1. Janne Salomäki and Jorma Luomi
Vector Control of an Induction Motor Fed by a PWM Inverter with Output LC Filter
Janne Salomäki and Jorma Luomi

2. Contents Introduction Filter and motor models Cascade control system
Full-order observer
Results
Conclusion

3. Introduction
The output voltage of a PWM inverter consists of rectangular voltage pulses
An LC output filter provides motor friendly voltage, but the control of the system becomes more difficult
The paper presents a vector control method that does not need additional measurements

4. Filter and motor modelsIM m w s u f C L i dc A

5. Cascade control system
Measurements needed: inverter current, DC link voltage and rotor speed

6. Full-order observer Estimated rotor flux reference frame
The observer gain selection:
pole placement
constant gain
Symmetric Euler discretization

7. Full-order observer (2)
Observer poles with constant gain
magnification

8. Experimental results
Experiments were made with 2.2-kW four-pole induction motor (400 V, 50 Hz)
The cutoff frequency of the LC filter was 566 Hz

9. Experimental results (2)
Inverter voltage
Stator voltage
Inverter current
Stator current

10. Experimental results (3)
Measured
Reference
Measured
Reference
Reference
Estimated

11. Conclusion
When the inverter output voltage is filtered by an LC filter, the vector control of the induction motor can be based on nested control loops
As the system states are estimated, the only required measurements are the inverter current, DC link voltage and rotor speed
Simulation and experimental results show that the proposed method works properly