Active phase coil inductance sensing

A circuit for commutating a conduction cycle of a motor phase of a switched reluctance motor comprising:

• a first switching device;
• a second switching device connected in series with said first switching device;
• a phase coil connected in series between said first switching device and said second switching device, said first and second switching devices connected in parallel to a power supply and provided for selectively adjusting a level of a current in said phase coil;
• means for closing said first and said second switching devices to initiate a conduction cycle by causing said current to flow through said phase coil;
• means for modulating only a selected one of said first and said second switching devices to control said current level between a local maximum level and a local minimum level;
• means for measuring a first rise time for said current level to rise from said local minimum level to said local maximum level;
• means for measuring a first fall time for said current level to fall from said local maximum level to said local minimum level;
• means for calculating a value of an active phase time ratio using said first rise time and said first fall time;
• and,
• means for opening said first and said second switching devices when said active phase time ratio value reaches a predetermined threshold value to thereby commutate said conduction cycle.

A circuit for commutating a conduction cycle of a motor phase of a switched reluctance motor comprising:

• a first switching device;
• a second switching device connected in series with said first switching device;
• a phase coil connected in series between said first switching device and said second switching device, said first and second switching devices connected in parallel to a power supply and provided for selectively adjusting a level of a current in said phase coil;
• a current sensor for monitoring a current level through said phase coil;
• and
• a microcontroller responsive to said current sensor for modulating only a selected one of said first and said second switching devices to control a level of said current between a local minimum level and a local maximum level, and for commutating said conducting cycle when an active phase time ratio derived from a first rise time and a first fall time of said current level reaches a predetermined threshold, wherein said microcontroller is programmed with a first set of program steps.