Variable speed drive with PFC front-end for three-phase induction motor



 A variable frequency drive for an induction motor is proposed. The drive uses a power factor (PF) correction bridgeless single-ended primary inductor converter-controlled rectifier operating in discontinuous inductor current mode as a front-end in order to improve the input power quality and a variation of the constant volts per hertz controller, with feedback to regulate the velocity of the motor shaft. The frequency slip is measured and compensated, since the input stage. Experiments with and without load are carried out and presented. Input power quality measurements are also presented. The proposed system is effective to regulate the velocity and achieving a close to unity PF.



Fig. 1 Proposed AC–DC–AC converter




Fig. 2 Results from experiments I and II

Fig. 3 Input voltage and current waveforms and input current harmonics

a Input voltage and current waveforms, Channel 1 for current and Channel 2 for voltage. Current is measured by V–I converter with 1 V:1.6 A conversion ratio

b First 39 non-fundamental current harmonics


The proposal of an SEPIC converter as the front-end of single-phase to three-phase AC–DC–AC converter for an induction motor for improving the input power quality is presented. It is also shown a variation of the CVH controller to regulate the angular velocity of the motor shaft using the aforementioned topology. The controller compensates the frequency slip, due to mechanical load, since the rectifying stage. The experimental results show that the topology is effective for regulating the velocity and that the topology can achieve a close to unity PF and low THD. The computed spectrum can be used to design passive input filters and further improve the THD and the PF of the circuit.


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