Method and device for determining a target value of a current
By determining the coefficients of permanent magnet flux and resistance torque based on the operating point and calculating the theoretical current value, the problem of imprecise current distribution in permanent magnet excitation electric motors is solved, and efficient motor torque adjustment and component protection are achieved.
Patent Information
- Application Number
- CN202010920977.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Priority Date
- 2019-09-04
- Filing Date
- 2020-09-04
- Publication Date
- 2024-12-10
- Estimated Expiration
- 2040-09-04
AI Technical Summary
In permanent magnet excited electric motors, it is difficult for the prior art to accurately and efficiently determine the current theoretical value to generate the desired motor theoretical torque, especially in rapid dynamic processes, resulting in inaccurate magnetic field current regulation.
Through the control device, the coefficients for the permanent magnet flux torque and the magnetic resistance torque are determined based on the current operating point and the expected motor theoretical torque, thereby calculating the current theoretical value of the torque forming and the current theoretical value of the weakening magnetic field, and adjusting the intermediate loop voltage to achieve optimal efficiency current distribution.
The optimal current distribution according to the efficiency of the operating point is achieved, ensuring efficient operation of the electric motor at each operating point, reducing material costs, and providing component protection through constraint coefficients.
Smart Images
Figure CN112532135B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method and a device for determining a target current value for generating a desired target motor torque at a permanently excited electric motor. Background Art
[0002] Due to the higher magnetic permeability in the transverse axis (q-axis, sometimes called quadrature axis) compared to the longitudinal axis (d-axis, sometimes called direct axis) oriented toward the permanent magnets, for synchronous machines (synchronous machines, sometimes called synchronous motors) with embedded magnets, in addition to the synchronous permanent flux moment (permanent flux moment, sometimes called permanent magnet torque), the reluctance torque can be used, which acts in particular in the field weakening region. Due to the additional reluctance torque, the machine can be designed with relatively less magnetic material, thereby reducing material costs.
[0003] In order to generate the motor target torque at a permanently excited electric motor, two target current values (q-axis current, d-axis current) must be determined in field coordinates. In order to optimally utilize the intermediate circuit voltage of the intermediate circuit (Zwischnkreis, sometimes called intermediate circuit) used to operate the electric motor, a control system is usually used here, which uses the d-axis current as a manipulated variable.
[0004] DE 10 2013 222 539 A1 discloses a method for operating a permanently excited synchronous machine, in which a torque-generating current and a field-weakening current are regulated in a rotor-fixed coordinate system, wherein the method should allow accurate and precise regulation even in fast and dynamic processes. To this end, it is provided that, for a predetermined torque requirement, an operating point of the synchronous machine is determined with the associated value of the torque-generating current, at which the field-weakening current has the smallest possible value. Summary of the invention
[0005] The object of the present invention is to improve a method and a device for determining a target current value for generating a desired target motor torque at a permanently excited electric motor.
[0006] According to the invention, this object is achieved by the method according to the invention and the device according to the invention.
[0007] In particular, a method is provided for determining a target current value for generating a desired target motor torque at a permanently excited electric motor, wherein by means of a control device:
[0008] - obtain the current operating point and the expected motor theoretical torque,
[0009] - Determination of the coefficient for the permanent magnet flux torque component depending on the operating point,
[0010] - determining the permanent magnet flux torque and the reluctance torque from the desired motor theoretical torque using the determined coefficients,
[0011] - starting from the determined permanent magnet flux torque, determine the theoretical value of the current for generating the torque,
[0012] - starting from the determined reluctance torque, a theoretical value of the current for weakening the magnetic field is determined, and
[0013] - The determined setpoint current value is provided for the control.
[0014] Furthermore, a device is provided in particular for determining a target current value for generating a desired target motor torque at a permanently excited electric motor, the device comprising a control device, wherein the control device is designed to:
[0015] - obtain the current operating point and the expected motor theoretical torque,
[0016] - Determination of the coefficient for the permanent magnet flux torque component depending on the operating point,
[0017] - determining the permanent magnet flux torque and the reluctance torque from the desired motor theoretical torque using the determined coefficients,
[0018] - starting from the determined permanent magnet flux torque, determine the theoretical value of the current for generating the torque,
[0019] - starting from the determined reluctance torque, a theoretical value of the current for weakening the magnetic field is determined, and
[0020] - The determined setpoint current value is provided for the control.
[0021] The method and the device make it possible to determine, in particular calculate, a theoretical current for forming a torque (d-axis current) and a theoretical current for weakening a magnetic field (q-axis current) depending on the operating point. This is done by determining a coefficient for the permanent magnetic flux torque component depending on the operating point. The permanent magnetic flux torque component indicates how large a share the permanent magnetic flux torque occupies in the total torque. With the aid of the coefficient, the share of the reluctance torque in the total torque can therefore also be determined. With the aid of the determined coefficient, the permanent magnetic flux torque and the reluctance torque are determined, in particular calculated, for the desired motor torque to be obtained. The theoretical value of the current for forming a torque (q-axis current) is determined based on the determined permanent magnetic flux torque. This is done in particular when using a motor torque equation for an electric motor. Accordingly, the theoretical value of the current for weakening a magnetic field (d-axis current) is determined based on the determined reluctance torque. For regulation, the theoretical current value thus determined is provided, for example, in such a way that the theoretical current value thus determined is output as a corresponding theoretical current value signal. The motor torque of the electric motor can then be regulated in a manner known per se by means of a control circuit.
[0022] The method and the device have the advantage that a setpoint current value is provided as a function of the operating point. By means of factors determined as a function of the operating point, the determination can be designed in such a way that an efficiency-optimized setpoint current value is provided for each operating point without great effort.
[0023] The variable referred to as torque in connection with the electric motor and the present disclosure is, in particular, torque.
[0024] The operating point includes in particular the current value of the intermediate circuit voltage in the intermediate circuit used for operating the electric motor and the motor angular velocity. The operating point here covers in particular the possible range of operating points or the power range of the electric motor. The current operating point can be detected, for example, at the intermediate circuit (intermediate circuit voltage) or at the electric motor (motor angular velocity) by means of suitable sensor devices. The associated sensor data are supplied to the control device.
[0025] To determine the target current value from the permanent magnet flux torque and the reluctance torque, for example, the following motor torque equation for the motor torque M can be used:
[0026] M=3 / 2*Z p *I q (Ψ pm +(L d -L q )*I d )=K*ψ pm *I q +K*(L d -L q )*I d *I q .
[0027] Where Z p is the number of pole pairs of the electric motor, ψ pm is the permanent magnetic flux (sometimes called permanent magnetic flux linkage), (L d -L q ) is the inductance difference of the electric motor due to the (magnetic) asymmetry of the electric motor, I q is the current that generates torque, I d is the current that weakens the magnetic field and K is the structure factor of the electric motor (where K = 3 / 2*Z p ).
[0028] Here, for the permanent magnetic flux torque M pm It turns out that:
[0029] M pm =K*ψ pm *I q ,
[0030] And for the magnetic drag moment M 磁阻 It turns out that:
[0031] M 磁阻 =K*(L d -L q )*I d *I q .
[0032] For the coefficients we get:
[0033] K pm =M pm / M.
[0034] The motor torque equations described are only simple examples and can in principle also be designed differently, in particular more complex. d and L q and hence the inductance difference (L d -L q ) can also be dependent on the operating point.
[0035] In addition, the following are particularly suitable for voltage:
[0036] U d =R s *I d +L d *(d / dt)I d -ω*L q *I q ,
[0037] U q =R s *I q +Lq *(d / dt)I q +ω*L d *I d +ω*ψ pm .
[0038] Limitations with intermediate circuit:
[0039] U d 2 +U w 2 ≤V DC 2 / 3.
[0040] Where R s is the resistance, U d is the stator voltage of the d-axis, U q is the stator voltage of the q axis, ω is the motor angular velocity and V DC is the intermediate circuit voltage.
[0041] The method is implemented by means of a control device. The control device can be designed as a combination of hardware and software, for example as a program code executed on a microcontroller or a microprocessor.
[0042] In one embodiment, it is provided that the maximum achievable motor torque is determined by means of the control device, in addition as a function of the operating point, wherein the desired motor setpoint torque obtained is limited to the determined maximum achievable motor torque. The maximum achievable motor torque is in particular the maximum achievable motor torque with the electric motor at a given operating point. This makes it possible to further improve the efficiency of the electric motor at a given operating point. In particular, this depends on the maximum achievable motor torque M max Coefficient of determination:
[0043] K pm =M pm / M max .
[0044] For a given operating point, the coefficients then remain constant independently of the desired motor setpoint torque. In particular, a good compromise can be achieved as a result between a high efficiency of the control device and the computing power required for determining the coefficients.
[0045] In one embodiment, it is provided that a characteristic map that is dependent on the operating point is used in each case to determine the maximum achievable motor torque and / or the coefficient. As a result, an optimal solution for the maximum achievable motor torque and / or the coefficient can be calculated for each or a predetermined number of operating points and stored in the characteristic map. When using the method, the optimal values for the maximum achievable motor torque and / or the coefficient for the operating point only need to be called up or read out from the respective characteristic map. As a result, the computing power required in the control device for carrying out the method can be reduced.
[0046] For example, a characteristic map can be determined for selected (for example 300 to 400) operating points, ie, for example, from pairs formed for the intermediate circuit voltage and the motor angular velocity, by solving the motor torque equation described above by way of example. q ,I d The motor torque equation is varied until the resulting motor torque reaches a maximum value. The motor torque that reaches the maximum value thus forms the maximum achievable motor torque for a given operating point. The coefficients are also determined using the same solution. If this is done for all operating points, an operating point-dependent overall characteristic curve for the maximum achievable motor torque and an operating point-dependent overall characteristic curve for the coefficients can be generated from this.
[0047] Furthermore, it can be provided that the characteristic curve thus determined is further or repeatedly optimized during use of the method by taking into account experimentally acquired measurement data, for example by adapting the characteristic curve. In addition, machine learning methods can also be used to create or optimize the characteristic curve.
[0048] In an improved embodiment, it is provided that the operating point-dependent characteristic curve for the maximum achievable motor torque and / or the operating point-dependent characteristic curve for the coefficients are temperature-dependent. Thus, temperature influences can also be taken into account in addition. This can further improve the efficiency-optimized provision of the current target value.
[0049] In one embodiment, it is provided that a restriction factor is determined by means of the control device and that the desired motor setpoint torque is limited by the restriction factor. In addition, a component protection or motor protection can be provided by means of which the electric motor is operated only at a reduced power. The restriction factor Lim includes in particular a value range of 0 to 1 and can be predefined, for example, in the form of a percentage indication (prozentangabe, sometimes referred to as a percentage value) (e.g. 80% . . .).
[0050] In one embodiment, it is provided that before the current target value is determined, the value for the permanent magnet flux is corrected as a function of the motor temperature determined. This makes it possible to further improve the provision of an efficiency-optimized current target value. In particular, it can be provided that, for this purpose, a linear, temperature-dependent characteristic curve is used, for example in a simple case.
[0051] In one embodiment, it is provided that a value for the inductance difference is determined as a function of the torque-generating current actual value obtained and the field-weakening current actual value obtained. This makes it possible to further improve the provision of efficiency-optimized current target values. The inductance difference is used in particular to calculate the target current value using the motor torque equation described.
[0052] Further features for the embodiment of the device emerge from the description of the embodiment of the method. The advantages of the device are respectively the same as in the embodiment of the method.
[0053] In particular, a motor vehicle is also provided which comprises at least one device according to any of the described embodiments. BRIEF DESCRIPTION OF THE DRAWINGS
[0054] The invention is explained in more detail below with reference to the drawings using preferred exemplary embodiments.
[0055] Figure 1 A schematic diagram of an embodiment of a device for determining a target current value for generating a desired target motor torque at a permanently excited electric motor is shown;
[0056] Figure 2 A schematic signal flow chart is shown for explaining one specific embodiment of a method for determining a target current value for generating a desired target motor torque at a permanently excited electric motor. DETAILED DESCRIPTION
[0057] exist Figure 1 The calculation method for determining the theoretical current value I is shown in d理论 ,I q理论 To generate the desired motor torque M at the permanently excited electric motor 理论 A schematic diagram of an embodiment of the device 1.
[0058] The device 1 is arranged, for example, in a motor vehicle 50 and is used there, for example, to provide a setpoint current value I d理论 ,I q理论 The purpose is to adjust the assist torque of an electric motor of a power steering system (not shown) of motor vehicle 50 .
[0059] The device 1 comprises a control device 2 which is designed as a combination of hardware and software, for example as a program code executed on a microcontroller or microprocessor.
[0060] The current operating point 3 of the electric motor and the desired motor setpoint torque M 理论 is supplied to the control device 2. The operating point 3 comprises the current values for the intermediate circuit voltage and the motor angular speed.
[0061] The control device 2 determines the desired motor torque M as a function of the operating point 3. 理论 The coefficient of the permanent magnet flux torque share in .
[0062] The control device 2 uses the determined coefficients to calculate the desired motor setpoint torque M 理论 Determine the permanent magnetic flux torque and reluctance torque.
[0063] Starting from the determined permanent magnet flux torque, the control device 2 determines the setpoint value I of the current which generates the torque. q理论 Taking the determined reluctance torque as a starting point, the control device 2 determines a target value I for the current which weakens the magnetic field. d理论 This determination is performed, for example, using the motor torque equation described above in the overview.
[0064] To regulate the setpoint torque I d理论 ,I q理论 The regulation takes place in a manner known per se by means of a control circuit (not shown).
[0065] In particular, it is provided that the control device 2 determines the maximum achievable motor torque as a function of the operating point 3. The control device 2 determines the desired motor setpoint torque M 理论 Limited to a certain maximum achievable motor torque.
[0066] exist Figure 2 The diagram is used to illustrate the method for determining the theoretical current value I d理论 ,I q理论 To generate the desired motor torque M at the permanently excited electric motor 理论 Schematic signal flow chart of an embodiment of the method.
[0067] Depends on the current operating point 3 (the operating point 3 includes the current intermediate circuit voltage V DC and the current motor angular velocity ω 实际 ) Determine the maximum achievable motor torque M max This determination takes place on the basis of a characteristic map 10 in which the associated maximum achievable motor torque M is stored for different operating points 3 . maxThe characteristic map 10 is stored, for example, in a memory of the control unit. If no maximum achievable motor torque M is found in the stored characteristic map 10 at the current operating point 3 max If the corresponding value is known, the interpolated value can be taken from the adjacent operating point as the starting point.
[0068] Furthermore, starting from the current operating point 3, the factor K for the permanent magnet flux torque component is determined: pm This determination is carried out on the basis of a characteristic map 11 in which the associated coefficients K are stored for different operating points 3 . pm The characteristic map 11 is stored, for example, in a memory of the control device. If no corresponding factor K is found in the stored characteristic map 11 at the current operating point 3 pm If the corresponding value is known, the interpolated value can be taken from the adjacent operating point as the starting point.
[0069] Before the method is carried out, characteristic curves 10 , 11 are generated and made available, for example by solving the already described motor torque equations for different operating point values.
[0070] By determining the maximum achievable motor torque M max The desired motor setpoint torque M is limited by means of the limiter 12 理论 , which means that if the desired motor theoretical torque M 理论 Exceeding the maximum achievable motor torque M max , the desired motor theoretical torque M 理论 Set to the maximum achievable motor torque M max Otherwise, the desired motor theoretical torque M 理论 Remain unchanged.
[0071] With the help of the determined coefficient K pm From the (possibly limited) desired motor torque M 理论 Determine the permanent magnetic flux torque M pm and magnetic drag torque M 磁阻 In order to calculate the permanent magnetic flux torque M pm , the (if necessary limited) desired motor theoretical torque M 理论 With coefficient K pm By multiplying the desired motor theoretical torque M 理论 Subtract the multiplication result to calculate the magnetic resistance moment M 磁阻 .
[0072] With the aid of the motor torque equation already described, the permanent magnet flux torque M can be determined from pm and the determined magnetic drag moment M 磁阻 Calculate the theoretical current value I d理论 ,Iq理论 In order to obtain the theoretical current value I of the q-axis current for generating torque q理论 , the determined permanent magnetic flux torque M pm Divided by the permanent magnetic flux ψ pm and structure factor K. In order to obtain the theoretical current value I for the d-axis current that weakens the magnetic field d理论 , the determined magnetic drag moment M 磁阻 Divided by the inductance difference (L d -L q ) and structure factor K.
[0073] Here, it can be provided that, depending on the torque-generating current actual value I q实际 and the actual value of the field weakening current I d实际 Determine the inductance difference (L d -L q In particular, this can be done based on the comprehensive characteristic curve 13.
[0074] In addition, it can be set that when determining the theoretical current value I d理论 ,I q理论 Previously, it was determined by the motor temperature T mot Correction for permanent magnetic flux ψ pm This is done, for example, with the aid of characteristic curve 14.
[0075] Furthermore, it can be provided that the characteristic curves 10, 11 are also temperature-dependent. In this case, the operating point 3 also includes the motor temperature T mot .
[0076] It can be set to obtain the constraint coefficient Lim and limit the desired motor theoretical torque M by the constraint coefficient Lim. 理论 In addition, a component protection or motor protection can be provided, by which the electric motor is operated only at a reduced power. The restriction factor Lim comprises in particular a value range of 0 to 1 and can be obtained, for example, as a percentage indication (0 to 100%). The limitation by the restriction factor Lim is carried out in the limiter 15.
[0077] Reference Numbers List
[0078] 1 device
[0079] 2. Control Equipment
[0080] 3. Operation status
[0081] 10 Comprehensive characteristic curve
[0082] 11 Comprehensive characteristic curve
[0083] 12 Limiter
[0084] 13 Comprehensive characteristic curve
[0085] 14 Characteristic curve
[0086] 15 Limiter
[0087] M 理论 Motor theoretical torque
[0088] I d理论 Theoretical current value (d-axis current)
[0089] I q理论 Theoretical current value (q-axis current)
[0090] L d -L q Inductance difference
[0091] ω 实际 Motor angular velocity
[0092] V DC Intermediate circuit voltage
[0093] M max Maximum achievable motor torque
[0094] K pm Coefficient (permanent magnet flux torque share)
[0095] M pm Permanent magnetic flux torque
[0096] M 磁阻 Reluctance torque
[0097] ψ pm Permanent magnetic flux
[0098] I q实际 Current actual value (q-axis current)
[0099] I d实际 Current actual value (d-axis current)
[0100] T mot Motor temperature
Claims
1. Used to determine the theoretical value of current (I q理论 ,I d理论 ) for generating the desired theoretical motor torque (M) at the permanent magnet excited electric motor 理论 ) method, wherein the desired motor theoretical torque (M 理论 ) is the permanent magnetic flux torque (M pm ) and magnetic drag torque (M 磁阻 ), wherein by means of the control device (2): - Obtain the current operating point (3) and the desired motor theoretical torque (M 理论 ), - Determine the factor for the permanent magnet flux torque component (K) depending on the operating point pm ), where in order to determine the coefficient (K pm ) uses an operating point-dependent characteristic map (11), wherein the characteristic map (11) stores associated coefficients (K) for different operating points (3) pm ), where the coefficient (K pm ) is generated in advance by solving the motor torque equation for different operating point values, - With the help of the determined coefficient (K pm ) from the desired motor theoretical torque (M 理论 ) to determine the permanent magnetic flux torque (M pm ) and magnetic drag torque (M 磁阻 ), - With the determined permanent magnetic flux torque (M pm ) is used as the starting point to determine the theoretical value of the current that generates the torque (I q理论 ), - Based on the determined magnetic drag torque (M 磁阻 ) is used as the starting point to determine the theoretical value of the current that weakens the magnetic field (I d理论 ),and - To provide a determined setpoint current value (I q理论 ,I d理论 ).
2. The method according to claim 1, characterized in that By means of the control device (2) the following is also achieved: - Determine the maximum achievable motor torque (M) depending on the operating point max ), - The desired motor theoretical torque (M 理论 ) is limited to the determined maximum achievable motor torque (M max ) within.
3. The method according to claim 2, characterized in that In order to determine the maximum achievable motor torque (M max ) and / or the coefficient (K pm ) respectively use the integrated characteristic curves (10, 11) depending on the operating point.
4. The method according to claim 3, characterized in that For the maximum achievable motor torque (M max ) of the operating point-dependent characteristic curve (10) and / or for the coefficient (K pm ) is temperature-dependent.
5. The method according to claim 1 or 2, characterized in that: The control device (2) determines a constraint factor (Lim) and limits the desired motor theoretical torque (M) by means of the constraint factor (Lim). 理论 ).
6. The method according to claim 1 or 2, characterized in that: In determining the theoretical current value (I q理论 ,I d理论 ) depends on the motor temperature (T mot ) correction for the permanent magnetic flux (ψ pm ) value.
7. The method according to claim 1 or 2, characterized in that: Depending on the actual value of the torque-generating current (I q实际 ) and the actual value of the field weakening current (I d实际 ) to determine the inductance difference (L d -L q ) value.
8. Used to determine the theoretical value of current (I q理论 ,I d理论 ) for generating the desired theoretical motor torque (M) at the permanent magnet excited electric motor 理论 ) of the invention, wherein the desired motor theoretical torque (M 理论 ) is the permanent magnetic flux torque (M pm ) and magnetic drag torque (M 磁阻 ), including: Control device (2), The control device (2) is configured to: - Obtain the current operating point (3) and the desired motor theoretical torque (M 理论 ), - Determine the factor for the permanent magnet flux torque component (K) depending on the operating point pm ), where in order to determine the coefficient (K pm ) uses an operating point-dependent characteristic map (11), wherein the characteristic map (11) stores associated coefficients (K) for different operating points (3) pm ), where the coefficient (K pm ) is generated in advance by solving the motor torque equation for different operating point values, - With the help of the determined coefficient (K pm ) from the desired motor theoretical torque (M 理论 ) to determine the permanent magnetic flux torque (M pm ) and magnetic drag torque (M 磁阻 ), - With the determined permanent magnetic flux torque (M pm ) is used as the starting point to determine the theoretical value of the current that generates the torque (I q理论 ), - Based on the determined magnetic drag torque (M 磁阻 ) is used as the starting point to determine the theoretical value of the current that weakens the magnetic field (I d理论 ),and - To provide a determined setpoint current value (I q理论 ,I d理论 ).
9. The device (1) according to claim 8, characterized in that The control device (2) is further configured to: - Determine the maximum achievable motor torque (M) depending on the operating point max ), - The desired motor theoretical torque (M 理论 ) is limited to the determined maximum achievable motor torque (M max ) within.
10. Motor vehicle comprising at least one device according to any one of claims 8 or 9.