WO2015088302A1

WO2015088302A1 - High-performance intelligently controlled solar lighting system with a plurality of charge stages

Info

Publication number: WO2015088302A1
Application number: PCT/MA2013/000050
Authority: WO
Inventors: Abdellatif BENABDELLAH; Mohsine BOUYA; Mohamed ELOUAHABI; Tarik LAGHMICH
Original assignee: Universite Internaltionale De Rabat
Priority date: 2013-12-09
Filing date: 2013-12-09
Publication date: 2015-06-18

Abstract

The invention concerns a public lighting system consisting of a high-luminance LED-based streetlamp provided with a solar panel and a battery charge controller, modified so as to enable optimum use to be made of the power supplied by the solar panel and enabling all the streetlamps to be monitored remotely. This optimization is brought about by automatically regulating the charge of two batteries arranged in series. The automatic regulation is performed by a microcontroller which efficiently charges the batteries by incorporating the principle of maximum power point tracking. The thermal control of the junctions is also taken in hand owing to appropriate dimensioning of the heat sinks and adaptation of the power transmitted to the LEDs according to the temperature. The streetlamp is provided with a radiofrequency transmitter connected to the microcontroller and enabling all the streetlamps to be monitored remotely, forming a wireless sensor network (WSN). This technology ensures a long service life owing to the intelligent control and system-monitoring functions. The streetlamp is also provided with an ultrasound transducer preventing birds from approaching and thus ensuring that the solar panel remains clean and transparent. In areas exposed to dust, such as building sites or desert regions frequently subject to sand storms, a dust detector is fitted in order to activate a vibration device for removing dust from the surface of the solar panel.

Description

The solar lighting system with high efficiency and intelligent control of several stages of charges relates to the field of lighting systems based on light emitting diodes (English: Light Emitting Diodes) or LEDs, powered by solar energy with centralized management.

The stand-alone solar street lights that currently exist essentially consist of a solar panel, an accumulator battery, a matrix of LEDs and electronic modules to control the charging / discharging of the battery and adapt the power supply to the LEDs.

There are also wind lamps that use a small wind turbine as a power source. Since wind energy is random, the use of this system is very rare because it requires a constant and steady wind resource throughout the year.

Finally, hybrid streetlights using both wind energy and solar energy as a source of energy supply.

The main issues related to autonomous LED lighting are:

the extraction of the maximum power provided by the photovoltaic panel, which has a direct impact on the autonomy of the batteries,

the efficient and optimal management of charge and discharge of batteries with detection of critical thresholds,

the thermal management of the junctions: the luminous flux of the LEDs decreases according to the increase of the temperature of the junctions, which limits the exploitation of this technology and imposes a specific dimensioning of the heatsinks which only partially solves the problem.

This invention integrates the latest scientific advances and technological innovations in the field of renewable energies and energy efficiency applied to lighting, capitalizing on certain achievements in electrical engineering, electronics, programming and telecommunications. . The characteristics that distinguish this lighting system, compared to the existing, are detailed in the following of this description.

The model described here is a stand-alone solar street lamp with high energy efficiency, compared to similar products, and requiring very little maintenance. It is intended to replace conventional street lights placed in public places: roads, squares, gardens, etc.

LED lighting has several advantages, such as low power consumption, long life, fast response and small footprint due to the small size of the LEDs.

Variations of this system can replace residential and industrial lighting, as well as the lighting of large surfaces: building sites, stadiums, ports, airports, etc.

The architecture of the system comprises according to FIG. 2:

a solar panel (1),

high luminance LEDs, or HBLEDs (High Brightness LEDs) (4), two 12V lead-acid batteries arranged in series (3) in three phases with automatic compensation of the power dissipated by Joule effect in the LEDs. The use of lithium-ion battery is possible,

a microcontroller (2) which controls the charging and discharging of the batteries,

a DC-DC voltage regulator (5) for the LEDs (4),

a radiofrequency transmitter (8) connected to the microcontroller (2), and which transmits the state of the circuit in real time to a web server (not shown in this figure),

a dust detector (10) associated with a vibrator (11), for removing dust, and optionally placed in a few areas,

an ultrasonic frequency transmitting device (9) which has a repulsive effect for birds, which can obstruct the transparency of the solar panels,

a photoresistor associated with a conditioner that enables the LEDS to be switched on when the brightness decreases,

a thermistor to read the temperature of the junctions of the LEDs.

The block diagram of the system is shown in FIG. 2: the solar panel, batteries, LEDs, light sensor, wireless transmitter, connect to the controller and allow complete management of the lamp. Photoresistance controls ambient light by activating the system at dusk and stopping it at sunrise.

According to FIG. 5, the main circuit of the system is composed of a microcontroller, around which orbit a wireless transmitter, DC-DC converters, a thermistor NTC (Negative Temperature Coefficient), a photoresistor LDR (Light-Dependent Resistor), an optocoupler, MOSFET electronic relays, operational amplifiers, an ultrasonic transducer and its emitter circuit, diodes, resistors and capacitors.

The controller can manage the charge and discharge functions of batteries by following the maximum power point delivered by the photovoltaic generator. It provides power to 12V LED lighting with constant power. The best efficiency is obtained when the power delivered by the photovoltaic panel is maximum.

When the ambient temperature varies from 0 to 40 ° C, the LED lighting varies slightly (1.7%) for the constant power control, compared to that of the constant current control (12%) and the constant voltage control (+ 50%).

The restriction on the number of watts of lighting and the duration of use depends mainly on the solar panels and their ability to recharge the batteries. A 10W solar panel is ideal for recharging two partially discharged 12V batteries, assuming the sun is available for at least six hours / day.

Batteries will be seriously damaged or rendered inoperative if they are completely discharged and / or left unloaded. Therefore, we have included load threshold detection logic. If the batteries discharge below 11V, the LEDs go out.

To extract the maximum power from the photovoltaic panel, the input resistance of the energy converter must be matched to the output resistance of the PV panel.

The microcontroller adjusts the output current supplied to the load so that the voltage of the PV panel is that which is set by the control pin of the maximum power point. In As a result, a programming resistor establishes the maximum power point, ensures the extraction of the maximum power of the PV panel and an optimal charging current at the output.

The batteries are charged in three stages. The first step, bulk loading, is applied when the battery voltage drops below 12.45V. This charge cycle transfers maximum power from the solar panel to the batteries until the voltage reaches 14.4V at 20 ° C.

Then the absorption phase, where the battery is kept at the threshold voltage for one hour, to ensure that the battery is fully charged. After that, the end of charge voltage: the battery is charged, but a voltage of 13.5V is maintained at its terminals. A battery that has been discharged below 10.5V will be charged with short current pulses until it reaches 10.5V, then the main charge phase will begin.

The maximum values of the charging voltages are reduced for temperatures above 20 ° C, in accordance with the specifications of the battery manufacturers. Typically, it is 19mV per ° C for a 12V battery.

Two of 50Ah and 12V batteries in series will give 100Ah-12V. But for parallel installations, it is imperative that the two batteries are perfectly identical: same capacity, same internal resistance, same manufacturer, same antecedents, etc. Otherwise, there is the risk of having the weakest in favor of the other: its internal resistance will increase and the battery in better conditions will take the largest part of the charging current, which will only increase the imbalance. We therefore prefer the series installation (addition of voltages), the parallel assembly (addition of capacities).

The batteries used are suitable for photovoltaic applications. They have anticorrosive properties thanks to thick positive plates of very good resistance, favor the slow discharge. Having a good reserve of electrolyte and a recycling cap that avoid losses in hot weather. Robust and economical, with monitoring levels every six months, they can last more than 10 years.

The temperature of the LED junctions is measured using a NTC (Negative Temperature Coefficient) thermistor located next to the LEDs, for a more accurate temperature measurement. The luminous flux and the LED yields given by the manufacturers are valid for a junction temperature of 25 ° C. In practice, the real values are always lower. LEDs always work better as their temperature decreases.

The system is designed to optimize the power provided by the solar panel. As shown in FIG. 3, a solar panel outputs current and voltage values that follow the curve. These values extend from the maximum point of the shortcurrent output current Isc to the maximum voltage when the output is open V ₀ c

It is the combination of the photogenerator with the battery that forces the photogenerator to work at a certain current and a certain tension. Contrary to a commonly held idea, the photovoltaic panel is therefore rather a current generator than a voltage generator, at least in the exploitable part of its characteristic between the l _sc and the P _m , because it is the current which is constant and not the tension. Beyond the P _m , the photogenerator is not exploitable, because the power drops very quickly.

When coupling the photogenerator to the battery, it is the voltage of the battery that imposes the operating point. The solar panel operates at full efficiency when it provides the maximum energy. And this is where the technique of tracking the maximum power point comes into play. It is essentially a step-down switching power converter, which couples the power available from the solar panel to the battery with minimal power loss. At the same time, it offers three stages of charge for the batteries.

The principle is explained in FIG. 5. The solar panel current flows through diode D4 and electronic relay Q4. When Q4 is on, the current flows in the inductance L1 to the capacitor C12 and the batteries. The magnetic field induced in the coil increases (the current increases to its maximum value) and after a short period, Q4 is extinguished and the energy stored in L1 maintains the flow of the current through the diode D7.

The duty cycle of the electronic relay Q4 is controlled so that the solar panel delivers its maximum power through pin RB3 of the microcontroller. The peak current in the inductor is provided by the 470 Ρ capacitor Cil. In the same way, the capacitor C12 acts as a reservoir to charge the battery when the current does not flow in the inductor. Moreover, these capacitors have a low effective ESR series resistance, adapted to the 31.24kHz switching frequency.

The voltage of the solar panel is monitored by the operational amplifier IC2a, while the current is monitored by measuring the voltage across a 0.1Ω resistor. This voltage is multiplied by -50 using the IC2b operational amplifier. These two operational amplifiers provide their IC microcontroller output signals that control the entire circuit.

The maximum power point tracking algorithm is fully automated and requires no user adjustment. The microcontroller firmware has been programmed to search for the maximum power point of the solar panel as it varies with weather conditions.

The batteries used are characterized by the nominal voltage which depends on the number of elements, the nominal voltage U is equal to the number of elements multiplied by 2.1 V. Generally it is considered that a lead accumulator is discharged when it reaches the voltage of 1.8 V per element, so a battery of 6 elements or 12 V is discharged, when it reaches the voltage of 10.8 V.

In a preferred embodiment, the use of lithium-ion battery, more compact and less cumbersome.

For loading, we use the step-down clipping previously described in FIG. 5. Q4 is a P-channel MOSFET transistor that switches with the negative voltage gate (G) with respect to the source (S). The voltage at the source of Q4 (from the solar panel and diode D4) can go up to about 21V when the solar panel does not provide power.

The gate is maintained at a negative voltage with respect to the source through transistor Q2, resistor R21 and diode D6. Transistor Q6 is PWM pulse width modulated by the IC output RB3 (pin 9) via a 4.7kΩ resistor (R16).

When RB3 is at 5V, Q6 is turned on and so the MOSFET Q4 is turned on. The resistor 10Ω (R20) at the Q6 collector limits the initial current at Zener diode ZD1 in case the gate voltage of Q4 is greater than 18V. This Zener diode protects the gate G of Q4 against overvoltages; an overvoltage at transistor Q6 will make it loosed.

When the output of RB3 is at 0V, the transistor Q.6 is blocked, and the base of Q.1 comes into contact with the source of Q4 via a resistor of 10kO (R22). Transistor Q1 turns on and puts the gate of Q4 in contact with its source, and therefore Q4 is blocked. This is how we control the on / off switching of the transistor Q4 through the pin RB3 of IC. The switching frequency that ensures the optimal transfer of power is 31.24kHz. The voltage of the battery is controlled by the ICI pin AN2 via the optocoupler IC3 and the resistive divider consists of a 22kO resistor and a 20kO VR2 potentiometer. This potentiometer is adjusted so that the voltage appearing at AN2 is 0.3125 times the voltage of the battery. This multiplicative voltage factor was chosen not to exceed the 5V limit of the analog input AN2, for example, a voltage of 14V at the battery terminals will be converted to only 4.375V.

The resistive divider is not directly connected to the battery, but via the transistor of the optocoupler IC3, which connects the battery to the divider each time the LED of IC3 is activated. The voltage between the collector and the emitter of the transistor has a minimal effect on the measurement of the voltage of the battery, because it is only about 200μν. The divided voltage, proportional to that of the batteries, is converted into a numerical value by the program housed in the microcontroller IC.

The optocoupler diode is driven from the 5V supply through a 470Ω resistor (R23) and at 0V when the Q3 MOSFET is activated. The NTC thermistor forms a voltage divider with a resistance of 10kΩ when Q3 is activated. Input AN6 d (pin 1) reads this voltage and converts it to a value in degrees Celsius. At the same time, the AN1 input (pin 18) reads the value of the R26 potentiometer that connects to the 5V power supply when Q3 is activated. Inputs AN1 and AN6 are converted to mV / ° C. They can vary from OmV / ° C when R26 is at 0V to 50 mV / ° C when R26 is at 5V.

Pulse Width Modulation PWM (PWM) modulation is part of the microcontroller's internal block: the CCP or Capture / Compare / PWM is used to manage the energy transmitted to the outside. Indeed, if a continuous signal corresponds to 100% of energy, a square signal whose high state duration equal to that of low state corresponds to 50% of energy. The percentage of energy transmitted is calculated by making the ratio of the duration of the high state over the duration of the period.

Two formulas make it possible to calculate the duration of the period and the width of the pulse:

Period = (PR2 + l) x4xT _0SC x (Timer 2 Predictor)

Width = (10 bits) xT _0Sc x (Timer 2 Primer)

T _osc is the period of the oscillator serving as clock to the microcontroller. The 10 bits correspond to the byte of the CCPR1L register and the 2 bits of DC1BX.

The Q2, Q3 and Q4 MOSFETs act as electronic relays, which in this situation have many advantages compared to the electromechanical relay; better switching speed, quiet operation and vibration insensitivity.

Network operation Fig. 4 and FIG. 1

The data collected by the nodes (transmitters and microcontrollers) are routed through a multi-hop routing. 1 (1) to a node considered as a "sink", which in turn transmits the information to the internet for oversight. 1 (2). This makes it possible to monitor the streetlight network and to detect if a battery is defective. This network can be exploited, in another embodiment, as a traffic management infrastructure for example.

The connection to the nodes of the network is done thanks to the information relayed gradually by the nodes of communication of the mesh network (mesh). This is the Zigbee industrial standard that is adopted here; the 802.15.4 protocol used by the transmitter module adds to the packets transmitted data, a source address and a recipient address.

The transmitter modules require prior configuration to operate in a Sink mode. A module is the coordinator of the network, which must be initialized with some special parameters, the other modules will be "End Device". This configures a Local Area Network (LAN) between each of the two transmitters. Each LAN module will have an id identifier that will be the same for the entire LAN. An "End Device" can associate with a coordinator in a LAN, without knowing either the LAN id or the Radio Frequency channel. The flexibility of the association is configured by the value of the parameter Al for the "End Device" and by the parameter A2 for the "Coordinator".

The transmitters used operate with a 2.4 GHz frequency that does not require a license. And feed with a voltage of 3.3V. We use a 2.8 - 3.4V output voltage regulator. The associated resistances make it possible to control this voltage according to the formula (FIG.

The quiescent current consumed by the assembly is low, and mainly due to the different sensors that equip the system.

Claims

Claims The embodiments of the invention, in respect of which an exclusive right of ownership or privilege is claimed, are as follows:

1. Solar lighting system characterized by high luminance LED street lights powered by two 12V acid lead acid batteries arranged in series connected to a microcontroller that controls the charging and discharging of batteries and a DC-DC voltage regulator for LEDs and using a radiofrequency transmitter connected to the microcontroller which transmits the circuit status in real time to a web server. Streetlights are protected by an ultrasonic transduction system. They are equipped with a dust detector that is linked to a vibrator.

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2. A solar lighting system according to claim 1 characterized by a microcontroller which automatically monitors the maximum power point delivered by the photovoltaic generator.

3. A solar lighting system according to claims 1 and 2 characterized by the charging of two batteries in series in three phases with automatic compensation of the power dissipated by Joule effect in the LEDs.

4. A solar lighting system according to claims 1, 2 and 3 characterized by an operating system of street lights wireless sensor network for controlling them via the Internet.

5. A solar lighting system according to claims 1, 2, 3 and 4 characterized in that the ultrasonic transduction system consists of a transmitter and a receiver detecting the approach of birds. The ultrasonic frequencies are adjusted so as to cause a repellent effect.

6. A solar lighting system according to claims 1, 2, 3, 4 and 5 characterized in that lithium-ion batteries can be used instead of lead acid batteries.