1、 Abstract The design of controller is the important part for static synchronous compensator(D-STATCOM).However,due to the strong decouple and non-linear characteristic of D-STATCOM,the traditional controller cannot meet the demand of the power system.This paper introduces linear auto disturbance rej
2、ection controller(LADRC)for D-STATCOM based on its mathematics model and design first-order LADRC for it;and then classical control theory is used to analyze convergence of two-order linear extended state observer(LESO)in frequency domain;at last,the simulation model is made for it,verification show
3、s that ADRC is superior to conventional proportional-integral-derivative controller,it has good tracking performance and immunity characteristics,this paper verify the feasibility ofLADRC controller and its controller.Index Terms STATCOM,linear active disturbance rejection control,linear extended st
4、ate observer.I.INTRODUCTION n recent years,with the large-scale application of clean energy,such as intelligent micro grid,wind power and photovoltaic,the structure of power grid has become more and more complicated.At the same time,the new energy which connected to the distribution network also pos
5、es a great threat to its stability.In addition,there are nonlinear power electronic Manuscript received July 15,2018.D.X.Wang is with the Tianjin electric power transmission and transformation engineering company,Tianjin 300161,China(corresponding author phone:86-15022722662;e-mail:wdx_).Y.T.Lin is
6、with the Customer service center of state grid Tianjin electric power company Y.Sun is with the Tianjin electric power transmission and transformation engineering company,Tianjin 300161,China Y.R.Fei is with the Tianjin electric power transmission and transformation engineering company,Tianjin 30016
7、1,China Z.Y.Zhang is with the Tianjin electric power transmission and transformation engineering company,Tianjin 300161,China C.L.Zhu is with the Tianjin electric power transmission and transformation engineering company,Tianjin 300161,China Z.W.Kou is with the Tianjin electric power transmission an
8、d transformation engineering company,Tianjin 300161,China devices such as electric arc furnace in the power grid.This also poses a great challenge to the grid structure and the safe operation of the distribution network.As a dynamic reactive power compensation device,the static compensator(STATCOM)c
9、an improve the system power factor and reduce the line loss.It is a major component in the field of power quality regulation,and as a link to improve the reliability of power supply,it is also an important device in the Flexible Alternative Current Transmission Systems(FACTS).In the distribution net
10、work,whether STATCOM can compensate the reactive power accurately and quickly and the ability to adjust the system voltage level or not,depending on the reactive current detection needed in the distribution network in real time.The reactive current compensation is connected to tracking control of th
11、e compensation current.Therefore,the tracking control of compensation current is the key technology of STATCOM.So the control strategy of STATCOM DC side voltage control and AC side current has become a hot research topic.At present,the main method of current loop control is the traditional linear c
12、ontrol strategy.This traditional control strategy is mainly used in the system where the nonlinear mathematical model of STATCOM has been linearized.A traditional linear control strategy that is widely used is PI controller.In the reference 3,the PI controller is used to adjust the reactive power.In
13、 the reference 4,the PI controller is used in the dq synchronous coordinate system to decouple the system.However,for PI controllers,it is difficult to find a suitable parameter to meet the needs of the system;and due to the increasing external disturbances,the dynamic characteristics of the PI cont
14、roller will become worse and worse.Therefore,so many intelligent control methods are proposed based on the defects of PI controllers,such as particle swarm optimization,neural networks,and artificial immunity.The combination of adaptive control and linear robust control against external disturbances
15、 is described in reference 5.An improved linear sinusoidal tracking controller based on Design of the Controller and Stability Analysis of Distributed Static Synchronous Compensator Based on LADRC 1Wang dexiang，2Lin yitong，1Sun yi，1Fei yarao，1Zhang ziyi，1Zhu chunlei，1Kou zhiwen 1.Tianjin electric po
16、wer transmission and transformation engineering company，Tianjin 300161，China 2.Customer service center of state grid Tianjin electric power company，Tianjin 300000，China I 2018 China International Conference on Electricity Distribution Tianjin,17-19 Sep.2018CICED2018 Paper No.201804270000663 Page1/4
17、746adaptive theory is mentioned in reference 6.This control method will improve the stability of STATCOM,but these control methods are not applicable to the cascaded STATCOM.In this paper,the schematic diagram of typical STATCOM structure is proposed,and its mathematical model and state equation are
18、 established to facilitate the design of subsequent controllers.Secondly,a first-order ADRC controller is designed for STATCOM on the AC side,and the classical control theory is used in the frequency domain.The convergence and band characteristics of the second-order linear expansion state observer
19、are demonstrated.II.STATCOM STRUCTURE AND MATHEMATICAL MODEL In order to obtain the STATCOM mathematical model,appropriate assumptions and equivalents need to be made while analyzing the structure:(1)Assume that all losses of the system are uniformly planned as equivalent resistance R,including tran
20、sformers,inverters,and power electronics loss;(2)It is assumed that the transformer on the AC side and the smoothing reactor on the AC side of the static synchronous compensation device are equivalent to the inductance L;(3)The higher harmonics of the output of the STATCOM device are ignored,and onl
21、y the fundamental wave is considered.RbRc非 线 性 三相 不 平 衡负 载C BACLRaUsaUsbUscUcaUcbUccIaIbIc Fig.1 STATCOM structure diagram for connecting with grid u sa,u sb,u sc respectively represent the three-phase voltage of the system,u ca,u cb,and u cc respectively represent the output voltage of STATCOM,and
22、u dc is the capacitor voltage of the DC side of STATCOM,which acts as a DC side voltage support for the inverter.The angle between the output of the compensator AC terminal and the grid voltage is.According to the adjustment of the angle,the inverter that controls and compensates the compensation de
23、vice absorbs or sends reactive power to the grid.According to the structural diagram of the compensator and the Kirchhoff voltage law,the STATCOM dynamic equations in the abc stationary coordinate system can be obtained,expressed as(1):)32sin()()32sin()()sin()(1)()()32sin(2)32sin()()()32sin(2)32sin(
24、)()()sin(2)sin()(t t i t t i t t iC dtt dut Ri t u t udtt diLt Ri t u t udtt diLt Ri t u t udtt diLc b adcc s dccb s dcba s dca（1）Analysis shows that the mathematical model of the obtained STATCOM is a set of differential equations with time-varying coefficients,which makes the design of the control
25、ler more complicated.In this paper,the classical Park transform is used to transform the mathematical model of STATCOM from abc coordinate system to dq0 coordinate system,which is convenient for system characteristic analysis and system parameter setting.After transformation,the mathematical model u
26、nder dq0 coordinate system is expressed as(2):3cos213 3sin 02033cos sin 022ddsqqdc dcRKLLiiU d R Kiidt L L LuuKKCC（2）III.DESIGN OF CONTROLLER AND ANALYSIS OF D-STATCOM A.Linear Auto Disturbance Rejection Controller The linear auto disturbance rejection controller consists of a Tracking Differentiato
27、r(TD),Linear Extended State Observer(ESO),and Linear State Error Feedback(LSEF).The tracking differentiator can extract the differential signal reasonably by arranging the excessive process,so that the fast tracking of the input signal can be realized,and the overshoot caused by the excessive contro
28、l force can be overcome;the linear extended state observer is used to solve the unknown part of the model and the external unknown disturbance.Integrating the influence on the control object,it designs an extended state quantity to track these total disturbances,and then compensates the control quan
29、tity.The biggest advantage is that it does not require accurate system mathematical model;linear state error feedback mainly gives control strategy of the control object,which can utilize the difference between the output and output of the ESO to obtain the compensation control amount,thereby elimin
30、ating the total disturbance of the system.In most of the existing coupled control systems,accurate mathematical models are applied.The idea of LADRC is to use the linear extended state observer LESO to estimate the 2018 China International Conference on Electricity Distribution Tianjin,17-19 Sep.201
31、8CICED2018 Paper No.201804270000663 Page2/4 747disturbance of the system from the input and output of the system in real time,so LADRC control is used to exact mathematical model that is not needed,the expression of LESO is expressed by equation(3):1,1,()iii i i iiix Ax Bu L x xy C x（3）In the expres
32、sion,1,2,1,ii i i n iL l l l is the observer gain,the observer bandwidth0 can be introduced to tune the matrix L parameters.In some special cases,the gain of the observer is defined as:1 21,2,1,0,1,0,2,0,1,iiini i n i i i i i i n il l l（4）The state observer can observe the state of the system in rea
33、l time,and by using if to eliminate the total disturbance of the system,LADRC can compensateif dynamically in time,and its control law is as follows:11,1,()(,)iin niini i i ni i i iu k r x k r x i r（5）The equationir represents the desired trajectory of the thi channel,and the feedforward is introduc
34、ed in the above equation to further reduce the tracking error of the system.B.CONVERGENCE AND BAND ChARACTERISTICS ANALYSIS OF SECOND ORDER LESO In this paper,a second-order linear state observer is designed for the control principle of STATCOM.The expression of LESO is as shown in(6):1 2 1 1 02 2 1
35、()()z z z i b uz z i（6）In the above equation,1，2 are the observer gain,b is the input control gain,but b can be estimated,assuming the estimated value is b0.Convert the differential equations of the above formula into the form of the transfer function,and bring the transformed equations into equatio
36、n(6)to obtain equation(7):20 0 01 2200220 0 02 22002Z()()()()Z()()()()w w s b ss Y s U ss w s ww s b ws Y s U ss w s w（）=（）=（7）Where Z 1(s),Z 2(s),U(s),and Y(s)are the pull-forms of z 1(t),z 2(t),y(t),and u(t)respectively.Let the tracking error:E1(s)=Z1(s)-Y(s),get the expression(8)and(9):210 2200()
37、()+()()()ssE s Y s b U ss w s w（8）110220()lim()0()lim()0ssssE s sE sE s sE s（9）It can be seen from the above equation that the tracking error and steady-state error of the LSEO are both 0,which fully demonstrates that the LESO has good convergence and can estimate the state variables of the system a
38、nd the error-free estimation of the semantic disturbance.Fig.2 Frequency domain characteristic of noise Similarly,the transfer function of the disturbance at the input of the system can be derived according to equation(7),as shown in the following equation(10):0 120()cbs zs（10）Equation(10)is express
39、ed as the transfer function of the disturbancec which at the input of the system.If the variable is c,then the values c are taken separately,and the change-50-40-30-20-10010Magnitude(dB)100101102103104-90-450Phase(deg)Bode DiagramFrequency(rad/sec)w0=50w0=40w0=30w0=20w0=10w0=50w0=40w0=30w0=20w0=1020
40、18 China International Conference on Electricity Distribution Tianjin,17-19 Sep.2018CICED2018 Paper No.201804270000663 Page3/4 748of the frequency domain characteristic curve in the frequency domain is observed when different values c are taken.If the parameter b0 of the LESO is 20,the frequency dom
41、ain characteristic curve in the frequency domain range can be obtained,as shown in FIG.3:Fig.4 Frequency domain characteristic of input disturbance IV.CONCLUSION In this paper,the controller of the static synchronous compensation device is designed.As for control strategy,LADRC is selected to contro
42、l the reactive current of the system.The method can track the grid frequency in real time when the grid voltage fundamental frequency is unstable,the grid voltage is unbalanced or distorted,which fundamentally solves the shortcomings of the traditional control method and improves the dynamic charact
43、eristics of the system.In addition,the paper also uses the classical control theory.The frequency domain characteristics of LADRC were analyzed in the frequency domain.Based on the proposed LADRC controller,the comparison with PID shows that LADRC can improve the dynamic characteristics of STATCOM a
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