Converter Prototype Research Articles

Nonlinear Modeling and Control Strategy Based on Type-II T-S Fuzzy in Bi-Directional DC-AC Converter

Bi-directional DC-AC converters are widely used in the field of electric vehicle-to-grid. However, the inductance of the grid-side interface filter is affected by the length of the grid connection and the power level, which presents nonlinear characteristics. This poses challenges for high-performance grid waveform control. In this paper, a modeling method for bi-directional DC-AC grid-connected converters based on type-II T-S fuzzy models is proposed, and the corresponding type-II T-S fuzzy control strategy is designed to address the parameter uncertainty and non-linearity issues. Simulation results show that type-II T-S fuzzy control offers superior control performance and better current waveform quality compared to type-I T-S fuzzy control under uncertainty parameter conditions. The effectiveness of the proposed strategy is further validated through a 1 kW prototype of a bi-directional DC-AC converter.

Dual-Coupled-Inductor-Based High-Step-Up Boost Converter with Active-Clamping and Zero-Voltage Switching

Many applications, such as photovoltaic systems, uninterruptible power supplies, and automobile headlamps, need a high step-up DC–DC converter without isolation. The conventional boost converter has the advantages of simple topology and easy control. However, it has some shortcomings, such as insufficient step-up voltage ratio and poor efficiency when operating at large duty-cycle conditions. One of the popular topologies used to overcome these problems is the coupled-inductor boost converter. It utilizes the turn ratio of the coupled inductor to realize a higher step-up voltage ratio. The drawback is that the leakage inductance of the coupled inductor causes a huge voltage spike when the power switches are turned off. Moreover, because coupled inductors are characterized by their large volume and high profile, a conventional coupled-inductor boost converter is unsuited for photovoltaic systems, such as the solar microinverter. This study proposes a novel high-step-up boost converter to solve these problems. This proposed converter uses dual coupled inductors instead of the conventional coupled-inductor boost converter. The secondary side of the coupled inductor is connected in series to increase the step-up voltage ratio. The proposed converter utilizes active clamping to achieve zero-voltage switching (ZVS) for suppressing voltage spike and improving conversion efficiency. In addition, low-profile designs can be fulfilled easily for solar microinverters. The proposed converter and its control method are introduced. The operation principle, circuit characteristics, and circuit analysis are presented. A prototype converter with 300 W output power 25–40 VDC input voltage and 200 VDC output voltage was tested. All functions, including high step-up voltage ratio, ZVS, and active clamping, were achieved, and the highest efficiency was around at 94.7%.

Experimental evaluation of virtual synchronous generators with high regulation performance to enhance AC–DC grid interconnections

In the recent years there has been a significant increase in the interest surrounding the interconnection of AC and DC networks due to its potential to improve the power systems reliability. Despite the potential advantages, however, the AC and DC grid coexistence can pose challenges if not appropriately managed. In this scenario, this paper presents an enhanced control scheme enabling the use of Virtual Synchronous Generators (VSGs) as elements of interconnection between AC and DC networks. The proposed solution enables VSG operation with both fast dynamics for DC voltage regulation and slow dynamics for AC inertia emulation. This approach accommodates the contrasting requirements arising from the distinct mechanisms of DC voltage regulation and AC frequency regulation. Simulation and experimental results obtained with a 8 kVA three-phase converter prototype are provided to validate the effectiveness of the proposed technique and prove its better performances with respect to the solutions currently presented in literature.

Comparative Evaluation of Dual-Purpose Converters Suitable for Application in DC and AC Grids

This paper presents a comparative evaluation of several topological solutions to the universal power electronics interface for the dc or single-phase ac grids using the same terminals. The idea of a dual-purpose approach lies in the utilization of the same semiconductors in the dc-dc and in the dc-ac configuration, resulting in minimal redundancy. Particular focus is on the power density improvement and control. Out of the three solutions under investigation, the first is the buck-boost cell with unfolding circuit presented earlier. The second solution is a conventional voltage source inverter with an intermediate boost cell considered as one of obvious competitors. The third design is based on a phase-modular solution with buck-boost cells. The design example and experimental prototypes of the universal power electronics interface converter rated for 3.6 kVA power in the ac mode and more than 5 kW in the dc mode are presented. Our experimental results demonstrate the ability of operation in the ac or dc grids with main corresponding modes. Possible applications along with main benefits are addressed in the conclusions.

A Novel Soft Switching Non-Isolated Bidirectional dc–dc Converter Without Any Extra Auxiliary Switch

In this paper, a new zero-voltage-switching (ZVS) non-isolated bidirectional DC-DC converter without any extra auxiliary switch is introduced. In the proposed converter, by applying an auxiliary circuit, soft switching condition is provided for all semiconductor elements regardless of the power flow direction and without any extra voltage stress. Each of the main switches provides soft switching conditions for the other switch. Additionally, each of the switches can be used as a synchronous rectifier switch in both power flow directions. The auxiliary circuit only consists of two coupled inductors with the converter main inductor and two diodes, which operate with a zero-current-switching (ZCS) condition. Since, all of the converter inductors are implemented on a single core, the presence of coupled inductors doesn’t increase the converter volume considerably. The detailed operating analysis of the proposed bidirectional converter and the design method of the main circuit is presented. Also, the theoretical analysis of the proposed bidirectional converter is verified with a 100W experimental prototype converter.

A Stacked Symmetrical Non-Isolated High Step-Up Voltage Gain Converter with High Efficiency and Low Voltage Stress on Components

This paper introduces a cascaded symmetrical non-isolated high step-up voltage gain converter with high efficiency and low voltage stress on components combining a non-isolated buck-boost converter and voltage doubler structure. In the proposed converter, the input source is connected in series to the output load; hence, a part of the source energy is directly delivered from source to load, not through the switching branch, improving efficiency. Furthermore, the appropriately stacked voltage doubler stage not only amplifies the high step-up voltage gain ratio but also considerably diminishes the voltage stress on all semiconductor devices and capacitors. As a result, the costless low internal resistance and low voltage components can be employed for higher efficiency, higher power density, and lower cost. To demonstrate the practicality of the proposed topology, the operating principle is outlined, and the steady-state characteristics are thoroughly analyzed. Furthermore, a 360 W prototype converter has been fabricated to confirm the efficiency of the proposed converter.

Design of Interleaved Winding for Multilayer Planar Inductor and Its Application in Reducing Current Ringing of LLC Resonant Converter

To enhance the power density of LLC resonant converters, multilayer planar inductors are required. However, multilayer planar inductors have high parasitic capacitance, which may cause inductor current ringing in LLC resonant converters, leading to EMI problems. In this paper, it is found that by using interleaved winding inductors, compared with traditional winding inductors, the parasitic capacitance of multilayer planar inductors is reduced, which can reduce current ringing, without sacrificing power density and increasing manufacturing complexity. The method used to analyze current ringing is to establish an impedance model, and the parasitic capacitance of the interleaved winding inductors is verified by FEM simulations. The analysis is validated in an LLC resonant converter prototype.

Very high step‐down coupled inductor two‐phase buck converter with single magnetic element and inherent clamp voltage capability

AbstractThis paper proposed a new two‐phase high step‐down DC–DC converter is proposed. This converter is derived from the two‐phase series‐capacitor converter. The proposed converter replaces the series capacitor with a new structure that integrates Valley‐Fill circuit and coupled‐inductors concepts. This replacement can improve the voltage gain of the converter as well as a considerable reduction of diodes voltage stress. The proposed structure implements a dual‐phase buck using a single magnetic element. Also, the proposed structure inherently limits the voltage spikes due to the leakage inductance of coupled inductors without any additional clamp circuit. The proposed converter is analyzed, and design guidelines are provided. A 300–24 V prototype converter is implemented to justify the validity of circuit operation and the theoretical analysis.

A Magnetic Integration Mismatch Suppression Strategy for Parallel SiC Power Devices Applications

A new magnetic integrated parallel current sharing control method for parallel silicon carbide (SiC) power devices is presented in this article. The problem of the application of parallel connected SiC power devices is analyzed. The coupled inductance method is adopted to solve the problem. Based on the active-back converter, we establish the theoretical model of the coupled inductance, and figure out its working mechanism. The integrated magnetic device is designed based on the working mechanism, and the effectiveness is determined through simulation. A 12 V/10 A output magnetic integrated active-flyback converter prototype is fabricated and tested to verify the strategy. Measurement results show that, with the proposed magnetic integrated method, the mismatch voltage is suppressed to 0.1 V under all load conditions, and the efficiency increases by at most 6.52% under full load conditions.

Multiobjective Design and Benchmark of Wide Voltage Range Phase Shift Full-Bridge DC/DC Converters for EV Charging Application

This paper presents an analysis, multi-objective design, and benchmark of three modified Phase-Shift Full-Bridge (PSFB) converters that are well-suited for Electric Vehicle (EV) battery charging applications, covering both typical battery voltage classes (400V and 800V). These three modified PSFB converters, denoted as the t-PSFB, r-PSFB, and i-PSFB converters, have the ability to reconfigure and provide better efficiency performance in the wide voltage range necessary for public EV battery charging applications. In this paper, the characteristics and design considerations of these reconfigurable PSFB converters are discussed in detail. A multi-objective converter design process is proposed to optimize the average efficiency, normalized cost, and power density of the magnetic components and heat sinks. This design process employs the correlations between the cost and performance indexes of the key components derived based on open and accessible components data to estimate the design objectives. In this way, the design process is not constrained by certain component choices, making it easier to identify the most advantageous design. A benchmark study is conducted among the re-configurable PSFB topologies and the conventional PSFB circuit using the proposed multi-objective design process. To validate the analysis, a close-to-Pareto-front 11kW, 45kHz r-PSFB converter prototype with 640-840V input voltage and 250-1000V output voltage ranges is developed and tested.

Maximum Efficiency Point Tracking Algorithm for Resonant Full-Bridge Converter in Charging Applications

In this paper, a novel maximum efficiency point tracking algorithm is proposed for a resonant DC-DC power converter in charging applications. Based on a total harmonic analysis (THA), a method for minimizing the harmonic content of the input AC current is investigated. An online algorithm is proposed for achieving the maximum efficiency at the whole charging spectrum, by controlling the angle under which zero-voltage switching occurs. The suggested control algorithm is simple to implement with very low computational complexity. Additionally, an effective winding method is proposed for increasing the leakage inductance without greatly increasing the air gap, thus eliminating the need for additional resonant inductors. A prototype converter of 2kW|20A is implemented for verifying the proposed method and 98% maximum efficiency is achieved.

A Reconfigurable Two-Stage 11 kW DC–DC Resonant Converter for EV Charging With a 150–1000 V Output Voltage Range

In this paper, a reconfigurable two-stage DC/DC resonant topology with a wide output voltage range of 150-1000V is proposed for Electric Vehicle (EV) charging with high efficiency over the entire load range. The proposed topology consists of an LLC resonant converter with dual secondary sides; two interleaved triangular current mode buck converters, and three additional auxiliary switches for reconfiguration. Two possible arrangements of the proposed topology are considered and compared. The analytical model of the topology is developed, which is used for the efficiency estimation of different configurations and the design of the prototype converter. An 11kW hardware demonstrator is built and tested. The maximum measured efficiency of the converter is 97.66%, with a >95% efficiency over the complete 150-1000V range at full power. The proposed two-stage converter achieves the widest output voltage range reported in literature for resonant power converters, thereby capable of charging existing and future EVs very efficiently over any charging cycle.

Effect of Metal Oxide Semiconductor Field-Effect Transistor Output Parasitic Capacitance on Efficiency in Full-Bridge LLC DC/DC Converters.

This study analyzed the efficiency impact of a MOSFET output parasitic capacitance (Coss) on a full-bridge LLC DC/DC converter. The core of the converter was the control chip for a half-bridge LLC DC/DC converter, and the output signal of the chip controlled the first-arm power transistors of the primary side of the converter. The coupling transformer reversed the output signal to control the primary side of the second arm of the power transistor. The full-bridge converter comprises a half-bridge control chip that converts the high-voltage DC power supply to a low-voltage DC power supply, which is then synchronously rectified and supplied to the load. The primary side of the power transistor achieves a zero-voltage switching (ZVS) state through the resonance of the LLC converter. This design gives the converter high power density and a simple structure. Furthermore, to determine the appropriate output parasitic capacitance for improving converter efficiency, this study analyzed the effect of the output parasitic capacitance on the switching loss and conduction loss of the power transistor on the basis of the output parasitic capacitance of the primary-side power transistor. A 1200 W converter prototype was fabricated in this study, and when the output was 300 W, efficiency increased from 92.603% to 93.462%, a 0.859% increase. The empirical results verified the feasibility of the proposed theory.

Wave Energy Conversion through Oscillating Water Columns: A Review

An oscillating water column (OWC) is designed for the extraction and conversion of wave energy into usable electrical power, rather than being a standalone renewable energy source. This review paper presents a comprehensive analysis of the mathematical modeling approaches employed in OWC systems, aiming to provide an in-depth understanding of the underlying principles and challenges associated with this innovative technology. A prominent classification within the realm of wave energy devices comprises OWC systems, which exhibit either fixed or floating configurations. OWC devices constitute a significant proportion of the wave energy converter prototypes currently operational offshore. Within an OWC system, a hollow structure, either permanently fixed or floating, extends below the water’s surface, creating an enclosed chamber where air is captured over the submerged inner free surface. This comprehensive study offers a thorough assessment of OWC technology in conjunction with air turbines. Additionally, the investigation delves into theoretical, computational, and experimental modeling techniques employed for analyzing OWC converters. Moreover, this review scrutinizes theoretical, computational, and experimental modeling methodologies, providing a holistic understanding of OWC converters. Ultimately, this work contributes a thorough assessment of OWC technology’s current state, accentuating its potential for efficient wave energy extraction and suggesting future research avenues.

High gain interleaved DC-DC converter with ripple-free input current and low device stress

ABSTRACT A non-isolated DC-DC converter which yields high voltage gain and suitable for photovoltaic (PV) applications is described in this research article. The high gain converter proposed in this paper is synthesised by combining several voltage gain extension techniques viz. coupled inductors, voltage-lift capacitor, and diode-capacitor multiplier (DCM) cells. Since the input stage is interleaved, and the switches are operated complimentarily, the source current ripple is nullified and switch current rating is minimised. Due to the hybrid voltage gain extension techniques adopted while synthesising the converter, the voltage stress on the switches is only 10.5% of the output voltage. To validate the proposed concept, experimental results are obtained from 18 V-380 V, 150W prototype converter which is operated at 50 kHz. The proposed converter yields a voltage gain of 21.11 at 92.83% efficiency under full-load condition. During closed-loop operation, the proposed converter quickly settles down to its nominal output voltage of 380 V when the input voltage and load current values are subjected to step variations. The superior features of the proposed converter are highlighted by comparing it with similar and recent state-of-the art high gain converters.

Dual LC parallel multi‐resonant DC‐DC converter with wide output‐voltage range

SummaryAlthough LLC converters have widespread applications due to their advantages of high efficiency, high power density, and soft switching, in wide voltage gain range applications, a large switching frequency range is inevitably required, which may bring difficulties in converter design and efficiency improvement. In this paper, a dual LC parallel multi‐resonant converter (MRC) is introduced. The converter contains two parallel LC resonant branches in the resonant tank, which exhibit the notch filter characteristic on the gain curve. It enables the converter to provide wide voltage gain regulation, soft startup, and overcurrent protection over a limited frequency range. Compared to other five‐element MRCs, since the converter provides different current loops for the fundamental wave and the third harmonic to transmit active power, the circulating reactive energy and stress on the resonant components are reduced. Finally, a detailed design procedure for a 3.3 kW converter prototype with an output voltage range of 250–450 V is provided.

Single Power-Conversion Active-Clamped AC/DC Converter Employing Si/SiC Hybrid Switch

This article proposes a single power-conversion voltage-fed active-clamped ac/dc converter that uses an Si IGBT/SiC MOSFET hybrid switch. By incorporating two switches at the primary side of the circuit, we removed the full-bridge diode rectifier, and thereby reduced the required number of power devices. Inherent bidirectional active-clamp circuit naturally limits the voltage spike at bottom switches and reuses the energy accumulated in the leakage inductor during both positive and negative grid half-cycles. Also, it offers dual-resonant power transfer paths, so it can deliver the high power with less circuit components. The alternating switching modulation makes one of the bottom switches turn off with hard switching per grid half-cycle while holding other bottom switch on to conduct the current. In contrast, top switches are softly switched with low root-mean-square current. Therefore, the converter with proposed switching modulation enables direct substitution of Si IGBT for an SiC MOSFET at the top on the primary side, and thereby which cuts down the circuit implementation cost. We built a 1 kW prototype converter and confirmed its validity.

Shared External Driver for VHF Converter With a Synchronous Rectifier Based on Matching Network Parameters Optimization

In order to reduce the conduction loss of diode, synchronous rectification is usually adopted in very-high-frequency (VHF) converters, in which the rectifier diode is replaced by a MOSFET with very low on-state resistance. And to ensure normal operation of the synchronous rectifier switch, it is necessary to design a suitable driver with accurate timing. The widely used self-oscillating resonant drive circuit has a limited range of duty cycle adjustment, and the body diode of synchronous rectifier switch has long on-state time and a large conduction loss. Therefore, based on the analysis and parameters optimization of matching network, a shared external drive circuit is put forward. That is, the drive signals of the inverter switch and the synchronous rectifier switch come from the same external oscillation signal. On the premise of ensuring accurate drive timing, it can improve the drive signal's duty cycle of synchronous rectifier switch, reduce the conduction loss of body diode, and improve the efficiency of converter. Then on the basis of the proposed drive circuit, a VHF converter prototype with operating frequency of 10 MHz, 13 V input and 8 V/10 W output is designed, and the feasibility of the proposed drive circuit is verified by simulations together with experiments.

A Bidirectional Direct AC-AC Resonant SCC

A direct ac-ac resonant switched-capacitor converter (SCC) for both noninverting and inverting output voltages is proposed here, which is suitable for bidirectional power transmission including different applications such as dynamic voltage restorer (DVR), constant voltage regulator (CVR), and constant current regulator (CCR). Zero voltage switching (ZVS) and zero current switching (ZCS) operation conditions are easily realized for its power switches, which effectively reduce the switching losses, as well as the electromagnetic interference (EMI) noise. Consequently, high-frequency operation is possible, which improves the converter power density, in practice. Continuous voltage-gain, transformerless connection of the converter output port to the gird, no commutation problems without using extra components, and improving the electrical specifications are some other advantages of the given resonant SCC. The converter operation principles, its key waveforms and different operational states, its mathematical analysis and normalized state-plane trajectories, simulation results, as well as its design procedure, are also given here, in detail. To verify the given theoretical analyses and simulation results, a 500 W prototype converter for a 2 kW DVR with 220 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> nominal output voltage has been implemented successfully, which realizes 96.55% efficiency at its rating power value.

High step up DC–DC converter with low conduction losses and reduced switching losses

AbstractThis article presents a novel high step up converter based on the active switch inductor (ASL) technique for renewable energy source applications. The coupled inductor technique provides an opportunity to increase the gain. The proposed converter exploited the leakage inductors to provide zero current switching (ZCS) turn‐on for both switches. Therefore, there is no need for an auxiliary circuit, which simplifies the structure. Also, all diodes turn off under ZCS, which eliminates the reverse recovery problem and results in reduced switching losses. The energy of the leakage inductor is recycled, and the voltage spike on the switches is limited. In addition, all semiconductor voltage stresses are clamped below the output voltage. Hence, components with lower on‐resistance can be utilized to reduce conduction loss. Because of the reduction in power loss, the efficiency rises to 97.2% at 250 W output power. It also benefits from the current sharing of the interleaved structure. The operating principles, design considerations, and comparison to other topologies are discussed. To verify the effectiveness of the proposed converter, a prototype converter with 250 W of output power, 50 V of input voltage, 500 V of output voltage, and 100 kHz of switching frequency is implemented.