A method for improving the impact of grid-connected distributed power sources on power grid quality

Abstract

The present invention belongs to the field of electric power technology. A method for improving the influence of grid-connected distributed power sources on the quality of power grid, characterized by comprising the following steps: 1) preparing an SVC compensation device; 2) connecting a 110 / 10kV step-down transformer to the outgoing line side of the 110kV busbar of each traction substation, and then installing SVC compensation devices on the three phases of the outgoing line on the low voltage side of the 110 / 10kV step-down transformer. The SVC compensation device includes a TCR branch, a first TSC branch, a second TSC branch, a first filter branch, and a second filter branch. This method can improve the influence of distributed power sources on the quality of power grid.

Description

Technical Field

[0001] The invention belongs to the technical field of electric power, and in particular relates to a method for improving the influence of a grid-connected distributed power source on the quality of a power grid. Background Art

[0002] Photovoltaic traction is different from traditional steam locomotive or diesel locomotive traction. It obtains electricity from the traction power supply system. The photovoltaic traction power supply system is to build several traction substations at a certain distance along the railway. The power is supplied by the 110kV (220kV) three-phase dual power supply of the power system. After the traction transformer steps down the voltage to 27.5kV (55kV), the single-phase power is supplied to the electric locomotive of the traction network. The electric locomotive uses a 25kV single-phase industrial frequency AC voltage and travels between the overhead contact wire and the rail.

[0003] The SS9 electric locomotive uses an unequally divided three-section half-controlled bridge rectifier circuit composed of high-power thyristors and diodes as the traction motor drive converter to achieve constant current and quasi-constant speed control. The locomotive uses thyristor shunts to achieve magnetic field weakening, and the braking method uses feeder resistor braking. The locomotive is a C0-C0 axle type, each bogie is independently powered, and uses a ZD115 six-pole series-excited pulse current traction motor.

[0004] Railway electric locomotives are high-power single-phase rectifier distributed power sources with large fluctuations. Their rectifiers are high-power rectifiers composed of diodes and thyristors, and are typical grid-connected distributed power sources. At the same time, the use of high-power power electronic devices causes the voltage and current waveforms to be distorted and contain a large number of harmonics. The shape of the voltage and current waveforms will not only be determined by the model, quantity, distribution and operating status of the locomotive equipment (such as acceleration, normal operation, coasting and braking), but also by the power supply circuit parameters.

[0005] The electric railway traction distributed power source is a special distributed power source that is mobile, has large and frequent amplitude changes, and its daily fluctuation characteristics are very obvious. Because the locomotive distributed power source often needs to change from zero to full load or from full load to zero in a few seconds or less, and there are large changes during the entire period. The random changes in slope, curvature and wind resistance generally make it impossible for the distributed power source current to remain constant, so the locomotive needs to be adjusted frequently to maintain its constant speed operation; in addition, the locomotive also needs to change speed according to the signal when it enters the station and stops. Therefore, the electric railway traction distributed power source is a typical daily fluctuating distributed power source with the characteristics of a short-term impact distributed power source.

[0006] The electric railway traction distributed power supply adopts single-phase power supply, so it is a typical asymmetric distributed power supply. Single-phase power supply will cause asymmetry in the three-phase power system. The current of the single-phase distributed power supply contains negative sequence current, which forms a negative sequence voltage drop on the system impedance.

[0007] In general, for the three-phase symmetrical power system power supply, the electric railway traction distributed power supply has the following characteristics:

[0008] 1) Asymmetry: Due to the use of two-phase (single-phase) power supply, a large amount of negative sequence components are injected into the system;

[0009] 2) Grid connection, which causes the power supply system to generate high-order harmonics;

[0010] 3) Volatility: large impacts on active and reactive power lead to voltage fluctuations in the power supply system.

[0011] The access of distributed power generation to the power grid will affect the safe, stable operation and control of the power grid, especially the power quality of the power grid. The access of distributed power generation to the electric railway will cause a large three-phase voltage imbalance at the public connection point. Summary of the invention

[0012] The object of the present invention is to provide a method for improving the influence of a grid-connected distributed power source on the quality of a power grid, and the method can improve the influence of the distributed power source on the quality of the power grid.

[0013] In order to achieve the purpose of the present invention, the technical solution adopted by the present invention is: a method for improving the influence of grid-connected distributed power sources on power grid quality, characterized by comprising the following steps:

[0014] 1) Prepare SVC compensation device;

[0015] 2) A 110 / 10kV step-down transformer 7 is connected to the outgoing line side of the 110kV busbar of each traction substation, and then SVC compensation devices are installed on the three phases of the outgoing line on the low voltage side of the 110 / 10kV step-down transformer.

[0016] The SVC compensation device includes a TCR branch 1, a first TSC branch 2, a second TSC branch 3, a first filter branch 4, and a second filter branch 5; the TCR branch 1 includes a first switch K1, a first reactor L1, a first thyristor VS1, a second thyristor VS2, and a sixth reactor L6, one end of the first switch K1 is connected to the access terminal 6, the other end of the first switch K1 is connected to one end of the first reactor L1, the other end of the first reactor L1 is respectively connected to the anode of the first thyristor VS1 and the cathode of the second thyristor VS2, the cathode of the first thyristor VS1 and the anode of the second thyristor VS2 are respectively connected to one end of the sixth reactor L6, and the other end of the sixth reactor L6 is connected to the ground terminal;

[0017] The first TSC branch 2 includes a second switch K2, a second reactor L2, a third thyristor VS3, a fourth thyristor VS4, and a first capacitor C1, one end of the second switch K2 is connected to the access terminal 6, the other end of the second switch K2 is connected to one end of the second reactor L2, the other end of the second reactor L2 is respectively connected to the anode of the third thyristor VS3 and the cathode of the fourth thyristor VS4, the cathode of the third thyristor VS3 and the anode of the fourth thyristor VS4 are respectively connected to one end of the first capacitor C1, and the other end of the first capacitor C1 is connected to the ground terminal;

[0018] The second TSC branch 3 includes a third switch K3, a third reactor L3, a fifth thyristor VS5, a sixth thyristor VS6, and a second capacitor C2, one end of the third switch K3 is connected to the access terminal 6, the other end of the third switch K3 is connected to one end of the third reactor L3, the other end of the third reactor L3 is respectively connected to the anode of the fifth thyristor VS5 and the cathode of the sixth thyristor VS6, the cathode of the fifth thyristor VS5 and the anode of the sixth thyristor VS6 are respectively connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the ground terminal;

[0019] The first filter branch 4 includes a fourth switch K4, a fourth reactor L4, and a third capacitor C3, one end of the fourth switch K4 is connected to the access terminal 6, the other end of the fourth switch K4 is connected to one end of the fourth reactor L4, the other end of the fourth reactor L4 is connected to one end of the third capacitor C3, and the other end of the third capacitor C3 is connected to the ground terminal;

[0020] The second filtering branch 5 includes a fifth switch K5, a fifth inductor L5, and a fourth capacitor C4. One end of the fifth switch K5 is connected to the access terminal 6, the other end of the fifth switch K5 is connected to one end of the fifth inductor L5, the other end of the fifth inductor L5 is connected to one end of the fourth capacitor C4, and the other end of the fourth capacitor C4 is connected to the ground terminal.

[0021] The three-phase lines on the high-voltage side of the 110 / 10kV step-down transformer are respectively equipped with high-voltage side switches 8, and the three-phase lines on the low-voltage side of the 110 / 10kV step-down transformer are respectively equipped with low-voltage side switches 9.

[0022] The beneficial effect of the present invention is that the method can improve the influence of distributed power sources on the quality of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the SVC compensation device of the present invention connected to the three-phase outgoing line on the low-voltage side of the step-down transformer.

[0024] Figure 2 It is a structural schematic diagram of the SVC compensation device of the present invention.

[0025] Numbers in the figure: 1-TCR branch, 2-first TSC branch, 3-second TSC branch, 4-first filter branch, 5-second filter branch, 6-access endpoint, 7-110 / 10kV step-down transformer, 8-high-voltage side switch, 9-low-voltage side switch. DETAILED DESCRIPTION

[0026] like Figure 1 , Figure 2 As shown, a method for improving the impact of grid-connected distributed power sources on power grid quality includes the following steps:

[0027] 1) Prepare SVC compensation device;

[0028] 2) On the outgoing line side of the 110kV busbar of each traction substation, connect a 110 / 10kV step-down transformer 7 (the input end of the 110 / 10kV step-down transformer is connected to the outgoing line of the 110kV busbar of the substation), and then install SVC compensation devices on the three phases of the outgoing line on the low voltage side of the 110 / 10kV step-down transformer (a step-down transformer that reduces 110V to 10kV) (the access terminal 6 of the SVC compensation device is connected to the outgoing line on the low voltage side of the 110 / 10kV step-down transformer by a wire; the outgoing line on the low voltage side can be multiple groups, such as 2-5 groups, Figure 1 Two groups of outgoing lines are drawn in the figure, and each group of outgoing lines is equipped with an SVC complete set of devices).

[0029] The SVC compensation device is a basic topology structure of a TCR+TSC type SVC, which is composed of one TCR, two TSCs and two passive filters. In an actual system, the number of TSCs and passive filters can be set as needed. The number of TSC branches and filter branches can be more than two (e.g., 2-6), and a switch is set on each branch to select the number of TSC branches and filter branches as needed.

[0030] The SVC compensation device comprises a TCR branch (thyristor controlled reactor) 1, a first TSC branch 2, a second TSC branch 3, a first filter branch 4, and a second filter branch 5; the TCR branch 1, the first TSC branch 2, the second TSC branch 3, the first filter branch 4, and the second filter branch 5 are connected in parallel;

[0031] The TCR branch 1 includes a first switch K1, a first reactor L1, a first thyristor VS1, a second thyristor VS2, and a sixth reactor L6, one end of the first switch K1 is connected to the access terminal 6 of the SVC compensation device, the other end of the first switch K1 is connected to one end of the first reactor L1, the other end of the first reactor L1 is respectively connected to the anode of the first thyristor VS1 and the cathode of the second thyristor VS2, the cathode of the first thyristor VS1 and the anode of the second thyristor VS2 are respectively connected to one end of the sixth reactor L6, and the other end of the sixth reactor L6 is connected to the ground terminal;

[0032] The first TSC branch 2 includes a second switch K2, a second reactor L2, a third thyristor VS3, a fourth thyristor VS4, and a first capacitor C1, one end of the second switch K2 is connected to the access terminal 6 of the SVC compensation device, the other end of the second switch K2 is connected to one end of the second reactor L2, the other end of the second reactor L2 is respectively connected to the anode of the third thyristor VS3 and the cathode of the fourth thyristor VS4, the cathode of the third thyristor VS3 and the anode of the fourth thyristor VS4 are respectively connected to one end of the first capacitor C1, and the other end of the first capacitor C1 is connected to the ground terminal;

[0033] The second TSC branch 3 includes a third switch K3, a third reactor L3, a fifth thyristor VS5, a sixth thyristor VS6, and a second capacitor C2, one end of the third switch K3 is connected to the access terminal 6 of the SVC compensation device, the other end of the third switch K3 is connected to one end of the third reactor L3, the other end of the third reactor L3 is respectively connected to the anode of the fifth thyristor VS5 and the cathode of the sixth thyristor VS6, the cathode of the fifth thyristor VS5 and the anode of the sixth thyristor VS6 are respectively connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is connected to the ground terminal;

[0034] The first filter branch 4 includes a fourth switch K4, a fourth reactor L4, and a third capacitor C3, one end of the fourth switch K4 is connected to the access terminal 6 of the SVC compensation device, the other end of the fourth switch K4 is connected to one end of the fourth reactor L4, the other end of the fourth reactor L4 is connected to one end of the third capacitor C3, and the other end of the third capacitor C3 is connected to the ground terminal;

[0035] The second filtering branch 5 includes a fifth switch K5, a fifth reactor L5, and a fourth capacitor C4. One end of the fifth switch K5 is connected to the access terminal 6 of the SVC compensation device, the other end of the fifth switch K5 is connected to one end of the fifth reactor L5, the other end of the fifth reactor L5 is connected to one end of the fourth capacitor C4, and the other end of the fourth capacitor C4 is connected to the ground.

[0036] The three-phase lines on the high-voltage side of the 110 / 10kV step-down transformer are respectively equipped with high-voltage side switches 8, and the three-phase lines on the low-voltage side of the 110 / 10kV step-down transformer are respectively equipped with low-voltage side switches 9.

[0037] Specific application in power grid:

[0038] 1. Use SVC compensation device for harmonic control and three-phase unbalance compensation. It consists of 1 TCR, 2 TSCs and 2 passive filters. TCR phase-splitting is used to compensate for the three-phase imbalance of the power grid. Passive filtering device is used for harmonic control. TCR, 2 TSCs and passive filters jointly implement reactive power compensation to achieve reactive balance during iron distributed power supply (or photovoltaic impact distributed power supply).

[0039] 2. Improvement measures for electric railways (when using electric railway distributed power sources to access the power grid)

[0040] 1) Considering the growth of traction distributed power sources in the future and the serious impact of harmonics generated after each traction station is connected to the power grid, and to improve the power factor, a 110 / 10kV step-down transformer 7 is connected to the outgoing line side of each traction substation (the input end of the 110 / 10kV step-down transformer is connected to the outgoing line of the substation 110kV bus), and then SVC compensation devices are installed on the three phases of the low-voltage side of the 110 / 10kV step-down transformer (a step-down transformer that reduces 110V to 10kV) (the access terminal 6 of the SVC compensation device is connected to the outgoing line of the low-voltage side of the 110 / 10kV step-down transformer by a wire).

[0041] 2) When the traction substation is connected to the power system, phase switching is required to make the three-phase distributed power supply of the system as balanced as possible to reduce the negative sequence interference to the power grid.

[0042] 3) The photovoltaic sector is required to use transformers that can reduce the impact of negative sequence and harmonic waves, and try to reduce negative sequence and harmonic waves from the source.

[0043] The effects after adopting the present invention are as follows:

[0044] 1) When the distributed power generation of the electric railway operates stably, the maximum voltage deviation of the power grid caused by it does not exceed 5% (10% before the improvement measures).

[0045] 2) When each traction station is connected to the power grid through a public connection point, the three-phase voltage imbalance of the relevant substation bus caused by the traction station is below 1.0% (1.3% before improvement measures), which is within the national standard limit.

[0046] 3) Voltage fluctuation:

[0047] The voltage fluctuation values ​​at the common connection point caused by each traction station with a power supply voltage of 220kV were all below 0.18% (0.24% before improvement measures), and did not exceed the national standard limit.

[0048] 4) Harmonics:

[0049] When both arms are in short-time maximum current operation mode, the total harmonic distortion rate of the bus voltage at the corresponding common connection point caused by the harmonic current injected by each traction station does not exceed 1.5% (2.0% before improvement measures), which is within the national standard limit.

Claims

1. A method for improving the impact of grid-connected distributed power sources on power grid quality, characterized in that The steps include: 1) Prepare SVC compensation device; 2) Connect a 110 / 10kV step-down transformer (7) to the outgoing line side of the 110kV busbar of each traction substation, and then install SVC compensation devices on the three phases of the outgoing line on the low voltage side of the 110 / 10kV step-down transformer; The SVC compensation device comprises a TCR branch (1), a first TSC branch (2), a second TSC branch (3), a first filter branch (4), a second filter branch (5), and a sixth reactor (L6); the TCR branch (1) comprises a first switch (K1), a first reactor (L1), a first thyristor (VS1), and a second thyristor (VS2); one end of the first switch (K1) is connected to an access terminal (6); the other end of the first switch (K1) is connected to one end of the first reactor (L1); the other end of the first reactor (L1) is respectively connected to an anode of the first thyristor (VS1) and a cathode of the second thyristor (VS2); the cathode of the first thyristor (VS1) and an anode of the second thyristor (VS2) are respectively connected to one end of the sixth reactor (L6); and the other end of the sixth reactor (L6) is connected to a ground terminal; The first TSC branch (2) comprises a second switch (K2), a second reactor (L2), a third thyristor (VS3), a fourth thyristor (VS4), and a first capacitor (C1); one end of the second switch (K2) is connected to an access terminal (6); the other end of the second switch (K2) is connected to one end of the second reactor (L2); the other end of the second reactor (L2) is respectively connected to an anode of the third thyristor (VS3) and a cathode of the fourth thyristor (VS4); the cathode of the third thyristor (VS3) and an anode of the fourth thyristor (VS4) are respectively connected to one end of the first capacitor (C1); and the other end of the first capacitor (C1) is connected to a ground terminal; The second TSC branch (3) comprises a third switch (K3), a third reactor (L3), a fifth thyristor (VS5), a sixth thyristor (VS6), and a second capacitor (C2); one end of the third switch (K3) is connected to the access terminal (6); the other end of the third switch (K3) is connected to one end of the third reactor (L3); the other end of the third reactor (L3) is respectively connected to the anode of the fifth thyristor (VS5) and the cathode of the sixth thyristor (VS6); the cathode of the fifth thyristor (VS5) and the anode of the sixth thyristor (VS6) are respectively connected to one end of the second capacitor (C2); and the other end of the second capacitor (C2) is connected to the ground terminal; The first filtering branch (4) comprises a fourth switch (K4), a fourth reactor (L4), and a third capacitor (C3); one end of the fourth switch (K4) is connected to the access terminal (6); the other end of the fourth switch (K4) is connected to one end of the fourth reactor (L4); the other end of the fourth reactor (L4) is connected to one end of the third capacitor (C3); and the other end of the third capacitor (C3) is connected to the ground terminal; The second filtering branch (5) comprises a fifth switch (K5), a fifth inductor (L5), and a fourth capacitor (C4); one end of the fifth switch (K5) is connected to the access terminal (6); the other end of the fifth switch (K5) is connected to one end of the fifth inductor (L5); the other end of the fifth inductor (L5) is connected to one end of the fourth capacitor (C4); and the other end of the fourth capacitor (C4) is connected to the ground terminal.

2. A method for improving the impact of grid-connected distributed power sources on power grid quality according to claim 1, characterized in that: The three-phase lines on the high-voltage side of the 110 / 10kV step-down transformer are respectively equipped with high-voltage side switches (8), and the three-phase lines on the low-voltage side of the 110 / 10kV step-down transformer are respectively equipped with low-voltage side switches (9).

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