Equivalent method for bilateral traction power supply system of electrified railway

Abstract

The invention belongs to the technical field of alternating-current traction bilateral power supply, and particularly relates to an equivalent method of an electrified railway bilateral traction power supply system. Based on a complex structure of an electrified railway double-side traction power supply system, a primary-side three-phase power grid power transmission system is simplified, and the primary-side three-phase power grid power transmission system is equivalent to a voltage source and resistance form through a linear source-containing two-port network equivalent method and participates in secondary-side single-phase traction electrical branch load flow calculation; and further analyzing the influence on the primary three-phase power grid electrical branch caused by the access of the secondary single-phase traction electrical branch. Compared with a traditional equivalent model, the model provided by the invention is more accurate, the theoretical analysis purpose is wider and clearer, the adopted linear source-containing two-port network equivalent method greatly simplifies the secondary side single-phase traction electrical branch load flow calculation process, and the calculation efficiency is improved. And great support is provided for the scheme design of a bilateral traction power supply system of an electrified railway in future.

Description

Technical Field

[0001] The present invention belongs to the technical field of AC traction bilateral power supply, and in particular relates to an equivalent method for an electrified railway bilateral traction power supply system. Background Art

[0002] Currently, dual-phase power supply technology is being adopted in domestic DC traction rail transit, but not in domestic AC electrified railways. Connecting traction loads as single-phase loads to the power system disrupts the existing three-phase symmetry of the power system, introducing negative-sequence and harmonics. To improve the power quality issues caused by the addition of traction loads, a phase rotation and zoned power supply solution is currently being implemented, with phase splitters installed at the traction substation exit and at the zoned substations. Phase splitters, as a weak link in the traction power supply system, not only reduce system reliability but also significantly impact line investment, routine operation and maintenance, and train operations. Implementing dual-phase power supply technology eliminates phase splitters located at the zoned substations, eliminating these dead zones. This improves system reliability, extends power supply distances, increases traction network voltage, and reduces losses. However, using dual-phase power supply technology also creates a parallel structure between adjacent traction substations and existing power system transmission lines, generating balanced current (circulating power), which can impact power flow control and railway electricity billing.

[0003] Therefore, the theoretical calculation of the relevant parameters of the bilateral traction power supply system is of urgent importance. Summary of the Invention

[0004] The purpose of this invention is to propose an equivalent method for the bilateral traction power supply system of an electrified railway. By constructing a new circuit structure of the bilateral traction power supply system of an electrified railway, the circuit calculation effect is simplified, which promotes the model construction and parameter calculation of the bilateral traction power supply system of an electrified railway, and provides a basis for the electrical characteristics analysis of a complex bilateral traction power supply system.

[0005] The technical solution adopted in the present invention is:

[0006] An equivalent method for a bilateral traction power supply system of an electrified railway comprises the following steps:

[0007] S1. Establish a bilateral traction power supply system for electrified railways, including a traction substation, a three-phase grid electrical branch, and a single-phase traction electrical branch. The three-phase grid electrical branch is connected to the primary side of the traction substation transformer, and the single-phase traction electrical branch is connected to the secondary side of the traction substation transformer. In addition, the B-phase circuit in the three-phase grid electrical branch is connected to the same-name terminal of the primary side, and the C-phase circuit is connected to the opposite-name terminal of the primary side.

[0008] Based on the above power supply system, an equivalent circuit is established, defining each traction substation as corresponding to a high-voltage power supply system. The high-voltage side incoming terminals of the transformers of two adjacent traction substations are taken as two-port network ports. The three-phase power grid electrical branch is equivalent to a linear source-containing two-port network including two power supply systems, and the single-phase traction electrical branch is equivalent to a linear passive two-port network.

[0009] S2. Use the generalized power equivalence theorem to process the linear two-port network with source, and equate it to a linear passive two-port network with two independent voltage sources added and the independent sources set to zero. Solve the transmission matrix of the linear passive two-port network with the independent sources set to zero and the equivalent power column vector coefficient matrix when applying the generalized Thevenin theorem;

[0010] S3, opening both ports of the linear two-port network with source at the same time, solving for the magnitudes of the two equivalent independent voltage sources, combining the linear passive two-port network transmission matrix with the independent sources set to zero obtained in step S2 with the equivalent power column vector coefficient matrix when applying the generalized Thevenin theorem, to obtain the port voltage-current relationship of the linear two-port network with source, and then obtaining the Z-parameter equivalent circuit of the linear two-port network with source;

[0011] S4. Combine the obtained Z-parameter equivalent circuit with a linear passive two-port network. Based on the electrical quantity relationship between the primary and secondary sides of the traction substation transformer, the electrical components of the primary-side Z-parameter equivalent circuit are equivalently transformed to the secondary side of the traction substation transformer. This simplifies the electrical branches of the three-phase power grid and constructs a new circuit structure for the bilateral traction power supply system for electrified railways. Based on this circuit structure, the balancing current and other required current, voltage, and power components are then solved.

[0012] Specifically, the specific method for solving the linear passive two-port network transmission matrix with independent sources set to zero in step S2 is:

[0013] Obtain relevant parameters of the electrical branch of the three-phase power grid, including the short-circuit impedance of the two power systems, the equivalent impedance of the transmission line, and the current at the two ports of the network. Calculate the mesh current using the mesh current method, then obtain the port voltage-current relationship, and finally obtain the transmission matrix.

[0014] Specifically, the specific method for solving the magnitudes of the two equivalent independent voltage sources in step S3 is:

[0015] The linear two-port network with source after opening is regarded as a symmetrical three-phase circuit. The voltages at both ends of each phase branch are equal. The currents of phase B and phase C branches are calculated respectively based on the short-circuit impedance, and then the open-circuit voltages of the two ports are solved respectively using KVL.

[0016] Specifically, the specific method of equivalently transforming the electrical components of the primary Z parameter equivalent circuit to the secondary side of the traction substation transformer in step S4 is:

[0017] The obtained Z parameter equivalent diagram is combined with the linear passive two-port network to obtain the current relationship between the four ports of the linear source-containing two-port network and the linear passive two-port network, and then converted into the balanced current of the single-phase traction branch and the traction transformer ratio of the traction substation, so that the controlled source is represented by resistance. Finally, the electrical components in the Z parameter equivalent diagram of the linear source-containing two-port network are converted to the secondary-side single-phase traction electrical branch by using the primary-secondary electrical quantity relationship of the traction transformer.

[0018] The beneficial effects of the present invention are as follows: based on the complex structure of the electrified railway bilateral traction power supply system, the primary three-phase power grid transmission system is simplified, and the primary three-phase power grid transmission system is equivalent to a voltage source plus a resistor through a linear source-containing two-port network equivalence method, and participates in the secondary single-phase traction electrical branch power flow calculation, and is then used to analyze the impact of the secondary single-phase traction electrical branch access on the primary three-phase power grid electrical branch. Compared with the traditional equivalent model, the model proposed by the present invention is more accurate, and the theoretical analysis is more widely used and clear. The linear source-containing two-port network equivalence method adopted greatly simplifies the secondary single-phase traction electrical branch power flow calculation process, providing great support for the future design of the electrified railway bilateral traction power supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a structural diagram of an electrified railway bilateral traction power supply system according to the present invention.

[0020] Figure 2 This is the equivalent circuit of the electrified railway bilateral traction power supply system of the present invention.

[0021] Figure 3 The linear source-containing two-port network and the linear passive two-port network of the present invention are

[0022] Figure 4 Schematic diagram of the linear passive two-port network mesh current method with independent source zeroing according to the present invention

[0023] Figure 5 The three-phase symmetrical circuit of the linear source-containing two-port network of the three-phase power transmission system of the present invention

[0024] Figure 6 This is the Z parameter equivalent circuit diagram of the linear two-port network with source according to the present invention.

[0025] Figure 7 The Z parameter equivalent circuit diagram of the linear source two-port network and the linear passive two-port network combination diagram of the present invention

[0026] Figure 8 This is the circuit structure of the new electrified railway bilateral traction power supply system described in the present invention.

[0027] Figure 9 This is a schematic diagram of the topology and basic parameters of a bilateral traction power supply system for an electrified railway according to the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is described in detail below with reference to the accompanying drawings:

[0029] like Figure 1 As shown, the first traction substation (TSS1) and the second traction substation (TSS2) are connected through a three-phase grid electrical branch. The secondary single-phase traction electrical branch, the primary three-phase grid electrical branch, the first power supply system, and the second power supply system together form an electrified railway bilateral traction power supply system. The above structure is equivalent to the circuit, and the equivalent circuit is as follows: Figure 2 shown.

[0030] Step S1 simplifies the bilateral traction power supply system of the electrified railway. The high-voltage side incoming terminals of the traction transformers of the two traction substations are selected as two-port network ports, and the bilateral traction power supply system of the electrified railway is decomposed into a combination structure of a linear source-containing two-port network of a three-phase power grid transmission system and a linear passive two-port network of a single-phase traction power supply system, as shown in the following example: Figure 3 shown.

[0031] Step S2 solves the linear passive two-port network transmission matrix with independent sources set to zero and the equivalent power column vector coefficient matrix when applying the generalized Thevenin theorem. Combined with step S1, the generalized power equivalence theorem is used to process the linear two-port network with sources in the three-phase power grid transmission system, and it is equivalent to a linear passive two-port network with independent sources set to zero with two independent voltage sources added. In order to solve the linear passive two-port network transmission matrix with independent sources set to zero at this time, as shown in FIG. Figure 4 As shown, the mesh current method is used to process it, as shown in formula (1):

[0032] (1)

[0033] in, and are the short-circuit impedances of the first power supply system and the second power supply system of the primary three-phase power grid transmission system, is the equivalent impedance of the three-phase power grid electrical branch transmission line, The current at port 1 of a linear passive two-port network with independent sources set to zero is, The current at port 2 of a linear passive two-port network with independent sources set to zero is, is the mesh 1 current, is the mesh 2 current, and the mesh current expression after solution is shown in formula (2):

[0034] (2)

[0035] Depend on Figure 4 The linear passive two-port network structure with independent sources set to zero is shown in Figure 3. Now we need to find the relationship between the port voltage and current, as shown in formula (3):

[0036] (3)

[0037] in, The voltage at port 1 of a linear passive two-port network with independent sources set to zero is, Voltage at port 2 of a linear passive two-port network with independent sources zeroed.

[0038] Combining equations (2) and (3), we get equation (4):

[0039] (4)

[0040] Solve the transfer matrix of a linear passive two-port network using the voltage-current relationship of the ports with independent sources set to zero As shown in formula (5) and (6):

[0041] (5)

[0042] (6)

[0043] When applying the generalized equivalent power theorem to a linear two-port network with a source, there are four equivalent circuits, corresponding to four different equivalent power column vector coefficient matrices. When using the generalized Thevenin theorem, the equivalent power column vector coefficient matrix of the linear two-port network with a source in the three-phase power transmission system is As shown in formula (7):

[0044] (7)

[0045] Step S3 determines the Z parameter equivalent circuit of the linear source-containing two-port network of the three-phase power grid transmission system. At the same time, open port 1 and port 2. At this time, the three-phase power grid transmission system is a symmetrical three-phase circuit, such as Figure 5 As shown, and The two points are equipotential, and the calculation of loops B and C is shown in formula (8):

[0046] (8)

[0047] in, and is the symmetrical voltage of the first power system of the three-phase power grid transmission system, and is the symmetrical voltage of the second power system of the three-phase power grid transmission system, and is the current of the first power supply system B and C branches of the three-phase power grid transmission system, and It is the current of branch B and branch C of the second power supply system of the three-phase power grid transmission system.

[0048] Combined with equation (8), using KVL, the open circuit voltages of port 1 and port 2 are solved respectively, as shown in equation (9):

[0049] (9)

[0050] in, and It is the open circuit voltage of the corresponding port when port 2 and port 1 are open.

[0051] Combining equations (6), (7) and (9), we get equations (10) and (11):

[0052] (10)

[0053] (11)

[0054] in, is the voltage of port 1 of the linear two-port network with source in the three-phase power transmission system, is the voltage at port 2 of the linear two-port network with source in the three-phase power transmission system, is the current of port 1 of the linear two-port network with source in the three-phase power transmission system, is the current of port 2 of the linear two-port network with source in the three-phase power transmission system, , .

[0055] Combined with formula (11), the voltage-current relationship of the linear two-port network with source in the three-phase power transmission system is solved, as shown in formula (12):

[0056] (12)

[0057] According to the voltage-current relationship of the linear two-port network with source in the three-phase power transmission system, the Z parameter equivalent circuit of the linear two-port network with source is obtained, as shown in Figure 6 shown.

[0058] Step S4 constructs a new circuit structure for the bilateral traction power supply system of the electrified railway, and calculates the balanced current based on this structure. The Z parameter equivalent circuit of the linear source two-port network of the three-phase power grid transmission system is combined with the linear passive two-port network of the single-phase traction power supply system, as shown in Figure 4. Figure 7 As shown. At this time, the relationship between the currents of the four ports is shown in formula (13):

[0059] (13)

[0060] in, is the current at port 3 of the linear passive two-port network of the single-phase traction power supply system, is the current at port 4 of the linear passive two-port network of the single-phase traction power supply system, is the balanced current generated by the single-phase traction power supply system when it is unloaded. The traction transformer ratios of the two adjacent traction substations are .

[0061] From formula (13), we can see that ,and and Can be It means that Figure 7 The controlled source is represented by resistance, as shown in formula (14):

[0062] (14)

[0063] in, The Z parameter equivalent circuit of the linear two-port network with source in the three-phase power transmission system is the equivalent resistance of the controlled source at port 1. It is the Z parameter equivalent circuit of the linear two-port network with source in the three-phase power transmission system and the equivalent resistance of the controlled source at port 2.

[0064] By using the relationship between the primary and secondary electrical quantities of the traction transformer, the electrical components in the Z-parameter equivalent circuit of the linear source-containing two-port network of the three-phase power grid transmission system can be converted to the secondary single-phase traction electrical branch, as shown in Equation (15):

[0065] (15)

[0066] in, The electromotive force of the power system of the three-phase power grid transmission system is converted from the linear source two-port network port 1 to the secondary single-phase traction electrical branch. The electromotive force of the power system of the three-phase power grid transmission system is converted from the linear source two-port network port 2 to the secondary single-phase traction electrical branch. is the incoming line resistance of the traction transformer of the first traction substation (TSS1), is the incoming line resistance of the traction transformer of the second traction substation (TSS2), The resistance of the traction transformer of the first traction substation (TSS1) converted to the secondary side single-phase traction electrical branch line. The resistance of the secondary single-phase traction electrical branch line of the traction transformer of the second traction substation (TSS2) is converted to the resistance. The equivalent self-impedance of port 1 of the linear two-port network with source in the three-phase power grid transmission system converted to the secondary single-phase traction electrical branch is: The equivalent self-impedance of port 2 of the linear two-port network with source in the three-phase power grid transmission system converted to the secondary single-phase traction electrical branch is: The Z parameter equivalent circuit of the linear two-port network with source in the three-phase power transmission system is converted from port 1 to the equivalent resistance of the controlled source of the secondary single-phase traction electrical branch. It is the Z parameter equivalent circuit of the linear two-port network with source in the three-phase power grid transmission system, and the equivalent resistance of the controlled source of the secondary single-phase traction electrical branch is converted from port 2.

[0067] Combined with formula (15), a new circuit structure of the bilateral traction power supply system for electrified railways is constructed, as follows: Figure 8 As shown in the figure, the equivalent model is used to calculate the balanced current of the single-phase traction power supply system, as shown in formula (16):

[0068] (16)

[0069] in, is the leakage reactance of the traction transformer of the first traction substation (TSS1), is the leakage reactance of the traction transformer of the second traction substation (TSS2), is the equivalent impedance of the traction network.

[0070] Through the above operations, the electrified railway bilateral traction power supply system is equivalent to a single-loop circuit structure from the original combination of a linear source two-port network and a linear passive two-port network, which greatly simplifies the original system model. It can provide assistance for the subsequent theoretical analysis of the electrified railway bilateral traction power supply system and the research on the balanced current suppression method.

[0071] Example

[0072] like Figure 9 As shown in the figure, this is a schematic diagram of the topological structure of a bilateral traction power supply system of an electrified railway. The first power supply system of the system provides a 220kV three-phase symmetrical voltage, and the second power supply system provides a phase difference with the first power supply system. The power system operates at a 220kV three-phase symmetrical voltage. Both power systems have a short-circuit capacity of 12,000MVA. Both traction substations utilize single-phase traction transformers with a transformer ratio of 220 / 27.5. The traction network between the two traction substations is 45km long, and the distance between the two power systems is 114km. The power lines to the first traction substation (TSS1) are 72km long, and to the second traction substation (TSS2) are 43km long.

[0073] The parameters of each part of the embodiment are set as follows:

[0074] Equivalent impedance of equivalent traction network per unit length , the equivalent impedance of the transmission line of the three-phase power grid electrical branch per unit length , the equivalent impedance of the power supply line per unit length of the first traction substation (TSS1) , the equivalent impedance of the power supply line per unit length of the second traction substation (TSS2) , the single-phase traction transformer has a rated capacity of 40MVA, a short-circuit loss of 130kW, and a short-circuit voltage of 10.5%.

[0075] The parameters of the electrified railway bilateral traction power supply system obtained from the above theory are as follows:

[0076] Three-phase power grid transmission system part: ; ; ; ; ; ; ; ; ; .

[0077] Single-phase traction power supply system: ; ; ; ; .

[0078] Part of the new electrified railway bilateral traction power supply system: ; ; ; ; ; ; ; .

[0079] The balanced current of the bilateral traction power supply system of the electrified railway is: .

[0080] After calculation, the error between the results and the actual simulation is not large, which verifies the correctness of the equivalent model.

Claims

1. An equivalent method for bilateral traction power supply systems of electrified railways, characterized in that: The following steps are involved: S1. Establish a bilateral traction power supply system for electrified railways, including a traction substation, a three-phase grid electrical branch, and a single-phase traction electrical branch. The three-phase grid electrical branch is connected to the primary side of the traction substation transformer, and the single-phase traction electrical branch is connected to the secondary side of the traction substation transformer. In addition, the B-phase circuit in the three-phase grid electrical branch is connected to the same-name terminal of the primary side, and the C-phase circuit is connected to the opposite-name terminal of the primary side. Based on the above power supply system, an equivalent circuit is established, defining each traction substation as corresponding to a high-voltage power supply system. The high-voltage side incoming terminals of the transformers of two adjacent traction substations are taken as two-port network ports. The three-phase power grid electrical branch is equivalent to a linear source-containing two-port network including two power supply systems, and the single-phase traction electrical branch is equivalent to a linear passive two-port network. S2. Use the generalized power equivalence theorem to process the linear two-port network with source, and equate it to a linear passive two-port network with two independent voltage sources added and the independent sources set to zero. Solve the transmission matrix of the linear passive two-port network with the independent sources set to zero and the equivalent power column vector coefficient matrix when applying the generalized Thevenin theorem; S3, opening both ports of the linear two-port network with source at the same time, solving for the magnitudes of the two equivalent independent voltage sources, combining the linear passive two-port network transmission matrix with the independent sources set to zero obtained in step S2 with the equivalent power column vector coefficient matrix when applying the generalized Thevenin theorem, to obtain the port voltage-current relationship of the linear two-port network with source, and then obtaining the Z-parameter equivalent circuit of the linear two-port network with source; S4. Combine the obtained Z parameter equivalent circuit with the linear passive two-port network. According to the relationship between the primary and secondary electrical quantities of the traction substation transformer, the electrical components of the primary side Z parameter equivalent circuit are equivalently transformed to the secondary side of the traction substation transformer, thereby simplifying the electrical branches of the three-phase power grid and constructing a new circuit structure of the bilateral traction power supply system for electrified railways. Based on this circuit structure, the balancing current and other required current, voltage and power component related parameters are solved.

2. The equivalent method of the bilateral traction power supply system of an electrified railway according to claim 1 is characterized in that: The specific method for solving the linear passive two-port network transmission matrix with independent sources set to zero in step S2 is: Obtain the relevant parameters of the three-phase power grid electrical branch, including the short-circuit impedance of the two power systems, the equivalent impedance of the transmission line, and the current at the two ports of the network. Calculate the mesh current using the mesh current method, then obtain the port voltage-current relationship, and finally obtain the transmission matrix, which is specifically: For a linear passive two-port network equivalent to two independent voltage sources with zero independent sources, the mesh current method is used to obtain: ， in, and are the short-circuit impedances of the first power supply system and the second power supply system of the primary three-phase power grid transmission system, is the equivalent impedance of the three-phase power grid electrical branch transmission line, The current at port 1 of a linear passive two-port network with independent sources set to zero is, The current at port 2 of a linear passive two-port network with independent sources set to zero is, is the mesh 1 current, is the mesh 2 current, and the mesh current expression is obtained after solving: ， For a linear passive two-port network with independent sources set to zero, the port voltage-current relationship is: ， in, The voltage at port 1 of a linear passive two-port network with independent sources set to zero is, The voltage at port 2 of a linear passive two-port network with independent sources set to zero; Combining the mesh current expression and the port voltage-current relationship, we can obtain: ， Solve the transfer matrix of a linear passive two-port network using the voltage-current relationship of the ports with independent sources set to zero : ， ， When applying the generalized equivalent power theorem to a linear two-port network with a source, there are four equivalent circuits, corresponding to four different equivalent power column vector coefficient matrices. When using the generalized Thevenin theorem, the equivalent power column vector coefficient matrix of the linear two-port network with a source in the three-phase power grid transmission system is : 。 3. The equivalent method of the bilateral traction power supply system of an electrified railway according to claim 2 is characterized in that: The specific method for solving the magnitudes of the two equivalent independent voltage sources in step S3 is: The linear two-port network with source after opening is regarded as a symmetrical three-phase circuit. The voltages at both ends of each phase branch are equal. The currents of phase B and phase C branches are calculated respectively based on the short-circuit impedance. Then, the open-circuit voltage of the two ports is solved respectively using KVL. Specifically, open port 1 and port 2. At this time, the three-phase power grid transmission system is a symmetrical three-phase circuit. The currents of phase B and phase C branches are: ， in, and is the symmetrical voltage of the first power system of the three-phase power grid transmission system, and is the symmetrical voltage of the second power system of the three-phase power grid transmission system, and is the current of the first power supply system B and C branches of the three-phase power grid transmission system, and The currents of branches B and C of the second power supply system of the three-phase power grid transmission system; Use KVL to solve the open circuit voltage of port 1 and port 2 respectively: ， in, and is the open circuit voltage of the corresponding port when port 2 and port 1 are open respectively; Combining the linear passive two-port network transmission matrix with independent sources set to zero obtained in step S2 with the equivalent power column vector coefficient matrix when applying the generalized Thevenin theorem, we obtain: ， ， in, is the voltage of port 1 of the linear two-port network with source in the three-phase power transmission system, is the voltage at port 2 of the linear two-port network with source in the three-phase power transmission system, is the current of port 1 of the linear two-port network with source in the three-phase power transmission system, is the current of port 2 of the linear two-port network with source in the three-phase power transmission system, , ; Thus, according to the port voltage-current relationship of the linear two-port network with source in the three-phase power grid transmission system, the Z parameter equivalent circuit of the linear two-port network with source is obtained.

4. The equivalent method of the bilateral traction power supply system of an electrified railway according to claim 3 is characterized in that: The specific method of equivalently transforming the electrical components of the primary Z parameter equivalent circuit to the secondary side of the traction substation transformer in step S4 is: Combining the obtained Z parameter equivalent diagram with the linear passive two-port network, the current relationship between the four ports of the linear source two-port network and the linear passive two-port network is obtained: ， in, is the current at port 3 of the linear passive two-port network of the single-phase traction power supply system, is the current at port 4 of the linear passive two-port network of the single-phase traction power supply system, is the balanced current generated by the single-phase traction power supply system when it is unloaded. The traction transformer ratios of the two adjacent traction substations are ; It is converted into the expression of the balanced current of the single-phase traction branch and the traction transformer ratio of the traction substation, so that the controlled source is expressed as a resistance: ， in, The Z parameter equivalent circuit of the linear two-port network with source in the three-phase power transmission system is the equivalent resistance of the controlled source at port 1. The Z parameter equivalent circuit of the linear two-port network with source in the three-phase power transmission system is the equivalent resistance of the controlled source at port 2; Finally, the electrical quantity relationship between the primary and secondary sides of the traction transformer is used to convert the electrical components in the Z parameter equivalent diagram of the linear source-containing two-port network into the secondary side single-phase traction electrical branch.

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