The practical mid-range wireless power transfer (WPT) system with high-quality resonant tanks is detuned easily due to the variation in parameters of the resonant tanks, leading to degradation of power transfer capability. For this reason, the frequency variation of the mid-range serial-serial (SS) topology WPT system under the condition of self-oscillation is analysed based on Hamel locus approach, considering the delays in devices. The delay-iteration method (DIM) to tune the transmitter (TX) is presented here. Use of this method can keep the overall TX delay equal to the self-oscillating cycle and the TX in the zero voltage switching state. When the DIM is applied, the disturbance observation method can be used to tune the capacitor of the TX, with no communication between the TX and the receiver. The experiment results validate the accuracy and stability of tuning mid-range loose-coupling WPT system using the proposed method.

Full-bridge neutral point clamped (NPC) non-isolated inverter topologies are used to mitigate leakage current at switching frequency due to non-ideal circuit parameters. Among these topologies, this current is the highest in optimised non-isolated inverter (oH5I) despite lowest switch count. This study analyses the limitations of oH5I in mitigating the leakage current by considering the junction capacitance of switches into account. This analysis elucidates the dependency of common-mode voltage (CMV) characteristics on circuit topology and dead time requirement. In order to ascertain this fact, a novel non-isolated full-bridge NPC inverter (NIFB-NPCI) is proposed. The CMV characteristics of this inverter are analysed during mode transitions and compared with that in oH5I. A 1 kVA unified prototype circuit of these inverters is designed and fabricated for experimental validation. The circuit topology and dead time requirement of oH5I cause a spike in CMV during each mode transition. However, these limitations are addressed in the proposed inverter, and CMV is maintained at a constant value. Hence, NIFB-NPCI evinces lower leakage current at switching frequency than oH5I. Therefore, the effect of topological limitation of full-bridge NPC non-isolated inverters on leakage current mitigation is validated.

Brushless DC (BLDC) motors are widely used in various low-power drive applications owing to their several advantages over conventional motors. This study describes a fuzzy logic-based improved loss minimisation technique for the BLDC motor drive system. The proposed algorithm uses selective harmonic elimination-based pulse-width modulation to optimise both the converter switching losses along with machine core and copper losses based on a speed- and load-dependent fuzzy rule matrix. The optimum switching angles eliminating lower-order harmonics are calculated offline and stored in microcontroller memory for online application. The suitability of the proposed control is well demonstrated through simulation and experimental results on a practical 350 W BLDC machine.

Two stage conversion systems (TSCSs) normally use either boost converter or high gain dc–dc converter along with dc–ac inverter in order to transfer power from low input voltage dc source to high voltage ac load. When these TSCSs operate at extremely low input voltages, the boost converter has to operate at extremely high duty ratios. This in turn results in more losses and reverse recovery problems. Usage of high gain dc–dc converter results in more number of components, increase in control complexity and decrease in reliability. Single-stage conversion systems (SSCSs) are formed by merging both dc–dc and dc–ac conversion processes. These SSCSs have advantages like low loss, more compactness and less reverse recovery problems. In this study, a high gain coupled inductor-based single-phase SSCS is presented. This SSCS topology has many desirable features such as high gain, less switching losses, free from leakage inductance adverse effects and compact. Principle of operation, steady-state analysis and design of the proposed topology are described in detail. MATLAB simulation results of the proposed topology and experimental results using DSP28335-based experimental setup are presented to validate the proposed scheme.

A novel and generalised three-phase multilevel inverter (MLI) with a minimum number of switches have been proposed. The number of voltage levels can be increased to a significant value by incorporating few switches and the DC voltage sources. In the proposed three-phase MLI, the number of phase-voltage levels can be increased twice as the number of switches increased. The detailed analysis of the proposed MLI, mathematical modelling of the inverter voltage and the switching loss calculation have been done for a seven-level inverter. Modelling and simulations of the proposed generalised three-phase inverter are carried out using MATLAB/SIMULINK. The simulation results of the proposed multilevel configuration corresponding to the different voltage levels as well as at different modulation index are presented. A laboratory prototype of the proposed five-level inverter has been developed and tested for the speed control of an induction motor. The experimental results for the different modulation indexes are presented, that verifies the simulation results. A detailed comparison of the proposed MLI with the other popular multilevel configuration is presented to reflect the merits of the proposed structure for the reduced component count.

Being one of the most used passive components in power electronics, electrolytic capacitors have the shortest life span due to their wear-out failure which is mainly caused by vaporisation and deterioration of capacitor electrolyte. Knowing these two phenomena increase equivalent series resistance (ESR) of the capacitor, tracking ESR value over the system operating time can be a good indicator for state of health of an electrolytic capacitor. To set the maintenance schedule, various ESR monitoring algorithms have been investigated in literature. These classical real-time algorithms lead the maintenance program to be either risky if the prediction is longer than the actual life-time or more expensive if it is shorter than the actual life span. This study presents a generalised equivalent model using fractional order (FO) element for electrolytic capacitor to estimate the ESR and impedance of faultless running capacitor. Furthermore, a novel failure predictive model using Mittag-Leffler function is proposed to track the ESR increment and estimate the failure time. Hence, the predictive maintenance of the system with capacitors nearing their failure time can be set more precisely. These two FO models are compared against classical ESR and life-time prediction models to illustrate the enhanced performances of the proposed models.

This study presents a backstepping direct power control (BS-DPC) strategy for the grid-connected AC/DC converter under both balanced and unbalanced grid conditions. The proposed BS-DPC adopts the non-linear BS controller to the DPC strategy in the stationary reference frame, thus phase-locked loop is unnecessary. A generalised power compensation method is applied to the proposed BS-DPC under unbalanced grid condition to achieve multiple control targets. To validate the effectiveness of the proposed BS-DPC, comparative experimental studies are conducted under both balanced and unbalanced grid conditions. Experimental results verify that the proposed BS-DPC inherits the excellent dynamic performance of the traditional DPC and has excellent steady-state performance as well. In addition, flexible control targets can be achieved and dynamically adjusted under unbalanced grid condition according to the grid safety operation requirement.

A cascade control strategy is employed in the boost inverter to generate a sinusoidal signal at grid frequency with very low distortion. The internal loop of the cascade employs a switching surface based on the difference of the inductor currents to induce sliding motions in the power stage. The outer loop in turn establishes the reference of the internal loop and ensures the tracking of an external sinusoidal signal at 50 Hz. The reported approach is analytical and is based on the equivalent control method. The root locus of the capacitor voltages at the equilibrium point of the inner loop is obtained assuming a constant value of the loop reference. In the particular case of a zero reference, sinusoidal variations at grid frequency are superposed to the corresponding equilibrium point and the resulting ideal dynamics are linearised yielding the control to output transfer function of the system. A proportional-integral (PI) compensator is designed for both large bandwidth and small phase error. Experimental results in a 500 W prototype are in perfect agreement with the analytical predictions.

A new outdoor photovoltaic (PV) module test platform was introduced to measure I–V characteristic curve of PV module in this study. The proposed test platform was designed centring on the programmable electronic load (E-load) which used the transfer characteristics of metal–oxide–semiconductor field-effect transistor (MOSFET) and controlled PV module output current by controlling the drain current I _D of MOSFET indirectly. Ultimately, controlling the PV module work on any operating point of the I–V curve. This test platform can automatically shift operation mode contraposing the I–V curve of PV module. It can continuously measure I–V curves and ambient data in the outdoors including the total irradiance, temperature of PV module back sheet and ambient temperature. The test results show the proposed test platform's accuracy meets the user's requirements, and more details of I–V curve can be obtained than by using traditional measurement mode.

This study presents a kind of three-phase three-wire double-star-type transformer-less modular multilevel converters (MMCs) in medium-voltage distribution static synchronous compensators (DSTATCOMs) application based on pulse-width-modulated cascaded half-bridge modules. An advanced steady-state analysis for arm current and capacitor voltage is presented to give the explicit converter performance evaluation in project installation. Two key equations based on first and second component equivalent circuits are formulated to obtain the undetermined circulating second harmonic current and actual modulation index. Based on the proposed analysis, the internal active and reactive power control and the external droop control for the voltage at the point of common coupling (PCC) are introduced for MMC-DSTATCOM, respectively. The droop control enlarges the operation area of the converter and the PCC voltage is allowed to vary in a larger acceptable range. Experiment tests acquired from a 60 V/2 kVA prototype in a simplified downscaled power distribution system verify the accuracy of the analysis and the feasibility of the PCC voltage droop control simultaneously.

In this study, the proposed configuration of input-series-output-parallel (ISOP) AC–DC–DC converter consists of a cascaded H-bridge (CHB) rectifier in the AC/DC stage and a parallel DC–DC converter in the DC/DC stage. This study reveals the relationship between input voltage sharing (IVS) and output current sharing (OCS) among the constituent modules. The factors causing DC-link voltage unbalance among series units in CHB rectifier are studied in detail. With the proposed operation method, the power balance including IVS, DC-link voltage balance and OCS can be achieved. In addition, the converter can always operate under a unity power factor with low-distortion grid current. The experimental results are presented to demonstrate the validity and features of the proposed operation method.

The coupled-inductor single-stage boost inverter (CI-SSBI) has been proposed and applied to photovoltaic (PV) power system. As previously presented, the CI-SSBI has the feature of stepping up input voltage to a higher voltage level by properly designing the turns ratio of coupled inductor and regulating the shoot-through duty cycle. The CI-SSBI based grid-connected PV system integrates some characteristics together in one stage, including boost inversion, feeding current into the grid with high power factor, and maximum power point tracking. Moreover, system reliability can be improved by using the shoot-through zero states as a normal operation mode. This study focuses on the power loss analysis of main elements, and control analysis of both bus voltage loop and inner current loop of the proposed PV system. Simulation and experimental results are presented to verify the analysis and show the real system performance.

Single-phase transformerless inverters are widely employed in grid-connected photovoltaic systems, because they are light, inexpensive and most importantly, have high conversion efficiencies. The highly efficient and reliable inverter concept (HERIC) is a well-known topology for transformerless inverters. Theses inverters, however, suffer from high-frequency leakage current generated by parasitic parameters. The mechanism behind the leakage current is described in this study. The concept of tri-direction clamping cell (TDCC) applied to HERIC-based transformerless inverters is proposed to eliminate the leakage current. This is achieved by clamping the freewheeling voltage to the midpoint voltage of the DC bus capacitors. A derived HERIC-based inverter has been selected to be connected with a TDCC that is constructed from three active switches in Y-type connection. This circuit is analysed in detail as an example in order to investigate the circuit performance. The experimental results show that the derived inverter has the advantages of leakage current elimination, high conversion efficiency and low grid current total harmonic distortion.

In this study, a new switched mode power supply (SMPS) for personal computers (PCs) with improved power quality and enhanced output voltage regulation is designed, modelled and implemented in the hardware. The normally used diode converter at the front end of any SMPS is eliminated in the present configuration by making use of two non-isolated power factor corrected (PFC) converters at the front end in a back to back manner. This is followed by an isolated dc–dc converter which yields multiple dc voltages required in the PCs. The front end converter is designed in discontinuous conduction mode with a single control loop to achieve both voltage control and PFC. A fair comparison between the conventional SMPS and the proposed SMPS is made to demonstrate the effectiveness of the proposed configuration which is verified by simulation results and corroborated with experimental results.

This study presents the control and modelling of modular multilevel converter (MMC) with grid-connected photovoltaic system. Synchronisation is an important issue in grid-connected system. Even though conventional proportional–integral (PI) controller used for synchronisation provides adequate performance, it yields poor transient response of the system because of poor tuning of controller gain values. In this study, the fuzzy tuned PI controller is designed and implemented to overcome this problem. The fuzzy logic controller refrains the controller gains based on the operating point of the system. The improved performance parameters such as faster transient response, tracking of the reference current with low overshoot and short settling time with system parameter changes under partial shading of the proposed controller are validated. The results are compared with conventional PI controlled grid-connected MMC with various PI gains. The developed controller algorithm is implemented through TMS320F28335 digital signal processor.

In the stand-alone brushless doubly-fed generator (BDFG) control system, there are two back-to-back converters composed of the machine-side converter (MSC) and the load-side converter (LSC). The LSC is a three-phase AC–DC pulse width modulation converter which usually adopts the double-loop control strategy with outer voltage loop and inner current loop. The introduction of the DC-link current feed-forward for improving the dynamic performance of the LSC can reduce the effect of the load disturbance to the system. However, the DC-link current has a complex harmonic spectrum with the MSC connected to the DC side, so its average value is not convenient to measure. This study presents a DC-link current estimation algorithm for the current feed-forward control in the LSC of the stand-alone BDFG. With the help of the equivalent circuit of the BDFG and the power balance, the rapid calculation of the average DC-link current can be estimated as well. With this estimation of the current instead of the actual DC-link current, the DC-link voltage and AC side current of the LSC can achieve stability quickly. The effectiveness and correction is validated by the simulation and experiments.

In this study, a novel soft-switched high step-up DC/DC converter is presented. This converter is suitable to be employed in photovoltaic and fuel cell systems. The proposed topology is based on coupled inductors and switched-capacitor techniques to provide high step-up gain. Also, due to high conversion ratio, and symmetrical structure of the proposed topology, the voltage stress of semiconductor elements is low; therefore, high performance metal–oxide–semiconductor field-effect transistors with low ON-resistance, and also low-voltage rating diodes can be utilised to reduce the circuit cost, conduction, and reverse-recovery losses which improve the converter efficiency and power density. Furthermore, by adopting an active clamp circuit, the stored energy in the leakage inductance of coupled inductors is recycled and zero-voltage-switching turn-on condition for both main and clamp switches are provided. Operating principle and steady-state analysis of the converter are discussed in detail. Finally, an experimental prototype of the proposed converter with 200 W output power is implemented which verifies the theoretical analysis.

The existing active power decoupling methods for single-phase current source rectifiers (SCSRs) usually involve a lot of additional semiconductor devices or energy storage units, which is adverse to cost and efficiency. This study proposes an active power decoupling method to buffer the double-frequency ripple power. The main circuit is configured by adding only a decoupling capacitor and a diode to the traditional SCSR. Compared with the existing ones, the added components are minimised. The operating principle and modulation scheme are described. A closed-loop control method is developed to enhance twice the line frequency ripple power compensation performance. The guide for the selection of the decoupling capacitance is also discussed. Simulations and experimental results are presented to show the effectiveness of the method.

The gallium-nitride (GaN) cascode switch has received much attention recently for line-operated medium–high frequency (200 to 500 kHz) medium-power (200–1000 W) applications. Owing to its device structure, there are two TO-220 package options available with regard to the tab internal connection, unlike the conventional vertical power MOSFET. It is pointed out in this study that using proper package combination of GaN cascode devices, the electromagnetic interferences can be reduced in power converters/inverters. A 240 W 200 kHz LLC power converter with a front-end power-factor-correction circuit was built for experimental verification of the theory. Significant reduction was observed. Same theory can be applied to other converter/inverter configurations.

In this study, a three-level hysteresis current-control (HCC) strategy is proposed for three-phase four-switch shunt active power filters. The four-switch topology which utilises four switching devices together with two series connected capacitors is able to reduce the cost, switching losses and improve the reliability of system. In this topology, when the current control of phases A and B is achieved successfully, the current control of phase C which is connected to the midpoint of the series connected capacitors is achieved automatically. The current control is achieved by using a three-level HCC strategy. An important consequence of using this control strategy is that it enables access to the zero level of the input voltage of active filter so that a switching device is only switched when the current error is negative, while it remains off when the current error is positive. Furthermore, the imbalance in the capacitor voltages is eliminated by adding a feedback term (the difference in the capacitor voltages multiplied by a suitable gain) to the current control. The proposed control strategy offers a reduced switching frequency, losses and cost. The steady-state and dynamic performance of the proposed control strategy is verified through simulations and experimental studies.

In this study, a new circuit topology of a three-phase half-bridge multilevel inverter (MLI) is proposed. The proposed MLI that consists of a cascaded half-bridge structure along with a modified full-bridge structure requires less number of dc-power supplies and power semiconductor devices, e.g. insulated gate bipolar transistors and diodes when compared with the existing MLI topologies, which significantly reduces the size and cost of the inverter. Two different structures: isolated and non-isolated dc-power supply-based three-phase half-bridge MLIs are investigated. A number of generalised methods are proposed to determine the magnitude of the input dc-power supplies that has a great impact on the number of levels of the output voltage waveform. To verify the feasibility of the proposed MLI topology, a scaled down laboratory prototype three-phase half-bridge MLI is developed and the experimental results are analysed and compared with the simulation results. Experimental and simulation results reveal the feasibility and excellent features of the proposed inverter system.

In this study, a new forward-type resonant bidirectional DC–DC converter is presented. Due to resonant technique and without employing any extra circuit element, zero current switching is achieved for all switches. The converter transformer is forward type and so the converter volume is low. This converter has one magnetic element and the transformer leakage inductance is used as the resonant inductor. Due to zero current switching, this structure is also appropriate for insulated gate bipolar transistor (IGBT) elements. The presented practical results confirm the converter performance.

In this study, the modelling methods are compared in terms of their accuracy and modelling simplicity for different types of components. And the principle of the equivalent circuit model is obtained from reference and is used in the proposed equivalent circuit models of other equipment of HVDC converter stations. Then, all the models are connected into an HVDC system, and simulations are conducted to verify the validity of the proposed model. A comparison with the traditional modelling method shows that the proposed method is more effective for studying entire HVDC converter stations, and is also better suited for equipment building and simulating. Simulation results show that the model is effective and acceptable.

The efficiency of wireless power transmission via electromagnetic induction is strongly dependent on the distance and the lateral misalignment between the sending and the receiving coils. In this study, the authors propose to adopt a multiple-input–single-output (MISO) coil system to increase the efficiency of energy transmission in case of large air gap misalignment between coils. The sending part consists of a matrix of air-core coils, in which only the four coils under the receiving coil, supplied with the same current, contribute to energy transmission. To orientate the magnetic field and to reduce the energy losses, they propose to power the two nearest neighbour coils with low, out-of-phase, excitation current. A simplified analytic model of the multi-coil system configuration is developed, whereas the mutual inductance and the coupling factor are determined by numerical simulations. To validate the analytical and simulation results, an experimental setup was built. Both simulation and experimental results at a distance of 83% of the receiving coil diameter show that the proposed MISO coil system improves the received power and reaches at the same time a much better efficiency than that of two-coil systems.