CN102904242B - Method for improving stability of doubly-indeed DC system - Google Patents

Abstract

The invention discloses a method for improving the stability of a doubly-indeed DC system in the technical field of monitoring and control of high-voltage DC transmission lines. The method comprises the following steps of: additionally arranging a static synchronous compensator subsystem in the doubly-indeed DC system, connecting the static synchronous compensator subsystem and a line-commutated-converter high-voltage DC subsystem of any one of two line-commutated-converter high-voltage DC subsystems to the same AC busbar in parallel and then connecting AC busbars of the two line-commutated-converter high-voltage DC subsystems by using impedance equivalent to a set electric distance. According to the method disclosed by the invention, the static synchronous compensator subsystem is accessed to the AC busbar of one DC subsystem inverter station of the doubly-indeed DC system with different points of fall, and the operation characteristics of the doubly-indeed DC system with different points of fall is effectively improved.

Description

A kind ofly improve the method that double-fed enters direct current system stability

Technical field

The invention belongs to high-voltage dc transmission electric wire Inspect and control technical field, particularly relate to and a kind ofly improve the method that double-fed enters direct current system stability.

Background technology

Line commutation high voltage direct current (Line-Commutated-Converter High Voltage DirectCurrent, LCC-HVDC) technology obtains a wide range of applications in long distance power transmission, Asynchronous Interconnection, seabed transmission of electricity etc.By the end of in August, 2012, China builds the LCC-HVDC engineering put into operation 20.LCC-HVDC converter adopts thyristor as commutation components, and LCC-HVDC runs needs AC system to provide converting commutating current, and the operational reliability of LCC-HVDC is affected by two ends AC network.Therefore, in order to reliable commutation, LCC-HVDC inverter side AC system must have enough intensity.

Along with implementing in full of " transferring electricity from the west to the east, north and south supplies mutually, on national network " strategy, many DC line are fed into areal through certain electrical distance and define multi-infeed HVDC (Multi-Indeed DirectCurrent, MIDC) system.According to alternating current-direct current Electric Power Network Planning, will the direct current system feed-in East China Power Grid of more than 8 times be had by 2015, more than 7 times direct current system feed-in south electric networks will be had.MIDC system will play significant role in alterating and direct current network operation.But the adjacent DC subsystem ac bus voltage fluctuation problem that a certain direct current subsystem AC fault causes, will become a great problem affecting multi-infeed HVDC system development.

STATCOM (Static Synchronous Compensator, STATCOM) has carries out the independent feature controlling fast and improve voltage stability to reactive power.STATCOM relies on its excellent dynamic characteristic, can significantly improve the dynamic property of transmission system, i.e. system Ability of Resisting Disturbance.According to different system requirements, STATCOM can realize the functions such as node voltage controls, power oscillation suppresses, raising systematic steady state/transient stability limit.

In view of above-mentioned background, the present invention proposes ac bus STATCOM being accessed different one of them direct current subsystem Inverter Station of drop point double feed-in d. c. power transmission system, STATCOM is utilized to carry out the independent advantage controlling fast and improve voltage stability to reactive power, the Steady state and transient state operation characteristic of local direct current subsystem can be improved, the Steady state and transient state operation characteristic of far-end direct current subsystem can be improved again through certain electrical distance, thus provide directive significance for the stable operation of alternating current-direct current electrical network and planning and development.

Summary of the invention

The object of the invention is to, propose a kind ofly to improve the method that double-fed enters direct current system stability, enter direct current system twice direct current subsystems influence each other for solving existing double-fed, local direct current subsystem AC fault can cause the problem of far-end another time direct current subsystem ac bus voltage fluctuation.

To achieve these goals, the technical scheme that the present invention proposes is, a kind ofly improve the method that double-fed enters direct current system stability, it is characterized in that, enter in direct current system to increase STATCOM subsystem in double-fed, any one line commutation high voltage direct current subsystem in STATCOM subsystem and two line commutation high voltage direct current subsystems is directly parallel on same ac bus, re-uses and with the impedance setting electrical distance equivalence, the ac bus of two line commutation high voltage direct current subsystems is connected.

Described STATCOM subsystem comprises change of current reactance connected in turn, Compensation subsystem converter transformer leakage reactance and voltage source converter.

Described line commutation high voltage direct current subsystem inverter side comprises equivalent susceptance and the inverter side converter of receiving end intercommunion subsystem, system impedance, high voltage direct current subsystem converter transformer leakage reactance, inverter side filter and the reactive power compensator be connected in turn.

STATCOM subsystem is accessed the ac bus that different drop point double-fed enters one of them direct current subsystem Inverter Station of direct current system in the present invention, the double-fed set up containing STATCOM subsystem enters direct current system model, and it effectively can improve the operation characteristic that different drop point double-fed enters direct current system.

Accompanying drawing explanation

Fig. 1 is that the different drop point double-feds containing STATCOM subsystem enter direct current system structural representation;

Fig. 2 (a) is not containing the first line commutation high voltage direct current subsystem maximum power MPC during STATCOM subsystem ₁curve chart;

Fig. 2 (b) is not containing the first line commutation high voltage direct current subsystem maximum transmitted active power MAP during STATCOM subsystem ₁curve chart;

First line commutation high voltage direct current subsystem maximum power MPC when Fig. 3 (a) is the change of STATCOM subsystem ₁curve chart;

First line commutation high voltage direct current subsystem maximum transmitted active power MAP when Fig. 3 (b) is the change of STATCOM subsystem ₁curve chart;

Fig. 4 is not containing the second line commutation high voltage direct current subsystem maximum transmitted active power MAP during STATCOM subsystem ₂curve chart;

Second line commutation high voltage direct current subsystem maximum transmitted active power MAP when Fig. 5 is the change of STATCOM subsystem ₂curve chart;

Fig. 6 (a) is not containing the temporary overvoltage curve chart of the first line commutation high voltage direct current subsystem load rejection during STATCOM subsystem;

The temporary overvoltage curve chart of the first line commutation high voltage direct current subsystem load rejection when Fig. 6 (b) is the change of STATCOM subsystem;

Fig. 7 (a) is not containing the temporary overvoltage curve chart of the second line commutation high voltage direct current subsystem load rejection during STATCOM subsystem;

The temporary overvoltage curve chart of the second line commutation high voltage direct current subsystem load rejection when Fig. 7 (b) is the change of STATCOM subsystem.

Embodiment

Below in conjunction with accompanying drawing, preferred embodiment is elaborated.It is emphasized that following explanation is only exemplary, instead of in order to limit the scope of the invention and apply.

Fig. 1 is that the different drop point double-feds containing STATCOM subsystem enter direct current system structural representation.In the present embodiment, two line commutation high voltage direct current subsystems double-fed being entered direct current system are denoted as the first line commutation high voltage direct current subsystem LCC-HVDC respectively ₁with the second line commutation high voltage direct current subsystem LCC-HVDC ₂.As shown in Figure 1, enter in direct current system to increase STATCOM subsystem STATCOM in double-fed, any one the line commutation high voltage direct current subsystem in STATCOM subsystem STATCOM and two line commutation high voltage direct current subsystem is directly parallel on same ac bus.Without loss of generality, in this enforcement, by STATCOM and the first line commutation high voltage direct current subsystem LCC-HVDC ₁directly be parallel on same ac bus.First line commutation high voltage direct current subsystem LCC-HVDC ₁with the second line commutation high voltage direct current subsystem LCC-HVDC ₂ac bus between there is certain electrical distance, therefore use LCC-HVDC with the impedance of this electrical distance equivalence in the present invention ₁and LCC-HVDC ₂ac bus be connected.

In Fig. 1, STATCOM comprises the change of current reactance X be connected in turn _s, converter transformer leakage reactance X _tSwith voltage source converter C _s.

LCC-HVDC ₁inverter side comprises the receiving end AC system E be connected in turn ₁, system impedance Z ₁, converter transformer leakage reactance X _t1, inverter side filter and reactive power compensator equivalent susceptance Bc ₁with inverter side converter C ₁.

LCC-HVDC ₂inverter side comprises the receiving end AC system E be connected in turn ₂, system impedance Z ₂, converter transformer leakage reactance X _t2, inverter side filter and reactive power compensator equivalent susceptance Bc ₂with inverter side converter C ₂.

In the present embodiment, LCC-HVDC is got ₁identical with international bulk power grid standard straight current test system (CIGRE) model parameter, capacity is 1000MW, its inverter side short circuit ratio SCR ₁=2.5; LCC-HVDC ₂according to LCC-HVDC ₁parameter is revised in proportion and is obtained, and capacity is 2000MW, its inverter side short circuit ratio SCR ₁=2.5; STATCOM subsystem is 300Mvar, and its AC voltage is 230kV, and DC voltage is ± 100kV.

Below according to Fig. 1, direct current system model is entered to the different drop point double-feds containing STATCOM, when STATCOM capacity, short circuit ratio (the Short Circuit Ratio of direct current subsystem inverter side, SCR) when the electrical distance and between direct current drop point is different, maximum power curve (Maximum Power Curve double-fed being entered to direct current system is emulated by MATLAB theory calculate and PSCAD/EMTDC, MPC), maximum transmitted active power (Maximum Available Power, MAP), temporary overvoltage (TransientOvervoltage, etc. TOV) operating index is assessed, and illustrate according to assessment result and increase STATCOM to enter direct current system improvement result to double-fed.

For independently single feed-in LCC-HVDC ₁mathematical Modeling can be described as

$I_{d1}=\frac{U_1[\cos {\mathrm{\γ}}_1-\cos ({\mathrm{\γ}}_1+{\mathrm{\μ}}_1)]}{\sqrt{2}{T}_1{X}_{T1}}---\left(1\right)$

$U_{d1}=\frac{3\sqrt{2}{U}_1}{\mathrm{\π}{T}_1}\cos {\mathrm{\γ}}_1-\frac{3}{\mathrm{\π}}{X}_{T1}{I}_{d1}---\left(2\right)$

P _d1＝U _d1I _d1(3)

Q _d1＝P _d1tanφ ₁(4)

$\cos {\mathrm{\φ}}_1=-\frac{\cos {\mathrm{\γ}}_1+\cos ({\mathrm{\γ}}_1+{\mathrm{\μ}}_1)}{2}---\left(5\right)$

$P_{\mathrm{ac}1}=[U_1^2\cos {\mathrm{\θ}}_1-E_1{U}_1\cos ({\mathrm{\δ}}_{U1}-{\mathrm{\δ}}_{E1}+{\mathrm{\θ}}_1)]/\left|Z_1\right|---\left(6\right)$

$Q_{\mathrm{ac}1}=[U_1^2\sin {\mathrm{\θ}}_1-E_1{U}_1\sin ({\mathrm{\δ}}_{U1}-{\mathrm{\δ}}_{E1}+{\mathrm{\θ}}_1)]/\left|Z_1\right|---\left(7\right)$

$Q_{c1}=B_{c1}{U}_1^2---\left(8\right)$

P _d1-P _ac1-P _c1＝0(9)

Q _d1-Q _ac1+Q _c1＝0(10)

In formula: U _d1, I _d1for LCC-HVDC ₁system dc voltage and current; P _d1, Q _d1for direct current is meritorious and reactive power; P _ac1, Q _ac1for AC is meritorious and reactive power; P _c1, Q _c1for active power consumption and the reactive compensation capacity of inverter side filter and reactive power compensator; X _t1for converter transformer leakage reactance; T ₁for converter transformer no-load voltage ratio; B _c1for the equivalent susceptance of inverter side filter and reactive power compensator; θ ₁for equivalent impedance angle; U ₁for ac bus voltage magnitude; δ _u1for ac bus voltage phase angle; E ₁for AC electromotive force amplitude; δ _e1for AC electromotive force phase angle; φ ₁for inverter side converter C ₁total power factor; Z ₁for system equivalent impedance; U ₁∠ δ _u1for ac bus voltage; E ₁∠ δ _e1for AC electromotive force; μ ₁it is the commutation overlap angle of converter; γ ₁for closing the angle of rupture.

Double-fed containing STATCOM enters the power delivery equation of direct current system, needs to consider STATCOM and LCC-HVDC ₁between reactive power transmission, also need simultaneously consider LCC-HVDC ₁with LCC-HVDC ₂between the meritorious and reactive power transmission of joint lines.Therefore, by LCC-HVDC ₁power equation is revised as

P _d1-P _ac1-P _c1-P ₁₂＝0(11)

Q _d1-Q _ac1+Q _c1-Q ₁₂+Q _S＝0(12)

In formula: P ₁₂and Q ₁₂be respectively LCC-HVDC in joint lines ₁to LCC-HVDC ₂meritorious and the reactive power of transmission; Q _sfor STATCOM is to LCC-HVDC ₁the reactive power of transmission.

If Q _sin STATCOM range of capacity, then STATCOM absorbs by reactive requirement or sends idle; If outside STATCOM range of capacity, then STATCOM regards as constant current source and treats.

LCC-HVDC ₂power equation is:

P _d2-P _ac2-P _c2+P ₁₂-ΔP ₁₂＝0(13)

Q _d2-Q _ac2+Q _c2+Q ₁₂-ΔQ ₁₂＝0(14)

In formula: Δ P ₁₂with Δ Q ₁₂for joint lines is meritorious and reactive power consumption.

LCC-HVDC ₁to LCC-HVDC ₂power delivery formula be

$P_{12}+j{Q}_{12}={\stackrel{\·}{U}}_1{\left(\frac{{\stackrel{\·}{U}}_1-{\stackrel{\·}{U}}_2}{Z_{12}}\right)}^{*}---\left(15\right)$

In formula: for LCC-HVDC ₁system inverter side ac bus voltage phasor value, for LCC-HVDC ₂system inverter side ac bus voltage phasor value, Z ₁₂it is the connection impedance of twice direct current subsystem inverter side.

Maximum power curve and maximum active power analysis.When maximum power curve M PC refers to the control not adopting special alternating voltage, the change curve that the direct current power of direct current system increases along with direct current.When direct current increase to certain some time, direct voltage decline speed be greater than direct current rise speed, direct current power will decline, and therefore there is maximum in MPC curve, is maximum transmitted active power MAP value.

According to the power delivery model entering direct current system containing STATCOM double-fed, the electrical distance L between research STATCOM capacity, twice direct current subsystem inverter side SCR and twice subsystem inverter side direct current drop point ₁₂time different, to LCC-HVDC ₁and LCC-HVDC ₂the impact of direct current subsystem MPC curve and MAP value.Wherein, SCR ₁and SCR ₂5.5 are changed to from 2.5; Electrical distance L ₁₂be taken as 39km and 117km, Z ₁₂line impedance compares X ₁₂/ R ₁₂=6, unitary impedance value is 0.41 Ω/km.

(1) STATCOM is to LCC-HVDC ₁maximum transmitted active power MAP ₁impact:

Change SCR ₁time, the capacity of filter and reactive power compensator remains unchanged.For ensureing the LCC-HVDC when rated condition ₁the active power of output of the system through-put power with CIGRE master pattern between identical and two direct current systems is zero, need recalculate LCC-HVDC ₁the electromotive force amplitude E of system inverter side AC system ₁with phase angle δ _e1, to ensure the phase angle δ of ac bus voltage _u1with LCC-HVDC ₂the phase angle δ of system ac bus voltage _u2identical.

First calculate different drop point double-fed and enter direct current system LCC-HVDC when not containing STATCOM ₁mPC ₁curve and MAP ₁value, power reference is 1000MW.LCC-HVDC ₂the parameter of system remains unchanged, SCR ₂=2.5, Q _s=0.LCC-HVDC ₁direct current I _d1increase gradually from zero.Simultaneous solution formula (1)-(15), can solve amplitude and the phase place U of twice direct current subsystem ac bus voltages ₁, U ₂, δ _u1, δ _u2and the exchange power P between twice direct current subsystem joint lines ₁₂, Q ₁₂.According to the variate-value of having tried to achieve, just LCC-HVDC can be calculated ₁direct current power, thus can obtain changing SCR without in STATCOM situation simultaneously ₁and L ₁₂time MPC ₁and MAP ₁, as shown in Figure 2.

Accompanying drawing 2 is known, electrical distance L ₁₂time constant, work as LCC-HVDC ₁the SCR of system ₁during increase, the stable operation zone of self increases, MAP ₁be worth also larger, MAP ₁corresponding DC current values I _d1also increase; SCR ₁time constant, electrical distance is less, LCC-HVDC ₁and LCC-HVDC ₂contact stronger, reach MAP ₁time, LCC-HVDC ₂to LCC-HVDC ₁reactive power support larger, self stable operation zone increase.MAP ₁corresponding DC current values I _d1also increase.Visible, SCR ₁larger, electrical distance is less, LCC-HVDC ₁operation stability higher.

STATCOM is accessed different drop point double-fed and enter direct current system, calculate LCC-HVDC when STATCOM capacity changes to 300Mvar from 0Mvar ₁the MPC of subsystem ₁curve and MAP ₁value, wherein SCR ₁=SCR ₂=2.5.

Can find out that STATCOM is linked into different drop point double-fed and enters direct current system LCC-HVDC from accompanying drawing 3 ₁after subsystem inverter side ac bus, STATCOM capacity is larger, and electrical distance is less, LCC-HVDC ₁operation stability higher.

Contrast accompanying drawing 2 (b) and accompanying drawing 3 (b) find, without MAP during STATCOM ₁mAP when value and STATCOM volume change ₁value has similar variation tendency.Visible, increase LCC-HVDC that can be equivalent after STATCOM access ₁the AC system intensity of subsystem inverter side.In accompanying drawing 3 (b), reach MAP ₁time, STATCOM and LCC-HVDC ₂be all LCC-HVDC ₁reactive power is provided.L ₁₂less, LCC-HVDC ₁and LCC-HVDC ₂contact stronger, LCC-HVDC ₂to LCC-HVDC ₁reactive power support larger, MAP ₁be worth larger.

(2) STATCOM is to LCC-HVDC ₂maximum transmitted active power MAP ₂impact:

LCC-HVDC ₂direct current I _d2increase gradually from zero, LCC-HVDC ₁the parameter of system remains unchanged, SCR ₁=2.5, now study STATCOM to LCC-HVDC ₂impact.In like manner, LCC-HVDC is calculated ₂subsystem is at STATCOM capacity, SCR ₂and L ₁₂mPC during change ₂curve, gets its maximum and can obtain MAP ₂value, power reference is 2000MW, as shown in figures 4 and 5.It should be noted that SCR ₂after change, LCC-HVDC need be recalculated ₂the electromotive force amplitude E of inverter side AC system ₂with phase angle δ _e2.

From accompanying drawing 4, SCR ₂larger, L ₁₂less, MAP ₂be worth also larger, LCC-HVDC ₂operation stability stronger.In accompanying drawing 5, STATCOM is equivalent to through L ₁₂with LCC-HVDC ₂subsystem is connected.The ordinate of contrast accompanying drawing 4 and accompanying drawing 5 can find, increase LCC-HVDC that also can be equivalent after STATCOM access ₂inverter side AC system intensity.Just this equivalent increase degree is less than LCC-HVDC ₁the increase degree of AC system intensity.Visible, after certain electrical distance, STATCOM is to the improvement reduced capability of direct current system.L ₁₂larger, this to weaken degree more obvious.

In addition, L ₁₂during=117km, after STATCOM capacity reaches 200Mvar, MAP ₂to no longer increase after STATCOM capacity increases to 200Mvar.The main cause of this phenomenon is caused to be LCC-HVDC ₁with LCC-HVDC ₂the contact of system is more weak, LCC-HVDC ₂subsystem direct current power causes LCC-HVDC when reaching maximum ₁the no-power vacancy of ac bus is about 200Mvar.Continue the capacity increasing STATCOM again, LCC-HVDC ₂subsystem direct current power maximum no longer changes.

MAP ₁and MAP ₂increase provide the ability of reactive power to determine by STATCOM.From the angle analysis providing reactive power, the AC system intensity of increase twice direct current subsystems of the access energy equivalence of STATCOM.

STATCOM enters the impact of direct current system temporary overvoltage to different drop point double-fed:

LCC-HVDC system is in the situations such as emergency outage, inverter side load rejection, converter trigger impulse loss, the reactive power of converter consumption reduces rapidly, the reactive power of current conversion station surplus will inject joined AC system, cause current conversion station ac bus voltage to raise, cause temporary overvoltage (TOV).TOV is the important indicator weighing direct current system performance.Time below by analysis twice direct current subsystem inverter side difference load rejections, STATCOM is to LCC-HVDC ₁and LCC-HVDC ₂the impact of temporary overvoltage.

(1) LCC-HVDC ₁tOV value during system load rejection:

Consider LCC-HVDC ₁system inverter side gets rid of whole load, and namely direct current system and inverter side AC system do not have flow of power, P _d1and Q _d1equal zero.Formula (11) and (12) change into

-P _ac1-P _c1-P ₁₂＝0(16)

-Q _ac1+Q _c1-Q ₁₂+Q _S＝0(17)

System is not containing STATCOM, Q _s=0.Work as LCC-HVDC ₁inverter side SCR ₁during increase, LCC-HVDC ₁and LCC-HVDC ₂the TOV calculated value of inverter side ac bus and PSCAD/EMTDC simulation result are as shown in accompanying drawing 6 (a).TOV calculated value when system contains different capabilities STATCOM and simulation value are as shown in accompanying drawing 6 (b).

LCC-HVDC ₁subsystem load rejection, its inverter side can produce temporary overvoltage TOV ₁, simultaneously superfluous reactive power flows to LCC-HVDC through joint lines ₂subsystem inverter side ac bus, causes temporary overvoltage TOV ₂.In accompanying drawing 6, solid line and dotted line are the calculated curves of MATLAB, and circle represents the simulation value of PSCAD/EMTDC.Calculated curve and simulation value basically identical, demonstrate the correctness of theory calculate and simulation result.Along with SCR ₁increase (accompanying drawing 6 (a)) and the increase (accompanying drawing 6 (b)) of STATCOM capacity, TOV ₁and TOV ₂all on a declining curve.And L ₁₂nearer, LCC-HVDC ₁and LCC-HVDC ₂between contact stronger, LCC-HVDC ₁the more reactive powers produced after load rejection inject another system by joint lines, thus the TOV caused ₁less, TOV ₂larger.

(2) LCC-HVDC ₂tOV value during system load rejection:

Research LCC-HVDC ₂during the temporary overvoltage that the load rejection of subsystem inverter side causes, P _d2and Q _d2equal zero.Formula (13) and (14) change into

-P _ac2-P _c2+P ₁₂＝0(18)

-Q _ac2+Q _c2+Q ₁₂＝0(19)

Same as above, SCR ₂during increase, system can be obtained not containing the LCC-HVDC under electrical distance different during STATCOM ₁and LCC-HVDC ₂the temporary overvoltage theoretical curves of inverter side ac bus and PSCAD/EMTDC simulation value, as shown in accompanying drawing 7 (a).Temporary overvoltage calculated curve during change STATCOM capacity under different electrical distance and simulation value are as shown in accompanying drawing 7 (b).

From accompanying drawing 7, along with SCR ₂increase and the increase of STATCOM capacity, TOV ₁and TOV ₂also all have a declining tendency.STATCOM is equivalent to absorb LCC-HVDC through certain electrical distance ₂inverter side surplus idle, carrys out ME for maintenance and stablizes.In addition, due to LCC-HVDC ₂reactive compensation capacity be LCC-HVDC ₁2 times, LCC-HVDC ₂overvoltage that load rejection causes obviously wants high.

TOV ₁and TOV ₂reduction to be determined by the ability of STATCOM absorbing reactive power.Known according to above research, from the angle analysis of absorbing reactive power, the intensity of the increase AC system that STATCOM also can be equivalent.

Above-mentioned calculating and simulation result show, utilize STATCOM the to improve method that different drop point double-fed enters direct current system operation characteristic invented, the exchanging degree of the local direct current subsystem of increase that can be equivalent, improves the Steady state and transient state operation characteristic of local direct current subsystem; The AC system intensity of increase far-end direct current subsystem that again can be equivalent, improves the Steady state and transient state operation characteristic of far-end direct current subsystem.Visible, the method has great significance to the operation characteristic that the different drop point double-fed of improvement enters direct current system.

The above; be only the present invention's preferably embodiment, but protection scope of the present invention is not limited thereto, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; the change that can expect easily or replacement, all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.

Claims (1)

1. one kind is improved the method that double-fed enters direct current system stability, it is characterized in that, enter in direct current system to increase STATCOM subsystem in double-fed, any one line commutation high voltage direct current subsystem in STATCOM subsystem and two line commutation high voltage direct current subsystems is directly parallel on same ac bus, re-uses and with the impedance setting electrical distance equivalence, the ac bus of two line commutation high voltage direct current subsystems is connected;

Described STATCOM subsystem comprises change of current reactance connected in turn, Compensation subsystem converter transformer leakage reactance and voltage source converter;

Described line commutation high voltage direct current subsystem inverter side comprises equivalent susceptance and the inverter side converter of receiving end intercommunion subsystem, system impedance, high voltage direct current subsystem converter transformer leakage reactance, inverter side filter and the reactive power compensator be connected in turn;

Calculate different drop point double-fed and enter direct current system LCC-HVDC when not containing STATCOM ₁mPC ₁curve and MAP ₁value; Again STATCOM is accessed different drop point double-fed and enter direct current system, calculate LCC-HVDC when STATCOM capacity changes to 300Mvar from 0Mvar ₁the MPC of subsystem ₁curve and MAP ₁value; Then analyze and obtain STATCOM to LCC-HVDC ₁maximum transmitted active power MAP ₁impact;

Calculate LCC-HVDC ₂subsystem is at STATCOM capacity, SCR ₂and L ₁₂mPC during change ₂curve, gets its maximum and can obtain MAP ₂; STATCOM is to LCC-HVDC ₂maximum transmitted active power MAP ₂impact;

Calculate LCC-HVDC respectively ₁tOV value during system load rejection and LCC-HVDC ₂tOV value during system load rejection; When analyzing twice direct current subsystem inverter side difference load rejections, STATCOM is to LCC-HVDC ₁and LCC-HVDC ₂the impact of temporary overvoltage.