A. Tonielli

Modeling and control strategies for a variable reluctance direct-drive motor

A high-performance ripple-free dynamic torque controller for a variable-reluctance (VR) motor intended for trajectory tracking in robotic applications is designed. A modeling approach that simplifies the design of the controller is investigated. Model structure and parameter estimation techniques are presented. Different approaches to the overall torque controller design problem are discussed, and the solution adopted is illustrated. A cascade controller structure consisting of a feedforward nonlinear torque compensator, cascaded to a nonlinear flux or current closed-loop controller is considered, and optimization techniques are used for its design. Although developed for a specific commercial motor, the proposed modeling and optimization strategies can be used for other VR motors with magnetically decoupled phases, both rotating and linear. Laboratory experiments for model validation and preliminary simulation results of the overall torque control system are presented. >

Robust control of a throttle body for drive by wire operation of automotive engines

The throttle control plays an important role in the development of drive by wire (DBW) systems. The position control of the throttle valve is quite a complex problem, due to application constraints and system characteristics. A cascaded control structure including a nonlinear trajectory generator filter is adopted, allowing each different control problem to be solved with the most suitable control algorithm and implementation technology. In this regard, the use of variable structure control techniques is the key element to reaching the solution. Extensive simulation tests are reported to show the performance of the proposed control algorithm. A prototype controller is presented. The experimental implementation of the controller for a step from 2.5/spl deg/ to 85.5/spl deg/ indicates a very smooth position trajectory with a maximum dynamic position error of 7/spl deg/. Application specifications are fully satisfied both in terms of control performance and controller cost.

Brief Nonlinear filters for the generation of smooth trajectories

A nonlinear variable structure (VS) system is presented, suitable for smooth trajectory generation in motion control system. Joined to a rough reference trajectory generator (step, ramp, etc.) it provides smooth output signals according to user-selectable bounds on trajectory derivatives. The bounds on output derivatives can be changed during system operation without impairing system stability. Moreover, minimum time response with guaranteed no overshoot is ensured both in the continuous and discrete-time implementations. The main contribution of the paper lies in the discrete-time version of the trajectory generator. The performance of the proposed nonlinear filters is tested through simulation experiments. Simulation results concerning the use of the discrete filter in a position tracking control system are also presented.

Power control of a doubly fed induction machine via output feedback

Abstract A new output feedback control algorithm for a doubly fed induction machine (DFIM) is presented. The asymptotic regulation of active and reactive power is achieved by means of direct closed-loop control of active and reactive components of the stator current vector, presented in a line-voltage-oriented reference frame. To get the maximum generality of the solution, the usual assumption of negligible stator resistance is not made. A full-order DFIM model is used for the control algorithm development. The proposed control system is robust with respect to bounded machine parameter variations and errors on rotor position measurement. In the paper, it is also shown how the proposed current control algorithm can be modified in order to achieve asymptotic active current tracking and zero reactive current stabilization during steady state. An extension for the speed control objective and output EMF control during the excitation–synchronization stage are also presented. Simulation and experimental tests demonstrate high dynamic performance and robustness of the control algorithm for typical operating conditions. The proposed controller is suitable for both energy generation and electrical drive application with restricted speed variation range.

Indirect stator flux-oriented output feedback control of a doubly fed induction machine

A new indirect stator flux field-oriented output feedback control for doubly fed induction machine is presented. It assures global exponential torque tracking and stabilization of the stator-side power factor at unity level, provided that electric machine physical constraints are satisfied. Based on the inner torque control system, a speed tracking controller, with load torque compensation is designed using passivity approach. In contrast to existing solutions, the stator voltage vector oriented reference frame is adopted in order to improve robustness properties with respect to induction machine parameters variation. To achieve smooth connection of electric machine to the line grid a synchronization algorithm is developed for excitation stage of the doubly fed induction machine operation. The solution proposed requires measurements of line voltages, rotor currents, rotor position and speed. Intensive experimental studies demonstrate high dynamic performance capabilities of the control algorithm proposed.

Robust current controller for three-phase inverter using finite-state automaton

A novel feedback current controller for a three-phase load driven by a power inverter is proposed. The main design specifications are robustness to load electrical parameters, fast dynamical response, reduced switching frequency, and simple hardware implementation. To meet previous specifications a multi-variable hysteresis type controller is proposed, designed as a finite-state automaton and implemented with a programmable logic device. After a general introduction, system analysis is performed, control targets are specified, and the proposed control strategy is presented and discussed. Further, actual controller architecture, based on simple analog-logic hardware, is shown and experimental results are presented using an induction motor as the inverter load. However, this does not limit the wider applicability of the proposed controller that is suitable for different types of three-phase AC loads. >

Robust control of permanent magnet motors: VSS techniques lead to simple hardware implementations

It is shown how very simple velocity-tracking robust controllers for permanent magnet motors driving nonlinear loads can be designed based on variable structure systems techniques. Very fast dynamics, accurate and robust velocity-tracking are achieved with very simple hardware components without resorting to powerful digital signal processors and related interface hardware. A cascade control structure is used to ensure maximum flexibility. The controller for a DC motor is considered in great detail. Extension to AC synchronous PM motors is also presented. At the different control levels robustness is addressed with specific algorithms and the simplest solution is always selected. The controller architecture for both DC and AC synchronous motor are presented and discussed in the paper. Experimental results related to the control of a DC motor driving a nonlinear load are also shown. They demonstrate feasibility and excellent performances of the proposed approach. >

Control of a camless engine electromechanical actuator: position reconstruction and dynamic performance analysis

Camless internal combustion engines offer major improvements over traditional engines in terms of efficiency, maximum torque and power, and pollutant emissions. Electromechanical valve actuators are very promising in this context, but they present significant control problems. Further, to keep system cost at an acceptable level, a control system without a valve position sensor needs to be adopted. Low valve seating velocity, small transition time for valve opening and closing, and unavailability of position sensor are conflicting objectives that need to be jointly considered. In this paper, a control system architecture is presented, capable of dealing with all these issues. It is shown that a position tracking controller is needed: a key point is the design of the reference trajectory to be tracked. Actuator physical limitations strongly influence the feasible trajectory when low valve seating velocity is required, thus affecting valve transition time. Owing to the same limitations, valve electromagnets have to be energized for a significant part of the trajectory, thus allowing valve position reconstruction starting from electrical measurements only. A method for position reconstruction is presented, which makes use of auxiliary coils to reconstruct electromagnets fluxes; it is shown via sensitivity analysis that the functional characteristics of position reconstruction and its accuracy are compatible with the required applications. The trajectory design is then addressed as an optimization problem that explicitly considers the tradeoff between fast dynamic performance and system robustness. The solution of this optimization problem enlightens the limitations on achievable dynamic performance, which are presented and discussed.

Theoretical and experimental comparison of indirect field-oriented controllers for induction motors

A theoretical and experimental comparison between standard and recently-developed improved indirect field-oriented controllers for induction motors is presented. It is shown that standard indirect field-oriented control algorithm provides asymptotic speed and flux regulation, while the improved one guarantees global exponential speed-flux tracking under condition of constant load torque. The difference between the flux sub-system design for the two controllers is analyzed. It is shown that the improved controller provides closed loop properties for flux subsystem when motor is rotating, leading to robust stabilization of the rotor flux vector space position and robust tracking of its modulus. It is demonstrated that both controllers have similar complexity and can be tuned using standard procedure for cascaded systems. Intensive experimental study shows that improved controller provides about one order higher speed tracking performance as compared with standard solution. Moreover, improved robustness with respect to rotor parameters variation leads to improved energy efficiency and robust stabilization of dynamic performance.

High-performance indirect field-oriented output-feedback control of induction motors

A new indirect field-oriented output feedback control for induction motors is presented which provides global asymptotic tracking of smooth speed and flux reference trajectories in the presence of unknown constant load torque. A tuning procedure for controller parameters is also developed. Transient performance and robustness properties with respect to structural unmodeled dynamics of the current control loops can easily be specified. Simulation and experimental tests demonstrate better dynamic performance compared to that of standard indirect field-oriented control. The proposed control algorithm can be viewed as an improvement of standard field-oriented controllers.