Improving power quality in restructured networks with the presence of scattered production resources

Dissertation

To obtain a master's degree

In the field of electrical-power engineering

Abstract:

     In recent years, attention to high productivity and efficiency in various industries has rapidly expanded the scope of application of power electronic equipment. These equipments have increased power quality problems in distribution networks due to their non-linear characteristics. On the other hand, due to the advancement of technology and the widespread use of computers in the control of industrial systems, the sensitivity to power quality phenomena has also increased many times.

     Now in such a situation, according to the plan of restructuring in the electricity industry, one of the parameters that can be very effective in the competitive environment of the electricity market is the provision of electricity of various quality and price for consumers with different degrees of sensitivity. Among the equipment used to improve the power quality is UPQC integrated power quality compensator, which consists of two series and parallel units. This equipment is placed near sensitive loads and while improving the quality of the voltage delivered to the consumer, it also improves the quality of the current drawn from the network.

In this thesis, inspired by the UPQC function, a new structure is introduced to improve the power quality (in networks that consist of different loads with different sensitivity levels), and its appropriate control method is introduced. They are placed in the vicinity of one of the sensitive loads in order to provide the power supply voltage of the sensitive loads in the event of an outage, while compensating the current harmonics. The simulations carried out in the environment of PSCAD software show the capability of the introduced equipment and its proposed control method in compensating voltage and current problems. Keywords: power quality, restructuring, active filter, integrated compensator of isolated power quality. Research topic: Today, active filters play an important role in improving power quality problems in distribution systems. The increasing number of non-linear loads, including diode and thyristor rectifiers, arc furnaces and distribution systems, lead to power quality problems and their mutual effect on the loads fed from that bus. On the other hand, due to the limitations considered by various international standards, especially for industrial consumers, the reduction of harmonic problems caused by the load is presented as a necessity [1]. To improve and upgrade the quality of power provided to consumers, various types of compensators have been introduced. Passive filters have been introduced as the first compensators in order to eliminate current harmonics and improve the power factor. Although this category of filters has simplicity and low cost, but due to the effect of line impedance and the possibility of resonance problems, the inability to remove several harmonic components and so on. They have little popularity [2]. For this reason, various and extensive researches have been conducted in the field of designing other compensating devices.

Active power filters are one of the compensating devices that are widely used in distribution systems today, which have the ability to remove all unwanted harmonics, improve the power factor and imbalance. In the last few decades, various structures of active filters have been presented, including series active filters, parallel filters, combined filters, UPQC, etc.     are Also, various control methods have been presented in the frequency domain and time domain in order to control active filters. In this research, a suitable method to improve power quality has been presented. In this connection, it is necessary to state some issues. Firstly, the overall improvement of the quality of the power provided to the consumer is the responsibility of the electricity selling companies. But the issue that can be raised here is that to what extent these companies are responsible for improving the quality of power, and if the consumers demand higher power quality than what is in the international standards, which the electricity selling companies are obliged to provide, how and how can this demand be met?

has done In this method, the overall improvement of power quality will be done for all consumers and some special features will be provided for sensitive consumers who need higher power quality.To achieve this goal, a new structure inspired by the structure of integrated power quality compensator will be introduced and a simple and efficient control method will be presented using the theory of instantaneous power. Due to its non-linear characteristics, these equipments cause the spread of power quality disturbances including harmonics in the distribution network. On the other hand, the increase of consumers has also led to the expansion of distribution networks and as a result of the increase in power quality disturbances, especially the lack and excess of voltage. According to the above, power quality is of great importance for consumers today, because the losses caused by low power quality are very high. For example, if due to the operation of a power switch, the production line of an average factory is out of order and it takes 4 hours to restart it, this factory will suffer about 10,000 thousand dollars [3]. Therefore, the use of compensation equipment such as active filters and integrated power quality compensator is inevitable.

Considering that in restructured networks, one of the tools of competition between power companies is to provide power quality at different levels and prices according to the needs of consumers, therefore, in this research, the goal is to achieve the above issue by using distributed production resources and the use of new structures of compensation equipment.

Power quality has been achieved by using different equipments, each of which has limitations. Among these researches, the use of passive filters and active filters such as parallel and series filters can be mentioned [4]. The combination of series and parallel active filters, i.e. integrated power quality compensator, was able to solve the deficiencies in both of these compensators to a large extent [5]. But the weakness of this equipment is the improvement of power quality for all consumers and to the same extent. Consumers need different power quality. A consumer may be highly sensitive to power quality disturbances, and as a result, demands the highest level of power quality, higher than the existing standards, and is ready to pay for it. But the consumer is no longer very sensitive and the power quality is sufficient for him at the standard level. Therefore, we will face the problem that we have to provide different levels of power quality required by consumers, and each consumer should pay for it according to the level of power quality they want.

For this purpose, a new structure called OPEN UPQC has been used. By using this new structure, it will be possible to provide a multi-level power quality at different prices and for different consumers. In this way, in the competitive environment in the restructured electricity market, suitable tools will be created to compete with other sellers.

1-3- Objectives of the thesis

The purpose of presenting this thesis is to provide a solution to improve the power quality required by consumers in the restructured networks. This improvement will be in such a way that every consumer will receive the power quality they need with the appropriate cost. Today, in the big and competitive electricity sales market, sales companies must increase their number and earn more profit by meeting the needs of their customers and increasing their satisfaction. In order to achieve this goal, it seems necessary to provide a method that can provide power quality at several levels and reduce the cost of providing it.

In this research, by using the integrated structure of isolated power quality compensator (OPEN UPQC) and its suitable controller design, the overall improvement of power quality for all consumers and also the increase of power quality for some customers who need higher power quality have been provided.

1-4- End organization Letter

In the first chapter, the introduction of the research and statement of the desired problem, the research conducted and the objectives of the thesis have been discussed.

At the beginning of the second chapter, the introduction of restructured and traditional networks has been discussed, and then the motives of restructuring have been examined. Then the effective factors in restructuring have been studied