Compensation of voltage flicker at the output of wind turbines based on induction generator by Statcom to improve power

Dissertation for Master's Degree in Electrical Engineering

Power Trend

Abstract:

The use of renewable energy to produce electrical energy has increased increasingly with the expansion of the use of flexible alternating current transmission systems (FACTS) to compensate for power and voltage qualities, the range of use of these energies has increased. In this project, the application of the static synchronous compensator (STATCOM) in the continuous operation of a wind farm has been evaluated and the effect of the presence of the STATCOM has been investigated and modeled. The simulation results show that the power of the network improves with the presence of the STATCOM, and constant speed wind turbines significantly affect the quality of the voltage of the electrical network connected to them due to the fluctuating nature of their output power. Rapid voltage fluctuations produced by these turbines occur. The voltage flickers in the network. According to the simulation done, it is possible to check the effect of different parameters of the electrical network on the amount of voltage flicker emitted by wind turbines. To evaluate the amount of voltage flicker emission, the flickermeter program was written based on the IEC 61400-4-15 standard. The study and simulation was done in the MATLAB/SIMULINK environment and considering three 3 MW turbines based on the induction generator in a wind farm.

Introduction

The issue of power quality, which is still one of the most important issues in power systems, has been discussed since the past, and power companies around the world have been working on this issue for several decades.

In 1970, power quality was raised as one of the important goals in the design of industrial power systems, in addition to safety, servicing with high reliability, and reducing initial and current costs were also among the issues that involved electrical engineers. made Almost at the same time, the issue of "voltage quality" was raised in the Scandinavian countries and in the former Soviet Union, whose main goal was to control low voltage range changes.

1-2: Factors affecting the increase in the importance of the issue of power quality

Today, several factors have caused the issue of power quality and the supply of electricity with appropriate quality to consumers to be considered important issues, some of which are mentioned below:

Equipment and devices compared to Voltage disturbances have become more sensitive. Power equipment has become much more sensitive in the last 10 to 20 years. Mr. Thomas Kay discusses the problems of voltage disturbances on the performance of electronic equipment in 1978. In addition to the sensitivity of equipment, companies also show more sensitivity to this problem due to the loss of time and decrease in income due to problems related to power quality phenomena. In an ideal electrical energy network, the continuous supply of electricity is a basic right for the subscribers, as a result, any power outage will be faced with more protests than in the past, even if it does not cause any damage or physical damage. [5]

Different equipment and devices alone cause voltage disturbances. Modern power electronic devices are not only sensitive to voltage disturbances, but also cause voltage disturbances themselves (increasing the use of converters). Consumer electronic equipment and computers to speed control equipment in motors) has led to an increase in disturbances in voltage. The main issue here is the non-sinusoidal current of rectifiers and inverters. In addition to having the main frequency of the network, the input current of these devices also contains harmonics. which are considered an important problem for the network due to the increase in their use.

Increasing the need for standardization and performance criteria: In the old days, from the point of view of many electricity companies, the consumer of electric energy was considered simple once, power outages and voltage disturbances were considered a normal thing, and the said company also acted according to its wishes, and any subscriber who needed higher quality and reliability had to pay an additional fee, but today, electricity supply companies treat the consumer as a Electricity is known as a product with its own characteristics that can be measured, predicted, guaranteed, improved and so on. This issue is due to the trend towards privatization and changing the structure of the electricity network.Free competition in electricity markets makes the matter of convenience even more complicated. In the old days, the consumer would sign a contract with the local electricity company and that company would provide the consumer with electric energy with its own quality and capability, but today, in the restructured systems and with the expansion of the electricity market, customers can buy electric energy from any company they want, so an organization is successful in this regard that can deliver electricity to customers with better quality and reliability. Therefore, the discussion of power quality and the reduction of its adverse effects shows its importance.

Power quality can be measured: with the availability of electronic devices to measure and display waveforms, power quality has received more attention. In the past, measuring power quality indicators was difficult and was limited to measuring the effective value of voltage, frequency, and long-term outages. Different power quality phenomena can be easily done. 1-3: What is power quality? Different definitions for power quality have been expressed from different points of view. For example, an electric company emphasizes power quality more than reliability, or from a manufacturer's point of view, power quality is the specifications of the power supplied for the proper operation of production devices.

Dictionary of the International Association of Electrical Engineers in the IEEE std 1100 standard defines power quality as follows: "Power quality is the electrification of sensitive equipment for the proper operation of that equipment." The more comprehensive definition stated in reference [5] raises power problems as follows: The supplied electricity, which occurs in the form of current, voltage or frequency deviations and leads to failure or improper operation of the subscriber's equipment". 1-4: Classification of power quality phenomena Despite the existence of agreements in the definitions of power quality phenomena, the two reference standards that are widely used are the IEEE1159 and IEC-61000 series, which are the famous phenomena introduced by these standards in It is further explained [4, 5, 6]:

1-4-1: Transient states:

The term transient is usually used for sudden changes in a sinusoidal waveform. The word shock is used to describe transient waves caused by lightning. The IEC61000-2-5-1990 standard divides transient waves into two subgroups depending on the sources that cause these disturbances:

1-4-1-1: Impulse transients:

Impact transients refer to a sudden change in stable conditions of current, voltage or both and with a frequency different from the grid frequency and unidirectional polarity. Impulse transients are usually with two The characteristics of "Decay Time" and "Rise Time" as well as their spectral contents are known. Figure (1-1) shows the shock wave on a sine wave. Shock transients, in addition to the adverse effects they have on insulators, also stimulate the natural frequency of the network and the occurrence of fluctuating transients. Figure (1-1): Shock voltage waveform on a sine wave

1-4-1-2: Transient states Oscillating:

Oscillating transient states refer to a sudden change in stable conditions of current, voltage, or both, with a frequency different from the grid frequency and with positive or negative polarity. In fact, transient oscillatory states include two voltages and

or a current whose polarity changes rapidly. Oscillating transient waves usually have their spectral content, their main frequency, amplitude and duration. Their occurrences are described. Common types of transient oscillatory waves in connection with types of switching in the network are divided into three categories: low frequency, medium frequency and high frequency. Figure (1-2) shows an example of the effect of the transient oscillatory waveform on the sine wave. Voltage:

Long-term changes in voltage include changes in the effective value of the nominal frequency of the network and for a period of more than one minute. Long-term changes include voltage reduction and voltage increase and permanent outages. The first two phenomena are usually caused by load changes in the system and not by errors.