Capacitor Voltage Balancing Research Articles

A Hybrid Multiobjective Control Strategy Based on Combination of Modulated Model Predictive Control and Phase‐Shifted Modulation for a Unidirectional Five‐Level Rectifier

ABSTRACTThe unidirectional multilevel rectifier has immense potential in high‐power medium‐voltage industrial applications. This paper proposes a multiobjective control method based on the combination of optimal‐vector‐pair modulated model predictive control (OVP‐M2PC) and a phase‐shifted modulation strategy for a unidirectional five‐level rectifier. This strategy takes both of the inductor current tracking and capacitor voltage balancing as the control objectives. First, an optimal vector pair is determined based on the AC‐side current variation rate, and then, through combining the calculated action duration of OVP with carrier phase‐shifted modulation, inductor current tracking is achieved. Second, capacitor voltage balancing control is carried out by compensating for the duty cycles which also decouples the input current tracking and output capacitor voltage balance control. Compared with traditional FCS‐MPC, under the proposed control strategy, complex cost function calculation and weighting factor tuning are not required, which much reduced computational burden. Multiobjective control is achieved with better performance in both steady‐state and dynamic conditions. The superiority of the proposed strategy over traditional FCS‐MPC are validated through simulations and hardware experiments.

A voltage-balancing algorithm based on the gating signal rotation and Separated Circulating Current Controller applied on a Modular Multilevel Converter

The Modular Multilevel Converter (MMC) is being used for many medium/high-power energy conversion applications due to its superior advantages such as modularity, scalability, and low harmonic generation. However, the MMC control can be challenging. If the submodule (SM) capacitors are not properly balanced, a circulating current is induced due to the voltage mismatch between the capacitor submodules. This circulating current adds to the arm current, which increases its RMS and peak value, and thus increases system losses. Therefore, controlling the submodule capacitor voltage and the circulating current is an important step in any MMC control. In this paper, a Gating Pattern Rotation algorithm is used for SM capacitor voltage balancing, and an independent circulating current controller in the double reference frame is used to eliminate the circulating current. Furthermore, a voltage-oriented control is employed to eliminate harmonics and regulate the grid power factor. MATLAB Simulink simulates the control technique, and various simulation results are presented. With results showing their effectiveness in managing and improving MMC behavior.

A novel and easy‐to‐implement modulation scheme for reducing modulation complexity in modular multilevel converter

AbstractModulation strategy plays a key role in the operation of modular multilevel converters (MMC). Although many studies have been carried out on its optimization in MMC, the limitations of hardware implementation are seldom considered. This paper presents a novel and easy‐to‐implement modulation strategy that simplifies both hardware design and application. From the analysis in this paper, the widely‐used modulation methods have the problems of pulse width modulation (PWM) signal feedback and complex carrier configuration in hardware implementation. By setting up a flexible insertion and removal submodule and proposing a capacitor voltage balance algorithm based on duty ratio allocation, the proposed modulation method can allow for the separate design of the Algorithm Unit and the PWM Unit in the hardware, which solves the problem of PWM feedback and reduces the hardware requirement of the trigger system. Moreover, the proposed method can broaden the selection range of processor chips. Finally, a downscaled MMC prototype is built; the proposed method is verified by both simulation and experiment.

A Novel Modular Multilevel Converter Topology with High- and Low-Frequency Modules and Its Modulation Strategy

To resolve the issue of the difficultly in effectively balancing the output performance improvement, cost reduction, and efficiency improvement of a medium-voltage modular multilevel converter (MMC), a novel MMC (NMMC) topology based on high- and low-frequency hybrid modulation is proposed in this study. Each arm of the NMMC contains a high-frequency sub-module composed of a heterogeneous cross-connect module (HCCM) and N − 1 low-frequency sub-modules composed of half-bridge converters. The high-frequency bridge arm of the HCCM in this study adopts SiC MOSFET devices, while the commutation bridge arm and low-frequency sub-module of the HCCM adopt Si IGBT devices. For the NMMC topology, this study adopts a high/low-frequency hybrid modulation strategy, which gives full play to the advantages of low switching loss in SiC MOSFET devices and low on-state loss in Si IGBT devices. In addition, a specific capacitor voltage balance strategy is proposed for the HCCM, and the working state of the HCCM is analyzed in detail. Furthermore, the feasibility and effectiveness of the proposed topology, modulation strategy, and voltage balancing strategy are verified by experiments. Finally, the proposed topology is compared with the existing MMC topology in terms of device cost and operating loss, which proves that the proposed topology can better balance the cost and efficiency indicators of the device.

Hybrid feedback control of PMSG-based WECS with multilevel flying-capacitor inverter enhanced by fractional order extremum seeking

This paper proposes an original hybrid control strategy for a three-phase multilevel flying capacitor inverter (FCI) used in wind energy conversion system (WECS). A state feedback law, computed using a Lyapunov function and an invariance principle, is designed to manage grid current control and capacitor voltage balancing, guaranteeing the asymptotic stability of the closed-loop system. Additionally, a fractional-order extremum seeking control (FOESC) algorithm for Maximum Power Point Tracking (MPPT) is introduced, which optimizes power capture by adjusting turbine speed from the DC side without requiring a detailed system model (model-free approach). The use of fractional-order calculus leads to improved convergence and more seamless performance while preserving the robust characteristics of the system. The proposed control strategies are validated through simulation, demonstrating improved transient response and stability under varying wind conditions and parameter uncertainties. These results highlight the potential of advanced control algorithms to enhance the efficiency and reliability of wind energy systems, contributing to global efforts to achieve sustainable energy goals.

Multilevel Middle Point Clamped (MMPC) Converter for DC Wind Power Applications

This manuscript introduces a novel multilevel middle point clamped (MMPC) DC-DC converter and its associated switching scheme aimed at maintaining the desired medium-voltage DC (MVDC) collector grid within offshore all-DC wind farms. Building upon previous work by the authors, which proposed an all-DC structure serving as a benchmark system, this study explores the application of the MMPC DC-DC converter within this framework. Within the all-DC wind generation system, a 9-phase hybrid generator (HG) integrated into the wind turbine is linked to the MVDC collector grid through an AC-DC stage, which is a passive rectifier. This passive rectifier offers elevated voltage ratings and protection against back power flow. The conventional neutral point clamped (NPC) converter concept has been thoroughly investigated and expanded upon to develop the proposed MMPC DC-DC converter. The proposed MMPC DC-DC converter integrates boosting capabilities, facilitating the connection of the generator’s rectified voltage to the MVDC collector grid while regulating variable rectified voltage to a fixed MVDC collector grid voltage. The MVDC collector grid is further interconnected with high-voltage DC (HVDC) through a DC-DC converter situated in an offshore substation. This paper further provides a comprehensive overview of the proposed MMPC DC-DC converter, detailing its operational modes and corresponding switching schemes. Through an in-depth examination of operational modes, duty cycles for each switch and mode are defined, subsequently establishing the relationship between rectified input voltage and MVDC output voltage for the MMPC DC-DC converter. Utilizing the middle point clamped architecture, this innovative converter offers several advantages, including low ripple voltage, a modular structure, and reduced switching stress because of the multilevel voltage and the incorporation of a hard point, which also facilitates the capacitor voltage balancing. Finally, the effectiveness of the proposed converter is evaluated via simulation studies of a wind turbine conversion system utilizing two cascaded MMPC DC-DC converters operating under variable input voltage conditions. The simulations confirm its efficacy, supported by promising results, and validating its performance.

Machine learning based fault detection technique for hybrid multi level inverter topology

AbstractMultilevel inverters (MLIs) have a significant contribution in many industrial sectors due to their improved power quality and lesser voltage stress, over the conventional three‐level inverters. However, the implementation of MLIs with an increased device count creates the scope of development in MLIs topologies. In this regard, a hybrid MLI topology is studied in this paper whose architecture is based on conventional two‐level inverters. This topology has lesser device count characteristics when compared to conventional and most of the recently presented configurations for nine‐level output voltage generation. The major issue of capacitor voltage balancing is resolved by employing an appropriate switching strategy. However, the semiconductor switches are the most vulnerable components and causes the open circuit faults frequently that creates issues in real time operation. Hence, it is important to detect the open circuit fault in switches in the least possible time. A new approach to open circuit fault detection technique based on the analysis of load voltage waveform is proposed in this paper. The wavelet transform technique has been implemented for feature extraction of load voltage. Later, the classification of the fault has been achieved by training an artificial neural network (ANN). The proposed work has been studied in MATLAB/simulation and the obtained results are verified experimentally.

Capacitor voltage balancing, capacitance monitoring, and fast fault detection in a nested neutral point clamped (NNPC) converter with the reduced number of sensors

In multilevel converters (MCs), system components such as capacitors and semiconductor switches are very susceptible to damage. Furthermore, utilizing voltage sensors to balance capacitor voltages increases the system's cost and complexity while decreasing reliability. This paper presents methods for voltage balancing of capacitors, capacitance monitoring and open-circuit fault detection in nested neutral point-clamped (NNPC) converter with a reduced number of voltage and current sensors. In the proposed method, converter capacitors' voltage and current sensors are eliminated, and only the output sensors are employed to control the converter. In order to balance the voltage of capacitors, their voltages are estimated in three cases without using individual sensors. Comparing the capacitors' measured and estimated voltage change ratios is used to assess their health in the monitoring method. Thus, the capacitors' status can be checked by considering the system's health indicator during each period. Furthermore, the open-circuit fault detection method can identify defective switches within one processing cycle by comparing the converter's measured and standard output voltages in all switching states. The proposed methods have been evaluated in an experimental study of the system, and the results confirmed the effectiveness of the methods based on the new system configuration.© 2017 Elsevier Inc. All rights reserved.

MPC Based TLSC-DSTATCOM with VIKOR Approach to Reduce Switching Frequency and Capacitor Voltage Balancing

MPC Based TLSC-DSTATCOM with VIKOR Approach to Reduce Switching Frequency and Capacitor Voltage Balancing

A single DC source, seven-level switched capacitor tripple boost inverter with fewer switches for renewable energy applications

This article presents a new SSTB-MLI with 3 times voltage boosting capability for medium voltage applications with optimal efficiency. Single DC source MLI topologies are more appropriate for many applications, including grid applications and renewable energy (RE) conversion systems than multiple DC source MLI topologies. The ability of switched-capacitor multi-level inverters (SCMLIs) to raise voltage has made them more and more popular in recent years. LS-PWM technique is used for the switching scheme. Two capacitors are employed in SSTB topology to operate alternatively in charging and discharging states at the carrier frequency of this LS-PWM algorithm for making the levels of output voltage. Comparing this innovative topology to those documented in the literature. It can also minimise the number of switches and capacitors needed, their voltage stresses, and switching loss. Since the suggested topology includes built-in capacitor voltage balancing, no additional voltage balancing circuit is required. Applications requiring industrial drives as well as grid-connected and R, RL loads can employ the suggested architecture. Based on less TSV (total standing voltage), MSV (Maximum standing voltage), the number of components used, optimum efficiency 98.43%, and other factors, a comparative analysis is done between the existing topology and the proposed topology. Experimental data and thorough simulation are used to verify the suggested switched capacitor multilevel topology.

Fuzzy Logic Control of Two-Stage Grid- Connected Photovoltaic System

In this paper, a two-stage grid-connected photovoltaic system is presented. The optimal performance of solar panels at varying temperatures and irradiance levels is achieved by the application of a fuzzy logic-based maximum power point tracking method. Space vector modulation is used to control the inverter; to achieve capacitor voltage balance, redundant switching states of a three level inverter are used. The grid side control regulates the power and the current injected to the grid, the conventional PI controllers are replaced by fuzzy PI. Simulations have been made using Simulink environment on MATLAB to validatethe control of the proposed system.

Transformer-Less Seven-Level Inverter with Triple Boosting Capability and Common Ground

This paper proposes a single-phase, transformer-less, seven-level inverter that utilizes eight switches, three capacitors, and two diodes to produce seven voltage levels with triple boosting ability. The availability of the common-ground point eliminates the leakage current in PV applications. The proposed Transformer-Less Triple-Boosting Seven-Level Inverter (TLTB7LI) has the ability to feed different types of loads from non-unity to unity power factors. The voltage balancing of capacitors takes place naturally without the need for auxiliary circuits and complicated control strategies. This paper investigates the appropriateness of the proposed TLTB7LI for grid-connected application. The Peak Current Controller (PCC) is employed to generate the switching pulses and regulate the active/reactive power transfer between the converter and the output, which guarantees the high quality of injected current to the output. Moreover, the operational principles, its control technique, as well as the design procedure of the key components of the proposed inverter have been presented. The superiority of the proposed inverter over existing counterparts has been verified through comparative analysis. The simulation and experimental analysis validated the proper operation of the proposed TLTB7LI.

Correction: Kim et al. Zero-Sequence Voltage Injection Method for DC Capacitor Voltage Balancing of Wye-Connected CHB Converter under Unbalanced Grid and Load Conditions. Energies 2021, 14, 1019

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Coordinated Capacitor Voltage Balancing Method for Cascaded H-Bridge Inverter with Supercapacitor and DC-DC Stage

Coordinated Capacitor Voltage Balancing Method for Cascaded H-Bridge Inverter with Supercapacitor and DC-DC Stage

An Active Virtual Space Vector Modulation Scheme for Three‐Level Neutral‐Point‐Clamped Converters

The performance of neutral‐point‐clamped (NPC) converters is subject to the regulation of neutral point balance. In the literature, researchers have addressed two main modulation methods: the active space vector PWM (SVPWM) technique and the virtual SVPWM (VSVPWM) method. However, those two approaches respectively suffer from reduced DC‐link voltage utilization and poor active regulation capability. To address this, an improved VSVPWM modulation scheme with actively strong voltage regulation capability is proposed in this paper. The fast and precise control of capacitor voltages is achieved by optimizing the synthesis scheme of the virtual vectors. When there is a voltage imbalance, the proposed technique can quickly restore and maintain the capacitor voltage balance till the full DC‐link voltage utilization without affecting the converter output quality. The experimental validation results on the NPC converter have demonstrated the benefits of the proposed active VSVPWM method. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

A new triple voltage gain seven level switched capacitor-based inverter with minimum voltage stress

Abstract This paper presents, a new seven level triple voltage gain inverter topology is proposed based on switched capacitor technique. The proposed inverter topology has minimum voltage stresses on the switches and balanced capacitor voltages. This paper briefs the operation of proposed topology, voltage stress analysis, capacitor sizing and generation gate signals for the switches. In addition, proposed topology is modeled in industrial based software PLECS with practical switches to study thermal behavior and efficiency analysis. Further, the proposed inverter topology is compared with competitive topologies in the recent literature. The proposed topology has merits like minimum total standing voltage, switching redundancy and inherent polarity generation. Furthermore, MATLAB based simulations and experimental analysis is done to validate the superior performance the proposed topology. The experimental results for the proposed seven-level inverter are presented and discussed in brief by considering different types of loads, amplitude modulation variations and frequency variations.

An FPGA-based balancing of capacitor voltage for multi-level inverter

ABSTRACT This paper introduces a novel cascaded multilevel inverter circuit configuration aimed at generating a five-level load voltage using a single DC source and a capacitor. In this inverter configuration, an additional switch is added to the charging circuit which helps to charge the capacitor from the DC source. Additionally, an inductor is incorporated to mitigate the substantial charging current during capacitor charging operation. A level-shifted pulse width modulation (LS-PWM) technique is implemented to generate gate pulses for both inverter and charging switches. The capacitor gets charged when an extra switch is enabled and discharged when it is connected to a load. Analysis of charging and discharging of capacitor is described thoroughly in this paper. Each operational mode of the inverter is thoroughly analysed. Furthermore, the proposed five-level inverter setup is designed, and its control logic is implemented using FPGA platform. Subsequently, simulation and experimental investigations are conducted under varied loads and different modulation indices to evaluate the efficacy of the proposed inverter configuration and the respective results are presented.

A Switched-Capacitor Multilevel Inverter With Modified Pulsewidth Modulation and Active DC-Link Capacitor Voltage Balancing

Although switched-capacitor (SC) multilevel inverters (MLIs) offer self-voltage balancing of flying capacitors and voltage gain higher than unity, the advantages come at the cost of high current stress and power loss in the SC circuit and DC source. Moreover, the voltage balancing is often restricted to a limited range of modulation index. Another problem of MLIs with neutral-point clamped (NPC) front end is with DC-link capacitor voltage balancing under unbalanced load conditions, imploring sensor-based closed-loop control. This paper proposes a unity gain five-level active-NPC SC-MLI with inrush charging current attenuation and actively balanced DC-link capacitor voltages under all load conditions and over the entire range of modulation index and power factor. The modified pulse-width modulation results in most switches operating at a low switching frequency, minimizing switching losses in the SC circuit. The proposed MLI attains a maximum efficiency of 98.04% at an output power of 510 W. Experiments on a 2 kVA laboratory prototype validate the theoretical analysis. Results from transformerless grid-connected solar PV system show that the proposed MLI can inject power into the grid with a unity power factor under conditions of varying irradiance and provide the grid with reactive power as well.

Topology and Hybrid Modulation of Six-Level Switched-Capacitor HC Converter With Improved DC-Link Capacitor Voltage Balancing

Topology and Hybrid Modulation of Six-Level Switched-Capacitor HC Converter With Improved DC-Link Capacitor Voltage Balancing

Model Predictive Control for Cascaded H-Bridge PV Inverter with Capacitor Voltage Balance

We designed an improved direct-current capacitor voltage balancing control model predictive control (MPC)for single-phase cascaded H-bridge multilevel photovoltaic (PV) inverters. Compared with conventional voltage balancing control methods, the method proposed could make the PV strings of each submodule operate at their maximum power point by independent capacitor voltage control. Besides, the predicted and reference value of the grid-connected current was obtained according to the maximum power output of the maximum power point tracking. A cost function was constructed to achieve the high-precision grid-connected control of the CHB inverter. Finally, the effectiveness of the proposed control method was verified through a semi-physical simulation platform with three submodules.