Electric drive

Abstract

Electric drive (1), comprising an electric machine (2), an inverter (3) and an intermediate circuit capacitor (C), wherein the intermediate circuit capacitor (C) is formed by at least two series-connected capacitors (C x1 , C x2 ), wherein the center tap is between the capacitors (C x1 , C x2) forms a neutral point (NP), wherein the electric drive (1) has a drive control device (6) which is designed to control the inverter (3) depending on input parameters, wherein the electric drive (1) has a single-phase mains connection (5) with a phase line (L) and a neutral conductor (N), wherein the phase line (L) is connected to a star point (S) of the electric machine (2) and the neutral conductor (N) is connected to the neutral point (NP) of the intermediate circuit capacitor (C), wherein the control for the electrical energy supply from the single-phase mains connection (5) is integrated into the drive control device (6), wherein the drive control device (6) is designed as a DQ control device with additional zero-current control, wherein the zero current (i z ) is the current through all windings of the electric machine (2), which is not equal to zero at least in AC charging mode.

Description

[0001] The invention relates to an electric drive.

[0002] Electric drives are available in a wide variety of designs for a wide range of applications.

[0003] A common design for electric drives comprises an electric motor, an inverter, and a DC link capacitor. The DC link capacitor is formed by at least two capacitors connected in series, with the center tap between the capacitors forming a neutral point. The electric drive has a drive control device designed to control the inverter depending on input parameters, for example, to generate a desired drive torque. The DC link capacitor can be connected to a battery as an energy source.

[0004] There is a desire to also provide the electric drive with energy from an AC electrical network, whereby, for example, the AC voltage is converted into a DC voltage via a separate rectifier and used to charge the intermediate circuit capacitors.

[0005] JP 2022-121 267 A discloses an electric drive comprising an electric machine, an inverter, and an intermediate circuit capacitor, wherein the intermediate circuit capacitor is formed by at least two capacitors connected in series. The center tap between the capacitors forms a neutral point. The electric drive further comprises a drive control device configured to control the inverter depending on input parameters. The electric drive comprises a single-phase mains connection with a phase line and a neutral conductor. The phase line is connected to a star point of the electric machine via a first switching element. The neutral conductor is connected to the neutral point via a second switching element. The control for the electrical energy supply from the single-phase mains connection is integrated into the drive control system.

[0006] A similar electric drive is known from US 2021 / 0 155 103 A1, where the phase line and star point are connected via an EMI filter and the neutral line and neutral point are connected via an EMI filter and a switching element.

[0007] From the technical article SENOL, Murat; DE DONCKER, Rik W.: Implementation of a drivetrain integrated DC-DC converter for 48 V vehicles. In: 2017 IEEE International Electric Machines and Drives Conference (IEMDC), 21-24 May 2017, Miami, Florida, USA, 2017, pp. 1-7. ISBN 978-1-5090-4282-1. DOI: 10.1109 / IEMDC.2017.8002247 a DC / DC converter integrated into the inverter is known, in which a zero current is regulated at the star point using an additional half-bridge.

[0008] The invention is based on the technical problem of creating an electric drive in which single-phase mains charging is possible with little circuitry effort.

[0009] The solution to the technical problem is provided by an electric drive having the features of claim 1. Further advantageous embodiments of the invention emerge from the subclaims.

[0010] For this purpose, the electric drive comprises an electric machine, an inverter and an intermediate circuit capacitor, wherein the intermediate circuit capacitor is formed by at least two capacitors connected in series, wherein the center tap between the capacitors forms a neutral point. The electric drive has a drive control device which is designed to control the inverter depending on input parameters. The electric drive has a mains connection with a phase line and a neutral conductor, wherein the phase line is connected to a star point of the electric machine and the neutral conductor is connected to the neutral point of the intermediate circuit capacitor, wherein the control for the electrical energy supply from the single-phase mains connection is integrated into the drive control device. This allows very simple integration without additional components, wherein only the star point of the electric machine orThe neutral point of the intermediate circuit capacitor must be removed. This illustrates this by showing that positive currents in the windings of the electric motor turn on the high-side transistors, and negative currents turn on the low-side transistors, charging the intermediate circuit capacitor and, via this, any connected battery.

[0011] The drive control system is designed as a DQ control system with additional zero-sequence current control, where the zero-sequence current is the current through all windings of the electric machine, which is not equal to zero, at least in the AC charging case. The term "zero-sequence current" stems from the fact that in purely motor operation, the currents through the windings are usually a +i b +i c =0 is assumed. Illustratively, the DQ control becomes a DQZ control (Z=Zero), ie the zero current, which is usually neglected in drive control, is controlled here as an active charging current.

[0012] Preferably, the single-phase mains connection has a ground connection which is connected to a ground connection of the electric drive.

[0013] In another embodiment, the lines of the single-phase mains connection are connected to an EMC filter, from which they are routed to the star point and the mains connection. The advantage is that the connections are easily accessible from the EMC filter, as all required connections (star point, neutral point, ground) are located there. For example, Y capacitors are arranged in the EMC filter, which are connected from the live lines to ground.

[0014] In one embodiment, the drive control device is designed to calculate a charging power to be set and the value of the mains voltage as input variables in AC charging operation and from this to calculate a zero current to be set as the charging current for the intermediate circuit capacitor.

[0015] In another embodiment, the drive control device is configured to simultaneously perform an AC charging process and generate a drive torque. For example, a fan or heat pump can be operated and charged simultaneously. The drive control device calculates a d, q, and z current.

[0016] In an alternative embodiment, the drive control device is designed such that no drive torque is generated during AC charging. In certain applications, such as electric drives of electric or hybrid vehicles, no drive torque should be generated during AC charging. In this case, the design of the drive control device is simplified because the zero-sequence current is zero during the drive mode and the d- and q-currents are zero during AC charging mode.

[0017] The electric drive is therefore suitable for a wide range of applications.

[0018] The invention is explained in more detail below using a preferred embodiment. The figures show: Fig. 1 a schematic representation of an electric drive and Fig. 2 a schematic block diagram of a drive control device.

[0019] In the Fig. 1 schematically shows an electric drive 1. The electric drive 1 has a three-phase electric machine 2 with a star point S. The electric drive 1 also has an inverter 3, which is symbolized by six switching elements S1-S6, which are connected in three half-bridges, with the center taps of the three half-bridges being connected to the three phases of the electric machine 2. Depending on the application, the switching elements S1-S6 can be designed as power transistors (e.g. MOSFET or IGBT), whereby the technology (Si, SiC, GaN) can also be selected according to the application. The electric drive 1 also has an intermediate circuit capacitor C, which is formed by a series connection of two capacitors C x1 , C x2is formed, with the center tap forming a neutral point NP. An EMC filter 4 is provided, which has various filters to reduce, on the one hand, feedback to an AC voltage network and, on the other hand, interference radiation from the electric drive 1. Furthermore, the electric drive 1 has a single-phase mains connection 5, which has a phase line L, a neutral conductor N as a return conductor and a ground line PE for earthing. The three lines L, N and PE are led to the EMC filter 4 and are distributed from there. The phase line L is connected to the star point S and the neutral conductor N to the neutral point NP. The ground line PE is connected to a ground connection of the electric drive 1. The three phase currents i a , i b , i c and the voltages U a , U b , U c measured at the center taps of the half bridges. U nis the mains voltage applied to the mains connection 5. Furthermore, the voltages U ZK+ and U ZK- on the intermediate circuit capacitor C.

[0020] The switching elements S1-S6 are then controlled via a drive control device 6, the drive control device 6 being shown as a block diagram in Fig. 2. The drive control device 6 has a reference calculation 7, which is calculated from the input variables U ZK+ , U ZK- , U n , n, m* and p* are the three current components i d* , i q* and i z* where n is the speed of electric machine 2, m* is a target torque of electric machine 2, and p* is a target charging power. The i d* and i q* Current components can be determined as in a known DQ control, where i z* for example through iz∗=p∗U⌢n2^⋅Un U n is determined. And^ the amplitude of the mains voltage U n . In parallel, a DQZ transformation 8 takes place, which converts the three measured phase currents i a , i b , i c into an i d -, i q - and i z -component. The differences i d* - i d , i q* - i q and i z* - i z are then fed to a controller 9, 10 and 11 respectively. Furthermore, a feedforward control 12 and a disturbance compensation 13 are provided, whereby the disturbance for the zero voltage is the mains voltage, i.e. U zs = U n(where the index s stands for disturbance). The feedforward control 12 takes the mutual inductive influence into account. Since, in contrast to a conventional DQ control, three currents instead of two currents must be considered, three three-dimensional characteristic maps result for the mutual influence of the inductances (instead of two two-dimensional characteristic maps in DQ control). The general rule is: Uzv=Lzd(id*,iq*,iz*)⋅Id*2+ Lzq(id*,iq*,iz*)⋅Iq*2+ Lzz(id*,iq*,iz*)⋅Iz*2

[0021] Clearly considers L zd the influence of L z by the d-component and L zq the influence of the q-component, where L zz which represents self-inductance.

[0022] The voltages U thus obtained d U q and U z are subjected to an inverse DQZ transformation 14, so that as a result the three voltages U a , U b , U con the three half bridges.

[0023] By means of this drive control device 6, a target torque m* can also be set during AC charging operation.

[0024] If, however, no target torque m* is to be generated during AC charging, the control is simplified, since no zero current is connected during motor operation (i z = 0) and in AC charging mode i d = i q = 0. In this case, in AC charging mode, all high-side switching elements S1, S3, S5 and all low-side switching elements S2, S4, S6 are each switched synchronously in the same way.

[0025] Thus, with minor adjustments, single-phase AC charging operation can be integrated into an electric drive, whereby mixed operation (AC charging + motor drive) is also possible. List of reference symbols 1 drive 2 electric machine 3 inverters 4 EMC filters 5 Mains connection 6 Drive control 7 Reference calculation 8 DQZ transformation 9, 10, 11 controls 12 Feedforward control 13 Disturbance compensation 14 DQZ.Transformation S star point S1-S6 switching elements C DC link capacitor C x1 , C x2 capacitors L phase line N neutral conductor PE ground wire NP Neutral Point

Claims

[1] Electric drive (1), comprising an electric machine (2), an inverter (3) and an intermediate circuit capacitor (C), wherein the intermediate circuit capacitor (C) is formed by at least two series-connected capacitors (C x1 , C x2 ), wherein the center tap is between the capacitors (C x1 , C x2) forms a neutral point (NP), wherein the electric drive (1) has a drive control device (6) which is designed to control the inverter (3) depending on input parameters, wherein the electric drive (1) has a single-phase mains connection (5) with a phase line (L) and a neutral conductor (N), wherein the phase line (L) is connected to a star point (S) of the electric machine (2) and the neutral conductor (N) is connected to the neutral point (NP) of the intermediate circuit capacitor (C), wherein the control for the electrical energy supply from the single-phase mains connection (5) is integrated into the drive control device (6), wherein the drive control device (6) is designed as a DQ control device with additional zero-current control, wherein the zero current (i z ) is the current through all windings of the electric machine (2), which is not equal to zero at least in AC charging mode. [2] Electric drive according to claim 1,characterized by that the single-phase mains connection (5) has a ground line (PE) which is connected to a ground connection of the electric drive (1). [3] Electric drive according to one of the preceding claims, characterized by that the lines (L, N, PE) of the single-phase mains connection (5) are connected to an EMC filter (4), from which they are led to the star point (S) and the neutral point (NP). [4] Electric drive according to one of the preceding claims, characterized by that the drive control device (6) is designed in such a way that, in AC charging mode, a charging line (p*) to be set and the value of the mains voltage (U n ) as input variables and to determine a zero current (i z ) as the charging current for the intermediate circuit capacitor (C). [5] Electric drive according to one of the preceding claims, characterized bythat the drive control device (6) is designed to simultaneously carry out an AC charging process and to generate a drive torque (m*). [6] Electric drive according to one of claims 1 to 4, characterized by that the drive control device (6) is designed such that no drive torque (m*) is generated during the AC charging process. [7] Electric drive according to claim 6, characterized by that the electric drive (1) is designed as a drive of an electric or hybrid vehicle.

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