General Aspects Of Emc Emissions - Danfoss FC 300 Design Manual

FC 300 Design Guide
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:
Step 1: Select only Proportional Control, meaning that the Integral time is selected to the
maximum value, while the differentiation time is selected to zero.
Step 2: Increase the value of the proportional gain until the point of instability is reached
(sustained oscillations) and the critical value of gain, K
Step 3: Measure the period of oscillation to obtain the critical time constant, P
Step 4: Use the table above to calculate the necessary PID control parameters.

General Aspects of EMC Emissions

"
Electrical interference is usually conducted at frequencies in the range 150 kHz to 30
MHz. Airborne interference from the drive system in the range 30 MHz to 1 GHz is
generated from the inverter, motor cable, and the 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 mains in the radio frequency range below approx. 5 MHz. Since
the leakage current (I
1
small electromagnetic field (I
The shield reduces the radiated interference but increases the low-frequency interference on the
mains. 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 frequencies,
which reduces the shield effect and increases the leakage current (I
If a shielded cable is used for Profibus, standard bus, relay, control cable, signal interface, and
brake, the shield must be mounted on the enclosure at both ends. In some situations, however,
it will be necessary to break the shield to avoid current loops.
40
Introduction to FC 300
Proportional Gain
0.45 * K
u
0.6 * K
u
0.33 * K
u
) is carried back to the unit through the shield (I
) from the shielded motor cable according to the below figure.
4
MG.33.B6.22 - VLT is a registered Danfoss trademark
Integral Time
0.833 * P
u
0.5 * P
u
0.5 * P
u
, is reached.
u
u
), there will in principle only be a
3
).
4
Differentiation Time
-
0.125 * P
u
0.33 * P
u
.