Search Results (24)

Transformerless inverters are increasingly becoming essential in renewable energy generation, particularly for grid-connected photovoltaic (PV) and other sustainable and alternative energy resources. The transformerless designs offer higher efficiency, compact size, and reduced cost compared to traditional inverters with bulky transformers. These inverters minimize energy losses and enable direct connection to the grid by removing the low-frequency transformer. This paper investigates a highly reliable single-phase common-ground inverter for solar panels and other alternative energy generation. The proposed PV inverter has the benefits of existing non-isolated common-ground PV inverters, including direct connection of an input source’s negative terminal to the AC neutral terminal, eliminating leakage ground currents. The inverter is an enhancement of the dual-buck inverter, incorporating one additional diode and a flying capacitor. The dual-buck structure with the inductor inserted between the inverter phase leg prevents short-circuiting. This increases the reliability of the entire power electronics system. Moreover, using external diodes to freewheel the current, the configuration has no reverse recovery issues, allowing power MOSFETs to be employed with safe commutation at higher DC-link voltage and achieve higher efficiency. Summarily, this design prevents short-circuit issues, enhancing reliability and efficiency, and relaxing pulse-width-modulation dead times. The derivation of the PV inverter is carefully analyzed. A 700 W prototype of power converter hardware has been built. The comparative study validates the operational performance, and the grid-connected experiment confirms its theoretical analysis. Experimental results of the hardware prototype are discussed to prove the feasibility and effectiveness of the proposed PV inverter. Full article

This paper presents a systematic experimental comparison of three sliding-mode-based current control strategies—traditional sliding mode control (SMC), fast terminal sliding mode control (FTSMC), and super-twisting sliding mode control (STSMC)—applied to a grid-connected five-level active neutral point clamped flying capacitor (5L-ANPC-FC) inverter. Unlike existing studies that typically investigate a single controller or topology, this work provides a fair, hardware-validated benchmark under identical operating conditions, enabling a clear assessment of convergence speed, harmonic performance, robustness, and implementation complexity. All controllers are designed within a unified framework and their stability is rigorously analyzed using Lyapunov theory. Experimental evaluations are conducted under steady-state operation, step changes in reference current, grid-voltage sag/swell, and DC-link voltage variations. The results demonstrate that while all three controllers ensure robust current tracking and inherent DC-side capacitor voltage balancing without additional control loops, FTSMC achieves the lowest grid-current total harmonic distortion (THD) and fastest convergence. STSMC effectively suppresses chattering, and traditional SMC offers a simple yet reliable baseline solution. The presented findings provide practical design guidelines for selecting appropriate sliding-mode controllers in high-performance multilevel inverter applications. Among the assessed control techniques, FTSMC has the most rapid dynamic response, characterized by a rise time of 0.1 ms and a minimal grid-current THD of 1.95%, indicating exceptional steady-state and transient performance. STSMC markedly diminishes chattering and ripple, attaining a THD of 2.04% with enhanced waveform smoothness relative to traditional SMC. Conversely, traditional SMC offers a more straightforward implementation but demonstrates elevated ripple and THD levels of around 2.29%, along with a peak current inaccuracy of 6–8%. The results underscore the trade-offs between implementation simplicity, dynamic responsiveness, and harmonic performance of the evaluated control techniques. Full article

This article proposes a parallel current-summing LCC multilevel inverter (MLI) to suppress harmonic distortion of radiated EMI for wireless power transfer. Traditionally, ZVS has been an issue for staircase voltage output multilevel inverters because a shared current output became faster than some of the voltage transitions in staircase voltage output. The other common problem was capacitor voltage imbalance and resultant output voltage distortion if a sophisticated voltage balancing function is not used. The proposed LCC MLI ensures ZVS by separating each voltage transition into multiple bridge legs. Each bridge leg outputs different phases of currents for each voltage transition. The individual output currents are summed at the matching network of wireless power transfer, generating a near-sinusoid output current to suppress harmonic distortions. In this way, each leg achieves ZVS even though the summed output current at the LCC network is faster than some of the voltage transitions. To avoid the capacitor voltage imbalance issue, the proposed MLI eliminated the flying capacitor. Instead, the four parallel legs are supplied by a shared DC input link. Therefore, the four legs can output identical voltages without using a typical DC flying capacitor. The necessity of multiple input voltage sources is, therefore, also eliminated. Measurement demonstrates that the proposed method effectively reduces radiated harmonic EMI by up to 14 dB. Full article

In flexible DC distribution systems, the three-phase four-leg (3P4L) converter demonstrates excellent performance in addressing three-phase load imbalance problems, but suffers from DC-side second harmonics and complex multi-parameter control coordination. In this paper, a flying capacitor zero-sequence leg-based 3P4L (FCZS-3P4L) converter is proposed, which introduces the three-level flying capacitor structure into the fourth zero-sequence leg, making it possible to suppress the DC-side second harmonics by using the flying capacitor for energy buffering. Meanwhile, a modulated model predictive control (MMPC) strategy for proposed FCZS-3P4L is presented. This strategy utilizes a dual-layer control strategy based on a phase-split power outer loop and a model predictive current inner loop to simultaneously achieve AC three-phase imbalance current compensation and the energy buffering of the flying capacitor, thereby eliminating the complex parameter coordination among multiple control loops in conventional control structures. A MATLAB-based simulation model and Star-Sim hardware-in-the-loop (HIL) semi-physical experimental platforms are built. The results show that the proposed FCZS-3P4L converter and corresponding MMPC control can effectively reduces three-phase current unbalance by 19.57%, and reduce the second harmonic amplitude by 57%, i.e., decreasing from 14.74 V to 6.31 V, simultaneously realizing DC-side second harmonic and AC-side three-phase unbalance suppression. Full article

The four-level nested neutral point clamped (4L-NNPC) inverter has recently become a promising solution for renewable energy generation, e.g., wind and photovoltaic power. The NNPC inverter can stabilize the flying capacitor (FC) voltages of each bridge through redundant switch states (RSSs). This paper presents an improved three-layer sequential model predictive control (3LS-MPC) method for 4L-NNPCs. This method eliminates weighting factors and removes the switch states that generate high common-mode voltage (CMV). Before selecting the optimal vector, we disable certain switch states which affect the FC voltages, continuing to deviate from the desired value. Then, adopting a two-stage optimal vector selection method, we select the optimal sector based on six specific vectors and choose the optimal vector from the seven vectors in the optimal sector. The feasibility of this method was verified in Matlab/Simulink and the prototype. The experimental results show that compared with classical FCS-MPC, the proposed 3LS-MPC method reduces the common-mode voltage and has better harmonic quality and more stable FCs voltages. Full article

Multilevel inverters (MLIs) have become fundamental in contemporary power electronics, providing enhanced performance compared to conventional two-level inverters regarding their output voltage quality, efficiency, and scalability. This study comprehensively assesses multilevel inverter technologies, including their topologies, control systems, and various applications. The study starts with a comprehensive examination of the core concepts of MLIs, subsequently embarking on a detailed evaluation of both conventional and innovative topologies, such as diode-clamped, flying capacitor, cascaded H-bridge, and modular multilevel converters. The study further examines the control systems used in MLIs, including Pulse Width Modulation (PWM), space vector modulation (SVM), and Model Predictive Control (MPC), emphasizing their benefits and drawbacks. The applications of MLIs in renewable energy systems, electric cars, industrial drives, and grid integration are comprehensively examined. The study closes by examining growing trends, difficulties, and future research paths, emphasizing the ability of MLIs to transform power conversion systems. Full article

The classical four-level nested neutral point-clamped (4L NNPC) inverter-leg is a hybrid of the flying-capacitor and diode-clamped 4L-inverter-leg configurations. Though uniform reduced voltage stress (1/3 of input voltage) on constituting switches is evident in the 4L NNPC inverter-leg, trails of the drawbacks of the diode-clamping concept still exist. With the significantly rated off-the-shelf IGBT switch modules (6.5 kV, 1200 A), chances of deployment of the newly evolved Four-Level Nested T-Type inverter (4L NTTI) in certain applications is high. Compared with the classical 4L NNPC inverter, 4L NTTI involves a smaller number of power switches and low conduction losses. However, in 4L NTTI, two of the six active switches have a blocking voltage rating of 2/3 of the input voltage. Considering this limiting topological feature in 4L NTTI, a six-switch inverter-leg for the four-level active neutral point-clamped (4L ANNPC) inverter is presented in this paper. In the proposed 4L ANNPC inverter-leg, only one switch has a voltage stress of 2/3 of the input voltage. This ameliorated voltage stress translates to low-cost and -loss inverter implementation. The operational characteristics and competitiveness of the 4L ANNPC inverter are analyzed in detail and demonstrated with a prototype. Full article

Conventional 5-level active neutral-point-clamped (5L-ANPC) topology and state-of-the-art 5-level hybrid active neutral-point-clamped (5L-HANPC) topology are popular for inverter applications. However, their dc-link voltage utilization is limited to only 50%. With the maximum voltage level generated by only half dc-link voltage, these inverters are not capable of boosting voltage in their ac output. To resolve these drawbacks, this paper proposes a family of four novel 5-level boost-active neutral-point-clamped (5L-BANPC) inverters. Without requiring any flying capacitors, the proposed topologies can generate five voltage levels by effectively using the dc-link capacitors. The dc-link voltage utilization of the proposed 5L-BANPC inverters is twice that of the 5L-ANPC and 5L-HANPC topologies. While generating the five-level ac output voltage, natural voltage balancing of both dc-link capacitors and voltage boosting are achieved. Ease of implementation is another noteworthy merit of the proposed 5L-BANPC inverters because they can be implemented using six widely available commercial half-bridge modules without requiring a dedicated circuit design. The operation of the proposed topologies is analyzed. Experimental results are presented for verification. Full article

This article presents a comprehensive comparative evaluation of a three-phase Three-Level (3L) Flying Capacitor Converter (FCC) and a Stacked Polyphase Bridge Inverter (SPBI), specifically a converter system formed by two Series-Stacked Two-Level three-phase Converters (2L-SSC), for the realization of a 7.5 kW Integrated Motor Drive (IMD) with a high short-term overload capability. The 2L-SSC requires a motor with two three-phase windings and a split DC-link, but uses standard six-switch, two-level transistor configurations. In contrast, the bridge legs of the 3L-FCC feature flying capacitors whose voltages must be actively balanced. Despite the 800 V DC-link voltage, both topologies employ the same set of 650 V GaN power transistors, i.e., the same total chip area, and if operated at the same switching frequency, show identical semiconductor losses. Electric Discharge Machining (EDM) damage of the motor bearings is a relevant issue caused by the common-mode (CM) voltages of the inverter stage. The high effective switching frequency of the 3L-FCC and the possibility of CM voltage canceling in the 2L-SSC facilitate mitigation of EDM by means of CM chokes, whereby a substantially smaller CM choke with lower losses suffices for the 2L-SSC; based on exemplary designs, the 2L-SSC features only about 75% of the total volume and 85% of the nominal losses of the 3L-FCC. If, alternatively, motor-friendliness is maximized by including DC-referenced sine-wave output filters, the 3L-FCC’s higher effective switching frequency and the 2L-SSC’s need for two sets of filters due to the dual-winding-set motor change the outcome. In this case, the 3L-FCC features only about 60% of the volume and only about 55% of the 2L-SSC’s nominal losses. Full article

In this article, a generalized control scheme is proposed to extend the operating range of three-phase hybrid cascaded H-bridge (HCHB) inverters into various voltage levels without necessitating alterations to the core structure or the integration of additional H-bridge submodules. This study addresses a critical challenge related to capacitor voltage drift at various modulation indices and power factors, which is a serious impediment to various applications. To overcome this challenge, a novel balancing control scheme has been developed based on the injection of two independent offset voltages to simultaneously control the DC-link and flying capacitors. A distinctive aspect of the proposed technique involves adjusting the common reference voltage to attain the nearest level in the same cluster, thereby mitigating the insufficiency of redundant switching states. The effectiveness of the proposed technique to regulate the capacitor voltages at various operating conditions has been verified through simulation and experimental results. Full article

Recently, multilevel converters (MLCs) have gained significant attention for stationary applications, including static compensators, industrial drives, and utility-grid interfaces for renewable energy sources. Compared to two-level voltage-source inverters (VSI) MLCs feature high-quality AC voltage with reduced harmonic content despite the lower switching frequency of the semiconductor devices. On the DC side, MLCs can integrate multiple isolated/non-isolated battery modules instead of a single battery pack. This helps to keep the system in service in case of a malfunction of one or more battery modules, as well as active balancing among the modules, a feature not possible with two-level VSI. In general, MLCs can be classified into two types: (i) two-port MLCs, which provide a single interface to connect with the battery pack, and (ii) multiport MLCs, which provide multiple interfaces to allow connection at the module or cell level. The classical topologies of both MLC types (e.g., neutral point clamped, flying capacitor, cascaded bridge) face limitations due to the high switch count. Consequently, many hybrid and reduced-switch topologies are reported in the literature. This paper presents a critical overview of both classical and recently reported MLC topologies and offers a better insight of MLC operation for grid-connected and standalone applications. In addition, the analysis thoroughly assesses various high-level control and modulation strategies while considering active balancing among the battery modules. Other salient features such as balancing speed during offtake/grid-injection mode and fault-ride-through capability are also incorporated. In conclusion, the key findings are summarized for a better understanding of the present and future integration of battery systems in stationary applications. Full article

Multilevel inverters (MLI) consist of a wide range of power converters. They have many designs and have been introduced with different circuit topologies such as neutral point clamped, diode clamped, cascaded H-bridges, and flying capacitors. Some of these MLIs have disadvantages, including design complexity, size, and losses due to the large number of switching devices required when they produce many output voltage levels. They are also bulky in size and may require several DC power sources. This paper presents a review of the various topologies of single-phase T-Type MLIs (T-MLIs). These MLIs are used to convert DC power from renewable energy sources (RES)” into AC with a near-sine waveform and low total harmonic distortion (THD). Simple and complex MLI designs are discussed. The major types of modulation techniques are discussed, including sinusoidal pulse width modulation (SPWM), selective harmonic elimination (SHE), and preprogrammed PWM. Various methods of output voltage control are taken into consideration as well. The aim of this comprehensive survey is to identify T-MLIs for researchers and those interested in the power conversion field, as well as to discuss the many topologies, identifying designs with superior characteristics that can be efficiently implemented with RESs to obtain better AC voltage with enhanced power quality. Full article

AC loads may demand a fixed or variable voltage at their input terminals. When using inverters to power such loads, the response of the inverter must be precisely controlled to suit the demands of the AC loads. Inverters with higher efficiency and sensitivity will play an increasingly essential role as the need for solar PV applications in prospective green technology grows. To increase power quality and provide a reliable power source, an inverter architecture with harmonic reduction approaches is proposed. The multilevel inverter (MLI), unlike conventional inverters, is developed by cascaded single inverter units and is often used to connect renewable energy sources. As a result, they can be utilized to efficiently reduce harmonics. Among the three topologies, the most widely used in industries is the neutral-point clamped MLI. When the levels are raised, however, they demand a larger number of diodes. When the level of the flying capacitor exceeds three, several capacitors are necessary. As a result, the optimum option for synthesizing the right output voltage from several DC sources is a cascaded multilevel inverter (CMLI). Each link in a CMLI is connected by a single DC source; therefore, there is no voltage imbalance. However, getting equal DC voltages at the input of each unit is once again a limitation. In this work, various existing multilevel inverter topologies including hybrid topologies with different switching strategies are investigated and reported. The performance of a solar PV-based seven-level quasi-Z-source cascaded H-Bridge MLI (qZS-CHBMLI) has been thoroughly examined with the best switching scheme and best topology of multilevel inverters using MATLAB/Simulink. Full article

This paper deals with a reduced switch multi-level inverter for the solar photovoltaic system-based 127-level multi-level inverter. The proposed technique uses the minimum number of switches to achieve the maximum steps in staircase AC output voltage when compared to the flying capacitor multi-level inverter, cascaded type multilevel inverter and diode clamped multi-level inverter. The use of a minimum number of switches decreases the cost of the system. To eliminate the switching losses, in this topology a square wave switch is used instead of pulse width modulation. Thereby the total harmonic distortion (THD) and harmonics have been reduced in the pulsating AC output voltage waveform. The performance of 127-level MLI is compared with 15 level, 31-level and 63-level multilevel inverters. The outcomes of the solar photovoltaic system-based 127-level multi-level inverter have been simulated in a MATLAB R2009b environment. Full article

Grid-connected inverters (GCI) are commonly used in PV system applications to generate a regulated AC current to feed into the grid. Transformerless inverters are the most advanced inverters that are used in industry, which provide efficiency with smaller size and lower cost. This paper proposes a grid-connected single-phase transformerless inverter with the technology of common ground and the virtual DC bus concept. In this topology, the grid neutral is connected directly to the PV ground, which generates a constant common mode voltage (CMV), thus leading to the elimination of the leakage current caused by the PV array’s parasitic capacitance. The proposed inverter has a buck–boost circuit with a flying capacitor to generate the DC bus for a negative power cycle, four switches, and two diodes. A unipolar sinusoidal pulse width modulation (SPWM) technique is used which reduces the output filter requirements. In addition, only one switch carries the load current during the active states of both the negative and positive power cycle, thus minimizing the conduction losses. One more advantage presented in the proposed inverter is its ability to charge the flying capacitor during all operation states due to the existence of the buck–boost circuit. Design and theoretical calculations were conducted in this paper to optimize the losses. Moreover, the PSIM simulation was used to validate the proposed topology inverter, verify the performance by showing leakage current elimination, and achieve unipolar voltage in the output bus. The simulation results show a peak efficiency of 98.57% for a 2 kW inverter, which agrees with the theoretical calculations. Full article