CN105576652A - Voltage control method and system for high-voltage direct-current power transmission end - Google Patents

Abstract

The invention discloses a voltage control method and system for a high-voltage direct-current power transmission end. The method comprises the steps of judging whether the transmission end is in an isolated island operation state or not; in an isolated island mode, performing active and reactive cooperative control based on adaptive voltage-reactive power sensitivity and voltage-active power sensitivity; in a networking mode, performing reactive voltage control according to a normal voltage regulation coefficient; according to a reactive power distribution method, calculating a reactive power setting value of each AVC (Automated Voltage Control) unit; and finally, performing local closed-loop control according to the reactive power setting value at an excitation regulator of each AVC unit. According to the voltage control method and system, the drastic fluctuation of a voltage of a high-voltage bus of a power plant in the isolated island mode due to AVC coefficient mismatching and active regulation is avoided according to different running conditions of a high-voltage direct-current power transmission end system. The voltage control method and system can be widely applied to the field of AVC of power systems.

Description

Voltage control method and system for high-voltage direct-current transmission end

Technical Field

The invention relates to the field of automatic voltage control of a power system, in particular to a voltage control method and a voltage control system for a high-voltage direct-current transmission end.

Background

The southwest and Guizhou of the west part of the southern power grid are large-scale sending end systems, and the west part of the power grid is transmitted to an east part of load center through a large-capacity extra/ultra-high voltage direct current line. The large-capacity direct current transmission system adopts a sending end island operation mode, so that the influence of power flow transfer after direct current tripping on an alternating current system can be reduced, and the large-capacity direct current transmission system has unique advantages in the aspects of improving the stability of a long-distance transmission system and improving the transmission capacity.

AVC (automatic voltage control of power plant) refers to a technique of automatically controlling a bus voltage of a power plant or a reactive power of a whole power plant according to predetermined conditions and requirements. Under the condition of ensuring the safe operation of the unit, the system is provided with fully-utilized reactive power, and the power loss of a power plant is reduced. The AVC substation system of the power plant receives the whole plant control targets (the voltage of a high-voltage bus of the power plant, the total reactive power of the whole plant and the like) issued by the AVC main station system, reasonably distributes the whole plant control targets to each unit according to the control method (the voltage curve, the voltage of a constant bus, the total reactive power of the whole plant and the like), achieves the whole plant target control value by adjusting the reactive power output of the generator, and realizes the voltage reactive power automatic control of a plurality of units of the whole plant, wherein the whole control process.

When the island operates the operating mode, the short circuit of system is smaller, and the same reactive variation will cause the voltage fluctuation bigger than the networking operating mode promptly, consequently reduces the voltage regulating coefficient of AVC system, makes the reactive adjustment amplitude that the same voltage deviation corresponds reduce, reaches the gain reduction, prevents the purpose of voltage by a wide margin oscillation. The lower voltage regulation coefficient can adapt to the requirement of steady-state voltage regulation, but in the island steady-state power lifting process, along with the reduction and the increase of the transmission power of an island system, the voltage of an island power plant and a converter station can also be greatly increased or reduced. Sensitivity analysis shows that the sensitivity of voltage of an island system to active power change is high, so that power plant power rise and fall can cause fluctuation of voltage with large amplitude.

Disclosure of Invention

In order to solve the technical problems, the invention aims to: a voltage control method for a high-voltage direct-current transmission terminal is characterized in that voltage-reactive sensitivity and voltage-active sensitivity are adaptively set through online network analysis, and the influence of active adjustment on voltage is considered, so that the large fluctuation of bus voltage of a power plant and a converter station is avoided.

In order to solve the above technical problems, another object of the present invention is to: a voltage control system of a high-voltage direct-current transmission terminal adaptively sets voltage-reactive sensitivity and voltage-active sensitivity through online network analysis, and considers the influence of active adjustment on voltage, so that the large fluctuation of bus voltage of a power plant and a converter station is avoided.

The traditional reactive regulation of AVC (automatic voltage control) cannot synchronously compensate voltage deviation caused by active power, and active regulation information needs to be introduced into AVC reactive regulation quantity and is improved into a voltage controller capable of compensating the active regulation.

The technical scheme adopted by the invention is as follows: a voltage control method for a high-voltage direct-current transmission terminal comprises the following steps:

A. detecting whether a sending end of the long-distance high-voltage direct-current transmission is in an island operation state or not through an island detection module;

B. if the sending end is in an island operation state, setting a power plant voltage regulation coefficient according to the voltage-reactive sensitivity of an island system, calculating a reactive compensation coefficient matched with active regulation according to the self-adaptive voltage-active sensitivity of the island system, further performing active and reactive cooperative control, and executing the step D;

C. if the sending end is in the networking state, the reactive voltage is controlled by using the normal voltage regulating coefficient in the networking state, and the step D is executed;

D. calculating a reactive power set value of each AVC unit according to a reactive power distribution method;

E. and each AVC unit excitation regulator carries out local closed-loop control according to the reactive power set value.

Further, the calculation formula for performing active and reactive cooperative control based on the adaptive voltage-reactive sensitivity and the voltage-active sensitivity in the step B is as follows:

$Q_{AVC}=Q_{ACT}+\mathrm{\Δ}V\·K_{V\_islanded}+\mathrm{\Δ}P\·K_P-Q_{\stackrel{\‾}{AVC}}$

wherein,

Q_AVCdistributing a value for the reactive AVC of the whole plant;

Q_ACTreactive power is generated for the current real time;

Δ V is the deviation of the actual bus voltage from the given voltage value;

K_{V_islanded}the voltage regulating coefficient of the power plant in an island mode;

ΔP·K_preactive compensation quantity for active regulation of island generator set, delta P is active regulation quantity of island generator set, K_PThe reactive compensation coefficient is matched with active power regulation;

the sum of reactive power generated by the AVC unit is not participated.

Further, K is_{V_islanded}And K_PThe values are determined from the voltage-active sensitivity matrix and the voltage-reactive sensitivity matrix of the power flow equation.

Further, the calculation formula for performing reactive voltage control according to the normal voltage regulation coefficient in the networking state in the step C is as follows:

$Q_{AVC}=Q_{ACT}+\mathrm{\Δ}V\·K_{V\_networked}-Q_{\stackrel{\‾}{AVC}}$

wherein,

Q_AVCdistributing a value for the reactive AVC of the whole plant;

Q_ACTreactive power is generated for the current real time;

Δ V is the deviation of the actual bus voltage from the given voltage value;

K_{V_networked}the normal voltage regulation coefficient;

the sum of reactive power generated by the AVC unit is not participated.

Further, the reactive power distribution method in step D distributes the reactive value of each AVC set according to an equal power factor principle, a reactive capacity proportional principle, a similarity adjustment margin principle, or a dynamic optimization principle.

Further, the reactive power distribution method in step D is to distribute reactive values of each AVC set according to a similar adjustment margin principle, and the distributed calculation formula is:

$Q_{iAVC}=Q_{AVC}\×\frac{Q_{iMax}-Q_i}{{\mathrm{\Σ}}_{i=1}^n(Q_{iMax}-Q_i)},(i=1,2,...,n)$

wherein,

n is the number of sets participating in AVC;

Q_iMax-Q_iadjusting the margin for the reactive power of the ith unit participating in AVC;

the sum of the current reactive power adjustment margins of the AVC units is obtained;

Q_iAVCand distributing reactive power output of the ith station participating in the AVC set for AVC.

The other technical scheme adopted by the invention is as follows: a voltage control system of a high-voltage direct-current transmission terminal comprises:

the island detection module is used for detecting whether a sending end of the long-distance high-voltage direct-current transmission is in an island operation state;

the island operation control module is used for setting a power plant voltage regulating coefficient on line according to the voltage-reactive sensitivity of an island system when a sending end is in an island operation state, calculating a reactive compensation coefficient matched with active regulation according to the self-adaptive voltage-active sensitivity of the island system, and performing active and reactive cooperative control;

the networking control module is used for performing reactive voltage control by using a normal voltage regulation coefficient in a networking state when the sending end is in the networking state;

the reactive power distribution module is used for calculating a reactive power set value of each AVC unit according to a reactive power distribution method;

and the AVC set in the system performs local closed-loop control by using an AVC set excitation regulator according to the reactive power set value.

The invention has the beneficial effects that: according to different operating conditions of the high-voltage direct-current transmission end system, reactive sensitivity is calculated according to island voltage under an island operating condition, and a smaller voltage regulation coefficient is adopted, so that voltage periodic oscillation of the island system is avoided; according to the active sensitivity of island voltage, the island voltage is matched with active adjustment information, and the voltage of a high-voltage bus of a power plant is prevented from being greatly reduced and increased along with the increase and decrease of system output power.

The invention has the following beneficial effects: the system of the invention is suitable for different operation working conditions of a high-voltage direct-current transmission end system, and adopts a normal voltage regulation coefficient to carry out reactive voltage control under the networking working condition; under an island working condition, AVC and active power adjustment information are matched to carry out active and reactive power cooperative control according to island voltage-reactive power sensitivity and island voltage-active power sensitivity, and the situation that the voltage of a high-voltage bus of a power plant is greatly reduced along with the increase and decrease of the output power of a system is avoided.

Drawings

FIG. 1 is a block diagram of the overall transfer function of a prior art voltage control;

FIG. 2 is a flow chart of the steps of the method of the present invention;

FIG. 3 is a schematic diagram of the system of the present invention;

FIG. 4 is a schematic diagram of an island system structure according to an embodiment of the present invention;

FIG. 5 is a block diagram of the overall transfer function of the voltage control of the present invention.

Detailed Description

The following further describes embodiments of the present invention with reference to the accompanying drawings:

referring to fig. 2, a voltage control method for a high voltage direct current transmission terminal includes the following steps:

A. detecting whether a sending end of the long-distance high-voltage direct-current transmission is in an island operation state or not through an island detection module;

B. if the sending end is in an island operation state, setting a power plant voltage regulating coefficient according to the self-adaptive voltage-reactive sensitivity of the island system, calculating a reactive compensation coefficient matched with active regulation according to the self-adaptive voltage-active sensitivity of the island system, performing active and reactive cooperative control, and executing the step D;

C. if the sending end is in the networking state, the reactive voltage is controlled by using the normal voltage regulating coefficient in the networking state, and the step D is executed;

D. calculating a reactive power set value of each AVC unit according to a reactive power distribution method;

E. and each AVC unit excitation regulator carries out local closed-loop control according to the reactive power set value.

Further as a preferred embodiment, in an island working condition constant value mode, AVC of the power plant calculates the reactive power output of the whole plant according to a given bus voltage value, and the aim is to maintain the bus voltage of the power plant at a given level; and B, performing active and reactive cooperative control based on the adaptive voltage-reactive sensitivity and the voltage-active sensitivity according to a calculation formula:

$Q_{AVC}=Q_{ACT}+\mathrm{\Δ}V\·K_{V\_islanded}+\mathrm{\Δ}P\·K_P-Q_{\stackrel{\‾}{AVC}}$

wherein,

Q_AVCdistributing a value for the reactive AVC of the whole plant;

Q_ACTreactive power is generated for the current real time;

Δ V is the deviation of the actual bus voltage from the given voltage value;

K_{V_islanded}the voltage regulating coefficient of the power plant in an island mode;

ΔP·K_preactive compensation quantity for active regulation of island generator set, delta P is active regulation quantity of island generator set, K_PThe reactive compensation coefficient is matched with active power regulation;

the sum of reactive power generated by the AVC unit is not participated.

Further preferably, K is_{V_islanded}And K_PThe values are determined from the voltage-reactive sensitivity matrix and the voltage-active sensitivity matrix of the power flow equation.

Reactive compensation coefficient K for matching active power regulation_PAnd performing online calculation to obtain a self-adaptive parameter value according to the system running state acquired by state estimation. Due to the fact thatCalculating K_PA voltage-active sensitivity matrix and a voltage-reactive sensitivity matrix are first obtained. The specific process is as follows.

The expanded power flow equation is listed,

$\left\{\begin{array}{c}{P}_i=V_i\underset{j=1}{\overset{n}{\Σ}}{V}_j(G_{ij}{\mathrm{cos\δ}}_{ij}+B_{ij}{\mathrm{sin\δ}}_{in})\\ Q_i=V_i\underset{j=1}{\overset{n}{\Σ}}{V}_j(G_{ij}{\mathrm{sin\δ}}_{ij}-B_{ij}{\mathrm{cos\δ}}_{in})\end{array}\right.$

partial derivatives of active and reactive power to the node voltage and phase angle are calculated to obtain a sensitivity matrix,

$\left[\begin{array}{c}\mathrm{\Δ}P\\ \mathrm{\Δ}Q\end{array}\right]=-\left[\begin{array}{cc}H& N\\ K& L\end{array}\right]\left[\begin{array}{c}\mathrm{\Δ}\mathrm{\δ}\\ V^{-1}\mathrm{\Δ}V\end{array}\right]=S\left[\begin{array}{c}\mathrm{\Δ}\mathrm{\δ}\\ V^{-1}\mathrm{\Δ}V\end{array}\right]$

to illustrate the PV nodes and balance nodes the following features,

${\mathrm{\θ}}_{slack}={\mathrm{\θ}}_{slack}^0$

$v_G=v_G^0$

the following operations are performed on S: zero-setting a column vector representing sensitivity with respect to a reference phase angle; zero-setting a column vector representing sensitivity with respect to the PV node and balance node voltages; setting a row vector representing the active sensitivity of the balance node to zero; zero setting of a row vector representing reactive sensitivity of the PV node and the balance node; the diagonal element at which the upper row vector and the column vector intersect is set to 1. In the power vector, elements corresponding to PV node reactive power, balance node active power and reactive power are set to zero.

Through the above operations, the S is inverted to obtain

$\left[\begin{array}{c}\mathrm{\Δ}\mathrm{\δ}\\ V^{-1}\mathrm{\Δ}V\end{array}\right]=\left[\begin{array}{cc}{S}_{\mathrm{\δ}P}& S_{\mathrm{\δ}Q}\\ S_{VP}& S_{VQ}\end{array}\right]\left[\begin{array}{c}\mathrm{\Δ}P\\ \mathrm{\Δ}Q\end{array}\right]$

Wherein, from S_VPAnd S_VQThe voltage-active sensitivity and voltage-reactive sensitivity information can be acquired separately.

Further as a preferred embodiment, the networking operating mode voltage-active sensitivity is negligible, the coordination with active regulation is not considered, and the voltage-reactive sensitivity does not change much with the power regulation, and the calculation formula of using the normal voltage regulation coefficient in the networking state to perform reactive voltage control in the step C is as follows:

$Q_{AVC}=Q_{ACT}+\mathrm{\Δ}V\·K_{V\_networked}-Q_{\stackrel{\‾}{AVC}}$

wherein,

Q_AVCdistributing a value for the reactive AVC of the whole plant;

Q_ACTreactive power is generated for the current real time;

Δ V is the deviation of the actual bus voltage from the given voltage value;

K_{V_networked}the normal voltage regulation coefficient;

the sum of reactive power generated by the AVC unit is not participated.

Further as a preferred embodiment, the reactive power allocation method in step D allocates the reactive value of each AVC unit according to an equal power factor principle, a reactive capacity proportional principle, a similarity adjustment margin principle, or a dynamic optimization principle.

Further as a preferred embodiment, taking a similarity adjustment margin principle as an example, the reactive power distribution method in step D distributes reactive values of the AVC sets according to the similarity adjustment margin principle, where the distributed calculation formula is:

$Q_{iAVC}=Q_{AVC}\×\frac{Q_{iMax}-Q_i}{{\mathrm{\Σ}}_{i=1}^n(Q_{iMax}-Q_i)},(i=1,2,...,n)$

wherein,

n is the number of sets participating in AVC;

Q_iMax-Q_iadjusting the margin for the reactive power of the ith unit participating in AVC;

the sum of the current reactive power adjustment margins of the AVC units is obtained;

Q_iAVCand distributing reactive power output of the ith station participating in the AVC set for AVC.

Taking the island system of fig. 4 as an example, a specific embodiment of the island system to which the method of the present invention is applied is illustrated as a chu ear direct current sending end system of southeast power grid of south China, a jin' an bridge and a small bay hydroelectric power plant at the sending end are respectively connected with a chu male converter station through double loops, and in addition, a peace station is connected in parallel between the small bay power plant and the chu male station through a single loop circuit during networking and is connected with a synchronous power grid. The Chu ear direct current island distinguishing system consists of a Chu male station, a bay power plant and an island distinguishing device of a peace station.

In a networking mode, according to the calculation result of the voltage-reactive sensitivity, the AVC voltage regulation coefficient of the Bay power plant is K_{V_networked}And 6MVar/kV, namely the voltage deviation is 1kV, reactive power is adjusted to 6MVar, and the active power sensitivity to the voltage sensitivity can be approximately ignored in a large power grid. The AVC of the networked working condition power plant calculates the reactive power according to the following formula:

$Q_{AVC}=Q_{ACT}+\mathrm{\Δ}V\·K_{V\_networked}-Q_{\stackrel{\‾}{AVC}}$

in an island mode, according to the result of the voltage-to-reactive sensitivity calculation, the actual voltage regulation coefficient K_{V_islanded}If the network is still regulated by using the constant voltage regulating coefficient of the networking working condition, the fluctuation caused by overshoot occurs, and the self-adaptive regulation is required to be carried out according to the network state.

Under the island mode, voltage is showing the increase to active sensitivity, and the continuous rising or the decline of power plant active causes obvious influence to power plant high voltage bus voltage amplitude, and AVC can compensate the influence of next control cycle active adjustment to voltage when the regulation of making reactive power volume, makes bus voltage more stable.

According to the sensitivity calculation result, under the 2500MW power level of an island system, the active power is increased by 1MW, the reactive power must be correspondingly increased by 0.25MVar for maintaining the constant voltage, and K is calculated on line_PWhen the value is 0.25, the calculation formula adopts:

$Q_{AVC}=Q_{ACT}+\mathrm{\Δ}V\·K_{V\_islanded}+\mathrm{\Δ}P\·K_P-Q_{\stackrel{\‾}{AVC}}$

the overall transfer function block diagram for AVC control in island mode is shown in fig. 5.

Referring to fig. 3, a voltage control system of a high voltage direct current transmission terminal includes:

the island detection module is used for detecting whether a sending end of the long-distance high-voltage direct-current transmission is in an island operation state;

the island operation control module is used for setting a power plant voltage regulating coefficient according to the self-adaptive voltage-reactive sensitivity of the island system when the sending end is in an island operation state, calculating a reactive compensation coefficient matched with active regulation according to the self-adaptive voltage-active sensitivity of the island system, and performing active and reactive cooperative control;

the networking control module is used for performing reactive voltage control by using a normal voltage regulation coefficient in a networking state when the sending end is in the networking state;

the reactive power distribution module is used for calculating a reactive power set value of each AVC unit according to a reactive power distribution method;

and the AVC set in the system performs local closed-loop control by using an AVC set excitation regulator according to the reactive power set value.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (7)

1. A voltage control method at the sending end of high-voltage direct current transmission, characterized in that: comprising the following steps: A. At the sending end of the long-distance HVDC transmission, the island detection module is used to detect whether the sending end is in an island operation state; B. If the sending end is in the island operation state, set the voltage regulation coefficient of the power plant according to the island system adaptive voltage-reactive power sensitivity, and calculate the reactive power compensation coefficient for active power adjustment according to the island system adaptive voltage-active power sensitivity, and then carry out Active and reactive power coordinated control, execute step D; C. If the sending end is in the networked state, use the normal voltage regulation coefficient in the networked state to control the reactive power voltage, and perform step D; D. Calculate the reactive power setting value of each AVC unit according to the reactive power distribution method; E. The excitation regulators of each AVC unit perform local closed-loop control according to the above reactive power setting value. 2. The voltage control method of a high-voltage direct current transmission sending end according to claim 1, characterized in that: in the step B, the calculation formula for active and reactive power cooperative control based on adaptive sensitivity is: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; C</span>}}}$ in, Q _AVC is the reactive AVC distribution value of the whole plant; Q _ACT is the current actual reactive power; ΔV is the deviation between the actual bus voltage and the given voltage value; K _{V_islanded} is the voltage regulation coefficient of the power plant under the island mode; ΔP K _p is the reactive power compensation amount of active power adjustment of the island generator set, ΔP is the active power adjustment amount of the island generator set, and K _P is the reactive power compensation coefficient for active power adjustment; It is the sum of reactive power generated by units not participating in AVC. 3. The voltage control method of a kind of HVDC transmission terminal according to claim 2, characterized in that: said K _{V_islanded} value is determined online according to the voltage-reactive power sensitivity of the power flow equation, and the K _P value is determined according to the voltage-reactive power sensitivity of the power flow equation. The active power sensitivity matrix is determined online. 4. The voltage control method of a high-voltage direct current transmission sending end according to claim 1, characterized in that: in the step C, the calculation formula for reactive voltage control using the normal voltage regulation coefficient under the networking state is: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; e</span>}\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; C</span>}}}$ in, Q _AVC is the reactive AVC distribution value of the whole plant; Q _ACT is the current actual reactive power; ΔV is the deviation between the actual bus voltage and the given voltage value; K _{V_networked} is the normal voltage regulation coefficient; It is the sum of reactive power generated by units not participating in AVC. 5. The voltage control method of a high-voltage direct current transmission sending end according to claim 1, characterized in that: the reactive power distribution method in the step D is based on the principle of equal power factors, the principle of proportionality of reactive power capacity, similar The adjustment margin principle or the dynamic optimization principle allocates the reactive power setting value of each AVC unit. 6. The voltage control method of a kind of HVDC sending end according to claim 5, characterized in that: the reactive power distribution method in the step D is to distribute the reactive power settings of each AVC unit according to the principle of similar adjustment margin. Fixed value, the distribution calculation formula is: ${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; V</span>}\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; \&times;</span>\frac{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>$ in, n is the number of crews participating in AVC; Q _iMax -Q _i is the reactive power adjustment margin of the i-th unit participating in AVC; is the sum of the current reactive power adjustment margins of participating AVC units; Q _iAVC is the reactive power output of AVC assigned to the i-th unit participating in the AVC unit. 7. A voltage control system at the sending end of high-voltage direct current transmission, characterized in that: it includes an island detection module for detecting whether the sending end of the long-distance high-voltage direct current transmission is in an island operation state; The island operation control module is used to set the voltage regulation coefficient of the power plant according to the island system adaptive voltage-reactive power sensitivity when the sending end is in the island operation state, and calculate the active power adjustment reactive power of the power plant according to the island system adaptive voltage-active power sensitivity power compensation coefficient, and then carry out active and reactive power coordinated control; The networking control module is used to control the reactive power voltage using the normal voltage regulation coefficient in the networking state when the sending end is in the networking state; The reactive power distribution module is used to calculate the reactive power setting value of each AVC unit according to the reactive power distribution method; The AVC unit in the system uses the excitation regulator of the AVC unit to perform local closed-loop control according to the above-mentioned reactive power setting value.