CN101252277A - Startup method of idle load long line - Google Patents

Abstract

Disclosed is a long unloaded line startup method, belonging to electricity transmission and distribution technical field and used to solve the problem in quickly starting up the long unloaded line during black startup. The invention adopts the technical scheme that: the inverting side of an VSC-HVDC inverter connected with internet is directly connected with the long unloaded line to be started through a switch; when to start up, first the switch is closed and then the AC side of the VSC-HVDC inverter is galvanized and the voltage of the line is controlled by the inverter to make the virtual value of the voltage to recover according to a specific curve. The method is capable of effectively eliminating power frequency overvoltage and overvoltage when closing the brake, and capable of improving black startup speed and shortening blackout time.

Description

A kind of startup method of idle load long line

Technical field

The present invention relates to a kind ofly in the black start-up course of electrical network, start the method for idle load long line fast, belong to the power transmission and distribution technical field.

Background technology

Along with the trans-regional interconnected continuous increase of electric power system, the scale of electrical network is increasing, and influencing each other between each subsystem is also strong further.The fault of subsystem part may lead to large-area power outage owing to the incorrect operation of protection or automatics.Although the possibility that this serious accident takes place is very little, in case take place, to lose hugely, consequence is hardly imaginable.Therefore, how to guarantee the operation of recovery system fast and effeciently after the accident of having a power failure on a large scale, be that power industry is extremely paid close attention to and pressed for the problem of solution always.

The power system restoration of having a power failure on a large scale generally is to realize by black start (Black-start), method is at first to start power supply with one idle load long line is carried out the zero load charging, start idle load long line, progressively start other generating set and load then, make whole power system restoration operation at last.At present, the general employing requires very low gas turbine set or water wheels unit that idle load long line is carried out the zero load charging to station service in the black start-up course, the shortcoming of this startup idle load long line method is can produce switching overvoltage when closing a floodgate unloaded long line, and start power supply when the long line of charging zero load, because the line capacitance effect can produce power-frequency overvoltage.For guaranteeing power grid security, the closing overvoltage of nonloaded line and the empty transformer fe magnetic resonance problem of filling must be through the calculating and the experimental verifications of strictness, otherwise might cause extremely serious consequence.The existence of these problems makes the speed of service of black startup scheme be subjected to very big restriction, has prolonged the interruption duration of load greatly.

Summary of the invention

The object of the present invention is to provide and a kind ofly can effectively suppress power-frequency overvoltage and the superpotential idle load long line of closing operation startup method.

The alleged problem of the present invention realizes with following technical proposals:

A kind of startup method of idle load long line, it directly links to each other the inverter of the VSC-HVDC of networking with the idle load long line XL that will start by circuit breaker BRK, the close circuit breaker BRK of elder generation during startup, make VSC-HVDC inverter AC side charged again, and, voltage effective value is recovered by assignment curve by inverter control circuit voltage.

The startup method of above-mentioned idle load long line, described inverter control circuit voltage recovers by following mode: in long transmission line starts 1～5 power frequency period of beginning, allow the ac bus voltage effective value of circuit breaker BRK access point evenly rise to 0.8～1p.u, and guarantee that the nonloaded line terminal voltage is no more than 1.1p.u from 0.3～0.6p.u.

The startup method of above-mentioned idle load long line, the modulation degree m of described inverter is determined by following formula:

$m=\frac{2\sqrt{u_{\mathrm{<figure-callout\; id="2"\; label="cd"\; filenames="S2007101854536E00021.png"\; state="\{\{state\}\}">cd</figure-callout>}}^2+u_{\mathrm{cq}}^2}}{U_d},$

The fundametal compoment U of converter output voltage _cWith ac bus voltage fundamental component U _sBetween phase angle difference determine by following formula:

$\mathrm{\&delta;}=\arctan \frac{u_{\mathrm{cd}}}{u_{\mathrm{cq}}};$

Wherein, u _Cd, u _Cq, be AC side voltage under the dq0 coordinate system; U _dBe direct voltage.

Black startup power supply when the present invention has a power failure on a large scale as AC system with the VSC-HVDC of networking operation, can realize " the flexible startup " of nonloaded line by VSC-HVDC, make and wait that the voltage that recovers AC system recovers by assignment curve, switching overvoltage and the transformer sky of having avoided interchange long transmission line combined floodgate to cause fill the ferro resonance of initiation; To idle independent quick control, produce power-frequency overvoltage in the time of also can avoiding long transmission line unloaded by VSC-HVDC, thereby can accelerate black toggle speed greatly.The present invention can effectively suppress power-frequency overvoltage and the superpotential generation of closing operation, improves black toggle speed, shortens and has a power failure on a large scale the time.

Description of drawings

The invention will be further described below in conjunction with accompanying drawing.

Fig. 1 is a VSC-HVDC structure electrical schematic diagram;

Fig. 2 starts the system construction drawing of idle load long line for voltage source converter;

Fig. 3 is a rectification side control algolithm schematic diagram;

Fig. 4 is for suppressing the terminal power-frequency overvoltage inversion of nonloaded line side control block diagram;

Fig. 5 is an inversion side control system block diagram when suppressing nonloaded line end switching overvoltage;

Unloaded line end produces the power-frequency overvoltage simulation waveform when directly starting with flexible the startup when Fig. 6 is 250km for line length;

Unloaded line end produces the power-frequency overvoltage simulation waveform when directly starting with flexible the startup when Fig. 7 is 500km for line length;

Unloaded line end produces the switching overvoltage simulation waveform when directly starting when Fig. 8 is 250km for line length;

Unloaded line end produced the switching overvoltage simulation waveform when flexibility started when Fig. 9 was 250km for line length;

Figure 10,11 is respectively the combined floodgate transient overvoltage emulation ripple figure after line length increases, before and after the flexible startup of employing.

Each symbol is among the figure: the generator of G, equivalence; R, line resistance; T ₁, converter transformer; T ₂, converter transformer; B ₁, the ac bus starting point; B ₂, the nonloaded line end; BRK, circuit breaker; XL, nonloaded line; PI, proportional integral link; PI ₁, the proportional integral link; PI ₂, the proportional integral link; AC Filter, filter circuit; VSC, voltage source converter high voltage direct current transmission; K1, gain coefficient.

Used symbol: U in the literary composition _c, the converter output voltage fundametal compoment; U _s, ac bus voltage fundamental component; δ, U _cAnd U _sBetween phase angle difference; M, modulation degree; u _Ca, u _Cb, u _Cc, the converter output voltage; u _Cd, u _Cq, AC side voltage under the dq0 coordinate system; L ₀, the single-phase inductance of circuit unit length; C ₀, circuit unit length single-phase capacitance; R ₀, circuit unit length single-phase transmission line resistance; G ₀, lead scatter admittance over the ground; γ, circuit propagation coefficient; Z _c, the line characteristics impedance; U _B1, ac bus starting point (B ₁) locate voltage; U _B2, line end voltage; U _B1ref, ac bus starting point (B1) locates the ac bus voltage reference value; The idle output of Q, converter; α, circuit propagation coefficient imaginary part; β, circuit propagation coefficient real part; U _Dref, the DC bus-bar voltage reference value; U _Dc, the DC bus-bar voltage measured value; i _1dref, i _1qref, rectification top-cross stream current reference value d axle component; i _1d, i _1q, rectification top-cross stream current measurement value d axle component; i _1qref, rectification top-cross stream current reference value q axle component; i _1q, rectification top-cross stream current measurement value q axle component; u _S1d, u _S1q, rectification side system alternating voltage d axle and q axle component; u _C1d, u _C1q, rectifier inverter output voltage d axle and q axle component; Q _1ref, rectification top-cross streaming system output reactive power reference qref; P.u is a phase voltage amplitude per unit value, U _dBe direct voltage.

Embodiment

The present invention has adopted the voltage source converter high voltage dc transmission technology, voltage source converter high voltage dc transmission technology (Voltage Source Converter based High Voltage Direct Current, be called for short VSC-HVDC) compare with traditional direct current transportation, have following major advantage:

(1) can provide power supply to passive network.

(2) can control fast meritorious and the idle independence of carrying out, may operate at meritorious and idle four quadrant states.

(3) can play the effect of STATCOM (STATCOM) for AC side provides idle fast support, STATCOM is an important component part of flexible AC transmitting system (FACTS), can realize static reactive.

Since the These characteristics of VSC-HVDC, the black startup power supply in the time of the VSC-HVDC of networking operation can being had a power failure on a large scale as AC system.If adopt the startup power supply of having a power failure on a large scale based on the VSC-HVDC conduct of interconnection operation, relating to many problems in black the startup can be readily solved, and can greatly accelerate load restoration speed.PWM technology by VSC-HVDC, realize VSC-HVDC " the flexible startup ", make the voltage effective value of waiting to recover AC system by specifying slope straight line or exponential function curve to increase, switching overvoltage and the transformer sky of having avoided interchange long transmission line combined floodgate to cause fill initiation ferro resonance problem; In conjunction with the idle characteristics that can independent quick control of VSC-HVDC, the power-frequency overvoltage problem in the time of also can avoiding long transmission line unloaded.

The idle load long line power-frequency overvoltage is idle load long line when charged, causes that by the line capacitance effect essence is because the power frequency capacitive reactance X of nonloaded line _cGreater than power frequency induction reactance X _L, under the effect of electrical source voltage, the pressure drop U of the capacitance current in the circuit on induction reactance _LWith the voltage U that makes in the capacitive reactance _cBe higher than the circuit electrical source voltage of beginning.

The generation of vibrating on its stable state power-frequency overvoltage basis of the terminal switching overvoltage of nonloaded line finally is stabilized in its power-frequency overvoltage, and terminal power-frequency overvoltage is high more, and the amplitude of switching overvoltage is high more.Therefore, the line end switching overvoltage is subjected to the influence of power-frequency overvoltage to a great extent during the combined floodgate nonloaded line, and its oscillatory process is very short.

By the mechanism of power-frequency overvoltage as can be known, power-frequency overvoltage is a kind of steady state phenomena, utilizes the inverter of VSC-HVDC can carry out deciding the characteristics that alternating voltage is controlled, when starting idle load long line, set its top voltage between 0.8～1p.u, then can suppress the terminal power-frequency overvoltage of nonloaded line.And conventional method is because the tap that transformer is regulated is limited, mechanical process during regulation voltage simultaneously, and governing speed is very slow, can not carry out high-precision fast control to top voltage, thereby can not the power-frequency overvoltage of idle load long line effectively be suppressed.

The terminal switching overvoltage of nonloaded line is owing to vibration on stable state power-frequency overvoltage basis produces, and therefore control relates to two main points: the one, and for the generation of minimizing electromagnetic viscosimeter waveform, therefore adopt the alternating voltage definite value to rise by assignment curve; The 2nd, beginning alternating voltage definite value is lower.Reasonably recovering rule should be, makes the ac bus voltage effective value rise to 0.8～1p.u from 0.3～0.6p.u by the straight line of index or certain slope, and the duration is a 1-5 cycle.

Control sequence is to suppress the terminal switching overvoltage of nonloaded line earlier, suppresses power-frequency overvoltage again.

The VSC-HVDC system configuration as shown in Figure 1.U _cFundametal compoment for the converter output voltage; U _sBe ac bus voltage fundamental component; δ is U _cAnd U _sBetween phase angle difference; Converter adopts PWM control, and m is a modulation degree.Converter output voltage u then _Ca, u _Cb, u _CcFor:

With u _Ca, u _Cb, u _CcThrough the Park conversion, get AC side voltage u under the dq0 coordinate system _Cd, u _CqFor:

$\left[\begin{array}{c}{u}_{\mathrm{cd}}\\ u_{\mathrm{cq}}\end{array}\right]=\frac{m{U}_{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="S2007101854536E00021.png"\; state="\{\{state\}\}">d</figure-callout>}}}{2}\left[\begin{array}{c}\sin \mathrm{\&delta;}\\ \cos \mathrm{\&delta;}\end{array}\right],$ So

$m=\frac{2\sqrt{u_{\mathrm{<figure-callout\; id="2"\; label="cd"\; filenames="S2007101854536E00021.png"\; state="\{\{state\}\}">cd</figure-callout>}}^2+u_{\mathrm{cq}}^2}}{U_d},$ $\mathrm{\&delta;}=\arctan \frac{u_{\mathrm{cd}}}{u_{\mathrm{cq}}};$

Among the present invention, the structure of the VSC-HVDC of networking startup nonloaded line as shown in Figure 2.Combined floodgate nonloaded line process is an electromagnetic transient, circuit is pressed distributed constant handle.Because the actual track parameter is with frequency change, and circuit is lossy circuit, for can be accurately, objectively respond its transient process, circuit adopts the road of modified line frequently model.

To simplify the analysis, can suppose that when calculating the power-frequency overvoltage that causes by the nonloaded line capacity effect circuit is harmless circuit, and and frequency-independent.Line length is 1, and the single-phase inductance of circuit unit length, electric capacity, conductor resistance, lead scatter admittance over the ground are respectively L ₀, C ₀, R ₀, G ₀, circuit propagation coefficient γ and characteristic impedance Z _cFor:

$\mathrm{\&gamma;}=\mathrm{\&beta;}+\mathrm{j\&alpha;}=\sqrt{(R_0+\mathrm{j\&omega;}{L}_0)(G_0+\mathrm{j\&omega;}{C}_0),}$ $Z_c=\sqrt{\frac{R_0+\mathrm{j\&omega;}{L}_0}{G_0+\mathrm{j\&omega;}{C}_0}};$ B1 place voltage U _B1With B2 place voltage U _B2Between the pass be: U _B1=U _B2Cos α l.Suppress the nonloaded line terminal voltage and raise, promptly keep busbar voltage U _B2Effective value is 1p.u. (p.u is the phase voltage amplitude (per unit value) of high operation, and 1p.u is 1 times a phase voltage .), promptly | and U _B1|=cos α l.VSC-HVDC adopts the rectification side to decide direct voltage, and the inversion side is decided the ac bus voltage control mode, and the control system block diagram as shown in Figure 3, Figure 4.Wherein, K ₁=-2Q/3U, U _B1refBe B1 place ac bus voltage reference value, U _B1Measured value for B1 place ac bus voltage.U _B1refSelected be normal startup at 1 o'clock, promptly B1 place ac bus voltage reaches 1p.u, is equivalent to the operation of ideal voltage source band nonloaded line; Work as U _B1refWhen being chosen as flexible the startup, promptly keep | U _B1|=cos α l, take this strategy to suppress the terminal power-frequency overvoltage of nonloaded line.

Among the present invention, rectification side control structure is seen Fig. 3, the outer remainder of PWM trigger impulse module and phase-locked loop is that control algolithm concerns schematic diagram among Fig. 3, unit 1 and unit 2 are the control function relation, detailed description sees below, and related physical quantity all is through the parameter under the dq0 coordinate system of Park conversion acquisition among Fig. 3.The meaning of each parameter is as follows.

U _Dref, U _DcBe respectively DC bus-bar voltage reference value and measured value; i _1dref, i _1d, i _1qref, i _1qBe respectively the d axle component of rectification top-cross stream current reference value and measured value; i _1qref, i _1qBe respectively the q axle component of rectification top-cross stream current reference value and measured value; u _S1d,, u _S1qBe respectively rectification side system alternating voltage d axle and q axle component; u _C1d, u _C1qBe respectively rectifier inverter output voltage d axle and q axle component; The functional relation of unit 1 is: $m=\frac{2\sqrt{u_{\mathrm{<figure-callout\; id="2"\; label="cd"\; filenames="S2007101854536E00021.png"\; state="\{\{state\}\}">cd</figure-callout>}}^2+u_{\mathrm{cq}}^2}}{U_d},$ The functional relation of unit 2 is: $\mathrm{\&delta;}=\arctan \frac{u_{\mathrm{cd}}}{u_{\mathrm{cq}}};$ Q _1refReactive power reference qref for the output of rectification top-cross streaming system.

VSC-HVDC to networking has carried out emulation direct the startup with the flexible situation that starts the unloaded long line of startup under two kinds of Starting mode, the line length of emulation is respectively 250km, 500km, consider on the basis of circuit for harmless and line parameter circuit value and frequency-independent, the line end power-frequency overvoltage was 1.04p.u when Theoretical Calculation directly started unloaded long line with VSC when line length was 250km, and the line end power-frequency overvoltage was 1.15p.u when Theoretical Calculation VSC directly started unloaded long line when line length was 500km.Simulation result is shown in Fig. 6,7.When VSC adopts direct Starting mode, at the terminal power-frequency overvoltage (Fig. 6) that produces of nonloaded line; After VSC adopted flexible Starting mode, power-frequency overvoltage obviously reduced (Fig. 7), and can maintain 1p.u basically.

The present invention's suppress to close a floodgate control strategy of switching overvoltage of nonloaded line end rises to 1p.u from 0.5p.u for control B1 place ac bus voltage effective value in a power frequency cycle, same Fig. 3 of rectification side control system at this moment, inversion side control system such as Fig. 5.Nonloaded line closes a floodgate when 1.5s, adopting VSC directly to start with VSC adopts the flexibility of the control system of Fig. 5 to start two kinds of Starting mode startups, line end A phase overvoltage factor K, be the overvoltage amplitude and the ratio (wherein steady state voltage is power-frequency overvoltage) of steady state voltage amplitude, shown in Fig. 8,9.

Obtain by line end switching overvoltage under comparison diagram 8,9 Starting mode, its terminal power-frequency overvoltage is 1.04p.u. when line length is 250km, switching overvoltage and not obvious (Fig. 8) of superposeing on this basis and producing, but rise to steady state voltage (Fig. 9) gradually through terminal switching overvoltage after the VSC Flexible Control, do not impact; After line length increased, the switching overvoltage of the moment of closing a floodgate obviously increased (Figure 10), and after VSC-HVDC adopted flexible the startup, as Figure 11, switching overvoltage obviously reduced.Proved that reducing power-frequency overvoltage in initial start stage can effectively suppress its switching overvoltage, it is effective taking this control strategy to suppress switching overvoltage.

Claims (3)

1, a kind of startup method of idle load long line, it is characterized in that, it be will networking the inversion side of VSC-HVDC directly link to each other with the idle load long line that will start (XL) by circuit breaker (BRK), elder generation's close circuit breaker (BRK) during startup, make VSC-HVDC inverter AC side charged again, and, voltage effective value is recovered by assignment curve by inverter control circuit voltage.

2, according to the startup method of the described idle load long line of claim 1, it is characterized in that, described inverter control circuit voltage recovers by following mode: in long transmission line starts 1～5 power frequency period of beginning, allow the ac bus voltage effective value of circuit breaker BRK access point evenly rise to 0.8～1p.u, and guarantee that the nonloaded line terminal voltage is no more than 1.1p.u from 0.3～0.6p.u.

According to the startup method of the described idle load long line of claim 1, it is characterized in that 3, the modulation degree of described inverter (m) is determined by following formula:

$m=\frac{2\sqrt{u_{\mathrm{cd}}^2+u_{\mathrm{cq}}^2}}{U_d},$

Fundametal compoment (the U of converter output voltage _c) and ac bus voltage fundamental component (U _s) between phase angle difference determine by following formula:

$\mathrm{\&delta;}=\arctan \frac{u_{\mathrm{cd}}}{u_{\mathrm{cq}}};$

Wherein, u _Cd, u _Cq, be AC side voltage under the dq0 coordinate system; U _dBe direct voltage.

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