Direct Eigen Control for Induction Machines and Synchronous Motors

4

Inverter Supply – LC Filter

We will follow the same approach as for the motors, applying the method to the inductance–capacitor power filter; in general this type of filter is used in series with the voltage inverter supply.

This filter makes it possible to prevent supply voltage variations being transmitted immediately to the inverter; it also filters consequences of the DC supply voltage switching by the inverter. It is a passive low-pass filter of the second order; its cut-off frequency must be lower than the frequencies to be filtered, in particular frequencies resulting from the rectification of the AC feeding voltage; the electromagnetic energy reserve of the LC filter is directly dependent on the duration of disturbances to be damped.

This kind of filter must have an excellent efficiency at the power which goes through it. For this, the inductance’s resistance has to be minimized. This results in the damping of this filter being very low and thus its Q-factor is high.

Any extraction of active power from the filter, higher than a small threshold, causes divergent oscillations at the natural filter frequency (Jacquot, 1995; Mosskull, 2005).

To avoid this phenomenon, it is thus necessary to damp these oscillations in an active way by using the only available control variable, which is the current feeding inverter (Délémontey, 1995; Délémontey et al., 1995).

We will now study its modeling.

4.1 Electrical Equations and Equivalent Circuit

4.1.1 Definitions and Notations

The filter inductance ...