Method of determining set torque of electric motor to allow control of consumed DC current

Abstract

A method (100) of determining a parameter representative of a set torque (XOUT) of an electric motor (12), comprising: a step (E2) of adjusting a command variable (IDCCom) as a function of a DC current threshold (IDCMax) and a measured DC current (IDCMes); a step (E3) of determining an upper limit (X LimMax) and a lower limit (XLimMin) of a parameter representing the set torque (XOUT) as a function of the command variable (IDCCom); an evaluation step (E4) of determining the parameter representing the set torque (XOUT) as a function of an upper limit (X LimMax) and a lower limit (XLimMin) of the parameter representing the set torque (XOUT) and of the parameter representing the desired torque (XIN).

Description

Technical Field

[0001] The present invention relates to the field of electric motors, and more particularly, to a method for determining a parameter representing a set torque of a motor.

[0002] The present invention is applicable to an electric motor, and more particularly to a brushless electric motor driven by a vector control method, regardless of the number of phases or windings. The electric motor receives an AC supply current from an inverter driven by a vector control method, the inverter being supplied with a DC supply current. Background Art

[0003] Hereinafter, the DC supply current will be referred to as direct current (DC current), and the alternating current supply current will be referred to as alternating current (AC current).

[0004] Hereinafter, the upstream system of the inverter responsible for providing or recovering DC current from the inverter is referred to as a DC power supply system or a DC system. For example, the upstream system may be a battery or a DC-DC converter.

[0005] The inverter converts DC current into AC current to power the electric motor.

[0006] Vector control, also known as field oriented control, is a known control method for electric motors in which the motor AC current is decomposed into two orthogonal components, one along axis q, hereinafter referred to as quadrature axis current, denoted Iq, and the other along axis d, denoted Id, denoted as direct axis current. The quadrature axis current Iq and the direct axis current Id are space currents of the so-called direct magnetizing axis (denoted d) and the quadrature axis (denoted q). The quadrature axis current Iq and the direct axis current Id correspond to the spatial projection of the three-phase current system on a rotating reference frame associated with the rotor of the motor. Therefore, the quadrature axis current Iq and the direct axis current Id are functions of the phase shift of the three-phase current system relative to the direct axis d and the amplitude of the three-phase system. For low reluctance motors, the direct axis current Id is generally able to reduce the perceptible magnetic flux to optimize high-speed operation, while the quadrature axis current Iq controls the torque applied by the motor (hereinafter referred to as motor torque). The direct-axis current Id and the quadrature-axis current Iq are determined, for example, as a function of the motor operating point, which is characterized by at least one of the following parameters: set torque, motor speed, motor temperature or voltage of the motor AC supply current.

[0007] The motor is powered by AC provided by an inverter, which includes a direct-axis component Id and a quadrature-axis component Iq. Summary of the invention

[0008] The invention is preferably applied in the field of power steering in vehicles, where car manufacturers are seeking to control the power consumption (ie the DC supply current) of the power steering system with greater precision.

[0009] The purpose of a vehicle's steering system is to enable the driver to control the vehicle's path by modifying the direction angle of the vehicle's wheels by means of the steering wheel. The power consumption of an electric power steering system is difficult to predict, as it depends on the forces transmitted by the wheels (parking maneuvers, driving, low grip conditions, etc.) and the driver's desire to turn the steering wheel. However, electric power steering systems have the ability and tendency to generate very high power consumption.

[0010] There are different solutions to control the power consumption of the power steering system. Some are based on controlling the motor supply voltage to the AC current level, others are based on the motor torque or the quadrature axis current Iq.

[0011] Solutions based on motor torque control or quadrature axis current Iq have the advantage of maintaining control of the set torque, which is not possible with the motor supply voltage. However, this control involves complex design and development to ensure performance and stability in all operating ranges (temperature, speed, etc.), since the DC current consumed depends on multiple inputs, including the motor torque (controlled), the voltage of the inverter DC supply current, the motor speed and, to a lesser extent, the variation of some parameters related to production and / or temperature and / or aging. Production should be understood as the use and / or manufacture of the motor. In fact, under the same environmental conditions, some parameters such as the resistance of the motor windings, the magnetic flux, etc. are dispersed from one motor to another during the manufacturing process, but these parameters also vary with temperature.

[0012] The present invention aims to remedy all or part of the above-mentioned drawbacks by determining a parameter representative of the set torque of the electric motor, thereby ensuring compliance with the constraints on the DC current consumed.

[0013] The object of the present invention is a method for determining a parameter representative of a set torque of an electric motor, the electric motor being powered by an AC current 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 powered by a DC current from at least one DC power supply system, the method being executed by at least one microcontroller, comprising:

[0014] a control step in which a control parameter is determined as a function of at least a DC current threshold value, a measured DC current and a limiting parameter;

[0015] a regulating step in which the command variable is determined as a function of at least a DC current threshold value and a measured DC current;

[0016] a determining step in which an upper limit and a lower limit of a parameter representing a set torque are determined as at least a function of a command variable;

[0017] an evaluation step in which a parameter representing the set torque is determined as a function of at least an upper limit and a lower limit of the parameter representing the set torque and a parameter representing the desired torque

[0018] The set torque is the torque that the motor must apply. The set torque is processed within the microcontroller in order to determine the direct-axis current and quadrature-axis current that allow the motor to provide the set torque. In normal operation, the set torque essentially corresponds to the torque applied by the motor, i.e. the motor torque.

[0019] Motor torque is the torque actually applied by the motor. Motor torque depends on the AC supply current of the motor. Motor users want the motor torque to be close to or equal to the set torque.

[0020] In the following, all elements capable of controlling an electric motor are referred to as a motor system. The motor system comprises in particular a motor-inverter assembly and a microcontroller.

[0021] The electric motor according to the invention is powered by an AC current provided by an inverter. The inverter itself is powered by a DC current.

[0022] The motor AC supply current is determined based on a parameter representing the set torque determined by the method according to the invention.

[0023] The method comprises a regulation step performed by a microcontroller.During this step, a command variable is determined as a function of a DC current threshold value and a measured DC current.

[0024] The DC current threshold is the maximum value of the consumed DC current which we do not wish to exceed. In other words, during operation of the motor, the DC current threshold corresponds to a DC current regulation value. The DC current threshold is determined by the user.

[0025] The measured DC current corresponds to the value of the DC current actually consumed by the motor during the previous iteration. The measured DC current is regulated according to the method of the invention so as to keep it less than or equal to a DC current threshold. The command variable corresponds to a virtual command DC current, making it possible to keep the maximum value of the consumed DC current less than or equal to the DC current threshold.

[0026] The regulation step makes it possible, on the one hand, to compensate for variations in parameters (in particular the magnetic flux and the motor resistance, whose values ​​vary as a function of temperature and production relative to the reference values ​​implemented in the control) and, on the other hand, to compensate for dynamics, since the lower-level regulation loops introduce a certain delay in the control of the desired torque.

[0027] The limiting parameter comprises an active and an inactive state, which indicates that the parameter representing the set torque is limited during the evaluation step. Thus, the state of the limiting parameter is determined during the evaluation step.

[0028] During the control step, the microcontroller activates or deactivates the regulation performance of the measured DC current, depending on the value assumed by the control parameter. In other words, it makes it possible to implement the regulation step according to certain conditions. To this end, the control parameter is switched into an active state or an inactive state, at least according to the DC current threshold value, the measured DC current and the limiting parameter. The control step makes it possible to continuously regulate the parameter representing the set torque via the limiting parameter. When the set torque is exceeded or limited, the method regulates the measured DC current. In other words, the regulation and determination steps are performed only when the measured DC current is greater than or equal to the DC current threshold value, until the limiting parameter indicates an invalid limitation.

[0029] The method comprises a determination step. During this step, at least an upper limit and a lower limit of a parameter representing a set torque are determined as a function of a command variable. Thus, the determination step follows the regulation step.

[0030] The upper and lower limits define a range of values ​​within which the parameter representing the set torque must ensure that the DC current measured or consumed by the motor remains less than or equal to the DC current threshold.

[0031] Since the command variables take into account the dispersion of the physical parameters of the motor system, this step does not perform calculations or adjustments of complex variables.

[0032] The method finally comprises an evaluation step. During this step, a parameter representative of the set torque is determined as a function of at least an upper limit and a lower limit of the parameter representative of the set torque and a parameter representative of the desired torque.

[0033] The desired torque is the torque that the user wants the electric motor to exert, regardless of the DC current consumed. The desired torque is determined by a high-level controller. In the case of a power steering system, the desired torque is determined based on, among other things, the steering wheel torque exerted by the driver on the steering wheel.

[0034] Therefore, the parameter representing the set torque must be as close as possible to the parameter representing the desired torque, taking into account the range of values ​​determined by the upper and lower limits. Therefore, the evaluation step may limit the parameter representing the set torque by the upper and lower limits.

[0035] According to one embodiment, the evaluation step determines at least the limiting parameter as a function of a parameter representing the set torque and a parameter representing the desired torque.

[0036] The limit parameter indicates whether a parameter representing the desired torque is limited during the evaluation step.

[0037] The regulating and determining steps are performed only when the measured DC current is greater than or equal to a DC current threshold value, or when the regulation loop limits the set torque indicated by the state of the limiting parameter.

[0038] According to one embodiment, the limiting parameter is active when the parameter representing the set torque differs from the parameter representing the desired torque.

[0039] According to one embodiment, when the parameter representing the set torque is equal to the parameter representing the desired torque, the limiting parameter is in an inactive state.

[0040] The principle of the method according to the invention is that, when it is necessary to limit the consumed DC current, the deviation of the physical parameters of the motor is taken into account via the command variable and then, on this basis, the range of values ​​of the parameter representing the set torque of the motor is determined, thereby making it possible to ensure that the consumed DC current is equal to or less than a DC current threshold value.

[0041] The present invention may also have one or more of the following features alone or in combination.

[0042] According to one embodiment, the electric motor is an electric motor of a power steering of a vehicle.

[0043] According to one embodiment, the control parameter has a value of 1 in the active state and a value of 0 in the inactive state.

[0044] The control step enables proper operation of the regulation of the measured DC current by activating the regulation step only when necessary.

[0045] According to one embodiment, the adjusting step is performed when the control parameter is in an active state.

[0046] Therefore, as long as the measured DC current is less than the DC current threshold, divergence of the command variable can be avoided.

[0047] When the control parameter is active, the parameter representing the set torque must be as close as possible to the parameter representing the desired torque, taking into account the range of values ​​determined by the upper and lower limits.

[0048] When the control parameter is in an inactive state, the parameter representing the set torque is equal to the parameter representing the desired torque, without taking into account the upper and lower limits. Therefore, there is no regulation of the DC current consumed.

[0049] The regulating and determining steps are only performed when the control parameter is active, that is to say when the method regulates or limits the measured DC current to a DC current threshold value, or as long as the set torque is limited.

[0050] According to one embodiment, the evaluation step determines a parameter representative of the set torque as a function of the control parameter.

[0051] According to one embodiment, the parameter representing the set torque and the parameter representing the desired torque correspond to the torque or the quadrature-axis current.

[0052] The method thus also determines the set torque or the set quadrature-axis current.

[0053] According to one embodiment, the method further comprises a driving step in which the microcontroller drives at least one inverter based on a parameter representing the set torque.

[0054] According to one embodiment, the regulating step determines the command variable by the sum of a DC current threshold value and a corrective action value, the corrective action value being determined by a controller, which is of the integral and / or differential and / or proportional type, and which receives as inputs the DC current threshold value and the measured DC current.

[0055] The command variable is obtained by the sum of a feedforward corresponding directly to the DC current threshold and a corrective action value generated by a closed-loop control of the proportional, integral, derivative type or a combination thereof. This closed-loop corrective action value makes it possible to compensate for parameter variations, in particular magnetic flux and motor resistance, whose values ​​vary with respect to temperature and generation with respect to the reference values ​​implemented in the control, as well as dynamic variations, since the lower order loops can generate a certain delay in the control of the desired torque.

[0056] According to one embodiment, the upper and lower limits of the parameter representing the set torque are obtained by solving an equation which is a function of at least the following parameters: the command variable, the motor speed, the voltage of the inverter DC supply current and the direct axis current of the motor AC supply current measured or determined during a previous iteration.

[0057] The equations solved in the determination step are derived from the general equations for the motor on the direct and quadrature axes.

[0058] According to one embodiment, the general equation is as follows:

[0059] [Mathematical formula 1]

[0060]

[0061] [Mathematical formula 2]

[0062]

[0063] [Mathematical formula 3]

[0064]

[0065] [Mathematical formula 4]

[0066] T=k*pI q .(Ψ+(L d -L q ).I d )

[0067] in:

[0068] V DC : Voltage of the inverter DC supply current (V);

[0069] I DC : Average DC supply current of the inverter (A);

[0070] Ψ: The selected Equivalent magnetic flux of the motor during conversion (Wb);

[0071] L d , L q : Direct-axis and quadrature-axis inductance of the motor (H);

[0072] R ac : Total equivalent resistance on the AC current side of the motor system (Ω);

[0073] p: number of pole pairs of the motor;

[0074] Ω: Motor speed (rad.s -1 );

[0075] k: the selected the transformation factor in the transformation (e.g. 3 / 2 or 1, depending on the chosen convention);

[0076] V d 、V q : DC and quadrature axis voltages of the AC supply current of the motor (A);

[0077] I d ,I q : Direct-axis and quadrature-axis currents of the motor AC supply current (A)

[0078] T: Electromagnetic torque of the motor (Nm)

[0079] According to one embodiment, the equation is a function of the physical parameters of the motor.

[0080] The physical parameters of the motor are, for example, the total equivalent resistance on the AC current side, the equivalent magnetic flux, the equivalent resistance, the direct and quadrature axis inductance, the number of pole pairs. These parameters are a result of the size of the motor. When solving the equations, they are assumed to be constants and, for simplicity, fixed reference values ​​are used.

[0081] The selected The transform factors in the transform are fixed gains corresponding to the chosen convention.

[0082] According to one embodiment, the method comprises a calculation step in which the transformation gain is determined as The transformation coefficient in the transformation, the number of pole pairs of the motor, A function of the equivalent magnetic flux of the motor being transformed, the direct-axis current of the motor's AC supply current measured or determined during a previous iteration, and the direct-axis and quadrature-axis inductances of the motor.

[0083] According to one embodiment, the conversion gain is calculated by the following formula:

[0084] [Mathematical formula 5]

[0085] G Iq2Trq =kp(ψ+(L d -L q ).I d )

[0086] in:

[0087] G Iq2Trq : conversion gain;

[0088] k: the selected the transformation factor in the transformation (e.g. 3 / 2 or 1, depending on the chosen convention);

[0089] p: number of pole pairs of the motor;

[0090] Ψ: The selected Equivalent magnetic flux of the motor during conversion (Wb);

[0091] L d , L q : Direct-axis and quadrature-axis inductance of the motor (H);

[0092] I d : Direct axis current of the AC supply current of the motor (A);

[0093] According to one embodiment, the upper and lower limits of the parameter representing the set torque are obtained by solving the following equation:

[0094] [Mathematical formula 6]

[0095]

[0096] in:

[0097] k: the selected the transformation factor in the transformation (e.g. 3 / 2 or 1, depending on the chosen convention);

[0098] R ac : Total equivalent resistance on the AC current side of the motor system (Ω);

[0099] G Iq2Trq : conversion gain;

[0100] Ω: Motor speed (rad.s -1 );

[0101] I d : Direct axis current of the AC supply current of the motor (A);

[0102] V DC : Voltage of the inverter DC supply current (V);

[0103] I DCCom : Command variable (A),

[0104] I qLim : Quadrature axis current limit of the motor AC supply current (A);

[0105] We get:

[0106] [Mathematical formula 7]

[0107]

[0108] and

[0109] [Mathematical formula 8]

[0110]

[0111] as well as

[0112] [Mathematical formula 9]

[0113] A=kR ac

[0114] [Mathematical formula 10]

[0115] B=G Iq2Trq .Ω

[0116] [Mathematical formula 11]

[0117]

[0118] [Mathematical formula 12]

[0119] Δ=B 2 -4.AC

[0120] in:

[0121] k: the selected the transformation factor in the transformation (e.g. 3 / 2 or 1, depending on the chosen convention);

[0122] R ac : Total equivalent resistance on the AC current side of the motor system (Ω);

[0123] G Iq2Trq : conversion gain;

[0124] Ω: Motor speed (rad.s -1 );

[0125] I d : Direct axis current of the AC supply current of the motor (A);

[0126] V DC : Voltage of the inverter DC supply current (V);

[0127] I DCCom : Command variable (A),

[0128] I qLimMin : The lower limit of the quadrature axis current of the motor AC supply current (A);

[0129] I qLimMax : The upper limit of the quadrature axis current of the motor AC supply current (A);

[0130] T LimMax : Set the upper limit of torque (Nm);

[0131] T LimMin : Set the lower limit of torque (Nm).

[0132] According to one embodiment, the control parameter is converted to an active state when the measured DC current is greater than or equal to a DC current threshold, and the control parameter is converted to an inactive state when the measured DC current is less than the DC current threshold and the parameter representing the set torque is equal to the parameter representing the desired torque.

[0133] Thus, when the measured DC current is greater than or equal to the DC current threshold, the limiting performed by the method is effective, and when the measured DC current becomes less than the DC current threshold, the method stops and the method no longer applies limiting.

[0134] According to one embodiment, the control parameter is activated in an inactive state.

[0135] By default, no limiting is performed on the parameter representing the set torque. Limiting is only implemented if exceeding of the DC current threshold is observed.

[0136] The invention also relates to a power steering system comprising at least one electric motor controlled by the method according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0137] The invention will be better understood through the following description, which relates to embodiments according to the invention, given as non-limiting examples and explained with reference to the accompanying drawings, in which:

[0138] [ Figure 1 ] is a schematic diagram of a power steering system including a method according to the present invention;

[0139] [ Figure 2 ] is a block diagram of the motor power supply;

[0140] [ Figure 3 ] is a schematic diagram of a method according to the present invention;

[0141] [ Figure 4 ] is an expression of the upper and lower limits of a parameter representing the set torque as a function of the motor speed;

[0142] [ Figure 5 ] is a time simulation of the motor speed, parameters representing the desired and set torques, measured DC current, DC current thresholds, command variables, limiting parameters and control parameters. DETAILED DESCRIPTION

[0143] like Figure 1 As shown, the steering system 1 of the vehicle 2 is intended to allow the driver to control the path of the vehicle 2 by changing the steering angle of the vehicle's wheels 10, 11 by means of a steering wheel 3. The steering angle of the wheels is particularly related to the angle θ3 of the steering wheel 3. The driver changes the angle θ3 of the steering wheel 3 by applying a force T3 (hereinafter referred to as "steering wheel torque") on the steering wheel 3. The force T3 applied to the steering wheel can be measured by a torque sensor 23.

[0144] Typically, the steering system 1 comprises a plurality of elements, including the steering wheel 3, a rack 6 and two wheels 10, 11, each of which is connected to tie rods 8, 9. The rack 6 is a component that allows the wheels 10, 11 to be steered, that is, so that the steering angle of the wheels 10, 11 can be changed by the tie rods 8, 9. The rack 6 converts the angular change of the steering wheel 3 into the angular change of the wheels 10, 11.

[0145] The electric power steering system 1 includes: Figure 2 The power supply system of the electric motor 12 shown. The power supply system comprises at least one microcontroller 20, which determines in detail the desired torque X based on the force T3 applied to the steering wheel 3 through the high-level controller 200 in a manner known to those skilled in the art. IN Parameter. Indicates the desired torque X IN The parameter is that the user wants the motor 12 to be independent of the DC current consumed by IDC The torque applied.

[0146] Then, the method 100 according to the invention is based on a representation of the desired torque X IN The parameter is used to determine the set torque X applied by the motor 12. OUT Parameters.

[0147] The modulation unit 300 represents the set torque X OUT The parameters are converted into variables M, so that the inverter 40 can be driven by a vector control method.

[0148] The inverter 40 is powered by a DC current I DC The power is supplied and converted into an AC current I which is supplied to the motor 12 AC . Motor AC supply current I AC It includes direct-axis component and quadrature-axis component. The direct-axis component is referred to as direct-axis current I in the following text. d The quadrature-axis component is represented by quadrature-axis current in the following text.

[0149] With supply voltage V DC The DC current I DC The power is provided by a DC power supply system 30 or DC system, which may be, for example, a battery or a DC-DC converter.

[0150] The motor 12 is based on the set torque X OUT The motor torque T12 is applied to the rack 6. The motor torque T12 depends on the AC current I supplied to the motor 12. AC The user of the motor 12 seeks to ensure that the motor torque T12 is close to or equal to the desired torque X represented by IN The parameter defines the desired torque.

[0151] All elements capable of controlling the electric motor 12 are referred to below as the motor system. The motor system comprises in particular a motor-inverter assembly and a microcontroller 20 .

[0152] The electric motor 12 is preferably a bidirectional electric motor, preferably a brushless rotary electric motor.

[0153] The invention is applicable, for example, to an electric motor 12 for mechanical power steering, i.e. in which there is a mechanical linkage, usually implemented by a steering column 4, which meshes via a steering pinion 5 with a rack 6, the rack 6 itself being guided in translation in a housing 7 fixed to the vehicle 2, or to electric power steering systems without a mechanical linkage, known as "steer-by-wire", in which the steering wheel is mechanically decoupled from the rack, not shown in the figures.

[0154] In the case of mechanical power steering, the electric motor 12 can be meshed through a gear reduction type reducer, or meshed on the steering column 4 itself, forming a so-called "single pinion" mechanism, or directly meshed on the steering rack 6, for example, by meshing with a second pinion 13 different from the steering pinion 5, so that the steering column 4 is meshed with the rack 6, thereby forming a so-called "double pinion" mechanism, such as Figure 1 shown.

[0155] The present invention relates in particular to a method of controlling a synchronous motor 12, which may be Figure 1 The electric motor 12 of a steering system or an electric motor 12 of another application is shown.

[0156] According to the method 100 of the present invention, Figure 3 shown.

[0157] According to the method 100 of the present invention, a torque X is determined OU The parameter can be torque or quadrature axis current. Similarly, the desired torque X IN The parameter corresponds to the torque or quadrature-axis current.

[0158] The method 100 comprises a control step E1. The step E1 receives a DC current threshold I DCMax , measured DC current I DCMes As input, and determine the control parameter CTL.

[0159] The control step E1 also receives as input the limit parameter LIM.

[0160] DC current threshold I DCMax is the DC current I consumed which we do not wish to exceed DC In other words, during the operation of the motor 12, the DC current threshold I DCMax Corresponding to DC current I DC The DC current threshold I DCMax Determined by the user.

[0161] The measured DC current I DCMes corresponds to the DC current I actually consumed by the motor 12 during the previous iteration DC The method 100 according to the present invention adjusts the measured DC current I DCMes , so that it remains less than or equal to the DC current threshold I DCMax .

[0162] During the control step E1 , the microcontroller 20 determines the actual DC current I DCIn other words, it allows the implementation of the method 100 according to the invention. For this purpose, the control parameter CTL is used as the DC current threshold I DCMax and the measured DC current I DCMes and the limit parameter LIM to be switched to the active state ON or the inactive state OFF.

[0163] According to one embodiment, the control parameter CTL has a value of 1 in the active state ON and a value of 0 in the inactive state OFF.

[0164] According to one embodiment, the control parameter CTL is activated in the inactive state OFF, that is to say:

[0165] [Mathematical formula 13]

[0166] CTL=OFF

[0167] According to one embodiment, when the measured DC current I DCMes Greater than or equal to the DC current threshold I DCMax When the control parameter CTL is switched to the active state ON, the measured DC current I DCMes Less than the DC current threshold I DCMax And when the limit parameter LIM is in the inactive state OFF, the control parameter CTL is converted to the inactive state OFF.

[0168] In other words:

[0169] [Mathematical formula 14]

[0170] IF I DCMes ≥I DCMax = > CTL = ON

[0171] [Mathematical formula 15]

[0172] If I DCMes DCMax AND LIM=OFF=>CTL=OFF

[0173] When the measured DC current I DCMes Greater than or equal to the DC current threshold I DCMax The limitation of method 100 is effective when the measured DC current I DCMes becomes less than the DC current threshold I DCMax , the limiting of method 100 stops and method 100 no longer performs limiting. In other words, by default, the setting torque X OUT The parameters are not limited. Only when the DC current threshold I DCMax Restrictions are only implemented when ​

[0174] The control step is achieved by activating the DC current I only when necessary DCMes , allowing the measured current I DCMes Make appropriate adjustments.

[0175] The method 100 comprises a regulation step E2. During this step, the command variable I DCCom is determined as the DC current threshold I DCMax and the measured DC current I DCMes function.

[0176] Command variable I DCCom corresponds to a commanded virtual DC current, so that the maximum value of the consumed DC current can be maintained at less than or equal to the DC current threshold I DCMax .

[0177] The regulation step can, on the one hand, compensate for parameter variations, in particular magnetic flux and motor resistance, whose values ​​vary as a function of temperature and production relative to the reference values ​​implemented in the control and, on the other hand, the dynamics in the lower-level regulation loops can produce a certain delay in controlling the desired torque.

[0178] According to one embodiment, the adjustment step E2 is performed when the control parameter CTL is in the active state ON.

[0179] Therefore, as long as the measured DC current I DCMes Less than the DC current threshold I DCMax , you can avoid the command variable I DCCom Divergence.

[0180] Regulation step E2 passes through the DC current threshold I DCMax and the correction action value ΔI DC The sum of the command variables I DCCom The correction action value is determined by the controller E21, which is an integral and / or differential and / or proportional controller. The controller E21 receives a DC current threshold value I DCMax and the measured DC current I DCMes as input.

[0181] The method 100 comprises a determination step E3. During this step, the set torque X OUT The upper limit of the parameter X LimMax and the lower limit X LimMin At least the command variable I is determined DCCom Therefore, the determination step E3 follows the regulation step E2 and they are only performed when the control parameter CTL is in the active state ON, that is, when the method 100 converts the measured DC current I DCMes Regulate or limit the DC current to the threshold IDCMax In other words, only when the measured DC current I DCMes Must be less than or equal to the DC current threshold I DCMax Or just set the torque X OUT The adjustment E2 and determination E3 steps are performed only when the conditions are restricted.

[0182] Upper limit X LimMax and the lower limit X LimMin Defines a range of values ​​within which the set torque X must be represented. OUT parameters to ensure that the measured DC current I DCMes Or the DC current consumed by the motor 12 remains less than or equal to the DC current threshold I DCMax Since the command variable I DCCom The dispersion of the physical parameters of the motor system 12 is taken into account, so that step E3 does not implement the calculation or adjustment of complex variables.

[0183] According to one embodiment, the set torque X is represented by OUT The upper limit of the parameter X LimMax and the lower limit X LimMin is obtained by solving an equation that is a function of at least the following parameters: command variable I DCCom , the speed Ω of the motor 12, the DC current V supplied to the inverter 40 DC and the AC current I supplied to the motor 12 measured or determined during the previous iteration. AC The direct axis current I d .

[0184] According to one embodiment, the equation is a function of the physical parameters of the motor.

[0185] The physical parameters of the motor are, for example, the total equivalent resistance on the AC current side, the equivalent magnetic flux, the equivalent resistance, the direct or quadrature axis inductance, the number of pole pairs. These parameters are a result of the size of the motor. They are assumed to be constant within the resolution of the equations and fixed reference values ​​are used for simplicity.

[0186] The selected The transform factors in the transform are fixed gains corresponding to the chosen convention.

[0187] Conversion gain G Iq2Trq As The conversion factor k in the conversion, the number of pole pairs p of the motor 12, The equivalent magnetic flux Ψ of the motor during the transformation, the AC current I supplied to the motor 12 measured or determined in the previous iteration AC The direct axis current I d and the direct axis L of the motor 12d and the cross axis L q The function of the inductance is determined during calculation step E5.

[0188] According to one embodiment, the conversion gain is calculated by the following formula:

[0189] [Mathematical formula 16]

[0190] G Iq2Trq =kp(ψ+(L d -L q ).I d )

[0191] in:

[0192] G Iq2Trq : conversion gain;

[0193] k: the selected the transformation factor in the transformation (e.g. 3 / 2 or 1, depending on the chosen convention);

[0194] p: number of pole pairs of the motor;

[0195] Ψ:: The selected Equivalent magnetic flux of the motor during conversion (Wb);

[0196] L d , L q : Direct-axis and quadrature-axis inductance of the motor (H);

[0197] I d : Direct axis current of AC supply current of motor (A)

[0198] The equations solved during determination step E3 are obtained from the general equations of the electric motor 12 on the direct and quadrature axes.

[0199] According to one embodiment, the general equation is as follows:

[0200] [Mathematical formula 17]

[0201]

[0202] [Mathematical formula 18]

[0203]

[0204] [Mathematical formula 19]

[0205]

[0206] [Mathematical formula 20]

[0207] T=k*pIq .(Ψ+(L d -L q ).I d )

[0208] in:

[0209] V DC : Voltage of the inverter DC supply current (V);

[0210] I DC : Average value of inverter DC supply current (A);

[0211] Ψ: The selected Equivalent magnetic flux of the motor during conversion (Wb);

[0212] L d , L q : Direct-axis and quadrature-axis inductance of the motor (H);

[0213] R ac : Total equivalent resistance on the AC current side of the motor system (Ω);

[0214] p: number of pole pairs of the motor;

[0215] Ω: Motor speed (rad.s -1 );

[0216] k: the selected the transformation factor in the transformation (e.g. 3 / 2 or 1, depending on the chosen convention);

[0217] V d 、V q : DC and quadrature axis voltages of the AC supply current of the motor (V);

[0218] I d ,I q : Direct-axis and quadrature-axis currents of the motor AC supply current (A)

[0219] T: Electromagnetic torque of the motor (Nm)

[0220] According to one embodiment, the set torque X is represented by OUT The upper limit of the parameter X LimMax and the lower limit X LimMin It is obtained by solving the following equation:

[0221] [Mathematical formula 21]

[0222]

[0223] in:

[0224] k: the selected the transformation factor in the transformation (e.g. 3 / 2 or 1, depending on the chosen convention);

[0225] R ac : Total equivalent resistance on the AC current side of the motor system (Ω);

[0226] G Iq2Trq : conversion gain;

[0227] Ω: Motor speed (rad.s -1 );

[0228] I d : Direct axis current of the AC supply current of the motor (A);

[0229] V DC : Voltage of the inverter DC supply current (V);

[0230] I DCCom : Command variable (A),

[0231] I qLim : Quadrature axis current limit of the motor AC supply current (A);

[0232] We get:

[0233] [Mathematical formula 22]

[0234]

[0235] and

[0236] [Mathematical formula 23]

[0237]

[0238] as well as

[0239] [Mathematical formula 24]

[0240] A=kR ac

[0241] [Mathematical formula 25]

[0242] B=G Iq2Trq .Ω

[0243] [Mathematical formula 26]

[0244]

[0245] [Mathematical formula 27]

[0246] Δ=B 2 -4.AC

[0247] in:

[0248] k: the selected the transformation factor in the transformation (e.g. 3 / 2 or 1, depending on the chosen convention);

[0249] R ac : Total equivalent resistance on the AC current side of the motor system (Ω);

[0250] G Iq2Trq : conversion gain;

[0251] Ω: Motor speed (rad.s -1 );

[0252] I d : Direct axis current of the AC supply current of the motor (A);

[0253] V DC : Voltage of the inverter DC supply current (V);

[0254] I DCCom : Command variable (A),

[0255] I qLimMin : The lower limit of the quadrature axis current of the motor AC supply current (A);

[0256] I qLimMax : The upper limit of the quadrature axis current of the motor AC supply current (A);

[0257] T LimMax : Set the upper limit of torque (Nm);

[0258] T LimMin : Set the lower limit of torque (Nm).

[0259] The method finally comprises an evaluation step E4. During this step, the set torque X OUT The parameters are at least determined to represent the set torque X OUT The upper limit of the parameter X LimMax and the lower limit X LimMin The control parameter CTL and represents the desired torque X IN A function of the parameters.

[0260] When the control parameter CTL is in the active state ON, it means the set torque X OUT The parameters must represent the desired torque X as closely as possible. IN parameters, while considering the upper limit X LimMax and the lower limit X LimMin所 Determine the range of values. In other words:

[0261] [Mathematical formula 28]

[0262] If CTL=ON=>X OUT =min(X LimMax , max (X LimMin , X IN ))

[0263] When the control parameter CTL is in the inactive state OFF, it means the set torque X OUT The parameter is equal to the desired torque X IN Parameters, ignoring the upper limit X LimMax and the lower limit X LimMin Therefore, the DC current I DC There is no regulation. In other words:

[0264] [Mathematical formula 29]

[0265] If CTL=OFF=>X OUT =X IN

[0266] According to one embodiment, the evaluation step E4 determines at least a limiting parameter LIM as representing the set torque X OUT The parameters and represent the desired torque X IN A function of the parameters.

[0267] The limit parameter LIM indicates whether the desired torque X is represented during the evaluation step E4. IN The parameters are restricted.

[0268] According to one embodiment, when the set torque X is represented OUT The parameter is different from the desired torque X IN When the limit parameter LIM is set to ON, the limit parameter LIM is active ON. In other words:

[0269] [Mathematical formula 30]

[0270] If X OUT ≠X IN = > LIM = ON

[0271] According to one embodiment, when the set torque X is represented OUT The parameter is equal to the desired torque X IN When the limit parameter LIM is in the inactive state OFF. In other words:

[0272] [Mathematical formula 31]

[0273] If X OUT =X IN = > LIM = OFF

[0274] Finally, the method includes a driving step in which the inverter 40 is driven by the microcontroller 20 based on a torque indicating a set torque X. OUT parameters to drive.

[0275] The principle of the method 100 according to the invention is that, when it is necessary to limit the consumed DC current IDC, via the command variable I DCCom Taking into account the deviation of the physical parameters of the motor 12, then, based on this, the set torque X representing the motor 12 is determined. OUT The parameter value range can ensure that the consumed DC current I DC Equal to or less than the DC current threshold I DCMax .

[0276] Figure 4 The solution I of the equation solved in the determination step is shown when the DC current threshold is 50A and 5A. qLimMax ,I qLimMin , the equation is a function of the rotational speed Ω of the motor 12.

[0277] Figure 5 shows the speed Ω of the motor 12, the desired torque T expressed in the form of torque IN and set torque T OUT Parameters, measured DC current I DCMes , DC current threshold I DCMax ., Command variable I DCCom , time simulation of the limit parameter LIM and the control parameter CTLL.

[0278] The limiting parameter LIM and the control parameter CTL are initially in the inactive state OFF, i.e. the value is 0. The DC current threshold I DCMax is set to 50A.

[0279] When the speed Ω of the motor 12 increases and the desired torque T IN When the measured DC current I DCMes increases and then exceeds the DC current threshold I DCMax This over-limit continues to lead to the activation state ON, that is, the value of the control parameter CTL is 1, and then the command variable I is calculated to be less than 50A. DCCom , and finally calculate the reduced set torque T OUT , and the limit parameter LIM enters the active state OFF, that is, the value is 1. As a result, the measured DC current I DCMes decreases until it returns to the DC current threshold I DCMax Nearby, this threshold is the regulation set point.

[0280] As the rotation speed Ω of the motor 12 decreases, the upper limit T of the parameter representing the set torqueLimMax and lower limit T LimMin will naturally become wider, in this example, plus the desired torque T IN The limit parameter LIM returns to the inactive state OFF. The measured DC current I DCMes has logically returned below the DC current threshold I DCMax , the control parameter CTL has also been switched to the inactive state OFF. The desired torque T IN Again equal to the set torque T OUT .

[0281] Of course, the invention is not limited to the embodiments described and represented in the accompanying drawings. Modifications are still possible, notably from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.

Claims

1. A method for expressing a set torque (X) of a motor (12) OUT ), wherein the electric motor (12) is supplied with an AC current (I AC ), the at least one inverter (40) being driven by at least one microcontroller (20) using a vector control method, the at least one inverter (40) being powered by a DC current (I DC ), the method (100) being executed by the at least one microcontroller (40) and comprising: - a control step (E1), in which a control parameter (CTL) is determined as at least a DC current threshold value (I DCMax ), the measured DC current (I DCMes ) and a function of the limiting parameter (LIM); - a regulation step (E2), in which the command variable (I DCCom ) is determined to be at least a DC current threshold (I DCMax ) and the measured DC current (I DCMes ) function; - Determination step (E3), wherein, represents the set torque (X OUT ) is the upper limit of the parameter (X LimMax ) and the lower limit (X LimMin ) is at least identified as a command variable (I DCCom ) function; - Evaluation step (E4), wherein, represents the set torque (X OUT ) is determined to represent at least the set torque (X OUT ) is the upper limit of the parameter (X LimMax ) and the lower limit (X LimMin ) and represents the desired torque (X IN ) is a function of the parameters.

2. The determination method (100) according to claim 1, wherein: Indicates the set torque (X OUT ) and represents the desired torque (X IN ) corresponds to the torque (T OUT , T IN ) or current cross axis.

3. The determination method (100) according to any one of the preceding claims, further comprising a driving step, wherein: The at least one inverter is controlled by the microcontroller (20) based on a voltage representing the set torque (X OUT ) parameter drive.

4. The determination method (100) according to any one of the preceding claims, wherein: The regulating step (E2) is performed by a DC current threshold (I DCMax ) and the correction action value (ΔI DC ) and determine the command variable (I DCCom ), the correction action value is received by the integral and / or differential and / or proportional controller E21 as a DC current threshold value (I DCMax ) and the measured DC current (I DCMes ) as input to determine.

5. The determination method (100) according to any one of the preceding claims, wherein: Indicates the set torque (X OUT ) is the upper limit of the parameter (X LimMax ) and the lower limit (X LimMin ) is obtained by solving an equation which is a function of at least the following parameters: the command variable (I DCCom ), the speed of the motor (Ω), the DC current voltage (V DC ), and the direct-axis current (I d ).

6. The determination method (100) according to the preceding claim, comprising a calculation step (E5) in which the transformation gain (G Iq2Trq ) was determined to be The transformation factor (k) in the transformation, the number of pole pairs of the motor (p), The equivalent magnetic flux (Ψ) of the motor being transformed, the direct-axis current (I d ) and the direct axis of the motor (L d ) or cross axis (L q ) is a function of the inductance.

7. The determination method (100) according to any one of the preceding claims, wherein: When the measured DC current (I DCMes ) is greater than or equal to the DC current threshold (I DCMax ), the control parameter (CTL) is switched to the active state (IN), and when the measured DC current (I DCMes ) is less than the DC current threshold (I DCMax ) and indicates the set torque (X OUT ) is equal to the desired torque (X IN ) parameter, the control parameter is converted to an inactive state (OFF).

8. The determination method (100) according to the preceding claim, wherein: The control parameter (CTL) is activated in the inactive state (OFF).

9. A power steering system (1) comprising at least one electric motor (12) which is driven by a method (100) according to any one of the preceding claims to determine a set torque (X OUT ) parameter control.

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