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High di/dt during the close-open operation process of hybrid dc breaker will cause differential mode interference (DMI) in the energy supply system of the breaker's driver units due to their inductive coupling. The generated DMI may lead to false action of the breaker, which is an important issue that should be carefully considered in design stage. A method to analyze DMI based on time-domain wideband circuit simulations is proposed in this article. First, a time-domain waveform expression of DMI voltage source is derived, and then wideband equivalent circuit models of major components in the energy supply system are established. Furthermore, a standardized design methodology to reduce DMI is suggested. Applying the method to a high-frequency energy supply system of a ±200 kV hybrid dc breaker, simulation results show that the DMI level for two DMI mitigation measures is reduced by about 90% and 80% of the initial value, respectively. [ABSTRACT FROM AUTHOR]