Nine-switch dual-output inverter stage two-stage matrix converter (NS-TSMC) has been widely applied in dual AC motors drive system, while it has the shortcoming of low voltage transfer ratio. Based on the NS-TSMC, a modified topology, named as series Z-source and nine-switch dual-output inverter stage two-stage matrix converter (ZS-NS-TSMC), is proposed, in which the series Z-source network is connected between the rectifier stage and nine-switch dual-output inverter stage (NS-DOI). In the presented topology, a brief shoot-through vector is employed, which can improve the voltage transfer ratio. Other advantages of the series Z-source network, such as low voltage stress of Z-source capacitor, zero dead-time of NS-DOI and limiting inrush current at startup, are discussed in the study. Furthermore, the dual space vector modulation is presented, which can achieve the merits of unity input power factor, sinusoidal input and outputs. Besides, the sinusoidal outputs, the capability of boosting voltage and adjustable output voltage amplitude are also discussed by the mathematical proof. Finally, an experimental prototype is set up based on the controllers of TMS320F28069 (DSP) and EPM570 (CPLD), the results of which verify the feasibility and desired advantages of the proposed topology and modulation strategy.

Owing to less conduction and switching power losses, the recently proposed Aalborg inverter has high efficiency within a wide range of input DC voltage for single-phase DC/AC power conversion. In theory, the conduction power losses can be further decreased, if an LLCL-filter is adopted instead of an LCL-filter for a voltage source inverter, mainly due to the reduced inductance. The Aalborg inverter shows the characteristic of a current source inverter, when working in the ‘boost’ state. Whether the LLCL-filter can meet the control requirement of this type inverter needs to be further explored. In this study, the small signal analysis for the modified-LLCL-filter-based Aalborg inverter is addressed. Through the modelling, it can be proven that compared with the LCL-filter, the modified-LLCL-filter causes no extra control challenge for the Aalborg inverter, and therefore more inductance in the power loop can be safely saved as well as a complete smaller filter size. A 220 V/50 Hz, 2000 W prototype is used to demonstrate the theoretical analysis.

The prime objective of this study is to achieve a highly efficient and reduced-cost configuration of a solar photovoltaic (PV)-based water pumping system using a canonical switching cell (CSC) converter employing a switched reluctance motor (SRM). A CSC converter with a maximum power point tracking controller utilises a continuous conduction mode (CCM), which helps in power optimisation of PV array and limiting the starting inrush current in the SRM by requisite control. The CCM operation of CSC converter considerably reduces the stresses on its components. The fundamental switching of a mid-point converter lowers its losses and it improves the system efficiency. The proper selection of perturbation size and initial duty ratio of CSC converter provide the soft starting to SRM drive. An experimental prototype of the proposed configuration is developed and it authenticates its suitability over varying irradiance and different environmental conditions.

To support many power management applications in wireless sensor networks, a previously developed model is modified to predict the terminal behaviour of a supercapacitor under a dynamic charging/discharging power profile. In addition, a robust model parameter identification method based on the genetic algorithm is developed to determine the model parameters using a dynamic test and a self-discharge experiment. On the basis of the supercapacitor power input model, charge redistribution related figures of merit are derived and used to evaluate the significance of charge redistribution for supercapacitors with various rated capacitance. The results show that supercapacitors with different sizes share similar charge redistribution phenomenon. Furthermore, the charge redistribution significance is studied from several perspectives to provide guidelines for designing power management techniques that can achieve full potential of the energy stored in the supercapacitors.

The main intent of this study is to integrate a solar photovoltaic (SPV) generating system to three-phase grid and to provide a clean and uninterrupted flow of power at abnormal and peak load conditions. To establish such an interface, a reliable, secure and high-performance control algorithm is the necessity. This study presents a three-phase single-stage grid tied SPV energy conversion system (SPECS) using phase locked loop-less (PLL-less) fast character of triangle function (CTF) control technique. This system configures an SPV array, voltage-source inverter (VSI), ripple filters and three-phase grid with connected linear and non-linear loads. Apart from supplying active power to the grid and connected loads, SPECS also provides functionalities of an active shunt filter such as reactive power compensation, harmonics attenuation, power factor correction, load balancing and zero voltage regulation. This system uses a single-stage perturb & observe approach for maximum power point tracking. Moreover, the VSI control is based on PLL-less fast CTF technique which enhances the functioning of SPECS. The presented system is modelled, designed and simulated on MATLAB/Simulink platform as well as its functioning is validated experimentally on a developed laboratory prototype.

Existing load monitoring methods for induction machines are generally effective, but suffer from sensitivity problems at low speeds and non-linearity problems at high supply frequencies. This study proposes a new non-invasive load monitoring method based on giant magnetoresistance flux sensors to trace stray flux leaking from induction motors. Finite element analysis is applied to analyse stray flux features of test machines. Contrary to the conventional methods of measuring stator and/or rotator rotor voltage and current, the proposed method measures the dynamic magnetic field at specific locations and provides time-spectrum features (e.g. spectrograms), response time load and stator/rotor characteristics. Three induction motors with different starting loading profiles are tested at two separate test benches and their results are analysed in the time-frequency domain. Their steady features and dynamic load response time through spectrograms under variable loads are extracted to correlate with load variations based on spectrogram information. In addition, the transient stray flux spectrogram and time information are more effective for load monitoring than steady state information from numerical and experimental studies. The proposed method is proven to be a low-cost and non-invasive method for induction machine load monitoring.

Industrial power system consists of several linear and non-linear loads. The proliferation of non-linear loads in power system causes the power system harmonics. Passive filters (PFs) are one of the ancient solutions to mitigate the harmonics. Some of the industrial power systems use PFs for harmonic compensation. Owing to dynamic load variation, the PFs are not the appropriate solution for harmonic compensation. To improve the system performance with existing PFs, this study presents the conservative power theory (CPT)-based hybrid active power filter (HAPF) with Type-II current controller for compensation of harmonics, reactive power and also the unbalance caused by different linear and non-linear loads of an industrial power system. In this system, the CPT is used as a harmonic reference generator and Type-II controller is designed for current control operation. The proposed HAPF overcomes the drawbacks of PFs and performs the compensation tasks effectively. The industrial power system with the proposed HAPF is modelled in MATLAB/Simulink environment and implemented in the real-time (RT) using OPAL-RT-based RT simulator. The RT results are in compliance with IEEE 519-2014 standard.

When applying the permanent magnetic synchronous motors (PMSM) to refrigerant system, the suppression of speed ripples of the PMSM in low-feed range becomes the focus of consideration. The authors start with the generation mechanism and the periodical characteristics of the speed ripples to propose an adaptive control method. In the proposed method, the authors place a frequency variable resonance controller in parallel with the conditional proportion and integral (PI) controller to form a PI-resonance (PI-RES) controller. The compensation torque current generated by the resonance controller and the main reference current generated by the PI controller constitute the reference torque current. Because of the existence of the compensation torque current, the electromagnetic torque can follow the variation of the load torque much better, thus the speed ripples are suppressed. Performance indices of the conventional PI controller and the PI-RES controller are compared and evaluated through experimental investigations. The results validate the effectiveness of the proposed method.

Commutation failure, primarily caused by voltage drops and distortion, may lead to high-voltage direct current (HVDC) power interruption and AC system oscillation. To date, there have been few studies on the mechanism and prevention of commutation failure based on voltage distortion caused by harmonics. This study analyses the influence of harmonic voltage on commutation failure based on voltage time area and proposes a method for quantitative analysis of harmonic effects. The analysis shows that limiting the DC current is an effective method to mitigate commutation failure caused by harmonics. A voltage distortion-dependent commutation failure prevention strategy is proposed, and the controller is applied on the inverter side. The selection of parameters is based on the influence of various harmonic orders. The validity and effectiveness of the proposed methods are verified by simulations, which show that voltage distortion-dependent commutation failure prevention strategy can improve the DC system recovery characteristics and suppress subsequent commutation failure caused by harmonics.

A single stage Z-source Neutral-Point-Clamped (NPC) inverter for buck-boost conversion is considered as a better alternative for the two-staged energy conversion in traditional inverters. The Dual Z-Source Network (DZSN) uses two distinct X-shaped impedance networks to connect two individual dc sources to the inverter circuit. The output voltage boosting can be achieved by selectively shooting-through the power sources in the dual networks. This study proposes a novel modulation method for integrating the shoot-through state to the traditional inverter switching. The performance of the proposed modulation method for DZSN is examined utilising attributes which include, voltage boosting, switching losses, efficiency, etc. In addition, this study also deals with non-ideal DZSN, where the circuit resistance and their respective voltage drops are considered. The presented modulation method uses a single carrier signal which is compared with two sets of sinusoidal reference signals to establish the switching. The theoretical findings of the proposed modulation method are verified using Matlab/Simulink and PSIM software. Moreover, an experimental NPC prototype was built and the results for the different values of modulation index are presented, which validate the applicability of proposed modulation method.

Owing to the inherent characteristics of grid-side inverters, a minimum dc-side voltage limit usually exists in grid-connected inverters. To solve this problem, this study proposes a convenient method of designing a novel LCL circuit for a grid-connected inverter, based on an LCL filter. The primary goal is to reduce the minimum dc-side voltage limit, while maintaining a considerably low harmonic content in the grid-side current. The design example of a photovoltaic grid-connected system demonstrates the convenience of the novel LCL circuit design, and the validity and effectiveness of the novel LCL circuit are verified by simulation and experiments.

This study presents a novel single-switch high step-up dc–dc converter employing a quasi-resonant operation with high efficiency and low ripple continuous input current characteristics. In order to achieve a high voltage gain, a combination of coupled inductor and switched capacitor techniques is used in the proposed dc–dc converter. Moreover, utilising a series resonance capacitor with the leakage inductance of the coupled inductor leads to a resonant circuit. Subsequently, by employing a quasi-resonant operation, the switching loss of the proposed dc–dc converter has been reduced significantly. Operational analysis, mathematical derivation, component voltage and current ratings are well demonstrated in this study. Finally, the performance of the proposed circuit is evaluated through a 200 W laboratory prototype with 25 V input voltage and 400 V output voltage. The maximum efficiency achieved at full load is 96.4%.

In this study, a novel zero voltage transition pulse width modulation (ZVT-PWM) DC–DC boost converter with an active snubber cell is proposed. All of the semiconductor devices in the converter turn on and off with soft switching (SS). The main feature of the proposed converter is the absence of extra current or voltage stress on the main switch and main diode. There is also no extra voltage stress on the auxiliary switch and the auxiliary diodes. The main switch turns on with ZVT and turns off with zero voltage switching. The auxiliary switch turns on with zero current switching and turns off with zero current transition. The proposed converter smoothly operates under light-load conditions. Having a simple structure at low cost is the main advantage of the proposed converter. This study also realises the theoretical analysis of the proposed converter. The experimental results, the operating stages and the key waveforms of the proposed converter, are given in detail for 500 W and 100 kHz switching frequency. Moreover, it is shown that the overall efficiency reaches a value of 97.8% at nominal output power. The proposed SS topology can be used in applications with the battery power source and low-voltage DC-link.

Hybrid cascaded multilevel inverters have been recognised as an important alternative in the medium-voltage inverter market due to their high-quality output and outstanding availability. To optimise the performance of voltage-source converters, modulation technologies have attracted more and more attention. With conventional modulation technologies, the switches within a cell are not utilised at a uniform switching frequency, which is not benefit for reliability and modularity. To solve this problem, a modified hybrid modulation strategy based on unipolar frequency doubling is proposed for H-bridge hybrid cascaded inverters. The equivalence of different multilevel carrier-based modulation strategies is revealed and corresponding implement methods are provided. Based on the equivalent hybrid modulation strategy, a modified hybrid modulation strategy is presented by using unipolar frequency doubling. Compared with the conventional modulation strategies, the proposed strategy makes a more uniform use of the switches within a cell. The proposed strategy keeps the output quality and efficiency while the maximum switching frequency is decreased by half. The strategy has been successfully substantiated by the simulation and experimental results of a seven-level hybrid cascaded inverter.