Switching Duty Cycle Research Articles

A High Step-Up PWM Non-Isolated DC-DC Converter With Soft Switching Operation

A high step-up PWM non-isolated dc–dc converter with soft switching is proposed in this paper. The converter has minimum auxiliary elements to achieve high power density and high voltage gain. The ZVS operation of the main power switch results in negligible capacitive turn-on losses. Since the duty cycle of the auxiliary switch is narrow and its operation is under ZCS condition, the losses that the auxiliary circuit imposes are not significant. Also, all the diodes are operated under soft-switching conditions solving the reverse recovery problem. All the inductors are coupled on only one magnetic core, reducing size and conduction losses. Compared to the hard switched counterpart, the electromagnetic interference of the proposed converter is reduced. Furthermore, the output voltage of the proposed converter is controlled by an integral sliding mode control strategy during the load variations. Also, the proposed integral sliding mode control strategy has been compared with the PI control strategy, improving the transient response and the robustness under load variations while the switching frequency is constant. The effectiveness and accuracy of the proposed converter are verified by practical laboratory results which are obtained from a 250W prototype.

Soft Switching Multiphase Interleaved Boost Converter With High Voltage Gain for EV Applications

In this paper, a soft switching interleaved boost converter (SS-IBC) using auxiliary resonant circuit for electric vehicles (EV) applications is proposed. Several phases of the proposed converter can be connected to make a multiphase interleaved boost converter. The operation of multiphase interleaved boost converter is identical to that of the one phase boost converter. All phases are ideally identical with shifted control signals and are controlled by PWM control strategy of equal switching frequency and duty cycle. The proposed converter can be considered as a cost effective retrofit to the grid integrated battery charging applications. It affords a steady electrical power for the load not only from the utility or classical energy storage systems as batteries, but also from renewable energy systems like photovoltaic (PV), wind or fuel cell systems. An appropriate design example demonstrates the size of the design circuit components and parameters are investigated. Analysis, design, and simulation of the presented converter are verified using PSIM simulation software on an 8.2 kW setup system with a conversion efficiency more than 97% over a wide output power conversion range from rated power to a minimum power of 460 W with complete soft switching operation. The converter performance is also validated experimentally on a downsized hardware rated 1.0 kW and the maximum efficiency is found to be 98.78%.

Implementation of PWM scheme for Z-Source inverter using embedded target on SIMULINK

The voltage source inverter (VSI) and current source inverter (CSI) have their own conceptual limitations. When operated as a dc-ac converter, the output voltage of a VSI is lesser compared to input dc voltage. On the other hand, when operated as a dc-ac converter the CSI can generate higher output voltage compared to input dc voltage. To overcome these limitations Z-source converter acts as a suitable alternative. The Z-source converter contains an impedance network connected at the dc link of the conventional 6-switch converter. This impedance network enables the Z-source inverter (ZSI) to overcome the traditional limitations in VSI and CSI. By controlling switching sequence and duty cycle through specific PWM schemes, the ZSI can produce desired output which can be above or below the input dc link voltage as per the requirement. As a result, the ZSI system provides operational capability during various practical conditions like input voltage fluctuation coupled with harmonic mitigation as well as power quality improvement capabilities. This paper dwells into the implementation of the control of ZSI on embedded target feature of MATLAB/SIMULINK for the ease of practical realization. The PWM scheme specific to ZSI requires it to use various hardware circuits for practical realization, the said problem has been addressed in this paper and hardware results of the implementation are also discussed.

Hierarchical Modular Battery Equalizer With Open-Loop Control and Mitigated Recovery Effect

In this manuscript, an advanced battery equalizer with open-loop control is proposed. This equalizer is based on a two-layer hierarchical modular architecture. The top stringto- module (S2M) layer consists of a half-bridge inverter and a voltage multiplier (VM) rectifier, and the bottom cell-to-cell (C2C) layer is implemented by bidirectional buck-boost units. Without state-of-charge (SOC) estimation, the battery charge can be automatically transferred from high-voltage cell-modules/cells to low-voltage ones. Only a pair of symmetrical pulse width modulation (PWM) driving signals with fixed switching frequency and duty cycle are required.This reduces the control complexity remarkably. Meanwhile, the balancing current of each balancing path naturally attenuates with the convergence of cell-module/ cell voltages. This ensures a fast balancing of cell-module/cell with large voltage mismatch. The battery-recovery-effect induced balancing error is also effectively mitigated. Moreover, simple control facilitates a simultaneous module and cell voltage balancing in static, charging, and discharging conditions. The operation principles are analyzed in detail. An experimental platform with eight series-connected batteries is built and tested. The measured results well validate the theoretical analysis. Both cell and module voltages automatically converge with clearly mitigated recovery effect.

Identification of DC Thermal Steady-State Differential Inductance of Ferrite Power Inductors

In this paper, we propose a method for the identification of the differential inductance of saturable ferrite inductors adopted in DC–DC converters, considering the influence of the operating temperature. The inductor temperature rise is caused mainly by its losses, neglecting the heating contribution by the other components forming the converter layout. When the ohmic losses caused by the average current represent the principal portion of the inductor power losses, the steady-state temperature of the component can be related to the average current value. Under this assumption, usual for saturable inductors in DC–DC converters, the presented experimental setup and characterization method allow identifying a DC thermal steady-state differential inductance profile of a ferrite inductor. The curve is obtained from experimental measurements of the inductor voltage and current waveforms, at different average current values, that lead the component to operate from the linear region of the magnetization curve up to the saturation. The obtained inductance profile can be adopted to simulate the current waveform of a saturable inductor in a DC–DC converter, providing accurate results under a wide range of switching frequency, input voltage, duty cycle, and output current values.

Steady State Behavior of a Single-Switch Non-isolated DC-DC SEPIC Converter Topology with Improved Static Voltage Gain

This paper presents the analysis of steady state behavior of a single switch non-isolated Single Ended Primary Inductance Converter (SEPIC) topology for achieving high DC voltage gain using diode-capacitor voltage multiplier. A voltage boosting module consisting of inductor and capacitor in addition with two diodes is introduced in the conventional SEPIC configuration in order to derive the DC-DC conversion technology proposed in this work. The voltage gain of the converter is extended using a diode-capacitor voltage multiplier cell. The converter suggested in this work has a single controlled switch. Hence, the conduction losses and the control complexity of the switch are very much reduced. The open loop configuration of the proposed non-isolated converter is described under continuous inductor current mode. The voltage boosting capability of the presented converter is compared with that of the existing modified SEPIC structure. The presented positive output converter topology has low switch voltage-current stress compared to the existing modified SEPIC topology given in the literature. The inductor and capacitor components of the suggested converter are so chosen that the DC output voltage and current waveforms show very low percentage of ripples. A DC voltage level of 24 V is given as input to the proposed converter. The DC voltage obtained across the load terminals is around 370 V which is achievable with low duty ratio (= 0.7) of the active switch. The voltage conversion ratio is very much influenced by the variation of the duty cycle of the power switch. In this work, the converter topology is presented and its various modes of operation are explained with equivalent circuits. The PSIM software platform is effectively and efficiently utilized to validate the performance of the converter. The obtained results convey that the proposed DC-DC conversion technology with extended voltage gain has the capability to maintain the steady-state output voltage and current profiles with almost negligible amount of ripples owing to the use of suitably designed non-dissipative elements in LC filter.

Design and Implementation a Single-Switch Step-Up DC-DC Converter Based on Cascaded Boost and Luo Converters

We designed and implemented a single-switch step-up DC-DC converter based on cascaded boost and Luo converters. The proposed converter demonstrated a quadratic voltage gain and a high efficiency, which makes it suitable for renewable energy applications, where a high voltage gain ratio is desired without imposing a high number of bulky items or employing a high duty cycle of the active switches. This converter benefits from the continuity of the input current waveform, which equips the maximum utilisation of renewable energy sources. While a transformer-less high voltage-gain was achieved, the voltage and current stresses of the power switch and diodes were kept low in comparison with the existing quadratic DC-DC converters. We analysed the converter in both continuous and discontinuous conduction modes. A non-ideal model of components was considered for power loss and efficiency calculations and comparisons. Finally, the simulation results were extracted with PLECS and validated with experiments on a 120 W prototype.

Computationally Efficient Optimal Switching Sequence Model Predictive Control for Three-Phase Vienna Rectifier Under Balanced and Unbalanced DC Links

Unbalanced dc links usually occur when a Vienna rectifier is used as a charger for series-connected battery packs. The redundant vector preselection optimal switching sequence model predictive control (OSS-MPC) scheme does not require weighting factor tuning and is applicable to unbalanced dc links. However, its use is complicated for switching sequence selections and duty cycle calculations. Therefore, this article proposes a computationally efficient OSS-MPC scheme for three-phase Vienna rectifier operating under balanced and unbalanced dc links. The scheme achieves the same performance as that achieved by the redundant vector preselection OSS-MPC scheme, however, its execution is significantly more efficient. In the proposed method, an unbalanced factor is proposed by considering unbalanced dc links, and a look-up table is derived to describe the equivalence relation among the six feasible switching sequences. Then, duty cycles are calculated for only one switching sequence, and the OSS and its duty cycles are reconstructed based on the predefined table. Unlike the redundant vector preselection OSS-MPC scheme, the enumeration process is eliminated in the proposed method, thus, the computational burden is significantly reduced. Experimental results are provided to validate the effectiveness of the proposed method. This article is accompanied by a PDF demonstrating the look-up tables.

A new dual‐input high step‐up DC–DC converter with reduced switches stress and low input current ripple

In this paper, a novel structure of non-isolated dual-input ultra-high step-up DC–DC converter with low voltage stress across semiconductor elements and low input current ripple is suggested. In the presented converter, when the power switches are turned-OFF, two inputs inductors become series and the input current ripple will be reduced. This topology benefits from the superiorities of voltage multiplier cell and coupled inductor. The voltage conversion ratio can be controlled by coupled inductor turns ratio and duty cycle of power switches. So, the voltage conversion ratio of the suggested structure is flexible. Using the voltage multiplier cell not only increases the voltage gain, but also the voltage stress across power switches and diodes is decreased. In order to confirm the presented structure performance, the theoretical study includes operation principle and steady-state analysis, and simulation results are provided. Also, the suggested converter has been compared with other similar converters versus voltage gain, efficiency, number of components, maximum voltage across switches and diodes. Finally, a 350 W experimental prototype of the converter is built to shows the effectiveness of the presented converter.

Constrained minimization of switched capacitor converter equivalent resistance by adjusting transistor sizes and duty cycles

This paper presents a novel optimization technique for Switched Capacitor Converters (SCCs). The optimization focuses on minimizing the SCC equivalent resistance by adjusting MOSFET widths and switching duty cycles. The optimized SCC parameters are obtained from numerical optimization with constant total transistor width and switching period constraints. The transistor carrier mobilities and gate-to-source voltages are accounted during the optimization. A Fibonacci SCC with two flying capacitors is used as an example and is simulated in a 65 ​nm low-power process. By comparing SCC parameters before and after the optimization, we obtain certain performance improvements. Particularly, at a switching frequency of 10MHz and 50Ω load, the optimized design shows improvement in average and minimum output voltage parameters by 2.5% and 4.1%, respectively, which are caused by 20.6% reduction of the equivalent resistance. The output voltage ripple is also decreased by 22.4%. By sweeping the duty cycle and transistor widths in simulation, the optimized parameters show nearly the best performance.

A GaN-HEMT Compact Model Including Dynamic RDSon Effect for Power Electronics Converters

In order to model GaN-HEMT switching transients and determine power losses, a compact model including dynamic RDSon effect is proposed herein. The model includes mathematical equations to represent device static and capacitance-voltage characteristics, and a behavioural voltage source, which includes multiple RC units to represent different time constants for trapping and detrapping effect from 100 ns to 100 s range. All the required parameters in the model can be obtained by fitting method using a datasheet or experimental characterisation results. The model is then implemented into our developed virtual prototyping software, where the device compact model is co-simulated with a parasitic inductance physical model to obtain the switching waveform. As model order reduction is applied in our software to resolve physical model, the device switching current and voltage waveform can be obtained in the range of minutes. By comparison with experimental measurements, the model is validated to accurately represent device switching transients as well as their spectrum in frequency domain until 100 MHz. In terms of dynamic RDSon value, the mismatch between the model and experimental results is within 10% under different power converter operation conditions in terms of switching frequencies and duty cycles, so designers can use this model to accurately obtain GaN-HEMT power losses due to trapping and detrapping effects for power electronics converters.

Design of PV MVDC Converter with Wide Output Voltage Range for Series DC System

This paper presents a topology of PV MVDC converter with wide output voltage range for a series DC system and its control strategy. In the series DC system, the PV MVDC converters are input-independent, and their outputs are series-connected. A high-level system voltage is achieved for power collection and transmission. This series boost system is flexible and very suitable for decentralized renewable energy application. A modular topology is present for the MVDC converter to improve its applicability. A reconfigurable topology and its modulation method are proposed for the module of the converter. By regulating of duty cycle of switches, the module can be reconfigured to step-up or step-down mode. The operating principles and theoretical derivations of the reconfigurable topology are discussed in detail in this paper. Multimode control strategy for the converter is designed to adapt to complex operation conditions in a series DC system. With the proposed topology and control strategy, the series-connected PV MVDC converter achieves wide input and output voltage range to adapt to the operating characteristics of the series DC system; 3 kV/80 kW DC–DC module and 20 kV/500 kW PV MVDC converter are developed and operating stably in practice. The operation results are presented in the paper.

Optimum Parametric Identification of a Stand-Alone Photovoltaic System with Battery Storage and Optimization Controller Using Averaging Approach

The dimensioning of photovoltaic systems is the major concern of researchers and power industry practitioners. This aims to improve energy efficiency and protect the conversion units by a consistent assessment of power conditioning circuits and interconnections for the PV application. In this context, this paper sets out to fulfill detailed modeling and control steps of a standalone photovoltaic (PV) power system with energy storage, according to practical specifications of the load, PV generation unit, and battery pack. The main goal is to estimate all unknown parameters, as the diode ideality factor and revers saturation current, the controller, and the PV link. The PV link interfacing the PV source circuit to the PV-side converter (PVSC) provides a filtering function to maintain a steady voltage at the link. The charge controller used in the PV-side converter is a DC/DC buck converter. It transfers the PV power to the battery and supplies the load. Using pulse- width modulation (PWM) technical, of which the switching duty cycle is the control-input variable; the PVSC power-conditioning circuit is permanently controlled by the maximum power point tracking (MPPT) algorithm to achieve the maximum energy. The battery pack voltage is properly maintained by the charge controller and specified to match the load voltage rating, to avoid a high ratio of voltage conversion. A method is proposed to integrate both the MPPT function and the battery cycle charge. The PV generator output and the power conditioning circuits, mainly constructed from switching- mode power converters, are nonlinear. An averaged model is then derived for dynamic analysis and controller synthesis, using the state-space averaging and linearization method. A PV array of nine PV modules configured into three strings is used in this application to demonstrate the effectiveness of modeling, design, control, and simulation. Simulation model for the controller and power interface is built and developed in short term, using the fundamental blocks of Matlab Simulink.

Robust Model Predictive Control of DC-DC Floating Interleaved Boost Converter With Multiple Uncertainties

DC-DC Floating Interleaved Boost Converter (FIBC) is recently introduced for converting low-level voltage generated by a renewable energy source to high-level voltage required for AC inverters. Although a desired voltage is expected at the output, designing a proper voltage gain for FIBC is challenging due to different types of uncertainties. For instance, the voltage generated by the energy source and, therefore, the input voltage of FIBC may change by a variety of parameters including external load. Furthermore, parametric uncertainty and measurement noise are other sources which can affect the control procedure. As a result, voltage gain for a fixed switching duty cycle may be uncertain. It demands a robust approach to guarantee the control performance under uncertainties without the need for individually tuning controller for each single converter. In this work, a robust model predictive control is employed to regulate the output voltage at the desired level despite the existing uncertainties. Controller parameters are fixed for any FIBC within the uncertainty range and further tuning is not required for individual converters. In addition, unlike the conventional controllers, the suggested controller is able to handle input-output constraints. Performance of the suggested controller is investigated through simulations carried out in MATLAB and the superiority of the proposed approach is verified over non-robust model predictive framework.

An Analog Control Strategy With Multiplier-Less Power Calculation Circuit for Flyback Microinverter

This letter proposed an analog control strategy for a flyback microinverter, which can calculate the output power by multiplier-less power calculation circuit, while the maximum power point tracking is realized by controlling the maximum duty cycle of the main switch. The proposed analog control method is quite simple with low cost. It is applied with a 100-W single-phase microinverter in a discontinuous conduction mode, and the simulation and experimental results demonstrate its feasibility.

Modulation Strategy and Controller for Grid-Tied Trinary Hybrid Multilevel Inverter

This article deals with the modulation and control of a trinary hybrid multilevel inverter (THMI), which is a cascade multilevel converter that maximizes the number of levels per full-bridge. The modulation presented defines the duty cycle of switches as piecewise functions of the desired output voltage, minimizing the processing time. In order to control this converter, it is modeled as a linear system with bounded disturbance. A quasi-sliding mode control (QSMC) is designed, simulated, and experimentally verified for the THMI operating in grid-tie mode obtaining better results when compared to a classic proportional–integral (PI) controller.

Flicker-Free Resonant LED Driver With High Power Factor and Passive Current Balancing

A flicker-free resonant LED driver with high power factor (PF) and passive current balancing is proposed and analysed in this paper. The proposed LED driver are composed a buck power factor correction (PFC) unit and a resonant dc-dc unit by sharing an active switch. Based on this topology, the low output current ripple can be achieved via small voltage ripple on bulk capacitor and fast voltage-mode control loop. By the charge balance for resonant capacitor, the output current of each LED string can be balanced. In a half line cycle, owing to the small voltage ripple on bulk capacitor of pre-stage output, the duty cycle of active switch is almost constant. Therefore, when the inductor current of buck PFC unit operates in discontinuous conduction mode, high PF can be realized. Moreover, as the resonance is existed between resonant capacitor and leakage inductor of transformer, the diodes in resonant dc-dc unit can achieve zero-current turn-off. Thus, the efficiency can be improved. Finally, an 82W LED driver prototype with three-output is built to verify the studied results.

Analysis of Cross-Connected Half-Bridges Multilevel Inverter for STATCOM Application

This paper suggested a single-phase cross-connected half-bridges multilevel inverter (cchb-mli) topology for static synchronous compensator (statcom) applications. The proposed mli structure consists of cross-connected multilevel cells connected in series with a more optimized number of devices to synthesize a higher number of voltage steps. Each cell in the structure consists of a set of switches and a dc-capacitor. Typically, when several dc-capacitors are used in an inverter, the dc voltages fluctuation occurs due to tolerance between passive element and asymmetric switch losses. A dual-loop control technique has been proposed with level-shifted pulse width modulation pwm to overcome these issues. The proposed methodology balances the dc-voltages using a proportional-integral controller by adjusting the switch duty cycle. The control method helps offset the issue of aggravated fluctuation while preserving the delivered reactive power distributed equally among the dc-capacitors at the same time. A thorough comparison is made between the proposed inverter concerning the number of components and efficiency to demonstrate the effectiveness of previous topologies. Moreover, a simulation model built in simulink and experimental results take from laboratory prototype to confirm the effectiveness of proposed structure and its control technique.

Parallel-charge series-discharge inductor-based voltage boosting technique applied to a rectifier-fed positive output DC-DC converter

The conventional power electronic boost converters have inherent limitations that they are not able to increase the low DC input voltage level into sufficiently high DC output voltage level. This is because of the fact that (1). the inductor used in the converter has certain amount of internal resistance, and (2). the power devices used in the converter are subjected to high potential stress which led to damage of the devices. A configuration of a non-isolated step-up rectifier-fed positive output power converter capable of converting low DC voltage into high DC output voltage-based on the concept of parallel-charge series-discharge inductors is proposed in this paper. The proposed converter is fed by an uncontrolled diode bridge rectifier to which an input sinusoidal AC voltage of magnitude 30 V (rms) is given. The converter is configured such that the input AC voltage of 30 V (rms) is stepped-up to around 900 V (DC) at the output of the converter, with extremely low duty ratio. The proposed converter configuration employs only two high power semiconductor switches with reduced complexity of control. In this work, the converter topology is presented, and its steady state behavior and dynamic modeling are discussed for continuous inductor current mode operation. Further, it is revealed that the voltage gain of the converter is influenced by the variation of the duty cycle of the power switches. The effectiveness of the converter is better understood through simulation in MATLAB/SIMULINK platform. The results demonstrate that the converter is able to maintain higher constant output voltage profile with significantly reduced overshoot and settling time. 
 

High Step-Up Quasi-Resonant Converter Featuring Minimized Switching Loss Over Wide Input Voltage Range

This article proposes a high step-up quasi-resonant converter that minimizes switching loss over a wide range of input voltages. By employing a bidirectional switch and corresponding switching modulation, the proposed converter achieves the main switch with almost zero voltage, and therefore incurs very little switching loss at all active switches. Moreover, no instantaneous reactive current flows through the circuit under wide variations of input voltages and loads. The duty cycle of primary-side switches is fixed to 0.5; then, the input and clamp capacitor voltages become identical, and thereby the following resonant capacitor voltages remain in balance. As a consequence, the proposed converter becomes compact and achieves high boost-ratio and high efficiency over a wide range of input voltages. The operating principle of the converter is presented along with its design procedure. 400-W/380-V prototype of the proposed converter has been implemented and tested at 40-60 V to verify its effectiveness.