Fahad Almasoudi

Integration of coherent optical OFDM with WDM

This paper proposes a system design that integrates CO-OFDM with WDM to reach a data rate of 400 Gbits/s over 1000 Km Single Mode Fiber (SMF). The 400 Gbits/s signal is generated by multiplexing eight OFDM with 50 Gbits/s for each OFDM. We present the performance of CO- OFDM WDM back to back design by measuring the BER and the OSNR (Optical Signal to Noise Ratio) and the constellation diagram of each user. We will also show the performance of CO-OFDM WDM for 1000 Km SMF by measuring the BER and the OSNR of different WDM channels and studying the constellation diagram of each user.

Highly efficient GaN-based single-phase transformer-less PV grid-tied inverter

Photovoltaic (PV) systems have been the focus of many scientific researches recently. The interest in grid-tied PV transformer-less inverters has increased rapidly, because of their higher efficiency and lower cost compared to traditional line transformer inverters. In this paper, a new modified transformer-less topology derived from H5 inverter is proposed. The proposed topology is equipped with GaN HEMTs to fully benefits from the superior performance of WBG devices. Detailed operation modes, inverter structure and switching strategy of the proposed topology are investigated and compared to conventional H5 topology. Furthermore, a comparison of the performance of the proposed inverter with Si IGBT and GaN HEMTs was presented to analyze the benefits of using WBG devices. The simulation results validate the theoretical that the proposed topology reduces the conduction losses of the system. The simulation results show that GaN HEMTs based inverter provides lower power losses and more than 5% increase in the efficiency when compared to Si IGBTs based inverter. Thus, prove the effectiveness of the proposed inverter for grid-tied PV applications.

High efficiency three level transformerless inverter based on SiC MOSFETs for PV applications

Transformerless inverters are widely employed in PV grid-tied inverter due to their capability of reducing power losses and enhancing the system efficiency. Several multilevel transformerless topologies are investigated to increase power quality and system efficiency. Wide bandgap power devices such as SiC MOSFETs can increase the system performance and reduce the total losses due to their superior features over Si switching devices. In this paper, a three level transformerless inverter based on H6 topology is proposed. The proposed topology is implemented with a silicon carbide (SiC) MOSFETs and a modulation approach is adopted to reduce the number of conducting switches. Simulation results show that total conduction and switching losses are reduced by about 50% and the efficiency of the system is increased by 3% at a high switching frequency of 100 kHz.

Performance enhancement of two-switch forward converter using GaN FETs

In this paper, a Two-Switch forward converter using enhancement mode Gallium Nitride transistors (GaN FETs) operating in CCM is designed for low power and high frequency applications. This topology provides a galvanic isolated, simple and efficient approach which will be suitable to use in battery charge circuits. The performance of the converter is evaluated using Si MOSFETs and GaN FETs. Comparison of the switching characteristics performance and the overall efficiency of the converter using Si MOSFTEs and GaN FETs are presented and discussed. The results are presented for a 100W, 200-24 V converter operating at two switching frequencies 100KHz and 500KHz.

Comparative study of Heatsink materials for Gallium Nitride HEMT modules using thermal modelling

Wide Bandgap (WBG) semiconductor devices are becoming the simpler and cheaper option as compared to the limited capabilities of Si devices because of their better blocking voltages, switching frequencies, thermal conductivities and operating temperatures. WBG semiconductors like Gallium Nitride (GaN) have better materials properties specifically suited for high power and high frequency electronics and they are slowly being favored for such applications. GaN High Electron Mobility Transistors (HEMTs) have demonstrated superior performance characteristics as compared to Si Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) in terms of switching characteristics and switching losses. One particular GaN HEMT module investigated by the authors has been calculated to have less than five times the switching losses as compared to a similar Si MOSFET module under the same operating conditions. The use of the GaN module instead of Si module in an inverter application has also shown reduction of power losses and heatsink volume by 60% and 30% respectively for the GaN module. This paper investigates the effect of different heatsink materials (Aluminum, Copper, AlSiC and E-Material) on the overall temperature profile of the GaN module. The heatsink structure used for the simulations were obtained from commercially available straight-fin heatsink designs. Comparisons among these heatsink materials were done for the same operating and ambient conditions by simulating the combined HEMT-Heatsink structure in the Finite Element Analysis (FEA) software COMSOL Multiphysics. The simulation results indicated Copper to be the best heatsink material among the four materials tested.

Highly efficient GaN HEMTs transformer-less single-phase inverter for grid-tied fuel cell

Transformer-less inverters are the most efficient approach to utilize renewable energy sources for grid tied applications. In this paper, a grid-tied fuel cell transformer-less single-phase inverter equipped with GaN HEMTs is proposed. The new topology is derived from conventional H5 inverter. The benefits of using GaN HEMTs are to enable the system to switch at high frequency, which will reduce the size, volume and cost of the system. Moreover, inverter control is designed and proposed to supply real power to the grid and to work as DSTATCOM to mitigate any voltage sag and compensate reactive power in the system. A comparison of the performance of the proposed inverter with Si IGBT and GaN HEMTs was presented to analyze the benefits of using WBG devices. The switching strategy of the new topology creates a new current path which reduces the conduction losses significantly. The analysis of the proposed system was carried out using MATLAB/SIMULINK and PSIM and the results show that the proposed controller improves voltage stability, power quality, mitigates voltage sag and compensates reactive power. Accordingly, the results prove the effectiveness of the system for grid-tied applications.

High efficiency H6 single-phase transformerless grid-tied PV inverter with proposed modulation for reactive power generation

Implementation of transformerless inverters in PV grid-tied system offer great benefits such as high efficiency, light weight, low cost, etc. Most of the proposed transformerless inverters in literature are verified for only real power application. Currently, international standards such as VDE-AR-N 4105 has demanded that PV grid-tied inverters should have the ability of controlling a specific amount of reactive power. Generation of reactive power cannot be accomplished in single phase transformerless inverter topologies because the existing modulation techniques are not adopted for a freewheeling path in the negative power region. This paper enhances a previous high efficiency proposed H6 trnasformerless inverter with SiC MOSFETs and demonstrates new operating modes for the generation of reactive power. A proposed pulse width modulation (PWM) technique is applied to achieve bidirectional current flow through freewheeling state. A comparison of the proposed H6 transformerless inverter using SiC MOSFETs and Si MOSFTEs is presented in terms of power losses and efficiency. The results show that reactive power control is attained without adding any additional active devices or modification to the inverter structure. Also, the proposed modulation maintains a constant common mode voltage (CM) during every operating mode and has low leakage current. The performance of the proposed system verifies its effectiveness in the next generation PV system.

Design of isolated interleaved boost DC-DC converter based on SiC power devices for microinverter applications

The power delivered by a photovoltaic (PV) to the grid must be modified in multiple stages. The operation concept of the micro-inverter is to increase the low output voltage received from a PV panel. Wide bandgap (WBG) power devices such as SiC MOSFETs offer multiple advantages over traditional silicon power devices when are used in a solar energy field due to their high switching frequency, high thermal conductivity and high power density that led to high efficiency and a smaller size of a converter. This paper demonstrates the implementation and design of an isolated interleaved boost DC-DC converter using a capacitor voltage doubler to achieve a high voltage step ratio. The performance of the design is analyzed and investigated at high switching frequency using different power switching devices, Si and SiC MOSFETs. The simulation results show that a 3% improvement achieved by SiC MOSFET at a higher switching frequency of 300 kHz.

Performance evaluation of a high power DC-DC boost converter for PV applications using SiC power devices

The development of Wide band gap (WBG) power devices has been attracted by many commercial companies to be available in the market because of their enormous advantages over the traditional Si power devices. An example of WBG material is SiC, which offers a number of advantages over Si material. For example, SiC has the ability of blocking higher voltages, reducing switching and conduction losses and supports high switching frequency. Consequently, SiC power devices have become the affordable choice for high frequency and power application. The goal of this paper is to study the performance of 4.5 kW, 200 kHz, 600V DC-DC boost converter operating in continuous conduction mode (CCM) for PV applications. The switching behavior and turn on and turn off losses of different switching power devices such as SiC MOSFET, SiC normally ON JFET and Si MOSFET are investigated and analyzed. Moreover, a detailed comparison is provided to show the overall efficiency of the DC-DC boost converter with different switching power devices. It is found that the efficiency of SiC power switching devices are higher than the efficiency of Si-based switching devices due to low switching and conduction losses when operating at high frequencies. According to the result, the performance of SiC switching power devices dominate the conventional Si power devices in terms of low losses, high efficiency and high power density. Accordingly, SiC power switching devices are more appropriate for PV applications where a converter of smaller size with high efficiency, and cost effective is required.

Switching performance and efficiency investigation of GaN based DC-DC Buck converter for low voltage and high current applications

The Wide band-gap (WBG) materials “such as Silicon Carbide (SiC) and Gallium nitride (GaN)” based power switching devices provide higher performance capabilities compared to Si-based power switching devices. The wide band-gap materials based power switching devices outperform Si-based devices in many performance characteristics such as: low witching loss, low conduction loss, high switching frequencies, and high operation temperature. GaN based switching devices benefit a lot of applications such as: future electric vehicles and solar power inverters. In this paper, a DC-DC Buck converter based on GaN FET for low voltage and high current applications is designed and investigated. The converter is designed for stepping down a voltage of 48V to 12V with high switching frequency. The capability of the GaN FET based buck converter is studied and compared to equivalent SiC MOSFET and Si-based MOSFET buck converters. The analysis of switching losses and efficiency was performed to compare the performance capabilities of GaN FET, SiC MOSFET and Si-based MOSFET. The results showed that the overall switching losses of GaN FET are lower than that of SiC and Si-based power switching devices. Also, the performance capability of GaN devices with higher frequencies is studied. GaN devices with high frequencies will reduce the total size and the cost of the power converter. In Addition, the overall efficiency of the DC-DC Buck converter is higher with the GaN FET switching devices, which make it more suitable for low voltage and high current applications.