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

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

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

Filter and motor models IM m w s u f C L i dc A

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

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

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

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

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

Experimental results (3) Measured Reference Measured Reference Reference Estimated

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