Cascaded H-bridge Multilevel Inverter Research Articles

Model predictive control of a microgrid with energy-stored quasi-Z-source cascaded H-bridge multilevel inverter and PV systems

This paper presents a new energy management system (EMS) based on model predictive control (MPC) for a microgrid with solar photovoltaic (PV) power plants and a quasi-Z-source cascaded H-bridge multilevel inverter that integrates an energy storage system (ES-qZS-CHBMLI). The system comprises three modules, each with a PV power plant, quasi-impedance network, battery energy storage system (BESS), and voltage source inverter (VSI). Traditional EMS methods focus on distributing the power among the BESSs to balance their state of charge (SOC), operating in charging or discharging mode. The proposed MPC-EMS carries out a multi-objective control for an ES-qZS-CHBMLI topology, which allows an optimized BESS power distribution while meeting the system operator requirements. It prioritizes the charge of the BESS with the lowest SOC and the discharge of the BESS with the highest SOC. Thus, both modes can coexist simultaneously, while ensuring decoupled power control. The MPC-EMS proposed herein is compared with a proportional sharing algorithm based on SOC (SOC-EMS) that pursues the same objectives. The simulation results show an improvement in the control of the power delivered to the grid. The Integral Time Absolute Error, ITAE, achieved with the MPC-EMS for the active and reactive power is 20 % and 4 %, respectively, lower than that obtained with the SOC-EMS. A 1,3 % higher charge for the BESS with the lowest SOC is also registered. Furthermore, an experimental setup based on an OPAL RT-4510 unit and a dSPACE MicroLabBox prototyping unit is implemented to validate the simulation results.

Modeling of Switching Power Losses in Cascaded H-Bridges With Unipolar PWM

This paper studies the extraction of an equivalent resistance for calculation of the switching power losses in cascaded H-bridge multilevel inverters with unipolar pulse width modulation. The concept of local and global rms currents and switching power losses are introduced in each H-bridge considering different frequencies of the inverter output and the switching network, i.e., transistor and diode. Energy conservation law has been utilized to show that the equivalent averaged local and global resistances for switching power losses are functions of load power factor angle, load rms current, and modulation index. This dependency is then reduced to only load rms current when the equivalent resistances are transformed to the inverter output branch based on the reflection rule. Consequently, a resistive model of switching power losses of the inverter is deduced, which depends neither on the knowledge of the physics of the switch, nor on complicated nonlinear equations of the semiconductor devices, and loop inductances. Double-pulse tests are conducted to acquire reliable data on the switching characteristics of the devices for different operating points.

Analysis of single-phase cascaded H-bridge multilevel inverters under variable power conditions

Easy modular I action is one of the benefits of a cascaded H-bridge (CHB) inverter. This study proposes an only one multilevel inverter comes with a unique H-bridge unit. The structure of the proposed topology is then enhanced in order to make use of switching devices and DC-link voltage inputs while creating a massive number of voltage steps. A cooperative active and reactive power control strategy is offered to earn a better real and reactive power management for every DC voltage source of a photovoltaic (PV) module, as well as boost systems power quality and reliability. A unique control approach and proportional pulse width modulation (PWM) modulation are described for the cascaded H-bridge multilevel inverters for grid-connected systems. Each Hbridge module can give different power levels thanks to this control. To supply the DC source, use the system's proportional, integral and derivative (PID) controller. The functionality and achievements of the proposed scheme with its associated algorithms in production of all operating voltage have been proven using experimental data from a nine-level single-phase inverter. Finally, to construct a cascaded H-bridge nine-level inverter, the proposed control strategy is developed and implemented in MATLAB software.

A Fault-Tolerant Strategy for Safe Operation of Cascaded H-Bridge Multilevel Inverter Under Faulty Condition

In the post-fault operation of cascaded H-Bridge (CHB) inverters, a common-mode voltage (CMV) is injected into the phase voltages of the converter to achieve the maximum balanced line-to-line voltages. However, when the non-regenerative CHB inverter feeds a low power factor load (PF), the fundamental component of CMV (FCMV) may cause real power to return from the load to the DC side. On the other hand, when the inverter feeds a high PF load, the real power of some H-bridge cells may exceed the rated value. This paper proposes a strategy consisting of two methods to tackle the mentioned problems. Also, three regions are determined, i.e., the non-overload area, the non-returnable power area, and the attainable zone for the FCMV. Then, A safe operating area (SOA) is obtained by overlapping these regions. The first method (Injecting Minimum FCMV (IMFCMV)) determines the CMV waveform with the least possible FCMV. This avoids the power flow back; however, it does not guarantee the non-overload operation of cells. So, it should be checked whether this FCMV is causing to overload operation of cells or not. If not, the proposed strategy uses the IMFCMV method. If yes, the second method (Shifting FCMV (SFCMV)) is used to shift FCMV into the SOA. In the SFCMV method, the determined CMV by the first method is modified so that its FCMV is located in the SOA. The simulation analysis and experimental results on the hardware prototype are provided to support the proposed strategy.

Automatic adaptive synchronization (A2S): A demand-based automatic synchronization for distribution generators in islanding mode

Synchronization is necessary for grid-connected islanded microgrid connection, but the existing methods solve the problem with high harmonics in the signal. Also, in many studies, the microgrid’s imbalanced voltage and frequency change rate is obtained by the sensor network or synchronizing relays, which is expensive. Hence to solve the problem, the paper introduced the automatic adaptive synchronization (A2S) scheme by using optimization and control techniques to synchronize the microgrid with the decentralized generators. The multiple decentralized generators serve the load through the microgrid, the voltage and phase are synchronized with the adaptive neuro-fuzzy inference system (ANFIS). The imbalance among them is sensed by the rain optimization algorithm (ROA). Thus the sensed changes are fed to the controller to provide gating signals accordingly to the cascaded H-bridge multi-level inverter with reduced harmonics. The distributed generator feeds the load through the 14 km feeder line and synchronizes the three-phase voltage at 1.9 ms with 2.28% distortion.

Total harmonic distortion reduction based energy harvesting using grid-based three phase system and integral-derivative

Distributed generation (DG) and solar photovoltaic (PV) systems are just two of the many places multilevel inverters have found a home. The total harmonic distortion (THD) of an inverter's output voltage or current is widely regarded as a useful quality indicator. In order to lessen THD while enhancing the performance of the network, the authors of this research presented a unified controller.An integrated controller consisting of PID (Proportional-Integral-Derivative),Fuzzy,and Artificial Neural Network (ANN) controllers is used in the 31-level multilevel inverter to reduce THD in the PV system. The fundamental frequency of the suggested integrated controller is 50 Hz,and the simulation results show that the THD is reduced to 0.94 percent. The proposed controller's performance shown a considerable decrease in 5th order harmonics for the Cascaded H-bridge Multilevel Inverter,as well as an average percentage reduction in line voltage total harmonic distortion of 17.04 compared to the existing approach.

High Reliable Medium Voltage Drive With Reduced Component Count of Converters

The rapid development of technology, particularly in the fields of medium-voltage drive applications, has led to the widespread and use of AC to DC multi-pulse and DC to AC multilevel converters. In recent years, multi-winding transformers (MWTs)-based multi-pulse converters have received significant attention, owing to the growing need to utilize the energy as per power quality standards with high reliability in medium voltage drive systems. The main issues of multi-pulse converters are the large complexity of winding connections, which directly degrades the reliability of the system and increases the requirement for conductor material. To address these issues of grid-end converters, this paper suggests a less complex structure of a multi-winding transformer (MWT) for a thirty-six pulse AC-DC converter, which demands the least conductor material for windings. Moreover, the reduction in the number of components of the multi-level inverters has a noticeable role in saving size, cost, and reliability improvement. To address these features in the drive system, a five-level hybrid symmetric cascaded H-bridge multilevel inverter (HSCHB-MLI) is presented, which performs a high-quality power conversion at the motor terminals of the drive system. Hence, the main concerns of this drive system are the reduction in the component count, weight, and losses of the system with excellent harmonics performance. The operational aspects of the topology such as circuit structure, design, and indirect field-oriented control (IFOC), and modulation technique (parabolic carrier wave-based level shifted pulse width modulation) are elaborated in detail. A detailed comparative assessment is performed with other multi-winding transformers and multi-level inverter structures to demonstrate the merits of the presented multi-winding transformer and multilevel inverter structures, respectively. Finlay, through Simulink modeling and hardware testing setup, the viability of the proposed architecture is verified.

Experimental Implementation of Cascaded H-Bridge Multilevel Inverter with an Improved Reliability for Solar PV Applications

This study presents the boost converter-based cascaded H-bridge (CHB) multilevel inverter with improved reliability for solar PV (photovoltaic) applications. The solar PV is associated with the boost converter to enhance DC link voltage by using the maximum power point tracking-perturb and observe (MPPT-P & O) technique. The proposed configuration is aimed toward the performance analysis of the boost converter-based CHB MLI by reducing the number of components, low total harmonic distortion (THD), reduced power, less cost function, low total standing voltage (TSV), improved reliability, and switching losses for solar PV application. In this study, a CHB multilevel inverter is used to obtain stepped pure sinusoidal AC from the solar PV array. The proposed boost converter extracts maximum power and enhances higher DC link voltage which provides high efficiency. The boost converter is integrated with a 27-level CHB multilevel inverter to generate near-sinusoidal output voltage with lower THD. The inverter is tested with linear and nonlinear loads for robustness, and during dynamic loads, inverter is stable and well suited to grid-connected applications. A detailed comparison is presented on the component count and reliability aspects with existing MLIs and 27-level MLIs. The simulation outcomes of the implemented arrangement are presented with the help of MATLAB/Simulink, an experimental prototype is developed using a dSPACE RTI1104 controller and also tested in the research laboratory for checking the possibility of the implemented arrangement.

Comparison between a Cascaded H-Bridge and a Conventional H-Bridge for a 5-kW Grid-Tied Solar Inverter

This paper compares the cost and efficiency of two inverter topologies for a 5-kW grid-connected solar inverter application: the Conventional H-Bridge Inverter (CHB) and the Cascaded H-Bridge Multilevel Inverter (CHBMLI). Emphasis is put on power switches and passive elements with a detailed study of the losses. Both designs respect the same constraints (cost, efficiency, and junction temperature of the transistors) to ensure a fair comparison between both topologies. The work highlights the important parameters when choosing the components (MOSFETs, capacitors, and magnetic cores for the inductors). The DC-link voltage ripple and the output AC current ripple are the key parameters for the design of the passive elements (capacitors and inductors). On top of that, the transistors MOSFETs are chosen, in both topologies, to limit the conduction losses (by selecting the Rdson) and the switching losses (by selecting the Qrr and dv/dt). Real components are picked in order to make the comparison as complete as possible. Numerical simulations are performed using the MATLAB platform. All equations and parameters are provided. A CHBMLI prototype was built with eight independent H-Bridges to validate the proposed design with thermal and efficiency measurements.

Four-state active fault diagnosis method for cascaded H-bridge multilevel inverter

The cascaded multilevel inverters have many semiconductor switches with high failure rate, which require timely diagnosis techniques. It is a difficult point that the diagonally positioned switches have similar fault characteristics. By analyzing the output characteristics under fault, it is found that the position and the cause of similar faults are related to the permutation of carrier in pulse width modulation. A four-state active fault diagnosis method is proposed in this article. First, the permutation of carriers is reconstructed to activate the fault behavior after the fault is detected. Under the specific four modulation states, the fault characteristics can be fully behaved. Next, based on the machine learning algorithm, the effective fault features are extracted from the voltage signals in four modulation states and the fault location is achieved. The experiments show that the proposed method could effectively distinguish similar faults, improve diagnostic accuracy and have better robustness.

Multiobjective Model-Free Predictive Control for Motor Drives and Grid-Connected Applications: Operating With Unbalanced Multilevel Cascaded H-Bridge Inverters

A multiobjective model-free predictive control (MO-MFPC) strategy is proposed in this article for multilevel cascaded H-bridge (MLCHB) inverters with unbalanced conditions. The compensated current variation (CCV), which allows the inclusion of the proportional and integral terms into the cost function, is generalized to improve the accuracy of MFPC over a wide range of applications. The new extended CCV is used to define the voltage control objective without involving the output voltage model of MLCHB. This voltage control objective is used to evaluate all state candidates to achieve a suitable subset for the current control objective. To achieve a better tradeoff between the current accuracy and the injected common-mode voltage (CMV), CMV is added to the cost function. Simulations and experimental evaluations show that, compared to existing MFPCs and classic model predictive control for MLCHB inverters, MO-MFPC achieves a better current accuracy over a wide range of applications and unbalanced MLCHB operating conditions.

A Comparative Study of Total Harmonic Distortion betweenTwo Topologies 27- and 31 Multi Level Inverter

In recent times, Multilevel inverters are considered an essential component of power electronics with widespread use in a wide range of high-voltage and high-power industrial and commercial applications. The use of multi-level inverters, also known as MLIs, has been preferred over conventional inverters due to the characteristics that these MLIs possess. These characteristics include low harmonic distortion caused by satisfacory performance of MLIs. This paper is concerned with analyzing harmonics to gain a deeper understanding of the performance of cascaded H-Bridge multilevel inverters (CHB-MLI). The model was constructed by using MATLAB/SIMULINK. A comparison was made between an asymmetrical cascaded 27 and 31-level multi-level inverter (MLI) by using the Phase disposition sinusoidal Pulse Width Modulation (PD-SPWM)and Phase Opposition Disposition sinusoidal Pulse Width Modulation (POD-SPWM) techniques. According to the outcomes of the simulations, 31 levels are better than 27 where Total Harmonic Distortion ( THD) in 31 levels is lower than 27 levels. The best result obtained during this study is 31 levels that use (PD-SPWM) technology, where the percentage of total harmonic distortion is small compared to the rest of the results and equal to 3.63%.

An Enhanced Space Vector PWM Strategies for Three Phase Asymmetric Multilevel Inverter

This work presents the two space vector pulse width modulation (SVPWM-I and SVPWM-II) strategies for eleven-level (11L) asymmetric cascaded H-bridge (CHB) multilevel inverter (MLI). Depending on the isolated structure and nonappearance of capacitor voltage balancing issues, the CHB MLI structure is favoured. These days, the SVPWM control method is accomplished superior consideration among the diverse PWM methods. In common, the SVPWM strategy is realized based on deteriorating higher-level hexagons into a lower level hexagon (2-level). Compared to the classical SVPWM strategy, the proposed SVPWM-I strategy decreases the memory and mathematical burden necessity included within the demonstration of eleven-level SVPWM devoid of losing the inverter output voltage (AC) contour by diminution the number of two-level hexagons. Also, the SVPWM-II strategy is presented, which incredibly diminishes the mathematical endeavours. The presented two SVPWM methods performed on an eleven-level asymmetric CHB multilevel inverter (MLI) by utilizing SIMULINK/MATLAB program tool and are compared with conventional sinusoidal PWM and Third harmonic injection (THI) PWM methods to confirm the proposed SVPWM methods. The proposed SVPWM methods give higher AC RMS voltage and lower harmonic distortion when compared to SPWM and THIPWM methods. To validate the presented two SVPWM control schemes, hardware results are taken on asymmetric eleven-level CHB MLI.

A Combinational Level-Shifted and Phase-Shifted PWM Technique for Symmetrical Power Distribution in CHB Inverters

In cascaded H-bridge (CHB) multilevel inverters (MLIs), phase-shifted pulse width modulation (PSPWM) and level-shifted pulse width modulation (LSPWM) are the two prominent techniques to attain multilevel and better performance. But both of them have certain drawbacks like in PSPWM the switching loss of all the semiconductors is high, and in LSPWM the power-sharing between the cascaded modules is not identical. These two drawbacks have been addressed in this article by proposing a novel modulation technique, named the phase opposed disposed phase-shifted PWM (PODPSPWM). In this technique, the level-shifted carriers have been rotated in such a way that there should not be any active power loss and simultaneously the carriers are phase-shifted as per the PSPWM technique. A detailed mathematical analysis of switching loss for all three methods has been presented. Moreover, the power-sharing and harmonic spectrum of the proposed PODPSPWM over other PWMs have been discussed. This novel modulation technique has been simulated in the MATLAB/Simulink software to validate the superiority of the operation. The 1.5-kW experimental prototype is developed to validate the performance of the proposed PODPSPWM modulation.

Mitigation Technique for Cascaded H-Bridge Multilevel Inverters Based on Pulse Active Width Modulation

This article considers <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${l}$ </tex-math></inline-formula> -level cascaded H-bridge (CHB) inverters and proposes a new modulation method based on pulse active width modulation (PAWM), capable to minimize all harmonics with order <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n&lt; 2l+1$ </tex-math></inline-formula> and to satisfy the European harmonic standards for medium-voltage-level applications EN 50 160 and CIGRE WG 36-05. A mathematical theorem and its proof are presented, stating the features of the procedure, which is an improvement of the selective harmonic elimination (SHE) PAWM proposed by Buccella et al. After a detailed description of the method, simulation and experimental results have been included, showing its capability to reduce low-order harmonics.

THD Minimization and Reliability Analysis of Cascaded Multilevel Inverter

Inverters are DC to AC power converters that are widely used in AC motor drives and distributed energy generation systems. Multi-Level Inverters (MLIs) have emerged as the preferred inverter technology because of their advantages of reduced switching losses and better harmonic profile. This paper deals with the Minimization of Total Harmonic Distortion (MTHD) of Symmetric Cascaded H-bridge Multi-Level Inverter (SCMLI) and Asymmetric Cascaded H-bridge Multi-Level Inverter (ACMLI). A hybrid memetic algorithm composed of heuristic PSO (Particle Swarm Optimization) algorithm and traditional MAS (Mesh Adaptive direct Search) is proposed to optimize the switching angles. In Photo Voltaic (PV) system, the input DC voltage generally varies from its nominal value due to the change in temperature and irradiance. Thus, the sensitivity analysis of THD and harmonics is also carried out considering the variations with non-integer magnitudes of input DC sources. The experimental prototype of SCMLI and ACMLI topology is developed and validated with simulation results. The reliability and Mean Time to Failure (MTTF) of SCMLI and ACMLI are investigated based on power losses of the MOSFET and thermal parameters.

Real-time hardware-in-loop based open circuit fault diagnosis and fault tolerant control approach for cascaded multilevel inverter using artificial neural network

Multilevel inverters (MLI) are finding widespread in various engineering and commercial applications owing to their immense performance. The cascaded H-bridge (CHB) inverter is the most potential MLI topology for renewable energy applications. The successful operation of the CHB-MLI depends on the integrity of the semiconductor devices and capacitors. Irrespective of its benefits the huge number of switches decreases the reliability of the inverter. Concerning reliability, this article proposes a fault-tolerant (FT) CHB MLI for solar photovoltaic applications. The proposed CHB MLI can withstand both the single and multiple open circuit faults in all the H-bridges of the CHB topology. The diagonally opposite switch pairs of CHB topology have similar fault features which lead to difficulty in finding the fault switches using the analytical fault diagnosis methods. Hence an artificial intelligence (AI) based fault diagnosis (FD) and FT operation of CHB MLI are interpreted. The proposed model offers complete FD and FT operation within one fundamental cycle which is advantageous relative to the existing methods. Compared to the existing methods, the proposed AI-based fault diagnosis strategy achieves a shorter diagnosis time and provides 96% classification accuracy between various fault conditions. Further, the simulation and HIL results demonstrated that the voltage magnitude and THD have been maintained at 8.24% before and after the fault state. In addition, the suggested FT structure ensures the constant output power over the post-fault operation for both single and multiple switch failure instances while improving the MLI resilience. The feasibility and performance of the proposed method have been investigated through related case studies using simulation and hardware-in-the-loop (HIL) tests on a single-phase fifteen-level CHB MLI.

Fault diagnosis in a five-level multilevel inverter using an artificial neural network approach

Introduction. Cascaded H-bridge multilevel inverters (CHB-MLI) are becoming increasingly used in applications such as distribution systems, electrical traction systems, high voltage direct conversion systems, and many others. Despite the fact that multilevel inverters contain a large number of control switches, detecting a malfunction takes a significant amount of time. In the fault switch configurations diode included for freewheeling operation during open-fault condition. During short circuit fault conditions are carried out by the fuse, which can reveal the freewheeling current direction. The fault category can be identified independently and also failure of power switches harmed by the functioning and reliability of CHB-MLI. This paper investigates the effects and performance of open and short switching faults of multilevel inverters. Output voltage characteristics of 5 level MLI are frequently determined from distinctive switch faults with modulation index value of 0.85 is used during simulation analysis. In the simulation experiment for the modulation index value of 0.85, one second open and short circuit faults are created for the place of faulty switch. Fault is identified automatically by means of artificial neural network (ANN) technique using sinusoidal pulse width modulation based on distorted total harmonic distortion (THD) and managed by its own. The novelty of the proposed work consists of a fast Fourier transform (FFT) and ANN to identify faulty switch. Purpose. The proposed architecture is to identify faulty switch during open and short failures, which has to be reduced THD and make the system in reliable operation. Methods. The proposed topology is to be design and evaluate using MATLAB/Simulink platform. Results. Using the FFT and ANN approaches, the normal and faulty conditions of the MLI are explored, and the faulty switch is detected based on voltage changing patterns in the output. Practical value. The proposed topology has been very supportive for implementing non-conventional energy sources based multilevel inverter, which is connected to large demand in grid.

Open circuit fault diagnosis and fault classification in multi-level inverter using fuzzy inference system

Multi-level inverters (MLIs) have been successfully used to integrated the renewable energy sources (RES) into microgrids. However, the operation of MLI is affected when an open circuit fault (OCF) or a short circuit fault occurs. Among these kinds of faults, there is a high prevalence of open circuit faults in MLI. Any fault in MLI must be identified and classified as soon as possible to maintain the reliability of the power supply. This work is focused on developing a Fuzzy Inference System (FIS) for detecting and classifying the open circuit faults in Cascaded H-Bridge Multi-Level Inverter (CHMLI), thereby improving the fault diagnosis accuracy and efficiency. In CHMLI, the gate pulse is generated by pulse width modulation (PWM) technique. The Mamdani Fuzzy Logic Controller (FLC) identifies and categorizes the different OCFs. Fuzzy logic rules are designed for detecting and classifying open circuit faults simultaneously using the fundamental Discrete Fourier components of voltage and current. Several combinations of open circuit faults have been studied in different switches of the MLI, along with the effect of fault inception angle. Furthermore, the test results support the feasibility of the proposed fuzzy-based fault diagnosis and classification scheme in a practical context. A real-time simulation obtained with the help of FPGA-based OPAL-RT 4510 demonstrates the robustness and effectiveness of the designed topology. All types and fault locations are considered in multiple cases of switch failure.

Performance of 7-level cascade H-bridge multi level inverter driven induction motor drive

In recent times, many of industrial applications require smooth control over a wide range of speeds or smooth torque control without effecting motor performance and efficiency. So, cascaded H-Bridge multilevel inverters convert the low or medium level voltage to medium or high level of output voltages. In this paper, a cascaded H-Bridge multilevel seven level inverter is operated by using sinusoidal pulse width modulation technique. This PWM technique will improves the smoothness of waveform by reducing the lower order harmonics. And analysed its performances like speed, torque, THD etc.