Inverter-side current feedback control (ICFC) has been extensively adopted in distributed generation systems because of its simple implementation and better consistency with actual operating conditions. At the same time, when there are a large number of background harmonics in the grid, capacitor voltage feedforward (CVF) is usually added to the system for its suppression. This method could make the system keep the first-order characteristics under the analogue control. However, under digital control, due to the digital control delay, a reverse resonance peak will be generated in the loop gain, which makes the system unstable in the weak grid. In order to solve the aforementioned problems, this study proposes a feedforward phase compensation method of LCL grid-connected inverter based on the all-pass filter (AF). By introducing AF into the CVF channel, the phase lag in the range of reverse resonance peak frequency is compensated, so as to enhance the robustness of the system in the weak grid. At the same time, this study gives the detailed design process of the proposed method. Experimental results on a 3-kW prototype are provided, and the effectiveness of the proposed control method is verified..

A new perspective of impedance matching is proposed to study the power flow operation of the three-phase four-wire (3P4W) unified power quality conditioner (UPQC) system. Specifically, the UPQC system is equivalent to an adjustable impedance network, when external conditions change, such as grid voltage sag/swell and unbalanced loads, the node impedances in the network will be dynamically matched. On the one hand, the three nodes of the series converter (SC) will be matched as positive or negative impedances with the change of grid voltages, which means that the SC operates in a rectifier or inverter state to absorb or transmit the energy. On the other hand, to compensate the unbalanced load currents, the three nodes of the parallel converter (PC) will be matched as positive and negative impedances at the same time, which means that the PC operates in both rectifier and inverter state to absorb and transmit the energy. After matching the node impedances, the system's output node impedances are equal to the load impedances, thus achieving the power balance of the whole system. Experimental results of the power flow and impedance matching from a laboratory-scale prototype hardware are presented to evaluate the correctness of the impedance analysis.

This paper presents a cascaded full-bridge resonant inverter configuration for different material vessel induction cooking. The proposed inverter configuration features simultaneous heating of three different material vessels, and independent power control. In this proposed work, three different induction heating loads are simultaneously operated at their respective resonant frequencies. Vessels of iron, steel, and aluminium materials are used. The output powers are independently controlled by an asymmetric duty cycle control. The proposed inverter is designed and hardware prototype has been implemented. Experimental results are validated with simulation results.

In this study, a non-isolated three-port high step-up/step-down DC–DC converter is proposed. The proposed converter has the capability of cancelling the input current ripple in the high current port, moreover, the voltage conversion ratios between the high voltage and low voltage are increased by coupled inductors. All the ports of the proposed converter have a common ground. In addition, any of the three ports can be used as an input voltage source, which can supply the other two ports. The number of DC voltage ports of the proposed converter can be more increased by using more inductor-switch cells. In this study, the theoretical results of the proposed converter are obtained and the voltage conversion ratios of the output ports, the voltage and current stress on switches, average currents of inductors, and the required condition of cancelling input current ripple at the low voltage side are calculated for the proposed three-port converter. The voltage gains of the developed converter with four ports are also calculated. Finally, the theoretical results are reconfirmed by the experimental results for 28 V input/150 and 460 V output ports.

DC transformer plays a significant role in DC distributed network. This study proposes a modular multilevel dynamic DC transformer (MMDT), which can realise smooth control of transformer ratio, multi-level voltage conversion, and reliable fault isolation without high-frequency transformers and extra loss. The inner circuit, formed by the capacitors, not only realises the energy exchange between different sides but also provides the capability of fault isolation. In the proposed MMDT, the voltage transforming is realised by switching to different numbers of control units (CUs) on each side. To realise multi-level voltage transforming, the multi-port MMDT is developed. Furthermore, this study offers analyses of the current and voltage characteristics in steady-state and investigates the parameter design method in detail. Finally, the simulation and experiment tests are conducted to verify the feasibility and superiority of the proposed MMDT.

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.

In this study, an innovative realisation of a heterodyne multiplier is proposed, in the field of power inverters, as an alternative to existing systems in the literature. It is shown that by proper choice of control signals, it is possible to reduce the number of components by a factor of three at least, as compared to existing applications. Additionally, it is possible to considerably reduce the amplitude of harmonics in the switching frequency. As a result, considerable improvement in frequency multiplier efficiency is seen, without detriment to the low total harmonic distortion (THD) achievable by the use of frequency multipliers. The advantages of this method have been shown in AC–AC converters as well as DC–AC converters. Finally, a 4.2-kW model was built with an efficiency of 98.7% and a THD of <2.2%.

In this study, modelling, implementation, and control of a hybrid renewables-based, scalable DC microgrid using multi-input multi-output dual active half-bridge (DAHB) converter is presented. The proposed microgrid architecture exhibits superiority and enhanced functionality in comparison to the existing conventional architectures in terms of the reduced number of converters for each resource integration, modularity, scalability, and bidirectional power flow capability, and local maximum power point tracking for each renewable resource. The proposed architecture is significant in terms that only a single converter is responsible for the whole operation of the DC microgrid. A dual half active bridge acts as a central hub for power processing while multiple renewable energy resources can be integrated through isolated input and output ports. The proposed microgrid is analysed for power flow, and the control scheme for different voltage and power-sharing scenarios is designed. The proposed architecture of the microgrid is simulated on the Power-SIM simulator, and a simplified hardware prototype is implemented in the laboratory with satisfactory results.

In this paper, Artificial Neural Networks (ANNs) for diagnosing multiple open-switch faults in three-phase PWM (Pulse Width Modulation) converters are designed. For single and double open-switch faults in the converters, there are 21 types of fault modes, causing distorted phase currents. Since these abnormal currents can induce secondary faults in peripherals, the open-fault diagnosis is essentially required. In this paper, a two-step technique based on ANNs is utilized for the diagnosis of the multiple open-switch fault. First, dc and harmonic components of the currents are extracted by using an ADALINE (Adaptive Linear Neuron). In the first step, the ANN categorizes fault modes into six sectors by using dc components in the three-phase plane. In the second step, the ANN localizes fault modes by using dc components and the ratio of d–q axes currents THDs (Total Harmonics Distortions) in each sector. Especially, both switches open-faults in the same legs are localised by counting the sampled zero current of the fault currents. The proposed two-step technique allows a simple design of the ANNs for the diagnosis, and a short execution time about 22 s. Simulations and experiments for a 3.7 kW three-phase PWM converter confirmed the validity of the proposed diagnostic method.

This study presents a performance assessment of a single photovoltaic (PV) array fed transformer-based five-level converter topology with optimal shift factor-based modified sinusoidal pulse width modulation (OSF-MSPWM) technique under a dynamic solar PV environment. The five-level converter output is generated using H bridge cells and single-phase transformers. A single PV array is fed to all cascaded H bridge cells and isolation is provided by cascading secondary windings of the transformers in the AC side. The separate DC sources requirement is eliminated and galvanic isolation is provided by single-phase transformers. The decoupled controller with modified in-phase disposition PWM technique is used for active power injection into the grid at unity power factor. This work uses a new carrier shape at the same input carrier frequency and modulation index m _f for improving the harmonics performance of the five-level converter. Hence, shift the dominant harmonics to the higher side for developed topology and performing optimal shift factor-based modulation is compared with the conventional SPWM technique. The steady-state and dynamic responses of the PV multilevel converter are observed in MATLAB simulation and tested in a real-time platform.

A systematic approach for synthesis and tuning of the controller for grid-connected inverters with LCL-filter is proposed in this study. The design objectives like current tracking, harmonics rejection, resonant damping and extended stability over wide grid variations are addressed. Controller structure is synthesised by direct synthesis approach which leads to a systematic design procedure and tuning method. Low-frequency approximation of the system under worst grid condition is used for the synthesis of the current controller and the resonance component is handled separately. Tunable parameters are identified to investigate grid variations in the process of augmenting the synthesised controller for realisability. Complete design, stability analysis and tuning are dealt with directly in the discrete domain. Detailed simulation and experimental validation are carried out on a 1 kW prototype inverter. The method proposed in this study serves as a simplified design tool for effective design of a multi-objective controller for grid-connected inverters.

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.

In this study, a phase shift controlled full-bridge series resonant converter (SRC) integrated with buck converters for light-emitting diode (LED) driver application is proposed. This LED driver supplies four LED loads simultaneously. The current through LED loads is controlled by phase shift control of the SRC, and its output is added to the input voltage. Zero-voltage switching (ZVS) switching of all the switches is achieved by operating the SRC at lagging power factor for all input voltage variations. As the only part of the output power is processed through the SRC and all the switches operating with ZVS, the efficiency of the converter is 95.7%, which is high. A 142 W LED driver is designed, and its performance is tested with PSPICE simulations and experimental prototype.

In this study, a procedure to evaluate the performance of a power converter under different operating conditions is presented. The technique takes into account the effect of the environmental conditions and the tolerance on each component and it provides a probability estimation that the converter will reach certain performance under definite operating condition. This feature allows to better understand the operation of the converter even outside the nominal operating conditions. Furthermore, by appropriately modelling the performance of each component, it is possible to understand from the early design stages which component technology is more suitable according to the environment in which the converter will work. The steps of the procedure are explained in detail and a case study applied on a Class-E inverter to provide a step-by-step explanation and to experimentally validate the accuracy of the probability estimation is presented.

The integration of remote renewable energy sources located near the long-distance HVDC transmission corridor to the HVDC system is an active area of research. This study presents a new fault-tolerant scheme using a modular soft-switched DC–DC converter with high-voltage gain to integrate renewable energy sources to LCC-based HVDC systems. The configuration, operating principle and mathematical modelling of the new DC–DC converter are described in this study. As both the charging and discharging processes takes place through resonant circuits, zero current switching of all the switches used in the converter is achieved. The proposed scheme has the inherent fault-tolerant capability and enables fast recovery from commutation failures in the main LCC HVDC system. The operation of the proposed scheme during various fault scenarios is analysed and explained in this study. The performance of the proposed scheme and its fault ride though the capability is verified using a simulation model built in PSCAD/EMTDC and an experimental prototype.

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.

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 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.

Parametric transformers are magnetic components which employ a variable inductance to generate parametric oscillations in a secondary resonant tank. Power conversion with parametric transformer can provide constant output voltage regulation, short-circuit protection, input over-voltage and under-voltage protection, and bidirectional filtering. In spite of these benefits, parametric transformers did only experience small scientific attention during the 1970s. Due to the low energy density and low efficiency of the topologies developed at the time, parametric transformers were discarded in favour of the more common power converters based on the magnetic amplifier. In spite of the great developments in power semiconductors, magnetic amplifier control still remains a competitive option in present-day power electronic applications benefiting from its high robustness. This publication presents a new topology of parametric transformer based on permanent magnet (PM)-inductors, presenting higher efficiency and higher energy density. Finite element method magnetics simulations are used to analyse the variable inductance mechanisms. A physical prototype is developed and tested empirically in an AC/DC power converter. The prototype verifies all the mentioned benefits of parametric power conversion, and presents an efficiency and energy density equivalent to presently employed solutions for voltage regulation, using power semiconductor magnetic amplifiers.

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.

A combination of shunt active harmonic filter (SAHF), and adjustable power factor correction (PFC) capacitors is generally employed in industrial applications to achieve cost effective solution for the load compensation. It has been experienced that SAHFs operating in conjunction with PFC capacitors may lose their stability while compensating certain harmonic components which are near the resonant frequency of the network. This resonant frequency is not known beforehand while designing the controller of the SAHF, and further it keeps on varying with time as the value of PFC capacitors vary based on the reactive power requirement of the load. Therefore, the conventional controllers having predetermined values for gains fail to stabilise the operation of the SAHF under varying operating conditions of the network. This necessitates the involvement of an adaptive control mechanism within the SAHF with which the SAHF exhibits stable operation even under varying network conditions. In order to accomplish this requirement an artificial neural network-based control scheme is proposed in this study. The proposed scheme is verified by conducting thorough simulation studies. The viability of the proposed scheme is also confirmed by carrying out detailed experimental studies on a laboratory prototype.

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.

The output power characteristic of the photovoltaic (PV) panel under partial shading condition (PSC) exhibits multiple peaks: a single global maximum peak (GMP) and several local maximum peaks, which adds more complexity to the maximum power point tracking (MPPT) system. Here, a deterministic modified Jaya (DM-Jaya)-based algorithm is proposed for tracking the GMP, where the updating solution formula and the step size in the vicinity of the GMP of the generic Jaya algorithm have been significantly improved, these improvements provide many pros, including quick convergence time, one parameter needs to be tuned, null oscillation in steady-state, and easily implemented in a low-cost microcontroller. The proposed DM-Jaya algorithm is implemented in the hardware prototype; in addition, it is compared to other state-of-the-art techniques under different PSC patterns. The obtained results revealed the effectiveness of the DM-Jaya and its overall superiority compared to other methods in terms of efficiency and tracking time.

This study proposes a new transformerless DC–DC step-down converter having the quadratic type of wider voltage gain, for point-of-load applications. In comparison to existent quadratic buck converter variants, the proposed topology offers better switch utilisation at small output voltages and reduced voltage/current stress on components. The stress minimisation benefit helps to select low ON-state resistance switch in the proposed converter, thereby decreasing its conduction losses. Qualitative steady-state analysis is carried out under continuous inductor current mode and design criteria for L-C components are established. State-space average model is derived and subsequently, an equivalent sliding mode control law based on just source side inductor current dynamics and integral of load voltage error is constituted to regulate the output. Salient operational characteristics of the converter are studied analytically and illustrated thereafter using experimental outcomes on a laboratory prototype.

DC–DC converters play an important role in electrical systems. The fault state of a DC–DC converter has a major impact on the operation of the back-end components and the entire electrical system. Therefore, the fault diagnosis is very necessary when the fault state of DC–DC is in the early stage. It can decrease the likelihood of happening the serious faults that may result in the enormous economic loss. To effectively diagnose the incipient fault in DC–DC converters, an incipient fault diagnosis method based on sensitive fault features is proposed. Firstly, for each type of the incipient fault, this study obtains the statistical features in time domain and the wavelet analysis local energy values in the frequency domain of the output. Then to further improve the incipient fault diagnosis accuracy, this study removes the redundant fault features based on overlap calculation, the unique fault features for each type of incipient fault will be selected. Finally, these sensitive fault features are used to build support vector data description models, which can diagnose the incipient faults. Simulation and hardware experimental results validate the practicability and effectiveness of the proposed method.

Due to the change of parameters caused by the dynamic longitudinal end effect, the operation characteristics of linear induction motors (LIMs) applied in an electromagnetic launch field are different from that of ordinary LIM. Due to the continuous increase of the LIM port voltage under high acceleration, the phase voltage is close to the inverter output limit. The conventional indirect field-oriented control (IFOC) strategies of LIM based on the flux attenuation compensation or maximum thrust control cannot solve the problem well. Based on the LIM mathematical model, this study analyses the output thrust characteristics of the LIM and discusses different control methods. This study presents an improved vector control strategy. By dynamically adjusting the value of ‘ k ’ based on the moving speed of the LIM, the maximum thrust output is maintained at medium and low speeds, and the voltage rise of a motor port is restrained at high speed. The effectiveness of the proposed control method is verified by simulation and experiment. The method proposed in this study is helpful to broaden the application of the LIM in the higher speed field.

This study focuses on considering battery one time constant model in the design of controllers of a two-stage AC/DC and DC/DC battery charger using the small-signal approach. For this aim, small-signal models of DC/DC and AC/DC converters and also the battery model are obtained. Moreover, the effect of disturbance terms are analysed to be omitted in controller loops. Simulation and experimental results of a 1 kW laboratory prototype show appropriate performance of designed controllers in tracking reference signals. Also, tuned controllers using this approach have guaranteed unity power factor and low total harmonic distortion. Furthermore, a complete charge cycle of a lithium-ion battery evaluates the performance of the converter in different constant current/voltage controlling modes. In comparison with restive model consideration, results show a more accurate model with grater damping ration and better stability characteristics.

Electric vehicle (EV) power system is the key to the development of EVs. If direct current (DC) arc occurs in the power system, it is difficult to extinguish at zero point. The arc fault will release a huge amount of energy and continuous sparking, which may cause spontaneous combustion or even explosion. In this study, an arc detection algorithm based on the classification of windowed Fourier transform and support vector machine (SVM) model is proposed for DC serial arc detection of EV power system. In order to optimise the arc detection algorithm, the authors use the pre-detection algorithm, which can effectively reduce the false detection rate of DC arc fault and ensure the reliability of detection algorithm. In addition, they propose an arc fault data enhancement model, which can generate arc fault current data. Finally, the experimental results show that the arc detection algorithm has a high accuracy and a false detection rate of 0%. After data enhancement, it has generalisation of the SVM classification model under the condition of high power experiment.

This study proposes a control technique for single-input dual-output three-level dc–dc converter (SIDO-TLC) using feedback (FB) and feedforward (FF) principles. Through the proposed control strategy, SIDO-TLC can smoothly function in both buck and boost operating conditions with a fast dynamic. Major duties of the designed FB control loops are to noticeably decrease the recovery time of transient responses under the load variations and accurately balance the boost capacitors voltages. To effectively decouple the introduced control inputs, an external FF controller is assigned that can also enhance the buck and boost voltage regulations. Furthermore, a step-by-step assessment is contemplated based on the proposed control loops to make an offline adjustment for the FB and FF coefficients. The proposed controller implemented on SIDO-TLC is highly suitable for portable applications, where efficiency, cost, and speed are of important factors. The simulation results and the laboratory test setup of SIDO-TLC using DSP TMS320F28335 are presented to prove the validity of the presented theoretical subjects.