Design of intelligent street lamp energy-saving device based on single chip microcomputer control

0 Introduction

With the continuous expansion of the scale of large and medium-sized cities and the improvement of urban appearance, the number of street lamps is increasing, and the proportion of their electricity consumption in the total electricity consumption of the city is increasing. In the past, street lamps were mostly powered directly, with manual power supply and manual shutdown. This method has many shortcomings: the voltage of the power supply system fluctuates at different times. During the peak period of power consumption, the voltage is lower than the rated value, and during the low period of power consumption, the power supply voltage is higher than the rated value. When the voltage is high, it not only affects the service life of the lighting equipment, but also greatly increases the power consumption (if the power supply voltage increases by 20% , the power consumption increases by 44% ). When it is low, the lighting equipment cannot work normally; using manual power supply, increasing the staff cost, and sometimes it cannot be turned on and off in time, which affects normal lighting and wastes electricity. Therefore, it is necessary to develop a convenient and energy-saving device to address the above problems. This device should have the following functions.

( 1 ) Voltage stabilization control: Whether in peak or low power consumption periods, the power supply voltage can always be kept stable within the rated value range;

( 2 ) Display function: can display input voltage, output voltage, three-phase current, power factor, active power, reactive power and other parameters;

( 3 ) Scheduled start and stop: The time of day and night alternation is different in different regions and seasons. The system can automatically adjust the time of opening and closing street lights according to the region and season;

( 4 ) Adjust the start and stop time according to weather conditions: The timed start and stop function can turn the street lights on and off according to weather conditions;

( 5 ) Automatic power factor compensation: With the continuous upgrading of lighting equipment, the system should have a power factor compensation function;

( 6 ) High efficiency, no waveform distortion, stable voltage regulation, adaptable to a wide range of loads, able to withstand instantaneous overload, able to work continuously for a long time, manual control and automatic control can be switched at will, and equipped with overvoltage and undervoltage automatic protection functions.

There are many AC voltage regulation methods, the most common ones are autotransformer voltage regulation, phase modulation, magnetic saturation voltage regulation, etc. These methods cannot meet the functional requirements of street lamp energy-saving devices. The autotransformer method cannot meet the requirements when supplying high current due to the limitation of its carbon brushes; the phase modulation method has waveform distortion, which interferes with the power grid and some new lighting equipment, and cannot meet the requirements; the magnetic saturation method cannot meet the requirements at high power due to its large size.

The compensation transformer method can be applied to AC voltage regulation. The electrical schematic diagram of this method is shown in Figure 1. Now, taking one phase as an example, the voltage regulation working principle is explained. If the impedance voltage drop of the compensation transformer is ignored, then

Where: Uo—output voltage of the voltage regulator;

Uo=Ui+Ub

Ui —regulator input voltage;

Ub — output voltage of compensation transformer.

The voltage regulating transformer is a double-contact output, and each contact can move within the full range. When contact A is on the top and contact B is on the bottom, the output voltage Ub of the compensation transformer is in the same phase as Ui ; when contact A is on the bottom and contact B is on the top, the output voltage Ub of the compensation transformer is in the opposite phase to Ui . When the input voltage Ui increases by ΔUi , the control circuit adjusts the movement of contacts A and B , so that contact B moves to the upper end and A moves to the lower end, and the compensation voltage Ub also changes accordingly by ΔUb , and ΔUb=-ΔUi , Uo = Ui-ΔUb , so that the output voltage Uo remains unchanged; when the input voltage Ui decreases by ΔUi , the control circuit moves contact A to the upper end and contact B to the lower end, at this time ΔUb=ΔUi , Uo =Ui+ΔUb , so that the output voltage Uo remains unchanged.

When the system is a three-phase power supply, the circuit consists of a three-phase compensation transformer TB , a three-phase voltage regulator TUV , a voltage detection unit, a servo motor control mechanism, a protection circuit, etc. The electrical schematic diagram is shown in Figure 2 .

The primary winding of the voltage regulating transformer TUV is connected in a Y shape and connected to the output end of the voltage stabilizer. The secondary winding is connected to the primary winding of the compensating transformer TB , and the secondary winding of the compensating transformer is connected in series in the main circuit.

The voltage stabilization process is as follows: according to the change of the output voltage, the voltage detection unit samples, detects and outputs the signal, controls the rotation of the servo motor, drives the brushes on the transformer TUV to adjust the secondary voltage of the transformer, so as to change the polarity and size of the compensation voltage, and realize the automatic stabilization of the output voltage within the range allowed by the voltage stabilization setting accuracy, thereby achieving the purpose of automatic voltage stabilization.

The compensating transformer method has the characteristics of small size, flexible control, the power and output current of the voltage regulating transformer can be reduced to a minimum, continuous operation and strong overload capacity.

2 Hardware Design of Control Circuit

The hardware circuit of the control system consists of a control microcontroller, an A/D converter, an LCD display, a clock circuit, a servo driver, etc. The hardware block diagram is shown in Figure 3 .

2.1 Microcontroller

The single- chip microcomputer adopts P89C51RD2 . P89C51RD2 single-chip microcomputer has 64K parallel programmable non-volatile FLASH program memory, and can realize serial in-system programming ISP and in-application programming IAP for the device . In-system programming ISP (In-system Programming), there is 1KB RAM inside, and the 6- clock /12 -clock mode can be selected through the parallel programmer (the default clock mode is 12 clocks after the chip is erased), 4 interrupt priorities, dual DPTR registers, programmable counter array PCA , PWM output and other functions. P89C51RD2 single-chip microcomputer is applied to this system without external expansion of program memory and data memory. All I/O ports of the single-chip microcomputer work in ordinary I/O working mode. In order to save port lines, peripheral devices are all selected with chips with serial data communication. In order to prevent interference, all signal lines dealing with strong signals are photoelectrically isolated. After level conversion, the serial port can be used as ISP function on the one hand, and on the other hand, it can communicate with the host computer in the future.

2.2 Analog-to-digital conversion circuit

The analog-to-digital conversion circuit consists of a signal conditioning circuit and an A/D conversion circuit. The main function of the signal conditioning circuit is to convert external signals such as voltage, current and ambient light into a signal range that the A/D can accept . The A/D conversion chip uses the TLC2543 converter. The TLC2543 is a 12 -bit A/D converter with 14 channels input . The chip uses 3 channels inside and 11 channels outside . The input voltage is 0~5V ( VER-=0 , VER+=5V ). The interface between TLC2543 and the CPU uses the SPI method. Its pins include conversion end EOC , chip select CS , data input DI , and data output DO . TLC2543 can work in 8- bit and 12- bit modes, which can be selected during initialization. The conversion starts using the command method. As long as the corresponding channel number is sent in the command, TLC2543 will start the conversion. After the conversion is completed, EOC has a low pulse sent to the microcontroller. After the microcontroller responds to the interrupt, it can read the conversion data from TLC2543 and send the next channel start command at the same time.

2.3 Stepper Motor Drive Circuit

The stepper motor driver uses a commercially available stepper motor driver module, which only requires 5 lines to interface with the microcontroller. The module pins include direction control, step pulse, brake signal, GND and VCC . After the microcontroller collects the three-phase voltage, it compares it with the set value and determines the running direction and number of step pulses of the stepper motor. Once the output voltage is within the error range, the stepper motor stops running.

2.4 Display and keyboard circuit

The display uses a 128 × 64 LCD display, and each data can be displayed on a split screen. The interface between the display and the microcontroller is a 4- wire serial data transmission method. The keyboard uses a 4 × 4 matrix keyboard with a total of 16 keys. The system time, stable voltage, longitude and latitude, and street light switch time can be set through the keyboard.

2.5 Ambient Light Detection Circuit

The function of the ambient light detection circuit is to detect the outdoor light. As long as this function is enabled during the setting, when the outdoor light is dim to a certain degree, the device can automatically turn on the street light. The circuit is shown in Figure 4 .

When the ambient light is very bright, the resistance of the photoresistor RS is very small, and the collector voltage of the transistor is very low. When the ambient light is dim to a certain extent, the output OUT voltage increases. When it is higher than the set value, the microcontroller controls the street light to turn on.

2.6 Power Factor Detection Circuit

After voltage and current are shaped, they are sent to INT0 and INT1 of the microcontroller . When INT0 (voltage signal) generates an interrupt, timer T0 count is started. When INT1 (current signal) generates an interrupt , T0 count is read. When INT0 interrupts again , T0 value is read and T0 is cleared at the same time . The frequency and power factor of the power supply can be calculated from the values ​​read twice from T0 .

3. Software Design of Control Circuit

The software program uses C51 language and is programmed in a modular way. The software consists of the main program, A/D sampling program, digital filter program, display program, key processing program, stepper motor driver, voltage regulation program, power factor compensation program, etc.

3.1 Main Program

After the system starts working, the main program first initializes the internal and external resources of the microcontroller, and then calls the programs of each functional module in turn.

3.2 A/D Sampling Procedure

The A/D sampling program is called by the main program in a loop, sampling 10 external analog quantities 12 times each time, and sending them to the data buffer after digital filtering for use by other programs.

3.3 Voltage Regulation Procedure

The voltage regulation program uses PID algorithm, and its input is the set voltage regulation value and the output voltage. After PID operation and then scaling transformation, it is converted into the number of pulses output by the stepper motor for use by the stepper motor driver. The stepper motor driver is relatively simple. According to the number and direction of pulses calculated by PID , the corresponding pulses are sent to the stepper motor driver through the I/O port. Since the voltage regulation accuracy of the system can be set within a certain range through the keyboard, there is no overshoot phenomenon in the voltage regulation process.

3.4 Display Program

The display program displays parameters such as voltage, current, power factor, system time, and working status on the LCD in split screens . Since the LCD module has a Chinese character library inside, the internal code of the Chinese characters can be directly sent when displaying Chinese characters. Dynamic numbers are also displayed using the fonts inside the LCD , and there is no need to create fonts in the program.

3.5 Power Factor Compensation Procedure

The power factor is calculated based on the data read back from interrupts INT0 and INT1 , and compared with the set power factor. After calculation, the external relay is controlled to switch the capacitor bank, so that the power factor of the street lamp power supply branch can be kept within the set range.

4 Conclusion

The intelligent street lamp energy-saving device adopts transformer compensation voltage stabilization method and utilizes the strong computing and control capabilities of the single-chip microcomputer. It has the advantages of small size, reliable operation, and energy saving. If it can be promoted and used, it will bring urban street lamp management to a new level. It not only saves energy, but also reduces the loss of lighting fixtures. Therefore, it has broad promotion prospects.

References:

[1] Tao Yonghua, Yin Yixin. New PID Control and Its Application [M] . Beijing: Machinery Industry Press, 2000 .

[2] Pu Zhaobang, Wang Baoguang. Measurement and Control Instrument Design [M] . Beijing: Machinery Industry Press, 2001 .

[3] P89C51RD2 Data Sheet ． http://www.zlgmcu.com ．

[4] TLC2543 Data Sheet ． http://www.zlgmcu.com ．