# How can I design a boost converter for a maximum power point tracking problem in a stand alone solar PV system?

Boost converter (or any dc-dc converter) connects PV array with load. MPPT algorithm modifies the duty ratio (of this converter) such that PV array is operated at voltage (or current) corresponding to maximum power point.

Normally, in applications other than Solar PV, input to boost converter is a constant dc voltage source. In such circuits duty ratio is calculated based on the amplification required and circuit parameters (R,L) are found based on allowable ripple. However in the case of photovoltaic applications the input is a PV array which is a non linear dependent current source.

Edit: What I mean by "How can I design" is how to calculate the design values (capacitance, inductance, duty cycle, etc. ).

When calculating for these values previously, I had a single input and output voltages in mind. I would use them to start off by solving for duty cycle, using Vout = Vin / (1-D), and move on from there with other boost design formulas. With PV input, there is no single Vin to calculate for Duty cycle, which I use for the other boost design formulas.

I have seen completed simulation circuits of boost converters with pv input, but they do not specify how duty cycle, inductor value, capacitor value etc. were calculated.

• Ripple will be worst at maximum power. Maximum power point tracking only makes sense when the load can make use of the power. This seems to mostly be during battery charging or grid tie. Perhaps there could be other cases, such as a variable speed pump that speeds up when more power is available. – mkeith Sep 25 '17 at 0:50
• Do have a specific question, other than the very broad (rhetorical?) one in your title? If not, this will have to be closed. – Dave Tweed Sep 25 '17 at 1:18
• @DaveTweed Sorry, I edited my post to clear up what I meant. – user163944 Sep 25 '17 at 3:58
• The question is still far too broad. A similarly broad answer would be that for every parameter that spans a range of values, you need to consider what the "worst case" value is for the particular thing that you're trying to calculate. It's an iterative process, and you'll have to make compromises along the way. In the end, you'll have a set of component values and other decisions, and then you can back-calculate the exact ranges of input parameters that the circuit can handle. This is what "engineering" is all about. It's trivial when all of the input parameters are fixed. – Dave Tweed Sep 25 '17 at 11:18
• There will still be a range of input voltages that are acceptable. You don't have to accept MPPT voltage from 0 to 500V. So you have to decide on the range of input voltages you want to accept, then design to that as your specification. – mkeith Sep 26 '17 at 3:01

There are several methods of computing MPPT, when demand exceeds supply;

1. measure Power transfer and hunt for max by regulating output load
2. using a pulsed Voc or Isc or both and estimate based on the known characteristics of the PV to matching impedance of the Source with the switched regulator
3. choose a battery that is 70 to 82% of the PV Voc and use a simply non-linear matched impedance with a non-linear load regulator ( I give an explanation and example of a small PV using this here )
4. using fuzzy logic to adapt a regulator for maximum output power (SMPS or impedance matched) d) using photo cells to monitor constant cloud changes and use the mean V(PD) like Voc to obtain a Solarity Index or potential power to track a load impedance to maximize Vs * Is
5. Each of these methods may also use a buck or buck boost regulator by converting to a different DC output voltage.
6. It can also include a battery charger with different CC , CV and float parameters. But the MPPT must regulate the output current such that the input current is optimized to achieve Vmpt. This is always a matched impedance condition averaged over one cycle.

Realize both out impedance load and input impedance of these regulators affects the MPT and cannot be done simply with a voltage regulator without sacrificing some efficiency.

• If you are battery charging you only need to look at the current going into the battery and optimize that. For low power applications the benefit may be outweighed by the power consumption and (in)efficiency of the controller. – Kevin White Sep 25 '17 at 1:08
• you always must monitor input voltage. If you see my transistor regulator you see that both current and voltage is limited. – Tony Stewart Sunnyskyguy EE75 Sep 25 '17 at 1:32
• Stewart - not necessarily. If you hill climb just on the output current. The input voltage and current is constrained by the PV cell - limiting of either is not necessary. The output voltage is constrained by the battery. The only degree of freedom is the duty cycle of the PWM modulator to give a maximum in the battery current. – Kevin White Sep 25 '17 at 2:05
• what about CV, OVP? – Tony Stewart Sunnyskyguy EE75 Sep 25 '17 at 2:42
• Agreed to avoid overcharging you need to monitor battery voltage - but it's not required as part of the MPPT. – Kevin White Sep 25 '17 at 14:26