CN102280881B - Three-phase static var compensator (SVC) device for electrified railway traction side - Google Patents

Abstract

The invention relates to a three-phase static var compensator (SVC) device for an electrified railway traction side. The device comprises an SVC having a three-phase structure which is connected in a delta connection mode, wherein each phase comprises a thyristor controlled reactor subcircuit and a fixed capacity subcircuit which are connected in parallel; a power supply arm for the device comprises power supply arms a and b; tree phases of the SVC is connected between a and c (the power supply arm a and a steel rail c), between b and c (the power supply arm b and the steel rail c) and between a and b (the power supply arm a and the power supply arm b); and the device is connected to a low-voltage side of a traction transformer. The device can comprehensively realize functions of supporting power supply arm voltage, controlling a power factor, suppressing harmonic waves and compensating a negative sequence on electrified railway load; and the defect that a single-phase SVC on a traction side cannot compensate negative-sequence current can be overcome, a step-up transformer for an SVC on a power grid side can be saved, and the device is a three-phase SVC device which integrates advantages of the SVC on the traction side and the SVC on the power grid side.

Description

A three-phase SVC compensation device for traction side of electrified railway

technical field

The invention belongs to the field of electrified railway power supply, power electronics technology and power quality control, and specifically relates to a three-phase SVC compensation device used on the traction side of electrified railway.

Background technique

With the rapid development of electrified railways, the impact of electrified railways on the power quality of power systems has become a problem that cannot be ignored. On the one hand, since the traction power supply system of electrified railways in my country adopts single-phase power supply mode, and the electric locomotive is a single-phase load, no matter what wiring mode the traction transformer adopts, it will inject a large negative sequence current into the power system; on the other hand, Electric locomotives use power electronic converters, which will generate harmonic currents and inject them into the power system. In addition, because the load of the traction substation fluctuates at any time with the number of trains in the power supply arm and the operating status of each train, the load of electrified railways also has random fluctuations.

With the development of high-speed passenger transport and heavy-haul freight railways, the above-mentioned problems will undergo new changes to varying degrees:

(1) The gradual increase of the traction load capacity will directly cause the increase of the negative sequence current injected into the system, and then aggravate the three-phase voltage imbalance problem of the power system. Especially in many areas of our country, the short-circuit capacity of electrified railway power supply system will lag behind the development of electrified railway load for a long time. Therefore, the negative sequence problem of electrified railway will become the primary problem in the power quality of electrified railway in my country in the future.

(2) DC drive electric locomotives are gradually replaced by AC drive electric locomotives. The reactive current and low-order harmonic current generated by the electric locomotive will be greatly reduced, and the power factor of the load side of the AC drive locomotive is very high, so the power quality problems caused by steady state and dynamic reactive power will also be significantly weakened, and the three-phase voltage The fluctuation will be mainly caused by the active impact of the single-phase electric iron load.

Aiming at the power quality problems of the above-mentioned electrified railways, various compensation measures have been taken at home and abroad. Among them, the more common method is to install fixed capacitor (Fixed Capacitor, FC) compensation equipment in the traction station. The common feature of this kind of equipment is to control the harmonic current while compensating reactive power. However, since this type of device is a fixed compensation method, it cannot be adjusted flexibly, and dynamic compensation cannot be realized. The compensation device will send reactive power back to the system when the power supply arm is empty or lightly loaded, causing the bus voltage to rise, which is not good for the locomotive. The reactive power compensation is not enough when the load is heavy.

With the development of power electronics technology and flexible power transmission and distribution technology, static var compensator (Static Var Compensator, SVC), static synchronous compensator (Static Synchronous Compensator, STATCOM) and large-capacity railway power regulation based on self-shutdown devices The Railway Static Power Conditioner (RPC) began to be applied to the power quality control of electrified railways. Since electrified railways are high-voltage and large-capacity loads, there is also a demand for high-voltage and large-capacity power quality devices. For governance devices such as STATCOM and RPC based on self-shutdown devices, it is necessary to increase the capacity of the device through technologies such as multi-level, multiplexing, and cascading. The design of the device is complex, the cost is high, and the control is difficult. Compared with STATCOM and RPC, the thyristor-based static var compensator SVC can easily meet the high-voltage and large-capacity requirements of the device, and has the advantages of simple structure, mature control method, and low engineering cost. Therefore, it has been widely used in electrified railway power quality control. a wide range of applications.

At present, there are usually two ways to use SVC for electrified railway compensation: one is to install a single-phase static var compensator SVC on the two power supply arms of the traction side, and a single-phase thyristor controlled reactor (Thyristor Controlled Reactor, TCR ) and a fixed capacitor FC are installed directly on the traction side, also known as direct-mounted SVC; the other is the system-side SVC, and a three-phase SVC composed of a single-phase thyristor control reactor TCR plus FC is installed on the traction transformer On the primary side, if it is installed in the power system substation, it can realize centralized power quality compensation in the power system.

The SVC on the traction side is directly installed on the power supply arm, and the reactive power generated by the TCR is smoothly adjusted by adjusting the trigger angle of the thyristor, so that the sum of the reactive power change of the load and the reactive power generated by the TCR is constant, and this constant has no inductive power. The active power and the capacitive reactive power of the FC are offset, and finally the power factor of the grid is kept at a high level, and the voltage of the traction grid is kept within the required range. In addition, the harmonic generated by the electric locomotive is filtered through the FC branch, so that the device has the comprehensive compensation effect of power supply arm voltage support, power factor control and harmonic suppression, and has the advantages of low access voltage level and simple design. However, this compensation method cannot realize negative sequence compensation because it cannot realize the energy flow between the power supply arms. The grid-side SVC is connected to the three-phase system, and its power factor control and harmonic suppression principles are basically the same as those of the traction-side SVC. It can further use the Steinmetz principle to realize compensation for unbalanced loads and play a role in compensating electrified railways. The effect of negative sequence current. However, since the voltage level of the three-phase system is higher (110kV), the SVC needs to be connected through a step-up transformer, which will increase the SVC's footprint and engineering cost, and also increase the complexity of SVC design and manufacturing.

Contents of the invention

Aiming at the power quality problems such as negative sequence, harmonics and low power factor of the electrified railway load, the present invention proposes a three-phase SVC compensation device for the traction side of the electrified railway. On the low-voltage side, each phase of the device adopts a single-phase thyristor-controlled reactor TCR in parallel with a fixed capacitor FC structure. According to the compensation requirements of electrified railway loads, each phase of the device can adopt an asymmetric design, which can comprehensively realize the functions of power supply arm voltage support, power factor control, harmonic suppression and negative sequence compensation for electrified railway loads; Phase SVC can not compensate the disadvantage of negative sequence current, and the step-up transformer of grid side SVC can also be omitted. It is a three-phase SVC compensation device integrating the advantages of traction side SVC and grid side SVC.

The object of the present invention is to adopt following technical scheme to realize:

A three-phase SVC compensation device for the traction side of an electrified railway, the device includes a static var compensator SVC; the improvement is that the static var compensator SVC is used for the traction side of an electrified railway, including a delta Three-phase structure connected by wiring; each phase includes parallel thyristor-controlled reactor TCR branch and fixed capacitor FC branch;

The power supply arm for the device comprises power supply arms a and b; the power supply arm a and rail c form ac; the power supply arm b and rail c form bc; the power supply arm a and power supply arm b form ab;

Each phase is respectively connected between ac, bc and ab;

The device is connected to the low voltage side of the traction transformer.

A preferred technical solution provided by the present invention is: the static var compensator SVC is connected to the traction transformer; the load electric locomotive is connected between the power supply arm a and the rail c.

The second preferred technical solution provided by the present invention is: the thyristor-controlled reactor TCR branch includes sequentially connected reactors and anti-parallel thyristor valves; the fixed capacitance FC branch includes sequentially connected reactors and capacitors.

The third preferred technical solution provided by the present invention is: the fixed capacitance FC branch circuit includes a reactor, a capacitor and a resistor connected in series in sequence.

The fourth preferred technical solution provided by the present invention is: the fixed capacitance FC branch is equivalent to capacitive reactance at power frequency, and is equivalent to low impedance at characteristic frequency; the fixed capacitance FC branch is equivalent to the thyristor control reactance The harmonic component generated by the TCR branch of the transformer and the load electric locomotive acts as a filter.

The fifth preferred technical solution provided by the present invention is: when the TCR branch of the thyristor-controlled reactor is working normally, the anti-parallel thyristors respectively trigger the conduction within the time interval from the voltage peak value to the zero-crossing point when the thyristors bear the forward voltage. Pass.

The sixth preferred technical solution provided by the present invention is: asymmetrically design the parameters of the FC branch of the fixed capacitor and the TCR branch of the thyristor-controlled reactor.

The seventh preferred technical solution provided by the present invention is: the traction transformer includes Ynd11, V/v and balance transformer.

Compared with prior art, the beneficial effect that the present invention reaches is:

(1) The three-phase SVC compensation device used in the traction side of the electrified railway provided by the present invention, each phase of the device adopts a single-phase thyristor-controlled reactor TCR parallel fixed capacitor FC structure, which can comprehensively solve the harmonics and negative sequence of the electrified railway load and low power factor issues;

(2) The three-phase SVC compensation device provided by the present invention is connected to the low-voltage side of the electrified railway traction transformer, without the need for a step-up transformer, which can reduce the footprint of the device, reduce design complexity and cost;

(3) The three phases in the three-phase SVC compensation device provided by the present invention adopt a delta connection mode, and the parameters of each phase are designed asymmetrically, which can minimize the overall capacity of the device;

(4) The three-phase SVC compensation device provided by the present invention suppresses the harmonics, negative sequence and low power factor problems of electrified railway loads on the traction side, not only reduces the traction transformer losses caused by harmonics and reactive power, but also reduces harmonics , the loss of high-voltage power supply lines and power transformers caused by the propagation of negative sequence and reactive power in the power system.

Description of drawings

Fig. 1 is a schematic diagram of the main circuit structure of a three-phase SVC compensation device used on the traction side of an electrified railway according to the present invention, wherein: 1: electric locomotive; 2: traction transformer; 3: three-phase static var compensator SVC; 4: thyristor Control reactor (TCR); 5: fixed capacitor/filter (FC); power supply arm a; power supply arm b; rail c;

Fig. 2 is a wiring diagram of a three-phase SVC compensation device on the traction side of a YNd11-connected traction transformer according to a specific embodiment of the present invention.

Detailed ways

The specific implementation of the present invention will be further described in detail below in conjunction with the drawings and specific examples.

Fig. 1 is a schematic diagram of the main circuit structure of the three-phase SVC compensation device used for the traction side of the electrified railway according to the present invention. As shown in Fig. Both adopt the structure of thyristor-controlled reactor TCR branch 4 paralleled with fixed capacitor FC branch 5. The power supply arm used in this device includes power supply arm a and b; each phase is respectively connected to ac (power supply arm a and rail c), bc ( Between power supply arm b and rail c) and ab (power supply arm a and power supply arm b).

Among them, the thyristor-controlled reactor TCR branch 4 is composed of a reactor and an anti-parallel thyristor valve in series. When the thyristor-controlled reactor TCR works normally, the time interval from the voltage peak value to the zero-crossing point of the anti-parallel thyristor when it bears the forward voltage is respectively The internal trigger is turned on.

The thyristor-controlled reactor TCR can only provide dynamic reactive power with a lagging power factor. In order to extend the dynamic range to the leading power factor region, a fixed capacitor FC branch 5 is connected in parallel with the thyristor-controlled reactor TCR branch 4. The fixed capacitance FC branch 5 is composed of two reactors and capacitors in series, and the two reactors are respectively on both sides of the capacitor. Sometimes the fixed capacitance FC branch 5 is also composed of reactors, capacitors and resistors in series. The fixed capacitance FC Branch 5 is equivalent to capacitive reactance at power frequency, and exhibits low impedance at characteristic frequency, which can filter the harmonic components generated by thyristor-controlled reactor TCR branch 4 and load electric locomotive 1 . In practice, it can be designed as a structure in which multiple sets of fixed capacitance FC branch circuits 5 and thyristor-controlled reactor TCR branch circuits 4 are connected in parallel according to the number of filtering required.

The compensation principle of the three-phase SVC compensation device on the traction side is: by injecting compensation current into power supply arm a and power supply arm b respectively and and the locomotive current on the two power supply arms and are superimposed separately, and the superimposed currents are respectively and Make the current on the two power supply arms after superposition and The three-phase current injected into the system after passing through the traction transformer 2 and The three phases are symmetrical, and the included angle with the three-phase voltage of the system is as small as possible, so as to ensure that the three-phase currents on the system side are symmetrical and the power factor meets the requirements. At the same time, the harmonic compensation function is realized through the fixed capacitance FC branch 5 to ensure that the harmonic index on the system side meets the requirements.

The three-phase SVC compensation device on the traction side is applicable to the traction transformer 2 of various wiring modes, and the traction transformer 2 can be any one of YNd11, V/v or balance transformer.

The key problem in the design of static var compensator SVC is to determine the compensation capacity. According to the theory of "general transformation relationship of electrical quantity at the port of traction substation" and the comprehensive compensation equation shown in formula (1) (reference: Li Qunzhan, " Traction Substation Power Supply Analysis and Comprehensive Compensation Technology", Beijing: China Railway Press, 2006.1), the compensation capacity required for each phase of the three-phase static var compensator SVC compensation device can be obtained, and then according to the required compensation Capacity and harmonic compensation requirements, the parameters of the fixed capacitor FC branch 5 and the thyristor-controlled reactor TCR branch 4 are designed.

in,

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det(T)=sin2(Ψ _T -Ψ _L )+sin2(Ψ _L -Ψ _K )+sin2(Ψ _K -Ψ _T );

In the formula:

S _K , S _L , S _T ——the compensation capacity of each phase of the SVC compensation device, K, L, T respectively represent the circuit port numbers connected to each phase of the SVC;

S _y —— traction load capacity of port y;

m——the number of loads, the wiring of the traction transformer provides two-phase or two-arm traction loads, but considering the phase commutation, generally m=3;

K _C —— reactive power compensation degree, when K _C = 1, it means that the reactive power generated by the load is fully compensated;

K _N —— Negative sequence compensation degree, when K _C = 1, it means that the negative sequence generated by the load is fully compensated;

Ψ _K , Ψ _L , Ψ _T , Ψ _y —— the phase angle lag of the voltage phasors of ports K, L, T, and y lagging behind the reference phasor is positive, generally the positive sequence voltage of phase A on the primary side of the traction transformer is taken, and its The value is related to the wiring mode of the traction transformer.

The following is YNd11 (where "Y" indicates that the high-voltage side is a star connection; "N" indicates a neutral point; "d" indicates that a low-voltage side is a delta connection; "11" indicates the line voltage on the low-voltage side of the transformer Lag high voltage side line voltage (or 30° in advance)) wiring a traction transformer and a typical traction load as an example, the implementation of the three-phase SVC compensation device on the traction side will be described. Fig. 2 is a wiring diagram of a three-phase SVC compensation device on the traction side of a YNd11-connected traction transformer according to a specific embodiment of the present invention.

Let the ports corresponding to the three phases of the SVC compensation device be K=4, L=5, T=6 respectively; the number of ports corresponding to the load m=3; and arrange S ₁ and S ₄ to be the same port, Ψ ₁ = Ψ ₄ = ξ , S ₂ and S ₅ are on the same port, Ψ ₂ =Ψ ₅ =120°+ξ, lagging behind Ψ ₁ ; S ₃ and S ₆ are on the same port, Ψ ₃ =Ψ ₆ =-120°+ξ, ahead of Ψ ₁ . Let the traction ports be ports 1 and 2, the corresponding load capacities of electric locomotives are S _L1 and S _L2 respectively, and the power factor angles are and The load of port 3 is 0, that is, S ₃ = 0, which can be brought into formula (1) to obtain the three-phase SVC comprehensive compensation model of the traction side of the V/V connection transformer as follows:

In the formula:

S _La , S _Lb ——the capacity of traction load carried by power supply arm a and power supply arm b;

——the power factor angle of the traction load carried by power supply arm a and power supply arm b.

When the SVC compensation device fully compensates reactive power and negative sequence, K _C =1, K _N =1, and its comprehensive compensation capacity model is:

The selected typical traction load power factor is 0.9, that is, the load power factor angle The load currents of power supply arms a and b are shown in Table 1 under typical operation mode. The most serious case of imbalance between the two arms is method 1. The heavy feeder takes the maximum current value, and the current of the light feeder is 0. Take the voltage of both power supply arms as 25kV, that is, Uab=Ubc=25kV, so the traction load capacity of the two arms can be calculated according to Table 1, as shown in Table 2. When the device fully compensates for negative sequence and reactive power, the compensation capacity of each phase of the three-phase SVC on the traction side under various operating modes can be calculated according to formula (3), as shown in Table 3, where the positive capacity means capacitive compensation , a negative capacity means inductive compensation.

Table 1 Current of power supply arm in typical operation mode

Table 2 Traction load capacity of power supply arm under typical operation mode

Table 3 Calculation of traction side three-phase SVC compensation capacity under typical operation mode

According to the maximum inductive compensation capacity and maximum capacitive compensation capacity required by each phase of the SVC calculated in Table 3, the capacity required by each branch of the SVC can be obtained. Considering the filtering function, assuming that there is an FC filter branch that can filter out the 3rd and 5th harmonics, the total capacity of the FC branch at port 4 is designed to be 19.7MVar, and the capacity of each filter branch is 9.85MVar, TCR The branch capacity is 19.7MVar+1.18MVar=20.88MVar. Similarly, it can be obtained that the capacity of the FC branch of port 5 is 36.2MVar, the capacity of each filtering branch is 18.1MVar, and the capacity of the TCR branch is also 36.2MVar; the capacity of the FC branch of port 6 is 2MVar, and the capacity of the TCR branch The road capacity is 2MVar+21.75MVar=23.75MVar. The above embodiments illustrate that the three-phase SVC compensation device on the traction side proposed by the present invention is designed with asymmetric parameters, which can minimize the capacity of the device and reduce unnecessary waste of capacity.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application rather than to limit its protection scope. Although the present application has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: After reading this application, those skilled in the art can still make various changes, modifications or equivalent replacements to the specific implementation methods of the application. These changes, modifications or equivalent replacements are all within the scope of the pending claims of the application.

Claims (4)

1. A three-phase SVC compensator for electrified railway traction side, said device comprises static var compensator (3); it is characterized in that said static var compensator (3) is used for electrified railway traction side , including a three-phase structure connected in a delta connection mode; wherein each phase includes a thyristor-controlled reactor branch (4) and a fixed capacitance branch (5) connected in parallel; The power supply arm for the device comprises a power supply arm (a, b); the power supply arm a and rail c form ac; the power supply arm b and rail c form bc; the power supply arm a and power supply arm b form ab; Each phase is respectively connected between ac, bc and ab; The device is connected to the low-voltage side of the traction transformer (2); The static var compensator (3) is connected to the low-voltage side of the traction transformer (2); the load electric locomotive (1) is connected between the power supply arm a and the rail c; The thyristor-controlled reactor branch (4) includes reactors connected in series and anti-parallel thyristor valves; the fixed capacitance branch (5) includes reactors and capacitors connected in series; The fixed capacitance branch (5) is equivalent to a capacitive reactance at power frequency, and is equivalent to a low impedance at a characteristic frequency; the fixed capacitance branch (5) is equivalent to the thyristor control reactor branch (4) and the The harmonic component produced by the load electric locomotive (1) acts as a filter; When the thyristor-controlled reactor branch (4) works normally, the anti-parallel thyristors are respectively triggered and turned on during the time interval from the voltage peak value to the zero-crossing point when the thyristors are subjected to forward voltage. 2. The three-phase SVC compensation device according to claim 1, characterized in that the parameters of the fixed capacitor branch (5) and the thyristor-controlled reactor branch (4) are designed asymmetrically. 3. The three-phase SVC compensation device according to claim 1, characterized in that, the traction transformer (2) includes Ynd11, V/v and balance transformers. 4. The three-phase SVC compensation device according to claim 1, characterized in that, the fixed capacitance branch (5) comprises a reactor, a capacitor and a resistor connected in series in sequence.