Here, a single-stage cascaded H-bridge (CHB) inverter is presented for grid-connected photovoltaic (PV) systems. The CHB inverter has separate DC links and allows individual control of PV arrays. The conversion efficiency is high and the harmonic generation is lower than conventional PV inverters. Although the CHB inverter is a good candidate for injection of solar power into grid, its control issues have not been completely solved. One of the main challenges in the CHB inverter is the harmonic generation when the connected PV arrays to the H-bridge cells have different amounts of insolation. This study deals with the asymmetrical operating conditions of PV arrays (or H-bridge cells) in the CHB inverter and presents an analytical equation for determination of cells’ modulation indices based on PV arrays data. Then, a control loop is added to the tracking algorithm of conventional control systems to determine whether an H-bridge cell is in the linear modulation or not. In the case of overmodulation, the corresponding DC link voltage is increased by the controller to bring it back to the linear region. The validity of new method is confirmed by simulations and experiments on a seven-level 1.7 kW CHB inverter.

This study deals with a speed sensorless induction motor drive (IMD) with efficiency optimisation. This drive is driven by a solar photovoltaic array for water pumping. The elimination of speed sensor increases the robustness and decreases cost of the IMD. The speed estimation is achieved by rotor flux-oriented control in stationary reference frame. Moreover, the parameters, namely stator resistance adaptation, make the system parameters insensitive. The efficiency of the drive system is enhanced by optimising the excitation current by using a particle swarm optimisation technique. The smooth operation of overall system during starting and steady-state condition is simulated in MATLAB/Simulink environment and validated on a prototype developed in the laboratory. The efficiency of the system with loss minimisation technique is compared with the conventional IMD. Simulated results comply with the test results and a comprehensive comparison is made to validate the suitability of proposed system.

Single-phase phase-locked loops (PLLs) are used in various types of power electronics applications, including voltage source inverters, pulse width modulation rectifiers and different types of grid-tied power converter utilities. The orthogonal signal generators (OSGs), used in single-phase PLLs, are generally based on various types of filters, and they need to operate robustly in relation to the grid voltage disturbances and frequency variations. In this study, a novel OSG is proposed based on a modified first-order all-pass filter, which enables the PLL phase detector to operate at different response speeds, tuned by means of a single parameter. The PLL is experimentally verified and compared with a number of conventional solutions. Tests include responses to phase angle disturbances, frequency steps, and PLL input voltage distortions. Results show that a novel OSG filter enables faster PLL responses when compared with several conventional OSG filters, all designed to have the same disturbance attenuation at double fundamental frequency.

In this study, two new high voltage gain dc–dc converters are proposed. In the proposed converters, two coupled inductors are used to increase and decrease the output voltage more than the traditional dc–dc converters in boost and buck operations, respectively. In these converters, by increasing the turns ratio of the coupled inductors, the voltage conversion ratio is increased for the whole range of duty cycles. The proposed topologies are analysed in all operating modes and the values of current stresses of all switches, voltage stresses on all switches, input current ripples and voltage gains are calculated for boost and buck operations. Finally, the accurate performance of the proposed converters is verified through experimental and Power System Computer Aided Design (PSCAD)/Electro Magnetic Transient Design and Control (EMTDC) simulation results.

Grid harmonic interactions due to aggregated flyback micro-inverters are investigated in this study. An impedance-based model based on the Norton model of flyback micro-inverters, which are with quasi-resonant peak-current control, is obtained by adopting the small-signal modelling approach. As a supplement to the existing output impedance modelling of string inverters with linear controllers, further study on micro-inverters under non-linear control is addressed in this study. Based on the derived impedance model, the admittance matrix of aggregated micro-inverters connected to the grid is formulated and the impedance-based analysis of the system stability is also presented. Consequently, by modelling the output admittance of the quasi-resonant peak-current controlled flyback micro-inverters, harmonic interactions with a distorted grid can be effectively forecasted. Results obtained from modelling, analysis and verifications have shown that the proposed method is a simple and valid way of dealing with the harmonic quasi-resonance problems.

This study presents the analysis, design, and implementation of a DC/DC boost resonant-inductor converter with the stable operation when using a sliding-mode control. In addition, the control scheme provides zero-current switching, fast transient response, and soft converter start-up. Thus, the resonant-inductor converter with the proposed control improves notably the performance of the conventional boost converter. The design of the control scheme is facilitated using an averaged large-signal model of the resonant converter. A laboratory prototype is built and tested to validate the expected features of the resonant converter. Selected experimental results are reported and discussed showing an excellent agreement with the results of the theoretical analysis.

Over the recent years, the modular multilevel converter has become the state-of-the-art technology for high-voltage (HV) alternating current (AC) to direct current (DC) converters and also upcoming HV DC to DC converters. Especially modular multilevel converters (MMCs) with half-bridge (HB) sub-modules (SMs) are already widely established. Due to the increasing requirements, such as a DC fault ride through and active DC fault current suppression, also MMCs with full-bridge (FB) SMs become more and more attractive. However, the higher losses of the FB SMs require further optimisation to achieve full market acceptance. With the new hybrid modulation technique, combining the advantages of HB and FB SMs, more efficient DC fault resilient converters can be designed. In this study, a new hybrid modulation technique is investigated and implemented for the new HV DC–DC auto transformer, to create a highly efficient, DC fault resilient HV DC–DC converter. A theoretical loss calculation method for hybrid MMCs is developed. The theoretical analysis is validated by means of a full-scale simulation model.

This study presents a new energy efficient V/f speed control of single-phase induction motor. The method is implemented with a single-phase inverter in which extreme learning machine technique is used to achieve selective harmonic elimination pulse width modulation. The objective is to adjust the speed of the single-phase induction motor while eliminating undesired low-order harmonics. Algorithm is developed using MATLAB/Simulink high-speed adaptation was obtained even at low- and high-speed regions. The results showed the effectiveness of the proposed method. The reduction in the total harmonic distortion is achieved in all operation range of V/f speed control.

One-cycle control technique has been a prominent and suitable solution for improving power quality with the help of three-phase rectifiers. This study proposes a generalised control strategy for the three-phase power factor rectifier based on both the one-cycle control technique and the hybrid pulse-width modulation (PWM) strategy. Improvement of the performance while providing very low-current total harmonic distortion (THD) is achieved with the proposed scheme. Discontinuous and/or continuous PWM operation is possible with advantages of simplicity, robustness, and low cost. Simulation and experimental results confirm the feasibility of the proposed controller.

A change regulation of variation in drain current (dI _D/dt) of silicon carbide (SiC) metal–oxide–semiconductor field-effect transistors (MOSFETs) and their temperature dependencies are examined. Experimental results show that the magnitude of turn-off dI _D/dt decreases with temperature and turn-on dI _D/dt increases with increasing temperature. Further analysis shows that turn-on dI _D/dt is better than turn-off dI _D/dt in terms of temperature dependency and exhibits good linearity. This behaviour results from the positive temperature coefficient of the intrinsic carrier concentration and the negative temperature coefficient of the effective mobility of the electrons in the SiC MOSFET. Other factors that affect the temperature dependency of dI _D/dt, such as supply voltage, load current, and gate resistance, are also discussed. A temperature-based analytical model of dI _D/dt for the SiC MOSFET is derived using fundamental device physics equations. The calculations generally fit the measurements well. These results are beneficial since they provide a potential approach for junction temperature estimation in the SiC MOSFET. In SiC MOSFET-based practical applications, if turn-on dI _D/dt is sensed, then the junction temperature can be derived from the relationship curve of turn-on dI _D/dt versus temperature drawn experimentally in advance.

Planar transformers (PTs) are becoming increasingly popular in high-power density, high-frequency SMPS in recent years due to their unique advantages including low profile structures and excellent thermal properties. This study focuses on detailed investigation of the effects of coil current distribution within each winding layer on leakage inductance and AC resistance of a PT, and an analytical derivation based on variational method is given. Then the optimal current distribution is proposed and verified through 3D finite element analysis simulation and physical experiments. The results show that the leakage inductance and AC resistance can be reduced further by optimising the current distribution. Accordingly, a practical implementation method is proposed to control the current distribution within a winding layer by adjusting the widths of conductors.

Higher transistor density in modern processors leads to an increase in computing power, which results in higher power consumption. To combat this, system-level power saving features like dynamic voltage transitions (DVTs) are introduced where the voltage required by the processor is varied according to computational load. In commercially available systems, the slew rate of the voltage transition is limited, which has the negative effect of increasing computational latency to ensure safe operation of the switch mode power converter. This study addresses the limitations of the existing techniques by introducing an adaptive DVT, which enables finer granularity of the operating voltage levels and promotes greater power savings. The switching surface-based analysis is performed to derive the conditions for (near) optimal voltage transitions constrained by inductor saturation limits. The results of an experimental prototype achieving the fastest safe transition response are shown to correlate well with the analysis across a wide range of DVT conditions.

Standalone power supplies using renewable energy resources become a key solution to address both energy consumption and environmental restrictions in remote locations. These standalone systems are weak low-voltage networks, wherein the presence of heavy non-linear and/or unbalanced loads may adversely affect the output voltage quality. Accordingly, four-leg voltage-source inverters play an important role by providing both balanced and unbalanced loads with clean power and balanced output voltage. The reported work proposes a sliding mode control (SMC) along with an iterative learning control (ILC) for harmonic compensation in the presence of critical load conditions such as unbalanced non-linear loads. Indeed, under substantial disturbances, the ILC harmonic compensator smoothly adjusts the input control signal of the SM controller in such a manner to properly reject the disturbing harmonics. The design methodology of the proposed SMC–ILC control scheme is detailed and its effectiveness is validated through simulation and experimental results.

A comparative study of two adaptive current-mode controllers for a high-order hybrid-type dc–dc boost converter is presented. The implementation of the traditional current-mode controller for this converter requires the knowledge of the nominal value of the load resistance to compute the control signal. As such, it is unable to handle systems with uncertain loads well. To address this, an adaptive law is used to estimate the load conductance in order to generate the reference current input. In this adaptive law, the derivative of the estimator is optimised as well as bounded. Moreover, the converter has two inductor currents which can be used for feedback purposes. Considering this, two adaptive current-mode controllers using the input and output inductor currents of the converter are separately designed to find the most appropriate inductor current for the implementation of the proposed controller. Finally, some simulation and experimental results comparing the performance of the adaptive controller using the output inductor current with that of the traditional current-mode controller are also presented.

A pulse skipping modulation (PSM) strategy is introduced to the primary-side regulating (PSR) fly-back converters operating under light load. The discrete-time state equations of the PSR fly-back converter works in discontinuous conduction mode are discussed. Based on the iterative map, the stability of PSR fly-back converter modulated by PSM scheme is analysed. A self-adaptive modulation factor control technique is proposed in response to the primary side sampling characteristics of the PSR fly-back converters. Theoretic analysis and simulation results show that by utilising the proposed PSM strategy, the power dissipation under light loads can be reduced, and that the modulation factor tolerance is 1.1% by maximum in comparison with its ideal value within 10–100% load range. By optimising the proposed technique, the output voltage ripple under light loads can also be well controlled to <1% (50 mV). The technique is realised by a 1 μm 5 V/40 V/700 V BCD process, and a 5 V/1 A PSR fly-back AC–DC converter prototype is built. The experimental results match the theoretical analysis. The technique proposed is believed to help improving the efficiency for refined regulating method in PSR fly-back converters under light loads.

This study presents a particular fuzzy-logic control (FLC) to produce the maximum power point of the photovoltaic system. The particularity of the single sensor FLC (SSFLC) method uses single current sensor and improves the drawbacks of response time and accuracy of the Perturb and Observe (P&O) method. Compared with the P&O method, the SSFLC improves the response time, precision at steady state and reduces the steady-state oscillation. To confirm its high performance, the proposed SSFLC and P&O algorithms have been evaluated by simulation utilising MATLAB/Simulink under linear and nonlinear profiles of weather conditions. The experimental results demonstrate that the effectiveness of the SSFLC method is an average 95.8% compared to 83.3%of the P&O method.

The contactless rotary transformer has been widely used in rotary ultrasonic machining because of less heat, less vibration, no friction and higher revolving speed. However, the power transfer efficiency of the rotary transformer is rather low. So it is necessary to adopt the method of capacitance compensation to maximum transfer efficiency, and more accurate compensation model will achieve better transmission performance. However, distributed capacitance existing in the primary and secondary winding current compensation models, which will seriously effect accuracy of capacitance compensation. In this study, a new mathematical model of four circuit compensation topologies is proposed, which takes distributed capacitance into consideration. Moreover, a series of experiments are conducted, which focus on the transmission efficiency and output power. The results of experiments have a good consistency with the new model and show higher accuracy compared with the previous models. In addition, the effect of distributed capacitance at different frequencies is also researched.

In this study, the feedback-linearisation (FBL) technique is employed to design a dc–dc boost voltage regulator feeding a grid-tied inverter for photovoltaic (PV) systems. The key feature of the proposed approach is that only a voltage control loop is used to generate the driving signal for the converter and no current control loop is required. Thereby, unlike the cascaded structure, the bandwidth of the voltage control loop can be specified only by the switching frequency as there is no need for an intermediate inner-loop. The major concern of this control scheme is its limited ability to eliminate completely the steady-state error under model uncertainty and unknown disturbance such as the PV current, which is considered as an unmatched disturbance. For this purpose, the unknown perturbation is estimated by a disturbance observer and compensated in the control law to drive the steady-state error to zero. With a fast disturbance estimation, the composite controller is able to retain the nominal transient performance specified with the FBL. The effectiveness of the proposed approach was verified by both simulation and experimental results, and a remarkable agreement was obtained while exhibiting excellent performances.

A third-order boost point of load converter capable of giving higher voltage gain, identical/similar to fifth-order converters, is proposed. In view of the lower order and higher boosting feature, the converter is more suitable to interface the given low voltage source to a high-voltage dc point of load or to a dc-bus. Furthermore, the proposed converter dynamics is simpler as its control-to-output transfer function is free from right half s-plane zeros. Component design expressions are formulated through a steady-state analysis. The boosting factor of the proposed converter is higher than the traditional boost and other reported fourth-order boost converters. The transfer functions are formulated from the state-space model and then a digital controller is designed in the z-domain. The proposed converter features are demonstrated through analysis and then compared with sample experimental observations.

In this study, a no-dead-time modulation method based on the H6 topology is proposed. The main objective is to reduce the total harmonic distortion (THD) of the inverter output voltage and improve the output-voltage waveform quality. On the basis of the working state of the main circuit, the proposed method selects an appropriate switch modulation, thereby realising the objective of not inserting a dead time, most of the time. Simulations and experiments demonstrate that the modulation method suppresses the THD better than the conventional modulation algorithm, at all power factors and power levels. Furthermore, with the increase in power, the output current increases, but the current commutation interval decreases and the output-voltage suppression effect THD is better. It can also be concluded that simultaneously there is a higher DC-link voltage utilisation efficiency in the no-dead-time modulation method than in the conventional modulation method.

Accidents related with high-order harmonic resonance seriously threaten the safety and stable operation of traction power supply systems (TPSSs). Generally, the resonant frequency of a TPSS, which is the crucial information for resonance suppression, cannot be accurately obtained through model-based methods due to the TPSS complexity. This study proposes a direct measuring method that harmonic currents at different frequencies and amplitudes are injected into the TPSS by a harmonic generator (HG). Then, the resonant frequency can be identified by measuring the harmonic response. The HG based on a single-phase cascaded H-bridge converter and its control algorithms are developed. Both simulations on a railway system model and experimental results on an equivalent resonant circuit are carried out to validate the feasibility and effectiveness of the proposed method.

This study presents variable structure system theory based robust integral controllers for class-D power amplifiers. These amplifiers are highly efficient switching type power amplifiers with negligible losses. Sensorless and current feedback based integral controllers with sliding modes are designed to provide robust tracking performance with negligible phase delays and distortions. The methods are capable of providing high-quality outputs by maximising gain and minimising the tracking error and phase shifts. The validity, feasibility and robustness performance of the controllers are investigated through circuit realisations.

Selective harmonic elimination pulse-width modulation (SHE-PWM) works at low-frequency switching, which reduces switching losses, device stress, and increases energy conversion efficiency. So, it can be an effective control strategy for multilevel inverter working on medium-voltage, high-power industrial energy conversion application. It provides desired output voltage by retaining the requested fundamental component as well as eliminating some low-order harmonics. The application of SHE-PWM in industries is having an influence on precise solvability of complex and non-linear equations. This study presents two recently reported optimisation techniques, namely backtracking search algorithm and differential search algorithm (DSA) for obtaining a more accurate solution of the harmonics elimination problem. The superiority of the proposed optimisation algorithms over the well known ancient algorithm such as genetic algorithm, BEE algorithm and particle swarm optimisation have been established by a comparative study with respect to the possibility of attaining global minima, the rank of convergence rate, and inverter performance analysis. Simulation and experimental results validate the efficacy of the DSA optimisation technique for calculating more precise switching angles that totally eliminate 5th- and 7th-order harmonics with fulfilling the requested fundamental component.

The model predictive control (MPC) is a promising control method for cascaded H-bridge (CHB) rectifiers. One well-known MPC method is the finite-control-set MPC (FCS-MPC). However, three main issues arise in FCS-MPC: heavy computational burden, low steady-state performance, and time-consuming tuning work of weighting factor. Here, an alternative MPC method, deadbeat (DB) control with a capability of voltage balance, has been proposed for a single-phase CHB rectifier. The proposed method is based on the DB solution to obtain zero current error at the sampling instant and the use of a redundancy-based modulation strategy for voltage balance, leading to the ease of controller design and elimination of tuning work. The proposed method has been evaluated against FCS-MPC method on a single-phase three-cell CHB rectifier. The experimental results show that a reduced computational burden, an improved steady-state performance, and a comparable dynamic response can be achieved in the proposed method in comparison with FCS-MPC method.

A high step-up cascade synchronous boost DC–DC converter with zero-voltage switching (ZVS) is proposed. The proposed converter is based on the conventional cascade boost converter with a single switch. In the first stage, a boost cell is modified to improve the voltage gain by utilising a coupled inductor. Additionally, turn ratio can be used to adjust voltage gain. In the second stage, a synchronous rectifier is adopted instead of the output diode to improve power efficiency. Moreover, ZVS is achieved using an auxiliary circuit, which consists of a coupled inductor and a small inductor. Therefore, total power efficiency is improved and high voltage gain can be obtained from a low turn ratio. The theoretical analysis and performance are proven from the experiment results using a prototype of the proposed converter with an output of 200 V–200 W.