Rankine cycle system

Abstract

A Rankine cycle system is provided in which, in order to make a pressure (P) of a gas-phase working medium at the inlet of an expander ( 13 ) coincide with a target pressure (P O ), a feedforward value (N FF ) is calculated on the basis of the target pressure (P O ) and a flow rate (Q) of the gas-phase working medium at the outlet of an evaporator ( 12 ), a feedback value (N FB ) is calculated by multiplying a deviation (ΔP) of the pressure (P) of the gas-phase working medium at the inlet of the expander ( 13 ) from the target pressure (P O ) by a feedback gain (kp) calculated on the basis of the flow rate (Q) of the gas-phase working medium, and the rotational speed of the expander ( 13 ) is controlled on the basis of the result of addition/subtraction of the feedforward value (N FF ) and the feedback value (N FB ). It is thereby possible to control the pressure of the gas-phase working medium at the inlet of the expander at the target pressure with high precision without changing the amount of liquid-phase working medium supplied to the evaporator.

1 . A Rankine cycle system comprising an evaporator ( 12 ) for heating a liquid-phase working medium with exhaust gas of an engine ( 11 ) so as to generate a gas-phase working medium, and a displacement type expander ( 13 ) for converting the thermal energy of the gas-phase working medium generated in the evaporator ( 12 ) into mechanical energy; 
 characterized in that, in order to make the pressure of the gas-phase working medium at the inlet of the expander ( 13 ) coincide with a target pressure, the system comprises control means ( 20 ) for calculating a feedforward value (N FF ) on the basis of the target pressure and the flow rate of the gas-phase working medium at the outlet of the evaporator ( 12 ), calculating a feedback value (N FB ) by multiplying a deviation of the pressure of the gas-phase working medium at the inlet of the expander ( 13 ) from the target pressure by a feedback gain (kp) calculated on the basis of the flow rate of the gas-phase working medium, and controlling the rotational speed of the expander ( 13 ) on the basis of the result of addition/subtraction of the feedforward value (N FF ) and the feedback value (N FB ).