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This paper investigates and technically demonstrates a capacitive power transfer (CPT) system applicable to the charging of emerging very‐low‐power portable devices. The constant‐current operation of the primary LCL compensation in CPT is implemented and analysed to simplify the system design process and minimize the configuration on the receiving side. Additionally, the system design considerations for the capacitive coupler and the diode rectifier are presented based on the battery charging specifications. All the design concepts and considerations are validated through experimentation with a 13.56 MHz CPT system, which achieves load‐independent constant‐current output from full‐load to light‐load (one‐tenth of the full load) charging operations. [ABSTRACT FROM AUTHOR]

In this paper, a new step‐up/down DC–DC converter based on switched capacitors (SCs) is proposed. This converter can provide highly variable voltage gain and merits like decreased voltage stress on power switches and capacitors. Besides, due to its modular configuration obtained by utilizing switched‐capacitor cells, it can generate high voltage gain in low‐duty cycles. In addition, the proposed converter has a continuous input current. The theoretical analysis of the proposed converter has been done, and its operating modes have been investigated. In addition, the proposed structure has been compared with some existing converters to highlight the advantages and disadvantages. Finally, to confirm the claims and theoretical results, a laboratory sample of the converter for 200 W has been implemented, with an efficiency of 91.34%. [ABSTRACT FROM AUTHOR]

This paper proposes a novel active power decoupling circuit (APDC) based on modified Buck converter to reduce the DC‐link voltage ripple of small capacitor motor drive systems. The APDC is placed between the Boost PFC circuit and the DC‐link, and has two energy flow paths, and the sum of the power decoupling capacitor and the DC‐link capacitor voltage equals to the output voltage of the Boost converter. With these configurations, the voltage of the decoupling capacitor can be precisely controlled to be the same as the AC component of the output voltage of the Boost converter, thereby effectively reducing the DC‐link voltage ripple. Another unique feature of the proposed APDC is that the inductor works in discontinuous current mode and only work for half of the time, which not only reduces the current stress of power switches, but also further improves the efficiency of the proposed APDC. Then, an instantaneous voltage control method is investigated to reduce the DC‐link voltage drop, which significantly improve the dynamic performance of the motor. The design guideline of key components is given in detail. The feasibility of the small capacitor motor drive system based on the proposed APDC is verified by experimental results. [ABSTRACT FROM AUTHOR]

Solid state transformer (SST) is designed as a power transmission device between AC grids and DC grids. However, the power fluctuation causes unbalanced power sharing among dual active bridge (DAB) converters and large voltage fluctuations on dc buses. Here, an adaptive virtual impedance control (AVIC) strategy is proposed to improve the balance performance of SST. Adaptive virtual impedance controller gets the same dynamic response for DAB converters, which matches dynamic impedance of DAB converters. Thereby the power balance can be achieved even the load changes. Meanwhile, an adaptive feedforward control scheme is proposed to reduce the influence of load fluctuation on DC bus voltage. The adaptive feedforward scheme also considers the parameter mismatch, thereby the balance of SST will not be destroyed. Moreover, the balanced power sharing achieved by adaptive controller eliminates the difference between actual transmission power and compensation power in each rectifier, which further suppresses the intermediate capacitor voltage fluctuations. Finally, simulation and StarSim experimental results verified the correctness and effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

The switched‐capacitor DC‐DC converters have been widely applied to convert energy from low voltage to DC bus for the power generation systems with fuel cells, photovoltaic array, and so on. However, the large capacitance is generally selected to eliminate the high current spike of switched‐capacitors in the hard‐switching switched‐capacitor (SC) DC‐DC converters, which will lead to the large volume and weight of capacitors and of converters. To solve this problem, a non‐resonant soft‐switching (NRSS) technique with linear current on switching cycle time‐scale for switched‐capacitor DC‐DC converters is first proposed in this paper, which achieves zero‐current‐switching (ZCS) turn‐on of switches and ZCS turn‐off of diodes with linear current on switching cycle time‐scale. In detail, the NRSS technique is proposed based on the idea that the current of an auxiliary inductor on switching cycle time‐scale is considered as the linear parts for the resonant current of the auxiliary inductor on resonant cycle time‐scale. The proposed NRSS technique is utilized into SC DC‐DC converter and the current spikes of switches can be reduced to two third by using the same capacitance compared with the hard‐switching SC DC‐DC converters and be reduced to a third compared with the resonant soft‐switching SC DC‐DC converters. Further, nine new soft‐switching SC DC‐DC converters, with single switch and double switches, are built based on the proposed non‐resonant soft‐switching technique. Finally, the non‐resonant soft‐switching technique is verified theoretically and experimentally by three of the nine proposed SC DC‐DC converters. This paper provides a new way to realize soft‐switching during the non‐resonant interval on switching cycle time‐scale and a new method to significantly reduce the required capacitance in SC DC‐DC converters. [ABSTRACT FROM AUTHOR]

Single‐stage switched boost inverter (SBI) with buck‐boost capability finds wide applications in renewable energy systems (RES). This paper aims at a comprehensive topological review of various single stage SBI circuits. The boosting techniques of SBI include switched inductor, switched capacitor, and transformer assisted switches. Each SBI derived structure has its own merits and demerits depending on the applications. The performance evaluation of SBIs, based on various perspectives like boost factor, voltage stress across active devices, passive elements count, DC link voltage, switching losses, voltage gain, and efficiency, are also discussed. A suitable modulation strategy is used to obtain the desired boosted and inverted ac output voltage in one stage SBI. Different modulation strategies adopted for SBIs are also included at the end of the topological review. This topological review's contribution enlightens the researchers in selecting appropriate SBI with effective modulation strategies suitable for renewable energy applications. Besides, the benefits and shortcomings of these converters are discussed in detail. [ABSTRACT FROM AUTHOR]

A high step‐up DC–DC converter which is applied to a voltage lift capacitor and coupled inductors to increase the voltage gain is proposed in this study. Moreover, the interleaved structure is applied in the converter to decrease the input ripple current. Besides, the voltage stress across the main and auxiliary switches is low. Furthermore, all switches and diodes have the soft‐switching condition by using an active clamp auxiliary cell. Consequently, the proposed converter has a high efficiency which is ideal for photovoltaic applications. Energy stored in the coupled inductors is transferred to the voltage lift capacitors and then transmitted to the output. Therefore, no voltage spikes caused by leakage inductors are created on the main switches. The converter operates in continuous current mode and its control remains in pulse width modulation. A 210 W laboratory prototype of the converter with 40 V input voltage and 420 V output voltage under 100 kHz switching frequency is constructed and experimental results confirm the theoretical analysis. Low voltage stress, low input ripple current and high efficiency (96.5%) show the superiority in the operation of the proposed converter in comparison with other similar structures. [ABSTRACT FROM AUTHOR]

The offline Switched Mode Power Supply (SMPS) draw non‐sinusoidal line current from the utility power supply, thereby introducing unwanted harmonics and also generate significant electromagnetic interference (EMI). Power factor correction (PFC) converters can be used to improve the power factor. But they also generate EMI in both Differential Mode (DM) and Common Mode (CM). In this paper, the EMI generated by the flyback PFC converter is addressed. A lumped circuit model for CM conducted EMI generated in a flyback converter, including the HF transformer's parasitics and the components, is considered. The parasitics of the HF transformer are calculated and measured experimentally. Using them, the resonant frequencies of the flyback converter are calculated for validation. A technique for determining the required balancing capacitor to mitigate CM conducted EMI is presented. A novel technique by splitting this balancing capacitor with their mid‐point grounded for further reduction of this EMI is presented. This technique can eliminate the Cy capacitors of the EMI line filter connected between line/neutral to the ground. Hence for the same amount of CM conducted EMI mitigation, the size and the cost of EMI line filters are reduced. Theoretical analysis, simulation results, and experimental verifications are presented. [ABSTRACT FROM AUTHOR]

In this work, the authors are considering the problem of compensation of harmonic current absorbed by a non‐linear load from a three‐phase grid voltage. The objective is twofold: the first is to reduce cost and control complexity by avoiding proportional–integral regulators and optimising measurement instrumentation while ensuring inverter capacitor voltage self‐balance and the second is to provide a robust control strategy against power grid problems. Without measuring current and capacitor voltages, the proposed control strategy generates accurate control signals able to ensure flying capacitor inverter self‐balance and full compensation of harmonics whatever the grid voltage problem. In this regard, the robustness of the proposed control against power grid problem such as sag, swell, grid voltage unbalance, and frequency variation have been tested while proving its efficiency to compensate for harmonic currents and ensuring capacitor voltage natural balance even in transient regimes. During balanced and unbalanced loads, the proposed method has exhibited an excellent transient response, represented by capacitor voltages tracking to their reference in the presence of large variation in the load. Finally, effectiveness of the proposed control strategy is verified by numerical simulations as well as realistic experiments, and its merits are showed in comparison with other methods. [ABSTRACT FROM AUTHOR]

This study proposes a new simple and fast space‐vector modulation scheme with the capability of balancing capacitor voltages in neutral‐point‐clamped converters. In the first step, transformations from the commonly used reference frames to the 60°‐frame are discussed. Next, a new method is presented to generate an appropriate switching sequence based on the voltage of the clamp point and direction of the phase currents. The proposed method is computationally efficient and its algorithm only needs knowledge of the load current directions, leading to further simplification of the hardware. This method can easily be generalised to control diode‐clamped multilevel inverters with an arbitrary number of levels. The feasibility, effectiveness, and performance of the method are investigated through simulation and experimental studies under various load conditions. [ABSTRACT FROM AUTHOR]

In this paper, a novel non‐isolated Single‐Switch Quadratic Boost Coupled‐Inductor (SSQBCI) DC/DC converter with continuous input current and low voltage stress on the switching component is presented. The suggested structure is based on the traditional quadratic boost converter. In this new topology, to achieve an ultra‐high voltage gain without large duty cycle, a Coupled‐Inductor (CI) along with a Voltage Multiplier (VM) are employed. The magnetic energy stored in the leakage inductor of the CI is recycled by a regenerative passive clamp capacitor that is connected with the switch in parallel, which helps to limit the maximum voltage across the switch. Therefore, to reduce the switch conduction loss and improve the efficiency, a switch with the low static drain‐to‐source ON‐resistance can be used. Moreover, the low voltage stress on the output side diode alleviates the reverse recovery loss. The steady‐state operating principle, comparisons with other related topologies and also design considerations in Continuous Conduction Mode (CCM) will be analyzed in detail. Finally, the performance of the proposed SSQBCI is verified by experimental results using a prototype with 30V input and 200V ‐ 160 W output operation at a constant switching frequency 50 kHz. [ABSTRACT FROM AUTHOR]

In this study, a new high step‐up non‐isolated three‐port DC–DC converter is proposed. A bidirectional buck–boost converter is used to interface photovoltaic battery and non‐isolated load port. Compared to the other three‐port converters, the presented topology has fewer component counts, which is the main merit of the proposed converter. The output voltage of the converter can be increased by using a three winding coupled inductor, a diode and a capacitor. Furthermore, since both main switches are turned on with zero voltage switching, switching losses is reduced and the efficiency of the converter is improved. Maximum power point tracking and maintaining the output voltage at a suitable level during the charging and discharging of the battery can be achieved by a simple controller. Moreover, according to the load power demand, three power flow paths will occur. The operation principle will be described in detail for three modes. Finally, the experiments with 400 W, 100 W, 40 V/400 V are implemented to verify the effectiveness of the converter. [ABSTRACT FROM AUTHOR]

This study introduces a boost multilevel inverter (MLI) based on a switched capacitor structure. The proposed inverter features high modularity as a result of which more levels and ratings of voltage can be obtained in the inverter AC terminals. The extension of this topology in both symmetric and asymmetric configurations are introduced and analysed. Taking advantage of the switched‐capacitor technique, only one DC source is utilised while the voltages of several capacitors are kept balanced without the adoption of any sophisticated balancing algorithm. A combination of two basic submodules named as boost switched capacitor submodule and dual switched capacitor submodule forms the proposed structure. Compared to the existing alternatives, the proposed one provides more voltage levels with a lower number of power switches and input DC sources. The performance of the presented MLI is verified through the MATLAB/Simulink environment. Finally, the experimental results are presented, validating the feasibility and effectiveness of the studied inverter. [ABSTRACT FROM AUTHOR]

Transformerless systems play an important role in many applications, such as photovoltaic generation systems and motor drives, since they present reduced size and high efficiency. On the other hand, the flying‐capacitor split‐source inverter (FC‐SSI) merges the boost and the inverter stage in a single power conversion system. It is important to point out that conventional modulation strategies applied to the FC‐SSI can result in unacceptable common‐mode voltage (CMV) which is one of the main causes of leakage currents. To overcome this problem, this paper proposes a virtual space vector modulation technique for FC‐SSI. The proposed modulation strategy manipulates the switching vectors in order to result in constant CMV enabling the transformerless operation. Simulation and experimental results, as well as a comparative analysis with existing modulation techniques, are provided to show the good features of the proposed modulation strategy. [ABSTRACT FROM AUTHOR]

In this study, a new zero‐voltage switching (ZVS) output inductor‐less bidirectional forward (OILBF) converter is presented. The OILBF has two diodes less than the conventional forward converter and is convenient for low‐power bidirectional applications. Moreover, the OILBF converter uses the leakage inductance of transformer as the forward inductor. In the proposed OILBF, two capacitors paralleled with main switches realise ZVS conditions for main switches in both directions without any auxiliary switches. Also, the reset of the converter transformer is done without any additional circuit. The proposed converter structure due to employing simultaneously OILBF topology with the simple auxiliary soft‐switching circuit is simple and low cost. The ZVS soft‐switching range is from light load to full load which enhances the converter efficiency. Phase shift is applied with the proposed converter. The proposed converter is completely analysed and its design approach is considered. Finally, an experimental prototype is implemented to verify theoretical results. [ABSTRACT FROM AUTHOR]

In this study, a seventeen‐level diode‐assisted hybrid multilevel inverter (DAH‐MLI) is proposed. The DAH‐MLI eliminates any external voltage balancing and/or sensing circuit by inherently balancing the capacitors using a series–parallel combination of capacitors and DC voltage source. The DAH‐MLI uses only one DC source and a reduced number of active and passive elements to generate a multilevel staircase output voltage. The proposed circuit can also be extended to obtain the higher number of voltage levels than seventeen by the addition of a single module comprising of two diodes, one switch, and one capacitor. The proposed DAH‐MLI can boost the input voltage and possesses reverse current carrying capability. The proposed DAH‐MLI is compared with several existing topologies on the basis of the number of active and passive components, total standing voltage, and peak inverse voltage to verify its advantages. A cost function is used in this study to compare the proposed DAH‐MLI and other existing typologies. Finally, the performance of the proposed DAH‐MLI is validated through a 570 W experimental prototype. [ABSTRACT FROM AUTHOR]

This study introduces a boost multilevel inverter (MLI) based on a switched capacitor structure. The proposed inverter features high modularity as a result of which more levels and ratings of voltage can be obtained in the inverter AC terminals. The extension of this topology in both symmetric and asymmetric configurations are introduced and analysed. Taking advantage of the switched-capacitor technique, only one DC source is utilised while the voltages of several capacitors are kept balanced without the adoption of any sophisticated balancing algorithm. A combination of two basic submodules named as boost switched capacitor submodule and dual switched capacitor submodule forms the proposed structure. Compared to the existing alternatives, the proposed one provides more voltage levels with a lower number of power switches and input DC sources. The performance of the presented MLI is verified through the MATLAB/Simulink environment. Finally, the experimental results are presented, validating the feasibility and effectiveness of the studied inverter. [ABSTRACT FROM AUTHOR]

In this study, a seventeen-level diode-assisted hybrid multilevel inverter (DAH-MLI) is proposed. The DAH-MLI eliminates any external voltage balancing and/or sensing circuit by inherently balancing the capacitors using a series–parallel combination of capacitors and DC voltage source. The DAH-MLI uses only one DC source and a reduced number of active and passive elements to generate a multilevel staircase output voltage. The proposed circuit can also be extended to obtain the higher number of voltage levels than seventeen by the addition of a single module comprising of two diodes, one switch, and one capacitor. The proposed DAH-MLI can boost the input voltage and possesses reverse current carrying capability. The proposed DAH-MLI is compared with several existing topologies on the basis of the number of active and passive components, total standing voltage, and peak inverse voltage to verify its advantages. A cost function is used in this study to compare the proposed DAH-MLI and other existing typologies. Finally, the performance of the proposed DAH-MLI is validated through a 570 W experimental prototype. [ABSTRACT FROM AUTHOR]

Transformerless systems play an important role in many applications, such as photovoltaic generation systems and motor drives, since they present reduced size and high efficiency. On the other hand, the flying-capacitor split-source inverter (FC-SSI) merges the boost and the inverter stage in a single power conversion system. It is important to point out that conventional modulation strategies applied to the FC-SSI can result in unacceptable common-mode voltage (CMV) which is one of the main causes of leakage currents. To overcome this problem, this paper proposes a virtual space vector modulation technique for FC-SSI. The proposed modulation strategy manipulates the switching vectors in order to result in constant CMV enabling the transformerless operation. Simulation and experimental results, as well as a comparative analysis with existing modulation techniques, are provided to show the good features of the proposed modulation strategy. [ABSTRACT FROM AUTHOR]

In this study, a new zero-voltage switching (ZVS) output inductor-less bidirectional forward (OILBF) converter is presented. The OILBF has two diodes less than the conventional forward converter and is convenient for low-power bidirectional applications. Moreover, the OILBF converter uses the leakage inductance of transformer as the forward inductor. In the proposed OILBF, two capacitors paralleled with main switches realise ZVS conditions for main switches in both directions without any auxiliary switches. Also, the reset of the converter transformer is done without any additional circuit. The proposed converter structure due to employing simultaneously OILBF topology with the simple auxiliary soft-switching circuit is simple and low cost. The ZVS soft-switching range is from light load to full load which enhances the converter efficiency. Phase shift is applied with the proposed converter. The proposed converter is completely analysed and its design approach is considered. Finally, an experimental prototype is implemented to verify theoretical results. [ABSTRACT FROM AUTHOR]

In this study, a new topology of grid‐connected four‐level inverter is introduced. The proposed structure, based on intermediate supercapacitors energy storage, is introduced to ensure two operation modes: to provide power to a microgrid from renewable energy sources and to regulate its voltage during short‐term power disturbances. The main idea is to replace ordinary capacitors of a four‐level flying capacitor (FC) inverter by supercapacitors and operate them under variable voltage conditions. The control strategy applies linear matrix inequalities approach as well as space vector modulation technique to generate the appropriate switching states. The latter part of this study is dedicated to the redundant state selection method for supercapacitors voltages balancing. Through experimental implementation, presented results highlight the efficiency of the proposed hybrid inverter in ensuring microgrid stability. [ABSTRACT FROM AUTHOR]

This study presents a STATic synchronous COMpensator (STATCOM) based on hybrid cascaded H‐bridge and full‐bridge neutral point clamped (HC‐FNPC) inverter. The advantages of HC‐FNPC over symmetric and asymmetric cascaded H‐bridge (HB) in STATCOM application are verified in terms of number of power components and voltage balancing capability. A control strategy is proposed to achieve control aims, i.e. reactive current compensation and balancing the voltages of capacitors. HC‐FNPC‐based STATCOM consists of two types of cells, i.e. full‐bridge neutral point clamped (FNPC) and HB cells with one and two capacitors in their DC side, respectively. A hierarchical balancing scheme is proposed to regulate the voltage of capacitors in mixed cells. In the first control layer, the voltage vector of cells is adjusted so that the active power is uniformly distributed among the cells. In the second control layer, the switching redundancies of FNPC are used to provide voltage balancing. The introduced balancing scheme not only provides voltage balance among capacitors, but also distributes the reactive power equally among the cells and increases the reliability in this way. The performance of the proposed control is validated through simulation in MATLAB/SIMULINK environment and experimental results based on a single‐phase nine‐level HC‐FNPC‐based STATCOM laboratory prototype. [ABSTRACT FROM AUTHOR]

Parasitic capacitances in transformers consist of three main groups: winding‐to‐winding, layer‐to‐layer, and stray capacitances. Stray capacitance is also made of turn‐to‐turn and turn‐to‐core capacitances. This study presents a novel analytical method for calculating the values of turn‐to‐turn, turn‐to‐core, and stray capacitances in each winding, and employs the results to calculate the equivalent parasitic capacitance especially for high‐voltage switching transformers. The proposed analytical method introduces an explicit formula in terms of the winding and core dimensions. This formula can be applied in performance analysis and design optimisation methods. By utilising the proposed formula, calculation of the equivalent parasitic capacitance neither takes a great deal of time nor requires a particular computer system. The analytical results are verified by simulation results using the finite‐element method and experimental results achieved by a practical prototype of a high‐voltage switching transformer employed in a 390 W, 15 kV inductor–capacitor–inductor–capacitor resonant converter. [ABSTRACT FROM AUTHOR]

This study presents active switched passive network‐based high‐gain DC–DC converters. The active switched network is formulated using two inductors, one capacitor and two diodes. Hence, the network is named as a 2L–C–2D network. Using ten components, an asymmetric high‐gain DC‐DC converter is proposed. This converter achieves a gain of 29 at an 80% duty ratio. In the asymmetric converter structure by replacing the inductor by another 2L–C–2D network, the symmetric converter structure is proposed using 14 components. This converter structure achieves the gain of 49 at the same 80% duty ratio. Apart from increasing the voltage gain, the 2L–C–2D network helps to reduce the voltage and current stresses of the converter. The utilisation of two semiconductor switches in the proposed converter structures permits a fault ride‐through capability even when any one of the switches fails. Operations of the converters in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) are discussed, and the boundary condition between CCM and DCM is derived. To limit the effect of parasitic elements on the converter performance, SiC‐based semiconductor devices are used in the 500 W hardware prototype. The maximum efficiency of 92.8% is achieved in the case of a symmetric converter. [ABSTRACT FROM AUTHOR]

A new non‐isolated high‐voltage gain single switch quadratic modified single‐ended primary‐inductor capacitor (SEPIC) DC–DC converter is proposed in this study. The proposed converter consists of a modified SEPIC converter along with a boosting module to obtain a high‐voltage gain at a low‐duty ratio. It has all advantages of the SEPIC converter such as continuous input current, which makes it applicable for renewable energy sources such as photovoltaic systems. The proposed converter is able to attain a higher voltage gain in comparison with similar previous transformer‐less DC–DC converters. Also, unlike high‐voltage transformer‐based DC–DC converters, it does not suffer from leakage inductances. Also, the proposed converter presents low‐voltage stress across the switch and output diode. The proposed converter is controlled through a single switch and there is no limitation for a range of duty ratios. The voltage gain analysis of the proposed converter is done in continuous conduction mode and discontinuous conduction mode, also comparative analysis is done with the existing topologies with similar features. The proposed converter is designed for 400 V DC microgrid applications. The theoretical analysis of the proposed converter is verified by the experimental investigation in the laboratory. [ABSTRACT FROM AUTHOR]

A conventional pulse frequency modulation (PFM) controlled LLC resonant converter requires a wide switching frequency operating range to regulate the output voltage. There are some disadvantages of PFM LLC resonant converters: (i) the design and optimisation of magnetic components and gate driver circuitry are challenging; (ii) due to the variable switching frequency operating range, electro‐magnetic interference performance of the converter is degraded; (iii) efficiency degradation; (iv) inability to achieve independent control in multiple‐output applications. To address the above‐mentioned problems and achieve fixed switching frequency operation, a variable magnetising inductance control (VMIC) strategy is proposed. In the proposed VMIC control strategy, the operating switching frequency of the primary switch is fixed and the duty cycle remains constant at 0.5. At the resonant frequency operating point, the output voltage is independent of both the magnetising inductance and load. In addition, the zero current turn‐off operation of the secondary rectifier requires that the switching frequency be designed below the resonant frequency. The operational principles and design considerations of the LLC resonant converter with VMIC are presented. Experimental results from a 200 W prototype are presented to validate the theoretical analysis and the effectiveness of the proposed VMIC control strategy. [ABSTRACT FROM AUTHOR]

This study presents a reduced switch three‐phase three‐level H‐Bridge‐based shunt active power filter (SAPF) for the mitigation of current harmonics, the reduction of current unbalance and the injection of reactive power. This recommended SAPF is developed by using two H‐bridge and two DC‐link capacitors. Compared to the conventional three‐level H Bridge‐based SAPF, the eight‐switch cascaded H bridge (ES‐CHB)‐based topology saves four semiconductor switches and one DC‐link capacitor. The ES‐CHB‐based SAPF saves the power electronic components and reduces voltage stress across each switch by introducing a small AC capacitor in series with coupling inductor in each phase. This LC circuit also reduces the harmonic stress of SAPF by tuning at the sixth order of current harmonics. The only drawback of the suggested SAPF is the DC link voltage unbalances. To address this problem, a modified feedback control strategy is proposed in this study. The modified controller regulates the DC link voltage at the desired voltage and mitigates the DC link voltage unbalances, by using reactive power flow control and active power flow control, respectively. The performance of the suggested eight‐switch three‐level CHB‐based SAPF is evaluated through MATLAB simulation and experimentally verified through the hardware implementation. [ABSTRACT FROM AUTHOR]

This study proposes a new structure of hybrid cascade coupled-inductor high step-up (HCCIHSU) DC/DC converter for renewable energy sources. The proposed topology can provide an ultra-high voltage gain under continuous input current and low voltage stress on semiconductor devices. This converter is a hybrid cascade connection of the boost and buck–boost converters. The HCCIHSU utilises a coupled-inductor (CI) and a voltage multiplier (VM) cell to enhance the voltage gain ratio as a semi-quadratic function. The magnetic energy of the leakage inductor of the CI is recycled to the VM capacitors that reduce the component voltage stress and improve the converter voltage gain. Additionally, the voltage stress on the main power switch is clamped by two passive clamp capacitors. Due to the very high voltage conversion ratio at a reduced turn's ratio, the maximum voltage stresses on the switches and diodes are significantly alleviated, which further improve the efficiency. In this study, detailed steady-state analysis and comparisons with other related converters are provided. Finally, a 160 W/200 V laboratory prototype is built with 24 V input voltage at a switching frequency of 50 kHz to verify the performance of the proposed converter. [ABSTRACT FROM AUTHOR]

The present work deals with the design of an efficient and inexpensive autonomous photovoltaic array-based water pumping system utilising a new configuration of a single-input balanced dual supply buck–boost DC–DC converter. A four-phase switched reluctance motor (SRM) drive is selected to pump the water effectively and to make the system reliable. The utilised DC–DC converter can provide two balanced outputs using a single solar power source. It offers continuous output supply with minimum ripple to the SRM pump. The new control logic is also discussed in this work to provide equal voltages for two capacitors of the split converter in both starting and steady-state conditions. An improved perturb and observer-based maximum power point tracking control is also utilised to enhance the solar output power at varying irradiance. Moreover, owing to the pulse-width modulation switching of a split converter, a reduction is achieved in the size of split DC-link capacitors. The MATLAB/Simulink-based simulation is done to validate the real-time implementation of a developed system. These obtained responses are again validated through test results obtained via the developed prototype. [ABSTRACT FROM AUTHOR]

The main contribution of this study is to show the effect of light-emitting diode (LED) modelling in the design of offline drives. The authors propose the use of a source voltage and resistance model (SVRM), consisting of a threshold voltage source in series with the characteristic resistance, for the modelling of the LED. The offline drive used for the analysis is the flyback converter operating in discontinuous conduction mode. The equivalent circuit is analysed by superposition and the AC circuit is analysed with phasors. The analysis has proven that the flyback converter can be modelled as a current source feeding the output capacitor in parallel with the load. Likewise, the analysis demonstrated that the current ripple is always greater than the voltage ripple when an LED is used as a load. In order to validate the theoretical analysis, a design methodology for the flyback converter with the SVRM as a load was developed. The designed circuit was simulated in Spice and implemented in a prototype. Experimental results using an LED as load are compared with the same circuit using a simple resistance as load. The experimental results confirm the theoretical analysis with an error of <6.6%. [ABSTRACT FROM AUTHOR]

A novel topological family of multi-level inverters with flyback high frequency link is proposed in this study. The inverters can transfer high DC voltage into regulated sinusoidal voltage with low total harmonic distortion (THD). The circuit configuration consists of high DC input voltage, DC-link capacitors, novel multi-level conversion unit, high frequency flyback transformer, cyclo-converter, output filter capacitor and AC load. This topological family includes diode-clamp type full-wave mode, hybrid-clamp half-bridge mode, multi-end mode and improved multi-end mode. To achieve reliable multi-level inversion and overcome DC-link capacitor voltages unbalance, multi-carrier modulation and DC-link capacitor voltage balancing strategy are presented. In addition, steady principle and AC small-signal model are analysed. Simulation and experimental results are given to prove that the novel flyback high frequency isolated multi-level inverters have the following advantages such as the high frequency electrical isolation, the bi-directional power flow, the two-stage power conversion (DC-high frequency AC (HFAC) - low frequency AC (LFAC)), the lower voltage stress of power switches and the low THD of output voltage. [ABSTRACT FROM AUTHOR]

A novel topological family of multi‐level inverters with flyback high frequency link is proposed in this study. The inverters can transfer high DC voltage into regulated sinusoidal voltage with low total harmonic distortion (THD). The circuit configuration consists of high DC input voltage, DC‐link capacitors, novel multi‐level conversion unit, high frequency flyback transformer, cyclo‐converter, output filter capacitor and AC load. This topological family includes diode‐clamp type full‐wave mode, hybrid‐clamp half‐bridge mode, multi‐end mode and improved multi‐end mode. To achieve reliable multi‐level inversion and overcome DC‐link capacitor voltages unbalance, multi‐carrier modulation and DC‐link capacitor voltage balancing strategy are presented. In addition, steady principle and AC small‐signal model are analysed. Simulation and experimental results are given to prove that the novel flyback high frequency isolated multi‐level inverters have the following advantages such as the high frequency electrical isolation, the bi‐directional power flow, the two‐stage power conversion (DC‐high frequency AC (HFAC) ‐ low frequency AC (LFAC)), the lower voltage stress of power switches and the low THD of output voltage. [ABSTRACT FROM AUTHOR]

This study proposes a new structure of hybrid cascade coupled‐inductor high step‐up (HCCIHSU) DC/DC converter for renewable energy sources. The proposed topology can provide an ultra‐high voltage gain under continuous input current and low voltage stress on semiconductor devices. This converter is a hybrid cascade connection of the boost and buck–boost converters. The HCCIHSU utilises a coupled‐inductor (CI) and a voltage multiplier (VM) cell to enhance the voltage gain ratio as a semi‐quadratic function. The magnetic energy of the leakage inductor of the CI is recycled to the VM capacitors that reduce the component voltage stress and improve the converter voltage gain. Additionally, the voltage stress on the main power switch is clamped by two passive clamp capacitors. Due to the very high voltage conversion ratio at a reduced turn's ratio, the maximum voltage stresses on the switches and diodes are significantly alleviated, which further improve the efficiency. In this study, detailed steady‐state analysis and comparisons with other related converters are provided. Finally, a 160 W/200 V laboratory prototype is built with 24 V input voltage at a switching frequency of 50 kHz to verify the performance of the proposed converter. [ABSTRACT FROM AUTHOR]

The present work deals with the design of an efficient and inexpensive autonomous photovoltaic array‐based water pumping system utilising a new configuration of a single‐input balanced dual supply buck–boost DC–DC converter. A four‐phase switched reluctance motor (SRM) drive is selected to pump the water effectively and to make the system reliable. The utilised DC–DC converter can provide two balanced outputs using a single solar power source. It offers continuous output supply with minimum ripple to the SRM pump. The new control logic is also discussed in this work to provide equal voltages for two capacitors of the split converter in both starting and steady‐state conditions. An improved perturb and observer‐based maximum power point tracking control is also utilised to enhance the solar output power at varying irradiance. Moreover, owing to the pulse‐width modulation switching of a split converter, a reduction is achieved in the size of split DC‐link capacitors. The MATLAB/Simulink‐based simulation is done to validate the real‐time implementation of a developed system. These obtained responses are again validated through test results obtained via the developed prototype. [ABSTRACT FROM AUTHOR]

Impedance characteristics of the floating capacitor in the submodule (SM) of a modular multilevel converter (MMC) change due to its chemical and aging characteristics. This can result in a rise of voltage ripple across SM capacitors, uneven power distribution among the SMs and could also interrupt the operation with prolonged use of degraded capacitors. Existing balancing approaches are presented for the MMC with equal SM capacitance and ignored the effect of capacitor degradation as well as parameter mismatch. Hence, a closed‐loop control scheme that incorporates the effect of capacitor degradation is much necessitated. This study aims to overcome this gap by proposing a new power balancing control algorithm for SM capacitors, which effectively controls and evenly distributes the power among SMs. The efficacy of the proposed strategy is substantiated through PLECS simulations and OPAL‐RT/OP4510 controller‐based experiments on a single‐phase MMC laboratory prototype. [ABSTRACT FROM AUTHOR]

This study deals with a new control strategy for flying capacitor (FC) based multilevel converter, in order to attain the desired reference value for five‐level output voltage in active neutral point clamped (ANPC) converter. The balancing of capacitor voltages is one of the crucial aspects of grid‐tied photovoltaic (PV) fed ANPC converter. The accurate reference voltage for FC is required to experience minimum power pulsation and capacitor voltage imbalance. An offset injection‐based FC voltage regulator is implemented to track the desired voltage reference for FC. A simple proportional–integral controller generates the offset signal, which is added to the sinusoidal modulating wave to eliminate the FC imbalance. Moreover, neutral point voltage (NPV) balancing is achieved with the help of DC component injection control. The DC–AC power transfer, FC balance, NPV balance and unity power factor operation are achieved simultaneously. The performance of the closed‐loop controller for grid‐tied PV‐fed ANPC converter is analysed at constant and variable irradiances. The system is modelled in MATLAB/Simulink for offline simulation. Furthermore, offline simulation results are validated using real‐time controller hardware in loop (HIL) test bench. Moreover, active power is injected into the AC grid seamlessly and results are found compliant with the IEEE 519 standard. [ABSTRACT FROM AUTHOR]

Two‐stage power conversion system (PCS) for energy storage systems has been considered in islanded operation mode. A three‐level T‐type three‐leg three‐phase four‐wire topology (3LT2 3L3P4W) is employed as AC/DC part and a three‐level buck/boost converter is used as DC/DC interface. This study is mainly focused on balancing the neutral‐point potential (NPP) of the PCS with asymmetrical load connection. An NPP low‐frequency ripple model of 3LT2 3L3P4 inverter is proposed considering various load conditions firstly, which includes detailed expression of low‐frequency ripple components at fundamental frequency and fundamental frequency multipliers. Then, a novel NPP balancing method based on front‐end three‐level buck/boost converter under proportional resonant control is presented, in which the resonance points are set at fundamental frequency and triple fundamental frequency to suppress the dominant components of NPP ripple. Furthermore, a small‐signal model of three‐level buck/boost NPP control system is established and stability analysis is carried out. Simulation and experimental results have been provided to verify the accuracy of the NPP low‐frequency ripple model and the effectiveness of the NPP balancing method. [ABSTRACT FROM AUTHOR]

A high step‐up/high‐efficiency converter is one of the essential requirements of a low power grid‐connected photovoltaic system that provides the maximum power point tracking ability and injects the low voltage extracted power to AC or DC distribution network. This study presents a common‐ground non‐isolated high‐gain DC/DC converter whit a naturally wide range of soft‐switching conditions. The proposed converter has two resonant loops, and a new simple structure consists of an active switch, three diodes, two inductors and two capacitors, work in two useful operation modes. In the optimum operation mode (OOM), the switch turns on/off in zero current switching (ZCS)/zero voltage switching condition, and at the sub‐OOM, the switch turns on in ZCS condition and turns off in hard switching condition. The mathematical analysis and MATLAB/SIMULINK simulation results are described in detail. Also, a prototype 100 W converter is built and tested to validate the simulation analysis on a 100 W photovoltaic panel. [ABSTRACT FROM AUTHOR]

A three‐phase interleaved high step‐up bidirectional DC–DC converter is proposed, which can achieve three times the voltage gain of the traditional three‐phase interleaved boost converter only by adding two capacitors. The proposed converter has the characteristics of low switch voltage and current stresses, low output voltage ripple, automatic voltage‐balancing and current‐sharing abilities. Compared with the traditional interleaved switching strategy, a 180° interleaved switching strategy is proposed, which is more suitable for the proposed converter by widening the working duty cycle range. Closed dual‐loop control is used to regulate the output voltage of the converter. The parameter determining the method of the closed‐loop controllers based on the Bode diagram is described in order to control the high‐order converter. Operating principle, modelling, steady‐state analysis, voltage‐balancing and current‐sharing ability analysis and closed‐loop design of the converter are studied in more detail. Finally, experimental verification and efficiency measurements are implemented by a 300 W, 24 V input to 230 V DC bus prototype, which proved that the proposed converter is more suitable than the traditional three‐phase interleaved boost converter for some applications where requiring about six to ten times the voltage conversion ratio. [ABSTRACT FROM AUTHOR]

Series and parallel resonance tend to occur and cause harmonic distortion when the distribution system contains a shunt power capacitor to compensate inductive load and dynamic capacitor (D-CAP) to suppress harmonics. This study focuses on the series and parallel resonance active damping of three-phase buck-type D-CAP, so as to achieve better power quality control. Two virtual resistor damping methods for series resonance, D-CAP power capacitor voltage or D-CAP front-end buffer inductor current feedback, are introduced and compared. Then, parallel resonance is damped by generating certain harmonic currents in the phase with the selective harmonic voltage at the point of common coupling (PCC), equivalent to controlling the D-CAP as a virtual harmonic resistor. In addition, the power balance of D-CAP is interpreted to ensure no additional energy control loop is needed for the active damping. To further improve the parallel resonance damping, the self-adjusted damping gain is proposed by the closed-loop regulation of harmonics in PCC voltage. Finally, coordinated control between reactive and multiple harmonic currents is introduced for the whole combined control to avoid over-modulation. A wide variety of experimental results from a 33 kVar/220 V laboratory prototype are provided to demonstrate the validity of the combined control. [ABSTRACT FROM AUTHOR]

This study presents a new boost DC-link integrated multilevel inverter (BDIMLI) topology for single-phase stand-alone photovoltaic applications. The BDIMLI is realised by the integration of two two-level boost DC-link converters (TBDCs) with a hybrid H-bridge inverter using symmetrical voltage sources. Conventional cascaded multilevel inverters require a large number of isolated DC source and circuit components. On the other side, switched capacitor multilevel inverter topologies require less number of sources and components, but need bulky capacitors. The proposed TBDC units charge the capacitors to the desired voltage with the high switching frequency, hence require less capacitance and component count. The proposed topology with proper selection of capacitor voltage levels can produce 9-, 11- and 13-level outputs without altering any circuit components. Besides, the proposed topology produces low-frequency common-mode voltage. The comprehensive analysis of BDIMLI in comparison with recent multilevel inverter topologies is presented. An experimental prototype of BDIMLI is built and its dynamic behaviour with different load conditions is presented for both 9- and 13-level operations. [ABSTRACT FROM AUTHOR]

In renewable energy generation systems, the DC–DC converter with high voltage gain is indispensable, which is used to convert the low output voltage of photovoltaic (PV) cells and fuel cells to the high DC bus voltage. In this study, a cost-effective clamping capacitor boost (CCB) converter with high voltage gain is proposed. In the basis of the conventional boost converter, a clamping capacitor cell with two capacitors and two diodes is embedded. Then, the voltage gain of the proposed CCB converter can be doubled compared with the conventional boost converter. Further, unlike the switched capacitor high voltage gain converter, there is no large current spikes on the capacitors in the proposed CCB converter, which can reduce the current stresses and the costs of capacitors a lot. The operation principles and characteristics of the proposed CCB converter are analysed in detail and verified by simulation. Finally, a 450 W prototype is implemented to validate the performances and advantages of the proposed CCB converter. The proposed CCB converter provides a cost-effective choice for high voltage gain converters in the renewable energy generation system with PV cells. [ABSTRACT FROM AUTHOR]

Switched capacitor multilevel inverter (SCMLI) with reduced components is attractive for higher number of voltage levels due to less implementation complexity and low cost. In this study, a new family of hybrid SCMLI for high frequency power distribution system is presented to eliminate the intermediate power conversion. Firstly, a five-level SCMLI employing a single voltage source is proposed, which is further extended to nine-level (9L) with its operation. Further extension/enhancement of the proposed 9L-SCMLI for generating a higher number of voltage levels with reduced number of components is achieved on the basis of structural modification. The mathematical analysis for determination of capacitance, power loss analysis and comparative analysis has been provided in detail. A comprehensive comparison with other similar topologies is also provided to highlight the merits of the proposed topology. Simulation and experimental results are discussed for various dynamic load conditions with different output frequencies to validate the suitability of the proposed SCMLI for various high-frequency AC applications, such as renewable energy systems, microgrids, electric vehicles and so on. [ABSTRACT FROM AUTHOR]

This study reports a miniaturised discontinuous conduction mode (DCM) variable on-time (VOT) buck converter providing an output of 1.8 V in the input range of 3–12 V to support applications with large wireless coupling. Conventionally, an additional large capacitor has been used as a bootstrap capacitor to drive the high-side switch of buck converters, which prevents minimisation. In this study, a standalone momentary power consumption level shifter is proposed to remove the additional bootstrap capacitor and increase the power conversion efficiency (PCE) in the buck converter. A Zener diode is utilised to reduce the power consumption of the level shifter. In addition, a dead-time-based off-time calibration circuit is proposed to further increase the PCE by reducing the low-side conduction loss. The proposed circuit is fabricated with a TSMC 0.18-µm BCD process, and the core circuit occupies an active area of 0.68 mm2 with two external components. It provides output currents in the range of 20 µA to 3 mA with a maximum switching frequency of 750 kHz. The maximum efficiency of the converter below 5 mW is 80.2%. [ABSTRACT FROM AUTHOR]

Errors in the injected high-frequency circulating currents are originally investigated for modular multilevel converters (MMCs) in low-speed drive operation. The mathematical analysis reveals that the magnitude and phase errors in the injected circulating currents cause serious energy imbalance in the MMC arms, resulting in large voltage fluctuations in the submodules. Furthermore, these fluctuations get larger when the circulating currents are injected at higher frequencies, which reduces the drive system stability and damages the submodule capacitors. A remedy approach is proposed to minimise the error effects by adjusting the circulating current command. A full-scale system comprising a 1 MVA MMC and a 1 MW induction machine is simulated to verify the theoretical analysis. The experimental investigation of a down-scale MMC feeding an inductor is also conducted to validate the theoretical results. [ABSTRACT FROM AUTHOR]

In order to meet the requirements of the fuel cell stack power interface converter applied in the fuel cell vehicles, a common ground wide voltage-gain range DC–DC converter is proposed. On the input voltage side, an interleaved structure is adopted in this converter to reduce the input current ripple. On the output voltage side, two series capacitors are combined with a diode–capacitor structure to improve the voltage gain and reduce the voltage stress of power semiconductors and capacitors. As a result, the efficiency and reliability of the proposed converter can be improved. The operating principle, steady-state characteristic, parameter design, efficiency calculation, and comparison with other converters are analysed. A 1.6 kW prototype of the proposed converter with the 400 V output voltage has been developed to validate the analytical results. Theoretical analysis and experimental results show that the proposed converter can meet the requirements of a fuel cell stack power interface converter and is suitable for use as a fuel cell stack power interface converter applied in fuel cell vehicles. [ABSTRACT FROM AUTHOR]

In this study, an over-current protection method for permanent magnet synchronous motor (PMSM) voltage source inverter (VSI) employing small DC-link capacitor is proposed. Since VSI with small DC-link capacitor has become popular for its long lifetime and compactness. However, the small DC-link capacitor brings the risk of excessive voltage in the DC-link capacitor when the traditional 'all-turn-off' over-current protection is utilised. In order to avoid the damage for VSI caused by excessive pumping-up voltage, based on the analysis for the 'all-turn-off' method, the proposed method could eliminate reversal current flowing into the DC-link capacitor through switching logic. Consequently, the electro-magnetic energy stored in PMSM windings is converted into mechanical energy and pumping-up voltage is cancelled. Detailed analysis of the proposed method is presented. The effectiveness of the proposed method is verified by simulation and experiments. [ABSTRACT FROM AUTHOR]

Digital implementation of current-mode control (CMC) considers the outer voltage-loop in the digital domain, whereas the inner current-loop is kept either in the analogue domain in mixed-signal CMC (MCMC) or in the digital domain in fully digital CMC (DCMC). Under finite voltage-loop sampling, this study reports that the selection of sampling point can completely change the stability status of a boost converter with non-minimum phase behaviour, particularly in the presence of the effective-seriesresistance of the output capacitor. A discrete-time framework is proposed for fast-scale stability analysis in a boost converter, operating under continuous conduction mode. Further, discrete-time small-signal models are derived and design guidelines are proposed for both MCMC and DCMC architectures with enhanced stability for fast transient performance. Keeping in mind software-controlled DCMC, a considerably large sampling delay is considered, and its effect on the performance and stability is discussed. A boost converter prototype is tested and various DCMC schemes along the proposed design techniques are implemented using a field-programmable-gate-array device. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) has attracted a large amount of attention due to its inherent advantages such as convenience, safety, low maintenance, weather proof and so on. Compensation topology is crucial for WPT system due to its function of reducing reactive power and improving system efficiency. Series-series (SS) compensation topology is widely employed due to a simple structure and the characteristic of constant current output (CCO). However, it has three serious drawbacks: high-voltage stresses on compensation capacitors, poor CCO characteristic under practical situations and significant dependence on coupling coils. This study proposes LC/CL (primary inductor-capacitor and secondary capacitor- inductor) compensation topology to eliminate aforementioned deficiencies of SS. The voltage stresses on compensation capacitors of LC/CL are much lower than those of SS. LC/CL also provides better CCO characteristics in imperfect scenarios. Load current of LC/CL compensated system only increases by 1.89% when the load is reduced by half. In contrast, the load current of SS compensated system increases by 6.87% with identical load reduction. An efficiency-based optimisation method is proposed for higher end-to-end efficiency as well. The validity of the optimisation is justified by both simulation and experiment. The efficiency of the optimised system is about 2% higher than that of a non-optimised system. [ABSTRACT FROM AUTHOR]

This study presents the modelling, analysis, and experimental results of a novel capacitive power transfer (CPT) structure with a single coupling capacitor. It is noticed that each charged object has a nature property called self-capacitance, which is a kind of capacitance with respect to infinity. Taking advantage of this property, the conventional CPT structure can be simplified. Instead of using two capacitors to form the closed coupling loop, one of them is replaced by two metallic blocks with relatively big self-capacitances. Even though there is no physical coupling between the two blocks, they can be considered as virtually connected through their self-capacitances to infinity, which forms the return route for the proposed CPT structure. To achieve precise analysis, the detailed circuit model is established with the consideration of self-capacitances for both the blocks and coupling plates. Moreover, the results of the applications with attached blocks replaced by robust reference grounds (RRG) are also analysed in order to extend the proposed structure to more scenarios. System performances with and without RRG are compared. Experiments with different capacitor plate sizes at various transfer distances are also conducted. Both the theoretical analysis and experimental results indicate the effectiveness of the proposed structure. [ABSTRACT FROM AUTHOR]