CASCADED H-BRIDGE INVERTER WITH

QUASI-SWITCHED BOOST NETWORK

FOR RENEWABLE ENERGY APPLICATION

Abstract— Recently, multilevel inverters have

Three general multilevel inverter topologies are:
become more attractive due to low total harmonic
flying capacitors, neutral point clamped (NPC), and
distortion (THD) in the output voltage and low
cascaded H-bridge (CHB) inverters. Among these
electromagnetic interference (EMI). This paper
topologies, the CHB inverter has unique advantages in
proposes a single stage cascaded H-bridge quasi
modularity and its contribution of high power.
switched boost inverter (CHB-qSBI) for renewable
Moreover, the CHB inverter can reach a higher
energy sources applications. The proposed inverter
reliability because of its modular topology. These
has the advantage over the cascaded H-bridge quasi-
advantages make the CHB inverter an attractive
Z-source inverter (CHB-qZSI) in reducing two
option for many applications such as uninterruptible
capacitors and two inductors. As a result cost, weight
power supplies (UPS), grid-connected system,
and size are reduced. Additionally, the proposed
StatCom system, motor drive, etc. However, the
qCHB-FLBI can work in the shoot-though state. A
traditional CHB multilevel inverter is a buck DC-AC
capacitor with low voltage rating is added to the
power conversion, where the peak AC output voltage
proposed topology to remove an offset voltage of the
is limited by the total DC source voltages.
output AC voltage when the input voltages of two
An additional DC-DC boost converter is
modules are unbalanced. The system is simulated
demanded for each module in the CHB topology to
using MATLAB/Simulink and the results validate the
achieve the high AC output voltage when the DC
effectiveness of the proposed system.
input voltages are low. Adding DC-DC boost power
converter results in low efficiency and high cost. Two
I. INTRODUCTION capacitors, two boost inductors, two diodes, ten
switches, one filter inductor and a resistive load are
utilized in the conventional CHB-BFLI. The boost
In the past decade, renewable energy sources such as
DC-DC converter is used to control the DC-link
photovoltaic (PV)-based systems have attracted much
voltage on each H-bridge circuit. Both the top and
more attention due to the advantages such as less
bottom switches in the same leg cannot be switched
environmental impact and improved economic
on simultaneously because the DC-link capacitor is
benefits. With the rapid growth of power electronics
connected to each leg in parallel. And a dead-time
technology, various converters topologies have been
between two switches in the leg must be used to avoid
developed for PV systems. Among these topologies,
short circuit in the DC source.
multilevel inverters have been receiving significant
A CHB quasi-Z-source inverter (qZSI) with
interest due to the reduced total harmonic distortion
single-stage power conversion has a qZS network with
(THD) and improved quality of output waveform. As
two capacitors and two inductors connected to each H-
the output voltage level increases, the output harmonic
bridge circuit. In the CHB-qZSI, a shoot-through (ST)
content of such inverters decreases, allowing the use
state is used to boost voltage without any damages in
of smaller output filters.
the power circuit. In one switching period,
the number of the ST states in the single-phase qSBI less inductor, one more diode and one more switch in
is two. Therefore, the operating frequency of the front of the main H-bridge circuit. In this paper, a new
inductors is twofold the switching frequency. In the single-stage quasi-cascaded H-bridge five-level boost
CHB-qZSI, the input DC current is continuous with inverter (qCHB-FLBI) is proposed. In the proposed
low ripple. Each module in the CHB qZSI can qCHB-FLBI, the qSB network is used in each module.
produce the same DC-link voltage by control the ST The main features of the proposed qCHB-FLBI are five-
duty cycle. However, the CHB-qZSI use a large level output voltage with boost voltage ability, reduction
number of passive elements with raises the size, cost, in a number of passive components and
and weight of the power cascaded system.
A quasi-switched boost (qSB) network is used
to replace the qZS network. In comparison to the qZS
network, the qSB network uses one less capacitor, one
the qBI module 1 is –𝑉𝐶1. Else, it equals zero. The qBI module 1 is –𝑉𝐶1.
inductor 𝐿1 is also charged in this state, and its In the NST state 3, as shown in Fig.2 (e), both
voltage is calculated as (1). 𝑆1 and 𝑆4 are turned ON. The output voltage of the
In the non-shoot-through (NST) state 1, as qBI module 1 is 𝑉𝐶1.
shown in Fig.2(c), both 𝑆1 and 𝑆3 are turned ON. In During the non-shoot-through (NST) states as
the NST state 4, as shown in Fig.2(f), both 𝑆2 and shown in Fig.2(c)–4(f), 𝐷𝑎1 and 𝐷𝑏1 are conducting.
𝑆4 are turned ON. The output voltage of the qBI The capacitor 𝐶1 is charged from 𝑉𝑑𝑐, while the
module 1 in both NST states 1 and 4 is zero. inductor 𝐿1 transfers energy from the DC voltage
In the NST state 2, as shown in Fig.2 (d), both source to the main circuit. The H-bridge circuit is
𝑆2 and 𝑆3 are turned ON. The output voltage of the equivalent as a current source, 𝑖𝑃𝑁1. We get:
shoot-through immunity.
𝐿1 𝑑𝑖𝐿1 = 𝑉𝑑𝑐1 - 𝑉𝐶1 (2)
II. PROPOSED TOPOLOGY 𝑑𝑡
The configuration of the proposed single-stage qCHB-
FLBI is illustrated in Fig.1. The proposed inverter
consists of two separate DC sources, two quasi-boost
inverter (qBI) modules and an inductor filter
connected to the resistive load in series. Each qBI
module contains one capacitor, one boost inductor,
four switches and two diodes. The output voltage of
the proposed qCHB-FLBI has five levels.

A.OPERATING PRINCIPLES
Assuming that two qBI modules have the
same parameters, the qBI module 1 in the proposed
system is used to analyze the operating principle. Fig.
2 shows the operating modes of the qBI module 1 in
the proposed inverter.
In the shoot-through (ST) state 1, as shown
in Fig.2 (a), both 𝑆1 and 𝑆2 are turned ON. 𝐷𝑎1 is
conducting, while 𝐷𝑏1 is blocking. If 𝑆3 is turned
ON, the output voltage of the qBI module 1 is –𝑉𝐶1.
Else, it equals zero. The inductor 𝐿1 is charged from Fig.1. Proposed qCHB-FLBI topology
the source. We have: In one switching period, T, each leg has twice
𝐿1 = 𝑉𝐶1 (1) short circuits alternatively. From (1) and (2), the
𝑑𝑖𝐿1
𝑑𝑡 average inductor
𝑇0
voltage is 𝑇
0
In the ST state 2, 𝑆3 and 𝑆4 are turned ON as 𝑉 = (1-2 )( 𝑉 - ) +2 (3)
𝑉 𝑉
𝐿1 𝐶1
shown in Fig.2(b). 𝐷𝑎1 is blocking, while 𝐷𝑏1 is 𝑇 𝑑𝑐1 𝑇 𝑑𝑐1
conducting. If 𝑆2 is turned ON, the output voltage of
0
where 𝑇 = 𝐷 is a ST duty ratio in each leg of module module 2. The output voltage 𝑉𝑎𝑐 of the cascaded
𝑇 1 system is a subtraction of 𝑉 and 𝑉 . Therefore, the
1; 𝑇0 is total ST time intervals in one leg. In a steady 𝑎𝑏 𝑐𝑏

state, the average inductor voltage should be zero. output voltage of the proposed qCHB-FLBI produces
We get: five levels as shown in Fig.3.
𝑉𝐶1 1 𝑇0 (4)
=1−2 = 1−2𝐷1 𝑉𝑑𝑐1
1
𝑇
Similarly, we obtain capacitor voltage on module 2 as
𝑉𝐶1 (5)
= 1−2𝐷2 𝑉𝑑𝑐2
1
 Fig. 2.Operating states of module 1. (a) ST state 1,
(b) ST state 2,(c) NST state 1, (d) NST state 2, (e)
NST state 3 and (f) NST state 4.

B.PWM SCHEME FOR THE PROPOSED SYSTEM

Fig.3 shows a phase-shifted sinusoidal pulse-
width modulation (PS-SPWM) strategy for the
proposed qCHB-FLBI. For module 1, two control
voltages, -𝑉𝑐𝑜𝑛𝑡𝑟𝑜𝑙 and 𝑉𝑐𝑜𝑛𝑡𝑟𝑜𝑙 are compared to a high-
frequency triangle voltage, 𝑉𝑡𝑟𝑖1, to produce control
signals for the 𝑆1 and 𝑆2 switches. Two DC voltages,
𝑉𝑆𝐻 and -𝑉𝑆𝐻, are compared to 𝑉𝑡𝑟𝑖1to produce the 𝑆0𝑎
control signal. Then 𝑆0𝑎 is added to the control signals
of switches 𝑆1 and 𝑆2 to produce the ST states.
Likewise, the 𝑉𝑡𝑟𝑖1 is shifted in 90° to create another
Fig.3 PWM scheme for the proposed qCHB-FLBI.
high-frequency triangle voltage,
𝑉𝑡𝑟𝑖2. 𝑉𝑐𝑜𝑛𝑡𝑟𝑜𝑙 and 𝑉𝑐𝑜𝑛𝑡𝑟𝑜𝑙 are compared to 𝑉𝑡𝑟𝑖2 to
produce control signals for the 𝑆3 and 𝑆4 switches. Because the number of the ST states in the
𝑉𝑆𝐻 and -𝑉𝑆𝐻 are compared to the 𝑉𝑡𝑟𝑖2 to produce a proposed qCHB-FLBI in one switching period is four
𝑆0𝑏 control signal. The 𝑆0𝑏 is then added to the control as shown in Fig.3, the operating frequency of the
signals of switches 𝑆3 and 𝑆4 to produce the ST states. inductors in the proposed inverter is fourfold the
As a result, the output voltage 𝑉𝑎𝑏 of H-bridge module switching frequency. In the CHB-qZSI, the operating
1 has three levels. frequency of the inductors is twofold the switching
Similar for the second H-bridge module, two frequency. Therefore, the high-frequency current
control voltages (𝑉𝑐𝑜𝑛𝑡𝑟𝑜𝑙 and 𝑉𝑐𝑜𝑛𝑡𝑟𝑜𝑙) are shifted in ripple on inductors of the proposed qCHB-FLBI is a
180° to produce the output voltage 𝑉𝑐𝑏 of the H-bridge half that of the CHB-qZSI.
C.SOLVING UNBALANCED DC SOURCE PROBLEM IN III. SIMULATION RESULTS
PROPOSED SYSTEM
In order to achieve a good quality of the The inverter is simulated using
output voltage as shown in Fig.3, the capacitor voltage MATLAB/Simulink. Table 1 shows the simulation
in each module must be the same. From (4) and (5),
parameters.
the ST duty cycles 𝐷1 and 𝐷2 in each module are used
to control the capacitor voltages 𝑉𝑐1 and 𝑉𝑐2, Table 1. Simulation parameters
respectively. When the DC input voltage in each
module is unbalanced, 𝐷1 is different from 𝐷2 to
keep
𝑉𝑐1= 𝑉𝑐2. The difference between 𝐷1 and 𝐷2 results in
generating the DC offset at the output voltage. To
remove the DC offset of the output voltage, a
capacitor 𝐶𝑑 is added to the output of the proposed
inverter. Fig.4 shows the proposed inverter under
unbalanced DC source condition, where the capacitor
𝐶𝑑 is connected between 𝑏1 and 𝑏2 nodes to filter the
DC component at the output. Assuming 𝑉𝐶 =𝑉𝑐1= 𝑉𝑐2,
the DC offset voltage is calculated as
 Input voltage 48V
Inductor (𝐿1, 𝐿2) 2mH
Capacitor (𝐶1, 𝐶2) 4.4 mH
Capacitor (𝐶𝑑) 4.7mH
Inductor (𝐿𝑓) 3mH
Resistor (R) 40 ohm
Switching frequency 10KHz

𝑉 =𝐷 𝑉
1
𝐷2 =( 𝐷 ) Fig.5. shows the Simulink model of the proposed
- 𝑉 -𝐷 𝑉
𝑐𝑑 1−2𝐷1 𝑑𝑐1 1−2𝐷2 𝑑𝑐2 1 2 𝐶 qCHB-FLBI. Switched are controlled using PWM
technique. PWM generation technique is shown in
Fig.6. First, we set 𝑉𝑑𝑐1 = 𝑉𝑑𝑐2 = 48V to confirm the
properties of the proposed inverter under balanced
DC-source condition. Fig. 8 shows the output voltage
of the proposed qCHB-FLBI when both input voltages
are the same. The output voltage has five levels ie
200V, 100V, 0V, -100V, -200V.

Fig.4.Proposed qCHB-FLBI with filter

capacitor Fig.5. Simulink model of qCHB-FLBI
Because the subtraction between 𝐷1 and 𝐷2 is
too small, the voltage stress on 𝐶𝑑 is very low.
Therefore, the effect the size and cost of the capacitor
𝐶𝑑 to overall cascaded system is trivial. Note that the
current rating of capacitor 𝐶𝑑 should carry the entire
load current during operation of the circuit.

Fig.6. Simulink model of PWM generation

Fig.7. PWM Control Scheme

 Input voltage of module 1 is changed to 60V. Output
voltage has five levels as before. The unbalanced DC
source problem is solved by the filter capacitor 𝐶𝑑.
Volatge across 𝐶𝑑 is shown in Fig.9.

IV. CONCLUSION

A new single-phase single-stage CHB five-

level inverter with boost voltage ability has been
proposed in this paper. The proposed inverter has a
Fig.8. Output Voltage of qCHB-FLBI five-level output voltage, reduced number of passive
components and shoot-through immunity. Modes and
PWM control strategy for the proposed system are
shown. A capacitor with low voltage rating is added to
the proposed topology to remove an offset voltage of
the output AC voltage when the input voltages of two
modules are unbalanced The system is simulated
using MATLAB/Simulink and the results validate the
effectiveness of the system.

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