Application of a high efficient voltage regulation system with MPPT algorithm

https://doi.org/10.1016/j.ijepes.2012.08.011Get rights and content

Abstract

In this study, an integrated voltage regulation system including Maximum Power Point Tracking Algorithm (MPPT) is introduced to store and efficient use of the energy produced by renewable sources. A dsPIC is used as the main controller to obtain a rapid and stable decision-making system and to decrease the cycle time of the MPPT operation. In order to minimize the oscillations on the output voltage, a cuk converter is used that can be operated as both buck and boost modes. Thus, efficiency of the system has been increased considerably by storing the energy consistently. The experimental results validates that the system developed operates highly stable and is faster than the similar ones presented in recent literature.

Highlights

► We designed a powerful voltage regulation system with MPPT application. ► We used dsPIC as the main controller and cuk converters to store the produced energy continuously. ► The system has very short response time against instant changes of input parameters. ► The system operates highly stable and faster.

Introduction

Efficient use of the energy is an important issue in these days as a result of increasing daily demand for energy and the consumption of energy sources. Therefore, renewable energy sources such as wind energy and solar energy have gained popularity nowadays. Storing the energy produced by renewable sources is as important as producing it. Although the efficiency of the solar power has been increased up to 46% in laboratory conditions [1], it is less than 30% for the most solar systems installed and used in current industrial applications. On the other hand, storing and using the energy produced by wind turbines is more difficult than the solar systems because the mechanical speed of the turbine may alter in a short time, and thereby voltage on the output side of the generator is usually unbalanced. This is a serious issue for loads and batteries because of causing such problems as the generator overloading, harmonics and unstable system forms. Therefore, designing of a high-speed voltage control unit for the output of the system is an indispensable requirement. In conclusion, since natural behavior of main energy source is quite stable in solar energy systems, the output voltage of the system is also very stable; however, especially in wind energy systems, the output voltage has instant oscillations because the natural behaviors of wind may alter momentarily. Therefore, it is an indispensable requirement that designing a quite rapid voltage regulation system for renewable energy systems like wind energy [2], [3], [4], [5].

In most energy systems, converters are used for regulating the output voltage; thus, the stability of the converter is an important factor to improve the energy efficiency. If any power system uses either only buck or only boost converters, the energy produced can be stored only in certain levels. For this reason, using a cuk converter is a better solution for this issue because it can be operated as both buck and boost modes [6]. In cuk converter based systems, if the voltage produced by the source is lower than desired level, the converter operates in boost mode. Otherwise, if the voltage produced is higher, the converter operates in buck mode. Therefore, the energy produced can be used without any interrupt, and thus efficiency of the system is increased. By taking into account all these reasons, a cuk converter is preferred in the system presented in this study.

Another important factor to increase the efficiency of the system is design of an optimum Maximum Power Point Tracking (MPPT) system. In most of the similar power systems presented in the literature, DSPs, PICs and FPGAs are generally used for achieving the MPPT system. Since the DSP is an expensive controller, its usage in such systems has a disadvantage. On the other hand, usage of PICs decreases the efficiency of the system due to their low speed response time [4], [7], [8]. Furthermore, using a low speed controller causes distortions on the output voltage of the systems including instant speed variations like wind turbines. By considering such issues, dsPIC is used in this study as the main controller to develop an efficient solution for such problems.

Recently, several studies have been presented in the literature to improve the efficiency of the energy produced by renewable sources such as MPPT operation for solar panels and application of SEPIC converter [2], design of a DC–DC resonant converter for wind turbines [9], response analyze of the converters against the load variations in uninterrupted operation conditions [10], improvement of the performances for wind energy conversion systems [11], dynamic power point tracking systems for solar energy [12], [13], [14]. These systems presented in [2], [7], [9], [10], [11], [12], [13], [14], [15] have used lower switching frequencies which are usually between 2 kHz and 50 kHz. As a difference, higher switching frequencies (about 100 kHz) are used in this study. Thus, oscillation on the output voltage is minimized considerably. Furthermore, analysis of the transient response time of the system against the oscillations on the output voltage and instant variations on the input voltage have also been analyzed in detail and the system has been verified successfully. As a result of experimental tests, it has been observed that the system achieved has more speed response time than the similar ones [10], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26].

Another superior feature of the system designed is uninterruptedly storage of the energy. While only boost or only buck converters have been used in similar studies for solar energy [7], [12] and wind energy [19], [27], the cuk converter has been used in this study which is capable to store the energy produced in both the buck and the boost modes. Additionally, while some similar studies such as control of fuel cells [10], [28], wind systems [11], and MPPT operations [29] have used traditional and ready to use converters, more flexible and original converter system and MPPT algorithm are designed and carried out in this study. Moreover, the converter system and MPPT algorithm developed can easily be adapted to new conditions that will be appeared in future like adding new solar panels or wind turbines to the system. Also, MPPT level can easily be set to any desired value that will be needed as a result of these new conditions.

In addition to novelties summarized above, a current protection unit against overloading situations has been added to the system because overloading to energy source may cause instant descents on output voltage and thus any part of the system may be damaged. Furthermore, software side of the system is very important for giving a rapid decision during undesired conditions like overloading [30]. In this study, control software of the system is developed using a flexible programming language.

Section snippets

Design of the cuk converter

Cuk converters are gained popularity in these days because oscillation on the output voltage of them is less than the other types of converters like the buck and the boost. Although using an external filter is a solution for minimizing the oscillations [31], [32], there are some disadvantages of this method such as increase of the cost and increase of the equipment used. In order to avoid from all these problems, cuk converter has been preferred in this study. Use of the cuk converter has made

dsPIC microcontroller

dsPIC is a powerful microcontroller which can be operated under high speed processes and especially designed for applications that are needed high performance such as voice recognition, heart sound acquisition, edge detection, and modems [33], [34], [35], [36]. In this study, dsPIC is preferred for such requirements as generating the switching signals of converters, measuring the analogue data of system, achieving MPPT operation and regulating the output voltage.

Since MPPT operation is mainly

Development of MPPT scheme

The maximum power point refers to a special point where the derivative of the ratio between the power variation and the voltage variation is equal to zero (Eq. (6)). Maximum Power Point Tracking (MPPT) operation is required to efficiently use the energy produced by several energy sources [45], [46]. Solar panels provide the output energy in direct proportion to the quantity of sunrays rebounding on the panel.MPP=dPdV0

The output power can be calculated by multiplying the current and the voltage

Application of the system

In this study, application of a high efficient voltage regulation system including MPPT operation has been achieved for renewable energy sources. Two main renewable energy sources are dealt with in the study as the solar and the wind energies. Experimental studies on both systems are given below. In general, the voltages of renewable energy sources are applied to converters and value of the voltages are measured by a controller at the same time to obtain voltage and current information required

Experimental results

Once the sub-parts of the system are designed and all parts are integrated to make it ready for operation, the system is tested under several experimental studies. These are evaluating the system performance by an analytical test of transition time for steady-state condition, analyzing the oscillations on the output voltage; and analyzing the response time of the system against the instant changes occurred on the input side. It has been observed from test results that the system operates with

Conclusion

In this study, a powerful voltage regulation system has been designed for renewable energy systems to obtain the best performance from the energy produced by them. For this, a dsPIC based cuk converter circuit with MPPT algorithm has been developed. Buck, boost and buck–boost modes of the designed converter have been examined experimentally under various switching frequencies. Initial response of the system and elapsed time for the steady state conditions have been tested and quite successful

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