DE102020106447B4 - Arrangement for current measurement - Google Patents

Abstract

Arrangement (1) for current measurement, in which a shunt resistor (7a, 7b, 7c) is arranged in a current path in which a current is measured, characterized in that at least a first partial shunt resistor (10) and a second partial shunt resistor (11) in are arranged in a series circuit, the partial shunt resistors (10, 11) being arranged together on one side of a printed circuit board (9) or on different, opposite sides of the printed circuit board (9), the partial shunt resistors (10, 11) having longitudinal axes (12) are arranged parallel to and at a distance from one another, and between a first soldering pad (17), which is connected to a first connection surface (13) of the first partial shunt resistor (10), and a second soldering pad (19), which is connected to a second connection surface (16) of the second partial shunt resistor (11) is connected, and a measuring amplifier (22) measuring lines (21) are arranged.

Description

The invention relates to an arrangement for current measurement, in which a shunt resistor is arranged in a current path in which a current is measured.

In many areas of technology, it is necessary to measure currents in lines, for example to make statements about these currents or to be able to control machines or electrical systems according to their requirements.
In particular in areas in which high currents, for example up to the order of magnitude of 20 A or more, are to be measured, the demands on such arrangements for current measurement are correspondingly high. On the one hand, the current flowing in a current path should not be influenced by the arrangement for current measurement and, on the other hand, the measurement should have a high level of accuracy.

Current measurements of this type are also carried out in vehicles, for example, this being necessary for the proper operation of assemblies on the one hand and corresponding statements being made, for example on the range of an electric vehicle or hybrid vehicle, on the other hand.

Methods for current detection are known from the prior art, in which at least one so-called shunt resistor R _shunt is used to measure a voltage U _shunt across the shunt resistor R _shunt and subsequently to calculate a current I _shunt therefrom. Such a current detection takes place, for example, in an inverter.

Inverters, also referred to as inverters, are required, for example, to convert a DC voltage on the input side into an AC voltage on the output side. Inverters of this type are used, among other things, to drive electric motors, particularly in motor vehicles with vehicle electrical system voltages of 48 V or more than 60 V. The electric motor can be used, for example, in an electric refrigerant compressor of an air conditioning system of a motor vehicle.

In order to control a three-phase electric motor controlled by an inverter, such as a motor of the electric refrigerant compressor, a current detection in at least two motor phases is required. A third phase can be determined by calculation. A known method for such a current measurement is a measurement of the currents of the three motor phases via a shunt resistor each. In this case, by means of so-called half-bridges of an inverter using a shunt resistor for each half-bridge, certain currents can be mathematically deduced from the currents in the individual motor phases.
The term shunt resistor refers to a low-impedance electrical measuring resistor or current measuring resistor, which is inserted directly into the current-carrying line.

The current I _shunt flowing through a shunt resistor R _shunt generates a voltage drop U _shunt at the shunt resistor, which is amplified and measured by means of a measuring amplifier, for example. Both analog and digital measurement technology can be used to record the voltage drop U _shunt . There is also the option of subsequently converting an analog measured value into a digital measured value. Such a digital measured value, for example, can be recorded via a central control unit, which among other things also controls the inverter, and the current I _{shunt 1} , I _shunt2 , I _{shunt 3} per motor phase of the inverter can be determined in this way. The currents I _{shunt 1} , I _{shunt 2} , I _{shunt 3} are used to control the drive of the motor by the inverter.

Since high currents, for example in a range of up to approximately 100 A, flow through such shunt resistors when used to detect a current in an inverter, the shunt resistor also inevitably heats up. In order to ensure that the current measuring arrangements function properly, the shunt resistor must be dimensioned with a correspondingly high performance. In addition, measures must be taken to dissipate the heat generated in the area of the shunt resistor. All of this leads to higher costs for a shunt resistor and the additional means to be designed for heat dissipation.

One way to reduce the amount of heat generated is to decrease the resistance of the shunt resistor. In this case, however, the voltage drop U _shunt measured across the shunt resistor also decreases, so that interference, such as what is known as noise, leads to greater measurement errors or less accuracy in the current detection.

A further problem of the known state of the art is the so-called interference immunity in the case of current detection. Electrical assemblies which are temporarily or permanently located in the vicinity of such a current measuring arrangement cause interference signals. The interference signals occur due to unwanted capacitive, inductive or galvanic coupling on the lines or the shunt resistor itself and affect the useful signal the current detection. Appropriate measures must be taken to reduce the occurrence of interference signals.

The state of the art known for this is, for example, in the book "EMV - Störfallsicherer Bauelektronischer Schaltung" by Joachim Franz; 5th edition; Springer Vieweg; ISBN978-3-8348-1781-5. Pages 43, 48 and 55 in particular are named here.

In the DE 10 2016 113 159 B4 discloses a circuit arrangement for detecting a current flowing through a current path of a motor drive device for a three-phase AC motor.

From the DE 10 2014 103 343 B4 disclose a multiple current sensing device and multiple current shunting device and method for providing a multiple current shunting device and multiple current sensing device, respectively.

Based on the prior art, there is a need for an improved current measurement arrangement.

The object of the invention is now to specify an arrangement for current measurement, which is inexpensive and easy to manufacture, has a high level of robustness against interference signals and enables improved heat dissipation. In addition, the arrangement for current measurement should be able to use only standard components.

The object is achieved by an object having the features according to patent claim 1 of the patent claims. Further developments are specified in the dependent patent claims.

The object is achieved by an arrangement for current measurement according to the invention, in which a shunt resistor is arranged in a flow path in which a current is measured. The shunt resistor is formed from at least two partial shunt resistors, it being possible for the two partial shunt resistors to have the same resistance value. According to a special embodiment of the invention, a partial shunt resistor has half the resistance value of the shunt resistor required for the current measurement.

According to the concept of the invention, the at least two partial shunt resistors are arranged in a series circuit, together on one side of a printed circuit board or on different, opposite sides of the printed circuit board and with longitudinal axes parallel and spaced apart from one another. Measuring lines are formed between a first soldering pad, which is connected to a first connection surface of a first partial shunt resistor, and a second soldering pad, which is connected to a second connection surface of a second partial shunt resistance, and a measuring amplifier.

According to a development of the invention, the at least two partial shunt resistors are arranged in a meandering manner, with the partial shunt resistors being arranged parallel and at a small distance from one another, in particular on the printed circuit board. The parallel arrangement of the at least two partial shunt resistors means that the cuboid or cylindrical partial shunt resistors are aligned parallel to one another with a longitudinal axis that extends in the direction of the greatest extent.

According to an advantageous embodiment of the invention, in the case of two partial shunt resistors arranged in parallel or in a meandering pattern, both partial shunt resistors are electrically conductively connected to one another at one end. In this case, for example, a soldering pad is formed on a printed circuit board, with which both partial shunt resistors are soldered at the respective first ends. The respective second ends of the two partial shunt resistors are preferably soldered to separate soldering pads which are electrically separate from one another and which produce the connections to the current path in which the current I _shunt is to be measured. This results in a meandering arrangement of the two partial shunt resistors with respect to the path to be covered by the current to be measured.

The partial shunt resistors are preferably in the form of SMD components, or surface-mounted devices for short, which have no connecting wires and are soldered directly onto the printed circuit board by means of solderable connecting surfaces. In this case, the connection surfaces are soldered onto soldering pads or contact surfaces arranged on the printed circuit board. This technique is also known as surface mounting.

According to an advantageous embodiment of the invention, the parallel or meandering partial shunt resistors are arranged on a first side or a first surface of the printed circuit board.

Alternatively, the partial shunt resistors arranged in parallel or in a meandering pattern can be provided on two opposite sides of the printed circuit board. In this case, one or more vias are formed to produce an electrically conductive connection of the respective first ends of the partial shunt resistors, which, for example, connect corresponding soldering pads to which the respective first ends of the partial shunt resistors are soldered.

Irrespective of the arrangement of the partial shunt resistors on one or both sides of the printed circuit board, it is provided that one soldering pad in a one-sided arrangement or the two opposite soldering pads in a two-sided arrangement of the partial shunt resistors are made larger than is necessary for contacting, in order to reach the common connection point of the first Ends of the partial shunt resistors to allow or improve heat dissipation from the partial shunt resistors. A surface is provided via the correspondingly large-area soldering pad or the two opposing soldering pads of correspondingly large-area design, via which heat transferred from the partial shunt resistors to the soldering pad or the soldering pads can be emitted to the environment. This improves the heat dissipation of the shunt resistor, which consists of at least two partial shunt resistors.

The improvement in heat dissipation leads to a reduced thermal load on the components and enables a selection of elements with lower thermal requirements or reduced power loss, which greatly reduces the costs of the required elements.

The soldering pads connected to the respective second ends of the partial shunt resistors can also be made larger than is necessary for contacting, in order to provide a further possibility for improved heat dissipation from the partial shunt resistors.

A further advantage of the parallel or meandering arrangement of the partial shunt resistors is that the inductance of such an arrangement, in particular of the shunt resistor, is reduced. By arranging the partial shunt resistors in a small space on one side or both sides of the printed circuit board, the smallest possible magnetically effective area is spanned or an antenna effect of the arrangement is reduced. This reduces the effect of interference fields or interference from other assemblies, since this effect is always related to the antenna effect of the arrangement. The sensitivity to interference of the parallel or meandering arrangement of the partial shunt resistors is reduced, while the robustness of the arrangement for current measurement is increased.
The lower inductance of the arrangement for current measurement also leads to an advantageous reduction in the interference signals emanating from the arrangement.

Furthermore, the measuring lines can be placed as connecting lines between the corresponding soldering pads and a measuring amplifier for amplifying the voltage U _shunt to be measured across the partial shunt resistors at a small distance from one another on the printed circuit board, since the soldering pads of the respective second ends of the partial shunt resistors are arranged closely adjacent to one another be able. The soldering pads can be arranged closely adjacent to one another both on one side of the printed circuit board and on the opposite sides of the printed circuit board. In the latter case, the minimum distance between the soldering pads is determined by the material thickness of the printed circuit board.

The arrangement of the measuring taps at a very small distance from one another, in conjunction with short measuring lines between the soldering pads and the measuring amplifier, also reduces the magnetically effective area or the antenna effect and leads to improved interference immunity.

Overall, the improvement in the interference immunity of the arrangement for current measurement leads to an improvement in the accuracy when measuring the current I _shunt . In this way, such an arrangement for current measurement can be used in areas in which there are high demands with regard to the accuracy of the current measurement and the robustness.

• 1: einen Wechselrichter aus dem Stand der Technik,
• 2: eine erfindungsgemäße Anordnung zur Strommessung in einer ersten Ausführungsform,
• 3: eine weitere erfindungsgemäße Anordnung zur Strommessung in einer zweiten Ausführungsform und
• 4: eine Darstellung von Lötpads und Messleitungen der erfindungsgemäßen Anordnung.

Further details, features and advantages of embodiments of the invention result from the following description of exemplary embodiments with reference to the associated drawings. Show it:

• 1 : a prior art inverter,
• 2 : an arrangement according to the invention for current measurement in a first embodiment,
• 3 : a further arrangement according to the invention for current measurement in a second embodiment and
• 4 : a representation of soldering pads and measuring lines of the arrangement according to the invention.

The current measurement arrangement according to the invention can be used, for example, to measure the phase currents or the currents I _{shunt 1} , I _{shunt 2} , I _{shunt 3} of motor phases U, V and W in an in 1 Inverter 2 shown as an example are used. A limitation however, the use of the arrangement for current measurement in an inverter does not exist.

A very common circuit arrangement for the controlled activation of electric drives by means of an inverter 2 is in 1 shown with a so-called B6 bridge or B6 bridge circuit.

The B6 bridge comprises three half-bridges 3a, 3b, 3c, each consisting of a high-side power switch 4 and a low-side power switch 5. The power switches 4, 5 or semiconductor power switches are, for example, MOSFETs : Metal-Oxide-Semiconductor Field-Effect Transistor or as IGBT, short for English: Insulated Gate Bipolar Transistor.

A connection of the high-side power switch 4 is connected directly to a connection of the low-side power switch 5 and an output of the half-bridge 3a, 3b, 3c or the inverter 2 within a half-bridge 3a, 3b, 3c. The voltage generated by the half-bridge 3a, 3b, 3c of a phase U, V, W, for example for operating a connected electric motor 6, is output via the output.

To measure the phase currents, phase current measuring shunt resistors or shunt resistors 7a, 7b, 7c are arranged in a series circuit with the half-bridges 3a, 3b, 3c. The first half-bridge 3a is assigned the first shunt resistor 7a, while the second half-bridge 3b is assigned the second shunt resistor 7b and the third half-bridge 3c is assigned the third shunt resistor 7c.

As is known from the prior art, the respective phase currents i _ph1 , i _ph2 , i _ph3 which in 1 shown currents I _{shunt 1} , I _{shunt 2} , I _{shunt 3} correspond, determined by means of the voltage drop across the respective shunt resistor 7a, 7b, 7c. For this purpose, a measuring amplifier 8a, 8b, 8c is arranged across the shunt resistor 7a, 7b, 7c to detect the voltages. On the basis of the voltages determined in this way and the known size of the respective shunt resistor 7a, 7b, 7c, Ohm's law is used and the respective phase current i _ph1 , i _ph2 , i _ph3 or the currents I _{shunt 1} , I _shunt2 , I _shunt3 calculated. The calculation can already take place in the measuring amplifiers 8a, 8b, 8c if they are equipped with the appropriate logic. This means that values for the currents I _{shunt 1} , I _{shunt 2} , I _{shunt 3 can already be} output by the measuring amplifiers 8a, 8b, 8c at the respective output of the measuring amplifiers 8a, 8b, 8c, for example in digital form, by means of which a 1 central control unit, not shown, controls the inverter 2. Alternatively, the signals at the outputs of the measuring amplifiers 8a, 8b, 8c are fed to a corresponding processing unit, which is 1 is also not shown.

A unit consisting of the shunt resistor 7a, 7b, 7c and the associated measuring amplifier 8a, 8b, 8c is referred to as an arrangement 1' for current measurement according to the prior art, as is shown in 1 is shown as an example with the shunt resistor 7c and the associated measuring amplifier 8c as an arrangement 1'. In the design of the arrangement 1' for current measurement according to the prior art, the disadvantages already described above occur, which are overcome by the present invention.

In 2 an arrangement 1 according to the invention for current measurement is shown in a first embodiment. A first partial shunt resistor 10 and a second partial shunt resistor 11 are arranged on a first side of a printed circuit board (not shown). In this case, the first partial shunt resistor 10 and the second partial shunt resistor 11 are aligned with the longitudinal axes 12 parallel to one another. In one embodiment, the partial shunt resistors 10, 11 have the same resistance value and thus each have half the resistance value of the shunt resistor required for the current measurement. However, such an equal division of the resistance value is not mandatory.

According to the embodiment of the arrangement 1 after 2 the two partial shunt resistors 10, 11 are designed as SMD components, which have corresponding solderable connection surfaces for contacting. The first partial shunt resistor 10 is electrically conductively connected or soldered to a first connection surface 13 with a first soldering pad 17 .

Such a soldering pad provides a soldering surface which creates a connection between a component, such as a partial shunt resistor 10, 11, and a conductor track on the printed circuit board 9.

The first partial shunt resistor 10 is electrically conductively connected or soldered to a second terminal surface 14 with a common soldering pad 18 to which a first terminal surface 15 of the second partial shunt resistor 11 is also soldered. A second connection surface 16 of the second partial shunt resistor 11 is connected to a second soldering pad 19 .

The first soldering pad 17 and the second soldering pad 19 establish the connections of the arrangement 1 for current measurement in the current path, in which the current should be measured as the in 1 shown current I _shunt3 .

As in 2 As shown, the common solder pad 18 is dimensioned with appropriate dimensions to maximize the dissipation of the heat generated in the partial shunt resistors 10,11. The arrows shown illustrate the heat spread 20 or the heat dissipation 20 from the partial shunt resistors 10, 11.

To measure the voltage U _shunt , which drops across the two partial shunt resistors 10, 11 and is measured to determine the current, the soldering pads 17, 19 are connected to the inputs of a measuring amplifier 22 by means of conductor tracks designed as measuring lines 21. At an output 23 of the measuring amplifier 22, either a value for the current to be measured, such as I _shunt3 , or a signal intended for further processing is output.

Due to the adjacent arrangement of the soldering pads 17, 19, there is the possibility of arranging the measuring lines 21 to the measuring amplifier 22 very closely spaced from one another. In addition, it is possible to place the measuring amplifier 22 very close to the soldering pads 17, 19, so that the length of the measuring lines 21 is minimal. The measures also result in a region 26 spanning a magnetically effective surface, via which disturbances can be coupled, being minimized. The resulting antenna effect is also minimized by means of the arrangement 1 for current measurement and the heat dissipation from the partial shunt resistors 10, 11 is maximized.

In 2 the current flow 24 through the arrangement 1 for current measurement is visualized by dash-dash lines, with a meandering current flow 24 being recognizable, which also supports the concept of a meandering arrangement of the partial shunt resistors 10, 11.

The arrangement 1 is not restricted to two partial shunt resistors 10, 11. Four or more partial shunt resistors could also be arranged, which together provide the value of the shunt resistor required for current measurement. Even if four partial shunt resistors are formed, the partial shunt resistors are preferably arranged with the longitudinal axes aligned parallel to one another.

In 3 a further embodiment of the arrangement 1 for current measurement is shown, in which the two partial shunt resistors 10, 11 are not on a common side of a printed circuit board 9, according to the embodiment of the arrangement 1 according to 2 , but are arranged on two different sides of the printed circuit board 9 .

The first partial shunt resistor 10 is arranged on a first side of the circuit board 9, while the second partial shunt resistor 11 is arranged on a second side of the circuit board 9 opposite the first side. The partial shunt resistors 10, 11 are thus arranged opposite one another with the smallest possible distance from one another. The longitudinal axes 12 of the partial shunt resistors 10, 11 are aligned parallel to one another.

The first partial shunt resistor 10 is electrically conductively connected or soldered to the first connection surface 13 to the first soldering pad 17 and to the second connection surface 14 to a first part of a common soldering pad 18a.

The first connection surface 15 of the second partial shunt resistor 11 is electrically conductively connected to a second part of a common soldering pad 18 b , while the second connection surface 16 of the second partial shunt resistor 11 is electrically conductively connected to a second soldering pad 19 .

A plurality of vias 25 are formed between the first part of the common soldering pad 18a and the second part of the common soldering pad 18b, which electrically conductively connect both parts of the common soldering pad 18a, 18b to one another and thus form a common soldering pad. The vias 25 enable both an electrically conductive and a thermally conductive connection of the parts of the common soldering pad 18a, 18b. The parts of the common soldering pad 18a, 18b are designed to be larger than is necessary for contacting the connection surfaces 14, 15 of the partial shunt resistors 10, 11 in order to maximize the heat dissipation 20, for example.

Also in 3 the meandering current flow 24 through the arrangement 1 for current measurement is visualized by dash-dash lines.

The first soldering pad 17 and the second soldering pad 19 in turn establish the connections of the arrangement 1 for current measurement in the current path in which the current is to be measured, as in 1 shown current I _shunt3 .

Due to the adjacent arrangement of the soldering pads 17, 19, there is the possibility of arranging the measuring lines 21 to the measuring amplifier 22 very closely spaced from one another. In addition, it is possible to 3 to place the measuring amplifier 22, not shown, very close to the soldering pads 17, 19, which results in a minimal length of the measuring lines 21. These measures also lead to how The result is that the area 26 spanning a magnetically effective surface, via which interference can be coupled in, is minimized. The resulting antenna effect is also minimized by means of the arrangement 1 for current measurement and the heat dissipation from the partial shunt resistors 10, 11 is maximized.

Also in the embodiment of the arrangement 1 for current measurement 3 the arrangement 1 can be expanded by a further two or more partial shunt resistors. For example, two partial shunt resistors could be arranged on the first side of the printed circuit board 9 and two partial shunt resistors on the second side of the printed circuit board 9 . In this case, a series connection of the partial shunt resistors arranged parallel to one another is provided, which in total provides the shunt resistor required for current measurement in the current path.

For a better understanding goes out 4 a representation of soldering pads 17, 18, 19 and measuring lines 21 of the arrangement 1 for current measurement without the partial shunt resistors 10, 11 on a surface of the printed circuit board 9, according to the in 2 illustrated embodiment of the arrangement 1 out.

The small distance between the first soldering pad 17 and the second soldering pad 19 and the resulting closely spaced routing of the measuring lines 21 to the measuring amplifier 22 with the output 23 become clear. Both the two soldering pads 17, 19 and the common soldering pad 18 are designed to be larger in the areas than is necessary for contacting the partial shunt resistors 10, 11, in order to maximize heat dissipation 20 in this way.

Reference List

1,

Arrangement for current measurement

2

Inverters / inverters

3a, 3b, 3c

half bridge

4

Circuit breakers, high-side circuit breakers

5

Circuit breaker, low side circuit breaker

6

electric motor

7a, 7b, 7c

shunt resistance

8a, 8b, 8c

measuring amplifier

9

circuit board

10

first partial shunt resistor

11

second partial shunt resistor

12

longitudinal axis

13

first pad first partial shunt resistor

14

second pad first partial shunt resistor

15

first pad second partial shunt resistor

16

second pad second partial shunt resistor

17

first solder pad, solder surface

18, 18a, 18b

common solder pad

19

second solder pad, solder surface

20

Heat spread, heat dissipation

21

Measurement line

22

measuring amplifier

23

Exit

24

current flow

25

via

26

area

Claims (8)

Arrangement (1) for current measurement, in which a shunt resistor (7a, 7b, 7c) is arranged in a current path in which a current is measured, characterized in that at least a first partial shunt resistor (10) and a second partial shunt resistor (11) in are arranged in a series circuit, the partial shunt resistors (10, 11) being arranged together on one side of a printed circuit board (9) or on different, opposite sides of the printed circuit board (9), the partial shunt resistors (10, 11) having longitudinal axes (12) are arranged parallel to and at a distance from one another, and between a first soldering pad (17), which is connected to a first connection surface (13) of the first partial shunt resistor (10), and a second soldering pad (19), which is connected to a second connection surface (16) of the second partial shunt resistor (11) is connected, and a measuring amplifier (22) measuring lines (21) are arranged. Arrangement (1) according to claim 1 , characterized in that the partial shunt resistors (10, 11) have the same resistance values. Arrangement (1) according to claim 1 or 2 , characterized in that the first partial shunt resistor (10) is electrically conductively connected to a first connection surface (13) to the first soldering pad (17) and to a second connection surface (14) to a common soldering pad (18), and that the second partial shunt resistance (11) with a first connection surface (15) is electrically conductively connected to the common soldering pad (18) and a second connection surface (16) to the second soldering pad (19). Arrangement (1) according to claim 1 or 2 , characterized in that the first partial shunt resistor (10) is electrically conductively connected to a first connection surface (13) to a first soldering pad (17) and to a second connection surface (14) to a first part of a common soldering pad (18a), and that the second partial shunt resistor (11) is electrically conductively connected to a first connection surface (15) to a second part of a common soldering pad (18b) and to a second connection surface (16) to a second soldering pad (19). Arrangement (1) according to claim 4 , characterized in that vias (25) are arranged between the first part of the common soldering pad (18a) and the second part of the common soldering pad (18b). Arrangement (1) according to one of Claims 1 until 5 , characterized in that the measuring amplifier (22) has an output (23) via which a measured value for the current to be measured is output. Arrangement (1) according to one of Claims 1 until 6 , characterized in that an arrangement for analog-to-digital conversion is arranged in the measuring amplifier (22). Arrangement (1) according to one of Claims 1 until 7 , characterized in that the partial shunt resistors (10, 11) are designed as SMD components.

Images