Fuji Electric FRENIC-MEGA, Instruction Manual

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5-74
Ch
ap
. 5
FUNCTION C
O
DES
F codes
„ V/f control with speed sensor
Applying any load to an induction motor causes a rotational slip due to the motor characteristics, decreasing the motor
rotation. Under V/f control with speed sensor, the inverter detects the motor rotation using the encoder mounted on the
motor shaft and compensates for the decrease in slip frequency by the PI control to match the motor rotation with the
reference speed. This improves the motor speed control accuracy.
„ Dynamic torque vector control with speed sensor
The difference from "V/f control with speed sensor" stated above is to calculate the motor torque matched to the load
applied and use it to optimize the voltage and current vector output for getting the maximal torque out of a motor.
This control is effective for improving the system response to external disturbances such as load fluctuations, and the motor
speed control accuracy.
„ Vector control without speed sensor
This control estimates the motor speed based on the inverter's output voltage and current to use the estimated speed for
speed control. It also decomposes the motor drive current into the exciting and torque current components, and controls each
of those components in vector. No PG (pulse generator) interface card is required. It is possible to obtain the desired
response by adjusting the control constants (PI constants) using the speed regulator (PI controller).
The control regulating the motor current requires some voltage margin between the voltage that the inverter can output and
the induced voltage of the motor. Usually a general-purpose motor is so designed that the voltage matches the commercial
power. Under the control, therefore, it is necessary to suppress the motor terminal voltage to the lower level in order to
secure the voltage margin required.
However, driving the motor with the motor terminal voltage suppressed to the lower level cannot generate the rated torque
even if the rated current originally specified for the motor is applied. To ensure the rated torque, it is necessary to increase
the rated current. (This also applies to vector control with speed sensor.)
This control is not available in MD-mode inverters, so do not set F42 data to "5" for those inverters.
„ Vector control with speed sensor
This control requires an optional PG (pulse generator) and an optional PG interface card to be mounted on a motor shaft and
an inverter, respectively. The inverter detects the motor's rotational position and speed according to PG feedback signals and
uses them for speed control. It also decomposes the motor drive current into the exciting and torque current components, and
controls each of components in vector.
It is possible to obtain the desired response by adjusting the control constants (PI constants) using the speed regulator (PI
controller).
The control enables speed control with higher accuracy and quicker response than vector control without speed sensor.
Since slip compensation, dynamic torque vector control, and vector control with/without speed sensor use motor
parameters, the following conditions should be satisfied to obtain full control performance.
• A single motor should be controlled per inverter.
• Motor parameters P02, P03, P06 to P23, P55 and P56 are properly configured. Or, auto-tuning (P04) is
performed.
• Under dynamic torque vector control, the capacity of the motor to be controlled is two or more ranks lower than
that of the inverter; under vector control with/without speed sensor, it is the same as that of the inverter.
Otherwise, the inverter may not control the motor due to decrease of the current detection resolution.
• The wiring distance between the inverter and motor is 164 ft (50 m) or less. If it is longer, the inverter may not
control the motor due to leakage current flowing through stray capacitance to the ground or between wires.
Especially, small capacity inverters whose rated current is also small may be unable to control the motor correctly
even when the wiring is less than 164 ft (50 m). In that case, make the wiring length as short as possible or use a
wire with small stray capacitance (e.g., loosely-bundled cable) to minimize the stray capacitance.