INTERNATIONAL JOURNAL OF PROFESSIONAL ENGINEERING STUDIES Volume 9 /Issue 3 / NOV 2017

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A PARALLEL RECTIFIER SERIES INVERTER TYPE SINGLE PHASE TO THREE PHASE POWER CONVERTER SYSTEM

1MR.ANIL KUMAR CHATAKONDA, 2CH. JAYAVARDHANARAO

1M.Tech, KUPPAM ENGINEERING COLLEGE 2Associate Professor, KUPPAM ENGINEERING COLLEGE

Abstract—Single-phaseto three-phase power conversion using power electronics converters is a well-known technology, when the configurations and control strategies are proposed in this paper. In this paper presents a single-phase to three-phase power conversion system with parallel rectifier and series inverter to cope with single-phase to three-phase asymmetry. In this paper we proposed better solution using SVPWM technique for single phase to three phase drive system by employing 2 parallel single phase rectifier stages, a 3-phase inverter stage. Parallel converters can be used to improve the power capability, reliability, efficiency and redundancy. Space vector modulation (SVM) is an algorithm for the control of pulse width modulation (PWM). It is used for the creation of alternating current (AC) waveforms; most commonly to drive 3 phase AC powered motors at varying speeds from DC using multiple class-D amplifiers. Such converter guarantees both reduction in the input current processed by rectifier circuit and reduction of the output voltage processed by the inverter circuit. A comprehensive model of the proposed converter, modulation strategy, and a general comparison with the conventional configuration is proposed in this paper. By using the Simulation results we can analyze the proposed method. Index Terms—Power conversion, power electronics converters, pulse width modulation converters.

I. INTRODUCTION Several solutions have been proposed when the objective is to supply a three-phase motor from single-phase ac mains [1]-[4]. It is quite common to have only a single phase power grid in residential, commercial, manufacturing, and mainly in rural areas, while the adjustable speed drives may request a three-phase power grid. In this paper, a single-phase to three-phase drive system composed of two parallel single-phase rectifiers and a three-phase inverter is proposed. The proposed system is conceived to operate where the single-phase utility grid is the unique option available. Compared to the conventional topology, the proposed system permits: to reduce the rectifier switch currents; the total harmonic distortion (THD) of the grid current with same switching frequency or

the switching frequency with same THD of the grid current; and to increase the fault tolerance characteristics. The semiconductor devices were the major technology used to drive the power processors. So power electronics plays an important role day by day. In the power distribution systems, the single-phase source has been considered as an alternative for rural or remote areas, due to its lower cost feature, especially when compared with the three-phase solution Beyond the improvement related to power switches, it was also identified a great activity in terms of the circuit topology innovations in the field of three-phase to three-phase, single-phase to single-phase, and three-phase to single-phase conversion systems. In present days, power electronics with silicon power diodes and thyristors are just emerging. In this paper, there is a need for single-phase to three-phase power conversion systems. The direct solutions for the single-phase to three-phase power converters are presented in Fig. 1.

(a)

(b)

Fig. 1. Conventional single-phase to three-phase configurations: (a) diode bridge at the input-converter

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side, and (b) controlled rectifier at the input converter side.

In the power distribution systems, the single-phase grid has been considered as an alternative for rural or remote areas, due to its lower cost feature, especially when compared with the three-phase solution. In addition, the losses of the proposed system may be lower than that of the conventional counterpart. The aforementioned benefits justify the initial investment of the proposed system, due to the increase of number of switches. In huge countries like Brazil, the single-phase grid is quite common due to the large area to be covered. On the other hand, loads connected in a three-phase arrangement presents some advantages when compared to single phase loads. This is especially true in three-phase motor systems with variable-speed drives due to their constant torque characteristic. Generally, a single-phase to three-phase power conversion presents an inherent asymmetry, i.e., constant power at the output-converter side (three-phase load) and pulsating power at the input-converter side (single-phase grid), as highlighted in Fig. 3(a). The direct consequence of this asymmetry is the low frequency voltage oscillation observed in the dc-link capacitors, as well as the power switches of the rectifier and inverter operate with different voltage and current ratings. Normally, the

(a)

(b)

(c)

Fig.2. Single-phase to three-phase power conversion. (a) Type of power processed by rectifier and inverter

circuits. (b) Solution employed.(c) Solution employed.

Another important characteristic observed in the single-phase to three-phase power converters that also has been considered in this paper is the irregular distribution of power losses among the switches of the converter, as observed in Fig. 3

Fig. 3. Converter power losses distribution in both rectifier and inverter units: 63% in the rectifier circuit and 37% in the inverter one. Power losses in each switch of the rectifier (15.7%) and inverter (6.1%). The current relation between input- and output-converter sides also implies in converter asymmetry, i.e., (iin >iout) solve the whole asymmetry inherent of the single-phase to threephase

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power conversion, i.e., higher input current (iin) and a demand for higher output voltage (vout). Indeed, the configurations observed in Fig. 3(b) and 3(c) reduce the current processed by the rectifier current, but the voltage at the output converter remains the same as in Fig. 1(b). This paper presents a single-phase to three-phase power conversion system with parallel rectifier and series inverter to cope with single-phase to three-phase asymmetry, as observed in Fig. 4.

Fig. 4. Proposed single-phase to three-phase

conversion system. Such converter guarantees both reduction in the input current processed by rectifier circuit (due to the parallel connection) and reduction of the output voltage processed by each inverter (due to the series connection). This paper presents a comprehensive model of the proposed converter, modulation strategy, and a general comparison with the conventional configuration.

Fig. 5. Simplified model of the proposed single-phase

to three-phase conversion system. II. SYSTEMMODEL

This section will present the model of the proposed configuration. Such a configuration is

constituted by a singlephase grid (eg), one open-end three-phase motor, inductor filters (L1a,L1b,L3b, andL3a), converters1, 2, 3, and4, and two dclink capacitor banks (C12andC34). If the legs are substituted by pulsed voltage sources, the proposed converter can be modeled as in Fig. 6. A. Grid-Side Converter Model From the system in Fig. 6, the following equations can be derived to converters 1 and 3 at the grid side: e = r i + l − r i − l + v (1)

e = r i + l − r i − l + v (2) i = i + i

With v = v o − v o (3) v = v o − v o (4) wherei1a andi1b are the input currents of the converter 1,i3a andi3b are the input currents of the converter 3, the symbols randl represent the resistance and inductance of inductors L1a,L1b,L3a, and L3b. The voltages v1a012 andv1b012 are the pole voltages of the converter 1, whilev3a034 andv3b034 are the pole voltages of the converter 3 andig is the grid current. B. Machine-Side Converter Model From the system in Fig. 6, the following equations can be derived to converters 2 and 4 at the machine side: v = v o − v o + v o − v o (5) v = v o − v o + v o − v o (6) v = v o − v o + v o − v o (7) wherev2a012 ,v2b012 , and v2c012 are the pole voltages of converter 2,v4a034 ,v4b034 , andv4c034 are the pole voltages of converter 4, andvab=va−vb,vbc =vb −vc, and vca =vc −va are line-to-line voltages of the machine. For the voltage control of the motor, the following relations are obtained: v = v o − v o = (8) v = v o − v o = (9) v = v o − v o = (10) v = v o − v o = − (11) v = v o − v o = − (12) v = v o − v o = − (13) C. Circulating Current Model Due to the parallel/series connection, the proposed system shown in Fig. 5 has a circulating

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current among the converts. The model of this circulating current can be defined as following:

0 = v + v o − v o + v o − v o + v 0 = v + v o − v o + v o − v o + v

The equations of the input circulating currents of the converters 1 and 3 (io1 andio3) and output circulating currents of the converters 2 and 4 (io2andio4) are defined as i = i + i (14) i = i + i + i (15) i = i + i (16) i = i + i + i (17) However, the circulating currentsio1,io2,io3, and io4 can be represented by a single circulating current io, which means i = i = i = −i = −i (18) From (15) and (16), it is possible to write v = v − v + (r + r )i + (l + i ) +∑ v (19)

D. Three-Phase Motor Model A typical three-phase machine has been used in this study. Selecting a fixed coordinate reference frame, the mathematical model that describes the dynamic behavior of the three-phase induction motor is given by

v = r i +ddt∅

v = r i +ddt∅ − j ∅

∅ = l i + l i ∅ = l i + l i

T = Pl i i − i + i (20) Where vsdq =vsd+jvsq, isdq =isd+jisq, and φsdq =φsd+ jφsq are the voltage, current, and flux dq vectors of the stator, respectively; vso and iso are the homo polar voltage and current of the stator, respectively (the equivalent rotor variables are obtained by replacing the subscript s by r); Te is the electromagnetic torque; ωr is the angular frequency of the rotor

III. MODULATIONSTRATEGY The converter pole voltages depend on the conduction states of the power switches. For example,v1a012 is given by v o = (2q − 1) (21) wherevC12 is the dc-link voltage connected between the converters 1 and 2; andq1a is the switching state of the top switch for the leg on

converter 1 connected to the inductorL1a. The reference pole voltagesv ∗ 1a012 to v ∗ 4c034 should be calculated from the reference voltages defined by controllers, i.e., v ∗ 1 ,v ∗ 3 ,v ∗ o, two among v ∗ 2ab ,v2bc, ∗ andv ∗ 2ca and two among v ∗ 4ab ,v ∗ 4bc , and v ∗ 4ca , which yields

v∗ = v∗ o − v∗ o v∗ = v∗ o − v∗ o

v∗ = v∗ o − v∗ o v∗ = v∗ o − v∗ o v∗ = v∗ o − v∗ o

v∗ = v∗ o − v∗ o (22) v∗ = −∑ v∗ o + ∑ v∗ o +∑ v∗ o −∑ v∗ o (23)

Since the proposed converter has ten power switches, to determine the reference pole voltages, then three auxiliary variablesv ∗ x ,v ∗ y, andv ∗ z are introduced, that is,

v∗ =12

(v∗ o + v∗ o )

v∗ =13

(v∗ o + v∗ o )

v∗ = (v∗ o + v∗ o + v∗ o ) (24) The reference pole voltages can now be obtained directly, that is

v∗ o =12 v∗ + v∗

v∗ o = −12 v∗ + v∗

v∗ o = v∗ + v∗ v∗ o = v∗ + v∗ v∗ o = v∗ + v∗

v∗ o =12 v∗ + v∗

v∗ o = − v∗ + v∗ (25) On the other hand, when μ=0orμ= 1leads a non sinusoidal reference pole voltages, however, the resultant voltage v∗1andv∗ab are sinusoidal as shown in Figs. 7(a), 7(c), 8(a), and 8(c). Additionally, with μ=0orμ=1, the distribution of zero instantaneous voltages are placed at the beginning or at the end of the switching period, respectively.

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(a)

(b)

(c)

Fig. 6. Modulation signals at the grid side with: (a)μx =0,(b)μx =0.5,and(c)μx =1

To solve the problem of how to determine the reference pole voltages as a function of the reference voltages (v ∗ 1 ,v ∗ 3 ,v ∗ o ,v ∗ 2ab ,v ∗ 2bc ,v4ab, ∗ and v ∗ 4bc ), it is necessary to choose the auxiliary variables v∗x ,vy,∗ and v∗z appropriately. The auxiliary variables can be chosen freely in a range defined by the limits of the pole voltages [vC12/2, −vC12/2]and [vC34/2, −vC34/2]. In order to simplify the auxiliary variables calculation, the voltagesv ∗ xandv ∗ y are first determined. the limit values forv ∗ x is

v∗ ≤ v∗ ≤ v∗

v∗ = v∗2 −max

v∗

2 ,−v∗

2

v∗ = −v∗2 −min

∗,−

∗ (26)

Now, from (52) and (53), the limit values forv ∗ y is Givenv ∗ xandv ∗ y

v∗ ≤ v∗ ≤ v∗

v∗ = v∗2 −max

v∗

2 ,−v∗

2

v∗ = −v∗2− min

∗,−

∗ (27)

the limits of voltage v ∗ z are determined i.e. v∗ ≤ v∗ ≤ v∗

v∗ = v∗2 − max{v }

v∗ = − v∗2 −min{v } (28)

Introducing the parametersμx,μy, and μz (0≤μ≤1), for instance, voltagev ∗ xcan be chosen equal to v∗ = μ v∗ + (1− μ )v∗ (26) The sequence for calculation of the reference pole voltages from v ∗ 1 ,v ∗ 3 ,v ∗ o ,v ∗ 2ab ,v ∗ 2bc ,v ∗ 4ab , and v ∗ 4bc is resumed in the following algorithm: Step 1: 1) Determine v ∗ x max and v ∗ x min; 2) choose μx; 3) determine v ∗ x. Step 2: 1) Determine v ∗ y max and v∗y min from (67) and (68); 2) choose μy; 3) determine v ∗ y from an equation Step 3: 1) Determine v ∗ z max and v ∗ z min from (70) and (71); 2) choose μz; 3) determine v ∗ z from an equation like (72). Step 4: 1) Determine the reference pole voltages. Once the reference pole voltages have previously developed, the gating signals can be obtained by a comparison of the pole voltages with a high-frequency triangular carrier signal

(a)

(b)

(c)

Fig. 7. Modulation signals at the machine side: (a)μz =0,(b)μz =0.5, and (c)μz =1

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In this paper, gating signals were obtained comparing pole voltages with a single or double-carrier-based pulse width modulation (PWM). The parameters μx,μy, and μz change the place of the voltage pulses related tov1,v3,vab,vbc, and vca. As an example, when μx=0orμx=1is selected, the pulses are placed at the beginning or at the end of the half period of the triangular carrier signal (Ts). .

(a)

(b)

Fig. 8. (a) Weighted total harmonic distortion (WTHD) of rectifier voltage for the proposed and

conventional configurations as a function ofμ.(b)WTHD of the inverter voltage for the

proposed and conventional configurations as a function ofμ.

The leading feature of PWM strategy with μ=0orμ=1is a reduction of the switching frequency. For the single-phase converter, there is no switching for a range of 180 ◦ while for the three-phase converter there is no switching for a range of 30 ◦ , reducing switching losses.

IV. CONTROLSTRATEGY A. Control Block Diagram The proposed converter has the same objectives as in the conventional converter, as observed in Fig. 1(b), i.e., 1) dc-link voltage control, 2) power factor correction, and 3) three-phase voltage generation at the output-converter side. Additionally, the converter control of the proposed system needs to control the circulating current. Fig. 9 presents the control block diagram for the proposed system.

Fig. 9. Control block diagram

In this paper we are using SVPWM technique to generate the pulses. The main objectives of space vector pulse width modulation generated gate pulse are the following. Wide linear modulation range Less switching loss Less total harmonic distortion in the spectrum of switching waveform Easy implementation and less computational calculations To control power factor and harmonic content at the input-converter side, the instantaneous reference currents i ∗ 1a andi ∗ 3a are synchronized with the grid voltage, as given in [23]. The blocksG−ig1 andG−ig3 have two functions, i.e., synchronization with the grid (through a phase locked loop scheme) and generation of the sinusoidal reference currents.

(a)

(b)

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(c)

(d)

(e)

(f)

(g)

(h)

Fig. 10. Simulation results: (a) voltage and current of the grid, (b) input current of the converter 1, (c) input current of the converter 2, (d) circulating current, (e) dc-link voltage inC12, (f) dc-link voltage in C34, (g)

load currents, and (h) load voltages. The capacitor dc-link voltagesvC12 andvC34 are adjusted to their reference valuesv ∗

C12 andv ∗ C34 using controllers RC12 andRC34 respectively. Those controllers provide the amplitude of reference currents i ∗ 1a and i ∗ 3a . The control of the rectifier currents are implemented by using the controllers indicated by blocksR1 and R3. Those current controllers can be implemented by using linear or nonlinear techniques. B. Double Sequence Synchronous Controller When the current is sinusoidal, a standard PI stationary controller does not guarantee zero sinusoidal steady-state error. A double sequence synchronous controller for ac variables were used to overcome such difficulty. 푑푥푑푡 = 푥 + 2푘 휖

푑푥푑푡 = −휔 푥

푣∗ = 푥 + 푘 휁 (27)

Fig 11 .Block diagram of simulation

V. HARMONICDISTORTION The WTHD has been computed by using

WTHD(p) = ∑ (28) wherea1 is the amplitude of the fundamental voltage, ai is the amplitude of ith, harmonic and p is the number of harmonics taken into consideration. Fig. 9(a) shows the WTHD of the voltage generated by rectifier [ v1+v3 2 for proposed configuration and vg =vg10− vg20for conventional configuration.

VI. SIMULATIONRESULTS The simulation results were obtained with the grid- and machine-phase voltages equal to 127 Vrms, dc-link voltage of 225 V, capacitance of 2200μF, and input inductor filters with resistance and inductance given respectively by 0.1Ωand 2.6 mH. The load power was of 5 kVA.

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(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Fig. 12. Simulation results with current transient: (a) grid current (ig), (b) circulating current (io), (c)

machine currents, (d) current components is d and is q,(e) output voltages without LPF, (f) dc-link voltage

(vC12), (g) dc-link voltage (vC34), and (h) input voltage

VIII. CONCLUSION A single-phase to three-phase drive system composed of two parallel single-phase rectifiers, a three-phase inverter and an induction motor was proposed. The system model and the control strategy, including the SVPWM technique, have been developed. The complete comparison between the proposed and standard configurations has been carried out in this paper. Such converter guarantees both reduction in the input current processed by the rectifier circuit (due to the parallel connection) and reduction of the output voltage processed by each inverter (due to the series connection). Compared to the conventional topology, the proposed system permits to reduce the rectifier switch currents, the THD of the grid current with same switching frequency or the switching frequency with same THD of the grid current and to increase the fault tolerance characteristics. The space vector PWM (SVM) method is an advanced computation-intensive PWM method and is possibly the best method among the all PWM techniques for variable- frequency drive application. Because of its superior performance characteristics, reduction of total harmonic distortion (THD) created by the rapid switching inherent to this PWM algorithm. By using the simulation results we can analyze the proposed method.

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REFERENCES [1] A. H. Maggs, “Single-phase to three-phase conversion by the ferrarisarno system,”Electr. Eng.—Part I, General, J. Inst., vol. 93, no. 32, pp. 133–136, Aug. 1946. [2] K. Hisano, H. Kobayashi, and T. Kobayashi, “A new type single-phase to three-phase converter,” IEEE Trans. Magn., vol. 2, no. 3, pp. 643–647, Sep. 1966. [3] S. Dewan and M. Showleh, “A novel static single-to three-phase converter,”IEEE Trans. Magn., vol. 17, no. 6, pp. 3287–3289, Nov. 1981. [4] M. Liserre, “Dr. Bimal K. Bose: A reference for generations [editor’s column],”IEEE Ind. Electron. Mag., vol. 3, no. 2, pp. 2–5, Jun. 2009. [5] F. Blaabjerg, A. Consoli, J. A. Ferreira, and J. D. van Wyk, “The future of electronic power processing and conversion,”IEEE Trans. Ind. Appl., vol. 41, no. 1, pp. 3–8, Jan./Feb. 2005. [6] F. W. Gutzwiller, “Thyristors and rectifier diodes-the semiconductor workhorses,”IEEE Spectrum, vol. 4, no. 8, pp. 102–111, Aug. 1967. [7] A. Elasser, M. H. Kheraluwala, M. Ghezzo, R. L. Steigerwald, N. A. Evers, J. Kretchmer, and T. P. Chow, “A comparative evaluation of new silicon carbide diodes and state-of-the-art silicon diodes for power electronic applications,”IEEE Trans. Indust. Appl., vol. 39, no. 4, pp. 915– 921, Jul./Aug. 2003. [8] M.-K. Nguyen, Y.-G. Jung, and Y.-C. Lim, “Single-phase AC–AC converter based on quasi-z-source topology,”IEEE Trans. Power Electron., vol. 25, no. 8, pp. 2200–2210, Aug. 2010 [9] M.-K. Nguyen, Y. cheol Lim, and Y.-J. Kim, “A modified single-phase quasi-z-source AC–AC converter,”IEEE Trans. Power Electron., vol. 27, no. 1, pp. 201–210, Jan. 2012. [10] B. Saint, “Rural distribution system planning using smart grid technologies,” inProc. Rural Electric Power Conf., Apr. 2009, pp. B3-1–B3-8.

MR.ANIL KUMAR CHATAKONDA

was born in Kurnool,AP on November 10, 1991. He graduated from the Jawaharlal Nehru Technological University, Anantapur. His special fields of interest included Power Electronics. Presently he is studying M.Tech in Kuppam Engineering College.

CH. JAYAVARDHANARAO has obtained his B.Tech Electrical Engineering from JNTUH, Hyderabad in the year 2002, M.Tech in power system emphasis on High voltage engineering from JNTUK Kakinada in the year 2009. He has 5 years of industrial experience, 2 years of research experience and 7 years of Teaching experience. Currently working as Associate Professor in Department of Electrical Engineering at Kuppam Engineering College, Kuppam, Chittoor district, Andhra Pradesh, INDIA. His Area Of Research Includes Power Systems, Power Electronics, High Voltage Engineering, Renewable Energy Sources, Industrial Drives, HVDC & FACTS Technology.