CN114421462B - Stable operation control method of flexible traction power supply system - Google Patents

Abstract

The invention introduces a stable operation control method of a flexible traction power supply system, which comprises the following steps: s1, selecting a flexible traction transformer as a main station, and connecting the flexible traction transformer to a traction network; s2, selecting other flexible traction transformers as slaves, and realizing phase synchronization tracking of the slave traction network side through a phase synchronization module to ensure that the slave traction transformers can be stably connected to the traction network; s3, setting a power control module to obtain a voltage reference value u _sref (ii) a S4, controlling the flexible traction transformer to stably output; and S5, a power coordination control module is arranged to increase or decrease the output of each flexible traction transformer appropriately along with the running condition of the train. The invention ensures that the output voltage of the flexible traction transformer is controllable, meets the through power supply requirement of the flexible traction power supply system, and realizes full-line through traction power supply; meanwhile, the loss of the flexible traction power supply system on the traction network side is kept at a small level, and the stable operation of the flexible traction power supply system after any flexible traction transformer is disconnected is ensured.

Description

A stable operation control method for a flexible traction power supply system

technical field

The invention belongs to the field of power supply control, and in particular relates to a stable operation control method of a flexible traction power supply system.

Background technique

At present, the current railway traction power supply systems in various countries in the world widely adopt the three-phase-two-phase power supply mode. The traction substation takes power from the three-phase power grid, and after being stepped down by the traction transformer, it is divided into two power supply arms to output power for the traction network. However, because the voltage phase, amplitude and frequency between the two power supply arms and the substations are difficult to be completely consistent, it is necessary to set up electric phase separation between the two power supply arms and each substation, and use partition power supply.

However, the partitioned power supply itself has parasitic problems that are difficult to solve, and it has serious constraints on the speed and load capacity of electric locomotives. Under this system structure, there is a close electromagnetic coupling relationship between the traction power supply system, the traction network, and the traction load, so the unbalance and impact of the traction load will be fed back to the three-phase grid side through the traction substation, seriously affecting the The power quality of the three-phase grid, and the power quality of the three-phase grid is directly related to the normal operation of the traction power supply system and traction load. This strong coupling relationship under the traditional power supply mode seriously reduces the operation efficiency and quality of the traction power supply system, and increases the difficulty of power quality governance in the three-phase power grid, and also threatens the safety and stability of the electric locomotive and traction power supply system , Reliable operation.

Chinese patent CN113224762A discloses a long-distance penetrating flexible traction power supply system and its optimal control method. The long-distance penetrating flexible traction power supply system includes multiple sets of power supply subsystems, and the multiple sets of power supply subsystems are connected electrically in separate phases. Each group of multiple power supply subsystems includes a three-phase power grid, multiple traction substations, multiple circuit breakers and traction network, and the output terminals of multiple traction substations correspond to the input terminals of multiple circuit breakers one by one The input ends of the multiple traction substations are connected to the three-phase grid, and the output ends of the circuit breakers are connected to the traction network, which is used to supply power to trains. The long-distance penetrating flexible traction power supply system and its optimized control method provided by it can realize long-distance energization of the traction network, and at the same time keep the voltage of the traction network in the power supply area of the traction substation stable.

Chinese patent CN110931222A discloses a four-winding traction transformer device for a flexible traction power supply system. The transformer TM4 includes four windings T1, T2, T3 and T4; the T1 winding is used as the high voltage side of the transformer TM4 in a three-phase △ connection, connected to the traction substation The bus bar on the 35kV side of the transformer; the T2 winding is one of the low-voltage sides of the transformer TM4, which is connected to the primary side of the rectifier device RN of the traction substation by using a three-phase Y-connection; the T3 winding is one of the low-voltage sides of the transformer TM4, which is connected in a three-phase △-type connection , connected to the primary side of the rectifier device RN in the traction substation; the T4 winding, as one of the low-voltage sides of the transformer TM4, is connected to the primary side of the bidirectional converter device PCS in the traction substation using a three-phase Y-connection. It can realize that the urban rail transit traction power supply system can use one transformer to supply power to the rectifier unit and the bidirectional converter device at the same time; it can save investment in transformer equipment and reduce the area occupied by the transformer in the traction station.

Although the above scheme provides an optimization scheme for the power supply system, it does not completely solve the power quality problem of the traction power supply system. Therefore, in order to solve the power quality problem of the traction power supply system, the electric phase splitting device is reduced or even eliminated, and the through-type cross-regional power supply is realized. Issues such as negative sequence, reactive power, and harmonics in the existing power supply system become particularly important.

Contents of the invention

In order to solve the above problems, the existing grid-connected control strategy is improved to realize that the flexible traction transformer can provide stable voltage for the traction grid side, keep the grid voltage consistent across the whole line, and achieve the purpose of connection; at the same time, it can realize the stability of each flexible traction transformer. Paralleling and decoupling; and realizing the reasonable distribution of load power among different flexible traction transformers, keeping the loss on the traction grid side small, and ensuring the efficient operation of the system; further solving the power quality problem of the traction power supply system, reducing or even canceling the electric phase splitting device.

In order to achieve the above effects, the present invention designs a stable operation control method of a flexible traction power supply system.

A stable operation control method for a flexible traction power supply system, comprising:

S1. First, choose a flexible traction transformer as the main station, provide a standard reference voltage of 27.5kV/50Hz, and connect it to the traction network;

S2. Select other flexible traction transformers as slaves, and use the phase synchronization module to realize phase synchronization tracking on the traction network side of the slave to ensure that it can be stably connected to the traction network;

S3. Setting the power control module to obtain the voltage reference value u _sref ;

S4, controlling the stable output of the flexible traction transformer;

S5. A power coordination control module is set to realize that the grid voltage on the traction grid side increases appropriately or decreases the output of each flexible traction transformer according to the train operation status.

Preferably, the phase synchronization module in the S2 step is completed by means of a single-phase phase-locked loop and a single-phase voltage coordinate system transformation module, mainly including:

S21. Use the single-phase voltage coordinate system transformation module to construct virtual α and β phases, and obtain the α phase voltage and the β phase voltage;

S22, the phase ω _g t of the traction grid side voltage obtained through the single-phase phase-locked loop;

S23. Use the traction grid side voltage phase ω _g t obtained in S2 to perform Park transformation on S21 α and β phase voltages to obtain u _sq .

Preferably, in the step S21, the single-phase voltage coordinate system transformation module adopts a 1/4 cycle delay algorithm to construct a virtual β phase, that is, using formula 1, which is

The angular frequency ω ₀ =2πf, f=50Hz, the voltage U _s =27.5kV; u _sα and u _sβ are respectively constructed virtual α-phase voltage and β-phase voltage, and j is an imaginary number sign.

Preferably, after the phase ω _g t of the traction network side is obtained through the single-phase phase-locked loop in the step S23, the formula 1 is transformed into the dq coordinate system through Park, that is, the formula 2 is used, and the formula 2 is:

The u _sd and u _sq are the voltage values in the dq coordinate system, and the deviation between u _sq and 0 is obtained through the PI controller to realize ω _g = ω ₀ , which satisfies the synchronization of the output phase of the flexible traction transformer with the phase of the traction network voltage track.

Preferably, the power control module in the step S3 includes a reactive power-amplitude control module and an active power-frequency control module.

Preferably, the specific method for obtaining the voltage reference value u _sref in the step S3 is:

S61. Collect the output voltage u _s and output current i _s of the flexible traction transformer;

S62. Calculate and obtain output active power P and reactive power Q;

S63. According to the actual current situation of the train, the flexible traction transformer obtains a corresponding voltage reference value u _sref according to its own output power.

Preferably, the step S4, ensuring the stable output of the flexible traction transformer, is realized through a voltage and current double closed-loop control module. The reference value u _sref obtained from S3 is decoupled by single-phase dq to obtain corresponding reference values U _sdref and U _sqref , and the implementation method is as follows:

Among them, LPF stands for low-pass filter.

Preferably, in the step S4, the output of the flexible traction transformer adopts an LC filter structure to obtain a control equation of voltage and current double closed-loop after dq decoupling.

Preferably, the step S5, setting the power coordination control module is specifically to adjust the given amplitude reference value of the power control module according to the train running position.

该模块设置自动调节参数va，幅值给定值为

其中

C为与系统自身特性相关的常数，dist为列车运行时与柔性牵引变压器的平均距离。Preferably, the reference value of the given amplitude of the power coordination control module is

This module sets the automatic adjustment parameter va, and the amplitude given value is

in

C is a constant related to the characteristics of the system itself, and dist is the average distance between the train and the flexible traction transformer during operation.

The advantages and effects of the application are as follows:

1. A stable operation control method suitable for flexible traction power supply systems proposed by this application ensures that the output voltage of flexible traction transformers is controllable, meets the requirements for through-through power supply of flexible traction power supply systems, and realizes through-line traction power supply for all lines.

2. This application proposes a power coordination control method suitable for the flexible traction power supply system, which can effectively keep the loss on the traction grid side of the flexible traction power supply system at a small level and ensure the friendly and stable operation of the system.

3. The combination of phase pre-synchronization control and power control method is applied to the flexible traction power supply system without synchronous communication between the stations, and can ensure the safe and stable connection and disconnection of the flexible traction transformer. At the same time, the master station is equipped with a complete set of control algorithms, which can realize any transformation between the master station and the slave station, and ensure the stable operation of the flexible traction power supply system after any flexible traction transformer is disconnected from the grid.

4. The flexible traction transformer used in this application can keep its output consistent according to the control, so the input side of the three-phase grid is relatively independent.

5. The output of the flexible traction transformer used in this application can provide a stable voltage for the traction network, and multiple flexible traction transformers can achieve the purpose of eliminating electrical phase separation due to their fully controllable advantages.

The above description is only an overview of the technical solution of the present application. In order to understand the technical means of the present application more clearly, it can be implemented according to the contents of the description, and in order to make the above and other purposes, features and advantages of the present application more obvious and understandable , the preferred embodiments of the application and accompanying drawings are described in detail below.

According to the following detailed description of specific embodiments of the application in conjunction with the accompanying drawings, those skilled in the art will be more aware of the above and other objectives, advantages and features of the application.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are For some embodiments of the present application, those of ordinary skill in the art can also obtain other drawings based on these drawings without creative effort. Throughout the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, elements or parts are not necessarily drawn in actual scale.

Fig. 1 is a schematic structural diagram of a flexible traction power supply system oriented to the present invention;

Fig. 2 is the overall schematic diagram of the stability control method provided by the present invention;

3 is a schematic diagram of a phase pre-synchronization module provided by the present invention;

4 is a schematic diagram of a voltage and current double closed-loop control module provided by the present invention;

Fig. 5 is a simulation diagram of the traction grid side voltage when two flexible traction transformers are operated synchronously according to the present invention;

Fig. 6 is a diagram of the corresponding relationship between the output power of the two flexible traction transformers and the running position of the locomotive provided by the present invention.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments It is a part of the embodiments of this application, not all of them. In the following description, specific details, such as specific configurations and components, are provided merely to help a comprehensive understanding of the embodiments of the present application. Accordingly, those of ordinary skill in the art should recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the application. Also, descriptions of well-known functions and constructions are omitted in the embodiments for clarity and conciseness.

It should be understood that references to "one embodiment" or "the present embodiment" throughout the specification mean that a particular feature, structure or characteristic related to the embodiment is included in at least one embodiment of the present application. Thus, appearances of "one embodiment" or "the present embodiment" in various places throughout the specification do not necessarily refer to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

Furthermore, the application may repeat reference numbers and/or letters in different instances. This repetition is for the purposes of simplicity and clarity and does not in itself indicate a relationship between the various embodiments and/or arrangements discussed.

The term "and/or" in this article is just an association relationship describing associated objects, which means that there may be three relationships, for example, A and/or B, which can mean: A exists alone, B exists alone, and A and B exist simultaneously. In the three cases of B, the term "/and" in this article is to describe another associated object relationship, which means that there can be two relationships, for example, A/ and B, which can mean: there is A alone, and there are two cases of A and B alone , In addition, the character "/" in this article generally indicates that the contextual objects are an "or" relationship.

The term "at least one" in this article is just an association relationship describing associated objects, which means that there can be three relationships, for example, at least one of A and B can mean: A exists alone, A and B exist simultaneously, There are three cases of B alone.

It should also be noted that in this article, relational terms such as first and second etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that these entities or operations Any such actual relationship or order exists between. Moreover, the terms "comprises", "comprises" or any other variation thereof are intended to cover a non-exclusive inclusion.

Example 1

This embodiment mainly introduces a stable operation control method of a flexible traction power supply system.

A stable operation control method for a flexible traction power supply system, comprising:

S1. First, choose a flexible traction transformer as the main station, provide a standard reference voltage of 27.5kV/50Hz, and connect it to the traction network;

S2. Select other flexible traction transformers as slaves, and use the phase synchronization module to realize phase synchronization tracking on the traction network side of the slave to ensure that it can be stably connected to the traction network;

S3. Setting the power control module to obtain the voltage reference value u _sref ;

S4, controlling the stable output of the flexible traction transformer;

S5. A power coordination control module is set to realize that the grid voltage on the traction grid side increases appropriately or decreases the output of each flexible traction transformer according to the train operation status.

Further, the phase synchronization module in the S2 step is completed by means of a single-phase phase-locked loop and a single-phase voltage coordinate system transformation module, mainly including:

S21. Use the single-phase voltage coordinate system transformation module to construct virtual α and β phases, and obtain the α phase voltage and the β phase voltage;

S22, the phase ω _g t of the traction network side obtained through the single-phase phase-locked loop;

S23. Use the traction grid side voltage phase ω _g t obtained in S2 to perform Park transformation on S21 α and β phase voltages to obtain u _sq .

Further, in the step S21, the single-phase voltage coordinate system transformation module uses a 1/4 cycle delay algorithm to construct a virtual β phase, that is, using formula 1, which is

The angular frequency ω ₀ =2πf, f=50Hz, the voltage U _s =27.5kV; u _sα and u _sβ are respectively constructed virtual α-phase voltage and β-phase voltage, and j is an imaginary number sign.

Further, after the phase ωgt of the traction network side obtained by the single-phase phase-locked loop in the step S23, the formula 1 is transformed into the dq coordinate system through Park, that is, the formula 2 is used, and the formula 2 is:

The u _sd and u _sq are the voltage values in the dq coordinate system, and the deviation between u _sq and 0 is obtained through the PI controller to realize ω _g = ω ₀ , which satisfies the synchronization of the output phase of the flexible traction transformer with the phase of the traction network voltage track.

Further, the power control module in the step S3 includes a reactive power-amplitude control module and an active power-frequency control module.

Further, the specific method for obtaining the voltage reference value u _sref in the step S3 is:

S61. Collect the output voltage u _s and output current i _s of the flexible traction transformer;

S62. Calculate and obtain output active power P and reactive power Q;

S63. According to the actual current situation of the train, the flexible traction transformer obtains the corresponding voltage reference value u _sref and angular frequency ω _sdref according to its own output power.

Further, the step S4, ensuring stable output of the flexible traction transformer, is realized through a voltage and current double closed-loop control module. The reference value u _sref obtained from S3 is decoupled by single-phase dq to obtain corresponding reference values U _sdref and U _sqref , and the implementation method is as follows:

Among them, LPF stands for low-pass filter.

Further, in the step S4, the output of the flexible traction transformer adopts an LC filter structure to obtain a control equation of voltage and current double closed-loop after dq decoupling.

Further, the step S5, setting the power coordination control module is specifically to adjust the given amplitude reference value of the power control module according to the train running position.

该模块设置自动调节参数va，幅值给定值为

其中

C为与系统自身特性相关的常数，dist为列车运行时与柔性牵引变压器的平均距离。具体结构，请参考图1-4；图1为本发明提供的面向的柔性牵引供电系统的结构示意图；图2为本发明提供的稳定控制方法整体示意图；图3为本发明提供的相位预同步模块示意图；图4为本发明提供的电压电流双闭环控制模块示意图。Further, the reference value of the given amplitude of the power coordination control module is

This module sets the automatic adjustment parameter va, and the amplitude given value is

in

C is a constant related to the characteristics of the system itself, and dist is the average distance between the train and the flexible traction transformer during operation. For the specific structure, please refer to Figures 1-4; Figure 1 is a schematic structural diagram of the flexible traction power supply system provided by the present invention; Figure 2 is an overall schematic diagram of the stability control method provided by the present invention; Figure 3 is a phase pre-synchronization provided by the present invention Module schematic diagram; FIG. 4 is a schematic diagram of a voltage and current double closed-loop control module provided by the present invention.

A stable operation control method suitable for a flexible traction power supply system proposed in this application ensures that the output voltage of the flexible traction transformer is controllable, meets the requirements of the flexible traction power supply system through power supply, and realizes the whole line through traction power supply.

This application proposes a power coordination control method suitable for a flexible traction power supply system, which can effectively keep the loss on the traction grid side of the flexible traction power supply system at a small level and ensure the friendly and stable operation of the system.

The combination of phase pre-synchronization control and power control method is applied to the flexible traction power supply system, without synchronous communication between the stations, and can ensure the safe and stable connection and disconnection of the flexible traction transformer. At the same time, the master station is equipped with a complete set of control algorithms, which can realize any transformation between the master station and the slave station, and ensure the stable operation of the flexible traction power supply system after any flexible traction transformer is disconnected from the network.

The flexible traction transformer used in this application can keep its output consistent according to the control, so the input side of the three-phase grid is relatively independent;

The output of the flexible traction transformer used in this application can provide a stable voltage for the traction network, and multiple flexible traction transformers can achieve the purpose of eliminating electrical phase separation due to their fully controllable advantages;

Example 2

Based on the above-mentioned embodiment 1, this embodiment mainly specifically introduces a stable operation control method of a flexible traction power supply system.

A stable operation control method for a flexible traction power supply system, comprising a phase pre-synchronization module, a power control module, a voltage and current double closed-loop control module, and a power coordination control module, through which the output of the flexible traction transformer is controlled, To realize the stability of the flexible traction power supply system, the specific steps are as follows:

S1: First, select one of the flexible traction transformers as the main station, provide the corresponding standard reference voltage of 27.5kV/50Hz to control its output voltage, connect to the traction network, and provide corresponding stable traction network voltage.

S2: The rest of the flexible traction transformers are used as slaves. Firstly, the phase synchronization module is used to realize the synchronous tracking of the phase of the traction network side of the slave to ensure that it can be stably connected to the traction network. This module requires the use of single-phase phase-locked loop and single-phase voltage The coordinate system transformation is completed; among them, the single-phase voltage coordinate system transformation module uses a 1/4 cycle delay algorithm to construct a virtual β phase, that is, formula 1:

The angular frequency ω ₀ =2πf, f=50Hz, the voltage U _s =27.5kV; u _sα and u _sβ are respectively constructed virtual α-phase voltage and β-phase voltage, and j is an imaginary number sign.

After the phase ω _g t of the traction grid side is obtained through the single-phase phase-locked loop, the formula 1 is transformed into the dq coordinate system through Park, that is, the formula 2 is used, and the formula 2 is:

The u _sd and u _sq are the voltage values in the dq coordinate system, then the deviation between u _sq and 0 can be obtained through the PI controller, and ω _g = ω ₀ can be realized, satisfying the output phase of the flexible traction transformer to the phase of the traction grid side network voltage At the same time, this module does not require synchronous communication between stations, which can greatly reduce the need for communication.

S3: setting a power control module, which includes a reactive power-amplitude control module and an active power-frequency control module. The output active power P and reactive power Q are calculated by collecting the output voltage u _s and output current i _s of the flexible traction transformer. This part needs to set the adjustment parameters according to the system stability control requirements: the power control coefficients Km and Kn are fixed and constant This part can ensure that the train obtains the corresponding voltage reference value u _sref and angular frequency ω _sdref according to the output power of the flexible traction transformer according to the actual current situation of the train.

S4: Control the stable output of the flexible traction transformer to ensure its good stability. This part is realized by the voltage and current double closed-loop control module. The reference value u _sref obtained by S3 is decoupled by single-phase dq to obtain corresponding reference values u _sdref and u _sqref , and the reference voltage u _sref can be decomposed into:

Formula 3:

u _sref = u _sdref cos(ω _sref t)+u _sqref sin(ω _sref t);

Formula 4:

Therefore, by adding a low-pass filter LPF, the double frequency component in formula 4 can be filtered out, and formula 5 can be obtained;

Formula 5:

Among them, LPF stands for low-pass filter, and the part of the output result lower than the cutoff frequency is reserved, and the cutoff frequency is set to 20Hz. In particular, the output of the flexible traction transformer adopts an LC filter structure, and the control equation of the voltage and current double closed-loop after dq decoupling is obtained as:

Among them, K is the dielectric constant, L and C are the equivalent inductance and capacitance, and S is the Poynting vector.

According to the control equation, the voltage and current double closed-loop control strategy is shown in Figure 4.

该模块设置自动调节参数va，幅值给定值为：公式6：S5: In particular, in order to ensure efficient and stable operation of the system, the power coordination control module adjusts the given amplitude reference value of the power control module according to the train running position. Under standard conditions, the given amplitude

This module sets the automatic adjustment parameter va, and the given value of the amplitude is: Equation 6:

In Formula 6, C is a constant related to the characteristics of the system itself, and dist is the average distance between the train and the flexible traction transformer during operation. This application can realize the appropriate increase or decrease of the power distribution of each flexible traction transformer according to the operation status of the traction network side network voltage, and effectively maintain the stability of the traction network side network voltage while ensuring the bilateral power supply of the flexible traction power supply system. Keep the loss on the traction grid side at a small level; moreover, when a flexible traction transformer is disconnected, setting special fault parameters can ensure the cross-regional power supply of the flexible traction transformer and ensure the reduced power operation of the train load under special working conditions.

Example 3

Based on the foregoing embodiments 1-2, this embodiment mainly introduces a simulation verification of a stable operation control method for a flexible traction power supply system.

The simulation is carried out according to the usage method of the present application, and the simulation diagrams of FIG. 5 and FIG. 6 are obtained.

Fig. 5 is a simulation diagram of the traction grid side voltage when two flexible traction transformers are operated synchronously according to the present invention;

Fig. 6 is a diagram of the corresponding relationship between the output power of the two flexible traction transformers and the running position of the locomotive provided by the present invention.

From Figure 5, it can be clearly judged that the output voltage of the flexible traction transformer presents standard sine wave fluctuations, indicating that the stable operation control strategy realizes the synchronous operation of multiple stations, and can provide stable network voltage for the traction network to achieve the purpose of power supply through.

Considering the "AC-DC-AC" locomotive as the load, the system mainly provides active power, and the simulation is shown in Figure 6: the figure shows that the locomotive runs between two flexible traction transformers, and four operating positions are set to obtain two flexible traction transformers. The relationship between transformer output power and locomotive running position. From the output active power of #1 and #2, it can be concluded that the output active power of #1 and #2 presents a symmetrical distribution. It can be clearly concluded that the distance between locomotives and its output can be effectively negatively correlated, and bilateral power supply can be guaranteed. At the same time, keep the traction network side loss small.

Therefore, the design of this application can realize any transformation between the master station and the slave station, ensuring the stable operation of the flexible traction power supply system after any flexible traction transformer is disconnected from the network.

The above descriptions are only preferred embodiments of the present invention, which do not limit the protection scope of the present invention. For those skilled in the art, the present invention may have various modifications and changes. Within the spirit and principles of the present invention, changes, modifications, substitutions, integrations and parameter changes of these embodiments without departing from the principles and spirit of the present invention by conventional substitutions or capable of achieving the same function fall within the scope of the present invention. Into the protection scope of the present invention.

Claims (6)

1. A stable operation control method of a flexible traction power supply system is characterized by comprising the following steps:

s1, firstly, selecting a flexible traction transformer as a main station, providing a standard reference voltage of 27.5kV/50Hz, and connecting the standard reference voltage to a traction network;

s2, selecting other flexible traction transformers as slaves, and realizing phase synchronization tracking of the slave traction network side through a phase synchronization module to ensure that the slave traction transformers can be stably connected to the traction network;

s3, setting a power control module to obtain a voltage reference value u _sref ；

S4, controlling the flexible traction transformer to stably output;

s5, a power coordination control module is arranged to increase or decrease the output condition of each flexible traction transformer appropriately along with the running condition of the train;

the phase synchronization module in the step S2 is completed by a single-phase-locked loop and a single-phase voltage coordinate system transformation module, and the method comprises the following steps:

s21, constructing virtual alpha and beta phases by using a single-phase voltage coordinate system transformation module, and acquiring alpha phase voltage and beta phase voltage;

s22, passing the billPhase omega of traction network side voltage obtained by phase-locked loop _g t；

S23, traction network side voltage phase omega obtained by using S2 _g t, in S21, alpha and beta phase voltages are subjected to Park conversion to obtain a voltage value u under a dq coordinate system _sq ；

S3, acquiring a voltage reference value u _sref The specific method comprises the following steps:

s61, collecting output voltage u of flexible traction transformer _s Output current i _s ；

S62, calculating to obtain output active power P and reactive power Q;

s63, obtaining a corresponding voltage reference value u according to the actual current taking condition of the train and the output power of the flexible traction transformer _sref And angular frequency ω _sdref ；

S5, setting a power coordination control module, namely adjusting a given amplitude reference value of the power control module according to the running position of the train;

the power coordination control module gives a reference value of amplitude

The module sets the automatic adjustment parameter v _a Given value of amplitude

Wherein

C is a constant related to the characteristics of the system, and dist is the average distance between the train and the flexible traction transformer when the train operates.

2. The stable operation control method of the flexible traction power supply system according to claim 1, wherein the single-phase voltage coordinate system transformation module in the step S21 adopts a 1/4 cycle delay algorithm to construct a virtual beta phase, that is, formula 1 is used, and the formula 1 is

Wherein the angular frequency ω ₀ =2 π f, f =50Hz, voltage U _s ＝27.5kV；u _sα ，u _sβ The virtual alpha phase voltage and the virtual beta phase voltage are respectively constructed, and j is an imaginary number sign.

3. The stable operation control method of the flexible traction power supply system according to claim 2, wherein the phase ω of the traction network side obtained by the single-phase-locked loop in the step S23 is the phase ω _g After t, converting the formula 1 into a dq coordinate system through Park, namely using a formula 2, wherein the formula 2 is:

wherein u is _sd And u _sq Obtaining u as the voltage value under dq coordinate system _sq The deviation from 0 is realized by a PI controller _g ＝ω ₀ And the synchronous tracking of the output phase of the flexible traction transformer to the network voltage phase at the side of the traction network is met.

4. The stable operation control method of the flexible traction power supply system according to claim 1, wherein the power control module in the step S3 comprises a reactive power-amplitude control module and an active power-frequency control module.

5. The stable operation control method of the flexible traction power supply system according to claim 1, wherein the step S4 of ensuring stable output of the flexible traction transformer is realized by a voltage-current double closed-loop control module; reference value u from S3 _sref Obtaining corresponding reference value U through single-phase dq decoupling _sdref 、U _sqref The realization method comprises the following steps:

where LPF represents a low pass filter and the output remains below the cut-off frequency, set to 20Hz.

6. The stable operation control method of the flexible traction power supply system according to claim 5, wherein in the step S4, the output of the flexible traction transformer adopts an LC filter structure to obtain a control equation of a voltage-current double closed loop after dq decoupling.

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