Circuit arrangement and method for detecting ground connection

Abstract

The invention relates to a circuit arrangement comprising a B6 bridge (1) for actuating an electric motor (M), the lower semiconductor switches (LS1 to LS3) of each half-bridge (HB1, HB2, HB3) of the B6 bridge (1) being connected to an electric motor ground (MGND) via a common main shunt (3), wherein the circuit arrangement further has a monitoring device for monitoring the current (ISUM) flowing through the main shunt (3) as a function of the voltage (USHUNT) dropped across the main shunt (3), the monitoring device being configured to monitor the current (ISUM) flowing through the main shunt (3), in the event of the occurrence of a reverse current flowing through the main shunt (3) which is greater than a predetermined threshold value and lasts for a predetermined duration, a ground connection is detected on the phase (U, V, W) at which the semiconductor switches (HS1, LS1, HS2, LS2, HS3, LS3) connected to the half-bridges (HB1, HB2, HB3) on the phase (U, V, W) have last been switched, in this way, the respective upper semiconductor switches (HS1 to HS3) are opened and the respective lower semiconductor switches (LS1 to LS3) are closed. The invention further relates to a method for detecting a ground connection of phases (U, V, W) of an electric motor.

Description

Field of the Invention

[0001] The present invention relates to a circuit arrangement for controlling an electric motor according to the preamble of claim 1 and a method for detecting a ground connection of a phase of an electric motor according to the preamble of claim 6. Background Art

[0002] It is known to monitor the phase conductors of an electric motor, such as a brushless DC motor, or the motor contacts of a control unit with respect to a ground connection. It is furthermore known to monitor the drain-source voltage at a field-effect transistor of a drive circuit for an electric motor. This monitoring strongly depends on a plurality of parameters, such as the type of the driver bridge circuit, its operating temperature, the type of short circuit (which has to be very low-ohmic), and the residual current through the electric motor. Furthermore, a temperature model has to be implemented for the components involved, such as FETs, IGBTs, which significantly increases the effort for implementation and maintenance. Summary of the Invention

[0003] Accordingly, it is an object of the present invention to provide an alternative solution for detecting a ground connection of a phase conductor of an electric motor.

[0004] According to the invention, this object is solved by a circuit arrangement having the features of claim 1 and by a method having the features of claim 6.

[0005] Advantageous refinements are the subject matter of the dependent claims.

[0006] The circuit arrangement according to the invention comprises a B6 bridge for controlling an electric motor, wherein the B6 bridge has three half-bridges, each of which has an upper semiconductor switch and a lower semiconductor switch, a center tap being formed between each of the half-bridges, to which the phases of the electric motor are or can be connected, wherein the upper semiconductor switch of each half-bridge is or can be connected to an operating voltage, and wherein the lower semiconductor switch of each half-bridge is or can be connected to the ground connection of the electric motor. According to the invention, the lower semiconductor switch of each half-bridge is or can be connected to the ground connection of the electric motor via a common total shunt, and the circuit arrangement furthermore has monitoring means for monitoring the current flowing through the total shunt on the basis of the voltage dropping across the total shunt, wherein the monitoring means are configured to detect a ground connection on the phase at which the semiconductor switch of the half-bridge connected to the phase was last switched such that the corresponding upper semiconductor switch is open and the corresponding lower semiconductor switch is closed in the case of a reverse current flowing through the total shunt that is greater than a pre-given threshold and persists for longer than a pre-given duration.

[0007] In one embodiment, the specific period is longer than 5 μs.

[0008] In one embodiment, the semiconductor switch is configured as a transistor, in particular a field-effect transistor or an IGBT.

[0009] In one embodiment, the monitoring device is configured to additionally monitor the drain-source voltage of a semiconductor switch configured as a field-effect transistor or an IGBT in order to detect a ground connection.

[0010] In one embodiment, the monitoring device is configured to turn off the B6 bridge in the event of a detected ground connection.

[0011] According to one aspect of the invention, a method for detecting a ground connection of a phase of an electric motor is proposed, wherein the phase of the electric motor is connected to the center tap of a respective half-bridge of a B6 bridge, wherein each half-bridge has an upper semiconductor switch and a lower semiconductor switch, and a center tap is respectively constructed between the half-bridges, wherein the upper semiconductor switch of each half-bridge is connected to the operating voltage, and wherein the lower semiconductor switch of each half-bridge is connected to the motor ground connection. According to the invention, the lower semiconductor switch of each half-bridge is connected to the motor ground connection via a common total shunt, wherein the current flowing through the total shunt is monitored based on the voltage dropped across the total shunt, and wherein in the case of a reverse current flowing through the total shunt that is greater than a pre-given threshold and lasts longer than a pre-given duration, a ground connection on the phase is detected at which the semiconductor switch of the half-bridge connected to the phase was last switched such that the respective upper semiconductor switch was turned off and the respective lower semiconductor switch was turned on.

[0012] In one embodiment, the specific time period is longer than 5 μs.

[0013] In one embodiment, in the case of a detected ground connection and the occurrence of a peak value of the reverse current, a low-ohmic ground connection and a low connection resistance between the motor ground and the ground are inferred, for which ground connection there is a ground connection of the phase, while in the case of the occurrence of a small peak value of the reverse current, a higher-ohmic ground connection and a higher connection resistance between the motor ground and the ground are inferred, for which ground connection there is a ground connection of the phase.

[0014] In one embodiment, in the case of a detected ground connection and a rapid drop in the reverse current, a low-inductance ground connection and a low connection inductance between the motor ground and the ground are inferred, for which ground connection there is a ground connection of the phase, while in the case of a slow drop in the reverse current, a high-inductance ground connection and a high connection inductance between the motor ground and the ground are inferred, for which ground connection there is a ground connection of the phase.

[0015] In one embodiment, the semiconductor switch is configured as a field effect transistor or an IGBT, wherein in order to detect a ground connection, the drain-source voltage of the semiconductor switch is additionally monitored.

[0016] If a ground connection occurs, this generates a reverse current flowing through the total shunt, which on the one hand depends on the type of short circuit (i.e., its impedance), but on the other hand also depends on various other parameters. Therefore, for the driver ASIC or other technical solutions, such as analog circuits, it is possible to detect an overcurrent that can be interpreted as a ground connection. After detecting the overcurrent, the system reacts as follows:

[0017] - At least briefly deactivate the B6 bridge driver and report the overcurrent.

[0018] - After debouncing, permanently turn off the B6 bridge and detect the ground connection.

[0019] - After a key cycle (reset control unit), the B6 bridge is in operation again.

[0020] - Occasional faults (short circuits) do not lead to permanent inoperability of the control unit.

[0021] The solution according to the invention has the following advantages:

[0022] - Lower cost for implementation compared to monitoring the drain-source voltage.

[0023] - No temperature model is required.

[0024] - Little or no adaptation of the software is required.

[0025] - No or lower temperature dependence compared to monitoring the drain-source voltage.

[0026] - Especially when making design changes (new pattern phase, new drive components, especially FETs or IGBTs), low maintenance cost throughout the product life cycle.

[0027] - Detection of a wide range of short circuits is possible, and higher-ohm short circuits are also possible compared to the case of monitoring the drain-source voltage.

[0028] - Improved reliability of the product.

[0029] - Improved detection rate of short circuits, especially in combination with monitoring the drain-source voltage.

[0030] - Improved protection of components (MOSFETs) is possible.

[0031] The solution according to the invention can also be applied to the drive stage for a solenoid valve or other electrical load, provided that the shunt is arranged accordingly. Description of the Drawings

[0032] Embodiments of the invention will be explained in more detail below with reference to the drawings.

[0033] Herein:

[0034] Figure 1 A schematic circuit diagram of a B6 bridge with a total shunt grounded towards the motor is shown,

[0035] Figure 2 A schematic diagram showing the duty cycle of pulse width modulation at the B6 bridge is shown,

[0036] Figure 3 A schematic diagram showing the phase voltage and the total current is shown,

[0037] Figure 4 A schematic circuit diagram of the B6 bridge in the case of a ground connection of the phase is shown,

[0038] Figure 5 A schematic circuit diagram of the B6 bridge after the semiconductor switches of the half - bridge involved in the ground connection have been switched is shown.

[0039] Parts corresponding to each other in all the figures are provided with the same reference numerals. Detailed Description of the Invention

[0040] Figure 1 is a schematic circuit diagram of a B6 bridge 1, including three half - bridges HB1, HB2, HB3, each of the half - bridges having two semiconductor switches HS1, LS1, HS2, LS2, HS3, LS3, such as transistors, in particular field - effect transistors or IGBTs. Center taps are respectively constructed between the semiconductor switches, and the phases U, V, W of a motor M, such as a brushless DC motor, are respectively connected or connectable to the center taps. The upper semiconductor switches HS1 to HS3 of each half - bridge HB1, HB2, HB3 are connected to the operating voltage VPS. The lower semiconductor switches LS1 to LS3 of each half - bridge HB1, HB2, HB3 are connected to the motor ground MGND via a total shunt 3. Thus, the current I flowing through all the lower semiconductor switches LS1 to LS3 SUM flows through the total shunt 3 and can be determined by measuring the voltage dropped across its two ends, provided that the resistance or impedance of the total shunt 3 is known.

[0041] For example, in normal operation, the B6 bridge 1 is controlled by pulse - width modulation with continuous sinusoidal modulation. Figure 2 is a schematic diagram of the duty cycle of pulse - width modulation as a function of the phase angle α.Figure 3 are the phase voltages of phases U, V, W and the current I SUM Schematic diagram. The shown shape of the pulse width modulation (in this example the shape "center aligned" is generated, i.e. the high level is made wider starting from the center of the PWM period) is not decisive for the functionality of the method.

[0042] Figure 4 is a schematic circuit diagram of the B6 bridge 1 in the case of a ground connection of phase W. The total shunt 3 is shown as a series circuit consisting of the shunt resistor R SHUNT and the shunt inductance L SHUNT The ground connection (Masseschluss) is a series circuit consisting of the ground connection resistor R SHORT and the ground connection inductance L SHORT The voltage source of the operating voltage VPS, for example a battery as current source 2, is shown in series with the parallel circuit of the capacitor C, for example the buffer capacitor of the B6 bridge 1, and the source resistor R DC and the source inductance L DC In the shown situation, the semiconductor switches HS1, LS2 and HS3 are closed, while the semiconductor switches LS1, HS2 and LS3 are open. The phase current I U flows via the semiconductor switch HS1 into phase U of the motor M. The phase current I V flows from phase U of the motor M via the semiconductor switch LS2 to the motor ground MGND. The short-circuit current I SHORT flows via the semiconductor switch HS3 to the ground GND. The ground GND can be, for example, a reference ground that can be formed by a metal substrate. The circuit arrangement can be part of a control device, for example a transmission control device for a motor vehicle, and the control device can be arranged on a substrate. The voltage U SHUNT drops across the total shunt 3, and the voltage can be determined according to the following equation:

[0043]

[0044] where I DC is the current flowing out of the voltage source.

[0045] Figure 5 is a schematic circuit diagram of the B6 bridge 1 after the semiconductor switches HS3, LS3 of the half-bridge HB3 involved in the ground connection have been switched, i.e. after the semiconductor switch HS3 has been opened and the semiconductor switch LS3 has been closed. A connection resistor R SH_PCB and a connection inductance L SH_PCBA series circuit formed (for example, the following connection between the ground GND and the motor ground MGND: the connection can, for example, extend partly on the metal substrate and partly on the printed circuit board). The discharge current flows partly through the ground connection and partly through the semiconductor switch LS3 from the phase conductor W.

[0046] Here, the following relationship applies:

[0047]

[0048] II : I DC = I U - I SHORT

[0049] II :

[0050] IV :

[0051] where:

[0052] - U SH_PCB is the voltage dropped across the series circuit composed of the connection resistance R SH_PCB and the connection inductance L SH_PCB

[0053] - U SHORT is the voltage dropped across the series circuit composed of the ground connection resistance R SHORT and the ground connection inductance L SHORT

[0054] - U L _ SH_PCB is the voltage dropped across the connection inductance L SH_PCB

[0055] - c is the initial current

[0056] Based on the above theoretical considerations, the following assumptions are made:

[0057] - Once the upper semiconductor switch HS3 is turned off and the lower semiconductor switch LS3 is turned on, the reverse current I SHUNT flows through the total shunt 3. This reverse current depends on the ground connection resistance R SHORT , the ground connection inductance L SHORT and the connection inductance L SH_PCB , as shown above in the formula. The reverse current I SHUNT is always negative, that is, it flows from the motor ground MGND through the shunt 3 into the B6 bridge 1.

[0058] - The ground connection inductance L SHORT and the connection inductance L SH_PCB ​​​Act as a current source.

[0059] - In the case of a low-ohmic short circuit and a low-ohmic connection resistance R SH_PCB a peak value of the short-circuit current I SHORT occurs. In the case of a higher-ohmic short circuit and a higher-ohmic connection resistance R SH_PCB a small peak value of the short-circuit current I SHORT occurs.

[0060] - In the case of a low-inductance short circuit and a low connection inductance L SH_PCB a rapid decline of the short-circuit current I SHORT takes place. In the case of a high-inductance short circuit and a high connection inductance L SH_PCB a slow decline of the short-circuit current I SHORT takes place.

[0061] - Since the brushless DC motor uses the absolute value of the current through the total shunt 3, as long as the negative current is high enough, the negative current also triggers the OC mechanism and shuts off the B6 bridge 1. The OC mechanism is configured to detect overcurrent (OverCurrent - OC) and can be constructed as an ASIC or a part thereof.

[0062] In particular, the reverse current I SHUNT can be determined by monitoring the voltage U SHUNT dropping across the total shunt 3, taking into account the resistance or impedance of the total shunt 3.

[0063] For example, if the voltage U SHUNT across the total shunt 3 is above a defined threshold for a specific period, for example longer than 5 μs, a short circuit towards the ground GND is detectable.

[0064] Experiments have shown that the detection of the ground connection can be effectively improved by the described detection of the reverse current I SHUNT

[0065] In an embodiment of the present invention, the detection of the ground connection by the described detection of the reverse current I SHUNT is used in a manner supplemented by the monitoring of the drain-source voltage.

[0066] List of reference signs

[0067] 1 B6 bridge

[0068] 2 Current source

[0069] 3 Total shunt

[0070] C Capacitor

[0071] DC Duty cycle ​

[0072] GND Ground

[0073] HB1 to HB3 Half-bridge

[0074] HS1 to HS3 Semiconductor switches, upper semiconductor switches

[0075] I DC Current flowing out from the voltage source

[0076] I SHORT Short-circuit current

[0077] I SUM Current

[0078] I U 、I V Phase current

[0079] LS1 to LS3 Semiconductor switches, lower semiconductor switches

[0080] L DC Source inductance

[0081] L SHORT Ground connection inductance

[0082] L SHUNT Shunt inductance

[0083] L SH_PCB Connection inductance

[0084] M Motor

[0085] MGND Motor ground

[0086] R DC Source resistance

[0087] R SHORT Ground connection resistance

[0088] R SHUNT Shunt resistance

[0089] R SH_PCB Connection resistance

[0090] U Phase

[0091] U L _ SH_PCB Voltage

[0092] U SHORT Voltage

[0093] U SHUNT Voltage

[0094] U SH_PCB Voltage

[0095] Phase V

[0096] VPS operating voltage

[0097] Phase W

[0098] α phase angle.

Claims

1. A circuit device, the circuit device comprising a B6 bridge (1) for controlling a motor (M), wherein the B6 bridge (1) has three half - bridges (HB1 to HB3), each of the half - bridges having an upper semiconductor switch and a lower semiconductor switch (HS1, LS1, HS2, LS2, HS3, LS3), center taps being respectively formed between the half - bridges, and phases (U, V, W) of the motor (M) being respectively connected or connectable to the center taps, wherein the upper semiconductor switches (HS1 to HS3) of each half - bridge (HB1, HB2, HB3) are connected or connectable to an operating voltage (VPS), and wherein the lower semiconductor switches (LS1 to LS3) of each half - bridge (HB1, HB2, HB3) are connected or connectable to a motor ground (MGND). Characterized in that, The lower semiconductor switches (LS1 to LS3) of each half-bridge (HB1, HB2, HB3) are connected or connectable via a common total shunt (3) to the motor ground (MGND), wherein the circuit arrangement furthermore has a monitoring device for monitoring the current (I SHUNT ) flowing through the total shunt (3) based on the voltage (U SUM ) dropping across the total shunt (3), wherein the monitoring device is configured to detect the ground connection on the following phases (U, V, W) in the case of a reverse current flowing through the total shunt (3) that is greater than a pre-given threshold and persists for longer than a pre-given duration, namely at the phase at which the semiconductor switches (HS1, LS1, HS2, LS2, HS3, LS3) of the half-bridge (HB1, HB2, HB3) connected to the phase (U, V, W) were last switched such that the respective upper semiconductor switches (HS1 to HS3) are open and the respective lower semiconductor switches (LS1 to LS3) are closed.

2. The circuit device according to claim 1, Characterized in that, A specific time period is longer than 5 μs.

3. The circuit device according to claim 1 or 2, Characterized in that, The semiconductor switches (HS1 to HS3, LS1 to LS3) are configured as transistors, in particular field - effect transistors or IGBTs.

4. The circuit device according to claim 3, Characterized in that, The monitoring device is configured to additionally monitor the drain - source voltage of the semiconductor switches (HS1 to HS3, LS1 to LS3) configured as field - effect transistors or IGBTs for detecting a ground connection.

5. The circuit device according to any one of the preceding claims, Characterized in that, The monitoring device is configured to turn off the B6 bridge (1) in the case of a detected ground connection.

6. A method for detecting a ground connection of phases (U, V, W) of a motor (M), the phases (U, V, W) of the motor (M) being connected to center taps of corresponding half - bridges (HB1 to HB3) of a B6 bridge (1), wherein each of the half - bridges (HB1 to HB3) has an upper semiconductor switch and a lower semiconductor switch (HS1, LS1, HS2, LS2, HS3, LS3), center taps being respectively formed between the half - bridges, wherein the upper semiconductor switches (HS1 to HS3) of each half - bridge (HB1, HB2, HB3) are connected to an operating voltage (VPS), and wherein the lower semiconductor switches (LS1 to LS3) of each half - bridge (HB1, HB2, HB3) are connected to a motor ground (MGND). Characterized in that, The lower semiconductor switches (LS1 to LS3) of each half-bridge (HB1, HB2, HB3) are connected to the motor ground (MGND) via a common total shunt (3), wherein the current (I SHUNT ) flowing through the total shunt (3) is monitored based on the voltage (U SUM ) dropping across the total shunt (3), and wherein in the case of a reverse current flowing through the total shunt (3) that is greater than a pre-given threshold and lasts longer than a pre-given duration, the ground connections on the following phases (U, V, W) are detected, i.e., at the phase where the semiconductor switches (HS1, LS1, HS2, LS2, HS3, LS3) of the half-bridge (HB1, HB2, HB3) connected to the phase (U, V, W) were last switched, such that the corresponding upper semiconductor switches (HS1 to HS3) have been opened and the corresponding lower semiconductor switches (LS1 to LS3) have been closed.

7. The method according to claim 6, Characterized in that, A specific time period is longer than 5 μs.

8. The method according to claim 6 or 7, Characterized in that, In the case of the detection of a ground connection and the occurrence of a peak value of the reverse current, a low-ohmic ground connection and a low-ohmic connection resistance (R SH_PCB ) between the motor ground (MGND) and the ground (GND) are inferred. For the ground (GND), there is a ground connection of the phases (U, V, W), and in the case of the detection of a ground connection and the occurrence of a small peak value of the reverse current, a higher-ohmic ground connection and a higher-ohmic connection resistance (R SH_PCB ) between the motor ground (MGND) and the ground (GND) are inferred. For the ground (GND), there is the phase (U, V, W) of the ground connection.

9. The method according to any one of claims 6 to 8, Characterized in that, In the case of a detected ground connection and a rapid drop in the reverse current, a low-inductance ground connection and a low connection inductance (L SH_PCB ) between the motor ground (MGND) and the ground (GND) are inferred. For the ground (GND), there is a ground connection of the phases (U, V, W). And in the case of a detected ground connection and a slow drop in the reverse current, a high-inductance ground connection and a high connection inductance (L SH_PCB ) between the motor ground (MGND) and the ground (GND) are inferred. For the ground (GND), there is a ground connection of the phases (U, V, W).

10. The method according to any one of claims 6 to 9, Characterized in that, The semiconductor switches (HS1 to HS3, LS1 to LS3) are configured as field effect transistors or IGBTs, wherein, in order to detect the ground connection, the drain-source voltage of the semiconductor switches (HS1 to HS3, LS1 to LS3) is additionally monitored.

Images