Device and method for actively discharging an intermediate circuit capacitor

Abstract

The present invention relates to a device (1) for actively discharging at least one intermediate capacitor (C), comprising at least one half-bridge circuit (HB), the half-bridge circuit having a high-side transistor (HST) and a low-side transistor (LST), wherein the half-bridge circuit (HB) is arranged in parallel with the intermediate circuit capacitor (C), wherein a voltage divider consisting of at least two resistors (R1, R2) is arranged in parallel with the intermediate circuit capacitor (C), wherein a tapping point of the voltage divider is connected to at least one differential element (3), and the half-bridge circuit (HB) is assigned at least one driver module (TB) for generating a gate drive signal and at least one controller (2), wherein the controller (2) is configured to control at least one transistor (HST, LST) of the half-bridge circuit (HB) in an active discharge mode according to an output signal of the differential element (3); and a corresponding method.

Description

Technical Field

[0001] The invention relates to a device and a method for actively discharging an intermediate circuit capacitor. Background Art

[0002] Intermediate-circuit capacitors are used, for example, in the traction systems of electric or hybrid vehicles, where they are arranged between the traction battery and the inverter for the electric motor. Especially in high-voltage systems using voltages exceeding 60V, rapid and reliable discharge of the intermediate-circuit capacitors is necessary if the system is shut down, such as in the event of a crash. Active discharge can be achieved by selectively switching on ohmic loads, which convert the energy stored in the intermediate-circuit capacitors into heat. The resulting load demands are not without their challenges, as the currents can be very high and the generated heat must be dissipated. Summary of the Invention

[0003] The technical problem underlying the present invention is therefore to provide an improved device for actively discharging an intermediate circuit capacitor and to provide a suitable method.

[0004] The solution to this technical problem is achieved by the device according to the invention and the method according to the invention. Further advantageous embodiments of the invention will be apparent from the following description.

[0005] To this end, a device for actively discharging at least one intermediate circuit capacitor includes at least one half-bridge circuit having a high-side transistor and a low-side transistor, wherein the half-bridge circuit is arranged in parallel with the intermediate circuit capacitor. Furthermore, a voltage divider consisting of at least two resistors is arranged in parallel with the intermediate circuit capacitor, wherein the tapping point of the voltage divider is connected to at least one differentiating element or differentiator. The half-bridge circuit is assigned at least one driver module for generating a gate drive signal and at least one controller, wherein the controller is configured to control at least one transistor of the half-bridge circuit in an active discharge mode based on an output signal of the differentiating element. The advantages of this device can be summarized as follows. Due to the high currents during normal operation, the transistors of the half-bridge circuit are very well thermally coupled to dissipate lost heat. On the other hand, these transistors cannot be operated in a permanent short circuit, as this could damage them. The discharge current of the intermediate circuit capacitor is determined by the differentiating element without direct current measurement; that is, the discharge current is proportional to the temporal change in the voltage at the intermediate circuit capacitor. If the current then becomes excessive, at least one transistor can be correspondingly blocked to limit the current flow. In principle, the manipulation can be continued.

[0006] However, this control is preferably performed in a pulsed manner, as in normal operation. To this end, a comparator is arranged downstream of the differentiating element. In active discharge mode, the at least one transistor is controlled according to the output signal of the comparator. Figuratively speaking, as long as the output voltage of the differentiating element is numerically less than the reference voltage, the transistor remains on. If the output voltage of the differentiating element exceeds the reference voltage, the transistor is temporarily turned off until the output voltage of the differentiating element again drops below the reference voltage. This forms a closed control loop.

[0007] In another embodiment, a switching element is associated with the differentiating element and / or the comparator, wherein the controller is configured to switch the differentiating element and / or the comparator on via the switching element in the active discharge mode and to switch the differentiating element and / or the comparator off outside the active discharge mode, thereby saving energy and avoiding possible adverse reactions. Preferably, the supply voltage is switched on and off via the switching element.

[0008] In another embodiment, the differentiating element and / or the comparator is designed as an operational amplifier circuit.

[0009] In another embodiment, the half-bridge circuit is assigned a differentiating element to only one transistor, with the controller being designed to permanently switch on the other transistor during active discharge mode. This reduces the circuit complexity. If the driver module is used for permanent switching for normal operation, short-circuit monitoring is also ensured.

[0010] Preferably, the differentiating element is assigned to the low-side transistor.

[0011] If multiple half-bridge circuits are present, it is generally sufficient to use only one half-bridge circuit for active discharge. However, it is possible to assign a differentiating element to at least one other half-bridge circuit, or even to all half-bridge circuits. This offers the advantage of redundancy and the possibility of distributing the load of the half-bridges.

[0012] A preferred field of application of the device is use in the traction system of a motor vehicle.

[0013] In another embodiment, the differentiating element and / or the comparator are integrated into a driver module of at least one transistor of the half-bridge circuit.

[0014] With regard to the design of the method aspect of the present invention, reference is made to the above embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The invention is explained in more detail below with reference to a preferred exemplary embodiment. The single FIGURE shows a schematic circuit arrangement of a device for actively discharging an intermediate circuit capacitor. DETAILED DESCRIPTION

[0016] exist Figure 1 Schematically shows a device 1 for actively discharging an intermediate circuit capacitor C. The intermediate circuit capacitor C is located between the positive high-voltage connection HV+ and the negative high-voltage connection HV-. A half-bridge circuit HB is arranged in parallel with the intermediate circuit capacitor C, which has a high-voltage side transistor HST and a low-voltage side transistor LST, wherein the freewheeling diode is not shown for reasons of clarity. The gate connections of the high-voltage side transistor HST and the low-voltage side transistor LST are each assigned a driver module TB, which each contains a driver circuit for generating a gate drive signal. However, these driver circuits can also be integrated in a common driver module. The driver module TB is controlled by the controller 2. In addition, a voltage divider is arranged in parallel with the intermediate circuit capacitor C, which has two ohmic resistors R1, R2. In addition, the device 1 has a differential element 3 and a comparator 4, both of which are constructed as operational amplifier circuits. The operational amplifier 5 of the differential element 3 acts as a conventional differentiator with the input capacitor C diff and the resistor R in the feedback branch diff Here, the differential element 3 has a switching element 6 between the supply voltage connection of the operational amplifier 5 and the supply voltage VCC, which is controlled by the controller 2. The input of the differential element 3 is connected to the center tap of the voltage divider. Correspondingly, the output voltage of the differential element 3 is calculated as U A =-R diff ·C diff ·dU / dt. This is a reflection of the discharge current of the intermediate circuit capacitor C. The output of the differential element 3 is connected to the negative input of the operational amplifier 7 of the comparator 4, and the reference voltage U ref A switching element 8 is also arranged at the supply voltage connection of the operational amplifier 7, which is also controlled by the controller 2. The output of the comparator 4 is connected (if necessary via a decoupling element (not shown), such as a diode) to the gate connection of the low-side transistor LST.

[0017] During normal operation, the controller 2 disconnects the switching elements 6 and 8, so that the differential element 3 and the comparator 4 are turned off. If the controller 2 now detects that the intermediate circuit capacitor C should be actively discharged, the controller 2 turns off the driver module TB of the low-voltage side transistor LST or switches it to high ohm and closes the switches 6 and 8. In addition, the controller 2 controls the driver module TB of the high-voltage side transistor HST so that the driver module turns on the high-voltage side transistor HST permanently. Initially, the voltage change at the intermediate circuit capacitor C is negligible, so that the comparator 4 turns on the low-voltage side transistor LST. Therefore, both transistors are turned on and a high current flows, so that the voltage change at the intermediate circuit capacitor C becomes larger. This causes the output voltage at the differential element 3 to increase. If the output voltage at the differential element 3 then reaches the reference voltage U at the comparator 4 ref , the comparator turns off the low-side transistor LST. As a result, the voltage change at the intermediate circuit capacitor C becomes smaller because the half-bridge circuit HB is cut off. If the output voltage at the differentiating element 3 then drops below the reference voltage U ref , the low-side transistor LST is turned on again. This process is repeated until the intermediate circuit capacitor C is discharged to a predetermined voltage. The advantages of this circuit are that it is designed using robust analog technology, is self-regulating, uses existing thermal connections, and is very fast.

[0018] Reference Signs List

[0019] 1 device

[0020] 2 Controllers

[0021] 3 Differential elements

[0022] 4 Comparators

[0023] 5. Operational Amplifier

[0024] 6 Switching elements

[0025] 7 Operational Amplifier

[0026] 8 Switching elements

[0027] HB Half-Bridge Circuit

[0028] C Intermediate circuit capacitor

[0029] R1, R2, R diff , R ohm resistance

[0030] C diff Input capacitance

[0031] TB driver module

[0032] HST High-Side Transistor

[0033] LST Low Side Transistor

Claims

1. A device (1) for actively discharging at least one intermediate circuit capacitor (C), comprising at least one half-bridge circuit (HB), the half-bridge circuit having a high-side transistor (HST) and a low-side transistor (LST), wherein the half-bridge circuit (HB) is arranged in parallel with the intermediate circuit capacitor (C), wherein a voltage divider consisting of at least two resistors (R1, R2) is arranged in parallel with the intermediate circuit capacitor (C), wherein a tapping point of the voltage divider is connected to at least one differentiating element (3), the half-bridge circuit (HB) is assigned at least one driver module (TB) for generating a gate drive signal, and at least one controller (2), wherein the controller (2) is configured to control at least one transistor (HST, LST) of the half-bridge circuit (HB) in an active discharge mode as a function of an output signal of the differentiating element (3).

2. The device according to claim 1, characterized in that A comparator (4) is arranged downstream of the differentiating element (3), wherein in the active discharge mode the at least one transistor (HST, LST) is driven as a function of an output signal of the comparator (4).

3. The device according to claim 2, characterized in that At least one switching element (6, 8) is assigned to the differential element (3) and / or the comparator (4), wherein the controller is configured to switch on the differential element (3) and / or the comparator (4) via the switching element (6, 8) in the active discharge mode and to switch off the differential element and / or the comparator outside the active discharge mode.

4. The device according to claim 2 or 3, characterized in that The differentiating element (3) and / or the comparator (4) are configured as an operational amplifier circuit.

5. The device according to any one of claims 1 to 3, characterized in that The half-bridge circuit is assigned a differentiating element (3) for only one transistor (HST, LST) of the half-bridge circuit (HB), wherein the controller (2) is designed to permanently switch on the other transistor (HST, LST) during the active discharge mode.

6. The device according to claim 5, characterized in that The differentiating element is assigned to the low-side transistor (LST) of the half-bridge circuit (HB).

7. The device according to any one of claims 1 to 3, characterized in that A plurality of half-bridge circuits (HB) are connected in parallel, wherein a differentiating element (3) is assigned to at least two half-bridge circuits (HB).

8. The device according to any one of claims 1 to 3, characterized in that The device (1) is arranged in a traction system of a motor vehicle.

9. The device according to claim 2 or 3, characterized in that The differentiating element (3) and / or the comparator (4) are integrated into a driver module (TB) of at least one transistor (HST, LST) of the half-bridge circuit (HB).

10. A method for actively discharging an intermediate circuit capacitor (C) by means of at least one controller (2), at least one half-bridge circuit (HB), at least one voltage divider and at least one differentiating element (3), wherein the controller (2) detects the need for active discharge of the intermediate circuit capacitor (C) and controls at least one transistor (HST, LST) of the half-bridge circuit (HB) as a function of an output signal of the differentiating element (3).

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