BATTERY SIMULATOR HAVING COMPENSATION IMPEDANCE

Abstract

The invention relates to a device for testing, in particular high-frequency testing, a test item, for example an electrical machine or a converter, comprising:

a simulation unit for simulating an electrical energy accumulator using a simulation model; and

an electrical connection line, via which the test item can be connected to the simulation unit; wherein the device comprises compensation impedance for compensating for an impedance in accordance with a line inductance of the connection line.

Claims

1. A device for the testing, of a test item comprising: a simulation unit for simulation of an electrical energy storage with the aid of a simulation model, and an electrical connecting line, by way of which the test item can be connected to the simulation unit, wherein, the device has a compensation impedance for compensation of an impedance resulting from a line inductance of the connecting line wherein, the compensation impedence is arranged such that, in a connected state of the test item, the compensation impedance is electrically arranged in parallel with the test item.

2. (canceled)

3. The device according to claim 1, wherein, the compensation impedance is arranged at an end of the connecting line facing towards the test item.

4. The device according to claim 1, wherein, the compensation impedance has an ohmic compensation resistor and a compensation capacitor.

5. The device according to claim 4, wherein, an adjustable resistor is provided as the compensation resistor, and/or, an adjustable capacitor is provided as the compensation capacitor.

6. The device according to claim 4, wherein, the compensation impedance adapts a source impedance, which source impedance is formed from a line impedance of the connecting line and an impedance of the simulation unit, such that the source impedance corresponds to a specified ohmic resistance.

7. The device (1) according to claim 6, wherein, the value of the compensation resistor essentially corresponds to the value of the specified resistance.

8. The device according to claim 7, wherein, the impedance of the simulation unit corresponds to an ohmic internal resistance, dimensioned according to the formula R.sub.I=R.sub.S−R.sub.L,wherein R.sub.S denotes the specified ohmic resistance, and R.sub.L denotes an ohmic line resistance of the connecting line.

9. The device according to one of the claim 4, wherein, the compensation capacitor is dimensioned according to the formula C.sub.P=L.sub.I/(R.sub.P.sup.2), wherein L.sub.L denotes a line inductance of the connecting line, and R.sub.P denotes the compensation resistor.

10. A method for the testing of a test item, in which the test item is connected to a simulation unit by way of an electrical connecting line, wherein the simulation unit simulates an electrical energy storage with the aid of a simulation model, wherein, a compensation impedance is used to compensate for an impedance, resulting from a line inductance of the connecting line, wherein the compensation impedance is electrically arranged in parallel with the test item.

11. The device according to claim 1, wherein the testing is a high frequency testing.

12. The device according to claim 1, wherein the test item is an electrical machine or a converter.

13. The device according to claim 3, wherein the compensation impedance is arranged between the end of the connecting line facing towards the test item, and the test item.

14. The device according to claim 3, wherein the compensation impedance is arranged in a connecting unit.

15. The device according to claim 4, wherein the compensation resistor and the compensation capacitor are electrically connected in series.

16. The method according to claim 10, wherein the testing is a high frequency testing.

17. The method according to claim 10, wherein the test item is an electrical machine or a converter.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0030] In what follows, the invention is described in more detail on the basis of figures, although there is no intention that the invention should be limited to these.

[0031] FIG. 1 shows a simplified representation of the device in accordance with the invention, with a test item connected to the device.

[0032] FIG. 2 shows an equivalent circuit diagram of the device in accordance with the invention, with a test item connected to the device.

[0033] FIG. 3 shows an amplitude response of the source impedance without compensation, and the amplitude response of the impedance of the simulation unit.

[0034] FIG. 4 shows an equivalent circuit diagram of the device in accordance with the invention, with a test item connected to the device, and a compensation impedance Z.sub.K.

DETAILED DESCRIPTION

[0035] FIG. 1 shows a simplified representation of the device 1 in accordance with the invention, to which is connected a test item 2 in the form of an electric drive unit. The device 1 has a simulation unit 3 for the simulation of an electrical energy storage, for example a battery or an accumulator, and an electrical connecting line 4, at the end of which is located a connecting unit 5, with a plug and/or coupling unit 6. However, screw terminals can also be provided on the connecting unit 5. The plug and/or coupling unit 6 is connected to the test item 2, and establishes an electrical connection between the test item 2 and the simulation unit 3.

[0036] The simulation unit 3 can be formed by a computer or a microprocessor, and can provide a current and a voltage in accordance with a simulation model by way of an output 7. Current and voltage are transferred to the test item 2 by way of the connecting line 4. The simulation unit 3 thus essentially corresponds to a feedforward controllable voltage source.

[0037] Such simulation units 3 are also called battery simulators or battery emulators, and enable the simulation of the operation of a test item 2 on an energy storage. With the aid of a simulation model, various operating points of an energy storage can be simulated, without the need to use a real energy storage. The use of a real energy storage would represent an enormous effort, as it would first have to be brought up to the desired operating point (temperature, charge, etc.). For this reason, simulation units 3 have become established for test purposes.

[0038] In many cases, modern electrical drive units are operated on fast-switching converters, that is to say, at high (fundamental) frequencies of current and voltage. However, what is problematic is that, especially at high frequencies, the voltage provided to the test item 2 sometimes deviates massively from the voltage at the output 7 of the simulation unit 3 as specified by the simulation model.

[0039] The following cause of this problem has been identified, and this will be illustrated by means of FIGS. 2 and 3.

[0040] FIG. 2 shows an equivalent circuit diagram of the device 1 in accordance with the invention, with a test item 2 connected to the device 1. The connecting line 4 essentially has a resistance per unit length and an inductance per unit length, which are shown in FIG. 2 as concentrated components R.sub.L and L.sub.L. R.sub.L denotes the line resistance, and L.sub.L denotes the line inductance, of the connecting line 4. Any capacitance per unit length is neglected in the further visualisation because of its minor influence. The actual values of the components R.sub.L and L.sub.L depend on the geometry of the connecting line 5. The anticipated value of the line resistance R.sub.L lies in the range of a few mΩ, while the anticipated value of the line inductance L.sub.L lies in the range of a few μH. Together the line resistance R.sub.L and the line inductance L.sub.L (neglecting any capacitive component) form a line impedance Z.sub.L. The simulation unit 3 is represented as a voltage source 8, and has an impedance Z.sub.S (shown by a dashed line), which ensues from the simulation model used, that is to say, is specified by the latter.

[0041] The resistance per unit length and the inductance per unit length now have an effect on the impedance of the device 1 that the test item “sees”. This impedance is called the source impedance Z.sub.Q, and to begin with is essentially composed of the impedance Z.sub.S of the simulation unit 3 and the line impedance Z.sub.L. By virtue of the resistance per unit length and the inductance per unit length, the source impedance Z.sub.Q “seen” by the test item deviates from the impedance Z.sub.S of the simulation unit 3, especially at frequencies >300 Hz. This can be seen in FIG. 3, which shows the amplitude response in dB of the source impedance Z.sub.Q as presented to the test item 2 (dashed line), and the amplitude response of the impedance Z.sub.S of the simulation unit 3 (solid line). Two phenomena can be observed here:

[0042] At low frequencies, the source impedance Z.sub.Q is slightly increased. This is caused by the line resistance R.sub.L,which is essentially constant over all frequencies.

[0043] 2) At high frequencies, the source impedance Z.sub.Q increases sharply. This is denoted as a high-frequency separation between the simulation unit 3 and the test item 2, and is primarily caused by the line inductance L.sub.L.

[0044] The increase of the source impedance Z.sub.Q caused by the line inductance L.sub.L cannot be corrected by alterations to the simulation model. It would be desirable if the source impedance Z.sub.Q as presented to the test item were to correspond to the impedance Z.sub.S of the simulation unit. In other words, the influence of the connecting line 4 should be eliminated, and the source impedance Z.sub.Q should correspond to a specified value, for example a general impedance, or the impedance Z.sub.S of the simulation unit 3. For this purpose, the impedance Z.sub.S of the simulation unit 3 is subsequently also adapted, that is to say, altered, which is why, if the source impedance Z.sub.Q is to correspond to the impedance Z.sub.S of the simulation unit 3, one also talks about the original impedance Z.sub.S of the simulation unit 3.

[0045] In accordance with the invention, a compensation impedance Z.sub.K is provided for the adaptation of the source impedance Z.sub.Q. With the aid of the compensation impedance Z.sub.K, the source impedance Z.sub.Q as presented to the test item 2 can be adapted, that is to say, altered. This will be explained with reference to FIG. 4.

[0046] FIG. 4 again shows an equivalent circuit diagram of the device 1 in accordance with the invention, with a connected test item 2. In accordance with the invention, however, the compensation impedance Z.sub.K is provided in the connecting unit 5. This consists of a compensation capacitor C.sub.P and an ohmic compensation resistor R.sub.P. The compensation capacitor C.sub.P and the compensation resistor R.sub.P are electrically connected in series. The compensation impedance Z.sub.K is electrically connected in parallel with the test item 2. In order to be able to make adaptations in a simple manner, the compensation capacitor C.sub.P and/or the compensation resistor R.sub.P can be designed to be adjustable.

[0047] The source impedance Z.sub.Q, formed from the point of view of the test item 2, is calculated from the parallel connection of the compensation impedance Z.sub.K and the series connection made up from the line impedance Z.sub.L and the impedance Z.sub.S of the simulation unit 3:

[00001]$\begin{array}{cc}{Z}_Q\left(s\right)=\frac{\left(Z_S\left(s\right)+R_L+s{L}_L\right)\left(R_P+\frac{1}{s{C}_P}\right)}{Z_S\left(s\right)+R_L+s{L}_L+R_P+\frac{1}{s{C}_P}}& \left(\mathrm{Equation}1\right)\end{array}$

[0048] Here the variable “s” corresponds to what is in general the complex Laplace variable of the Laplace transformation. To make it clear that the impedances Z.sub.Q and Z.sub.S can in general take the form of frequency-dependent impedances, the variable (s) has been added to these impedances in the equations. If the source impedance Z.sub.Q is to correspond to a specified value Z.sub.SOLL, the following must apply:

[00002]$\begin{array}{cc}{Z}_{SOLL}\left(s\right)=Z_Q\left(s\right)=\frac{\left(Z_S\left(s\right)+R_L+s{L}_L\right)\left(R_P+\frac{1}{s{C}_P}\right)}{Z_S\left(s\right)+R_L+s{L}_L+R_P+\frac{1}{s{C}_P}}.& \left(\mathrm{Equation}2\right)\end{array}$

[0049] Equation 2 can be transformed into

[00003]$\begin{array}{cc}{Z}_S\left(s\right)=\frac{\begin{array}{c}{Z}_{\mathrm{SOLL}}\left(s\right)\left[s^2{L}_L{C}_P+s\left(R_L+R_p\right)C_P+1\right]-\\ \left[s^2{L}_L{R}_P{C}_P+s\left(R_L{R}_P{C}_P+L_L\right)+R_L\right]\end{array}}{s\left(R_P-Z_{\mathrm{SOLL}}\left(s\right)\right)C_P+1}& \left(\mathrm{Equation}3\right)\end{array}$

[0050] and indicates how the impedance Z.sub.S of the simulation unit 3 must be selected for a given source impedance Z.sub.Q =Z.sub.SOLL. Here Equation 3 applies quite generally for the impedance Z.sub.S of the simulation unit 3.

[0051] Simply stated, provision must now be made for the source impedance Z.sub.Q to correspond to a constant specified ohmic resistance Z.sub.SOLL=R.sub.S. The specified resistance R.sub.S can be, for example, the value that the simulation model would have provided for the test item 2, but which would have been falsified by virtue of the connecting line 4. With this in mind, Equation 3 can be transformed as follows:

[00004]$\begin{array}{cc}{Z}_S\left(s\right)=\frac{\begin{array}{c}{s}^2\left(R_S-R_P\right)L_L{C}_P+\\ s\left[\left(R_S-R_P\right)R_L{C}_P+R_S{R}_P{C}_P-L_L\right]+\left(R_S-R_L\right)\end{array}}{s\left(R_P-R_S\right)C_P+1}.& \left(\mathrm{Equation}4\right)\end{array}$

[0052] By virtue of the higher degree numerator (see the Laplace variable s) in Equation 4, one is dealing here with an impedance Z.sub.S that cannot be implemented. If now R.sub.P is chosen to be equal to R.sub.S, one obtains

Z.sub.S(s)=s(R.sub.SR.sub.PC.sub.P−L.sub.L)+(R.sub.S−R.sub.L),   (Equation 5)

[0053] which, however, is still an impedance that cannot be implemented.

[0054] By means of the selection

[00005]$\begin{array}{cc}{C}_P=\frac{L_L}{R_S{R}_P}=\frac{L_L}{R_P^2}& \left(\mathrm{Equation}6\right)\end{array}$

[0055] Equation 5 advantageously simplifies to

Z.sub.S(s)=(R.sub.S−R.sub.L).   (Equation 7)

[0056] This at last represents an impedance Z.sub.S of the simulation unit 3 that can be implemented, and which corresponds to a frequency-independent, ohmic resistance. The impedance Z.sub.S of the simulation unit in Equation 6 corresponds to the specified resistance R.sub.S reduced by the line resistance R.sub.L. By the above selection of the parameters R.sub.P and C.sub.P, the influence of the line inductance can therefore be eliminated, and there ensues an ohmic resistance value of the impedance Z.sub.S of the simulation unit 3 that is particularly easy to form. By the subtraction of R.sub.L from R.sub.S, compensation is made for the ohmic line resistance R.sub.L.

[0057] The above assumptions and results serve as an example of embodiment, and can be summarised and interpreted as follows: in order to alter the source impedance Z.sub.Q of the device as presented to the test item 2, such that it corresponds to a predetermined ohmic resistance value R.sub.S, it is opportune if the impedance Z.sub.S of the simulation unit 3 corresponds to the resistance value R.sub.S−R.sub.L. In other words: the impedance Z.sub.S of the simulation unit should correspond to the specified resistance R.sub.S, reduced by the line resistance R.sub.L. Furthermore, the capacitance of the compensation capacitance C.sub.P should be selected in accordance with Equation 6, and the compensation resistance R.sub.P should correspond to the specified resistance R.sub.S.