AC-DC Converter Research Articles

Behavior of Residual Current Devices at Earth Fault Currents with DC Component.

Low-voltage electrical installations are increasingly saturated with power electronic converters. Due to very high popularity of photovoltaic (PV) installations and the spread of electric vehicles (EV) as well as their charging installations, DC-AC and AC-DC converters are often found in power systems. The transformerless coupling of AC and DC systems via power electronic converters means that an electrical installation containing both these systems should be recognized from the point of view of earth fault current waveform shapes. In such installations, various shapes of the earth fault current may occur-a DC component of a high value may especially flow. The DC component included in the earth fault current influences the tripping threshold of residual current devices (RCDs)-the devices which are mandatory in certain locations. This paper presents results of the AC-type, A-type, and F-type RCDs sensitivity testing under residual currents of various compositions of the DC component. This testing has shown that the DC component may both degrade and improve the sensitivity of RCDs. Moreover, unexpected positive behaviors of RCDs in some circumstances under DC residual current is discussed. Therefore, recognizing the real sensitivity and behavior of RCDs from the point of view of the DC component is important for effective protection against electric shock, in particular, in PV installations and EV charging systems. The research results provide a new insight into the real behavior of RCDs in modern power systems and, consequently, the safety of people.

Quasi-Single-Stage Current-Fed Resonant AC–DC Converter Having Improved Heat Distribution

This article presents a quasi-single-stage current-fed resonant ac–dc converter having improved heat distribution. Secondary-side switches are turned <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> with the voltage closed to zero at high instantaneous power and with the voltage closed to the half of the output voltage at low instantaneous power. Switching losses at the primary-side bottom switches are reduced; this change improves the heat distribution over the switches. The primary-side duty-cycle fixed at 0.5 results in negligible input current ripple; this trait can significantly reduce the size of filter inductor at the grid side. Experimental results show the effectiveness of the proposed ac–dc converter and its improved heat distribution against a conventional solution.

A Scalable Filter Topology for $N$-Parallel Modular Three-Phase AC–DC Converters by an Arrangement of Coupled Inductors

Modularity in hardware improves the manufacturability of power electronics systems and reduces maintenance costs. By paralleling modular ac–dc converters, the current capacity of SiC-based power conversion systems can be easily expanded. However, it is questionable which filter topology can be chosen for an arbitrary number of the converters ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> ). Considering interleaving, filters without any coupling may result in an overdesign. Meanwhile, filters that magnetically couple the paralleled converters may suffer from complexity in mechanical structure and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N-1$</tex-math></inline-formula> redundancy. Based on these observations, this article proposes a filter structure that can be easily scaled to any number of converters. The proposed structure is comprised of a coupled inductor (CI) forming a loop of secondary windings, a single boost inductor on that loop, and a normally <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> normally closed (NONC) contactor per converter. Circulating currents are attenuated by the CI for any <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> . A single inductor rated for each channel realizes a boost inductor for a whole <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> -converters, which can bring a significant benefit on power density and cost. When one of the converter faults, the faulty converter can be easily isolated from the system by the NONC contactor, thus achieving <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N-1$</tex-math></inline-formula> redundancy. The proposed filter topology is experimentally verified with a 20-kW full-SiC modular ac–dc converter.

Design of an Indirectly Coupled Filter Building Block for Modular Interleaved AC–DC Converters

This article presents the analysis and realization of a modular interconnected filter building block (FBB) operating under a single and multichannel (parallel three-phase converter blocks) configuration without loss of attenuation to any harmonic components. Emphasis is on the design of coupled inductor (CI) and boost inductor. In order to achieve a modular scheme with interleaved operation, indirect coupling between converters is realized using the secondary loop (SL)-based interconnection with inserted impedance. Here the “SL” serves as an additional pass for average grid side currents for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> channels. A building block type configuration has been proposed using this topology, inspired by the power electronics building block (PEBB) nature. The purpose of the loop is to interconnect the parallel converters in series using an arrangement of CIs. In addition, a boost inductor has been introduced in the SL to realize a power factor correction rectifier operation. The CI serves as the circulating current filter while reflecting channel currents toward the SL. To meet conducted electromagnetic interference (EMI) limits, a two-stage <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCLC</i> filter has been integrated with the FBB by introducing the point of common coupling (PCC) connection between two stages for filter size reduction. A design procedure is presented to meet power quality, circulating current, and EMI limits as per industry standards (EN-55011 and IEEE-519/1594). The proposed FBB has been characterized using 3L-NPC converters enabled with 1.2 kV Silicon Carbide based modules with comprehensive performance validation up to three channels in parallel with 15-kW power rating per channel.

Principles, design and implementation of a direct AC-to-AC power converter-Regulated electronic transformer.

In the last three decades, the energy conversion market has been dominated by switching power converters due to reduction of size and cost of electronic components. This market includes four types of conversion: DC-DC, DC-AC, AC-DC, and AC-AC. While the first three types are applied directly in a single conversion, the AC-AC converter is comprised of two serial converters leading to an AC-DC-AC conversion. This article introduces, for the first time, a real direct single-stage AC-AC conversion electronic transformer. The single stage AC-AC converter is fabricated using a unique high efficiency topology, combined with the advantages of dual-stage power-quality protection. This single-stage AC-AC regulated electronic transformer is stabilized, controlled, protected, and can lock onto any line voltage (110 or 220V) with a frequency of 45-65Hz. Stabilization is achieved by fast pulse-width modulation technology, applied by two-way fast solid-state switches. The transformer is controlled by a 150MHz digital signal processor and is fully protected against overcurrent and output short circuits. Our first stage transformer is a single-phase device with 5 kW power with an efficiency of better than 97% with one-tenth of the weight and volume of present conventional electromechanical transformers.

Single-Stage Isolated and Bidirectional Three-Phase Series-Resonant AC–DC Converter: Modulation for Active and Reactive Power Control

Single-stage isolated and bidirectional (SSIB) AC–DC converters have a high potential for future solid-state transformers and smart battery chargers due to their reduced volume and high efficiency. However, there is a research gap for SSIB reactive power injection. This article introduces an SSIB three-phase AC–DC converter composed of three low frequency rectifiers linked by tiny film capacitors with a quad-active-bridge series-resonant (QABSR) DC–DC. A novel QAB modulation is proposed to solve three issues: (1) Three DC inputs with high ripple compensation, (2) active–reactive power injection, and (3) minimization of high-frequency (HF) transformers currents. The rectified grid voltages were modulated by time-variant duty ratio (DR) angles. In contrast, the DC source was modulated by a fixed DR (FDR) angle along with a phase-shift angle which changes according to the grid current amplitude. A constant HF current amplitude with minimum value was obtained. It is shown that the HF current amplitude is increased for reactive power injection. Hence, the FDR angle was used to compensate for this increase. Active and reactive power control were validated in a 2 kW prototype. Compared with other structures, tiny DC-link capacitors and smaller L filters were used. Moreover, higher efficiency (96%) and smaller grid currents THDi (3%) were obtained.

A novel suppression method for input current distortion of the Vienna rectifier under unbalanced grid conditions

The Vienna rectifier is an excellent Power Factor Correction (PFC) AC–DC converter which has low Total Harmonic Distortion (THD) of input current, resistance to high-voltage, and high efficiency. Based on the structural characteristics of Vienna rectifier under the unbalanced grid conditions, considering the influence of grid voltage negative sequence component, the reference modulation wave of Vienna rectifier will lead or lag the input current, and the input current will be distorted which affects the power quality of Vienna rectifier. In this paper, a novel modulation waves clamping method by modifying the current command of the rectifier is proposed to eliminate the input current distortion under unbalanced grid conditions. By analyzing the distortion mechanism of the input current for a Vienna rectifier in unbalanced grid, the drawback of the conventional modulation waves clamping method for suppressing the input current distortion is illustrated, which shows that the method is ineffective in certain non-ideal grid conditions. Moreover, the proposed method modifies the current command, which realizes adjusting the clamping interval for modulation waves. So signs of the reference modulation wave and the input current are avoided to be inconsistent, and the input current distortion is suppressed. Besides, the quality of the input current is improved effectively. Finally, experimental results show that the proposed method can suppress the input current distortion obviously under the unbalanced grid conditions. Compared with conventional modulation wave clamping method, the THD value of the input current for a Vienna rectifier is reduced effectively (below 2%) with the proposed method.

A Review on Hydrogen-Based Hybrid Microgrid System: Topologies for Hydrogen Energy Storage, Integration, and Energy Management with Solar and Wind Energy

Hydrogen is acknowledged as a potential and appealing energy carrier for decarbonizing the sectors that contribute to global warming, such as power generation, industries, and transportation. Many people are interested in employing low-carbon sources of energy to produce hydrogen by using water electrolysis. Additionally, the intermittency of renewable energy supplies, such as wind and solar, makes electricity generation less predictable, potentially leading to power network incompatibilities. Hence, hydrogen generation and storage can offer a solution by enhancing system flexibility. Hydrogen saved as compressed gas could be turned back into energy or utilized as a feedstock for manufacturing, building heating, and automobile fuel. This work identified many hydrogen production strategies, storage methods, and energy management strategies in the hybrid microgrid (HMG). This paper discusses a case study of a HMG system that uses hydrogen as one of the main energy sources together with a solar panel and wind turbine (WT). The bidirectional AC-DC converter (BAC) is designed for HMGs to maintain power and voltage balance between the DC and AC grids. This study offers a control approach based on an analysis of the BAC’s main circuit that not only accomplishes the function of bidirectional power conversion, but also facilitates smooth renewable energy integration. While implementing the hydrogen-based HMG, the developed control technique reduces the reactive power in linear and non-linear (NL) loads by 90.3% and 89.4%.

Intelligent control of integrated on-board charger with improved power quality and reduced charging transients

This paper proposes an intelligent control scheme for a two-stage integrated onboard electric vehicle (EV) battery charger connected to a single-phase household outlet which offers a close to ideal battery charging profile with power factor correction feature. Generally, the front-end AC–DC​ conversion stage is controlled by dual loop proportional–integral (PI) controllers, and tuning their gain constants is a difficult task. Furthermore, to achieve a close to ideal charging profile for an EV battery, the DC–DC conversion stage switches from constant current (CC) and constant voltage (CV) mode after a certain state of charge (SOC) which may lead to discontinuity in the charging current and voltage. This paper attempts to solve these issues by proposing an intelligent control scheme that includes the dynamic estimation of PI controller gain constants as well as provides a seamless mode transfer feature for battery charging. It is achieved by using fuzzy-PI-based control in the AC–DC conversion stage and Bayesian Regularization (BR) algorithm trained artificial neural network (ANN)-based control in the DC–DC conversion stage. The performance of the proposed control scheme is assessed both in steady-state and transient conditions in MATLAB® Simulink environment by comparing it against similar control schemes. The proposed intelligent control approach improves the dynamic response of DC link voltage, offers unity power factor operation and maintains the line current harmonics within IEEE 519 standards even during the switchover from CC to CV charging mode. Also, there is a decrease of 85% in the third harmonic component of the source current, 23.2% improvement in DC link voltage undershoot and 6.5% reduction in DC link voltage overshoot with reduced settling times using the proposed unified control scheme.

Systemic optimal control of wind energy system regulating conjointly generator speed and battery recharging current

In this paper is presented an optimal control technology of wind energy system recovering energy in a battery energy accumulator. This control technology makes it possible to regulate the speed of the electric generator at its optimum value, to avoid any over-speed problems leading to strong increases in current in the electrical components of the wind turbine, and subsequently to its destruction. This control technology also makes it possible to maintain the induced electromotive forces in phase with the phase’s currents of the generator to have an additive electromagnetic torque, and in this way the recovered energy will be optimal. This control technology is based on two conversions, one is an Alternative-Continuous conversion performed by an AC-DC converter with IGBTs, and the other is a DC-DC conversion performed by a booster chopper to regulate the voltage of recharges batteries at its nominal value.

Analyses of charging power and performance in electric vehicles using Fuzzy Type-II approach

Nowadays, there is a need for charging electric vehicles (EVs) wirelessly, since it provides a more convenient, reliable, and safer charging option for the EV customers. A wireless charging system using a double-sided LCC compensation topology is proven to be highly efficient. In this paper, considering the importance of wireless charging of electric vehicles, using a circuit equivalent to the wireless power Transfer (WPT) system, the behavior of electric vehicles in the power grid only in technical analysis is investigated. Accordingly, two different scenarios have been used in modeling and simulation. In the first scenario, the charge of electric vehicles was controlled using an [Formula: see text] controller to stabilize the charging frequency. The model predictive control (MPC) controller was used to identify the optimum power factor for electric vehicles and determine the optimal power values and efficiency. In the second scenario, a two-way AC-DC converter was designed using a Fuzzy type-II controller under uncertainty to provide precise control over the vehicle charge exchange in terms of voltage, current, and stage of control (SOC). So, type-II fuzzy controller is used to control the process of charging and discharging vehicles. The results show that the final efficiency is 0.98, and the power will be 1480 W.

Non-Isolated Power Factor Corrected AC/DC Converter with High Step-Down Voltage Ratio for Low-Power Applications

This paper proposes a high step-down ratio AC-DC converter employing a quadratic buck converter with power factor correction. Conventional active power factor correction topologies employ boost-based correction schemes for unity power factor operation. This will require a steeper step-down ratio and higher switch voltage stress apart from complexity in the control scheme with sensors. The structure of the proposed topology is developed by combining the power factor correction stage with a high step-down stage. The passive input filter is split up into two for the purpose of reducing the thermal heating apart from offering a higher power factor. A single switch operation reduces the complexity of the control scheme. In addition, the number of conducting devices during the current path is also the same as the conventional buck converter due to cascading and hence offers lower conduction losses. The need for the converter to operate at an extremely low duty cycle is reduced due to the quadratic stage structure. The proposed converter operates at a moderate duty cycle, offering higher step-down voltage apart from reducing filtering requirements. MATLAB R2020b is used for carrying out simulation studies. Xilinx FPGA-based controller using system generator is implemented for the generation of pulses of appropriate duty cycle. Simulation and experimental results for a 150 W prototype are presented. An investigation and comparative evaluation of the conventional bridgeless buck system with the quadratic buck converter are carried out. The proposed structure offers the benefit of a higher step-down voltage ratio incorporating an inherent power factor correction stage along with the AC/DC stage.

A Single-Phase Compact-Sized Matrix Converter with Symmetrical Bipolar Buck and Boost Output Voltage Control

The development of single-phase symmetrical bipolar voltage gain matrix converters (MC) is growing rapidly as they find their application in power systems for dynamic restoration of line voltages, high voltage AC–DC converters, and variable frequency controllers for many industrial processes. However, the existing trend in matrix converter technology is a buck–boost operation that has inherently serious issues of high voltage and current surges or stresses. This is a big source of the high voltage and current rating of semiconductor switching devices. There is also a problem of high ripples both for voltage as well for current, requiring large size of filtering capacitors and inductors. The non-symmetrical control of the voltage gain increases the control complication. A large count of operating transistors is critical regarding their cost, size, and power conversion losses, as the space and cost required by their gate control circuits are much larger than the size and cost of the switching transistors. Thus, in this research work, a new single-phase MC is introduced only employing six fully controlled switching devices, ensuring similar operation or outputs as is obtained from the existing topologies that require the use of eight or more fully controlled switching devices, and the reduction by two or more switching transistors helps to compact the overall size and lower the overall cost. The separation in its voltage buck and boost operation enables smooth control of the voltage gain through duty cycle control. The low values of the voltage and current surges reduce the power rating and losses of the switching devices. The flow of the current in the filtering inductor is kept unidirectional to avoid the current interruption and reversal problem once the operation of the converter is abruptly switched from inverting to non-inverting and vice versa. All these factors are comprehensively detailed through the circuit’s description and comparative analysis. Simulation and practical results are presented to confirm the effectiveness of the developed circuit topology.

Simulation and design of an energy accumulator around the hydrogen energy vector

This work demonstrates the study of the numerical modelling and a design of a compact energy generator based on green hydrogen. This generator aims allowing the energy storage, electricity, cold and heat productions as well as a supply the energy for the production of the sanitary hot water. The generator is considered to be powered by 30 solar cells panels and will mainly consist of a Proton Exchange Membrane (PEM) electrolyzer compiled with a Metal Hydride (MH) tank, a PEM fuel cell, and a system of heat exchangers sized to recover the heat from the electrolyzer, PEM fuel cell and MH tank. Furthermore, the generator will contain an adsorber to manage air conditioning (cooling and heating) and a production of the sanitary hot water. A converter block is included in the generator, in particular, a Buck-booster to raise the voltage of the solar panels and the DC-AC converter for the electricity consumption in the household. The desorption of the hydrogen contained in the tank MH will take place using the heating resistance. In overall, the designed generator is foreseen to have a dimension of 1800 × 1000 × 500 mm and its role is to allow integration of the hydrogen energy for the tertiary and residential sectors. As such it is a suitable choice of components for the cost reduction and high yield hydrogen production, storage, and consumption.

A PCB-Embedded 1.2 kV SiC MOSFET Half-Bridge Package for a 22 kW AC–DC Converter

This article presents the design and analysis of a double-side-cooled printed circuit board (PCB) embedded silicon carbide (SiC) MOSFET half-bridge package with low loop inductances and an integrated gate driver. The 1.2 kV SiC MOSFET dies used in the half-bridge package are embedded in the PCB using AT&S's patented technique. The dies are cooled and electrically connected to traces in the PCB through copper-filled microvias. The design methodology accounts for both electrical and thermal performance, limiting the power-loop inductance to 2.3 nH and the maximum package temperature to less than the 175 °C limit. The integration of the gate drive circuitry allows for a high power density and 2.2 nH gate-loop inductances. At 0.12 K/W, the measured junction-to-case thermal resistance with double-sided cooling is 57% lower than that of a TO-247 package. Under similar operating conditions, the PCB-embedded half-bridge package also achieves a 5.6 times lower voltage overshoot and a 0.5% higher peak efficiency than a TO-247-based half-bridge. This article reports the first demonstration of PCB-embedded 1.2 kV SiC MOSFET packages in buck, boost, and ac–dc converters. The prototype three-phase ac–dc converter for an electric vehicle on-board charger is composed of six PCB-embedded half-bridge packages and achieves an efficiency of 98.2% and a power density of 182 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

Large signal stability criterion of AC–DC hybrid microgrids with constant power loads considering reference current limitation

Islanded AC–DC hybrid microgrids composed of new energy sources, constant power loads and energy storage system are typical non-linear systems, and guaranteeing large signal stability is a key issue. In this paper, the non-linear model of islanded AC–DC hybrid microgrids is established, and large signal stability criteria are obtained. Considering reference current limitation of the energy DC–AC converter, the derived large signal stability criterion gives important constraints on the constant power loads power, the power of energy storage unit, DC bus voltage, the inductor and equivalent resistance of the AC filter, DC capacitor, the proportional parameter of the inner current controller and the maximum instantaneous power of the DC–AC converter. The paper is summarized as follows. Firstly, the equivalent model of the AC–DC hybrid microgrids in DQ rotating frame is established. Then based on mixed potential theory, the mixed potential model is constructed, and large signal stability criterion is derived and optimized considering the reference current limitation of the DC–AC converter. Finally, the presented criterion is verified by simulation and experimental results.

Self-Powered Single-Inductor Rectifier-Less SSHI Array Interface With the MPPT Technique for Piezoelectric Energy Harvesting

Piezoelectric energy harvester (PEH) arrays are practical solutions to the low and unreliable power output of a single PEH. However, most PEH circuits are developed for addressing the one-channel ac input from a single PEH. In this article, an extensible rectifier-less synchronized switch harvesting on inductor (ReL-SSHI) array interface with the maximal power point tracking (MPPT) function to manage the multiple ac inputs from the PEH arrays is designed. The ac–dc conversion is performed by the ReL-SSHI topology with passive peak switches featured with self-powered characteristic and fast cold-start. Only one shared inductor is employed, greatly reducing the circuit volume and cost. The MPPT module for each channel is implemented by a simple envelope detector and an ultra-low power hysteresis controller and achieves continuous energy extraction by adapting the fractional normal-operation voltage method. A developed discrete array interface able to handle three PEHs effectively executes the MPPT for each channel with the uphill and downhill response speeds of 2.0 and 7.1 V/s, and a maximal MPPT efficiency of 97.1%. This circuit boosts the power output by 485% compared with that by the traditional full-bridge rectifier, around 33% higher than that from existing synchronous electric charge extraction array interfaces.

Nonlinear Control of a Two-Stage Single-Phase DC–AC Converter

In this article, a multi-input multi-output nonlinear control strategy for a two-stage single-phase dc–ac converter is introduced. The design technique is based on a multi-input multi-output feedback linearization strategy. A change of coordinates is used for obtaining a decoupled two-input two-output linear description. It allows us to design a linear controller in a transformed domain. Finally, this linear controller is expressed in original coordinates, resulting in the proposed nonlinear controller. Using this nonlinear controller allows improving the performance of the converter in presence of large excursions of reference and disturbance signals. The performance of the whole system is tested via simulation and experimental results using both linear and nonlinear loads.

Comparative Model of Single-phase AC Cycloconverter for 1000Wp Photovoltaic Grid-connected 220VAC-50Hz

Currently, the Electrical Engineering Laboratory (EEL) of Universitas Jenderal Achmad Yani has a 1 kWp photovoltaic (PV) system. However, in order to fulfill the overall load, the hybrid link to the grid must be improved. The PV system and the grid must be synchronized in terms of voltage, frequency, and phase. This article presents comparative simulations of AC-AC converter models of power electronics component variants using MATLAB 2019a. Among other stages is to model the DC-DC Converter in order to enhance the output voltage of the solar panel by identifying the circuit characteristics. The second stage involves simulating the MOSFET-based DC-AC Converter circuit, which is used to convert DC to AC. The use of switching Thyristor, Gate Turn-Off Thyristor (GTO), and Insulated Gate Bipolar Transistor (IGBT) in an AC-AC phase converter to connect to the grid is examined in this range. Non-linear and linear loads are used to represent the load on the AC Cycloconverter range. Based on the results of the modeling and analysis of the PV 1 kWp system, the AC Cycloconverter in the first stage may provide a frequency of 50 Hz with a voltage drop of 235.4 V for the line and 231.9 V for the non-linear, which meets the AC Cycloconverter criterion.

Adaptive super-twisting sliding mode for DC-AC converters in very weak grids

ABSTRACT This paper presents the design of a direct-type adaptive control structure for current regulation of a single-phase grid-tied Voltage-Source Inverter (VSI) with an LCL filter under very weak grid condition. The initial content of this work was previously published, where the controller was presented and its discrete-time stability proof was provided. Power converters connected to weak grids bring challenges to the control system, since the grid can change abruptly from a strong to a very weak condition , degrading system power quality. This study evaluates the feasibility of a RMRAC-based robust adaptive Super-Twisting Sliding Mode controller for current control of VSI when the grid inductance changes substantially, from 0 mH (strong grid) to 10 mH (very weak grid). To show the benefits of the control strategy and its robustness, hardware-in-the-loop (HIL) simulation results are presented, comparing its performance with two other controllers..