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This article presents a new hybrid three-phase cascaded modular multilevel inverter developed with a reduced switch count concept for harvesting renewable energy. The basic module of the proposed inverter consists of six switches, three asymmetric dc links, and two blocking diodes. The inverter can generate six positive voltage states, which are negatively polarized by the end-side H-bridge unit. As a result, a higher number of voltage levels are obtained with a minimum number of switches that ensure reduced total harmonic distortion in the grid current. Additionally, the proposed inverter can operate at a comparatively lower switching frequency, which decreases the switching losses. Most of the switches in each individual module conduct for a small period resulting in low conduction losses. The reduced switch count with the low switching and conduction losses increases the compactness and the efficiency of the proposed inverter. Multiple high-frequency magnetic links are utilized for the dc sources required for the proposed inverter to achieve inherent dc-link voltage balancing ability and galvanic isolation. The performance of the proposed inverter is validated by simulation and experimental investigations. [ABSTRACT FROM AUTHOR]

In this article, a multioutput-based transformerless hybrid solar inverter (TLHSI) with no right half-plane zero (RHPZ) and reduced common-mode leakage/ground current is presented for photovoltaic (PV) based microgrid applications. In the proposed multioutput TLHSI, two magnetically coupled inductor coils are placed between the input and dc output sides along with a dc-link capacitor to continuously provide the stored energy to the dc load so that the RHPZ is eliminated and, thus, makes it a minimum phase system. Furthermore, a hybrid unipolar sinusoidal pulsewidth modulation technique is established to nullify the high-frequency components of common-mode voltage across the PV to ground stray capacitor. Also, it normalizes both dc and ac loads at the same instant from a single dc input during each operating state of the proposed TLHSI. The shoot-through issue is resolved in the proposed TLHSI, which increases the system reliability. Furthermore, as the deadtime is not required in between the switching pulses, the quality of the inverter output voltage improves. The performance analysis of the proposed TLHSI is compared with the existing topologies. To validate the performance of TLHSI, a scaled down 340 W laboratory prototype is developed. [ABSTRACT FROM AUTHOR]

In this article, a 13-level switched capacitor multilevel inverters (SC-MLI) based single-phase inverter is proposed in which desired levels of output ac voltage are realized with reduced number of switch counts. The proposed inverter requires 12 switches, three diodes, one input dc source, and three capacitors. The requirement of less number of switches reduces the requirement of gate drivers, which enhances power density of converter. The second challenge in SC-MLI is to maintain self-voltage balancing across the capacitors. The self-voltage balancing capability becomes poor at low values of modulation index. The capacitors connected in proposed SC-MLI are capable to maintain the self-voltage balancing without requiring auxiliary circuits or complex control strategies. The operation of capacitors is self-balanced at all regions of modulation index values. The comparison of the proposed SC-MLI is carried out with state-of-art SC-MLIs discussed in the literature using the parameters like peak inverse voltage and total standing voltage. The switches connected in the proposed 13-level SC-MLI undergoes less voltage stress as compared to the SC-MLI configurations discussed in the literature. The proposed SC-MLI is highly competent to achieve good power quality and is capable to ensure voltage balancing of capacitors even at low values of modulation index. The validation of the proposed inverter topology is carried out using a laboratory prototype. The efficiency of the converter claimed using the simulation results is observed to be 96.2% while the efficiency evaluated using the experimental results is 94.1% at 500 W. [ABSTRACT FROM AUTHOR]

An isolated multilevel bidirectional dc–dc converter is presented in this article to interface the low-voltage (LV) battery and the high-voltage (HV) propulsion inverter in electric vehicles. The proposed topology achieves a HV step-up ratio in the motoring mode by reconfiguring two split capacitor half-bridge circuits in series/parallel through the symmetrical modulation of a voltage bidirectional, two quadrant switch. This reconfiguration generates a high-frequency multilevel voltage output at the dc-bus side of the inverter, which reduces the output filter volume. The dc-bus voltage is regulated by the duty cycle modulation of the intermediary switch in the motoring mode, simplifying the sensing and control. During regenerative braking, the converter is operated with phase shift modulation between the HV half bridges and the LV full bridge to regulate the battery voltage. The presented modulation strategies achieve zero voltage switching for the full-bridge devices over a wide load range. A comprehensive analysis of the proposed multilevel converter in motoring and braking modes along with the design constraints and soft switching boundary conditions is presented in this article. Detailed experimental results on a 1.5-kW laboratory prototype are presented to verify the design approach and illustrate the converter performance. [ABSTRACT FROM AUTHOR]

This article presents a novel ring-shaped hybrid fractal antenna for detection of partial discharge (PD) in inverter-fed machines. PD is known as a source of degradation and lifetime reduction in the machines winding insulation. PD activity is becoming a major concern in high performance drives, especially due to the increased use of repetitive impulse voltage with short rise-time (high dv/dt) from pulsewidth modulation-controlled inverters. The proposed hybrid fractal antenna is designed and experimentally demonstrated to show a high sensitivity in the ultrahigh-frequency bandwidth of interest for PD detection as well as an ability to discriminate PD signals from other sources of high-frequency disturbances. Additionally, the proposed PD sensing solution features a unique ring-shape geometry that facilitates its physical integration into a live machine, making it suitable as a noninvasive solution for online condition monitoring and PD detection of any inverter-fed electrical machine. [ABSTRACT FROM AUTHOR]

The integration of single-phase microgrids (MG) and unbalanced loads to three-phase MGs results in power quality issues at the point of common coupling (PCC). These issues include unbalanced voltage, unequal power flow, and inaccurate reactive power sharing. In this article, an energy storage system (ESS) has been proposed with novel control methods to help mitigate unbalance issues in these islanded multimicrogrids (MMGs). It presents two novel control methods: modified reverse droop control and multifunction control to compensate the reactive power of the MMG and generate the needed active and reactive power references of the ESS. The developed control methods mitigate PCC voltage and power unbalance of the MMG and also achieve the load power sharing proportionally among different rated photovoltaics (PV) inverters. In addition, the system stability with the proposed control is also presented under different scenarios. The proposed multifunction controller operation is validated using Opal-RT real-time simulator and experimentally using control hardware-in-the-loop. The results demonstrate that the PCC unbalanced voltage and power are reduced significantly by 97.8%, and the proper reactive power sharing is achieved among the different PV inverters in the proposed system. [ABSTRACT FROM AUTHOR]

Direct electrical heating (DEH) is a well-established method for preventing hydrate formation inside subsea oil transfer pipelines. However, poor efficiency and high reactive power requirement of the existing line-frequency DEH systems have necessitated high-frequency power processing along with reactive power compensation. To meet these design objectives, a dc–ac converter using an LCCL resonant tank is presented in this article to function as a high-frequency alternating current source. The LCCL resonant tank is tuned at the frequency of the maximum tank current gain to maximize the heat generation and reduce the VA rating of the tank. The maximum tank current gain operation also ensures zero-voltage switching of the bridge inverter devices. Detailed frequency domain analysis and design guidelines are presented for the proposed LCCL resonant inverter (RI). Experimental results on a 10-A laboratory prototype and controller hardware-in-the-loop results for a 350-A system illustrate the advantages of the LCCL RI in DEH application. [ABSTRACT FROM AUTHOR]

Impedance-source inverters (ZSIs) are getting more attention in renewable energy generation over conventional inverters due to their inherent boosting ability and shoot-through immunity. However, most of the ZSI expansion abilities are somehow limited by the component stresses and poor performance, particularly at a low modulation index. In this article, a new coupled inductor-based switched quasi-ZSI is proposed to accomplish enhanced boost inversion at a high modulation index. It offers a robust boosting feature even with a very low turns ratio, which significantly reduces the passive circuit element's size. The working principle, steady-state analysis, and the design guidelines for selecting circuit parameters are addressed. The proposed inverter significantly improves the input current ripple with enhanced boosting with appropriate control of the impedance-network active switch. A comprehensive comparative analysis with allied topologies is presented to show the proposed inverter's effectiveness. The superior features offered are more suitable for renewable energy generation from low- and variable-voltage renewable sources, such as solar PV and fuel cells. A laboratory prototype is made for experimental verification. Analytical, MATLAB simulation and experimental results are presented to validate the proposed theory. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) due to high dv/dt pulsewidth modulation has been identified as one of the leading causes of insulation failure in low voltage (LV) variable frequency drive (VFD) fed motors with random wound stator windings. With the recent increase in electrical stress with faster risetime wide bandgap power semiconductor devices and higher dc link voltage for higher efficiency and power density of the system, PD-induced insulation failures are expected to increase. Since LV motor insulation is not resistant to PD, an increasing number of VFD motors are being qualified for PD-free operation. However, the PD inception voltage of qualified motors decreases with insulation aging making LV motors susceptible to failure. In this article, an offline standstill test method is proposed for automated inverter-embedded PD testing under impulse excitation. The main concept is to perform the impulse PD test using the VFD at increased voltage levels for providing advanced warning of PD activity for preventing forced outage of VFD motors. Options for application of increased impulse test voltage and automated detection of PD for implementing the proposed concept are presented. Testing on an 800 V VFD driven motor shows that the proposed method can provide automated impulse PD testing whenever the motor is at standstill to warn the end user of impending PD activity that can lead to failure. [ABSTRACT FROM AUTHOR]

This article presents the design and demonstration of an all silicon carbide (SiC) 2×250 kW dual inverter for heavy-duty traction applications. Through the use of a formal electrothermal-control co-design approach, the maximum power density of the proposed inverter system is 60 kW/L, which is accomplished by. More specifically, to analyze the thermal performance of the inverter, a lumped thermal model is developed based on the characteristics of the power modules and the cold plate. To analyze the complicated interaction between the power losses and module junction temperatures, a closed-loop iterative estimation scheme is proposed to estimate the inverter power loss and module junction temperature. Based on the proposed thermal model and estimation scheme, a detailed optimization procedure on the selection of switching frequency and dc-link capacitor is presented to maximize power density. Furthermore, design optimization of the busbar was conducted to minimize the stray inductance, thus reducing the voltage overshoot during switching transients. Comprehensive experimental studies were performed on a physical converter prototype built based on the optimization results, which validate both the effectiveness of the presented design approach. [ABSTRACT FROM AUTHOR]

The Class-E inverter is appropriate for wireless power transfer system due to its high efficiency and high inverting frequency. Meanwhile, the Class-E inverter is sensitive to the changes in load characteristics, which leads to the weak adaptability to a variable distance of the coupling coils. This article aims at providing a secondary side static zero compensation switching method. The load characteristics based on the S-S (Series-Series) compensation type coupling system were analyzed. It was found that when the compensation capacitor on the secondary side is switched off, the equivalent parameters of the load on the secondary side tend to vary with an increase in coupling strength. At the same time, the equivalent parameters satisfy the conditions where the Class-E inverter works in the ZVS state. The discussion is then extended to the output power and efficiency of the system. The result showed that a significant increase in both output power and efficiency when the coupling strength is far higher than the default standards. The correctness of the theoretical analysis and the feasibility of the method were verified by a 500 kHz experimental prototype with 10 W output while the coupling coefficient varies from 0.02 to 0.07. [ABSTRACT FROM AUTHOR]

Impedance-source-based solar PV systems are capable of achieving both voltage boosting and inversion in a single stage, resulting in a simple design thereby enhancing reliability. One of the major concerns of PV systems is their leakage current, as it can cause hazardous operational insecurity and reliability. This article introduces a quasi-Z-source (qZS)-based five-level inverter, which displays the following advantages: 1) reactive power handling capability, 2) single-stage boosting, 3) shoot-through immunity, and 4) reduced leakage current based on VDE 0126-1-1. The proposed single-stage power converter is constituted by the fusion of a boosting stage, consisting of two back-to-back connected qZSs, with a five-level inverter produced by the combination of T-type and neutral point clamped arms. The problem of the leakage current is addressed by a modified modulation technique and a passive filter structure, which filters high-frequency variations in the common mode voltage. The working principle of the proposed power converter and the effectiveness of the modulation scheme to reduce the leakage current are assessed with the aid of simulation studies in both standalone and the grid-connected modes. The simulation results are experimentally validated with the aid of a laboratory prototype of 500 W rating. [ABSTRACT FROM AUTHOR]

Selective harmonic minimization-pulse amplitude modulation (SHM-PAM) generates a waveform that minimizes some selected low-order harmonics instead of eliminating them completely. This approach is highly beneficial for medium-voltage high-power inverters, where allowable amplitudes for individual harmonics (mentioned in power quality standard) are required with low switching frequencies. This work applies improved SHM-PAM proposing four new types of formulations utilizing quarter-wave (QW) and half-wave (HW) symmetry-based waveforms for three-phase five-level cascaded H-bridge (CHB) multilevel inverter (MLI) to satisfy the requirements of two well-known power quality standards, namely IEC 61000-2-12 and ER G4/5. Recently reported dragonfly algorithm (DA) is used for computing the optimum switching angles and dc-link voltages required to control the CHB MLI. The effectiveness and practicality of the proposed techniques have been investigated through extensive simulations and experimentation on a laboratory scale CHB MLI. While fulfilling the IEC 61000-2-12 and ER G4/5 voltage harmonic standards, the solutions provided by QW and HW symmetry-based waveforms are compared based on several performance indices such as waveform quality and power losses. It is found that HW symmetry waveforms provide better waveform quality and power loss profile than QW symmetry waveforms. The proposed SHM-PAM has also been compared with some existing modulation techniques to justify its mastery. Finally, the practicability of the proposed SHM-PAM technique is verified on an induction motor drive application. [ABSTRACT FROM AUTHOR]

This article presents a current limitation technique for a multiphase bearingless machine featuring a combined winding system. This winding structure allows the machine to produce both suspension force and motoring torque. The main challenges with the combined winding configuration consist of decoupling the suspension force and torque generation and designing a proper current limitation algorithm. The former topic has been already tackled and presented in previous publications, while the latter will be addressed in this article. In particular, the proposed suspension force control technique will allow to prioritize either suspension force or torque generation. In this article, the priority is given to the rotor levitation, hence the suspension force rather than the torque is essential. Finally, simulation results and experiment validation on a $\text{1.5}\,\text{kW}/3000\,\text{r/min}$ prototype machine are provided. [ABSTRACT FROM AUTHOR]