Pulse or digital communications – Spread spectrum – Frequency hopping
Reexamination Certificate
2000-08-02
2004-01-06
Ghayour, Mohammad H. (Department: 2634)
Pulse or digital communications
Spread spectrum
Frequency hopping
C330S010000
Reexamination Certificate
active
06674789
ABSTRACT:
BACKGROUND OF THE INVENTION
All commercial electrical systems must meet specific Electro-Magnetic Interference (EMI) limits. EMI solutions are usually quite expensive. In some systems 30% of the whole cost is related to EMI/EMC (compatibility) for large filters, shielding, etc. In the Electric Power Steering (EPS) system the main contributor to RF noise is the Pulse Width Modulation (PWM) operation used for current control. PWM generates narrow-band noise in the form of a spike at every integer harmonic of the PWM switching frequency. The vehicle's radio is a serious victim to narrow-band noise, since the above harmonics can appear as distinct tones at the output of the radio. This invention converts the narrow-band noise into broadband noise and reduces the peak amplitude thereof by varying the switching frequency of the PWM within a small range.
The PWM harmonic spikes have an amplitude given by:
(
At/T
s
)·|(sin(&pgr;
f
n
t
)/(&pgr;
f
n
t
)| (1)
where A is the amplitude of the pulses, t is the PWM “on” time, T
s
is the PWM switching period and f
n
, is an integer multiple of 1/T
s
, the switching frequency, f
s
. The spectrum is a series of spikes spaced apart by f
s
, bounded by the modulus of a sine-shaped envelope as seen in FIG.
1
.
BRIEF SUMMARY OF THE INVENTION
A method of controlling the bandwidth of electromagnetic interference generated by a pulse modulation controlled automotive motor is disclosed. The method comprises providing a controller including at least one register thereof; the controller in signal communication with the motor for controlling the motor based upon operating parameters thereof; selecting a first clock frequency; selecting a first switching frequency; initializing the at least one register, establishing thereby a prescribed at least one number; selecting a first hopping period; based upon the prescribed at least one number of the at least one register, the first clock frequency and the first hopping frequency randomly modulating the switching frequency of the pulse modulation.
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Comstock Luke
Fardoun Abbas
Rakouth Heritianarisoa
Delphi Technologies Inc.
Ghayour Mohammad H.
Smith Michael D.
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