Nonlinear Effect of Deadtime in Small-Signal Modeling of Power-Electronics System Under Low Load Conditions

Abstract

Deadtime is required to ensure that switches of a synchronous switching inverter leg never conduct at the same time. During deadtime, the current commutates to an anti-parallel 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 injection frequency due to the deadtime. The error depends on the perturbation amplitude, inductor current ripple and the fundamental current amplitude. This paper proposes a describing-function method to model the deadtime effect under low load conditions. It is shown that a nonlinear damping effect from the deadtime 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 deadtime effect.