Overview of Inverter Selection Overview of Braking Resistor Selection ■ Applications Requiring Braking Resistors ■ Simple Method for Braking Resistor Selection In applications where excessive regenerative motor energy is produced during deceleration or descent, the main-circuit volt- age in the Inverter may rise high enough to damage the Inverter. Standard Inverters are equipped with an overvoltage protection function so the main-circuit overvoltage (OV) is detected and operation is stopped to prevent damage.
Although the Inverter will be protected, the overvoltage protection function will gener- ate an error and the motor will stop; this system configuration will not provide stable continuous operation. This is a simple method for determining the braking resistance from the percentage of time that regenerative energy is produced during a normal operating pattern. ● About Regenerative Energy The load connected to the motor has kinetic energy if it is rotat- ing or potential energy if it is at a high level. The kinetic or poten- tial energy is returned to the Inverter when the motor decelerates or lowers the load.
This phenomenon is known as regeneration and the returned energy is called regenerative energy. T t Use rate (duty) = t/T x 100 (%ED) t: Deceleration time (regenerative time) T: Time for 1 cycle of operation Inverter Load Motor Kinetic energy Potential energy Regenerative energy During deceleration, the Inverter acts as a generator and converts kinetic and potential energy to regenerative energy. ● Avoiding the Use of a Braking Resistor The following methods can be used to avoid having to connect a Braking Resistor. These methods require the deceleration time to be extended, so you must evaluate whether extending the deceleration time will cause any problems in the application.
• Enable the "stall prevention during deceleration" function; the default setting for this function is enabled. (The deceleration time is extended automatically to prevent main-circuit overvolt- age from occurring.) • Set a longer deceleration time. (This reduces the rate at which the regenerative energy is produced.) • Select "coast to stop" as the stopping method. (Regenerative energy will not be returned to the Inverter.) 60 Overview of Inverter Selection