A. W. F. V. Silveira

Switched reluctance machine modeling including core magnetic saturation - the self-excited operation mode

This paper presents a switched reluctance machine (SRM) modeling including core magnetic saturation. The self-excited operation mode switched reluctance generator (SRG) as example application. In addition, following an extensive bibliographic review about self-excited switched reluctance generator (SSRG), the mathematical model, principle of operation and simulation results of the generator dynamics is presented. To correctly represent the self excitation operation the mathematical model must take into account the core magnetic saturation, and that is observed here. Experimental results are included to validate the discussions presented.

Study on an alternative converter performance for Switched Reluctance Generator

The subject of this paper is an alternative converter for switched reluctance generators (SRG) and its applications. The performance of the conventional half-bridge converter is compared with the performance of this alternative one. In both cases the machine is excited by a rectified DC link. Mathematical model and simulation results are presented. Both the power converters topologies implemented worked well but the alternative converter is cheaper and more efficient than the conventional half-bridge converter. Furthermore, only the alternative converter allows feed the load from the grid even when the SRG is not running. This is good for an unstable renewable complementary power source like wind power. Also this kind of machine can be competitive for small hydropower plants where the power electronics is necessary to control the output voltage under not constant water flux conditions. Experimental results are presented. It is shown here that the SRG worked as expected and that the alternative converter topology reached expectations.

Self-excited switched reluctance generator

This paper presents a study on the behavior of the self-excited switched reluctance generator (SSRG). Following an extensive bibliographic review about SSRGs, the mathematical model, principle of operation and simulation results of the generator dynamics is presented. A capacitor partially charged, in parallel with the load is used as a mean to provide the necessary amount of magnetic flux and start the generators voltage built up. The arrangement is such that the generated voltage and current is delivered to the load in D.C. mode. To correctly represent the self excitation operation the mathematical model must take into account the core magnetic saturation, and that is observed here. Experimental results are included to validate the discussions presented.

Control of the SRM operating as a motor/generator

This paper deals with switched reluctance machine used as a motor/generator drive. The motoring operation is achieved with a half-bridge converter. A strategic modification in the electronic converter topology is required to allow the generator operation mode. It is achieved automatically as well as the phase switching angles control is simultaneously provided. Three different techniques to control the voltage delivered to the load when the machine is operating as a generator are evaluated. All of them exert control on the machine magnetization level. Simulated results are included to show the feasibility of the proposed techniques and to confirm the applicability of the switched reluctance machine as a motor/generator device.

Dependence of the switched reluctance generator output on the speed and the excitation voltage

This paper analyses the dependence of the output power and voltage of a switched reluctance generator prototype on its angular speed and excitation voltage. Simulations and experimental results are presented. Many operational tests were conduced to state clearly the behavior of a prototype triggered by a half-bridge (HB) converter. Variable excitation voltage and angular speed relationship dependences are clearly established. It shows that the suitable excitation control for a wind powered switched reluctance generator must adjust the operational parameters to match the desired point on certain surfaces of control.

A voltage control strategy for Switched Reluctance Generator

This paper presents a strategy to control the terminal voltage of a Switched Reluctance Generator. It is implemented using a closed loop feedback that senses the shunt capacitor smoothed generated voltage at the generator terminals. The voltage error feeds a PI controller that in turn governs the switches of the electronic converter used to drive the generator. With this approach the amount of energy stored in the winding in each cycle is controlled and leads directly to the control of the generated voltage. A mathematical model that considers magnetic saturation is used to represent the reluctance generator, which is driven by an asymmetric half bridge converter. An appropriate sequence of turning off the switches of each phase of the generator is shown to allow for a better usage of mechanical power in the electromechanical conversion process. Comparison with a standard switching strategy is included. An efficient technique to detect the right moment of firing the controlled switches is shown. Experimental and simulated results are compared and found to be in good agreement. The feasibility of the proposed strategy is demonstrated.

A Comparative Study Between Tree Philosophies of Stator Flux Estimation for Induction Motor Drive

This paper shows and compares three different flux estimator algorithms developed for use in high- performance sensorless ac motor drives. The first algorithm uses a low pass filter with a very low cut off frequency to integrate the back electromotive force (emf). The second one uses a high pass filter to remove the offset present in the signal before its integration. The third algorithm uses current and voltage model to estimate the flux of induction motor. These algorithms can be used to accurately measure the motor flux including magnitude and phase angle over a wide speed range. The performance of the algorithms is investigated, compared, and verified using simulation. Preliminary experimental results are also included.

Generated voltage control of the SRM operating as motor/generator

This article treats the switched reluctance motor/generator drive for general purpose. A typical half-bridge converter topology is used to attain the motor operation mode. Although, the converter topology is strategically modified to make possible the generator operation mode. It is achieved automatically through a relay and so the phase demagnetization generates power to the load. Also the switching angles control must be simultaneously provided. Three techniques are proposed here to control the load voltage when the machine is operating as a generator. All of them exert control on the machine magnetization level. Some simulated results are presented here to show that the proposed techniques are capable of been dealt with successfully. It is showing the applicability of the switched reluctance machine as a motor/generator device.

A grid connection scheme of a Switched Reluctance Generator for active power injection

This paper presents a study of the Switched Reluctance Generator dynamics when connected to a single-phase AC power grid. A mathematical model that includes magnetic saturation is used to represent the reluctance generator, which is driven by an asymmetric half bridge converter. Output generated voltage is smoothed with a shunt capacitor leading to a DC link voltage. This voltage is regulated using a PI compensator that governs the magnetizing angle of the generator phases. It is shown that introducing a freewheeling stage between the magnetizing and the demagnetizing states of each phase, allows for a better usage of mechanical power in the electromechanical conversion process. Injection of active power in the grid is performed by a current controlled PWM inverter synchronized by phase locked loop. The complete system is simulated and the results are shown and discussed. The feasibility of the proposed strategy is demonstrated.

Controlled self-excited switched reluctance generator

This paper deals with switched reluctance generators. Two aspects of operation are investigated: self excitation and control of terminal generated voltage. Self excitation is attractive as it does not require external energy sources. Investigations in a self excited generator ask for magnetic saturation of iron core to be considered and that is observed in the paper. A technique based on the governance of the magnetization level of the machine phases to control the terminal voltage is proposed. It incorporates a strategy to improve the electromechanical conversion by means of adequate sequence of switching of the generators electronic converter. Achieving the generated voltage build up as well as the ability to control the terminal voltage in the presence of oscillations in the generator speed shaft are shown to be feasible with the proposed approaches. Theoretical and experimental results are included to validate the investigations.