Control device and control method for an electric drive system and electric drive system

Abstract

The invention relates to a kind of operation of electric drive system, wherein, in the consideration of the rotation frequency of motor or the trend of torque, the adjustment range of switching frequency for converter can be adapted in such drive system. In this way, mental-acoustic irritation can be avoided.

Description

Technical Field

[0001] This invention relates to an apparatus and method for controlling an electric drive system. Furthermore, this invention relates to an electric drive system. Background Technology

[0002] Electric drive systems are used, for example, in vehicles that are fully or at least partially electric. Here, electrical energy is provided by a so-called traction battery and converted into an alternating current voltage by means of an electrical converter, which is suitable for operating the motor according to a desired target value preset.

[0003] Publication DE 10 2017 203 668 A1 describes a method and apparatus for operating an inverter for a drive system. The method described herein includes a step for determining the inverter switching frequency using an operating point signal. Furthermore, the method includes a step for providing a frequency signal to set a predetermined switching frequency at the inverter. Summary of the Invention

[0004] The present invention realizes a control device and a method for operating an electric drive system, as well as an electric drive system.

[0005] The following settings were configured accordingly:

[0006] Control equipment for electric drive systems, particularly electric drive systems with converters and motors. The control equipment includes a monitoring device and a control device. The monitoring device is designed to determine the motor's rotational frequency. As an additional or alternative, the monitoring device can also determine the motor's torque. Furthermore, the monitoring device is designed to determine variations in the determined rotational frequency and / or the determined torque. The control device is designed to determine the adjustment range for the converter's switching frequency. This adjustment range can be determined, especially when using variations in the rotational frequency or torque determined by the monitoring device. Furthermore, the control device is designed to operate the converter using a switching frequency within the determined adjustment range.

[0007] In addition, the following settings were configured:

[0008] An electric drive system comprising: an electric motor, a converter designed to control the electric motor, and a control device according to the invention.

[0009] Finally, the following settings were made:

[0010] A method for controlling an electric drive system, particularly an electric drive system having a converter and a motor. The method includes steps for determining the current rotational frequency and / or current torque of the motor. Furthermore, the method includes steps for determining changes in the determined rotational frequency and / or the determined torque. Additionally, the method includes steps for determining an adjustment range for the switching frequency of the converter. Specifically, the adjustment range for the switching frequency of the converter can be determined using changes in the rotational frequency and / or the torque. Finally, the method includes steps for controlling the converter using a switching frequency within the determined adjustment range.

[0011] The present invention is based on the understanding that electric drive systems typically include a converter containing switching elements that are operated at a predetermined switching frequency. This switching frequency results in the generation of specific noises within the electric drive system. Specifically, in modern electric drive systems, the switching frequency used to operate the switching elements can be varied. This variation in switching frequency affects several operating characteristics of the electric drive system. For example, the choice of switching frequency negatively impacts electrical losses within the drive system or voltage ripples that may occur at the input of the converter. Furthermore, the choice of switching frequency also affects the acoustic characteristics and noise emissions of the electric drive system. The resulting noise emissions are particularly perceptible to people in the surrounding environment of the drive system, such as drivers of electric vehicles.

[0012] Here, a vehicle driver typically anticipates noise typical of the current driving conditions. Thus, a driver might expect noise with an increasing or at least constant frequency during acceleration, while noise with a decreasing frequency during acceleration is more likely to be perceived as stimulating. Conversely, a driver is more likely to expect noise with a decreasing or at least constant frequency during deceleration, while noise with an increasing frequency during deceleration is more likely to be stimulating.

[0013] Therefore, the concept of this invention is to adapt the switching frequency, used to control the switching elements in the converter for an electric drive system, in a suitable manner, taking into account this understanding and the corresponding operating characteristics. Specifically, the switching frequency used to control the converter should appropriately take into account the operating characteristics of the electric drive system, such as variations in speed or torque. In this way, the noise generation of the electric drive system corresponding to the switching frequency is similarly adapted to the operating characteristics, such as variations in rotational frequency or torque. Therefore, it is possible to achieve noise generation in the electric drive system that induces a positive psychoacoustic experience. Thus, for example, the driver of an electric vehicle experiences noise generation corresponding to the vehicle's driving characteristics. This, in particular, avoids irritation to the driver.

[0014] An electric drive system equipped with the control device according to the invention can be, for example, a drive system for a fully or at least partially electrically driven vehicle. Such a drive system can be powered by an energy storage device, such as a traction battery, using a DC voltage. In this case, the converter can convert the DC voltage provided by the energy storage device into a suitable single-phase or multi-phase AC voltage and provide this AC voltage at the motor. Here, the converter can particularly take into account target value presets, such as, for example, the motor's set rotational frequency or the torque to be provided. Furthermore, it goes without saying that the converter can also take into account any other target value presets in order to provide a correspondingly suitable voltage at the motor.

[0015] The electrical converter can include, for example, one or more half-bridges each having two switching elements, which are controlled and thus opened or closed according to a target value preset. These switching elements can be, for example, bipolar transistors with insulated gate junctions (IGBTs) or MOSFET switching elements. In particular, modern silicon carbide (Si-C) based transistors can be used in this context over a wide frequency range for switching frequencies. For example, switching frequencies in the range of 5 to 40 kHz are feasible.

[0016] The control device of the control apparatus according to the invention can therefore adapt the switching frequency of the switching elements in the converter to a suitable manner according to the corresponding current framework conditions. For example, the control frequency can be adjusted to minimize losses in the electric drive system, keep disruptive effects, such as voltage ripple at the input of the transformer, below predetermined limits, or follow any other framework conditions. For this purpose, the adjustment range for the switching frequency can be predetermined based on the current direction of the motor speed or motor torque. In this way, the noise generation of the electric drive system can be affected. In particular, adverse psychoacoustic effects that could cause irritation to the user can be avoided or at least minimized.

[0017] In one embodiment, the monitoring device can be designed to calculate the change in rotational frequency using the gradient of the currently detected rotational frequency trend. As an additional or alternative, the change in torque can also be calculated using the gradient of the currently detected torque trend. The gradient here typically corresponds to the first derivative of the function with respect to time. Furthermore, in principle, any other suitable calculation method is also feasible, such as calculating the second derivative with respect to time.

[0018] In one embodiment, the monitoring device is designed to detect the current rotational frequency based on measured values. As an additional or alternative solution, torque can also be detected based on measured values ​​of the current actual torque. As an additional or alternative solution for detecting actual values, the monitoring can also receive target values ​​for rotational frequency and / or torque. Accordingly, the adjustment range for switching frequencies can thus be preset based on the current actual values ​​and / or target values.

[0019] In one embodiment, the control device is designed to determine the current switching frequency as the lower limit frequency of the adjustment range for the switching frequency if the rotational frequency and / or torque increases. As an additional or alternative, if the rotational frequency and / or torque decreases, the control device can determine the current switching frequency as the upper limit frequency of the adjustment range for the switching frequency. The lower or upper limit frequency of the adjustment range can, if necessary, deviate from the current switching frequency by a predetermined threshold. For example, if the rotational frequency increases, the lower frequency can be lower than the current limit frequency by a predetermined threshold. Correspondingly, if the rotational frequency decreases, a frequency higher than the current switching frequency by a predetermined threshold can be used as the upper limit frequency. In this way, it can be ensured that the noise generation of the electric drive system, especially the frequency of noise generation, changes in a manner consistent with the dynamic characteristics of the drive system.

[0020] In one embodiment, the control device is designed to determine a predetermined maximum switching frequency as the upper limit frequency of the adjustment range for the switching frequency if the rotational frequency and / or torque increases. Alternatively, if the rotational frequency and / or torque decreases, a predetermined minimum switching frequency can be determined as the lower limit frequency of the adjustment range for the switching frequency. In this way, the adjustment range for the switching frequency can be fully utilized over a wider range when the rotational frequency changes, without causing any adverse psychoacoustic effects on the user.

[0021] In one embodiment, the control device is designed to adapt the modulation method used to control the converter when a desired rotational frequency and / or a desired torque is used. As feasible modulation methods, in addition to conventional pulse width modulation (PWM), especially SVPWM, other special modulation methods, such as block operation and flat-top modulation, can also be applied. Here, the selection of the modulation method used can also take into account the current rotational frequency or current torque, as well as the current changes in the rotational frequency or current torque.

[0022] In one embodiment, the control device includes a characteristic curve memory. This characteristic curve memory is designed to store and provide at least one characteristic curve suitable for controlling the converter. The control device is particularly designed to control the converter using the characteristic curves stored in the characteristic curve memory. The characteristic curves can represent any suitable relationship between operating parameters and / or target values. For example, the characteristic curves stored in the characteristic curve memory can represent relationships previously obtained through measurement techniques or simulation, such as electrical losses (e.g., switching losses in semiconductor switching elements), motor losses, expected voltage ripple, temperature trends, etc. However, it goes without saying that any other relationships can also be stored in the characteristic curve memory.

[0023] In one embodiment, the control device is designed to adapt to the operation of the converter when using at least one additional operating parameter. This additional operating parameter may be, for example, voltage ripple at the converter's input obtained technically or mathematically. Furthermore, the temperature or temperature profile of the drive system, obtained technically or mathematically, such as the temperature or temperature profile in the motor rotor or at the converter's switching elements, may also be considered. Moreover, it goes without saying that any other operating parameters are also feasible and can be considered simultaneously for controlling the converter.

[0024] The above-described design schemes and improvements can be combined with each other arbitrarily as long as they are meaningful. Other design schemes, improvements, and implementations of the present invention also include combinations of features not explicitly mentioned in the foregoing or following descriptions of the embodiments. In particular, those skilled in the art will also add various aspects as improvements or supplements to the corresponding basic form of the present invention. Attached Figure Description

[0025] The invention will now be explained in more detail with reference to embodiments specified in the schematic illustrations of the accompanying drawings. Here are shown:

[0026] Figure 1 A schematic block diagram of an electric drive system with control equipment according to one embodiment is shown.

[0027] Figure 2 A schematic diagram is shown according to one embodiment for adapting an adjustment range for switching frequencies; and

[0028] Figure 3 A flowchart is shown based on a method for controlling an electric drive system according to one embodiment. Detailed Implementation

[0029] Figure 1A schematic block diagram of an electric drive system according to one embodiment is shown. The electric drive system includes a motor 3. The motor 3 can be fed by a converter, particularly a single-phase or multi-phase inverter 2. The converter 2 is fed at its input side by a power source 4, particularly by an energy storage device (such as, for example, a traction battery of an electric vehicle). The converter 2 converts the electrical energy supplied by the power source 4 into a voltage suitable for setting a desired operating state at the motor 3, such as a desired rotational frequency or a desired torque. For this purpose, the converter 2 can include multiple switching elements, particularly semiconductor switching elements, such as bipolar transistors with insulated gate junctions (IGBTs) or silicon carbide transistors. The switching elements of the converter 2 can be opened and closed by means of appropriate control signals. For this purpose, each switching element of the converter 2 can be controlled by a corresponding control signal. This control signal can be provided, for example, by a control device 1. In particular, the control signal can be generated at a predetermined clock frequency. Specifically, semiconductor switching elements can be controlled by means of pulse width modulation (PWM). Presets for setting specific operating states, such as rotational frequency or torque, can be provided, for example, by means of a target value preset S at the corresponding control device 1.

[0030] Furthermore, control device 1 can detect the current rotational frequency f_M of motor 3 and / or the current torque M provided by motor 3. For this purpose, suitable sensor devices, such as a resolver, can be provided. However, it goes without saying that the current rotational frequency f_M, or torque M, can also be detected in any other way. For example, a transmitterless method for determining the rotational frequency f_M is also feasible.

[0031] The control device 1 may include a monitoring device 11 that receives a target value preset S and, if necessary, a signal of the current rotation frequency f_M and / or the current torque M of the motor 3. Specifically, the monitoring device 11 can monitor the trend of the rotation frequency f_M or torque M of the motor 3 and detect changes or alterations in the rotation frequency f_M or torque M. For this purpose, it may calculate, for example, the gradient, that is, the first derivative with respect to time, or, if necessary, any other suitable parameter, such as, for example, the second derivative with respect to time. For this purpose, it may detect, for example, the actual value of the rotation frequency f_M or torque M and store the actual value for a predetermined duration. For example, these values ​​may be stored in a cyclic memory. For example, the cyclic memory may store a predetermined number of measurements. After a predetermined number of measurements have been written into the memory, the next value is overwritten with the previously stored value. Needless to say, any other suitable method for storing these values ​​or for determining changes in the rotation frequency f_M or torque M is also feasible.

[0032] In addition to considering the actual value of the rotation frequency f_M or torque M of motor 3, a target value for the rotation frequency or torque can also be preset as an additional or alternative solution.

[0033] The monitoring device 11 provides the obtained data, i.e., the detected value, and the results obtained, particularly from the analysis of changes in the rotational frequency f_M or torque M, to the control device 12 of the control equipment 1. The control device 12 can determine, based on the data provided by the monitoring device 11, a feasible adjustment range for the switching frequency used to operate the switching elements in the converter 2. Here, the control device 12 can, for example, limit the adjustment range for the switching frequency so that a decrease in the switching frequency is avoided when the rotational frequency f_M increases. Similarly, when the rotational frequency f_M at the motor 3 decreases, an increase in the switching frequency can be avoided by correspondingly adapting the adjustment range for the switching frequency. In this way, the frequency component of noise generation in the electric drive system can be prevented from responding inversely to changes in the motor's speed.

[0034] The control device 12 can then appropriately operate the transformer 2, and in particular the switching elements within the transformer 2, taking into account the determined adjustment range for the switching frequency. For this purpose, the control device 12 can, for example, employ feasible characteristic curves or a family of characteristic curves stored in the characteristic curve memory 13 of the control device 1. These characteristic curves or family of characteristic curves can, for example, characterize electrical losses according to the switching frequency, possible or anticipated voltage ripple at the input of the transformer 2 according to other operating parameters, temperature trends according to other operating parameters, etc.

[0035] Figure 2 A schematic diagram of an adjustment range for frequency switching, according to one embodiment, is shown. Here, curve 100 shows the current target or actual rotational speed of motor 3. As can be identified here, motor 3 operates at a constant or at least approximately constant rotational speed in the first time segment I, the third time segment III, and the fifth time segment V, respectively. In the second time segment II, the rotational speed f_M of motor 3 increases. In the fourth time segment IV, the rotational speed f_M of motor 3 decreases.

[0036] The graph shown below illustrates the adjustment range of the switching frequency for the switching element of transformer 2. Here, curve 200 shows the corresponding current switching frequency. The upper curve 210 plots the upper limit frequency of the adjustment range for the switching frequency, and the lower curve 220 plots the lower limit frequency of the adjustment range for the switching frequency.

[0037] In the first time interval I, where motor 3 rotates at an approximately constant speed, the switching frequency can vary entirely between the minimum switching frequency f_min and the maximum switching frequency f_max. After determining that the speed f_M of motor 3 should be increased, or should be increased, this adjustment range is limited in time interval II. For example, the lower limit of the adjustment range for the switching frequency can be limited to the corresponding current switching frequency. Therefore, the only remaining adjustment range for the switching frequency is the range between the current switching frequency and the maximum permissible switching frequency f_max. In this way, it is possible to avoid lowering the switching frequency when increasing the rotational frequency f_M of motor 3, thus generating noise that would acoustically conflict with the characteristics of motor 3.

[0038] After determining in section III that the rotational frequency f_M of motor 3 is constant or at least approximately constant, the adjustment range for the switching frequency can be expanded. For example, in this stage, the switching frequency can be made to vary entirely between the minimum switching frequency f_min and the maximum switching frequency f_max.

[0039] If a decrease in the rotational frequency f_M of motor 3 is subsequently detected in time segment IV, then the adjustment range for the switching frequency can be limited accordingly. In this case, for example, the current switching frequency can be defined as the maximum permissible switching frequency. Therefore, the switching frequency can move only between the current switching frequency and the minimum permissible switching frequency f_min during the decrease in rotational frequency f_M. After it is subsequently determined in segment V that the rotational frequency f_M of motor 3 is constant or at least approximately constant, the adjustment range can be expanded to the full adjustment range between the minimum switching frequency f_min and the maximum switching frequency f_max.

[0040] In addition to the aforementioned limitations on the switching frequency considering the rotational frequency or torque of motor 3, other operating parameters can also be considered as an additional option. Specifically, these additional operating parameters can, for example, pre-define additional limitations on the adjustment range for the switching frequency. For instance, to limit the voltage ripple at the input of transformer 2, it may also be necessary to appropriately limit the switching frequency for transformer 2. Furthermore, the selection of the switching frequency corresponds to the switching losses in the switching elements of transformer 2 and other losses in motor 3. This can also lead to further limitations on the adjustment range for the switching frequency if necessary. Possible temperature effects, such as, for example, the temperature rise of the rotor of motor 3, may also necessitate further limitations on the adjustment range for the switching frequency. Needless to say, other operating parameters can also be considered to adapt the adjustment range for the switching frequency accordingly.

[0041] Figure 3 A schematic diagram of a flowchart based on one embodiment of a method for controlling an electric drive system is shown. This method can, in principle, include any steps, as previously described in conjunction with the electric drive system. Correspondingly, the electric drive system can also have any components, as will be described below in conjunction with the method for control.

[0042] In step S1, the current rotational frequency and / or current torque of the motor can be determined first. In step S2, the changes in the determined rotational frequency and / or torque can then be determined. Next, in step S3, the adjustment range for the switching frequency of the converter can be determined. Specifically, the adjustment range for the switching frequency can be determined using changes in the rotational frequency and / or torque. Based on this adjustment range, the converter can be controlled in step S4, wherein the switching frequency can be set within the previously determined adjustment range.

[0043] In summary, this invention relates to the control of an electric drive system in which the adjustment range of the switching frequency for the converter can be adapted in such a drive system, taking into account the rotational frequency or torque direction of the motor. This avoids psychoacoustic stimulation.

Claims

1. Control device (1) for an electric drive system having a current converter (2) and an electric machine (3), wherein The control device (1) comprises: a monitoring device (11) designed to determine a rotational frequency and / or a torque of the electric machine (3) and to determine a change in the determined rotational frequency and / or the determined torque; and a control device (12) designed to determine an adjustment range for a switching frequency of the inverter (2) using the change in the rotational frequency and / or the change in the torque and to operate the inverter (2) with a switching frequency in the determined adjustment range, wherein the control device (12) is designed to determine the current switching frequency as a lower limit frequency for the adjustment range for the switching frequency if the rotational frequency and / or the torque increases and / or to determine the current switching frequency as an upper limit frequency for the adjustment range for the switching frequency if the rotational frequency and / or the torque decreases, and / or wherein the control device (12) is designed to determine a predetermined maximum switching frequency as an upper limit frequency for the adjustment range for the switching frequency if the rotational frequency and / or the torque increases and / or to determine a predetermined minimum switching frequency as a lower limit frequency for the adjustment range for the switching frequency if the rotational frequency and / or the torque decreases.

2. The control device (1) according to claim 1, wherein The monitoring device (11) is designed to calculate the change in the rotational frequency and / or the torque using a gradient of the rotational frequency and / or the torque.

3. The control device (1) according to claim 1 or 2, wherein The monitoring device (11) is designed to detect a current actual rotational frequency and / or a current actual torque and / or to receive a target rotational frequency and / or a target torque.

4. The control device (1) according to claim 1 or 2, wherein The control device (12) is designed to adapt a modulation method for operating the inverter (2) using the determined rotational frequency and / or the determined torque.

5. The control device (1) according to claim 1 or 2, having a characteristic curve memory (13) designed to store and provide at least one characteristic curve for operating the inverter (2), wherein The control device (12) is designed to operate the inverter (2) using a characteristic curve stored in the characteristic curve memory.

6. The control device (1) according to claim 1 or 2, wherein The control device (12) is designed to adapt the operation of the inverter (2) using at least one further operating parameter.

7. An electric drive system having: an electric machine (3); an inverter (2) designed to operate the electric machine (3); and a control device (1) according to one of claims 1 to 6.

8. A method for operating an electric drive system having an inverter (2) and an electric machine (3), the method having the following steps: S1: determining a current rotational frequency and / or a current torque of the electric machine (3); S2: determining a change in the determined rotational frequency and / or the determined torque; S3: determining an adjustment range for a switching frequency of the inverter (2) using the change in the rotational frequency and / or the change in the torque; and S4: operating the inverter (2) with a switching frequency in the determined adjustment range. S3: determining an adjustment range for the switching frequency of the converter (2) using the change in the rotational frequency and / or the change in the torque; and S4: operating the converter (2) with the switching frequency in the determined adjustment range; wherein, if the rotational frequency and / or the torque increases, the current switching frequency is determined as a lower limit frequency for the adjustment range for the switching frequency, and / or if the rotational frequency and / or the torque decreases, the current switching frequency is determined as an upper limit frequency for the adjustment range for the switching frequency, and / or wherein, if the rotational frequency and / or the torque increases, a predetermined maximum switching frequency is determined as an upper limit frequency for the adjustment range for the switching frequency, and / or if the rotational frequency and / or the torque decreases, a predetermined minimum switching frequency is determined as a lower limit frequency for the adjustment range for the switching frequency.

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