Research on temperature monitoring system of photovoltaic power plant power generation equipment based on LabVIEW

Abstract: Based on the LabVIEW software development platform, this paper designs a real-time temperature monitoring system for photovoltaic power plant power generation equipment. By monitoring the temperature of the PV modules and the ambient temperature, it not only guarantees the safety and stability of the system operation, but also provides a strong basis for the prediction of the PV power generation. The system can also monitor the lightning-preventing bus box and the grid-connected inverter in real time. The transformer temperature, transformer operation status, fault information, etc., to grasp the situation of power generation equipment on the job site, thus effectively reducing the failure rate of the power generation system.

1 Introduction

Photovoltaic power generation system mainly consists of photovoltaic modules, combiner boxes, grid-connected inverters, and transformers. In the actual operation of a photovoltaic power plant, sometimes due to equipment failure, its operating temperature is too high, such as transformer axial fan failure can not start, resulting in transformer operating temperature is too high; or due to the high operating temperature of the equipment, affect photovoltaic power generation The lifetime and failure rate of the equipment, such as high inverter operating temperature, will affect the working life of its internal devices, especially IGBT devices, and increase the failure rate. In view of the above two situations, if the temperature of the equipment during operation can be grasped in real time, not only the prediction of the operating status of the photovoltaic power generation equipment can be made, but also effective preventive measures against the fault can be taken in time to reduce the system failure rate and improve the system operation. Safety and reliability.

However, at present, most photovoltaic power plants use man-powered regular inspections, which not only increases the workload of operating personnel, but also reduces the reliability and safety of system operation. To solve the above problems, this paper develops a temperature monitoring system for photovoltaic power plant power generation equipment based on LabVIEW. The system can achieve the following functions:

(1) Real-time monitoring of the temperature of PV modules, combiner boxes, inverters, transformers, and outdoor environments, as well as alarms over temperature, ultra-high temperature alarms, and other functions;

(2) Transformer equipment that is very important to the normal operation of the photovoltaic power plant adopts fault priority alarm mode;

(3) It has functions such as data storage, curve storage, report printing, and historical data return visits, plus its friendly and simple upper computer interface provides great convenience for user operations.

The application of this system can effectively reduce the failure rate of photovoltaic power plants, improve the safety and reliability of photovoltaic power plants, reduce the workload of operating personnel, improve the automation degree of operation management, and promote the scientific and technological progress of photovoltaic power generation industry for the future of photovoltaic power generation. Development plays a demonstration role.

2 monitoring system hardware architecture

2.1 System Hardware Structure

The system hardware is mainly composed of outdoor temperature sensors, combiner boxes, inverters, transformer temperature control tables, 485 hubs, and RS485-RS232 serial port converters.

An outdoor temperature sensor is designed for the 5# power generation unit to collect the PV module temperature and the outdoor ambient temperature for the research of the PV power generation forecasting system; each junction box is designed with a temperature sensor to collect the internal temperature of the cabinet, because If the design parameters of the box do not meet the requirements or the wiring process does not conform to the standard, the internal temperature of the box may be abnormal. The temperature of the internal device and the temperature of the terminal of the inverter are mainly monitored to prevent the temperature from affecting the life of the device and the cable. It mainly collects its three-phase temperature, and has alarm function for fan startup, over temperature, and tripping. The communication mode of this system adopts RS485 communication, which has a simple structure, reliable communication and low cost.

2.2RS485 topology design

The topological structure of RS485 communication mainly includes hand-in-hand bus structure, star topology, tree topology, etc., as shown in Figure 1.

The star topology has the advantages of simple structure and high communication speed. However, this method has many wirings and is not economical, and when the line is long, it will generate reflected signals, thus affecting the quality of 485 communication.

The advantage of the tree topology is that the cabling is relatively simple and the scalability is good, but this method requires the auxiliary implementation of the 485 repeater and the cost is high.

Hand-in-hand bus structure is a common method. Although the wiring is more complex, it has the advantages of high transmission reliability, simple structure, low cost, etc. Moreover, the photovoltaic power plant has a large area, the distance between the equipment and the control room is far, and the bus is hand-in-hand. The method can extend the transmission distance and ensure the transmission quality.

Since there are many monitoring devices in this system, a hybrid topology with the main bus topology and supplemented by the star topology is adopted. System hardware structure framework shown in Figure 2.

From Figure 2, we can see that the bus topology between the bottom equipment (temperature sensor, combiner box, inverter and transformer temperature control table) makes the communication safe and reliable; the communication between the five inverter stations and the control room adopts a star topology. The structure can effectively increase the data transmission rate. Here, the 485 hub is used to enhance the load capacity and anti-jamming capability, making the communication more stable, accurate, and rapid.

3 monitoring system software design

3.1 Introduction to Programming Environment

This software is implemented in the LabVIEW environment. LabVIEW is a program development environment developed by National Instruments (NI) Corporation. The significant difference from other computer languages ​​is that other computer languages ​​use a text-based language to generate code, while LabVIEW uses a graphical editing language G to write programs. The resulting program is in the form of a block diagram.

The main features of LabVIEW: 1 as far as possible the use of general-purpose hardware, the difference between various instruments is mainly software; 2 can give full play to the computer's ability, have powerful data processing functions, can create a more powerful instrument. 3 Users can define and manufacture various instruments according to their own needs; 4 Fully modularized program, no need to write complicated code, easy to learn.

3.2 Communication Protocol Introduction

This system uses the standard RS485ModBusRTU communication protocol, ie "9600, n, 8, 1", baud rate 9600 (optional), no parity, 8 data bits, 1 stop bit. With CRC check, all bytes from the address byte before the check are used. The system uses the upper computer to send the query command, the lower computer response and return the response command mode.

The host computer query command frame format is:

The lower computer response command frame format is:

3.3 System Software Implementation

The inverter and transformer temperature control table communicate with the host computer using RS485 communication. Therefore, it is necessary to call the serial port communication module in LabVIEW and configure it correctly according to the communication protocol. The main program flow of the system software is shown in Figure 3.

During the running of the main program, the Serial-Read subroutine is called. The main function of this subroutine is to complete the serial communication function between the upper computer and the bottom device. The flowchart of Serial-Read is shown in Figure 4. The CRC-16 checksum calculation subroutine is called again in the Serial-Read program.

CRC check code calculation block diagram and calculation process shown in Figure 5.

4 experiments and debugging

The system has been applied in the Shenzhou Power 5MW Photovoltaic Demonstration Power Station in Hohhot, Inner Mongolia Autonomous Region. The demonstration power station is divided into 5 power generation units with a total of 172 confluence boxes, 28 inverters and 5 transformers. The inverters and transformers are respectively arranged in five inverter rooms. Among them, the furthest distance from the main control room reaches more than 400 meters.

Utilize the software that has compiled to carry on the on-the-spot monitoring to the photovoltaic module temperature, ambient temperature, 172 sets inside the box temperature, 28 working temperatures of the inverter and 5 transformers working temperature of the 5 districts power generation area, the debugging interface is shown as in Fig. 6 As shown. In order to verify the correctness of the data read by the serial port of the upper computer, a field-viewing person is arranged during the experiment and checked by the walkie-talkie and the debugger of the main control room. And through the artificial setting of the transformer fan start, over temperature, trip temperature threshold to test the alarm function is normal.

After debugging, the system can realize the real-time monitoring display of PV module temperature, ambient temperature, junction box temperature, inverter temperature and transformer three-phase temperature, and can conduct data analysis through curve mode; it can realize transformer status display and fault alarm (including Voice alarm) and other functions; and transformer temperature data, status information can be stored, printed, and information can also be visited (due to limited space, not shown in pictures here).

5 Summary

In this paper, a real-time temperature monitoring system for photovoltaic power plant power generation equipment is developed using the National Instruments LabVIEW software development platform. The system adopts a modular design concept and uses sub-program calls in a hierarchical manner to improve the program's scalability and maintainability. It also develops a visual and friendly human-computer interaction interface, which is more convenient for user system management. The application of this system to large-scale photovoltaic power stations not only greatly reduces the inspection intensity of operators, but also significantly increases the operating efficiency of photovoltaic power plants, effectively guarantees the safety and reliability of the power stations, and provides a basis for the development, operation, and maintenance of photovoltaic power generation systems. To demonstration role.