DE102007051106B4 - Inverter for supplying an electric motor and method for operating an inverter - Google Patents

Abstract

Inverter for supplying an electric motor,
wherein the converter comprises a first and a second inverter, each of which is supplied from a unipolar DC link voltage and the respective DC link voltage is generated by means of a respective rectifier or controllable AC / DC converter from a supply network,
wherein at least one of the inverters feeds the electric motor,
characterized in that
- The first inverter (6) switch much lower blocking voltage than the second inverter (2),
- below a critical value of the motor voltage at least the first inverter (6) and above a critical value of the motor voltage of the second inverter (2) feeds the electric motor (3), and
- Between the first inverter (6) and motor (3) a separating device (5) is arranged; which is controllable by a control electronics.

Description

The The invention relates to a converter for supplying an electric motor and a method of operating an inverter.

inverter comprise a rectifier, which consists of a supply voltage a unipolar voltage that generates DC link voltage, from which an inverter is supplied, which feeds an electric motor. The inverter is in this case of two or more half-bridges, ie Branch pairs, formed by power semiconductor switches, of be controlled by a control electronics. This is usually a pulse width modulated method used.

From the DE 197 26 161 A1 a converter for supplying an electric motor is known, wherein a first and a second inverter are supplied from a unipolar DC link voltage, which is generated from a rectifier. The interaction of the inverters should favorably influence the reactive power ratios.

From the US 5 047 909 A a converter for supplying an electric motor is known, wherein a first and a second inverter are supplied from a unipolar DC link voltage, which is generated from a rectifier. It should be achieved by the interaction of the inverter harmonic compensation.

Of the Invention is therefore the object of a converter in cost Way to develop, with a motor, a suitable and cost-effective Inverter provided shall be.

According to the invention Task with the inverter according to claim 1 and in the method solved according to the features specified in claim 11.

• – der erste Wechselrichter Schalter viel geringerer Spannungsfestigkeit aufweist als der zweite Wechselrichter,
• – unterhalb eines kritischen Wertes der Motorspannung zumindest der erste Wechselrichter und oberhalb eines kritischen Wertes der Motorspannung der zweite Wechselrichter den Elektromotor speist, und
• – zwischen erstem Wechselrichter und Motor eine Trennvorrichtung angeordnet ist, die von einer Steuerelektronik steuerbar ist.

Important features of the invention in the inverter are that it comprises at least a first and a second inverter, which are each supplied from a unipolar DC link voltage and the respective DC link voltage is generated by means of a respective rectifier or controllable AC / DC converter from a supply network,
wherein at least one of the inverters feeds the electric motor,
in which

• The first inverter has a much lower dielectric strength switch than the second inverter,
• - below a critical value of the motor voltage at least the first inverter and above a critical value of the motor voltage of the second inverter feeds the electric motor, and
• - Between the first inverter and motor, a separator is arranged, which is controlled by an electronic control unit.

From The advantage here is that the first and second inverter on different voltage ranges can be interpreted. The second inverter is equipped with switches that have a much higher reverse voltage capability and smaller maximum allowable Current values are interpretable. The switches of the first inverter are on the other hand much higher current values interpretable and to a much smaller reverse voltage resistance. Consequently is a much cheaper Realization of the inverter available. Because in different operating areas Different inverters are operable, whereby these adaptable are on these respective operating areas. For example, the first inverter on the operating range of low voltage and high currents interpretable while the second inverter can be designed for medium voltage and lower currents is. Preferably the low voltage is less than 50 volts and the medium voltage is up to 1000 volts.

at The invention thus the respective DC link voltage means a respective rectifier or controllable AC / DC converter generated a supply network. The advantage here is that means of the rectifier, a DC link voltage can be generated, the the peak voltage corresponds to the AC voltage of the supply network and by means of the controllable AC / DC converter an intermediate circuit voltage can be generated from the supply network, which is a unipolar low voltage of, for example, less than 50 volts.

at The invention is also between the first inverter and motor arranged a separator, which is controllable by a control electronics. It is advantageous that destructive high voltages can be kept away from the switches of the first inverter are.

In an advantageous embodiment, that intermediate circuit voltage from which the first inverter is supplied, generated by means of an uncontrolled rectifier from a supply network
and that intermediate circuit voltage from which the second inverter is supplied, generated by means of a controllable AC / DC converter, in particular a phase-angle controlled rectifier, from the supply network. The advantage here is that the rectifier can be built from passive low-cost components and the controllable converter is operable with a simple phase control.

at In an advantageous embodiment, the electric motor is a three-phase motor and / or the supply network a single- or multi-phase AC mains. The advantage here is that industry standard rotary current drivable Asynchronous or synchronous motors are used in the invention, especially in the range between 10 watts and 10 megawatts, and off A three-phase network can be supplied. But the invention is also for single-phase supply network and single-phase electric motors applicable.

at an advantageous embodiment is the reverse voltage resistance the switch of the first inverter at least more than five times, in particular more than ten times, less than the reverse voltage capability of Switch of the second inverter. The advantage here is that for the first inverter simpler, cheaper Switch are usable because the reverse voltage resistance far lower must be than the second inverter.

at An advantageous embodiment is the maximum permitted DC link voltage of the first inverter at least more than five times, in particular more than ten times, less than the maximum permitted DC link voltage of the second inverter. The advantage here is that a respective provided smoothing capacitor only to the appropriate voltage must be designed. Thus is this one for the first DC link much cheaper than the second.

at an advantageous embodiment, the AC / DC converter for Generating the DC link voltage for the first inverter phase-gapped Thyristors. The advantage here is that a simple arrangement for the generation of unipolar low voltage is providable, from the the first inverter can be supplied.

at an advantageous embodiment, the drive signals of Inverter generated by the control electronics. Is an advantage in that the control makes the inverter controllable in this way, that it is pulse width modulated operable.

at an advantageous embodiment, the drive signals for the first and second and / or for all inverters are synchronous or they become the same control signals for the supplied first and second and / or all inverters, in particular the associated Signal lines are laid parallel. The advantage here is that no separate control for the different inverters are necessary but a common Control is sufficient.

at an advantageous embodiment are means for detecting the Motor voltage provided and / or there are means for detecting the DC link voltage with means for detecting the pulse width modulation duration connected such that the motor voltage is modeled, in particular from the control electronics. The advantage here is that the motor voltage directly or at least model, ie indirectly, can be determined and thus the voltage at the motor to a critical exceeding Value monitorable is and a corresponding actuation of the Isolating circuit is effected.

• – der erste Wechselrichter Schalter viel geringerer Sperrspannungsfestigkeit aufweist als der zweite Wechselrichter,
• – unterhalb eines kritischen Wertes der Motorspannung zumindest der erste Wechselrichter und oberhalb eines kritischen Wertes der Motorspannung der zweite Wechselrichter den Elektromotor speist, und
• – oberhalb des kritischen Wertes die elektrische Verbindung zwischen Motor und erstem Wechselrichter aufgetrennt wird.

Important features in the method for operating an inverter are that at least one of the inverters feeds the electric motor, wherein

• The first inverter has a switch with much lower blocking voltage resistance than the second inverter,
• - below a critical value of the motor voltage at least the first inverter and above a critical value of the motor voltage of the second inverter feeds the electric motor, and
• - Above the critical value, the electrical connection between the motor and the first inverter is separated.

From The advantage here is that not an inverter with its switches on all operating range, ie low voltages with high currents and at the same time high voltages with low currents, interpreting is but that for the respective operating area a respective inverter can be interpreted.

Especially So is in the invention above the critical value of the electric Connection between motor and first inverter separated. The advantage here is that the switches of the first inverter Estimated against excessive voltages are. Because after disconnecting the first inverter from the motor supply lines The second inverter generates an increasingly higher and higher output critical value lying motor voltage, because of the low reverse voltage resistance the switch of the first inverter could lead to their destruction.

The Separating device is designed as a contactor in a first embodiment. In other embodiments But it is also an execution executable by other means.

In an advantageous embodiment, the first and second inverters feed in parallel and / or synchronously below the critical value Engine and
above the critical value only the second feeds the motor. The advantage here is that the generation of high currents at low voltages is parallel executable, so distributed to two inverters. Thus, the first inverter does not have the high current value. but slightly lower current values are designed.

at In an advantageous embodiment, the first inverter supplying DC link voltage limited to a value that at least five times, in particular ten times, is smaller than the value of the intermediate circuit voltage in the unloaded case, from which the second inverter is supplied. Advantageous is that by means of the controllable AC / DC converter, the DC link voltage limited to the critical value or an underlying value is. Thus, a destruction the switch of the first inverter preventable despite the low Voltage blocking capability.

1

rectifier

2

inverter

3

electric motor

4

control unit

5

separating device

6

inverter

7

AC / DC converter

8th

supply network

The invention will now be explained in more detail with reference to figures:
In the 1 a device according to the invention is schematically sketched.

As a supply network 8th is a single- or multi-phase supply network, so AC network, provided. For example, this is designed as a 380 V three-phase network.

Overall, a first and a second inverter 6 and 2 intended.

One from the supply network 8th powered rectifier 1 generates a unipolar DC link voltage. In this case, the rectifier is composed of a number of diode half-bridges corresponding to the number of phases, that is to say branch pairs. Preferably, passive uncontrolled power semiconductor components are therefore used for this purpose.

From the unipolar voltage, ie intermediate circuit voltage, becomes the second inverter 2 supplied, which generates a three-phase system of three-phase voltage, from which the electric motor 3 is dinable.

The intermediate circuit voltage has values of more than 500 volts in the unloaded operating state. Thus, the intermediate breakdown voltage then corresponds to the peak voltage of the supply network. For regenerative operation of the engine 3 even higher voltages of over 800 volts occur.

The inverter 2 comprises three half-bridges, that is to say branch pairs, in each of which electronic power switches, that is to say power semiconductors such as IGBT or MOSFET, are provided. The blocking voltage of these power switches is so high that the said intermediate circuit voltage values can be controlled.

Similarly, one is via a separator 5 also for feeding the same engine 3 connected first inverter 6 can be supplied from a DC link voltage, that of the supply network 8th power supply AC / DC converter 7 is supplied.

The first inverter 6 also comprises three half-bridges, that is to say branch pairs, in each of which electronic power switches, that is to say power semiconductors such as IGBT or MOSFET, are provided. The reverse voltage capability of these circuit breakers, however, is lower than that of the switches of the second inverter 2 , Thus, the inverter 6 much cheaper switch than the second inverter 2 used.

Both inverters 2 and 6 become from a control unit 4 supplied with drive signals, which are preferably carried out synchronously. The control unit 4 also generates a control signal indicating the closing and opening of the separator 5 allows. In this case, the operation of the separator 5 caused as a function of exceeding or falling below a critical value of motor voltage. For this purpose, the motor voltage is detected directly or indirectly.

The AC / DC converter 7 is designed such that it comes from the AC voltage of the supply network 8th a unipolar voltage, ie DC link voltage generated, which is much lower than that of the second inverter 2 supplying DC link voltage. Preferably, this DC link voltage 5 times or up to 10 times smaller than the first inverter 2 supplying DC link voltage, this applies to the unloaded state.

In a first embodiment of the invention, the AC / DC converter 7 designed as a rectifier, which includes not only diodes but also controllable power semiconductors, such as phase-gapped thyristors. Every phase of the supply network 8th So it's a half bridge, so Pair of branches, assigned, which consists of two series-connected phase-gapped thyristors or at least one diode, which is connected to a phase-gapped thyristor in series.

It will be the AC / DC converter 7 detected DC link voltage detected and regulated by means of adjusting the phase angle to the desired target value, in particular less than 50 volts.

advantageous DC link voltages are 12 volts, 24 volts or 48 volts. The reverse voltage resistance is correspondingly low selectable.

When starting the motor supplied by the inverter 3 In particular, a high current is needed to overcome the breakaway torque. The voltage required at startup, on the other hand, is low.

With the device according to the invention it is thus possible with closing the separator 5 a high current to the motor from at least the first inverter 6 supply. The low DC link voltage of less than 50 volts makes this possible cost-effective types of electronic circuit breakers.

After overcoming the breakaway torque, the speed increases increasingly. The power is proportional to the product of speed and torque and increases accordingly. As soon as the necessary voltage to be supplied from the converter to the motor reaches the critical value, the disconnecting device is opened, ie the first inverter 6 disconnected from the engine. The engine will then only be powered by the second inverter 2 fed, which provides the then necessary high voltage values. This second inverter 2 but does not have to deliver those high current values by means of the first inverter 6 are available.

Of the critical value is by the stated value of the AC / DC converter maximum generated DC link voltage given or determined by this.

All in all is thus cheaper Do a high current at low voltage levels and a lower one Current at high voltages available from each other Inverter.

The inverters 2 and 6 are thus alternatively operated depending on whether the voltage to be set on the motor is greater or less than the critical value.

In a further embodiment according to the invention, a hysteresis is taken into account when switching over by the critical value in order to suppress oscillation tendency. Thus, so when switching from the second inverter 2 on the first inverter 6 a higher value is provided as a critical value than when switching from the first inverter 6 to the second inverter 2 ,

In a further embodiment of the invention, the two inverters are not operated alternatively but below the critical value in parallel. Above the critical value is only the second inverter 2 operated. In this way, a very high current can be operated at low voltages below the critical value.

The separator 5 is executed in a further embodiment as a contactor. In other embodiments, however, an embodiment with other means for protecting the switch of the power amplifier executable, for example, comprising diodes and / or other passive components.

Claims (13)

Inverter for supplying an electric motor, wherein the inverter comprises a first and a second inverter, each of which is supplied from a unipolar DC link voltage and the respective DC link voltage is generated by means of a respective rectifier or controllable AC / DC converter from a supply network, wherein at least one of Inverter feeds the electric motor, characterized in that - the first inverter ( 6 ) Switch has much lower reverse voltage capability than the second inverter ( 2 ), Below a critical value of the motor voltage at least the first inverter ( 6 ) and above a critical value of the motor voltage of the second inverter ( 2 ) the electric motor ( 3 ), and - between the first inverter ( 6 ) and engine ( 3 ) a separating device ( 5 ) is arranged; which is controllable by a control electronics. Converter according to claim 1, characterized in that the intermediate circuit voltage from which the second inverter ( 2 ) is powered by means of an uncontrolled rectifier ( 1 ) is generated from the supply network and that intermediate circuit voltage from which the first inverter ( 6 ) is supplied by means of a controllable AC / DC converter (7), in particular a phase-angle controlled rectifier from the supply network ( 8th ) is produced. Converter according to one of the preceding claims, characterized in that the electric motor ( 3 ) is a three-phase motor and / or the supply network ( 8th ) a single- or multi-phase AC mains. Converter according to one of the preceding claims, characterized in that the blocking voltage resistance of the switch of the first inverter ( 6 ) is at least more than five times, in particular more than ten times, lower than the blocking voltage resistance of the switches of the second inverter ( 2 ). Converter according to one of the preceding claims, characterized in that the maximum permitted intermediate circuit voltage of the first inverter ( 6 ) is at least more than five times, in particular more than ten times, less than the maximum permitted intermediate circuit voltage of the second inverter ( 2 ). Converter according to one of the preceding claims, characterized in that the first inverter ( 6 ) to low voltage and the second inverter ( 2 ) is designed for medium voltage. Converter according to one of the preceding claims, characterized in that the AC / DC converter (7) for generating the intermediate circuit voltage for the first inverter ( 6 ) comprises phase-gapped thyristors. Converter according to one of the preceding claims, characterized in that the drive signals of the inverters ( 6 ; 2 ) from the control electronics ( 4 ) be generated. Converter according to one of the preceding claims, characterized in that the drive signals for the first and second inverters ( 6 ; 2 ) synchronously or the same drive signals for the first and second inverters ( 6 ; 2 ), in particular the associated signal lines are laid in parallel. Converter according to one of the preceding claims, characterized in that means for detecting the motor voltage are provided and / or means for detecting the DC link voltage are connected to means for detecting the pulse width modulation duration such that the motor voltage can be modeled, in particular by the control electronics ( 4 ). A method for operating an inverter, wherein the converter comprises a first and a second inverter, each of which is supplied from a unipolar DC link voltage and the respective DC link voltage is generated by means of a respective rectifier or controllable AC / DC converter from a supply network, wherein at least one of Inverter feeds the electric motor, characterized in that - the first inverter ( 6 ) Switch has much lower reverse voltage capability than the second inverter ( 2 ), Below a critical value of the motor voltage at least the first inverter ( 6 ) and above a critical value of the motor voltage of the second inverter ( 2 ) feeds the electric motor, and - above the critical value, the electrical connection between the engine ( 3 ) and first inverter ( 6 ) is separated. Method according to claim 11, characterized in that below the critical value first and second inverters ( 6 ; 2 ) parallel and / or synchronously the motor ( 3 ) Food. Method according to one of claims 11 or 12, characterized in that the first inverter ( 6 ) supply voltage is limited to a value which is at least five times, in particular ten times, smaller than the value of the intermediate circuit voltage in the unloaded case, from which the second inverter ( 2 ) is supplied.