Three-level Converter Research Articles

A Novel Analysis of the Influence of Zero-Axis Control on Neutral-Point Potential Self-Balancing of Three-Level Converters

The neutral-point potential balance issues in three-level converters have obtained great attention. The popular view thinks that the neutral-point voltage deviation can be suppressed by regulating the injected zero-sequence component, whether via carrier modulation or space vector modulation techniques. However, this paper presents a novel finding: the efficacy of different frame controllers on the self-balancing of neutral-point potential in three-level converters differs when a comprehensive analysis of zero-sequence dynamics, including neutral-point current and PWM modulation, is conducted. That is, the proportional-resonant (PR) controller in the abc frame effectively introduces a zero-axis PR control of the zero-sequence component, which subsequently degrades the stability of neutral-point potential self-balancing. In contrast, the PI control in the dq frame does not incorporate any additional control of the zero-sequence component, thereby enhancing the self-balancing capability of the neutral-point potential. To substantiate this novel finding, a series of simulations and experimental validations were performed.

6.5 kV SiC PiN and JBS Diodes’ Comparison in Hybrid and Full SiC Switch Topologies

This work investigates the performance of state-of-the-art non-commercial 6.5 kV Silicon Carbide (SiC) PiN and Junction Barrier Schottky (JBS) diodes in hybrid (Si IGBT with SiC diode) and full SiC (SiC MOSFET with SiC diode) switch topologies. The static and dynamic performance has been systematically evaluated at distinct temperatures, gate resistances and currents for each configuration. The SiC PiN diode presented higher current density capability and lower leakage current density than the JBS diode. Moreover, in most cases, the SiC PiN diode-based topologies demonstrated slightly higher total switching losses compared to the SiC JBS diode-based equivalent configurations. A loadability analysis in a three-level NPC converter is presented to evaluate the potential of each configuration in a converter application. The SiC PiN technology presented a 25% power extension compared to the SiC JBS technology with similar efficiency at typical industrial drives switching frequency operation when comparing same-active-area diode technologies. Finally, a long-term reliability test (H3TRB) is presented to demonstrate the SiC PiN diode technology’s potential for operation in harsh environments. Such characteristics show the advantage of the 6.5 kV SiC PiN diode when a high current density (>100 A/cm2), high efficiency and reliability are required.

A fuzzy-predictive current control with real-time hardware for PEM fuel cell systems

This research study presents the application of the FC-PCC (Fuzzy Logic Predictive Current Control) algorithm in the context of maximum power point tracking (MPPT) for a proton exchange membrane fuel cell system employing a three-level boost converter (TLBC). The proposed approach involves the integration of an intelligent fuzzy controller with a predictive current control strategy in order to improve the performance of MPP tracking. Initially, the utilization of fuzzy logic involves the utilization of data values obtained from the PEMFC. The maximum point (P-I) of the PEMFC polarization curve is determined, followed by the selection of the reference current. A predictive current control technique employs the reference current to ensure the voltage balance of the output capacitor in the three-level converter. The hardware-in-the-loop system utilizes a real-time and high-speed simulator, specifically the PLECS RT Box 1, to obtain the findings. The computational cost of the overall system is rather low, making it feasible to construct using PLECS RT Box 1. The new MPPT algorithm quickly finds the maximum power point (MPP) and balances the voltage of capacitors in a number of different proton exchange membrane fuel cells. The suggested MPPT technique has been verified to demonstrate rapid tracking of the maximum power point (MPP) location, as well as precise balancing of capacitor voltage and robustness to environmental variations. This approach was tested and found to outperform conventional MPPT methods like Perturb and Observe (P&O) and Incremental Conductance (IC) in terms of tracking duration, precision, and voltage balancing, achieving a 15% reduction in tracking duration, a 5% deviation from the MPP value for voltage, and superior stability under changing temperature and pressure.

Three-Level Double LLC Resonant Converter with Ripple-Free Input Current for DC Microgrid Application

DC distribution systems have garnered interest in recent years due to their advantages over AC distribution systems, such as their high power conversion efficiency and lack of harmonic issues. An isolated DC-DC converter with low-input noise, high efficiency, and high-power density is required for DC microgrids within DC distribution systems. Although existing DC to DC converters have high efficiency and high power density, they still have input noise problems due to pulsating input currents. Thus, a large input filter should be inserted, which increases the cost and degrades the power density. In this study, a novel three-level double LLC resonant converter with zero-input-current ripple is presented for DC microgrid application with a high-voltage DC bus. The input-current ripple of the proposed converter theoretically decreases to zero without adding large input filters. Moreover, the voltage stress on each main switch is only half of the input voltage when using the modified three-level structure, which enables the use of low-voltage-rated power switches for high-voltage input applications. In addition, all the primary switches and secondary diodes are softly switched over a wide input voltage range. The experimental results of the prototype are presented to verify the performance of the proposed converter.

Enhanced Active Voltage Regulation Capability for Three-Level NPC Converters with the Space Vector Modulation Method

Enhanced Active Voltage Regulation Capability for Three-Level NPC Converters with the Space Vector Modulation Method

ISOS-SAB DC/DC Converter for Large-Capacity Offshore Wind Turbine

This study offers a modular isolated grid-connected DC/DC medium-voltage DC aggregation converter to support offshore full DC wind farms’ need for lightweight and highly efficient power aggregation and transmission. The converter can simultaneously have a smaller transformer size and lower switching frequency during operation through the dual-voltage stabilization three-loop control strategy and phase-shift modulation strategy, which greatly reduces the space occupied by the converter and lowers the switching loss, Additionally, the use of a two-level structure at a lower switching frequency has lower loss, which effectively reduces the cost of the power device compared with the commonly used three-level converter. The input series output series connection between the converter sub-modules effectively lowers the voltage stress on each power switching device and facilitates expansion into a multi-module structure, expanding its application in high-voltage and large-capacity environments. This study analyzes the two working modes of the DC/DC converter and its control approach, in addition to providing a detailed introduction to the application scenarios of this converter. Ultimately, the efficacy and practicability of the suggested topology and control scheme are confirmed by simulations and experiments.

A Modified Carrier-Based PWM Strategy for Common Mode Voltage Elimination and Neutral Point Voltage Balance in a Unidirectional Three-Level Converter for AC Motor Drives

A Modified Carrier-Based PWM Strategy for Common Mode Voltage Elimination and Neutral Point Voltage Balance in a Unidirectional Three-Level Converter for AC Motor Drives

Novel Two-Stage Three-Level Converter With Inherently Balanced DC Voltage for EV Fast-Charging Applications

Novel Two-Stage Three-Level Converter With Inherently Balanced DC Voltage for EV Fast-Charging Applications

Online condition monitoring for DC-link capacitors of three-level NPC converters using noninvasive signal injection

This paper introduces an online method for monitoring the health condition of the DC-link in three-level NPC converters. This method does not require hardware changes or modifications to the control algorithm. It involves injecting a zero-sequence signal, added to the system reference voltages to generate a neutral-point current injection. A square waveform with an interharmonic cycle frequency is used for the signal injection to minimize estimation errors caused by existing signals. This combined signal allows for the simultaneous estimation of the capacitor equivalent series resistance (ESR) and capacitance (C) at different frequency components using wavelet decomposition. Additionally, a balance between the magnitudes of the system reference voltage and the signal injection is established to prevent power quality issues. Besides, the capacitor parameters are estimated in the time-frequency domain, enabling tracking of capacitor degradation and wear-out failure. A comparison with a Fourier-based approach shows that this method provides highly accurate capacitor parameter estimation with less than 2% errors, instilling confidence in its results. Experimental results from a three-level NPC converter’s laboratory setup demonstrate the proposed method’s effectiveness.

A Trapezoidal Current Mode to Reduce Peak Current in Near-CRM for Three-Level DC–DC Converter

A Trapezoidal Current Mode to Reduce Peak Current in Near-CRM for Three-Level DC–DC Converter

A composite control method of PWM and phase shift for a three-level DC-DC converter

Abstract This research introduces a control strategy for the Three Level Active Half Bridge (TL-DAHB) DC-DC converter that integrates PWM combined with phase-shift control. This composite control method precisely regulates the output voltage by adjusting the phase-shift duty cycle between the input and output sides. Additionally, the application of the PWM control loop optimizes the duty cycle of the switches, effectively reducing the current stress on the converter during operation, improving transmission efficiency, and decreasing conduction losses of the switches. These enhancements boost the overall performance and the reliability of the converter. With its excellent voltage regulation capabilities and safety features, this converter is an ideal choice in the field of power conversion, especially in applications that demand high levels of stability and safety.

Integration Modulation for Current Ripple and High-Frequency Zero-Sequence Circulating Current Reduction on Two-Parallel Three-Level Converters

Integration Modulation for Current Ripple and High-Frequency Zero-Sequence Circulating Current Reduction on Two-Parallel Three-Level Converters

A single-bridge interleaved three-level LLC resonant converter with current sharing capability for fuel cell system

This paper propose a wide gain single-bridge interleaved three-level LLC resonant converter with current sharing capability. This novel converter offers numerous advantages, including low cost, low current ripple, reduced voltage and current stress, widely gain range, high efficiency, good current sharing capability and versatile application scalability. Utilizing the three-level inverter + full-wave rectifier LLC converter as a representative case, the paper conducts an in-depth analysis and research on the proposed method. Finality, a 600 W experimental prototype was constructed and tested. Experimental results reveal that the proposed converter exhibits lower current ripple and a broader gain range. Moreover, the converter shows good current sharing capability (with a resonant element tolerance of 10%, the current error between the two phases does not exceed 12%) and high efficiency (peaking at 95.8%).

An efficient implementation of three-level boost converter with capacitor voltage balancing for an advanced MPPT approach in PV Systems

Ensuring optimal extraction of power from photovoltaic (PV) systems under diverse climatic circumstances is a significant challenge, which requires an efficient Maximum Power Point (MPP) Tracking (MPPT) algorithm and an adequate conversion stage. Therefore, this paper proposes an advanced MPPT strategy implemented by a Three-Level Boost converter (TLB), which serves as the interface between the PV generator and the DC load, offering advantages such as reduced output voltage distortion, minimized inductor current ripple, and decreased switching losses. To achieve more accurate tracking, a robust voltage balance control across the TLB converter capacitors is also suggested. The proposed system is meticulously implemented and evaluated using MATLAB/Simulink, demonstrating its robust control capabilities in MPP tracking and voltage balancing across the TLB converter capacitors under diverse climatic scenarios. Furthermore, comparative analysis under various test circumstances including static and dynamic insolation conditions and sudden load variations, shows that the suggested MPPT algorithm offers noteworthy improvements over the InC algorithm. Additionally, a thorough comparison with existing research methods proves its effectiveness over these methods. The advanced MPPT strategy achieves a steady-state error of 0 W, an average tracking efficiency between 99.13 % and 99.44%, and fast-tracking velocity. Further, a comprehensive real-time evaluation using the cutting-edge RT-LAB platform confirms the consistency of the results with the simulation outputs, emphasizing the robustness and low implementation complexity of the overall proposed control strategy.

Control of dual star induction generator based on multi-level inverter used in wind energy conversion system

This paper presents vector control of dual star induction generator (DSIG) integrated into variable speed wind energy and supplied by three-level NPC converters. Now the DSIG is the most common among multiphase machines when used in high power generation systems, which is associated with two converters. Maximum power point tracking (MPPT) for extracting a maximum of power fluctuating wind speed is illustrated. In order to decrease the fluctuations that appear in the currents generated by DSIG to the electrical network, we propose the NPC structure three-level inverter. Simulation results of a 1.5 MW Wind turbine are presented to illustrate the validity of this application.

A reduced vector model predictive controller for a three-level neutral point clamped inverter with common-mode voltage suppression

This paper presents a novel, state-of-the-art predictive control architecture that addresses the computational complexity and limitations of conventional predictive control methodologies while enhancing the performance efficacy of predictive control techniques applied to three-level voltage source converters (NPC inverters). This framework's main goal is to decrease the number of filtered voltage lifespan vectors in each sector, which will increase the overall efficiency of the control system and allow for common mode voltage reduction in three-level voltage source converters. Two particular tactics are described in order to accomplish this. First, a statistical approach is presented for the proactive detection of potential voltage vectors, with an emphasis on selecting and including the vectors that are most frequently used. This method lowers the computational load by limiting the search space needed to find the best voltage vectors. Then, using statistical analysis, a plan is presented to split the sectors into two separate parts, so greatly limiting the number of voltage vectors. The goal of this improved predictive control methodology is to reduce computing demands and mitigate common mode voltage. The suggested strategy's resilience is confirmed in a range of operational scenarios using simulations and empirical evaluation. The findings indicate a pronounced enhancement in computational efficiency and a notable diminution in common mode voltage, thereby underscoring the efficacy of the proposed methodology. This increases their ability to incorporate renewable energy sources into the electrical grid.

Segmented-Vector Pulse Frequency Modulated Three-Level Converter for Wireless Power Transfer

Segmented-Vector Pulse Frequency Modulated Three-Level Converter for Wireless Power Transfer

Three-level DC-DC converter with fuzzy logic-based MPPT controller for photovoltaic applications

Three-level DC-DC converter with fuzzy logic-based MPPT controller for photovoltaic applications

A Novel Bidirectional Three-Level LCL-T Resonant Converter Applied to Onboard ESHS Based on Quasi-Constant-Current

A Novel Bidirectional Three-Level LCL-T Resonant Converter Applied to Onboard ESHS Based on Quasi-Constant-Current

Waveform Optimization Control of an Active Neutral Point Clamped Three-Level Power Converter System

Currently, the escalating integration of renewable energy sources is causing a steady weakening of grid strength. When grid strength is weak, interactions between inverters or those between inverters and grid line impedance can provoke widespread oscillations in the power system. Additionally, the diverse DC voltage application characteristics of power converter systems (PCS) may lead to over-modulation, generating narrow pulse issues that further impact control of the midpoint potential balance. Existing dead-time elimination methods are highly susceptible to current polarity judgments, rendering them ineffective in practical use. PCS, due to inherent dead-time effects, midpoint potential imbalances in three-level topologies, and narrow pulses, can elevate low-order harmonic content in the output voltage, ultimately distorting grid-connected currents. This is particularly susceptible to causing resonance in weak grids. To enhance the output voltage waveform of PCS, this article introduces a comprehensive compensation control strategy that combines dead-time elimination, midpoint potential balance, and narrow pulse suppression, all based on an active neutral point clamped (ANPC) three-level topology. This strategy gives precedence to dead-time elimination and calculates the upper and lower limits of the zero-sequence available for midpoint potential balance while fully compensating for narrow pulses. By prioritizing dead-time elimination, followed by narrow pulse suppression and finally midpoint potential balance, this method decouples the coupling between these three factors. The effectiveness of the proposed method is validated through semi-physical simulations.