Danfoss FC 300 Design Manual page 41

FC 300 Design Guide
K is the gain at which the oscillation is obtained.
u
Type of Control
PI-control
PID tight control
PID some overshoot
Table 1: Ziegler Nichols tuning for regulator, based on a stability boundary.
Experience has shown that the control setting according to the Ziegler Nichols rule provides a
good closed-loop response for many systems. The process operator can perform final tuning of
the control iteratively to yield satisfactory control.
Step-by-step Description:
Step 1:
mum value, while the differentiation time is selected to zero.
Step 2:
tained oscillations) and the critical value of gain,
Step 3:
Step 4:
3.4.1. General Aspects of EMC Emissions
Electrical interference is usually conducted at frequencies in the range of 150 kHz to 30 MHz.
Airborne interference from the drive system in the range of 30 MHz to 1 GHz is generated from
the inverter, motor cable and motor.
As shown in the illustration below, capacitive currents in the motor cable coupled with a high dV/
dt from the motor voltage generate leakage currents.
The use of a shielded motor cable increases the leakage current (see illustration below), because
shielded cables have higher capacitance to ground than non-shielded cables. If the leakage current
is not filtered, it will cause greater interference on the line power supply in the radio frequency
range below approximately 5 MHz. Because the leakage current (I
through the shield (I
shielded motor cable according to the below figure.
The shield reduces the radiated interference, but increases the low-frequency interference in the
line power supply. The motor cable shield must be connected to the adjustable frequency drive
enclosure as well as on the motor enclosure. This is best done by using integrated shield clamps
so as to avoid twisted shield ends (pigtails). These increase the shield impedance at higher fre-
quencies, which reduces the shield effect and increases the leakage current (I
If a shielded cable is used for the serial communication bus, relay, control cable, signal interface
and brake, the shield must be mounted on the enclosure at both ends. In some situations, how-
ever, it will be necessary to break the shield to avoid current loops.
Proportional Gain
K
0.45 *
u
K
0.6 *
u
K
0.33 *
u
Select only proportional control, meaning that the integral time is selected to the maxi-
Increase the value of the proportional gain until the point of instability is reached (sus-
Measure the period of oscillation to obtain the critical time constant,
Use the table above to calculate the necessary PID control parameters.
), there will in principle only be a small electro-magnetic field (I
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3. Introduction to FC 300
Integral Time Differentiation
Time
P
0.833 * -
u
P
0.5 * 0.125 *
u
P
0.5 * 0.33 *
u
K
, is reached.
u
) is carried back to the unit
1
P
u
P
u
P .
u
) from the
4
).
4
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