H-bridge Multilevel Converter Research Articles

Passivity-based adaptive current control loop of cascaded H-bridge multilevel converter for grid-tied photovoltaic system

This paper proposes an algorithm to passivity-based control (PBC) for the current control loop of the cascaded H-bridge converter (CHB) connecting the grid-connected PV system with the space vector modulation (SVM) algorithm using the law of expanding any number of voltage levels. The algorithm SVM in this paper is suitable for CHB converters. It can create a number of high levels of alternating voltage that other methods cannot do. Passivity-based control (PBC) algorithm aims to create a flexible controller that can change its structure or parameters to adapt to changes in the system, ensuring stable system quality, reducing switching losses and gaining energy conversion efficiency. It enhances the capability of accurately delivering power on demand to the grid with the CHB inverter in situations in which the grid demands the mobilization of maximum power from the photovoltaics (PV) system. The simulation results of the 9-level CHB system performed by MATLAB/Simulink software have proved the feasibility of the proposed algorithm.

Selective Harmonic Elimination Technique Improvement for Cascaded H-Bridge Multilevel Converters Under DC Sources Uncertainty

The performance of multilevel converters (MLCs) is at the risk of uncertainty of DC sources. This issue has a more negative effect on three-phase cascaded H-bridge MLCs (CHB-MLCs) due to more isolated DC sources. DC voltage variation can take place in all phases, but in this paper, the effect of DC voltage variation of one phase on line voltages is considered. This problem can lead to unbalanced line voltages and a lack of third harmonic elimination in a spontaneous way. Therefore, these problems cause to modify the formulation of quarter-wave symmetrical selective harmonic elimination (SHE) for three-phase CHB-MLCs so that the line voltages become resistant to DC voltage variations as well as mitigating third harmonic. To keep line voltages amplitude fixed under variation of DC voltages, it is necessary to take advantage of non-identical modulation indices to exploit the maximum capacity of DC voltages. Furthermore, regarding unequal DC voltages that can appear in numerous states in a phase, a new method based on the average of DC voltages (ADCV) per phase is employed in the formulation of SHE to reduce these states. Finally, both simulation and experimental results are presented to validate the performance of the proposed method.

A Comprehensive Review of Compensation Control Techniques Suitable for Cascaded H-Bridge Multilevel Inverter Operation with Unequal DC Sources or Faulty Cells

A cascaded H-bridge multilevel converter topology is the ultimate solution for energy conversion in various industrial applications due to its exceptional features, such as high modularity and fault-tolerant capability. However, two circumstances can lead to unbalanced operation of the inverter, potentially causing a decrease in its reliability and survivability: unequal DC voltage sources and faulty cells. In recent decades, scientists and engineers have conducted intensive research and meaningful studies to propose control solutions capable of maintaining the stable and continuous operation of the inverter under these operational concerns. Typically, each challenge is addressed separately using a distinct compensation control scheme in the existing literature. The paper aims to offer a comprehensive review of the existing compensation control schemes appropriate for CHBMIs operating under unbalanced conditions. It overviews the most popular control schemes and summarizes their usefulness in such scenarios. The theoretical foundations of each control scheme are presented and discussed, including their operating principles, implementation schemes, advantages, and disadvantages. The paper concludes with suggested future trends that require further research for CHBMIs’ continued growth and adoption in various industrial applications.

Diagnosis and Resilient Control for Multiple Sensor Faults in Cascaded H-Bridge Multilevel Converters

Diagnosis and Resilient Control for Multiple Sensor Faults in Cascaded H-Bridge Multilevel Converters

A Study on the Distributed-Control Architecture of a DSP-Based Solid-State Transformer System with Implementation

This article proposes a Distributed-control Architecture (D-CA) and an operation sequence with start-up strategies for a Digital Signal Processor (DSP)-based Solid-State Transformer (SST). Although various control techniques for SSTs have been reported in earlier studies, there is still a lack of research covering comprehensive content, including hierarchical control architectures and operation sequences with start-ups considering the implementation of DSPs. Therefore, this article addresses the following factors of SST. First, the D-CA is described for the design of the hierarchy between control boards. With the D-CA, because sub-boards are in charge of their corresponding DC-link voltage balancing control individually, the computational burden on the master board can be reduced. Second, the operation sequence of the SST system is explained based on the SST with D-CA. The step of DC-link voltage balance is considered throughout the entire operation sequence for safe driving. Furthermore, the PWM start-up strategies for a Cascade H-bridge Multilevel (CHM) converter and Dual Active Bridge (DAB) converter are proposed to prevent switching pulse errors caused by DSP operating characteristics. These start-up strategies reduce the current surges. The validity of the proposed D-CA and operation sequence with start-up strategies are verified by experimental results.

A Hybrid Symmetric Cascaded H-Bridge Multilevel Converter Topology

This paper presents a hybrid symmetric cascaded multilevel converter capable of generating nearly twice the number of output levels as that generated by a conventional symmetric cascaded H-bridge multi-level converter. In the proposed converter topology, each phase comprises one five-level transistor-clamped H-bridge power cell, and the remaining are three-level H-bridge power cells, with all the power cells having equal cell dc-link voltages. Because of the cascade connection of the power cells with equal dc-link voltages, the H-bridge power cells share equal power and is nearly equal to the power shared by the transistor-clamped power cell. The near-equal power sharing condition further helps in effective suppression of the lower-order harmonics present in the input source current waveform if a suitable phase-shifting transformer is employed at the converter input. In this paper, the operating principle and the modulation strategy for the generalized configuration of the proposed topology is explained in detail. The analysis of the capacitor voltages in transistor-clamped H-bridge power cell and converter power loss calculations are also presented. To investigate the performance of the converter system, detailed simulation studies are carried out and the results are validated through experimental results obtained from nine- and thirteen-level laboratory prototypes.

Cascaded H-Bridge Multilevel Converter Applied to a Wind Energy Conversion System with Open-End Winding

With the growing expansion of renewable sources around the world, wind energy is among those that stand out. With the advances of technology, wind turbine projects have considerably increased their power, reaching higher power, mainly for offshore installations. One of the main challenges is the power converters, more specifically the semiconductor components, which have limited voltage and current capabilities. Thus, the concept of multilevel converters emerged, increasing the voltage levels and thus carrying higher power levels. In addition to the application of multilevel converters, it is possible to increase the voltage and power levels employing an open-end winding (OEW) connection to the generator. In this context, the present work investigated the application of a multilevel converter (three-level cascaded H-bridge back-to-back) driving a squirrel-cage induction machine in an open-end winding configuration, connected to a wind energy conversion system (WECS). The analysis of the proposed system was developed through dynamic simulation of a 1.67 MW WECS, using PLECS software, including the modeling of the main system components: generator, power converters, system control, filter, and grid connection. The results show that the objective of obtaining a 5-level behavior in the output voltage is achieved by using the OEW connection. Furthermore, a low harmonic content is achieved in the machine current as in the current injected into the grid. In addition, it is possible to verify the power distribution between the converters, demonstrating that converters with smaller power can be combined to reach higher WECS power.

Multi-objective control strategy for multilevel converter based battery D-STATCOM with power quality improvement

Differences in battery state-of-charge (SOC) in a cascaded H-bridge multilevel converter (CHB-MLC) based distribution static synchronous compensator (D-STATCOM) in battery storage system (BSS) applications could result in undesirable efficiency and performance reductions, and even system failure. Moreover, faults occurring on batteries and/or H-bridges (modules) of CHB-MLC severely increase the risk of failure. Power quality at the output of CHB-MLC is reduced as results of those faults. Therefore, active power differences that are introduced by SOC balancing among modules and bypassing the faulty modules yield to undesired harmonics at the output of CHB-MLC. This paper proposes a multi-objective control strategy for CHB-MLC based BSS D-STATCOM. The proposed control strategy includes a bidirectional power flow controller with unity power factor operation (UPF) feature, a fault-tolerant (FT) controller, a SOC balancing scheme that is designed to work on fault conditions, and a harmonic minimization strategy to enhance the power quality at the output of the CHB-MLC. Performance of the proposed method is validated through different operating conditions including faults, unbalanced SOCs and dynamic load changes. Results indicate that charging and discharging of the batteries with 5 kW rated power are held successfully along with maintaining UPF operation under both normal and fault conditions. Moreover, grid currents are balanced with the help of the FT controller and SOC balancing is properly operated even in fault conditions. Negative impacts of faults and unbalanced operating conditions on the power quality are also mitigated with the help of the harmonic reduction controller with significant decreases on total harmonic distortion reaching up to 47% and 69% during normal operation and faulty operations, respectively.

A New Model-Based Dead-Time Compensation Strategy for Cascaded H-Bridge Converters

Cascaded H-bridge multilevel converter can generate high-voltage and high-power output with low harmonics. However, the error voltage caused by dead time effect will distort the output waveform, which depends on the phase current polarity. Since the normal dead time compensation method based on current sampling is often disturbed by sampling error and transmission delay, a novel current prediction method is proposed for dead time compensation of cascaded H-bridge converter in this paper. This method, based on phase shift carrier pulse width modulation, reconstructs the switch pattern, and combined with the system model, can easily predict the phase currents. Excellent compensation performance can be obtained by dead time compensation according to the predicted current. Simulation and experiments are built to validate the excellent performance of the proposed method applied to cascaded H-bridge converters.

Seven Level Symmetric Cascaded H-Bridge Multilevel Inverter for Solar Photovoltaic System

Among different types of Non-Conventional Energy Sources, Solar Power has become highly prominent with exhausting suitable to innovation in Power Electronic Systems. The primary intention of the advised performance must limit the number of switches to enhance the output waveforms with a preferred harmonic profile. This topology moderates the estimate about switches, isolated DC origin, expenditure, and intensity of the circuit substantially as correlated to other topologies. The proposed method uses the MPPT approach to exploit the maximum energy from solar photovoltaic to load entirely. The Proposed method provides almost sinusoidal output waveforms by developing a few power switches. The SPV arrangement was simulated and constitution through SPV arrays, a DC-DC buck converter, and a sliding mode MPPT regulation. Based on the cascaded H-Bridge multilevel converters, The strong constraint enforced confined DC voltage sources considering separately Cascaded H-Bridge. This constitution converter worth along with diminishing the constancy based on the system. The system gives boosting voltages with improves the harmonic profile. Performance of the arrangement demonstrated in MATLAB SIMULINK as well as PROTEUS.

Dynamic Addition of Common Mode Voltage in Post Fault Operation of Cascaded H-Bridge Converter Fed Induction Motor Drive

In this article, a postfault control technique is proposed for a rotor field-oriented induction motor (RFO-IM) drive fed from a cascaded H-bridge multilevel (CHB-ML) converter. The control strategy is to vary the magnitude and phase shift of the injected fundamental common mode voltage (FCMV) according to the motor’s operating condition. The addition of the proposed FCMV with the reference phase voltages, not only ensures maximum line voltage in the postfault operating condition but also shares equal power among the remaining healthy cells of the converter. Moreover, in the postfault operation, a detailed analysis is performed on both motor and converter, and an integrated control is presented to maintain the command speed and load torque of the RFO-IM. This includes the mathematical equation explaining the new operating point of the motor for different fault configurations, traversal of operating point, and the variation in power factor of each leg of the converter in postfault conditions. From the above analysis, the dynamic FCMV is calculated from the new operating point of the stator current components in the current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -plane and the fault configuration of the CHB-ML converter. The proposed control technique is validated using simulation and experimental results conducted on a 3-hp IM.

A novel power balance control scheme for cascaded H-bridge multilevel converters with battery energy storage

Battery energy stored quasi-Z source cascaded H-bridge based photovoltaic power generation system combines advantages of quasi-z-source inverter, cascaded H-bridge, and battery energy storage system. However, the battery state of charge imbalance between the cascaded H-bridge inverter modules would reduce the system's performance and efficiency and potentially cause the system to fail. An integrated control technique of adaptive state of charge balancing based on gain scheduling and three-phase power balance of third harmonic injection based on fundamental frequency whole zero sequences is suggested for the quasi-Z source cascaded H-bridge battery storage system. Based on the mathematical relationship between the instantaneous state of charge of battery energy stored quasi-z-source cascaded H-bridge and the voltage reference value, this method updates the proportional controller gain in each sampling period. It combines the third harmonic injection method based on the fundamental frequency zero sequence to select the optimal modulation ratio Mn. Rapid state of charge balancing is accomplished without overmodulation while increasing the power balance range and decreasing DC link voltage swings. The simulation results validate the method's usefulness. The simulation results validate the proposed control method for ensuring power distribution between each phase and achieving a balanced state of charge of the battery energy stored quasi-Z source cascaded H-bridge photovoltaic system's battery energy storage.

Multiple Fault Tolerant Control Strategy for Rotor Field Oriented Induction Motor Drive Fed From CHB Converter With Redundant Cells

The article proposes a postfault control strategy for a rotor field oriented induction motor (RFO-IM) drive fed by a cascaded H-bridge multilevel converter (CHB-MLC) with redundant cells in each phase. The objective of the control strategy is to maintain the torque and speed of the RFO-IM in postfault operation and to maximize the converter's power capability by adding a maximum number of power cells during postfault operation. Furthermore, maximum line voltage is utilized from the redundant cells without increasing the dc-link voltage of power cells, and the motor's operating point in the voltage plane is analyzed and determined for various loading conditions during prefault and postfault operation. In the postfault operation, a common mode voltage of fundamental frequency is also added depending on the motor's loading condition and postfault configuration to distribute power evenly among the remaining healthy cells. Theoretical and graphical analyses include the equation of the operating point in the voltage plane, traversal of the operating point from prefault to postfault operation, and selection of common mode voltage of fundamental frequency based on the fault configuration and the motor's loading. The simulation and experimental data are used to validate the proposed fault-tolerant control approach.

Driving Asynchronous Induction Launchers: Design and Simulation of a Novel Power Conditioner with a Brief Review

The design and implementation of an asynchronous coilgun’s structure is relatively simple compared with other types of linear induction launchers. In order to drive rotating electrical machines, multilevel converter structures have attracted much attention in recent decades as a result of their unique advantages. A linear induction launcher has an identical theoretical background to rotating electrical machines; therefore, multilevel converter structures can be applied to them as well. The stator of a launcher can be excited by generators or capacitor groups whose voltage and frequency might be fixed or changeable by a power conditioner. The aim of this study is to design and simulate a novel power conditioner as a multilevel converter topology for the power source of an asynchronous coilgun. Cascaded H-Bridge multilevel converter topology constitutes the proposed power conditioner in which a level-shifted pulse-width modulation method is used to generate appropriate pulses for the power switches of the converter. Additionally, variable-voltage variable-frequency control is involved in the converter’s modulation.

Battery Energy Support to Cascaded H-Bridge Converter-Fed Large-Scale PV System During Unbalanced Power Generation

The cascaded H-bridge (CHB) multilevel converter is an attractive solution for integrating photovoltaic (PV) generators with the ac grid. However, the power generated in the PV panels may be unequal due to partial shading, temperature change, and dust layer accumulation leading to unequal and unbalanced power between the phases and possible violation of power quality constraints. Fundamental frequency zero-sequence voltage (FFZSV) injection can be applied, but this method can produce overmodulation in conditions with high PV power mismatch. A new FFZSV is proposed in this article assuming a CHB with a battery energy support (BES) to compensate for the effects of unbalanced PV power generation. A barycentric coordinate representation helps to determine the capacity of the BES required. A coordinated control between the PV system and BES is also proposed in the article. Additionally, a novel approach to deliberate FFZSV injection is discussed in this article by which the maximum charge and discharge rate for the BES can be obtained along with balanced current injection into the grid. The effectiveness of the proposed technique is verified in numerical simulations and with experimental results.

A novel adaptive state-of-charge balancing control scheme for cascaded H-bridge multilevel converter based battery storage systems

Variations in state-of-charges (SOCs) of batteries in a cascaded H-bridge multilevel converter (CHB-MLC) based battery storage system (BSS) could lead to undesired efficiency and performance drops, even failure of the whole system. Hence, SOC balancing is crucial for BSSs. Avoiding over-modulation region, ensuring zero common-mode voltage and reaching balanced SOC condition as quickly as possible are the key points to consider while performing SOC balancing. In this paper, a gain-scheduling based adaptive SOC balancing method is proposed for single-phase CHB-MLC based BSSs. In the proposed method, gains of the proportional controllers are updated at each sampling time based on the mathematical relationship between instantaneous SOCs and voltage reference of the CHB-MLC. Performance of the proposed method is validated through a Monte Carlo simulation based numerical analysis and experimental studies on a single-phase three-module CHB-MLC based BSS. Results reveal that the proposed method achieves SOC balancing at least two times faster than the traditional constant gain methods while avoiding over-modulation region and having zero common-mode voltage.

A Voltage-Based Multiple Fault Diagnosis Approach for Cascaded H-Bridge Multilevel Converters

This article proposes a fast and robust open-circuit fault diagnosis method without additional sensors for cascaded H-bridge multilevel converters (CHBMCs). The method is based on the error between the actual input-side voltage and the estimated one, with one detection threshold and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2n$ </tex-math></inline-formula> comparators in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> cascaded H-bridges. Benefitted from the simple design of the fault location, spike elimination, and parameter estimation, with the lower implementation burden, the single and multiple faults in arbitrary positions are accurately identified within a fundamental cycle, and the diagnostic robustness is guaranteed under different transient changes. In view of the low complexity, the proposed scheme can be easily applied to the CHBMCs with arbitrary modules. The experimental results from a CHBMC prototype verify the effectiveness of the proposed method under different operating conditions and fault scenarios.

Nonlinear Control of a Two-Stage 1-MWh Grid-Connected Battery Energy Storage System by Exact Linearization via State Feedback

This paper presents modeling and nonlinear control of a two-stage 1-MWh battery energy storage system (BESS) connected to a distribution grid. The BESS is based on a cascaded H-bridge (CHB) multilevel converter offering the distribution of the batteries among multiple submodules which provides safer operation and more flexibility in the voltage design of the batteries. The main function of the BESS is to exchange active and reactive power by controlling the current of the CHB using voltage oriented control strategy. Moreover, this paper proposes a nonlinear state feedback exact linearization controller to control the bidirectional buck–boost converter in each submodule to charge/discharge the batteries and stabilize the dc-link capacitor voltage throughout the operation of the BESS. The proposed controller performance is compared with the conventional PI controller and validated through simulation results.

An Open-Circuit Fault Detection and Localization Scheme for Cascaded H-Bridge Multilevel Converter Without Additional Sensors

In this article, a new model-based fault detection and localization scheme is proposed for cascaded H-bridge (CHB) multilevel converter to localize the open-circuit faults without needing any additional sensors. The grid current is estimated from the gird voltage, switching states, and dc bus voltages, and compared with the measured grid current. Any significant deviations in the estimated and actual grid currents of the CHB trigger an open-circuit (OC) fault. Once the fault is detected, modulation scheme is switched from phase-shifted unipolar SPWM to phase-shifted bipolar sine pulse width modulation (SPWM) to localize the OC faults. At selected time instants, the change in measured grid current for a specific period is calculated and compared with the estimated change in grid current from the system model. The abovementioned comparisons are used to localize the OC faults in the CHB. The proposed method is validated on a scale-down CHB prototype developed in the laboratory environment, and experimental results are presented to demonstrate the effectiveness of the proposed method.

Hierarchical Single-Objective Model Predictive Control With Reduced Computational Burden in Cascaded H-Bridge Converter Based on 3-Level Flying Capacitor Unit Cell

This paper presents a control algorithm to reduce the computational burden of model predictive control in a grid-connected single-phase N-cell cascaded flying capacitor H-bridge (CFCHB) multilevel converter of a solid-state transformer. The proposed control algorithm is a finite-control-set model predictive control (FCS-MPC) that is based on a hierarchical structure controlling the grid current, DC-link voltage, and flying capacitor voltage, using each cost function through three layers. Unlike the conventional multi objective cost function that evaluates and compares all candidates to determine the optimal state, the proposed method uses a single-objective cost function by separating the control variables to determine the optimal state through calculation without comparison. Therefore, the amount of computation is significantly reduced compared with that of the conventional method, and the execution time is shortened. Thus, the sampling period can be shortened and the switching frequency can be increased. Further, it can lead to using a smaller inductor to produce a high-quality grid current, which can help reduce the system size and cost. The execution time is not large, even if the voltage level increases and the effect of time reduction is large compared to the existing method, because the computational burden of the proposed method is linearly proportional to the number of cells. The voltage level expansion is easy and suitable for digital system implementation, and the control performance is not affected. The effectiveness of the proposed method is verified through the simulation of a single-phase 250 kW 9-cell CFCHB multilevel converter using PSIM and an experiment with a single-phase 2 kW 3-cell CFCHB multilevel converter at the laboratory scale.