The additional signal can be obtained
by a suitable estimation of the motor CMcurrent by sensing
the CM voltage at the inverter terminals and applying it to a simple equivalent circuit reproducing the CM high-frequency
motor impedance. In practice, the need for the knowledge of
the CM high-frequency motor model is not a limitation, since
the most relevant CM phenomenon, to be reproduced, is tied to
the front-end capacitance toward ground. Therefore, the motor
model can be approximated by only this capacitance, whose
value is nearly constant for induction motors belonging to a
Fig. 2 shows a block diagram of the proposed active filter,
where F(s) is a low-pass filter, T(s) is a transfer function,
including a linear amplifier, a power amplifier, and a commonmode
transformer (CMT) and G(s) is the transfer function of
the CM current estimator. Each block is described in detail in
the next section.
The additional signal can be obtained
by a suitable estimation of the motor CMcurrent by sensing
the CM voltage at the inverter terminals and applying it to a simple equivalent circuit reproducing the CM high-frequency
motor impedance. In practice, the need for the knowledge of
the CM high-frequency motor model is not a limitation, since
the most relevant CM phenomenon, to be reproduced, is tied to
the front-end capacitance toward ground. Therefore, the motor
model can be approximated by only this capacitance, whose
value is nearly constant for induction motors belonging to a
Fig. 2 shows a block diagram of the proposed active filter,
where F(s) is a low-pass filter, T(s) is a transfer function,
including a linear amplifier, a power amplifier, and a commonmode
transformer (CMT) and G(s) is the transfer function of
the CM current estimator. Each block is described in detail in
the next section.
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