This paper proposes a novel 4-level converter and
instantaneous switching angle detector for a high speed SRM
(Switched Reluctance Motor) drive. The excitation current cannot be sufficiently built up . the demagnetization
current can be easily extended to the negative torque region.The 4-level converter proposed here has additional charge capacitor and an active power switch compare than a conventional asymmetric converter. the high charged voltage of additional capacitor is supplied to the phase winding in the fast excitation mode. Also the demagnetization phase current is decreased fast during the recharging of capacitor in demagnetization mode.

THE CHARACTERISTICS OF HIGH SPEED SRM
The Asymmetric converter is simple and is free for arm-short problem of the power. Its mode 1 is the wheeling mode which can supply zero voltage and the mode 2 is the demagnetization mode and the mode 3 when the stored magnetic energy is feed-back to the source. In order to secure enough time to build-up the desire phase current the advance angle can be adjusted according to the motor speed. According to increasing speed, the advance angle is larger and turn-on position may be advanced the previous negative torque region. But in the high speed range, the actual excited phase current could not properly build-up due to switching position
errors.

THE PROPOSED SPEED CONTROLLER
-4-level inverter:
In order to have a fast build-up of the excitation current,high switching voltage is required. The proposed 4-level converter supplies the high voltage from the additional charge capacitor.

The instantaneous switchingposition detector:
As stated, switching position error decreases the control perfornance in a high speed range. There is a 16bit QEP counter and 3-channel comparator, the encoder pulse is multiplied by four and the counter value is shifted according to the mechanical structure of the motor.

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