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A review of modulation techniques for hybrid multilevel inverter
Abstract
This paper presents the overview of modulation methods for hybrid multilevel inverters. Modulation techniques consider modulation index with respect to amplitude and frequency which are to be defined. These modulation techniques can be applied to various multilevel inverters. Some techniques can be applied directly to multilevel inverters while some modifications are required in some techniques for various multilevel inverters. Therefore, a given modulation technique can synthesize several multilevel configurations, significantly increasing flexibility and decreasing total harmonic distortion (THD). The purpose of the modulation techniques presented here is to observe effect of different techniques on different multilevel inverter topology. This paper presents a survey of different modulation techniques for different multilevel inverter for different level output.
... Generally, all the carrier signals have equal amplitude and frequency and lie in one phase. PD method is usually used for asymmetric MLI, and with the increase in the number of voltage levels, the harmonic contents are decreased [224]. ...
... This method involves all the carriers to be in phase opposition by 180 • to the nearest carriers [224]. ...
... This triangular carrier possesses identical frequency and amplitude; however, adjacent carriers have a definite phase shift between them [225]. The gate signals of the MLI switches are produced with the help of the on/off state of some logic circuit switches [224]. ...
In recent years, multilevel inverters (MLIs) have emerged to be the most empowered power transformation technology for numerous operations such as renewable energy resources (RERs), flexible AC transmission systems (FACTS), electric motor drives, etc. MLI has gained popularity in medium- to high-power operations because of numerous merits such as minimum harmonic contents, less dissipation of power from power electronic switches, and less electromagnetic interference (EMI) at the receiving end. The MLI possesses many essential advantages in comparison to a conventional two-level inverter, such as voltage profile enhancement, increased efficiency of the overall system, the capability of high-quality output generation with the reduced switching frequency, decreased total harmonic distortions (THD) without reducing the power of the inverter and use of very low ratings of the device. Although classical MLIs find their use in various vital key areas, newer MLI configurations have an expanding concern to the limited count of power electronic devices, gate drivers, and isolated DC sources. In this review article, an attempt has been made to focus on various aspects of MLIs such as different configurations, modulation techniques, the concept of new reduced switch count MLI topologies, applications regarding interface with renewable energy, motor drives, and FACTS controller. Further, deep insights for future prospective towards hassle-free addition of MLI technology towards more enhanced application for various fields of the power system have also been discussed. This article is believed to be extremely helpful for academics, researchers, and industrialists working in the direction of MLI technology.
... The zero reference is placed in the middle of the carrier sets. PD-PWM modulation commonly implemented in asymmetric multilevel topology and as the number of voltage levels is increased the harmonic for five contents are decreased [48]. ...
... In APOD-PWM all carries are alternatively in opposite disposition [48]. ...
... In this modulation, all the triangular carriers have the same frequency and the same amplitude, but with a definite phase shift between each adjacent carriers. The gate signals of the inverter switches are generated by comparing the modulating signals with the carrier waves then throughout a certain logic circuit switches are either turned on or off [48]. ...
... The well-known modulation techniques are pulse width modulation (PWM), space vector pulse width modulation (SVPWM), sinusoidal pulse width modulation (SPWM), phase shifted carrier PWM (PSC-PWM) and the selective harmonic elimination pulse width modulation technique (SHE-PWM). Many articles for improving modulation strategies have been investigated [1,14,15]. The researchers [16,17] have adopted a SiC technology instead of Si semiconductor switches. ...
The paper presents the practical design and implementation of a three-level neutral point clamped (TNPC) six-phase inverter rated at 100 kVA. The study initiates with prior work review, whereby most research work done earlier was mainly simulation-based. Based on the simulation results, this paper focuses on the practical aspects of inverter design, such as the development of a power board on an Insulated Metal Substrate, a gate driver board, an interconnect board, and the main control board. An inverter physical prototype has been built and tested at 500 V and 20 kW of output power. The SiC semiconductor technology is the base of the inverter, which represents the main merit of the work. Finally, high power density, compact design, and high efficiency are shown, which are major contributions of the paper. Tests performed proved that the designed converter was operating reliably and efficiently. While a simple Sinusoidal Pulse Width Modulation (SPWM) control algorithm has been implemented, the overall performance of the inverter showed great promise for higher-power applications. Compact and high-efficiency TNPC converters are developed for meeting increasing demands of advanced energy, automotive, and industrial applications.
... Moreover, it has been demonstrated that they can produce semiconductor switches with lower power dissipation and electromagnetic interference (EMI) [23]- [26]. Based on its architecture, MLIs are often classified into three fundamental topologies: Cascaded H-Bridge (CHB), Flying Capacitor (FC), and Neutral Point Clamped (NPC) [27]. Because of its versatility and easy modification to several levels, the CHB is widely used. ...
A multilevel inverter is a type of electrical equipment that converts a DC voltage to a higher AC value by creating a stepped waveform using several voltage levels. Multilevel inverters may create waveforms with three or more voltage levels, although regular inverters cannot. This separation results in lower harmonic distortion, decreased electromagnetic interference, and higher efficiency. An innovative MLI design that makes use of fewer switches and PV sources solves this problem. The Perturbation and Observation (P&O) approach is used to derive the Maximum Power Point Tracking (MPPT) from these PVs. The MC-SPWM technique was used in the design, simulation, and construction of single-phase and three-phase multilevel inverters with inverter levels ranging from three to twenty-five. The technique's cornerstones are phase disposition (PD-PWM) and power quality improvement. The main goal of the paper objectively analyzing the issue of power-system harmonics, providing information on causes, effects, and useful harmonic mitigation strategy.
... In this class, the Packed U-cell multilevel converter becomes one of the most advantageous topologies, which provide the fewest devices for the same number output voltage levels over the traditional inverters. This inverter topology was introduced by Al-Haddad in 2008 as a combination of the benefits of the (FC) and the (CHB) topologies [6]. PUC inverter can generate different multilevel voltages while using only six active power devices, one isolated direct source, and one capacitor as the second source to achieve seven-level output voltage by adapting the auxiliary capacitor to one-third of the first DC source. ...
... The essential aim of a modulation technique is to provide synchronized pulses for each switching device of an MLI [50]. Also, they are used to decrease the harmonic content of the output current and voltage waveforms. ...
Multilevel inverters (MLI) consist of a wide range of power converters. They have many designs and have been introduced with different circuit topologies such as neutral point clamped, diode clamped, cascaded H-bridges, and flying capacitors. Some of these MLIs have disadvantages, including design complexity, size, and losses due to the large number of switching devices required when they produce many output voltage levels. They are also bulky in size and may require several DC power sources. This paper presents a review of the various topologies of single-phase T-Type MLIs (T-MLIs). These MLIs are used to convert DC power from renewable energy sources (RES)” into AC with a near-sine waveform and low total harmonic distortion (THD). Simple and complex MLI designs are discussed. The major types of modulation techniques are discussed, including sinusoidal pulse width modulation (SPWM), selective harmonic elimination (SHE), and preprogrammed PWM. Various methods of output voltage control are taken into consideration as well. The aim of this comprehensive survey is to identify T-MLIs for researchers and those interested in the power conversion field, as well as to discuss the many topologies, identifying designs with superior characteristics that can be efficiently implemented with RESs to obtain better AC voltage with enhanced power quality.
... Cascaded inverter topology in comparison to a conventional three-level inverter allows a decrease in current and voltage harmonics and reduced switching losses of the inverter by distributing power over two inverters. In the proposed reactive power compensator, the hybrid modulation technique [22][23][24] is used for the forming of the compensator output voltage. In order to reduce switching losses, the majority of inverter power is produced using the first cascade operating at low (grid) frequency. ...
The topology of the static synchronous compensator of reactive power for a low-voltage three-phase utility grid capable of asymmetric reactive power compensation in grid phases has been proposed and analysed. It is implemented using separate, independent cascaded H-bridge multilevel inverters for each phase. Every inverter includes two H-bridge cascades. The first cascade operating at grid frequency is implemented using thyristors, and the second one—operating at high frequency is based on the high-speed MOSFET transistors. The investigation shows that the proposed compensator is able to compensate the reactive power in a low-voltage three-phase grid when phases are loaded by highly asymmetrical reactive loads and provides up to three times lower power losses in the compensator as compared with the situation when the compensator is based on the conventional three-level inverters implemented using IGBT transistors.
... These modern optimized methodologies offer numerous advantages, Although Newton-Raphson iterative (NRI) method remains the preferred primary choice because its algorithm is very simple with fast convergence rate, it requires appropriate firing angles initialization (Massrur et al. 2016) because an inappropriate initialization may increase the number of iterations and even cause divergence (Chandwani and Matnani 2012;Mohammadi and Akhavan 2014;Renu and Scholar 2014). Thus, the proposed technique is implemented using fmincon which helps the NRI technique to locate global minima region and then the modified NRI will find the exact convergence angles in just a few iterations. ...
This paper aimed at the prospect of an optimized algorithm for Selective Harmonic Elimination (SHE) through a hybrid control mechanism using fmincon and Newton-Raphson iterative method. In search of minimizing the Total Harmonic Distortion (THD), appropriate multi-level sequences and firing angles are used. This technique not only reduces the execution time but also improves the convergence rate. MATLAB simulations confirm that the algorithm is robust and the desired response is achieved within a few iterations for any range of modulation index. PSpice simulation verifies the successful removal of harmonics and confirms THD lies within limits specified by IEEE 519 standard. The implementation of this SHEPWM algorithm will improve the working of cascaded multi-level inverters by increasing their efficiency rate with respect to their speed.
... The performance of the inverter depends on the form of pulse width modulation schemes [7]. Continuous research is going on to introduce the high efficient PWM schemes. ...
- Considerable research is being carried out on the effect of the choice of PWM scheme on inverter performance. Discontinuous PWM schemes, initially developed by “Depenbrock” in 1977, has become one of the most promising modern PWM methods. This modulation scheme is also known as “Depenbrock PWM” scheme. In this paper the discontinuous modulation schemes are applied on the recently introduced five level Packed U-Cell (PUC-5) inverter. The THD index, common mode voltage (CMV) and utilization of DC link voltage are analyzed as they are important parameters of a typical inverter. To control theses parameters and output voltage, PWM is a best option for it. A comprehensive analysis of these modulation schemes are shown on the basis of the output THD and common mode voltage applied for PUC-5 inverter. A single phase prototype model is also presented which is used for validation of the concept.
... It is common to observe in power converters several modulating techniques, especially for multilevel converters. In order to generate the AC waveform in these kind of converters, it is possible to name the most widespread methods, such as Phase-Shifted (PS) Sinusoidal Pulse Width Modulation (SPWM), Staircase Nearest Level Modulation (NLM), Space Vector Modulation (SVM), among others [7], [8]. ...
... En convertidores de potencia es común ver muchas técnicas de modulación, particularmente en convertidores multinivel. Para generar la forma de onda en este tipo de convertidores, comúnmente se puede encontrar la modulación S-PWM, modulación escalera, modulación por vectores espaciales, etc [9], [10]. ...
... For asymmetric multilevel converters, the best modulation method is the hybrid modulation [23] that uses different frequencies for each power module. This allows a reduction in switching frequency, which leads to a reduction in the converter losses [19,24]. ...
Problems related to power quality, which in the last years were responsible only for small losses in low-voltage distribution systems, are now causing damage to power apparatuses and financial losses also in medium-voltage systems. The necessity of a better quality of power supply encourages the development of new specific custom power devices directly connected in medium-voltage distribution systems. It is well know that the multilevel converters are capable of being installed directly in the medium voltage, and presents several advantages when compared with conventional two-level converters. Some topologies, like the asymmetric cascaded multilevel converter, presents difficulties in regulating the voltages of all isolated dc-link capacitors. In this context, this article presents an asymmetric nineteen-level D–STATCOM (Distribution Static Synchronous Compensator) with a reactive power and dc-link regulation control loops for generic cascaded multilevel converters in order to improve the power quality in medium-voltage distribution systems. The performance of the proposed control method for a multilevel D–STATCOM is presented and evaluated in a downscaled prototype.
Wide attention from academia and industry has been received for Multilevel Inverters (MLIs) as they offer high power capacity, lower harmonics, and lower switching losses. The usage of many switches in the conventional configuration causes a limitation, which leads to the development of a new topology with a switch count. This paper presents the development of Reduced Switch Single Source (RSSS) MLI, which can produce all voltage levels. The analysis of RSSS MLI is done using nine-level MLI, which consists of a few components compared to conventional topologies, thereby ensuring reduced size, minimum switching loss, and installation cost. The harmonic contents of the output voltage are obtained and compared using the carrier-based PWM technique. MATLAB/Simulink environment and experimental tests in the laboratory are used to validate the results.
In this paper, an Adaptive Neuro Fuzzy Inference System (ANFIS) is proposed to the multilevel inverter to eliminate the Total Harmonic Distortions (THD) with a modified cascaded inverter. This method prohibits the variations presents in the output voltage of the modified cascaded inverter. The work is directed to prove that the importance of ANFIS is integrated learning for alteration of learning content affording to learners desires. The concert of the ANFIS model was calculated by means of standard error quantities which shows the ideal setting needed for better certainty. The MATLAB Simulink performance point out that it is affordable and easy to implement the performance of the ANFIS process. The study of different modified cascaded inverter consisting of five-level, seven-level, and nine- level is carried out for evaluating the THD with ANFIS controller and without ANFIS controller is implemented. The learning outcomes are based on the study of various system settings; it demonstrates the usability of the m-learning application. However, it must be noted that the number of inputs increased being considered by the model increases the system response time of the system.
Multilevel inverters (MLI) are aligned with lower harmonics and less commutation losses, which offer high power capacity. MLI is one of the best widespread converters due to its ability to eliminate the harmonic distortion without dropping the converter power output. The cascaded MLI is utilized for a reduced number of switches. In this topology, the switching angles at fundamental frequency are attained by solving the selective harmonic eliminations using sine cosine algorithm. This attains the desired output voltage with the elimination of certain lower order harmonics. In this paper, the analysis of seven-level cascaded MLI is presented with the scheme of carrier-based modulation techniques i.e. Phase-Disposition (PD), Phase-Opposition Disposition (POD) and Alternative Phase-Opposition Disposition (APOD). The Artificial intelligence (AI) is carried out for PD technique. These techniques are capable of defining the required switching angles to eliminate the preferred values of harmonics. The harmonic contents of output voltage in carrier-based modulation are observed with the indices, such as the modulation index with frequency modulation index and amplitude modulation index. The simulation results are obtained for seven-level inverter using MATLAB/SIMULINK. The hardware implementation is carried out using Main Power Management IC TPS65217C Beagle Bone Black Board for seven-level open loop control to justify the achievement of the suggested topology.
This paper aimed at the prospect of an optimized algorithm for Selective Harmonic Elimination (SHE) through a hybrid control mechanism using fmincon and Newton–Raphson iterative method. In search of minimizing the Total Harmonic Distortion (THD), appropriate multi-level sequences and firing angles are used. This technique not only reduces the execution time but also improves the convergence rate. MATLAB simulations confirm that the algorithm is robust and the desired response is achieved within a few iterations for any range of modulation index. PSpice simulation verifies the successful removal of harmonics and confirms THD lies within limits specified by IEEE 519 standard. The implementation of this SHEPWM algorithm will improve the working of cascaded multi-level inverters by increasing their efficiency rate with respect to their speed.
Nowadays multilevel converter topology has been growing since last few decades because it consists of lesser number of switches and DC sources. Multilevel converter topology integrates the stepped waveform to produce waveform nearly equal to sinusoidal waveform. To reduce switching losses and increasing efficiency of multilevel inverter the core idea is to minimize the number of switches. The proposed topology is based on minimum number of switches along with less number of voltage sources used. By using this hybrid topology with modified stair case modulation method THD obtained 18.38% for 7 level inverter and 5.61% for 21-level inverter without using passive filter. A comparison is made on THD and power loss of MLI on SSPWM and modified stair case modulation method. Using proposed method the power loss is 86.82% reduced as compare to CHB method for same level. A modified stair case modulation is used for triggering of switches. A MATLAB/SIMULINK model is used for the purpose. Hardware arrangement is yet to be realized.
Several control strategies have been proposed for diode clamped and flying capacitor multilevel inverters topologies which have their advantages. The observation for multicarrier modulation is quite similar for the above mentioned topologies, where as phase disposition technique has a superior line-to-line harmonic performance over alternative phase opposition disposition and phase opposition disposition techniques. Marx multilevel inverter derived from the Marx generator topology with the features of voltage balancing and boosting capability may find various applications in the field of renewable applications. This paper analyzes and propose the most suitable control strategy for the aforementioned topology. The detailed mathematical analysis and simulation results for various control algorithms for Marx inverter are presented in the paper.
This paper deals with a novel natural sampled pulse width modulation (PWM) switching strategy for voltage source inverter through carrier modi-fication. The proposed inverted sine carrier PWM (ISCPWM) method, which uses the conventional sinusoidal reference signal and an inverted sine carrier, has a better spectral quality and a higher fundamental component compared to the conventional sinusoidal PWM (SPWM) without any pulse dropping. The ISCPWM strategy enhances the fundamental output voltage particularly at lower modulation index ranges while keeping the total harmonic distortion (THD) lower without involving changes in device switching losses. The presented mathemati-cal preliminaries for both SPWM and ISCPWM give a conceptual understanding and a comparison of the strategies. The detailed comparison of the harmonic content and fundamental component of the ISCPWM output for different values of modulation index with the results obtained for the SPWM is also presented. Finally, the proposed modulator has been implemented in field programmable gate array (FPGA-Xilinx Spartan 3) and tested with the proto-type inverter.
Fuel cells have been considered as the primary energy source for the distributed power generation as they are highly efficient, modular and clean. The main drawback is that the dc voltage generated by a single fuel cell varies from 0.7V to 1V. Due to the low input voltage in fuel cells, a suitable power conditioner is required to interface to the utility grid or local loads. To meet this requirement, this paper presents the design, development and performance of a hybrid cascaded multilevel inverter. The advantage of the proposed topology is that the modulation, control and protection requirements of each bridge are modular and it requires only a single dc source in each phase leg. A two-level H-bridge inverter using variable frequency inverted sine wave carrier modulation technique has been studied for total harmonic distortion (THD) and switching losses for fuel cell applications. A detailed study of the technique was carried out through MATLAB/SIMULINK for switching losses and THD. The results were verified experimentally. It was noticed that the proposed modulation strategy results in lower switching losses for a chosen THD as compared to the conventional strategies.
Multilevel inverters have emerged as the state of the art power conversion systems for high power medium voltage applications. Many topologies and modulation methods are commercially available. This paper presents a new adaptive duty cycle modulation algorithm, that reduces the switching frequency and consequently the switching losses. This can be important for high power applications, where high frequency modulation methods like PWM are not suitable. Results are shown for a nine level asymmetric cascaded inverter. Output voltage waveforms obtained for references with variable frequencies and amplitudes show a similar switching pattern, with a reduced and near constant number of commutations per cycle, regardless the reference frequency and amplitude. The proposed modulation is compared to a multiple carrier PWM method, achieving the same fundamental reference tracking performance with a reduced number of commutations
Multilevel cascaded and hybrid inverter systems conventionally use
three level bipolar PWM for each individual inverter, with their
carriers phase shifted to achieve maximum harmonic cancellation within
each phase leg. This has been shown to give a harmonic performance
equivalent to APOD modulation of a NPC multilevel inverter, when the
switching frequencies are scaled to achieve the same number of overall
switch transitions. In contrast, PD modulation of a NPC inverter is
harmonically superior, because it places harmonic energy directly into
the carrier harmonic for each phase leg, and relies on cancellation of
this harmonic across phase legs as the line-to-line voltage is
developed. Using this understanding, a new discontinuous modulation
strategy is proposed for a hybrid inverter which achieves a similar
level of improvement in line-to-line harmonics compared to conventional
three level modulation of this type of inverter
Analytical solutions of pulse width modulation (PWM) strategies
for multilevel neutral point clamped (NPC) and cascaded inverters are
presented. These solutions show that the alternative phase opposition
disposition (APOD) PWM strategy for NPC inverters produces the same
spectral components as the phase shifted carrier PWM (PSCPWM) strategy
for cascaded inverters, when the carrier frequencies are adjusted to
achieve the same number of total switch transitions for each inverter
over one fundamental cycle. From this understanding, a method is
proposed to apply the harmonically superior phase disposition (PD) PWM
strategy for NPC inverters to cascaded inverters, to achieve improved
harmonic performance for the modulation of cascaded inverters. Both
theoretical and experimental results confirming this understanding are
presented
PWM strategies have been the subject of many years of research
effort, and the merits of the various alternatives investigated have
been argued extensively. In general, it is now accepted that natural or
asymmetrical regular sampled PWM with a third harmonic injected or a
space vector centered reference waveform gives the best harmonic
performance, with discontinuous modulation having some advantages for
higher modulation ratios. This paper uses a general analytical solution
for carrier based PWM to mathematically identify the harmonic
cancellation that occurs in various PWM implementations and converter
topologies. This solution provides a formal justification for the
superiority of natural and asymmetrical regular sampling techniques in
eliminating half of their sideband harmonics simply by virtue of their
phase leg switching. Then the use of fundamental reference phase
shifting between phase legs to create single and three phase I-I output
voltages is reviewed, and the harmonic cancellation that occurs is
identified. One significant result from this analysis is the realisation
that an odd/triplen carrier/fundamental ratio has no intrinsic harmonic
benefit, contrary to the generally accepted wisdom. Finally,
opportunities for harmonic elimination in multi-level cascaded inverter
systems by carrier phase shifting are investigated, and the optimum
phase shift is identified
The use of multilevel inverters has become popular in recent years
for high power applications. Various topologies and modulation
strategies have been reported for utility and drive applications in the
recent literature. This paper is devoted to the investigation of a 500
hp induction motor drive based on a seven-level 4.5 kV hybrid inverter.
The topological structure and operating principles of the proposed
approach are presented. Various design criteria, spectral structures and
other practical issues such as capacitor voltage balancing are
discussed. The feasibility of the proposed approach is verified by
computer simulations
Pulsewidth modulation (PWM) strategies have been the subject of
many years of research effort, and the merits of the various
alternatives investigated have been argued extensively. In general, it
is now accepted that natural or asymmetrical regular sampled PWM with a
third harmonic injected or a space-vector centered reference waveform
gives the best harmonic performance, with discontinuous modulation
having some advantages for higher modulation ratios. This paper uses a
general analytical solution for carrier-based PWM to mathematically
identify the harmonic cancellation that occurs in various PWM
implementations and converter topologies. This solution provides a
formal justification for the superiority of natural and asymmetrical
regular sampling techniques in eliminating half of their sideband
harmonics simply by virtue of their phase leg switching. Then, the use
of fundamental reference phase shifting between phase legs to create
single- and three-phase 1-1 output voltages is reviewed, and the
harmonic cancellation that occurs is identified. One significant result
from this analysis is the realization that an odd/triplen
carrier/fundamental ratio has no intrinsic harmonic benefit, contrary to
the generally accepted wisdom. Finally, opportunities for harmonic
elimination in multilevel cascaded inverter systems by carrier phase
shifting are investigated, and the optimum phase shift is identified
Trends in power semiconductor technology indicate a tradeoff in
the selection of power devices in terms of switching frequency and
voltage-sustaining capability. New power converter topologies permit
modular realization of multilevel inverters using a hybrid approach
involving integrated gate commutated thyristors (IGCTs) and insulated
gate bipolar transistors (IGBTs) operating in synergism. This paper
investigates a hybrid multilevel power conversion system typically
suitable for high-performance high-power applications. This system,
designed for a 4.16 kV⩾100 hp load is comprised of a hybrid
seven-level inverter, a diode bridge rectifier, and an IGBT rectifier
per phase. The IGBT rectifier is used on the utility side as a real
power flow regulator to the low-voltage converter and as a harmonic
compensator for the high-voltage converter. The hybrid seven-level
inverter on the load side consists of a high-voltage slow-switching IGCT
inverter and a low-voltage fast-switching IGBT inverter. By employing
different devices under different operating conditions, it is shown that
one can optimize the power conversion capability of the entire system. A
detailed analysis of a novel hybrid modulation technique for the
inverter, which incorporates stepped synthesis in conjunction with
variable pulsewidth of the consecutive steps is included. In addition,
performance of a multilevel current-regulated delta modulator as applied
to the single-phase full-bridge IGBT rectifier is discussed. Detailed
computer simulations accompanied with experimental verification are
presented in the paper
Multilevel inverter is an effective and practical solution for increasing power and reducing harmonics of ac waveforms. Several multilevel topologies are reported and the most popular topology is Cascaded Multilevel Inverter (CMLI). This paper focuses on asymmetric cascaded multilevel inverter employing variable frequency inverted sine PWM technique (VFISPWM). This technique combines the advantage of inverted rectified sine wave and variable frequency carriers for a seven level inverter for balancing the switch utilization. A detailed study of the technique was carried out through MATLAB/SIMULINK for switching losses and THD. Furthermore, a PI controller is used to control the MLI using the proposed PWM technique. The results were verified experimentally and FPGA processor is used for PWM. It was noticed that the proposed modulation strategy results in lower switching losses for a chosen THD as compared to the conventional strategies.
This paper presents a new variation of hybrid phase disposition pulse width modulation technique suitable for cascaded multilevel inverter. A hybrid PDPWM is developed based on low frequency PWM and high frequency Sinusoidal PWM. An optimized sequential switching scheme introduced in this proposed method to equalize electro static and electro magnetic stress among the power devices. It is confirmed that the proposed technique offers significantly lower switching losses and switching transitions. Furthermore, the proposed hybrid PDPWM offers better harmonic performance compared to its conventional PWM counterpart. Simulation results are included in this paper in order to confirm the effectiveness of the proposed technique.
Various topologies and modulation strategies of multi-level inverters have been proposed for utility and drive applications. This paper studies multi-carrier PWM methods for asymmetric multi-level inverter. Phase disposition, phase opposition disposition and alternative phase opposition disposition methods are discussed considering switching frequencies, spectrum of the output waveform and the use of inverter state redundancies.
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Carrier-based methods have been used widely for switching of multilevel inverters due to their simplicity, flexibility and reduced computational requirements compared to space vector modulation (SVM). Several multi-carrier modulation methods with miscellaneous properties have been already known. The paper also proposes another three new multi-carrier techniques being more efficient for high-power inverter applications. While evaluating and comparing these new methods with all basic methods, such as PS, PD, POD and APOD through measures like THD, WTHD, WTHDO, switching losses and DC bus utilization, the paper shows their advantages for applications of diode-clamped and cascade multi-level topologies by simulation results. The validity of obtained results is approved by experimental results.
This paper develops a detailed analysis about the impact of hybrid multilevel modulation strategy on the harmonic content of the input currents and output voltages. Advantages and limitations of this modulation strategy are firstly discussed from the load point of view. After, this paper proposes a new modulation strategy for hybrid multilevel inverters, which can be used with asymmetrical multipulse connection of uncontrolled rectifiers to improve the input harmonic performance of adjustable-speed drives for any operating point. This new modulation strategy maintains the original capability to synthesize output voltages with reduced harmonic distortion and makes possible to eliminate undesired low-frequency harmonics from input currents in all operating range, even when the series-connected cells process distinct active power levels.
Multilevel inverters are becoming popular in the past few years for high voltage and high power applications. Various topologies and modulation strategies have been investigated for utility and drive applications in the recent literature. However, most of the reported topologies for multilevel structures employ DC voltage sources of equal magnitudes. This paper is devoted to the investigation of a generalized structure of multilevel power converter where these discrete voltage sources are not necessarily equal. The topological structures, operating principles and performance characteristics resulting from this general approach are presented. Various design criteria and issues like spectral structure are discussed. A comparative evaluation of various alternatives obtained from the generalized structure is presented.
This paper investigates and analyses different multicarrier PWM
methods for a single phase five level cascaded inverter. Carrier
disposition methods, phase shifted and a hybrid method are discussed
with respect to resulting switching frequencies, complexity of
implementation, spectrum of the output waveform, and the use of inverter
state redundancies to perform additional application specific control
tasks, such as power flow control from each DC source. A concept of
separating the waveshaping function from the switch selection is
explored and selected experimental results are presented
A generalization of the PWM (pulse width modulation) subharmonic method for controlling single-phase or three-phase multilevel voltage source inverters (VSIs) is considered. Three multilevel PWM techniques for VSI inverters are presented. An analytical expression of the spectral components of the output waveforms covering all the operating conditions is derived. The analysis is based on an extension of Bennet's method. The improvements in harmonic spectrum are pointed out, and several examples are presented which prove the validity of the multilevel modulation. Improvements in the harmonic contents were achieved due to the increased number of levels.
Analytical solutions of pulsewidth-modulation (PWM) strategies for multilevel inverters are used to identify that alternative phase opposition disposition PWM for diode-clamped inverters produces the same harmonic performance as phase-shifted carrier PWM for cascaded inverters, and hybrid PWM for hybrid inverters, when the carrier frequencies are set to achieve the same number of inverter switch transitions over each fundamental cycle. Using this understanding, a PWM method is then developed for cascaded and hybrid inverters to achieve the same harmonic gains as phase disposition PWM achieves for diode-clamped inverters. Theoretical and experimental results are presented in the paper.
Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate DC sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed.
A new neutral-point-clamped pulsewidth modulation (PWM) inverter composed of main switching devices which operate as switches for PWM and auxiliary switching devices to clamp the output terminal potential to the neutral point potential has been developed. This inverter output contains less harmonic content as compared with that of a conventional type. Two inverters are compared analytically and experimentally. In addition, a new PWM technique suitable for an ac drive system is applied to this inverter. The neutral-point-clamped PWM inverter adopting the new PWM technique shows an excellent drive system efficiency, including motor efficiency, and is appropriate for a wide-range variable-speed drive system.
Use of multilevel converters in ship propulsion drives
- K A Corzine
- S D Sudhoff
- E A Lewis
- D H Schmucker
- R A Youngs
- H J Hegner
Application specific harmonic performance evaluation of multilevel pwm techniques