EEE M.tech Project on Elimination of RHP Zero for the improvement of performance of Boost Converter:
The key idea is to utilize the current loops for the variables to be controlled to achieve maximum bandwidth. The tristate boost converter circuit, shown in Fig. 3. The basic operation is briefly described with the help of Fig. 4.
At the start of the clock period, switch S1 turns on and S2 turns off and the inductor current iL rises. This interval is termed as the “boost interval,” denoted as “mode 1,” and the corresponding duty ratio is denoted as don.When iL reaches a peak value iref+, S1 turns off. Then, iL starts falling until it reaches some lower threshold iref−. This interval is known as the “capacitor charging interval,” denoted as “mode 2” and doff is the related duty ratio. Switch S2 turns on when iL reaches iir e f − and remains on until the arrival of the next clock pulse. This is the additional interval, termed as the “freewheeling interval” denoted by “mode 3.” The cycle then repeats. During mode 1, mode 2, and mode 3, m1 , −m2 , and−m3 are the respective slopes of the inductor current. T is the switching period or the clock interval.
Fig 4. Typical inductor current waveform of a tri-state boost converter.
In the proposed current control scheme, iref+ is controlled using peak current mode control whereas iref− is made dependent on the reference voltage and the supply voltage. As would be shown later, the values of iref+ and iref− need to be carefully chosen from the voltage loop or the current loop to prevent the RHP zero from reappearing. It is also confirmed analytically as well as by simulations that the presence of freewheeling mode makes the operation completely free from subharmonic oscillations even without using a stabilizing ramp.
Generalization to Other Converter Topologies
Apart from a boost converter, there exist other dc-dc converters (like the buck-boost converter, the flyback converter etc.), which suffer from the similar RHP zero problem. The proposed scheme can be generalized for those converter topologies for eliminating the RHP zero. The proposed scheme can be also be used in a single-inductor-multipleoutput converter for minimizing the cross coupling, and it can also be used in a non-minimum phase converter (like the buck converter) for improving closed loop bandwidth further.
Download Elimination of RHP Zero for the Improvement of Performance of Boost Converter Project Report and PPT.