Soutenance mémoire
Impact of DG on Losses
One of the most common impacts of DG is the losses on the distribution feeder. Locations of DG units have an important role to reduce the losses in the power grid. Barker and De Mello, (2000) cited that optimal locations of DG can minimize losses as well as capacitor bank can minimize losses if it can be installed in a suitable location. The basic difference between DG and capacitor bank are, DG can inject both active and reactive power (P and Q) to the power network. On the other hand, capacitor bank can give reactive power (Q) flow to the power network. The ideal areas of DG can be found using the load flow analysis, which can easily determine the optimum positions of DG in the network to reduce the losses. If any feeder creates large losses, installing a small DG on the system can have positive impact to reduce the losses. Impact of DG on the Feeder Protection The most main characteristics of distribution networks is that the power flows radially, from the principal location of power generation to the feeders to maintain all loads. In this model it showed that protection device is connected to the feeders of the power network, in order to keep continues power supply to the loads and protect different types of equipment of power network from unbalance power flow (Khan, 2008).
During the modeling of these protection devices, some features should be considered. It is true that the protection of whole power network is not possible using only of one kind of protection device. In large power network the protection is given by different types of protection devices based on the length of power network which can cover maximum length of protection. When modeling the protection strategy of a power network, operation between indicated protection devices should be able to reach a high range of reliable power network which can isolate the faulted portions of the networks and maintain the regular power flow in healthy parts of the networks. With this strategy, the global reliability of power network can be increased (Khan, 2008). The DG in the power network will have a major impact on the operation of the protection devices, which affects the protection of distribution side feeder. The large penetration of DG in a distributed power network can increase the chance of fault in the whole power systems. This fault has also an impact on the protection devices. The protection devices can break down into two different ways: mal-trip (unplugging non-faulted parts) or fail-to-trip (by not unplugging faulted parts). A mal-trip is a case where a protection devices trip in place of other devices. This tripping happens when the protection device is outside of the protection zone while fault occurs. Figure 1.4 (a) shows mal-trip operation where a DG unit feeds a high level of fault. This type of operation isolates the healthy parts of the network to safe from the danger. Figure 1.4 (b) shows fail-to-trip operation where DG unit in a downstream fault condition (Häger et al., 2006).
Impact of the power converters to the DG Renewable sources are generally connected to the main power networks via power converters, inverters and rectifiers. Under the effect of the dynamic interaction between the power grid and converter, the power quality is decreasing. DG connected to the distribution network can create a harmonic distortion to the system depending on which type of DG technology and power converters are connected. The implementation of passive filters can limit the effect of this phenomenon by increasing the penetration rate of distributed generations. The purpose of this simulation is made by Kadir et al., (2012). They have modeled the system consisting of DC voltage source of DG, passive filter, inverter and P-Q control system.
Intentional islanding
Intentional islanding is a case where the reliability of power can be increased if a DG configured to maintain ‘backup-islands’ during upstream power outages. Barker and De Mello, (2000) described in their paper that during upstream faults the switch should open and generator should be able to maintain the demand of load on the islanded region and maintaining acceptable frequency and voltage levels in the islanded area. It is highly accepted that to support an island, DG must be assigned to be able to restart and carry the load of island after the switch has opened. Philip and Barker, (2000) also mention, to detect a fault in downstream of a switching area the switch has to be sensed and send a signal automatically to isolate the DG portions from the islanded fault zone.
Islanding detection In the present time, to detect the islanding situation in a network, several methods and techniques are used based on the output of DG parameters and decision is taken to determine whether these parameters detect an islanding condition or not. The islanding determination methods may be defined into two main classes; local islanding and remote islanding methods. Pai and Huang (2001) and Mahat et al., (2008) mention that the local methods are divided into active and passive detection methods. Remote islanding detection method is based on communication between the main power networks and DGs. This method is highly reliable than local detection methods, but it is expensive to apply in DG system. Local islanding detection method is depends on the measurement of system parameters in DGs area (i.e. voltage, frequency, etc). Active methods operation is directly connected to the power system but on the other hand passive methods are based on detecting the fault on the measurement of the system parameters (Pai and Huang, 2001). Passive methods observe the variation of parameters of power systems like phase displacements, levels of short circuit and rate of output power. In most situations disconnection of DG from power network affects the nominal network voltage, frequency and current. There is some negligible change in the power flow and the frequency when DG is connected to the main power network and it will not be enough for the beginning of a protective relay that is responsible for a DG disconnection from the network. One other side, if DG is not connected with the main power network, the variation in the output power and frequency will be enough to energize the protective relay to isolate the DG that preventing the occurrence of an islanding situation (Ropp et al., 2000). Active methods identify the islanding situation even there is perfect balance between loads and generation but in passive detection methods, it is not possible. Active detection methods directly cooperate with the operation of power system when small disturbance is introduced in the system.
Control of frequency
The balance between the load and the output power determines the frequency of the power system. In large interconnected networks, output power increases with frequency drop and vice versa. The first frequency control line is the local governor, which provides » reserve power flow » to the system. For DG, this type of control will be required for the operation of insulation. Frequency control in open loop always gives a constant value but in higher droop. For the case of closed loop control, the frequency is very sensitive with the actual energy (minimum droop), which requires control the governor to control the frequency.
|
Table des matières
INTRODUCTION
0.1 General
0.2 Motivation
0.3 Objective
CHAPTER 1 LITERATURE REVIEW
1.1 Concept of Traditional Power Systems
1.2 Concept of New Power System
1.3 The Distributed Generation (DG)
1.3.1 Definition
1.3.2 Benefits of DG
1.3.3 Drawbacks of DG
1.3.4 The technologies of DG
1.3.5 Impact of DG on Power System
1.3.6 Impact of DG on Voltage Regulation
1.3.7 Impact of DG on Losses
1.3.8 Impact of DG on the Feeder Protection
1.3.9 Impact of the power converter on the DG
1.3.10 Protection coordination
1.4 Islanging of power network
1.4.1 Intentional islanding
1.4.2 Islanding dectection
1.5 Control of Frequency
1.6 Micro grid
CHAPTER 2 CONNECTION OF WIND POWER IN THE POWER NETWORK
2.1 Introduction
2.1.1 Overview
2.1.2 Principle of wind generation
2.2 Conversion system of wind energy
2.3 The technical operation of wind turbine
2.3.1 Types of wind turbines
2.3.1.1 The variable speed squirrel cage wind turbines
2.3.1.2 Wind turbine induction generator (WTIG)
2.3.1.3 Doubly-fed induction generator (DFIG)
2.3.1.4 Permanent magnet synchronous generator (PMSG) at variable speed
2.4 Connection of wind power to the grid
2.4.1 Network stability
2.4.2 The network frequency
2.4.3 Case study: connecting a wind turbine to the power grid without stroge system
CHAPTER 3 FLUCTUATION BEHAVIOR OF FREQUENCY FOR A HYBRID / WIND POWER BASED BATTERY STORAGE SYSTEM WITH DIFFERENT CONTROLLERS
3.1 Introduction
3.2 The system of WDHS
3.2.1 The operation modes of WDHS system
3.2.2 System combination of WDWS
3.2.2.1 The synchronous machine SM
3.2.2.2 The Wind turbine
3.2.2.3 Secondary load system
3.2.2.4 The energy storage system BESS
3.3 The network control system of WDHS
3.3.1 The frequency control system of WDHS
3.3.2 The control of BESS
3.4 Case study: connecting a wind turbine to the power grid with storage system
3.5 Simulation: Scenario 1
3.5.1 Frequency control by PID, When (PT > PL) where, PS fully charged
3.5.2 Fuzzy logic controller
3.5.2.1 Introduction
3.5.2.2 Fuzzy logic membership function and rules
3.5.3 Frequency control using Fuzzy logic controller, When (PT > PL) where, PS fully charged
3.5.4 Comparison between PID and fuzzy logic controller to control the frequency, when (PT > PL) where, PS fully charged
3.6 Simulation: Scenario 2
3.6.1 Frequency control by PID, When (PT > PL) where, PS is charged
3.6.2 Frequency control using Fuzzy logic controller, When (PT > PL) where, PS is charged
3.6.3 Comparison between PID and fuzzy logic controller to control the frequency, when (PT > PL) where, PS is charged
3.7 Simulation: Scenario 3
3.7.1 Frequency control by PID, When (PT > PL) where, PS is discharged
3.7.2 Frequency control using Fuzzy logic controller, When (PT > PL) where, PS is discharged
3.7.3 Comparison between PID and fuzzy logic controller to control the frequency, when (PT > PL) where, PS is discharged
CONCLUSION
RECOMMANDATIONS
BIBLIOGRAPHIE
Télécharger le rapport complet
