The off grid inverter can work independently after leaving the grid, which is equivalent to an independent mini-grid and mainly controls its own voltage source. It can carry loads such as resistance, capacitance, motor inductance, fast strain and anti-interference, strong adaptability and practicality. It is the preferred power supply product for power outage emergency power and outdoor power supply.
In a PV off-grid system, the power of the off-grid inverter is usually determined according to the customer's load type and power.
Load type
- Resistive load. The load with no voltage phase difference is a resistive load, such as rice cooker, light bulb, electric furnace, electric ferrochrome, etc.
- Inductive load. When the current lag voltage is a phase difference, the load is an inductive load, such as washing machines, air conditioners, refrigerators, water pumps, range hoods and other loads with motors, transformers, relays, compressors, etc.
- Capacitive load. The load with the phase difference of the voltage ahead of the current is a capacitive load, such as compensation capacitors, computers, TVs, etc.
The starting power of inductive loads such as motors is 5-7 times the rated power. The starting power of these loads should be considered when estimating the power of the inverter.
If the load is an elevator, etc., it cannot be directly connected to the output end of the inverter. When the elevator falls, the motor reverses, and back electromotive force will occur, which will enter the inverter and the inverter will be easily damaged. In case of disconnection, the mains system must be used, it is recommended to add a frequency converter between the frequency converter and the elevator motor.
The waveform of the inverter can be mainly divided into two categories, one is pure sine wave inverter, and the other is modified wave inverter. The modified sine wave inverter uses the PWM pulse width modulation method to generate the modified wave output. Due to the harmonic distortion of about 20%, it cannot carry inductive loads such as air conditioners, but can carry resistive loads such as lights.
The rectified sinusoidal inverter uses a non-isolated coupling circuit, which is simple in installation and high in efficiency. Pure sine inverters are designed with isolated coupling circuits, which are complex and costly, and can be connected to any common electrical equipment (including TVs, LCD monitors, etc., especially inductive loads such as refrigerators) without interference.
The inverter can be divided into high frequency machine and power frequency machine according to the degree of isolation. The back of the inverter is equipped with a 50Hz power frequency isolation transformer, which is called a power frequency inverter; The isolation transformer replaces the power frequency transformer in the inverter, which is called a high frequency inverter.
The advantages of the power frequency inverter are that the power components are stable and reliable, the overload capacity is strong, and the shock resistance is strong. The disadvantages are low efficiency, heavy weight and high price. There are two types of high-frequency inverters: high-frequency isolation and low-frequency isolation. The advantages are small size, high efficiency, and low price. The disadvantage is that the impact resistance is slightly lower.
The output power of the inverter is greater than the load power. For applications with strict requirements such as monitoring stations and communication stations, the output power is the sum of all load powers. But for a normal family, considering that all loads cannot be turned on at the same time, in order to save costs, the coefficient 0.7-0.9 can be multiplied by the sum of the load power.
If you are building a PV off-grid system and do not know how to choose an off grid inverter, please contact us, and we will choose the most suitable inverter for you according to your needs.
