The demand for electric vehicles is increasing, mainly due to the decrease of fossil fuel reserves. In addition, it is economical to choose an electric vehicle, because it requires less operating costs and will not cause harm to the environment. Considering these facts, it is logical to improve the efficiency of batteries and components. One of the methods is to use wide band gap, gallium nitride and silicon carbide instead of silicon in the power converter, because the traditional DC-DC converter will cause huge power loss.

Recent research shows that compared with SiC, the switching power loss of GaN transistor is lower, so the efficiency is higher. Because power density is very important for general DC-DC converters and power electronic converters in PEV, and commercial GaN transistors with lateral structure cannot be used due to high power limit.

After using the universal converter, the number of modules used will be reduced, which will improve the power density and reliability and help us improve the efficiency and design of PEV. In order to solve the limitation of lateral GaN transistors, a general DC-DC converter can be applied in PEV with multiphase topology. However, this will bring a series of problems. The problem is that multiphase converters with high phase numbers are not suitable for power electronics.

In order to solve these problems, we have studied a novel two-phase interleaved bidirectional boost converter, in which one phase is based on GaN and the other phase is based on SiC. The principle behind it is that only GaN-based phases are used for power conversion in the range of 1-15Kw. The other phase provides conversion of power exceeding 15kw.

Modern applications (such as multi-input and zero-voltage switching) use multiphase topology to share current between two phases, and power converters also use the same technology. However, unlike other converters, this design uses different types of active devices. The configuration of the converter is shown in Figure 1.

Fig. 1 layout of sic-gan based converter

People may think that due to the mismatch of current sharing in this configuration, the diode with higher current will have higher temperature and eventually lead to instability. Although this is not the case due to the bidirectional topology, there are transistors on both sides of the converter. In addition, this technology has proved to be a great progress because it does not need body diodes and anti-parallel diodes.

In order to design the inductor, it is important to consider the conduction mode of the converter, which is set to be continuous in this example. With this in mind, the number of inductors can be calculated as shown in Formula 1:

Equation 1

Here, Vo is the DC bus voltage, Vin is the battery voltage, FS is the switching frequency, and IL(min) is the minimum inductor current. Because the minimum current is only provided by the GaN phase, there is no advantage of small inductance size compared with single-phase converter. At the same time, the high voltage capacitance can be calculated according to Formula 2:

Equation 2

1. Mathematical calculation of the model

We studied the interval to obtain the mathematical model of the converter. Therefore, we analyzed the boost mode, in which a voltage ratio equivalent to 2 (Vin = 300 [V] and Vo = 600 [V]) is required. The duty cycle of the boost converter and its voltage are as follows:

Equation 3

In the above formula, eta is the efficiency of the converter. Since the efficiency is always less than 1, the duty cycle of the converter is greater than 50%. On the other hand, the switching command in the interleaved two-phase converter has a time offset of T/2, where T = 1/fs is the time period. With this in mind, the possible inductor currents are as follows:

Fig. 2 Inductive current