Nowadays, in the world of power generation, conventional power generation is still the mainstay. Conventional power generation has three types: thermal power generation, hydroelectric power generation, and nuclear power generation. Among them, thermal power generation is the mainstay, but thermal power generation is accompanied by massive combustion of huge amounts of non-renewable fossil fuels. With environmental pollution caused by the consumption of conventional energy such as coal, oil and natural gas, and environmental problems such as the greenhouse effect caused by the emission of large amounts of CO2, global sea level rise and global climate anomalies, fossil energy reserves are limited, and soon The future will be exhausted. Therefore, whether it is from the perspective of human living environment or energy consumption, it forces us to look for renewable energy to replace the conventional energy.
In recent years, solar photovoltaic power generation systems have received more and more attention from various countries. The relevant plans announced in China propose that distributed photovoltaic power generation should reach 10 million kilowatts in 2015. At the same time, it is explicitly proposed to encourage construction and construction in the central and eastern regions.
A combined photovoltaic power generation system. Therefore, distributed photovoltaic power generation is an important development direction in the future. It is foreseeable that in the near future, the primary energy-based solar energy and terminal energy-based energy pattern will become a reality. The design of the LabVIEW-based photovoltaic power generation remote power monitoring system can be realized anytime, anywhere. Network access to the system completes monitoring of system power.
1 overall design of the system
The application of solar photovoltaic system (PV system) is mainly divided into two parts: ground application and space application. In the future, solar photovoltaic power generation system is mainly based on land application. At present, the structure of photovoltaic power generation system mainly has three forms: no battery Countercurrent power generation system, no battery no-countercurrent power generation system, and battery-free countercurrent power generation system. The so-called countercurrent refers to the phenomenon that surplus electric energy is reversed to the grid. This paper proposes a DC bus-type battery with reverse current power supply system. The main task is to establish a remote power monitoring system for photovoltaic power generation. Specifically, the power generated by the distributed power generation device is determined by using a smart meter or a corresponding power sensor. Information (voltage, current, electric energy, active power, reactive power, power factor, etc.) is collected and sent to the local client via 485 communication or power carrier technology using MOD-BUS-RTU protocol, running on the local client. Control the display interface of the whole system, monitor the status of the terminal in real time, and pay attention to the market and grid information dynamics in a timely manner. When the user needs to sell excess power to the grid company, send a transformer grid connection control command, which will be passed through the XBee wireless module. Command transmission to transformer test drive
The dynamic control circuit drives the control circuit with the AVR microcontroller as the controller, accepts the command of the upper computer and issues the command, so as to realize the grid-connected control of photovoltaic power generation. At the same time, if the power produced by the user cannot meet his own needs, it can also be carried out from the power grid. At the time of purchase, the host computer sends relevant instructions to the single-chip microcomputer through the wireless module according to the required electric energy value and related information, thereby controlling the power exchange between the transformer and the power grid, and realizing the power monitoring at any time and any place through remote release.
Based on the above analysis, it can be seen that the whole system includes four parts: power supply module, energy storage module, load module and control module. The power supply module includes a photovoltaic power generation battery and a power grid; the energy storage module is a battery; the load includes a DC load and an AC load; and the control module further includes control of the battery, control of the inverter, and control of the power distribution box. This article focuses on the design of the control module, which mainly includes hardware design and software design. The following sections will explain the hardware and software design separately.
2 system hardware design
The system must complete the acquisition and transmission of power signals such as voltage, current, electric energy, active power, reactive power and power factor in hardware: XBee wireless transmission module design; field drive control module design.
The power signals involved in the system mainly include: voltage, current, electric energy, active power, reactive power, power factor, etc. For the whole system, the front-end measurement acquisition device is the first unit of data acquisition, which is the lowest level. The data acquisition terminal is also the front-end equipment of the whole system. The system selects the digital electric energy meter. The specific electric energy meter is the intelligent single-phase electric energy meter model PD1150-E-3J produced by Dandong Innote Electric Co., Ltd. The series electric energy meter adopts advanced energy metering chip and combines the advantages of mechanical meter. The product has the advantages of high precision, high reliability, long life and small volume. It is a kind of programmable measurement, display and digital. Multi-function power meter with communication and energy pulse, transmission output and other functions, can complete power measurement, energy metering, data display, acquisition and transmission, connect three energy meters together by network connection, and transfer to RS485 via USB /RS232 converter is connected to the host computer.
The various control commands issued by the system host computer are transmitted to the various units in the field through the XBee wireless module. Therefore, we need to establish the XBee wireless network first. We choose MaxStream's XBee-PRO OEM RF module. We can easily connect the XBee module to the Arduino by using the wireless expansion board we built for XBee, so that the Arduino board can be easily utilized. The wireless module communicates. The selection switch on the board can configure the communication mode of the wireless module. You can choose to communicate with the host computer through the USB/serial converter, or communicate directly with the Arduino (microcontroller).
Some control commands of the host computer, such as the grid connection control command, the battery charge and discharge command, the switching command in the distribution box, etc. are transmitted to the MCU control module through the XBee wireless transmission module, and the MCU is given to each unit according to the instruction of the host computer.
The field unit issues a corresponding command signal. This design selects the ATmega8 MCU in the AVR MCU series, which inherits some features of the AT90, and on the basis of the AT90, adds more interface functions, and the performance is more stable, power saving, flexibility, anti-interference High sex. ATmega8 integrates a large-capacity data memory, non-volatile program and working memory on-chip. It is a RISC-based 8-bit MCU manufactured by low-power CMOS technology. In addition, it needs attention. The Flash memory of this series of microcontrollers is divided into two sections in space: the application segment and the bootstrapping segment. The update of the program in the application segment can be realized by using the SPM instruction for the boot program residing in the bootstrapping segment. This allows the program to be written to the application segment by serial online programming or by parallel programming (written by the programmer).
3 system software design
3.1 MCU control program design
The microcontroller program uses a new programming software, Arduino, a development platform that enables computers to measure and control more physical devices. It is a development environment for writing software code. Its programming language is a kind of "line implementation", similar to a physical computing platform based on processing multimedia programming environment, it can run under some operating systems such as Windows, Linux, Mac OS, etc. Its programming environment is simple and clear. It is easy to use for novices. The most important thing is that its source code is open. Some C++ libraries or source code can be used directly, and the programs written are easy to read. Figure 3 is a flow chart of the program controlled by the single chip microcomputer.
3.2 XBee communication program design of host computer and single chip microcomputer
In fact, the XBee wireless module after the configuration is equivalent to a “serial cableâ€. The middle of the serial cable is a wireless connection. The two ends are the corresponding serial terminals. One end is connected to the MCU control module, and the other end is connected. Connected to the host computer serial port. Therefore, we can use LabVIEW to write a serial port read/write program to realize the communication between the host computer and the control terminal of the field MCU, as shown in Figure 4.
3.3 Remote release
If the user wants to implement remote login access and operation, it needs a link, and the link is implemented by the local LabVIEW program WEB. The client can use different methods for remote access. For example, browsing the HTML file on the webpage; browsing the front panel of the program on the webpage, by opening the web server of LabVIEW, you can publish the LabVIEW program on the webpage, so that the local or remote client computer can browse or control the remote panel in the web server in real time. To achieve remote control of the production environment. Use the Web publishing tool of LabVIEW: Tools/Options, complete the settings related to the Web server and the release of the LabVIEW program in the pop-up dialog box to set the Web server: configuration; Web server: Visible VI; Web server: Browser access. Through the Tools/Web Publishing Tools dialog box, the programs in the Web memory can be published in the form of web pages, and browsed on the client side. The system uses the method of browsing the front panel of the program on the webpage to realize remote monitoring.
4 system test results
After the system is built and the remote release is implemented, the user enters the corresponding URL in the address bar of the remote client browser and presses Enter to enter the system login interface of the remote front panel. Click in the blank space and a dialog will appear. Box, select "Request VI control right", after the application is successful, the system's various operation rights are given to the remote client, the user clicks to run, after entering the correct user name and password, the page will automatically transfer to the entire system monitoring Interface, the user first configures parameters according to requirements (mainly 485 communication serial port parameters and XBee wireless communication parameters). When the user lacks power and needs to buy power from the grid, the grid connection command is sent to the upper position to display the control command status. Figure 5 is The entire system controls the front panel of the main interface.
5 Conclusion
The remote monitoring system uses the intelligent single-phase electric energy meter as the power signal collecting terminal, realizes signal transmission through the 485 bus; realizes the transmission of various control commands between the upper computer and the field single-chip control unit by using the XBee-based wireless transmission module; Based on LabVIEW-based development system, the machine uses LabVIEW's own toolkit or function module to complete the data communication function, write the power monitoring interface of the whole system, and use the built-in WEB publishing technology to remotely release the system. Realized remote access and monitoring of users. The whole system has simple structure, flexible setting, high reliability and stable operation, and has a good reference for the case of power monitoring.
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