The full bridge of MMC-HVDC（modular multilevel converter based high voltage direct current systems）can rapidly isolate DC line faults

which is widely used. Losses are an important indicator of converter valves. Thispaper analyzes the losses of the full bridge and proposes a piecewise analytical formula method for loss calculation ofconverters. Firstly

the total losses of MMC converter valves are divided into two parts:conduction losses and switch-ing losses. Secondly

according to the direction of the bridge arm current and the relationship between the bridge armvoltage and the numbers of input sub-modules

we can get the conduction losses of the MMC converter by using thepiecewise analytical method. Thirdly

according to each sub-module’s energy losses in switching state

the specificexpression of switching losses can be acquired by a piecewise analytical formula method. The total losses of the fullbridge are obtained by the conduction losses adding the switching losses. Simulation results verify the accuracy of the proposed method in this paper.