Dynamic Input Current Low-Frequency Ripple Evaluation and Reduction by Inverter with Variable-Speed, Sensor less Induction Motor Drive

Abstract

The control of IM variable speed drives often requires control of machine currents, which is normally achieved by using a voltage source inverter. We propose a modified control scheme that includes the torque control and a current regulated PWM inverter to avoid the undesirable trips due to transient currents. In this system, two PI controllers are used to regulate the average value of torque and speed. The output of the P-I regulators forms the q-axis reference in a synchronously rotating reference frame. The open loop control strategy in an existing v/f drive can be replaced by the proposed close-loop control strategy without requiring any additional power components or the physical sensors. The proposed strategy appears to be a good compromise between the high-cost, high-performance field-oriented drives and the low-cost, low-performance v/f drives. In this paper, a new speed sensor less control strategy for IM is proposed that includes the speed control, torque control and current regulation. The drive is operated under torque control with an phase voltages, line currents, flux, torque and rotor speed. An active or passive-type low-pass filter (LPF) with narrow bandwidth is used to filter out the high frequency components in the ac current waveform.