Inverter is a power control device that applies frequency conversion technology and microelectronics technology to control AC motor by changing the frequency of motor working power supply. Inverter is mainly composed of rectifier (AC to DC), filter, inverter (DC to AC), brake unit, drive unit, detection unit microprocessor unit and so on. The inverter also has many protection functions, such as overcurrent, overvoltage, overload protection and so on. With the increasing degree of industrial automation, the inverter has also been very widely used.
When an AC motor is started "across the line", the starting motor and load may require up to 7 to 8 times the full load current of the motor. The vfd rated motors start the motor at zero frequency and voltage. As the frequency and voltage "build up", the VFD converter "magnetizes" the motor windings, which typically draws 50 to 70% of the motor's full load current. The additional current above this level also depends on the connected load, acceleration rate and acceleration.
Starting an AC motor across the line, and the subsequent demand for 300 to 600% of the motor's full load current, places a significant drain on the power distribution system connected to the motor. When the supply voltage dips, depending on the size of the motor and the capacity of the distribution system, the voltage dips can cause sensitive equipment connected to the same distribution system to go offline due to low voltage. Items such as computers, sensors, proximity switches and contactors are voltage sensitive and may drop out when subjected to large AC motor lines that start nearby. Using a VFD inverter eliminates this voltage dip as the motor starts and accelerates at zero voltage.
If power is proportional to current multiplied by voltage, the power required to start an AC motor across the line is significantly higher than with a vfd synchronous motor. This holds true only at start-up. The main problem is that some distribution systems may be at their limits at certain times of the day (often considered "peak hours"). When industrial customers start their motors during these peak hours, the customer is often stung by power surges during peak hours. These demand factors do not become an issue with VFD inverters.