Self-Adaption Dead-Time Setting for the SiC MOSFET Boost Circuit in the Synchronous Working Mode

Abstract

To improve the DC-bus voltage and the switching frequency of the boost circuit and reduce the volume of the passive filter element and the heatsink, the SiC MOSFET should be used as the main switching device. It is necessary to keep the SiC MOSFET working in the synchronous working mode to minimize the on-state loss of the SiC MOSFET. In this mode, the dead-time should be inserted into the gate signals of two SiC MOSFETs in the bridge. However, because of the high switching frequency and the output capacitance of the SiC MOSFET and the freewheeling SiC diode, there will be a large loss during the dead-time. Thus, a self-adaption dead-time setting has been proposed in this paper. Firstly, it analyzes the detailed switching process and establishes the models around dead-times when the SiC MOSFET boost circuit works in the continuous and discontinuous mode respectively. Secondly, based on the analyses and models, the dead-time before the active SiC MOSFET turns on can be set as a fixed value calculated by the parameters of the SiC MOSFET and the driver board in the continuous mode ( $T_{\text {d1}}{}^{\text {con}}$ ) and can be set as a variable value relevant to the duty cycle, the switching period, the input and output voltage in the discontinuous mode ( $T_{\text {d1}}{}^{\text {discon}}$ ). Thirdly, also based on the analyses and models, the dead-time after the active SiC MOSFET turns off can be set as a variable value in the continuous mode ( $T_{\text {d2}}{}^{\text {con}}$ ), which depends on the real-time measured output voltage, the real-time measured maximum current in the boost inductor and the value of $T_{\text {d1}}{}^{\text {con}}$ . In the discontinuous mode, it can be set as a variable value relevant to the real-time measured output voltage, the inductance value, the duty cycle, the switching period, the input voltage and the value of $T_{\text {d1}}{}^{\text {con}}$ ( $T_{\text {d2}}{}^{\text {discon}}$ ). The dead-times before the active SiC MOSFET turns on and after the active SiC MOSFET turns off in the continuous and discontinuous mode constitute the self-adaption dead-time, which can be automatically adjusted according to circuit parameters and decrease the loss around the dead-time especially at the high switching frequency. The effectiveness of the proposed self-adaption dead-time setting is proved by the experiment finally, which can reduce the loss by 12.5% in the continuous mode when the output voltage is 400V, the output power is 880W and the switching frequency is 100kHz and can reduce the loss by 12.0% in the discontinuous mode when the output voltage is 400V, the output power is 440W and the switching frequency is 20kHz.

Keywords

• SiC MOSFET boost circuit
• synchronous working mode
• self-adaption dead-time
• continuous mode
• discontinuous mode
• loss