Abstract
In this paper, the effect of 3-level inverter’s MOSFET switching at 33
different PWM frequencies, has been compared from 15 kHz to 2 MHZ, in
relation to control loop stability, transfer function’s coefficients
variation, system response and speed characteristics. The position of
rotor in 8 pole, wye-winding 7.5 Hp i.e., 5.5 kW with service factor of
1.15 (≈8.6 Hp), 72VDC, 85.6A, 14.27 Nm torque, with per phase insulation
temperature of 311 ◦ F, at an efficiency of 89.2% is estimated without
sensor using sliding mode observer implemented with field oriented
control algorithm. The decoupled flux and torque components are
controlled by discrete PI with anti-windup/reset and IIR filters. The
coefficients of IIR applied in the speed and SMO control block, and
other parameters like gain, ADC are mentioned along with the resulting
without SMO or with SMO closed loop transfer functions at each of these
33 frequencies along with the change in the coefficients of PI (errors,
Ki, Kp), of Iq, Id, field weakening, speed controllers are mentioned.
The 132 values, 33 values of e, Ki, Kp for each of these four
controllers at these 33 PWM frequencies are tabulated, which can be used
to design prototypes with higher power densities. The relative control
loop stability with SMO is analyzed and tabulated with gain, phase
margins along with eigen values of the characteristic equation.