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 Pn = 3 kW, Un = 380 V (Y connected), and In = 6.4 A. The inverter DC supply voltage is 540 V, transistor switching frequency is fimp = 3.3 kHz, and inverter output maximal frequency is fout 1h = 100 Hz. The desired system property is switching ripple current ΔIs = 20%.
Solution: First the inductor is selected. The motor ripple current is
The L1 inductance is
The voltage drop on L1 for the motor nominal frequency fn and nominal load is
The assumed L1 = 9.5 mH satisfies the limiting current ripple and permitted voltage drop.
The L1 nominal current is equal to the motor nominal IL1n = In = 6.4 A.
Next the C1 is selected. The C1 is related to the assumed resonant frequency fres. The value of the fout 1h should satisfy:
so the resonant frequency is selected:
For the capacitor, the nominal ...