Improvement of spot welding control system Dolinar, D; Klopcic, B; Stumberger, G
Proceedings of 14th International Power Electronics and Motion Control Conference EPE-PEMC 2010,
2010-Sept.
Conference Proceeding
This paper deals with the control improvement of a middle-frequency resistance spot welding system. This is achieved by a combined closed-loop control of the welding current and closed-loop control ...of the iron core saturation level. The proposed control assures a very short rise time of the welding current and the best possible utilization of the transformer iron core.
Three phase transformers used in the electric power applications are composed either of three single phase transformers or they are three limb core type. The majority of three phase core-type ...transformer dynamic models neglect magnetic nonlinearity and saturation. This paper presents two magnetically nonlinear iron core models of three phase three-limb transformer. Iron core model I is determined by described simultaneous excitation of three windings, where two currents are always constant, or by special single-phase excitaion.Iron core model II is determined by simultaneous three phase excitation with different currents. The comparison between measured and calculated currents confirms that results agree much better when the proposed iron core model II with included cross saturation is used in the dynamic transformer model instead of the iron core model I. Even more, the values of measured and calculated currents using iron core model II are almost the same.
The paper proposes an IM torque control based on the stator current vector reference frame. The introduced control concept rejects the paradigm of decoupled control with constant rotor flux vector. ...Instead of this widespread assumption the proposed control is derived from the augmented dynamic equilibrium conditions assuring the existence and uniqueness of the inverse mapping between the required torque end stator current vector. By manipulating simultaneously the magnitude and the rotation speed of the stator current vector in an appropriate way the rotor flux trajectories are forced to change only inside the globally stable sector under all operating conditions. Additional features as maximal torque per ampere steady state ratio, almost perfect command tracking at non-zero rotor flux and insensitivity to the bounded perturbation of the rotor time constant, characterize introduced control. Implementation of this control requires estimation of the machine torque and cascaded current controllers. Experimental results confirm the key expectations and show the potential and benefits of the proposed control.
Pulsating torque reduction for permanent magnet AC motors Grcar, B.; Cafuta, P.; Stumberger, G. ...
Proceedings of the 2001 IEEE International Conference on Control Applications (CCA'01) (Cat. No.01CH37204),
2001
Conference Proceeding
Control methods for the pulsation of torque reduction for the surface-mounted permanent magnet motors are discussed. The pulsation torque is a consequence of the non-sinusoidal flux distribution and ...due to interaction of the rotor's permanent magnets with the changing stator reluctance. The proposed control method is an estimator based. To ensure parameter convergence the Lyapunov direct method is used in the estimator design for the flux Fourier coefficients. A novel nonlinear torque controller based on the flux/torque estimate is introduced to reduce the influence of the flux harmonics. The influence of the cogging torque is considerably reduced at lower motor speed using the internal model principle and adaptive feedforward compensation technique. An overall control scheme and experimental results are also presented.
In the paper induction machine (IM) torque control is studied as an example of a three-dimensional non-holonomic integrator that includes drift terms. By expanding Brockett's controller derived for ...the driftless systems, a control structure is proposed that guarantees natural adjustment of both the amplitude and the frequency modulation of the sinusoidal stator current vector. The rotor flux linkage vector is implicitly forced to track required periodic orbits satisfying non-holonomic constraints of the IM. Main features of the proposed control include fast dynamics of the torque response, maximal torque per amp ratio for nominal parameters, asymptotic stability, and robustness regarding expected parameter variations. Simulation and experimental results illustrate the main characteristics of the proposed control.
In the paper, the interaction of numerical protective relays with a complex power system operation during transients and faults is studied. The presented approach, which incorporates the analysis of ...pre- and post-fault conditions as well as those during transients, enables a deeper insight in the protection operation and allows more accurate parameter settings. Additionally it offers a practical tool for checking the existing and new protection schemes. As an example the dynamical model of the Crete power system was used in the authors' simulations. The Crete power system is an autonomous medium-sized power system, comprising power generation of various types including renewable and high voltage transmission. Essentially new numerical differential and conventional distance relays were modelled to demonstrate the benefits of the proposed integral approach.
Non-holonomy in im torque control Grcar, B.; Cafuta, P.; Stumberger, G. ...
9th IEEE International Workshop on Advanced Motion Control, 2006,
2006
Conference Proceeding
In the paper IM torque control is studied as an example of non-holonomic system with drift terms. Following the famous Brockett integrator problem several control propositions are introduced. The ...paper extends the control scheme from the state to the output control in several steps. By introducing adjusted amplitude, frequency and phase modulation of the IM stator current vector, the rotor flux linkage vector is implicitly forced to generate required periodic orbits that satisfy nonholonomic constraint. Improvements in the transient feedback performance, maximal steady-state efficiency, avoidance of singularities and sufficient robustness are actually achieved by making the current modulation dependent from the torque error signal. In the contrast with the original work instead of global only local stability could be assured. Simulation and experimental results illustrate main characteristics of the proposed control
The current and position dependence force and flux linkage characteristics of the studied radial active bearings are determined by the finite element computations in the entire operating range. Based ...on results of the performed computations the considerable impact of magnetic nonlinearities and cross coupling effects on properties of radial active magnetic bearings is established. The obtained characteristics are incorporated into the dynamic mathematical model, which is based on the current and position dependent radial forces and partial derivatives of flux linkages.
