DE102022204381A1 - Inverter unit for a multi-phase electrical machine and electrical machine with such an inverter unit - Google Patents

Abstract

The invention relates to an inverter unit (10) for a multi-phase electrical machine (100), having a bridge circuit (20) with several half-bridges (22), the half-bridges each having a low-side (24) and a high-side switch (26 ), and wherein the inverter unit (10) has a control unit (30), wherein the control unit (30) has a high-side driver (36) for controlling the respective high-side switch (26), and wherein at least two Half bridges (22) each have a bootstrap unit (40) for supplying energy to the respective high-side driver (36). One aspect of the invention is that at least two bootstrap units (40) are coupled to one another. The invention also relates to an electrical machine (100) with an inverter unit (10) according to the invention.

Description

State of the art

The invention relates to an inverter unit for a multi-phase electrical machine, having a bridge circuit with several half-bridges, the half-bridges each having a low-side and a high-side switch, and the inverter unit having a control unit, the control unit having a high for each half-bridge -Side driver for controlling the respective high-side switch, and at least two half bridges each have a bootstrap unit for supplying energy to the respective high-side driver.

Such an inverter unit is known to those skilled in the art. If the high-side and low-side switches are alternately switched on, the potential at the center tap of the half bridges changes between 0V and an input voltage provided for the inverter unit by a power supply unit. In particular, n-channel MOSFETs generally have low resistance when the potential at the gate is more positive than at the source terminal by the threshold voltage UGS-on, typically 6 to 15 V. With the low-side switch, if the input voltage is sufficiently high or with little additional effort, it is no problem to alternately set the gate to 0 V and to values of approx. 15 V to reach the threshold voltage. However, in order to be able to control the high-side switch, gate potentials that are the threshold voltage higher than the voltage of the power supply unit are necessary. This is often achieved using a so-called bootstrap unit, which has a diode and a capacitor in combination with a high-side driver. The high-side driver's reference potential is connected to the center tap of the half bridge. To initialize the bootstrap circuit, also known as precharge, the capacitor is charged to the input voltage of the power supply unit by turning the low-side switch on for a certain minimum time while the high-side switch is open. The capacitor is charged to the input voltage of the power supply unit during this half-period while the low-side switch is conducting.

In the second half cycle, the capacitor supplies the high-side driver and the gate terminal of the high-side switch, causing it to turn on while the low-side switch is open. If the high-side switch is then closed, the voltage at the center tap is close to the voltage of the energy supply unit and the upper connection of the capacitor, which supplies the energy to the high-side driver, is at a potential which corresponds approximately to twice the input voltage.

Since the capacitor can only store a finite amount of charge, discharges via the high-side driver and after a certain period of time can no longer provide a sufficiently large voltage to keep the high-side switch closed, the charging process of the capacitor must be stopped be repeated periodically by opening the high-side switch and closing the low-side switch and thus clocking the half bridge accordingly.

The bootstrap circuit is therefore not suitable if the high-side switch is to remain on for a long time.

In the case of high-voltage arrangements, instead of bootstrap units, potential-free DC-DC converters designed as so-called fly-back circuits can be used to supply the high-side drivers with the appropriate energy. However, these fly-back circuits are expensive and require a lot of space due to the complex circuit arrangement.

The invention also relates to an electrical machine with such an inverter unit.

Disclosure of the invention

The invention relates to an inverter unit for a multi-phase electrical machine, having a bridge circuit with several half-bridges, the half-bridges each having a low-side and a high-side switch, and the inverter unit having a control unit, the control unit (per half-bridge) has a high-side driver for controlling the respective high-side switch, and at least two half bridges each have a bootstrap unit for supplying energy to the respective high-side driver.

One aspect of the invention is that at least two bootstrap units are coupled to one another.

The advantage here is that, through the coupling, a power supply to a bootstrap unit of a half-bridge with a closed high-side switch can be supported by another bootstrap unit of a half-bridge with an open high-side switch, whereby the half-bridge with a closed high-side switch lasts longer than can remain in this state usually or even permanently. This means that the pumping properties of the individual half-bridges are coupled to the associated bootstrap units and thereby a clocked half-bridge controls the coupled half-bridges cken can supply accordingly. Simple bootstrap units can be used for this and a complex fly-back circuit can be omitted, which can improve the cost and space requirements of the inverter unit. In addition, the control of the half bridges can be selected more flexibly than before.

The electric machine can in particular be designed as an electric motor, for example as a permanently excited synchronous machine, as an electrically excited synchronous machine, or as an asynchronous machine.
This electric motor has, for example, a stator and a rotor. In addition, the electric motor has an inverter unit to appropriately control the machine to generate a rotating magnetic field in the stator coils.

The term inverter unit is understood to mean an electronic circuit that can be used to convert direct current into alternating current, with the direct current being supplied by a supply voltage of a power supply unit or via an intermediate circuit voltage.

In particular, the inverter unit implements a corresponding control of stator coils using a bridge circuit in order to generate a rotating magnetic field. The switches of the bridge circuit can be opened or closed by the control unit as required. This magnetic rotating field, in conjunction with magnetic components of the rotor, drives the rotor and ultimately the rotor shaft. For this purpose, the bridge circuit has several half-bridges, with a half-bridge consisting of a low-side switch and a high-side switch and the center tap between the two switches leads to a stator coil. The low-side switches and high-side switches can be designed as semiconductor switches, in particular as MOSFETs or as IGBTs.
A half bridge with the associated stator coil forms a corresponding phase of the motor. For example, if the half-bridge circuit has three half-bridges, this corresponds to a total of six switches, which then form a so-called B6 bridge, in turn forming a three-phase electrical machine. In principle, the electrical machine can be designed with any number of phases.

The control unit can be designed, for example, as one or more microcontrollers. There can be various separate control circuits or control partitions, particularly within the control unit. In particular, the control unit has corresponding high-side drivers and low-side drivers for the respective high-side switches and low-side switches for switching the corresponding switches of the half bridges, which in turn can be controlled using a PWM method .

A bootstrap unit is an electrical circuit in which a change in potential in one part of the circuit suddenly becomes effective in another. This takes advantage of the effect that capacitors only change their voltage slightly at low currents. They transfer a change in potential on one side to the other (bootstrap effect). Another application of the bootstrap effect is starting a semiconductor switch, in particular an NMOS transistor as a high-side switch of a half bridge. By maintaining the voltage of the capacitor, voltages can even be realized that are above the input voltage of the inverter unit through the power supply unit and the high-side switches can therefore be switched accordingly.

By coupled to one another is meant that the bootstrap units are electrically connected to one another in order to improve the power supply to the respective bootstrap units.

Energy supply in turn means the provision and maintenance of a voltage that is high enough to continue to be able to control the respective high-side switches when the high-side switch of the respective half-bridge is closed, or the high-side -To be able to keep the switch closed.

One embodiment of the invention provides that the bootstrap units are coupled to one another in such a way that the power supply to the high-side driver of a half-bridge with a closed high-side switch can be at least partially taken over by the bootstrap unit of a half-bridge with an open high-side switch.

The advantage here is that the energy supply of the corresponding high-side driver is improved compared to the prior art and the control of the half bridges can therefore be selected more freely, which in turn can lead to improved performance of the inverter unit.

A further embodiment of the invention provides that the bootstrap units each have at least a first bootstrap circuit and that at least one of the bootstrap units has a second bootstrap circuit.

The advantage here is that the second bootstrap circuit can be used for the corresponding energy supply to the first bootstrap circuit of another bootstrap unit. For this purpose, the bootstrap unit with a first and a second bootstrap circuit is coupled via its second bootstrap circuit to a first bootstrap circuit of another bootstrap unit.

According to a further embodiment of the invention, it is provided that the first bootstrap circuit and the second bootstrap circuit are each arranged between the center tap of the respective half bridge and a voltage source of the inverter unit, with the first bootstrap circuit being arranged between a first diode and a first capacitor has a first circuit node, which is connected to the respective high-side driver of the half bridge, and wherein in each case the second bootstrap circuit between a second diode and a second capacitor has a second circuit node, which is connected via a further diode to the first circuit node first bootstrap circuit of another bootstrap unit is connected.
The advantage here is that this enables a simple circuit design of the corresponding coupling of the bootstrap units.

It is important to ensure that the second circuit node is not connected to the respective high-side driver of the associated bootstrap unit and only serves to couple the associated bootstrap unit to other bootstrap units.

According to a further embodiment of the invention, it is provided that the inverter unit has at least one fly-back circuit for supplying energy to the respective high-side driver, the fly-back circuit being arranged on a half bridge without a bootstrap unit.
The advantage here is that a fly-back circuit can be used for individual phases if, for example, no coupling is desired.

The fly-back circuit is a DC-DC converter and is used to transmit electrical energy between an input and an output side of galvanically isolated DC voltages in order to ensure the energy supply when the high-side switch is closed and is used in particular in high-voltage arrangements with a voltage of used over 60V.

The invention also relates to an electrical machine with an inverter unit according to the invention.
The electric machine can in particular be designed as an electric motor, for example as a permanently excited synchronous machine, as an electrically excited synchronous machine or as an asynchronous machine. Such an electric machine can be used, for example, in a steering system to move the steering axle accordingly.

drawings

• 1 shows schematically an exemplary embodiment of an electrical machine according to the invention with an inverter unit according to the invention.
• 2 shows an inverter unit from the prior art in detail.
• 3 shows an exemplary embodiment of an inverter unit according to the invention in detail.

Description of exemplary embodiments

1 shows schematically an exemplary embodiment of an electrical machine according to the invention with an inverter unit according to the invention.

An electrical machine 100 is shown, for example for a steering system (not shown). The electric machine 100 is designed as a three-phase electric motor and has a rotor-stator unit 110 on which a rotor shaft, not shown in the picture, is arranged. Furthermore, the electrical machine 100 has an inverter unit 10, which is electrically connected to the rotor-stator unit 110.

The inverter unit 10 in turn has a bridge circuit 20 and a control unit 30 and is in the 2 and 3 described in detail.

The control unit 30 is electrically connected to the switches of the bridge circuit 20 (not shown) in order to be able to control them accordingly. The control unit 30 is set up to control the switches of the bridge circuit 20 in such a way that a rotating magnetic field is generated by means of coils of the stator, which drives the permanently magnetic rotor.

The inverter unit 10 is supplied with energy by means of a power supply unit 120. The energy supply unit 120 can be, for example, a vehicle battery or another energy storage device.

2 shows an inverter unit from the prior art in detail. An inverter unit 10 with a bridge circuit 20, as is known to those skilled in the art, is shown. The bridge circuit 20 has three half bridges 22, wherein each half bridge 22 in turn has two switches, which are arranged and connected as low-side switches 24 and as high-side switches 26 in such a way that they form a B6 bridge, which in turn can drive a three-phase electric motor. However, depending on the type of electrical machine 100, any number of further half bridges would also be conceivable. The low-side switches 24 and high-side switches 26 of the half bridges 22 can in particular be designed as semiconductor switches, for example as MOSFETs. However, IGBTs would also be conceivable as switches 24, 26.

The control unit is divided into several control units 30, each of which has a high-side driver 36 for switching the respective high-side switch 26 and a low-side driver 34 for switching the respective low-side switch 24. However, it would also be conceivable to combine the control units 30 in a single component or in fewer components.

The low-side drivers 34 are each supplied with energy from a voltage source 80 of the inverter unit 10.

The high-side drivers 36 are each supplied with energy via a bootstrap unit 40, which is connected to the voltage source 80. However, it would also be conceivable that the voltage source 80 is replaced by the energy supply unit 120 and accordingly supplies the drivers 34 and 36 with energy.

Each of the bootstrap units 40 correspondingly has a first bootstrap circuit 50. The first bootstrap circuit 50 in turn has a first upper circuit node 54, a first circuit node 53, a first diode 51 and a first capacitor 52. Here, the first upper circuit node 54 is connected to the voltage source 80 and also to the first circuit node 53 via the first diode 51. Furthermore, the first circuit node 53 is connected both to the high silk driver 36 and via the first capacitor 52 to a center tap 28 of the respective half bridge 22.

The high-side driver 36 is connected to the center tap 28 with its reference potential. To initialize the bootstrap unit 40 with the first bootstrap circuit 50, the first capacitor 52 is charged by turning the low-side switch 24 on for a certain minimum time, with the high-side switch 26 being switched off accordingly during this period of time. If the high-side switch 26 is then switched, with the low-side switch 24 then being switched off accordingly, the voltage of the energy supply unit 120 is present at the center tap 28 and the first circuit node 53 is in turn at a potential which is around that of the first Capacitor 52 provided voltage is increased compared to the input voltage of the power supply unit 120. Since the first capacitor 53 can only store a finite amount of charge and discharges via the high-side driver 36, this charging process of the first capacitor 53 must be repeated periodically by the first of the capacitors 53 in the half-period during the low-side Switch 24 is conductive and the high-side switch 26 is open, is charged. In the second half period, the first capacitor 53 supplies the high-side driver 36 and the gate connection of the high-side switch 26, whereby it is switched on and kept closed. The bootstrap unit 40 with the first bootstrap circuit 50 is therefore not suitable if the high-side switch 26 is to remain switched on for a longer period of time.

3 shows an exemplary embodiment of an inverter unit according to the invention in detail.
Shown as in 2 an inverter unit 10 with a bridge circuit 20, which in turn has three half bridges 22 with corresponding high-side switches 26 and low-side switches 24. The high-side switches 26 and low-side switches 24 are in turn controlled by control units 30 with corresponding high-side drivers 36 and low-side drivers 34.

The difference to 2 is now, among other things, that the bootstrap units 40 each have, in addition to the first bootstrap circuit 50, a second bootstrap circuit 60 and a third bootstrap circuit 70.

Here, the second bootstrap circuit 60 has a second upper circuit node 64, a second diode 61, a second circuit node 63 and a second capacitor 62. The second upper circuit node 64 is connected to the voltage source 80 and also to the second circuit node 63 via the second diode 61. Furthermore, the second circuit node 63 is connected via the second capacitor 62 to the center tap 28 of the respective half bridge 22 and via a further diode 65 to the first circuit node 53 of the first bootstrap circuit 50 of another bootstrap unit 40.

Furthermore, the third bootstrap circuit 70 has a third upper circuit node 74, a third diode 71, a third circuit node 73 and a third capacitor 72. Here, the third upper circuit node 74 is connected to the voltage source 80 and also via the third diode 71 to the third circuit node 73. Furthermore, the third circuit node is 73 connected via the third capacitor 72 to the center tap 28 of the respective half bridge 22 and via a further diode 75 to the first circuit node 53 of the first bootstrap circuit 50 of yet another bootstrap unit 40.

As a result, all bootstrap units 40 are coupled to one another in such a way that the power supply to the high-side driver 36 of a half-bridge 22 with a closed high-side switch 36 can be at least partially taken over by the bootstrap unit 40 of a half-bridge 22 with an open high-side switch 36.

The first diode 51, second diode 61 and third diode 71 are each connected on the anode side to the first upper circuit node 54, second upper circuit node 64 and third upper circuit node 74 and on the cathode side to the first circuit node 52, second circuit node 62 or
third circuit node 72 connected.
The further diodes 65 and 75 are connected on the anode side to the second circuit node 62 or third circuit node 72 and on the cathode side to the first circuit node 52 of the first bootstrap circuit 50 of another bootstrap unit 40.

What is not shown in the picture is that optionally between the first upper circuit node 54 and the first diode 51 or between the second, the second upper circuit node 64 and the second diode 61 or between the third upper circuit node 74 and the third diode 71 a resistor can be arranged.
Furthermore, it is not shown in the picture that an additional resistor can optionally be arranged between the second circuit node 63 and the further diode 65 or between the third circuit node 73 and the further diode 75.

In an exemplary embodiment not shown in the picture, it is also conceivable that not each of the half bridges has a bootstrap unit and in particular that not each of the bootstrap units is coupled to the other bootstrap units. Less coupling reduces the circuit complexity of the inverter unit, but also reduces the flexibility of the control of the half bridges.

In addition, in an exemplary embodiment not shown in the picture, the inverter unit 10 can have at least one fly-back circuit for supplying energy to the respective high-side driver 36, the fly-back circuit being arranged on a half bridge 22 without a bootstrap unit 40.

Claims (6)

Inverter unit (10) for a multi-phase electrical machine (100), comprising a bridge circuit (20) with a plurality of half-bridges (22), the half-bridges each having a low-side (24) and a high-side switch (26), and wherein the inverter unit (10) has a control unit (30), wherein the control unit (30) has a high-side driver (36) for controlling the respective high-side switch (26), and wherein at least two half bridges (22) each have a bootstrap unit (40) for supplying energy to the respective high-side driver (36), characterized in that at least two bootstrap units (40) are coupled to one another. Inverter unit (10). Claim 1 , characterized in that the bootstrap units (40) are coupled to one another in such a way that the energy supply to the high-side driver (36) of a half bridge (22) with a closed high-side switch (36) is at least partially supplied by the bootstrap unit (40). a half bridge (22) with the high-side switch (36) open. Inverter unit (10). Claim 1 or 2 , characterized in that the bootstrap units (40) each have at least a first bootstrap circuit (50) and that at least one of the bootstrap units (40) has a second bootstrap circuit (60). inverter unit Claim 3 , characterized in that the first bootstrap circuit (50) and the second bootstrap circuit (60) are each arranged between a center tap (28) of the respective half bridge (22) and a voltage source (80) of the inverter unit (10), where in each case the first bootstrap circuit (50) between a first diode (51) and a first capacitor (52) has a first circuit node (53), which is connected to the respective high-side driver (36) of the half bridge (22). , and wherein in each case the second bootstrap circuit (60) has a second circuit node (63) between a second diode (61) and a second capacitor (62), which is connected via a further diode (65) to the first circuit node (53). first bootstrap circuit (50) of another bootstrap unit (40). Inverter unit (10) according to one of the preceding claims, characterized in that the inverter unit (10) has at least one fly-back circuit for supplying energy to the respective high-side driver (36), the fly-back circuit being connected to a half bridge (22) is arranged without a bootstrap unit (40). Electric machine (100), in particular electric motor, with an inverter unit (10) according to one of the preceding claims.

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