DE102014210627A1 - Electric drive system and method for operating an electric drive system - Google Patents

Abstract

The invention relates to an electric drive system with a DC intermediate circuit, a first n-phase inverter, n> 1, which is fed by the DC voltage intermediate circuit with DC voltage, and which is designed to generate a first n-phase AC voltage, a second n-phase inverter. phase inverter, which is fed by the DC intermediate circuit with DC voltage and which is adapted to generate a second n-phase AC voltage, a 2n-phase electric machine, the first n phase terminals with output terminals of the first inverter and the second n phase terminals with output terminals of the second inverter, and a control circuit coupled to the first n-phase inverter and the second n-phase inverter. In this case, the 2n-phase electric machine has two n-phase winding sets each of opposite polarity. The control circuit is designed to control in each case a half-bridge of the first n-phase inverter and a corresponding half-bridge of the second n-phase inverter such pulse width modulated, that the phase voltage generated by the half-bridges of the first n-phase inverter to the respective corresponding thereto Half bridges of the second n-phase inverter phase voltage generated are oppositely poled, and that the switching edges of the pulse width modulated control of the half-bridges of the first n-phase inverter coincide in time with the switching edges of the pulse width modulated driving the half-bridges of the second n-phase inverter.

Description

Technical area

The invention relates to an electric drive system and to a method for operating an electric drive system, in particular for use in an electrically operated vehicle such as an electric car or a hybrid vehicle.

State of the art

In an electric drive system, the feeding of multi-phase current into an electric machine usually takes place by means of a converter, for example in the form of a pulse-controlled inverter. For this purpose, an energy storage device such as a high-voltage battery can feed a DC intermediate circuit, which in turn provides a DC voltage that can be converted into a multi-phase AC voltage, for example, a three-phase AC voltage. The DC intermediate circuit can be fed by a string of serially connected battery modules or any DC voltage sources.

The inverter usually operates with pulse width modulated drive signals to produce the multi-phase output voltage. By the timing of the individual half-bridges in the inverter transient electrical common mode quantities are generated, which spread over the phase connections in the direction of the electric machine in the drive system. In the electrical machine, these transient common-mode quantities can also capacitively or to a lesser extent inductively couple to electrically conductive parts of the electrical machine or the housing of the electrical machine. As a result, these unwanted outcouplings may cause dielectric breakdowns of the lubricating film in the bearings of the electric machine, emission of electromagnetic disturbances to the environment via the powertrain, for example via shafts and axles, and conducted interference emissions into the DC supply system of the converter come.

One way to counteract these undesirable effects is to provide adequate shaft grounding by appropriate galvanic connections of the shaft of the electric machine to the housing. Furthermore, shielding measures can be taken on the phase conductors of the electrical machine. In addition, conducted noise emissions can be reduced by using Y capacitors or other active or passive filters. Finally, it is possible to use insulating bearings (for example, ceramic bearings) for the electric machine.

However, since such measures are complicated and expensive and only combat the symptoms of transient electrical common mode variables occurring, it is desirable not to let arise transient electrical common mode variables in the control of converters in an electric drive system in the first place.

The publication US 2010/0071970 A1 proposes, for example, to equip a polyphase motor with two electrically insulated winding sets of opposite polarity per phase, and to supply the winding sets of opposite polarity in pairs via two corresponding half bridges of an inverter via a common phase drive with a phase voltage.

Disclosure of the invention

The present invention therefore according to a first aspect provides an electric drive system with a DC intermediate circuit, a first n-phase inverter, n> 1, which is fed by the DC voltage intermediate circuit with DC voltage, and which is adapted to a first n-phase AC voltage a second n-phase inverter, which is fed by the DC voltage intermediate circuit with DC voltage and which is adapted to generate a second n-phase AC voltage, a 2n-phase electric machine whose first n phase terminals with output terminals of the first inverter and whose second n phase terminals are connected to output terminals of the second inverter, and a control circuit which is coupled to the first n-phase inverter and the second n-phase inverter. In this case, the 2n-phase electric machine has two n-phase winding sets each of opposite polarity. The control circuit is designed to control in each case a half-bridge of the first n-phase inverter and a corresponding half-bridge of the second n-phase inverter such pulse width modulated, that the phase voltage generated by the half-bridges of the first n-phase inverter to the respective corresponding thereto Half bridges of the second n-phase inverter phase voltage generated are oppositely poled, and that the switching edges of the pulse width modulated control of the half-bridges of the first n-phase inverter coincide in time with the switching edges of the pulse width modulated driving the half-bridges of the second n-phase inverter.

According to a second aspect, the present invention provides a method for operating an electric drive system which has a DC intermediate circuit, a first n-phase inverter, n> 1, which is supplied with DC voltage by the DC voltage intermediate circuit and which is designed to generate a first n-phase inverter. To generate phase AC voltage, a second n-phase inverter, which is fed by the DC voltage intermediate circuit with DC voltage, and which is adapted to generate a second n-phase AC voltage, and a 2n-phase electric machine having its first n phase terminals with Output terminals of the first inverter whose second n phase terminals are connected to output terminals of the second inverter, and which comprises two n-phase winding sets each having opposite polarity. The method comprises the steps of driving the half bridges of the first n-phase inverter with a pulse width modulated drive signal for generating first phase voltages, and driving the half bridges of the second n-phase inverter with a pulse width modulated drive signal for generating second phase voltages. In this case, the first phase voltages are opposite polarity to the second phase voltages, and the switching edges in the pulse width modulated driving the half-bridges of the first n-phase inverter with the switching edges in the pulse width modulated driving the half-bridges of the second n-phase inverter coincide in time.

Advantages of the invention

One idea of the present invention is to prevent transient common-mode currents, which occur briefly when a converter is switched, by using two antisymmetric converter modules which generate equal but opposite-flowing transient common-mode currents when switching. The half bridges of the converter modules can then be controlled synchronously so that common mode currents causing switching edges of both converter modules occur simultaneously and the resulting common mode currents of both converter modules cancel each other out.

By extinguishing the transient common mode currents, several advantages can be realized: Storage-damaging electrostatic discharges and radiation of electromagnetic interference by the mechanical components of the electric machine can be significantly reduced or completely avoided. Furthermore, the emission of electromagnetic disturbances along the machine shaft and thus the decoupling of such disturbances in the environment by axle or gear parts in hybrid and electric vehicles is effectively suppressed. It is also possible to dispense with active or passive filter elements for wave grounding or at least greatly reduce the use of such. In addition, it is not necessary to resort to electrically insulating bearings such as ceramic bearings, whereby the cost of manufacturing the electrical machine can be significantly reduced.

Reverse currents from the electric machine into the DC voltage network are likewise prevented efficiently, as a result of which Y capacitors may possibly be completely dispensed with. Under certain circumstances, it is also possible to dispense with toroidal common mode filters such as throttle valve filters in the DC voltage line and the phase line to the electrical machine. By eliminating or reducing filter measures, electrical power losses through the filters can also be reduced, so that the electric drive system has an improved energy balance or energy efficiency.

In addition, steeper switching edges can be driven without favoring the formation of common mode currents. This leads to reduced switching losses and the possibility of setting higher phase currents for the same semiconductor area in the power semiconductor switches.

According to one embodiment of the drive system according to the invention, the drive system may further comprise an energy storage device which is coupled to the DC intermediate circuit and which is adapted to supply the DC intermediate circuit with a DC voltage.

According to one embodiment of the drive system according to the invention, the first inverter may comprise a self-commutated inverter having a plurality of symmetrical half-bridges of two power semiconductor switches in series, and the second inverter comprising a self-commutated inverter with a plurality of balanced half-bridges of two power semiconductor switches in series.

According to a further embodiment of the electric drive system according to the invention, the power semiconductor switches of the inverters may each comprise MOSFET switches or IGBT switches.

According to one embodiment of the method according to the invention, the pulse width modulated drive signal for driving the Half bridges of the second n-phase inverter is formed by inverting the pulse width modulated drive signal for driving the half-bridges of the first n-phase inverter.

Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings.

Brief description of the drawings

Show it:

1 a schematic representation of an electric drive system according to an embodiment of the present invention;

2 a schematic diagram of an exemplary voltage waveform of a through a first half-bridge of the first inverter in the electric drive system according to 1 generated phase voltage;

3 a schematic diagram for an exemplary voltage waveform of a through a first half-bridge of the second inverter in the electric drive system according to 1 generated phase voltage;

4 a schematic diagram for an exemplary voltage waveform of a through a second half-bridge of the first inverter in the electric drive system according to 1 generated phase voltage;

5 a schematic diagram of an exemplary voltage waveform of a through a second half-bridge of the second inverter in the electric drive system according to 1 generated phase voltage; and

6 a schematic representation of a method for operating an electric drive system according to another embodiment of the present invention.

Like reference numerals generally designate like or equivalent components. The schematic representations shown in the figures are only exemplary in nature, which are idealized for reasons of clarity. It is understood that the illustrated components are merely illustrative of principles and functional aspects of the present invention.

Detailed description of embodiments

1 shows a schematic representation of an electric drive system 10 with a six-phase electric machine 8th , which may be, for example, a switched reluctance machine or a rotating field machine. The electric machine 8th has two three-phase windings 8a and 8b on, which can be coupled with each other in their star point. The electric drive system 10 also has a first inverter or inverter 7a , which at its output terminals 6a a first of the three-phase winding strands 8a the electric machine 8th powered in motor operation, as well as a second inverter or inverter 7b on, at its output terminals 6b a second of the three-phase winding strands 8b the electric machine 8th fed in motor operation.

The first and the second inverter 7a respectively. 7b each have a B6 full bridge topology, that is, the inverters 7a respectively. 7b have a three-phase self-commutated inverter comprising three symmetrical half-bridges B1, B2, and B3 or B4, B5 and B6 each consisting of two power semiconductor switches H1 and H2, H3 and H4 or H5 and H6 connected in series. The power semiconductor switches may be, for example, MOSFET switches or IGBT switches. However, it is also possible to use any other type of switching elements as switches H1 to H6 and to switch parallel to each switching element H1 to H6 a freewheeling diode. At a center tap of a first half-bridge B1 of the first inverter 7a is a first of the phases of the electric machine 8th at a center tap of a second half-bridge B2 of the first inverter 7a a second of the phases of the electric machine 8th , and at a center tap of a third half-bridge B3 of the first inverter 7a a third of the phases of the electric machine 8th coupled. Analogously, at a center tap of a first half-bridge B4 of the second inverter 7a is a fourth of the phases of the electric machine 8th at a center tap of a second half-bridge B5 of the second inverter 7a a fifth of the phases of the electric machine 8th , and at a center tap of a third half-bridge B6 of the second inverter 7a a sixth of the phases of the electric machine 8th coupled.

The phases of the electric machine 8th are arranged so that the six-phase electric machine 8th two three-phase winding sets 8a and 8b each having opposite polarity, that is, that each two of the windings are arranged antiparallel to each other.

For controlling the power semiconductor switches H1 to H6 of both inverters 7a and 7b can be a control circuit 5 used, for example, on a common control board with the inverters 7a and 7b can be implemented.

The inverters 7a and 7b become from a DC voltage intermediate circuit 2 powered, in turn, by an energy storage device 1 such as a DC voltage source 1 For example, a traction battery of an electric vehicle is supplied with electrical DC voltage. The DC voltage source 1 can do this, for example, a series connection of battery modules 1a to 1k have, the number in 1 only exemplified by three - any other number of battery modules 1a to 1k may also be possible. It is also clear that the number of phases of the inverter 7a and 7b from the in 1 may vary depending on the required number of phases of the electric machine 8th whose number of phases can take any (even) number.

In the drive system 10 of the 1 can the electric machine 8th For example, a synchronous or asynchronous machine, a reluctance machine or a brushless DC motor (BLDC) of an electrically powered vehicle such as an electric car or a hybrid vehicle. It may also be possible, the electric drive system 10 of the 1 Use in stationary systems, for example in power plants, in electrical energy production systems such as wind turbines, photovoltaic systems or cogeneration plants, in energy storage systems such as compressed air storage plants, battery storage power plants, flywheel storage, pumped storage or similar systems. Another possible use of the electric drive system 10 of the 1 are passenger or goods transport vehicles, which are designed for locomotion on or under the water, for example, ships, motor boats or the like.

The control circuit 5 , which with the first inverter 7a and the second inverter 7b coupled, is used to generate drive signals for the operation of the inverter 7a respectively. 7b , In this case, the control circuit can in particular use the principle of pulse width modulation, for example a center-centered pulse width modulation, in order to control signals for the individual half bridges B1, B2, B3 or B4, B5, B6 of the inverters 7a and 7b to create. Corresponding half-bridges of the inverters 7a and 7b are each half bridges whose output terminals with phase connections of two antiparellel or connected in opposite polarity windings of the winding sets 8a . 8b are connected. In the example of 1 For example, windings connected in opposite polarity are each shown in pairs - the two upper windings are connected in opposite polarity, as are the two middle windings and the two lower windings. Corresponding half bridges in the sense of this disclosure are the half bridges B1 and B4, the half bridges B2 and B5 and the half bridges B3 and B6.

Corresponding half bridges are each from the control circuit 5 so pulse width modulated driven, that by the respective half-bridge B1, B2 or B3 of the first inverter 7a generated phase voltage Ua to the corresponding respectively by the respective half bridges B4, B5 and B6 of the second inverter 7b generated phase voltages Ub are oppositely poled. The 2 to 5 each show a schematic voltage-time diagram for an exemplary voltage waveform at a first or second half-bridge of the first and second inverters, respectively 7a . 7b of the electric drive system 10 in 1 ,

2 shows the exemplary voltage waveform U _B1 through a first half-bridge B1 of the first inverter 7a generated phase voltage Ua. This phase voltage is subjected to a center-centered pulse width modulation, that is, after an initial low potential T-, which is set at the beginning, with a first switching edge Sa ("low-high switching edge") the potential from the low potential T- to a high Potential T + set. This switching operation produces transient common-mode currents in the phase line connected to the half bridge B1 and connected to the electric machine 5 , In an analogous manner, after maintaining the high potential T + according to the specification of the pulse width modulation with a second switching edge Sb ("high-low switching edge"), the potential of the high potential T + to the low potential T + is lowered again. This switching process also produces transient common-mode currents in the phase line assigned to the half bridge B1 and connected to the electrical machine 5 ,

3 shows the exemplary voltage waveform U _B4 one through a first half-bridge B4 of the second inverter 7b generated phase voltage Ub. This phase voltage is also subjected to center-centered pulse width modulation. However, the half-bridge B4 is a half-bridge corresponding to the half-bridge B1, which is controlled by the control circuit 5 is controlled so that the switching edges Sa, Sb the pulse width modulated control of the half-bridge B4 with the Switching edges Sa and Sb of the pulse width modulated control of the half-bridge B1 coincide in time. This can be achieved, for example, by virtue of the fact that the pulse width modulated drive signals are used to drive the half bridges B4, B5 and B6 of the second inverter 7b by inverting the pulse width modulated drive signals for driving the half bridges B1, B2, and B3 of the first inverter 7a be formed.

The transient common-mode currents in the phase line of the half-bridge B4, which are produced at the switching edges Sa and Sb, are just dimensioned by the inversion of the high-low switching edges or low-high switching edges such that they match the transient common-mode currents in the phase line of the half-bridge B1 extinguish.

Similarly, the show 4 and 5 schematic diagram of exemplary voltage waveforms of corresponding half bridges B2 and B5 of the first and second inverter 7a . 7b in the electric drive system 10 to 1 generated phase voltages Ua and Ub. In each case, a shorter duration of the pulses generating the phase voltages is provided by the center-centered pulse width modulation. By suitable staggering of the pulse width modulation in all of the n half-bridges of the inverters 7a and 7b can be an n-phase AC voltage in the phase lines of the electric machine 8th are provided, wherein in each case two of the phase voltages are formed in pairs inverted.

Each switching edge Sa or Sb, which in the first inverter 7a is generated, is an inverted and temporally with the respective considered switching edge Sa or Sb of the first inverter 7a coincident switching edge Sa or Sb in the second inverter 7b opposite. The respective resulting transient common-mode currents therefore cancel in the phase lines and thus also in the electrical machine 8th mutually exclusive. The common mode noise current is thus kept at all times at zero or at least at a very low level. For the complete elimination of the transient common mode currents it is necessary to ensure symmetrical machine stray sizes and equal stray capacitances. This can be in the design of the 2n-phase electric machine 8th be taken into account.

4 shows a schematic representation of a method 20 Operating an electric drive system, in particular an electric drive system 10 , as related to the 1 to 5 explained. The procedure 20 can be done by the control circuit 5 in the generation of pulse width modulated drive signals for the inverter 7a respectively. 7b of the electric drive system 10 in 1 be implemented.

In a first step 21 there is a drive 21 the half bridges B1, B2 and B3 of the first inverter 7a with a pulse width modulated drive signal for generating first phase voltages Ua. In a second step 22 there is a drive 22 the half bridges B4, B5 and B6 of the second inverter 7b with a pulse width modulated drive signal for generating second phase voltages Ub. The first phase voltages Ua are oppositely poled to the second phase voltages Ub. The control signals can be generated in such a way that the pulse width modulated drive signal for driving the half bridges B4, B5, B6 of the second inverter 7b by inverting the pulse width modulated drive signal for driving the half bridges B1, B2, B3 of the first inverter 7a is formed. This can be achieved that the switching edges Sa in the control of the first inverter 7a each with the switching edges Sb in the control of the second inverter 7b coincide in time, that is, that corresponding half-bridge pairs of the first and second inverters 7a . 7b be switched at the same time.

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

• US 2010/0071970 A1 [0006]

Claims (6)

Electric drive system ( 10 ), comprising: a DC voltage intermediate circuit ( 2 ); a first n-phase inverter ( 7a ), n> 1, which by the DC voltage intermediate circuit ( 2 ) is supplied with DC voltage and which is adapted to generate a first n-phase AC voltage; a second n-phase inverter ( 7b ), which by the DC voltage intermediate circuit ( 2 ) is supplied with DC voltage and which is adapted to generate a second n-phase AC voltage; a 2n-phase electric machine ( 8th ), whose first n phase connections with output connections ( 6a ) of the first inverter ( 7a ) and its second n phase terminals with output terminals ( 6b ) of the second inverter ( 7b ) are connected; and a control circuit ( 5 ), which are connected to the first n-phase inverter ( 7a ) and the second n-phase inverter ( 7b ), wherein the 2n-phase electric machine ( 8th ) two n-phase winding sets ( 8a ; 8b ) each having opposite polarity, and wherein the control circuit ( 5 ) is designed in each case to have a half-bridge (B1; B2; B3) of the first n-phase inverter ( 7a ) and a corresponding half-bridge (B4; B5; B6) of the second n-phase inverter ( 7b ) in such a pulse-width-modulated manner that the signals caused by the half-bridges (B1, B2, B3) of the first n-phase inverter ( 7a ) generated phase voltages (Ua) to the respective corresponding half bridges (B4; B5; B6) of the second n-phase inverter ( 7b ), and that the switching edges (Sa, Sb) of the pulse-width-modulated control of the half-bridges (B1, B2, B3) of the first n-phase inverter ( 7a ) with the switching edges (Sa; Sb) of the pulse-width-modulated activation of the half-bridges (B4; B5; B6) of the second n-phase inverter ( 7b ) coincide in time. Electric drive system ( 10 ) according to claim 1, further comprising: an energy storage device ( 1 ), which with the DC voltage intermediate circuit ( 2 ) and which is adapted to the DC link ( 2 ) with a DC voltage (Uc) to supply. Electric drive system ( 10 ) according to one of claims 1 and 2, wherein the first inverter ( 7a ) comprises a self-commutated inverter having a plurality of symmetrical half-bridges (B1; B2; B3) each comprising two power semiconductor switches (H1, H2; H3, H4; H5, H6) connected in series, and wherein the second inverter ( 7b ) comprises a self-commutated inverter having a plurality of symmetrical half-bridges (B4; B5; B6) each comprising two power semiconductor switches (H1, H2; H3, H4; H5, H6) connected in series. Electric drive system ( 10 ) according to claim 3, wherein the power semiconductor switches (H1, H2, H3, H4, H5, H6) each comprise MOSFET switches or IGBT switches. Procedure ( 20 ) for operating an electric drive system ( 10 ), which comprises: a DC voltage intermediate circuit ( 2 ), a first n-phase inverter ( 7a ), n> 1, which by the DC voltage intermediate circuit ( 2 ) is supplied with DC voltage and which is designed to generate a first n-phase AC voltage, a second n-phase inverter ( 7b ), which by the DC voltage intermediate circuit ( 2 ) is fed with DC voltage and which is designed to generate a second n-phase AC voltage, and a 2n-phase electric machine ( 8th ), whose first n phase connections ( 8a ) with output connections ( 6a ) of the first inverter ( 7a ), whose second n phase connections ( 8b ) with output connections ( 6b ) of the second inverter ( 7b ) and which two n-phase winding sets ( 8c ; 8d ) of opposite polarity, the method ( 20 ) comprises the following steps: 21 ) of the half-bridges (B1, B2, B3) of the first n-phase inverter ( 7a ) with a pulse width modulated drive signal for generating first phase voltages (Ua); and driving ( 22 ) of the half-bridges (B4; B5; B6) of the second n-phase inverter ( 7b ) with a pulse width modulated drive signal for generating second phase voltages (Ub), the first phase voltages (Ua) being oppositely poled to the second phase voltages (Ub), and wherein the switching edges (Sa; Sb) in the pulse width modulated driving ( 21 ) of the half-bridges (B1, B2, B3) of the first n-phase inverter ( 7a ) with the switching edges (Sa; Sb) in the pulse width modulated driving ( 22 ) of the half-bridges (B4; B5; B6) of the second n-phase inverter ( 7b ) coincide in time. Procedure ( 20 ) according to claim 5, wherein the pulse width modulated drive signal for driving the half bridges (B4; B5; B6) of the second n-phase inverter ( 7b by inverting the pulse width modulated drive signal for driving the half bridges (B1, B2, B3) of the first n-phase inverter ( 7a ) is formed.

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