JPH05211451A - Radio noise reduction system - Google Patents

Abstract

PURPOSE:To prevent a radio noise caused by harmonics generated by a PWM power controller by setting a switching frequency so that a frequency at a beat signal is higher than an audible frequency band width. CONSTITUTION:The system is provided with a PWM system power controller 40 switched at a frequency f0 and generating a noise spectrum comprising plural harmonics with respect to a fundamental wave of the frequency f0 and with an AM receiver 50. Thus, the frequency f0 is set so that a frequency fB of a beat signal calculated by an absolute value ¦F0-nf0¦ of a difference between the carrier frequency F0 of a radio broadcast received by the receiver 50 and a frequency nf0 of a harmonic component (n is an integer) closest to the carrier frequency F0 is higher than an upper limit of an audible frequency band fA of the receiver 50. That is, the leak of a beat signal to the sound signal outputted from the AM receiver 50 is avoided by satisfying the condition of fA<fB.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a PWM type power control device and an AM type receiver.
The present invention relates to a radio noise reduction system that prevents a receiver of a radio system from effectively becoming noise.

[0002]

2. Description of the Related Art Conventionally, in order to continuously and optimally control the power level of a load such as a motor and to reduce the power loss of a control device, a power control device of a PWM (Pulse Width Modulation) system (hereinafter referred to as PWM A power control device) has been devised and is being installed in automobiles.

However, an automobile has a medium-wave band (535-1605 k).
When an AM radio of (Hz) is installed, harmonics of the switching frequency generated by the PWM power control device are mixed into the AM radio as radio noise and interfere with broadcast radio waves to emit a beat sound or the like. There's a problem. As a solution to this problem, there is a method in which a noise filter is inserted in the power supply line of the PWM power control device or the device is wrapped in a shield case so that radio noise is not emitted from the PWM power control device to the outside. ing. That is, radio noise is eliminated by taking measures against only the noise source.

[0004]

However, the above-mentioned method for preventing radio noise in which a noise filter is inserted in the power supply line or the device is wrapped in a shield case is a method for preventing the noise and radio wave from the inductor, the capacitor, the physique, and the like. A heavy metal case is required, and it is necessary to take measures for each PWM power control device, which causes a problem of high cost. Moreover, even if these measures were taken, it was not possible to completely prevent radio noise. Further, the recent AM radio has an automatic tuning function using a synthesizer, and there is a problem in that harmonics of the fundamental frequency of the switching operation generated by the PWM power control device are mistakenly recognized as an AM radio broadcasting station and tuned. ..

The problems of this prior art will be described in detail with reference to the drawings. FIG. 3 includes a conventional PWM power controller 10, a load motor 30, and a battery 31,
The configuration will be described in detail. The duty control circuit 16 receives the reference signal of the frequency f ₀ from the reference signal generation circuit 24 and the duty control signal from the duty setting terminal 11.
A signal of a predetermined duty is the gate of the power MOSFET 18.
Input to the input terminal 17. The source terminal 19 of the power MOSFET 18 is grounded, the drain terminal 20 is connected to the node of the flywheel diode 21, and the motor 30 via the terminal 13.
Is connected to one terminal. The cathode terminal of the flywheel diode 21 is connected to the other terminal 14 of the motor 30, one terminal of the capacitor 22, and one terminal of the inductor 23. The other terminal of the capacitor 22 is grounded, and the other terminal of the inductor 23 is connected to the positive terminal of the battery 31 via the terminal 15. The negative terminal of the battery 31 is grounded. The capacitor 22 and the inductor 23 form a noise filter on the power supply line.

The operation of the above structure will be described with reference to the time chart shown in FIG. FIG. 4A shows the waveform of the gate voltage V _{G at} the gate terminal 17, which is supplied with a voltage of 10 V when it is on and 0 V when it is off from the duty control circuit 16.
FIG. 4B shows the waveform of the drain voltage V _D of the drain terminal 20, which has an inverted logic relationship with the waveform of the gate voltage V _G. FIG. 4C shows the waveform of the drain current I _D , which flows only during the gate-on period, and the current value thereof tends to increase with the passage of time. FIG. 4 (d) shows a flywheel current I _F flowing through the flywheel diode 21, which flows only during the gate-off period, and its current value tends to decrease with the passage of time. FIG. 4 (e) is the motor current I _M flowing through the motor 30, and the waveform during the gate-on period of FIG. 4 (c) and the gate of FIG. 4 (c).
The waveform is equal to the waveform obtained by combining the waveforms in the toff period and exhibits a triangular wave. FIG. 4 (f) shows the battery current I _B flowing through the battery 31.
That is, the waveform of the drain current I _D shown in FIG. 4C is a waveform formed by being smoothed by the noise filter including the capacitor 22 and the inductor 23.

The waveforms shown in FIGS. 4 (b), 4 (c), and 4 (d) contain high-harmonic components of high intensity because of their large amplitudes, and the PWM power is supplied via the wires to which these voltages and currents are applied. Control device
Although it leaks to the outside of 10 and mixes into an AM radio (not shown) as radio noise, most of it is shielded by a shield case (not shown) provided in the PWM power control device 10,
The amount leaked to the outside is small. The current waveform shown in Fig. 4 (e) flows through the wires L1 and L2 that connect the motor 30 and the terminals 13 and 14, and generates a strong harmonic component.
Since 1 and L2 are outside the PWM power control device 10, they are not shielded by the shield case, and the AM (not shown) has a strong intensity.
Mix into the radio. In addition, the current waveform shown in Fig. 4 (f) flows through the wire L3 that connects the terminal 15 and the positive terminal of the battery 31, and the amplitude is smaller than other current waveforms, but the wire L3
Is outside the PWM power controller 10, so the shield case
As is the case with the electric wires L1 and L2, it is easily shielded by an AM radio (not shown) as is the case with the electric wires L1 and L2.

The switching frequency shown in FIGS. 4 (b) to 4 (f)
Number f₀The frequency spectrum of the (= 1 / T) waveform is
From the theory of Fourier transform, it is a fundamental wave as shown in FIG.
Switching frequency f₀And has a frequency that is an integer multiple of that
It is composed of multiple harmonics that gradually decrease in degree. Not illustrated now
Carrier frequency of the AM radio broadcast that the AM radio is receiving
To F₀And F on the frequency axis₀Two harmonics adjacent to
The lower frequency is nf ₀Then, the higher one is (n + 1) f₀To
Become. Also, F₀And nf₀The difference frequency of f_B1, F₀And (n + 1) f₀
The difference frequency of f_B2Then, from the principle of AM modulation,
Not from AM radio speaker f_B1And f_B2To the frequency of
A corresponding beat sound is output (actually, not shown AM
Audio frequency bandwidth to the radio f_AAnd f_AThe following frequencies
Only a few beat sounds are output).

In the conventional PWM power controller 10,
Since the switching frequency f ₀ is set by the AM radio (not shown) independently of the carrier frequency F ₀ of the AM radio broadcast being received, the difference frequencies f _B1 and f _B2 are indefinite, and the audio frequency band of the AM radio (not shown) is set. The value is often less than the width f _A , and there is a problem that a beat sound is generated as radio noise from the speaker. Further, as shown in FIG. 5, the harmonics are arranged at intervals of f ₀ on the frequency axis, and in an AM radio (not shown) having an automatic tuning function by a synthesizer, these harmonics are referred to as an AM radio broadcasting station. There was a problem of misidentifying and synchronizing.

The present invention has been made in view of the above-mentioned problems of the prior art, and a PWM power control device and an AM radio, which can be a radio noise source as represented by an automobile, are installed close to each other with a common power source. Even in an environment where
It is an object of the present invention to provide a complete radio noise prevention system that does not require a high-performance noise filter that is bulky and costly, and eliminates the problem of misidentifying harmonics of radio noise as an AM radio broadcasting station and causing tuning. ..

[0011]

According to the present invention for solving the above-mentioned problems, a switching operation is performed at a frequency f ₀ ,
A PWM (Pulse Width Modulation) system power control device for generating a noise spectrum composed of a plurality of harmonics with f ₀ as a fundamental wave, and an AM system receiver are provided, and the receiver receives radio broadcasts. The frequency f of the beat signal calculated by the absolute value | F ₀ −nf ₀ | of the difference frequency between the carrier frequency F ₀ and the harmonic component nf ₀ (n is an integer) closest to the carrier frequency F _0. The gist of a radio noise reduction system is characterized in that the frequency f ₀ is set so that _B is higher than an upper limit of a voice frequency bandwidth f _A of the receiver.

The radio noise reduction system described above is
It is desirable to generate a reference signal by signal processing based on the carrier frequency F ₀ and to determine the switching frequency f ₀ based on the reference signal.

Furthermore, the reference signal, after generating a signal of a frequency with respect to the carrier frequency F ₀ (F ₀ + Δf) or (F ₀ -.DELTA.f), there the frequency signal by dividing the signal Is desirable.

[0014]

[Function] The audio frequency bandwidth f _A of the AM receiver is several
The frequency of the beat signal is f _B (= | F ₀ − nf
₀ |) is by setting the switching frequency f ₀ to be higher than the audio frequency bandwidth f _A, i.e. f _A <f _B
If the condition of is satisfied, the beat signal is not mixed in the audio signal output from the AM receiver, and the PW
It is possible to prevent harmonics generated from the M type power control device from effectively becoming noise with respect to the AM type receiver.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to FIGS. First of all, FIG. 1 is a block diagram of an embodiment of the present invention, which schematically comprises a PWM power controller 40, a load motor 30, a battery 31, and an AM radio 50. The configuration of the PWM power control device 40 is similar to that of the conventional PWM power control device 10 shown in FIG.
The flywheel diode 21 and the inductor 23 are omitted in the circuit configuration, and the same reference numerals are given to other same components.

Next, the AM radio 50 has a structure in which a reference signal generating circuit 70 is added to an AM radio of a synthesizer system which generally uses a general PLL (Phase Locked Loop). The detailed configuration of the AM radio 50 is that the antenna 80 receives the radio broadcast wave of the carrier frequency F ₀ and the antenna terminal
It is input to MIX (Mixer, frequency mixer) 54 via 51. Frequency that is higher than F ₀ by the intermediate frequency F _I
(F ₀ + F _I ) to VCO (Voltage Controlled Oscillator,
Voltage controlled oscillator) 59 and oscillates this signal with MIX54
And outputs the intermediate frequency signal F _I from the MIX54. The intermediate frequency signal F _I is IF (Intermediate Frequenc
y amplifier (intermediate frequency amplifier) 55, and after being amplified, demodulated by a DET (Detector) 56 to output a voice signal. This audio signal is AF (Audio Frequency ampl
ifier, audio frequency amplifier) 57 and SP (Speaker,
Speaker) 58 outputs.

An oscillation signal of an XTAL (Crystal Oscillator) 62 is frequency-divided by a DIV (Divider) 63 at a constant ratio and a comparison signal having a frequency F _S is output. PC (Phase Comparator) 61 is VC
The output signal (F ₀ + F _I ) of O59 is set to PD (Programmable Divid
er, programmable frequency divider) 60 compares the phase of the output signal divided by a predetermined ratio with the output signal F _S of the DIV63,
A voltage signal corresponding to the phase difference is output. The oscillation frequency of the VCO 59 is controlled by the voltage signal output from the PC 61.
VCO59, PD60, and PC61 constitute a PLL,
The PLL operation is performed so that the frequency of the output signal of PD60 and the frequency of the output signal F _S of DIV63 are always the same. The frequency division ratio of PD60 is the reception frequency F ₀ determined by an external circuit (not shown).
Signal corresponding to CONT (Controlle
r, controller) 64 and input to PD60. As a result, the oscillation frequency of VCO 59 is always equal to (F ₀ + F _I ).

Next, the structure of the reference signal generating circuit 70 will be described. PL consisting of VCO77, PD76, and PC75
L is the same as the PLL composed of the VCO 59, PD 60, and PC 61 described above in that the comparison signal F _S input from the terminal 71 is used, but L is connected via the terminal 72 to CON.
The division ratio of PD76 input to PD76 from T64 is different.
That is, the CONT64 makes the PD so that the oscillation frequency F _R of the VCO 77 becomes equal to (F ₀ + f _B ) or (F ₀ -f _B ).
A division ratio of 76 is set. Here, f _B is the frequency of the beat signal described above.

The oscillation frequency F _R of the VCO 77 is divided by the PD 78 with the division ratio m, and the signal of the frequency F _R / m is fed to the terminals 74 and 53.
P is output as a reference signal f ₀ via an electric wire L4.
It is led to a terminal 41 of the WM power controller 40. Where PD
The division ratio m of 78 is set by the CONT 64 via the terminal 73, and the value of m is selected so that the frequency F _R / m is higher than the audible frequency band.

Since the operation of the PWM power controller 40 is similar to that of FIG. 3 described above, the description of the same parts will be omitted. The different part is that the PWM power controller 40 is switched at the frequency of the reference signal f ₀ generated by the AM radio 50. That is, the reference signal output from the terminal 53
f ₀ is input to the duty control circuit 16 via the electric wire L4 and the terminal 41, and a signal of a predetermined duty is supplied to the power MOSFET.
Input to 18 gate terminals and power MOS at frequency f ₀
FET 18, motor 30, and flywheel diode
21 performs switching operation.

The operation of the above arrangement will be described with reference to (a) to (e) of the time chart shown in FIG. 4 and the frequency spectrum shown in FIG. Here, the waveform of each part in the embodiment of the present invention shown in FIG. 1 is the same as that of the conventional example shown in FIG. 3 except for the waveform of the battery current in FIG. 4 (f). Similar to the above-mentioned conventional example, the frequency spectrum provided in the waveform of the switching frequency f ₀ (= 1 / T) shown in FIGS. 4B to 4E is as shown in FIG. 2 from the theory of Fourier transform. The switching frequency f _0, which is the fundamental wave, and a plurality of harmonic waves having a frequency that is an integral multiple thereof and whose intensity gradually decreases. The carrier frequency of the AM radio broadcast currently being received
If F ₀ is set and nf ₀ is the lower one of the two harmonics adjacent to F ₀ on the frequency axis, the higher one is (n + 1) f ₀ .

The difference between the embodiment of the present invention and the prior art is that the difference frequency between F ₀ and nf ₀ is f _B1 and the difference frequency between F ₀ and (n + 1) f ₀ is f _B2. Beat signal frequency f _B1 , f
_{In order} to make both _B2 sufficiently higher than the audio frequency bandwidth f _A of AM radio and not to be output from the speaker as radio noise, set f ₀ so that f _B1 ≈ f _B2 is satisfied. Is. At this time, the frequency f of the beat signal
The relationship between _B and the switching frequency f ₀ is clear from Fig. 2.
Is a _B ≒ f _0/2. For example, if f ₀ = 20 kHz and f _A = 6 kHz, then f _B ≈10 kHz, and since f _A <f _B is satisfied, beat noise as radio noise is not output from the speaker and the It means that noise is prevented.

Also, the electric wire L4 may be broken or the AM radio 50
In order to operate the PWM power control device 40 normally even when is not operated, the reference signal generation circuit 24 that oscillates at a frequency close to the reference signal f ₀ is provided in the PWM power control device 40, and the reference signal is continuously supplied. By inputting to the duty control circuit 16, the switching operation of the PWM power control device 40 can be continued. At this time, needless to say, it is not necessary to strictly set the reference signal f ₀ so as to satisfy the above relationship in order to prevent radio noise.

In the above embodiment, the PWM power control device and the AM radio mounted on the automobile are described. However, the radio noise generated by the PWM power control device is not limited to the automobile and is mixed in the AM radio. Also has the same effect.

[0025]

As described in detail above, according to the present invention, the switching frequency is set so that the frequency f _B (= | F ₀ −nf ₀ |) of the beat signal becomes higher than the voice frequency bandwidth f _A. f ₀
Is set, there is an excellent effect that radio noise caused by harmonics generated by the PWM power control device can be effectively eliminated completely.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

2 is a frequency spectrum showing the relationship between the harmonic noise generated by the PWM power control apparatus shown in FIG. 1 and the carrier frequency of the AM radio broadcast received by the AM radio shown in FIG.

FIG. 3 is a configuration diagram of a conventional PWM power control device, a motor, and a battery.

4 is a voltage and current waveform of each part of the embodiment of the present invention shown in FIG. 1 and the conventional PWM power control device shown in FIG.

5 is a frequency spectrum showing a relationship between harmonic noise generated by the PWM power control apparatus shown in FIG. 3 and a carrier frequency of an AM radio broadcast received by an AM radio (not shown).

[Explanation of symbols]

 10 PWM power control device 16 Duty control circuit 18 Power MOSFET 21 Flywheel diode 22 Capacitor 23 Inductor 24 Reference signal generation circuit 30 Motor 31 Battery 40 PWM power control device 50 AM Radio 70 Reference signal generation circuit VCO Voltage controlled oscillator PD Programmable frequency divider PC Phase comparator

Claims (3)

[Claims] 1. A switching operation at the frequency f _0, and a PWM (Pulse Width Modulation) method of power control apparatus for generating a noise spectrum comprising a plurality of harmonics and the fundamental wave of the frequency f _0, AM scheme reception And a carrier frequency F ₀ of the radio broadcast being received by the receiver, and the harmonic component nf ₀ (where n is the closest to the carrier frequency F _0).
The absolute value of the difference frequency is an integer) | F ₀ - nf ₀ | frequency f _B of the beat signal is calculated by the frequency f ₀ to be higher than the upper limit of the audio frequency bandwidth f _A of the receiver A radio noise reduction system characterized by setting. 2. The radio noise reduction according to claim 1, wherein a reference signal is generated by signal processing based on the carrier frequency F ₀ , and the switching frequency f ₀ is determined based on the reference signal. system. Wherein the reference signal, after generating a signal of a frequency with respect to the carrier frequency F ₀ (F ₀ + Δf) or (F ₀ -.DELTA.f), there the frequency signal by dividing the signal The radio noise reduction system according to claim 2, wherein: