Permanent magnet motor short circuit fault protection strategy determination method and system considering load characteristics

Abstract

The invention provides a permanent magnet motor short-circuit fault protection strategy determination method and system considering load characteristics. The method comprises the following steps: constructing a finite element model of a permanent magnet motor; determining a critical torque of the finite element model considering the potential constant torque load under a single-phase short circuit; determining a short-circuit peak current ratio of the finite element model under the potential constant torque load as a first short-circuit peak current ratio; determining a short-circuit peak current ratio of the finite element model under a reactive constant torque load as a second short-circuit peak current ratio; and according to the first short-circuit peak current ratio and the second short-circuit peak current ratio, short-circuit fault protection strategies of the permanent magnet motor in different load torque and inertia intervals are determined. The influence of the load characteristics on the short-circuit current is considered, the change characteristics of the single-phase short circuit and the three-phase short circuit of the permanent magnet motor under different load characteristics are obtained, the protection strategy is selected according to the ratio of the peak current and the short-circuit characteristics, and the situation that the protection strategy is mistakenly selected is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of motor fault diagnosis, and in particular relates to a method and system for determining a short-circuit fault protection strategy for a permanent magnet motor taking load characteristics into consideration. 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 cause motor performance degradation. In order 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 operation, permanent magnet motors may experience irreversible demagnetization due to various reasons, among which short-circuit faults caused by the drive are a major cause. They will generate a short-circuit current much larger than the rated current, thereby generating a huge magnetic field that causes permanent magnet demagnetization. A short-circuit fault caused by the drive means that when one switch of the inverter is short-circuited, the remaining switches receive control signals normally. For short-circuit faults caused by the drive, forced transition to single-phase short circuit and three-phase short circuit are two commonly used short-circuit protection strategies. Traditional protection strategies give priority to three-phase short circuits, because the peak current of a single-phase short circuit is greater than that of a three-phase short circuit at a constant speed, which will cause more serious demagnetization.

[0004] However, the above conclusions are based on the assumption that the inertia is infinite. In practical applications, the rotor speed usually cannot remain constant. The load characteristics including load torque and inertia will affect the short-circuit current. If the traditional protection strategy determination method is still followed, that is, only comparing the single-phase short-circuit and three-phase short-circuit peak currents at constant speed, the wrong protection strategy may be selected, resulting in serious permanent magnet demagnetization. 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 taking load characteristics into consideration, so as to solve the problem that only comparing the single-phase short-circuit and three-phase short-circuit peak currents at a constant speed may result in the selection of an erroneous protection strategy, thereby causing 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 taking into account load characteristics, comprising:

[0007] 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;

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

[0009] 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;

[0010] 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;

[0011] 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;

[0012] According to the first short-circuit peak current ratio and the second short-circuit peak current ratio, a short-circuit fault protection strategy of the permanent magnet motor in different load torque and inertia ranges is determined.

[0013] Optionally, determining 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 includes:

[0014] S31, 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; L d is the d-axis inductance;

[0017] S32, 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;

[0018] S33, 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, and judging whether the rotation speed of the finite element model is stable;

[0019] S34, if it is unstable, replacing 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;

[0020] S35, if stable, replacing 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;

[0021] S36, determining whether the difference between the maximum value and the minimum value in the new load torque interval is greater than a preset difference;

[0022] S37, if it is greater than the preset difference, return to execute the operation of S13;

[0023] S38: If the difference 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 used as the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit.

[0024] Optionally, the determining of 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 comprises:

[0025] 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;

[0026] Dividing the first inertia interval into a plurality of inertia subintervals at equal intervals;

[0027] 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;

[0028] 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 :

[0029] ;

[0030] 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;

[0031] 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 :

[0032] ;

[0033] 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;

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

[0035] Optionally, determining 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:

[0036] Dividing the first load torque interval into a plurality of load torque sub-intervals at equal intervals;

[0037] Dividing the first inertia interval into a plurality of inertia subintervals at equal intervals;

[0038] 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;

[0039] 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 :

[0040] ;

[0041] 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;

[0042] 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 :

[0043] ;

[0044] 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;

[0045] 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.

[0046] Optionally, 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 includes:

[0047] 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;

[0048] 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.

[0049] In a second aspect, the present invention provides a system for determining a short-circuit fault protection strategy for a permanent magnet motor taking into account load characteristics, comprising:

[0050] 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;

[0051] An acquisition module, used for acquiring a first load torque interval and a first inertia interval of a finite element model;

[0052] 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;

[0053] 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;

[0054] 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;

[0055] The fourth determination module is used to determine 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.

[0056] Optionally, the first determining module includes:

[0057] 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 :

[0058] ;

[0059] 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;

[0060] 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;

[0061] 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;

[0062] 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;

[0063] 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;

[0064] 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;

[0065] 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;

[0066] 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.

[0067] Optionally, the second determining module includes:

[0068] 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;

[0069] A second division unit is used to divide the first inertia interval into a plurality of inertia subintervals at equal intervals;

[0070] A third determination unit is used 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;

[0071] 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 :

[0072] ;

[0073] 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;

[0074] 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 :

[0075] ;

[0076] 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;

[0077] The fourth determining unit is used to As the short-circuit peak current ratio of the finite element model under potential constant torque load.

[0078] Optionally, the third determining module includes:

[0079] A third dividing unit, used for dividing the first load torque interval into a plurality of load torque sub-intervals at equal intervals;

[0080] A fourth dividing unit, used for dividing the first inertia interval into a plurality of inertia subintervals at equal intervals;

[0081] 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;

[0082] 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 :

[0083] ;

[0084] 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;

[0085] 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 :

[0086] ;

[0087] 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;

[0088] 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.

[0089] Optionally, the fourth determining module includes:

[0090] 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;

[0091] 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.

[0092] The present invention provides a method and system for determining a short-circuit fault protection strategy for a permanent magnet motor taking into account load characteristics, wherein the method takes into account the influence of load characteristics on short-circuit current, obtains the changing 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, selects a protection strategy according to the ratio of peak currents and short-circuit characteristics, and avoids the situation where the protection strategy is selected incorrectly. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0094] Figure 1 A flow chart of a method for determining a short-circuit fault protection strategy for a permanent magnet motor taking into account load characteristics provided by an embodiment of the present invention;

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

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

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

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

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

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

[0101] Figure 8 A schematic diagram of a three-phase short-circuit circuit structure of a permanent magnet motor provided in an embodiment of the present invention;

[0102] Fig. 9 A schematic diagram of a rotation speed losing a steady state provided by an embodiment of the present invention;

[0103] Fig.10 A schematic diagram of a rotation speed in a steady state provided by an embodiment of the present invention;

[0104] Fig.11 A structural schematic diagram of a system for determining a short-circuit fault protection strategy for a permanent magnet motor taking load characteristics into consideration provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0105] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

[0107] However, the protection method proposed in this prior art solution is determined under constant speed, and is based on the assumption of infinite inertia, which does not actually exist. In practical applications, current distortion during short circuits leads to electromagnetic torque distortion, which often causes changes in the speed of the permanent magnet motor. The change in speed will affect the short-circuit current. At this time, the short-circuit current is very different from the short-circuit current under constant speed. In this case, the motor speed and current during the short circuit process depend largely on the load characteristics. Common load types for permanent magnet synchronous motors include potential constant torque loads and resistance constant torque loads, and their torque-speed curves are as follows: Figure 4 and Figure 5 shown.

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

[0109] Therefore, in order to solve the above problems, the present invention takes into account the influence of load characteristics on short-circuit current, obtains the changing characteristics of single-phase short circuit and three-phase short circuit of permanent magnet motor under different load characteristics, eliminates unnecessary calculations, saves calculation time, and selects protection strategy according to the ratio of peak current and short-circuit characteristics to avoid the situation of incorrect selection of protection strategy. Example 1

[0110] like Figure 1 As shown, this embodiment provides a method for determining a short-circuit fault protection strategy for a permanent magnet motor taking into account load characteristics, including:

[0111] Step S1, 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 of the load characteristics are considered as variables of the finite element model.

[0112] like Figure 6 As shown, the permanent magnet motor is modeled using finite element simulation software.

[0113] Step S2, obtaining a first load torque interval and a first inertia interval of the finite element model.

[0114] In this embodiment, the minimum value of the first load torque interval is 0. For example, the first load torque interval is [0 Nm, 10 Nm]; the minimum value of the first inertia interval is J r , 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 value, where the threshold value of the angular acceleration is a safe value that the permanent magnet motor cannot exceed in commercial applications. For example, the angular acceleration of permanent magnet motors used in precision control applications such as robots and CNC machine tools generally does not exceed 10,000 rad / s², the angular acceleration of permanent magnet motors used to drive equipment with large load inertia such as conveyor belts and cranes generally does not exceed 5,000 rad / s², and the angular acceleration of permanent magnet motors used to drive large loads such as wind turbines or electric vehicles generally does not exceed 2,000 rad / s². The maximum load torque is determined according to the equation of motion:

[0115] T max =α max J totalmax .

[0116] Among them, T max is the maximum load torque; α max is the maximum angular acceleration; J totalmax is the maximum inertia.

[0117] Step S3, 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.

[0118] In this step, the dichotomy method is used to determine the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit.

[0119] Exemplarily, a three-phase short-circuit equation is constructed to calculate the size of the three-phase short-circuit critical torque 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 permanent magnet motor speed is in a steady state.

[0120] Construct the three-phase short-circuit voltage equation expression:

[0121] .

[0122] Where 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; f is the permanent magnet flux; ω is the angular velocity; t is the time; represents the time derivative of the d-axis current; It represents the time derivative of the q-axis current.

[0123] When the three-phase short circuit is in steady state, the d-axis current and the q-axis current no longer change, and the voltage equation becomes:

[0124] .

[0125] Construct the equation of motion for the motor:

[0126] .

[0127] 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 time derivative of angular velocity.

[0128] To simplify the calculation, assume that the damping coefficient is 0 and the motor speed remains constant when in steady state, and the motion equation becomes:

[0129] .

[0130] 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 :

[0131] .

[0132] The condition for the existence of steady-state angular velocity is that the square root part is greater than 0.

[0133] Exemplarily, this step includes:

[0134] S31, calculate the three-phase short-circuit critical torque T of the finite element model according to the following formula 3PSC :

[0135] .

[0136] S32, 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.

[0137] S33, 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, judging whether the rotation speed of the finite element model is stable; from S32 to S33, the current load torque interval is the second load torque interval.

[0138] S34, if it 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; in S32 to S34, the new load torque interval is the third load torque interval.

[0139] S35, if 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 to obtain a new load torque interval; in S32, S33 and S35, the new load torque interval is the third load torque interval.

[0140] S36, determining whether the difference between the maximum value and the minimum value in the new load torque interval is greater than a preset difference;

[0141] 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.

[0142] S38: If the difference 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 used as the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit.

[0143] To make the solutions of S31-S38 clearer, this embodiment further discloses specific examples:

[0144] The critical torque of single-phase short circuit is determined by the dichotomy method, and the inertia of the finite element model is set to the maximum value J in the first inertia interval. totalmax ; The dichotomy method is that when the speed of the finite element model is calculated for the first time, the load torque is set to the average value (first average value) of the maximum value and the minimum value in the second load torque interval. If the speed is unstable at this time, the average value (first average value) is used to replace the maximum value in the second load torque interval to form a third load torque interval. If the speed is stable, the average value (first average value) is used to replace the minimum value in the second load torque interval to form a third load torque interval. Then the speed of the finite element model is calculated again, and the load torque is set to the average value of the maximum value and the minimum value in the third load torque interval. The speed is observed to form a new load torque interval until the preset conditions are met.

[0145] When considering the potential constant torque load, the finite element model is switched to single-phase short-circuit operation, and the inertia is set to 40J. r , use the dichotomy 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 as follows: Figure 7 and Figure 8 As shown. Figure 6 The 10-pole / 12-slot permanent magnet synchronous motor finite element model is shown in the figure. First, the critical torque of the three-phase short circuit is determined to be 9Nm according to the formula, so the new load torque range is [0Nm, 9Nm], the load torque is set to 4.5Nm, and the speed is as follows: Fig. 9 As shown in the figure, the speed is out of balance, so 4.5Nm is used to replace the maximum value of the load torque interval to form a new interval [0Nm, 4.5Nm]. Then set the load torque to 2.25Nm, and the speed is as follows Fig.10 As shown, the speed is in a steady state, so 2.25Nm is used to replace the minimum value of the load torque interval to form a new interval [2.25Nm, 4.5Nm]. Then the load torque is set to 3.375Nm, and the speed is continuously observed to see whether it is in a steady state, and a new load torque interval is continuously formed, and this cycle is repeated until the difference between the maximum and minimum values ​​of the load torque interval is less than or equal to 0.05Nm, and then the average value of the maximum and minimum values ​​of the interval is taken. In this embodiment, the single-phase short-circuit critical torque is determined to be 4Nm.

[0146] Step S4, according to the critical torque of the finite element model under the potential constant torque load under the single-phase short circuit, determine 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.

[0147] Exemplarily, this step includes:

[0148] The load torque interval [0, T SPSC ] is divided into multiple load torque sub-intervals with equal spacing; T SPSC This is the critical torque of the finite element model considering potential constant torque load under single-phase short circuit.

[0149] The first inertia interval is divided into a plurality of inertia subintervals at equal intervals. The greater the number of load torque subintervals and the number of inertia subintervals, the more accurate the subsequent peak current calculation is.

[0150] The average value of the maximum value and the minimum value in the target load torque sub-interval is used as the load torque of the finite element model as the first load torque. Under the first load torque, the inertia of the finite element model is set to x2, and the single-phase short-circuit peak current of the finite element model under this condition is calculated using the finite element software. Then, the inertia of the finite element model is set to y2, and the single-phase short-circuit peak current of the finite element model under this condition is calculated.

[0151] 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 :

[0152] .

[0153] 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.

[0154] The single-phase short circuit and three-phase short circuit are given in the finite element model by modifying the circuit settings; the three-phase short circuit peak current I under the target load torque sub-interval and the target inertia sub-interval is calculated according to the following formula 3PSC_max1 :

[0155] .

[0156] 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 represents the three-phase short-circuit peak current corresponding to the load torque being the first load torque and the inertia being y2.

[0157] Will As the short-circuit peak current ratio of the finite element model under potential constant torque load.

[0158] In order to make the scheme of this step clearer, this embodiment further discloses a specific example:

[0159] When considering the potential constant torque load, the load torque range is [0Nm, 4Nm], and the inertia range is [J r ,40J r In this embodiment, the load torque is divided into four intervals, as shown in Table 1, where T load is the load torque. Optionally, more intervals are divided according to the accuracy requirements. The finite element model is switched to single-phase short circuit and three-phase short circuit operation respectively, and the short-circuit peak current ratio in different load torque and inertia intervals is calculated.

[0160] Table 1 Load torque interval division table considering potential constant torque load

[0161]

[0162] In a certain load torque and inertia range, the load torque is set to the average value of the maximum and minimum values ​​in the range, and the corresponding relationship is shown in Table 2. Then, the peak current when the inertia is the maximum and minimum values ​​in the range is calculated respectively, and the average value is taken.

[0163] Table 2 Correspondence between load torque range and load torque setting value considering potential constant torque load

[0164]

[0165] The peak currents of single-phase short circuit and three-phase short circuit are shown in Table 3 and Table 4 respectively. For example, the 2nd row and 2nd column in Table 3 correspond to the interval 0Nm≤T Load <1Nm and J r ≤J total <10J r The single-phase short-circuit peak current under load torque of 0.5Nm and total inertia of J r The peak current and load torque are 0.5Nm and the total inertia is 10J. r The average value of the peak current.

[0166] Table 3 Single-phase short-circuit peak current table in different load torque and inertia ranges considering potential constant torque load

[0167]

[0168] Table 4 Three-phase short-circuit peak current table in different load torque and inertia range considering potential constant torque load

[0169]

[0170] Finally, the peak current ratio of the corresponding interval, that is, the ratio of the single-phase short circuit and three-phase short circuit peak currents, is calculated, as shown in Table 5.

[0171] Table 5 Short-circuit peak current ratios in different load torque and inertia ranges considering potential constant torque loads

[0172]

[0173] Step S5, determining 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.

[0174] Exemplarily, this step includes:

[0175] The first load torque interval is divided into a plurality of load torque sub-intervals at equal intervals.

[0176] The first inertia interval is divided into a plurality of inertia subintervals at equal intervals.

[0177] The average value of the maximum value and the minimum value in the target load torque sub-interval is used as the load torque of the finite element model as the second load torque.

[0178] 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 :

[0179] .

[0180] 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 represents the total number of inertia subintervals (when the interval length of a single inertia subinterval is T); 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.

[0181] 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 :

[0182] .

[0183] 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;

[0184] 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.

[0185] In order to make the scheme of this step clearer, this embodiment further discloses a specific example:

[0186] Considering the resistive constant torque load, the motion force condition is modified to give it in the finite element model. The calculation method is to set the load torque of the finite element model in the corresponding load torque interval [x3, y3] as:

[0187] .

[0188] Starting from the maximum inertia interval, assuming that the length of each inertia interval is T, then from the inertia interval [J totalmax -T,J totalmax ], that is, first calculate the load torque interval [x3, y3] and the inertia interval [J totalmax -T,J totalmax ], the calculation method is the same as that in the formula and step S4, except that the force motion conditions of the finite element model are different; if the ratio is less than 1, the peak current ratios of other inertia subintervals in the load torque subinterval do not need to be calculated; if the ratio is greater than or equal to 1, continue to calculate the peak current ratios in the load torque subinterval [x3, y3] and the inertia subinterval [J totalmax -2T,J totalmax -T], and so on, until the peak current ratio is less than 1, and then calculate the peak current ratios in other load torque sub-intervals.

[0189] Set the load torque interval to [0Nm, 10Nm] and the inertia interval to [Jr, 40Jr]. Calculate the peak current in different sub-intervals according to the calculation method in step S4. The difference is that this step first calculates the ratio, and calculates the short-circuit peak current ratio in a certain load torque sub-interval in the order from the maximum inertia sub-interval to the minimum inertia sub-interval (which can be understood as sorting from large to small according to the maximum value of the sub-interval). When the short-circuit peak current ratio is less than 1, stop the calculation, and the ratios in other inertia sub-intervals do not need to be calculated. Then calculate the short-circuit peak current ratio in other load torque sub-intervals. In a certain load torque sub-interval and inertia sub-interval, the load torque is set to the average of the maximum and minimum values ​​in the sub-interval. The corresponding relationship is shown in Table 6, and the corresponding interval short-circuit peak current ratio is shown in Table 7. Among them, "\" indicates an interval that does not need to be calculated.

[0190] Table 6 Correspondence between torque range and load torque setting value considering resistive constant torque load

[0191]

[0192] Table 7 Short-circuit peak current ratios for different load torques and inertia ranges considering resistive constant torque loads

[0193]

[0194] Step S6, determining a 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.

[0195] When considering the potential constant torque load, when the finite element model load torque is greater than the single-phase short-circuit critical torque, the transition to three-phase short circuit is determined; 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, the transition to single-phase short circuit is determined; 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, the transition to three-phase short circuit is determined.

[0196] 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.

[0197] In summary, the method for determining the short-circuit fault protection strategy of a permanent magnet motor taking into account load characteristics provided in this embodiment determines a reasonable range of load torque and inertia, meets the needs of permanent magnet motors in practical applications, and avoids meaningless interval calculations; when determining the critical torque under a potential constant torque load, the maximum value in the inertia interval is selected to obtain the minimum critical torque; the key point in determining the critical torque is to judge whether the speed is stable; under a resistive constant torque load, within a certain load torque interval, the peak current ratio is calculated in the order from the maximum inertia interval to the minimum inertia interval to reduce the amount of calculation; under a potential constant torque load, when the load torque is greater than the critical torque, directly select the transition to three-phase short circuit as the protection strategy, and under a resistive constant torque load, the interval that is not calculated directly selects the transition to single-phase short circuit as the protection strategy. In addition, the peak current ratio is used to select a short circuit with a smaller peak current as the protection strategy. Example 2

[0198] Based on the same inventive concept as Example 1, this embodiment provides a system for determining a short-circuit fault protection strategy for a permanent magnet motor taking into account load characteristics. Since the principle of solving the problem by this system is similar to the method for determining a short-circuit fault protection strategy for a permanent magnet motor taking into account load characteristics provided in the aforementioned Example 1, the implementation of this system can refer to the implementation of the method for determining a short-circuit fault protection strategy for a permanent magnet motor taking into account load characteristics provided in Example 1.

[0199] like Fig.11As shown, a permanent magnet motor short-circuit fault protection strategy determination system considering load characteristics includes:

[0200] 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; wherein the load torque and inertia of the load characteristics are considered as variables of the finite element model.

[0201] The acquisition module 20 is used to acquire a first load torque interval and a first inertia interval of the finite element model.

[0202] The first determination module 30 is used to 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.

[0203] 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 the single-phase short circuit, as the first short-circuit peak current ratio.

[0204] The third determination module 50 is used to determine 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.

[0205] The fourth determination module 60 is used to determine 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.

[0206] Exemplarily, the first determining module includes:

[0207] 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 :

[0208] ;

[0209] 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.

[0210] 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 the second load torque interval.

[0211] The first judgment 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.

[0212] 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 to obtain a new load torque interval when the first judgment unit determines that the speed of the finite element model is unstable.

[0213] The 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.

[0214] The second judgment unit is 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.

[0215] The first determination unit is used to determine to return to execute the operation of the first determination unit 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 a preset difference.

[0216] 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.

[0217] Exemplarily, the second determining module includes:

[0218] 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 This is the critical torque of the finite element model considering potential constant torque load under single-phase short circuit.

[0219] The second dividing unit is used to divide the first inertia interval into a plurality of inertia subintervals at equal intervals.

[0220] The third determining unit is used 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 as the first load torque.

[0221] 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 :

[0222] .

[0223] 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.

[0224] 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 :

[0225] .

[0226] 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 represents the three-phase short-circuit peak current corresponding to the load torque being the first load torque and the inertia being y2.

[0227] The fourth determining unit is used to As the short-circuit peak current ratio of the finite element model under potential constant torque load.

[0228] Exemplarily, the third determining module includes:

[0229] The third dividing unit is used to divide the first load torque interval into a plurality of load torque sub-intervals with equal intervals.

[0230] The fourth dividing unit is used to divide the first inertia interval into a plurality of inertia subintervals at equal intervals.

[0231] The fifth determining unit is configured to use an average value of a maximum value and a minimum value in a sub-interval of the target load torque as a load torque of the finite element model, so as to serve as a second load torque.

[0232] 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 :

[0233] .

[0234] 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.

[0235] 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 :

[0236] .

[0237] in, It indicates the three-phase short-circuit peak current corresponding to the second load torque and the inertia is x4; It represents the three-phase short-circuit peak current corresponding to the second load torque and the inertia is y4.

[0238] 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.

[0239] Exemplarily, the fourth determining module includes:

[0240] 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, considering the potential constant torque load; 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 less than 1; determine the transition to three-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.

[0241] 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.

[0242] For more specific working processes of the above modules, please refer to the corresponding contents disclosed in Example 1, which will not be repeated here. Example 3

[0243] This embodiment provides a computer device, including a processor and a memory; wherein, when the processor executes a computer program stored in the memory, the steps of the method for determining a permanent magnet motor short-circuit fault protection strategy considering load characteristics described in Embodiment 1 are implemented.

[0244] For more specific details of the above method, please refer to the corresponding contents disclosed in Example 1, which will not be repeated here. Example 4

[0245] 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 a permanent magnet motor short-circuit fault protection strategy considering load characteristics described in Embodiment 1 are implemented.

[0246] For more specific details of the above method, please refer to the corresponding contents disclosed in Example 1, which will not be repeated here. Example 5

[0247] 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 a permanent magnet motor short-circuit fault protection strategy considering load characteristics described in Example 1 are implemented.

[0248] For more specific details of the above method, please refer to the corresponding contents disclosed in Example 1, which will not be repeated here.

[0249] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the 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 description is relatively simple, and the relevant parts can be referred to the method part description.

[0250] Those skilled in the art can clearly understand that the technology in the embodiments of the present invention can be implemented by means of software plus a necessary general hardware platform. Based on this understanding, the technical solution in the embodiments of the present invention can be essentially or partly contributed to the prior art in the form of a software product, which can be stored in a storage medium such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in the various embodiments of the present invention or certain parts of the embodiments.

[0251] In some embodiments, computer executable instructions may 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 may be deployed in any form, including as a stand-alone program or as a module, component, subroutine or other unit suitable for use in a computing environment.

[0252] As an example, computer-executable instructions may, but need not, correspond to a file in a file system, may be stored as part of a file storing other programs or data, such as in one or more scripts in a HyperText Markup Language (HTML) document, in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files storing one or more modules, subroutines, or code portions).

[0253] As an example, computer executable instructions may be deployed to be executed on one electronic device, or on multiple electronic devices located at one site, or on multiple electronic devices distributed at multiple sites and interconnected by a communication network.

[0254] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached 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; According to the first short-circuit peak current ratio and the second short-circuit peak current ratio, a short-circuit fault protection strategy of the permanent magnet motor in different load torque and inertia ranges is determined.

2. 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 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: S31, 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; S32, 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; S33, 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, and judging whether the rotation speed of the finite element model is stable; S34, if it is unstable, replacing 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; S35, if stable, replacing 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; S36, determining whether the difference between the maximum value and the minimum value in the new load torque interval is greater than a preset difference; S37, if it is greater than the preset difference, return to execute the operation of S33; S38: If the difference 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 used as the critical torque of the finite element model considering the potential constant torque load under single-phase short circuit.

3. 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.

4. 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.

5. 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.

6. 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; The fourth determination module is used to determine 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.

7. The permanent magnet motor short-circuit fault protection strategy determination system according to claim 6, characterized in that: The first determining module comprises: 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.

8. The permanent magnet motor short-circuit fault protection strategy determination system according to claim 6, 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.

9. The permanent magnet motor short-circuit fault protection strategy determination system according to claim 6, 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.

10. The permanent magnet motor short-circuit fault protection strategy determination system according to claim 6, 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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