Request for Guidance on MPPT Circuit Design - Page 1
Forum section: electronics / beginners

author: GlassWindow
author_rank: Newbie
timestamp: February 02, 2025, 01:55:25 am
content: Hello everyone,I'm currently working on a project where I am trying to design an MPPT (Maximum Power Point Tracking) circuit by myself, and I’m looking for some guidance. I would really appreciate it if someone could explain how MPPT circuits work, the key components involved.If anyone has experience with MPPT circuit design, could you please share your insights or resources that could help me in building and understanding these circuits?Thank you in advance for any help!

author: eTobey
author_rank: Super Contributor
timestamp: February 02, 2025, 07:35:54 am
content: Hi,what are your current research efforts so far?I can easily find schematics and open source mppt controllers:https://www.instructables.com/DIY-1kW-MPPT-Solar-Charge-Controller/And why do you want to build one? They start at 50€.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 02, 2025, 05:36:06 pm
content: You realize that maximum power point tracker is not a circuit, it's a software algorithm?

author: 30Penny
author_rank: Newbie
timestamp: February 02, 2025, 08:09:50 pm
content: There are quite a few analog mppt circuits out there and I think it's a great project to make your own. While it's true mppt is usually done in software and are cheap and readily available where's the fun in that? I think i will spend sometime on this. perhaps this could be as simple as a couple ntc's to measure panel output and some discrete trannies setup as differentials to adjust the output power of a smps charging some batteries.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 04, 2025, 09:29:53 am
content: Oh, fixed voltage with temperature compensation is possible to do in analog, but that's not what's usually called MPPT (thetrackingpart specifically). It ignores effect of irradiation, and even more seriously, partial shading. Sure it can be an interesting project of course.

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: February 04, 2025, 03:55:03 pm
content: Quote from: Siwastaja on February 02, 2025, 05:36:06 pman mpp tracker (in the true sense of the word, not just voltage monitoring) can very well be done solely in hardware.it is not by any means a "software algorithm" thing.

author: Peabody
author_rank: Super Contributor
timestamp: February 04, 2025, 04:06:28 pm
content: I have the same questions as the OP. Does anyone know of a video which explains in detail how a Perturb and Observe MPPT solar charging circuit works? I've looked at the Instructables schematic, but don't really know what's going on there.Specifically, I see one inductor in the charging part of the circuit, which I assume is part of the switching circuit that keeps the solar output at the MPP. But I don't see how the resulting power gets converted to the voltage and current the battery needs for charging. Shouldn't there be another switching circuit to do that? Well, obviously not, but it sure would be helpful to see scope captures showing what exactly is going on. Has anyone seen such an explanation?

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 04, 2025, 04:38:49 pm
content: A simple algorithm that I used for a home project, take it as a starting point only, it can be optimized:-INITIALIZE set the PWM to 50%, read the power.-PERTURB increase (or decrease, your choice) the DC by a small amount, say 1%.-OBSERVE read the power. Did it increase/ decrease as compared to the previous reading?-PERTURB if power increases, continue to increase/decrease the DC. Otherwise go into the opposite direction.-OBSERVE read the power. Did it increase/ decrease as compared to the previous reading?...Continue foreverWith any small micro the software is trivial. You may also want to use discrete logic, if you are proficient with state diagrams.

author: Faranight
author_rank: Unknown
timestamp: February 04, 2025, 05:09:22 pm
content: Having done some research on this subject, I was disappointed to learn that there are several IC's out there that call themselves MPPT, but aren't actually doing the tracking, just fixing the voltage.Analog Deviceshas many of these, and they sometimes call it MPPC (maximum power point control). It's basically a scheme where you're supposed to manually adjust the voltage that you're expecting a solar panel should be operating at. The IC will then adjust the current draw of the panel to match the given voltage, which is typically set to a fixed value of 80% of the panel's open circuit voltage. This has a drawback in low-light conditions because the maximum power vs illumination curve (not IV curve) is not linear in that region, and the system is operating in sub-optimal conditions.Texas Instrumentsalso have some "MPPT" IC's which are somewhat better, but still fall short as they don't actually do the real tracking. While they technically track, they don't truly track the maximum power point. Instead, they periodically disconnect the panel from the system for a few moments to measure its Voc, and then adjust the switch duty-cycle to fix the panel voltage to about 80% of the measured Voc. They do this like every 12 seconds, if I remember correctly. A real MPPT will continuously measure the panel voltage and current to calculate the actual power draw of the panel. Next, the algorithm will try to slightly vary the duty-cycle of the DC-DC switch in one direction to see, if the power draw increases. If yes, then it continues to adjust the PWM in the same direction, otherwise it nudges the duty-cycle in the opposite direction until the maximum is found. When found, the duty-cycle lingers there until there is some deviation in the panel illumination, to which the algorithm reacts by following the same pattern continuously. This algorithm is calledPerturb & Observe.

author: 30Penny
author_rank: Newbie
timestamp: February 04, 2025, 08:50:35 pm
content: So I was thinking about this for a bit and came to the conclusion I will have to get a panel and test my idea out. The panel itself provides the only two variables you need to track power. Voltage divider from panel into an opamp, hall effect sensor measuring current negative proportion to the same op amp, so as either the voltage or the current increases the op amp output voltages increases proportionately which you feed into a ka7500 ic, or whatever you like. So I'll put a slight positive bias on the controller so it requires a slight negative drop on the control voltage to stop the duty cycle from increasing and hence current increasing. So start up would be minimum duty, then if there is battery connected for charging the duty cycle will start to increase due to positive feedback from hall effect sensor and the panel voltages is high and the positive bias on the controller creates a runaway duty cycle increase until the voltage starts to drop when the panel can no longer sustain the voltage which it will hold at until the voltage the panel is providing either drops (less light) or increases (more light) and forces the duty cycle up or down until feedback equilibrium is reached again. Obviously you need to size it correctly for panel power and work out the particulars for hall effect and dividers and such and stabilize the feedback network and rate of change, blah blahMost panels maximum power output is right where the voltage starts to droop or a little after (panel dependent of course) so I think minimal tweaking would be needed to at least get something going in the ball park.Sounds fun, and I'm thinking this must be more or less how it's done in the analog domain.

author: eTobey
author_rank: Super Contributor
timestamp: February 05, 2025, 12:41:45 pm
content: An opamp does amplify adifference, doesnt it?What is the definition of power? P = U * IThat does not really compare.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 05, 2025, 07:10:52 pm
content: Quote from: Le_Bassiste on February 04, 2025, 03:55:03 pmA pedantic answer - you are of course correct. Then again, I don't believe anyone is crazy enough to seriously do analog MPPT (in the full correct meaning). It can be done as an interesting project, similarly how people today build computers out of logic gates even if it does not "make sense"; or use disk drives to play music. MPPT would be an excellent example of an algorithmic task which is much easier to develop and test on a microprocessor than analog, but you sure can implement e.g. perturb and observe with some analog building blocks like oscillators, amplifiers, sample&hold circuits, and error integrators. You can even add global scan in analog. It would be interesting to see; just like doing analog induction motor vector control (the concept of which is from before 1970's, but really gained traction with affordable microcomputers).

author: Peabody
author_rank: Super Contributor
timestamp: February 05, 2025, 10:40:31 pm
content: Quote from: KerimF on February 05, 2025, 01:19:34 pmThis is a very interesting point. The output voltage is fixed at or slightly above the battery voltage, so the only thing that varies is the charging current.Why is MPPT tracking better than @KerimF's method?

author: johansen
author_rank: Super Contributor
timestamp: February 06, 2025, 04:18:19 am
content: Quote from: Siwastaja on February 05, 2025, 07:10:52 pmnot crazy, and not a super high parts count eitherhttps://www.edn.com/solar-array-controller-needs-no-multiplier-to-maximize-power/https://www.edn.com/solar-day-lamp-with-active-mppt-and-no-ballast-resistors/

author: Siwastaja
author_rank: Super Contributor
timestamp: February 06, 2025, 06:36:27 am
content: Quote from: johansen on February 06, 2025, 04:18:19 amI especially like the log function implemented from discrete transistors, to convert voltage*current multiplication into a simpler summation. It is intriguing to see someone did this in 2008. Most people would have said it makes no sense to do it analog.

author: eTobey
author_rank: Super Contributor
timestamp: February 06, 2025, 08:04:53 am
content: Quote from: Peabody on February 05, 2025, 10:40:31 pmI could not answer it at first, but i googled it. I hope i got that right:PWM directly connects the battery to the panel with the PWM duration. So the panel then operates for example with 30% at an arbitrary efficiency, and 70% with 0% efficiency. Or in the best case with 100% at an arbitrary efficiency. The effiency then would depend on the difference between the battery voltage and the panel voltage.MPPT does look for the best efficiency, eliminating the difference between the battery and the panel, and imposing the proper voltage on the panels, to get the higest output.I would compare the pwm with a car that has an engine, but no gears: you can drive the car at the speed where the motor has the highest efficiency, but with a gear box (aka MPPT) you would have an advantage.

author: MrAl
author_rank: Super Contributor
timestamp: February 06, 2025, 09:31:25 am
content: Quote from: GlassWindow on February 02, 2025, 01:55:25 amHello,To do this with an analog circuit is not easy because you really need a way to perturb the system so it can search for the max power point.To start, you could use an analog multiplier chip. That would multiply a scaled voltage times a scaled current which would represent the power. To perform the perturbation, you would measure the power and then have the system increase some value that changed the output power, then compare the two power measurements to see if the power increased or decreased. If it increased you step up the output power a little bit more, then make another measurement and repeat the comparison. If the power went down, then you step back, then try to decrease the control setting, then repeat the measurement, then repeat the comparison. You keep doing this.You do need a load that can actually take the maximum power though or else it does not mean anything. This would normally be a line-tied inverter that converts the solar power into AC power that is fed back into the power line. If it is a battery, then the battery has to be able to take the maximum power all the time, which would be unusual unless it had power constantly drawn from it. You may not have to measure the voltage just the current, but that's only if the voltage does not change too much. Since current is the main quantity it may not help to measure the voltage anyway. The voltage could go to whatever it needed to, but only if the battery could take the full load current all the time.This is a little tricky because you do not want to overcharge the battery.Just to note, I worked on a project a long time ago with Sandia Labs and they concluded that the best way to manage the power from an array and a line-tied converter was to use a separate solar cell to measure the insolation. That was mostly because of harmonics that appear on the power line when there are a lot of line-tied max power tracking systems online in the same local area. There are drawbacks to this, but it was their decision. I suppose if we were just charging a battery that would not be an issue.What happens with the perturbed system is that it may go offline sometimes when the increment in power is too high. It tries to draw too much power from the converter and so it cannot put out the required voltage. This happens when the max power tracker tracks off the deep end of the curve because the test increment pushes it too far. This applies to the line-tied converter application also.There were also issues with the timing that came up with variable cloud cover. When a cloud rolls in, the insolation level falls but the max power tracker does not know this immediately. That means that the output power changes by something other than the max power tracker perturbation cycle, which confuses the max power tracker because it relies on the output power changing due to it's own control in order to be able to measure the output power. This also brings up the question of how much of an increment should be used to perturb the system. Too much means it can fall off the deep end, and too little makes it harder to measure any changes.This all may not matter with battery charging though.Some systems simply set the voltage and that's that. There is some reasoning behind this due to the relationships present in solar panels.When we did the work for Sandia Labs we had a huge solar panel to work with worth a million dollars. When I did my own personal panel it was just about 100 watts or something. I found that the biggest issue with battery charging was to not overcharge the battery, yet get enough current to charge it when it was needed. Cloudy days were the worst, because there was little power available.What I used as a guide was the voltage. If the voltage got too high, I could shut off the current. But then I found that if I selected the right current level, it would never overcharge. This was with a system that did not have to actually draw power from the battery every single day, yours may be different.

author: eTobey
author_rank: Super Contributor
timestamp: February 06, 2025, 10:15:32 am
content: Quote from: MrAl on February 06, 2025, 09:31:25 amYou have invested quite a bit of time it seems. But the guy that asked, never answered a question that was directed to him, allthough he was online after those have been asked...

author: Peabody
author_rank: Super Contributor
timestamp: February 06, 2025, 03:07:43 pm
content: Quote from: eTobey on February 06, 2025, 08:04:53 amWell I guess I've misunderstood what a PWM controller is. I thought PWM controller had an inductor and diode like a regular buck converter does, but with feedback from the battery side controlling the duty cycle. As opposed to MPPT, which essentially uses feedback from the panel to control the duty cycle. But if PWM is just switching current to the battery on and off directly. I don't see what advantage it has over a plain linear charger, except maybe to reduce dissipation in the charger when the sun is really bright.But I really don't understand how MPPT works. I'm still looking for a scope capture showing panel voltage when MPPT is going on. Would it show constant voltage at the MPP voltage? Or would I see switching going on, and if so, between what values?Edit: I still don't see why MPPT is better than @KerimF's method. If you have a switching circuit that uses P&O to maximize charging current, how could that possibly be worse than MPPT for charging a battery? For a battery, it's all about charging current.

author: eTobey
author_rank: Super Contributor
timestamp: February 06, 2025, 07:37:47 pm
content: Quote from: Peabody on February 06, 2025, 03:07:43 pmEven if someone explains something very well, dont just believe that. Especially if someone just googled it, and "believes" its right.Quote from: Peabody on February 06, 2025, 03:07:43 pmSo neither do i really. Information is quite often only superficial. My information i got, is from another forum.Quote from: Peabody on February 06, 2025, 03:07:43 pmI believe its benefit (only benefit?) comes into play, when there is less sunlight. ( i got that from a forum as well...)Id love to know more about it, but finding good resources is not that easy.

author: globoy
author_rank: Frequent Contributor
timestamp: February 06, 2025, 08:40:18 pm
content: I've designed some small (35-50W) MPPT solar chargers for Lead Acid and LiFePO4 battery types.Historically, PWM chargers were an improvement over simply connecting a solar panel (through a blocking diode) to a battery and getting whatever current the panel could generate at the battery voltage. They were developed and commercialized before MPPT. Their primary advantage is the ability to regulate the current going into the battery by changing the duty cycle. I attached a marketing blurb by a PWM charger manufacturer below.MPPT chargers, as everyone here knows, try to optimize the power out of the panel by keeping the power (watts) at its highest point using a SMPS (e.g. a buck converter). In my systems this is a software PWM controlled buck (mosfet, inductor, diode). These systems get up to about 93% measured efficiency (of course they get much lower efficiency at low power). They measure panel voltage, panel current and battery voltage (other stuff too but those are what are necessary for the MPPT algorithm). The fact that a battery is a large reservoir whose voltage doesn't quickly change makes buck control amenable to software control (stability). The algorithm implements the classic P&O strategy. It works hand-in-hand with the charge control algorithm which - in the case of a lead acid battery - is taking the battery through several charge states and voltage levels (BULK, ABSORPTION, FLOAT) and managing things like temperature compensation. The buck control then can work in several states. For example, it can be attempting to provide as much current as possible to bring the battery up to a charge level (for example 14.7V for BULK, 13.65V for FLOAT) or it can be managing current to keep the battery at a charge level (ABSORPTION, FLOAT). The P&O algorithm is initialized (and periodically) re-initialized by controlling the buck so the panel transits through a range of voltages to find the point of maximum power. It also deals with stuff like the fact that the P&O algorithm can sometimes wonder off (localized maxima) when conditions are changing (for example a cloud transits across the sun for a few seconds). In my system the buck control and the P&O algorithm coordinate in the case where the buck is limiting current to hold a battery voltage since it isn't looking for maximum output at that time. And finally the algorithm dynamically adjusts the step size used in the perturb phase based on power requirements (lower power requires larger steps to find a significant change).As an experiment I implemented PWM on essentially the same hardware. For my little systems, where panel voltage is close to battery voltage, I saw 15-20+% improvement using MPPT. Of course for high power/voltage systems or systems that feed the grid MPPT is a requirement. In these systems, from what I understand, the algorithms are fairly complex (way beyond what you read about online).

author: eTobey
author_rank: Super Contributor
timestamp: February 07, 2025, 11:04:23 am
content: Quote from: globoy on February 06, 2025, 08:40:18 pmBut the MPPT is doing the exact same? How then is it more efficient?

author: MrAl
author_rank: Super Contributor
timestamp: February 07, 2025, 11:21:05 am
content: Quote from: eTobey on February 06, 2025, 10:15:32 amThat's an interesting thought. I don't have too much problem with it though because I can type very fast, so that previous reply probably took me five to ten minutes to complete. I don't mind sharing experience and information and maybe it will benefit others besides the original poster.

author: MrAl
author_rank: Super Contributor
timestamp: February 07, 2025, 11:27:14 am
content: Quote from: eTobey on February 07, 2025, 11:04:23 amHi,I see the idea that PWM regulators are "more efficient" all the time on the web in various forums. I guess this misconception started because they regulate something and that makes it seem more "efficient". As to the energy wasted, they are no more efficient than an equivalent series resistor and I bet you already knew that.The word "efficient" can apply to different things, but in the power control area of electronics it is almost always referring to the energy wasted. Something that wastes less energy is more efficient. It can be taken in other contexts though, although I don't think it should. For example, PWM can be loosely said that it is more 'efficient' because we don't have to use a giant rheostat which would be required to adjust current if we did not use PWM. I would not refer to it like that though, and just say that PWM is better than using a rheostat unless there is some probably with a pulsing power source or something.

author: Peabody
author_rank: Super Contributor
timestamp: February 07, 2025, 02:55:41 pm
content: Quote from: globoy on February 06, 2025, 08:40:18 pmCan you explain how your system maintains output voltage at 14.7V while also maintaining the panel at the MPP? Do you have two switching circuits (two inductors)? If not, it's hard for me to understand how one duty cycle setting can contol both input and output. The Instructables circuit posted earlier only has one inductor, but claims to be a P&O MPPT charger.Also, is anyone aware of a video that explains EXACTLY and in detail how MPPT works, including scope captures at every stage? I've had no luck finding that.

author: globoy
author_rank: Frequent Contributor
timestamp: February 07, 2025, 03:01:29 pm
content: Quote from: eTobey on February 07, 2025, 11:04:23 amBecause MPPT  operates the panel at its optimal *power output* level while when the transistor turns on in a PWM charger the panel voltage drops to the battery + transistor-drop voltage and is not operating at its optimal level so less power is output.

author: globoy
author_rank: Frequent Contributor
timestamp: February 07, 2025, 03:24:35 pm
content: Quote from: Peabody on February 07, 2025, 02:55:41 pmI have one switching circuit. I think the thing I didn't make clear is that (at least in my implementation) there is no need to try to operate the panel at its MPPT point when holding an output voltage or limiting current because at that time the panel is putting out enough power to satisfy the needs of the [now limiting] buck converter. At the point where energy production falls off enough to no longer satisfy the needs of the buck converter then we start to look for the MPP again. In this case either the battery voltage has dropped below the regulation point because the current going into it has fallen off or we're no longer limiting current because the power is less. The system can quickly move between these states as needed (IIRC every 250 mSec). The MPPT algorithm has some other special features to try to allow it to start back up quickly since the solar conditions may have changed while it was suspended.I took a quick look at the code for the Instructables project. It looks like it does the regulation in the file4_Charging_Algorithm.ino. You can see that it seems to operate with and without MPPT active.Code://///////////////////// CC-CV BUCK PSU ALGORITHM //////////////////////////////if(MPPT_Mode==0){ //CC-CV PSU MODEif(currentOutput>currentCharging) {PWM--;} //Current Is Above → Decrease Duty Cycleelse if(voltageOutput>voltageBatteryMax){PWM--;} //Voltage Is Above → Decrease Duty Cycleelse if(voltageOutput<voltageBatteryMax){PWM++;} //Increase duty cycle when output is below charging voltage (for CC-CV only mode)else{} //Do nothing when set output voltage is reachedPWM_Modulation(); //Set PWM signal to Buck PWM GPIO}/////////////////////// MPPT & CC-CV CHARGING ALGORITHM ///////////////////////else{if(currentOutput>currentCharging){PWM--;} //Current Is Above → Decrease Duty Cycleelse if(voltageOutput>voltageBatteryMax){PWM--;} //Voltage Is Above → Decrease Duty Cycleelse{ //MPPT ALGORITHMif(powerInput>powerInputPrev && voltageInput>voltageInputPrev) {PWM--;} // ↑P ↑V ; →MPP //D--else if(powerInput>powerInputPrev && voltageInput<voltageInputPrev){PWM++;} // ↑P ↓V ; MPP← //D++else if(powerInput<powerInputPrev && voltageInput>voltageInputPrev){PWM++;} // ↓P ↑V ; MPP→ //D++else if(powerInput<powerInputPrev && voltageInput<voltageInputPrev){PWM--;} // ↓P ↓V ; ←MPP //D--else if(voltageOutput<voltageBatteryMax) {PWM++;} // MP MV ; MPP Reached -powerInputPrev = powerInput; //Store Previous Recorded PowervoltageInputPrev = voltageInput; //Store Previous Recorded Voltage}PWM_Modulation(); //Set PWM signal to Buck PWM GPIO}

author: Peabody
author_rank: Super Contributor
timestamp: February 07, 2025, 03:55:13 pm
content: So then when MPPT is in effect, it's assumed that the battery will absorb all of the current produced by the panel, and the output voltage will automatically be the battery voltage or slightly higher? So the output doesn't need to be regulated in any way. But once you do need to regulate anything about the output, either the current or the voltage, you can no longer keep the panel at the MPP.Also, with respect to your other post:QuoteAre you saying that a PWM charger does not have a normal switching circuit with an inductor, that it just switches the current on and off? My understanding was that a PWM circuit does have a normal buck circuit, but the duty cycle is controlled by the output voltage or current rather than by the input. @KerimF may be thinking of PWM the way I am, which would mean he and I are referring to a different type of circuit than you are when we refer to a PWM charger. I've never actually used either type of charger, so I may just have it wrong.

author: globoy
author_rank: Frequent Contributor
timestamp: February 07, 2025, 05:34:30 pm
content: Quote from: Peabody on February 07, 2025, 03:55:13 pmI don't know about other systems, but with mine during times the battery will absorb all amps thrown its way and we can regulate the panel voltage using MPPT. When the battery doesn't want those amps or is at a charge threshold we want to keep then I regulate to the desired battery voltage and don't have to worry about MPPT (the system will automatically go back to MPPT if the power falls off enough that the battery wants more current - indicated by the fact that its voltage droops).Quote from: Peabody on February 07, 2025, 03:55:13 pmThe PWM chargers I know about do not implement a buck converter. They are essentially a chopper with averaged current and voltage reading. They collapse the panel voltage whenever the switch is closed. They were designed before MPPT was developed but were an improvement on simply connecting the panel to the battery (at least in my world of 12V battery charging).I dunno if this is true or not but maybe the term PWM is confusing. Both the PWM charger I'm referring to and a SMPS-based MPPT charger use PWM to control the switching element.

author: eTobey
author_rank: Super Contributor
timestamp: February 07, 2025, 09:35:26 pm
content: I think i have now a good explanation:"The MPPT charger is simply converting the voltage of the panel to the battery voltage, and thus increasing the current."Look at the picture in this link:https://www.solarpowermanufacturer.com/de/FAQ/mppt-solar-charge-controller.htmlThis is just like my example:Quote from: eTobey on February 06, 2025, 08:04:53 amThere are also boost chargers, that could charge a battery with higher voltage.

author: Peabody
author_rank: Super Contributor
timestamp: February 07, 2025, 10:06:09 pm
content: Quote from: globoy on February 07, 2025, 05:34:30 pmIt looks like I was wrong about PWM chargers using a regular buck circuit with an inductor. At least Julian Ilett says I'm wrong. His six-part series just does the switching, like you described. Well then we have yet another type of charger - the KerimF charger. Speaking of which, if it really is able to adjust the duty cycle to maximize charging current, it's hard to see the circumstance under which MPPT would be better.

author: lakis70
author_rank: Contributor
timestamp: February 07, 2025, 10:11:39 pm
content: Can someone enlight why voltage monitoring isnt proper way?Datasheet saysOpen Circuit Voltage (Voc) 45.6VShort Circuit Current (Isc) 9.45VOpt. Operating Voltage (Vmp) 37.2VOpt. Operating Current (Imp) 8.88ASo monitoring voltage and regulate current for no voltage drop from 37.2V isnt proper? e.g. the cloudy hours it will give only 1A, other hours gives the most it can if it was wanted.

author: Peabody
author_rank: Super Contributor
timestamp: February 07, 2025, 10:20:53 pm
content: It will only be 37.2V at the MPP at the standard insolation level assumed in the specs. Every other level will have a different (lower) voltage at its MPP. However, the voltage doesn't vary a lot with insolation, so there are a number of "MPPT" chargers that do use voltage. The results are not quite as good as P&O, but the difference isn't great, and it's easier to just sense the voltage. Sometimes it's a fixed voltage, and sometimes it's a percentage of the open circuit voltage at the current sun brightness.

author: lakis70
author_rank: Contributor
timestamp: February 07, 2025, 10:31:47 pm
content: Quote from: Peabody on February 07, 2025, 10:20:53 pmi haven't do experiments with my panels, but i thought the same.Another thought if someone put a constant voltage mppt controller only, to power the simple pwn charger

author: eTobey
author_rank: Super Contributor
timestamp: February 08, 2025, 11:02:50 am
content: Quote from: lakis70 on February 07, 2025, 10:11:39 pmI believe, you can go with a fixed percentage of the actual Voc that is measured. It may however not be at the exact maximum power point.Quote from: KerimF on February 08, 2025, 06:48:46 amI can not find such thing as MCCT topology. Have you got some links?

author: lakis70
author_rank: Contributor
timestamp: February 08, 2025, 09:37:39 pm
content: Peabody look microchip AN1521A they have the circuit and software for pic.

author: Peabody
author_rank: Super Contributor
timestamp: February 08, 2025, 10:53:08 pm
content: Thanks. I'll have to look through the app note, but at first sight, the circuit is not typical. They call it an inverse SEPIC. Right.

author: eTobey
author_rank: Super Contributor
timestamp: February 09, 2025, 07:38:03 am
content: Quote from: KerimF on February 08, 2025, 02:19:54 pmYou described "The" ... "topology"."The" usually describes an entity, that exists, or is well nown (topology). You should have said like "A (imaginary) MCCT topology". You got me confused there.

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: February 09, 2025, 11:47:12 am
content: maybe you guys get your defintions of "regulator topology" vs. "control strategy" straight before discussing them.just saying.

author: TheoB
author_rank: Regular Contributor
timestamp: February 09, 2025, 06:56:07 pm
content: The goal of MPPT is to maximize power. Not Voltage or current. Finding the maximum is straightforward. Short the panel and you have the maximum current. The maximum power you get when you draw 95% of this current from the panel/string. And this is the global maximum, not the local maximum. Nearly every panel has three sections that can each be bypassed if the section is hit by shadow.This is a simulation of a string of 8 panels and thus 24 sections that can be bypassed:The top chart shows no shadow and full sunlight, 10A, 3kW. The middle chart shows two optima the tracker can find. Simple trackers will stick to the local maximum, the red arrow. A good tracker will (eventually) find the green arrow. The perturb and optimize method will not find the global optimum.The method of shorting the panel introduces a short time without any power delivered. That's why it's not done continuously but only a few times per hour. The P&O or differential power method is used to track change of insolation.If you want to build yourself a MPPT, and put the energy in a battery, then optimum power equals maximum current into the battery. You have to control the PWM of a buck converter starting at max. That means the panel is connected directly to the panel. This is very close to Isc. Now lower the duty cycle (of the PWM). The panel current stays constant but the battery current will increase. Stop when you find the maximum output current.And have fun

author: Peabody
author_rank: Super Contributor
timestamp: February 10, 2025, 06:11:41 pm
content: Doesn't this go back to @KerimF's idea? You have a buck converter, and the duty cycle is controlled by the charging current, presumably through a P&O algorithm that maximizes the voltage across a very tiny series resistor, with some ADC reading that voltage after it's been amplified. Or possibly using some current sensing chip.But the point is that this should work as well as, or possibly better than, MPPT. I guess it depends on whether the "optimum power point" is always the same as the "maximum power point". Well I guess we know they are not always the same. In your middle graph, going left from the local MPP reduces power, but increases current. And it's the current that matters.Anyway, I know things like MPPT are important to getting maximum efficiency for charging car batteries and solar paneled roof tops, but for small projects using something like a single 18650, a 5V panel and a linear charger come pretty close to MPPT performance, with much less complexity and cost.

author: TheoB
author_rank: Regular Contributor
timestamp: February 10, 2025, 07:41:46 pm
content: Quote from: Peabody on February 10, 2025, 06:11:41 pmNope it's not current but power that matters. The maximum power point also delivers the maximum power (and thus current) to the battery. You might not want that when your battery is full, but that a different story. You seem to forget that the current charging the battery is always larger than the panel current. At least when the output voltage is lower than the panel voltage.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 10, 2025, 07:53:49 pm
content: Quote from: Peabody on February 10, 2025, 06:11:41 pmThis is getting pretty philosophical, but for any sensible person, yes, maximum power is optimum - most of the time.Sometimes you have to limit power - for example, when the battery is getting full (or when feeding to grid is sanctioned), possibly all the way down to zero. In such case, zero power could be "optimum", for these external reasons, and non-zero power could, for example, cause a fire, quite non-optimum!Sure maximum power point tracking is more complex than not doing it, but that's what this thread is supposedly about. And the whole idea is to get as much power out of the cell(s) as possible. You can't do better than the best. But of course how you exactly implement the tracking does affect the result. As does conversion losses from the power conversion topology, which is again a different thing than control strategy, as Le_Bassiste points out.

author: Peabody
author_rank: Super Contributor
timestamp: February 11, 2025, 03:54:10 pm
content: Quote from: TheoB on February 10, 2025, 07:41:46 pmOk. But if charging current is maximized with the panel at its MPP, then it seems you should be able to set the duty cycle based on charging current instead of panel power. Is that right? It would have to be P&O, but if you were going to use that method anyway, then it seems measuring charging current would be simpler than measuring panel power.

author: eTobey
author_rank: Super Contributor
timestamp: February 11, 2025, 05:48:03 pm
content: Quote from: eTobey on February 07, 2025, 09:35:26 pmI just like to qoute myself again, since i think some people still have the wrong understanding:In a MPPT charger, the current of the panel does not go directly into the battery.

author: TheoB
author_rank: Regular Contributor
timestamp: February 11, 2025, 09:59:41 pm
content: To measure power, both the voltage and current needs to be known. At the panel side both need to be measured. At the output (battery or grid) the voltage can be assumed to be constant and only the current varies significantly.

author: KerimF
author_rank: Frequent Contributor
timestamp: February 12, 2025, 10:09:43 pm
content: I uploaded LTspice files (Solar88VChrg24V_02.zip) which simulate an example of what we may call Solar Maximum Charging Current, SMCC.In this example, the maximum charging current and the panel maximum power occur when the duty cycle is around 34%.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 13, 2025, 09:35:38 am
content: Quote from: TheoB on February 11, 2025, 09:59:41 pmThis is correct. Tomeasurepower, there is no way around measuring both current and voltage. But the aim of MPPT is not to measure and report power value, it is tomaximizepower. When the tracking cycle is short enough, battery voltage stays constant over the cycle, and power is directly proportional to current. Even if not, even the battery voltage is directly and monotonically (not inversely after some point, like on PV panel!) proportional to battery current. Therefore, maximizing battery current indeed maximizes battery power, which is what we are interested in. It achieves exactly the same result as measuring panel current and voltage, multiplying them, and tracking maximum of that.

author: Peabody
author_rank: Super Contributor
timestamp: February 13, 2025, 06:07:38 pm
content: So then why has the industry settled on measuring panel power to control the duty cycle instead of measuring battery current? (I'm speaking of the P&O algorithm here. I don't think there is an equivalent method on the battery side to just using panel voltage as an approximation of the MPP.)Looking at a lithium rechargeable, for example, you have to measure charging current for the CC phase, and battery voltage as well for the CV phase. So why have any sensors on the panel at all?

author: TheoB
author_rank: Regular Contributor
timestamp: February 14, 2025, 08:19:22 am
content: All four wires go to a controller. For me there is no way to tell how a black box implements a charge controller with MPPT. Measuring points is a no brainer especially voltage.I think panel voltage is always measured as that will tell if there is any light at all. Don't try to regulate in the middle of the night for example. This thread is about someone wanting to implement a MPPT for sake of learning. That does not need to be state of the art and does not need to optimize speed of tracking (fast shadows due to clouds) or trying to find the global optimum. What is important is to understand that power out to the battery is about power in from the panel. Any difference need to be spend on cooling. Even for a hobby project efficiency becomes an issue quickly. There is no alternative for a buck converter as PWM alone without buck converter does not track the maximum power point. It just limits the overall power.

author: globoy
author_rank: Frequent Contributor
timestamp: February 14, 2025, 04:33:40 pm
content: Quote from: Peabody on February 13, 2025, 06:07:38 pmThis doesn't work because panel voltage at MPPT depends on other factors such as light level and temperature and will vary for a particular panel.Quote from: Peabody on February 13, 2025, 06:07:38 pmAs TheoB said there are other reasons to know panel voltage as well in a real device.But I am intrigued by the idea of using just the buck output current to see if one could regulate to MPP and one of my chargers is the perfect software-defined charger platform to play with this. Maybe if I get some time I'll see how this works.

author: Peabody
author_rank: Super Contributor
timestamp: February 14, 2025, 06:44:00 pm
content: Quote from: globoy on February 14, 2025, 04:33:40 pmBut for a given panel, it doesn't vary much over a wide brightness range. Which is why there are a number of "MPP" chargers that use this method. It's cheating, but it works pretty well, and it's pretty simple to sense voltage. And the voltage is usually set by an external divider, which lets you adjust for the particular panel. But temperature might be more of a problem.QuoteIf you find the time, that would be great.

author: TheoB
author_rank: Regular Contributor
timestamp: February 15, 2025, 08:26:15 am
content: If you really want to only use the panel voltage, then you can use the same trick as with the current, measure at zero load. Zero load (Open voltage) depends on temperature and insolation. Once that is measured load the panel up to 90-95% of that voltage and you have a rough estimate of the MPP. Repeat this every now and then as temperature and light conditions will vary. Although voltage does not vary as much as current as a function of insolation, so this method is even simpler compared to the method of shorting the panel to measure Isc. Drawback is that it will never find the real MPP as you will find when shorting the panel. So if you don't bother about partial shading, go for the voltage mode.