Electric locomotive and power supply system thereof, and method for suppressing overvoltage at network side

Abstract

The application discloses an electric locomotive, a power supply system thereof and a network side overvoltage suppression method. The system comprises a control unit, a first voltage detector and a traction power supply network, a traction transformer, a rectifier unit, an intermediate direct current link, an inverter unit and a traction motor connected in sequence. The first voltage detector, the rectifier unit and the inverter unit are connected with the control unit respectively. The first voltage detector is used for detecting a network side voltage. When the locomotive is in an electric braking condition and the network side voltage is greater than a set maximum limit voltage, the control unit blocks power switching tubes of the inverter unit, simultaneously increases a set reference value of the intermediate direct current link, and enables energy flow to be changed from the traction power supply network to the intermediate direct current link, so that the network side energy is consumed, and the network side overvoltage suppression is realized.

Description

Technical Field

[0001] This invention belongs to the field of electric locomotive power supply protection technology, and particularly relates to an electric locomotive and its power supply system, and a grid-side overvoltage suppression method. Background Technology

[0002] Most electric locomotives on mainline railways use AC drive systems powered by AC. The AC voltage from the traction power grid is stepped down by a grid-side transformer and then converted from AC to DC to AC by a traction converter to obtain an adjustable voltage to drive the traction motor. In traction mode, electrical energy is transferred from the traction grid to the traction motor, which exerts traction force. Conversely, in electric braking mode, the traction motor exerts braking force, generating electrical energy that is fed back to the traction power grid.

[0003] During operation on railway lines, electric locomotives switch between traction and electric braking modes. When the traction system operates in electric braking mode, it feeds energy back to the grid. If the traction power grid experiences a power outage due to a fault, the energy cannot be delivered or consumed in time, leading to an accumulation that causes a rapid increase in grid voltage. In severe cases, this voltage may exceed the maximum grid voltage limit, damaging high-voltage components on the grid side. Therefore, electric locomotives need to have grid-side overvoltage suppression protection under electric braking conditions.

[0004] Typically, the converter control unit collects the grid-side voltage in real time. When the locomotive is operating under electric braking and a grid voltage interruption is detected, it immediately blocks the pulse signals of the power switches of the four-quadrant rectifier and the inverter, cutting off the energy transmission return path. Traditional grid voltage interruption detection logic relies on the detection unit detecting abnormal grid voltage waveforms or grid voltage RMS values ​​exceeding the normal range. Under electric braking conditions, although traction power supply is interrupted, the energy fed back to the traction power grid by the locomotive's electric braking can maintain the grid-side voltage for a short time, preventing the detection unit from promptly identifying the grid voltage interruption. Furthermore, due to stray inductance and capacitance in the traction power grid and the locomotive's grid-side circuits, and the inductance in the traction transformer windings, even after detecting a grid voltage interruption and cutting off the energy return path, the grid voltage will not immediately drop with the blocking of the pulse signals. This results in uncontrollable overvoltage during this transient process, potentially damaging high-voltage grid-side components. Summary of the Invention

[0005] The purpose of this invention is to provide an electric locomotive and its power supply system, and a grid-side overvoltage suppression method, in order to solve the problem of transient grid-side overvoltage caused by the energy generated by electric braking being injected into the traction power supply network due to the interruption of the traction power supply network voltage, thereby causing damage to the grid-side high-voltage devices.

[0006] The present invention solves the above-mentioned technical problems through the following technical solution: an electric locomotive power supply system, the power supply system comprising a control unit, a first voltage detector, and a traction power supply network, a traction transformer, a rectifier unit, an intermediate DC link, an inverter unit, and a traction motor connected in sequence; the first voltage detector, the rectifier unit, and the inverter unit are respectively connected to the control unit; the first voltage detector is used to detect the grid-side voltage;

[0007] When the locomotive is in electric braking mode and the grid-side voltage is greater than the upper limit of the normal grid voltage range, the control unit blocks the pulse signals of all power switching transistors in the inverter unit, and at the same time increases the set reference value of the intermediate DC link, so that the energy flow direction changes from the traction power supply network to the intermediate DC link, consuming grid-side energy, thereby quickly suppressing grid-side overvoltage.

[0008] Furthermore, the first voltage detector is a voltage transformer, which is located between the high-voltage incoming end and the grounding end of the traction power supply network.

[0009] Furthermore, a current transformer is provided between the traction power supply network and the traction transformer, and the current transformer is used to detect the current.

[0010] Furthermore, a high-voltage circuit breaker is provided between the traction power supply network and the current transformer.

[0011] Furthermore, the rectifier unit is a four-quadrant rectifier.

[0012] Furthermore, the intermediate DC link includes a DC capacitor and a second voltage detector, with the second voltage detector connected in parallel across the two ends of the DC capacitor.

[0013] Based on the same concept, the present invention also provides a method for suppressing overvoltage on the grid side of an electric locomotive, applied to the power supply system of an electric locomotive, the suppression method comprising:

[0014] When the locomotive is in electric braking mode and the grid-side voltage is greater than the upper limit of the normal grid voltage range, the pulse signals of all power switching transistors in the inverter unit are blocked, and the set reference value of the intermediate DC link is increased, so that the energy flow direction changes from the traction power supply network to the intermediate DC link, consuming grid-side energy, thereby quickly suppressing grid-side overvoltage.

[0015] Furthermore, the improved setting reference value is 1.05 to 1.15 times the original setting reference value.

[0016] Furthermore, when the locomotive is in a non-electric braking condition and the grid-side voltage is greater than the upper limit of the normal grid voltage range, the pulse signals of all power switching transistors in the rectifier unit and inverter unit are blocked.

[0017] Furthermore, after raising the set reference value of the intermediate DC link, when the grid voltage is lower than the lower limit of the normal grid voltage range, the pulse signals of all power switching transistors in the rectifier unit are blocked, and the set reference value of the intermediate DC link is restored.

[0018] After increasing the set reference value of the intermediate DC link, when the grid-side voltage is higher than the lower limit of the normal grid voltage range, the current state is maintained for a set time.

[0019] Furthermore, after maintaining the current state for a set time, when the grid-side voltage is within the normal grid voltage range, the pulse signals of all power switching transistors in the inverter unit and the set reference values ​​of the intermediate DC link are restored.

[0020] After maintaining the current state for a set time, when the grid voltage is not within the normal grid voltage range, the pulse signals of all power switching transistors in the rectifier unit are blocked, and the set reference value of the intermediate DC link is restored.

[0021] Based on the same concept, the present invention also provides an electric locomotive, the locomotive including the electric locomotive power supply system as described above.

[0022] Beneficial effects

[0023] Compared with the prior art, the advantages of the present invention are as follows:

[0024] When an electric locomotive is operating under electric braking conditions and the grid-side voltage is detected to be higher than the upper limit of the normal grid voltage range, this invention blocks the power switch pulse signal of the inverter unit, cuts off the energy flowing back from the traction motor to the traction power grid, and simultaneously raises the set reference value of the intermediate DC link. The rectifier unit switches its operating state from inverter mode to rectification mode, and the energy flow changes from the intermediate DC link to the traction power grid and from the traction power grid to the intermediate DC link. This allows the voltage of the intermediate DC link to quickly track the change of the set reference value, thereby instantly consuming the grid-side energy and rapidly reducing the grid-side voltage to the normal grid voltage range. This avoids the problem of damage to grid-side high-voltage devices caused by transient grid-side overvoltage.

[0025] This invention can quickly suppress grid-side overvoltage caused by grid voltage interruption under electric braking conditions, further improving the safety and reliability of electric locomotives under abnormal operating conditions. Attached Figure Description

[0026] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only one embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a structural block diagram of the electric locomotive power supply system in an embodiment of the present invention;

[0028] Figure 2 This is an energy flow diagram under different operating conditions in the embodiments of the present invention, wherein the solid line represents the energy flow under the electric braking condition and the dashed line represents the energy flow under the traction condition;

[0029] Figure 3 This is a flowchart of the overvoltage suppression method on the grid side of electric locomotives in an embodiment of the present invention. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The technical solutions of this application will be described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0032] like Figure 1 As shown, an electric locomotive power supply system provided in this embodiment of the invention includes a control unit, a first voltage detector, and a traction power supply network, a traction transformer T, a rectifier unit, an intermediate DC link, an inverter unit, and a traction motor connected in sequence; the first voltage detector, the rectifier unit, and the inverter unit are respectively connected to the control unit; the first voltage detector is used to detect the grid-side voltage.

[0033] When the locomotive is in electric braking mode and the grid voltage is less than or equal to the upper limit of the normal grid voltage range, the control unit (e.g., TCU) controls the power switches of the inverter and rectifier units, causing the energy generated by the traction motor to be injected into the intermediate DC link through the inverter unit, resulting in a brief voltage rise in the intermediate DC link. To maintain the intermediate DC link voltage at a set reference value, the rectifier unit simultaneously injects the energy from the intermediate DC link into the traction power grid through the traction transformer T. Through the coordinated operation of the rectifier and inverter units, precise control is achieved over the inflow and outflow of energy into the intermediate DC link, ensuring that the intermediate DC link voltage remains stable near the set reference value. At this point, the intermediate DC link voltage is considered to be in a steady state. Figure 2 As shown. In this embodiment, setting the reference value to be near means setting the reference value ±50V.

[0034] To address the abnormal situation where a locomotive operating under electric braking encounters a sudden interruption of the traction power grid voltage, causing energy generated by electric braking to be injected into the traction power grid, resulting in transient grid-side overvoltage, a first voltage detector monitors the grid-side voltage in real time. When the locomotive is under electric braking and the grid-side voltage exceeds the upper limit of the normal grid voltage range, the control unit immediately blocks the pulse signals of all power switches in the inverter unit (the power switches in the rectifier unit are not blocked at this time), causing the inverter unit to stop operating. Simultaneously, the set reference value of the intermediate DC link is increased. At this time, to achieve a higher set reference value for the intermediate DC link, the control unit supplies the grid-side voltage to the intermediate DC link through the traction transformer T and the rectifier unit, reversing the energy flow from the intermediate DC link to the traction power grid, thus dissipating grid-side energy and suppressing grid-side overvoltage. During locomotive movement, it is impossible to know whether a grid voltage interruption has occurred; the detection and protection rely solely on the occurrence of grid-side overvoltage.

[0035] When the locomotive is in non-electric braking condition and the grid voltage is greater than the upper limit of the normal grid voltage range, the pulse signals of all power switching transistors in the rectifier unit and inverter unit are blocked.

[0036] After raising the reference value of the intermediate DC link, during the transition of the grid-side voltage to the intermediate DC link, it is determined whether the grid-side voltage is lower than the lower limit of the normal grid voltage range. When the grid-side voltage drops below the lower limit of the normal grid voltage range (i.e., drops to the point where normal operation cannot be maintained), the control unit blocks the pulse signals of all power switches in the rectifier unit and simultaneously restores the reference value of the intermediate DC link. Figure 2 As shown, after raising the set reference value of the intermediate DC link, during the process of the grid-side voltage transferring to the intermediate DC link, it is determined whether the grid-side voltage is lower than the lower limit of the normal grid voltage range. When the grid-side voltage is higher than the lower limit of the normal grid voltage range, the current state is maintained for a set time. In this embodiment, the set time is 200ms.

[0037] In one specific embodiment of the present invention, the first voltage detector is a voltage transformer, which monitors the grid-side voltage in real time.

[0038] In one specific embodiment of the present invention, a current transformer is provided between the traction power supply network and the traction transformer T. The current transformer is used to detect the current so as to realize overcurrent protection and determine whether the current is DC or AC.

[0039] In one specific embodiment of the present invention, a high-voltage circuit breaker K is provided between the traction power supply network and the current transformer, and the high-voltage circuit breaker K realizes the on-off control of the traction power supply network.

[0040] In one specific embodiment of the present invention, the rectifier unit is a four-quadrant rectifier.

[0041] In one specific embodiment of the present invention, the intermediate DC link includes a DC capacitor and a second voltage detector, the second voltage detector being connected in parallel across the two ends of the DC capacitor and used to detect the voltage of the DC capacitor.

[0042] like Figure 3 As shown, this embodiment of the invention also provides a method for suppressing overvoltage on the grid side of an electric locomotive, applied to the power supply system of an electric locomotive, the suppression method comprising:

[0043] Step 1: Obtain locomotive operating conditions and grid-side voltage;

[0044] Step 2: Determine whether the locomotive is in electric braking mode and whether the grid voltage is greater than the upper limit of the normal grid voltage range;

[0045] Step 3: When the locomotive is in electric braking mode and the grid voltage is less than or equal to the upper limit of the normal grid voltage range, the control unit controls the power switching transistors of the inverter unit and the rectifier unit, so that the energy generated by the traction motor is injected into the intermediate DC link through the inverter unit. At the same time, the rectifier unit injects the energy of the intermediate DC link into the traction power supply network through the traction transformer T. The inflow and outflow of energy in the intermediate DC link are controlled so that the voltage of the intermediate DC link is always stable near the set reference value.

[0046] When the locomotive is in electric braking mode and the grid-side voltage is greater than the upper limit of the normal grid voltage range, the control unit immediately blocks the pulse signals of all power switching transistors in the inverter unit, and at the same time increases the set reference value of the intermediate DC link, so that the energy flow is reversed, from the traction power supply network to the intermediate DC link, consuming grid-side energy, thereby quickly suppressing grid-side overvoltage.

[0047] When the locomotive is in non-electric braking condition and the grid voltage is greater than the upper limit of the normal grid voltage range, the pulse signals of all power switching transistors in the rectifier unit and inverter unit are blocked.

[0048] Step 4: After raising the set reference value of the intermediate DC link, when the grid voltage is lower than the lower limit of the normal grid voltage range, block the pulse signals of all power switching transistors in the rectifier unit, and restore the set reference value of the intermediate DC link.

[0049] After increasing the set reference value of the intermediate DC link, when the grid-side voltage is higher than the lower limit of the normal grid voltage range, the current state is maintained for a set time.

[0050] Step 5: After maintaining the current state for a set time, when the grid-side voltage is within the normal grid voltage range, restore the pulse signals of all power switching transistors in the inverter unit and the set reference values ​​of the intermediate DC link;

[0051] After maintaining the current state for a set time, when the grid voltage is not within the normal grid voltage range, the pulse signals of all power switching transistors in the rectifier unit are blocked, and the set reference value of the intermediate DC link is restored.

[0052] Different traction converter systems have different reference values ​​for the intermediate DC link, which are specifically related to the voltage level selected during the design of the traction converter system. For traction converter systems using 3.3kV power switching devices, the reference value for the intermediate DC link is usually set to 1800V. In this embodiment, the increased reference value is 1.05 to 1.15 times the original reference value, with a preferred value of 1.1 times.

[0053] Different traction power supply systems have different normal grid voltage ranges. For a 25kV traction power supply system, the upper limit of the normal grid voltage range can be set to 42kV, and the lower limit of the normal grid voltage range can be set to 17kV.

[0054] The above description only discloses specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or modifications that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A power supply system for an electric locomotive, the power supply system comprising a control unit, a first voltage detector, and a traction power supply network, a traction transformer, a rectifier unit, an intermediate DC link, an inverter unit, and a traction motor connected in sequence; the first voltage detector, the rectifier unit, and the inverter unit are respectively connected to the control unit; the first voltage detector is used to detect the grid-side voltage; characterized in that: When the locomotive is in electric braking mode and the grid-side voltage is greater than the upper limit of the normal grid voltage range, the control unit blocks the pulse signals of all power switching transistors in the inverter unit, and at the same time increases the set reference value of the intermediate DC link, so that the energy flow direction changes from the traction power supply network to the intermediate DC link, consuming grid-side energy, thereby quickly suppressing grid-side overvoltage. The intermediate DC link includes a DC capacitor and a second voltage detector, with the second voltage detector connected in parallel across the two ends of the DC capacitor.

2. The electric locomotive power supply system according to claim 1, characterized in that: The first voltage detector is a voltage transformer, which is located between the high-voltage incoming line and the grounding end of the traction power supply network.

3. The electric locomotive power supply system according to claim 1, characterized in that: A current transformer is installed between the traction power supply network and the traction transformer, and the current transformer is used to detect the current.

4. A method for suppressing overvoltage on the grid side of an electric locomotive, applied to the electric locomotive power supply system as described in claim 1, characterized in that, The suppression method includes: When the locomotive is in electric braking mode and the grid-side voltage is greater than the upper limit of the normal grid voltage range, the pulse signals of all power switching transistors in the inverter unit are blocked, and the set reference value of the intermediate DC link is increased, so that the energy flow direction changes from the traction power supply network to the intermediate DC link, consuming grid-side energy, thereby quickly suppressing grid-side overvoltage.

5. The method for suppressing overvoltage on the grid side of an electric locomotive according to claim 4, characterized in that, The improved setting reference value is 1.05 to 1.15 times the original setting reference value.

6. The method for suppressing overvoltage on the grid side of an electric locomotive according to claim 4, characterized in that, When the locomotive is in non-electric braking condition and the grid voltage is greater than the upper limit of the normal grid voltage range, the pulse signals of all power switching transistors in the rectifier unit and inverter unit are blocked.

7. The method for suppressing overvoltage on the grid side of an electric locomotive according to claim 4, characterized in that, After raising the set reference value of the intermediate DC link, when the grid voltage is lower than the lower limit of the normal grid voltage range, the pulse signals of all power switching transistors in the rectifier unit are blocked, and the set reference value of the intermediate DC link is restored. After increasing the set reference value of the intermediate DC link, when the grid-side voltage is higher than the lower limit of the normal grid voltage range, the current state is maintained for a set time.

8. The method for suppressing overvoltage on the grid side of an electric locomotive according to any one of claims 4 to 7, characterized in that, After maintaining the current state for a set time, when the grid-side voltage is within the normal grid voltage range, restore the pulse signals of all power switches in the inverter unit and the set reference values ​​of the intermediate DC link. After maintaining the current state for a set time, when the grid voltage is not within the normal grid voltage range, the pulse signals of all power switching transistors in the rectifier unit are blocked, and the set reference value of the intermediate DC link is restored.

9. An electric locomotive, characterized in that, The locomotive includes the electric locomotive power supply system as described in any one of claims 1 to 3.

Images