Due to the large number of PV power plant components and strings, in the actual operation of the power station, due to the quality of the components themselves, the adverse environmental impact, the pre-design and construction defects, etc., each string inverter or combiner power generation unit will inevitably have a low The phenomenon of power generation, the search, analysis and resolution of low-efficiency power generation units are very important for the power generation of power stations. In order to promote the attention of PV power plant operators in the industry, the main idea of this paper is based on O2O operation. The concept of dimension, guides the operation and maintenance personnel to effectively use the centralized monitoring system for online analysis and offline diagnosis, and can carry out the search and analysis processing of inefficient units.
Inefficient power generation unit characteristics and troubleshooting ideas
■Inefficient power generation unit: It is determined by the fixed attribute of a string of components, that is, if there is an inefficient component in a string or there is a low-power hybrid component, the inverter corresponding to the string will generate electricity or power for several consecutive days. The number of hours will be lower than the normal string, and there will be no high or low.
■ string inefficient operation: environmental factors, construction factors, design factors, orientation problems, grid power constraints, others, etc.
Before looking for inefficient strings, the operation and maintenance personnel need to be very familiar with the basic situation of the power station, such as the installed capacity of the power station, the inverter model, the number of access strings of the inverter, the number of components in each string, and the component specifications. For power plants using string inverters, all inverters must be analyzed first to find inefficient inverter power generation units. For fast positioning of inefficient units, here is a string inverter or DC combiner box. As a preliminary troubleshooting unit, it can be locked to a certain group branch or component through on-site verification or other diagnostic methods. Of course, this idea is also applicable to centralized power stations using combiner boxes. The following ideas and methods do not have to be copied. In-situ inspections can also be judged according to their own experience. Although the process of searching varies from person to person, it is recognized that different methods are used to obtain the same result.
Simple analysis of inverter inefficient power generation through data analysis and site survey:
1) Step 1: Use the background to analyze whether the capacity of each inverter is consistent with the actual capacity. For inconsistent situations, you need to reconfigure and export the daily effective power generation hours data of each inverter for about one month (needed according to It is very important to calculate the actual inverter square array capacity to prevent false positives. It is very important that each power station should compile a string capacity information table, that is, the string inverter number, the access string. Quantity, component serial number, component power level, etc., must be verified with the site one by one), to determine the existence of inefficient inverter, the original data needs to be saved.
2) Second: Lock the inefficient string or component: 1 Diagnose online through monitoring system, discrete rate analysis, current benchmark analysis, etc. 2 If you do not pass the background system, you can also skip the line according to your own ideas. Discrete rate analysis, etc., directly through the on-site investigation to analyze the causes of inverter inefficient power generation.
3) Third: According to the second step, on-site diagnosis of the surrounding environment, if necessary, carry out voltage and current tests, analyze the reasons (starting from internal and external factors), and make relevant records (photographing).
4) Fourth: Propose the solution and evaluate the operability. According to the feasible measures, rectify the inefficient group and make corresponding records.
For power plants with centralized inverters, the following methods are available:
1) With the centralized inverter as the analysis unit, there is an inefficient inverter unit through the analysis of the number of hours of inverter power generation for one month.
2) For the inefficient inverter unit, derive the historical 5 minute branch current data and use the string current dispersion rate analysis. Focus on the string with large dispersion rate. If the dispersion rate is normal, but the branch of the combiner box as a whole The current is low (by the current pairing method below). This situation requires on-site verification of the specific cause, and the possibility of inefficient branch components is greater.
For the western power station with power limitation, when the PV output exceeds the planned output period of the provincial transfer, it is not recommended to analyze the data. At this time, the factors caused by the power cut are difficult to exclude. Therefore, it is necessary to wait until the irradiance is good, PV When the output is less than the output value of the AGC plan, analyze it or query the historical power generation data, and select the time period in which the proportion of the whole day power limit is very small for analysis.
Inefficient string or component position locking method
1 online diagnostic method
The purpose of online diagnosis is to conduct preliminary analysis and screening of low-efficiency power generation units (components or strings) of power stations, especially the comparison method of power generation hours, and the analysis of string current dispersion rate, current calibration and other methods require operation and maintenance personnel. Certain big data analysis ability. Operation and maintenance personnel can judge by offline diagnosis, and may need to be supplemented with certain testing methods (such as multimeter, clamp meter, etc.), or by viewing the surrounding environment of the string, whether there is shadow blocking Wait for confirmation to analyze the reasons for inefficiency.
1.1 Monitoring system transient analysis
As shown in Figure 1, a sub-array inverter, from the figure, the fifth branch, the sixth branch has a low operating voltage, the voltage value is only 290V, the voltage of the normal branch is 587V, but the current is basically In line with the rest of the branch roads. In this case, the operation and maintenance personnel need to carry a multimeter, a clamp meter and other tools to the site to check the problems of the two branches.
Figure 1 shows the current and voltage display values of each inverter string inverter in the background
1.2 Discrete rate analysis
Use the background management system to compare the data of each branch current, voltage and other data of the inefficient inverter with the normal inverter to find the string with lower current or voltage. Take a power station as an example, such as a square matrix inverse The transformer has the lowest number of hours of power generation, and it is necessary to analyze the string current dispersion rate. The analysis of the current dispersion rate is best to choose sunny, that is, the weather with better irradiance. Because of the rainy days, the string current is small, the difference between the strings It is difficult to reflect. If you observe the current data of each inverter, it is found that the current of the second channel is low during the time between 15:00 and 18:00, so you can lock the problem to the second branch. You need to record it. The serial number of the inverter, to be verified on site, there needs to be a pre-judgment in the heart. According to experience, if the current of the string is normal at noon irradiation, and it is lower in the afternoon, it may be Due to occlusion. (If we can find the problem through the real-time data of the monitoring system, this is best, the site will only be checked, and the work will be targeted. If the real-time monitoring data in the background cannot be judged, you can go to the site. Go check it out).
1.3 current benchmark analysis
If it is impossible to lock a string from the discrete rate analysis, we need to further analyze whether the low number of power generation hours is caused by the overall low string current. If the overall current of the string corresponding to the inverter is low, then the string The current dispersion rate may be normal, and the deviation from the discrete rate is biased; that is, the normal dispersion rate does not necessarily have no problem, and the discrete rate is not normal, there must be a problem, which requires the attention of the operation and maintenance personnel.
The purpose of current benchmarking is to find out the actual string of problems from the actual characteristics of the string. In general, we need to find the date or time period when the irradiance is stable. If the irradiance is unstable, it will be high or low. , will have an impact on our analysis, mainly because when the irradiation changes faster, the actual tracking response accuracy of the string inverter is different, and the obtained output current does not necessarily reflect the output current under actual irradiation. It will affect our judgment. The premise of current calibration is that the component models must be the same between the strings. The high-power components have larger output currents than the low-power components, but their grades are different and cannot be compared. Actual In the analysis, the string inverter with lower average current is compared with the string inverter with higher current. If the deviation is found to be large, the string capacity information table needs to be retrieved to check the component power used by the string. If the current is low because it is caused by a low-power component, please note that if the component type and the high-current component type are the same, then Low current string is there are certain problems, we need to verify the site.
1.4 online diagnosis summary
1) Verify the system back-end inverter capacity is faulty. If it is correct, the number of power generation hours calculated automatically by the background. If the system background capacity is wrong, the actual inverter capacity needs to be calculated according to the actual inverter capacity.
2) Export the number of power generation hours of each inverter in the past one month from the system background (if the capacity is not correct, calculate according to the actual capacity), rank from small to large, and filter the inverter with the highest number of hours.
3) On-line initial diagnosis: Select the weather with better irradiation, and derive the 5-minute historical data of the inefficient inverter (mainly the current of each branch of the string) to obtain the current dispersion rate of each branch. If the dispersion rate is normal, The overall current of the inverter group branch is low, which can be confirmed by the current calibration method described above.
2-line diagnostic method
1.1 Viewing the surrounding environment
Mainly check whether the string corresponding to the string inverter has external environment effects, such as shadow obscuration, dust shielding, weeds, iron towers, utility poles, etc. For the mountain photovoltaic power station, check whether the string is in the mountain, Whether the orientation of the string is positive south, whether the installation inclination of the string is consistent with other strings, and actively taking pictures to retain.
1.2 test string or component
The current system background system diagnoses low current series. The current value measured by the clamp meter may deviate from the background. Check whether the PV module is damaged, such as the glass surface of the component, whether the internal battery of the component is broken, the junction box, Photovoltaic cable insulation, etc. Check if the string wiring is wrong, the wiring error is likely to cause a certain string voltage to be low. Use the clamp ammeter to test the working current of each branch of the string inverter corresponding to the string, and test the power generation. A good inverter is used as the benchmark. The serial number of the test and its test data are used for subsequent analysis. If there is an infrared camera, it can detect the presence of hot spot components, whether the open circuit voltage is normal, and the component junction box bypass diode. Whether the fever is serious, etc.
3 inefficient treatment measures
■ String MPPT wiring optimization: At present, the string optimizer is generally a two-way string of one MPPT. Check whether the photovoltaic cable at the input of the inverter has a margin. If there is a margin, the inefficient group can be placed. Into the same MPPT. Especially for inverters that are not full of strings, it is necessary to fully use the remaining terminals. If necessary, you need to use a photovoltaic cable and MC4 connector to connect the strings.
■ Grass cover problem: For the southern region, during the rainy season, the grass is lush, and there are large areas of weeds around the square. At this time, we need to focus on it, adjust our investigation focus reasonably, and formulate a suitable weeding plan. When there are sporadic weeds in the component, it needs to be removed immediately. In addition, the weeding tools are equipped in time, and wear and tear are replaced in time. Pay attention to personal safety when weeding.
■Change the wiring method: For the type of brackets installed in the vertical row, the disadvantages of the traditional U-shaped wiring will cause the photovoltaic components of the entire bracket to be shielded from the shadow of the front square array, especially in winter, the shielding effect is greater. The wiring can be changed to a 'one' shape, that is, the adjacent upper row of the brackets are connected in series to form a string, and the lower row of components are connected into a string. It is necessary to prepare enough cables and MC4 connectors.
■Installing power optimizer: It is required to count the string or component unit of the power optimizer that can be installed in each power station, mainly the tall tower, the utility pole, the front and rear block of the component, the parapet block (distributed power station), and the block of the integrated building. , trees cover (in the case of trees can not be felled) and other shadow occlusion, statistical occlusion can affect the number of components.
4 inefficient treatment case introduction
Figure 2 shows a mountain photovoltaic power plant. Its components are installed in a vertical double row and adopt C-type wiring. The design of the mountain photovoltaic power station is more challenging than the traditional desert power station. Due to the fluctuation of the terrain, the azimuth of the slope It is not the same as the slope angle. It is difficult to balance all aspects of the front and rear of the module. Especially for complex mountainous areas, there may be more than ten kinds of slope types, even more than twenty kinds. The front and back distance of some areas may be Too small, then the front row has a certain shadow block on the back row, especially in the winter, the early spring and other periods of low solar altitude. From the operational dimension, whether it is congenital design and construction, or the outside world 2. The traditional C - type wiring method has certain defects.
Table 1 shows that before the retrofit, the daily power generation data of the inverter is statistically analyzed. The time span is more than 5 months. We found that the experimental inverter has a difference in power generation hours compared to the benchmark inverter. 1.65%, in view of the fact that the lower row of components is susceptible to a certain degree of occlusion, after the evaluation, the wiring method is refined. After the transformation, the difference in the number of hours of power generation of the inverter is reduced to -0.16%. The power generation capacity has increased by about 1.5%. After the transformation of the single string inverter, the average number of power generation hours per day is 0.05h, equivalent to 1.82 degrees of power generation, and 665 degrees of electricity is increased throughout the year, that is, a single inverter is available throughout the year. The number of hours of power generation is increased by 20h. If the array is shaded by shadows or other obstacles before and after the array, the room for lifting can be increased, although this number may be small for a single inverter, but if the power station The number of inverters reaches 1,000, so the amount of electricity that can be increased every day is expected to reach more than 1000 kWh, and the annual amount is more than 360,000 kWh.
figure 2
Table 1 Comparison of power generation hours before and after inverter retrofit
5 summary
Inefficient unit analysis and processing of photovoltaic power plants is a long-term work, which belongs to the field of refined management and operation and maintenance. The traditional extensive operation and management mode will be a big challenge for inefficient analysis and processing, so it is inefficient. The analysis and processing of the unit is inseparable from the intelligent monitoring system and the data analysis and processing platform. From the inefficient definition, the inefficient type and the string inverter, the centralized inverter and other different types of power stations, how to find the low analysis The efficiency unit has been elaborated in detail, and at the end of the economic evaluation of the typical case, I hope that this paper can give the domestic power station professional operation and maintenance play a role.
