Method for controlling an electric motor, control device and motor arrangement

Abstract

The invention relates to a method for controlling an electric motor, wherein the method, at least in one field weakening mode, compares a torque request with an actual torque and, based on this, generates a controller output variable which serves to obtain motor control variables by means of which the motor is controlled, and wherein motor operating variables are measured and used to calculate the actual torque. The invention further relates to an associated control device and an associated motor arrangement.

Description

[0001] The invention relates to a method for controlling an electric motor, a control device for an electric motor and a motor arrangement with such a control device.

[0002] Electric motors are typically used to perform various drive tasks. For example, they can be used to power a motor vehicle or for auxiliary tasks such as electric power steering. At high power levels, field weakening is typically used, which is a mode of control for the electric motor. In this field weakening mode, the electric field within the electric motor is deliberately weakened to ensure continued controllability.

[0003] It is an object of the invention to provide a method for controlling an electric motor which is implemented as an alternative or improved method compared to known designs. It is a further object of the invention to provide an associated control device and an associated motor arrangement. This is achieved according to the invention by a method, a control device, and a motor arrangement as defined in the respective main claims. Advantageous embodiments can be found, for example, in the respective dependent claims. The content of the claims is incorporated into the description by express reference.

[0004] The invention relates to a method for controlling an electric motor. The method comprises, at least in one field weakening mode, the following steps: - Providing a torque request, - Determining a controller output variable based on the torque requirement and an actual torque, - Calculating motor control parameters based on the controller output parameter, - Controlling the electric motor based on the motor control parameters, - Measuring one or more motor operating parameters, and - Calculating the actual torque based on the engine operating parameters.

[0005] Using this method, a controller output for driving the electric motor can be determined directly based on a torque request and the actual torque. Conventional controllers can be used for this purpose. In particular, this eliminates the need to generate motor control variables based on a torque request using lookup tables. Such lookup tables are not only complex to create but also fail to account for variations between individual electric motors. The actual torque, which should typically match the torque request as closely as possible, is used directly within the control system and can thus contribute to particularly accurate and rapid adjustments to the desired torque.

[0006] An electric motor is understood to be, in particular, an electric machine that is powered by electrical energy and generates a rotary motion. The electric motor can, for example, be the primary drive system of a motor vehicle, or it can be a supplementary or intermittent drive system, such as in hybrid vehicles. Likewise, the electric motor can perform other drive functions, which in a motor vehicle might include assisting with steering or operating a transmission. The torque requirement is typically a target value derived from a suitable source. For example, the torque requirement might depend on how much torque is desired to drive a vehicle in order to accelerate, decelerate, or maintain a specific speed.In field weakening mode, the electric motor typically delivers its maximum power output, but not its maximum torque. This is typically the case at higher speeds, which can be referred to as the field weakening range. Below this, there is typically a base speed range, in which the torque is maximum and constant, but the power output can be varied.

[0007] The controller output typically indicates the extent to which the actual torque deviates from the torque requirement. The controller output can be determined, in particular, using a controller. Specifically, a proportional-integral controller or a proportional-integral-differential controller can be used. Such controller types have proven advantageous for typical applications. However, other controller types are also possible. The controller output is typically a scalar value. Based on the controller output, motor control parameters are then calculated, whereby one, two, three, or more motor control parameters can be used. The motor control parameters are quantities used to control the motor and by means of which the electric motor can be controlled. In particular, these can be d- and q-voltages, which can be used within the framework of a Clarke-Park transformation.Controlling the electric motor based on its control parameters results in the motor behaving as desired, i.e., generating a specific torque. Motor operating parameters can then be measured, such as the current flowing through the motor or a phase, or the applied voltage. The actual torque can be calculated based on these motor operating parameters. This provides feedback on the torque currently being generated by the electric motor.

[0008] In particular, it can be implemented that only one controller and / or one controller system is used in field weakening mode. Additional controllers can then be advantageously dispensed with. This results in reduced application and functional complexity and increases efficiency and voltage utilization.

[0009] In particular, the motor control variables can be calculated as two-dimensional quantities. Specifically, a first scalar and a second scalar can be used, which together form the two-dimensional quantity. Specifically, a first motor control variable can be calculated as the sine of the controller output multiplied by a given voltage value. Specifically, a second motor control variable can be calculated as the cosine of the controller output multiplied by a given voltage value. This allows the aforementioned trigonometric functions to be used to calculate the motor output variables. These can be used in a d / q diagram or system, as typically used in a Clarke-Park transformation, to control the electric motor. The d-axis typically represents flux, and the q-axis typically represents torque.

[0010] In particular, the motor control variables can be fed to an inverse Clarke-Park transform. Specifically, the output variables of the inverse Clarke-Park transform can be used to control the electric motor. The inverse Clarke-Park transform is a transformation that is the inverse of a Clarke-Park transform.

[0011] In particular, the motor operating parameters can be phase currents or phase voltages of the electric motor. Typically, an electric motor has three phases, although other numbers of phases are also possible. Phase currents and / or phase voltages can be measured for each of these phases, or for a subset of them, and these measurements can then be used to calculate the actual torque.

[0012] In particular, the motor operating parameters can be fed into a Clarke-Park transformation, with the output parameters of the Clarke-Park transformation being used to calculate the actual torque. This allows for a reliable calculation of the actual torque. The output parameters of the Clarke-Park transformation can be, in particular, a first current value and a second current value. The actual torque can be determined, in particular, based on the first current value and the second current value. This has proven to be a useful approach for calculating the actual torque.

[0013] In particular, an additional mode may be provided besides the field weakening mode, namely a maximum torque mode. In such a maximum torque mode, the method may comprise the following steps: - Provision of a torque request, - Determining a first target current and a second target current based on the torque requirement, - Determining a first controller output variable based on the first setpoint current and a first actual current, and determining a second controller output variable based on the second setpoint current and a second actual current, - Controlling the electric motor based on the first controller output and the second controller output, - Measuring one or more motor operating parameters, and - Calculating the first actual current and the second actual current based on the motor operating parameters.

[0014] In this mode of maximum torque, the base speed range mentioned earlier is particularly relevant. The torque remains constant, while the power output is varied. Here, target currents are calculated and compared with actual currents. This approach enables optimal control of the electric motor in this mode.

[0015] Furthermore, a maximum power mode can be provided. In such a mode, the electric motor should always deliver its maximum power, regardless of any other parameters. An extreme value controller can be used for this purpose. In this mode, the process can include the following steps: - Varying a control parameter of the electric motor, while monitoring a system quantity generated by the electric motor, and - Changing the control parameter in such a way that the system size generated by the electric motor is optimized.

[0016] The system parameters in question can be, for example, an optimizable system parameter such as DC power, efficiency, or torque. Such system parameters can be monitored, and even a slight variation can reveal a maximum value. The control parameter can then be adjusted to this maximum value, ensuring that the electric motor delivers its maximum power output or the maximum of the system parameter to be optimized, which could be, for example, torque, efficiency, or power.

[0017] The invention further relates to a control device for an electric motor. This motor can, in particular, be configured to execute a method as described herein. With regard to the method, all embodiments and variants described herein can be used. The invention further relates to a non-volatile, computer-readable storage medium configured to execute a method as described herein. With regard to the method, all embodiments and variants described herein can be used.

[0018] The invention further relates to a motor arrangement comprising an electric motor and a control device as described herein. With regard to the control device and, in particular, with regard to the method implemented therein, reference can be made to all embodiments and variants described herein.

[0019] The process steps described herein are typically to be understood as being executed continuously and repeatedly. In particular, quantities such as actual torque or actual current are calculated in certain process steps and used in other, possibly previously mentioned, process steps. Typically, the process steps mentioned first are executed again after the calculation of quantities such as actual torque or actual current, and the value calculated immediately before is then used.

[0020] This paper describes an operating strategy for maximizing power and efficiency through the use of voltage angle control. Specifically, it addresses the control of electrical machines in the field weakening regime. Previous solutions, which rely on multiple controllers, cannot achieve optimal utilization of the available DC link voltages. This results in losses in power output and efficiency.

[0021] In particular, it can be provided that a single controller (especially a voltage angle controller) is used for the field weakening region, and that a comprehensive operating strategy is preferably developed. Because only one controlled variable exists, the available DC link voltage can be optimally utilized. An extreme value controller can also be implemented using the voltage angle. This makes it possible to optimize the system for maximum power, torque, or efficiency.

[0022] The mechanisms described herein can be applied to all inverter-fed electrical machines, and are not limited to specific applications such as the automotive industry.

[0023] Further features and advantages will be evident to those skilled in the art from the exemplary embodiment described below with reference to the accompanying drawing. These show: Fig. 1: a division of areas, Fig. 2: a control device, Fig. 3: a division of areas with sections from a control device, and Fig. 4: Excerpts from a control device.

[0024] Fig. Figure 1 schematically illustrates different operating ranges of an electric motor. The horizontal axis represents the angular velocity ω. The vertical axis represents power P and torque T. Up to a transition angular velocity ω base The electric motor is operating at its base speed range GD, where the power P increases linearly with increasing angular velocity, while the torque T remains constant. When the transition angular velocity ω is exceeded... base The electric motor enters the field weakening region FB, in which the power P remains constant and the torque T decreases. In this region, field weakening is implemented to prevent the electric motor from entering an undefined or uncontrollable state. The procedure for field weakening is generally known to those skilled in the art.

[0025] Fig. Figure 2 shows a control device 10 schematically in a functional representation. Only some modules of the control device 10 are labelled with reference symbols; some are shown with regard to their functionality.

[0026] The input variable is initially a torque requirement T. e *. The torque requirement T e * is calculated using an actual torque T e The calculation of which will be discussed in more detail below is compared. Specifically, a difference is calculated between the torque requirement T. e * and the actual torque T e This difference serves as the input for a proportional-integral controller PI, whose functionality is well-known. Alternatively, a proportional-integral differential controller, also known as a PID, can be used. The controller PI generates a controller output b, which in turn is used to generate a first motor control variable u.q and a second engine control variable u d is used. This is done using the given formulas, where the first motor control variable u q This is obtained by applying a predetermined voltage V to the sine of the controller output variable b. s is multiplied, and where the second motor control variable u d This is obtained by multiplying the cosine of the controller output variable b by the specified voltage V. s is multiplied. The two motor control variables u q , u d are fed to an inverse Clarke-Park transform, the outputs of which, in the present implementation, are fed to a space vector circuit 20. This, in turn, controls an inverter 30, which, based on an input voltage U, DCAn operating voltage is generated for a three-phase electric motor 40. In principle, electric motors with more than three phases can also be used. A motor angle θ is measured or estimated for each motor motor and used in control tasks such as the previously discussed inverse Clarke-Park transform and a Clarke-Park transform, which will be discussed subsequently. Furthermore, motor operating parameters in the form of phase currents U, V, W of the electric motor 40 are measured and fed into a Clarke-Park transform. The output of the Clarke-Park transform is a first current value I. q and a second current value I d These are then fed to a torque estimator 50, which calculates the actual torque T from the obtained values. e calculated. The actual torque T e It will then be used as described above.

[0027] Overall, this results in a control loop for the electric motor 40 in field weakening operation, in which an actual torque T e directly with a torque requirement T e * is compared and used as a controller input variable. Therefore, it is unnecessary to specify the torque requirement T. e * First, the data is converted into suitable control parameters for the electric motor using lookup tables, and a control system is implemented based on current values. This has proven to be simpler and more reliable overall.

[0028] Fig. 3 already shows this in Fig. 1 Diagram shown for the division of the operating ranges of the electric motor 40 and related excerpts from the in Fig. 2. Circuit shown. One such section is depicted on the right. An alternative is shown on the left. The section shown in the right ellipse corresponds exactly to a part of the Fig. 2. The section shown in the left ellipse represents an alternative that can be used in the basic speed range. This involves a torque requirement T. e * first via lookup tables to determine an initial target current I q * and a second target current I d * implemented, which are then compared with actual values ​​calculated from motor operating parameters. The differences determined accordingly serve as input variables for two separate PI controllers, which in turn output voltage variables as motor control variables. q , u d generate. In this case, two controllers are therefore required, and the implementation of a torque request T is achieved. e* required using lookup tables. In principle, this control mechanism can also be applied in the field weakening range, which is typically done in the prior art. However, it has been found that the control described herein, which is shown on the right in Fig. Figure 3 shows that it delivers better results in the field weakening range and requires less effort. As an alternative to PI controllers, PID controllers, for example, can be used.

[0029] A transition between the two areas and the use of the respective control procedure can be achieved, for example, using the parameter m, which indicates the modulation level, i.e., in particular the current voltage utilization. If this parameter is greater than or equal to 0.9, the following applies to the execution described herein: Fig. 2 changed. If the parameter is less than or equal to 0.85 and at the same time the condition I is met d is greater than -I qx tan(θ MTPA ), where θ MTPA If a motor constant is used that specifies the maximum torque per ampere, then the classic version shown on the left is used. In other words, this means that the measured d-axis current is greater than a calculated d-current value, which is multiplied by -I. q × tan(θ MTPA ). However, other transition criteria can also be used.

[0030] Fig.Figure 4 shows a transition between the field weakening control described herein and an extreme value controller. An extreme value controller is understood to be a controller designed to optimize a specific operating parameter, such as power. This is achieved by modulating a certain superposition onto a control variable, which can be, for example, a sinusoidal superposition. This results in a change to a variable monitored by the electric motor, such as power. The superimposed change also allows monitoring of the direction in which the modulated parameter should be changed to maximize the operating parameter. Thus, the extreme value controller can always control the electric motor in such a way as to maximize the operating parameter.

[0031] A transition from the controller-based control described herein to the extreme value controller can occur, for example, when a torque reference M* is greater than or equal to the current torque M and, furthermore, the current torque M is less than the torque in the last cycle k-1. A transition back to the controller-based control described herein from the extreme value controller can occur, in particular, when the current torque M is greater than or equal to the torque reference M*. However, other transition criteria are also fundamentally applicable.

[0032] The approach described herein allows for improved control of the electric motor, particularly in the field weakening range. Transitions between different modulation types can be implemented seamlessly. Valid transitions to the base speed range and to the use of an extreme value controller are described. However, it should be noted that the implementation described herein can also be used independently of these. The described control methods in the base speed range and the extreme value controller are generally known in the prior art, which is why they are not discussed in detail here. It should be understood that other transition criteria besides those described herein can also be used.

[0033] The steps of the method according to the invention can be carried out in the specified order. However, they can also be carried out in a different order, provided this is technically feasible. In particular, they can be repeated continuously and / or carried out simultaneously. The method according to the invention can be carried out in one embodiment, for example with a specific combination of steps, in such a way that no further steps are performed. However, further steps can also be carried out in principle, including those not mentioned.

[0034] It should be noted that features may be described in combination in the claims and description, for example to facilitate understanding, even though they can also be used separately. The person skilled in the art recognizes that such features can also be combined independently with other features or combinations of features.

[0035] References in dependent claims may indicate preferred combinations of the respective features, but do not exclude other combinations of features. Reference symbol list 10 Control device 20 Space vector circuit 30 Inverter 40 electric motor 50 torque estimators T e * Torque requirement T e Actual torque b Controller output size V s specified voltage u q first engine control parameter ud second engine control parameter U DC Input voltage U, V, W motor operating parameters I q first current value I d second current value I q * first target current I d * second target current T torque P Performance GD basic speed range FB Field Weakness Area ω base Transition angular velocity m Modulation level θ MTPA Motor constant M* Torque reference M current torque k-1 last cycle

Claims

[1] Method for controlling an electric motor (40), wherein the method comprises at least one field weakening mode comprising the following steps: - Providing a torque request (T e *), - Determining a controller output variable (b) based on the torque requirement (T) e *) as well as an actual torque (T e ), - Calculation of engine control parameters (u q , u d ) based on the controller output variable (b), - Controlling the electric motor (40) based on the motor control variables (Uq, Ud), - Measuring one or more motor operating parameters (U, V, W), and - Calculating the actual torque (T) e ) based on the engine operating parameters. [2] Method according to claim 1, - wherein the controller output variable (b) is determined using a proportional integral (PI) controller or a proportional integral differential controller. [3] Method according to any one of the preceding claims, - where in field weakening mode only one controller (PI) and / or only one controlled system is used. [4] Method according to any one of the preceding claims, - where the engine control parameters (u q , u d ) can be calculated as a two-dimensional quantity. [5] Method according to any one of the preceding claims, - where a first motor control variable (u q ) as the sine of the controller output variable (b) multiplied by a predetermined voltage value (V) s ) is calculated, and / or - where a second engine control variable (u d ) as the cosine of the controller output variable (b) multiplied by a predetermined voltage value (V) s ) is calculated. [6] Method according to any one of the preceding claims, - where the engine control parameters (u q , u d) are fed to an inverse Clarke-Park transformation, with the output variables of the inverse Clarke-Park transformation being used to control the electric motor (40). [7] Method according to any one of the preceding claims, - where the motor operating parameters (U, V, W) are phase currents of the electric motor (40). [8] Method according to any one of the preceding claims, - wherein the motor operating variables (U, V, W) are fed to a Clarke-Park transformation, with output variables of the Clarke-Park transformation being used to calculate the actual torque (T) e ) be used. [9] Method according to claim 8, - where the output variables of the Clarke-Park transformation are a first current value (I q ) and a second current value (I d ) are, and - where the actual torque (T e ) based on the first current value (I q ) and the second current value (I d) is determined. [10] A method according to any of the preceding claims, which in a mode of maximum torque comprises the following steps: - Providing a torque request (T e *), - Determining an initial target current (I q *) and a second target current (I d *) based on the torque requirement, - Determining a first controller output variable based on the first setpoint current (I) q *) and a first actual current and determining a second controller output variable based on the second setpoint current (I d *) and a second actual current, - Controlling the electric motor (40) based on the first controller output and the second controller output, - Measuring one or more motor operating parameters (U, V, W), and - Calculating the first actual current and the second actual current based on the motor operating parameters (U, V, W). [11] A method according to any of the preceding claims, which in a maximum power mode comprises the following steps: - Varying a control parameter of the electric motor (40), while monitoring a system quantity generated by the electric motor (40), and - Changing the control parameter in such a way that the system size generated by the electric motor is optimized. [12] Control device (10) for an electric motor (40) which is configured to perform a method according to one of the preceding claims. [13] Motor arrangement comprising - an electric motor (40), and - a control device (10) according to claim 12.

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