WO2019105795A1

WO2019105795A1 - Method for controlling an electric machine

Info

Publication number: WO2019105795A1
Application number: PCT/EP2018/081870
Authority: WO
Inventors: Felix EGBERT
Original assignee: Robert Bosch Gmbh
Priority date: 2017-12-01
Filing date: 2018-11-20
Publication date: 2019-06-06
Also published as: DE102017221638A1; EP3718203A1; CN111713003A

Abstract

The invention relates to a method for controlling an electric machine via an inverter, which comprises a number of switches (102, 104), wherein the switches (102, 104) are controlled by a driver circuit (106), an electrical parameter of the inverter is monitored by an evaluating unit (110), in order to detect an exceeding of a threshold value, the evaluating unit (110) outputs an output signal (134), which carries information about the electrical parameter, and wherein the output signal (134) of the evaluating unit (110) acts directly on the switch (102, 104), such that a countermeasure is initiated upon detecting an exceeding of the threshold value of said electrical parameter.

Description

description

title

Method for controlling an electrical machine

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

State of the art

To control an electrical machine that is to provide ver with an AC variable or such supplies, such as, for example, a synchronous or an Asyn chron machine, so-called inverter or inverter are used, which set the required for driving the electrical machine electrical currents , An inverter is an electrical device that converts a direct current into an alternating current or an alternating current into a direct current. In particular special in motor vehicles, in which in many cases only an electric DC is available, such inverters are often used.

Electric machines in the motor vehicle, which are actively actuated via an inverter, usually have an overvoltage protection which is intended to limit the intermediate circuit voltage of the inverter to a maximum value. A DC link is by definition an energy storage device between two inverters. In an inverter, an energy storage is also referred to as inter mediate circuit.

Such electrical machines with appropriate overvoltage protection functions find application at various voltage levels in motor vehicles. In particular, in the 48 V electrical system, in which the maximum operating voltage is 54 V, there is for the electrical machine with inverter due the small distance of 6 V the technical challenge to be able to meet the contact protection voltage of 60 V in the event of a fault.

Under a vehicle electrical system is to be understood in particular in the automotive use, the totality of all electrical components in a motor vehicle. Thus, both electrical consumers and sources of supply, such as. Generators or electrical storage, z. As batteries includes. In the motor vehicle care must be taken to ensure that electrical energy is available so that the vehicle can be started at any time and a sufficient power supply is ensured during operation. But even when parked, electrical consumers should still be operable bar for a reasonable period, without a subsequent start is affected. 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 may be damaged.

Inverters typically comprise a number of switches, for example, arranged in a half-bridge or bridge and controlled by a driver circuit, which is also referred to herein as drive, i. E. H. switched on and off or closed and opened. In known Ansteuerungskonzep th bridges or half bridges for driving the electrical Maschi ne driven by bridge drivers, which in turn receive the PWM drive signal through a microcontroller.

A schematic structure of an electronic drive unit in connexion with a separately excited five-phase electric machine is shown, for example, in Fi gur 1. In such a machine, the DC link voltage is monitored by a comparator circuit. If this voltage exceeds a defined limit, appropriate protective measures are initiated by the microcontroller. This is necessary because too high an intermediate circuit voltage can lead to an excessive vehicle electrical system voltage, which in turn can cause damage or even destruction of components in this vehicle network. In known methods, error responses are known, which are initiated by the microcontroller, which drives the driver circuit, to limit the voltage over. Thus, it is known to quickly reduce the exciter field with a fast excitation, so that no more Polradspannung is generated, whereby the overvoltage is limited. Furthermore, it is known to cause a Pha senkurzschluss. Thus, either all high-side or all low-side MOSFETs of the half-bridges in the inverter are short-circuited to control the electrical machine, so that no energy is transmitted from the stator winding to the intermediate circuit of the inverter. Furthermore, it is known to limit the inter mediate circuit voltage by diodes. These become conductive starting from a certain voltage and in this way reduce the maximum attainable intermediate circuit voltage.

Electrical machines in the 48 V electrical system can not comply with known methods in the event of a load shedding in the system, the contact protection voltage for a short period, eg. A few milliseconds, in most operating situations and generate voltages greater than 60 V. One reason is the time to error detection is too long. Furthermore, the fast de-excitation is not fast enough to break down the exciter field before reaching the overvoltage. In addition, the rapid excitation and the phase short circuit in known methods by an electronic control unit, typically triggered by a microcontroller. Due to the delay of the microcontroller, it is not possible to initiate the phase short circuit fast enough. When using Zener diodes, there is the problem that they heat up during the stress and thereby further increases the voltage at the connection pin of the machine. It should also be noted that the time requirements in this area are steadily increasing.

Disclosure of the invention

Against this background, a method according to claim 1 and an Anord tion with the features of claim 9 are presented. Embodiments emerge from the dependent claims and the description. The method presented herein is for driving an electric machine via an inverter comprising a number of switches and typically a DC link in which electrical energy is stored. It is intended to monitor whether an electrical variable exceeds a threshold value and thus, for example . An overvoltage is present in order to initiate a countermeasure or a protective measure in this case. This typically consists of causing a phase short circuit.

As an electrical variable can, for example, the DC voltage over the switches are monitored. It is also possible to monitor the so-called DC link voltage. Alternatively or additionally, the phase voltage between the switches, the DC current flow change from the inverter or a phase current change or a comparable size can be used. Thus, typically a physical quantity is monitored that is proportional to the voltage or voltage change of the DC voltage, whereby an overvoltage can be detected.

In the method, the switches are driven by a driver circuit and it is the monitoring of the monitored electrical variable by means of an evaluation, for example. By means of a comparator performed. This Auswer teeinheit recognizes, in an embodiment of the comparator eg. By comparison with a reference size or reference voltage or threshold voltage, whether an oversize or overvoltage, d. H. a value or voltage lying above a limit exists, for example, in the intermediate circuit.

The evaluation unit outputs an output signal which carries information about the intermediate circuit voltage. For example, the signal may carry the information as to whether an overvoltage exists or not. The output signal of the evaluation unit acts directly on the switches of the converter, for example, mediated by the driver circuit. Immediately means that the information on the presence of an overvoltage is not first given to the microcontroller, which then outputs a corresponding drive signal for the driver circuit. Immed directly means that the output of the evaluation is passed directly to the switch or its driver circuit. This can mean that the output signal of the evaluation unit has an immediate effect on an input signal of the driver circuit, an output signal of the driver circuit or else on the internal function or mode of operation of the driver circuit. Thus, the evaluation unit, for example. The comparator can also be provided in the driver circuit. The output signal then directly influences the processes in the driver circuit or their function.

Upon detection of an exceeding of the threshold value, for example, in an overvoltage voltage of the DC link voltage, a countermeasure is initiated. This consists z. Example, in that a phase short circuit is brought about by all highside or all lowside switches of a bridge or half-bridge, which can represent the driver circuit are closed.

The presented method is used, for example, in a vehicle electrical system of a motor vehicle in which an electric machine is operated. However, the method is also applicable in other areas whenever an electrical machine is controlled.

The presented method now makes it possible to significantly reduce the error reaction time in the event of an overvoltage event and thus to reduce the maximum voltage reached by the electrical machine so as not to exceed the contact protection voltage of 60 V as far as possible. Furthermore, the method currently used for the overvoltage protection Zen diodes in the inverter superfluous by the process.

The proposed method is characterized by the initiation of Pha senkurzschlusses not initiate as error response of the inverter via the microcontroller, but directly bind to the measurement of the DC link voltage to ver. The primary initiation of the protective reaction, such. B. the phase short circuit, is thus realized only by a pure hardware circuit that bypasses the microcontroller. In this way, the error reaction time can be significantly reduced. Previously needed zener diodes to reduce the maximum overvoltage are superfluous, since the timely initiation of the phase short circuit is sufficient. The presented device is used to carry out the procedure described procedural and is, for example, integrated in a control unit.

The presented method and apparatus have the following advantageous effects, at least in some of the embodiments:

- Cost reduction by eliminating unneeded components to Redu cation of the overvoltage, z. Zener diodes,

- Faster error response and thereby reduce the maximum voltage reached.

Further advantages and embodiments of the invention will become apparent from the loading and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained not only in the particular combination specified, but also in other combinations or alone, without departing from the scope of the present invention.

Brief description of the drawings

Figure 1 shows an embodiment of an electric machine with drive circuit according to the prior art.

Figure 2 shows the arrangement for carrying out the presented method.

FIG. 3 shows a further possible embodiment of the described arrangement.

Embodiments of the invention

The invention is illustrated schematically on the basis of embodiments in the drawings and will be described below in detail with reference to the drawings. FIG. 1 shows an electrical machine 10, which is controlled by an inverter 12. The electric machine comprises a stator 20, a rotor 22 with Ro torwicklung 24 and a pulley 26. The inverter 12 includes a half-bridge 30 with a number 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, an exciter bridge 42, a Komparatorschal device 44 with a voltage divider 45, which includes a first resistor 46 and a second resistor 47, and a diode 48. The intermediate circuit, which is given, for example, by a capacity , is not shown in the illustration. An intermediate circuit voltage 50 is connected between a first terminal 52 and a second terminal 54.

The illustration thus shows the schematic structure of the electronic control unit or to the inverter 12 in connection with the externally excited five-phase electric machine 10. The half bridges 30 for driving the electric machine 10 are driven by bridge driver 38, 40, in turn, the PWM drive signal through received the 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, appropriate protective measures are initiated by the microcontroller 36.

According to the prior art, the following error responses are primarily initiated by the microcontroller 36 in order to limit the overvoltage:

Fast de-excitation: With the aid of the fast de-excitation, the excitation field is reduced very quickly, so that no more pole-wheel voltage is generated, which limits the overvoltage.

Phase short circuit: There are either all high-side switch 32 or all lowside switch 34, which are realized, for example. By MOSFETs, the half-bridge 30 in the inverter 12 to control the electric machine 10 short-circuited. As a result, no energy is transmitted from the stator winding into the DC link of the inverter 12. Furthermore, the DC link voltage is limited by diodes 48. These become conductive above a certain voltage and thereby reduce the maximum DC link voltage 50 reached.

In contrast, it is proposed herein, in the presence of an overvoltage in the intermediate circuit, bypassing the microcontroller directly or directly initiate a protective measure. This procedure is explained below in connection Ver with Figure 2.

It should be noted that the presented method will be described below mainly in connection with the monitoring of an intermediate circuit voltage. However, this represents only one of many possibilities. It is fundamentally Lich a physical, especially electrical, monitored size. This can be the DC link voltage.

FIG. 2 shows a half-bridge 100 with five high-side switches 102 and five low-side switches 104, which are embodied, for example, as MOSFETs or IGBTs, a driver circuit 106, in this case a bridge driver, a microcontroller 108 and an evaluation unit 110 is formed as a comparator or compa ratorschaltung with a voltage divider 112 with a first resistor 114 and a second resistor 116 and an operational amplifier 118 out. Between a first terminal 120 and a second terminal 122 is an intermediate circuit voltage 124 at.

Inputs of 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 representing the output signal 134 of the evaluation unit 110. The output 134 carries information as to whether an overvoltage exists or not. This output signal 134 is now more directly via a connection 140 to the driver circuit 106 gege ben. In this case, the output signal 134 of the evaluation unit 110 acts directly on an input signal 142 of the driver circuit 106. As a countermeasure, if an overvoltage is present in the intermediate circuit, at this output phase short circuit by either closing all the high side switches 102 or all the low side switches 104.

In the presented method, it is thus fundamentally provided that a phase short circuit is not first initiated via the microcontroller 108.

Instead, the output of the evaluation unit 110, in this case the voltage comparator, overwrites the PWM output signal of the microcontroller 108, so that a duty cycle of 100% of all low-side MOSFETs is set. This thus causes the phase short circuit as soon as an overvoltage has been detected by the comparator.

FIG. 3 shows a circuit arrangement 200 as a possible arrangement for carrying out the method presented here, by means of which a comparator can directly overwrite the PWM signal of a microcontroller in order to initiate a protective measure 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, which represents a hysteresis circuit 209 for setting a hysteresis, a transistor 210, a PWM output signal 212 of a microcontroller 214 and a Driver circuit 216, in this case a bridge driver. Between a first terminal 220 and a second terminal 222, typically a ground terminal GND, is a Zwischenkreisspan voltage 226 at. The capacitance 204 and the resistor 208 are optional measures.

The circuit arrangement 200 in FIG. 3 enables PWM operation by the microcontroller 214 as long as the voltage at the tap of the voltage divider 202 does not exceed a reference voltage. When exceeding the clamping voltage limit GND is applied to the output of the operational amplifier 206, whereby the transistor 210 blocks and thereby the PWM signal is set to "low" ge.

The low pass filter 205 may be provided to prevent false triggering. This can be due to the very small distance of the voltage limit for Operating voltage range occurrences. The hysteresis circuit 209 ensures that the phase short circuit is not canceled immediately after falling below the specified voltage limit again.

The interconnection of the comparator and the influence on the control of the circuit breaker, for example. The high-side switch and the low-side switch, are highly dependent on the selected control of the respective inverter. Therefore, there are various ways to initiate the hardware short-circuit hardware directly through a comparator. Furthermore, for example, there is the possibility to bypass the bridge driver and through the evaluation unit, for example. The comparator directly to influence the control terminal activation of the power switch.

It is conceivable in addition to the initiation of the phase short circuit to initiate by a hardware circuit as well as a de-energizing of the electric machine.

It should be noted that this measure alone might possibly have few advantages over prior art methods.

The presented method is particularly suitable for electrical machines, such as. Foreign-excited synchronous machine, which are set up for use in motor vehicle witnesses. In addition, an application in an asynchronous machine is conceivable.

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

The method and the arrangement can also be used as part of the boost recuperation system (BRS) in the electric machine, the so-called boost recuperation machine.

Claims

claims

A method of driving an electrical machine via an inverter comprising a plurality of switches (102, 104), the switches (102, 104) being driven by a driver circuit (106, 216) having an electrical size of the inverter an evaluation unit (110) is monitored to detect that a threshold value is exceeded, the evaluation unit (110) outputs an output signal (134) which carries information about the electrical variable, and wherein the output signal (134) of the evaluation unit (110) is instantaneous acting on the switches (102, 104) of the inverter, so that upon detection of an exceeding of the threshold value of this electrical quantity, a countermeasure is initiated.

2. The method of claim 1, wherein the electrical size of a DC voltage across the switches (102, 104) of the inverter is monitored.

3. The method of claim 1 or 2, wherein the output signal (134) of the evaluation unit (110) acts on the driver circuit (106, 216) of the switch of the order judge.

4. The method of claim 3, wherein the output signal (134) of the Auswer teeinheit (110) directly to an input signal (142) of the driver circuit (106, 216) acts.

5. The method of claim 3, wherein the output signal (134) of the Auswer teeinheit (110) directly to an output signal (134) of the driver circuit (106, 216) acts.

6. The method of claim 3, wherein the output signal (134) of the Auswer teeinheit (110) acts directly on the internal function of the driver circuit (106, 216).

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

8. The method according to any one of claims 1 to 7, wherein in the presence of exceeding the threshold value in addition by a hardware circuit, a de-energizing of the electric machine is initiated.

9. An arrangement for driving an electrical machine, wherein the arrangement (200) for performing a method according to one of claims 1 to 8 is addressed.

10. Arrangement according to claim 9, which additionally comprises a low-pass filter (205), with which to filter an input signal of the evaluation unit (110) which characterizes the electrical cal size.

11. Arrangement according to claim 9 or 10, which additionally comprises a hysteresis circuit (209).