Key Technologies For Silicon Carbon Power Device In High Speed Application

Silicon carbide power device has the characteristic of the high-switching speed,which leads to the low-switching loss and the high-switching frequency,and has obvious advantage to achieve high efficiency and high power density of the power electronic converter.Therefore,it is hoped that silicon carbide power device can be widely used in the power electronic converter.However,some application problems are brought by the high-switching speed of silicon carbide power device.At present,those problems haven't been studied in depth and thus the research of the technologies in the high-switching speed application for silicon carbon power device is significant.The main contents in this paper are as following:Based on the relations between the voltage rate,the current rate and parameters of the silicon carbide power device,the design ranges of the gate resistance,the gate parasitic inductor and the power loop parasitic inductor are deduced to design the PCB layout of the gate loop and the power loop.According to the maximum voltage rate of the silicon carbide power device,the parasitic capacitors of the freewheel diode and the load inductor are limited.Test points selection and test equipment direction are specified to reduce the impact of less-standard test on the results of the switching performance when testing the switching waveforms by the double-pulse-test circuit.In order to predict the switching behavior of silicon carbide power device,this paper proposes an analytical model based on the mathematical modeling method.This paper utilizes mathematics iteration method for solving the analytical model and the piecewise mathematical formula for fitting the nonlinear characteristics of the junction capacitors and the transconductance coefficient to acquire more accurate results of prediction,which avoid solving the simplified time domain expression in which the junction capacitors and the transconductance coefficient are constant.Based on the proposed analysis model,the channel current of the silicon carbide power device can be obtained to evaluate the switching loss.The sensitivities of the switching performance of silicon carbide power device to parameters in the circuit are compared to provide theoretical guidance for optimizing the performance of the power electronic converter.The crosstalk mechanisms of the non-Kelvin package and the Kelvin package of silicon carbide power device are analyzed respectively.The displacement current of the gate-drain capacitor and the drop-voltage on the common source inductor are the principal factors inducing crosstalk.From above analysis,this paper proposes a low gate turn-off impedance driver for suppressing crosstalk,by which the common source parasitic inductor is decoupled from the gate loop and the displacement current of the gate-drain capacitor bypasses.This driver is simple and the control logic is plain.The mechanisms of the overvoltage and oscillation occurring to the turn-off voltage are analyzed respectively using the terminal impedance of the freewheel diode and silicon carbide power device during the turn-off transition..It is concluded that reducing the terminal impedance or switching speed can suppress the overvoltage and oscillation.For decoupling a portion of the parasitic inductors from the power loop to reduce the terminal impedance during the turn-off transition,the design principle of the high-frequency decoupling capacitor paralleled with the phase-leg configuration is deduced.Since the problem that the low-frequency oscillation and the high-frequency oscillation overlay on the turn-off voltage after the high-frequency decoupling capacitor paralleled needs to be solved,the range of the damping in series with the high-frequency decoupling capacitor is deduced.This paper proposes a novel method that the high-frequency decoupling capacitor in parallel with the capacitor and damping branch,and deduces the design principle of this damping,so that the decoupling effect of the high-frequency decoupling capacitor lowered by the damping can be improved.In order to avoid switching delay and the switching loss increasing dramatically as a result of the gate resistor increasing for reducing the switching speed,a variable-voltage and variable-gate-resistor driver is proposed to suppress the overvoltage and oscillation.This driver can reduce the driver voltage and increase the gate resistor when the overvoltage and oscillation occur to the turn-off voltage.However,the switching loss caused by this method must be assessed to guarantee the acceptable range.