The present invention refers to a method and to a system for controlling an electric machine.

In particular, the invention refers to a control method and to a control system of the torque of an electric machine, more in particular a synchronous reluctance electric machine, of the type with permanent magnets, but can be used with any type of electric machine.

In electric machines, and in particular in high-performance electric motors with permanent magnets, an important parameter which must be controlled is given by the torque supplied as output from the machine.

In order to control the torque, a method is known for estimating the value of the torque supplied by the electric machine, by using: the measure of the angular position of the rotor detected with a position sensor, and the value of the three-phase electric power computed using current values measured by current sensors, next to the steps of the electric supply circuit of the electric machine.

Such known methods for controlling the torque supplied by an electric machine have the problem that they do not allow verifying the presence of errors in the computed torque value, which can be caused by reading errors of position and current sensors, which would bring about a wrong estimation of the torque value supplied by the electric machine, in particular by the motor, with following driving errors.

An object of the present invention is obtaining a method and a system for controlling an electric machine which allow verifying the value of the torque supplied by the electric machine, detecting the presence of possible errors.

The above and other objects and advantages of the invention, as will result from the following description, are obtained with a method and a system for controlling an electric machine as claimed in the independent claims.

Preferred embodiments and non-trivial variations of the present invention are the subject matter of the dependent claims. It is intended that all enclosed claims are an integral part of the present description.

It will be immediately obvious that numerous variations and modifications (for example related to shape, sizes, arrangements and parts with equivalent functionality) can be made to what is described, without departing from the scope of the invention, as appears from the enclosed claims.

The present invention will be better described by some preferred embodiments thereof, provided as a non-limiting example, with reference to the enclosed drawings, in which:

Figure 1 shows a schematic view of a system and of the control method of an electric machine according to the invention.

With reference to the Figure, the control method of an electric machine 20, preferably a high-performance electric motor with permanent magnets, of the invention comprises the following steps: a first step of detecting the angular position

Θ of a rotor of the electric machine 20 through a position sensor 11 of a known type, for example an encoder or a resolver; a second step, simultaneous with the first step, of detecting the values of the alternate current i _a , i _b , i _c next to at least two phases of the input current to the electric machine 20 through at least two alternate current sensors 12, each of said alternate current sensors 12 being electrically connected to a phase of the supplying circuit of the electric machine 20, in turn electrically connected to an inverter 30 configured to transform a direct voltage supplied by electric supply means into an alternate voltage for supplying power to the electric machine 20; a third step, simultaneous with the first and the second step, of detecting the values of the direct voltage V _DC and of the direct current i _DC supplied as input to the inverter 30 by the electric supply means, respectively through a direct voltage sensor 32 and a direct current sensor 31 electrically connected to the supplying circuit of the inverter 30; a fourth step of estimating the torque

Teestimatingted supplied by the electric machine 20, performed by processing, preferably through an information program executed by a microprocessor, data detected by the position sensors 11, and the alternate current sensors 12 in the first and in the second step, and data obtained by means of known simulations of the electric machine 20; a fifth step 5 of computing the torque Tcheck supplied by the electric machine 20 performed by processing, preferably through an information program executed by a microprocessor, data detected by the direct current sensor 31, the direct voltage sensor 32 (anyway necessary and present for controlling the machine) and the position sensor 11 from which the rotation speed is obtained (through processing from an information program) respectively in the previous third and first steps, and parameters of the electric machine 20; a sixth step 6 of comparing the value of the torque Tcheck computed in the fifth step 5 and the value of the torque Teestimatingted estimated in the fourth step, to verify that the difference between the two values is lower than a pre-set value, for example not greater than 10% or 10Nm (taking into account that usually the required accuracy for controlling the torque Teestimatingted is 5% or 5Nm).

In a preferred way, in the fifth step 5, computing of the torque Tcheck supplied by the electric machine 20 is performed by using the following formula; wherein: ω is the speed of the rotor of the electric machine

20 computed in a first sub-step 5a starting from the angular position Θ of the rotor of the electric machine 20 detected by the position sensor 11; P _DC is the value of the power supplied to the electric machine 20 by the electric supply means, for example by the battery, obtained in a known way by multiplying the voltage Voc supplied by the electric supply means for the current i _DC detected by the direct current sensor 31 in the third step, and η is the efficiency of the electric machine 20.

In particular, the efficiency of the electric machine is known, since it can be computed with specific bench tests, and afterwards it can be tabulated in order to be used by the information program.

Preferably, the fourth step of estimating the torque Teestimatingted supplied by the electric machine

20 comprises a first sub-step 4a wherein, using known Clarke Park transforms, direct current i _d and quadrature current i _q are computed. In a preferred way, if the electric machine 20 is a synchronous motor with permanent magnets, the fourth step further comprises a second sub-step 4b wherein the estimation of the torque Teestimattngted supplied by the electric machine 20 is performed by using the following formula, in the reference rotating system synchronous with the rotor: wherein: p is the number of polar torques of the motor, i _d and i _q are respectively the direct current and the quadrature current computed in the first sub-step

4a, L _d is the direct inductance where the direct current i _d passes, and Lq is the quadrature inductance where th quadrature current iq passes, λ is the concatenated flow, produced by the rotor permanent magnets and concatenated by the stator windings.

The system 10 for controlling an electric machine 20, preferably a high-performance electric motor with permanent magnets, of the invention comprises: a position sensor 11 of a known type, for example an encoder or a resolver, configured to detect the angular position of a rotor of the electric machine 20; at least two alternate current sensors 12, each of said alternate current sensors

12 being configured to detect the value of the alternate current i _a , ib, ic next to an input phase to the electric machine 20, and electrically connected to a phase of the supplying circuit of the electric machine 20, in turn electrically connected to the inverter 30 configured for transforming a direct voltage supplied by the electric supply means into an alternate voltage for supplying power to the electric machine 20; a direct voltage sensor 32 and a direct current sensor 31 configured to respectively detect the direct voltage V _D C and the direct current i _DC supplied by the electric supply means, for example a battery, as input to the inverter 30.

The system 10 for controlling an electric machine 20 of the invention further comprises an electronic control unit of a known type, comprising a microprocessor and memory means, configured to process, through suitable information programs, data detected by the sensors and drive the electric machine 20 to perform the previously described control method of the invention. The invention further comprises a high- performance electric motor with permanent magnets comprising the previously described control system

10.