hello,
--- Is it possible to always get the maximum power that can be fed from a pv panel if i am imposing a stable voltage at a certain value on DC bus (by a certain controller) ?
Hi there, yes it is necessary to keep DC-link voltage at a constant level. To achieve MPPT you would need to regulate the current of a DC-DC converter while keeping its output voltage at a constant level.
Adam Tomaszuk
thank you, yes you are right but if we say that the DC bus voltage should be maintained at a certain level this means that the maximum power drawn from the pv panel is the maximum that corresponds to this level of DC voltage and not the absolute maximum (that can be obtain if we have a load with a characteristic resistance connected to the PV ) ?? this is related to the idea if the MPPT should always give us the maximum power that can be given disregarding the voltage or the load at the output, because the relation is between Vout, Vin and duty cycle and if the Vout is already determined how the MPPT is working in these two conditions (Vout determined and Vin determined ) ?
i am a little bit confused by this idea
Dear Sarah,
If it is possible or not, it depends on the electrical load on the DC bus.
If the load is constant and resistive, then it is not possible to maintain a constant voltage and obtain MPPT unless the resistance matches the characteristic resistance of the module.
If the load is a battery for example, then the voltage can be kept constant and vary the current to obtain MPPT (provided the battery is not fully charged or its maximum current limit is reached).
MPPT with constant voltage can also be achieved if the DC bus is supplied by two or more power sources (including the PV) which can adjust their output power based on the PV output. For example, if the PV power increases, the other soucre decreases its power.
It is possible to regulate its current while keeping the output voltage at a constant level, thus having the opportunity to track MPP (P = U * I). It all depends on the topology of the DC-DC converter you would choose. The other way is to incorporate two control loops: inner voltage loop and outer current loop. You may also have a look at the discussions on the RG on that/similar topic.
Michalis Florides
thank you so much
you said that "it depends on the electrical load on the DC bus", is this true also when we have a pv panel provided by an MPPT algorithm ? shouldn't i expect always the maximum power from pv (with MPPT alg) whatever the load is ?
as i know that with MPPT algorithm we will get maximum power whatever the weather conditions are and whatever the load is.. am i wrong ?
Seyed Majid Hashemzadeh
your reply is really very interesting, thank you so much !!
Concerning the two power switches converter, you mean that we can control both sides in this way (input side for MPPT) and output side (for constant voltage) each switch for its corresponding goal right ?
Sarah,
An MPPT will try to track the maximum power whatever the weather conditions are. However, this is true if the load is within certain limits.
Assume the load is a resistor. If the resistance is too low, the MPPT converter will reach its rated output current before tracking the maximum power. On the other hand, if the resistance is too high, the MPPT converter will reach is rated voltage before tracking the maximum power.
Therefore, if the power converter will be able to track the maximum power depends on its design specifications and also on the load.
Use a DC-DC converter with an appropriate topology and control system for connection of the PV array to the DC bus. It's as simple as that. The only question is: are there other sources connected to the same DC bus? How the power balance will be attained in case of changing PV irradiance conditions? If the PV array is the only source, voltage regulation will not be possible when required load power is greater than PV power at MPP.
Slah Farhani merci pour la reponse
donc on ne peut pas dire que avec MPPT nous obtenons la puissance maximale (correspondante a une irradiation et une temperature bien determinées) qlq soit la charge , c juste ?
You need two converters: the 1st converter can take care of the MPPT and the second converter can be leveraged for the DC bus stabilization by linear (PI) or non-linear (ANN, fuzzy logic, MPC) controller.
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