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Test method of 1-12kw solar inverter dynamic MPPT efficiency
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Test method of 1-12kw solar inverter dynamic MPPT efficiency

  • Categories:Industry news
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  • Time of issue:2022-11-21 11:27
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Test method of 1-12kw solar inverter dynamic MPPT efficiency

  • Categories:Industry news
  • Author:
  • Origin:
  • Time of issue:2022-11-21 11:27
  • Views:
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In real life, due to the influence of various factors such as the angle, cloud layer, and shadow of sunlight, the sunlight radiation degree and corresponding temperature received by the photovoltaic array will be very different under different conditions. Under clear and cloudy weather, especially the impact of clouds, it may cause severe changes in radiation in a short period of time. Therefore, for the solar inverter, it must have the strategy of responding to the continuous change of sunlight radiation, always maintain, or restore a higher MPPT accuracy level, and higher conversion efficiency in a short time as possible. Only in order to achieve good power generation effects in real life.

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At present,some solar inverter have basically demonstrated a high level of handling of static MPPT tracking algorithms, which can be accurately maintained at a very close to 100% level, which provides good in the process of back -end DC communication. The basics also reflected in the overall efficiency parameters of the inverters of each model, and the nominal value is generally high. In the actual working environment of the inverter, the external conditions such as sunshine and temperature are in the process of real -time dynamic changes. The inverter works under such conditions, and its dynamic efficiency has become a measuring actual performance important indicators.

 

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In the laboratory testing environment, the high -efficiency simulator of photovoltaic simulator that can directly simulate various types and configuration photovoltaic arrays has been widely used in the test of the inverter. However, the previous tests are more concentrated in simulation of various static conditions (that is, maintain a given IV curve during the test process), or limited low -intensity changes (such as the two given two in the test process will be Or a few IV curve switching), less involved the simulation of long -term and high -intensity real working conditions. Now pay attention to the use of photovoltaic simulator to simulate the output of dynamic changes over time, explore the practicality of this dynamic MPPT test function and the main points that need attention.

Because the combination of dynamic weather is almost endless, the first question is what typical types of weather documents are provided by the photovoltaic simulator, and whether there is sufficient flexibility for customers to generate new weather documents by themselves, whether it provides enough time Resolution to support fast radiation changes. We take the photovoltaic simulator as photovoltaic simulation and the test industry as an example. It provides a typical weather condition for sunny, cloudy, cloudy and other conditions (as shown in Figure 1 below). In addition, it supports it directly in the software Formulate or use external data processing software (such as Excel) to generate custom weather documents with a time resolution of 1 second. There is no limit on the length of the weather document, which can support long -term tests, such as a week or even longer.

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                             Sunny day                                                   Cloudy day

Figure 1 The degree of radiation and temperature changes in sunny and cloudy days, the horizontal axis is time, the yellow line is radical, and the purple line is the temperature.

 

Some organizations in the industry also define some "standard" test forms in order to compare different inverters in accordance with the same standards, such as:

 

  1. Sandia National Laboratory defines several different modes of radiation and temperature changes:
  1. Quickly change (3 seconds of radiation from 100W/m² linear to 800W/m² and reverse decrease in reverse));
  2. Slowly changes (the radiation degree rose from 0W/m² to 1000W/m², and then fell to 0 at the same rate, and the temperature returned from 5 degrees to 5 degrees at the same time);
  3. Triangular changes (splicing 30 seconds from 100W/m² linear to 800W/m², and then fell to 100W/m² at the same rate, repeated 60 times);
  4. Temperature changes (linearly increased from 35 degrees to 75 degrees from 10 seconds, and then fell 35 degrees at the same rate, repeated 15 times);

 

  1. IEC/EN50530 defines different test mode in Appendix B:
  1. Different rates from low -spoke to medium radiation degrees (from 100W/m² to 500W/m², 11 different rates, the slowest 800 seconds, the fastest 8 seconds);
  2. Different rates from the degree of spoke to high -spoke degree changes (from 300W/m² to 1000W/m², 6 different rates, the slowest 70 seconds, the fastest 7 seconds);

 

  1. The definition of the test mode of dynamic efficiency is the same as the EN50530 test mode for dynamic efficiency.

It should be said that these standards provide good reference conditions to facilitate the study of targeted improvement of dynamic MPPT performance. These standards are more concerned about changes in radiation rather than temperature. This is because the output power of photovoltaic components is particularly severely affected by radiation, while the effect of temperature is relatively small. It should be noted that these standards do not provide compulsory requirements for the time resolution of the changes in radiation, but it will essentially require further linear internal interpolations while using seconds to meet this species Test form.

Taking EN50530 as an example, the fastest requirement for the rate of radiation degree is 100W/m²/s, and changes from 300W/m² to 1000W/m² in 7 seconds. If we only adopt a method of changing the radiation degree 1 second, we will get the following step -like radiation change diagram of the step -by -step step (Figure 2), not the linear change spokes required by the standard Diagram(Figure 3).

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Figure 2 The step -shaped radiation degree change with 1 second as a step -by -step Figure 3 The ideal linear radiation degree change of the ideal

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Figure 3 The ideal linear radiation degree change

 

Through simple mathematical calculations, a inverter with 1kW in a standard test state (STC, 1000W/m², 25 degrees Celsius) is used as an example to evaluate how much the impact of this step -like change method can be. According to the photovoltaic array I/V curve defined in EN50530 Appendix C, the corresponding maximum power point list of the theoretical maximum power point of the corresponding crystal silicon model and the film model under the corresponding radiation degree is as follows.

 

 

Radioactivity (W/M²)

Crystal Silicon Pmp(W)

Film Pmp(W)

300

291.6

300.7

400

394.3

404.8

500

497.0

507.9

600

599.3

609.9

700

700.8

710.3

800

801.4

808.9

900

900.9

905.7

1000

999.3

1000.3

 

 That is to say, the changes in the radiation degree of 100W/m² each time will cause the maximum power point of the output IV curve of the photovoltaic simulator (hereinafter referred to as PMP). In addition, through simple mathematical calculations, you can draw the difference in the actual supply of the inverter between this step -shaped change method and ideal situation. Within 7 seconds of the linearity of the radiation, the crystal silicon model is It is 707W less, which is 700W less, that is, the supply of about 100W is supplied by about 10%per second, and the supply of about 10%of the nominal power is insufficient. Similarly, when the radiation degree is reduced linearly, it will supply more than 100W per second, and about 10%of the nominal power supply. The difference in supply power of up to 10%is completely due to the algorithm of the photovoltaic simulator itself. For high -speed inverters, this difference may seriously affect its performance, making it unable to play its own real ability, and unable to distinguish it from other relatively low -speed inverters.

The method of solving this problem is to perform linear internal interpolations per second, so that the IV curve given by photovoltaic simulator is as good as possible to the ideal linear change as much as possible. For example, the photovoltaic simulator can be inserted 128 times linearly per second, that is a new IV curve will be automatically changed every 7.8 milliseconds, which is equivalent to almost seamless switch between the curve. Essence However, such a high -speed change will introduce another problem, that is, the calculation of MPPT tracking accuracy.

At present, various manufacturers basically rely on the MPPT accuracy measurement function provided by the photovoltaic simulator itself to directly calculate the MPPT efficiency of the inverter. The calculation method is to multiply the output voltage of the current moment to obtain the current actual output power. Then Except PMP with the current IV curve. Among them, the current actual output voltage and current value acquisition requires real -time measurement. There is a problem of measured time window length. Theoretically, the length of the time is better, such as 20ms or more To obtain high -precision reading; and another more important, impact is a synchronous problem.

When the IV curve is in the condition of high -speed automatic linear internal insertion (for example, it is updated every 7.8 milliseconds), it is clear that the conventional 20MS measurement window cannot be matched. When the measurement sampling time of 20ms is completed and a output power value is obtained, at this time The IV curve has been updated two to three times. We take this measurement value to remove the PMP value of the current IV curve, and the obtained MPPT efficiency will obviously have distortion. Therefore, when the radiation degree is rising, the MPPT efficiency reported by photovoltaic simulator will be low; when the radiation degree is in a decline, the MPPT efficiency of photovoltaic simulator reports will be high. As shown in the figure below (Figure 4), a test result of a test result from 1000W/m² to 300W/m² at a rate of 100W/m², at the same time, the test results of the photovoltaic simulator per second per second. We can clearly see that the actual output power of the photovoltaic simulator report represented by the red line is higher than the PMP of the ideal IV curve representing the linear decline representing the blue line, so that the calculated MPPT efficiency will exceed 100%.

Figure 4 In the case of linear decline in the radical degree of 100W/m /s, the MPPT efficiency reported by the photovoltaic simulator with high -speed linear interpolation function has a large error.

To solve this problem, we need to select the appropriate IV curve update rate and measure the time window. For example, the photovoltaic simulator allows users to set up a disabled instrument to automatically insert the IV curve function of 128 times per second, and the method of enabling the unified control of the IV curve per 100 milliseconds is enabled. Reading back, this can ensure that the current output power measurement is synchronized with the IV curve update. In this way, the update rate of the IV curve is 10 times per second, which can reduce the power jump of the supply to the inverter, and the difference between the supply of energy and the ideal situation to 1%of the order. Test Results. We can see that the red trajectory representing the actual output power measurement results excellently matches the blue trajectory that represents the change of ideal PMP. Figure 6 is a longer test result icon, which contains two situations that decline and rise in radiation. It shows that the current inverter can be very good to adapt to the radiation rate of this 1000W/ m², maintaining the MPPT efficiency of more than 99%.

Figure 5. When the radiation degree of 100W/m /s has a linear decline, the MPPT efficiency reported by the photovoltaic simulator of 10 times/second of the internal insertion function of the software.

Figure 6 In the case of linear decline of 100W/m²/s, the MPPT reported by the photovoltaic simulator of 10 times/second of the internal insertion function of the software.

In summary, when we need to simulate the dynamic weather conditions in the laboratory, we need to build or load typical test modes of various complex weather conditions and international specifications. The actual IV curve update rate needs to be faster (such as 10 times per second) to meet the requirements of smooth changes and meet the actual conditions. At the same time, when the high -speed IV curve is updated We can get enough accurate and reliable test results.

 

For our 1-12kw low frequency solar inverter with inside mppt solar charge controller , the key features as below :

  1. Low frequency based on Pure Copper Transformer 
    2. Compatible to mains voltage or generator power.
    3. Built-in 40A/60A/120A optional MPPT solar charger controller.
    4. Optional Solar or AC or DC priority mode
    5. Adjustable charge current, solar and AC charger
    6. Optional remote LCD display
    7. 80-270vac Wide Input AC Voltage
    8. Generator restart signal. (Dry contact).
    9. LCD display can show Solar generation
    10. 3 times peak power ensure strong protection
    11,Wifi monitor
    12,Charger adjustable for AGM/LifePO4 battery
    Certificates:ISO9001 for factory,CE for inverter 1-12KW,UL1741 for inverter 4-12KW.
    Applications:Air conditions,fridge,printers,pump and normal household equipments

                               Solar Inverter companySolar Inverter company 

If you want to know more about the inverter, you can contact me through : sales06@zlpower.com or 86-13622352906

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