Patent ID: 12224690

EMBODIMENTS

FIG.1shows a circuit diagram of an on-board power system100, in particular of a (motor) vehicle, with an electric machine102with stator winding104and rotor winding106as well as a battery or an energy storage device108with a positive on-board power system connection B+ and a negative on-board power system connection B− (ground), which serve as positive (plus pole) and negative supply connection (minus pole), respectively. In addition, a DC link capacitor C is provided.

By way of example, this is a five-phase electrical machine102having five phases U, V, W, X and Y or corresponding phase windings. It will be understood that the invention may also be used with other electrical machines having a different number of phases, e.g., three or six, etc.

Furthermore, a drive device110is provided, which comprises a voltage regulator (or regulator)120, which is provided to apply an excitation current to the rotor winding106or to control the same. For this purpose, the rotor winding can be connected with its first terminal F+ and its second terminal F− to the regulator120. For this purpose, the regulator120has two switches (a high-side switch and a low-side switch), which are shown inFIG.2.

Furthermore, a power converter (or inverter)130is provided having one half-bridge per phase comprising two switches (one highside and one lowside switch), e.g. MOSFETs, IGBTs. These switches are designated TU_Hand TU_Lfor highside and lowside switches of phase U, respectively; the same applies to the switches of the other phases V, W, X and Y.

Furthermore, two drive circuits or gate drive circuits140and142are provided. Each of the two drive circuits140,142can drive six semiconductor switches, by way of example, and is for this purpose connected to one of the respective control or gate terminals (indicated by arrows). By way of example, the drive circuit140controls the two switches of the regulator120as well as the switches of the phases X and V. Correspondingly, the drive circuit142controls the switches of the phases U, V and W. The drive circuits140,142can each receive signals from a higher-level computing unit150, such as an MCU, or transmit signals thereto.

FIG.2shows a more detailed view of part of the drive device110fromFIG.1, in particular the regulator120. In particular, the high-side switch TF_Hand the low-side switch TF_Lare shown there, which are controlled via the control circuit140, illustrated here as an example by pulses.

The high-side switch TF_His arranged between the first terminal F+ of the rotor winding106and the positive supply terminal B+ of the drive device. The lowside switch TF_Lis arranged between the first terminal F+ of the rotor winding and the negative supply terminal B− of the drive device. Furthermore, a de-energizing switch S1is arranged between the second terminal F− of the rotor winding and the negative supply terminal B− of the drive device.

In normal operation, by closing (switching to conducting state) the lowside switch TF_Land opening (switching to non-conducting state) the de-energizing switch S1, a de-energizing circuit can be formed via which the rotor winding106can be de-energized. Such a de-excitation circuit is designated K and includes a de-excitation resistor R connected in parallel with the de-excitation switch S1.

The drive device110is further arranged to assume or enter a safe state in the presence of at least one fault by disconnecting and/or de-energizing the rotor winding106from the positive supply terminal B+. For this purpose, the highside switch TF_Hcan be opened and/or the de-energization switch S1can be opened.

It is provided that, in the presence of an error, the control circuit144for the de-energizing switch is controlled in order to open the de-energizing switch. For this purpose, a series of error signals (present, for example, four, F1to F4) can be evaluated. Depending on the type of error signal (e.g., “1” or “0” indicates error), a suitable logic operation is provided.

For example, an error signal, e.g. F1, F2, is assigned to each of the two control circuits140,142(i.e. the respective control circuit outputs the respective error signal if there is an error there). Another error signal, e.g., F3, may be an external error signal, e.g., coming from outside (e.g., from a unit155, at least outside the drive circuits140,142, but not from outside the entire power converter), and one, e.g., F4, may be a general permission signal, e.g., coming from the MCU150.

In addition, a measuring or shunt resistor Rshis provided in series with the parallel circuit comprising the de-energizing switch S1and the de-energizing resistor, and a current measuring device152is associated with this resistor for measuring the excitation current.

With reference toFIG.1, the control circuits140,142are each supplied with a safety signal SF1and SF2, respectively, on the basis of which it can be judged whether everything is in order and the control circuits are to be operated regularly.

As explained, various faults or problems can occur in such a drive device which cannot be rectified or cannot be rectified sufficiently using conventional means, i.e. a safe state cannot be entered. Based on the drive circuit110shown inFIGS.1and2, various embodiments of the invention will now be explained with reference to the following figures.

FIG.3shows an embodiment of a drive device210according to the present disclosure. The drive device210corresponds in principle to the drive device110according toFIGS.1and2, so that in this respect reference can also be made to the description there. The reference signs are each increased by 100. Differences will be discussed in particular below. A power converter (or inverter) is not explicitly shown, but this can be designed in accordance with the power converter130.

In particular, the drive device210also comprises a regulator220, which is provided for applying an exciter current to the rotor winding106or controlling the same. The regulator220is shown enlarged inFIG.4a, in particular with regard to the interconnection of the individual switching elements.

In addition toFIG.1, an additional highside switch Q1is connected in series with the highside switch TF_H, so that the highside switch TF_Hhas a redundant design. In the absence of a fault or defect, the additional highside switch Q1is closed or conductive. If a safe state is to be entered, but the TF_Hhighside switch was defective and could not be opened, the safe state can be entered via the additional Q1highside switch. A separate control circuit243is provided for the additional highside switch Q1.

Furthermore, an additional de-energizing switch S2is connected in series with the de-energizing switch S1, so that the de-energizing switch S1is designed redundantly. In the absence of a fault or defect, the additional de-energizing switch S2—like the regular de-energizing switch S1—is closed or conductive. If a safe state is to be entered or the rotor winding is to be de-energized, but one of the de-energizing switches is defective and cannot be opened, the safe state can be entered via the other de-energizing switch. Two control circuits244and245are provided for controlling the de-energizing switches S1and S2.

Furthermore, two diodes each, D21and D22, or D31and D32, respectively, e.g. TVS or Zener diodes, are connected in parallel to the de-energizing switch S1and to the additional de-energizing switch S2. As can be seen, the diodes are located in the de-energizing circuit K. Due to the diodes, the de-energizing resistor shown inFIG.2is not (no longer) necessary.

Furthermore, two diodes, DF1and DF2, are connected in parallel to the TF_Llowside switch. This also provides a certain redundancy for the TF_Llowside switch and increases its robustness. If the TF_Llowside switch should be defective, the de-energization process is ensured by these diodes.

The regulator220also has two parallel measuring resistors Rsh1and Rsh2(measuring points) connected between the second terminal F− of the rotor winding and the negative supply terminal B− of the drive device. Thus, the parallel connection of the measuring resistors Rsh1and Rsh2is connected in series with the de-energizing switches S1and S2.

In the regulator220shown inFIG.4a, the measuring resistors Rsh1and Rsh2are also each connected in such a way that they are located in the de-energizing circuit K. Thus, the parallel connection of the measuring resistors Rsh1and Rsh2is also connected in series with the diodes D21, D22, D31and D32. In this way, the de-excitation runs faster.

FIG.4bshows a regulator320in a further embodiment. There, the parallel connection of the two measuring resistors Rsh1and Rsh2is also connected between the second terminal F− of the rotor winding and the negative supply terminal B− of the drive device. However, the measuring resistors Rsh1and Rsh2are not connected in the de-energizing circuit K, so they are not connected in series with the diodes D21, D22, D31and D32. It should be noted, however, that in the case of the regulator320, providing only the measuring resistor Rsh1would also be sufficient, since there is no series connection with the diodes D21, D22, D31, D32here.

Furthermore, the drive device210comprises two current measuring devices252and253, each of which is arranged to measure a current in the excitation winding106via a respective one of the measuring resistors Rsh1and Rsh; the overcurrent measuring devices254,255can then cause the safe state to be entered, at least when the measured current exceeds a predetermined threshold value. Although this is shown inFIG.3only for the regulator220, it is intended to apply mutatis mutandis to the regulator320. As already mentioned, in the case of the regulator320also only one measuring resistor—and thus also only one current measuring device252—is sufficient. Thus, if a circuit with only one measuring resistor or one current measuring device is to be realized, the regulating circuit device320is recommended.

Further, the drive device210comprises a plurality of overvoltage measuring devices260,261,262, each of which is arranged to measure a voltage and to cause the safe state to be entered at least when the measured voltage exceeds a predetermined threshold.

The overvoltage measuring device260is adapted to measure a voltage between the positive supply terminal B+ and the negative supply terminal B− of the driving circuit. The overvoltage measuring device261is adapted to measure a voltage in the driving circuit240, and an overvoltage measuring device262is adapted to measure a voltage in the driving circuit242. In particular, the voltage in the drive circuits240,242is also the voltage between the positive supply terminal B+ and the negative supply terminal B−.

Three diodes D1, D2and D3, e.g. TVS diodes, are connected in series and are provided as an example between the positive supply terminal B+ and the negative supply terminal B− of the drive device. There can also be more than three. These diodes can absorb excess energy that needs to be dissipated, if required; in particular, they serve as a voltage limiting circuit or overvoltage protection device. The functionality of these diodes can be detected or monitored, for example, by a monitoring device270.

FIG.3also shows various error signals which, in addition to those already known fromFIGS.1and2, also include other error signals.

Safety signal SF1: This is the output of the first safety interrogation circuit501(seeFIG.5). If all input signals of the safety interrogation circuit are “1” (logical value), this means that there is no fault in the drive device and the MCU has checked the other conditions and the programmed logic and gives permission to operate the drive device.

Safety signal SF2: This is the output of the second safety interrogation circuit502(seeFIG.5). If all input signals of the safety interrogation circuit are “1” (logical value), this means that there is no fault in the drive device and the MCU has checked the other conditions and the programmed logic and gives permission to operate the drive device.

Fault signal F1: When a fault such as an overvoltage (FOV, can be detected by the overvoltage measuring device262), an overcurrent, an internal fault, etc. is detected in the drive circuit242(OR circuit), this logic level becomes “0”, otherwise it is “1”.

Fault signal F2: When a fault such as an overvoltage (FOV, can be detected by the overvoltage measuring device261), an overcurrent, an internal fault, etc. is detected in the drive circuit240(OR circuit), this logic level becomes “0”, otherwise it is “1”.

Fault signal FOC1(overcurrent in the excitation winding): The current through Rsh1is sent (from the current measuring device252) to a comparator (overcurrent measuring device254) and compared with the desired setting. If the current exceeds the set threshold, the protection output becomes “0”, otherwise it is “1”.

Error signal FOC2(overcurrent in the excitation winding): The current through Rsh2is sent (from the current measuring device253) to a comparator (overcurrent measuring device255) and compared with the desired setting. If the current exceeds the set threshold, the protection output becomes “0”, otherwise it is “1”.

Error signal F4(general permission signal): Signal from the MCU; e.g. if all control logics programmed in the MCU are fulfilled, the signal is “1”, otherwise “0”.

Error signal F5: The MCU gives the additional highside switch Q1permission to close, so that the excitation circuit becomes ready for operation.

Signal IF1: Value of the measured excitation current at the measuring resistor Rsh1determined by the current measuring device252.

Signal IF2: Value of the measured excitation current at the measuring resistor Rsh2determined by the current measuring device253.

So-called SPI and gate signals GS, for example, can be exchanged between the drive devices240,242and the MCU250: The monitoring signal and the setting are transmitted and received via SPI. The generated PWM signals (to drive the switches) are sent to the drive circuits.

Safety state signal SF3of the MCU: There may be special conditions within the logic programmed in the MCU; if these conditions are met, the signal is “1”, otherwise it is “0”.

Error signal FOV1(overvoltage): Output of the overvoltage measuring device260, which monitors the voltage of the DC link. If the voltage exceeds a certain threshold and drops at a certain time, this signal changes from “1” to “0”.

Supply signal SF4: If all power supplies for SPI and digital I/O of the drive circuits and the MCU are available, this signal is “1”, otherwise “0”.

FIG.5also shows the two safety interrogation circuits501,502for the aggregation (AND circuit) of fault signals to generate the safety signals SF1and SF2. The safety interrogation circuits501,502are independently arranged to cause the safe state to be entered, in particular by de-energizing the rotor winding. If, for example, one of the error signals SF1, SF2at the input does not correspond to the desired or regular value (e.g. has the logical value “0” instead of “1”), the safety signal concerned can change from “1” to “0”, for example. These safety interrogation circuits501,502may in particular be part of the drive device210according toFIG.3.

An exemplary operation of the electric machine using the drive device210will now be explained below.

A normal state means that there is no error and the drive device can control the electric machine regularly. In this mode the following actions are performed: All switches of the power converter are triggered, for example, by a PWM signal from the MCU (or another type of modulation signal generated by the MCU). To operate the electrical machine, the excitation must be on, so switches Q1, S1and S2are closed (conducting). Switches TF_Hand TF_Lare controlled by the MCU via drive circuit240. The excitation current is controlled.

When one of the signals F1, F2, SF3, SF4, FOC1, FOC2, FOV1, FOV2becomes “0”, one or both of the safety signals SF1or SF2also becomes “0”. Then the safe state is activated or initiated and the power converter enters the safe state, which means that all lowside switches, both of the power converter and the regulator, are closed (conductive state) and all highside switches are opened (non-conductive state).

The mechanism is activated by the safety signals SF1(for the drive circuit240) and SF2(for the drive circuit242); a suitable input terminal may be provided on the relevant drive circuit for this purpose.

The de-energizing process starts and continues until the energy stored in the rotor winding (excitation coil) reaches zero. The switches Q1, S1and S2are open. The de-excitation current (a circular current) flows through the switch TF_Land the antiparallel diodes DF1and DF2, then through the excitation coil and finally through the TVS diodes. The circular current is represented by a dashed line inFIGS.4aand4b, respectively.

A transient overvoltage on TVS diodes D21, D22, D31and D32turns on these TVS diodes and the excitation current flows through them during this mode. It should be noted that a suitable number of TVS diodes can be selected depending on the excitation voltage, the transient overvoltage in de-excitation mode, the thermal resistance of the components and the power dissipation of the TVS diodes. The nearly constant voltage of the TVS diodes helps to de-energize the coil much faster than when using a discharge resistor, as shown inFIG.2.

As mentioned, the proposed circuit provides several ways (or mechanisms) to ensure the safe state of the drive device as well as the electrical machine in case of a fault.

Safety interrogation circuits (or state aggregators): Even though there are no exact redundancies to each other due to the two safety sensing circuits, the fault signals F1and F2are inputs to both safety sensing circuits; if one of the safety sensing circuits fails, the other can reach the safe state initiated by the drive circuits, as explained with reference toFIG.5.

Overvoltage detection by the overvoltage measuring devices: There are three overvoltage measuring devices. These overvoltage measuring devices or their functions should be coordinated with each other in order to be able to react accordingly and protect the drive device. As mentioned, the overvoltage measuring devices are, for example, each implemented once in one of the two drive circuits and provided once externally. In case of a problem in one of these overvoltage measuring devices, two remaining overvoltage measuring devices can ensure a safe state of the drive device.

Diodes or TVS diodes for de-excitation: For example, there are two sets of TVS diodes and their parallel de-excitation switches (e.g., MOSFETs), namely de-excitation switch S1with diodes D21and D22, and another de-excitation switch S2with diodes D31and D32. In the event of a fault in one of the sets, the other set can ensure the de-energization process, albeit at a lower voltage (two TVS diodes instead of four TVS diodes in series), resulting in a slower de-energization process compared to four TVS diodes.

Diodes DF1and DF2in parallel with the lowside switch, TF_L, of the regulator: during the de-energizing process, switch TF_Lis closed. If this switch cannot be opened for some reason, the current flows through the parallel diode(s) and also the body diode of switch TF_L. By using two parallel diodes, each of which can carry the entire current, complex diagnostics for switch TF_Lcan be avoided.

Active short circuit with de-energization due to the safety signals SF1and SF2via the drive circuits240and242: The active short circuit for the drive circuit242can be defined, for example, as the generation of a short circuit by the lowside switches of the phases U, W and Y, which means that the lowside switches TU_L, TW_Land TY_Lare closed (cf.FIG.1). The drive circuit242performs this active short circuit when an input connection request of the drive circuit242is activated via the safety signal SF2or, if necessary, directly by an important protective measure such as the overvoltage measuring device262. The active short circuit for the drive circuit240may be defined, for example, as the generation of a short circuit by the lowside switches of the phases V and X, which means that the lowside switches TV_L, TXLas well as TF_Lare closed. The drive circuit240performs this active short circuit when an input connection request of the drive circuit240is activated via the safety signal SF1or, if necessary, directly by an important protective measure such as the overvoltage measuring device261.

It should be noted that due to the thermal load on the lowside switches during the active short circuit, it is possible to switch such an active short circuit between highside and lowside switches (switching between highside and lowside switches). To achieve this switching function, for example, an oscillating circuit with adjustable frequency is required to change the gate signals of highside and lowside switches. Since switch Q1is used to disconnect the excitation coil from the positive supply voltage in the safe state, switching between TF_Hand TF_Lis not a problem for the de-excitation process.

The de-energizing mechanism can be defined, for example, as the disconnection of the coil from the positive supply terminal B+ by opening switch Q1and opening the two de-energizing switches S1and S2. Switch TF_Lis closed because of the active short circuit in question; even if switch TF_Lremains open, the de-energizing current can flow through DF1and DF2(or the body diode if a MOSFET TF_Lis used).

(External) voltage limiting or overvoltage protection device: This especially represents a backup overvoltage protection device to cope with the overvoltage. If other mechanisms to suppress or detect the overvoltage (caused by other faults) in the system—for example, the active short circuits—fail, the TVS diodes D1, D2, D3can absorb the residual energy and limit the voltage. The number of TVS diodes used and their characteristics depend on the voltage level of the DC network and also on the coordination of voltage and time as backup of other over-voltage measuring or protection devices.

The operability of these diodes can be checked via the aforementioned monitoring device270(or monitoring circuit) e.g. on instigation by the signals TVS1, TVS2and TVS3. By bridging individual TVS diodes via a resistor (within270), the voltage between the anode and cathode of the un-shorted TVS diodes can then be monitored, for example, particularly during the start-up process. The MCU then determines, for example, the state or functionality of the TVS diodes.

Excitation current measurement and overcurrent detection of the excitation circuit by the mentioned measuring resistors and overcurrent measuring devices: As shown inFIG.3, the excitation current can be measured using two shunt or sense resistors (Rsh1and Rsh2). The output of the measured current is sent to the MCU for control purposes (i.e. signal IF1and IF2). Two overcurrent (OC) measuring devices monitor the field current. For example, if the field current exceeds a certain threshold (e.g., set point) for a certain time, the output of these detection mechanisms changes from “1” to “0” (in terms of logic levels). This leads to a safe state by activating the safety signals SF1and SF2.

If one of the sensing resistors fails, the MCU detects the sudden change in excitation current and considers that as a sensor failure. It should be mentioned that if there is only one sensing resistor and this resistor would become non-conductive, the entire de-energizing circuit would be an open circuit; therefore, two paths for current sensing are appropriate. Depending on system requirements and ambient temperature, other types of current sensors such as Hall-effect sensors (or other suitable types) can be used at appropriate (e.g. two) measurement points, for example.

To create a more reliable de-energizing circuit, diode D32can be connected directly to the negative supply terminal or directly to the relevant busbar (as shown inFIG.4b). If the sense resistors fail, the de-energizing circuit is not disconnected and the de-energizing current always flows through the TVS diodes (i.e. D21, D22, D31and D32). A minor disadvantage here is that it is not possible to measure the de-energizing current, but as a general rule this is not relevant, especially when the circuit transitions to a safe state. This direct connection of TVS diodes to B− would be essential when using a single measuring resistor.