Control of a brushless electrical machine
AssigneeNidec SR Drives Ltd.
InventorsSteven Paul Randall, Mark John Cherney
Life of this patent
Estimating the term…
Abstract
A brushless electrical machine has at least one phase winding which produces torque to drive a load. The control system for the machine is able to vary the flux and current supplied to a phase so as to vary the torque output as a function of the rotor position. The energization is reduced at particular angles to produce a dip in the torque profile, thus ensuring that, if the drive stalls, it does so at a predetermined position, for example where the losses in the drive are minimized.
Claims20
A method of controlling a brushless electrical machine to produce an output, wherein the output is a torque or a force, the method comprising:
- energising a first phase of the machine in a conduction region between a switch-on point and a switch-off point and in response to an output demand, compensating for a nonlinear relationship between the output of the brushless electrical machine and a current in the first phase to produce a first output between an upper and a lower output limit, respectively higher and lower than the output demand,
- wherein the first phase is energised to produce the first output between the upper and lower output limits from a beginning of the conduction region to a detent region and from the detent region to an end of the conduction region and to produce a second output at a detent level in the detent region below the lower output limit, thereby favouring stalling of the machine at a detent position within the detent region, and
- wherein, for a constant output demand, the current drawn by the first phase is above a level in a second and a fourth portion of the conduction region between, respectively, a first and a third portion of the conduction region and the third portion and a fifth portion of the conduction region, the current being below the level in the first, third and fifth portion of the conduction region.
A drive, comprising:
- a brushless electrical machine;
- and
- a control system coupled to the brushless electrical machine, the control system comprising a processor configured to cause the control system to control the brushless electrical machine to produce an output, wherein the output is a torque or a force by causing the control system to:
- energise a first phase of the machine in a conduction region between a switch-on point and a switch-off point and in response to an output demand, compensating for a nonlinear relationship between the output of the brushless electrical machine and a current in the first phase to produce a first output between an upper and a lower output limit, respectively higher and lower than the output demand,
- wherein the first phase is energised to produce the first output between the upper and lower output limits from a beginning of the conduction region to a detent region and from the detent region to an end of the conduction region and to produce a second output at a detent level in the detent region below the lower output limit, thereby favouring stalling of the machine at a detent position within the detent region, and
- wherein, for a constant output demand, the current drawn by the first phase is above a level in a second and a fourth portion of the conduction region between, respectively, a first and a third portion of the conduction region and the third portion and a fifth portion of the conduction region, the current being below the level in the first, third and fifth portion of the conduction region.
Dependencies are inferred from the claim text.