Harmonic injection method for reducing LCC DC voltage fluctuation

Abstract

The invention relates to a harmonic injection method for reducing LCC DC voltage fluctuation, each voltage control module is provided with different three-phase harmonic voltage control signals, the three-phase harmonic voltage control signals in each voltage control module are used for controlling the output voltage of a controlled voltage source, the output voltage of the controlled voltage source is changed, and the output voltage of the controlled voltage source is adjusted. The alternating current side voltage waveform of the 6-pulse LCC converter is changed, so that the direct current voltage fluctuation of the 6-pulse LCC converter is reduced, and reactive power and harmonic waves injected into a power grid are reduced. The method has the advantages that the method is used for changing the network side voltage waveform of the 6-pulse LCC converter and reducing the voltage pulsation generated on the direct current side when the 6-pulse LCC converter works, and in the direct current transmission project using the LCC converter, a filter and a smoothing reactor are not used, so that the loss of a direct current line is reduced, and the investment of the direct current transmission line is reduced; the grid-side voltage waveform can provide a stable commutation voltage for the 6-pulse LCC converter, and the commutation process of the 6-pulse LCC converter is controlled.

Description

Technical Field

[0001] The present invention relates to the technical field of high voltage direct current transmission, and in particular to a harmonic injection method for reducing LCC direct current voltage fluctuation. Background Art

[0002] Conventional DC transmission, i.e., Line Commutated Converterbase High Voltage Direct Current (LCC-HVDC), has the advantages of long-distance and large-capacity transmission, weak synchronous oscillation characteristics, and low energy loss, and is widely used in long-distance power transmission. Due to the working characteristics of the LCC phase-commutated converter itself, the DC voltage on the DC side of the LCC converter fluctuates greatly, and a large amount of harmonic current and reactive power is generated on the AC side of the LCC converter. Therefore, in LCC-HVDC DC transmission projects, the investment in AC filters, DC filters, smoothing reactors, and reactive power compensation accounts for a large proportion.

[0003] To solve the above problems, SVG is connected in parallel on the AC side of the LCC to filter harmonics and compensate reactive power on the AC side of the LCC. This method does not essentially change the working characteristics of the LCC, so there will still be DC voltage fluctuations on the DC side of the LCC, and it is still necessary to add a DC filter and a smoothing reactor on the DC side of the LCC. Summary of the invention

[0004] The purpose of the present invention is to provide a harmonic injection method for reducing LCC DC voltage fluctuations. By controlling the voltage waveform of a three-phase controlled voltage source, the AC side voltage of a 6-pulse LCC converter is changed, thereby reducing the voltage pulsation generated on the DC side when the 6-pulse LCC converter is working, thereby reducing the investment in DC filters, smoothing reactors and DC transmission lines of a DC transmission project using a 6-pulse LCC converter. It can be seen from the test waveform that the method can improve the AC harmonics and reactive power of the LCC converter.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A harmonic injection method for reducing LCC DC voltage fluctuations, wherein each voltage control module is respectively set with a different three-phase harmonic voltage control signal, and the three-phase harmonic voltage control signal in each voltage control module is used to control the output voltage of a controlled voltage source, and the AC side voltage waveform of a 6-pulse LCC converter is changed by changing the output voltage of the controlled voltage source, so that the DC voltage fluctuation of the 6-pulse LCC converter is reduced, and the reactive power and harmonics injected into the power grid are reduced;

[0007] According to the A phase voltage u of the three-phase voltage on the valve side of the converter transformera The phase selects the corresponding voltage control module and acts on the controlled voltage source.

[0008] The A phase voltage phase (θ a ), the three-phase current on the valve side of the converter transformer (i a 、i b 、i c ), the trigger angle α of the 6-pulse LCC converter is the input signal, and the corresponding voltage control module is selected. The content is as follows:

[0009] When the A phase voltage u a The phase θ a At α+30°<θ a <α+90°, if the three-phase current i c The absolute value of the error current I err , select voltage control module 1, if the valve side three-phase current i of the converter transformer c The absolute value of the error current I err , select voltage control module 2;

[0010] When the A phase voltage u a The phase θ a In α+90°<θ a <α+150°, if the three-phase current i b The absolute value of the error current I err , select voltage control module 3, if the valve side three-phase current i of the converter transformer b The absolute value of the error current I err , select voltage control module 4;

[0011] When the A phase voltage u a The phase θ a At α+150°<θ a <α+210°, if the three-phase current i a The absolute value of the error current I err , select voltage control module 5, if the valve side three-phase current i of the converter transformer a The absolute value of the error current I err , select voltage control module six;

[0012] When the A phase voltage u a The phase θ a At α+210°<θ a<α+270°, if the three-phase current i c The absolute value of the error current I err , select voltage control module seven, if the valve side three-phase current i of the converter transformer c The absolute value of the error current I err , select voltage control module eight;

[0013] When the A phase voltage u a The phase θ a At α+270°<θ a <α+330°, if the three-phase current i b The absolute value of the error current I err , select voltage control module nine, if the valve side three-phase current i of the converter transformer b The absolute value of the error current I err , select voltage control module ten;

[0014] When the A phase voltage u a The phase θ a At α+330°<θ a <α+390°, if the three-phase current i a The absolute value of the error current I err , select voltage control module 11, if the valve side three-phase current i of the converter transformer a The absolute value of the error current I err , select voltage control module twelve;

[0015] Error current I err The range of values ​​is 0.001-0.01.

[0016] Voltage control module 1, the formula is as follows:

[0017] U vA =(u c -u a +2*V p ) / 2

[0018] U vB =(-u b +0.5*(u c +u a ))-U dc

[0019] U vC =(u a -u c ) / 2 ①

[0020] Voltage control module 2, the formula is as follows:

[0021] U vA =(u c -u a +V p ) / 2

[0022] U vB =(-u b +0.5*(u c +u a ))-U dc

[0023] U vC =(u a -u c +V p ) / 2②.

[0024] Voltage control module three, the formula is as follows:

[0025] U vA =U dc -(u a -0.5*(u b +u c ))

[0026] U vB =(u c -u b ) / 2

[0027] U vC =(u b -u c -2*V p ) / 2 ③

[0028] Voltage control module 4, the formula is as follows:

[0029] U vA =U dc -(u a -0.5*(u b +u c ))

[0030] U vB =(u c -u b +V p ) / 2

[0031] U vC =(u b -u c -2*V p ) / 2④.

[0032] Voltage control module five, the formula is as follows:

[0033] U vA =(u b -u a ) / 2

[0034] U vB =(u a -u b +2*V p ) / 2

[0035] U vC = (-u c +0.5*(u a +u b ))-U dc ⑤

[0036] Electric control system model 6, official information below:

[0037] U vA =(u b -u a -V p ) / 2

[0038] U vB =(u a -u b +V p ) / 2

[0039] U vC = (-u c +0.5*(u a +u b ))-U dc ⑥.

[0040] Electric control system model 7, official information below:

[0041] U vA =(u c -u a -2*V p ) / 2

[0042] U vB = U dc -(u b -0.5*(u c +u a ))

[0043] UvC = (u a -u c ) / 2 ⑦

[0044] Electric control system model 8, official information below:

[0045] U vA =(u c-u a -V p ) / 2

[0046] U vB = U dc -(u b -0.5*(u c +u a ))

[0047] U vC =(u a -u c +V p ) / 2⑧.

[0048] Electric control system model 9, official information below:

[0049] U vA = (-u a +0.5*(u b +u c ))-U dc

[0050] U vB =(u c -u b ) / 2

[0051] U vC =(u b -u c +2*V p ) / 2 ⑨

[0052] Electric power control model 10, official information below:

[0053] U vA = (-u a +0.5*(u b +u c ))-U dc

[0054] U vB =(u c -u b -V p ) / 2

[0055] U vC =(u b -u c +V p ) / 2⑩.

[0056] Electric control system model 11, official information below:

[0057] U vA =(u b -u a ) / 2

[0058] U vB =(u a -u b -2*Vp) / 2

[0059] U vC =U dc -(Uc1-0.5*(u a +u b ))

[0060] Voltage control module twelve, the formula is as follows:

[0061] U vA =(u b -u a +V p ) / 2

[0062] U vB =(u a -u b -Vp) / 2

[0063] U vC =U dc -(Uc1-0.5*(u a +u b ))

[0064] Among them, UvA, U vB , U vC Represents the three-phase harmonic voltage control signal, u a 、u b 、u c represents the three-phase voltage on the valve side of the converter transformer, i a 、i b 、i c Indicates the three-phase current on the valve side of the converter transformer; U dc represents the DC voltage of the 6-pulse LCC converter; Vp represents the commutation voltage of the 6-pulse LCC converter, and Vp is a constant DC value.

[0065] The device for reducing LCC DC voltage fluctuation comprises a converter transformer, a three-phase controlled voltage source, and a 6-pulse LCC converter. The grid side of the converter transformer is connected to the power grid, the valve side of the converter transformer is connected to the positive pole of the three-phase controlled voltage source, the negative pole of the three-phase controlled voltage source is connected to the AC side of the 6-pulse LCC converter, and the DC side of the 6-pulse LCC converter is connected to a DC transmission line.

[0066] The 6-pulse LCC converter is composed of three-phase bridge arms A, B, and C connected in parallel. Each phase arm includes a thyristor 1 and a thyristor 2 connected in series. Of the two thyristors connected in series, the thyristor 1 at the upper end is the upper bridge arm thyristor, and the thyristor 2 at the lower end is the lower bridge arm thyristor.

[0067] The voltage control module 1 is used to change the commutation voltage of the upper arm thyristors of the A phase and the C phase of the 6-pulse LCC converter, and to modify the operating voltage of the lower arm thyristors of the B phase of the 6-pulse LCC converter;

[0068] The voltage control module 2 is used to modify the operating voltage of the thyristors of the upper bridge arm of phase A and the lower bridge arm of phase B of the 6-pulse LCC converter;

[0069] The voltage control module 3 is used to change the commutation voltage of the lower arm thyristors of the B phase and the C phase of the 6-pulse LCC converter, and to modify the operating voltage of the upper arm thyristors of the A phase of the 6-pulse LCC converter;

[0070] The voltage control module 4 is used to modify the operating voltage of the thyristors of the upper bridge arm of phase A and the lower bridge arm of phase C of the 6-pulse LCC converter;

[0071] The voltage control module 5 is used to change the commutation voltage of the upper arm thyristors of the A phase and the B phase of the 6-pulse LCC converter, and to modify the operating voltage of the lower arm thyristors of the C phase of the 6-pulse LCC converter;

[0072] The voltage control module 6 is used to modify the operating voltage of the thyristors of the upper bridge arm of the B phase and the lower bridge arm of the C phase of the 6-pulse LCC converter;

[0073] The voltage control module 7 is used to change the commutation voltage of the lower arm thyristors of the A phase and the C phase of the 6-pulse LCC converter, and to modify the operating voltage of the upper arm thyristors of the B phase of the 6-pulse LCC converter;

[0074] The voltage control module eight is used to modify the operating voltage of the thyristors of the upper bridge arm of the B phase and the lower bridge arm of the A phase of the 6-pulse LCC converter;

[0075] The voltage control module nine is used to change the commutation voltage of the upper arm thyristors of the B phase and the C phase of the 6-pulse LCC converter, and to modify the operating voltage of the lower arm thyristors of the A phase of the 6-pulse LCC converter;

[0076] The voltage control module 10 is used to modify the operating voltage of the thyristors of the upper bridge arm of the C phase and the lower bridge arm of the A phase of the 6-pulse LCC converter;

[0077] The voltage control module eleven is used to change the commutation voltage of the lower arm thyristors of the A phase and the B phase of the 6-pulse LCC converter, and to modify the operating voltage of the upper arm thyristors of the C phase of the 6-pulse LCC converter;

[0078] The voltage control module twelve is used to modify the operating voltage of the thyristors of the upper bridge arm of the C phase and the lower bridge arm of the B phase of the 6-pulse LCC converter.

[0079] Compared with the prior art, the present invention has the following beneficial effects:

[0080] 1. By injecting harmonic voltage on the grid side of the LCC harmonic injection device, the grid-side voltage waveform of the 6-pulse LCC converter is changed, thereby greatly reducing the voltage pulsation generated on the DC side when the 6-pulse LCC converter is working. In the DC transmission project using the LCC converter, no filter and smoothing reactor are used, the loss of the DC line will be reduced, and the investment in the DC transmission line can be reduced;

[0081] 2. By injecting harmonic voltage on the grid side of the LCC harmonic injection device, the grid-side voltage waveform of the 6-pulse LCC converter is changed. The grid-side voltage waveform can provide a stable commutation voltage for the 6-pulse LCC converter, control the commutation process of the 6-pulse LCC converter, and significantly reduce the harmonic current and reactive power consumed during the operation of the 6-pulse LCC converter;

[0082] 3. The LCC harmonic injection device includes a converter transformer, a three-phase controlled voltage source, and a 6-pulse LCC converter. The grid side of the converter transformer is connected to the power grid, the valve side of the converter transformer is connected to the positive electrode of the three-phase controlled voltage source, the negative electrode of the three-phase controlled voltage source is connected to the AC side of the 6-pulse LCC converter, and the DC side of the 6-pulse LCC converter is connected to the DC transmission line. The three-phase controlled voltage source can inject a controlled voltage between the LCC and the converter transformer, thereby controlling the AC side voltage of the 6-pulse LCC converter, so that the commutation process and operation process of the 6-pulse LCC converter can be controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 It is a schematic diagram of the structure of the LCC harmonic injection device;

[0084] Figure 2 is a schematic diagram of the voltage control module selection process;

[0085] Figure 3 It is the harmonic injection timing diagram for reducing the DC voltage fluctuation of LCC;

[0086] Figure 4 It is the harmonic injection voltage waveform that reduces the LCC DC voltage fluctuation;

[0087] Figure 5 This is a comparison chart of the DC voltage and AC current waveforms of the conventional LCC waveform and the waveforms after LCC harmonic injection;

[0088] Figure 6 This is the structural diagram of a 6-pulse LCC converter. DETAILED DESCRIPTION

[0089] The present invention is described in detail below in conjunction with the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0090] The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0091] [Example 1]

[0092] See Figure 1 , an LCC harmonic injection device for reducing LCC DC voltage fluctuations, comprising a converter transformer, a three-phase controlled voltage source, and a 6-pulse LCC converter, wherein the grid side of the converter transformer is connected to the power grid, the valve side of the converter transformer is connected to the positive electrode of the three-phase controlled voltage source, the negative electrode of the three-phase controlled voltage source is connected to the AC side of the 6-pulse LCC converter, and the DC side of the 6-pulse LCC converter is connected to a DC transmission line.

[0093] The converter transformer is a step-down transformer, which is used to provide AC voltage to the 6-pulse LCC converter, and the 6-pulse LCC converter is used to convert AC power into DC power.

[0094] The three-phase controlled voltage source is composed of three-phase cascaded H-bridge submodules, and the number of H-bridge submodules is determined according to the actual AC voltage. The three-phase controlled voltage source includes a three-phase input control signal U v , by controlling the three-phase input control signal U v , changing the output voltage of the three-phase controlled voltage source.

[0095] [Example 2]

[0096] On the basis of Example 1, a harmonic injection method for reducing LCC DC voltage fluctuation is provided, including 12 voltage control modules and a voltage control module selection process; each voltage control module contains different three-phase harmonic voltage control signals for controlling the output voltage of a controlled voltage source; by changing the output voltage of the controlled voltage source, the AC side voltage waveform of the 6-pulse LCC converter is changed, so that the DC voltage fluctuation of the 6-pulse LCC converter is reduced, and the reactive power and harmonics injected into the power grid are reduced; the voltage control module selection process, with the A-phase voltage phase (θ a ), the three-phase current on the valve side of the converter transformer (i a 、i b 、i c ), the trigger angle α of the 6-pulse LCC converter is the input signal, and one of the voltage control modules is selected in turn. The process is as follows:

[0097] When the A phase voltage u a The phase θ a At α+30°<θ a <α+90°, if the three-phase current i c The absolute value of the error current I err , select voltage control module 1, otherwise select voltage control module 2;

[0098] When the A phase voltage u a The phase θ a In α+90°<θ a <α+150°, if the three-phase current i b The absolute value of the error current I err , select voltage control module 3, otherwise select voltage control module 4;

[0099] When the A phase voltage u a The phase θ a At α+150°<θ a <α+210°, if the three-phase current i a The absolute value of the error current I err , select voltage control module 5, otherwise select voltage control module 6;

[0100] When the A phase voltage u a The phase θ a At α+210°<θ a <α+270°, if the three-phase current i c The absolute value of the error current I err , select voltage control module 7, otherwise select voltage control module 8;

[0101] When the A phase voltage u a The phase θ a At α+270°<θ a <α+330°, if the three-phase current i b The absolute value of the error current I err , select voltage control module 9, otherwise select voltage control module 10;

[0102] When the A phase voltage u a The phase θ a At α+330°<θ a<α+390°, if the three-phase current i a The absolute value of the error current I err , select voltage control module 11, otherwise select voltage control module 12;

[0103] Error current I err It is a smaller current value, which can be set to 0.01 to eliminate system misjudgment.

[0104] Voltage control module 1, the formula is as follows:

[0105] U vA =(u c -u a +2*V p ) / 2

[0106] U vB =(-u b +0.5*(u c +u a ))-U dc

[0107] U vC =(u a -u c ) / 2 ①

[0108] Voltage control module 2, the formula is as follows:

[0109] U vA =(u c -u a +V p ) / 2

[0110] U vB =(-u b +0.5*(u c +u a ))-U dc

[0111] U vC =(u a -u c +V p ) / 2 ②

[0112] Voltage control module 3, the formula is as follows:

[0113] U vA =U dc -(u a -0.5*(u b +u c ))

[0114] U vB =(uc -u b ) / 2

[0115] U vC =(u b -u c -2*V p ) / 2③

[0116] Electric control system model 4, official information below:

[0117] U vA = U dc -(u a -0.5*(u b +u c ))

[0118] U vB =(u c -u b +V p ) / 2

[0119] U vC =(u b -u c -2*V p ) / 2 ④

[0120] Electric control system model 5, official information below:

[0121] U vA =(u b -u a ) / 2

[0122] U vB =(u a -u b +2*V p ) / 2

[0123] U vC = (-u c +0.5*(u a +u b ))-U dc ⑤

[0124] Electric control system model 6, official information below:

[0125] U vA =(u b -u a -V p ) / 2

[0126] U vB =(u a -u b +V p ) / 2

[0127] U vC = (-u c +0.5*(u a +u b ))-U dc ⑥

[0128] Electric control system model 7, official information below:

[0129] U vA =(u c -u a -2*V p ) / 2

[0130] U vB = U dc -(u b -0.5*(u c +u a ))

[0131] UvC = (u a -u c ) / 2 ⑦

[0132] Electric control system model 8, official information below:

[0133] U vA =(u c -u a -V p ) / 2

[0134] U vB = U dc -(u b -0.5*(u c +u a ))

[0135] U vC =(u a -u c +V p ) / 2 ⑧

[0136] Electric control system model 9, official information below:

[0137] U vA = (-u a +0.5*(u b +u c ))-U dc

[0138] U vB =(u c -u b ) / 2

[0139] U vC =(ub -u c +2*V p ) / 2 ⑨

[0140] Electric control system model 10, official information below:

[0141] U vA = (-u a +0.5*(u b +u c ))-U dc

[0142] U vB =(u c -u b -V p ) / 2

[0143] U vC =(u b -u c +V p ) / 2 ⑩

[0144] Electric control system model 11, official information below:

[0145] U vA =(u b -u a ) / 2

[0146] U vB =(u a -u b -2*Vp) / 2

[0147] U vC = U dc -(Uc1-0.5*(u a +u b ))

[0148] Electric control system model 12, official information below:

[0149] U vA =(u b -u a +V p ) / 2

[0150] U vB =(u a -u b -Vp) / 2

[0151] U vC = U dc -(Uc1-0.5*(u a +u b ))

[0152] Among them, formula ①- Medium, UvA, U vB , U vC Represents the three-phase harmonic voltage control signal, u a 、u b 、u c represents the three-phase voltage on the valve side of the converter transformer, i a 、i b 、i c Indicates the three-phase current on the valve side of the converter transformer; U dc represents the DC voltage of the 6-pulse LCC converter; Vp represents the commutation voltage of the 6-pulse LCC converter, and Vp is a constant DC value.

[0153] like Figure 6 The pulse LCC converter is composed of three-phase bridge arms A, B, and C connected in parallel. Each arm is composed of two thyristors connected in series. Among the two thyristors in series, the one at the upper end is called the upper bridge arm thyristor, and the one at the lower end is called the lower bridge arm thyristor.

[0154] The voltage control module 1 is used to change the commutation voltage of the upper arm thyristors of the A phase and the C phase of the 6-pulse LCC converter, and to modify the operating voltage of the lower arm thyristors of the B phase of the 6-pulse LCC converter.

[0155] The voltage control module 2 is used to modify the operating voltage of the thyristors of the upper bridge arm of phase A and the lower bridge arm of phase B of the 6-pulse LCC converter.

[0156] The voltage control module 3 is used to change the commutation voltage of the lower arm thyristors of the B phase and the C phase of the 6-pulse LCC converter, and to modify the operating voltage of the upper arm thyristors of the A phase of the 6-pulse LCC converter.

[0157] The voltage control module 4 is used to modify the operating voltage of the thyristors of the upper bridge arm of the A phase and the lower bridge arm of the C phase of the 6-pulse LCC converter.

[0158] The voltage control module 5 is used to change the commutation voltage of the upper arm thyristors of the A phase and the B phase of the 6-pulse LCC converter, and to modify the operating voltage of the lower arm thyristors of the C phase of the 6-pulse LCC converter.

[0159] The voltage control module 6 is used to modify the operating voltage of the thyristors of the upper bridge arm of the B phase and the lower bridge arm of the C phase of the 6-pulse LCC converter.

[0160] The voltage control module 7 is used to change the commutation voltage of the lower arm thyristors of the A phase and the C phase of the 6-pulse LCC converter, and to modify the operating voltage of the upper arm thyristors of the B phase of the 6-pulse LCC converter.

[0161] The voltage control module 8 is used to modify the operating voltage of the thyristors of the upper bridge arm of the B phase and the lower bridge arm of the A phase of the 6-pulse LCC converter.

[0162] The voltage control module 9 is used to change the commutation voltage of the upper arm thyristors of the B phase and the C phase of the 6-pulse LCC converter, and to modify the operating voltage of the lower arm thyristors of the A phase of the 6-pulse LCC converter.

[0163] The voltage control module 10 is used to modify the operating voltage of the thyristors of the upper bridge arm of the C phase and the lower bridge arm of the A phase of the 6-pulse LCC converter.

[0164] The voltage control module 11 is used to change the commutation voltage of the lower arm thyristors of the A phase and the B phase of the 6-pulse LCC converter, and to modify the operating voltage of the upper arm thyristors of the C phase of the 6-pulse LCC converter.

[0165] The voltage control module 12 is used to modify the operating voltage of the thyristors of the upper bridge arm of the C phase and the lower bridge arm of the B phase of the 6-pulse LCC converter.

[0166] According to the above three-phase harmonic voltage control signal process with different settings, the harmonic injection voltage waveform of the three-phase controlled voltage source is obtained, such as Figure 4 As shown, the first figure is the injection voltage waveform of the A-phase controlled source, the second figure is the injection voltage waveform of the B-phase controlled source, and the third figure is the injection voltage waveform of the C-phase controlled source; according to such voltage injection waveform, the AC voltage of the commutation and operation process of the 6-pulse LCC converter can be changed, thereby greatly reducing the voltage pulsation generated on the DC side when the 6-pulse LCC converter is working. In the DC transmission project using the LCC converter, the loss of the DC line will be reduced without using filters and smoothing reactors, which can reduce the investment in the DC transmission line; and the commutation process of the 6-pulse LCC converter is controlled, thereby Figure 3 and Figure 5 It can be seen that the phase of voltage and current is controllable, and the harmonics of current are significantly reduced. Therefore, the harmonic current and reactive power consumed during the operation of the 6-pulse LCC converter can be controlled according to such a voltage injection waveform.

[0167] Compare the DC voltage and AC current waveforms of conventional LCC and LCC harmonic injection, such as Figure 5As shown, the upper left corner is the DC voltage waveform of the conventional LCC, the lower left corner is the AC current waveform of the conventional LCC, the upper right corner is the DC voltage waveform of the LCC harmonic injection, and the lower right corner is the AC voltage waveform of the LCC harmonic injection. It can be seen that compared with the conventional LCC, the DC voltage of the conventional LCC is a DC waveform with larger pulsation, while the DC voltage pulsation of the LCC harmonic injection is greatly reduced and tends to be a straight line. Therefore, there is no need to add any filter and smoothing inductor on the DC side of the LCC, and the AC current waveform is significantly improved.

Claims

1. A harmonic injection method for reducing LCC DC voltage fluctuations, characterized in that: A different three-phase harmonic voltage control signal is set for each voltage control module. The three-phase harmonic voltage control signal in each voltage control module is used to control the output voltage of the controlled voltage source. By changing the output voltage of the controlled voltage source, the AC side voltage waveform of the 6-pulse LCC converter is changed, so that the DC voltage fluctuation of the 6-pulse LCC converter is reduced, and the reactive power and harmonics injected into the power grid are reduced; According to the A phase voltage u of the three-phase voltage on the valve side of the converter transformer a The phase selects the corresponding voltage control module and acts on the controlled voltage source.

2. A harmonic injection method for reducing LCC DC voltage fluctuation according to claim 1, characterized in that: The A phase voltage phase (θ a ), the three-phase current on the valve side of the converter transformer (i a 、i b 、i c ), the trigger angle α of the 6-pulse LCC converter is the input signal, and the corresponding voltage control module is selected. The content is as follows: When the A phase voltage u a The phase θ a At α+30°<θ a <α+90°, if the three-phase current i c The absolute value of the error current I err , select voltage control module 1, if the valve side three-phase current i of the converter transformer c The absolute value of the error current I err , select voltage control module 2; When the A phase voltage u a The phase θ a In α+90°<θ a <α+150°, if the three-phase current i b The absolute value of the error current I err , select voltage control module 3, if the valve side three-phase current i of the converter transformer b The absolute value of the error current I err , select voltage control module 4; When the A phase voltage u a The phase θ a At α+150°<θ a <α+210°, if the three-phase current i a The absolute value of the error current I err , select voltage control module 5, if the valve side three-phase current i of the converter transformer a The absolute value of the error current I err , select voltage control module six; When the A phase voltage u a The phase θ a At α+210°<θ a <α+270°, if the three-phase current i c The absolute value of the error current I err , select voltage control module seven, if the valve side three-phase current i of the converter transformer c The absolute value of the error current I err , select voltage control module eight; When the A phase voltage u a The phase θ a At α+270°<θ a <α+330°, if the three-phase current i b The absolute value of the error current I err , select voltage control module nine, if the valve side three-phase current i of the converter transformer b The absolute value of the error current I err , select voltage control module ten; When the A phase voltage u a The phase θ a At α+330°<θ a <α+390°, if the three-phase current i a The absolute value of the error current I err , select voltage control module 11, if the valve side three-phase current i of the converter transformer a The absolute value of the error current I err , select voltage control module twelve; Error current I err The range of values ​​is 0.001-0.

01.

3. A harmonic injection method for reducing LCC DC voltage fluctuation according to claim 2, characterized in that: The voltage control module 1 has the following formula: U vA =(u c -u a +2*V p ) / 2 IN vB =(-u b +0.5*(in c +in a ))-IN dc IN vC =(in a -in c ) / 2 ① The voltage control module 2 has the following formula: U vA =(u c -u a +V p ) / 2 IN vB =(-u b +0.5*(in c +in a ))-IN dc U vC =(u a -u c +V p ) / 2②。 4. A harmonic injection method for reducing LCC DC voltage fluctuation according to claim 2, characterized in that: The voltage control module three has the following formula: IN vA =U dc -(in a -0.5*(in b +in c )) IN vB =(in c -in b ) / 2 U vC =(u b -u c -2*V p ) / 2 ③ The voltage control module 4 has the following formula: IN vA =U dc -(in a -0.5*(in b +in c )) U vB =(u c -u b +V p ) / 2 U vC =(u b -u c -2*V p ) / 2④。 5. A harmonic injection method for reducing LCC DC voltage fluctuation according to claim 2, characterized in that: The voltage control module 5 has the following formula: IN vA =(in b -in a ) / 2 U vB =(u a -u b +2*V p ) / 2 IN vC =(-u c +0.5*(in a +in b ))-IN dc ⑤ The voltage control module 6 has the following formula: U vA =(u b -u a -V p ) / 2 U vB =(u a -u b +V p ) / 2 IN vC =(-u c +0.5*(in a +in b ))-IN dc ⑥。 6. A harmonic injection method for reducing LCC DC voltage fluctuation according to claim 2, characterized in that: The voltage control module seven has the following formula: U vA =(u c -u a -2*V p ) / 2 IN vB =U dc -(in b -0.5*(in c +in a )) UvC=(u a -in c ) / 2 ⑦ The voltage control module eight has the following formula: U vA =(u c -u a -V p ) / 2 IN vB =U dc -(in b -0.5*(in c +in a )) U vC =(u a -u c +V p ) / 2⑧。 7. A harmonic injection method for reducing LCC DC voltage fluctuation according to claim 2, characterized in that: The voltage control module nine has the following formula: IN vA =(-u a +0.5*(in b +in c ))-IN dc IN vB =(in c -in b ) / 2 U vC =(u b -u c +2*V p ) / 2 ⑨ The voltage control module 10 has the following formula: IN vA =(-u a +0.5*(in b +in c ))-IN dc U vB =(u c -u b -V p ) / 2 U vC =(u b -u c +V p ) / 2⑩。 8. A harmonic injection method for reducing LCC DC voltage fluctuation according to claim 2, characterized in that: The voltage control module 11 has the following formula: IN vA =(in b -in a ) / 2 YOU vB =(you a -you b -2*Vp) / 2 The voltage control module twelve has the following formula: U vA =(u b -u a +V p ) / 2 YOU vB =(you a -you b -Vp) / 2 Among them, UvA, U vB , U vC Represents the three-phase harmonic voltage control signal, u a 、u b 、u c represents the three-phase voltage on the valve side of the converter transformer, i a 、i b 、i c Indicates the three-phase current on the valve side of the converter transformer; U dc represents the DC voltage of the 6-pulse LCC converter; Vp represents the commutation voltage of the 6-pulse LCC converter, and Vp is a constant DC value.

9. The device for reducing LCC DC voltage fluctuations used in the method according to any one of claims 1 to 8, characterized in that: It includes a converter transformer, a three-phase controlled voltage source, and a 6-pulse LCC converter. The grid side of the converter transformer is connected to the power grid, the valve side of the converter transformer is connected to the positive pole of the three-phase controlled voltage source, the negative pole of the three-phase controlled voltage source is connected to the AC side of the 6-pulse LCC converter, and the DC side of the 6-pulse LCC converter is connected to the DC transmission line.

10. The device for reducing LCC DC voltage fluctuation according to claim 9, characterized in that: The 6-pulse LCC converter is composed of three-phase bridge arms A, B, and C connected in parallel, and each phase arm includes a thyristor 1 and a thyristor 2 connected in series. Of the two thyristors connected in series, the thyristor 1 at the upper end is the upper bridge arm thyristor, and the thyristor 2 at the lower end is the lower bridge arm thyristor; The voltage control module 1 is used to change the commutation voltage of the upper arm thyristors of the A phase and the C phase of the 6-pulse LCC converter, and to modify the operating voltage of the lower arm thyristors of the B phase of the 6-pulse LCC converter; The voltage control module 2 is used to modify the operating voltage of the thyristors of the upper bridge arm of phase A and the lower bridge arm of phase B of the 6-pulse LCC converter; The voltage control module 3 is used to change the commutation voltage of the lower arm thyristors of the B phase and the C phase of the 6-pulse LCC converter, and to modify the operating voltage of the upper arm thyristors of the A phase of the 6-pulse LCC converter; The voltage control module 4 is used to modify the operating voltage of the thyristors of the upper bridge arm of phase A and the lower bridge arm of phase C of the 6-pulse LCC converter; The voltage control module 5 is used to change the commutation voltage of the upper arm thyristors of the A phase and the B phase of the 6-pulse LCC converter, and to modify the operating voltage of the lower arm thyristors of the C phase of the 6-pulse LCC converter; The voltage control module 6 is used to modify the operating voltage of the thyristors of the upper bridge arm of the B phase and the lower bridge arm of the C phase of the 6-pulse LCC converter; The voltage control module 7 is used to change the commutation voltage of the lower arm thyristors of the A phase and the C phase of the 6-pulse LCC converter, and to modify the operating voltage of the upper arm thyristors of the B phase of the 6-pulse LCC converter; The voltage control module eight is used to modify the operating voltage of the thyristors of the upper bridge arm of the B phase and the lower bridge arm of the A phase of the 6-pulse LCC converter; The voltage control module nine is used to change the commutation voltage of the upper arm thyristors of the B phase and the C phase of the 6-pulse LCC converter, and to modify the operating voltage of the lower arm thyristors of the A phase of the 6-pulse LCC converter; The voltage control module 10 is used to modify the operating voltage of the thyristors of the upper bridge arm of the C phase and the lower bridge arm of the A phase of the 6-pulse LCC converter; The voltage control module eleven is used to change the commutation voltage of the lower bridge arm thyristors of the A phase and the B phase of the 6-pulse LCC converter, and to modify the operating voltage of the upper bridge arm thyristors of the C phase of the 6-pulse LCC converter; The voltage control module twelve is used to modify the operating voltage of the thyristors of the upper bridge arm of the C phase and the lower bridge arm of the B phase of the 6-pulse LCC converter.

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