Power supply switching method for reducing traction loss of long-stator linear synchronous motor of high-speed maglev train

Abstract

The invention discloses a power supply switching method for reducing traction loss of a high-speed maglev train long-stator linear synchronous motor, and belongs to the technical field of traction power supply of high-speed maglev trains. According to the method, the absolute position of a train is obtained in real time, power is supplied to a lower stator section in advance when the train is not completely separated from a current stator section, power supply tasks are dynamically distributed through a plurality of converters, motor inductance and flux linkage parameters are corrected in real time in combination with a coupling coefficient, and voltage feedforward of a current loop is calibrated. And the traction loss of the motor during step changing of the stator section is reduced. By reducing the traction loss in the step changing process, the speed increasing time can be shortened, meanwhile, the current fluctuation is reduced, and the traction stability during high-speed operation is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of conventional high-speed maglev trains, and in particular relates to a power supply switching method for reducing the traction loss of a long-stator linear synchronous motor of a high-speed maglev train. Background Art

[0002] Maglev trains use long-stator linear synchronous motors for traction. The core structure of these motors uses the track with the armature windings as the stator and the vehicle body as the mover. During operation, only the stator segment covered by the vehicle generates traction. The remaining uncovered portion, which accounts for a large proportion of the stator, generates a large amount of energy loss. Continuously supplying power to the entire track would result in significant energy waste. To this end, the system adopts a segmented power supply strategy: the stator is divided into several independent sections, and real-time positioning technology is used to energize only the section where the train is located. This on-demand power supply mode reduces energy consumption in uncovered sections. Only the stator windings of the maglev train are energized, significantly improving the overall energy efficiency of the system.

[0003] Among the segmented power supply switching methods for high-speed maglev trains, the short-circuit method, the leapfrog method, the two-step method, and the three-step method each have their own unique characteristics. The short-circuit method requires only a single converter and has a simple structure, but the traction force returns to zero during switching, making it suitable for low-speed test lines. The leapfrog method uses dual converters to alternately power the stator segments, with each converter providing full power. The traction force fluctuates during the switching process, making it suitable for medium-speed scenarios. The two-step method uses dual converters working in parallel. During switching, power is relayed through a three-step process of "release-switch-load." During switching, the total traction force of the train drops to 50% of the pre-switch state, affecting the acceleration performance of high-speed trains. Traction loss can easily cause the train to stall in mountainous or undulating terrain. However, due to its balanced cost and reliability, it has become the mainstream choice for commercial lines in the 400 km / h range. The three-step method uses three converters to achieve seamless switching without loss of traction, providing more stable power output. However, equipment redundancy and high costs limit its application, and it is mostly used on ultra-high-speed lines above 500 km / h. In current engineering practice, the two-step method is widely used due to its cost-effectiveness, while the three-step method represents the technical direction of future ultra-high-speed maglev and needs to be further optimized between efficiency and cost. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a power supply switching method for reducing the traction loss of the long-stator linear synchronous motor of a high-speed maglev train. The method is based on a three-step method and adopts multiple converters to work in coordination.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A power supply switching method for reducing traction loss of a long-stator linear synchronous motor of a high-speed maglev train, comprising:

[0007] Step 1. Calculate the length of the train body according to the number of train formations. Obtain the absolute position of the train on the track through the positioning mark plate, on-board relative position sensor and absolute position sensor set up beside the track, and then determine the stator segment the train is in and whether it is about to enter the next stator segment. If it is to enter the next stator segment, enable the converter corresponding to the stator segment in advance to power the stator segment. The converter supplies power to the stator segment through cables 1, 2 and 3 and the switch station set up beside the track. A total of 6 stator segments on both sides constitute a power supply cycle. In each power supply cycle, each converter needs to power two stator segments, one stator segment on each left and right track, and the stator segment number values ​​differ by 3, which is different from the two-step converter that fixedly powers the stator segment on one side.

[0008] The train makes its step-changing decisions based entirely on its absolute position. Maglev trains are simultaneously powered by long-stator linear synchronous motors on both the left and right sides. The left and right stator segments are staggered, so only one motor on each side will enter the step-changing phase at a given time. If the train is at the center of the left stator segment, the motor on the right is about to enter the step-changing state. Similarly, if the train is at the center of the right stator segment, the motor on the left is about to enter the step-changing state. The time it takes for the switch station to close and the current in the next stator segment to rise to the target current is estimated. Combined with the length of the vehicle body and the current speed, the train determines where on the track the next stator segment should be powered. The expression for the step-changing position is:

[0009] ;

[0010] In the above formula, S trigger represents the absolute position of the train when power is supplied to the next stator segment, n represents the stator segment number where the train is located, l s Represents the length of each stator segment, L M represents the train length, v represents the current train speed, t switch Represents the closing time of the switch station, t rise Represents the current rise time.

[0011] Step 2: When the train is in the step-changing state, multiple converters are in operation at the same time, supplying power to different stator segments respectively; this is equivalent to three long-stator linear synchronous motors providing traction for the train, and the total traction is equal to the sum of the traction of the long-stator linear synchronous motors on the left and right sides when the step is not changed. During this period, the parameters of the motor on the step-changing side are greatly perturbed. The stator and rotor coupling part of the train leaving the stator segment gradually decreases, and the motor inductance and magnetic flux decrease, while the stator and rotor coupling part entering the stator segment gradually increases, and the motor inductance and magnetic flux increase. The rate of change of motor inductance and magnetic flux is closely related to the train speed. It is necessary to calculate the stator and rotor coupling coefficient of the train step-changing side motor according to the train position. The long-stator linear synchronous motor on the step-changing side can be divided into two motors, one for the motor leaving the stator segment, and the other for the motor entering the stator segment. The coupling coefficient of the stator segment leaving and the rotor is P c , and the coupling coefficient between the stator segment and the mover is 1-P c , specifically, the coupling coefficient of the departure section gradually decreases, while the coupling coefficient of the entry section increases synchronously. The coupling coefficient P c The expression is:

[0012] ;

[0013] In the above formula, S represents the absolute position of the train on the track.

[0014] When the train is in single-ended power supply mode, only the converter at one end of the trackside supplies power to the motor. Therefore, changes in motor parameters during the step-changing process need to be considered. To simplify the model, the motor parameters can be assumed to change linearly, similar to the coupling coefficient. The current loops of the motors in the exit and entry sections of the step-changing side use the same target current value, which is output by the speed loop. The motor model corresponding to the exit stator section is:

[0015] ;

[0016] In the above formula, u d and u q Represents the motor dq axis voltage, i d and i q Represents the motor dq axis current, R s Represents the motor stator resistance, R k and L k Represents the resistance and inductance of the feeder cable, L dis and L qis Represents the dq-axis inductance of the stator and mover coupling part, L dos and L qos represents the dq-axis inductance of the uncoupled part of the stator and the mover, ω represents the motor angular velocity, ψ m represents the excitation flux, and p represents the differential operator.

[0017] The motor model corresponding to the driving-in stator segment is:

[0018] ;

[0019] When the train is in dual-end power supply mode and has not yet entered the step-changing phase, the motor model on one side is:

[0020] ;

[0021] In the above formula, u d1 ,u q1 ,u d2 and u q2 Represents the dq axis voltage output by the head-end converter and the tail-end converter, i d1 ,i q1 ,i d2 and i q2 Represents the dq axis current output by the head-end converter and the tail-end converter, R s Represents the motor stator resistance, R k1 and L k1 Represents the resistance and inductance of the feeder cable between the head-end converter and the motor, R k2 and L k2 represents the resistance and inductance of the feeder cable between the tail converter and the motor, L ds and L qs Represents the total dq-axis inductance of the motor, including the inductance of the coupled part between the mover and stator and the inductance of the uncoupled part.

[0022] Similarly, when the train leaves the stator segment, the coupling length between the stator and the mover gradually decreases, and the corresponding motor parameter expression is:

[0023] ;

[0024] In the above formula and Represents the motor dq axis inductance corresponding to the stator segment leaving the motor, Represents the excitation flux of the motor. When the train enters the next stator segment, the coupling length between the stator and the mover gradually increases, and the corresponding motor parameter expression is:

[0025] ;

[0026] In the above formula and Represents the motor dq axis inductance corresponding to the stator segment, Represents the excitation flux of the motor.

[0027] By substituting different parameter expressions into the voltage equation of the long-stator linear synchronous motor in the above-mentioned double-end power supply mode, the voltage equation expressions of different motors can be obtained.

[0028] Single-side motor traction F x The expression is:

[0029] ;

[0030] In the above formula, τ represents the motor pole pitch.

[0031] Because taking i d =0 field oriented control, and the long stator linear synchronous motor L ds ≈L qs , the second part to the right of the equal sign in the above formula can be omitted. Taking the single-ended power supply mode as an example, assuming that the motor on the right side of the train enters the step-changing state, the sum of the traction forces of the three traction motors is:

[0032] ;

[0033] In the above formula, F x_total Represents the total traction force of the train, i ql1 represents the q-axis current of the left motor, i qr1 represents the q-axis current of the motor in the right departure section, i qr2 Represents the q-axis current of the motor in the right-side driving section.

[0034] Because when entering the step-changing stage, the current target values ​​of different motors are the same, it can be considered that i qr1 =i qr2 Total traction force F when not changing steps x_total_un The expression is:

[0035] ;

[0036] So we can get the equation:

[0037] ;

[0038] Step 3: When the train fully enters the next stator section, the switch station is controlled to disconnect the power supply to the departing stator section and use the standby converter to supply power to the next stator section during the step change on the other side. A time delay protection is set to wait until the current is completely stable before disconnecting the power supply to the departing section.

[0039] The beneficial effects of the present invention are:

[0040] (1) Reduce the loss of traction during train step change and ensure the stability and continuity of traction;

[0041] (2) Calculate the energy loss during the switching process of the next stator segment based on the real-time train speed, switch switching time, and target current rise time;

[0042] (3) Considering the motor parameters that change with the coupling coefficient during the step-changing process and applying them to the voltage feedforward in the current loop can reduce the current fluctuation caused by the motor parameter mismatch. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a diagram showing the connection relationship between the stator segment, converter unit, and switch of the long-stator linear synchronous motor of the high-speed maglev train of the present invention;

[0044] Figure 2 This is a waveform diagram of the overall target speed and actual train speed of the high-speed maglev train of the present invention when it accelerates from 0 km / h to 600 km / h and then decelerates to 0 km / h;

[0045] Figure 3 The current target curve output by the speed loop during the operation of the high-speed maglev train of the present invention;

[0046] Figure 4 A comparison curve of the total traction force applied to the high-speed maglev train during operation of the present invention and the prior art method;

[0047] Figure 5 The target current curve of each motor during the operation of the high-speed maglev train of the present invention;

[0048] Figure 6 The excitation flux variation curves of each motor during the operation of the high-speed maglev train of the present invention;

[0049] Figure 7 The d-axis inductance variation curves of each motor during the operation of the high-speed maglev train of the present invention are as follows;

[0050] Figure 8 The graph shows the change curve of the q-axis inductance of each motor during the operation of the high-speed maglev train of the present invention. DETAILED DESCRIPTION

[0051] The present invention will be further described below with reference to the accompanying drawings and examples.

[0052] The present invention provides a power supply switching method for reducing the traction loss of the long stator linear synchronous motor of a high-speed maglev train, such as Figure 1As shown, a high-speed maglev system with a long-stator linear synchronous motor (LSM) is equipped with a substation, switchyard, and feeder cables at each end of the trackside. The traction converter unit in the substation includes input switchgear, input transformer, converter, output transformer, and output switchgear. Each substation is equipped with three converters (ConverterA-1L to 3L and ConverterA-1R to 3R). Through the feeder cables and the stator switchyard, and other trackside feeding equipment, power is supplied in sections to the LSLSM, specifically the stator segment where the train is located. This power supply cycle is based on six stator segments, achieving segmented stator power supply. When the train is running at low speed, only the three converters in the traction converter unit at one end of the trackside supply the stator segment. As the speed increases, to reduce losses and reduce the power burden on each converter, the six converters at both ends are activated simultaneously. When the train is about to leave a stator segment, power is pre-delivered to the next stator segment on the same side. On the other side of the track, because the train is currently at the center of the stator segment, there's no need to pre-energize the next stator segment on the same side. The three-step method requires that the three converters be connected to their respective stator segments through a switch station according to a specific pattern, minimizing traction loss during the step-changing process. For example, at the starting point of the track, single-ended power supply is used. Stator segments 0 and 1 are energized, and the stator segments are arranged in a staggered pattern. The right side enters the step-changing process first. During the step-changing process, stator segments 0, 1, and 2 are energized. Stator segment 0 corresponds to converter Converter A-3L, stator segment 1 corresponds to converter Converter A-1L, and stator segment 2 corresponds to converter Converter A-2L. After the step-changing process is complete, power to stator segment 0 is disconnected. The converters are connected to one end of the three-phase windings of the stator segments, while the other ends of the three-phase windings are connected together. Figure 2 The target speed and actual speed waveform of the high-speed maglev train, which was accelerated from 0 km / h to 600 km / h and then decelerated to 0 km / h, were displayed using this method.

[0053] Without loss of generality, the present invention is applicable to equipping multiple converters on both sides for control, and here only three converters on each side are used as an example for illustration.

[0054] Specifically, the method includes the following steps:

[0055] Step 1. Calculate the length of the train body according to the number of train formations. Obtain the absolute position of the train on the track through the positioning mark plate set beside the track and the on-board position sensor, and then determine the stator segment the train is in and whether it is going to enter the next stator segment. If it is to enter the next stator segment, enable the corresponding converter in advance to power the next stator segment. The converter supplies power to the given segment through cables 1, 2 and 3 and the switch station set beside the track. A total of 6 stator segments on both sides constitute a power supply cycle. In each power supply cycle, each converter needs to power two stator segments, one stator segment on each left and right track, and the stator segment number values ​​differ by 3, which is different from the existing method in which the converter is fixed to power the stator segment on one side.

[0056] The train makes its step-changing decisions based entirely on its absolute position. Maglev trains are simultaneously powered by long-stator linear synchronous motors on both the left and right sides. The left and right stator segments are staggered, so only one motor on each side will enter the step-changing phase at a given time. If the train is at the center of the left stator segment, the motor on the right is about to enter the step-changing state. Similarly, if the train is at the center of the right stator segment, the motor on the left is about to enter the step-changing state. The time it takes for the switch station to close and the current in the next stator segment to rise to the target current is estimated. Combined with the length of the vehicle body and the current speed, the train determines where on the track the next stator segment should be powered. The expression for the step-changing position is:

[0057] ;

[0058] In the above formula, S trigger represents the absolute position of the train when power is supplied to the next stator segment, n represents the stator segment number where the train is located, l s Represents the length of each stator segment, L M represents the train length, v represents the current train speed, t switch Represents the closing time of the switch station, t rise Represents the current rise time.

[0059] Multiple converters are installed on each side of the track. When only the converter at one end of the track supplies power to the motor, it's single-ended powering mode. When converters at both ends of the track supply power to the motor, it's dual-ended powering mode. In dual-ended powering mode, when the corresponding converter is connected to the approaching section, the converter switches at both ends of the track must operate simultaneously. When power is disconnected to the stator section, the converter switches at both ends also need to operate simultaneously. In single-ended powering mode, only the converter switch at one end of the track operates, while the converter at the other end remains inoperative. The switching logic for both modes is consistent.

[0060] Step 2: When the train is in the step-changing state, multiple converters are in operation at the same time, supplying power to different stator segments respectively, which is equivalent to three long-stator linear synchronous motors providing traction for the train. The total traction is equal to the sum of the traction of the long-stator linear synchronous motors on the left and right sides when the step is not changed. During this period, the parameters of the motor on the step-changing side are greatly perturbed. The length of the stator and rotor coupling part of the train leaving the stator segment gradually decreases, and the motor inductance and magnetic flux decrease, while the length of the stator and rotor coupling part entering the stator segment gradually increases, and the motor inductance and magnetic flux increase. The rate of change of motor inductance and magnetic flux is closely related to the train speed. It is necessary to calculate the stator and rotor coupling coefficient of the train step-changing side motor according to the train position. The long-stator linear synchronous motor on the step-changing side can be divided into two motors, one for the motor corresponding to the leaving stator segment and the other for the motor corresponding to the entering stator segment. The coupling coefficient of the leaving stator segment and the rotor is P c , and the coupling coefficient between the stator segment and the mover is 1-P c , specifically, the coupling coefficient of the departure section gradually decreases, while the coupling coefficient of the entry section increases synchronously. The coupling coefficient P c The expression is:

[0061] ;

[0062] In the above formula, S represents the absolute position of the train on the track.

[0063] When the train is in single-ended power supply mode, only the converter at one end of the trackside supplies power to the motor. Therefore, the changes in motor parameters during the step-changing process need to be considered. To simplify the model, the change in motor parameters can be assumed to be linear, just like the coupling coefficient. The current loops of the motors in the outgoing and incoming sections of the step-changing side use the same target current value, which is output by the speed loop (e.g. Figure 3 , Figure 5 As shown in the figure), the motor model corresponding to the stator segment is:

[0064] ;

[0065] In the above formula, u d and u q Represents the motor dq axis voltage, i d and i q Represents the motor dq axis current, R s Represents the motor stator resistance, R k and L k Represents the resistance and inductance of the feeder cable, L dis and L qis Represents the dq-axis inductance of the stator and mover coupling part, L dos and L qos represents the dq-axis inductance of the uncoupled part of the stator and the mover, ω represents the motor angular velocity, ψ mrepresents the excitation flux, and p represents the differential operator.

[0066] The motor model corresponding to the driving-in stator segment is:

[0067] ;

[0068] When the train is in dual-end power supply mode and has not yet entered the step-changing phase, the motor model on one side is:

[0069] ;

[0070] In the above formula, u d1 ,u q1 ,u d2 and u q2 Represents the dq axis voltage output by the head-end converter and the tail-end converter, i d1 ,i q1 ,i d2 and i q2 Represents the dq axis current output by the head-end converter and the tail-end converter, R s Represents the motor stator resistance, R k1 and L k1 Represents the resistance and inductance of the feeder cable between the head-end converter and the motor, R k2 and L k2 represents the resistance and inductance of the feeder cable between the tail converter and the motor, L ds and L qs Represents the total dq-axis inductance of the motor, including the inductance of the coupled part between the mover and stator and the inductance of the uncoupled part.

[0071] Similarly, when the train leaves the stator section, the coupling length between the stator and the mover gradually decreases, and the corresponding motor parameter expression is (such as Figure 6 , Figure 7 , Figure 8 shown):

[0072] ;

[0073] In the above formula and Represents the motor dq axis inductance corresponding to the stator segment leaving the motor, Represents the excitation flux of the motor. When the train enters the next stator segment, the coupling length between the stator and the mover gradually increases, and the corresponding motor parameter expression is:

[0074] ;

[0075] In the above formula and Represents the motor dq axis inductance corresponding to the stator segment, Represents the excitation flux of the motor.

[0076] Substituting different parameter expressions into the voltage equation of the long-stator linear synchronous motor in the above double-end power supply mode, the voltage equation expressions of different motors can be obtained:

[0077] Single-side motor traction F x The expression is:

[0078] ;

[0079] In the above formula, τ represents the motor pole pitch.

[0080] Because taking i d =0 field oriented control, and the long stator linear synchronous motor L ds ≈L qs , the second part to the right of the equal sign in the above formula can be omitted. Taking the single-ended power supply mode as an example, assuming that the motor on the right side of the train enters the step-changing state, the sum of the traction forces of the three traction motors is:

[0081] ;

[0082] In the above formula, F x_total Represents the total traction force of the train, i ql1 represents the q-axis current of the left motor, i qr1 represents the q-axis current of the motor in the right departure section, i qr2 represents the q-axis current of the right-side approaching motor. In the single-ended power supply mode, the q-axis currents of the traction motors on the left and right sides of the train correspond to the q-axis current values ​​output by the single-ended converter of the track. In the double-ended power supply mode, the q-axis currents of the traction motors on the left and right sides are the sum of the q-axis currents output by the converters at both ends of the track.

[0083] During the whole operation, the current target values ​​of different motors are always the same. When entering the step-changing stage, the current target values ​​of the motor entering the segment, the motor leaving the segment and the current segment are the same, so it can be considered that i qr1 =i qr2 Total traction force F when not changing steps x_total_un The expression is:

[0084] ;

[0085] So we can get the relationship (such as Figure 4 shown):

[0086] ;

[0087] Step 3: When the train fully enters the next stator section, the switch station is controlled to disconnect the power supply to the departing stator section and use the standby converter to supply power to the next stator section during the step change on the other side. A time delay protection is set to wait until the current is completely stable before disconnecting the power supply to the departing section.

[0088] Example

[0089] Stator segments are arranged every 1200 meters, with stator segments arranged alternately on both sides. Each stator segment is connected to its corresponding switchyard via a feeder cable. The switchyard is controlled and powered by three converters within the substation (ConverterA-1L / 2L / 3L at the head end and ConverterA-1R / 2R / 3R at the tail end). Trackside positioning markers are installed, and train-mounted position sensors provide real-time information on the train's precise position on the track. The converters are pre-started and in standby mode, with the switchyard initially operating in single-ended power supply mode (for example, the head-end ConverterA-1L / 2L / 3L supplies stator segments 0 and 1). Onboard sensors read the positioning marker information and integrate the running speed to calculate the train's absolute position, S. The control system uses the S value to determine the train's current stator segment number, n (for example, stator segment 4).

[0090] According to the expression , the train enters the step-changing state. According to the current speed v, the switch station closing time t is calculated switch , current rise time t rise And the body length L M , determine the advance power supply distance S1=v×(t switch +t rise )+L M , ensuring that power supply switching is synchronized with the train position, e.g. Figure 1 As shown in the figure, when the train enters the step-change trigger area, the control system allocates the standby converter (such as ConverterA-3R) to pre-power the next stator segment (such as stator segment 6). At this time, as the train speeds up and enters the double-ended power supply state, ConverterA-1L and ConverterA-1R continue to power the current segment (stator segment 4). ConverterA-3L and ConverterA-3R gradually increase the current of stator segment 6 to the target value i qref ,like Figure 5 As shown. According to the coupling coefficient , real-time correction of motor parameters:

[0091] Departure section (stator section 4):

[0092] ;

[0093] Driving section (stator section 6):

[0094] ;

[0095] Through field-oriented control (i d =0), the output current i ql1 (left), i qr1 (Right exit section), i qr2 (Right-side entry section) satisfies i qr1 =i qr2 , the total traction force during step change remains the same as that during step change, and there is no traction loss during step change in the two-step method. Figure 4 As shown:

[0096] ;

[0097] When the train tail is completely separated from the original stator segment, that is, S≥nl s , the control system disconnects the power supply to the original segment (stator segment 4), releases ConverterA-1L and ConverterA-1R, and enters the standby state, ready to supply power to the subsequent step change (such as stator segment 7).

[0098] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A power supply switching method for reducing traction loss of a long-stator linear synchronous motor of a high-speed maglev train, characterized in that: include: Step S1: Monitor the train position and running speed in real time, calculate the step-changing position based on the train body length, determine the next stator segment, and start the converter that supplies power to the next stator segment in advance to establish a pre-power supply state; Step S2: During the step change process, multiple converters are coordinated to simultaneously power the departing segment, the current segment, and the incoming segment, and motor parameters are dynamically adjusted to match the change in coupling coefficient to ensure that the total traction force is consistent with that before the step change; Step S3: When the train completely enters the next stator section, the power supply to the departure section is disconnected, completing the power supply switching process.

2. The power supply switching method for reducing traction loss of a long-stator linear synchronous motor of a high-speed maglev train according to claim 1 is characterized in that: In step 1, the length of the train body is calculated according to the number of train formations, and the absolute position of the train on the track is obtained through the positioning mark plate set beside the track and the on-board position sensor. The stator segment in which the train is located and whether it is about to enter the next stator segment are determined. If it is about to enter the next stator segment, the corresponding current transformer is used to power the stator segment in advance.

3. The power supply switching method for reducing traction loss of a long-stator linear synchronous motor of a high-speed maglev train according to claim 1, characterized in that: In step 1, the calculation formula for the step-changing position is: ； In the above formula, S trigger represents the absolute position of the train when power is supplied to the next stator segment, n represents the stator segment number where the train is located, l s Represents the length of each stator segment, L M represents the train length, v represents the current train speed, t switch Represents the closing time of the switch station, t rise Represents the current rise time.

4. The power supply switching method for reducing traction loss of a long-stator linear synchronous motor of a high-speed maglev train according to claim 3 is characterized in that: In step 2, the coupling coefficient P c The expression is: ； In the above formula, S represents the absolute position of the train on the track.

5. The power supply switching method for reducing traction loss of a long-stator linear synchronous motor of a high-speed maglev train according to claim 4, characterized in that: In step 2, multiple converters are provided on both sides of the track. When only the converter at one end of the track supplies power to the motor, it is a single-ended power supply mode of the motor. When the converters at both ends of the track supply power to the motor at the same time, it is a double-ended power supply mode of the motor. In the double-ended power supply mode, when the corresponding converter is connected to the approaching section, the switch stations of the converters at both ends of the track are simultaneously actuated. When the power supply to the stator section is disconnected, the switch stations of the corresponding converters at both ends are also actuated simultaneously. In the single-ended power supply mode, only the switch station of the converter at one end of the track is actuated, and the converter at the other end of the track does not work. The switching logic of the two power supply modes is consistent.

6. The power supply switching method for reducing traction loss of a long-stator linear synchronous motor of a high-speed maglev train according to claim 5, characterized in that: In single-ended power supply mode, the motor model corresponding to the stator segment is: ； In the above formula, u d and u q Represents the motor dq axis voltage, i d and i q Represents the motor dq axis current, R s Represents the motor stator resistance, R k and L k Represents the resistance and inductance of the feeder cable, L dis and L qis Represents the dq-axis inductance of the stator and mover coupling part, L dos and L qos represents the dq-axis inductance of the uncoupled part of the stator and the mover, ω represents the angular velocity of the motor, ψ m represents the excitation flux, and p represents the differential operator.

7. The power supply switching method for reducing traction loss of a long-stator linear synchronous motor of a high-speed maglev train according to claim 6, characterized in that: In single-ended power supply mode, the motor model corresponding to the stator segment is: 。 8. The power supply switching method for reducing traction loss of a long-stator linear synchronous motor of a high-speed maglev train according to claim 5, characterized in that: In the dual-end power supply mode, before entering the step-changing phase, the motor model on one side of the track is: ； In the above formula, u d1 ,u q1 ,u d2 and u q2 Represents the dq axis voltage output by the head-end converter and the tail-end converter, i d1 ,i q1 ,i d2 and i q2 Represents the dq axis current output by the head-end converter and the tail-end converter, R s Represents the motor stator resistance, R k1 and L k1 Represents the resistance and inductance of the feeder cable between the head-end converter and the motor, R k2 and L k2 represents the resistance and inductance of the feeder cable between the tail converter and the motor, L ds and L qs Represents the total dq-axis inductance of the motor, including the inductance of the coupled part between the mover and stator and the inductance of the uncoupled part; When the train leaves the stator segment, the corresponding motor parameter expression is: ； In the above formula and Represents the motor dq axis inductance corresponding to the stator segment leaving the motor, Represents the excitation flux of the motor; When the train enters the stator section, the corresponding motor parameter expression is: ； In the above formula and Represents the motor dq axis inductance corresponding to the stator segment, Represents the excitation flux of the motor.

9. The power supply switching method for reducing traction loss of a long-stator linear synchronous motor of a high-speed maglev train according to claim 8, characterized in that: In step 2, the total traction force of the train remains unchanged before and after the step change, and the traction force of the single-side motor F x The expression is: ； In the above formula, τ represents the motor pole pitch; Total traction force F when not changing steps x_total_un The expression is: ； Where i ql1 represents the q-axis current of the left motor, i qr1 represents the q-axis current of the motor on the right departure section. In single-ended power supply mode, the q-axis currents of the traction motors on the left and right sides of the train correspond to the q-axis current values ​​output by the single-ended track converter. In dual-ended power supply mode, the q-axis currents of the traction motors on the left and right sides are the sum of the q-axis currents output by the converters at both ends of the track. During the whole operation, the current target values ​​of different motors are always the same; when entering the step-changing stage, the current target values ​​of the motor entering the segment, the motor leaving the segment and the current segment are still the same, then i qr1 =i qr2 , so we get the equation: 。 10. The power supply switching method for reducing traction loss of a long-stator linear synchronous motor of a high-speed maglev train according to claim 1, characterized in that: The step 3 includes setting a preset time delay protection, and disconnecting the power supply of the departure section after the current is completely stable.

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