Power Conversion Stage Research Articles

Predictive Control Applied to Matrix Converters: A Systematic Literature Review

Power electronic devices play an important role in energy conversion. Among the options, matrix converters, in combination with predictive control, represent a good alternative for the power conversion stage. Although several reviews have been undertaken on this topic, they have been conducted in a non-systematic manner, without indicating how the studies considered were chosen. This paper presents results from a systematic literature review on predictive control applied to matrix converters that included 142 primary papers, which were selected after applying a defined protocol with clear inclusion and exclusion criteria. The study provides a detailed classification of predictive control methods and strategies applied to different matrix converter topologies. Research findings require to be understood in combination to develop a common understanding of the topic and ensure that future research effort is based on solid premises. In light of this, this study identifies and characterizes different predictive control techniques and matrix converter topologies through systematic literature review. The results of the review indicate that interest in the area is increasing. A number of open questions in the field are discussed.

Single-Stage Multi-Input Buck Type High-Frequency Link's Inverters With Multiwinding and Time-Sharing Power Supply

A circuit structure, topological family, and unipolar phase-shift SPWM master-slave power distribution energy management control strategy (EMCS) of the single-stage Buck type multi-input high-frequency (HF) link's inverters with multiwinding time-sharing power supply are proposed in this article, in order to reduce the power conversion stage, volume and weight, and increase conversion efficiency and reliability. The key technologies of this kind of inverter, such as circuit structure and topological family, EMCS, power supply mode (PSM), and steady-state principle characteristics, are deeply studied. The circuit structure is composed of multiple isolated HF inverting bridges, a HF transformer with multi-input single-output, a cycloconverter and an output <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filter. The EMCS is to generate the bipolar tristate multilevel SPWM waves by phase-shift between the right arm and the left arm of multiple HF inverting bridges; the cycloconverter demodulates it into the unipolar tristate multilevel SPWM wave, and performs zero voltage commutation. The experimental results of the designed and developed 1kVA multi-input inverter prototype have shown it has the advantages of single-stage power conversion, HF electrical isolation, high conversion efficiency, small volume and weight, high reliability, stable output voltage, multi-input source master-slave power distribution, and smooth switching of different PSMs.

Performance Analysis of LED Driver Circuit using DC-DC Converter Topology

High Pressure Sodium (HPS) lamp has been extensively employed in outdoor lighting. But the need of time is to save electricity since HPS has high consumption of electricity. Light Emitting Diodes (LEDs) are better choice to replace HPS. Since they are compact and with very low power ratings, they have very high illumination. The basic difference between LED and HPS is that, HPS works on normal AC voltage supply whereas LED requires low DC voltage to operate. Hence a converter circuit with low voltage rating is required for proper functioning of LED. In this paper, simulation and hardware implementation of an LED driver base on a permutation of the buck converter as the DC-DC power conversion (PC) stage and buck-boost converter as the power factor rectification (PFR) stage is presented. This paper presents the hardware implementation of LED driver circuit for 12 V LED lighting strip.

Interfacing Standalone Loads With Renewable Energy Source and Hybrid Energy Storage System Using a Dual Active Bridge Based Multi-Port Converter

Batteries used for providing backup power in renewable energy sources (RES) fed standalone power systems often suffer from a limited lifetime because of high charging and discharging currents arising from sudden changes in load and/or generation. To prevent this, supercapacitors (SCs) are used to supply the high-frequency (HF) power surges. In this article, a new way of interfacing hybrid energy storage systems (HESSs) (Battery + SC) with RES and loads by employing a current fed dual active bridge (DAB) converter based multi-port converter (MPC) is proposed. The proposed approach enables the MPC to regulate the load voltage while tracking the maximum power point (MPP) of the RES and protecting the battery from transients arising from variations in load and/or renewable generation. The SC is used for tracking MPP so that the transient changes in RES generation do not cause a sudden rise/fall in the battery current. The employed MPC structure is designed in such a way that most of the power processing takes place in one stage only resulting in lower losses. The number of switches is reduced by merging the power conversion stages, which helps in keeping the cost low. Experimental results on a laboratory prototype under various static and dynamic conditions are presented.

A Single-Stage Wireless Power Transfer Converter With Hybrid Compensation Topology in AC Input

Miniaturization and low cost contribute to the development and popularization of wireless power transfer (WPT). Reducing the number of power conversion stages can reduce the volume and cost of the WPT converter, and even make it possible to improve the efficiency. A single-stage WPT converter with constant current (CC) and constant voltage (CV) output and its asymmetric modulation method are proposed in this paper. A direct AC-AC converter is applied to the primary side of the WPT converter to directly convert line-frequency AC to high-frequency AC. The applied direct AC-AC converter that can replace the commonly used multi-stage primary converter reduces the number of circuit devices, thereby reducing the volume and cost of primary converter. The proposed WPT converter can realize zero voltage switching (ZVS) and power factor correction (PFC). In order to achieve CC and CV output, a switchable hybrid compensation topology is applied to the proposed WPT converter. A 720-W experimental prototype was manufactured to verify the rationality of the proposed WPT converter and the correctness of the theoretical analysis.

A Study of MPPT Charge Controller Roles in Photovoltaic Energy Management

Nowadays, the world's demand the energy is increasing. So, we need a good energy management system to use the available energy. An energy management system consists of maximum power point tracking (MPPT) charge controller, battery management, and the power conversion stage to control and reduce energy consumption. Solar energy is used solar radiation and is converted into electrical energy. In photovoltaic (PV) system consists of a PV module, charge controller, battery storage, and load. Arduino NANO is used in this project because it's low cost and has an efficient microcontroller in the MPPT charge controller to prevent the battery from overcharging and display the maximum power point (MPP). Perturb and Observe (P&amp;O) and Incremental Conductance (InC) algorithm is used in the MPPT charge controller to transfer maximum power from the PV module which is executed using a microcontroller. The voltage, current, and power from the MPPT charge controller, are shown on a liquid crystal display (LCD). The benefit of this project is to achieve high efficiency and low cost of photovoltaic modules for the design of photovoltaic systems with a simple MPPT.

A High-Power-Density High-Efficiency Soft-Switched Single-Phase Universal Input to 28-V Isolated AC–DC Converter Module Designed for Paralleled Operation

This article presents a high-power-density high-efficiency soft-switched single-phase universal input to 28-V isolated ac–dc converter module designed for parallel operation. The proposed two-stage converter utilizes a totem-pole bridgeless boost power factor correction (PFC) ac–dc converter stage followed by an isolated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant dc–dc converter stage. A comprehensive design and optimization methodology is presented that compares various designs and operating modes for the converter's power stages and selects the optimal design based on overall power density and efficiency. Additionally, a control scheme is presented for the PFC stage to minimize current distortion by accounting for various sensor, control, and gate-drive delays while ensuring zero-voltage switching (ZVS) of the transistors. Moreover, a new droop control strategy is presented, which utilizes the input current of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> dc–dc stage to ensure equal output current distribution between paralleled modules powering a common output load. To validate the proposed design and control strategy, two 1-kW universal input to 28-V isolated ac–dc converter modules are built and tested. Each prototype converter module achieves a high power density of 84 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and a peak efficiency of greater than 93% while ensuring a current distribution error of less than 0.3% when operating in parallel to deliver the maximum output power of 2kW.

Dual-Boost Inverter for PV Microinverter Application—An Assessment of Control Strategies

Photovoltaic (PV) microinverters have grown rapidly in the small-scale PV market, where typical two-stage converters are used to connect one PV module to the single-phase AC grid. This configuration achieves better performance in terms of energy yield compared with other PV configurations. However, the conversion efficiency of a two-stage system is the main drawback, especially when a high-voltage gain effort is required. In this context, single-stage microinverter topologies have been recently proposed since only one power conversion stage is required to extract the maximum power of the PV module and inject the AC power to the grid. This single-stage configuration allows considerable improvement of the overall efficiency of microinverters by reducing the number of elements in the system. However, the main challenge of these topologies is their control, since all variables of the converter are composed by the AC waveform with DC-bias. In this paper, four control strategies are analyzed for the mainstream single-stage topology, which is the dual-boost inverter (DBI). Classical linear control and three non-linear strategies, namely finite control set–model predictive control, flatness-based control, and sliding mode control, are detailed. The main contribution of this work is a complete comparison of the control strategies, to give insights into the most suitable control strategy for the DBI in PV microinverter application.

Virtual Intermediate Bus CPU Voltage Regulator

This article presents a merged two-stage 48-V-to-1-V point-of-load (PoL) architecture with a 24-V virtual intermediate bus (VIB) for CPU voltage regulator applications. The VIB-PoL architecture includes two power conversion stages linked by a 24-V VIB with a significant voltage ripple. The first stage is a 2:1 interleaved charge pump, which converts 48 to 24 V. The second stage comprises multiple interleaved four-level series-capacitor buck modules with coupled inductors, converting 24 V to regulated 1 V with an equivalent voltage conversion ratio of 6:1. The VIB-PoL architecture achieves high efficiency and high power density by reducing the power conversion stress of both stages and eliminating the intermediate bus capacitors. A 48-V-to-1-V 640-A CPU voltage regulator with a peak power stage efficiency of 95.2% (93.3%, including gate driver loss), a full-load efficiency of 84.4% (83.1%, including gate driver loss), and a power density of 463 W/in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^3$</tex-math></inline-formula> (at 1-V output with liquid cooling) is built and tested to demonstrate the VIB-PoL architecture.

Pulse-Amplitude-Modulation Full-Bridge Diode-Clamped Multilevel LLC Resonant Converter Using Multi-Neighboring Reference Vector Discontinuous PWM

A full-bridge diode-clamped multilevel LLC resonant converter suitable for power conversion systems that use high input voltage, such as railway vehicles, is proposed in this paper. In order to eliminate the voltage deviations of the capacitors connected in series to the high voltage input DC link, a novel modulation strategy referred to as multi-neighboring reference vector discontinuous pulse-width modulation (MNRV DPWM) is proposed. Unlike the existing two-level resonant converter that varies the operating frequency to hold the output voltage constant, the proposed multilevel resonant converter modulates the amplitude of the fundamental wave input to a resonance tank while fixing the operating frequency at the resonance point. Therefore, the design of passive elements becomes easier, and stable operation is possible over a wide operating range with only one power conversion stage. In this paper, the control algorithm and operation characteristics of the newly proposed full-bridge diode-clamped four-level LLC resonant converter are analyzed in detail and design guidelines are presented. The feasibility of the proposed converter is verified through a simulation and an experiment with a prototype converter.

Reduction of power conversion losses in AC-DC coupled hybrid micro-grid under grid distorted voltage scenario

As the power consumption rate is high, the supply from fossil fuels is not enough to meet consumer demand. Further, the depletion of fossil fuels and environmental concern forces the extraction of power from low carbon fuels causes generation problems due to its uncertainty and intermittent in nature. So, low carbon fuels such as wind, solar, etc. can therefore, be incorporated into a more efficient hybrid micro-grid system. In the current dominated AC coupled hybrid micro-grid system, a significant amount of power conversion losses is increased due to more power conversion stages. Therefore, this research paper proposes an appropriate loss calculation method (i) to validate AC-DC coupled hybrid micro-grid system has minimum power conversion losses than the AC coupled hybrid micro-grid system, (ii) appropriate power sharing between AC and DC bus and (iii) grid current harmonics mitigation. To validate this method, different case studies are performed in MATLAB simulation by considering undistorted and distorted grid conditions with variation in renewable energy sources. The observed results demonstrate that the merits of the AC-DC coupled hybrid micro-grid system has been validated over AC coupled hybrid micro-grid system.

Wave-to-grid (W2G) control of a wave energy converter

Grid integration of wave energy involves various power train stages from device to grid, such as a power take-off stage, a power conversion stage, and a power conditioning stage. The coupled performance of the complete wave-to-grid system depends heavily on the dynamics of each stage and their respective controllers. However, the control objectives of various stages may not align with each other and pose a potential problem, in terms of economic performance and grid integration. This study presents a complete wave-to-grid control approach for a wave energy converter, ensuring that the system performs optimally under variable wave resource conditions. The proposed system comprises a point absorber wave energy converter oscillating in heave, a linear permanent magnet generator, and back-to-back power converters for connection to the grid. Additionally, short term energy storage, based on an ultra-capacitor, is also added to the DC link between the back-to-back converters for power quality improvement. In the paper, a mathematical model is derived for the individual components of the wave-to-grid system. Then, the controllers for each stage of the power train are designed. A LiTe-Con controller is used for maximum power extraction on the device side, while Lyapunov-based nonlinear controllers are designed for power converter control in order to achieve the full range of control objectives. The result shows that the proposed controllers accomplish the desired control objectives and perform well under various operating conditions.

Maximum Power Point Tracking of an Off-Grid Photovoltaic System Consisting of a Series Connected Supercapacitor with a Step-Down Converter

An off-grid photovoltaic (PV) system's PV array is connected with a charge controller as the first power conversion stage. The average efficiency of the power stage of charge controllers is around 90%. Supercapacitor (SC) battery hybrid PV system is a novel PV system that utilizes some of the wasted energy of a typical system and enhances the system's efficiency up to 98%. However, the feasibility of maximum power point tracking (MPPT) for this system is yet to be validated. This paper presents a comparative study to adapt MPPT for the proposed system consisting of a series-connected SC bank with PV array and step-down DC-DC converter. The step-down converter is used as the impedance matching network. Different solar irradiance profiles were emulated to check the feasibility and efficiency of MPPT. Experimentally, it was shown that the typical MPPT could be adapted to the proposed PV system with very high MPPT efficiency.

Double Adaptive PI-Structure for Regulating a Microgrid DC Bus Using a Flyback-Based Battery Charger/Discharger Converter

DC microgrids are composed of loads, renewable sources, and storage devices that require control and protection to operate safely. The flyback converter is an alternative to connect paralleled batteries with nominal voltage DC buses; however, until now, complex controllers have been proposed, making difficult their implementation. On the other hand, when the voltage of a DC microgrid is not properly controlled, the loads may be damaged due to the voltage outside of the safe range. Therefore, proposed in this paper are two adaptive PI-structures to control a battery charger based on a flyback converter to be used in DC microgrids. The first adaptive current controller regulates the magnetizing current for stabilizing the system, and the second adaptive voltage controller regulates the voltage of the DC bus to protect the elements of the microgrid. The methodology to design the adaptive parameters of the PI-structures is developed as follows: first, the power stage of the flyback converter is introduced to derive a control-oriented model. The battery and the DC bus of the microgrid, which are interfaced by the flyback converter, are represented with widely accepted approaches. The second step is focused on modeling the system. The flyback converter, which includes a capacitance to model the DC microgrid, is represented by a dynamic model. The differential equations are averaged, and several transfer functions of the main variables are obtained. In the third step, the transfer functions are used to design the PI adaptive current controller and the PI adaptive voltage controller. In the last step, several recommendations are made to implement the power and control stages in low-cost hardware. An application example with realistic parameters is carried out in PSIM to validate the controller loops design. A battery of 12 V is connected to a DC microgrid of 48 V through a flyback converter with a switching frequency of 50 kHz. The settling time and deviation of the DC microgrid voltage, after a perturbation, are 0.845 ms and 2.04 V respectively, while the maximum values are adjusted to be 1 ms and 2.4 V. The simulation results validate the proposed procedure and the effectiveness of the PI-structures in regulating the magnetizing current and the DC bus voltage.

Continuous Simulation of the Power Flow in AC–DC Hybrid Microgrids Using Simplified Modelling

This paper reports the development of a model for continuous simulation of the power flow into AC–DC hybrid microgrids operating for different generation–consumption scenarios. The proposed application was assembled using a multiple-input multiple-output model which was built using blocks containing simplified models of photovoltaic (PV) modules, wind turbines (WT), battery arrays (energy storage units, ESU), and power loads. The average power was used as the input/output variable of the blocks, allowing flexibility for easy reconfiguration of the microgrid and its control. By defining a generation profile, PV and WT were modeled considering environmental conditions and efficiency profiles of the maximum power point tracking (MPPT) algorithms. ESUs were modeled from intrinsic characteristics of the batteries, considering a constant power charge regime and using the State of Energy (SoE) approach to compute autonomy. To define a consumption profile, DC and AC loads were modeled as a constant real power. As an innovative characteristic, unidirectional and bidirectional power conversion stages were modeled using efficiency profiles, which can be obtained from experiments applied to the real converters. The outputs of the models of generation, consumption, and storage units were integrated as inputs of the mathematical expressions computing the power balance of the buses of the microgrid. The proposed model is suitable to analyze efficiency for different configurations of the same microgrid architecture, and can be extended by integrating additional elements. The model was implemented in LabVIEW software and three examples were developed to test its correct operation.

A Topological Advancement Review of Magnetically Coupled Impedance Source Network Configurations

Magnetically coupled impedance source networks provide a wide range of applications, such as dc to dc, dc to ac, ac to ac, ac to dc unidirectional or bi-directional power conversion. Various impedance source networks are reported in the literature to overcome the barriers of conventional voltage source inverters. They offer high boost with buck-boost capabilities and reduce power conversion stages. Thus, they provide an economical solution to expanding power systems, and are most suitable for renewable sources having low output. The goal of this study is to provide an in-depth comprehensive review of the major topologies of magnetically coupled impedance source networks. The review is more focused towards the fast-growing niche area, which has seen many advancements in the last few years. Best efforts are made to include relevant major topological advancements, with the aim of providing relevant and accessible information for researchers. This research provides a detailed comparison of essential factors and presents a full assessment of major topological improvements in MCIS networks.

Dual Active Bridge Based Reduced Stage Multiport DC/AC Converter for PV-Battery Systems

Standalone power systems are significant for electrifying the remote areas where extending the grid connectivity is not feasible, either economically or logistically. Solar Photovoltaic (PV) systems with battery backup are among the most popular candidates to serve as an energy source in standalone systems. This article presents a novel multiport converter (MPC) for PV-battery systems powering standalone loads. The proposed converter is a reduced stage power converter based on current fed dual active bridge (CF-DAB) topology. CF-DAB offers galvanic isolation and a high voltage ratio without sacrificing efficiency. Switching losses are further reduced by a modified modulation scheme that reduces the average switching frequency of some of the switches. The proposed converter performs the functions of tracking maximum power point of the solar panel and regulating the load voltage while using fewer power conversion stages. This is done by sharing components among the various stages performing maximum power point tracking, voltage boosting, and dc/ac conversion. A small-signal model of the proposed MPC required for its closed-loop control is also proposed, which can also be utilized for other CF-DAB-based converters. A lab prototype of the proposed MPC has been fabricated and its operation has been validated under various static and dynamic conditions.

Single-Stage Buck–Boost Inverters: A State-of-the-Art Survey

Single-stage buck–boost inverters have attracted the attention of many researchers, due to their ability to increase/decrease the output voltage in one power conversion stage. One of the most important uses of these inverters is in photovoltaic applications, where the voltage of the solar panels varies in a wide range. In recent years, many new inverters have been proposed to improve the performance of existing structures. In this paper, the state of the art of these single-stage buck–boost inverters is discussed. The advantages and disadvantages of each structure are examined from different perspectives, such as the number of components, losses, and performance. Finally, in a general comparison, the properties of all structures are discussed and summarized in a table.

Single Stage Power Control Strategy for Nanogrid Connected Solar PV System

The focus on reduction of converter size in nanogrid connected Photo-Voltaic(PV) systems increases to obtain the various advantages. This paper proposesa single stage nanogrid connected solar PV system that works with DC-ACinverter along with the closed loop control strategy to send the maximumpower from the PV array. The proposed scheme controls the power deliveryof the PV system to nanogrid in a single stage power conversion along withthe incorporated Maximum Power Point Tracking (MPPT) controller. Thedecoupled control strategy has been designed and developed for the proposedsystem using synchronous reference frame theory. The developed hardwareprototype in the laboratory has been used to validate MATLAB/Simulink sim-ulation results. The simulation and experimental results have been observed for dynamic changes in irradiation by maintaining the Total Harmonic Dis-tortion (THD) within the standard limits while operating at unity powerfactor. The successful validation of the proposed control strategy shows itsusefulness in real-time nanogrid applications.

Reactive Power Compensation in a Hybrid Renewable Energy System through Fuzzy Based Boost Converter

The reactive power compensation is essential during hybrid grid connected system, because the overall power factor of the power systems is reduced due to DC energy fed to the grid using electronic energy inverters. Increased load on the grid due to poor power factor triggers losses in the grid. The main objective of the work related to control the Reactive Power flow in grid connected Hybrid Renewable Energy System (PV-wind-battery). The objectives of the work were achieved by satisfying the load demand, injecting the reactive power from hybrid sources to the grid. First, the proposed technique with fuzzy based boost converter is implemented. It reduced power conversion stages, decreases the losses compared to existing Hybrid Grid-connected systems. The most significant result of the work is the conclusion that the fuzzy based boost converter should increase the Maximum power from solar PV Panel, The speed control of wind energy system is control by speed controller-fuzzy rule, and it created with low speed to high speed. The significance of the obtained results is that the used methodology allowed maximum energy utilized by hybrid renewable energy system to grid. The reactive power is maintained at zero level in order to ensure the unity power factor operation. But rather significantly enhances the small voltage fluctuation in the grid. In addition, to reduces the current total harmonic distortion to 1.9 %, which is good lower than the requirement for network operation. The proposed method is verified using MATLAB/Simulink. The simulation results were supported experimentally.