Method and safety shutdown arrangement for operating a generator unit

Abstract

Method for operating a generator unit which has an electrical machine with a rotor winding (16) and a stator winding (12) and a rectifier (14) connected thereto, via which the electrical machine can be connected to an on-board network (10), wherein, when an excitation voltage is applied to the rotor winding (16) to generate an excitation current through the rotor winding (16) and thus provide an output voltage at the rectifier (14), a level of the output voltage is determined, wherein the rotor winding (16) is de-energized via a first shutdown path when the output voltage reaches or exceeds a predetermined first safety threshold for more than a predetermined first safety time, and wherein a regulator output to which the rotor winding (16) is connected is short-circuited via a second shutdown path when the output voltage reaches or exceeds a predetermined second safety threshold for more than a predetermined second safety time.

Description

[0001] The present invention relates to a method for operating a generator unit, a safety shutdown arrangement, a voltage regulator with such a safety shutdown arrangement, an arrangement with a generator unit and such a voltage regulator and an on-board power supply system, in particular a vehicle on-board power supply system, with such an arrangement. Background of the invention

[0002] Electrical machines, especially generators, can be used to convert mechanical energy into electrical energy in motor vehicles. Claw-pole generators, which are usually equipped with electrical excitation, are typically used for this purpose. Since such generators generate three-phase current, usually three-phase, rectification is required for standard automotive DC electrical systems. Rectifiers based on semiconductor diodes or semiconductor switches can be used for this purpose.

[0003] To regulate the vehicle electrical system voltage, an excitation current can be controlled or regulated through the generator's rotor winding. This means that the manipulated variable for voltage regulation in automotive generators is the excitation current, i.e., the current that flows through the generator's rotor winding and generates the excitation field. This is typically implemented using a switching unit of a voltage regulator (field regulator), which can, for example, comprise at least one switching transistor. The switching unit can switch the excitation current on and off. The excitation current or an excitation current-pulse ratio can be changed such that the generator's output voltage is adjusted to the desired value.

[0004] In the event of a fault, e.g., a defective voltage regulator, the generator voltage and thus the vehicle electrical system voltage can become too high, which can cause undesirable malfunctions of components and / or electrical devices in the vehicle electrical system. For example, some components in the vehicle electrical system may limit their functionality or shut down completely for their own protection. This can even cause damage to components and / or electrical devices in the vehicle electrical system.

[0005] DE 31 44 043 A1 discloses a method for de-energizing a generator's rotor winding via a shutdown path. DE 15 38 316 A also discloses safety measures for generators, such as short-circuiting the rotor winding via a second shutdown path. Disclosure of the invention

[0006] According to the invention, a method for operating a generator unit, a safety shutdown arrangement, a voltage regulator with such a safety shutdown arrangement, an arrangement with a generator unit and such a voltage regulator, and an on-board electrical system, in particular a vehicle on-board electrical system with such an arrangement, are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0007] The invention concerns the prevention or reduction of overvoltage events in on-board electrical systems. To this end, it proposes, in the event of an excessively high output voltage at the rectifier, firstly, de-energizing the rotor winding via a first shutdown path, in particular, rapidly de-energizing it. Secondly, short-circuiting a regulator output to which the rotor winding is connected via a second shutdown path—thereby also short-circuiting the rotor winding and de-energizing it. This provides two different, particularly redundant shutdown paths or shutdown precautions, which can be implemented, in particular, as independent safety shutdown devices and used together as a safety shutdown arrangement, but in principle also independently—in a voltage regulator or generator unit.For the basic operation of the generator unit - and thus the application of an excitation voltage to the rotor winding of the electrical machine - the use of a (conventional) voltage regulator is particularly suitable.

[0008] For de-energization and short-circuiting, the use of a dedicated safety shutdown device is then considered. This device can be integrated into the voltage regulator, but can particularly be connected as an add-on to a conventional voltage regulator or to the actual control circuit device there. This can, in particular, involve two essentially separate safety shutdown devices, which, however, can be used particularly advantageously together or combined in a common safety shutdown arrangement.

[0009] De-excitation is achieved in particular by conducting the current in the excitation winding through a diode, e.g. a Zener diode or one or more conventional diodes. The one or more diodes are also connected to the freewheeling path of the excitation winding for de-excitation. For this purpose, the diode can be connected in parallel to a switch in the current path of the excitation winding, which is closed or conductive during normal operation. The diode is then inoperative. If the output voltage is too high - this can be determined using a voltage measuring device, for example - this switch is then switched to non-conductive or opened. The current then flows through the diode, where it is dissipated more quickly (or converted into heat).

[0010] Short-circuiting the excitation terminal means, in particular, that the voltage applied to it (e.g., vehicle electrical system or battery voltage) is removed from the excitation winding. To do this, as mentioned, the excitation output of the voltage regulator used, via which the excitation voltage is normally applied to the excitation winding, is connected to ground or short-circuited. If the output voltage is too high - this can be determined, for example, using a voltage measuring device - a switch connected in parallel to the rotor winding can be switched on or closed. Depending on the configuration, this will also mean short-circuiting the excitation winding. This short-circuiting usually causes irreversible damage to the voltage regulator, as it is not designed for such current strength; it is thus sacrificed, so to speak.Preferably, however, instead of destroying the voltage regulator, an additional safety element, such as a fuse, located in the voltage regulator's current path is destroyed. In any case, the short-circuiting should ultimately lead to the current being cut off from the excitation winding.

[0011] Both de-energization and short-circuiting occur when the output voltage reaches or exceeds a respective predetermined safety threshold for more than a predetermined, respective safety time. A first safety threshold and a first safety time can be used for de-energization, and a second safety threshold and a second safety time can be used for de-energizing. These safety times can both be the same or different. The same applies to the safety thresholds.

[0012] The two shutdown paths are preferably activated one after the other, i.e., a cascaded shutdown is provided. For this purpose, the second safety time can be selected to be longer than the first safety time. Alternatively or additionally, it is preferred if the second safety threshold is also selected to be higher than the first safety threshold.

[0013] In particular, the first safety time can also be zero, i.e. de-excitation is triggered immediately in the event of an overvoltage, but can also be, for example, up to 100 ms. The second safety time is preferably less than 1 s, e.g. between 100 ms and 500 ms. The safety times can be specified in particular as a function of the dielectric strength of the on-board power supply consumers, i.e. how long they can withstand which overvoltages. The first safety threshold is preferably specified as a function of a nominal on-board power supply voltage and can, for example, be from approximately 110% to approximately 150% of the nominal on-board power supply voltage. For a nominal voltage of 12 V, the first safety threshold can, for example, be between 15.0 V and 16.7 V. The second safety threshold is then, for example, between 0.3 V and 1.0 V higher than the first safety threshold. Both can be specified in particular as a function of the dielectric strength of the on-board power supply consumers, i.e.i.e. how long they can withstand which surges.

[0014] A particular advantage of this cascaded tripping is that the de-energization, which is performed first, is reversible. Only the de-energization is irreversible due to the resulting damage to the voltage regulator or a fuse. This ensures a high level of safety integrity for multiple faults, e.g., ASIL C or ASIL D. The cascading capability can be further enhanced with additional switches and additional redundancies.

[0015] Preferably, the two switches or circuit breakers for de-energization or de-energizing, but especially also for the necessary controls or control circuits, are equipped with different technologies and / or component manufacturers due to possible "common cause" faults. Although a (common) voltage measuring device is generally considered for both switches or shutdown paths, it is particularly preferable to use two different ones to increase redundancy.

[0016] The controls for both switches are advantageously designed to have a very low quiescent current when the generator is off (the generator is not rotating). For this purpose, the control for the de-energizing switch is designed as 'high active' and the control for the de-energizing switch is designed as 'low active'. To further protect the independently redundant circuit components against polarity reversal for greater safety integrity, a polarity reversal element, such as a diode, can be used. This element is connected between the positive input terminal and the at least one voltage measuring device.

[0017] In summary, this enables special protection of the on-board electrical system and its loads against overvoltage caused by a malfunction of the generator. The generator can be transferred to a defined state in which overvoltage is no longer possible. This allows the generator to be used in safety-relevant on-board electrical systems and to meet high safety integrity requirements through multiple redundant cascading. By varying the number of cascades, a modular system is created for different safety integrity requirements. Furthermore, a reduction in the quiescent current and the fulfillment of the generator function even in the event of external starting with more than 20 V are achieved.

[0018] Short-circuit protection of the internal control circuit and the independently redundant circuit components can be achieved using the aforementioned additional fuse element, such as a fuse. Reverse polarity protection of the independently redundant circuit components can be achieved using a diode, further increasing safety integrity. The invention offers the further advantage that safety shutdown functionality, particularly in the form of safety shutdown devices, can be retrofitted. Existing control circuit devices, e.g., in the form of ICs or ASICs, do not need to be modified. This enables the implementation of a modular safety system from which suitable products can be combined to meet specific safety requirements. In other words, the invention offers the advantage that safety shutdown can be provided individually in or for voltage regulators as needed.

[0019] Furthermore, the invention offers the advantage that, for example, a mass production of uniform safety shutdown devices can be carried out, which can then be added to voltage regulators as required.

[0020] Preferably, an on-board power supply or output voltage provided by the rectifier is applied to the rotor winding as the excitation voltage. Then, by monitoring the magnitude of the excitation voltage, the on-board power supply voltage can be monitored simultaneously. This embodiment is very easy to implement, since the excitation voltage usually corresponds to the on-board power supply voltage.

[0021] Preferably, the excitation or output voltage is also used to power the safety shutdown arrangement or devices. This eliminates the need for a separate power supply, which particularly improves robustness against disturbances in the on-board electrical system and reduces the risk of a short circuit between the supply potential (B+) and ground.

[0022] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0023] The invention is illustrated schematically in the drawings using exemplary embodiments and is described below with reference to the drawings. Short description of the drawings Fig. 1 shows a circuit diagram of an on-board electrical system with a safety shutdown arrangement with two safety shutdown devices. Embodiment of the invention

[0024] Fig.1 shows a circuit diagram of an on-board network 10, in particular of a (motor) vehicle, with a voltage source 11 and consumers or battery 1.

[0025] The voltage source 11 comprises an electric machine or a generator with a stator 12, a rectifier 14 connected downstream of the stator, a rotor with a rotor winding 16, which can in particular be driven by a vehicle engine, and a preferred embodiment of a voltage regulator 20 according to the invention (also referred to as a field regulator) for specifying an excitation current through the rotor winding 16 or for regulating a generator voltage. The voltage regulator 20 serves to regulate the generator voltage between the B+ terminals and ground to a desired value, e.g., approximately 14-15 V for a so-called 12 V vehicle electrical system with a nominal voltage of 12 V. The generator voltage is thus the rectified output voltage of the generator or the vehicle electrical system voltage.

[0026] The voltage regulator 20 comprises the actual control circuit 22, which can be implemented, for example, as an application-specific integrated circuit (ASIC), and a preferred embodiment of a safety shutdown arrangement 24 according to the invention, which comprises two safety shutdown devices 24.1 and 24.2 for two shutdown paths. The voltage regulator 20, the control circuit 22, and the safety shutdown arrangement 24 are each identified by circumferential dashed lines. The two safety shutdown devices are preferably separate in terms of circuitry and components, but can nevertheless be arranged, for example, on a common circuit carrier.

[0027] The control circuit device 22 has a switch 22c, e.g., a semiconductor switch such as a MOSFET, IGBT, or thyristor, by means of which the current flowing through the rotor winding 16 can be switched, and also a diode 22a for freewheeling the excitation current. The diode 22a can also be designed as a semiconductor switch. A communication connection 20b is also provided, for example, to specify a target voltage.

[0028] The voltage regulator 20 is connected to the rotor winding 16 via a first terminal 16a and a second terminal 16b. These terminals also represent output terminals of the safety shutdown device 24. It should be emphasized that the rotor winding is arranged on the rotor of the electrical machine and not within the voltage regulator 20.

[0029] The safety shutdown arrangement 24 has a positive potential terminal 24a, an excitation terminal 24b, and a negative potential terminal 24c, which are connected to corresponding terminals of the control circuit device 22 (or are to be connected if retrofitted). The positive potential terminal 24a is used for connection to B+, the negative potential terminal 24c is used for connection to ground, and the excitation terminal is used for connection to the excitation output (so-called DF) of the control circuit device in order to apply voltage to the excitation winding. These terminals are supplied to both safety shutdown devices 24.1 and 24.2 independently of each other.

[0030] During normal operation of the voltage regulator, switch 24.1d is closed. The first voltage measuring device 24.1a monitors or determines the output voltage at B+. If this increases, e.g., due to a load dump (load shedding) or a fault in the regulator, and the first safety threshold is exceeded, a first control circuit 24.1c turns switch 24.1d off or non-conductive. In normal operation, switch 22c of the control circuit 22 is also opened due to the overvoltage. Due to the inductance, the current continues to flow through the Zener diode 24.1e and the freewheeling diode 22a. Due to the Zener effect, the energy in the excitation circuit or the excitation winding 16 is dissipated more quickly. By quickly dissipating the excitation current, the overvoltage duration can be reduced in the event of a load dump. After the voltage has decayed, switch 24.1d is closed again, allowing the safe state to be reversibly activated and deactivated.The diode 24.1e could also optionally be designed not as a Zener diode, but with one or more diodes in order to reduce the error rate of the individual components.

[0031] In addition, an independent, second voltage measuring device 24.2a is provided, which can also determine the output voltage. If the associated second safety threshold is exceeded (e.g., if the voltage regulator is defective and the switch 22c does not open), a second control circuit 24.2c is controlled via a time delay element 24.2b, which allows a second safety time to elapse, and via which the second switch 24.2d can be closed or switched on. When the switch 24.2d is activated, the excitation input terminal 24b is conductively connected to ground. This causes a high current to flow through the control circuit device 22, which will generally lead to its damage or destruction. Alternatively, this can lead to the triggering of a fuse element 20a.In any case, the excitation winding 16 is subsequently de-energized, thus reaching a safe state (voltage at B+ below the second safety threshold). At the same time, the excitation winding is short-circuited. The current can then be dissipated via diode 24.1e, which is still present in the freewheeling path; or, if the circuit or shutdown path 24.1 had not functioned, via a normal short circuit.

[0032] As mentioned, it is possible to integrate a fuse element 20a, such as a fuse, into the B+ supply, which is triggered in the event of a short circuit. This fuse element has the advantage of preventing a potential overvoltage and even circuit destruction in the event of an internal short circuit in the regulator IC or in the independently redundant circuit components.

[0033] The first and second safety threshold values ​​are set in such a way that the first safety threshold is lower than the second safety threshold by a difference of, for example, 0.3 V to 1.0 V. The absolute value of the first safety threshold can be in the range from 15.0 V to 16.7 V. This has the advantage that a reversible state is assumed first and only when the first redundancy fails or becomes ineffective (switch 24.1d, for example due to a short circuit, i.e. if, for example, the first shutdown path 24.1 is not functioning and / or, for example, switch 22c is defective) does it transition to an irreversible state. This ensures a high level of safety integrity for multiple faults. The cascading can also be increased with additional switches and additional redundancies.

[0034] The two switches – these can each be power switches such as MOSFETs or IGBTs – and their control systems are preferably equipped with different technologies or component manufacturers due to possible common-cause faults. The control systems for the two switches are designed, for example, to have a very low quiescent current when the generator is off (the generator is not rotating). For this purpose, the control system for switch 24.2d is designed as "high active" and the control system for switch 24.1d as "low active."

[0035] In order to protect the independently redundant circuit components against polarity reversal for higher safety integrity, an additional polarity reversal element can be constructed using diode 24.3.

Claims

[1] Method for operating a generator unit which has an electrical machine with a rotor winding (16) and a stator winding (12) and a rectifier (14) connected thereto, via which the electrical machine can be connected to an on-board network (10), wherein, when an excitation voltage is applied to the rotor winding (16) to generate an excitation current through the rotor winding (16) and thus provide an output voltage at the rectifier (14), a level of the output voltage is determined, wherein the rotor winding (16) is de-energized via a first shutdown path when the output voltage reaches or exceeds a predetermined first safety threshold for more than a predetermined first safety time, and wherein a regulator output to which the rotor winding (16) is connected is short-circuited via a second shutdown path when the output voltage reaches or exceeds a predetermined second safety threshold for more than a predetermined second safety time. [2] The method of claim 1, wherein the second safety time is longer than the first safety time. [3] The method of claim 1 or 2, wherein the second security threshold is higher than the first security threshold. [4] Method according to one of the preceding claims, wherein the rotor winding (16) is de-energized, in particular rapidly energized, by making a switch (24.1c) non-conductive, which switch is connected in a freewheeling path of the rotor winding (16), in particular between the rotor winding (16) and ground or between the rotor winding (16) and the excitation terminal, and to which a diode (24.1d) is connected in parallel. [5] Method according to one of the preceding claims, wherein the excitation terminal is short-circuited by switching a switch (24.1d) between the excitation terminal and ground on, so that the rotor winding (16) is short-circuited. [6] Method according to one of the preceding claims, wherein the level of the output voltage for de-excitation is determined by means of a first voltage measuring device (24.1a), and wherein the level of the output voltage for short-circuiting is determined by means of a second voltage measuring device (24.2a) which is different from the first voltage measuring device (24.1a). [7] A method according to any one of the preceding claims, wherein output voltage is applied as the excitation voltage to the rotor winding (110). [8] Safety shutdown arrangement (24) for use in a voltage regulator (20) which is designed to operate a generator unit which has an electrical machine with a rotor winding (16) and a stator winding (12) and a rectifier (14) connected thereto, via which the electrical machine can be connected to an on-board network (10), wherein the safety shutdown arrangement (24) has two output terminals (16a, 16b) between which the rotor winding (16) is to be connected, and which has a positive (24a), a negative (24c) and an excitation input terminal (24b), wherein the safety shutdown arrangement (24) is configured to determine a voltage between the positive (24a) and negative input terminal (24c), and to carry out the de-excitation via the first shutdown path and the short-circuiting via the second shutdown path of a method according to one of the preceding claims. [9] Safety shutdown arrangement (24) according to claim 8, with at least one voltage measuring device (24.1a, 24.2a) for determining the voltage between the positive (24a) and negative input terminal (24c), and / or with a diode (24.3) between the positive input terminal (24a) and the at least one voltage measuring device (24.1a, 24.2a). [10] Voltage regulator (20) for operating a generator unit, which has an electrical machine with a rotor winding (16) and stator winding (12) and a rectifier (14) connected thereto, via which the electrical machine can be connected to an on-board network (10), with a safety shutdown arrangement (24) according to claim 8 or 9. [11] Voltage regulator (20) according to claim 10, comprising a fuse device (20a) at a positive potential terminal. [12] Arrangement with a generator unit which has an electrical machine with a rotor winding (16) and stator winding (12) and a rectifier (14) connected thereto, via which the electrical machine can be connected to an on-board network (10), and with a voltage regulator (20) according to claim 10 or 11. [13] On-board network (10) with a voltage source (11) and at least one consumer (1), wherein the voltage source (11) has an arrangement according to claim 12.

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