A Low Cost Demonstration Platform for Reducing Energy Consumption by Regulating Building Controls through VLC

Transcription

1 A Low Cost Demonstration Platform for Reducing Energy Consumption by Regulating Building Controls through VLC KOFI NYARKO, CHRISTIAN EMIYAH Electrical Engineering Morgan State University 700 East Cold Spring Lane Baltimore, MD 225, US Abstract: - LEDs are continually replacing traditional light fixtures such as incandescent light, fluorescent and CFLs in lighting because of their low energy consumption, longer lifetime and application for visible light communication (VLC). In this research, we demonstrate a low cost VLC platform for reducing building energy consumption through the intelligent regulation of building controls. We are using the differential pulse position modulation (DPPT) scheme for data synchronization between the transmitter and the receiver. The VLC system will be used to control a lamp (turn ON/OFF and dimming) by interfacing the VLC system with an existing home automation platform used to control the lamp. Key-Words:-Reducing Energy Consumption, Visible Light Communication, differential Pulse Position Modulation, Arduino; LED Introduction Reducing energy consumption by doing more with less continues to be an objective for the commercial and residential building industry. Lighting is a major source of electric energy consumption. According to the US Energy Information Administration (EIA), about 7% of total electricity consumed in the residential and commercial sector is used for lighting. [] The primary method of reducing this energy consumption is by replacing traditional incandescent and compact fluorescent light fixtures with low-energy consuming LED light fixtures. In recent years, the proliferation of LEDs in lighting has greatly increased because of the development of the white LEDs. Recent research shows that if all existing bulbs were replaced by WLED sources, within 0 years, we would have the following benefits: energy savings of joules, US$.83 trillion financial savings, 0.68 gigatons reduction of carbon dioxide emissions, and 962 million barrels less consumption of crude oil. [2] Moreover, LEDs provide efficient yet highly controllable light that can be used for visible light communication. The VLC system can be interfaced with existing building management platforms for building resource control. The U.S. Department of Energy estimates that 73% of electricity usage is consumed by buildings. The Heating, Ventilation and Air Conditioning (HVAC) systems account for almost 50% of the total energy budget [3]. Reducing unnecessary use of building resources through home automation can reduce domestic energy consumption. 2 Background VLC is data communication using radiation visible (safe) to the human eye. Currently, wireless networking is dominated by the use of radio frequency (RF) techniques. A few of the limitations to RF wireless communication are: interference, limited bandwidth, exposure to electromagnetic radiation, which can be hazardous in some cases, and eavesdropping. On the other hand, in visible light communication, there is no interference with other radio frequency, no regulation on bandwidth allocation, eavesdropping is limited since communication is confined by opaque walls, and radiation is safe for the human eye.[4] However, when considering the use of LEDs as both a light source and a communication medium, it is important to achieve effective communication data rates while limiting flickering visible to the human eye. Like other communication systems, VLC requires a transmitter and a receiver. The transmitter transmits an encoded signalthrough the modulation of visible light intensity, which is sensed by the receiver and processed accordingly. This work is funded by the Smart Lighting Research Center, under NSF Cooperative Agreement No. EEC ISBN:

2 LEDs are efficient light sources with a short response time. [4] Data can be encoded by modulating the on and off states of the LED. On the other hand, a reverse biased photodiode can be used to convert the modulated light into an electrical signal. With fast response time photodiodes such as the OSRAM - SFH23 photodiode, which has a 5ns rise and fall time, higher bit rates can be achieved. The radio frequency (RF) community, have utilized pulse position modulation (PPM) for various applications since the early 960s. A variation of PPM that has been proven efficient and less complex is the differential PPM (DPPM) in which data encoding is done regardless of clock. The delay between the pulses does not take reference from the rising edge of the clock; instead, each delay takes reference from the falling edge of the previous pulse. secondarduinodevice, which decodes the received signal. To use this system to control a building resource such as an office lamp, the VLC system will be interfaced with an existing building automation platform. There are several building automation platforms already in use e.g. Z-Wave, X0, LonnWorks and Bacnet. For many of these systems, there is a programmable controller and there is module to which the building appliance will be connected. Depending on the nature of the building automation solution, this module could be consumer oriented (i.e. a Z-Wave lamp module) or oriented towards commercial structures (i.e. LonWorks interface module). Z-Wave is the first protocol implemented in the demonstration platform. In the U.S., the Z-Wave operating frequency is MHz; therefore, it does not interfere with other household devices. An example Z-Wave controller and lamp module are displayed in figure 2 and 3, respectively. Figure : A DPPM signal for 000 As illustrated in figure, when the bit is 0, the pulse is delayed for some time t 0 while when the bit is,the pulse is delayed for some time t which is greater than t 0 as seen from the figure. According to Rufo et al., other modulation techniques require complex synchronization system to ensure correct detection.[5] Consequently, the DPPM technique was chosen as the preferred encoding schemeforthis research.with the requirements for VLC data encoding clearly identified, an appropriate low cost platform was selected to implement thebit sequence encoding and decoding of the transmitted signal. Arduino is a low cost open-source electronics prototyping platform. The microcontroller on the board can be programmed in arduino programming language, which is simply a set of C/C++ functions. [6] In this demonstration platform, an Arduino device is used to module the power applied to a set of white LEDs., The Arduino platform also comes with the ability to sense input voltages to several input pins on the board.[6]on the receiver end, a reverse biased photodiode is connected to a voltage amplifier circuit whose output is input to a 2 pin port to connect lamp Figure 2: HA07 Z-Wave controller Figure 3: HA03 Z-Wave lamp Module Control buttons (ON/OFF/DIM) ISBN:

3 The HA07 Z-Wave controller in figure 2 can control up to 2 different lamp modules. To control a lamp using the controller and a module, the module is first associated with a channel on the controller. The state of the lamp can now be controlled using the button corresponding to this channel. With the HA03 module, you can dim the lamp, turn it OFF or ON. The approach used by this platform for building control is to leverage the existing building controllers and modules as the last-mile of the VLC building control communication process. The command sequences that are sent by the VLC transmitter are received and sent to an interface layer that translates the VLC command sequences into compatible RF, Ethernet, or Powerline instructions for a given control platform. 3 Methodology 3. Functionality of the photodiode and photodiode circuit The photodiode is the sensing element of the VLC system that enables the receiver to detect the modulated incident light emanating from the transmitter. A photodiode consists of an active p-n junction operated in reverse bias. When light falls on the junction, External photons that is, light strike the semiconductor and separate the electrons and holes. The flow of these free charge carriers produces current. External voltage (reverse bias) enhances this effect. [7] the more charge carriers that will be created (more photocurrent). The photocurrent from the photodiode is the order of milliamperes. Therefore, there is a need to amplify the output from the photodiode. Figure 5: Photodiode Circuit The figure above represents the photodiode amplifier circuit developed for the demonstration test-bed. To test the functionality of the photodiode circuit, the photodiode is placed before an LED powered by a 50% 8V peak to peak square wave signal. Transmitted signal Received signal Figure 6: Testing the Photodiode From figure 6, there is a fall or a rise time t d, which is the minimum delay that should be used during the pulse modulation. If a delay less than t d is used there integrity of the transmitted signal will most likely be compromised. The implementation of DPPM is described in the next section. Figure 4: active p-n junction [9] From figure 4, as light (photons) fall on the p-n junction, electrons and holes are created from atoms in the depletion region. The carriers move towards either side of the depletion leading to the flow of current (photocurrent). Moreover, the more photons that strike the active area of a photodiode, 3.2 AchievingVLC with the Arduio platform To execute the DPPM scheme, the Arduino transmitter was programmed to convert an n-bit sequence, where n is currently set at 4, into an encoded signal such that when the bit is, a pulse is sent with a delay t and when the bit is 0, a pulse is sent with a delay, t 0. For this research, we set t = 2t 0. To signify the end of a bit sequence (or the start of a bit sequence), a pulse is delayed for t = 3t 0. ISBN:

4 Logic Level ( mA) will flow through R 3. A pull-down resistor is added between the Arduino and the positive lead input pin of the op-amp because the LOW state of the Arduino output pin appears as a short circuit and the op-amp is designed to output the maximum possible voltage and current at this state time 50 (us) 60 Figure 7: Encoded Signal (DPPM) However, because the LED is also used for illumination, it is required that the LED is on for the most time. Therefore, the system is inverted. Since the signal is mostly high, as show in Figure 8, the LED is mostly ON, so flickering is minimized. logic level time (us) Figure 8: Inverted DPPM Signal 3.3 Achieving higher luminosity Initial VLC communication tests were performed with a 20mA white LED, which was readily available in the lab. However this LEDis not well suited to provide sufficient elimination to mimic commercial LED luminaires (even in an array). In order to providethe necessary luminance, a set of four Luxeon neutral white LED were purchased and used to replace the 20mA LED. The LuxeonLEDs provides 0lm at 350mA and 220lm at 700mA. By combining these high power LEDs in an array, sufficient luminosity was attained. In addition, the Texas Instrument high power op-amp (OPA549s) was used to drive the amplifier for the LED array. A specialized circuit was built to drive the LED array, where the Arduino modulates the power drawn. This circuit is illustrated in figure 9. It is important to note that the resistor R 3 used in the circuit is a high power resistor, capable of handling 5W. With this circuit design, high current Figure 9: Driver circuit for LED array 3.4 Interfacing with Building Controls 3.4. Protocol For this research, a protocol similar to that of the Ethernet is used, where data is sent in packets or frames. For this demonstration platform, a frame consists of the following sections, which is also illustrated in figure 0: i. Start-of-delimiter ( : 0000 ): This confirms the beginning of a frame. ii. Destination Device ID ( e.g. 0 ): This is the receiver s ID. It is added in order to ensure that each receiver in a multi-receiver setup, is uniquely addressable. iii. Command Sequence ID ( ; range: -255 ): This is used to identify the number of command frames that have been sent. iv. Command Code ( e.g. 00 ): This is used to communicate the action to be executed by the receiver, e.g. change dim level to 50%, turn lamp full ON, or turn lamp full OFF. v. End-of-frame delimiter ( : ): This represents the end of a frame. Start of Delimeter Receiver's ID/Address Command Sequence # Command Code End of Delimeter ISBN:

5 Figure 0: A Command Frame Error Check In order to ensure that VLC commands are transmitted without error, initial thoughts for the design of the demonstration platform included a Cyclic Redundancy Check. However, this approach was modified to both reduce complexity and ensure higher tolerance for communication errors based on the expected sources of error. Since the communication medium requires line of sight, it is anticipated that certain errors may be due to physical obstructions within the environment. To mitigate these types of errors, the following procedure was implemented: i. A command frame is sent continuous for five (n) seconds, where n is adjustable ii. A command is only executed if the frame iii. has been received three consecutive times. The command sequence number must be incremented by one before a new command frame can be executed. This approach enables the system to be very tolerant of both physical obstruction as well as momentary channel integrity errors. However there is a cost of a significant reduction in the speed at which commands can be sent. That being said, the intended application for this demonstration test-bed does not require high volume control operations Interfacing with Z-Wave controller Most building control platforms support standalone controllers that can interface through Ethernet, serial or simple electrical connections. The first control platform incorporated into the demonstration platform is Z-Wave. For simplicity, a standard Z-Wave controller was simply modified with electrical relays to achieve control. A relay is an electrically operated switch. The channel control button on the Z-Wave controller also works in a similar manner toa switch. When a button is pressed, a circuit is closed and vice versa. Also, the dim level depends on how long the button is pressed. To automate this using Arduino, a relay is needed. Figure : Operating Z-Wave controller using Arduino From Figure, Nodes N and N 2 are connected to the contacts of the channel control button. When the arduino output pin is low, there is no contact between nodes N and N 2. This is the same as the button not pressed. When the arduino output pin is HIGH (about 5V), N and N 2 are connected simulating a button press. By controlling how long arduino output pin remains HIGH, different dim levels can be accomplished. The Z- Wave controller was modified by soldering the relay s N and N2 pins to the appropriate Z-Wave circuit board traces. 4 Results The demonstration platform discussed in this paper consists of several components, the most visible of which is the 2x2 high power LED array that is capable of 700lm (shown in figure 2). The array is mounted 8 feet from the ground to emulate the typical height of a building luminaire. The array is connected via two wires to the desktop setup of the test-bed. This setup includes the lab power supply, measurement equipment, and the Arduino powered encoding circuit. The Arduino, which is interfaced to a standard PC (for programming) is connected to the power amplifier circuit so that the light intensity of the LED array can be modulated based on push button switches connected to the input pins of the Arduino. Pushing a button causes the Arduino to send a frame consisting of a command sequence over the VLC channel to a receiving Arduino. This Arduino has a photodiode, connected to an amplifier circuit provided by Rensselaer Polytechnic Institute s Smart Lighting Research Center. The receiving Arduino receives and decodes the command frame and activates the relay addressed in the command frame to initiate Z- Wave command. This command is received by the ISBN:

6 Z-Wave command module, which turns a connected floor lamp on/off or adjusts the dimming level. Figure 2: 2X2 LED array The bitrates achieved are on the order of 4kbps 6kbpswithBit Error Rates (BER) as low as 9 from every 0 7 bits (with ambient light). The demonstration setup described in this paper is displayed in figure 3. Figure 3: Lab Setup B LED Array C Receiver with Z-Wave Controller L Controlled Lamp P Power source 4 Discussion One of the key capabilities yet to be developed in this platform is VLC propagation, where a single control signal can be propagated from luminaire to luminaire across an entire zone (or even an entire floor). This capability will enable building wide control with the limited use of RF transmissions (RF power can be kept to the minimum required to reach the control module depending on transmitter location). This will provide the added benefit of limiting RF leakage beyond the building perimeter, which should thereby improve security. References: [] How Much Energy is Used for Lighting, EIA, =3 [2] Kavehrad, Mohsen, "Sustainable energyefficient wireless applications using light," Communications Magazine, IEEE, vol.48, no.2, pp.66,73, December 200 [3] Energy Efficiency Trends in Residential and Commercial Buildings, Department of Energy ons/pdfs/corporate/bt_stateindustry.pdf [4] Yu Yang; Xiongbin Chen; Zhu Lin; Bo Liu; Chen HongDa, "Design of indoor wireless communication system using LEDs," Communications and Photonics Conference and Exhibition (ACP), 2009 Asia, vol., no., pp.,2, 2-6 Nov [5] Rufo, J.; Quintana, C.; Delgado, F.; Rabadan, J.; Perez-Jimenez, R., "Considerations on modulations and protocols suitable for visible light communications (VLC) channels: Low and medium baud rate indoor visible ligth communications links," Consumer Communications and Networking Conference (CCNC), 20 IEEE, vol., no., pp.362,364, 9-2 Jan. 20 [6] Arduino Homepage, Web. Jul 2, 203 [7] Mynbaev, D. K.; Scheiner, L.L., Fibre-Optic Communiations Technology, Prentice Hall PTR, 2006 [8] Feng-Li Lian; Moyne, James R.; Tilbury, D.M., "Performance evaluation of control networks: Ethernet, ControlNet, and DeviceNet," Control Systems, IEEE, vol.2, no., pp.66,83, Feb 200 ISBN: