Inverters generally have multiple protection circuits.
1. Reverse polarity protection
Reverse polarity protection prevents improper connection to the battery, albeit at the cost of reduced efficiency, but is still valuable for mobile applications. It should be noted that not all inverters have reverse polarity protection.
2. Overload protection
The most important thing for overload protection is to control the maximum current output by the inverter, which can avoid damage to the inverter due to overload or short-circuit fault.
It is very important that the inverter should be designed to pass large inrush currents without damage. When the transistors are destroyed in a surge or short circuit situation, the inverter is also damaged. In this case the transistor temperature will increase rapidly and is proportional to the square of the transistor junction resistance. To make matters worse, this resistance increases with temperature, and the positive feedback effect is fairly rapid, so the inverter circuit must quickly determine if the current exceeds a safe limit and control it.
Protection circuits based on sensing temperature increases are often too slow to protect against massive overload currents.
When the inverter is overloaded, most circuits sense AC current and respond quickly by shortening the pulse width, thereby limiting the maximum current.
Another strategy is a sine wave inverter for series resonant capacitor control. In this type of inverter, the output circuit has been configured so that it has limited impedance and cannot pass current beyond a safe level. Since there is no requirement for active control circuitry, this strategy is very reliable. The disadvantage of this strategy is the lack of surge capability, especially when inductive loads are connected.
3. Overheating protection
Below the surge limit, moderate overloads can cause overheating and require temperature sensors for protection.
Fans are usually controlled by such temperature sensing circuits to improve cooling capacity in environments with high power output and high outside temperatures.
4. Overvoltage protection and low voltage protection
Voltage cut-offs are provided on most inverters to prevent damage to the inverter, battery and load. Excessive input voltage will stress the switching devices and cause the output waveform of the low frequency transformer down-modified square wave inverter to peak. Most manufacturers limit the input voltage to 130%~135% of the rated input voltage.
When the battery voltage is too low, the battery circuit needs to be cut off to prevent damage to the battery due to excessive discharge. In response to heavy loads, some inverters automatically adjust the voltage before tripping the low-voltage circuit, and many inverters warn of impending shutdown before interrupting output. In some devices, the cut-off voltage level can be adjusted manually.
Some inverters monitor the output AC voltage and will shut down if the output voltage remains too low for a preset time. This feature helps prevent damage to unstartable loads.