Photovoltaic power generation can provide sustainable energy for mankind, for the survival and protection of the environment, but its low-efficiency power generation, power generation is still relatively high cost of full control of its large-scale application of the important factors. 。 In the absence of a highly efficient photovoltaic cells materials, the development of practical value of solar concentrators and auto-tracking system to achieve low-cost, is to promote solar wider use of one of the main ways. General biaxial system can increase generating capacity of about 35%, single system can be increased by 20 percent, condenser-tracking system will be higher.
Abroad in the 1980s on the solar tracking system have been studied, such as the United States, Germany in a single biaxial automatic tracking, F1 in the condenser lens to track the Philippine legislature Seoul, Spain 2 times in the condenser reflection tracking and so on to develop the corresponding The commercialization of automatic solar tracking device. China in the 1990s also about a lot of their research, in October 2006 in Tibet Yangbajing installed a total of four sets of different forms of 13.2 kW single, biaxial grid solar power generation automatic tracking system. Has not been stable and reliable before the commercialization of our products, The reasons are:
(1) system reliability can not meet the requirements
As most of photovoltaic power stations are installed in remote areas, the environment is very bad, maintenance difficulties, tracking system to increase the rotating bodies and the corresponding machinery, reliability decreased significantly, if it can not guarantee that the whole system in various circumstances can be reliable And stable operation of the entire photovoltaic power plant, could be disastrous blow.
(2) the tracking error
In particular, the condenser reflection of the tracking system, if the tracking error, will not only fail to improve the efficiency of power generation, instead of small battery-both by the board, the yield Pottinger hot spots and so on, greatly shorten the life of the battery plate.
(3) cost too high
All buy foreign mature technology, will greatly enhance the hardware costs and maintenance costs.
Based on the PIC16F877 microprocessor as the core, for photovoltaic power generation systems, developed a biaxial automatic automatically track the sun, he is stable and reliable operation, the tracking error of small, low cost advantages.
1 automatically track the sun for the basic principles of [1-3]
Automatically track the sun, Gu Ming Si Yi basic function is to make photovoltaic arrays with the sun and the rotation, the basic tenets of diagram as shown in Figure 1.
Detection system at all times and photovoltaic solar arrays and their input into the location of the control unit, this control unit to compare two signals and produce an output signal to drive the rotation, so that sunlight at normal incidence to the photovoltaic array Out of the surface.
Although the sun's position in space is changing all the time, but it has run its strict laws, and coordinates the horizon, the sun's position may be a high degree of angle and azimuth φ to determine, the following formula [2-3]:
Type in: δ Declination angle to the sun; φ latitude for the local angle; ω too Kok.
Declination angle with the sun angle can be identified by the local time, and to determine the location, the local angle is also determine latitude, as long as the importation of the local geographical and time-related information on the location of the sun can be identified at this point in time.
2 of its overall design plan
PIC16F877A is a structure with a high-performance midrange RISC MCU, only 35 words directive, 8 k × 14 bytes FLASH program memory, 368 × 8 bytes of data RAM memory, 256 × 8 bytes E2PROM data memory, 14 Interrupt sources, eight depth of the hardware stack, the internal watchdog timer, low-power sleep mode, the inhalation of up to 25 mA / pull current, external timer with three modules, two 16-bit capture / 16 comparison / 10 PWM module, over 10-channel A / D converter, Universal Asynchronous simultaneously receive / transmitter features such as module [5].
Automatically track the sun for control of main microprocessor-controlled, PLC control, DSP control and analog circuits control four kinds of forms, in accordance with the above principle, this cost-effective option for the control of the PIC16F877A microcontroller core, the system to achieve the specific Principle diagram shown in Figure 2.
The controller from the main control unit and drive the implementation of Part 2 of body composition. 。 Control unit from the perspective of calculation and feedback control, start signal, motor-driven signal, signal processing and protection of human-machine communication five parts. System functions as follows: MCU cycle of photovoltaic arrays detect the location and the time and calculated the height of the local sun and the azimuth angle compared to determine whether photovoltaic arrays track the sun on the location, if Did not meet the launch and start signal conditions, SCM issued a directive on the drive motor rotation; protection signal is the guarantee system in the outside world, as well as other factors Feiren Wei enforced by the circumstances of the operation of a directive to ensure that systems from damage, thereby enhancing The overall system reliability. Driving the implementation of modules main function is to achieve motor drive and the rotation, and driven by mechanical transmission mechanism photovoltaic array rotation.
2.1 The control unit hardware design
As a result of the SCM as the main control unit, most of the work by the SCM software to achieve, thus simplifying the hardware design of the control circuit, an outline of the main control part of the implementation process.
(1) point of calculation and feedback control
SCM through the expansion of three-state latch input module clock access to the time signal and optoelectronic rotary encoder signal the location, use of rapid processing capacity of SCM software used to be realized;
(2) motor drive signals generated
This article is based on stepper motor, driven by the pulse of its own internal MCU 10 PWM wave in a module, simply set the appropriate software can change the parameters of the motor speed;
(3) Computer Monitoring System is to use asynchronous microcontroller within the built-in acceptance / transmitter features such as modules, hardware just to increase MAX 232-level conversion, can be realized between PC and SCM data transmission ;
(4) taking into account the photovoltaic power generation only in strong sunlight intensity to meet a certain time to power generation, start signal is detected by photodiodes light intensity to ensure that systems at night or rainy days does not meet power generation conditions, to stop tracking system , Detection circuit as shown in Figure 3. Mainly by the amplification, Optocoupler compared with the three isolated parts.
(5) protection system including wind protection, power grids brown-out protection, the protection of excessive vibration, limit switches and proximity switches protection component, the protection of SCM detected a signal when it issued a directive will be parked in the security system Position to ensure that the entire system from damage. Figure 4 is the grid brown-out detection circuit schematics, mainly by the buck, rectification and isolation Optocoupler three parts.
3 control unit software design
Software is the core of the control system, with the exception of some self-locking function through the protection of hardware, most features are achieved by software, the software used C programming language modular, easy integration with the transplant system.
Main program and interrupt service routines process shown in Figure 5. First to initialize the microcontroller, after reading the initial system as a checksum of the photoelectric encoder rotating the location of the benchmark. The main circulation procedures to continue the operation of state testing system, if the conditions meet the reduction will be issued directives into reset routines, the battery rapidly to the appropriate board after the standby position to wait for new instructions; calibration routines to re-check system And a new location to store test of its own internal MCU in the E2PROM as a new benchmark position, he can be used to eliminate the accumulated error, but also facilitates the installation and commissioning of the system; systems usually run on auto - Tracking Status, SCM moment of testing solar battery panels and the difference between the actual location of launch conditions and a corresponding PWM pulse, to control the motor rotation; main cycle of testing procedures also continue with the current solar battery panels position, location Information through the data bus and the RS 232 were sent to the LCD monitor and PC software system, the location of the relevant parameters and time deposit to the MCU in the E2PROM.
。 To make full use of PIC16F877 MCU system resources, improve the detection rate of SCM, SCM receiving a PC using the data to achieve interruption, the flow diagram shown in Figure 5.
4 anti-jamming system of measures
Can be a reliable and stable operation is automatically track the sun for a mature product on the premise that the system software and hardware from the two sides to enhance anti-jamming measures, the main means:
(1) external input signal and control system did not signal a total;
(2) some external input into the internal MCU before undergo strict Optocoupler circuit to be isolated;
(3) optimize the PCB wiring structure, reducing the hole to reduce the parasitic capacitance stray inductance;
(4) ensure that the entire system reliable grounding;
(5) external signal by shielding cable transmission;
(6) software filtering software on the increase, can trap door timer and software, and other measures to ensure that software in the event of crashes, such as run-down self-restoration.
(7) system as an important protection limit protection from both software and hardware to double protection, to enhance its reliability.
5 Conclusion
Automatically track the sun for the stability and reliability has been its large-scale application has not been one of the main issues.
Based on the PIC16F877A SCM for the control of the core, a design automatically track the sun azimuth angle and a high degree of automatic rotation of the sun track, running results show that the accurate tracking system, low energy consumption, high reliability and system performance and stability, Power generation efficiency above 35 percent increase, after the construction of large power station network and the Gobi Desert of guiding significance.