Drive system, method for operating a drive system and use

Abstract

Drive system comprising electric motor, inverter, energy storage device, wherein the electric motor can be powered by the inverter, which can be supplied from the energy storage device, wherein the inverter has upper and lower controllable semiconductor switches, wherein the electric motor is designed as a three-phase motor in star point connection, characterized in that current can be supplied to the star point of the electric motor from a rectifier, which is supplied by a secondary winding, wherein the secondary winding can be supplied from a primary winding, which is inductively coupled to the secondary winding, wherein the primary winding is inductively coupled to the secondary winding from outside the drive system, wherein the stator winding of the electric motor, as the inductor of a charging circuit designed as a buck converter or boost converter, charges the energy storage device, wherein the rectifier is directly connected to the energy storage device by means of a diode.that when a first critical value of the voltage at the neutral point is exceeded, the charging current is carried directly from the rectifier to the energy storage device(s) via a diode, in particular wherein the first critical value corresponds to the charging voltage for the energy storage device(s), wherein an additional inductor is arranged between the neutral point and the rectifier supplying it, wherein the inverter with the stator windings together with the additional inductor forms a boost converter, to which current from the rectifier is supplied and which provides charging current to the energy storage device, wherein, as protection against overcharging, one or more switches of the inverter switch the stator winding to the lower potential or a further switch is provided which connects the neutral point of the stator winding to the lower potential.

Description

The invention relates to a drive system, a method for operating a drive system and a use.It is known to feed electric motors from an inverter which is supplied from an energy store, such as, for example, an intermediate circuit capacitor of a converter. It is also obvious, in battery-supplied vehicles with electromotive drive, to feed the electric motor from an inverter which is supplied by the battery.From DE 198 57 645 A1, an electrical system for electric vehicles is known as the closest prior art.DE 698 36 468 T2 discloses a method for contactless power supply.US 020060274468 A1 discloses an active in-current control.US 020020101750 A1 discloses a power factor correction.US 000905563781 A discloses a dual mode power converter.Further documents relating to the prior art are U.S. Pat. No. 6,058,032 A, JP 2002-165 370 A, DE 10 2006 043 960 A1, US 2005 / 0 105 311 A1, DE 41 28 962 A1 and US 2005 / 0 258 796 A1.The object of the invention is therefore to provide a cost-effective charging circuit for an energy store.According to the invention, the object is achieved in the drive system according to the features specified in claim 1 and in the method for operating a drive system according to the features specified in claim 8 and in use according to the features specified in claim 12.Important features of the invention in the drive system are that the drive system comprises an electric motor, an inverter and at least one energy store, wherein the electric motor can be supplied by the inverter which can be supplied from the energy store, wherein the electric motor is designed as a three-phase motor in a star-point connection, wherein current can be supplied to the star point of the electric motor from a rectifier which is fed by a secondary winding, wherein the secondary winding can be supplied from a primary winding which is provided in an inductively coupled manner to the secondary winding.It is advantageous in this case that a very compact charging circuit can be realized, wherein even at the secondary winding a far lower voltage level may exist than the voltage required for charging the energy store. This is because, because the stator winding is connected to the energy store via the inverter and can thus be used as an inductance for the charging circuit, for example in the manner of a buck converter, it is even possible to set the voltage level up from the secondary voltage to the required charging voltage. In other words, a wide-voltage-supplied charging circuit is thus made possible.If the secondary voltage is sufficiently high, i.e. lies above a first critical value, a direct charging of the energy stores from the secondary winding is made possible.If the secondary voltage is too high, i.e. lies above a second critical value, from which the energy store is endangered with a certain probability, a dissipation of the current via the inverter is made possible, i.e. a diversion of the current from the energy store is made possible. Thus, a deterioration, early aging or other risk, such as overheating of the energy store, can be avoided.If the secondary voltage is greater than a third critical value, a further current path can additionally be enabled, which can be implemented without active activation, via which the current can then be derived with high certainty in order to protect the energy store reliably, in particular with a higher safety category.If the secondary voltage is thus below the first critical value, it is advantageous that the stator windings also have at least partially the function of an additional energy store and moreover also contribute to smoothing of the charging current.A wide voltage can thus be used. Therefore, charging is made possible even in the event of a deterioration of the coupling or in the case of a primary-side supply network with fluctuating or variable voltage. Even wide-voltage operation is made possible, i.e. the charging in the case of different supply grids which differ not only in their frequency but also in the effective voltage.In an advantageous embodiment, the primary winding is supplied from a voltage-current converter, in particular a gyro, which is fed with an alternating voltage by an inverter, wherein the voltage-current converter comprises at least one capacitance and an inductance in such a way that the associated resonant frequency substantially corresponds to the frequency of the alternating voltage, in particular wherein the capacitance and inductance are connected in series. It is advantageous here that the voltage source-like behavior of the single-phase inverter feeding the primary winding is converted into a current source-like behavior, whereby a substantially constant current can be made available. In this way, even with weak inductive coupling, a high efficiency can be achieved in the contactless energy transmission to the secondary coil.In an advantageous embodiment, when a first critical value of the voltage at the neutral point is exceeded, the charging current is carried out by means of a diode directly from the rectifier to or to the energy stores, in particular wherein the first critical value corresponds to the charging voltage for the energy store or stores. It is advantageous here that no further losses occur, but rather the full energy transmitted in contactless fashion is available for charging the energy store.In an advantageous embodiment, when the voltage falls below the first critical value of the voltage at the neutral point, the charging current is conducted from the rectifier to or to the energy stores via at least one stator winding and the inverter, in particular wherein the inverter can be operated together with the stator windings as a step-up converter. It is advantageous here that the low voltage at the secondary coil can be boosted and charging is thus made possible despite this low voltage.In an advantageous embodiment, when a second critical value, which is greater than the first critical value, is exceeded, a switch is closed, via which current is derived from the neutral point to the lower potential. It is advantageous here that protection of the energy stores against overcharging can be provided.In an advantageous embodiment, one of the energy stores is a capacitor, an ultracap capacitor or a battery. It is advantageous here that, depending on requirements, a capacity can be selected which guarantees the operation of the planned application.In an advantageous embodiment, the stator windings of the electric motor are connected in a star-point connection. It is advantageous here that all stator windings can be used in a simple manner as inductances of the charging circuit. In particular, when using the inverter connected to the stator windings as a step-up converter, a distribution of the charging current to the stator windings is made possible. The ohmic heat losses can thus be reduced.In an advantageous embodiment, an additional inductance is provided between the neutral point and the rectifier. It is advantageous here that lower switching frequencies of the inverter can be used for generating current of equal magnitude in the individual stator windings, as a result of which the switching losses of the semiconductor switches comprised by the inverter can then also be reduced. In addition, greater voltage differences between the charging voltage and the voltage level of the energy source are made possible. It is also advantageous that the current can be divided between the stator windings and thus lower losses can be achieved.In an advantageous embodiment, the effective value or peak value of the secondary voltage supplying the rectifier is smaller than the charging voltage for the energy store, i.e., is smaller than the voltage necessary for charging the energy store, i.e., in particular the input voltage of the inverter. It is advantageous here that a wide-voltage energy source can be used as the energy source supplying the switch.Important features in the method for operating a drive system are that current is supplied to the neutral point of the electric motor from a rectifier, which is fed by a secondary winding, wherein the secondary winding is supplied in a contactless manner from a primary winding, wherein charging current for the energy store is formed from an inverter, via which the stator windings of the electric motor can be fed, in particular with a rotary voltage system, which is generated from the energy store during motor operation when the inverter is fed, as long as the voltage occurring at the neutral point is below a first critical value.It is advantageous here that a charging method can be used for charging the energy source, which charging method uses the stator windings of the electric motor that is present in any case. Thus, not only a wide voltage is usable as the secondary voltage and thus as the power source for the charging circuit, but also a very compact construction because the stator windings of the motor are used for driving a charging circuit.In an advantageous embodiment, the charging current is supplied to the energy store directly from the rectifier as long as the voltage occurring at the neutral point is above the first critical value. It is advantageous that no further losses occur.In an advantageous embodiment, at least one of the lower switches of the inverter is placed in the conductive state, as a result of which current is discharged from the rectifier via the associated stator winding to the lower potential of the energy store, that is to say in particular the energy store is protected from current from the rectifier, as long as the voltage occurring at the neutral point is above a second critical value which is greater than the first critical value and, starting from the exceeding thereof, the energy store is at risk with a certain probability. It is advantageous that a high level of safety can be achieved.In an advantageous embodiment, a further current path is enabled, via which current is discharged from the rectifier directly or via the associated stator winding to the lower potential of the energy store, i.e. in particular the energy store is protected from current from the rectifier, as long as the voltage occurring at the neutral point is above a third critical value, which is greater than the second critical value and, starting from the exceeding thereof, the energy store is more likely at risk.in particular wherein the further current path is formed from a passive circuit arrangement, in particular wherein the further current path comprises a thyristor, in the drive path of which a Zener diode or a corresponding component which has a switching threshold-like behavior is provided. It is advantageous here that a very high level of safety can be achieved since the current diversion path can be implemented twice.In an advantageous embodiment, the stator windings can be fed with a rotational voltage system that can be generated from the energy store. It is advantageous here that a conventional inverter can be used which consists of three half bridges of in each case a series circuit of two semiconductor switches and thus pulse-width-modulated actuation for achieving the motor or generator operation of the semiconductor switches can be achieved.In an advantageous embodiment, the inverter is controlled in a pulse-width modulated or block-commutated manner, in particular for motor-driven or generator-driven operation of the electric motor. It is advantageous that simple methods can be used.In an advantageous embodiment, the switches of the inverter are controlled in a pulse width modulated manner. It is advantageous that a simple and inexpensive mode of operation can be realized; in particular, a regulation of the charging voltage to a setpoint value is also made possible, in that the pulse width modulation ratio can be used as the actuating variable.In an advantageous embodiment, the inverter is of polyphase design and the control signals for the switches of the inverter are of synchronous, second-offset synchronous or asynchronous design. It is advantageous in this case that particularly simple actuation can be carried out in the case of synchronous operating mode, uniform and independent load on the half bridges of the inverter and of the stator windings can be carried out in the case of asynchronous operating mode, and uniform load on the half bridges and the stator windings is made possible in a simple manner in the case of synchronous operating mode with time offset.In an advantageous embodiment, the recharging of the energy store is repeated cyclically, in particular the recharging is carried out alternately with the motor or generator operation of the electric motor. It is advantageous here that the stator windings are made possible only to the maximum of the current occurring in the operating modes. Alternatively, a simultaneous generation of charging current is also made possible in the case of motor and generator operating modes of the electric motor, wherein, however, the stator windings have to be dimensioned correspondingly more strongly.Further advantages are evident from the dependent claims.The invention will now be explained in more detail with reference to the drawings:FIG. 1 shows an apparatus according to the invention with a schematic circuit diagram.Here, from the energy stores B and C connected in parallel, which are preferably designed as a battery and / or capacitor, an inverter is provided for feeding the electric motor M. The stator windings of the electric motor M are designed as a three-phase winding in a star-point connection. The electric motor can thus be supplied with a supply frequency determinable by the inverter, i.e. a rotational voltage system rotating with this supply frequency, and in this way the rotational speed of the electric motor can be controlled or alternatively, upon attachment of a rotational angle or rotational speed sensor, controlled to a desired rotational speed or a desired torque.In the generator mode, the energy generated by the electric motor M can be supplied to the energy store via the inverter.The inverter consists of three half bridges, i.e. branch pairs, each of which comprises a series circuit of an upper and lower drivable semiconductor switch, to each of which a diode is in turn connected in parallel. The semiconductor switches are preferably controlled in a pulse width modulated manner. The control electronics A generate the control signals for the semiconductor switches. In motor operation, a rotational voltage system with a predefinable frequency is thus supplied to motor M and motor M is thus set in rotational motion.Conversely, in the generator mode, energy can be supplied from the engine via the inverter to the energy stores B and C and can thus be charged.However, the loading can also be carried out when the engine M is not rotating. Thus, for example, when the vehicle is in the parking position, a primary winding L 2 can be brought into inductive coupling with a secondary winding L 1 from the outside. This secondary winding L 1 is part of a charging unit 2 which is connected in a plug-in manner to the remaining motor-converter unit 1.The primary winding is fed by a gyro G which is in turn fed by a single-phase inverter which comprises the switches S1, S2, S3, S4 and which is fed by the DC voltage applied to the capacitor C2. At this time, the gyro G converts the voltage source-like behavior of the output side of the single-phase inverter into a current source-like behavior toward the secondary winding L 1. To shut off the supplied energy, a short-circuiting device R is provided in parallel with the secondary winding. When this short-circuiting device R is open, the secondary alternating current is supplied to the rectifiers comprising the diodes D 2, D 3, D 4, D 5 and the rectified current is supplied via the diode D 1 to the energy stores B and C.In the event of an overvoltage or also for the other protection of the energy stores B and C, for example as protection against overcharging, the inverter is used to end the charging by setting one or more lower switches of the inverter, that is to say switches arranged at a lower potential of the energy stores, in the conductive state, as a result of which the rectified alternating current is derived via the star point SP of the motor M and the one or more stator windings of the motor M and the lower switch or switches.If all switches of the inverter are open, a portion of the rectified alternating current is supplied via the neutral point SP and the stator windings of the motor M to the diodes of the inverter, which rectify the alternating current and make a unipolar current available therefrom for charging the energy stores B and C. The stator windings reduce high-frequency components and contribute to smoothing.Charging of the energy stores is also made possible if the voltage SP present at the neutral point is less than the required charging voltage. This is because a step-up converter operation is then made possible by means of the inductances of the stator winding. For this purpose, the motor with inverter is not only used for the purpose of merely rectifying, but is operated as a step-up converter. For this purpose, the switches are controlled accordingly, so that a far higher voltage can be generated at the energy store than the peak voltage value of the unipolar voltage that can be generated by the rectifier. In this case, the inductances of the stator windings bring the semiconductor switches of the inverter together during switching operations and make the level of the voltage at the energy store controllable or regulable when a means for detecting the voltage at the energy store is provided. An important parameter here is the switching frequency of the switches of the inverter. Despite a mains voltage whose peak value and / or effective value is smaller than the charging voltage required for the energy store, charging of the energy store is thus made possible.During motor and / or generator operation of the motor, the inverter is controlled in such a way that a rotary voltage is present at the motor. In this case, the control signals are therefore dependent on one another, so that the rotary voltage is present at the stator windings. In the charging operation described and with the motor M not driving or driven, the drive signals for the switches of the half bridges may be generated independently of one another.The driving of the three half bridges, i.e. branch pairs, of the inverter can be carried out synchronously. In the case of an asynchronous embodiment of the control signals, a further improved more uniform utilization of the switches is made possible. Asynchronous means here that the drive signals assigned to the respective half bridges have a different frequency and are therefore not synchronous with one another.By means of the unipolar current, which is generated during charging of the energy store and boost converter operation, a holding torque is generated in the electric motor, in particular when embodied as a synchronous motor.By closing the lower switches of the inverter, the battery can be protected from overcharging or overvoltage.According to the invention, a further electronic switch is provided which is provided between the neutral point and the lower potential, that is to say is arranged parallel to one of the lower switches. In this way, the safety can be further increased. In particular, when this further switch is designed as a thyristor, a passive circuit, for example comprising a Zener diode or the like, can be implemented, with which the current can be derived from the neutral point into the lower potential of the energy stores B and C from exceeding a critical voltage which is greater than the critical voltage at the exceeding of which the lower switches of the inverter are closed.In a further exemplary embodiment according to the invention, the switches of the inverter are controlled in a block-commutated manner by the control not shown in FIG. 1, rather than in a pulse-width-modulated manner.In a further exemplary embodiment according to the invention, even in the case of motor operation of the motor M, the energy store can be supplied in the described manner, with the result that the capacity of the energy store is used up more slowly, that is to say the above-mentioned charging current can be used for at least partially supplying the inverter. However, for this purpose, the stator windings and the diodes of the rectifier must be dimensioned in a correspondingly robust manner.In a further exemplary embodiment according to the invention, a plurality of inverters are supplied from the energy store, each of which supplies an electric motor, wherein, via a stator winding of a first or a plurality of electric motors, the energy store has in each case a switch for the controlled supply of current to the respective stator winding in the manner described above.In further exemplary embodiments according to the invention, an additional inductance L is inserted between the neutral point SP and the rectifier (D 2, D 3, D 4, D 5), the current of which can be influenced by a controllable switch. The switch essentially works in accordance with a buck converter, wherein, however, at least the stator windings and the inductance L are provided as the inductance at the neutral point of the stator windings and the inverter with energy store is effective as the load.A diode is connected in parallel with the switch, preferably a semiconductor switch, wherein this parallel circuit is connected to the lower potential of the unipolar voltage via the diode connected in series.In this way, it is now possible to supply an alternating current to the neutral point by means of the switch, so that a charging current can be supplied to the energy store via the diodes of the inverter 1. Charging of the energy store is thus made possible.In the invention, the stator windings have a smoothing effect on the current supplied via the switch and also represent an additional energy store.List of reference characters1 Converter-motor unit 2 Charging unit, secondary part 3 Charging unit, primary part D 1 Diode D 2 Diode D 3 Diode D 4 Diode D 5 Diode S 1 Switch S 2 Switch S 3 Switch S 4 Switch C 2 Capacitor B Energy store, for example battery C Energy store, for example capacitor S Plug connection M Electric motor in neutral connection R Relay G Gyrotor L 1 Secondary inductance L 2 Primary inductance MC 1 First microcontroller MC 2 Second microcontroller A Control electronics

Claims

Drive system comprising an electric motor, inverter, energy store, wherein the electric motor can be fed by the inverter which can be supplied from the energy store, wherein the inverter has upper and lower drivable semiconductor switches, wherein the electric motor is designed as a three-phase motor in a star-point connection, characterized in that current can be supplied to the star point of the electric motor from a rectifier which is fed by a secondary winding, wherein the secondary winding can be supplied from a primary winding which is provided in inductively coupled fashion to the secondary winding, wherein the primary winding is brought into inductive coupling with the secondary winding from outside the drive system, wherein the stator winding of the electric motor charges the energy store as an inductance of a charging circuit designed as a buck converter or boost converter, wherein the rectifier is connected directly to the energy store in this way by means of a diode, that, when a first critical value of the voltage at the star point is exceeded, the charging current is carried out by means of a diode directly from the rectifier to or to the energy stores, in particular wherein the first critical value corresponds to the charging voltage for the energy store or stores, wherein an additional inductance is arranged between the star point and the rectifier feeding it, wherein the inverter together with the stator windings forms a step-up converter, to which current is supplied from the rectifier and which provides charging current to the energy stores, wherein one or more switches of the inverter switch the stator winding to the lower potential or a further switch is provided as a protection against overcharging, which connects the star point of the stator winding to the lower potential.Drive system according to Claim 1, characterized in that the primary winding is supplied from a voltage-current converter which is fed with an alternating voltage by an inverter, wherein the voltage-current converter comprises at least one capacitor and one inductor in such a way that the associated resonant frequency corresponds substantially to the frequency of the alternating voltage, in particular wherein the capacitor and inductor are connected in series.Drive system according to at least one of the preceding claims, characterized in that, if the voltage falls below the first critical value of the voltage at the neutral point, the charging current is conducted from the rectifier to or to the energy stores via at least one stator winding and the inverter, in particular wherein the inverter can be operated together with the stator windings as a step-up converter.Drive system according to at least one of the preceding claims, characterized in that, when a second critical value which is greater than the first critical value is exceeded, the further electronic switch is closed, via which current is derived from the neutral point to the lower potential, in particular for protecting the energy stores from overcharging.Drive system according to at least one of the preceding claims, characterized in that at least one energy store is designed as a capacitor, an ultracap capacitor and / or a battery.Drive system according to at least one of the preceding claims, characterized in that the stator windings of the electric motor are interconnected in a star-point connection.Drive system according to at least one of the preceding claims, characterized in that the effective value or peak value of the voltage which supplies the rectifier and occurs at the secondary winding is less than the charging voltage for the energy store, that is to say is in particular less than the voltage which is necessary for charging the energy store, in particular input voltage of the inverter.Method for operating a drive system according to one of the preceding claims, wherein one of the lower switches of the inverter is placed in the conductive state, whereby current is dissipated from the rectifier via the associated stator winding to the lower potential of the energy store, in particular that is to say the energy store is protected from current from the rectifier as long as the voltage occurring at the neutral point is above a second critical value which is greater than the first critical value and, from when it is exceeded, the energy store is endangered with a certain probability, wherein a further current path is enabled by a further electronic switch, via which current is dissipated from the rectifier directly or via the associated stator winding to the lower potential of the energy store, in particular that is to say the energy store is protected from current from the rectifier as long as the voltage occurring at the neutral point is above a third critical value, which is greater than the second critical value and from the exceeding of which the energy store is more likely at risk.Method according to Claim 8, characterized in that the charging current is fed directly from the rectifier to the energy store as long as the voltage occurring at the neutral point is above the first critical value and / or in that the further current path is formed from a passive circuit arrangement, in particular wherein the further current path comprises a thyristor, in the drive path of which a Zener diode or a corresponding component which has a switching threshold-like behavior is provided.Method according to Claim 8 or 9, characterized in that the inverter is actuated in a pulse-width-modulated or block-commutated manner, in particular for motor-driven or generator-driven operation of the electric motor, and / or in that the inverter is of polyphase design and, when the energy store is charged, the actuation signals for the switches of the inverter are of synchronous, second-offset synchronous or asynchronous design.Method according to one of Claims 8 to 10, characterized in that the recharging of the energy store is repeated cyclically, in particular the recharging is carried out alternately with the motor or generator operation of the electric motor.Use, according to a method according to one of Claims 8 to 10, of a stator winding of an electric motor of a drive system according to one of Claims 1 to 7 as an inductance of a charging circuit, in particular a buck converter or boost converter, for charging an energy store.

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