Loads are classified according to the nature of impedance: resistive load, inductive load, capacitive load. Resistive load: the load with no phase difference between current and voltage is resistive load, such as rice cooker, light bulb, electric stove, electric iron, etc. Inductive load: current lagging voltage a phase difference for inductive load, such as washing machine, air conditioner, refrigerator, water pump, range hood and other loads with motor and transformer, relay, compressor, etc. Capacitive load: current ahead of the voltage a phase difference negative load for capacitive loads, such as compensation capacitors, computers, televisions and other home use switching power supply. Motor and other inductive loads start power is 5-7 times the rated power, in the calculation of the power of the inverter, to take into account the starting power of these loads.
If the load is an elevator or something like that, it cannot be directly connected to the inverter output because when the elevator is descending, the motor reverses and a counter-electromotive force is generated, which will damage the inverter when it enters the inverter. If an off-grid system must be used, it is recommended to add a frequency converter between the inverter and the elevator motor.
If the PV system is only used for pumping water and a water tower can be built, it is recommended to use a PV water lifting inverter, which can save cost. For example, a 2P water pump, if an ordinary inverter is used, it takes more than 5kW off-grid inverter to drive it, and it has to be equipped with more than 200AH battery, the total cost is more than 10,000 RMB, but if a water lifting inverter is used, it only needs 2kW and the price is less than 3000 yuan.
The waveform of the inverter is mainly divided into two categories, one is the sine wave inverter, the other is the correction wave inverter. Repair sine wave inverter, using PWM pulse width modulation to generate correction wave output, due to the existence of about 20% harmonic distortion, can not take inductive loads such as air conditioners, but can take resistive loads such as electric lamps. The modified sine wave inverter uses a non-isolated coupling circuit with simple devices and high efficiency. The pure sine wave inverter is designed with isolated coupling circuit, which is more complex and costly, and can connect any common electrical devices (including TV, LCD, etc., especially inductive loads such as refrigerators) without interference.
Inverter is divided into high frequency machine and industrial frequency machine according to isolation. Inverter with a 50Hz industrial frequency isolation transformer at the back is called industrial frequency inverter; using high frequency switching technology, replacing the industrial frequency transformer in the inverter with high frequency switching components or high frequency isolation transformer is called high frequency inverter. The advantages of IFB inverter are stable and reliable power components, strong overload capability and shock resistance, and the disadvantages are low efficiency, relatively heavy weight and higher price. High frequency inverter has high frequency isolation and not isolated two, the advantage is small size, high efficiency, lower price, the disadvantage is slightly lower shock resistance. If the load is a large impact is an inductive load such as an electric motor, but not often move, it is recommended to choose the industrial frequency inverter, if the load is a smaller impact resistive load, to often move, it is recommended to choose the high frequency inverter.
The output power of the inverter should be greater than the power of the load. For monitoring stations, communication stations and other occasions with strict requirements, the output power is according to the sum of all the load power. However, for a general poor family, considering that all the loads cannot be turned on at the same time, the sum of the load power can be multiplied by a factor of 0.7-0.9 in order to save cost.
