Method for controlling a current setpoint value for an electric motor in a hybrid drive train of a hybrid vehicle

Abstract

The invention relates to a method for controlling a current setpoint value for an electric motor in a hybrid drive train of a hybrid vehicle, wherein the hybrid drive train also has an internal combustion engine and the electric motor is rotationally fixedly coupled to the internal combustion engine for torque transmission, characterized in that, starting the internal combustion engine from the standstill of the internal combustion engine, the current setpoint value for the electric motor follows a predefined start-up characteristic curve (100) for tow-starting and starting the internal combustion engine by means of the electric motor, and the rotor position angle is thereby determined by means of an injection-based sensorless method.

Description

[0001] P241355 DE 01

[0002] - 1 - Method for controlling a current setpoint signal to an electric motor in a hybrid powertrain of a hybrid vehicle

[0003] The invention relates to a method having the features according to the preamble of claim 1.

[0004] The application of the invention: In sensorless operation of an electric motor, the rotor position sensor, which is usually used to determine the current angle of the rotor, is omitted. Current sensor signals and measured and estimated phase voltages are used to deduce the rotor position and the motor speed via a model and / or by exploiting anisotropy. Using the estimated speed and rotor position in the control of the electric motor means that the estimated values ​​must be stably and robustly determinable at all possible operating points of the electric motor.

[0005] WO 2022233384 A1 discloses a method for identifying the anisotropy of an electric rotating field machine comprising a rotor and a stator, wherein the rotating field machine is controlled by pulsed terminal voltages using pulse width modulation and the current of the rotating field machine is measured cyclically, wherein a periodic injection voltage is superimposed on the fundamental voltage, and the current inductance and / or admittance of the rotating field machine is calculated from the applied voltage and the measured current, with the purpose of determining the current rotor position. For this purpose, it is provided that the period of the injection voltage is shorter than twice the cycle time of the current measurement.

[0006] Below a certain speed threshold of the absolute rotational speed, it is necessary to inject so-called injection signals to estimate the rotor position and speed. These signals enable the identification of the rotor position and speed in this speed range, as the sole evaluation of induced voltages at the motor is insufficient in this range due to the decreasing signal-to-noise ratio.

[0007] INTERNALP241355 DE 01

[0008] -2 - does not function reliably. Specifically, this means that if the rotational speed decreases and approaches zero, the terms used for evaluation become less dominant compared to the other terms in the equation, and eventually disappear. Injection signals often have negative effects on the acoustics of the system and may be audible, for example, as a disturbing noise in the interior of a vehicle.

[0009] EP2144362B1 presents an injection method that is intended to be suitable for small absolute rotational speeds.

[0010] A method that can be used to initialize the rotor position angle and also at small absolute rotational speeds is published in DE 102022 110304 A1.

[0011] A robust method requires a pronounced anisotropy. This is defined by the ratio of Ld / Lq, which should be greater than 1.5. Prototype studies show that the method can also function with smaller values ​​of this ratio. Ultimately, the robustness depends on whether a favorable ratio can be guaranteed at all possible operating points.

[0012] Unfortunately, an increasing current has a negative impact on the Ld / Lq ratio; it usually becomes smaller and often almost reaches 1.

[0013] Since the electric motor is intended to be used, for example, to start an internal combustion engine, it is necessary to accelerate the electric motor from a standstill, potentially with a high torque, i.e., a high current. When using loss-optimized current setpoints, such as MTPA (Maximum Torque Per Ampere), the ratio Ld / Lq can decrease further due to the increasing current, and the resulting insufficient ratio during motor start-up leads to a loss of the angle signal. Without a correctly determined angle signal, the motor cannot be operated in a controlled manner.

[0014] The reason for this is that the MTPA characteristic curve for the current setpoint is traversed during engine start-up, and this results in excessively low Ld / Lq ratios in certain areas.

[0015] INTERNALP241355 DE 01

[0016] - 3 - (i.e., close to 1). Experiments with these electric motors have shown that at high currents even a quotient less than 1 can be reached; thus, the requirement for sensorless operation with sufficient anisotropy is not met in such ranges.

[0017] The invention is based on the objective of ensuring sufficient anisotropy for motor start-up by selecting a current setpoint that deviates from the MTPA characteristic curve in the injection-based sensorless method. In this case, the electric motor operates in a less efficient range when deviating from the MTPA characteristic curve.

[0018] A special current setpoint strategy is proposed for starting the engine.

[0019] The problem is solved by a method having the features according to claim 1.

[0020] According to the invention, a method for controlling a current setpoint to an electric motor in a hybrid powertrain of a hybrid vehicle is provided, wherein the hybrid powertrain also includes an internal combustion engine and the electric motor is rotationally fixed to the internal combustion engine for torque transmission. It is provided that, for starting the internal combustion engine from a standstill, the current setpoint to the electric motor follows a predetermined start-up characteristic curve for towing and starting the internal combustion engine using the electric motor, and the rotor position angle is determined by means of an injection-based sensorless method.

[0021] In a preferred embodiment of the invention, it is provided that, for starting from a standstill, the current setpoint follows the start-up characteristic curve and is specified by the course of a first characteristic curve during starting from a standstill.

[0022] In a particularly preferred embodiment of the invention, it is provided that when a first predetermined value of the quotient Ld / Lq is undershot for the first time, the current setpoint for towing and starting the combustion engine-

[0023] INTERNALP241355 DE 01

[0024] - 4 -tors, the current setpoint follows the start-up characteristic curve and is specified from the first time the first specified value of the quotient Ld / Lq is undercut by the course of a second characteristic curve, on which for each point of the second characteristic curve, the quotient Ld / Lq is greater than a second specified value.

[0025] In a further particularly preferred embodiment of the invention, it is provided that when a predetermined minimum speed of the electric motor is reached, the system switches from the injection-based sensorless method to a back-EMF-based sensorless method, leaving the predetermined start-up characteristic curve and returning to the first characteristic curve.

[0026] In a preferred embodiment of the invention, the first characteristic curve is an MTPA characteristic curve, an MTPF characteristic curve, or an MTPL characteristic curve.

[0027] In a preferred embodiment of the invention, the first predetermined value of the quotient Ld / Lq is a value between 1.0 and 1.6, preferably 1.2.

[0028] In a preferred embodiment of the invention, the second predetermined value of the quotient Ld / Lq is a value between 1.0 and 1.6, preferably 1.2.

[0029] In a further preferred embodiment of the invention, it is provided that the electric motor forms a unit with the combustion engine.

[0030] In this way, when towing and starting the combustion engine from a standstill using the electric motor, sufficient anisotropy in the current setpoint to the electric motor is present during towing and starting the combustion engine by the electric motor, due to the inventive shape of the start-up characteristic curve of the current setpoint. The electric motor is only used during-

[0031] INTERNALP241355 DE 01

[0032] - 5 -rend of the time the deviation of the start-up characteristic curve from the MTPA characteristic curve is operated in a less efficient range.

[0033] Further advantages and advantageous embodiments of the invention are the subject of the following figure and its description.

[0034] They show in detail:

[0035] Figure 1 Electric motor characteristic map 10 with start-up characteristic curve 100 according to the invention for the current setpoint specification to an electric motor for towing and starting an internal combustion engine from standstill using the injection method for rotor position determination, as well as MTPA characteristic curve 50.

[0036] Figure 1 shows a start-up characteristic curve 100 for an electric motor in a hybrid powertrain and an MTPA characteristic curve 50 in an engine map of the electric motor. The start-up characteristic curve (100) can also be referred to as the combustion engine start-up characteristic curve.

[0037] In a hybrid vehicle's powertrain, the electric motor and combustion engine are rigidly coupled to each other, enabling torque transfer. Alternatively, the electric motor and combustion engine could be coupled and completely decoupled as needed using a disconnect clutch. In the following, it is assumed that the electric motor and combustion engine are rigidly coupled, specifically rotationally fixed, forming a single unit. The hybrid vehicle may also have a second electric motor that can be coupled or disconnected from the unit consisting of the first electric motor and combustion engine via a disconnect clutch.

[0038] The motor controller of the electric motor typically regulates the target currents id (x-axis) and iq (y-axis) using field-oriented control, typically with a rotor position sensor, in such a way that the MTPA characteristic curve is not deviated from. This ensures very efficient operation of the electric motor.

[0039] The further the MTPA characteristic curve 50, starting with Id = Iq = 0A (Fig. 1 bottom right), at

[0040] INTERNALP241355 DE 01

[0041] - 6 - The higher the currents increase, the worse the Ld / Lq ratio becomes. This is characterized by the height profile 200, i.e., the lines of the points with the same Ld / Lq ratio. For operation of the electric motor using the injection method, it can only be operated without a sensor in the range where the ratio is greater than 1.2. The value 1.2 is already very borderline; ideally, it should be greater than 1.5. Up to that point, the start-up characteristic curve 100 corresponds to the MTPA characteristic curve.

[0042] Unfortunately, the MTPA characteristic curve extends into a range where the ratio drops from 1.2 to values ​​below 1. The current limit is reached at a ratio of 0.95. Sensorless operation using the injection method is therefore not possible in this range, as the rotor angle can no longer be reliably estimated and the control becomes unstable.

[0043] The electric motor is therefore operated on the MTPA characteristic curve using the sensorless injection method as long as the ratio Ld / Lq is sufficiently large. If the operating point enters the range where the ratio becomes too small, i.e., less than 1.2, then the MTPA characteristic curve 50 is abandoned in order to reach the current limit and thus near-maximum torque with a sufficiently large ratio greater than 1.2. In Figure 1, the point where the start-up characteristic curve 100 deviates from the MTPA characteristic curve 50 is marked with an X, and the current setpoint continues to follow the start-up characteristic curve 100 from that point onward. By leaving the MTPA characteristic curve 50, the motor operates slightly less efficiently for the short interval of the combustion engine's start-up.Once the combined combustion engine and electric motor reaches a minimum speed, the system switches from the injection-based sensorless method to the back-EMF-based sensorless method, returning to the MTPA characteristic curve. In Figure 1, this switch back is marked with a W and an arrow pointing 150.

[0044] The point W at which a switch back to the MTPA characteristic curve 50 occurs can vary greatly, as the combustion engine typically generates very different load torques depending on the temperature.

[0045] INTERNALP241355 DE 01

[0046] - 7 -

[0047] The use of the MTPA characteristic curve 50 (Maximum Torque Per Ampere) in the preceding description can be generalized to MTPF characteristic curve (Maximum Torque Per Flux) or MTPL characteristic curve (Maximum Torque Per Loss).

[0048] INTERNALP241355 DE 01

[0049] - 8 - List of reference symbols

[0050] 10 Electric motor characteristic map

[0051] 50 MTPA characteristic curve

[0052] 100 Start-up characteristic curve: Characteristic curve of the current setpoint for starting an internal combustion engine using the electric motor with an injection-based sensorless method for determining the rotor position

[0053] Arrow 150: Change of the current setpoint from the start-up characteristic curve 100 back to the MTPA characteristic curve 50.

[0054] 200 lines of points with the same quotient Ld / Lq (elevation profile)

[0055] 250 lines of points with the same magnetic flux (in volts * seconds) in the motor or the same voltage at constant speed

[0056] 300 lines of points with the same engine torque (in kNm)

[0057] Point X in the electric motor map 10 that lies on both the MTPA characteristic curve 50 and the start-up characteristic curve 100, and up to which the course of the start-up characteristic curve 100, which describes the current setpoint, corresponds to the course of the MTPA characteristic curve 50. Point at which the current setpoint to the electric motor leaves the MTPA characteristic curve 50 and continues only on the start-up characteristic curve 100.

[0058] W is the point on the start-up characteristic curve 100 in the electric motor map 10, at which the current setpoint specification to the electric motor leaves the start-up characteristic curve 100 and, as shown by the arrow 150, returns to the course of the MTPA characteristic curve 50.

[0059] INTERNAL

Claims

P241355 DE 01 - 9 - Patent claims 1. Method for controlling a current setpoint to an electric motor in a hybrid powertrain of a hybrid vehicle, wherein the hybrid powertrain also includes an internal combustion engine and the electric motor is rotationally fixed to the internal combustion engine for torque transmission, characterized in that, for starting the internal combustion engine from standstill, the current setpoint to the electric motor follows a predetermined start-up characteristic curve (100) for towing and starting the internal combustion engine by means of the electric motor, and the rotor position angle is determined by means of an injection-based sensorless method.

2. Method according to claim 1, characterized in that, for starting from standstill, the current setpoint follows the start-up characteristic curve (100) and is specified by the course of a first characteristic curve when starting from standstill.

3. Method according to claim 2, characterized in that when the current setpoint for towing and starting the internal combustion engine falls below a first predetermined value of the quotient Ld / Lq for the first time, the current setpoint follows the start-up characteristic curve (100) and from the first time the first predetermined value of the quotient Ld / Lq falls below a predetermined value, it is determined by the course of a second characteristic curve, on which, for each point of the second characteristic curve, the quotient Ld / Lq is greater than a second predetermined value.

4. Method according to claim 3, characterized in that when a predetermined minimum speed of the electric motor is reached, the process switches from the injection-based sensorless method to a back-EMF-based sensorless method and leaves the predetermined start-up characteristic curve (100) (W) and returns to the first characteristic curve (150). INTERNALP241355 DE 01 - 10 - 5. Method according to one of the preceding claims, characterized in that the first characteristic curve is an MTPA characteristic curve (50) or an MTPF characteristic curve or an MTPL characteristic curve.

6. Method according to one of the preceding claims, characterized in that the first predetermined value of the quotient Ld / Lq is a value between 1.0 and 1.6, preferably 1.

2.

7. Method according to one of the preceding claims, characterized in that the second predetermined value of the quotient Ld / Lq is a value between 1.0 and 1.6, preferably 1.

2.

8. Method according to claim 1, characterized in that the electric motor forms a unit with the internal combustion engine. INTERNAL

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