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Multilevel voltage source inverters/converters (ML-VSIs) with an integrated voltage-boosting feature have been popular in recent years as an interface between the provided low-magnitude DC voltage and standard 220V rms grid voltage. The voltage-boosting feature is achieved with an integrated switched-capacitor (SC) or a switched-boost (SB) technique, while the circuit configuration of the resulting ML-VSIs can be based on a standard half-bridge-based design or a common-ground/midpoint-clamp-based structure. The critical challenges for SC-based ML-VSIs are the discontinuous nature of the input current, pulsating current stress over devices, and the static ratio of the voltage-conversion gain. These challenges require that researchers go through either a two-stage-based boost-integrated design with a front-end DC–DC boost converter or a single-stage SB-based ML-VSI with inherent dynamic voltage-conversion gain. This chapter investigates the state-of-the-art contributions of boost-integrated ML-VSIs and provides insights for overcoming critical challenges like excessive current stress and the inrush current problem. The chapter also outlines the relatively new concept of SB-based MLIs, while the working principles of several recently proposed structures are reviewed and compared.

Although switched-capacitor (SC) multilevel inverters (MLIs) offer self-voltage balancing of flying capacitors and voltage gain higher than unity, the advantages come at the cost of high current stress and power loss in the SC circuit and DC source. Moreover, the voltage balancing is often restricted to a limited range of modulation index. Another problem of MLIs with neutral-point clamped (NPC) front end is with DC-link capacitor voltage balancing under unbalanced load conditions, imploring sensor-based closed-loop control. This paper proposes a unity gain five-level active-NPC SC-MLI with inrush charging current attenuation and actively balanced DC-link capacitor voltages under all load conditions and over the entire range of modulation index and power factor. The modified pulse-width modulation results in most switches operating at a low switching frequency, minimizing switching losses in the SC circuit. The proposed MLI attains a maximum efficiency of 98.04% at an output power of 510 W. Experiments on a 2 kVA laboratory prototype validate the theoretical analysis. Results from transformerless grid-connected solar PV system show that the proposed MLI can inject power into the grid with a unity power factor under conditions of varying irradiance and provide the grid with reactive power as well.

Multilevel inverters (MLIs) with a common-ground (CG) circuit design and a switched-boost (SB) technique are of interest in transformerless grid-connected applications due to the enhanced overall efficiency, higher power density and reduced leakage current concern. Utilization of the SB technique in MLIs leads to obtaining a single-stage power conversion platform with a dynamic voltage boosting feature. Drawing a continuous input current and spike-free current stress of the devices are two additional features of SB-based MLIs. Regarding the current state-of-the-art contributions, an interleaved CGSB-based MLI is introduced in this work. The main benefits of the proposed topology are larger injected grid current handling capability with a reduced current stress, uniform peak voltage stress across the devices, bidirectional power flow operation, controllable power sharing, and generalization capability to realize any number of output voltage levels. Through a modular design with a phase-shifted PWM technique, the injected grid current is shared among the modules, while the size of the grid-interface filters is reduced, leading to establishing a practical design with enhanced overall efficiency. The working principle of the proposed converter is discussed in detail. Design guidance, comparative study and extensive closed-loop experimental results obtained from a 5.1 kW grid-tied laboratory-built prototype are then given to validate the feasibility and performance of the proposed solution.

Multilevel inverters with common-ground feature have been getting attention especially for grid-tied photovoltaic systems. These inverters have the grid neutral line connected to the negative pole of the dc bus, eliminating the common-mode leakage current which is a critical issue in grid-connected PV systems. This paper proposes a common-ground five-level transformerless inverter with a reduced switch count for solar photovoltaic applications. The proposed inverter comprises only four power switches, three diodes, two capacitors and two inductors. Moreover, only two switches operate at high-frequency, enabling the reduction of switching losses. The interleaved operation of a coupled inductor enhances the quality of the output current, as the first group of harmonic components is around twice the switching frequency. Additionally, a full dc- bus voltage utilization is provided and the reactive power capability is achieved. The paper details the operation modes, the design guidelines as well as a control and modulation strategy for the proper operation of the inverter. Finally, experimental results are obtained to validate the performance of the proposed grid-tied inverter.

Boost multilevel inverters (MLIs) with front-end switched-capacitor (SC) modules are popular in applications like solar system and electric vehicles. This work proposes a three-phase SC boost MLI (TSCBI) employing single-input. The SCs are employed in parallel charging and series discharging path to create a two-fold boosted output. The SC voltage is self-balanced and maintained at half of the input voltage magnitude, which assist in synthesizing a nine-level line voltage output. Multi-carrier pulse-width modulation technique is further developed that used to control the switches. Benefits of the proposed TSCBI are justified in comparison to other SC MLIs. Including detailed operation analysis and power loss calculation, the suggested topology is validated through MATLAB/Simulink simulations under dynamic test conditions and through real-time using a laboratory-scale experimental setup.

This paper presents a new six-level switched-capacitor multilevel inverter, which can generate six output voltage levels with 2.5 times voltage gain from a single dc source. The design is motivated by the need for an overall compact and efficient inverter with a smaller line filter without an additional boost converter and line transformer. The capacitor voltages remain balanced as the constant dc input voltage source directly charges them. The suppression of inrush capacitor charging current using charging inductors and voltage boosting capability make this inverter a significant contender for a transformerless grid-connected photovoltaic system. The closed-loop dq current control and dc-link voltage control have been discussed theoretically to control the active power fed to the grid and voltage across the dc-link capacitors. The hardware implementation demonstrates lower harmonics and reactive power handling capability. The simulation and experimental results are analyzed and presented for the grid-connected mode of operation. The maximum measured efficiency is 95.79% at 448.8 W of output power. The ability of multiphase expansion from a single dc source and 2.5 times voltage gain makes the proposed MLI suitable for interfacing distributed energy generation systems with the electrical grid.

This chapter presents an overview of control and modulation techniques for Z-source converters (ZSCs) used for electric power conversion. ZSCs are categorized into four main categories: DC/DC converters, DC/AC inverters, AC/AC converters, and AC/DC rectifiers. ZSCs are further classified into voltage-fed or current-fed, and non–transformer based or transformer coupled-inductor based. Modulation techniques for traditional three-phase H-bridge topologies (two-level) are classified as sine pulse width modulation and space vector modulation, with several modifications available in the literature. Modulation techniques for three-phase multilevel topologies, matrix topologies, and DC/DC converters with an intermediate H-bridge are also discussed. The impact of modulation strategies on the reliability and harmonics of impedance-source inverters is analyzed. The control strategy of ZSCs is also discussed, with various closed-loop control methods presented in the literature. The chapter concludes that proper modulation and control techniques are necessary to achieve the maximal voltage boost and minimal harmonic distortion, lower semiconductor stress, and minimal number of devices commutation per switching cycle in ZSCs.

This article proposes a novel three-port converter with a fault-tolerant (FT) capability to reconfigure automatically under different switching fault conditions, i.e., open circuit fault (OCF) and short circuit fault (SCF) of the power transistors, and to continue achieving different control objectives such as effective battery charging, maximum power point tracking (MPPT), and output voltage regulation. The proposed fault-tolerant design with a one-level redundancy structure enhances the reliability of traditional three-port converters (TPCs). Experimental results of a laboratory prototype has proven the effectiveness of the proposed converter.

Impedance-source networks have gained attention as promising power conversion stages owing to their flexible step-up/down conversion ratios and high reliability with shoot-through protection. However, there are still limitations that hinder their further applications in renewable energy systems. This chapter provides an overview of Z-source converters, a type of impedance-source converter, and their classifications. It discusses the limitations of traditional voltage source inverters and current source inverters, leading to the emergence of Z-source converters. The features, operation principle, and classification of various topologies are then discussed, including DC/DC converters, DC/AC inverters, two-level H-bridge topologies, multilevel/neutral point clamped AC/AC converters, and AC/DC converter topologies. The chapter highlights the need to design and optimize impedance source networks and presents an example of a quasi-Z-source inverter design. Finally, the chapter discusses possible future directions and applications of Z-source converters.

The new four port quadratic DC DC boost converter with high gain FPQBC has the advantages of continuous input current at both inputs and high output voltage gain due to its quadratic nature with low component count The proposed converter has a wide range of operation modes i e Dual input Dual output DIDO and Dual input Single output DISO All of these converter operating modes are analyzed under steady state conditions to understand the working of the proposed converter Numerous simulations were carried out in the simulator to verify the advantages as mentioned earlier of the proposed converter To verify the simulation results the hardware prototype experimentation is under investigation

Single-inductor single-input dual-output (SI-SIDO) dc–dc converters with a higher power density and fewer components are attractive for various applications such as renewable energies, portable chargers, PFC, HVdc, LED lightening, and electric vehicles (EVs). However, the voltage balancing of the output capacitors is a big challenge and always limits the application of these converters. In this regard, an enhanced SI-SIDO three-level dc–dc converter with a high voltage gain, inherited common ground condition, and voltage balancing capability is proposed in this article. A time-multiplexed control scheme is designed for the proposed converter to charge two output capacitors independently and provide different voltage levels for different requirements. Hence, the proposed converter can provide balanced or nonbalanced output voltages for various applications, maintaining constant output voltages even under unbalanced loads. Furthermore, it can be designed to support bidirectional operation. Because of the voltage balancing feature, the proposed converter can provide the dc-link voltage balancing for different applications, such as the bipolar low-voltage dc distribution system and the neutral-point-clamped inverter. The performance of the proposed topology is verified by the PLECS simulation program and experimentally in an 800-W prototype.

A novel modular four port dc dc converter FPC is proposed in this paper which is capable of integrating the photo voltaic PV voltage balancing and charging of multiple batteries using a single inductor in a modular converter structure for the battery management system BMS The proposed topology is competent to work under single input single output SISO dual input single output DISO and single input dual output SIDO modes based on the PV battery and load availability These operating modes are analyzed under various conditions of the sources PV and battery and load and the steady state analysis is performed for the proposed FPC to obtain the output voltage expressions Finally the simulation results are presented using the LTspice simulator under various operating modes to verify the working of the proposed modular FPC

Bidirectional dc-dc converter (BDC) is an integral part of energy storage interface, where high efficiency, high voltage transfer ratio and small input ripple current are essential for application, such as dc microgrid and electric vehicle. In this article, a new approach is proposed to achieve reduced input ripple current at the low voltage side, which potentially replaces the necessity of using interleaved circuit structure. Parallel coupled inductor and capacitor circuit are utilized for charging and discharging the two parallel paths in a complementary fashion using a mosfet. The proposed solution helps to increase the voltage conversion ratio unlike interleaved structure. Additionally, in proposed BDC, zero voltage switching turn on operation of all active switches are possible utilizing synchronous rectification principle in both the operating modes. Parallel path structure not only reduce the input current ripple, but also helps to share the input current, thereby reducing the coil size and associated losses. A 250 W BDC is designed to validate performance in 1kW dc microgrid system

Multilevel inverters (MLIs) featuring reactive power ability and common ground (CG) have become much popular in transformerless grid-tied photovoltaic applications. A switched-capacitor (SC) based five-level transformerless inverter configuration is thus proposed in this article, which requires only six switches, one diode, three capacitors, and one input dc voltage supply. Notably, only four power switches are operated in high frequency, thus, the switching losses are reduced. Moreover, the presented topology can effectively tackle the leakage current problem using a CG architecture. A multicarrier phase disposition pulsewidth modulation strategy is employed to achieve reactive power regulation and SC voltage self-balancing. To achieve the neutral point voltage balance of the presented five-level inverter, a simple closed-loop voltage-balancing control method is proposed. The operation principles with modulation strategy and voltage self-balancing of SC are discussed in depth. Comparisons between the proposed and the state-of-the-art MLIs are presented in detail. Finally, experimental tests on a single-phase 1.1-kW prototype validate the appropriate performance of the proposed inverter.

This article introduces a new nonisolated soft-switching coupled-inductor (CI) step-up dc/dc converter. The presented topology utilizes a three-winding CI (TWCI) along with a voltage multiplier circuit to increase the voltage conversion ratio without needing a high duty cycle. Using this circuit, a high voltage gain can be achieved without requiring a large number of turns ratio in the CI. The input current ripple of the introduced converter is very low, which is very desirable for renewable energy sources applications. The TWCI also creates an additional design freedom to increase the voltage gain, which indicates more circuit flexibility. Additionally, the voltage stress across the single power switch is limited with the help of a regenerative clamp capacitor. The leakage inductor of the CI is used to create a resonant tank to reduce power losses further. The leakage inductances help provide the zero-current switching conditions for the single power switch and decrease the reverse-recovery issues for all diodes, leading to an efficiency improvement. The operation principle, steady-state analysis, and design considerations are discussed thoroughly. Finally, the theoretical analysis is validated through experimental results obtained from a 200 W prototype with 250 V output voltage.

This paper proposes a dual input single output DISO step up dc dc converter exhibiting high voltage gain for grid connected applications The main advantage of the proposed concept is the common ground between input and output ports with a continuous input current profile at both input ports The operating principle and steady state analysis are presented in detail The voltage gain expressions for both inputs are obtained using equivalent circuit analysis The voltage and current stresses of all components and the design equations for L C elements are derived Preliminary simulation results are presented using the LTspice simulator to demonstrate the key operational characteristics of the proposed DISO step up converter Finally the converter operation and analytical studies are verified through sample experimental results captured using a prototype converter

Distributed generation systems integrated into the modern electrical grid demand novel circuit architectures that can combine high efficiency and high power density together. The transformerless highly efficient and reliable inverter concept (HERIC) topologies are notable due to their mitigated leakage current concerns, constant common-mode voltage, and high efficiency. Nonetheless, the HERIC-based structures feature a maximum of three-level ac output voltage, forcing the conversion system to integrate large output filters to meet the grid codes. This article introduces a novel HERIC active-clamped converter with bidirectional power flow and full reactive power capabilities that can achieve five-level output voltage. This is accomplished by means of a phase-shifted pulsewidth modulation technique that effectively doubles the apparent switching frequency of the inverter and improves the quality of the injected ac power. Consequently, the topology can achieve higher power conversion efficiency, while using the same or a smaller output filter. To verify the feasibility of the proposed converter, a 2.5-kW SiC-based prototype was built and tested in the laboratory under different operation conditions.

Grid-connected inverters with a multilevel output voltage and an integrated dynamic voltage boosting feature are promising to achieve higher overall efficiency/power density, reduced output filter size, and better power quality. However, the input current of such a single-stage system might be pulsating with low- and high-frequency ripple contents in a single-phase grid-connected application. To tackle this challenge, active power decoupling (APD) can be used to keep the input current flat and reduce the current stress of the devices with an efficient performance. On the other hand, the grid voltage is usually nonideal in practice, polluted with the harmonics. This causes additional complexity in the closed-loop control system to maintain the injected power quality. The aim of this article is to apply a tailored closed-loop APD control on a recently proposed single-source single-stage switched-boost (SB) five-level converter leading to further enhancing its overall efficiency without adding any extra circuit components. A distinctive feature of the proposed solution is using a single proportional-resonant controller with a filtered feedforward term to achieve APD, even under a distorted grid voltage condition. This solution can also be applied to other single-stage SB-based converters as long as their input current before integration of the APD control contains a low-frequency ripple content. A 2-kW SiC-based prototype is built to validate the feasibility and accurate performance of the proposed method via experiments when connected to a grid with harmonic pollution.

This paper proposes two single-phase boost inverters that are capable of mitigating the high-frequency common-mode voltage (CMV). The conventional two-stage topology that consists of a frontend boost converter and a backend H-bridge inverter is restructured. While retaining the advantages of the conventional topology such as continuous input current and dynamic voltage gain, the proposed 3-level boost inverter achieves constant CMV without requiring any additional components. An extended 5-level boost inverter is also proposed by integrating another capacitor controlled by 4 switches to the 3-level topology. For the same inductor charging duty-cycle and inverter modulation index, the voltage gain of the proposed 5-level boost inverter is double compared to the 3-level counterpart. The operation of the proposed 3-level and 5-level boost inverters is comprehensively analyzed and verified by simulation results.

Electromagnetic Compatibility (EMC) has gained an evident importance with the evolution and optimization of power electronics and power systems. With the ease of access to a variety of power converters to be used in our daily life, the EMC standardization is a growing concern. This study compares and evaluates the conducted Electromagnetic Interference (EMI) performance of some off-the-shelf power supplies using pre-compliance EMC testing facility. Furthermore, the results are verified with a calibrated EMC facility and evaluated under AS/NZS 61000.6.3. Various insights are highlighted which are important to consider whilst moving towards the realization of EMC in power electronics.

The latest single-stage boost inverter has many advantages such as continuous input or dc source current, high-frequency common-mode voltage mitigation and generation of three-level boosted ac voltage. However, it requires a dedicated circuit design, which cannot be implemented using commercial power modules such as half-bridge. To resolve this drawback, this letter proposes an improved topology designed using three half-bridges. While retaining the advantages of the latest boost inverter, the proposed topology reduces the number of conducting switches for load current during positive voltage level that enhances efficiency. The proposed three-level boost inverter can be extended to generate five levels by merely adding a half-bridge and a capacitor. The derivation of the proposed single-stage boost inverters and their operation are analyzed. Simulation and experimental results are presented for verification.

Grid-connected AC/DC power converters play a crucial role in integrating renewable energies, smart grids, and motor drives. Consequently, high-performance control techniques have constantly attracted the interest of researchers. Predictive direct power control (P-DPC) strategies are promising control techniques for these converters, due to their fast transient response. However, standard P-DPC strategies cannot effectively compensate for steady-state errors when the switching frequency is reduced, due to model inaccuracies. This work proposes a new optimal switching sequence direct power control (OSS-DPC) strategy, which enhances the converter discrete-time model by estimating the grid currents and voltages at each commutation instant within a sampling period. As a result, the proposed OSS-DPC provides a fast dynamic response with reduced overshoot and improved steady-state performance, outperforming the standard P-DPC strategies.

This paper proposes two novel 5-level active neutral-point-clamped (ANPC) inverters that double the voltage gain of the conventional topology from half to unity. Each phase of the proposed topologies is constituted by three half-bridges that control a flying capacitor to generate 5 symmetrical ac voltage levels. The natural voltage balancing of dc-link and flying capacitors in the proposed topologies implies that the sensors and voltage balancing controller commonly used in the conventional ANPC inverter are no longer necessary. In addition to switch count reduction, the most noteworthy merit of the proposed topology is its ease of implementation with commercial half-bridge modules, where the design of dedicated circuit is not needed. The operation of the proposed 5-level unity-gain ANPC (5L-UG-ANPC) inverters is analyzed and validated through simulation and experimental tests.

This article proposes a new Zero-Voltage Switching (ZVS) high step-up DC/DC converter based on a built-in transformer for renewable energy applications. The proposed topology utilizes a Three-Winding Built-In Transformer (TWBT) to increase the voltage gain, but unlike most coupled-inductor-based DC-DC converters, high output voltages can be obtained under a lower magnetic turns ratio. In this circuit, with the help of a regenerative active clamp circuit, the energy of the leakage inductor from the TWBT is absorbed and transferred to the output, therefore, the ZVS conditions at turn-on time are achieved for switches. The voltage stresses across the switches of the proposed topology are limited, and the diodes reverse-recovery issue are eliminated. Due to the low input current ripple, the suggested topology can be used for renewable energy sources. Furthermore, because of the low number of components along with the soft-switching operation, the proposed circuit can offer enough high efficiency. The operational principle, steady-state analysis, and characteristics of the proposed converter are provided. Finally, a 200 W prototype with 25 V input and 400 V output voltage is built to validate the analytical results.

Active neutral point-clamped (ANPC) multilevel converters with integrated flying-capacitor (FC) technique are widely used in many industrial applications owing to their low losses, reduced stress on devices, bidirectional operation, and leakage current attenuation capability. Their major setback related to the half dc-link voltage utilization at the ac output has also recently been addressed using the concept of active boost neutral point-clamped (ABNPC) converters with a switched-capacitor (SC) technique. Nonetheless, such a voltage-boosting capability in ABNPCs causes an excessive voltage stress on devices, when the provided dc-link voltage is larger than double of the grid peak voltage. To address this critical challenge, the concept of dual-mode (DM) converter that can retain the quality of ac output with a reduced voltage stress on devices over a wide range of the input dc voltage is introduced. Following this concept, a family of three DM-ANPC five-level (5L) converters is presented in this article, where they can be operated in either buck or boost mode. This allows to operate the converters with a wide range of input dc voltage utilization and an improved performance. Each of the proposed DM-ANPC-5L converters requires 10 power switches, while they offer a bidirectional power flow feature with an integrated FC and/or SC technique. Extensive analysis, comparative study, and several simulation and experimental results obtained from a laboratory-built prototype operating in the grid-connected condition are presented to validate the performance of the proposed converters.

The conventional active neutral-point-clamped (ANPC) multilevel inverters are popular for single-phase applications owing to their advantage of mitigating high-frequency common-mode voltage (CMV). With the ac neutral connected to the midpoint of dc link, their voltage gain is restricted to only half. For boosting output voltage, a two-stage structure by adding a frontend dc-dc boost converter is commonly used. This article investigates the performance of the conventional two-stage 5-level ANPC inverter and proposes an improved topology by splitting the dc-link midpoint and cross clamping them to the dc-link capacitors. While using the same number of power devices and retaining the advantages of the conventional two-stage 5-level ANPC topology, such as high-frequency CMV mitigation and continuous dc source current, the proposed 5-level split-midpoint cross-clamped (5L-SMCC) inverter achieves several advantages, such as higher voltage gain, lower voltage across dc-link capacitors, lower inverter voltage stress, and natural voltage balancing for all capacitors without requiring any balancing controller or sensor. In addition, it saves one capacitor by eliminating the flying capacitor of the conventional 5-level ANPC inverter. The operation of the proposed 5L-SMCC inverter is thoroughly analyzed. For validation, simulation and experimental results are presented.

This article proposes a new single switch trans-inverse high step-up converter applicable in sustainable sources of energies such as photovoltaic (PV) and fuel cell (FC). Through developing a single-ended primary-inductor converter by a three-winding built-in transformer (BIT) mixed with a switched-capacitor voltage multiplier cell, high voltage gains as well as low voltage stress across the mosfet can be achieved to reduce the required duty cycle and the conduction losses. The third winding of the BIT acts in a trans-inverse manner whose turns ratio should be lower than unity. Hence, with a lower number of windings the voltage gain can also be improved. Furthermore, the quasi-resonance operation of the proposed converter, reduces the associated switching losses of the mosfet and also guarantees zero current switching of diodes through the whole switching cycle. Meanwhile, low input current of the proposed converter serves as an interesting feature to maintain PV and FC lifetime. The detailed steady-state analysis of the proposed high-efficiency converter is presented with an extensive performance comparison to explore its advantages. Finally, a 200-W prototype with 20-250-V voltage conversion is developed in the laboratory to examine the carried steady-state analysis.

This paper proposes a novel three-port converter using a single-shared inductor for output voltage regulation and a single-shared inductor for battery management. The converter is capable to not only perform MPPT but it can also perform battery charging for multiple storage units and control the amount of current going into each storage unit individually. The detailed circuit configuration is provided in this paper, and the concept was verified using simulation results in LTSpice Simulator. The final prototype is in progress; full experimental results included in the final paper.

In this brief, comparison of coupled inductors with two and three windings is presented. For this, an implementation of two simple hybrid topologies was carried out, which will be presented with their principle of operation, and performance analysis, e.g., comparison of voltage and current stress. A design guideline is presented to reduce the effect of leakage inductance and winding resistance. Five prototypes each with 250 W, were built in the laboratory to verify the performance of the converters for different values of duty cycle (D) and turns ratio (N).

Transformerless grid-connected inverters with highly efficient and reliable inverter concept (HERIC) and positive-negative neutral point-clamped (PN-NPC) circuit configurations exhibit excellent performance in terms of overall efficiency, common-mode voltage, and alleviated leakage current concern. These inverters are designed to generate only a three-level (3L) output voltage waveform, thereby reducing the power density of a conversion system. On the other hand, it is well-known that increasing the inverter output voltage levels entails the reduction of the output filter size. In this regard, this article aims to develop a five-level (5L) inverter output voltage for the improved versions of HERIC-clamped and original PN-NPC inverters. This is achieved with either phase-shifted or level-shifted pulse width modulation technique leading to further quality improvement of ac voltage and current waveforms through increasing the number of output voltage levels. Therefore, a much smaller output filter size can be utilized, while the overall efficiency of the entire system is enhanced. Two laboratory-built SiC-based prototypes for both the proposed HERIC-clamped (1.8 kW) and PN-NPC-5L (2 kW) inverters have been fabricated to show the feasibility and effectiveness of the proposed solution via experiments.

Integration of supercapacitor alongwith battery in electric vehicles (EVs) improves the life cycle of the battery. Additionally, supercapacitor supplies or absorbs a large amount of instantaneous power during sudden demand such as acceleration or regenerative braking operation, hence also improve the dynamics of the internal power system. However, a major challenge with supercapacitor is that its terminal voltage is low and varies in a wide range during charging and discharging operation. Thus, a high voltage conversion ratio based bidirectional DC-DC converters are required to connect the lower supercapacitor voltage to higher DC-link voltage. The steep voltage conversion ratio with continuous gain based bidirectional DC-DC converters are an integral part of such applications. Various high gain converters exist in the literature such as isolated, non-isolated, cascaded, switched, flying capacitor, and coupled inductor based DC-DC converters, however all these converters have some limitations in context to high gain/high power applications. Therefore, to understand the development of next-generation high voltage gain bidirectional DC-DC converter, this paper focus to comprehensively review and classify various bidirectional step-up DC-DC converters based on their characteristics and voltage-boosting techniques. Further, practical suitability of the reviewed converters and future research directions in switched capacitor converters in context to EVs are also discussed in detail.

In this article, we present a family of multilevel converters with the single-stage dynamic voltage-boosting feature, reduced number of circuit components, modular structure, bidirectional operation, continuous input current, and acceptable overall efficiency. The proposed structure is based on a three-level single-stage boost integrated inverter with an embedded quasi-H-bridge (QHB) cell. It is comprised of five unidirectional power switches and a floating capacitor. By differential connection of two or three QHB cells and with the aim of a single inductor/input dc source, several derived topologies for both the single and three-phase applications with different multilevel output voltage performances have been achieved. The aforementioned advantages make this converter a suitable candidate for renewable energy applications. Theoretical analysis, design consideration, comparative study, and several experimental results for a 3-kW laboratory-built system are presented to validate the effectiveness and feasibility of this proposal.

Zero-sequence injection (ZSI) techniques are widely adopted in Wye- and Delta-connected cascaded H-bridge (CHB) three-phase systems to cope with the unbalanced power generation from each phase. Recent studies have shown that a ZSI can allow a $\triangle-$connected CHB converter to cope with a large range of power imbalances among phases when compared to a standard Y-connected CHB converter. The superiority in the electrical performance under unbalanced input power has been well investigated, however the comparative thermal performance for both configurations under same power imbalance condition has not been investigated. In this work, the thermal performance of a CHB converter connected in both $\triangle-$configuration and Yconfiguration operating under an unbalanced power condition is studied. For this, the enquired ZSI for both $\triangle-$ and Y-connected CHB converters is firstly analyzed. Then, the impact of ZSI on the thermal performance and lifetime expectancy of the power switches in each phase is evaluated and compared for both configurations. The thermal analysis carried out in this work shows that even though a $\triangle-$connected CHB converter offer a wider power imbalance operation than Y-connected counterpart from the electrical viewpoint, this is achieved by thermally stressing the power switches in each phase in an uneven manner, and in some case overstressing them. Consequently, there is a trade-off between electrical performance and thermal stress when dealing with power imbalances in $\triangle$-connected and Y-connected CHB converters.

Multilevel inverters (MLIs) with switched-capacitor (SC) units have been a widely rehearsed research topic in power electronics since the last decade. Inductorless/transformerless operation with voltage-boosting feature and inherent capacitor self-voltage balancing performance with a reduced electromagnetic interference make the SC-MLI an attractive converter over the other available counterparts for various applications. There have been many developed SC-MLI structures recently put forward, where different basic switching techniques are used to generate multiple (discrete) output voltage levels. In general, the priority of the topological development is motivated by the number of output voltage levels, overall voltage gain, and full dc-link voltage utilization, while reducing the component counts and stress on devices for better efficiency and power density. To facilitate the direction of future research in SC-MLIs, this article presents a comprehensive review, critical analysis, and categorization of the existing topologies. Common fundamental units are generalized and summarized with their merits and demerits. Ultimately, major challenges and research directions are outlined leading to the future technology roadmap for more practical applications.

Multilevel inverter demonstrates advantages over conventional topologies to meet the grid codes and standards. Compared to 3-level inverters, multilevel inverter exhibits significantly better harmonic performance, better efficiency, lower filter size, and less dv/dt and di/dt in the switches. In this regard, a modified HERIC-based topology with a 5-level modulation technique is derived from the conventional 3-level passive midpoint clamped HERIC-based topology and introduced in this paper. A circuit description and working principles of the proposed converter with simulation results, and experimental results are given to demonstrate the feasibility of the concept.

This paper shows how to exploit the degree of freedom represented by the common-mode voltage, which is inherent in three-phase Cascaded H-Bridge (CHB) converters, to minimize the total Root Mean Square (RMS) current value of the distributed dc sources. An optimal common-mode voltage injection law is derived, constituting a Maximum Power Per Ampere (MPPA) modulation strategy with respect to the currents of the dc sources. The potential benefits introduced by the proposed algorithm are analyzed in the context of battery-fed CHB converters and validated experimentally with a three-time-constant Randles model of a battery cell. The MPPA strategy is compared with traditional common-mode voltage injection methods, and battery loss reduction is demonstrated. The obtained battery energy saving is dependent on the converter modulation index and power factor. Experimental tests on a 36-cell full-bridge CHB converter validates the simulation and numerical derivation. To demonstrate the efficacy of the proposed method in practical applications, a 3 MW Energy Storage System (ESS) and a 110 kW Battery Electric Vehicle (BEV) undergoing standard drive cycles are presented as case studies. Compared to traditional modulation strategies, the MPPA strategy reduces the battery losses by up to 10.9% in the ESS and 27.5% in the BEV application.

Voltage source multilevel inverters with reduced leakage current, single-stage voltage step-up feature, compact design, and an efficient performance are a promising technology for high-frequency ac (HFac) microgrids feeding through renewable energy sources. This article proposes a novel single-source common-grounded (CG) step-up nine-level (9L) inverter, which can be applied in HFac microgrid applications. The proposed CG-based boost inverter is comprised of only nine switches (9S) and three self-balanced capacitors. Using the switched-capacitor (SC) technique, a double voltage boosting feature within a single power processing stage is achieved, while the leakage current concern is eliminated due to a CG-based configuration between the input dc source and the null of the grid. With the help of an LC input filter, the input current profile is free from large discontinuous inrush spikes. The working principles of the proposed 9L9S-CGSC inverter are discussed in this article. The modulation and closed-loop control strategy, as well as a comparative study, are presented. Finally, the open and closed-loop grid-tied performances of the proposed topology are evaluated by both simulation and experimental results obtained from a 1.2-kW laboratory-built prototype.

The circuit performance of conventional active neutral point-clamped (ANPC) inverter is widely accepted in many renewable energy-based applications like photovoltaic (PV) or electric vehicle grid-connected systems. This is mainly because of its excellent characteristics in terms of voltage/current stress profile of the switches, bidirectional power flow capability, and efficient operation. Nonetheless, due to its half-dc link voltage utilization in the ac output voltage, another power processing stage with additional active and passive elements is required to make its output voltage compatible with the grid when low and wide varying input dc source is available. In this paper, a novel ANPC-based five-level (ANPC5L) inverter with a single-stage boost-integrated circuit design is presented. The proposed topology is able to make the peak output voltage of the conventional ANPC5L inverter followed by a front-end bidirectional boost converter double using the same number of power switches but with less total standing voltage across semiconductors. The working principles of the proposed topology is discussed. Experimental results obtained from 1.3 kW laboratory-built prototype under the grid-connected condition are also given to support the discussion.

This paper presents a common-ground five-level transformerless inverter for solar photovoltaic (PV) applications. In the proposed inverter, the grid neutral line is directly connected to the negative pole of the dc bus eliminating the common-mode leakage current which is a critical problem in grid-connected PV systems. Moreover, the proposed inverter has only four power switches, making the first five-level common-ground topology with less than six switches found in the recent literature. In addition to low switch count, only two switches are operating in high-frequency. The operation modes, the design guidelines as well as a modulation strategy are presented. Simulation and experimental results are obtained to demonstrate the performance of the proposed inverter.