Abstract: Conventionally, standard proportional and integral (PI) controllers with constant PI gains are commonly used for the dc-link voltage control of single-phase grid-connected converters (GCCs). For such controllers, the selection of the PI gains will lead to a tradeoff between two control objectives: 1) the reduction of the dc-link voltage fluctuations caused by random swings of the active power drawn by the single-phase GCC; and 2) the reduction of the grid current harmonics mainly caused by the 2 f oscillation of the active power in single-phase applications. To solve this tradeoff, this paper presents a systematic approach for the design of an adaptive PI controller for the dc-link voltage control of single-phase GCCs. The proposed design approach is simple and it provides a convenient method to properly determine the adaptive PI controller parameters. Representative simulation and experimental results are presented and discussed in order to show the effectiveness of the proposed dc-link voltage controller.

Abstract: DC–DC boost converters have been widely employed at the dc input of grid-tied photovoltaic (PV) inverters. In order to comply with grid standards, their control systems must usually work in two operation modes: Maximum power point tracking (MPPT) mode and limited power tracking (LPT) mode. MPPT algorithms reach high dynamic and static efficiencies when they operate with high-speed PV voltage control, because PV voltage is not significantly dependent on solar irradiance variations. On another hand, high-speed LPT mode can be obtained by controlling inductor current, which is proportional to the power injected into the dc bus. Both modes can be integrated in a cascade control scheme with an inner and fast current loop and an outer voltage loop. The main challenge is that both voltage and current small-signal models are highly dependent on the operation point of the PV array, temperature, and solar irradiance. This may cause control interactions between both loops and instability, especially when small film capacitors are used in parallel with the PV array. A common approach is to increase the input capacitance and design a low-speed PV voltage controller, which is not the best solution when high MPPT dynamic efficiency is necessary. To overcome these challenges, this paper proposes a cascade control structure based on an inner non-linear current controller and an outer adaptive voltage controller with fast detection of the PV array's model without requiring extra current sensor. A control design methodology and a MATLAB stability analysis tool are presented to support application engineers. The proposed control system has been experimentally validated using a PV array and a boost converter switched at 40 kHz. PV voltage settling time lower than 8 ms has been achieved for low and high solar irradiance, demonstrating the efficacy of the proposed technique.

Abstract: Since a DC micro-grid consists of power converters connected through different line impedances, tuning of the voltage controller provides a simple and intuitive tradeoff between the conflicting goals of voltage regulation and current sharing. A highly flexible distributed control strategy is proposed to achieve the balanced control between the two control objectives, which includes the containment-based voltage controller and consensus-based current controller. The terminal voltage can be bounded within a prescriptive range which means each terminal voltage is controllable instead of only controlling the average voltage; meanwhile, the current-sharing performance can be regulated among converters. The two objectives, including either bounding voltages tightly or decreasing current sharing errors, can be compromised between each other by tuning the weightings of controllers. The large-signal model is developed to analyze the tuning principle about different control parameters. The proposed strategy can provide flexible control performance according to various control requirements. Experimental results and comparisons are illustrated to verify the effectiveness of the proposed method and compromised tuning under resistive loads and constant power loads, dynamic voltage boundary conditions.

Abstract: Conventional Energy Resources (CER) are being rapidly replaced by Renewable Energy Resources (RER) due to their abundant, environmentally friendly, clean, and inexhaustible nature. In recent years, Solar Photovoltaic (SPV) energy installation is booming at a rapid rate among various RER. Grid-Connected PVS required advance DC-link controllers to overcome second harmonic ripple and current controllers to feed-in high-quality current to the grid. This paper successfully presents the design of a Fuzzy-Logic Based PI (F-PI) and Fuzzy-Logic based Sliding Mode Controller (F-SMC) for the DC-link voltage controller and Proportional Resonant (PR) with Resonant Harmonic Compensator (RHC) as a current controller for a Single-Phase Two-Stages Grid-connected Transformerless (STGT) Photovoltaic (PV) Inverter. The current controller is designed with and without a feedforward PV power loop to improve dynamics and control. A Second Order General Integral (SOGI)-based Phase Lock Loop (PLL) is also designed that has a fast-dynamic response, fast-tracking accuracy, and harmonic immunity. A 3 kW STGT-PV system is used for simulation in Matlab/Simulink. A comparative assessment of designed controllers is carried out with a conventionally well-tuned PI controller. The designed controllers improve the steady-state and dynamic performance of the grid-connected PV system. In addition, the results, performance measure analysis, and harmonics contents authenticate the robustness, fastness, and effectiveness of the designed controllers, related to former works.

Abstract: This paper proposes an optimal design algorithm for distributed secondary voltage control in islanded microgrids (MGs), including communication topology and controller gains First, upon the consensus-based secondary voltage control, the sufficient condition for network connectivity of communication topology is revealed by the reachability matrix A multi-objective optimization criterion is first proposed for the network design, taking the convergence performance, network-relevant time delays, and communication costs into consideration After obtaining the Pareto frontier of this multi-objective model, an optimal network is selected to meet the practical requirements Based on static output feedback, a small-signal dynamic model of an MG installed with a secondary voltage controller is established, where the distributed secondary voltage controller can be converted into an equivalent decentralized controller Thereby, a linear quadratic regulator is formulated for the near-optimal design of controller parameters Our approach customizes the optimal design framework of the topology and controller, which have been largely ignored in the existing literatures Therefore, it promises to improve the performance of distributed secondary control The effectiveness of the proposed methodology is verified by a simulation study

Abstract: State-space control could provide both high dynamic performance and sufficient stability margin to voltage source converters with LC filter However, an inherent digital delay induced by a digital control system deteriorates performance and even induces instability In this paper, a discrete-time voltage controller is proposed based on a discrete state-space model First, a state feedback control with a reference feedforward path is designed in the discrete-time domain with consideration for the digital delay Second, an output current decoupling path is augmented to minimize the effects of an output current disturbance Controller gains are derived as the functions of system parameters and design specifications, which is based on a direct pole placement and pole-zero cancellation method in a rotating reference frame Moreover, a parameter sensitivity and digital implementation are discussed to improve the performance and stability of the proposed controller The effectiveness of the proposed controller is verified with various experimental results It shows that a filter resonance is well damped out while maintaining wide voltage control bandwidth

Abstract: In this paper, a simplified control scheme is introduced for permanent magnet synchronous motors (PMSMs). The control strategy consists of a direct voltage controller that capitalizes on the motor's model to achieve accurate speed tracking. As such, no explicit currents loop regulation is needed which simplifies the control structure and unlike other control strategies, no motor's parameter knowledge, voltage or current transducer is required. But, the absence of current regulation loops yields higher energy consumption, which limits the motor's range of operation. Therefore, a genetic algorithm is presented to determine control gains with optimal current consumption ensuring operation at the full range of the machine. Simulation and experimental results for different situations highlight the performance of the proposed controller in transient, steady-state, and standstill conditions. Furthermore, the simplicity of the control scheme makes it a good candidate for a low-cost implementation of real-time PMSM drives.

Abstract: DC power distribution systems typically consist of several source converters supplying load converters through single or multiple dc buses. Such complex systems are prone to stability issues caused by the interactions among feedback-controlled converters. Additionally, dc interconnected systems typically undergo considerable changes in their operating points. This can cause a system that is well-stabilized at a certain operating point to go unstable for another operating condition. Therefore, a stabilization method that is capable of adapting to variations in system operating conditions is highly desirable. This paper presents an adaptive stabilization method implemented on the source-side. The system stability is periodically analyzed by real-time measurement of the system bus impedance, which is dominated by the source impedance. Accordingly, the source converter control is modified by the proposed method to guarantee stability and high performance of the entire system after system changes. The approach has several advantages, including ease of design and implementation, minimal deviation from the nominal controller, and robustness due to the real-time adaptive implementation. Simulation and experimental results are presented that confirm the effectiveness of the proposed method.

Abstract: This paper proposes a novel nonlinear control method for the input-parallel output-series modular dual active bridge (DAB) dc/dc converter which regulates the dc-bus voltage and individual module voltages together. At first, a state space form of the DAB converter model is derived. Next, the output voltage controller of the modular DAB converter is designed with the hierarchical sliding-mode control theory. Furthermore, due to the robustness of the sliding-mode control, the control performance is insensitive to the mismatch of leakage inductances of the DAB transformers. The feasibility of the proposed control scheme has been proved by simulation and experimental results.

Abstract: Passivity theory provides a promising approach to guarantee microgrid system stability. If all converters in the system can be made passive, prevention of electrical resonance can be achieved. To that end, a passivity-oriented discrete-time voltage controller for grid-forming inverters is proposed in this –paper. Compared with existing methods, the approach ensures not only –superior reference tracking performance and load disturbance rejection capability, but also provides passive output impedance, and therefore, guaranteed stable inverter operation under weak grid condition. A comparison study is carried out and the proposed controller design method is validated by hardware-in-the-loop (HIL) experiments.

Abstract: The back-to-back (BTB) converter is one of the most popular converter topologies for the control of electrical machines, power transmission systems, and power quality applications. The conventional cascade control structure is commonly used due to its simple design procedure and reliable operation. However, the bandwidth of the dc-link voltage controller has to be limited in order to avoid instability issues and be restrictive in high-performance applications. This paper presents a differential- and common-current (power)-based state-feedback control for BTB converters. This controller features a fast control of active and reactive powers, and a stiff regulation of the dc-link voltage. A theoretical analysis of the proposed controller along with a strategy for current limiting is presented. Its robustness was tested against variations of the filter parameters, the dc capacitance, the grid inductance, and the grid voltage values. The controller was experimentally validated under nominal operation, voltage sags, and connected to a weak grid by using a 15-kVA BTB converter in a laboratory test network.

Abstract: In this paper, a coordinated control method is proposed for three-phase ac/dc hybrid microgrid power electronic interlinking unit with dual converters sharing both dc and ac links. Unlike the conventional dual converters-based system where the same control strategy is applied to both converters, converter1 in this proposed system is controlled by a closed-loop current regulation algorithm while converter2 employs voltage controller with coupled adaptive virtual impedance. With the flexible control of the coupled virtual impedance, the system performance is enhanced in the following three aspects. First, in grid-tied operation mode, the output power difference between dual converters is used as an input to tune the coupled virtual impedance of converter2 for a rapid dynamic power response. Second, the proposed coordinated control with inherent voltage support is able to achieve a seamless transfer without additional efforts. Third, during system islanded operation, a generalized power sharing and an active PCC voltage harmonic and unbalanced components mitigation are achieved via the adjustment of the coupled virtual impedance. Finally, the scalability of the proposed method in a system with more converters is briefly discussed and verified.

Abstract: A boost converter exhibits a nonminimum phase behavior while operating in continuous conduction mode. This is due to the existence of a right-half-plane zero that significantly restricts the closed-loop bandwidth. Using the phase–plane geometry, this paper proposes a nonlinear tuning approach in a digitally current-mode controlled boost converter with a proportional–integral voltage controller. Considering a load current feed-forward with a normalized gain $k_{n}$ , optimal proportional gains are analytically derived in order to achieve near time optimal recovery under both load and reference step transients. The optimal gain is shown to be equally applicable for a (nonminimum phase) noninverting buck-boost converter by suitably updating $k_{n}$ . Large-signal stability analysis is carried out, and the effects due to finite sampling and parameter variations are discussed. The proposed tuning significantly improves the transient response over existing small-signal-based tuning methods. The constraints on the current overshoot and/or voltage deviation are also considered, and their effects on the transient performance are studied. A boost converter prototype is tested using resistive and dimmable (white) LED array loads. The proposed tuning is realized using a field-programmable gate array device; improved performance and efficiency are demonstrated using test results.

Abstract: This paper proposes a robust current controller (CC) and dc-link voltage controller based on $\mu $ -synthesis and $H_{\infty }$ method, respectively, for a single-phase photovoltaic (PV) converter with an LCL -filter under weak grid operation. The $\mu $ -synthesis CC guarantees system robustness against weak grid uncertainties such as grid impedance variations and voltage harmonics. Moreover, the controller compensates the system delays arising from the calculation, pulsewidth modulation, and zero order hold, as well as delay uncertainties. The CC only uses the grid current feedback which eliminates the requirement for additional loops or state measurements utilized in partial or full state-feedback systems. In addition, the $H_{\infty }$ dc-link voltage controller minimizes the bus voltage fluctuations caused by variations of PV system power generation. Also, the controller ensures system robustness against such power variations, which conventional controllers fail to perform. Moreover, power decoupling is achieved by the control system without any auxiliary circuit. In addition, the stability and robust performance of the phase-locked loop in a weak grid with major impedance changes is verified. Simulation and experimental results prove the superior performance of the proposed controllers in both cases of a nominal system and a system with deviated parameters.

Abstract: The 9-Level Packed U-cell (PUC9) inverter topology is presented in this paper. It uses eight switches, one DC voltage source and two auxiliary capacitors to generate a 9-level voltage at the output. Obtaining two small size of flying capacitors through proper voltage balancing technique integrated into the modulation unit and without using the complicated external control system that may increase its reliability is the innovation of this article. This topology offers a low-cost inverter compared to the other similar 9-level inverters due to the reduced number of devices and simple voltage controller. PUC9 topology is chosen by trade off between redundancy of states and voltage levels at the output of inverter by selection of suitable proportion of voltage at capacitors than each other and DC source. The stand-alone operation of the PUC9 inverter with implemented voltage balancing technique is investigated through simulation analysis in Matlab-Simulink and results are discussed in details.

Abstract: Ripple-based constant on -time and off -time control techniques can achieve fast step-down and step-up transient performance along with an improved light-load efficiency. However, they suffer from varying switching frequency at the steady state and often require a phase-locked loop for frequency regulation. This paper proposes a constant on/off -time hybrid modulation technique in a digitally current-mode controlled synchronous buck converter. The proposed technique considers an event-based sampling mechanism using one sample per switching cycle, which makes it useful for high-frequency implementation. This requires a monoshot timer and a digital voltage controller $G_c(z)$ . The proposed technique can be configured to a constant on -time or off -time modulator with seamless transition because of sharing $G_c(z)$ ; thus, improved step-up/down transient performance can be retained. Furthermore, a discrete-time framework is proposed for fast-scale stability analysis, and the effects of finite sampling and practical parasitics are discussed. Discrete-time small-signal models are derived for the direct digital control design with enhanced stability and performance. A frequency adaptation method is discussed to customize the switching frequency in real time. A buck converter prototype is tested, and the usefulness of the proposed modulation technique is verified experimentally.

Abstract: Diode and thyristor-based rectifier circuits have been widely used in the industry. Due to non-linear structures of these circuits, they draw non-sinusoidal current from AC network as well as cause a low power factor in the AC side. The DC-link voltage of rectifier is affected by the changes in AC network or by the load variations on the DC side. Pulse-width modulated (PWM) rectifiers can eliminate the mentioned power quality problems if they control properly. This study proposes a controller with an adaptive and robust structure based on proportional + derivative type-2 fuzzy neural network (PD-T2FNN) for DC-link voltage control of PWM rectifier. Dynamic performance of PWM rectifier using the proposed controller is evaluated via dSPACE based experimental setup under different operation conditions: set-point change, step load change in the DC side of the rectifier, set-point change under load and capacitive operation mode. The experimental results are given for traditional PD and proportional + integral and T2FNN controllers to validity performance of the proposed controller. Performances of controllers are evaluated regarding settling time, overshoot, steady-state error and total harmonic distortion. PWM rectifier with PD-T2FNN DC-link voltage controller has superior performance for all operating conditions according to performance criteria when compared with other controllers.

Abstract: In this paper mathematical model of electrolyzer is elaborated. A mathematical model of the Proton Exchange Membrane (PEM) electrolyzer powered by an interleaved Buck converter is developed in this study. A pulse width-modulation-based sliding-mode controllers (SMPWM) is used to solve the problem of instability of the PEM electrolyzer voltage. The performances of the proposed electrolyzer system - controller are analysis and validated by a series of simulation in MATLAB – SIMULINK.

Abstract: This paper investigates dc-link capacitor optimization for three-phase photovoltaic-based microinverters. This concept minimizes the storage capacitance by allowing greater voltage ripple on the dc link. Therefore, the microinverter reliability can be significantly increased by replacing electrolytic capacitors with film capacitors. However, this intentionally increased voltage ripple can introduce harmonic distortion on the output current of the inverter stage if it is not mitigated by the dc-link voltage controller. For this purpose, a robust and accurate dc-link voltage control is proposed to filter this ripple while regulating the dc-link voltage without using any additional circuit components. The experimental results on a 400-W three-phase half-bridge microinverter prototype validate the theoretical analysis of the dc-link capacitor optimization and show that a significant reduction of the dc-link capacitor requirement can be achieved. The proposed high-accuracy dc-link voltage controller is also implemented on this prototype to demonstrate very low harmonic distortion of the inverter output current while tightly regulating the dc-link voltage even during transients.

Abstract: This study proposes an adaptive second order generalized integrator based quadrature signal generator-frequency locked loop (SOGI-QSG-FLL) and fuzzy tuned proportional integral (FPI) in grid interconnection of photovoltaic (PV) system with shunt power quality conditioner (SAPF) for quality of power enhancement. The SOGI-QSG-FLL adaptive controller is simple in structure, more flexible, and it has been utilized for many applications like grid synchronization, frequency estimation, and harmonic extraction. The FPI voltage controller is used to stable DC bus voltage at a reference value. The combination of both controllers gives a better performance at steady state, dynamic load, grid voltage unbalancing, voltage fall, deformed voltage, raises voltage, and eliminated load states. The frequency locked loop (FLL) used for frequency estimation; the hysteresis current controller utilized for generating PWM signals to SAPF inverter. The proposed controller executed on MATLAB/SIMULINK software platform under steady state, dynamic load, grid voltage unbalancing, sag, distorted, swell grid voltage, and load removed conditions. And the simulation results are found adequate within IEEE-519 limits.

Abstract: Direct online starting inrush current of induction motors results in voltage dip across the distribution network. The voltage sensitive loads that are connected to such networks tend to trip and disconnect from the networks during such voltage disturbances. There has been rising installation of rotary and static distributed generator DG units that include diesel generators, combined heat and power generators, small wind turbines, and solar photovoltaics. This paper presents control strategy to minimize the impact of induction motor starting on the network voltage using voltage feedback based reactive power support from the existing DGs. Simulation studies are presented to validate the theoretical framework. It is shown that DGs can restore the motor starting transient voltage dip quickly due to the fast response of the voltage controller designed for the DG.

Abstract: Many power electronics applications require a power calculation in the control system. To get a suitable output, engineers need to control the process and regulate the power exchange with the grid. Since real and reactive power calculations are so crucial a topic, a novel control strategy for a single-phase photovoltaic (PV) inverter has been developed. Therefore, Direct power control (DPC) and a single-phase three-level space vector pulse width modulation (SVPWM) combine as a control and modulation system. In this paper, predictive real and reactive power control and SVPWM method are conferred in the inner loop. A voltage controller based on a proportionalintegral (PI) scheme is used in the outer loop to acquire constant output voltage and provide power refers to the DPC. The performance of the proposed method is verified by using MATLAB/SIMULINK.

Abstract: This paper presents a new lightning search algorithm (LSA) to enhance the piezoelectric energy harvesting system converter (PEHSC) using the dSPACE DS1104 controller board as the proportional-integral voltage controller (PIVC). To extract the energy from the vibration is challenging and difficult due to the uncertain behavior of vibration. Since the piezoelectric vibration transducer generates low AC voltage output with fluctuations and harmonics, it is difficult to control this low-level signal of various magnitudes. Therefore, the behavior of the converter is governed by its controller. The traditional PIVC process for improved parameter values of proportional gain (Kp) and integral gain (Ki) is commonly implemented via trial and error, which does not lead to an acceptable response in several conditions. Hence, this paper offers a method for finding the optimal Kp and Ki values for PIVC that eliminates the time-consuming conventional trial-and-error process. This method is applied to PEHSC development by producing values of Kp and Ki performed in the PIVC depending on the estimated outcomes of the objective function defined via LSA. The mean absolute error (MAE) is used as the objective function for reducing the output error of the PEHSC. The LSA optimizes the Kp and Ki values that give the minimum MAE, and the effect on the PEHSC is in terms of the rising and settling times. The development process and efficiency of the PIVC are demonstrated and examined via simulations using the MATLAB tools. The LSA-based PIVC (LSA-PI) is compared with the particle swarm optimization (PSO)-based PIVC (PSO-PI) and the backtracking search algorithm (BSA)-based PIVC (BSA-PI). The performance of the LSA-PI-based PIVC is then validated through hardware implementation using the dSPACE DS1104 control board. The simulation results are compared with the hardware results of PEHSC to validate the overall efficiency of the system. Finally, the results are regulated at an output of 7 V DC from an input range of 150 mV~250 mV AC at 30 Hz through a closed-loop using the LSA-PIVC.

Abstract: This paper introduces the control of the parallel operation of two voltage source converter (VSC)-HVdc links interconnecting an offshore wind farm. The aim of the study is to propose and validate a control system that allows the parallel operation of two VSC-HVdc links by controlling the currents injected by the VSC converters. The currents set points are established by a voltage controller in order to maintain constant voltage and frequency in the capacitor of the output filter and therefore within the offshore wind farm (OWF). It is demonstrated that the decoupled control of the d-q component of the voltage at the capacitor allows achieving the direct control of voltage and frequency, respectively. The voltage and frequency control is implemented by orienting the capacitor voltage toward a synchronous axis that is generated within the controller and therefore is not subjected to any grid disturbance. Both converters collaborate therefore in maintaining constant voltage and frequency, achieving in this way the parallel operation of the converters. The validation of this approach is demonstrated by simulation where the OWF and the VSC-HVdc rectifier have been modeled. Simulation results demonstrate that the proposed control system allows the parallelization of the converters while maintaining constant voltage and frequency within the OWF, even during transient faults.

Abstract: This paper investigated the performance of the sliding mode control technique for dc/dc converter using frequency response method. The applications of the step down type switching regulator) buck converter (are found in the devices that use batteries as power source like laptop, cell phones, electric vehicle, and recently, it has also been used in the renewable energy processing, as a maximum output power can be achieved at higher efficiency. In order to optimize the efficiency and for convenient power management, the issues like power on transients, the effect of load variation, Switching and Electromagnetic interference (EMI) losses has to be overcome for which controllers are used. In the proposed method, pulse width modulation (PWM) based on proportional-integral-derivative sliding mode voltage controller (PID SMVC) is designed for a buck converter and the response for appropriate control parameters has been obtained. The system stability has been examined and analyzed from the performance characteristics, which shows clearly that the buck converter controlled by the sliding mode controller has fast dynamic response and it’s very efficient for various applications.

Abstract: In this paper, a novel voltage controller of energy storage system (ESS) in DC microgrids (DC-MG) is proposed to enhance the DC-bus voltage stability. At first, a mathematical model of the DC-MG is developed in a state-space form. Then, the voltage controller of the ESS is designed by using the methodology of the IDA-PBC (interconnection and damping assignment-passivity-based control) with an integral action. System stability has been analyzed with passivity-based stability criterion (PBSC). The proposed controller gives the robust performance to the parameters variation. The validity of the proposed control scheme has been verified by the hardware-in-the-loop simulation (HILS) results.