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Firmware version: M-01-12-01-000
This article explains how to set an AKD for driving an asynchronous machine, using an open loop V/Hz strategy. The article contains:
Table of Contents
Introduction
The open loop volts/Hz (also known as Volt/Frequency) scalar control of an induction motor is by far a popular method of sped control because of its simplicity. For adjustable speed applications, frequency control is natural. However voltage is required to be proportional to frequency so that the flux (Fs = Vs/w) remains constant (see Fig. 1), neglecting the stator resistance Rs drop. MOTOR.VOLTRATED and MOTOR.VRATED have to be set according to machine parameters from data sheet. Then, the output V/Hz is automatically adjusted. This will work as long as the supplied voltage is high enough to allow the induction machine to reach the speed command. Since the algorithm neglects the voltage drop in the resistance, a boost voltage should be added so that the rated flux and corresponding full torque are available at zero or low speed. In AKD, this boost voltage is set through MOTOR.VOLTMIN.
Figure 1: Relationship Voltage/Frequency
Figure 2 shows the block diagram of the volts/Hz speed control method that is implemented in AKD.
Figure 2: V/Hz scheme
The velocity command can be obtained from three different sources, depending on DRV.CMDSOURCE:
- 0: Service
- 1: Field bus
- 3: Analog
Initial settings
| DRV.OPMODE = 1 | Velocity mode |
| MOTOR.TYPE = 2 | V/Hz speed control |
| FB1.SELECT = 1 | None feedback |
| DRV.ACC & DRV.DEC | Set according to induction machine mechanical dynamics |
Parameters
The following table shows which MOTOR parameters should be also configured for driving induction machines under V/Hz open-loop operation:
|
Keyword |
Induction Motor V/f Open Loop |
Description |
|
MOTOR.NAME |
Yes |
Set a name for customer motor |
|
MOTOR.TYPE |
Yes |
Set to motor type. For V/Hz, MOTOR.TYPE = 2 |
|
MOTOR.AUTOSET |
No |
No available in V/Hz |
|
MOTOR.IPEAK |
Yes |
Set to motor peak current (A). 150% of continuous current for NEMA motors |
|
MOTOR.ICONT |
Yes |
Set to motor continuous current (A) |
|
MOTOR.INERTIA |
Yes |
Set the motor inertia in kg cm2 |
|
MOTOR.KT |
No |
No necessary for Induction Motor |
|
MOTOR.LQLL |
No |
No necessary for V/Hz |
|
MOTOR.POLES |
Yes |
Set to motor poles |
|
MOTOR.VMAX |
Yes |
This is the maximum mechanical speed of the motor in RPM |
|
MOTOR.R |
Yes |
Set the stator winding resistance phase-to-phase in Ohms |
|
MOTOR.VOLTMAX |
Yes |
Motor max winding voltage. Ex: 230 VAC or 460VAC |
|
MOTOR.PHASE |
No |
No necessary for Induction Motor |
|
MOTOR.CTF0 |
Yes |
This is used to configure the thermal constant of the motor coil |
|
MOTOR.KE |
No |
No necessary for Induction Motor |
|
MOTOR.IMTR |
No |
No necessary for V/Hz |
|
MOTOR.IMID |
No |
No necessary for V/Hz |
|
MOTOR.VOLTRATED |
Yes |
This is the rated voltage for the V/HZ curve. |
|
MOTOR.VRATED |
Yes |
This is the rated velocity for the V/Hz curve |
|
MOTOR.VOLTMIN |
Yes |
V/Hz drive, this is the starting voltage of the V/Hz curve in %. Ex: 5V is 2.1% of 230V so set MOTOR.VOLTMIN to “2%” for 5V |
Variables for analysis
Following variables are available for analysis and supervision:
|
IL.CMD |
Since there is no cascade structure, no current loop is present. However, this shows a track similar to the speed command. The relationship is dependent on MOTOR.VRATED |
|
IL.FB |
Currently current at motor terminals |
Further information
KOLLMORGEN Europe Product Wiki : Induction Machine -General
KOLLMORGEN Europe Product WIKI : Sensorless Control for Induction Machines with S300-S700
KOLLMORGEN Europe Product WIKI : Operating Induction Machines S300-S700
Example
Considering the following IM:
|
Nominal voltage = 230/460V |
Nominal current = 8.75/5.05A |
4 poles |
|
Power: 2.20Kw |
Nominal speed = 1395 rpm |
|
|
cos(phi) = 0.82 |
Nominal frequency = 50Hz |
|
We set following parameters in AKD:
|
Parameter |
Value |
Parameter |
Value |
|
DRV.ACC & DRV.DEC |
10000rpm/s |
MOTOR.POLES |
4 |
|
DRV.OPMODE |
1 |
MOTOR.VMAX |
1600 rpm |
|
FB1.SELECT |
1 |
MOTOR.R |
1.12 ohm |
|
MOTOR.NAME |
NORD-ASM |
MOTOR.VOLTMAX |
240V |
|
MOTOR.TYPE |
2 |
MOTOR.VOLTRATED |
230 |
|
MOTOR.IPEAK |
13 A |
MOTOR.VRATED |
1395 rpm |
|
MOTOR.ICONT |
8.75 A |
MOTOR.VOLTMIN |
2% |
|
MOTOR.INERTIA |
6.2 kg cm2 |
|
|
Speed command: 1395 rpm
