Digital PWM technique for increased resolution
- 1. DPWM RESEARCH PAPER PRESENTATION Anas Zohrab M.Uzair Arshad Huzaifa Ibrahim Ammar Sadiq
- 2. Problems with DC PWM Output Voltage Accuracy is limited Resolution is finite THD of SPWM is higher
- 3. PWM resolution Number of different steps you can have from zero power to full power. 10 bit resolution means that you can have 1024 steps from zero to full power
- 4. Basic working Principle High frequency switching and low frequency modulating DPWM adds a lower-frequency PWM (2nd order) into conventional PWM (fundamental PWM)
- 7. B. Spectral Characteristics Fundamental PWM: Function of Fundamental PWM. Its Fourier Transform is: V1(ω)
- 8. B. Spectral Characteristics (cont.) 2nd Order PWM: Function of 2nd Order PWM.
- 9. B. Spectral Characteristics (cont.) Fourier of 2nd Order PWM. V2(ω)
- 10. B. Spectral Characteristics (cont.) Double PWM: Function of Double PWM.
- 11. B. Spectral Characteristics (cont.) Fourier of Double PWM. V(ω)
- 12. B. Spectral Characteristics (cont.) Conclusion: DC component is added. More harmonics (𝑘 ≠ 𝑛, 2𝑛, 3𝑛,∙∙∙) are introduced by 2nd Order PWM. The magnitudes of 𝑘 = 𝑛, 2𝑛, 3𝑛,∙∙∙ harmonics, contained in both fundamental and 2nd Order PWM, are added.
- 13. B. Modulating Resolution of DPWM Conventional PWM controlling DC-DC converters have resolution of Tb in T. Due to addition of 2nd order PWM in the fundamental PWM, the resolution is improved by “n” times and error is reduced to (Tb/(nT)) x 100%. Higher the frequency division modulus “n”, Better the resolution of DPWM.
- 14. C. Filter Parameters Maximum RMS of total harmonics of DPWM is the same as conventional PWM when pulse width Tk is among the switching period T. Various order harmonics amplitudes drop generally when frequency rises, same as the fundamental PWM. For conventional PWM, lowest order harmonic has the highest amplitude, about 63.66% of Vm. However, the amplitudes of 2nd order PWM harmonics are much less than one tenth of maximum fundamental harmonic of conventional PWM. When the Tk changes among switching period T, the maximum change in amplitude is no more than 2% of Vm. 2nd Order PWM Conventional PWM Double PWM
- 15. C. Filter Parameters continued As long as the frequency division modulus n is less than 8, same filtering technique can be applied to output waveform of DPWM as the conventional PWM. If n is greater than or equals to 8, LC filter parameters need to be increased to obtain good filtering effect. However, n is not required very high as it is set to improve the resolution of PWM. In conclusion, addition of 2nd order PWM does not effect design considerations about filter.
- 16. Experimental Circuit Experimental Buck - Boost converter
- 17. Three Operating States Vs<Vo, boost converting state Vs>Vo, buck converting state Vs=Vo, direct transmitting state
- 18. Duty Ratio Curves Boost converting state: D1= 0 ~ (1-Vsmin/Vo), D2= 1. Direct transmitting state:D1= 0, D2 = 1. Buck converting state: D1=0, D2 =Vo/Vsmax ~ 1.
- 20. Experimental Verification The dynamic waveforms of output voltage and load current when load changes
- 21. Features of DPWM (i) to increase the modulating accuracy of high-frequency PWM with finite timer resolution (ii) to reduce over-shoot value and to improve dynamic response (iii) to obtain the same filtering effect as conventional PWM with same filter when the DPWM frequency division modulus n is not too high, and (iv) to be a control method with higher ratio of performance to cost compared to the increase of microprocessor operating frequency
- 22. Any Question?
- 23. Thank You!