WO2016079296A1

WO2016079296A1 - Circuit for limiting common-mode voltages

Info

Publication number: WO2016079296A1
Application number: PCT/EP2015/077214
Authority: WO
Inventors: Gerhard Müller
Original assignee: Avl List Gmbh
Priority date: 2014-11-21
Filing date: 2015-11-20
Publication date: 2016-05-26
Also published as: AT514765A2; AT514765A3; AT514765B1

Abstract

The invention relates to a circuit for reducing common-mode voltages in indirect converter systems having a d.c. voltage intermediate circuit (1) for rotary current or three-phase alternating current motors (10), wherein the d.c. voltage intermediate circuit (1) has a first diode (3) having a pass direction and a series-connected second diode (4) having the same pass direction as the first diode (3), by means of the two series-connected diodes (3, 4) a negative string (5) of the d.c. voltage circuit (1) is connected to a positive string (6) of the d.c. voltage intermediate circuit (1) and a point (7) between the first diode (3) and the second diode (4) is connected to earth (9) by means of at least one capacitor (8).

Description

Circuit for limiting common-mode voltages

The present invention relates to a circuit for limiting common-mode voltages in indirect converter systems with direct voltage intermediate circuit for three-phase AC or three-phase AC machines. In the field of three-phase or three-phase AC machines is the

Use of converters which generate an alternating voltage different in frequency and amplitude, other AC voltage widely known.

As is known, these converter systems consist of a network converter and a machine converter with a DC intermediate circuit therebetween. The power converter is usually preceded by a so-called Hochsetzerdrossel. These are inductors that are used for attenuation, radio interference suppression, commutation, current limitation, suppression of unwanted frequencies or energy storage. Basically, the switching processes in the line converter and in the machine converter lead to voltage jumps in the DC link to ground. Due to the inductance of the boost converter choke and the capacitance to earth, which are mainly found in the shielded motor supply lines and the motor winding, a parasitic oscillating circuit is created by the switching operations of the power converter and the machine converter.

Since resulting interference voltages are "passed" through the machine converter to the motor, between motor windings and ground

Common-mode voltages occur. Depending on their height, this damage can be

Motor windings and winding temperature sensors cause.

To reduce the common-mode voltages, DE 10 2007 008 765 A1 shows the use of an inductive-capacitive filter between the converter output and the motor winding. The feedback occurs via a line with damping resistor which leads to the star point of three capacitors, which are connected to the input terminals of the inverter. The circuit also sees additional capacitors on the

Output connections of the inverter before. The disadvantage is that the filter shown is not limited beyond a certain limit and thus only occasionally active, but is activated for reduction throughout the operation, creating a corresponding power loss during the entire operation.

Furthermore, the space required for the components leads to a correspondingly large

Cabinet design and is poorly suited for retrofitting. The object of the present invention is therefore to limit the

Common mode voltage with low space requirement and easy retrofitting to

enable.

The object is achieved according to the invention in that the DC intermediate circuit has a first diode with a forward direction and a second diode connected in series with the same forward direction as the first diode, that via the two series connected diodes a negative leg of the DC circuit with a positive leg of DC intermediate circuit is connected and that a point between the first diode and second diode is connected via at least one capacitor to the ground. In fact, this only allows a limit on those who exceed the limit

Common-mode voltages, which fall between positive strand of the DC intermediate circuit and ground or negative strand of the DC intermediate circuit and ground. The upper or lower limit, which are determined by the dimensioning of the two diodes, thereby represents the positive or negative value of

DC link voltage is.

As is known, a diode has an n-doped region as the cathode and a p-doped region as the anode. The forward direction is an interconnection in which the anode is connected to the positive potential and the cathode is connected to the negative potential. Advantageously, an anode of the first diode with the negative strand and a cathode of the second diode are connected to the positive leg of the DC intermediate circuit. The two diodes connected in series are thus operated in the reverse direction.

An advantageous embodiment provides that in front of the DC voltage intermediate circuit, each of the three phases of a three-phase network present on the input side of the converter system is connected to the ground via in each case at least one feedback capacitor.

As a result, the circuit according to the invention can also be used for known TT (Terre Terre) and IT (Isole Terre) networks, with TN (Terre Neutre) networks also being used

electromagnetic compatibility is improved. In TT networks, a transformer node is connected via the ground to a system ground and thus to the ground of the inverter. For IT networks, no common ground is provided. In TN systems, in contrast to TT and IT systems, common earthing is provided at which the star point of the transformer and the inverter are connected via the PE cable (earthing conductor provided for earthing). The subject invention will be explained in more detail with reference to Figures 1 to 4, which shows an exemplary, schematic and not limiting an advantageous embodiment of the invention. It shows

A section of an indirect converter system with

DC intermediate circuit according to the prior art,

Fig.2 Voltage curves in the DC voltage intermediate circuit in a positive voltage jump,

3 shows voltage profiles in the DC voltage intermediate circuit in the case of a negative voltage jump, FIG. 4 shows a section from an indirect converter system with FIG

DC voltage intermediate circuit with the common mode filter according to the invention.

Figure 1 shows an indirect converter with DC voltage in the intermediate circuit, consisting of a three-phase rectifier or the power converter 1 1, a

DC voltage intermediate circuit 1 and an output-side inverter or the machine converter 12. The advantage of the indirect converter consists in a substantial decoupling of the output from the input via the DC voltage intermediate circuit first

The DC voltage intermediate circuit 1 is thus in a known manner between the

input side three-phase rectifier or the network converter 1 1 and the

output side inverter or the machine converter 12 is arranged. Such converter systems find to drive a three-phase or

Three-phase AC machine 10 multiple use. The illustrated

DC link capacitor 13, which connects the negative strand 5 to the positive strand 6 of the DC intermediate circuit 1, is known to be used for energetic coupling to a common DC voltage level or for smoothing the

DC voltage in the DC intermediate circuit.

Figure 2 shows a voltage waveform in the DC voltage intermediate circuit 1 at a positive voltage jump. Such voltage jumps arise, as already mentioned, by the switching operations of power converter 1 1 and / or machine inverter 12th

Figure 3 shows in a very analogous manner, voltage waveforms in the DC voltage intermediate circuit 1 at a negative voltage jump.

Both in Figure 2 and in Figure 3 it can be seen that, depending on the positive or negative voltage jump, the intermediate circuit voltage U _Z K is exceeded or fallen below. the aim is However, to avoid such overrun or underruns and limit the voltage level at the three-phase AC or three-phase AC machine 10 to the intermediate circuit voltage UZK ZU.

FIG. 4 shows, in a schematic form and based on FIG. 1, the block diagram of an inverter system 2 for a three-phase AC machine 10 in an advantageous embodiment according to the invention.

The invention relates in particular to the DC voltage intermediate circuit 1 already mentioned in connection with FIG.

As can be seen in Figure 4 are in the DC voltage intermediate circuit 1 of an indirect

Inverter system 2 for a three-phase AC or three-phase AC machine 10, a first diode 3 with a forward direction and a series-connected second diode 4 in the same forward direction as the first diode 3 is provided. The diodes 3, 4 in this case have n-doped regions as cathodes and p-doped regions as anodes in a known manner. The forward direction refers to a connection in which the anode is connected to a positive strand 6 and the cathode to a negative strand 5. In the embodiment illustrated in FIG. 4, the anode of the first diode 3 is connected to the negative leg 5 of the DC intermediate circuit 1, and the cathode of the second diode 4 is connected to the positive leg 6 of the DC intermediate circuit 1. Via the two series-connected diodes 3, 4, a negative strand 5 is connected to a positive strand 6 of the DC intermediate circuit 1 and a point 7 between the first diode 3 and second diode 4 is connected via a capacitor 8 to the ground 9. The two series connected diodes 3, 4 are so in the

DC intermediate circuit 1 arranged so that the anode of the first diode 3 with the negative strand 5 and the cathode of the second diode 4 are connected to the positive strand 6 of the DC intermediate circuit 1. The two series-connected diodes 3, 4 are operated in the reverse direction due to their installation position in the DC intermediate circuit 1.

The illustrated circuit is due to the two diodes 3 and 4 a

Limiting circuit is and is therefore active only when exceeding or falling below an intermediate circuit voltage U _Z K and therefore causes no additional power loss in normal operation. The common-mode voltages U1 and U2 shown in FIG. 4 are limited to the intermediate circuit voltage +/- U _ZK in the following manner:

Limit 1: -U _ZK <U1 <0V

Limitation 2: OV <U2 <U _ZK The range stated under Limit 1 thus states that, although the voltage U1 may be less than or equal to zero, it does not fall below the value -U _Z K. The range stated under Limit 2 states that the voltage U2 may be greater than or equal to zero, but does not exceed the value + U _ZK . When the intermediate circuit _voltage U _ZK is exceeded or undershot, a current flow via the capacitor 8 to ground 9 is set by the suitable selection of the two diodes 3 and 4. When selecting, or

Dimensioning of the two diodes 3 and 4 is to be noted, in which it is on

input side three-phase rectifier or the network converter 1 1 and the

output side inverter or the machine converter 12 comes to a simultaneous switching operation. In this case, it can lead to significant peak currents, since the already mentioned oscillatory system is doubly excited. The height of the corresponding peak currents depends, among other things, on the sum amplitude of the exciting voltage. Furthermore, the dimensioning of the network converter 1 1 usually upstream Hochsetzerdrossel 17 and the possibly provided return capacitors 14, 15, 16 on the said peak currents corresponding influence. Merely by way of example, it should be mentioned that, for example, at average currents of about 6 amperes peak currents can occur, which are in the region of 120 amperes.

The capacitor 8 decouples the DC intermediate circuit from the ground and acts at high frequencies known as a short circuit. If there is a short circuit at or on one of the two diodes 3, 4, the capacitor 8 acts to limit the current. In the absence of the capacitor 8 would at a defective diode 3, 4, a short-circuit current of the three phases u, v, w flow to the already mentioned transformer easter point and possibly destroy the power converter 1 1.

In this way, the circuit according to the invention limits the common-mode voltages U1 and U2 to the level of the intermediate circuit voltage U _ZK, whereby the voltage load of the windings of the three-phase AC machine 10, but also of sensors not shown, is correspondingly reduced.

As already mentioned, Figure 4 shows an advantageous embodiment in which before the DC voltage intermediate circuit 1 each of the three phases u, v, w of an input side on Inverter system adjacent three-phase network, via at least one recirculation capacitor 14, 15, 16 is connected to the ground 9. The occurring

About voltages Ux, so that voltage components, which U + _Z K exceed or fall below -ΙΙζκ, the input side of the inverter on the

Return capacitor 14, 15, 16 recycled.

The advantage of the feedback capacitors 14, 15 and 16 results in connection with the respective used three-phase network for energy supply. Regarding the

Energy supply, is differentiated in a known manner between TN (Terre Neutre), TT (Terre Terre) and IT (Isole Terre) networks. If the return capacitors 14, 15, 16 are always used, there is no further one

Grid viewing necessary and therefore easy integration possible. This makes it possible to use the circuit according to the invention also for known TT (Terre Terre) and IT (Isole Terre) networks.

For TT and IT networks, no common ground is provided. For this reason, there is also no common connection of the groundings which would allow a previously mentioned return of the overvoltage Ux. As mentioned, a reduction of the aforementioned overvoltages Ux across the respective separate grounds would be possible. However, since their properties are highly dependent on the laying of the lines and their length, can be made with respect to the times within which compensation or reduction of the overvoltage Ux no accurate statement. By using the

However, return capacitors 14, 15, 16 is a unique compound whose length and properties are known. This allows a correspondingly defined reduction or compensation of the overvoltage Ux.

For TN (Terre Neutre) networks, their use is advantageous. In such systems, unlike TT and IT systems, a common ground is provided to which also the neutral point of the transformer is connected. Without the capacitors 14, 15, and

16, the equalizing current would be fed back via the neutral point of the transformer.

This is a defined compound known in its properties.

Their use can lead to problems in terms of electromagnetic compatibility, ie the mutual influence of different devices by electromagnetic effects. For this reason, the use of the feedback capacitors is also in TN networks

14, 15, 16 of advantage. In this connection, it should be mentioned that capacitors in the arrangement of the feedback capacitors 14, 15, and 16 in FIG. 4 can already be provided in the case of a circuit, as shown, for example, in FIG.

Their task is usually to improve the electromagnetic compatibility (EMC) of the circuit. The aim is that electrical equipment or devices do not adversely affect each other by unwanted electrical, magnetic or electromagnetic effects. In particular converters generate due to the

Pulse width modulation Interference, which affects adjacent devices accordingly. For the high-frequency oscillations, the capacitors are a short circuit to earth, which is why they are derived or attenuated accordingly.

Usually, the dimensioning of such capacitors, to improve the electromagnetic compatibility in the range> 10μΡ. This size or dimensioning is completely sufficient for the transmission or return of the overvoltage Ux. Retrofitting with the feedback capacitors 14, 15, and 16 is therefore not necessary and there is an advantageous double use of existing components.

Due to the small number of necessary components, the space requirement with simultaneous high integrability in existing circuits is correspondingly low. Another advantage is that such a common mode filter solution is independent of one

Supply voltage, clock frequency and height of the intermediate circuit voltage U _Z K can be used.

These advantages thus result in an optimal retrofitting of existing systems.

Claims

claims

1 . Circuit for reducing common mode voltages in indirect

Inverter systems with a DC intermediate circuit (1) for three-phase or three-phase AC machines (10), characterized in that the

DC intermediate circuit (1) has a first diode (3) with a forward direction and a series connected second diode (4) with the same forward direction as the first diode (3), that on the two series connected diodes (3, 4) a negative Strand (5) of the DC voltage circuit (1) with a positive strand (6) of the

DC intermediate circuit (1) is connected and that a point (7) between the first diode (3) and second diode (4) via at least one capacitor (8) to the ground (9) is connected.

2. A circuit according to claim 1, characterized in that an anode of the first diode (3) with the negative strand (5) and a cathode of the second diode (4) to the positive strand (6) of the DC intermediate circuit (1) is connected.

3. A circuit according to claims 1 or 2, characterized in that before the

DC intermediate circuit (1) each of the three phases (u, v, w) of an input side of the inverter system adjacent three-phase network, each having at least one

Return capacitor (14, 15, 16) is connected to the mass (9).