Article source: ROHM Semiconductor
Abstract: A Trans-link interleaved inverter circuit (1) that takes advantage of the high-frequency characteristics of silicon carbide (SiC) MOSFETs achieves a power conversion efficiency of more than 99% at 5kW. In this circuit topology, the inductance of the smoothing reactor can be reduced. Since the number of turns of the reactor is reduced, the copper loss is greatly reduced, and high efficiency is achieved. In this document, an example of this new inverter design is presented. In addition, the new inverter circuit was developed in collaboration with Power-Assist-Tech Co., Ltd. (https://www.power-assist-tech.co.jp/).
Comparison with conventional circuits
Figure 1 shows a comparison between the conventional full-bridge type and the Trans-link interleaved circuit described in this document, with both circuits having an output power of 5 kW.
Although the conventional bridge parallel 2PCS IGBT (STGW60H65DGB) is used as a switching device, the efficiency at 5KW is 97.4% (total loss is 133W), and a cooling fan is necessary. The staggered efficiency is 99% (a total loss of 51W) because the downsizing radiator that suppresses heat generation and does not use a cooling fan can be cooled. And because it is a staggered type, it is clear that the switching frequency can be doubled, the smoothing filter is miniaturized, and the size and weight are halved.
Circuit composition
Figure 2 shows the composition of an interleaved circuit
There are three half-bridges in an inverter circuit, each containing two transistors (QHk and QLk, k = 1, 2, 3). Schottky diodes are connected in parallel as freewheeling diodes and transistors. B2 and B3 operate in 180° reversed phase PWM mode. The QH1と and QL1 of B1 switch alternately at 50 Hz and act as a low-frequency switch bridge. The outputs of B2 and B3 interact with each other via a coupled reactor (LC), and the currents flow through the LC and are added. The outputs of B2 and B3 and the center point of B1 are connected to the output capacitance (CO).
The equivalent circuit of the coupling reactor is shown in Figure 3.
It can be divided into two leakage inductances (L1 and L2), excitation inductance (Lm), and an ideal reverse transformer. As shown in Figure 3, VL1, VL2, V1, and V2 are the self-induced electromotive forces of each inductor, and in Figure 3, iL1, iL2, i1, i2, and im are the defined currents. Because this is a PWM circuit, QH2 operates at duty cycle d when it is turned on. Since it is an inverter action, d varies according to time. The inductance of L1 and L2 is the same, and L is used for simplicity. In the inverter process, all half-bridges in the inverter circuit operate according to the principle of synchronous rectification, except for the dead time.
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Source: SIC SiC MOS transistor and power module applications
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