DE102013016960A1 - Inverter unit for electric machine has control device to control inverter switches and bridge switches to close, and to cause free-wheel to control one of bridge switches and other inverter switches to open in response to error signal - Google Patents

Abstract

The inverter unit (1) has direct current (DC)/DC transducer (4) including bridge with two bridge legs which comprise bridge switch (S-dcdc-1,S-dcdc-2). A current intermediate circuit (5) is connected to inverters (6) with several inverter branches with inverter switches (S1-S6). A control device controls bridge switches and inverter switches. The control device controls inverter switches and bridge switches to close and causes a free-wheel and controls one of the bridge switches and the other inverter switches to open in response to an error signal. An independent claim is included for method for operating inverter unit.

Description

The invention relates to an inverter unit for an electrical machine with a DC / DC converter including a bridge with two bridge branches, each having a bridge switch, a power link at the output of the bridge, a connected to the power link inverter with multiple phases, each two inverter switches per branch, and a controller for controlling the bridge switch and the inverter switch. Moreover, the present invention relates to a method for operating such an inverter unit.

An inverter unit with current intermediate circuit can be used as a power element for a traction drive. In the event of a fault, all system components (electrical machine, inverter unit and battery) must be brought to a safe state. During the shutdown process, very high overvoltages and currents may occur due to the passive components in the system. These must be controlled by suitable switch-off strategies in order to protect the components during the switch-off process. It is therefore desirable to find corresponding switch-off strategies for the use of an inverter unit with current intermediate circuit.

From the publication DE 10 2006 003 254 A1 is a method for switching off an electrical machine with pulse inverter in case of failure known. Unwanted side effects when switching off the electric machine can be minimized and the regular machine operation can be maximized when the electric machine first in a disconnection operation in which all switches of the pulse inverter are open, and subsequently switched to a short-circuit mode in which The high-potential connected switch is open and the switches connected to the low potential are closed. However, this document relates only to an application of an inverter unit with voltage intermediate circuit and is not transferable due to the basic structure for the application of an inverter unit with current intermediate circuit.

The object of the present invention is thus to provide an inverter unit with current intermediate circuit, which can be operated safely and in particular safely switched off. In addition, a corresponding operating method should be provided.

• – einem DC/DC-Wandler einschließlich einer Brücke mit zwei Brückenzweigen, die jeweils einen Brückenschalter aufweisen,
• – einem Stromzwischenkreis am Ausgang der Brücke,
• – einem an den Stromzwischenkreis angeschlossenen Wechselrichter mit mehreren Phasen, die jeweils zwei Wechselrichterschalter aufweisen, und
• – einer Steuereinrichtung zur Steuerung der Brückenschalter und der Wechselrichterschalter, wobei
• – die Steuereinrichtung dazu ausgelegt ist, in Abhängigkeit von einem Fehlersignal in einem ersten Schritt einen aktiven Kurzschluss zu bewirken, indem alle Wechselrichterschalter geschlossen werden und ein Brückenschalter geschlossen wird, und in einem zweiten Schritt einen Freilauf zu bewirken, indem die Wechselrichterschalter eines Brückenbeins geschlossen und die übrigen Wechselrichterschalter geöffnet werden.

According to the invention this object is achieved by an inverter unit for an electric machine

• A DC / DC converter including a bridge with two bridge branches, each having a bridge switch,
• A current intermediate circuit at the output of the bridge,
• A multiphase inverter connected to the power link, each having two inverter switches, and
• - A control device for controlling the bridge switch and the inverter switch, wherein
• - The control device is adapted to cause in response to an error signal in a first step, an active short circuit by all inverter switches are closed and a bridge switch is closed, and to effect a freewheel in a second step by the inverter switches a bridge leg closed and the remaining inverter switches are opened.

• – Erfassen eines Fehlersignals,
• – Bewirken eines aktiven Kurzschlusses von Anschlüssen der elektrischen Maschine in Abhängigkeit von dem Fehlersignal, indem alle Wechselrichterschalter geschlossen werden und ein Brückenschalter geschlossen wird, und
• – Bewirken eines Freilaufs der elektrischen Maschine, indem die Wechselrichterschalter eines der Brückenbeine geschlossen und die übrigen Wechselrichterschalter geöffnet werden.

In addition, the invention provides a method for operating an inverter unit for an electrical machine with a DC / DC converter including a bridge with two bridge branches, each having a bridge switch, a power link at the output of the bridge and a connected to the power link inverter with multiple Phases, each having two inverter switch through

• Detecting an error signal,
• - causing an active short circuit of terminals of the electric machine in response to the error signal by all inverter switches are closed and a bridge switch is closed, and
• - To cause a freewheel of the electric machine by the inverter switch one of the bridge legs closed and the other inverter switches are opened.

In the event of a fault, when an error signal is detected, an active short circuit at the output of the inverter is advantageously effected first, followed by a freewheeling of the electrical machine. This has the advantage that initially low overvoltages occur during the active short circuit and the high peak torques occurring during this process are reduced by the subsequent switching to the freewheeling system.

Preferably, a battery contactor is arranged at the input of the DC / DC converter, which is opened in the first step in order to disconnect the battery in the event of a fault.

In addition, the current intermediate circuit may comprise a coil, and the Control device may be configured to open in a third step subsequent to the second step, all bridge switches and inverter switches when the coil is demagnetized to a predetermined extent. In this state, the system can be shut down safely.

In addition, the inverter unit may comprise voltage estimation means for estimating a voltage at the output of the inverter or a filter means connected thereto, and the controller may then be configured to switch from the first step to the second step depending on the estimated voltage , As a result, the switching from the active short circuit to the freewheel can take place as a function of the maximum permissible component voltages.

The present invention will now be explained in more detail with reference to the accompanying drawings, in which:

1 an inverter unit according to the invention with current intermediate circuit in a system with battery and electric machine in the off state;

2 a circuit diagram of the system of 1 in the state of an active short circuit; and

3 a circuit diagram of the system of 1 in the state of a freewheel.

The embodiments described in more detail below represent preferred embodiments of the present invention.

1 gives a schematic diagram of one about an inverter unit 1 from a battery 2 powered electric machine 3 again. The battery 2 can be represented by an ideal voltage source V_Batt in series with a battery resistor R_Batt. To the terminals of the battery 2 a backup capacitor C_Stütze is connected.

The inverter unit 1 here has a DC / DC converter 4 on whose two input poles each have a battery protection S_Battschutz_1 and S_Battschutz_2 to the terminals of the battery 2 are connected. The DC / DC converter 4 has a bridge with two bridge branches connected in parallel to its input terminals. The first bridge branch consists of a series connection of a switch S_dcdc_1 and a diode D1. The second bridge branch consists of a series connection of a diode D2 and a switch S_dcdc_2. The center taps of the two bridge branches lead to the current intermediate circuit 5 having an inductance L_ZK. Through the switches S_dcdc_1 and S_dcdc_2 of the DC / DC converter 4 can the current in the power link 5 be regulated. For this purpose, the switches are controlled by a control device, not shown.

The two lines of the current intermediate circuit 5 lead to an inverter 6 from the direct current an alternating current (here a three-phase alternating current) for the electrical machine 3 generated. For example, it is the electric machine 3 around a three-phase electric motor.

The inverter 6 is in the example of 1 typically shown with three phases in parallel with its input terminals. Each bridge leg has in the usual way two series-connected switches S1, S2 and S3, S4 and S5, S6. The center taps between the respective switches of each inverter branch represent the inverter outputs and are connected to the terminals of the electric machine 3 connected. That's what the three leaders are for 7 . 8th . 9 intended. This ladder 7 . 8th . 9 are with a filter 10 with a star point 11 connected. This is every leader 7 . 8th . 9 with a respective filter capacitor C_Filter to the neutral point 11 connected.

Both the bridge switches S_dcdc_1, S_dcdc_2 and the inverter switches S1 to S6 but also the battery contactors S_Battschutz_1, S_Battschutz_2 are opened here so that the system is in the "off" state. This state should be able to be safely reached from a normal operating state in the event of a fault. The DC / DC converter is used for recuperation purposes.

If an error occurs in a normal operating state of the system, the in 1 unillustrated control device, which controls all circuit breakers, bridge switches and inverter switches, to be able to safely place the system in the in 1 displayed "off" state to switch. So it has to be both the electric machine 3 as well as the power electronics of the inverter unit 1 be switched off. It is important to protect the battery, the power electronics and passive components from overvoltages and overcurrents. Particularly critical are overvoltages on the filter capacitances C_Filter and resulting phase-to-phase voltages between the conductors 7 . 8th and 9 that can damage the power electronic components.

According to the invention, therefore, in the event of a fault, ie in the case of the present error signal, initially an active short-circuit at the outputs of the inverter 6 and then causes a freewheeling means of the inverter switch S1 to S6. For switching from active short circuit to freewheeling a surge estimator is used, which provides a corresponding control function for switching. Such a surge estimator is preferably integrated in the control device. Input variables of the overvoltage estimator are, for example, machine parameters and measured currents and voltages. Output variables are maximum expected capacitance and phase-to-phase voltages.

So it is in the event of an error, first from the control device in the in 2 shown active short circuit switched. In this case, all inverter switches S1 to S6 are closed and a bridge switch of the DC / DC converter 4 (here the bridge switch S_dcdc_1) is also closed. The battery contactors S_Battschutz_1 and S_Battschutz_2 are opened from the normal operating state. An advantage of the active short circuit is that only small to no overvoltages occur at the inductances of the electric machine, the filter components and the switches. A disadvantage of the active short circuit, however, is that a high peak torque and high peak currents occur.

Due to the disadvantages of the active short circuit is in the freewheel according to 3 connected. So two fault strategies are combined: the active short circuit and the freewheel. In the freewheel is a branch of the inverter 6 (Here, the switches S1 and S2) closed, while the remaining switches S3 to S6 are open. In addition, the bridge switch S_dcdc_1 is closed, while the other bridge switch S_dcdc_2 remains open. The battery contactors S_Battschutz_1, S_Battschutz_2 remain open. The advantage of the freewheeling state is now the low peak torque and the low peak currents. The disadvantage, however, are high overvoltages in the filter and at the switches.

Both strategies (active short circuit and freewheeling) have advantages and disadvantages. The active short circuit must, starting from a static state, usually first be activated, otherwise there is a risk of a component destruction. The advantage of freewheeling is that the inverter is disconnected from the electrical machine, there is no current flow from the machine to the inverter and the DC link inductance is demagnetized via the switch and the DC link, which enables a subsequent "off" state.

Thus, according to the invention, both strategies (active short-circuit and free-wheeling) are combined, with the active short circuit initially taking place and, after meeting certain criteria, switching to the free-wheeling mode. After switching to freewheel, wait until the DC link is demagnetized. After that, all switches can be switched off to the safe state. Critical is the switch from the active short circuit in the freewheel. There is a forced opening of the inverter branches. The flowing electricity has to pass on to the filter capacities. After switching to the freewheel results in an electrical network with capacities of the filter 10 and inductors of the electric machine 3 in row. This results in resonant circuits with sinusoidal currents and voltages fed by induced voltages of the electric machine.

With the aid of the above-mentioned overvoltage estimator, it is now estimated whether the respective overvoltages in the filter or at the switches are in free-running at the respective current point in time below a predetermined permissible voltage. In particular, it can be monitored whether all the peak voltages at the filter capacitors are below a permissible maximum voltage. This decision criterion can be used for the regulated switching from active short circuit to freewheeling.

Another decision criterion for controlled switching from active short to freewheeling is in terms of phase-to-phase voltages between the conductors 7 . 8th and 9 , Each of these phase-to-phase voltages must not exceed a permissible maximum value.

If both of the above-mentioned decision criteria are met, the control device can switch from the active short circuit to the freewheel.

• a) Statischer Betrieb: Das System befindet sich in einem normalen Betriebsmodus. Eine Fehlerfallregelung ist inaktiv.
• b) Aktiver Kurzschluss: Im Fehlerfall wird der aktive Kurzschluss aktiviert. Die Batterie wird zunächst mit Hilfe von Leistungsschützen von der Leistungselektronik abgetrennt. Die Fehlerfallregelung wird aktiv und die Spannungen an den kritischen Bauteilen werden geschätzt. Der Regler bzw. die Steuereinrichtung löst ein Umschalten in den Freilauf aus, sobald vordefinierte Bedingungen bezüglich der geschätzten Spannungen erfüllt sind.
• c) Freilauf: Es erfolgt kein Stromfluss mehr von der elektrischen Maschine und den Filtern in den Wechselrichter. Der Zwischenkreis wird entmagnetisiert. Der Regler bzw. die Steuereinrichtung schaltet um in den „aus”-Zustand, sobald der Zwischenkreis entmagnetisiert ist.
• d) „aus”-Zustand: Alle Schalter sind ausgeschaltet. Die Batterie ist abgetrennt und der Zwischenkreis ist entmagnetisiert. Es liegt ein sicherer Zustand vor.

A fault control of the battery-powered electric machine 3 could be done in four states according to the following scheme:

• a) Static operation: The system is in a normal operating mode. An error control is inactive.
• b) Active short circuit: In the event of a fault, the active short circuit is activated. The battery is first disconnected from the power electronics with the help of power contactors. The fault control becomes active and the voltages at the critical components are estimated. The controller or the control device triggers a switchover to the freewheel as soon as predefined conditions with regard to the estimated voltages are fulfilled.
• c) Freewheel: There is no current flow from the electrical machine and the filters in the inverter. The DC link is demagnetized. The controller or the control device switches to the "off" state as soon as the DC link is demagnetized.
• d) "off" state: all switches are off. The battery is disconnected and the DC link is demagnetized. There is a safe state.

Special features of fault control or control can occur at operating points of high mechanical performance. These include high currents and / or high induced voltages that lead to excessively high overvoltages. In addition, a switch to the freewheel can only be made possible when the speed drops sufficiently and thus the induced voltage is correspondingly low. This would be another decision criterion in addition to the maximum allowable voltages. With such operating points, the system can therefore remain for a longer time in the active short circuit, whereby the disadvantages of such an active short circuit would not be fully compensated.

In summary, the fault control in the event of a fault thus separates the electrical machine and the filter capacitors from the power electronics. In such an error case, switching to the active short-circuit occurs without additional conditions. A control or control for switching from the active short circuit in the freewheel is based on a prediction of the expected voltage spikes in the filter and the power electronics. This can avoid critical overvoltages and high negative torque peaks can be reduced by the active short circuit. After the demagnetization of the DC link all switches are turned off and the power electronics is thus completely disconnected.

Advantageously, the present invention thus combines the advantages of both failure strategies and at the same time avoids the disadvantages by properly determining the switchover time by a surge estimator so that the electrical machine can be safely shut down by the DC link inverter unit without destroying other system components by overvoltages.

LIST OF REFERENCE NUMBERS

1

Inverter unit

2

battery

3

electric machine

4

DC / DC converter

5

Current intermediate circuit

6

inverter

7

ladder

8th

ladder

9

ladder

10

filter

11

star point

V_Batt

ideal voltage source

R_Batt

battery resistance

S_Battschutz_1

battery contactor

S_Battschutz_2

battery contactor

S_dcdc_1

bridge switch

S_dcdc_2

bridge switch

D1

diode

D2

diode

L_ZK

inductance

S1 to S6

Inverter switch

c_filter

filter capacitor

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• DE 102006003254 A1 [0003]

Claims (5)

Inverter unit ( 1 ) for an electric machine ( 3 ) with - a DC / DC converter ( 4 ) including a bridge with two bridge arms, each having a bridge switch (S_dcdc_1, S_dcdc_2), - a power link ( 5 ) at the output of the bridge, - one at the current intermediate circuit ( 5 ) connected inverters ( 6 ) having a plurality of inverter branches, each having two inverter switches (S1 to S6), and - a control device for controlling the bridge switches (S_dcdc_1, S_dcdc_2) and the inverter switch (S1 to S6), characterized in that - the control device is adapted to Depending on an error signal in a first step to cause an active short circuit by all inverter switches (S1 to S6) are closed and a bridge switch (S_dcdc_1, S_dcdc_2) is closed, and in a second step to cause a freewheel by the inverter switches (S1 to S6) one of the bridge legs closed and the other inverter switches (S1 to S6) are opened. Inverter unit ( 1 ) according to claim 1, characterized in that at the input of the DC / DC converter ( 4 ) a battery contactor (S_Battschutz_1, S_Battschutz_2) is arranged, which is opened in the first step. Inverter unit ( 1 ) according to claim 1 or 2, characterized in that the current intermediate circuit ( 5 ) has a coil (L_ZK), and the control device is further configured, in a third step following the second step, to open all the bridge switches (S_dcdc_1, S_dcdc_2) and inverter switches (S1 to S6) when the coil (L_ZK) reaches up to demagnetized to a predetermined degree. Inverter unit ( 1 ) according to one of the preceding claims, characterized in that it comprises a voltage estimator, with which a voltage at the output of the inverter ( 6 ) or on a connected filter device ( 11 ), and the controller is adapted to switch from the first step to the second step in response to the estimated voltage. Method for operating an inverter unit ( 1 ) for an electric machine ( 3 ) with a DC / DC converter ( 4 ) including a bridge with two bridge branches, each having a bridge switch (S_dcdc_1, S_dcdc_2), a power link ( 5 ) at the output of the bridge and one at the current intermediate circuit ( 5 ) connected inverters ( 6 ) having a plurality of phases, each having two inverter switches (S1 to S6), characterized by - detecting an error signal, - causing an active short circuit of terminals of the electric machine ( 3 ) in response to the error signal by closing all the inverter switches (S1 to S6) and closing a bridge switch (S_dcdc_1, S_dcdc_2), and - causing a freewheel of the electric machine ( 3 ) by closing the inverter switches (S1 to S6) of one of the bridge legs and opening the remaining inverter switches (S1 to S6).

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