Detailed Parameter Description; Symbols; Introduction; Control Modes - WEG CFW08 Vector inverter User Manual

6.1 SYMBOLS

6.2 INTRODUCTION

6.2.1 Control Modes

6.2.2 V/F Control

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DETAILED PARAMETER DESCRIPTION

This chapter describes in detail all CFW-08 parameters and functions.
Please find below some symbols used in this chapter:
AIx = Analog input number x.
AO = Analog output.
DIx = Digital input number x.
F* = Frequency reference. This is the frequency value that indicates the
desired motor speed at the inverter output.
F = Input frequency of the acceleration and deceleration ramp.
e
F = Maximum output frequency, defined at P134.
max
F = Minimum output frequency, defined at P133.
min
F = Output frequency - frequency applied to the motor.
s
I = Rated inverter output current (rms), in Ampères (A). This value is
nom
defined in P295.
I = Inverter output current.
s
I = Active current at inverter output, i.e., it is the compoment of the total
a
motor current proportional to active electric power absorbed by the motor.
RLx = Relay output number x.
U = DC link voltage in the DC link circuit.
d
This section describes the main concepts related to the CFW-08 frequency
inverter.
As already informed in section 2.3, CFW-08 has in the same product a
V/F control and a sensorless vector control (VVC: "voltage vector control").
The user must choose one of them. Please find below a description of
each control mode.
This control mode is based on the constant V/F curve(P202=0 - linear V/
F curve). Its performance is limited at low frequencies as function of the
voltage drop in the stator resistance, that causes a significant magnetic
flow reduction in the motor air gap and consequently reducing the motor
torque. This deficiency should be compensated by using manual and
automatic boost torque (IxR compensations), that are set manually and
depend on the user experience.
In most applications (for instance: centrifugal pumps and fans) the setting
of these functions is enough to obtain the required performance. But there
are applications that require a more sophisticated control. In these cases
it´s recommended the use of the sensorless vector control, that will be
described in the section below.
In V/F control, the speed regulation, that can be obtained by setting
properly slip compensation can be maintained within 1 to 2% of the rated
speed. For instance, for a IV pole motor/60Hz, the minimum speed variation
at no load condition and at rated load can be maintained between 18 and
36rpm.
CHAPTER 6