Conventional Converter Research Articles

A New Fifth-Order Boost Converter With Dual Operating Modes and Wider Conversion Ratios for Renewable Energy Applications

Conventional DC-DC converters for renewable energy systems work in large duty cycle conditions, which will lead to the inductor saturations and decrease the system efficiencies and stabilities. In this brief, a new fifth-order boost converter, which can work in dual operating modes when different control technologies are adopted, is proposed. To obtain a wider conversion ratio, the required duty cycle for the proposed converter with synchronous controller is smaller than 0.333 while with interleaved controller is smaller than 0.5. Also, dual modes of this converter both have lower switches voltage stress. Then, the inductor saturation issues can be avoided and the system efficiencies and stabilities can be improved. Besides, the lower topological order and simple grounded structure of this converter are benefit to reduce the modeling complexity, topology volume and system noises. Detailed analyses, comparisons and prototype are implemented to study the improved conversion ratio, efficiency and power density of the proposed converter in-depth, and to validate its feasibilities for renewable energy applications.

An Extended Control of the Input Angle for Matrix Converters Connected With the Nonunity Power Factor Loads

This article proposes a novel pulsewidth modulation (PWM) modulation algorithm for multiphase conventional matrix converters, with three inputs and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$k$</tex-math></inline-formula> outputs, using the transfer function of the load angle. The proposed approach extends the range of power angle control at the input during the operation with a maximum voltage transfer ratio. The proposed concept is based on the direct analytic voltage PWM modulation with an elliptical trajectory of reference load voltages. The proposal has been verified using the circuit simulation in PSIM software, symbolic analysis using MATLAB, and finally through an experiment.

A Low Voltage Stress PFC Rectifier Based on Nonoverlapping Strategy Using Resonant Switched-Capacitor Converter

In order to break limited step-down ratio range and poor regulation capacity in the conventional resonant switched-capacitor converters for rectifier application, a single-stage ac/dc rectifier based on the dual-resonance switched-capacitor converter is proposed in this article. Through utilizing a dual-resonant structure and nonoverlapping strategy to realize wide continuous voltage gain of the proposed converter, high power factor (PF) and low total harmonic distortion (THD) based on the narrow dead zone are guaranteed by operating at high step-down conversion ratio in this converter topology. Moreover, the voltage gain is concentrated between resonant frequency and double resonant frequency to achieve a narrow switching frequency range for rectifier application. Furthermore, operating at flat voltage stress curves to obtain low voltage stress character. Comprehensive mode analysis, input PF and THD, and stress analysis are given, and analysis results indicate that the proposed power factor correction converter can work with soft turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> and zero-current turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> ; high efficiency is realized. Finally, an experimental prototype with 85–130 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ac</sub> input and 47 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> /44 W output is built and tested for verifying the operation modes and PFC performance, and the comparison between different rectifiers and the proposed one is provided.

Analysis and Design of Series Voltage Compensator for Differential Power Processing

Differential power processing (DPP) has been proven effective in many applications. This article explores a series voltage compensator (SVC) architecture for voltage regulation of DPP systems. An SVC is connected in series between the input dc bus and the DPP system to compensate for the voltage difference. It only processes a fraction of the overall power. The inclusion of an SVC changes the power flow of the DPP system and changes the loss distribution. We theoretically investigated the SVC power rating and the additional power conversion stress that SVC brings to the DPP converter. Accordingly, we identified the operation range where an SVC is more attractive than a conventional DPP pre-regulation converter that has to process the full power. Our analysis provides insights into system design and control strategy of SVC-DPP topologies. To validate the principles of SVC, a buck SVC is designed and applied to a ten-port DPP converter. The buck SVC can efficiently convert an input voltage ranging from 50 V to 65 V into a regulated 50 V for the DPP system. The size of the SVC is only 20% of the DPP converter, and the peak efficiency of the SVC-DPP system achieves 98.8%.

Comparative Study Between Sliding Mode Controller and PI Controller for AC/DC Bridgeless Converter Under Uncertain Parameters

Abstract In this paper, a comparative study between nonlinear sliding mode controller (SMC) and standard PI controller for stabilizing bridgeless AC/DC converter under uncertain parameters is presented. This type of converters is widely used in harvesting low energy systems as in wind turbine, piezoelectric transducers and heat exchange transducers. Designing robust controllers to enhance the efficiency and accuracy of these converters has become a promising track in control engineering field. The traditional bridge rectifier is widely used in the majority types of AC/DC conventional converters to gain the rectified DC voltage from the low AC input voltage source. However, these traditional converters are not effective for the low output voltage of renewable sources due to the voltage drops across rectifier’s diodes. The proposed SMC-PI controller is used to enhance the stability and the response of these converters under uncertain parameters comparing with the standard PI controller. The proposed approach consists of both Boost and Buck-Boost converters with two controllers in order to maximize the useful output energy from the source. The graphical method has been used to obtain the limitation of the coefficients of the standard PI controller. A parameter space approach is used to find all robust stabilization PI coefficients and the stability regions. A comparative study using simulations in MATLAB is presented to ensure the effectiveness and robustness of the proposed SMC-PI controller under some external disturbances.

Diode rectifier‐based hybrid high‐voltage direct current converter for offshore wind farms

This paper presents a diode rectifier (DR)-based hybrid converter topology for high-voltage direct current (HVDC) transmission system with offshore wind farms (OWFs). The hybrid converter consists of a DR and an auxiliary converter. A high conversion ratio ac/dc converter is designed as the auxiliary converter, which can form the offshore grid voltage for OWFs to achieve black-start. Under steady state, all the active power output from OWFs is delivered through the DR. Meanwhile, the auxiliary converter is able to compensate the reactive power and harmonic currents of the system. Comparing with the conventional modular multilevel converter (MMC), the number of submodules (SM) of the proposed hybrid converter is significantly reduced, which decreases the construction cost and size of the system. The topology and operation principle of the hybrid HVDC converter are introduced. Then the corresponding control strategy is designed to achieve energy balance and power transmission. Based on the mathematic model, a design method for the parameters of the auxiliary converter is proposed. Finally, the feasibility of the proposed hybrid HVDC converter is verified by both the simulation and hardware-in-the-loop experiment results.

ДОСЛІДЖЕННЯ ПЕРЕХІДНИХ ПРОЦЕСІВ У КОЛІ УМОВНО ДВАНАДЦЯТИФАЗНОГО ТИРИСТОРНОГО КОМПЕНСАТОРА ДЛЯ КОРЕКЦІЇ ПЕРЕХІДНИХ ПУСКОВИХ РЕЖИМІВ В ЕЛЕКТРИЧНІЙ МЕРЕЖІ

Electromagnetic transient processes in a network with a conventionally twelve-phase thyristor compensator designed to adjust the value of the starting transient current of the network in the case of direct start from the network of asynchronous motors of comparable power to the network with a jump-like change in the control angle of the thyristors in the bridges were studied. A comparison was made with such a change in the control angle of thyristors of transient currents in the circuits of a two-bridge controlled thyristor compensator with parallel connection of bridges with transient currents in a conventionally twelve-phase thyristor compensator, where these bridges are switched on in series with each other relative to the supply voltage. The advantages of the technical and economic and mass-dimensional parameters of the conventional twelve-phase converter and its operational characteristics when applied in practice in comparison with analogues are indicated. Ref. 5, fig. 6, table.

Terahertz polarization conversion from optical dichroism in a topological Dirac semimetal

Topological Dirac semimetals (TDSMs), such as Cd3As2 and Na3Bi, exhibit strong optical dichroism with contrasting dielectric permittivity along different crystal axes. However, such optical dichroism is often overlooked in the study of TDSM-based optoelectronic devices and whether such optical dichroism can lead to unique functionalities not found under the isotropic approximation remains an open question, thus far. Here, we show that the optical dichroism in TDSM lead to starkly different terahertz (THz) responses and device performance as compared to the isotropic case. Using finite-difference time-domain simulations of a Cd3As2-based metasurface, we demonstrate that such optical dichroism can lead to an unexpected THz wave polarization conversion even if the metasurface structure remains fourfold rotationally symmetric, a useful feature not achievable under the isotropic model of TDSM. Our findings concretely reveal the contrasting spectral response between isotropic and anisotropic media and shed important light on the capability of anisotropic TDSM in THz applications, leading not just to the more accurate device modeling but also a new route in realizing THz wave polarization conversion without the need for complex device morphology commonly employed in conventional polarization converters.

Modular Multi-Input DC/DC Converter for EV Fast Charging

In this paper, a modular multi-input, single output DC/DC converter is proposed to enhance the energy management of a fast-charging station for electric vehicles (EVs). The proposed bidirectional converter can work in different modes of operation with fewer components and a modular design to extend the input power sources and increase the charging power rate. The converter has several merits compared to the conventional converters, such as centralizing the control, reducing power devices, and reducing power conversion stages. By using MATLAB/Simulink, the converter was tested in many operation modes and was used to charge a Nissan Leaf EV’s battery (350 V, 60 Ah) from hybrid sources simultaneously and individually in power up to (17 kW). In addition, it was tested on a hardware scale at a low power rate (100 W) for the validation of the simulation work and the topology concept. In addition, its different losses and efficiency were calculated during the different operation modes.

Integrated Multi Mode Converter With Single Inductor for Fuel Cell Electric Vehicles

Fuel cell electric vehicles have batteries to mitigate problems such asthe inability to store energy, poor response speed, and low power density. In the conventional power conversion system, the fuel cell (FC) and battery can be connected to the output load via two independent converters, namely a unidirectional converter for powering with the FC and a bidirectional converter for powering and regenerating via the battery. The conventional converter has a simple structure; it achieves specific operating modes that are required in various driving situations. However, it has two inductors and many operating switches when both the FC and battery are simultaneously used. In addition, all the switches have high voltage stresses. These factors can degrade the overall power density and efficiency. Thus, an integrated converter with single inductor is proposed in this article. By employing a battery mode selection cell, the two converters can be integrated with only one inductor. Moreover, the number of operating switches is reduced during powering, and low voltage-rated semiconductor devices can be used. Therefore, the proposed converter can achieve a high power density and low conduction and core losses. The validity of the proposed converter was demonstrated by the experiments under various operating conditions.

Highly Efficient Full-Bridge Resonant AC/DC Converter Using T-Type Voltage Doubler

This article presents full-bridge resonant ac/dc converter that minimizes switching loss over entire grid voltage cycle. By using the voltage fluctuation at T-type voltage doubler, the existing hard-switched components are turned- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> with almost zero-voltage switching at high instantaneous output power and with less than half of the output voltage at low instantaneous output power. Moreover, no instantaneous reactive current flows through the circuit under wide variations of grid voltages and loads. Furthermore, the proposed converter has balanced loss distribution over the primary-side and secondary-side switches, which ensures high power transfer capability with improved overall switch utilization. A 1-kW prototype is developed and tested to demonstrate the circuit functionality. Finally, the efficiency improvement is investigated; comparisons show the benefit of the proposed converter over conventional converters that use unfolders.

Analysis and small-signal modeling of simplified cascade multiphase DC-DC buck converter

One of the power converters that are often implemented in renewable energy applications is a DC-DC power converter. One of such converters is a step-down converter or buck converter whose output voltage is lower than its input. A novel DC-DC buck converter for low output-voltage and high output current applications is presented in this paper. When compared to the conventional buck converter, the voltage ratio of the proposed topology is higher. The output of this converter also has lower ripple. Thus, the proposed topology is appropriate for renewable applications. The operating principle and small-signal model analysis are discussed in detailed. Finally, a simulation studies is carried out by PSIM to verify performances of the offered topology

Dual-Buck Three-Switch Leg Converters With Reduced Number of Passive Components

Like conventional two-switch leg converters, the three-switch leg converters also have short-circuit risks and a dangerous shoot-through current is generated if switches of the same leg are turned <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> simultaneously. In this article, a new dual-buck structure is proposed for three-switch leg converters. The proposed structure is reliable because of no shoot-through concerns and high quality of output waveforms can be obtained due to the reduction in pulsewidth modulation deadtime. Unlike the conventional dual-buck three-switch leg that uses many passive components such as four current limiting inductors and three external diodes, the new dual-buck three-switch leg uses only one current limiting inductor with two external diodes. To verify the performance, the proposed three-switch legs are used in single-phase dual-output inverter and detailed theoretical analysis, simulation, and experiments are performed. Both continuous and discontinuous modulation schemes are applied and it has been figured out that discontinuous modulation scheme can improve the dc-link voltage utilization in the common-frequency mode of operation.

An Ultrahigh Step-Down DC–DC Converter Based on Switched-Capacitor and Coupled Inductor Techniques

In this article, high step-down dc–dc converters are widely employed in data center applications. Due to the higher step-down conversion ratio in the new generation 48 V voltage regulator module, a conventional buck converter is not suitable for such applications. To conquer this problem, a novel dc–dc converter is proposed in this article to achieve an ultrahigh step-down voltage conversion ratio for data centers. The nonisolated topology can be optimally designed to integrate both the switched-capacitor and coupled inductor techniques, which allows zero-voltage-switching (ZVS) of all active switches to be achieved and improves high efficiency. In addition, the converter presents the advantages of lower voltage stress, ultrahigh voltage gain, common ground, and simple control strategy. A comprehensive analysis of the steady-state analysis, derivation of voltage gain, voltage stress, and ZVS condition is presented in detail. Finally, a 30 W, 48-to-1 V experimental prototype is built and tested, which validates the ultrahigh step-down voltage gain and soft-switching characteristic of the proposed converter. The maximum efficiency of the prototype is 89.1% and the efficiency is 81.4% in full-load condition.

An active power coordination control strategy for hybrid doubly-fed DC system based on actual project

A coordinated control strategy for parallel hybrid doubly-fed DC power transmission system based on the actual project is proposed, which makes full use of the unique advantage of continuous power transmission of LCC-HVDC and VSC-HVDC. This project includes Longquan conventional DC converter station, Yichang back-to-back flexible DC converter station in Hubei province of China and their near AC gird. The control requirements of frequency recovery, damping oscillation and reducing excision of generator sets after the fault are realized by means of VSC/LCC emergency power control, power modulation and frequency modulation. The proposed control strategy is simulated and analyzed in PSCAD/EMTDC, and the effectiveness of that is verified.

Current Mode Control of Non-Isolated Multi-Phase Interleaved Buck-Boost Converter for Military Battery Charging Application.

Power conversion devices are essential in a remote off-grid site, typically for military purposes where several types of equipment with varying input characteristics are supplied essentially by the same energy source, necessitating the use of a buck-boost converter for DC-DC applications. Because the conventional buck-boost converter's inverting output voltage is incompatible with some applications, the two-switch buck-boost converter is recommended for battery charging in military applications. The nominal input voltage range of the five-phase interleaved buck-boost converter is 9 – 36 V, the output voltage is 28 V, the output power is 3.3 kW, and the switching frequency is 100 kHz. The simulation of the converter with current mode control in the MATLAB/Simulink simulation environment was performed to confirm validity of the operational theory and the simulation results show consistency with theoretical values. Maximum of 74.41 ms and 51.35 % were recorded under all conditions of operation for the settling and overshoot respectively. The obtained data indicates a 1–2 % variation between the measured and theoretical duty cycle.

Modular SEPIC-Based Isolated dc–dc Converter with Reduced Voltage Stresses across the Semiconductors

This paper presents the theoretical analysis, experimental results and generalized structure for N modules of an isolated dc–dc SEPIC converter. The structure comes from the integration of N conventional SEPIC converters based on the input-series and output-parallel connection. The main advantages provided by the proposed structure are reduced voltage stress across the semiconductors and division of the current stress in the output diodes. The proposed converter is presented in a generalized approach, varying the voltage stress across the semiconductors according to the number of modules used. As the converter uses more than one switch, the commands can be either equal or phase-shifted by 360∘/N degrees. When operating with phase-shift modulation, a multilevel converter is obtained, which brings another advantage of the structure, since there is a reduction in the volume of the input inductors (Li1 and Li2) and the output capacitor (Co). In this paper, the steady-state analysis, a dynamic model, system control and experimental results are presented for phase-shift modulation and discontinuous conduction mode (DCM). The performance of the proposed converter was verified in a prototype with four modules and the following specifications: 500 W output power, 800 V input voltage, 120 V output voltage and 50 kHz switching frequency. The converter achieved 94.42% efficiency at rated power.

A three‐level isolated dc‐dc SEPIC converter with parallel‐connected output

AbstractThis paper presents a comprehensive theoretical analysis and experimental results for three‐level isolated dc‐dc converter based on the single‐ended primary‐inductance converter (SEPIC) topology. The main advantage of this structure is the reduction of voltage stress on semiconductors comparing it to the conventional SEPIC converter. Voltage stress is the major challenge associated with the conventional SEPIC structure, and contributions in this area can extend the range of applications for the family of SEPIC converters. The analyzed structure contains two switches, and their commands can be either equal or phase‐shifted by 180°. This provides four different modes of operation in discontinuous conduction mode (DCM), which have different operating stages, waveforms, and design equations. In this paper, the topology with parallel‐connected output and the static and dynamic theoretical analysis in DCM, for the four command signal profiles, are presented. The advantages and disadvantages, control strategy, experimental results, and a comparative analysis with the conventional SEPIC converter are discussed. The dc‐dc SEPIC converter was verified by experimental results from a proof‐of‐concept prototype with 500 W rated power, 400 V input voltage, 120 V output voltage, and 50 kHz switching frequency. The converter achieved 94.72% efficiency at rated power.

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 study on improving the efficiency of non-isolated buck-boost bidirectional DC–DC converter

ABSTRACT In battery-based systems such as hybrid electric propulsion system for ships that use electric propulsion and DC grid, bidirectional converters are often used as interfaces between high-voltage power sources and low-voltage batteries for the purpose of storing excess energy and the fields of application for bidirectional converters are steadily expanding. This study proposes a new bidirectional converter with a high voltage conversion rate and low switch voltage stress. The proposed converter allows current to flow between modules by adding only one capacitor compared to a conventional bidirectional converter. To check the effectiveness of the proposed method, PSIM software by Powersim co. Ltd. was used to perform simulation tests. It was confirmed that the high voltage conversion rate was 4 times that of a conventional bidirectional converter in step-up mode and 1/4 that of a conventional bidirectional converter in step-down mode. Therefore, low-voltage components, such as MOSFETs, GTOs, etc., can be applied in the DC–DC converters thanks to the 1/4 voltage that is required in each switching time.