APPLICATION OF Z-SOURCE INVERTER IN
FUEL-CELL VEHICLES
Abstract:
The objective of this paper is to
demonstrate a low-cost, efficient, and reliable
inverter for traction drives of fuel cell vehicles
(FCVs). Because of the wide voltage range of
the fuel cell, the inverter and the motor need to
be oversized to accommodate the great
constantpowerspeedratio.
The
Z-source
inverter could be a cheap and reliable solution
for this application.
FCVs. As the automotive industry has been
urged to develop HEVs based on a
combination of internal combustion engine and
batteries as a bridging technology to FCVs,
issues and possibilities are addressed for the
use of the Z-source inverter in ICE HEV
traction drive systems.
Currently, two types of inverters are
used in FCV and hybrid electric vehicle (HEV)
tractiondrives:
 The
traditional
pulse
width
modulation (PWM) inverter
 Thedc/dcboostedPWMinverter.
For FCVs, the fuel cell voltage to the
inverter decreases with an increase in
power drawn
from the fuel cell. Therefore, the obtainable
output voltage of the traditional PWM inverter
is low
at high power for this application, so an
oversized inverter and motor must be used to
meet therequirement of high-speed, highpower operation.
The dc/dc–boosted PWM inverter does
nothave this problem; however, the extra dc/dc
stage increases the complexity of the circuit
and the
cost and reduces the system efficiency.
To demonstrate the superiority of the
Z-source inverter forFCVs, a comprehensive
comparison between the three inverters has
been made for the efficiency, price and
switchingdevicepowercomparision(sdpc).
Several PWM schemes with shoot-through are
proposed and compared. The PWM scheme
with the maximum constant boost, different
from other PWM schemes proposed, results in
less switching loss. The test results
demonstrated that the original objective of the
paper had been achieved: high efficiency
(greater than 97%), low cost (with minimal
device ratings), improved reliability (because
no deadtime is needed), and wide constant
power speed ratio (1.55 times that of the
traditional PWMinverter, thanks to the voltage
boost).
The results of this paper
demonstrate the many unique features of the Zsourceinverter and its high feasibility for use in
1|Page
4. Input fuel cell voltage: 0–420 V dc
INTRODUCTION:
z-sourceinverter is a low-cost, efficient, and
reliable inverter for traction drives of fuel cell
vehicles (FCVs). Because of the wide voltage range
TRADITIONAL INVERTERS:
Currently, there are two existing inverter topologies
usedfor hybrid electric and fuel cell vehicles:

of the fuel cell, the inverter and the motor need to be
oversized to accommodate the great constant power
speed ratio. The Z-source inverter could be a cheap
the conventional 3-phase Pulse Width
Modulation (PWM) inverter and

3-phasePWM inverter with a dc-dc
boost converter, which is alsovery
and reliable solution for this application.
WHY NEED A INVERTER FOR FUELCELLVEHICLE:
Fuel cells, as one of the most
promising energy sources,
Have been using such as, utility applicationsand
traction applications .Unlike batteries that havefairly
constant output voltage, the fuel cell has a unique VIcharacteristic and wide voltage change range as
shown in Fig.
popular in other applications. 3.Because of the
widevoltage range and limited voltage level of
1.
As can be seen from the figure, the output voltage of
thefuel cell decreases as the output current increases.
This
results in difficulty for high-speed, and high-power
operation to achieve a great Constant Power Speed
Ratio (CPSR). Inaddition, a larger inverter is
required.
fuel cell stack, the conventional PWMinverter
topology imposes high stressesto the switching
devices and motor, and limits the
motor’sconstant power speed ratio. 4.The dc/dc
boosted PWM inverter topology can alleviate the
stresses and limitations, however,suffers
problems such as high cost and complexity
associatedwith the two-stage power conversion.
Specifications of the inverter for fuel cell FCVs are
as follows:
1. Continuous power: 30 kW
2. Peak power: 55 kW for 18 seconds
3. Inverter efficiency >97% at30kW
2|Page
2.
With this unique feature, the Z-source
inverter provides a cheaper,simpler, single
stage approach for applications of fuel cell.
3. Thus, the Z-source inverter system can minimize
stresses andsize of the motor and increase output
power greatly.
4. Moreover, it highly enhances because
theshoot through can no longer destroy the
inverter.
EEEEEEEEEEEEEEEE
li
mitations of the Traditional Converters:
• Limited output voltage
(> or < Vdc)
• Either buck or boostoperation only
• Not interchangeable main circuits
• Vulnerable to EMI noise
• Difficult to use IGBT
module and IPM for ISource
• Start-up difficulty
• Shoot-through or opencircuit problem –reliability
EXISTENCE OF Z-SOURCEINVERTER:
EEEEWe need a new type of inverter
to solve the following problems for fuel cell:
• Two-stage power conversion
• High cost
• Low efficiency
• Difficult to start up (in-rush)
• Reliability problem (vulnerable to EMI)

To have a new power conversion technology
The newly proposed Z-source inverter has the
capacity to solve the above problems and unique
feature that
1.
it can boost the output voltage by
introducing shoot through operation mode,
. The Z-source inverter outputs a required
voltageby adjusting the shoot through duty cycle with
the restrictionto keep the voltage across the switches
not to exceed its limit.
Shoot through for PWMcontrol:
Control methods for z-source inverter :
Several control methods have been proposed:
simple control , maximum boost control ,and
maximum constant boost control .
Compared with a traditional voltage source inverter,
the Z-source inverter has an extraswitching state:
shoot-through. During the shoot-though state, the
output voltage to the loadterminals is zero, the same
as traditional zero states. Therefore, to maintain
sinusoidal outputvoltage, the active-state duty ratio
has to be maintained and some or all of the zero
states turnedinto shoot-through state.
which is forbidden in traditional voltage
source inverters.
3|Page
simple control:
The simple control uses two straight lines to control
the shoot-through states, as shown in
Fig. 4.1. When the triangular waveform is greater
than the upper envelope, Vp, or lower than the
bottom envelope, Vn, the circuit turns into shootthrough state. Otherwise it operates just astraditional
carrier-based PWM. This method is very straight
forward; however, the resultingvoltage stress across
(a) Maximum boost control.
the device is relatively high because some traditional
zero states are not
utilized.
(b) Maximum boost control with third harmonic
injection.
Maximum Constant Boost Control
Maximum Boost Control
The sketch map of maximum constant boost control
To fully utilize the zero states so as to minimize the
is shown in Fig. 4.3.
voltage stress across the device,maximum boost
This methodachieves maximum boost while keeping
control turns all traditional zero states into shoot-
the shoot-through duty ratio always constant; thus
through state, as shown inFig. 4.2. Third harmonic
itresults in no line frequency current ripple through
injection can also be used to extend the modulation
the inductors.
index range.Indeed, turning all zero states into shoot-
The sketch map of maximumconstant boost control
through state can minimize the voltage
with third harmonic injection is shown in Fig. 4.3(b).
stress;however, doing so also causes a shootthrough
With this method, theinverter can buck and boost the
duty ratio varying in a line cycle, which causes
voltage from zero to any desired value smoothly
inductor current ripple [10]. This will require high
within the limitof the device voltage.
inductance for low-frequency orvariable-frequency
applications.
4|Page
.Act
ual price comparision:
Again, the Z-source has thelowest price among
the three
inverters. In addition, because it has fewer
components, a higher mean time between failures
canbe expe cted, which leads to better reliability.
comparision between the inverters:
Switchingdevice powercomparision:
The Z-source inverter’s average SDPR is the
smallest among the three, while theconventional
PWM inverter’s SDPRs are the highest in both
average and peak values. average SDPR also
indicates thermal requirementfrom a distributor are
EFFICIENCY COMPARISION:
listed in table2.
1..The Z-source inverter can increase inverter
The Z-source also reduces the total averageSDP by
conversion efficiency by 1% over the two existing
15%, which leads to costreduction.
systems
2.Invertermotorsystem efficiency by 1% to 15% over
the conventionalPWM inverter.
5|Page
• A new type of inverter has been presented.
• The Z-source inverter is specially suited forfuel cell
applications.
• Unique features include buck-boost
inversion by single power-conversion stage,improved
reliability, strong EMI immunity,and low EMI.
• The Z-source technology can be applied tothe entire
spectrum of power conversion.
.ADVANTAGES:
• Provides the buck-boost function by
onestageconversion;
References:
• Is immune to EMI noise and misgating(i.e., mis-
1. F. Z. Peng, Li Hui, Su Gui-Jia, J. S. Lawler, “A
gating on and off by EMI noisewill not destroy the
new ZVS bidirectional dc-dc converter forfuel cell
converter)
and battery application,” IEEE Transactions on
• Has the advantages of both traditional
Power Electronics, 19
converters: V- and I- converters;
pp. 54–65.
• Solves the problems of the traditional
2. S. E. Gay, Gao Hongwei, M. Ehsani, “Fuel cell
converters;
hybrid drive train configurations and motordrive
• Has low or no in-rush current compared with the V-
selection,” presented at Vehicular Technology
converter; and
Conference, 2002, 2(24–28), Sept. 2002,pp. 007–
• Has low common-mode noise
1010.
.Improves power factor and reduces
3. Tadaichi Matsumoto, Nobuo Watanabe, Hiroshi
harmonic currentand common-mode voltage.
Sugiura, Tetsuhiro
CONCLUSION:
6|Page