DE102022201539A1 - Determination of a safe state of a power converter - Google Patents

Abstract

A power converter (105) for an electrical machine (110) comprises a plurality of half-bridges (140), each comprising a first and a second current valve (145, 150); each half-bridge (140) being assigned a device for current determination (155) for determining a current flowing through the terminal (135); and a control device (170) for controlling the flow control valves (145, 150). The first current valve (145) of a half-bridge (140) controls a current between a high potential (120) and a connection (135) of the machine (110) and the second current valve (150) controls a current between the connection (135) and a low potential (125). The control device (170) is set up to detect a defect in one of the flow control valves (145, 150) on the basis of flows through all connections (135); and preventing a condition in which both flow control valves (145, 150) of a half-bridge (140) are closed.

Description

The present invention relates to the protection of a power converter. In particular, the invention relates to the detection of a fault in the power converter and the selection of the associated safe state.

A power converter converts electrical energy from constant to alternating quantities or vice versa and can thus be used to control an electrical machine. In order to provide an alternating current, the power converter includes a half-bridge that includes an upper and a lower power valve. The upper flow valve is configured to connect a terminal of the electric machine to a high potential and the lower flow valve to connect the terminal to a low potential. The high potential can also be called plus potential and the low potential minus potential. A voltage is present between the potentials, which frequently represents an intermediate circuit voltage. The current valves of a half-bridge are activated alternately in order to provide the electrical machine with a predetermined voltage.

The electric machine can be used for a safety-critical application, for example in a drive train of a motor vehicle. In this case, the power converter can be designed for an electrical output which, in the event of a fault, can lead to a hazard to material or persons.

If a significant error occurs, the drive system, consisting of at least the electrical machine and the power converter, must assume a safe state. The usual safe states of an inverter are the inverter lock, in which all control signals of the current valves are switched off, and the active short circuit, in which the connections of the electrical machine are either all connected to the high potential or all to the low potential. If the error relates to a defect in one of the flow control valves, so that it cannot open or close, assuming one of the states mentioned can lead to a subsequent error with even greater potential damage. In particular, a current can be released through both flow control valves of a half bridge, which is also referred to as a bridge short circuit. Another component that is connected to the drive system, for example an energy store for providing the voltage, can also be damaged as a result.

An object on which the present invention is based is therefore the intelligent selection of the safe state of a power converter in the event of a fault. The invention solves this problem by means of the subject matter of the independent claims. Subclaims reflect preferred embodiments.

According to a first aspect of the present invention, a power converter for an electrical machine comprises a plurality of half bridges, each comprising an upper and a lower flow control valve; each half-bridge being assigned a device for current determination for determining a current flowing through the connection of the electrical machine; and a control device for controlling the flow control valves. In this case, the connection of the electrical machine is connected to the high potential via the upper current valve of a half-bridge and the low potential is connected to the same connection of the electrical machine via the lower current valve of the same half-bridge. The control device is set up to implement required controlled variables in the power converter. These controlled variables usually include phase currents of the electrical machine.

According to the invention, an asymmetrical current can be prevented from flowing in the power converter or in the electrical machine by selecting an unsuitable state. In particular, the current valves can be prevented from causing a short circuit between the potentials. The optimized safe state selection of the present invention relates to the detection of valve failures based on the current profiles of each individual phase. In addition, the power converter can monitor a controlled safe state, ie ensure that a controlled safe state is actually assumed.

In one embodiment, operation of the electrical machine on the power converter cannot be interrupted despite the defective power valve. The prevention can only relate to switching off the electrical machine.

In one embodiment, the electrical machine is disconnected from the intermediate circuit voltage due to the detected defect in one of the flow control valves. In this case, the current valves of all half-bridges can be controlled in such a way that a current from the high potential to the low potential dries up. The power converter can be brought into a safe state and the electrical machine can be switched off safely.

For the analysis of the current profile, the currents at the connections are considered over at least one period of the fundamental frequency. In normal operation, the power converter also regulates phase-shifted alternating currents in the electrical machine the same fundamental frequency. By considering the currents over a complete period, transient effects in particular can be taken into account, which can result in particular from an inductance of the electrical machine or a parasitic capacitance, for example. The effects of a reverse feed, in which the electrical machine delivers energy to the DC voltage side of the power converter, can also be taken into account.

The valve defect in the power converter or a defect in the electrical machine can be determined on the basis of the ratios of positive components, negative components and zero components of the currents of the machine. In particular, such a ratio can be formed for each phase current, from which it can be read whether one of the flow control valves has a defect or not.

A failure may include a flow control valve that will not open or close. A flow valve that cannot be opened can also be called low-impedance and a flow valve that cannot be closed can also be called high-impedance. The behavior of the flow control valve can be assessed with reference to its specification when open or when closed. In this way, a flow control valve that cannot be opened can be determined if its resistance does not rise above a predetermined value, regardless of its activation. Conversely, a flow control valve that cannot be closed can be determined if its resistance does not fall below a predetermined value, regardless of its activation. The predetermined values may depend on an embodiment or technology of the flow control valve. Exemplary technologies include FET, bipolar, or IGBT transistors. The specification can depend on a semiconductor technology of the flow control valve, for example whether the flow control valve is made on the basis of silicon, germanium, gallium nitride or silicon carbide.

A plurality of safe states are preferably predetermined, in which the electrical machine is separated from at least one of the potentials, so that no voltage is present. Depending on the specific defect, one of the safe states is activated. According to the invention, a safe state is selected that can be controlled despite the defect in the flow control valve or in which no consequential damage is to be feared.

In the safe state "active short circuit in the high side" all upper flow valves are closed and all lower flow valves are open. All connections of the electrical machine are connected to the high potential of the intermediate circuit. This safe state can be assumed when an upper flow valve of one of the half-bridges cannot be opened and/or a lower flow valve of one of the half-bridges cannot be closed. A flow control valve that cannot be opened and a flow control valve that cannot be closed can be assigned to different half bridges.

A state in which the current valves are controlled in such a way that the connections of the electrical machine are connected to the same potential is also referred to herein as a “supposedly safe state” if it is not ensured that no bridge short circuit is controlled as a result.

For another safe condition, all upper flow valves are open and all lower flow valves are closed. This condition can also be referred to as "active short circuit in the low side". This safe state can be assumed when an upper flow valve of one of the half-bridges cannot be closed and/or a lower flow valve of one of the half-bridges cannot be opened. Here, too, the flow control valves can be assigned to different half bridges.

When an active short circuit is activated, the electrical machine cannot be completely short-circuited due to a current valve that cannot be closed.

In the third case of safe conditions, all of the upper and lower flow valves may be open. This condition can also be called inverter lock. The third safe state can be adopted in particular when any number of flow control valves cannot be closed.

If one of the current valves in one of the half-bridges cannot be opened, the inverter lock can still be activated. The electrical machine can still not draw any energy from the intermediate circuit and a short circuit through the power converter can be prevented.

It should be noted that in the event of certain defects in more than one flow control valve, one of the safe states can still be assumed. In one embodiment of the present invention, the power converter can be operated despite a defect in one of its flow control valves as long as a safe state can still be assumed. In a further preferred embodiment, operation can be permitted as long as a single additional defect in a flow control valve that has not yet been determined to be defective still allows at least one of the safe states to be assumed. In this embodiment, the safe state is preferred already initiated if a flow control valve could fail in such a way that it would no longer be possible to control a safe state.

According to a second aspect of the present invention, a drive device includes an electrical machine and a power converter described herein. The electric machine can be used in particular in a drive train, for example a motor vehicle. According to a further aspect of the present invention, a motor vehicle includes a drive train with an electric machine which is controlled by means of a power converter described herein. The power converter can be used with or without an electric machine in any context, for example in a power supply system, in a battery charging system, in a battery storage system or in a converter. The power converter can be used stationary or on board a ship, an airplane, a rail vehicle or a land vehicle.

According to yet another aspect, a vehicle includes a drive device as described herein. The vehicle can in particular include a motorcycle, a passenger car, a truck or a bus.

According to yet another aspect of the present invention comprises a method for controlling a power converter for an electrical machine, wherein the power converter comprises a plurality of half-bridges, each comprising an upper and a lower flow valve; wherein the upper current valve of a half-bridge controls a current between a high potential and a terminal of the machine and the second current valve controls a current between the terminal and a low potential; each half-bridge being assigned a device for current determination for determining a current flowing through the connection; steps of determining currents through all ports; detecting a failure of one of the flow valves based on the currents; and preventing a condition where both flow valves of a half-bridge are closed.

The method can be carried out in particular by means of a control device of a power converter described herein. For this purpose, the control device can include a programmable microcomputer or microcontroller, and the method can be in the form of a computer program product with program code means. The computer program product can also be used in other ways to implement the method, for example to configure a logic module (ASIC). The computer program product can also be stored on a computer-readable data carrier. Features or advantages of the method can be transferred to the control device or the power converter or vice versa.

The method can determine the location of a defect, ie assign a malfunction to one of the half-bridges and possibly also to an upper or lower flow control valve. The method can also determine the type of defect that is present, that is to say whether the flow control valve has a low resistance or a high resistance. A high-impedance flow valve cannot be closed and a low-impedance valve cannot be opened. In this case, threshold values for a current flowing through the flow control valve can be predetermined in each case. A high-impedance valve can thus be determined if a current of a predetermined magnitude cannot be reached, or a low-impedance valve if the flowing current cannot be reduced below a further predetermined magnitude.

• 1 einen Stromrichter mit einer elektrischen Maschine; und
• 2 ein Ablaufdiagramm eines Verfahrens

darstellt.The invention will now be described in more detail with reference to the attached figures, in which:

• 1 a power converter with an electrical machine; and
• 2 a flowchart of a method

represents.

1 shows a system 100 that includes a power converter 105 and an electrical machine 110 . Electric machine 110 is preferably set up for use in a drive train, for example of a motor vehicle. In one specific embodiment, the electrical machine 110 includes a permanently excited synchronous machine PSM; in other specific embodiments, for example, a three-phase asynchronous machine ASM or a reluctance machine are also possible.

The power converter 105 is operated with a DC voltage 115 which is present between a high potential 120 and a low potential 125 . The voltage 115 can also be called the intermediate circuit voltage and can be provided on the basis of an electrical energy store, in particular a high-voltage battery. An intermediate circuit capacitor 130 can be connected between the potentials 120 and 125 .

The electric machine 110 generally includes N phases, as exemplified in FIG 1 three electrical phases are shown, which are connected together in a triangular shape by way of example. A different connection, in particular in a star configuration, is also possible. Each phase of electrical machine 110 is connected to a connection 135 of power converter 105 .

For each of the connections 135 , the power converter 105 includes a half-bridge 140 which includes an upper flow valve 145 and a lower flow valve 150 . The upper flow valve 145 connects the high potential 120 of the converter 105 to the associated connection 135 of the electrical machine 110. The associated connection 135 of the electrical machine 110 is connected to the low potential 125 of the converter 105 via the lower flow valve 150 of the converter 105. In addition, each half-bridge 140 or each connection 135 is preferably assigned a device for current determination 155 in order to determine the current flowing through the connection 135 . The device for current determination 155 can work, for example, on the basis of a voltage drop across a resistance, an induction in a current-carrying line or a magnetic field caused by the current. In a further embodiment, the device can also determine a flowing current using a mathematical model, for example on the basis of voltages at the phases of the electrical machine 110.

A control device 170 is set up to control the flow control valves 145, 150 of one or more half-bridges 140 in order to regulate the electrical machine 110. The activation can take place depending on a request for a speed, a torque or a converted power of the electrical machine 110 . Optionally, a return (recuperation) of electrical energy from the electrical machine 110 into the providing energy store can be supported.

To control the electrical machine 110 , the power converter 105 provides electrical voltages or currents that are phase-shifted with respect to one another at the connections 135 . In order to set a predetermined voltage or a predetermined current through a connection 135, the control device 170 controls the flow control valves 145, 150 of the associated half-bridge 140, preferably in alternation. A frequency with which the flow control valves 145, 150 are controlled is preferably at least one order of magnitude higher than a basic frequency that a current or voltage profile at the connection 135 has. The fundamental frequency depends on a speed of the electrical machine 110 .

It is proposed that control device 170 be set up to determine, on the basis of the currents through terminals 135 of electrical machine 110 determined by means of current determination devices 155, whether one of flow control valves 145, 150 of half-bridges 140 is defective. There can be a defect if a flow control valve 145, 150 can no longer be fully controlled. In the event of a defect, the flow control valve 145, 150 can no longer be opened or closed.

The control device 170 is preferably set up to determine the type of defect, which half-bridge 140 is affected by the defect and/or whether the defect relates to an upper flow valve 145 or a lower flow valve 150 . Furthermore, the control device 170 is preferably set up to prevent a state in which both flow control valves 145, 150 of a half-bridge 140 are closed at the same time. In particular, a state in which energy is exchanged between electrical machine 110 and the energy store, which provides voltage 115, can be selected from a plurality of predetermined safe states such that it can be assumed without causing a short circuit through one of half bridges 140 include. In particular, the predetermined safe states may include an active short circuit to high potential 120, an active short circuit to low potential 125, or an inverter lockout. A supposedly safe state, which actually cannot be assumed due to a defect in one of the flow control valves 145, 150 without creating a short circuit, can be prevented.

2 shows a flow chart of a method 200 for controlling a power converter 105. The method 200 can be carried out in particular by means of a control device 170. The description is given using the example of a three-phase electrical machine.

In a step 205 a current through a connection 135 of the electrical machine 110 can be detected. This step is preferably carried out for each connection 135 provided, with the acquisition times for the currents being as close together as possible.

Each stream can be determined whether it exceeds a positive threshold so that it can be counted as a positive component, or falls below a negative threshold so that it can be counted as a negative component. Furthermore, it can be determined whether the current lies between two other threshold values which have different signs and are closer to zero, so that it can be evaluated as a zero component. The threshold values are preferably selected to be the same for all currents in the electrical machine.

Then ratios between the current components determined for the individual phases can be calculated. Should an asymmetry be determined that is greater than a predetermined Value is, it can be concluded that one of the flow control valves 145, 150 is defective. This determination can be made at any point in time and does not require consideration of flows over a predetermined period of time. This determination can therefore also be called “Fast Path”.

Furthermore, it can be determined whether one of the determined currents is below a lower threshold value, while at the same time the other two currents are above an upper threshold value. It can be determined in a corresponding manner. whether one of the determined currents is above an upper threshold while the other two currents are below a lower threshold. The magnitudes of the threshold values are usually different from one another in both tests. Three permutations are possible for each of the tests, each comparing one of the specified streams to a different threshold than the other two streams. A total of six tests can be carried out in this way. If one of the tests is answered positively, then a fault in one of the flow control valves 145, 150 can be determined. The error can be determined in the half-bridge 140 controlling the current, which is compared to a different threshold than the other two currents. The error can be precisely localized, in particular with regard to the half-bridge 140 in which it occurred and with regard to the flow control valve 145, 150.

As a reaction to such a fault, an active short circuit can be brought about by the affected half-bridge 140 being controlled in such a way that the current provided reverses its sign. Such a defect can be detected immediately, regardless of a period of the fundamental frequency of the currents.

The currents can be viewed in a step 210 over a period of a fundamental frequency. The currents through terminals 135 are typically phase shifted AC currents having the same fundamental frequency. Steps 205 may be repeated for a predetermined duration depending on the fundamental frequency being controlled.

In a step 215, it may be determined whether the AC currents have predetermined proportions of currents that are positive, negative, or zero. In a typical sequence, positive and negative currents alternate at a terminal 135 with no current flowing therebetween for a predetermined period of time.

If only a positive current flows through a connection 135 during a period of the fundamental frequency, then a defect in one of the flow control valves 145, 150 can be inferred. The situation is similar if only a negative current flows during the period. The trend may also take an unintended form, such as when the current flowing through terminal 135 is positively or negatively limited. In this case, the sinusoidal shape of the current waveform is disturbed and contains an increased proportion of direct current.

In a step 220, a defect in one of the flow control valves 145 can be determined on the basis of the determined ratios of the flows. The type of defect can be determined, i.e. whether a flow control valve 145 cannot be opened or closed due to its activation, whether the defect relates to an upper flow control valve 145 or a lower flow control valve 150 and/or in which of the half-bridges 140 the defective flow control valve is located 145, 150 lies.

In a first example of a defect, one of the upper flow control valves 145 has low resistance, ie it cannot be opened. This can be determined when currents at one port 135 associated with the failed upper flow valve 145 are only positive and the other two are only negative over a period of the fundamental frequency. In this case, an amount of the positive current is usually greater than an amount of one of the negative currents. In a second example of a defect, the pulse pattern freezes at the flow control valves 145, 150, so that certain phase currents flow invariably. This can be determined by observing the phase currents over a phase - or the time that corresponds to a phase. For example, the currents can each be integrated over time. If the integral of a phase current over time is not exactly zero, the defect can be determined. Even if the integrated currents do not match each other precisely enough, a defect can be inferred.

In a step 225 it can be determined which of several predetermined safe states can still be assumed despite the defective flow control valve 145, 150. In a first safe state, all of the upper flow valves 145 are closed and all of the lower flow valves 150 are open. Conversely, in a second safe state, all of the upper flow valves 145 are open and all of the lower flow valves 150 are closed. In a third safe state, all of the upper flow valves 145 and all of the lower flow valves 150 are open. A supposedly safe state, which cannot be assumed due to a defective flow control valve 145, 150, or in which the assumption would cause a short circuit through one of the half-bridges 140, can be prevented.

In a step 230 it can be determined whether a safe state should be assumed. The assumption of the safe state can depend on an external signal or be triggered based on internal determinations.

If the safe state is to be assumed, then in a step 235 a safe state that was not determined as an allegedly safe state can be assumed. Current valves 145, 150 of the half-bridges 140 can be controlled according to the specific safe state. When driving, an opening of a flow control valve 145, 150 that cannot be closed or a closing of a flow control valve 145, 150 that cannot be opened can be omitted.

Reference List

100

system

105

power converter

110

electric machine

115

intermediate circuit voltage

120

high potential

125

low potential

130

intermediate circuit capacitor

135

Electrical machine connection, phase connection

140

half bridge

145

upper flow valve (to the high potential / high side)

150

lower flow valve (to the low potential / low side)

155

Device for current determination

170

control device

200

Proceedings

205

Capture current through connector

210

view over a period

215

create a power balance

220

Determine the defect in a flow control valve and its location

225

Determine safe state, only block supposedly safe state

230

Determining whether to enter a safe state

235

control safe state

Claims (13)

A power converter (105) for an electrical machine (110), the power converter (105) comprising: a plurality of half-bridges (140) each comprising an upper (145) and a lower flow valve (150); wherein the upper flow valve (145) of a half-bridge (140) carries a current between a high potential (120) and a terminal (135) of the machine (110) and the lower flow valve (150) generates a current between the terminal (135) of the electrical machine (110) and a low potential (125); each half-bridge (140) being assigned a device for current determination (155) for determining a current flowing through the terminal (135); and a control device (170) for controlling the flow control valves (145, 150); wherein the control device (170) is set up to detect a defect in one of the flow control valves (145, 150) on the basis of flows through all ports (135); and preventing a condition in which both flow control valves (145, 150) of a half-bridge (140) are closed. Power converter (105) according to claim 1 , wherein the current valves (145, 150) of all half-bridges (140) are controlled in such a way that a current from the high potential (120) to the low potential (125) dries up. Power converter (105) according to claim 1 or 2 wherein the currents are considered (210, 215) over at least one period of a fundamental frequency. A power converter (105) according to any one of the preceding claims, wherein the defect is determined (205) on the basis of ratios of positive components, negative components and zero components of the currents. Power converter (105) according to one of the preceding claims, wherein a defect comprises a flow control valve (145, 150) which cannot be opened or which cannot be closed. Power converter (105) according to one of the preceding claims, wherein a plurality of safe states are predetermined in which the electrical machine (110) is separated from at least one of the potentials (120, 125); and depending on the specific defect, one of the safe states is activated. A power converter (105) according to any one of the preceding claims, wherein in a first safe condition all upper flow valves (145) are closed and all lower flow valves (150) are open. Power converter (105) according to any one of the preceding claims, wherein in a second safe State or all upper flow valves (145) open and all lower flow valves (150) are closed. A power converter (105) according to any one of the preceding claims, wherein in a third safe state all of the upper and lower flow valves (145, 150) are open. Drive device (100), comprising an electric machine (110) and a power converter (105) according to one of the preceding claims. Vehicle, comprising a drive device (100). claim 10 . A method (200) for controlling a power converter (105) for an electrical machine (110), the power converter (105) comprising: a plurality of half-bridges (140), each comprising an upper and a lower flow valve (145, 150); wherein the upper flow valve (145) of a half-bridge (140) carries a current between a high potential (120) and a terminal (135) of the machine (110) and the lower flow valve (150) carries a current between the terminal (135) and a low potential (125) controls; each half-bridge (140) being assigned a device for current determination (155) for determining a current flowing through the terminal (135); the method (200) comprising the steps of: (205) determining currents through all ports (135); (220) detecting a failure of one of the flow control valves (145, 150) based on the flows; and preventing (225) a condition in which both flow control valves (145, 150) of a half-bridge (140) are closed. Method (200) according to claim 12 , wherein it is determined (205) which flow control valve (145, 150) is defective or whether the fault includes a non-opening or a non-closing flow control valve (145, 150).

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