Cascaded Multilevel Inverter Research Articles

A Single DC Source Cascaded Seven-Level Inverter Integrating Switched-Capacitor Techniques

In this paper, a novel cascaded seven-level inverter topology with a single input source integrating switched-capacitor techniques is presented. Compared with the traditional cascade multilevel inverter, the proposed topology replaces all the separate dc sources with capacitors, leaving only one H-bridge cell with a real dc voltage source and only adds two charging switches. The capacitor charging circuit contains only power switches, so that the capacitor charging time is independent of the load. The capacitor voltage can be controlled at a desired level without complex voltage control algorithm and only use the most common carrier phase-shifted sinusoidal pulse width modulation strategy. The operation principle and the charging–discharging characteristic analysis are discussed in detail. A 1-kW experimental prototype is built and tested to verify the feasibility and effectiveness of the proposed topology.

Investigation on cascade multilevel inverter with symmetric, asymmetric, hybrid and multi-cell configurations

In recent past, numerous multilevel architectures came into existence. In this background, cascaded multilevel inverter (CMLI) is the promising structure. This type of multilevel inverters synthesizes a medium voltage output based on a series connection of power cells which use standard low-voltage component configurations. This characteristic allows one to achieve high-quality output voltage and current waveforms. However, when the number of levels increases switching components and the count of dc sources are also increased. This issue became a key motivation for the present paper. The present paper is devoted to investigate different types of CMLI which use less number of switching components and dc sources and finally proposed a new version of Multi-cell based CMLI. In order to verify the proposed topology, MATLAB – simulations and hardware verifications are carried out and results are presented.

A Modular Cascaded Multilevel Inverter Based Shunt Hybrid Active Power Filter for Selective Harmonic and Reactive Power Compensation Under Distorted/Unbalanced Grid Voltage Conditions

A Modular Cascaded Multilevel Inverter Based Shunt Hybrid Active Power Filter for Selective Harmonic and Reactive Power Compensation Under Distorted/Unbalanced Grid Voltage Conditions

A Modular Cascaded Multilevel Inverter Based Shunt Hybrid Active Power Filter for Selective Harmonic and Reactive Power Compensation Under Distorted/Unbalanced Grid Voltage Conditions

In recent years, shunt hybrid active power filters are being increasingly considered as a viable alternative to both passive filters and active power filters for compensating harmonics. In literature, their applications are restricted to balanced systems and low voltage applications and therefore not for industrial applications. This paper investigates the performance of a modular cascaded multilevel inverter based Shunt Hybrid Active Power Filter (SHAPF) for reactive power compensation and selective harmonics elimination under distorted/unbalanced grid voltage conditions in medium voltage levels. In the proposed control method, reactive power compensation is achieved successfully with a perceptible amount and the performance results of harmonic compensation are satisfactory. Theoretical analysis and simulation results are obtained from an actual industrial network model in PSCAD. The simulation results are presented for a proposed system in order to demonstrate that the harmonic compensation performance meets the IEEE-519 standard.

Negative Harmonics Injection Cuddled Equal Area Criteria Based Selective Harmonic Elimination Pulse Width Modulation Techniques for Multilevel Cascaded Inverters

Selective Harmonics Elimination (SHE) technique of power electronic converters can be generally defined as calculation of the optimized switching angles at any desired output (fundamental) voltage component to eliminate a set of preferred lower order harmonic components. This low switching frequency method adds values to Multilevel Inverter (MLI) based systems for the reason that MLI’s have the ability to synthesize waveforms closer to sinusoidal with a better harmonics spectrum. The traditional method for finding the optimized switching angles is by solving the Fourier non-linear transcendental equations of the MLI output voltage and various algorithms like Newton-Raphson (NR) algorithm, Genetic algorithm (GA), Resultant theory, Walsh function etc. are available. This paper proposes a novel approach for performing SHE in MLI working with both equal and unequal dc voltages. The basic principle in which the proposed technique works is a combined effect of equal area criteria and negative harmonics injection techniques. The major advantage is that the proposed methodology comprises of four simple equations for performing SHE instead of solving the complex non-linear transcendental equation. The computational efficiency of this algorithm is evaluated through comparison with traditional NR and GA. In addition, a prototype of three-phase seven-level cascaded MLI is designed through which several informative results are investigated and the effectiveness of the proposed algorithm is proved.

A Modified Switched-Diode Topology for Cascaded Multilevel Inverters

In this paper, a single phase modified switched-diode topology for both symmetrical and asymmetrical cascaded multilevel inverters is presented. It consists of a Modified Switched-Diode Unit (MSDU) and a Twin Source Two Switch Unit (TSTSU) to produce distinct positive voltage levels according to the operating modes. An additional H-bridge synthesizes a voltage waveform, where the voltage levels of either polarity have less Total Harmonic Distortion (THD). Higher-level inverters can be built by cascading MSDUs. A comparative analysis is done with other topologies. The proposed topology results in reductions in the number of power switches, losses, installation area, voltage stress and converter cost. The Nearest Level Control (NLC) technique is employed to generate the gating signals for the power switches. To verify the performance of the proposed structure, simulation results are carried out by a PSIM under both steady state and dynamic conditions. Experimental results are presented to validate the simulation results.

Optimum Structures of a Cascaded Multilevel Inverter for Minimum Number of Power Electronic Devices

Optimum Structures of a Cascaded Multilevel Inverter for Minimum Number of Power Electronic Devices

Capacitor-Voltage Balancing for a Modular Multilevel DSCC Inverter Driving a Medium-Voltage Synchronous Motor

This paper provides a comprehensive discussion on voltage balancing of all the floating capacitors in a modular multilevel cascade inverter based on double-star chopper cells (DSCC) or a modular multilevel DSCC inverter. It intends to use the inverter for driving a medium-voltage synchronous motor. Theoretical and numerical design considerations on both amplitude and phase of the three-phase motor currents achieve better capacitor-voltage balancing in a low-power low-frequency range. A three-phase DSCC inverter with phase-shifted-carrier pulse width modulation is designed, constructed, and tested to drive the 370-V 15-kW 75-Hz six-pole interior-permanent-magnet synchronous motor loaded with a hypothetical centrifugal compressor. Experimental results verify the validity of the theoretical analysis, as well as the effectiveness and viability of the DSCC inverter for such a specific electrical drive.

Interfacing renewable energy sources to the ac grid by a 43-level CMLI with many advantages

This paper proposes a 43-level asymmetric cascaded multilevel inverter (CMLI) as an interface between renewable energy sources and the grid, that has the following advantages:1.The CMLI consists of only four H-bridges per phase, with separate dc sources. Renewable energy sources of different types are treated as the dc sources of the CMLI (e.g., dc voltage from PV panels, rectified ac voltage from wind turbines, etc.).2.It can interface different types of renewable energy sources instantaneously to feed the ac grid with a nearly sinusoidal voltage with very low total harmonic distortion (THD).3.It can accommodate natural fluctuations in the renewable energy sources and provide output voltage regulation against many fluctuations in these sources while keeping very low value of the THD for its output voltage.An approach using a mixed integer linear programming (MILP) optimization model is applied to determine the switching angles of the power switches of this CMLI to minimize the values of the undesired low order harmonics. A mathematical model is proposed, that can be applied for uniform step CMLIs, and this is applied for normal operation cases. Then a modification to this model is given that can be applied for some disturbance cases in the dc sources These models are applied for the single phase and three phase cases. For each case, an output voltage amplitude is selected first for normal operation at the nominal values of the dc sources, whose harmonics absolute values agree with the IEEE Standards 519-1992 for voltage distortion limits. Then the following disturbance cases are analyzed:1.Fluctuations of all the dc sources within ±20% of their nominal values.2.Dropping some dc sources below 80% of their nominal values.The models are applied under the required value of the output voltage with an allowed deviation within ±5%. Solutions are obtained that give the switching angles of the inverter at these disturbances in the dc sources while keeping low values of the output voltage THD, and still satisfying the IEEE standards for voltage distortion limits up to 59kV for single phase case and up to 161kV for three phase case.

Harmonic Elimination of Seven Level Inverter with Switching Pattern Reconfiguration Technique Using Hybrid BBO/MAS Algorithm

<p>A hybrid optimization algorithm is proposed in this paper to find the optimum switching angles in a Cascaded Multilevel Inverter (CMLI). A seven level cascaded inverter is considered and optimum switching angles are found by hybrid Biogeographical Based Optimization search (BBO) / Mesh Adaptive Direct Search (MAS) algorithm. The fundamental frequency Selective Harmonic Elimination-Pulse Width Modulation (SHE-PWM) technique is applied in order to reduce the switching losses.Reconfiguration technique is also proposed to achieve harmonic elimination for entire Modulation index(M). The various performance indices like phase THD, line THD, lower order harmonics eliminated in a CMLI are calculated based on the optimized switching angles. A seven level CMLI is simulated in MATLAB/SIMULINK by using switching angles calculated from BBO/MAS algorithm and the FFT analysis of traditional SHE-PWM and reconfiguration SHE-PWM methods are compared and verified with the calculated values from BBO/MAS algorithm.</p>

Transformer-Less Unified Power-Flow Controller Using the Cascade Multilevel Inverter

The conventional unified power-flow controller (UPFC) that consists of two back-to-back inverters requires bulky and often complicated zigzag transformers for isolation and reaching high voltage. This paper proposes a completely transformer-less UPFC based on an innovative configuration of two cascade multilevel inverters (CMIs). The unique configuration and control of the two CMIs as a power-flow controller make it possible to independently control active and reactive power flows over a line. The new UPFC offers several advantages over the traditional technology, such as transformer-less, light weight, high efficiency, high reliability, low cost, and fast dynamic response. The transformer-less UPFC is thereby very suited for fast and distributed power flow control, such as wind and solar power transmission. Experimental results based on 13.8-kV/2-MV·A transformer-less UPFC prototype are shown to validate the theoretical analysis and operating principle.

A Predictive Capacitor Voltage Control of a Hybrid Cascaded Multilevel Inverter With a Single DC-Link and Reduced Common-Mode Voltage Operation

For cascaded multilevel inverter topologies with a single dc supply, closed-loop capacitor voltage control is necessary for proper operation. This paper presents zero and reduced common-mode voltage (CMV) operation of a hybrid cascaded multilevel inverter with predictive capacitor voltage control. Each phase of the inverter is realized by cascading two- three-level flying capacitor inverters with a half-bridge module in between. For the presented inverter topology, there are redundant switching states for each inverter voltage levels. By using these switching state redundancies, for every sampling instant, a cost function is evaluated based on the predicted capacitor voltages for each phase. The switching state that minimizes cost function is treated as the best and is switched for that sampling instant. The inverter operates with zero CMV for a modulation index upto 86%. For modulation indices from 86% to 96%, the inverter can operate with reduced CMV magnitude ( $V_{\rm dc}/18$ ) and reduced CMV switching frequency using the new space-vector pulsewidth modulation (SVPWM) presented herein. As a result, the linear modulation range is increased to 96% as compared to 86% for zero CMV operation. Simulation and experimental results are presented for the inverter topology for various steady state and transient operating conditions by running an induction motor drive with open loop $V/f$ control scheme.

Cascaded multilevel inverter using series connection of novel capacitor‐based units with minimum switch count

This paper presents a new family of cascaded multilevel inverters (CMLIs) which can generate a considerable number of output voltage levels with minimum number of required accompanying switching devices. Conceptually, each stage of proposed CMLI is composed of using a novel capacitor-based unit including two floating capacitors, one embedded dc voltage source and three power switches. In this case, the balanced voltage of integrated capacitors can be precisely provided as self-voltage balancing without using any auxiliary circuits, close loop systems and intricate modulation techniques. In addition, to reach different number of output voltage levels, four different algorithms pertaining to the symmetrical, binary asymmetrical, trinary asymmetrical and also hybrid patterns for determining the magnitude of isolated dc voltage sources are presented. Hereby, proposed hybrid structure is capable of working under mixed switching frequency without aiming the conventional full H-Bridge cell. Therefore, a high quality of output waveforms with reduced switching devices as well as power loss dissipation can be alternatively achieved. To confirm the validity of proposed CMLI, a complete comparison with several recently presented topologies besides several simulation and experimental results based on trinary asymmetrical and hybrid evolved structures will be also given.

Economical design of H-bridge multilevel inverter drive controlled by modified fast algorithm

Traditional cascaded multilevel inverter needs n DC voltage sources to give 2n+1 levels. As number of levels increased, the amount of switching devices, their proper related drive circuits and their controllers and other components are also increased excessively, making the inverter more complex and costly. A simple and low cost single-phase cascade multilevel inverter with no transformers can be implemented using only single-DC source with n-1 DC sources represented by capacitors and with reduced switches. So, current inverter hardware cost can be reduced abruptly as compared with conventional one.When the number of DC sources is increased, inverter output has higher harmonic content characterized by their transcendental equations that become more complicated and required more time to be solved. New technique is exhibited to find the inverter switching angles by executing modified fast recursive algorithm providing an on-line precise solution for the Harmonic Elimination (HE) problem. The suggested optimized algorithm technique have been used to find optimum switching angles necessary to eliminate any number of lowest order harmonics and maintain the desired fundamental voltage for driving an AC motor. Simulation results of cascade 7-level inverter with single-DC source under the optimized HE stepped waveform technique is used to eliminate the 3rd and 5th harmonics. Prototype design for the proposed inverter loaded by single-phase fan motor is built.

A New Topology for Regulation of Active Power by Battery Storage System with Cascaded Multilevel Inverter using Three Phase System

The battery plays a major role for energy storage in non conventional energy systems. This paper proposed an AC-DCAC converter using Pulse Width Modulation Technique for Multilevel inverter. Normally the voltage drop increases when the load increases. Because the load voltages are consume more than the source voltages. To overcome this problem, the battery energy depot system is linked to the converter for controlling the active power. The performance of the proposed topology is a present active power regulates in battery energy depot scheme has been verified by simulation MATLAB/SIMULINK environment.

A simple modular multilevel inverter topology for the power quality improvement in renewable energy based green building microgrids

The advent of multilevel inverter topologies paves path for the realization of renewable energy based microgrids for various classes of consumers. But, these topologies are offering concerns with design complexity, power quality, dv/dt stresses, capacitor voltage balancing, etc. In view of these challenges, this paper proposes a simple Modular Cascaded Multilevel Inverter with modified Uni-Polar Shifted Carrier Pulse Width Modulation (MCMI-mUPSC PWM) topology for microgrids. The proposed MCMI topology eliminates the use of clamping diodes, capacitors, and requires only 1/4th (25%) of the DC input voltage that is used in any conventional topology to produce the same amount of output voltage. This leads to the reduction in switching devices’ rating and dv/dt stresses. The proposed mUPSC PWM reduces the magnitude of hazardous lower order harmonics by shifting them to higher order components around the region of integral multiples of switching frequency. Thus, the proposed MCMI-mUPSC PWM topology simplifies the design of multilevel inverters along with aforesaid advantages. For the analysis, microgrid modelling and simulations are carried out in MATLAB/Simulink®. The effectiveness of the proposed topology is evaluated by calculating various power quality indices under dynamic and non-linear loading conditions. These indices are compared with the conventional topology with respect to standard tolerances. From results, it is observed that the proposed topology has improved the power quality along with the elimination of some of the inherent problems of the multilevel inverters. This enhances the plausibility of microgrid installations towards smart and net-zero energy buildings.

Minimization of Total Harmonic Distorsion for Cascaded Multilevel Inverter with Reduced Number of Switches

Minimization of Total Harmonic Distorsion for Cascaded Multilevel Inverter with Reduced Number of Switches

Fuzzy Logic Controlled Harmonic Suppressor in Cascaded Multilevel Inverter

<p>This paper presents an investigation of seven level cascaded H-bridge (CHB) inverter in power system for compensation of harmonics.For power quality control a Fuzzy Logic Control (FLC) giving comparatively better harmonic reduction than the conventional controllers. Harmonic distortion is the most important power quality problem stirring in multilevel inverter, the harmonics can be eliminated by an optimal selection of switching angles. A hybrid evaluation technique evaluates the obtained optimal switching angles that are attained from the fuzzy inference system as well as neural network. The proposed method will be implemented in MATLAB working platform and the harmonic elimination performance will be evaluated.</p>

Improved Output Voltage Quality using Space Vector Modulation for Multilevel Inverters

Space vector modulation (SVM) has received wide acceptance due to many benefits over other techniques such as higher output voltages, lower total harmonic distortion (THD), high-efficiency and flexible to be implemented in vector control systems. In digital implementation, the SVM equations can be optimally computed by eliminate the use of complex forms. In this paper, the simple SVM based on twolevel inverter is employed for higher levels of inverters. This is to retain the simplicity of SVM computation for three-level and five-level cascaded H-bridge multilevel inverter (CHMI). Moreover, the proposed method utilizes two controller boards to perform high computational workloads and to eliminate glitch and error problems. Experiment results show that the THD of output voltage in five-level CHMI gives the smallest value among the results obtained from other levels.

Validation of a Three-Phase Cascaded Multilevel Inverter based on Newton Raphson (N.R.)

Objective: This paper discusses the configuration three-phase Cascaded H-Bridge Multilevel Inverter (CHBMLI) based on Newton Raphson (N.R.) method to produce obtain five-levels of output voltage by reduce Total Harmonic Distortion (THD). Method: The proposed method had been comprised of 5-level multilevel inverter, while the control system was based on the Newton Raphson (N.R.) method. Moreover, the main purpose of the research was to investigate the effectiveness of the proposed method by using NR for harmonic analysis in high voltage electrical distribution system. Besides, the optimization of the controller based on modulation indexes was employed in order to optimize and non-optimize the switching angle of the CHBMLI for different modulation indexes. Findings: An inverter is used to convert DC power generator from the DC supply into AC power. The five-level inverter resulting in increased voltage levels of the output waveform. As the levels of output waveform increase, the percentage of THD reduced and switching losses decreased to improves power quality have been done compared with conventional three phase Dc supply connected PWM cascaded H-bridge multilevel inverter. Based on Newton Raphson (N.R.) five-level of output voltage is produced by the inverter zero, +1/2Vdc, +Vdc, -1/2Vdc and -Vdc. Improvements: Apart from that, the proposed scheme was modelled with MATLAB software and the Simulation results were verified via hardware experimental by using Digital Signal Processing (DSP) TMS320F2812. The experimental results showed that the proposed method had been effective in verifying the NR control in terms of Total Harmonic Distortion (THD).