Hi, Can someone please explain how a boost converter controlled via PWM allows you to not only output a constant voltage to the batteries, but also perform the function of an MPPT?
there are two methods to control. first MPP the control depend on the insolation level to control of the switch of converter. Other control depend on the value of voltage load (as voltage regulator)
I do not see any problem if the battery voltage is higher than the PV cell voltage. As the output of the converter is approximatgely constant, limited by the battery, the output voltage is not controlled: the MPPT controller has to adjust the output current of the boost converter to get the optimal PV cell load. It seems a good application for a boost converter, as at every pulse it delivers a fixed energy, independently of the output voltage.
there are two methods to control. first MPP the control depend on the insolation level to control of the switch of converter. Other control depend on the value of voltage load (as voltage regulator)
Dears Professor Nashed and Mr Casanellas
Thank you for your clear and helpful explanations.
Mppt circuit is uasually added into converter, however, you should distinguish the differencies oh two these concepts. In your problems, Mppt always try to regulate input impedance which seen at input of converter to get the highgest power from PV cell.
There are three issues involved
1. Drawing maximum power from PV.
2. charging profile of the battery
3 Avoiding overcharging of the battery.
Current drawn from PV should not exceed the maximum recommended charging current of the battery. Design your control which addresses these issues.
Hi Mohammad,
In MPPT applications with battery you are not regulating the output, which is however almost constant (at least considering the response time constant of a dc-dc converter), as correctly said by Francesc. This voltage will "slowly" vary depending on size of battery, loads attached to the battery and energy transferred by the converter.
Now, you have the common Vout/Vin=1/(1-D) relation where Vout and D are fixed by the battery and by you, so that you can control your Vin depending on your MPPT strategy.
hi
I think you have to give up the idea that an MPPT charger outputs a constant voltage.
It outputs a controlled voltage that
(a) is safe for charging the batteries
(b) results in a safe charging current for the batteries
(c) gives the highest current to the batteries that the solar cells can provide at the moment.
In practice this means measuring the input voltage and current, calculating the power, and adjusting the output voltage to maximise power (goal c) while also considering the output voltage and current AND the state of charge of the batteries to meet goals (a) and (b).
State (b) probably means you need a bigger battery with a higher charging rate - or it is close to fully charged (and only permits trickle charging) and state (a) means the battery is fully charged. The rules for these depend on the battery technology. Lead acid batteries have characteristics allowing safe MPPT charging; lithium batteries may have stricter charging regimes... In either case these rules give you some leeway to charge at different rates, and the MPPT charger uses that.
Normally an MPPT controller will be in state (c) - the MPPT state - until the batteries are close to fully charged. And here it is controlling the charging current to the batteries - by adjusting the charge voltage.
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hi
I think you have to give up the idea that an MPPT charger outputs a constant voltage.
It outputs a controlled voltage that
(a) is safe for charging the batteries
(b) results in a safe charging current for the batteries
(c) gives the highest current to the batteries that the solar cells can provide at the moment.
In practice this means measuring the input voltage and current, calculating the power, and adjusting the output voltage to maximise power (goal c) while also considering the output voltage and current AND the state of charge of the batteries to meet goals (a) and (b).
State (b) probably means you need a bigger battery with a higher charging rate - or it is close to fully charged (and only permits trickle charging) and state (a) means the battery is fully charged. The rules for these depend on the battery technology. Lead acid batteries have characteristics allowing safe MPPT charging; lithium batteries may have stricter charging regimes... In either case these rules give you some leeway to charge at different rates, and the MPPT charger uses that.
Normally an MPPT controller will be in state (c) - the MPPT state - until the batteries are close to fully charged. And here it is controlling the charging current to the batteries - by adjusting the charge voltage.
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