This paper introduces two types of single-stage high-frequency isolated converters named isolated modular multilevel converter (I-M2C) and isolated modular cascaded converter (I-MC2), which are both based on the high-frequency-link concept. The two converters can totally reduce the individual DC-link capacitors at the high-voltage (HV) side and simplify the voltage balancing control. The fundamental principle and applied modulation strategy scheme of I-M2C and I-MC2 are given in details. The operation mode of I-M2C is analysed as an example. Experimental results are given respectively to illustrate the efficient operating characteristics of the two new types of converters.