CN105914741A - UPFC line side reactive power flow optimization control method - Google Patents

Abstract

The invention relates to a UPFC line side reactive power flow optimization control method. The core idea is that reactive power consumed by lines is provided by a UPFC, and the sending end and receiving end power grids do not provide reactive power. The method comprises the following steps: calculating the reactive power loss of a line according to the current effective value of the line and the power grid impedance, and taking the reactive power loss as a line reactive power flow instruction of a series side converter of a UPFC; and performing subtraction between the reactive power of a sending end power grid and zero, and carrying out closed-loop control to get a reactive power instruction of a parallel side converter. Through the method, the capability of the UPFC to control the active power flow of lines is enhanced under constant capacity of the UPFC. Moreover, as the UPFC provides reactive power for lines, the influence of the reactive power loss of lines to the power grid voltage is reduced, and the stability of the sending end and receiving end power grids is improved.

Description

A kind of UPFC line side reactive power flow optimal control method

Technical field

The present invention relates to a kind of UPFC line side reactive power flow optimal control method, belong to Power System Flexible transmission of electricity neck Territory.

Background technology

THE UPFC (unified power flow controller, UPFC) is based on voltage source converter Series and parallel mixed type FACTS device, can quickly, flexibly, the trend of continuous print adjusting circuit, improve Section Tidal Current of Power Transmission and divide The phenomenon that cloth is uneven, improves the utilization ratio of transmission line of electricity, also can be to electrical network injection reactive power, systems stabilisation node voltage, Improve power supply reliability.

Line Flow control system is as it is shown in figure 1, by shunt transformer, parallel inverter, series transformer, the series connection change of current Device and by-pass switch etc. form.Parallel inverter is for stablizing the DC bus-bar voltage of transverter, and injects to electrical network or absorb Reactive power；Series connection transverter, by adjusting its output voltage vector amplitude and phase place, changes the meritorious of circuit and reactive power flow.

For the problem that the instruction of UPFC series side Line Flow is given, traditional Line Flow control method is, meritorious tide Stream instruction is issued by dispatcher according to the load of system, the ruuning situation etc. of circuit；Reactive power flow instruction is given as zero.Use When this reactive power flow controls, the regulating power of circuit effective power flow is reduced by UPFC, and the reactive loss of circuit is by receiving end electricity Source provides, the idle absorption by sending end power supply of UPFC series side output, and the stability of sending end and receiving end line voltage reduces, in addition The active power that UPFC series side and top-cross in parallel are changed is big.

Summary of the invention

It is an object of the invention to provide a kind of UPFC line side reactive power flow optimal control method, in order to strengthen UPFC to line The control ability of road effective power flow, the impact on line voltage of the reactive power of reduction circuit reactive loss and UPFC output, carry High sending end and the stability of receiving end line voltage, and reduce the active power that UPFC series side changes with top-cross in parallel.

A kind of UPFC line side reactive power flow optimal control method, including

The control of UPFC series side converter: the line reactive power of UPFC series side transverter instructs according to line current Virtual value and electric network impedance are calculated；

UPFC parallel connection side converter Control: reactive power idle according to sending end electrical network of instruction of UPFC parallel connection side transverter Power closed-loop control obtains.

Further, the line reactive power instruction computational methods of described UPFC series side are Q_{ref_se}=3I_lrms ²X_R, formula In: X_RFor line impedance, I_lrmsFor line current virtual value.

Further, the reactive power instruction of described side in parallel transverter is done with zero according to the reactive power of sending end electrical network Difference, utilizes pi regulator closed-loop control to obtain.

Present contribution to the art essentially consists in the control mode of series side.Control when using line reactive power When being zero, there is UPFC and decline the regulating power of circuit effective power flow, sending end and receiving end Network Voltage Stability reduce, UPFC The problem that active power that series side and top-cross in parallel are changed is big, the Line Flow control method that therefore present invention provides has following Advantage: improve the UPFC control ability to circuit effective power flow, enhances sending end and receiving end voltage stability, UPFC series side Little with the active power that top-cross in parallel is changed, and realize simple.

Accompanying drawing explanation

Fig. 1 is Line Flow control system schematic diagram；

Fig. 2 is that Line Flow controls equivalent circuit；

Fig. 3 is that Line Flow controls polar plot；

Fig. 4 is line reactive power optimal control block diagram；

Fig. 5 is the present invention carried line side reactive power flow optimisation strategy and the comparison diagram of conventional measures.

Detailed description of the invention

The UPFC line side reactive power flow optimal control method that the present invention provides comprises the following steps:

(1) the line reactive power instruction of UPFC series side, it is calculated according to line current virtual value and electric network impedance；

(2), the reactive power closed-loop control of sending end electrical network is obtained the reactive power instruction of UPFC parallel connection side transverter.

As shown in Figure 4, concrete, the line reactive power instruction computational methods of described UPFC series side are Q_{ref_se}= 3I_lrms ²X_R, in formula: X_RFor line impedance, I_lrmsFor line current virtual value.The reactive power instruction of described side in parallel transverter Reactive power according to sending end electrical network and zero does difference, utilizes pi regulator closed-loop control to obtain.

Q_{ref_se}=3I_lrms ²X_RIt is fundamental formular, as other embodiments, it is also possible to it is carried out deformation and obtains other Formula.

Below this control method is specifically described:

Adding after UPFC, the equivalent circuit of transmission line of electricity is as in figure 2 it is shown, with sending end electrical network phase voltage v₁On the basis of, system Polar plot as it is shown on figure 3, sending end voltage v₁, circuit v₂Put and by terminal voltage v_RDq axle component be respectively

$\left\{\begin{array}{c}{v}_{1d}=V_1\\ v_{1q}=0\end{array}\right.---\left(1\right)$

$\left\{\begin{array}{c}{v}_{2d}=V_1+V_{12}{\mathrm{cos\θ}}_{12}\\ v_{2q}=V_{12}{\mathrm{sin\θ}}_{12}\end{array}\right.---\left(2\right)$

$\left\{\begin{array}{c}{v}_{Rd}=V_{R}cos\mathrm{\δ}\\ v_{Rq}=-V_{R}sin\mathrm{\δ}\end{array}\right.---\left(3\right)$

In formula: V₁For sending end electrical network phase voltage virtual value, V_RFor receiving end electrical network phase voltage virtual value, V₁₂For UPFC series side The virtual value of incoming line voltage distribution, θ₁₂For UPFC series side output voltage phase place, δ is sending end line voltage and receiving end line voltage Phase difference.

The dq axle component of line current is

$\left\{\begin{array}{c}{i}_d=\frac{V_{R}sin\mathrm{\δ}}{X_R}+\frac{V_{12}{\mathrm{sin\θ}}_{12}}{X_R}\\ i_q=-\frac{V_1-V_R\cos \mathrm{\δ}}{X_R}-\frac{V_{12}{\mathrm{cos\θ}}_{12}}{X_R}\end{array}\right.---\left(4\right)$

Sending end power network current i₁Dq axle component be

$\left\{\begin{array}{c}{i}_{1d}=i_{shd}+i_d\\ i_{1q}=i_{shq}+i_q\end{array}\right.---\left(5\right)$

Wherein X_RFor line impedance, i_shdFor the d shaft current of UPFC parallel connection side, i_shqQ shaft current for UPFC parallel connection side.

The power of UPFC series side is

$\left\{\begin{array}{c}{P}_{12}-\frac{3V_{12}}{X_R}\left(V_{R}sin\right({\mathrm{\θ}}_{12}+\mathrm{\δ})-V_1{\mathrm{sin\θ}}_{12})\\ Q_{12}=\frac{3V_{12}}{X_R}(V_1{\mathrm{cos\θ}}_{12}-V_R\cos ({\mathrm{\θ}}_{12}+\mathrm{\δ}))+\frac{3{V_{12}}^2}{X_R}\end{array}\right.---\left(6\right)$

The active power of line transmission is

$P_{line}=\frac{3V_R}{X_R}(V_{1}sin\mathrm{\δ}+V_{12}sin({\mathrm{\θ}}_{12}+\mathrm{\δ}\left)\right)---\left(7\right)$

The reactive power of sending end electrical network is

$Q_1=\frac{3V_1(V_1-V_{R}cos\mathrm{\δ})}{X_R}+\frac{3V_1{V}_{12}{\mathrm{cos\θ}}_{12}}{X_R}-Q_{sh}---\left(8\right)$

The reactive power of receiving end electrical network is

$Q_R=\frac{3V_R}{X_R}(V_R-V_{1}cos\mathrm{\δ}-V_{12}cos({\mathrm{\θ}}_{12}+\mathrm{\δ}\left)\right)---\left(9\right)$

Circuit v₂The reactive power of point is

$Q_2=\frac{3V_1(V_1-V_{R}cos\mathrm{\δ})}{X_R}+\frac{3V_{12}}{X_R}(2V_1{\mathrm{cos\θ}}_{12}-V_{R}cos({\mathrm{\θ}}_{12}+\mathrm{\δ}\left)\right)+\frac{3{V_{\mathrm{12}}}^2}{X_R}---\left(10\right)$

It is idle by power supply v that line reactance consumes₁、v₁₂And v_RCommon offer, such as following formula

Q_L=-(Q_R+Q₁+Q₁₂) (11)

Traditional UPFC control method is by circuit v₂The Reactive Power Control of point is zero

Q₂=0 (12)

Can be in the hope of, when reducing line transmission active power, the angle of UPFC series side output voltage is

${\mathrm{\θ}}_{12}=arcsin\left(\frac{V_1(V_{R}cos\mathrm{\δ}-V_1)-{V_{12}}^2}{V_{12}\sqrt{{(2V_1-V_{R}cos\mathrm{\δ})}^2+{\left(V_{R}sin\mathrm{\δ}\right)}^2}}\right)-arctan\left(\frac{2V_1-V_{R}cos\mathrm{\δ}}{V_{R}sin\mathrm{\δ}}\right)---\left(13\right)$

When promoting circuit transmitting active power, the angle of UPFC series side output voltage is

${\mathrm{\θ}}_{12}=\mathrm{\π}-arcsin\left(\frac{V_1(V_{R}cos\mathrm{\δ}-V_1)-{V_{12}}^2}{V_{12}\sqrt{{(2V_1-V_{R}cos\mathrm{\δ})}^2+{\left(V_{R}sin\mathrm{\δ}\right)}^2}}\right)-arctan\left(\frac{2V_1-V_{R}cos\mathrm{\δ}}{V_R\sin \mathrm{\δ}}\right)---\left(14\right)$

UPFC control program in this paper is by circuit v₂The reactive loss that Reactive Power Control is circuit of point, i.e.

Q₂=Q_L (15)

Can be in the hope of, when reducing line transmission power, the angle of UPFC series side output voltage is

${\mathrm{\θ}}_{12}=-arccos\left(\frac{V_R-V_{1}cos\mathrm{\δ}}{V_{12}}\right)-\mathrm{\δ}---\left(16\right)$

When promoting circuit transmitting active power, the angle of UPFC series side output voltage is

${\mathrm{\θ}}_{12}=arccos\left(\frac{V_R-V_{1}cos\mathrm{\δ}}{V_{12}}\right)-\mathrm{\δ}---\left(17\right)$

The capacity of UPFC is

S=3V₁₂I_lrate (18)

Wherein I_lrateFor circuit rated current.

Deriving according to above, when using two kinds of different control strategies, UPFC is to the change ability of circuit effective power flow, right The active power that sending end and the impact of receiving end power supply and UPFC series side and top-cross in parallel are changed is as shown in Figure 5.

During conducting transmission line power flowcontrol, the present invention carried line reactive power optimisation strategy is compared with the advantage of conventional measures For, when changing identical Line Flow, required UPFC capacity is less, and the reactive loss of circuit is provided by UPFC, sending end and Receiving end power supply is without output or absorbing reactive power, and Network Voltage Stability is more preferable, and UPFC series side and top-cross in parallel are changed Active power is less.

The control program of UPFC mainly includes two parts, i.e. series side and side in parallel is respectively adopted different reactive power flows Instruction: for series side, be calculated the reactive loss of circuit according to line current virtual value and electric network impedance, as The line reactive power instruction of UPFC series side transverter.For side in parallel, the reactive power and zero of sending end electrical network is done difference, right It carries out closed-loop control, obtains the reactive power flow instruction of side in parallel transverter.The main contributions of prior art is by the present invention The control of series side, controls for side in parallel, it would however also be possible to employ other control strategies of the prior art.

Claims (2)

1. a UPFC line side reactive power flow optimal control method, it is characterised in that: include

The control of UPFC series side converter: the line reactive power instruction of UPFC series side transverter is effective according to line current Value and electric network impedance are calculated；The line reactive power instruction computational methods of described UPFC series side are Q_{ref_se}= 3I_lrms ²X_R, in formula: X_RFor line impedance, I_lrmsFor line current virtual value；

UPFC parallel connection side converter Control: the reactive power instruction of UPFC parallel connection side transverter is according to the reactive power of sending end electrical network Closed-loop control obtains.

UPFC line side the most according to claim 1 reactive power flow optimal control method, it is characterised in that described side in parallel The reactive power instruction of transverter does difference according to the reactive power and zero of sending end electrical network, utilizes pi regulator closed-loop control to obtain.