Nonlinear Effect of Dead Time in Small-Signal Modeling of Power-Electronic System Under Low-Load Conditions

Dead time is required to ensure that the switches of a synchronous switching inverter leg never conduct at the same time. During dead time, the current commutates to an antiparallel diode that can cause a voltage error depending on the instantaneous current direction. To measure a frequency response from a system, external injections are commonly required to perturb the system. The perturbation can change the current direction at the frequency of the injection, causing a voltage error at the injection frequency due to the dead time. The error depends on the perturbation amplitude, inductor current ripple, and fundamental current amplitude. This article proposes a describing-function method to model the dead-time effect under low-load conditions. It is shown that a nonlinear damping effect from the dead time can occur under low-load conditions and cannot be modeled with a resistor-like element. Real-time hardware-in-the-loop-simulation results are presented and used to demonstrate the effectiveness of the proposed method. Experimental measurements are used to verify the nonlinear dead-time effect.