阅读说明：本技术 用于操控电机的方法 (Method for controlling an electric machine ) 是由 F·埃格伯特 于 2018-11-20 设计创作，主要内容包括：本发明涉及一种用于经由换流器操控电机的方法,所述换流器包括多个开关(102,104),其中开关(102,104)由驱动器电路(106)操控,借助评估单元(110)监控换流器的电变量,以便识别是否超过阈值,评估单元(110)输出输出信号(134),所述输出信号载有电变量的信息,并且其中评估单元(110)的输出信号(134)直接地作用于换流器的开关(102,104),使得在识别到超出该电变量的阈值时采取对策。(The invention relates to a method for controlling an electric machine via a converter, which converter comprises a plurality of switches (102, 104), wherein the switches (102, 104) are controlled by a driver circuit (106), an electrical variable of the converter is monitored by means of an evaluation unit (110) in order to detect whether a threshold value is exceeded, the evaluation unit (110) outputs an output signal (134), which carries information of the electrical variable, and wherein the output signal (134) of the evaluation unit (110) acts directly on the switches (102, 104) of the converter in such a way that a countermeasure is taken when the threshold value of the electrical variable is detected to be exceeded.)

1. A method for operating an electric machine via a converter comprising a plurality of switches (102, 104), wherein

The switches (102, 104) are operated by driver circuits (106, 216),

monitoring an electrical variable of the converter by means of an evaluation unit (110) in order to identify whether a threshold value is exceeded,

the evaluation unit (110) outputs an output signal (134) which carries information of the electrical variable, and wherein

The output signal (134) of the evaluation unit (110) acts directly on the switches (102, 104) of the converter, so that countermeasures are taken when a threshold value of the electrical variable is identified as being exceeded.

2. A method according to claim 1, characterized by monitoring the direct voltage over the switches (102, 104) of the converter as an electrical variable.

3. The method according to claim 1 or 2, characterized in that the output signal (134) of the evaluation unit (110) acts on a driver circuit (106, 216) of a switch of the current transformer.

4. A method according to claim 3, characterized in that the output signal (134) of the evaluation unit (110) acts directly on an input signal (142) of the driver circuit (106, 216).

5. A method according to claim 3, characterized in that the output signal (134) of the evaluation unit (110) acts directly on the output signal (134) of the driver circuit (106, 216).

6. A method according to claim 3, characterized in that the output signal (134) of the evaluation unit (110) acts directly on an internal function of the driver circuit (106, 216).

7. The method according to any one of claims 1 to 6, characterized in that a comparator is used as the evaluation unit (110), which comparator is used to compare the detected electrical variable with a reference value.

8. Method according to any of claims 1 to 7, characterized in that the electrical machine is de-excited additionally by a hardware circuit in case there is a exceeding of the threshold value.

9. A device for operating an electric machine, wherein the device (200) is configured to perform the method according to any one of claims 1 to 8.

10. The device according to claim 9, additionally having a low-pass filter (205) by means of which an input signal of the evaluation unit (110) which characterizes the electrical variable is filtered.

11. The apparatus of claim 9 or 10, additionally comprising a hysteresis circuit (209).

Technical Field

The invention relates to a method and a device for controlling an electric machine.

Background

A so-called converter or inverter, which sets the current required for operating the electric machine, is used for operating the electric machine, which is supplied with or is provided with an alternating variable, for example a synchronous machine or an asynchronous machine. An inverter is an electrical device that converts direct current to alternating current or alternating current to direct current. Such converters are often used in particular in motor vehicles in which in many cases only one electrical direct current variable is provided.

In motor vehicles, the electric machine actively operated via an inverter usually has an overvoltage protection device, which is intended to limit the intermediate circuit voltage of the inverter to a maximum value. The intermediate circuit is by definition an energy store between the two converters. In the inverter, the energy store is likewise referred to as an intermediate circuit.

Such electric machines with corresponding overvoltage protection functions are used in motor vehicles at various voltage levels. In particular in a 48V vehicle electrical system with a maximum operating voltage of 54V, there is a technical requirement for an electric machine with an inverter to be able to comply with a contact protection voltage of 60V in the event of a fault, because of the small distance of 6V.

In particular, in automotive use, an onboard power supply system is understood to be a totality of all electronic components in a motor vehicle. It therefore includes not only the electrical consumer but also the power supply, i.e. for example a generator or an electrical storage, for example a battery. In motor vehicles, it is important to note that electrical energy is made available so that the vehicle can be started at any time and an adequate supply of electricity is ensured during operation. However, even in the stopped state, the appliance should still be able to operate for a reasonable period of time without compromising subsequent starts. At the same time, it must be ensured that the vehicle electrical system voltage does not exceed a maximum value, since otherwise components in the vehicle electrical system would be damaged.

Inverters typically comprise a plurality of switches, which are arranged for example as a half bridge or a bridge and are controlled, i.e. switched on and off or closed and opened, via a driver circuit, which is also referred to herein as a steering device. In known actuation designs, the bridge or half-bridge for actuating the electric motor is driven by a bridge driver, which in turn receives a PWM actuation signal via a microcontroller.

For example, fig. 1 shows a schematic configuration of an electronic control unit associated with a five-phase separately excited motor. In such machines, the intermediate circuit voltage is monitored by a comparator circuit. If this voltage exceeds a defined limit value, corresponding protective measures are taken by the microcontroller. This is necessary because an excessively high intermediate circuit voltage can lead to an excessively high vehicle electrical system voltage, which in turn can cause damage or even destruction of components in the vehicle electrical system.

In the known method, it is known to take fault reactions by a microcontroller which operates a driver circuit in order to limit overvoltages. It is therefore known that, by means of rapid de-excitation, the excitation field is rapidly degraded so that the pole wheel voltage is no longer generated, thereby limiting the overvoltage. It is also known to induce phase shorts. Thus, for the operation of the electric machine, all high-side or all low-side MOSFETs of the half-bridge in the inverter are short-circuited, so that no energy is transferred from the stator windings into the intermediate circuit of the inverter. It is also known to limit the intermediate circuit voltage by means of a diode. The diode becomes conductive from a certain voltage and in this way reduces the maximum attainable intermediate circuit voltage.

In the known method, in the event of load shedding in the system, the electric machine in the 48V on-board electrical system cannot comply with the contact protection voltage in most operating situations during a short period of time, for example, during a few milliseconds, and generates a voltage of more than 60V. The reason for this is that the time period until a fault is identified is too long. Furthermore, the fast de-excitation is not fast enough to degrade the excitation field before the overvoltage is reached. Furthermore, in the known method, rapid deactivation of the magnetic field and phase short-circuiting is triggered by an electronic control unit, typically by a microcontroller. It is not feasible due to the delay of the microcontroller to trigger a phase short fast enough. In the case of the use of zener diodes, there is the problem that they generate heat strongly under load and thus further increase the voltage at the connecting bolts of the machine. It is also noted that the time requirements in this respect are constantly increasing.

Disclosure of Invention

Against this background, a method according to claim 1 and an apparatus having the features of claim 9 are proposed. Embodiments emerge from the dependent claims and the description.

The method proposed herein is for operating an electric machine via an inverter comprising a plurality of switches and typically comprising an intermediate circuit in which electric energy is stored. In this case, it is monitored whether the electrical variable exceeds a threshold value and thus, for example, whether an overvoltage is present, in order to be able to take countermeasures or protective measures in this case. The countermeasures or protective measures are typically to cause phase shorts.

For example, the dc voltage across the switch can be monitored as an electrical variable. So-called intermediate circuit voltages can also be monitored. Alternatively or additionally, the phase voltage between the switches, the dc current flow change or the phase current change in the converter or similar variables can also be taken into account. A physical variable is therefore typically monitored which is proportional to the voltage or voltage change of the direct voltage, as a result of which overvoltages can be detected.

In the method, the switch is actuated by a driver circuit and the monitoring of the monitored electrical variable is carried out by means of an evaluation unit, for example by means of a comparator. The evaluation unit identifies, in the embodiment of the comparator, for example by comparison with a reference variable or a reference voltage or a threshold voltage, for example whether an excess variable or an overvoltage, i.e. a variable or a voltage above a limit value, is present in the intermediate circuit.

The evaluation unit outputs an output signal which carries information of the intermediate circuit voltage. Thus, the signal can carry information, for example, whether an overvoltage is present. The output signal of the evaluation unit acts directly on the switches of the converter, for example, by means of a driver circuit. Directly, the information that an overvoltage is present is not first provided to the microcontroller, which then outputs a corresponding control signal for the driver circuit. Directly, the output signal of the evaluation unit is forwarded directly to the switch or its driver circuit.

This can mean that the output signal of the evaluation unit has a direct effect on the input signal of the driver circuit, the output signal of the driver circuit or also on the internal function or mode of operation of the driver circuit. Thus, an evaluation unit, for example a comparator, can also be provided in the driver circuit. The output signal then directly affects the driver circuit or the flow in its function.

If a threshold value is detected to be exceeded, for example if the intermediate circuit voltage is overvoltage, countermeasures are taken. The countermeasures consist, for example, in causing a phase short by closing all high-side switches or all low-side switches of a bridge or half-bridge, which can be a driver circuit, for example.

The proposed method is used, for example, in the onboard power supply system of a motor vehicle, in which the electric machine is operated. However, this method can be used in other fields as long as the motor is operated.

With the proposed method, it is now achieved that the fault response time in the event of an overvoltage is significantly reduced, so that the maximum voltage reached by the electric machine is reduced in order to not exceed a contact protection voltage of 60V as far as possible. In addition, the zener diodes currently used for overvoltage protection functions in the converter are rendered superfluous by this method.

The proposed method is characterized in that the triggering of a phase short is not taken via a microcontroller as a fault reaction of the converter, but is directly connected to the measurement of the intermediate circuit voltage. The protective reaction, i.e. the initial initiation of a phase short, for example, is thus achieved by a purely hardware circuit which bypasses the microcontroller. In this way, the failure reaction time can be significantly reduced. The zener diodes necessary to date for reducing the maximum overvoltage become superfluous, since it is sufficient to initiate a phase short circuit in time.

The proposed device is used to carry out the described method and is integrated, for example, in a control device.

The proposed method and the described apparatus have the following advantageous effects at least in some embodiments:

cost reduction by eliminating components for overvoltage reduction, such as zener diodes, which are no longer required,

faster fault reaction and thus reduced maximum reached voltage.

Drawings

Further advantages and embodiments of the invention emerge from the description and the enclosed drawing.

It is to be understood that the features mentioned above and those yet to be explained below can be used not only in the respectively stated combination, but also in different combinations or individually without departing from the scope of the present invention.

Fig. 1 shows an embodiment of an electric machine with a control circuit according to the prior art.

Fig. 2 shows an apparatus for performing the proposed method.

Fig. 3 shows another possible embodiment of the described device.

Detailed Description

The invention is schematically illustrated in the drawings according to embodiments and is described in detail below with reference to the drawings.

Fig. 1 shows an electric machine 10 operated by means of an inverter 12. The motor includes a stator 20, a rotor 22 having rotor windings 24, and a pulley 26. The inverter 12 includes a half bridge 30 having a plurality of high side switches 32 and an equal number of low side switches 34, a microcontroller 36, a first bridge driver 38, a second bridge driver 40, a field bridge 42, a comparator circuit 44 having a voltage divider 45 including a first resistor 46 and a second resistor 47, and a diode 48. The intermediate circuit, for example provided by a capacitor, is not shown in the figure. An intermediate circuit voltage 50 is applied between a first terminal 52 and a second terminal connection 54.

The diagram thus shows a schematic configuration of an electronic control unit or inverter 12 associated with the five-phase separately excited electrical machine 10. The half bridge 30 for controlling the electric motor 10 is driven by bridge drivers 38, 40, which in turn receive PWM control signals from a microcontroller. As shown in fig. 1, the intermediate circuit voltage 50 is monitored by the comparator circuit 44. If this voltage exceeds a defined limit value, corresponding protective measures are taken by the microcontroller 36.

According to the prior art, the following fault reactions are mainly undertaken by the microcontroller 36 in order to limit the overvoltage:

-fast de-excitation: by means of the rapid de-excitation, the excitation field is degraded so rapidly that the pole wheel voltage is no longer generated, thereby limiting the overvoltage.

-phase short circuit: for controlling the electric machine 10, all high-side switches 32 or all low-side switches 34 of the half-bridge 30 in the inverter 12 are short-circuited, which are realized, for example, by MOSFETs. Whereby no energy is transferred from the stator windings into the intermediate circuit of the converter 12.

Furthermore, the intermediate circuit voltage is limited by a diode 48. The diode becomes conductive from a certain voltage and thereby reduces the maximum reached intermediate circuit voltage 50.

In contrast, it is proposed here that: in the event of an overvoltage in the intermediate circuit, the microcontroller is bypassed and protective measures are taken directly or immediately. This process is described below in conjunction with fig. 2.

Note that: the proposed method is described below mainly in connection with the monitoring of the intermediate circuit voltage. However, this is only one of many possibilities. In principle, physical, in particular electrical variables are monitored. This can be the intermediate circuit voltage.

Fig. 2 shows a half bridge 100 with five high-side switches 102 and five low-side switches 104, in this case a bridge driver, a microcontroller 108 and an evaluation unit 110, which is designed as a comparator or comparator circuit with a voltage divider 112 with a first resistor 114 and a second resistor 116, for example in the form of a MOSFET or an IGBT. An intermediate circuit voltage 124 is applied between the first terminal 120 and the second terminal 122.

The inputs to the operational amplifier 118 are a reference voltage 130 and a voltage value 132 of the voltage divider 112. The operational amplifier 118 outputs an output signal 134 which is the output signal 134 of the evaluation unit 110. The output signal 134 carries information as to whether an overvoltage is present. The output signal 134 is now provided directly to the driver circuit 106 via connection 140. In this case, the output signal 134 of the evaluation unit 110 acts directly on the input signal 142 of the driver circuit 106. As a countermeasure, if there is an overvoltage in the intermediate circuit, in this embodiment, a phase short circuit is caused by closing all of the high-side switches 102 or closing all of the low-side switches 104.

Thus, it was originally proposed in the proposed method that a phase short is not induced by the microcontroller 108. Instead, the output of the evaluation unit 110, in this case a voltage comparator, overrides the PWM output signal of the microcontroller 108 such that the pulse duty cycle of all low-side MOSFETs is set to 100%. As soon as an overvoltage is detected by the comparator, a phase short circuit is caused.

Fig. 3 shows a circuit arrangement 200 as a possible device for carrying out the method proposed here, by means of which the PWM signal of the microcontroller can be directly overwritten by a comparator in order to take protective measures in this way sufficiently quickly.

The circuit arrangement 200 comprises a voltage divider 202, a capacitor 204 for setting a low-pass filter 205, an operational amplifier 206, a resistor 208 being a hysteresis circuit 209 for setting the hysteresis, a transistor 210, a PWM output signal 212 of a microcontroller 214 and a driver circuit 216, in this case a bridge driver. An intermediate circuit voltage 226 is applied between the first terminal 220 and the second terminal 222, typically the ground terminal GND. The capacitance 204 and the resistance 208 are optional measures.

The circuit arrangement 200 in fig. 3 enables a PWM operation by the microcontroller 214 as long as the voltage at the tap of the voltage divider 202 does not exceed the reference voltage. When the voltage limit value is exceeded, GND is present at the output of the operational amplifier 206, whereby the transistor 210 is switched off and the PWM signal is thus set "low".

A low pass filter 205 can be provided to prevent false triggering. This may be due to the very small distance of the voltage limit values from the operating voltage range. The hysteresis circuit 209 ensures that the phase short is not eliminated immediately after falling below the preset voltage limit.

The connection of the comparators and the influence on the operation of the power switches, e.g. the high-side and low-side switches, is closely related to the selected operation of the respective converter. Thus, there are various possibilities to induce a phase short in hardware directly by the comparator. Furthermore, for example, there is the possibility of bypassing the bridge drive and directly influencing the actuation of the control terminals of the power switches by means of an evaluation unit, for example a comparator.

In addition to the induction of a phase short circuit, it is also conceivable for the deexcitation of the electric machine to be induced by a hardware circuit. It should be noted that this measure may itself have only some advantages over the method according to the prior art.

The proposed method is particularly suitable for electric machines, i.e. for example separately excited synchronous machines, which are designed for use in motor vehicles. Furthermore, use in asynchronous machines is also conceivable.

The controlled electric machine can be in generator mode or engine mode.

The method and the device can also be used in the context of a power recovery system (BRS) in an electric motor, a so-called power recovery motor.