Step-down Voltage Research Articles

Improving the Dimming Performance of Low-Power Single-Stage AC–DC HBLED Drivers

The design of efficient single-stage high-brightness light-emitting diodes (HBLEDs) ac–dc drivers with power factor correction (PFC) in low-power applications is addressed in this paper. The PFC is achieved by using a switching converter with both step-up and step-down voltage capability. It is well known that a good tracking of the input reference current close to the zero crossing is challenging, in particular when the LED output current is low, hence jeopardizing the power quality at low power levels. A solution is proposed to improve the power quality in ac–dc LED drivers under inner current loop based on a variable hysteresis modulation scheme. An adaptive hysteresis window modulated by the input voltage and the output LED current reference is used. The double modulation strategy helps to avoid the distortion near the zero crossings of the input current and to improve the dimming performance of the HBLEDs. This results in a low value of total harmonic distortion (THD) under low current/power conditions and therefore in a very good dimming performance in single-stage ac–dc HBLEDs drivers with PFC. The operation principle of the proposed technique is presented and numerical simulations are shown to demonstrate its functionality. A laboratory prototype is designed and tested to verify its feasibility obtaining a significant improvement in terms of power quality. Under universal input voltage operation, good efficiency and low THD can be achieved even for low power levels.

A Matrix-Based Nonisolated Three-Phase AC–DC Rectifier With Large Step-Down Voltage Gain

This paper presents a matrix-based nonisolated three-phase ac–dc converter with a current-doubler rectifier (CDR) circuit. Buck-type rectifiers are normally used for step-down ac-to-dc conversion. However, for three-phase buck rectifiers, the lower bound of rectified dc voltage is limited as the converter is severely underutilized by operating at lower modulation index. Moreover, at lower modulation index, the rms values of current increases contributing to higher conduction losses. However, by using a matrix (3 × 1) topology followed by a CDR, the desired dc output voltage can be reduced by half. The matrix topology directly converts three-phase line frequency ac voltages into intermediate high-frequency ac voltage which is subsequently, rectified using a CDR to obtain the required output dc voltage. A modified space vector modulation based modulation scheme especially suited for the proposed converter is presented for superior input power quality with reduced power loss. Comprehensive analysis and design of the proposed converter is carried out followed by simulation and laboratory-based experimental tests. Subsequently, the loss analysis of the proposed converter is carried out and a comparative evaluation of the proposed converter with the traditional six-switch buck rectifier is provided to demonstrate the suitability of the proposed converter for large step-down voltage gain. Digital implementation of the proposed modulation scheme is carried out at 40-kHz switching frequency. A hardware prototype of 500 W is developed to validate the theoretical and simulation results.

A Dual Series-Resonant DC–DC Converter

A dual series-resonant dc-dc converter with zero-voltage switching and zero-current switching features is proposed in this paper. The topology consists of two switches and a clamping capacitor on the primary side of an isolating transformer. The two switches are operated in a complementary mode under a pulse width modulation (PWM) scheme. The secondary side of the transformer is connected to the load through two series-resonant circuits and a half-bridge diode rectifying stage, in which the rise and fall slopes of the diode currents are limited by the slope of the currents in the resonant circuits, resulting in reduced switching losses in the diodes. The two series-resonant circuits provide power transfer to the output load without interruption throughout the positive and negative cycles of operation. It is shown that the output voltage of the proposed converter can be regulated using either PWM control or frequency modulation control. Both step-down and step-up voltage conversions can be achieved using the proposed topology. Programmable system-on-chip is used as the controller platform to implement a 40 W laboratory prototype. A complete steady-state analysis is presented and the experimental results of the prototype of the proposed converter are discussed.

A New Interleaved Bidirectional Zero Voltage Switching DC/DC Converter with High Conversion Ratio

In this paper, a new interleaved nonisolated bidirectional zero voltage switching (ZVS) dc–dc converter by using one three-windings coupled inductor is proposed. The proposed topology can provide high step-up and high step-down conversion ratios for boost and buck operations, respectively. Moreover, because of interleaving, the proposed converter has low input current ripple at low voltage side in both buck and boost operations. The proposed converter uses lower number of switches to have bidirectional power flow in comparison with other interleaved bidirectional converters. All used switches in the proposed converter are turned on under ZVS. The advantages of the proposed converter in comparison with the conventional interleaved converters are included in the capability of bidirectional power flow, ZVS operation for all switches and high step-up and high step-down voltage gain for boost and buck operations. In this paper, the proposed converter is analyzed completely and all equations of components are extracted as well as the ZVS conditions of all switches. Moreover, a comprehensive comparison between the proposed converter and conventional topologies is presented. To verify the accuracy performance of the proposed converter, the experimental results are given.

A Single-Phase Buck–Boost Matrix Converter With Only Six Switches and Without Commutation Problem

In this paper, a single-phase buck–boost matrix converter is proposed which can both buck and boost the input voltage with step-changed frequency. It consists of only six unidirectional current flowing bidirectional voltage blocking switches, two input and output filter capacitors, and one inductor. It has following advantages over the existing single-phase matrix converters: 1) it can both buck and boost input voltage solving the limited voltage transfer ratio (only boost or buck) problem; 2) it also has enhanced reliability as it is immune from shoot-through problem of voltage source when all switches are turned-on simultaneously, and, therefore, it has no need of PWM dead times and RC snubbers or dedicated soft-commutation strategies to solve the commutation problem; 3) it can also use high-speed power MOSFETs as their body diodes never conduct, which eliminate their poor reverse recovery problem. The operation principle of the proposed converter is given, and switching strategies are developed to obtain various multiples and submultiples of input frequency. To verify its performance, a laboratory prototype is fabricated and experiments are performed to produce step-down and step-up voltage with three different frequencies of 120, 60, and 30 Hz.

Optimal Switching of DC-DC Power Converters Using Approximate Dynamic Programming.

Optimal switching between different topologies in step-down dc-dc voltage converters, with nonideal inductors and capacitors, is investigated in this paper. Challenges including constraint on the inductor current and voltage leakages across the capacitor (due to switching) are incorporated. The objective is generating the desired voltage with low ripples and high robustness toward line and load disturbances. A previously developed tool, which is based on approximate dynamic programming, is adapted for this application. The scheme leads to tuning a parametric function approximator to provide optimal switching in a feedback form. No fixed cycle time is assumed, as the cycle time and the duty ratio will be adjusted on the fly in an optimal fashion. The controller demonstrates good capabilities in controlling the system even under parameter uncertainties. Finally, some modifications on the scheme are conducted to handle optimal switching problems with state jumps at the switching times.

An Expandable Four-Phase Interleaved High Step-Down Converter With Low Switch Voltage Stress and Automatic Uniform Current Sharing

In this paper, a novel four-phase interleaved high step-down converter is presented. The proposed converter can provide an extremely high step-down voltage conversion ratio within a moderate duty cycle. There are four main advantages of the proposed converter. First, the blocking capacitors can store energy as usual. Therefore, they are used as voltage sources to reduce the input voltage as well as to reduce the switch voltage stresses. Second, due to the charge balance of the dc blocking capacitors, the converter possesses an automatic uniform current sharing characteristic of the interleaved phases without adopting any extra circuitry. Third, due to the phase shift between the interleaved phases, the architecture provides a low output current ripple. Fourth, the number of phases can be expanded or reduced to any even phases; therefore, the converter has a wide range of applications. Finally, the operating principles and analysis of this architecture are given, and an experimental prototype is also provided to verify the effectiveness of the proposed converter.

A New High Step-down DC-DC Converter for Renewable Energy System Applications

This paper proposes a new topology of a high step-down dc-dc converter with a conversion ratio of approximately 20 times for high-input and low-output voltage applications such as renewable system applications. This proposed converter employs only one single switch with low control complexity. In this paper, the converter configuration is presented and its operating principle under continuous conduction mode (CCM) is described. The relationship between the step-down voltage ratio and the duty cycle is also presented in order to illustrate the performance of the proposed converter. In addition, the laboratory phototype of the proposed converter is implemented. The simulation and experimental results are shown to demonstrate the effectiveness of the proposed high step-down single-switch dc-dc converter.

Analysis of a Bidirectional DC-DC Converter with High Voltage Gain

A novel bidirectional DC-DC converter with high conversion ratio is proposed in this paper. The proposed converter uses the three windings coupled-inductor to achieved high voltage conversion ratio. The primary side consist of a winding and secondary side consist of two windings, which these two windings are series to achieved high voltage gain.In the boost mode, a capacitor is parallel charged and series discharged by the coupled inductor. Thus, high step-up voltage gain can be achieved with an appropriate duty ratio. In the buck mode, a capacitor is series charged and parallel discharged by the coupled inductor. The bidirectional converter can have high step-down voltage gain.The stress voltage of main switches can be reduced, and efficiency can be improved. The operating principle and the steady-state analyses of the voltage gain are discussed. Finally, in 24V for low voltage, and 400V for high voltage, and 200W for output power, this converter is simulated in MATLAB.

Step‐down converter with wide voltage conversion ratio

A non-isolated dc–dc converter with a wide step-down voltage gain is presented, which combines one coupled inductor and two energy-transferring capacitors. The corresponding voltage conversion ratio is much lower than that of the traditional synchronously rectified buck converter, and the proposed converter can achieve an extremely low output voltage by adjusting the turns ratio and duty cycle. Furthermore, the proposed converter can achieve zero-voltage-switching turn-on, and the leakage inductance energy of the coupled inductor can be recycled to the capacitors, thereby causing the voltage spikes on some of the switches and all diodes to be quite low. In this study, theoretical deductions and experimental results are given to verify the feasibility and effectiveness of the proposed converter.

A Topology of Step-Down Resonant Switched-Capacitor-Based AC–DC Converter for High-Frequency AC Distribution

This paper proposes a switched-capacitor (SC)-based step-down AC–DC power converter with high-frequency feed without rectifier or transformer. The operational principle of the circuits and the design considerations are described. The main advantage of the circuit is that step-down voltage can be achieved in the circuit by simply configuring with cascaded stages, which will be much more convenient to be modular development and easy for replacement and maintenance; the voltage and current stresses of most components are smaller than the conventional converter. Using buffer capacitor to reserve energy, there are no magnetic energy storage elements in the circuits. Weight and size can be further reduced due to high-frequency-power line operation. Zero current switching (ZCS) is achieved by introducing small resonant inductors. Therefore, higher efficiency and power density can be achieved. The performance of the converter has been demonstrated by an experiment with 50 kHz 50 V power feed which is emulated by a signal generator and high-frequency amplifier to prove the concept.

비절연형 양방향 탭인덕터 부스트 플라이백 컨버터

This paper proposes a new bidirectional DC–DC converter with high efficiency. The proposed converter is composed of a flyback and a tapped-inductor boost converter to satisfy extreme operating conditions with low cost. The outputs are connected in series to achieve a high-voltage step-up. In the reverse direction, the proposed converter has an extreme step-down voltage. In this study, the proposed converter was employed with a 100 W hardware prototype. To design the controller, a small-signal transfer function of the proposed converter is derived. For PV power conditioning systems, a maximum power point tracking method is applied with perturb and observe method. To verify the operation of the bidirectional power flow, the current controller is applied. All of the controllers are employed with a digital signal processor.

A New Single Active Switch Quadratic Buck Converter

A new dc-dc converter consisting of one active switch (transistor), three diodes, two inductors and two capacitors is proposed. The new converter is theoretically analyzed in continuous conduction mode (CCM) operation, in which the converters are used in most applications. Then, the feasibility is studied using a simulation tool and a practical prototype. All these prove that the convertor operates as expected and that it has a second-order (quadratic) dc conversion ratio. Its applicability is related to conversion where a small step-down voltage is needed. Also current mode control can be easily implemented in this topology, when output current is of interest.

Formation and Effect of Moisture Contents to Kraft Paper’s Life of In-Service Power Distribution Transformer

Examples of solid and liquid electrical insulations for power transformer are mineral oil and cellulose based paper. As transformers performed their function to step-up or step-down voltage level, its’ insulations will be degraded. Paper insulation is considered the most critical component in a transformer insulation system because it is not easily replaced if compared to oil where it is easily reconditioned in-order to remove water and contaminants. Studies show that temperature, moisture contents and oxygen contributed to paper insulation degradation. Moisture and furanic compound were produced from these deterioration processes. This paper is focused on the formation and effect of moisture to Kraft paper’s life. Levels of moisture contents were obtained from in-service power distribution transformers. These data then is used to assess the Kraft paper’s life by means of Weibull plot. This study shows that level of moisture contents can be used to assess the life of Kraft paper insulation.

A Review of Non-Isolated High Step-Down Dc-Dc Converters

In this paper, a review of the common techniques used for high step-down dc-dc voltage conversion is presented. First, the limitations of conventional buck & synchronous rectifier buck converters used for high step down dc-dc voltage conversion which include narrow duty cycle, high voltage stress, large ripple and low efficiency are briefly discussed. Then various topologies of non-isolated step-down dc-dc converters are reviewed and discussed. The topologies/techniques used for high step down dc-dc conversion are divided into various groups which include interleaved, quadratic, tapped, switched capacitor, switched inductor, coupled inductor, multi level and buck converter with three state switching cells. Each group of converters is briefly discussed, main circuit structure of each topology is given and their features and limitations are given. Finally a comparison of all the discussed topologies is carried out based on some common features.

Comparison of Filter with Fuzzy Controlled Three Level DC-DC Converter Fed Drive

A simple Fuzzy logic controller (FLC) applied to buck converter is presented in this paper. This approach uses FLC which performs better when compared with the conventional PI controllers. In proposed buck converters, high voltage dc supply is switched at very high frequency and inductively transferred to dc load via a high frequency transformer and rectifier. In this converter four power switches are connected in series to primary of high frequency transformer for large load currents. To achieve large step-down voltage ratios the power switches are turned ON and OFF alternatively with a time gap. The voltage step-down ratios, Total Harmonic Distortion and angular velocity of drive are the parameters to be analyzed. The comparison with the original FLC and comparison of three level DC-DC converter with capacitor and pi filter is carried out by MATLAB-Simulink simulation and Model is designed to verify the proposed method performance.

A Family of Multiport Buck–Boost Converters Based on DC-Link-Inductors (DLIs)

A systematic method for derivation of a multiport converter (MPC) based on the dc-link inductor (DLI) concept is proposed in this paper. The MPC is generated by interconnecting multiple pulsating voltage cells (PVCs) through the DLIs. The PVCs can be input type, output type, and bidirectional type, and bidirectional MPC topologies can be harvested if all the PVCs are bidirectional type. As a result, a family of novel MPCs, including multiinput converters, multioutput converters, and bidirectional MPCs, are derived. With the proposed MPCs, step-up and step-down voltage conversion between any two of the ports can be implemented. As an example, the three-port bidirectional buck-boost (TP-B 3 ) converter is analyzed and applied to a stand-alone renewable power system for interconnection of three dc subsystems. The operation principles, pulse width modulation, and feed-back control strategies are presented and analyzed in depth. The analysis indicates that, compared to the traditional common dc-bus-based solution, bulky dc-link capacitor is eliminated and single-stage conversion between any two of the three dc-buses are achieved with the TP-B 3 converter, which is beneficial for higher efficiency, power density, and reliability. Experimental results are given to verify the feasibility and effectiveness of the developed TP-B 3 converter.

A Buck-Boost Type Charger with a Switched Capacitor Circuit

In this paper, a buck-boost type battery charger is developed for charging battery set with a lower voltage. This battery charger is configured by a rectifier circuit, an integrated boost/buck power converter and a switched capacitors circuit. A boost power converter and a buck power converter sharing a common power electronic switch are integrated to form the integrated boost/buck power converter. By controlling the common power electronic switch, the battery charger performs a hybrid constant-current/constant-voltage charging method and gets a high input power factor. Accordingly, both the power circuit and the control circuit of the developed battery charger are simplified. The switched capacitors circuit is applied to be the output of the boost converter and the input of the buck converter. The switched capacitors circuit can change its voltage according to the utility voltage so as to reduce the step-up voltage gain of the boost converter when the utility voltage is small. Hence, the power efficiency of a buck-boost type battery charger can be improved. Moreover, the step-down voltage gain of the buck power converter is reduced to increase the controllable range of the duty ratio for the common power electronic switch. A prototype is developed and tested to verify the performance of the proposed battery charger.

High-Conversion-Ratio Bidirectional DC–DC Converter With Dual Coupled Inductors

In this paper, a high-conversion-ratio bidirectional DC–DC converter with dual coupled inductors is proposed. In the boost mode, two capacitors are parallel charged and series discharged by the dual coupled inductors. Thus, high step-up voltage gain can be achieved with an appropriate duty ratio. In the buck mode, two capacitors are series charged and parallel discharged by the dual coupled inductors. The bidirectional converter can have high step-down voltage gain. The stress voltage of all switches can be reduced, and the switching loss and efficiency can be improved. The operating principle and the steady-state analyses of the voltage gain are discussed. Finally, in 24V for low voltage, and 400V for high voltage, and 200W for output power, this converter simulated in MATLAB.

Design and Implementation of a Power Converter to Process Renewable Energy for Step-down Voltage Applications

In this study a power converter to process renewable energy is proposed, which can not only process solar energy but deal with wind power. The proposed converter is derived from two series modified forwards to step down voltage for charger system or dc distribution application, so as called Modified-Forward Dual-Input Converter (MFDIC). The MFDIC mainly contains an upper Modified Forward (MF), a lower MF, a common output inductor and a DSP-based system controller. The upper and lower MFs can operate individually or simultaneously to accommodate the variation of atmospheric conditions. Since the MFDIC can process renewable power with interleaved operation, the ripple of output current is suppressed significantly and thus better performance is achieved. In the MFDIC only a common output inductor is needed, instead of two separated inductors, so that the volume of the converter is reduced significantly. To draw maximum power from PV panel and wind turbine, perturb-and-observe method is adopted to achieve the feature of Maximum Power Point Tracking (MPPT). The MFDIC is constructed, designed, analyzed, simulated and tested. Simulations and practical measurements have demonstrated the validity and the feasibility of the proposed dual-input converter.