Mitsubishi Electric FR-A700 Technical Manual page 442

3.1 Inverter selection
3.1.1 Principle and control method of the inverter
(1) Principle
common
AC Voltage
MCCB
Power
supply
Converter circuit
Inverter structure
The inverter rectifies commercial power into a DC
Voltage once in the converter circuit and converts it
into an AC Voltage of desired frequency in the
inverter circuit.
The speed N of the induction motor is expressed by
the following formula:
120 f(frequency)
N =
P(number of motor poles)
Where S is motor slip
By changing the frequency (f) with the inverter, the
motor speed can be changed freely.
Actually, when the frequency (f) is changed, the
output voltage (V) is also changed to produce a
sufficient motor torque.
Item V/F Control
Motor used with Standard motor
inverter (Mitsubishi, others)
Start several motors
Enabled
at the same time
Auto tuning function Not necessary
1Hz: 30% or less
Starting torque
3Hz: 30%
low speed torque
6Hz: 80%
Speed detector Not necessary
Speed control range 1 : 10
2 to 5%
Speed variation ratio Depends on load
magnitude
Torque control Disabled
Speed control Enabled
Position control Disabled
Control response
10 to 20rad/s
level
Fan, pump,
Applications General industrial
machines, etc.
Applicable Inverters
common
Inverter
AC Voltage
DC
Voltage
Inverter circuit
(1-S) [r/min]
Comparison between Mitsubishi Inverter Control Method
Simple Magnetic General-Purpose
Flux Vector Magnetic Flux
Control Vector Control
Standard motor Standard motor
(Mitsubishi, others) (Mitsubishi, others)
Disabled
Not necessary
3Hz:120%
(when slip
compensation is set)
compensation is set)
Not necessary Not necessary
1 : 15 1 : 60 (driving)
2 to 5%
Depends on load Depends on load
magnitude
Disabled
Enabled
Disabled
20 to 30rad/s
General industrial
Fan, pump,
machines, transfer
General industrial
machines, etc.
applications, etc.
F700 E700
common
(common)
(2) Control Method
1) V/F control
When changing the frequency (f), the inverter
controls to make the ratio (V/f) of output frequency
(f) to output voltage (V) constant. This method is
IM
the basic inverter control method and called V/F
control.
Motor
In this method, a sufficient torque will not be
developed since the actual effective voltage
decreases due to a voltage drop in the wiring and
motor's primary winding. This phenomenon has
greater influence as the speed gets lower. (Low-
speed torque will be short)
Hence, a voltage drop is pre-estimated to increase
the voltage (torque boost
continuous line in the figure below to compensate
for the torque shortage at low speed.
To make up for this disadvantage, we developed
Advanced magnetic flux vector control and Real
sensorless vector control.
Torque
boost
* If the torque boost is too large, the torque is developed
sufficiently but an excessive current flows, causing the inverter
to be more easily resulting in an overcurrent (OCT) trip.
Advanced
Magnetic Flux
Vector Control
Standard motor
(Mitsubishi, others)
Disabled Disabled
Equipped as Equipped as
standard standard
1Hz:150%
3Hz:200%
(3.7K or less) 0.5Hz: 150%
(when slip
Not necessary
1 : 120 (driving)
2 to 5% 1%
Not influenced by
magnitude load
Disabled Disabled
Enabled Enabled
Disabled Disabled
20 to 30rad/s 20 to 30rad/s
General industrial
machines, transfer
machines, lift machines, lift
applications, etc
D700 A700 E700
476
SELECTION
common
) as indicated by the
*
V/f = constant
0 Frequency (f)
Real Sensorless
Vector Control
Vector Control
Standard motor Dedicated motor (Mitsubishi)
(Mitsubishi, others) Standard motor (Mitsubishi, others)
Disabled
Equipped as
Equipped as standard
standard
Dedicated motor
0.3Hz: 200/150% 0Hz:150%
(3.7K or less/5.5K or Standard motor
more) 0Hz:200/150%
(3.7k or less/5.5k or more)
Not necessary
1 : 200 (driving)
1%
Not influenced by
Not influenced by load
load
Enabled
Enabled
Disabled
120rad/s
(standard motor)
General industrial
machines, transfer Transfer machines, lift application
machines, lift line control, etc.
applications, etc.
A700 A700+A7AP
Disabled
Necessary
1 : 1500
0.01%
Enabled
Enabled
Enabled
300rad/s