Abstract: The invention is a system and method for smoothly starting and controlling an ORC power plant. The system comprises a cascaded closed loop control that accounts for the lack of relationship between pump speed and pressure at startup so as to control pump speed and pressure, and that smoothly transitions into a steady state regime as a stable operating condition of the system is attained. The cascaded loop receives signals corresponding to a superheat setpoint, a pressure at an evaporator exit, and a temperature at an evaporator exit, and controls the pump speed and pressure upon startup to provide smooth operation. The system and method can further comprise a feed-forward control loop to deal with conditions at start-up and when external disturbances are applied to the ORC power plant.

Abstract: The invention is a system and method for synchronizing an induction machine to an electrical grid. The embodiment described is an ORC power plant having a motor-generator in mechanical communication with a turbine. The motor-generator is operated with open windings (e.g., freewheeling) by driving the turbine with a variable speed pump. The rotational speed of the motor-generator is sensed. When the motor-generator is operating at a rotational speed near the steady state rotational speed that corresponds to operation of the ORC power plant, the contacts between the motor-generator windings and the grid are closed, and the motor is synchronized with the grid.

Abstract: In a waste heat recovery system having a superheat controller, a reference superheat controller operating trajectory is established and compared with operational superheat controller trajectories from time to time and measuring the deviation therebetween to determine whether a low charge condition exists. If such a condition does exist, warning steps and possibly shut down steps can be taken. As a verification of a low charge condition, the absence or presence of oscillations in the pressure and/or pump power conditions can be observed.