Large-scale photovoltaic (PV) plants may be destabilised by the large grid impedance introduced by transformers and long transmission lines. When considering the digital control delay of grid-connected inverters, the problem will become more serious. In this study, the equivalent impedance model of digitally controlled large-scale PV plants is established, considering that the values of the parameters of the LCL filter follow Gaussian distributions. Then, the system stability can be analysed conveniently, and the stability analysis shows that the digital control delay will make the system robust to large grid impedance worse. To enhance the stability-robustness of the system, an H _∞ robust controller is proposed in this study. By properly selecting the weighting functions, the desired tracking error performance and robustness are achieved on the basis of the mixed-sensitivity optimisation control design. Compared with the traditional dual current loop control strategy, the H _∞ robust controller improves significantly the system stability-robustness against large grid impedance. Finally, simulation and experimental tests are carried out in this study, and the results demonstrate the effectiveness of the proposed H _∞ robust controller.

This study proposes a power conversion interface for a DC grid and a single-phase utility. The proposed power conversion interface is configured using an interleaved AC–DC power converter and a DC hybrid power filter. The interleaved AC–DC power converter controls the real power between the DC grid and the single-phase utility in both directions. The interleaved AC–DC power converter can effectively reduce the high-frequency harmonic currents at both the AC side and DC side. A new current-sharing control method is used to equalise the currents in the interleaved power-electronic arms using only one current sensor in the interleaved AC–DC power converter. The DC hybrid power filter is connected between the DC bus of the interleaved AC–DC power converter and the DC grid. The DC hybrid power filter is controlled to be operated as a virtual low-frequency AC resistor connected to the DC grid in series and the low-frequency harmonic for the DC input current of the interleaved AC–DC power converter is suppressed. Accordingly, the problems of harmonic currents for a power conversion interface used between the DC grid and the single-phase utility are attenuated. A hardware prototype is developed to verify the performance of the proposed power conversion interface.

This study presents an improved super-twisting sliding mode (SSM) approach to a stand-alone doubly fed induction generator (DFIG) for direct current (DC) generation system. By taking the uncertainties into consideration, an improved SSM regulator based on an extended state observer (ESO) is proposed to enhance the robustness of DC-voltage regulation. Moreover, a novel sinusoidal rotor current calculation method is proposed to generate sinusoidal reference of rotor current. A resonant-based ESO (R-ESO) SSM approach is proposed to regulate rotor current. By applying the R-ESO to estimate the model-related part of DFIG, the tracking performance with respect to a sinusoidal reference is improved. Then, the suppression ability to fifth and seventh harmonic currents are enhanced. Finally, both simulations and experiments on a 6-kW DFIG-DC system are provided to show the effectiveness of DC-voltage regulation and harmonic current suppression of the proposed approach.

This study presents a family of novel high gain non-isolated hybrid dc–dc converter for dc micro grid application. The proposed family of the converter is developed by employing both inductor-capacitor-inductor (LCL) based switched inductor (SI) and switched capacitor (SC) technique to achieve high voltage gain. Appropriate increase in the number of LCL-based SI cells in the power circuits in order to achieve ultra-high voltage gain allows formulating a generalised structure of the circuit. Incorporation of SI & SC techniques and the structure of the circuit with one stage power transfer ensure high voltage gain at low voltage stress across the switches and diodes. The study includes the principle of operation, steady-state analysis and performance analysis in detail for the converters. Experimental results from the developed hardware prototype of 380 V/250 W validate the adopted concept, design and exemplify that the proposed family of converter operates at a full load efficiency of 94%.

Considering the time delay introduced by the digital control, it turns out that capacitor current proportional feedback active damping (AD) is equivalent to a frequency-dependent virtual impedance in parallel with the filter capacitor. Unstable open-loop poles will arise due to the presence of virtual negative resistor, which causes that the system stability is highly sensitive to grid-impedance variation. Therefore, this study proposes a novel capacitor current quasi-integral feedback AD method. Theoretical analysis shows the proposed AD method can extend the region of the virtual positive resistor, i.e. damping region to the half of sampling frequency (f _s/2). Hence, strong robustness against the grid-impedance variation is achieved. Finally, experimental results including the proposed AD method as well as capacitor current proportional feedback AD method are given and compared, which validates the superior damping performance of the proposed scheme.

This study proposes a novel high step-up non-isolated dc–dc converter based on the classical Ćuk converter with coupled inductor and voltage multiplier techniques. To further increase its voltage gain, the load is differentially connected between the input source and the output capacitor. The proposed converter presents reduced voltage stresses over the active switches and allows the design of low-volume magnetic devices. Its quasi-resonant operation mode guarantees zero-current-switching (ZCS) turn-off of diodes, whereas the current ripple of the magnetic devices can be utilised to assist zero-voltage-switching (ZVS) turn-on of active switches. A prototype circuit with 25–40-V input voltage, 400-V output voltage, and 200-W output power is built and tested to verify its performance. The highest obtained efficiency is 97.2% and the weighted California Energy Commission (CEC) efficiencies are >95.7% over the entire input voltage range.

In this study, a family of isolated boost DC–DC converters is proposed and evaluated. This family is built by the combination of an isolated current fed converter with high-voltage gain techniques. The evaluated cells are switched inductor, switched capacitors, reduced redundant power processing and a mixed of switched inductor and switched. So, the proposed family has four different isolated high step-up DC–DC converters. To evaluate this family, a comparative study of the significant features was performed. This study comprises features such as principle of operation, derivation of static voltage gain, current and voltage stress on the components, component stress factor, number of components, power losses, power density and cost. By these evaluations, the key features, limitations and restrictions of each converter were acknowledged. In this way, one can gather all the theoretical knowledge of each of the analysed converters and estimate which one will have better performance in the laboratory. To validate the theoretical analysis, four prototypes were built according to PV AC-module specifications 200 W.

Nowadays new silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) are available in the market and they are expected to replace, in the next few years, the insulated gate bipolar transistor (IGBT) and Si-MOSFET in power electronic converters. SiC MOSFET transistors must be controlled by a dedicated circuit called ‘gate driver’ which ensures the switching orders transmission, the users’ safety and the switching cell integrity. The design of a gate driver dedicated to a SiC MOSFET module for applications up to 1200 V is described in this study. Galvanic isolation of control signals and power supplies, the power supply structure, SiC MOSFET switching orders and protection functions are detailed. Essential functions such as the short circuit detection and the implementation of the soft shut down are expanded. The developed gate driver is tested and validated. Experimental measurements allow for the validation of the good functioning of the developed gate driver in a highly disturbed environment.

In the bipolar (multiple) receiver inductive power transfer (IPT) system, the delivered power sharply drops with detuning due to the coupling between the two receiver coils. As a remedy to this problem, a new self-decoupled model of bipolar receiver by adding decoupling coils (sub-coils) to the receiver coils is proposed. First, the IPT system topology with a bipolar receiver has been analysed. Then, the self-decoupled model of bipolar receiver has been built. Furthermore, a quantitative calculation model of decoupling coils has been given. Finally, a series of IPT system comparison experiments for a single receiver, a bipolar receiver, and the decoupled bipolar receivers by using overlap, and the presented method are carried out separately. The results show that the presented self-decoupled model of bipolar receiver can effectively overcome the electromagnetic coupling between the dual receiver coils on the system resonance. The results further verified that the presented model is also suitable for the case with core plates.

A modular structured 12-kW resonant converter with effective zero voltage switching (ZVS) is proposed to integrate renewable energy lower voltage source to the microgrid. In this study, duty cycle control is adopted until ZVS fails and thereafter, sequential and parallel adjustment of duty cycle and the switching frequency is proposed for effective output voltage regulation. The proposed control logic ensures ZVS and output voltage regulation over wide load range even at very light loads compared to conventional control methods. Further, it maintains very high system efficiency with narrow range of frequency operation. Hence, it is easy to implement using a conventional digital controller. To minimise ripple current, each of the four converters is provided with phase delayed gate pulses under the proposed control scheme. This study presents an optimal design of the tank circuit elements assimilating high permeable powder cores to reduce magnetic loss and operation with IGBT switches at an optimum point to reduce conduction loss for enhanced system efficiency. A 12-kW, 400–1600 V developed prototype is tested and experimental results are discussed.

For power electronic systems, adding filters to eliminate harmonic interference is a general and effective method, but the position and parameters of filters in wireless power transmission (WPT) system will greatly affect the system characteristics of WPT. The main reason for the harmonic interference in WPT is that the harmonics in the output square wave are loaded on the resonant coil of the transmitter, so in this study, a method of harmonic elimination by adding a second-order LCR filter to the resonant part (LCR-WPT) is studied. However, the WPT resonant part is precisely matched and designed; if a filter is added at the resonant part, it inevitably affects the resonance state, system output power and efficiency of the WPT. To ensure that the LCR-WPT has good system characteristics, this study analyses the mathematical model of the LCR-WPT and deduces a design method for the filter and an efficiency optimisation formula. This study also introduces LCR-WPT applications in two different control schemes. The experimental results show that the harmonic interference of the system is significantly attenuated after the filter is added; additionally, the efficiency of the system decreases by <10%, and the system still maintains sufficient output power.

Hierarchical schemes are widely used for the designing of the inverter-based AC microgrids control strategies. To ensure reliable operation, hierarchical control must consider together all the functionalities that allow the regulation of key variables and guarantee a safe transition between operation modes. Conventionally, in the literature are proposed three-layer schemes which present relevant drawbacks: they include limited functionalities and they use droop method for the primary layer which, despite its decentralised nature, suffers from issues that have motivated the development of alternative strategies. Considering this, the contribution of this study is two-fold. First, a droop-free hierarchical control strategy that satisfies a proper operation of AC microgrids is proposed. Control objectives such as power-sharing, frequency regulation, optimal power dispatch and voltage regulation are considered. Second, a closed-loop small-signal model, which facilitates the control parameters design and fills a gap in the literature is presented. Differences between the proposal and previous controls are discussed. Selected tests are carried out in a laboratory microgrid under different conditions, including normal operation and the response to failures in the central controller and to communication impairments. The experimental results show a good performance of the proposal even in adverse conditions.

To increase the efficiency of the grid-connected inverter, this study proposes an L + LCL-filtered dual-frequency single-phase grid-connected inverter. The proposed inverter consists of the low-frequency unit and high-frequency unit. The low-frequency unit transmits power to the grid at the low switching frequency. The high-frequency unit uses the feed-forward method to eliminate grid switching current ripples without current harmonics detection. The passive damping LCL filter is used to attenuate high-frequency unit switching harmonics. The operation principle of the proposed inverter is analysed, and the parameter design method of the inverter is introduced. An experimental prototype is built to test the performances of the inverter. Simulation and experimental results show that the grid current harmonics are effectively suppressed, and the efficiency of the proposed inverter can be higher than that of the L-type inverter and LCL-type inverter.

Pulse width modulation (PWM) converters generate switching common-mode voltages (CMV) across the load terminals. These voltages cause common mode currents, leading to bearing failure in motor loads and electromagnetic interference problems. This study proposes a novel space vector PWM strategy to reduce the CMV in the dual three-phase permanent magnet synchronous motor (PMSM) driven by two-level six-phase inverter. The novel space vector PWM algorithm discards the use of zero vectors. Firstly, the two largest voltage vectors of each sector are selected as main vectors to synthesise reference vector. Then, three groups voltage vector, which are opposite to the main vectors, have been selected as auxiliary vectors. Appropriate auxiliary vector selected is based on the length of zero voltage vector working time. Next, zero vector working time is distributed to the main and selected auxiliary vectors based on voltage-second principle. In addition, CMV and the harmonic component in z1z2 subspace of the proposed space vector PWM are analysed in detail. Finally, the expected CMV reduction to one-sixth of DC voltage and change rate of CMV in each cycle promised by the proposed novel space vector PWM are demonstrated with simulation and experimental results.

A bridgeless single-ended primary inductance converter (SEPIC) is a highly preferred single-stage front-end AC–DC converter for applications requiring a wide variation of DC voltage because it also gives improved performance in terms of the quality of supply current. This study presents the design of coupled inductors for the bridgeless SEPIC using the split winding scheme. With coupling incorporated the required value of self-inductances of the input and output inductors for the same performance is reduced. Also, they can be wound on the same core, thereby resulting in a reduction in size. The conventional method of tuning the coupling coefficient by adjusting the air-gap is tedious. A split winding scheme for the distribution of windings over three limbs of E-core for obtaining the desired coupling coefficient is presented. The split winding scheme for the design of coupled inductors for bridgeless SEPIC converter rated for 500 W, 20 kHz is illustrated. The effect of coupling on the volume, weight, cost, and efficiency of the converter is compared with the conventional SEPIC converter without coupling for a similar performance. The performance of the proposed converter is evaluated using MATLAB/Simulink simulation and experimental results with a laboratory prototype rated for 500 W.

An improved multilevel inverter (MLI) topology using a new basic unit structure with a reduced number of components is proposed in this study. Its single compact module is made up of two basic units connected to the left and right sides of a packed H-bridge. The topology produces 9-Level output when operated symmetrically and 17-Level output when operated asymmetrically. Identical magnitude of DC sources is used for the symmetrical operation, while non-identical magnitudes in a trinary sequence are used for the asymmetrical operation. The low-frequency modulation scheme is applied for the switching control where the switching angles are pre-calculated. The mathematical formulations for the switching are also considered to reduce the total harmonic distortion (THD) at the output. The proposed topology is also found to be superior in terms of the required number of switches per output level and total blocking voltage compared to conventional and recently reported MLIs. With these merits, real-time installation of the proposed topology will potentially require lesser space and become cheaper. The feasibility of the proposed topology is validated for its 9-Level and 17-Level operations through experimental verification on output characteristics, THD, blocking voltage, power-sharing and efficiency.

In this study, a soft-switched buck converter is proposed and analysed. In this structure, by adding an auxiliary inductor and two auxiliary capacitors, zero-voltage switching condition for switch's turn on and near to soft-switching condition for switch's turn off are provided. Furthermore, the power diode turns off under zero-current switching condition. As a result, switching losses and reverse recovery losses have been eliminated, and the proposed converter can provide high efficiencies. To prove the mentioned advantages, a 200 W laboratory prototype of the proposed converter is built and its results are investigated completely. On the basis of these results, the proposed converter can provide 96.1% experimental efficiency at 200 W output power, which proves the 96.78% theoretical efficiency. Also, in comparison results, it is shown that this converter not only provides higher efficiency in comparison with other structures, but also it has less components and simpler structure than other related buck converters.

Modulated model predictive control (M2PC) approaches have been widely investigated owing to their improved steady-state performance and constant switching frequency operation. However, most of these methods either increase control complexity or cannot obtain optimal solutions under certain operating conditions such as lower modulation index and near the boundary of linear and over-modulation regions. To overcome these limitations, this study proposes a new modulated predictive current control technique based on a novel virtual vector synthesis. The optimal duty cycle is obtained by solving the optimisation problem defined by the cost function. To minimise the tracking error of the input current, a simple non-linearity compensation method for the converter is also demonstrated. The experimental results confirm that the proposed technique significantly reduces the steady-state error of the controlled objective and the ripples in the input current without sacrificing the transient performance compared to other existing M2PC methods.

This Letter proposes a novel control and optimisation strategy for a bi-directional, three-stage, on-board battery charger (OBC) achieving 80 PLUS Titanium efficiency. The proposed strategy utilises the benefits of silicon carbide (SiC) devices and is based on direct current hysteretic control (DCHC) with optimisation of switching patterns and dead time. The OBC first stage is a solid-state transformer that provides the isolation barrier and is operated under zero-current switching/zero-voltage switching (ZVS) conditions. The second stage is a bi-directional buck–boost converter that operates in critical conduction mode (CRM) with automatic dead time optimisation to achieve ZVS operation. The third stage is an H-bridge inverter with a DCHC controlled current loop to optimise dynamic and steady-state performance and provide a smooth transition between CRM and continuous conduction mode. The DCHC is implemented using a hybrid software/hardware approach. The experimental results show that the OBC can not only change the power flow direction within a few milliseconds but can also provide reactive power support for the grid. Additionally, the OBC achieves a peak efficiency of 96.65% and a minimum total harmonic distortion equal to 1%.

The superior power quality of the multilevel inverter (MLI) compared to the two-level counterpart has increased its suitability for medium and high power applications. In the present work, a switched capacitor MLI topology has been presented, which utilises lesser switches and dc power supply and generates a 13-level output voltage. The detailed analysis along with simulation and hardware results have been presented. The comparative performance of the proposed topology has also been presented.