GA tuned PI controller for grid synchronization using MLI

Renewable energy provides a reliable source of electricity and fuel efficiency and also reduces the demand of imported fuels. Grid operated inverters are used to connect renewable energy sources (RES) to the grid. Although these types of inverters were having many difficulties in beginning due to th

Project Title

GA tuned PI controller for grid synchronization using MLI

Project Area of Specialization

Electrical/Electronic Engineering

Project Summary

Renewable energy provides a reliable source of electricity and fuel efficiency and also reduces the demand of imported fuels. Grid operated inverters are used to connect renewable energy sources (RES) to the grid. Although these types of inverters were having many difficulties in beginning due to their control techniques and its difficulty. Studies on grid-based inverters are increasing rapidly and with the results of the development of power electronics equipment these inverters are widely used in many applications. RES is now used to generate photovoltaic (PV), wind energy, hydro and tidal energy etc. Interfacing these inverters with grid lead to many complications such and voltage and frequency fluctuations which compromise the overall reliability of the powersystem. RES uses different type of inverters for grid interference and the popular among them are Multilevel inverters (MLI). Grid connected RES of MLI is complex due to its composite design so a conventional controller led to total harmonic distortion (THD) which is the difference between original and applied voltage. Voltage fluctuation in MLI may lead to the load variation which results in the increase in current and rapid increase in current will rise the temperature. So, the voltage of both grid and inverter should be in the specified range so RES may easily be transmitted and distributed in the national grid. PI and PID controllers are used for the grid interference of multilevel converters (MMC). But the gains of the PI controller cannot be fixed due variable response of the power system. The modulation techniques in multilevel inverters are commonly classified according to their switching frequency range. There is a restraint to use high-frequency modulations techniques in medium voltage range as the switching losses will reduce the inverter rating and its overall efficiency. The typical level PWM (SPWM) modulation technique is commonly adopted in industrial applications as the distortions on the produced waveform are less.n this research PI controller with continuously changing gains for grid interference of MLI will be implemented along with the hybrid modulation technique of PWM (pulse width modulation) to control the switching of the MLI in order to have less switching losses. Furthermore, the total harmonic distortion (THD) will be analyzed to meet the international standard for grid interference.

Project Objectives

1) The new MLI topology will be designed with the aim of having less electrical components and greater efficiency.

2) The hybrid modulation techniques will be applied to the MLI to decrease the switching losses and THD of the inverter in order to increase the overall reliability of the power system.

3) The  Genetic algorithm (GA) tuned PI controller whose gains will change continuously according to the system requirement will be designed.

Project Implementation Method

First and foremost the proposed inverter model consists of 6 switches and two DC supplies which will give us 7 levels at the output.The beauty of this proposed solution is that by increasing only one cell (2 switches and one battery), the increase in number of level of proposed multi-level inverter output increases tremendously as compared to cascaded multi-level inverter.

                                                                                                        

For one voltage level we will have one form of switching configuration and for second level we will have to set the second form of switching configuration. Table below shows the all the switching configurations for the proposed seven level inverter. The switches S1’, S2’ and S3’ are just the complement of the switches S1, S2 and S3 respectively.

                                                                                           Switching Configuration of proposed 7 level inverter for the half cycle (180°)

                                                                                               
We have proposed hybrid of Selective Harmonic Elimination Pulse Width Modulation (SHEPWM) and Selective Harmonic mitigation Pulse Width Modulation (SHMPWM). In this technique we have used both elimination and mitigation for the harmonic control of multi-level inverter. Some of the lower order harmonic are completely eliminated with  Selective Harmonic Elimination PWM and some are mitigated as per the IEEE mitigation standards using Selective Harmonic mitigation PWM, with the constraint that Total Harmonic Distortion (THD) is minimum and the fundamental amplitude is maximum. This becomes an optimization problem in which we have to find the optimal switching angles to maintain the Total Harmonic Distortion (THD) minimum and the Fundamental amplitude maximum.To impose this technique we will first find harmonic equation or more accurately define its objective function to find optimal angles by Genectic Algorithm. All this will be done on Arduino board or by means of micro controller.

Genetic algorithm, sometimes called revolutionary algorithm. It is not an intelligent and smart algorithm, but it response to the changes very fast. GA preffered over other gradient methods because they get stuck in local minima, while GA finds out the maxima’s.

The steps for parameter tuning of PI controller using the proposed GA can be summarized as follows:

Step 1: Create a population with the size of M chromosomes, in which the chromosomes [Kp KI] are randomly generated from ?.

Step 2: Evaluate the value of ITAE in (2) for each chromosome in the population.

Step 3: If the pre-specified number of generations G is reached or there is a chromosome in the population with ITAE value less than e, then stop.

Step 4: Carry out operations of reproduction, multiple crossover in (4), and mutation in (5). If the resulting chromosome during operations is outside the ?, then the original one is retained.

                                                                  

Project Block Diagram:

                                                                           

Benefits of the Project

The existing powersystem needsto be more reliable and efficient. A fault may occur in power system equipment such as motors and protective devices. The technology of high voltage direct current (HVDC) transmission based on Multilevel converter (MMC) draws many concerns. Due to its special structure, MMC presents different performance compared with conventional voltage source converters(VSC). MMC is used to eliminate harmonics and make the output more suitable to the desired level of output. Grid interference of renewable resources the power system faces various power quality problems such as sag, swell, unbalance current, voltage flicker and frequency deviation. The issue of voltage mismatch and to make a flexible and effective renewable power production ,the PI controller is used for synchronization. It offers excellent steady state error elimination, it is commonly connected with grid but due to its fixed gains it causes high settling time and maximum overshoot. To overcome these issues a continuous change in gains is required so that with system variation the overall operation of power system is not affected. In this research a PI controller with continuous changing gains will be implemented along with the hybrid modulation technique to reduce the switching losses of inverter along with the speedy response. And increase the overall efficiency of the power system.

Technical Details of Final Deliverable

1) The proposed inverter model is cost effective as opposed to other MLI and gives as many levels as we want.

                                                                                       

2) We shall imply hybrid modulation technique to bring Total Harmonic Distrotion down to only 5% according to IEEE strandards for good switchong inverter.

3) PI controller and inverter switching angles will be genetically optimized to avoid swelling, lagging and fluctuations in grid synchronization.

Final Deliverable of the Project

HW/SW integrated system

Core Industry

Energy

Other Industries

Others

Core Technology

Others

Other Technologies

Artificial Intelligence(AI)

Sustainable Development Goals

Affordable and Clean Energy, Responsible Consumption and Production

Required Resources

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