Modeling and simulation of static compensator based on DQ model

Number of pages: 89 File Format: word File Code: 30922
Year: 2014 University Degree: Master's degree Category: Electrical Engineering
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    Dissertation for Master's Degree in Electrical Engineering

    Power Orientation

    Abstract

    Flexible power transmission systems known as FACTS[1] compensators are modern tools that have been used in power systems to enhance controllability and develop the transmission capacity of power networks based on power electronic converters during the last decade. In fact, FACTS systems are able to control the parameters and characteristics of transmission lines, such as series impedance, parallel impedance, phase angle, which act as the main limitation on the way to increase network capacity. The basic idea behind the concept of FACTS is to enable the transmission system by activating its elements and components. In fact, FACTS has a fundamental role in increasing the flexibility of power transmission and the security of the dynamic stability of power systems. In this thesis, the control structure of STATCOM (Static Reactive Power Compensator) is investigated. First, the STATCOM model is simulated based on the dq model. Then, with the appropriate fuzzy controller design, the reactive power management problem in the power network and the analysis of the STATCOM behavior during the fault are presented. The simulation results show that the proposed control method can perform reactive power control in power networks under different operating conditions.     

    [1] Flexible AC Transmission Systems (FACTS)

    Voltage imbalances are short-term reductions in effective voltage caused by short circuits in the system, overloads, and starting large motors. Attention to voltage sags is primarily related to issues that affect several types of components: Adjustable speed drives, process control components and computers that are problematic due to their sensitivity. Exciting capacitors and switching electronic loads also lead to short-term overcurrent. But because the length of overcurrent is so short, it does not lead to an effective voltage reduction.  These factors are not referred to as voltage drop and Lee classifies it as voltage cut or voltage transient. Voltage drop caused by short circuit and ground fault are the most important factors of equipment problems. In this chapter, the problem of voltage errors in distribution networks will be examined first, and then, according to the sensitivity of electronic power converters to this error, the control methods of electronic power converters will be investigated.

    Figure (1-1): An example of voltage sag and imbalances in the distribution network

    is a common way to show the voltage sag through the effective voltage as a function of time. Effective voltage over a time window which is basically a time cycle and repeats itself for one or more times each cycle. According to figure (1-1), the voltage drop is the result of a ground-to-ground fault in an underground cable. The undervoltage as a result of the error leads to a decrease in the power transfer from the generator to the engine, the result of which is a decrease in the speed of the engine and an increase in the speed of the generator. These phenomena lead to limiting the error recovery time in transmission systems as well as the rules for connecting wind farms to the grid. Although protection methods have been suitable for consumers for many years, recently many issues and problems have arisen in relation to customers due to voltage dips. Basically, the necessary limits for stability in the distribution system are 70% voltage during one second. Many power electronic devices such as computers, process controllers and adjustable speed drives have a voltage drop of 85% for 45 seconds. 1-2 Characterization and indicators related to voltage drop In order to describe events related to voltage drop, processing should be done on the sampled voltage waveforms. In the IEC-61000-4-30 standard, two important characteristics, voltage and duration are defined as evaluating the quality of voltage dip. Both of these parameters are obtained from the effective voltage as a function of time. By having the profile of a single event, it is possible to describe the performance of a situation and even the entire network. The importance of discussing the indicators of voltage drop and considering information related to measurement (power quality monitoring) and simulation. Measurement is a good way to evaluate the performance of a situation or a system.But measurements have limitations in predicting for year to year or situation to situation. A large number of monitoring devices for a long period of time are required to predict voltage sag performance. Random prediction methods are very suitable for performance prediction, for example, it is suitable for comparing different improvement methods. There are usually methods to reduce the effectiveness of equipment from voltage drops, some of which are listed below:

    Reducing the number of errors

    Accelerating the time to fix the error

    Improving the design and performance of the network

    Using improvement tools in the connection: a very common method is to connect a UPS or a constant voltage transformer between the system and sensitive loads. For large loads, static compensators based on three-phase inverters are possible as a solution.

    Improvement of components on the part of customers: making equipment safe against all voltage drops is a solution to solve the problem, but it is not possible for most equipment.

    According to the provided references, the methods of improving voltage quality caused by interruptions and voltage drops can be divided as follows

    Reducing the number of short-circuit errors

    Reducing the time to fix the error

    Change the system so that short-circuit errors lead to less severe events in the terminals of components or in communication with customers.

    Improved component connection between sensitive devices and power supply

    Improving equipment security

    1-3 Reducing the number of short-circuit errors and its connection Voltage unbalance

    Reducing the number of short circuit faults in a system not only reduces the frequency of sags but also reduces the frequency of imposed outages. Therefore, this method is an effective factor for improving the quality of nutrition, and many consumers consider it as an effective solution when voltage drops occur. Since the short circuit causes damage to the operating equipment and the network, therefore, many efforts have been made to reduce the frequency of the error as far as it is economically viable. Some of the methods that have been used so far for this purpose are as follows:

    Replacing overhead lines with underground cables

    Using protective wires for overhead lines

    Installing more protective wires to prevent faults during lightning

    Increasing insulation levels

    Increasing more inspection and maintenance periods

    Reducing the time to fix Error

    Decreasing error resolution time does not reduce the number of events, only their severity. Therefore, it does not affect the duration of outages and their number. By clearing the fault faster, it also does not affect the number of voltage dips, but it can reduce the duration of the dip. Maximum reduction in fault clearing time is achieved by using current limiting fuses. These fuses are able to clear the fault in half a cycle, so the voltage drop period rarely exceeds one cycle. In time transmission systems, fault elimination is often characterized by transient stability limitations. 1-4 Effect of changes in the power system on voltage imbalances By making changes in the power supply system, the intensity of events can be reduced. Here the cost can be very high. Especially for transmission and sub-transmission voltage levels. The most important way to improve against outages is to install additional backup devices. Some of the possible methods to improve the voltage sag are as follows:

    Installing a generator near sensitive loads, in order to keep the voltage high during the sag period.

    Dividing buses or posts in the feeding path to limit the number of feeders that are exposed to faults.

    Installing current limiting coils in strategic positions to increase the electrical distance related to the fault.

    Bass feed with sensitive equipment from two or more posts. In this case, the voltage drop in one post is improved by feeding from other posts. 1-5 Installation of improving devices Recent advances have been directed towards the use of devices to improve the voltage drop. Some of the improvement tools are as follows: Uninterruptible power supplies are widely used for computers and process control components. Motor-generator sets are often used in industrial environments.

  • Contents & References of Modeling and simulation of static compensator based on DQ model

    List:

    Table of Contents

    Title

    Page

    Abstract..1

    Chapter One: An overview of research conducted in the field of three-phase inverter control

    1-1 Introduction ..2

    1-2 Characterization and indicators related to voltage sag.4

    1-3 Reducing the number of short-circuit faults and related voltage imbalance. 5

    1-4 The effect of changes in the power system on voltage imbalance. 5

    1-5 Installing improvement tools. 6

    1-6 Improving equipment security. Constant..9

    1-7-2 Voltage regulation..10

    1-7-3 Voltage flicker..10

    1-7-4 Voltage drop..10

    1-7-5 Harmonics..11

    1-8 Examining the types of structures of connection to the network of distributed generation sources and control of electronic power converters.12

    1-9 Methods based on the processing of voltage and current signals.21

    Chapter Two: Familiarity with FACTS tools

    2-1 Introduction..26

    2-2 Introduction of SVC static Var compensator.26

    2-2-1 Applications of SVC..27

    2-2-2 The most common types of SVC.28

    2-3 introduction and simulation of static compensator STATCOM.29

    2-3-1: applications of STATCOM.30

    2-3-2 simulation of STATCOM.31

    2-3-3: comparison of STATCOM and SVC.33

    2-4 introduction of TCSC thyristor control series capacitor.35

    2-4-1 objectives of compensation Transmission lines by series capacitors. 35

    2-4-2 Subsynchronous resonance damping. 36

    2-5 Introduction of PST phase shifting transformer. 36

    2-5-1 PST applications..37

    2-5-2 Dynamic and transient applications. 38

    2-6-1 SSSC applications..38

    2-7 introduction of UPFC integrated power controller. 39

    2-8 introduction of inter-line power controller (IPFC).

    3-1-2 External controller.

    3-2 Modeling of three-phase inverters connected to the network in STATCOM compensator.

    Chapter Four: Design of phase control system for three-phase inverters

    4-1 Introduction..48

    4-2 Design of phase control for reactive power control.

    4-3 Loop Phase lock (PLL) Inverter in reactive power injection mode .62

    5-3 Conclusion..67

    References..68

    List of Blacks

    Sources Title

    Figure (1-1): An example of the collapse and immortality of the wallet in the distribution network.

    Figure (1-2): The proposed structure to improve the voltage sag. 12

    Figure (1-3): The structure of connecting distributed generation sources to the grid in the event of a voltage sag. 13

    Figure (1-4): ITI/CBEMA curves to determine the tolerable levels of sensitive loads. 14

    Figure (1-5): A micro turbine based MSDG system. 14

    Figure (1-6): The structure of the inverter presented in the load connection mode. 16

    Figure (1-7): The general block diagram of the controller. 16

    Figure (1-8): The structure of the connection to the inverter grid. 18

    Figure (1-9): The control strategy related to the connection to the inverter grid. 18

    Figure (1-10) The structure of the three-phase inverter connected to Network. 19. Figure (1-11): Proposed compensator for micro-grid. Figure (1-12): Voltage and current control loop proposed for parallel inverter. Figure (1-13): Voltage and current control loop proposed for series inverter.

    Figure (1-15): Block diagram of the presented processing system. 25

    Figure (1-16): Block diagram of the proposed method for tracking symmetric components based on the energy operator. 25

    Chapter Two

    Figure (0-1): SVC structure and its V-I characteristic. 27

    Figure (0-2): Types29

    Figure 2-3 STATCOM :( and its V-I characteristic. 29

    Figure (2-4): STATCOM transient stability model with PWM voltage control. 30

    Figure (2-5) PWM voltage control of a STATCOM. 32

    Figure (2-6): Permanent state model. 32

    Figure (2-7): Control limitations STATCOM.33

    Figure (2-8): Comparison of V-I characteristic of SVC and STATCOM.34

    Figure (2-9): TCSC and P-V diagram.36

    Figure (2-10): PST and voltage phasor diagram.

    Figure (2-11): SSSC structure.

    Figure (2-12): UPFC and multi-type working area FACTS on P-Q page.40 Figure (2-13): Structure of IPFC.41 Chapter Three Figure (3-1): Block diagram of STATCOM control system 4th Figure (4-1): Designed control structure. Figure (4-2) Structure of phase lock loop for frequency estimation. Figure (4-3): Structure of a pure fuzzy system. Figure (4-4): Main structure of TSK fuzzy system. Instrument. 54

    Figure (6-4): It shows the membership function ? in terms of e(t).  55

    Figure (4-7): Non-fuzzy graphical representation of center of gravity. 57

    Figure (4-8): Non-fuzzy graphical representation of average centers. 57

    Chapter 5

    Figure (5-1): Characteristics of reactive power requested by the load. 59

    Figure (5-2): Reactive produced by inverter power generation system STATCOM.59

    Figure (5-3): reactive power produced by the network.59

    Figure (5-4): currents injected into the network by the compensator STATCOM.60

    Figure (5-5) asymmetric voltage drop.61

    Figure (5-6): injected reactive power during asymmetric voltage drop.62

    Figure (5-7) of the three-phase currents injected into the grid during asymmetric voltage drop without considering the phase jump. 62

    Figure (5-8): Grid voltages. 63

    Figure (5-9): Changes of the output reactive power of the compensator. 63

    Figure (5-10): Variations of the output current of the inverter (kA) of the compensator during the changes of reactive power. 64

    Figure (5-11) Changes in the q component of the currents injected by the compensator during changes in reactive power.64

    Figure (5-12): Changes in the d component of the currents injected by the compensator during changes in the reactive power.65

    Figure (5-13): Changes in q in the PLL output.65

    Figure (5-14): Frequency changes in the PLL output.66

    Figure (5-15): Changes of frequency and angle in the field of grid voltage disturbance. 66

    Source:

    [1] Koen J. P. Macken, Math H. J. Bollen, Ronnie J. M. Belmans, "Mitigation of Voltage Dips Through Distributed Generation Systems", IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 40, NO. 6, NOVEMBER/DECEMBER 2004

    [2] Mahesh Illindala, Giri Venkatamnanan, “Control of Distributed Generation Systems to Mitigate Load and Line Imbalances”, Power Electronics Specialists Conference, 2002. pesc 02. 2002 IEEE 33rd Annual.

    [3] G. Venkaiaramanan, D. M. Divan, T. M. Jahns, "Discrete Pulse Modulation Strategies for High-Frequency Inverter Systems," IEEE Trans on Power Electronics, Vol. 8, No. 3, July 1993, pp. 279-287.

    [4] Milan Prodanovic and Timothy C. Green, "Control and Filter Design of Three-Phase Inverters for High Power Quality Grid Connection", IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 18, NO. 1, JANUARY 2003.

    [5] Amirnaser Yazdani, Reza Iravani, "A Unified Dynamic Model and Control for the Voltage-Sourced Converter Under Unbalanced Grid Conditions", IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 21, NO. 3, JULY 2006.

    [6] J. He, Y. W. Li and M. S. Munir "A flexible harmonic control approach through voltage-controlled DG-grid interfacing converters", IEEE Trans. Ind. Electron., vol. 59, no. 1, pp.444-455 2012.

    [7] S. Yang, Q. Lei, F. Z. Peng and Z. Qian "A robust control scheme for grid-connected voltage source inverters", IEEE Trans. Ind. Electron., vol. 58, no. 1, pp.202-212 2011 [8] A. Yazdani and R.

Modeling and simulation of static compensator based on DQ model