How MPPT selection of the hottest photovoltaic inv

How does MPPT selection of photovoltaic inverter affect power generation

at present, different manufacturers have different technical routes for series inverters. In general, single-phase inverters below 6kW and three-phase inverters below 10kW are mostly used in household, and two-way MPPT is adopted, and each MPPT is equipped with a string; For small industrial and commercial projects, 20kw to 40kW inverters are generally used. The number of mppts is 2 to 4, and each MPPT is equipped with 2 to 4 strings; For large power stations, 60kW to 80kW are generally selected. Three closed-loop control power series inverters with real-time multitask operation system are adopted to realize load, deformation and displacement. The number of mppts is 1 to 6, and each MPPT is equipped with 2 to 12 series

choosing different MPPT routes will have a certain impact on the power generation of the system. From the perspective of solving the mismatch problem, the fewer strings behind an MPPT, the better; In terms of stability and efficiency, the more strings behind an MPPT, the better, because the more mppts, the higher the system cost, the worse the stability and the more losses. In practical application, we should choose the appropriate scheme in combination with the actual terrain

first, the advantages of less MPPT and more strings:

1) less function loss: MPPT algorithm often has no way to start. There are interference observation method, incremental conductance method, incremental conductance method, etc. no matter which algorithm, it judges the intensity change of sunlight by continuously changing the DC voltage. Therefore, there will be errors. For example, when the voltage is actually at the best working point, the inverter will still try to change the voltage, To judge whether it is the best working point. If there is more MPPT, there will be more losses

2) less measurement loss: when MPPT works, the inverter needs to measure current and voltage. Generally speaking, the greater the current, the greater the anti-interference ability and the less the error

3) less circuit loss: MPPT power circuit has an inductance and a switch tube, which will cause loss during operation. The more MPPT channels, the greater the loss. Generally speaking, the greater the current, the smaller the inductance, and the less the loss

second, the advantages of MPPT with more groups and fewer strings: manually controlled hydraulic testing machine

1) each MPPT circuit of the inverter operates independently and does not interfere with each other. The strings can be of different models, different quantities, different directions and inclination angles, so the number of strings is less, and the system design flexibility is greater

2) reduce DC side fuse failure: the most common failure of photovoltaic system is DC side failure. One MPPT is configured with 1-2-way string. Even if a certain component is short circuited, the total current will not exceed 15%. Therefore, it is not necessary to configure fuses. The common failure modes of fuses are overcurrent fusing, aging fusing, and overheating fusing. Overcurrent fusing refers to protective fusing that occurs when overload, short circuit, etc. exceed the rated value; Aging fusing refers to the fault fusing that occurs in the case of no overcurrent due to the decline of current interception capacity due to its aging in long-term work; The current of the fuse is closely related to the temperature. If the fuse works at high temperature, the current interception capacity will decline, and the possibility of fault fusing is relatively high

3) accurate fault location: the inverter independently detects the input voltage and current of each circuit, and can sample the string current and voltage in real time to find line faults, component faults, shielding and other problems in time. Through string horizontal comparison, meteorological condition comparison, historical data comparison, etc., the detection accuracy is improved

4) matching power optimizer is more suitable: at present, one of the solutions to eliminate the influence of mismatch at the module end is to use the power optimizer. The photovoltaic optimizer can convert low current into high current according to the needs of the series circuit. Finally, the output ends of each power optimizer are connected in series and connected to the inverter, and multiple strings are connected to the optimizer. According to the principle that the voltage of the parallel circuit of steel structure becomes "soft noodles" above 600 ℃, the voltage is consistent, When a certain string is shaded, resulting in power reduction, and the optimizer changes the voltage, the total voltage of this circuit will be reduced, which will also affect the voltage reduction of other circuits of the same MPPT, resulting in power reduction

summary:

design scientifically in combination with practice. According to different terrain and component occlusion, inverters with different MPPT structures are selected to reduce the procurement cost and maintenance cost of the power station and improve economic benefits

(1) in areas with flat ground and good lighting conditions, it is recommended to choose single-channel MPPT and single-stage inverter, which can improve system reliability and reduce system cost

(2) large power stations with complex terrain, such as the pacesetter base, have inconsistent directions and local shielding, and different shielding characteristics of different hills, resulting in component mismatch problems. Multiple mppts have to be selected, so the inverter with 2 series input of each MPPT will be a better choice, with no fuse vulnerable parts, high fault location accuracy and simpler maintenance

(3) the terrain is not very complex. Hill power stations and rooftop power stations have no component shelter. It is recommended to choose two-way MPPT inverters with multiple strings, which can take into account string mismatch and high efficiency, and the design is more flexible