The introduced FCMLI gives that it consists of less number of switches and gate drivers. And also it has features of voltage balancing property, purge the more dc source, double the output voltage levels, get better the output frequency range. The phase shift PWM technique can be used to achieve nine level output voltage. But in a new structure of FCMI the two low frequency switches makes to provide the full DC input i.e., for both the peak levels. And also produce a double RMS and increasing the output levels. And it is decreases the count of flying capacitors. The output voltages with nine level FCMI as shown in the figure. The THD and other parameters analysis are taken as from the simulation itself. The simulation output give a efficient, no distortions and without losses in the output levels. The proposed structure has a possibility to withstand in high power rating applications, such as ac drives, filters, FACTS controllers and etc., both the simulation and hardware results provide good performance and feasibility of proposed FlyingCapacitorMultilevelInverter (FCMI).
KEYWORDS: FlyingCapacitorMultilevelInverter, Multilevelinverter, Phase Opposition Disposition –Pulse Width Modulation, Sinusoidal Pulse Width Modulation, Total Harmonic Distortion
The Multilevel voltage source inverter topologies are the best suited for medium and high voltage applications in the industries . Mainly, there are three topologies of multilevel voltage source inverters [1–5]: neutral point clamped (NPC) ,flyingcapacitor (FC) and cascaded H-bridge (CHB). The flyingcapacitor topology allows the conventional inverter to produce higher output voltages by using standard low-voltage switches available in the market, controlling the real and reactive power flow easily.
for PD scheme.
IV. C OMPARISON WITH O THER T OPOLOGIES
A Comparison between the proposed topology and different 5-level topologies in terms of component count and loss distribution is listed in table II. The 5-level NPC has low switch count but the major problems are unbalanced operation of dc-link capacitors, poor loss distribution among switches, and excessive number of diodes. 5-Level FC provides low switch count and excellent loss distribution but requires high number of flying capacitors that can adversely affect the initial cost, maintenance and replacement surcharges, and reliability of the inverter. Capacitors’ precharge requirement in some applications is also a drawback of this topology. The 5-level SMC topology provides lower capacitor count compared to FC and good loss distribution. However, high switch count and high frequency switches in series are the main issues of this topology. The 5-Level FC ANPC provides a good balance between the number of semiconductors and capacitors. The major issue with this topology is the poor loss distribution among the switches. The topology proposed in this paper,
The control system presented in this paper has a wide range of applicability. It is used in a DVR system to eliminate voltage sags, harmonic voltages, and voltage imbalances within a band- width. Unlike other control schemes with a comparable range of applicability, only one controller is needed to cancel out all three disturbances simultaneously, while exhibiting good dynamic performance. On the one hand, a closed-loop controller, which consists of a feedback of the load voltage and the repetitive controller, guarantees zero tracking error in steady state. On the other hand, the applied control strategy for the voltage balancing of the flying capacitors, along with a feed forward term of the grid voltage and a controller for the output voltage of the DVR filter, provides excellent transient response.This paper is organized as follows. The model of a five-level flying- capacitor DVR is presented in Section II. The complete control-scheme structure is studied in Section III, including the three different control subsystems, namely, the filter output voltage controller, the repetitive control structure for the load voltage, and the flying-capacitor voltage regulator scheme, as well as the modulation method used to operate the multilevel converter.
Sonam Gehlot 1 , J.S. Shakya 2
1,2 Electrical Engineering, Samrat Ashok Technological Institute, (India)
The paper proposes a new five-level hybrid Topology combination feature of natural point clamped and flyingcapacitor inverters. The future topology provides good loss distribution; avoid direct series connection of semiconductor devices. The five level Flyingcapacitor(FC) based on active neutral point clamped (ANPC) Inverter .The voltage across the FC’s and dc link capacitors be simultaneously controlled at their reference Voltage levels. NPC and FC inverters are the Most widely used topology of multilevel inverters In high power application. This paper present Basic operation and most used modulation and Control techniques developed to date. The discuses the main field of application and presents some technological Problems such as capacitor balance and losses. The features of this topology are investigated and Compared to other available topology and implement the induction motor of this paper.
Analysis of Modified Five Level FlyingCapacitor Based MultilevelInverter
P.Siva Prasad, Dr.G.Annapurna
Abstract- Multilevelinverter concept gained importance because of high power handling capability and lower harmonic content in the output voltage. As the output voltage of multilevel inverters is synthesized from several levels of dc voltages, the harmonic distortion is minimum. Now -a- days, Carrier Based Pulse Width Modulation (CBPWM) technique gained importance as it can be easily extended to higher inverter levels and applied to Sinusoidal and Space Vector modulation schemes for control of multilevel inverters. This paper presents modified topology of Five level FlyingCapacitorMultilevelInverter with reduced number of dc bus capacitors and clamping capacitors.
2. 5-level flyingcapacitormultilevel inverters
The diodes in the diode-clamped topology can be replaced by clamping capacitors or floating capacitors to clamp the voltages. Such a topology is called flyingcapacitormultilevelinverter (FCMLI). FCMLI topologies are relatively new compared to the diode-clamped the cascaded H-bridge cell inverter topologies. Redundancy in the switching states is available by using flying capacitors instead of clamping diodes. This redundancy can be used to regulate the capacitor voltages and obtain the same desired level of voltage at the output. Figure2 shows a single- phase five-level FCMLI topology. The voltage across the capacitors is considered to be half of Dc source voltage Vdc. The output voltage consists of five different voltage levels + Vdc, Vdc/2, 0, -Vdc/2, and - Vdc. Similar to the other multilevel converter topologies, FCMLI also has complementary switch pairs. In the present considered circuit, switches Sa1 &Sa1 ׳, and Sa2 &Sa2 ׳ are complementary to each other.Similarly on the other limb, switches Sb1 &Sb1 ׳, and Sb2 &Sb2׳ are complementary to each other. The switching states available for such a topology are higher than that of the diode clamped. The number of voltage levels at the output can be increased by adding a pair of complementary switches and a capacitor. However, all the capacitors used in such topologies must be rated identically which can prove to be expensive and bulky in size. Single-phase five-level FCMLI topology VdcCa CbSa1Sa2
II. REVIEW OF FLYINGCAPACITOR AND MODULAR MULTILEVEL CONVERTER
A. FLYINGCAPACITORMULTILEVELINVERTER The topology of three phase three level flyingcapacitormultilevelinverter is shown in figure 1.It is also called as Capacitor Clamped or Imprecated cell inverter. It is similar to that of diode clamped multilevelinverter. The only difference is that here the clamping diodes are replaced by flying capacitors. The flyingcapacitor is also called as imprecated cell inverter. The flyingcapacitor is so called because the capacitors float with respect to earth’s potential. In flyingcapacitormultilevel inverters the switching combination or
² Department of Electronics & Telecommunication Engineering R. T. M. N. U, India
1 email@example.com; 2 firstname.lastname@example.org
Abstract— This paper is a simulation study of modulation strategies in three-phase three-level flyingcapacitor inverters in MATLAB Simulink. The flyingcapacitormultilevel converter is a recently developed converter topology assuring a flexible control and modular design. To improve the performance of FlyingCapacitorMultilevelInverter (FCMLI) implement the switching pattern selection scheme. This scheme reduces capacitor voltage fluctuation. This method is developed for sinusoidal voltage generation using the sinusoidal pulse width modulation technique the computer model allows a thorough investigation of all possible switching pattern permutations that produce the desired output and maintain steady state capacitor voltage balancing. Results show that the total harmonic distortion in a sinusoidal synthesised output can be minimised by the correct selection of the switching mode sequence.
Since, there are similarities between the flyingcapacitor and modular multilevel inverters in their structures, operational principles and pulse width modulation techniques. In addition to, both inverters are depending on phase voltage redundancies to balance dc link capacitors rather than line-to-line redundancies as in case of diode clamped. Nonetheless, modular multilevel inverters perform better than flyingcapacitorinverter as number of levels increases. Therefore, detail comparisons between flyingcapacitor and modular multilevelinverter are investigated in this paper. Several operating conditions have been considered to demonstrate the abilities of both inverters in improving system reliability and their limitations. Computer simulation has been used to confirm the validity of the results.
St.Johns College of Engineering &Technology, Yerrakota,Yemmiganur,Kurnool ,Andhra Pradesh ABSTRACT: This thesis aims to extend the
knowledge about the performance of different multilevelinverter induction motor drives through harmonic analysis. Large electric drives and utility applications require advanced power electronics converter to meet the high power demands. As a result, multilevel power converter structure has been introduced as an alternative in high power and medium voltage situations. Hybrid multilevel converters combine features of conventional multilevel topologies to provide an acceptable tradeoff between the advantages and disadvantages of these converters. For many industrial applications, common dc link is a requirement that limits the choice of topologies to neutral point clamped (NPC) and flyingcapacitor multicell (FCM) hybrid types. This paper investigates the operation of a hybrid five-level topology and proposes a modulation method that takes the advantage of the combined features of NPC and FCM. The dual flyingcapacitor (FC) active-neutral-point-clamped (DFC-ANPC) converter provides certain advantages such as natural soft switching of line frequency switches, elimination of the transient voltage balancing snubbers, and a more even loss distribution. Simulation results and verification of the five-level DFC-ANPC converter are presented to validate the performance of the converter as well as the applied modulation technique.. In particular, aspects of total harmonic distortion (THD) and modulation which are required or desirable for multilevel converters are discussed.
Key Words: PD-SPWM, POD-PWM, THD, Modulation Index.
1. INTRODUCTION 1.1 Multilevel Inverters
Multilevel inverters have drawn tremendous interest in power industry owing to their advantages such as higher efficiency, lower common mode voltage, lower voltage stress on power switches, lower dv/dt ratio, no EMI problems & its suitability for high voltage and high current applications .There are three types of multilevel inverters. They are Diode clamped or Neutral clamped, Flyingcapacitor or Capacitor clamped &. Cascaded H bridge multilevel inverters -.During the 1980s the development of the Multilevel Converters did not move much forward. Only after ten years, at the turn of the decade, finally appeared articles about new applications, e.g. nuclear fusion, and new control methods.
15. Peng, F. Z., J.-S. Lai, J. McKeever, and J. Van Coevering, “A multilevel voltage — source converter system with balanced DC voltages,” IEEE PESC Conf. Record, 1144–1150, June 1995.
16. Shukla, A., A. Ghosh, and A. Joshi, “Flying-capacitor-based chopper circuit for dc capacitor voltage balancing in diode-clamped multilevelinverter,” IEEE Trans. Ind. Electron., Vol. 57, No. 7, 2249–
KEYWORDS: Multilevelinverter, series inverters, series– parallel connection, switched capacitor.
Multilevel inverters have been under research and development for more than three decades and have found successful industrial applications. However, this is still a technology under development, and many new contributions and new commercial topologies have been reported in the last few years. Large electric drives and utility applications require advanced power electronics converter to meet the high power demands. As a result, multilevel power converter structure has been introduced as an alternative in high power and medium voltage situations . A multilevel converter not only achieves high power ratings, but also improves the performance of the whole system in terms of harmonics, dv/dt stresses, and stresses in the bearings of a motor. Several multilevel converter topologies have been also developed i) diode clamped, ii) flying capacitors, and iii) cascaded or H-bridge. Referring to the literature reviews, the cascaded multilevelinverter (CMI) with separated DC sources is clearly the most feasible topology for use as a power converter for medium & high power applications due to their modularization and extensibility .
In this paper, the proposed controller for the SAPF current loop is based on an ANN whose parameters (weights and biases) are optimized by PSO. This control scheme is combined with simple proportional control to balance the floating capacitor voltage of FCI to achieve good performance of the SAPF-FCI and maintain the flyingcapacitor voltages around their references. This ensures a balanced voltage sharing on the converter switches of the FCI even under variations in the system parameters.
It is assumed that the main dc capacitor and FCs were initially charged at 300 kV and 150 kV, respectively, prior to enabling both converter stations. Both converters were enabled at 0.05 s and then various reactive and active power orders were applied to the APC. Reactive and active power orders of 100 MVar at a rate of 100 MVar/20 ms and 200 MW (inverter operation) at a rate of 100 MW/20 ms were applied at 0.1 s and 0.2 s, respectively. A single-phase-to-ground fault was applied to the APC side at 0.8 s and cleared at 1.0 s. The proposed FC voltage balancing control was initially enabled but was disabled at 0.57 s and re-enabled at 0.69 s. The maximum peak converter current was set at 2 kA. Selected simulation results for the APC side are shown in Fig. 12 when the APC operated as an inverter. It has been found that the waveforms for the DCVC are very similar to those shown in Fig. 12 but not shown in the paper due to space limitations.
A. Diode clamped inverter B. Flyingcapacitorinverter C. Cascaded inverter
The most commonly efficient inverter is cascaded multilevelinverter (CMLI). It provides higher output voltage and power levels. It is one of the methods used for drive application which meet the requirements such as high power rating with reduced THD and switching losses. The CMLI consists of number of levels as the levels gets increase the number of switches gets increase. In order to overcome this problem, we use the concept of “switch reduction”. In this work, the new topology called reduced switch diode bridge topology is used to reduce the switches and separate dc-source in CMLI. The MOSFETs used as semiconductor switches.
Figure 3.1 shows the proposed FCMFC in a series configuration for pulsed power applications.
DCM operation is used here due to the pulse nature of the output voltage required. This also allows for maximum energy transfer because the inductor current reaches zero when discharging into flying capacitors. Both the upper and lower converters within the structure function in unison to provide high voltage peaks to the load. There are also diodes added to the phase leg of the secondary side of the transformer to prevent reverse current while charging the magnetizing inductor. Similar to the single FCMFC, this series configuration was simulated in PLECS to demonstrate operation. The converter was sized to match that of the case in  and parameters are shown in Table 6. The converter is defined by the number of voltage levels, N, for a given FCMFC, and by the number of series connected converters, M. This makes for MxN possible configurations. A 3x2 configuration is shown in Figure 3.1.