Solar Energy Smart Hybrid Inverter

In this article we are going to discuss that how to design Smart Hybrid Inverter Using Solar Energy.The main idea, is to propose a design for an uninterrupted power supply (UPS) to drive the load using non-conventional energy source i.e Sunlight and AC power coming from the grid using a hybrid mechanism so that the system is not entirely dependent on just one source.

Solar Based Smart Hybrid Inverter.

In Smart Hybrid Inverter First of all we design a solar charge controller which would regulate the upcoming charge (voltage) from solar panels to 14 volt using a microcontroller. 220v AC from the Grid is step down to 12 volt and is rectified to 15v DC using bridge diodes and LM7015 ICs. A 12 volt battery is put so as to store the charge from both the sources and is used to feed the inverter when there is cut-off power. At the end, an inverter converts DC-AC via an assembly of H-bridge.

Uninterruptable Power Supply production is the most important power problem faced by many industries and utilities in the current era where almost every equipment/machine requires power to function. So, our task is not to run load by solar energy but also store this energy when there is no sunlight or energy from grid.

Basic topology of a smart hybrid inverter system

We will divide our project of Smart Hybrid Inverter into two parts. In the first part, we will discuss the Designing of buck converter to produce constant voltage output, from varying input coming from PV panels, to charge the battery. In the second part, we will discuss the Designing of Inverter which produces constant AC Supply to drive the Load.

Components Description

Components needed for the project are as follows,

  • PIC 18f452
  • 8051 microcontroller
  • Gate drivers (IRF2112)
  • MOSFET(2N222, IRF610)
  • LM7015
  • 555 Timer
  • Inductor.
  • Capacitor.

Complete Circuit Diagrams of Smart Hybrid Inverter

Complete project schematic for solar energy based Smart Hybrid Inverter

Hardware Setup

To explain the hardware part of Smart Hybrid Inverter, I am going to break the project into two parts so that it will be easier to understand. Let’s start with the Designing of Buck Converter which will charge the battery using input from PV Panels or AC grid using Hybrid Technique.

Hardware Setup of solar based Smart Hybrid Inverter (final year project)

Designing of Buck Converter:

Buck converter is designed to step down 25V (which is the average output) to 14.2V which is required for battery charging. For this purpose, inductor, capacitor and feedback for buck converter should also be designed accordingly. The control unit for the converter used is PIC18f452. Initially, 10% duty cycle PWM with switching frequency 20kHz is fed into the switch. At the output, a feedback is fed back in the micro-controller which checks if it is equal to required. It changes the duty cycle according to the output. The Diode used in Buck converter is IN5822 having average rectified current of 3A and Max reverse voltage of 30V.

For complete calculations and details on ferrite core inductor design, you can read this article.

buck converter in Smart Hybrid Inverter for solar and grid

Designing of Inductor:

Toroid type inductor is used because it is cost effective, smaller in size and easy to design. The idea behind the use of ferrite core in inductor was that it is most suitable when subjected to high frequency i-e 20Khz because of its negligible losses.

No of turns were calculated as follows:

$L \approx 0.01257 N^2 (R- \sqrt{R^2 – a^2}) \mu \; H$

Where L=68uH, a=2.5mm, R=12mm. Substituting these values, N came out to be 27(approximately)

Designing of Capacitor:

The Purpose of Capacitor in Buck Circuitry is to filter the ripple current of Inductor so as to minimize ripple present at the output of Buck Converter. The output capacitor should be large enough to absorb stored inductor energy so as to prevent output voltage from overshooting above the specified maximum output voltage. The formula for value calculation is below:

$$C_c =\frac{1-k}{16Lf^2}$$

Where L should be greater than critical inductance. Putting the values in above equation, $C_c=1.01\mu \;F$.

Battery Charging

The output of the PV panel when passed through buck converter is maintained at the constant level of 14 Volts. This constant Voltage is then fed into the Battery to charge it. The specifications of the battery are:
Battery ratings: 12V, 25Ah.
This battery would then serve as a source to the inverter.

Designing of Inverter

The Second Part of project comprises of Inverter, Rectifier and Transformer Designing. There are variety of inverter topologies that could be used but the one I selected is H-Bridge.In a Full H-Bridge, the alternate output voltage is obtained by the difference between two branches of switching cells. To maximize the fundamental component of the output voltage, the fundamental component of the voltage on each branch must be 180º out of phase. The semiconductors of each branch are complementary in performance, which is to say when one is conducting the other is cut-off and vice versa. Therefore, The main components of Inverter with their values are below.

  • IRFz44 MOSFET – max current rating (continuous Drain-Source) of 50A and Drain to source voltage limit of 60V
  • MOSFETs Gate Resistance – R=10 Ohms
  • HCPL-3120Gate Driver – having maximum peak output current of 2.5A
Smart Hybrid Inverter

Designing of Rectifier for Smart Hybrid Inverter:

An electrical device which converts an alternating current into a direct one by allowing the current to flow through it in one direction only. In this project, after 1st H-bridge, a high frequency transformer steps up the voltage to 60V and rectifier make this into 60V DC. Which goes to input of the 2nd H-bridge. Hence, the diodes used in rectifier are Rg 416 which has rating of 120V and 5A max forward current.

Rectifier circuit for Inverter

Designing of Transformer:

The core purpose of transformer in Smart Hybrid Inverter is to step up the voltage. As the switching frequency of the 1st H-bridge is 20kHz, that’s why ferrite core is used. The Core used is ETD34. The calculation is below.

$$N_P = \frac{V_{in}\times 10^8}{4f_s \; B_{max} \; A}$$
$V_{in}=12V \\
f_s = 20\;kHz \\
B_{max} \approx 1500 \\ A= 0.97 \\
N_P = 10.3 \;turns $
in order to get 10 turns. Therefore,

$N_s = \frac{V_s}{V_P} \times N_P$
Where, $V_s =60 V \; V_P= 12 V $ and $N_P = 10$. Hence, $N_s =50$

Hence, we will use 2 parallel wires of 19 AWG for primary winding.
and
22 AWG for secondary winding.

You can read Detailed designing calculation and hardware construction of transformer here.

Coding Part:

Here is complete arduino code for smart hybrid inverter. this is for educational purposes only and for understanding basics. by learning you can explore new worlds by yourself

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