Single Converter Research Articles

New single‐stage bidirectional three‐phase ac‐dc solid‐state transformer

AbstractHigh‐power applications with low‐voltage (LV) dc loads, for example, fast charging stations for electric vehicles (EVs), are typically supplied from the medium‐voltage (MV) grid. Aiming for low volume, MVac‐LVdc solid‐state transformers (SSTs) that provide galvanic separation with medium‐frequency transformers (MFTs) are thus considered, which are conventionally realized as two‐stage systems that consist of an ac‐dc power‐factor‐correction (PFC) rectifier and an isolated dc‐dc converter. This letter extends a new single‐stage isolated bidirectional PFC rectifier concept to MV levels, resulting in an SST that performs MVac‐LVdc conversion in a single converter stage and, unlike many modular SST concepts, employs only a single MFT. The SST's primary side operates modular‐multilevel‐converter (MMC) bridge legs, whose input voltages contain large ac components, in the quasi‐two‐level mode to minimize the cell capacitors. The secondary side employs a standard LV three‐phase rectifier, and a dual‐active‐bridge‐(DAB)‐like modulation strategy allows power flow regulation and ensures sinusoidal grid currents. The concept is explained and validated using detailed circuit simulations of an exemplary 1‐MW system operating between a 10‐kV three‐phase grid and an 800‐V dc output. The component stresses are evaluated, and an efficiency of 98.1% and a power density of up to 0.6 kW/dm3 are estimated.

Hydrodynamic analysis and optimization of a floating wave energy converter with moonpool using OpenFOAM®

This paper presents the hydrodynamic analysis and optimization of a novel axisymmetric single cylindrical Wave Energy Converter (WEC) equipped with a moonpool, called MoonWEC. The primary aim of the study is to optimize the design of the MoonWEC by minimizing pitch rotations, enhancing heave motion, and facilitating moonpool oscillations. A set of new laboratory experiments was conducted to characterise the hydrodynamic response of the MoonWEC. These experiments were reproduced using a Numerical Wave Tank (NWT) in OpenFOAM. Qualitative and quantitative data were recorded, and the heave and pitch response was analysed by comparing experimental and numerical data. Good agreement between experimental and numerical data was observed throughout all the simulations. The results showed that the MoonWEC device can achieve the preferred excitation in heave, but it can also undergo the unpreferred excitation in pitch. By shifting the centre of mass, MoonWEC was numerically optimized to reduce the pitch rotations without affecting the heave oscillations. The moonpool motion was also analysed for the optimised prototype. The study shows that the CFD model in OpenFOAM coupled with the MooDy library can be used to simulate the hydrodynamics of the MoonWEC accurately. The optimization study shows that the centre of mass of the device is a key parameter in controlling the natural period of the device in pitch. The analysis of the moonpool shows that the MoonWEC has the potential to generate significant power.

Hybrid Energy Generation System with Brushless Generators

Important technical and financial hurdles exist when attempting to extend the power system to remote areas. Decentralized power generation utilising renewable energy sources (RES) has been promoted and is being further investigated as a result. This project showcases a microgrid architecture that uses brushless generators and a single voltage source converter (VSC). Wind and solar photovoltaic arrays are two of the renewable energy sources that power the microgrid system. But to keep the system reliable, there is also a battery energy storage system (BESS) and a diesel generator set. The simplified control and decreased number of switching devices are two benefits of the suggested architecture. In the current architecture, DG is configured as an AC source. The DC connection of the VSC is connected to the wind generator and the solar PV array, both of which are DC sources. Additionally, the BESS is utilised at the DC connection to assist with the dynamic instantaneous power balancing. In addition to integrating systems, VSCs may reduce power quality issues including harmonic currents, imbalance loads, and regulate voltage. To showcase all the aspects of the proposed system, we offer a diverse range of matlab/simulink simulation results.

Integration of multiple sources for fuel cell hybrid electric vehicles using single inductor multi-input converter

Fuel Cell Hybrid Electric Vehicles (FCHEV) use batteries and Photo Voltaic (PV) arrays to overcome Fuel Cell (FC) limitations like slow reaction times and low power densities. In a traditional power conversion system, three converters link FC, PV array, and battery to the output load. Despite using the FC, PV array, and battery, it has three inductors and several switches. Each switch also endures high voltage stress, possibly lowering power density and efficiency. This paper proposes a single-inductor multi-input converter (SI-MIC) that achieves 550 V as output where the input is variable. The fuzzy logic controller enables the integration of multiple power sources by selectively turning the ON and OFF switches in various operating modes. Fewer active switches during the powering process make it possible to employ semiconductors with a lower voltage. Thus, the converter generates high power with low conduction and switching losses. The state space model verifies the validity and stability of the converter under various operating modes.

Droop-Based DC Microgrids Analysis and Control Design Using a Weighted Dynamic Aggregation Modeling Approach

In this paper, Weighted Dynamic Aggregation (WD agg) approach is used for modeling, analyzing and control loop design of islanded DC microgrids. The proposed approach models <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><inline-formula><tex-math notation="LaTeX">$ \textbf {n}$</tex-math></inline-formula></i> DC-DC converters and their controllers with a single equivalent converter and an equivalent control system, which without sacrificing the accuracy, reduces the complexity of such large-scale system studies. It is shown that the model equivalent converter and control system parameters can be determined by the weighted average of the corresponding parameters of the large-scale system. The weight of each converter is quantified based on the contribution of that converter in the overall dynamic behavior of the large-scale system. WD agg model can accurately predict the transient response and can be employed in power planning, stability and sensitivity analyses with high accuracy. It is also shown that the proposed model can be used in designing the controller parameters of the large-scale system to ensure desirable system performance. The accuracy and applications of the proposed WD agg model are evaluated through time-domain simulations, and experiments of an islanded microgrid consisting of three paralleled converters with different control parameters connected to a Constant Power Load (CPL) emulating a challenging system stability case.

Design and implementation a novel single switch high gain DC-DC converter based on coupled inductor with low-ripple input current

A novel high-gain and high-efficiency direct current to direct current (DC-DC) converter is introduced in this paper. The presented converter is suitable for low-voltage renewable energy resources such as photovoltaic (PV) and fuel cell (FC). The existence of series inductance with the input source ensures continuous and low-ramp input current, which is important for extracting maximum power from resources. Using coupled inductor technology and an intermediate capacitor in the suggested converter leads to a high gain voltage. In the presented topology for recovering energy from the leakage inductor, reducing voltage stress on the power switch, and so decreasing overall converter losses, a passive clamp circuit is used. The suitable operation range of duty cycle in the converter, besides the leakage inductor, decreases the problem of reverse recovery in diodes. The low value of the leakage inductor and the low volume and cost of the proposed converter are due to the low turn ratio of the coupled inductor. Details of the operation principles of the proposed converter have been discussed in this paper. The presented simulation and laboratory prototype results verify the theoretical analysis and performance of the suggested topology.

Investigation of single and multiple MPPT structures of solar PV-system under partial shading conditions considering direct duty-cycle controller

Partial shading of solar panels diminishes their operating efficiency and energy synthesized as it disrupts the uniform absorption of sunlight. To tackle the issue of partial shading in photovoltaic (PV) systems, this article puts forward a comprehensive control strategy that takes into account a range of contributing factors. The proposed control approach is based on using multi-string PV system configuration in place of a central-type PV inverter for all PV modules with a single DC-DC converter. This adaptation enhances overall efficiency across varying radiation levels. Also, the proposed technique minimizes the overall system cost by reducing the required sensors number by utilizing a radiation estimation strategy. The converter switching strategy is synthesized considering direct duty-cycle control method to establish the maximum power point (MPP) location on the P–V curve. The direct duty-cycle tracking approach simplifies the control system and improves the system’s response during sudden partial shading restrictions. To validate the effectiveness of the suggested MPPT method, two system configurations were constructed using MATLAB/SIMULINK software and assessed under various partial shading scenarios. Additionally, a multi-string system was subjected to real irradiance conditions. The sensor-less MPPT algorithm proposed achieved an impressive system efficiency of 99.81% with a peak-to-peak ripple voltage of 1.3V. This solution offers clear advantages over alternative approaches by reducing tracking time and enhancing system efficiency. The system findings undoubtedly support the theoretical scrutiny of the intended technique.

Enhanced Cascaded Converters for Switched Reluctance Motor-Fed Electric Vehicles

This manuscript proposes an optimization technique for electric vehicles (EVs) operated through solar photovoltaic (PV) panels by enabling the drive of a switched reluctance motor (SRM) and an enhanced cascaded converter (ECC). The proposed method is an improved Tunicate Swarm Algorithm (ITSA). The Lévy flight distributions are emerging at the conventional Tunicate Swarm Algorithm (TSA) in the modified Tunicate Swarm Algorithm, which enhances the capabilities of diversification searching and avoids the potential for stagnation. The major objective of the proposed method is to minimize the ripple present in the supply current and give optimal photovoltaic power extraction to the solar module. The proposed enhanced cascaded converter method consists of a single main converter and one auxiliary converter combined as a series structure for the distribution of minimal voltage across the switch to restrict the switch stress of dv/dt. These quantities of error are lessened by the controller of Proportional–integral; the PI gain controller is tuned to the error and provides a reference current signal by using the proposed method. An optimum voltage gain and continuous input current minimize the impact of less solar irradiation in EV applications. Finally, the performance of the proposed method is implemented in the MATLAB platform and compared with existing methods.

PID-Based control of sepic power stage with QS bacterial-based search algorithm for renewable energy applications

In response to the growing need for efficient power conversion in renewable energy applications, this study addresses the issue of harmonic distortion and low Power Factor (PF) values caused by non-linear loads, such as electronic devices. Low PF results in reduced efficiency, increased energy consumption, and higher costs for both consumers and utilities. Active correction, typically involving an active circuit implemented using a power converter, provides an optimal solution by offering high performance, precise regulation, and low harmonic distortion. This research proposes a Power Factor Correction (PFC) solution utilizing an Interleaved DC-DC Single Ended Primary Inductance Converter (SEPIC) for the power stage and a Proportional Integral Derivative (PID) controller for the control block, tuned by a Quorum Sensing (QS) bacterial-based search algorithm. The PID controller parameters are derived using a frequency-domain approach, which presents advantages such as reduced design complexity, improved stability margins, and enhanced SEPIC performance. Simulation results indicate reduced overshoot, settling time, rise time, and Total Harmonic Distortion (THD) percentage, as well as increased efficiency and power factor nearing unity. The proposed scheme also demonstrates improved dynamic performance for variations in load, line, and reference voltage. Owing to its high efficiency, precise voltage regulation, and minimized impact on the electrical grid, this solution is well-suited for renewable energy applications, where optimizing energy conversion and ensuring stable operation are crucial for the overall performance of renewable energy systems.

Design and implementation of hybrid MPPT controller for FC based EV system with boost DC-DC converter

The fuel cell-dependent electric vehicle systems are giving an important role in the present automotive systems because their features are less air pollution, high flexibility, reduced oil dependency, and more reliability. However, the fuel stack delivers nonlinear output V-I characteristics. So, the extraction of peak power from the fuel source is very difficult. In this work, a Variable Step Size Radial Basis Functional Network-based Adaptive Fuzzy Logic Controller (VSSDE-AFLC) is proposed for tracking the peak power point of the fuel cell system. The merits of the proposed Maximum Power Point Tracking (MPPT) controller are high tracing speed of functioning point of the fuel cell, more flexibility, high abundant, acceptable oscillations across MPP, and less dependency on modeling of the fuel stack. Also, the single switch converter is utilized for increasing the voltage supply of the fuel cell. The features of the proposed converter are wide input operation, less voltage stress, high supply voltage conversion ratio, and good dynamic response. The proposed fuel cell-dependent boost converter is implemented by utilizing the MATLAB/Simulink software, and the converter is tested successfully by using the desired programmable DC supply.

An adaptive dynamic power management approach for enhancing operation of microgrid with grid ancillary services

The increasing prevalence of photovoltaic (PV)-wind-battery-based microgrids and their integration into distribution networks have brought new challenges in grid ancillary services, such as poor power quality (PQ), grid instability, voltage and current fluctuations, and low efficiency of microgrids. These adverse effects are due to the intermittent nature of PV and wind power generation. The present work proposes an adaptive dynamic power management (ADPM) approach and enhanced instantaneous symmetrical component theory (EISCT) to improve the microgrid operation and grid ancillary services. The proposed ADPM-based EISCT not only utilizes a single grid side converter (GSC) but also reduces the sensor requirement and control structure complexity and thereby eliminates communication mismatch. The control structure, proposed in this research, has two major segments. The first segment focuses on active power management control through ADPM to facilitate efficient power flow between the utility grid and microgrid sources which helps in ensuring efficient power sharing. The second component is dedicated to synchronizing the renewable energy sources of the microgrid with the utility grid and simultaneously maintaining PQ compliance as per IEEE 519–2022 standards. The efficacy and adaptability of the proposed structure are validated through MATLAB®/Simulink® environment and the practical superiority of the system has been tested by using MicroLabBox® DS1202-based real-time hardware set-up. The experimental result shows improved performance of the developed structure under various microgrid operating conditions including dynamic loading situations, and battery system state-of-charge (SOC). The simulation and experimental results suggested that the DC-link ripples have been reduced to 2%, peak overshoot to 1.8%, settling time during the transition to 1.2s, battery response time to 0.3s, and the total harmonic distortion (THD) to less than 5%. These results demonstrated the superiority of the ADPM-based EISCT over conventional strategies.

A Hybrid Interleaved DC-DC Converter Based on Buck-Boost topologies for Medium Voltage Applications

DC-DC power converters with high voltage gain are primary components for renewable energy generation such as offshore wind farms. As the DC-DC converters installed in these farms should have limited size and weight, the non-isolated DC-DC converters are the most suitable choose for the offshore wind farms. Although, several DC-DC converters with high voltage gain have been developed for offshore wind farms. Most of them includes large count of semiconductors or experiences high voltage stresses. In this paper, a reduced components count converter is proposed for the collector system of offshore wind farms. The proposed topology is a modular input parallel output series non-isolated DC-DC converter. It is a hybrid interleaved structure which combines two buck-boost topologies into a single converter. The proposed converter aims to offer high voltage gain with reduced voltage and current stress on the converter's components. Moreover, the interleaved PWM offers limited output voltage ripple and supply current ripple. The operation modes and the steady-state performance of the proposed converter are analysed. In addition, a small signal model based on the state space averaged method is developed for the proposed converter. The accuracy of the developed model is verified using the converter's switching model. Furthermore, the output voltage control scheme utilizing a simple PI controller for the proposed converter is presented.

Design and analysis of multiple input single output converter for hybrid renewable energy system with energy storage capability

This paper proposes the design and analysis of a multiple-input-single-output (MISO) DC-DC converter suitable for a hybrid renewable energy system with energy storage capability. The converter design and control strategy validated in this research can be used to regulate the output dc voltage obtained from multiple-source renewable energy systems. The design is realized using a non-isolated double boost converter as it can handle bidirectional power flow at the storage port and has other advantages like compact structure, reduced number of components, and double boosting capability. The converter can also work without transformers, enabling the input renewable energy sources to operate individually. An inverted decoupler control strategy is adopted in the design of this novel converter. Mathematical models were developed to obtain the decoupler matrix, and the proposed control strategy is utilized to analyze the output. Simulations were performed on MISO converters with load and reference variations and is validated with the prototype. The current ripple percentage at the dual source side is found to be reduced by 2.6%. Also, the rise time, settling time, and percent overshoot of the output voltage were reduced by 0.03 s, 45 ms, and 3.6%, respectively. The performance of the proposed MISO converter is validated on a 50 W hardware prototype. The results validate the MISO converter's superior dynamic performance, output voltage regulation and reduced dual source ripple current, all of which are in agreement to the results of the simulation. A comprehensive comparison with the traditional controller is also conducted to further illustrate the advantages of the proposed inverted decoupler. The inverted decoupler validated in this work can be effectively used in hybrid renewable energy systems with energy storage capability, as it is found to be immune to the disturbances from the source end.

Vulnerability analysis and modeling false data injection attack against voltage source converter in renewable generation power system

With the increasing penetration of renewable resources, more power electronic devices that need communication with control centers may bring a novel risk of cyber attacks. This paper investigates the vulnerability of the hierarchical control and proposes a false data injection attack (FDIA) constructing algorithm against voltage source converters. The attack can be accomplished via a physical attack generator or falsification via attacking supervisory control and data acquisition system. By developing the FDIA model against state estimation, the proposed attack model can circumvent bad data detection in the secondary control loop. The tests are carried out on a single converter infinite bus benchmark and an IEEE 34-bus system. The results show that the proposed attack model can mislead the system to produce threatening oscillation.

Large-Signal Stability of the Quadratic Boost Converter Using a Disturbance Observer-Based Sliding-Mode Control

The quadratic boost (QB) converter is a fourth-order system with a dc gain that is higher than the traditional second-order step-up configuration. The modern controllers that control these high-order dc–dc converters often only guarantee local stability around a steady-state equilibrium point, which is one of their primary drawbacks. In this article, a non-linear robust control law design to attain large-signal stability in this single switch QB converter is presented. In the presence of an unpredictable load, the control objective is to maintain the regulation of an output voltage. The Brunovsky canonical model of the converter was derived first, and the non-linear disturbance observer-based sliding-mode (SM) control law is designed based on it. An observer variable precisely estimates the output disturbances. The detailed process for deriving the control signal is described in this paper and the large-signal stability of the closed-loop converter system is ensured via the Lyapunov function. Finally, some simulation results are shown to validate the usefulness of the given controller.

Sigma Converter Family With Common Ground for the 48 V Data Center

The 48 V bus architecture has become a standard in modern Data Centers, due to the increasing power demands of digital loads. This requires low-profile, high-density Intermediate Bus Converters, able to efficiently step-down the input bus. Usually, this bus has a wide variation (40 V to 60 V), and the VRM must withstand the whole converted range, with a negative impact on efficiency due to design oversizing. A regulated IBC can address this issue, enabling a fine-tuned VRM design. In this paper, a novel regulated Regulated Hybrid Switched Capacitor sigma converter family (RHSC) is proposed, which enables regulation without sacrificing efficiency or power density. This is enabled by a new architecture featuring the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sigma</i> connection of a high-efficiency, unregulated converter with a low-power, regulated one sharing the same <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GND</i> domain, i.e. without the need of functional isolation. With this approach, efficiency and regulation can coexist in a single converter. This work includes the full analysis and design tools for the new RHSC family, together with two demonstrators: a 1.2 kW, 48 V to 12 V down-solution and a 750 W, 48 V to 5.1 V 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{th}$</tex-math></inline-formula> brick module, both exceeding a power density of 1 kW/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> .

Single-Phase AC-DC-AC Multilevel Five-Leg Converter Based on a High-Frequency Transformer

This paper investigates a single-phase ac-dc-ac multilevel five-leg converter based on a high-frequency transformer. The system consists of a three-leg module with a full-bridge module connected to the shared part of the system. In the proposed configuration, the dc link of the three-leg module is supplied by the full-bridge module through a single active bridge converter. This feature improves the power quality and efficiency of the structure and simplifies the design of the control strategy compared to the conventional solution that uses floating capacitors. The proposed system is composed of a shunt unit and a series unit. The first one is responsible for compensating reactive power and harmonic currents, while the second one provides load voltage compensation against voltage sags and harmonics in the grid voltage. In addition, the proposed converter operates with low dc-link voltages in applications with the same input and output frequency, such as unified power quality conditioner. The model of the system, a space-vector pulse-width modulation and the overall control scheme are addressed. Simulations and experimental results are presented to confirm the feasibility of the proposed converter and the correctness of the design methodology.

Power Dispatch Capacity of a Grid-Forming Control Based on Phase Restoring Principle

The concept of grid-forming control is driving system operators to define this technology's capabilities and requirements to maintain grid stability, reliability, and the need to provide some of the services previously provided by synchronous generators. The novel control strategy, called the “Phase Restoring Principle” (PRP), was recently introduced for converter operated power systems. This article provides further insights and confirmation of the PRP grid-forming capabilities based on the response requirements from the perspective of the power system. It describes the extension of the control by supplementing PRP with active power control allowing the control to cooperate with other sources. The generalized small-signal solution of the control is derived and evidenced. Analytical deductions supported by simulative evidence of the power dispatch based on PRP are displayed in single, double, and triple converter configurations. The development of steady-state operating point and, hence, drift frequency using the principle of PRP with active power control is examined and discussed based on reference values and weighted gain selection. The enhanced PRP control structure also displays controller stability for sufficiently small drift frequencies and achieves nominal frequency with dedicated parameters.

Frequency-Locked Loop Based New Automatic Phase-Shift Method for Active Islanding Detection of Three-Phase MicroGrid

This paper proposes an active Islanding Detection Method (IDM) integrating Frequency Locked-Loop (FLL) for the detection of voltage phase and frequency at the point of common coupling (PCC) and a modified Auto Phase Shift (APS) method for three-phase Distributed Energy Resource (DER) serving a local RLC load. The FLL is composed of a double second-order generalized integrator (DSOGI) to attenuate the harmonics and pass the fundamental positive sequence components in a frequency adaptive manner. Different from traditional APS methods, a new variable frequency term with an exponential factor is injected into the phase shift algorithm to reduce the region of Non-Detection Zone (NDZ). This modified approach enables the decentralized power generation system to detect the islanding phenomenon more quickly. Simulations and experimental tests conducted on a DG system on OPALRT (OP5600) and hardware test-bed demonstrate the behaviour of the proposed model within IEEE Standards. Additionally, a comparative evaluation was performed on the seamless transition of a microgrid (MG) from Grid-connected mode to Islanded mode and vice versa, using two different MGs, each having a single voltage source converter (VSC) and a local load but with control circuits incorporating DSOGI-FLL and ROGI-FLL respectively. Hardware testing results indicated that the control circuit based on ROGI-FLL demonstrated superior performance.

Stability Analysis and Control Strategy Optimization of a Paralleled IPOS Phase-Shifted Full-Bridge Converters System Based on Droop Control

The application of high-power DC equipment further increases the power supply scale of DC systems. But, it is difficult for a single converter to support high transmission power, so multiple converters must operate in parallel for efficient power transmission. In a parallel system comprising many IPOS phase-shifting full-bridge converters, current sharing can be realized via droop control. However, the stability of the parallel system using current-sharing control will appear poor in light load conditions, so it is necessary to analyze the stability of parallel systems in light load conditions. Firstly, a single IPOS phase-shifted full-bridge control system is modeled; on this basis, the state space model of the n-module paralleled IPOS phase-shifted full-bridge converters system is derived. Then, the influence of load power and the number of parallel IPOS phase-shifted full-bridge converters on the system stability is analyzed via eigenvalue analysis, and an optimal control strategy based on a particle swarm optimization algorithm is proposed. The control parameters are optimized for the parallel system of eight IPOS phase-shifted full-bridge converters. Finally, the above results are simulated to verify the accuracy of the stability analysis and the feasibility of the optimized control strategy.