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Influence of photovoltaic inverter MPPT’s number on system power generation
- Jul 17, 2018 -

Maximum Power Point Tracking (MPPT) is a core technology in photovoltaic power generation system. It refers to adjusting the output power of the photovoltaic array according to different ambient temperature and light intensity, so that the photovoltaic array is always Output maximum power. What is the impact of the number of MPPT circuits on the PV inverter power generation?

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Number of MPPT

At present, the string inverter has a number of MPPTs ranging from 1 to 5 channels. The centralized inverter is generally a 1-channel MPPT, a distributed inverter, integrating the combiner box and the MPPT boost, and there are multiple channels. MPPT, there is also a high frequency modular inverter, each module has an MPPT.

From the perspective of solving the mismatch problem, the more MPPT is, the more favorable it is; the smaller the number of MPPT, the better the stability and efficiency, because the more MPPT, the higher the system cost, the worse the stability, the more the loss many. Therefore, it is necessary to select an appropriate solution in combination with actual terrain requirements. In theory, the inconsistency of components exceeds 0.5%, and the value of use is used.

1) Functional loss: There are many MPPT algorithms, such as interference observation method, incremental conductance method, conductance increment method, etc. No matter which algorithm is used, it is to continuously change the DC voltage to judge the intensity change of sunlight. There will be errors. For example, when the voltage is actually at the optimal operating point, the inverter will try to change the voltage to determine whether it is the best working point. If there is more than one MPPT, there will be more loss.

2) Measurement loss: When the MPPT is working, the inverter needs to measure current and voltage. In general, the larger the current, the greater the anti-interference ability, and the less the error. The 2-channel MPPT is twice as large as the 4-channel MPPT current, and the error is doubled. For example, a 50KW inverter of a company uses an open-loop DC current sensor HLSR20-P with a current of 20A and an error of 1%. When the input current is less than 0.5A, the error often occurs. When the input current is less than 0.2A, Basically can't work anymore.

3) Circuit loss: The MPPT main circuit has an inductor and a switch tube, which also generates losses during operation. In general, the larger the current, the smaller the inductance and the less the loss.

The diversity of inverter MPPT technology has brought great convenience to power station design. Combine the actual, scientific design, different terrain, lighting conditions, select different inverters, reduce power station costs, and improve economic efficiency. Mountain power stations and rooftop power stations have inconsistent and partial occlusion phenomena, and different hills have different shielding characteristics, which brings component mismatch problems. It is recommended to select multi-channel MPPT and wide-range two-stage inverters. Can increase the power generation time in the morning and evening. In areas with no flat ground and good lighting conditions, it is recommended to select single-channel MPPT and single-stage inverter to improve system reliability and reduce system cost.