multi level inverter with ac and boost dc outputs for ... · converter and a multi -level inverter...

Multilevel inverter with AC and Boost DC

Outputs for Microgrid Applications

P.Sathyanathan1, Dr.P.Usha Rani

2, R.Niranjan Kumar

3, S.R.Akshaya

4

1 Asst Prof, Department of EEE, Vel Tech, Chennai

2 Professor, Department of EEE, R.M.D Engineering College, Chennai

3,4 Asst Prof, Department of EEE, Vel Tech, Chennai

Abstract—In microgrids, integration of multiple renewable energy

sources to AC and DC buses of grid require a boost and multi-level

inverters. Depending on the requirement, these boost and multi-level

converters are connected either in parallel or in cascaded. In this

parallel or cascaded arrangement the device count and control

complexity increases. And, also it requires a separate AC and DC

output control (for modulation index and duty ratio). So, these

arrangement cannot give the fully controlled simultaneous DC and

AC outputs. With this intent, this paper proposes a simplified

converter with simultaneous AC and DC outputs. This proposed

converter topology is derived by modifying the DC-DC boost

converter power switch with a multi-level inverter. This resulting

simplified topology requires less number of devices (switches) to

produces a simultaneous boost DC and multi-level AC waveforms

with a shoot through protection for a multi-level converter. A

suitable pulse width modulation (PWM) control strategy is described

and simulation results are presented using MATLAB. And also, the

mathematical analysis of the proposed converter has been derived

and compared with conventional/already existing designs.

Index Terms—Hybrid microgrid, multi-port converter, boost

converter, multilevel inverter

integrated inverters. And presents the hybrid multilevel

inverter. But, boost integrated multilevel inverters are not

discussed in literature.

I. INTRODUCTION

Power converter architectures having multiple input ports or multiple

output ports are used in a wide variety of appli-cations. Typical examples

are hybrid electric vehicles (EV), DC/AC-based hybrid microgrids and

power supplies. Recent developments in the operation and control of

microgrids and widespread use of power electronics challenging the

researchers to design new power converter topologies with less number

of devices and reduced complexity. During this pro-cess, in hybrid

microgrids, integration of multiple renewable energy sources to AC and

DC buses of grid requires a two individual converters, a DC-DC boost

converter and a multi-level inverter (MLI). Depending on requirement

these boost and multi-level converters are arranged in parallel as shown

in Fig. 1(a) or arranged in cascaded as shown in Fig. 1(b). In this

arrangement the device count and control complexity increases. And also

it requires a separate AC and DC output control (for modulation index

and duty ratio). So, simultaneous wide control on AC and DC outputs are

not possible in cascaded and parallel arrangements. To overcome these

issues, discussed the boost derived hybrid converters, proposed the

different multi port converters deals with boost

Fig. 1. Arrangement of boost and multilevel inverter for AC and DC outputs

a) Parallel b) Cascaded c) Proposed

International Journal of Pure and Applied MathematicsVolume 119 No. 15 2018, 681-687ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

681

This paper proposes a simplified converter for achieving

simultaneous AC multi-level and DC boost outputs as shown in

Fig. 1(c). This proposed converter topology is derived by

replacing the DC-DC boost converter power switch with a MLI.

The resulting simplified converters require less switches count to

provide simultaneous desired multi-level AC and boost DC

outputs with an inherent shoot through protection in MLI stage. This paper organizes as follows: Section II discuss about proposed

topology control and operation. Section III discuss the simulation

results. And, the comparative analysis are discussed in Section IV.

And, Section V concludes the paper.

II. PROPOSED TOPOLOGY OPERATION AND CONTROL A. Modeling of Proposed Converter

The controlled switch S of a conventional DC-DC boost converter as shown in Fig. 2(a) is replaced by the multilevel inverter topology to obtain the proposed converter as shown in Fig. 2(b). This proposed converter produces a simultaneous multi-level AC output and boost DC output using five con-trolled

switches S1 S5 and diode. Thus the control of the duty ratio (D)

control the boost converter operation and control of the

modulation index (ma) control the MLI operation. The input DC

voltage is Vdc = Vdc1 +Vdc2. Inductor (L) is used for store the

energy in shoot through (ST) operation. AC load is connected across H-bridge and DC load is connected across capacitor C.

Fig. 3. The control design of proposed converter

Stage-1: Triangular signal compared with Vm1, Vm2

(Vm2 = Vm1=2) to generate the control pulse for positive and negative half cycles and Triangular signal compared

with Vst to generate the control pulse in shoot through operation. Stage-2: The aggregate signal is generated from control pulses

with addition of +1 or -1. This aggregate signal leads to

generation of inverter’s desired output level.

Stage-3: Finally, look-up table shown in Table I is for-

mulated based on the topology that produces gate signals

required for proposed converter operation. C. Operation of Proposed Converter

The gate signals required for the operation of the proposed

converter is shown in Fig. 4. The voltage and current wave form in

different locations with different intervals are shown in Fig. 5. The

overall operation of proposed converter with power, zero and shoot

through intervals are explained as follows:

Fig. 2. a) Boost converter b) Proposed simplified converter derived from

boost converter

B. Control of Proposed Converter

The control scheme used for controlling the proposed con-verter is

shown in Fig. 3. It consists of three stages as follows:

TABLE I

SWITCHING STATES DURING DIFFERENT LEVELS OF VOLTAGE

Level Switches (1 ON; 0 OF F ) F ig:#

S1 S2 S3 S4 S5

+2Vdc 1 1 0 0 0 6(a)

+1Vdc 0 1 0 0 1 6(b)

0Vdc 1 0 0 1 0 6(c)

ST 1 0 0 1 0 6(d)

1Vdc 0 0 1 0 1 6(e)

2Vdc 0 0 1 1 0 6(f)

a) Power intervals (+Vdc, -Vdc , +2Vdc, 2Vdc): These

intervals (+Vdc, -Vdc , +2Vdc, 2Vdc) are shown in Fig. 6(a), 6(b), 6(e), 6(f) occurs when current leaving or entering the multilevel inverter. The diode is forward bias in power interval. In this

interval, S1 S5, S3 S5, S1 S2, S3 S4 are ON for producing +Vdc, -

Vdc, +2Vdc, 2Vdc respectively. This sequence produces a five level AC output.

International Journal of Pure and Applied Mathematics Special Issue

682

Fig. 4. Generation of gate signals

b) Shoot through (ST) interval: The circuit diagram of

the ST interval is shown in Fig. 6(d). In this interval both the

switches (either S1 S4 or S3 S2) are ON at the same instant.

The duration of ST interval depends on duty ratio of boost converter. The inductor current circulates in switches (either

S1 S4 or S3 S2). In this interval diode is in reverse bias c) Zero interval: The circuit diagram of zero interval is

shown in Fig. 6(c). In this interval the multi-level inverter current

circulates in the switches (either S1 S2 or S3 S4). The diode is in

forward bias during the zero interval.

From Fig. 5, it is shown that the sum of AC output current iab

and current passing through diode id is equal to the current

through inductor L. And, the input voltage is equal to the aggregate sum of the AC and DC output voltages.

D. Mathematical Formation for Implementation of Proposed

Converter

The relationship between DC input Vdc, AC and DC output (Vaco,

Vdco) are derived as follows: From Fig 6(d), during the shoot

through operation, the increase in the inductor current (iL) depend on

duty ratio and the total time (T ) as follows:

Fig. 5. Current and voltage waveforms of proposed converters

D T

iL

= L

Vdc

(1)

From Fig 6(e), it is observed that stored energy in inductor

is dissipated through capacitor. During this time, the DC

voltage gain is given by (2).

V

dco = 1 (2)

1 D V

dc The modulation index (ma) controls the inverter output

voltage. The relation between peak AC output voltage to the

DC input voltage (Vdc) is given by (3). V

aco

= ma

1

(3) V

dc 1 D From (3), the AC gain depends on modulation index for any

constant value of D. The switching control must satisfy the following equation (4).

ma + D 1 (4) Hence, the multilevel output AC voltage is equal to the

input DC voltage and this output AC voltage is not depends

on D and ma. From (2) and (3), the output DC power (Pdc) and AC power

(Pac) is derived as follows:


683

Fig. 6. The equivalent circuit of the proposed TPHSMC during different voltage levels (a) +2Vdc-level. (b) +Vdc-level. (c) 0Vdc-level. (d) Shoot through

operation. (e) -Vdc-level. (f) -2Vdc-level.

V 2

(5) P

dc

= dc

Rdc (1 D)2

Pac = 0:5 Vdc2 ma

2

(6)

Rac (1 D)2

Here, Rdc and Rac are the DC and AC load resistance

respectively. From (5) and (6) it is observe that the Pdc

depends D and Pacdepends on both D and ma.

III. SIMULATION RESULTS

TABLE II

SIMULATION PARAMETERS

Simulation Parameter Value

Inductor L 5mH,

Capacitors C1 380µF

Capacitors C2 2000µF

DC source voltage (Vdc = 100V ) Vdc1 = 50V ; Vdc1 = 50V

Carrier frequency fc 5kHz

Reference frequency fr 50Hz

Modulation index ma 0:5 0:9

Duty ratio D 0:4 0:9

AC load 10 , 10mH

DC load 15

The proposed converter is simulated using

MATLAB/Simulink. The simulation parameters considered for

simulation are Tabulated in Table II. And, modulation index and

duty ratio are consider based on (4).

Fig. 7. Output voltage of AC and DC with different duty ratio 0.4, 0.2

Fig. 8. Output current of AC and DC with different duty ratios and loads

Fig. 7 shows the five level AC output voltage waveform and DC boost output voltage waveform with duty ratios of 0.2

and 0.4. The output DC voltages are 166V and 125 V achieved with duty ratios of 0.2 and 0.4 for a given input

voltage of 100V. The AC output voltage is 100V for ma of 0.8

and 0.6. Fig. 8 shows the multilevel AC and boost DC output

current waveforms with duty ratios of 0.2, 0.4 when it is loaded with R and R-L loads.

Fig. 9 shows the five level AC output voltage waveform and DC

boost output voltage waveform with duty ratios of 0.3 and 0.5. The

output DC voltages are 176V and 135 V achieved with duty ratios of

0.3 and 0.5 for a given input voltage of 100V. The AC output voltage

is 120V for ma of 0.8 and 0.6.


684

Fig. 9. Output voltage of AC and DC with different duty ratio 0.3, 0.5

Fig. 12. Comparison of AC gains

Fig. 10. Output current of AC and DC with different duty ratios (0.3, 0.5) and

loads

Fig. 10 shows the multilevel AC and boost DC output current

waveforms with duty ratios of 0.3, 0.5 when it is loaded with

R and R-L loads.

Fig. 7 shows the fifteen level AC output voltage waveform and DC boost output voltage waveform with duty ratios of 0.2

and 0.4. The output DC voltages are 70V and 100 V achieved with duty ratios of 0.2 and 0.4 for a given input voltage of 45V. The AC output voltage is 100V for ma of 0.8 and 0.6.

Fig. 11 shows the 3D-plot between ma, D and AC voltage

gain. AC voltage gain is increases exponentially for increasing of

duty ratio and increasing linearly with ma. Fig. 11. 3d-plot between AC voltage gain, duty ratio and modulation index

The Fig. 12 and Fig. 13 shows the AC and DC voltage gains against the duty ratio of separate boost and MLI, boost

converter cascaded with MLI, and proposed converters. The modulation index satisfies condition (4) for achieving higher

AC gains. The DC gain is same for all topologies. The proposed converter used for different AC or DC conversion

ratios with a controlled maand D.

IV. COMPARISON OF THE PROPOSED TOPOLOGY WITH THE

EXISTING TOPOLOGIES

The comparison of proposed simplified converter topology with

the existing topologies like, boost converter, multi-level inverter,

invidual boost and multi-level inverter, boost con-verter cascaded

with MLI and [2] are given in Table II. The proposed converter has

the following advantages: A shoot-through protection for multilevel stages.


685

TABLE III COMPARISON OF PROPOSED CONVERTER TOPOLOGY WITH EXISTING TOPOLOGIES

Boost Converter Multi level Inverter

Cascaded Separated Topology Proposed Topology

in [2]

F ig 1(b) F ig 1(a) F ig 2(b)

No.of switches 2 5 10 10 4 5

DC Voltage gain 1

1 1 1 1 1

1 D 1 D 1 D 1 D 1 D

AC Voltage gain

1 1 1

ma ma

ma ma

ma

1 D 1 D 1 D

Range of ma - 0 ma 1 0 ma 1 0 ma 1 0 ma (1 D) 0 ma (1 D)

Degree of freedom 1 1 2 2 2 1

Control parameters 2 2 5 5 5 4

Dead time Yes Yes Yes Yes No No

Multilevel AC Output No Yes No No No Yes

High boost DC Output Yes No No No No Yes

The proposed topology implemented without any dead-time. The switches count is less compared to conventional

topologies.The duty ratio and modulation index of the AC

multi level inverter and DC boost structures can be controlled

independently.The current during shoot through operation

circulate between alternative switches (S1 S4 or S2 S3).

V. CONCLUSION

The paper proposes a new converter with simultaneous AC and

DC outputs for microgrid applications. It is derived by replacing the

boost converter power switch with a multilevel inverter. The features

of this simplified topology are shoot through protection, multi-level

AC output, boost DC output without any dead-time. Number of

switches are also reduced compared to the existing topologies.

REFERENCES [1] A. Ravindranath, O. Ray, S. Mishra, and A. Joshi, “Single phase utility

interactive switched boost inverter for renewable energy based residential

power applications,” 28TH IEEE Applied power electronics conference and

exposition (APEC), pp. 3283-3287, 2013.

[2] O. Ray and S. Mishra, “Boost derived hybrid converter with simultaneous DC and AC outputs,” IEEE Trans. Ind. Applicat., vol. 50, no. 2, pp. 1082–1093, 2014.

[3] B. Axelrod, Y. Berkovich, A. Ioinovici, “A cascade boost-switched-capacitor-

converter -two level inverter with an optimized multilevel output waveform,” IEEE

Trans. Circuts Syst., vol. 52 (12), pp. 2763-2770, 2005.

[4] K. Gupta and S. Jain, “A novel universal control scheme for multilevel

inverters,” 6TH IET International conference on power electronics, ma-

chines and drives, 2012. [5] S. Mishra, R. Adda, and A. Joshi, “Inverse Watkins-Johnson topology

based inverter,” IEEE Trans. Power Electron., vol. 27, no. 3, pp. 1066-

1070, Mar. 2012. [6] G. Ceglia, V. Guzman, C. Sanchez, F. Ibanez and J. Walter, “A new

simplified multilevel inverter topology for DC-AC conversion,” IEEE

Trans. Power Electron., vol. 21, no. 5, pp. 1311-1319, 2006. [7] Y. V. Pavan Kumar and Ravikumar Bhimasingu, “A simple modular

multilevel inverter topology for the power quality improvement in renewable

energy based green building microgrids,” Elsevier Journal of Electric Power

Systems Research., vol. 140, pp. 147-161, 2016.


686

multi level inverter with ac and boost dc outputs for ... · converter and a multi -level inverter...

Documents