Abstract—Power Line Communication (PLC) is a communication method where the existing Power Line carries data. The home automation associates the usual electrical cabling to the renewable plants for smart home, smart grid. The use of PLC technology permits the use of the existing electrical network for data transfer. The use of renewable energy helps to reduce the electrical energy consumption. The user can also sell back energy to the utility during his off time, daylight. The different components of a low voltage low wattage solar photovoltaic system are monitored by the end user. The characterization of the inverter as medium of communication permits the deployment of PLC technology over the solar photovoltaic energy system. Combined BFSK modulation and Manchester coding were implemented. At 120 bps, data were transferred over a 230 W modified sine wave inverter, simplex from the DC bus.
Keywords—H-Bridge inverter, PWM control, Manchester coding, FSK modulation
I. INTRODUCTIONThe rapid progression of home automation in the last years has been enabled by the use of Power Line Communication technology. When renewable energies are integrated into the grid (grid tied), the monitoring of the different modules demands communication technologies. Communication technologies are also needed when the different parameters of the renewable system are controlled by the user. Two options are available: Wireless technology and wire technology. Wireless technology refers to the transmission of data wireless-based. It is possible to control a solar photovoltaic system and grid tied systems, by controlling the inverter modules (this is actually present on the market). it is also possible to monitor the Maximum Power Point (MPP) of the solar photovoltaic. As Highlighted in [16], among wireless technologies, Zigbee appears as being the leading standard for home network communication, against the other Wireless technologies. Wi-Fi is leading the standards for laptops and phones communication. Wi-Fi is the synonym for IEEE 802.11, while WiMAX is based on the IEEE 802.16. Wire technology refers to the transmission of data over a wire-based. Among wire technologies, Power Line Communications is a special technology in which, the low frequency power line carries a high frequency communication signal. That signal can
be recovered at any point of the same network. Power Line Communications are leaded by the IEEE 1901 standards for broadband PLC, by CENELEC, G3 and PRIME etc. for narrowband PLC. F. Richard in [16] has described the interoperability between the communication technologies and the applications of each of them. In wire technologies, the standard telephone technology has been proved. There is a cable between the satellite dish on the roof and the decoder inside the house carrying simultaneously the DC energy from the decoder to power the LNB (low Noise Blocks), and the TV signal from the LNB to the decoder. The smart grid and the smart house use the existing electrical network to connect devices (PLC technology) despite the noise level as well as the attenuation which is as a result of the low impedance of the power line.
Problem statement
The question to arise is; why is wireless technology used in solar system when there are wires connecting devices? The answer leads us to the use of the existing electrical wires betweendifferent modules to communicate. Actually, the use of PLC technology in smart grid smart home will cover the weakness points of wireless technologies. Some of them are presented in [17] where the authors classified the different technologies used in home automation and smart grid, they presented for Zigbee, WiFi and PLC, the advantages and the notable weakness points. It is to notice that, wire technology for home automation can work where wireless technology can not, for example the basement of tall buldings. It is known that wireless signal hardly pass through thick walls and slab.
Figure 1: Block diagram of the system
Solar PV
Boost-er
Invert-er
Laod ®
Tx Rx
2013 IEEE 17th International Symposium on Power Line Communications and Its Applications
To achieve transmission in the case of this work, the inverter needs to become a medium of propagation of the communication signal. A BFSK modulator was built using a VCO chip, combined with Manchester coding techniques for DC free communication, and connected to the couplers to make the transceiver. A booster and an H-bridge inverter was built for the project. The transmitter and the receiver are connected to communicate with each other through the inverter, when the system is fed by a 250 W-18V solar panel and powering a resistive load, the block diagram of the system is presented on Figure 1. The focus in this paper is on the inverter and the communication system.
II. INVERTER DESIGN Designing an inverter implies the choice of three important parameters:
The shape of the output voltage;
The topology;
The type of control.
Figure 2: H-bridge inverter power stage
In this case, the output is a modified sine wave. The topology is H-Bridge (Figure 2), controlled by a self-oscillator integrated circuit or by a microcontroller. H-bridge topology is indicated for renewable energy [1]. The model proposed in [2] motivated the choice of the number of switches and the number of phases as calculated in the following equations. = − 12 = 1= 2 = 4M is the number of phase, N is the system level; N = 3 in this case; k is the number of switches.
A. PWM Control and gate drivers
The IR2154 produces a square wave at calculated frequency. To control the H-Bridge inverter, 2 IR2154 are needed. There is noneed for using any other gate driver, IR2154 being a gate driver itself. Another external control using a microchip were design to show the impact of the inverter control on the communication system. The PIC used in this second control is PIC16F887; especially its CCP module.
B. H-Bridge inverter Power stage
The power stage is made of 4 switches connected as showed on Figure 2. they are closed and opened two by two. Each pair receives an input gate signal from a gate driver. The gates close and opend at switching frequency fsw. One MOSFET receives the signal from the high-side driver output while the other one receives the signal from the low-side driver output causing one to be on and the other to be off during one half-cycle [18], [19]. They then change states for the other half cycle. The other pair of MOSFETs will be driven by a gate driver with a 50 Hz square wave input. One of the pair of MOSFETs will be driven by an inverted signal so that only one is on at a time. The output signal will be a zero centered. Tthe switching frequency is 40kHz for the control using the PIC microchip. Component selection was done with tact to give the inverter more than 70% efficiency at nominal load. IRF740 was used as switch. A snubber filter was design to reduce the noise magnitude in the inverter. Figure 3 shows the inverter output captured on an oscilloscope using a 100 times probe.
Figure 3: Modified sine wave inverter output measured with a 100 times probe.
III. COMMUNICATION SYSTEM Five main modules constitute a communication system: the data source, the transmitter, the medium, the receiver and the recipient. The transceiver was set up the maner in which it will best cope with the noises. The medium accommodates different types of noises. The noise spectrum is dominated by a high concentration of low frequency noise. BFSK is used to modulate the signal produced by the coder. Manchester coding was the
coding technique used to encrypt the message. The PIC16F887 microchip includes many modules for communication; among them, Manchester module is capable of encoding a message according to the Manchester coding techniques and produces a binary signal ready to be modulated and transmitted. XR2206 and XR2211 are two VCO chips used in FSK Modems. In this experimentation, the first one is used to produce the BFSK signal and the second is the demodulator. Generally, both chips have a very low power output. An amplifier steps up the current and the voltage from the XR2206 in order to challenge the noise magnitude in the inverter. The output power of the amplifier is 5 W. The PWM modulated message is a data signal (Square wave) with variable duty cycle according to the different positions of “1” and “0. The two frequencies produced by the VCO are 100 kHz and 125 kHz. The system is non-coherent and non-orthogonal. The transmission is characterized by the following parameters:
Figure 4 gives the frequencies classification foe this transmission system. This communication system was tested over 2 m Power Line channel dominated by periodic impulse noise and the transmission was achieved with less than 30% bit error.
IV. PROPAGATION MEDIUM The transmission medium is a crucial link in any communication system. Without it, there would be little or no issues to battle with in the propagation of information from one point to another. In commutation, the transmission medium may include the ionosphere, the troposphere, free space, or simply a transmission line (cable of any type). In the case of this research, the transmission medium is the inverter. Every medium ofcommunication is a source of impairment. The modified sine wave inverter presents many sources of noise and the switches used can cause attenuation and distortion of the carrier signal. The impedance drain-source of the MOSFETs used to build the medium (ZDS) is made of many virtual components (capacitors,
resistors and inductors). That impedance attenuates the signal. Figure 5 is the simplified diagram of the H-bridge inverter. ZDS1
and ZDS2 are respectively the input impedance of the two MOSFETs that are “on” at the same time. The value of ZDS1 and ZDS2 are 0.55Ω [3] when the switch is closed. For a 230W inverter, the load resistance is about 210.43Ω; as the load power grows, its resistance decreases; for 10 kW, the resistance is 4.8 Ω, associated with the two serial drain source impedance. The signal is facing 5.9Ω, which is very low. This last situation is typically comparable to the Power Line Communication channel [4]. Figure 6 shows how a single MOSFET attenutes a small signal when the in diagram Figure 5 is used.
A. Attenuation
Figure 5: Illustration of the communication path in the inverter
Figure 6: Attenuation in a single IRF740, gate connected to the ground
B. Noise The inverter in its operation as any other converters produces noises. These noises are likely to affect the modulated signal when the inverter is used as a channel of communication.
1) Generation-recombination noise:
Generation-recombination (G-R) noise is the result of the fluctuation in the material in conductance due to a series of discrete event provoked by the release of the trapped carriers after a while. G-R noise is a low frequency noise [20]. This noise is present in inverters.
Δf Δf
Tracking bandwidth
99241.2Hz
111803.4 Hz
125621.79 Hz
100 kHz 125 kHz
25000 Hz
Figure 4: Frequencies classification for the reception system
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2) Delta-I noise:
Delta-I noise is also called simultaneous switching noise (SSN), Ground Bounce (Vdd Bounce) Noise (G-B-N), dI/dt noise, simultaneous switching output noise (SSO) [9]. The sources of the current surges are the input/output drivers and the internal logic circuitry; as a result of the self-inductance of the off-chip bonding wires and the on-chip parasitic inductance inherent to the power supply rails, the fast current surges result in voltage fluctuations in the MOSFET [8]. [9], [10], [11], and [12].
3) Flicker noise: (1/f noise)
1/f is a frequency dependent noise, it occurs at low frequencies switching. The magnitude of 1/f noise is very significant at frequencies less than 100 Hz. It results in long-term drift in electronic components [6], and [7].
4) Crosstalk:
Crosstalk (XT) is the result of unwanted capacitive, inductive or conductive coupling from one circuit to another.
5) Shot noise:
The shot noise is independent of the frequency (white noise), itis due to the statistical variation of the flow of electrons across junctions.
6) Thermal noise:
The Johnson noise is due to different velocities and movements of electrons in electrical components [5] it is a white noise.
7) Intermodulation noise
When two or many signals at different frequencies are mixed in the same medium, harmonic frequencies, sum or difference of the original frequencies, or multiples of those frequencies can be produced, which can interfere with the intended signal; this occurs in converters.
The inverter as communication medium can easily be compared to PLC channel modeled by Hooijen and Vinck in [13]. The model is presented on figure 7.
Figure 7: Model of inverter as a communication medium
Where ∑rest represents the others noises except 1/f noise and SSN. The converter channel is characterized by the following transmission equation:
( ) = ( ) + ( ) + ( ) + The noise spectrum measured in the inverter is presented in Figure 8, the maximum peak is about 5.43 dB in the range of frequencies between 0 Hz and 1 MHz, when the inverter is not driving any load. After that range of frequencies, the spectrum shows a white noise with a magnitude corresponding to about -40.2 dB; those value increase with the load. For a 230W load, the peak magnitude of the noise reaches the value of 40 dB. For the input signal fixed at 6dB, a fixed bandwidth, the channel capacity is defined for the environment as a function of the frequency by the curve on Figure 9. For the carrier frequencies in the range of 0 to 100 kHz (narrowband PLC), the channel presents a very low capacity of transmitting a signal. From 1 MHz (Broadband PLC), the channel starts to be capable of transmitting a signal. This is the direct consequence of the domination of the low frequency noise in the system. This situation can predict the quality of the result that is produced. The noise spectrum in figure 8 may be transferred to the PLC channel in case of grid tied.
Figure 8: Noise spectrum measured inside the inverter
Figure 9: Channel capacity as a function of the frequency
Inverter channel
Transmitted signal s(t)
Received signal r(t)
1/f noise SSN
+++
500 kHz/div
Frequency (Hz)
Cha
nnel
cap
acity
(bits
/s/H
z)
117
It is proved taking into account the noise spectrum Figure 8 that the capacity of the channel varies with the input signal frequency as in the case of PLC channel. For the frequencies in the range of 0 Hz to 500 Hz, the channel is characterized by a very low capacity of transmitting the signal. The picture of the setup on Figure 10 shows the transmitter and the receiver next to each other with two LCDs displaying the messages sent and received. The couplers can be seen on figure 11 (5,6), as well as the modulator and the demodulator (3,4). The AC link coupler is built according to [14] while the DC link coupler is built using the technicques proposed in [15].
V. SETUP
Figure 10: Block diagram
Figure 11: picture of the setup
Figure 12: Spectrum of the DC link showing how the two frequencies
The two FSK frequencies sent are showed on figure 12,representing the snapshot of the DC link of the inverter.
The bit error probability is influenced by the input frequency; see Figure 13 shows. For the frequencies in the range between 0 Hz and 500 Hz (narrowband PLC), the channel presents a very low capacity of signal transmission; confirming what had being noticed when characterizing the channel. As well, the input signal level determines the capacity of transmitting a signal. Figure 14 compares four distinct cases: the inverter powering three different loads: 60 W, 200 W and 300 W; as well a 60 W case when the inverter is controlled by the microchip. This confirms that more the control is accurate, more capable is the channel (Figure 14). In any of these cases, as the input signal increases, the system presents more capabilities. The question now is, what level are we allowed to increase the input signal to?
VI. RESULT
Figure 13: Effect of the input frequency on the bit error probability
Figure 14: Effect of the input signal level on the bit error probability
VII. CONCLUSION The error presented in Figure 15 shows that between 0 and 30 dBV, the probability of the channel of transmitting a signal is less than 10%, which is very low for a reliable communication.
5 10 15 20 25 30 350
2
4
6
8
10
12
Input signal (dBV)
Out -
N (d
BmV)
60W PIC60W IR2153200W IR2153300W IR2153
Display DisplayCoding Decoding
Modulator
Coupler CouplerInverter Channel
Amplifier Demod
l
34
561
2
100 kHz125 kHz
harmonics
118
The reason of this being the flicker noise and the SSN, which are very high when the inverter is driving the nominal load (250 W). The solution might be found in the scheme of modulation or the coding techniques. Many other schemes of modulation and coding techniques are available and must be tested over the inverter at a chosen frequency. The accuracy of the inverter control must be improved. The component selection of the inverter must be done with tact. Low noise switching architecture and low noise components must be chosen. Broadband Power Line Communication (BPLC) frequencies look to be better than narrowband Power Line Communications (NPLC), because in the range of 2 to 30 MHz, the noise floor upper limite is around -30dB.
Figure 15: Comparing Error probability for three different sizes of load: 250 W, 100 W and 60 W, the inverter being controlled with the microchip
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