DC Voltage Source Research Articles

A new submodule‐based generalized multilevel inverter topology with reduced switches and DC sources

SummaryMultilevel inverters are known as essential converters in renewable sources. First, in this paper, a new submodule is presented, and based on it, a new sub‐multilevel inverter is presented. The proposed sub‐multilevel inverter consists of several unidirectional and bidirectional switches and DC voltage sources. Then, the generalized topology, developed in two modular and cascaded modes, is presented to increase production levels. The proposed submodules are connected in series in the modular topology, increasing production levels. The proposed topology to produce the maximum output levels has the minimum number of IGBTs, drivers, DC voltage sources, etc. Mathematical analyses for conduction and switching losses are provided, and mathematical analyses for the number of devices and voltage across the switches are also presented. In addition to the mathematical analysis of losses, the simulation results are also presented. A general comparison of proposed topology components is presented to demonstrate their advantages. This comparison shows that the proposed topology has the minimum number of power electronic devices. In this paper, nearest level modulation is used to control the proposed topology. The simulation and experimental results of the proposed sub‐multilevel verify the performance of the proposed topology.

Capacitor based topology of cross-square-switched T-type multi-level inverter

In this paper, a new topology is introduced for capacitor-based multi-level inverters. The proposed topology is based on combination of two Cross-Square-Switched T-Type inverters. This structure can be generalized in two modular and cascaded modes. In the cascaded mode, higher voltage levels are produced with low power switches. The main features of the proposed topology include the level generation without the utilization of the H-bridge module, the low number of switching components, a lower number of DC voltage sources, and low total blocking voltage. Besides, in the proposed topology, the number of conducting switches in the current path for each different voltage level is low, which leads to a conduction loss decrement. The loss simulations are performed, and the results are presented. A study provides a detailed comparison of the proposed topology in terms of various parameters. In this paper, the nearest level modulation switching, which is low-frequency switching, is utilized to generate voltage levels. To confirm the performance of the proposed topology, a simulation was performed with MATLAB/Simulink software, and a laboratory sample was implemented. Comparative results, simulation results, and implementation results indicate the appropriate performance of the proposed structure in different steady-state and dynamic conditions.

A Comprehensive Review of Compensation Control Techniques Suitable for Cascaded H-Bridge Multilevel Inverter Operation with Unequal DC Sources or Faulty Cells

A cascaded H-bridge multilevel converter topology is the ultimate solution for energy conversion in various industrial applications due to its exceptional features, such as high modularity and fault-tolerant capability. However, two circumstances can lead to unbalanced operation of the inverter, potentially causing a decrease in its reliability and survivability: unequal DC voltage sources and faulty cells. In recent decades, scientists and engineers have conducted intensive research and meaningful studies to propose control solutions capable of maintaining the stable and continuous operation of the inverter under these operational concerns. Typically, each challenge is addressed separately using a distinct compensation control scheme in the existing literature. The paper aims to offer a comprehensive review of the existing compensation control schemes appropriate for CHBMIs operating under unbalanced conditions. It overviews the most popular control schemes and summarizes their usefulness in such scenarios. The theoretical foundations of each control scheme are presented and discussed, including their operating principles, implementation schemes, advantages, and disadvantages. The paper concludes with suggested future trends that require further research for CHBMIs’ continued growth and adoption in various industrial applications.

A dual source fed eleven level switched capacitor multilevel inverter with voltage boosting capability

This work introduces an 11-level switched-capacitor multilevel inverter (SCMLI) designed for solar photo-voltaic (PV) applications, capitalizing on the growing popularity of multilevel inverters due to their superior power quality. With a 1.67-times boosting capability, the proposed SCMLI employs 10 switches, 2 DC supplies, and 2 capacitors to achieve an 11-level output voltage waveform. The topology requires only seven driver circuits, incorporating 2 bidirectional switches and 3 complementary pairs of switches. The proposed inverter has intrinsic capacitor self-balancing features since the capacitors are connected across the DC voltage source at different times throughout a basic cycle to charge the capacitors at a level of input voltage. A thorough comparison between the topology and recently developed SCMLI’s has been presented. The comparison demonstrates the effectiveness in terms of switches, capacitors, sources, efficiency, total standing voltage (TSV), and boosting capacity. To experimentally validate its performance, the suggested SCMLI undergoes testing using a frequency-based switching method. The topology exhibits low total harmonic distortion (THD) of 7.65% in its output voltage waveform and 0.89% in the output current waveform.

A Novel Limited Grid-Forming Strategy to Support Power System Stability under Primary Energy Source Limitations

The available literature on grid-forming converters often assumes an unlimited primary energy source, for example by postulating a constant DC voltage source. However, this assumption is not justified in real-world scenarios as soon as primary energy source limitations are reached. Therefore, it is imperative for grid-forming control strategies to take such limitations into account and ensure that they support robust system stability even under primary source limitations. In this work, a novel concept of limited grid-forming control is introduced that supports the stability of the network, even under primary energy source power as well as energy constraints. Moreover, the control concept also allows for a seamless transition between full grid-forming and limited grid-forming behavior without any control mode switching. The proposed scheme is tested on a modified IEEE 9-bus test system with one synchronous machine replaced by a droop-based grid-forming controlled battery system incorporating the proposed control scheme. The simulation of a couple of dynamic events provides results that demonstrate promising performance, thereby substantiating the feasibility of the proposed control scheme.

Multiresolution Models of DC Traction Power Supply Systems With Reversible Substations

Reversible substations (RSs) permitting bidirectional power flows can recover the regenerative braking energy of trains in DC traction power supply systems (TPSSs), increasing the energy efficiency of railway systems. To predict their effects on system dynamics and energy savings, the paper develops multiresolution models (MRMs) to simulate the RS roles with different fidelities. A high‐resolution model for the transient simulation replicates a particular topology where a three‐level voltage source inverter is connected to the secondary winding of an existing 12‐pulse rectifier transformer and regulated to keep a constant DC voltage in the inverting mode. Furthermore, it can model the transient effects of pantograph‐to‐line arcing by inserting arc voltage profiles at the train’s input stage. To increase the computation speed in the long‐term energy flow simulation, a low‐resolution model simplifies the rectifiers into a series connection of a diode and a controlled voltage source depicting their nonlinear output characteristics and then places a DC voltage source in parallel to form a reverse path for braking power recovery. In addition, nonlinear conversion efficiencies are introduced to calculate energy flows across substations. The MRMs are tested based on a 1.5 kV DC TPSS and discussed alongside system dynamics under normal operation or pantograph arcing and the consistencies between different models. The RS using bidirectional voltage source converters only is additionally modelled to compare the technical performance of the two topologies in terms of system dynamics and energy efficiencies.

Design and Implementation of Transformer-less Common-Ground Inverter With Reduced Components

Nowadays, common-ground-type (CGT) based transformer-less inverters (TIs) are gaining more popularity in photovoltaic (PV) applications owing to their low cost, weight of the systems, losses and zero ground leakage current. For PV applications, a separate boost converter is often used to boost the low PV array voltage, resulting in increased component count, cost and lower efficiency. To resolve this issue, switched-capacitor (SC) based CGT inverter with reduced component count is proposed in this paper. The proposed amalgamation of CGT and SC technique, results in inherent boosting and zero ground leakage current. In the proposed inverter, SCs are connected in series/parallel with the dc voltage source for several instances in a fundamental cycle preserving the self-voltage balancing ability. Therefore, the proposed topology is devoid of voltage sensors to balance the voltage across SCs. Further, A simplified logic gatebased pulse-width-modulation strategy is developed. In addition, the benefits of proposed inverter are highlighted and compared with the other recent SC inverter topologies with regard to boosted voltage, elimination of leakage current and reduced component count. A laboratory prototype is developed by using DS1202/1302 dSPACE controller and experimental results are presented for both steady state and dynamic conditions and verifying the feasibility of the proposed TI.

Implementation of the Fuzzy Logic Controlled 31‐Level Diode Switched Multilevel Inverter with Optimal Components for Solar PV‐Fed System

This work presents a novel architecture for the 31‐level asymmetrical DC voltage source configured diode switched multilevel inverter, which has a single phase and fewer components. Using asymmetric DC sources and an H‐bridge, the proposed topology generates a maximum output voltage of 31 levels. This 31‐level topology is suitable for both renewable energy source conversion (RES) and electric vehicle (EV) applications. This topology requires fewer total components, lower cost, and smaller size. Along with the numerous benefits of MLIs, reliability issues are critical due to the larger number of devices required to minimize THD. Several characteristics, such as total standing voltage (TSV), reliability, cost function (CF), efficiency, and overall power losses, are investigated for the developed 31‐level MLIs. The TSV and CF of the proposed MLI are critical factors in demonstrating that the proposed topology is cost‐effective when compared to other recent topologies. Many parameters are thoroughly compared and tabulated, as well as represented graphically. The suggested MLI has lower TSV and component demand. Total harmonic distortion complies with IEEE specifications. The reliability aspects were also calculated and validated. The proposed MLI is controlled by a fuzzy logis controller (FLC) to achieve efficient results. The topology is simulated in MATLAB/Simulink software under a variety of conditions and dynamic load changes, and a prototype with a dSPACE controller is also implemented.

Multi-material additive manufacturing through electrostatic metal powder attraction and laser-induced forward transfer

The possibility to produce multi-materials and functionally graded materials opens new opportunities within material development, not only to explore new possibilities for combinations of different materials, but also to develop entirely new materials. Materials that are customized for individual applications and purposes down to the level of a single product. Here a process is described, where applied voltage onto a machine element results in an electrostatic attraction of powder. The machine element has certain electrical abilities and is transparent to certain wavelengths of light. The powder attraction is relatively uncomplex using a high DC voltage source with low amperage. The attracted powder on the machine element is selectively transferred to the workpiece by using laser-induced forward transfer (LIFT). The final goal is to melt the transferred powder onto the workpiece with the laser from LIFT. This part of the process and its developments are discussed in detail. Thereby, the powder is selectively added to the workpiece surface, making it possible to apply a combination of different materials without contaminating the powder stock.

Soft start‐up control of four‐level hybrid‐clamped converters with DC voltage source

SummaryThe four‐level hybrid clamp converter (4L‐HCC) is one of the next‐generation multilevel topologies due to its simplified structure and excellent performance. However, it consists of several DC‐link and flying capacitors, which must be precharged to the rated voltage before the normal operation. Without proper control, those internal capacitors could easily induce inrush currents and cause system fatal failure due to the unsymmetrical circuit structure. This paper proposes soft start‐up control methods for both single‐phase and three‐phase HCCs. The precharging mathematical models of DC‐link and flying capacitors are established. A straightforward algorithm using the selected switching states and rotating regions is developed to build precharging circuits properly. A full‐scale simulation model and a downscale laboratory prototype of the 4L‐HCC are established to validate the superiority of the proposed method. Results demonstrate that the proposed approach is effective in charging all capacitors through internal elements rapidly with suppressed and controllable charging currents.

Active Power Allocation Strategy for a Novel Wireless Open-Winding Motor System With Improved Antimisalignment Capability

This paper proposes a wireless open-winding motor (WOWM) system, where noncontact operation can be achieved with the magnetic coupler. Thus, the flexibility and reliability of the WOWM system can be improved. Two isolated DC voltage ports for the open-winding motor can be obtained with only one DC voltage source, which facilitates the application of the system. The zero-sequence current in the motor winding can be suppressed and the DC link voltage utilization rate can be maximized owing to the isolated DC link structure. Besides, the operation characteristics of the WOWM system are analyzed in detail. The decoupled dual-receivers are designed, which ensures that the ratio of DC link voltages is load-independent. Moreover, the influences of misalignment on the WOWM system, including the overmodulation and increased phase current ripple are presented. The DC link voltage regulation (DVR) and active power allocation (APA) strategy are further proposed. The DC link voltage reference is identified based on the operating state of the motor for high performance operation. The allocation coefficient, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> is adjusted according to the extent of misalignment, which improves the anti-misalignment capability. The feasibility of the WOWM system and the effectiveness of the DVR and APA strategy are verified by experiments.

A novel generalized multi input boosting multi-level inverter (MIB-MLI) for high-frequency AC (HFAC) power distribution

The simplified topology for the high-frequency ac (HFAC) power distribution method with a multi-level inverter (MLI) hybrid switched capacitor (SC) is introduced. Capacitors, switches, diodes, and DC sources are among the components that are reduced in the designed MIB-MLI (Multi Input Boosting Multi-level Inverter). Where asymmetric dc voltage sources are available, such as in renewable energy farm-based ac microgrids and current electric vehicle, this architecture is advantageous. The proposed inverter has the feature of self-balancing the capacitor voltages and voltage boosting by using the series-parallel conversion scheme. The quality of output power is increased when a dc source array is connected with the unidirectional switched converter. Moreover, if a major phase variation betwixt the output current along with the voltage is no more mandatory, multiple alive switches may be recouped with diodes. In the switched capacitor group ripple volatge is reciprocal to the output frequency, so the MIB-MLI is favorable for HFAC implementations. Also, this paper clarifies the operating theory of the complete network and switching condition covered by the sinusoidal pulse width modulation (SPWM) technique. Mathematical equation related to power loss and capacitor voltages are provided. The modeling and simulation results of the proposed seventeen-level (17-L) inverter are depicted in this paper. The findings have shown that the proposed inverter is superior at HFAC along with the power efficiency of the inverter is adequate with SPWM technique.

Dynamic multi‐agent dc‐bus reconfiguration in modular motor drives with a stacked polyphase bridge converter

AbstractA stacked polyphase bridge converter consists of multiple standard, three‐phase two‐level voltage source inverters connected in series to the same dc voltage source. The authors present a decentralised and dynamic dc‐bus reconfiguration strategy for this type of converter. The innovation of the proposed strategy lies in its ability to isolate or reactivate one of the inverters in the series connection online, even in motoring mode, enabling increased fault tolerance and an extended speed range. Both the required hardware alterations and the multi‐agent control strategy are addressed. Its major benefits compared to the state‐of‐the‐art are that only two additional active, unidirectional semiconductor switches are required per inverter, and that the control is based on local computations, local measurements and neighbour‐to‐neighbour communication only. Hence, the scalability and reliability of the hardware are extended towards the control. Simulations and experimental results on a 4 kW modular axial‐flux PMSM prove the feasibility of the concept, and validate that the dc‐bus can be reconfigured in 100 ms, without torque interruption.

Switched capacitor based 7-level and 9-level multilevel inverters with single DC source and reduced voltage stress

This paper proposes two different switched capacitor based Multilevel Inverter topologies having single dc voltage source. One of the proposed MLIs is a seven-level structure whereas the other circuit successfully generates a nine-level output voltage. The special features of the seven-level topology consist of reduced number of circuit elements, lower voltage stress on switches, and boosted output voltage. The nine-level MLI having unity gain also possess the reduced switch count along with lower value of switch voltage stress. Fundamental frequency based Nearest Level Control modulation and Level-Shifted Pulse Width Modulation have been used for generating the required voltage levels. Successful implementation of the proposed MLI circuits has been done with the help of a laboratory prototype and its results are presented and explained in the paper to show its practical suitability. Other type of analysis include loss analysis which has been done in PLECS software. From this analysis, the efficiency has been estimated. A comparative analysis of both the proposed structures has been carried out with some other similar topologies on different performance parameters. From the analysis and comparison, it is evident that the proposed MLIs are better than some of the existing topologies and can be used for industrial applications.

Comparative analysis of NR and DE methods for multilevel inverters: An experimental case study

This paper presents an experimental performance comparison between differential evolution (DE) algorithm and Newton Raphson (NR) method for solving the optimal switching problem for multilevel inverters with the objective of improving the output AC voltage quality. The methods are used to compute optimal switching angles to control a multilevel inverter in such way that allows the elimination of low order harmonics; this control technique is called selective harmonic elimination. The proposed inverter in this article is composed of two H-bridge cells with non-equal DC voltage sources in order to generate seven voltage levels. The differential evolution (DE) optimization and the Newton Raphson (NR) algorithm is used to solve non-linear transcendental equations necessary for the (SHPWM). Computational results obtained from computer simulations presented a good agreement with the theoretical predictions. A laboratory prototype based on STM32F407 microcontroller was built in order to validate the simulation results.

THD Reduction of Improved Single Source MLI Using Upgraded Black Widow Optimization Algorithm

An upgraded Black Widow Optimization algorithm for obtaining the ideal switching angles of a reduced structure multilevel inverter is proposed in this paper with minimum voltage THD. The conventional BWO algorithm has been modified and proposed to solve the THD minimization problem with faster convergence rate, lesser tuning variables, and lesser number of equations than the other existing nature inspired algorithms. The reduced structure MLI is designed with three asymmetrical DC voltage sources of ratio 1 : 2 : 4 to generate 15-level output voltage which requires reduced number of switching devices in comparison with the existing topologies of equivalent voltage level. The asymmetrical DC voltage sources to the MLI are derived from a single DC voltage source using a multisecondary winding DC-DC converter in order to provide the isolation between the load side and source side. The proposed modified BWO algorithm reduces the complexity of solving the nonlinear equations to achieve the best result by avoiding the local optima. To verify the effectiveness of the upgraded BWO algorithm, the optimization problem for three phase fifteen level MLI has been solved using the genetic algorithm, BFO algorithm, and PSO algorithm. The results for the above three applied algorithms are compared with the upgraded BWO and presented. The proposed algorithm has minimized the output voltage THD to 1.83% at 0.88 modulation index. The developed scheme has been corroborated with the help of MATLAB simulation and the results have been verified through a hardware model developed in laboratory.

High power T-type-based multi-level inverter for electric vehicles

This paper presents an extension of a 5-level T-Type inverter to a high-power multi-level inverter that can be implemented in electric vehicles and trucks. The proposed inverter possesses several advantages over standard topologies such as Neutral Point Clamped, Flying Capacitor, and Cascaded H-bridge. The main advantages are a low number of components, an estimated lower price and weight, smaller dimensions, and the implementation of only one DC voltage source per phase. The proposed topology can be implemented for any required odd number of voltage levels. Due to the estimated reduced dimensions and weight, the proposed topology is especially suitable for electric transportation applications. The operation of the proposed topology was validated for 9- and 13-level configurations under PD, POD, and APOD PWMs. The simulation results show the inverter’s practicability for supplying motors of electric trucks.

DC Voltage Source Based on a Battery of Supercapacitors with a Regulator in the Form of an Isolated Boost LCC Resonant Converter

Studies have been conducted on Energy storage systems (ESS) that replaced lithium-ion batteries (LIB) by the thermal runaway of the existing LIB. Using only the supercapacitor (SC) as a direct current power source in applications such as supercapacitor-based ESSs and mobile electric vehicle charging stations (MCSs) reduces the output voltage of the SC linearly. To solve this problem, this paper combines a boost converter capable of achieving regulatable constant voltage from an input of an SC bank to an output of a rectifier and an inductor/capacitor/capacitor (LCC) resonance converter. In this paper, an electrical double-layer capacitor (EDLC) known as SC was constructed as 64.8-V 400-FEDLC for experimental analysis. This EDLC is a high-capacity EDLC bank using 120 EDLCs with 30 serial connections and 4 parallel connections. In addition, resonance compensation circuits are analyzed and designed using a first-order harmonic approximation method (FHA). The analysis shows that the LCC resonance compensation converter is more suitable for EDLC standalone systems as an energy storage system, for LCC resonance converter topologies combined with EDLC discharge characteristics, constant voltage discharge is designed under an efficient discharge strategy, i.e., variable load conditions after the first constant voltage discharge. Based on LCC compensation analysis, the system has an optimum frequency, which allows the system to operate at the maximum efficiency point. By combining constant voltage power characteristics, constant voltage power becomes the same as the optimal power point, and thus high efficiency could be maintained in the constant voltage stage. Finally, the above design is verified through experiments.

Agar-based optical sensors for electric current measurements

Biodegradable optical waveguides are breakthrough technologies to light delivery and sensing in biomedical and environmental applications. Agar emerges as an edible, soft, low-cost, and renewable alternative to traditional biopolymers, presenting remarkable optical and mechanical characteristics. Previous works introduced agar-made optical fibers for chemical measurements based on their inherent response to humidity and surrounding concentration. Therefore, we propose, for the first time, an all-optical, biodegradable electric current sensor. As flowing charges heat the agar matrix and modulate its refractive index, we connect the optical device to a DC voltage source using pin headers and excite the agar sample with coherent light to project spatiotemporally deviating speckle fields. Experiments proceeded with spheres and no-core fibers comprising 2 wt% agar/water. Once the increasing current stimulates the speckles’ motion, we acquire such images with a camera and evaluate their correlation coefficients, yielding exponential decay-like functions whose time constants provide the input amperage. Furthermore, the light granules follow the polarization of the applied voltage drop, providing visual information about the current direction. The results indicate a maximum resolution of sim 0.4 upmu A for electrical stimuli le 100 upmu A, which fulfills the requirements for bioelectrical signal assessment.

A Family of Single-Phase Single-Stage Boost Inverters

H-bridge inverter is a common topology used for single-phase applications. Due to its limited voltage gain, a two-stage power conversion with a front-end dc-dc converter is usually adopted to accommodate the low dc source voltage. Recently, single-stage boost inverters are gaining significant interest due to their higher power efficiency and compactness. This paper presents a family of boost inverters with continuous dc source current. By the incorporation of merely a power switch and a boost inductor to the first leg of H-bridge, voltage-boosting and 3-level generation can be simultaneously achieved within a single-stage operation. All potential topologies using the same number of components are derived. An extension to generate five voltage levels with voltage gain enhancement is also proposed. The operation of the proposed boost inverters is thoroughly analyzed. Simulation and experimental results are presented for verification.