Method for determining a target torque for a motor that enables control of the consumed direct current.

Abstract

Method (100) for determining a parameter representative of a target torque (XOUT) for a motor (12) comprising: a control step (E2) that determines a reference variable (IDCCom) as a function of a DC threshold value (IDCMax) and a measured DC current (IDCMes); a determination step (E3) that determines an upper limit (XLimMax) and a lower limit (XLimMin) of the parameter representative of the target torque (XOUT) as a function of the reference variable (IDCCom); an evaluation step (E4) that determines the parameter representative of the target torque (XOUT) as a function of the upper limit (XLimMax) and the lower limit (XLimMin) of the parameter representative of the target torque (XOUT) and a parameter representative of the desired torque (XIN).

Description

The invention relates to the field of electric motors and, more particularly, to a method for determining a parameter representative of a desired torque of an electric motor.The present invention relates to an electric motor, and more particularly to a brushless electric motor that is driven independently of a number of phases or windings by a vector control method. The electric motor receives an alternating current from an inverter driven by the vector control method, the inverter being supplied with direct current.Hereinafter, the DC power supply current is referred to as direct current (DC current) and the AC power supply current is referred to as alternating current (AC current).Hereinafter, a system upstream of the inverter, which is responsible for supplying or recovering the direct current from the inverter, is referred to as a direct current supply system or a direct current system. This upstream system can be, for example, a battery or a DC-DC converter.The inverter converts the direct current into alternating current, which supplies the motor.Vector control, also called field-oriented control, is a known control method for electric motors, in which the motor alternating current is divided into two orthogonal components, one along an axis q, called transverse axis current below, which is denoted by I q and the other along an axis d, called longitudinal axis current, which is denoted by I d. The transverse axis current I q and the longitudinal axis current I d are spatial currents of the so-called longitudinal magnetization axis, which is marked d, and the transverse axis, which is marked q. The cross-axis current I q and the longitudinal-axis current I d correspond to a spatial projection of the three-phase current system onto a rotating reference system related to a rotor of the electric motor. The cross axis current I q and the longitudinal axis current I d are therefore a function of the phase shift of the three phase current system with respect to the longitudinal axis d and the amplitude of the three phase system. In low reluctance motors, the longitudinal axis current I d generally allows for a reduction in perceived magnetic flux to optimize high speed operation, while the transverse axis current I q controls motor applied torque, referred to herein as motor torque. The longitudinal axis current I d and the transverse axis current I q are determined, for example, as a function of an operating point of the motor, which is characterized by at least one of the following parameters: a setpoint torque, a rotational speed of the motor, a temperature of the motor or a voltage of the motor supply alternating current.The motor is supplied with alternating current comprising a longitudinal axis component I d and a transverse axis component I q provided by the inverter.The invention is preferably applied in the field of power steering for vehicles, where automobile manufacturers are striving to control the power consumption of the power steering system, i.e. the DC supply current, with increasing precision.The object of a steering system of a vehicle is to enable the driver to steer the travel path of the vehicle by changing the orientation angle of the wheels of the vehicle using a steering wheel. The electric power consumption of the electric power steering system is difficult to predict because it depends on the forces transmitted from the wheels (parking maneuvers, driving style, low grip, etc.) and the driver's desire to turn the steering wheel. However, the electric power steering system has the capability and convenience of generating a very high power consumption.There are various solutions by which the power consumption of the power steering system can be controlled. Some are based on the control of the motor supply voltages at AC level, others on the motor torque or the cross axis current I q.The solutions based on motor torque control or on the cross axis current I q have the advantage that they maintain control over the target torque, which is not possible when acting on the motor supply voltages. However, this control requires complex designs and developments to ensure performance and stability over all operating ranges (temperature, speed, etc.) since the DC current consumed depends on several input signals, including motor torque (which is controlled), inverter DC supply voltage, motor speed, and to a lesser extent variation of some parameters related to production and / or temperature and / or aging. Production is understood to mean the use and / or production of the motor. Indeed, some parameters such as the electrical resistance of the motor winding and the magnetic flux during manufacture vary from one motor to another under the same environmental conditions, but these parameters also vary with temperature.It is an object of the invention to eliminate all or part of the aforementioned disadvantages by determining a parameter representative of a desired torque of the motor and thus making it possible to ensure compliance with a limitation of the consumed direct current.This object is achieved by the features of claims 1 and 9.The invention discloses a method for determining a parameter representative of a desired torque of a motor, the motor being supplied with alternating current coming from at least one inverter, the at least one inverter being driven by at least one microcontroller using a vector control method, the at least one inverter being supplied with direct current coming from at least one direct current supply system, the method being executed by the at least one microcontroller (20) and comprising:a control step in which a control parameter is determined at least as a function of a DC threshold value, a measured DC current and a limiting parameter;a control step in which a command variable is determined at least as a function of a DC threshold value and the measured DC current;a determining step in which an upper limit value and a lower limit value of the parameter representative of the setpoint torque are determined at least as a function of the reference variable;an evaluation step in which the parameter representative of the desired torque is determined at least as a function of the upper limit value and the lower limit value of the parameter representative of the desired torque and of a parameter representative of the desired torque.The desired torque is the torque that the motor must apply. The desired torque is processed in the microcontroller to determine a longitudinal and transverse axis current that allows the motor to provide the desired torque. In normal operation, the setpoint torque corresponds substantially to the torque which the motor applies, that is to say the motor torque.The motor torque is the torque actually applied by the motor. The motor torque depends on the alternating supply current of the motor. An engine user desires the engine torque to be close to or equal to the desired torque.In the following, all elements that enable control of the electric motor are referred to as motor system. The motor system includes, in particular, the motor-inverter assembly and the microcontroller.The electric motor according to the invention is supplied with alternating current, which is provided by the inverter. The inverter itself is electrically supplied with direct current.The motor alternating current is determined from the parameter representative of the desired torque determined by the method of the invention.The method comprises a control step performed by the microcontroller. During this step, a command is determined as a function of the DC threshold and the measured DC current.The DC threshold is the maximum value of the consumed DC current that is not to be exceeded. In other words, the DC threshold value corresponds to the DC control value during engine operation. The DC threshold is set by the user.The measured DC current corresponds to the value of the DC current actually consumed by the motor during the previous iteration. The method according to the invention regulates the measured direct current such that it remains less than or equal to the direct current threshold value. The command value corresponds to a virtual command DC current that makes it possible to keep the maximum value of the consumed DC current less than or equal to the DC threshold value.The control step allows, on the one hand, the compensation of parameter fluctuations, in particular of the flux and of the motor resistance, the values of which change as a function of the temperature and in production compared to a setpoint value implemented in the controller, and, on the other hand, the compensation of the dynamics, since subordinate control loops can generate a certain delay in the control of the desired torque.The limiting parameter comprises an active state and an inactive state which indicates that a limiting of the parameter representative of the desired torque is carried out during the evaluation step. The state of the limitation parameter is therefore determined during the evaluation step.During the control step, the microcontroller activates or deactivates the execution of the regulation of the measured direct current according to a value assumed by the control parameter. In other words, it allows the execution of the control step according to certain conditions. For this purpose, a control parameter is put into an active or inactive state as a function of at least the DC threshold value, the measured DC current and the limiting parameter. The control step makes it possible to continuously control the parameter representing the desired torque by means of the limiting parameter. The method controls the measured direct current when the desired torque is exceeded or limited. In other words, the steps of controlling and determining are only performed when the measured DC current is greater than or equal to the DC threshold and until the limit parameter indicates inactive limit.The method comprises the determining step. During this step, an upper limit value and a lower limit value of the parameter representative of the target torque are determined at least as a function of the command variable. The determination step thus follows the regulation step.The upper limit and the lower limit define a range of values in which the parameter representative of the desired torque must be located to ensure that the DC current measured or consumed by the engine remains less than or equal to the DC threshold.Since the dispersion of the physical parameters of the engine system by the command variable is taken into account, no calculations or adaptations of complex variables are carried out in this step.The method finally comprises the evaluation step. During this step, the desired torque representative parameter is determined at least as a function of the upper limit and lower limit of the desired torque representative parameter and a desired torque representative parameter.The washed torque is the torque that the motor should exert for the user regardless of the DC current consumed. The desired torque is determined by a higher-order control unit. In a power steering system, the desired torque is determined in particular on the basis of a steering wheel torque exerted by the driver on a steering wheel.The parameter representative of the desired torque must therefore be as close as possible to the parameter representative of the desired torque, while maintaining the value range defined by the upper and lower limit values. The evaluation step can therefore carry out a limitation of the parameter representative of the setpoint torque by the upper and lower limit values.According to one exemplary embodiment, the evaluation step ascertains the limiting parameter at least as a function of the parameter representative of the setpoint torque and of the parameter representative of the desired torque.The limiting parameter indicates whether a limiting of the parameter representative of the desired torque has been carried out during the evaluation step.The control and determination steps are only performed when the measured DC current is greater than or equal to the DC threshold or when the control loop limits the desired torque, which is indicated by the state of the limit parameter.According to one exemplary embodiment, the limiting parameter is in the active state if the parameter representative of the setpoint torque differs from the parameter representative of the desired torque.According to one exemplary embodiment, the limiting parameter is in the inactive state if the parameter representative of the setpoint torque corresponds to the parameter representative of the desired torque.The invention may also have one or more of the following features, individually or in combination.According to one exemplary embodiment, the electric motor is a motor of a power steering system of a vehicle.According to one exemplary embodiment, the control parameter has a value of 1 in the active state and a value of 0 in the inactive state.The control step enables proper operation of the control of the measured direct current by activating the control step only when needed.According to one embodiment, the control step is carried out when the control parameter is in the active state.Divergence of the command variable is thus avoided as long as the measured direct current is less than the direct current threshold value.In the active state of the control parameter, the parameter representative of the desired torque must therefore be as close as possible to the parameter representative of the desired torque, the value range defined by the upper and lower limit values having to be observed.In the inactive state of the control parameter, the parameter representative of the desired torque corresponds to the parameter representative of the desired torque, the upper and lower limit values not being taken into account. No regulation of the consumed direct current then takes place.The control and determination steps are performed only when the control parameter is in an active state, i.e. when the method controls or limits the measured direct current to the direct current threshold value, or as long as the desired torque is limited.According to one exemplary embodiment, the evaluation step determines the parameter representative of the setpoint torque as a function of the control parameter.According to one embodiment, the parameter representative of the desired torque and the parameter representative of the desired torque correspond to a torque or a cross-axis current.Thus, the method similarly determines a desired torque or transverse axis current.According to one exemplary embodiment, the method additionally comprises a control step, wherein the at least one inverter is controlled by the microcontroller on the basis of the parameter representative of the setpoint torque.According to one exemplary embodiment, the control step ascertains the reference variable by a sum of the DC threshold value and a correction measure value, which is ascertained by an integral and / or derivative and / or proportional controller, which receives the DC threshold value and the measured DC current as input signal.The command value is obtained by the sum of a pilot control directly corresponding to the DC threshold value and a corrective action value resulting from a proportional, integral, closed loop differential control, or a combination thereof. This closed loop corrective action value allows compensation for both parametric variations, in particular the flux and the motor resistance, whose values change as a function of temperature and production with respect to the setpoint implemented in the controller, and dynamics, in that the subordinate loops can generate a certain delay in the control of the washing torque.According to one embodiment, the upper limit and the lower limit of the parameter representative of the desired torque are determined by solving an equation that defines a function of at least the command variable, a speed of the motor, a voltage of the inverter DC supply current, and a longitudinal axis current of the motor AC supply current measured or determined during a previous iteration.The equation solved in the determination step results from the general equations of the motor in the longitudinal and transverse axes.According to one embodiment, the general equations are as follows: wherein V DC is the voltage (V) of the inverter DC supply current; I DC is the average inverter DC supply current (A); ψ is an equivalent magnetic flux of the electric motor in a selected uvw ↔ dqo transformation (Wb); L d, L q are longitudinal and transverse axis inductances of the electric motor (H); R ac is the total equivalent resistance on the AC side of the motor system (Ω); P is a number of pole pairs of the electric motor; Ω is a rotational speed of the motor (rad·s -1); k is the transformation factor in the chosen uvw ↔ dqo transformation (e.g., 3 / 2 or 1), depending on the convention chosen; V d, V q is the longitudinal axis and transverse axis voltages of the motor AC supply current (V); I d, I q are the longitudinal axis and transverse axis currents of the motor AC supply current (A); T is an electromagnetic torque of the motor (Nm).According to one embodiment, the equation is a function of physical parameters of the motor.The physical parameters of the motor are, for example, total equivalent resistance on the AC side, equivalent magnetic flux, equivalent resistance, longitudinal and transverse axis inductances, the number of pole pairs. These parameters are a result of the dimensioning of the motor. They are assumed constant in solving the equations and fixed reference values are used for simplicity.The transformation factor in a chosen uvw ↔ dqo transformation is a fixed gain that corresponds to a chosen convention.According to an embodiment, the method comprises a calculation step in which a transformation gain is determined as a function of the transformation factor in a uvw ↔ dqo transformation, a number of pole pairs of the motor, an equivalent magnetic flux of the motor in the uvw ↔ dqo transformation, the longitudinal axis current of the motor supply alternating current measured or determined during the previous iteration, and the longitudinal axis and transverse axis inductances of the motor.According to an embodiment, the transformation gain is calculated using the formula: wherein G Iq2Trq is the transformation gain; k is the transformation factor in the chosen uvw ↔ dqo transformation (e.g., 3 / 2 or 1), depending on the chosen convention; p is a number of pole pairs of the electric motor; ψ is an equivalent magnetic flux of the electric motor in a chosen uvw ↔ dqo transformation (Wb); L d, L q are longitudinal and transverse axis inductances of the electric motor (H); I is d of the longitudinal axis current of the motor supply alternating current (A).According to one embodiment, the upper limit and the lower limit of the parameter representative of the desired torque are obtained by solving the following equation: wherein k is the transformation factor in the chosen uvw ↔ dqo transformation (e.g., 3 / 2 or 1), depending on the chosen convention; R ac is an equivalent total resistance on the AC side of the motor system (Ω); G Iq2Trq is the transformation gain; Ω is a speed of the motor (rad·s -1) ; I d is the longitudinal axis current of the motor AC supply current (A); V DC is the voltage of the inverter DC supply current (V); I DCCom is the command variable (A), I qLim is the transverse axis current limit value of the motor alternating supply current (A);We obtain: and with k being the transformation factor in the chosen uvw ↔ dqo transformation (e.g. 3 / 2 or 1), depending on the chosen convention; R ac is an equivalent total resistance on the AC side of the motor system (Ω); G Iq2Trq is the transformation gain; Ω is a speed of the motor (rad·s -1) ; I is d the longitudinal axis current of the motor supply AC current (A); V is DC: the voltage of the inverter supply DC current (V); I DCCom is the command quantity (A), I qLimMin is the lower limit value of the transverse axis current of the motor supply alternating current (A); I qLimMax: is the upper limit value of the transverse axis current of the motor supply alternating current (A); T LimMax is the upper limit value of the setpoint torque (Nm); T LimMin is the lower limit value of the setpoint torque (Nm).According to one embodiment, the control parameter is placed in an active state when the measured direct current is greater than or equal to the direct current threshold value and in an inactive state when the measured direct current is less than the direct current threshold value and the parameter representative of the desired torque corresponds to the parameter representative of the desired torque.The limitation performed by the method thus becomes effective when the measured direct current is greater than or equal to the direct current threshold value, and is stopped when the measured direct current becomes less than the direct current threshold value and the method no longer applies any limitation.According to one exemplary embodiment, the control parameter is initiated in the inactive state.As standard, no limitation of the parameter representative of the desired torque takes place. Only when an exceeding of the DC threshold is detected is the limiting implementedThe invention also relates to a power steering system comprising at least one motor controlled according to the method of the invention.Further details, features and advantages of the invention are evident from the following description of an exemplary embodiment with reference to the drawings. The following shows: FIG. 1 is a schematic illustration of a power steering system that includes a method according to the present invention; FIG. 2 is a block diagram showing a power supply of a motor; FIG. 3 is a schematic illustration of the method according to the invention; FIG. 4 is a graph showing upper and lower limits of the desired torque representative parameter as a function of a rotational speed of an engine; FIG. 5 is a time-based simulation of the rotational speed of the motor, a parameter representing desired and desired torques, a measured direct current, a direct current threshold value, a command variable, a limiting parameter and a control parameter.A steering system 1 of a vehicle 2 as illustrated in FIG. 1 is intended to allow a driver to steer the path of a vehicle 2 by changing an orientation angle of the vehicle wheels 10, 11 using a steering wheel 3. The orientation angle of the wheels is particularly related to an angle θ 3 of the steering wheel 3. The driver changes the angle θ 3 of the steering wheel 3 by applying a force T 3 to the steering wheel 3, which is hereinafter referred to as "steering wheel torque". The force T 3 exerted on the steering wheel can be measured by means of a torque sensor 23.Typically, a steering system 1 comprises a plurality of elements including the steering wheel 3, a rack 6 and two wheels 10, 11 each connected to a tie rod 8, 9. The rack 6 is the element that allows manoeuvring of the wheels 10, 11, i.e. it allows to change the orientation angle of the wheels 10, 11 by means of the tie rods 8, 9. The rack 6 converts a change in the angle of the steering wheel 3 into a change in the orientation angle of the wheels of the vehicle 10, 11.An electric power steering system 1 comprises, as shown in FIG. 2, a power supply system of the motor 12, which power supply system comprises at least one microcontroller 20 which, in particular by means of a higher-order control unit 200, determines a parameter representative of the washed torque X IN based on the force T3 exerted on the steering wheel 3 in a manner known to the person skilled in the art. The representative torque of the washed torque X IN is the torque that the motor 12 is to exert independently of the consumed direct current I DC as desired by the user.Then, based on the parameter representative of desired torque X IN method 100 according to the present invention determines the parameter representative of desired torque X OUT to be applied by an electric motor 12.The parameter representing the target torque X OUT is converted into variables M by a modulation unit 300 that enables driving of an inverter 40 by a vector control method.The inverter 40 is electrically supplied with direct current I DC which converts it into alternating current I AC which is supplied to the motor 12. The motor alternating current I AC includes a longitudinal axis component, referred to herein as a longitudinal axis current I d and a transverse axis component, referred to herein as a transverse axis current.The direct current I DC with a supply voltage V DC is provided by a direct current supply system 30 or direct current system, which can be a battery or a direct current-to-direct current converter, for example.The motor 12 applies motor torque T 12 to the rack 6 based on the parameter representative of the target torque X OUT. The motor torque T 12 depends on the alternating current IACapplied to the motor 12. A user of the engine 12 attempts to ensure that the engine torque T 12 is near or equal to the desired torque defined by the parameter representative of the desired torque X IN.In the following, all elements that enable control of the electric motor 12 are referred to as motor system. The motor system includes, in particular, the motor-inverter arrangement and the microcontroller 20.The electric motor 12 is preferably an electric motor having two operating directions, and is preferably a rotary brushless electric motor.The invention relates, for example, to an electric motor 12 of a mechanical power steering system in which there is a mechanical connection which is generally produced by a steering column 4 which engages via a steering pinion 5 with the rack 6, which in turn is displaceably guided in a housing 7 fastened to the vehicle 2, or to an electric power steering system without a mechanical connection, referred to as "steer-by-wire", in which the steering wheel is mechanically separated from the rack, which is not illustrated in the figures.In a mechanical power steering system, the electric motor 12 can engage via a reduction gear or on the steering column 4 itself to form a so-called "single pinion" mechanism or directly on the rack 6, for example by means of a second pinion 13 which is different from the steering pinion 5 and which enables the steering column 4 to engage with the rack 6 to form a so-called "double pinion" mechanism as shown in Fig. 1.The invention relates in particular to a method for controlling a synchronous electric motor 12, which may be an electric motor 12 of the steering system shown in FIG. 1 or another application.The method 100 according to the invention is illustrated in FIG. 3.Method 100 according to the present invention determines the parameter representative of setpoint torque X OUT which may be a torque or a transverse axis current. Similarly, the parameter representative of desired torque X IN corresponds to a torque or a cross-axis current.The method 100 comprises a control step E 1. This step E1 receives as input a DC threshold value I DCMax, a measured DC current I DCMes and determines a control parameter CTL.The control step E1 also receives as input signal a limiting parameter LIM.The DC threshold value I DCMax is the maximum value of the consumed DC current I DC, which is not to be exceeded. In other words, during operation of the motor 12, the DC threshold value I DCMax corresponds to the regulation value of the DC current I DC. The DC threshold I DCMax is determined by a user.The measured DC current I DCMes corresponds to the value of the DC current I DC, which was actually consumed by the motor 12 during a previous iteration. The method 100 according to the invention regulates the measured direct current I DCMes such that it remains less than or equal to the direct current threshold value I DCMax.During the control step E 1, the microcontroller 20 activates or deactivates execution of the regulation of the actually consumed direct current I DC. In other words, it enables the implementation of the method 100 according to the invention. For this purpose, the control parameter CTL is set to an active state ON or an inactive state OFF as a function of the DC threshold value I DCMax and the measured DC current I DCMes and the limiting parameter LIM.According to one exemplary embodiment, the control parameter CTL has the value 1 in the active state ON and the value 0 in the inactive state OFF.According to one embodiment, the control parameter CTL is initiated in the inactive state OFF, i.e.:According to an embodiment, the control parameter CTL is placed in the active state ON when the measured direct current I DCMes is greater than or equal to the direct current threshold value I DCMax and in the inactive state OFF when the measured direct current I DCMes is less than the direct current threshold value I DCMax and the limiting parameter LIM is in an inactive state OFF.In other words:The limiting of the method 100 is effective when the measured DC current I DCMes is greater than or equal to the DC threshold I DCMax and is terminated when the measured DC current I DCMes becomes less than the DC threshold I DCMax and the method 100 does not perform any further limitations. In other words, no limitation of the parameter representative of the setpoint torque X OUT is carried out by default. Only when the DC threshold value I DCMax is exceeded is the limiting implemented.The control step enables proper operation of the regulation of the measured direct current I DCMes in that it is activated only when required.The method 100 comprises a control step E 2. During this step, a command variable I DCCom is determined as a function of the DC threshold value I DCMax and the measured DC current I DCMes.The command variable I DCCom corresponds to a virtual DC current setpoint value that makes it possible to keep the maximum value of the consumed DC current less than or equal to the DC current threshold value I DCMax.The control step allows, on the one hand, the compensation of parameter variations, in particular of the flux and of the motor resistance, the values of which change as a function of the temperature and during production with respect to a reference value implemented in the controller, and, on the other hand, of the dynamics, in that subordinate control loops can generate a certain delay in the control of the desired torque.According to one embodiment, the control step E2 is carried out when the control parameter CTL is in the active state ON.Divergence of the command variable I DCCom is thus avoided as long as the measured direct current I DCMes is less than the direct current threshold value I DCMax.The control step E2 determines the reference variable I DCCom by a sum of the DC threshold value I DCMax and a corrective action value ΔI DC, which is determined by an integral and / or differential and / or proportional controller E21 which receives as input signal the DC threshold value I DCMax and the measured DC current I DCMes.The method 100 comprises a determination step E 3. In this step, an upper limit value X LimMax and a lower limit value X LimMin, of the parameter representative of the setpoint torque X OUT are determined at least as a function of the reference variable I DCCom. The determination step E 3 therefore follows the regulation step E 2 and is carried out only if the control parameter CTL is in an active state ON, i.e. if the method 100 regulates or limits the measured direct current I DCMes to the value of the direct current threshold value I DCMax. In other words, the steps of control E2 and determination E3 are executed only if the measured direct current I DCMes has to be less than or equal to the direct current threshold value I DCMax or as long as the desired torque X OUT is limited.The upper limit value X LimMax and the lower limit value X LimMin define a range of values in which the parameter representative of the desired torque X OUT must be located in order for the measured direct current I DCMes or direct current drawn by the motor 12 to remain less than or equal to the direct current threshold value I DCMax. Since the dispersion of the physical parameters of the engine system 12 is taken into account by the command variable I DCCom no calculations or adaptations of complex variables are carried out in this step E 3.According to an embodiment, the upper limit value X LimMax and the lower limit value X LimMin of the parameter representative of the target torque X OUT are obtained by solving an equation that is a function of at least the following quantities: the command variable I DCCom, a rotational speed Ω of the motor 12, a voltage of the direct current V DC, which is supplied to the inverter 40, and a direct current I d of the alternating current I AC, which is supplied to the motor 12 and measured or determined during a previous iteration.According to one embodiment, the equation is a function of the physical parameters of the motor.The physical parameters of the motor are, for example, an equivalent total resistance on the alternating current side, the equivalent magnetic flux, the equivalent resistance, the inductances of the longitudinal axis or the transverse axis, the number of pole pairs. These parameters are a result of the dimensioning of the motor. They are assumed constant at the resolution of the equations and fixed reference values are used for simplicity.The transformation factor in a chosen uvw ↔ dqo transformation is a fixed gain that corresponds to a chosen convention.The transformation gain G Iq2Trq is determined during a calculation step E 5 as a function of the transformation factor k in a uvw ↔ dqo transformation, a pole pair number p of the motor 12, an equivalent magnetic flux ψ of the motor in the uvw ↔ dqo transformation, the longitudinal axis current I d of the alternating current I supplied to the motor 12 AC, which was measured or determined during the previous iteration, and the longitudinal axis inductance L d and transverse axis inductance L q of the motor 12.According to an embodiment, the transformation gain is calculated according to the following formula: wherein G Iq2Trq is the transformation gain; k is the transformation factor in the chosen uvw ↔ dqo transformation (e.g., 3 / 2 or 1), depending on the chosen convention; p is a number of pole pairs of the electric motor; ψ is an equivalent magnetic flux of the electric motor in a chosen uvw ↔ dqo transformation (Wb); L d, L q are longitudinal and transverse axis inductances of the electric motor (H); I is d of the longitudinal axis current of the motor supply alternating current (A). The equation solved during the determination step E 3 results from the general equations of the motor 12 in the longitudinal and transverse axes.According to one embodiment, the general equations are as follows: wherein V DC is the voltage (V) of the inverter DC supply current; I DC is the average inverter DC supply current (A); ψ is an equivalent magnetic flux of the electric motor in a selected uvw ↔ dqo transformation (Wb); L d, L q are longitudinal and transverse axis inductances of the electric motor (H); R ac is the total equivalent resistance on the AC side of the motor system (Ω); P is a number of pole pairs of the electric motor; Ω is a rotational speed of the motor (rad·s-1); k is the transformation factor in the chosen uvw ↔ dqo transformation (e.g., 3 / 2 or 1, depending on the convention chosen); V d, V q is the longitudinal axis and transverse axis voltages of the motor AC supply current (V); I d, I q are the longitudinal axis and transverse axis currents of the motor AC supply current (A); T is an electromagnetic torque of the motor (Nm).According to one embodiment, the upper limit value X LimMax and the lower limit value X LimMin of the parameter representative of the desired torque X OUT are determined by solving the following equation: where k is the transformation factor in the chosen uvw ↔ dqo transformation (e.g., 3 / 2 or 1), depending on the chosen convention; R ac is an equivalent total resistance on the AC side of the motor system (Ω); G Iq2Trq is the transformation gain; Ω is a speed of the motor (rad·s-1); I is d the longitudinal axis current of the motor AC supply current (A); V DC is the voltage of the inverter DC supply current (V); I is DCCom is the command value (A); I is qLim the cross axis current limit value of the motor AC supply current (A); I is;We obtain: where k is the transformation factor in the chosen uvw ↔ dqo transformation (e.g., 3 / 2 or 1), depending on the chosen convention; R ac is an equivalent total resistance on the AC side of the motor system (Ω); G Iq2Trq is the transformation gain; Ω is a speed of the motor (rad·s -1) ; I is d the longitudinal axis current of the motor AC supply current (A); V is DC: the voltage of the inverter DC supply current (V); I DCCom is the command quantity (A), I qLimMin is the lower limit value of the transverse axis current of the motor supply alternating current (A); I qLimMax: is the upper limit value of the transverse axis current of the motor supply alternating current (A); T LimMax is the upper limit value of the setpoint torque (Nm); T LimMin is the lower limit value of the setpoint torque (Nm).The method finally comprises an evaluation step E 4. In this step, the parameter representative of the target torque X OUT is determined at least as a function of the upper limit value X LimMax and the lower limit value X LimMin the parameter representative of the target torque X OUT the control quantity CTL, and the parameter representative of the target torque X IN.Therefore, when the control parameter CTL is in the active state ON, the parameter representative of the target torque X OUT needs to be as close as possible to the parameter representative of the desired torque X IN while satisfying the range of values determined by the upper limit value X LimMax and the lower limit value X LimMin. In other words:When the control parameter CTL is in the inactive state OFF, the parameter representative of the target torque X OUT corresponds to the parameter representative of the washed torque X IN and the upper limit value X LimMax- and the lower limit value X LimMin are not taken into account. No control of the consumed direct current I DC. is then effected. In other words:According to one exemplary embodiment, evaluation step E 4 ascertains limiting parameter LIM at least as a function of the parameter representative of setpoint torque X OUT and the parameter representative of washed torque X IN.The limiting parameter LIM indicates whether a limiting of the parameter representative of the desired torque X IN has been carried out during the evaluation step E 4.According to one embodiment, the limiting parameter LIM is in the active state ON when the parameter representative of the desired torque X OUT is different from the parameter representative of the washed torque X IN. In other words:According to one embodiment, the limiting parameter LIM is in the active state ON when the parameter representative of the desired torque X OUT corresponds to the parameter representative of the washed torque X IN. In other words:Finally, the method comprises a control step in which the inverter 40 is controlled by the microcontroller 20 on the basis of the parameter representative of the setpoint torque X OUT.The principle of the method 100 according to the invention consists in taking into account the deviation of the physical parameters of the motor 12 via the reference variable I DCCom when limiting the consumed direct current I DC is required and then determining on the basis thereof the value range of the parameter representative of the desired torque X OUT of the motor 12, whereby it can be ensured that the consumed direct current I DC is equal to or less than the direct current threshold value I DCMax.FIG. 4 illustrates solutions I qLimMax, I qLimMin of the equation solved during the determining step as a function of the speed Ω of the motor 12 for a DC threshold of 50 A and 5 A.FIG. 5 illustrates a time simulation of the rotational speed Ω of the motor 12, the parameter representative of a desired torque T IN and a target torque T OUT expressed in terms of a torque, the measured direct current I DCMes, the direct current threshold value I DCMax, the command value I DCCom, the limiting parameter LIM, and the control parameter CTL.The limiting parameter LIM and the control parameter CTL are initially in the inactive state OFF, i.e. at a value of 0. The DC threshold value I DCMax is set to 50 A.As the rotational speed Ω of the motor 12 increases and the desired torque T IN increases, the measured direct current I DCMes increases and then exceeds the direct current threshold value I DCMax. This overflow leads successively to the transition to the active state ON, i.e. to a value of 1 of the control parameter CTL, then to a calculation of the reference variable I DCCom, which is less than 50 A, and finally to a decreasing desired torque T OUT and a transition to the active state ON, i.e. to a value of 1, of the limiting parameter LIM. As a result, the measured DC current I DCMes decreases until it again approaches the DC threshold I DCMax representing the regulation target value.Since the drop in the rotational speed Ω of the motor 12 naturally causes the upper and lower limit values T LimMax, T LimMin of the parameter representative of the target torque to expand, in this example combined with a drop in the desired torque T IN, the limit parameter LIM returns to the inactive state OFF. Since the measured DC current I DCMes has logically decreased below the DC threshold value I DCMax the control parameter CTL has also entered the inactive state OFF. The washed torque T IN again corresponds to the desired torque T OUT-Of course, the invention is not limited to the exemplary embodiments described and illustrated in the appended figures. Modifications remain possible, in particular with regard to the composition of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.In summary, it can be stated:The invention discloses a method (100) for determining a parameter representative of a desired torque (X OUT) for an engine (12), comprising: a step of controlling (E2) determining a command value (I DCCom) as a function of a threshold DC current value (I DCMax) and a measured DC current value (I DCM,s) ; a step of determining (E3) determining an upper limit value (X LimMax) and a lower limit value (X LimMin) of the parameter representative of the desired torque (X OUT) as a function of the command value (I DCCom); an evaluating step (E4) determining the parameter representative of the desired torque (X OUT) as a function of the upper limit value (X LimMax) and the lower limit value (X LimMin) the parameter representative of the desired torque (X OUT) and a parameter representative of the desired torque (X IN).LIST OF REFERENCE CHARACTERS1 Steering system 2 Vehicle 3 Steering wheel 4 Steering column 5 Steering pinion 6 Rack 7 Housing 8, 9 Tie rod 10, 11 Wheels 12 Motor 13 Second pinion 20 Microcontroller 23 Torque sensor 30 Direct current supply system 40 Inverter 100 Determination method 200 Superordinate control unit 300 Modulation unit E 1 Control step E 2 Control step E 3 Determination step E 4 Evaluation step E 5 Calculation step

Claims

Method (100) for determining a parameter representative of a desired torque (X OUT) of a motor (12), said motor (12) being supplied with alternating current (I AC) coming from at least one inverter (40), said at least one inverter (40) being driven by at least one microcontroller (20) using a vector control method, said at least one inverter (40) being supplied with direct current (I DC) coming from at least one direct current supply system (30), said method (100) being carried out by said at least one microcontroller (20) and comprising: - a control step (E1) in which a control parameter (CTL) is controlled at least as a function of a direct current threshold value (I DCMax), a step (E2) of determining a command value (I DCMes) and a limiting parameter (LIM); a step (I2) of determining a command value (I DCCom) at least as a function of a threshold value (I DCMax) of the current measured (I DCMes) ; a step (E3) of determining an upper limit value (X LimMax) and a lower limit value (X LimMin) of the parameter representative of the desired torque (X OUT) at least as a function of the command value (I DCCom) ; an evaluation step (E4) in which the parameter representative of the desired torque (X OUT) is determined at least as a function of the upper limit value (X LimMax) and of the lower limit value (X LimMin) of the parameter representative of the desired torque (X OUT) and of a parameter representative of the desired torque (X IN).Determination method (100) according to Claim 1, in which the parameter representative of the desired torque (X OUT) and the parameter representative of the desired torque (X IN) correspond to a torque (T OUT, T IN) or a transverse current axis.Determination method (100) according to one of the preceding claims, which also comprises a control step in which the at least one inverter is controlled by the microcontroller (20) on the basis of the parameter representative of the setpoint torque (X OUT).Determination method (100) according to one of the preceding claims, wherein the control step (E2) determines the reference variable (I DCCom) by a sum of the DC threshold value (I DCMax) and a corrective action value (ΔI DC) which is determined by a proportional and / or integral and / or differential regulator (E21), which receives as input signal the DC threshold value (I DCMax) and the measured DC current (I DCMes).Determination method (100) according to one of the preceding claims, wherein the upper limit value (X LimMax) and the lower limit value (X LimMin) of the parameter representative of the desired torque (X OUT) are obtained by a resolution of an equation which is a function of at least the following variables: the reference variable (I DCCom), a rotational speed (Ω) of the motor, a direct current voltage (V DC) supplied to the inverter (40), and a longitudinal axis current (I d) of the motor alternating current supply current which was measured or determined during a previous iteration.Determination method (100) according to the preceding claim, comprising a calculation step (E5) in which a transformation gain (G Iq2Trq) is determined as a function of the transformation factor (k) in a uvw ↔ dqo transformation, a number of pole pairs (p) of the motor, an equivalent magnetic flux (ψ) of the motor in the uvw ↔ dqo transformation, the longitudinal axis current (Id) of the motor alternating current supply current measured or determined during the preceding iteration, and the longitudinal axis inductance (Ld) or the transverse axis inductance (Lq) of the motor.Determination method (100) according to one of the preceding claims, wherein the control parameter (CTL) is placed in an active state (IN) if the measured direct current (I DCMes) is greater than or equal to the direct current threshold value (I DCMax) and in an inactive state (OFF) if the measured direct current (I DCMes) is less than the direct current threshold value (I DCMax) and the parameter representative of the desired torque (X OUT) corresponds to the parameter representative of the desired torque (X IN).Determination method (100) according to the preceding claim, wherein the control parameter (CTL) is initiated in the inactive state (OFF).A power steering system (1) comprising at least one motor (12) controlled by the parameter representative of a desired torque (XOUT) determined by the method (100) according to any of the preceding claims.

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