Welcome to my solar charge controller tutorials series.I have posted two version of my PWM charge controller.If you are new to this please refer my earlier tutorial for understanding the basics of charge controller.
This instructable will cover a project build for a Arduino based Solar MPPT charge controller.It has features like: LCD display,Led Indication,Wi Fi data logging and provision for charging different USB devices.It is equipped with various protections to protect the circuitry from abnormal condition.
The microcontroller used is in this controller is Arduino Nano. This design is suitable for a 50W solar panel to charge a commonly used 12V lead acid battery. You can also use other Arduino board like Pro Mini,Micro and UNO.
Now a days the most advance solar charge controller available in the market is Maximum Power Point Tracking (MPPT).The MPPT controller is more sophisticated and more expensive.It has several advantages over the earlier charge controller.It is 30 to 40 % more efficient at low temperature.But making a MPPT charge controller is little bit complex in compare to PWM charge controller.It require some basic knowledge of power electronics.
I put a lot of effort to make it simple, so that any one can understand it easily.If you are aware about the basics of MPPT charge controller then skip the first few steps.
The Maximum Power Point Tracker (MPPT) circuit is based around a synchronous buck converter circuit..It steps the higher solar panel voltage down to the charging voltage of the battery. The Arduino tries to maximize the watts input from the solar panel by controlling the duty cycle to keep the solar panel operating at its Maximum Power Point.
1.Based on MPPT algorithm
2. LED indication for the state of charge
3. 20×4 character LCD display for displaying voltages,current,power etc
4. Overvoltage / Lightning protection
5. Reverse power flow protection
6. Short Circuit and Over load protection
7. Wi Fi data logging
8.USB port for Charging Smart Phone /Gadgets
Electrical specifications :
1.Rated Voltage= 12V
2.Maximum current = 5A
3.Maximum load current =10A
4. In put Voltage = Solar panel with Open circuit voltage from 12 to 25V
5.Solar panel power = 50W
This project is consists of 40 steps.So for simplicity I divided the entire project in to small sections.Click on the link which you want to see.
I have spent a lot of time to make this charge controller project.If you like it ,please vote for me in all the competitions.It will be very helpful for me.Thank you in advance.
Step 1: PARTS AND TOOLS REQUIRED:
1. Arduino Nano ( eBay)
2.Current Sensor ( ACS712-5A )
3.Buck Converter ( LM2596 )
4.Wifi Module ( ESP8266 )
5. LCD display ( 20×4 I2C )
6 .MOSFETs ( 4x IRFZ44N )
7. MOSFET driver ( IR2104 )
8. 3.3V Linear regulator ( AMS 1117 )
9. Transistor ( 2N2222 )
11.TVS diode ( 2x P6KE36CA )
12.Resistors ( 3 x 200R ,3 x330R,1 x 1K, 2 x 10K, 2 x 20K, 2x 100k, 1x 470K )
13.Capacitors ( 4 x 0.1 uF, 3 x 10uF ,1 x100 uF ,1x 220uF)
14.Inductor ( 1x 33uH -5A )
15. LEDs ( 1 x Red ,1 x Yellow ,1 x Green )
17.Wires and Jumper wires ( Female -Female )
19. DIP Socket ( 8 pin )
20.Fuses ( 2 x 5A)
21. Fuse Holders (2 nos)
22. Push Switch ( 2 nos)
23.Rocker /Toggle Switch ( 1 no)
24.Female USB port ( 1no)
25. JST connector ( 2pin male -female )
28.Plastic Base and studs
TOOLS REQUIRED :
2. Glue Gun
8. Ruller and pencil
Step 2: Basics on MPPT charge controller
A solar panel will generate different voltages depending on the different parameters like :
1.The amount of sun light 2.The connected load 3.The temperature of the solar panel.
Throughout the day, as the weather changes, the voltage produced by the solar panel will be constantly varying. Now, for any given voltage, the solar panel will also produce a current (Amps). The amount of Amps that are produced for any given voltage is determined by a graph called an IV curve, which can be found on any solar panel’s specification sheet and typically looks like the figure-1 shown above.
In the above figure-2, the blue line shows a solar panel voltage of 30V corresponding to a Current of about 6.2A. The green line shows a Voltage of 35V corresponds to a current of 5A.
We know that Power = V x I
In the picture shown above as you move along the red curve above you will find one point where the Voltage multiplied by its corresponding Current is higher than anywhere else on the curve. This is called the solar panel’s Maximum Power Point (MPP).
What Is MPPT ?
MPPT stands for Maximum Power Point Tracking. MPPT charge controllers used for extracting maximum available power from PV module under certain conditions.In order to understand this in details we first need to look at the power curve characteristics of a solar panel.Look at the image shown above.I have downloaded this images from web to explain the MPPT. Till now we have seen that the maximum power point (MPP) of a solar panel lies at the knee of the current and voltage curve.
A 12V solar panel is not really a 12V panel at all.Its really a somewhere in between 12V and 21V panel depending on what load is connected to it and how bright the sunlight is.The panel has an internal resistance which changes dynamically with differing irradiance levels. Solar panels will only deliver their rated power at one specific voltage and load, and this voltage and load moves around as the sunlight intensity changes.
For example take a solar panel rated at 100 watts, 18V at 5.55 amps.
The 18 V at 5.5 amps means that the Solar panel wants to see a load of 18/5.5 = 3.24 ohms.
With any other load the panel will deliver less than 100 watts.So if a static load is connected directly to a panel and its resistance is higher or lower than the panels internal resistance at MPP, then the power drawn from the panel will be less than the maximum available.
Taking a simple example say we connected the above 100W panel directly to a 12V lead acid battery, the panel voltage would be dragged down near to the load voltage of the battery as the batteries resistance is lower than the panels, but the current stays the same at 5.55 amps.This happens because Solar Panels behave like current sources, so the current is determined by the available sunlight.
Now the power (P)= V x I = 12×5.55=66.6W. So the Solar panel is now behaving like a 66 watt panel.
This equates to a loss of 100W-66.6W = 34W ( 33.4%).
This is where MPPT comes into play. MPPT circuits can be based on various switch mode power supply (SMPS) topologies, they generally have a fixed frequency but varying duty cycle. The duty cycle is controlled via an algorithm so as to track the changing MPP.
Step 3: BUCK CONVERTER WORKING
A buck converter is basically a DC to DC converter. The main principle at work in a buck converter, is the tendency for an inductor to resist changes in current. A buck converter output voltage will always be lower or the same as the input voltage. A simplified schematic of a buck converter is shown in the above picture.
Working Principle :
When the MOSFET is ON
When the mosfets is ON, current flows through the inductor (L) in a clockwise direction into the load (R) and also charging the output capacitor (C). At this point the voltage on the cathode of the diode is positive, therefore the diode (D) is blocking any flow of current and is said to be reverse biased. The Initial current flow into the load from Vin is slow, as energy is stored in the inductor as it’s magnetic field increases. So during the ON state of the mosfet, energy is stored in the inductor.
When the MOSFET is OFF
When the mosfet is switched OFF, the voltage across the inductor is reversed. The inductors magnetic filed begins to collapse, this collapse releases the stored energy allowing current to flow from the inductor into the load. The diode now has a negative voltage on the cathode so becomes forward biased. Therefore the inductors discharge current flows in a clockwise direction through the load and back through the diode. Once the inductors energy has fallen below a certain threshold, the load voltage falls and the capacitor becomes the main source of current, ensuring the load is still supplied until the next switching cycle begins. To ensure continuous conduction mode the inductor is must not be fully discharged before the mosfet is switch on again, and the cycle repeats.
What is Synchronous Buck Converter ?
The synchronous design simply replaces the diode with a second mosfet, this eliminates the losses incurred by the forward voltage drop across the diode, thus making the circuit more efficient. This is slightly more complex to implement, as the second mosfet switching needs to be carefully timed with the switching of the first mosfet. It is essential to ensure that both are never on at the same time, or the current will have a direct path to ground, effectively causing a short circuit. The mosfet switching is effectively 180 degrees out of phase, with a short delay period between each transition referred to as a Dead-Band.
Step 4: BUCK CONVERTER DESIGN
The first step was to design the buck converter circuit, this is determined by the output parameters of the system and it’s load. It designed for a 50W solar panel, it was decided to aim for a 12 V output ( battery voltage)
When calculating a buck circuit the frequency of operation, inductor size and output capacitor size are important, as they determine the current and voltage ripple size. It is desirable to have as smaller current and voltage ripple as possible.
A general rule is the higher the frequency the smaller the size of the inductor and output capacitor, and a smaller inductor and capacitor size generally lowers the system cost. However higher PWM frequencies decrease the system efficiency due to switching losses in the mosfets, so a trade off has to be reached which meets the design constraints of the end system.
For this design a PWM frequency of 50kHz was chosen.
From the earlier discussion we have conclude that a buck converter is consist of
In the next few steps I will discuss how to choose these components.
Step 5: INDUCTOR CALCULATION
Calculating the inductor value is most critical in designing a buck converter. First, assume the converter is in continuous current mode( CCM), which is usually the case. CCM implies that the inductor does not fully discharge during the switch-off time. The following equations assume an ideal switch (zero on-resistance, infinite off-resistance and zero switching time) and an ideal diode.
We are designing for a 50W solar panel and 12V battery
Input voltage (Vin) =15V
Output Voltage (Vout)=12V
Output current (Iout) =50W/12V =4.16A = 4.2A (approx)
Switching Frequency (Fsw)=50 KHz
Duty Cycle (D) =Vout/Vin= 12/15 =0.8 or 80%
L= ( Vin-Vout ) x D x 1/Fsw x 1/ dI
Where dI is Ripple current
For a good design typical value of ripple current is in between 30 to 40 % of load current.
Let dI =35% of rated current
dI=35% of 4.2=0.35 x 4.2 =1.47A
So L= (15.0-12.0) x 0.8 x (1/50k) x (1/1.47) = 32.65uH =33uH (approx)
Inductor peak current =Iout+dI/2 = 4.2+(1.47/2) = 4.935A = 5A (approx)
So we have to buy or make a toroid inductor of 33uH and 5A.
You can also use a buck converter design calculator
So 33uH is enough for our design.
Step 6: HOW TO WIND A TOROIDAL INDUCTOR
I have collected a bunch of toroidal cores from old computer power supply.So I thought to made the inductor at my home.Though it took a lot of time to make,but I learned a lot and enjoyed during making.These are few tricks what I learned during the making,so that you can make it easily.
How to Wind the wire :
Winding by hand is very painful for skin as well as you can’t make the winding so tight.So I made a simple tool from popscile stick for winding the toroidal core.This simple tool is very handy and you can make perfect and tight winding.Before making the inductor you have to know the core specification and number of turns.
The important parameters of toroidal core are
1. Outer diameter(OD)
As I did not know the part number,I used a indirect method to identify it.First I measure the OD and ID of the unknown core by using my vernier caliper,it was around
OD= 23.9mm (.94′”) , ID= 14.2mm(.56″) ,H= 7.9mm( .31″) and yellow white in color.
I used a toroid core chart (page-8) to identify the unknown core.I have attached this toroid size chart in the bellow.It contains a lot of information for the inductor design.The PDF version is attached bellow.
Finding the part number :
I searched the Physical dimension table from the chart. From the table it was found that the core is T94
Finding the mix number :
The color of the core is indication for mix number.As my core is is yellow/white in color,it is confirmed that the mix number is 26
So the unknown core is T94-26
Finding Al value :
From the Al value table for a T94-26 core it is 590 in uH/100 turns.
After selecting the core now time to find out the number of turns required to obtain the desired inductance.
Number of turn (N) = 100 x sqrt( desired inductance in uH / Al in uH per 100 turns)
=> N= 100 sqrt(33/590) = 23.65 = approximately 24 turns
You can also use this online calculator for finding the number of turns.Only you have to know the part number and mix number.
Then I wind a 20 AWG copper wire (24 turns) around the the toroid core.At the both end of the winding leave some extra wire for connection lead.After this remove the enamel insulation from the lead. I used my leatherman file for removing the insulation. See the above picture for better understanding.
Note : Making a good inductor is not so simple.I am still in learning stage.If you are not so confident I will recommend to buy a ready made inductor.
Step 7: CAPACITOR CALCULATION
Output capacitance is required to minimize the voltage overshoot and ripple present at the output of a buck converter. Large overshoots are caused by insufficient output capacitance, and large voltage ripple is caused by insufficient capacitance as well as a high equivalent-series resistance (ESR) in the output capacitor. Thus, to meet the ripple specification for a buck converter circuit, you must include an output capacitor with ample capacitance and low ESR.
The out put capacitor ( Cout)= dI / (8 x Fsw x dV)
Where dV is ripple voltage
Let voltage ripple( dV ) = 20mV
Cout= 1.47/ (8 x 50000 x 0.02 ) = 183.75 uF
By taking some margin, I select 220uF electrolytic capacitor.
The equations used for calculation of inductor and capacitor is taken from a article LC Selection Guide for theDC-DC Synchronous Buck Converter
Step 8: MOSFET SELECTION
The vital component of a buck converter is MOSFET.Choosing a right MOSFET from the variety of it available in the market is quite challenging task.
These are few basic parameters for selecting right MOSFET.
1.Voltage Rating : Vds of MOSFET should be greater than 20% or more than the rated voltage.
2.Current Rating: Ids of MOSFET should be greater than 20% or more than the rated current.
3.ON Resistance (Rds on) : Select a MOSFET with low ON Resistance (Ron)
4.Conduction Loss : It depends on Rds(ON) and duty cycle.Keep the conduction loss minimum.
5.Switching Loss: Switching loss occurs during the transition phase.It depends on switching frequency,voltage ,current etc.Try to keep it minimum.
These are few links where you can get more information on selecting the right MOSFET.
In our design the maximum voltage is solar panel open circuit voltage(Voc) which is nearly 21 to 25V and maximum load current is 5A.
I have chosen IRFZ44N MOSFET. The Vds and Ids value have enough margin as well as it has low Rds(On) value.
You can check the other parameters of IRFZ44N from the data sheet
Step 9: MOSFET DRIVER
Why we need a gate driver ?
A Mosfet driver allows a low current digital output signal from a Microcontroller to drive the gate of a Mosfet. A 5 volt digital signal can switch a high voltage mosfet using the driver.A MOSFET has a gate capacitance that you need to charge so that the MOSFET can turn on and discharge it to switch off,the more current you can provide to the gate the faster you switching on/off the mosfet, that is why you use a driver.
Fore more details you can read about MOSFET Basics
For this design I am using a IR2104 Half Bridge driver. The IC takes the incoming PWM signal from the micro controller, and then drives two outputs for a High and a Low Side MOSFET.
How to use it ?
From the data sheet I have taken the image shown above.
First we have to provide power to the gate driver.It is give on Vcc (pin-1) and its value is in between 10-20V as per data sheet.
The high frequency PWM signal from Arduino goes to IN (pin-2) . The shut down control signal from the Arduino is connected on SD ( pin 3).
The 2 output PWM signals are generated from HI and LO pin. This gives the user the opportunity to fine tune the dead-band switching of the MOSFETs.
Charge Pump Circuit :
The capacitor connected between VB and VS along with the diode form the charge pump.This circuit doubles the input voltage so the high switch can be driven on. However this bootstrap circuit only works when the MOSFETs are switching.
The data sheet of IR2104 is attached here
Step 10: SCHEMATIC AND WORKING
The input power connector to the solar panels is the screw terminal JP1 and JP2 is the output screw terminal connector to the battery.The third connector JP3 is connection for the load.
F1 and F2 are the 5A safety fuses.
The buck converter is made up of the synchronous MOSFET switches Q2 and Q3 and the energy storage devices inductor L1 and capacitors C1 and C2 The inductor smooths the switching current and along with C2 it smooths the output voltage.Capacitor C8 and R6 are a snubber network,used to cut down on the ringing of the inductor voltage generated by the switching current in the inductor.
The third MOSFET Q1 is added to allow the system to block the battery power from flowing back into the solar panels at night.In my earlier charge controller,this is done by a diode in the power path. As all diodes have a voltage drop a MOSFET is much more efficient.Q1 turns on when Q2 is on from voltage through D1. R1 drains the voltage off the gate of Q1 so it turns off when Q2 turns off.
The diode D3 (UF4007) is an ultra fast diode that will start conducting current before Q3 turns on. It is supposed to make the converter more efficient.
The IC IR2104 is a half bridge MOSFET gate driver. It drives the high and the low side MOSFETs using the PWM signal from the arduino (Pin -D9) .The IR2104 can also be shut down with the control signal (low on pin -D8) from the Arduino on pin 3. D2 and C7 are part of the bootstrap circuit that generates the high side gate drive voltage for Q1 and Q2. The software keeps track of the PWM duty cycle and never allows 100% or always on. It caps the PWM duty cycle at 99.9% to keep the charge pump working.
There are two voltage divider circuits( R1,R2 and R3,R4) to measure the solar panel and battery voltages.The out put from the dividers are feeds the voltage signal to Analog pin-0 and Analog pin-2 .The ceramic capacitors C3 and C4 are used to remove high frequency spikes.
The mosfet Q4 is used to control the load.The driver for this mosfet is consists of a transistor and resistors R9 ,R10.
The diode D4 and D5 are TVS diodes used for over voltage protection from solar panel and load side.
The current sensor ACS712 sense the current from the solar panel and feeds to the Arduino analog pin-1.
The 3 LEDs are connected to the digital pins of the microcontroller and serve as an output interface to display the charging state.
Reset switch is helpful if the code gets stuck.
The back light switch is to control the back light of LCD dislay.
Step 11: Test the gate driver and MOSFETs Switching
Hey I think I have talked a lot on the theory.So lets do some practical.
As I have told earlier the heart of the MPPT charge controller is Buck Converter.As per me if your buck converter circuit work perfectly.You can do the rest thing easily.So first lets test the Mosfets switching and the driver.
Before soldering ,I request to do it on a bread board.I have blown lot of MOSFETs during my testing.So be careful during the connection.
Connect the everything as per schematic given above.Now you can omit the TVS diode,current sensor and voltage divider.
After connecting everything test the resistance between the input rail.It should be several KOhm. If you get resistance bellow 1K then recheck the circuit connection.
Upload the test sketch to the Arduino.The code in the form of text file is attached bellow.
Then connect the scope in between the source of Q1 and GND.
The result should be a PWM with frequency 50KHz.
The waveform obtained during my testing are shown above.
If everything goes right then proceed to complete the bulk converter circuit.( i.e adding inductor and capacitor)
Step 12: Test the Buck Converter
In the previous steps we have calculated the inductor and capacitor rating.Now it is time to using and testing it.
Add the 33uH inductor and 100uf input and 220uF out put electrolytic capacitor as per schematic.You can also use 0.1uF ceramic capacitors parallel with input and output capacitors.It will give better result.But it is not mandatory.
Then make the snubber circuit by using a 0.1uF ceramic capacitor and 200ohm resistor.
Again check the resistance in between the input rail.It should be order of K ohm.
Now give power to the input rail and Arduino.
Connect the probe of your scope in between the output capacitor.
The result is shown above .The out put should be a steady DC.
Vout = Duty Cycle x Vin
For example if i give 50% duty cycle to a 12 input supply, the output should be 6V in the scope.
After confirmed that everything working fine,now we can add the blocking mosfet Q1.It is used to block reverse power from battery to the solar panel during night.
Add the third mosfet Q3 as per schematic.Then place the 470k resistance and diode IN4148.
Again check the output it should be same.
At last put the scope in between the gate of Q1 and Gnd.
Do you know ? you have done the most critical part of this project.
Step 13: VOLTAGE MEASUREMENT
Voltage Measurement :
As you may well know, Arduino’s analog inputs can be used to measure DC voltage between 0 and 5V (when using the standard 5V analog reference voltage) and this range can be increased by using two resistors to create a voltage divider. The voltage divider decreases the voltage being measured to within the range of the Arduino analog inputs. We can use this to measure the solar panel and battery voltages.
For a voltage divider circuit
Vout = R2/(R1+R2) x Vin
Vin = (R1+R2)/R2 x Vout
The analogRead() function reads the voltage and converts it to a number between 0 and 1023
Example code :
// read the input on analog pin 0 ( You can use any pin from A0 to A5)
int Value = analogRead(A0);
The bove code gives an ADC value in between 0 to 1023
We’re going to read output value with one of the analog inputs of Arduino and its analogRead() function. That function outputs a value between 0 (0V in input) and 1023 (5V in input)
that is 0,0049V for each increment (As 5/1024 = 0.0049V)
Vin = Vout*(R1+R2)/R2 ; R1=100k and R2=20k
Vin= ADC count*0.0049*(120/20) Volt // Highlighted part is Scale factor
Note : This leads us to believe that a reading of 1023 corresponds to an input voltage of exactly 5.000 volts.
In practical you may not get 5V always from the arduino pin 5V .So during calibration first measure the voltage between the 5v and GND pins of arduino by using a multimeter,and use
1ADC = measured voltage/1024 instead of 5/1024
Check your voltage sensor by a test code attached bellow
Step 14: CURRENT MEASUREMENT
For current measurement I used a Hall Effect current sensor ACS 712 (5A).
The ACS712 sensor read the current value and convert it into a relevant voltage value, The value that links the two measurements is sensitivity.You can find it on the datasheet.
As per data sheet for a ACS 712 (5A) model :
1. Sensitivity is 185mV/A.
2. The sensor can measure positive and negative currents (range -5A…5A),
3. Power supply is 5V
4. Middle sensing voltage is 2.5V when no current.
Value = (5/1024)*analog read value
// If you are not getting 5V from arduino 5V pin then, value = ( Vmeasured/1024 ) * analog read value
// Vmeasured is the voltage in between Arduino pin 5V and GND. You can measure it by a multimeter.
But as per data sheets offset is 2.5V (When current zero you will get 2.5V from the sensor’s output)
Current in amp = (value-2.5)/0.185
Test it by a sample code for ACS712 attached bellow.
For more detail: ARDUINO MPPT SOLAR CHARGE CONTROLLER ( Version-3.0)