DE102014223224A1 - Drive device and method for operating a drive device - Google Patents

Abstract

The invention relates to a drive device with an electric motor, which has a plurality of partial motors, with a plurality of inverters, each connected to a partial motor, which can be connected to a common DC voltage network and with a connection device for connecting the inverters to the common DC voltage network, which has at least two connection states. wherein, in a first connection state, all inverters are connected in series to the direct voltage network and, in a second connection state, all inverters are connected in parallel to the direct voltage network. Furthermore, the invention relates to a method for operating such a drive device.

Description

The invention relates to a drive device with an electric motor, which has a plurality of partial motors, and with a plurality of in each case connected to a motor part inverters which can be connected to a common DC voltage network. The invention further relates to a vehicle with an electric traction drive device. In addition, the invention relates to a method for operating a drive device with an electric motor, which has a plurality of sub-motors, and with a plurality of in each case connected to a motor part inverters which can be connected to a common DC voltage network.

The invention can be applied, inter alia, in electric or hybrid vehicles and in machine tools.

In the US Pat. No. 8,497,648 B2 a drive device is described, which has a designed as a permanent magnet synchronous motor electric motor with a plurality of pole pairs. The coils associated with a pole pair of this electric motor each form a partial motor, which is controlled via a separate inverter. The inverters are connected in parallel to each other and connected to a common DC voltage network.

In such a drive device, the voltage of the DC voltage network is applied to all inverters, which is usually selected such that it corresponds to the DC voltage required in full load operation of the electric motor. In partial load operation, in order to limit the currents impressed by the inverters into the electric motor, it is necessary to operate the inverters in such a way that pulsed voltages with very short pulse widths are provided. In this context, it has proved to be disadvantageous that the combination of a high voltage of the DC voltage network and the short pulse widths leads to high switching losses in the inverters as well as current overshoots and harmonic current harmonics, which cause losses to the coils of the electric motor.

Against this background, it is an object of the present invention to reduce losses in part-load operation.

In a drive device of the type mentioned above, the object is achieved by a connection device for connecting the inverter to the common DC network, which has at least two connection states, in a first connection state all inverters are connected in series connected to the DC voltage network and in a second connection state all Inverters connected in parallel to the direct voltage network.

Via the connection device, the connection of the inverters to the common DC voltage network can optionally be changed in order to set the DC voltage applied to the inverters. In the second connection state of the connection device all inverters are connected in parallel. When the inverters are connected in parallel, a DC voltage which is increased in comparison to the series connection is applied to the inverters, so that an increased power of the respective partial motors can be called up. In the first connection state, all inverters are connected in series via the connection device to the DC voltage network. In comparison with the parallel connection, the voltage drop across the power semiconductors of the inverters is reduced so that the switching losses are reduced. In series connection, a voltage is applied across the inverters, which corresponds to the voltage divided by the number of series-connected inverters in the DC voltage network. Thus, it is optionally possible to adjust the voltage applied to the inverters DC voltage to reduce losses in partial load operation.

The electric motor can have any desired number of partial motors, in particular two, four, six, eight or ten partial motors. The partial motors of the electric motor preferably act on a common drive shaft of the drive device. Advantageously, the partial motors have a common stator and / or a common rotor. Particularly preferably, the partial motors comprise a partial winding of the stator and / or the rotor of the electric motor. The electric motor may have a plurality of pole pairs, wherein a partial motor in each case has at least one pole pair of the electric motor. Alternatively it can be provided that the partial motors have separate rotors and / or separate stators and / or are arranged in separate housings.

The inverters are preferably designed as self-commutated inverters. It is advantageous if the inverters are configured in such a way that an at least approximately sinusoidal current profile with adjustable frequency can be generated on the motor side. Particularly preferably, a three-phase three-phase system can be generated by the inverters so that partial motors designed as three-phase three-phase motors can be driven.

The DC voltage network of the drive device can be designed as a vehicle electrical system of a vehicle, in particular of an electric or hybrid vehicle. Alternatively, the DC voltage network as DC voltage intermediate circuit, in particular as a DC voltage intermediate circuit of a DC voltage intermediate converter, be formed.

According to an advantageous embodiment, it is provided that the connection device has at least one third connection state, in which the inverters can be connected to the direct voltage network as a plurality of series-connected groups of parallel-connected inverters or as several parallel-connected groups of series-connected inverters. This has the advantage that an interconnection of the inverters can be provided by the connection device, in which a DC voltage is applied to the inverters, which is reduced compared to the parallel connection of all inverters and is higher than the voltage applied to a series connection of all inverters DC voltage. In this respect, at least three voltage levels of the applied DC voltage, in particular load-dependent, can be set at the inverters. Optionally, the connection device can have further connection states in which the inverters can be connected to the direct voltage network as a plurality of series-connected groups of parallel-connected inverters or as a plurality of parallel-connected groups of series-connected inverters. In particular, in such drive devices, which have more than four inverters, further connection states can be provided in order to provide more than three voltage levels of the DC voltage applied to the inverters.

Preferred is an embodiment in which the drive device has a plurality of capacitors, wherein each inverter is associated with at least one capacitor, so that the stability of the voltage applied to the inverters DC voltage can be improved. The capacitors may be DC link capacitors of a DC intermediate circuit.

Particularly preferably, the drive device has a control unit via which the connection states of the connection device can be set as a function of a load state of the electric motor, in particular of the load states of the partial motors. In this respect, the control unit can detect the load state of the electric motor and set a connection state suitable for the load state. The control unit may be connected to at least one sensor for detecting the load state, wherein the sensor is designed for example as a current sensor for detecting a winding current or as an angle sensor for detecting the rotational position and / or the rotational speed of the rotor. In addition, it can be provided that the inverters of the drive device are additionally controlled via the control unit, so that both the load-dependent setting of the DC voltage applied to the inverters and the control of the power semiconductors of the inverters can be effected by the control unit.

In a vehicle of the type mentioned above, it contributes to the solution of the problem that the traction drive device is designed as a drive device described above.

In a method of the type mentioned, the object is achieved in that the inverters are connected via a connection device to the common DC voltage network, which has at least two connection states, in a first connection state all inverters are connected in series connected to the DC network and in a second connection state all inverters connected in parallel to the DC power supply.

In the vehicle and the method, the same advantages as they have already been described in connection with the drive device according to the invention.

According to an advantageous embodiment of the method is provided that the connection device is placed in the first connection state when the speed of the electric motor is smaller than a predetermined first speed threshold. The series connection of the inverters on the one hand reduces the DC voltage applied to the inverters. On the other hand, the windings of the partial motors connected to the inverters are also connected in series, which increases the inductance in the current path. This leads to a decrease in the current gradients and consequently to a reduction of losses due to current overshoots and current harmonics in the electric motor. The series connection of all inverters enables low-loss operation of the drive device at low speeds below the first speed threshold. Due to the series connection of the inverters, the maximum battery current is available to all inverters so that a high torque can be generated for a short time. In this respect, the first connection state forms a start-up mode, which enables both a low-loss partial load operation and the short-term provision of a high torque.

A further advantageous embodiment provides that the connection device is placed in the second connection state when the speed of the electric motor is greater than the first speed threshold or greater than a predetermined second speed threshold. The parallel connection of the inverters on the one hand creates the highest possible DC voltage at the inverters. On the other hand, the windings of the partial motors are connected in parallel, so that the inductance is reduced in the current path. The parallel connection of all inverters makes it possible to achieve full engine power at high speeds above the first or second speed threshold, which is why the second connection state can also be referred to as a high-speed mode.

It has also proven to be advantageous in an embodiment in which the connection device is placed in a third connection state in which the inverters as several series-connected groups of several parallel-connected inverters or as multiple parallel-connected groups of several series-connected inverters to the DC voltage network are connected when the speed of the electric motor is between a predetermined first speed threshold and a predetermined second speed threshold. In a middle speed range between the first and the second speed threshold, an interconnection of the inverters can thus be provided in which a DC voltage is applied to the inverters which is reduced compared to the parallel connection of the inverters and the inductance in the current path assumes an average value. Optionally, it can be provided that the connection device is placed in further connection states in which the inverters are connected as a plurality of series-connected groups of inverters connected in parallel or as a plurality of parallel-connected groups of series-connected inverters to the DC voltage network, if the rotational speed of the electric motor between two other predetermined speed thresholds. Depending on the number of sub-motors or inverters of the drive device can thus be adjusted depending on other predetermined speed thresholds further voltage levels at the inverters.

It is also advantageous if only one inverter of several series-connected inverters is operated for current limitation with pulse width modulation, so that increased switching losses occur only in the inverter operated with pulse width modulation. The other inverters connected in series can be switched according to the phase sequence so that no increased switching losses occur in the other inverters.

Furthermore, an embodiment is preferred in which the connection device has a plurality of switches which are operated pulsed when switching between a closed state and an opened state. By pulsing the switches can be reduced when switching between a parallel connection and a series connection of the inverter resulting losses. As switches are advantageously power semiconductor switch with low on resistance, such. As IGBTs or MOSFETs used.

The advantageous features described in connection with the drive device can also be used alternatively or in combination in the method according to the invention for operating the drive device.

Further details and advantages of the invention will be described below with reference to the embodiments illustrated in the drawings. This shows

1 1 is a schematic block diagram of a drive system according to a first embodiment,

2 a circuit diagram of the drive system according to 1 and

3 a circuit diagram of a drive device according to a second embodiment.

In the 1 is a first embodiment of a drive system 1 shown, which is used as a traction drive in an electric or hybrid vehicle. The drive system 1 has a higher pole trained electric motor 2 on, which is designed as a permanent-magnet synchronous motor. The coils of the electric motor 2 are connected such that a first partial motor TM1 and a second partial motor TM2 is formed, each partial motor TM1, TM2 each having a group of coils, which are a pole pair of the common electric motor 2 provide. The coils of the partial motors TM1, TM2 are arranged on a common stator and act on a common rotor, so that via the partial motors TM1, TM2 a common drive shaft of the drive system 1 is drivable.

The first sub-motor TM1 is controlled by a first inverter WR1 connected to the first sub motor TM1, while the second sub motor TM2 is controlled by a second inverter WR2 connected to the second sub motor TM2. The inverters WR1, WR2 supply the partial motors TM1, TM2 with three-phase alternating current of adjustable frequency. The inverters WR1, WR2 are in a common housing with the electric motor 2 or arranged with the partial motors TM1, TM2. Alternatively it is possible, the inverters WR1, WR2 in one of the electric motor 2 to arrange independent housing.

As the illustration in 1 Furthermore, the inverters WR1, WR2 can be connected to a common DC voltage network 4 be connected, which may be designed as DC voltage intermediate circuit. The direct voltage network 4 provides a substantially constant DC voltage between a positive pole + UB and a negative pole -UB which can be applied to the DC terminals of the inverters WR1, WR2.

For connecting inverters WR1, WR2 to the direct voltage network 4 has the drive device 1 a connection device 3 which is configured such that both inverters WR1, WR2 are either connected in parallel with the respective other inverter WR1, WR2 or connected in series with the respective other inverter WR1, WR2 to the common DC voltage intermediate circuit 4 are connectable. In this respect, the connection device 3 two connection states, wherein in a first connection state, all inverters WR1, WR2, WR3, WR4 connected in series to the DC network 4 are connected and in a second connection state, all inverters WR1, WR2, WR3, WR4 connected in parallel to the DC voltage network 4 are connected. About the connection device 3 Thus, the voltage applied to the inverters WR1, WR2 DC voltage can be adjusted. In the parallel connection of the two inverters WR1, WR2 is located at the DC voltage terminals of the inverter WR1, WR2, the full DC voltage of the DC voltage network 4 so that the full power of the two partial motors TM1, TM2 is retrievable. When the two inverters TM1, TM2 are connected in series, half of the voltage of the DC voltage network is dropped across the inverters WR1, WR2 4 so that the switching losses are reduced.

To operate in the 1 shown drive system 1 For example, a method is used in which a change is made between the parallel connection and the series connection of the two inverters WR1, WR2. In a speed range in which the speed of the electric motor 2 is less than a predetermined speed threshold, are via the connection device 3 both inverters WR1, WR2 connected in series to the DC voltage network 4 tethered. Furthermore, all inverters WR1, WR2 are connected in parallel to the DC voltage network 4 Tailed when the speed of the electric motor 2 is greater than or equal to the predetermined speed threshold. Below the speed threshold, a first connection state, also referred to as start-up mode, is provided, in which the switching losses are reduced. In the start-up mode, there is an increased inductance in the current path through the series connection of the partial motors TM1, TM2, which limits the current increase speeds, so that additional losses in the electric motor 2 be reduced. Above the speed threshold, a second connection state, also referred to as a high-speed mode, is provided in the method, in which the electric motor 2 reached a high speed.

The following is based on the representation in 2 the construction of in 1 shown connection device 3 be explained, which is to be understood by a closed switch position, a switch position, in which a switch is electrically conductive and under an open switch position, a position in which the switch is not conductive.

The connection device 3 has a total of three switches S1, S2, S3, which are designed as a power semiconductor switch. The first switch S1 is connected to a negative DC pole of the first inverter WR1 and a negative DC pole of the second inverter WR2. The negative DC voltage pole of the second inverter WR2 is connected to the negative pole -UB of the DC voltage network 4 connected. The second switch S2 is connected to a positive DC pole of the first inverter WR1 and a positive DC pole of the second inverter WR2. The positive DC pole of the first inverter WR1 is connected to the positive pole + UB of the DC network 4 connected. The third switch S3 is connected to the negative DC pole of the first inverter WR1 and to the positive DC pole of the second inverter WR2. For series connection of the two inverters WR1, WR2 in the starting mode, the first switch S1 and the second switch S2 are opened and the third switch S3 is closed, so that the inverter WR1, WR2 in series between the two poles + UB, -UB of the DC network 4 lie. In the high-speed mode, the inverters WR1, WR2 are connected in parallel between the two poles + UB, -UB of the DC mains 4 in which the first switch S1 and the second switch S2 are closed and the third switch S3 is opened.

In the 3 is a second embodiment of a drive device according to the invention 1 which has four partial motors TM1, TM2, TM3, TM4 in contrast to the first embodiment. While the first partial motor TM1 is connected to a first inverter WR1, the second partial motor TM2 is connected to a second one Inverter WR2, the third partial motor TM3 with a third inverter WR3 and the fourth partial motor TM4 connected to a fourth inverter WR4. Furthermore, a connection device 3 provided, which has a total of nine switches S1, S2, S3, S4, S5, S6, S7, S8, S9.

The positive DC pole of the first inverter WR1 is connected to the positive pole + UB of the DC network 4 connected while the negative DC voltage pole of the fourth inverter WR4 is connected to the negative pole -UB. The first switch S1 is connected to a negative DC pole of the first inverter WR1 and a negative DC pole of the second inverter WR2. The second switch S2 is connected to a positive DC pole of the first inverter WR1 and a positive DC pole of the second inverter WR2. The third switch S3 is connected to the negative DC pole of the first inverter WR1 and to the positive DC pole of the second inverter WR2. The fourth switch S4 is connected to a negative DC pole of the third inverter WR3 and a negative DC pole of the fourth inverter WR4. The fifth switch S5 is connected to a positive DC pole of the third inverter WR3 and a positive DC pole of the fourth inverter WR4. The sixth switch S6 is connected to the negative DC pole of the third inverter WR3 and to the positive DC pole of the fourth inverter WR4). The seventh switch S7 is connected to the negative DC pole of the second inverter WR2 and to the negative DC pole of the fourth inverter WR4. The eighth switch S8 is connected to the positive DC pole of the first inverter WR1 and to the positive DC pole of the third inverter WR3. The ninth switch S9 is connected to the negative DC pole of the second inverter WR2 and to the positive DC pole of the third inverter WR3.

About the connection device 3 In addition to the series connection of all inverters WR1, WR2, WR3, WR4 in a first connection state and the parallel connection of all inverters WR1, WR2, WR3, WR4 in a second connection state optionally further circuit configurations are possible. Thus, the connection device can be placed in a third connection state, in which the first inverter WR1 and the second inverter WR2 are connected in parallel and form a first group. In the third connection state, the third inverter WR3 and the fourth inverter WR4, also connected in parallel, can form a second group. By selecting the switching position of the seventh, eighth and ninth switches S7, S8, S9, the interconnection of these two groups can be selected. In this respect, it is optionally possible to use the four inverters WR1, WR2, WR3, WR4 as two series-connected groups of two parallel-connected inverters WR1, WR2, WR3, WR4 or as two parallel-connected groups of two series-connected inverters WR1, WR2, WR3, WR4 to interconnect.

To operate in the 3 shown drive system 1 A method is used in which between the parallel connection of all inverters WR1, WR2, WR3, WR4, the series connection of all inverters WR1, WR2, WR3, WR4 and a circuit is changed, in which the inverters WR1, WR2, WR3, WR4 as two series-connected groups of two parallel inverters WR1, WR2, WR3, WR4 to the DC network 4 be connected.

In a speed range in which the speed of the electric motor 2 is less than or equal to a predetermined first speed threshold - ie a start-up mode - are via the connection device 3 all inverters WR1, WR2, WR3, WR4 are connected in series to the direct current network 4 tethered. In this start-up mode, each inverter WR1, WR2, WR3, WR4 is the maximum of the DC voltage network 4 deliverable power available so that a short time high torque can be generated. In the starting mode, the first switch S1, the second switch S2, the fourth switch S4, the fifth switch S5, the seventh switch S7 and the eighth switch S8 are opened. The third switch S3, the sixth switch S6 and the ninth switch S9 are closed.

Furthermore, all inverters WR1, WR2, WR3, WR4 are connected in parallel in a high-speed drive mode to the DC voltage network 4 Tailed when the speed of the electric motor 2 is greater than or equal to a predetermined second speed threshold. In fast-drive mode, each inverter WR1, WR2, WR3, WR4 has only a quarter of the maximum possible current in start-up mode. At the same time lies the full DC voltage of the DC voltage network 4 over the windings of the partial motors TM1, TM2, TM3, TM4. In the high-speed driving mode, the first switch S1, the second switch S2, the fourth switch S4, the fifth switch S5, the seventh switch S7 and the eighth switch S8 are closed. The third switch S3, the sixth switch S6 and the ninth switch S9 are open.

The second speed threshold is greater than the first speed threshold. When the speed of the electric motor 2 is between the first speed threshold and the second speed threshold, the inverters WR1, WR2, WR3, WR4 as two series-connected groups of two inverters WR1, WR2, WR3, WR4 connected in parallel to the DC network 4 tethered. In this respect, a normal operating mode is provided, in which each inverter WR1, WR2, WR3, WR4 is half of the maximum current possible in the start-up mode available. In the normal operating mode, the first switch S1, the second switch S2, the fourth switch S4, the fifth switch S5 and the ninth switch S9 are closed. The third switch S3, the sixth switch S6, the seventh switch S7 and the eighth switch S8 are open.

The electric motor 2 is designed for normal operating mode. This means that a compromise between the highest possible torque at low speeds and a field control range with sufficient torque at high speeds is achieved when the electric motor 2 is operated with two series-connected groups of two parallel-connected inverters WR1, WR2, WR3, WR4. In the normal operating mode, the inverters WR1, WR2, WR3, WR4 each fall half the voltage of the DC voltage network 4 which corresponds to the release voltage of the partial motors TM1, TM2, TM3, TM4.

In the drive systems described above 1 In addition, a plurality of DC link capacitors may be provided, wherein each inverter is associated with a DC link capacitor. The DC link capacitors can be connected, for example, to the positive DC pole and the negative DC pole of the inverters WR1, WR2, WR3, WR4.

For the series connection of all inverters WR1, WR2, WR3, WR4 of a drive system 1 In the start-up mode, it is advantageous if only one of the inverters WR1, WR2, WR3, WR4 is operated for current limitation with pulse width modulation.

When switching between the starting mode, the normal operating mode and the high-speed driving mode, the switches S1, S2, S3, S4, S5, S6, S7, S8, S9 can optionally be operated pulsed.

The drive devices described above 1 each have an electric motor 2 with several partial motors TM1, TM2, TM3, TM4. Furthermore, a plurality of inverters WR1, WR2, WR3, WR4, each connected to a partial motor TM1, TM2, TM3, TM4, are provided which are connected to a common DC voltage network 4 are connectable. For connection to the direct voltage network 4 have the drive devices 1 in each case a connection device 3 with at least two connection states. In a first connection state, all inverters WR1, WR2, WR3, WR4 are connected in series, and in a second connection state, all inverters WR1, WR2, WR3, WR4 are connected in parallel to the DC voltage network 4 tethered.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• US 8497648 B2 [0003]

Claims (10)

Drive device with an electric motor ( 2 ) having a plurality of partial motors (TM1, TM2, TM3, TM4) and a plurality of inverters (WR1, WR2, WR3, WR4) each connected to a partial motor (TM1, TM2, TM3, TM4) connected to a common DC network ( 4 ) are connectable, characterized by a connection device ( 3 ) for connecting the inverters (WR1, WR2, WR3, WR4) to the common DC voltage network ( 4 ), which has at least two connection states, wherein, in a first connection state, all the inverters (WR1, WR2, WR3, WR4) are connected in series to the direct voltage network ( 4 ) and in a second connection state all inverters (WR1, WR2, WR3, WR4) are connected in parallel to the direct voltage network ( 4 ) are connected. Drive device according to claim 1, characterized in that the connection device ( 3 ) has at least one third connection state, in which the inverters (WR1, WR2, WR3, WR4) as a plurality of series-connected groups of parallel-connected inverters (WR1, WR2, WR3, WR4) or as a plurality of parallel-connected groups of series-connected inverters (WR1, WR2, WR3, WR4) to the DC network ( 4 ) are connected. Drive device according to one of claims 1 or 2, characterized by a plurality of capacitors, wherein each inverter (WR1, WR2, WR3, WR4) is associated with a capacitor. Vehicle with an electric traction drive device, characterized in that the traction drive device is designed as a drive device according to one of claims 1 to 3. Method for operating a drive device ( 1 ) with an electric motor ( 2 ) having a plurality of partial motors (TM1, TM2, TM3, TM4) and a plurality of inverters (WR1, WR2, WR3, WR4) each connected to a partial motor (TM1, TM2, TM3, TM4) connected to a common DC network ( 4 ) are connectable, characterized in that the inverters (WR1, WR2, WR3, WR4) via a connection device ( 3 ) to the common DC network ( 4 ), which has at least two connection states, wherein, in a first connection state, all the inverters (WR1, WR2, WR3, WR4) are connected in series to the direct voltage network (FIG. 4 ) and, in a second connection state, all the inverters (WR1, WR2, WR3, WR4) are connected in parallel to the direct current network ( 4 ). Method according to claim 5, characterized in that the connection device ( 3 ) is placed in the first connection state when the speed of the electric motor ( 2 ) is smaller than a predetermined first speed threshold. Method according to one of claims 5 or 6, characterized in that the connection device ( 3 ) is placed in the second connection state when the speed of the electric motor ( 2 ) is greater than the first speed threshold or greater than a predetermined second speed threshold. Method according to one of claims 5 to 7, characterized in that the connection device ( 3 ) is placed in a third connection state, in which the inverters (WR1, WR2, WR3, WR4) as a plurality of series-connected groups of a plurality of parallel inverters (WR1, WR2, WR3, WR4) or as a plurality of parallel-connected groups of several in Series connected inverters (WR1, WR2, WR3, WR4) to the direct current network ( 4 ) are connected when the speed of the electric motor ( 2 ) is between a predetermined first speed threshold and a predetermined second speed threshold. Method according to one of Claims 5 to 8, characterized in that only one inverter (WR1, WR2, WR3, WR4) of several inverters (WR1, WR2, WR3, WR4) connected in series is operated with pulse width modulation for current limitation. Method according to one of claims 5 to 9, characterized in that the connection device ( 3 ) has a plurality of switches (S1, S2, S3, S4, S5, S6, S7, S8, S9) which are pulsed when switching between a closed state and an open state.

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