Grid-tied inverters are the key components of distributed generation system because of their function as an effective interface between renewable energy sources and utility. Recently, there has been an increasing interest in the use of transformerless inverter for low-voltage single-phase grid-tied photovoltaic (PV) system due to higher efficiency, lower cost, smaller size and weight when compared to the ones with transformer. However, the leakage current issues of transformerless inverter, which depends on the topology structure and modulation scheme, have to be addressed very carefully. This review focuses on the transformerless topologies, which are classified into three basic groups based on the decoupling method and leakage current characteristics. Different topologies under the three classes are presented, compared and evaluated based on leakage current, component ratings, advantages, and disadvantages. An examination of demand for the inverter, the utility grid, and the PV module are presented. A performance comparison in MATLAB/Simulink environment is done among different topologies. Also an analysis has been presented to select a better topology. Finally, based on the analysis and simulation results, a comparison table has been presented. Furthermore, some important experimental parameters have been summarized.

Single phase transformerless inverter topologies for grid-tied photovoltaic system: A review

Energy storage systems have been widely applied in power distribution sectors as well as in renewable energy sources to ensure uninterruptible power supply. This paper proposes a modified model predictive control (MMPC) method based on the Lyapunov function to improve the performance of a bidirectional ac–dc converter, which is used in an energy storage system for bidirectional power transfer between the three-phase ac voltage supply and energy storage devices. The proposed control technique utilizes the discrete behavior of the converter, considering the unavoidable quantization errors between the controller and the control actions selected from the finite control set of the bidirectional ac–dc converter. The proposed control method reduces the execution time delay by 18% compared with the conventional model predictive control. Moreover, the nonlinear system stability of the proposed MMPC technique is ensured by the direct Lyapunov method and a nonlinear experimental system model. Detailed experimental results with a 2.5-kW downscaled hardware prototype are provided to show the efficacy of the proposed control system.

Modified Model Predictive Control of a Bidirectional AC–DC Converter Based on Lyapunov Function for Energy Storage Systems

Due to the expansion of distributed renewable energy resources, peer to peer energy trading (P2P DET) is expected to be one of the key elements of next generation power systems. P2P DET can provide various benefits such as creating a competitive energy market, reducing power outages, increasing overall efficiency of power systems and supplementing alternative sources of energy according to user preferences. Because of these promising advantages, P2P DET has attracted the attention of several researchers. Current research related to P2P DET include demand response optimization, power routing, network communication, security and privacy. This paper presents a review of the main research topics revolving around P2P DET. Particularly, we present a comprehensive survey of existing demand response optimization models, power routing devices and power routing algorithms. We also identify some key challenges faced in realizing P2P DET. Furthermore, we discuss state of the art enabling technologies such as Energy Internet, Blockchain and Software Defined Networking (SDN) and we provide insights into future research directions.

Peer to Peer Distributed Energy Trading in Smart Grids: A Survey

Induction motor (IM) drives, specifically the three-phase IMs, are a nonlinear system that are difficult to explain theoretically because of their sudden changes in load or speed conditions. Thus, an advanced controller is needed to enhance IM performance. Among numerous control techniques, fuzzy logic controller (FLC) has increasing popularity in designing complex IM control system due to their simplicity and adaptability. However, the performance of FLCs depends on rules and membership functions (MFs), which are determined by a trial-and-error procedure. The main objective of this paper is to present a critical review on the control and optimization techniques for solving the problems and enhancing the performance of IM drives. A detailed study on the control of variable speed drive, such as scalar and vector, is investigated. The scalar control functions of speed and V/f control are explained in an open- and closed-loop IM drive. The operation, advantages, and limitations of the direct and indirect field-oriented controls of vector control are also demonstrated in controlling the IM drive. A comprehensive review of the different types of optimization techniques for IM drive applications is highlighted. The rigorous review indicates that existing optimization algorithms in conventional controller and FLC can be used for IM drive. However, some problems still exist in achieving the best MF and suitable parameters for IM drive control. The objective of this review also highlights several factors, challenges, and problems of the conventional controller and FLC of the IM drive. Accordingly, the review provides some suggestions on the optimized control for the research and development of future IM drives. All the highlighted insights and recommendations of this review will hopefully lead to increasing efforts toward the development of advanced IM drive controllers for future applications.

Optimization techniques to enhance the performance of induction motor drives: A review

For a reliable dynamic system and significant amount of savings in energy usage, adjustable speed drives (ASD) can play a vital role. The proper control of motor drives can give a good system response and also increase the efficacy of the drive. Recently the direct torque control (DTC) strategy has drawn great attention for motor drives due to its simplicity, insensitivity to the motor parameters, high reliability and improved dynamic response. Many control strategies have been developed for the improvement of conventional DTC drives focusing specifically on torque and flux. A number of techniques have been formulated and successfully implemented for induction motor (IM) control. This paper aims to provide a substantial updated review, albeit by no means complete, for those who are interested in keeping track of the present state-of-the-art in this field and working further. The review focuses on different control algorithms of DTC IM drives and their applications to minimize the energy losses and improve the system efficacy.

A review of reliable and energy efficient direct torque controlled induction motor drives

Since the discovery of nonlinear dynamics and chaotic behaviors of basic power converter circuits, stability analysis has been extended to more complex converter structures, paralleled and interconnected converters, microgrids, and power systems. While the analysis has long been identifying the parameters that cause various nonlinear phenomena, some work has shown direct relevance toward practical design of power converters, and control circuits. In this article, a review is conducted to highlight the key contributions of bifurcation analysis for power converter circuits and systems, and to discuss the ongoing work in this area.

Recent Progress and Future Research Direction of Nonlinear Dynamics and Bifurcation Analysis of Grid-Connected Power Converter Circuits and Systems

This paper aims to improve the performance of conventional direct torque control (DTC) drives proposed by Takahashi by extending the idea for 5-level inverter. Hybrid cascaded H-bridge topology is used to achieve inverter voltage vector composed of 5-level of voltage. Although DTC is very popular for its simplicity but it suffers from some disadvantages like- high torque ripple and uncontrollable switching frequency. To compensate these shortcomings conventional DTC strategy is modified for five levels voltage source inverter (VSI). Multilevel hysteresis controller for both flux and torque is used. Optimal voltage vector selection from precise lookup table utilizing 12 sector, 9 torque level and 4 flux level is proposed to improve DTC performance. These voltage references are produced utilizing a hybrid cascaded H-bridge multilevel inverter, where inverter each phase can be realized using multiple dc source. Fuel cells, car batteries or ultra-capacitor are normally the choice of required dc source. Simulation results shows that the DTC drive performance is considerably improved in terms of lower torque and flux ripple and less THD. These have been experimentally evaluated and compared with the basic DTC developed by Takahashi.

https://www.koreascience.kr:443/article/JAKO201509057413829.pdf

Modeling and experimental validation of 5-level hybrid H-bridge multilevel inverter fed DTC-IM drive

Direct Torque controlled induction motor (DTC-IM) drives have been used widely over last few decades. DTC-IM drives use the stator resistance of the motor for stator flux estimation which directly depends on the stator resistance of IM. Proper estimation of the stator resistance is very important because stator resistance varies due to the increase in temperature of the machine during operation. An online estimation of the stator resistance of the induction motor using model reference adaptive system (MRAS) and fuzzy logic for the direct torque control drive is modeled and verified in this paper. The error between the actual state variable of the machine and the estimated value of the reference model and rate of change of this error is used as input by the fuzzy estimator which gives the change in resistance value as output. From simulation it has been proved that the estimator can track the stator resistance value within 70 ms when a step change of stator resistance has been applied. The efficacy of the estimator is investigated in simulation by varying the stator resistance from the nominal value which has been done in MATLAB/SIMULINK.

Stator resistance estimation scheme using fuzzy logic system for direct torque controlled induction motor drive

Recently proposed power packet (PP) distribution system can reduce stand-by power, improve the traditional power distribution system efficiency using less power processing stages, and monitor load demand intelligently from source side to keep the power system stable. Each PP includes header and footer bits which are used to distribute the PP. Reduced footer bit can save the transitional switching loss. A modified PP format with reduced footer bit and an improved algorithm to route the PP to the objective loads are proposed in this paper and verified by the experimental results.

C. M. F. S. Reza

Papers

A review of reliable and energy efficient direct torque controlled induction motor drives

Recent Progress and Future Research Direction of Nonlinear Dynamics and Bifurcation Analysis of Grid-Connected Power Converter Circuits and Systems

Modeling and experimental validation of 5-level hybrid H-bridge multilevel inverter fed DTC-IM drive

Stator resistance estimation scheme using fuzzy logic system for direct torque controlled induction motor drive

Improved power routing algorithm for power packet distribution system