This paper proposes a novel multifunctional topology for a grid-connected voltage source inverter to control the speed and power flow of a squirrel-cage induction motor. For high-inertia loads during startup, the issues faced include a large transient current and high heat generation. However, the solutions proposed by existing startup methods are inadequate. The topology presented in this study not only addresses the problems related to these methods, i.e., creating a smooth startup, but also presents a flexible alternative for power factor correction using capacitor banks. First, the proposed technique accelerates the motor smoothly to its operating point through the sinusoidal voltage provided by an inverter with an LC filter in its output. In the second step of the control method, after achieving stability in the desired operating point, a converter with an LC filter is assigned the task of power factor correction. Thus, the proposed topology achieves a smooth startup and unity power factor. It includes a new control strategy in which the rotor fieldoriented control method is employed for the speed control mode. Finally, the validity of the proposed theory is verified.INDEX TERMS field-oriented control, grid-connected inverter, induction motors, power factor correction, startup process.
NOMENCLATURE
Grid: uGrid voltage in the bus bar. v g , i gGrid voltage and current in coupling point. R g , L gGrid resistance and inductance. Ï g , f gGrid frequency in rad/s and Hz. Ξ g Voltage phase measured in rad. Power converter with filter: v, i Filter output voltage and current. v i , i i Inverter output voltage and current. i c , i r Capacitance and damping resistance currents. R f , L f , C f Filter resistance, inductance, and capacitance. f r Resonance frequency. f s Switching frequency. V dc DC link voltage.