Method for actuating an electric motor

Abstract

The invention relates to a method for operating an electric machine (10), in which the electric machine (10) is actuated with a modulation signal which is characterized by a modulation degree M, during operation of the electric machine (10), at least one influencing parameter is detected, and the modulation degree M is determined on the basis of the at least one influencing parameter.

Description

Technical Field

[0001] The present invention relates to a method for controlling an electric motor, particularly a method for controlling an electric motor in a motor vehicle electrical system, and an apparatus for implementing the method. Background Technology

[0002] In automotive applications, the proportion of motors designed for 48V electrical systems is increasing. Compared to traditional 12V electrical systems, these motors pose increased electrical safety risks. Therefore, standard ISO 6469-3:2021 standardizes measures to ensure electrical safety in automotive environments.

[0003] Accordingly, voltage levels are divided into three grades: Grade A, Grade B1, and Grade B2, which impose different levels of stringency on electrical safety measures. The difference between these grades lies in their underlying voltage level.

[0004] For electromechanical actuators, if the control unit containing power electronics is not directly mounted on the motor (this is also known as a discrete ECU (electronic control unit), then the current used to drive the motor must be guided through a so-called phase cable. The phase current or phase voltage supplied in this case is an alternating current (AC) parameter.

[0005] A method for obtaining the actual torque of a multiphase motor is known from document DE102010031435A1, in which the motor is controlled by a pulse width modulation signal.

[0006] Document DE102021214517A1 describes a method for operating an electric motor (also called an electric motor) and determining the temperature of its components.

[0007] Document DE102008042978A1 describes a method for determining the phase current of a multiphase motor connected to an inverter. In this method, the motor temperature is determined. Summary of the Invention

[0008] Against this backdrop, a method having the features of claim 1 and an apparatus according to claim 12 are proposed. Embodiments are derived from the dependent claims and the description.

[0009] The proposed method is used to operate a motor, which is controlled by a modulated signal. This modulated signal is characterized by the modulation grad (also called modulation rate or modulation depth) M. This means that the modulation grad is a parameter that describes the modulated signal to a particularly large extent. During motor operation, at least one influencing parameter is detected. The modulation grad is then determined based on the at least one detected parameter. This specifically means that the modulation grad is limited, and the motor is then controlled by the modulated signal characterized by that modulation grad. Here, "influence" means that the parameter or condition affects the operation of the motor.

[0010] At least one influencing parameter can be selected from the following set of parameters: supply voltage, temperature, resistance, and estimated values ​​of MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) parameters. This means that one or any combination of the above parameters, or even all of them, can be used as an influencing parameter.

[0011] These parameters are used to model the actual object being regulated—that is, the entity or physical component that follows the control unit's logic, i.e., the components, cables, and motors within the control unit—as well as possible. Based on this, the modulation can be optimized as much as possible without violating the voltage class limitations of the control unit's output voltage. For example, the resistance of the cable and the resistance of the motor components (MOSFETs) within the control unit. These resistances are temperature-dependent, therefore the corresponding, and especially the estimated, temperature is also important.

[0012] The proposed apparatus is used to perform the method and is equipped with an evaluation unit with a corresponding configuration.

[0013] Therefore, the design specifies that the supply voltage should be measured using a suitable device, and the phase voltage should be limited to the effective value of Class A or the RMS level (rms: root means square) by limiting the modulation based on the measurement results.

[0014] In one particular implementation, the operation is monitored in order to detect or identify potential faults.

[0015] If the motor is part of a redundant system, such as in a redundantly designed steering system, and a fault in another system prevents the redundancy level from functioning properly, then the relevant restrictions can be removed.

[0016] If a fault is detected, remove any restrictions that may have been imposed on the modulation scheme in the design and utilize the available power reserves.

[0017] Other advantages and design solutions of the present invention can be derived from the specification and the accompanying drawings.

[0018] It should be understood that the features mentioned above and described below can be used not only in the given combinations, but also in other combinations or individually, without departing from the scope of the invention. Attached Figure Description

[0019] Figure 1 A separately excited motor with a control unit is shown in schematic form.

[0020] Figure 2 Two diagrams illustrate a separately excited roll stabilizer (also called a sway stabilizer).

[0021] Figure 3 The variation process of sinusoidal phase voltage is shown in the form of a chart.

[0022] Figure 4 The process of the sinusoidal target signal changing and the resulting PWM (pulse width modulation) signal changing are illustrated in the form of a chart.

[0023] Figure 5 A three-phase permanent magnet synchronous motor with a star connection is shown in the form of a circuit diagram.

[0024] Figure 6 The process of signal variation used to illustrate sinusoidal-triangular modulation is presented in the form of a chart.

[0025] Figure 7 The process of sine variation under different modulations M is shown in the form of a chart. Detailed Implementation

[0026] The present invention has been illustrated with reference to the embodiments shown in the accompanying drawings, which will now be described in detail with reference to the drawings.

[0027] Figure 1 A separately excited electric motor is shown, generally indicated by reference numeral 10 in the attached figure. The illustration also shows the control unit 12 and the housing 14.

[0028] like Figure 1 As shown, in this configuration, the motor 10 is not directly connected to the control unit 12, but rather connected to the control unit via cable 18. This principle is also feasible in safety-critical components such as brakes and steering systems.

[0029] It is important to consider that for systems in vehicles powered by 48V or higher electrical system voltages, the connection between the electric motor and the discrete or autonomous control unit (ECU), i.e., phase cables, plugs, and other aspects such as markings, should be protected at least according to the measures defined in Level B1 of ISO 6469-3:2021. Compared to Level A measures, this would involve a considerable amount of work and cost at the vehicle level.

[0030] The proposed method lowers the relevant voltage levels, enabling the system, consisting of an autonomously operating control unit, motor, and its connecting devices, to meet Class A requirements, thereby achieving cost savings. Crucially, the voltage between two of the three phases, the so-called phase voltage, has an effective value or RMS value (RMS: root mean square) that is higher than the RMS value of a single phase voltage.

[0031] Figure 2 An example of a separately excited motor with a voltage level of 48V in the housing is shown, indicated by reference numeral 50. In addition to the control unit 52, cable 54, which is part of the electrical safety measures, can also be seen.

[0032] B1 voltage can also be avoided by reducing the power supply voltage level specification from 48V to about 42V.

[0033] In the design, phase voltage control is achieved through pulse-width modulation (PWM) of power electronic components. This involves applying a periodic, typically sinusoidal, voltage to the phase cable. Please refer to [reference needed]. Figure 3 .

[0034] Figure 3 A graph 100 is shown, with time on the horizontal axis 102 and normalized voltage on the vertical axis 104. The graph illustrates the changes in sinusoidal phase voltage 110, 112, and 114. The three sinusoidal signals shown are illustrated with a uniform phase difference.

[0035] Figure 4 A graph 150 is shown, with time on the horizontal axis 152 and normalized voltage on the vertical axis 154. The graph shows the change process 160 of the sinusoidal target signal and the change process 164 of the resulting PWM signal.

[0036] Based on the supply voltage and required power, the corresponding RMS value of the AC voltage is obtained within one cycle.

[0037] Now, the supply voltage is measured according to the proposed method, and the phase voltage is limited to the RMS level of Class A by limiting the modulation based on the measurement results.

[0038] The following explanation is based on the following assumptions, and the extensions will be explained later:

[0039] This is a three-phase permanent magnet synchronous motor with a star connection;

[0040] In an ideal scenario, each phase is excited by a sinusoidal voltage with a phase difference of 120°;

[0041] As the modulation method for PWM, sinusoidal-triangular modulation is used;

[0042] The voltage level is 48V.

[0043] Figure 5 A motor, generally indicated by reference numeral 200, is shown. It is constructed as a three-phase permanent magnet synchronous motor with a star connection, including phases A 202, B 204, and C 206. The illustration further shows the converter 210, the load 212 given by the motor 200, and the grounding conductor N214.

[0044] The arrow is marked as follows: Arrow 220U A0 Arrow 222U B0 Arrow 224U C0 Arrow 226U N0 Arrow 228U A Arrow 230U B Arrow 232U C0 Arrow 234U AB Arrow 236U BC Arrow 238U CA Arrow 240U S1 Arrow 242U S2 Arrow 244U S3 Arrow 250I A Arrow 252I B Arrow 254I C Arrow 256I S1 Arrow 258I S2 And arrow 260I S3 .

[0045] The proposed method will now be described in more detail with reference to the accompanying figures shown above.

[0046] Figure 1 The electrical circuit of a three-phase permanent magnet synchronous motor with a star connection is shown.

[0047] The corresponding normalized sinusoidal target phase voltage has been Figure 3 This was explained in the text.

[0048] The RMS value of the AC component of one phase voltage is determined according to the following formula:

[0049]

[0050] The RMS value of the voltage difference between the two phases is determined accordingly in the integration term using the voltage difference between the two phases. The RMS voltage between the two phases is greater than the RMS voltage of a single phase, thus it is critical for electrical safety measures. In practical applications, the RMS value of the voltage is affected by the pulse width modulation of the target voltage.

[0051] Here, for the AC component, we assume that the average value of u(t) is zero.

[0052] Figure 6 A graph 300 is shown, with time on the horizontal axis 302 and voltage on the vertical axis 304. The graph shows the target signal 310 and the triangular modulation signal 312, used to illustrate sinusoidal-triangular modulation. When the triangular signal 312 is greater than the target signal 310, the resulting PWM signal is 1.

[0053] Similar to the formula above, the RMS value of the phase-to-phase voltage obtained within one cycle can be determined. This value will be increased compared to the ideal target signal. Now, the power supplied to the actuator can be influenced by the modulation index M. The modulation index is here determined according to the following formula for the amplitude of the sinusoidal signal:

[0054]

[0055] Figure 7 A graph 350 is shown, with time on the horizontal axis 352 and voltage on the vertical axis 354. The graph shows the sinusoidal change process under different modulation degrees M, namely the first change process 360 when the modulation degree M is 0%, the second change process 362 when the modulation degree M is 25%, the third change process 364 when the modulation degree M is 50%, and the fourth change process 366 when the modulation degree M is 100%.

[0056] At a voltage level of 48V, the phase-to-phase voltage RMS value is 35.64V, which makes the system compliant with Class B1 standards in ISO 6469-3:2021. To reduce the voltage level under normal operating conditions and achieve Class A standards (which would significantly reduce electrical safety measures), the following methods were employed:

[0057] Monitoring parameters affecting the system:

[0058] Power supply voltage;

[0059] Temperature and resistance;

[0060] Estimated values ​​of MOSFET parameters.

[0061] Dynamic limiting modulation ensures that the corresponding voltage limits in the phase cable remain below the critical voltage level during each cycle.

[0062] The maximum modulation obtained thus is determined by the following relationship:

[0063]

[0064] Alternatively, the modulation schemes outlined above can be used:

[0065]

[0066] And accordingly, solve the equation based on the modulation scheme M. Where:

[0067] U Eff,max This is the maximum voltage for the corresponding voltage level (30V in this case);

[0068] U nom It is the power supply voltage.

[0069] Since temperature, resistance, and MOSFET parameters still affect actual behavior, and the actual effective voltage provided differs from that in the ideal formula, these factors can be further utilized to better adapt the modulation to the current state.

[0070] Other implementation methods involve:

[0071] Unlike other alternative ideal control signals with a pure sinusoidal shape (e.g., when manipulated in the dq coordinate system (Parker transformation), the current component i_d is not 0 → e.g., field weakening operation);

[0072] Other alternative phase differences;

[0073] Other alternative modulation methods;

[0074] Other alternative voltage levels;

[0075] Other alternative motor connection methods that differ from the star connection described above;

[0076] -More alternative motor phases;

[0077] -Other alternative motor types;

[0078] - As an alternative to using modulation to adjust power, for example, to flexibly enhance the target signal;

[0079] - Unlike other voltage levels or other voltage grades, 48V.

[0080] The proposed method is designed to increase the system's power level in the event of a failure, serving as a backup and providing power reserves for motor control. This is particularly important for steering control, which typically uses a six-phase motor controlled by two three-phase motors.

[0081] The starting point is the PWM control performed under separately excited conditions using the adaptive method mentioned above.

[0082] The implementation described below addresses a fault condition, such as a phase short circuit in a six-phase steering motor. Since ISO 6469-3:2021 pertains to normal operating conditions, the electrical safety requirements described therein are not relevant in this case, and the effective value of the phase-to-phase voltage can be increased in this fault condition.

[0083] Therefore, other costly safety measures in the control unit can be omitted.

[0084] The described implementation uses a mechanism that:

[0085] Fault detected;

[0086] Based on this, the mechanism is modified so that instead of reducing the still controllable phase voltage, the remaining power reserves are used by making full use of the modulation to ensure the vehicle's necessary steering capability.

[0087] The following implementation will be described based on the following assumptions:

[0088] This is a three-phase permanent magnet synchronous motor with a star connection;

[0089] In an ideal scenario, each phase is excited by a sinusoidal voltage with a phase difference of 120°;

[0090] As the modulation method for PWM, sinusoidal-triangular modulation is used;

[0091] The voltage level is 48V;

[0092] This is a 2x3 phase steering motor;

[0093] The fault scenario under consideration is a short circuit in two of the six phases.

[0094] In the previously described control strategy, the phase voltage is limited by the modulation index M. The modulation index is determined by the amplitude of the sinusoidal signal according to the following formula:

[0095]

[0096] Please refer to Figure 7 The diagram illustrates the sine variation process under different modulation schemes M.

[0097] In the event of a fault, the restrictions on the switching system will now be lifted, allowing power reserves to be utilized.

[0098] This implementation method can be summarized as follows:

[0099] 1) The nominal behavior as described at the beginning

[0100] a. Monitor influencing parameters during operation:

[0101] Power supply voltage;

[0102] Temperature and resistance;

[0103] Estimated values ​​of MOSFET parameters.

[0104] b. Dynamically adjust the modulation scheme to ensure that the corresponding voltage limits in the phase cable remain below the critical voltage level during each cycle.

[0105] c. The maximum adjustable modulation index is obtained by solving the following equation based on the modulation index:

[0106]

[0107] 2) A malfunction occurred

[0108] a. A fault was detected;

[0109] b. While removing modulation restrictions, estimate and monitor the motor phase temperatures so that limiting measures can be taken based on this information to prevent demagnetization. This can be achieved by specifying a reduction in the current flowing through the motor to prevent demagnetization.

[0110] c. Cancel the restrictions on the adjustment system in 1)c.

[0111] Other implementation methods involve:

[0112] - Unlike other alternative ideal control signals that are purely sinusoidal (e.g., when manipulated in the dq coordinate system (Parker transformation), the current component i_d is not 0 → e.g., field weakening operation);

[0113] -Other alternative phase differences;

[0114] -Other alternative modulation methods;

[0115] -Other alternative voltage levels;

[0116] -Other alternative connection methods;

[0117] -More alternative motor phases;

[0118] -Other alternative motor types;

[0119] - Alternatives to the adjustment mechanism, such as flexibly increasing the target signal;

[0120] - Unlike other voltage levels or other voltage grades, 48V;

[0121] - Alternatives to steer-by-wire: for rack actuators and / or steering wheel actuators; - Other different failure scenarios in the steering motor.

Claims

1. A method for operating motors (10, 50, 200), wherein: The motors (10, 50, 200) are controlled by modulation signals (164, 312); The modulation signals (164, 312) are characterized by the modulation index M; During the operation of the motors (10, 50, 200), at least one influencing parameter is detected; and The modulation scheme M is determined based on the at least one influence parameter.

2. The method according to claim 1, wherein, The at least one influencing parameter is selected from the following set of parameters: supply voltage, temperature, resistance, and estimated values ​​of MOSFET parameters.

3. The method according to claim 1 or 2, wherein the method is used for a separately excited motor (50).

4. The method according to claim 1 or 2, wherein the method is used for a permanent magnet synchronous motor (200).

5. The method according to any one of claims 1 to 4, wherein, The PWM modulation signal (164) is used as the modulation signal (164, 312).

6. The method according to claim 5, wherein, The modulation signal (312) is generated using sinusoidal-triangular modulation.

7. The method according to any one of claims 1 to 6, wherein, Additional monitoring is performed to identify faults.

8. The method according to claim 7, wherein, Additionally, monitor another connected subsystem, or use the results of such monitoring in another location to identify faults.

9. The method according to claim 8, wherein, By utilizing a fault identified in another system or subsystem, the available power reserves can be utilized by increasing the modulation M.

10. The method according to claim 9, wherein, Monitor the phase temperature of the motor.

11. The method of claim 10, wherein limiting measures are taken based on the monitored motor phase temperature.

12. An apparatus for controlling a motor (10, 50, 200), the apparatus having an evaluation unit configured to perform the method according to any one of claims 1 to 11.

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