Fuji Electric FRENIC-Ace series - Page 266

5.3 Description of Function Codes
5-96
F43, F44
Current limiter (Mode selection and Level)
Related function codes: H12 Instantaneous overcurrent limiting (Mode selection)
When the output current of the inverter exceeds the level specified by the current limiter (F44), the inverter
automatically manages its output frequency to prevent a stall and limits the output current. According to limit value
based on Inverter’s rated current, the default setting of the current limiter is 160% for HHD/HD mode, and 130% for
HND/ND mode, respectively (Initial value is automatically written when selecting ND/HD/HND/HHD by function
code F80) If overload current, higher than the current limiter level, flows instantaneously so that the output
frequency decrease due to the current limiter causes a problem, consider to increase the current limiter level.
The current limiter mode should be also selected with F43. If F43 = 1, the current limiter is enabled only during
constant speed operation. If F43 = 2, it is enabled during both of acceleration and constant speed operation.
Choose F43 = 1 if you need to run the inverter at full capability during acceleration and to limit the output current
during constant speed operation.
■ Mode selection (F43)
F43 selects the motor running state in which the current limiter becomes active.
F43 data
Running states that enable the current limiter
During acceleration During constant speed During deceleration
0 Disabled Disabled Disabled
1 Disabled Action Disabled
2 Action Action Disabled
■ Level (F44)
F44 specifies the operation level at which the output current limiter becomes activated, as a ratio of the inverter
rating.
• Data setting range: 20 to 200 (%) of rated current of the inverter
(Inverter’s rated current changes according to the setting value of function code F80.)
■ Instantaneous overcurrent limiting (Mode selection) (H12)
H12 specifies whether the inverter invokes the current limit processing or enters the overcurrent trip when its
output current exceeds the instantaneous overcurrent limiting level. Under the current limit processing, the inverter
immediately turns OFF its output gate to suppress the further current increase and continues to control the output
frequency.
H12 data Function
0 Disable (An overcurrent trip occurs at the instantaneous overcurrent limiting level.)
1 Enable (An instantaneous overcurrent limiting operation is activated)
If any problem could occur when the motor torque temporarily drops during current limiting processing, it is
necessary to cause an overcurrent trip (H12 = 0) and actuate a mechanical brake at the same time.
• Since the current limit operation with F43 and F44 is performed by software, it may cause a delay in
control. If you need a quick response current limiting, also enable the instantaneous overcurrent
limiting with H12.
•
If an excessive load is applied when the current limiter operation level is set extremely low, the
inverter will rapidly lower i
ts output frequency. This may cause an overvoltage trip or dangerous
turnover of the motor rotation due to undershooting. Depending on the load, extremely short
acceleration time may activate the current limiting to suppress the increase of the inverter ou
tput
frequency, causing hunting (undesirable oscillation of the system) or activating the inverter
overvoltage trip (alarm 0u
). When specifying the acceleration time, therefore, you need to take into
account machinery characteristics and moment of inertia of the load.
• The torque limiter and current limiter are very similar in function. If both are activated concurrently,
they may conflict with each other and cause hunting. Avoid concurrent activation of these limiters.
•
Vector control with speed sensor
itself contains the current control system, so it disables the current
limiter specified by F43 and F44, as well as automatically disabling the instantaneous overcurrent
limiting (specified by H12). Accordingly, the inverter causes an ove
rcurrent trip when its output current
exceeds the instantaneous overcurrent limiting level.