Power flow control device, comprehensive compensation device and comprehensive compensation method for same-phase power supply of railway

Abstract

The invention discloses a power flow control device and a comprehensive compensation device and method for railway in-phase power supply, and relates to the technical field of alternating current electrified railway power supply. The power flow control device comprises a converter, the comprehensive compensation device comprises a transformer and the power flow control device, the three-phase voltage unbalance degree, the power factor and the traction bus voltage serve as compensation target values, comprehensive compensation of the electric energy quality and the power supply capacity is achieved at the same time, and the power supply capacity is improved by changing the value of a port wiring angle according to the known train load. The active power and the reactive power of each converter under different compensation schemes can be obtained, the comprehensive compensation optimization of the in-phase power supply system of the railway is realized, and the long-distance power supply advantage of the in-phase power supply system can be further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply for AC electrified railways, and particularly to a power flow control device, a comprehensive compensation device for in-phase power supply of railways, and a comprehensive compensation method.

[0002] Background and Significance

[0003] As an efficient, high-speed, and low-carbon long-distance transportation mode, electrified railways are widely used for passenger and freight transportation. As the sole power source for electrified railway trains, the traction power supply system is crucial for ensuring the safe and reliable operation of trains. The traditional single-phase AC 25 kV traction power supply system has been widely adopted in most countries such as China, France, the United Kingdom, and Japan, showing good performance. However, the high power and single-phase load characteristics of trains cause serious three-phase voltage imbalance on the power system side, threatening the operation of generators, relay protection devices, communication lines, and the safe and stable operation of the entire system. The traditional method of reducing the three-phase voltage imbalance is to rotate the phase sequence of the traction substation connected to the power system and set electric phase separation at the traction substation and the section post between adjacent traction substations. The electric phase separation is a no-power area. When the train passes through the electric phase separation, transient overvoltage and overcurrent will be generated, which will affect the operation state of the pantograph and the traction network. At the same time, the train cannot obtain electric energy, and passing through the electric phase separation by inertia will cause speed loss, increase the running time of the train, and in severe cases, the train may stop or the braking may fail. In addition, the electric phase separation also blocks the energy flow between different power supply arms, resulting in a large amount of regenerative braking energy that cannot be utilized by locomotives in the traction mode, and the reverse power sent to the power system exacerbates the imbalance impact on the power system.

[0004] In addition to the influence of the electric phase separation, for the improvement of the transportation capacity of existing lines and the problem of high-power traction of trains on long and steep slopes, it is necessary to ensure the qualified traction network voltage of the train. In order to eliminate the adverse effects of the electric phase separation, further improve the power supply capacity of the traction power supply system, and give full play to the long-distance power supply advantage of in-phase power supply, it is necessary to conduct research on a power flow control device, a comprehensive compensation device, and a method with the three-phase voltage imbalance degree, power factor, and traction bus voltage of the system as the compensation target values. Summary of the Invention

[0005] Aiming at the above problems, the present invention aims to provide a power flow control device, a comprehensive compensation device for in-phase power supply of railways, and a comprehensive compensation method, specifically relating to a comprehensive compensation device and method for the three-phase voltage imbalance degree, power factor, and traction bus voltage of the railway in-phase power supply system, and solving the power quality problem mainly dominated by negative sequence while improving the power supply capacity of the system.

[0006] One object of the present invention is to provide a power flow control device, which includes converters β1, β2, β3 and a DC bus. One side of each of the converters β1, β2, β3 is connected to the DC bus, and the other sides of the converters β1, β2, β3 are respectively connected to the β port on the secondary side of transformer TT1, the primary side of transformer TT2, and the primary side of transformer TT3; the primary side of transformer TT1 is connected to a three-phase power grid, and the secondary side is provided with α and β ports. Two terminals are fed out from the α port, one of which is connected to the traction bus after being connected in series with the secondary side of transformer TT3, and the other is grounded; the two terminals on the secondary side of transformer TT2 are respectively connected to the traction bus and the ground; the traction bus supplies power to train loads on the railway traction network through traction feeders; by adjusting the active power and reactive power of the converters β1, β2, β3, comprehensive compensation is performed on the load power on the secondary side of transformer TT1 and the voltage of the traction bus.

[0007] In the present invention, by adjusting the active power and reactive power of the converters β1, β2, β3, the active power and reactive power of the load on the secondary side of transformer TT1 can be changed, so as to adjust the three-phase voltage unbalance degree and power factor of the railway single-phase power supply system. At the same time, adjusting the active power and reactive power of the converters β1, β2, β3 can also change the voltage of the traction bus of the railway single-phase power supply system, thereby achieving comprehensive compensation of the three.

[0008] Another object of the present invention is to provide a comprehensive compensation device for railway single-phase power supply, which includes transformers TT1, TT2, TT3 and a power flow control device. Both transformers TT2 and TT3 are single-phase transformers; transformer TT1 is a three-phase-two-phase traction transformer, and the three-phase-two-phase traction transformer includes Vv, Scott and YNvd connection transformers, and also includes a three-phase-two-phase transformer composed of a single-phase transformer and a YNd connection transformer; according to the train load, control the converters β1, β2, β3 to output adjustable active power and reactive power, so that the three-phase voltage unbalance degree of the load on the secondary side of transformer TT1 at the common connection point of the three-phase power grid, the power factor of the secondary side of transformer TT1, and the voltage increment of the traction bus meet the compensation target values.

[0009] Preferably, the compensation target value of the three-phase voltage unbalance degree of the load on the secondary side of transformer TT1 at the common connection point of the three-phase power grid can be a value that meets the railway design standard, or a preset value that meets the safe and stable operation of the three-phase power grid and the railway.

[0010] Preferably, the compensation target value of the power factor of the secondary side of transformer TT1 can be a value that meets the railway design standard, or a preset value that meets the safe and stable operation of the three-phase power grid and the railway, such as 0.9, 0.95, 0.98, etc.

[0011] Preferably, the compensation target value of the voltage increment of the traction busbar can be a value that meets the railway design standard, or a preset value that meets the safe and stable operation of the railway.

[0012] Preferably, the integrated compensation device of the present invention is applicable to the direct power supply mode or the direct power supply mode with a return line in the railway traction network power supply mode.

[0013] The third object of the present invention is to provide a comprehensive compensation method for in-phase power supply of railways, including the following steps:

[0014] S1. Set the complex powers of the converters β2 and β3 to be P β2 +jQ β2 and P β3 +jQ β3 , and define the direction in which the power flows from the DC busbar of the power flow control device to the traction network as the positive direction;

[0015] Set the complex power of the converter β1 to be P β1 +jQ β1 , and define the direction in which the power flows from the three-phase to two-phase traction transformer TT1 to the DC busbar of the power flow control device as the positive direction;

[0016] Set the port connection angles ψ α and ψ β to be the angles by which the α and β port voltages on the secondary side of the transformer TT1 lag behind the reference voltage of phase A of the three-phase power grid respectively;

[0017] The calculation formula for the three-phase voltage unbalance degree at the common connection point of the secondary side load of the transformer TT1 in the three-phase power grid is

[0018]

[0019] where ε U and δ are the amplitude and phase angle of the three-phase voltage unbalance degree at the common connection point; S d is the short-circuit capacity at the common connection point; j is the imaginary unit; P α , Q α are the active power and reactive power of the load at the α port on the secondary side of the transformer TT1;

[0020] S2. Set the compensation target value of the power factor on the secondary side of the transformer TT1 to be The active and reactive power relationships between different ports of the transformer TT1 are

[0021]

[0022] where P L , Q LIt is the active power and reactive power provided to the train load through the traction bus;

[0023] S3. Combining equations (1) and (2), we can get the active power and reactive power of converter β1:

[0024]

[0025] Substituting equation (3) into equation (2), we get the active power and reactive power constraints of converters β2 and β3 as

[0026]

[0027] The voltage increment of the traction bus caused by the converter β3 is affected by the introduction of the traction bus voltage regulation coefficient ρ. If constraints are imposed, then

[0028]

[0029] Among them, ρ x and ρ y are the real and imaginary parts of ρ; is the voltage of the traction bus;

[0030] Furthermore, according to equation (5), the complex power of converter β3 is

[0031]

[0032] Combining equations (4) and (6), we can obtain the active power and reactive power of converters β2 and β3 as follows:

[0033]

[0034] S4. Setting ε U ,δ, The values of and ρ are substituted into equations (4) and (7) to determine the active power and reactive power of converters β1, β2 and β3, thus realizing the comprehensive compensation of the three-phase voltage imbalance of railway co-phase power supply, the power factor of the secondary side of transformer TT1 and the voltage increment of the traction bus.

[0035] As a preferred embodiment, the port connection angle ψ in equation (4) and equation (7) is determined respectively according to various connection modes of the three-phase to two-phase connection transformer TT1. α and ψ β The value of controls the converters β1, β2, and β3 to output active power and reactive power that match the wiring mode of transformer TT1.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1) The power flow control device of the present invention can adjust the active power and reactive power of the converters β1, β2, and β3, change the active power and reactive power of the load on the secondary side of the transformer TT1, and change the traction bus voltage of the railway single-phase power supply system, so as to achieve the comprehensive compensation of the three-phase voltage unbalance degree, power factor, and traction bus voltage of the railway single-phase power supply system;

[0038] 2) The comprehensive compensation device and method proposed in the present invention take the three-phase voltage unbalance degree, power factor, and traction bus voltage as the compensation target values, and simultaneously achieve the comprehensive compensation of power quality and power supply capacity, which helps to further enhance the long-distance power supply advantage of the railway single-phase power supply system;

[0039] 3) The comprehensive compensation device and method proposed in the present invention can ensure that the traction bus voltage works within a reasonable voltage range, avoid the occurrence of over-limit traction network voltage, and improve the reliability of power supply;

[0040] 4) The comprehensive compensation device and method proposed in the present invention can make the converter power change with different wiring modes of the three-phase to two-phase transformer, ensure that the three-phase voltage unbalance degree, power factor, and traction bus voltage are always in the optimal compensation state, achieve the optimal compensation effect, avoid the occurrence of excessive three-phase voltage unbalance degree, non-compliance of power factor, and over-limit traction network voltage, and improve the reliability of power supply;

[0041] 5) The comprehensive compensation device and method proposed in the present invention supply power to the traction bus through the transformer and the power flow control device to achieve comprehensive compensation, and transmit electric energy with consistent phases to the traction network through the traction bus, realizing single-phase power supply of the traction network. The structure is simple, the technology is reliable, the performance is excellent, and it is easy to implement.

[0042] 6) The comprehensive compensation device and method proposed in the present invention are applicable to the direct power supply mode or the direct power supply mode with a return line of the railway traction network, and improve the power supply capacity of the direct power supply mode or the direct power supply mode with a return line. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 FIG. is a schematic diagram of a comprehensive compensation scheme for a railway single-phase power supply system with a return line in the present invention.

[0044] Figure 2 FIG. is a schematic diagram of a structure for jointly performing comprehensive compensation by using a Scott connection transformer and a power flow controller in the present invention.

[0045] Figure 3 FIG. is a schematic diagram of a structure for jointly performing comprehensive compensation by using a Vv connection transformer and a power flow controller in the present invention.

[0046] Figure 4It is a schematic structural diagram of comprehensive compensation jointly carried out by a three-phase-two-phase connection transformer composed of a single-phase connection transformer and a YNd connection transformer and a power flow controller according to the present invention. Specific embodiments

[0047] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The accompanying drawings do not represent all embodiments.

[0048] As Figure 1 shown, there is provided a schematic diagram of a comprehensive compensation scheme for a railway cophase power supply system with a direct power supply method with a return line. An external power source (such as a three-phase power grid) transmits electric energy to a traction substation TS through three-phase transmission lines. After the traction substation TS steps down the voltage and conducts comprehensive compensation, it transmits electric energy with the same phase to the traction network through a traction busbar and a traction feeder, realizing cophase power supply for the traction network.

[0049] This embodiment provides a power flow control device, including converters β1, β2, β3 and a DC busbar. One side of each of the converters β1, β2, β3 is connected to the DC busbar, and the other sides of the converters β1, β2, β3 are respectively connected to the β port on the secondary side of a transformer TT1, the primary side of a transformer TT2, and the primary side of a transformer TT3; the primary side of the transformer TT1 is connected to a three-phase power grid, and the secondary side is provided with α and β ports. Two terminals are fed out from the α port, one of which is connected to the traction busbar after being connected in series with the secondary side of the transformer TT3, and the other terminal is grounded; the two terminals on the secondary side of the transformer TT2 are respectively connected to the traction busbar and the ground; the traction busbar supplies power to train loads on the railway traction network through the traction feeder; by adjusting the active power and reactive power of the converters β1, β2, β3, comprehensive compensation is carried out on the load power on the secondary side of the transformer TT1 and the voltage of the traction busbar.

[0050] This embodiment also provides a comprehensive compensation device for railway cophase power supply, including transformers TT1, TT2, TT3 and a power flow control device. Both the transformers TT2 and TT3 are single-phase transformers; the transformer TT1 is a three-phase-two-phase traction transformer, and the three-phase-two-phase traction transformer includes Vv, Scott and YNvd connection transformers, and also includes a three-phase-two-phase transformer composed of a single-phase transformer and a YNd connection transformer; according to the train load, control the converters β1, β2, β3 to output adjustable active power and reactive power, so that the three-phase voltage unbalance degree of the load on the secondary side of the transformer TT1 at the common connection point of the three-phase power grid, the power factor of the secondary side of the transformer TT1, and the voltage increment of the traction busbar meet the compensation target values.

[0051] As an optional embodiment, the comprehensive compensation device of the present invention is applicable to a direct power supply method or a direct power supply method with a return line for the railway traction network power supply method.

[0052] This embodiment also provides a comprehensive compensation method for railway in-phase power supply, including the following steps:

[0053] S1. Set the complex powers of converters β2 and β3 to be P β2 +jQ β2 and P β3 +jQ β3 , and define the direction in which power flows from the DC bus of the power flow control device to the traction network as the positive direction;

[0054] Set the complex power of converter β1 to be P β1 +jQ β1 , and define the direction in which power flows from the three-phase to two-phase traction transformer TT1 to the DC bus of the power flow control device as the positive direction;

[0055] Set the port connection angles ψ α and ψ β to be the angles by which the α and β port voltages on the secondary side of transformer TT1 lag the reference voltage of phase A of the three-phase power grid respectively;

[0056] The calculation formula for the three-phase voltage unbalance degree at the common connection point of the secondary side load of transformer TT1 and the three-phase power grid is

[0057]

[0058] where ε U and δ are the amplitude and phase angle of the three-phase voltage unbalance degree at the common connection point; S d is the short-circuit capacity at the common connection point; j is the imaginary unit; P α , Q α are the active power and reactive power of the load on the α port of the secondary side of transformer TT1;

[0059] S2. Set the compensation target value of the power factor on the secondary side of transformer TT1 to be The relationship between the active power and reactive power between different ports of transformer TT1 is

[0060]

[0061] where P L , Q L are the active power and reactive power provided to the train load through the traction bus;

[0062] S3. Combine equations (1) and (2) to obtain the active power and reactive power of converter β1 as

[0063]

[0064] Substituting equation (3) into equation (2), we get the active power and reactive power constraints of converters β2 and β3 as

[0065]

[0066] The voltage increment of the traction bus caused by the converter β3 is affected by the introduction of the traction bus voltage regulation coefficient ρ. If constraints are imposed, then

[0067]

[0068] Among them, ρ x and ρ y are the real and imaginary parts of ρ; is the voltage of the traction bus;

[0069] Furthermore, according to equation (5), the complex power of converter β3 is

[0070]

[0071] Combining equations (4) and (6), we can obtain the active power and reactive power of converters β2 and β3 as follows:

[0072]

[0073] S4. Setting ε U ,δ, The values of and ρ are substituted into equations (4) and (7) to determine the active power and reactive power of converters β1, β2 and β3, thus realizing the comprehensive compensation of the three-phase voltage imbalance of railway co-phase power supply, the power factor of the secondary side of transformer TT1 and the voltage increment of the traction bus.

[0074] As an optional embodiment, the port connection angles ψ in equations (4) and (7) are determined according to various connection modes of the three-phase to two-phase traction transformer TT1. α and ψ β The value of controls the active power and reactive power output of converters β1, β2, and β3 to match the connection mode of transformer TT1. Port connection angle ψ α and ψ β Different values will result in different connection methods of the three-phase-two-phase traction transformer TT1, and different output powers of the corresponding converters β1, β2, and β3. This solution can output power that matches different connection methods of the three-phase-two-phase traction transformer to achieve optimal compensation.

[0075] As an optional embodiment, by determining the port connection angle ψ in equation (4) and equation (7): α and ψ βThe values of are used to determine the active power and reactive power of the converters β1, β2, and β3 under different compensation schemes. As Figure 2 shown, according to the known train load, an integrated compensation scheme consisting of a Scott-connected transformer and a power flow controller is adopted, and ε U , δ, and ρ are set, and the port connection angles ψ α and ψ β are set to -30° and -120° respectively, and substituted into equations (4) and (7) to determine the active power and reactive power of the converters β1, β2, and β3. As Figure 3 shown, according to the known train load, an integrated compensation scheme consisting of a Vv-connected transformer and a power flow controller is adopted, and ε U , δ, and ρ are set, and the port connection angles ψ α and ψ β are set to -30° and 90° respectively, and substituted into equations (4) and (7) to determine the active power and reactive power of the converters β1, β2, and β3. As Figure 4 shown, according to the known train load, an integrated compensation scheme consisting of a three-phase to two-phase traction transformer composed of a single-phase transformer and a YNd-connected transformer and a power flow controller is adopted, and ε U , δ, and ρ are set, and the port connection angles ψ α and ψ β are set to -30° and 120° respectively, and substituted into equations (4) and (7) to determine the active power and reactive power of the converters β1, β2, and β3. The present invention takes the three-phase voltage unbalance degree, power factor, and traction bus voltage as the compensation target values. By changing the values of the port connection angles, the active power and reactive power of the converters β1, β2, and β3 under different compensation schemes can be obtained, realizing the optimization of the integrated compensation of the traction power supply system.

[0076] The above is only the preferred embodiment of the present invention. It should be noted that the above preferred embodiment should not be regarded as a limitation of the present invention. The protection scope of the present invention should be subject to the scope defined by the claims. For those of ordinary skill in the art, without departing from the spirit and scope of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A current control device, characterized in that, It includes converters β1, β2, β3 and a DC bus, one side of the converters β1, β2, β3 are connected to the DC bus, and the other sides of the converters β1, β2, β3 are respectively connected to the β port of the secondary side of the transformer TT1, the primary side of the transformer TT2, and the primary side of the transformer TT3; The primary side of transformer TT1 is connected to the three-phase grid, and the secondary side is provided with α and β ports. The α port feeds two terminals, one of which is connected in series with the secondary side of transformer TT3 and then connected to the traction bus, and the other terminal is grounded; The two terminals of the secondary side of transformer TT2 are connected to the traction bus and the ground respectively; The traction busbar supplies power to train loads on the railway traction network through traction feeders; Adjust the active power and reactive power of converters β1, β2, and β3 to comprehensively compensate for the secondary side load power and traction bus voltage of transformer TT1.

2. An integrated compensation device for in-phase power supply of railways, characterized in that, It comprises transformers TT1, TT2, TT3 and the power flow control device according to claim 1, wherein transformers TT2 and TT3 are both single-phase transformers; The transformer TT1 adopts a three-phase to two-phase traction transformer, which includes Vv, Scott and YNvd connection transformers, and also includes a three-phase to two-phase transformer composed of a single-phase transformer and a YNd connection transformer; According to the train load, the converters β1, β2, and β3 are controlled to output adjustable active power and reactive power, so that the three-phase voltage imbalance of the secondary side load of transformer TT1 at the common connection point of the three-phase power grid, the power factor of the secondary side of transformer TT1, and the voltage increment of the traction bus meet the compensation target values.

3. The integrated compensation device according to claim 2, wherein The comprehensive compensation device is suitable for a railway traction network power supply mode which is a direct power supply mode or a direct power supply mode with a return line.

4. A comprehensive compensation method for in-phase power supply of railways using the comprehensive compensation device described in claim 2 or 3, characterized in that The following steps are involved: S1. Set the complex powers of the converters β2 and β3 to be P β2 +jQ β2 and P β3 +jQ β3 , and define the direction in which the power flows from the DC bus of the power flow control device to the traction network as the positive direction; Set the complex power of the converter β1 as P β1 +jQ β1 , and define the positive direction as the power flowing from the three-phase to two-phase traction transformer TT1 to the DC bus of the power flow control device; Set the connection angle ψ of the port α and ψ β are respectively the angles by which the voltages of the secondary side α and β ports of the transformer TT1 lag behind the reference voltage of phase A of the three-phase power grid; The three-phase voltage unbalance degree of the secondary side load of transformer TT1 at the common connection point of the three-phase power grid The calculation formula is where ε U and δ are the magnitudes and phase angles of the three-phase voltage unbalance at the common connection point; S d is the short-circuit capacity at the common connection point; j is the imaginary unit; P α , Q α are the active and reactive powers of the load at the α port on the secondary side of transformer TT1; S2. Set the compensation target value of the power factor on the secondary side of transformer TT1 to be The active and reactive power relationships between different ports of transformer TT1 are Among them, P L , Q L are the active power and reactive power supplied to the train load through the traction busbar; S3. Combining equations (1) and (2), we can get the active power and reactive power of converter β1: Substituting equation (3) into equation (2), we get the active power and reactive power constraints of converters β2 and β3 as Introduce the traction bus voltage adjustment coefficient ρ to constrain the voltage increment of the traction bus caused by the converter β3, then there is ​ where ρ x and ρ y are the real and imaginary parts of ρ; is the voltage of the traction busbar; Furthermore, according to equation (5), the complex power of converter β3 is Combining equations (4) and (6), we can obtain the active power and reactive power of converters β2 and β3 as follows: S4. Set ε U , δ, and the values of ρ, substitute them into equations (4) and (7) to determine the active power and reactive power of the converters β1, β2, and β3, and achieve the comprehensive compensation of the three-phase voltage unbalance degree of the railway single-phase power supply system, the power factor on the secondary side of transformer TT1, and the traction bus voltage increment.

5. The integrated compensation method according to claim 4, wherein Determine the values of the port connection angles ψ in equations (4) and (7) respectively according to various connection modes of the three-phase to two-phase connection transformer TT1, and control the active power and reactive power output by the converters β1, β2, and β3 to match the connection mode of the transformer TT1. α and ψ β , and control the active power and reactive power output by the converters β1, β2, and β3 to match the connection mode of the transformer TT1.

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