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According to the operating modes of three‐phase line‐voltage cascaded boost high power factor rectifier topology, the operating characteristics of the rectified output voltage of each module and the characteristics of the topology for automatically balancing the input current under the unbalanced grid are analyzed in this article. Based on the analysis to the unique feature, a simple dual‐loop PI control strategy in the rotating coordinate system is designed with no need to deal with the negative sequence component of grid voltage. In response to the issue of unbalanced DC‐link capacitor voltage of each module caused by unbalanced grid, injection of the zero‐sequence voltage component is adopted in the designed control system, which make the output power of each module be able to be independently regulated, so that the balancing control to the DC‐link capacitor voltage of each module is realized. At the same time, the three‐phase input currents always remain in balance automatically operating under unity power factor. Simulations and experiments have verified the superiority of the topology structure and the feasibility of the control strategy. [ABSTRACT FROM AUTHOR]

In this paper, taking into account the unidirectional conduction property of diodes, with an emphasis on the enhancement of system tolerance and robustness, a modified passivity-based control (PBC) method is introduced to three-phase cascaded unidirectional multilevel converters. This is the first time the PBC method has been utilized in cascaded unidirectional multilevel converters. This paper applies the PBC method to the current control loop and the overall DC bus voltage control loop. Meanwhile, considering that the classical PBC method regulates DC voltage with a steady-state error, the overall DC bus voltage is regulated via a combination of the PBC method and a PI controller to ensure zero-voltage tracking error. Moreover, the tolerance and robustness of the modified PBC method are verified by a theoretical analysis. Simulation results are furnished for assessing the correctness of the theoretical analysis, and the performance of the modified PBC method for three-phase cascaded unidirectional multilevel converters. [ABSTRACT FROM AUTHOR]

This paper presents studies of the four maximum power point tracking (MPPT) algorithms of a single-phase grid-connected photovoltaic (PV) inverter based on single loop voltage control (VC) and cascaded voltage and current control (CVCC). The purpose of this research was to evaluate four techniques for maximum power tracking control: (1) the Perturbation and Observation (P&O) MPPT&VC, (2) the Incremental Conductance (InC) MPPT&VC, (3) the P&O MPPT&CVCC and (4) the InC MPPT&CVCC. The MPPT efficiency values of each technique were affected by sudden changes in various irradiances. The CVCC was found to reduce the oscillating PV power and have a faster response time of MPPT from the PV array than the VC configuration. The InC MPPT&CVCC technique can track maximum power when irradiance changes rapidly. The simulation results showed that the InC MPPT&CVCC technique can decrease oscillation at a steady state around the set point and has a fast response time of MPPT, reduced electrical power ripple, and less power loss. The average efficiency of MPPT was 99.98%. [ABSTRACT FROM AUTHOR]

This work presents an automated design methodology for time-mode proportional and integral (PI) controllers aimed for an on-chip switched-capacitor (SC) dc/dc converter system. The basis of this design is the use of evolutionary optimization algorithms to find the near-optimal set of sizings for the time-mode PI controller. It is motivated due to the difficulty faced when tuning the controller parameters at a circuit level, which arise as a result of the presence of modeling inaccuracies and the small region for the linearized model where it is defined. Moreover, this design proposes the required modifications for the original design presented for the inductor-based dc/dc converter. These modifications are necessary to operate the SC dc/dc converter in slow switching limit (SSL). The addition of a pulse-width-modulated (PWM)-to-pulse frequency-modulated (PFM) conversion block is presented and elaborated in this article. The controller is codesigned using the differential evolution algorithm for the circuit level implementation to mitigate the issues prior mentioned. The optimized controller is then tested in a simulation environment using TSMC $0.18~\mu \text{m}$ technology. The results of the optimized controller were superior to those of a conventional controller. The optimized system achieved an overall efficiency of 79.1%. [ABSTRACT FROM AUTHOR]

In the operation of battery energy storage systems (BESSs) based on the cascaded H-bridge (CHB) converters, it is desirable to balance the state of charge (SoC) among the submodules (SMs) within each phase arm. However, there are constraints on the active power distribution among the SMs that intend to balance the SoC. For instance, each SM in a practical system is designed with a specific power rating and can be damaged if it is exceeded. Therefore, a novel rule-based method is proposed in this article to achieve a fast SoC balancing, while respecting the power constraints of the SMs. The proposed method is general and readily applicable to hybrid BESSs, where the SMs are integrated with heterogeneous energy storage. Experimental results are obtained to verify the effectiveness of the proposed algorithm and to compare its performance with respect to existing methods. [ABSTRACT FROM AUTHOR]

Globally,wind power plants (WPPs) installations are dramatically increasing, leading to a large-scale integration into the power grids. Huge endeavors are devoted to achieving an efficient operation of WPPs. This paper offers a novel chaotic-billiards optimizer (C-BO) algorithm to properly design the fuzzy logic control (FLC) strategy for stability enhancement of grid-integrated WPPs. The C-BO algorithm has distinct features such as simple construction, low numbers of parameters required to design, high convergence speed, and low computational burden. The permanent-magnet synchronous generator (PMSG)-based WPP is interlinked into the electric power grid through power converters. A cascaded FLC approach, which is optimally fine-tuned by the C-BO, is offered as the control methodology for these converters. The C-BO algorithm fine-tunes the gain factors of multiple FLCs at a rapid convergence speed. A simulation-based optimization approach is applied, in which the integrated square error criterion is chosen as an objective function. For the sake of preciseness, the PMSG-based WPP is connected to the IEEE 39-bus New England test system. The effectiveness of the optimal FLC using the C-BO algorithm is compared with that achieved using the water cycle algorithm-based optimal FLC, the genetic algorithm-based optimal FLC, and the marine predator algorithm-based optimal proportional-integral controller, taking into account severe grid disturbances. Moreover, real wind speed measured data captured from Zaafarana Station in Egypt are extensively performed in the system studies. The validity of the offered control approach is widely verified by the simulation analyses using the MATLAB/Simulink environment. [ABSTRACT FROM AUTHOR]

The proportional-integral (PI) control method is long well-known because of its simplicity as well as effectiveness. Although the PI control method overwhelmingly dominates engineering applications, the issue of developing a general PI control for nonlinear systems remains open. This article considers the PI control problem for a family of unknown nonlinear systems. A structurally simple and computationally inexpensive PI-type control approach with constant gains is provided to solve the problem, which maintains preassigned transient as well as steady-state performance and guarantees the global stability of closed-loop systems. The key to possessing such properties comes down to the transformation and modification of tracking errors. The effectiveness of the presented control approach is assessed via the experiment on a pneumatic artificial muscle, and the results corroborate the theoretical findings. [ABSTRACT FROM AUTHOR]

Since current controllers are implemented digitally, digital current controllers need to be established for pursuing high performance alternating current (ac) machine drives. Considering to enhance the dynamic response, disturbance rejection and stability both, this article proposes a simple three-degree-of-freedom (3DOF) digital current controller. In the proposed structure, three needed coefficients have been theoretically designed, which stand for the dynamic response ability, disturbance rejection, and rejection of the instability caused by machine parameters mismatch, respectively. In addition, the proposed 3DOF current controller can own dead beat response characteristic with one-step delay compensation. Experimental results validate the effectiveness of the proposed 3DOF digital current controller in a ac machine drive test rig. [ABSTRACT FROM AUTHOR]

Vector control plays a critical role in a permanent magnet synchronous motor (PMSM) drive to deliver the desired torque in electrified vehicle applications. Motor speed and stator current control depend on various nonlinear motor parameters that influence the performance of PMSM. Moreover, tuning of speed and current controller parameters using conventional control techniques also depends on these PMSM parameters. To enhance the robustness of vector control and tracking methodology against PMSM parameter uncertainties and load disturbances, a novel deep reinforcement learning (DRL) based advanced speed and current control technique is proposed in this article. The proposed method mitigates the effects of disturbance due to parameter variations as well as the load torque. The novel architecture delivers closed-loop reinforcement learning agents trained with the deep deterministic policy gradient learning algorithm in the plant environment where the cost of exploration is expensive. First, an overview and need for the proposed DRL vector control architecture are provided. Subsequently, the design and training methods for the proposed DRL controller are elicited. Thereafter, the proposed control scheme is validated with real-time software-in-the-loop testing under various conditions and compared against adaptive proportional–integral control of the same PMSM in OPAL-RT simulator. [ABSTRACT FROM AUTHOR]

High dynamic performance is an essential requirement for the dual-active-bridge (DAB) dc/dc converters. As dc voltage sources, they should maintain the desired output voltage instantly under all working conditions. However, the previous literature mainly focus on the dynamic control of the voltage-fed DAB converters, and the existing control schemes for the current-fed DAB converters achieve limited dynamic performance. Aiming at improving the dynamic performance, a direct actual-power control (DAPC) scheme based on virtual impedance estimation (VIE) is proposed for the current-fed DAB converters in this article. The proposed DAPC scheme is based on a parallel structure instead of the series structure of existing control schemes, and it realizes fast dynamic control through combining actual power control with the VIE method. The proposed DAPC scheme can obtain the fastest transient response for the output voltage without voltage overshoot in transient conditions, such as load step change, input voltage fluctuation, and the desired output voltage step change. Besides, a leakage inductor precharging method is integrated into the DAPC scheme to avoid the current mismatching. Finally, the proposed DAPC schemes are compared with two existing control schemes and tested in a scale-down experimental prototype. Experimental results verify the effectiveness of the proposed DAPC scheme. [ABSTRACT FROM AUTHOR]

In this article, the control of hybrid off-grid configuration based on a variable-speed diesel generator and solar photovoltaic array, is implemented. To ensure a stable operation with the ac voltages and system frequency regulation, back-to-back connected converters are controlled using vector-based control, and stator flux-oriented frame-based control. To adjust the speed of diesel engine according to specific fuel consumption, an effective control strategy is developed. In addition, to compensate for the slow dynamics of variable speed operation and to balance the power in the system the dc-link voltage and battery current are controlled using a double-loop control strategy. Furthermore, the dynamic model of the dc–dc boost converter is integrated with the perturbation and observation method for obtaining smooth and efficient maximum power point tracking (MPPT). To prevent overshoots during the sudden transition, all proportional-integral controllers are reinforced with a back-calculation antiwindup scheme. The performance is obtained using MATLAB/Simulink and validated on real-time hardware to demonstrate the effectiveness of coordinated control under variations of loading and weather conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a unified active power filter (UAPF), which control the current Total Harmonic Distortion (THD) in low voltage distribution networks. The UAPF strategy implements photovoltaic (PV) generation as its source and uses a boost power converter. The IEEE 13-bar system is the test-bench, and a nonlinear load is in the 7th busbar. Thus, the results are based on the voltage, current and THD behavior in the system. The current (THDi) and voltage (THDv) harmonics reduces significatively. Where the 7th busbar THDi initially has a 13.5 percent, and after the implementation it went 6 percent, while the THDv started from 14 to 3 percent. Those resulted values are within the allowed limits in IEEE 1159 standards and resolution No. ARCERNNR -017/2020. [ABSTRACT FROM AUTHOR]

In a typical wireless power transfer (WPT) system, the load, the mutual inductance, and the required tuning frequency can vary in a particular range. Variation of each parameter can substantially impact the dynamic characteristics of the system. Thus, they can be considered as sources of uncertainty in the system. To address this, robust control methods such as μ-synthesis are developed to deal with possible system uncertainties. This article first undertakes the generic dynamic analysis of the series–series WPT compensation network for two modes of operation, i.e., constant output voltage (COV) mode and constant output current (COC) mode, in the presence of three aforementioned uncertainty sources. Subsequently, the frequency detuning as a function of the compensation capacitor variation is explored and broadened as a technique to obtain the optimized compensation capacitor value that can lead to a plant with minimized dynamic deviations from its nominal system in the operating range between COC and COV modes. As such, this approach offers a design procedure for a least conservative robust controller, which can significantly improve the system performance. The optimized structure and the corresponding designed μ-synthesis controller are comprehensively elaborated. The theoretical achievements and experimental results show superior dynamic performance of the optimized structure and the corresponding designed controller in the presence of three uncertainty sources compared to the COC and COV modes of operation. [ABSTRACT FROM AUTHOR]

In this article, a novel cascade model-predictive control for a three-phase unity power factor rectifier is presented. Unlike the traditional control techniques for rectifiers, the proposed method uses a cascade dual-model-predictive control for the inner and outer control loops. The three-phase currents of the rectifier are controlled with the inner control loop, while the desired output voltage is achieved with the outer control loop. In this proposal, the output power is used as a feedforward to enhance the transient dynamics of the output dc voltage. Several advantages can be highlighted such as a fixed switching frequency, and output voltage variations are avoided when a sudden change in the load or a voltage sag appears. The overall control proposal has been fully integrated into a digital signal processor. Selected experimental results are introduced to validate the theoretical contributions of this article. [ABSTRACT FROM AUTHOR]

In this paper, it is identified that unstable weak grid connection of voltage source inverters (VSIs) is dominantly caused by the current control. In particular, it is found the proportional gain $ k_p$ of conventional PI controller cannot balance the grid voltage impact and damping capability especially when a very weak grid with short circuit ratio (SCR) $ < $ 1.3 is connected. This issue is solved in this paper by simply restructuring the PI controller as an IP controller for current control. This IP controller will not change the tuning method of current control and make this VSI indeed connect to a very weak grid with rated power injection. [ABSTRACT FROM AUTHOR]

This article presents a new control strategy merging a sliding mode control (SMC) with a linear extended state observer (LESO) to regulate the output voltage of the buck–boost power converter system affected by matched and mismatched disturbances. The SMC–LESO schema uses the input–output linearization approach and the equivalent control method to determine the boundary layer around the sliding surface. This boundary layer depends on the sliding surface and the equivalent control value, depending on the estimated variables obtained through a LESO. With this schema, the unknown matched, and mismatched disturbances are observed and compensated by an adaptation of the SMC. The proposed approach minimizes the sliding surface chattering and improves the performance against sudden static and dynamic load changes as well as voltage variations on the power supply input. An experimental comparison with traditional sliding mode control and classical proportional–integral–derivative control is performed, confirming the proposal's effectiveness. The closed-loop stability (observer-controller-plant) is guaranteed in the input-to-state stability framework. [ABSTRACT FROM AUTHOR]

Fault characteristics analysis normally provides a theoretical foundation for the protection design. Although conventional fault analysis of inverter-interfaced renewable energy sources (IIRESs) can characterize post-fault steady-state at the power frequency, it might not effectively present the fault transient. This can negatively affect the protection based on fault transient data within 20–30 ms after a grid fault. Thus, the fault transient of IIRESs needs to be fully investigated. Given this, the nonlinear effect of controller saturation is considered in this study. The domain of attraction (DOA) is first established to estimate the practical working state of the controller within the current loop. The transient fault current (TFC) analytical model is then proposed in accordance with the nonlinear control response of the controller under different working stages, which reveals a detailed transient transition of the fault current. Meanwhile, the proposed model is low-order and presents high applicability in different fault scenarios. Simulation results indicate that the TFC analytical accuracy obtained using the proposed method is improved by at most 50% relative to the accuracy reported in published studies. Field short-circuit test data are ultimately used to verify the performance of the proposed TFC analytical model. [ABSTRACT FROM AUTHOR]

This article presents the analysis and implementation of a predictive control method for dc-link regulation and voltage balance in a cascaded modular reduced dc-link solid-state transformer (SST). Passive components like bulky dc links limit the power density of power converters, especially medium-voltage (MV) SST. Reduced dc-link or low-inertia converters can dramatically reduce the size, cost, and weight by tolerating larger dc-link ripples and improve the reliability with electrolytic capacitor-less dc link. However, a small dc link leads to tight coupling between the input and the output stages, which is a challenge for control design. In stacked low-inertia converters (SLIC), the low-inertia converter modules are stacked for MV applications, resulting in coupling between the modules and making the control more challenging. A new model predictive control method that can achieve deadbeat regulation on the dc link without weighting factors has been proposed to address this novel problem. This article focuses on analyzing the condition of the low-inertia dc link up to 80% ripple, the robustness of the control under parameter mismatches, high-order terms, and important implementation issues, such as model-based sampling and computation delay compensation. Significantly, the high-order terms are introduced because of the large dc-link ripple. These high-order terms are unique to the SLIC and negligible in conventional high-inertia converters. A discrete-time large-signal model is built to capture the dc-link's nonlinear dynamics, and the eigenvalues of a small-signal Jacobian matrix are analyzed with Floquet theory to evaluate stability, using the modular soft-switching SST (M-S4T) as an example of the SLIC. Simulation and experimental results of an MVDC M-S4T verify the analysis and the predictive control method. Finally, the general application of the predictive control to low-inertia converters is compared against a conventional PI controller using a reduced dc-link active-front-end rectifier as an example. [ABSTRACT FROM AUTHOR]

With the feedback rotor speed outer-loop PI control, the mechanism analysis of SMES-based power oscillation damping is derived by the small signal and classical electric torque method in this research. Theoretical analysis shows that adjusting the proportional and integral can equivalently dominate the damping ability and synchronization level. However, the conventional PI may cause the deep charging-discharging so that the power oscillation damping failure. To this end, the proportional integral controller with integral alleviation (PI-IA) controller is designed to address this issue, which not only ensures energy deviation-free of SMES, but also holds the advantage of PI controller. Moreover, the effectiveness of the proposed controller and the validity of the mechanism analysis are performed by the time-domain simulation. [ABSTRACT FROM AUTHOR]

DC-link voltage control is a key issue for the reliable operation of hybrid distribution transformers (HDTs). This article uncovers the basic power flow principle of HDT based on the established dynamic power balance equations and the proposed power flow diagrams. Based on the derived differential equations and the transfer function models, the dc-link voltage control system with PI controller is developed. With the pure PI controller, the grid currents distortion and asymmetry cannot be well eliminated. To address this, an improved controller that includes a low-pass filter and three notch filters is designed. A disturbance feedforward loop is integrated into the improved controller, thus formulating a novel controller. This novel controller not only controls the dc-link voltage and grid currents with better dynamic performance but also eliminates distortion and asymmetry. Simulation and experiment results verify the correctness of the analyses and proposed methods. [ABSTRACT FROM AUTHOR]

In DC microgrids, constant power loads (CPLs) reduce the effective damping of the DC-DC converter and may induce destabilizing effects into the DC-DC converter. To overcome such problems regarding CPL and ensure large-signal stability of DC-DC converters in DC microgrids, some feedforward terms are added to $V$ - $I$ droop-based dual-loop controller for a DC-DC converter based on the large-signal model. It is proven that the feedforward terms can not only improve the transient response but also guarantee the exponential stability of the closed-loop system in the whole operating range in regards to a large-signal manner, which is verified by using a singular perturbation model. Moreover, a disturbance observer is designed to estimate the output current, thereby enabling the removal of the current measurement sensor. The proposed technique can be easily plugged into a pre-defined $V$ - $I$ droop-based dual-loop controller without an additional sensor being required. Ultimately, both simulation and experimental tests verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, a novel distributed active power control method for interlinking converters (ICs) in an islanded hybrid ac/dc microgrid (IHMG) is proposed. The goal is to implement power sharing among all distributed generators (DGs) in an IHMG and among the ICs in a distributed manner, without the need for additional proportional-integral controllers. A mathematical formula for the active power references of the ICs is derived to achieve these objectives. Then, an estimator providing the data required for the reference calculation is proposed based on the modified dynamic consensus algorithm. In addition, a unified state-space model is derived for the entire IHMG, including the cyber-physical interactions, and a design method is presented for the parameters of the estimator. Finally, the effectiveness of the proposed method is verified by performing small-signal analysis and controller-hardware-in-the-loop verification. Compared to a previous distributed control method, the proposed method significantly improves the robustness in terms of communication delay and variation in the status of DGs while achieving the objectives. [ABSTRACT FROM AUTHOR]

The tracking of power in solar PV systems depends on controlling the voltage or current to the optimum level irrespective of changes in solar irradiation. There are two aspects of maximum power point tracking (MPPT), first is to control the voltage or current and second is to find the peak power with an algorithm. This work deals with both the aspects, using current control which provides fast control response and a momentum-based MPPT algorithm for improved peak tracking. Since current programmed control gives a simple implementation and fast response of converters, it would seem obvious to link it with current referenced MPPT but this method is prone to fail when irradiation drops suddenly, leading to control loss. Voltage oriented MPPT control (which has logarithmic dependance on irradiation), with an inner current control loop is used, as it maintains control even with step changes in irradiation. The second part of this work discusses the perturb and observe (hill climbing) algorithm for finding the power peak, which is known for its simple and effective implementation. A simple modification of this algorithm by adding momentum to the hill climbing is shown to improve the speed of tracking while maintaining the oscillations around maximum power point to acceptable levels. [ABSTRACT FROM AUTHOR]

In a dc microgrid, several batteries with their converters are controlled to share the bus deficient/excessive power among themselves. A battery management system is required to improve the reliability and appropriate power-sharing. A novel control strategy is proposed in this article that ensures power sharing among the various batteries in accordance with their power rating and state of charge (SOC). In the proposed scheme, a common time reference (Tref) is generated using the conventional dc-bus voltage control loop and SOC information of the batteries with the help of communication. An attractive feature of the proposed scheme is that it does not depend on output current of the converters. Voltage regulation is also maintained within limits in case of wide deviation in the converter output voltage at interfacing point by monitoring and using corrective measures. A low-speed communication is sufficient to convey the reference time to the controllers of the batteries. The batteries are charged or discharged in the same time interval irrespective of the initial SOC, which significantly increases their life and performance. The proposed system is more reliable as it is tolerant to various fault scenarios. All the analytical, simulation and experimental results are presented. [ABSTRACT FROM AUTHOR]

As the output power of wind farm is fluctuating, it is one of the important ways to improve the schedule ability of wind power generation to predict the output power of wind farm. The operation mode of tracking planned output takes the planned value issued by the grid dispatching as the control basis of wind power generation. This operation mode is easy to control, which not only meets the needs of power grid dispatching, but also improves the reliability and controllability of new energy generation. This paper introduces the traditional PI control strategy of SMES and combines the advantages of SMES and the characteristics of application scenarios, and introduces sliding mode variable structure control into SMES. Through simulation and comparison of two different control modes, it is verified that SMES adopting sliding mode variable structure control have the advantages of fast response speed and strong robustness, which can make the wind farm output stable power according to the planned value. [ABSTRACT FROM AUTHOR]

This article presents an implementation of a fast and accurate control strategy for a synchronous generator driven by a diesel engine and a two-stage solar photovoltaic (PV) with a battery storage-based microgrid (MG) system. This MG feeds active power from a solar PV array to the distribution network by operating it at its maximum power point (MPP). The MPP of the solar PV array is estimated by using an incremental conductance control. An adaptive control of volterra least mean square/fourth (VLMS/F) is applied to an islanded hybrid MG to control the power converter that is interconnecting dc sources to the ac system, to improve various power quality indices such as harmonics suppression, compensation of reactive power, balancing of output currents from the diesel generator set, and neutral current compensation in a three-phase four-wire system. The simulation and experimental investigations of the developed MG show the performance superiority of the VLMS/F control strategy over the conventional controls. [ABSTRACT FROM AUTHOR]

This article highlights a voltage instability when the bidirectional interlinking converter (BIC) of a hybrid ac–dc microgrid operates as a constant power load (CPL). The instability is attributed to the impedance interactions seen at the dc port of the BIC. The BIC is operated with two different controllers, viz., a PI controller and a model predictive controller (MPC). In order to avert the instability, prohibiting impedance interactions is proposed as a design objective while determining the bandwidth of the PI controller. However, since a flexible control over bandwidth is not available with MPC, an active damping technique is proposed to address the instability. The proposed technique works equally well for the PI controllers with fixed or predetermined bandwidths. An important feature of the proposed technique is that it does not interfere with the original objectives of the controllers, once the instability is addressed. The technique comprises only one tuning factor, which does not depend on the BIC's internal parameters. As a result, it can easily be implemented as a general stabilizing scheme in any BIC. The efficacy of the proposed technique is verified through simulations, frequency-domain impedance analyses as well as experiments on a laboratory prototype of the BIC. [ABSTRACT FROM AUTHOR]

This paper investigates the Multilevel Current Source Converter (MCSC) STATCOM. It proposes a new method of modulation. The new modulation method produces less THD and di/dt at the terminals of the MCSC STATCOM when compared to the widely used Phase-Shifted Carrier SPWM (PSC-SPWM). To ensure the inductors' currents remain balanced, a Current Balancing Algorithm (CBA) is presented. The CBA does not require any controls. It relies on assigning optimum switching states to each CSC module in real-time. In addition, two control strategies are presented in this paper. The first one assumes the STATCOM to be a SISO. Therefore, it only requires one PI controller. However, the gains for the controller must be changed if the STATCOM was to transition from capacitive mode to inductive mode, or vice versa. The second control strategy overcomes this problem by implementing a TITO integral state feedback controller. The contributions of this paper are validated via simulation and experimental results. [ABSTRACT FROM AUTHOR]

In permanent-magnet synchronous motor (PMSM), the winding current consists of different orders of harmonics due to the manufacture error, deadtime, and disturbances. This article proposes a winding current harmonic suppression method for PMSM by reducing the dominant fifth- and seventh-order current ripples. First, with reference frame transformation, the fifth- and seventh-order current ripples convert to sixth-order ripples in the synchronous reference frame (SRF). Then, with further transformation, these sixth-order ripples turn to dc signals. Next, the type-II Chebyshev filter is designed to extract these dc signals. Also, the proportional–integral (PI) controller is adopted to generate the current harmonic control voltage, which is setting the dc current harmonic signals reference to be zero. Finally, the current harmonic control voltage is compensated to the voltage reference in the SRF. Both the simulation and experimental results are presented to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article presents control strategies developed with two-level coordinated and double loop control for a standalone microgrid. The interfacing inverter is controlled to perform multifunctions. It incorporates the compensation for power quality problems at the point of common coupling and controls the voltage and frequency deviation to provide a constant voltage and frequency to connected ac loads in standalone and grid-connected operating modes. The power demand during battery charging and discharging is controlled using a buck–boost converter. To control overshoot and settling time while following a dc and sinusoidal references without losing control during the transition, proportional-integral, and proportional-resonant controllers with optimal gain designs are reinforced by antiwindup feedback. To ensure a soft and secure transition, even under disturbances, such as distortions and notches, an enhanced phase-locked loop is used. The performance of this system is simulated in MATLAB and validated on a 2-kW laboratory prototype. [ABSTRACT FROM AUTHOR]

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]

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 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]

This study confers a novel approach towards fuzzy‐PI (proportional–integral) controlled pulse width modulation (PWM) controlled permanent magnet synchronous motor (PMSM) drive operated through a conventional voltage source inverter (VSI) supplemented with buck‐converter fed current source inverter (CSI). It is observed that in a PWM controlled VSI, output voltage and current obtained contains certain harmonic distortion. A buck‐converter fed CSI is capable of minimising the voltage and current ripples prominently even with the application of PWM. Thereby, in this study, an economic, as well as robust design procedure for the buck converter, fed CSI is proposed. Moreover, a particle swarm optimisation (PSO) mechanism is introduced to optimise the performance of the proposed fuzzy logic controller. Additionally, an over‐current protection scheme of the PMSM motor is proposed. The performance of a PMSM drive is analysed in MATLAB/SIMULINK platform. Furthermore, the proposed concept is tested and verified in a real‐time test‐bench developed in the laboratory. Finally, from the performed test conditions, it can be confirmed that the proposed current control strategy of the drive system shows excellent performance in various operating conditions and can be employed in light‐weight electric vehicles. [ABSTRACT FROM AUTHOR]

In a photovoltaic array (PVA) tied grid system, PVA and the grid are connected at AC bus (ACB) to feed the power to the grid and the load connected locally at the ACB. The photovoltaic energy conversion system (PVECS) requires an improved dynamic controller to control the grid voltage harmonics under variable solar power and nonlinear unbalanced load conditions. The conventional filtering controllers are unable to remove the sub‐harmonics and DC‐offset in the input signal. Moreover, their attenuation for the dominant lower order harmonics is unsatisfactory for unbalanced loading conditions and highly nonlinear loads. A MMLSTOGI (mixed multi‐level second and third order generalized integrator) based control is used in this work. It effectively mitigates the dominant lower‐order harmonics and the DC‐offset of load currents and extracts their in‐phase and quadrature‐phase fundamental components (FCs). The PVA is connected at ACB through interfacing voltage source converter (VSC). The DC‐link voltage is ascertained by generating its reference value using an incremental conductance (InC) based maximum power point tracking. The PVA power is feed‐forwarded in the control to enhance the dynamics of the system. The control is validated on a developed model in MATLAB SIMULINK background, and using a developed prototype. [ABSTRACT FROM AUTHOR]

A voltage-controlled canonical switching cell-derived DC–DC converter with improved power quality feeding a variable speed permanent magnet brushless direct current (PMBLDC) motor-drive system for home appliances, is presented in this study. The converter is operating in the continuous conduction mode (CCM). This converter has less stress on the converter devices due to CCM of operation. A single converter is used for both the power factor correction (PFC) and the speed control of the drive, thus reducing the number of elements in the system. The speed control, along with PFC in this system is achieved via a PI controller having speed reference as an input. This system is capable of providing the low speed to rated speed operation while maintaining a unity power factor. The Hall-effect sensor-based electronic commutation of a PMBLDC motor-drive is implemented at the fundamental frequency. This significantly improves efficiency by reducing the switching losses of the voltage source inverter. A prototype of it is developed in the laboratory for implementation of the scheme. Simulated and real-time experimental results of the scheme are presented here for performance validation at various dynamic and steady-state operating conditions. [ABSTRACT FROM AUTHOR]

Hybrid distribution transformer (HDT) is a promising device for constructing the future active distribution network. To overcome the limitations of the existing HDT control schemes, a compound control scheme is proposed for an HDT with improved circuit design. In this design, the voltage source converter (VSC) for low-voltage side voltage regulation is moved to the medium-voltage side. The compound control scheme is developed based on the dynamic model of this new HDT, which explicitly considers the external disturbances. In this control scheme, two compound controllers are established to regulate the grid current and load voltage, respectively. For each compound controller, feedforward loops are integrated with the PI regulator, thus suppressing the disturbances. The key feature of this control scheme is that, by using the feedforward loops, the effect of external step disturbance can be equivalently weaken to an impulse disturbance and, hence, the system robustness can be improved. Simulation and experimental results validate the effectiveness of the proposed control scheme. [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]

In this study, the current mode control strategy for a Cuk converter assisted self‐excited induction generator‐based wind energy conversion system (WECS) for DC nanogrid is proposed. The sliding mode controller (SMC) is a non‐linear controller and, is preferred because of good static and dynamic response for input ‐output disturbance rejections. However, the knowledge of all the state variables is required, which increases the number of sensors and control complexity. To reduce the number of sensors, reduced‐order SMC (ROSMC) can be implemented. Conventionally design of the voltage loop in ROSMC does not consider the uncertainty of the control parameter. However, the accuracy of the control signal generated by the ROSMC also depends on how accurately the reference current is generated. Therefore, a genetic algorithm tuned PI controller is proposed to generate the ripple‐free reference current. Artificial intelligence assisted ROSMC (AIROSMC) is proposed because of its advantages over SMC, which are a reduced number of sensors, improved dynamic response and easy implementation. The extensive simulation study is carried in MATLAB\Simulink for comparative analysis of fixed frequency SMC, two variable SMC, ROSMC, and AIROSMC. The harmonic spectrum analysis is carried out to justify the selection of DBR instead of the controlled rectifier. [ABSTRACT FROM AUTHOR]

Dual-active-bridge (DAB) enabled dc microgrids stabilization is investigated in this article. DAB has two control objectives: load current regulation and the dc-bus voltage stabilization. In multiobjective control applications, the conventional proportional integrator (PI)-based controllers face challenges in the control loop coordination. The saturation of the loops largely deteriorate the control performance. Moreover, the system impedance has to be measured before designing the active damping control. In this article, a moving discretized control set—model predictive control (MDCS-MPC) is proposed for DAB. The proposed MDCS-MPC is inherently a good choice for multiobjective control. It provides several advantages, such as a good tradeoff between two control objectives and adaptive performance on system impedance. The evaluation and comparison of the proposed MDCS-MPC and PI are carried out. Experiments on a 270–270V, 20 kHz, 1 kW DAB converter are conducted to verify the theoretical claims. [ABSTRACT FROM AUTHOR]

This study deals with a new control strategy for flying capacitor (FC) based multilevel converter, in order to attain the desired reference value for five‐level output voltage in active neutral point clamped (ANPC) converter. The balancing of capacitor voltages is one of the crucial aspects of grid‐tied photovoltaic (PV) fed ANPC converter. The accurate reference voltage for FC is required to experience minimum power pulsation and capacitor voltage imbalance. An offset injection‐based FC voltage regulator is implemented to track the desired voltage reference for FC. A simple proportional–integral controller generates the offset signal, which is added to the sinusoidal modulating wave to eliminate the FC imbalance. Moreover, neutral point voltage (NPV) balancing is achieved with the help of DC component injection control. The DC–AC power transfer, FC balance, NPV balance and unity power factor operation are achieved simultaneously. The performance of the closed‐loop controller for grid‐tied PV‐fed ANPC converter is analysed at constant and variable irradiances. The system is modelled in MATLAB/Simulink for offline simulation. Furthermore, offline simulation results are validated using real‐time controller hardware in loop (HIL) test bench. Moreover, active power is injected into the AC grid seamlessly and results are found compliant with the IEEE 519 standard. [ABSTRACT FROM AUTHOR]

In the traditional control strategy for single-phase PWM converter applications, the proportional-integral (PI) controller has the role of voltage tracking in the outer loop voltage controller, which has limited capability to provide acceptable dynamic performance and disturbance rejection. With regard to this, this article proposes a voltage control strategy based on the active disturbance rejection control (ADRC) for single-phase cascaded H-bridge rectifiers, aiming at achieving satisfactory dynamic performance and strong robustness to the disturbances. First, the extended state observer is used for the state and disturbance estimations. Then, the nonlinear state error feedback deals with the system error and makes the dynamic compensation to the disturbances. More specifically, an improved continuous nonlinear function is adopted to mitigate the jitter behavior of the traditional ADRC and provide immunity to large disturbance errors. Furthermore, the performance and stability analysis of the proposed strategy are implemented. A parameter tuning guideline of the proposed strategy is detailed. The effectiveness of the proposed ADRC-based voltage control strategy is verified through extensive experimental tests and is compared to that of the conventional PI-based voltage control strategy. [ABSTRACT FROM AUTHOR]

A non-linear control structure for a Photovoltaic (PV), battery and supercapacitor based stand-alone DC-microgrid is presented in this paper. Most of the conventional PI-based linear control structures reported in the literature have been designed around a single operating point and also supercapacitor voltage has not been regulated. Though supercapacitor voltage is regulated in some of the works, a dedicated controller has been used which increases controller count and makes designing/tuning of controllers together for desired system performance complicated. However, due to self-discharge or frequent discharge during operation, supercapacitor voltage can reach the lowest value which affects controller performance and even makes the system unstable. So, a robust non-linear controller: Interconnection Damping Assessment-Passivity Based Controller (IDA-PBC) is implemented as an outer loop controller to regulate DC-link and supercapacitor voltages. Also, a Finite Control Set-Model Predictive Control (FCS-MPC) which is intuitive in nature is implemented as inner current controllers. The proposed control structure is digital-friendly and can address the limitations of linear PI-control structure such as (i) Controller conflicts in designing the multiple controllers, (ii) Small region of stability (iii) Supercapacitor voltage regulation. Finally, the proposed control structure is verified through simulation and experimental results. [ABSTRACT FROM AUTHOR]

The centralized output-parallel dual-active-bridge (OP-DAB) dc–dc system is a promising candidate for achieving isolated dc–dc energy conversion with large current and power rating. To implement the flexible power sharing performance of the OP-DAB dc–dc converter, a simple tunable power sharing (TPS) strategy is proposed with the single-phase-shift method in this article. Based on the TPS strategy, the excellent dynamic performance under disturbances of input voltage for each module and load resistor can be provided. However, inaccurate circuit-parameter information always damages the power sharing performance among different DAB converters. Therefore, the comprehensive circuit-parameter estimating schemes proposed for different conditions of the OP-DAB dc–dc system including the start-up process, the working process and plugging-in a new DAB dc–dc converter, respectively. Moreover, the hot swap (plug-in and plug-out) control methods of the DAB converter without large influence on output voltage is also discussed in detail. Experimental results are obtained to verify the analysis in this article and the excellent performance of the proposed methods. [ABSTRACT FROM AUTHOR]

This paper presents a robust adaptive PI voltage controller (PIVC) that effectively eliminates the impact of disturbances and distorted model parameters for a three-phase constant voltage constant frequency (CVCF) inverter with an output LC filter. The proposed controller contains an adaptive control stage to enhance its tracking performance by compensating for distorted model parameters and a feedback control stage to stabilize the error dynamics to converge to zero. Unlike a conventional PIVC, the proposed adaptive method automatically updates its gains using the adaptive control stage. The stability of the proposed controller is proven by the Lyapunov stability theory. Even without information regarding the load current, the proposed adaptive PIVC achieves a fast dynamic response, small steady-state error, and low total harmonic distortion under critical load conditions. Experimental results demonstrate the efficacy of the proposed control method on a prototype three-phase CVCF inverter using a TI TMS320F28335 DSP. [ABSTRACT FROM AUTHOR]

This study aims to propose optimised and robust current controller for the transformerless grid‐integrated photovoltaic inverter. Challenge of ensuring improved power quality while minimising the DC‐component under non‐ideal grid condition is at the forefront in the photovoltaic system. In this context, an advanced current controller is designed and developed in the stationary reference frame with proportional‐integral (PI) plus four‐vector PI (4VPI) controllers. The PI‐controller modulates the shape of fundamental current to follow its reference induced from outer DC‐link loop. Meanwhile, 4VPI controllers are tuned at the multiple of grid frequencies including third‐(3ω0), fifth‐(5ω0), seventh‐(7ω0), and ninth‐(9ω0) to introduce infinite gain and thereby alleviating stationary errors in the current loop of the photovoltaic inverter. The most distinguishing feature of the proposed controller is its inherent control robustness, and therefore, it operates satisfactorily against control delay time and frequency excursion. Traditionally, cumbersome trial‐and‐error techniques have been largely employed to adjust the PI‐VPI controller gains. Nonetheless, tuning of these parameters has made many practitioners switch‐off from employing the proposed controller. Given this, the particle swarm optimisation algorithm is proposed. Finally, the practicality of the proposed controller is verified through comprehensive set of simulation and experimental tests conducted on a laboratory‐developed prototype using dSPACE‐1104. [ABSTRACT FROM AUTHOR]

This paper presents the proposal of using two bio-inspired metaheuristics—genetic algorithms (GAs) and particle swarm optimization (PSO)—to adjust the free coefficients of a Gaussian adaptive proportional–integral–derivative (GAPID) controller. When a specific adaptation rule is imposed to a conventional proportional–integral–derivative (PID) controller, either by means of a hyperbolic tangent function or a Gaussian function, the solution is left exposed to the function restrictions/impositions. Finding the correct proportionality between the parameters is an arduous task, which often does not have an algebraic solution. Each Gaussian function of each control action has three parameters, resulting in a total of nine parameters to be defined. This paper proposes making the parameters linked to the linear PID gains, in order to keep the GAPID the same design requirements as for the PID. Then, two metaheuristics (GA and PSO) were employed in order to find the best parameters for the GAPID. A comparison between these two strategies is presented. In this investigation, a well-known plant of a step-down dc–dc converter is used, which represents a typical second-order system, where the absence of significant nonlinearities helps focus the study on the control behavior. Simulation and experimentation were performed, and both have been successful, but PSO stood out due to its simplicity and low-computational effort. [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]

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.

The static VAR compensator is widely applied in large-scale grid-connected photovoltaic (PV) generation to participate in voltage regulation of power system, which ignores the reactive power regulation capability of PV inverter. In this study, firstly, the constraints of maximum operating current and output voltage's amplitude of PV inverter are considered, and the reactive power regulation capability of the PV generation is evaluated; secondly, an active participation in voltage regulation and control strategy of PV generation is proposed considering reactive power demand of system. This control method through the real-time detection and comparison with reference value of point of common coupling (PCC) voltage, automatically obtain the reactive demand to maintain PCC voltage by PI controller and realises the dynamic adjustment; finally, a time-domain small-signal model for PV generation is established, and based on this small-signal model, eigenvalue analysis is employed to study the influence of the grid strength, operating condition, and the reactive power control strategy on operating stability. Based on the time-domain simulation example in EMTDC/PSCAD, the validity of the theoretical analysis and the feasibility of the control strategy are verified.