Post on 27-Mar-2020
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.
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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:
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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.
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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.
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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.
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