Search

Abstract This paper presents an auto‐tuning method for dc‐ac voltage source converters (VSCs) with an inductive load that is based on the modified relay feedback test (MRFT). Controllers tuned by the proposed method can produce near‐optimal dynamic performance for dc–ac VSCs without requiring knowledge of the plant's parameters. The controller consists of a PID cascaded with a digital notch filter. The tuning involves two steps. In the first step, the MRFT is used to tune the digital notch filter to compensate for the LCL resonance resulting from the LC filter's interaction with the inductive load. In the second step, one more MRFT is used to tune the PID controller using optimal tuning rules that are derived in advance (offline). The proposed optimal for the class of the dc–ac VSCs tuning rules can guarantee a specified phase margin and near optimal transient performance for any randomly picked VSC. The performance of the proposed tuning of the PID + notch filter is verified by simulations and experiments. The dynamic response of the auto‐tuned controller compares well to the response of a theoretically optimal but non‐auto‐tuned PID + notch filter designed using the full knowledge of the LC filter and the load.

This paper presents an auto‐tuning method for dc‐ac voltage source converters (VSCs) with an inductive load that is based on the modified relay feedback test (MRFT). Controllers tuned by the proposed method can produce near‐optimal dynamic performance for dc–ac VSCs without requiring knowledge of the plant's parameters. The controller consists of a PID cascaded with a digital notch filter. The tuning involves two steps. In the first step, the MRFT is used to tune the digital notch filter to compensate for the LCL resonance resulting from the LC filter's interaction with the inductive load. In the second step, one more MRFT is used to tune the PID controller using optimal tuning rules that are derived in advance (offline). The proposed optimal for the class of the dc–ac VSCs tuning rules can guarantee a specified phase margin and near optimal transient performance for any randomly picked VSC. The performance of the proposed tuning of the PID + notch filter is verified by simulations and experiments. The dynamic response of the auto‐tuned controller compares well to the response of a theoretically optimal but non‐auto‐tuned PID + notch filter designed using the full knowledge of the LC filter and the load. [ABSTRACT FROM AUTHOR]

Abstract This study considers a control problem related to the regulation of fractional‐order systems controlled by fractional order proportional‐integral‐derivative controllers (PIλDμ). The stability result of PIλDμ‐based control systems is provided, such that the closed‐loop systems can accomplish global stabilisation under some suitable conditions related to the system uncertainties. Finally, a simulation is demonstrated to verify the results.

Abstract This study proposes a generic mathematical modelling and decoupling fault‐tolerant vector control for dual three‐phase permanent magnet synchronous machine (PMSM) with one phase open based on the conventional dual three‐phase voltage source inverters, accounting for the mutual coupling between two sets of three‐phase windings and the second harmonic inductance. When the dual three‐phase PMSM has one phase open, the permanent flux‐linkages are asymmetric and there are second harmonic components in the conventional synchronous reference frame (dq‐frame). Based on the proposed mathematical modelling, both permanent magnet flux‐linkages and currents become DC values in the dq‐frame, and therefore, the conventional proportional integral (PI) controller can be used to regulate the dq‐axis currents. Then, a decoupling fault‐tolerant vector control with/without a dedicated feed‐forward compensation is proposed to validate the correctness of the proposed mathematical modelling. Experimental results on a prototype dual three‐phase PMSM with one phase open show that the second harmonic dq‐axis currents can be well suppressed simply by the conventional PI controller and dedicated feed‐forward compensation. It also shows that the decoupling fault‐tolerant control based on the proposed modelling and control method has excellent dynamic performance, which is equivalent to the vector space decomposition control for the healthy machine.

In this work, the authors are considering the problem of compensation of harmonic current absorbed by a non‐linear load from a three‐phase grid voltage. The objective is twofold: the first is to reduce cost and control complexity by avoiding proportional–integral regulators and optimising measurement instrumentation while ensuring inverter capacitor voltage self‐balance and the second is to provide a robust control strategy against power grid problems. Without measuring current and capacitor voltages, the proposed control strategy generates accurate control signals able to ensure flying capacitor inverter self‐balance and full compensation of harmonics whatever the grid voltage problem. In this regard, the robustness of the proposed control against power grid problem such as sag, swell, grid voltage unbalance, and frequency variation have been tested while proving its efficiency to compensate for harmonic currents and ensuring capacitor voltage natural balance even in transient regimes. During balanced and unbalanced loads, the proposed method has exhibited an excellent transient response, represented by capacitor voltages tracking to their reference in the presence of large variation in the load. Finally, effectiveness of the proposed control strategy is verified by numerical simulations as well as realistic experiments, and its merits are showed in comparison with other methods. [ABSTRACT FROM AUTHOR]

A combination of shunt active harmonic filter (SAHF), and adjustable power factor correction (PFC) capacitors is generally employed in industrial applications to achieve cost effective solution for the load compensation. It has been experienced that SAHFs operating in conjunction with PFC capacitors may lose their stability while compensating certain harmonic components which are near the resonant frequency of the network. This resonant frequency is not known beforehand while designing the controller of the SAHF, and further it keeps on varying with time as the value of PFC capacitors vary based on the reactive power requirement of the load. Therefore, the conventional controllers having predetermined values for gains fail to stabilise the operation of the SAHF under varying operating conditions of the network. This necessitates the involvement of an adaptive control mechanism within the SAHF with which the SAHF exhibits stable operation even under varying network conditions. In order to accomplish this requirement an artificial neural network‐based control scheme is proposed in this study. The proposed scheme is verified by conducting thorough simulation studies. The viability of the proposed scheme is also confirmed by carrying out detailed experimental studies on a laboratory prototype. [ABSTRACT FROM AUTHOR]

Good power quality cannot be achievedwithout the frequency stability of power systems. Nevertheless, with the large‐scale integration of highly flexible renewable energy sources (RESs) such as wind and solar energy, frequency stability is threatened by RES‐generated disturbances due to their volatility and intermittency especially in the very short time scale. Therefore, a new frequency control scheme should be designed to attenuate these highly time‐varying disturbances. In this study, load frequency control (LFC) considering flexible RES suppression is investigated. Inspired by the idea of disturbance estimation and compensation, a novel active disturbance rejection (ADR) scheme is proposed. Unlike previous ADR‐based LFC schemes, the proposed one can significantly reduce estimation errors via a novel extended state observer. Then a sliding mode control scheme is used to force the area control error to slide along the equilibrium, thus significantly attenuating the power imbalance. Simulation results show the effectiveness of the proposed schemes. [ABSTRACT FROM AUTHOR]

There is a consistent demand for reliable, efficient, small‐sized, and light weight power supply for electronics devices. To meet the aforesaid requirements, Quasi Resonant converters are being used due to low switching losses, high efficiency, small size and weight. With these motivations, in this paper, two different methodologies of passivity‐based controllers namely (EL‐PBC and PCH‐PBC) are proposed for Zero Voltage Switching Quasi Resonant (ZVS‐QR) boost converter to regulate the output voltage. First, the Euler‐Lagrange (EL) formulation is used to derive state‐space equations for ZVS‐QR boost converter under different operating modes and then, average state‐space model is developed using generalized state space average (GSSA) technique. In order to improve the dynamic performance of the ZVS‐QR boost converter, the aforesaid passivity‐based controllers are designed and its stability analysis is carried out. The entire system is developed with Sim Power System toolbox of MATLAB software and validated through OP‐5142 real time simulator. Steady state and dynamic performances are examined under several operating conditions. It is observed that the passivity‐based controllers of the paper achieve robustness against the uncertainties at the input and the load side. It is compared with benchmark PI controller as well. [ABSTRACT FROM AUTHOR]

This study is concerned on the design of a quasi‐linear parameter varying (qLPV) proportional–integral (PI) controller for twin rotor multiple‐input multiple‐output systems (TRMS). The non‐linear model is represented as a qLPV polytopic plant with an affine dependence on a non‐linear parametric function of the pitch angle. This representation retains the exact model as opposed to the conventional linearisation around an operating point. Due to the availability of the pitch angle measurement, the non‐linear parameter can be obtained in real‐time and the controller is designed using qLPV technique. To deal with limited control input for such systems, the proposed controller design also considers the actuator saturation that yields controller with practical gains without any additional gain bound criterion. Further, the transient tracking performance is also considered in the design by using closed‐loop eigenvalues assignment in desired damping regions. The control synthesis problem is formulated in the form of linear matrix inequalities for L2 gain based performance criterion. The designed controller is validated on a two‐degree of freedom helicopter experimental setup. Finally, to demonstrate the effectiveness of the proposed design, a comparative analysis is done with the existing algorithms. Also, the efficacy of the decentralised controller vis‐a‐vis the centralised one is presented. [ABSTRACT FROM AUTHOR]

The parameter perturbation of grid‐side equivalent inductance is a significant feature of the uncertainty in the single‐phase pulse‐width modulation rectifiers system for the electric locomotive. This characteristic tends to reduce the robustness of the rectifier system. This study handles these problems in the framework of the structured singular value, which helps to reduce the influence of model parameter perturbation, caused by measurement error and operation condition change, on the robustness. However, the conventional μ‐synthesis robust controls only reflect tracking and anti‐disturbance performance by weighting functions and ignoring the dynamic response performance. Herein, a direct current control (DCC) scheme based on improved μ‐synthesis is proposed. A desired closed‐loop transfer function is introduced to the conventional μ‐synthesis control structure to ameliorate the performance of the dynamic response. Furthermore, considering the external disturbances on the system control output, a suitable weighting function is used to restrict the external disturbance. The input–output relationship of the generalised open‐loop plant can thus be constructed accordingly. The proposed control scheme is compared with the widely applied proportional–integral‐based DCC scheme and the conventional μ‐synthesis DCC scheme. Hardware‐in‐the‐loop experiment results show promising dynamic performance as well as stronger robustness against parameter perturbation and external disturbances. [ABSTRACT FROM AUTHOR]

This study proposes a control technique based on integral switching surface sliding‐mode control for three‐phase pulse‐width modulation (PWM) rectifier. The proposed control system is based on the combination of a conventional proportional–integral (PI) controller and with two decoupled first‐order sliding‐mode (PI‐FOSM) current controller. A set of integral switching surfaces based on the state‐space equation are designed in the internal loop to force the grid currents to track their desired values. The proposed control approach improves the transient response and minimises the steady‐state error under uncertainty. In addition, a conventional PI controller is also employed for the voltage regulation loop and generating the current reference of inner loops. In the controller design, all parameters of the system are considered with bounded perturbations in the design of control law. The main advantage of the proposed controller is robustness property against variations of entertained PWM rectifier parameters and external disturbances. The proposed PI‐FOSM can improve transient performance and can decrease of the harmonic components under steady‐state condition. In order to validate the theoretical contributions of this study, the performance of the proposed controller has been investigated by using a prototype laboratory. [ABSTRACT FROM AUTHOR]

The contribution of power because of the nonconventional energy sources is enhancing day by day. This gives rise to power converter connected to the grid for an integration and to utilize the nonconventional energy sources economically and efficiently. However, this causes the distortion in the grid voltages and currents. All advanced high precision operating machines and measuring instruments are sensitive to the harmonics of the grid voltages. Therefore, this work illustrates an improved control to supress the grid voltage and current harmonics caused by an integration of non‐conventional energy source and nonlinear loads. An enhanced resonant two‐degree of freedom proportional–integral–derivative (ER‐2‐DOF‐PID) controller is used to extract fundamental components from load currents. It uses a resonant controller in shunt with PI controller to suppress the multi‐order harmonics and steady state error. A DC‐offset is used in parallel of this combination to suppress the sub‐order harmonics. To suppress the peak overshoot during the load transients and insolation changes, a 2‐DOF‐PID controller is used. The presented control is investigated by developing its model in MATLAB environment and this is validated on a prototype developed in the laboratory. The controller is modelled and investigated for stability analysis using a Bode mathematical tool.. [ABSTRACT FROM AUTHOR]

This study presents the optimisation of fractional‐order proportional–integral (FOPI) controllers for a bidirectional quasi‐Z‐source inverter (QZSI) in an electric vehicle (EV) off‐road application. An ant colony optimisation Nelder–Mead (ACO‐NM) algorithm is used for the optimisation of the controller parameters. This optimisation method is applied to enhance the performance of FOPI control for bidirectional QZSI. Ziegler–Nichols (ZN) with relay and the pole placement tuning method are also used for the FOPI controller design for comparison purposes. The modelling and the control design of bidirectional QZSI for an electric traction system are presented and discussed. Simulations are performed to verify the efficacy of the proposed controller structure with the bidirectional QZSI for two standardised driving cycles. The result shows that the FOPI controller designed with the ACO‐NM algorithm provides more suitable ageing performance index values for the battery. The ACO‐NM algorithm permits to reduce the root‐mean‐square value and the standard deviation by 2 and 5% of the battery current compared to the ZN tuning method and direct battery supply topology, respectively. The bidirectional QZSI with this type of controller can globally enhance the performance of EVs by optimising the electric power consumption and extending its driving range. [ABSTRACT FROM AUTHOR]

The capacitive current feedback active damping strategy has a limited damping region. When the grid‐side impedance is large, the digital control inductor–capacitor–inductor (LCL) grid‐connected inverter system with grid‐side current loop control and capacitive current feedback active damping cannot run stably. To address this issue, this study proposes an improved capacitive current feedback active damping strategy, namely the capacitive current fractional proportional–integral feedback strategy (CCFPIFS), which increases the upper‐frequency limit of the system damping region and approaches to the Nyquist sampling frequency. Furthermore, this study analyses the constraints of fractional‐order proportional–integral controller parameters to ensure the stability of the system. The simulation analysis is performed by Simulink. The experimental results are consistent with theoretical expectations. Consequently, the proposed CCFPIFS can not only achieve better control performance and improve the robustness of the LCL grid‐connected inverter system, but also improve the output power quality of the system. This damping strategy can make the LCL grid‐connected inverter system work stably under the environment of high grid impedance. [ABSTRACT FROM AUTHOR]

Processes including one or more integrators in their transfer functions can frequently be encountered in industry. In this study, integral–proportional–derivative (I‐PD) controllers are proposed to control these type of processes. Analytical and optimal tuning rules are derived to tune the I‐PD controllers for setpoint tracking of integrating plus first order plus dead time (IFOPDT) processes and double IFOPDT processes. Optimal tuning rules for setpoint tracking are achieved by minimising time moment weighted integral performance criteria. Obtained I‐PD tuning formulas are in terms of process' transfer function parameters, namely the gain, time delay and time constant. Simulation examples are given to demonstrate the use of the proposed method. Comparisons are provided to show the superior closed‐loop performance of the proposed approach than existing proportional–integral–derivative and I‐PD controller designing methods. In addition, the practical implementation of the proposed designing method is presented by controlling the position of a cart on an experimental setup. [ABSTRACT FROM AUTHOR]

This study reveals the energy shaping port‐controlled Hamiltonian passivity‐based control (PCH‐PBC) technique for an interleaved boost power factor correction (IBPFC) converter. First, the mathematical modelling of an IBPFC converter is developed under all possible operating modes. Then, the average state‐space model of the system is established with the help of averaging state‐space technique. Further, the PCH technique is applied for controller design and the stability analysis of the proposed system is carried out. A proportional‐integral (PI) controller is integrated with the PCH‐PBC controller to achieve minimum steady‐state errors. Finally, a Simulink model of the proposed system is developed using the Simulink toolbox of MATLAB software and its performances are studied under several operating conditions and verified through experimentation. To assess the system performance in terms of efficiency and input current total harmonic distortion (THD), the comparative study is also carried out under different controllers. Based on the simulation outcomes, the proposed controller is compared with the benchmark PI controller, adaptive passivity‐based controller in terms of different control parameters. The performances of the controller are also investigated against dynamic variations at the input voltage and the load. It is observed that the proposed PCH‐PBC controller achieves robustness against the aforesaid variations. [ABSTRACT FROM AUTHOR]

Renewable energy resources energy is widely collected from the natural resources of wind, photovoltaic, and geothermal heat energy. Generally, the hybrid system is affected by the unwanted power quality issues such as harmonics, voltage sag, and swell. The proportional resonant (PR) controller is optimised with an Elephant herding optimisation (EHO) algorithm to investigate the dynamic performance of buck–cuk power converters in hybrid renewable energy sources. The proposed power converter is used to regulate the level of voltages by controlling the switching pulse of the converter depending on the duty cycle ratio. An EHO algorithm is employed for tuning the PR controller gain parameters. In the grid side, shunt active power filters are integrated, and the inductor–capacitor–inductor filter is utilised for solving the overshoot and settling time problems. The total harmonic distortion (THD) and steady‐state error are reduced by the proposed technique. The proposed system is designed with the help of MATLAB/Simulink platform, and the output response is determined with the simulated results. The dynamic response of the proposed system is examined based on simulated outcomes, and THD comparison analysis is performed with the existing controllers such as proportional–derivative, proportional–integral–derivative, and fuzzy controller. [ABSTRACT FROM AUTHOR]

This study proposes a modified internal model control (IMC) structure in which an additional controller is added to the standard IMC structure to improve the closed‐loop system bandwidth. The resulting structure is evaluated to satisfy standard IMC objectives of nominal performance and robust stability. The novelty of the work is to design a fractional order (FO) filter in the IMC structure so that gain margin (Am) and phase margin (ϕm) specifications could be independently satisfied for a first‐order plus time delay (FOPTD) process control plant. The proposed modified IMC (m‐IMC) is simulated for three different FOPTD systems to validate and substantiate the theoretical analysis. The proposed m‐IMC is compared with different integer order as well as FO controllers. The transient performance are compared in terms of rise time (Tr), settling time (Ts), maximum overshoot (% Mp) and the effectiveness is measured in terms of integral square error. To validate the viability of the proposed control scheme, it is implemented on a laboratory DC servo‐system. [ABSTRACT FROM AUTHOR]

In this study, a new sampling strategy for networked control systems, called regular quantification with hysteresis (RQH), is proposed. This alternative presents some benefits with respect to symmetric‐send‐on‐delta sampling, which is one of the most used strategies in the event‐based proportional–integral–derivative (PID) control loops. The behaviour of the RQH is defined by two parameters, the signal quantification and hysteresis, whose effect on the overall system performance is studied and guidelines about its choice are given in terms of noise measurement and steady‐state error. The limit cycle oscillations that could be induced by this sampling strategy are studied and new robustness measures to avoid them are proposed based on the describing function approach. The suitability of some tuning rules for continuous PI when applied to control systems with a RQH sampling is evaluated using the proposed measures. The results show that these tuning rules can be applied under certain conditions. [ABSTRACT FROM AUTHOR]

A new approach is proposed here to control the two‐level three‐phase grid side converter. The proposed control strategy is an extended state observer (ESO)‐based adaptive control, consists of two cascaded control loops. The adaptive‐multi‐input multi‐output controller is employed in the inner control loop, which is used to regulate the active and reactive component of the grid currents. The outer‐loop consists of an adaptive controller augmented with an ESO to regulate the DC bus voltage. The goal of the proposed control strategy is to maintain a unity power factor while keeping the DC bus voltage constant under a sudden change in load demand at DC side, i.e. change in the resistive load connected across the DC bus. The proposed adaptive controller in the inner control loop does not require any information about the parameters associated with the grid filter (L‐filter), and hence, it is found to be more robust towards parametric variations. The ESO‐based adaptive controller is compared with the classical proportional–integral control in real‐time, and the comparison indicates that the proposed controller not only accomplishes a nearly flawless tracking performance but also delivers a complete robust performance against resistive load variation across the DC bus. [ABSTRACT FROM AUTHOR]

The hybridisation of two or more algorithms is recently emerging to detect superior solutions to the optimization troubles. In this study, a new hybrid cuckoo search algorithm and grey wolf optimiser (CSA–GWO) optimisation technique is exercised and exhibited to optimally design and tune the controller parameters installed in the voltage source converter (VSC) of an offshore wind farm (OWF). One of the widely used control strategies for VSC is the proportional–integral (PI) closed‐loop control system. The new hybrid optimisation algorithm is used to design and tune the PI controllers' parameters to improve the performance of OWF. It shall be mentioned that these parameters are usually hard to obtain owing to the high level of embedded non‐linearity in such energy systems. The performance of such optimally designed PI controllers is presented in both dynamic and transient conditions. To examine the realistic stability of the proposed algorithm, real wind speed pattern has been captured from Egypt wind farm at Zafarrana and simulated. The obtained results from this new hybrid optimisation CSA ‐GWO control system reflect its superiority over other traditional algorithms, such as genetic algorithm, especially during symmetrical and unsymmetrical faults. CSA–GWO algorithm was examined using MATLAB/Simulink. [ABSTRACT FROM AUTHOR]

This study proposes an optimal control scheme for a permanent‐magnet linear synchronous generator (PMLSG) using the state feedback control (SFC) method plus the grey wolf optimisation (GWO) algorithm. First, A novel state‐space model of linear PMLSG is established in order to obtain desired dynamics and enough power when used for the smooth wave energy. Second, the GWO algorithm is adopted to acquire weighting matrices Q and R in the process of optimising linear quadratic regulator (LQR). What is more, a penalty term is brought into the fitness index to reduce the overstrike of output voltage and keep the rate of work more stable. Finally, optimal LQR‐based SFC with and without penalty term and proportional‐integral (PI) controllers are compared both in simulations and in experiments. Results clearly prove that the proposed optimal control strategy performs a better response when compared to other strategies. [ABSTRACT FROM AUTHOR]

For low‐voltage autonomous microgrids, the essential goal is maintaining stable voltage and frequency throughout its network for the smooth operation of distributed loads. The other goal is to maintain proportionate power‐sharing between multiple sources connected through voltage source converters (VSCs). For the particular case of a heavily loaded microgrid, any further increase in demand poses new problems. The VSCs proximate to the loads may overshoot beyond its maximum ratings. Owing to which the stability of the power supply, as well as the longevity of VSCs, may get compromised. Also, these sources provide power under varying composite loading conditions comprising both linear and non‐linear loads resulting in unbalancing in its network. To overcome these problems, a decentralised fast terminal sliding mode control strategy for active power‐sharing between parallel VSCs has been proposed. A detailed mathematical model based on Lyapunov's stability theory‐based study is designed to establish the operating stability of the proposed controller. To validate the proposed control strategy, MATLAB‐based simulation results are provided for possible loading scenarios. A comparative study for performance evaluation between the proposed controller and a conventional proportional ‐integral‐based controller is further carried out. Finally, the performance of the proposed controller is also validated in real‐time scenario. [ABSTRACT FROM AUTHOR]

This research proposed the methods based on the neural network (NN) to build the digital twins (DT) of the inverter model. The proposed methods can be divided into two groups: firstly, an online tuner for the proportional–integral (PI) controller is formulated through backpropagation (BP) algorithm; and secondly an NN‐based identifier is used to approximate the non‐linear functional dynamics of the targeted control loop of the inverter. The design of PI tuner is based on the deviation between the output of the model and the reference output from measurement data. Then, according to the difference, the tuner can calculate the appropriate parameter of the current and voltage controller to track the dynamic behaviour of the reference model. The NN identifier is, however, to replicate the dynamic character of the reference model by NN which is initially trained offline with extensive test data and afterwards is applied to online tuning. In order to compare the advantages of the methods by NN with the traditional ones, the system identification and parameter estimation are also utilised to build the DT of inverter model. The performance of these methods will contribute to illustrating that NN identifier is effective in the building of DT. [ABSTRACT FROM AUTHOR]

This work proposes a design method for robust state feedback H∞ grid current controller applied to single‐phase grid‐connected photovoltaic (PV) systems. The proposed method achieved high system reliability even dealing with grid distorted voltages and other power quality issues. The robustness of the H∞ controller was verified in the face of parametric uncertainties at the first‐order output filter, and also a satisfactory disturbance rejection performance was achieved. The proposed design is based on linear matrix inequalities associated with constraints involving H∞ optimisation and a pole placement analysis on the continuous‐time domain. A discrete‐time analysis is also presented in order to indicate the simplicity of its implementation by a microcontroller or similar devices. Based on the presented results and in order to validate the proposed controller, its robust performance was compared with two linear and well‐known control methods: a classical PI controller, in terms of robustness; and a robust H∞ resonant controller, regarding the power quality at the connection point with the grid‐utility. Although the conclusions were listed regarding a low voltage PV grid‐interactive multilevel power converter, the proposed H∞ control design (and its concepts) can be applied to a great variety of renewable energy resources systems. [ABSTRACT FROM AUTHOR]

This study presents the quadratic boost converter (QBC) as a power electronic interface between the fuel cell (FC) stack and the DC bus of the FC vehicle (FCV). QBC provides the high voltage gain to interface the low voltage, high current and non‐linear FC stack to higher voltage DC bus of the proposed architecture. The output voltage of FC is variable and is a function of cell chemistry, load variations and atmospheric conditions. Therefore, a genetic algorithm assisted fixed frequency sliding mode controller (SMC) based two‐loop control strategy is proposed and developed in this study. The accuracy of the control signal generated by the SMC depends on the accuracy of reference current generation. Therefore, genetic algorithm tuned proportional–integral controller is proposed to generate the ripple‐free reference current generation which follows the load‐side or source‐side variations. Further, a control algorithm is integrated with SMC which uses the design constants such that the chattering amplitude is suppressed and generates the control signal with fixed frequency. Consequently, the dynamic performance of the proposed controller is compared in terms of the tracking error, control effort and sliding surface error. The extensive studies are carried out under different dynamic conditions to analyse the robustness of the proposed controller for QBC‐based FCV. [ABSTRACT FROM AUTHOR]

This study introduces two fractional‐order proportional–integral (FOPI) controllers optimised by harmony search (HS) optimisation algorithm, for direct power control of switched reluctance generator (SRG) through regulating the off‐delay angle of the generator. These two proposed FOPI controllers aim at improving the integration of SRG into the wind energy conversion system (WECS) through two control modes. The two control modes are maximum power point tracking during healthy operation with wind speed variation and fault ride‐through capability during faulty conditions. On the basis of the voltage magnitude at the point of common coupling between the SRG and grid, each mode, and consequently, the corresponding FOPI controller is activated. Comparison between FOPI controllers and classical PI controllers optimised by HS is introduced. Simulation results show the capability of the two modes of control proposed for improving the SRG‐WECS performance in both healthy and faulty operating conditions with the superiority of FOPI controller over conventional PI controllers. An experimental platform is built to show the adequacy of the proposed FOPI controller of SRG. [ABSTRACT FROM AUTHOR]

High‐performance current control is critical for obtaining smooth output torque in permanent‐magnet synchronous motors (PMSMs). To this end, a new proportional–integral (PI) tuning method based on multivariable sliding‐mode extremum seeking is proposed in this study and applied for current control of a PMSM. In the proposed method, a sliding‐mode extremum seeking optimiser varies the PI gains by minimising a cost function based on the feedback error term. The resulting PI controller can achieve fast and accurate tracking response, high disturbance rejection, and low sensitivity to PMSM parameter variations. The stability of the proposed control strategy is investigated through a Lyapunov analysis and its performance is evaluated through experimental studies. The results indicate that the proposed controller can offer improved performance in terms of accuracy, parametric variations, and load torque disturbances when compared with a conventional PI and a recently proposed PI controller using the gradient‐based extremum seeking tuning method. [ABSTRACT FROM AUTHOR]

Contribution of Photovoltaic (PV) systems is rapidly growing and great attention is given to the design of PV controllers to enhance both the performance of PV systems and the low voltage ride through (LVRT) capability during abnormal operational conditions. This article presents a novel application of the salp swarm algorithm (SSA) in order to optimally tune the PV controllers to enhance the LVRT of grid‐connected PV systems. Enhancement of LVRT is indicated in percentage undershoots or overshoots, settling time and steady‐state error of voltage response. A control strategy is applied to the DC‐DC converter to obtain a maximum power point tracking operation through a proportional‐integral (PI)‐based open fractional voltage control. The grid side inverter controls both the point of common coupling voltage and the DC‐link voltage through PI‐based cascaded‐voltage control. To get PI controller parameters that guarantee the optimum design of the controllers, the fitness function is optimized by using the SSA. The proposed optimal control scheme is tested under various fault scenarios and compared with other conventional optimization‐based PI controllers to examine its validity under PSCAD environment. The effectiveness of the optimal control scheme is verified by comparing the simulation results with the practical results of the PV system. [ABSTRACT FROM AUTHOR]

This article considers the robust control problem of non-linear magnetic levitation system with parameter uncertainties and external disturbance. To obtain a simple and practical controller that does not depend on the exact model information, a generalised-proportional-integral observer is constructed to estimate the velocity and disturbance. Then, based on mild assumptions and the estimated values, an output feedback tracking controller is proposed such that the reference position tracking task could be realised. The obtained control approach is confirmed strictly by theoretical analysis. Finally, simulation results are provided to show the effectiveness of the proposed control method.

In this study, a novel disturbance observer-based (DOB) [inline-formula] robust anti-disturbance tracking control problem is discussed for a kind of single-link flexible-joint manipulator with separate types of disturbances. On the one hand, a disturbance observer is imported to estimate the modelable disturbances. On the other hand, the introduction of [inline-formula] performance index optimises the impact of unmodelled disturbances on the system. A DOB proportional-integral control input is proposed such that the stability of single-link flexible-joint manipulator can be ensured. Furthermore, the satisfactory disturbance rejection and attenuation performance with [inline-formula] index can be obtained simultaneously. Finally, the simulation results verify this feasibility and effectiveness of the proposed control method.

The rail pressure control in diesel high-pressure common rail (HPCR) system is considered as one of the key issues for precise control of fuel injection. This study investigates the application of generalised proportional integral observer (GPIO)-based control in diesel HPCR system. Firstly, a non-linear mathematical model of HPCR system which uses the metering unit as the actuator is established based on hydromechanics under some proper simplifications. Secondly, a GPIO is developed to estimate the mismatched disturbance caused by the injection process. Then a composite controller combining GPIO and backstepping control method is designed. By introducing the disturbance estimations into the control design process, the disturbance rejection capability of the system is promisingly enhanced. The effectiveness of the proposed control method is validated by the simulation results.

This paper presents a cascaded closed-loop control of a five-phase induction motor (IM) drive system with common-mode voltage reduction capability. The outer loop uses standard PI regulators for speed reference tracking, while the inner control loop is implemented using a reduced order finite-state model-based current predictive approach. Establishing certain constraints, different combinations of switching state vectors are obtained, leading to the generation of different magnitudes of common-mode voltages. As a result, precise speed and current control is achieved in addition to the reduction of common-mode voltage and computational burden. Experimental results are presented to validate the concept.

Conventional automatic voltage regulator (AVR) schemes use thyristor-based rectifiers in which the generator field voltage is varied by changing the thyristor's firing angle. The conventional AVR has been known to cause voltage sags and extended under-voltages, especially under fault conditions. Several control schemes such as digital proportional–integral–derivative (PID) controllers, adaptive control schemes, and intelligent control schemes have been proposed in the literature. However, these schemes increase the complexity of the system. This work proposes a DC−DC converter-based AVR as an alternative to the rectifier-controlled AVR. The DC−DC converter is arranged in step-down (buck-type) configuration. The DC−DC converter uses metal-oxide-semiconductor field-effect transistor/insulated-gate bipolar transistors and has a faster response than the thyristors, thereby resulting in faster and precise control of the generator field voltage. The DC−DC converter is connected to the field circuit of the generator, and the terminal voltage of the generator is regulated by a PI controller by varying the converter duty cycle to control the generator field voltage. Simulation and experimental investigation has shown that the proposed scheme exhibits a better transient response and is robust under DC input voltage variation and generator load changes.

Switch reluctance motor is suitable for an electric vehicle driving system, which has the advantages of simple structure, high reliability of system and wide range of speed adjustment. In order to reduce the torque ripple of the system and improve the dynamic performance, a strategy of direct instantaneous torque control (DITC) based on a fractional-order proportion integration differentiation (PID) controller is proposed. According to the mathematical characteristics of the fractional-order controller, the form of the fractional-order speed loop controller is determined. Also, the parameters of the speed regulator are designed using the frequency-domain design theory of the control system. Then, the fractional-order controller is discretised. Compared with the traditional proportion integration (PI) controller, the fractional-order controller can have a better control effect. Simulation experimental results of the system show that the DITC control method has effectively reduced the torque ripple and the fractional-integral controller has reduced the overshoot and adjustment time and improved the robustness and disturbance resistance of the system.

High-voltage direct current (HVDC) techniques play an important role in the power transmission, especially for the distance district. For the HVDC, control system is necessary to the operation of flexible transmission system, so it is significant to research its control strategy. Normally, the traditional control method is proportional integral (PI) control under the dq frame system, but if the grid voltage is unbalanced, the traditional control method cannot reach the required aim. So the article proposed the full-order terminal sliding mode (TSM) control under the [inline-formula] frame system. In the proposed control strategy, the cross-coupled term of current in two-phase stationary reference frame is avoided; thus, the feed-forward decoupling is not needed and the whole control system becomes simple. At last, the proposed control strategy is simulated in PSCAD/EMEDC, and simulation results show that the proposed control strategy is correct and effective.

A control topology input-parallel–output-series converter system is investigated, which is suitable for high-voltage and high-output power applications. In this control method input current sharing (ICS) and output current sharing (OVS) taken into account. As observed, ICS is automatically attained as OVS sharing is controlled. In this design, two modules are connected in series, Module 1 provided variable voltage but in Module 2 by using three-level neutral-point-clamped converter and designing a comprehensive control feedback system, which regulates the DC voltages at the constant magnitude and constant frequency, helps to provide constant output voltages in the event of uncertain disturbance and load variation, A feedback double closed-loop control topology (inner current loop control and outer voltage loop control) with the combination of sliding mode control and a proportional–integral control method. A simulation model is built, by using MATLAB/Simulink, and the simulation results show excellent performance and feasibility of this system. This will be beneficial for research and improvement for the grid-connected converter.

The design of space vector control (SVC) systems suitable for flux‐weakening operation of permanent magnet brushless DC machines (PMBDCMs) is presented in this study. The proposed design approach enables overcoming the critical issues arising from the non‐linearities of PMBDCM voltage and torque equations; these issues derive from the trapezoidal shapes of back‐emfs and affect PMBDCM constraint management significantly. The SVCs presented in this study have been developed within two different synchronous reference frames, both of which enable distinguishing torque and demagnetising current components clearly. Therefore, reference torque current component is determined in accordance with PMBDCM torque demand, while reference demagnetising current component is computed through a voltage follower PI regulator, which processes the voltage deficit detected on the DC‐link. In this regard, a novel synchronous reference frame is proposed in this study, which improves PMBDCM constraint management and results into a wider constant‐power speed range, but at the cost of some torque ripple. The enhanced performances achievable by SVC approaches are highlighted by numerical simulations, which regard the comparison among the SVCs and an SVC with no flux‐weakening capability, at different operating conditions. [ABSTRACT FROM AUTHOR]

Speed controllers may be employed to provide safer along with more secure vehicles. They may also be used to minimise environmental pollution, e.g. speed controllers can be employed to track speed optimal velocity profile based on energy consumption minimisation. Consequently, accurate speed tracking is important. However, despite soft‐computing techniques have been proved successful in controller tuning, there is a limited amount of research on these techniques applied to speed controller optimisation. Therefore, this study performs a comparison study on PI cruise controller tuning for an off‐road electric vehicle. A cost function is designed to reach an accurate EV speed tracking while considering safety aspects, such as no reverse speed. The ACO‐NM algorithm has been demonstrated to be the most efficient compared to GA, ALO, DE, and PSO. Indeed, ACO‐NM reached high‐quality solutions for lower computational cost for three driving cycles. Moreover, contrary to the majority of published work on the subject, experimental validations have been carried out with the optimised PI cruise controllers. The experimental results have validated the ACO‐NM efficiency with a maximum overshoot average <10% for the hardest acceleration of the real driving cycle. [ABSTRACT FROM AUTHOR]

In two‐stage grid‐integrated photovoltaic (PV) system, usually a DC–DC converter is employed between the PV modules and the inverter. The dynamic interactions between the DC–DC converter, inverter, and the maximum power point tracking (MPPT) controller may affect the system performances. This study gives an integral procedure to design a stable sliding‐mode controller (SMC) based on fixed frequency equivalent control approach to improve the transient response of PV system and to track the reference voltage supplied by the voltage‐oriented MPPT controller in the presence of environmental and load perturbations and converter output sinusoidal perturbations imposed by the second harmonic of the grid frequency. The controller consists of fast current tracking inner current loop based on SMC law whose sliding surface is defined by the input capacitor and inductor current and outer PI controller maintains required PV voltage regulation. The superiority of the controller is validated at different operating conditions through PSIM software and its performance is compared with variable frequency hysteresis‐based SMC. To check the static and transient performances of the system, various experiments are conducted. The results obtained show very fast transient response in settling time and alleviation of chattering magnitude at various operating conditions. [ABSTRACT FROM AUTHOR]

Conventional automatic voltage regulator (AVR) schemes use thyristor-based rectifiers in which the generator field voltage is varied by changing the thyristor's firing angle. The conventional AVR has been known to cause voltage sags and extended under-voltages, especially under fault conditions. Several control schemes such as digital proportional–integral–derivative (PID) controllers, adaptive control schemes, and intelligent control schemes have been proposed in the literature. However, these schemes increase the complexity of the system. This work proposes a DC−DC converter-based AVR as an alternative to the rectifier-controlled AVR. The DC−DC converter is arranged in step-down (buck-type) configuration. The DC−DC converter uses metal-oxide-semiconductor field-effect transistor/insulated-gate bipolar transistors and has a faster response than the thyristors, thereby resulting in faster and precise control of the generator field voltage. The DC−DC converter is connected to the field circuit of the generator, and the terminal voltage of the generator is regulated by a PI controller by varying the converter duty cycle to control the generator field voltage. Simulation and experimental investigation has shown that the proposed scheme exhibits a better transient response and is robust under DC input voltage variation and generator load changes. [ABSTRACT FROM AUTHOR]

This paper presents a cascaded closed-loop control of a five-phase induction motor (IM) drive system with common-mode voltage reduction capability. The outer loop uses standard PI regulators for speed reference tracking, while the inner control loop is implemented using a reduced order finite-state model-based current predictive approach. Establishing certain constraints, different combinations of switching state vectors are obtained, leading to the generation of different magnitudes of common-mode voltages. As a result, precise speed and current control is achieved in addition to the reduction of common-mode voltage and computational burden. Experimental results are presented to validate the concept. [ABSTRACT FROM AUTHOR]

This paper presents the design of a non‐linear recurrent artificial neural network (ANN) based load frequency control (LFC) of a two‐area power system interconnected via HVDC tie‐line in parallel with EHVAC line. The control design is based on the combination of robust LFC and optimisation of recurrent ANN so that designed LFC scheme is suitable to handle the diverse operating conditions of power system. The various structures of the state cost weighting matrix (Q), i.e. controllability and observability aspects which affect the dynamics of the power system are used for the LFC design. The feedback gains achieved by the implementation of robust LFC using the different structures of Q are used to effectively train the recurrent ANN‐based LFC design and its performance is analysed with and without system non‐linearity's for 1% step load disturbance in one of the control areas to show the superiority of one design over the others. The closed‐loop system eigenvalues obtained for the system ensure the system stability. Furthermore, the recurrent ANN‐based LFC performance is evaluated for the diverse system operating conditions and compared with multi‐layer perceptron (MLP) ANN‐based and conventional PI control schemes to demonstrate the effectiveness of proposed LFC design scheme. [ABSTRACT FROM AUTHOR]

A dynamic output feedback (DOF) controller design is proposed for an indirect vector‐controlled induction motor (IVCIM). The proposed controller is an alternative to the conventional proportional integral (PI) one and can be used for improving the dynamic performance of the IVCIM system. A sequential design method is used in which, first, the inner‐loop controllers are designed. Then, the designed inner‐loop controller is employed to design the outer speed‐loop controller. The procedure incorporates the iron loss dynamics of the induction motor model to fetch the benefit of better performance than conventional controller designs neglecting the same. The DOF controller is designed in an H∞ control framework by solving the iterative linear matrix inequality that makes stator currents and speed response to be robust against load disturbances and parameter variations. A first‐order dynamic controller is tested to highlight its superiority over the PI controller. Comparison between the proposed dynamic and conventional PI controller is shown through several experimental results. It depicts enhanced performance by the proposed controller and suitability to industrial use. [ABSTRACT FROM AUTHOR]

One of the major issues in the operation of an islanded microgrid is the frequency deviations caused by the variation of power production coming from non‐dispatchable renewable energy sources. Using an appropriate control system may allow the system to deal with the frequency deviation and allow the system frequency to be restored to its rated value. A wide‐area system frequency controller sends a control signal to each of the dispatchable generating sources to enforce the frequency control by using communication channels. However, the communication channels are susceptible to the time delays, which affect the performance of the frequency control system and potentially the system security. Also, the system parameters are uncertain due to the error in the modelling, variation in network topology, generations, loads etc. This study proposes a robust proportional and integral (PI) system frequency controller based on Kharitonov theorem (KT) considering the time delay of the communication system and the system parametric uncertainties. Simulation results demonstrate that the KT‐based controller model has enhanced robustness compared to the conventional approaches of controller design. [ABSTRACT FROM AUTHOR]

This study proposes a fractional‐order (FO) improved fast terminal sliding mode controller for permanent‐magnet synchronous motor speed regulation system. By designing an FO proportional–integral controller for current loops, an FO model between reference q ‐axis current and speed output is proposed. By introducing an FO terminal sliding mode surface, a novel FO terminal sliding mode controller is designed for speed loop to improve the speed tracking performance. The proposed FO controller can make speed reach reference value in finite time. Moreover, it is proved that the control time of the FO sliding mode controller is shorter than integer‐order (IO) sliding mode controller. To further enhance the convergence speed, the fast terminal sliding mode control method is used. Meanwhile, FO disturbance observer is utilised to enhance the disturbance‐rejection ability. The control law of the proposed controller is designed according to Lyapunov stability theorem. Finally, Simulation and experimental results demonstrate the effectiveness, high control performance and high disturbance‐rejection ability of the proposed composite FO controller in comparison with IO controller. [ABSTRACT FROM AUTHOR]

The operation of variable speed wind turbine (VSWT) greatly affects the efficiency and quality of wind power generation. The conventional controllers are not able to improve VSWT performance in the presence of higher degree of non‐linearity, uncertain changes in wind speed, and coupling effects in the dynamical modelling. This study presents a controller design based on dynamic surface control (DSC) for a three‐bladed, horizontal axis VSWT. The DSC design provides the robust performance while considering the problem of irregularity of wind speed, extraction of maximum available power from the wind, and vibration effect due to tower dynamics. The boundedness and the convergence of the proposed control have been ensured through a formal proof, leading to minimum tracking error. A comparative evaluation of a VSWT performance from the proposed DSC scheme has been analysed with the performances using quantitative feedback theory control, standard wind turbine controller, and conventional proportional integral control. The simulation results confirm that the application of DSC control has effectively produced maximum power and least tracking error than the other three existing controllers, performing robustly in presence of parametric variations upto ±15% and external disturbances. [ABSTRACT FROM AUTHOR]

To utilise load‐side control for frequency regulation in transmission networks, the designed control schemes need to be granulated down to the subtransmission level as only aggregate loads are used on the transmission level. Moreover, due to a higher R/X ratio in subtransmission networks, the active power changes caused by frequency control will influence bus voltages. To achieve the required active power response and regulate bus voltages, a control scheme is proposed for subtransmission networks by adopting electric spring (ES) aggregators consisting of ESs and non‐critical loads. To implement the dual goals, the ES voltage of each ES aggregator is decoupled into d and q components. A distributed leader‐following consensus algorithm is adopted for ES aggregators to control its active power consumption by sharing information with neighbouring aggregators. The d component of the ES voltage is adjusted accordingly to provide the required active power cooperatively. To avoid the consequent voltage variation, decentralised proportional–integral (PI) control is adopted for ES aggregators to adjust the q component of the ES voltage accordingly. Simulation results show that ES aggregators manage to achieve the required coordinated active power response to regulate frequency and keep bus voltages within the acceptable region under the proposed control method. [ABSTRACT FROM AUTHOR]

In this Letter, a hybrid particle swarm optimisation and gravitational search algorithm (PSO–GSA) to tune the parameters of proportional–integral (PI) controller operating in cascade with sliding mode controller (SMC) is proposed for the design of Cuk converter for low‐voltage electric vehicle application. The PI controller in the outer loop regulates the voltage and SMC in the inner loop regulates the current of converter operating in continuous conduction mode. The main objective of Cuk converter with PSO–GSA tuned PI & SMC controller is to track the reference voltage amidst disturbances, and to reduce the performance indices such as integral absolute error (IAE) and integral time absolute error. Initially, PI controller was tuned using Routh Hurwitz and root locus method. Then to improve its steady‐state performance index, PSO–GSA technique is applied to tune the proportional and integral gains. To validate the effectiveness of the proposed scheme, the performance indices such as IAE, integral squared error was measured and compared. The results obtained reveal that IAE is reduced to minimal value and the solution converges at a faster rate with the proposed controller than the conventional control methods. Moreover, the stability analysis was carried out using the Lyapunov method of stability. [ABSTRACT FROM AUTHOR]

Hybrid distribution transformer (HDT) is a novel transformer that has a powerful control on grid current and load voltage, and it is significant for the construction of the smart grid. The load voltage control is the key part in HDT control system. Here, a load voltage control strategy based on fuzzy PI controller is proposed, since the traditional PI controller cannot achieve satisfying dynamic performance under the operation of grid voltage change. The fuzzy controller can respond faster than PI controller for the outputs that is only determined by inputs and independent with time, when the grid voltage rags or swells. While combining the fuzzy controller with the PI controller, the fuzzy control will cover the shortage of PI control in transient process and the PI control ensures that the static performance will not be affected. In the end, the simulation model of HDT is carried out, and the result shows that the load voltage can track the reference faster than the traditional PI controller, which improves the performance of voltage control system. [ABSTRACT FROM AUTHOR]