Principle and precautions of inverter dummy load application

In the application of inverter, dummy load is an important auxiliary equipment, mainly used to test and protect inverter module.

I. Principle of inverter dummy load

The principle of inverter dummy load is mainly to protect the module through current limiting resistor to prevent module short circuit and damage to equipment. When the module drive is abnormal and the module short circuit occurs, the current limiting resistor can limit the current, thereby protecting the module from damage. Usually, light bulbs are used as dummy loads because they have the characteristics of luminescence and can intuitively judge the working status of the inverter.

II. Application of inverter dummy load

1. Connection method: The dummy load should be connected between the DC energy storage capacitor and the three-phase IGBT, and two 25w 220V powered light bulbs are added to the disconnection point. When there is a problem with the inverter circuit, the light bulb has the function of current limiting to protect the inverter module.

2. Power-on process: After powering on without load, judge whether the module is normal according to different situations. For example, if the light bulb is on, it means that there is a problem with the insulation inside the module; if there is no problem after power-on, but it lights up as soon as it is running, it means that one phase of the upper bridge or lower bridge in the three-phase module is damaged.

3. Troubleshooting: If the light bulb is not on when powered on or running, and the voltage measured for the three-phase output is unbalanced, it means that the internal circuit of a phase IGBT is open, causing the on-resistance to increase and approach the open circuit state.

III. Precautions

1. The dummy load should be connected between the capacitor and the module, not between the rectifier and the capacitor, because the discharge of the capacitor may burn the module.

2. When the switching power supply is supplied through a fast fuse, the dummy load cannot be placed on the fast fuse, otherwise the light bulb will light up after power is supplied, and the switching power supply sometimes does not work.

3. The dummy load should also be connected behind the DC voltage detection point, so that when the inverter output is abnormal and the light is on, the inverter will not jump to "low voltage", and then it can be checked which output is faulty.