Penrose Cofie - Academia.edu (original) (raw)

Papers by Penrose Cofie

World Journal of Advanced Engineering Technology and Sciences, Mar 30, 2022

Multilevel H-bridge inverters have grown in popularity in electronic direct current (DC) to alter... more Multilevel H-bridge inverters have grown in popularity in electronic direct current (DC) to alternating current (AC) power conversion. In the renewable energy field, H-bridge inverters are used for converting DC voltage obtained from solar panels to AC voltage. However, H-bridge inverters produce undesirable odd harmonics in their output. Several Hbridges are, therefore, usually cascaded to reduce the total harmonic distortion (THD) in their output, but the results aren't satisfactory in most cases. In this paper, both active and passive filters are incorporated in a cascaded H-bridge inverter to reduce the THD further. Then cost comparison is made of cascaded H-bridge inverters (3, 5, 7, 9, and 11levels) without a filter and multilevel cascaded H-bridge inverters (3, 5, 7, 9, and 11-levels) with a passive filter or active filter. Powersim (PSIM) platform is used to perform the THD analysis.

American Journal of Optics and Photonics, 2019

Hybrid organic-inorganic perovskite solar cells have attracted the attention of researchers and s... more Hybrid organic-inorganic perovskite solar cells have attracted the attention of researchers and scientists throughout the world. From 2009, when actual research work began on photovoltaic perovskite applications, a lab power conversion efficiency above 23.3% have been achieved. Whereas, silicon solar cells have only achieved power conversion efficiencies around 17.5% in both residential and commercial applications. A typical perovskite solar cell consists of 6 main layers of different materials: a glass layer, a thin layer of fluorine-doped tin oxide substrate (FTO), an electron transport layer of TiO 2 , a perovskite active layer known as methylammonium lead iodide (CH 3 NH 3 PbI 3), a hole transport layer of Spiro-Ometad, and a gold (Au) electrode. This paper summarizes the research that focused on the selective use of the perovskite solar cell's composite materials, specifically, the Spiro-Ometad layer, the methylammonium lead iodide layer (CH 3 NH 3 PbI 3), and the TiO 2 layer with a variation of the thickness of the perovskite layer. Initial simulation results show a power conversion efficiency of 20.34% when using a gold (Au) electrode. Further research is needed, in which new technology for device fabrication will create homogeneous thin-film layers that will be tested for increased efficiency.

Circuits and Systems, 2016

This paper presents the design and implementation of a Stepper Motor using Nexys2 circuit board b... more This paper presents the design and implementation of a Stepper Motor using Nexys2 circuit board based on a Xilinx Spartan 3E Field Programmable Gate Array (FPGA) device with VHDL code. The algorithm implemented on FPGA allows a substantial decrease of the equivalent processing time developed by different velocity controllers. The Stepper Speed control is achieved using VHDL code, and the hardware digital circuit is designed for a programmable rotational stepper motor using VHDL as a tool and FPGA as a target technology. The 50 MHZ provided by the starter kit is divided to obtain the necessary delay time between the motor phases that ranges between 2-10 m seconds. Though output selections, the direction of rotation of the stepper motor besides the magnitude of the angle of movement and the rotation speed can be controlled. The major advantage of using reconfigurable hardware (FPGA) in implementing the Stepper Motor instead of a discrete digital component is that it makes modifications to the design easy and quick and also, the total design hence represents an embedded system (works without computer). The total programmable hardware design that controlled on the stepper motor movement, occupied an area that did not exceed 12% of the chip resources.

Energy and Power Engineering, 2015

Load flow is an important tool used by power engineers for planning, to determine the best operat... more Load flow is an important tool used by power engineers for planning, to determine the best operation for a power system and exchange of power between utility companies. In order to have an efficient operating power system, it is necessary to determine which method is suitable and efficient for the system's load flow analysis. A power flow analysis method may take a long time and therefore prevent achieving an accurate result to a power flow solution because of continuous changes in power demand and generations. This paper presents analysis of the load flow problem in power system planning studies. The numerical methods: Gauss-Seidel, Newton-Raphson and Fast Decoupled methods were compared for a power flow analysis solution. Simulation is carried out using Matlab for test cases of IEEE 9-Bus, IEEE 30-Bus and IEEE 57-Bus system. The simulation results were compared for number of iteration, computational time, tolerance value and convergence. The compared results show that Newton-Raphson is the most reliable method because it has the least number of iteration and converges faster.

2010 IEEE/ASME International Conference on Advanced Intelligent Mechatronics, 2010

ABSTRACT Our technological demands today require extremely challenging control solutions such as ... more ABSTRACT Our technological demands today require extremely challenging control solutions such as real-time applications of Networked Control System (NCS). However, due to communication protocol and shared data bus, NCS always experiences uncertain and unpredictable time delays in both input and output channels. These delays cause asynchronization between controller and plant thereby degrading the performance of closed-loop control systems. To address the concern of stability improvement in real-time, this paper proposes to utilize digital redesign technique to compensate for these network induced delays.

2012 24th Chinese Control and Decision Conference (CCDC), 2012

ABSTRACT This paper proposes a discretization scheme and an optimal digital cascaded plus state-f... more ABSTRACT This paper proposes a discretization scheme and an optimal digital cascaded plus state-feedback controller for Multiple-Input-Multiple-Output (MIMO) continuous-time systems with multiple time delays in both inputs and outputs. Firstly, an equivalent discrete-time model is obtained from the MIMO analog time-delayed system. The equivalent discrete-time model and a partially predetermined digital cascaded controller are formulated as an augmented discrete-time state-space system for state-feed forward and state-feedback Linear Quadratic Regulator (LQR) design. As a result, the parameters of the cascaded controller and its associated state-feedback controller can be determined by tuning the weighting matrices in the LQR optimal design. Then a discrete-time optimal observer for the MIMO analog time-delayed system is constructed for the implementation of the designed state-feedback digital controller. The proposed methodology has been verified through both simulation and experiment on the induction motor drive system.

International Journal of Systems Science, 2006

This paper presents a new fault tolerant control scheme for unknown multivariable stochastic syst... more This paper presents a new fault tolerant control scheme for unknown multivariable stochastic systems by modifying the conventional state-space self-tuning control approach. For the detection of faults, a quantitative criterion is developed by comparing the innovation process errors occurring in the Kalman filter estimation algorithm, which, for faulty system recovery, a weighting matrix resetting technique is developed by adjusting and resetting the covariance matrices of the parameter estimate obtained in the Kalman filter estimation algorithm to improve the parameter estimation of the faulty systems. The proposed method can effectively cope with partially abrupt and/or gradual system faults and/or input failures with fault detection. The modified state-space self-tuning control scheme can be applied to the multivariable stochastic faulty system without requiring prior knowledge of system parameters and noise properties.

Fusion Science and Technology, 2016

Abstract In order to accommodate high thermal loading of single-side-heated (SSH) components, rob... more Abstract In order to accommodate high thermal loading of single-side-heated (SSH) components, robust thermal management and high-heat-flux-removal approaches are essential to prevent thermal instability, thermal runaway, or a thermal spiral toward component failure. This paper presents multidimensional steady-state heat transfer measurements for a high-strength-copper SSH monoblock (heat sink) coolant flow channel with a helical wire insert (HI) and thermally developing internal laminar and turbulent water (coolant) flow. In the present case, the term “monoblock” refers to a solid parallelepiped with a central coolant flow channel along the axial centerline. In addition to producing local two-dimensional (axial and circumferential) flow boiling curves, multidimensional monoblock wall temperature distribution comparisons were made between flow channels with and without a HI. Further, flow boiling curves were measured up to ∼4.0 MW/m2 at the inside flow channel wall. For the same inside flow channel temperature, the HI enhanced (1) the incident heat flux by >70% when compared with the flow channel without the insert and (2) the inside flow channel wall heat flux by up to a factor of 5 near the monoblock heated side and at all axial locations. These results can be used for validation of computational fluid dynamics codes.

The design and selection of a heater material of reasonable thickness to provide peak surface hea... more The design and selection of a heater material of reasonable thickness to provide peak surface heat flux of 15 MW per square meter is one of the major requirements in the high heat flux experiment. The heater receives power from a 40 V direct current (DC) supply. The surface area of the heater is dictated by the dimensions of the test section. Because of its excellent dielectric strength and electrical resistivity, Aluminum Nitrite (AIN) is used in the design to electrically insulate the heater from the test section. The computations, analysis, and a clear display of the electro-physical properties of several heater candidates are discussed to provide the rationale for the final selection of copper and graphite as heater materials for the design. The procedure for sizing the copper bus, which transfers the power to the heater is also discussed.

A novel design implementation of PID equivalent controller using state observer based Extended Ka... more A novel design implementation of PID equivalent controller using state observer based Extended Kalman Filter (EKF) for Permanent Magnet Synchronous Motor (PMSM) is proposed. The EKF is constructed to achieve accurate estimation of the speed and current from the noisy measurement. Then, a PID controller is developed based on Linear Quadratic Regulator (LQR) to achieve speed command tracking performance. In the approach, the speed and the q-axis current are estimated using the EKF algorithm. The steady state and the transient response of the system is enhanced and also effective speed control is achieved under load disturbance. The experimental results for the speed response and the q-axis current as well as the control signal variations when the PMSM is subjected to the load disturbance are presented.. The results verify the effectiveness of the method.

Fusion Technology, 2001

The optimized design of one-side-heated plasma-facing components (PFC) is dependent on knowing th... more The optimized design of one-side-heated plasma-facing components (PFC) is dependent on knowing the local distribution of inside wall heat flux in the flow channels. The local inside wall heat flux can be obtained from selectively chosen local PFC wall temperatures close to the inside boundary of the flow channel. To this end, three-dimensional thermal measurements for a one-side-heated monoblock were made and show: (1) the three-dimensional variation of the wall temperature close to both the heated and fluid-solid surface boundaries, (2) the resultant effects of local subcooled flow boiling on the 3-D wall temperature/outside heat flux relationship – one of which is the 3-D wall temperature profile is almost unchanged in the vicinity for incident heat flux levels between the onset to fully developed boiling and CHF, and (3) the occurrence of local CHF and local post-CHF. The monoblock has a 180.0 mm heated length, has a 10.0 mm inside diameter, and has a circular-like cross-section with a 30.0 mm nominal outside diameter.

American Journal of Optics and Photonics, 2020

Proceeding of International Heat Transfer Conference 12, 2002

International Journal of Engineering Research, 2017

The study of electromagnetic scattering by two-dimensional rough surface remains a challenging su... more The study of electromagnetic scattering by two-dimensional rough surface remains a challenging subjects for scientists due to its bidirectional scattering field computation. In this paper, Gibbs Sampler approach is applied to study electromagnetic scattering by two-dimensional rough surface. This work consists of generating a two-dimensional random rough surface. From that bivariate random distribution data generated, Gibbs Sampler method is applied to iteratively draw samples from the full conditional distribution. As we are dealing with a bivariate data two conditional probabilities distribution will be determined. They are respectively the probability distribution of given) and the probability distribution given. If sampling from those conditional distributions is possible then we can use Gibbs sampling method. For our study we consider a situation where it can be sampling from those two conditional distribution. The purpose of this sampling method is to estimate the marginal distributions and. And these marginal distributions are employed to compute the scattering field in direction and in direction. As results, a very high-frequency fluctuation is observed on scattering coefficient. Comparing with other works that exist literature this technique of Gibbs sampling shows an agreement.

Energy and Power Engineering, 2017

The availability of non-renewable energy sources such as crude oil, natural gas, coal etc., is fa... more The availability of non-renewable energy sources such as crude oil, natural gas, coal etc., is fast diminishing. So the renewable energy sources such as solar, hydropower, geothermal, wind, tidal energy, are gaining more and more importance. Many new developments to convert these renewable energy sources into usable forms are taking place. Most renewable energy sources are used to produce electricity. In this paper, a performance and efficiency simulation study of a smart-grid connected photovoltaic system using Chroma DC programmable power supply, AC programmable source and an Aurora Inverter is proposed. The simulation is performed in MATLAB environment where the Current-Voltage (I-V) and Power-Voltage (P-V) curves from the solar array simulator are generated and plotted. The proposed topology has been verified with satisfactory results. In addition, temperature and irradiance effects on I-V and P-V characteristic curves are verified. Also, the efficiency curves of the photovoltaic grid interface inverter are generated in the study. The MATLAB code developed in this paper is a valuable tool for design engineers comparing different inverters, calculating the optimum efficiency of a given inverter type.

2016 Saudi Arabia Smart Grid (SASG), 2016

Fusion Science and Technology, 2002

In the development of plasma-facing components (PFC) for fusion reactors and high heat flux heat ... more In the development of plasma-facing components (PFC) for fusion reactors and high heat flux heat sinks (or components) for electronic applications, the components are usually subjected to a peripherally non-uniform heat flux. Even if the applied heat flux is uniform in the axial direction [which is unlikely], both intuition and recent investigations have clearly shown that both the local heat flux and the eventual critical heat flux (CHF) in this three-dimensional case will differ significantly from similar quantities found in the voluminous body of data for uniformly heated tubes and flow channels. Although this latter case has been used in the past as an estimate for the former case, more study has become necessary to examine the three-dimensional temperature and heat flux distributions and related CHF. Work thus far has shown that the non-uniform peripheral heat flux condition enhances CHF in some cases. In order to avoid the excess costs associated with using electron- or ion-beams to produce the non-uniform heat flux, a new facility was developed which will allow three-dimensional conjugate heat transfer measurements and two-dimensional local subcooled flow boiling heat flux and related critical heat flux measurements. The configurations under study consist of: (1) a non-uniformly heated cylindrical-like test section with a circular coolant channel bored through the center, and (2) a monoblock which is a square cross-section parallelepiped with a circular drilled flow channel through the center line along its length. The theoretical or idealization of the cylindrical-like test section would be a circular cylinder with half (−90 degrees to +90 degrees) of its outside boundary subjected to a uniform heat flux and the remaining half insulated. For the monoblock, a uniform heat flux is applied to one of the outside surfaces and the remaining surfaces are insulated. The outside diameter of the cylindrical-like test section is 30.0 mm and its length is 200.0 mm. The monoblock square has lengths 30.0 mm. The inside diameter of the flow channel for both types of test sections is 10.0 mm. Water is the coolant. The inlet water temperature can be set at any level in the range from 26.0 °C to 130.0 °C and the exit pressure can be set at any level in the range from 0.4 MPa to 4.0 MPa. Thermocouples are placed at forty-eight locations inside the solid cylindrical-like or monoblock test section. For each of four axial stations, three thermocouples are embedded at four circumferential locations (0, 45, 135, and 180 degrees, where 0 degrees corresponds to that portion of the axis of symmetry close to the heated surface) in the wall of the test section. Finally, the mass velocity can be set at any level in the range from 0.6 to 10.0 Mg/m2s.

IASTED Technology Conferences / 705: ARP / 706: RA / 707: NANA / 728: CompBIO, 2010