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Co-Surge in Bi-Turbo Engines: Measurements, Analysis and Control
Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, The Institute of Technology.
2014 (English)In: Control Engineering Practice, ISSN 0967-0661, Vol. 32, 113-122 p.Article in journal (Refereed) Published
Abstract [en]

In parallel turbocharged V-engines, with two separate air paths connected before the throttle, an oscillation in the flow can occur.If the compressor operates close to the surge line, typically during low speed and high load, and a disturbance alters the massflow balance, the compressors can begin to alternately go into surge. This phenomenon is called co-surge and is unwanted due tohigh noise and risk for turbocharger destruction. Co-surge is measured on a test vehicle in a chassis dynamometer and the systemanalyzed and modeled using a mean value engine model. The investigation shows that the alternating compressor speeds have animportant role in the prolonged oscillation. A reconstruction of the negative flow from measurements is made and compared tosimulation results, showing similar amplitudes, and supports the model validation. A new co-surge detection algorithm is presented,suitable for a pair of sensors measuring either mass flow, boost pressure or turbo speed in the two air paths. Furthermore, a newcontroller is proposed that uses a model based feedforward for the throttle, together with wastegate actuation to force the compressorspeeds together and improve balance at the recovery point. This has shown to be sufficient with moderate to high pressure ratiosover the throttle, only for zero or very low pressure drop the use of bypass valves are necessary. The advantage of not opening thebypass valves is a smaller drop in boost pressure which also reduces the torque disturbance. The performance of the controller is evaluated both in simulation and in the test vehicle.

Place, publisher, year, edition, pages
Elsevier, 2014. Vol. 32, 113-122 p.
Keyword [en]
Compressor surge, surge detection, surge control, engine modeling, engine control
National Category
Control Engineering
URN: urn:nbn:se:liu:diva-105686DOI: 10.1016/j.conengprac.2014.08.001ISI: 000344435200009OAI: diva2:709524
Available from: 2014-04-02 Created: 2014-04-02 Last updated: 2014-12-09Bibliographically approved
In thesis
1. Modeling and control of actuators and co-surge in turbocharged engines
Open this publication in new window or tab >>Modeling and control of actuators and co-surge in turbocharged engines
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The torque response of the engine is important for the driving experience of a vehicle. In spark ignited engines, torque is proportional to the air flow into the cylinders. Controlling torque therefore implies controlling air flow. In modern turbocharged engines, the driver commands are interpreted by an electronic control unit that controls the engine through electromechanical and pneumatic actuators. Air flow to the intake manifold is controlled by an electronic throttle, and a wastegate controls the energy to the turbine, affecting boost pressure and air flow. These actuators and their dynamics affect the torque response and a lot of time is put into calibration of controllers for these actuators. By modeling and understanding the actuator behavior this dynamics can be compensated for, leaving a reduced control problem, which can shorten the calibration time.

Electronic throttle servo control is the first problem studied. By constructing a control oriented model for the throttle servo and inverting that model, the resulting controller becomes two static compensators for friction and limp-home nonlinearities, together with a PD-controller. A gain-scheduled I-part is added for robustness to handle model errors. The sensitivity to model errors is studied and a method for tuning the controller is presented. The performance has been evaluated in simulation, in test vehicle, and in a throttle control benchmark.

A model for a pneumatic wastegate actuator and solenoid control valve, used for boost pressure control, is presented. The actuator dynamics is shown to be important for the transient boost pressure response. The model is incorporated in a mean value engine model and shown to give accurate description of the transient response. A tuning method for the  feedback (PID) part of a boost controller is proposed, based on step responses in wastegate control signal. Together with static feedforward the controller is shown to achieve the desired boost pressure response. Submodels for an advanced boost control system consisting of several vacuum actuators, solenoid valves, a vacuum tank and a vacuum pump are developed. The submodels and integrated system are evaluated on a two stage series sequential turbo system, and control with system voltage disturbance rejection is demonstrated on an engine in a test cell.

Turbocharged V-type engines often have two parallel turbochargers, each powered by one bank of cylinders. When the two air paths are connected before the throttle an unwanted oscillation can occur. When the compressors operate close to the surge line and a disturbance alters the mass flow balance, the compressors can begin to alternately go into surge, this is called co-surge. Measurements on co-surge in parallel turbocharged engines are presented and analyzed. A mean value engine model, augmented with a Moore-Greitzer compressor model to handle surge, is shown to capture the cosurge behavior. A sensitivity analysis shows which model parameters have the largest influence of the phenomena. The compressor operation in the map during co-surge is studied, and the alternating compressor speeds are shown to have a major impact on the continuing oscillation. Based on the analysis, detection methods and a controller are proposed, these detect co-surge and control the turbo speeds to match during co-surge. The controller is evaluated both in simulation and on a test vehicle in a vehicle dynamometer, showing that co-surge can be detected and the oscillations quelled.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. 28 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1590
National Category
Engineering and Technology
urn:nbn:se:liu:diva-105687 (URN)10.3384/diss.diva-105687 (DOI)978-91-7519-355-7 (print) (ISBN)
Public defence
2014-05-16, Visionen, ing 27-29, B-huset, våning 1, Campus Valla, Linköpings Universitet, Linköping, 10:15 (English)
Available from: 2014-04-11 Created: 2014-04-02 Last updated: 2014-04-11Bibliographically approved

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