Discontinuous Input Current Research Articles

An MV Hybrid Isolated DC Transformer for Wide Output Voltage Range Applications

DC transformer (DCT) is the key energy conversion equipment that converts medium voltage dc to low voltage dc. Aiming at the industrial loads requiring wide output voltage range and unidirectional power flow, a hybrid isolated DC transformer (HIT) as an alternative to the traditional MMC-DCT is proposed in this paper. It is composed by thyristors, diodes, and submodule (SM) based arms. The operation principle, circuit performance, and control strategy are introduced in detail. Particularly, a discontinuous input and continuous output currents (DICO) operation mode is further proposed to suppress submodule capacitor voltage ripple. Compared with the traditional MMC-DCT, HIT can save 50% SMs, 28% semiconductor cost and 46.3% total SM capacitance. The effectiveness and the theoretical analysis have been confirmed by both simulation and experimental results.

Dual‐input single‐output high step‐up DC–DC converter for renewable energy applications

AbstractThis paper introduces a dual‐input single‐output (DISO) non‐isolated DC–DC converter with the capability to accommodate multiple input ports. It supports both bidirectional and unidirectional power flows. The proposed converter employs the switched‐capacitors (SC) technique, resulting in a high‐ voltage transfer gain. Although the use of the SC technique leads to discontinuous input current, this issue has been addressed by incorporating an inductor at the input side. The DISO high‐voltage gain converter offers flexible control options, reduces current and voltage stress on semiconductors, and imposes no duty cycle limitations due to the proposed switching methods. Furthermore, when Port 2 fails, the proposed converter can transfer energy to the load by sources in Port 1 without interruption. The steady‐state model and small‐signal analysis (SSA) of the proposed converter are examined at continuous conduction mode (CCM). To evaluate accurately, the proposed converter is compared with the recently presented converters based on important characteristics. Additionally, a comprehensive power loss analysis is performed. Following the design specifications, an evaluation and testing of a prototype are conducted to verify the feasibility and performance of the converter.

Low-Voltage Photovoltaic System Based on a Continuous Input/Output Current Converter

Low-voltage photovoltaic systems are being widely used around the world, including their introduction into the power grid. The development of these systems requires the adaptation of several power converters, their static and dynamic modeling, the design of passive elements, and the design of the controller parameters, among other actions. Today, power converters are key elements in the development of photovoltaic systems, and classical power converters such as buck converters produce discontinuous input and output currents, requiring a high input capacitance and impacting the output power quality of these systems. This paper presents a proposal for a low-voltage photovoltaic system that uses a continuous input/output current buck converter, which enhances the operation of the classical buck converter in photovoltaic systems. The methodology describes the proposed photovoltaic system, including the power converter, its detailed operation, and the analysis of its waveforms. Moreover, the methodology includes a mathematical model of the photovoltaic system’s dynamic behavior and the design of a sliding-mode controller for maximum power extraction and perturbation rejection. The photovoltaic system is validated in two ways: first, a comparison with the classical buck converter highlighting the advantages of continuous input/output currents is presented; then, an application example using commercial devices is described in detail. The application example uses a flowchart to design the power converter and the sliding-mode controller, and a circuit simulation confirms the advantages of the continuous input/output current buck converter with its controller. In the circuit simulation, the control strategy is formed by a perturb and observe algorithm that generates the voltage reference for the sliding-mode controller, which guarantees the system stability, tracks the maximum power point, and rejects the double-frequency oscillations generated by an intended microinverter.

A family of switched-impedance network enhanced-boost quasi-Z-source inverters

This paper proposes a family of novel enhanced-boost quasi-Z-source inverters (EB-qZSIs). For the similar input voltage and shoot-through duty ratio, similar to that of enhanced-boost Z-source inverter/enhanced-boost qZSIs, the presented topologies provide very high voltage boost at high modulation index with improved quality output waveform. Compared to EB-ZSI and EB-qZSIs, these topologies provide less capacitors stress, which reduce the volume and cost of the system. Akin to traditional EB-qZSIs, the presented novel impedance networks share joint ground with the source and inverter bridge, also reduces the initial inrush current. Among the four types of proposed configurations, the type-1 of discontinuous input current (DIC) EB-qZSIs offers fewer stress athwart the capacitors and little inrush current at start-up condition. Consequently, type-1 is considered and illustrated for the examination, simulation, and hardware execution. The steady-state operation and derivation of boost factor, peak direct current-link (DC-link) voltage and capacitor voltages are derived for both continuous conduction mode (CCM) and discontinuous conduction modes (DCM). The Z-network elements design, and evaluation with other Z-networks are also carried out. Lastly, the hypothetical investigation is confirmed with simulation and experimental tests.

Non-Isolated Interleaved Hybrid Boost Converter for Renewable Energy Applications

DC-DC boost converters are necessary to extract power from solar panels. The output voltage from these panels is far lower than the utility voltage levels. One of the main functions of the boost converter is to provide a considerable step-up gain to interface the panel to the utility lines. There are several techniques used to boost the low panel voltage. Some of the issues faced by these topologies are a high duty ratio operation, complex design with multiple active switches and discontinuous input current that affects the power drawn from the panel. This paper presents a boost converter topology that combines the advantages of an interleaved structure, a voltage lift capacitor and a passive voltage multiplier network. A mathematical analysis of the proposed converter during its various modes of operation is presented. A 100 W prototype of the proposed converter is designed and tested. The prototype is controlled by a PIC16F18455 microcontroller. The converter is capable of achieving a gain of 10 without operating at extremely high duty ratios. The voltage stress of the switch is far lower than the maximum output voltage.

Modeling and Control of Single-Stage Quadratic-Boost Split Source Inverters

This paper aims to develop the recently introduced Spilt-Source Inverter (SSI) topology to improve its boosting characteristics. New SSI topologies with high voltage gain are introduced in this paper. The proposed converters square the basic SSI’s boosting factor by utilizing an additional inductor, capacitor, and two diodes. Thus, the proposed converters are called Quadratic-Boost (or Square-Boost) SSIs (QBIs or SBIs). Four different QBI topologies are presented. One with continuous input current (CC-QBI), and the other draws a discontinuous input current (DC-QBI) but with reduced capacitor voltage stresses. This paper also introduces the small-signal model of the CC-QBI using state variables perturbance. Based on this model, the closed-loop voltage and current control approach of the dc-boosting factor are designed. Moreover, a modified space vector modulation (MSVM) scheme is presented to reduce the input current ripples. To evaluate the performance of the proposed topologies, a comparative study between them and the other counterpart from different perspectives is introduced. It can be found that the CC-QBI topology has superior boosting characteristics when operating with low input voltage compared with their counterparts. It has a higher boosting capability, lower capacitor voltages, and semiconductor stresses, especially when high voltage gains are required. These merits make the proposed topologies convenient to the Photovoltaic and Fuel-Cell systems. Finally, the feasibility of the suggested topology and the introduced mathematical model is verified via simulation and experimental results, which show good accordance with the theoretical analysis.

Novel Interleaved High Gain Boost Converter Using Switched Capacitor

The increase in global energy demand has led to increased research in harvesting solar energy. Solar energy is widely used in homes, electric vehicles and is a great solution to power remote areas. DC–DC converters are essential in extracting power from solar panels. One of the main problems in designing converters for solar energy applications is boosting the low output voltage of the solar panel to meaningful levels. While there are several topologies to achieve high gain, some of the problems faced by them are the extreme duty ratio, complex design and discontinuous input current. This paper presents a novel topology that uses an interleaved input, a voltage lift capacitor and a hybrid switched capacitor network to achieve high gain without an extreme duty ratio or bulky magnetics. The proposed converter is controlled using a microcontroller which regulates the output voltage. The voltage lift capacitor and the switched capacitor network enhances the voltage gain over a conventional boost converter without an extreme duty ratio. The analysis and design of the proposed converter are presented and verified with a 100 W prototype. The results show that the converter provides a gain of 10, at a duty ratio of 30%, while delivering the designed output power with considerably high efficiency.

A non‐isolated quasi‐Z‐source‐based high‐gain DC–DC converter

AbstractTo overcome the problems associated with Z‐source‐based DC–DC converters, a quasi‐Z‐source (QZS)‐based high‐gain DC–DC boost converter with switched capacitors is proposed in this work. Z‐source‐based DC–DC converters have problems like low‐voltage gain, discontinuous input current, and high‐voltage stress on the active and passive components. The proposed converter can produce a high‐voltage gain of more than 10 times for a duty cycle of less than 0.5. The converter has other desirable features like reduced voltage stress across the switching components and continuous input current (CIC). It comprises a QZS cell made up of switched inductors and a voltage multiplier cell (VMC) made up of switched capacitors. The power loss analysis is done using PLECS software by incorporating the real parameters of switches and diodes from the datasheet. A hardware prototype of 200 W is developed in the laboratory to verify the working of the converter. In experimental results for an output power of 200 W, the converter is operated with a source voltage of 33 V at a duty ratio of 0.4 providing an output voltage of 395 V. The converter performance is good in open‐loop conditions and is verified through experimental results.

Z‐source inverter topologies with switched Z‐impedance networks: A review

The Z-source inverter is one of the most interesting power electronic converters. Over the past decades, research and development have been in high demand to meet the challenges for improving the converter performance with reduced weight and cost while having high efficiency along with high gain or boost factor. Since the inception, tons of resolutions, customizations, and improvements have appeared to achieve these performance goals. To overcome the most common drawback, i.e. the low boost factor of classical Z-source inverters, the switched inductor/capacitor and switched boost Z-source inverter topologies have become predominant in the recent epoch. Furthermore, the higher component voltage stress, discontinuous input current, and high inrush start-up current issues have also been addressed and solved in various literature as part of this topical advancement. In this study, a comprehensive review of various switched impedance network-based Z-source inverter topologies has been accomplished for providing a quick report to researchers and engineers so that they can consider this as a one-stop solution for selecting inverters from this group. The overall study covers the methodology, features, and relevant important results of the latest switched Z-source inverter models in order to demonstrate the coordination between pitfalls and improvements.

A New Hybrid Zeta-Boost Converter With Active Quad Switched Inductor for High Voltage Gain

For renewable sources application like smart grids, microgrids, etc. high voltage gain converter becomes a fundamental unit. In this article, a new hybrid circuit of zeta and boost converter based on active-quad-switched-inductor (AQSL) is proposed. The discontinuous input current in classical zeta circuit determines the less consumption of input source. However, the proposed hybrid zeta-boost converter provides a higher voltage gain with continuous input and output currents. It achieves higher voltage gain devoid of the high-frequency transformer, and multiple stages of diode and capacitor circuit. The mode of operation, boundary region, and non-ideal model of the proposed converter are presented. Design consideration and a comparison study with recent circuits are provided. The design circuitry of the proposed converter investigated and the functionality of the suggested circuit is validated.

A Non-Pulsating Input Current Step-Up DC/DC Converter With Common Ground Structure for Photovoltaic Applications

Many of the High Gain Step-Up DC/DC converters proposed in the literature do not share common ground and have a pulsating or discontinuous input current, making the converter unsuitable for solar photovoltaic applications. In this article, a non-pulsating input current (NPIC) with a high-gain DC/DC step-up converter is proposed and analyzed in detail. The converter shares a common ground structure and a voltage conversion ratio more than twice that of the Traditional quadratic boost converter (TQBC). The converter has two switches that operate in phase, which makes it easy to control. Also, the voltage stress across all semiconductor devices is lower than the output voltage, which enhances the efficiency of the converter. The loss analysis is carried out with the PLECS software, integrating the real models of switches and diodes from the technical datasheet. To confirm and validate the functionality of the proposed converter, a 200 W hardware prototype is being developed in the laboratory. It was observed that the maximum efficiency was 94.5% with an input voltage of 16V. The converter achieves high gain at low duty cycles and has been shown to perform well in open loop conditions.

A Family of Coupled Dual-Winding Impedance-Source Inverters With Continuous Input Currents and No DC-Link Voltage Spikes

Impedance-source inverters with coupled inductors can provide much higher voltage gains, but occasionally at the expense of discontinuous input currents and large voltage spikes at their dc-links. The former is caused by the absence of inductances at their inputs, while the latter is due to unintentional interruptions of leakage currents through their coupled inductors. These problems have now been solved here by a new family of dual-winding impedance-source inverters (DW-ISIs). Each DW-ISI can recycle the leakage energy from its two windings to a few clamping capacitors, which in turn help prevent the voltage spikes. This, together with the presence of an inductance for smoothing its input current, renders the family of DW-ISIs to be highly effective, while not compromising the voltage and current stresses when compared with other precedent inverters. In addition, to simplify the circuit analysis, a reactive component elimination method has been proposed in this article. Simulation and experimental results have confirmed the validity of the proposed topologies.

Input Filter-Based Ripple Injection for Mitigating Limit Cycling in Buck Converters Driving CPL

In a two-stage dc-dc intermediate bus architecture (IBA), an LC input filter with a series parasitic resistance is often used in an intermediate bus converter (IBC) because of its discontinuous input current, which is designed using Middlebrook's impedance criteria. Using the ripple voltage of the input filter capacitor, this article proposes a closed-loop pulsewidth modulation (PWM) control method in the IBC to mitigate limit-cycle oscillations (LCOs) in an IBA. This ripple voltage is shown to indirectly carry inductor current information of the IBC and offers a virtual damping in the closed-loop system. Small-signal models are derived, and stability conditions are established. A simple PI controller is shown to be sufficient to achieve tight output voltage regulation and fast transient response. The proposed technique is extended to a multiphase IBC to achieve equal current sharing among the phases. Hardware prototypes are developed, and the analytical claims are verified using experimental results.

An Improved PWM Technique to Achieve Continuous Input Current in Common-Ground Transformerless Boost Inverter

A latest common-ground transformerless inverter for photovoltaic (PV) system has demonstrated its superiority over its existing counterpart due to its merits of single-stage structure and voltage boost capability. The exploited modulation scheme, however, led to discontinuous input current that draws high peak current from the source and causes high input power fluctuation in the converter. Such discontinuous and high peak current are detrimental to the PV source. Addressing this concern, this brief proposes a new modulation technique that achieves continuous input current with reduced peak magnitude while in the meantime ensures a good quality ac output voltage. Simulation and experimental results of a laboratory prototype are provided to verify the effectiveness of the proposed modulation technique.

A Novel Parameter Tuning Method for a Double-Sided LCL Compensated WPT System With Better Comprehensive Performance

Wireless power transfer (WPT) has attracted a large amount of attention owing to its inherent advantages such as convenience, safety, low maintenance, being weather proof, etc. A parameter tuning method is crucial for a WPT system due to its function of reducing reactive power and improving system efficiency. Three deficiencies of the conventional double-sided inductor–capacitor–inductor (DS- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> ) compensated system, i.e., low design freedom, weak high-order harmonic suppression capability, and discontinuous input current of a full-wave diode rectifier (FDR), are first analyzed by means of theoretical derivation, numerical calculation, and Pspice simulation. In order to overcome these disadvantages, a novel parameter tuning method is proposed. The characteristic of constant current output of the proposed DS- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> system is analyzed, followed by a detailed derivation about secondary compensation inductance. Theoretical analysis indicates that the proposed system has four attractive characteristics: higher design freedom, reduced coil current, enhanced high-order harmonic suppression capability, and continuous input current of the FDR. The overall efficiencies of two comparative WPT prototypes, tuned by conventional and proposed methods, are 87.3% and 90.2%, respectively. Experimental results show great coincidence with theoretical analysis, demonstrating the superiority of the newly proposed parameter tuning method.

Circuit for clamping bridge overvoltages in voltage‐fed quasi‐ Z ‐source converter

Unlike the voltage source converter, the Z-source converter can boost as well as buck the input voltage. However, the presence of physically large components in the impedance network introduces large parasitic inductances into power device commutation paths. This leads to consequent overvoltages at power device turn-off. A simple circuit for addressing this is presented. Practical results are given for a voltage-fed quasi- Z-source inverter with discontinuous input current.

A single stage three-level full bridge resonant AC/DC converter

This article presents a new three-level full bridge resonant single stage AC/DC converter. The converter is operated with a variable frequency pulse width modulation controller (PWM). A PWM is used to provide the required input current shaping as well as regulating the DC-bus voltage, whereas variable frequency control is used to tightly regulate the output voltage. Zero voltage switching (ZVS) is achieved for all switches. The proposed topology can operate with either continuous or discontinuous input current while maintaining high power factor. Owing to ZVS operation, reduced component stresses and low circulating currents the proposed converter has high conversion efficiency making it suitable for higher power operations compared to existing single stage AC/DC topologies as well as operating with universal input voltage. Operation, analysis and performance of the converter will be presented in this article.