This paper proposed a command-filtered backstepping controller to improve the dynamic performance of back-to-back voltage-source-converter high voltage direct current (BTB VSC-HVDC). First, the principle and model of BTB VSC-HVDC in abc and d-q frame are described. Then, backstepping method is applied to design a controller to maintain the voltage balance and realize coordinated control of active and reactive power. Meanwhile, command filter is introduced to deal with the problem of input saturation and explosion of complexity in conventional backstepping, and a filter compensation signal is designed to diminish the adverse effects caused by the command filter. Next, the stability and convergence of the whole system are proved via the Lyapunov theorem of asymptotic stability. Finally, simulation results are given to demonstrate that proposed controller has a better dynamic performance and stronger robustness compared to the traditional PID algorithm, which also proves the effectiveness and possibility of the designed controller.
National Natural Science Foundation of China6150315651405198Fundamental Research Funds for the Central UniversitiesJUSRP11562JUSRP51406ANJ20150011National Key Research and Development Program2016YFD0400300Science and Technology Funds for Jiangsu ChinaBY2015019-24Science and Technology project of Jiangsu Electric Power Company1. Introduction
With the rapid development of economy, the demand for energy is rising [1]. There is a great technological development in the power generation, transmission, distribution, and other aspects [2]. However, with the development of power energy, there are a lot of new technical problems in terms of transmission, such as economic grid-connected technology of decentralized and small renewable energy power generation, power supply technology of isolated island and other passive load, expansion of urban electric load capacity and reconstruction technology of urban power grid, remote power supply, and grid connection of nonsynchronous power grid and microgrid. The traditional AC and DC transmission technology is still unable to effectively solve the above problems in the technical and economic benefits [2]. With the development of power electronics and control technology, the above problems can be solved by using voltage-source-converter high voltage direct current (VSC-HVDC) composed of IGBT, IGCT, and other new full controlled power electronic devices, which can realize the independent control of active power and reactive power [3]. VSC-HVDC has the following two main advantages, one is that VSC-HVDC transmission technology supplies power to the passive load without the commutation voltage of the AC system, the other one is that VSC-HVDC does not need AC power grid to provide reactive power to stabilize DC voltage, which can work as static synchronous compensator (STATCOM) [2–4]. Moreover, the other advantages are the following: large transmission capacity, small harmonic of output voltage, low cost and little loss, and the current of the AC-side being controlled so that the short-circuit capacity of the system can not be added [2–5]. Therefore, VSC-HVDC play a very significant role in the gird-connection of large-scale wind farm and the development of new technologies such as urban power supply and isolated island power supply, which meet the energy demand of continued rapid growth and efficient use of energy.
Nowadays, the back-to-back VSC-HVDC (BTB VSC-HVDC) is playing a significant part from the start of HVDC, which gets extensive attention in the field of interconnection of synchronous and asynchronous AC system, wind power networking, and so forth [6]. Power flow control range of BTB VSC-HVDC is greater than unified power flow controller (UPFC); meanwhile UPFC is a series structure, so it will withstand large short-circuit current for series part when the feeder is fault, while the BTB VSC-HVDC is parallel structure, which has the higher security. So BTB VSC-HVDC technology has become a hot research topic in the field of transmission [7–10].
Recently, there are many relevant researches about BTB VSC-HVDC [7–12]. In [7], a DC side capacitor voltage balance control based on space vector modulation (SVM) is proposed, which is used for five-level BTB VSC-HVDC to control and maintain the voltage balance of the DC side capacitors. In [8], a phase-disposition sine-wave pulse-width modulation (SPWM) strategy including voltage balancing strategy is applied for modular multilevel BTB VSC-HVDC, which focuses on the dynamic performance of system under both balanced and unbalanced operation condition. Reference [9] proposed a model predictive control for BTB VSC-HVDC to eliminate the circulating currents of converter arm, control real and reactive power, and maintain the voltage balance of DC-link. These methods improve the control performance and have good stability and fast dynamic response. However, their control scheme has added complexity and cost to the system, which contributes to the fact that the design scheme of the controller and the determination of the parameters are more difficult.
In recent years, the backstepping method, as a design tool for nonlinear control [13], has received great attention from scholars, which has become an effective method for nonlinear control design. The method is designed on the basis of nonlinear system, which can retain some useful nonlinear terms. The basic idea of backstepping is to decompose the complex nonlinear system into several subsystems; then Lyapunov function and virtual control are designed in each subsystem. Finally, they go “back to” the entire system until the completion of the entire control law [13, 14]. The whole design process and the adjustment of parameter in backstepping controller are convenient, which is easy to be accepted by the engineering staff. Backstepping is widely used in the control system design of VSC-HVDC, which has obtained some achievements [15–22]. But this kind of controller has the following two main disadvantages: (1) the derivative of each virtual controller needs to be analyzed and calculated, and the calculation process is very complicated, so it is difficult to be applied in practical engineering; (2) physical limitations in practical systems are not considered in the design process of controller, which may cause the problem of control saturation [14]. Currently, there are many ways to solve the above problems, such as dynamic surface control [23, 24] and command filter [25, 26]. Among them, command filter is a more effective method compared to the dynamic surface control, because the constraint of amplitude, rate, and bandwidth are introduced in the filter process of command filter, which is more convenient to modulate and limit the virtual control signal and the actual control signal to meet the actual control requirements. By adding constraints on input control signals, the control effect and stability of the controller can be effectively guaranteed, which increases the feasibility of the controller in engineering application. Moreover, filter compensation is introduced in the control, which can realize the asymptotic tracking of reference signal rather than bounded tracking in dynamic surface control.
The rest of paper is organized as follows. In Section 2, the model of BTB VSC-HVDC in abc and d-q frame are described. In Section 3, command-filtered backstepping control is designed for BTB VSC-HVDC and the stability of system is proved by Lyapunov stability theory. In Section 4, simulation results are shown to demonstrate the effectiveness of the designed controller. Finally, some conclusions are discussed in Section 5.
2. Model of Back-to-Back VSC-HVDC
Mathematical modeling is the basis of the research on control strategy, so in this section, the mathematical models of main circuit of BTB VSC-HVDC in abc and d-q reference frame are described, which lays the foundation for the research of coordinated control of active and reactive power and the voltage balance of BTB VSC-HVDC.
2.1. Model of Back-to-Back VSC-HVDC in <inline-formula>
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M7">
<mml:mi>a</mml:mi>
<mml:mi>b</mml:mi>
<mml:mi>c</mml:mi></mml:math>
</inline-formula> Frame
The equivalent system model for BTB VSC-HVDC is shown in Figure 1 [7], which is composed of two VSC converter stations, DC side capacitor C and reactor (L1 and L2). Among them, the DC capacitor provides voltage support for the VSC and reduces the DC side harmonics, the reactor is used to filter out the harmonic of output current, and the loss of the converter and line is represented by equivalent resistances R1 and R2.
Equivalent physical model for BTB VSC-HVDC system.
The dynamic mathematical model of AC-side voltage in the abc frame can be expressed as follows [15]:(1)Lkdika,b,cdt=-Rkika,b,c+uska,b,c-urka,b,c,where k=1 as AC1 and VSC1 system, k=2 as AC2 and VSC2 system, uska,b,c is the vector of the grid-side phase voltages (uska,uskb,uskc), ika,b,c is the vector of the grid-side currents voltages (iska,iskb,iskc), Lk is the vector of equivalent inductance, Rk is the vector of equivalent resistance, and urka,b,c is the vector of phase voltages in the AC-side of the VSC. Meanwhile, the active power Pk and reactive power Qk can be expressed as follows [15]:(2)Pk=uskaika+uskbikb+uskcikcQk=13uabic+ubcia+ucaib,where uab, ubc, uca are the grid-side line voltages and ia, ib, ic are the grid-side line currents.
The dynamic changes of DC-bus voltage can be drawn from Figure 1 as follows:(3)Cdudcdt=idc1+idc2-udcRp,where Rp is the total estimation of switching losses of VSC.
2.2. Model of Back-to-Back VSC-HVDC in <inline-formula>
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M39">
<mml:mi>d</mml:mi>
<mml:mtext>-</mml:mtext>
<mml:mi>q</mml:mi></mml:math>
</inline-formula> Frame
VSC-HVDC is transformed to d-q synchronous rotating reference frame as follows [16]:
VSC-2 converter stations:(5)L2did2dt=ω2L2iq2-R2id2+usd2-urd2L2diq2dt=-ω2L2id2-R2iq2+usq2-urq2,where ω1, ω2 are the angular frequencies of two sides’ AC system, respectively, idk, iqk are the d-axis and q-axis currents of the power grid, respectively, usdk and usqk are the d-axis and q-axis grid-side voltages, respectively, and urdk and urqk are the d-axis and q-axis voltages in the AC-side of the VSC.
When the losses in the converters are ignored, the active power balance equation can be described as follows [17]:(6)Pdc=Pr1+Pr2,where Pr1,Pr2 are the active power supplied by VSC-1 and VSC-2, respectively, and Pr1,Pr2 can be given as(7)Pr1=32urd1id1+urq1iq1Pr2=32urd2id2+urq2iq2.
Generally, the losses in the transformer are very small, so (7) can be approximated as follows [17]:(8)Pr1≈P1=32usd1id1+usq1iq1Pr2≈P2=32usd2id2+usq2iq2.
Then, the d-axis is located in the direction of the voltage vector of the AC system by phase-locked loops (PLL); therefore usq1,usq2 are equal to 0, while usd1,usd2 are equal to the magnitude of usk; therefore, (8) can be calculated as follows:(9)P1=32usd1id1(10)P2=32usd2id2.
Similarly, reactive power can be calculated as follows:(11)Q1=-32usd1iq1(12)Q2=-32usd2iq2.
In the synthesis, according to (6), (8)–(10), the power balance equation for the DC-bus voltage can be derived as follows:(13)Cudcdudcdt=32usd1id1+usd2id2.
Remark 1.
In steady state, usd1 and usd2 are constant, so the active and reactive power exchanging between VSC1 and AC1 can be adjusted by controlling the currents id1 and iq1. Similarly, the active and reactive power exchanging between VSC2 and AC2 can be adjusted by controlling the currents id2 and iq2.
Remark 2.
In order to ensure the safe operation of system, it is necessary to maintain the DC side capacitor voltage near its rated value in the process of operation. And we can see from (13) the operation constraint that the exchange of active power between the two sides AC system and back-to-back converter must be kept balanced.
So the control problem of power exchanging between BTB VSC-HVDC and two sides AC system can be converted to power tracking problem under the constraint condition of the constant voltage balance of DC capacitor voltage.
3. Design of Command-Filtered Backstepping Controller
In this section, command-filtered backstepping controller is designed for BTB VSC-HVDC. First, backstepping control technique is applied to the overall controller design of the system. Then, the command filter is used to overcome complex problems of derivation of virtual control signal in the design of conventional backstepping control law, which avoids the unacceptable defects of differential operation in engineering applications. Moreover, constrained command filter can also handle problem of input saturation in backstepping controller. However, command filter will generate filter error which can affect the performance of the controller, so filter compensation signal is designed to eliminate this effect.
The BTB VSC-HVDC usually adopts constant DC voltage control and reactive power control in the one-side converter, and active and reactive power control are adopted in the other side of the converter. The outer loop control is used to determine the current reference, and the inner loop control is used to realize the fast tracking of the current reference.
The design procedure of the controller for BTB VSC-HVDC is deduced as follows. First, the controller of VSC-1 controlling the DC voltage and reactive power is derived step by step as follows.
Step 1.
For the VSC-1, the tracking errors are defined as(14)e1=udc-udcce2=id1-id1ce3=iq1-iq1c,where udcc is the reference voltage of DC side, iq1c is the reference current in q-axis which can be obtained from (11), and id1c is the filtered command from virtual controller id1d.
From (4), (13), and (14), the differential of the tracking errors can be computed as(15)e˙1=32Cudcusd1id1+usd2id2-u˙dcc(16)e˙2=ω1L1iq1-R1id1+urd1-usd1-i˙d1c(17)e˙3=-ω1L1id1-R1iq1+urq1-usq1-i˙q1c.
Step 2.
The candidate Lyapunov function is chosen to stabilize (15) as follows:(18)V1=12e12.
And the time derivative of Lyapunov function V1 is derived as(19)V˙1=e1e˙1=-k1e12+e132Cudcusd1id1+usd2id2-u˙dcc+k1e1.
So the virtual controller id1d can be chosen as(20)id1d=2Cudc3usd1u˙dcc-k1e1-usd2id2usd1,where k1 is a designed positive constant. Substituting (20) into (19), we can obtain that V˙1<0. Therefore, the subsystem is asymptotically stable according to Lyapunov stability theory.
Step 3.
A command filter is applied to solve the effect of differential expansion of time derivative of (20) and input saturation of the controller, which is shown in Figure 2. Passing id1d through the command filter, we can obtain the filtered command id1c and its derivative i˙d1c. Moreover, the state space expression of constrained command filter is represented as(21)q˙1q˙2=q22ξωnSRωn22ξωnSMu-q1-q2,where q1=xdc, q2=x˙dc, u=xd, ξ is the damping of the command filter, ωn is the bandwidth, and SR· and SM· represent the rate and magnitude limit, respectively.
Structure of constrained command filter.
Remark 3.
According to (21), if the input xd is bounded, xdc and x˙dc are bounded and continuous. The error xc-xd can be adjusted by bandwidth ωn. With the increase of the bandwidth ωn, the signal xdc implemented by the controller can be faster and more accurate to converge to xd. And the first-order differential signal is obtained by the integral method, which can effectively overcome the effect of the amplified noise signal caused by the differential operation to the desired signal.
However, there is a filtering error generated by command filter, which will increase the difficulty to get minor tracking error and degrade the dynamic response of system. So the influence of filter error is considered in the controller design and the tracking error needs to be redefined as(22)e-1=e1-ψ.
And the filter compensation signal is designed as(23)ψ˙=-k1ψ˙+3usd1Cudcid1c-id1d.
Step 4.
In order to stabilize (16) and (17), Lyapunov function V2 is designed as(24)V2=12e-12+e22+e32.
The time derivative of Lyapunov function V2 can be computed as(25)V˙2=e-1e-˙1+e2e˙2+e3e˙3.
According to (13), (20), and (23), the time derivative of e-1 can be calculated as(26)e-˙1=32Cudcusd1id1+usd2id2-u˙dcc+k1ψ-3usd12Cudcid1c-2Cudcu˙dcc-k1e1-3usd2id23usd1=3usd12Cudce2-k1e-1.
Substituting (16), (17), and (26) into (25), V˙2 can be calculated as(27)V˙2=-k1e-12-k2e22-k3e32+e23usd12Cudce-1+ω1iq1-R1L1id1+urd1-usd1L1-i˙d1c+k2e2+e3-ω1id1-R1L1iq1+urq1-usq1L1-i˙q1c+k3e3,where k2 and k3 are the designed positive constant. Finally, we choose two control inputs for VSC-1 as(28)urd1=L1-3usd12Cudce-1-ω1iq1+R1L1id1+usd1L1+i˙d1c-k2e2(29)urq1=L1-ω1id1+R1L1iq1+usq1L1+i˙q1c-k3e3.
Then, we can obtain(30)V˙2=-k1e-12-k2e22-k3e32<0.
Thus, it is proven that the subsystem for VSC-1 is asymptotically stable by Lyapunov stability theory. In order to clarify the design of subsystem, the block diagram of the designed controller for VSC-1 is displayed in Figure 3.
Block diagram of command-filtered backstepping designed for VSC-1.
Remark 4.
Since the command filter is applied in the backstepping controller to avoid the derivation signal i˙d1d of the virtual control by use of the integrated signal i˙d1c, the designed controller in this paper is more concise than the traditional backstepping controller [18], which simplifies the program and reduces the amount of calculation of the controller. Therefore, command-filtered backstepping is more suitable for engineering applications.
Then, the controller that controls the active and reactive power for VSC-2 is derived as follows.
The tracking errors about the VSC-2 are defined as(31)e4=id2-id2ce5=iq2-iq2c,where id2c and iq2c are the reference current in d-axis and q-axis which can be obtained from (10) and (12), respectively.
The candidate positive definite Lyapunov function V3 is designed as(32)V3=12e42+12e52.
According to (5) and (31), the time derivative of e4 and e5 can be calculated as(33)e˙4=ω2iq2-R2L2id2+usd2-urd2L2-i˙d2ce5=-ω2id2-R2L2iq2+usq2-urq2L2-i˙q2c.
Then, from (32)–(33), the time derivative of Lyapunov function V3 is derived as follows:(34)V˙3=e4e˙4+e5e˙5=-k4e42-k5e52+e4ω2iq2-R2L2id2+usd2-urd2L2-i˙d2c+k4e4+e5-ω2id2-R2L2iq2+usq2-urq2L2-i˙q2c+k5e5,where k4 and k5 are the designed positive constant. Finally, based on (34), the two control inputs for VSC-2 are designed as(35)urd2=L2ω2iq2-R2L2id2+usd2-urd2L2-i˙d2c+k4e4(36)urq2=L2-ω2id2-R2L2iq2+usq2-urq2L2-i˙q2c+k5e5.
Thus, based on the above analysis, we can reach the goal of stability by Lyapunov stability theory because(37)V˙3=-k4e42-k5e52<0.
In summary, the whole system is proved to be asymptotically stable.
The block diagram of the designed controller for VSC-2 is shown in Figure 4 to obtain a clear thought.
Block diagram of designed controller for VSC-2.
4. Simulation Results
In order to verify the effectiveness of the designed command-filtered backstepping controller for the BTB VSC-HVDC, some simulations are carried out in this section. The structure of the system and control scheme of VSC on both sides are shown in Figures 1, 3, and 4, respectively. The main parameters of BTB VSC-HVDC are summarized in Table 1 [11]. In addition, with the purpose of making the proposed controller have better control effect, the remaining control parameters are selected as k1=260, k2=100, k3=60, k4=100, k5=60. The parameters of constrained command filter are chosen as ξ=0.707, ωn=300, and the magnitude limit and rate limit are 500 A and 50000 A/s.
The main parameters of BTB VSC-HVDC.
Parameters
Value
Equivalent resistances R1 and R2
40 mΩ
Equivalent inductances L1 and L2
6 mH
DC-link capacitor C
4000 μF
Nominal net DC voltage
60 kV
Each AC system nominal voltage
138 kV
Each transformer voltage ratio
138 kV/30 kV(Y/Δ)
Nominal frequencies f1
50 Hz
Nominal frequencies f2
60 Hz
Switching frequency fs
10 kHz
The whole system simulation process is 1 s, which is divided into 5 intervals. Originally, the system runs in the standby phase from 0 to 0.05 seconds. Then, at t=0.05 s, P2 is set as a step response to 10 MW from AC system 1 to AC system 2. At t=0.3 s, Q1 is changed as a step response to −5 MVar. At t=0.5 s, P2 is ramped from 10 MW to −10 MW, which changes as a power flow reversal from AC system 2 to AC system 1. At t=0.7 s, Q2 is step changed from 0 to 3 MVar for AC system 2. Meanwhile, in order to demonstrate the advantages of the designed controller, the command-filter backstepping is compared with the commonly used PID controller [12] and H∞ controller [27], and the simulation results are shown in Figure 5. The parameters of PID controller applied for VSC-1 and VSC-2 of BTB VSC-HVDC are listed in Table 2, and the parameter γ1=0.1 of H∞ controller is used for VSC-1, and γ1=0.2 of H∞ controller is used for VSC-2.
The parameters of PID controller in BTB VSC-HVDC.
PID controller
kp
Ti (ms)
Td (ms)
DC-link voltage
40
2
0
Real power in VSC-1
400
20
1
Reactive power in VSC-1
400
20
1
Real power in VSC-2
100
2
1
Reactive power in VSC-1
100
2
1
System response results of command-filtered backstepping control compared with PID control and H∞ controller.
DC-link voltage
Real power components of AC system 1
Reactive power components of AC system 1
Real power components of AC system 2
Reactive power components of AC system 2
As can be seen from Figure 5(a), the DC-bus voltage is maintained closely to reference by use of the proposed control. The proposed controller and H∞ controller have better voltage balancing performance and robustness than conventional PID control. In addition, command-filter backstepping controller has faster response speed than H∞ controller; however, the H∞ controller has smaller overshoot when the power flow changes suddenly. Figure 5(b) shows the dynamic response of P1 under the different step change. From Figure 5(b) we can see that proposed control has nonovershoot, smaller tracking error, and faster dynamic performance than PID control and H∞ controller. Figure 5(c) shows the dynamic response of reactive power components Q1 of AC system 1. Figure 5(d) shows the dynamic response of real power components P2 of AC system 2. Figure 5(e) shows the dynamic response of reactive power components Q2 of AC system 2. Moreover, three-phase AC-side currents of AC system 1 and AC system 2 controlled by command-filter backstepping controller are shown is Figure 6.
Three-phase AC-side currents via command-filter backstepping controller.
Three-phase AC-side currents of AC system 1
Three-phase AC-side currents of AC system 2
Detail of three-phase AC-side currents of AC system 1
Detail of three-phase AC-side currents of AC system 2
Figures 5 and 6 show that the control system tracks the desired signal correctly and controls the actual and reactive power requirements independently. From Figure 5, we can see that the designed controller has better dynamic performance and stronger robustness compared with the traditional PID controller and has faster response speed than H∞ controller. And the tuning of the parameters of proposed command-filtered backstepping controller is easier than that of the traditional PID controller. Figure 6 shows that the currents change their phases during the power flow reversal period and the operation state is well controlled according to the power reference; meanwhile, the current harmonics meet requirement of grid connection.
5. Conclusion
In this paper, a command-filtered backstepping controller has been designed successfully to maintain DC voltage balance and coordinated control of active and reactive power in BTB VSC-HVDC. First, the design process of the controller is very simple and clear, because the controller is derived from backstepping method step by step. Then, the problems of input saturation and tedious calculation of time derivative of virtual control in conventional backstepping are solved by use of command filter. Meanwhile, a filter compensation signal is considered to eliminate the adverse effects caused by command filter. Next, the stability and astringency of whole system are proved theoretically by Lyapunov method. Finally, simulation results clearly verify that the designed controller can improve the dynamic performance of the system compared to the conventional PID controller and H∞ controller and has stronger robustness compared with the traditional PID controller, which proves the effectiveness of proposed controller.
Competing Interests
The authors declare that they have no competing interests.
Acknowledgments
This work is supported by National Natural Science Foundation of China (61503156, 51405198) and the Fundamental Research Funds for the Central Universities (JUSRP11562, JUSRP51406A, and NJ20150011) and National Key Research and Development Program (2016YFD0400300) and the Science and Technology Funds for Jiangsu China (BY2015019-24) and Science and Technology project of Jiangsu Electric Power Company.
BianZ.XuZ.Fault ride-through capability enhancement strategy for VSC-HVDC systems supplying for passive industrial installationsLiB.JingF.JiaJ.Research on saturated iron-core superconductive fault current limiters applied in VSC-HVDC systemsBorovikovY. S.GusevA. S.SulaymanovA. O.UfaR. A.VasilevA. S.AndreevM. V.RubanN. Y.SuvorovA. A.A hybrid simulation model for VSC HVDCChenL.ChenH.ShuZ.ZhangG.XiaT.RenL.Comparison of inductive and resistive SFCL to robustness improvement of a VSC-HVDC system with wind plants against DC faultDaoudM. I.MassoudA. M.Abdel-KhalikA. S.ElserougiA.AhmedS.A flywheel energy storage system for fault ride through support of grid-connected VSC HVDC-based offshore wind farmsChavesM.MargatoE.SilvaJ. F.PintoS. F.SantanaJ.HVDC transmission systems: bipolar back-to-back diode clamped multilevel converter with fast optimum-predictive control and capacitor balancing strategySaeedifardM.IravaniR.PouJ.A space vector modulation strategy for a back-to-back five-level HVDC converter systemSaeedifardM.IravaniR.Dynamic performance of a modular multilevel back-to-back HVDC systemQinJ.SaeedifardM.Predictive control of a modular multilevel converter for a back-to-back HVDC systemZhangL.HarneforsL.NeeH.-P.Interconnection of two very weak AC systems by VSC-HVDC links using power-synchronization controlBouafiaS.BenaissaA.BouzidiM.BarkatS.Backstepping control of three-levels VSC based back-to-back HVDC systemProceedings of the 3rd International Conference on Systems and Control (ICSC '13)October 2013Algiers, Algeria90090510.1109/icosc.2013.67509642-s2.0-84896642038NikkhajoeiH.IravaniR.Dynamic model and control of AC–DC–AC voltage-sourced converter system for distributed resourcesKanellakopoulosI.KokotovicP. V.MorseA. S.Systematic design of adaptive controllers for feedback linearizable systemsYanW.HuangJ.XuD.Adaptive command-filtered backstepping control for linear induction motor via projection algorithmWangG.-D.WaiR.-J.LiaoY.Design of backstepping power control for grid-side converter of voltage source converter-based high-voltage dc wind power generation systemSunQ.ZhouJ.GuerreroJ. M.ZhangH.Hybrid three-phase/single-phase microgrid architecture with power management capabilitiesAjamiA.ShotorbaniA. M.AagababaM. P.Application of the direct Lyapunov method for robust finite-time power flow control with a unified power flow controllerRuanS.-Y.LiG.-J.JiaoX.-H.SunY.-Z.LieT. T.Adaptive control design for VSC-HVDC systems based on backstepping methodAyariM.GharianiM. A.BelhaouaneM. M.Benhadj BraiekN.Integral backstepping control design for VSC-HVDC systemsProceedings of the 15th International Conference on Sciences and Techniques of Automatic Control and Computer Engineering (STA '14)December 201469870310.1109/sta.2014.70867822-s2.0-84983151054WuJ.WangZ.-X.WangG.-Q.LuX.-F.ZouJ.-L.Backstepping control for voltage source converter-high voltage direct current grid side converterLiaoY.WangG.A new control strategy for DFIG wind farm with VSC-HVDC integrationParkhidehB.BhattacharyaS.Vector-controlled voltage-source-converter-based transmission under grid disturbancesQiuY.LiangX.DaiZ.CaoJ.ChenY.Backstepping dynamic surface control for a class of non-linear systems with time-varying output constraintsTongS.-C.LiY.-M.FengG.LiT.-S.Observer-based adaptive fuzzy backstepping dynamic surface control for a class of MIMO nonlinear systemsWangY.CaoL.ZhangS.HuX.YuF.Command filtered adaptive fuzzy backstepping control method of uncertain non-linear systemsCuiG.XuS.LewisF. L.ZhangB.MaQ.Distributed consensus tracking for non-linear multi-agent systems with input saturation: a command filtered backstepping approachLiangH.LiG.LiG.LiP.YinM.Analysis and design of H∞ controller in VSC HVDC systemsProceedings of the IEEE/PES Transmission and Distribution Conference and Exhibition: Asia and PacificAugust 20051610.1109/TDC.2005.1547069