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This article studies the control problem for a class of stochastic nonlinear time-delay systems with uncertain output functions. Under the appropriate assumptions, a stabilization controller is explicitly constructed by applying the adding a power integrator method. Then, using the Lyapunov-Krasovskii functionals to address time-delay, it is proven that the designed controller can guarantee the closed-loop system to be globally asymptotically stable (GAS) in probability. Finally, two simulations show that the control strategy is effective and can be applied to the actual system.

A fixed-time trajectory tracking control of autonomous surface vessels (ASVs) subject to unmeasured speed is studied in this work. By using the homogeneity-based Lyapunov method, the unknown system states, including the unmeasured speed and lumped disturbances, are estimated by using a novel extended state observer (ESO) within fixed time. Subsequently, using the estimated states, the task of fixed-time tracking is completed with the aid of a newly proposed output-constrained power integrator method, which makes the vessel position and heading strictly within the predefined output constraints, and the tracking errors can be reduced to a range of zero under the continuous control action. The practical fixed-time stability (FTS) of the closed-loop system is analyzed in the sense of Lyapunov, while the output constraints can be well maintained during maneuvering. Finally, the ascendancy of the designed scheme is exhibited by simulation comparisons.

This paper studies an optimal formation control problem of general integrator chain multi-agent systems with strongly convex local cost functions. The control goal is to design appropriate controllers for the agents such that they reach a desired formation shape and the global cost function is minimized. To achieve the goal, a modular control scheme with two modules is proposed. First, in Module I, an optimal formation signal generator is designed, whose outputs asymptotically converge to the minimizer of the global cost function. Second, in Module II, by employing the outputs into the feedback loop as the agents reference trajectories, some linear tracking controllers are designed for the agents to track the references asymptotically. With both modules, the proposed control scheme realizes the optimal formation control goal asymptotically. Moreover, the proposed control scheme is also applied to solving an optimal formation control problem of multiple mobile robots, where the robots total relative weighted squared moving distance requires minimization. Both simulations and experiments validate the effectiveness of the proposed control scheme.

This article focuses on global finite-time output feedback stabilization for uncertain nonlinear systems with unknown measurement sensitivity. The existence of the continuous measurement error resulting from limited accuracy of sensors invalidates the existing design strategies depending on the use of the precise output in the construction of an observer, which highlights the contribution of this article. Essentially, different from related works, we propose a new finite-time convergent observer by avoiding the use of the information on nonlinearities. By combining the homogeneous domination with the addition of a power integrator method, an output feedback controller composed of multiple nested sign functions is successfully developed. Finally, the effectiveness of the presented scheme is exhibited by a numerical example.

This paper proposes an enhanced time delay based current component identification method for single-phase systems to overcome the absence of filtering and poor grid frequency response of conventional method. The proposed technique integrates a delayed signal cancellation (DSC) with a time delay unit, to incorporate a dc offset rejection feature, while maintaining speedy and precise extraction of orthogonal current components. The frequency adaption is also developed through the incorporation of linear interpolation. The dynamic and steady-state performance of the proposed method is analysed and compared with two advanced second-order generalised integrator (SOGI) based methods, namely, modified SOGI and cascaded SOGI under different operating scenarios. The simulation and experimental results substantiate the advantage of zero steady-state error and lower settling time of the proposed solution while exhibiting comparable overshoot with advanced SOGI based methods.

This article studies the issue of adaptive event-triggered output-feedback control for switched p -normal nonlinear systems with the unknown homogeneous growth rate. A homogeneous output-feedback controller is first designed for nominal nonlinear systems based on adding one power integrator technique. Then, a dynamic gain technique is introduced to deal with the difficulty caused by the unknown homogeneous growth rate. With an elaborate design of the adaptive law of the dynamic gain, a novel adaptive event-triggered output-feedback controller is developed to ensure that the closed-loop system is globally asymptotically stable. Meanwhile, a new analysis way is proposed to prove that the Zeno behavior is excluded in the event-triggered control system. Finally, two examples are provided to indicate the effectiveness of the proposed control method.

In this technical note, free-will arbitrary time terminal sliding mode control design is proposed. With such a design, it is possible to control the time duration of sliding in the sliding phase. Under the assumption that the chosen arbitrary time is greater than the reaching phase time (tr), it is shown that the nth order chain of integrators converges to zero within the selected arbitrary time. An algorithm is also proposed for the case when tr is not known to the designer. Stability analysis based on Lyapunov theory has been provided.

In this paper, the high-order nonlinear system is commonly studied in an underactuated weakly coupled mechanical system, the control design is difficult from the tractional control design for nonlinear systems. Thus, we study the finite-time fuzzy adaptive error constraint control problem for stochastic high-order nonlinear nonstrict feedback systems. Fuzzy logic systems (FLSs) are utilized to identify the unknown nonlinear dynamics, a new error transfer variable is used to achieve the prescribed performance. Based on adding a power integrator technique and adaptive backstepping recursive control, a novel adaptive fuzzy finite-time prescribed performance control scheme is developed. By utilizing stochastically finite-time stable theory, the proposed control method can guarantee that the high-order system is semi-global finite-time stable in probability (SGFSP). Finally, both numerical and practical simulations are provided to verify the feasibility and effectiveness of the developed control method.

Considering that the traditional linearization method can not accurately analyze the grid-tied inverter (GTI) system with nonlinear nature. In the single-phase case, a novel nonlinear model for GTI system considering nonlinear factors including synchronous reference frame phase-locked loop (SRF-PLL) and duty cycle saturation in pulsewidth modulation (PWM) is proposed, and the corresponding global asymptotic stability condition is given. Specifically, some system nonlinear factors, e.g. duty cycle saturation phenomenon, and Park (dq-) transformation and cosine operation in second-order generalized integrator-based PLL (SOGI-PLL), are investigated respectively, and their sector-bounded conditions are derived. In order to seek less conservative results, the system state of SOGI-PLL is restructured such that the linear part of PLL system can be stabilized. Then the nonlinear state-space model with sector-bounded for the whole GTI system is formulated. Furthermore, the deduced sector-conditions are introduced into derivation of Lyapunov function by using S-procedure lemma, and the global asymptotic stability condition of inverter system is thus obtained. The system stability regions (SRs) under different grid impedance, current reference, and control parameters are further analyzed. Finally, the effectiveness of proposed theories is fully supported by transient experimental results.

This article proposes a finite-time adaptive containment control scheme for a class of uncertain nonlinear multiagent systems subject to mismatched disturbances and actuator failures. The dynamic surface control technique and adding a power integrator technique are modified to develop the distributed finite-time adaptive containment algorithm, which shows lower computational complexity. In order to overcome the difficulty from the mismatched uncertainties, the disturbance observers are constructed based on the backstepping technique. Moreover, the uncertain actuator faults, including loss of effectiveness model and lock-in-place model, are considered and compensated by the proposed adaptive control scheme in this article. According to the Lyapunov stability theory, it is demonstrated that the containment errors are practically finite-time stable in the presence of actuator faults. Finally, a simulation example is conducted to show the effectiveness of the proposed theoretical results.

The output constraints are widespread in physical systems. Violation of output constraints may result in system damage and performance degradation. This paper investigates the design issue of adaptive fuzzy second-order sliding mode (SOSM) controller, which aims to handle a class of nonlinear systems with output constraints. The unknown bounds of uncertainties are approached dynamically by fuzzy logic systems. Through designing a new barrier Lyapunov function, the output constraint problem has been well solved. Then, by integrating adding a power integrator (API) technology and adaptive fuzzy control, a novel adaptive fuzzy SOSM controller is proposed. It is proved that the proposed method makes the output variable not violate the specified constraint region. At the same time, it can be shown based upon the Lyapunov approach that the finite-time stability of the resulting closed-loop system under output constraint is ensured. Finally, a numerical example and a practical pendulum system are presented to demonstrate the validity of the proposed SOSM control strategy.

This paper proposes a zero-tracking second-order generalized integrator-based frequency-locked loop (ZT-SOGI-FLL) with better dynamics and stability than conventional SOGI-FLL. Unlike the internal model principle, the ZT-SOGI-FLL reconstructs the input signal under frequency deviation by tracking the zeros. Also, it has the same compact structure as the conventional SOGI-FLL. A linearized model is then derived to show that the ZT-SOGI-FLL is always an over-damped or a critical-damper system. More importantly, the derived model proves that the ZT-SOGI-FLL has a larger damping factor and higher bandwidth than SOGI-FLL when the same SOGI gain is tuned. Finally, the input-to-state stability of ZT-SOGI-FLL is analyzed to support the high robustness to severe grid faults. Comparative experimental results show that the ZT-SOGI-FLL has a faster and smoother dynamic response with a higher stability margin than some commonly-used SOGI-based methods under grid faults.

In this paper a super-twisting algorithm based sliding mode observer (STA-SMO) with a complex vector generalized integrator (CVGI) for sensorless control of an interior permanent magnet synchronous motor (IPMSM) is proposed. The STA-SMO exists the compromise between chattering and estimation accuracy under limited control frequency in practice. In order to solve this problem, a CVGI is introduced to guarantee the accuracy of the back-EMF estimation while alleviating chattering. The proposed STA-SMO with CVGI can be used not only in the normal operation but also in the flying start operation based on virtual resistance. The accuracy of the estimated rotor position is not influenced by the value of the virtual resistance during flying start. Furthermore, the proposed STA-SMO with CVGI is designed based on the discrete model of the IPMSM in the discrete-time domain. The stability of the proposed method in the discrete-time domain is further analyzed. Finally, the effectiveness of proposed method is verified by experiments.

This paper focuses on the modeling and stability analysis of the typical single-phase phase-locked loop (PLL) based on second-order generalized integrator (SOGI). Traditionally, SOGI-based PLL (SOGI-PLL) is linearized as the linear time-invariant (LTI) model for the stability analysis and parameter design. Yet, the PLL has periodical nature due to the periodical variation of the grid voltage. The traditional LTI model for PLL thereby reduces the precision of stability analysis. For addressing this problem, an accurate linear time-periodic (LTP) model of the single-phase SOGI-PLL is proposed in this paper. The proposed model can precisely characterize the coupling nature of phase, frequency, and amplitude estimated by SOGI-PLL. A precise stability region of SOGI-PLL thereby can be derived from the proposed LTP model. The effectiveness of the proposed LTP model for SOGI-PLL is verified by simulation and experimental tests.

This paper develops a new control strategy for voltage source converter (VSC) based multi-terminal high voltage dc (MT-HVDC) grids for enhancing the mutual frequency support between MT-HVDC interconnected asynchronous ac systems. The existing droop control structure of VSCs is augmented with an additional feedback voltage-based loop that generates a voltage shifting term to be added to the original dc voltage reference. The addition of this integrator-based controller nullifies the difference between voltage errors seen at adjacent converter stations. This action helps to overcome inaccuracies in the mutual frequency support caused by the uneven voltages across a dc system. The proposed strategy uses only local variables for the continuous-time control; thus, it does not rely on a high-bandwidth communication network, and its performance is not affected by the change of ac systems parameters. Modal analysis is carried out to investigate the stability of the proposed controller. Finally, comprehensive simulation studies are used to verify the proposed strategys performance and compare it with recently reported alternative controllers.

In this work, a synchronverter-based D-STATCOM with self-synchronization and voltage imbalance compensation capability with operation independent of the power operating modes is proposed. The S-STATCOM's synchronverter base model is firstly presented in space-vector representation together with its control strategy with standard D-STATCOM control structure. Then, the Voltage Imbalance Compensation Loop (VICL) is proposed, which uses two well known resonant control structures, the Double Second-Order Generalized Integrator (DSOGI) and a Proportional plus Resonant controller (PR), in an innovative way to effectively turn the S-STATCOM into a specialized active filter for negative sequence voltage, compensating the voltage imbalance at the PCC by supplying the corresponding oscillating power locally. Simulation and experimental results on a small scale prototype are presented to validate the control strategy, which successfully reduced voltage imbalances from up to 10% to bellow the 2% acceptable levels.

This paper analyzes the effect of discretization in the frequency-adaptive flux observer (FAO). Although FAO has structural simplicity and ease of implementation, the discrete-time FAO has phase and gain errors in fundamental flux estimation. As a result, the estimated flux might be erroneous, especially in the high-speed region. For accurate flux estimation, this paper analyzes how the voltage synthesis in the pulse-width-modulation (PWM) affects the stator flux. Through the analysis, the backward Euler method is selected for the primitive stator flux estimation. To mitigate the FAOs discretization error, the proposed FAO utilizes the integrators constructed at the rotor reference frame. Since the discretization error comes from the approximation error of the continuous-time integrator at the operating frequency, the proposed FAO conducts the fundamental flux extraction at the rotor reference frame, where the operating frequency components are treated as a dc signal. Thanks to the coordinate transformation, the FAO can be discretized with no error while keeping the structure of double integrators. The proposed method is verified through the computer simulation and experimental test.

This brief deals with the distributed consensus observer design problem for high-order integrator multi-agent systems on directed graphs, which intends to estimate the leader states accurately in a prescribed time interval. A new kind of distributed prescribed-time observers (DPTO) on directed graphs is first formulated for the followers, which is implemented in a cascading manner. Then, the prescribed-time zero-error estimation performance of the above DPTO is guaranteed for both time-invariant and time-varying directed interaction topologies, based on strictly Lyapunov stability analysis and mathematical induction method. Finally, the practicability and validity of this new distributed observer are illustrated via a numerical simulation example.

An improved nonlinear virtual synchronous control for three-phase grid-connected inverters, that can maintain a reliable operation under both normal and faulty grid conditions, i.e. balanced grid voltage sags, is proposed. The proposed controller can ensure a desired RMS current limitation at all times, provide virtual inertia and damping via the DC-link voltage and AC system frequency coupling, and realize the desired real and reactive power regulation without requiring accurate knowledge of the system parameters. Opposed to the conventional methods that use saturated PI controllers with or without anti-windup techniques to limit the reference value of the inverter current, the proposed controller includes a nonlinear bounded integrator, which limits the actual value (instead of the reference) of the inverter RMS current and leads to a fast system recovery even after significant grid voltage sags. The closed-loop stability of entire system is rigorously proven using nonlinear singular perturbation theory. Moreover, analytic conditions for the controller parameter selection to guarantee the stability of entire inverter system with the DC-link dynamics are provided. To prove the effectiveness of proposed controller and its superior performance compared to the traditional approaches, extensive Matlab/Simulink-based simulations are performed, followed by Typhoon-HIL hardware-in-the loop implementation using a TI microcontroller.

This paper investigates the distributed fixed-time attitude coordinated control problem for multiple spacecraft subject to actuator saturation under the directed topology. First, a distributed fixed-time observer is presented for each follower spacecraft to estimate the leader spacecraft’s states. Compared with the commonly used fixed-time observer, the settling time of the proposed fixed-time observer can be easily adjusted by some free design parameters. Next, a distributed fixed-time control scheme is derived by using the estimates of the leader spacecraft's states and the adding a power integrator technique. When considering actuator saturation, an auxiliary system is utilized to compensate the saturation. Further, a rigorous theoretical proof is provided to show that the practical fixed-time stability of the closed-loop system is ensured. Finally, simulation results illustrate the benefits and effectiveness of the developed control scheme.

The filtered split-path nonlinear integrator (F-SPANI) is a generic nonlinear controller designed to improve the transient performance of linear (motion) systems in terms of overshoot. The main idea underlying F-SPANI is that the amplitude and phase of an integrator can be tuned using independent filters, resulting in more efficient use of the buffer of the integrator. In this article, a general description of F-SPANI is presented. In addition, a stability analysis result is presented that provides sufficient conditions in the form of linear matrix inequalities (LMIs) for closed-loop stability analysis on the basis of construction of a common quadratic Lyapunov function (CQLF). The ease of the design, implementation, and the potential of the proposed controller are illustrated both in simulations and in experiments on an industrial pick-and-place machine.

The complex and ever-changing harmonics in grid voltage will cause performance deterioration of the frequency-locked loops (FLLs). Although various measurements had been adopted to attenuate the deterioration, they had to make the trade-off between the dynamic and steady-state characteristics generally. Consequently, a novel single-phase FLL that can adaptively adjust the dynamic and steady-state performance was proposed in this paper. The proposed FLL regards the damping ratio of second-order generalized integrator-FLL (SOGI-FLL) as a time-varying parameter rather than a constant, and adjusts the damping ratio adaptively, so the proposed FLL was named SOGI-FLL with damping ratio adaptation (DASOGI-FLL). The adaptive mechanism is to decrease the damping ratio as frequency estimation error decreases and vice versa. To realize the mechanism, a novel variable was constructed to indirectly correlate the damping ratio with frequency estimation error. An objective function containing the constructed variable for damping ratio adaptation was designed, and the adaptive algorithm was derived by using the gradient ascent method. Then the convergence analysis, parameter design, and digital implementation of the algorithm were elaborated. Finally, the results of simulation and experiment reveal that, benefits from the damping ratio adaptation, DASOGI-FLL can achieve rapid convergence, strong filtering capability, and high estimation accuracy simultaneously.

In the high-power traction system, such as rail transit, the switching frequency is relatively low. The bandwidth of the current controller and the frequency of the injected signal are both limited under low switching frequency, which hinder the sensorless control of interior permanent magnet synchronous motor (IPMSM) in the zero-and low-speed regions. This paper presents an IPMSM sensorless control for zero-and low-speed regions under low switching frequency condition based on the fundamental model. The position can be estimated from the estimated virtual back electromotive force (EMF) with sinusoidal current injection. An internal model control (IMC) and a vector PI (VPI) control are designed to solve the problem of current controller bandwidth limitation. The multiple adaptive filters (AFs) based on the second-order second-order generalized integrator (SO-SOGI) are designed to eliminate the harmonics related to the injection frequency and the fundamental frequency in the stationary frame (SF) to improve the control performance. Meanwhile, the proposed sensorless control strategy is extended from the SF to the rotating frame (RF) which is easier to implement. The rotor position and speed are estimated by a third-order super-twisting extended state observer. The effectiveness of the both proposed strategies are verified by experiments.

In order to reduce the adverse effect of the large thrust ripple of permanent magnet linear synchronous motor (PMLSM) on mover position estimation accuracy and solve the sliding mode chattering problem of the traditional sensorless algorithm based on sliding mode observer (SMO), this paper proposes a systematic method to solve above issues. First, the high-order SMO method is used to suppress harmonic generation from the source of sliding mode chattering. Second, an adaptive filter based on a second-order generalized integrator (SOGI) is constructed to filter out the harmonics. Then, the normalized quadrature phase-locked loop (PLL) method is used to realize the closed-loop extraction of position information. Finally, the deadbeat predictive current control (DPCC) with the current feedforward compensation strategy is proposed to further improve the dynamic performance and mover position estimation accuracy. The simulation model and experimental platform are built. The simulation analyses and test results show that the proposed method has better performance than conventional techniques.

In the sensorless control system of an induction machine, the rotor speed value is not measured but reconstructed by an observer structure. The rotor speed value can be reconstructed by the classical adaptive law with the integrator. The second approach, which is the main contribution of this paper, is the non-adaptive structure without an integrator. The proposed method of the rotor speed reconstruction is based on an algebraic relationship – the rank of the mathematical model of the observer system is not increased. However, the problem with the stabilization of the observer structure does exist. For near to zero rotor speed or in the regenerating mode of an induction machine, the speed observer structure can be unstable. Therefore, in this paper, the new stabilization functions are proposed. The stability is provided by the Lyapunov theorem and the practical stability theorems in which the uncertainty of parameters is considered. In the proposed solution, the newly introduced stabilization functions guarantee observer stability during both the motoring and regenerating conditions at the chosen low rotor speed ranges and for different load torque values. All the theoretical considerations were confirmed by simulation and experimental tests during the chosen working modes and uncertainties of nominal parameters of the induction machine.

In this article, an adaptive fuzzy control design strategy is presented for p -norm nontriangular stochastic high-order nonlinear systems with asymmetric output constraints and unknown nonlinearities. To prevent the violation of the asymmetric output constraint, a novel barrier Lyapunov function (BLF) is constructed. Then, combining the constructed BLF with adding a power integrator approach, the adaptive fuzzy control algorithm is developed by the backstepping technique. Simultaneously, the rigorous proof displays that the designed controller can ensure that all variables of the closed-loop system are bounded in probability with the achievement of the output constraint. Eventually, the theoretical result is further demonstrated via the simulation results.

The global fixed-time control problem is studied for uncertain nonlinear systems whose dead-zone input and control coefficients are unknown. Unlike the previous results, the control coefficients are unknown and their bounds are also not required. Firstly, a modified adaptive controller is proposed with the assistance of the adding a power integrator technique. And a logic switching mechanism is developed based on the framework of the fixed-time stability theorem to compensate the uncertain control coefficients and dead zone. Then it is proved that the fixed-time stability can be ensured for the closed-loop systems based on the proposed algorithm. Furthermore, the effectiveness of the proposed controller is verified by a simulation result.

It is well-known that a phase-locked loop (PLL) technique is widely used in engineering scenarios, recovering and synthesizing the phase and frequency values. The loop filter is the core part of the PLL. This article proposes a class of nonlinear active disturbance rejection loop filters for the PLL. First, we present the detailed nonlinear mathematical model of PLL in consideration of the phase unbalancing, the voltage harmonics, and the voltage offset. Next, based on the model, a class of nonlinear active disturbance rejection loop filters with different nonlinearity degree-of-freedom are proposed in the synchronous reference frame, which can make the PLL in possession of better performance in comparison with that of PLL designed by traditional methods. Moreover, the parameter tuning rules of the nonlinear loop filters are given. Furthermore, hardware-in-the-loop experiments are finished in the dSPACE platform so as to check the real-time performance of the loop filters in more electronic aircraft power grid system scenario. At last, we conclude that the loop filter with the nonlinear generalized integrator extended state observer type2 possesses the best performance among the three loop filters for PLL in this article.

Unbalanced grid voltages, appearing at stator terminals of a doubly fed induction generator (DFIG) based wind energy conversion system (WECS) deteriorate its performance, by instigating unwanted oscillations and distortions in output grid power and rotor currents, respectively, as well as by introducing unbalanced currents in the stator and the grid. This paper aims to address these challenges using a coordinated control strategy based on an improved reduced order generalized integrator (IROGI) for positive and negative sequence estimation (PNSE). The IROGIPNSE further enhances the control performance, by eliminating the effects of any DC component or unbalance in sensed voltages, on grid synchronization. The coordinated control strategy uses hysteresis scheme for current control. The hysteresis based current control requires fewer rotational transformations, and eliminates the need for PI/PIR regulators and notch filters for inner current control loops. This renders the control, computationally efficient. Moreover, the presented system is equipped to exhibit wind power levelling functionality, through a battery energy storage (BES). An approach, employing the region-specific wind speed frequency distribution graph, is utilized to constitute the power levelling operation modes. The effectiveness of the control scheme is demonstrated through test results on a prototype developed in the laboratory.

This paper is a research related to finite-time stability. Different from traditional fixed-time, predefined-time, and prescribed time stability that more or less have some conservativeness, we manage to stabilize system states onto the equilibrium at an arbitrarily selected time instant irrespective of initial system states and parameters. In another word, the conservativeness of convergence time in our proposed control method is proved to be zero. Moreover, the control is bounded and also gradually goes to zero at the selected instant. It is obviously an improvement compared with the existing finite-time stabilization (FNTS), such as fixed-time stabilization (FTS), predefined-time stabilization (PDTS), and prescribed-time stabilization (PSTS).The FNTS property is of great interest for scenarios where real-time constraints need to be satisfied, e.g., in missile guidance, the impact time control guidance laws require stabilization in a desired time. Our proposed PSIS can deal with the FNTS problems. For other tasks with more accurate requirement on time, the FTS, the PDTS, and the PSTS are insufficient. For instant, two robot arms playing the piano. Music has its’ rhythm, each note is expected to appear at a specific time instant, or the music will sounds terrible. There are many other tasks that are easy for human beings but difficult for robots, e.g.. dancing and sports. The author think it is because human have rhythm feeling, while robots have not. Hence, it is important to develop such control methodologies.

Because of the complexities of tire-road interaction, the wheels of a multi-wheel distributed electric drive vehicle can easily slip under certain working conditions. As wheel slip affects the dynamic performance and stability of the vehicle, it is crucial to control it and coordinate the driving force. With this aim, this paper presents a driving force coordination control strategy with road identification for eight-wheeled electric vehicles equipped with an in-wheel motor for each wheel. In the proposed control strategy, the road identification module estimates tire-road forces using an unscented Kalman filter algorithm and recognizes the road adhesion coefficient by employing the recursive least-square method. According to road identification, the optimal slip ratio under the current driving condition is obtained, and a controller based on sliding mode control with a conditional integrator uses this value for acceleration slip regulation. The anti-slip controller obtains the adjusting torque, which is integrated with the driver-command-based feedforward control torque to implement driving force coordination control. The results of hardware-in-loop simulation show that this control strategy can accurately estimate tire-road forces as well as the friction coefficient, and thus, can effectively fulfill the purpose of driving force coordinated control under different driving conditions.

This note investigates a unified finite-time output feedback control strategy for a class of planar switched systems with an asymmetric output constraint. A fraction-type asymmetric barrier Lyapunov function (BLF) is constructed firstly. Based on relaxed assumptions on system nonlinearities together with the developed BLF, a set of finite-time state feedback controllers are designed systematically by revamping the technique of adding a power integrator. By incorporating the state controllers with switched reduced-order observers developed delicately, the task of finite-time stabilization for planar switched systems can be realized by the resultant output feedback controllers in consideration of asymmetric output constraints imposed on switched systems simultaneously. The proposed method enjoys the unification property such that it is workable for the scenarios of constrained and unconstrained cases, without the need of changing/redesigning the structures of controllers and observers. Finally, simulation results are presented to verify the proposed scheme.

Model-based sensorless field-oriented control (FOC) suffers from overparameterization and can be laborious to use for a five-phase permanent magnet synchronous motor. On the other hand, insulated gate bipolar transistor (IGBT) frequently fails in an electric drive. Under IGBT failure, a freewheeling current is observed, and, above all, it carries the failed phase back electromotive force information. Based on this observation, this article presents the design of a brand new sensorless FOC by exploiting the freewheeling current to accommodate both IGBT and position sensor failures, which is expected to further enhance the drive's fault-tolerant capability. The mathematical model of this current is first established to provide a theoretical basis and a comprehensive understanding of the presented sensorless FOC. By virtue of this model, a second-order generalized integrator with a frequency-locked loop can be used as a simple and elegant way to extract position/speed estimates. Experimental results are provided to validate the proposed sensorless FOC philosophy.

The fixed-length transfer delay-based adaptive frequency-locked loop (TD-AFLL) has drawn much attention with concise structure and faster response speed compared with the conventional second-order generalized integrator-based FLL. However, the application of TD-AFLL is still limited due to the poor performance in terms of phase-angle detection under distorted grid conditions. This letter proposes an enhanced TD-AFLL (ETD-AFLL) with high phase-angle detection accuracy under distorted grid conditions. The ETD-AFLL employs a filter in parallel with the FLL rather than using a pre-filer before the FLL, so that the constructed phase-angle detection keeps a fast response speed. In addition, this filter fully utilizes the inherent samples of TD-AFLL, thus it requires the slightly additional computational cost. Experimental results are given to support the proposed ETD-AFLL.

In this article, we deal with the development of a fractional-order notch filter (FONF) for a grid-connected solar photovoltaic (PV) system. The developed FONF control approach is used to estimate fundamental active constituents from the distorted load currents, and hence, gating pulses for operating voltage source converter (VSC) are used in the PV system. This control approach for the grid-connected solar PV system is designed to achieve several purposes, such as feeding active power demand of the load/grid and countercurrent-related power quality issues at the common connecting point. The power quality issues taken into consideration are harmonics distortion, reactive power burden on the system, and unbalancing of connected loads. The FONF-based control proposes a modified structure of an integer-order notch filter. The integer-order filters have a limitation due to the fixed integrator and differentiator terms. In FONF, the power of integrator used in a notch filter can be modified according to the application required for obtaining the accurate response of the system. A prototype of the grid-connected solar PV system is developed in the laboratory using IGBTs based VSC and dSPACE MicroLabBox (DS-1202) to demonstrate the behavior of the FONF-based control. Simulation and experimental results are obtained for steady-state and unbalanced loads with variation in the solar irradiance. The harmonic distortions in the system are observed as per the IEEE-519 standard.

Active disturbance rejection controller (ADRC) has achieved soaring success in motion controls featured by rapid dynamics. However, it turns obstreperous to implement it in the power plant process with considerable time-delay, largely because of the tuning difficulty. To this end, this article proposes a quantitative tuning rule for the time-delayed ADRC (TD-ADRC) structure based on the typical first order plus time delay (FOPTD) model. By compensating the FOPTD process as an integrator plus time delay in low frequencies, the gain parameter of TD-ADRC can be related to a scaled time constant which shapes the closed-loop tracking performance. Bandwidth parameter of extended state observer is scaled as a dimensionless parameter. A sufficient stability condition of TD-ADRC is theoretically derived in terms of the scaled parameter pair, the range of which falls within the practical interest. Relative delay margin is revealed as a critical robustness metric among others, a default pair of scaled parameter setting is recommended as well as an explicit retuning guideline according to the user's preference for performance or robustness. Simulation and laboratory water tank experiment validate the tuning efficacy and a coal mill temperature control test depicts a promising prospective of the proposed method in process control practice.

This paper investigates the leader-following consensus problem of second-order nonlinear multi-agent systems with directed graph. A novel reset control approach is proposed for the aim of improving transient consensus performance, e.g., settling time. By introducing consensus error into reset conditions, the output of reset integrator will keep the same sign with the consensus error, thus, the desired states can be compensated preferentially and the system transient performance is improved accordingly. To appropriately describe the closed-loop system with reset-induced jump dynamics, a hybrid system model consisting of both flow dynamics and jump dynamics is constructed. Based on this model, and combined with backstepping method, Lyapunov-based consensus analysis is presented under hybrid system framework. Finally, a numerical example is provided to show the effectiveness of the obtained results.

When the permanent magnet synchronous motor (PMSM) works in the high-speed region with low carrier ratios, the performance of the rotor flux observer has a great influence on the loading capacity and stability of the speed sensorless vector control system. The problem of the adaptive compensation flux observer (ACFO) of the PMSM at low carrier ratios is analyzed in this paper, and an ACFO with a feedback delay component is presented. After retuning the PI regulator parameters, the new expression related to carrier ratio is obtained, which can improve the performance of the flux observer at low carrier ratios and make the torque and current loop response faster. Meanwhile, the stability of different Euler approaches of the integrator for ACFO in the discrete domain is analyzed, and a new Euler with a coefficient is proposed to combine the merits of the backward Euler and the trapezoid Euler. It shows better performance at low carrier ratios. Finally, the effectiveness of the discrete ACFO is verified by experiments.

In the permanent magnet synchronous motor speed regulation system, the dynamic performance of the conventional active disturbance rejection control (ADRC) system will be deteriorated by using a low bandwidth speed filter. To solve this problem, two ADRC controllers considering the speed measurement noise are proposed in this article. One proposed ADRC system is based on the extended state observer (ESO), the other proposed ADRC system is based on phase-locking loop observer (PLLO). In the proposed two ADRC systems, an integrator is employed as the speed filter so that the measured position can be directly used for observing the speed and disturbance without speed calculation. Meanwhile, by using an integrator as the speed filter, the dynamic performance of the proposed ESO-based ADRC system is not affected since it is independent of the speed filter, and the proposed PLLO-based ADRC system has a better rejection ability for the low-frequency disturbance. Experimental results validate the proposed methods. Ministry of Education (MOE) Accepted version This work was supported in part by the Academic Research Fund Tier 1 from Ministry of Education, Singapore, under Grant 04MNP000588C140, and in part by the Natural Science Foundation of China under Grant 51807080.

Three-phase grid-connected voltage-source inverters (VSIs) are widely used for renewable energies integration. Cost reduction and suitable operation under nonideal grid conditions are their important technical challenges. Accordingly, this paper proposes an efficient adaptive neural filter-based virtual flux (ANF-VF) estimator for sensorless control of a grid-connected VSI under unbalanced and distorted grid conditions. To perform sensorless predictive direct power control (PDPC), the grid voltage sensors are substituted by the ANF-VF estimator. This estimator includes an emulated ideal integrator in series with two simple ANFs. Lyapunov’s theory-based convergence analysis is conducted for its optimal tuning. This is resulted in an accurate extraction of VF fundamental components. For more effectiveness under unbalanced grid conditions, an extension of original instantaneous power theory is introduced in the proposed VF-based PDPC (VF-PDPC). Effectiveness of the VF-PDPC is verified through simulation and experimental tests. A direct and smooth startup without initialization is accomplished under unbalanced grid conditions. Superiority of the VF-PDPC compared to the conventional PDPC is demonstrated. The proposal presents sinusoidal grid currents with low total harmonic distortion under unbalanced and distorted grid conditions. Moreover, the ANF-VF estimator illustrates best performances compared to the second-order generalized integrator-based VF estimator that uses measured grid voltages under nonideal grid conditions.

This paper presents a practical approach to developing a speed limiter using a disturbance observer (DOB) and a speed observer. A nominal plant model is designed assuming that the vehicle is a lumped mass. The plant uncertainty and external disturbance are lumped into a disturbance term and compensated for by the DOB. With the contribution of the DOB, the proposed controller can reduce overshoot and minimize steady-state error without feedforward and integrator control. In addition, the speed observer is also designed to reduce the overshoot due to noise such as offset, lag, and communication delay between the display speed and wheel speed, because the proposed controller operates according to the display speed. The proposed controller was validated by vehicle experiments performed on a C-segment hybrid electric vehicle (HEV) and achieved superior performance compared to conventional controllers.

The purpose of this study is to offer an adaptive hybrid controller for the formation control of multiple unmanned aerial vehicles (UAVs) leader-follower configurations with communication delay. Although numerous studies about the control of the formation exist, very few incorporate the delay in their model and are adaptive as well. The motivation behind this article is to bridge that gap. The strategy consists of an adaptive fuzzy logic controller and a Proportional, Integral, and Derivative (PID) controller where the logic controller fines/tunes the PID controller gains. The controller also consists of an integrator that raises the order of the system which helps reduce the noise and steady-state errors. The simulations confirm that the proposed technique is robust and satisfies mission requirements. Moreover, the flying formations of the swarm were created by a B-spline curve based on a simple waypoint. The main contribution of this study is to present a model where the formation remains stable during the whole flight, errors are within the optimal range, and the time delays are manageable.

In this paper, we consider a robust control problem for a quadrotor that has uncertain time-varying mass and external disturbance. In solving our control problem, we suggest a new $$\gamma$$ -sliding mode controller coupled with an integrator to tackle both uncertain time-varying mass and disturbance issues in the system. Through Lyapunov analysis of the controlled system, we show that the gain-scaling factor $$\gamma$$ can effectively reduce the ultimate bound of each controlled state. The performance of the proposed controller is verified under the mass change during the experiment.

This article focuses on the control based on an extended second-order generalized integrator with a frequency locked loop (Ext-SOGI-FLL) to provide satisfactory performance for synchronization of microgrid (MG). In the existing phase-locked loop (PLL) based control, the loop filter used is not capable to entirely remove harmonics. Hence, the harmonics in voltage considerably affect the frequency as well as phase extraction, both in the dynamics and steady-state situations. To deal with this problem in this system, the voltage source converter is controlled using Ext-SOGI-FLL. This control algorithm extracts the fundamental voltage and current for assessment of phase angle and reference source current (maintaining the required IEEE power quality standard-519 & 1547). This FLL-based control is also capable of estimating the exact frequency and phase magnitude, which suffer from phase offset due to frequency change. The comparative results validate that the response of Ext-SOGI-FLL control in comparison to the existing control algorithms is faster at loads and generation perturbations. Simulated and test results for MG system combining a solar photovoltaic, pico-hydropower generation, and battery validate its performance while feeding local loads uninterruptedly.

In order to improve the dynamic performance of the sensorless permanent magnet synchronous motor drive system, the modified pulsating high frequency voltage injection method is proposed. Firstly, the second order generalized integrator can be used to extract the high frequency voltage signal instead of band-pass filters. The specific frequency harmonic elimination unit is applied to obtain the rotor position error signal to avoid using the low-pass filter. Therefore, the system dynamic performance can be improved. In addition, the system parameter is easier to adjust than traditional methods with band-pass filters and low-pass filters. Finally, the simulation model and experimental platform are built to verify the effectiveness of the proposed method. The simulation and experimental results present that the dynamic performance of motor drive system can be improved.

This study presents a time-invariant feedforward (FF) element design for the high-speed and high-precision tracking control of an ultrahigh-acceleration, high-velocity linear synchronous motor (LSM). The linear motor can generate an acceleration greater than 70 G (= 686 m/s2) and move at a velocity above 10 m/s. To take advantage of this performance and realize high response, the design and usage of suitable FF elements is crucial. However, as the LSM includes highly nonlinear characteristics, it is difficult to provide an exact dynamic model for FF design. To overcome this problem, a control system with a learning controller (LC) as the FF element has been designed previously, demonstrating high-precision and high response motion. However, the motion performance can be achieved only with sufficient pre-learned motions. The integrator and the disturbance observer that were effective in suppressing disturbances were removed from the control system. In addition, the control system has some FF time-invariant elements along with the LC. This study proposes a design method for easy design of all FF elements using an LC. The designed FF elements are time invariant and are used with an integrator and a disturbance observer, without pre-learning. Using the proposed method, two sets of time-invariant FF elements are designed. The performances of two control systems, which include a set of time-invariant FF elements for each, and a simple disturbance observer are experimentally examined and compared with two previously designed control systems. Experimental results demonstrate that the performance of one of the control systems with a set of time-invariant FF elements designed in this study and a disturbance observer is good and almost comparable with that of the previously designed control system with high-precision and high response motion.

This article addresses the problem of finite-time stabilization for a class of high-order nonlinear stochastic systems with asymmetric output constraints. A novel barrier Lyapunov function (BLF) is first presented to handle such asymmetric constraints. Further, based on the proposed BLF and the adding a power integrator technique, a controller design approach is developed by the backstepping method. It can be rigorously proved that the designed controller can not only make the system states finite-time converge to the origin in probability but also ensure that the constraint on system output is not violated. Another novelty of this approach is that it is a unified tool owing to its simultaneous application to the systems without output constraints. Finally, the validity of the proposed scheme can be verified by a simulation example.