Virtual Control Variables Research Articles

Control performance of a road vehicle with four independent single-wheel electric motors and steer-by-wire system

This article presents a motion controller for a road vehicle equipped with a steer-by-wire system and four independent electric rim-mounted drives. The motion controller separates the control law from the specific actuator setup by the usage of virtual global control variables acting on the vehicle centre of gravity. A control allocation algorithm distributes the virtual control variables to the available actuators. An approximation of the real actuator dynamics is used to analyse the performance of different motion controller types in the linear and nonlinear driving regions. In addition, a vehicle state observer consisting of a traction force observer and an unscented Kalman filter is discussed to analyse the control behaviour in the case of a real sensor setup.

An algebraic method for designing controllers for multi-input multi-output linear systems via s-domain input-output decoupling

The method introduced here is applicable for multi-input multi-output, linear, and time-invariant systems. The state and output equations of the system, which are originally expressed in the t-domain, are first transformed into the s-domain. Then, input-output decoupling is achieved by generating the actual control variables as combinations of virtual control variables in such a way that each output is controlled by only the dedicated one of the virtual control variables. As the next stage, appropriate linear controllers are designed to generate the virtual control variables with feedback, feedforward, and disturbance rejection features. The design method is algebraic and involves the assignment of not only the closed-loop poles but also the type numbers associated with the reference and disturbance inputs. The multivariable transformation filter that converts the virtual control variables into actual ones is formed properly to prevent any possibility of internal instability.

Suppression of stick-slip in drillstrings: A control approach based on modeling error compensation

An approach for the robust suppression of stick-slip oscillations in oil drillstrings is presented. Two control configurations are derived: a cascade control scheme, where a favorable choice of virtual input control variables is demonstrated, and a decentralized control scheme, where two control inputs are manipulated. The control approach is based on modeling error compensation techniques to provide robustness against uncertain parameters and friction terms. Numerical simulations are provided to illustrate the control performance.