Control circuit of an Electronically Controlled Capacitor for the Optimization of the Single Phase Induction Motor


The control circuit of an Electronically Controlled Capacitor (ECC) for the optimization of the Single Phase Induction Motor (SPIM) with auxiliary winding is presented. The control circuit is based on a fixed value AC capacitor within a full bidirectional switches bridge PWM controlled at much higher than line frequency (in kHz range). The power bridge circuit and its embedded pulse driver circuit are presented within the theoretical sections of the paper. In the experimental section, using a small electric motors test bench and a two speed SPIM with auxiliary winding, are analyzed the main influences of the pulse drive circuit over the ECC. Firstly, being considered that the optimum is reached at the maximum motor torque, the optimal pulses frequency has been established around 4 kHz. Secondly, the switches over-voltages at the ommutations
moments being a serious drawback of the ECC, are analyzed the influence of the fixed capacitor value and the dead time of the pulse shape over the MOS-FET power transistors
of the bidirectional switches over-voltages. The overvoltages diminish as both the capacitor value and the dead time diminish. More than that, in contrast with some authors, there are no disadvantages as dead time became zero. These issues are the main contributions of this paper.