DE102010043492A1 - Control method for stator and rotor in electric machine that is utilized in pure electric car and hybrid vehicles, involves reducing reference torque by torque value if one of reference values reaches or exceeds corresponding maximum values - Google Patents

Abstract

The method involves making reference values for stator and rotor currents (Is.ref, If.ref), where the reference value for the stator current and the reference value for the rotor current or an auxiliary parameter representing the reference value of the stator current and an auxiliary parameter representing the reference value of the rotor current is dependent on predefined reference torque (Tref). The reference torque is reduced by a torque value if one of the reference values reaches or exceeds corresponding maximum values (Is.max, If.max). An independent claim is also included for a control device comprising a memory unit.

Description

The present invention relates to a control method and a device for controlling synchronous machines, in particular externally excited synchronous machines.

The synchronous machine is one of the most important types of electrical machines. Traditionally, the synchronous machine is used, for example, to generate electrical energy. Increasingly, the electric machine, in particular the synchronous machine, is gaining importance as a drive unit in motor vehicles. In this case, the synchronous machine can be used, for example, in purely electric vehicles but also in hybrid vehicles. Essentially, a distinction is made between permanent-magnet synchronous machines and separately excited synchronous machines. Permanent-magnet synchronous machines have a rotor in which permanent magnets are arranged. In a separately excited synchronous machine, a rotor with a winding is used, which is flowed through slip rings by an excitation current, whereby the rotor side, a magnetic excitation flux or rotor flux is generated, which interacts with a field generated by energized stator windings rotating field.

Externally excited synchronous machines are used, for example, in hybrid vehicles, in particular in hybrid axle drive systems. The hybrid technology is essentially characterized in that two drive units, an internal combustion engine and an electric machine are arranged in the vehicle. The engine can be connected, for example, axially parallel via a two-stage spur gear with an axle differential. Especially in motor vehicle propulsion units, safety is a special criterion that must be taken into account when choosing the type of electrical machine. The engine should ideally be switched off anytime. An advantage of the externally excited synchronous machine is that the rotor-side excitation current can be switched off, whereas in permanent magnet-excited synchronous machines, the rotor-side magnetic excitation flux can not be switched off in normal operation. An important aspect of electric machines in motor vehicles are the losses occurring during operation, since they either have to be supplied completely from an accumulator or via a generator coupled to a combustion unit. Together with the inverter losses one speaks for example of driving cycle losses. When designing the electrical machine, in particular the externally excited synchronous machine and the associated control with inverter, the loss characteristic is a special criterion.

It is an object of the present invention to provide a control method and a corresponding device that enables a loss-optimized operation of a separately excited synchronous machine with high control dynamics.

The object is achieved by a method according to claim 1 or by a device according to claim 10. Refinements and developments of the inventive concept are the subject of dependent claims.

In particular, the object is achieved by a control method for a separately excited synchronous machine having a stator and a rotor, comprising the steps: providing reference values for stator and rotor currents, wherein the reference value for the stator current and / or the reference value for the rotor current or the reference value Auxiliary variable representing the stator current and / or an auxiliary variable representing the reference value of the rotor current is dependent on a predetermined reference torque, providing maximum values for stator and rotor currents, comparing the reference values for the stator and / or rotor currents or an auxiliary variable representing the reference value of the stator current and or an auxiliary variable representing the reference value of the rotor current with the corresponding maximum values and reducing the reference torque by a torque value if at least one of the reference values reaches its corresponding maximum value he passes.

A control device according to the invention has the following components: A memory unit which is designed to provide reference values for stator and rotor currents, the reference value for the stator current and / or the reference value for the rotor current or an auxiliary variable representing the reference value of the stator current and / or Auxiliary unit representing the reference value of the rotor current is dependent on a predetermined reference torque, and providing maximum values for stator and rotor currents, and a processing unit configured to compare the reference values for stator and rotor currents with the corresponding maximum values for stator and rotor currents, and is further adapted to reduce the predetermined reference torque when at least one reference value for stator and rotor currents reaches or exceeds the corresponding maximum value.

The present invention will be explained in more detail with reference to the embodiments illustrated in the figures, wherein the same or equivalent elements are provided with the same reference numerals. It shows

1 2 schematically shows the rotor of a separately excited synchronous machine and a magnetic rotor flux oriented dq coordinate system,

2 in a signal flow diagram, an example of the structure of a current control for a separately excited synchronous machine,

3 in a Sankey diagram, the essential loss components of a separately excited synchronous machine

4 schematically in a diagram, a principle for torque reduction for the current control of a separately excited synchronous machine and

5 in a signal flow plan an exemplary for torque control with a superimposed torque control for the current control of a separately excited synchronous machine according to the scheme in 4 .

6 schematically a drive train for an electric vehicle with a synchronous machine, a converter, a control device and an energy storage and

7 schematically essential components of a control device for the current control of a synchronous machine.

Electrical machines, in particular synchronous machines, are commonly controlled by means of a vector control, also called field-oriented control, using an inverter. To implement a field-oriented control, a Cartesian coordinate system is used 10 introduced, which has a d and a q-axis, wherein the d-axis at the magnetic rotor flux (or exciting flux) is oriented, so that the coordinate system rotates rotor-fixed with the rotor speed. This simplifies the control of the model equations. In 1 is an example of a rotor 11 a foreign-excited synchronous machine with pronounced rotor poles in the form of a salient pole rotor shown. This rotor has a rotor winding 12 on, with the direction of current flow (cross: current flows into the plane of the drawing; point: current emerges from the plane of the drawing).

From the direction of energization results a rotor flux Ψ _f , which is placed on the d-axis of the dq coordinate system. Orthogonal to the d-axis is the q-axis of this coordinate system. In this dq reference system, a stator current vector I _s can be expressed via a d component (current vector) I _d and a q component (current vector) I _q . In the following, the vector notation is omitted for reasons of simplification in the case of vector variables. A pole wheel voltage U _{p of} the synchronous machine is oriented as shown in the q-axis of the dq reference system. In the example shown, the current vector I _{d is located} on the negative d-axis in opposition to the rotor flux Ψ _f . In this case, one speaks of field-weakening operation, since the current (-zeiger) I _d generates a flux component (eg, Ψ _d ) which is directed counter to the excitation flux Ψ _f , so that the resulting flux is reduced. In the case of separately excited synchronous machines, the field weakening can be carried out via the additional degree of freedom of a variable excitation current I _f compared to permanent-magnet machines.

In 2 By way of example, the signal flow diagram of a possible current or torque control for a separately excited synchronous machine with respect to the dq reference system is shown. This control structure includes reference current processing and derating 50 which _provides reference _values I _q.ref and I _d.ref for current regulation, that is to say a current vector for a current vector-based field-oriented torque regulation. For I _q.ref , the reference value of the q-component of the stator current, and for I _d.ref , the reference value for the q-component of the stator current, in each case a PI current regulator 21 . 23 intended. A feedforward control 22 For the d as well as for the q-component of the stator current, the two PI controllers are subjected to a value that is independent of the states of the controlled system (controlled system: eg synchronous machine and converter), in particular independent of the determined in the machine active currents I _q.akt , I _d.akt is. The active currents I _q.akt , I _d.akt represent the stator current actually flowing in the control system in the dq reference system. The feedforward control allows the consideration of the manipulated variable demand to be expected on the basis of the setpoint curve, whereby the d and q components can be regarded as actuating or reference variables in a current control. The pilot control thus essentially serves to improve the guiding behavior of the current regulation by compensation of switching dead times, without endangering the stability of the regulation.

From the reference current processing according to the invention with derating 50 results in an excitation current I _f.ref , which also has a PI controller 24 is regulated. The PI current regulator 21 . 23 . 24 provide corresponding voltages U _f.ref , U _d.ref and U _f.ref , where the stator _voltages such as U _f.ref , U _d.ref the currents are described in the dq system. The voltages U _f.ref , U _d.ref and U _f.ref become a switching time _processor 25 . 26 fed. Output signals t _U , t _V , t _W , t _{f of} the switching time processors 25 . 26 turn the power level with inverter 27 fed, which ultimately controls the power supplied to the synchronous machine. For the stator sizes, in particular the stator _voltages U _f.ref , U _d.ref , a transformation from the dq- System, for example, take place in a stator-oriented coordinate system. For this example, the switching time processor 25 the rotor angle φ _P supplied. The rotor angle φ _P (also load angle) is the angle at which the flywheel of a synchronous machine (usually the rotor) leads or lags the phase generated by the stator winding depending on whether the machine is in motor or generator mode , Such a transformation from the dq system, for example, into a fixed-stator coordinate system can be, for example, an inverse Park-Clark transformation.

An essential aspect in the current regulation of synchronous machines, in particular of externally-excited synchronous machines used as a drive unit in motor vehicles, is the loss reduction of the drive system or of the drive train (for example, the drive train includes: electric machine, shaft, differential gear, inverter, electrical energy storage (eg B. in mobile applications), control device). In 3 are shown on the basis of a Sankey diagram, the main loss components in a separately excited synchronous machine in motor operation. The stator is supplied with a power P _S = 3U _S * I _S * cosφ, where U _{S is} the stator voltage, I _S in this case the magnitude of the stator current and φ the (temporal) phase shift between stator current and voltage. The stator is lossy, with a dissipated in the stator power dissipation P _VS from copper losses P _Cu.S , iron losses (in particular _{Ummagnetisierungsverlusten} ) P _Fe.S and scattering losses P _σ.S composed. The rotor reaches the air gap power P _δ = P _S - P _VS. The air gap power P _δ is narrowed down by rotor losses P _VR , wherein a mechanical power P _mech = M _mech · ω _mech (M _mech torque at the shaft; ω _mech : angular speed of the shaft) delivered at the rotor shaft reduces the air gap power P _δ minus the rotor losses P _VR is. The rotor losses P _VR are essentially composed of copper losses P _{Cu.R of} the rotor winding, _leakage losses P _σ.R in the rotor and friction losses P _Fr.R , such as, for example, B. bearing and air friction.

In a separately excited synchronous machine, the rotor is supplied with a power P _f = U _f * I _f = P _Cu.R , where U _{f is} the voltage at the rotor winding and I _{f is} the exciting current in the rotor winding. Usually, the electrical quantities supplied to the rotor are constant; ie, they are DC currents and voltages. In the design of the current control, in particular the stator currents I _S and the rotor current I _{f are} regulated. Via the rotor current I _f the one hand, the copper losses in the rotor P _Cu.R which are proportional to the square of the exciting current I _f, and on the other hand, the iron losses in the stator P _Fe.S can be influenced. The magnetic excitation flux Ψ _f formed in the rotor is proportional to the excitation current I _f in the rotor.

The rotor flux Ψ _f is predominantly responsible for the stator iron losses P _Fe.S , since the stator lamination with rotating rotor undergoes a changing over time magnetic field, which in addition to passing through the material hysteresis (the BH curve) additionally eddy currents are formed. Thus, in particular the iron losses in the stator P _Fe.S can be influenced via the exciting current in the rotor I _f . From the magnitude of the excitation current, the copper losses or the ohmic losses in the rotor winding P _Cu.R are directly dependent. The amount of the stator current is responsible in particular for the copper losses or the resistive losses P _Cu.S in the stator winding. In particular, the maximum losses in the electric machine are limited with the present invention. This serves on the one hand to prevent thermal overload of the machine and, since electric machines can be used for example in electric vehicles, the consumption of electrical energy z. B. from a rechargeable battery, which is very important for mobile applications.

In 4 is exemplified by a diagram, such as the losses of the synchronous machine via a current-derating method 40 can be limited. The starting point here is generally a three-dimensional lookup table, in which the currents I _d.ref , _Iq.ref , _{If.ref are} respectively _stored as functions of a reference torque T _ref , speed n or intermediate _{circuit voltage} U _DC . For a certain speed n, a specific reference torque T _ref and a certain intermediate _{circuit voltage} U _DC , the reference _values for stator currents I _d.ref , I _q.ref (respectively with respect to the dq reference system) and for the rotor-side excitation current I _f.ref , _result . which are fed to the current control. With the determination of the reference values for the individual currents ultimately matching values for desired and actual torque are to be made available to the loss-optimal operation according to the invention with respect to the essential loss components of the synchronous machine (see 3 ) taking into account the limiting parameters, such as the DC link voltage. The loss optimization itself is performed, for example numerically using a simulation model iteratively for the three currents I _d.ref , I _q.ref , I _f.ref depending on the speed n, the reference torque T _ref and the intermediate _{circuit voltage} U _DC . It can be provided, the three reference _currents I _d.ref , I _q.ref , I _f.ref in a lookup table 51 as a function of the reference torque T _ref , the speed n and the intermediate circuit voltage U _DC store, ie I _d.ref , I _q.ref , I _f.ref = (T _ref , n, U _DC ), so that the loss-optimal reference values for the currents can be interpolated. This results in an offline simulation of a lookup table with loss-optimized reference currents for maximum possible torques.

The reference values do not necessarily have to be explicit reference values for stator and / or rotor currents, for example in the dq reference system. Alternatively or additionally, auxiliary quantities which are representative of stator and / or rotor currents can also be used. Such auxiliary variables may result, for example, from the mathematical or numerical models used to generate lookup tables. An auxiliary variable can be determined, for example, from the ratio of the rotor current and the q component and / or the d component of the stator current. The use of auxiliary quantities may be advantageous in that, in certain cases, a transformation into the dq reference system of the rotor becomes superfluous, which means reduced computational effort. The permissible maximum values are converted accordingly to the auxiliary values.

The use of look-up tables is very advantageous in the regulation, in particular of electrical machines, since the magnetically active constituents have pronounced nonlinear behavior over a wide range. Nonlinear characteristics can be mapped by numerical approximation using a variety of suitable machine models and stored in lookup tables. In particular, the numerical approximation using FE models (numerical machine models according to the finite element method) are able to accurately map nonlinearities even in the saturation region. While these strategies require considerable memory overhead for the resulting lookup tables, they offer the benefits of higher stability, higher dynamics, and better steady state control over closed loop control concepts with fixed, analytically-estimated parameters.

aus den Referenzwerten für die einzelnen Statorstromkomponenten bezüglich des dq-Systems gebildet werden. Aus Betriebsparametern, die den Zustand der Regelstrecke, also insbesondere der Synchronmaschine, repräsentieren, z. B. der Drehzahl n, der Zwischenkreisspannung U_DC und einer Vielzahl von Temperaturen θ₁, θ₂, etc. können über ein Strom-Derating 53 Maximalwerte, beispielsweise für die Beträge des Statorstroms I_S.ref und des Erregerstroms I_f.ref gebildet werden. Das Strom-Derating 53 ist so ausgelegt, dass diese Maximalwerte beispielsweise zuvor festgelegte maximale Verluste P_V.S, P_V.R der Synchronmaschine charakterisieren. Wie hoch diese Verluste im Einzelnen sein dürfen, ist abhängig davon, wo die Maschine verbaut ist und wie sie bezüglich ihres Designs (z. B: Wicklungstyp, Rotortyp usw.) beschaffen ist. Die Maximalwerte für die Ströme werden erfindungsgemäß mit den Referenzwerten aus der Lookup-Tabelle 53 verglichen. Erreicht oder übersteigt zumindest einer der Referenzwerte aus der Lookup-Tabelle die aus dem Strom-Derating ermittelten Maximalwerte, dann ist das vorgegebene Referenzdrehmoment zu hoch und muss um einen bestimmten Wert T' reduziert werden, so dass die Maximalwerte für die Ströme und damit die maximal zulässigen Verluste erreicht oder unterschritten werden.In order to achieve a high dynamics of the current control in loss-optimal operation during the operation of a separately excited synchronous machine in real time, a feedback via a superimposed torque control is proposed according to the invention, which reduces the reference torque T _ref as needed, thereby using the lookup table 51 ultimately the reference currents are lowered. For this purpose, for example, the amount 52 of the stator current

are formed from the reference values for the individual stator current components with respect to the dq system. From operating parameters that represent the state of the controlled system, ie in particular the synchronous machine, z. As the rotational speed n, the _DC link voltage U _DC and a plurality of temperatures θ ₁ , θ ₂ , etc. can be a current derating 53 Maximum values, for example, for the amounts of the stator current I _S.ref and the excitation current I _{f.ref are} formed. The current derating 53 is designed such that these maximum values characterize, for example, predetermined maximum losses P _VS , P _{VR of} the synchronous machine. The exact amount of these losses depends on where the machine is installed and how it is designed (eg winding type, rotor type, etc.). The maximum values for the currents according to the invention with the reference values from the lookup table 53 compared. If at least one of the reference values from the look-up table reaches or exceeds the maximum values determined from the current derating, then the given reference torque is too high and must be reduced by a specific value T 'so that the maximum values for the currents and thus the maximum permissible losses are reached or fallen below.

In 5 is an example in a signal flow plan with a reference current processing with derating 50 shown in particular a current derating 53 with a superimposed torque control 56 for torque reduction for the current control of a separately excited synchronous machine can be implemented control technology. Thus operating parameters representing an operating point are specified as reference variables and from the lookup table 51 Reference values for the individual streams, for example, with respect to the dq system formed and the current regulation 20 fed. From the reference _values for the d and q components of the stator current, the magnitude of the reference value of the stator current I _S.ref can be formed. With suitable measuring devices (for example, speed and temperature sensors) operating parameters representing the state of the controlled system such as the rotational speed n, the intermediate circuit voltage U _DC and a multiplicity of temperatures θ ₁ , θ ₂ , etc. prevailing in the synchronous machine are determined. These are real operating conditions or conditions prevailing in the machine.

In particular, the temperatures determined can be a measure of the losses in the machine. About the current derating 53 are determined from these operating conditions maximum values for stator current I _S.max and excitation current I _f.max . Decisive are especially the temperatures of the individual components, so for example, the stator and the rotor of the synchronous machine, the inverter and the Exciter stage (eg the power semiconductors). These temperatures can be measured and / or modeled during operation. A modeling of the temperatures can be particularly advantageous if a metrological determination is associated with great expense. For example, it may be necessary to mount a multiplicity of temperature sensors in the rotor, in particular on the rotor winding, in order to map the thermal conditions in the rotor as realistically as possible. In this case, these temperature sensors must be made electrically accessible via slip rings, for example. However, the possible number of slip rings and thus the number of measuring points is very limited. A thermal model can be used here in addition to sensors or alone. From the reference values for the currents and the corresponding maximum values, a control difference is formed in each case and a control difference module 55 fed.

At least the difference between the reference value for the stator current and the maximum value for the stator current ΔI _S = I _S.ref - I _{S. max} can be used for the control difference _block 55 over a scale 54 are supplied to the control difference from the excitation currents .DELTA.I _f = I _f.ref - I _{f.max reach} identical conditions. The magnitudes of the thermally effective stator current (rms value of the stator current) and the rotor DC current are different. By way of example, the stator current can assume rms values of approximately 300 A, while the rotor direct current can, for example, only have values in the region of 18 A. In order nevertheless to achieve a suitable control behavior of the superimposed torque control according to the invention, a normalization of the currents to either the stator or the rotor current respectively. In the present example, the control difference of the stator current ΔI _{S is} scaled, whereby a standardization of the stator current is achieved on the rotor current. A superimposed torque controller 56 Received via the rule difference block 55 an instruction to reduce the reference torque T _ref by a torque value T 'when the control differences ΔI _S , ΔI _{f have reached} a certain extent, which depends on the application. The threshold determination is preferably designed so that the superimposed torque controller 56 the reference torque T _{ref can} only reduce arbitrarily, but can not increase.

In order to achieve the highest possible control dynamics in the torque control according to the invention, a fast control loop for the rotor current (excitation current) is required. Since the stator time constant is much lower than the rotor time constant, the dynamics of the control circuit for the rotor current acts as a limiting factor for the entire current control. The time constants relevant for the control are determined by the rotor or stator inductance as well as the rotor inertia. Therefore, in particular the control reserve for the rotor current contributes essentially to the dynamics of the corresponding control loop.

For determining the maximum values for the stator current and the rotor-side exciter current via the current derating 53 An estimate of the rotor temperature can be used. Since the rotor is actively heated by the ohmic losses (copper losses) in the rotor winding and the rotor-side leakage losses, a reduction of the rotor current according to the invention during operation of the synchronous machine may be required. The rotor temperature can be estimated, for example, using a plurality of temperature sensors placed in the rotor, on average. However, this has the disadvantage that these sensors must be made electrically accessible, for example via slip rings, which is complicated and prone to failure. Alternatively, the rotor temperature may be above the measured excitation current and that through the rotor current regulator 26 determined rotor voltage (eg, the target voltage) are determined. In this way, approximately the average rotor temperature can be determined from the temperature-dependent ohmic resistance of the rotor winding. In order to achieve sufficient accuracy in particular the non-linearity of the power level 27 and the voltage drop across the slip rings, which make the rotor winding electrically accessible, be compensated in a suitable manner. Normally, this type of rotor temperature estimation is only possible from a certain exciter current.

The implementation of a current control according to the invention with derating (with respect to torque and reference currents) approximately according to the signal flow plans in the 2 and the 5 can be realized for example by means of analog or digital circuit technology with a microprocessor. In a processing unit of the microprocessor, the signal flow plans with their components can then be implemented digitally by means of a suitable program code.

Since the field-oriented torque control allows relatively high control dynamics, this principle is used in synchronous machines, even and especially in externally-excited synchronous machines. An object of the present invention is to provide a loss-optimized control, in particular a loss-optimized torque control, with respect to conventional field-oriented control methods of high control dynamics available. Therefore, according to the invention, a predictive or predictive torque or rotor flux control is proposed, which is particularly suitable for the loss-optimal operation of a separately excited synchronous machine is suitable.

As already stated, the time constant decisive for the dynamics of the torque control of a separately excited synchronous machine is the rotor time constant, which is much larger than the stator time constant. Thus, the rotor circuit is the limiting component for the control dynamics of the torque control. Predictive torque control is to predictively increase or decrease the rotor current before the relevant parameters prevailing in the machine (eg, torque, stator current, rotor current) would result in a corresponding feedback response of the controller Depending on the operating state, the requirement of increased dynamics or higher or lower torque is foreseeable. The requirement for greater dynamics, in particular increased driving dynamics when using the proposed control method in motor vehicles, can be determined, for example, by known methods for detecting the driving situation (eg overland or city driving). This can be done, for example, based on the driver behavior by means of suitable algorithms. If the torque is increased, for example by means of an increase in the rotor current, before it is actually required on the motor shaft, then the large rotor time constant can be bridged so that only the stator time constant for the control dynamics remains decisive. If the torque provided on the shaft, the actual torque, should remain constant, the stator current must be adjusted accordingly. If more torque is required on the shaft, then only the stator current must be increased quickly. This applies accordingly also in the case that less torque is ordered, in which case the currents are lowered. By influencing the rotor current, the rotor or exciter flux is directly changed and thus the torque is changed.

In the drive train of an electrical machine, in particular a separately excited synchronous machine, a plurality of components, such as stator and rotor winding and stator and rotor core are arranged. The thermal load capacity, ie the maximum temperature which may prevail in the individual components (over a certain period of time), is very different in each case. The temperatures that are reached in the individual components during operation depend, on the one hand, on the supplied current (in the stator and rotor) and on the other hand on how well the individual components can be cooled. In electric machines with rotor winding, for example, the rotor winding tends to be axially in the middle of points in the middle to thermal overload, since the cooling there is the worst.

Individual components can also be selectively thermally overloaded in the loss-optimal operation according to the invention. A large number of sensors and / or a suitable thermal model can provide information about the instantaneous thermal load of individual components, ie instantaneous temperatures. If it is above the thermal load capacity, ie above the permissible maximum temperatures, then measures must be taken to prevent damage to the corresponding components. A separately excited synchronous machine, for example, offers the advantage of an additional degree of freedom over the exciting current compared to a permanent-magnet synchronous machine. If, for example, a component is thermally overloaded at loss-optimized currents and torques at a specific operating point, then the thermal load of this component, ideally with constant torque at the shaft, should be reduced. For this purpose, in a separately excited synchronous machine, the ratio between stator and rotor currents can be changed in such a way that the torque which can be tapped off from the shaft remains constant, but the thermal load, for example, is made uniform. Specifically, this would mean that the rotor current is reduced, for example, in the case of a thermally overloaded rotor winding, but the stator current is correspondingly increased in order to ensure a constant torque output. Ideally, nothing changes on the shaft during this procedure, although the loss-optimized operation of the machine generally has to be suspended at least temporarily.

In 6 are exemplary the essential components of a drive train 60 shown for an electric vehicle. In principle, however, the powertrain of an electric vehicle does not differ from other applications of synchronous machines that require an electrical energy storage. The essential components of the drive train 60 are an inverter 63 , a control device 61 with a sensor cable 65 , a synchronous machine 62 with a wave 66 , For the exemplary case of a mobile application in a hybrid vehicle or pure electric vehicle is in place of a power grid additionally an electrical energy storage 64 necessary as energy source. However, the present invention is not limited to mobile applications. The synchronous machine 62 As with any concentric rotating electrical machine, it has a stator 67 on, be arranged in the stator windings for generating a rotating field. In addition, a rotor is rotatably mounted in the synchronous machine 68 arranged, which has a winding which is energized, for example via slip rings such that a rotor-side excitation field is formed that can interact with the rotating field of the stator. As a rule, the rotor-side excitation current is a direct current. The synchronous machine 62 can provide together with an internal combustion engine for the propulsion of the vehicle; this is called a hybrid vehicle.

There are numerous drive concepts for hybrid vehicles, which will not be discussed further here. On the other hand, the synchronous machine 62 be provided without internal combustion engine in a pure electric vehicle as the sole drive unit. The synchronous machine 62 belongs to the type of three-phase machines. For three-phase machines, the speed and torque control is via a converter 63 widespread. About the inverter 63 becomes the synchronous machine 62 for generating mechanical torque on the shaft 66 supplied necessary electrical power. The inverter 63 draws this power in a motor vehicle in the form of DC voltage and current typically from the electrical energy storage 64 , This energy storage 64 may be an electrochemical energy storage, such as an accumulator. It is quite conceivable an electro-chemical energy storage with electrostatic energy storage, eg. B. capacitor banks to combine. The inverter 66 is from a control device 61 driven, which ultimately ensures that the synchronous machine 62 the electrical power which is currently required for the operating state of the motor vehicle (of which, incidentally, the losses in the drive train must also be covered) is supplied. In order to limit the losses according to the invention, in particular in the electrical machine, the control device requires, in addition to the active currents in the machine, for example, also information as to which operating conditions prevail in the machine. There are for this purpose, for example, temperature sensors 651 and speed sensors 652 provided in the machine whose measured values of the control device 61 via a sensor cable 65 be supplied.

The control device 61 In an advantageous embodiment, as in FIG 7 exemplified, essentially a memory unit 71 and a microprocessor 72 , where the microprocessor 71 the inverter 63 controls. In the microprocessor 71 For example, the current regulation according to the invention can be implemented digitally. The microprocessor 71 For this purpose, the measured values representing the operating conditions prevailing in the machine must also be transmitted via the sensor line 65 be supplied. In order to realize the current regulation according to the invention, in particular the dynamic determination of loss-optimized reference values for currents and torques via suitable lookup tables, one has to work with the microprocessor 71 connected storage unit 71 be provided. The storage space on the storage unit 71 must be sufficiently large to the inventive lookup tables, to which the microprocessor 71 must access, save.

Although the examples discussed above particularly relate to hybrid vehicles, the present invention is not limited to mobile applications such as automobiles but has many uses.

LIST OF REFERENCE NUMBERS

10

dq coordinate or reference system

11

externally excited rotor with pronounced poles

12

Rotor winding with current supply direction

U _S

Internal voltage

I _S

stator

I _q

q-component of the stator current (q-current)

I _d

d-component of the stator current (d-current)

_F

Rotor or exciter flux

P _f

Excitation power in the rotor

P _S

supplied power in the stator

P _δ

Air gap power

P _Cu.S

Copper losses (ohmic losses) in the stator winding

P _Fe.S

Iron or magnetic reversal losses in the stator

P _σ.S

Scatter losses in the stator

P _VS

entire stator losses

P _VR

total rotor losses

P _Cu.R

Copper losses (ohmic losses) in the rotor winding

P _σ.R

Scatter losses in the rotor

P _Fr.R

friction

20

Current control of a synchronous machine

21

PI controller for q-current

22

Feed forward control

23

PI controller for d-current

24

PI controller for excitation current

25

Switching time processor

26

Switching time processor

27

Power level with inverter

50

Reference current processing and derating

51

Lookup table (LUT)

52

Amount formation of the stator current

53

Current derating

54

Scaling (of control differences)

55

Control difference block

56

torque controller

Claims (11)

A control method for a stator-excited and a rotor-driven, externally excited synchronous machine, comprising the steps of: Providing reference values for stator and rotor currents (I _S.ref , I _f.ref ), wherein the reference value for the stator current and / or the reference value for the rotor current or an auxiliary variable representing the reference value of the stator current and / or a reference value of the rotor current representing auxiliary variable is dependent on a predetermined reference torque (T _ref ), providing maximum values for stator and rotor currents (I _S.max , I _f.max ), comparing the reference values for the stator and / or rotor currents (I _S.ref , I _f.ref ) or an auxiliary variable representing the reference value of the stator current and / or an auxiliary variable representing the reference value of the rotor current with the corresponding maximum values (I _S.max , I _f.max ) and reducing the reference _torque (T _ref ) by a torque value ( T ') if at least one of the reference values reaches or exceeds its corresponding maximum value (I _S.max , I _f.max ). A control method according to claim 1, wherein the reference values are in a look-up table ( 51 ), these reference values respectively corresponding to a loss minimum operating point, represented by corresponding operating parameters (T _ref , n, U _DC ). Control method according to one of the preceding claims, wherein the maximum values for stator and rotor currents (I _S.max , I _f.max ) are dependent on temperatures of certain components of the synchronous _machine (θ ₁ , θ ₂ , ...), of the rotational speed (n) as well as the intermediate circuit _voltage (U _DC ). Control method according to claim 3, wherein the temperature of at least one of the following components of the synchronous machine is taken into account: stator winding, rotor winding, stator lamination stack, rotor lamination stack and rotor bearing. Control method according to claim 4, wherein additionally the rotational speed (n) is taken into account. Control method according to one of the preceding claims, in which the torque value (T ') by which the reference torque (T _ref ) is reduced depends on the deviation of the reference value of the rotor current (I _f.ref ) from the permissible maximum value of the rotor current (I _{f. max} ) and / or the deviation of the reference values of the stator current (I _S.ref ) from the permissible maximum value of the stator current (I _S.max ). Control method according to one of the preceding claims, wherein prior to reducing the reference torque (T _ref ), the deviation of the reference value of the stator current from the maximum value of the stator current is scaled. A control method according to any one of the preceding claims, wherein a plurality of temperatures of the synchronous machine is compared to a plurality of maximum allowable temperatures and wherein the stator current and / or the rotor current varies upon reaching and / or exceeding at least one of the plurality of maximum temperatures is that at least one of the plurality of maximum allowable temperatures again falls below. Control method according to one of the preceding claims with a predictive torque control in which the rotor current is predictively increased or decreased, if a higher or lower load on the shaft and / or a high control dynamics is to be expected. A control method according to claim 1, wherein the auxiliary value representing the reference value of the stator current and / or the reference value of the rotor current is formed from the ratio of the rotor current and the q-component of the stator current. A control device, which is designed to control a sparsely-excited synchronous machine with a stator and a rotor with low loss, comprising: a memory unit, which is designed to reference values for stator and rotor currents, wherein the reference value for the stator current and / or the reference value for the Rotor current or an auxiliary variable representing the reference value of the stator current and / or an auxiliary variable representing the reference value of rotor current is dependent on a predetermined reference torque (T _ref ) and provide maximum values for stator and rotor currents and a processing unit which is adapted to the reference values for To compare stator and rotor currents with the corresponding maximum values for stator and rotor currents and which is further adapted to reduce the predetermined reference torque when at least one reference value for stator and rotor currents reaches the corresponding maximum value or ü Bersch rides.

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