An Equivalent Method for Through-Connect Power Supply System of Electrified Railway

Abstract

The present invention discloses an equivalent method for an electrified railway through-power supply system. This method uses two-port circuit theory and Carson theory to equate the ring network power supply structure under the through-power supply system to an open power supply network. This method accurately analyzes the power flow distribution when different types of high-voltage power supply lines, trains operating in multiple working conditions on the traction network, and new energy power generation units are connected to the traction network. This method facilitates the theoretical derivation of power distribution, power loss, voltage at each node, and current distribution patterns in the network, laying a theoretical foundation for the electrical characteristic analysis of complex through-power supply systems. The method includes the following steps: S1, determining the equivalent circuit of the high-voltage power supply line; S2, determining the equivalent circuit of the traction network; S3, determining the equivalent circuit of the entire through-power supply system; and S4, performing equivalent transformation of the equivalent circuit of the ring network of the through-power supply system.

Description

Technical Field

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

[0002] Currently, electrified railways mostly use out-of-phase traction power supply. To reduce the unbalanced impact of traction load on the power system, phase splitting is generally installed at the exit and substation of the traction substation. Phase splitting is a weak link in the traction power supply system. Its existence can easily lead to excessive phase loss of train power, threatening the safety of railway system operation and, to a certain extent, limiting the reliable power supply of the railway system and improving the utilization rate of regenerative braking energy. With the rapid development of high-speed railways and the increasing in-depth research of domestic scholars on traction power supply systems, the proposal of a through-type power supply system provides new opportunities to solve these problems.

[0003] Based on power supply solutions such as the new cable-through power supply system and the high-voltage dedicated line-through power supply system, which are currently being researched, the use of combined, same-phase power supply technology effectively addresses power quality issues such as negative sequence, harmonics, and reactive power. Furthermore, by extending the power supply distance through bilateral connectivity, the phase separation between sub-zones can be effectively eliminated (or reduced), thereby eliminating power supply bottlenecks, improving railway power supply and transportation capabilities, and achieving phase-free, through-the-line power supply for the traction network.

[0004] The traction network of the through-line power supply system is fully connected. The parallel operation of the traction network and high-voltage power supply lines through the transformer magnetic circuit will form multiple ring network power supply structures. Therefore, theoretical analysis and research on the ring network power supply structure of the through-line power supply system is also an important part. In recent years, the scale of the railway system has gradually expanded. To accommodate the planning and design of new railways such as urban rail and remote areas in western China, the integration and layout of different types of equipment, such as new energy and energy storage, must be comprehensively considered. The impact of the external environment on the ring network architecture of the through-line power supply system will become more complex and variable. Therefore, it is urgent to establish a theoretical system for the power flow of the through-line power supply system to lay a theoretical foundation for practical engineering applications. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an equivalent method for the electrified railway through-power supply system, to equate the ring network power supply structure under the through-power supply system to an open power supply network structure, to accurately analyze the power flow distribution when different forms of high-voltage power supply lines, multi-operating trains on the traction network and new energy power generation units are connected to the traction network, to facilitate the theoretical derivation of power distribution, power loss, voltage at each node and current distribution rules in the electrified railway through-power supply system, and to lay a theoretical foundation for the electrical characteristics analysis of complex through-power supply systems.

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

[0007] An equivalent method for an electrified railway through-power supply system comprises the following steps:

[0008] S1. Determine the equivalent circuit of the high-voltage power supply line and perform equivalent transformation based on the electrical coupling relationship between the two-phase high-voltage power supply lines (transmission line and return line) and the circuit two-port theory;

[0009] S2. Determine the equivalent circuit of the traction network. Based on the overhead line-rail power supply network diagram and combined with Carson theory, simplify the traction network circuit structure and calculate the basic parameters of the equivalent traction network.

[0010] S3. Determine the equivalent circuit of the entire through-connection power supply system. Based on the through-connection power supply system structure and in combination with the partial network equivalent circuits obtained in steps S1 and S2, construct a simplified through-connection power supply system equivalent circuit.

[0011] S4. Equivalent transformation of the equivalent circuit of the through-power supply system. According to the ring network power supply structure under the through-power supply system, the split potential method is used at the access point between the external power supply and the through-power supply system to convert the complex ring network power supply structure of the through-power supply system into a two-terminal power supply network structure, and determine the position of the power distribution point, and further convert the two-terminal power supply network into two open power supply networks.

[0012] The beneficial effects of the present invention are as follows: based on the complex structure of the electrified railway through-line power supply system, the various network components are transformed and simplified, and the ring network power supply structure of the through-line power supply system is ultimately equivalent to an open power supply network structure, which facilitates the calculation of the through-line power supply system's power flow and is then used to theoretically analyze the power distribution, power loss, node voltage, and current distribution patterns in the through-line power supply system. Compared with the traditional lumped parameter equivalent model, the model proposed by the present invention is more accurate, the theoretical analysis is more extensive and clear, and it also facilitates the design of new through-line power supply systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The figure is a schematic structural diagram of an electrified railway through-power supply system according to the present invention.

[0014] Figure 2 This is a circuit model diagram of the high-voltage transmission line-return line coupling per unit length described in the present invention.

[0015] Figure 3 This is the equivalent circuit model diagram of the contact wire-rail per unit length described in the present invention.

[0016] Figure 4 This is the equivalent circuit of the electrified railway through-power supply system described in the present invention.

[0017] Figure 5It is the equivalent circuit of the open power supply network after the through power supply system ring network is equivalent to the present invention.

[0018] Figure 6 This is a schematic diagram of the topology and basic parameters of a high-voltage dedicated line through-power supply system in the example described in the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments:

[0020] like Figure 1 As shown in Figure 1, the first traction substation (SS1) and the second traction substation (SS2) are connected by a high-voltage power supply line (HTL). The high-voltage power supply line (HTL) is divided into a high-voltage transmission line and a high-voltage return line. The basic parameters of the two-phase lines are the same. First, a unit-length high-voltage transmission line-return line circuit model is constructed, as shown in Figure 1. Figure 2 As shown, the KVL voltage equation is written for the above circuit model, as shown in formula (1):

[0021]

[0022] in, is the potential at point A, is the potential at point B, is the potential at point C, is the potential at point D, is the input current at point A, is the output current at point C, is the voltage between terminals A and B, is the voltage between terminals C and D, Y Z is the self-admittance of the single-phase high-voltage power supply line to ground, Z Z is the equivalent self-impedance of the single-phase high-voltage power supply line. After solving, the relationship between the port voltage and current is obtained, as shown in equations (2) and (3):

[0023]

[0024]

[0025] According to the two-port network theory, the above Y parameter circuit model uses T parameters to describe the external characteristics of the port, as shown in formulas (4) and (5):

[0026]

[0027]

[0028] Where, det(Y ZZ ) represents Y ZZ Determinant of the parameter matrix.

[0029] When the high voltage power line (HTL) is an overhead line, the mutual admittance Y between the two phases needs to be considered. ZM , parameter matrix T of unit length overhead line ZZ-O , as shown in formula (6):

[0030]

[0031] When the high voltage power line (HTL) is a cable, there is no mutual capacitance between the two phase cables due to the effect of the cable shielding layer. The T parameter matrix per unit length of cable is T ZZ-C =T ZZ .

[0032] In summary, the parameter matrix T′ of the unit length high voltage power line (HTL) is ZZ , as shown in formula (7):

[0033]

[0034] According to the specified line length L km, the T parameter two-port cascade is performed to obtain the T parameter matrix of the entire high-voltage power supply line (HTL) As shown in formula (8):

[0035]

[0036] According to the relationship between the T parameter matrix and the π-type equivalent circuit, the above-mentioned high-voltage power supply line (HTL) is further transformed into a π-type equivalent circuit model, as shown in formula (9):

[0037]

[0038] Where, express Determinant of the parameter matrix;

[0039] Step S2 determines the traction network (OCS) equivalent circuit, such as Figure 3 As shown, the equivalent traction network (OCS) unit length impedance z is determined according to Carson theory C , as shown in formula (10):

[0040]

[0041] Among them, z T is the impedance per unit length of the contact network (T)-ground (G) loop, z R is the impedance per unit length of the rail (R)-ground (G) loop, z TR It is the mutual impedance per unit length between the contact network (T)-ground (G) loop and the rail (R)-ground (G) loop.

[0042] Based on the above-mentioned unit impedance of the equivalent traction network (OCS), the unit ground capacitance C of the equivalent traction network (OCS) line is considered. C , as shown in formula (11):

[0043] C C =C T +C TR (11)

[0044] Where C T is the capacitance per unit length of the contact line (T) to the ground, C TR is the mutual capacitance per unit length between the catenary (T) and the rail (R).

[0045] According to the specified traction network (OCS) length of 11km, the corresponding traction network (OCS) impedance Z C , admittance Y C , as shown in formula (12):

[0046]

[0047] Where f is the 50Hz power frequency.

[0048] Step S3 determines the equivalent circuit of the entire through power supply system. The excitation admittances of the two single-phase traction transformers (TT1, TT2) in the through power supply system are both negligible. The impedance Z′ of the single-phase traction transformer is calculated to the high voltage side. TT Instead, consider that the transformation ratio k of the two traction transformers is the same, and the traction network (OCS) parameters are converted to the high-voltage side voltage level according to the transformation ratio k, that is, Z′ C =k 2 Z C , Y′ C =Y C / k 2 ,like Figure 4 shown.

[0049] Trains running on the traction network (OCS) and connected new energy power generation units are all treated as load points.

[0050] Step S4 is to perform equivalent transformation of the power supply system equivalent circuit, such as Figure 5 As shown, the voltage at the access point of the external power supply (VSS) and the through-power supply system The voltages after equipotential splitting are have

[0051] Equivalent system power Split into two equal power branches The ring network structure of the through-line power supply system is converted into a two-terminal power supply network. In order to further accurately calculate the power distribution and node voltage in the network, the location of the power distribution point must be determined first.

[0052] Let the rated voltage of the high voltage side of the single-phase traction transformer be The rated voltage of the low voltage side is The power relationship at each position of the line is shown in formula (13):

[0053]

[0054] Where, They are the parallel admittances Y on the left and right sides of the high voltage power line (HTL) Z1 、Y Z2 Equivalent load power generated; Q Cm The length of the mth segment is l m Charging power generated by the parallel admittance of km-long traction network (OCS) lines; The load power at points N1, N2, and N3 respectively (the connection point between the equivalent traction network line and the first traction transformer is N1, the connection point between the equivalent traction network line and the second traction transformer is N2, and the connection point between the second traction transformer and the high-voltage power supply line is defined as N3); S′ Lm is the total load power at the mth load point on the traction network (OCS) line.

[0055] Ignoring the power loss in the network, when the traction network (OCS) line is connected to n loads, calculate the two power supply points The output power As shown in formula (14):

[0056]

[0057] Where Z ∑ is the total impedance of the entire line; Z i , Z′ i are the total impedance from the i-th load point to the two power supply points on the traction network (OCS) line, is the load power of the i-th load on the traction network (OCS) line.

[0058] After determining the power output at the power supply point, the power distribution throughout the entire line can be calculated based on the power conservation principle. When power flows from two directions at a load point, this load point is the power distribution point in the line. (When only one train is pulling the traction network (OCS), the voltage at the train terminal is typically the lowest, and the network power distribution point is at the location of the pulling train.)

[0059] Assume that the power distribution point is located at the load Position, divide the load at the power distribution point into Two parts, there are

[0060] Through the above operations, the power supply network at both ends is untied into It is a two-open power supply network for terminal loads, so as to facilitate the subsequent theoretical analysis of the electrical characteristics of the through-power supply system.

[0061] Example:

[0062] like Figure 6 The figure shows the topology of a dedicated high-voltage power supply system. The system's central traction substation is powered by a 220kV three-phase power supply. Both the central traction substation and the ordinary traction substations utilize single-phase traction transformers with a 220 / 27.5 ratio. The high-voltage power supply line between the two substations is connected by a two-wire, single-phase dedicated external power line. The central traction substation, high-voltage power supply line, traction network, and ordinary traction substations form a ring network. The dedicated high-voltage external power line utilizes single-core cross-linked polyethylene cable. The 220kV high-voltage power supply line is 40km long. A train is operating in traction mode in the middle of the traction network. The train simulates a constant power condition, with P = 20MW and a power factor of 0.98.

[0063] The network parameters of each part of the embodiment are set as follows:

[0064] Equivalent system power output voltage U S The contact line self-impedance per unit length is Z T =0.167+j0.595Ω; self-impedance of rail per unit length Z R =0.140+j0.581Ω; mutual impedance Z between the contact network and the rail TR =0.05+j0.339Ω; Equivalent contact network unit ground admittance C C =8.7123×10 -9 F; self-impedance per unit length of high-voltage traction cable Z Z =0.1106+j0.7232Ω; Admittance per unit length of high-voltage traction cable to ground Y Z =j4.0608×10 -5 s; 220 / 27.5 single-phase traction transformer with rated capacity of 40MVA, short-circuit loss of 130kW and short-circuit voltage of 10.5%.

[0065] The above theoretical calculations yield the following parameters for the equivalent circuit of the ring network of this high-voltage dedicated line through-line power supply system:

[0066] High voltage power supply line part: Z Z =4.8798+j18.1983Ω; Y Z1=Y Z2 =1.3510×10 -7 +j4.0658×10 -4 , S Z1 =S Z2 =0.0065-j19.6787MVA;

[0067] Single-phase traction transformer part: Z' TT =3.9325+j 1.2705×10 2 Ω.

[0068] Equivalent traction network part: Z' C1 =Z' C2 =1.9956×10 2 +j 5.2216×10 2 Ω; Y' C1 =Y' C2 =j4.2767×10 -7 s;Q C1 =Q C2 =-j0.0103Mvar;

[0069] Train power: S L =20+j4.0612MVA;

[0070] Power at load point: S N1 =Q C1 =-j0.0103Mvar; S N2 =Q C2 =-j0.0103Mvar; S N3 =S Z2 =0.0065-j19.6785MVA; S' L =S L +2jQ C1 =20+j4.0405MVA.

[0071] Substitute the above-mentioned parameter values ​​into the following formula:

[0072]

[0073] Calculate the two power points U S1 、U S2 The power output to the load side is S1=10.1266+j1.7632MVA and S2=9.8799-j17.4220MVA respectively.

[0074] Further calculation of the power distribution on the line shows that the train power can be divided into S' L1 =10.1266+j1.7735MVA, S' L2=9.8734+j2.2670MVA, so the two-terminal power supply network is equivalent to two open power supply networks at the train. The error between the calculated result and the actual simulation is very small, which does not affect the actual theoretical analysis.

Claims

1. An equivalent method for an electrified railway through-power supply system, characterized in that: The following steps are involved: S1. Determine the equivalent circuit of the high-voltage power supply line, and perform equivalent transformation based on the electrical coupling relationship between the two-phase high-voltage power supply lines and the circuit two-port theory; S2. Determine the equivalent circuit of the traction network. Based on the overhead line-rail power supply network diagram and combined with Carson theory, simplify the traction network circuit structure and calculate the basic parameters of the equivalent traction network. The specific method is as follows: Determination of equivalent traction network unit length impedance based on Carson theory : ， in, is the impedance per unit length of the contact network-ground loop, is the unit length impedance of the rail-ground loop, is the mutual impedance per unit length between the catenary-ground loop and the rail-ground loop; On the basis of obtaining the equivalent traction network unit length impedance, the unit ground capacitance of the equivalent traction network line is considered. : ， in, is the capacitance per unit length of the contact line to ground, is the mutual capacitance per unit length between the catenary and the rail; Calculate the corresponding traction network impedance based on the specified traction network length of 11km , admittance : ， Where, f is the power frequency of 50Hz; S3. Determine the equivalent circuit of the entire through-power supply system. According to the power supply structure of the through-power supply system and in combination with the equivalent circuits of the partial network obtained in step S1 and step S2, a simplified equivalent circuit of the through-power supply system is constructed. When determining the equivalent circuit of the entire through-power supply system, for the through-power supply system composed of the first traction substation and the second traction substation, ignore the excitation admittance of the single-phase traction transformer in the first traction substation and the second traction substation, and use the impedance of the single-phase traction transformer to be converted to the high-voltage side. Instead, consider that the transformation ratio k of the two traction transformers is the same, and the traction network parameters are converted to the high-voltage side voltage level according to the transformation ratio k, that is, , At the same time, trains running on the traction network and connected new energy power generation units are all treated as load points; S4. Equivalent transformation of the equivalent circuit of the through-power supply system. According to the ring network power supply structure under the through-power supply system, the split potential method is used at the access point between the external power supply and the through-power supply system to transform the complex ring network power supply structure of the through-power supply system into a two-terminal power supply network structure, and determine the position of the power distribution point, and further transform the two-terminal power supply network into two open power supply networks.

2. The equivalent method of an electrified railway through power supply system according to claim 1, characterized in that: The specific method of step S1 is: Define the first traction substation and the second traction substation as connected by a high-voltage power supply line. Define the two ports of the first traction substation connected to the high-voltage power supply line as points A and B, and the two ports of the second traction substation connected to the high-voltage power supply line as points C and D. The high-voltage power supply line is divided into a high-voltage transmission line and a high-voltage return line. Define the current to flow from point A to point C. The basic parameters of the two-phase line are the same. Construct a unit-length high-voltage transmission line-return line circuit model, and write the KVL voltage equation for the circuit model: ， in, is the potential at point A, is the potential at point B, is the potential at point C, is the potential at point D, is the input current at point A, is the output current at point C, is the voltage between terminals A and B, is the voltage between terminals C and D, It is the self-admittance of the single-phase high-voltage power supply line to the ground. is the equivalent self-impedance of the single-phase high-voltage power supply line. After solving, the relationship between the port voltage and current is obtained: ， ， According to the two-port network theory, the Y parameter circuit model uses T parameters to describe the external characteristics of the port: ， ， in, express Determinant of the parameter matrix; When the high-voltage power supply line is an overhead line, the mutual admittance between the two phase lines needs to be considered. , T parameter matrix of unit length overhead line : ， When the high-voltage power supply line is a cable, there is no mutual capacitance between the two-phase cables due to the effect of the cable shielding layer. The T parameter matrix of the unit length cable is ; The T parameter matrix of the unit length high-voltage power supply line can be obtained : ， According to the specified line length L km, the T parameter two-port cascade is performed, and the T parameter matrix of the entire high-voltage power supply line is obtained after cascading. : ， according to Parameter matrix and The relationship between the high-voltage power supply line and the equivalent circuit is further transformed into Equivalent circuit model of type: ， in, express Determinant of the parameter matrix.

3. The equivalent method of an electrified railway through power supply system according to claim 2, characterized in that: The specific method of step S4 is: Define the voltage at the access point of the external power supply and the through-power supply system The voltages after equipotential splitting are 、 ,have ;Equivalent system power Split into two equal power branches 、 , the ring network power supply structure of the through-power supply system is converted into a two-terminal power supply network structure. In order to further accurately calculate the power distribution and node voltage in the network, the location of the power distribution point must be determined first: Let the rated voltage of the high-voltage side of the single-phase traction transformer be , the rated voltage of the low voltage side is , define the connection point between the equivalent traction network line and the first traction transformer as N1, the connection point between the equivalent traction network line and the second traction transformer as N2, and the connection point between the second traction transformer and the high-voltage power supply line as N3. The power relationship at each position of the line is: ， Where, 、 They are the parallel admittances on the left and right sides of the high-voltage power supply line 、 Equivalent load power generated; The length of the mth segment is l m Charging power generated by the parallel admittance of km-long traction network lines; 、 、 are the load powers at points N1, N2, and N3 respectively; is the total load power at the mth load point on the traction network line; Ignoring the power loss in the network, when the traction network line is connected to n loads, calculate the two power supply points 、 Output power 、 : ， in, is the total impedance of the entire line; 、 are the total impedances from the i-th load point to the left and right power supply points on the traction network line, is the load power of the i-th load on the traction network line; After finding the power output of the power supply point, the power distribution in the entire line can be calculated based on the power conservation condition. When power flows into a certain load point from two directions, the position of this load point is the power distribution point in the line.

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