A waste heat recovery system, comprising a Brayton cycle system and a Rankine cycle system: the Brayton cycle system comprising: a heater configured to circulate an inert gas in heat exchange relationship with a heating fluid to heat the inert gas; a first expansion unit/group coupled to the heater and configured to expand the inert gas; a heat exchanger configured to cool the inert gas from the first expansion unit/group by evaporating a working fluid of the Rankine cycle system; a cooler configured to further cool the inert gas from the heat exchanger; and a compression unit/group configured to compress the inert gas fed through the cooler; characterized in that the first expansion unit/group and the compression unit/group are mechanically coupled reciprocating machines; and the Rankine cycle system comprising: a second expansion unit/group coupled to the heat exchanger and configured to expand the working fluid vapor; a condenser; and a pump configured to compress the working fluid fed through the condenser, wherein the second expansion unit/group is a reciprocating machine mechanically coupled with the first expansion unit/group and the compression unit/group of the Brayton cycle system, wherein the first expansion unit/group and the compression unit/group of the Brayton cycle system and the second expansion unit/group of the Rankine cycle system are connected to a common shaft. a heater configured to circulate an inert gas in heat exchange relationship with a heating fluid to heat the inert gas; a first expansion unit/group coupled to the heater and configured to expand the inert gas; a heat exchanger configured to cool the inert gas from the first expansion unit/group by evaporating a working fluid of the Rankine cycle system; a cooler configured to further cool the inert gas from the heat exchanger; and a compression unit/group configured to compress the inert gas fed through the cooler; characterized in that the first expansion unit/group and the compression unit/group are mechanically coupled reciprocating machines; and the Rankine cycle system comprising: a second expansion unit/group coupled to the heat exchanger and configured to expand the working fluid vapor; a condenser; and a pump configured to compress the working fluid fed through the condenser, wherein the second expansion unit/group is a reciprocating machine mechanically coupled with the first expansion unit/group and the compression unit/group of the Brayton cycle system, wherein the first expansion unit/group and the compression unit/group of the Brayton cycle system and the second expansion unit/group of the Rankine cycle system are connected to a common shaft. a second expansion unit/group coupled to the heat exchanger and configured to expand the working fluid vapor; a condenser; and a pump configured to compress the working fluid fed through the condenser, wherein the second expansion unit/group is a reciprocating machine mechanically coupled with the first expansion unit/group and the compression unit/group of the Brayton cycle system, wherein the first expansion unit/group and the compression unit/group of the Brayton cycle system and the second expansion unit/group of the Rankine cycle system are connected to a common shaft.