Speed-variable maximum delay clamping when using variable-delay random PWM switching
View Patent ↗A control system and a method of using the same for an electric machine having a random number generating module generating a random number ranging from a first value to a second value, a multiplying module multiplying the random number and a sample rate to generate an random delay value; and a delay limiter module limiting the random delay value as a function of speed of the electric machine and generating a limited delay value.
1. A control system for an electric machine, comprising:
a random number generating module that generates a random number ranging from a first value to a second value;
a multiplying module that multiplies said random number and a sample rate to generate a random delay value; and
a delay limiter module that limits said random delay value as a function of speed of said electric machine and generates a limited delay value, wherein a pulse width modulated drive signal is generated for said electric machine based on said limited delay value.
2. The control system according to claim 1 further comprising:
a switch module that receives said limited delay value from said delay limiter module, that adds said sample rate, that subtracts a delay period of a previous cycle, and that outputs a calculated switching period.
3. The control system according to claim 2 further comprising:
a max checking module that compares said calculated switching period to a predetermined minimum switching period, that outputs a final switching period that is equal to said calculated switching period if said calculated switching period is greater than said minimum switching period and that is equal to said minimum switching period if said calculated switching period is less than said minimum switching period.
4. The control system according to claim 3 further comprising: a delay calculating module that receives said final switching period from said max checking module, that subtracts said sample rate, that adds said delay period of said previous cycle and that outputs a delay period for a current cycle.
5. The control system according to claim 1 wherein said delay limiter module further limits said random delay value as a function of speed for speeds greater than a predetermined value.
6. The control system according to claim 5 wherein said delay limiter module limits said random delay value in an inversely proportional manner relative to said speed of said electric machine for speeds greater than said predetermined value.
7. The control system according to claim 1 wherein said first value is 0 and said second value is 1.
8. A control system for an electric machine, said control system comprising:
a random number generating module that generates a random number ranging from a first value to a second value;
a multiplying module that multiplies said random number and a sample rate to generate a random delay value; and
a delay limiter module that limits said random delay value as a function of speed of said electric machine and generates a limited delay value, that limits said random delay value as a function of speed for speeds great than a predetermined value, which is greater than a minimum speed of said electric machine and less than a maximum speed of said electric machine, wherein a pulse width modulated drive signal is generated for said electric machine based on said limited delay value.
9. The control system according to claim 8 further comprising:
a switch module that receives said limited delay value from said delay limiter module, that adds said sample rate and subtracts a delay period of a previous cycle, and that outputs a calculated switching period.
10. The control system according to claim 9 further comprising: a max checking module that compares said calculated switching period to a predetermine minimum switching period, that outputs a final switching period that is equal to said calculated switching period if said calculate switching period is greater than said minimum switching period and that is equal to said minimum switching period if said calculated switching period is less than said minimum switching period.
11. The control system according to claim 10 further comprising: a delay calculating module that receives said final switching period from said max checking module, that subtracts said sample rate and adds said delay period of said previous cycle, and that outputs a delay period for a current cycle.
12. The control system according to claim 8 wherein said delay limiter module limits said random delay value in an inversely proportional manner relative to said speed of said electric machine for speeds greater than said predetermined value.
13. The control system according to claim 8 wherein said first value is 0 and said second value is 1.
14. A control method comprising:
generating a random number ranging from a first value to a second value;
multiplying said random number and a sample rate to generate a random delay value;
limiting said random delay value as a function of speed of electric machine;
generating a limited delay value; and
generating a pulse width modulated drive signal for said electric machine based on said limited delay value.
15. The control method according to claim 14 further comprising:
receiving said limited delay value;
adding said sample rate to said limit delay value; and
subtracting a delay period of a previous cycle from said limit delay value to output a calculated switching period.
16. The control method according to claim 15 further comprising:
comparing said calculated switching period to a predetermine minimum switching period; and
outputting a final switching period that is equal to said calculated switching period if said calculated switching period is greater than said minimum switching period and that is equal to said minimum switching period if said calculated switching period is lesser than said minimum switching period.
17. The control method according to claim 16 further comprising:
receiving said final switching period;
subtracting said sample rate; and
adding said delay period of said previous cycle to output a delay period for a current cycle.
18. The control method according to claim 14 wherein said limiting said random delay value as a function of speed of said electric machine and generating a limited delay value includes limiting said random delay value as a function of speed for speeds greater than a predetermined value.
19. The control method according to claim 18 wherein said limiting said random delay value is inversely proportionally to said speed of said electric machine for speeds greater than said predetermined value.
20. The control system according to claim 1 wherein said function of speed of said electric machine establishes an upper limit for said random delay value.
21. The control system according to claim 8 wherein said function of speed of said electric machine establishes an upper limit for said random delay value.
22. The control method according to claim 14 wherein said function of speed of said electric machine establishes an upper limit for said random delay value.