(13) Protection function
Inverters should be equipped with short-circuit protection, overcurrent protection, overvoltage protection, undervoltage protection, and phase loss protection.
(14) Interference and anti-interference
The inverter should be able to withstand electromagnetic interference in general environments under the specified normal operating conditions. The anti-interference performance and electromagnetic compatibility of the inverter should comply with the relevant standards.
(15) Noise
Inverters that are not frequently operated, monitored, and maintained should have<95db; inverters that are frequently operated, monitored, and maintained should have<80db.
(16) The display inverter should be equipped with data displays for parameters such as AC output voltage, output current, and output frequency, as well as signal displays for input live, energized, and fault states. When selecting inverters for photovoltaic/wind complementary systems, the first and foremost step is to determine the following key technical parameters of the inverter:
Input DC voltage range, such as DC24V, 48V, 110V, 220V, etc; Rated output voltage, such as three-phase 380V or single-phase 220V; output voltage waveform, such as sine wave, trapezoidal wave, or square wave.
Three phase bridge inverter circuit and its control mode
1. Circuit principle:
The most basic circuit for inverters is the bridge circuit. The principle circuit of the three-phase bridge inverter circuit is shown in the diagram.
The switches S1-6 in the figure represent power electronic power switching devices in actual circuits. As long as the switch opens and closes according to a certain pattern, it can convert direct current into alternating current. In practical circuits, the switching (commutation) of switches is achieved through commutation circuits or control pulses. Phase change is a very important concept in inverter circuits, because the power electronic switching devices in actual circuits are not ideal switches, and their turn-on and turn off must be carried out under certain control conditions. Whether it is a fully controlled or semi controlled power electronic device, as long as an appropriate signal is given to the control electrode, it can be turned on; However, the situation when turning off is different. Fully controlled devices can be turned off with a control electrode signal, while semi controlled devices must adopt certain external conditions or measures to turn off. For devices with self turn off capability, commutation can be completed by themselves, which is called device commutation; Otherwise, other means must be used to achieve commutation, such as grid commutation, load commutation, and capacitor commutation.