

Articles
by
Z. Yeo 
Total Records (
14 ) for
Z. Yeo 





O. Asseu
,
M. Koffi
,
Z. Yeo
,
X. LinShi
,
M.A. Kouacou
and
T.J. Zoueu


This study presents a feedback linearization strategy
and a robust controller to permit a decoupling and regulation of the motor
states in order to assure a good dynamic performance and stability of
the global system. As the control required the knowledge of the instantaneous
flux of the rotor and the rotor parameter estimation can improve the control
quality, a sixdimensional discretetime extended sliding mode observer
is proposed for online estimation of rotor fluxes and rotor time constant.
The simulation results for a 1.8 kW induction motor are presented to illustrate
the validity and the high robustness of the proposed approach against
parameter variations and disturbances. 




O. Asseu
,
T.R. Ori
,
K.E. Ali
,
Z. Yeo
,
S. Ouattara
and
X. LinShi


The aim of this study is to present a high dynamic current control and speed estimation strategy for Permanent Magnet Synchronous Motor (PMSM) drives without a speed transducer. The strategy is based on the exact linearization methodology and Extended Sliding Mode Observer (ESMO) algorithm. The performances of the proposed control strategy are analysed by simulations for a 1.6 kW PMSM. The obtained results show the effectiveness of the proposed robust current control approach and speed observation algorithm under load torque and stator resistance variation. 




O. Asseu
,
A. Tanoh
,
M. Koffi
,
Z. Yeo
,
T.R. Ori
and
X. LinShi


In this study, a reducedorder discretetime Extended Sliding Mode Observer (ESMO) is introduced for online estimation of rotor fluxes and rotor time constant. The satisfying simulations and experimental results carried out on a 5.5 kW induction motor demonstrate the excellent performance and high robustness of the proposed ESMO against parameter variations, modeling uncertainty and measurement noise. It is concluded that the implementation in realtime of this reducedorder ESMO in the industrial applications, compared with the fullorder ESMO, permit on the one hand to overcome the heavy computational effort, complexity and hard tuning of the estimation algorithm and on the other hand, to reduce the execution time of the observation with a good accuracy and considerable rapidity. 





M.A. Kouacou
,
A.A. Koua
,
Z. Yeo
,
A. Akichi
,
A. Tanoh
and
M. Koffi


The aim of this study is to investigate magnetic properties of an example of halfmetallic and ferromagnetic compounds, namely, the half Heusler PtMnSb. From the magnetic measurements, it can be shown a change from a localized magnetism due to the spin waves thermally excited, to an itinerant magnetism with spin fluctuations is to reduce the moments in this compound. Furthermore, the electrical and thermal resistivity measurements were performed. The resistivity results with respect to the magnetic properties are confirmed and a transition of a halfmetallic state to a metallic state at 100 K is observed. 




M. Koffi
,
Z. Yeo
,
A. Tanoh
,
A.D. Ochou
,
O. Asseu
,
D.K. Konan
and
M.A. Kouracou


The raindrop size distribution (DSD) measurements were
collected in the tropical and midlatitude rain system. Comparisons of
measured values and estimated values of polarimetric parameters (Z_{H}
and Z_{DR}) shows that kinematic peaks are the main cause of the
variability of Z_{H} but they do not influence much Z_{DR}.
The influence of the peak number on the variance of the radar parameters
is based on the relations between time and averaging. It consists to examine
how many DSDs have to be averaged in order to suppress the peaks and what
are the consequences on the radar parameters. The study shows that averaging
improves the validity of the polarimetric parameters. 




Z. Yeo
,
M. Koffi
,
M.A. Kouacou
,
O. Asseu
,
A. Tanoh
and
D. Konan


This study built a computer program in order to carry
out accurate calculations of the magnetic field according to time, space
and the load of a threephase line (3 or 6 conductors). The theorem of
Ampere and the superposition one were used. We obtained the variations
of the magnetic field according to time at a given space point and the
magnetic field at a given moment on both sides of the line. These results
enabled us to define security distance with respect to critical values
used in the literature. The number of parameters did not allow
us to calculate standard security distances. For the tested pylons, if
reference value is 0.2 μT, the security distance can exceed several
hundred meters. 




A. Tanoh
,
D.K. Konan
,
M. Koffi
,
Z. Yeo
,
M.A. Kouacou
,
B.K. Koffi
and
K.R. N`guessan


This study deals with the early detection of damages
in rolling bearings of an asynchronous machine. It presents a neuronal
network based application for motor bearing fault diagnosis. Vibration
simulation is used to assist in the design of various motor rolling bearing
fault strategies. These simulation results indicate that neural networks
can be effective agents in the diagnosis of motor bearing fault through
vibration signature. 




O. Asseu
,
Z. Yeo
,
M. Koffi
,
M.A. Kouacou
and
K.E. Ali


This study proposes a novel method to achieve good performance for rotor time constant and flux estimation in induction motor sensorless control, using a reduced order Extended Kalman Filter (EKF) instead of a fullorder EKF. This new algorithm uses a reduced order statespace model that is discretized in a particular and innovative way proposed in this study. With this model structure, only the rotor flux components are estimated while the full order EKF also estimates stator current components. Thus, as compared with the full order EKF, this new approach strongly reduces the execution time of the observation and simplifies the tuning of covariance matrices, since, the number of elements to be adjusted is reduced. The satisfying simulations results on MatlabSimulink environment for a 1.8 kW induction motor, demonstrate the good performance and stability of the proposed reduced order EKF algorithm against parameter variation, modeling uncertainty, measurement and system noises. 





B.K. Koffi
,
D.K. Konan
,
R.K. N’guessan
,
J.K. Saraka
,
A. Tanoh
,
M.A. Kouacou
,
Z. Yeo
,
M. Koffi
and
A.A. Koua


This study presents theoretical consideration and results of solar water distiller system. Device was composed of glass which served as a condenser and an aluminium plate in black paint as an absorber. It was also composed of a tank of brine and a tank of distilled water. Solar water distiller system was modelled and simulated using an implicit numerical scheme, the DiaboloSablier algorithm. Simulation results showed that accumulated mass water greatly depended on the ambient temperature. Thus, for an increasing of 5°C of the ambient temperature, accumulated mass water roughly doubled. This inexpensive device permitted to produce 6 kg of water per day with a commonly used of collector of 2 m^{2}. Condensed mass water became significant for relative humidity of 40% at 308K temperature corresponding to conditions of dry season in the Abidjan zones. 





Z. Yeo
,
M. Koffi
,
O. Asseu
,
A. Tanoh
,
D. Konan
and
B. Koffi


Some discharge models suppose that the discharge is
developed mainly according to an electric field`s line. In this study,
a computer program is built in order to carry out accurate determination
of the electric field`s lines. Finite element method is implemented to
solve the Laplace equation and then the electric field is derivate. Field`s
lines are built by successive jumps and their parameters are calculated
by a polynomial approximation. Results are successfully compared to empirical
formula established by earlier researches in rod to plane geometry. The
field`s lines and what could be a discharge line for an aerial insulator
are also investigated and discussed. 




D.K. Konan
,
B.K. Koffi
,
A. Tanoh
,
M. Koffi
,
Z. Yeo
,
K. Konan
and
R.K. N`guessan


This study presents a new technique to measure the phase
difference between two diffracted fields: The field diffracted by a reference
object and the field diffracted by an unknown object. For that we use
the interferential technique of Young slits. We measured the phase difference
between the diffracted fields of two rods of resin. And knowing the phase
of the diffracted field of the reference object helps deducing the phase
of the field diffracted by the sample. This setup is simple and it is
very strong in the presence of disturbances because both objects are illuminated
with the same incident beam. Moreover, this technique allows us measuring
the phase of the diffracted field on a wide range of angle so that a high
resolution of the image can be obtained. 




O. Asseu
,
S. Ouattara
,
K.E. Ali
,
Z. Yeo
and
M. Koffi


This study uses a robust inputoutput linearization via feedback control in order to assure a good dynamic performance, stability and a decoupling of the stator currents for an induction motor in a fieldoriented (d, q) coordinate. However, this control requires the knowledge of certain variables (rotor flux, torque) that are difficult to access or simply impossible to measure and also the rotor time constant variation can induce a performance degradation of the system. Thus, a fifthorder Discretetime extended Kalman filter approach is proposed for online estimation of rotor flux, currents, rotor time constant and torque in an induction motor. The interesting simulations and experimental results obtained on a testing bench for a 5.5 kW induction motor permit to validate the effectiveness and good performance of the proposed nonlinear control and extended Kalman filter algorithm in the presence of parameter variation, modeling uncertainty and measurement noise. 





