Power Line Communications – Technologies and Problems: Requirements for their Control and Open Issues

Get Complete Project Material File(s) Now! »

Main applications for the control and handling of electric power distribution

One goal for distribution systems is to accomplish higher reliability and quality while optimizing the resources. Another goal should be improvement in system efficiency by reducing system losses. The evolutionary growth in microprocessor based devices and telecommunication equipments and networks have brought the possibility of integrating protection, control, metering, automation and monitoring systems cost-effectively.
The first kind of application concerns the control and the supervision functionalities. Su-pervisory Control and Data Acquisition (SCADA) systems and Distribution Automation (DA) systems are representative of this category. A second area for application is directly related to customer-related functions, such as remote load control, AMR(Automated Me-ter Reading), and remote connect/disconnect. Finally, a common trend aims to integrate several platforms across many utility departments (standard mapping systems, customer information systems, work management systems, etc.).
The future trends are to shift from a very limited control of load and demand response to utilities that should provide a certain level of Quality of Service (QoS) and should de-liver the electricity safely, reliably and cost-effectively. In order to supply a high-quality electricity product, the utility must reduce the number and the length of interruptions in supply to customers, minimize the consequences of them and avoid disruptions such as voltage and frequency fluctuations. Customers will have to participate in the energy and reliability services market. In the following, we present some functions that should be implemented in the future power electric distribution system [16] [18][17][19] [20]:
In the development of tomorrow’s electric infrastructure, a self-healing transmission and distribution system that is capable of automatically anticipating and responding to dis-turbances while continually optimizing its own performance, will be critical for meeting the future electricity needs of an increasingly transactional society.
For instance, real-time pricing (RTP) system provides customers with dynamic pricing in-formation of electric power. The objective of this dynamic pricing scheme is to encourage customers to perform load management strategies to lower their electric demands during high price periods. Distributed generation (DG) is able to encompass any small-scale electricity generation technologies that provide electric power at a site close to consumers. Proponents of DG further suggest that it will enable utilities to expand into new markets, minimize invest-ment in existing infrastructure, increase flexibility, increase reliability and power quality, optimize asset utilization, and reduce the overall cost of providing power to end users. These trends will increase the number of Intelligent Electric Devices (IEDs) and Remote Terminal Units (RTUs) associated with the operation and control of DG units and their interconnection with the distribution system.
Electric utilities will be able to expand the portfolio of their business services to include communication, Internet access, real-time online monitoring, and other associated service. Customers will gain real-time access to energy markets and thus control energy cost and energy utilization better. All of these are based on the integration of electricity with communication system.
The implementation of these applications has to ensure reliability and availability of the electric power distribution system. These properties that are expressed at a functional level must be guaranteed by the implementation of these applications. The reliability and dependability purpose has to be translated, on the one hand, by equivalent reliability and dependability properties imposed on each devices and the architecture and, on the other hand, by timing properties on data exchanges and function execution. These properties can therefore be expressed as schedulability properties on each CPU, end-to-end response time, data freshness, etc. Some of these properties required by applications are given in Section 2.3. More specifically, if we focus on the data exchanged within one application or between several applications, we have to take into account the communication architecture between computers supporting these applications and to evaluate the network technology for ensuring these exchanges in a reliable way.

Communication networks

The reliable and economic operation of power electrical distribution systems relies heavily on its efficient communications system. There are many communication methods avail-able. As aforementioned, the high-speed Ethernet is applied widely. Herein, we focus on Wide Area Network (WAN) between DCC and RTUs/IEDs distributed widely along the feeder. The fundamental requirements for communication infrastructure [21] [24] [25] are given below.
• The requisite amount of data and multitasking can be handled.
• Data throughput and system response times should meet various application re-quirements.
• A reliable (i.e. acknowledged) transmission within a bounded time should be pro-vided.
• There should be support for priorities to allow distinction between urgent and non-urgent message.
• Both periodic and aperiodic (asynchronous) traffic types should be supported.
• Regular topology changes on the distribution system should be adapted.
• A long distance communication should be supported.
• It should allow for network growth and added applications.
The communication media can either be wired (cable, fiber, telephone) or wireless (wire-less local area network(802.11), radio etc.) [26] [27].

Historical development of data communication over power line

Power utilities began to be used additionally for data transmission for operations man-agement and optimum energy distribution soon after full-coverage electrification. Carrier Transmission over power lines (CTP) is used on the High Voltage (HV) power line, and provides a long distance and bi-directional transmission with low transmit power. In con-trast, Ripple Carrier Signalling (RCS) on Medium Voltage (MV) and Low Voltage (LV) power line allows only a very low bit rate and unidirectional transmission with enormous transmit powers[4].
These PLC systems aimed mainly for the distributors’ own requirements and they were not publicly available. PLC systems on HV power line are used for protection signaling and voice and data communications. A typical PLC communication network consists of one or multiple point-to-point links that can cover a distance of hundreds of kilometers without repeaters. To avoid interference between different links, they are typically sepa-rated by line traps. The voice services are still in use today, despite that reliable radio transmitters are now available.
Also the utilities have used RCS systems for many years, mainly to address load distri-bution, i.e. the avoidance of extreme load peaks and the smoothing of the load curve. RCS works at low frequencies near the power frequency. Low frequencies used as carriers for the packets allow information to flow over the transformers between the MV and LV segments without particular and generally costly coupling measures. Despite that data rate is low and less than 120 bps, it is sufficient for the tasks involved in load distribution, because often only enabling or disabling commands have to be issued.
In the past, only the supply utilities could make use of PLC as the communication method for their own purposes. Recently, the situation has changed fundamentally.

READ  Theoretical bases for influence of creativity on writing task-based language teaching

Regulatory of PLC communication

The PLC technology as telecom services over the electric grid makes regulation both in the energy and the telecommunication sectors relevant for PLC development. In addition, PLC should comply with EMC (Electro Magnetic Compatibility) regulations for sharing the same frequency bands with wireless services.
In Europe the allowed bandwidth is regulated by the CENELEC standard (EN50065-1, Signaling on low-voltage electrical installations in the frequency range 3 kHz to 148.5 kHz). The standard only allows frequencies between 3 kHz and 148.5 kHz. Fig. 3.1 shows the bandwidth specified by the CENELEC standard. The frequency range is divided into five sub-bands.
• 3-9 kHz for use by energy providers.
• 9-95 kHz (A-band) for use of energy providers.
• 95-125 kHz (B-band) for use of consumers.
• 125-140 kHz (C-band) for use of consumers, CSMA protocol defined.
• 140-148.5 kHz (D-band) for use of consumers.
The EN 50065 limits the signal amplitude. This puts a hard restriction on power-line communications, and the maximum data rate is up to 144 kb/s over distances around 500m. It might not be enough to support high speed rate applications, such as real-time video. In addition, EN 50065 differs considerably from other regulations, e.g., those applicable in the United States or Japan, where a frequency spectrum of approximately 500 kHz.

Present PLC technologies and applications

Deregulation of the telecommunications and energy markets was initiated in 1998. Power utilities have to adapt the future competition in the electric power market, and they want to open up new business fields with growth potential in the deregulated telecommuni-cations market. Those new applications focus on the MV and LV grids. However, in contrast to overhead lines on the HV power line, MV and LV power lines are hostile com-munication media. The principal property of the channel is that the noise and attenuation has time and frequency varying [34] [35]. However, modern modulation and coding tech-niques allow using PLC as a high speed, robust and reliable transmission media. With the specification of well-suited and efficient services, in particular a suitable medium access control (MAC) algorithm, a PLC network can provide data, voice and video services.

Physical layer

Power line is originally devised for distribution of power at 50-60 Hz. The use of this medium for communications at higher frequencies presents some technically challenging problems. Power line networks are usually made of a variety of conductor types, joined almost at random, and terminating into loads of varying impedance. Such a network has an amplitude and phase response that varies widely with frequency. At some frequencies, the signal may arrive at the receiver with relatively very small loss, while other frequencies may be driven below the noise floor. Furthermore, the channel characteristics can also vary with time when the load on the network changes [36][37].
Power line networks are also affected by interference. Electric appliances with brush mo-tors, switching power supplies and halogen lamps produce impulse noise that can reduce the reliability of communication signals. Due to high attenuation over the power line, the noise is also location-dependent. Apart from these, ingress sources such as amateur radio transmission can render certain frequencies unfit for communications [38].
Due to the above mentioned power line channel characteristics, it is necessary to carefully select modulation schemes and sophisticated error correction and detection technologies for forming up reliable physical layers as a basis for robust power line communications.
In [4], a comparison of the major modulation schemes in PLC is reported in Table 3.1 and they include:
• Spread-spectrum modulation, particularly Direct Sequence Spread Spectrum (DSSS).
• Broadband single-carrier modulation without equalizing.
• Broadband single-carrier modulation with broadband equalizing.
• Broadband multicarrier modulation with adaptive decision feedback equalizing.
• Multicarrier modulation in the form of “Orthogonal Frequency Division Multiplex-ing” (OFDM).

Table of contents :

Chapter 1 Introduction
1.1 Why do we need a new PLC
1.2 Perimeter of our study and its context: REMPLI
1.3 Research problems
1.4 Our Approaches, contributions and the organization of the thesis
Chapter 2 Electric Power Distribution and Consumption
2.1 Power electric distribution system
2.2 Main applications for the control and handling of electric power distribution
2.3 System requirements
2.3.1 Functions
2.3.2 Timing constraints
2.4 Communication networks
2.5 Conclusion
Chapter 3 Power Line Communications – Technologies and Problems: Requirements for their Control and Open Issues
3.1 Historical development of data communication over power line
3.2 Regulatory of PLC communication
3.3 Present PLC technologies and applications
3.3.1 Physical layer
3.3.2 MAC layer
3.3.3 Current PLC applications
3.4 Standards
3.5 Identification of problems in PLC technology for utility applications
3.6 REMPLI project and architecture
3.7 Conclusions
Chapter 4 Routing Algorithms
4.1 Routing protocols
4.1.1 DLC 1000
4.1.2 SFN
4.2 Performance metrics
4.3 Theoretical analysis
4.3.1 Average polling cycle duration of DLC 1000
4.3.2 Theoretical analysis of SFN
4.4 Numerical comparison between SFN and DLC 1000
4.4.1 Five channel models
4.4.2 Average duration of a polling cycle
4.4.3 Bandwidth consumed for routing signaling
4.4.4 Routing overhead
4.4.5 Conclusion
4.5 Simulation and performance evaluation
4.5.1 Physical Layer Emulator
4.5.2 Simulation parameters for routing protocols
4.5.3 Simulation results of DLC 1000
4.5.4 Simulation results of SFN
4.6 Improvement of SFN protocol
4.6.1 Methods to decide the number of repeater levels
4.6.2 Simulation results
4.6.3 Conclusion
Chapter 5 REMPLI Performance Evaluation
5.1 Logical channel
5.2 Network layer services
5.3 Performance Evaluation
5.3.1 Performance in an autonomous PLC network
5.3.2 End to end performance in REMPLI PLC network
5.4 Conclusion
Chapter 6 Dispatcher
6.1 Traffic classes and priority levels in network layer
6.2 System constraints
6.3 Aperiodic traffic
6.4 Periodic traffic
6.4.1 Execution time Ci
6.4.2 Static Periodic Polling
6.4.3 Dynamic polling approach
6.5 Simulation results
6.5.1 Static schedule vs dynamic schedule
6.5.2 DP vs DP with deadline relaxation
6.6 Towards dispatcher implementation
6.7 Conclusion
Chapter 7 Random Access Protocol Based on SFN
7.1 Characteristic of random access protocol based on SFN
7.2 Random access protocols design
7.2.1 Time slot partition in random access logical channel
7.2.2 ARQ mechanism
7.2.3 Repeating in SFN protocol
7.2.4 Protocol description
7.3 Simulation results
7.3.1 Repeater level
7.3.2 Two protocols comparison
7.4 Conclusion
Chapter 8 Conclusions and Future Works
Appendix A Calculation Program
A.1 DLC 1000
Appendix B Simulation Model
B.1 Interface Visual C++ Physical Layer Emulator and OPNET Simulator .
B.2 REMPLI simulation in OPNET
B.2.1 Medium node
B.2.2 Master node
B.2.3 Slave node
B.2.4 Bridge node
B.2.5 ALOHA-master node
B.2.6 ALOHA-slave node
B.2.7 CSMA-master node
B.2.8 CSMA-slave node
B.3 Configuration
B.4 Statistics tools
List of my Publications


Related Posts