What is the principle and design of photovoltaic grid-connected monitoring system?

What is the principle and design of photovoltaic grid-connected monitoring system?

1. Structure design of photovoltaic grid-connected monitoring system
At present, there are three common implementations of remote monitoring systems, namely:

①After data collection is carried out through the RS485 bus, it communicates directly with the local master computer, and the local master computer is connected to the Internet, so as to realize remote monitoring.

②The collected data is converted into an analog signal through the modulation function of the Modem, which is transmitted on the public telephone network, received in different places, and then converted into a digital signal through the demodulation function of the Modem, so that the remote computer can identify and process the data. .

③Using the GSM/GPRS wireless remote monitoring system to complete the data transmission by applying for the data communication service of the mobile communication GSM/GPRS, so as to realize the remote monitoring of the photovoltaic power station.

In the actual application of this project, the RS485 bus is used to detect each device, and the obtained data is transmitted to the communication management machine in the message format of the Modbus protocol. After transmission by optical cable, the optical transceiver sent to the remote end is converted into electrical signal, and then transmitted to the server through the switch, and the obtained data is stored in the database in the server. text in order to communicate with the power dispatch center. The RS485 bus and Modbus protocol are used for communication reliability, and the optical cable transmission speed is fast. The structure diagram of the 100MWp photovoltaic grid-connected monitoring system is shown in Figure 1.

What is the principle and design of photovoltaic grid-connected monitoring system?
Figure 1 Overall structure of photovoltaic grid-connected monitoring system

The 100MWp photovoltaic grid-connected monitoring system is mainly composed of three parts: on-site monitoring, host computer monitoring and remote monitoring. The lower computer mainly includes 500kW grid-connected inverter, environmental collector, combiner box, local controller and other equipment. On-site monitoring is to monitor the equipment through the MCGS display screen and emergency start and stop buttons. The value of monitoring parameters, local host computer monitoring refers to the local monitoring computer, web server and application software deployed in the above servers, remote monitoring refers to connecting to the local monitoring server through Ethernet, the operator of the power dispatch center can Internet and IE browser to implement remote monitoring

2. Functional design of photovoltaic grid-connected monitoring system
The state quantities that need to be monitored in the photovoltaic grid-connected power generation system are: power country voltage, grid frequency, town phase, DC voltage, DC current, driving current, driving voltage, equipment temperature, etc. When these state quantities are normal, it indicates that the system is in normal working state. The data to be collected by the photovoltaic grid-connected power generation system are: photovoltaic cell instantaneous output voltage, photovoltaic cell instantaneous output current, grid-connected phase voltage, grid-connected phase current, The start and stop status of the system, the grid rate, the daily power generation of the photovoltaic grid-connected system, the cumulative power generation of the photovoltaic grid-connected system, wind direction, wind speed, sunshine intensity, and ambient temperature. Some of these data are collected raw quantities, and some are calculated from raw quantities The obtained on-site monitoring can reflect the real-time working status and set parameters of the monitored equipment, and can control the start and stop of the equipment at the same time. , On-site monitoring has the following functions.

(1) Data display
Display the operating status of the power station in time on site, and display the output voltage and current, grid-connected voltage and current, inverter voltage and current, grid-connected power, total power factor, grid compliance rate, inverter efficiency, ambient temperature, etc. of the photovoltaic cell array in real time.

(2) Fault monitoring
Real-time monitoring of the operation status of the solar photovoltaic grid-connected power station. When the power station is faulty, the monitoring system will immediately send an alarm signal and notify the power station management personnel to deal with it in time.

(3) Data management
Store the operating data of the solar photovoltaic power station. When the photovoltaic power station fails, the stored operating data of the power station can be transmitted to the remote monitoring center, which is convenient for the management personnel to analyze the fault and make corresponding processing. In addition, it also includes historical data storage. , data export, etc.

(4) Password management
The operator needs to enter the user name and password when carrying out commands such as parameter setting and start-stop control.
The host computer monitoring is in the local monitoring room of the power station, using the C/S mode on the local monitoring computer to realize the monitoring of each equipment, the function division is shown in Figure 2, it includes real-time display and statistics of each DC voltage, current , instantaneous power, daily power generation, total power generation and CO) emission reduction, fault records, alarms and circuit breaker status and other parameters and state quantities; real-time monitoring of the voltage, current and operating conditions of the step-up transformer and combiner box; Real-time monitoring of all operating parameters and power generation parameters of the inverter, and monitoring of its fault information; operations such as start-stop and parameter setting of the inverter can be performed, and grid-connected power management control of each grid-connected inverter: can be drawn every day The solar radiation intensity curve, wind speed change curve, photovoltaic cell power generation parameter curve, inverter voltage and current curve, power time curve: it has the functions of parameter setting, system analysis, power accumulation and printing various parameter curves; real-time monitoring and display of the scene Environmental data, meteorological data can be collected through the underlying intelligent instruments, such as; ambient temperature, component temperature, light intensity, wind speed, rainfall and other related data.

What is the principle and design of photovoltaic grid-connected monitoring system?
Figure 2 C/S mode monitoring software function structure

The functions of the local monitoring software can be divided into the following parts:

①Start the simultaneous system self-check and display the relevant information of the manufacturer. After logging in, the main operating parameters and window information of the power station are displayed on the main interface.

②As a local monitoring computer, it is mainly for maintenance personnel. Maintenance personnel can modify control parameters, and can compare the theoretical value of operating parameters after modifying the control parameters with the actual value of the power station. The interface and debugging interface give the main operating parameter values.

③Due to the user’s misoperation and modification of the control parameters, the photovoltaic power station equipment will fail. In order to avoid this situation, it is necessary to set the management authority of the system. In addition, if you are not logged in, you cannot view the internal information of the power plant such as system information and user parameters.

④The real-time curve interface of the monitoring system is a more important interface, and it is required to display the operating parameters and environmental parameters of the photovoltaic power station in real time, such as grid-connected three-phase voltage and current, ambient temperature, grid-connected power, etc.

⑤ It can record the historical operating parameters of the power station, and can select the curve type and time for later statistical analysis.

⑥For fault information and alarm signal, it can be displayed on the local monitoring terminal in the form of image and sound in time. The network remote monitoring is the B/S mode provided by Visual Studio, which mainly receives various data in the local monitoring of the host computer. The MySQL database is used to store these data, which is connected to the server through Ethernet, and the data can be viewed through the IE browser, so as to realize the requirements of unattended photovoltaic power plants or the data viewing requirements of production departments, maintenance departments and leading departments in different places, and log in to the website With different permissions set, the relevant operators can view and analyze the operation status according to different permissions, and can also perform remote control, such as equipment start and stop and parameter setting, etc. These control commands can also be stored in the database in time to facilitate Check back later.

The remote monitoring also incorporates the concept of enterprise management, with the functions of password protection, user authority classification, and the addition of personnel post salary management modules and benefit management function modules, which make the management of the power station more convenient and provide the top management personnel of the power station with all the information. It needs information so that senior managers can make timely and effective decisions on various planning, monitoring and control activities that they should be responsible for anytime and anywhere. The function design of remote monitoring is shown in Figure 3.

What is the principle and design of photovoltaic grid-connected monitoring system?
Figure 3 Design of remote B/S mode browser terminal monitoring function

When the inverter fails, not only the on-site MCGS LCD screen will display the sound and light alarm in real time, but also the fault alarm function in the Web server monitoring software can automatically notify the relevant personnel through E-mail and SMS, including the fault time and fault name. and fault description, etc., and E-mail and SMS recipients are set in the user management. Multiple E-mail addresses and SMS numbers can be set to remind operators to troubleshoot faults in time, and try to avoid and reduce losses. This project also set up in advance. For some reading values, when the real-time data exceeds these thresholds, obviously no alarm signal will be issued, but the Web server will send E-mail or SMS to the relevant personnel, and the operator will do some processing in advance according to these values, so that the Avoid major failures to achieve the effect of failure assessment and pre-maintenance.