•Microgrid is a small grid that uses renewable energy sources to generate power.•Performance of microgrid may deteriorate due to the uncertainty in load dynamics.•A controller is proposed to control ...the voltage, current and power of a microgrid.•The controller is designed for both single and three phase islanded microgrid.•Performance of the controller is measured and compared against various loads.
Future grids will consist of many small and large microgrids that will require complex control of grid interaction as well as islanding operation. This paper addresses the control of islanded microgrids under dynamic system conditions. In this paper, a robust model reference modified adaptive proportional integral derivative (PID) controller is designed for voltage and current control augmentation of islanded microgrid against various load dynamics. The variation of load dynamics may cause the unsafe operation of the microgrid. The objective of the designed controller is to confirm the safe operation against voltage and current control under different load dynamics. The controller is designed based on selecting the desired reference model and controlling parameters. The effectiveness of the proposed controller is evaluated against the presence of load dynamics, harmonic sources, asynchronous machines, nonlinear and unknown loads. The results show that the proposed controller is capable of providing high tracking performance and safe operation for both the single and three phase islanded microgrid system.
In virtual synchronous generator (VSG)-related discussions, the inner voltage and current controls are always omitted due to their fast dynamics. However, converters require a lower switching ...frequency as their power rating increases, which constrains the cascaded controls' bandwidths. Hence, the interactions between the controls at different time-scales should be analyzed. Specifically, the aim is to reveal the effects of inner control loops on the VSG system from the torque perspective. First, this paper derives a linearized model of the internal voltage phase and amplitude, which accurately depicts the VSG system characteristics. Subsequently, based on this linearized model, we derive an equivalent single-input single-output motion-equation- based model. The proposed model can be used to investigate the change in damping and synchronizing torque components under low control bandwidths and weak grid conditions. Finally, simulation results are presented to validate the proposed modeling and effects analysis. Our model is general and can be used for any power ratings, and the study also provides a guide to designing control parameters for VSG systems.
Hybrid single-phase ac/dc microgrids (MGs) consist of a dc MG and a single-phase ac MG, interconnected through an interlinking converter (IC). In this configuration, the dc MG naturally experiences a ...second harmonic current injection caused by the double-frequency component of the ac side instantaneous power. This paper proposes a new decentralized control method by utilization of the injected harmonic for power sharing. The proposed method enables accurate power sharing among dc sources and precise global power sharing among dc and ac sources without imposing any dc side voltage deviation. In this method, each dc source adjusts its power based on the frequency of the harmonic component. Additionally, the IC ensures that the voltage level of the dc MG remains at the rated value. Capacitive virtual impedances are integrated into the dc sources to facilitate second harmonic current sharing among them and prevent the circulation of harmonic current flow between the dc sources and the IC's dc side capacitor. To fulfill the objectives, each dc source simultaneously regulates the second harmonic voltage of its output filter capacitor and the dc component current of its output filter inductor. The effectiveness of the proposed control strategy is demonstrated through time-domain and frequency-domain simulations.
The sharing of nonlinear loads among different distributed generation units (DGs) is always a tradeoff between accuracy and voltage quality. This paper proposes a virtual harmonic conductance for ...each harmonic as a family of droop characteristics in terms of conductance versus current. Assigning a variable conductance for each harmonic current improves the DG controllability, thus offering accurate nonlinear load sharing, which is crucial at the near-rated loading and enhanced voltage quality. This paper also unveils a tuning methodology for the droop characteristics that sets a maximum permissible value for each individual harmonic to comply with international standards. Lastly, a hybrid voltage and current control system is suggested to accurately track the DG harmonic conductance designated by the proposed droop characteristics. While the proposed algorithm is capable of accurately distributing common nonlinear loads among DGs, it also enjoys the advantage of supplying local nonlinear loads by their dedicated DGs. A comprehensive performance evaluation assures the effectiveness of the proposed control strategy.
An effective hybrid technique is proposed for enhancing the efficiency of photovoltaic (PV) system by an extended boost inverter called active-switched boost quasi-Z source inverter (ASB-qZSI). The ...hybrid approach is the combination of quasi-oppositional chemical reaction optimization (QOCRO) and golden eagle optimizer (GEO), and later called Q2OGEO approach. The main objective of the proposed system is “to increase the proficiency of PV system and the extraction of maximum power.” Here, ASB-qZSI method is used to increase the voltage gain of converter in less duty cycles. The objective of the system is defined as controller-based parameters and limitations like voltages, modulation index, current, and power. The QOCRO method is utilized to regulate the system voltage, and GEO is used to regulate the current of system. The proposed Q2OGEO method efficiently controls the voltage, current, and DC link voltage and then extracts maximal power of PV system. Additionally, increasing the power delivery, voltage profile, but minimizing the total harmonic distortion (THD). By using the ASB-qZSI, control the shoot-through duty ratio to minimize the modulation burden. Then, the proposed approach is enthused on the MATLAB software, and the effectiveness is observed with existing techniques.
This paper provides a systematic review of advanced control strategies for the two mostly acclaimed standalone/off-grid distributed generation (DG) systems, i.e., wind energy conversion systems ...(WECSs) and solar photovoltaic energy systems (PVESs). The existing literature individually studies each DG system and does not provide an appropriate categorization of available advanced control strategies. Thus, it is quite difficult to systematically comprehend the control requirements of overall standalone/off-grid DG systems. Unlike the existing literature, this paper conducts a systematic study based on a useful distinctive organization of the advanced control strategies for the standalone permanent magnet synchronous generator (PMSG)-/doubly-fed induction generator (DFIG)-based WECSs and PVESs. The generalized control configurations for both standalone/off-grid DG systems are specifically exhibited by assigning a control system (CS) with its inherent inputs and outputs for every power conditioning unit (PCU) in the corresponding generation system. The advanced control techniques for all CSs are distinctively classified based on the presented generalized control configurations for both DG systems. Then, a comprehensive review is performed on every control technique with regard to its control functionality in the particular CS. Last, significant future research recommendations are provided for both standalone DG systems keeping in view the improved control strategies and PCUs.
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•A systematic review of the advanced control strategies is presented for the standalone/off-grid wind and solar photovoltaic (PV) energy systems.•The generalized control configurations for both systems are presented distinctively in the form of control systems (CSs).•Based on the specified CSs, the control strategies for each energy system are uniquely classified and then comprehensively studied considering the essential control operation of each CS.•The appropriate numerical data analysis, tables and graphical results are presented to properly understand the pros and cons of every advanced control strategy.•The useful future research recommendations are provided to achieve the improved control strategies and hardware components for the wind and solar PV energy systems.
Summary
A hybrid AC/DC microgrid takes advantages of both DC and AC microgrids with distributed generation (DG) units in both the respective grids connected through a bidirectional interlinking ...converter (BIC). Control of hybrid AC/DC microgrid presents a significant research and engineering challenge and hence needs increased research efforts. Existing control algorithms restrict individual controllers to control only designated parameters. This paper proposes MPC‐based distributed control algorithm that will analyze grid conditions, and it would designate BIC to regulate the highest deviated parameter (AC/DC voltage or current) in all nonlinear conditions by performing multivariable optimization using variable control scheme in MPC. Other parameters would be controlled by individual controllers as per their capability. MPC being a nonlinear control technique having an excellent dynamic response and constraint inclusion feature has advantage as compared to other linear and nonlinear techniques. The performance of the proposed algorithm has been compared against other techniques and proved in MATLAB/SIMULINK simulation.
MPC Control of BIC in hybrid microgrid.
A modular multilevel converter (MMC) is an advanced voltage source converter applicable to a wide range of medium and high-voltage applications. It has competitive advantages such as quality output ...performance, high modularity, simple scalability, and low voltage and current rating demand for the power switches. Remarkable studies have been carried out regarding its topology, control, and operation. The main purpose of this review is to present the current state of the art of the MMC technology and to offer a better understanding of its operation and control for stationary applications. In this study, the MMC configuration is presented regarding its conventional and advanced submodule (SM) and overall topologies. The mathematical modeling, output voltage, and current control under different grid conditions, submodule balancing control, circulating current control, and modulation methods are discussed to provide the state of the MMC technology. The challenges linked to the MMC are associated with submodule balancing control, circulating current control, control complexity, and transient performance. Advanced nonlinear and predictable control strategies are expected to improve the MMC control and performance in comparison with conventional control methods. Finally, the power losses associated with the advanced wide bandgap (WBG) power devices (such as SiC, GaN) are explored by using different modulation schemes and switching frequencies. The results indicate that although the phase-shifted carrier-based pulse width modulation (PSC-PWM) has higher power losses, it outputs a better quality voltage with lower total harmonic distortion (THD) in comparison with phase-disposition pulse width modulation (PD-PWM) and sampled average modulation pulse width modulation (SAM-PWM). In addition, WBG switches such as silicon carbide (SiC) and gallium nitride (GaN) devices have lower power losses and higher efficiency, especially at high switching frequency in the MMC applications.
Based on the standardization in the automotive industry, systems require extensive testing, which represents significant costs regarding personnel and equipment. The testing systems must be built in ...such a way that a bidirectional power flow is possible between the power source and the tested system. Additionally, applied testing systems have to possess high disturbance immunity. Classical current programmed control performed using an analogue approach suffers from low disturbance rejection during switching operation. The digital control of DC–DC converter can solve this problem with the use of digital integration in a measurement chain. The integrals of values are obtained by using a Voltage Control Oscillator (VCO) and appropriate counters. Digital control of an interleaving operated bidirectional buck-boost synchronous converter can be applied in the testing system for automotive powertrains. The voltage and current measurements with the application of an integral-measurement principle act as low-pass filters, which remove the disturbances from the measured values. The digital implementation of a compensation ramp (current mode control) and method for choice of control parameters are described. All the tasks for measurements, as well as current and voltage control, were implemented within the FPGA (Field Programmable Gate Array). The presented converter can operate as a close to ideal voltage or current source, and satisfies the requirements of testing electric motor drive-trains with bidirectional DC–AC converters that are applied in automotive applications. The proposed system was verified by simulation
In this study, a novel blended state estimated adaptive controller is designed for voltage and current control of microgrid against unknown noise. The core feature of the microgrid (MG) is its ...ability to integrate more than one distributed energy resource into the main grid. The state of a microgrid may deteriorate due to many reasons, for example malicious cyber-attacks, disturbances, packet losses, etc. Therefore, it is necessary to achieve the true state of the system to enhance the control requirement and automation of the microgrid. To achieve the true state of a microgrid, this study proposes the use of an algorithm based on the unscented kalman filter (UKF). The proposed state estimator technique is developed using an unscented-transformation and sigma-points measurement technique capable of minimizing the mean and covariance of a nonlinear cost function to estimate the true state of a single-phase, three-phase single-source and three-phase multi-source microgrid system. The advantage of the proposed estimator over using extended kalman filter (EKF) is investigated in simulations. The results demonstrate that the use of the UKF estimator produces a superior estimation of the system compared with the use of the EKF. An adaptive PID controller is also developed and used in system conjunction with the estimator to regulate its voltage and current against the number of loads. Deviation in load parameters hamper the function of the MG system. The performance of the developed controller is also evaluated against number of loads. Results indicate the controller provides a more stable and high-tracking performance with the inclusion of the UKF in the system.
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