Showing papers on "Inverter published in 2020"

Grid-Forming Inverters: A Critical Asset for the Power Grid

Abstract: Increasing inverter-based sources reduces the system’s inertia resulting in possible frequency stability issues. Understanding low-inertia systems and their stability properties is of crucial importance. This article introduces fundamental ways to integrate high levels of renewable energy (RE) and distributed energy resources (DERs) in the power system while creating a more flexible power system. Using RE and DER in the distribution system has many advantages such as reducing the physical and electrical distance between generation and loads, bringing sources closer to loads contributes to the enhancement of the voltage profile, reduction in distribution and transmission bottlenecks, improved reliability, lower losses, and enhances the potential use of waste heat. A basic issue for high penetration of DER is the technical complexity of controlling hundreds of thousands to millions of inverters. This is addressed through autonomous techniques using local measurements eliminating the need for fast control systems. The key issues addressed in this article include using inverter damping to stabilize frequency in systems with low or no inertia, autonomous operation, methods for relieving inverter overload, energy reserves, and their implementation in photovoltaics (PV) systems. This article provides important insight into the interactions between inverter bases sources and the high-power system. The distinction between grid-forming (GFM) inverter and grid-following (GFL) inverter is profound. GFM inverters provide damping to frequency swings in a mixed system, while GFL inverter can aggravate frequency problems with increased penetration. Rather than acting as a source of inertia, the GFM inverter acts as a source of damping to the system. On the other hand, the application of inverters in the power system has two major issues. One is the complexity of controlling hundreds of thousands to millions of inverters. This is addressed through autonomous techniques using local measurements. The other is the potential of high overcurrent in GFM inverters and techniques for explicitly protecting against overloading. To exploit the innate damping of GFM inverters, energy reserves are critical.

Transformerless Inverter Topologies for Single-Phase Photovoltaic Systems: A Comparative Review

Abstract: In photovoltaic (PV) applications, a transformer is often used to provide galvanic isolation and voltage ratio transformations between input and output. However, these conventional iron- and copper-based transformers increase the weight/size and cost of the inverter while reducing the efficiency and power density. It is therefore desirable to avoid using transformers in the inverter. However, additional care must be taken to avoid safety hazards such as ground fault currents and leakage currents, e.g., via the parasitic capacitor between the PV panel and ground. Consequently, the grid connected transformerless PV inverters must comply with strict safety standards such as IEEE 1547.1, VDE0126-1-1, EN 50106, IEC61727, and $\text{A}S/N$ ZS 5033. Various transformerless inverters have been proposed recently to eliminate the leakage current using different techniques such as decoupling the dc from the ac side and/or clamping the common mode (CM) voltage (CMV) during the freewheeling period, or using common ground configurations. The permutations and combinations of various decoupling techniques with integrated voltage buck–boost for maximum power point tracking (MPPT) allow numerous new topologies and configurations which are often confusing and difficult to follow when seeking to select the right topology. Therefore, to present a clear picture on the development of transformerless inverters for the next-generation grid-connected PV systems, this paper aims to comprehensively review and classify various transformerless inverters with detailed analytical comparisons. To reinforce the findings and comparisons as well as to give more insight on the CM characteristics and leakage current, computer simulations of major transformerless inverter topologies have been performed in PLECS software. Moreover, the cost and size are analyzed properly and summarized in a table. Finally, efficiency and thermal analysis are provided with a general summary as well as a technology roadmap.

Current-driven magnetic domain-wall logic.

Abstract: Spin-based logic architectures provide nonvolatile data retention, near-zero leakage, and scalability, extending the technology roadmap beyond complementary metal-oxide-semiconductor logic1-13. Architectures based on magnetic domain walls take advantage of the fast motion, high density, non-volatility and flexible design of domain walls to process and store information1,3,14-16. Such schemes, however, rely on domain-wall manipulation and clocking using an external magnetic field, which limits their implementation in dense, large-scale chips. Here we demonstrate a method for performing all-electric logic operations and cascading using domain-wall racetracks. We exploit the chiral coupling between neighbouring magnetic domains induced by the interfacial Dzyaloshinskii-Moriya interaction17-20, which promotes non-collinear spin alignment, to realize a domain-wall inverter, the essential basic building block in all implementations of Boolean logic. We then fabricate reconfigurable NAND and NOR logic gates, and perform operations with current-induced domain-wall motion. Finally, we cascade several NAND gates to build XOR and full adder gates, demonstrating electrical control of magnetic data and device interconnection in logic circuits. Our work provides a viable platform for scalable all-electric magnetic logic, paving the way for memory-in-logic applications.

A Single-Phase Transformer-Less Grid-Tied Inverter Based on Switched Capacitor for PV Application

Abstract: In this paper, a transformer-less grid-tied single-phase inverter is proposed which is directly connected to the topology. The voltage across the leakage capacitor has the base frequency, which decreases the leakage current under the defined value in the standards. This inverter’s active switches are high- and low-frequency types. High-frequency switches control the inductor’s current. In addition, the low-frequency switches are synchronous with the grid and operate in the base frequency. Since no power electrolytic decoupled capacitor is utilized between the high- and low-frequency switches, the system’s total efficiency and lifespan are improved. The proposed inverter has the capability of stepping up/down the output voltage, making it suitable for operating in a wide range of voltages and also providing large range of powers to the grid. This topology is directly connected to the grid, without any output filter, leading to elimination of the losses caused by the filter and increased efficiency. In the proposed inverter, a digital current controller is employed to control the injected current to the grid. Furthermore, P&O algorithm is adapted to extract the maximum power from the input source. For proving the proposed converter’s performance, a 770-W prototype has been implemented and comprehensive experimental results are presented.

Doping-free complementary WSe2 circuit via van der Waals metal integration.

Abstract: Two-dimensional (2D) semiconductors have attracted considerable attention for the development of ultra-thin body transistors. However, the polarity control of 2D transistors and the achievement of complementary logic functions remain critical challenges. Here, we report a doping-free strategy to modulate the polarity of WSe2 transistors using same contact metal but different integration methods. By applying low-energy van der Waals integration of Au electrodes, we observed robust and optimized p-type transistor behavior, which is in great contrast to the transistors fabricated on the same WSe2 flake using conventional deposited Au contacts with pronounced n-type characteristics. With the ability to switch majority carrier type and to achieve optimized contact for both electrons and holes, a doping-free logic inverter is demonstrated with higher voltage gain of 340, at the bias voltage of 5.5 V. Furthermore, the simple polarity control strategy is extended for realizing more complex logic functions such as NAND and NOR.

Five-Level Transformerless Inverter for Single-Phase Solar Photovoltaic Applications

Abstract: Transformerless inverters are extensively employed in grid-connected photovoltaic (PV) generation systems due to its advantages of achieving low cost and high efficiency. However, the common-mode voltage issues have been motivated the proposition of new topologies, control, and modulation schemes. In common ground PV inverters, the grid neutral line is directly connected to the negative pole of the dc bus. Therefore, the parasitic capacitances are bypassed and the leakage current can be eliminated. In this paper, a five-level common ground transformerless inverter with reduced output harmonic content for PV systems is proposed. In addition, the proposed inverter can process reactive power and it presents a maximum dc-voltage utilization in opposition to half-bridge-based topologies. The operation modes of the proposed inverter, a simple modulation strategy, as well as the design guidelines are analyzed in detail. Finally, experimental results demonstrate the feasibility and good performance of the proposed inverter.

A Seven-Level Inverter With Self-Balancing and Low-Voltage Stress

Abstract: Based on the switched-capacitor (SC) principle, a seven-level inverter is proposed, which can synthesize seven levels containing a single dc source. Moreover, it can further generate more levels by a cascaded extension. Meanwhile, the proposed topology does not require any sensor due to the use of SC technology. Furthermore, the capacitor voltage is self-balanced without utilizing the complicated control strategy and additional control circuits. The phase disposition pulsewidth modulation is adopted to reduce the total harmonic distortion. The topology can generate different levels with a wide range of modulation index. In addition, the topology can also work in overmodulation. Compared with the traditional SC multilevel inverter, the absence of H-bridge makes low-voltage stress in proposed topology. The voltage stress of all switches is not more than the input voltage. Operational principles, modulation strategy, and voltage stress analysis are discussed. Simulation and experiment are conducted in low power to verify the feasibility of the proposed topology.

Overview on Grid-Forming Inverter Control Methods

Abstract: In this paper, different control approaches for grid-forming inverters are discussed and compared with the grid-forming properties of synchronous machines. Grid-forming inverters are able to operate AC grids with or without rotating machines. In the past, they have been successfully deployed in inverter dominated island grids or in uninterruptable power supply (UPS) systems. It is expected that with increasing shares of inverter-based electrical power generation, grid-forming inverters will also become relevant for interconnected power systems. In contrast to conventional current-controlled inverters, grid-forming inverters do not immediately follow the grid voltage. They form voltage phasors that have an inertial behavior. In consequence, they can inherently deliver momentary reserve and increase power grid resilience.

A New Switched Capacitor 7L Inverter With Triple Voltage Gain and Low Voltage Stress

Abstract: In this brief, a new switched capacitor based multilevel inverter topology is proposed. The proposed topology generates seven level (7L) output voltage using a single dc voltage source along with two floating capacitors. The output voltage of the proposed topology is three-times higher than the input voltage (i.e., gain factor of $\text{V}_{\mathrm{ in}}$ : $\text{V}_{\mathrm{ out}} = 1:3$ ) along with self-voltage balancing of capacitors. The proposed seven level triple voltage gain boost inverter (7L-3GBI) inherently generates a bipolar waveform without backend H-bridge that reduces the total standing voltage of the topology. The practicability of the proposed topology has been demonstrated by having a quantitative and cost comparison with similar topologies. Furthermore, the workability of the proposed 7L topology has been validated through different results taken from a prototype laboratory setup.

Modelling, Implementation, and Assessment of Virtual Synchronous Generator in Power Systems

Abstract: As more and more power electronic based generation units are integrated into power systems, the stable operation of power systems has been challenged due to the lack of system inertia. In order to solve this issue, the virtual synchronous generator (VSG), in which the power electronic inverter is controlled to mimic the characteristics of traditional synchronous generators, is a promising strategy. In this paper, the representation of the synchronous generator in power systems is firstly presented as the basis for the VSG. Then the modelling methods of VSG are comprehensively reviewed and compared. Applications of the VSG in power systems are summarized as well. Finally, the challenges and future trends of the VSG implementation are discussed.

A New Transformer-Less Five-Level Grid-Tied Inverter for Photovoltaic Applications

Abstract: A new fundamental structure of a single-phase transformer-less grid connected multilevel inverter based on a switched-capacitor structure is presented in this study. By employing the series-parallel switching conversion of the integrated switched-capacitor module in a packed unit, attractive features for the proposed inverter can be obtained such as high efficiency and boosting ability within a single stage operation. Also, using a common grounding technique provides an additional advantage of reducing the leakage current. Moreover, the presented structure generates a multilevel waveform at the output voltage terminals which reduces the harmonics in the system. A peak current controller is utilized for triggering the gate of the power switches and controlling both the active and reactive powers. This results in a tightly controlled current with an appropriate quality that can be injected to the grid using a single source renewable energy resource. Operating procedures, design considerations, comparison studies and test results of a 620 W prototype are also presented to validate the accuracy and feasibility of the proposed multilevel inverter.

Reduced-Order Transfer Function Model of the Droop-Controlled Inverter via Jordan Continued-Fraction Expansion

Abstract: This article proposes a reduced-order small-signal closed-loop transfer function model based on Jordan continued-fraction expansion to assess the dynamic characteristics of the droop-controlled inverter and provide the preprocessing method for the real-time simulation of power systems. Firstly, dynamic phasors, time delay and zero-order hold are embedded into the small-signal model at the same time, then the closed-loop transfer function of the droop-controlled inverter is built. Compared with the existing closed-loop transfer function approaches, the accuracy of the built transfer function model is dramatically enhanced. Meanwhile, the inner cascaded voltage/current controller parameters are also designed. In order to directly obtain and preserve the maximum overshoot and settling time, which are main features to evaluate the system input-output dynamic response characteristics, the reduced second order closed-loop transfer function is proposed through the continued-fraction expansion regarding arbitrary points on the real frequency axis. Therein, this second order closed-loop transfer function with dynamic response of the original inverter is reduced to the lowest order. Furthermore, combined with the impedance-based approach, the proposed stability assessment approach is utilized to analyze the stability of the microgrid with multiple converters. Finally, simulations and experimental results demonstrate the convenience and accuracy of the proposed approach.

An Improved Seven-Level PUC Inverter Topology With Voltage Boosting

Abstract: In this brief, a seven-level (7L) improved packed U-cell (IPUC) inverter with reduced power electronic components is proposed. The presented IPUC inverter has low voltage stress on switches and is capable of voltage boosting. A new voltage balancing method based on logic form equations is developed for regulating the inherent floating capacitor voltage to half the input dc voltage. The proposed 7L IPUC is compared with other state-of-the-art 7L inverters in terms of number of IGBTs, blocking voltage, and driver circuits for attesting its superior merits. The performance of the proposed voltage balancing is verified through a laboratory prototyped 7L IPUC inverter considering varying load conditions and the corresponding results are elucidated.

A Wireless Power Transfer System With Dual Switch-Controlled Capacitors for Efficiency Optimization

Abstract: This article proposes a novel wireless power transfer (WPT) system with switch-controlled capacitor (SCC) where variable capacitance and efficiency optimization are realized. The optimum asymmetrical voltage cancellation (OAVC) control is applied to realize wide-ranging soft-switching operation for the active bridge converters. The pulsewidth of the active bridge inverter regulates the output voltage, and the pulsewidth of the active bridge rectifier optimizes power delivery efficiency. The SCCs in the transmitter and the receiver sides are regulated for the zero-voltage switching operation and the resonant condition, respectively. The online estimation of mutual inductance is carried out to adapt the coupling deviations of the WPT system in real time. A 650-W prototype is built to verify the feasibility of the proposed WPT system and the effectiveness of the OAVC control. The experimental results show quite good performance and efficiency improvement for the WPT system at various loads.

Design and development of symmetrical super-lift DC–AC converter using firefly algorithm for solar-photovoltaic applications

Abstract: The super-lift technique is an exceptional contribution to DC-DC conversion technology. A replacement approach of symmetrical super-lift multilevel inverter (SLMLI) DC/AC technology is proposed with a reduced number of elements compared with the traditional multilevel inverter. In this method, the firefly algorithm conveys a leading task for the SLMLI topology for solar-photovoltaic applications. It generates low distortion output and consumes the harmonic band of the fast Fourier transform framework by the employment of the proposed algorithm. The simulation circuit for 15 levels output uses single switch super-lift inverter feed with different kinds of load (R, RL and RLE) conditions. The power quality is improved in SLMLI with minimised harmonics underneath the various modulation indices while varied from 0.1 up to 0.8. The circuit is designed in a field-programmable gate array, which includes the firefly rule to help the multilevel output, to reduce the lower order harmonics and to find the best switching angle. As a result, the minimum total harmonic distortion from the simulation and hardware circuit is achieved. Due to the absence of bulky switches, inductor and filter elements expose the effectiveness of the proposed system.

An Online Data-Driven Method for Simultaneous Diagnosis of IGBT and Current Sensor Fault of Three-Phase PWM Inverter in Induction Motor Drives

Abstract: This article presents an online data-driven diagnosis method for multiple insulated gate bipolar transistors (IGBTs) open-circuit faults and current sensor faults in the three-phase pulsewidth modulation inverter. The fast Fourier transform (FFT) algorithm is used to extract the fault frequency spectrum features of the three-phase currents. Then, a feature selection method named ReliefF is introduced to select the most critical features by removing redundant and irrelevant features. In addition, as novel fast learning technology, a random vector functional link network is applied to learn the faulty knowledge from the historical dataset. Based on the well-learned model, the fault type and location of the converter can be accurately identified as long as the three-phase current signals are measured. Offline test results verify that the proposed method can identify the IGBT and sensor faults with an accuracy of 98.83% and outperforms the state-of-the-art learning algorithms. Moreover, the real-time hardware-in-the-loop test results show that the proposed method can successfully identify the IGBT faults and current sensor faults within 22 ms. It is robust to the dc-link voltage fluctuations, model parameters, and speed or load variations. The extensibility of the proposed method is also validated based on the test results in terms of other fault modes and drive systems.

Device and Circuit-Level Assessment of GaSb/Si Heterojunction Vertical Tunnel-FET for Low-Power Applications

Abstract: This article investigates the performance of a vertically grown GaSb/Si tunnel field effect transistor (V-TFET) with a source pocket to enhance the performance of the device. The commercially available Silvaco TCAD has been used for simulating the proposed V-TFET structure. A low bandgap material, GaSb, is used in the source region for the first time to enhance the carrier tunneling through the source (GaSb)-channel (Si) heterojunction. The proposed V-TFET with a pocket shows the improved subthreshold swing (SS) of 26 mV/decade at ${V}_{{\textit {DS}}}= 0.5$ V over the V-TFET without any pocket. The effects of temperature on SS and ${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ ratio along with the analog/RF figures of merit (FOMs) are also analyzed for V-TFETs with and without a pocket. The results are also compared with some recently reported TFETs. The dc and analog/RF performances of V-TFET with a pocket are shown to be better than those of the V-TFET without a pocket and other reported TFET structures. Finally, the applications of V-TFETs with and without a pocket in designing inverter and ring oscillator circuits have been demonstrated. The dc and transient responses of the V-FET-based inverter and ring oscillator circuits have been analyzed using the Verilog-A model in the CADENCE tool.

Review and Comparison of Grid-Tied Inverter Controllers in Microgrids

Abstract: Grid-tied inverters are widely used for interfacing renewable energy sources or storage devices to low-voltage electrical power distribution systems. Lately, a number of different control techniques have been proposed to address the emerging requirements of the smart power system scenario, in terms of both functionalities and performance. This article reviews the techniques proposed for the implementation of current-controlled or voltage-controlled inverters in microgrids. By referring to a voltage source inverter with an ${LCL}$ output filter, different control architectures are classified as single, double, and triple loop. Then, the functionalities that are needed or recommended in the grid-connected, islanded, and autonomous operating modes of the grid-tied inverter are identified and their implementation in the different control structures is discussed. To validate the analysis and to better illustrate the merits and limitations of the most effective solutions, six control strategies are finally implemented and experimentally compared on a single-phase, grid-connected inverter setup.

Simultaneous Common-Mode Voltage Reduction and Neutral-Point Voltage Balance Scheme for the Quasi-Z-Source Three-Level T-Type Inverter

Abstract: The conventional three-level inverter only has voltage buck capability. The quasi-Z-source three-level T-type inverter (QZS 3LT $^2$ I) has been proposed to realize voltage buck–boost operation. In this paper, we further propose a novel modulation scheme for the QZS 3LT $^2$ I to realize voltage boosting, reduce the common-mode voltage (CMV), and control the neutral-point voltage balance simultaneously. The proposed scheme adopts a large vector, a medium vector, a small vector with low CMV magnitude, a zero vector, and a shoot-through vector to generate the output voltage. According to sector number and neutral-point voltage difference, a p-type or n-type small vector with low CMV magnitude is properly selected to balance the neutral-point voltage. Shoot-through states are inserted within zero vector to boost the dc input voltage without affecting the ac output voltage. Dwell times of basic vectors are calculated through the revised volt–second balance equation. Furthermore, a coordinate control strategy between neutral-point voltage balance and voltage boosting is proposed. Doing so, the CMV magnitude can be restricted within one-sixth of dc-link voltage and neutral-point voltage imbalance can be effectively mitigated. The effectiveness of the proposed scheme is verified by simulations and experiments.

Sequence-Based Control Strategy With Current Limiting for the Fault Ride-Through of Inverter-Interfaced Distributed Generators

Abstract: Three-phase three-leg inverters represent the majority of inverters that are integrated into low voltage power grids. They can develop positive- and negative-sequence components during unbalanced conditions including asymmetrical faults, but not zero-sequence components. This indicates that a sequence-based control strategy is required for comprehensive control of inverter currents and voltages. Positive- and negative-sequence components must be controlled separately with their own dedicated controllers in such a scheme. Given this critical need, a sequence-based control technique for grid-forming and grid-feeding inverter-interfaced distributed generators is proposed. As a necessary part of the fault ride-through capability of inverter-interfaced distributed generators, a current limiter is developed, which can limit inverter currents at a pre-defined threshold for both balanced and unbalanced faults. Whilst the current regulators work in the synchronous reference frame with simple PI controllers, the limiter works in the natural reference frame and thus treats each phase current separately, which results in current limiting at the threshold for all phases. The advantage of the proposed limiter is that it acts instantaneously such that the inverter current can be limited from the start of the disturbance. The simulation results in MATLAB/SIMULINK reveal promising performance of the proposed control strategy with the proposed current limiting.

Finite Control Set Model Predictive Control for LCL-Filtered Grid-Tied Inverter With Minimum Sensors

Abstract: Recently, finite control set model predictive control (FCS-MPC) has been successfully applied in the grid-tied inverter with the LCL filter. However, to achieve active damping and grid synchronization, many sensors are required, increasing cost, and complexity. In addition, a considerable computational delay should be addressed when it is experimentally implemented, which may degrade the performance of the overall system. In order to reduce the number of sensors, eliminate the computational delay, and enhance the control reliability of the system, a novel FCS-MPC strategy with merely grid-injected current sensors is proposed, which contains four compositions: virtual flux observer, state observer, delay compensation, and FCS-MPC algorithm based on estimations. A 3-kW/3-phase/110-V experimental platform is established to validate that utilizing the proposed observations-based control method with only grid-injected current sensors is capable to obtain satisfactory performance of grid synchronization and high-quality grid-injected current both under balanced and unbalanced grid voltage condition.

A New Switched-Capacitor Five-Level Inverter Suitable for Transformerless Grid-Connected Applications

Abstract: Transformerless grid-connected inverters have been extensively popular in renewable energy-based applications owing to some interesting features such as higher efficiency, reasonable cost, and acceptable power density. The major concern of such converters is the leakage current problem and also the step-down feature of the output voltage, which causes a costly operation for a single-stage energy conversion system. A new five-level transformerless inverter topology is presented in this study that is able to boost the value of the input voltage and can remove the leakage current problem through a common-ground architecture. Here, providing the five-level of the output voltage with only six power switches is facilitated through the series–parallel switching of a switched-capacitor module. Regarding this switching conversion, the self-voltage balancing of the integrated capacitors over a full cycle of the grid's frequency can be acquired. Additionally, to inject a tightly controlled current to the local grid, a peak current controller-based technique is employed, which can regulate both the active and reactive power support modes. Theoretical analyses besides some experimental results are also given to corroborate the correct performance of the proposed topology.

On Grid-Interactive Smart Inverters: Features and Advancements

Abstract: Traditionally, a grid-interactive inverter providing ancillary services is called a smart inverter. However, broader features will be required for the next generation of inverters that can be categorized as self-governing, self-adapting, self-security, and self-healing. For grid-interactive inverters, the self-governing feature can be identified as the capability of inverters to operate in grid-following and grid-forming control modes, where the self-adapting is referred to as more flexibility realized by adaptive controllers for stable dynamics of inverters under various grid conditions. Moreover, for supervisory control and economic dispatch in a grid with high-penetration of inverter-based power generators, a minimum communication might be necessary, but it can place grid-interactive inverters in danger of being hacked when self-security becomes essential to identify malicious setpoints. Furthermore, the self-healing is defined as fault-tolerance and stress reduction under abnormal conditions. It suggests that after realizing these features, an inverter is called a smart inverter. In this paper, the advancements toward achieving these features for grid-interactive inverters are reviewed.

High Gain Active Neutral Point Clamped Seven-Level Self-Voltage Balancing Inverter

Abstract: This brief presents a novel seven-level (7L) inverter topology for grid-connected renewable applications. It consists of ten active switches and one inner flying-capacitor unit forming a structure similar to conventional active neutral point clamped inverter. The proposed unique arrangement reduces the number of active, passive components and it does not require any sensor to balance the floating capacitor voltage, thereby reduces cost and complexity in the control system design. In addition, compared to major conventional 7L inverter topologies, the proposed topology is capable of boosting the input voltage by a factor of 1.5, thereby, eliminating the need for an intermediate boosting stage. In other words, it reduces the dc-link voltage requirement by 50%. To prove the advantage of the proposed topology over other recent topologies, a comparative study in terms of power components and cost is presented. The operation and performance of the proposed topology for various loading conditions are validated through experimental tests and measurements.

Passivity-Based Design of Plug-and-Play Current-Controlled Grid-Connected Inverters

Abstract: Stable operation of LCL filtered grid-connected inverters can be achieved using active damping. However, the stability can be threatened by non-ideal conditions such as delay in digitally controlled systems and grid impedance variation at the point of common coupling (PCC). In a grid-side current controlled inverter, the computational and pulsewidth modulation delays cause an unintentionally negative virtual resistance when the resonance frequency is higher than one-sixth of the sampling frequency $(f_{s}/ 6)$ . This paper proposes a delay compensation method to address this issue, which can expand the effective damping region up to Nyquist frequency $(f_{s}/ 2)$ . Also, it is shown that the negative real part of the inverter output admittance will make the system unstable under specific grid condition. Therefore, a PCC voltage feedforward method is proposed to cancel the negative real part of the inverter output admittance according to passivity-based stability. Thanks to the proposed methods, the inverter output admittance will be passive in all frequencies and can be connected to the grid regardless of grid impedance. It means that the inverter has robust plug-and-play functionality. The validity of the theoretical analysis and the effectiveness of the proposed approaches are verified using experimental results on a laboratory prototype.

Analysis and Design of a Novel Six-Switch Five-Level Active Boost Neutral Point Clamped Inverter

Abstract: This article presents an analysis and design of a new boost type six-switch five-level (5L) active neutral point clamped (ANPC) inverter based on switched/flying capacitor technique with self-voltage balancing. Compared to major conventional 5L inverter topologies, such as neutral point clamped, flying capacitor, cascaded H-bridge, and ANPC topologies, the new topology reduces the dc-link voltage requirement by 50%. Whilst reducing the dc-link voltage requirement, the number and the size of the active and passive components are also reduced without compromising the reactive power capability. The analysis shows that the proposed topology is suitable for wide range of power conversion applications (for example, rolling mills, fans, pumps, marine appliances, mining, tractions, and most prominently grid-connected renewable energy systems). Experimental results from a 1.2 kVA prototype justifies the concept of the proposed inverter with a conversion efficiency of around 97.5% ± 1% for a wide load range.

Topology and Control of a Four-Level ANPC Inverter

Abstract: Four-level hybrid-clamped inverter is a newly proposed topology that can operate under a wide voltage range without switches connected in series. However, when it is applied in medium voltage high power conversions, the flying capacitors in each phase will occupy a huge volume and a high switching frequency is required to restrain the voltage ripples. In order to overcome this drawback, a four-level active neutral-point clamped inverter is discussed in this paper, which consists of only six switches and no diodes or flying capacitors are required. In order to balance the neutral-point voltages under the full power factor and modulation index range, a capacitor voltage balance method based on carrier-overlapped pulsewidth modulation is proposed in this paper. The upper and lower dc-link capacitor voltages are balanced by zero-sequence voltage injection and the central dc-link capacitor voltage is balanced by adjusting the duty cycles of switching signals slightly. Simulation and experimental results are presented to confirm the validity of this method.

A New Single-Phase Transformerless Grid-Connected Inverter With Boosting Ability and Common Ground Feature

Abstract: A new scheme of single-phase transformerless grid-connected inverter is presented in this article. By employing the series–parallel switching conversion of the integrated switched-capacitor module in a packed unit, some attractive features for the proposed inverter can be obtained. Such promising features can be quantified as more than 97% overall efficiency for a wide range of output power, two-time boosting ability within a single-stage operation and almost total suppression of the leakage current through using the common grounding technique. In this case, a peak current controller strategy is used in order to trigger the gate of power switches and control both the active and reactive powers. Therefore, a tightly controlled current with an appropriate quality can be injected to the grid from a single source renewable energy resource. Operating procedure, design consideration, comparison study, and a 513 W built prototype results are also given to prove the correctness and feasibility of the proposed circuit.

PMSM Open-Phase Fault-Tolerant Control Strategy Based on Four-Leg Inverter

Abstract: Open-phase fault is a common failure in permanent magnet synchronous motor (PMSM), which would degrade motor performance and increase its loss due to the unbalanced phase currents However, conventional fault-tolerant strategies suffer from the tracking problem of sinusoidal current references In this paper, different from previous fault-tolerant strategies, a new fault-tolerant method for open-phase PMSM is proposed by designing a novel transformation matrix for current/voltage references With the new transformation matrix, the voltage/current references in the d–q frame can be transformed to the phase voltage/current references of the two remaining phases With the proposed method, open-phase fault-tolerant implementation can be much easier (proportional-integral controller is enough) and its performance can be much higher Besides, as the tolerant method is designed based on the four-leg inverter, stronger fault-tolerance capability can be obtained compared with the three-phase inverter-based method Finally, the experimental results confirm the validity of the proposed fault-tolerant method

A Novel Configuration of Cross-Switched T-Type (CT-Type) Multilevel Inverter

Abstract: This article introduces a novel configuration of multilevel inverter (MLI) with low number of power electric components. The inverter is a combination of two back to back T-type modules using two cross-connected switches. This inverter can operate using dc sources having either same or different voltage ratings. The proposed inverter can also be extended using cascaded connection to obtain higher voltage levels. This MLI and its extensions are suitable for other applications where high voltage is required. The major feature of this MLI is the formation of negative voltage levels without using any H-bridge circuit. Some other advantages of this MLI are low total harmonic distortion and highly efficient output voltage. A low-frequency modulation technique known as nearest level control is applied to produce the high-quality output voltage. The simulation was done using MATLAB/Simulink, while the hardware prototype is build using TMS320F28335 digital signal processor. The performance of the proposed MLI is validated by obtaining the accurate simulation and experimental results.