimum value in the current load torque interval when the first judgment unit determines that the speed of the finite element model is unstable, so as to obtain a new load torque interval.

[0215] A third replacement unit, configured to, when the first determination unit determines that the rotational speed of the finite element model is stable, replace the minimum value in the current load torque interval with the average value of the maximum value and the minimum value in the current load torque interval, so as to obtain a new load torque interval.

[0216] A second determination unit, configured to determine whether the difference between the maximum value and the minimum value in the new load torque interval is greater than a preset difference.

[0217] A first determination unit, configured to, when the second determination unit determines that the difference between the maximum value and the minimum value in the new load torque interval is greater than the preset difference, determine to return to execute the operation of the first determination unit.

[0218] A second determination unit, configured to, when the second determination unit determines that the difference between the maximum value and the minimum value in the new load torque interval is not greater than the preset difference, determine to use the average value of the maximum value and the minimum value in the new load torque interval as the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit.

[0219] Exemplarily, the second determination module includes:

[0220] A first partitioning unit, configured to equally and spacedly partition the load torque interval [0, T SPSC into a plurality of load torque sub-intervals; T SPSC is the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit.

[0221] A second partitioning unit, configured to equally and spacedly partition the first inertia interval into a plurality of inertia sub-intervals.

[0222] A third determination unit, configured to use the average value of the maximum value and the minimum value in the target load torque sub-interval as the load torque of the finite element model, so as to be used as the first load torque.

[0223] A second calculation unit, configured to calculate the single-phase short circuit peak current I under the target load torque sub-interval and the target inertia sub-interval according to the following formula SPSC_max1 :

[0224]

[0225] wherein, x 1 is the minimum value in the target load torque sub-interval; y 1 is the maximum value in the target load torque sub-interval; x 2 is the minimum value in the target inertia sub-interval; y 2 is the maximum value in the target inertia sub-interval; indicates that the load torque is the first load torque and the inertia is x 2The single-phase short-circuit peak current corresponding thereto; Indicates that the load torque is the first load torque and the inertia is y 2 The single-phase short-circuit peak current corresponding thereto.

[0226] A third calculation unit for calculating the three-phase short-circuit peak current I under the target load torque sub-interval and the target inertia sub-interval according to the following formula 3PSC_max1 :

[0227]

[0228] Wherein, Indicates that when the load torque is the first load torque and the inertia is x 2 The corresponding three-phase short-circuit peak current; Indicates that when the load torque is the first load torque and the inertia is y 2 The corresponding three-phase short-circuit peak current.

[0229] A fourth determination unit for using As the short-circuit peak current ratio of the finite element model under the potential constant torque load.

[0230] Exemplarily, the third determination module includes:

[0231] A third division unit for equally spacing the first load torque interval into a plurality of load torque sub-intervals.

[0232] A fourth division unit for equally spacing the first inertia interval into a plurality of inertia sub-intervals.

[0233] A fifth determination unit for using the average of the maximum value and the minimum value in the target load torque sub-interval as the load torque of the finite element model to be the second load torque.

[0234] A fourth calculation unit for calculating the single-phase short-circuit peak current I under the target load torque sub-interval and the inertia sub-interval [J totalmax -nT, J totalmax -(n - 1)T] according to the following formula SPSC_max2 :

[0235]

[0236] Wherein, J totalmax Is the maximum inertia; T is the interval length of a single inertia sub-interval; n = 1, 2, 3,..., N; the initial value of n is 1; N is the total number of inertia sub-intervals; x 3 Is the minimum value in the target load torque sub-interval; y 3 Is the maximum value in the target load torque sub-interval; x 4 Is the interval [J totalmax-nT, J totalmax The minimum value in [-(n - 1)T]; y 4 is the interval [J totalmax -nT, J totalmax The maximum value in [-(n - 1)T]; Indicates that the load torque is the second load torque and the inertia is x 4 The corresponding single-phase short-circuit peak current when Indicates that the load torque is the second load torque and the inertia is y 4 The corresponding single-phase short-circuit peak current when

[0237] The fifth calculation unit is used to calculate the target load torque sub-interval and the inertia sub-interval [J totalmax -nT, J totalmax The three-phase short-circuit peak current I under [-(n - 1)T] is 3PSC_max2 :

[0238]

[0239] Wherein, Indicates that when the load torque is the second load torque and the inertia is x 4 The corresponding three-phase short-circuit peak current when Indicates that when the load torque is the second load torque and the inertia is y 4 The corresponding three-phase short-circuit peak current when

[0240] The sixth determination unit is used to take As the short-circuit peak current ratio of the finite element model under the counteractive constant torque load. Wherein, when Stop calculating the short-circuit peak current ratio of the remaining inertia sub-intervals within the target load torque sub-interval.

[0241] Exemplarily, the fourth determination module includes:

[0242] The seventh determination unit is used to, when considering the potential constant torque load, determine to transition to three-phase short circuit when the load torque of the finite element model is greater than the single-phase short-circuit critical torque; determine to transition to single-phase short circuit when the load torque of the finite element model is less than or equal to the single-phase short-circuit critical torque and the short-circuit peak current ratio within the corresponding load torque interval and inertia interval is less than 1; determine to transition to three-phase short circuit when the load torque of the finite element model is less than or equal to the single-phase short-circuit critical torque and the short-circuit peak current ratio within the corresponding load torque interval and inertia interval is greater than or equal to 1.

[0243] An eighth determination unit, configured to determine to transition to single-phase short circuit when the ratio of the short-circuit peak current within the corresponding load torque range and inertia range is less than 1 considering a resistive constant-torque load; and determine to transition to three-phase short circuit when the ratio of the short-circuit peak current within the corresponding load torque range and inertia range is greater than or equal to 1; wherein, for the inertia range that does not require calculation, it is determined to transition to single-phase short circuit.

[0244] For the more specific working processes of the above various modules, reference can be made to the corresponding content disclosed in Embodiment 1, and details will not be elaborated here.

[0245] Embodiment 3

[0246] This embodiment provides a computer device, including a processor and a memory; wherein, when the processor executes the computer program stored in the memory, the steps of the method for determining the short-circuit fault protection strategy of a permanent magnet motor considering load characteristics described in Embodiment 1 are implemented.

[0247] For the more specific process of the above method, reference can be made to the corresponding content disclosed in Embodiment 1, and details will not be elaborated here.

[0248] Embodiment 4

[0249] This embodiment provides a computer-readable storage medium for storing a computer program; when the computer program is executed by a processor, the steps of the method for determining the short-circuit fault protection strategy of a permanent magnet motor considering load characteristics described in Embodiment 1 are implemented.

[0250] For the more specific process of the above method, reference can be made to the corresponding content disclosed in Embodiment 1, and details will not be elaborated here.

[0251] Embodiment 5

[0252] This embodiment provides a computer program product, including computer-executable instructions or a computer program. When the computer-executable instructions or the computer program are executed by a processor, the steps of the method for determining the short-circuit fault protection strategy of a permanent magnet motor considering load characteristics described in Embodiment 1 are implemented.

[0253] For the more specific process of the above method, reference can be made to the corresponding content disclosed in Embodiment 1, and details will not be elaborated here.

[0254] In this specification, the various embodiments are described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the systems, devices, storage media, and computer program products disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and the relevant parts can be referred to the description of the method part.

[0255] Those skilled in the art can clearly understand that the technologies in the embodiments of the present invention can be implemented by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solutions in the embodiments of the present invention, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in various embodiments or some parts of the embodiments of the present invention.

[0256] In some embodiments, the computer-executable instructions can be in the form of a program, software, software module, script, or code, written in any form of programming language (including compiled or interpreted languages, or declarative or procedural languages), and can be deployed in any form, including being deployed as an independent program or being deployed as a module, component, subroutine, or other unit suitable for use in a computing environment.

[0257] As an example, the computer-executable instructions may or may not correspond to files in a file system, and may be stored as part of a file that stores other programs or data. For example, they can be stored in one or more scripts in a Hyper Text Markup Language (HTML) document, stored in a single file dedicated to the program being discussed, or stored in multiple cooperating files (for example, files that store one or more modules, subroutines, or code portions).

[0258] As an example, the computer-executable instructions can be deployed to execute on one electronic device, or on multiple electronic devices located at one location, or on multiple electronic devices distributed at multiple locations and interconnected through a communication network.

[0259] The present invention has been described in detail above in combination with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications, or improvements can be made to the technical solutions and their implementation manners of the present invention, and all of these fall within the scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A method for determining a short-circuit fault protection strategy for a permanent magnet motor considering load characteristics, characterized in that: include: Perform finite element simulation modeling on the permanent magnet motor to obtain a finite element model of the permanent magnet motor; wherein the load torque and inertia considering the load characteristics are used as variables of the finite element model; Obtaining a first load torque interval and a first inertia interval of a finite element model; According to the first load torque interval and the three-phase short-circuit critical torque of the finite element model, determining the critical torque of the finite element model under the single-phase short circuit considering the potential constant torque load; According to the critical torque of the finite element model under the potential constant torque load under the single-phase short circuit, the short-circuit peak current ratio of the finite element model under the potential constant torque load is determined as the first short-circuit peak current ratio; Determining a short-circuit peak current ratio of the finite element model under a resistive constant torque load as a second short-circuit peak current ratio; Determining a short-circuit fault protection strategy for the permanent magnet motor in different load torque and inertia ranges according to the first short-circuit peak current ratio and the second short-circuit peak current ratio; The method of determining the critical torque of the finite element model under single-phase short circuit considering the potential constant torque load according to the first load torque interval and the three-phase short circuit critical torque of the finite element model comprises: The three-phase short-circuit critical torque T of the finite element model is calculated according to the following formula 3PSC : Where p is the number of pole pairs of the permanent magnet motor; ψ f is the permanent magnet flux; L d is the d-axis inductance; Replacing the maximum value in the first load torque interval with the three-phase short-circuit critical torque of the finite element model to obtain a second load torque interval; The average value of the maximum value and the minimum value in the current load torque range is used as the load torque of the finite element model to determine whether the speed of the finite element model is stable; If it is unstable, the maximum value in the current load torque interval is replaced by the average value of the maximum value and the minimum value in the current load torque interval to obtain a new load torque interval; If it is stable, the minimum value in the current load torque interval is replaced by the average value of the maximum value and the minimum value in the current load torque interval to obtain a new load torque interval; Determine whether the difference between the maximum value and the minimum value in the new load torque interval is greater than a preset difference; If it is greater than the preset difference, the operation of "taking the average of the maximum value and the minimum value in the current load torque interval as the load torque of the finite element model to determine whether the speed of the finite element model is stable" is returned; If it is not greater than the preset difference, the average value of the maximum value and the minimum value in the new load torque interval is taken as the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit.

2. The method for determining a short-circuit fault protection strategy for a permanent magnet motor according to claim 1, characterized in that: The method of determining the short-circuit peak current ratio of the finite element model under the potential constant torque load as the first short-circuit peak current ratio according to the critical torque of the finite element model under the potential constant torque load under the single-phase short circuit includes: The load torque interval [0, T SPSC ] is divided into multiple load torque sub-intervals with equal spacing; T SPSC The critical torque of the finite element model considering the potential constant torque load under single-phase short circuit; Dividing the first inertia interval into a plurality of inertia subintervals at equal intervals; Taking the average value of the maximum value and the minimum value in the sub-interval of the target load torque as the load torque of the finite element model as the first load torque; The single-phase short-circuit peak current I under the target load torque sub-interval and target inertia sub-interval is calculated according to the following formula SPSC_max1 : Among them, x1 is the minimum value in the target load torque sub-interval; y1 is the maximum value in the target load torque sub-interval; x2 is the minimum value in the target inertia sub-interval; y2 is the maximum value in the target inertia sub-interval; It indicates the single-phase short-circuit peak current corresponding to the load torque being the first load torque and the inertia being x2; It indicates the single-phase short-circuit peak current corresponding to the load torque being the first load torque and the inertia being y2; The three-phase short-circuit peak current I under the target load torque sub-interval and target inertia sub-interval is calculated according to the following formula 3PSC_max1 : in, It indicates the three-phase short-circuit peak current corresponding to the load torque of the first load torque and the inertia of x2; It indicates the three-phase short-circuit peak current corresponding to the load torque being the first load torque and the inertia being y2; Will As the short-circuit peak current ratio of the finite element model under potential constant torque load.

3. The method for determining a short-circuit fault protection strategy for a permanent magnet motor according to claim 1, characterized in that: The determining of the short-circuit peak current ratio of the finite element model under the resistive constant torque load as the second short-circuit peak current ratio includes: Dividing the first load torque interval into a plurality of load torque sub-intervals at equal intervals; Dividing the first inertia interval into a plurality of inertia subintervals at equal intervals; taking the average value of the maximum value and the minimum value in the sub-interval of the target load torque as the load torque of the finite element model as the second load torque; The target load torque sub-interval and inertia sub-interval are calculated according to the following formula [J totalmax -nT,J totalmax -(n-1)T] single-phase short-circuit peak current I SPSC_max2 : Among them, J totalmax is the maximum inertia; T is the interval length of a single inertia subinterval; n=1,2,3,…,N; the initial value of n is 1; N is the total number of inertia subintervals; x3 is the minimum value in the target load torque subinterval; y3 is the maximum value in the target load torque subinterval; x4 is the interval [J totalmax -nT,J totalmax -(n-1)T]; y4 is the minimum value in the interval [J totalmax -nT,J totalmax -(n-1)T]; It indicates the single-phase short-circuit peak current corresponding to the second load torque and the inertia is x4; It indicates the single-phase short-circuit peak current corresponding to the load torque being the second load torque and the inertia being y4; The target load torque sub-interval and inertia sub-interval are calculated according to the following formula [J totalmax -nT,J totalmax -(n-1)T] three-phase short-circuit peak current I 3PSC_max2 : in, It indicates the three-phase short-circuit peak current corresponding to the second load torque and the inertia is x4; It indicates the three-phase short-circuit peak current corresponding to the load torque being the second load torque and the inertia being y4; Will As the short-circuit peak current ratio of the finite element model under the resistive constant torque load, when Stop calculating the short-circuit peak current ratio of the remaining inertia subinterval within the target load torque subinterval.

4. The method for determining a short-circuit fault protection strategy for a permanent magnet motor according to claim 1, characterized in that: The method of determining the short-circuit fault protection strategy of the permanent magnet motor in different load torque and inertia ranges according to the first short-circuit peak current ratio and the second short-circuit peak current ratio includes: When considering the potential constant torque load, when the load torque of the finite element model is greater than the single-phase short-circuit critical torque, it is determined to transition to three-phase short circuit; when the load torque of the finite element model is less than or equal to the single-phase short-circuit critical torque and the short-circuit peak current ratio in the corresponding load torque interval and inertia interval is less than 1, it is determined to transition to single-phase short circuit; when the load torque of the finite element model is less than or equal to the single-phase short-circuit critical torque and the short-circuit peak current ratio in the corresponding load torque interval and inertia interval is greater than or equal to 1, it is determined to transition to three-phase short circuit; When considering the resistive constant torque load, when the short-circuit peak current ratio in the corresponding load torque interval and the inertia interval is less than 1, it is determined to transition to a single-phase short circuit; when the short-circuit peak current ratio in the corresponding load torque interval and the inertia interval is greater than or equal to 1, it is determined to transition to a three-phase short circuit; among them, the inertia interval that does not need to be calculated determines the transition to a single-phase short circuit.

5. A system for determining a short-circuit fault protection strategy for a permanent magnet motor considering load characteristics, characterized in that: include: A modeling module is used to perform finite element simulation modeling on the permanent magnet motor to obtain a finite element model of the permanent magnet motor; wherein the load torque and inertia of the load characteristics are considered as variables of the finite element model; An acquisition module, used for acquiring a first load torque interval and a first inertia interval of a finite element model; A first determination module is used to determine the critical torque of the finite element model considering the potential constant torque load under the single-phase short circuit according to the first load torque interval and the three-phase short-circuit critical torque of the finite element model; A second determination module is used to determine the short-circuit peak current ratio of the finite element model under the potential constant torque load according to the critical torque of the finite element model under the single-phase short circuit, as the first short-circuit peak current ratio; A third determination module is used to determine the short-circuit peak current ratio of the finite element model under the resistive constant torque load as a second short-circuit peak current ratio; A fourth determination module, configured to determine a short-circuit fault protection strategy of the permanent magnet motor under different load torque and inertia intervals according to the first short-circuit peak current ratio and the second short-circuit peak current ratio; Wherein, the first determining module includes: The first calculation unit is used to calculate the three-phase short-circuit critical torque T of the finite element model according to the following formula 3PSC : Where p is the number of pole pairs of the permanent magnet motor; ψ f is the permanent magnet flux; L d is the d-axis inductance; A first replacement unit is used to replace the maximum value in the first load torque interval with the three-phase short-circuit critical torque of the finite element model to obtain a second load torque interval; A first judging unit is used to use the average value of the maximum value and the minimum value in the current load torque interval as the load torque of the finite element model to judge whether the rotation speed of the finite element model is stable; A second replacement unit is used to replace the maximum value in the current load torque interval with an average value of the maximum value and the minimum value in the current load torque interval to obtain a new load torque interval when the first judgment unit determines that the speed of the finite element model is unstable; A third replacement unit is used to replace the minimum value in the current load torque interval with the average value of the maximum value and the minimum value in the current load torque interval to obtain a new load torque interval when the first judgment unit determines that the speed of the finite element model is stable; A second judgment unit, used to judge whether the difference between the maximum value and the minimum value in the new load torque interval is greater than a preset difference; A first determining unit, configured to determine to return to executing the operation of the first determining unit when the second determining unit determines that the difference between the maximum value and the minimum value in the new load torque interval is greater than a preset difference; The second determination unit is used to determine the average value of the maximum value and the minimum value in the new load torque interval as the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit when the second judgment unit determines that the difference between the maximum value and the minimum value in the new load torque interval is not greater than the preset difference.

6. The permanent magnet motor short-circuit fault protection strategy determination system according to claim 5, characterized in that: The second determining module comprises: The first division unit is used to divide the load torque interval [0, T SPSC ] is divided into multiple load torque sub-intervals with equal spacing; T SPSC The critical torque of the finite element model considering the potential constant torque load under single-phase short circuit; A second division unit is used to divide the first inertia interval into a plurality of inertia subintervals at equal intervals; A third determination unit, configured to use an average value of a maximum value and a minimum value in a subinterval of the target load torque as a load torque of a finite element model, as a first load torque; The second calculation unit is used to calculate the single-phase short-circuit peak current I under the target load torque sub-interval and the target inertia sub-interval according to the following formula SPSC_max1 : Among them, x1 is the minimum value in the target load torque sub-interval; y1 is the maximum value in the target load torque sub-interval; x2 is the minimum value in the target inertia sub-interval; y2 is the maximum value in the target inertia sub-interval; It indicates the single-phase short-circuit peak current corresponding to the load torque being the first load torque and the inertia being x2; It indicates the single-phase short-circuit peak current corresponding to the load torque being the first load torque and the inertia being y2; The third calculation unit is used to calculate the three-phase short-circuit peak current I under the target load torque sub-interval and the target inertia sub-interval according to the following formula 3PSC_max1 : in, It indicates the three-phase short-circuit peak current corresponding to the load torque of the first load torque and the inertia of x2; It indicates the three-phase short-circuit peak current corresponding to the load torque being the first load torque and the inertia being y2; The fourth determining unit is used to As the short-circuit peak current ratio of the finite element model under potential constant torque load.

7. The permanent magnet motor short-circuit fault protection strategy determination system according to claim 5, characterized in that: The third determination module comprises: A third dividing unit, used for dividing the first load torque interval into a plurality of load torque sub-intervals at equal intervals; A fourth dividing unit, used for dividing the first inertia interval into a plurality of inertia subintervals at equal intervals; a fifth determining unit, configured to use an average value of a maximum value and a minimum value in a subinterval of the target load torque as a load torque of a finite element model, as a second load torque; The fourth calculation unit is used to calculate the target load torque sub-interval and inertia sub-interval according to the following formula [J totalmax -nT,J totalmax -(n-1)T] single-phase short-circuit peak current I SPSC_max2 : Among them, J totalmax is the maximum inertia; T is the interval length of a single inertia subinterval; n=1,2,3,…,N; the initial value of n is 1; N is the total number of inertia subintervals; x3 is the minimum value in the target load torque subinterval; y3 is the maximum value in the target load torque subinterval; x4 is the interval [J totalmax -nT,J totalmax -(n-1)T]; y4 is the minimum value in the interval [J totalmax -nT,J totalmax -(n-1)T]; It indicates the single-phase short-circuit peak current corresponding to the second load torque and the inertia is x4; It indicates the single-phase short-circuit peak current corresponding to the load torque being the second load torque and the inertia being y4; The fifth calculation unit is used to calculate the target load torque sub-interval and the inertia sub-interval according to the following formula [J totalmax -nT,J totalmax -(n-1)T] three-phase short-circuit peak current I 3PSC_max2 : in, It indicates the three-phase short-circuit peak current corresponding to the second load torque and the inertia is x4; It indicates the three-phase short-circuit peak current corresponding to the load torque being the second load torque and the inertia being y4; A sixth determining unit is used to As the short-circuit peak current ratio of the finite element model under the resistive constant torque load, when Stop calculating the short-circuit peak current ratio of the remaining inertia subinterval within the target load torque subinterval.

8. The permanent magnet motor short-circuit fault protection strategy determination system according to claim 5, characterized in that: The fourth determination module comprises: The seventh determination unit is used to determine the transition to three-phase short circuit when the finite element model load torque is greater than the single-phase short circuit critical torque under the condition of considering the potential constant torque load; when the finite element model load torque is less than or equal to the single-phase short circuit critical torque and the short-circuit peak current ratio in the corresponding load torque interval and inertia interval is less than 1, determine the transition to single-phase short circuit; when the finite element model load torque is less than or equal to the single-phase short circuit critical torque and the short-circuit peak current ratio in the corresponding load torque interval and inertia interval is greater than or equal to 1, determine the transition to three-phase short circuit; The eighth determination unit is used to determine the transition to single-phase short circuit when the short-circuit peak current ratio in the corresponding load torque interval and the inertia interval is less than 1 under the condition of considering the resistive constant torque load; and to determine the transition to three-phase short circuit when the short-circuit peak current ratio in the corresponding load torque interval and the inertia interval is greater than or equal to 1; wherein the transition to single-phase short circuit is determined in the inertia interval that does not need to be calculated.

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