10 Questions
What is the primary concern when applying -Vdc/2 to the converter during the fall time?
To avoid negative torque generation
What is the expression for the output torque of a synchronous reluctance machine?
Te = (Ld - Lq)Is2 sin 2δ
What is the main difference between an interior permanent magnet synchronous machine and a synchronous reluctance machine?
The presence of magnets in the rotor cavity
What is the characteristic of the rotor of a synchronous reluctance motor?
It contains no magnets or copper
What is the purpose of d-axis excitation in a synchronous reluctance machine?
To generate reluctance torque
What is the advantage of synchronous reluctance machines in high-speed applications?
Their robust rotor design
What is the direction of the excitation in a synchronous reluctance machine?
Both d-axis and q-axis
What is the characteristic of the inductance in a synchronous reluctance machine?
High inductance in the d-axis
What is the type of torque generated by a synchronous reluctance machine?
Reluctance torque
What is the advantage of using a synchronous reluctance machine instead of an interior permanent magnet synchronous machine?
Robust rotor design
Study Notes
Permanent Magnet Assisted Synchronous Reluctance Machine
- Induced voltage by rotor magnets opposes the voltage drop across the q-axis inductance, improving the power factor.
- The machine has Ld > Lq and the output torque can be maximized at a torque angle of 45°.
Synchronous Reluctance Motor
- Terminal voltage can be represented by V = RI + jX d I d + jX q I q.
- The machine operates at low power factor (PF = cos Φ), requiring a larger inverter compared to the induction machine.
Power Factor Improvement
- Adding permanent magnets in the rotor q axis can improve the power factor of the synchronous reluctance machine.
SRM Drive System
- The current fall time is longer than the classical converter, as only -Vdc/2 is applied through this period.
- To avoid negative torque generation, the phases current should go down to zero before dL/dθ becomes negative.
Synchronous Reluctance Machines
- The machine can still operate with the reluctance torque when the magnets are removed from the rotor cavity.
- The output torque can be represented by Te = Tr = (Ld - Lq)Is^2 sin 2δ.
Characteristics
- The rotor is very robust, containing no magnets or copper, making it suitable for high speed applications.
- High inductance is present on the d-axis.
Examples
- 4-pole synchronous reluctance motor.
- ABB synchronous reluctance motor.
This quiz covers the concept of permanent magnets in AC machines, focusing on the phasor diagram and the voltage equations. It explains how the induced voltage by the rotor magnets improves the power factor.
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