APPARATUS AND METHOD FOR ACTIVELY DISCHARGING A DC LINK CAPACITOR

Abstract

An apparatus for actively discharging at least one DC link capacitor, comprising 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 DC link capacitor, wherein a voltage divider comprising at least two resistors is arranged in parallel with the DC link capacitor, wherein a tap of the voltage divider is connected to at least one differentiator, wherein at least one driver module for generating gate driver signals is assigned to the half-bridge circuit, and at least one control unit, wherein the control unit is designed in such a way that, in an active discharge mode, at least one transistor of the half-bridge circuit is controlled as a function of an output signal of the differentiator, as well as to an associated method.

Claims

1. An apparatus for actively discharging at least one DC link capacitor, the apparatus comprising: at least one half-bridge circuit having a high-side transistor and a low-side transistor, the half-bridge circuit being arranged in parallel with the DC link capacitor; a voltage divider comprising at least two resistors is arranged in parallel with the DC link capacitor; a tap of the voltage divider being connected to at least one differentiator; at least one driver module to generate gate driver signals is assigned to the half-bridge circuit; and at least one control unit configured such that, in an active discharge mode, the control unit controls at least one transistor of the half-bridge circuit as a function of an output signal of the differentiator.

2. The apparatus according to claim 1, wherein a comparator is arranged downstream of the differentiator, wherein the at least one transistor is controlled in active discharge mode as a function of an output signal of the comparator.

3. The apparatus according to claim 1, wherein at least one switching element is assigned to the differentiator and/or the comparator, wherein the control unit is designed such that the differentiator and/or the comparator are switched on via the switching element in the active discharge mode and switched off outside the active discharge mode.

4. The apparatus according to claim 1, wherein the differentiator and/or the comparator are designed as an operational amplifier circuit.

5. The apparatus according to claim 1, wherein only one differentiator for one transistor of the half-bridge circuit is assigned to the half-bridge circuit, wherein the control unit is designed such that the other transistor is permanently switched through during the active discharge mode.

6. The apparatus according to claim 5, wherein the differentiator is associated with the low-side transistor of the half-bridge circuit.

7. The apparatus according to claim 1, wherein a plurality of half-bridge circuits are connected in parallel, and wherein at least two half-bridge circuits are assigned a differentiator.

8. The apparatus according to claim 1, wherein the apparatus is arranged in a traction network of a motor vehicle.

9. The apparatus according to claim 1, wherein the differentiator and/or the comparator are integrated in a driver module of at least one transistor of the half-bridge circuit.

10. A method for actively discharging a DC link capacitor via at least one control unit, at least one half-bridge circuit, at least one voltage divider and at least one differentiator, the method comprising: detecting by the control unit a need for active discharge of the DC link capacitor; and controlling at least one transistor of the half-bridge circuit as a function of an output signal of the differentiator.

11. The method according to claim 10, wherein the control unit controls the at least one transistor as the function of the output signal of the differentiator.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0015] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawing which is given by way of illustration only, and thus, are not limitive of the present invention, and wherein the sole FIGURE schematically shows an apparatus according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION

[0016] The FIG. 1 schematically shows an apparatus 1 for active discharging of a DC link capacitor C. The DC link capacitor C is located between a positive high-voltage terminal HV+ and a negative high-voltage terminal HV−. A half-bridge circuit HB with a high-side transistor HST and a low-side transistor LST is arranged in parallel with the DC link capacitor C. For clarity, the freewheeling diodes are not shown. The gate terminals of the high-side transistor HST and the low-side transistor LST are each assigned a driver module TB, each of which contains driver circuits for generating gate driver signals. However, the driver circuits can also be integrated in a common driver module. The driver modules TB are controlled by a control unit 2. Further, a voltage divider with two resistors R1, R2 is arranged in parallel with the DC link capacitor C. Further, the apparatus 1 has a differentiator 3 as well as a comparator 4, both of which are designed as operational amplifier circuits. The operational amplifier 5 of the differentiator 3 is connected as a classical differentiator with an input capacitance C.sub.diff and a resistor R.sub.diff in the feedback branch. In this case, the differentiator 3 has a switching element 6 between a supply voltage terminal of the operational amplifier 5 and the supply voltage VCC, which is controlled by the control unit 2. The input of the differentiator 3 is connected to the center tap of the voltage divider. Accordingly, the output voltage of differentiator 3 is calculated to be U.sub.A=−R.sub.diff.Math.C.sub.diff.Math.dU/dt. This represents an image of the discharge current of the DC link capacitor C. The output of the differentiator 3 is connected to the negative input of the operational amplifier 7 of the comparator 4, to the positive input of which a reference voltage U.sub.ref is applied. A switching element 8 is also arranged at the supply voltage terminal of the operational amplifier 7, which is also controlled by the control unit 2. The output of the comparator 4 is connected (possibly via a decoupling element, not shown, such as a diode) to the gate terminal of the low-side transistor LST.

[0017] In normal operation, the control unit 2 opens the switching elements 6 and 8 so that differentiator 3 and comparator 4 are switched off. If the control unit 2 now detects a situation where the DC link capacitor C is to be actively discharged, the control unit 2 switches the driver module TB of the low-side transistor LST off, or to high impedance, and closes the switches 6, 8. Furthermore, the control unit 2 controls the driver module TB of the high-side transistor HST in such a way that it permanently switches through the high-side transistor HST. Initially, the voltage change at the DC link capacitor C is negligible, so that the comparator 4 switches through the low-side transistor LST. Thus, both transistors are connected through, and a large current flows so that the voltage change at the DC link capacitor C becomes larger. This leads to an increasing output voltage at the differentiator 3. If the output voltage at the differentiator 3 then reaches the reference voltage U.sub.ref at the comparator 4, the latter switches off the low-side transistor LST. As a result, the voltage change at the DC link capacitor C becomes smaller, since the half-bridge circuit HB blocks. If the output voltage at the differentiator 3 then drops below the reference voltage U.sub.ref, the low-side transistor LST is switched on again. This is repeated until the DC link capacitor C is discharged to a predetermined voltage. The advantage of the circuit is that it uses robust analog technology, is self-regulating, uses an existing thermal link, and is very fast.

[0018] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.