Seven-level Converter Research Articles

Optimized integration of renewable energy sources using seven-level converter controlled by ANFIS-CS-GWO

The global energy landscape is undergoing a significant transformation, driven by the need to reduce greenhouse gas emissions, enhance energy security, and provide sustainable and clean power solutions. Renewable energy sources (RES) such as Solar Photovoltaic (SPV), wind, fuel cells, and tidal power play a crucial role in this transition due to their abundant availability and low environmental impact. However, integrating these diverse energy sources into power systems requires advanced control strategies to ensure stability, efficiency, and reliability. Existing systems, however, face significant challenges such as unstable voltage profiles, prolonged fault settling time (FST), and high total harmonic distortion (THD), which compromise their efficiency and reliability. To overcome these limitations, a novel methodology is proposed, integrating Solar PV (SPV), wind, fuel cell, and tidal energy sources into a seven-level converter (SLC) system, which is named as Four Level RES based SLC (FLRES-SLC) system. This system is managed by an Adaptive Neuro-Fuzzy Inference System (ANFIS), fine-tuned by Cuckoo Search adopted Grey Wolf Optimizer (CS-GWO). This hybrid control strategy ensures a robust voltage profile, significantly reduces FST, and lowers THD, thereby markedly improving the overall performance of the converter system. The innovative approach offers a reliable and efficient solution for modern power systems, enhancing their integration with diverse RES and ensuring high-quality power delivery.

A 6h ± 1 Repetitive Scheme for the Three-Phase CHB Seven-Level Converter Used in an APF Application

A 6<i>h</i> ± 1 Repetitive Scheme for the Three-Phase CHB Seven-Level Converter Used in an APF Application

Circulating current mitigation for renewable-based modular seven-level converter using deep learning-optimized fractional-order proportional resonant controller

Circulating current mitigation for renewable-based modular seven-level converter using deep learning-optimized fractional-order proportional resonant controller

An Active Hybrid Modulation Strategy for a Si/SiC Hybrid Multilevel Converter

This paper proposes a hybrid modulation strategy for a medium-voltage hybrid seven-level (7-L) converter, which consists of a three-phase silicon (Si) IGBT-based active-neutral-point-clamped (ANPC) stage and a cascaded silicon carbide (SiC) MOSFET-based H-bridge (HB) stage in each phase. Within the framework of the proposed modulation strategy, three floating HB converters are controlled using a high-frequency three-level (3-L) space-vector-modulation (SVM), while a low-frequency modulation is applied to the ANPC converter. To regulate the DC voltages across floating capacitors, a zero-sequence voltage (ZSV) injection method is adopted. The proposed method possesses three major advantages. First, it enables the simplification from a 7-L to a 3-L SVM, which significantly reduces the computational burden. Second, with all the high-frequency switching actions assigned to SiC devices in the HB stage, the power loss of the hybrid 7-L converter is reduced. Third, the hybrid modulation together with the ZSV injection enables a wider stable operating range compared to the existing 7-L SVM method. Finally, both simulation and experimental results performed on the scale-down and the full-scale 1 MVA prototype validate the effectiveness of the proposed hybrid modulation strategy.

Analysis and Control of PV Cascaded H-Bridge Multilevel Inverter With Failed Cells and Changing Meteorological Conditions

This article proposes an approach to control a photovoltaic cascaded H-bridge multilevel inverter with failed cells and changing meteorological conditions for large-scale grid-connected applications. The controller development is based on an analysis of the interaction between the inverter common-mode and differential-mode quantities, which is done in the time domain, supported by a space vector representation analysis. The proposed approach is able to produce balanced three-phase line-to-line voltages and currents even if there is a failed cell or if the fluctuating meteorological conditions cause uneven power distribution among the bridges. This is achieved through the modification of the pulsewidth modulation reference phase voltage angles combined to the injection of a dynamic homopolar component. Such an approach avoids tripping the system due to the protective functions #25 and #87 for per grid applicable codes and standards. Numerical simulations and laboratory experiments performed on a seven-level converter with different abnormal conditions to confirm the effectiveness of the suggested control strategy.

Switch count reduced structure for symmetric bi‐directional multilevel inverter based on switch‐diode‐source cells

Inverters as one of the most important elements of power systems have been profoundly developed in recent decades and their performance has attracted researches in control and structure point of view. In this study, a novel structure based on the switch-diode-source cell is proposed for a multilevel converter that is capable of bidirectional feeding. The proposed structure is presented for symmetrical mode and the number of power electronic devices is decreased in comparison with similar works. Considering recent proposed symmetrical structures, the proposed structure has the superior condition in terms of semiconductor switches and drivers count as well as switching loss. Also, total blocked voltage (TBV) of the proposed converter is compared with conventional and novel symmetrical converters. Then, switch costs of the proposed converter are compared with the structure that its TBV is the lowest. The performance of the proposed symmetrical seven-level converter is analysed and simulated in MATLAB/Simulink for both PWM and selective harmonic elimination switching methods. Not only the results are desirable, but also the experimental results of laboratory prototype validate the simulation results.

A novel hybrid seven-level converter for permanent magnet synchronous motor driving system based on model predictive control

A novel hybrid seven-level converter for permanent magnet synchronous motor driving system based on model predictive control

Satisfactory model predictive control for a hybrid single-phase seven-level converter

Satisfactory model predictive control for a hybrid single-phase seven-level converter

Hybrid Seven-Level Converter Based on T-Type Converter and H-Bridge Cascaded Under SPWM and SVM

This paper presents a hybrid seven-level converter based on T-type converter and H-bridge cascaded suitable for low-voltage and high-power-density applications. The operation principles and conduction paths are analyzed comprehensively. Voltage balance control of the floating capacitors is the key point of this paper. Mathematical expressions of capacitor voltage balance conditions are deduced based on sinusoidal pulse width modulation (SPWM). The results show that floating capacitor voltages are only balanced when the modulation index is below 0.82 under SPWM. In order to enlarge the modulation index ensuring the capacitor voltage balance, space vector modulation (SVM) is also applied to regulate floating capacitor voltages taking advantage of redundant switching vectors. Meanwhile, in SVM, there are no additional control requirements for the capacitor voltage. Taken both SPWM and SVM into consideration, the limit to the range of operation for this seven-level converter is presented, which is a function of the modulation index and the power factor. The merit of dc voltage utilization improvement in this topology is also analyzed based on simulation results. Simulations and experimental results under different modulation index and RL load are presented to verify the modulation strategies illustrated in this paper.

Rapid and generalised space vector modulation algorithm for cascaded multilevel converter based on zero‐order voltage constraint

To simplify space vector modulation (SVM) algorithm, reduce zero-order voltage, and find the shortest switching path of the switching state vectors, a rapid and generalised SVM algorithm for cascaded multilevel converter is proposed. Using coordinate transformation which leads to all basic vectors locating in the integer grids in new coordinates, the algorithm simplifies the locating of basic vectors synthesising reference vectors and also their dwell time calculation. Switching state vectors calculation based on minimum zero-order voltage criteria reduces the workload of SVM. To find a most suitable switching path, the switching state vectors are mapped in three-dimensional (3D) space coordinates. Switching frequency is minimal along adjacent two sides of a unit cube's surface in 3D space coordinates, which improves performance of the converter. Finally, a three-cell seven-level converter experimental prototype is built and tested. Simulation and experimental results are consistent with the theoretical prediction, which verifies the correctness and effectiveness of the proposed algorithm.

A New SVPWM Modulated Input Switched Multilevel Converter for Grid-Connected PV Energy Generation Systems

This paper proposes a new space vector pulsewidth modulation (SVPWM) strategy for a hybrid input switched multilevel converter for photovoltaic energy generation systems. The converter topology is a cascaded connection of input switched and H-bridge converters, which can provide 2N + 1 voltage levels for each phase. The proposed SVPWM strategy treats the multilevel converter as a two-level converter by introducing an offset vector. With a generated switching pattern, it is possible to obtain minimum number of switching-state transitions and switch the H-bridge close to line frequency; thus, the switching losses can be significantly reduced. The proposed SVPWM strategy has been realized on a seven-level converter to demonstrate the principle of operation. The advantages of the proposed scheme and architecture are verified by both simulation and experimental results.

Implementation of a 84-pulse voltage-source converter for special applications

This study presents the experimental results on the implementation of a 84-pulse voltage-source converter (VSC), assembled by combining a 12-pulse VSC in conjunction with an asymmetric single-phase seven-level converter. The phase-locked-loop strategy used ensures the determination of the system&apos;s frequency and phase-angle of the fundamental positive sequence voltage of the controlled AC bus. The injection transformer added to the configuration allows the total harmonic distortion on the VSC&apos;s output to be compliant with the IEEE STD 519-1992, for its use in special applications. The amount of switches and capacitors employed on the implementation, and the wide turn ratios allowed to the re-injection transformer, constitute an attractive array in terms of cost and reduced output voltage distortion and notching.

Operation and Control of a Hybrid Seven-Level Converter

This paper introduces a novel hybrid seven-level converter that is based on the upgrade of the five-level active neutral-point-clamped converter concept and is suitable for high-power applications. The paper provides a comprehensive analysis for the operation of the converter. Based on the analysis, a space vector modulation (SVM)-based switching strategy that takes advantage of redundant switching vectors of the SVM strategy to counteract the voltage drift phenomenon of the proposed converter is proposed. The limit to the range of operation of the seven-level converter based on the proposed SVM strategy is also presented. It is shown that the ability to stabilize the dc-link capacitor voltages and the per-phase flying capacitors is a function of the converter operating indices, i.e., the load power factor and modulation index. The salient feature of the proposed SVM-based control strategy is that it enables proper operation of the converter with no requirements for additional controls or auxiliary power circuitry, within the specified range of operation. Performance of a converter under various operating conditions, based on the proposed SVM strategy, in the MATLAB/Simulink environment, is evaluated and experimentally demonstrated.

3-D Space Modulation With Voltage Balancing Capability for a Cascaded Seven-Level Converter in a Solid-State Transformer

The solid-state transformer (SST) is an alternative for existing power transformer due to its advantage in low volume, bidirectional power flow, power factor control, and fault management capability. In this paper, a three-stage cascaded-type SST, which utilizes the cascaded seven-level rectifier as the interface with a 7.2 kV distribution system, is presented. In the described system, dc voltage balancing of the cascaded seven-level rectifier is a necessity for stable operation. Previous PI-based voltage balancing control has intrinsic disadvantage in compromise between fast regulation and PI saturation. Besides, the addition of a voltage balancing controller may also change the system loop and bring unexpected performance. This paper aims at giving an alternative view of voltage balancing mechanism in a cascaded multilevel converter. A novel 3-D space modulation technique with voltage balancing capability is proposed for a cascaded seven-level rectifier stage of SST. By choosing the most suitable switching pairs for dc voltage balance, this method has a very good voltage balancing capability that can realize fast regulation of dc voltages in all operation modes, including unity power factor operation, capacitive operation, and inductive operation. Simulation and experimental results in a scaled-down system are provided to verify the effectiveness of the proposed method.

A Novel Voltage Source Converter Behind the StatCom

This article analyzes the structure of an 84-pulse voltage source converter, assembled by one 12-pulse voltage source converter in conjunction with an asymmetric single-phase seven-level converter with the addition of an injection transformer. Through the application of this novel structure, the total harmonic distortion in the voltage source converter's output is reduced, allowing its use in special applications or as the basement for FACTS devices. The proposition allows savings on the total amount of switches employed and a few capacitors to ward off unbalance problems. Emphasis is given on the automatic control of the reactive power exchange, providing a detailed and explicit explanation of the used blocks. A synchronizing strategy to match phase and frequency in an automatic way is also included. Simulations and experimental results are given to show the proposal appropriateness.

DStatCom regulation by a fuzzy segmented PI controller

This paper presents a segmented PI controller for the 84-pulses DStatCom connected to the electric power system (EPS) and subjected to several common disturbances in voltage and load levels. The 84-pulses signal is obtained by combining one twelve-pulses voltage source converter (VSC) with an asymmetric single-phase seven-level converter, adding an injection transformer. This structure allows a reduced VSC output's total harmonic distortion. The synchronizing strategy ties the DStatCom to the EPS in an automatic way, preventing phase and frequency problems. PI controllers exhibit good performance around nominal conditions but they do not tolerate severe disturbances. Thus, a segmented PI strategy based on the error and error's variation is utilized and selected according to fuzzy rules. Simulations demonstrate the appropriateness of the proposal.

Control of a multilevel converter using resultant theory

In this work, a method is given to compute the switching angles in a multilevel converter to produce the required fundamental voltage while at the same time cancel out specified higher order harmonics. Specifically, a complete analysis is given for a seven-level converter (three dc sources), where it is shown that for a range of the modulation index m/sub I/, the switching angles can be chosen to produce the desired fundamental V/sub 1/=m/sub I/(s4V/sub dc///spl pi/) while making the fifth and seventh harmonics identically zero.