Ensuring the operation of electrical equipment during short-time voltage sags or power outage

This paper describes the situation of a modern electric drive (induction machine supplied from indirect frequency converter with voltage source inverter) in industry (paper mills, etc.), where a voltage sag can bring significant problems with long-time interruption of the production process. One method of operation is a direct increase of voltage in the DC-link of a frequency converter with a step-up converter during voltage sag. A transistor designed for braking is often used. It is used often present transistor designed for braking. The article presents the waveforms of voltages and currents in the circuit of an indirect frequency converter in the case of voltage sags without the intervention of a step-up converter. Then it presents waveforms with the use of a boost converter and its various control options.