Abstract:
Adjustable speed drives are essential for energy savings in industries. The availability of modern permanent magnets (PM) with considerable energy density led to the development of dc machines with PM field excitation in 1950s.Traditionally DC motors have been used for the adjustable speed drives. Now-a-days vector controlled ac drives are replacing the do drives because ac motors are more robust and need minimum maintenance due to absence of commutators and brushes. Among the ac motors permanent magnet synchronous motors (PMSM) are superior to squirrel cage induction motors for servo applications as it has fast response, higher torque to inertia ratio, higher power, density and higher efficiency. Further, the permanent magnet ac motors do not need magnetizing current from stator side. The magnets on rotor are of high resistivity materials thus losses in the rotor are negligible.
In the PWM inverter fed PMSM control structure, the rotor position and speed are sensed. The actual rotor speed is subtracted from a reference speed and speed error is processed in speed controller to obtain a reference torque. The torque command is divided with the PMSM torque constant to obtain torque component (q-axis component) of the reference current. The field component (d-axis component) of the reference current is kept zero as the PMSM surface mounted type in which demagnetization is avoided. Using torque and field components of the reference current and rotor position angle, the park's transformation is applied to transform dq-axis references currents to abc-axis reference currents. The actual three phase stator currents are subtracted from the abc-axis references currents and the currents errors are passed through fed to sinusoidal pulse width modulated (SPWM) current controller, which provides controlled switching signals to.the inverter switches. The controlled switching of the inverter feeds regulated current to the .PMSM.
Mathematical models of the PMSM and vector control of the drive is developed. The models are used for. associate controller designs and simulation of the drive. The PMSM speed controller is investigated with PI, Fuzzy, Hybrid and FPPI speed controllers. And the drive performance is compared with these speed controllers. The SPWM technique is implemented with I-8438 embedded controller.
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