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.
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.
KEYWORDS: Photovoltaics, Silicon carbide, Field effect transistors, Solar cells, Switches, Switching, Renewable energy, Solar energy, Energy efficiency, Reliability
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.
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.
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.
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.
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