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GSM-based network monitoring system of solar street light

In Electronic Infomation Category: G | on April 22,2011

Abstract: The characteristics of solar PV panels and SAA7115H datasheet and the maximum power point tracking for photovoltaic principle analysis, based on CUK circuit photovoltaic maximum power point tracking method, the working mechanism of the analysis of solar street light, the introduction of A new network monitoring system of solar street light, solar street lamp controller described the overall design ideas, and SAA7115H price and focuses on the slave communication link between the host and SAA7115H suppliers and the host and the wireless communication between control center connections. The system has the ability to control, high reliability and flexible features and applications, with a high practical value.

0 Introduction

Order to promote the use of renewable energy, accelerate the construction of resource-saving and environment-friendly society, solar energy is gradually get peoples attention, solar street light as the high-tech products are gradually replacing traditional energy-saving lamps.

Characteristics for solar lights, solar street lamps presents a network monitoring system, that is, from the machine and the host through the RS485 interface connection, different from the host machines solar panels, batteries and LED work lamp status and monitor various operating parameters, and then, the host module through MC39i test results to the form of text messages or voice transmission to the monitoring center or related technical staff to achieve the interconnection of solar street light control.

1 system hardware design

Current control system is independent of solar photovoltaic street light control system, mainly consists of six parts: solar cells, batteries, LED lights, controller, charging circuit, discharge / load drive circuit [1]. The host system structure shown in Figure 1. Solar panel output by CUK circuit adjusted directly from the battery, the system uses DSPIC30F3011 master chip microcontroller, voltage acquisition of solar panels, battery voltage acquisition, control CUK circuit, control LED lamp, 485 communication between master and slave, host and monitoring Centre or the connection between the staff and other functions.

Figure 1, the host system architecture

1.1 PV maximum power point settings

Photovoltaic power system due to the sunlight intensity and ambient temperature changes, the voltage (current) vary widely. The larger the load resistance to the system greater flexibility and higher efficiency, the systems main circuit used CUK circuit, the principle for the Boost-Buck circuit, a voltage regulator circuit levels.

The system uses CCM mode, the characteristics of the working mode is very close to one turns ratio adjustable DC-DC transformer. Energy storage and transmission during the same time in two and two switching circuits for the converter with high efficiency. CUK circuit switch conduction duty cycle of change, in terms of the performance of photovoltaic arrays change their output impedance, output impedance of the change will affect the output characteristics of photovoltaic arrays. Which corresponds to a certain output impedance of the output voltage and output current values. The MPPT technology that is the circuit by adjusting the duty cycle CUK change the output impedance of the PV array to the output current and output voltage for the product that the maximum output power.

1.2 control circuit hardware design Master control circuit

DSPIC30F3011 microcontroller chip, the main control functions include: solar panels, voltage acquisition; CUK strobe control circuit; battery voltage acquisition; unloading circuit control; LED lamp control; RS485 communication; GSM module to send SMS control ; lamp switch control; work mode control. Host schematic diagram in Figure 2, Figure 3 and Figure 4, where the main chip DSPIC30F3011 Figure 2 schematic. Figure 3 shows the voltage sampling circuit and CUK circuit, the solar panel voltage and battery voltage are changes in the 0 ~ 35 V, while the microcontroller A / D input voltage range is 0 ~ 5 V, so the partial pressure of handling the sampling voltage After the transfer to the microcontroller A / D converter channel, CUK circuit used to adjust the solar panel maximum power point, the MCU PWM3 by strobe output control switch.

Figure 2 DSPIC30F3011 principle

Figure 3, the voltage sampling circuit and CUK Circuit

Figure 4 LED lamp control circuit and unloading circuits, microcontroller through the solar panel and battery voltage monitoring to control the LED lamp, respectively, through the PWM0 and PWM1 to adjust the LED light switch and brightness. When the battery voltage high-voltage 30 V, the MCU to control the foot through the PWM2 start unloading, to achieve the discharge of the battery.

Figure 4 LED lamp control circuit and unloading circuits

2 Communication System Design Network monitoring system of solar street light

the overall communication link shown in Figure 5, DSPIC30F3011 microcontroller with dual serial ports, host port all the way from the machine with the RS-485 communication, the other way serial GSM module for control, ie MC39i module communication links, control MC39i send text messages to the monitoring center.

Figure 5, the overall communication link

2.1 Communication between master and slave design

The spacing of tens of meters of solar street lights, so the system between master and slave communication link through the RS-485, RS-485 communication distance can reach several hundred meters or even kilometers, the maximum transmission rate of 10 Mb / s, but also multi-point communication, which can set up a small range of local area network [3]. Figure 6 DSPIC30F3011 microcontroller connected with the MAX485 hardware connection diagram, DSPIC30F3011 and MAX485 isolation between the through 6N136, to ensure the accuracy of data transmission. Lord, aside from the machine serial port and MAX485 are connected, each MAX485 chip, A, B, and GND pins connected to each other. Lord, from the machine constantly on the solar panel voltage and battery voltage detection, of low power from the machine will be promptly sent to the host information.

2.2 host and the monitoring center communication design

GSM-based wireless communication technology, measurement and control system has the common good, a wide geographical coverage, maintenance-free commissioning, operation and control of flexible low-cost characteristics, so between the host and the monitoring center using GSM communication module to transmit information.

DSPIC30F3011 microcontroller on the solar panel voltage and battery voltage sampling comparison, when the sample is lower than the set value, send text messages, "solar panel voltage is less than" or "the battery voltage is less than" to the monitoring center, the microcontroller can also work status lights monitor exception occurs, the message transmitted to the monitoring center.

Figure 6 DSPIC30F3011 and MAX485 Connection

GSM modules MC39i, MC39i is a support of the Chinese industrial GSM short message module, voice and data signals can be transmitted through the interface connector and antenna connector are connected to SIM card reader and antenna. MC39i data interface can be two-way transmission through AT command instructions and data, selectable baud rate ranging from 300 b / s ~ 115 kb / s, support Text and PDU format SMS (ShortMessage Service, Short Message Service), available through AT commands on or off signal to achieve the restart and recovery [4].

MC39i module has 40 pins through a ZIF (Zero InsertionForce, zero resistance socket) connector leads. These 40 pins can be divided into five categories, namely, power supply, data input / output, SIM card, audio interface and control. MC39i 1 of the 5 pin is the positive power supply input pin, 6 to 10 pin is the power ground, 15 feet is to start foot IGT, after the system power state to enter the work MC39i must be given a greater than 100 ms IGT low pulse duration decreased level should not exceed 1 ms. 18-pin RXD, 19 pin TXD pin to TTL serial communication, needs, and microcontroller or PC communication. MC39i SIM card with an external 24 to 29 for the SIM card, pin, MC39i the first 32 feet SYNC pin to control the foot, there are two modes, one is indicative of the power transmitting state growth, the other is indicates the working status of MC39i, available AT commands AT + SYNC switch, 35 to 38 for the voice interface [5].

MC39i power input with adjustable high-performance microwave circuit switching voltage regulator chip dedicated LM2941S. IGT can start pin microcontroller software control can also be keys to control its potential level of change control, 18-pin RXD, 19 pin TXD directly with the asynchronous serial RXD2 DSPIC30F3011 microcontroller and TXD2 are connected to the MCU to send and receive instructions MC39i control, 24 to 29 pin SIM card directly to the corresponding pins to connect, easy to detect SIM card is inserted, and the completion of the function of SMS, SYNC pin can be used to detect an external light-emitting diode module is in working condition.

3 Software Design

3.1 system software design

The system for monitoring treatment DSPIC30F3011 microcontroller, the microcontroller on the solar panel voltage and battery voltage in real time monitoring. If the solar panel voltage is greater than the set value, indicating that light intensity is large enough, single chip LED lamp off power, solar panels charge the battery; if the solar panel voltage is less than the value of the LED lamp powered by batteries, the first test battery voltage, if large enough power from the battery to the LED lamp, if less than the lower limit, the microcontroller control module to send SMS MC39i "low battery power", if the battery voltage is higher than the upper limit, will have to start unloading circuit avoid battery overcharge. System flow chart shown in Figure 7.

Figure 7, the system processes

3.2 GSM software design

Can use AT commands to control the module on MC39i. MC39i by AT commands to the microcontroller module initialization and receive short messages sent. Control of short message has two modes: PDU mode and Text mode, but does not support Text mode text, designed with PDU mode. Through the MCU to send asynchronous serial AT commands "AT CRLF" to MC39i module (which represents a carriage return CR; LF line), if MC39i module Send "CRLFOKCRLF" to the microcontroller, then the modules MC39i normal; then microcontroller sends "AT + CMGF = 0CRLF "to MC39i module, set the SMS format PDU mode, if the module MC39i reply" CRLFOKCRLF "that set successfully; then microcontroller sends" AT + CMGS = 26 CRLF "to MC39i module, set the total message length is 26 bytes, if received "CRLF> 26" that set up, the last single chip to send a specific message MC39i module information, such as sending SMS "low power solar panels" to the monitoring center, monitoring center of the SIM card, the corresponding numbers for 1364217302X, the corresponding PDU data To: 0891683108200205F011000B813146123720 FX0008A712592A963380FD677F4F4E75351A. Of which: 08: SMSC address length; 91: SMS center number type; 68: Chinese code (after swap); 3108200205F0: Tianjin SMS center number (fill in at the end of F, every two reversed, the actual number is "13800220500"); 11: the first byte of the file, the default is 11; 00: Information type, default is 00; 0B: called number length; 81: called number type; 3146123720FX: called number (through the swap, the actual for the 1364217302X); 0008 : 00 signs agreement 08 that the use of Unicode encoding; A7: the effective number of days = A7-A6; 12: message content length; 592A too; 9633 Yang; 80FD can; 677F plate; 4F4E low; 7535 electricity; last message content 1A at the end, 1A to send end of the flag.

4 Conclusion

Where the system controller on the existing street lights to transform solar energy, photovoltaic maximum power point will be set into solar controller, serial communication is realized by means of master and slave communication link, using GSM technology to achieve host and the communication link between the monitoring center, and ultimately the solar street light control system network monitoring. Thus, the system not only improves the efficiency of solar energy, solar controller also implements wireless data transmission between the improved use of existing solar street lamp controller value.

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