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This article presents a method for calculating all the proportional–integral/proportional–derivative controllers with a low-pass filter of a given order, which satisfy gain–phase margins and sensitivity (or complementary sensitivity) specifications. The method is explicit and requires solving a set of a polynomial and two linear equations. It is shown how to extend the method to design all the proportional–integral–derivative or cascaded controllers with a low-pass filter assuming that a minimum value of one of the controller components is given. [ABSTRACT FROM AUTHOR]

This article presents an automated, model-free, data-driven method for the safe tuning of PID cascade controller gains based on Bayesian optimization. The optimization objective is composed of data-driven performance metrics and modeled using Gaussian processes. The safety requirement is imposed via a barrier-like term in the objective, which is introduced to account for operational changes in the system. We further introduce a data-driven constraint that captures the stability requirements from system data. Numerical evaluation shows that the proposed approach outperforms relay feedback autotuning and quickly converges to the global optimum, thanks to a tailored stopping criterion. We demonstrate the performance of the method through simulations and experiments. For experimental implementation, in addition to the introduced safety constraint, we integrate a method for automatic detection of the critical gains and extend the optimization objective with a penalty depending on the proximity of the current candidate points to the critical gains. The resulting automated tuning method optimizes system performance while ensuring stability and standardization. [ABSTRACT FROM AUTHOR]

In this article, a speed control scheme based on an analytically designed fractional-order PID with Bode’s ideal cutoff (FOPID-BICO) filter is proposed. The FOPID controller is designed to track the speed references and the BICO suppress is applied to filter the high-frequency noise. Considering the difficulty of parameters tuning of the FOPID controller, a comprehensive analytical design method based on frequency specifications-defined loop-shaping for the FOPID-BICO controller is first proposed for the permanent magnet synchronous motor speed control. The designed speed servo system satisfies five frequency-domain specifications: gain crossover frequency, phase margin, phase crossover frequency, gain margin, and a “flat phase” constraint. Moreover, the influence of phase crossover frequency on control system is fully exposed through the frequency-domain analysis. The proposed designed method ensures that the control system is robust to loop gain variations and guarantees the optimal performance on rejecting noise in high-frequency and disturbance in low-frequency. The effectiveness of the proposed FOPID-BICO controller has been verified by experimental results. [ABSTRACT FROM AUTHOR]

The speed and radial displacement of the rotor have the obvious ripples due to the strong coupling between torque and suspension force of a single-winding bearingless flux-switching permanent magnet motor, and the traditional PID/PI controller is difficult to suppress the disturbance of the unbalanced magnetic force. A linear active disturbance rejection control method based on model compensation is proposed in this article. First, the topology and operation principle of the motor are described, and then the dynamic model of the rotor and flux linkage model of the motor are analyzed. Accordingly, the integral-series standard mathematical models of the displacement and speed are deduced, and then the mathematical expressions of the controller gain and radial disturbance are obtained. Second, the linear extended state observer with known model perturbation information and the linear feedback control law are designed, and the parameters tuning method is given. Finally, the simulation and experimental results verified that the proposed method can significantly reduce the rotor displacement and torque ripples, and it has better disturbance rejection performance than the traditional PID/PI control method in the same stability margin. [ABSTRACT FROM AUTHOR]

A high-performance triaxial fast tool servo (FTS) with the hybrid electromagnetic–piezoelectric actuation and the hybrid parallel–serial-kinematic structure is reported. Featuring the balanced and uniform actuation, in this article, a novel axis-symmetric linearized reluctance actuator is proposed to generate the planar motion in parallel, and the piezoactuated vertical motion is then serially carried by the planar motion within a limited space. Verified by the finite-element analysis, a two-stage design strategy is developed to optimally determine the multiphysical system parameters for the triaxial FTS, assisted by an analytical model of the electromagnetic circuit as well as the mechanical mechanism. As for the trajectory tracking, the loop-shaping tuned PID controller with a feedforward compensator is employed for each axis, and a damping controller is additionally designed for the planar motion. Finally, both open-loop and closed-loop performance of the prototype are carefully demonstrated. [ABSTRACT FROM AUTHOR]

In this article, a hybrid algorithm of Levenberg–Marquardt (LM) and proportional-integral-derivative neural network (PIDNN) with the relay feedback (LM-PIDNN-RF) is proposed to solve control problems for unknown discrete nonlinear systems. First, the PIDNN is initialized by the relay feedback to solve the problem of assigning initial weights; meanwhile, the LM neural network is regarded as an identifier to fit system input/output quickly and accurately. Second, the partial derivative of the system output to system input is transferred to the PIDNN, which ensures that the weights of the PIDNN can be updated correctly in time. The hybrid algorithm can update the weights of the neural network controller correctly against the errors caused by system instantaneous disturbance, and the controller has only one parameter to be tuned manually. Moreover, the stability of the closed-loop system is proven by using the Lyapunov stability theory. The proposed hybrid algorithm can significantly improve tracking performance in comparison with PIDNN and RF-PID. The results of three simulation examples and a physical experiment are presented to show superior tracking performance of the proposed algorithm. [ABSTRACT FROM AUTHOR]

In this article, a modified reduced order generalized integrator-based frequency-locked loop (MROGI-FLL) is proposed for controlling the interfacing inverter of the grid-tied photovoltaic system to mitigate the harmonics. Additionally, a fuzzy tuned PID controller is integrated in the proposed scheme to minimize the steady-state error, which results the voltage level is maintained constant at the common dc-link bus terminals. The MROGI-FLL is designed to evaluate the three-phase reference currents by extracting the fundamental constituents from the load currents and grid voltages. The proposed MROGI-FLL has several advantages such as better harmonic mitigation capability, control adaptivity, adaptive frequency and phase, grid synchronization, and low computation burden. The proposed reference current generator is simulated on MATLAB/Simulink platform under steady state and various transient conditions.The comparative study of proposed scheme is compared with the existing and adaptive control techniques, which assures the potency of the proposed control algorithm in-terms of harmonic mitigation, dc-offset rejection, frequency variation, and computation burden. Finally, the experimental results are verified through an experimental platform by using the dSPACE evaluation kit and both the simulation and hardware characteristics are well justified to the IEEE-519 standard limits. [ABSTRACT FROM AUTHOR]

In this article, we introduce an adaptive strictly negative-imaginary (SNI) autopilot for a low-cost quadrotor aerial vehicle, specifically designed to achieve high precision hovering and perform accurate trajectory tracking under time-varying dynamic load (i.e., displacement, velocity, and acceleration). Leveraging the learning ability of an artificial neural network, our adaptive SNI controller is robustly designed to overcome uncertainties in flight environments such as variations in the centre-of-gravity, modeling errors, and unpredictable wind gusts. The efficacy of the proposed adaptive control system is investigated under extensive flight tests in addition to numerous computer simulations and rigorous comparison with other control techniques, namely, fixed-gain SNI, fuzzy-SNI, and conventional PID controllers. We also conduct a stability analysis of the proposed control system using the SNI theorem. [ABSTRACT FROM AUTHOR]

In the context of disturbance-estimation (DE)-based control, it is reported that including desired dynamics into the nominal model yields a simple and compact control law that is easier to implement. The resulting control structure unifies the nominal feedback controller and feed-forward disturbance compensator to formulate an overall feed-forward disturbance compensation problem. Based on this, two popular DE-based techniques, namely active disturbance rejection control (ADRC) and uncertainty and disturbance estimator (UDE)-based control, are restructured into a unified form. By reformulating the controllers in the frequency domain, it is shown that the two structures are equivalent provided the UDE filter is selected based on the observer designed for ADRC. For an easier understanding of practitioners who are familiar with the conventional control structures, the designed controllers are reinterpreted in the framework of two-degree-of-freedom (2DoF) internal model control and 2DoF proportional-integral-derivative (PID) controller to show the equivalence among them. Tuning rules for PID controllers in terms of unified ADRC parameters are also presented to aid practical implementation in industry. Performance of the unified control scheme is evaluated on a non-minimum phase dc–dc boost converter that is operating under line and load disturbances using simulation and experimental study. [ABSTRACT FROM AUTHOR]

In this article, we propose an analytical method to design a robust nonfragile controller for load voltage regulation of high-gain boost converter exhibiting nonminimum phase behavior due to right-half plane (RHP) zero. The proposed single-loop voltage-mode controller design technique is based on the stability boundary locus and Kharitonov's theorem. Using this approach, a robust performance region having guaranteed gain margin and phase margin criteria for nominal and 16 Kharitonov's plants are generated in the controller parameter plane. Controller robustness-fragility analysis due to the tolerance of analog compensator passive components is done with the help of a delta 20 robustness fragility index. Controller robustness, performance, and nonfragility are tested on a 200-W laboratory prototype against the load and source perturbations. Experimental results validate the effectiveness of the robust controller to regulate the load voltage of the converter in spite of the limit on performance set by RHP zero. [ABSTRACT FROM AUTHOR]

In this article, we investigate the tuning problem of digital proportional-integral-derivative (PID) parameters for a dc motor controlled via the controller area network (CAN). First, the model of the dc motor is presented with its parameters being identified with experimental data. By studying the CAN network characteristics, we obtain the CAN-induced delays related to the load rate and the priorities. Then, considering the system model, the network properties, and the digital PID controller, the tuning problem of PID parameters for the CAN-based dc motor is transformed into a design problem of a static-output-feedback controller for a time-delayed system. To solve this problem, particle swarm optimization algorithm and linear-quadratic-regulator method are adopted by incorporating the sufficient condition of time-varying delay system. Finally, the effectiveness of the proposed PID tuning strategy is validated by experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a neural tuning technique is proposed and applied to a fractional-order proportional-integral-derivative (FOPID) controller. The proposed controller is applied to a radar-guided missile which is used for tracking high-speed moving targets in defense systems. The proposed neural tuning along with $\text{H}_{2}\text{/} \text{H}_{\infty }$ optimization method is intended to improve the tracking performance of the proportional navigation (PN) system and the stability of the missile trajectory during flight time. Due to the coupled and nonlinear dynamics of the considered missile, we propose a new control structure that integrates the FOPID controller into the PN system of the missile which results in better stability properties for the missile. In order to tune the FOPID, we propose a neural tuning technique that starts with a genetic algorithm-based optimizer and continues with a neural network-based scheme. This speeds up finding a near-optimal solution and refining it effectively. Then, $\text{H}_{2}\text{/} \text{H}_{\infty }$ optimization process is applied within the neural tuning technique to achieve better stability and tracking performance for the missile during the whole flight time. The proposed controller is compared with the standard PID controller tuned by the conventional Ziegler–Nichols (ZN) tuning method as well as particle swarm optimization (PSO) method, and the simulation results proved the superiority of the proposed tuning method over ZN- and PSO-based tuning approaches. [ABSTRACT FROM AUTHOR]

The proportional-integral-derivative (PID) controller is a widely used controller in automation industries. Several advanced PID tuning/design methods, such as response-based design, internal model control, and controller optimization by stochastic algorithms, have been proposed in the literature. However, regardless of the advantages and accuracy of developed tuning methods, due to the process modeling error and parametric uncertainties, the experimental response always differs from the theoretical response, which required online fine-tuning of the PID parameter. Manual adjustment of three PID parameters disturbs the robustness of the controller from its desired value; also, it does not guarantee the stability of the process. Therefore, this paper focuses on online PID controller tuning with the guaranteed robustness of the controller. A new single variable tuning method is developed for the online robustness and performance adjustment. Moreover, the proposed rules only depend upon the previously optimized PID parameters. The proposed method is an additional feature to all existing PID tuning methods, including optimal PID controller with stochastic optimization algorithms. The proposed method is validated with the help of optimal PID controller design by existing optimal tuning rules, optimized PID with particle swarm optimization and experimental validation on the canonical tank system. [ABSTRACT FROM AUTHOR]

In this paper, a fractional-order model of pneumatic servo system is introduced by replacing the integer-order dynamic equation with the corresponding fractional order one. Then, a fractional-order proportional-integer-differential (FPID) controller is optimized for the servo system using an online multivariable multiobjective genetic algorithm (MMGA). The proposed MMGA searches in five-dimensional parameter space based on Pareto rank to balance multiobjectives. In order to provide a basis for comparison, the parameters of a integer order proportional-integer-differential (IPID) controller are also optimized using the same method. The performance indices defined for comparison are the steady-state tracking accuracy and the control energy consumption. Additionally, seven other methods from the literature are compared. The experimental results obtained show that the optimized FPID controller results in a better performance than the optimized IPID controller and the other existing approaches. [ABSTRACT FROM AUTHOR]

Charge control is a well-known sensorless approach to operate piezoelectric actuators, which has been proposed for more than 30 years. However, it is rarely used in industry because the implemented controllers suffer from the issues of limited low-frequency performance, long settling time, floating-load, and loss of stroke, etc. In this paper, a novel controller circuit dedicated to overcome these issues is presented. In the proposed scheme, a grounded-load charge controller with decoupled configuration is developed, which separates high-frequency and low-frequency paths, thus achieving arbitrarily low transition frequency without increasing the settling time. Based on this, a self-compensating configuration is further proposed and integrated into the controller circuit, which makes full use of controller output to improve its own control performance at low frequencies. Experimental results show that the presented charge controller can effectively reduce more than 88% of the hysteretic nonlinearity even when operating close to the transition frequency. To demonstrate its practical value, we then integrate it into a custom-designed high-speed atomic force microscope system. By comparing images obtained from using voltage drive and charge controller, it is clear that the piezoelectric hysteresis has been significantly reduced in a wide bandwidth. [ABSTRACT FROM AUTHOR]

General linear active disturbance rejection control (LADRC) is studied in the paper. First, it is shown that there are some limitations in the conventional LADRC, and then some properties of general LADRC are analyzed. It is proved that any strictly proper controller with integration can be implemented via a general LADRC, thus extends the application range of LADRC. Finally, a method is proposed to tune the general LADRC using the same bandwidth idea as the conventional LADRC. [ABSTRACT FROM AUTHOR]

In this paper, a model-based current control strategy with virtual time constant is proposed for three-phase grid-connected LCL-filtered voltage source inverters. The proposed control strategy is based on controlling the inverter currents in the rotating dq frame by using current-oriented proportional-integral (PI) controllers rather than voltage-oriented PI. The PI controllers determine the inverter current references in the d- and q-axes by regulating the grid current. It is shown that the proposed strategy decouples the inverter current from other variables provided that the inverter-side inductance and its resistance values used in the control variable match the actual values in the system. In addition, the virtual time constant is introduced in the control variables to offer flexibility for adjusting the inverter current dynamics as desired. Moreover, the integral gain of PI controller has the ability to keep the LCL-resonance peak below 0 dB. Unlike the existing methods, the proposed strategy does not require a dedicated active damping. Computer simulations and experimental studies show that the proposed control strategy exhibits a good performance in achieving fast dynamic response and sinusoidal grid current with low THD under balanced, unbalanced, and distorted grid conditions. [ABSTRACT FROM AUTHOR]

This paper is concerned with the problem of data-driven fault-tolerant control for multiple simultaneous sensor drift faults in variable-gain digital PID systems with very large time constants and long dead time, which are exceedingly common characteristics of process control systems. No existing data-driven residual generation method can allow building (with low computational costs) residual variables independent of the state of these systems, and meanwhile guarantee that each of the sensor faults is mapped uniquely and entirely onto the associated residual variable. To solve the aforementioned technical difficulty, a novel residual generation technique is devised via the dead time as well as the coefficients and state of the variable-gain PID controller. On this basis, a methodology is developed for the purpose of the full-decoupling estimation of several sensor malfunctions from the residual variables. Finally, a resulting data-driven approach to compensate for the aforesaid faults is applied to a dual-chamber electric heating furnace (which is a typical process plant), so that the effectiveness and advantages of the proposed methods are verified by experiment. [ABSTRACT FROM AUTHOR]

Existing charging techniques for lithium-ion batteries use a largely open-loop approach, where the charge profile is predecided based on a priori knowledge of cell parameters. There is a need for closed-loop charging techniques that use instantaneous cell voltage and/or temperature to modulate the charging current magnitude. This paper addresses this gap by proposing a constant-temperature constant-voltage (CT-CV) charging technique, considering cell temperature as a key degradation metric. The proposed CT-CV charging scheme employs a simple and easy-to-implement proportional-integral-derivative (PID) controller aided by a feed-forward term. The charging current is dynamically adjusted in response to the battery temperature, which indirectly reflects its aging and thermal environment. As per experimental results, the proposed method achieves 20% faster charging with the same total temperature rise as constant-current constant-voltage (CC-CV) technique. Alternatively, it causes 20% lower cell temperature rise for given total charge time. It can easily accommodate applications that demand even faster charging by simply raising the set temperature. This paper establishes the benefits of the proposed CT-CV charging at cell level and raises the possibility of extending it to the pack level by integrating it with battery management systems. [ABSTRACT FROM AUTHOR]

This paper presents a novel cascade proportional-integral (PI) continuous second-order sliding mode control (SMC) for induction motor in the presence of operational constraints. The inner-loop SMC is designed to control the current dynamics of the motor, while the outer-loop control is the PI control of speed. The main advantage of the proposed method is that the PI control provides reference to the inner-loop SMC with constraints according to the system requirements in terms of maximum current and speed limits. Moreover, because the inner-loop dynamics of the motor are nonlinear, SMC design has more importance in terms of robustness and disturbance rejection capability. The proposed control is a continuous-time design strategy with fixed-time convergence, while its discretization is performed at the implementation stage. The performance of the developed controller is validated by carrying out real-time experimental studies on an industrial size induction machine. Experimental results demonstrate remarkable robust tracking performance of the controller in terms of transient speed response and steady-state accuracy. [ABSTRACT FROM AUTHOR]

This paper studies the practical use of discrete-time direct adaptive control in a high-precision inertially stabilized platform's turbulence isolation system for the purpose of enhancing isolation performance. Under low-frequency and low-velocity environments, the velocity-stabilized loop of the platform shows severe nonlinear characteristic; therefore, its isolation performance is limited. In previous research, we constructed a nonlinear model of the velocity-stabilized loop by using an improved Stribeck friction model, and also designed a feed-forward compensation strategy. Both have obtained outstanding performance during practical experiments. However, errors still exist as disturbance of the unmodeled part and environmental change causes the system's parameter to vary. To solve this, a novel discrete-time direct model reference adaptive control based on nonlinear friction compensation is introduced to the original proportional-integral control system. An improved projection algorithm and a recursive least-square algorithm with fading memory are respectively used to design the adaptive law. By using a turbulence observer to provide a reference signal, both types of controls are applied to the carrier turbulence isolation system. Results of the practical experiments prove that model reference adaptive control can further enhance the system's isolation ability. [ABSTRACT FROM AUTHOR]

Piezoelectric-actuator-driven nanopositioning stages, with large stroke and low crosstalk, are quite appealing for fulfilling the through-silicon via lithography etching task. The motivation of this paper is to combine the ability to enable the nanopositioning stage running in a manner of millimeter scale workspace and nanometer scale positioning accuracy. Two pairs of flexure-guided kinematic modules with high displacement amplification ratio are adopted to construct a 4-PP (P is prismatic) XY nanopositioning stage. A new decoupling design is implemented to realize the decoupling behavior between the input actuators and output compliant limbs, respectively. Kinematics modeling including output compliance, input stiffness, displacement amplification ratio modeling, and workspace determination are carried out. After a series of mechanism dimension optimizations via particle swarm optimization algorithm, the performance of the optimized mechanism is analyzed and assessed by using the ANSYS workbench. Then, a repetitive-compensated PID controller and a single-input and single-output closed-loop control strategy are designed. Finally, a series of experimental tests in terms of crosstalk test, frequency characteristic analysis, damping property analysis, dynamic hysteresis nonlinearity characterization, signal trajectory tracking, workspace determination, and Bode diagram plotting are carried out in details. It indicates that the workspace of fabricated prototype has reached to 1.035 mm $\times$ 1.035 mm, the crosstalk ratio is kept within 0.5%, and the closed-loop positioning accuracy is determined as 400 nm. [ABSTRACT FROM PUBLISHER]

The attitude control of quadrotor unmanned aerial vehicle (UAV) is investigated. The aim of this paper is to develop a continuous multivariable attitude control law, which drives the attitude tracking errors of quadrotor UAV to zero in finite time. First, a multivariable super-twisting-like algorithm (STLA) is proposed for arbitrary order integrator systems subject to matched disturbances. A discontinuous integral term is incorporated in the control law in order to compensate the disturbances. A rigorous proof of the finite time stability of the close-loop system is derived by utilizing the Lyapunov method and the homogeneous technique. Then, the implementation of the developed method in an indoor quadrotor UAV is performed. The remarkable features of the developed algorithm includes the finite time convergence, the chattering suppression and the nominal performance recovery. Finally, the efficiency of the proposed method is illustrated by numerical simulations and experimental verification. [ABSTRACT FROM PUBLISHER]

This paper proposed a combined method for wind energy conversion system using pressure coupling (PC) hydrostatic transmission. The operation strategy is the combination of maximizing power point tracking at the input power and stabilizing the output power. The maximum power point tracking method is to control the turbine speed for tracking the optimal tip speed ratio (TSR). For maximizing the input power, a PID controller and a sliding mode controller are applied for speed control to track a predefined speed that is calculated from the optimal TSR. The output power is stabilized by using a high-pressure accumulator for accumulating and compensating the power. The driven speed of the generator is controlled by the PC principle, using a PID controller and an adaptive fuzzy sliding mode controller. Experiments are carried out to verify the proposed method. The overall efficiency in several wind speed profiles is about 40%. [ABSTRACT FROM PUBLISHER]

Torque ripple caused by stator current and flux harmonics is one of the main issues in the doubly fed induction generator (DFIG)-dc system, which inherently has to operate with distorted waveforms produced by the diode commutation. This paper proposes a torque-ripple mitigation strategy based on a predictive estimation of the reciprocal of flux linkage. The predictive estimation compensates for the intrinsic delay in the actuation of the torque-ripple rejection signal through the rotor current control loops. Unlike other approaches relying on complex current regulators with selective harmonic tracking, this strategy is based on well-established proportional-integral (PI) controllers for the rotor currents. PI current controllers can then still have bandwidth values typical of usual DFIG systems. Simulations and experiments on a test-rig show that the compensation strategy achieves a strong torque ripple reduction and is very robust against stator frequency variations. [ABSTRACT FROM PUBLISHER]

In this paper, the constrained control problem of the prescribed performance control technique is discussed in discrete-time domain for single input-single output dynamical systems. The goal of this design is to maintain the tracking error trajectory in a predefined convergence zone described by a performance function in the presence of the uncertainties. In order to achieve this goal, the discrete-time quasi-sliding-mode control with a new sliding variable is proposed. Additionally, by using a modified convergence zone, the transient response of the system can be adjusted without producing the offset error in the steady state. The effectiveness of the proposed method is confirmed by experiments on a piezo-actuated positioning system. [ABSTRACT FROM PUBLISHER]

Randomness from the power load demand and renewable generations causes frequency oscillations among interconnected power systems. Due to the requirement of synchronism of the whole grid, load frequency control (LFC) has become one of the essential challenges for power system stability and security. In this paper, by modeling the disturbances and parameter uncertainties into the LFC model, we propose an adaptive supplementary control scheme for the power system frequency regulation. An improved sliding mode control (SMC) is employed as the basic controller, where a new sliding mode variable is specifically proposed for the LFC problem. The adaptive dynamic programming strategy is used to provide the supplementary control signal, which is beneficial to the frequency regulation by adapting to the real-time disturbances and uncertainties. The stability analysis is also provided to guarantee the reliability of the proposed control strategy. For comparison, a particle swarm optimization-based SMC scheme is developed as the optimal parameter controller for the frequency regulation problem. Simulation studies are performed on single-area and multiarea benchmark systems, and comparative results illustrate the favorable performance of the proposed adaptive approach for the frequency regulation under load disturbances and parameter uncertainties. [ABSTRACT FROM AUTHOR]

This paper presents a methodology to control a two-staged ac/dc converter, which is a cascade combination of a three-phase ac–dc boost power factor correction (PFC) rectifier and a phase-shifted full-bridge (PSFB) dc/dc converter. This paper explains the issues of instability and losing unity power factor operation, i.e., high reactive power transfer with conventional PI compensator due to the sensitive variation of output impedance of the PFC stage at different loads. In this paper, this instability issue is resolved by the proposed state-feedback control methodology, which shows that there exists a load-insensitive range of controller parameters, providing unity PFC. As an additional benefit of this control, total number of sensors are reduced by three (an input phase current, a dc/dc primary current, and an output dc voltage), in comparison to the conventional PI-based control. This reduction is achieved by introducing two augmented state variables followed by their reduced state observer design. A 6-kW laboratory prototype of the integrated three-phase PFC and PSFB dc/dc is developed and designed to validate the proposed control algorithm. The experimental results show a conversion efficiency of 95.4% at full load, input total harmonic distortion of 4.1%, power factor of 0.998, and output voltage ripple of ±1%. [ABSTRACT FROM PUBLISHER]

This paper presents the design, implementation, and performance testing of a nonlinear proportional-integral (PI) predictive controller for a grid-tied inverter used in photovoltaic systems. A conventional cascade structure is adopted to design the proposed controller, where the outer loop is used to regulate the dc-link voltage, and the inner loop is designed as a current controller for adjusting the active and reactive powers injected into the grid. For each loop, the controller is derived based on combining a continuous-time nonlinear model predictive control and nonlinear disturbance observer techniques. It turns out that the composite controller reduces to a nonlinear PI controller with a predictive term that plays an important role in improving tracking performance. The salient feature of the proposed approach is its ability to approximately preserve the nominal tracking performance during the startup phase. Both simulation and experimental results are provided to demonstrate the effectiveness of the proposed approach in terms of nominal performance recovery, disturbance rejection, and current control. [ABSTRACT FROM AUTHOR]

Neutral-to-ground overvoltage may occur in noneffectively grounded power systems because of the distributed parameters asymmetry and resonance between Petersen coil and distributed capacitances. Thus, the constraint of neutral-to-ground voltage is critical for the safety of distribution networks. In this paper, an active grounding system based on a single-phase inverter and its control parameter design method is proposed to achieve this objective. Relationship between its output current and neutral-to-ground voltage is derived to explain the principle of neutral-to-ground voltage compensation. Then, a practical current detection method is proposed to specify the reference of compensated current. A current control method consisting of proportional resonant and proportional integral (PI) with capacitive current feedback is then proposed to guarantee sufficient output current accuracy and stability margin subjecting to large range of load change. The PI method is taken as the comparative method and the performances of both control methods are presented in detail. Experimental results prove the effectiveness and novelty of the proposed grounding system and control method. [ABSTRACT FROM AUTHOR]

To realize high-performance control for a two-axis inertially stabilized platform (ISP), a nonlinear dynamic model based on the geographic coordinate and a compound control method based on the back-stepping sliding mode control and adaptive radial basis function neural network (RBFNN) are proposed. Compared with the traditional dynamic model based on the inertial coordinate, the nonlinear dynamic model based on the geographic coordinate constructs the direct relationship among the control inputs and criteria of the ISP. Moreover, the back-stepping sliding mode control method is proposed to handle the system nonlinearity, parameter variations, and disturbances. Furthermore, the adaptive RBFNN is constructed and optimized to estimate the upper bound of the residual error on line to reduce the chatting phenomenon. The asymptotic stability of the proposed control method has been proven by the Lyapunov stability theory. The effectiveness of the proposed method is validated by a series of simulations and flight tests. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel disturbance-rejection tracking controller for ball screw feed drives. First, active-disturbance-rejection control (ADRC) and proportional-integral (PI) control are employed to ensure the performance of the closed-loop system. In this control framework, the extended state observer estimates and compensates for unmodeled dynamics, parameter perturbations, variable cutting load, and other uncertainties, which improves the disturbance-rejection performance and robustness of the system. Then, based on ADRC feedback linearization, a novel equivalent-error-model-based feedforward controller is designed to further improve the tracking performance of the system. This equivalent error model is independent of the mechanical model, simple to design and easy to tune. Simulations and experimental results demonstrate that the proposed control method has better tracking performance and robustness against the internal and external disturbances compared with the conventional P-PI controller. [ABSTRACT FROM AUTHOR]

In this paper, the full bridge-based modular multilevel converter (MMC) is discussed for the application of tundish induction heating power supply (TIHPS). TIHPS features three-phase to single-phase ac/ac conversion and variable output frequency, and has intense demand for the power transmission stability and output current control precision. MMC is suitable for this application and especially the bulky and costly transformer and ac filter in the conventional topology can be dispensable. Therefore, it is interesting to investigate the applicable control method for MMC-TIHPS. According to the instantaneous power theory, a hierarchical direct power control based on the improved deadbeat current control is presented to assure the energy balance inside and outside MMC-TIHPS and reduce the sensitiveness of the current controller to parameter uncertainties. The proposed control strategy dispenses with the phase-locked loop, and does not exist the coupling among control variables of internal and external currents. Then, parameters design of energy controller is studied for stability analysis. Finally, MMC-TIHPS and proposed control method are verified by experimental results of a down-scaled physical prototype. [ABSTRACT FROM AUTHOR]

In this paper, a walking robot that consists of its body and six legs is considered for trajectory control. The leg mechanism is a 1-UP&2-UPS (U-universal joint, P-prismatic joint, and S-spherical joint) parallel mechanism with the arm–leg conversion function. Due to the nonlinearity and uncertainties of the robot, it is difficult to obtain its exact dynamic model, therefore this paper utilizes the decentralized control strategy to design a dynamic hybrid controller, in which the outer loop is an impedance controller, the middle and inner loops are designed by using the sliding-mode control and the nonlinear proportional–integral–derivative (PID) control, respectively. The inverse kinematics of one leg is derived for mathematic model, based on which three control methods including the classical PID control, position–velocity loops cascade control, and dynamic hybrid control are examined. Contrast tracking experiments were performed with one robotic leg. The experimental results are shown to identify their differences and prove the effectiveness and applicability of the proposed dynamic hybrid control. [ABSTRACT FROM PUBLISHER]

In this paper, a continuous–discrete time observer which simultaneously estimates the unmeasurable states and the uncertainties for the electro-hydraulic actuator (EHA) system is presented. The main feature of the proposed observer is the use of an intersample output predictor which allows the users to increase the frequency acquisition of the piston position sensor without affecting the convergence performance. The stability analysis of the proposed observer is proved using Lyapunov function adapted to hybrid systems. To show the efficiency of our proposed observer, numerical simulations and experimental validation involving a control application, which combines the designed observer and a proportional–integral (PI) controller for the purpose of piston position tracking problem, are presented. [ABSTRACT FROM PUBLISHER]

A cascaded dc–dc boost converter is one of the ways to integrate hybrid battery types within a grid-tie inverter. Due to the presence of different battery parameters within the system such as, state-of-charge and/or capacity, a module-based distributed power sharing strategy may be used. To implement this sharing strategy, the desired control reference for each module voltage/current control loop needs to be dynamically varied according to these battery parameters. This can cause stability problem within the cascaded converters due to relative battery parameter–variations when using the conventional proportional–integral (PI) control approach. This paper proposes a new control method based on Lyapunov functions to eliminate this issue. The proposed solution provides a global asymptotic stability at a module level avoiding any instability issue due to parameter variations. A detailed analysis and design of the nonlinear control structure is presented under the distributed sharing control. At last thorough experimental investigations are shown to prove the effectiveness of the proposed control under grid-tie conditions. [ABSTRACT FROM PUBLISHER]

This paper presents the design and implementation of leaping control methods for replicating high-speed dolphin leaping behavior. With full consideration of both mechanical configuration and propulsive principle of a physical robot comprising one neck joint, two propulsive joints, and a pair of two-degrees-of-freedom (2-DOF) mechanical flippers, closed-loop pitch, roll, yaw, and depth control methods are integrated to accomplish precise attitude control. Specifically, two pitch control strategies are proposed to separately satisfy small and large pitch requirements based on the real-time feedback of the pitch angle, while the roll controller is further implemented as a proportional-integral-derivative (PID) loop. A combination of pitch and roll control is utilized to regulate the desired pitch maneuvers. Finally, a parameterized five-phase leaping control algorithm instead of Weihs’s three-phase porpoising model is implemented on the self-contained real robot, enabling the examination of biological leaping phenomena which are hard to observe or measure. Latest experimental results reveal that besides high speeds exceeding the minimum exit speeds, the pitch control closely related to pitch angle and submersion depth is another critical factor contributing to effective dolphin leaping. [ABSTRACT FROM PUBLISHER]

This paper presents a control strategy of a flyback microinverter with hybrid operation mode for photovoltaic ac modules. The proposed control strategy consists of two components: the proportional-resonant (PR) controller with the harmonic compensator (HC) and the hybrid nominal duty ratio. Compared to the conventional control strategy using the proportional-integral controller, the PR controller with HC provides a higher system gain at the fundamental and harmonic frequencies of the grid without using a high proportional gain in both operation modes. Then, it enhances the tracking speed and disturbance rejection performances satisfying the desired stability. Moreover, by applying the hybrid nominal duty ratio yielded from the proposed operation mode selection, the disturbance rejection is achieved more effectively, and the control burden is reduced. Finally, the simulation and experimental results were shown to verify the tracking speed and disturbance rejection performances of the proposed control strategy. [ABSTRACT FROM PUBLISHER]

In this paper, a modified zero-voltage-switching pulsewidth-modulation inverter with a digital-signal-processor-based proportional–integral–derivative (PID)-like fuzzy controller (PIDFC) is implemented. The switches of the inverter can achieve a soft-switching feature that can largely reduce switching losses and improve the converting efficiency. In order for the online control of the proposed dc–ac inverter to be feasible, a fuzzy control is designed to be a PID-like fuzzy mechanism with the complexity significantly reduced. From the results, it is shown that the PIDFC can not only stabilize the output at 110 V rms but can also improve the performance when the system load has been changed from 600 to 100 $\Omega$. Comparing with a traditional PID controller, the responding speed can be improved by 75% in the simulation, and the speed can still be improved by 35% in the practice experiment. [ABSTRACT FROM AUTHOR]

One of the most attractive features of multiphase machines is the fault-tolerant capability due to the higher number of phases. Different postfault control strategies based on hysteresis, proportional integral (PI)-resonant, and predictive techniques have been recently proposed. They all proved their capabilities to withstand fault situations and to preserve the fundamental component of the air-gap field, while achieving minimum losses, maximum torque per ampere, and reducing torque vibrations. Nonetheless, due to their recent introduction, no thorough study has yet appeared comparing the performance of these controllers. In this paper, two open-phase fault-tolerant control schemes are experimentally compared in a real five-phase induction machine. The controllers being compared are based on PI-resonant and predictive control techniques, respectively. The experiments include pre- and postfault situations. Obtained results show that both control methods offer nearly the same performance. When compared, predictive control provides faster control response and superior performance at low-speed operation but is found to be less resilient to fault detection delays and to have higher current ripple. Regarding the controller implementation, it is shown that the transition from prefault to postfault operation involves modeling the nonlinear effects observed when an open-phase fault occurs for the predictive controller and proper retuning of the PI trackers for the PI-resonant controller, to ensure postfault operation. [ABSTRACT FROM AUTHOR]

In a paper written by Choi and Lee (IEEE Trans. Ind. Electron., vol. 56, no. 6, pp. 2039–2046, Jun. 2009), the authors propose a new antiwindup strategy for the proportional–integral speed controller, to suppress the undesired side effect known as integrator windup when large set-point changes are made. In this paper, we point out that there are obvious errors in the paper. Our paper corrects these errors and informs of further study to improve the antiwindup method. The proposed method is demonstrated by experimental results. [ABSTRACT FROM PUBLISHER]

Proportional–integral–derivative (PID) controllers with constant gains seldom meet desired performance when system dynamics rapidly changes due to unknown disturbances. A gain tuning method for variable PID controllers is presented in this paper. First, the equivalence relationship between a discrete PID control and a discrete backstepping control with time-delay estimation and nonlinear damping is clarified, and the variable gains of the PID controller are automatically tuned with a nonlinear damping component. The nonlinear damping terms directly affect system performance and make PID gains vary. The system performance of a variable PID controller with the proposed method is compared with that of a constant PID controller. The experimental results show that the proposed method is adaptive, robust, and effective. [ABSTRACT FROM PUBLISHER]

In this paper, the positioning control problem of pneumatic muscle actuators (PMAs) is being considered. A two-degree-of-freedom nonlinear proportional–integral–derivative structure is being synthesized, providing ameliorated compensation of the PMAs’ nonlinear hysteretic phenomena and advanced robustness through disturbance cancellation. Experimental studies are being utilized to prove the overall efficiency of the proposed control scheme with regard to set-point tracking performance for the position control of a single PMA, torsion angle control of a nonsymmetrical antagonistic PMA setup, and disturbance rejection in both single and antagonistic control scenarios. [ABSTRACT FROM PUBLISHER]

Control Parameters design of a three-phase synchronous reference frame phase locked loop (SRF-PLL) with a prefiltering stage (acting as the sequence separator) is not a trivial task. The conventional way to deal with this problem is to neglect the interaction between the SRF-PLL and prefiltering stage, and treat them as two separate systems. This approach, although very simple, is not optimum as the prefiltering stage and the SRF-PLL may have comparable dynamics. The aim of this paper is to develop a systematic and efficient approach to design the control parameters of the SRF-PLL with prefiltering stage. To this end, the paper first optimizes the performance of the prefiltering stage in detection of the sequence components. The paper then proceeds to reduce the interaction between the prefiltering stage and SRF-PLL, which is achieved by employing a derivative-filtered proportional-integral-derivative controller as the loop filter (instead of the commonly adopted proportional-integral controller) and arranging a pole-zero cancellation. The suggested method is simple and efficient, and is applicable to the joint operation of different sequence separation techniques and the SRF-PLL. The effectiveness of the suggested design approach is confirmed through extensive experimental results. [ABSTRACT FROM PUBLISHER]

In grid connected photovoltaic (PV) systems, lowpass filters are utilized to reduce injected current harmonics. LCL filters have recently drawn attention for PV system grid interfaces due to their small size and they have shown better attenuation to switching harmonics than simple L filters. However, the LCL filter causes resonance resulting in oscillation and instability issues. This paper proposes an effective active damping technique by introducing a two-degree-of-freedom (2DOF) PID control structure. The 2DOF control structure allows the independent action of PI and D terms giving two degrees of freedom. The design is based on a typical three-phase grid-tied PV system. The active damping control loop is formed by using the existing grid side inductor currents and thus eliminating the need of additional sensors. The relative stability is illustrated in frequency domain by using bode plots. A real-time hardware-in-loop study is performed to validate the performance of the proposed 2DOF technique to damp out the LCL filter resonance. [ABSTRACT FROM AUTHOR]

Sensorless and sensor-fault-resilient control of a networked dc motor system (NDCMS) with an optimal integral-square-error proportional–integral (PI) controller is considered, while network-induced delays and packet dropouts are taken into account. A sliding-mode observer is developed to estimate rotor speed and unknown load torque for the networked system. Then, a PI controller is designed such that the overall NDCMS with complete or partial sensor failure is stabilized and a linear quadratic cost function is sufficiently minimized. Optimal controller parameters are determined by solving bilinear matrix inequalities. The numerical and experimental tests are performed to evaluate the feasibility and applicability of the networked sensorless or sensor-fault-tolerant controller. The results show good performance in both estimation and control objectives. [ABSTRACT FROM AUTHOR]

The design and the implementation of a fuzzy output tracking control applied to a boost converter that operates in large-signal domain are presented. Unlike conventional fuzzy controller design which addresses only small-signal system control and stability, the proposed controller ensures good tracking performances and overall large-signal stability of the system over the whole operating space. This is thanks to: i) The high prediction accuracy of the Takagi–Sugeno fuzzy approximator (TSFA) with twelve affine functions; ii) the possibility to automatically derive the corresponding small-signal model under a wide range of operating conditions; iii) the advantage of integral controllers; and iv) the LMI approach to carry out the overall large-signal stability. After introducing an added integral state of the output tracking error, the resulting augmented system is represented into a Takagi–Sugeno fuzzy model (TSFM). Parallel distributed compensation (PDC) concept is applied to design the state-feedback based control law whereby the control gains are off-line pre-solved by the mean of the linear quadratic regulator (LQR) technique. Sufficient stability conditions are expressed in terms of LMIs. Experimental results using dSPACE DS1104 and a boost converter for different operating conditions, both in tracking and regulation mode; illustrate the efficiency, the robustness and the flexibility of the proposed approach relatively to a classical PID controller. [ABSTRACT FROM PUBLISHER]

In this paper, a saturation-based tuning method for fuzzy proportional–integral–derivative (PID) controller is proposed. The key feature is that this tuning method adopts an inherent saturation property resulting from finite rules in practical application. Based on the saturation, fuzzy PID controller can be expressed as a sliding-mode controller that has two nonlinear terms: One plays as an equivalent control, and the other acts as a switching control. A nominal tuning is first presented to design a stable equivalent control using gain margin and phase margin. Then, a robust tuning is presented to design the switching control by using maximum sensitivity function or compensation sensitivity function. The maximum bound of uncertainty is given by the robust analysis. Finally, this proposed tuning method is used to control a clamp rotation of a forging manipulator. The simulations and real-time experiments demonstrate the effectiveness of the proposed tuning method. [ABSTRACT FROM PUBLISHER]

The increasing number of distributed generation units has led to the development of microgrids, to which the distributed generators are commonly interfaced by means of a voltage-source inverter (VSI). When the microgrid is operating independently of the power system, i.e., in islanded mode, two levels of control can be distinguished for these VSIs: power control and voltage control (frequency and amplitude). The set-point values for the voltage controller are obtained from the power controller. This paper investigates theoretically and experimentally the benefits of using several PID control structures for the voltage control. Theoretical insights into the dynamics of such a system emphasize the benefits of measuring current signals for control purposes and adding voltage measurements to the output of the controllers. Direct voltage control and cascade voltage control are compared both with and without forward compensation of the grid voltage. Simulation and experimental results are given showing that such PID-type controllers on a digital signal processor are simple yet effective strategies for an accurate voltage control in islanded microgrids. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel control scheme for the fast current control of permanent magnet synchronous machines. The proposed method mainly works in the transient state of current control without deteriorating steady-state characteristics. The proposed method is applicable in a wide range of speed: in the speed below the base speed and in the flux weakening region. Using the proposed method, the reference values of d-q currents are modified so that the currents follow the so-called “shortcut” trajectory in the d-q coordinate plane. The effectiveness of the proposed method is confirmed by computer simulations and experiments. The settling time is reduced by 55% compared with that of the conventional method. [ABSTRACT FROM AUTHOR]