Asymmetrical Duty Research Articles

Three-Phase Three-Level Isolated DC-DC Soft Switching Converter For Solar Applications

Three-level isolated DC-DC converter is an attractive topology in high input voltage applications, which can provide the voltage stress of the power devices to only a half of the dc voltage and also reduce the size of dc filter requirement. But major limitations in the existing three level ZVS converter topologies are brought out with an increased inductance in the primary side and it required to provide complete ZVS of all primary devices down to light loads. By employing an external inductance in the primary of the transformer, total leakage inductance of the transformer increases which is required for realization of soft switching of the converter switches but there are some disadvantages of connecting external inductance in the primary of the transformer. To overcome all these drawbacks, the three-phase three-level isolated DC-DC soft switching converter has been proposed in order to reduce voltage and current stresses. This converter topology requires less number of control switches and operates with an asymmetrical duty cycle control. The proposed three level DC-DC converters provide two- level voltage waveform before dc output filter, which significantly reduce the size of dc output filter. The proposed work has been implemented using MATLAB/SIMULINK and the performance of the proposed converter is verified through simulation results.

Closed-Form Asymmetrical Duty-Cycle Control to Extend the Soft-Switching Range of Three-Phase Dual-Active-Bridge Converters

The three-phase dual-active-bridge (DAB) converter is a promising topology for high-power dc–dc conversion in dc grids and industrial applications. However, the conventional single-phase-shift modulation shows a limited soft-switching range and large reactive currents under light-load operation especially with large voltage variations. This article proposes an asymmetrical duty-cycle control method for the three-phase DAB to extend the soft-switching range and reduce reactive currents by realizing three-phase triangular- and trapezoidal-current-mode operation. Closed-form solutions of the proposed modulation schemes are derived that enable a simple online calculation of the control parameters. The proposed modulation schemes can substantially reduce losses of both power semiconductor devices and the medium-frequency transformer. Thus, the three-phase DAB converter can realize high efficiency over a wide operation range, especially under light-load conditions. Considering the practical implementation, a compensation method is presented to correct the distorted current waveforms caused by the dead time and ensure the desired soft-switching operation. Besides, the power loss imbalance between top and bottom switches induced by the asymmetrical duty cycle is addressed by an active thermal balancing strategy. The effectiveness of the proposed method is validated by simulation results and experiments on a downscaled converter prototype.

Cascaded full‐bridge resonant inverter configuration for different material vessel induction cooking

This paper presents a cascaded full-bridge resonant inverter configuration for different material vessel induction cooking. The proposed inverter configuration features simultaneous heating of three different material vessels, and independent power control. In this proposed work, three different induction heating loads are simultaneously operated at their respective resonant frequencies. Vessels of iron, steel, and aluminium materials are used. The output powers are independently controlled by an asymmetric duty cycle control. The proposed inverter is designed and hardware prototype has been implemented. Experimental results are validated with simulation results.

Optimal Asymmetric Duty Modulation to Minimize Inductor Peak-to-Peak Current for Dual Active Bridge DC–DC Converter

Asymmetric duty modulation (ADM), as a recently proposed modulation scheme, provides new chance to improve the performance of dual active bridge (DAB) converter. On this basis, an optimal ADM (OADM) scheme is proposed in this article to minimize the inductor peak-to-peak current over the whole voltage and power range. First, the DAB converter adopting ADM scheme is analyzed in frequency-domain and time-domain, and four operating modes are established. Then, the minimum peak-to-peak inductor current for each operating mode is obtained under Karush-Kuhn-Tucker condition, and the corresponding optimal closed-loop control with low calculation complexity is derived. Then, the key values and features of the OADM scheme are compared with recent state of the art, mainly including the inductor root mean square current and soft-switching performance. Finally, an experimental prototype was built to validate the efficiency enhancement of the converter by adopting the proposed OADM scheme.

An NDT Model for Block Designs Operating Under Asymmetrical Duty Cycling

Reducing energy consumption is of paramount importance in wireless networks, particularly now with the increasing popularity of the Internet of Things. One of the most effective tools for that is duty cycling the radio. In particular, asynchronous methods have been repeatedly studied in the literature. In this letter, we consider the asymmetrical case of asynchronous duty cycling, i.e., when nodes operate under different duty cycles because of different energy requirements. More specifically, we derive upper and lower bounds, as well as an approximate model for the neighbor discovery time of nodes operating under asymmetrical block designs. We further validate our model by comparing it to empirical data.

A level shifted asymmetric duty cycle controlled half-bridge series resonant LED driver configuration

ABSTRACT This paper proposes an efficient LED lamp converter circuit incorporating dimming feature and multiple lamp independent control. The converter consists of a half-bridge resonant converter in series with a DC source. This converter operates at 200 kHz. Soft switching is employed with resonant power conversion. With modulation of the low frequency pulse width, the dimming feature is incorporated. The proposed configuration provides lower voltage stress for switching devices as well as lower switching losses resulting in increased efficiency. It is possible to independently control the current of each lamp. For two lamps operating in parallel with a total power of 25 W, a laboratory prototype has been designed. It can be used in residential applications. The proposed circuit is presented with detailed operation of the circuit, simulation and experimental results.

High-Efficiency Asymmetrical Half-Bridge Converter With a New Coupled Inductor Rectifier (CIR)

A conventional asymmetrical half-bridge (AHB) converter is one of the most promising topologies in low-power applications because of the zero-voltage switching (ZVS) of all switches and the small number of components. However, when it operates with an asymmetrical duty ratio, it has a large dc-offset current in the transformer, which increases the size and core loss of the transformer. Moreover, because the dc-offset current decreases ZVS energy for one of the half-bridge switches, it has low efficiency in a light load condition. In addition, because most of the output current is concentrated in high-voltage-rating diodes that have large forward voltage drops, large conduction loss occurs in the secondary rectifier. To solve these problems, a new AHB converter with a coupled inductor rectifier (CIR) is proposed in this paper. By adopting the CIR structure in the AHB converter, the proposed converter not only eliminates the dc-offset current in the transformer, but it also has equalized current stress in the rectifier diodes. As a result, the proposed converter achieves high efficiency in entire load condition, compared to an AHB converter with a full-bridge rectifier. The effectiveness and feasibility are verified with a 250–400 V input and 100 V/200 W output prototype.

A Novel NPC Dual-Active-Bridge Converter With Blocking Capacitor for Energy Storage System

In recent years, dc microgrids have been widely concerned for natural interface with renewable energy sources, dc loads, and energy storage systems (ESS). A novel neutral point clamped (NPC) dual-active-bridge (DAB) converter with a blocking capacitor is proposed for ESS in dc microgrids. By inserting a blocking capacitor in primary loop of the traditional NPC DAB converter, the voltage amplitudes across the primary and the secondary windings of the transformer can be matched when the voltage ratio is equal to 0.25, 0.5, 0.75, and 1. Therefore, the proposed topology can adapt to a wide range of energy storage battery voltage variations. Asymmetric pulsewidth modulation plus phase shift modulation are applied to improve the dynamic performance of the proposed converter. The phase-shift ratio between the two bridges and the asymmetric duty ratio are regulated to control the power flow of the proposed NPC DAB converter. Compared with the traditional NPC DAB converter, the proposed topology has lower transformer rms current and wider soft-switching region. Finally, experimental results from a 500-W hardware prototype are presented to verify the feasibility and the advantage of the proposed converter. Compared with the traditional NPC DAB converter, the maximum promotion of efficiency is up to 3.8%.

A three‐leg resonant converter for two output LED lighting application with independent control

SummaryA three‐leg resonant converter is proposed to drive two light emitting diode (LED) lamps of different power ratings. This may be required when both main and local lighting are essential. The proposed converter is operated simultaneously at two different frequencies. Two series resonant circuits are used to allow two different frequency currents. Each lamp is powered through a series resonant circuit and is controlled independently. LED lamp currents are regulated at the desired operating current by using phase‐modulation control and asymmetrical duty ratio control. In addition, pulse‐width modulation (PWM) dimming control is implemented for two LED lamps independently. The proposed topology has advantages of zero‐voltage switching (ZVS), regulation of lamp currents, independent illumination control, and high efficiency. A 126‐W prototype has been developed experimentally to confirm its working principle, performance, and validity.

ZVS-Operation of LLC Resonant Inverter with Phase Limit Control for Induction furnace

This paper presents an LLC resonant inverter with phase limit control to guarantee zero voltage switching (ZVS) operation and protect switching devices from spike current during the heating process. The output power is controlled by using the asymmetrical duty cycle (ADC) modulation. With phase limit control, the non-ZVS operation and spike current caused by a change of duty cycle with fixed frequency and load Curie’s temperature can be eliminated. The proposed method is confirmed through computer simulation and hardware experiment. The experimental results are provided with the heating of a 300 g of Tin from room temperature until melting at 232 ˚C.

Revisiting Probabilistic Schedule-Based Asynchronous Duty Cycling

Schedule-based asynchronous duty cycling is a simple duty cycling technique that requires no synchronization, control traffic or expensive computation. Thus, it is an interesting choice for WSNs. However, most of the literature on the design of asynchronous schedules has been limited by the exaggerated restriction that the schedules present a property named rotation closure. While more flexible probabilistic schedules have been proposed, they were considered inferior under the argument that they do not provide an upper bound on the communication latency. In this paper we revisit the probabilistic schedules with the goal of showing they may be the preferred method in several scenarios. We argue that under realistic assumptions no schedule can guarantee a latency upper bound. We show that probabilistic schedules better support asymmetric duty cycle operation, while also providing unlimited duty cycle granularity and range. Finally, by means of simulation, we compare a probabilistic schedule belonging to the family of Birthday Protocols, the Birthday–Listen–and–Transmit (BLT), with traditional deterministic schedules. Results show that, on top of its other qualitative advantages, BLT achieves competitive latencies.

Multichannel Broadcast in Duty-Cycling WBANs via Channel Hopping

We formulate and study a broadcast problem arising in multichannel duty-cycling wireless body area networks (WBANs) which the sink needs to broadcast control information to all sensor nodes on or implanted in the human body. Despite its fundamental importance for the network configuration and secure key management, the multichannel broadcast problem is largely unaddressed in duty-cycling WBANs. In this paper, we devise novel 2-D scheduling specifying the rule of channel hopping and wake-up time slot selection, which achieves the order-minimal worst-case broadcast delay while guaranteeing the full broadcast diversity regardless of clock drifts and asymmetric duty cycles and channel perceptions. Specifically, we first employ the Chinese remainder theorem to design an effective multichannel broadcast (MCB) algorithm and further propose improved MCB that enhances the granularity of MCB in matching actual duty cycles and number of channels, reducing the theoretically worst-case broadcast delay of MCB by up to 75%. We demonstrate the performance of the proposed algorithms through theoretical analysis and extensive simulations.

Block combination–based asynchronous wake-up schedule in wireless sensor networks

In wireless sensor networks, when sensor nodes are operated with different ratios of active slots, this is called asymmetric duty cycles. Furthermore, cycles with the same ratio of active slots per cycle for all nodes are called symmetric duty cycles. In wireless sensor networks, most applications require both symmetric and asymmetric duty cycles. The balanced incomplete block design–based wake-up schedule is known to be the optimal solution for symmetric duty cycles. However, because this schedule cannot support asymmetric duty cycles, the balanced incomplete block design–based wake-up schedule is not suitable for wireless sensor networks. Herein, we propose a new scheme called the block combination–based asynchronous wake-up schedule to resolve this issue for asymmetric duty cycles. Block combination–based asynchronous wake-up schedule combines different blocks using a block combination operation. The combined schedule guarantees common active slots between sensor nodes in asymmetric duty cycles. To demonstrate the superior performance of block combination–based asynchronous wake-up schedule, we implement a TOSSIM-based simulation and compare the experimental results with recent neighbor discovery protocols such as balanced incomplete block design, prime-based block design, Disco, U-Connect, SearchLight, Hedis, and Todis. We then prove that block combination–based asynchronous wake-up schedule outperforms the others.

Output Voltage Control of the SP topology IPT system based on Primary side Controller operating at ZVS

This paper presents a technique to control the output voltage of a series-parallel (SP) topology inductive power transfer (IPT) system using only a controller, located on the primary side. This reduces the cost, size, complexity and loss of the system compared to conventional IPT dual-side controllers. An asymmetrical duty cycle control (ADC) of full-bridge inverters was used to control the DC output voltage to its designed value. Additionally, a zero voltage switching (ZVS) operation can be obtained at all power levels by varying the switching frequency of the inverter. Theoretical analysis was performed through a mutual inductance coupling model and verified by computer simulation. Experimental results of the circular magnetic structure IPT system with an adjustable air-gap confirm the validity of the proposed controller. The system efficiency was improved throughout the operation and the improvement became obvious as the output power was decreased.

Three-Phase Three-Level Soft Switching Dc-Dc Converter for Industrial Applications

In high power DC applications, the single-phase DC-DC converter will face large voltage and current stress in each control switch and thereby the power handling capacity is less. To overcome this problem, three-phase DC-DC converter is used and it is suitable for high power applications with reduced number of switches as compared with the conventional topologies. The asymmetrical duty cycle control is considered to operate the switches under soft switching and hence the switching losses are reduced. The transformer leakage inductances are used along with junction capacitances in order to form resonance and hence ZVS commutation is possible in a wider load range. The modified phase shift control method is used for the proposed converter.The operational modes and design equations of the proposed converter have been observed. The simulation is carried out with a load of 1000W for validating the proposed work.

High‐power bidirectional resonant DC–DC converter with equivalent switching frequency doubler

A high-power double frequency bidirectional symmetrical DC–DC resonant converter is proposed to reduce the sizes of the passive components and increase the cost-effectiveness. Inspired by the bipolar and unipolar modulations for the single-phase inverter, an asymmetrical duty cycle double frequency modulation is originated for high-power bidirectional resonant converters whose switching frequency and power density are significantly limited by the high-power devices. The equivalent operating frequency of the resonant tank becomes twice of the switching frequency, which effectively reduces the volumes and costs of the passive components, especially for high-power high-voltage applications. Moreover, the proposed converter has the same output characteristics for the two power flow directions, which not only symmetrises the bidirectional frequency control, but also simplifies the design of the resonant components. The converter operation principle is illustrated and the converter performances are analysed including the principle of the double frequency modulation, output characteristics and soft switching condition. Finally, a 5 kW prototype is built to verify the analysis, and the resonant components for the conventional bidirectional resonant converter are also designed and compared to illustrate the advantages of the proposed converter.

Code-Based Neighbor Discovery Protocols in Mobile Wireless Networks

In mobile wireless networks, the emerging proximity-based applications have led to the need for highly effective and energy-efficient neighbor discovery protocols. However, existing works cannot realize the optimal worst-case latency in the symmetric case, and their performances with asymmetric duty cycles can still be improved. In this paper, we investigate asynchronous neighbor discovery through a code-based approach, including the symmetric and asymmetric cases. We derive the tight worst-case latency bound in the case of symmetric duty cycle. We design a novel class of symmetric patterns called Diff-Codes, which is optimal when the Diff-Code can be extended from a perfect difference set. We further consider the asymmetric case and design ADiff-Codes. To evaluate (A)Diff-Codes, we conduct both simulations and testbed experiments. Both simulation and experiment results show that (A)Diff-Codes significantly outperform existing neighbor discovery protocols in both the median case and worst case. Specifically, in the symmetric case, the maximum worst-case improvement is up to 50%; in both symmetric and asymmetric cases, the median case gain is as high as 30%.

Prime Block Design for Asynchronous Wake-Up Schedules in Wireless Sensor Networks

Due do the various requirements of sensor applications, it is desired to design a neighbor discovery protocol that supports both the symmetric and asymmetric duty cycles. This letter proposes a new block-based neighbor discovery protocol for asymmetric sensor networks by adapting the theory of balanced incomplete block designs and the Chinese remainder theorem. Through the simulation study, it is demonstrated that the proposed block-based neighbor discovery protocol outperforms other neighbor discovery methods, such as Disco, U-Connect, SearchLight, Hedis, and Todis.

Asymmetrical Duty-Cycle and Phase-Shift Control of a Novel Multiport CLL Resonant Converter

In this paper, a novel multiport CLL resonant converter with a phase shift and asymmetrical duty-cycle control is analyzed. The power flow can be maintained with the phase shift between ports, whereas the asymmetric duty cycle manages the output voltage at the load terminals. Series connected transformers at the secondary side enable to split the power in each port and reduce the voltage stresses on the switches compared with the parallel connected transformers. Even under the unbalanced input conditions, the power flow between ports can be managed by the central control without any need for communication devices. In order to investigate the power distribution in each port, two different isolated dc sources and a variable load are used. The converter operation is tested at 40, 80, or 120 V inputs, with the output of 200 V at a full power of 1 kW with a maximum efficiency of 97.4%. The experimental results show that the multiport CLL resonant converter with the proposed controller is an appropriate topology for sustainable energy platforms, which are supplied by different types of energy sources, such as photovoltaic, fuel cell, wind, and so on, at various power capacities.

Three‐leg inverter configuration for simultaneous dual‐frequency induction hardening with independent control

Parts of certain objects need hardening. Hardening is a heat treatment process which can be achieved by induction heating. Certain objects like gears require alternating source with two different frequencies. Simultaneous application of dual frequencies is desirable for proper hardening of a gear. This study proposes a three-leg inverter topology with a load resonant circuit which can provide independent and simultaneous control of low-frequency (LF) and high-frequency (HF) currents through the load coil. The load circuit is a combination of two series resonant circuits which operates at the desired LF and HF. Power control is achieved with phase modulation and asymmetric duty cycle control techniques. A 240 W prototype of the proposed dual-frequency inverter is implemented and tested. Experimental results obtained are in good agreement with the simulation results.