Method and apparatus for flux and torque sensing in electrical machines

A method of determining the air gap flux in an electrical machine of the type having a stator with a plurality of stator slots therein and a plurality of coils in the slots, the coils forming the winding for each phase of the machine arranged in at least one phase belt having series connected coils distributed over at least two slots, and also including a rotor spaced from the stator to define an air gap therebetween, comprising the steps of:

• (a) measuring the voltages across two of the distributed coils in a phase belt for at least one phase of the machine;
• (b) subtracting the measured voltage across one coil in each such phase belt from the measured voltage across the other coil in the phase belt to provide a voltage difference for each such phase;
• and
• (c) integrating the voltage differences for each such phase to provide signals which are indicative of flux in the air gap.

Apparatus for determining the electromagnetic torque in an electrical machine of the type having a stator with a plurality of stator slots therein and a plurality of coils in the slots, the coils forming the winding for each phase of the machine arranged in at least one phase belt having series connected coils distributed over at least two slots, a rotor spaced from the stator to define an air gap therebetween, and also including electrical leads extending to connection to ends of two of the distributed coils in a phase belt for each phase of the machine such that the voltage across each such coil can be measured at the leads, comprising:

• (a) means for subtracting the voltage at the leads across one coil in each phase belt from the voltage across the other coil in the phase belt to provide a voltage difference signal for a number of phases sufficient to determine the flux in the machine;
• (b) means for integrating the voltage difference signal for each phase to provide signals which are indicative of air gap flux in an axis along one phase chosen as the q axis and the air gap flux along an axis in quadrature therewith chosen as the d axis;
• (c) means for measuring the stator phase currents and providing signals indicative thereof;
• and
• (d) means, receiving the signals indicative of flux in the q and d axes and the stator phase currents, for determining electromagnetic torque and providing a signal indicative thereof as a function of the signals indicative of the flux in the q and d axes and of the stator phase currents.

A method of determining the electromagnetic torque in an AC electrical machine of the type having a stator with a plurality of stator slots therein and a plurality of coils in the slots, the coils forming the winding for each phase of the machine arranged in at least one phase belt having series connected coils distributed over at least two slots, and also including a rotor spaced from the stator to define an air gap therebetween, comprising the steps of:

• (a) measuring the voltages across two of the distributed coils in a phase belt for a number of phases sufficient to determine the flux in the machine;
• (b) subtracting the measured voltage across one coil in each phase belt from the measured voltage across the other coil in the phase belt to provide a voltage difference for each phase;
• (c) integrating the voltage differences for each phase to provide signals which are indicative of air gap flux in an axis along one phase chosen as the q axis and of the air gap flux along an axis in quadrature therewith chosen as the d axis;
• (d) measuring the stator phase currents and providing signals indicative thereof;
• and
• (e) calculating the electromagnetic torque of the machine as a function of the signals indicative of the flux in the q and d axes and of the stator phase currents.

A control system for regulating an inverter supplying variable frequency power to an electrical machine of the type having a stator with a plurality of stator slots therein and a plurality of coils in the slots, the coils forming the windings for each phase of the machine arranged in at least one phase belt having series connected coils distributed over at least two slots, a rotor spaced from the stator to define an air gap therebetween, and also including electrical leads extending to connection to ends of two of the distributed coils in a phase belt for at least one phase of the machine such that the voltage across each such coil can be measured at the leads, comprising:

• (a) means for subtracting the voltage at the leads across one coil in each phase belt from the voltage across the other coil in the phase belt to provide a voltage difference signal for a sufficient number of phases to determine the flux in the machine;
• (b) means for integrating the voltage difference signal for each phase to provide signals which are indicative of air gap flux in an axis along one phase chosen as the q axis and the air gap flux along an axis in quadrature therewith chosen as the d axis;
• (c) means for measuring the stator phase currents and providing signals indicative thereof;
• (d) means, receiving the signals indicative of flux in the q and d axes and the stator phase currents, for determining the electromagnetic torque and providing a signal indicative thereof as a function of the signals indicative of the flux in the q and d axes and of the stator phase current;
• and
• (e) control means responsive to the signals indicative of flux and electromagnetic torque for controlling the operation of the inverter to provide power to the electrical machine to drive it to produce flux and torque signals which are controlled to follow selected values of torque and flux.