Power blending device for power supply partition of electrified railway traction

Abstract

The present application belongs to the field of traction power supply technology of electrified railway, and particularly relates to a power blending device for traction power supply partition of electrified railway. Compared with the prior art, the present application mainly adds a transformer and a single-phase PWM rectifier, but compared with the prior art, the present application can reduce the capacity of the transformer and the rectifier to less than 1 / 2 of the original capacity when transmitting the same power, thereby reducing the equipment and construction cost of the blending device, reducing the loss by not less than 65.5%, and improving the efficiency of the power blending device.

Description

Technical Field

[0001] This invention belongs to the field of electrified railway traction power supply technology, specifically relating to a power fusion device for electrified railway traction power supply substations. Background Technology

[0002] Electrified railway traction uses single-phase 27.5kV AC to power trains. In order to reduce the impact on the power grid, three-phase power supply is used along the railway line to keep the three-phase load of the power grid basically balanced. Figure 1 This is a typical traction power supply system structure containing two traction substations (N and N+1) and one sectioning substation. The traction substations convert three-phase 110kV or 220kV high voltage into single-phase 27.5kV voltage via traction transformers to supply power to the traction network. A sectioning substation is located between the two traction substations. The sectioning substation has an insulation section separating the left and right traction networks, and a switch QF that can connect the two traction networks. Under normal circumstances, to suppress circulating current, QF is disconnected, and the traction networks on both sides of the sectioning substation independently supply power to trains in their respective power supply sections. When a substation on one side fails and goes out of service, the sectioning substation switch QF can be closed to connect the two traction networks, achieving cross-regional power supply.

[0003] Electrified railways currently primarily employ AC-DC-AC electric traction systems. During train traction, the traction system draws power from the traction grid via a pantograph to drive the train. When the train brakes, the traction system returns regenerative braking energy to the traction grid. While some of this regenerative braking energy is absorbed by other trains operating on the same traction grid, excess energy is returned to the high-voltage grid. However, the grid either does not charge for the returned energy or only charges for it, increasing operating costs. Furthermore, adjacent traction substations are isolated by sectioning stations, and train loads are random. Therefore, situations may arise where one substation is overloaded while the other is unloaded or lightly loaded, necessitating an increase in the capacity of the traction transformers. Increasing the traction transformer capacity increases capacity occupancy fees paid to the grid, further increasing operating costs.

[0004] To solve the above problems, a power switching device can be used to allow energy to flow between the traction networks on both sides of the sectioning station. This power switching device, also known as a railway static power conditioner (RPC) or power flow controller, has the following structure: Figure 2 As shown. The power fusion device consists of two step-down transformers TR1 and TR2 and two back-to-back single-phase PWM rectifiers. The high-voltage sides of transformers TR1 and TR2 are connected to the traction networks on both sides of the substation, respectively, and the low-voltage sides are connected to the AC sides of PWM1 and PWM2, respectively; the DC sides of the two PWM rectifiers are connected in parallel.

[0005] Because of the isolation provided by the transformer, the two traction networks are electrically isolated. Through control, the power flow between the left and right traction networks of the section substation can be achieved. If a train on the left traction network is braking, or its traction power supply is less than that of the trains on the right traction network, it is desirable for energy to flow from the left traction network to the right traction network. Figure 2 The path for energy to flow to the right-hand traction network is given.

[0006] The power P from the left traction network flows through transformer TR1 to the AC side of PWM rectifier #1, then through the DC side of PWM rectifier #1 to the DC side of PWM rectifier #2, then through the AC side of PWM rectifier #2 to transformer TR2, and finally through transformer TR2 to the right traction network. By changing the control command, the current direction can be controlled, and the flow of energy from the right traction network to the left traction network can also be controlled.

[0007] As can be seen from the above, the power balancing device can balance the load between the two traction substations, reduce the peak power of the traction substation transformers, and allow more regenerative braking energy to be absorbed and utilized by other traction trains. The two PWM rectifiers in the power balancing device can also compensate for reactive power and harmonic currents in the traction network.

[0008] Depend on Figure 2 As shown in the energy flow path, the combined capacity of the two transformers and the two PWM rectifiers in the power fusion device are equal to the fusion power P between the two traction networks. The sum of the transformer capacities and the sum of the PWM rectifier capacities in the fusion device are both 2P.

[0009] The capacity of the power fusion device depends on the power of the trains running on the traction network during traction and braking. The traction and braking power is usually in the range of several MW to tens of MW. Therefore, the transformer of the fusion device will be very large in size, weight and cost. The problem is that the one-time investment is too large, which affects its promotion and application. Summary of the Invention

[0010] To address the aforementioned problems, this invention proposes a power fusion device suitable for electrified railway substations. Under the condition of transmitting the same power, the capacity of transformers and converters is reduced to less than half of the original capacity, thereby reducing the equipment and construction costs of the fusion device, reducing losses by no less than 65.5%, and improving the efficiency of the power fusion device.

[0011] The technical solution of this invention is as follows:

[0012] A power balancing device for traction power supply substations in electrified railways, characterized by comprising a first transformer, a second transformer, a third transformer, a first single-phase PWM rectifier, a second single-phase PWM rectifier, and a third single-phase PWM rectifier; defining the traction networks on both sides of the substation as the first-side traction network and the second-side traction network respectively; one end of the primary winding of the first transformer is connected to the first-side traction network, and the other end is grounded; the secondary winding of the first transformer is connected to the AC side of the first single-phase PWM rectifier; one end of the primary winding of the second transformer is connected to the second-side traction network, and the other end is grounded; the secondary winding of the second transformer is connected to the second single-phase PWM rectifier. The AC side of the M rectifier; the DC sides of the first single-phase PWM rectifier and the second single-phase PWM rectifier are connected in parallel; both ends of the primary winding of the third transformer are connected to the traction network, and the connection point between the primary winding of the third transformer and the traction network is located between the connection point between the primary winding of the first transformer and the traction network and the connection point between the primary winding of the second transformer and the traction network. An insulation section is provided between the two connection points to prevent the two traction networks from being directly connected. The secondary winding of the third transformer is connected to the AC side of the third single-phase PWM rectifier, and the DC side of the third single-phase PWM rectifier is connected in parallel with the DC sides of the first single-phase PWM rectifier and the second single-phase PWM rectifier.

[0013] Furthermore, the voltage on the primary winding side of the third transformer is the difference between the voltage on the first traction network and the voltage on the second traction network.

[0014] Furthermore, the sum of the capacities of the first transformer, the second transformer, and the third transformer is 1.03P, where P is the power transmitted from the first traction network to the second traction network.

[0015] Furthermore, the combined capacity of the first single-phase PWM rectifier, the second single-phase PWM rectifier, and the third single-phase PWM rectifier is 1.03P.

[0016] This invention also proposes the following two simplified implementation methods based on practical considerations:

[0017] The first type of power sharing device for traction power supply substations of electrified railways includes a first transformer, a second transformer, a first single-phase PWM rectifier, and a second single-phase PWM rectifier. The traction networks on both sides of the substation are defined as the first traction network and the second traction network, respectively. One end of the primary winding of the first transformer is connected to the first traction network, and the other end is grounded. The secondary winding of the first transformer is connected to the AC side of the first single-phase PWM rectifier. Both ends of the primary winding of the second transformer are connected to the traction network, and the connection point between the primary winding of the second transformer and the traction network is closer to the second traction network than the connection point between the primary winding of the first transformer and the traction network. An insulating section is provided between the two connection points to prevent direct connection between the two traction networks. The secondary winding of the second transformer is connected to the AC side of the second single-phase PWM rectifier, and the DC side of the second single-phase PWM rectifier is connected in parallel with the DC side of the first single-phase PWM rectifier.

[0018] The second type of electrified railway traction power supply substation power sharing device includes a first transformer, a second transformer, a first single-phase PWM rectifier, and a second single-phase PWM rectifier. The traction networks on both sides of the substation are defined as the first traction network and the second traction network, respectively. One end of the primary winding of the first transformer is connected to the second traction network, and the other end is grounded. The secondary winding of the first transformer is connected to the AC side of the first single-phase PWM rectifier. Both ends of the primary winding of the second transformer are connected to the traction network, and the connection point between the primary winding of the second transformer and the traction network is closer to the first traction network than the connection point between the primary winding of the first transformer and the traction network. An insulating section is provided between the two connection points to prevent direct connection between the two traction networks. The secondary winding of the second transformer is connected to the AC side of the second single-phase PWM rectifier, and the DC side of the second single-phase PWM rectifier is connected in parallel with the DC side of the first single-phase PWM rectifier.

[0019] Furthermore, the voltage on the primary winding side of the second transformer is the difference between the voltage on the first traction network and the voltage on the second traction network.

[0020] The beneficial effects of the present invention are as follows: Compared with existing power switching devices, when transmitting the same power, the present invention can reduce the capacity of transformers and converters to less than 1 / 2 of the original capacity, thereby reducing the equipment and construction costs of the switching device, reducing losses by no less than 65.5%, and improving the efficiency of the power switching device. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the traction power supply system.

[0022] Figure 2 This is a schematic diagram of an existing power fusion device.

[0023] Where: U1 is the first traction network voltage; U2 is the second traction network voltage; TR1 is the first transformer; TR2 is the second transformer; 1#PWM rectifier is the first PWM rectifier; 2#PWM rectifier is the second PWM rectifier; IS is the insulation section between the two traction networks; P is the power flowing from the first traction network to the second traction network.

[0024] Figure 3 This is a schematic diagram of the power fusion device of the present invention.

[0025] Where: U1 is the first traction network voltage; U2 is the second traction network voltage; TR1 is the first transformer; TR2 is the second transformer; TR3 is the third transformer; 1#PWM rectifier is the first PWM rectifier; 2#PWM rectifier is the second PWM rectifier; 3#PWM rectifier is the third PWM rectifier; IS is the insulation section between the two traction networks; P is the total power transmitted from the first traction network to the second traction network; P1 is the power directly transmitted from the first traction network to the second traction network; P2 is the power transmitted from the first traction network to the second traction network through the third transformer and the third PWM rectifier; I1 is the current flowing from the first traction network to the second traction network; U3 is the low-voltage side voltage of the third transformer.

[0026] Figure 4 for Figure 3 The equivalent circuit diagram for controlling the energy flow direction. Wherein: This refers to the voltage phasor of the first traction network. For the second traction network voltage phasor; The voltage phasor of the low-voltage side of the third transformer is converted to the high-voltage side; k is the turns ratio of the third transformer; L is the phasor of the current flowing from the first traction network to the second traction network; L is the leakage inductance of the third transformer referred to the high-voltage side (resistance is ignored).

[0027] Figure 5 For the corresponding Figure 3 The phasor diagram corresponding to the equivalent circuit. Where: This refers to the voltage phasor of the first traction network. For the second traction network voltage phasor; The voltage phasor of the low-voltage side of the third transformer is converted to the high-voltage side; k is the turns ratio of the third transformer; L is the phasor of the current flowing from the first traction network to the second traction network; L is the leakage inductance of the third transformer referred to the high-voltage side (resistance is ignored); Let θ be the voltage phasor on L; θ is and The included angle.

[0028] Figure 6 This is a simplified structural diagram of the power fusion device of the present invention. Figure 6 (a) to omit Figure 3 The structure after TR2 and PWM rectifier #2 is as follows: U1 is the first traction network voltage; U2 is the second traction network voltage; TR1 is the first transformer; TR3 is the second transformer; PWM rectifier #1 is the first PWM rectifier; PWM rectifier #3 is the second PWM rectifier; (b) is omitted. Figure 3 The structure after TR1 and PWM rectifier #1 is as follows: U1 is the first traction network voltage; U2 is the second traction network voltage; TR2 is the first transformer; TR3 is the second transformer; PWM rectifier #2 is the first PWM rectifier; and PWM rectifier #3 is the second PWM rectifier. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings.

[0030] The power fusion device structure proposed in this invention is as follows: Figure 3 As shown, with Figure 2 The power fusion device shown differs in that it includes an additional transformer TR3 and a #3 PWM rectifier. When analyzing its energy flow path, the phase and effective value of the traction network voltage on both sides of the substation will be explained first.

[0031] The voltage phase difference between the two sides of the traction network at the substation. To reduce the voltage difference between the two sides of the substation and lower the voltage across the substation equipment, traction transformers with different wiring can alternate their power supply sequence to ensure that the voltages of the traction networks on both sides of the substation come from the same phase voltage of the high-voltage grid. Therefore, the voltage phase difference between the two sides of the traction network at the substation is very small, at most only a few degrees. For ease of analysis and description, they are considered to be in phase.

[0032] The effective voltage difference between the two sides of the sectioning station. According to the TB10009-2005 National Railway Electric Traction Power Supply Design Specification, the allowable voltage fluctuation range of the electrified railway traction network is 19kV-29kV. Therefore, the maximum effective voltage difference between the two sides of the sectioning station is 10kV.

[0033] By adjusting Figure 3 The voltage magnitude and phase of the AC side of the #3 PWM rectifier can control the direction and magnitude of energy flow in the traction networks on the left and right sides of the partition. The following example illustrates the principle by showing the energy flow from the first traction network on the left to the second traction network on the right.

[0034] Figure 4 It is the equivalent circuit for power flow control when controlling energy flow. Figure 5 It corresponds Figure 4 The phasor diagram of voltage and current in the transformer TR3. The leakage reactance of transformer TR3 is much greater than its resistance; for simplicity of analysis, in... Figure 4 In this context, the transformer winding resistance is ignored.

[0035] from Figure 5 The phasor diagram shows that the voltage of the traction network on the left side... and the voltage of the right traction network When the traction power on the right side is greater than that on the left side, in order to balance the power supply of the traction networks on both sides of the section, energy is transferred from left to right. Therefore, the effective value of the voltage on the left side is greater than that on the right side. When controlling energy transfer, in order to reduce the capacity of the transfer device, the output current of the left traction network is... With voltage In phase, the voltage across inductor L Leading current The low-voltage side voltage of transformer TR3 (PWM control transformer #3) can be observed. When the following relationship is satisfied, the current of the left traction network can be controlled to be... Right now:

[0036]

[0037] In Equation 2-1, the voltages form a right triangle, therefore:

[0038]

[0039] In Equation 2-1, voltage With voltage In phase, with a maximum difference of 10kV; the transformer short-circuit impedance is designed to be 10%, voltage The amplitude is the high voltage of TR3. 10%, which is significantly less than the high-voltage side voltage of TR3. Equation 2-2 can be written as:

[0040]

[0041] The maximum voltage on the high-voltage side of transformer TR3 can be calculated as follows:

[0042]

[0043] It can be seen that the high-voltage side voltage of transformer TR3 can be 10kV, which is related to the voltage... With voltage The maximum voltage difference is very close.

[0044] The power transferred from the left traction network to the right traction network is expressed as:

[0045] P=U1I1 (2-5)

[0046] Depend on Figure 3 It can be seen that there are two ways for the left traction net to transfer energy to the right traction net:

[0047] Firstly, the power P1 directly transmitted to the right-side traction network has the following magnitude:

[0048] P1=U2I1 (2-6)

[0049] Secondly, the power is transmitted through TR3 to the AC side of PWM rectifier #3, then through the DC side of PWM rectifier #3 to the DC side of PWM rectifier #2, and finally from the AC side of PWM rectifier #2 through transformer TR2 to the right traction network side. The power is P2, and its magnitude is:

[0050] P2=kU3I1cosθ=(U1-U2)I1 (2-7)

[0051] The ratio of energy transferred via the second route to the total energy transferred is:

[0052]

[0053] As shown in 2-8, the closer the voltage of the right traction grid is to the voltage of the left traction grid, the smaller the proportion of power transmitted through the second path; conversely, the greater the voltage difference between the right and left traction grids, the larger the proportion of power transmitted through the second path. When the left traction grid voltage is at its maximum U1 = 29kV and the right traction grid voltage is at its minimum U2 = 19kV, the proportion of power transmitted through the second path to the total transmitted power is the largest, which is:

[0054]

[0055] That is, the power P1 directly transmitted via the first path accounts for the minimum of 65.5% of the total transmitted power, making it the main transmission channel.

[0056] Based on the energy transfer path, it can be seen that the maximum capacity of TR2, TR3, and converters #2 and #3 is 0.345 times the transmission power, which is 0.345P.

[0057] Similarly, it can be analyzed that when the load on the left traction network is less than the load on the right traction network, energy can be controlled to be transferred from the right traction network to the left traction network. The maximum capacity of both the TR1 transformer and the #1 PWM rectifier is 0.345P.

[0058] The above analysis shows that the first transmission path has no loss, while only the second transmission path has losses. Assuming that the transformer and PWM rectifier in the improved power transfer scheme have the same efficiency as those in the existing scheme, the power transmission loss is 34.5% lower than that in the existing scheme, a reduction of no less than 65.5%.

[0059] Based on the above analysis, the combined capacity of the three transformers TR1, TR2, and TR3 in the proposed power fusion device is 3 × 0.34P = 1.03P; the combined capacity of the three PWM rectifiers (1#PWM, 2#PWM, and 3#PWM) is also 3 × 0.34P = 1.03P. Compared with existing power fusion devices, the transformer and converter capacities are reduced to approximately 50% of the original capacity when transmitting the same power. This reduction in capacity not only lowers the size, weight, and cost of the equipment but also brings two benefits: firstly, it saves a significant amount of civil engineering costs for equipment installation, reducing the overall construction cost; secondly, the main power between the two traction networks is directly transmitted by the fusion device, resulting in a maximum equipment loss that is 34.5% lower than that of the existing scheme.

[0060] The power balancing device of the present invention, like the existing power balancing device, can compensate for the traction network harmonics and reactive current on both sides of the partition through 1#PWM and 2#PWM rectifiers.

[0061] In practical applications, the present invention also has the following characteristics:

[0062] 1) Lower capacity power switching devices are required in practical applications.

[0063] The capacity of the novel power fusion device proposed in this invention depends on the voltage difference between the two sides of the section. The voltages of the two traction networks are in phase, and the voltage difference is mainly affected by the traction load.

[0064] The aforementioned maximum 10kV voltage difference is only possible when the load difference between the two traction networks is significant. For example, one traction network is under heavy load, while the other is under regenerative braking or no-load conditions. Activating the power balancing device will balance the load on both traction networks, and the voltage difference will immediately decrease. Therefore, in practical applications, the required transformer and converter capacities for the power balancing device will be lower than the balancing power calculated based on the maximum voltage difference, resulting in a capacity reduction of over 50% compared to existing power balancing devices.

[0065] 2) The structure of the power fusion device can be simplified.

[0066] Figure 3 The power fusion device shown includes three transformers (TR1, TR2, and TR3) and three PWM rectifiers (1#PWM rectifier, 2#PWM rectifier, and 3#PWM rectifier). The purpose is to ensure that the power absorbed by 3#PWM can be transmitted to the target traction network through either 2#PWM or 3#PWM rectifier during power transmission, aligning with the desired power transmission direction. Otherwise, omitting TR1 and 1#PWM or TR2 and 2#PWM would cause some power to be transmitted back to the source side, affecting the capacity of the power fusion device and increasing losses.

[0067] As in Figure 3 As shown, during the energy transfer from left to right, without transformer TR2 and PWM rectifier #2, the following would occur: Figure 6 As shown in a), the power directly transmitted is P1. The transformer TR3 and the 3# PWM rectifier absorb the power P2, which can only be sent back to the left traction network through the 1# PWM rectifier and the transformer TR1. In the actual fusion device, only the power P1 is transmitted to the right traction network, and P2 is sent back to the left traction network.

[0068] In practical applications, due to the power switching function of the power switching device, the voltage difference between the two sides of the substation decreases rapidly. Transformer TR3 and PWM rectifier #3 absorb relatively little energy, and the power transmitted by PWM rectifiers #1 and #2 accounts for a very small proportion of the total transmitted power. Therefore, Figure 3 The fusion device shown can eliminate the need for transformer TR1 and PWM rectifier #1, resulting in the following: Figure 6 The simplified structure shown in a) can also be omitted, resulting in the following: Figure 6 The simplified structure shown in b)

Claims

1. A power switching device for traction power supply sections of electrified railways, characterized in that, This includes a first transformer, a second transformer, a third transformer, a first single-phase PWM rectifier, a second single-phase PWM rectifier, and a third single-phase PWM rectifier. The traction networks on both sides of the substation are defined as the first-side traction network and the second-side traction network, respectively. One end of the primary winding of the first transformer is connected to the first-side traction network, and the other end is grounded. The secondary winding of the first transformer is connected to the AC side of the first single-phase PWM rectifier. One end of the primary winding of the second transformer is connected to the second-side traction network, and the other end is grounded. The secondary winding of the second transformer is connected to the AC side of the second single-phase PWM rectifier. The first single-phase PWM rectifier and the second single-phase PWM rectifier... The DC side of the WM rectifier is connected in parallel; both ends of the primary winding of the third transformer are connected to the traction network, and the connection point of the primary winding of the third transformer to the traction network is located between the connection point of the primary winding of the first transformer to the traction network and the connection point of the primary winding of the second transformer to the traction network. An insulation section to prevent short circuit is provided between the connection point of the primary winding of the first transformer to the traction network and the connection point of the primary winding of the second transformer to the traction network. The secondary winding of the third transformer is connected to the AC side of the third single-phase PWM rectifier, and the DC side of the third single-phase PWM rectifier is connected in parallel with the DC side of the first single-phase PWM rectifier and the second single-phase PWM rectifier. The voltage on the primary winding side of the third transformer is the difference between the voltage on the first traction network and the voltage on the second traction network.

2. The power fusion device for traction power supply sections of electrified railways according to claim 1, characterized in that, The sum of the capacities of the first transformer, the second transformer, and the third transformer is 1.03P, where P is the power transmitted from the first traction network to the second traction network.

3. The power fusion device for traction power supply sections of electrified railways according to claim 2, characterized in that, The combined capacity of the first single-phase PWM rectifier, the second single-phase PWM rectifier, and the third single-phase PWM rectifier is 1.03P.

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