A Comparative Evaluation of Wide-Bandgap Semiconductors for High-Performance Domestic Induction Heating

Abstract

This paper presents a comparative evaluation of wide-bandgap power semiconductor devices for domestic induction heating application, which is currently a serious alternative to traditional heating techniques. In the induction heating system, the power transferred to the output depends on the equivalent resistance of the load, and the resistance depends on the operating frequency. Due to the switching characteristics of wide-bandgap power semiconductor devices, an induction heating system can be operated at higher operating frequencies. In this study, SiC and Si semiconductor devices are used in the comparison. These devices are compared according to different evaluation issues such as the turn-off energy losses, turn-off times, current fall time, the power losses of the internal diodes, and the conduction voltage drops issues. To perform the proposed evaluation, the series-resonant half-bridge inverter, which is frequently used in state-of-the-art induction heating systems, has been selected. The device suitability in an induction heating system is analyzed with the help of a test circuit. A comparison is made in terms of criteria determined by using the selected switches in the experimental circuit, which is operated in the 200 W to 1800 W power range and 45 kHz to 125 kHz switching frequency range. System efficiency is measured as 97.3% when Si IGBT is used. In the case of using SiC cascode JFET, the efficiency of the system is increased up to 99%.

1. Introduction

The semiconductor materials used in power devices determine the current and voltage values of the devices. The features expected from semiconductor power devices are low thermal resistance, wide energy bandgap, and operation at high frequencies [1]. The low thermal resistance of the semiconductor power devices results in a shorter thermal time constant.

Operating the switches at high frequencies reduces the passive component sizes and the circuit volume. The operation of the circuit at high frequencies is possible with power devices with high electron drift velocity. Power devices with wide energy bandgap have thinner layers, low internal resistance, fewer power losses, and leakage currents, so they have higher package thermal resistances and can operate at higher voltages. The Si element is often preferred in power devices because of its stable and easy production. Silicon carbide (SiC) and gallium nitrate (GaN) are materials with wide bandgap (WBG) used in semiconductor power devices [2,3].

Silicon (Si) power devices have undergone many changes from the date they were first used to the present day. In terms of maximum voltage that can be applied, operating temperature, conduction, and switching properties, these devices are getting close to their theoretically permitted limits for the materials. State-of-the-art Si-insulated gate bipolar transistors (IGBTs) have a voltage rating of five kV because of their restricted performance, and switching speeds are still slow because of tail currents. In addition, most of the commercial Si-based devices currently have a maximum junction temperature below 175 °C. The thermal limitation is due to the liquid temperature of the solder layer. The thermal performance of the device is lower than soldering when sintering or gluing is used [4]. Obtaining converters with higher power densities is difficult because of these inherent physical constraints [5].

Along with the commercial production of wide-bandgap semiconductor devices, these devices have begun to be used in state-of-the-art power converters. In contrast to Si devices, WBG devices have a large breakdown electric field, a low conduction resistance, a high switching speed, and a high junction temperature tolerance. These properties affect the conversion’s efficiency, power density, output power, and reliability [3].

As a result of the advancement in SiC technology, SiC metal-oxide field-effect transistors (MOSFETs) operating at higher powers and with better temperature strength than Si MOSFET have been produced [6]. In SiC MOSFET, the thickness of the area holding the voltage is made 10 times thinner than Si MOSFET, as shown in Figure 1, while the additive density can be increased 10 times. In this way, the on-state resistance of the SiC MOSFET decreases to one percent of the resistance of the Si MOSFET with the same properties. Thus, the on-state resistance, the main disadvantage of Si MOSFETs, is reduced. Drive circuits must include protection against the uncontrolled operation of the device caused by environmental noise [5].

JFETs have a rated voltage of 1200 V to 1700 V and a rated current of up to 48 A [7]. SiC MOSFETs are normally off power devices. In the MOSFET, the gate is insulated because there is an oxide layer between the gate and the drain. Practically no current passes from gate to source. On the other hand, generally, JFET has a reverse polarized pn junction that causes leakage current from gate to source. This causes the device to be normally on, unlike MOSFETs. Since SiC JFET is a normally on device, the negative voltage must be applied between the gate and source for the device to be off. The main disadvantage of normally on JFET is that negative voltage can cause a short circuit in the drive part of the device. For this reason, it is not preferred to be used in power electronics circuits [8].

To eliminate the disadvantage of SiC JFETs caused by the driver circuit, a SiC cascode JFET structure was created by connecting a Si MOSFET in series with the device. Here, the serial MOSFET has low conduction resistance [9,10]. This structure has the JFET’s conduction characteristics and the driving characteristics of Si MOSFET. However, due to high di/dt and dv/dt, high-frequency oscillations occur between the Si MOSFET’s parasitic capacitance and the circuit path’s leakage inductance [9]. These high-frequency oscillations can be avoided by using a snubber circuit [11]. The driving voltage of SiC cascode JFET has a wide range. Another advantage of SiC cascode JFET is that it can be used without changing the driving circuit of the Si device.

Due to their superior high efficiency, safety, cleanliness, and quick heating over conventional heating processes, domestic induction heating systems (DIHS) are becoming more and more popular on the market. In DIHS, when SiC power devices are used instead of Si, the total volume of the system decreases and power density and circuit efficiency increase [12,13,14,15,16].

The importance of efficient use of energy in terms of sustainability is increasing day by day. Therefore, it is important to increase the efficiency of domestic induction cookers, which are increasingly used in homes. The main novelty of the current study is the comparative analysis using SiC semiconductor devices, which were not compared with each other in IH systems in previous studies. Furthermore, to contribute to developing a system that operates at high frequencies with high efficiency to transmit power to nonferromagnetic metals.

The rest of the paper is structured as follows. In the “Literature Review” section, studies using WBG devices in induction heating systems were examined, and the research gap in the literature was defined. In the “Performance Parameters” section, the criteria for comparing the selected devices are given. Brief information about the general operation of the converter to be used in the device comparison and the design of the resonance tank is given in the “System Description” section. The results are given and discussed in the “Experimental Results” section. The last section, “Conclusion”, provides the concluding remarks of the present study.

2. Literature Review

The use of IH technology in home appliances first started with MOSFET in half -bridge (HB) and full-bridge (FB) topologies. In the following years, with the discovery of the high voltage value MOSFET, the lower-cost single-switched quasi-resonant (SSQR) topology was used in home applications [12,14].

With the development of the IGBT with low conduction resistance, the efficiency of topologies has increased [17]. In IH systems, the system’s efficiency is increased by using resonance topologies in which switching power losses do not occur or are reduced [18]. In IH systems, serial resonant (SR), FB, HB, and SSQR topologies are commonly used [19,20]. Figure 2 shows the topologies and power devices used in domestic IH systems over the years. The FB topology is suitable for industrial IH systems with an output power higher than 5 kW. In domestic IH systems, low-cost SSQR topology is up to 2 kW, and HB topology is used in a cost-performance balance of up to 5 kW [21].

There are some disadvantages to SR HB topology, commonly realized with Si IGBT in DIHS [22]. These can be listed as follows:

• Circuit volume cannot be reduced since IGBTs cannot be operated above 100 kHz;
• Semiconductor power devices with wide bandwidth can operate at high voltages;
• Nonferromagnetic materials cannot be heated because of the IGBT’s switching frequency, and voltage values are not high enough.

When SiC power devices are used instead of Si in IH applications, the above disadvantages are eliminated. As a result, the system’s total volume decreases and power density and circuit efficiency increase. In addition to those advantages, nonferromagnetic materials can be heated using SiC power devices [12,13,14,15,16].

Various studies have been conducted on using WBG devices in IH systems, as summarized in

Table 1. Survey of IH with WBG devices.

Reference	Topology	Si	Si	SiC	SiC	SiC	SiC
		IGBT	MOSFET	MOSFET	BJT	JFET	Cascode JFET
[23]	FB			X
[2]	FB			X
[24]	HB + FB			X
[25]	FB			X
[26]	CSRI			X
[27]	SS QR	X				X
[28]	QR					X
[12]	FB					X
[14]	SR HB						X
[15]	FB		X	X
[29]	SR FB		X	X
[30]	LLC	X	X	X
[31]	Boost HB	X		X
[32]	HB			X
[33]	HB	X		X	X	X
PS	HB	X		X			X

PS: Present Study.

[2,12,14,15,22,23,24,25,26,27,28,29,30,31,32]. In these studies, a single WBG device was mostly examined. In a limited number of studies, Si and WBG devices were examined comparatively.

Si and SiC MOSFETs were compared in FB topology used for surface hardening of irregular cylindrical parts. It has been observed that the turn-off power loss of SiC MOSFET is less than that of Si MOSFET, and the power loss of turn-on is decreased by 90% [14]. To verify the proposed multi-modulation technique in which a QR AC-AC topology was used, SiC JFET with a high voltage value was used in [12]. SiC JFET was used to achieve high performance and efficiency in the multi-output IH system realized with an FB AC-AC topology [12].

The behavior of the Si and SiC MOSFETs realized with SR FB topology has been investigated. It has been observed that the turn-off time of SiC MOSFET is 10 times lower than Si MOSFET [15]. SiC MOSFET is operated at a switching frequency of 400 kHz realized with an FB topology to separate foreign metal materials. In this case, the heatsink volume has decreased by 78% [33].

The switches’ power losses are investigated using Si IGBT, Si MOSFET, and SiC MOSFET, in which LLC topology with resonance is used. It has been observed that the lowest power loss is in SiC MOSFET [2,29]. The circuit’s efficiency and performance have been investigated using a three-phase SiC module in a new IH power supply using an interleaved resonance booster topology. The efficiencies of IH systems realized with HB and FB topologies using the SiC power module have been examined. Si IGBT module and SiC MOSFET module are used in high frequency [24]. It has been observed that the efficiency of the circuit increases with the SiC module [30]. The conduction and switching losses of SiC JFET and Si IGBT realized with a SS QR topology have been investigated [27]. SiC MOSFET is operated with FB topology at high frequency and power [25]. SiC cascode JFET is used in the domestic IH, which is realized with SR HB topology [34].

Details of the comparative studies are given in

Table 2. Comparative studies.

Ref.	Device				Topology				Analyses
	Type	η	Voltage	Current	Pn	fSW	Type	Frequency
		(%)	(V)	(A)	(kW)	(kHz)
[15]	Si MOSFET	97.3	1200	29	5	100	FB	Constant	tOFF, tON,
	2Si MOSFET	98	1200	24					POFF, PON,
	SiC MOSFET	99.2	1200	33					PT, η
[30]	Si IGBT	95.2	1200	100	2.6	32	Boost HB	Constant	POFF, PT,
	SiC MOSFET	97.2	1200	120					η
[27]	Si IGBT	N/A	1200	30	2-1	21.3–314	SSQR	Variable	VON, tOFF,
	SiC JFET-nON	N/A	1200	17					T(°C)
[29]	Si IGBT	84	600	75	6	50	LLC	Variable	PT, η
	Si MOSFET	91	600	65
	SiC MOSFET	94	1200	45
[22]	Si IGBT	96.1	N/A	N/	2	20	HB	Constant	tOFF, POFF,
	SiC MOSFET	95.1	1200	42					PON, PT,
	SiC BJT	97.8	1200	50					η,VON
	SiC JFET-nON	96.3	1200	48
	SiC JFET-nOFF	95.7	1200	30
PS	Si IGBT	97.3	600	48	0.2–1.8	125–45	HB	Variable	PT, PCON,
	SiC MOSFET	97.6	650	27					PSW, POFF,
	SiC MOSFET	98.3	650	35					PON, PBD,
	SiC MOSFET	96.4	1200	28					tOFF, tf,
	SiC MOSFET	91.5	1200	16					di/dt, VON,
	SiC cascode JFET	98.1	650	62					η,
	SiC cascode JFET	99	1200	47

PS: Present Study.

[15,22,27,29,30]. In these studies, Si devices and SiC devices were compared in general. Although all of the studies have been examined from different aspects, the system efficiency has been examined in all except [27]. It is seen that the SiC cascode JFET, which is a combination of the superior features of the Si MOSFET and SiC JFET devices, is not compared with other devices in DIHS. As a result, the lack of comparison using the SiC cascode JFET device in the literature is seen as a research gap.

The main contribution of this work is to examine the performance of SiC cascode JFET in a DIHS using the SR HB topology and to compare it with the SiC MOSFET and Si IGBT devices used in these systems. The selected devices were compared according to the determined performance criteria. A power circuit has been created for the experimental realization. The performances of power devices in the selected 45–125 kHz switching frequency range are examined. In addition to the main contribution, this article makes four additional contributions to DIHS:

• SiC devices that have not been compared with each other before being compared;
• A device suitability analysis is performed using SiC power devices according to different manufacturers and voltage ratings;
• The advantages of high switching speed SiC devices are examined;
• A wide range and high-efficiency operation have been achieved at high frequencies, which is important for heating all metals in state-of-the-art induction heating systems.

3. Performance Parameters

Semiconductor power devices are controlled switches that have the ability to turn on and off speedily in power electronics circuits. The voltage across the power device is low during the conduction time and high during the blocking time. There are two power losses in power devices, conduction loss and switching loss. Switching loss consists of turn-on power loss and turn-off power loss. The power devices’ current, voltage, and power loss waveforms are given in Figure 3 for one switching period [35].

The time between removing the control signal and reducing the current to 90% is called the delay time. The time that the current falls from 90% to 10% is called the falling time. The turn-off time is the sum of these times.

The power and energy losses equations are given in Equations (1)–(7). As shown in Equations (2) and (3), switching power losses are calculated by multiplying the switching frequency of the power device with the switching energy losses. Switching power losses change proportionally with the switching frequency. At high frequencies, the device can be damaged by overheating caused by the switching power loss. Therefore, choosing the suitable power device to be used at high frequency is crucial in terms of switching power loss.

The conduction losses occur depending on the conduction voltage drop or the conduction resistance of the device, as shown Equation (4). It is the primary source of power loss, especially at maximum output power. Switching and conduction losses directly affect the power converter efficiency. Therefore, these losses will be examined as the basic performance parameters in comparing the selected devices.

$$P_{CON}=\frac{1}{T_p}{\int }_0^{t_{CON}}{V}_{CON}{i}_{CON}$$

(1)

$$P_{ON}=f_{SW}{E}_{ON}$$

(2)

$$P_{OFF}=f_p{E}_{OFF}$$

(3)

$$P_{SW}=P_{ON}+P_{OFF}$$

(4)

$$E_{ON}={\int }_0^{t_{ON}}{V}_{ON}{i}_{ON}dt$$

(5)

$$E_{OFF}={\int }_0^{t_{OFF}}{V}_{OFF}{i}_{OFF}dt$$

(6)

$$E_{sw}=E_{ON}+E_{OFF}$$

(7)

4. System Description

(a)

Reference application

The serial resonant HB topology, which is balanced in terms of cost and performance, is frequently used in DIHS [36]. Figure 4 shows the circuit diagram of SR HB topology. In this topology, inductance current and switch voltage are in sinusoidal and square wave form, respectively. SR HB topology is usually operated above the resonant frequency in the inductive region. In the inductive region, when the freewheeling diode is in the on state, the control signal is applied to the switch. Thus, switching loss does not occur in the turn-on process of the switch. Snubber capacitors are connected in parallel with switches to reduce turn-off switching power losses. To use Si IGBTs at high frequencies, snubber capacitors must be used [37].

(b)

Resonance tank design

The equivalent series resistance R_EQ and inductance L_EQ are used to model the IH load (inductor-pot system). A C_RES resonance capacitor is used to generate series resonance with the L_EQ. The equivalent resistance and inductance vary depending on the switching frequency, load materials, temperature, and alignment [38].

In the literature, there are many studies on the SR HB inverter circuit design, and different methods are used in the design process of the resonant tank [36]. One of these methods is to determine the L_EQ and C_RES according to the power, the minimum value of the input AC voltage (V_ACmin), and the selected resonance frequency (f_RES) values. The input current (I) is equal to the average of the resonant current in one operating period and calculated from Equation (8).

C_RES is calculated from Equation (9). By arranging the resonance frequency equation given in Equation (10), Equation (11) of the resonance inductance is obtained. The value of the resonance inductance is determined using C_RES and f_RES. Iteration is performed using these values, and the final values of the resonance tank are obtained. The inverter is operated above 20 kHz so that the users are not disturbed by noise while the DIHS operates [39,40].

$$I=\frac{2\pi P}{V_{ACmin}}$$

(8)

$$C_{RES}=\frac{I}{2\pi f{V}_{ACmin}}$$

(9)

$$f_{RES}=\frac{I}{2\pi \sqrt{L_{EQ}{C}_{RES}}}$$

(10)

$$L_{EQ}=\frac{I}{{\left(2\pi f\right)}^2{C}_{RES}}$$

(11)

5. Experimental Results

To compare the performances of power devices in DIHS, the SR HB circuit shown in Figure 5 has been realized. The main supply voltage is selected 220 V. The resonant capacitance value is 540 nF, and the equal resonant inductance and resistance values are 45 µH and 4.3 Ω, respectively. Moreover, the filter capacitance and inductance values are 5 µF and 100 µH, respectively, which are suitable for home appliance usage. The circuit was operated in a 200 W to 1800 W power range and a 45 kHz to 125 kHz switching frequency range. After 50 kHz switching frequency, a negligibly low (220 pF) capacitor is added to the switch terminals as a snubber capacitor.

Firstly SiC cascode JFET, which has not been used before, was chosen to compare semiconductor devices in DIHS systems. Then, Si and SiC power devices with nearly the same current and voltage values were selected for comparison. In addition, SiC devices from the same manufacturer at different voltage levels were used for comparison. The type, material, manufacturer company, product code of devices, and electrical and thermal values of selected power devices are given in

Table 3. Some electrical and thermal characteristics of the power devices used in the experimental circuit.

Company	Product Code	Material/Type	In (A)	Vn (V)	RDSon (mΩ)	PM (W)	VG (V)	RJC (°C/W)	Tm (°C)
Infineon	IRGP4068D	Si IGBT	48	600	VCEon = 2 V 48 A/150 °C	170	(0)–(+15)	0.45	(−55)–(+175)
Rohm	SCT3060AL	SiC MOSFET	27	650	79.2 mΩ 13 A/125 °C	80	(−4)–(+22)	0.91	(−55)–(+175)
Rohm	SCT2080KE	SiC MOSFET	28	1200	100 mΩ 20 A/25 °C	130	(−6)–(+22)	0.57	(−55)–(+175)
ST	SCT35N65	SiC MOSFET	35	650	55 mΩ 20 A/125 °C	90	(−6)–(+22)	0.72	(−55)–(+175)
ST	SCT20N120	SiC MOSFET	16	1200	189 mΩ 10 A/150 °C	175	(−10)–(+25)	1	(−55)–(+200)
USCi	UJ3C065030K3S	SiC Cascode JFET	62	650	40 mΩ 20 A/175 °C	210	(−25)–(+22)	0.34	(−55)–(+175)
USCi	UJ3C120040K3S	SiC Cascode JFET	47	1200	60 mΩ 20 A/175 °C	210	(−25)–(+22)	0.35	(−55)–(+175)

.

To examine the switching characteristics of the selected devices, the SR HB converter circuit is operated under a 52 kHz switching frequency and 17 A output current. The investigation of switching performance is concentrated on the turn-off transition. Since the SR HB topology operates in the inductive region, the switches turn on without loss. For this reason, the turn-on behavior of power devices has not been examined in this study. A Tektronix DPO5034B oscilloscope was used to take the measurements.

The experimental waveforms during the turn-off transition for the selected devices are given in Figure 6a–g. In these waveforms, the power device’s current, voltage, and control signals are shown in green, red, and blue colors, respectively. The switch current waveforms were obtained using the Rogowski CWT Mini 15 PEM current probe. The voltage waveforms at the switch terminals were obtained by using the PMK PHV-1000RO 1000 V 400 MHz voltage probe. Control signals were measured using a Tektronix TPP0500B 500 MHz 300 V.

From these results, at the 650 V voltage rating, it can be seen that the fastest device is the Si cascode JFET with a switching time of 168 ns, whereas the tail current of the Si IGBT almost doubles this value with 310 ns. It has been observed that the speeds of MOSFETs belonging to different companies are almost the same and are approximately 190 ns. Among the 1200 V devices, it is seen that SCT20N120 SiC MOSFET is the fastest with 140 ns, while the other SiC MOSFET SCT2080KE is the slowest with 238 ns.

Due to the significant di/dt of the SiC Cascode JFET, excessive voltage oscillations occurred during turn-off, as seen in Figure 6f,g. The power device’s parasitic capacitance and the circuit’s leakage inductances cause these oscillations. The devices’ connections should be designed so that leakage inductance is minimal [41]. It is seen that the device with the shortest current drop time of 68 ns and the highest di/dt ratio is the SiC cascode JFET of the UJ3C120040K3S. The turn-off time of the 1200 V SCT20N120 SiC MOSFET is shorter than of the 650 V SCT3060AL. SiC power devices perform worse than Si IGBT in terms of electromagnetic interference noise because of their high di/dt value.

It has been observed that the switching losses are significantly reduced with the SiC technology, which has a low switching time. Another significant loss that affects efficiency is conduction power loss. Measurements of the on-state voltage drops have been made from Figure 6, and the results are presented in

Table 4. Values are taken from waveforms of power devices.

		toff (ns)	tf (ns)	di/dt (A/µs)	VON (V)	PBD (W)	EOFF (µJ)
Si IGBT	IRGP4068D	310	131	130	1.26	1.16	497.7
SiC MOSFET	SCT3060AL	182	92	184	1.37	2.31	374
SiC MOSFET	SCT2080KE	238	110	154	3.09	2.21	368
SiC MOSFET	SCT35N65G	195	90	189	1.57	1	380.15
SiC MOSFET	SCT20N120	140	71	241	3.33	1.83	371
SiC Cascode JFET	UJ3C065030K3S	168	74	230	0.93	1.17	313
SiC Cascode JFET	UJ3C120040K3S	193	67	253	0.34	1.75	460

. The highest and lowest conduction voltage drops occurred in the SiC MOSFET and SiC cascode JFET devices, respectively. The IGBT device with Si is in the middle range. These values are especially important at high currents. In MOSFET devices, on the other hand, the conduction voltage drop is high because of the higher conduction on-resistance. Since the on-resistance of the MOSFET increases depending on the cube of the voltage rating, the on-resistances of 1200 V SiC MOSFETs are bigger than of the 650 V devices. As a result of this, the voltage drop values are higher than for other devices. It is seen that the device with the lowest conduction voltage drop of 0.34 V is UJ3C120040K3S, and the one with the highest is the SCT20N120 with 3.33 V.

The current and voltage values during the turn-off process are taken from the oscilloscope. The variation of the power loss that occurred during the turn-off transition was obtained using these values. Figure 7 shows the change in turn-off switching power losses of devices with respect to time. From here, it is seen that the turn-off process of the IRGP4068 is 270 ns, with the current falling from 90% to 10%, and more power loss occurs under the same conditions compared to other devices. It is seen that the least power loss occurs in the UJ3C065030K3S device, and the turn-off time is approximately 100 ns.

Body diode losses are obtained by multiplying the voltage value of the diode at the moment of conduction with the current. The obtained values are given in Table 4. In terms of power loss in body diodes, it is seen that the least loss is in SCTW35N65, and the highest loss is in SCT3060AL. Although these two devices are 650 V SiC MOSFETs, they belong to different manufacturers. In addition, the power device’s turn-off energy losses are calculated by taking the derivative of the turn-off power loss waveforms according to time, as given in Equation (6). All obtained values are combined and given in Table 4.

After comparing the devices’ 52 kHz switching frequency, the power devices were operated between 45 kHz and 125 kHz. The power transferred to the output with frequency has been changed. The device’s conduction and switching power losses were measured in this case. Conduction, turn-off, and total power losses of the power devices at different frequencies are given in Figure 8, Figure 9 and Figure 10, respectively. As the switching frequency moves away from the resonant frequency, that is, as the switching frequency increases, as in

Table 5. Frequency-dependent power values.

fSW (kHz)	Output Power (W)
45	1800
52	1500
59	1300
66	700
77	500
91	400
111	300
125	200

, the power transferred to the output decreases and the current passing through the circuit decreases. As can be seen from Figure 8, the conduction losses of the power devices decrease with increasing frequency. As seen in Figure 3, the current value before turning off affects the switching power loss. Since the current decreases with increasing switching frequency, the switching power loss decreases with current, but increases proportionally with frequency, as can be seen from Equation (3). In addition, the small value snubber capacitor connected after 50 kHz has an effect on reducing losses. As a result, in Figure 9, the variation of the switching losses does not follow an increase in direct proportion to the frequency.

In the case of operation with a 45 kHz switching frequency, that is, at 1800 W output power, the current passing through the circuit is high. From Figure 8, in this case a conduction loss of approximately 80 W occurred in the SCT20N120 device with the highest conduction voltage drop. A loss of about 8 W occurred in the UJ3C120040K3S, which has the lowest conduction voltage drop. It has been determined that the ratio of the losses of the two devices is 1/10. Similar results are valid for high frequencies. There is the same ratio between the conduction voltage drops given in Table 4.

From Figure 9, the highest switching loss occurs in the IRGP4068 in the determined operating frequency range. There is a loss of about 9.4 W at 125 kHz operating frequency. The lowest loss belongs to the SiC cascode JFET device with 1.9 W. In Figure 10, the frequency-dependent variation of the sum of the power losses in the switch is given. The SiC cascode JFET, the UJ3C120040K3S, has the lowest total losses compared to other devices in the selected frequency range. About 2 W at 200 W power and about 10 W at 1800 W power is lost. The rate of losses in the device decreases at high powers.

The efficiency of DIHS is obtained for different switching frequencies. The input and output powers of the circuit were measured using a power analyzer. Efficiency values are calculated by proportioning the measured output and input powers. To compare the efficiency of the selected devices, the tests are carried out under the same conditions.

The efficiency curves of the system depending on the switching frequency are given in Figure 11 for each switch. As seen from Figure 11, efficiency value increases significantly when the circuit is realized with SiC devices instead of Si IGBT. At all operating frequencies, the circuit efficiency with SiC cascode JFET is higher than other devices. At maximum output power, i.e., 45 kHz switching frequency, the system efficiency is 99% with the UJ3C120040K3S. The most efficient operation has been achieved with this device in all of the selected frequency ranges. In the case of using the IRGB4068 as a switch, the efficiency was measured as 97.2% at low frequencies and 89.4% at high frequencies.

6. Discussion

In this study, performance criteria for selected SiC-based devices were defined and evaluated. WBG devices will play an important role in the realization of high-performance IH systems in the near future. Engineers working in the field of design and application should know the features of these devices well. The devices were compared according to the performance criteria determined using the DIHS application circuit in Figure 12.

Experimental results show that SiC cascode JFET gives the best performance among the power devices selected for use in the DIHS. In addition, the SiC cascode JFET is advantageous in terms of applicability compared to other SiC devices, as it can be driven with the drive circuit of the Si IGBT. SiC cascode JFET has a flat efficiency curve, as well as highly efficient operation throughout the selected switching-frequency range. This feature allows efficient energy transfer to ferromagnetic and nonferromagnetic metals using the same DIHSs. Efficient operation can be achieved without overheating and without damaging the system in nonferromagnetic loads with low resistance value at high frequencies by using WBG devices in the HB converter.

The switching power losses of the SiC power devices are lower than the Si IGBT. Especially the high voltage rating SiC MOSFET has high conduction losses because of its high on-state resistance. The switching speed of Si IGBT is lower than the SiC device because of the tail current.

As a result, the turn-off power loss is higher than SiC devices. It has been determined that the parameters examined in devices with the same values belonging to different companies, except for PBD, are approximately similar. Considering the voltage and cost the device will be exposed to in the circuit, selecting the appropriate device is important in terms of efficiency and cost balance. The increasing use of SiC cascode JFET is due to industrial interest and reduced oscillations in switching.

7. Conclusions

This article presented an experimental comparative evaluation of different SiC power devices in DIHS with a state-of-the-art Si device. Detailed analyses were made using different SiC devices with the same and different voltage values from different manufacturers. The efficiency of DIHS has been investigated by operating the devices under different frequencies at the range of 45 kHz–145 kHz. As a conclusion of this study, several differential features have been identified:

• As with the state-of-the-art Si IGBTs, the SiC Cascode JFET device, which combines the good features of two different devices, showed the best performance;
• SiC cascode JFET is advantageous in terms of applicability compared to other SiC devices, as it can be driven with the drive circuit of the Si IGBT;
• SiC cascode JFET has a flat efficiency curve, as well as a not only highly efficient operation throughout the selected switching frequency range.

In device selection, cost/performance balance is as effective as electrical parameters and efficiency values. Despite the cost disadvantage, using SiC power devices is increasing in industrial applications.

One of the main goals in state-of-the-art DIHS is to efficiently transfer power to all metals, ferromagnetic or nonferromagnetic. In future studies, power transfer to all metals in a converter operating efficiently at high frequency with WBG devices will be experimentally investigated. In addition, the use of WBG devices in DIHS is of great importance for sustainability and reducing carbon footprints.