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How to choose inverter for PV off-grid system?
In photovoltaic off-grid system, the power of off-grid inverter is generally confirmed according to the user's load type and power.
Loads are classified into resistive loads, inductive loads and capacitive loads according to impedance properties.
1. Resistive load: the load with no phase difference between current and voltage is resistive load, such as rice cooker, light bulb, electric furnace, electric soldering iron, etc.
2. Inductive load: load with a phase difference of current lag voltage is inductive load, such as washing machine, air conditioner, refrigerator, water pump, range hood and other loads with motors, transformers, relays, compressors and so on.
3. Capacitive load: current leading voltage a phase difference negative load for capacitive load, such as compensation capacitor, computer, TV and other home used switch power supply. The starting power of inductive loads such as motors is 5-7 times of the rated power. The starting power of these loads should be taken into account when calculating the power of the inverter.
The waveform of the inverter is mainly divided into two categories, one is the pure sine wave inverter, the other is the modified wave inverter.
1. Modified sine wave inverter: PWM pulse width modulation method to generate corrected wave output, due to the existence of about 20% harmonic distortion, can not take the inductive load such as air conditioning, but can take the resistive load such as lights. The modified sine wave inverter adopts unisolated coupling circuit, which has simple components and high efficiency.
2. Pure sine wave inverter: Isolated coupling circuit design, circuit is more complex, high cost, can be connected to any common electrical equipment (including TV, LIQUID crystal display, especially refrigerators and other inductive load) without interference.
The inverter is divided into high frequency machine and power frequency machine according to isolation. Behind the inverter, there is a 50Hz power frequency isolation transformer called power frequency inverter. Using high frequency switching technology, high frequency switching components or high frequency isolation transformer to replace the inverter in the power transformer, called high frequency inverter.
1. Power frequency inverter has the advantages of stable and reliable power components, strong overload capacity and impact resistance, while its disadvantages are low efficiency, heavy weight and high price.
2. High frequency inverter has two kinds of high frequency isolation and no isolation. The advantage is small size, high efficiency, low price, and the disadvantage is that the impact resistance is slightly lower. If the load is a inductive load such as a motor with high impact but does not move often, it is recommended to choose a power frequency inverter. If the load is a resistive load with low impact and often moves, it is recommended to choose a high frequency inverter.
Fangpusun's XTM, XTH, PSM and PSH inverters are all pure sinuse-wave and power-frequency inverters, which can withstand about 3 times the rated power within 5S and can be connected to almost all types of loads. Of course, the heavy weight is difficult to overcome at present, so Fangpusun inverters are suitable for use in fixed positions. Such as home, rv, yacht, factory, etc. With many more features, these inverters can meet any usage scenario of any kind of battery!
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