IMO Precision Controls Jaguar VXS - 9.3 Calculations for Braking Resistors; 9.4 Minimum Braking Resistor Values

9.3 Calculations for Braking Resistors
The data necessary for the calculations:
Inverter Jaguar VXS 150-1, (1.5kW,
240V 1-phase)
Motor* Rated power, P = 1.5kW
Speed, N
L
= 1420rpm
Inertia, J
M
= 0.0035 kg m
2
Load* Inertia, J
L
= 0.205 kg m
2
Resistive torque M
R
= 0.49 Nm
*Manufacturers’ data
Maximum DC bus voltage
Nominal DC bus voltage = AC input line volt-
age multiplied by √2. A margin above nomi-
nal voltage is necessary to allow for the
switching level of the braking transistor.
∴ Max. DC bus voltage is:
(240 x √2) + 40 = 380V DC
Desired braking performance
Duty cycle = 30 seconds
Deceleration time to standstill (ramp
down), ∆t = 2 seconds
56
The working:
Angular shaft speed, ω
N
ω
N
=
2πN
L
=
2π x 1420
= 148.7 rad/s
60 60
∴ maximum torque
=
P
=
1500
= 10.08 Nm
ω
N
148.7
Total system inertia J
T
J
T
= J
M
+ J
L
= 0.2085 kg m
2
and required braking torque, M
b
=
J
T
x
∆ω
= 0.2085 x
148.7
= 15.5 Nm
∆t2
Motor braking torque
M
M
= M
b
- M
R
= 15.01 Nm
Instantaneous braking power
P
b
= M
M
x ω
N
= 15.01 x 148.7 = 2232 W
Average power during one cycle (rating of the
resistor)
= 2232 x
2
= 149W
30
Resistor ohmic value
=
(DC bus max. V)
2
=
380
2
=65Ω
P
b
2232
These are the optimum values for the resistor
to be selected. As resistors are manufactured
in standard sizes, choose a rating of 150W or
above, and the closest ohmic value to 65Ω.
For further advice, and for a supply of braking
resistors, please consult IMO Precision
Controls Ltd.
9.4 Minimum Braking Resistor Values
Inverter type VXS… 20-1 40-1 75-1 150-1 220-1 40-3 75-3 150-3 220-3 400-3
Rating Ω NA 100 100 40 40 200 200 160 160 130
CAUTION The Jaguar VXS inverter will be damaged if a
braking resistor is applied having an ohmic value less than
the appropriate minimum shown in the table below.