Energy Monitoring With Power Line Communication

Transcription

1 Energy Monitoring With Power Line Communication Design Review Matthew Feddersen Evan Richards Saheed Rosenje Project #33 TA: Kevin Chen ECE 445 Senior Design Project Laboratory October 1st, 2014

2 1.0 Introduction 1.1 Statement of Purpose The purpose of our project is to create an efficient home appliance energy monitoring system. There are plenty of energy monitoring devices on the market. Currently all of these devices use wireless signals to transmit their energy consumption data. We believe this is a waste of energy and less efficient data transmission method. Our alternative is to use power line communication to transmit our data. We hope to design a product that is both affordable and energy efficient. 1.2 Objectives Goals Develop two working transmitter modules Develop one working receiver module Interface receiver module with internet to view data Functions Monitor power and energy usage of multiple appliances and devices Aggregate system wide usage data in central location Display data in user friendly format Benefits Easy to install No batteries or external power supplies needed Visualize both instantaneous power and energy usage over time Monitor multiple, distinct appliances and devices Features Compatible with all 120VAC appliances and electronic devices Modular, allowing for monitoring of numerous appliances and devices Store and view all data in one central location

3 2.0 Design 2.1 Block Diagrams Two distinct devices are needed for operation of the system: the Measurement and Transmitter Module, and the Receiver Module. The modular nature of our system allows the user to add any number of the Measurement and Transmitter Modules while only needing one receiver module. For demonstration purposes, we intend to build two Measurement and Transmitter Modules and one Receiver Module. In the block diagrams for each device, solid lines represent 120VAC 60Hz power, dashed lines represent DC power, and dot dashed lines represent the flow of measurement data. Figure 1 Top Level System Layout Figure 2 Measurement and Transmitter Module

4 Figure 3 Receiver Module 2.2 Block Descriptions and Circuits Measurement and Transmitter Module Overall: The Measurement and Transmitter Module acts as the device in between the wall outlet and the home appliance being monitored. Power from the 120VAC line is converted to DC by the AC/DC Power Circuit and then sent to power the PLC circuit, which in turn powers the microcontroller. The Measurement Circuit receives power from the 120VAC line and measures the voltage and current. It then passes the power along to the home appliance and sends the measured values to the Microcontroller. The Microcontroller converts the analog measurements to digital values using a built in ADC. It sends this data to the PLC chip, which then injects a message into the 120VAC power line in the form of a modulated signal. Power Circuit: This circuit provides the dc power needed by the PLC chip and the microcontroller. The PLC chip operates at 12V while the microcontroller operates at 3.3V. The power supply circuit only needs to provide the 12V power to the PLC chip, however, as the chip has a built in linear regulator which can output 3.3V at up to 50mA. According to [1] and [2], both devices combined can draw an approximate maximum current of 500mA. The power supply circuit was designed according to these specifications. An overall schematic of the power circuit can be seen in Figure 4 below. Power will enter the circuit via a standard NEMA 5 15 male connector, the type that plugs into a wall outlet. From there it

5 will pass through a 250V, 15A fuse for user safety and internal circuit protection. After passing through the fuse, the power will split into two separate circuits, the power circuit and the measuring circuit. Continuing with the power circuit, a transformer with turns ratio 115:16 will step down the line voltage to approximately 17V RMS. At this point a standard bridge rectifier is used to achieve full wave rectification of the voltage. The rectifier was picked to have a blocking voltage higher than 17V RMS and a maximum output current higher than 500mA. In order to adjust the voltage to the final desired level of 12Vdc, a capacitor and a linear regulator were added after the rectifier. The linear regulator, although inefficient, is an effective way to achieve a constant output voltage without having to implement a switching power converter with feedback. As long as the input to the regulator remains above the desired output by the regulator s designated dropout voltage, the output voltage will remain essentially constant. For the linear regulator chosen, the dropout voltage is 2.5V, meaning that the input must be at least 14.5Vdc in order to obtain an output voltage of 12Vdc. From this requirement it is possible to calculate the necessary value of the rectifier output capacitor. Assuming a worst case scenario of line voltage equal to 115V RMS, the secondary voltage of the transformer will be 16V RMS, with a peak voltage of 22.6V. The diode bridge has a total forward voltage of 1V, so the peak of the rectified voltage is 21.6V. In order for the capacitor to cover one full cycle of the output of the linear regulator, it must provide energy E = P T = V I 1 f = = 0.05 J (1) The energy stored in a capacitor is 1 2 E = 2 CV (2) Combining equations (1) and (2), we see that C = V 2 = 214 μf (3) 2E = (21.6) 2 The closest standard capacitor value is 220 μf. The other two capacitors are included as additional filters for the linear regulator as seen in [3]. Figure 4 Power Supply circuit for Measurement and Transmitter Module Measurement Circuit: This circuit will perform the necessary measurements of the line voltage and the current drawn by the home appliance. The circuit must be designed to output voltage levels which are within the

6 tolerance of the analog microcontroller inputs. As will be discussed later, we are using a version of the MSP430 microcontroller to convert the measurements to digital values, as well as perform calculations and interpret them before sending the data to the PLC circuit. As a result, the design of the measurement circuit in Figure 5 is based upon the design found in [2]. The voltage measuring circuit is essentially the same, whereas a few changes were made to the current measuring circuit. Instead of measuring the current with a current transformer, we have chosen to use a shunt resistor. The first impression of this choice is that it is inherently inefficient. With the choice of a very small, precise resistor, though, the losses can be minimized. We have chosen to use a precision resistor with a resistance of Ω. This will result in a maximum voltage of V = I R = = 75 mv (4) and the power dissipated will be P = I 2 R = = 1.13 W (5) This is still a relatively small power loss and the voltage will be within the measurable range of the MSP430. Figure 5 Measurement Circuit

7 Microcontroller: Acting as an ADC between the Measurement Circuit and the Powerline Communication module will be an MSP430FE4272 microcontroller. This particular MSP430 is extremely low power and is specifically tailored for voltage and current measurement, which is the main reason we chose it. The MSP430 that we chose takes approximately 3V and 400 microa as input. It will connect directly with our PLC chip, communicating via UART asynchronously. Quite simply, it takes the current and voltage values from the measurement circuit, digitizes them to one 24 bit message, and sends that to the PLC chip for transmission every 2 seconds. The 24 bit messages are formatted as one 16 bit current value and one 8 bit voltage value. The 16 bit current value is formatted with 14 value bits and 2 parity bits, while the voltage value is formatted with 7 value bits and 1 parity bit. The parity bits, in addition to redundant transmission, allows for rudimentary error checking in the receiving microprocessor. The format can be seen in the table below: I: I0 I1 I2 I3 I4 I5 I6 P0 I7 I8 I9 I10 I11 I12 I13 P1 V: V0 V1 V2 V3 V4 V5 V6 P2 P0 is the even parity of I0 I6, P1 is the even parity of I7 I13, and P2 is the even parity of V0 V6. The most relevant connections shown in the figure below are the RX/TX lines coming from the MSP to the ST, the input current and voltage values coming from the measurement circuit to the MSP, and the RX_IN and TX_OUT connections coming from the ST to the external filter circuitry. Interface between MSP430 (left) and ST7540 (right) Powerline Communication Chip:

8 A commercial Power Line Communication chip that acts as a transmitter to the power line. This will add a modulated carrier signal to the 60 Hz power line with our encoded messages. The modulated signal will arrive at the receiver to be demodulated. Example of FSK, from Wikipedia To transmit and receive data from our module we have selected the ST7540 transceiver FSK chip [5]. Our data will be sent using a frequency modulation scheme named binary frequency shift keying. When transmitting data, BFSK uses two frequencies to transmit binary information.with this scheme, the 1 is called the mark frequency and the 0 is called the space frequency. The figure above illustrates how the data signal is modulated across the carrier wave. We have selected the ST7540 default communication frequency of 132.5kHz which is within the FCC allow frequency C band [1]. We are also selecting a Baud Rate of 4800bps and a standard deviation of 1. This deviation widens the range between our mark and space frequencies of Hz and Hz. The data transmission and reception mode will be set to asynchronous since we are using a UART microcontroller to handle the transmission and reception timing. During transmission and reception, external signals at interfering frequencies or noise from other devices turning on and off, can cause distortion in our signal. In order to eliminate some of these distortions, we must strengthen our Rx and Tx signal. In transmission, the ST7540 filters our output signal spectrum and reduces the harmonic distortion. In addition, there is a variable gain amplifier with a gain range of 0db to 30db. The following figure depicts our transmission signal flow

9 PLC internal filter and liner injection diagram for Tx, from the ST7540 documentation [1] In addition to the internal filters, the ST7540 has an external filter for the transmission signal. The filter introduces attenuation approximately an octave above the transmission channel frequency. The following diagram depicts the flow of the transmission signal. PLC external filter and line injection circuitry, from the ST7540 documentation [1]

10 2.2.2 Receiver Module Overall: The Receiver Module is the central device responsible for receiving and aggregating the transmitter messages from the power line. Like the Transmitter Module, the Receiver has an AC/DC Power Circuit to power each of its components. It also has a PLC chip to receive and digitize the communication from the power line, and a microcontroller to decode this communication into a useful format. The microcontroller sends this information to the cloud through a wifi module. AC/DC Power Circuit: This circuit will be exactly the same as the one in the Measurement and Transmitter Module. It will convert the AC voltage from the wall outlet to the DC voltage necessary to power each component in the Receiver Module. PLC Chip: This is the same as the chip on the Transmitter Module, except it is set to specifically receive messages instead of sending them. This will interface directly with the microcontroller unit, sending any messages there for processing. This utilizes the same filter and line injection circuits as on the Transmitter. Similarly, in reception, the ST7540 receives signals and filters the signals to improve the sound to noise ratio before it reaches the demodulator. In addition, the ST7540 provides carrier/preamble detection which identifies signals with a harmonic component close to the signal frequency and detects whether a carrier is modulated at the Baud Rate. The following diagram depicts the flow of the received signal. PLC internal filter and liner injection diagram for Rx, from the ST7540 documentation [1]

11 Microcontroller and Wifi Module: The microcontroller takes in the data stream from the PLC chip, performs checks on the data parity as well as calculations for power and energy use, then sends the data to the cloud as a JSON object. We plan to use a Spark Core, an ARM based microcontroller with a built in TI CC3000 wifi module. We chose this because it fits within our power requirements of our receiver module and vastly simplifies the problem of wireless data transfer. The Spark Core is specifically built to simplify the interface between electronics and the internet, and there isn t a compelling enough reason for us to design and build our own interface when this one conveniently exists already. The Spark Core will take 5V as input from our power circuit, and anywhere from 30mA to 300mA of current, depending on its wifi connection and computational load. We will connect the microcontroller directly to our PLC chip to communicate via the UART serial protocol. Since the PLC chip will receive voltage and current data every 2 seconds from each transmitter, the spark core will be able to calculate an instantaneous power usage as well as an approximate energy metric relatively frequently. Even though we are not updating the values constantly, we expect such little variation in the voltage and current values that a 2 second sampling period will be sufficiently accurate. Interface between Spark Core (left) and ST7540 (right) Data Display: This will be a simple web page to show various metrics as tracked by the Spark Core. These metrics will be available for the overall power use as well as per transmitter, displayed in text form. The

12 metrics are current power usage, peak usage in the past 24 hours, peak usage in the past week, total usage over the past 24 hours, and total usage from the past week.

13 3.0 Requirements and Verification Measurement and Transmitter Module AC/DC Power Circuit Requirements V out = 12 V dc V ripple < 5% of V out I out,max = 500 ma Verification Test AC/DC power circuit with a multimeter and oscilloscope under no load, half load, and full load (500mA) to verify correct voltage and ripple. PLC Circuit Requirements PLC successfully receives data from MSP430 with no more than 5% error PLC successfully transmits data across powerline Draws no more than 500 ma at 12V Verification Feed data to chip and test with an oscilloscope to verify message modulation.verify the output signal s peak to peak voltage ranges from 1.75V to 3.5V Monitor powerline with signal analyzer and detect the data signal frequency modulation Measure consumed voltage and current on oscilloscope. Measurement Circuit Requirements 0.5 V and 0.5 A accuracy Voltage range of V rms Current Range of 0 15 A Verification Test measurement circuit with a function generator as input at low voltage levels, and use an oscilloscope to verify output at expected level. Test measurement circuit at minimum voltage, no load, then increase voltage to maximum, while taking down measured values. Repeat for 5A increments of load up to 15A Receiver Module

14 AC/DC Power Circuit Requirements V out = 5Vdc and 12Vdc V ripple < 5% of V out I out = 300mA at 5V and 100mA at 12V Verification Test AC/DC power circuit with a multimeter and oscilloscope under no load, half load, and full load to verify correct voltage and ripple. Test one voltage level first, then the other, then test together. PLC Circuit Requirements Able to filter and demodulate signal from power line Output correct data from demodulated signal, with 95% accuracy Verification Test with a function generator as input, and use an signal analyzer to verify message reception output. Test demodulated signal with oscilloscope to verify accuracy of received data. Microcontroller, Wifi, and Data Display Requirements Microcontroller can identify and ignore incorrectly transmitted data, with at least a 50% accuracy rate Webpage displays each of the required values as reported by the microcontroller with no mistakes Verification Test microcontroller with function generator as input, and use an oscilloscope or visual debugger to verify data correctness. Test wifi module with function generator as input, and use an internet browser to verify data upload. Program the Spark Core with test values to send to the webpage, then verify that they appear by refreshing the webpage. All values should match. 3.3 Tolerance Analysis

15 A part of project that we have concerns is the filtering of interfering signals. It is our hope we will have little to no interference but if this were to occur, we would first check for proper zero crossing with the three phases on the main line.this would involve synchronizing the transmission to the phase itself. In addition, we would also attempt to decrease the signal frequency. This would slow down the data speed but enable for for greater signal strength. the frequency of 110kHz has the highest gain but with in the B band. the following graph shows gain across the PLC s frequency band. We can not use the highest gain at 72kHz because it is in the A band held for electricity providers. Frequency response of the Tx active filter, from the ST7540 documentation

16 4.0 Ethics and Safety 4.1 Ethics Our project has some inherent safety risks that become ethical concerns in accordance with the IEEE Code of Ethics. Specifically, the 1st and 9th points: 1. to accept responsibility in making decisions consistent with the safety, health, and welfare of the public, and to disclose promptly factors that might endanger the public or the environment; 9. to avoid injuring others, their property, reputation, or employment by false or malicious action; As such, we will be sure to address any safety risks involved in working directly with mains power, ensuring our own safety while working on the project as well as the safety of others while using it. In addition, as a group, we will strive to improve our understanding of the formal engineering design process while offering constructive feedback to each other throughout. While this may be a capstone design project, there is still plenty to learn and improve upon for each of us. This is consistent in points 6, 7, 8, and 10 from the IEEE Code of Ethics: 6. to maintain and improve our technical competence and to undertake technological tasks for others only if qualified by training or experience, or after full disclosure of pertinent limitations; 7. to seek, accept, and offer honest criticism of technical work, to acknowledge and correct errors, and to credit properly the contributions of others; 8. to treat fairly all persons and to not engage in acts of discrimination based on race, religion, gender, disability, age, national origin, sexual orientation, gender identity, or gender expression; 10. to assist colleagues and co workers in their professional development and to support them in following this code of ethics.

17 4.2 Safety Since our project involves working with mains power, which is about 120V and 15A, there is a clear safety risk that we must address. Fortunately, the General Electrical Safety for Labs provided by the UIUC Division of Research Safety covers the basics of working with these levels of power. We have gone through the materials, and will adhere to the relevant safety protocols. For our end users, we will have to ensure that there is no further risk from electric shock with our project than normally present with wall sockets. For testing purposes, this can be achieved with proper insulation and protection around our 120V NEMA plug connectors. If we decide to produce a housing for the project, we can simply cover up the entire board with the housing material, which will give adequate protection to the end user.

18 5.0 Cost and Schedule 5.1 Cost Analysis Name Hourly Rate ($) Hours Total ($) = 2.5 * Rate * Hours Matthew Feddersen Evan Richards Saheed Rosenje Total 33, Item Quantity Unit Price ($) Total Price ($) ST7540 PLC MSP430FE4272 MCU NEMA 5 15 B male NEMA 5 15 B female Op amps and comparators Resistors, capacitors, inductors, diodes Spark Core wifi controller PCB's Hammond 164G16 XFMR Linear Regulator UA BAS3007A rectifier HXP Fuse Total

19 Item Total ($) Labor Cost 33, Parts Cost Total Cost 34, Schedule Week Task Responsibility 9/14/2014 Finish Proposal Matt Research commercial PLC chips Saheed Research current and voltage sensor parts Evan Design ADC circuit Matt 9/21/2014 Choose and purchase PLC Tx/Rx pair Saheed Order current and voltage sensor parts Evan Design monitoring circuit Evan Choose and order a microcontroller Matt Work on Design Review material Saheed 9/28/2014 Finish Design Review material Evan Eagle a microcontroller board Saheed Breadboard ADC circuit Matt Breadboard monitoring circuit Evan 10/5/2014 Design housing for transmitter and receiver pairs Saheed Eagle monitoring board Evan Set up and program microcontroller Matt 10/12/2014 Eagle schematic for ADC Matt Learn how to operate PLC chips Saheed PCB manufacturing of monitoring board Evan 10/19/2014 PCB manufacturing of ADC board Matt Assemble and verify monitoring board Evan

20 Demonstrate PLC chips working with virtual power lisaheed 10/26/2014 Test microcontroller with PLC chips Saheed Assembly and verification of ADC board Matt 11/2/2014 Further receiver testing with microcontroller Saheed Monitor/Transmitter assembly and testing Evan 11/9/2014 Test microcontroller with end user data display Matt Test transmitter/receiver interactions over PLC Saheed 11/16/2014 Prepare Demo, Presentation, and Paper Evan

21 References [1] AN2451 Application Note: ST7540 FSK Power line Transceiver Design Guide for AMR CD pdf [2] MSP430FE42x2: Mixed Signal Microcontroller datasheet [3] ua78m00 Series Positive Voltage Regulators datasheet [4] Power line Modems, Power Supplies, and Cleaning Up the Neighborhood [5] ST7540 FSK power line transceiver datasheet web ui/static/active/en/resource/technical/document/datasheet/ CD pdf [6] AN4068 Application Notes: ST7540 Power line Communication SOC Design Guide DM pdf