In this study, a hybrid high-voltage direct current (HVDC) topology with line commutated converter (LCC) and modular multilevel converter (MMC) in series-connection is proposed, which is suitable for bulk power overhead line transmission. This topology is of operational flexibility in terms of active and reactive power controls, and is able to withstand ac and dc faults by the cooperative control of LCC and MMC. First, the operation principle and mathematical model are presented. Then, the control strategies for ac faults at rectifier and inverter side are discussed, which can prevent current cut-off under ac fault at rectifier side as well as maintain part of active power if commutation failure of LCC occurs under ac fault at inverter side. In addition, the feasibility on dealing with dc fault is theoretically demonstrated by analysing the characteristic of MMC under blocking state. A detailed control strategy for dc fault is further proposed combined with a test system. Finally, the effectiveness of the control strategy for ac and dc faults is verified and further compared with LCC-based HVDC topology through time-domain simulation.

Direct current (DC) electrical grids are already a reality in low voltage (LV) telecom distribution systems and point-to-point high voltage DC transmission. Medium voltage (MV) domain, despite its big potential, still suffers from a lack of suitable conversion and protection technologies. This study presents a bidirectional, galvanically isolated, high power converter for interface of emerging MVDC grids with readily available LVAC grids. To achieve high conversion efficiency, the integration of a line frequency transformer into the structure of the modular multilevel converter (MMC) is analysed and described in a systematic manner. Two configurations of the galvanically isolated modular converter: (i) interleaved and (ii) stacked, are derived and presented. Differences and similarities, compared to the classical MMC, are presented on the system design level, while control performances are evaluated by means of simulations.

In the past two decades, many different multilevel converters have been presented. Usually, these comprise a large number of semiconductors. Some converters try to reduce the amount of semiconductors by using some of them for the three phases. This study presents a different approach: a converter where all the switching semiconductors are common for the three phases. This approach reduces the amount of high-frequency switching semiconductors and can use cheaper semiconductors for low-frequency switching ones, which may lead to a reduction of the total cost of the converter. Different options are described throughout this study and the advantages and disadvantages of each one of them are discussed. Finally, some simulation results illustrate the correct operation of the proposed new topology.

Static power converters have various applications, such as static ground power units (GPUs) for airplanes. This study proposes a new configuration of a static GPU based on a novel nine-level flying capacitor h-bridge active-neutral-point-clamped (FCHB_ANPC) converter. The main advantages of the proposed converter in comparison with conventional nine-level ANPC converter are decreasing the number of switches and flying capacitors (FCs) in the proposed converter, doubling the output voltage level of a traditional ANPC converter and reduction of output L-C filter sizes which results in significant improvement in GPU dynamic performances. This progress is achieved by utilising the proposed FCHB converter to an ANPC converter and using the suggested modulation method. This leads to diminish the size and cost and enhance the feasibility and reliability of the converter. Applying the proposed modulation method for FCs in the FCHB_ANPC converter guaranties self-balancing and voltage level regulation of FCs without using closed-loop control. Improved output voltage spectrum leads to inductance reduction of output L-C filter which enhances static GPU performance. The simulation and experimental results demonstrate the validity and feasibility of the proposed converter and the modulation method under various operating conditions.

This study details a three-level hybrid fault-tolerant converter. The definition of an original decoupling solution between the fourth flying capacitor (FC) leg and the three neutral point (NP) clamped-based phases overcomes topology hybridisation issues. Under normal conditions, a control strategy of the FC-based leg leads to a converter NP voltage balance, and decreases the DC side capacitors’ volume and cost. Under fault conditions, the presented fault isolation and converter reconfiguration strategies generate a post-fault converter, which is able to operate safely with the added FC-based leg. The proposed topology is an interesting trade-off between converter fault-tolerant capability and its complexity and offers the ability to be simply reconfigured and controlled in the case of switch fault occurrence. Two operation modes under fault conditions are presented and their performances are shown and discussed through simulation results and first experimental tests.

This study presents the experimental evaluation of a proposed new three phase hybrid converter topology for medium voltage applications. The topology is based on the interconnection of a low switching frequency voltage source inverter (VSI), rated at medium voltage, with a high switching frequency low-power rated current source inverter (CSI). The main function of the shunt connected CSI is to cancel the large switching current ripple produced by the VSI while operating at a reduced fundamental voltage enabled by the use of series connected capacitors. The simulations and design procedure outline the possibility of achieving high output grid current quality whilst the added installed power by the CSI remains at <4% compared with the VSI. The experimental results show good correlation between analytical/simulated targets of 20% maximum CSI voltage stress albeit with added installed power of 6.7% due to a larger amount of current ripple processed.

This study presents a new LLC resonant converter with two transformers in parallel for the electric vehicle battery charger. This topology achieves the zero-voltage switching for main switches in the entire charging profile. In addition, the zero-current switching for output rectifier diodes is extended under charging condition. The proposed charger provides a wide range output voltage for the battery system. Moreover, in order to maintain the high efficiency under charging, the charger adopts a bidirectional switch. At low-output power condition, the charger uses one transformer to transfer the energy. Finally, the design procedure is provided and implemented in a prototype charger with the input DC link 400 V and the output voltage of 36–58 V. Experimental results are presented to demonstrate the system performance. The maximum power is up to 700 W and the peak efficiency is as high as 93.6%.

A three-winding transformer based asymmetrical dual active bridge (TWT-ADAB) isolated dc–dc converter is proposed in this study. The converter comprises of three stages: primary, isolation, and secondary. The primary stage consists of an H-bridge converter, the isolation stage consists of a three-winding transformer with one primary and two secondary windings, and the secondary stage consists of a bridge converter having three legs and six active switches. The load current is shared equally by the secondary windings of the transformer resulting in reduced currents through switches of the secondary converter. Therefore, the turn-off losses of these switches get reduced. Further, zero voltage switching turn-on can be achieved for all switches of the TWT-ADAB converter to reduce the switching losses. A detailed analysis of the modelling and control of the proposed TWT-ADAB converter is presented. The theoretical analysis is verified using the simulation and experimental results. These demonstrated results show that the proposed TWT-ADAB converter offers wider ranges of the output voltages and powers and higher efficiency as compared with the existing dual bridge isolated dc–dc converters. Therefore, it can be an eminent structure for high-power isolated dc–dc power conversion applications.

Cascaded H-bridge multilevel inverter with isolated dc sources is a suitable choice as an interface between grid and distributed generation (DG) sources. The main duty of the interface inverter is to adapt voltage of the grid and DG source while active and reactive power exchange is also controlled by it. Conventional fundamental frequency switching methods have been studied so far only for quality improvement of the inverter output voltage. However, for the grid-connected applications, voltage quality at the point of common coupling (PCC) is more important than the inverter output voltage. This study presents a modified harmonic mitigation fundamental frequency switching method for the grid-connected cascaded H-bridge multilevel inverters. The goal is to calculate optimum switching angles of the inverter which satisfy the standard limits for the total harmonic distortion and harmonic contents of the voltage waveform at PCC considering specifications of the grid. This is also to be achieved with minimum required amount of the coupling impedance. Genetic algorithm optimisation program based on the modified switching method is employed for a sample system including a three-phase cascaded H-bridge seven-level inverter connected to a harmonic polluted grid. Computer simulation using Simulink/MATLAB is performed, the results of which confirm effectiveness of the proposed method.

In this study, a new high step-up dc–dc converter is proposed. The proposed converter has two switches that operate in two operational modes. In the first case, both switches are turned on simultaneously, where the voltage gain would be similar to cascaded boost converter but the input current ripple will not be removed. Thus, the high voltage conversion ratio can be achieved with a suitable duty-cycle. In this case, the performance of the converter has been investigated in two continuous and discontinuous conduction modes. In the second case, two switches operate inversely. In this case, in addition to having high voltage conversion ratio, the input current ripple is removed by a pre-selected duty cycle. The results of the steady-state operation of the converter are studied in both discontinuous conduction mode and continuous conduction mode. Finally, a 100 W prototype of the proposed converter has been implemented in the laboratory for evaluating its performance.

This paper focuses on the design and development of power factor corrected (PFC) interleaved canonical switching cell (I-CSC) converter-based switched mode power supply (SMPS) for arc welding. By interleaving CSC converters, input current is shared amongst them so that high reliability and efficiency is obtained for high-power applications. I-CSC converter is designed to operate in discontinuous conduction mode (DCM) to achieve unity power factor inherently at utility interface. DCM operation together with interleaving technique bring additional size and performance benefits such as reduced reverse recovery loss, less switching stress, high efficiency, etc. I-CSC converter is followed by three full bridge buck converters in parallel to perform DC-DC conversion and to provide galvanic isolation desired for safe operation during welding. The modularity of SMPS allows flexibility in current, voltage and power levels, usage of devices of lower rating and ease of maintenance. The proposed SMPS operates in constant voltage mode; however, during extreme overload condition it maintains constant current at the output to improve the weld bead quality. Test results confirm the effectiveness of proposed SMPS in maintaining power quality indices within the acceptable limits of international standards over wide load range while over-current handling capability leads to improved welding performance.

In this study, a physics-based model for emitter controlled (EMCON) p–i–n diode is proposed. The model is based on the one-dimensional Fourier-based solution of ambipolar diffusion equation (ADE) implemented in MATLAB and Simulink. The ADE is solved for all injection levels based on the design concepts of EMCON diode. The deep field stop layer utilised in the EMCON diode is also considered in the solution. Moreover, the depletion behaviour in the N-base during reverse recovery is redescribed. To be self-contained, a parameter extraction method is proposed to extract all the parameters of the model. In the end, the static and reverse recovery experiments for a commercial EMCON diode are used to validate the proposed model. The simulation results are compared with experiment waveforms and good agreement is obtained.

This study deals with the design of a load sensorless multi-loop control system for the stand-alone inverter. In the proposed strategy, only the inverter current is measured, which is practically required for both control and protection purposes, then the load voltage and current are both estimated using the linear Kalman filter algorithm, and the gradient descent adaptive control method, respectively. The estimated quantities are used as feedback signals of an inner-outer double-loop controller, which uses a proportional-resonant outer-controller to regulate the output voltage with minimum steady-state error and a simple proportional inner-controller to provide active damping and improve the transient performance. The controller parameters are designed in the frequency domain based on the required bandwidth and stability margin. Furthermore, the controllability and observability, as well as the stability of overall digital control system, including the dynamics of estimators, are analytically investigated. Simulation and experimental results, with a 600 VA prototype, confirm the theoretical achievements and illustrate the excellent performance of the proposed estimation and control scheme.

This study investigates a multiple input buck dc–dc converter. Different operational modes of the converter for two-, three- and four-input sources are studied then, for each item the relation of critical inductance between continuous conduction mode and discontinuous conduction mode is calculated. Finally, a generalised relationship is proposed for calculation of critical inductance of n-input topology, which is true for any number of input sources. Experimental and simulation results in power systems computer-aided design/EMTDC are presented to validate the theoretical concepts and proposed generalised relation of converter critical inductance.

This study proposes a novel method to eliminate the limit cycle caused by low resolution analogue-to-digital converter (ADC) in digitally controlled DC–DC converter. The reduced state Kalman filter is proposed to get the optimum estimate of the output voltage from the noisy measurement provided by the low resolution ADC. The proposed scheme is simulated with 6 bit resolution of ADC and the validation is performed with different resolutions using a prototype model which is implemented in16 bit digital signal processor. The results show that the proposed scheme eliminates limit cycle oscillation completely and is computationally more efficient.