Abstract: EMBEDDED SYSTEM FOR REAL TIME ENERGY MANAGEMENT system which includes Utility

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Aleesha Joan Welch
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1 EMBEDDED SYSTEM FOR REALTIME ENERGY MANAGEMENT UDHAYARANI.T 2/8 Flowers apartment, G1 B Block, Flowers Road, Purasawakkam, Chennai, Tamilnadu, India The author is affiliated to Department of Applied Electronics, School of Electronics, College of Engineering, Guindy, Chennai, Tamilnadu, India Abstract: Embedded system for real time energy management is the most significant automatic meter reading system which saves money, time and reduce overhead. This system not only calculates energy consumed and also announces the amount to be paid by the consumer when he is accessing the system through phone. It provides fast information retrieval, eliminates human error, and reduces overall administration and maintenance cost. Indexing terms: Embedded systems applications, DTMF, Frequency modulation &demodulation, Interactive voice response system. 1.Introduction: In Electricity Billing we find the following type of errors such as wrong utility rates, miscalculated bills, mistaken meter readings, broken meters etc.. When we identify such billing errors we negotiate a resolution with our utility. But here we do not need such negotiations This EMBEDDED SYSTEM FOR REAL TIME ENERGY MANAGEMENT system which includes Utility accounting, Energy and rate analysis, Bill Processing, and Payment that will help us to reduce administration overhead while decreasing the utility cost. So we can Save time and money by steam lining utility payment process and reduce overhead by making informed energy management decisions. The main features of the system are Access information through Telephone System. Fast information retrieval System announces both the Consumer Account No. keyed and corresponding Electricity tariff to be paid by the consumer. 24hours service possible. Eliminates the human operator and human error. The system reduces the over all Administration and Maintenance cost 2.An automated meter reading system can offer the following benefits to electric utilities: More efficient meter reading - With an automated system, meter readers can significantly improve their productivity over a manual system. Improved meter reader safety - Meter readers are less susceptible to the dangers of meter reading, including crime, dogs, heat, and other issues. Tamper detection - With an AMR system, meter reading can be done for most utilities within several days, enabling the utility to have a better view of consumption levels and identify possible meter tampering. Billing accuracy - Increased accuracy of an AMR system ensures that readings are done correctly the first time, which improves customer satisfaction. Hard-to-reads - Hard-to-read meters can be read from a safe distance. Eliminate estimated reads - Many utilities can justify going to a monthly read schedule for residential reads, eliminating estimated reads which can often lead to dissatisfied customers. More efficient use of personnel - Meter readers can be re-deployed into other, higher value and enjoyable functional areas which can improve morale and reduce turnover among staff.

Compatibility with existing equipment - This system offers a wide range of compatibility with other components of an advanced metering solution, including electronic meters, handheld computers, and

2 Compatibility with existing equipment - This system offers a wide range of compatibility with other components of an advanced metering solution, including electronic meters, handheld computers, and billing software. 3.OPERATIONAL DIAGRAM (OVERVIEW) in the form of audio files in response to the consumer call through IVRS. In this application we consider only one user with maximum consumption of four digits. Therefore the transmitted signal consists of five pulses one is c consumer ID, Other four is Consumption reading. However it can be extended to any number of consumers by coding. 4.TRANSMITTER SECTION (consumer side) : Operation of the transmitter can be explained by splitting it into three section. 1. LOADING SECTION Fig.1 This application comprises two sections One in consumer side and other in distribution side. The consumer section consists of a transmitter where the amount of energy consumed by the consumer is converted into pulses using an application specific integrated circuit ADE The ADE 7751 supplies average real power information on its low frequency outputs. These logic pulses are counted in a microcontroller 89C51 by interfacing using an optocoupler. The number of pulses may be calibrated to increment the seven-segment display, which indicates the number of units consumed. These counted pulses are encoded into DTMF form by an IC UM The DTMF tones are frequency modulated and transmitted.any specific frequency band may be allotted for transmission. In receiver side the frequency modulated signals are demodulated, amplified and decoded using a DTMF decoder IC M8870.The received logic data is stored in a computer database by interfacing a microcontroller 89C51.The consumed units are calibrated for utility billing. The data stored in the database will be outputted The actual load is connected in this section is where the load get the supply through an application specific integrated circuit ADE 7751 which is a power measurement integrated dedicated chip as it gets the input V and I through the potential and current transformers Fig 2. Transmitter Block Diagram respectively. With these inputs the ADE 7751 will issue the train of square pulses where frequency is determined by the load. These pulses are proportional to the average real power consumed. 2. ENERGY CALCULATION SECTION This section consists of a 8 bit micro controller (89C51) which act as a counter and counting the number of pulses from the ADE The micro controller has been programmed such a way that when its count value is equal to

1188000 it will increment another counter by one (ie) 1188000 pulses = 1kwh (1 unit) and the first counter get resets and the next counting starts and the process is cumulative.

3 it will increment another counter by one (ie) pulses = 1kwh (1 unit) and the first counter get resets and the next counting starts and the process is cumulative. The same will be outputted to seven segment LED display. 2. TRANSMITTING SECTION When the Energy transmit signal is applied ( by pressing energy transmit switch) the Energy (number of unit consumed) counted in previous section in the micro controller has been send to DTMF Encoder through the analog switch which is used to short circuiting the required column and rows. This dual tone multiple frequency (DTMF) signal has been mixed with the carrier frequency of 100 MHZ by the mixing transistor. This modulated wave has been transmitted through the antenna serially. 5.Application Specific Integrated Circuit (IC- ADE7751) Fig 3. Single Phase Energy Metering IC with On- Chip Fault Detection The ADE7751 is an accurate fault tolerant electrical energy measurement IC intended for energy distribution systems. It provides instantaneous and average real power based on line. The part specifications surpass the accuracy requirements as quoted in the IEC The only analog circuitry used in the ADE7751 are in the ADCs and reference circuit. All other signal processing is carried out in digital domain. This approach provides superior stability and accuracy over extreme environmental conditions and over time. The ADE7751 continuously monitoring both the phase and neutral currents. A fault is indicated if fault current differ by more than 12.5% and billing is continued using the larger of the two calibrations. High Accuracy, Surpasses 50 Hz/60 Hz IEC 687/1036 Less than 0.1% Error over a Dynamic Range of 500 to 1 Supplies Average Real Power on the Frequency Outputs F1 and F2. High-Frequency Output is intended for Calibration and Supplies Instantaneous Real Power Continuous Monitoring of the Phase and Neutral Current. The ADE7751 includes a power supply monitoring circuit on the AV dd supply pin. The ADE7751 will remain in a reset condition until the supply voltage on AV dd reaches 4 V. If the supply falls below 4 V, the ADE7751 will also be reset and no pulses will be issued on F1, F2, and CF. Internal phase matching circuitry ensures that the voltage and current channels are matched whether the HPF in Channel 1 is on or off. The ADE7751 also has anticreep protection. The ADE7751 is available in 24-lead DIP and SSOP packages. 6.Theory of operation The two ADCs digitize the voltage and current signals from the current and voltage transducers. These ADCs are 16-bit second order sigma-delta converters with an oversampling rate of 900 khz. This analog input structure greatly simplifies transducer interfacing by providing a wide dynamic range for direct connection to the transducer and also by simplifying the antialiasing filter design. A programmable gain stage in the current channel further facilitates easy transducer interfacing. A high-pass filter in the current channel removes any dc component from the current signal. This eliminates any inaccuracies in the real power calculation due to offsets in the voltage or current signals. The real power calculation is derived from the instantaneous power signal. The instantaneous power signal is generated by a direct multiplication of the current and voltage signals. In order to extract the real power component (i.e., the dc component), the instantaneous power signal is low-pass filtered. Figure 4 illustrates the instantaneous real power signal and shows how the real power information can be extracted by low-pass filtering the instantaneous power signal. This scheme correctly

calculates real power for nonsinusoidal current and voltage aveforms at all power factors. All signal processing is carried out in the digital domain for superior stability over temperature and time.

The low-frequency output of the ADE7751 is generated by accumulating this real power information. This low frequency inherently means a long accumulation time between output pulses.

4 calculates real power for nonsinusoidal current and voltage aveforms at all power factors. All signal processing is carried out in the digital domain for superior stability over temperature and time. Signal processing diagram Fig 4. This is the correct real power calculation. DC component of instantaneous power signal conveys real power information PF < 1 Fig 5. The low-frequency output of the ADE7751 is generated by accumulating this real power information. This low frequency inherently means a long accumulation time between output pulses. The output frequency is therefore proportional to the average real power. This average real power information can in turn be accumulated (e.g., by a counter) to generate realenergy information. Because of its high output frequency, and hence shorter integration time, the CF output is proportional to the instantaneous real power. This is useful for system calibration purposes that would take place under steady load conditions. Fig 6. 7.ANALOG INPUTS Channel V2 (Voltage Channel) The output of the line voltage transducer is connected to the ADE7751 at this analog input. Channel V2 is a fully differential voltage input. The maximum peak differential signal on Channel 2 is ±660 mv. Figure 7 illustrates the maximum signal levels that can be connected to the ADE7751 Channel 2. Maximum signal level at channel 2 Power Factor Considerations The method used to extract the real power information from the instantaneous power signal (i.e., by low-pass filtering) is still valid even when the voltage and current signals are not in phase. Figure 3 displays the unity power factor condition and a DPF(displacement power factor) = 0.5, i.e., current signal lagging the voltage by 60...If we assume the voltage and current waveforms are sinusoidal, the real power component of the instantaneous power signal (i.e., the dc term) is given by: Fig 7. Channel 2 must be driven from a commonmode voltage, i.e., the differential voltage signal on the input must be referenced to a common mode (usually AGND). The analog inputs of theade7751 can be driven with common-mode voltages of up to 100 mv with respect to AGND. However, best results are achieved using a common mode equal to AGND.

5 Channel V1 (Current Channel) The voltage outputs from the current transducers are connected to the ADE7751 here. Channel V1 has two voltage inputs, namely V1A and V1B. These inputs are fully differential with respect to V1N. However, at any one time, only one is selected to perform the power calculation Fault Detection section. The analog inputs V1A, V1B, and V1N have the same maximum signal level restrictions as V2P and V2N. However, Channel 1 has a programmable gain amplifier (PGA) with user-selectable gains of 1, 2, 8, or 16. These gains facilitate easy transducer interfacing. Figure 7 illustrates the maximum signal levels on V1A, V1B, and V1N. The maximum differential voltage is ±660 mv divided by the gain selection. Again, the differential voltage signal on the inputs must be referenced to a common mode, e.g., AGND. The maximum common-mode signal is ±100 mv as shown in Figure 7. Maximum signal level at channel 1 and burden resistor (Rb) are selected to give a peak differential voltage of 660 mv/gain. Connection Diagram for channel 1 Fig 9. Figure 10 shows two typical connections for Channel V2. The first option uses a PT (potential transformer) to provide complete isolation from the mains voltage. In the second option, the ADE7751 is biased around the neutral wire and a resistor divider is used to provide a voltage signal that is proportional to the line voltage. Adjusting the ratio of Ra and Rb is also a convenient way of carrying out a gain calibration on the meter. Connection diagram for channel 1 Fig 8. 8.Typical Connection Diagrams Figure 9 shows a typical connection diagram for Channel V1. Here the analog inputs are being used to monitor both the phase and neutral currents. Because of the large potential difference between the phase and neutral, two CTs (current transformers) must be used to provide the isolation. Notice both CTs are referenced to AGND (analog ground), hence the common-mode voltage is 0 V. The CT turns ratio Fig 10. The output logic pulses from ADE7751 are given to the microcontroller 89C51 are counted by a counter. This counter increments another counter when the count value reaches one unit. The same may be displayed in a MCU interface 8279 to display the amount of units consumed. At any particular time the consumed data may be transmitted by using a pushbutton (optional) or the same may be done by coding using a RTC. Before transmission the pulses are converted to analog signals by a DTMF encoder

6 UM91214 and transmitted through frequency modulation. 9.Receiver section : Fig 11. In the receiver section there are two modes of operation : Receive mode and IVRS (Interactive Voice Response System) mode.this can be done by a switch. When the distribution section is in the receive mode (i.e) getting power consumption from the transmitters the IVRS section is deactivated. When the processing of utility billing is over the IVRS section can be activated by placing the switch in IVRS mode. In receive mode the frequency modulated signals are demodulated, decoded by a DTMF decoder IC M8870. The BCD output from the M8870 are given to the micro-controller 89C51 and stored in the computer database. The received readings are calculated for billing using Visual Basic coding and the same is stored in the computer database. In IVRS mode the telephone lines are interfaced to the computer through the microcontroller using proper telephone interface circuit. When someone calls the distribution section the ring detector circuit is activated, the dialed tones are decoded using M8870, amplified and applied to the system through the micro-controller. The ring detector also connected to the microcontroller activates the hook off relay thereby indicating the inward transmission. After getting welcome message the consumer is requested to dial the consumer number after the beep. Now the signal out relay is activated thereby indicating the outward transmission. The IVRS section informs the amount to be paid to the called subscriber. A security code may be added to avoid unwanted accessing. An optional LCD display may be added to display the actual processing. Thus the EMBEDED SYSTEM FOR REAL TIME ENERGY MANAGEMENT is an easy accessing, low cost and easy to implement system. 10.conclusions: The Energy Consumption of each consumer can be received in the local receiving center with in a short distance which may called as Local Data Center, from that transmitted data is stored in its data base is also made available for the central data base which is main data base center where all the local data centers are connected.the Energy Consumption data of more No. of consumers say hundred consumers are connected to the Local HUB through wire from which all the data are serially transmitted. At the receiving center, the serially received data can be chopped at the predetermined length, there by Hundred valid data of respective consumer can be recovered and each consumer can be identified using the consumer ID in the sectioned data.this system is high sensitive to small change in load, at a time, all meter readings at different locations are down loaded which enables the electricity utility company to realize the revenues and high accuracy of data is obtained. 11.REFERANCES: [1]JOHN B. PEATMAN, Design with Micorcontrollers Mc Graw Hill international Ltd. [2]ATMEL manual an 8 and 16 bit [3]KENNEDYG. Electronic Communication Systems, Mc Graw Hill international Ltd. 4 th Edition, [4}IEEE Transactions on consumer Electronics. [5]MALVINO AND LEACH, Digital principles and applications Mc Graw Hill international Ltd [6]Mohammed Rafiquzzaman., Micro processor and micro computer based system design [7] AirBorn Electronics Circuit Design Library - microcontroller circuits based on AT89C2051

7 [8] AVR Embedded Microcontroller Resources - very good AVR link page [9] DonTronics Atmel page - lots of Atmel resources [10]Analog Devices datasheet for ADE 7751 [11]Computer telephone interface by Mohsen banan

Energy Metering IC with On-Chip Fault Detection AD7751*

Energy Metering IC with On-Chip Fault Detection AD7751* a FEATURES High Accuracy, Supports 50 Hz/60 Hz IEC 51/1036 Less than 0.1% Error Over a Dynamic Range of 500 to 1 The AD7751 Supplies Average Real Power On the Frequency Outputs F1 and F The High Frequency