Troubleshooting method for variable frequency inverter overvoltage

The previous article focused on the analysis of variable frequency inverter overvoltage faults, and this article focuses on some processing methods.

1. Input side processing method
Since there is an impulse voltage on the input side, it will usually lead to an overvoltage fault of the variable frequency inverter. Therefore, before the lightning strike and the change of the compensation capacitor switch state generate an overvoltage, the impulse voltage should be absorbed. The frequency of the overvoltage fault after the absorption treatment will be significantly reduced. Specifically increasing impact
The voltage absorbing device can be connected in parallel or in series. One method is to reduce the impact of the impact voltage on the variable frequency inverter through a parallel surge absorbing device, and the other method is to realize it through a series reactor.

2. Adjust the setting parameters of the variable inverter
The overvoltage fault can also be eliminated by adjusting the setting parameters of the variable inverter. The deceleration time of the variable inverter can be extended appropriately. When the load deceleration time is appropriately extended, the load kinetic energy will not be released quickly. The parameter adjustment is based on the intermediate DC of the variable frequency inverter. Whether there is an overvoltage fault in the circuit, when the inertia of the load is large, the extension of the deceleration time of the load should also be appropriately increased.

3. Increase the bleeder resistance
Take the 7.5kW variable inverter as an example. When the variable frequency drive specification is less than 7.5kW, the original factory usually has a bleed resistor configuration. Adding the bleeder resistor in the DC circuit is to convert the excess electric energy in the loop into heat energy and consume it. Although adding the bleeder resistor can effectively solve the problem of excess energy, at the same time, it can also generate a lot of heat when the current flows through the resistor, causing the temperature of the bleeder resistor to continue to rise, and the resulting high temperature may cause damage to the equipment.

4. Vfd inverter circuit adjustment method
In addition to the methods mentioned above, the situation that the energy in the system exceeds the standard value can also be solved by other methods. This kind of problem can be solved by changing the circuit structure. The specific measure is to change the circuit to have an variable frequency drive circuit module In this way, the useless energy in the equipment can be fed back to the main circuit network. This work can only be realized with the help of an variable frequency drive bridge. The vfd inverter bridge is expensive, difficult to install, and cumbersome. Installing an variable frequency drive bridge is not a simple and practical way. Therefore, the production cost and installation cost of the vfd inverter bridge determine that it can only be used in some high-level frequency converter applications.

5. Capacitance improvement method
Adding capacitance to the intermediate DC circuit has many advantages. After adding capacitance, the voltage of the vfd inverter will be more stable than before. Due to the increase in capacitance, the inverter’s ability to withstand overvoltage is also significantly improved. Therefore, for capacitors that have been used for a long time and use There are different solutions for short-term capacitors. If the capacitor on an intermediate DC circuit is originally small, you can only solve this problem by increasing the capacitor. If the capacitor has a significant drop in capacity due to years of use , you should directly replace a new capacitor. From the above analysis, we can think that it is very important to design the capacitor reasonably in the design stage. It is more reasonable to increase the capacity of the capacitor as much as possible under the condition of cost and other design requirements.

6. DC bus sharing method
When the frequency converter uses its own DC bus, the phenomenon of overvoltage is easy to appear. The solution is to share one bus with multiple devices, which can solve the problems described in this article very well. Because the occurrence of overvoltage phenomenon is due to the instantaneous increase of current or voltage, it indicates that the inflow current and outflow current have not been well coordinated. If multiple devices use a bus at the same time, the inflow current and outflow The currents can cancel each other out, which can solve such problems to the greatest extent. As long as two or more devices share one bus at the same time, it can ensure that the current taken is greater than the feedback current, and the DC bus will not be over-voltaged under common working conditions. However, if multiple devices share the same busbar, there are some problems. It is more common that the protection of the busbar cannot be taken into account when using this method to prevent overvoltage faults, which makes it possible to damage the busbar when sharing the busbar. Therefore, When using this method to solve the problem, it is important to consider how to protect the safety of the busbar.