9.10 Problems

Problem 9.1

Design the differential filter (normal mode filter) with L, C, and R dampings for the drive with a voltage inverter, and induction motor. The filter topology is presented in Figure 9.29. The three-phase induction motor data is P_{n} = 3 kW, U_{n} = 380 V (Y connected), and I_{n} = 6.4 A. The inverter DC supply voltage is 540 V, transistor switching frequency is f_{imp} = 3.3 kHz, and inverter output maximal frequency is f_{out 1h} = 100 Hz. The desired system property is switching ripple current ΔI_{s} = 20%.

Solution: First the inductor is selected. The motor ripple current is

(9.185)

The L_{1} inductance is

(9.186)

The voltage drop on L_{1} for the motor nominal frequency f_{n} and nominal load is

(9.187)

The assumed L_{1} = 9.5 mH satisfies the limiting current ripple and permitted voltage drop.

The L_{1} nominal current is equal to the motor nominal I_{L1n} = I_{n} = 6.4 A.

Next the C_{1} is selected. The C_{1} is related to the assumed resonant frequency f_{res}. The value of the f_{out 1h} should satisfy:

(9.188)

so the resonant frequency is selected:

(9.189)

hence:

(9.190)

For the capacitor, the nominal ...

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