ANALYSIS OF MULTILEVEL INVERTER IN DIFFERENT LEVELS

Transcription

1 K A BABU, et al, International Journal of omputers lectrical and Advanced ommunication nineerin [IJA] TM Volume, Issue 6, PP:, DMBR 04. ANALYSIS OF MULTILVL INVRTR IN DIFFRNT LVLS K ANIL BABU *, V SINGARAIAH *. II.M.Tech, Dept of, AM Reddy Memorial ollee of nineerin & Technoloy, Petlurivaripalem.. Assoc.Prof,Dept. of, AM Reddy Memorial ollee of nineerin & Technoloy, Petlurivaripalem. Abstract This paper analyses the structure of new type of multilevel inverters suitable for hih voltae and hih power applications. The proposed topoloies sinificantly reduces the number of dc voltae sources, switches, IGBTs, and power diodes as the number of output voltae levels increases. Two type of multilevel inverters have been compared in this paper. The objective of this paper is to understandin the workin and simulation study of pulse 7 level and pulse 7 level multilevel inverter by PWM technique usin MATLAB/SIMULINK software. Keywords Multipulse converters, Voltae source converters, Multilevel inverters, FATS devices. I. INTRODUTION The voltae source inverters produce a voltae or a current with levels either 0 or ±V dc they are known as two level inverters. To obtain a quality output voltae or a current waveform with a minimum amount of ripple content, they require hih switchin frequency alon with various Pulse Width Modulation (PWM) strateies. In hih power and hih voltae applications, these two level inverters, however, have some limitations in operatin at hih frequency. It may be easier to produce a hih power, hih voltae inverter with the multilevel structure because of the way in which device voltae stresses are controlled in the structure. Increasin the number of voltae levels in the inverters without requirin hiher ratins on the individual devices can increase the power ratin. The unique structure of Multilevel voltaes sources inverters allow them to reach hih voltaes with low harmonics without the use of transformer or series connected synchronized switchin devices. As the number of voltae levels increases, the harmonic content of output voltae waveform decreases sinificantly. The capability of proposed structure in producin all odd and even output voltae levels is proved by simulation result for a pulse 7 level multilevel inverter and a pulse 7 level multilevel inverter. II. MULTILVL INVRTR An inverter is an electrical device that converts direct current (D) to alternatin current (A); the converted A can be at any required voltae and frequency with the use of appropriate transformers, switchin, and control circuits. Static inverters have no movin parts and are used in a wide rane of applications, from small switchin power supplies in computers, to lare electric utility hihvoltae direct current applications that transport bulk power. Inverters are commonly used to supply A power from D sources such as solar panels or batteries. III. INVRTR TOPOLOGIS The eneral structure of multilevel converter is to synthesize a near sinusoidal voltae from several levels of dc voltaes, typically from capacitor voltae sources. As number of levels increases, the synthesized output waveform has more steps, which provides a staircase wave that approaches a desired waveform. Also, as steps are added to International Journal of omputers lectrical and Advanced ommunications nineerin Vol. (6), ISSN: 09, DMBR 04.

2 K A BABU, et al, International Journal of omputers lectrical and Advanced ommunication nineerin [IJA] TM Volume, Issue 6, PP:, DMBR 04. waveform, the harmonic distortion of the output wave decreases, approachin zero as the number of voltae levels increases. This increases the power quality. Numerous methods have been investiated to increase the number of levels in the multilevel inverter s output. Multilevel voltae source inverter is reconized as an important alternative to the normal two level voltae source inverter especially in hih voltae application. Usin multilevel technique, the amplitude of the voltae is increased, stress in the switchin devices is reduced and the overall harmonics profile is improved. It exhibits several attractive features such as simple circuit layout, less components counts and modular in structure. However as the number of output level increases, the circuit becomes bulky due to the increase in the number of power devices. In this paper, a pulse 7 level multilevel inverter and a pulse 7 level multilevel inverter employ a new technique to obtain a multilevel output usin less number of power semiconductor switches when compared to ordinary cascaded multilevel inverter. The comparisons between the topoloies that have been made in this paper are as follows pulse 7 level multilevel inverter pulse 7 level multilevel inverter ) Pulse 7 Level Multilevel Inverter The Pulse 7 Level Multilevel Inverter consists of less number of switches when compared to the other familiar topoloies. The initial cost reduces because of the switch reduction. So, it looks attractive and an apt one for industrial applications. The eneral circuit diaram of the proposed multilevel inverter is shown in the fi.. The switches are arraned in the manner as shown in the fiure. For this topoloy, we just need to add only one switch for every increase in levels, so initial cost ets reduced. Let us see operation in the next subdivision in detailfor the Pulse 7 Level inverter as shown in fi.. S.NO onductinswitches Outp S,S,S,S7,S9,S utvolta S,S,S,S6,S9,S V S,S4,S7,S8,S9,S0 4 S,S,S7,S8,S9,S0 S,S,S7,S8,S9,S0 4 6 S,S4,S,S7,S9,S0 7 S,S,S,S7,S9,S0 6 8 S,S,S,S7,S9,S0 7 9 S,S4,S,S6,S9,S0 8 S,S,S,S6,S9,S0 0V 9 D 0 V International Journal of omputers lectrical and Advanced ommunications nineerin 4 Vol. (6), ISSN: 09, DMBR S,S,S,S6,S9,S 7 lock u ontinuous powerui fcn y mbedded MATLAB Function dc dc dc T T4 T T8 T9 T T T T7 T6 T T0 Fi. MATLAB/Simulink circuit for Pulse 7 Level inverter. Simulation results are shown here by the help of MATLAB/Simulink for Pulse 7 Level inverter in fi.the results are shown by PWM control technique. The batteryof volts D each is chosen for input supply. The load connected here is the same R load. The IGBTs are used in this topoloy forhiher stability of the circuit. D voltaes are compared with different types of trianular waves to obtain the ate. The relational operators areused. The pulse width of the required determines thevalue of the constants. Pulse width is determined by the ontime of each switch and these sinals are used for switchinthe IGBT s. The below table shows the various different switchin states in this proposed topoloy. Table I Switchin states i I Load V v sinal rms RMS Scope Display

3 [A] 7level [] yy [B] A B c yd L L L 6 pulse Generator yy 6 pulse Generator yd 7 Level Generator Discrete, Ts = e00 s. powerui Pi Section Line Pi Section Line Pi Section Line del wt Sinal conditionin PLL Freq wt Va Interator s DSP ref TMS0F8 T/f Kki A K Kkp A B B B B Sinal conditionin voltae function 660 s660 rror Vref L L L A A B B A A B B yy yd B B B B R R R v Voltae Measurement Goto [B] [A] Pulses YD Pulses YY [Vsixpulse] [Vsevenlevel] From [Vsixpulse] Vref From From Scope Add 6 Scope Vdc_ v [Vsevenlevel] V star Voltae Measurement Goto V delta [] Ul Pulses _7Level Vdc_ Vdc_ Vdc_4 D D A a a4 a a D D4 B a8 a6 a7 a K A BABU, et al, International Journal of omputers lectrical and Advanced ommunication nineerin [IJA] TM Volume, Issue 6, PP:, DMBR 04. Values of VD for different switchin states are as shown in Table I. The firin are obtained from the embedded Matlab function. These are iven to Pulse 7 Level inverter. ) pulse 7 level multilevel inverter Numerous methods have been investiated to increase the number of levels in the multilevel inverter s output. Stron efforts have been made in order to reach minimum harmonic distortion in the VSI s output voltae. A stratey to build an pulse 7 level equivalent output voltae waveform, which employs a twelvepulse alon with an sevenlevel inverter is presented in [4] this paper. The pulse 7 level multilevel inverter operation is assembled by connectin two identical threephase brides to threephase transformers in a parallel VS confiuration. ach branch in the sixpulse converter must have a displacement of 0 amon them. The upper switch is conductin while the lower one is open and vice versa (80 voltae source operation) []. A 0 displacement in the firin sequence of both converters should be considered. This produces the output and the levels required to enerated output waveform. The phase transmission line is the source and the pulse and 7 level voltae waveform with improved power quality and less Total Harmonic Distortion (THD) is the output voltae. The MATLAB/Simulink circuit for Pulse 7 Level inverter is shown in fi.. The Total Harmonic Distortion (THD), which is defined by THD VU MATLAB for a value n = 700, with increments of a = With these parameters, the minimum THD becomes.8% with a = 0.609, value employed in previous fiures. Accordin to the I Std. 9, the distortion limits indicate that the allowed THD voltae is 0% in dedicated systems, % in eneral systems, and % for special applications as hospitals and airports [].. PhaseLockedLoop (PLL) The Synchronizin ircuit is responsible for determinin the system frequency and the phaseanle of the controlled A bus fundamental positive sequence voltae [6]. The PhaseLockedLoop (PLL) utilizes the Stationary Reference Frame in order to reduce the computational cost, and helps to improve the system s dynamic performance [7]. The diital PLL is an alorithm able to detect the phase of the fundamental voltae, throuh the synchronization of the output sinal to the frequency and phase of the input one, without requirin a zero crossin subroutine at the input voltae, or to enerate an internal reference sinal for the input current [8]. The proposed stratey employs a tan function added to a correction value determined by the sins α and β,fi. Sin_os Fi. MATLAB/Simulink circuit for Pulse 7 Level inverter. SixPulse Generator Fi. Optimized PLL scheme. The second block is the sixpulse enerator, responsible for eneratin the pulse sequence to fire the threephase IGBT array. It consists of an array of International Journal of omputers lectrical and Advanced ommunications nineerin Vol. (6), ISSN: 09, DMBR 04.

4 K A BABU, et al, International Journal of omputers lectrical and Advanced ommunication nineerin [IJA] TM Volume, Issue 6, PP:, DMBR 04. sixpulse spaced 60 each other. The IGBT will operate at full 80 for the on period and 80 for the off period. Any disturbance on the frequency will be captured by the synchronizin block, preventin malfunctionin. The fallin border in the synchronizin block output sinal is added to a series of six 60 spaced sinals. The modulus operator with the arument ives the needed on sequence that will be sent to the ate optocoupler block,which will feed each six pulse converter. The off sequence turns out on a similar way but waitin 80 to keep the same on and off duration in each IGBT.. SevenLevel Pulse Generator To operate the sevenlevel inverter, six times the frequency of the sixpulse enerator must be ensured. This is achieved by monitorin the fallin border in the novel PLL output sinal, usin it alon with the modulus operator with the arument. This sinal will be the period for the sevenlevel enerator which will chane its state each 4 rad. To examine the performance of pulse 7 level and pulse 7 level multilevel inverter in eneration of a desired output voltae waveform it is simulated in MATLAB SIMULINK environment. This inverters can enerate staircase output voltae waveform. Table I shows the switchin pattern of structure in Fi. to produce different output voltae levels for pulse 7 level multilevel inverter. Fi. shows the control block diaram of pulse 7 level multilevel inverter. Fi. 4 Mixin sevenlevel, sixpulse sinals IV. SIMULATION RSULTS Fi.. pulse 7 level multilevel inverter output voltae, current waveform and THD value Fi.6 pulse 7 level multilevel inverter output voltae and THD value International Journal of omputers lectrical and Advanced ommunications nineerin Vol. (6), ISSN: 09, DMBR 04.

5 K A BABU, et al, International Journal of omputers lectrical and Advanced ommunication nineerin [IJA] TM Volume, Issue 6, PP:, DMBR 04. The main idea in control stratey is to deliver the load a voltae that minimizes the total harmonic distortion with respect to reference voltae.the simulation results for a pulse 7 level multilevel inverter and a pulse 7 level multilevel inverter is shown in the fi. and fi 6 respectively [6] A. Karnik, Performance of TP conestion control with rate feedback: TP/ABR and rate adaptive TP/IP, M. n. thesis, Indian Institute of Science, Banalore, India, Jan [7] J. Padhye, V. Firoiu, and D. Towsley, A stochastic model of TP Reno conestion avoidance and control, Univ. of Massachusetts, Amherst, MA, MPSI Tech. Rep. 990, 999. Table II Total Harmonic Distortion. INVRTR THD (%) pulse 7 level.94 pulse 7 level.6 V. ONLUSION The simulation of pulse 7 level and pulse 7 level multilevel inverter by PWM technique usin MATLAB/SIMULINK softwareis successfully done. Acomparison betweenthe pulse 7 level multilevel inverter and 7 level multilevel inverter topoloy is shown in Table II Which clearly shows the percentae reduction in the Total Harmonic Distortion. The results of the simulation the pulse 7 level multi level inverter and pulse 7 level multilevel inverter demonstrate that the later confiuration has prominent feature compared to other multilevel inverters.the exhibited low THD, permits the system to be used in especial applications suitable for hih voltae and hih power applications. The pulse 7 level multilevel inverter has ability to synthesize waveforms with better harmonics spectrum.the output waveform of multilevel inverter follows the sinusoidal waveform hence the harmonic contents are less. The power loss in the circuit is less due to less number of switches. RFRNS [] Liu, Y. H., Arrillaa, J., Watson, N. R.: A New STATOM onfiuration Usin MultiLevel D Voltae Reinjection for Hih Power Application, I Transactions on Power Delivery, Vol. 9, No. 4, October 004, pp [] Arrillaa, J., Liu, Y. H., Watson, N. R.: Flexible Power Transmission, The HVD Options. (John Wiley & Sons, Ltd, 007, pp. 69.) [] Liu, Y. H., Perera, L. B., Arrillaa, J., and Watson, N. R.: Harmonic Reduction in the Double Bride Parallel onverter by MultiLevel DVoltae Reinjection, 004 lnternational onference on Power SystemTechnoloy POWRON 004, 4 November 004 [4] Arrillaa, J., Liu, Y. H., Watson, N. R.: Flexible Power Transmission, The HVD Options. (John Wiley & Sons, Ltd, 007, pp. 69.) [] Aredes, M., Santos Jr., G.: A Robust ontrol for MultipulseStatoms, Proceedins of IP 000, Vol. 4, pp. 6 68, Tokyo, 000. International Journal of omputers lectrical and Advanced ommunications nineerin Vol. (6), ISSN: 09, DMBR 04.