In boost converter there are two operation mode such as continuous-conduction mode (CCM) and discontinuous-conduction mode (DCM). However, could anyone explain when we would like to design the converter to work in CCM or DCM? What is the advantage of each operation mode?
Thanks for help!
efficiency is key factor. (Light load and heavy load operating conditions).
Rgs
According to the values of your converter's parameters including the L,C,R, input voltage and desired output voltage, and mainly the switching frequency, you should know whether your converter will operate in CCM or DCM. In general, if your load isn't variable do not hesitate to design your converter to operate in CCM. (inductor current does not go to zero) , but in the case of variable load, in light load, your converter will be forced to DCM and you should take this into account for the controller design
In addition to already said, it depends on the application. If you want to correct the power factor, the simplest form is DCM in case that you are not interested in current efforts of your devices.
Each mode has its own advantage and disadvantage based on the application you are using. Comparitively , the control of the DCM is easier than the CCM. But, the Ripple content of the DCM will be higher. There is a third mode called critical conduction mode. You can find various papers on these modes of operation.
Added to the mentioned notes.
One important feature of boost converter that sometimes gets less attention is the non-minimum phase (NMP) characteristic, which is due to the right half plane (RHP) zero in its control to output voltage transfer function.
If you want to avoid NMP effect that will deteriorate the control and stability behavior of the converter, sometimes DCM operation is an available alternative to CCM. In this case ,the RHP zero places in high frequencies usually higher than the switching frequency and the boost converter mainly behaves like a converter with single pole.
Moreover, considering the disadvantages of DCM operation like high current ripple and low efficiency, in some special applications when control is important, power circuit designers intentionally design the converter to operate in DCM operation.
Thank you all for the info.
One thing I would like to confirm and calculate myself is about efficiency. I read some articles and they say opposite things about this. Some say that DCM has higher efficiecy than CCM. The other say the opposite. What are your opinions about this? Thanks.
The efficiency depends on the application or the power rating of the converter you are designing for. The diode reverse recovery losses and switch on loss of our deivce will be less in DCM but you may see a higher inductor loss due to higher ripple content. And it is different in CCM. You can also see interleaved approaches for higher efficiency.
Need of minimum input ripple current is the deciding factor for selection of boost converter topology. Because step-up of voltage level can also be done by using buck-boost converter. Thus, operating boost converter in DCM robs its ability to have low input ripple current. So operating boost converter in DCM is not suggested.
In case of very wide range of input voltage and output load variations requires, retaining efficient operation and good line shaping qualities can be addressed by interleaved topology with variable number of active phases, regarding the power output demand and the input voltage level and the number of active phases (more active phases results in lower current ripple, but can also reduce efficiency of the converter for the same operating point regarding input voltage and output load) . Furthermore, AC line-interfaced topologies constantly employ both CCM and DCM (mixed mode of operation), and high-performance controllers are regularly supported by appropriate feed-forward control subsystems (with some specific issues regarding boundary operating conditions).
for low output voltage and high current application Ccm is used & for high voltage and low current application Dcm is use
You can check https://www.hpe.ee.ethz.ch/uploads/tx_ethpublications/PhD_Thesis_main_christen.pdf. There is a chapter on the same problem concerning buck converters also dealing with the optimal number of phases for interleaving. I guess the models etc. can also be applied to boost converters...
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