Heat Energy Calculation Of Braking Resistor - Fuji Electric FRENIC-HVAC User Manual

3.1.3.3

Heat energy calculation of braking resistor

If the inverter brakes the motor, the kinetic energy of mechanical load is converted to electric energy to
be transmitted into the inverter circuit. This regenerative energy is often consumed in so-called
braking resistors as heat. The following explains the braking resistor rating.
[ 1 ] Calculation of regenerative energy
In the inverter operation, one of the regenerative energy sources is the kinetic energy that is generated
at the time an object is moved by an inertial force.
Kinetic energy of a moving object
When an object with moment of inertia J (kg·m
follows:
2
J 2π •
N 2
E = •
( )
2
60
1
≈ J 2
N
• •
2
182 4 .
When this object is decelerated to a speed N

J 2
 π 
N
•
2
E =
  
•
2 60
 


1
≈ J ( N
• •
2
182 4 .
The energy regenerated to the inverter as shown in Figure 3.9 is calculated from the reduction-gear
efficiency η and motor efficiency η
G
1 (
E ≈ +
J J
•
182 4 .
1 2
[ 2 ] Calculation of energy able to regenerate per inverter
Energy able to regenerate per inverter is determined by the power source voltage and capacitance of
the DC link bus capacitor(s).
1
2
Ec = C V (J)
• •
2
If the value E obtained by the equation (3.14) does not exceed the value Ec obtained here, the inverter
is able to decelerate its load.
(J = Ws)
( ) J

2 2
 π 2

N
•
1
− ( ) J
  
60
 


2
− 2 ) ( ) J
N
1
as follows:
M
( )
)
η η
2 − 2
N N
• • •
2 1
G M
2
) rotates at a speed N
(r/min), the output energy is as follows:
1
( ) J
3-10
(r/min), its kinetic energy is as
2
(3.12)
(3.12)'
(3.13)
(3.13)'
(3.14)
(3.15)