WO2003058807A1

WO2003058807A1 - Device and method for reducing noise

Info

Publication number: WO2003058807A1
Application number: PCT/NL2003/000008
Authority: WO
Inventors: Jan Abraham Ferreira; Pieter Dorland; Jan Willem Verheij; Fred Govert De Beer
Original assignee: Nederlandse Organisatie Voor Toegepast- Natuurwetenschappelijk Onderzoek Tno
Priority date: 2002-01-09
Filing date: 2003-01-08
Publication date: 2003-07-17
Also published as: NL1019715C2; AU2003207133A1

Abstract

The invention relates to a method for filtering disturbing frequencies in an electrical power supply for an electrical driving device with a variable speed, comprising: determining at least one dominant disturbing frequency and filtering out this disturbing frequency by means of a notch filter whose zero frequency is settable. The method finds application in an electrical driving device, comprising: an electrical driving device with a variable speed; a supply for supplying electrical power to the electrical driving device; a settable notch filter to filtering a dominant disturbing frequency out of the supply voltage of the supply; and a control device for controlling the filter. Preferably, the device comprises a unit for measuring an acoustic dominant frequency, which unit is in communication with the control device, so that its controls the filter depending on the measured frequency.

Description

Title: Device and method for reducing noise

The invention relates to a method for filtering disturbing frequencies in an electrical power supply for an electrical driving device with a variable speed.

The electrical power supply for such an electrical driving device comprises, in addition to active frequency components, inactive components which can cause objectionable mechanical and/or acoustic vibrations. To prevent or limit such objectionable vibrations, a number of techniques are known, such as sound reduction and/or the application of electrical filters, in particular low-pass filters. However, none of the known techniques yields satisfactory results. The filters applied all have as a disadvantage that they are expensive or voluminous and often entail considerable power losses. Accordingly, the object of the invention is to avoid the above disadvantages of the known techniques and to provide a method in which an effective filtering is provided for filtering disturbing frequencies in the supply voltage for an electrical driving device. This object is achieved in that a method according to the above- mentioned preamble comprises the steps of: during the operation of an electrical driving device, determining at least one frequency in the electrical power supply that is causative of disturbing acoustic and/or mechanical vibrations of the electrical driving device; setting a zero frequency of a notch filter arranged in the power supply, so that the notch filter filters the at least one disturbing frequency out of the power supply; and during the operation of the electrical driving device, adjusting the set zero frequency, so that at all times a disturbing acoustic and/or mechanical vibration of the electrical driving device is suppressed.

Such a notch or resonance filter in a known design has an LC circuit and has a high impedance for one bandwidth of frequencies. In the invention, the notch filter is included in a switching network of inductances and capacities, the switching frequency being considerably higher than the zero frequency of the notch filter. This results in a variable zero frequency. Through the method of the invention, it is possible to filter out varying disturbing frequency components in an electrical driving device with a variable speed, so that a strongly improved noise reduction is provided.

In the method according to the invention, it is possible to make a directed determination of disturbing frequency components, and to filter these out by means of the notch filter. Due to the high Q-value of the notch filter, the reduction at the filter frequency is high and the power loss is relatively low. It was found in practice that filtering out only one frequency component leads to good results.

In a preferred embodiment, determining a dominant disturbing frequency comprises the steps of determining a dominant acoustic frequency, and relating this dominant acoustic frequency to a disturbing frequency in the electrical power of the power supply. Through a modeled analysis, the outcome of an acoustic measurement can be related to a frequency component in the electrical power supply that causes the acoustic vibration and it proves possible to successfully filter out the correct electronic frequency. Determining a dominant disturbing frequency can comprise performing a frequency analysis of the electrical power supply.

The invention further relates to an electronic driving device, comprising: an electrical driving device with a variable speed; a supply for supplying electrical power to the electrical driving device; a settable notch filter, for filtering a dominant disturbing frequency out of the supply voltage of the supply; and a control device, for controlling the filter. The device according to the invention enables adequate filtering at the relatively high powers that are used, with a relatively small power loss.

Preferably, the device comprises a unit for measuring the speed of the electrical driving device, which unit is in communication with the control device, so that the latter controls the filter depending on the measured speed.

In a further preferred embodiment, the device comprises a unit for measuring an acoustic dominant frequency, which unit is in communication with the control device, so that the latter controls the filter depending on the measured frequency.

The device can comprise a unit for analyzing the constituent frequencies of the supply voltage, which unit is likewise in communication with the control device, so that the latter controls the filter depending on the measured constituent frequencies. The device can further comprise a vibration sensor, which is connected with the electrical driving device, for measuring a dominant vibration frequency of the electrical driving device, which vibration sensor is in communication with the control device, so that the latter controls the filter depending on the measured dominant vibration frequency. In a still further preferred embodiment, the filter comprises a switching network coupled between two terminals, for electronically switching a capacitive component on and off by means of a pulse width modulation, such that in one switching condition the capacitive component is switched between the terminals, and in another switching condition the capacitive component is switched off and the terminals are short-circuited.

The switching network can form a series connection with a second capacitive component. The series connection can be connected in parallel with an inductive component. The switching network can comprise unidirectional semiconductor switches each connected in parallel with a diode for providing a free run of electrical voltage oriented against the direction of the switch.

The switching network can switch with a duty cycle between a first and a second switching condition, where in the first switching condition a unipolar capacity is charged unipolarly by means of a diode bridge circuit coupled between two terminals, and is discharged by means of semiconductor switches connected in parallel with the diodes of the diode bridge circuit; and a second switching condition in which the bridge circuit between the terminals is short-circuited. The advantage of a unipolar capacity over a bipolar capacity is the small dimension and low cost price. In the case of unidirectional semiconductor switches, the advantage is thereby achieved that the number of diodes and switches used is limited, in that during the short-circuit phase the voltage across the switches can be opposite. In a preferred embodiment, the semiconductor switch is a Field Effect Transistor (FET).

In a further preferred embodiment, the filter comprises a unipolar capacity, connected between two junctions, with a positive and a negative terminal, of which the positive terminal is connected with the drains of a first and fourth unidirectional FET, respectively, and of which the negative terminal is connected with the sources of a second and third unidirectional FET, respectively, which FETs are each connected in parallel with a free running diode, so that a free run is provided in the direction of the source to the drain of each of the FETs, while further a first terminal is connected with the source and drain, respectively, of the first and second FET, respectively, and wherein a second terminal is connected with the source and drain, respectively, of the fourth and third FET, respectively, while further in a positive voltage phase across the terminals the first and second transistor are alternately open and closed, respectively, with a duty cycle D of the first FET, the third FET is in closed conductive condition, and the fourth FET is in open condition, while in a negative voltage phase across the terminals, the first and second FET are alternately open and closed, respectively, with a duty cycle 1-D of the first FET, the third FET is in open condition and the fourth FET is in closed condition, and wherein switching takes place between the positive and the negative voltage phase on the zero axis crossing of the unipolar capacity.

Since in a pulse width modulation switching takes place with a frequency which is at least a few times and preferably a number of orders of magnitude higher than a base frequency of the electrical power current, the switched electronic components have an effective impedance which varies between the value of one of the capacities and the value of two series- connected capacities, which impedance is regulable by regulating the pulse width modulation (varying the duty cycle).

As no mechanical parts are included in the filter, high switching frequencies can be realized. Further, the above-mentioned embodiments of the notch filter have as an advantage that always a free run path for the inductive current of a coil is offered. As a result, the energy of the coil and the capacity is not dissipated in the switches.

Further, the filter functions autonomously with a filter frequency to be set, which provides an advantage because the components to be filtered in the supply voltage are difficult to implement in the time domain in terms of signal technique, and therefore cannot be used for driving the filter.

The invention further relates to a settable notch filter for use in a driving device according to any one of the above aspects.

The invention will be further elucidated with reference to the drawing. In the drawing:

Fig. 1 shows a system diagram of a device according to the invention;

Fig. 2 shows a schematic embodiment of a notch filter for use in a driving device according to the invention; Fig. 3 shows a first embodiment of a notch filter for use in a driving device according to the invention;

Fig. 4 shows a second embodiment of a notch filter for use in a driving device according to the invention.

In the figures, the same reference numerals have been used for the same or corresponding parts.

Fig. 1 shows a system diagram of a device 1 according to the invention. The device comprises an electrical power supply 2 for supplying power 3 to an electrical driving device 4. The electrical driving device 4 is fed with the power 3, while the speed of the device 4 is determined by the supplied voltage frequency of the power supply 2. The power supply 2 thereby generates not only the desired voltage gradient, but also distortions which are to be filtered out by the electrical filter 5. The distortions cause mechanical and acoustic vibrations and are generally experienced as being a nuisance and/or harmful.

The filter 5 is an electronic notch filter according to the invention, and will hereinafter be further elucidated with reference to Figs. 2-4. During the operation of the electrical driving device, i.e. while the electrical driving device is in operation with a (variable) speed, a signal processing system 6 determines at least one frequency in the electrical power supply that is causative of disturbing acoustic vibrations of the electrical driving device. The processing system 6 is coupled with the electrical filter 5, so that a zero frequency of the filter can be set, i.e. a frequency for which the impedance of the filter is maximal. By adjusting the set zero frequency during the operation of the electrical driving device 4, a disturbing acoustic and/or mechanical vibration of the electrical driving device can always be suppressed. In a preferred embodiment, the signal processing system 6 comprises a converter 7 for converting acoustic signals or mechanical vibrations 8 into electronic signals 9. By means of a modeled calculation, a dominant acoustic frequency can be related to a disturbing frequency in the electrical power of the power supply. In a supplemental or alternative embodiment, the signal processing system 6 can comprise a speedometer 10, thereby enabling the disturbing frequency to be filtered out depending on a measured speed. Additionally, or alternatively, the signal processing system can comprise an electronic analysis unit 11 for analyzing the constituent frequency components of the electrical power signal itself.

The signal processing system 6 is connected with a control device 12, which provides a control signal 13 to the filter 5 for setting the zero frequency of the filter 5.

Fig. 2 represents in what manner the filter 5 can be represented in schematic form. The invention is based on the insight that acoustic noise can be reduced by filtering out a single frequency component in the electrical power supply. However, due to the variable speed, this single frequency component shifts, and the filter should be settable. As is represented in Fig. 2, the filter according to the invention comprises a switching network 16 coupled between two terminals 14, 15 for electronically switching a capacitive component 17 on and off by means of a pulse width modulation, such that in one switching condition the capacitive component is switched between the terminals 14, 15; and that in another switching condition the capacitive component is switched off and terminals 14, 15 are short-circuited. Thus, a settable capacity is provided, with a value which increases inversely quadratically with the duty cycle D.

By connecting the switching network 16 in series with a second capacity component 18, a capacity settable by means of the duty cycle is provided. Connected in parallel therewith is an inductive component 19, with which the settable filter 5 has thus been formed. Fig. 3 shows an embodiment where the switching network comprises unidirectional FETs 20 which are each connected in parallel with a diode 21 for providing a free run of electrical voltage oriented against the direction of the FET. This prevents the unidirectional FET 20 from being exposed to a voltage of the wrong polarity: it is taken over by the free running diode 21. To enable switching for positive and negative voltage phases, a series connection 22 of two of such switches is needed. The circuit diagram of Fig. 3 has a relatively simple implementation for driving the FETs 20. The diagram of Fig. 4 is slightly more complex, but has as an advantage that a current path is provided for the induction current at all times, so that the circuit, in view of the fact that high powers are being used, is safer. Further, it permits working with a single type of transistors, which can be controlled by means of a standard available integrated circuit. Further, a relatively small number of transistors and diodes are used with a unipolar capacity, which is more suitable for high powers.

Fig. 4 represents how the switching network 16 switches with a dutycyele between a first and a second switching condition, where in the first switching condition a unipolar capacity 23 is charged unipolarly by means of a diode bridge circuit coupled between two terminals 14, 15 and is discharged by means of FETs (S1-S4) connected in parallel with the diodes (D1-D4) of the diode bridge circuit; and a second switching condition in which the bridge circuit is short-circuited between the terminals 14, 15.

The switching diagram of Fig. 4 is as follows

The interval is here indicated as the phase in the voltage of terminal 14 minus the voltage of terminal 15. The switching signal for the pulse width modulation is provided by a standard timing circuit, such as the TL494 IC. To provide the switching signal for switching S3 and S4, the polarity of the voltage across the terminals 14, 15 must be known. This voltage is measured by measuring the voltage difference across the unipolar capacity, which goes to zero upon a voltage change across the terminals.

The invention is not limited to the exemplary embodiments elaborated in the figures, but can comprise all kinds of modifications. Such variations are understood to fall within the scope of protection of the following claims.

Claims

1. A method for filtering disturbing frequencies in an electrical power supply for an electrical driving device with a variable speed, comprising: - during the operation of an electrical driving device, determining at least one frequency in the electrical power supply that is causative of disturbing acoustic and/or mechanical vibrations of the electrical driving device; setting a zero frequency of a notch filter arranged in the power supply, so that the notch filter filters the at least one disturbing frequency out of the power supply; and during the operation of the electrical driving device, adjusting the set zero frequency, so that at all times a disturbing acoustic and/or mechanical vibration of the electrical driving device is suppressed.

2. A method according to claim 1, characterized in that determining a dominant disturbing frequency comprises the steps of determining a dominant acoustic frequency, and relating this dominant acoustic frequency to a disturbing frequency in the electrical power of the power supply.

3. A method according to claim 1 or 2, characterized in that determining a dominant frequency can comprise performing a frequency analysis of the electrical power supply.

4. An electrical driving device, comprising: an electrical driving device with a variable speed; a supply for supplying electrical power to the electrical driving device; a notch filter with settable zero frequency, for filtering a dominant disturbing frequency out of the supply voltage of the supply; and a control device which provides a control signal to the filter for setting the zero frequency of the filter.

5. A driving device according to claim 4, characterized in that the device comprises a unit for measuring the speed of the electrical driving device, which unit is in communication with the control device, so that the latter controls the filter depending on the measured speed.

6. A driving device according to claim 4 or 5, characterized in that the device further comprises a unit for measuring an acoustic dominant frequency, which unit is in communication with the control device, so that the latter controls the filter depending on the measured frequency.

7. A driving device according to at least one of claims 4-6, characterized in that the device comprises a unit for analyzing the constituent frequencies of the supply voltage, which unit is in communication with the control device, so that the latter controls the filter depending on the measured constituent frequencies.

8. A driving device according to at least one of claims 4-7, characterized in that the device further comprises a vibration sensor, which is connected with the electrical driving device, for measuring a dominant vibration frequency of the electrical driving device, which vibration sensor is in communication with the control device, so that the latter controls the filter depending on the measured dominant vibration frequency.

9. A driving device according to at least one of claims 4-8, characterized in that the notch filter comprises a switching network coupled between two terminals, for electronically switching a capacitive component on and off by means of a pulse width modulation, such that in one switching condition the capacitive component is switched between the terminals, and that in another switching condition the capacitive component is switched off and the terminals are short-circuited.

10. A driving device according to claim 9, characterized in that the switching network forms a series connection with a second capacitive component.

11. A driving device according to claim 9 or 10, characterized in that the series connection is connected in parallel with an inductive component.

12. A driving device according to claims 9-11, characterized in that the switching network comprises unidirectional semiconductor switches each connected in parallel with a diode for providing a free run of electrical voltage oriented against the direction of the switch.

13. A driving device according to claims 9-12, characterized in that the switching network switches with a duty cycle between a first and a second switching condition where in the first switching condition a unipolar capacity is charged unipolarly by means of a diode bridge circuit coupled between two terminals and is discharged by means of semiconductor switches connected in parallel with the diodes of the diode bridge circuit; and a second switching condition in which the bridge circuit is short- circuited between the terminals.

14. A driving device according to claims 9-13, characterized in that the semiconductor switch is a Field Effect Transistor (FET).

15. A driving device according to claims 9-14, characterized in that the filter comprises a unipolar capacity, connected between two junctions, with a positive and a negative terminal, of which the positive terminal is connected with the drains of a first and fourth unidirectional FET, respectively, and of which the negative terminal is connected with the sources of a second and third unidirectional FET, respectively, which FETs are each connected in parallel with a free running diode, so that a free run is provided in the direction of the source to the drain of each of the FETs, wherein, further, a first terminal is connected with the source and drain, respectively, of the first and second FET, respectively, and wherein a second terminal is connected with the source and drain, respectively, of the fourth and third FET, respectively, while further in a positive voltage phase across the terminals the first and second FET are alternately open and closed, respectively, with a duty cycle D of the first transistor, the third FET is in closed conductive condition, and the fourth FET is in open condition, while in a negative voltage phase across the terminals, the first and second FET are alternately open and closed, respectively, with a duty cycle 1-D of the first transistor, the third FET is in open condition and the fourth FET is in closed condition; and wherein switching takes place between the positive and the negative voltage phase on the zero axis crossing of the unipolar capacity.

16. A settable notch filter for use in a driving device according to at least one of the preceding claims.