Comparison of GAN, SIC, SI Technology for High Frequency and High Efficiency Inverters

Power semiconductor devices plays a major role in efficient power conversion. As we have Silicon (Si), Silicon Carbide (SiC) and Gallium Nitride (GaN) based power devices, GaN technologies are ideal for working in high frequency power electronic systems (in MHz). Because the GaN has superior electron mobility and bandgap than the SiC and Si it has superior characteristics like low conduction losses, high switching rate so that there is better power efficiency than SiC, Si based inverter. Here we are using the Gan based High-Electron-Mobility Transistor (HEMT) and SiC and Si based mosfet in the inverter. The proposed inverter of different topologies is designed to transfer the power at >1MHz range. Comparison of the three different switches is done by the output power and the efficiency of the inverter. This paper presents the SPICE simulation results of the class d and class e inverter of output power 1KW.


Introduction
Inverters are most important in power conversion of DC to AC as they consist of the solid state devices such as Si, SiC, GaN based mosfet. Based on the material properties different devices used in inverter has different applications such as Si based devices in power frequencies and SiC and GaN based devices in high frequency applications such as wireless power transfer in medical and electric vehicles. Silicon band gap (the gap between the valence and conduction bands) is too small and is the energy required to excite an electron from the valence to conduction band. Silicon's band gap is around 1.1 eV, whereas the GaN band gap is around 3.4 eV (depending on temperature) and the band gap for the SiC is 3.25eV. Therefore for high power transistors, GaN is the clear winner due to its high efficiency. The following Table1 shows the electron band gap and different properties of the devices.  As from the above Figs. you can see that the band gap is more for GaN and SiC rather than Si. The wide band gap of GaN and SiC device produces high power output at high frequency operation with more efficiency than the Si device. The comparison of different topologies of inverters is done by taking a fixed voltage breakdown of the GaN, SiC and Si devices. The following Table 2 shows the parameters of the devices. The following Fig.2 shows the different types of devices based on the Comparison of output power and the frequency. In this paper we are going to implement a singlephase H-bridge class d inverter using the wide band gap devices of GaN and SiC, Si and following for the class e inverter using the same devices. These devices produce high efficiency inverters due to the higher breakdown voltage, lower input and output capacitances, and lower drain-source on-resistance. The Silicon Carbide (SiC) MOSFET and enhancement-mode Gallium Nitride (GaN) FET are the WBG devices which are used in high frequency applications i.e in multi-MHZ inverters.
The inverters have wide range of applications in automobile industry and are creating a change of positivity in the electric vehicles. Electric vehicles require more output power so as to deliver and the inverters which are proposed in this literature are quite same as the requirement of it [7] [8]. The charging of the electric vehicles is done mainly through the WPT (Wireless Power Transfer) which is more comfortable than the conventional charging stations [6] and for that WPT these inverters are used for their efficiency. There are so many types of amplifiers which are used around the world like class d, class e, class e 2 , class ef, class f, class Ф, class ef 2 and so on. Each converter has its frequency range and the power output of the converter. There are so many converters for different applications and mostly selected converters are used. In recent days, one type converter is used to drive the switch so that the efficiency and the power output and the quality of the converters and in nearby future, we are going to implement all types of inverters and compare the power efficiency.
There are two types of switching techniques in any converter design hard switching and soft switching. Hard switching is one which refers to the turn on-off of the switch based on the relationship of the current and voltages, during the on-off transitions of the switch voltage and current of the switch occurs at the drain and source side where the switching noise and losses are produced. In recent days, the applications are based on the high switching frequencies which produce more switching losses as result of increase in the junction temperatures so in order to reduce the switching losses soft switching techniques are implemented. In this method, the addition of the LC parameters to the circuit tends the circuit to operate in the safe way and reduce the switching losses and the conduction losses. In this soft switching i.e Zero Voltage Switching (ZVS), the switch will be in on state when the voltage applied to switch is zero which reduce the transition time of the voltage and current in on state and the reduce the losses in the switch. By the zvs the operation only the turn losses are eliminated.
A 13.56MHz zvs class d using dynamic dead time is presented in the [1] which is limited to the less power output and in the most of the papers, hardly trying to implement a power output >1kw. Regarding the class e inverter, so many converters are proposed with more output power and the efficiency is little less than which we have gained. In this paper, we are going to implement zvs class d and zvs class e inverter which operates in MHz frequency with a power output of >1kw. Both the class d and class e inverter simulation are done in the LTPSPICE software simulation.

Analysis of a Class D and Class E Inverter
Most of the modern-day electronics are depending upon the zvs and zcs based inverters for the better optimization. In this section the zvs based class d and class e inverter are presented in detail with the simulation results. For the applications of the electric vehicles which are having frequency of operation in MHz and the power output of the >1kw which is clear region of the type of class d and class e inverter as they fall in this category and also produces the greater efficiency which is an advantage for wpt applications.

Comparison of Devices using ZVS Class D Inverter Topology
In this part we are going to see the Comparison of different devices of a class d inverter topology. By comparing the inverters with the parameter of output power and efficiency. The class d topology is done using a H-bridge inverter. Class d triggering is done through unipolar switching and bipolar switching. In unipolar type of triggering, two switch's which conduct at a time are triggered with one signal which is generated by the carrier wave generator whereas in the bipolar independent triggering of switch will be done. As efficiency is criteria, we are going implement unipolar type of triggering method and it also reduces the electro-magnetic interference (EMI). We are going to implement a singlephase H-bridge inverter using the unipolar switching technique. The Fig. 3 shows the class H-bridge inverter.

Fig 3:
Class d h-bridge inverter using different type of technologies. [1] In this the inverter consists of 4 mosfet's and the series RLC resonance circuit in which Resistor (Rl) is taken as load and, Inductor (L1) and capacitor (C1). The supply to the circuit is given through a DC voltage. The following Table 3 gives the input circuit parameters of the inverter.  Fig. 4 shows the modes of operation.  The Fig. 7 shows the voltage and current across the different switch's (GaN, SiC, Si) and the output voltage and output current. The Figs. show the voltage and current at the switch Q1 and Q2 because remaining switches are same (i.e) voltage and current of switch Q4 is same as Q1 and the same for the switch Q3 is as Q2. The following Table 4 shows the values of the voltage and currents at the different points in the circuit of class d inverter for different switches of GaN, SiC, Si.  Table 3 used in inverter, by the use of the GaN, SiC and Si switches results are obtained. The following Table 5 shows the output parameters of the circuit using the different technologies.

Comparison of devices using ZVS Class E inverter topology
In this section we are going to see the different devices Comparison of class e inverter topology. The Fig. 4 shows the typical class e inverter with series rlc resonant circuit.

Fig 5: Class E inverter using different type of technologies.[2]
In this type of topology, the no of switches used are one. This consists of a series RLC resonant circuit in which the Resistor (Rl) is taken as the load. The Following Table VI shows the input circuit parameters of the inverter. In the table, the value of the shunt capacitor is varied according to the switch output capacitance (Coss)so that the energy dissipated from the switch is stored in the capacitor.
The following Fig. 6 shows the modes of operation and the two modes of operation are during the time at which is in on position and off position. During the switch on position, the current passes through the switch to the load and during the off position, the energy stored in the shunt capacitor during the on position is passes to load.   1445nH Inductor The Fig. 8 shows the voltage and current across the switch (GaN, SiC, Si) and across capacitor, the output voltage and output current of the load. The following table 7 represents the values of the voltages and currents at different switches of GaN, SiC, Si and at the capacitor in the circuit. The simulation of the soft switching single phase h-bridge inverter is done and following are the results. The results of class E are obtained as from Table 8. As clearly, the GaN switch produces more output power and the efficiency is more than the SiC and Si.

Simulation Results Of Class D Inverter Topology
In this section we are going to present the simulation results i.e wave forms of the zvs based class d inverter using GaN, SiC, Si.

Simulation Results of Class E Inverter Topology
In this section we are going to present the simulation results i.e wave forms of the zvs based class e inverter using GaN, SiC, Si.

4.2
Class e inverter using SiC switch

4.3
Class e inverter using Si switch

Conclusion
In this paper, the comparison of different types of technologies of class d and class e inverter are done and the simulation results are obtained for the use of converters which consists of different technology of GaN, SiC and Si. The output power of the inverter greater than 1kw for a switching frequency of 13.56MHz is obtained. The efficiency of the GaN technology used inverters are more efficient compared than that of SiC and Si.