Nonlinear Prefilter to Prevent Pilot-Induced Oscillations due to Actuator Rate Limiting

Proceedings of the 2010 American Control Conference

2010

Abstract-This paper proposes a control allocation technique that can help pilots recover from pilot induced oscillations (PIO). When actuators are rate-saturated due to aggressive pilot commands, high gain flight control systems or some anomaly in the system, the effective delay in the control loop may increase depending on the nature of the cause. This effective delay increase manifests itself as a phase shift between the commanded and actual system signals and can instigate PIOs. The proposed control allocator reduces the effective time delay by minimizing the phase shift between the commanded and the actual attitude accelerations. Simulation results are reported, which demonstrate phase shift minimization and recovery from PIOs. Conversion of the objective function to be minimized and constraints to a form that is suitable for implementation is given.

Section: Remarkmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A control allocation technique to recover from pilot-induced oscillations (capio) due to actuator rate limiting

Proceedings of the 2010 American Control Conference

2010

“…In the literature, there are several successful approaches for phase compensation such as the "Differentiate-Limit-Integrate" (DLI) method [3], [4], [5], [6], [7], logic or feedback based based methods Yildiray [8], [9], [10] and methods such as [11] that use describing function relationships developed in [12].…”

Section: Introductionmentioning

confidence: 99%

A control allocation system for automatic detection and compensation of phase shift due to actuator rate limiting

Proceedings of the 2011 American Control Conference

Acosta

2011

Abstract-This paper proposes a control allocation system that can detect and compensate the phase shift between the desired and the actual total control effort due to rate limiting of the actuators. Phase shifting is an important problem in control system applications since it effectively introduces a time delay which may destabilize the closed loop dynamics. A relevant example comes from flight control where aggressive pilot commands, high gain of the flight control system or some anomaly in the system may cause actuator rate limiting and effective time delay introduction. This time delay can instigate Pilot Induced Oscillations (PIO), which is an abnormal coupling between the pilot and the aircraft resulting in unintentional and undesired oscillations. The proposed control allocation system reduces the effective time delay by first detecting the phase shift and then minimizing it using constrained optimization techniques. Flight control simulation results for an unstable aircraft with inertial cross coupling are reported, which demonstrate phase shift minimization and recovery from a PIO event.

“…Differentiate-limit-integrate (DLI) approach [8][9][10][11][12] is one of the approaches that is implemented using a "software rate limiter" as shown in figure 3, where the software limiter is placed between the command signal and the input signal to the actuator. This method eliminates the effective time delay introduced by the rate saturation as seen in figure 4 and hence the onset of a PIO can be avoided.…”

Section: -7mentioning

confidence: 99%

Stability Properties and Cross Coupling Performance of the Control Allocation Scheme CAPIO

AIAA Infotech@Aerospace 2010

2010

This paper presents a stability analysis and an application of a recently developed Control Allocator for recovery from Pilot Induced Oscillations (CAPIO). When actuators are rate-saturated due to either aggressive pilot commands, high gain flight control systems or some anomaly in the system, the effective delay in the control loop may increase. This effective delay increase manifests itself as a phase shift between the commanded and actual system signals and can instigate Pilot induced Oscillations (PIO). CAPIO reduces the effective time delay by minimizing the phase shift between the commanded and the actual attitude accelerations. We present a stability analysis of CAPIO for a scalar system. In addition, we present simulation results for aircraft with cross-coupling which demonstrates the potential of CAPIO serving as an effective PIO handler in adverse conditions.