WO2002008574A1

WO2002008574A1 - Energy conversion system and method for operating the same

Info

Publication number: WO2002008574A1
Application number: PCT/US2000/019592
Authority: WO
Inventors: Heinz Bausch; Otmar Bitsche; David J. Rausen
Original assignee: Daimlerchrysler Ag
Priority date: 2000-07-19
Filing date: 2000-07-19
Publication date: 2002-01-31
Also published as: JP2004505586A; EP1311744A1; EP1311744A4

Abstract

An energy conversion system system includes a powertrain (21, 1, 6, 7, 8, 11) capable to transfer mechanical power to (MP2) other devices (24, 10). An electromechanical system (20, 2, 3) is coupled to said powertrain and this system is operable to convert mechanical power provided by said powertrain into a form (SP) that can be stored by an energy storage element (22, 5), drawing energy stored by the energy storage element, and transforming the power drawn from the storage element into mechanical power. The powertrain is capable of transferring mechanical power to and from the electromechanical system. The energy storage element is coupled to said electromechanical system for exchanging power with the electromechanical system and is operable to store energy provided by the electromechanical system, and acts as ballast to stabilize system operation. A controller (23, 4) is provided for regulating powertrain mechanical power, regulating electrical power provided by the electromechanical system to other devices, and regulating the power transferred with the energy storage element in order to regulate the amount of energy stored in energy storage element.

Description

Energy conversion system and method for operating the same

The invention relates to an energy conversion system and a method for operating the same.

DE 197 48 423 Al discloses a motor/generator assembly in which a vehicle having an auxiliary unit can be driven by the drive shaft of the motor vehicle. The auxiliary unit may, in the form of an alternator, supply the on-board electrical system with electrical energy or, in the form of a starter, start the internal combustion engine or output braking energy as electrical energy into a vehicle battery.

An object of the invention is to specify an energy conversion system and a method for operating the same which energy conversion system is capable of supplying electrical energy to various electrical loads .

This object is achieved in the case of an apparatus by providing a method for operating an energy conversion system comprising a powertrain capable of exchanging mechanical power with other devices; an electromechanical system coupled to said powertrain for converting mechanical power provided by said powertrain into controllable electrical power to other devices, converting mechanical power provided by said powertrain into a form that can be stored by the energy storage element, drawing energy stored by an energy storage element, and transforming the power drawn from the storage element into mechanical power, the powertrain being capable of transferring mechanical power to and from the electromechanical system; an energy storage element coupled to said electromechanical system for exchanging power with said electromechanical system, storing energy provided by said electromechanical system, and acting as ballast to stabilize system operation; and a controller for regulating powertrain mechanical power, regulating electrical power provided by said electromechanical system to other electrical devices, and regulating the power transferred with the energy storage element in order to regulate the amount of energy stored in said energy storage element.

This object is achieved in the case of a method by providing an energy conversion system comprising a powertrain capable of exchanging mechanical power with other devices; an electromechanical system coupled to said powertrain for converting mechanical power provided by said powertrain into controllable electrical power to other devices, converting mechanical power provided by said powertrain into a form that can be stored by the energy storage element, drawing energy stored by an energy storage element, and transforming the power drawn from the storage element into mechanical power, the powertrain being capable of transferring mechanical power to and from the electromechanical system; an energy storage element coupled to said electromechanical system for exchanging power with said electromechanical system, storing energy provided by said electromechanical system, and acting as ballast to stabilize system operation; and a controller for regulating powertrain mechanical power, regulating electrical power provided by said electromechanical system to other electrical devices, and regulating the power transferred with the energy storage element in order to regulate the amount of energy stored in said energy storage element , said method comprising: decoupling the other mechanical devices from the powertrain and, with the powertrain decoupled, driving an electromechanical system by the powertrain; and wherein an output AC voltage of the electromechanical system is regulated by a field current, made available by a controller, as a function of an electrical load on the electromechanical system.

The energy conversion system combines a powertrain delivering mechanical power to other devices and an electromechanical system to and from which the powertrain can transfer mechanical power. The electromechanical system can convert mechanical power provided by that powertrain into controllable electrical power to other devices as well as convert mechanical power provided by said powertrain to energy that is storable in an energy storage element as well as draw energy from said storage element and transform this energy into mechanical power.

One advantage of the invention is that this conversion of energy can be performed by a single electrical machine coupled to an electric controller which results in a simple and compact energy conversion system.

In a first preferred embodiment, the energy conversion system is part of a motor vehicle and has, successively along a drive shaft of the vehicle, an internal combustion engine, a transmission, an element with a motor/generator, a separating means and a wheel drive shaft, the separating means being provided for separating the wheel drive shaft from the drive shaft when the vehicle is at a standstill . The auxiliary units of a motor vehicle can be operated by the energy conversion system and electrical energy can also be made available for electrical loads external to the vehicle. The motor/generator is preferably provided with a converter which is suitable for regulating a field current and/or a slip in the motor/generator in accordance with different electrical load situations.

The advantage resides in the fact that the rotor/generator can be used as a power unit, which power unit can be used to operate electrical loads with different powers. It is favorable that, in the driving mode, the motor/generator can be used for recuperating braking energy or for boosting the drive, as in a customary parallel hybrid vehicle. It is particularly advantageous that the vehicle can provide a power unit which enables power to be supplied to electrical loads even outdoors. In this case, the vehicle infrastructure and the vehicle facilities are available, such as for instance emission-gas controls, noise insulation and the like.

Further advantages and refinements of the invention emerge from the claims and the description.

These together with other objects of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a first preferred embodiment of an energy conversion system according to the invention with two operation modes, in a first mode for regulating power exchange with other mechanical devices (Fig. la) e.g. in a hybrid vehicle, and in a second mode with other electrical devices (Fig. lb) of external electrical loads, and

Figure 2 shows a plan view of another preferred arrangement in a vehicle.

DETAILED DESCRIPTION OF THE DRAWINGS The invention can be advantageously used in motor vehicles but is not restricted to an automotive application.

The control system described below in figures la and lb advantageously uses the same system components to exchange mechanical power with mechanical devices via the powertrain and exchange electrical power with electrical devices via the electromechanical system. This allows for a simplification of such a system and a reduction the number of components and costs. The control system is the same in the embodiments according to figures la and lb except that the control law and the data used as input and output for the control law differ between the two modes .

Figure la illustrates a first mode of operation of a preferred embodiment of the energy conversion system according to the invention. The system operation is suitable for regulating power exchange with other mechanical devices, e.g. vehicle wheels as in a hybrid vehicle.

An electromechanical system 20 is connected with a powertrain 21. The powertrain 21 exchanges mechanical power MP2 with other mechanical devices 24, e.g. vehicle wheels as in a hybrid vehicle.

The electromechanical system 20 is directly or indirectly driveable by the powertrain 21. Mechanical power MP1 is exchanged between the electromechanical system 20 and the powertrain 21, An energy storage element 22 is also connected with the electromechanical system 20. Storage power SP is exchanged between the electromechanical system 20 and the energy storage element 22.

The electromechanical system 20 receives system controls signals EMC from controller 23. The powertrain 21 receives powertrain controls signals PTC from the controller 23. The controller 23 receives system feedback signals EMF from the electromechanical system 20 and powertrain feedback signals PTF from the powertrain 21 and energy storage feedback signals SPF from the energy storage element 22, e.g, a battery.

The operation of the energy conversion system in this mode is a follows. Mechanical device or devices 24 demand mechanical power of the system. Controller 23 delivers the required torque according to a control law that regulates' the delivered torque and /or speed by regulating the powertrain torque and the electromechanical system torque. Controller 23 monitors energy storage element 22 and readjusts control law as necessary to ensure that its energy level is within desirable limits .

An example of a preferred specific implementation of controller input-output for the described mode is listed below:

Inputs for controller 23 :

Desired mechanical power (e.g. desired torque at certain speed or desired torque and speed) ;

Energy storage element level (e.g. calculated via battery voltage and current) ;

Outputs from controller 23 :

Electromechanical system torque (e.g. electric motor torque for acceleration or regeneration) ; Powertrain torque (e.g. for acceleration) .

Figure lb illustrates a second mode of operation of the preferred embodiment described in fig. 1. Similar elements are referenced by the same reference numbers. Additionally or alternatively to the other mechanical devices 24, the electromechanical system 20 is connected with other electrical devices 25 and exchanges electrical power EP with the electromechanical system 20.

Signal flow and power flow are similar to the operation as described in fig. la.

The operation of the energy conversion system in this mode is a follows. Electrical device or devices 25 demand electrical power of the system. Controller 23 regulates flow of electrical power between the electromechanical system 20 and external electrical devices 25 so that the electrical power

EP is delivered at the required level, including voltage and frequency. Controller 23 regulates powertrain torque in order to provide the necessary mechanical power to allow the electromechanical system 20 to continue deliver the required electrical power. Energy storage element 22 can act as ballast as necessary.

The electrical devices 25 could include any electrically powered loads, including, but not limited to such as electrical pumps, compressors and the like.

An example of a preferred specific implementation of the input and output for the control means for the described mode is listed below:

Inputs for controller 23;

Desired electrical voltage; Desired electrical frequency;

Actual electrical voltage;

Actual electrical frequency;

Outputs from controller 23 :

Electrical power flow to device 25 (e.g. via switching of semiconductor devices) to maintain desired voltage;

Powertrain (engine) torque to maintain desired electrical frequency.

The energy conversion system as described in figure 1 is capable of powering mechanical and electrical devices 24, 25. Preferably to power the electrical devices 25, the other mechanical devices 24 are decoupled from the powertrain 21 and, with the powertrain 21 decoupled, the electromechanical system 20 is driven by the powertrain 21, and an output AC voltage U_A of the electromechanical system 20 is regulated by a field current I_F, made available by the controller 23, as a function of an electrical load on the electromechanical system 20.

Figure 2 illustrates a first preferred embodiment of an apparatus for operating auxiliary units of a motor vehicle in accordance with the invention wherein the energy conversion system is arranged in a motor vehicle 13.

In a vehicle 13, a powertrain comprises combustion engine 1 which is connected to a transmission 11 in the direction of a drive shaft 6. The drive shaft 6 is provided for driving a mechanical device such as a wheel drive shaft 8 with driving wheels 10.1, 10.2 and a differential 9. Further wheels 10.3, 10.4 on a second wheel axle are not driven in this preferred configuration. The invention, however, can also be used in a vehicle where more than one or all wheels axles are driven.

An electromechanical system comprises an auxiliary unit 3 which can be operated via an element 2 connected to the drive shaft 6 and which can be driven by the drive shaft 6. The auxiliary unit 3 can either be directly driven by the drive shaft 6 or indirectly driven via another shaft connected with the drive shaft 6. The auxiliary unit 3 is preferably a single electric machine with a single stator assembly and a single rotor assembly.

The electric machine 3 may also be arranged between the internal combustion engine 1 and the transmission 11. In this case, a clutch or a torque converter may also be provided before or after the motor/generator 3. The advantage is that a separate separator 7 is not necessary for separating the motor/generator 3 from the wheel drive axle 8. The separation may also be effected by the transmission 11. However, a separator 7 may also be provided.

It is also possible to use an electric machine 3 which is concentrically arranged around the drive shaft 6 instead of connecting the machine via an element 2 with the drive shaft 6.

A battery 5 is provided for an energy storage element. Control means comprises a controller or converter 4.

The internal combustion engine 1, the transmission 11, the element 2, a separator 7 and a wheel drive shaft 8 are arranged successively along the drive shaft 6. The separator 7 is provided for separating the wheel drive shaft 8 from the drive shaft 6 when the vehicle is at a standstill. A clutch or a torque converter may also be provided between internal combustion engine 1 and transmission 11.

The element 2 has a motor/generator 3 as auxiliary unit. The motor/generator 3 is connected to the converter 4. The motor/generator 3 is connected to a draw point 12 for electrical power for supplying electrical loads outside and/or inside the vehicle 13, to which electrical loads can be connected as they would be to a customary local voltage supply .

In this case, an isolator 14, preferably a switch, for decoupling the converter 4 from the motor/generator 3 may be provided between the converter 4 and the motor/generator 3. Furthermore, the converter 4 may be connected to a vehicle battery 5.

In the driving mode, the arrangement may advantageously be operated like a customary parallel hybrid. In this case, the motor/generator can be used in four-quadrant operation. As a result, in the driving mode, energy yielded by the motor/generator 3 operation can be stored in the battery 5. Braking energy of the vehicle can be fed into the battery 5 by the motor/generator 3 and can thus be recuperated. In the driving mode, once again in motive operation, the motor/generator 3 can be fed by the battery 5 and additionally have a driving effect. If the motor/generator 3 is designed adequately, it can also act as an electric drive motor, so that the vehicle 13, with the internal combustion engine 1 turned off, can be driven electrically.

In a second preferred embodiment the motor/generator 3 is located in a series of the engine 1 followed by the transmission 1.1 and the motor/generator 3 along the drive shaft of the vehicle.

In a third preferred embodiment the motor/generator 3 is located between the engine 1 and the transmission 1.1.

In a further preferred development of the invention, the drive shaft 6 and/or the wheel drive shaft 8 and/or the driving wheels 10.1, 10.2 may additionally be connected to an electrical drive machine. It is also possible for all the driving wheels 10.1, 10.2, 10.3, 10.4 to be driven, preferably electrically at least in part.

According to the invention, the motor/generator 3 coupled to the internal combustion engine 1 forms a power unit when the vehicle is at a standstill. When the vehicle is at a standstill it is possible for the coupling 7 to be opened, with the result that the drive shaft 6 is separated from the wheel drive shaft 8. The motor/generator 3 coupled to the internal combustion engine 1 forms a power unit. The internal combustion engine 1 can be matched to an optimum operating point by the transmission 11 and can preferably be operated with speed regulation in order to keep the frequency of the output voltage of the power unit constant . Typical electrical powers of the power unit of up to 50 kW are thus available in the case of a customary passenger vehicle, and an even higher electrical power in the case of a commercial vehicle, corresponding to the higher engine power. As a result, loads can be supplied with electrical power as they would be in customary local electricity supply systems, even if the loads are not connected to such supply networks .

The vehicle 13 is brought to a park position and then the wheel drive shaft 8 is decoupled from the drive shaft 6 and, with the wheel drive shaft 8 decoupled, the motor/generator 3 is driven by the internal combustion engine 1.

If a preferably three-phase synchronous machine is used as the motor/generator 3, it is advantageous to provide a delta connection for the winding sections of the machine for traction purposes in the driving mode. A star connection is expedient for the generator mode, preferably in the case of use as a power unit when the vehicle is at a standstill. In this case, it is possible to use both single-phase and three- phase load . There are a number of advantages in using a synchronous machine. Such electric machines exhibit two operation ranges. The first range is from standstill to a principal number of revolutions and in which range the machine is operated in a constant field mode . The electric current and the torque remain constant whereas the electric voltage and the electric power vary proportional to the number of revolutions. The electric voltage reaches a maximum value at the principal number of revolutions. The principal number of revolutions is a characteristic parameter for the design and size of the electric machine. The second range of operation of the machine is the so called field weakening range from the principal number of revolutions up to the maximum possible number of revolutions of the machine. In this range, the electric voltage remains constant as well as the electric current and the electric power. In this range of operation the magnetic field decreases inversely proportional with increasing number of revolutions. The torque decreases in the same way.

The synchronous machine has an advantageously wide field weakening range, up to 1:5, which is the ratio between the principal number of revolutions to the maximum possible number of revolutions, and is highly efficient.

The machine is relatively simple to regulate. The machine is particularly well-suited to the generator mode. The machine permits inductive loads and asymmetrical loads in the generator mode, and it requires only a relatively small converter .

If a synchronous machine is used as the motor/generator 3, in a preferred embodiment the converter 4 comprises a six-pulse bridge circuit and, in addition, a field controller.

The output AC voltage U_A, of the motor/generator 3 is regulated by the field current I_F, made available by the converter 4 , as a function of a desired electrical voltage across the motor/generator 3.

Although a three-phase generator does not allow simultaneous provision of 120 V and 240 V, or 115 V and 230 V, it is possible to generate the required voltage at the draw point 12 by field control . Such voltage values are commonly used e.g. for domestic power supply and electrically powered loads in various countries worldwide. By using a four-pole machine, it is possible to provide the voltage at 60 Hz given typically 1800 revolutions at the transmission output. By choosing the transmission ratio in a suitable manner, it is possible to operate the internal combustion engine at an optimum operating point with regard to prescribed boundary conditions, preferably a primary energy consumption, emission of noise and/or pollutant emissions .

It is possible for the three motor phases to be disconnected from the converter 4 by isolation means 14, in order that peak voltages that are not tolerated by the battery 5 cannot occur.

If the electric machine is designed as an electric drive motor and if a converter 4 having a maximum output current I_max=600 A is used, a peak power of 115 kW can be generated in such star connections, and up to 80 kW in the case of a 400 A converter. In this case, the star connection requires a battery voltage of about 300 V for the respective peak load.

In the case of a delta connection of the motor winding sections, the battery 5 is required to have a voltage of about

170 V for peak load. In the case of a delta connection, a peak power of 66 kW can be achieved with a 600 A converter, and 46 kW in the case of a 400 A converter. With this design for the driving mode, it is accordingly possible for similarly large electrical powers to be made available by the power unit according to the invention in the generator mode as well. If an asynchronous machine or a permanently excited machine is used as the motor/generator 3, in a preferred embodiment the converter 4 comprises a six-pulse bridge circuit.

The advantages of an induction motor are a relatively wide field weakening ranges, up to 1:3, a high efficiency, a good availability of hardware components and of open-loop and closed-loop control programs for traction purposes. The output voltage TJ_Acan be set simply by a corresponding data processing program in the converter 4. No additional hardware is necessary for the generator mode, in contrast to a synchronous machine.

In the case of an induction machine, just like in the case of a synchronous machine, a star connection or delta connection is possible for traction purposes and a star connection is favorable for the generator mode. In this case, converter 4 and battery 5 act actively as controllable phase shifters in order to set the field current I_F and hence the output voltage U_A in the motor/generator 3.

The electrical power of the motor/generator 3 that can be drawn at the draw point 12 is set by the slip, that is to say the difference between the frequency of the stator and that of the rotor of the motor/generator 3. To that end, the speed of the internal combustion engine 1 is preferably regulated, with the result that a voltage of constant frequency can be guaranteed at the power unit in accordance with the invention.

Similar conditions to those in the case of synchronous machines apply in the generator mode. Simultaneous provision of 120 V and 240 V, or 115 V and 230 V, is not possible but it is possible to generate the required voltage at the draw point 12 by field control. If a four-pole machine is used, an electrical voltage having a frequency of 60 Hz can also be provided at an induction machine given a typical transmission output speed of 1800 revolutions /min. Other frequencies are set at other transmission output speeds. The battery voltage is nominally above 340 V, corresponding to a mains voltage of 240 V. The peak power results from the respective design for the traction application.

In motor operation, in the case of a star connection of the motor winding sections, the peak power is 105 kW in the case of a 600 A converter, and 75 kW in the case of a 400 A converter. The battery 5 must tolerate a peak voltage of 340 V.

Overall, with the connected transmission 11, the partial shaft 6.1, the element 2 with motor/generator 3 and the converter 4, the internal combustion engine 1 forms a power unit or emergency power unit which is particularly suitable for operating decentralized electrical loads remote from local electricity supply systems, for instance when camping as a leisure pursuit, or electrical equipment on construction sites and the like. Loads in the vehicle can also be operated thereby, preferably with a high power consumption, such as stationary air-conditioning of the vehicle. Thus it becomes unnecessary to carry a separate power unit. At the same time, highly developed vehicle technology is used in the arrangement according to the invention, for instance catalytic converters for exhaust-gas cleaning, sound-proofing that is present, and vehicle security features can be employed by the invention when it functions as a generator.

Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Claims

WE CLAIM :

1. An energy conversion system comprising a powertrain ^(21, 1, 6, 7, 8, 11) capable of exchanging mechanical power (MP2) with other devices (24, 10) ; an electromechanical system (20, 2, 3) coupled to said powertrain (21, 1 , 6, 7, 8, 11) for converting mechanical power (MPl) provided by said powertrain (21, 1, 6, 7, 8, 11) into controllable electrical power (EP) to other devices (25), converting mechanical power (MPl) provided by said powertrain (21, 1, 6, 7, 8, 11) into a form (SP) that can be stored by the energy storage element (22, 5) , drawing energy stored by an energy storage element (22, 5) , and transforming the power

(SP) drawn from the storage element (22, 5) into mechanical power (MPl, MP2) , the powertrain (21, 6) being capable of transferring mechanical power (MPl) to and from the electromechanical system (20, 2, 3); an energy storage element (22, 5) coupled to said electromechanical system (20, 2, 3) for exchanging power (SP) with said electromechanical system (20, 2, 3) , storing energy provided by said electromechanical system (20, 2, 3), and acting as ballast to stabilize system operation; and a controler (23, 4) for regulating powertrain mechanical power (MPl, MP2) , regulating electrical power (EP) provided by said electromechanical system (20, 2, 3) to other electrical devices (25) , and regulating the power (SP) transferred with the energy storage element (22, 5) in order to regulate the amount of energy stored in said energy storage element (22, 5) .

2. An energy conversion system as set forth in claim 1, wherein the mechanical power (MPl, MP2) is used for driving a vehicle.

3. An energy conversion system as set forth in Claim 1 wherein the electromechanical system (20, 2, 3) consists of a single electric machine (3) , electrical interconnections, and means to regulate electrical energy flow to and from the electric machine (3) .

4. An energy conversion system as set forth in claim 2, wherein the powertrain (20, 1, 6, 7, 8, 11) comprises a combustion engine (1), the vehicle (13) having an electric machine (3) and a transmission (11) connected to the engine

(1) in the direction of a drive shaft (6), the drive shaft (6) being provided for driving at least one wheel drive shaft (8) with driving wheels (10.1, 10.2), wherein the combustion engine (1) , the transmission (11), an element (2) via which the electric machine (3) can be operated by the drive shaft (6), a separator (7) and a wheel drive shaft (8) are arranged along the drive shaft (6), or wherein the combustion engine (1) , the electric machine (3), the transmission (11) and a wheel drive shaft (8) are arranged along the drive shaft (6), and wherein a separator (7) or the transmission (11) is provided for separating the wheel drive shaft (8) from the drive shaft (6) when the vehicle is at a standstill.

5. A system according to Claim 4, wherein the separator (7) is provided for separating the wheel drive shaft (8) from the drive shaft (6) when the vehicle is at a standstill.

6. A system according to Claim 4, wherein the electric machine (3) is driveable by the drive shaft (6) .

7. A system according to Claim 4, wherein the electric machine (3) is a motor/generator.

8. A system according to claim 4, wherein the motor/generator (3) is electrically connected to a converter (4) .

9. A system according to Claim 4, wherein the motor/generator (3) is connected to a draw point (12) for electrical power for supplying electrical loads outside the vehicle (13) .

10. A system according to Claim 8, wherein electrical isolator (14) for decoupling the converter (4) from the motor/generator (3) are provided between the converter (4) and the motor/generator (3) .

11. A system according to Claim 8, wherein the converter (4) is electrically connected to a vehicle battery (5) .

12. A system according to Claim 4, wherein the drive shaft (6) and/or the wheel drive shaft (8) and/or driving wheels (10.1, 10.2) are connected to an electrical drive machine (9).

13. A system according to Claim 4, wherein the motor/generator (3) coupled to the internal combustion engine (1) forms a power unit having a maximum output power which corresponds approximately to that of the internal combustion engine (1) in the idling range.

14. A system according to Claim 4, wherein the motor/generator (3) is an asynchronous machine or a permanently excited machine and the converter (4) comprises a six-pulse bridge circuit .

15. A system according to Claim 4, wherein the motor/generator (3) is a machine and the converter (4) comprises a six-pulse bridge circuit with a field controller.

16. Method for operating an energy conversion system comprising a powertrain (21, 1, 6, 7, 8, 11) capable of exchanging mechanical power (MP2) with other devices (24, 10); an electromechanical system (20, 2, 3) coupled to said powertrain (21, 1, 6, 7, 8, 11) for converting mechanical power (MPl) provided by said powertrain (21, 1, 6, 7, 8, 11) into controllable electrical power (EP) to other devices (25), converting mechanical power (MPl) provided by said powertrain

(21, 1, 6, 7, 8, 11) into a form (SP) that can be stored by the energy storage element (22, 5) , drawing energy stored by an energy storage element (22, 5) , and transforming the power

(SP) drawn from the storage element (22, 5) into mechanical power (MPl, MP2) , the powertrain (21, 6) being capable of transferring mechanical power (MPl) to and from the electromechanical system (20, 2, 3) ; an energy storage element (22, 5) coupled to said electromechanical system (20, 2, 3) for exchanging power (SP) with said electromechanical system (20, 2, 3), storing energy provided by said electromechanical system (20, 2, 3), and ^• acting as ballast to stabilize system operation; and a controler (23, 4) for regulating powertrain mechanical power (MPl, MP2), regulating electrical power (EP) provided by said electromechanical system (20, 2, 3) to other electrical devices (25) , and regulating the power (SP) transferred with the energy storage element (22, 5) in order to regulate the amount of energy stored in said energy storage element (22, 5) ; said method comprising: decoupling the other mechanical devices (24) from the powertrain (21) and, with the powertrain (21) decoupled, driving an electromechanical system (20) by the powertrain (21); and wherein an output AC voltage (U_A) of the electromechanical system (20) is regulated by a field current (I_F), made available by a controller (23), as a function of an electrical load on the electromechanical system (20) .

17. Method according to Claim 16, wherein a vehicle (13) is brought to a park position, the wheel drive shaft (8) is decoupled from the drive shaft (6) and, with the wheel drive shaft (8) decoupled, a motor/generator (3) is driven by the internal combustion engine (1) ; and wherein an output AC voltage (U_A) of the motor/generator (3) is regulated by a field current (I_F) , made available by a converter (4), as a function of an electrical load on the motor/generator (3) .

18. Method according to Claim 16, wherein the field current of the motor/generator (3) is regulated by the converter (4), and wherein the electrical power of the motor/generator (3) that can be drawn is set by the difference between the rotational speed of the stator and the rotational speed of the rotor.

19. Method according to Claim 16, wherein the motor/generator (3) coupled to the internal combustion engine (1) is operated as a power unit for external electrical loads when the vehicle is at a standstill.

20. Method according to Claim 16, wherein the vehicle is operated as a parallel hybrid in driving mode.

21. Method according to Claim 16, wherein the motor/generator (3) is used to recuperate braking energy.

22. Method according to Claim 21, wherein the motor/generator (3) is used for electrical driving of the vehicle.