Schneider Electric MNA01M001EN manual Energy balance basics

3 Engineering LXM32

3.1Energy balance

To be able to estimate the effect of an interconnection of drives via a common DC bus, create an energy balance of the individual drives over a movement cycle. A movement cycle typically consists of the fol- lowing phases: acceleration, continuous movement and deceleration.

The energy generated during deceleration can be used by other drives connected via a common DC bus. Excess energy can be absorbed by the braking resistors.

The assessment of the energy balances of the individual drives per movement cycle and of the cyclic sequence of the movement cycles allows you to draw a conclusion regarding the efficiency of a common DC bus.

3.1.1Energy balance basics

The energy balance is influenced by the following factors:

•Energy absorption of capacitors Evar in the drive

•Electrical losses of the drive system Eel

•Mechanical losses of the facility and the drive system Emech

•Braking resistor EB

Energy absorption of the capaci- The higher the mains voltage, the lower the energy absorption of the tors Evar capacitors Evar. In your calculation, use the values for the highest

mains voltage that is used in your application, see chapter "2.3 Braking resistor".

The energy absorption of the capacitors Evar is the square difference between the voltage prior to the start of the deceleration and the switch-on voltage of the braking resistor.

Electrical losses Eel The electrical losses Eel of the drive system can be estimated on the basis of the peak power of the drive. The maximum power dissipation is approximately 10% of the peak power at a typical efficiency of 90%. If the current during deceleration is lower, the power dissipation is reduced accordingly.

Mechanical losses Emech The mechanical losses result from friction during operation of the sys- tem. Mechanical losses are negligible if the time required by the sys- tem to coast to a stop without a driving force is considerably longer than the time required to decelerate the system. The mechanical los- ses can be calculated from the load torque and the velocity from which the motor is to stop.

Braking resistor EB Two characteristic values determine the energy absorption of a brak- ing resistor:

•	The continuous power PPR is the amount of energy that can be
	continuously absorbed without overloading the braking resistor.
•	MNA01M001EN,V1.01, 08.2014
	The maximum energy ECR limits the maximum short-term power
	that can be absorbed.

22 Common DC bus