Power semiconductor module with interference-insensitive measurement of its shunt voltage

Abstract

The invention relates to a power semiconductor module with a power current path (17) in which a shunt resistor (1), in particular a resistor ≤50mOhm, is arranged, wherein the shunt resistor (1) has two main measurement contacts (2, 3) spaced apart from one another and having different polarities (+,-) and an auxiliary measurement contact (4) is arranged in the direct vicinity of the shunt resistor (1) without being in direct electrical connection to same, wherein a measurement line (20, 21, 22) leads from each measurement contact (2, 3, 4) to an evaluation unit (6) and forms loops (18, 19) which are practically identical in terms of area.

Description

[0001] Description

[0002] Power semiconductor module with interference-insensitive measurement of its shunt voltage

[0003] The invention relates to a power semiconductor module with interference-insensitive measurement of its shunt voltage, as well as a method for interference-insensitive measurement of a shunt voltage in a power semiconductor module.

[0004] Due to the increasing demand for ever higher power densities in power electronics, current measurement in converters is realized with the help of compact shunt resistors that are integrated in the power semiconductor module.

[0005] The shunt resistors within the power semiconductor module are positioned very close to the power semiconductors. This proximity causes interference to the measurement lines leading to the shunt resistor, resulting in inaccurate measurements.

[0006] A known, effective solution to this interference is a twisted-pair cable. This solution can only be implemented manually during the manufacture of power semiconductor modules. Automated production of this solution is very complex. Furthermore, parallel wiring remains at the power module pins. Despite twisted-pair cables, this area remains a window for interference.

[0007] Another solution to reduce this interference is to increase the desired signal. However, with shunt resistors, this leads to an increase in the resistance value. This reduces the ratio of interference to the measured signal.

[0008] Previously known and commonly used analog-to-digital converters have a measuring range of 50 mV or 200 mV. The shunt design for the 50 mV measuring range results in comparatively high interference due to the low voltage drop.

[0009] However, a change to the higher measuring range, especially the 200 mV range, means a multiplication, in particular a quadrupling, of the shunt's ohmic resistance. This also increases the power loss, in particular by a factor of four. To dissipate these losses, the shunt resistors must be connected in parallel. This, however, increases costs and space requirements in a power semiconductor module.

[0010] Based on this, the object of the invention is to provide a compact power semiconductor module with interference-insensitive measurement.

[0011] The solution to the problem is achieved through the features of the independent claims.

[0012] Advantageous embodiments can be found in the dependent claims.

[0013] According to the invention, interference-insensitive current detection is enabled in a power semiconductor module with a power current path in which a shunt resistor, in particular a resistor <50 mOhm, is arranged. This comprises two spaced-apart main measuring contacts of different polarity (+, -) and an auxiliary measuring contact in the immediate vicinity of the shunt resistor, whereby the auxiliary measuring contact is not in direct electrical connection with the shunt resistor. This arrangement enables interference-insensitive current detection at the shunt resistor in that a measuring line leads from each measuring contact - both the main measuring contact and the auxiliary measuring contact - to an evaluation unit, forming loops with almost identical areas.

[0014] Power semiconductors are semiconductor components used in power electronics for controlling and switching high electrical currents and voltages (more than 1 ampere and voltages greater than approximately 24 volts). The upper limits of these values ​​are several thousand amperes and volts.

[0015] Adapted versions of normal semiconductor components are used for this purpose, as high currents and voltages would destroy them. The following components are preferably used: power diodes (are switching elements that basically only allow current to flow in one direction or only above a certain voltage value), thyristors, GTO ("Gate Turn Off" or SCR, "Silicon Controlled Rectifier" are switching elements that allow the switching point to be set flexibly and as required by a controllable voltage on a control electrode), triacs (are two thyristor elements in one component that are connected in parallel in opposite directions and controlled together) and power MOSFETs and IGBT components (are transistors with special switching and performance properties due to their atomic semiconductor structure).

[0016] The power semiconductors are electrically connected to the power contacts of the respective power semiconductor module.

[0017] According to the invention, a shunt resistor is referred to as a current measuring resistor, i.e. a low-ohm electrical measuring resistor, often equipped with separate current and voltage terminals. This is inserted directly into the current-carrying line, i.e. the power current path of the power semiconductor. The evaluation unit connected in parallel to this type of shunt resistor thus diverts only a comparatively small current and records the voltage "dropped" across it. For high currents, e.g. greater than 10A, the current measurement is carried out by measuring the electrical voltage across a shunt. To measure very high currents (>100A), the shunt resistors are mechanically robust, for example from metal strips or rods with strong screw contacts for the load circuit (consumer circuit) and two smaller measuring contacts for connecting e.g. a measuring device.Large shunt resistors made of parallel metal bars can also be screwed directly between busbars. Materials for such shunt resistors include manganin, isotan, and isabellin, which are characterized by a low temperature coefficient of specific electrical resistance and a low thermoelectric voltage against copper. Adequate heat dissipation must be ensured.

[0018] These shunts are often designed for a voltage of 50mV or 200mV at the nominal current in the power path. The current in the shunt is calculated using Ohm's law.

[0019] The shunt resistor is installed in the line carrying the current to be measured. The voltage drop caused by this resistance is measured. The contact resistances in the current terminals are often greater than the measuring resistance, and the quantity is unknown.

[0020] Since currents with short rise times or high frequencies must be measured in power electronics and converters, shunt resistors are designed with low parasitic inductance. Axial or axially wound resistors are only suitable to a limited extent. Better suited for such shunt resistors are bifilament wound resistors or special designs, such as a coaxial shunt consisting of two tubes inserted into one another through which current flows in opposite directions. Other low-inductance designs are well-known as Möbius resistors and wave-shaped resistor foils.

[0021] Shunt resistors are an inexpensive and accurate method of current measurement and are generally used not only in measuring devices but also in power electronics assemblies for current monitoring and control.

[0022] Such a power semiconductor module is installed in a power converter. A power converter can be, for example, a rectifier, an inverter, a converter, or a DC-DC converter.

[0023] According to the invention, an auxiliary measuring contact is created directly on the shunt resistor, in particular by means of a bridge, which is at the same potential as a second measuring contact.

[0024] By alternating the measuring signals ( -+- , or alternatively : +-+ ) , it is possible to make the measurement of the voltage drop insensitive to interference .

[0025] Three measuring lines run from the shunt resistor to the evaluation unit in such a way that loops of equal size are formed. In particular, the measuring lines run parallel and as close to one another as possible. Due to the arrangement in which the two main measuring contacts are at different potentials and the auxiliary measuring contact is at the potential of the second main measuring contact, i.e., either "+" or alternatively, loops of equal area are formed between the now three measuring lines, through which an interference field couples into these measuring lines.

[0026] This interference can currently be reduced, as described above, but cannot be easily prevented.

[0027] According to the invention, interference is explicitly allowed first. This interference (dB / dt) preferably occurs in a plane spanned by the loops. This interference signal induces an electric field (dE / dt) in the conductor loops formed by the measuring lines and causes an interference voltage with a different direction at the inputs of the evaluation unit.

[0028] In one operational amplifier of the evaluation unit, the disturbance increases the actual measurement signal, while in the other operational amplifier of this evaluation unit, the disturbance acts in the opposite direction to the measurement signal.

[0029] By subsequently summing both signals analogously, e.g. using a resistor circuit, the interference signal is cancelled out before entering an A / D converter.

[0030] Strong gradients in the interference field can induce different levels of interference voltage in the two loops. This effect can be avoided, or at least significantly reduced, by routing the measuring lines as closely parallel as possible.

[0031] With the proposed solution, small voltage signals from the shunt resistors can still be measured without interference. This allows the use of relatively small resistors, especially <50 mOhm for the 50 mV measuring range of the A / D converter.

[0032] The advantages and preferred embodiments listed below with regard to the power semiconductor can be transferred analogously to the method for interference-insensitive current measurement.

[0033] According to the invention, the following advantages arise: Faster current measurements on the power semiconductor module are possible because the filter cutoff frequency of an anti-aliasing filter can be increased. Furthermore, shunt resistors are saved by using the 50 mV voltage measuring range. The compact design of the current measurement reduces the required assembly area in the power semiconductor module. The design and method according to the invention reduce power loss, among other things, within the power semiconductor module. Such a design can be manufactured automatically, which is advantageous compared to previous designs.

[0034] The invention and further advantageous embodiments of the invention are explained in more detail using exemplary embodiments shown in principle, in which:

[0035] FIG 1 basic structure and arrangement of the shunt resistor,

[0036] FIG 2 Mode of operation of the measuring method,

[0037] FIG 3 Signal curve .

[0038] For the sake of clarity, in some cases where components are present more than once, not all of the components shown are provided with reference symbols.

[0039] The described embodiments can be combined in any way. Individual features of the respective embodiments can also be combined without departing from the essence of the invention.

[0040] FIG. 1 shows a shunt resistor 1 arranged in a power current path of a power semiconductor. Directly at the shunt resistor 1, an auxiliary measuring contact 4—that is, a third connection—is formed, in particular by means of a bridge 5, in addition to the two main measuring contacts, the first main measuring contact 2 and the second main measuring contact 3. The auxiliary measuring contact 4 is at the same potential as the second main measuring contact 3.

[0041] By alternating the arrangement of the measuring signals ( -+- , or alternatively : +-+ ), it is possible to make the measurement of the voltage drop across the shunt resistor 1 insensitive to interference.

[0042] According to the invention, three measuring lines 20, 21, 22 run parallel and close to one another. The -+- (or alternatively +-+) arrangement forms loops 18, 19 of equal size (see also FIG. 2), through which an interference signal 7 couples into these measuring lines 20, 21, 22.

[0043] This interference coupling (dB / dt) occurs in the plane as shown in FIG. 2. This interference signal 7 induces an electric field 8 (dE / dt) in the loops 18, 19 and causes an interference signal 14, in particular an interference voltage, at the inputs of an evaluation unit 6, which is preferably located directly at the pins 15 of a housing 16 of the power semiconductor module. The operational amplifiers 9, 10, to which these measurement signals are fed as shown in FIG. 2, are arranged in this evaluation unit 6.

[0044] In the first operational amplifier 9, the interference signal 7 amplifies the useful signal 13, while in the second operational amplifier 10, the interference acts in the opposite direction to the useful signal 13. The interference signal 7 (see FIG. 3) is canceled out by the analog summation downstream of the operational amplifiers 9, 10, in particular by a resistor circuit 11 of both signals.

[0045] Strong gradients in the interference field can induce interference voltages of different values ​​in the two loops 18, 19. This effect can be avoided or at least significantly reduced by particularly close parallel routing of the measuring lines 20, 21, and 22. It is important that the voltages on the taut surfaces of the loops 18, 19 are as identical as possible in order to obtain the same magnitude of signal 14.

[0046] With the proposed solution, even small voltage signals from the shunt resistors 1 can be measured without interference. This makes it possible to use small shunt resistors 1 for the 50 mV measuring range of the A / D converter 12.

[0047] The following advantages result from the power semiconductor module, the shunt resistor 1 and the method for measuring the current in the power current path 17 :

[0048] According to the invention, a comparatively fast current measurement is now possible since the filter cutoff frequency of an anti-aliasing filter can be increased from approximately <100kHz to >300kHz.

[0049] The variance of shunt resistors 1 can be reduced, so there is a saving of shunt resistors 1 due to the 50mV voltage measuring range.

[0050] The required mounting area in the power semiconductor module can be reduced, which benefits a more compact design.

[0051] The structure according to the invention leads to a reduction in power loss, particularly at the shunt resistor 1. The structure according to the invention also allows for automated production, at least in this area of ​​the power semiconductor module.

Claims

Patent claims 1. Power semiconductor module with a power current path (17) in which a shunt resistor (1), in particular a resistor <50 mOhm, is arranged, wherein the shunt resistor (1) has two spaced-apart main measuring contacts (2, 3) of different polarity (+, -) and an auxiliary measuring contact (4) is arranged in the immediate vicinity of the shunt resistor (1) without being in direct electrical connection therewith, wherein from each measuring contact (2, 3, 4) a measuring line (20,21,22) to an evaluation unit (6) and forms loops (18,19) which are almost identical in area, so that three measuring lines (20,21,22) are present which form two symmetrical loops (18,19) with respect to one another, so that interference coupling at the inputs of the evaluation unit (6) causes an interference voltage with a different direction.

2. Power semiconductor module with a power current path (17) according to claim 1, characterized in that the distance between the auxiliary contact (4) and the first main measuring contact (2) is the same as the distance between the first main measuring contact (2) and the second main measuring contact (3).

3. Power semiconductor module with a power current path (17) according to claim 1 or 2, characterized in that the auxiliary measuring contact (4) is formed by means of an electrical bridge (5) from the second main measuring contact (3).

4. Power semiconductor module with a power current path (17) according to one of the preceding claims, characterized in that the measuring lines (20, 21, 22) run essentially in one plane.

5. Power semiconductor module with a power current path (17) according to one of the preceding claims, characterized characterized in that the measuring lines (20, 21, 22) are laid parallel to and adjacent to the evaluation unit (6).

6. Power semiconductor module with a power current path (17) according to one of the preceding claims, characterized in that the evaluation unit (6) has at least two operational amplifiers (9, 10) and a summation circuit.

7. Power converter of a drive unit, with at least one power semiconductor module according to one of the preceding claims 1 to 6.

8. A method for interference-insensitive current detection in a power semiconductor module with a power current path (17) in which a shunt resistor (1), in particular a resistance <50 mOhm, is arranged, wherein the shunt resistor (1) has two spaced-apart main measuring contacts (2, 3) of different polarity (+, -) and an auxiliary measuring contact (4) is arranged in the immediate vicinity of the shunt resistor (1) without being in direct electrical connection with it, wherein a measuring line (20, 21, 22) leads from each measuring contact (2, 3, 4) to an evaluation unit (6) and forms loops (18, 19) with almost identical areas, so that three measuring lines (20, 21, 22) are present, which form two symmetrical loops (18, 19) with respect to one another, so that interference coupling at the inputs of the evaluation unit (6) causes an interference voltage with a different direction, by the following steps: - Recording of the measuring signals at the measuring contacts (2,3,4), - the measuring signals are provided to an evaluation unit (6) via measuring lines (20, 21, 22), - within the evaluation unit (6) via operational amplifiers (9, 10) and analog summation of the two outputs of the operational amplifiers (9, 10), in particular by means of a resistance circuit generates a cleaned measuring signal (useful signal) which is fed to an A / D converter (12) for further processing in a control system, in particular drive control.

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