The conventional microinverters with transformers and multiple-stage system increases the cost, weight and size, lowering the effectiveness and power density of PV system. It is therefore desirable to prevent using these methods for a microinverter. However, extra care must be taken to prevent component stress, excess switching and conduction losses, ground leakage currents and harmonics. Several transformerless buck–boost inverters have lately been suggested to address various issues. Due to the availability of a number of buck–boost inverter-topology for the solar PV system, it is often difficult to identify when to choose the appropriate topology. Therefore, in order to present a clear view of the advancement of transformerless buck–boost inverters for next-generation grid-integrated PV systems, this article seeks to explore multiple buck–boost topologies with an extensive analytical comparison. Computer simulations for the 70 W system have been conducted in PLECS software to strengthen the results and comparisons, as well as to provide more insight into the features of the distinct topologies for the building-integrated photovoltaic implementation. At the later part, voltage and current stress in each component, efficiency and total harmonic distortion of the system are provided with a general summary, as well as, a technology roadmap.

In this article, basic concepts, operating principles and important characteristics of continuous control set-predictive controllers (CCS-PCs) applied to AC motors are explained in detail. Based on the existence or absence of cost function as well as the method used to find the optimal control action, CCS-PCs can be categorised into the following three categories: predictive controllers without cost function, predictive controllers with a cost function (or model predictive controllers) and deadbeat controllers. To identify the advantages and disadvantages of each category, one of the recent algorithms of each category is selected and implemented experimentally. Then, various experimental tests are conducted where performances of all the algorithms are assessed in a comprehensive manner by evaluating stator-flux ripple, torque ripple, stator current harmonics, robustness against parameter changes, computational complexity, memory requirement and torque dynamic response. To achieve general and meaningful conclusions, the analysis is performed on a traditional three-phase two-level voltage source inverter used to control an interior permanent-magnet synchronous motor. Based on the theoretical discussions and experimental results, it is indicated that which category of CCS-PCs can be adopted in high performance AC motor drives.

This study proposes a charging/discharging system of energy storage devices (ESDs) to regulate the voltage of a dc bus. The proposed charging/discharging system is formed by a zeta/sepic converter and a sliding mode controller (SMC). The SMC uses a single sliding surface to regulate the dc bus voltage for the three operating modes of the charger/discharger converter (charging, discharging, and stand-by) and for ESD voltages lower, equal, or higher than the dc bus voltage. This study includes the stability analysis of the SMC and a design procedure of the SMC parameters. The charging/discharging system is simulated in PSIM, where the results confirm that the proposed SMC regulates the bus voltage in charging, discharging, and stand-by modes for different operating points of the system. Finally, the proposed charging/discharging system was constructed for demonstrating the feasibility of the solution for real applications. Moreover, the experimental results obtained in such a platform put into evidence the accuracy of the proposed SMC in regulating the bus voltage in all the possible conditions: bus voltage lower, equal or higher than ESD voltage, and during charge, discharge, and stand-by modes of the ESD.

Low-voltage battery energy storage system and dual active bridge (DAB) converter control method for DC bus connection in DC microgrid. To use power efficiently in a DC microgrid, power must be easily transferred in both directions. DAB converters can easily transfer power in both directions using only the phase shift of the gate at 50% fixed duty on the primary and secondary sides. In the transient state, however, an overcurrent occurs to charge the output capacitor. A soft start algorithm is used to overcome this overcurrent problem. In the conventional method, the control complexity and response characteristics are slow because the duty control is included and the algorithm is performed in several stages. In this study, a gate drive circuit is constructed using a pulse transformer for 50% fixed duty control and short circuit protection. A soft start control algorithm is proposed, including a first-order phase shift scheme for the stable soft start at 50% fixed duty. The 3 kW prototype DAB converter is designed and implemented for bidirectional power conversion testing. The experimental results show that stable power transfer is achieved in the initial transient state through bidirectional output control and soft start.

During voltage sags, distributed generation systems must fulfil specific grid-code requirements for reactive current injection. This ancillary service can produce overvoltage problems in networks operating in unbalanced conditions when the amplitude of one of the phase voltages is higher than the others and a balanced reactive current is injected through large grid impedance. This study proposes a control scheme to avoid these overvoltage problems, thus reducing the risk of cascade disconnection that this incident may produce. The derivation of the control scheme starts from the flexible oscillating-power control, introduces the necessary modifications so that this control meets the grid-code requirements for current injection and combines it with a slope voltage control to achieve a good voltage regulation. A theoretical analysis is included to determine the expressions that quantify the voltage support characteristics of the proposal. Finally, selected experimental results are reported to validate the characteristics of the proposed control.

This study aims at the DC-link capacitor voltage imbalance problem of independent double three-phase common bus five-level neutral point-clamped/H-bridge inverter, which is applied to an electromagnetic launch system under instant high-power and high-current conditions. First, the traditional method of voltage balance strategy based on redundant vectors is described, and the key factors leading to the DC-link capacitor voltage fluctuation is analysed in detail. Second, the objective function is constructed to predict the variation trend of DC-link capacitance voltage difference. Third, an optimised voltage balance strategy is proposed. At first, the optimised strategy calculates the variation trends of the voltage difference for all three-phase switch vector combinations. Then, the results make up a voltage balance finite control set. At last, compare the results in the set to select the vector combination corresponding to the minimum variation for output. Finally, tested by the semi-physical real-time simulation platform, and the proposed optimised voltage balance strategy is verified effective for improving DC-link capacitor voltage imbalance and inhibiting the voltage difference fluctuation.

This study presents a hierarchical control strategy for an auxiliary power unit (APU) for aircraft to coordinate multiple power sources and control developed power electronic interfaces. The study benefits from the presence of a hybrid energy system in paralleled structure to the main generator as the complementary system. The employed structure enhances power quality and improves the voltage profile of the high-voltage DC bus. Furthermore, the developed bi-directional topology provides the possibility of interaction with the grid. Considering the APU features in an aircraft, a hierarchical control strategy with different levels of control, timescale, dynamic response, and significance are developed. The developed controller consists of a power management algorithm in the higher level, and local voltage and current controllers in the lower one. The algorithm aims to maximise the PV sub-system utilisation, overcome voltage fluctuations, increase power density, reduce operation costs, and increase system availability while allowing further development to larger systems. Simulation and experimental results confirm the robustness of the algorithm. The result shows that the proposed power sharing strategy optimises the system utilisation while achieving a high-quality voltage profile under severe fluctuations. Moreover, the stress on the battery pack is reduced to improve the life cycle and reduce operation costs.

This study introduces a dual range flyback converter, which overcomes low efficiency of the conventional flyback converter for universal mains voltages, i.e. 220 and 110 V AC mains. The topology comprises of reconfigurable primary power loops enabled by additional state switches. This combination allows the converter to run in parallel or series modes, enhancing the performance at 220 V AC high line or 110 V AC low line mains. It reduces the voltage rating of devices, supports two working points that operate in boundary conduction mode under fixed frequency and improves the utilisation of the devices. A 100 kHz, 60 W, 110 V AC or 220 V AC to 13 V DC converter has been designed and tested. The experimental results of the proposed converter have been compared against a conventional flyback converter. The results show a small improvement of performance at low voltage (110 V AC) and considerable performance improvement at high voltage (230 V AC): 0.6 and 2.3% efficiency improvement at full load, respectively.

In this study, a novel ‘’ dual-control modulation is proposed for the MHz-level CLLC converters in battery charging applications. Phase shift between the primary and secondary switches is utilised as an additional control variable to effectively reduce the power losses, especially in light- and medium-load conditions. Compared to other state of the art, a more generalised theoretical model is developed to characterise the converter with higher accuracy based on extended harmonic approximation. Furthermore, a numerical algorithm is utilised to thoroughly examine the converter performance under various operating conditions and systematically search for the optimised design parameters under the proposed modulation scheme. The modelling and optimisation are verified by simulation on a 3.3 kW onboard charger design for electric vehicles, which shows an estimated efficiency enhancement between 1 and 4%. Finally, a laboratory prototype has been developed using gallium nitride semiconductor devices, at the resonant frequency of 1 MHz. The converter measured efficiencies are 96.4, 96.2 and 94% for the selected heavy, medium- and light-load conditions, respectively. This system would allow insights into the practical implementation and evaluation of utilising wide bandgap semiconductors to achieve both high power density and enhanced efficiency for emerging power electronic systems.

Recently, LLC resonant converters have attracted significant research from industry and academia for AC–DC and DC–DC power conversion with high efficiency and remarkable power density. They are appealing candidates for numerous vehicular and renewable energy applications including battery chargers for electric vehicles and drivers of LED lights. This study introduces a mathematical model of LLC resonant half-bridge DC–DC converter, which captures its steady-state behaviours for both continuous conduction mode and discontinuous conduction mode operations. One major advantage of the proposed model lies in accurate estimation of the switching frequency of power switches under a wide range of parametric variations. This benefit is, however, not offered by the prevailing method based on the first harmonic approximation (FHA). The analytical derivations of the system's state-space model, as well as equations for calculating the switching frequency by FHA, are discussed in details. For illustration, a 340 W digitally controlled LLC resonant converter is targeted in this study. The simulation analyses of current and voltage waveforms for light and heavy load conditions are presented. Moreover, the experimental results, along with the comparison of switching frequency estimation for both methods, are demonstrated and discussed, which confirms the validity and effectiveness of the proposed model.

In this study, a new transformer-less multi-port dc–dc converter with bidirectional capability is proposed. The proposed converter has dual inputs and dual outputs in which one of the inputs is considered energy storage (ES) such as a battery. Owing to the bidirectional capability, charging and discharging of the ES are provided. In the charging mode, the energy of the regenerative braking can charge the battery. These features make the proposed converter suitable for hybrid energy systems. Continuous charging and discharging current of the battery, low normalised peak voltage stress (NPVS) on semiconductors, and step-up capability are other advantages of the proposed converter. Reduced NPVS causes the semiconductors with low turn-on resistance and reduced rating voltage to be utilised. The performance analysis of the proposed converter in charging and discharging modes is described. Finally, the performance of the converter and mathematical analysis are validated by experimental results.

This study proposes a non-isolated quadratic boost converter (QBC) that features a low-output-voltage ripple with respect to traditional QBCs. This advantage is in contrast with other topologies that require a higher amount of stored energy by capacitors to achieve the same output-voltage ripple specification. This benefit permits to design a compact converter, since the size of capacitors is proportional to their energy storage rating. Moreover, the proposed transformerless topology is suitable for applications that require high-voltage gains as in the case of renewable energy applications. The main properties of the converter are corroborated as well as its advantages by providing mathematical models, analytical waveforms and experiments.

Despite the ability of type-3 phase-locked loop (PLL) to provide zero steady-state error when a three-phase voltage experiences frequency ramp change, its major drawback is slow dynamic performance and instability during voltage sag condition. In this paper, by obtaining the linearised model of PLL, instability associated with the presence of voltage amplitude within the PLL control loop is illustrated. Furthermore, analysis of two common techniques employed in improving PLL stability (high phase margin design and use of phase-lead compensator) is presented and their inapplicability to three-phase type-3 PLL is revealed. Thus, to address the said problems, a gain compensation technique is proposed in this paper. In the proposed approach, the PLL loop gain is adjusted by inserting a DC gain within the PLL control loop when the frequency of supply voltage deviates from its nominal value. The inserted DC gain compensates for reduction in voltage amplitude within the PLL control loop, thus, enhancing PLL's stability especially during voltage sags. Also, the gain increases PLL's bandwidth thereby improving its estimation speed. Effectiveness of the proposed solution is confirmed through experimental studies and it is compared with five existing type-3 PLL schemes and a type-2 PLL.

Commutation torque ripple is an important factor affecting the performance of brushless DC (BLDC) motor drives. In order to suppress this torque ripple, an alternating conduction control strategy between the two-phase and three-phase conduction mode has been proposed in this study. During the non-commutation periods, the conventional two-phase conduction mode is selected to drive the BLDC motor. While during the commutation period, the commutation torque ripple is reduced by employing an alternating two-phase and three-phase conduction mode. By calculating the duty cycle of the three-phase conduction mode, which indicates whether the rate of change in current in the incoming and outgoing phase is equal during the commutation interval, the commutation torque ripple is effectively reduced, while the current in the non-commutated phase is maintained constant. Simulation and experimental results show that the proposed method can suppress the commutation torque ripple efficiently, particularly at high rotational speeds of the motor.

A novel modulation strategy for improving the voltage gain of a dual-active-bridge converter is proposed herein. Under the strategy, the converter performs a high-voltage gain under a low transformer turns ratio, thereby improving the transmission efficiency of the transformer because the large turns ratio typically results in large parasitic parameters, such as leakage inductance or distributed capacitance. In addition, voltage spikes can be avoided as the energy caused by leakage inductance is recycled to the output side. The operating principle of the proposed modulation strategy is discussed in detail herein. Moreover, the zero-voltage switching conditions in both buck and boost modes are analysed and derived. Finally, a prototype with a 350 V high voltage, 48 V low voltage, and 1 kW output power is established, and the conversion efficiencies of 94.2% in buck mode and 93.2% in boost mode are obtained. Experimental results verify the validity of the proposed modulation strategy.

This paper presents a new mathematical approach to design an asynchronous pulse width modulation (APWM) for the switched mode power supply (SMPS). Unlike the conventional APWM that utilises a Hysteretic comparator based Asynchronous Pulse Width Modulation (HAPWM) to provide the self-oscillating property, the proposed APWM is based on a Binary comparator based Asynchronous Pulse Width Modulation (BAPWM) and a delay cell. This way, compared to the HAPWM, the mathematical analysis of the modulator is significantly simplified. This was achieved by replacing the describing function (DF) -based graphical method with a ?linearised mathematical model. The introduced mathematical approach is extended to study the behaviour of the higher order self-oscillating modulators in terms of the harmonic distortion. To confirm the effectiveness of the analytical derivations, the BAPWMs are employed in a classic DC–DC buck converter and the system-level simulation results are provided. It is concluded that there is an acceptable degree of similarity between the simulation results and the deployed analytical calculations for different orders of the modulators. Finally, to validate these analytical and simulation results and also to compare the BAPWM performance with its HAPWM counterpart, both modulators are implemented using off-the-shelf components and their measurement results are presented.

Three-level dual-active bridge (3L-DAB) DC–DC converter under conventional phase-shift (CPS) control would produce large reflux power and current stress, especially when the voltage conversion ratio is varied in a wider range, which will lead to high power loss and low system efficiency. An optimised phase-shift (OPS) control strategy is proposed to control the 3L-DAB operating at the point with minimum reflux power. The power characteristics of 3L-DAB under CPS control are analysed. Then the mathematical model of the reflux power is established, and the relationship equations among the reflux power, phase-shift (PS) ratios, and voltage conversion ratio are deduced. The minimum reflux power and optimal PS ratio are calculated by using the segmentation optimisation algorithm in different ranges of transmission power and voltage conversion ratio. Performance comparative analysis between CPS and OPS controls is carried out later. Adopting the proposed OPS control strategy, the reflux power of 3L-DAB is minimised, as well as reducing the current stress and increasing the efficiency in a wide voltage conversion ratio range. An experimental prototype was developed to verify the effectiveness of the OPS control strategy and the correctness of the theoretical analysis.

Adjustable speed motor drives are among the most representative types of non-linear systems which can exhibit rich varieties of complex dynamic behaviours. This study presents the investigation of chaotic phenomena in the switched reluctance (SR) motor drive employing digital speed regulator and hysteresis current controller. For conducting stability analysis, a small signal discrete-time model of the SR drive has been derived and analysed for a range of control parameters. The simulation results of time-domain and frequency-domain analysis and phase portraits of the SR drive system are also demonstrated and discussed. Two influencing factors for chaotic behaviour in the SR drive system are identified and examined in detail: the feedback delay of the speed regulator and measurement imperfection from a rotary incremental encoder. For verification, an 8/6 pole 2.3 kW SR drive is employed in experimental tests. The bifurcation diagrams of the reference signal, waveforms of phase current, and the corresponding frequency spectra are recorded and illustrated for both normal and chaotic operations, which reveal the pattern of chaos exhibited from this type of electric drive system.

In this study, a filter-based control scheme is developed for a single-phase grid-connected inverter system with the local load. Improving the quality of the local load voltage in the grid-connected mode and injecting clean current to the grid at the same time is the main objective of the proposed scheme. Moreover, unity power factor at the grid side for different types of the local load is ensured by the proposed controller. Furthermore, this control approach ensures the seamless transfer between grid-connected and stand-alone operation modes without adjusting the controller structure and without any resynchronisation scheme. The proposed scheme is validated by the Lyapunov stability analysis. Moreover, an experimental testbed has been implemented to further validate the controller in the real-time environment, as well as, the performance is compared to a conventional approach.

Inverters as one of the most important elements of power systems have been profoundly developed in recent decades and their performance has attracted researches in control and structure point of view. In this study, a novel structure based on the switch-diode-source cell is proposed for a multilevel converter that is capable of bidirectional feeding. The proposed structure is presented for symmetrical mode and the number of power electronic devices is decreased in comparison with similar works. Considering recent proposed symmetrical structures, the proposed structure has the superior condition in terms of semiconductor switches and drivers count as well as switching loss. Also, total blocked voltage (TBV) of the proposed converter is compared with conventional and novel symmetrical converters. Then, switch costs of the proposed converter are compared with the structure that its TBV is the lowest. The performance of the proposed symmetrical seven-level converter is analysed and simulated in MATLAB/Simulink for both PWM and selective harmonic elimination switching methods. Not only the results are desirable, but also the experimental results of laboratory prototype validate the simulation results.