Nur Uddin

Bond graph modeling of centrifugal compression systems

A novel approach to model unsteady fluid dynamics in a compressor network by using a bond graph is presented. The model is intended in particular for compressor control system development. First, we develop a bond graph model of a single compression system. Bond graph modeling offers a different perspective to previous work by modeling the compression system based on energy flow instead of fluid dynamics. Analyzing the bond graph model explains the energy flow during compressor surge. Two principal solutions for compressor surge problem are identified: upstream energy injection and downstream energy dissipation. Both principal solutions are verified in bond graph modelings of single compression system equipped with a surge avoidance system (SAS) and single compression system equipped with an active control system. Moreover, the bond graph model of single compressor equipped with SAS is able to show the effect of recycling flow to the compressor upstream states which improves the current available model. The bond graph model of a single compression system is then used as the base model and combined to build compressor network models. Two compressor networks are modeled: serial compressors and parallel compressors. Simulation results show the surge conditions in both compressor networks.

Active Compressor Surge Control Using Piston Actuation

A novel approach to active surge control in compressors using piston actuation is presented. Two control laws are compared in order to evaluate the feasibility of implementing the concept. The first control law is a nonlinear feedback control derived by using backstepping and the second one is a linear feedback control derived by analyzing the eigenvalues of the linearized system around the operating point. The nonlinear feedback control law makes the closed loop system globally asymptotically stable (GAS) and uses full states feedback. The linear feedback control is only using feedback from plenum pressure and piston velocity and the removal of the mass flow feedback is advantageous for implementation. The closed loop system with the linear feedback control is locally asymptotically stable around the operating point. Simulations show that both controllers are capable of stabilizing surge.© 2011 ASME

Introducing Back-up to Active Compressor Surge Control System

A novel method for introducing a back-up system to an active compressor surge control system is presented in this paper. Active surge control is a promising method for extending the compressor map towards and into the unstable area at low mass flow by stabilizing the surge phenomenon. The method also has potential for allowing operation at higher efficiencies. However, a failure in the active surge control system may endanger the compressor by entering deep surge as the compressor is allowed to operate in the stabilized surge area. We propose the use of a back-up system applied to the active system to keep the compressor safe should the active system fail. This paper present an active compressor surge control system with piston actuation combined with a blow off system as the back-up. Performance of the combined system is evaluated by simulating the system in situations where the piston is saturated or jammed. The combination results in a system with increased performance by taking advantage of both systems.

Two general state feedback control laws for compressor surge stabilization

Active surge control system (ASCS) can be classified into two types: upstream energy injection and downstream energy dissipation [1]. Two novel state feedback control laws termed φ-control for the upstream energy injection and ψ-control the downstream energy dissipation are presented. Both state feedback control laws are derived by using the Lyapunov based control method such that the closed loop systems are global asymptotic stable (GAS). The φ-control applies feedback from the compressor mass flow sensor to generate extra pressure to the compressor upstream line, while the ψ-control generates an extra flow out of the plenum using feedback from the compressor discharged pressure and the plenum pressure. Both state feedback control laws offer a minimum number of sensors requirement. Moreover, the ψ-control requires feedback from pressure sensors only which are readily available and make real-time implementation of the system to be easier.

Passivity-Based Control for Two-Wheeled Robot Stabilization

A passivity-based control system design for two-wheeled robot (TWR) stabilization is presented. A TWR is a statically-unstable non-linear system. A control system is applied to actively stabilize the TWR. Passivity-based control method is applied to design the control system. The design results in a state feedback control law that makes the TWR closed loop system globally asymptotically stable (GAS). The GAS is proven mathematically. The TWR stabilization is demonstrated through computer simulation. The simulation results show that the designed control system is able to stabilize the TWR.

Compressor surge control design using linear matrix inequality approach

A novel design for active compressor surge control system (ASCS) using linear matrix inequality (LMI) approach is presented and including a case study on piston-actuated active compressor surge control system (PAASCS). The non-linear system dynamics of the PAASCS is transformed into linear parameter varying (LPV) system dynamics. The system parameters are varying as a function of the compressor performance curve slope. A compressor surge stabilization problem is then formulated as a LMI problem. Solving the LMI problem results in a feedback control gain for the compressor surge stabilization and stability proof of the closed loop system in the whole compressor operating area. Simulation results show that the designed surge control system is able to stabilize compressor surge. Significant improvement of the control system performance is achieved by combining the LMI approach and linear quadratic regulator (LQR).