Winding connection selection method and device for reducing the risk of short-circuit demagnetization of permanent magnet motors

Abstract

The present invention relates to the technical field of permanent magnet motors, and specifically refers to a winding connection selection method and device for reducing the risk of short-circuit demagnetization of permanent magnet motors, including: when the permanent magnet motor is in a three-phase short-circuit state, based on the relationship between the torque loss ratios of star connection and delta connection at different permanent magnet temperatures and different starting rotor positions, a target permanent magnet temperature threshold is found; if the permanent magnet temperature is higher than the target permanent magnet temperature threshold, delta connection is selected, otherwise star connection is selected; when the permanent magnet motor is in a two-phase short-circuit state, based on the relationship between the torque loss ratios of star connection and delta connection at the current permanent magnet temperature and different starting rotor positions, after finding the first intersection rotor position and the second intersection rotor position at the current permanent magnet temperature, a suitable winding connection method is selected according to the intersection rotor position. The present invention can improve the reliability of the operation of the permanent magnet motor and ensure the effective reduction of the risk of short-circuit demagnetization of the permanent magnet motor.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet motors, and in particular to a winding connection selection method and device for reducing the risk of short - circuit demagnetization of permanent magnet motors. Background Art

[0002] Permanent magnet motors play an important role in industrial applications due to their high torque density, efficiency, and simple structure. However, the irreversible demagnetization risk of permanent magnet materials cannot be ignored. Irreversible demagnetization will lead to a decrease in the average torque of the motor and an increase in torque ripple, which is unacceptable in high - cost applications such as large - scale offshore wind turbines. Usually, demagnetization is caused by the transient large - peak current generated by short - circuit faults, including two common types: three - phase short - circuit and two - phase short - circuit. Therefore, studying how to reduce the demagnetization risk brought by short - circuit faults is very important for reducing the maintenance cost of permanent magnet motors and improving their reliability.

[0003] The winding connection selection of permanent magnet motors is crucial, which can change the magnitude of the short - circuit peak current. Usually, there are two connections: star connection and delta connection. Existing technical solutions generally choose delta connection because star connection will generate a larger magnetomotive force, which leads to more serious demagnetization. However, this conclusion is drawn under the normal operating state of the motor and does not consider short - circuit faults. When the motor is in the normal operating state, the peak current is small. At this time, the demagnetization risk reduced by choosing delta connection is relatively small compared with star connection. When a short - circuit fault occurs, the demagnetization risks of delta connection and star connection cannot be determined. If only delta connection is selected, the motor may be placed under a demagnetization risk much higher than that of star connection. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problems in the prior art that only consider the delta connection mode of the winding of the permanent magnet motor under normal working conditions, do not consider short - circuit faults, cannot effectively reduce the demagnetization risk, and when a short - circuit fault occurs in practical applications, it is impossible to determine which winding connection should be selected to reduce the demagnetization risk.

[0005] To solve the above - mentioned technical problems, the present invention provides a winding connection selection method for reducing the short - circuit demagnetization risk of a permanent magnet motor, including:

[0006] Establish a finite - element model of the permanent magnet motor;

[0007] Modify the circuit settings of the finite element model of the permanent magnet motor to make the permanent magnet motor in a three-phase short-circuit state. By adjusting the temperature of the permanent magnet, when the permanent magnet is at different temperatures, calculate the torque loss ratios at each starting rotor position within the first starting rotor position range for the star connection and delta connection of the permanent magnet motor winding respectively, and then find the target permanent magnet temperature threshold. When the permanent magnet temperature is less than or equal to the target permanent magnet temperature threshold, at each starting rotor position within the first starting rotor range, the torque loss ratio of the star connection of the permanent magnet motor winding is lower than that of the delta connection. When the permanent magnet temperature is greater than the target permanent magnet temperature threshold, at each starting rotor position within the first starting rotor range, the torque loss ratio of the star connection of the permanent magnet motor winding is higher than that of the delta connection.

[0008] When the permanent magnet motor is in a three-phase short-circuit state, if the permanent magnet temperature is greater than the target permanent magnet temperature threshold, the connection of the permanent magnet motor winding selects the delta connection method. If the permanent magnet temperature is less than or equal to the target permanent magnet temperature threshold, the connection of the permanent magnet motor winding selects the star connection method.

[0009] Modify the circuit settings of the finite element model of the permanent magnet motor to make the permanent magnet motor in a two-phase short-circuit state. At the current permanent magnet temperature, calculate the torque loss ratios at each starting rotor position within the second starting rotor position range for the star connection and delta connection of the permanent magnet motor winding respectively, and then find the first intersection rotor position at the current permanent magnet temperature. When the starting rotor position is less than or equal to the first intersection rotor position, the torque loss ratio of the star connection of the permanent magnet motor winding is lower than that of the delta connection. When the starting rotor position is greater than the first intersection rotor position, the torque loss ratio of the star connection of the permanent magnet motor winding is higher than that of the delta connection.

[0010] At the current permanent magnet temperature, calculate the torque loss ratios at each starting rotor position within the third starting rotor position range for the star connection and delta connection of the permanent magnet motor winding respectively, and then find the second intersection rotor position at the current permanent magnet temperature. When the starting rotor position is less than or equal to the second intersection rotor position, the torque loss ratio of the star connection of the permanent magnet motor winding is higher than that of the delta connection. When the starting rotor position is greater than the second intersection rotor position, the torque loss ratio of the star connection of the permanent magnet motor winding is lower than that of the delta connection.

[0011] By adjusting the temperature of the permanent magnet, obtain the first intersection rotor position and the second intersection rotor position ;

[0012] When the permanent magnet motor is in a two-phase short-circuit state, at the permanent magnet temperature Under the condition that when the starting rotor position is within one cycle, if the starting rotor position is less than or equal to or greater than , the permanent magnet motor winding connection selects the star connection method; if the starting rotor position is greater than and less than or equal to , the permanent magnet motor winding connection selects the delta connection method, where the interval represents one cycle; is an integer.

[0013] Preferably, the first starting rotor position interval is [0, 60°]; the second starting rotor position interval is [30°, 60°]; the third starting rotor position interval is [120°, 150°].

[0014] Preferably, the method for adjusting the temperature of the permanent magnet so that when the permanent magnet is at different temperatures, the torque loss ratios corresponding to each starting rotor position in the first starting rotor position interval for the star connection and delta connection of the permanent magnet motor winding are calculated respectively, and then the target permanent magnet temperature threshold is found includes:

[0015] Set the initial temperature of the permanent magnet temperature, and based on the first starting rotor position interval, obtain each starting rotor position corresponding in the first starting rotor position interval at a first preset interval;

[0016] When the permanent magnet temperature is the initial temperature, calculate the torque loss ratios corresponding to each starting rotor position in the first starting rotor position interval for the star connection and delta connection of the permanent magnet motor winding respectively;

[0017] Judge the relationship between the torque loss ratio of the star connection of the permanent magnet motor winding and the torque loss ratio of the delta connection at each starting rotor position corresponding in the first starting rotor position interval when the permanent magnet temperature is the initial temperature;

[0018] If when the permanent magnet temperature is the initial temperature, the torque loss ratio of the star connection of the permanent magnet motor winding is lower than the torque loss ratio of the delta connection at each starting rotor position corresponding in the first starting rotor position interval, then increase the permanent magnet temperature, recalculate the torque loss ratios corresponding to each starting rotor position in the first starting rotor position interval for the star connection and delta connection of the permanent magnet motor winding, and judge the relationship between the torque loss ratio of the star connection of the permanent magnet motor winding and the torque loss ratio of the delta connection at this time, until when the permanent magnet temperature is at each starting rotor position corresponding in the first starting rotor position interval, the torque loss ratio of the star connection of the permanent magnet motor winding is higher than the torque loss ratio of the delta connection, and when the permanent magnet temperature is When, at each starting rotor position corresponding to the first starting rotor position interval, the torque loss ratio of the star connection of the permanent magnet motor winding is lower than that of the delta connection, the increase in the permanent magnet temperature is terminated, and is used as the target permanent magnet temperature threshold; where is an integer multiple of; represents the temperature change value.

[0019] Preferably, if when the permanent magnet temperature is the initial temperature, at each starting rotor position corresponding to the first starting rotor position interval, the torque loss ratio of the star connection of the permanent magnet motor winding is higher than that of the delta connection, the permanent magnet temperature is reduced, and the torque loss ratios of the star connection and the delta connection of the permanent magnet motor winding at each starting rotor position corresponding to the first starting rotor position interval are recalculated, and the relationship between the torque loss ratio of the star connection and the torque loss ratio of the delta connection of the permanent magnet motor winding at this time is judged until when the permanent magnet temperature is at each starting rotor position corresponding to the first starting rotor position interval, the torque loss ratio of the star connection of the permanent magnet motor winding is lower than that of the delta connection, and when the permanent magnet temperature is at each starting rotor position corresponding to the first starting rotor position interval, the torque loss ratio of the star connection of the permanent magnet motor winding is higher than that of the delta connection, the reduction of the permanent magnet temperature is terminated, and is used as the target permanent magnet temperature threshold; where is an integer multiple of; represents the temperature change value.

[0020] Preferably, the first preset interval does not exceed 10°.

[0021] Preferably, after calculating the torque loss ratios of the star connection and the delta connection of the permanent magnet motor winding at each starting rotor position corresponding to the second starting rotor position interval at the current permanent magnet temperature, finding the first intersection rotor position at the current permanent magnet temperature includes:

[0022] Set the initial temperature of the permanent magnet temperature to , based on the second starting rotor position interval, and obtain each starting rotor position corresponding to the second starting rotor position interval according to the second preset interval;

[0023] When the current permanent magnet temperature is the initial temperature , calculate the torque loss ratios of the star connection and the delta connection of the permanent magnet motor winding at each starting rotor position corresponding to the second starting rotor position interval respectively;

[0024] If the starting rotor position is , the torque loss ratio of the star connection of the permanent magnet motor winding is lower than that of the delta connection; when the starting rotor position is , the torque loss ratio of the star connection of the permanent magnet motor winding is higher than that of the delta connection;

[0025] Then, based on the starting rotor positions of and , the first intersection rotor position at the current permanent magnet temperature is obtained, and its expression is:

[0026] ;

[0027] Among them, represents the first intersection rotor position at the initial temperature of the current permanent magnet; is a multiple of , belongs to the second starting rotor position interval; represents the second preset interval.

[0028] Preferably, after calculating the torque loss ratios corresponding to each starting rotor position in the third starting rotor position interval for the star connection and delta connection of the permanent magnet motor winding respectively at the current permanent magnet temperature, finding the second intersection rotor position at the current permanent magnet temperature includes:

[0029] Set the initial temperature of the permanent magnet temperature to , and based on the third starting rotor position interval, obtain each starting rotor position corresponding in the third starting rotor position interval according to the second preset interval;

[0030] When the current permanent magnet temperature is the initial temperature , calculate the torque loss ratios corresponding to each starting rotor position in the third starting rotor position interval for the star connection and delta connection of the permanent magnet motor winding respectively;

[0031] If the starting rotor position is , the torque loss ratio of the star connection of the permanent magnet motor winding is higher than that of the delta connection; when the starting rotor position is , the torque loss ratio of the star connection of the permanent magnet motor winding is lower than that of the delta connection;

[0032] Then, based on the starting rotor positions of and , the second intersection rotor position at the current permanent magnet temperature is obtained, and its expression is:

[0033] ;

[0034] Among them, represents the second intersection rotor position at the initial temperature of the current permanent magnet; under the second intersection rotor position; is a multiple of and belongs to the third starting rotor position interval; represents the second preset interval.

[0035] Preferably, by introducing the B-H curves of the permanent magnet at different temperatures, the temperature of the permanent magnet is adjusted.

[0036] Preferably, the expression of the torque loss ratio is:

[0037] ;

[0038] Among them, represents the torque loss ratio; represents the average torque output during the normal operation of the permanent magnet motor before demagnetization occurs; represents the average torque output when the permanent magnet motor operates for one electrical cycle under a short-circuit fault and returns to the normal operating state again after demagnetization occurs.

[0039] The present invention also provides a winding connection selection device for reducing the risk of short-circuit demagnetization of a permanent magnet motor, including:

[0040] a memory for storing a computer program;

[0041] a processor for implementing the steps of the above-mentioned winding connection selection method for reducing the risk of short-circuit demagnetization of a permanent magnet motor when executing the computer program.

[0042] The above technical solutions of the present invention have the following beneficial effects compared with the prior art:

[0043] The winding connection selection method for reducing the risk of short-circuit demagnetization of a permanent magnet motor according to the present invention, by modifying the circuit settings of the finite element model of the permanent magnet motor, enables the permanent magnet motor to be in different short-circuit conditions; for different short-circuit conditions, the torque loss ratios of star connection and delta connection at different permanent magnet temperatures and starting rotor positions are calculated and analyzed. Under three-phase short-circuit conditions, the target permanent magnet temperature threshold is found, and under two-phase short-circuit conditions, the first intersection rotor position and the second intersection rotor position at different permanent magnet temperatures are found, so as to provide a basis for selecting the appropriate winding connection method during three-phase short-circuit and two-phase short-circuit, and can quickly and correctly select the winding connection method of the permanent magnet motor under three-phase short-circuit and two-phase short-circuit; at the same time, it can comprehensively consider various factors, more scientifically determine the winding connection, improve the operating reliability of the motor, and ensure effective reduction of the risk of short-circuit demagnetization of the permanent magnet motor. Description of the Drawings

[0044] To make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in conjunction with the accompanying drawings, where:

[0045] Figure 1 is the current waveform diagram of the star connection and delta connection of the windings when the permanent magnet motor is operating normally;

[0046] Figure 2 is the demagnetization ratio distribution diagram of the star connection of the windings when the permanent magnet motor is operating normally;

[0047] Figure 3 is the demagnetization ratio distribution diagram of the delta connection of the windings when the permanent magnet motor is operating normally;

[0048] Figure 4 is the equivalent circuit diagram of the star connection of the windings of the three-phase short-circuit permanent magnet motor;

[0049] Figure 5 is the equivalent circuit diagram of the delta connection of the windings of the three-phase short-circuit permanent magnet motor;

[0050] Figure 6 is the equivalent circuit diagram of the star connection of the windings of the two-phase short-circuit permanent magnet motor;

[0051] Figure 7 is the equivalent circuit diagram of the delta connection of the windings of the two-phase short-circuit permanent magnet motor;

[0052] Figure 8 is the flow chart of a method for selecting winding connections to reduce the risk of short-circuit demagnetization of a permanent magnet motor provided by the present invention;

[0053] Figure 9 is the finite element model of the permanent magnet motor;

[0054] Figure 10 is the three-phase short-circuit torque loss ratio diagram of the star connection and delta connection of the windings of the permanent magnet motor at a permanent magnet temperature of 80 °C;

[0055] Figure 11 is the three-phase short-circuit torque loss ratio diagram of the star connection and delta connection of the windings of the permanent magnet motor at a permanent magnet temperature of 90 °C;

[0056] Figure 12 is the three-phase short-circuit torque loss ratio diagram of the star connection and delta connection of the windings of the permanent magnet motor at a permanent magnet temperature of 100 °C;

[0057] Figure 13 is the three-phase short-circuit torque loss ratio diagram of the star connection and delta connection of the windings of the permanent magnet motor at a permanent magnet temperature of 110 °C;

[0058] Figure 14It is a diagram of the ratio of two-phase short-circuit torque losses between the star connection and the delta connection of the permanent magnet motor winding at the starting rotor positions [30°, 60°];

[0059] Figure 15 It is a diagram of the ratio of two-phase short-circuit torque losses between the star connection and the delta connection of the permanent magnet motor winding at the starting rotor positions [120°, 150°]. Specific embodiments

[0060] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the illustrated embodiments are not intended to limit the present invention.

[0061] The prior art believes that under the same conditions, the star connection of the winding will cause more serious demagnetization than the delta connection. As Figure 1 shown, when a certain 10-pole / 12-slot permanent magnet motor is operating normally, the peak current of the star connection is 4A, which is greater than the peak current of 3.1A of the delta connection. Figure 2 And Figure 3 give the demagnetization ratio distribution diagram of the permanent magnet motor after running one electrical cycle. Among them, the demagnetization ratio is defined as the ratio of the residual magnetism loss value to the initial value of the residual magnetism. It can be seen from the figure that the demagnetization ratio of the star connection is only higher than that of the delta connection at the edge of the permanent magnet, and the difference is less than 0.5%.

[0062] This technical solution is determined when the permanent magnet motor is operating normally and does not consider short-circuit faults. In this case, the demagnetization difference caused by the star connection and the delta connection is very small, and even if the delta connection is selected, it cannot effectively reduce demagnetization. In practical applications, short-circuit faults are generally considered to be the main cause of demagnetization, because a short circuit can generate a peak current that is 3-4 times the rated current. At this time, the demagnetization generated is much more serious than when operating normally. Therefore, the choice of winding connection method is crucial and determines whether the demagnetization risk can be effectively reduced. Common short-circuit faults include three-phase short circuit and two-phase short circuit, and their equivalent circuit diagrams under different winding connections are as Figure 4 、 Figure 5 、 Figure 6 And Figure 7 shown.

[0063] In summary, the prior art is based on the conclusion under normal operating conditions, believing that using the delta connection compared to the star connection can reduce the demagnetization risk, but the effect is very limited, and the difference in demagnetization rates between the delta connection and the star connection basically does not exceed 0.5%; and the prior art does not consider short-circuit faults. In practical applications, short-circuit faults are the main cause of demagnetization, and the demagnetization caused by short-circuit faults is much more serious than when operating normally. The single selection method of the prior art, that is, selecting the delta connection, is very likely to place the permanent magnet under a higher demagnetization risk.

[0064] Therefore, in order to solve the problem that when a short - circuit fault occurs in a permanent - magnet motor during actual application, it is impossible to determine which winding connection should be selected to reduce the risk of demagnetization, that is, when a short - circuit fault occurs, it is impossible to determine which of the star connection and the delta connection causes more serious demagnetization, the present invention provides a method for selecting a winding connection to reduce the risk of short - circuit demagnetization of a permanent - magnet motor.

[0065] Refer to Figure 8 as shown in Figure 8 is a flowchart of a method for selecting a winding connection to reduce the risk of short - circuit demagnetization of a permanent - magnet motor provided by the present invention; specifically including:

[0066] S1: Establish a finite - element model of the permanent - magnet motor;

[0067] S2: Modify the circuit settings of the finite - element model of the permanent - magnet motor to make the permanent - magnet motor in a three - phase short - circuit state, and select the winding connection mode of the permanent - magnet motor, including:

[0068] S21: By adjusting the temperature of the permanent magnet, when the permanent magnet is at different temperatures, calculate the torque loss ratios at each starting rotor position corresponding to the star connection and the delta connection of the permanent - magnet motor winding in the first starting rotor position interval respectively, and then find the target permanent - magnet temperature threshold, including:

[0069] Set the initial temperature of the permanent - magnet temperature, and based on the first starting rotor position interval, obtain each starting rotor position corresponding to the first starting rotor position interval at a first preset interval; wherein, by importing the B - H curve of the permanent magnet at different temperatures, adjust the temperature of the permanent magnet; the first starting rotor position interval is [0, 60°]; the first preset interval does not exceed 10°; in a specific embodiment of the present invention, when finding the target permanent - magnet temperature threshold, set the initial temperature of the permanent - magnet temperature to 80 °C, and select an interval of 10°, that is, at different permanent - magnet temperatures, calculate the torque loss ratios of the star connection and the delta connection of the permanent - magnet winding every 10° respectively;

[0070] When the permanent - magnet temperature is the initial temperature, calculate the torque loss ratios at each starting rotor position corresponding to the star connection and the delta connection of the permanent - magnet motor winding in the first starting rotor position interval respectively; wherein, the expression of the torque loss ratio is:

[0071] ;

[0072] wherein, represents the torque loss ratio; represents the average torque output by the permanent - magnet motor during normal operation before demagnetization; It represents the average torque output when the permanent magnet motor operates for one electrical cycle under a short - circuit fault and returns to the normal working state again after demagnetization occurs.

[0073] Judge the relationship between the torque loss ratios of the star - connected winding and the delta - connected winding of the permanent magnet motor at each starting rotor position within the first starting rotor position interval when the temperature of the permanent magnet is the initial temperature.

[0074] If, when the temperature of the permanent magnet is the initial temperature, the torque loss ratio of the star - connected winding of the permanent magnet motor is lower than that of the delta - connected winding at each starting rotor position within the first starting rotor position interval, then increase the temperature of the permanent magnet, recalculate the torque loss ratios of the star - connected winding and the delta - connected winding of the permanent magnet motor at each starting rotor position within the first starting rotor position interval, and judge the relationship between the torque loss ratio of the star - connected winding and the delta - connected winding of the permanent magnet motor at this time, until when the temperature of the permanent magnet is At this time, the torque loss ratio of the star - connected winding of the permanent magnet motor is higher than that of the delta - connected winding at each starting rotor position within the first starting rotor position interval, and when the temperature of the permanent magnet is At this time, the torque loss ratio of the star - connected winding of the permanent magnet motor is lower than that of the delta - connected winding at each starting rotor position within the first starting rotor position interval, then terminate increasing the temperature of the permanent magnet, and take as the target permanent magnet temperature threshold; where is an integer multiple of; represents the temperature change value;

[0075] If, when the temperature of the permanent magnet is the initial temperature, the torque loss ratio of the star - connected winding of the permanent magnet motor is higher than that of the delta - connected winding at each starting rotor position within the first starting rotor position interval, then decrease the temperature of the permanent magnet, recalculate the torque loss ratios of the star - connected winding and the delta - connected winding of the permanent magnet motor at each starting rotor position within the first starting rotor position interval, and judge the relationship between the torque loss ratio of the star - connected winding and the delta - connected winding of the permanent magnet motor at this time, until when the temperature of the permanent magnet is At this time, the torque loss ratio of the star - connected winding of the permanent magnet motor is lower than that of the delta - connected winding at each starting rotor position within the first starting rotor position interval, and when the temperature of the permanent magnet is At this time, the torque loss ratio of the star - connected winding of the permanent magnet motor is higher than that of the delta - connected winding at each starting rotor position within the first starting rotor position interval, then terminate decreasing the temperature of the permanent magnet, and take as the target permanent magnet temperature threshold; where is an integer multiple of; representing a temperature change value; in a specific embodiment of the present invention, i.e., increasing the temperature of the permanent magnet by 10 °C or decreasing the temperature of the permanent magnet by 10 °C;

[0076] At this time, the found target permanent magnet temperature threshold satisfies the condition that when the temperature of the permanent magnet is less than or equal to the target permanent magnet temperature threshold, at each starting rotor position corresponding to the first starting rotor range, the torque loss ratio of the star connection of the permanent magnet motor winding is lower than that of the delta connection; when the temperature of the permanent magnet is greater than the target permanent magnet temperature threshold, at each starting rotor position corresponding to the first starting rotor range, the torque loss ratio of the star connection of the permanent magnet motor winding is higher than that of the delta connection; wherein, by modifying the circuit settings of the finite element model of the permanent magnet motor, the star connection and delta connection of the permanent magnet motor winding are realized;

[0077] S22: When the permanent magnet motor is in a three-phase short-circuit state, if the temperature of the permanent magnet is greater than the target permanent magnet temperature threshold, the connection of the permanent magnet motor winding selects the delta connection method; if the temperature of the permanent magnet is less than or equal to the target permanent magnet temperature threshold, the connection of the permanent magnet motor winding selects the star connection method;

[0078] S3: Modify the circuit settings of the finite element model of the permanent magnet motor to make the permanent magnet motor in a two-phase short-circuit state, and select the connection method of the permanent magnet motor winding, including:

[0079] S31: At the current permanent magnet temperature, after calculating the torque loss ratios of the star connection and delta connection of the permanent magnet motor winding at each starting rotor position corresponding to the second starting rotor position interval respectively, find the first intersection rotor position at the current permanent magnet temperature, including:

[0080] Set the initial temperature of the permanent magnet temperature as , based on the second starting rotor position interval, and obtain each starting rotor position corresponding to the second starting rotor position interval at a second preset interval; wherein, the second starting rotor position interval is [30°, 60°];

[0081] At the current permanent magnet temperature of the initial temperature , calculate the torque loss ratios of the star connection and delta connection of the permanent magnet motor winding at each starting rotor position corresponding to the second starting rotor position interval respectively;

[0082] If when the starting rotor position is , the torque loss ratio of the star connection of the permanent magnet motor winding is lower than that of the delta connection; when the starting rotor position is When the permanent magnet motor winding is star - connected, the torque loss ratio is higher than that of the delta - connected winding.

[0083] Then, based on and the starting rotor position, the first intersection rotor position at the current permanent magnet temperature is obtained, and its expression is:

[0084] ;

[0085] where, represents the first intersection rotor position at the initial temperature of the current permanent magnet; is a multiple of , belongs to the second starting rotor position interval; represents the second preset interval;

[0086] At this time, the first intersection rotor position at the current permanent magnet temperature is found, and it satisfies the condition: when the starting rotor position is less than or equal to the first intersection rotor position, the torque loss ratio of the star - connected winding of the permanent magnet motor is lower than that of the delta - connected winding; when the starting rotor position is greater than the first intersection rotor position, the torque loss ratio of the star - connected winding of the permanent magnet motor is higher than that of the delta - connected winding.

[0087] S32: At the current permanent magnet temperature, after calculating the torque loss ratios of the star - connected and delta - connected windings of the permanent magnet motor at each starting rotor position within the third starting rotor position interval respectively, find the second intersection rotor position at the current permanent magnet temperature, including:

[0088] Set the initial temperature of the permanent magnet temperature to , and based on the third starting rotor position interval, obtain each starting rotor position within the third starting rotor position interval at the second preset interval; where the third starting rotor position interval is [120°, 150°];

[0089] When the current permanent magnet temperature is the initial temperature , calculate the torque loss ratios of the star - connected and delta - connected windings of the permanent magnet motor at each starting rotor position within the third starting rotor position interval respectively;

[0090] If when the starting rotor position is , the torque loss ratio of the star - connected winding of the permanent magnet motor is higher than that of the delta - connected winding; when the starting rotor position is , the torque loss ratio of the star - connected winding of the permanent magnet motor is lower than that of the delta - connected winding;

[0091] Then, based on and The starting rotor position is obtained to get the second intersection rotor position at the current permanent magnet temperature, and its expression is:

[0092] ;

[0093] Wherein, represents the second intersection rotor position at the initial temperature of the current permanent magnet ; is a multiple of , and belongs to the third starting rotor position interval; represents the second preset interval;

[0094] At this time, the second intersection rotor position at the current permanent magnet temperature found satisfies the condition: when the starting rotor position is less than or equal to the second intersection rotor position, the torque loss ratio of the star connection of the permanent magnet motor winding is higher than that of the delta connection; when the starting rotor position is greater than the second intersection rotor position, the torque loss ratio of the star connection of the permanent magnet motor winding is lower than that of the delta connection;

[0095] S33: By adjusting the permanent magnet temperature, the first intersection rotor position and the second intersection rotor position at different permanent magnet temperatures are obtained; wherein, in a specific embodiment of the present invention, when finding the first intersection rotor position and the second intersection rotor position, the initial temperature of the permanent magnet temperature is set to 90 °C, that is ; the second preset interval is selected as 5 °, that is , then at different permanent magnet temperatures, the torque loss ratios of the star connection and the delta connection of the permanent magnet winding are calculated every 5 °; at this time, and and are both multiples of 5;

[0096] S34: When the permanent magnet motor is in a two-phase short-circuit state, at the permanent magnet temperature , when the starting rotor position is within one cycle, that is, within the interval, if the starting rotor position is less than or equal to or greater than , then the star connection method is selected for the permanent magnet motor winding connection; if the starting rotor position is greater than and less than or equal to , then the delta connection method is selected for the permanent magnet motor winding connection, wherein, interval represents one cycle; is an integer.

[0097] In summary, under the three-phase short-circuit condition, the present invention takes the magnitude relationship between the torque loss ratios of the star connection and the delta connection at different permanent magnet temperatures and starting rotor positions as an important basis to find the temperature threshold. For three-phase short-circuit, if the permanent magnet temperature is higher than the temperature threshold, the delta connection is selected; otherwise, the star connection is selected. Under the two-phase short-circuit condition, the present invention takes the magnitude relationship between the torque loss ratios of the star connection and the delta connection at different starting rotor positions as an important basis to find the rotor position intersection point. For two-phase short-circuit, the winding connection selection method is closely related to the rotor position intersection point. Therefore, the winding connection selection method provided by the present invention for reducing the short-circuit demagnetization risk of permanent magnet motors can quickly and correctly select the winding connection modes of permanent magnet motors under three-phase short-circuit and two-phase short-circuit conditions. The rapidity is reflected in that the temperature calculation range and the starting rotor position calculation range are reduced according to the torque loss ratio change characteristics of different winding connection modes of permanent magnet motors at different permanent magnet temperatures and different starting rotor positions, eliminating unnecessary calculations and saving calculation time. The correctness is reflected in that the technical solution selects the winding connection mode based on the magnitude of the torque loss ratio, which can ensure effective reduction of the demagnetization risk.

[0098] Based on the steps of S1-S3, the present invention also provides a specific embodiment, including:

[0099] Step 1: Establish a finite element model of the permanent magnet motor, and the model is as Figure 9 shown;

[0100] Step 2: When the permanent magnet motor is in a three-phase short-circuit state, select the winding connection mode of the permanent magnet motor, including:

[0101] (1) Under the three-phase short-circuit condition, calculate the torque loss ratios of the star connection and the delta connection at different permanent magnet temperatures and starting rotor positions, and find the target permanent magnet temperature threshold, including:

[0102] First, set the permanent magnet temperature to 80 °C, and calculate the torque loss ratios of the star connection and the delta connection at different starting rotor positions. As Figure 10 shown, the torque loss ratio of the star connection is always lower than that of the delta connection. Therefore, increase the permanent magnet temperature by 10 °C. Set the permanent magnet temperature to 90 °C, and calculate the torque loss ratios of the star connection and the delta connection at different starting rotor positions. As Figure 11 shown, the torque loss ratio of the star connection is always lower than that of the delta connection. Therefore, continue to increase the permanent magnet temperature by 10 °C. Until the condition is met: when the permanent magnet temperature is 100 °C, the torque loss ratio of the star connection is always lower than that of the delta connection, and when the permanent magnet temperature is 110 °C, the torque loss ratio of the star connection is always higher than that of the delta connection. Stop the calculation and determine 100 °C as the temperature threshold, as Figure 12 and Figure 13 shown;

[0103] (2) If the permanent magnet motor is in a three-phase short-circuit state, when the temperature of the permanent magnet is higher than 100 °C, then the delta connection is selected; otherwise, the star connection is selected.

[0104] Step 3: When the permanent magnet motor is in a two-phase short-circuit state, select the winding connection method of the permanent magnet motor, including:

[0105] (1) Under the condition of two-phase short circuit, calculate the torque loss ratio of the star connection and the delta connection at different permanent magnet temperatures and starting rotor positions, and find the first intersection rotor position and the second intersection rotor position, including:

[0106] Set the permanent magnet temperature to 90 °C, and calculate the torque loss ratio of the star connection and the delta connection at different starting rotor positions, as Figure 14 and Figure 15 shown; when the starting rotor position is between [30°, 60°], when the starting rotor position is 45°, the torque loss ratio of the star connection is less than that of the delta connection, and when the starting rotor position is 50°, the torque loss ratio of the star connection is greater than that of the delta connection. Therefore, the first intersection rotor position is 47.5°; when the starting rotor position is between [120°, 150°], when the starting rotor position is 145°, the torque loss ratio of the star connection is greater than that of the delta connection, and when the starting rotor position is 150°, the torque loss ratio of the star connection is less than that of the delta connection. Therefore, the second intersection rotor position is 147.5°;

[0107] (2) If the permanent magnet motor is in a two-phase short-circuit state, when the permanent magnet temperature is 90 °C, when the starting rotor position is within one cycle, that is, within the interval, is an integer, when the starting rotor position is less than or equal to or greater than then the star connection is selected, and when the starting rotor position is greater than and less than or equal to then the delta connection is selected.

[0108] In a specific embodiment of the present invention, a winding connection selection device for reducing the risk of short-circuit demagnetization of a permanent magnet motor is further provided, including:

[0109] A memory for storing a computer program;

[0110] A processor for implementing the steps of the above-mentioned winding connection selection method for reducing the risk of short-circuit demagnetization of a permanent magnet motor when executing the computer program.

[0111] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0112] The present application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, as well as the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate a means for implementing the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0113] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing devices to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including an instruction means that implements the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0114] These computer program instructions can also be loaded onto a computer or other programmable data processing devices, such that a series of operation steps are executed on the computer or other programmable devices to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable devices provide steps for implementing the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0115] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A winding connection selection method for reducing the risk of short-circuit demagnetization of a permanent magnet motor, characterized in that: include: Establish a finite element model of a permanent magnet motor; Modify the circuit setting of the finite element model of the permanent magnet motor so that the permanent magnet motor is in a three-phase short-circuit state. By adjusting the temperature of the permanent magnet so that the permanent magnet is at different temperatures, respectively calculate the torque loss ratio of the permanent magnet motor winding star connection and triangle connection at each starting rotor position corresponding to the first starting rotor position interval, and then find the target permanent magnet temperature threshold; When the permanent magnet temperature is less than or equal to the target permanent magnet temperature threshold, at each corresponding starting rotor position in the first starting rotor position interval, the torque loss ratio of the permanent magnet motor winding in star connection is lower than the torque loss ratio of the triangle connection; when the permanent magnet temperature is greater than the target permanent magnet temperature threshold, at each corresponding starting rotor position in the first starting rotor position interval, the torque loss ratio of the permanent magnet motor winding in star connection is higher than the torque loss ratio of the triangle connection; wherein the first starting rotor position interval is [0,60°]; When the permanent magnet motor is in a three-phase short-circuit state, if the permanent magnet temperature is greater than the target permanent magnet temperature threshold, the permanent magnet motor winding connection selects a delta connection mode; if the permanent magnet temperature is less than or equal to the target permanent magnet temperature threshold, the permanent magnet motor winding connection selects a star connection mode; Modify the circuit setting of the finite element model of the permanent magnet motor so that the permanent magnet motor is in a two-phase short-circuit state. Under the current permanent magnet temperature, respectively calculate the torque loss ratios of the permanent magnet motor winding star connection and the triangle connection at each starting rotor position corresponding to the second starting rotor position interval, and then find the first intersection rotor position under the current permanent magnet temperature; when the starting rotor position is less than or equal to the first intersection rotor position, the torque loss ratio of the permanent magnet motor winding star connection is lower than the torque loss ratio of the triangle connection; when the starting rotor position is greater than the first intersection rotor position, the torque loss ratio of the permanent magnet motor winding star connection is higher than the torque loss ratio of the triangle connection; wherein, the second starting rotor position interval is [30°, 60°]; At the current permanent magnet temperature, after respectively calculating the torque loss ratios of the permanent magnet motor winding star connection and the triangle connection at each starting rotor position corresponding to the third starting rotor position interval, find the second intersection rotor position at the current permanent magnet temperature; when the starting rotor position is less than or equal to the second intersection rotor position, the torque loss ratio of the permanent magnet motor winding star connection is higher than the torque loss ratio of the triangle connection; when the starting rotor position is greater than the second intersection rotor position, the torque loss ratio of the permanent magnet motor winding star connection is lower than the torque loss ratio of the triangle connection; wherein, the third starting rotor position interval is [120°, 150°]; By adjusting the permanent magnet temperature, the The first intersection rotor position under and the second intersection rotor position ; When the permanent magnet motor is in a two-phase short-circuit state, the permanent magnet temperature In this case, when the starting rotor position is within one cycle, if the starting rotor position is less than or equal to or greater than , the permanent magnet motor winding connection selects the star connection mode; if the starting rotor position is greater than and less than or equal to , then the permanent magnet motor winding connection selects the triangle connection method, where, An interval represents a period; is an integer.

2. A winding connection selection method for reducing the risk of short-circuit demagnetization of a permanent magnet motor according to claim 1, characterized in that: The method of adjusting the permanent magnet temperature so that the permanent magnet is at different temperatures and respectively calculating the torque loss ratios of the permanent magnet motor windings at respective starting rotor positions corresponding to the star connection and the delta connection within the first starting rotor position interval, then finding the target permanent magnet temperature threshold comprises: Setting an initial temperature of the permanent magnet temperature, based on the first starting rotor position interval, and obtaining corresponding starting rotor positions within the first starting rotor position interval according to a first preset interval; When the permanent magnet temperature is the initial temperature, the torque loss ratios of the permanent magnet motor windings at the corresponding starting rotor positions in the first starting rotor position interval under star connection and triangle connection are calculated respectively; Determine the relationship between the torque loss ratio of the star connection of the permanent magnet motor winding and the torque loss ratio of the delta connection at each starting rotor position corresponding to the first starting rotor position interval when the permanent magnet temperature is the initial temperature; If when the permanent magnet temperature is the initial temperature, at each starting rotor position corresponding to the first starting rotor position interval, the torque loss ratio of the permanent magnet motor winding star connection is lower than the torque loss ratio of the triangle connection, then the permanent magnet temperature is increased, and the torque loss ratio of the permanent magnet motor winding star connection and triangle connection at each starting rotor position corresponding to the first starting rotor position interval is recalculated, and the relationship between the torque loss ratio of the permanent magnet motor winding star connection and the torque loss ratio of the triangle connection is determined at this time, until when the permanent magnet temperature is When the torque loss ratio of the permanent magnet motor winding in star connection is higher than that of the triangle connection at each starting rotor position corresponding to the first starting rotor position interval, and when the permanent magnet temperature is When the torque loss ratio of the star connection of the permanent magnet motor winding is lower than the torque loss ratio of the triangle connection at each starting rotor position corresponding to the first starting rotor position interval, the permanent magnet temperature is stopped from being increased, and the As the target permanent magnet temperature threshold; where, for An integer multiple of ; Indicates the temperature change value.

3. A winding connection selection method for reducing the risk of short-circuit demagnetization of a permanent magnet motor according to claim 2, characterized in that: If, when the permanent magnet temperature is the initial temperature, at each corresponding starting rotor position in the first starting rotor position interval, the torque loss ratio of the permanent magnet motor winding in star connection is higher than the torque loss ratio of the triangle connection, then the permanent magnet temperature is reduced, and the torque loss ratio of the permanent magnet motor winding in star connection and triangle connection at each corresponding starting rotor position in the first starting rotor position interval is recalculated, and the relationship between the torque loss ratio of the permanent magnet motor winding in star connection and the torque loss ratio of the triangle connection is determined at this time, until the permanent magnet temperature is When the torque loss ratio of the permanent magnet motor winding star connection is lower than that of the triangle connection at each starting rotor position corresponding to the first starting rotor position interval, and when the permanent magnet temperature is When the torque loss ratio of the star connection of the permanent magnet motor winding is higher than the torque loss ratio of the triangle connection at each starting rotor position corresponding to the first starting rotor position interval, the permanent magnet temperature reduction is terminated and the permanent magnet temperature is As the target permanent magnet temperature threshold; where, for An integer multiple of ; Indicates the temperature change value.

4. A winding connection selection method for reducing the risk of short-circuit demagnetization of a permanent magnet motor according to any one of claims 2-3, characterized in that: The first preset interval does not exceed 10°.

5. A winding connection selection method for reducing the risk of short-circuit demagnetization of a permanent magnet motor according to claim 1, characterized in that: After respectively calculating the torque loss ratios of the permanent magnet motor windings at the respective starting rotor positions corresponding to the star connection and the delta connection in the second starting rotor position interval at the current permanent magnet temperature, finding the first intersection rotor position at the current permanent magnet temperature comprises: Set the initial temperature of the permanent magnet to , based on the second starting rotor position interval, obtaining each starting rotor position corresponding to the second starting rotor position interval according to the second preset interval; When the current permanent magnet temperature is the initial temperature , respectively calculating the torque loss ratios of the permanent magnet motor windings in star connection and delta connection at each starting rotor position corresponding to the second starting rotor position interval; If the starting rotor position is When the starting rotor position is When , the torque loss ratio of the permanent magnet motor winding in star connection is higher than that in delta connection; Based on and The starting rotor position is obtained by calculating the first intersection rotor position at the current permanent magnet temperature, and its expression is: ； in, Indicates that the current permanent magnet temperature is the initial temperature The first intersection rotor position under ; for multiples of Belongs to the second starting rotor position interval; Indicates the second preset interval.

6. A winding connection selection method for reducing the risk of short-circuit demagnetization of a permanent magnet motor according to claim 1, characterized in that: After respectively calculating the torque loss ratios of the permanent magnet motor windings at the respective starting rotor positions corresponding to the star connection and the delta connection within the third starting rotor position interval at the current permanent magnet temperature, finding the second intersection rotor position at the current permanent magnet temperature comprises: Set the initial temperature of the permanent magnet to , based on the third starting rotor position interval, obtaining each starting rotor position corresponding to the third starting rotor position interval according to the second preset interval; When the current permanent magnet temperature is the initial temperature , respectively calculating the torque loss ratios of the permanent magnet motor windings at various starting rotor positions corresponding to the star connection and the delta connection in the third starting rotor position interval; If the starting rotor position is When the starting rotor position is When , the torque loss ratio of the permanent magnet motor winding in star connection is lower than that in delta connection; Based on and The starting rotor position is obtained by calculating the second intersection rotor position at the current permanent magnet temperature, and its expression is: ； in, Indicates that the current permanent magnet temperature is the initial temperature The second intersection rotor position below; for multiples of Belongs to the third starting rotor position interval; Indicates the second preset interval.

7. A winding connection selection method for reducing the risk of short-circuit demagnetization of a permanent magnet motor according to claim 1, characterized in that: The permanent magnet temperature can be adjusted by importing the BH curve of the permanent magnet at different temperatures.

8. A winding connection selection method for reducing the risk of short-circuit demagnetization of a permanent magnet motor according to claim 1, characterized in that: The expression of torque loss ratio is: ； in, Indicates the torque loss ratio; It indicates the average torque output by the permanent magnet motor during normal operation before demagnetization occurs; It indicates the average torque output by a permanent magnet motor when it runs for one electrical cycle under a short circuit fault and recovers to a normal working state after demagnetization occurs.

9. A winding connection selection device for reducing the risk of short-circuit demagnetization of a permanent magnet motor, characterized in that: include: Memory for storing computer programs; A processor, configured to implement the steps of a winding connection selection method for reducing the risk of short-circuit demagnetization of a permanent magnet motor as claimed in any one of claims 1 to 8 when executing the computer program.

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