DE102008040920A1 - Method for controlling electric motor by pulse-width modulated control signals, involves generating control pulse with target-duty cycle and temporally varying pulse width and pulse spacing - Google Patents

Abstract

The method involves generating control pulse with target-duty cycle (AA) and temporally varying pulse width and pulse spacing. The temporally varying pulse width and pulse spacing are generated as a function of load or thermal load of the electric motor or its control mechanism. The electric motor is controlled by the control pulse. A minimum and a maximum cycle duration is defined as a function of load or thermal load of the electric motor or its control mechanism. An independent claim is included for a device for controlling an electric motor by pulse-width modulated control signals.

Description

State of the art

The The invention relates to a method and a device for driving an electric motor by means of pulse width modulation.

A Such pulse width modulation control can be low-frequency, which represents a relatively inexpensive solution up to 100 Hz. Will the pulse width modulation frequency be inaudible high-frequency ultrasonic range of over 20 kHz, is this associated with increased costs, especially as the case EMC requirements to be observed (electromagnetic compatibility) difficult to meet, so far this procedure rarely used.

The conventional cost effective driving method generate by the associated low-frequency keying the Pulse width modulation electromechanical noise emissions. The resulting noise emissions are high energy and have a narrow bandwidth. Due to the narrow bandwidth and the high energy are these noise emissions from human ear can be clearly perceived. Especially if the ambient noise is lower, drowned out the annoying narrowband electric motor noise due to the pulse width modulation control the ambient noise, so that it is practically impossible, this noise to ignore.

The JP 2006191756 A describes a control method of a DC motor, wherein for noise suppression a spectral diffusion modulation of the PWM frequency is made.

Advantages and effects the invention

According to the invention, a method for controlling a
Electric motor by means of pulse width modulated drive signals according to claim 1 and a corresponding device according to claim 6 is provided.

According to the invention made the modulation of the pulse intervals dependent from a power requirement of the engine and / or the thermal Loading of its components or its control. The physical Conditions in the control of electric motors see in most Cases like this, from the point of view of noise and controllability driving with higher driving frequencies is desirable, which is usually higher Power loss leads. To the thermal design the motor path to proceed cost-optimal, takes place therefore a compromise in such a way that a noise optimal Control only in certain situations or limited Periods is carried out. In particular, will better in low thermal stress situations Noise performance than in situations of high thermal Load can be achieved.

According to one be preferred depending on the load and / or thermal load of the electric motor and / or its control device set a minimum and a maximum period.

The minimum and maximum period are preferably set so that with increasing load and / or thermal load of the Electric motor and / or its control device increase.

preferred Further developments are the subject of the respective subclaims.

Of the Electric motor, for example, a DC or AC motor be with commutator or an AC motor without commutator. Further, the electric motor, a rotary motor or a linear motor be.

there can be achieved by varying the time intervals the drive pulses, d. H. by a variation of the pulse width modulation frequency a shift in the acoustic emission spectrum of the electric motor, especially in the direction of a sound emission spectrum of ambient noise to reach.

By the variation of the pulse width modulation frequency according to the invention is it possible to use the sound emission spectrum of the electric motor to a sound emission spectrum of ambient noise advantageously adapt so that the noise emissions the electric motor practically not from the ambient noise are to be distinguished and thus the by varying the pulse width modulation frequency controlled electric motor also no narrow-band high-energy Noise generated, so that the noise pollution is reduced is.

The narrow-band noise emission of the controlled electric motor, as occurs at fixed pulse width modulation frequency in the audible range, is preferably replaced by an adaptation to the noise frequency of the environment, whereby the acoustic emission spectrum of the electric motor is almost completely obscured by the ambient noise. Thus, the invention designs the motor drive in such a way that the noise emissions generated by the keying in the pulse width modulation better in one Ambient noise can be hidden.

Further can by a previous sound frequency analysis of ambient noise a Motor control can be realized, their noise emissions tailored to the noise spectrum of the environment is and thus not only masked by an ambient noise but for the human ear from these environmental sounds is no longer distinguishable. Thus, the invention differs significantly from the common motor drive concepts that at least temporarily on a fixed pulse width modulation frequency are based, with the modulation of the control over setting the pulse width ratio (PWM-duty) he follows.

The Invention is thus based on the one hand on the modulation of the control via adjusting the pulse width modulation clock ratio and additionally, the pulse width modulation frequency becomes so modulates that generated by the keying electromagnetic generated noise emissions and preferably the EMC emissions a desired spectral ratio and acoustic emission spectrum exhibit.

On this way is a predictable and customizable emission behavior reachable. Especially in the automotive sector, the vehicle environments differ clearly different from each other, such as diesel, gasoline or electric vehicles, whereby the adaptability of the invention Method allows advantageous functionality. So can continue with increasing power requirement and increasing thermal load by increasing the minimum pulse durations used both power dissipation and Temperature of the electric motor can be reduced.

Further can decrease with decreasing power requirement and decreasing thermal load on the electric motor through a reduction the minimally used pulse duration on-board network load and controllability be optimized of the electric motor.

The The invention will now be more apparent from the accompanying drawings explained.

Brief description of the figures

1 shows a schematic block diagram of an example motor drive;

2 shows comparative schematic diagrams of motor drive signals;

3 shows comparative schematic diagrams of frequency analyzes of the drive signals;

4 shows further comparative schematic diagrams of frequency analyzes of the drive signals;

5 shows a schematic block diagram of a motor drive according to an embodiment of the present invention;

6a shows a minimum and maximum period in dependence on the temperature of the semiconductor switch;

6b shows a minimum and maximum period depending on the engine load; and

7 FIG. 12 is a flowchart for explaining a motor driving method according to another embodiment of the present invention. FIG.

Explanation of the figures in detail

1 shows a schematic block diagram of an exemplary motor drive 3 an electric motor.

First, in a circuit block 1 a target drive emission spectrum is provided, which is obtained for example by a sound analysis of the ambient noise. Alternatively or additionally, different acoustic emission spectra may be stored, for example, by internal combustion engines or by driving and rolling noise of vehicles as desired drive emission spectra in tabular form. In this case, a memory may be provided in which various acoustic emission spectra are stored. For example, for different engine types such. B. die-sel-, electric or gasoline engines to be stored a corresponding acoustic emission spectrum, which is taken into account in the choice of pulse width modulation frequencies. In addition, the operating state of a vehicle, in particular the engine speed, the speed or the road condition can be taken into account in the choice of the pulse width modulation frequency.

The circuit block 1 is a desired duty cycle also called "Duty" fed to the modulation of engine performance. Depending on the desired duty cycle and the desired target drive emission spectrum, as stored in tabular form and / or predetermined via tables in cooperation with a random number generator, a variation of the pulse width modulation frequency in conjunction with corresponding values of the duty cycle becomes a circuit block 2 fed.

In the circuit block 2 a variation of the pulse widths and pulse intervals is generated and then a pulse width modulation frequency sequence or sequence is supplied to a motor switch for driving the electric motor.

The basis of the variation of the pulse widths and pulse intervals is based on the construction of a desired spectral behavior Spec _total of the totality of the spectrums of the set pulse width modulation _frequencies Spec (f _pwm (i)) spec total = (Σα i · Spec (f pwm (i)) with α i as weighting. (1)

If the radiated spectrum grows to a single pulse width modulation _frequency , Spec (f _pwm (i)) z. B. can be determined by a measurement. In addition, the individual transfer functions can be modeled and the pulse width modulation _frequency Spec (f _pwm (i)) calculated model-based. A determination of the weighting α _i can be made as back-calculation with the aid of the following formula (2) from the desired spectrum. spec total = (Σα i · Spec (f pwm (i) = Spec Should = Σβ j · Spec (f (j)) (2)

A detailed construction of the weighting α _i with equation (2) and the subsequent equal distribution of the pulse width modulation drive frequency in a time domain can lead to systems with tailored acoustic emission spectra, which are then realized by tables and / or tables and random number generators.

In the simplest case, an equally distributed weighting α _i can be selected. As a rule, the resulting _{acoustic emission spectrum will} not be white, especially as the pulse width modulation _frequencies Spec (f _pwm (i)) are folded in real complete systems. In certain cases, an approach with equally distributed weighting α _{i may} suffice. By the variation of the pulse width modulation frequency, frequency values and duty ratio values in the circuit block become dependent on a target duty ratio and the desired target drive emission spectrum 2 generated for the pulse width modulation of the motor control and forwarded to a motor switch.

at a motor drive with a variable pulse width modulation frequency is an active noise adjustment possible, so that fewer narrow-band components are included in the acoustic emission spectrum are. The electric motor noise is subjectively as less annoying because it is from the normal driving noise hard to distinguish.

2 shows comparative schematic diagrams of electric motor drives. In addition shows 2A a motor drive with a fixed pulse width modulation frequency of 400 Hz. In this oscillogram, the time t is given in milliseconds on the abscissa and the voltage U on the ordinate. The fixed pulse width modulation frequency of 400 Hz can be recognized by the completely uniform, temporally successive pulses. Here, for example, a duty cycle of 50% is maintained. This duty cycle of 50% is also in 2 B shown, but here is the pulse modulation frequency variable, which can be seen at the different time intervals of individual pulse sequences. While a motor with the drive signals according to 2A causes marked narrow-band noise emissions caused by a motor with signals according to 2 B is controlled, noises that are covered by the ambient noise. This is shown even more clearly with the following figures.

3 shows comparative schematic diagrams of frequency analyzes of the drive signals. In addition shows 3A a control with a fixed pulse width modulation frequency of 200 Hz. The abscissa shows the frequency in Hz again, while the ordinate indicates the electrical voltage as the drive signal. While in 3A With 200 Hz for the drive signal significant peaks with amplitudes of 30 dB - and thus clearly audible - can be seen, is due to the variation of the pulse width modulation frequency, as it 3B shows, reaches a spectrum that corresponds approximately to the normal sound emission spectrum of a moving vehicle, the maximum amplitude difference is only 18 dB.

4 shows further comparative schematic diagrams of frequency analyzes of the drive signals. In 4A The control is shown with a fixed pulse modulation frequency of 400 Hz and the associated electrical voltages and frequencies of the drive signal, which in turn at the characteristic locations for 400 Hz, an amplitude of about 30 dB is clearly visible, extending from the ground and thus of the Ambient sound emissions takes off. In contrast, shows 4B as already in 3B shown a voltage spectrum of the drive signal having no narrow-band characteristic peaks, since the teachings of the invention are advantageously used by varying the pulse width modulation frequency. For example, frequencies for pulse width modulation in the range between 1 kHz and 6 kHz can be used.

With the described variation of the frequency of the pulse width modulation is the generation of acoustic signals by the electric motor avoided with a frequency width smaller than 300 Hz. Preferably Become acoustic signals of the electric motor with a frequency width less than 200 Hz in the control of the electric motor by the Variation of the pulse width modulation frequency avoided.

In Another variant is the generation of acoustic signals a frequency width less than 10 Hz during operation of the electric motor by the variation of the pulse width modulation frequency avoided.

5 shows a schematic block diagram of a motor drive according to the fourth embodiment of the present invention.

In this fourth embodiment, the drive pulses are at a target duty cycle 30 and time varying pulse widths and pulse intervals as a function of a measured ambient noise level modulated.

This is done via a corresponding ambient noise level measuring device 31 , z. A microphone, the ambient noise level 32 detected and for determining the ambient noise spectrum to a detection device 33 transmitted.

The determined ambient noise spectrum 34 and the target duty cycle 30 are used to select a corresponding Ansteuerspektrums from a data store 35s to a corresponding selection device 35 transmitted. The read control spectrum 36 is used to set a corresponding drive frequency to a fixing device 37 transmitted. The drive frequency 38 is determined by the fixing device 37 transmitted to the motor relay.

Alternatively, the selection device could 35 also a calculation of the drive spectrum 36 carry out.

Selecting the driving spectrum 35 takes place according to the described additionally in dependence of a load parameter 41 (eg current times supply voltage) of the electric motor and / or a temperature in the motor path. For this purpose, a device for measuring or calculating the load situation 40 provided in the engine. To determine the thermal state in the motor path is a temperature measuring device 42 for detecting the temperature and outputting a corresponding signal 43 intended.

Generally the pulse widths and pulse intervals are at high thermal Load or under high mechanical load changed so that a lower power loss arises, in particular the drive frequency decreased.

Thereby However, in situations of low thermal Load or under low mechanical load better noise adjustments as in situations of high thermal stress or high mechanical stress can be achieved.

Especially be detected in this embodiment with reference to the Load and / or temperature a minimum and a maximum period the PWM control set and accordingly the Ansteuerspektrum selected or calculated.

6a shows a minimum and maximum period duration depending on the temperature of a semiconductor switch.

For this purpose, the period T of the motor drive is plotted on the y-axis and the temperature t of the semiconductor switch is plotted on the x-axis. With increasing temperature increases from a temperature t * both minimum period T _min and maximum period T _max up to the maximum allowable temperature t _{max of} the semiconductor switch to optimize the power loss and thus the temperature of the semiconductor switch.

Conversely, for the optimization of noise, EMC radiation, electrical system load and controllability, the lower the temperature t the smaller both the minimum period T _min and the maximum period T _max .

Between minimum period T _min and maximum period T _max is a permitted band of period lengths.

6b shows a minimum and maximum period depending on the engine load.

For this purpose, the period T of the motor control is plotted on the y-axis and the load L of the motor on the x-axis. To optimize the power loss and thus the temperature rise with increased load both minimum period T _min and maximum period T _max .

Conversely, the lower the load L in the motor path, the smaller the minimum period T _min and the maximum period T _max . Thus, an optimization of noise, EMC emissions, vehicle electrical system load and controllability is possible.

Between minimum period T _min and maximum period T _max is a permitted band of period lengths.

7 FIG. 12 is a flowchart for explaining a motor driving method according to another embodiment of the present invention. FIG.

In step S1, via the ambient noise level measuring device 31 , z. A microphone, the ambient noise level 32 detected and for determining the ambient noise spectrum to the detection device 33 transmitted.

In step S2, the load 41 in the engine and the thermal state 43 recorded in the motor path.

The determined ambient noise spectrum 34 , the target duty cycle 30 and the load 41 in the engine and the thermal state 43 in the motor path to select a corresponding Ansteuerspektrums from a data memory 35s to the selection device 35 transmitted in step S3.

The selection device determines 35 first off the load 41 in the engine and the thermal state 43 in the engine path
a permitted band of periods between a minimum period T _min and a maximum period T _max and then selects in step S4 a corresponding control spectrum.

The read control spectrum 36 is used to set a corresponding drive frequency to a fixing device 37 transmitted in step S5. The drive frequency 38 is determined by the fixing device 37 transmitted to the motor relay in step S6.

preferred Applications of the above-mentioned embodiments in the car, for example, windows, vacuum pumps, windscreen wipers, gasoline pumps, Fan motors, level control, electric heating, hybrid control Etc.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - JP 2006191756 A [0004]

Claims (15)

Method for driving an electric motor by means Pulse width modulation with the following steps: Generating Driving pulses with a desired duty cycle and in time varying pulse widths and pulse intervals, the temporal varying pulse widths and pulse intervals depending on from a load and / or thermal load of the electric motor and / or its control device are generated; and head for of the electric motor by means of the drive pulses. The method of claim 1, wherein depending on from the load and / or thermal load of the electric motor and / or Its control device a minimum and a maximum period be determined. The method of claim 2, wherein the minimum period duration is set so as to increase with increasing load and / or thermal load of the electric motor and / or its control device increases. Method according to claim 2, wherein the maximum period duration is set so as to increase with increasing load and / or thermal load of the electric motor and / or its control device increases. Method according to one of the preceding claims, wherein the pulse widths and the pulse intervals are varied so that generated by the driving of the electric motor by means of the drive pulses Sound emission spectrum a spectrum of ambient noise is approximated. Method according to one of the preceding claims, further with the following step: Performing a sound frequency analysis from ambient noise to a sound emission spectrum of the To preserve the environment; wherein varying the pulse widths and the pulse intervals as a function of the acoustic emission spectrum the environment takes place. Method according to one of the preceding claims, regardless of the modulation of the pulse widths Duty cycle remains constant. Device for driving an electric motor by means Pulse width modulation with: a generating device for generating of drive pulses with a desired duty cycle and in time varying pulse widths and pulse intervals, causing the time-varying pulse widths and pulse intervals depending on from a load and / or thermal load of the electric motor and / or its control device can be generated; and one Control device for driving the electric motor by means of Driving pulses. Apparatus according to claim 8, wherein the generating means depending on the load and / or thermal load the electric motor and / or its driving device a minimum and a maximum period can be specified. Apparatus according to claim 9, wherein the minimum Period is set so that they increase with increasing Load and / or thermal load of the electric motor and / or its Control device increases. Apparatus according to claim 9, wherein the maximum Period is set so that they increase with increasing Load and / or thermal load of the electric motor and / or its Control device increases. Device according to one of claims 8 to 11, whereby the pulse widths and the pulse intervals are so variable are that one by the driving of the electric motor by means of Ansteuerpulse generated sound emission spectrum a spectrum of Ambient noise is approximated. Device according to one of claims 8 to 11, further comprising a sound frequency analyzer for Performing a sound frequency analysis of ambient noise, to obtain a sound emission spectrum of the environment, wherein the Pulse widths and the pulse intervals as a function of the sound emission spectrum of the environment are variable. Device according to one of claims 8 to 12, further comprising a detection device for detecting the thermal load of the electric motor. Apparatus according to claim 14, wherein the detection means is present as a thermometer.