NORDAC PRO (SK 500P) – Users Manual for Frequency Inverters
64 BU 0600 en-2319
4.2 Selecting the operating mode for motor control
The frequency inverter is able to control motors with all efficiency classes (IE1 to IE4). Motors which
we manufacture are produced as asynchronous motors in efficiency classes IE1 to IE3, whereas IE4
motors are produced as synchronous motors.
Operation of IE4 motors has many special features with regard to the control technology. In order to
enable the optimum results, the frequency inverter was specially designed for the control of NORD IE4
motors, whose construction corresponds to an IPMSM type (Interior Permanent Magnet Synchronous
Motor). In these motors, the permanent magnets are embedded in the rotor. The operation of other
brands must be checked by NORD as necessary. Also refer to the technical information TI 80-0010
"Planning and commissioning guidelines for NORD IE4 motors with NORD frequency inverters“.
4.2.1 Explanation of the operating modes (P300)
The frequency inverter provides different operating modes for the control of a motor. All operating
modes can be used with either an ASM (asynchronous motor) or a PMSM (Permanent Magnet
Synchronous Motor), however various constraints must be complied with. In principle, all these
methods are "flux oriented control methods.
1. VFC open-loop mode (P300, setting "0")
This operating mode is based on a voltage-governed flux oriented control method (Voltage Flux
Control Mode (VFC)). This is used for both ASMs as well as PMSMs. In association with the
operation of asynchronous motors this is often referred to as "ISD control".
Control is carried out without the use of encoders and exclusively on the basis of fixed parameters
and the measurement results of actual electrical values. No specific control parameter settings are
necessary for the use of this mode. However, parameterisation of the precise motor data is an
essential prerequisite for efficient operation.
As a special feature for the operation of an ASM there is also the possibility of control according to
a simple V/f characteristic curve. This mode of operation is important if several motors which are
not mechanically coupled are to be operated with a single frequency inverter, or if it is only possible
to determine the motor data in a comparatively imprecise manner.
Operation according to a V/f characteristic curve is only suitable for drive applications with relatively
low demands on the quality of speed control and dynamics (ramp times ≥ 1 s). For machines which
tend to have relatively large mechanical vibrations due to their construction, control according to a
V/f characteristic curve can also be advisable. Typically, V/f characteristic curves are used to
control fans, certain types of pump drives or agitators. Operation according to a V/f characteristic
curve is activated via parameters (P211) and (P212) (each set to "0").
2. CFC closed-loop mode (P300, setting "1")
In contrast to the "0" setting "VFC open-loop mode" this is a form of control with current controlled
flux orientation (Current Flux Control). For this operating mode, which for ASMs is functionally
identical to the previously used designation "servo control", use of an encoder is essential. The
precise speed behaviour of the motor is detected and included in the calculation for control of the
motor. Determination of the position of the rotor is also possible through the use of the encoder,
whereby the initial value of the rotor position must also be determined for the operation of a PMSM.
This enables even more precise and rapid control of the drive unit.
This operating mode provides the best possible results for the control behaviour of both ASMs and
PMSMs and is especially suitable for lifting equipment applications or applications with
requirements for the highest possible dynamic behaviour (ramp times ≥ 0,05 sec). The greatest
advantage of this operating mode is gained in combination with an IE4 motor (energy efficiency,
dynamics, precision).
3. CFC open-loop –mode (P300, setting "2")
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