WO2011045192A2 - Method and system for electrically powering a vehicle - Google Patents

Abstract

The invention relates to the operation of a multiphase electric motor designated to be a vehicle drive, comprising the generation of PWM pulses for actuating circuit elements of an inverter for providing phase currents (Iu, Iv, Iw) for the electric motor, wherein a corresponding PWM pulse sequence (Pu, Pv, Pw) having a prescribed pulse frequency (fpwm = 1 / Tpwm) is generated for each phase current (Iu, Iv, Iw). In order to reduce acoustic noise, according to the invention, the pulse frequency (fpwm) of at least one of the PWM pulse sequences (Pu, Pv, Pw) is operationally varied in a continuous manner.

Description

description

Method and system for electric drive of a vehicle The present invention relates to methods and systems for electric drive vehicles, and more particularly to operation ^{information model} according to the preamble of claim 1 and an electric drive system according to the preamble of claim 8. Such a method and such a system are, for example known from DE 10 2008 052 923 AI. According to this prior art a Kraftfahrzeu ^¬ ges a three-phase AC motor is provided for driving. A supplied by a battery electric vehicle inverter provides the three required to operate the motor elekt ^¬ step phase currents. For this are electrical

Switching elements of the inverter by pulse width modulated pulses, briefly "PWM pulses" driven, the provided for the Pha ^¬ senströme PWM pulse train are generated with a predetermined as "switching frequency of the inverter" pulse frequency.

The concrete choice of the pulse frequency of the inverter results in the following conflict in practice:

On the one hand it is advantageous if the pulse frequency is mög ^¬ lichst selected large so that a desired (ideal) timing phase current curve by the fact ^¬ neuter from the inverter provided phase current curve can be approximated as well as possible. If z. B. a sinusoidal

Phase current waveform in a multi-phase three-phase motor at maximum motor speed is to be provided with a phase current frequency of about 100 to 200 Hz, so this requires a PWM pulse frequency, well above that Phase current frequency is. From a practical point of view, for example in order to avoid harmonic components of the motor torque which are disturbing in the drive train, the PWM pulse frequency should even be larger by some orders of magnitude than the phase current frequency. The ratio between the pulse rate (the PWM pulse train) and the phase current frequency is often referred to as the pulse ratio. In typical motor ^¬ controls, for example, a pulse ratio of about 10 ¹ to 10 ^{3 is} provided. In the above example, this results in a pulse frequency which is already in the kHz range (the larger, the better).

On the other hand, the pulse rate should be as small as possible namely that inevitably associated with each switching operation of the inverter electrical switching losses mini ^¬ mieren. This aspect is very important for the energy efficiency of the relevant electric drive system.

In the known electric drive system mentioned above, a value of the pulse frequency of 8 kHz is proposed as a compromise, wherein in a very specific operating situation, namely at above a predetermined torque level driving torque, the inverter is set to ei ^¬ ne contrast lowered pulse rate. This is advantageous in terms of energy efficiency

Choice of pulse rate made depending on the current engine operating situation.

Also, in the known electric power system, however, remains a serious drawback, consisting in that the pulse ^¬ frequency always lies in the acoustically audible range, which in practice (eg. As in so-called hybrid vehicles and pure electric vehicles for road transport) as a disturbing Makes buzzing or whistling noticeable. Due to the mechanical design of the vehicle-related mechanical resonances can this z. B. by the driver as disturbing perceived effect even more.

It is an object of the present invention to improve a method and a system of the type mentioned above with respect to the generation of acoustic noise. This object is achieved according to the invention by an operating method according to claim 1 and an electric drive system according to claim 8. The dependent claims relate to advantageous developments of the invention. The operating method according to the invention is characterized in that the pulse frequency of at least one of the PWM pulse sequences is continuously varied in operation.

Instead of a rigid pulse frequency, which is possibly lowered in a very specific engine operating situation, an operationally continuous Variati ^¬ on the pulse rate is provided to reduce the acoustic interference in the invention. Due to the continuous variation, the acoustic interference spectrum is distributed over a larger frequency range, which correspondingly reduces the corresponding acoustic interference amplitudes. The continu ^¬ ous variation also reduces the risk of mechanical resonances, as the "excitation frequency" is constantly changing. The remaining noise is distributed over a larger frequency range and significantly reduced, in particular with regard to human-acoustic perception. The invention can be used particularly advantageously for road vehicles with a purely electric drive or a hybrid drive ^(¬ from internal combustion engine and the electrical machine), however, is by no means limited to these applications.

The electric drive may comprise one or more electrical machines, of which at least one, in particular all, can be controlled in accordance with the invention.

With regard to the design of a multi-phase electric machine as well as the inverter used for this purpose can be used advantageously to known concepts of the prior art. In this respect, it is not contrary to the use of the invention, if the electrical machine in question is also operable as an electrical generator, for example, for regenerative energy recovery during braking (in general: delay) of the vehicle.

The electric machine can be, in particular, a multi-phase, in particular three-phase, three-phase motor or motor / generator. The inverter may be implemented in a simple manner as a bridge circuit formed a plurality of times in accordance with the number of phases, such as, for example, a bridge circuit. B. in the above-mentioned DE 10 2008 052 923 AI represented. The switching elements are preferably designed as switching transistors, optionally with freewheeling diodes connected in parallel.

Each of the pulse frequencies provided for the PWM pulse sequences may have a time average z. B. in the range of 5 to 15 kHz. In one embodiment, it is provided that the pulse frequency is varied within a fixed, predetermined, for example, Fre ^¬ quenzbereiches.

The upper limit and / or the lower limit of the frequency ranges ^¬ ches differs preferably by at most 20%, in particular more than 10% of the time-averaged pulse rate from. In a particular embodiment the upper limit and / or the lower limit is not fixed but in response to a mo ^¬ mentanen engine operating condition (such. As speed, torque, etc.) Is given.

In one embodiment, it is provided that the pulse frequency is varied periodically.

It is preferred that the period of Pulsfrequenzva ^¬ riation is less than 100 ms, in particular less than 50 ms, and / or that the frequency of the pulse frequency variation is smaller than 1/10, more preferably less than 1/100 of the time-averaged pulse rate.

In a specific embodiment of the periodic pulse frequency variation, it is provided that the value of the pulse frequency is varied sinusoidally (over time). According to another specific embodiment, it is provided that the pulse frequency is varied in a triangular manner. In general, it is preferred that the periodic pulse rate ^¬ course is symmetrical, that has identical "positive and negative half-waves", as z. B. for a sinusoidal or a symmetrical (not sawtooth) triangular ^¬ form is the case. Alternatively or in addition to a periodic pulse frequency variation, it is considered that the pulse frequency is varied in a random manner. For example, it can be provided for this purpose that the Pulsfre ^acid sequence according to a so-called "random walk" method, under the constraint of a predetermined maximum pulse frequency (upper limit) and a predetermined minimum pulse rate (lower limit) is changed. In one embodiment variant of this "random walk" method, the pulse frequency (or equivalently: the temporal pulse interval) is changed after every nth pulse in a random manner, for For example, a specific frequency increment or frequency decrement, where n denotes a small natural number (eg, n in the range of 1 to 4, either fixed, or also chosen randomly from change to change). The provided with every change of the pulse frequency increment or decrement can be precisely ^¬ if random, but preferably made to fall in a fixed predetermined range.

In a development of the "random walk" method with predetermined upper and lower limits of the pulse rate, it is provided that, when the upper limit for the further course of the random change is reached, the probability for a decrement is greater than the probability for an increment the lower limit is reached, these are reversed ^¬ probabilities, that is more likely than a decrement is provided for an increment. Such "biased" randomness results in a similar pulse rate variation to a strictly periodic pulse rate variation, but involves an additional random element. The vorbelaste ^¬ th probabilities and the corresponding increment or decrement values can hereby z. B. be chosen so that the statistical expected value of a "frequency" of the Pulsfre ^¬ quenzvariation meets the criteria described above for a periodic Pulsfrequenzva ^¬ riation. If the "random walk" method is carried out in real time, ie during the operation of the electric machine to be controlled, this requires more or less computational effort (including the generation of random numbers). Calculations must be carried out within a relatively short time span, depending on the selected (time-averaged) pulse rate. This effort can z. B. be justified if one or more parameters of the "random walk" (probabilities, increments, decrements, pulse rate limits) of one or more only available in real time operating parameters of the electric machine (eg current speed, etc.) or the relevant Vehicle (eg current driving time speed, etc.) should be dependent. Particularly in the case that no such a function should be provided such a variant of the "random walk" is method is preferred in which the varied in zufälli ^¬ ger way pulse rate is not calculated in real time, but already calculated in advance (or in other Set way) and was stored in a memory device. The pulse frequency variation to be performed in real time can then be carried out very simply on the basis of information which is read out from the relevant memory device (eg memory device in an electronic control device). A pre-stored "random sequence" can only have a finite length of all ^¬ dings. In this case, however, such a sequence can be retrieved repeatedly in practice to realize a longer lasting pulse rate variation. A "mixed form" of a real-time calculation and a previously performed calculation is also conceivable. For example, sequences of random numbers for use in determining probabilities and / or increments and decrements may be pre-determined and stored to facilitate partial real-time computation. In another variant, it is provided that a plurality of different pulse ^¬ rate variations have been determined in advance and stored (which is z. B. respect to their pulse rate limit and / or pulse rate lower limit different from each other), in which case only been determined in real time, on wel ^¬ che of stored pulse frequency variations (eg, depending on current operating parameters).

The particularity of the invention is that the Fre ^acid sequence at least one of the PWM pulse trains is varied operatively continuously, with which the respective (n) PWM pulse train (n) is (are). The "pulse rate" can z. B. be defined by the temporal positions of the rising edges of the PWM pulses. Deviating from the pulse rate could also be defined by another, each pulse immanent temporal position, ie z. B. by the time-borrowed positions of the waste edges, or z. B. by the time positions pulse centers.

In a development of the invention, it is provided that at the same time the pulse frequencies of at least two of the PWM pulse sequences are varied in the same way in order to synchronize the pulses of these PWM pulse sequences to one another. In particular, the pulse frequency of all PWM pulse sequences (ie, for example, the three PWM pulse sequences in a three-phase three-phase motor) for the synchronization of all PWM pulse trains can be varied.

Such, common for two or more PWM pulse trains pulse rate can, for. B. define the temporal positions of the leading edges of the PWM pulses, so that these rising edges for all PWM pulse trains are on a common "temporal grid". Such a synchronization of the PWM pulse trains with each other has advantages hinsich- tlich the load on the drive power source (eg. B. traction battery and the intermediate circuit capacitor) and the time tend to be more uniform torque curve of elekt ^¬ step machine. In addition, under certain circumstances, such a syn chronization ^¬ simplifies the effort to produce the pulse trains (eg. As by means of a microcontroller).

The electric drive system according to the invention is characterized in that the control device provided for generating the PWM pulses is designed to continuously vary the pulse frequency of at least one of the PWM pulse trains in an operational manner.

With regard to the manner of this pulse-frequency variation, it is possible to fall back on all the above-described special features and embodiments, individually or in combination.

In an embodiment, it is provided that the control device carries out the generation of the PWM pulse trains and the pulse frequency variation in a program-controlled manner. Here, the control device z. B. as a processor-controlled electronic control unit containing a micro-controller or be designed as a functionality of such a control unit. The generation of the PWM pulse trains, ie in particular the actual pulse width modulation, as well as the inventively provided pulse frequency variation (equivalent: Pulsab- prior variation) can be advantageously carried out by a common software algorithm, which serves as a ^¬ engine operating parameters gear sizes sensorially determined (in particular, instantaneous values of the phase currents and / or phase ^voltages ) and operating parameters (in particular eg pedal position, etc.), in order to generate output variables which in particular contain control signals for generating the PWM pulse sequences or the PWM pulse sequences themselves.

Alternatively or in addition to the above-described generation of the PWM pulse sequences and the pulse rate variation in a program-controlled manner, it can also be provided that this pulse train generation and / or pulse frequency variation is realized by means of a "hardwired logic" (or also "programmable logic"). This can z. B. the burden of a processor in a programmable controller are advantageously reduced.

The invention will be described below with reference to Ausführungsbei ^¬ games with reference to the accompanying drawings. They show:

1 is a block diagram of an electric drive system for a hybrid vehicle, Fig. 2 is a detailed block diagram of some compo ^¬ nents of the electric drive system of Fig. 1, Fig. 3 is a timing chart illustrating a conventional provision of a phase current through an inverter, a time course illustration to illustrate an inventive control of the inverter, a plot of the pulse rate as a function of time, according to a first Ausführungsva ^¬ variant, a plot of the pulse rate in dependence from the time, according to a second Ausführungsva ^¬ variant, and a plot of the pulse rate as a function of time, according to a third Ausführungsva ^¬ variant.

1 illustrates an electric drive system 10 including an electric motor 12, an inverter ("inverter") 16 powered by an electric traction battery 14, and a controller 18 for driving the inverter 16.

The electric drive system 10 is integrated in this example in a drive system of a hybrid vehicle, wel ^¬ chem to the vehicle drive in addition to the electric motor 12 and an internal combustion engine 20, z. B. a gasoline engine or diesel ^¬ engine, is provided in a drive train of the vehicle in question (so-called parallel hybrid). In a known manner, on the will not be discussed in detail here, the vehicle drive according to various ^¬ Dener operating modes can be carried out in which a set of wheels 22 (eg. B. front wheels or rear wheels of a motor vehicle) by either the engine 20 or by the electric motor 12 or combined by both sources of power is driven. When decelerating the vehicle, z. B. during active braking, a regenerative energy recovery can be provided, in which the electric motor 12 is operated as an electric generator to convert kinetic energy of the vehicle into electrical energy and store it in the Traktionsbat ^¬ terie 14. With regard to the various possibilities with regard to the arrangement of the drive sources and their coupling (eg via controllable couplings, gearboxes, etc.), as well as the activation of the aforementioned operating modes, reference is made to the relevant prior art.

Essential to the present invention is the type and Wei ^¬ se of by controlling the inverter 16 implemented operation of the electric motor 12. In this Ansteurerung is therefore discussed in more detail below.

The controller 18 receives user commands and controls c on this basis, taking into account sensory ER- summarized operating parameters p of the hybrid drive system in particular ^¬ sondere the inverter 16 and, optionally, z. B. also the internal combustion engine 20th

The operating commands c can z. B. include an accelerator pedal position, which is representative of acceleration or Verzö ^¬ gerungswünsche the driver.

The sensor-determined operating parameters p include, in particular, those described with reference to FIG. 2 electrical characteristics, which are detected in the region of the electric motor 12 and / or the inverter 16 by appropriate Sen ^¬ soreinrichtungen. FIG. 2 shows in more detail the structure of the electric drive system 10 according to one exemplary embodiment.

In this example, the electric motor 12 is designed as a three-phase AC motor and connected via a line arrangement 24 to the inverter 16. In operation of the motor 12, the line arrangement leads 24 (positive or negative) Pha ^¬ mass flows Iu, Iv and Iw.

The inverter 16 provided for providing these phase currents Iu, Iv and Iw contains a triplex bridge circuit made up of switching transistors T1 to T6. This bridge circuit is supplied via a so-called intermediate circuit capacitor Cl from the battery voltage U of the traction battery 14.

By a PWM (Pulsweitenmodulati ^¬ on) known in principle -Ansteuerung the switching transistors Tl to T6 desired temporal profiles of the phase currents Iu, Iv and Iw can be approximated. This is done by appropriately switching on and off the switching transistors T1 to T6 whose control inputs (in this case eg gate terminals) are supplied with a corresponding PWM pulse train Pu, Pv or Pw for each of the phase currents. The controller 18 generates the PWM pulse trains Pu, Pv, Pw takes place in program-controlled manner by means of a microcontroller coupler 26 in which a corresponding control program (Algo ^¬ algorithm). The microcontroller 26 is connected to an interface module 28, which in turn is connected to the inverter 16. As shown in the figure, 16 measurements of the intermediate circuit voltage and the phase currents and / or phase voltages by means of a measuring device 30 of the interface module 28 are performed and communicated to the microcontroller 26 in the field of Wechsel ^¬ richters.

Taking account of these operating parameters p and on the basis of the also supplied operating commands c of Fahrzeugbe ^¬ user, the microcontroller is calculated 26 for engine operation ge ^¬ suitable pulse sequences Pu, Pv, Pw and outputs them via a Trei- prepared direction 32 of the interface module 28 to the Wech ^¬ selrichter 16 out.

3 illustrates the conventional principle of the approximation of this ideal course through a PWM pulse sequence Pu activating the switching transistors T1 and T2 (in FIG. 3 t denotes the time), ^taking the example of an assumed ideal sinusoidal phase current Iu (dashed line). The temporally successive individual pulses of the pulse train Pu are generated at a fixed predetermined pulse frequency fpwm, corresponding to the reciprocal of a fixed pulse interval Tpwm (fpwm = 1 / Tpwm). To approximate the ideal sinusoidal current curve, the pulse widths are suitably modulated.

The solid line in FIG. 1 represents the resulting actual phase current waveform Iu. This results from the type and arrangement of the pulses and the (typically inductive) electrical properties of the relevant electrical machine.

In FIG. 3, for the sake of clarity of illustration, a very large pulse interval Tpwm (measured on the period of the sinusoidal shape of the current) is shown. In practice ei ^¬ ne typical pulse frequency is about 10 kHz, corresponding to a pulse interval Tpwm of about 0.1 ms. The frequency of the current is typically on the order of about 100 Hz, so that each period of the sinusoid is actually about 100

Pulse, so much more than shown in Fig. 3, gebil ^¬ det is.

The temporally equidistant successive rising edges of the pulse train Pu cause the "lower peaks" of the illustrated actual current curve in the generated phase current Iu. These abrupt changes in current lead in practice to acoustic interference containing in particular z. B. a humming or whistling on the selected pulse frequency (eg., 10 kHz).

To prevent such interference, the control means is adapted to 18 (Fig. 2) according to the invention, the Pulsfre ^acid sequence fpwm least one of the PWM pulse trains Pu, Pw to vary Pv of functionally continuously. Such a Variati ^¬ on the pulse rate is exemplified Fig. 4 is illustrated ^¬ light.

FIG. 4 shows in the upper part the approximation of an ideal course drawn back in dashed lines through the actual phase current Iu drawn again in solid lines. The lower part of Fig. 4 is a corresponding representation for another, here the phase current Iv. As can be seen from FIG. 4, the pulse frequency fpwm is continuously reduced in the illustrated range of time t

(equivalent: the pulse interval Tpwm continuously magnification ^¬ ßert). Thus, one recognizes an initially relatively short pulse interval (see, for example, Tpwml), which increases more and more to the right (see, for example, Tpwm2). In the example shown, the pulse interval Tpwm even from pulse to pulse is ver enlarges ^¬. In the example shown, there is a linear increment of the pulse interval Tpwm.

In a later, in Fig. 4, however, no longer shown range of time t, the pulse frequency fpwm is increased again (accordingly, the pulse interval Tpwm reduced again). Due to the operationally continuous variation of the pulse frequency fpwm, the acoustic interference is advantageously reduced.

In the example shown, the pulse frequency of both PWM pulse trains Pu and Pv is varied in the same way in such a way at the same time that the pulses of these pulse sequences Pu, Pv are synchronized with each other (see FIG. Dashed lines Vertika ^¬ le lines at the positions of the rising edges). The Fig. 5, 6 and 7 illustrate various possible answer ^¬ th or embodiments of the pulse rate variation.

In Figs. 5 and 6, for example, each have a periodi cal ^¬ variation of the pulse frequency represented fpwm (period of the variation: Tv). The variation is sinusoidal in FIG. 5 and symmetrical-triangular in FIG. 6, wherein the pulse frequency fpwm is varied in each case within a frequency range which is predetermined by fixed upper and lower limits fmax and fmin. In FIG. 7, the pulse rate variation also takes place within a predetermined frequency range between an upper limit fmax and a lower limit fmin, but the variation is not provided periodically but in a random manner.

In all of the examples described above, the pulse rate variation may be based, at least in part, on pre-stored information to reduce or substantially eliminate the computational burden required in real time. Both periodic and non-periodic pulse rate variations may be e.g. B. in the form of suitable rows of numbers or tables in an electronic storage device are stored in advance, in which case during the operation of the electrical machine only to determine the manner of retrieval of this information. As an alternative to a fixed specification, fmax and / or fmin could also be variable in the examples described above, for example. B. in response to a current torque and / or a current speed of the electric motor 12th

Claims

claims Method for operating a multi-phase electric machine (12) provided as a vehicle drive, comprising generating PWM pulses for driving switching elements (Tl - T6) of an inverter (16) for providing phase currents (Iu, Iv, Iw) for the electric machine (12), wherein for each phase current (Iu, Iv, Iw) a respective PWM pulse train (Pu, Pv, Pw) with a predetermined pulse frequency (fpwm) is generated, characterized in that the pulse frequency (fpwm) we ^¬ least one the PWM pulse trains (Pu, Pv, Pw) is continuously varied in operation. The method of claim 1, wherein the pulse rate (fpwm) is varied within a predetermined frequency range. Method according to Claim 2, wherein an upper limit (fmax) of the frequency range deviates by a maximum of 20%, in particular a maximum of 10%, from a time-averaged pulse frequency. A method according to claim 2 or 3, wherein a lower limit (fmin) of the frequency range deviates by a maximum of 20%, in particular a maximum of 10% from a time-averaged pulse rate. 5. The method according to any one of claims 1 to 4, wherein the pulse frequency (fpwm) is periodically varied. 6. The method according to any one of claims 1 to 4, wherein the pulse frequency (fpwm) is varied in a random manner. Method according to one of the preceding claims, wherein at the same time the pulse frequencies (fpwm) of at least two of the PWM pulse trains (Pu, Pv, Pw) are varied in the same way to the pulses of these PWM pulse trains (Pu, Pv, Pw) to each other synchronize. An electric drive system (10) for a vehicle, comprising - A multi-phase electric machine (12) in one  Powertrain of the vehicle, an inverter (16) supplied by an electric vehicle power source (14) for providing phase currents (Iu, Iv, Iw) to the electric machine (12), - A control device (18) for generating PWM pulses (Pu, Pv, Pw) for driving switching elements (Tl - T6) of the inverter (16), wherein for each phase ^¬ current (Iu, Iv, Iw) a respective PWM Pulse sequence (Pu, Pv, Pw) with a predetermined pulse frequency (fpwm) is generated, characterized in that the control device (18) is adapted to the pulse frequency (fpwm) of at least one of the PWM pulse trains (Pu, Pv, Pw) operationally vary continuously. The electric drive system (10) according to claim 8, wherein the control means (18) performs the generation of the PWM pulse trains (Pu, Pv, Pw) and the pulse frequency variation in a program-controlled manner.