A method for preventing circulation of current in rail transit traction power supply

Abstract

The application provides a method for preventing circulation of rail transit traction power supply, which comprises the following steps: S1. verifying whether the rail transit traction power supply system has external droop characteristics according to a power flow calculation principle, and the verification process is as follows: (1) based on the power flow calculation principle, the output active and reactive power expressions of any traction substation i can be obtained, that is, formula (1) and formula (2). The method for preventing circulation of rail transit traction power supply provided by the application can suppress the generation of circulation, so as to solve the problems of system current distortion, increase of system additional loss and influence on the overall performance of the system.

Description

Technical Field

[0001] This invention belongs to the field of rail transit technology, and in particular relates to a method for preventing circulating current in rail transit traction power supply. Background Technology

[0002] With the continuous expansion of urban rail transit, urban rail transit plays an increasingly important role in alleviating urban traffic congestion and energy conservation and emission reduction. Therefore, ensuring the safe and reliable operation of the urban rail transit traction power supply system is becoming increasingly important.

[0003] Urban rail transit traction power supply systems typically include an AC power grid, a DC contact network, and multiple traction substations. Each traction substation includes a power supply unit and a diode rectifier unit. Since the DC sides of the power supply unit and the diode rectifier unit are connected, and their AC sides are on the same busbar, the power supply unit and the diode rectifier unit can form a circuit.

[0004] However, when the existing system is subjected to factors such as AC power grid fluctuations, circulating currents are likely to occur. The generation of circulating currents will cause current distortion in the system, which can increase the additional losses of the system and thus seriously affect the overall performance of the system.

[0005] Therefore, it is necessary to provide a new method for preventing circulating current in rail transit traction power supply to solve the above-mentioned technical problems. Summary of the Invention

[0006] The technical problem solved by this invention is to provide a method for preventing circulating current in rail transit traction power supply that can suppress the generation of circulating current, thereby solving the problems of system current distortion, increased system losses, and impact on the overall system performance.

[0007] To solve the above-mentioned technical problems, the present invention provides a method for preventing circulating current in rail transit traction power supply, comprising the following steps:

[0008] S1. Based on the principle of power flow calculation, verify whether the rail transit traction power supply system has external droop characteristics. The verification process is as follows:

[0009] (1). Based on the principle of power flow calculation, the active and reactive power output expressions of any traction substation i can be obtained, namely, formula (1) and formula (2):

[0010]

[0011] .

[0012] From the above formulas (1) and (2), it can be seen that the impedance of the traction network in the rail transit traction power supply system is very small relative to the load impedance, and there is an approximate relationship, that is... and Therefore, formulas (1) and (2) can be simplified to obtain formulas (3) and (4), which are:

[0013]

[0014] .

[0015] Combining formulas (3) and (4), we can verify whether it has external droop characteristics. If so, we can introduce droop control to eliminate circulating current. The idea of ​​current sharing control is to obtain the current output information of the neighboring inverter and itself, introduce this information into the circulating current control, and use this information to control the output current amplitude and phase to be equal, so as to reduce and eventually eliminate the circulating current. Its expression formula (5) is as follows:

[0016]

[0017] Therefore, by using a current sharing control strategy, the inverter output current can be made equal, thereby reducing the circulating current to zero and reducing additional power consumption.

[0018] As a further aspect of the present invention, in the above formula, since Therefore, reactive power For load current With substation current The amplitude difference has a significant impact on the active power output of the substation. For load current With substation current phase angle difference The impact is significant.

[0019] As a further embodiment of the present invention, the rail transit traction power supply system is composed of a traction network, multiple traction substations, and rail vehicles. The traction substation includes a three-phase power inverter and an LCL filter circuit.

[0020] As a further embodiment of the present invention, the traction substation adopts a dual-side power supply, and the busbars of the traction substation are all connected together to supply power to the power supply network. The trains in the power supply network draw power from two adjacent substations.

[0021] As a further embodiment of the present invention, bilateral power supply refers to the situation where the contact network power supply section between adjacent traction substations simultaneously draws current from the substations at both ends.

[0022] Compared with related technologies, the anti-circulating current method for traction power supply in rail transit provided by this invention has the following beneficial effects:

[0023] 1. This invention can suppress the generation of circulating current, thereby solving the problems of system current distortion, increased system losses, and impact on overall system performance. Attached Figure Description

[0024] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0025] Figure 1 In this invention A curve graph;

[0026] Figure 2 Q in this invention A graph of V;

[0027] Figure 3 This is a diagram of the circulating flow control strategy in this invention. Detailed Implementation

[0028] Please refer to the following: Figure 1 , Figure 2 and Figure 3 ,in Figure 1 In this invention A curve graph; Figure 2 Q in this invention A graph of V; Figure 3 This is a diagram illustrating the circulating current control strategy in this invention. The method for preventing circulating current in rail transit traction power supply includes the following steps:

[0029] S1. Based on the principle of power flow calculation, verify whether the rail transit traction power supply system has external droop characteristics. The verification process is as follows:

[0030] (1). Based on the principle of power flow calculation, the active and reactive power output expressions of any traction substation i can be obtained, namely, formula (1) and formula (2):

[0031]

[0032] .

[0033] From the above formulas (1) and (2), it can be seen that the impedance of the traction network in the rail transit traction power supply system is very small relative to the load impedance, and there is an approximate relationship, that is... and Therefore, formulas (1) and (2) can be simplified to obtain formulas (3) and (4), which are:

[0034]

[0035] .

[0036] In the above formula, since Therefore, reactive power For load current With substation current The amplitude difference has a significant impact on the active power output of the substation. For load current With substation current phase angle difference The impact is significant.

[0037] Combining formulas (3) and (4), we can verify whether it has external droop characteristics. If so, we can introduce droop control to eliminate circulating current. The idea of ​​current sharing control is to obtain the current output information of the neighboring inverter and itself, introduce this information into the circulating current control, and use this information to control the output current amplitude and phase to be equal, so as to reduce and eventually eliminate the circulating current. Its expression formula (5) is as follows:

[0038]

[0039] Therefore, by using a current sharing control strategy, the inverter output current can be made equal, thereby reducing the circulating current to zero and reducing additional power consumption.

[0040] The rail transit traction power supply system consists of a traction network, multiple traction substations, and rail vehicles. The traction substation includes a three-phase power inverter and an LCL filter circuit.

[0041] The traction substation uses a dual-side power supply, and all the busbars of the traction substation are connected together to supply power to the power supply network. The trains in the power supply network draw power from the two adjacent substations.

[0042] Bilateral power supply refers to a situation where the contact network power supply section between adjacent traction substations simultaneously draws current from substations at both ends.

[0043] Depend on Figure 1 and Figure 2 It is known that active power is approximately proportional to the change in phase angle, and reactive power is approximately proportional to the change in output current amplitude. When the locomotive load is at a certain point, The slope of the QV curve remains basically constant. When the track load position changes, the slope of the curve is always negative, so the system has a drooping characteristic.

[0044] As can be seen from equation (5), if the output current at each converter terminal can be made equal, circulating current can be suppressed. Based on this, a proposal is made... Figure 3 The diagram shows an equal current circulating current suppression strategy based on a master-slave control strategy. C These are the inductance and capacitance of the LC filter circuit, and the equivalent inductance of the interface circuit, respectively. Figure 3There are three converters operating in parallel, using current control mode. The control objective is to maximize the output current. Proximity converter 1 output current To suppress circulation.

[0045] This invention can suppress the generation of circulating current, thereby solving the problems of system current distortion, increased system losses, and impact on overall system performance.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preventing circulating current in traction power supply for rail transit, characterized in that, Includes the following steps: S1. Based on the principle of power flow calculation, verify whether the rail transit traction power supply system has external droop characteristics. The verification process is as follows: (1). Based on the principle of power flow calculation, the active and reactive power output expressions of any traction substation i can be obtained, namely, formula (1) and formula (2): ； From the above formulas (1) and (2), it can be seen that the impedance of the traction network in the rail transit traction power supply system is very small relative to the load impedance, and there is an approximate relationship, that is... and Therefore, formulas (1) and (2) can be simplified to obtain formulas (3) and (4), which are: ； Combining formulas (3) and (4), we can verify whether it has external droop characteristics. If so, we can introduce droop control to eliminate circulating current. The idea of ​​current sharing control is to obtain the current output information of the neighboring inverter and itself, introduce this information into the circulating current control, and use this information to control the output current amplitude and phase to be equal, so as to reduce and eventually eliminate the circulating current. Its expression formula (5) is as follows: The current sharing control strategy can make the inverter output current equal, thereby reducing the circulating current to zero and reducing additional power consumption.

2. The method for preventing circulating current in rail transit traction power supply according to claim 1, characterized in that: In the above formula, since Therefore, reactive power For load current With substation current The amplitude difference has a significant impact on the active power output of the substation. For load current With substation current phase angle difference The impact is significant.

3. The method for preventing circulating current in rail transit traction power supply according to claim 1, characterized in that: The rail transit traction power supply system consists of a traction network, multiple traction substations, and rail vehicles. The traction substation includes a three-phase power inverter and an LCL filter circuit.

4. The method for preventing circulating current in rail transit traction power supply according to claim 1, characterized in that: The traction substation uses a dual-side power supply, and all the busbars of the traction substation are connected together to supply power to the power supply network. The trains in the power supply network draw power from the two adjacent substations.

5. The method for preventing circulating current in rail transit traction power supply according to claim 1, characterized in that: Bilateral power supply refers to a situation where the contact network power supply section between adjacent traction substations simultaneously draws current from substations at both ends.

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