Traction network impedance simulation system and control method based on voltage source converter

Abstract

The application discloses a kind of traction network impedance simulation system and control method based on voltage source converter, and main substation is simulated by three-phase transformer, and traction substation is simulated by single-phase transformer.Three-phase transformer steps down power supply voltage, and the voltage on the high-voltage side of the single-phase transformer of the traction substation group comes from the same two-phase voltage of the three-phase transformer, which supplies the traction network after stepping down the voltage. Among them, for the impedance simulation of the traction network, the movement of the train is equivalent to the change of the line impedance, and the VSC is used to simulate the impedance of the traction network. The VSC is used to realize the change of the impedance of the traction network on both sides of the train during the train operation. The VSC device is used to simulate the impedance of the traction network on both sides of the train during the train operation, and relevant researchers can use the invention to carry out experimental verification of the related theory of the new type of substation group bilateral traction power supply system, and promote the development of the new type of substation group bilateral traction power supply technology.

Description

Technical Field

[0001] This invention relates to the field of railway traction power supply technology, and in particular to a traction network impedance simulation system and control method based on a voltage source converter. Background Technology

[0002] Currently, my country's electrified railways use a 25kV single-phase AC power supply system. Rail transit traction power supply systems typically have multiple traction substations along the track. These substations are powered by external power sources in their respective areas, and the three-phase AC power is converted into single-phase AC power by traction transformers to supply the traction network.

[0003] In the rugged mountainous areas of western China, due to complex terrain and weak external power supply, it is difficult to set up electrical phase separation. When trains rely on inertia to pass through electrical phase separation, the speed loss is quite severe. At present, the new double-sided traction power supply system of the depot can reduce electrical phase separation and ensure the stability of train operation.

[0004] Since the new double-sided traction power supply system is in the theoretical exploration stage, it is necessary to construct a physical model to conduct experimental verification of the relevant theoretical research. However, during actual train operation, the traction network impedance between the train and the departing and arriving stations changes with the train's position. Therefore, it is difficult to simulate the dynamic change process of the traction network impedance between the train and the departing and arriving stations in the physical model due to the dynamic change of the train's position. Summary of the Invention

[0005] The purpose of this invention is to provide a traction network impedance simulation system and control method based on a voltage source converter (VSC). The voltage source converter is used to simulate the traction network impedance at both ends of the train in the physical system, so as to realize the experimental simulation of the dynamic operation process of the train.

[0006] The technical solution of the present invention is as follows:

[0007] A traction network impedance simulation system based on a voltage source converter includes a three-phase transformer, a first single-phase transformer, a second single-phase transformer, a first voltage source converter, a second voltage source converter, and a power resistor. Both the first and second single-phase transformers are powered by the three-phase transformer. The first output terminal of the first single-phase transformer is connected in series with the first and second voltage source converters and then connected to the first output terminal of the second single-phase transformer. The second output terminals of both the first and second single-phase transformers are grounded. The series connection point of the first and second voltage source converters is connected to one end of the power resistor, and the other end of the power resistor is grounded. The power resistor is used to simulate a train, and the first and second voltage source converters are used to simulate the traction network impedance on both sides of the train. The system also includes a controller for controlling the first and second voltage source converters.

[0008] Further technical solutions also include a third single-phase transformer, a third voltage source converter, and a fourth voltage source converter; the third single-phase transformer is also powered by the three-phase transformer, and the first output terminal of the third single-phase transformer is connected in series with the fourth voltage source converter and the third voltage source converter and then connected to the first output terminal of the second single-phase transformer, and the second output terminal of the third single-phase transformer is also grounded.

[0009] The control method for the above simulation system is as follows:

[0010] Step 1: Let the simulated traction network impedance between the train and the first single-phase transformer be R1+jX1=(R0+jX0)×l1, and the simulated traction network impedance between the train and the second single-phase transformer be R2+jX2=(R0+jX0)×l2; where l1 is the length of the traction network between the train and the first single-phase transformer, l2 is the length of the traction network between the train and the second single-phase transformer, and R0+jX0 is the impedance per unit length of the traction network between the first single-phase transformer and the second single-phase transformer.

[0011] Let the secondary voltages of the first and second single-phase transformers both be U∠0°, and the power of the power resistor be P0.

[0012] Step 2: Calculate the voltage at both ends of the train. Specifically:

[0013] Current flowing through the train

[0014] according to

[0015] Since the train is a resistive load, the voltage across the train is in phase with the current flowing through it.

[0016] Phase

[0017] Combining the above equations, we obtain the voltage across the two ends of the train;

[0018] Step 3: Calculate the voltage drop across the traction network between the train and the first single-phase transformer. Voltage division of the traction network between the train and the second single-phase transformer U1 and U2 are the effective values ​​of the voltage division between the train and the first and second single-phase transformers, respectively. These are the phases of the voltage division between the train and the first and second single-phase transformers in the traction network;

[0019] Step 4: Calculate the power P1+jQ1 of the traction network between the train and the first single-phase transformer, and the power P2+jQ2 of the traction network between the train and the second single-phase transformer.

[0020] Among them, active power reactive power

[0021] Step 5: After P1+jQ1 and P2+jQ2 are decoupled by DQ respectively, the first voltage source converter and the second voltage source converter are controlled by PID to simulate the traction network impedance on both sides of the train.

[0022] The beneficial effect of this invention is that by using a VSC device to simulate the impedance of the traction network on both sides during train operation, relevant researchers can use this invention to conduct experimental verification of the relevant theories of the new type of double-sided traction power supply system, and promote the development of the new type of double-sided traction power supply technology. Attached Figure Description

[0023] Figure 1 This is a topology diagram of a new type of dynamic simulation system for bilateral traction power supply in a cluster of institutes.

[0024] Figure 2 This is the control flow diagram of VSC in the simulation system.

[0025] Figure 3 This is a schematic diagram of DQ decoupling and P, Q control of VSC.

[0026] Figure 4 This is a schematic diagram of a traction network impedance simulation system based on VSC. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] A novel dynamic simulation system for bilateral traction power supply in a substation cluster includes a main substation, a group of traction substations, a traction network (simulated by equivalent VSC), and trains (simulated by equivalent power resistance). Three traction substations under one main substation form one traction substation group, and two traction substations under a second main substation form another. The main substation is simulated by a three-phase transformer, and the traction substations by single-phase transformers. The three-phase transformers step down the power supply voltage, while the high-voltage side voltage of the single-phase transformers in the traction substation group comes from the same two-phase voltages of the three-phase transformers, and is then stepped down before being supplied to the traction network.

[0029] In the impedance simulation of the traction network, the movement of the train is equivalent to the change in the line impedance. VSC is used to simulate the impedance of the traction network and to realize the change in the impedance of the traction network on both sides of the train during the operation of the train.

[0030] The control methods that VSC can use are as follows (but not limited to the control methods described below):

[0031] The dynamic operation of the train is equivalent to the change in the impedance of the traction network on both sides of the train. The impedance of the traction network on both sides of the train is controlled by the active power P and reactive power Q consumed by the calculated impedance of the traction network on both sides of the train.

[0032] The impedance of the traction network on both sides of the train is obtained by measuring the length of the track at both ends of the train and the impedance per unit length of the traction network. The active power P and reactive power Q of the traction network impedance on both sides of the train are then calculated. The obtained active power P and reactive power Q are then used to control the VSC, thereby simulating the change of the traction network impedance on both sides of the train during train operation.

[0033] By decoupling through DQ, PID control achieves constant power control of VSC, making its AC port equivalent impedance a specific value.

[0034] The grid voltage Us is selected as the reference vector, and the current is subjected to Park transformation;

[0035] Treating id and iq as reference values ​​for active and reactive components, and decoupling the current so that the d-axis current is independently controlled by the d-axis voltage, respectively.

[0036] After solving for the active power P and reactive power Q, the parameters are passed to the VSC, which controls the AC port to achieve a specific equivalent impedance. Since P and Q are continuously changing at each moment, the impedance changes continuously at each moment, thus realizing the dynamic simulation of the traction network impedance.

[0037] The advantages of this invention are:

[0038] 1. Using the VSC device to simulate the impedance changes of the traction network on both sides during train operation can effectively simulate the impedance of the traction network, thereby simulating the new type of double-sided traction power supply system.

[0039] 2. Using DQ decoupling and PID control for closed-loop control of the VSC, the changes in line impedance can be simulated by utilizing the changes in active power P and reactive power Q when the simulated train is running. Through embedding functions, continuous changes in traction network impedance are achieved, thus realizing dynamic simulation of traction network impedance.

[0040] 3. By presetting the train's location and the impedance per unit length of the traction network, the distances from the train to the departure and arrival traction substations are obtained based on the train's location. The impedance of the traction network between the departure and arrival stations is then obtained. The voltages at both ends of the traction network (VSC) between the departure and arrival stations are obtained through network solving. The active power P and reactive power Q consumed by the VSC between the departure and arrival stations are then obtained. Finally, the control objective is achieved through DQ decoupling, PID control, and constant PQ control, enabling the system to simulate changes in train position.

[0041] 4. Relevant researchers can use this invention to conduct experimental verification of the relevant theories of the new institute group bilateral traction power supply system, thereby better promoting the development of the new institute group bilateral traction power supply technology.

[0042] Example:

[0043] A novel dynamic simulation system for bilateral traction power supply in a railway substation includes two three-phase transformers (380V:380V), five single-phase transformers (220V:55V), a train, and a VSC device. The topology is as follows: Figure 1 As shown. One three-phase transformer has three single-phase transformers to replace three traction substations, and another three-phase transformer has two single-phase transformers to replace two traction substations. There are no breaks in the traction network between single-phase transformers under the same three-phase transformer, but breaks are set in the traction network between single-phase transformers under different three-phase transformers to replace phase separation.

[0044] A three-phase transformer is connected to the power supply voltage on one side, converting the power supply voltage into a voltage that can be used by a single-phase transformer. The high-voltage side of a single-phase transformer under the same three-phase transformer is connected to the voltage of the same two phases of the three-phase transformer, thus enabling continuous power supply within the group.

[0045] The low-voltage side of a single-phase transformer is connected to the traction network, which supplies the stepped-down voltage to the traction network and then to the train.

[0046] Using VSC to control the impedance changes of the traction network at both ends of the train, the movement of the train is equivalent to the impedance changes of the lines on both sides. The impedance of the lines on both sides of the train is then derived using the lengths of the lines at both ends. Assume that the secondary voltages of both transformers are U∠0°, and the voltage across the trolley is... Given that the impedance per unit length of the traction network is R0 + jX0, and the distance from the trolley to the departure-side traction substation is l1, the impedance of the departure-side line can be calculated as R1 + jX1 = (R0 + jX0) × l1; given that the distance from the trolley to the arrival-side traction substation is l2, the impedance of the arrival-side line can be calculated as R2 + jX2 = (R0 + jX0) × l2. Assume the voltage division of the departure-side line impedance is... The voltage division of the line impedance on the driving side is If the power resistance of the simulated train is R, then the current equations for the line impedance between the train and the departing station, and between the train and the destination station, are as follows:

[0047]

[0048]

[0049] The current I0 flowing through the car is:

[0050]

[0051] The equation for the voltage division on the departure side is:

[0052]

[0053] The equation for the voltage division on the driving-side line is:

[0054]

[0055] The relationship between the voltage, current, and resistance at both ends of the train is as follows:

[0056]

[0057] Assuming the trolley is a resistive load with constant power, then the trolley's power P0 is:

[0058]

[0059] Since the trolley is a resistive load, the voltage across the trolley and the current flowing through it are in phase.

[0060]

[0061] Given the known line impedances R1+jX1 and R2+jX2, the current flowing through the trolley, and the trolley power P0, the voltage across the trolley can be calculated. Let the power of the car on the departure side be P1+jQ1, and the power on the arrival side be P2+jQ2, then:

[0062]

[0063]

[0064]

[0065]

[0066] The VSC is controlled based on the active power P1, P2 and reactive power Q1, Q2 of the required line impedance to simulate the line impedance.

[0067] To enable the VSC to control line impedance changes by utilizing active power P and reactive power Q, the VSC needs to be decoupled from its input voltage (DQ).

[0068] The specific DQ decoupling steps are as follows:

[0069] Since this system uses single-phase rectification, it is necessary to delay the single-phase AC system by 90° to construct a virtual orthogonal component.

[0070]

[0071] Rotation coordinates: Let the single-phase sinusoidal quantity be:

[0072]

[0073] The β virtual component is obtained by delaying by 1 / 4 period: x(t) = X q cos(ω0t)+X d sin(ω0t)

[0074]

[0075] Choosing the grid voltage Us as the reference vector, according to the Park transformation matrix, we can obtain:

[0076]

[0077]

[0078] ] Treat id and iq as reference values ​​for active and reactive components, respectively.

[0079]

[0080]

[0081] d-axis: q-axis:

[0082]

[0083]

[0084] Applying Laplace transform to the d-axis and q-axis currents yields:

[0085] (R+sL)i sd (s)=ω0L s i sq (s)+u sd (s)-u abd (s)

[0086] (R+sL)i sq (s)=-ω0L s i sd (s)+u sq (s)-u abq (s)

[0087] The relationship between d-axis and q-axis voltages and currents is defined as follows:

[0088] U df (s)=ω0L s i sq (s)+u sd (s)-u abd (s)

[0089] U qf (s)=-ω0L s i sd (s)+u sq (s)-u abq (s)

[0090] achievable

[0091] (R+sL)i sd (s)=U df (s)

[0092] (R+sL)i sq (s)=U qf (s)

[0093] Will U df (s), U qf (s) is constructed as follows:

[0094]

[0095]

[0096] The final DQ decoupling result is:

[0097]

[0098] The schematic diagram of using DQ to decouple and control VSC is as follows: Figure 3 As shown;

[0099] The active power P and reactive power Q at each moment are calculated and transmitted to the VSC, which controls the AC port to achieve a specific equivalent impedance. Since P and Q change continuously at each moment, the traction network impedance also changes continuously, enabling dynamic simulation of the traction network impedance.

Claims

1. A voltage source converter based traction network impedance emulation system, characterized in that, The system includes a three-phase transformer, a first single-phase transformer, a second single-phase transformer, a first voltage source converter, a second voltage source converter, and a power resistor. Both the first and second single-phase transformers are powered by the three-phase transformer. The first output terminal of the first single-phase transformer is connected in series with the first and second voltage source converters and then connected to the first output terminal of the second single-phase transformer. The second output terminals of both the first and second single-phase transformers are grounded. The series connection point of the first and second voltage source converters is connected to one end of the power resistor, and the other end of the power resistor is grounded. The power resistor is used to simulate a train, and the first and second voltage source converters are used to simulate the traction network impedance on both sides of the train. It also includes a controller for controlling the first voltage source converter and the second voltage source converter.

2. The voltage source converter based traction network impedance emulation system of claim 1, wherein, It also includes a third single-phase transformer, a third voltage source converter, and a fourth voltage source converter; the third single-phase transformer is also powered by the three-phase transformer, and the first output terminal of the third single-phase transformer is connected in series with the fourth voltage source converter and the third voltage source converter and then connected to the first output terminal of the second single-phase transformer, and the second output terminal of the third single-phase transformer is also grounded.

3. The control method of the voltage source inverter based traction network impedance emulation system as claimed in claim 1, characterized in that, include: Step 1: Let the simulated traction network impedance between the train and the first single-phase transformer be R1+jX1=(R0+jX0)×l1, and the simulated traction network impedance between the train and the second single-phase transformer be R2+jX2=(R0+jX0)×l2; where l1 is the length of the traction network between the train and the first single-phase transformer, l2 is the length of the traction network between the train and the second single-phase transformer, and R0+jX0 is the impedance per unit length of the traction network between the first single-phase transformer and the second single-phase transformer. Let the secondary voltages of the first and second single-phase transformers both be U∠0°, and the power of the power resistor be P0. Step 2, find the voltage at both ends of the train Specifically: Current flowing through the train According to Since the train is a resistive load, the voltage across the train is in phase with the current flowing through it. i.e. phase Combining the above equations, we obtain the voltage across the two ends of the train; Step 3: Calculate the voltage drop across the traction network between the train and the first single-phase transformer. Voltage division of the traction network between the train and the second single-phase transformer U1 and U2 are the effective values ​​of the voltage division between the train and the first and second single-phase transformers, respectively. These are the phases of the voltage division between the train and the first and second single-phase transformers in the traction network; Step 4: Calculate the power P1+jQ1 of the traction network between the train and the first single-phase transformer, and the power P2+jQ2 of the traction network between the train and the second single-phase transformer. Among them, active power reactive power Step 5: After P1+jQ1 and P2+jQ2 are decoupled by DQ respectively, the first voltage source converter and the second voltage source converter are controlled by PID to simulate the traction network impedance on both sides of the train.

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