Grid tie inverter

One of the many challenges that the modern world is facing is the mounting energy requirements. Pakistan as well faces an energy crisis which is hindering its industrial and economic growth. Short fall of power is becoming one of the biggest threats to the prosperity of Pakistan. The use of generato

Project Title

Grid tie inverter

Project Area of Specialization

Electrical/Electronic Engineering

Project Summary

One of the many challenges that the modern world is facing is the mounting energy requirements. Pakistan as well faces an energy crisis which is hindering its industrial and economic growth. Short fall of power is becoming one of the biggest threats to the prosperity of Pakistan. The use of generators is increasing our fuel consumption and UPS systems are putting unnecessary load on national power systems.

The alternative solution is an MPPT controlled Solar Grid Tied Inverter. The solar array output voltage is first fed to a DC-DC converter. Maximum power point tracking (MPPT) is implemented which ensures the maximum power output from the solar array. The subsequent DC voltage is produced and then used for the DC-AC conversion. Afterwards, the AC voltage is stepped up, using a step-up transformer, to the grid voltage level. The phase and frequency of the produced voltage is synchronized with that of the grid. There is a switch which controls whether to put the produced energy into the grid or just use it for the household requirements as a standalone system.

Pakistan meets most of its electrical power needs from variety of sources like hydel, thermal and nuclear energy. In this scenario, the solution is to implement an MPPT controlled Solar Grid Tied Inverter as it fulfills our electrical needs in a reliable and environment friendly way. Solar power does not require any fuel and is environment friendly. Baluchistan and North-Eastern parts of Sindh have been identified as the most suitable places for solar harvesting with sunshine of 2300-2700h per annum.

           

Project Objectives

With the current prevailing energy crisis, the world is moving towards the renewable energy sources as they are cheaper and have no negative environmental impact. The one of the best possible solution to this problem is the grid tied inverter.

Our main objective is to reduce energy crisis by converting solar energy into electrical energy which can be then used for the household use and the exceeding amount of energy can be sent into the grid which can cause low electricity bills.

If we decompose this project into smaller components we can get the following sub stages. We can achieve our final objectives by implementing these stages:

• Dc-Dc stage (Boost converter)  
• Dc-Ac stage (Inverter)
• Grid connecting stage(PLL etc.)

In the first stage, we aim to convert solar energy into electrical energy by means of solar cells. In order to get max energy from the solar panel we use the MPPT algorithm then we boost the low Dc voltages to high Dc voltages by implementing the boost converter.

In the second stage, we aim to convert the high dc voltages to ac voltages by means of implementing a dc to ac inverter after this by applying appropriate filters we can get the desired output voltage waveform will then supply power to the load.

After completing the two stages we will then connect these two power stages to the utility grid. We aim to make the inverter bidirectional which may be able to send and receive power from the utility grid according to the requirements. For this purpose, we will be using the concept of Phase Locked Loop (PLL).

PLL is implemented in order to match the phase of our generated ac signal and the phase of the grid. For this purpose we use the sensing transformer and the PI controller which will be used to increase or decrease the phase of our generated ac signal until it is fully matched to the signal of the grid.

Our final objective is to successfully integrate all these components and test their working at the optimum conditions. After we develop this prototype in the desired frame of time, we wish to commercialize this product so that the energy crisis of our country can be reduced. 

Project Implementation Method

The methodology for implementation of our final year project is based on two power stages named as, interleaved isolated DC-DC converter stage and mixed frequency DC-AC converter stage. The controlled section of the entire system is on microcontroller STM32F103C8T6 that ensure the Maximum Power Point Tracking (MPPT) of the input and controlled active and reactive power of the output.

In the first power stage we use interleaved transistors topology that are connected with the high frequency transformer. The output of the transformer is connected with two rectifier diodes and two capacitors (commonly known as voltage doubler topology circuit).

 The second power stage DC-AC stage is implemented as a full bridge inverter which is characterized as high frequency leg and low frequency leg. The high frequency leg is synchronized with sinusoidal PWM and the low frequency leg with grid frequency.

Finally, for grid synchronization Hall effect current sensors are used to sense the current of inverter and voltage transformer for voltage sensing. These voltages and current are feed into microcontroller STM32f103C8T6 for Phase Locked Loop programming.

Benefits of the Project

Following are the benefits of using a Grid-Tie Inverter:

1) Production of clean electricity from renewable energy sources(solar) & also cheaper as compared to electricity produced from petroleum products.

2) Another important benefit of Grid-Tie Inverter is that it can energize the national grid, when excess electricity is produced.

3) Electricity bills will be reduced as most of the energy can be drawn from solar cells.

4) The efficiency of Solar Grid-Tie Inverters is higher than off-grid inverters, and they are also easy to    install as they don’t require batteries.

5) These can be used as an alternative of UPS in our homes.

Following are the benefits of using a Grid-Tie Inverter:

1) Production of clean electricity from renewable energy sources(solar) & also cheaper as compared to electricity produced from petroleum products.

2) Another important benefit of Grid-Tie Inverter is that it can energize the national grid, when excess electricity is produced.

3) Electricity bills will be reduced as most of the energy can be drawn from solar cells.

4) The efficiency of Solar Grid-Tie Inverters is higher than off-grid inverters, and they are also easy to    install as they don’t require batteries.

5) These can be used as an alternative of UPS in our homes.

Technical Details of Final Deliverable

Following are the technical details:

1. Solar panel is used as an input source which is of 250W and provides an input voltage of 18 to 55V.
    
2. Switching frequency of interleaved boost converter (DC-DC Converter) is 35kHz and is controlled using STM32F103C8T6 micro-controller.
    
3. DC-DC stage has an output voltage of 380V which is used as an input for the DC-AC stage(inverter).
    
4. The DC-AC stage converts 380V DC voltage into an output 220V AC (rms) voltage.
    
5. The switching frequency of DC-AC stage is controlled using a sinusoidal PWM, with frequency of 17.4kHz.
    
6. A first order filter made using capacitors and resistors is used to filter the output from DC-AC stage, to produce a pure sinusoidal wave.
    
7. Relay circuit has also been used to protect the system from short circuit and electrical fluctuations.

Final Deliverable of the Project

Hardware System

Core Industry

Energy

Other Industries

Core Technology

Others

Other Technologies

Sustainable Development Goals

Affordable and Clean Energy

Required Resources

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