DE102012109283A1 - Power converter of electrical machine used for feeding three-phase motor of motor vehicle, has electrical resistance that is provided in circuit portion at same time through decoupling element - Google Patents

Abstract

The power converter (1) has a voltage intermediate circuit (7) that is configured for supplying an intermediate circuit voltage (UZK). A power unit (2) configured for converting electrical energy. A second voltage tap configured for picking up a second component voltage from the intermediate circuit voltage. A decoupling element configured to execute function of the circuit portion in a first switching state. An electrical resistance is provided in the circuit portion at the same time through the decoupling element. Independent claims are included for the following: (1) an electrical machine; (2) a motor vehicle; and (3) a method for operating a power converter.

Description

The present invention is in the field of power electronics and relates to a power converter for feeding an electrical machine with an operating voltage, and a method for operating such a power converter.

BACKGROUND OF THE INVENTION Against the background of dwindling fossil resources, modern motor vehicles are increasingly being equipped with an electric or hybrid drive. In view of the required driving force drive machines of motor vehicles must be operated with a considerably higher operating voltage of for example 400 to 900 volts compared to the electrical system, which is typically provided by DC sources such as batteries or fuel cells. In vehicle technology, predominantly three-phase motors (permanent or externally excited asynchronous or synchronous motors) are used, which are fed by an inverter. Due to the inverter, the direction of rotation and the speed of the drive machine can be adjusted as needed to the respective driving situation.

In a typical design, inverters have a voltage link with a charge storage to power a power unit in which the DC is converted to AC. Through the charge storage voltage support and smoothing for the operation of the drive machine is achieved. The basic structure of an inverter with voltage intermediate circuit is known per se to the person skilled in the art and has already been described in detail in the patent literature. For example only in this context, the German patent DE 19710371 C1 directed.

The object of the present invention is to develop conventional power converters so that different functions of the power converter, which are related to the voltage intermediate circuit, in a very compact and less complex manner and with low error rate can be realized. These and other objects are achieved according to the proposal of the invention by a power converter and a method for operating a power converter with the features of the independent claims. Advantageous embodiments of the invention are indicated by the features of the subclaims.

As used herein and hereinafter, the term "power converter" refers to devices known per se for the conversion of electrical energy. Converters in this sense are in particular single-phase or multi-phase DC / AC converters (DC / AC converters) or inverters, for example 3-phase inverters.

The power converter according to the invention is used to power an electrical machine with an operating voltage. As usual, the power converter comprises a power unit, which can be controlled by a control circuit, for converting electrical energy, which in particular serves to generate one or more alternating current phases from direct current. By means of a voltage intermediate circuit with a charge storage device, an intermediate circuit voltage for the power unit can be provided.

The power converter includes for this purpose, for example, a bridge circuit with one or more half-bridges, in each of which two power switches are arranged with their load current paths in series. Here, a first power switch ("TOP switch") with its load current input to an upper or higher potential (DC +) of the voltage intermediate circuit and a second power switch ("BOT switch") with its load current output to a lower or lower potential (DC -) connected to the voltage intermediate circuit. A center tap between the TOP and BOT switches forms a load output of the half-bridge for connecting the AC phase to an electrical load. Such circuit breakers are typically designed to carry electrical currents of several hundred amps and block voltages up to about 1000 volts. In practice, bipolar transistors with insulated gate electrode (IBGT) or field effect transistors (FET), in particular metal oxide field effect transistors (MOSFET), are usually used for this purpose.

The control circuit for driving the power switch is divided into a primary-side circuit part and a secondary-side circuit part, wherein the primary-side circuit part (low-voltage side) and the secondary-side circuit part (high-voltage side) are electrically isolated by at least one galvanically isolating transmission device, but data-technically connected to each other. The primary-side circuit part comprises a control logic module for generating control signals for driving the power switches. As usual, the control signals in the secondary-side circuit part are converted by driver circuits into control voltages for switching the power switches on or off.

According to the invention, the power converter has an additional circuit which comprises a voltage divider (resistance chain) connected to voltage intermediate circuit with at least two ohmic resistors. By the Voltage dividers are shorted to the two DC link lines of the voltage intermediate circuit.

In addition, the additional circuit comprises a first voltage tap on the voltage divider for tapping a first partial voltage from the intermediate circuit voltage, wherein the first voltage tap is electrically connected to a circuit part having a functional element for performing a function. Furthermore, the additional circuit comprises at least one second voltage tap on the voltage divider for tapping a second partial voltage from the intermediate circuit voltage, wherein the second voltage tap is electrically connected to at least one further circuit part with a further functional element for performing a further function. The first voltage tap and the second voltage tap can be designed as a common voltage tap. Preferably, the second voltage tap is different from the first voltage tap, wherein the second voltage tap taps off a second partial voltage from the intermediate circuit voltage, which is different from the first partial voltage tapped from the first voltage tap. The functions of the functional elements are different from each other.

It is essential here that the circuit parts each have a switchable decoupling element for electrical decoupling of the other circuit parts, wherein the decoupling elements each have a switch and are designed so that in a first switching state of the switch, the function of the associated circuit part is executable and in one second switching state of the switch, the function of the associated circuit part is not executable and at the same time in the second switching state is defined by the decoupling element electrical resistance in the associated circuit part.

As used herein, the term "decoupling" refers to a state of a circuit portion of the supplemental circuit in which the associated function is not executable and the switch portion has a predetermined electrical resistance (impedance) predetermined by the decoupling member.

The power converter according to the invention thus advantageously allows the execution of various functions in connection with the intermediate circuit voltage, in particular the provision of a measuring and / or supply voltage or control voltage, which are tapped as a partial voltage (s) of the intermediate circuit voltage to a single voltage divider. The power converter can thus be made very compact, the design is simplified by avoiding complex creepage distances and clearances.

In an advantageous embodiment of the power converter according to the invention, the decoupling members are each designed to electrically connect the associated voltage tap with a DC link. Typically, the decoupling members are in each case to those intermediate circuit line, which is acted upon by the lower or lower potential of the intermediate circuit voltage. For this purpose, the decoupling members advantageously each comprise a series connection of an ohmic ballast resistor, wherein the functional element is electrically connected to a connection point between the ballast resistor and the transistor. With this design, the decoupling elements in mass production can be realized inexpensively and technically particularly simply and reliably.

In a further advantageous embodiment of the power converter according to the invention, the voltage divider at least three ohmic resistors, wherein the first voltage tap picks up the first partial voltage between a first pair of ohmic resistors and the second voltage tap picks up the second partial voltage between a second pair of ohmic resistors, wherein the two pairs Ohmic resistances are different from each other. By this measure, the functional elements can be acted upon in a simple manner with different partial voltages of the DC link voltage, wherein the partial voltages are reduced so far that the functional elements and decoupling must have only a low dielectric strength. As a result, costs can be saved in series production. In particular, in this case, it is advantageous if the two pairs of ohmic resistors have a common ohmic resistance, which can then simultaneously serve as a ballast resistor for a functional element.

In a further advantageous embodiment of the power converter according to the invention, the second voltage tap is connected to a plurality of circuit parts which are each provided with a functional element for performing a function. As a result of this measure, a plurality of functions in which a partial voltage is tapped from the intermediate circuit voltage can be realized in the power converter in a technically simple and cost-effective manner.

In a further advantageous embodiment of the power converter according to the invention, a connected to the first voltage tap first circuit part is adapted to measure the DC link voltage, and / or a to the second voltage tap connected second circuit part adapted to supply a start-up circuit with a supply voltage, and / or connected to the second voltage tap third circuit part is designed to actively (controllably) to discharge the voltage link. In this case, particularly important functions of the power converter are realized in a simple manner. Advantageously, for this purpose, the first circuit part comprises an analog-to-digital converter, and / or the second circuit part a charge storage, and / or the third circuit part comprises a series circuit of power transistor and PTC resistor.

In an alternative embodiment of the power converter according to the invention, the voltage divider consists of only two ohmic resistors, wherein the first voltage tap and the second voltage tap are designed as a common voltage tap.

The invention further extends to an electric machine with a power converter designed as described above for feeding with an operating voltage.

Furthermore, the invention extends to a motor vehicle with an electric or hybrid drive, which is equipped with such an electric machine with power converter as a drive machine.

• – Abgreifen einer ersten Teilspannung von der Zwischenkreisspannung (U_ZK) zum Beaufschlagen eines Funktionselements zum Ausführen einer Funktion eines ersten Schaltungsteils einer Zusatzschaltung mit der ersten Teilspannung,
• – Abgreifen einer zweiten Teilspannung von der Zwischenkreisspannung (U_ZK) zum Beaufschlagen mindestens eines weiteren Funktionselements zum Ausführen einer weiteren Funktion eines zweiten Schaltungsteils der Zusatzschaltung mit der zweiten Teilspannung,

Furthermore, the invention extends to methods for operating a power converter with a voltage intermediate circuit for providing an intermediate circuit voltage for a power unit for converting electrical energy. The method comprises the following steps:

• Picking up a first partial voltage from the intermediate circuit voltage (U _ZK ) to apply a functional element for carrying out a function of a first circuit part of an additional circuit with the first partial voltage,
• - Picking up a second partial voltage from the intermediate circuit voltage (U _ZK ) for applying at least one further functional element for carrying out a further function of a second circuit part of the additional circuit with the second partial voltage,

wherein at least one functional element of at least one other functional element is electrically decoupled when the other functional element performs its function, wherein a defined electrical resistance in the circuit part of the one functional element is generated. In particular, in this case additionally execution of the function of the one functional element can be blocked.

In an advantageous embodiment of the method, a defined electrical resistance in the circuit part of a functional element by electrically connecting a Spannungsabgriffs for tapping the circuit part associated partial voltage with a potential, in particular the lower potential, the intermediate circuit voltage is generated.

• – Messen der Zwischenkreisspannung,
• – Beaufschlagen einer Anlaufschaltung mit einer Versorgungsspannung,
• – aktives Entladen des Zwischenkreises.

In a further advantageous embodiment of the method, one or more of the following functions are performed by the functional elements:

• - measuring the intermediate circuit voltage,
• - applying a start-up circuit with a supply voltage,
• - Active unloading of the DC link.

The advantages achieved with the method according to the invention and its embodiments have already been described in connection with the converter according to the invention, so that reference is made to the statements there to avoid repetition.

It is understood that the various embodiments of the invention can be implemented individually or in any combination in order to achieve improvements of conventional power converters and their operating methods. In particular, the features mentioned above and to be explained below can be used not only in the specified combinations but also in other combinations or in isolation, without departing from the scope of the present invention.

embodiment

The invention will now be explained in more detail with reference to an embodiment, reference being made to the accompanying drawings. Show it:

1 a schematic representation of a 3-phase inverter;

2 a schematic representation of the additional circuit of the 3-phase inverter of 1 ,

In the figures, an embodiment of a total with the reference number 1 designated, 3-phase inverter according to the invention for the conversion of a DC voltage in three AC phases for feeding an electric machine illustrated. For example, the 3-phase inverter is used 1 for feeding a three-phase motor of a motor vehicle with electric or hybrid drive.

Specifically shows 1 the secondary or high-voltage side of the 3-phase inverter 1 . which usually has a working voltage of several hundred volts. The (not shown) primary or low-voltage side contains a control logic whose working voltages correspond to the usual logic and vehicle electrical system voltages and are typically in the range of 1 to 24 volts. Primary and secondary side of the 3-phase inverter 1 are galvanically isolated, but connected together in terms of data technology.

As in 1 shown has the 3-phase inverter 1 For example, a modular structure and includes a plurality of parallel modules, of which in 1 only those are shown which serve the understanding of the invention. So includes the 3-phase inverter 1 a power module 2 with three half-bridges 3 each of which is for generating an alternating current phase, abbreviated to u, v and w, respectively. Every half bridge 3 has in a conventional manner via a switch pair of two series-connected circuit breakers 4 , which are designed as power transistors, such as insulated gate bipolar power transistors (IGBTs) or power MOSFETs. Every circuit breaker 4 is a freewheeling diode 6 connected in parallel with opposite passage direction. The alternating current phases u, v, w are each by a center tap 5 between two series-connected circuit breakers 4 a half bridge 3 tapped. The center taps 5 are connected to winding strands (not shown) of the electric machine, wherein the winding strands for controlling the direction of rotation and speed each a potential of predetermined polarity for a certain period of time is supplied. For this purpose, the circuit breakers 4 controlled by the control logic of the primary circuit by control signals accordingly.

The power module 2 is from a voltage link 7 supplied with a DC link voltage U _ZK (DC voltage). For this purpose, the parallel half-bridges 3 with two DC link lines 8th . 8th' electrically connected to a capacitor 9 are connected so that the one DC link 8th a higher potential (DC +) and the other DC link 8th' has a lower potential (DC-). From the difference between the two potentials (DC +, DC-) results in the intermediate circuit voltage U _ZK , which of the half-bridges 3 is converted to the AC phases u, v, w. In order to have sufficient motor power for the operation of the motor vehicle, the intermediate circuit _voltage U _ZK must be sufficiently large. For example, the intermediate circuit voltage U _{ZK is} in the range of 400-900 volts. The capacity of the capacitor 9 is for example 1000 μF.

In operation, the capacitor 9 through one to the two DC link lines 8th . 8th' connected DC power source (not shown), such as an accumulator or a fuel cell, electrically charged.

In 1 not shown are other modules of the 3-phase inverter 1 , which are connected in parallel to the power module 2 to the two DC link lines 8th . 8th' are electrically connected, for example, filter modules and reactor modules for the AC phases u, v, w. Likewise not shown are current sensors for the three alternating current phases u, v, w.

An essential aspect of the 3-phase inverter 1 is a total with the reference number 10 designated additional circuit, which in 2 is shown in detail. The parallel to the power module 2 to the two DC link lines 8th . 8th' connected additional circuit 10 fulfills several functions in connection with the intermediate circuit _voltage U _ZK , which are explained in more detail below.

As in 2 shown includes the additional circuit 10 a voltage divider 11 , the two DC link lines 8th . 8th' electrically shorts. The voltage divider 11 consists of a plurality n ohmic resistors connected in series (resistance chain), here denoted R1, R2, R3, R4 ... Rn. For example, the voltage divider has 11 over five, six or more ohmic resistors, with a relatively large number of ohmic resistors (eg, 10 to 12) being preferred due to concomitant reduced ohmic power dissipation.

The voltage divider 11 is connected to a connection point V1 of the intermediate circuit line adjacent to the resistor R1 8th' and with a connection point V2 of the intermediate circuit line adjacent to the nth resistor Rn 8th electrically connected. The resistors R1 and R2 have a relatively low resistance value, which is in the one to two-digit kilo-ohm (kΩ) range (eg 1 to 20 kΩ). For example, resistor R1 has a resistance of 3 kΩ and resistor R2 has a resistance of 10 kΩ. The resistors R3, R4 ... Rn are each relatively high-impedance, the resistance value of which is in each case in the range from 100 kΩ to 1 megaohm (MΩ).

Through the voltage divider 11 can be a passive (non-controllable) discharge of the voltage intermediate circuit 7 be achieved. Here, the size of the ohmic resistors in the voltage divider 11 chosen so that a discharge over a sufficiently long period of, for example, at least one or more hours, so that the operability of the 3-phase inverter 1 is not or not significantly affected by the passive discharge. In addition, excessive heating of the ohmic resistors in the voltage divider 11 avoided by a relatively low discharge current.

Due to the passive discharge of the voltage intermediate circuit 7 can the operational safety of the 3-phase inverter 1 can be improved because the applied high voltage is reduced in case of failure or a longer shutdown of the vehicle, for example, for a repair in a workshop.

Next to the voltage divider 11 has the additional circuit 10 via a first circuit part 12 , which allows a further function, namely the measurement of the intermediate circuit _voltage U _ZK . Typically (but not necessarily), the intermediate _circuit voltage U _ZK is measured during operation of the 3-phase inverter 1 ,

For this purpose, the first circuit part comprises 12 an analog-to-digital converter (ADC) 13 with a first ADC input 14 and a second ADC input 15 , The first ADC input 14 is through a first voltage tap 16 (Intermediate tap) to the voltage divider 11 connected. The first voltage tap 16 is connected to a junction V3 between resistor R1 and resistor R2 of the voltage divider 11 electrically connected. The second ADC input 15 is connected to a connection point V4 of the intermediate circuit line 8th' electrically connected.

Accordingly, the first ADC input is located 14 a potential that results from the voltage drop of the intermediate circuit voltage U _ZK via the ohmic resistors R2, R3, R4 ... Rn. The second ADC input 15 is the reference potential, the lower potential (DC) of the intermediate circuit voltage U _ZK , so that through the analog-to-digital converter 13 the voltage drop across resistor R1 is measured, which is typically so low that the analog-to-digital converter 13 can be performed with low dielectric strength. In general, the ohmic resistors of the voltage divider 11 dimensioned so that a first partial voltage can be tapped, which allows a simple and inexpensive processing by digital circuitry, here, for example, a voltage in the range of 0 to 3 volts.

At an ADC output (not shown) of the analog-to-digital converter 13 a digital value is provided in accordance with the voltage dropped across the ohmic resistor R1, from which the intermediate circuit voltage U _ZK can be derived.

The first circuit part 12 further comprises a transistor assembly of a transistor T1 with antiparallel connected diode D1. The transistor T1 is connected to its load terminals (input and output terminals) with a connection point V17 of the first voltage tap 16 and a connection point V16 of the intermediate circuit line 8th' electrically connected. Due to the relatively low voltage which drops across the resistor R1, the transistor T1 can be designed with low dielectric strength.

A control of the transistor T1 is effected by a T1 control logic 17 which is connected to the control terminal of the transistor T1. The T1 control logic 17 is connected to a connection point V18 of the DC link 8th' electrically connected, wherein the lower potential (DC-) serves as a reference potential. Through the T1 control logic 17 For example, the control terminal of the transistor T1 can optionally be supplied with a control voltage for switching to the conductive or on-state, for example 5 volts, or with a control voltage, for example 0 volts, for switching to the open or blocking state.

If the transistor T1 is switched to passage, then the first voltage tap 16 with the lower potential (DC-) of the DC link 8th' connected so that across the resistor R1 no voltage drops and the first ADC input 14 is tension-free. The intermediate circuit voltage U _ZK can be measured when the transistor T1 is switched to its off state, wherein the tapped partial voltage to the analog-to-digital converter 13 is supplied as input or measuring voltage.

Furthermore, the additional circuit 10 a second circuit part 18 on, which allows a further function in connection with the intermediate circuit voltage U _ZK , namely the provision of a supply voltage for a non-illustrated starting circuit 19 ,

For this purpose, the additional circuit includes 10 a second voltage tap 20 (Intermediate tap) connected to a connection point V5 of the voltage divider 11 between resistor R2 and resistor R3 is electrically connected. An unspecified input of the starting circuit 19 is with the interposition of an ohmic resistor RV1 serving as a ballast resistor with a connection point V6 of the second voltage tap 20 electrically connected.

The second voltage tap 20 is further connected via a series circuit of ballast resistor RV1 and a downstream transistor assembly consisting of a transistor T2 and antiparallel-connected diode D2, with the intermediate circuit line 8th' electrically connected. The transistor T2 is with its two load terminals with the series resistor RV1 and with a connection point V19 of the DC link 8th' electrically connected. Due to the relatively low voltage which drops across the two resistors R1 and R2, the transistor T2 can be designed with low dielectric strength.

The startup circuit 19 is connected to a connection point V7 between the series resistor RV1 and the transistor T2 of the series circuit of ballast resistor RV1 and transistor T2, with a reverse-biased diode D5 is interposed. Passes the startup circuit 19 in the simplest case of a capacitor (not shown), it can be prevented by the diode D5, a discharge of the capacitor via the series resistor RV1.

A control of the transistor T2 is effected by a T2 control logic, not shown, which is connected to the control terminal of the transistor T2. The T2 control logic is here, for example, in the start-up circuit 19 integrated, it being understood that it may equally be embodied as a separate component. By means of the T2 control logic, the control terminal of the transistor T2 can optionally be supplied with a control voltage for switching into the on-state or off-state.

If the transistor T2 is switched to its blocking state, then the start-up circuit 19 acted upon by a voltage applied at the connection point V7 supply voltage. In general, the ohmic resistors of the voltage divider 11 dimensioned so that a partial voltage can be tapped, which is a supply of the starting circuit 19 with a suitable supply voltage (eg 10 volts). By the ballast resistor RV1 can be made a further adjustment of the supply voltage. If the transistor T2 is switched to its on state, then the lower potential (DC-) of the intermediate circuit line 8th' the connection point V7 of the start-up circuit 19 at. In this case, by the series resistor RV1 a defined electrical resistance in the second circuit part 20 given.

Furthermore, the additional circuit 10 a third circuit part 21 on, which allows a further function, namely an active (ie controllable) fast discharge of the intermediate circuit voltage U _ZK . Generally, by the third circuit part 21 a much faster discharge of the voltage intermediate circuit 7 as over the voltage divider 11 be achieved. In contrast to the voltage divider 11 , which only a passive discharge of the voltage intermediate circuit 7 allows, the third circuit part 21 be actively controlled to select either only a slow discharge of the voltage intermediate circuit 7 or in combination a slow and fast discharge of the voltage intermediate circuit 7 to reach. For this purpose, a total with the reference number 22 designated discharge circuit with the interposition of an ohmic resistor RV2 serving as a ballast resistor with a connection point V8 of the second voltage tap 20 electrically connected.

The discharge circuit 22 comprises a series connection of a PTC thermistor or resistor with a positive temperature coefficient, hereinafter referred to as "PTC resistor" 23 and a power transistor T4. This series connection closes the two DC link lines 8th . 8th' short, wherein the resistance-side end with a connection point V9 of the DC link 8th and the transistor-side end with a connection point V10 of the intermediate circuit line 8th' electrically connected. The input terminal of the power transistor T4 is connected to the PTC resistor 23 , the output connection with the DC link 8th' electrically connected. The second voltage tap 20 is connected with the interposition of the ballast resistor RV2 to the control terminal of the power transistor T4. The power transistor T4 is formed, for example, as an insulated gate bipolar power transistor (IGBT) or power MOSFET.

For example, the PTC resistor 23 at a temperature of 25 ° C, an electrical resistance of 350 ohms, which increases due to the electrical properties of the resistance material with increasing temperature. The electrical resistance of the PTC resistor 23 is significantly lower at least at room temperature, for example at least by a factor of 500, than the electrical sum resistance of the ohmic resistors of the voltage divider 11 , Accordingly, the discharge current through the series circuit of PTC resistor 23 and power transistor T4 much larger than via the voltage divider 11 ,

The third circuit part 21 further includes a series circuit of ballast resistor RV2 and a Zener diode 24 , through the second voltage tap 20 to the intermediate circuit line 8th' connected. Here, the diode-side end of the series circuit is connected to a connection point V11 of the second intermediate circuit line 8th' electrically connected so that the Zener diode 29 directly with the DC link 8th' electrically connected. Relative to the intermediate circuit voltage U _ZK is the Zener diode 24 arranged in the reverse direction, but is at an intermediate circuit voltage U _ZK above a predetermined breakdown voltage electrically conductive. The control terminal of the power transistor T4 is connected to a connection point V12 of the series connection between the series resistor RV2 and the Zener diode 23 electrically connected, so that by the voltage divider 11 tapped voltage control of the power transistor T4 can be done.

Furthermore, in the third circuit part 21 the second voltage tap 20 via a series connection of series resistor RV2 and a downstream transistor module, consisting of a transistor T3 and antiparallel connected diode D3, with the intermediate circuit line 8th' electrically connected. The transistor T3 is with its load terminals with the series resistor RV2 and the DC link 8th' electrically connected, wherein the transistor-side end of the series circuit with a connection point V13 of the intermediate circuit line 8th' electrically connected.

A control of the transistor T3 is done by a T3 control logic 25 which is connected to the control terminal of the transistor T3. The T3 control logic 25 is connected to a connection point V14 of the intermediate circuit line 8th' electrically connected, wherein the lower potential (DC-) serves as a reference potential. Through the T3 control logic 25 The control terminal of the transistor T3 can optionally be supplied with a control voltage for switching to the on or off state. Due to the relatively low voltage at the voltage divider 11 is tapped, the transistor T3 can be performed in contrast to the power transistor T4 with low dielectric strength. The control terminal of the power transistor T4 is electrically connected to a connection point V15 between the ballast resistor RV2 and transistor T3 of the series circuit of the ballast resistor RV2 and transistor T3.

If the transistor T3 is in the on state, the lower potential (DC-) of the voltage intermediate circuit is present 7 at the control terminal of the power transistor T4. Control and output terminal of the power transistor T4 are thus at the same potential (DC-), so that the power transistor T4 is in the blocking state. In this situation is an active discharge of the voltage intermediate circuit 7 via the PTC resistor 23 not possible. Such deactivation of the rapid discharge of the capacitor 9 is for the proper functioning of the 3-phase inverter 1 desired during normal operation of the electric machine. For example, the transistor T3 is controlled by the T3 control logic 25 switched to the on state when starting the electric machine and in the blocking state when stopping.

The transistor T3 is in the off state, the potential of the connection point V12 is located at the control terminal of the power transistor at T4, wherein the ohmic resistors are chosen so that the power transistor T4 is switched by the tapped from the intermediate circuit voltage U _ZK voltage in its conducting state. The discharge of the voltage intermediate circuit 7 via the PTC resistor 23 due to the low electrical resistance much faster than via the voltage divider 11 , preferably within a time interval in the single-digit second range, for example within less than 5 Seconds. This can cause excessive heating of the PTC resistor 23 be avoided by increasing the electrical resistance with increasing temperature due to the high discharge current occurring. In practice it turns out that the temperature of the PTC resistor 23 up to a maximum operating temperature, with the PTC resistor 23 is designed in accordance with the intermediate circuit voltage U _ZK to be discharged so that its maximum operating temperature is a non-destructive discharge of the voltage intermediate circuit 7 allows. For example, the maximum operating temperature of the PTC resistor is 23 in the range of 130 to 160 ° C.

A fast discharge of the voltage intermediate circuit 7 can thus be achieved in an advantageous manner by a voltage tap on the intermediate _circuit voltage U _ZK , provided that the transistor T3 is in the blocking state. Such a situation occurs when the control terminal of the transistor T3 is controlled by the T3 control logic 25 is acted upon, for example, 0 volts, which is provided by control technology when stopping the electric machine.

The zener diode 24 is designed so that it breaks through if the voltage applied at the connection point V12 voltage exceeds a predetermined threshold. As a result, the control terminal of the power transistor T4 is protected from overvoltages in the voltage intermediate circuit 7 protected.

On the other hand, the power transistor T4 goes into its blocking state when the intermediate circuit voltage U _{ZK is} so low that at the connection point V12, the required switching voltage is no longer applied. Another active discharge of the voltage intermediate circuit 7 via the PTC resistor 23 is thus no longer possible, so that a (harmless for persons) residual voltage of for example 10 to 50 volts in the voltage intermediate circuit 7 remains over the voltage divider over a much longer period of time 11 can be unloaded. The residual voltage is preferably less than 20%, in particular less than 10%, of the intermediate circuit voltage U _ZK im normal operation of the 3-phase inverter 1 , A residual voltage in the voltage intermediate circuit 7 has the advantage that the capacitor 9 faster to those for the operating state of the 3-phase inverter 1 desired intermediate _circuit voltage U _ZK can be loaded, so that an accelerated resumption of operation is possible.

A special advantage of the additional circuit 10 is that by switching the transistors T1, T2 and T3, the various circuit parts 12 . 18 . 21 can be electrically decoupled.

As already stated, a measurement of the intermediate circuit voltage U _ZK by the first circuit part is generally carried out during the operation of the 3-phase inverter 12 , In this case, the transistor T1 is switched to its off state. At the same time, the transistor T2 of the second circuit part 18 and the transistor T3 of the third circuit part 21 each switched to their on state, so that both the second circuit part 18 as well as the third circuit part 21 have a defined electrical resistance, which is given by the respective ballast resistor RV1 and RV2. In this respect, the measurement of the intermediate circuit voltage U _ZK by the second circuit part 18 and third circuit part 21 not adversely affected or the defined resistances of these circuit parts can be taken into account in the measurement of the DC link voltage.

Ballast resistor RV1 and transistor T2 of the second circuit part 18 on the one hand, and ballast resistor RV2 and transistor T3 of the third circuit part 21 On the other hand, each form a decoupling member 26 for electrically decoupling the second circuit part 18 and / or third circuit part 21 from the first circuit part 12 ,

On the other hand, a supply of the starting circuit 19 and an active discharge of the voltage intermediate circuit 7 usually performed during the start and / or stop operations of the electric machine, wherein a measurement of the intermediate circuit voltage U _{ZK is} usually not required. Here, the transistors T2 and T3 of the second circuit part 18 or third circuit part 21 each switched to their blocking state, wherein at the same time the transistor T1 of the first circuit part 12 is switched to its on state. This can be achieved on the one hand, that during operation of the start-up circuit 19 and / or discharge circuit 22 in the first circuit part 12 there is a defined electrical resistance, which is given by the ohmic resistor R2. Resistor R2 effectively serves as a ballast resistor of the first circuit part 14 , On the other hand, the analog-to-digital converter 13 before any overvoltage in the first voltage tap 16 protected, which by the second circuit part 18 or third circuit part 21 can be caused. Resistor R2 and transistor T1 form a decoupling element 26 for electrically decoupling the first circuit part 12 from the second circuit part 18 and third circuit part 21 ,

The additional circuit 10 thus advantageously allows a measurement of the intermediate circuit voltage U _ZK and / or a supply of the starting circuit 19 with a tapped from the intermediate circuit voltage U _ZK supply voltage and / or an active discharge of the voltage intermediate circuit, each function of the other two functions by a decoupling element, consisting of a series circuit of ballast resistor and transistor, which the respective voltage tap to the DC link 8th' connects electrically, is electrically decoupled. The different functions are due to two voltage taps on a single voltage divider 11 realized. It is therefore not necessary for the various functions that multiple voltage dividers (high-voltage resistance chains) for short-circuiting the two DC link lines 8th . 8th' in the voltage intermediate circuit 7 must be provided. Such a design would have the disadvantage that the required air and creepage distances must be complied with, which requires a considerable amount of space and thus contradicts the demands for more and more compact power converters. In addition, the concrete design of the clearances and creepage distances is very complex and represents a potential source of error.

The additional circuit 10 can be modified in many ways. It would be conceivable only two ohmic resistors R1 and R2 in the voltage divider 11 to provide, in which case the first voltage tap 16 and the second voltage tap 20 be combined to form a common voltage between the two resistors R1 and R2. In this case, it would be advantageous if in the first circuit part 12 the transistor T1 is connected via an additional ballast resistor to the common voltage tap.

In the additional circuit 10 each decoupling element consists of a series circuit of ballast resistor and transistor, the series circuit the associated voltage tap with the DC link 8th' connects electrically. It would be conceivable to implement the decoupling elements differently in each case, for example, solely by a transistor having a defined electrical resistance in the off state.

The inventive 3-phase inverter 1 Thus, it is possible for the first time to provide a plurality of functions in connection with the intermediate circuit voltage U _ZK by means of a single voltage divider 11 to realize, wherein the various functions by respective decoupling members are electrically decoupled from each other, so that the functions do not adversely affect each other. The 3-phase inverter 1 can be made very compact, since only a single voltage divider 11 is required, so that in particular there is no space requirement for the creepage distances and creepage distances of several high-voltage resistance chains. The technical implementation of the air and creepage distance of the single voltage divider 11 is relatively simple and subject to low susceptibility to errors.

LIST OF REFERENCE NUMBERS

1

 3-phase inverter

2

 power module

3

 half bridge

4

 breakers

5

 center tap

6

 Freewheeling diode

7

 Voltage link

8, 8 '

 Link cable

9

 capacitor

10

 additional circuit

11

 voltage divider

12

 first circuit part

13

 Analog to digital converter

14

 first ADC input

15

 second ADC input

16

 first voltage tap

17

 T1 control logic

18

 second circuit part

19

 start-up circuit

20

 second voltage tap

21

 third circuit part

22

 discharge circuit

23

 PTC resistor

24

 Zener diode

25

 T3 control logic

26

 decoupling member

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19710371 C1 [0003]

Claims (14)

Power converter ( 1 ) with a voltage intermediate circuit ( 7 ) for providing a DC link voltage (U _ZK ) for a power unit ( 2 ) for converting electrical energy and an additional circuit ( 10 ), the additional circuit ( 10 ) comprises: - one to the voltage intermediate circuit ( 7 ) connected voltage divider ( 11 ) having at least two ohmic resistors (R1, R2, R3 ... Rn), - a first voltage tap ( 16 ) at the voltage divider ( 11 ) for tapping a first partial voltage from the intermediate circuit voltage (U _ZK ), wherein the first voltage tap ( 16 ) with a circuit part ( 12 ) with a functional element ( 13 ) is electrically connected to perform a function, - at least one second voltage tap ( 20 ) at the voltage divider ( 11 ) for tapping a second partial voltage from the intermediate circuit voltage (U _ZK ), wherein the second voltage tap ( 20 ) with at least one further circuit part ( 18 . 21 ) with another functional element ( 19 . 22 ) is electrically connected to perform another function, wherein the circuit parts ( 12 . 18 . 21 ) each via a switchable decoupling member ( 26 ) for the electrical decoupling of the other circuit parts, wherein the decoupling members ( 26 ) each having a switch (T1, T2, T3) and are formed so that in a first switching state of the switch (T1, T2, T3), the function of the associated circuit part ( 12 . 18 . 21 ) is executable and in a second switching state of the switch (T1, T2, T3), the function of the circuit part ( 12 . 18 . 21 ) is not executable and at the same time by the decoupling member ( 26 ) defined electrical resistance in the circuit part ( 12 . 18 . 21 ) is present. Power converter according to Claim 1, in which the decoupling members ( 26 ) are each adapted to the associated voltage tap ( 16 . 20 ) with a DC link ( 8th . 8th' ) electrically connect. Power converter according to one of Claims 1 or 2, in which the decoupling members ( 26 ) each comprise a series connection of an ohmic ballast resistor (R2, RV1, RV2) and a transistor (T1, T2, T3), wherein the functional element ( 13 . 19 . 22 ) is electrically connected to a connection point (V17, V7, V12) between the ballast resistor (R2, RV1, RV2) and the transistor (T1, T2, T3). Power converter according to one of Claims 1 to 3, in which the voltage divider ( 11 ) has at least three ohmic resistors (R1, R2, R3 ... Rn), wherein the first voltage tap ( 16 ) picks up the first partial voltage between a first pair of ohmic resistors (R1, R2) and the second voltage tap ( 20 ) picks up the second partial voltage between a second pair of ohmic resistors (R2, R3), wherein the two pairs of ohmic resistors are different from each other. A power converter according to claim 4, wherein the two pairs of ohmic resistors (R1, R2; R2, R3) have a common ohmic resistance (R2). Power converter according to one of Claims 1 to 5, in which the second voltage tap ( 20 ) with a plurality of circuit parts ( 18 . 21 ), each with a functional element ( 19 . 22 ) are provided for performing a function, is electrically connected. Power converter according to one of claims 1 to 6, in which - a to the first voltage tap ( 16 ) connected first circuit part ( 12 ) is designed to measure the intermediate _circuit voltage (U _ZK ), and / or - a to the second voltage tap ( 20 ) connected second circuit part ( 18 ) is adapted to supply a starting circuit with a supply voltage, and / or - a to the second voltage tap ( 20 ) connected third circuit part ( 21 ) is adapted to the voltage intermediate circuit ( 7 ) to actively unload. A power converter according to claim 7, wherein - the first circuit part ( 12 ) an analog-to-digital converter ( 13 ), and / or - the second circuit part ( 18 ) comprises a charge storage, and / or - the third circuit part ( 21 ) a series circuit of power transistor (T4) and PTC resistor ( 23 ). Power converter according to one of Claims 1 or 2 and 5 to 8, in which the voltage divider ( 11 ) comprises two ohmic resistors, the first voltage tapping ( 16 ) and the second voltage tap ( 20 ) are designed as a common voltage tap. Electric machine with a power converter ( 1 ) according to one of claims 1 to 9 for feeding with an operating voltage. Motor vehicle with an electric or hybrid drive, which is equipped with an electric machine with power converter according to claim 10 as a drive machine. Method for operating a power converter ( 1 ) with a voltage intermediate circuit ( 7 ) for providing a DC link voltage (U _ZK ) for a power unit ( 2 ) for converting electrical energy, comprising the following steps: - picking up a first partial voltage from the intermediate circuit voltage (U _ZK ) for applying a functional element for performing a function of a first circuit part of an additional circuit with the first partial voltage, - tapping a second partial voltage from the intermediate circuit voltage (U _ZK ) for applying at least one further functional element for carrying out a further function of a second circuit part of the additional circuit with the second partial voltage, wherein at least one functional element of at least one other functional element is electrically decoupled when the other functional element performs its function, wherein a defined electrical Resistance is generated in the circuit part of a functional element.  Method according to Claim 12, in which a defined electrical resistance is generated in the circuit part of the one functional element by electrically connecting a voltage tap for tapping the partial voltage associated with the circuit part with a potential, in particular the lower potential, of the intermediate circuit voltage.  Method according to one of claims 12 or 13, in which one or more of the following functions are performed by the functional elements: - measuring the intermediate circuit voltage, - applying a start-up circuit with a supply voltage, - Active unloading of the DC link.

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